bluuebunny/crossref_metadata_2025 huggingface dataset:
Perfect non-specular reflection with polarization control by using a locally passive metasurface sheet on a grounded dielectric slab
Authors: Yepes C. , Faenzi M. , Maci S. , Martini E.
Published: June 2021

This paper investigates the conditions for a perfect anomalous reflection through a modulated metasurface consisting of a metallic cladding printed over a grounded slab. Differently to what has been previously published, the problem is rigorously addressed by modeling the metallic cladding through an equivalent penetrable impedance and accounting for the grounded slab through the problem's Green's function. It is shown that without polarization transformation, the exact solution exists only for the special case of retroreflection, and, in that case, it can be done simultaneously for the two orthogonal polarizations, with an arbitrary phase shift among the two. On the other hand, changing the polarization of the reflected wave allows one to find an exact solution for arbitrary combinations of incidence and reflection angles. The exact solution is found by imposing that the induced currents radiating with the Green's function of the background problem simultaneously create the desired reflected beam and cancel the specular reflection from the grounded slab. This approach leads to the derivation of a closed-form expression for the homogenized penetrable impedance profile providing perfect anomalous reflection, i.e., ensuring the vanishing of all the coefficients of the waves associated with unwanted diffraction orders, including the specular reflected wave and the evanescent waves. This result is of great practical interest, since the derived penetrable impedance profile can be readily implemented through a simple distribution of metallic patches. The feasibility of this approach is verified through full wave simulations of both the ideal impedance and the patch-based structure, which confirm the effectiveness of the proposed solution.
Anisotropic ultrafast spin dynamics in epitaxial cobalt
Authors: Unikandanunni Vivek , Medapalli Rajasekhar , Fullerton Eric E. , Carva Karel , Oppeneer Peter M. , Bonetti Stefano
Published: June 2021

We investigate the ultrafast spin dynamics in an epitaxial hcp(11¯00) cobalt thin film. By performing pump–probe magneto-optical measurements with the magnetization along either the easy or hard magnetic axis, we determine the demagnetization and recovery time for the two axes. We observe an average of 33% slower dynamics along the easy magnetization axis, which we attribute to magneto-crystalline anisotropy of the electron–phonon coupling, supported by our ab initio calculations. This points toward an unambiguous and previously undisclosed role of anisotropic electron–lattice coupling in ultrafast magnetism.
Accurate frozen core approximation for all-electron density-functional theory
Authors: Yu Victor Wen-zhe , Moussa Jonathan , Blum Volker
Published: June 2021

We implement and benchmark the frozen core approximation, a technique commonly adopted in electronic structure theory to reduce the computational cost by means of mathematically fixing the chemically inactive core electron states. The accuracy and efficiency of this approach are well controlled by a single parameter, the number of frozen orbitals. Explicit corrections for the frozen core orbitals and the unfrozen valence orbitals are introduced, safeguarding against seemingly minor numerical deviations from the assumed orthonormality conditions of the basis functions. A speedup of over twofold can be achieved for the diagonalization step in all-electron density-functional theory simulations containing heavy elements, without any accuracy degradation in terms of the electron density, total energy, and atomic forces. This is demonstrated in a benchmark study covering 103 materials across the Periodic Table and a large-scale simulation of CsPbBr3 with 2560 atoms. Our study provides a rigorous benchmark of the precision of the frozen core approximation (sub-meV per atom for frozen core orbitals below −200 eV) for a wide range of test cases and for chemical elements ranging from Li to Po. The algorithms discussed here are implemented in the open-source Electronic Structure Infrastructure software package.
Electronic and optical properties of Zn-doped β-Ga2O3 Czochralski single crystals
Authors: Jesenovec Jani , Varley Joel , Karcher Samuel E. , McCloy John S.
Published: June 2021

β-Ga2O3 has several soluble deep acceptors that impart insulating behavior. Here, we investigate Zn doping (0.25 at. %) in bulk Czochralski and vertical gradient freeze β-Ga2O3. Representative crystals were assessed for orientation (electron backscatter diffraction and Raman spectroscopy), purity (glow discharge mass spectrometry and secondary ion mass spectrometry), optical properties (ultraviolet to near infrared absorption), and electrical properties (resistivity and current–voltage). Purity measurements indicate that Zn evaporation is insufficient to inhibit doping of Zn into β-Ga2O3. Hybrid functional calculations show Zn substitutes nearly equally on tetrahedral and octahedral sites, with less than ∼0.1 eV preference for the octahedral (GaII) site. Furthermore, calculations show that ZnGa acts as a deep acceptor with trapping levels ∼1.3 and ∼0.9 eV above the valence band for one and two holes, respectively. The solubility and electronic behavior of Zn dopants are consistent with measured concentrations >1 × 1018 atoms/cm3 and electrical measurements that show resistivity 1011–1013 Ω cm, with no p-type conduction.
Charge transport through molecular ensembles: Recent progress in molecular electronics
Authors: Liu Yuru , Qiu Xinkai , Soni Saurabh , Chiechi Ryan C.
Published: June 2021

This review focuses on molecular ensemble junctions in which the individual molecules of a monolayer each span two electrodes. This geometry favors quantum mechanical tunneling as the dominant mechanism of charge transport, which translates perturbances on the scale of bond lengths into nonlinear electrical responses. The ability to affect these responses at low voltages and with a variety of inputs, such as de/protonation, photon absorption, isomerization, oxidation/reduction, etc., creates the possibility to fabricate molecule-scale electronic devices that augment; extend; and, in some cases, outperform conventional semiconductor-based electronics. Moreover, these molecular devices, in part, fabricate themselves by defining single-nanometer features with atomic precision via self-assembly. Although these junctions share many properties with single-molecule junctions, they also possess unique properties that present a different set of problems and exhibit unique properties. The primary trade-off of ensemble junctions is complexity for functionality; disordered molecular ensembles are significantly more difficult to model, particularly atomistically, but they are static and can be incorporated into integrated circuits. Progress toward useful functionality has accelerated in recent years, concomitant with deeper scientific insight into the mediation of charge transport by ensembles of molecules and experimental platforms that enable empirical studies to control for defects and artifacts. This review separates junctions by the trade-offs, complexity, and sensitivity of their constituents; the bottom electrode to which the ensembles are anchored and the nature of the anchoring chemistry both chemically and with respect to electronic coupling; the molecular layer and the relationship among electronic structure, mechanism of charge transport, and electrical output; and the top electrode that realizes an individual junction by defining its geometry and a second molecule–electrode interface. Due to growing interest in and accessibility of this interdisciplinary field, there is now sufficient variety in each of these parts to be able to treat them separately. When viewed this way, clear structure–function relationships emerge that can serve as design rules for extracting useful functionality.
From bending of light to positive mass: A non-PDE perspective
Authors: He Xiaokai , Wu Xiaoning , Xie Naqing
Published: June 2021

Penrose et al. investigated the physical incoherence of the spacetime with negative mass via the bending of light. Precise estimates of the time-delay of null geodesics were needed and played a pivotal role in their proof. In this paper, we construct an intermediate diagonal metric and reduce this problem to a causality comparison in the compactified spacetimes regarding timelike connectedness near conformal infinities. This different approach allows us to avoid encountering the difficulties and subtle issues that Penrose et al. met. It provides a new, substantially simple, and physically natural non-partial differential equation viewpoint to understand the positive mass theorem. This elementary argument modestly applies to asymptotically flat solutions that are vacuum and stationary near infinity.
New mechanisms of cavity facet degradation for GaN-based laser diodes
Authors: Wang Xiao-Wei , Liu Zong-Shun , Zhao De-Gang , Chen Ping , Liang Feng , Yang Jing
Published: June 2021

We investigated the cavity facet degradation of unsealed GaN-based laser diodes (LDs). It was found that the decrease of optical output power accompanied by undulation for unsealed LDs is related to the facet degradation. Deposits containing Ga, Al, Si, and O were observed on the LD facet for the first time, explaining the reason for the degradation behavior. Considering the shorter wavelength of GaN-based laser diodes, we propose that the splitting of water molecules induced by high-energy photons triggers the oxidation of the facets and the deposition of SiO2. The shape of the deposits is closely correlated with the field distribution on the facet, influencing the LDs’ output power. Improving the tightness of the package is necessary to avoid the fast degradation of GaN-based LDs.
Structure prediction in high-entropy alloys with machine learning
Authors: Zhao D. Q. , Pan S. P. , Zhang Y. , Liaw P. K. , Qiao J. W.
Published: June 2021

High-entropy alloy is an alloy design concept without a principal component. This concept not only refers to the complexity of alloy compositions but also means that when the high-entropy alloy transits from a high-energy state to low-energy state, there will be more intermediate metastable states. Corresponding to different states are the changes in the degree and manner of order in the microstructure. In this study, we used machine learning to combine elemental characteristics with long-term ordering and established 87% of prediction accuracy. This data-driven method can correlate elemental characteristics and metastable states and accelerate the discovery of potential compositions.
Imaging the small with the small: Prospects for photonics in micro-endomicroscopy for minimally invasive cellular-resolution bioimaging
Authors: Untracht Gavrielle R. , Karnowski Karol , Sampson David D.
Published: June 2021

Many bioimaging studies, including those in engineered tissue constructs, intravital microscopy in animal models, and medical imaging in humans, require cellular-resolution imaging of structures deep within a sample. Yet, many of the current approaches are limited in terms of resolution, but also in invasiveness, repeatable imaging of the same location, and accessible imaging depth. We coin the term micro-endomicroscope to describe the emerging class of small, cellular-resolution endoscopic imaging systems designed to image cells in situ while minimizing perturbation of the sample. In this Perspective, we motivate the need for further development of micro-endomicroscopes, highlighting applications that would greatly benefit, reviewing progress, and considering how photonics might contribute. We identify areas ripe for technological development, such as micro-scanners and small lens systems, that would advance micro-endomicroscope performance. With the right developments in photonics, many possibilities exist for new minimally invasive translatable imaging tools across the scientific, pre-clinical, and clinical spectrum: from longitudinal studies of engineered tissue constructs, to tracking disease progression in animal models, to expanding the ability to diagnose and develop treatments for diseases without the need for invasive medical procedures.
Computational optimization of transcranial focused ultrasound stimulation: Toward noninvasive, selective stimulation of deep brain structures
Authors: De Angelis A. , Leonetti M. , Apollonio F. , Liberti M. , Aglioti S. M. , Ruocco G.
Published: June 2021

Low-intensity focused ultrasound is emerging as a high-resolution highly selective alternative to standard noninvasive transcranial brain stimulation techniques. A major challenge in using ultrasound devices is designing a stimulator capable of efficiently focusing the acoustic wave to selectively target a specific brain region by compensating for the wavefront distortions induced by the intact skull. Single-element transducers are efficient in stimulating cortical areas in both non-human and human primates. However, reaching deeper brain structures with millimeter resolution and high specificity requires the use of ad hoc multi-element devices characterized by a specific number of piezoelectric elements that optimize the energy deposition in the focal region while simultaneously minimizing the off-focus dispersion. The high cost and complexity of adequately controlling the thousands of elements used generally for such stimulators have limited their use in neuromodulation applications. This study defines the optimal configuration of a multi-element stimulator for low-intensity focused ultrasound through a full-wave realistic numerical model that includes both the stimulator geometry and a detailed anatomical head model. The performance of the device was evaluated. We investigated the influence of the number of piezoelectric elements in the stimulator on its transcranial focusing capabilities. Our results confirm that the focusing optimization improves as the number of elements increased (from 16 to 256). With only 96 point-sources, there was a good trade-off between cost and focusing efficiency. Our study provides a cost-effective stimulator design that enables a standard focusing procedure and a steering technique enacted without prior knowledge about the skull's local acoustic impedance.
Characteristics of cavity collapse behind a high-speed projectile entering the water
Authors: Zhang Q. , Zong Z. , Sun T. Z. , Yu Y. Q. , Li H. T.
Published: June 2021

We investigate cavity collapse regimes behind high-speed projectiles entering the water. Using numerical simulations, we confirmed two different collapse phenomena: deep pinch-off and consecutive collapse. We performed a theoretical analysis to develop the relationship between projectile motion and cavity evolution. We found that projectile acceleration is the most significant factor determining the initial cavity collapse. There is a critical acceleration determining the direction of cavity collapse at the location of deep pinch-off. The pressure field is obviously affected by the collapse. The increase in pressure induced by surface pinch-off accelerates the collapse at the cavity tail. Because of the impact of surface pinch-off, consecutive collapse can be seen if a projectile reaches critical acceleration near a free surface. Otherwise, the cavity will pinch off at a distance from the surface of the water and form a deep pinch-off. Particular attention is paid to the impact of consecutive collapse on the projectile. Numerical calculations show that cavity collapse and a high-speed water jet have an obvious impact on the stability of the projectile. The jet exerts great pressure on the projectile, and the accompanying splash droplets contaminate the cavity wall. Cavity pulsation and the asymmetric geometry of the projectile-cavity system aggravate attitude deflection.
Three dimensional wave group dynamics of ion acoustic waves in electron–positron–ion plasmas in the presence of an external uniform magnetic field
Authors: Biswas Akash , Chakraborty Debkumar , Pramanik Sourav , Ghosh Samiran
Published: June 2021

Three dimensional (3D) wave group dynamics of ion acoustic wave is studied in electron–positron–ion (EPI) plasmas incorporating the effects of an external uniform magnetic field through the Laedke–Spatschek equation. In the presence of self-interaction (self-focusing effect), the wave group dynamics is shown to be governed by a (3 + 1) nonlinear Schrödinger equation. The derived nonlinear equations are solved analytically and the solutions predict a wide class of nonlinear structures in EPI plasma in the presence of magnetic field. The boundaries of stable and unstable solutions are also specified in parametric space. The results are expected to provide deeper insights into the ionic processes occurring in both astrophysical and laboratory plasmas.
On the exceptional temperature stability of ferroelectric Al1-xScxN thin films
Authors: Islam Md. Redwanul , Wolff Niklas , Yassine Mohamed , Schönweger Georg , Christian Björn , Kohlstedt Hermann , Ambacher Oliver , Lofink Fabian , Kienle Lorenz , Fichtner Simon
Published: June 2021

Through its dependence on low symmetry crystal phases, ferroelectricity is inherently a property tied to the lower temperature ranges of the phase diagram for a given material. This paper presents conclusive evidence that in the case of ferroelectric Al1−xScxN, low temperature has to be seen as a purely relative term, since its ferroelectric-to-paraelectric transition temperature is confirmed to surpass 1100 °C and thus the transition temperature of virtually any other thin film ferroelectric. We arrived at this conclusion through investigating the structural stability of 0.4–2 μm thick Al0.73Sc0.27N films grown on Mo bottom electrodes via in situ high-temperature x-ray diffraction and permittivity measurements. Our studies reveal that the wurtzite-type structure of Al0.73Sc0.27N is conserved during the entire 1100 °C annealing cycle, apparent through a constant c/a lattice parameter ratio. In situ permittivity measurements performed up to 1000 °C strongly support this conclusion and include what could be the onset of a diverging permittivity only at the very upper end of the measurement interval. Our in situ measurements are well-supported by ex situ (scanning) transmission electron microscopy and polarization and capacity hysteresis measurements. These results confirm the structural stability on the sub-μm scale next to the stability of the inscribed polarization during the complete 1100 °C annealing treatment. Thus, Al1−xScxN, there is the first readily available thin film ferroelectric with a temperature stability that surpasses virtually all thermal budgets occurring in microtechnology, be it during fabrication or the lifetime of a device—even in harshest environments.
Performance of a black-box-type rovibrational method in comparison with a tailor-made approach: Case study for the methane–water dimer
Authors: Martín Santa Daría Alberto , Avila Gustavo , Mátyus Edit
Published: June 2021

The present work intends to join and respond to the excellent and thoroughly documented rovibrational study of X. G. Wang and T. Carrington, Jr. [J. Chem. Phys. 154, 124112 (2021)] that used an approach tailored for floppy dimers with an analytic dimer Hamiltonian and a non-product basis set including Wigner D functions. It is shown in the present work that the GENIUSH black-box-type rovibrational method can approach the performance of the tailor-made computation for the example of the floppy methane–water dimer. Rovibrational transition energies and intensities are obtained in the black-box-type computation with a twice as large basis set and in excellent numerical agreement in comparison with the more efficient tailor-made approach.
Fluorescent ruby nanocrystals for biocompatible applications
Authors: Alkahtani Masfer H , Almuqhim Anas A. , Alshehri Abdullah A. , Almughem Fahad A. , AlHazaa Abdulaziz N. , Hemmer Philip
Published: June 2021

Chromium-doped aluminum oxide (ruby) micro- and nanocrystals have shown a sharp and strong fluorescence emission that linearly depends on pressure and temperature. They also have an exceptional photostability and a high quantum efficiency. In spite of their widespread use as pressure sensors, only a few earlier studies have used ruby nanocrystals as efficient fluorescent bioimaging probes. However, their use at biocompatible excitation/detection wavelengths and toxicity assessment against human living cells remain unexplored. In this work, we show that ruby nanocrystals can be efficiently excited and detected within the biological transparency window. We also examined the biocompatibility of ruby nanocrystals in human living cells, which exhibited no detectable cytotoxicity. This makes ruby nanocrystals among the best alternative fluorescent probes for promising biological applications.
Phenomenological analysis of transverse thermoelectric generation and cooling performance in magnetic/thermoelectric hybrid systems
Authors: Yamamoto Kaoru , Iguchi Ryo , Miura Asuka , Zhou Weinan , Sakuraba Yuya , Miura Yoshio , Uchida Ken-ichi
Published: June 2021

We phenomenologically calculate the performance of the recently observed Seebeck-driven transverse thermoelectric generation (STTG) for various systems in terms of the thermopower, power factor, and figure of merit to demonstrate the usefulness of STTG. The STTG system consists of a closed circuit comprising thermoelectric and magnetic materials which exhibit the Seebeck and anomalous Hall effects, respectively. When a temperature gradient is applied to the hybrid system, the Seebeck effect in the thermoelectric material layer generates a longitudinal charge current in the closed circuit, and the charge current subsequently drives the anomalous Hall effect in the magnetic material layer. The anomalous Hall voltage driven by the Seebeck effect has a similar symmetry to the transverse thermoelectric conversion based on the anomalous Nernst effect. We find that the thermoelectric properties of STTG can be much better than those of the anomalous Nernst effect by increasing the Seebeck coefficient and anomalous Hall angle of the thermoelectric and magnetic materials, respectively, as well as by optimizing their dimensions. We also formulate the electronic cooling performance in the STTG system, thereby confirming the reciprocal relation for the hybrid transverse thermoelectric conversion.
Externally driven broadband transmission in strongly disordered materials
Authors: Bachelard Nicolas , Ropp Chad , Yang Sui , Zhang Xiang
Published: June 2021

In classical and quantum systems, order is of fundamental importance to many branches of science. Still, disorder is prevalent in our natural world. It manifests in various ways, and overcoming its limitations would open up exciting applications. In this work, we numerically show that disorder-induced Anderson localization can be mitigated and transmission systematically restored in random media through a self-organization process relying on energy dissipation. Under the scattering pressure produced by a driving optical field, a colloidal suspension composed of strongly polydisperse (i.e., random size) particles spontaneously assembles a Bloch-like mode with a broad transmission band. This mode displays a deterministic transmission scaling law that overcomes the statistical exponential decay expected in random media. This work demonstrates that, through the continuous dissipation of energy, amorphous materials can collectively synchronize with a coherent drive field and assemble a crystalline order. Self-organization, thus, offers a robust approach for addressing the physical limitations of disorder and immediately opens the door to applications in slow-light engineering and the development of “bottom-up” photonic materials.
Narrating organisational identity
Authors: Holmgreen Lise-Lotte
Published: June 2021

Organisational identity may be understood as the result of communication processes, e.g. in the form of narratives and stories, that continuously intertwine and compete for the right to define the organisation (Boje, 1995;Humle & Frandsen, 2017). This understanding forms the background of the article which analyses the narrative struggles in a local Danish airport whose collective identity was challenged in light of organisational changes that led to a large and dispersed organisation. Combining positioning theory (Davies & Harré, 1990,1999) with close linguistic analysis, data from a focus group interview are analysed, showing that through stories and narratives, top-management and staff members construct several positions along a cline that make it possible to achieve consensus across organisational levels and divisions. Furthermore, the article argues for analysing participants’ linguistic choices in detail to come closer to how participants do positioning work.
Cooperative binding ensures the obligatory melibiose/Na+ cotransport in MelB
Authors: Hariharan Parameswaran , Guan Lan
Published: June 2021

MelB catalyzes the obligatory cotransport of melibiose with Na+, Li+, or H+. Crystal structure determination of the Salmonella typhimurium MelB (MelBSt) has revealed a typical major facilitator superfamily (MFS) fold at a periplasmic open conformation. Cooperative binding of Na+ and melibiose has been previously established. To determine why cotranslocation of sugar solute and cation is obligatory, we analyzed each binding in the thermodynamic cycle using three independent methods, including the determination of melting temperature by circular dichroism spectroscopy, heat capacity change (ΔCp), and regulatory phosphotransferase EIIAGlc binding with isothermal titration calorimetry (ITC). We found that MelBSt thermostability is increased by either substrate (Na+ or melibiose) and observed a cooperative effect of both substrates. ITC measurements showed that either binary formation yields a positive sign in the ΔCp, suggesting MelBSt hydration and a likely widening of the periplasmic cavity. Conversely, formation of a ternary complex yields negative values in ΔCp, suggesting MelBSt dehydration and cavity closure. Lastly, we observed that EIIAGlc, which has been suggested to trap MelBSt at an outward-open state, readily binds to the MelBSt apo state at an affinity similar to MelBSt/Na+. However, it has a suboptimal binding to the ternary state, implying that MelBSt in the ternary complex may be conformationally distant from the EIIAGlc-preferred outward-facing conformation. Our results consistently support the notion that binding of one substrate (Na+ or melibiose) favors MelBSt at open states, whereas the cooperative binding of both substrates triggers the alternating-access process, thus suggesting this conformational regulation could ensure the obligatory cotransport.
Research on dynamics of bouncing ball in triboelectric nanogenerator
Authors: Huang Chaoming , Li Qingtao , Li Jie , Guo Huize , Hao Wenhan , Sheng Kexin , An Yunsheng , Chen Jiayi , Zhang Xinyi , Xu Minyi
Published: June 2021

Bouncing ball based Triboelectric Nanogenerator (BB-TENG) can be used to harvest vibrational energy and sense signal for self-powered sensor in the non-resonant zone because of its non-spring vibration system. The energy harvesting efficiency and sensing effectiveness are significantly affected by the dynamics of the bouncing ball. However, due to the chaotic and nonlinear mechanics, the dynamics of the bouncing ball inside BB-TENG and the corresponding influencing factors have not yet been revealed, which restricts the development of high-efficiency BB-TENG. In this work a method based on dynamics simulation and test bench experiment is to be proposed and the ‘Takeoff’, ‘Well-Contact’, ‘Self-Spin’, and ‘Rich-Contact’ of the bouncing ball with the plate electrodes will be investigated. The kinetic model established based on the Automatic Dynamic Analysis of Mechanical Systems (ADAMSs) is verified through experiments to confirm the reliability of the simulation results. It is found that ‘Well-Contact’ of the bouncing ball makes BB-TENG harvest energy efficiently. The factors for ‘Well-Contact’ and their influence are investigated, and the critical frequencies for ‘Well-Contact’ of the bouncing ball at each vibration excitation amplitude are obtained. ‘Self-Spin’ of the bouncing ball produced by unbalanced excitation torque is found to increase energy harvesting, and the excitation frequency significantly determines the energy of the ‘Self-Spin’. When the external excitation acceleration reaches a critical value, the ‘Rich-Contact’ of the bouncing ball is found, and the amount of charge transfer for BB-TENG will not increase, which is termed saturated condition. Therefore, the results of this work help improve the design and application of high-efficiency BB-TENG.
Simulations of resonant tunnelling through InAs/AlSb heterostructures for ULTRARAM™ memory
Authors: Lane Dominic , Hayne Manus
Published: June 2021

ULTRARAM™ is a III–V semiconductor memory technology which allows non-volatile logic switching at ultra-low energy (per unit area). This is achieved by exploiting triple-barrier resonant tunnelling (TBRT) through a series of InAs/AlSb heterojunctions specifically engineered for this purpose. Electrons tunnelling through the barriers at low bias are trapped in a floating gate, in which the presence or absence of charge defines the memory logic. Here, we report detailed non-equilibrium Green’s functions simulations of the InAs/AlSb TBRT heterostructure, which is the principal source of ULTRARAM™’s extraordinary performance benefits. The effects of variations to the heterostructure layer thickness are investigated for performance optimization, and for assessing growth and process tolerances for commercial implementation on 12″ Si wafers. Trade-offs between power, speed, logic disturbance and data retention time are identified. Importantly, most one monolayer alterations to the tunnelling region show the required characteristics for ULTRARAM™ memory operation, thus some tolerance in any future commercial fabrication process is identified.
Effects of gate work function on E-mode AlGaN/GaN HEMTs with stack gate β-Ga2O3/p-GaN structure
Authors: Ge Mei , Li Yi , Zhu Youhua , Chen Dunjun , Wang Zhiliang , Tan Shuxin
Published: June 2021

This research investigates electrical properties of E-mode AlGaN/GaN HEMTs with n-type β-Ga2O3/p-GaN gate stack under different gate work functions of 4.6, 5.1 and 5.7 eV, respectively. The simulated results show that the device with gate work function of 5.7 eV exhibits the largest threshold voltage of 2.8 V while having the lowest saturation drain current of 0.15 A mm−1, which can be ascribed to the device having the highest Schottky barrier, leading to the least electrons collected at the AlGaN/GaN interface. Moreover, the device with gate work function of 5.7 eV shows the largest gate breakdown voltage as well as the lowest off-state gate leakage, which can be attributed to the least strength of electric field in the Ga2O3 layer. Additionally, the Fowler–Nordheim equation was used to study the mechanisms of off-state leakage.
Spheres rolling on an inclined track
Authors: D’Anna Michele , Fuchs Hans U , Corni Federico
Published: June 2021

A quantitative experiment where we measure the acceleration of spheres of radius R rolling on an inclined U-shaped profile of width 2D is presented. For a given inclination, we examine the behaviour of four solid spheres having different diameters; in contrast to what is usually assumed to be the case, the experimental findings show that the dissipative component of the ball—track interaction can be neglected only in a limited range of the D/R parameter. We develop two interpretative models which are at the level of advanced high school students. The comparison between model predictions and measurements is quite satisfactory.
From contact electrification to triboelectric nanogenerators
Authors: Wang Zhong Lin
Published: June 2021

Although the contact electrification (CE) (or usually called ‘triboelectrification’) effect has been known for over 2600 years, its scientific mechanism still remains debated after decades. Interest in studying CE has been recently revisited due to the invention of triboelectric nanogenerators (TENGs), which are the most effective approach for converting random, low-frequency mechanical energy (called high entropy energy) into electric power for distributed energy applications. This review is composed of three parts that are coherently linked, ranging from basic physics, through classical electrodynamics, to technological advances and engineering applications. First, the mechanisms of CE are studied for general cases involving solids, liquids and gas phases. Various physics models are presented to explain the fundamentals of CE by illustrating that electron transfer is the dominant mechanism for CE for solid–solid interfaces. Electron transfer also occurs in the CE at liquid–solid and liquid–liquid interfaces. An electron-cloud overlap model is proposed to explain CE in general. This electron transfer model is extended to liquid–solid interfaces, leading to a revision of the formation mechanism of the electric double layer at liquid–solid interfaces. Second, by adding a time-dependent polarization term
P

s created by the CE-induced surface electrostatic charges in the displacement field
D
, we expand Maxwell’s equations to include both the medium polarizations due to electric field (
P
) and mechanical aggitation and medium boundary movement induced polarization term (
P

s). From these, the output power, electromagnetic (EM) behaviour and current transport equation for a TENG are systematically derived from first principles. A general solution is presented for the modified Maxwell’s equations, and analytical solutions for the output potential are provided for a few cases. The displacement current arising from ε∂E/∂t is responsible for EM waves, while the newly added term ∂
P

s/∂t is responsible for energy and sensors. This work sets the standard theory for quantifying the performance and EM behaviour of TENGs in general. Finally, we review the applications of TENGs for harvesting all kinds of available mechanical energy that is wasted in our daily life, such as human motion, walking, vibration, mechanical triggering, rotating tires, wind, flowing water and more. A summary is provided about the applications of TENGs in energy science, environmental protection, wearable electronics, self-powered sensors, medical science, robotics and artificial intelligence.
Entanglement distribution in multi-platform buffered-router-assisted frequency-multiplexed automated repeater chains
Authors: Askarani Mohsen Falamarzi , Chakraborty Kaushik , Castro do Amaral Gustavo
Published: June 2021

Realization of a globe-spanning quantum network is a current worldwide goal, where near and long term implementations will benefit from connectivity between platforms optimized for specific tasks. Towards this goal, a quantum network architecture is herewith proposed whereby quantum processing devices based on NV− colour centers act as quantum routers (QR) and, between which, long-distance entanglement distribution is enabled by spectrally-multiplexed quantum repeaters based on absorptive quantum memories in rare-earth ion-doped crystals and imperfect entangled photon-pair sources. The inclusion of a quantum buffer structure between repeaters and routers is shown to, albeit the increased complexity, improve the achievable entanglement distribution rates in the network. Although the expected rate and fidelity results are presented for a simple linear network (point-to-point), complex topologies are compatible with the proposed architecture through the inclusion of an extra layer of temporal multiplexing in the QR’s operation. Figures of merit are extracted based on parameters found in the literature for near-term scenarios and attest the availability of the proposed buffered-router-assisted frequency-multiplexed automated repeater chain network.
Thermoelastic Problem for a Free Square Plate: Exact Solution
Authors: Kerzhaev A P
Published: June 2021

The paper presents a method for determining thermal stresses in an elastic free square plate (the plane problem). First, we construct the solution to the nonhomogeneous temperature problem for an infinite plane. Then, we add to this solution the solution for a square, with the help of which the required boundary conditions on its sides are satisfied. The temperature factors are obtained in the form of explicit series in Papkovich–Fadle eigenfunctions.
Interactive Mechanical Systems Using Mathematica
Authors: Santiago Acosta R D , Hernández Cooper E M , Hernández Medina A , Gómez Castillo R
Published: June 2021

This work shows a new proposal for teaching mechanical systems (SM) modelled through differential equations (SED) using the Mathematica package. The adopted strategy considers four stages. In the first, simple SMS, such as the mass-spring system on a plane or the simple pendulum, are analysed. The Lagrangian of each system is determined and the Euler-Lagrange equations are used to obtain the equations of motion. In other cases, the Hamiltonian of the systems is determined and the Hamilton equations are used. Afterwards, the resulting EDS are solved analytically. During the second stage, SED solution programs in Mathematica are developed by using classical numerical methods such as a fourth order Runge-Kutta method (Rk4) and a Runge-Kutta-Feldberg method of order 4-5 (RKF45). The programs are tested with the examples from the previous stage. In the next stage, a set of programs is elaborated in order to determine the equations of motion for any system by using the Euler-Lagrange equations (Hamilton) from the Lagrangian (Hamiltonian) of the system. In the last stage, complex problems such as the movement of planets in the solar system or the movement of a particle over a conical surface are solved. The programs developed during stages 2 and 3 are used in order to obtain a numerical solution to these examples. Finally, interactive graphical interfaces are constructed for each proposed system, and are used to study and analyse the physical phenomena. As a result, engineering students who use and build graphical interfaces have improved their understanding of SED and their use in classical mechanics. In addition, they change their previous ideas about the scope of mechanics and SEDs, they gain confidence in their knowledge and they are able to find solutions to dynamical systems through the use of simple numerical techniques.
Wigner functions and coherent states for the quantum mechanics on a circle
Authors: Kowalski K , Ławniczak K
Published: June 2021

The Wigner functions for the coherent states of a particle on a circle are discussed. The nontrivial analytic forms of these functions are derived. The classicality of the circular coherent states existing in the literature as well as the new ones constructed by means of the Fourier transformation of the Gaussian is compared based on negativity of the Wigner function.
Centralization and decentralization for resilient infrastructure and complexity
Authors: Helmrich Alysha , Markolf Samuel , Li Rui , Carvalhaes Thomaz , Kim Yeowon , Bondank Emily , Natarajan Mukunth , Ahmad Nasir , Chester Mikhail
Published: June 2021

The capacities of our infrastructure systems to respond to volatile, uncertain, and increasingly complex environments are increasingly recognized as vital for resilience. Pervasive across infrastructure literature and discourse are the concepts of centralized, decentralized, and distributed systems, and there appears to be growing interest in how these configurations support or hinder adaptive and transformative capacities towards resilience. There does not appear to be a concerted effort to align how these concepts are used, and what different configurations mean for infrastructure systems. This is problematic because how infrastructure are structured and governed directly affects their capabilities to respond to increasing complexity. We review framings of centralization, decentralization, and distributed (referred to collectively as de/centralization) across infrastructure sectors, revealing incommensurate usage leading to polysemous framings. De/centralized networks are often characterized by proximity to resources, capacity of distribution, volume of product, and number of connections. De/centralization of governance within infrastructure sectors is characterized by the number of actors who hold decision-making power. Notably, governance structures are often overlooked in infrastructure de/centralization literature. Next, we describe how de/centralization concepts are applied to emerging resilient infrastructure theory, identifying conditions under which they support resilience principles. While centralized systems are dominant in practice and decentralized systems are promoted in resilience literature, all three configurations—centralized, decentralized, and distributed—were found to align with resilience capacities in various contexts of stability and instability. Going forward, we recommend a multi-dimensional framing of de/centralization through a network-governance perspective where capabilities to shift between stability and instability are paramount and information is a critical mediator.
Isomorphism of the cubical and categorical cohomology groups of a higher-rank graph
Authors: Gillaspy Elizabeth , Wu Jianchao
Published: June 2021

We use category-theoretic techniques to provide two proofs showing that for a higher-rank graph

Λ
\Lambda

, its cubical (co-)homology and categorical (co-)homology groups are isomorphic in all degrees, thus answering a question of Kumjian, Pask and Sims in the positive. Our first proof uses the topological realization of a higher-rank graph, which was introduced by Kaliszewski, Kumjian, Quigg, and Sims. In our more combinatorial second proof, we construct, explicitly and in both directions, maps on the level of (co-)chain complexes that implement said isomorphism. Along the way, we extend the definition of cubical (co-)homology to allow arbitrary coefficient modules.
Estimates of Childhood Overweight and Obesity at the Region, State, and County Levels: A Multilevel Small-Area Estimation Approach
Authors: Zgodic Anja , Eberth Jan M , Breneman Charity B , Wende Marilyn E , Kaczynski Andrew T , Liese Angela D , McLain Alexander C
Published: June 2021

Local-level childhood overweight and obesity data are often used to implement and evaluate community programs, as well as allocate resources to combat overweight and obesity. The most current substate estimates of US childhood obesity use data collected in 2007. Using a spatial multilevel model and the 2016 National Survey of Children’s Health, we estimated childhood overweight and obesity prevalence rates at the Census regional division, state, and county levels using small-area estimation with poststratification. A sample of 24,162 children aged 10–17 years was used to estimate a national overweight and obesity rate of 30.7% (95% confidence interval: 27.0%, 34.9%). There was substantial county-to-county variability (range, 7.0% to 80.9%), with 31 out of 3,143 counties having an overweight and obesity rate significantly different from the national rate. Estimates from counties located in the Pacific region had higher uncertainty than other regions, driven by a higher proportion of underrepresented sociodemographic groups. Child-level overweight and obesity was related to race/ethnicity, sex, parental highest education (P < 0.01 for all), county-level walkability (P = 0.03), and urban/rural designation (P = 0.02). Overweight and obesity remains a vital issue for US youth, with substantial area-level variability. The additional uncertainty for underrepresented groups shows surveys need to better target diverse samples.
A sparse negative binomial mixture model for clustering RNA-seq count data
Authors: Li Yujia , Rahman Tanbin , Ma Tianzhou , Tang Lu , Tseng George C
Published: June 2021

Clustering with variable selection is a challenging yet critical task for modern small-n-large-p data. Existing methods based on sparse Gaussian mixture models or sparse $K$-means provide solutions to continuous data. With the prevalence of RNA-seq technology and lack of count data modeling for clustering, the current practice is to normalize count expression data into continuous measures and apply existing models with a Gaussian assumption. In this article, we develop a negative binomial mixture model with lasso or fused lasso gene regularization to cluster samples (small $n$) with high-dimensional gene features (large $p$). A modified EM algorithm and Bayesian information criterion are used for inference and determining tuning parameters. The method is compared with existing methods using extensive simulations and two real transcriptomic applications in rat brain and breast cancer studies. The result shows the superior performance of the proposed count data model in clustering accuracy, feature selection, and biological interpretation in pathways.
Exploratory Study of the Resettlement Experiences of Burmese Refugees Children in the USA
Authors: Tonsing Jenny C
Published: June 2021

The purpose of this study is to explore the educational and resettlement experiences of Burmese refugee children in the USA. Transition and migration in itself are a difficult task for refugees due to the demands associated with adjustment to a new way of life in a different environment, and even more so for children, as the events co-occur with the developmental changes they experience. The study has employed qualitative research methods in the form of in-depth interviews to examine the subjective experiences of the participants. Using the purposive sampling method, twenty-eight Burmese refugee children participated in a one-on-one in-depth interview. Respondents ranged in age from ten to seventeen years, with the majority being girls (53.6 per cent). The average length of time in the USA was 5.8 years. Analysis of the data revealed three key themes that relate to school experience, bi-cultural dynamics and changing role expectations, and future hopes and aspirations. Implications for practice and future research are discussed.
Response Inhibitory Control Varies with Different Sensory Modalities
Authors: Ikarashi Koyuki , Sato Daisuke , Fujimoto Tomomi , Edama Mutsuaki , Baba Yasuhiro , Yamashiro Koya
Published: June 2021

Response inhibition plays an essential role in preventing anticipated and unpredictable events in our daily lives. It is divided into proactive inhibition, where subjects postpone responses to an upcoming signal, and reactive inhibition, where subjects stop an impending movement based on the presentation of a signal. Different types of sensory input are involved in both inhibitions; however, differences in proactive and reactive inhibition with differences in sensory modalities remain unclear. This study compared proactive and reactive inhibitions induced by visual, auditory, and somatosensory signals using the choice reaction task (CRT) and stop-signal task (SST). The experiments showed that proactive inhibitions were significantly higher in the auditory and somatosensory modalities than in the visual modality, whereas reactive inhibitions were not. Examining the proactive inhibition-associated neural processing, the auditory and somatosensory modalities showed significant decreases in P3 amplitudes in Go signal-locked event-related potentials (ERPs) in SST relative to those in CRT; this might reflect a decreasing attentional resource on response execution in SST in both modalities. In contrast, we did not find significant differences in the reactive inhibition-associated ERPs. These results suggest that proactive inhibition varies with different sensory modalities, whereas reactive inhibition does not.