bluuebunny/crossref_metadata_2025 huggingface dataset:
Discriminating power of milli-lensing observations for dark matter models
Authors: Loudas Nick , Pavlidou Vasiliki , Casadio Carolina , Tassis Konstantinos
Published: November 2022

Context. The nature of dark matter (DM) is still under intense debate. Subgalactic scales are particularly critical, as different, currently viable DM models make diverse predictions on the expected abundance and density profile of DM haloes on these scales.

Aims. We investigate the ability of subgalactic DM haloes to act as strong lenses on background compact sources, producing gravitational lensing events on milli-arcsecond scales (milli-lenses), for different DM models. For each DM scenario, we explore whether a sample of ∼5000 distant sources is sufficient to detect at least one milli-lens.

Methods. We developed a semi-analytical model to estimate the milli-lensing optical depth as a function of the source’s redshift for various DM models. We employed the Press-Schechter formalism, as well as results from recent N-body simulations to compute the halo mass function, taking into account the appropriate spherically averaged density profile of haloes for each DM model. We treated the lensing system as a point-mass lens and invoked the effective surface mass density threshold to calculate the fraction of a halo that acts as a gravitational lens. We studied three classes of dark matter models: cold DM, warm DM, and self-interacting DM.

Results. We find that haloes consisting of warm DM turn out to be optically thin for strong gravitational milli-lensing (zero expected lensing events). Cold DM haloes may produce lensing events depending on the steepness of the concentration-mass relation. Self-interacting DM haloes can efficiently act as gravitational milli-lenses only if haloes experience gravothermal collapse, resulting in highly dense central cores.
Rolle der Chirurgie bei solitären Wirbelsäulenmetastasen
Authors: Ryang Yu-Mi , Schaser Klaus-Dieter
Published: November 2022

Moderne onkologische Therapien insbesondere im Bereich der Immuntherapien und targeted Therapien konnten deutliche Fortschritte in Bezug auf die Lebenserwartung von Patienten mit disseminiertem Tumorleiden erzielen.

Die chirurgische Therapie solitärer spinaler Metastasen stellt hier eine besondere Herausforderung dar. Mit der Technik der sogenannten en bloc Spondylektomie wird seit vielen Jahren für ausgewählte solitäre Läsionen prognostisch günstiger Tumorbiologien das Ziel einer extraläsionalen Resektion und kurativen Behandlung verfolgt.

Nach heutiger Datenlage scheint der Nutzen jedoch limitiert und muss kritisch bewertet werden. Bei wenigen prognostisch günstigen Tumorentitäten wie dem Nierenzell- und Schilddrüsenkarzinom konnte in Studien mit niedriger Evidenz ein signifikanter Überlebensvorteil 1
2 nachgewiesen werden. Entwicklungen, insbesondere der stereotaktischer Bestrahlungstechniken scheinen jedoch vergleichbare Ergebnisse hinsichtlich lokaler Tumorkontrolle und Gesamtüberleben zu erzielen, was zumindest im US-amerikanischen Raum dazu geführt hat, dass die en bloc Spondylektomie quasi nicht mehr für diese Indikation empfohlen oder durchgeführt wird, sondern die primäre Therapie in der Radiochirurgie liegt.

Die en bloc Spondylektomie könnte bei einem hochselektiven Patientengut in wenigen spezialisierten Zentren einen marginalen Stellenwert behalten. Die Entwicklung sollte primär jedoch nicht nur in Richtung Verbesserung operativer v.a. weniger invasiver Techniken, sondern in Richtung Verbesserung molekularer Diagnostik und Therapien (Strahlentherapie, Chemo-, Immun- und targeted Therapien) gehen.
Global migration: Implications for international business scholarship
Authors: Hajro Aida , Brewster Chris , Haak-Saheem Washika , Morley Michael J.
Published: November 2022

Migration is increasingly viewed as a high-priority policy issue among politicians, intergovernmental organizations, NGOs, and civil society throughout the world. Its implications for the private sector, for economic prosperity, and for the cross-border activities of firms are undeniable and likely to grow in importance. Yet, despite its relevance to International Business, treatment of migration in the mainstream International Business literature has been limited. In this contribution, we set out key aspects of migration that are germane to International Business. Specifically, we suggest recent migratory shifts are transforming important elements of the context in which multinational enterprises operate, with significant implications for their international human resource management practices, for firms’ entry modes and market selection approaches, and for the manner in which international strategies are formulated and implemented. We offer a research agenda to motivate International Business scholars to study global migration in more depth and to reevaluate the generalizability of aspects of their theories in light of developments in global migration.
Is the continuum SSH model topological?
Authors: Shapiro Jacob , Weinstein Michael I.
Published: November 2022

The discrete Hamiltonian of Su, Schrieffer, and Heeger (SSH) [Phys. Rev. Lett. 42, 1698–1701 (1979)] is a well-known one-dimensional translation-invariant model in condensed matter physics. The model consists of two atoms per unit cell and describes in-cell and out-of-cell electron-hopping between two sub-lattices. It is among the simplest models exhibiting a non-trivial topological phase; to the SSH Hamiltonian, one can associate a winding number, the Zak phase, which depends on the ratio of hopping coefficients and takes on values 0 and 1 labeling the two distinct phases. We display two homotopically equivalent continuum Hamiltonians whose tight binding limits are SSH models with different topological indices. The topological character of the SSH model is, therefore, an emergent rather than fundamental property, associated with emergent chiral or sublattice symmetry in the tight-binding limit. In order to establish that the tight-binding limit of these continuum Hamiltonians is the SSH model, we extend our recent results on the tight-binding approximation [J. Shapiro and M. I. Weinstein, Adv. Math. 403, 108343 (2022)] to lattices, which depend on the tight-binding asymptotic parameter λ.
Modular pulsed power supply for characterization of high-power microwave devices
Authors: Ram Subhash Kumar , Verma Brijendra Kumar , Abhishek Anand , Devassy Sachin , Mishra Sukumar
Published: November 2022

Developing a robust and reliable high-voltage (HV) pulse power system (PPS) is essential for the characterization and testing of microwave tubes and industrial applications. This paper presents the design, simulation, and implementation of a modular and versatile high-voltage pulse power supply used in microwave device characterization and testing. A microcontroller-based digitally controlled pulse generation unit is also developed to generate the trigger pulses for high-voltage switching modules to control the turn-ON and turn-OFF of the switching devices. The digitally controlled pulse generation unit provides better resolution of pulse width, pulse repetition frequency, and system protection over the entire range of operations. The pulse generation and control circuit controls the pulse repetition frequency (PRF) and pulse wide (PW). The PRF and PW can be varied from 100 to 1000 Hz and 10 to 100 µs, respectively. The experimental prototype with ten series-connected high-voltage modules is connected to achieve a 25 kV pulsed output voltage. The experimental results of HV-PPS on a resistive dummy load and 5 GHz klystron tube are presented in this work.
Development of a photoelectron spectrometer for hard x-ray photon diagnostics
Authors: Laksman Joakim , Dietrich Florian , Liu Jia , Maltezopoulos Theophilos , Planas Marc , Freund Wolfgang , Gautam Randeer , Kujala Naresh , Francoual Sonia , Grünert Jan
Published: November 2022

The development and characterization of an angle-resolved photoelectron spectrometer, based on the electron time-of-flight concept, for hard x-ray photon diagnostics at the European Free-Electron Laser, are described. The instrument is meant to provide users and operators with pulse-resolved, non-invasive spectral distribution diagnostics, which in the hard x-ray regime is a challenge due to the poor cross-section and high kinetic energy of photoelectrons for the available target gases. We report on the performances of this instrument as obtained using hard x-rays at the PETRA III synchrotron at DESY in multibunch mode. Results are compared with electron trajectory simulations. We demonstrate a resolving power of 10 eV at incident photon energies up to at least 20 keV.
Topography of bent crystals with microradian resolution in one dimension
Authors: Pereira N. R. , Macrander A. T. , Harding E. C.
Published: November 2022

Optimum performance in x-ray imaging and spectroscopy of plasmas with bent crystals is achievable only when the crystal reflects the x rays theoretically perfectly across its entire surface. However, typical thin quartz (101̄1) crystal samples kept flat by direct attachment to a flat substrate reflect 8 keV x rays differently across their surface, on a scale comparable to the ideal rocking curve. Additional processing improves the uniformity. Irradiation of flat crystals with collimated, monochromatic x rays in rocking curve topography shows such problems directly, with microradian resolution. Nonuniform x-ray reflection is more difficult to document for strongly bent crystals because, then, monochromatic, collimated x rays satisfy the Bragg condition only along a narrow stripe that may be too narrow to resolve with the available cameras. However, it can be resolved with a knife edge that moves through the reflected x rays with the necessary spatial precision as demonstrated here for a bent silicon crystal. This shows qualitatively similar imperfections in the reflection as flat quartz and as the bent quartz analyzers reported on previously with lower resolution.
Evaluation of a novel mid-infrared pyrometer for dynamic material experiments
Authors: Dutra E. C. , Akin M. C. , Guyton R. , Hawkins M. C. , La Lone B. M. , Mance J. , Tiangco R. , Wolff Z. , Rodriguez E.
Published: November 2022

Temperature is a complicated thermodynamic parameter to measure in dynamic compression experiments. Optical pyrometry is a general-purpose “work-horse” technique for measuring temperature from a radiant surface on these experimental platforms. The optical pyrometry channels are commonly held to the visible or Near-Infrared spectrum, which provides high fidelity temperature measurement for shock temperature above ∼1200–1500 K. However, low temperature (T < 1200 K) dynamic material experiments, including low pressure or quasi-isentropic studies, as well as experiments with complex thermodynamic paths, require Mid-Infrared (Mid-IR) for high fidelity measurements. This article outlines the design, testing, and characterization of a novel Mid-IR pyrometer system that can be configured between 2.5 and 5.0 µm, suitable for lower temperature measurements and for increasing the fidelity and precision of higher temperature measurements. Experimental validation was done on two separate gas gun platforms, with two separate impact velocities, achieving temperatures between 450 and 1100 K.
Constraining time-dependent ion temperature measurements in inertial confinement fusion (ICF) implosions with an intermediate distance neutron time-of-flight (nToF) detector
Authors: Moore A. S. , Schlossberg D. J. , Eckart M. J. , Hartouni E. P. , Hilsabeck T. J. , Jeet J. S. , Kerr S. M. , Nora R. C. , Kilkenny J.
Published: November 2022

A concept for using an intermediate distance (0.3–3.0 m) neutron time-of-flight (nToF) to provide a constraint on the measurement of the time-dependence of ion temperature in inertial confinement fusion implosions is presented. Simulated nToF signals at different distances are generated and, with a priori knowledge of the burn-averaged quantities and burn history, analyzed to determine requirements for a future detector. Results indicate a signal-to-noise ratio >50 and time resolution <20 ps to constrain the ion temperature gradient to ∼±25% (0.5 keV/100 ps).
3D metal powder additive manufacturing phased array antenna for multichannel Doppler reflectometer
Authors: Tokuzawa T. , Nasu T. , Inagaki S. , Moon C. , Ido T. , Idei H. , Ejiri A. , Imazawa R. , Yoshida M. , Oyama N. , Tanaka K. , Ida K.
Published: November 2022

Measuring the time variation of the wavenumber spectrum of turbulence is important for understanding the characteristics of high-temperature plasmas, and the application of a Doppler reflectometer with simultaneous multi-frequency sources is expected. To implement this diagnostic in future fusion devices, the use of a phased array antenna (PAA) that can scan microwave beams without moving antennas is recommended. Since the frequency-scanning waveguide leaky-wave antenna-type PAA has a complex structure, we have investigated its characteristics by modeling it with 3D metal powder additive manufacturing (AM). First, a single waveguide is fabricated to understand the characteristics of 3D AM techniques, and it is clear that there are differences in performance depending on the direction of manufacture and surface treatment. Then, a PAA is made, and it is confirmed that the beam can be emitted in any direction by frequency scanning. The plasma flow velocity can be measured by applying the 3D manufacturing PAA to plasma measurement.
Measurement of Pa
α line from pellet ablation cloud in Heliotron J
Authors: Iwata A. , Kado S. , Murakumo M. , Shikama T. , Motojima G. , Mori A. , Feng C. , Okada H. , Minami T. , Ohshima S. , Kobayashi S. , Ishizawa A. , Nakamura Y. , Konoshima S. , Mizuuchi T. , Nagasaki K.
Published: November 2022

The Paα line (1875.13 nm) in the near-infrared (NIR) region was evaluated to apply Stark broadening of the line spectrum to the electron density measurement of the small-pellet ablation cloud in Heliotron J, a medium-sized helical-axis heliotron device. Paα is three-to-four times broader than the visible Hβ line (486.13 nm) for the same electron density. Using a portable NIR spectrometer, preliminary proof-of-concept experiments determined the marginal density, below which the broadening was undetectable. The lower detection density limit can be decreased using a narrower entrance slit or a denser grating.
Research on nonlinear isometric L-shaped cantilever beam type piezoelectric wind energy harvester based on magnetic coupling
Authors: He Lipeng , Yu Gang , Han Yuhang , Liu Lei , Hu Dianbin , Cheng Guangming
Published: November 2022

Harvesting wind energy using piezoelectric materials is expected to be an alternative solution for powering wireless sensing networks. This paper proposed a nonlinear isometric L-shaped cantilever beam type piezoelectric wind energy harvester based on magnetic coupling (L-PWEH). The transducer consists of an array of equidistant L-shaped piezoelectric vibrators that are sealed inside the shell. It greatly improves the equivalent piezoelectric coefficient, robustness, and wind speed range for reliable operation. Theoretical and simulation analyses of the structural parameters related to the widening of the L-PWEH were performed. The prototype was built and the experimental system was constructed to verify the feasibility of the L-PWEH and the results of the analyses. Experiments have shown that increasing the magnetic force, additional springs, and the appropriate quantity of excitation magnets can effectively increase the output voltage and widen the wind speed range at high voltage output. When the wind speed is 16.35 m/s and the load resistance is 2 MΩ, the best output power of the piezoelectric vibrator is 142.3 µW. At this time, the height of the middle excitation magnet of the prototype is 12 mm, the number is 5, and the wire diameter of the additional spring is 1 mm. The prototype can successfully make the electronics work properly.
Tripolar guide magnetic fields due to island coalescence in solar wind current sheets: Simulation and theory
Authors: Newman David L. , Eriksson Stefan , Lapenta Giovanni
Published: November 2022

Reconnecting current sheets (CSs) in the solar wind near 1 AU have been previously identified that exhibit a modified Hall magnetic field perturbation of the nominal guide field characterized by a “tripolar” structure with depressions on both sides of a central maximum [Eriksson et al., Astrophys. J. 805, 43 (2015)]. Such CSs were inferred to contain multiple interacting islands based on measurements from all four Cluster satellites. A new set of 2D particle-in-cell simulations have been performed providing the foundation for a theoretical model for the origin of the tripolar guide-field perturbation. The simulations are initialized with a thin CS unstable to the formation of many small islands that undergo pairwise coalescence and growth. The guide field depressions develop as the result of a balance between the electrostatic (curl-free or irrotational) and electromagnetic (divergence-free or solenoidal) components of the parallel electric field. Field-line and flow-line tracing provide additional support for the model by demonstrating how a level of charge separation sufficient to support a large electrostatic potential can be maintained following island coalescence. A parameter study reveals that the plasma beta is the primary quantity controlling the evolution of the tripolar field. Dependence on the initial guide-field strength is also investigated.
The effect of noise in an HIV infection model with cytotoxic T-lymphocyte impairment
Authors: Majumder Abhijit , Sardar Shibani , Bairagi Nandadulal
Published: November 2022

The human immunodeficiency virus (HIV) interacts with the immune cells within the human body, where the environment is uncertain and noisy. Stochastic models can successfully encapsulate the effect of such a noisy environment compared to their deterministic counterparts. The human immune system is complex but well-coordinated with various immune cells like CD4+T cells, dendritic cells, and cytotoxic T-lymphocyte (CTL) cells, among many others. The CTL can kill the antigenic cells after its recognition. However, the efficacy of CTL in removing the infected CD4+T cells is progressively compromised in HIV-infected individuals. This paper considers a noise-induced HIV-immune cell interaction model with immune impairment. A multiplicative white noise is introduced in the infection rate parameter to represent the fluctuations around the average value of the rate parameter as a causative effect of the noise. We analyzed the deterministic and stochastic models and prescribed sufficient conditions for infection eradication and persistence. It is determined under what parametric restrictions the asymptotic solutions of the noise-induced system will be a limiting case of the deterministic solutions. Simulation results revealed that the solutions of the deterministic system either converge to a CTL-dominated interior equilibrium or a CTL-free immunodeficient equilibrium, depending on the initial values of the system. Stochastic analysis divulged that higher noise might be helpful in the infection removal process. The extinction time of infected CD4+T cells for some fixed immune impairment gradually decreases with increasing noise intensity and follows the power law.
A newly designed femtosecond KBe2BO3F2 device with pulse duration down to 55 fs for time- and angle-resolved photoemission spectroscopy
Authors: Zhong Haoyuan , Bao Changhua , Lin Tianyun , Zhou Shaohua , Zhou Shuyun
Published: November 2022

Developing a widely tunable vacuum ultraviolet (VUV) source with a sub-100 fs pulse duration is critical for ultrafast pump–probe techniques such as time- and angle-resolved photoemission spectroscopy (TrARPES). While a tunable probe source with a photon energy of 5.3–7.0 eV has been recently implemented for TrARPES by using a KBe2BO3F2 (KBBF) device, the time resolution of 280–320 fs is still not ideal, which is mainly limited by the duration of the VUV probe pulse generated by the KBBF device. Here, by designing a new KBBF device, which is specially optimized for fs applications, an optimum pulse duration of 55 fs is obtained after systematic diagnostics and optimization. More importantly, a high time resolution of 81–95 fs is achieved for TrARPES measurements covering the probe photon energy range of 5.3–7.0 eV, making it particularly useful for investigating the ultrafast dynamics of quantum materials. Our work extends the application of the KBBF device to ultrafast pump–probe techniques with the advantages of both a widely tunable VUV source and ultimate time resolution.
High-resolution optical magnetic resonance imaging of electronic spin polarization in miniaturized atomic sensors
Authors: Wu Zekun , Chai Zhen , Mao Yunkai , Tian Hao , Liu Zhanchao
Published: November 2022

Miniaturized atomic sensors of magnetic field and inertia have great potential to be applied as geophysical instruments and in the detection of biomolecules. The distribution of the electronic spin polarization plays a key role as it defines the amount of noble gas that can achieve a state of hyperpolarization, which in turn determines the technique's accuracy and, consequently, its resolution. However, the current techniques for electronic spin polarization imaging are unsuited for the operating conditions of miniaturized atomic sensors besides only accomplishing submillimeter spatial resolution. In this study, optical magnetic resonance is applied to obtain electronic spin polarization images with a spatial resolution of 60 μm experimentally and 10 μm theoretically. This corresponds to an increase by one order of magnitude in resolution when compared to previous reports of electronic spin polarization imaging. By sweeping the RF frequency of the magnetic field while applying a magnetic field gradient of 0.22 μT/mm, it is possible to measure electronic spin polarization images for different average photon spins and pump beam positions. Spin polarization images present a high degree of correlation with pump beam images. Furthermore, this image method can be applied to suppressing the inhomogeneities in miniaturized cells, leading to a gain in signal-to-noise ratio. It also offers an opportunity to experimentally perform two-dimensional atomic polarization manipulation in the gas phase, optically transparent solids, and liquids.
A promising outlook on the development of lead halide perovskites as spin-orbitronic materials
Authors: Filippetti A. , Wadhwa P. , Caddeo C. , Mattoni A.
Published: November 2022

Hybrid lead halide perovskites have progressively overcome the horizon of materials for novel, highly efficient solar cells and are now proposed for a variety of optoelectronic, nanoelectronic, and thermoelectric applications. In this Perspective, we focus on a still scarcely explored and yet extremely thrilling playground: the use of lead halide perovskites to design efficient magneto-electronic and magneto-optic applications. Our analysis is pointed to emphasize the unique combination of strong spin–orbit coupling and wide structural and chemical flexibility, which characterize the lead halide perovskites. Using model calculations, we furnish a qualitative evidence of their capabilities for what concerns the charge–spin conversion mechanism, which is basic to some of the most visionary spin-orbitronic implementations, such as the magnetoelectric switching and the spin-diffusive transistor.
Thomson microwave scattering for diagnostics of small plasma objects enclosed within glass tubes
Authors: Ranjan Apoorv , Patel Adam , Wang Xingxing , Shashurin Alexey
Published: November 2022

In this work, coherent microwave scattering in the Thomson regime was demonstrated for small-scale plasmas enclosed within a glass tube and validated using a well-known hairpin resonator probe technique. The experiments were conducted in a DC discharge tube with a diameter of 1.5 cm and a length of 7 cm. Thomson microwave scattering (TMS) diagnostics yielded electron number densities of about 5.9 × 1010 cm−3, 2.8 × 1010 cm−3, and 1.8 × 1010 cm−3 for air pressures in the discharge tube of 0.2, 0.5, and 2.5 Torr, respectively. Measurements using the TMS technique were consistent across the tested microwave frequencies of 3–3.9 GHz within the margin of error associated with non-idealities of the IQ mixer utilized in the circuit. The corresponding densities measured with the hairpin resonator probe were 4.8 × 1010, 3.8 × 1010, and 2.6 × 1010 cm−3. Discrepancies between the two techniques were within 30% and can be attributed to inaccuracies in the sheath thickness estimation required for correct interpretation of the hairpin resonator probe results.
Periodic solutions of coupled Boussinesq equations and Ostrovsky-type models free from zero-mass contradiction
Authors: Khusnutdinova K. R. , Tranter M. R.
Published: November 2022

Coupled Boussinesq equations are used to describe long weakly nonlinear longitudinal strain waves in a bi-layer with soft bonding between the layers (e.g., a soft adhesive). From a mathematical viewpoint, a particularly difficult case appears when the linear long-wave speeds in the layers are significantly different (high-contrast case). The traditional derivation of the uni-directional models leads to four uncoupled Ostrovsky equations for the right- and left-propagating waves in each layer. However, the models impose a “zero-mass constraint”; i.e., the initial conditions should necessarily have zero mean, restricting the applicability of that description. Here, we bypass the contradiction in this high-contrast case by constructing the solution for the deviation from the evolving mean value, using asymptotic multiple-scale expansions involving two pairs of fast characteristic variables and two slow time variables. By construction, the Ostrovsky equations emerging within the scope of this derivation are solved for initial conditions with zero mean, while initial conditions for the original system may have non-zero mean values. Asymptotic validity of the solution is carefully examined numerically. We apply the models to the description of counter-propagating waves generated by solitary wave initial conditions, or co-propagating waves generated by cnoidal wave initial conditions, as well as the resulting wave interactions, and contrast with the behavior of the waves in bi-layers when the linear long-wave speeds in the layers are close (low-contrast case). One local (classical) and two non-local (generalized) conservation laws of the coupled Boussinesq equations for strains are derived and used to control the accuracy of the numerical simulations.
GaN-based resonant cavity micro-LEDs for AR application
Authors: Huang Jinpeng , Tang Minglei , Zhou Binru , Liu Zhiqiang , Yi Xiaoyan , Wang Junxi , Li Jinmin , Pan Anlian , Wang Liancheng
Published: November 2022

Augmented reality (AR) is emerging as a next-generation interactive display that promotes the interaction between users, digital content, and the real world. Although micro-LED is regarded as the most promising light engine candidate for AR, its inherent Lambertian radiation characteristics and relatively broader emission spectrum result in low optical coupling efficiency and diffraction dispersion-related “rainbow” phenomenon when combined with a waveguide combiner. Here, we numerically and experimentally demonstrate resonant cavity (RC) micro-LEDs by incorporating SiO2/TiO2 distributed Bragg reflectors with chip sizes of 60, 100, and 150 μm. The device has a divergence angle of 78.7° and a narrow spectrum width of 6.8 nm, which is significantly lower than that of the controlled micro-LEDs. The reported GaN-based RC micro-LEDs have the potential to be used in the display panel for AR applications in a variety of scenarios, including AR glasses, and head up display for cars and airplanes.
Improved electrical performance of lateral β-Ga2O3 MOSFETs utilizing slanted fin channel structure
Authors: Liu Hongyu , Li Jianing , Lv Yuanjie , Wang Yuangang , Lu Xiaoli , Dun Shaobo , Han Tingting , Guo Hongyu , Bu Aimin , Ma Xiaohua , Feng Zhihong , Hao Yue
Published: November 2022

In this Letter, lateral slanted-fin-channel β-Ga2O3 metal-oxide-semiconductor field effect transistors (MOSFETs) are demonstrated. A 600-nm thick n-type doped channel layer is adopted to improve output characteristics. The tri-gate structure enhances gate control in the proposed β-Ga2O3 MOSFETs, showing an on/off ratio as high as 109. In particular, the slanted-fin-channel structure, mainly located in the gate region, reduces the peak electric field in the Ga2O3 channel due to the gradual regulation of a threshold voltage. The slanted-fin-channel β-Ga2O3 MOSFETs show a breakdown voltage (Vbr) of 2400 V and a power figure-of-merit of 193 MW/cm2, which are almost 2 and 5.5 times larger, respectively, than those of conventional straight-fin-channel devices. These results imply that the slanted-fin channel structure provides a viable way of fabricating high-performance β-Ga2O3 MOSFET power devices.
A field-programmable gate array (FPGA)-based data acquisition system for closed-loop experiments
Authors: Delgadillo Bonequi Ian , Stroschein Abraham , Koerner Lucas J.
Published: November 2022

We describe a custom and open source field-programmable gate array (FPGA)-based data acquisition (DAQ) system developed for electrophysiology and generally useful for closed-loop feedback experiments. FPGA acquisition and processing are combined with high-speed analog and digital converters to enable real-time feedback. The digital approach eases experimental setup and repeatability by allowing for system identification and in situ tuning of filter bandwidths. The FPGA system includes I2C and serial peripheral interface controllers, 1 GiB dynamic RAM for data buffering, and a USB3 interface to Python software. The DAQ system uses common HDMI connectors to support daughtercards that can be customized for a given experiment to make the system modular and expandable. The FPGA-based digital signal processing (DSP) is used to generate fourth-order digital infinite impulse response filters and feedback with microsecond latency. The FPGA-based DSP and an analog inner-loop are demonstrated via an experiment that rapidly steps the voltage of a capacitor isolated from the system by a considerable resistance using a feedback approach that adjusts the driving voltage based on the digitized capacitor current.
Investigation of self-trapped excitonic dynamics in hematite nanoforms through non-degenerate pump–probe transmission spectroscopy
Authors: N M Anjan Kumar , Mukherjee Soumya , Sunny Anoop , Karthikeyan B. , Kamaraju N.
Published: November 2022

Non-degenerate pump–probe transmission spectroscopy is used to examine the ultrafast dynamics of photo-excited carriers in hematite nanoforms at various pump fluences. Using coupled rate equations, the kinetics of self-trapped exciton (STE) formation and its interaction with free excitons resulting in exciton annihilation were studied. It is shown from this model that the majority of the excitons were trapped by polaronic trap states to form self-trapped excitons within ∼3.5 ps. The findings indicate that free excitons and STEs interact non-linearly, similar to trap-assisted bi-molecular Auger recombination to annihilate one another. It is observed that there is substantial dependence of kinetics of STE formation and exciton decay on photo-excited exciton density, and the nature of this dependence indicates the reduced screening of electron–phonon interaction. Using the screening model applied to the rate constants of STE formation and decay, we estimate the saturation exciton density to be ∼3.3 × 1017 cm−3 and the average STE density to be ∼3.8 × 1018 cm−3 in the hematite nanoforms. We also noticed that doping K and Ni to hematite nanoforms up to 5% did not remarkably change the nature of the exciton dynamics.
On nonlinear effects in holographic-modulated ultrasound
Authors: Sallam Ahmed , Shahab Shima
Published: November 2022

Holographic acoustic lenses (HALs), also known as acoustic holograms, are used for generating unprecedented complex focused ultrasound (FU) fields. HALs store the phase profile of the desired wavefront, which is used to reconstruct the acoustic pressure field when illuminated by a single acoustic source. Nonlinear effects occur as the sound intensity increases, leading to distorted and asymmetric waveforms. Here, the k-space pseudospectral method is used to perform homogeneous three-dimensional nonlinear acoustic simulations with power law absorption. An in-depth analysis is performed to study the evolution of holographic-modulated FU fields produced by HALs as the excitation amplitude increases. It is shown that nonlinear waveform distortion significantly affects the reconstruction of the pressure pattern when compared to the linear condition. Diffraction and nonlinear effects result in an asymmetric waveform with distinct positive and negative pressure patterns at the target plane. Peak positive pressure distribution becomes more localized around the areas with the highest nonlinear distortion. The peak signal-to-distortion ratio (PSDR) at the target plane falls while the nonuniformity index (NUI) rises. As a result of harmonic generation, the heat deposition distribution becomes highly localized with a significant increase in the NUI. Nonlinear effects have also been shown to flatten the peak negative pressure distribution while having minimal effect on the PSDR or NUI. However, nonlinear effects are shown to be critical for accurately predicting cavitation zones. Findings will pave the way for HALs implementation in high-intensity applications and prompt the incorporation of nonlinear acoustics into the notion of computer-generated holography.
β
-Ga2O3 Schottky barrier diodes with 4.1 MV/cm field strength by deep plasma etching field-termination
Authors: Dhara Sushovan , Kalarickal Nidhin Kurian , Dheenan Ashok , Joishi Chandan , Rajan Siddharth
Published: November 2022

In this work, we demonstrate a deep mesa etch design for efficient edge field termination in β-Ga2O3 Schottky barrier diodes (SBDs). The proposed design enabled parallel plate fields higher than 4.1 MV/cm with negligible change to the device ON characteristics. The effect of BCl3/Cl2-based dry etch on (100) and (010) etched vertical sidewalls is also analyzed. A remarkable anisotropy in depletion was observed for etch along (100) and (010) sidewalls. This work provides insight into the impact of etching on n-type Ga2O3 and shows a promising method to realize efficient field termination for high breakdown field strength SBDs.
Sensing performance of sub-100-nm vanadium oxide films for room temperature thermal detection applications
Authors: Scott Ethan A. , Singh Manish K. , Barber John P. , Rost Christina M. , Ivanov Sergei , Watt John , Pete Douglas , Sharma Peter , Lu Tzu-Ming , Harris C. Thomas
Published: November 2022

Vanadium oxide films are widely employed as thermal detectors in uncooled infrared detection systems due to their high temperature coefficient of resistance near room temperature. One strategy toward maximizing detectivity and reducing the thermal time constant in these systems is to minimize the system platform dimensions. This approach necessitates thinner film thicknesses (≪100 nm), for which there is little information regarding thermal sensing performance. Herein, we report on the sensitivity of reactively sputtered vanadium oxide thin film resistive thermometers nominally ranging from 100 to 25 nm and assess the influence of thermal annealing. We demonstrate that films in this minimum limit of thickness maintain a high temperature coefficient while additionally providing an enhancement in characteristics of the noise equivalent power.
Dual-band polarized optical switch with opposite thermochromic properties to vanadium dioxide
Authors: Guo Yanming , Zhu Liangwei , Chen Shuni , Zhou Sihong , Pan Qinghui , Zhao Junming , Shuai Yong
Published: November 2022

A dual-band polarized wavelength-selective optical switch whose thermochromic transmission property is opposite to VO2 itself is proposed. The switch shows a low and high transmittance during phase transition from insulating VO2 to metallic VO2, respectively. The multi-mode coupled circuit model is employed to calculate and tailor the operating frequency of the switch in xz sections for TM waves and yz sections for TE waves. The switch exhibits a transmittance difference of more than one order of magnitude between “on” and “off” modes when the structure is same in the x and y directions under circularly polarized light incidence. For the condition that the structure is not same in the x and y directions, thermochromic transmittance becomes polarization-dependent. By superimposing two polarization states, a dual-band as well as broadband thermochromic transmission property is obtained. The mechanisms of suppressed and enhanced transmission lie in the excitation of MPC and MPV2, respectively. This study may have theoretical guiding significance for design and tailoring of metamaterials with wavelength-selective broadband thermochromic transmission property and potentially apply in active filters and architectural energy-efficient glass.
How graphenic are graphynes? Evidence for low-lying correlated gapped states in graphynes
Authors: Lleopart Genís , Lopez-Suarez Miquel , de P. R. Moreira Ibério , Bromley Stefan T.
Published: November 2022

Graphynes can be structurally envisioned as 2D extensions to graphene, whereby linearly bonded carbon linkages increase the distance between trigonal carbon nodes. Many graphynes have been predicted to exhibit a Dirac-like semimetallic (SEM) graphenic electronic structure, which could potentially make them competitive with graphene for applications. Currently, most graphynes remain as attractive synthetic targets, and their properties are still unconfirmed. Here, we demonstrate that the electronic structure of hexagonal α-graphyne is analogous to that of biaxially strained graphene. By comparison with accurate quantum Monte Carlo results on strained graphene, we show that the relative energetic stability of electronic states in this correlated 2D system can be captured by density functional theory (DFT) calculations using carefully tailored hybrid functionals. Our tuned hybrid DFT approach confirms that α-graphyne has a low energy correlated Mott-like antiferromagnetic insulating (AFI) state, which competes with the SEM state. Our work shows that the AFI-SEM crossover in α-graphyne could be tunable by in-plane biaxial strain. Applying our approach to other graphynes shows that they should also exhibit correlated AFI states, which could be dominant even at zero strain. Calculations using an onsite Coulombic repulsive term (i.e., DFT + U) also confirm the predictions of our hybrid DFT calculations. Overall, our work strongly suggests that graphynes are not as graphenic (i.e., Dirac-like) as often previously predicted by DFT calculations using standard generalized gradient approximation functionals. However, due to the greater electronic versatility (e.g., tunable semiconducting bandgaps and accessible spin polarized states) implied by our study, graphynes could have novel device applications that are complementary to those of graphene.
Radiation-enhanced acoustically driven magnetoelectric antenna with floating potential architecture
Authors: Yun Xiaofan , Lin Wenkui , Hu Rui , Liu Yizhang , Wu Dongmin , Zhang Xinping , Zeng Zhongming , Zhang Baoshun
Published: November 2022

A magnetoelectric (ME) antenna driven by a high-overtone bulk acoustic resonator (HBAR) can play a potentially positive role in the bandwidth enhancement benefit from its narrow harmonic frequency interval, in which radiation characteristics remain to be explored. HBAR ME antennas with floating potential architecture (FPA) and grounded are fabricated and demonstrated separately. The measured far-field radiation characteristics show that the FPA can significantly enhance the gain and radiation efficiency of the HBAR ME antenna by more than 10 dB compared to the grounded setup. Meanwhile, the time domain amplitude sweep demonstrates the high-power tolerance (>23.2 dBm) of the HBAR ME antenna. Two-dimensional finite element method analysis reveals that the FPA-induced electric field excites additional longitudinal-wave resonance, resulting in the coupling of dual longitudinal and shear waves, which is the intrinsic mechanism of its radiation enhancement from the perspective of acoustic excitation. Not only limited to HBAR antennas, the mechanism of FPA described here is also a promising candidate for radiation enhancement in acoustically driven antennas.
Relating McArthur fire danger indices to remote sensing derived burned area across Australia
Authors: Shah Sami Ullah , Yebra Marta , Van Dijk Albert I. J. M. , Cary Geoffrey J.
Published: November 2022

The McArthur grassland and forest fire danger indices, widely used in Australia, predict six fire danger classes from ‘Low-Moderate’ to ‘Catastrophic.’ These classes were linked to the rate of fire spread and difficulty of suppression. However, the lack of rate of fire spread data, especially for elevated fire danger classes, has hindered improvement of the McArthur methodology or an alternate approach. We explored the relationship between fire danger classes and burned areas (derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite instrument) within six climate zones during the 2000–2016 Australian fire seasons. A negative binomial linear regression model was used to explore this relationship. The fire danger classes demonstrated a corresponding increase in burned area from ‘Low-Moderate’ to ‘Very High’ classes in Australia’s inland regions. The elevated fire danger classes did not contribute to this trend. In coastal regions, the satellite-derived burned area showed no relationship between fire danger classes and satellite-derived burned area. We used accumulated burned area from the daily MODIS product, which could be subjected to lagged detection as observed in the Kilmore East fire. Thus, the satellite-derived total burned area may not be a suitable metric for informing the McArthur fire danger classes across Australia.
Accelerating the discovery of novel magnetic materials using machine learning–guided adaptive feedback
Authors: Xia Weiyi , Sakurai Masahiro , Balasubramanian Balamurugan , Liao Timothy , Wang Renhai , Zhang Chao , Sun Huaijun , Ho Kai-Ming , Chelikowsky James R. , Sellmyer David J. , Wang Cai-Zhuang
Published: November 2022

Magnetic materials are essential for energy generation and information devices, and they play an important role in advanced technologies and green energy economies. Currently, the most widely used magnets contain rare earth (RE) elements. An outstanding challenge of notable scientific interest is the discovery and synthesis of novel magnetic materials without RE elements that meet the performance and cost goals for advanced electromagnetic devices. Here, we report our discovery and synthesis of an RE-free magnetic compound, Fe
3
CoB
2
, through an efficient feedback framework by integrating machine learning (ML), an adaptive genetic algorithm, first-principles calculations, and experimental synthesis. Magnetic measurements show that Fe
3
CoB
2
exhibits a high magnetic anisotropy (
K
1
= 1.2 MJ/m
3
) and saturation magnetic polarization (
J
s
= 1.39 T), which is suitable for RE-free permanent-magnet applications. Our ML-guided approach presents a promising paradigm for efficient materials design and discovery and can also be applied to the search for other functional materials.
Preserved soft anatomy confirms shoulder-powered upstroke of early theropod flyers, reveals enhanced early pygostylian upstroke, and explains early sternum loss
Authors: Pittman Michael , Kaye Thomas G. , Wang Xiaoli , Zheng Xiaoting , Dececchi T. Alexander , Hartman Scott A.
Published: November 2022

Anatomy of the first flying feathered dinosaurs, modern birds and crocodylians, proposes an ancestral flight system divided between shoulder and chest muscles, before the upstroke muscles migrated beneath the body. This ancestral flight system featured the dorsally positioned deltoids and supracoracoideus controlling the upstroke and the chest-bound pectoralis controlling the downstroke. Preserved soft anatomy is needed to contextualize the origin of the modern flight system, but this has remained elusive. Here we reveal the soft anatomy of the earliest theropod flyers preserved as residual skin chemistry covering the body and delimiting its margins. These data provide preserved soft anatomy that independently validate the ancestral theropod flight system. The heavily constructed shoulder and more weakly constructed chest in the early pygostylian
Confuciusornis
indicated by a preserved body profile, proposes the first upstroke-enhanced flight stroke. Slender ventral body profiles in the early-diverging birds
Archaeopteryx
and
Anchiornis
suggest habitual use of the pectoralis could not maintain the sternum through bone functional adaptations. Increased wing-assisted terrestrial locomotion potentially accelerated sternum loss through higher breathing requirements. Lower expected downstroke requirements in the early thermal soarer
Sapeornis
could have driven sternum loss through bone functional adaption, possibly encouraged by the higher breathing demands of a
Confuciusornis
-like upstroke. Both factors are supported by a slender ventral body profile. These data validate the ancestral shoulder/chest flight system and provide insights into novel upstroke-enhanced flight strokes and early sternum loss, filling important gaps in our understanding of the appearance of modern flight.
PAHSAs reduce cellular senescence and protect pancreatic beta cells from metabolic stress through regulation of Mdm2/p53
Authors: Rubin de Celis Maria F. , Garcia-Martin Ruben , Syed Ismail , Lee Jennifer , Aguayo-Mazzucato Cristina , Bonner-Weir Susan , Kahn Barbara B.
Published: November 2022

Senescence in pancreatic beta cells plays a major role in beta cell dysfunction, which leads to impaired glucose homeostasis and diabetes. Therefore, prevention of beta cell senescence could reduce the risk of diabetes. Treatment of nonobese diabetic (NOD) mice, a model of type 1 autoimmune diabetes (T1D), with palmitic acid hydroxy stearic acids (PAHSAs), a novel class of endogenous lipids with antidiabetic and antiinflammatory effects, delays the onset and reduces the incidence of T1D from 82% with vehicle treatment to 35% with PAHSAs. Here, we show that a major mechanism by which PAHSAs protect islets of the NOD mice is by directly preventing and reversing the initial steps of metabolic stress–induced senescence. In vitro PAHSAs increased Mdm2 expression, which decreases the stability of p53, a key inducer of senescence-related genes. In addition, PAHSAs enhanced expression of protective genes, such as those regulating DNA repair and glutathione metabolism and promoting autophagy. We demonstrate the translational relevance by showing that PAHSAs prevent and reverse early stages of senescence in metabolically stressed human islets by the same Mdm2 mechanism. Thus, a major mechanism for the dramatic effect of PAHSAs in reducing the incidence of type 1 diabetes in NOD mice is decreasing cellular senescence; PAHSAs may have a similar benefit in humans.