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Achieving long‐term device stability is one of the most challenging issues that impede the commercialization of perovskite solar cells (PSCs). Recent studies have emphasized the significant role of the cathode interfacial layer (CIL) in determining the stability of inverted p‐i‐n PSCs. However, experimental investigations focusing on the influence of the CIL on PSC degradation have not been systematically carried out to date. In this study, a comparative analysis was performed on the PSC device stability by using four different CILs including practical oxides like ZnO and TiOx. A new implemented co‐doping approach was found to results in high device performance and enhanced device stability. The PSC with a thick film configuration of chemically modified TiOx CIL preserves over 77 % of its initial efficiencies of 17.24 % for 300 h under operational conditions without any encapsulation. The PSCs developed are among the most stable reported for methylammonium lead iodide (MAPbI3) perovskite compositions., In for the CIL: Highly stable inverted perovskite solar cells (PSCs) are assembled by using chemically modified titanium suboxide (TiOx) as the cathode interfacial layer (CIL). Codoping enhances the electrical properties of the TiOx CIL, providing better inner encapsulation with thick film configuration. The PSCs exhibit significantly improved operational stability, maintaining >77 % of their initial efficiencies for up to 300 h without encapsulation.

An experimental investigation into the nonlinear optical properties of rhenium diselenide (ReSe2) was conducted at a wavelength of 1.9 μm using the open-aperture and closed-aperture Z-scan techniques for the nonlinear optical coefficient (β) and nonlinear refractive index (n2) of ReSe2, respectively. β and n2 measured at 1.9 μm were ~ − 11.3 × 103 cm/GW and ~ − 6.2 × 10–2 cm2/GW, respectively, which to the best of our knowledge, are the first reported measurements for ReSe2 in the 1.9-μm spectral region. The electronic band structures of both ReSe2 and its defective structures were also calculated via the Perdew–Becke–Erzenhof functional to better understand their absorption properties. A saturable absorber (SA) was subsequently fabricated to demonstrate the usefulness of ReSe2 for implementing a practical nonlinear optical device at 1.9 μm. The 1.9-μm SA exhibited a modulation depth of ~ 8% and saturation intensity of ~ 11.4 MW/cm2. The successful use of the ReSe2-based SA for mode-locking of a thulium–holmium (Tm–Ho) co-doped fiber ring cavity was achieved with output pulses of ~ 840 fs at 1927 nm. We believe that the mode-locking was achieved through a hybrid mechanism of saturable absorption and nonlinear polarization rotation.

Metallic 2D materials can be promising saturable absorbers for ultrashort pulsed laser production in the long wavelength regime. However, preparing and manipulating their 2D structures without layer stacking have been nontrivial. Using a combined experimental and theoretical approach, we demonstrate here that a metallic titanium carbide (Ti3C2Tx), the most popular MXene 2D material, can have excellent nonlinear saturable absorption properties even in a highly stacked state due to its intrinsically existing surface termination, and thus can produce mode-locked femtosecond pulsed lasers in the 1.9-μm infrared range. Density functional theory calculations reveal that the electronic and optical properties of Ti3C2Tx MXene can be well preserved against significant layer stacking. Indeed, it is experimentally shown that 1.914-μm femtosecond pulsed lasers with a duration of 897 fs are readily generated within a fiber cavity using hundreds-of-layer stacked Ti3C2Tx MXene saturable absorbers, not only being much easier to manufacture than mono- or few-layered ones, but also offering character-conserved tightly-assembled 2D materials for advanced performance. This work strongly suggests that as-obtained highly stacked Ti3C2Tx MXenes can serve as superb material platforms for versatile nanophotonic applications, paving the way toward cost-effective, high-performance photonic devices based on MXenes.

The thickness of the film produced by spin coating is different from the theoretically calculated thickness based on the Newtonian fluid equation. In this study, the rotational time and rotational speed (in revolutions per minute [RPM]) were used as the control parameters, and the thickness differences between the actual and theoretical results were analyzed based on statistical analyses. Furthermore, we investigated the effects of the aging time (i.e., time after spin coating before heat treatment curing) independently from the parameters of the theoretical equation for spin coating of Newtonian fluids mentioned above. The thickness of the film formed by the spin coater within a period of 300 s was smaller than the theoretically predicted thickness at all rotation speeds irrespective of aging. Based on statistical analyses of the measured thickness values, we confirmed that rotational speeds in the range of 2000–6000 RPM within a period of 300 s did not yield thickness differences owing to aging time. However, below 1500 RPM, the thickness without aging time was smaller than the thickness with aging time. In addition, the thicknesses of the edge and center of the substrate were unequal but became uniform as the aging time increased. Additionally, the estimated thickness based on the constructed plots yielded completely different results from those predicted by the existing equation about Newtonian fluids. Based on the analyses of the thickness as a function of aging time and speed, we confirmed that the aging time—which was not accounted for in the conventional equation—was the parameter that primarily affected the thickness.

With the increasing demands of indoor air quality monitoring, highly sensitive and selective gas sensor arrays consisting of metal oxide semiconductors have been increasingly studied. As an effective strategy to obtain the desired performance, noble metal functionalization is frequently chosen owing to its target-specific sensing mechanisms. However, the lack of a comprehensive analysis on the sensing mechanisms of different combinations of metal oxides and noble metals limit the versatility of these sensor arrays for use in selective gas sensor arrays. In this study, we fabricate a 3 × 3 gas sensor array to obtain a reliable comparison of the sensing mechanism through the use of three metal oxides—WO3, SnO2 and NiO—in three different nanostructure forms: a thin film and dome-like nanostructures with and without Au nanoparticle (NP) decoration. The responses of the sensor arrays to four target gases (CH3COCH3, C6H5CH3, NH3, and H2S) are generally enhanced by the dome-like nanostructure and show distinctively enhanced responses when the sensors are decorated with Au NPs. Moreover, the dome-like SnO2 with Au NPs shows an increase of up to 121 times for C6H5CH3 compared with the pristine SnO2 thin film. Additionally, the sensitization effects of Au NPs depend on the types of metal oxides and gases, which improve the gas discrimination capability by diversifying the gas selectivity of the sensor units in the array. The prepared sensor array can distinguish four target gases by principal component analysis (PCA). The contributions of different enhancement mechanisms, which are dependent on the gases and metal oxides, are investigated by comparing the activation energy of each gas response with and without Au. The comparison among the chosen gases reveals that the decoration of Au NPs is effective for C6H5CH3 and NH3 regardless of the type of metal oxide. Among the metal oxides, the effects of Au NPs on gas responses are in the order of SnO2, NiO, and WO3, in which the energy level difference between the Au NPs and metal oxide are 0.2, 0.1, and −0.6 eV, respectively. These results confirm that the dominant enhancement mechanism of Au NPs for each combination of gases and metal oxide is a decrease in activation energy. Therefore, this study provides a systematic understanding of the sensitization mechanism of Au NPs on metal oxides toward gases for the fabrication of selective gas sensor arrays.

Amine-containing polyelectrolytes such as polyethyleneimine (PEI) are commonly used as cathode interfacial materials (CIMs); however, they are rarely found in non-fullerene acceptor (NFA) organic solar cells due to undesirable chemical reactions between PEI and NFAs. Unveiling the nature of these chemical interactions and developing chemically stable amine-containing polyelectrolytes is inevitable for achieving highly efficient and stable NFA organic solar cells. Herein, the reaction between PEI and 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (INCN)-based NFAs was investigated using a model system. 15N-isotope labeling experiments and 2D nuclear magnetic resonance (NMR) studies revealed that the products were generated by the Michael addition reaction and existed as the keto–enol tautomers. Based on the identified undesirable reaction, we developed a series of functionalized PEIs that are compatible with INCN-based NFAs by protecting the reactive amine functional groups. Highly efficient and stable NFA organic solar cells were successfully fabricated by the use of functionalized PEIs with broad work function tunability and improved chemical stability, which led to NFA organic solar cells with high power conversion efficiency (PCE) values of over 15% and thermally stable device operation for more than 360 hours at 100 °C.

Various redox-active organic molecules can serve as ideal electrode materials to realize sustainable energy storage systems. Yet, to be more appropriate for practical use, considerable architectural engineering of an ultrathick, high-loaded organic electrode with reliable electrochemical performance is of crucial importance. Here, by utilizing the synergetic effect of the non-covalent functionalization of highly conductive non-oxidized graphene flakes (NOGFs) and introduction of mechanically robust cellulose nanofiber (CNF)-intermingled structure, a very thick (≈ 1 mm), freestanding organic nanohybrid electrode which ensures the superiority in cycle stability and areal capacity is reported. The well-developed ion/electron pathways throughout the entire thickness and the enhanced kinetics of electrochemical reactions in the ultrathick 5,10-dihydro-5,10-dimethylphenazine/NOGF/CNF (DMPZ-NC) cathodes lead to the high areal energy of 9.4 mWh·cm−2 (= 864 Wh·kg−1 at 158 W·kg−1). This novel ultrathick electrode architecture provides a general platform for the development of the high-performance organic battery electrodes.

We report the first investigation results of the nonlinear optical properties of As2Te3. More specifically, the nonlinear optical absorption properties of the prepared α-As2Te3 were investigated at wavelengths of 1.56 and 1.9 μm using the open-aperture (OA) Z-scan technique. Using the OA Z-scan technique, the nonlinear absorption coefficients (β) of α-As2Te3 were estimated in a range from (− 54.8 ± 3.4) × 104 cm/GW to (− 4.9 ± 0.4) × 104 cm/GW depending on the irradiance of the input beam at 1.56 μm, whereas the values did from (− 19.8 ± 0.8) × 104 cm/GW to (− 3.2 ± 0.1) × 104 cm/GW at 1.9 μm. In particular, the β value at 1.56 μm is an order of magnitude larger than the previously reported values of other group-15 sesquichalcogenides such as Bi2Se3, Bi2Te3, and Bi2TeSe2. Furthermore, this is the first time report on β value of a group-15 sesquichalcogenide at a 1.9-μm wavelength. The density functional theory (DFT) calculations of the electronic band structures of α-As2Te3 were also conducted to obtain a better understanding of their energy band structure. The DFT calculations indicated that α-As2Te3 possess sufficient optical absorption in a wide wavelength region, including 1.5 μm, 1.9 μm, and beyond (up to 3.7 μm). Using both the measured nonlinear absorption coefficients and the theoretically obtained refractive indices from the DFT calculations, the imaginary parts of the third-order optical susceptibilities (Im χ(3)) of As2Te3 were estimated and they were found to vary from (− 39 ± 2.4) × 10–19 m2/V2 to (− 3.5 ± 0.3) × 10–19 m2/V2 at 1.56 μm and (− 16.5 ± 0.7) × 10–19 m2/V2 to (− 2.7 ± 0.1) × 10–19 m2/V2 at 1.9 μm, respectively, depending on the irradiance of the input beam. Finally, the feasibility of using α-As2Te3 for SAs was investigated, and the prepared SAs were thus tested by incorporating them into an erbium (Er)-doped fiber cavity and a thulium–holmium (Tm–Ho) co-doped fiber cavity for both 1.5 and 1.9 μm operation.

MoO3 has potential advantages in price and weight over more widely studied WO3 for electrochromic devices, but it typically suffers from inferior electrochromic performance. Here, it is demonstrate...

Physicochemical properties between colloidal engineered nanomaterials (ENMs) and aerosols released from consumer spray products were characterized. A dynamic light scattering (DLS), transmission electron microscopy (TEM), and inductively coupled plasma mass spectrometer (ICP-MS) were used to evaluate the suspended ENMs in the products. Direct-reading instruments, TEM, and ICP-MS were used to characterize the properties of aerosolized ENMs. The aerosolized organic compounds with ENMs were assumed to be vaporized for a short time after spraying. The median diameter of ENMs in product solutions measured by DLS was about 200-350 nm, while individual particle was confirmed from 3 to 50 nm by TEM. The size of aerosolized ENMs was ranged from 7 to 44 nm, and their aggregates were about 100-1000 nm in near distance. Some inorganic substances including raw nanomaterials were also found in the aerosol. The particles released from the propellant sprays were identified in far distance, while they were not found in far distance when pump sprays were used. The number concentration from the propellant sprays increased up to 6000 particles/cm3 /g at near distance and dispersed to far distance, while the most of droplets emitted from pump sprays were settled down near sprayer's location. We found other metals besides labeled ENMs are included in each product and the characteristics of the particles are different when they are sprayed.

Recent breakthroughs in molecular design have allowed for remarkable achievement in the field of non-fullerene acceptor (NFA)-based organic solar cells (OSCs) with high power conversion efficiencies (PCEs) of over 15%. However, despite such promising advances, the inferior stability of OSCs under operating conditions remains a prominent challenge that must be overcome for their practical realization. Here, versatile ternary photoactive systems with simultaneously enhanced efficiency and photostability are developed by introducing a small amount of fullerene (PC71BM) into a narrow band gap NFA-based bulk heterojunction nanocomposite (PTB7-Th:IEICO-4F); this approach leads to an enhanced PCE of 10.55% and a prolonged lifetime, retaining approximately 80% of the initial PCE after 500 h of operation under continuous illumination. Based on the energy levels and surface energies of the component materials, cascade energetic alignment facilitates electron transfer without trapping. The PTB7-Th/PC71BM interface provides an energy barrier to suppress recombination between holes in PTB7-Th and electrons in IEICO-4F. Moreover, a small amount of PC71BM promotes favorable molecular packing and orientation of IEICO-4F, leading to enhanced electron mobility and balanced charge transport. A study using transient absorption spectroscopy reveals that the ternary blend effectively suppresses the evolution of charge recombination.

The ternary chalcogenide, ZnIn2S4, is known to exhibit various polymorphic expressions: from the cubic spinel phase to various polytypic layered hexagonal structures, commonly known as α, β, IIa, a...

An efficient method for the formation of hexagonal disk shape C60 crystals at desired positions on a solid substrate has been achieved. The detailed growth behavior was studied through in-situ observation and series of control experiments. Our position selective growth technique enabled a fabrication of bottom electrode type C60 single crystal devices which exhibited n-type field-effect transistor behavior and photo response. Moreover, the C60 single crystal devices were further exploited to study alkali metal doped C60 crystal and its superconductivity.

In recent years, three-dimensional (3-D) printing has presented a new manufacturing paradigm and attracted considerable attention since it allows for products to be fabricated as solid objects by printing successive layers of material following instructions produced through computer-aided design. Here, for the first time, the 3-D printing technology based on fused deposition modeling is demonstrated to be readily useful in the fabrication of a fiberized saturable absorber (SA) intended for use in ultrafast mode-locking of an all-fiberized laser. The fiberized SA was fabricated on a side polished fiber platform by printing a low-cost composite of graphene and polylactic acid (PLA). The insertion loss and modulation depth of the fabricated SA were measured to be ∼3.8 and 1.2 dB, respectively. The saturation power and the modulation depth for the transverse electric (TE) mode were estimated to be ∼16 W and ∼2.2% , respectively, while the values for the transverse magnetic (TM) mode were ∼24 W and ∼1.5%, respectively. Using the fabricated SA in an erbium fiber ring cavity, stable femtosecond soliton pulses was readily produced at 1560.2 nm. To the best of the authors’ knowledge this is the first experimental demonstration using 3-D printing technology to implement a fiberized saturable absorber.

It is generally recognized that most nosocomial infections are spread by exposure to expelled particles at close range (usually within 1 m) or through contact. Although the Korea Centers for Disease Control established a 2-m cut-off for transmittance from patients during the Middle East Respiratory Syndrome (MERS) outbreak in Korea in 2015, questions have been raised regarding possible infection due to aerosols transported beyond this distance. The aim of this study was to characterize cough-generated aerosol emissions from cold patients and to determine the transmission distance of cough particles in indoor air. The study was conducted using subjects with acute upper respiratory infections. The number and size distribution of the particles generated from each cough were measured after participants coughed into a stainless steel chamber in a clean room. The total particle concentration was measured for each subject in the near field ( 2 m). The number of particles emitted by the cough of an infected patient was 560 ± 5513% greater than that generated by patients after recovery (P < 0.001). The number of particles was also significantly higher (P < 0.001) than the background concentration when infected patients were coughing, even in the far field. These results suggest that the 2-m cut-off should be reconsidered to effectively prevent airborne infections.

In this paper, we present GradPIM, a processing-in-memory architecture which accelerates parameter updates of deep neural networks training. As one of processing-in-memory techniques that could be realized in the near future, we propose an incremental, simple architectural design that does not invade the existing memory protocol. Extending DDR4 SDRAM to utilize bank-group parallelism makes our operation designs in processing-in-memory (PIM) module efficient in terms of hardware cost and performance. Our experimental results show that the proposed architecture can improve the performance of DNN training and greatly reduce memory bandwidth requirement while posing only a minimal amount of overhead to the protocol and DRAM area., Accepted to HPCA 2021

This study reports a Q-switching-based, 2058-nm holmium (Ho) fiber laser incorporating a saturable absorber (SA) based on graphene oxide (GO). The SA was prepared with a side-polished fiber, while GO particles were deposited onto the fiber-polished surface to realize an all-fiber SA. A continuous-wave thulium-doped all-fiber laser, which was configured with a master-oscillator power-amplifier (MOPA) structure, was constructed as a pumping source. By inserting the fabricated SA into an all-fiber ring resonator based on 1-m length of Ho-doped fiber, Q-switched pulses could readily be obtained at a wavelength of 2058 nm. The pulse width was observed to vary from 2.01 to 1.56 &mu, s as the pump power was adjusted from ~759 to 1072 mW, while the repetition rate was tunable from 45.56 to 56.12 kHz. The maximum values of average optical power and pulse energy were measured as ~11.61 mW and 207.05 nJ, respectively, at a ~1072 mW pump power.

Much of what is known about high-temperature cuprate superconductors stems from studies based on two surface analytical tools, angle-resolved photoemission spectroscopy (ARPES) and spectroscopic imaging scanning tunneling microscopy (SI-STM). A question of general interest is whether and when the surface properties probed by ARPES and SI-STM are representative of the intrinsic properties of bulk materials. We find this question is prominent in thin films of a rarely studied cuprate DBCO. We synthesize DBCO films by oxide molecular beam epitaxy and study them by in situ ARPES and SI-STM. Both ARPES and SI-STM show that the surface DBCO layer is different from the bulk of the film. It is heavily underdoped, while the doping level in the bulk is close to optimal doping evidenced by bulk-sensitive mutual inductance measurements. ARPES shows the typical electronic structure of a heavily underdoped CuO2 plane and two sets of one-dimensional bands originating from the CuO chains with one of them gapped. SI-STM reveals two different energy scales in the local density of states, with one corresponding to the superconductivity and the other one to the pseudogap. While the pseudogap shows large variations over the length scale of a few nanometers, the superconducting gap is very homogeneous. This indicates that the pseudogap and superconductivity are of different origins.

One of the well‐known strategies for achieving high‐performance light‐activated gas sensors is to design a nanostructure for effective surface responses with its geometric advances. However, no study has gone beyond the benefits of the large surface area and provided fundamental strategies to offer a rational structure for increasing their optical and chemical performances. Here, a new class of UV‐activated sensing nanoarchitecture made of highly periodic 3D TiO2, which facilitates 55 times enhanced light absorption by confining the incident light in the nanostructure, is prepared as an active gas channel. The key parameters, such as the total 3D TiO2 film and thin‐shell thicknesses, are precisely optimized by finite element analysis. Collectively, this fundamental design leads to ultrahigh chemoresistive response to NO2 with a theoretical detection limit of ≈200 ppt. The demonstration of high responses with visible light illumination proposes a future perspective for light‐activated gas sensors based on semiconducting oxides., The high‐performance light‐activated NO2 gas sensors using 3D TiO2 nanostructures are achieved by the unique light harvesting properties of the nanoporous structures. The light scattering effects from optical maze‐like nanostructures and numerous intermediate energy states from atomic layer deposition of the film electronically activate 3D TiO2 and enhance its gas sensing performance under UV illumination.

We propose FlexReduce, an efficient and flexible all-reduce algorithm for distributed deep learning under irregular network hierarchies. With ever-growing deep neural networks, distributed learning over multiple nodes is becoming imperative for expedited training. There are several approaches leveraging the symmetric network structure to optimize the performance over different hierarchy levels of the network. However, the assumption of symmetric network does not always hold, especially in shared cloud environments. By allocating an uneven portion of gradients to each learner (GPU), FlexReduce outperforms conventional algorithms on asymmetric network structures, and still performs even or better on symmetric networks.

We demonstrate the implementation of a temperature sensor based on mechanically induced long period fiber gratings (MILPFGs) using a 3-D printer. The temperature sensitivities are measured to be –97 pm/°C and 0.33 dB/°C, respectively.

Significance By making a variety of quantitative comparisons between electronic visualization experiments and a theory describing coexisting pair density wave and superconductive states in cuprates, we find striking correspondence throughout. Our model can thus explain the microscopic origins of many key atomic-scale phenomena of the cuprate broken-symmetry state. These observations are consistent with the possibility that a short-range pair density wave (PDW) state coexists with superconductivity below a critical hole density in Bi2Sr2CaCu2O8, that the charge density wave modulations in cuprates are a consequence of the PDW state, that the cuprate pseudogap is the antinodal gap of the PDW, and that the critical point in the cuprate phase diagram occurs due to disappearance of the PDW., The defining characteristic of hole-doped cuprates is d-wave high temperature superconductivity. However, intense theoretical interest is now focused on whether a pair density wave state (PDW) could coexist with cuprate superconductivity [D. F. Agterberg et al., Annu. Rev. Condens. Matter Phys. 11, 231 (2020)]. Here, we use a strong-coupling mean-field theory of cuprates, to model the atomic-scale electronic structure of an eight-unit-cell periodic, d-symmetry form factor, pair density wave (PDW) state coexisting with d-wave superconductivity (DSC). From this PDW + DSC model, the atomically resolved density of Bogoliubov quasiparticle states Nr,E is predicted at the terminal BiO surface of Bi2Sr2CaCu2O8 and compared with high-precision electronic visualization experiments using spectroscopic imaging scanning tunneling microscopy (STM). The PDW + DSC model predictions include the intraunit-cell structure and periodic modulations of Nr,E, the modulations of the coherence peak energy Δpr, and the characteristics of Bogoliubov quasiparticle interference in scattering-wavevector space q-space. Consistency between all these predictions and the corresponding experiments indicates that lightly hole-doped Bi2Sr2CaCu2O8 does contain a PDW + DSC state. Moreover, in the model the PDW + DSC state becomes unstable to a pure DSC state at a critical hole density p*, with empirically equivalent phenomena occurring in the experiments. All these results are consistent with a picture in which the cuprate translational symmetry-breaking state is a PDW, the observed charge modulations are its consequence, the antinodal pseudogap is that of the PDW state, and the cuprate critical point at p* ≈ 19% occurs due to disappearance of this PDW.

Wavelength-selective harvesting by organic solar cells (OSCs) has attracted significant research attention due to the unique potential of these materials for smart photovoltaic window applications. Here, a visibly transparent OSC is demonstrated by utilizing both near-infrared (NIR)-absorbing polymer donor and nonfullerene acceptor (NFA) materials with narrow optical band gaps of less than 1.4 eV. Despite the substantial overlap in absorption spectra between the donor and acceptor, sufficient lowest unoccupied molecular orbital (LUMO) and highest occupied molecule orbital (HOMO) energy offsets for efficient charge separation with concurrent very low voltage losses yield a power conversion efficiency (PCE) of 9.13%. Moreover, with the introduction of an ultrathin Ag film (8 nm) as a transparent top electrode, semitransparent OSCs exhibit an excellent dual-side photovoltaic performance of 5.7 and 3.9% under bottom and top illumination, respectively, with high transmittance reaching 60% at wavelengths from 400 to 600 nm. This approach is expected to provide a new perspective in developing the highly efficient and transparent OSCs.

We investigate the recovery-time impact of a saturable-absorber on mode-locking performance of a fiber laser. The recovery-time was found to have a significant impact in a fiber cavity with normal GVD rather than anomalous GVD. © 2020 The Author(s)

Morphology-retained solid-state photoconversion of anthracene (AN) to 9,10-anthraquinone (PC-ANQ) and dipara-anthracene (PC-DPA) was accomplished by irradiating mercury lamp light to plate-shaped AN single crystal in oxygen and argon atmosphere, respectively. The photoconverted crystals retained the original plate shape morphology of the starting AN crystal, whereas the emission profile and crystal structure were significantly changed. The electrical conductivity of PC-ANQ crystal is 5 orders of magnitude greater than that of the starting AN crystal, whereas the PC-DPA crystal exhibits a decreased conductivity. The AN/PC-ANQ/PC-DPA heterostructures with smooth interface were successfully obtained by inducing the photoconversion only at the desired area.

An atomically thin two-dimensional (2D) covalent organic framework (COF) was successfully synthesized via the photon-assisted imine condensation reaction within 1 h from the highly uniform and homogeneous precursor solution layer floating on the water surface. The polarity optimization of the precursor solution was the key step for the successful formation of the high-quality 2D COF because only the precursor solution consisting of polarity-controlled solvents allows ideal floating on the water surface. The polarity-controlled solution not only prohibits the agglomeration of the organic precursors on the water surface but also facilitates the wafer scale and layer number-controllable synthesis of the 2D COF. The resulting 2D COF has a uniform porous structure and highly oriented layered structure along the out-of-plane direction as observed by microscopy analysis and X-ray diffraction, respectively. In addition, we successfully fabricated field effect transistor type polyimine-based COF (pi-COF) electronic devices to demonstrate the prompt electrical responses to photo-exposure and water vapor exposure, suggesting the potential applications of the pi-COF in electrical photodetector or moisture-detector devices.

A sonobuoy is an underwater acoustic sensor primarily deployed by airdrop. An acoustic sensor plays a significant role in conducting anti-submarine warfare for detecting underwater sounds. As a future underwater acoustic sensor, sonobuoy is expected to have an ability of self-movement, i.e., autonomous sonobuoy. In this study, we consider an optimal linear array deployment of autonomous sonobuoys when detecting an unknown underwater sound, assuming that the initial locations of sonobuoys are random in a specified operational area. Deploying sonobuoys from the initial locations onto a specific line requires to first determine the line and positions on that line. Under the interval equivalence between two adjacent sonobuoys, we propose two lines, one that is perpendicular from the underwater sound source location and the other based on the linear regression analysis using the initial locations of sonobuoys. With these two lines onto which sonobuoys will be deployed, we provide two optimization models, total distance minimization and maximum distance minimization, which turn out to be assignment and bottleneck assignment problems, respectively, with nonlinear cost coefficients in the objectives. Due to non-convexity of the objectives, we solve these problems for a fixed interval repetitively as a linear program and integer program, respectively. Computational results show that regression-based line provides higher solution qualities for both problems. Finally, we suggest an approximate interval in a heuristic manner, which guarantees a highly near-optimality as the number of sonobuoys increases. Our results may support a decision-making and provide practitioners with insight on more variety of effective use of autonomous sonobuoys.

In this paper, we report an efficient alkali metal doping system for organic single crystals. Our system employs an enhanced diffusion method for the introduction of alkali metal into organic single crystals by controlling the sample temperature to induce secondary thermal activation. Using this system, we achieved intercalation of potassium into picene single crystals with closed packed crystal structures. Using optical microscopy and Raman spectroscopy, we confirmed that the resulting samples were uniformly doped and became K2picene single crystal, while only parts of the crystal are doped and transformed into K2picene without secondary thermal activation. Moreover, using a customized electrical measurement system, the insulator-to-semiconductor transition of picene single crystals upon doping was confirmed by in situ electrical conductivity and ex situ temperature-dependent resistivity measurements. X-ray diffraction studies showed that potassium atoms were intercalated between molecular layers of picene, and doped samples did not show any KH- nor KOH-related peaks, indicating that picene molecules are retained without structural decomposition. During recent decades, tremendous efforts have been exerted to develop high-performance organic semiconductors and superconductors, whereas as little attention has been devoted to doped organic crystals. Our method will enable efficient alkali metal doping of organic crystals and will be a resource for future systematic studies on the electrical property changes of these organic crystals upon doping.

We have previously shown that an activated carbon-supported ruthenium catalyst promoted with ReO x (RuRe/AC) is highly active for the hydrodeoxygenation (HDO) of lignin-derived phenols (e.g., guaiacol). In this work, we have investigated the effect of carbon supports on the structure and HDO activity of bimetallic RuRe particles using three different carbon supports, i.e., activated carbon (AC), carbon black (Vulcan carbon, VC), multi-walled carbon nanotube (MWCNT). The MWCNT- and VC-supported catalysts show remarkably enhanced activity and hydrocarbon selectivity for the HDO of a range of phenolic molecules (i.e., guaiacol, eugenol, benzyl phenyl ether) compared to RuRe/AC. STEM-EDS and XPS analyses reveal that bimetallic RuRe particles are more common than monometallic Ru or Re particles in the VC- and MWCNT-supported catalysts, and hexavalent rhenium species are more easily reduced to tetravalent rhenium during the HDO reactions in these catalysts, suggesting that Ru and Re in close proximity are required for the efficient hydrogenolysis of phenols. The formation of bimetallic particles on the AC surface is likely hindered by high microporosity and high surface oxygen functionalities, both of which restrict the mobility of Re and Ru for assembly.

Elimination of charge trapping at defects is highly challenging for poly-crystalline organometal halide perovskites. Here, we report a new architecture for reinforcing the built-in electric field (Ein) across the photoactive layer with a pair of strong electric dipole layers (EDLs). The paired EDLs significantly intensify the Ein across the perovskite layer, resulting in suppressed charge trapping of photogenerated charges. As a result, our low-temperature processed P–I–N planar PeSC devices using the paired EDLs exhibit a higher power conversion efficiency (ηmax ∼ 19.4%) and a smaller device-to-device variation with a standard deviation (S.D.) of 0.70%, which far surpass those (ηmax ∼ 17.8%, S.D. ∼ 1.1%) of the devices with typical charge transport layers.

Here we report on the development of thin film manufacturing processes based on new and sustainable green solutions. We focused on utilizing green based surface solutions. The peroxo titanium complex (PTC) solution-based thin film fabrication method used does not require additional heat treatment and complex processes to remove organic matter. Conditions suitable for thin film fabrication were derived through optimization of precursor concentration and reaction temperature. As a result of I-V test of TiN/TiO2/FTO samples fabricated by applying this technology, it has been proven that it can operate as a resistive random-access memory (RRAM). The measured I-V curve suggests that TiN/TiO2/FTO RRAM exhibits bipolar resistive switching (RS) characteristics through the formation of oxygen vacancy (Vo) filament conduction paths. We also used the double logarithmic plot analysis to confirm that the dominant conduction mechanism of the device is the space charge limited conduction (SCLC) model.

Nanostructured Si is a promising material for photoelectrochemical water splitting, but it has the problem of being well oxidized in water. Depositing a TiO2 layer on the Si surface is an effective way to protect it from oxidation and increase light absorption. However, the lattice mismatch between Si and TiO2 acts as a defect that causes an efficiency reduction. To improve the interface and electrical properties of TiO2/Si, nitric acid oxidation of Si (NAOS) is used to form a high-density SiO2 layer and analyze the effect of photoelectrochemical properties. Due to the lattice mismatch, the TiO2/Si sample (−3.12 mA/cm2) decreases about 1.8 times when using SiO2. In TiO2/SiO2/Si samples (-5.70 mA/cm2) further decrease after post-oxidation annealing (POA) (−7.70 mA/cm2). As a result, it can be seen that by fabricating an ultra-thin high-density SiO2 layer, the lattice mismatch at the TiO2/Si interface is reduced and the photocurrent density is improved.

In this study, we conduct a numerical evaluation of the impact of the recovery time of a saturable absorber (SA) on the output performance of an Yb-doped fiber laser operating in the dissipative soliton regime. Particularly, we evaluate the output pulse characteristics, such as the pulse width, spectral bandwidth, pulse peak power, and pulse energy depending on the change in recovery time. Applying a too-slow SA recovery time above a certain critical value is shown to make the output pulse unstable and broken. Furthermore, we demonstrate that there is an optimum recovery time range for stable dissipative soliton pulse generation, depending on the cavity dispersion and modulation depth of the SA. Further, we perform an additional numerical simulation of the pulse compression to demonstrate the relationship between the output dechirped pulse width and SA recovery time. The optimum approach for the generation of the shortest dechirped pulses in the dissipative soliton regime will be to construct a fiber laser cavity with a small normal cavity group velocity dispersion and use an SA with an appropriate recovery time.

In this paper, we propose ExtraV, a framework for near-storage graph processing. It is based on the novel concept of graph virtualization , which efficiently utilizes a cache-coherent hardware accelerator at the storage side to achieve performance and flexibility at the same time. ExtraV consists of four main components: 1) host processor, 2) main memory, 3) AFU (Accelerator Function Unit) and 4) storage. The AFU, a hardware accelerator, sits between the host processor and storage. Using a coherent interface that allows main memory accesses, it performs graph traversal functions that are common to various algorithms while the program running on the host processor (called the host program) manages the overall execution along with more application-specific tasks. Graph virtualization is a high-level programming model of graph processing that allows designers to focus on algorithm-specific functions. Realized by the accelerator, graph virtualization gives the host programs an illusion that the graph data reside on the main memory in a layout that fits with the memory access behavior of host programs even though the graph data are actually stored in a multi-level, compressed form in storage. We prototyped ExtraV on a Power8 machine with a CAPI-enabled FPGA. Our experiments on a real system prototype offer significant speedup compared to state-of-the-art software only implementations.

Background: GCSB-5, an herbal drug composition with an anti-inflammatory effect, is prepared by boiling, which is the most common herbal extraction method in traditional Korean medicine. Several parameters are involved in the process, i.e., extractant type, herb-to-extractant ratio, extraction temperature and pressure, and total boiling time. Objectives: The aim of this study was to examine the influence of boiling time on index compound amount and the antioxidative and anti-inflammatory activities of GCSB-5. Materials and Methods: Different samples of GCSB-5 were obtained by decocting for 30, 60, 90, 120, 150, and 240 min. Each sample was tested for hydrogen ion concentration (pH), total soluble solid content (TSSC), marker compound profiles, and antioxidative and anti-inflammatory activity. Results: pH was found to decrease while TSSC increased with extended decoction. Marker compound contents for GCSB-5 (acanthoside D for Acanthopanax sessiliflorus Seem, 20-hydroxyecdysone for Achyranthes japonica Nakai, and pinoresinol diglucoside for Eucommia ulmoides Oliver) remained relatively constant regardless of the length of boiling. Total D-glucose amount increased with longer boiling. The antioxidative and anti-inflammatory potentials of GCSB-5 were not substantially affected by decoction duration. Conclusion: Biological characteristics and marker compound content of GCSB-5 were not altered significantly in prolonged boiling. SUMMARY Longer boiling duration of GCSB-5 did not increase yield in a time-dependent manner, but yields of 210 and 240 min samples were significantly higherHydrogen ion concentration of GCSB-5 samples decreased while total soluble solid content and D-glucose concentration levels increased with boiling durationAlthough concentrations of some index compounds increased with extended boiling duration of GCSB-5, increase was small and not in a direct proportional relationshipAntioxidative and anti-inflammatory properties of GCSB-5 were not substantially affected by decoction duration. Abbreviations used: CAM: Complementary and alternative medicine; KIOM: Korea Institute of Oriental Medicine; KMD: Korean medicine doctor; TSSC: Total soluble solid content; pH: Hydrogen ion concentration; HPLC: High-performance liquid chromatography; NO: Nitric oxide; NO2: Nitric dioxide; LPS: Lipopolysaccharide; DMSO: Dimethyl sulfoxide.

We propose an approach called buffered compares , a less-invasive processing-in-memory solution that can be used with existing processor memory interfaces such as DDR3/4 with minimal changes. The approach is based on the observation that multibank architecture, a key feature of modern main memory DRAM devices, can be used to provide huge internal bandwidth without any major modification. We place a small buffer and a simple ALU per bank, define a set of new DRAM commands to fill the buffer and feed data to the ALU, and return the result for a set of commands (not for each command) to the host memory controller. By exploiting the under-utilized internal bandwidth using ‘compare-n-op’ operations, which are frequently used in various applications, we not only reduce the amount of energy-inefficient processor-memory communication, but also accelerate the computation of big data processing applications by utilizing parallelism of the buffered compare units in DRAM banks. We present two versions of buffered compare architecture-full-scale architecture and reduced architecture-in trade of performance and energy. The experimental results show that our solution significantly improves the performance and efficiency of the system on the tested workloads.

Even after 30 years of discovery of the high temperature superconductivity (HTSC) from the cuprate compounds by Bednorz and Muller, the mechanism of the formation of Cooper pairs well above the liquid nitrogen boiling temperature is still remained to be elucidated. The discovery of a yet another HTSC family of the iron-based superconductors seemed to add more complexity to this puzzle, but also seems to render a prospect of finding a universal principle shared by the entire HTSC family. The tunneling experiments, on the other hand, also witnessed remarkable breakthroughs ever since Giaever succeeded the first tunneling experiment on a superconducting aluminum. The scanning tunneling microscopy (STM) invented by Binnig and Rohrer began to be heavily applied to the research of the condensed matter and became one of the most versatile spectroscopic tools as well as the most powerful microscope available also in the HTSC research field as of today. In this review, we would like to convey a snapshot of the current application of the STM in the research of HTSC, mainly focusing on the studies using the spectroscopic imaging scanning tunneling microscopy (SI-STM) which eventually led to the scanning Josephson tunneling microscopy (SJTM) by which we can visualize the superconducting Cooper pairs in an atomic scale.

We evaluated the spatial-temporal dispersion of airborne nanomaterials during the use of spray consumer products and estimated the level of consumer inhalation exposure. A total of eight spray products including five propellant and three pump types were selected to evaluate the dispersion of airborne nanoparticles across time and space in a cleanroom which could control the background particles. Four products were advertised to contain silver and one contained titanium nanoparticles, while three products were specified no ENM but as being manufactured through the use of nanotechnology. We used direct-reading instruments with a thermodesorber unit to measure the particles (number, mass, surface area), as well as filter sampling to examine physicochemical characteristics. Sampling was conducted simultaneously at each location (1 m, near-field; 2, 3 m, far-field) by distance from the source. We estimated the inhaled doses at the breathing zone, and the doses deposited in each part of the respiratory tract using the experimental data and mathematical models. Nanoparticles released from the propellant sprays persisted in the air and dispersed over a large distance due to their small size (1466-5565 particles/cm

Increasing the open circuit voltage (Voc) is one of the key strategies for further improvement of the efficiency of perovskite solar cells. It requires fundamental understanding of the complex optoelectronic processes related to charge carrier generation, transport, extraction and their loss mechanisms inside a device upon illumination. Herein we report the important origin of Voc losses in methylammonium lead iodide perovskite (MAPI) based solar cells, which results from undesirable positive charge (hole) accumulation at the interface between the perovskite photoactive layer and the PEDOT:PSS hole transport layer. We show strong correlation between the thickness-dependent surface photovoltage and device performance, unraveling that the interfacial charge accumulation leads to charge carrier recombination and results in a large decrease in Voc for the PEDOT:PSS/MAPI inverted devices (180 mV reduction in 50-nm-thick device compared to 230-nm-thick one). In contrast, accumulated positive charges at the TiO2/MAPI interface modify interfacial energy band bending, which leads to an increase in Voc for the TiO2/MAPI conventional devices (70 mV increase in 50-nm-thick device compared to 230-nm-thick one). Our results provide an important guideline for better control of interfaces in perovskite solar cells to improve device performance further.

When Cooper pairs are formed with finite center-of-mass momentum, the defining characteristic is a spatially modulating superconducting energy gap $\Delta(r)$. Recently, this concept has been generalized to the pair density wave (PDW) state predicted to exist in a variety of strongly correlated electronic materials such as the cuprates. Although the signature of a cuprate PDW has been detected in Cooper-pair tunnelling, the distinctive signature in single-electron tunneling of a periodic $\Delta(r)$ modulation has never been observed. Here, using a new approach, we discover strong $\Delta(r)$ modulations in Bi$_2$Sr$_2$CaCu$_2$O$_8$+$\delta$ that have eight-unit-cell periodicity or wavevectors $Q=2{\pi}/a_0(1/8,0)$; $2{\pi}/a_0(0,1/8)$. This constitutes the first energy-resolved spectroscopic evidence for the cuprate PDW state. An analysis of spatial arrangements of $\Delta(r)$ modulations then reveals that this PDW is predominantly unidirectional, but with an arrangement of nanoscale domains indicative of a vestigial PDW. Simultaneous imaging of the local-density-of-states $N(r,E)$ reveals electronic modulations with wavevectors $Q$ and $2Q$, as anticipated when the PDW coexists with superconductivity. Finally, by visualizing the topological defects in these $N(r,E)$ density waves at $2Q$, we discover them to be concentrated in areas where the PDW spatial phase changes by $\pi$, as predicted by the theory of half-vortices in a PDW state. Overall, this is a compelling demonstration, from multiple single-electron signatures, of a PDW state coexisting with superconductivity at zero magnetic field, in the canonical cuprate Bi$_2$Sr$_2$CaCu$_2$O$_8$+$\delta$., Comment: Final submitted version. arXiv admin note: text overlap with arXiv:2109.14031

We applied Deep Q-Network with a Convolutional Neural Network function approximator, which takes stock chart images as input, for making global stock market predictions. Our model not only yields profit in the stock market of the country where it was trained but generally yields profit in global stock markets. We trained our model only in the US market and tested it in 31 different countries over 12 years. The portfolios constructed based on our model's output generally yield about 0.1 to 1.0 percent return per transaction prior to transaction costs in 31 countries. The results show that there are some patterns on stock chart image, that tend to predict the same future stock price movements across global stock markets. Moreover, the results show that future stock prices can be predicted even if the training and testing procedures are done in different countries. Training procedure could be done in relatively large and liquid markets (e.g., USA) and tested in small markets. This result demonstrates that artificial intelligence based stock price forecasting models can be used in relatively small markets (emerging countries) even though they do not have a sufficient amount of data for training., 12 pages, 2 figures

We demonstrate a ligand-free green chemical method for the rapid growth of nanoporous Ca0.35CoO2 thin films on sapphire and mica substrates from a water-based precursor ink, formulated by dissolving the precursor solid, composed of in situ prepared Ca2+-DMF and Co2+-DMF complexes. Mica serves as the flexible substrate as well as the sacrificial layer for the film transfer. Despite the presence of nanopores, the power factor of the flexible film Ca0.35CoO2-on-mica is above 0.50 x 10(-4) W m(-1) K-2 at around room temperature. The present technique is simple and cost-effective. Funding Agencies|Science and Engineering Research Board, the DST "GPU", Government of India [SERB/1759/2014-15]; Basic Science Research Program through the National Research Foundation of Korea (NRF) - Ministry of Education [2016R1D1A1B03931391]; Aforsk foundation [17-578]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

Here, we report a discussion on the development of a new and sustainable green surface modification process to improve environmental pollution by modifying the surface and structural properties of nanostructured materials. Homo-core/shell TiO2 (HCST) was successfully synthesized through a peroxo titanium complex (PTC) solution-based surface modification process. The PTC solution is easily synthesized by the interfacial ion diffusion-redox reaction of Ti-metal and successfully forms an ultra-thin TiO2 shell (~2 nm) on the P-25 surface. The presence of these TiO2 shells not only causes high organic pollutant adsorption properties but also accelerates the photocatalytic activity along with the rich hydroxyl groups and oxygen vacancies present on the shell surface. The photocatalytic properties depend on the mixing ratio of the PTC solution and the heat treatment temperature and exhibited methylene blue (MB) removal efficiency of up to 99% or more and excellent recycling properties. Under optimal conditions, the rate constant value of HCST was calculated to be 17.14 × 10−3 min−1, about 2.7 times higher than P-25 through the Langmuir-Hinshelwood (L-H) equation.

The redshift of the long wavelength plasmonic absorption band is essential to the use of gold nanorods (GNRs) for the implementation of the infrared broadband saturable absorbers (SAs). A common method to obtain the GNR-based SAs with a substantially broad absorption bandwidth from 1 to 2 μm is to use GNRs with a large aspect ratio. Here, a simple self-assembly technique is demonstrated, which enables us to obtain a significant redshift of the long wavelength plasmonic absorption peak of GNRs with a small aspect ratio, together with substantial spectral broadening of the absorption band. The proposed technique is based on an end-to-end self-assembly of the GNRs through hot air induced rapid drying of the GNRs in a deionized water solution, which makes the GNRs reassemble by attaching to one another by their ends. Using the proposed end-to-end self-assembly method for GNRs with an aspect ratio of 5.1, a single broadband SA that can operate from 1.5 to 1.9 μm was fabricated on a fiber ferrule based sandwich platform. The saturable absorption performance was tested by incorporating the fabricated GNR-based SA into two different optical fiber based ring cavities: One was based on an erbium-doped fiber and the other was a thulium–holmium codoped fiber. Our fabricated single SA readily produced stable Q-switched pulses from both the cavities.

A key to improve the electrochemical performance of anode materials is to exploit the rational nanostructure designing beneficial for structural toughness and high rate capability. As a nanostructure design in accordance with this criterion, we introduced GeSe nanocomb architecture with well-developed nanocomb teeth on the backbone. In this unique nanocomb architecture, the free space between nanocomb teeth effectively alleviates tremendous volume expansion during lithiation, and anisotropic structure with a short Li+ diffusion length of tens of nanometer scale guarantees the favorable lithiation/delithiation kinetics. These structural advantages of GeSe nanocomb architecture lead to significantly improved electrochemical performance compared to the GeSe nanopowder counterpart. This GeSe nanocomb architecture exhibits electrochemical performance with the reversible capacity of 726 mA·h·g–1, showing superior capacity retention of 89% even after 1000 cycles at 1.0 C (1.01 A·g–1).

Printed polymer solar cells (PSCs) were demonstrated by doctor-blade coating a zinc oxide (ZnO) material, slot-die coating photoactive and PEDOT:PSS materials, and screen-printing a silver (Ag) electrode. To make a PEDOT:PSS film on a hydrophobic photoactive layer, we tried to modify various types of commercial PEDOT:PSSs (Clevios P, N 1005, S 305, AI 4083) with the surfactants Zonyl FS-300 and FS-31 (Capstone® Dupont™). The addition of the FS-31 surfactant successfully reduced the contact angle of PEDOT:PSS on the hydrophobic photoactive layer, and the wetting property was sufficiently developed, even using a slot-die coating method. A relatively thick PEDOT:PSS layer, Clevios P modified by FS-31, prevents the penetration of the Ag ink solvent into the photoactive layer. Accordingly, a power conversion efficiency of 4.06% was attained in the printed PSCs.