bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarization manipulation of surface acoustic waves by metallization patterns on a piezoelectric substrate
Authors: Weser R. , Darinskii A. N. , Schmidt H.
Published: October 2020

Surface acoustic waves (SAWs) with large normal (vertical) surface displacement at the surface are commonly utilized in microfluidic actuators in order to provide the desired momentum transfer to the fluid. We present an alternative concept using a SAW with comparatively small vertical displacement. Such a SAW passes underneath the microfluidic vessel walls with minimum losses but it needs to be converted inside the vessel into surface vibrations with large vertical displacements. The principal operability of the above idea is illustrated by experimental and numerical studies of the polarization conversion of a leaky SAW on 64° rotated Y-cut of lithium niobate owing to the partial metallization of the substrate surface. In particular, it is found that vertical displacements on the metallized surface can be up to 3.5 times higher as compared to their values on the free surface. Results of computations agree reasonably well with measurements carried out with a laser Doppler vibrometer and allow the clarification of some specific features of this polarization conversion by means of spatial frequency analysis.
Generalized Grad–Shafranov equation for non-axisymmetric MHD equilibria
Authors: Burby J. W. , Kallinikos N. , MacKay R. S.
Published: October 2020

The structure of static MHD equilibria that admit continuous families of Euclidean symmetries is well understood. Such field configurations are governed by the classical Grad–Shafranov equation, which is a single elliptic partial differential equation in two space dimensions. By revealing a hidden symmetry, we show that in fact all smooth solutions of the equilibrium equations with non-vanishing pressure gradients away from the magnetic axis satisfy a generalization of the Grad–Shafranov equation. In contrast to solutions of the classical Grad–Shafranov equation, solutions of the generalized equation are not automatically equilibria, but instead only satisfy force balance averaged over the one-parameter hidden symmetry. We then explain how the generalized Grad–Shafranov equation can be used to reformulate the problem of finding exact three-dimensional smooth solutions of the equilibrium equations as finding an optimal volume-preserving symmetry.
Thermal evolution of ferroelectric behavior in epitaxial Hf0.5Zr0.5O2
Authors: Adkins J. W. , Fina I. , Sánchez F. , Bakaul S. R. , Abiade J. T.
Published: October 2020

Herein, we report a cryogenic-temperature study on the evolution of the ferroelectric properties of epitaxial Hf0.5Zr0.5O2 thin films on silicon. Wake-up, endurance, and fatigue of these films are found to be intricately correlated, strongly hysteretic, and dependent on available thermal energy. Field-dependent measurements reveal a decrease in polarization with temperature, which has been determined not to be an intrinsic change of the material property, rather a demonstration of the increase in the coercive bias of the material. Our findings suggest that a deficiency in thermal energy suppresses the mobility of defects presumed to be oxygen vacancies during wake-up and trapped injected charge during fatigue, which is responsible for polarization evolution during cycling. This permits accelerated wake-up and fatigue effects at high temperatures where thermal energy is abundant but delays these effects at cryogenic temperatures.
Relaxation of competing electromechanical couplings in murine artery
Authors: Jiang Peng , Huang Boyuan , Wei Liyu , Li Aolin , Ou Yun , Yan Fei , Zheng Hairong , Li Jiangyu
Published: October 2020

Piezoelectricity and pyroelectricity in biological tissues, which originate from oriented fibrous proteins with a polar axis, have long been suggested to play important roles in physiological functions. The possible manipulation of their polarity by external mechanisms, however, remains unsettled. We revisit this problem here using piezoresponse force microscopy (PFM) as the tool and the intima layer of murine artery as a model system. By carefully examining first and second harmonic piezoresponses at both selected points and through spatial mapping, we establish that electromechanical coupling probed by PFM is predominantly piezoelectric in the intima layer, while the quadratic effect makes only minor contributions. More importantly, we observe competition between the linear and quadratic effects after removal of DC biases applied to the sample surface, revealing not only interesting relaxation dynamics, but also highly asymmetric piezoresponse. Positive DC rotates dipoles in tropoelastin monomers away with reduced alignment, while negative DC aligns dipoles more leading to enhanced piezoresponse. The electric manipulation of biological polarity is thus demonstrated, with the relaxation time constant determined on the order of 0.1 s, much slower than classical ferroelectrics.
A multiple liquid metal switching mechanism in a single flow microfluidic channel as a reconfigurable bandpass filter
Authors: Park Eiyong , Lee Minjae , Phon Ratanak , Lim Sungjoon
Published: October 2020

We propose a novel microfluidic channel wherein three different liquid metal switches can be operated via a single fluidic flow. Liquid metals with movable metallic properties have been used in antenna filters, sensors, etc. In previous works of the liquid metal switch, each switch requires each channel with an inlet and outlet. For instance, three liquid metal switches must employ three channels with three flows. However, the proposed mechanism needs only single flow for three liquid metal switches. The proposed mechanism applies to a novel filter that achieves the frequency reconfigurability by using the variation of inductive coupling of a half-mode substrate-integrated waveguide (HMSIW) rather than capacitive coupling. The proposed filter consists of three layers, namely, top microfluidic channel, middle conductive, and bottom ground layers. The middle conductive layer has an HMSIW with two microstrip step impedances (SIs) and two microstrip 50-Ω feeding lines. A pair of defected ground structures (DGSs) was realized on the bottom ground layer. The HMSIW and DGS were designed to determine the low-cutoff and high-cutoff frequencies, respectively. Because two of the liquid metal switches are located above the SI lines with the DGSs, they enable switching of the high-cutoff frequency. However, as the remaining liquid metal switch is located on the HMSIW to change its width, it enables switching of the low-cutoff frequency. For instance, when the SI switches are on, the 1-dB passband of the filter is 2.95 GHz–4.76 GHz, and when the HMSIW switch is on, the 1-dB passband of the filter is 4.8 GHz–6.6 GHz.
Resolution of the paradox discovered by Freidberg in the Shafranov's theory on plasma equilibrium
Authors: Pustovitov V. D.
Published: October 2020

Predictions of the Shafranov's analytical theory are so highly respected that some of them are reprinted without any check for consistency. One example of such a kind is considered here: the equation for the plasma shift in a tokamak first introduced in Shafranov, J. Nucl. Energy C 5, 521 (1963). Since then, it has entered a number of review papers and textbooks, though, when tested by Freidberg [Freidberg, Rev. Mod. Phys. 54, 801 (1982)], it revealed some peculiar features. The main (long unnoticed) discovery was that the external vertical magnetic field required by that equation at zero shift was significantly different from the value given by the other famous Shafranov's formula for the same field in the same configuration. It is the tremendous scale of disagreement in the very core of the otherwise perfect theory that attracts attention. Here, a wrong element in the construction is found and repaired. It is established that it must be the incorrectly imposed boundary conditions for the magnetic field at the vacuum vessel wall treated as an ideal conductor. The proposed replacement eliminates the contradiction and extends the model by incorporating the resistive-wall effects.
Rotational relaxation model for nitrogen and its application in free jet expansion problem
Authors: Yakunchikov Artem , Kosyanchuk Vasily , Iuldasheva Aliya
Published: October 2020

This paper studies a rotational relaxation process in nitrogen. A series of more than 200 × 106 classical trajectory calculations (CTCs) of collisions of nitrogen molecules were carried out. Based on the CTC results, a collision model accounting for rotational relaxation was proposed and used for three-dimensional event-driven molecular dynamics simulation of a free jet expansion. It was shown that the collision model parameterized by the CTCs can produce results in good agreement with the existing experimental measurements.
Charge transport mechanism in La:HfO2
Authors: Gritsenko V. A. , Gismatulin A. A.
Published: October 2020

Currently, it is generally accepted that the charge transport in dielectrics is limited by the Coulomb trap ionization in a strong electric field (Frenkel effect). In the present work, the charge transport mechanism in La:HfO2 was experimentally studied, and four theoretical conductivity models—the Frenkel effect of Coulomb trap ionization, Hill-Adachi model of overlapping Coulomb potentials, Makram–Ebeid and Lannoo model of multiphonon isolated trap ionization, and Nasyrov-Gritsenko phonon-assisted tunneling between traps—were quantitatively analyzed. It was shown that the charge transport mechanism in La: HfO2 is qualitatively described by the Frenkel effect, but the Frenkel effect predicts an abnormally low trap concentration value and a large high-frequency dielectric constant value, which is not consistent with the experiment. The charge transport in La:HfO2 is quantitatively described by the model of phonon-assisted tunneling between neighboring traps.
Analytic energy gradients for the self-consistent direct random phase approximation
Authors: Thierbach Adrian , Görling Andreas
Published: October 2020

Analytic energy gradients with respect to nuclear coordinates are derived and implemented for the self-consistent direct random phase approximation (sc-dRPA) method. In contrast to the more common non-self-consistent dRPA methods, the sc-dRPA method does not require a choice for the approach to generate the Kohn–Sham orbitals and eigenvalues serving as input for the dRPA correlation functional. The fact that the sc-dRPA total energy is variational facilitates the calculation of analytic gradients. The analytic gradients are tested against numerical ones and then used to calculate equilibrium geometries and vibrational frequencies for various molecules including weakly bonded dimers and transition metal compounds. The sc-dRPA method can compete in accuracy with Møller–Plesset perturbation theory of second order and with conventional density-functional methods within the generalized gradient approximation or of hybrid type. Indeed, sc-dRPA geometries and vibrational frequencies are most accurate in many cases. Moreover, the sc-dRPA method is robust in the sense that it is applicable to all considered molecules, whereas conventional density-functional methods are not applicable to dispersion bonded dimers, and Møller–Plesset perturbation theory of second order erroneously predicts a number of molecules to be unbound and yields completely wrong vibrational frequencies in some cases. The coupled cluster singles doubles methods yield geometries and vibrational frequencies of a quality that is inferior to that of the other considered methods.
On the flow characteristics in different carotid arteries
Authors: Chen Yu , Yang Xiaolei , Iskander Andrew John , Wang Ping
Published: October 2020

Hemodynamics plays an important role in the cause of atherosclerotic disease. In this work, we simulated the flow fields in six human carotids using the sharp-interface immersed boundary method. We compare the axial velocity, the secondary flow, the vortex structures, the area with reversed flows, and the standard deviation of velocity fluctuations for different carotids. The computed results show similarities among different carotids for the overall pattern of different flow characteristics. More importantly, differences are observed in terms of the details of the area of the reversed flow region, the size and shape of the region dominated by reversed flows, and the length of time with reversed flow or dominated by secondary flows, which are strongly correlated with the formation of plaques. Further analysis shows that patient-specific features of the carotid geometry, e.g., the flare and proximal curvature of the carotid, have significant effects on these flow characteristics. This suggests that a patient-specific program is needed for the prevention and treatment of atherosclerosis.
Scale-by-scale energy transfer in a dual-plane jet flow
Authors: Hao Keli , Nagata Koji , Zhou Yi
Published: October 2020

We numerically investigate the scale-by-scale energy transfer along all three directions (i.e., streamwise, vertical, and spanwise directions) at three specifically selected centerline locations (i.e., X/L0 = 7, 12, and 20) in a dual-plane jet flow by using the Karman–Howarth–Monin–Hill (KHMH) equation, where X and L0 are the streamwise distance from the inlet and the initial jet width, respectively. Unlike the well-known Karman–Howarth equation, the fully generalized KHMH equation allows us to study the scale-by-scale energy balance without any assumptions (i.e., homogeneity and isotropy). We calculate each term in the KHMH equation by using the data from a direct numerical simulation [Zhou et al., “Dual-plane turbulent jets and their non-Gaussian velocity fluctuations,” Phys. Rev. Fluids 3, 124604 (2018)]. At X/L0 = 7, where the flow is inhomogeneous and anisotropic, the scale-by-scale energy transfer is quite different in the streamwise, vertical, and spanwise directions. One interesting finding is that a negative production term in the vertical direction can be found in the reversal flow region. Unlike most flows previously investigated, the linear energy cascade plays an important role in the energy cascade. The linear energy transfer is heavily dependent on the direction: in the streamwise direction, it is forward (from the large scale to the small scale), but in the vertical direction, it is backward (from the small scale to the large scale). A physical model is proposed and also verified, which suggests that the forward linear energy cascade corresponds to fluid compression, and the backward linear energy cascade corresponds to the fluid stretching. At X/L0 = 12, where the energy spectrum exhibits a well-defined −5/3 scaling, there is no equilibrium energy cascade. The linear energy cascade is still dominant and shows a backward cascade in the streamwise direction and a forward cascade in the vertical direction, while the non-linear energy cascade remains forward. At X/L0 = 20, where the flow becomes much more homogeneous and isotropic, within a short scale-range around the Taylor microscale, the dissipation term can be balanced by the combination of the non-linear energy transfer term and advection term. This observation to some extent echoes Kolmogorov’s hypothesis, but limited only to length scales around the Taylor microscale, and the persistence of the advection term can find its root in the low local Reynolds number at that length scale.
N-polar GaN/AlN resonant tunneling diodes
Authors: Cho YongJin , Encomendero Jimy , Ho Shao-Ting , Xing Huili Grace , Jena Debdeep
Published: October 2020

N-polar GaN/AlN resonant tunneling diodes are realized on a single-crystal N-polar GaN bulk substrate by plasma-assisted molecular beam epitaxy growth. The room-temperature current–voltage characteristics reveal a negative differential conductance (NDC) region with a peak tunneling current of 6.8 ± 0.8 kA/cm2 at a forward bias of ∼8 V. Under reverse bias, the polarization-induced threshold voltage is measured at ∼−4 V. These resonant and threshold voltages are well explained with the polarization field, which is opposite to that of the metal-polar counterpart, confirming the N-polarity of the resonant tunneling diodes (RTDs). When the device is biased in the NDC-region, electronic oscillations are generated in the external circuit, attesting to the robustness of the resonant tunneling phenomenon. In contrast to metal-polar RTDs, N-polar structures have the emitter on the top of the resonant tunneling cavity. As a consequence, this device architecture opens up the possibility of seamlessly interfacing—via resonant tunneling injection—a wide range of exotic materials with III-nitride semiconductors, providing a route towards unexplored device physics.
A universal framework for microscope sensorless adaptive optics: Generalized aberration representations
Authors: Hu Q. , Wang J. , Antonello J. , Hailstone M. , Wincott M. , Turcotte R. , Gala D. , Booth M. J.
Published: October 2020

Adaptive optics (AO) methods are widely used in microscopes to improve image quality through correction of phase aberrations. A range of wavefront-sensorless AO schemes exist, such as modal, pupil segmentation zonal, and pixelated piston-based methods. Each of these has a different physical implementation that makes direct comparisons difficult. Here, we propose a framework that fits in all sensorless AO methods and facilitates systematic comparisons among them. We introduce a general model for the aberration representation that encompasses many existing methods. Through modeling and experimental verification in a two-photon microscope, we compared sensorless AO schemes with a range of aberration representations to correct both simulated and sample induced aberrations. The results show that different representations can provide a better basis for correction in different experimental scenarios, which can inform the choice of sensorless AO schemes for a particular application.
Effect of Basset’s hereditary force on bubble dynamics in liquid oxide-based diffusion-bubbling membranes
Authors: Belousov Valery V. , Fedorov Sergey V.
Published: October 2020

Innovative liquid oxide-based diffusion-bubbling membranes are a key perspective for efficient oxygen separation from air. The oxygen bubble motion in these membranes is usually described within the framework of a quasi-stationary model allowing negligible characteristic time and characteristic distance of the bubble dynamic relaxation. Here, we show that Basset’s hereditary force, associated with the existence of an unsteady boundary layer around the bubble, affects the oxygen bubble dynamics and increases the characteristic time and distance of the bubble dynamic relaxation by two and three orders of magnitude, respectively. An important application of this result is thin-film diffusion-bubbling membranes whose thickness is comparable with the characteristic distance of the bubble dynamic relaxation.
Magnetic (electric) drop deformation in uniform external fields: Volume averaged methods and formation of static and dynamic conical tips
Authors: Misra Kaartikey
Published: October 2020

Analytical relationships describing droplet deformation in external magnetic (electric) fields rely on spheroidal and ellipsoidal shape approximations. We show that the ellipsoidal shape approximations that assume a uniform internal magnetic field are only valid for small deformations (aspect ratio a/b ≈ 4). For large droplet deformations, the non-uniformity in the field within the droplet becomes substantial, rendering such approximations to be invalid. To overcome the limitations of ellipsoidal theory, we perform numerical simulations to determine volume averaged demagnetization factor and fields. Based on the numerical simulations, we propose semi-analytical relationships to describe small and large deformations for magnetic droplets using volume averaged methods. We test and validate our results with the existing experimental results and find an excellent agreement between our model and experimental studies. We extend our analysis and investigate static and dynamic droplets with conical tips. We show that droplets with conical tips could be defined solely by the characteristic half cone angle. We analyze unstable droplets with extremely high susceptibility χ → ∞ and find that conical tips with a half cone angle of θc ≈ 30° and an aspect ratio of ≈3.7 are formed prior to breakup, in agreement with the prior experimental studies of charged electric droplet breakup. We show that the volume averaged methods derived for droplets with finite tip curvature are also valid and in good agreement with the computational and previous experimental studies of magnetic droplets with conical tips.
Photoinduced charge transfer in Zn(II) and Au(III)-ligated symmetric and asymmetric bacteriochlorin dyads: A computational study
Authors: Aksu Huseyin , Maiti Buddhadev , Ptaszek Marcin , Dunietz Barry D.
Published: October 2020

The excited-state properties and photoinduced charge-transfer (CT) kinetics in a series of symmetrical and asymmetrical Zn- and Au-ligated meso–meso-connected bacteriochlorin (BChl) complexes are studied computationally. BChl derivatives, which are excellent near-IR absorbing chromophores, are found to play a central role in bacterial photosynthetic reaction centers but are rarely used in artificial solar energy harvesting systems. The optical properties of chemically linked BChl complexes can be tuned by varying the linking group and involving different ligated metal ions. We investigate charge transfer in BChl dyads that are either directly linked or through a phenylene ring (1,4-phenylene) and which are ligating Zn or Au ions. The directly linked dyads with a nearly perpendicular arrangement of the BChl units bear markedly different properties than phenylene linked dyads. In addition, we find that the dielectric dependence of the intramolecular CT rate is very strong in neutral Zn-ligated dyads, whereas cationic Au-ligated dyads show negligible dielectric dependence of the CT rate. Rate constants of the photo induced CT process are calculated at the semiclassical Marcus level and are compared to fully quantum mechanical Fermi’s golden rule based values. The rates are calculated using a screened range separated hybrid functional that offers a consistent framework for addressing environment polarization. We study solvated systems in two solvents of a low and a high scalar dielectric constant.
Thermoelectric Si1−xGex and Ge epitaxial films on Si(001) with controlled composition and strain for group IV element-based thermoelectric generators
Authors: Taniguchi Tatsuhiko , Ishibe Takafumi , Hosoda Ryoya , Wagatsuma Youya , Alam Md. Mahfuz , Sawano Kentarou , Uenuma Mutsunori , Uraoka Yukiharu , Yamashita Yuichiro , Mori Nobuya , Nakamura Yoshiaki
Published: October 2020

This study presents the material design of Si1−xGex epitaxial films/Si for thin film thermoelectric generators (TFTEGs) by investigating their thermoelectric properties. The thermoelectric films composed of group-IV elements are advantageous due to their compatibility with the Si process. We fabricated Si1−xGex epitaxial films with various controlled x values and strains using various growth methods. Ge epitaxial films without strains exhibited the highest thermoelectric power factor (∼47 μW cm−1 K−2) among various strain-controlled Si1−xGex (x ≠ 1) epitaxial films, which is higher at room temperature than SiGe alloy-based bulks ever reported. On the other hand, strained Si1−xGex epitaxial films showed an ultralow thermal conductivity of ∼2 W m−1 K−1, which is close to the value for amorphous Si. In addition to strained SiGe films with the ultralow thermal conductivity, unstrained Ge films with a high thermoelectric power factor can also be used for future TFTEGs by applying a nanostructuring technique. A preliminary TFTEG of Ge epitaxial films was realized, which generated a maximum power of ∼0.10 μW cm−2 under a temperature difference of 20 K. This demonstrates that epitaxial films composed of group-IV semiconductors are promising materials for TFTEG applications.
Temperature-dependent phase noise properties of a two-section GaSb-based mode-locked laser emitting at 2
μ
m
Authors: Li Xiang , Wang Hong , Qiao Zhongliang , Sia Jia Xu Brian , Wang Wanjun , Guo Xin , Zhang Yu , Niu Zhichuan , Tong Cunzhu , Liu Chongyang
Published: October 2020

The temperature-dependent phase noise properties of a monolithic two-section mode-locked semiconductor laser are first investigated. This is performed on a GaSb-based quantum well laser emitting at ∼2 μm. Stable mode locking operation with a fundamental repetition frequency of ∼13.3 GHz is achieved on this laser up to 60 °C. At a fixed temperature, there is no monotonous dependence of integrated jitter on the bias condition. For a given gain current or absorber voltage, there exists a corresponding optimal absorber voltage or gain current, respectively, that minimizes the integrated jitter. More important, the phase noise properties improve obviously at elevated temperatures with the lowest achievable jitter reducing obviously from 3.15 ps at 20 °C to 1.39 ps at 60 °C (100 kHz–1 GHz). We consider that the reason is reduced amplified spontaneous emission noise at high temperatures. This is confirmed by the extracted peak-to-valley ratio of the involved laser modes. We believe that this study provides an important insight into the carrier behaviors and noise performance of mode-locked semiconductor lasers, which is meaningful to their applications especially at high temperatures.
Room-temperature magnetic skyrmion in epitaxial thin films of Fe2−xPdxMo3N with the filled
β
-Mn-type chiral structure
Authors: Qiang B. W. , Togashi N. , Momose S. , Wada T. , Hajiri T. , Kuwahara M. , Asano H.
Published: October 2020

We report experimental observations of chiral magnetic skyrmion phases in thin films of molybdenum nitride with a filled β-Mn-type structure. A series of Fe2−xPdxMo3N (x = 0.15, 0.32, and 0.54) thin films are grown epitaxially with the (110) orientation on c-plane sapphire substrates by reactive magnetron sputtering, and their structural, magnetic, and transport properties are investigated. Studies using the Topological Hall effect and Lorenz transmission electron microscopy imaging for films with x = 0.32 identified the existence of two types of skyrmion phases with a size as small as 60 nm; one is a dense skyrmion phase at temperatures below 100 K, and the other is an isolated skyrmion phase in a higher temperature range to well beyond room temperature. These epitaxial thin films in the family of molybdenum nitrides open the way for the study of skyrmions, manipulation of their properties, and the exploration and optimization for skyrmion-based applications.
Features of the secondary runaway electron flow formed in an elongated, atmospheric pressure air gap
Authors: Yalandin M. I. , Sadykova A. G. , Sharypov K. A. , Shpak V. G. , Shunailov S. A. , Zubareva O. V. , Zubarev N. M.
Published: October 2020

We investigate the formation of a secondary flow of runaway electrons with energies on the order of 100 keV in an air gap after the passage of a primary picosecond flow of similar fast particles, arising in the cathode region where the distribution of the electric field is very inhomogeneous. The dependence of the secondary flow onset delay on the gap length and the field strength is demonstrated. The reasons for the discrimination of the two flows in time are considered analytically. The occurrence of fast secondary electrons in an anode-located part of the gap is demonstrated under conditions when the ionization wave generated in the cathode region by the primary runaway electrons is cutoff. For this, an intermediate aluminum foil electrode under a floating potential has been used. This third electrode, which divides the gap into two sections, is partially transparent for the runaway electrons. It has been also shown that runaway electrons demonstrate the earliest arrival to the anode if they arise due to the photoionization of the gas by bremsstrahlung of the primary particles bombarding an intermediate electrode made of tantalum foil.
Tunable second harmonic generation from bianisotropic plasmonic metamolecule via utilizing phase change materials
Authors: Guo Kai , Zhou Keya , Guo Zhongyi
Published: October 2020

In this work, we utilize phase change materials to achieve tunable second harmonic generation from magnetic resonance in bianisotropic plasmonic metamolecules. As a proof-of-concept, we fill the gap of gold split ring resonators (SRRs) with Ge2Se2Te5 (GST); the second harmonic wavelength can be tuned over 400 nm in the telecom regime when GST gradually changes from amorphous to crystalline state. According to the equivalent circuit model, we demonstrate that the second harmonic wavelength and its tunable range can be engineered through the capacitance coupling strength in gold SRRs. Our results may suggest a wide range of potential applications of nonlinear nanooptics.
Importance of phenolics in populations of Teucrium chamaedrys (Lamiaceae) from serpentine soils
Authors: Zhiponova Miroslava , Yordanova Zhenya , Pavlova Dolja , Rogova Mariya , Dimitrova Milena , Dragolova Daniela , Tasheva-Terzieva Elena , Kapchina-Toteva Veneta
Published: October 2020

The genus Teucrium includes perennial herbs or shrubs widespread all around the world. The wall germander (Teucrium chamaedrys L.) is widely used in traditional and modern medicine for various health disorders and recent research revealed that serpentine populations of this herb have increased antioxidant and respective medical potential compared with calcareous population. The present study aims to elucidate further the role of phenolic compounds for T. chamaedrys growth on serpentine soil. Methanol extracts from two serpentine and two non-serpentine (calcareous and siliceous) Bulgarian populations were obtained and analysed for total quantity of phenolics and flavonoids, and antioxidant activity. The serpentine soils acted as an elicitor of the antioxidant response in T. chamaedrys plants and the increased phenolics level correlated with enhanced antioxidant activity. The calcareous population had lower values but still higher than the siliceous population which had the lowest antioxidant values, although the flavonoid quantity that was equal to the serpentine populations. A gas chromatography-mass spectrometry (GC-MS) assay for identifying phenolic acids pointed to caffeic acid as a dominant compound, with additional cinnamic and benzoic acid derivatives with putative roles as antioxidants, in cell wall lignification for heavy metals chelation, and for interspecies interactions.
Response time of temperature measurements at automatic weather stations in Australia
Authors: Ayers G. P. , Warne J. O.
Published: October 2020

Bureau of Meteorology automatic weather stations (AWS) are employed to record 1-min air temperature data in accord with World Meteorological Organization recommendations. These 1-min values are logged as the value measured for the last second in each minute. The Bureau explains that this is appropriate because the inherent measurement system time constant means the 1-s data are not instantaneous, but are an average smoothed over the previous 40–80 s. To test this proposition in the field air temperature data were measured at 1-Hz at two Bureau AWS sites between April and June 2018. The frequency distribution of the differences between each 1-s value and the 60-s average centred on that value provided information on the overall measurement system response time constant. Expressed in terms of an e-folding measurement system response time, the data from the two measurement systems studied yielded response times in the range 50–150 s, largely consistent with the Bureau’s explanation.
“I guess anyone would do that wouldn’t they?”
Authors: Johansen Stine Hulleberg
Published: October 2020

Hedging is a complex phenomenon with an indefinite number of potential realisations. The complexity and versatility of
hedging strategies make them particularly interesting to study across languages. This contrastive study compares the realisations of the
pragmatic function of hedging in everyday Norwegian and English conversations using data from four corpora of Norwegian and English informal
spoken conversations (the Norwegian Speech Corpus, the Nordic Dialect Corpus, the BigBrother corpus, and the BNC2014). The results show that
speakers of both languages mainly use pragmatic particles, adverbs, and first-/second-person pronouns + cognitive verbs [1/2 pers. + Cog. V]
to express hedging. Furthermore, English speakers use significantly more [1/2 pers. + Cog. V] and modal verbs than Norwegian speakers, who
use significantly more adjectives, prepositional phrases and clauses to hedge their utterances.
Asymptotic structure of the Pauli–Fierz theory in four spacetime dimensions
Authors: Fuentealba Oscar , Henneaux Marc , Majumdar Sucheta , Matulich Javier , Troessaert Cédric
Published: October 2020

The asymptotic structure of the Pauli–Fierz theory at spatial infinity is investigated in four spacetime dimensions. Boundary conditions on the massless spin-2 field that are invariant under an infinite-dimensional group of non-trivial ‘improper’ gauge symmetries are given. The compatibility of these boundary conditions with invariance of the theory under Lorentz boosts is a subtle issue which is investigated in depth and leads to the identification of the improper gauge symmetries with the pure BMS supertranslations. It is also shown how rigid Poincaré transformations and improper gauge symmetries of the free Pauli–Fierz theory merge into the full BMS group as one switches on the gravitational coupling. Contrary to the massless spin-1 case, where invariance under boosts is implemented differently and where important differences between the free and the interacting cases have been exhibited recently, the free Pauli–Fierz theory and general relativity show very similar behaviors at spatial infinity.
Projectile angular distribution for electron capture in p + H2 collision considering the vibrational motion
Authors: Igarashi A
Published: October 2020

We show the results calculated with improved treatment for the interaction between incident proton and nuclei in H2 over our previous work [2019 J. Phys. B: At. Mol. Opt. Phys.
52 075204] for electron capture process from H2 by proton with including the vibrational motion of molecules. Moreover, the differential cross sections with respect to the projectile scattering angle are calculated and the results are compared with experimental data. It is found that the inclusion of vibrational motion of molecules is essential to reproduce the experimental angular distribution for the fixed molecular orientation parallel to the transverse momentum transfer.
Numerical modeling of ignition enhancement using repetitive nanosecond discharge in a hydrogen/air mixture I: calculations assuming homogeneous ignition
Authors: Wang Yuan , Guo Peng , Chen Haitao , Chen Zheng
Published: October 2020

Ignition enhancement using repetitive nanosecond discharge (NSD) is studied in a stoichiometric hydrogen/air mixture. Numerical simulations are conducted for the homogeneous ignition process using code incorporating ZDPlasKin and CHEMKIN. The objective is to examine how the characteristics of the NSD affects the ignition delay time and why the NSD promotes a homogeneous ignition process. The influence of pulse number, discharge frequency, reduced electric field, total input energy and input energy per pulse on the ignition process is investigated. It is found that the characteristics of NSD have a significant impact on the ignition delay time. The ignition delay time changes non-monotonically with the reduced electric field, and it depends on both the total input energy and the input energy per pulse. Furthermore, it is shown that the ignition enhancement by NSD is mainly due to the kinetic effects while the thermal effects (Joule heat) are negligible. The ignition enhancement is mainly caused by radicals, especially H and O, produced by NSD. A reaction pathway analysis is conducted to identify the key elementary reactions involved in the ignition enhancement using NSD. The electron impact reactions and quenching reactions of excited species are found to help to produce H and O radicals and thereby promote the homogeneous ignition process.
Analysis of runaway electron discharge formation during Joint European Torus plasma start-up
Authors: de Vries P C , Gribov Y , Martin-Solis R , Mineev A B , Sinha J , Sips A C C , Kiptily V , Loarte A
Published: October 2020

Joint European Torus (JET) plasma initiations that form a significant quantity of runaway electrons have been studied. It is shown that there is no direct relationship between the prefill pressure and breakdown electric field and signs of runaway electrons during the plasma initiation. Runaway electron generation is determined by the electric field and density development at and after burn-through. A clear criterion of density and electric field at one given point in time, which would ensure the avoidance of runaway electron generation, cannot be determined, because the timescales for the formation of runaway electrons and for the dynamics of the density differ significantly. Moreover, the formation process can be reversed, reducing the influence of runaway electrons on the discharge. Ensuring a high enough density will reduce the likelihood that runaway electron discharges are formed. It is also found that at JET the electric field often exceeds the critical electric field during the early stages of the current ramp-up phase, even when no signs of runaway electrons are present. Expected runaway current dynamics have been analysed using the discharge circuit equation. The comparison of the expected runaway electron current dynamics shows it to be significantly slower compared to theoretical expectations in the presence of a hot and dense thermal background plasma. This could be explained by an enhanced critical electric field and/or a reduced confinement of runaway electrons. The latter is shown to be affected by bursts of magnetohydrodynamic activity that are characteristic during the current ramp-up. The development of discharges in which the current is fully carried by runaway electrons happens on a slow timescale of several seconds, limited by the available flux. Such timescales are sufficient for improved active control of these events, avoiding runaway currents at plasma initiation exceeding values at which they could damage in-vessel components. The results provide insight into the improvement and interpretation of self-consistent modelling of runaway electron generation during the start-up of International Thermonuclear Experimental Reactor discharges.
III-nitride blue light-emitting diodes utilizing hybrid tunnel junction with low excess voltage
Authors: Wang Jianfeng , Young Erin C , Ho Wan Ying , Bonef Bastien , Margalith Tal , Speck James S
Published: October 2020

Tunnel junctions (TJs) offer alternative designs and promise in some cases improved performances for nitride-based light-emitting diode (LEDs) and laser diodes (LDs) and are widely used in academic studies. However, the voltage penalty of the LEDs and LDs, in comparison with standard contact technologies, has been a major concern especially for commercial applications. In this study, we investigated methods to achieve low excess voltage. Using ammonia molecular beam epitaxy (NH3 MBE), GaN TJs were grown on commercial metalorganic chemical vapor deposition (MOCVD) grown blue LED wafers. Atom probe tomography (APT) and secondary ion mass spectrometry (SIMS) indicate 1 min buffered HF (BHF) clean of the regrowth interface reduced Mg and impurity incorporation into the n++ regrown TJ layers. The wafers were processed and measured in parallel to reference wafers using both university processes and industry processes. At 20 A cm−2, TJ LEDs grown with Si δ-doping at the junction interface processed in the university cleanroom had a forward voltage of 3.17 V in comparison to 2.86 V for LEDs processed with a standard indium tin oxide (ITO) contact. Unencapsulated TJ LEDs processed by industrial process without ITO or current blocking layer had about 0.3 V excess voltage compared to reference LEDs. The TJ LEDs also had more uniform light emission profile. The low excess voltage and consistent results acquired in both settings suggest that TJ can be scaled for industrial processes.
Bistability study of buckled MEMS diaphragms
Authors: Ratnayake Dilan , Derakhshani Masoud , Berfield Thomas A , Walsh Kevin M
Published: October 2020

Bistable elements are candidate structures for the evolving field of MEMS-based no-power event-driven sensors. In this paper, we present a strategy for producing bistable elements and investigate two compatible bilayer material systems for their realization using MEMS technology. Both bilayer systems leverage thermally-grown silicon dioxide as the principal stress-producing layer and a second material (either polyimide or aluminum) as the main structural layer. Arrays of buckled circular diaphragms, ranging in diameter from 100 μm to 700 μm in 50 μm increments, were fabricated and their performances were compared to modeled and FEA-simulated results. In all cases, the diaphragms buckled when DRIE-released as expected, and their buckled experimental heights were within 9.1% of the theory and 1.8% of the FEA prediction. Interestingly, the smaller diameter structures exhibited a directional bias which we investigate and forecast using FEA. These bistable mechanical elements have the ability to serve as building blocks for no-power threshold-driven smart switches. New contributions to the field include: (a) introduction of a new bistable material system made from aluminum and compressive oxide, (b) investigation of diaphragm diameter size as it related to the phenomena of bistability versus non-bistability, (c) FEA analysis of the critical transition between bistability and non-bistability, and (d) introduction of the ‘dome factor’ term to describe dome quality.
Statistical Estimation of the Reproductive Number From Case Notification Data
Authors: White Laura F , Moser Carlee B , Thompson Robin N , Pagano Marcello
Published: October 2020

The reproductive number, or reproduction number, is a valuable metric in understanding infectious disease dynamics. There is a large body of literature related to its use and estimation. In the last 15 years, there has been tremendous progress in statistically estimating this number using case notification data. These approaches are appealing because they are relevant in an ongoing outbreak (e.g., for assessing the effectiveness of interventions) and do not require substantial modeling expertise to be implemented. In this article, we describe these methods and the extensions that have been developed. We provide insight into the distinct interpretations of the estimators proposed and provide real data examples to illustrate how they are implemented. Finally, we conclude with a discussion of available software and opportunities for future development.
An optimal kernel-based multivariate U-statistic to test for associations with multiple phenotypes
Authors: Wen Y , Lu Qing
Published: October 2020

Set-based analysis that jointly considers multiple predictors in a group has been broadly conducted for association tests. However, their power can be sensitive to the distribution of phenotypes, and the underlying relationships between predictors and outcomes. Moreover, most of the set-based methods are designed for single-trait analysis, making it hard to explore the pleiotropic effect and borrow information when multiple phenotypes are available. Here, we propose a kernel-based multivariate U-statistics (KMU) that is robust and powerful in testing the association between a set of predictors and multiple outcomes. We employed a rank-based kernel function for the outcomes, which makes our method robust to various outcome distributions. Rather than selecting a single kernel, our test statistics is built based on multiple kernels selected in a data-driven manner, and thus is capable of capturing various complex relationships between predictors and outcomes. The asymptotic properties of our test statistics have been developed. Through simulations, we have demonstrated that KMU has controlled type I error and higher power than its counterparts. We further showed its practical utility by analyzing a whole genome sequencing data from Alzheimer’s Disease Neuroimaging Initiative study, where novel genes have been detected to be associated with imaging phenotypes.
Epidemiological Trends of Racial Differences in Early- and Late-onset Group B Streptococcus Disease in Tennessee
Authors: Hamdan Lubna , Vandekar Simon , Spieker Andrew J , Rahman Herdi , Ndi Danielle , Shekarabi Emily S , Thota Jyotsna , Rankin Danielle A , Haddadin Zaid , Markus Tiffanie , Aronoff David M , Schaffner William , Gaddy Jennifer A , Halasa Natasha B
Published: October 2020

Background

The rates of early-onset group B Streptococcus (GBS) disease (EOGBS) have declined since the implementation of universal screening and intrapartum antibiotic prophylaxis guidelines but late-onset (LOGBS) rates remain unchanged. Racial differences in GBS disease rates have been previously documented, with Black infants having higher rates of EOGBS and LOGBS, but it is not known if these have persisted. Therefore, we sought to determine the differences in EOGBS and LOGBS disease by race over the past decade in Tennessee.

Methods

This study used active population-based and laboratory-based surveillance data for invasive GBS disease conducted through Active Bacterial Core surveillance in selected counties across Tennessee. We included infants younger than 90 days and who had invasive GBS disease between 2009 and 2018.

Results

A total of 356 GBS cases were included, with 60% having LOGBS. EOGBS and LOGBS had decreasing temporal trends over the study period. Overall, there were no changes in temporal trend noted in the rates of EOGBS and LOGBS among White infants. However, Black infants had significantly decreasing EOGBS and LOGBS temporal trends (relative risk [95% confidence interval], .87 [.79, .96] [P = .007] and .90 [.84–.97] [P = .003], respectively).

Conclusions

Years after the successful implementation of the universal screening guidelines, our data revealed an overall decrease in LOGBS rates, primarily driven by changes among Black infants. More studies are needed to characterize the racial disparities in GBS rates, and factors driving them. Prevention measures such as vaccination are needed to have a further impact on disease rates.