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For atmospheric argon RF dielectric barrier discharges, a self-consistent one-dimensional fluid model based on the drift-diffusive approximations of the particles is established to investigate the role of the neutral gas temperature on the discharge process and the plasma characteristics. A finite difference method is used to solve numerically the model, and the numerical results are obtained for the cases that the neutral gas temperature varies from 300 to 600 K. It shows that an increase in the neutral gas temperature causes a decrease in the ionization rate peak and a decrease in the plasma density, but the electric field and the electron temperature do not change very much. Moreover, the discharge mode transition from α mode to α-γ mode occurs because the growing ion flux induces more secondary electron flux, even if the ions entering the sheaths decrease. In addition, the ground state ionization and the ground state excitation are the main collisions in the argon discharges. When metastable atoms are focused on, the three-body quenching is also an important collision progress. [ABSTRACT FROM AUTHOR]

This study utilized high-speed camera and large eddy simulation methods to explore the cavitating flow mechanisms and turbulence structures of R134a refrigerant inside a Venturi tube under varying cavitation numbers (CNs). Data-driven modal analysis approaches, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), were introduced to identify and extract the energy hierarchy and transient characteristics within the cavitating flow. The analysis of grayscale images indicated that the cavitating flow gradually transitioned from quasi-periodic to unsteady flow as the CN decreased, and the severity of cavitation correlates with lower peak frequencies. The POD analysis facilitated the extraction of coherent structures in the cavity's temporal evolution, and the results indicate that the quasi-ordering shedding and collapse of large-scale cavity clouds predominantly occur under low cavitation intensity conditions. As the CN increases, the influence of small-scale cavity shedding becomes more significant. The first 30 most energetic modes occupied over 75% of the entire energy, and they were used to reconstruct the cavitating flow, achieving good consistency with transient flow snapshots. Additionally, the DMD results of the cavitating flow yield three frequency spans, including several prominent characteristic frequencies. These spans are closely linked to the cavity cloud structures of varying scales, unveiling the structural characteristics of unsteady cavitating flow. [ABSTRACT FROM AUTHOR]

Medical devices are becoming more and more significant in our daily life. For implantable medical devices, good biocompatibility is required for further use in vivo. Thus, surface modification of medical devices is really important, which gives a wide application scene for a silane coupling agent. The silane coupling agent is able to form a durable bond between organic and inorganic materials. The dehydration process provides linking sites to achieve condensation of two hydroxyl groups. The forming covalent bond brings excellent mechanical properties among different surfaces. Indeed, the silane coupling agent is a popular component in surface modification. Metals, proteins, and hydrogels are using silane coupling agent to link parts commonly. The mild reaction environment also brings advantages for the spread of the silane coupling agent. In this review, we summarize two main methods of using the silane coupling agent. One is acting as a crosslinker mixed in the whole system, and the other is to provide a bridge between different surfaces. Moreover, we introduce their applications in biomedical devices. [ABSTRACT FROM AUTHOR]

Gas spark switches had been applied extensively in the field of pulse power technology on account of the advantages of a simple structure, short breakdown time, and high through-current capability. This paper investigates the streamer breakdown process in a two-electrode switch in a nitrogen environment under atmospheric pressure using a numerical method. First, a two-dimensional fluid simulation was carried out for the streamer generated under the negative and positive trigger voltages, and the difference in the breakdown mechanism in the two modes was analyzed. The study showed that when a negative trigger voltage is applied to the rod electrode, a negative streamer from the cathode to the anode will first be formed, and then a positive streamer from the anode to the cathode will be formed. When a positive trigger voltage is applied to the rod electrode, the streamer propagation mechanism is significantly different from that obtained when a negative voltage is applied. In this case, the breakdown mode is a cathode-directed streamer. Finally, we investigated the effect of circuit parameters on the breakdown process. The time scale of breakdown varies greatly with the capacitance. The significant difference in the breakdown process may come from the charging process of the capacitor. The larger the capacitance is, the slower the charging process will be. [ABSTRACT FROM AUTHOR]

Phase change memory has been considered as the next generation in non-volatile electronic data storage. The property modulation of such materials by the doping of rare-earth elements has drawn a lot of attention, which motivates us to search for the optimal dopants and reveal the underlying mechanisms. Here, we investigate the role of Gd as a dopant in Ge2Sb2Te5, which exhibits higher crystalline resistance and better thermal stability and antioxidant capacity than the undoped counterpart. Moreover, Gd dopants suppress both the processes of phase transition and grain growth. The crystalline structure remains unchanged with Gd dopants and vacancies are randomly distributed. Furthermore, the bonding mechanism was theoretically investigated. In the amorphous state, Gd atoms modify the local structures around Ge, Sb, and Te atoms. The large coordination number of Gd and the "Gd–Te distorted pentagonal bipyramidal-like" structure can be attributed to the good thermal stability. These microscopic findings figure out some of the key issues about the bonding mechanism, electrical properties, and crystallization behaviors of Gd doped phase change memory materials, which could be useful for storage devices. [ABSTRACT FROM AUTHOR]

To reveal if universal rules may exist in face centered cubic (FCC) concentrated solid solution (CSS) alloys for strength and plastic deformation at room and cryogenic temperatures, we select a FCC CSS superalloy Haynes 188 to demonstrate the deformation mechanisms from atomic to micrometer scales. In FCC CSS alloys, the yield strength (YS) is intrinsically determined by atomic/modulus mismatches and affected extrinsically by grain size; the tensile strength and elongation to fracture (EF) are governed by the plastic process where low stacking fault energy is beneficial. Moreover, almost all CSS alloys show that YS and EF increase simultaneously with the decrease in the temperature. Our findings may expand alloy application and can be used as a design strategy for stronger and tougher alloys. [ABSTRACT FROM AUTHOR]

Imaging of optical phenomena at the sub-nanometer scale can offer fundamental insights into the electronic or vibrational states in atomic-scale defects, molecules, and nanoparticles, which are important in quantum information, heterogeneous catalysis, optoelectronics, and structural biology. Several techniques have surpassed the traditional Abbe diffraction limit and attained spatial resolutions down to a few nanometers, but sub-nanometer scale optics has remained elusive. Here, we propose an approach that combines spectrally specific photoabsorption with sub-nanometer scale resolution transmission electron microscopy (TEM) of photoexcited electrons. We first estimate the signal level and conditions required for imaging nanoscale optical phenomena in core-shell quantum dots (QDs) like CdS/CdTe. Furthermore, we show the possibility of imaging photoexcited states of atomic-scale defects in a monolayer hexagonal boron nitride (h-BN) using ab initio and high resolution (HR)TEM simulations. The ability to directly visualize photoexcited states at the sub-nanometer scale opens opportunities to study properties of individual quantum dots and atomic defects. [ABSTRACT FROM AUTHOR]

High temperature materials usually serve under extreme conditions. In order to ensure the safety and reliability of industrial application, it is very significant to clarify the microstructural evolution and mechanical properties at high temperature. The in situ experiment combining mechanical tensile testing and heating in the scanning electron microscope (SEM) is a feasible method to study the relationship between the microstructure, mechanical properties, and temperature. However, it was challenging to acquire images of high quality when the temperature exceeded 800 °C due to the effect of thermal electrons and the instability of loading conditions at high temperature. In this study, a mini-tensile apparatus was devised and installed in an ordinary SEM, which can achieve a stable loading of 0–2200 N and obtain high quality images in the temperature range of 1150 °C. A highly efficient heat source with multi-layer thermal insulation was designed to prevent the other parts of the apparatus from being affected by high temperature. A symmetrical tensile structure was developed to ensure that the region of interest was always within the field of view of the microscope during testing. Thermal electrons were suppressed to ensure that the sample can be clearly distinguished at 1150 °C. In order to ensure the testing reliability, standard carbon steel was used to calibrate the instrument. Finally, a Ni-based single crystal superalloy, as an example, was tested using this in situ tensile testing system at 1150 °C to verify the main functions and reliability of the apparatus. [ABSTRACT FROM AUTHOR]

Amorphous Ge1-xMnx magnetic semiconductor films with high Mn concentrations were prepared on liquid-nitrogen (LN2)-cooled glass substrates by ultrahigh vacuum thermal coevaporation. Hysteresis loops measured at 5 K show coexistence of ferromagnetism and paramagnetism. The maximum Curie temperature of 220 K was found in Ge0.48Mn0.52 film. Moreover, exchange bias occurs in magnetization hysteresis loops for samples with higher Mn concentrations, which can be explained by the antiferromagntic exchange coupling between ferromagnetic phase and antiferromagnetic phase. All the Ge1-xMnx magnetic semiconductor films show semiconducting transport behavior and anomalous Hall effects below the Curie temperature, indicating carrier-mediated ferromagnetism. [ABSTRACT FROM AUTHOR]

We design and demonstrate what we called shape-preserving "optical pin beams" (OPBs) that possess stable wavefronts against diffraction and ambient turbulence during free-space long distance propagation. Theoretically, we show that a laser beam passing through properly assembled phase elements paired with opposite transverse wavevectors can morph quickly into a stable optical field, exhibiting "self-focusing" dynamics during propagation without optical nonlinearity. The overall shape of such OPBs remains invariant, while their width can in principle be inversely proportional to the propagation distance, in contradistinction to conventional Bessel beams and radially symmetric Airy beams. Experimentally, utilizing a single photoetched mask, we demonstrate efficient generation and robust propagation of the OPB through atmospheric turbulence beyond kilometer distances. We envisage exciting opportunities arising from such OPBs, especially when propagation through turbulent environments is unavoidable. [ABSTRACT FROM AUTHOR]

Biomass (straw) gasification with oxygen-enriched air was studied in a lab-scale entrained-flow gasifier. Effects of oxygen concentration (OC), equivalence ratio (ER), and reactor temperature on the produced gas composition, gasification index and tar yield were investigated. Compared with air, oxygen-enriched air as gasifying agent was beneficial to increase the H2 content, H2/CO ratio, and lower heating value (LHV) of the gas, and decrease the yield of tar contained in the flue gas. The H2/CO reached 1 when OC was 50%, which was an optimal value for dimethyl ether, methanol, and higher alcohol production in the process of alcohols synthesis. A reference value of OC was given approximately to 40% according to economic consideration. A reference value of ER was given around 0.25 when OC was 40%, achieved a relatively high LHV of 8.2 MJ/Nm3 and low tar yield of 2.6 mg/g. In addition, high reaction temperature could improve both gas quality and gasification indexes significantly. The better gasification performance achieved in the paper verified that the oxygen-enriched gasification was a good option for the improvement of direct air gasification. [ABSTRACT FROM AUTHOR]

In situ electrical measurement experiments were carried out in individual SiC nanowires (NWs) subjected to tensile strain using a transmission electron microscope. Fracture strain approaching 10% was achieved for a diamond-structure SiC NW with a <111> direction. With an increase in the tensile strain, the conductance increased monotonously. The current rate of increase remained constant prior to fracture. The calculated piezoresistance coefficient of this SiC NW was -1.15 × 10-11 Pa-1, which is similar to the coefficient of the bulk material. Our results indicate that these SiC NWs can be used as pressure sensors even in very high-pressure environments. [ABSTRACT FROM AUTHOR]

A detailed in situ investigation of dislocation processes has been rare for nanograined materials with grain sized near or less than 10 nm. Here, we report a time-resolved and atomic-scale in situ transmission electron microscopy observation of the nucleation, motion, annihilation, and storage of full dislocations in nanograins with diameters less than ∼10 nm. Annihilation of dislocation dipoles appears to be a major contributor to the reduction in dislocation density, in addition to annihilation at grain boundary sinks. The accumulation of a high density of dislocations inside nanograins is found to be possible when they are surrounded by neighboring grains. [ABSTRACT FROM AUTHOR]

The Co valence state and the location of Co dopant atoms in ZnO:Co thin films revealing anomalous Hall effect below 50 K have been determined by electron energy-loss spectroscopy (EELS) measurements and atom location by channeling enhanced microanalysis (ALCHEMI), respectively. The method of ALCHEMI-EELS to investigate the dopant in materials was brought. It was used to determine that the intrinsic ferromagnetism in ZnO:Co thin films derives from the +2 Co which substitute for Zn atoms at Zn sites in the ZnO matrix. The divalent Co state in ZnO:Co has been unambiguously proven by modeling the corresponding EELS data. [ABSTRACT FROM AUTHOR]

We report the superconductivity near 35 K in magnesium-doped boron nanowires, BMgx(x≈0.1), which were synthesized via the reaction of well-aligned amorphous boron nanowires with magnesium vapor in vacuum-sealed quartz tubes. Electron microscopy and electron energy-loss spectroscopy reveal that the BMgx nanowires have an amorphous structure with magnesium content of ∼10 at. %, far less than that in crystalline MgB2, and magnesium distributes uniformly in the nanowires. Our results provide a base material not only for low-temperature nanodevice applications but also for theoretical investigations on the mechanism of its superconductivity. [ABSTRACT FROM AUTHOR]

In this letter, we report the electrical properties of hollow polyaniline (PANI) microspheres. β-naphthalene sulfonic acid (NSA) and salicylic acid (SA) doped PANI microspheres were synthesized by a self-assembly method. The room-temperature conductivity is 8.6×10[sup -2] S/cm for PANI–NSA microspheres (0.8–2 μm in outer diameter) and 5.6×10[sup -4] S/cm for PANI–SA microspheres (3–7 μm in outer diameter). The conductivity of an individual PANI–SA microsphere is measured directly by a two-probe technique, about 8×10[sup -2] S/cm (which is two orders of magnitude higher than that of a PANI–SA microsphere’s pellet). The measurements of conductivity, I–V curve, and magnetoresistance demonstrate that the electrical properties of PANI microspheres are dominated by the intersphere contacts due to the sample’s microscopic inhomogeneity. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

GaN films were grown in pairs on two opposite c faces of Al[sub 2]O[sub 3] substrate by low-pressure metal-organic vapor phase epitaxy, and studied by scanning electron microscopy and converged beam electron diffraction. It is found that GaN film on the c-Al[sub 2]O[sub 3] whose c face is forward to its crystal seed has [0001] polarity, and the other film on the c-Al[sub 2]O[sub 3] whose c face is backward to its crystal seed has [0001¯] polarity. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This letter reports the effect of distortion of crystal structure on the superconductivity of Y-Ba-Cu-O compounds. The result shows that the cooling rate is responsible for the superconductivity in the range of LN2 temperature with the same composition and heat treatment temperature. The changes of intensity of three dominant x-ray diffraction peaks caused by structural distortion in the perovskite orthorhombic phase may become an important criterion of superconductivity. [ABSTRACT FROM AUTHOR]

The letter presents an explanation for the reversal of peak intensities in x-ray diffraction patterns of Y-Ba-Cu-O compounds with the same nominal compositions but distinctive properties of superconductivity due to different cooling conditions. Structural differences between the phases caused by different lattice distortions as well as the effect of these distortions on superconductivity are also discussed. [ABSTRACT FROM AUTHOR]

By in situ uniaxial-tensile tests with dynamic and atomic scale observation, we report the quantitative investigation of strain-induced deformation-twinning process through incoherent twin boundary propagation in nanocrystalline Au. The consecutive and quantitative strain maps revealed that a strong compressive strain, up to 5.8%, was formed. A screw-rotation twinning mechanism by consecutive and collective screw-rotations of triple-partials along a [111] screw-axis is proposed. This twin generates a macro-strain of 0.707, same as the conventional shear twins, but in a helical manner. [ABSTRACT FROM AUTHOR]

A technique, laser vaporization by ablating at a solid target in the vapor phase, is developed to produce encapsulated titanium nanocrystals. By vaporizing sponge titanium in benzene vapor, the single titanium crystals encapsulated in carbon nanocages have been synthesized in good yields. The sizes of the encapsulated crystals are around 5-15 nm and the numbers of the wrapped graphitic layers are on the order of 3-10 layers. Characteristic lattice spacings and angles observed by high-resolution transmission electron microscopy identify two phases of the nanocrystals inside the carbon onion cavities as α-Ti and β-Ti. The latter has never been stable below 850 °C until the experiment. The encapsulated titanium crystals adsorbed a large amount of hydrogen released in the synthesis. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Microstructures of Si nanowires (SiNW’s) synthesized using laser ablation were investigated by transmission electron microscopy. The SiNW’s have a high density of structural defects, which may play an important role in the formation of SiNW’s and in the determination of the morphology of the nanowires. A model for the growth mechanism of the SiNW’s was discussed on the basis of the observation. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]