bluuebunny/crossref_metadata_2025 huggingface dataset:
State-resolved rotational distributions and collision dynamics of CO molecules made in a tunable optical centrifuge
Authors: Michael Tara J. , Ogden Hannah M. , Mullin Amy S.
Published: April 2021

State-resolved distributions and collision dynamics of optically centrifuged CO molecules with orientated angular momentum are investigated by probing the CO J = 29–80 rotational levels using high-resolution transient IR absorption spectroscopy. An optical centrifuge with tunable bandwidth is used to control the extent of rotational excitation in the sample. The rotational distributions are inverted with a maximum population in J = 62. Rotational levels with J > 62 have populations that correlate with the intensity profile of the optical trap. The full bandwidth trap excites CO up to the J = 80 level, while J = 67 is the highest level observed in the reduced bandwidth trap. Polarization-sensitive transient spectroscopy shows that the initial orientational anisotropy is r = 0.8 for levels with J ≥ 55, while anisotropy values are near r = 0.4 for levels with J < 50. The rotational distribution for J > 50 is broadened slightly by collisions, consistent with small |ΔJ| propensity rules for rotational energy transfer. Doppler-broadened line profiles show that the J = 60–80 levels have translational temperatures near Ttrans = 300 K and that these temperatures remain constant for as much as 24 gas kinetic collisions. Doppler linewidths for levels with J < 60 are broadened by non-resonant rotation-to-translation energy transfer. Kinetic analysis of transient signals shows that collisions with thermal bath molecules are the predominant relaxation pathway.
p-type conductivity in GaN:Zn monocrystals grown by ammonothermal method
Authors: Zajac M. , Konczewicz L. , Litwin-Staszewska E. , Iwinska M. , Kucharski R. , Juillaguet S. , Contreras S.
Published: April 2021

Zinc is often regarded as an alternative to magnesium p-type dopants in gallium nitride. However, besides many theoretical predictions, at present, there are poor data on experimentally revealed p-type conductivity and evaluation of Zn activation energy by means of electrical transport measurements. In this paper, ammonothermal crystallization of bulk GaN:Zn monocrystals is reported. Despite a high doping level of Zn (up to 2 × 1020 cm−3), p-type conductivity with hole concentration as low as of 4 × 1015 cm−3 at room temperature and mobility about 3 cm2/V s was observed. A deep nature of the Zn acceptor was proved, as the ionization energy can exceed 260 meV. In addition, conduction in the impurity band appeared at temperatures as high as room temperature.
Self-integrating current sensor for fast pulsed current monitor in transmission line
Authors: Wang Jiachen , Ding Weidong , Su Fangfei , Zhang Xiwen , Wan Zhenbo , Qiu Aici
Published: April 2021

The fast linear transformer driver (FLTD) utilizes a water-insulated transmission line as its secondary. To monitor the fast pulsed current and locate the fault, a compact self-integrating current sensor is developed. Print circuit board (PCB) coils and PCB integrating resistors are used to form the current sensor. By soldering a large number of chip resistors, PCB integrating resistors with various resistance and low inductance can be obtained. The current sensor is designed in a coaxial structure to reduce its inductance and size and can be installed on the inner conductor of the FLTD’s secondary water-insulated transmission line with a small opening. The principle and matching schemes for the current sensor are theoretically analyzed with the circuit principle. Both simple matching and two-stage division can be used to obtain signals without oscillation. The time constant of the two schemes is the same. However, the sensitivity of the current sensor with two-stage division is lower than that with simple matching. A 100 kV step pulse generator is used as the pulsed high current generator to verify the properties of the current sensor. The designed current sensor could respond to the step current pulse with the rise time of 4 ns. The matching scheme is verified to be effective with step response experiments. Finally, the influence of the parameters, which are the coil type, the angle between the PCB coil and the magnetic flux, the resistance of the integrating resistor, and the length of the measuring cable, on the output signal of the current sensor is studied.
Entropy charts and bifurcations for Lorenz maps with infinite derivatives
Authors: Malkin M. , Safonov K.
Published: April 2021

This paper deals with one-dimensional factor maps for the geometric model of Lorenz-type attractors in the form of two-parameter family of Lorenz maps on the interval I=[−1,1] given by Tc,ν(x)=(−1+c⋅|x|ν)⋅sign(x). This is the normal form for splitting the homoclinic loop with additional degeneracy in flows with symmetry that have a saddle equilibrium with a one-dimensional unstable manifold. Due to L. P. Shilnikov’ results, such a bifurcation (under certain conditions) corresponds to the birth of the Lorenz attractor. We indicate those regions in the parameter plane where the topological entropy depends monotonically on the parameter c, as well as those for which the monotonicity does not take place. Also, we indicate the corresponding bifurcations for the Lorenz attractors.
Enhanced multiferroic characteristics in hexagonal ScMn1−xFexO3 ceramics
Authors: Zhu Xiao Li , Dai Hao Ming , Sun Tu Lai , Liu Xiao Qiang , Chen Xiang Ming
Published: April 2021

In the present study, enhanced antiferromagnetic characteristics and room temperature magnetoelectric coupling are achieved by Fe-substitution for Mn in h-ScMnO3. The antiferromagnetic Néel temperature (TN) increases from 131 K for ScMnO3 up to 140 K for ScMn0.8Fe0.2O3. Electric field controlled magnetism is confirmed for ScMn0.8Fe0.2O3 at room temperature, combining with the short-range magnetic spin ordering. The Rietveld structural refinement and selected area electron diffraction confirm the noncentrosymmetric P63cm structure for the present ceramics. The ferroelectric domain walls at the atomic scale are determined by the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy; meanwhile, the spontaneous polarization of 5.6 μC/cm2 is determined. The noticeable magnetoelectric coefficient αME ∼ 0.78 mV/cm Oe (measured under a magnetic field up to 3000 Oe) is obtained in ScMn0.8Fe0.2O3, which is quite stable with the applied magnetic field, reflecting coupling of the short-range spin ordering with the ferroelectric ordering. The enhanced antiferromagnetic behaviors are discussed with the effect of Fe-substitution, which reduce the magnetic frustration and enhance the exchange interaction.
Electromagnetic torque measurements in DIII-D using internal/external magnetic field decomposition
Authors: Strait E. J. , Munaretto S. , Sweeney R. M. , Logan N. C. , Nelson A. O.
Published: April 2021

Given spatially resolved measurements of normal and tangential components of the magnetic field just outside the surface of a magnetically confined plasma, the field at the measurement location can be uniquely decomposed into contributions from the plasma and from external sources. This principle allows direct measurement of the electromagnetic torque on the plasma without knowledge of the distribution of the internal and external currents, similar to the more well-known formalism using the Maxwell stress tensor. The internal/external field decomposition also enables a mixed approach that incorporates any explicitly known current distributions (e.g., from non-axisymmetric coils). We discuss the requirements and limitations of such an approach to torque measurements. Experimental measurements of the torque evolution as a rotating tearing mode locks to the wall in the DIII-D tokamak are consistent with a simple model.
Full-scale simulation of self-propulsion for a free-running submarine
Authors: Liu Liwei , Chen Meixia , Yu Jiawei , Zhang Zhiguo , Wang Xianzhou
Published: April 2021

It is important to predict the self-propulsion performance of full-scale marine vessels during the design stage. With the development of high-performance computational techniques, full-scale ship-free running simulations focused on self-propulsion performance are receiving increased attention. This study presents the results of computational fluid dynamics (CFD) simulations for a full-scale submarine propelled by a high-skew propeller. An in-house CFD code with the dynamic overset grid approach is used to simulate the rotational motion of the propeller. First, model- and full-scale simulations focused on submarine resistance and propeller open-water performance are conducted, enabling a systematic convergence study of the model. The self-propulsion performance is then predicted at the model scale, and comparisons with other available results show only small discrepancies. Finally, full-scale submarine self-propulsion simulations are conducted and the results are compared with those from the model-scale simulations with the addition of skin friction correction. Discussions on the differences between model- and full-scale self-propulsion results are presented including propeller performance, pressure distribution, boundary layer, and wake flow.
Coupled nuclear and electron dynamics in the vicinity of a conical intersection
Authors: Schnappinger Thomas , de Vivie-Riedle Regina
Published: April 2021

Ultrafast optical techniques allow us to study ultrafast molecular dynamics involving both nuclear and electronic motion. To support interpretation, theoretical approaches are needed that can describe both the nuclear and electron dynamics. Hence, we revisit and expand our ansatz for the coupled description of the nuclear and electron dynamics in molecular systems (NEMol). In this purely quantum mechanical ansatz, the quantum-dynamical description of the nuclear motion is combined with the calculation of the electron dynamics in the eigenfunction basis. The NEMol ansatz is applied to simulate the coupled dynamics of the molecule NO2 in the vicinity of a conical intersection (CoIn) with a special focus on the coherent electron dynamics induced by the non-adiabatic coupling. Furthermore, we aim to control the dynamics of the system when passing the CoIn. The control scheme relies on the carrier envelope phase of a few-cycle IR pulse. The laser pulse influences both the movement of the nuclei and the electrons during the population transfer through the CoIn.
Biaxial atomically resolved force microscopy based on a qPlus sensor operated simultaneously in the first flexural and length extensional modes
Authors: Kirpal Dominik , Qiu Jinglan , Pürckhauer Korbinian , Weymouth Alfred J. , Metz Michael , Giessibl Franz J.
Published: April 2021

Frequency-modulation atomic force microscopy (AFM) with a qPlus sensor allows one to atomically resolve surfaces in a variety of environments ranging from low-temperature in ultra-high vacuum to ambient and liquid conditions. Typically, the tip is driven to oscillate vertically, giving a measure of the vertical force component. However, for many systems, the lateral force component provides valuable information about the sample. Measuring lateral and vertical force components simultaneously by oscillating vertically and laterally has so far only been demonstrated with relatively soft silicon cantilevers and optical detection. Here, we show that the qPlus sensor can be used in a biaxial mode with electrical detection by making use of the first flexural mode and the length extensional mode. We describe the necessary electrode configuration as well as the electrical detection circuit and compare the length extensional mode to the needle sensor. Finally, we show atomic resolution in ambient conditions of a mica surface and in ultra-high vacuum of a silicon surface. In addition to this, we show how any qPlus AFM setup can be modified to work as a biaxial sensor, allowing two independent force components to be recorded.
Machine learning of free energies in chemical compound space using ensemble representations: Reaching experimental uncertainty for solvation
Authors: Weinreich Jan , Browning Nicholas J. , von Lilienfeld O. Anatole
Published: April 2021

Free energies govern the behavior of soft and liquid matter, and improving their predictions could have a large impact on the development of drugs, electrolytes, or homogeneous catalysts. Unfortunately, it is challenging to devise an accurate description of effects governing solvation such as hydrogen-bonding, van der Waals interactions, or conformational sampling. We present a Free energy Machine Learning (FML) model applicable throughout chemical compound space and based on a representation that employs Boltzmann averages to account for an approximated sampling of configurational space. Using the FreeSolv database, FML’s out-of-sample prediction errors of experimental hydration free energies decay systematically with training set size, and experimental uncertainty (0.6 kcal/mol) is reached after training on 490 molecules (80% of FreeSolv). Corresponding FML model errors are on par with state-of-the art physics based approaches. To generate the input representation for a new query compound, FML requires approximate and short molecular dynamics runs. We showcase its usefulness through analysis of solvation free energies for 116k organic molecules (all force-field compatible molecules in the QM9 database), identifying the most and least solvated systems and rediscovering quasi-linear structure–property relationships in terms of simple descriptors such as hydrogen-bond donors, number of NH or OH groups, number of oxygen atoms in hydrocarbons, and number of heavy atoms. FML’s accuracy is maximal when the temperature used for the molecular dynamics simulation to generate averaged input representation samples in training is the same as for the query compounds. The sampling time for the representation converges rapidly with respect to the prediction error.
Localization of ultrasound in 2D phononic crystal with randomly oriented asymmetric scatterers
Authors: Dhillon Jyotsna , Bozhko Andrey , Walker Ezekiel , Neogi Arup , Krokhin Arkadii
Published: April 2021

A phononic crystal of aluminum rods with an asymmetric cross section in water is used for the study of Anderson localization of sound. Due to asymmetry, these scatterers may be arranged in three different configurations: a periodic 2D structure, a random structure with 2D disorder, and a random structure with 1D disorder. The last configuration where the rods are equally oriented within the columns and disoriented along the rows is fabricated for the experimental study of 1D Anderson localization in the 2D random system. An exponentially weakening transmission of the ultrasound is demonstrated for the waves propagating along the direction of disorder. In the perpendicular direction where the scatterers are ordered, sound propagates as an extended (delocalized) wave. The localization length is controlled by the degree of disorder. For weak disorder, when orientations of the rods weakly fluctuate around a given direction, Thouless’s theoretical prediction for the scaling of the Lyapunov exponent with disorder is experimentally observed for a mode within the transmission band. For the sound mode close to the band edge, anomalous scaling is confirmed.
Rapid β-human chorionic gonadotropin detection in urine with electric-double-layer gated field-effect transistor biosensors and a handheld device
Authors: Liao Liang-Wen , Chen Po-Hsuan , Tsai Shu-Yi , Tripathi Adarsh , Paulose Akhil K. , Chang Shing-Jyh , Wang Yu-Lin
Published: April 2021

In this experimental study, a portable biosensor was developed to detect β-human chorionic gonadotropin (β-hCG), which is extensively used in pregnancy tests and serves as a biomarker for ectopic pregnancy. The sensor used is an electric-double-layer field-effect transistor biosensor with the extended-gate design. Bias voltage is applied on the sensor to measure the resulting drain current signals. Gold electrode surface is functionally activated with an anti-β-hCG antibody to capture β-hCG protein. Fluorescence imaging technique is utilized to confirm the surface functionalization. The biosensor demonstrates a dynamically wide range of molecules as detection targets at very low sample concentrations, which shows the potential to detect ectopic pregnancy in very early stages and easily keep track of its periodic changes. It can be produced en masse and does not use additional labels/reagents or pre-processing techniques for the sample. This biosensor can significantly reduce the manufacturing costs and is comparable with the currently available commercial ß-hCG assays. It is suitable for early diagnosis of ectopic pregnancy with low cost and easy operation at home with urine samples.
Probing the lattice structure of dynamically compressed and released single crystal iron through the alpha to epsilon phase transition
Authors: Hawreliak James A. , Turneaure Stefan J.
Published: April 2021

Experiments using broadband Laue x-ray diffraction (XRD) were used to examine the lattice structure of dynamically compressed [100]-oriented single crystal iron samples at the Dynamic Compression Sector at the Advanced Photon Source. These experiments used 1 μm thick iron single crystal samples sandwiched between a polyimide ablator and a polycarbonate window. A 100 J, 10 ns duration laser pulse incident on the polyimide ablator was used to shock compress the iron samples to initial stresses greater than 25 GPa, exceeding the ∼13 GPa alpha (body-centered-cubic or bcc structure) to epsilon (hexagonal-close-packed or hcp structure) phase transition stress. XRD measurements were performed at various times relative to the shock wave entering the iron sample: early times, <∼150 ps while the initial shock waves propagated through the iron; intermediate times, after the iron equilibrated with the ablator and window reaching a plateau stress state (12 or 17 GPa) lasting several nanoseconds; and late times, during uniaxial strain release. The early time measurements show that in <∼150 ps, the high-pressure hcp phase is relaxed with a c/a ratio of 1.61, contrary to previous laser shock experiments where a c/a ratio of 1.7 was inferred. In the plateau stress state and partially released states, XRD measurements showed that the hcp structure retained a c/a ratio of 1.61 with no observable changes in the microstructure. Upon stress release at ∼1 GPa/ns release rate, the reverse phase transition (hcp to bcc) to the original single crystal orientation (implying a transformation memory effect) was observed to reach completion somewhere between 13 and 11 GPa, indicating little stress hysteresis under rapid uniaxial strain release. A similar memory effect for the reverse hcp to bcc transformation has been previously observed under hydrostatic compression. However, the bcc/hcp orientation relationships differ somewhat between dynamic and static compression experiments, implying that the transformation pathway under uniaxial dynamic strain differs from the Burgers mechanism.
Investigation of quantum structure in N-polar deep-ultraviolet light-emitting diodes
Authors: Jia Hongfeng , Yu Huabin , Kang Yang , Ren Zhongjie , Memon Muhammad Hunain , Guo Wei , Sun Haiding , Long Shibing
Published: April 2021

This study systematically investigates the optical performance of N-polar deep-ultraviolet light-emitting diodes (DUV LEDs) in consideration of different quantum structures in the active region, with a highlight on various thicknesses of quantum barrier (QB), quantum well (QW), and the electron-blocking layer (EBL). The results show that the internal quantum efficiency (IQE), as well as light output power (LOP) of N-polar DUV LED, is not sensitive to QB thickness. On the contrary, the LOP and IQE performance can be significantly enhanced by increasing the QW thickness from 2 to 4 nm. Moreover, a saturated LOP in the N-polar DUV LEDs can be observed after QW thickness increased to a certain level as there is a trade-off between boosted carrier concentration and decreased wave function overlap in the active region. Lastly, the impact of the EBL on the optical performance of the N-polar DUV LED is also investigated. Specifically, a thicker EBL or a higher Al composition in the EBL leads to an increase in the turn-on voltage and series resistance while the LOP value remains unchanged. These findings lay the foundation for the development of high-performance N-polar DUV LEDs of the future.
Tutorial on the elastic theory of spin crossover materials
Authors: Popa Alexandra-Ioana , Stoleriu Laurentiu , Enachescu Cristian
Published: April 2021

In this paper, we present the ingredients that allow the building-up of the elastic model, one of the approaches that successfully describes the phenomena observed in complex spin-crossover systems at both the micro- and macroscopic level and we review its challenges and some of its main applications. After discussing the usefulness and the drawbacks of some of the previous models (such as mean-field and Ising-like ones), we introduce the premises that imposed the elastic approach in the study of spin-crossover compounds and present the steps to follow in order to build-up and implement the model. As illustrative applications, we first discuss the simulations of relaxation, thermal transition, and the nucleation phenomena and then introduce the effects of anisotropy in two-dimensional systems. Special sections are dedicated to particular structures like three-dimensional, spin-crossover micro- or nanoparticles as layers on substrates or embedded in polymer or surfactant matrices as well as to the study of ultra-fast phenomena.
A broadband metamaterial absorber design using characteristic modes analysis
Authors: Wu Yanjie , Lin Hai , Xiong Jie , Hou Junjie , Zhou Rui , Deng Feng , Tang Rongxin
Published: April 2021

In this paper, a broadband metamaterial absorber with a fractional bandwidth of 126.88% was presented. The characteristic mode theory was used to guide the design of the absorber. According to the analysis of characteristic mode and characteristic current, the resistance value of resistive films can be determined. The different modal information obtained through parameter changes can also better guide the design of the absorber. To study its operation mechanism, the equivalent impedance and surface current distribution of the proposed absorber have been analyzed. The final simulation and measurement results show that the proposed absorber has a wide absorbing bandwidth which is from 3.21 to 14.35 GHz, and the absorptivity is greater than 90%, covering the S, C, X, and Ku bands. In addition, for TE and TM polarization, it can achieve an absorptivity of more than 85% at 45° oblique incident and has good angular stability. Hence, the absorber has great potential applications in the field of electromagnetic stealth technology and Radar Cross Section reduction.
Control of non-equilibrium Casimir force
Authors: Iizuka Hideo , Fan Shanhui
Published: April 2021

We introduce the concepts of the control theory into the study of non-equilibrium Casimir forces and radiative heat transfer. As an illustration, we consider the plate-plate system for non-equilibrium Casimir forces, where two dielectric plates having different temperatures are separated by a vacuum gap. Previous works have indicated that this system only supports an unstable mechanical equilibrium. Here, we prove analytically and confirm numerically that the equilibrium can be made stable through a feedback control process involving temperature measurement and modulation. Our results show that it should be fruitful to explore the concepts from control theory in the study of the Casimir force and radiative heat transfer.
Exotic optoelectronic behaviors in CH3NH3PbCl3 perovskite single crystals: Co-existence of free and bound excitons with structural phase transitions
Authors: Jung Hye Ri , Bari Maryam , Cho Yunae , Kim Yeon Soo , Nguyen Trang Thi Thu , Kim Yejin , Yoon Seokhyun , Jo Young Chan , Kim Jae Hoon , Yuldashev Shavkat , Ye Zuo-Guang , Jo William
Published: April 2021

CH3NH3PbCl3 (MAPbCl3) perovskite single crystal is attractive for the ultra-violet detector due to its wide bandgap and comparative stability over iodine or bromine systems. Single crystals of MAPbCl3 perovskite are also intriguing owing to its generic type of materials for fundamental photophysical properties and excitonic behaviors for its use in devices. Furthermore, recent progress using crystal-based device fabrication will shed light on semiconducting devices like III–V compounds. In this study, a structurally well-defined crystal is grown and examined to reveal free and bound excitonic behaviors depending on the structural phase transition. We classified the free and bound excitonic behaviors by temperature- and power density-dependent photoluminescence and optical transmission spectra. The single emission peak located at 3.1 eV and blueshift depending on decreasing the temperature is attributed to the radiative recombination of the free exciton at the cubic and the tetragonal phases, whereas the several peaks from the bound excitonic transition are just revealed under 120 K of the orthorhombic phase. We also determined the work function distribution and band structures with excitonic bound states via Kelvin probe force microscopy. The optoelectronic properties resulted in the excitonic behaviors can be a fundamental approach for the construction of perovskite-based optoelectronic and photonic applications.
Comprehensive imaging of C-2W plasmas: Instruments and applications
Authors: Granstedt E. M. , Gupta D. , Sweeney J. , Tobin M. , Dikovsky M. ,   TAE Team
Published: April 2021

The C-2W device (“Norman”) [Gota et al., Nucl. Fusion 59, 112009 (2019)] has produced and sustained beam-driven field-reversed configuration (FRC) plasmas embedded in a magnetic mirror geometry using neutral beams and end-bias electrodes located in expander divertors. Several discrete vessels comprise this device, and many imaging instruments are required in order to view the plasma throughout. To meet this need, a suite of spatially and radiometrically calibrated, high-speed camera systems have been deployed. Besides global visualization of the plasma evolution and macro-stability, this imaging suite has been used in a variety of applications. One example application is a tomographic reconstruction of passive impurity emission. Calculation of the magnetic field in the equilibrium vessel is complicated by eddy currents in conducting structures and internal currents in the high-β FRC plasma. In addition, thus far non-perturbative measurements of internal field have not been available. The tomographic reconstruction of O4+ impurity emission enables an independent visualization of the plasma geometry, serving as a check on magnetic modeling and indirect evidence for field reversal within the FRC. A second application uses the cameras to view the Balmer-α emission throughout the plasma in order to estimate the ionization rate in each region. These rates can then be incorporated into particle balance calculations and a circuit model for currents from the end-bias electrodes. Finally, arcing on the electrode surfaces is identified through automated image processing of carefully selected spectral line emission.
Magnetic, conductive textile for multipurpose protective clothing and hybrid energy harvesting
Authors: Wan Ji , Guo Hang , Wang Haobin , Miao Liming , Song Yu , Xu Chen , Xiang Zehua , Han Mengdi , Zhang Haixia
Published: April 2021

In this paper, we report a magnetic and conductive textile made from a mixture of NdFeB microparticles, multi-walled carbon nanotubes, and polydimethylsiloxane. The textile can (i) shield 99.8% of electromagnetic signals ranging from 30 MHz to 3 GHz, thereby protecting people from damage caused by the electromagnetic radiation, (ii) be hydrophobic and fire retardant, making it a possible choice for raincoat and fire protection clothing, and (iii) convert mechanical energy into electricity through both electromagnetic induction and triboelectrification. The textile creates many opportunities in the fields of multifunctional protective equipment and energy harvesting.
Neovascularization of engineered tissues for clinical translation: Where we are, where we should be?
Authors: Nazeer Muhammad Anwaar , Karaoglu Ismail Can , Ozer Onur , Albayrak Cem , Kizilel Seda
Published: April 2021

One of the key challenges in engineering three-dimensional tissue constructs is the development of a mature microvascular network capable of supplying sufficient oxygen and nutrients to the tissue. Recent angiogenic therapeutic strategies have focused on vascularization of the constructed tissue, and its integration in vitro; these strategies typically combine regenerative cells, growth factors (GFs) with custom-designed biomaterials. However, the field needs to progress in the clinical translation of tissue engineering strategies. The article first presents a detailed description of the steps in neovascularization and the roles of extracellular matrix elements such as GFs in angiogenesis. It then delves into decellularization, cell, and GF-based strategies employed thus far for therapeutic angiogenesis, with a particularly detailed examination of different methods by which GFs are delivered in biomaterial scaffolds. Finally, interdisciplinary approaches involving advancement in biomaterials science and current state of technological development in fabrication techniques are critically evaluated, and a list of remaining challenges is presented that need to be solved for successful translation to the clinics.
An implicit kinetic inviscid flux for predicting continuum flows in all speed regimes
Authors: Cao Junzhe , Liu Sha , Zhong Chengwen , Zhuo Congshan
Published: April 2021

In this study, the kinetic inviscid flux (KIF) is improved and coupled with an implicit strategy. The KIF is a recently proposed numerical method, which is a dynamic combination of the kinetic flux vector splitting (KFVS) method and the totally thermalized transport (TTT) method. The inherent microscopic mechanism of the KFVS makes the KIF good at solving shock waves and avoiding the numerical shock instability phenomenon. When developing the implicit KIF, it is noticed that, in boundary layers, the KFVS part of the KIF not only reduces the accuracy but also seriously reduces the Courant–Friedrichs–Lewy (CFL) number. As a result, a new weight is proposed in this paper to combine the KFVS method with the TTT method properly. Besides admitting the use of larger CFL numbers, this new weight also contributes to more accurate numerical results like pressure, friction coefficient, and heat flux when solving shock waves, boundary layers, and complex supersonic/hypersonic flows. To examine the validity, accuracy, and efficiency of the proposed method, six numerical test cases covering the whole speed regime are conducted, including the hypersonic viscous flow past a cylinder, the hypersonic double-cone flow, the hypersonic double-ellipsoid flow, the laminar shock-boundary layer interaction, the supersonic flow around a ramp segment and the subsonic lid-driven cavity flow.
Local force calculations by an improved stress tensor discontinuity-based immersed boundary–lattice Boltzmann method
Authors: Suzuki Kosuke , Ishizaki Kou , Yoshino Masato
Published: April 2021

In the immersed boundary method, the volume force that is applied to enforce the no-slip boundary condition is equivalent to a discontinuity in the stress tensor across the boundary. In the stress tensor discontinuity-based immersed boundary–lattice Boltzmann method, which was proposed in our previous study [Suzuki and Yoshino, “A stress tensor discontinuity-based immersed boundary–lattice Boltzmann method,” Comput. Fluids 172, 593–608 (2018)], the boundary is represented by Lagrangian points that are independent of the background grid, and the discontinuity in the stress tensor is calculated on these points from desired particle distribution functions that satisfy the no-slip boundary condition based on the bounce-back condition. Although this method allows computation of the force locally acting on the boundary, the local force has a spurious oscillation along the boundary. In the present study, we remedy this problem by relaxing the bounce-back condition. To confirm the improvement achieved by using the new method, we apply it to simulate typical benchmark problems involving two- and three-dimensional flows with stationary or moving boundaries. We find that the proposed approach can effectively eliminate the spurious oscillation of the local force, and the results obtained with the improved method show good agreement with other numerical and experimental results. In addition, as an application of the proposed method to local force calculation, we investigate the effect of lift enhancement due to wing–wake interaction on a two-dimensional butterfly-like flapping wing.
Enhanced electro-osmosis in propylene carbonate salt solutions
Authors: Russell Wilfred Shelby , Siwy Zuzanna
Published: April 2021

Properties of solid–liquid interfaces and surface charge characteristics mediate ionic and molecular transport through porous systems, affecting many processes such as separations. Herein, we report experiments designed to probe the electrochemical properties of solid–liquid interfaces using a model system of a single polyethylene terephthalate (PET) pore in contact with aqueous and propylene carbonate solutions of LiClO4. First, the existence and polarity of surface charges were inferred from current–voltage curves recorded when a pore was placed in contact with a LiClO4 concentration gradient. Second, the electro-osmotic transport of uncharged polystyrene particles through the PET pore provided information on the polarity and the magnitude of the pore walls’ zeta potential. Our experiments show that the PET pores become effectively positively charged when in contact with LiClO4 solutions in propylene carbonate, even though in aqueous LiClO4, the same pores are negatively charged. Additionally, the electro-osmotic velocity of the particles revealed a significantly higher magnitude of the positive zeta potential of the pores in propylene carbonate compared to the magnitude of the negative zeta potential in water. The presented methods of probing the properties of solid–liquid interfaces are expected to be applicable to a wide variety of solid and liquid systems.
Anisotropic spin-driven ferroelectricity and magnetoelectric effect in a Y-type hexaferrite
Authors: Li L. Y. , Wang W. , Li P. Z. , Xian J. B. , Zeng M. , Liu M. F. , Hou Z. P. , Fan Z. , Chen D. Y. , Qin M. H. , Gao X. S. , Lu X. B. , Liu J.-M.
Published: April 2021

We report a systematic study on the magnetic, dielectric, and magnetoelectric (ME) properties of the Y-type hexaferrite (Ba0.4Sr1.6)Zn2(Fe11.3Al0.7)O22 single crystal. The phase diagrams were established by the observed magnetic anomalies under magnetic field and temperature scans for the in-plane and out-of-plane cases. Intrinsic large anisotropy in the magnetodielectric and converse ME effects was revealed. The spin-driven electric polarizations induced in the ab-plane and out-of-plane were found to be closely related to the transverse conical and alternating longitudinal conical spin structures, respectively. The amplitudes of varied magnetization ΔM are about ∼0.128 μB/f.u and ∼0.0178 μB/f.u. in the E oscillating between ±1 MV/m at 100 K, corresponding to the converse ME effect coefficient of ∼3500 ps/m and ∼480 ps/m for the in-plane and out-of-plane cases, respectively. All these results demonstrate the essential and unique spin-order-induced anisotropic ferroelectricity and ME properties in these Y-type hexaferrites.
Performance dependence of a stick-slip piezoelectric actuator on the angle between the piezoelectric stack and mover
Authors: Wang Kuifeng , Xu Zhi , Li Xuan , Sun Wuxiang , Yang Zhixin , Huang Hu
Published: April 2021

The angle between the piezoelectric stack (PES) and the mover would significantly affect the output performances of stick-slip piezoelectric actuators in theory; however, this issue has not been explored. Accordingly, in this paper, to investigate the effects of the angle, a stick-slip piezoelectric actuator with a changeable angle between the PES and the mover was proposed, and its structure was briefly introduced first. Then, the relationship between the angle and the parasitic motion was theoretically calculated. After that, the output performances of the actuator were characterized under different angles between the PES and the mover. The results indicated that the angle between the PES and the mover significantly affected the one-step maximum displacement and the backward motion. After comprehensive analysis, the best output performances of the actuator were obtained under the angle of 0°.
Thermal and field-rate dependence of multi-step magnetization switching of synthetic antiferromagnetic multilayers
Authors: Pan Zizhao , Ma Mangyuan , Chen Zhendong , Ma Fusheng
Published: April 2021

Synthetic antiferromagnetic (SAF) multilayers are a kind of functional materials with great potential for spintronic devices. Many excellent properties of SAF multilayers have been widely reported in previous works. Here, we experimentally found that the magnetization switching steps n of [Pt/Co]2/Ru/[Co/Pt]4 SAF multilayers with perpendicular magnetic anisotropy are highly dependent on the temperature and magnetic field sweeping rate by magneto-optic Kerr effect and anomalous Hall resistance measurement. It is found that the contribution of the upper and lower layers of the SAF multilayers to the anomalous Hall coefficients is different. The switching steps n change from 2 to 3 by reducing the thickness of the non-magnetic spacer, decreasing the sweeping rate of the magnetic field, and increasing the temperature of the measuring environment. Our findings could provide a method to achieve multi-step magnetization switching for functional spintronic devices.
Ordered GaAs quantum dots by droplet epitaxy using in situ direct laser interference patterning
Authors: Han Im Sik , Wang Yun-Ran , Hopkinson Mark
Published: April 2021

We report the fabrication of highly ordered arrays of GaAs/AlGaAs quantum dots (QDs) by droplet epitaxy using in situ direct laser interference patterning. Two-dimensional arrays of Ga droplets with a periodicity of ∼300 nm are initially formed on nanoisland structured AlGaAs surfaces due to the localized surface diffusion under the influence of a thermal gradient imposed by the light pulse. After crystallization under an arsenic flux, precisely ordered arrays of GaAs single dots are obtained. The size distribution and optical properties of the ordered GaAs QDs are shown to be optimized by the careful choice of parameters for nucleation and droplet formation.
Accomplishment of one-step specific PCR and evaluated SELEX process by a dual-microfluidic amplified system
Authors: Chen Jing , Liu Xiaohui , Xu Meng , Li Zhoumin , Xu Danke
Published: April 2021

One of the main obstacles for systematic evolution of ligands by exponential enrichment (SELEX) failure is the generation of a non-specific product, as selection-inherent amplification procedures tend to form by-products, which prevents the enrichment of target-binding aptamers. Herein, we reported a dual-microfluidic amplified system (dual-MAS) based on the real-time polymerase chain reaction (PCR) detection chip and the large volume PCR chip for one-step specific PCR and for evaluating the SELEX process. First, it is a simple method to accomplish analytical PCR and amplification PCR in one step, and the optimal number of cycles for generating the specific PCR product is the cycles when the slope of the linear amplification period of the real-time PCR curve begins to decrease. Second, the time used by the dual-MAS for generating a specific PCR product is reduced to 30 min, and the multi-functional dual-MAS can simultaneously evaluate the SELEX process by providing important information on the amounts of enriched sequences and the library diversity in every round of SELEX. In addition, pollution contamination and fragment loss can be significantly avoided in the closed chip. Last, the specific PCR product, the amounts of enriched sequences, and the library diversity can be obtained for every single SELEX in just 30 min. Compared with current methods, this system can reduce the time for generating a specific PCR product and SELEX, and it is easier to choose the optimal number of cycles for a specific PCR product. In a word, it is a sensitive, simple, and rapid strategy to improve the specificity of the PCR product and make the process of SELEX in a controlled way.
Maximal kinetic energy and angular distribution analysis of spatial map imaging: Application to photoelectrons from a single quantum state of H2O
Authors: Yifrach Yair , Rahimi Rami , Portnov Alexander , Baraban Joshua H. , Bar Ilana
Published: April 2021

Dynamical or spatial properties of charged species can be obtained using electrostatic lenses by velocity map imaging (VMI) or spatial map imaging (SMI), respectively. Here, we report an approach for extracting dynamical and spatial information from patterns in SMI images that map the initial coordinates, velocity vectors, and angular distributions of charged particles onto the detector, using the same apparatus as in VMI. Deciphering these patterns required analysis and modeling, involving both their predictions from convolved spatial and velocity distributions and fitting observed images to kinetic energies (KEs) and anisotropy parameters (βs). As the first demonstration of this capability of SMI, the ensuing photoelectrons resulting from (2 + 1) resonant ionization of water in a selected rotational state were chosen to provide a rigorous basis for comparison to VMI. Operation with low acceleration voltages led to a measured SMI pattern with a unique vertical intensity profile that could be least-squares fitted to yield KE and β, in good agreement with VMI measurement. Due to the potential for improved resolution and the extended KE range achievable by this new technique, we expect that it might augment VMI in applications that require the analysis of charged particles and particularly in processes with high KE release.
Lattice Boltzmann multicomponent model for direct-writing printing
Authors: Monteferrante Michele , Montessori Andrea , Succi Sauro , Pisignano Dario , Lauricella Marco
Published: April 2021

We introduce a mesoscale approach for the simulation of multicomponent flows to model the direct-writing printing process, along with the early stage of ink deposition. As an application scenario, alginate solutions at different concentrations are numerically investigated alongside processing parameters, such as apparent viscosity, extrusion rate, and print head velocity. The present approach offers useful insights on the ink rheological effects upon printed products, susceptible to geometric accuracy and shear stress, by manufacturing processes such as the direct-writing printing for complex photonic circuitry, bioscaffold fabrication, and tissue engineering.
Nondestructive readout of holographic memory in Ag/TiO2 heterojunction via carbon-dots and hydrogel co-modification
Authors: Wang Yiqian , Li Xin , Fu Shencheng , Wang Xiuli , Zhou Jiahui , Liu Hongfang , Zhang Xintong , Liu Yichun
Published: April 2021

Effective utilization of light energy is essential for the storage and conversion of optical information. Plasmonic nanoparticles are regarded as an optical energy antenna for their spectrum-tuning ability, while the multi-wavelength response and interface electron flow, in turn, weaken the stability in reading information. Herein, we propose a smart route of carbon dot/hydrogel co-modified silver nanoparticles in titania to construct a large-area Schottky heterojunction. The diffraction efficiency is increased by three times, and the readout stability is even increased by 240 times, compared with those for undecorated Ag/TiO2 heterostructures. The readout fluctuation ratio of the holographic signal is less than 3% in the area of 1.5 × 1.5 cm2. The enhanced performance benefits from the interface electron regulation by carbon dots and the high stability of Ag+ ions in hydrogel. Based on such properties, an 8-cm plasmonic holographic disk is fabricated, opening a bright way to the application of high-density information memory.
Unidirectional coherent energy transport via conjugated oligo(p-phenylene) chains
Authors: Leong Tammy X. , Qasim Layla N. , Mackin Robert T. , Du Yuchen , Pascal Robert A. , Rubtsov Igor V.
Published: April 2021

We discovered a way to funnel high-frequency vibrational quanta rapidly and unidirectionally over large distances using oligo(p-phenylene) chains. After mid-IR photon photoexcitation of a —COOH end group, the excess energy is injected efficiently into the chain, forming vibrational wavepackets that propagate freely along the chain. The transport delivers high-energy vibrational quanta with a range of transport speeds reaching 8.6 km/s, which exceeds the speed of sound in common metals (∼5 km/s) and polymers (∼2 km/s). Efficiencies of energy injection into the chain and transport along the chain are found to be very high and dependent on the extent of conjugation across the structure. By tuning the degree of conjugation via electronic doping of the chain, the transport speed and efficiency can be controlled. The study opens avenues for developing materials with controllable energy transport properties for heat management, schemes with efficient energy delivery to hard-to-reach regions, including transport against thermal gradients, and ways for initiating chemical reactions remotely.
Plug-in tubes allow tunable oil removal, droplet packing, and reaction incubation for time-controlled droplet-based assays
Authors: Sun Meng , Maryu Gembu , Wang Shiyuan , Yang Qiong , Bailey Ryan C.
Published: April 2021

Here, we report a unique microfluidic technique that utilizes a membrane filter and plug-in tubes to remove oil and pack water-in-oil droplets for controlled incubation of droplet-based assays. This technique could be modularly incorporated into most droplet-generation devices without a need to alter the original designs. Our results show that removing excess oil to form tightly packed droplets allows for extended and controllable incubation for droplets traveling in microchannels. The efficiency of this technique was evaluated and confirmed using a time-dependent enzyme assay with a fluorometric readout. The system is also readily generalizable to control inter-droplet distance, crucial for studying droplet communication and pattern formation.
Highly active and stable Ir nanoclusters derived from Ir1/MgAl2O4 single-atom catalysts
Authors: Yang Jingyi , Zhang Jingcai , Jiang Qike , Su Yang , Cui Yitao , Li Xianquan , Zhang Shengxin , Li Weizhen , Qiao Botao
Published: April 2021

Single-atom catalysts (SACs) prepared by the atom trapping method often possess high stability yet have limited advantages regarding catalytic performance due to the strong metal–support interaction. Using these SACs as seeds to develop supported nanoclusters or nanoparticles has, however, been proven to be effective in improving the catalysts’ intrinsic activity. Herein, we have prepared extremely stable Ir SACs supported by MgAl2O4 via atomic trapping and used them as seeds to fabricate highly active and stable Ir nanocluster catalysts by high-temperature reduction. The activity toward N2O decomposition increased by more than ten times compared with that of the parent Ir SACs. This study provides a new avenue to design and develop highly active and stable catalysts for industrial use.