Search

The massive amount of wasted heat energy from industry has pushed the development of thermoelectric (TE) materials that directly convert heat into electricity to a new level of concern. Recently, multicomponent alloys such as GeTe-based and PbSe-based high-entropy (HE) chalcogenides have attracted a great deal of attention due to their potential application as TE materials. The nature of the interatomic bonding, lattice distortion (LD), and the electronic structure in this class of materials is not fully understood. Herein, we report a comprehensive computational investigation of nine GeTe-based HE alloys with eight metallic elements (Ag, Pb, Sb, Bi, Cu, Cd, Mn, and Sn) with large supercells of 1080 atoms each; seven PbSe-based HE solid solutions: Pb0.99−ySb0.012SnySe1−2xTexSx (x = 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, with y = 0) with supercells of 1000 atoms each; and five Pb0.99−ySb0.012SnySe1−2xTexSx (y = 0.05, 0.1, 0.15, 0.2, 0.25 with x = 0.25) solid solutions with supercells of 1000 atoms each. All these HE models are theoretically investigated for the first time. The electronic structure, interatomic bonding, charge transfer, and lattice distortion (LD) are investigated by first-principles calculations based on density functional theory. Multicomponent HE alloys can cause a significant LD, which affects their mechanical, thermal, and TE properties. The calculations for the GeTe-based HE chalcogenides showed that they are semiconductors with a narrow bandgap, except for m8, which has a semi-metallic characteristic, and this makes them good candidates for TE applications. For most of these models, the Fermi level shifts upward and locates deeply in the conduction bands, resulting in the enhancement of the electrical conductivity (σ). The bonding properties showed that most bonds in m5 are more dispersed, indicating highest LD and lower lattice thermal conductivity. For PbSe-based HE solid solutions, the LD calculations showed that the models Pb0.99Sb0.012Se0.5Te0.25S0.25 and Pb0.89Sb0.012Sn0.1Se0.5Te0.25S0.25 have the higher LD, and thus a lower lattice thermal conductivity. Such investigations are in high demand since it enables us to design new HE chalcogenides for TE applications. We use the novel concept of total bond order density as a single quantum mechanical metric to characterize the internal cohesion of these HE alloys and correlate with calculated properties, especially the mechanical properties. This work provides a solid database for HE chalcogenides and a road map for many potential applications. Moreover, the computational procedure we developed can be used to design new HE chalcogenides for specific TE applications. [ABSTRACT FROM AUTHOR]

The presence of gradient softer outer layers, commonly observed in biological systems (such as cartilage and ocular tissues), as well as synthetic crosslinked hydrogels, profoundly influences their interactions with opposing surfaces. Our prior research demonstrated that gradient-stiffness hydrogel layers, characterized by increasing elasticity with depth, control contact mechanics, particularly in proximity to the layer thickness. We postulate that the distribution of polymers within these gradient layers imparts extraordinary stretch and adhesion characteristics due to network adaptability and stress-induced reorganization. To investigate this phenomenon, we utilized Atomic Force Microscopy nanoindentation to assess the depth-dependent adhesion behavior of polyacrylamide hydrogels with varying gradient layer thicknesses. Two gradient layer thicknesses were achieved by employing different molding materials: glass and polyoxymethylene (POM). Glass-molded hydrogels exhibited a thinner gradient layer alongside a stiffer bulk layer compared to their POM-molded counterparts. In indentation experiments, the POM-molded hydrogel had larger adhesion compared to glass-molded hydrogel. We find that indenting within the gradient layer engenders increased load-unload hysteresis due to heightened fluid transport in the sparse outer polymer network. Consequently, this led to augmented adhesion and work of separation at shallow depths. We suggest that the prominent stretching capability of the sparse outer polymer network during probe retraction contributes to enhanced adhesion. The Maugis–Dugdale adhesive model only fits well to indentations on the thin layer or indentations which engage significantly with the bulk. These results facilitate a comprehensive characterization of adhesion mechanics in gradient-stiffness hydrogels, which could foster their application across emerging contexts in health science and environmental domains. [ABSTRACT FROM AUTHOR]

Recent advancements in perovskite-based solar energy conversion technologies require materials having enhanced optoelectronic properties and stability. Harnessing density functional theory (DFT), we have investigated here a novel orthorhombic phase of a recently synthesized oxynitride perovskite, SrTaO2N, and its uniaxial strain-tunable electronic and optical properties. Phonon dispersion and formation energy calculations are utilized to determine lattice dynamic stability and exothermic formation feasibility of the structure, correspondingly. The predicted bandgap at the Heyd–Scuseria–Ernzerhof [generalized gradient approximation Perdew–Burke–Ernzerhof (GGA-PBE)] level is ∼2.125 eV (∼1.125 eV), which is highly receptive to uniaxial strains. The bandgap formed in between X and G points with high symmetry at the first Brillouin zone was further dissected using the atomic orbital projected density of states (PDOS). The PDOS showed that the N-pz orbital dominantly contributes to valence band maxima and the Ta-dz2 orbital to conduction band minima. Compressive uniaxial strain widens the bandgap by ∼1.21 times, while tensile uniaxial strain lowers the bandgap by ∼1.1 times from the intrinsic value, suggesting strain switchable bandgap nature in the material. An elastic constant matrix also evaluates the mechanical stability of strained structures, and we found that in the strained structures from −6% to +6%, SrTaO2N is mechanically stable and ductile. Optical absorption reveals an increased absorption coefficient in the visible spectrum. These strain-tuned optoelectronic properties through the DFT approach thus suggest an evident route to a wide range of optoelectronics applications of the SrTaO2N perovskite material. [ABSTRACT FROM AUTHOR]

The objective of our study was to analyze the mechanical, magnetic, elastic, electrical, and optical characteristics of the halide-based perovskite FrSnX3 (X = Cl, Br, and I) at hydrostatic pressures ranging from 0 to 6 GPa. We conducted this analysis using first-principles calculations based on density functional theory. The thermodynamic and mechanical stability of the complex FrSnX3 (X = Cl, Br, and I) were calculated based on its formation enthalpy and elastic constant characteristics. The compound was found to be ductile and stable. FrSnCl3, FrSnBr3, and FrSnI3 are all classified as semiconductors according to band calculations. Their respective bandgaps are 1.046, 0.675, and 0.485 eV, respectively. These values remain constant when hydrostatic pressure is not applied. The bandgap and density of states of the three halides were examined to observe their variations with increasing induced pressure. The bandgaps of FrSnCl3, FrSnBr3, and FrSnI3 were measured to be 0 eV at pressures of 6, 4, and 2 GPa, respectively. In addition, a comprehensive study was conducted on the optical properties of cubic perovskites FrSnX3 (X = Cl, Br, and I) under different hydrostatic pressures ranging from 0 to 6 GPa. The investigation focused on analyzing the optical absorption, reflectivity, and refractive index, as well as the imaginary and real components of the dielectric functions. Under high pressure, the compound exhibited higher absorption capabilities for all compounds within the 10–13 eV range, transforming into a conductor. This property makes it well-suited for utilization in the UV spectrum. Chlorine exhibits the greatest absorption among all chemicals, whereas iodine demonstrates the least absorption. The reflectance values of all compounds range from 12% to 16% and increase with increasing pressure. At the energy level of zero, the refractive index's real component ranges from 1.25 to 1.7, and it increases with increasing pressure. Chlorine has a relatively low refractive index compared to iodine. Bromine has the most pronounced variance. The dielectric characteristics typically vary from 4.5 to 7.5 F/m. As pressure increases, the charge storage capacities of all compounds increase. However, among these compounds, iodine has the highest capacity, while chlorine (Cl) has the lowest. The hydrostatic pressure applied to the structure FrSnX3 (X = Cl, Br, and I) causes it to become harder and more ductile. This is evident from the increasing values of the bulk, Young's, and shear modulus, as well as the elastic constants (C11 and C12). We optimized the band structure and density of states by aligning the electrons in a co-linear location and assessed the magnetic properties. The diamagnetic characteristic of the FrSnX3 compound (where X = Cl, Br, and I) remained unchanged when subjected to increasing pressure. The results indicate that the perovskite material has exceptional absorption properties, indicating a change in its behavior from a transistor to a metal. The numerical findings highlight the potential applications of this material in photovoltaic cells, ultraviolet light absorbers, and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have great potential to be used as porous adsorbents and membranes to achieve high-performance methane purification. Although the continuous increase in the number and diversity of MOFs and COFs is a great opportunity for the discovery of novel adsorbents and membranes with superior performances, evaluating such a vast number of materials in the quickest and most effective manner requires the development of computational approaches. High-throughput computational screening based on molecular simulations has been extensively used to identify the most promising MOFs and COFs for methane purification. However, the enormous and ever-growing material space necessitates more efficient approaches in terms of time and effort. Combining data science with molecular simulations has recently accelerated the discovery of optimal MOF and COF materials for methane purification and revealed the hidden structure–performance relationships. In this perspective, we highlighted the recent developments in combining high-throughput molecular simulations and machine learning to accurately identify the most promising MOF and COF adsorbents and membranes among thousands of candidates for separating methane from other gases including acetylene, carbon dioxide, helium, hydrogen, and nitrogen. After providing a brief overview of the topic, we reviewed the pioneering contributions in the field and discussed the current opportunities and challenges that we need to direct our efforts for the design and discovery of adsorbent and membrane materials. [ABSTRACT FROM AUTHOR]

This experimental study investigates the effect of blade phase angle on noise attenuation in two adjacent, electronically synchronized propellers. Acoustic measurements were performed in an aeroacoustic wind tunnel with a distributed electric propulsion system that involved the adjustment of relative phase angles of 2-bladed propellers between Δψ = 0° and 90°. Ranges of advance ratios (J = 0–0.73) were investigated at a fixed propeller rotation speed of 5000 rpm. The investigation explored the impact on noise directivity and frequency characteristics. The findings reveal significant reductions in noise directivity and tonal noise at the blade pass frequency (BPF). A relative phase angle of Δψ = 90° demonstrated the maximum noise reduction, with an 8 dB decrease at the first BPF and a 2 dB reduction in overall sound pressure level at J = 0. For in-flow conditions (J > 0), a relative phase angle of Δψ = 90° resulted in significant noise reductions of about 24 dB in the first BPF and 6 dB in overall sound pressure level, compared to Δψ = 0°. These observations offer critical insights into the use of the propeller's relative phase angle as an effective noise control method in the distributed electric propulsion system. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) MXenes, having comparable transport properties like graphene and a wide spectrum application, are often limited to being used in optoelectronics due to metallic bandgap. Here, by employing density functional theory we report the bandgap engineering and tuning optoelectronic properties through modulating the anions of novel 2D spinel Hf3X2O2 (X = N, P and As) MXenes structures and show that the material class can be among the few semiconducting MXenes. Phonon spectra and cohesive energies confirm that these structures are dynamically stable and chemically exothermic. Modulating anions X = N, P, and As in Hf3X2O2, the electronic bandgaps are found ∼0.46 eV for N, metallic for P, and ∼48 meV for As atoms, suggesting the semiconducting, metallic, and semi-metallic MXenes. The biaxial strains are incorporated to tune the features: In the Hf3N2O2 structure, the bandgap is increased with both compressive and tensile strains, while for the Hf3As2O2 structure, the gap decreased at the GGA-PBE level. For Hf3P2O2 structures, the bandgaps are all metallic irrespective of pristine or biaxial strain. Spin–orbit coupling SOC+GGA reveals that Hf3N2O2 is highly spin responsive while Hf3As2O2 shows semi-metal-to-metallic bandgap transition for pristine as well as biaxial strained conditions. From optical properties analysis, optical absorptions are found located in the visible spectral regions that are also highly receptive to biaxial strains. These properties we have unleashed for the novel Hf3X2O2 (X = N, P, As) semiconducting MXene, thus, show the potentiality of the utilization of the material class in nanoelectronics and optoelectronics applications. [ABSTRACT FROM AUTHOR]

An in situ metal-organic chemical vapor phase epitaxy is used to grow a complete AlGaN/GaN metal oxide semiconductor heterojunction field effect transistor (MOSHFET) structure, gated by a gallium oxide (Ga2O3) layer; we observed reduction in the interfacial trap density compared to its version wherein the Ga2O3 was grown ex situ, after breaking the vacuum, all else being the same. A remarkable decrease in the interfacial charge density for in situ MOSHFET structures in the range of 70%–88% for 10–30 nm oxide layer thickness and improvements in other electrical parameters required for high-performing devices were observed. [ABSTRACT FROM AUTHOR]

Using first-principles calculations based on density functional theory, this work investigated the mechanical, magnetic, elastic, electrical, and optical characteristics of the halide-based perovskite FrGeX3 (X = Cl, Br, I) at different hydrostatic pressures ranging from 0 to 9 GPa. It was determined that the compound FrGeX3 (X = Cl, Br, I) is stable and ductile in nature by calculating its thermodynamic and mechanical stability using the parameters of its formation enthalpy and elastic constant. When no hydrostatic pressure is applied, the band computations reveal that FrGeCl3, FrGeBr3, and FrGeI3 all remain in the semiconductor region with bandgaps of 1.14, 0.8, and 0.645 eV, respectively. The study examined how increasing induced pressure affects the bandgap and density of states of the structure for all three halides. The bandgap of FrGeCl3, FrGeBr3, and FrGeI3 fell to 0 eV at 9, 6, and 5 GPa, respectively. In addition, the optical absorption, reflectivity, refractive index, and imaginary and real components of dielectric functions were all studied in detail for cubic perovskites FrGeX3 (X = Cl, Br, I) under varying hydrostatic pressures, from 0 to 9 GPa. Due to increased pressure, the compound transitioned into a conductor and improved its absorption capabilities for all compounds within the 8–14 eV range, making it suitable for use in the UV spectrum. Cl has the largest absorption among all compounds, whereas I displays the lowest. Reflectivity ranges from around 14% to 18% for all compounds and increases w%ith pressure. The actual component of the refractive index ranges from around 2.25 to 2.7 at 0 eV and increases with pressure. Chlorine has a low refractive index, whereas iodine demonstrates the greatest. The highest fluctuation is shown for Br. The dielectric characteristics vary from around 5 to 7.5 F/m. Chlorine (Cl) has the least charge storage capacity, while iodine (I) demonstrates the most, of which both increase with pressure in all compounds. Structure FrGeX3 (X = Cl, Br, I) is hardened and made more ductile by applying hydrostatic pressure, as seen by the increasing bulk, Young's, and shear modulus values, as well as the elastic constants (C11 and C12). While the electrons were in a co-linear position, the magnetic property was also studied by optimizing the band structure and density of states. The diamagnetic property of the combination FrGeX3 (where X = Cl, Br, I) remained unchanged even when subjected to increased pressure. According to the findings, this perovskite material has remarkable absorption properties, which point to a change in its behavior from semiconductor to metal. Their potential uses in solar cells, UV absorbers, and optoelectronic devices are highlighted by these computational results. [ABSTRACT FROM AUTHOR]

Polymer crystallization is a long-standing interesting problem both in fundamental polymer physics and in polymer manufacturing. Fundamentally, the connectivity of the macromolecules provides a unique feature for the study of nucleation and growth of crystals in contrast to the crystallization of smaller molecules. In addition, understanding the crystallization in polymers is industrially important due to the necessity of its control to achieve mechanically durable plastic materials. Molecular dynamics simulations offer a suitable way of studying this phenomenon due to their capability to probe the small time and length scales that are characteristic of nucleation. In this paper, we use a long alkane chain model to study nucleation and the growth of polyethylene crystals both within bulk and nano-droplets whose diameters range from about 6 to 11 nm. It is found that the droplets approach being more spherical during the nucleation whereas they deviate from this shape during the growth regime. Strikingly, a mean first passage time analysis indicates that the nucleation rate per unit volume decreases as the droplet size is increased. Finally, visual inspection of the simulation snapshots suggests that nuclei majorly emerged from the surface of the droplets. [ABSTRACT FROM AUTHOR]

The interaction between superconductivity and spin-polarized surface states of topological materials provides an exciting platform for the research and development of proximity induced coupling effects, Majorana fermions, spin valves, spintronics, etc. and so on. In this work, the inverse proximity effect observed exactly at the super conducting transition temperature of indium (3.5 K) demonstrates the complex interplay between robust 2D spin-polarized surface states observed in our (002n) oriented MoTe2 nanolayer sheets with that of superconducting states. Interestingly, our phenomenological model based on the Werthamer-Helfand-Hohenberg (WHH) model and Ginzburg–Landau formalism, invoked to validate the experimental observations, indicates a competition between superconductivity and topological order, marked by a close correspondence between the temperature of crossover (Tcr = 2.45 K) of their respective length scales, ξ and Lφ, and the saturation temperature in resistivity. [ABSTRACT FROM AUTHOR]

In the starting phases of laminar, axisymmetric, continuously blowing under-expanded jets, the evolution of a counter rotating vortex ring (CRVR) over the periphery of the primary vortex ring (PVR) is numerically investigated. During CRVR evolution, the circulation dynamics of both these vortex rings is also studied. The effect of jet Reynolds number (Rej), jet Mach number (Mj), and pressure ratio ( p j p a ) on these phenomena is also shown. The CRVR evolution involves the rolling of the CRVR over the PVR periphery followed by the shock–vortex interaction between the CRVR and vortex induced shock (VIS) of the PVR. The PVR and CRVR circulations attain quasi-constancy as the CRVR starts to roll over the PVR periphery. The PVR circulation is shown to attain quasi-constancy even in the absence of its pinch-off (detachment) from the shear layer, which is a manifestation of Kelvin's theorem. The slip-stream strength is found to govern the magnitude of CRVR circulation. New type of discontinuities (induced shocks and vortex sheet) are observed inside the rolling CRVRs, which are generated from medium/high strength slip-streams. Due to the vorticity imparted from such slip-streams, there is self-roll-up of the CRVR leading to the generation of transient spiral stagnation point and vortex sheet which causes the formation of the transient saddle stagnation point. The formation of induced shocks inside CRVRs is due to the combination of two different constraints, i.e., (a) cyclic distribution of fluid properties inside the CRVR and (b) quasi-constancy of the CRVR circulation. The shock–vortex interaction between CRVR and VIS is a weak shock-strong vortex interaction, which occurs due to the constraint of quasi-constancy of net-circulation enclosing both vortex rings (i.e., PVR and CRVR) and causes the weakening of VIS. [ABSTRACT FROM AUTHOR]

Drug distribution is a vital parameter for depicting the pharmacokinetic properties of therapeutic agents. Magnetic nanoparticles (MNPs) conjugated with anti-cluster of differentiation 3 (anti-CD3) monoclonal antibody (MNPs-Ab) is a promising immunotherapeutic agent. Magnet-guided targeted delivery of MNPs has been studied exclusively in oncology. The distribution of MNPs is routinely analyzed by measuring Fe levels using inductively coupled mass spectrometry (ICP-MS). However, the ICP-based methods measure the total iron content, including endogenous iron. We used an efficient approach that measured MNPs-Ab distribution after intravenous administration using an in vivo imaging system. The fluorescent-labeled anti-CD3s are conjugated with dextran-coated magnetic nanoparticles (50 nm diameter) by the glutaraldehyde conjugation method. MNPs-Ab was intravenously administered to BALB/c mice. The fluorescence intensity in live animal and organs were analyzed after 0, 1, and 24 h. The conjugation of fluorescently labeled antibodies with MNPs was validated. The attachment of a permanent magnet on the dorsal skin area successfully guided the intravenously injected Ab-MNPs within 24 h. However, after 1 h, no observable fluorescence was seen at the target site. The in vitro organ distribution study confirms nanoparticles' predominant distribution in the liver and kidneys-the intensities of the fluorescence increase after 24 h than 1 h. Our in vivo imaging studies confirmed the external magnet-driven targeted distribution of the antibody-conjugated nanoparticle. Besides, the in vivo imaging system enables rapidly identifying the distributed nanoparticles. [ABSTRACT FROM AUTHOR]

Iron oxide nanoparticles (NPs) are biocompatible, have excellent magnetic properties, respond to external magnetic fields, and have been used in many studies on drug delivery systems. In this study, hyaluronic acid (HA)–superparamagnetic microneedles containing superparamagnetic iron oxide nanoparticles were manufactured using HA as the matrix material. Optical and scanning electron microscopy (SEM) were used to investigate the characteristics of the magnetized microneedles (MMNs). The mechanical rigidity of MMNs for in vivo evaluation is expected to be sufficient, as evidenced by a transmittance greater than 90%. Additionally, the superconducting quantum interference device-vibrating sample magnetometer measurement results confirmed that the magnetic characteristics did not change, even after the magnetic nanoparticles (MNPs) were manufactured. The hysteresis curves of the NPs confirmed the maintenance of the magnetic properties, including a coercivity of 60 Oe and susceptibility of 4 × 10-6 emu/gOe. Based on these results, MNPs are expected to be useful as a delivery material for transdermal drug delivery systems, magnetic resonance imaging, and molecular imaging. [ABSTRACT FROM AUTHOR]

Artificial synaptic devices made from natural biomaterials capable of emulating functions of biological synapses, such as synaptic plasticity and memory functions, are desirable for the construction of brain-inspired neuromorphic computing systems. The metal/dielectric/metal device structure is analogous to the pre-synapse/synaptic cleft/post-synapse structure of the biological neuron, while using natural biomaterials promotes ecologically friendly, sustainable, renewable, and low-cost electronic devices. In this work, artificial synaptic devices made from honey mixed with carbon nanotubes, honey-carbon nanotube (CNT) memristors, were investigated. The devices emulated spike-timing-dependent plasticity, with synaptic weight as high as 500%, and demonstrated a paired-pulse facilitation gain of 800%, which is the largest value ever reported. 206-level long-term potentiation (LTP) and long-term depression (LTD) were demonstrated. A conduction model was applied to explain the filament formation and dissolution in the honey-CNT film, and compared to the LTP/LTD mechanism in biological synapses. In addition, the short-term and long-term memory behaviors were clearly demonstrated by an array of 5 × 5 devices. This study shows that the honey-CNT memristor is a promising artificial synaptic device technology for applications in sustainable neuromorphic computing. [ABSTRACT FROM AUTHOR]

In this research paper, our primary objective is centered around the creation, characterization, and evaluation of zinc sulfate (ZnSO4) nanoparticles through the utilization of Nigella sativa as a natural reducing agent. We embraced an environmentally conscious and uncomplicated green synthesis approach to synthesize these ZnSO4 nanoparticles. For a comprehensive examination of their structural and physical properties, we employed techniques such as x-ray diffraction, Raman spectroscopy, scanning electron microscopy, and dynamic light scattering analysis. Our results unequivocally confirmed the successful production of ZnSO4 nanoparticles with well-defined crystalline structures, distinct wavelength patterns, prominent peak values, and specific particle sizes. This study underscores the impressive efficacy of Zn nanoparticles in the context of bio-electrolyte power generation systems. In addition, it introduces an economically feasible and environmentally friendly method for their fabrication. The Zn nanoparticles display great potential as a solid basis for advancing bio-electrochemical cells, underscoring the significance of further exploration into their effects on these cells. [ABSTRACT FROM AUTHOR]

In order to have a precise knowledge on how pressure gradients and buoyancy force affect fluid flow and energy distribution in a bending channel, it is important to perform a comprehensive study on flow characteristics and heat transfer mechanisms that trigger out the transition of fluids into a turbulent state, subject to a sustained pressure gradient. The present paper explores a computational modeling on two-dimensional fluid flow and thermal characteristics in a bent square channel of strong curvature. The Newton–Raphson (N-R) iteration method is applied to obtain a bifurcation structure depending on the pressure-driven force, the Dean number (De), covering 0 < De ≤ 5000. As a consequence, four branches of asymmetric steady solutions are identified for each of the cases of the Grashof number, Gn (=1000, 1500, and 2000), where only the first branch is found to exhibit asymmetric two-vortex solutions while the remaining branches encompass twoto four-vortex solutions. The similarity and disparity in the branching structure are also demonstrated. Then, adopting the Adam–Bashforth (A-B) method together with Crank–Nicholson (C-N) formula, the unsteady solutions (US) have been explored, validated by power spectrum density (PSD) and phase space Within the realm of US, two- and three-vortex solutions are found and these solutions exhibit transitions from steady to chaotic behavior profoundly. Effects of the Grashof number with convective heat transfer (CHT) are also compared. By analyzing the Nusselt number (Nu), it is observed that in case of highly chaotic flow, CHT experiences substantial enhancement. This intensified CHT arises from increased turbulence and mixing, facilitating more efficient thermal energy exchange under such chaotic flow conditions. [ABSTRACT FROM AUTHOR]

High electron mobility transistors (HEMTs) based on gallium nitride (GaN) with a wide range of application potentials need to be rigorously examined for reliability to take advantage of their intrinsically extraordinary properties. The most vital parameter of the reliability, the hotspot, or Tmax, resides in the two-dimensional electron gas (2DEG) temperature profile inside the device where optical access is often restricted. The device surface temperature can be measured by widespread IR thermography with the limitation of diffraction-based IR transmission losses. However, Tmax on the sub-surface cannot be reached thermographically. Although finite element analysis (FEA)-based thermal simulations can easily reveal the 2DEG temperature profile, accuracy is tightly dependent on the realistic modeling of material/structure parameters. Because these parameters are rather sensitive to fabrication and processing, it is quite difficult to specify them accurately. To overcome these drawbacks, a method integrating both IR thermography and FEA thermal analysis is demonstrated on a fabricated high-power 40 × 360 μm packaged GaN HEMT as a proof-of-concept. Utilizing the simulation and measurement temperature profiles, a correlation algorithm is developed so that accuracy of the FEA thermal simulation is improved by calibrating the parameters specific to fabrication/process conditions by thermographic measurement. Then, it is quantitatively shown that the proposed method is able to find the 2DEG temperature profile and Tmax with an accuracy that best suits the intrinsic and extrinsic characteristics of the device under test. The method sheds light on GaN reliability engineering by providing a feasible and reliable alternative to realistically reveal hotspot information for device lifetime assessments. [ABSTRACT FROM AUTHOR]

Recently, semiconductor photocatalysts for green hydrogen (H2) fuel require two-dimensional (2D) material with semiconducting direct bandgap and enhanced visible light absorptions. In this study, the first-principles calculation of the 2D layered nanostructure of SnGe2N4 is presented for photocatalysis applications, which has a direct bandgap of 1.73 eV/2.64 eV (Perdew–Burke–Ernzerhof/Heyd–Scuseria–Ernzerhof with generalized gradient approximation) with enhanced optical absorptions. The structure is checked to confirm the chemical formidability and dynamical steadiness by formation energy calculations and phonon dispersions. To attain the tunability of electronic and optical properties, biaxial strains, together with tensile and compressive strains, are incorporated, and it is found that compressive strain widens the bandgap, whereas tensile strain causes bandgap reduction. Biaxial strains also improve the optical absorption and the highest absorption coefficient is obtained at ∼1.47 ⨯ 105 cm−1 for 6% compressive strain, comparable to conventional perovskite materials. However, in the visible spectrum, the highest absorption coefficient is obtained for 6% tensile strain. The calculated photocatalytic band edges suggest that this material has sufficient kinetic overpotential for photo redox at compressive strains in both pH = 7 and pH = 0. In addition, the spatial carrier separation is achieved due to having a large intralayer effective potential deviation of ∼6.96 eV, as well as intralayer spatial atomic group contribution in the valance band maximum and conduction band minimum. Conclusively, the analysis in this study can be a theoretical background of this layered nanostructure as a potent photocatalyst for water splitting. [ABSTRACT FROM AUTHOR]

The detailed optical and electronic characteristics of 2D GeC and 2D PtO2 under biaxial strains and electric fields across the plane are studied systematically using the density functional theory (DFT) based first-principles framework. The six different stacking patterns of the stacked van der Waals (vdW) GeC/PtO2 hetero-bilayers were DFT screened, and HBL 4 and HBL 5 are found both dynamically stable and energetically favorable, evident from the non-zero phonon frequency and negative binding energy from phonon dispersion and binding energy calculations, respectively. The bandgap of 2D GeC and 2D PtO2 is found to be ∼2.08 eV (direct) and ∼1.63 eV (indirect), while the bandgaps in vdW HBL 4 (HBL 5) are found to be 0.51 eV (0.49 eV). Biaxial strain lowered the bandgap by ∼11.13 (∼1.81) times at 6% compressive (tensile) biaxial strain in HBL 4 (HBL 5). Semiconductor-to-metal switching is found in both HBLs at ±0.6 V/Å of the cross-plane electric field. All the HBLs show type-II band-alignment, evident from the difference in charge density and projected density of state contour, indicating spatial carrier separation capability. The peak of the optical absorption coefficient is found to be ∼3.1 × 105 cm−1 at 310 nm for both HBL 4 and HBL 5, which is comparable to high-absorbing perovskite material. Moreover, the optical absorption is sensitive to the biaxial strains and electric fields, and increased visible band optical absorption is found for tensile strains in both HBLs. These exceptional findings and engineered bandgap in GeC/PtO2 vdW HBL indicate the promising application of this material in 2D advanced nanoelectronics. [ABSTRACT FROM AUTHOR]

We report on a novel scissor-like electromechanical metamaterial (SEMM) with enhanced and tunable damping properties, stemming from its electromechanical resonant effects. The displacement amplification mechanism of the scissor-like structure in SEMM is exploited to amplify the damping ratio for stronger vibration mitigation through the enhanced electrical dissipation of the amplified voltage of the piezoelectric element. The relative dissipation performance, termed as metadamping, is quantified based on complex band structures, which allow frequencies to be complex valued. Using different shunting circuits, the overall damping performance of SEMM is demonstrated to be higher than a statically equivalent traditional systems, such as acoustic metamaterials and monatomic lattices. The dissipation performance of SEMM is numerically verified via finite structure analysis and found to be in an excellent agreement with Bloch's wave analysis. Furthermore, the electromechanical nature of the piezoelectric material in SEMM provides a convenient way to tune the metadamping by adjusting the piezoelectric shunting circuit. [ABSTRACT FROM AUTHOR]

The three-dimensional flow transition is examined in the wake of a heated square cylinder subjected to horizontal cross-flow perpendicular to gravity utilizing a direct numerical simulation approach. The surface of the square cylinder is heated uniformly to an elevated temperature Tw, and the amount of excess temperature is represented as the over-heat ratio ε = (T w − T ∞) / T ∞ , where T ∞ represents the surrounding temperature. The effects of large-scale heating on the transport properties and thermal straining of the fluid particles are captured using an in-house non-Oberbeck–Boussinesq compressible model. The compressible flow governing equations (in a body-fitted coordinate system) are solved using a variant of flux-based particle velocity upwind-modified+ (PVU-M+) technique [Ahmad et al., "On the formation and sustenance of the compressible vortex rings in starting axisymmetric jets: A phenomenological approach," Phys. Fluids 32, 126114 (2020)]. In this investigation, all computations are conducted at a low Mach number (Ma = 0.1) and air (Prandtl number, Pr = 0.71) is used as the working fluid. As the heating level rises, the shape and wavelength of the vortical structure undergo significant alterations. At Re = 250, the mode-B transition with a shorter spanwise wavelength and the mode-D transition with a longer wavelength are observed, respectively, for heating levels ε = 0.0 − 0.2 and ε = 0.8 − 1.0. Furthermore, for heating levels in the range 0.4 ≤ ε ≤ 0.6 , an intermediate wavelength of the mode-E transition is detected. The temporal variation of fluid properties such as the force coefficient (CL, CD) and the Nusselt number (Nu) are shown at various heating levels. In addition, surface vorticity is examined in order to comprehend the flow dynamics near the surface of a heated square cylinder. [ABSTRACT FROM AUTHOR]

To obtain improved thermal performance of flat plate solar collectors, the effect of square and rectangular riser tubes of a flat plate collector (FPC) were numerically investigated and compared with circular riser tube FPC in the present study. For this purpose, a three-dimensional numerical model for FPC collectors has been developed and simulated in CFD software ANSYS FLUENT. Transient thermal performance analysis is carried out to find out the optimum geometrical configuration of the FPC riser tube. The numerical results indicated that using the square-shaped riser tube in FPC improves the collector's useful heat exchange rate as well as thermal efficiency as compared to the use of circular and rectangular riser tubes. There is a maximum 8.1% higher heat exchange rate of the collector with a square riser tube than a circular riser tube under the same operating conditions. The average efficiency of the collector with the circular tube is 65.95%, whereas the square tube has the highest efficiency of 70.44%. However, the pressure drops through the square and rectangular riser geometry are higher than the circular tube. By making a balance between enhanced heat exchange rate and increased pressure drop, the performance evaluation criterion was evaluated and the square-shaped riser tube having the highest value of 2.65 is better than the other configurations. The results clearly indicate that the collector's performance is notably influenced by the shape of the riser tube, with a square shape yielding superior performance. [ABSTRACT FROM AUTHOR]

We describe an apparatus for investigating the excited-state dissociation dynamics of mass-selected ion–molecule clusters by mass-resolving and detecting photofragment-ions and neutrals, in coincidence, using an ultrafast laser operating at high repetition rates. The apparatus comprises a source that generates ion–molecule clusters, a time-of-flight spectrometer, and a mass filter that selects the desired anions, and a linear-plus-quadratic reflectron mass spectrometer that discriminates the fragment anions after the femtosecond laser excites the clusters. The fragment neutrals and anions are then captured by two channeltron detectors. The apparatus performance is tested by measuring the photofragments: I−, CF3I−, and neutrals from photoexcitation of the ion–molecule cluster CF3I·I− using femtosecond UV laser pulses with a wavelength of 266 nm. The experimental results are compared with our ground state and excited state electronic structure calculations as well as the existing results and calculations, with particular attention to the generation mechanism of the anion fragments and dissociation channels of the ion–molecule cluster CF3I·I− in the charge-transfer excited state. [ABSTRACT FROM AUTHOR]

This study examined the impact of Boger droplets on spherical surfaces, considering the various properties of liquids and surfaces for the first time. The experimental setup involved spheres with three different diameters composed of hydrophilic and hydrophobic surfaces. The main innovative aspect of the present study lies in the examination of the effects of rheological properties including elasticity, elongational viscosity, and the first normal stress difference on the impact of Boger droplets on solid surfaces via stress analysis. For this purpose, the results of the impact of Boger droplets are compared to the impact of equivalent Newtonian droplets with the same viscosity and surface tension coefficient. The research also explored the influences of Weber number, diameter ratio, and surface wettability on the dynamic behaviors of viscoelastic droplets during the spreading and receding stages. The results suggested that increasing the Weber number increases the maximum spreading factor of the droplets. A smaller diameter ratio required more time to reach this factor. The surface wettability significantly affected the receding phase, while its effect on the spreading stage was minimal. Droplets exhibited more retraction on surfaces with higher contact angles. The Newtonian fluids showed greater spreading and retraction than viscoelastic fluids with the same viscosity, highlighting the influence of fluid elasticity. It is shown that the normal stress caused by extensional viscosity during droplet spreading is significantly higher than the normal stress difference resulting from shear deformation, showing different behaviors between these two types of stress concerning droplets. [ABSTRACT FROM AUTHOR]

This document explores the use of Boomwhackers, a musical instrument, as a teaching tool for physics concepts related to sound waves. The author suggests using Boomwhackers to play Beethoven's "Ode to Joy" and then delving into the speed of sound. The focus is on the relationship between sound frequency and tube length, as well as the concepts of pitch and octaves. The document provides a step-by-step procedure for conducting experiments with Boomwhackers to help students grasp these concepts. It concludes that students can learn about fundamental frequency, pitch, octave, and the speed of sound through this activity, even without prior knowledge of physics. [Extracted from the article]

Three-dimensional numerical simulations are performed to study the migration dynamics of a deformable bubble that is spherical at an initial time near a corner formed by two vertical walls. Near-wall dynamics of this rising bubble are studied by investigating its path, wake, shape and velocity. A finite volume approach coupled with VOF (volume-of-fluid) method is adopted to solve the incompressible Navier–Stokes equation and track the gas–liquid interface. From the study, it is found that bubble inertia is dictated by initial bubble–walls interaction as bubble progressively migrates away in a diagonal direction from both the vertical walls in three-dimensional space. This influenced bubble inertia, in turn, affects the conformity of the bubble to a specific bubble regime. Five regimes are identified based on the bubble's migrating trajectory among which three of them are fully developed-steady, zigzag, and spiral and two of them are transitional-steady to zigzag and zigzag to spiral. The point of complete transformation of bubble from steady to zigzag transition to fully developed path instability is evaluated by varying a certain dimensionless parameter, Galilei number Ga. It is found that the path instability occurs at a lower Ga than what it is for the unbounded situations, and the onset of planar zigzag motion is not the result of vortex shedding rather the critical amount of wake accumulation on bubble surface and bubble inertia modulated by walls. Furthermore, the overall dynamics found in the current study show distinguishable characteristics when compared to single wall and unbounded situations. [ABSTRACT FROM AUTHOR]

This study focuses on the buckling behavior of composite microshells inside pacemakers to select the most durable material. Due to the strong electromagnetic forces encountered by pacemaker microshells, comprehensive research is needed to identify suitable materials. This study analyzes the buckling behavior of a porous sandwich cylindrical microshell attached to electrodes, which is supported by an elastic foundation and reinforced with functionally graded carbon nanotubes. Three porosity models are considered for the core material, and the equilibrium equations are derived using Hamilton's principle based on third order shear deformation theory. This study compares the critical buckling loads with those from the literature and examines the effects of various parameters, such as thickness stretching and non-stretching. The findings indicate that the thickness stretching effect has a significant influence on the critical buckling load. In addition, a lower functionally graded power index and higher porosity volume fraction result in higher critical buckling loads. These results are relevant for micro-electromechanical systems and can aid in the selection of appropriate materials for pacemaker microshells to improve their durability and performance. [ABSTRACT FROM AUTHOR]

Airborne and deposited water microdroplets can carry viruses including coronaviruses. The evaporation of microdroplets containing virus particles often leads to virus inactivation. Microdroplet evaporation involves various mechanisms such as diffusion, the Kelvin effect, infrared irradiation, and the role of solutes. For the evaporation of airborne water microdroplets, temperature and relative humidity of ambient air are important factors. However, for sessile droplets deposited on solid surfaces, wetting and porosity become important factors that control evaporation on regular, superhydrophobic, and photocatalytic surfaces. An experimental study of the effect of wetting properties and porosity on the evaporation rates on the polypropylene non-woven medical fabric was consistent with the theoretical models. Highly porous tile surfaces exhibited 2.2–4 times faster evaporation rates than nonporous surfaces. [ABSTRACT FROM AUTHOR]

Based on the motivation of the recent advancement of the van der Waals heterostructure (vdW HBL), we have studied the tunable optoelectronic properties of the two-dimensional (2D) boron phosphide–platinum di-oxide (BP/PtO2) heterostructure using dispersion corrected density functional theory (DFT). Six different stackings are considered to stack the 2D BP upon 2D PtO2 and are tested through DFT. Phonon spectra and binding energy calculation validate the dynamical and chemical stability of the constructed heterostructures. It is found that HBL1, HBL3, and HBL4 have type-II indirect band gaps of 0.001, 0.027, and 0.021 eV, respectively whereas the other HBLs 2, 4, and 5 show a semiconductor–metal transition. The variation in the interlayer distances, cross-plane electric field, and biaxial strain can effectively tune the bandgap, although type-II band alignment remains unaffected in all cases. A large built-in electric field, of ∼15 eV in electrostatic potential between the 2D structures and type-II band alignment of the HBL, suggests efficient separation of charges in all the HBLs. The bandgaps are highly responsive to the interlayer distances, electric field, and biaxial strain in the HBL. It is found that the bandgap increases under the application of compressive strain and an external electric field along the negative z-direction up to −0.4 V/Å. Interestingly, a semiconductor–metal transition occurs for tensile strain and the external electric field along the positive z-direction. All HBLs have efficient optical absorption in the visible and UV portions of the solar spectra, which is highly anticipated for optoelectronics applications. These unrivaled properties of the vdW BP/PtO2 HBL that we have explored make them a promising candidate for nano-electronic devices and infrared detector applications. [ABSTRACT FROM AUTHOR]

The article discusses the importance of understanding organ-specific vasculature and its implications for tissue-specific vascular therapies and bioengineering human organs. It highlights recent advances in microfabrication techniques and organ-on-a-chip systems that allow for the study of tissue-specific blood and lymphatic vasculature in a physiologically relevant context. The article also explores the use of vascularized organ-on-a-chip systems for studying host-bacteria interactions and cellular responses related to bacterial infections. Additionally, it presents microfluidic platforms that enable the investigation of how the liver endothelium changes in response to its microenvironment and how the liver responds to changes in the endothelium. The article concludes by emphasizing the potential of these models to improve drug development and investigate organ-specific cancer metastasis. [Extracted from the article]

The theoretical study of one-dimensional-infinite systems of elastically coupled parallel waveguides has established the existence of band structures with pseudo-spin characteristics. Those systems, which are named ϕ -bits, have been shown to exhibit a spinor character associated with directional degrees of freedom, which makes them potential quantum mechanical analogs. The realization of such systems is challenged by the three-dimensional and finite nature of physical elastic waveguides. We address this problem, and with it the design of ϕ -bits in general, by developing finite elements models based on COMSOL Multiphysics®. We model systems of one or more coupled finite length Al rods. The analysis of their dispersion relations, transmission spectra, and amplitudes establishes their ϕ -bit character. For three coupled finite length Al rods, the elastic field is associated with wavefunctions, tensor products of a spinor part related to the directional degrees of freedom, and an orbital angular momentum part representing the phase of the coupled waveguides. We demonstrate the possibility of creating non-separable states between these degrees of freedom. [ABSTRACT FROM AUTHOR]

We discuss the dependence of the propagon contribution to thermal conductivity on the medium range order (MRO) in amorphous silicon. Three different amorphous structures with the same size of 3.28 nm were studied. Among these three structures, two structures were constructed with experimentally observed MRO [M. M. J. Treacy and K. B. Borisenko, Science 335, 950 (2012)], and the other structure is from continuous random network (CRN), which lacks MRO and thus represents a randomized amorphous structure [G. Barkema and N. Mousseau, Phys. Rev. B 62, 4985 (2000)]. Using the simulated fluctuation electron microscopy and dihedral angle distribution, we confirm that the first two structures contain MRO in the length scale of 10–20 Å while the CRN structure does not. The transport of propagons in the MRO and CRN structures is compared using the dynamic structural factor calculation and normal mode decomposition of the molecular dynamics simulation data, showing noticeably longer lifetime of propagons in MRO structures than in the CRN structure. The propagon thermal conductivity in MRO structures is estimated to be 50% larger than that in the CRN structure. [ABSTRACT FROM AUTHOR]

Cytokine storm is characterized by increased levels of proinflammatory cytokines. Magnetic nanoparticles (MNPs)-conjugated antibody therapy is promising in treating cytokine storms. This study will evaluate the time-dependent distribution of the silica-coated MNP (MNP-Si) in the spleen and consequent serum cytokine changes for 30 days. MNP-Si were administered to female BALB/c mice via the tail vein injection. The distribution of Fe in the spleen tissue was analyzed by ICP-MS both in control and MNP-Si-treated mice. Moreover, the acute immune toxicity in serum was investigated by analyzing IFN-γ and IL-6 levels. Fe in the control spleen is 0.98 × 106μg/mg of dry weight. The highest average concentration of Fe in the spleen was measured on day 10 (1.4 × 106μg/mg). And at day 30, Fe levels decreased to 1.0 × 106μg/mg. IFN-γ levels significantly increase to a maximum on day 6 and remain elevated until day 30. IL-6 levels are not elevated after MNP-Si administration. Although the cytokines in tissue homogenates were elevated at day 20, the data are statistically non-significant. In conclusion, the proinflammatory cytokine IFN-γ levels were increased on day 6, indicating induced activation of macrophages and systemic inflammation after MNP-Si administration. Therefore, the dose and composition of the MNP-Si should be revised for potential usage for therapeutic purposes. [ABSTRACT FROM AUTHOR]

The pressure–strain interaction describes the rate per unit volume that energy is converted between bulk flow and thermal energy in neutral fluids or plasmas. The term has been written as a sum of the pressure dilatation and the collisionless analog of viscous heating referred to as Pi − D , which isolates the power density due to compressible and incompressible effects, respectively. It has been shown that Pi − D can be negative, which makes its identification as collisionless viscous heating troubling. We argue that an alternate decomposition of pressure–strain interaction can be useful for interpreting the underlying physics. Since Pi − D contains both normal deformation and shear deformation, we propose grouping the normal deformation with the pressure dilatation to describe the power density due to converging/diverging flows, with the balance describing the power density purely due to shear deformation. We then develop a kinetic theory interpretation of compression, normal deformation, and shear deformation. We use the results to determine the physical mechanisms that can make Pi − D negative. We argue that both decompositions can be useful for the study of energy conversion in weakly collisional or collisionless fluids and plasmas, and implications are discussed. [ABSTRACT FROM AUTHOR]

How energy is converted into thermal energy in weakly collisional and collisionless plasma processes, such as magnetic reconnection and plasma turbulence, has recently been the subject of intense scrutiny. The pressure–strain interaction has emerged as an important piece, as it describes the rate of conversion between bulk flow and thermal energy density. In two companion studies, we presented an alternate decomposition of the pressure–strain interaction to isolate the effects of converging/diverging flow and flow shear instead of compressible and incompressible flow, and we derived the pressure–strain interaction in magnetic field-aligned coordinates. Here, we use these results to study pressure–strain interaction during two-dimensional anti-parallel magnetic reconnection. We perform particle-in-cell simulations and plot the decompositions in both Cartesian and magnetic field-aligned coordinates. We identify the mechanisms contributing to positive and negative pressure–strain interaction during reconnection. This study provides a roadmap for interpreting numerical and observational data of the pressure–strain interaction, which should be important for studies of reconnection, turbulence, and collisionless shocks. [ABSTRACT FROM AUTHOR]

In weakly collisional and collisionless magnetized plasmas, the pressure–strain interaction describes the rate of conversion between bulk flow and thermal energy density. In this study, we derive an analytical expression for the pressure–strain interaction in a coordinate system with an axis aligned with the local magnetic field. The result is eight groups of terms corresponding to different physical mechanisms that can contribute to the pressure–strain interaction. We provide a physical description of each term. The results are immediately of interest to weakly collisional and collisionless magnetized plasmas and the fundamental processes that happen therein, including magnetic reconnection, magnetized plasma turbulence, and collisionless shocks. The terms in the field-aligned coordinate decomposition are likely accessible to measurement with satellite observations. [ABSTRACT FROM AUTHOR]

The time evolution in open quantum systems, such as a molecular aggregate in contact with a thermal bath, still poses a complex and challenging problem. The influence of the thermal noise can be treated using a plethora of schemes, several of which decompose the corresponding correlation functions in terms of weighted sums of exponential functions. One such scheme is based on the hierarchical equations of motion (HEOM), which is built using only certain forms of bath correlation functions. In the case where the environment is described by a complex spectral density or is at a very low temperature, approaches utilizing the exponential decomposition become very inefficient. Here, we utilize an alternative decomposition scheme for the bath correlation function based on Chebyshev polynomials and Bessel functions to derive a HEOM approach up to an arbitrary order in the environmental coupling. These hierarchical equations are similar in structure to the popular exponential HEOM scheme, but are formulated using the derivatives of the Bessel functions. The proposed scheme is tested up to the fourth order in perturbation theory for a two-level system and compared to benchmark calculations for the case of zero-temperature quantum Ohmic and super-Ohmic noise. Furthermore, the benefits and shortcomings of the present Chebyshev-based hierarchical equations are discussed. [ABSTRACT FROM AUTHOR]

In quantum transport across molecular junctions, time-dependent effects arise mainly due to interactions with external perturbations such as pulsed laser fields or fluctuating environments. While the calculation of the charge dynamics in such an open quantum system is a complex problem, it is highly relevant for engineering nanoscale devices. Several theoretical approaches to this problem including some based on quantum master equations, hierarchical schemes, or non-equilibrium Green's functions (NEGFs) rely on assuming a molecule-lead coupling composed of Lorentzian functions and a decomposition of the Fermi function. The underlying assumptions in this strategy lead to limitations in the functional form of the molecule-lead coupling and to an inefficiency at low temperatures. To overcome these restrictions, a Chebyshev expansion is applied to derive a set of coupled ordinary differential equations within the NEGF formalism. The numerical efficiency of this approach is independent of temperature and band structure of the electrodes. Moreover, since the scheme deals with a single particle basis set, it is possible to replace all auxiliary matrices present in the equations by vectors. Test setups for this new scheme include molecular junctions under the influence of strong time-dependent perturbations leading, for example, to coherent destruction of tunneling. [ABSTRACT FROM AUTHOR]

We theoretically investigate the electronic transport and Klein tunneling in AA-stacked bilayer graphene (AA-BLG) encapsulated by dielectric materials. Using the four-band continuum model, we evaluate the transmission and reflection probabilities along with the respective conductances. We find that the interlayer mass-term difference induced by the dielectric materials opens a gap in the energy spectrum and couples the upper and lower Dirac cones in AA-BLG. This cone coupling induces an inter-cone transport that is asymmetric with respect to the normal incidence in the presence of the asymmetric mass-term. The energy spectrum of the gapped AA-BLG exhibits electron-hole asymmetry that is reflected in the associated intra- and inter-cone transport channels. We also find that even though Klein tunneling exists in gated and biased AA-BLG, it is precluded by the interlayer mass-term difference and instead Fabry-Pérot resonances appear. [ABSTRACT FROM AUTHOR]

Here, we report on the structural, vibrational phonon, electrical, and magnetic properties of undoped strontium titanate SrTiO3, Ce doped Sr1−xCexTiO3, and (Ce, Fe) co-doped Sr1−xCexTi1−yFeyO3 samples synthesized through solid state reaction route. The Rietveld refined powder x-ray diffraction analysis confirmed the cubic Pm-3m phase in our as-synthesized samples. We observed grain size reduction in SrTiO3 from scanning electron micrographs due to the incorporation of Ce and Fe dopants. The sample purity in terms of chemical species identification has been confirmed from energy-dispersive x-ray spectroscopy. The characteristic phonon modes in our samples are identified using room temperature Raman spectroscopy and benchmarked against existing relevant experimental observations. The incorporation of Ce and Fe as substitutional dopants in SrTiO3 unit cell was confirmed from the absence of absorption at 480, 555, 580, and 1635 cm−1 band in Fourier transform infrared spectra. The 3% Ce doping in Sr0.97Ce0.03TiO3 sample may have induced ferroelectric order, whereas the undoped SrTiO3 (STO) revealed lossy paraelectric nature. In the case of (Ce = 3%, Fe = 10%) co-doped Sr0.97Ce0.03Ti0.90Fe0.10O3 sample, we observed ferromagnetic hysteresis with orders of magnitude enhancement in remnant magnetization and coercivity as compared to undoped STO sample. This long range robust ferromagnetic order may have originated from F-center mediated magnetic interaction. [ABSTRACT FROM AUTHOR]

In this study, a computational fluid dynamics model was employed to simulate the impact of a breaking wave on the foundation of an offshore wind turbine. The accuracy of the numerical simulation was validated in comparison with published experimental results for the Large Wave Channel (GWK) at Hannover, Germany. To understand the influence of the wave-breaking location on the monopile support structure, a series of shoaling waves with different spilling and plunging breaking wave types were considered in terms of the surf-similarity parameter ( ξ 0 ) and relative breaking distance ( x b ′ ). After processing the total wave load with an empirical mode decomposition method and a low-pass filter, the instantaneous nature of the slamming wave load generated by different breaking wave types was obtained. Subsequently, an exponential-type refined dynamic model was established to consider the characteristics of the filtered slamming wave load. ξ 0 and x b ′ were found to be dominant factors for the run-up phenomena, slamming characteristics, and wave-dependent parameters. The results demonstrated that these two coefficients can be applied to determine the nature of the run-up and slamming wave loads. [ABSTRACT FROM AUTHOR]

A comparative study on mechanical, thermodynamic, electronic, and optical properties has been performed on various compounds having an ABO3, where A = Ba, Ca, Sr and B = Ce, Ti, Zr, perovskite structure using first-principles calculations. These materials' properties have been thoroughly investigated for their ground states under the same computational parameters. The computed lattice parameters in the ground state agreed with other theoretical studies. Elastic moduli, ductility or brittleness, elastic anisotropy, mechanical stability, and stiffness of solid materials are studied. Enthalpy (H), entropy (S), and free energy (F) were reported from the vibrational properties of the materials. The temperature-dependent heat capacity and Debye temperature are investigated. The electronic band structure as a function of energy, of different perovskite structures at the ground state, is also studied. From this study, the ABO3 perovskite has emerged as the most promising material for applications in optoelectronics, photonics, and mechanical and thermoelectric devices. [ABSTRACT FROM AUTHOR]

The stretching of plasma membranes of cells and lipid bilayers of vesicles affects the physical properties of the membrane as well as the functions of proteins/peptides in the membranes. Here, we examined the effect of membrane tension on the rate constant of the transbilayer movement (kFF) of fluorescent probe-labeled lipids using a new method. Specifically, we recently reported [Hasan et al., Langmuir 34, 3349 (2018)] the development of a technique that employs giant unilamellar vesicles (GUVs) with asymmetric lipid compositions in two monolayers. In the present work, we found that the kFF greatly increased with tension without leakage of water-soluble fluorescent probes from the GUV lumen (i.e., without the formation of pores in the GUV membrane). We discussed the plausible mechanisms for the effect of tension on the transbilayer movement of lipids. As one of the mechanisms, we hypothesized that the transbilayer movement of lipids occurs through the lateral diffusion of lipids in the walls of hydrophilic pre-pores. [ABSTRACT FROM AUTHOR]

In the starting phases of continuously blowing under-expanded jets, this numerical study investigates the effect of co-flow ( U a U j ) (a) on the circulation and evolution of primary vortex ring (PVR) and (b) on the occurrence of Mach reflection, slipstream generation, and subsequent formation of counter rotating vortex rings (CRVRs). With increase in co-flow ( U a U j ), the PVR circulation gradually decreases. The size of supersonic PVR gradually decreases with increase in co-flow ( U a U j ), and at high magnitudes of co-flow ( U a U j ≳ 0.3), the supersonic PVR attains a circular shape. The strengths of embedded shock (ES) and vortex-induced shock are found to decrease with increase in co-flow ( U a U j ), and at high magnitudes of co-flow ( U a U j ≳ 0.3), these shocks may even cease to form inside the supersonic PVR. An increase in co-flow ( U a U j ) causes the expansion fan to become more and more narrow. This reduces the acceleration of the supersonic flow inside the inviscid core, thereby weakening the incident oblique shock (IOS), which in turn increases the pressure prevailing downstream of this shock inside the inviscid core. The increase in co-flow ( U a U j ) also leads to a simultaneous decrease in the pressures prevailing in front of the downstream marching PVR and Mach disk (MD) of the inviscid core due to the reduction in the strength of precursor shock. As the magnitudes of pressures prevailing in the upstream and downstream of Mach disk approach each other, hence, MD also weakens. This shows that with the increase in co-flow ( U a U j ), there is weakening of the different shocks (i.e., ES, IOS, and MD) involved in Mach reflection. This causes a reduction in the strength of the resulting slipstream, thereby affecting the formation of CRVR patterns. [ABSTRACT FROM AUTHOR]

Compared with the local correlation-based shear stress transport (SST) γ − Re θ transition model (where SST k − ω transport equations are coupled with intermittency γ and transitional momentum-thickness Reynolds number Re θ transport equations), relatively simple and convenient modifications are applied to the parent SST k − ω model for computing natural and separation-induced transitions over the hydrofoil at a low-Reynolds number (LRN). The curiosity toward hydrofoil performance at an LRN has been enhanced by increasing attention to autonomous marine systems, deserving numerical simulations for transitional flow using computational fluid dynamics. With the newly devised transitional SST (T-SST) model, the viscous sublayer blending function F 2 is slightly modified, and a stress-intensity parameter as a function of eddy-to-laminar viscosity ratio R T is introduced; intended formulations are plausible and have significant impacts on the transition prediction. Owing to the inherent potential for predicting bypass transition, two anisotropic versions of the v ¯ 2 − f (V2F) turbulence model are selected to evaluate their competencies in capturing separation-induced and natural transitions. Results demonstrate that natural transition prediction is more challenging than separation-induced transition for the V2F model. Nonetheless, the T-SST model performs consistently well in replicating both transitional phenomena. [ABSTRACT FROM AUTHOR]

A significant structural modification and enhancement of the electrical and magnetic properties with dilute substitution of Zr (≤1mol.%) in the Bi0.8La0.2Fe1-xZrxO3 system has been reported. A mixture of rhombohedral and orthorhombic phases was detected in these conventionally sintered ceramics. Transition from a leaky state to an insulating state was observed upon Zr substitution. This is the first time that a drop in the electrical conductivity as large as 6 orders of magnitude for doping as small as 0.25mol. % in bismuth ferrite systems has been reported. An investigation on the nature of this abrupt transition revealed the dominant role of defects. A proper consideration of possible defect reactions taking place during and after sintering satisfactorily accounts for the observed modulation in the electrical properties. Both AC and DC measurements indicate that, before Zr substitution, ptype hopping conduction prevails with an activation energy as low as ~0.57 eV, whereas the Zr substitution makes oxide ion migration the central mechanism for conduction with the activation energy of ~0.96-1.08 eV. In contrast to that, the magnetic properties of the compounds experience a more subtle effect; a gradual modification of saturation magnetization and coercivity with Zr substitution is observed. Curve fitting of the magnetic hysteresis loops not only allowed extraction of three separate contributions from the magnetic response but also helped to explain the effects of Zr on the magnetic properties. Modifications of structural characteristics and magnetic anisotropy of the samples are believed to be the primary driving force behind the improvement in the magnetic properties. [ABSTRACT FROM AUTHOR]

We introduce a new technique for designing quasi-optical, reflective-type spatial filters. The proposed filter is a reflective metasurface with a one dimensional, frequency-dependent phase gradient along the aperture. By careful design of each unit cell of the metasurface, the phase shift gradient provided by the adjacent unit cells can be engineered to steer the beam towards a desired, anomalous reflection direction over the passband region of the filter. Outside of that range, the phase shift gradient required to produce the anomalous reflection is not present and hence, the wave is reflected towards the specular reflection direction. This way, the metasurface acts as a reflective filter in a quasi-optical system where the detector is placed along the direction of anomalous reflection. The spectral selectivity of this filter is determined by the frequency dispersion of the metasurface’s phase response. Based on this principle, a prototype of the proposed metasurface filter, which operates at 10 GHz and has a bandwidth of 3%, is designed. The device is modeled using a combination of theoretical analysis using the phased-array theory and full-wave electromagnetic simulations. A prototype of this device is also fabricated and characterized using a free-space measurement system. Experimental results agree well with the simulations. [ABSTRACT FROM AUTHOR]

Flexible materials embedded with hard magnetic particles have recently gained widespread recognition as small-scale actuators due to their capacity to be a rapid and precise shape-shifting material. Strontium ferrite (SrFe12O19) particles have been shown as a great candidate for such applications, since it is an inert hard magnetic material that, in contrast to barium ferrite and neodymium, is also biocompatible. The preparation of such material is done by mixing the magnetic particles into the uncured elastomer (polydimethylsiloxane (PDMS)), in liquid form, and then pouring the mixture in a mold for curing. If the samples are subjected to a magnetic field during the curing process, chains of particles are formed in the direction of the applied field, thus creating an easy axis in this same direction. The magnetic properties of such composite cannot yet be found in literature. In this study, we analyzed three concentrations of strontium ferrite particles in PDMS under three field configurations, resulting in 9 different samples. The concentrations used were 1:1, 2:1, and 4:1 ratios of PDMS to strontium ferrite per weight. All three types of samples were cured either in a zero magnetic field, or over the north pole of a neodymium permanent magnet, or over the side of said magnet. A biaxial vibrating sample magnetometer (VSM) was used to measure hysteresis curves parallel and perpendicular to the curing field. The samples cured in a field show a squareness ratio of up to 0.94 while the samples cured in zero field, only close to 0.5. The samples cured in a field show a magnetic anisotropy with an easy axis parallel to the curing field. Harvesting these modified properties, a mobile robot manufacturing method is proposed that bypasses the need of applying a high intensity magnetic field. [ABSTRACT FROM AUTHOR]

Self-consistent numerical modeling was performed of a micro-glow discharge in helium self-organizing into 3D symmetrical patterns over a metallic cathode in the range of pressures of 600 to 800 Torr, for a constant gas temperature of 300 K. The 3D model employed comprised of Poisson's equation, equations of conservation of flux density, transport, and reactions, for a single ion species and electrons, assuming the drift-diffusion and local-field approximations. Multiple solutions to the model were found for the same range of discharge current, describing modes with different configurations of cathode spots. Stable transitions from the fundamental mode to the modes corresponding with self-organized patterns were identified as current was reduced from a discharge in the abnormal glow. At 600 Torr, the self-organized patterns comprised of symmetrically ordered, similarly sized, circular spots of current density that closely resembled patterns already identified in experiments and by modeling at lower pressures (in, e.g., xenon). At atmospheric pressure and above, the patterns emerged with one large central circular spot with small spots emerging uniformly around its periphery, resembling the shape of a gear. Modeling was also performed at atmospheric pressure for two constant temperatures above 300 K, of 600 and 1150 K. Qualitative changes to the patterns of current density on the cathode were observed. At 600 K, the first stable self-organized mode manifested similarly sized circular spots of current density on the cathode. At 1150 K, no self-organized patterns of spots emerged. The results indicate that self-organized patterns may emerge in atmospheric pressure micro-glow discharges but that gas temperature should be considered in an experiment attempting to characterize the phenomenon. [ABSTRACT FROM AUTHOR]