Geometrical Dependences Research Articles

Comprehensive Modulation of Conductance Anisotropy in Low-Symmetry ReS2 Transistors

The anisotropic nature of the electrical conductance in low-symmetry two-dimensional materials is of great interest for emerging devices, as the existence of anisotropy potentially offers an additional degree of freedom. The comprehensive modulation of the conductance anisotropy in electronic devices is highly desired. However, so far, only tuning of the magnitude has been reported. Here, we report the comprehensive electrical modulation of conductance anisotropy in low-symmetry ${\mathrm{Re}\mathrm{S}}_{2}$ transistors. Device design ensures two comparable processes, i.e., thermionic emission and carrier drift, involved in device transport, which have opposite in-plane anisotropic distributions of conductance. Application of a gate voltage could switch over the dominance between these two processes, therefore, reversing the polarization directions of the maximum conductance. Systematic investigations also show the strong geometrical and temperature dependences of gate modulation. Conductance anisotropy can be tuned from a fourfold difference, with the maximum polarization in the direction of the light effective mass, to a sevenfold difference polarized in the perpendicular direction, i.e., the direction of the heavy effective mass. The demonstrated modulation facilitates the conductance anisotropy as an additional degree of freedom for exploring functionalities for future electronics in low-symmetry semiconductors.

The study of slide-valve throttle orifice’s geometry influence on control surface actuator’s dynamical capabilities of maneuverable aircraft

The study of slide-valve throttle orifice’s geometry influence on required dynamical capabilities at the low angular deflection of maneuverable aircraft’s actuator has been carried out. To find the correlation dependences of slide-valve throttle control area opening to its transfer, the six configurational forms of fluid flow throttle regulation orifices were considered, the geometrical dependences were obtained and mathematical model were designed. The Bode plots of control surface actuator at six different geometrical forms of orifices have been achieved. Main findings of slide-valve orifice influence on the actuator dynamical sensitivity have been stated. The obtained results have a theoretical benefit for the designers of aircraft control systems and actuators.

Microstructure Role in Permanent Magnet Eddy Current Losses

The impact of granular microstructure on permanent magnets on eddy current losses is investigated. A numerical homogenization procedure for electrical conductivity is defined. Then, an approximated simple analytical model for the homogenized conductivity able to capture the main features of the geometrical and material dependences is derived. Finally, analytic calculations of eddy current losses are given, and the two asymptotic expressions for losses in the stationary conduction limit and advanced skin effect limit are derived and discussed.

Systematic Orbital Geometry-Dependent Variations in Satellite Solar-Induced Fluorescence (SIF) Retrievals

While solar-induced fluorescence (SIF) shows promise as a remotely-sensed measurement directly related to photosynthesis, interpretation and validation of satellite-based SIF retrievals remains a challenge. SIF is influenced by the fraction of absorbed photosynthetically-active radiation at the canopy level that depends upon illumination geometry as well as the escape of SIF through the canopy that depends upon the viewing geometry. Several approaches to estimate the effects of sun-sensor geometry on satellite-based SIF have been proposed, and some have been implemented, most relying upon satellite reflectance measurements and/or other ancillary data sets. These approaches, designed to ultimately estimate intrinsic or physiological components of SIF related to photosynthesis, have not generally been applied globally to satellite measurements. Here, we examine in detail how SIF and related reflectance-based indices from wide swath polar orbiting satellites in low Earth orbit vary systematically due to the host satellite orbital characteristics. We compare SIF and reflectance-based parameters from the Global Ozone Mapping Experiment 2 (GOME-2) on the MetOp-B platform and from the TROPOspheric Monitoring Instrument (TROPOMI) on the Sentinel 5 Precursor satellite with a focus on high northern latitudes in summer where observations at similar geometries and local times occur. We show that GOME-2 and TROPOMI SIF observations agree nearly to within estimated uncertainties when they are compared at similar observing geometries. We show that the cross-track dependence of SIF normalized by PAR and related reflectance-based indices are highly correlated for dense canopies, but diverge substantially as the vegetation within a field-of-view becomes more sparse. This has implications for approaches that utilize reflectance measurements to help account for SIF geometrical dependences in satellite measurements. To further help interpret the GOME-2 and TROPOMI SIF observations, we simulated cross-track dependences of PAR normalized SIF and reflectance-based indices with the one dimensional Soil-Canopy Observation Photosynthesis and Energy fluxes (SCOPE) canopy radiative transfer model at sun–satellite geometries that occur across the wide swaths of these instruments and examine the geometrical dependencies of the various components (e.g., fraction of absorbed PAR, SIF yield, and escape of SIF from the canopy) of the observed SIF signal. The simulations show that most of the cross-track variations in SIF result from the escape of SIF through the scattering canopy and not the illumination.

MODELS OF ROBOT’S WHEEL-MOVER BEHAVIOR ON FERROMAGNETIC SURFACES

The mobile robots which can move on complicated working surfaces play a significant role in the automation of various technological processes, in particular, ship repair, fire fighting, inspection of welding quality, rescue operations, etc. This work is a continuation of the authors’ investigation of the mobile robot’s moving on inclined and vertical ferromagnetic surfaces based on a magnetically operated wheel-mover. Special attention is paid to constructing magnetically operated wheel-mover with twelve legs and modeling of the robot’s wheel-mover behavior in different working modes including investigations of the wheel-mover center trajectory, behavior of control signals, etc. Geometrical dependences between a number of wheel-mover legs and deviation of the wheel center path from horizontal line are described. In the present article the modeling results for movement of the wheel-mover on both plain and non-plain surfaces are discussed. For this purpose, the mathematical model of the wheel-mover was created and analyzed and the results were verified using a simulation approach.

Angular Effects on Single-Event Mechanisms in Bulk FinFET Technologies

Angular single-event (SE) mechanisms and experimental upset data for 14-/16-nm bulk fin field-effect transistor (FinFET) technologies are presented and analyzed. The discrete structure of FinFETs introduces unique geometrical and orientation dependences for angular SE mechanisms and SE upset (SEU) responses of FinFET circuits. Geometric analyses and 3-D technology computer-aided design results effectively explain the angular mechanisms behind experimentally observed SE cross-sectional responses. Results show that angular SEU cross-sectional characteristics can be attributed to the proportional contributions of charge deposition regions in the fin structure and the subfin bulk substrate.

Specific Features of Friction-Type Traction Gear of Rotating Machines Drives

The paper reviews specific operational features of the friction-type traction gear typically used in track-guided vehicles when applied to the drives of rotating machines. A design of the friction-type traction gear that uses a circular rail is presented. The provided layout drawing shows the position of the traction gear wheels against the circular rail as well as the pattern of forces acting on the traction gear. Basic geometrical, kinematic, and force dependences are established for the traction gear mounted on a circular rail. Based on the performed analysis, the recommendations regarding the use of friction-type traction gears as drives for the rotating machines are provided.

“Imaging” LEIS of micro-patterned solid oxide fuel cell electrodes

Understanding the kinetics of oxygen exchange between the gas phase and a ceramic electrode is key to optimising the performance of electrochemical energy conversion devices such as Solid Oxide Fuel Cells. Clearly the surface chemistry of these materials is important, and surface sensitive techniques such as Low Energy Ion Scattering (LEIS) can provide important compositional information key to unravelling electrode kinetics.In this work, we use high lateral resolution LEIS to perform local analyses of a micropatterned electrode structure, of the type often used for studies of the geometrical dependences of electrode performance. We find that the results are comparable to those for bulk materials, but detect evidence of cation interdiffusion from the electrode to the electrolyte. Finally, we note that this preliminary study could open the prospect of in situ measurements of cells near operating conditions.

AC Power Losses Model for Planar Windings With Rectangular Cross-Sectional Conductors

In this letter, a method to calculate the ac losses, including skin effect and proximity losses, in planar windings with rectangular cross-sectional conductors is proposed. The aim is proposing proper ac losses expressions similar to the formulas available for round cross-sectional wires, to be used for the calculation of the ac losses and the optimization of planar magnetic windings implemented in the printed circuit board. The proposed model is based on the decomposition into conduction and proximity losses. Conduction losses only depend on the properties of the conductor, whereas proximity losses are calculated by using the orthogonal decomposition of the magnetic fields in which the conductors are immersed. Functions including the frequency and geometrical dependences of the both types of losses are extracted by means of finite element method simulation. Finally, several prototypes are used to verify the proposed expressions and some design considerations are also outlined.

Capillary study on geometrical dependence of shear viscosity of polymer melts

ABSTRACTGeometrical dependence of viscosity of polymethylmethacrylate (PMMA) and high density polyethylene (HDPE) are studied by means of a twin‐bore capillary rheometer based on power‐law model. Contrary geometrical dependences of shear viscosity are observed for PMMA between 210 and 255°C, but similar geometrical dependences are revealed for HDPE between 190 and 260°C. The fact that wall slip can not successfully explain the irregular geometrical dependence of PMMA viscosity is found in this work. Then, pressure effect and dependence of fraction of free volume (FFV) on both pressure and temperature are proposed to be responsible for the geometrical dependence of capillary viscosity of polymers. The dependence of shear viscosity on applied pressure is first investigated based on the Barus equation. By introducing a shift factor, shear viscosity curves of PMMA measured under different pressures can be shifted onto a set of parallel plots by correcting the pressure effect and the less shear‐thinning then disappears, especially at high pressure. Meanwhile, the FFV and combining strength among molecular chains are evaluated for both samples based on molecular dynamics simulation, which implies that the irregular geometrical dependence of PMMA viscosity can not be attributed to the wall slip behavior. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39982.

Precise practical measurements of 90Y used in radiopharmaceuticals using re-entrant ionization chambers

For diagnostic nuclear medicine, radiopharmaceuticals are labeled with γ-ray emitting nuclides. Routine activity measurements for these drugs are mainly performed with re-entrant ionization chambers. For radiotherapeutic applications, β-ray emitting nuclides are also used. Since very few gamma transitions are involved in these nuclides, an ionization chamber responds only to weak bremsstrahlung. In order to apply the re-entrant chamber method to routine activity assay for these β-ray emitting nuclides, detailed studies were carried out. It was determined that the response was strongly affected by the choice of thickness of the inner wall of the well in the measurement of high energy beta particle emitting nuclides. The geometrical dependences were successfully reduced. Accordingly, routine assay of radioactivity of 90Y therapeutic pharmaceuticals can be performed within an acceptable uncertainty with ordinary re-entrant dose calibrators that are commercially available and equipped in most hospitals.

DIII-D contributions towards the scientific basis for sustained burning plasmas

DIII-D is making significant contributions to a scientific basis for sustained burning plasma operation. These include explorations of increasingly reactor-relevant scenarios, studies of key issues for projecting performance, development of techniques for handling heat and particle efflux, and assessment of key issues for the ITER research plan. Advanced scenarios are being optimized in DIII-D via experiments to empirically determine the relationship between transport and the current profile, which in turn can provide essential input to inform improvement of the theory-based models that do not currently capture the observed behaviour. Joint DIII-D/JET ρ* scans in the hybrid regime imply Bohm-like confinement scaling. Startup and shutdown techniques were developed for the restrictive environment of future devices while retaining compatibility with advanced scenarios. Towards the goal of a fully predictive capability, the DIII-D program emphasizes validation of physics-based models, facilitated by a number of new and upgraded diagnostics. Specific areas include transport, rotation, energetic particles and the H-mode pedestal, but this approach permeates the entire research programme. Concerns for heat and particle efflux in future devices are addressed through studies of ELM control, disruption avoidance and mitigation, and hydrogenic retention in DIII-D's carbon wall. DIII-D continues to respond to specific needs for ITER. Recent studies have compared H-mode access in several different ion species, identifying not only isotopic, but density, rotation and geometrical dependences that may guide access to H-mode during ITER's non-activated early operation. DIII-D used an insertable module to simulate the magnetic perturbations introduced by one of ITER's three test blanket module sets, demonstrating that little impact on performance is seen at ITER equivalent levels of magnetic perturbation.

Experimental evidence for an angular dependent transition of magnetization reversal modes in magnetic nanotubes

We report on the experimental and theoretical investigation of the magnetization reversal in magnetic nanotubes that have been synthesized by a combination of glancing angle and atomic layer deposition. Using superconducting quantum interference device magnetometry the angular dependence of the coercive fields is determined and reveals a nonmonotonic behavior. Analytical calculations predict the crossover between two magnetization reversal modes, namely, the movement of different types of domain boundaries (vortex wall and transverse wall). This transition, already known in the geometrical dependences of the magnetization reversal in various nanotubes, is found within one type of tube in the angular dependence and is experimentally confirmed in this work.

Plasmonic metallic nanostructures for efficient absorption enhancement in ultrathin CdTe-based photovoltaic cells

The effects of incorporating metal nanodiscs (NDs) and nanospheres on optical absorptions of a CdTe solar cell are theoretically investigated by finite-difference time-domain calculations. Significant broadband absorption enhancements have been demonstrated in CdTe layers with various metals, among which Al-ND arrays result in the best photon absorption performance of up to 50% enhancement with respect to bare CdTe materials. The origins of increased absorptions are believed to be the effects of the enormous electric field enhancement and increased scattering upon the excitation of localized surface plasmon resonance. The geometrical dependences of photon absorption in plasmonic CdTe thin films are also studied, from which the relatively optimal geometrical parameters leading to the ultimate solar cell efficiency of ∼36% are extracted. Besides, this work offers a clue to using low-cost plasmonic metals for potential photovoltaic applications.

Temporal variations of the CaXIX spectra in solar flares

Standard model of solar flares comprises a bulk expansion and rise of abruptly heated plasma (the chromospheric evaporation). Emission from plasma ascending along loops rooted on the visible solar disk should be often dominated, at least temporally, by a blue-shifted emission. However, there is only a very limited number of published observations of solar flares having spectra in which the blue-shifted component dominates the stationary one. In this work we compare observed X-ray spectra of three solar flares recorded during their impulsive phases and relevant synthetic spectra calculated using one-dimensional hydro-dynamic numerical model of these flares. The main aim of the work was to explain why numerous flares do not show blue-shifted spectra. The synthesized BCS spectra of the flares were compared with the relevant observed BCS spectra. We conclude that stationary component of the spectrum should be observed almost for all flares during their early phases of evolution. In opposite, the blue-shifted component of the spectrum could be not detected in flares having plasma rising along the flaring loop even with high velocity due to the geometrical dependences only. After the start of the up-flow motion, the blue-shifted component dominate temporally the synthetic spectra of the investigated flares at their early phases.

Ionization of oriented elliptic Rydberg states by half-cycle pulses

We calculate the ionization of elliptic Rydberg states by half-cycle unipolar electromagnetic-field pulses and examine the dependence of ionization probabilities on the eccentricity and the orientation of the ellipse with respect to the field direction of the pulse. It is suggested that the predicted large geometrical dependences be tested experimentally.

Geometrical and algebraical invariances and general angular dependences of sets of s-p hybrid orbitals. Their angular overlap model relevance

An s-p hybrid orbital can be conceived as a linear combination of a scalar and a vector and can be written as h p ( θ, φ) = h(sp p , θ, g4) = h( χ, θ, ϕ)= s sin χ + p σ ( θ, φ) cos χ where ρ = cot 2 χ determines the shape of the hybrid and p σ ( θ, φ) = p x 〈p x |p σ ( θ, φ)〉 ang+p y 〈p y |p σ ( θ, φ) 〉 ang+p z 〈p z |p σ ( θ, φ)〉 ang determines its direction. The coefficients to the unit vectors along the three Cartesian axes, written as p functions, are the angular overlaps between these unit vectors and the unit vector along the direction of the hybrid. The situation of four mutually orthogonal s-p hybrids has been analyzed by using these concepts and it has been found that these hybrids invariably lie pairwise in perpendicular planes. Moreover, if each hybrid h i with shape parameter χ i is replaced by a vector with the direction of the hybrid and the length sin2 χ i , then their vector sum is vanishing. The four-hybrid problem has three degrees of freedom determining shapes and relative directions. Formulas are given for a general analysis of the situation, and particularly for the analysis — on the basis of three experimentally determined angles — of the shape and direction of a single lone-pair, which is necessary in an angular overlap model (AOM) context. The formalism of the AOM is shown to function on the basis of hybrid orbitals, and this property of the AOM gives the clue to its handling of non-linearly ligating ligands.

Magnetic phase transitions and crystal-field splitting in K2UX5 (X=Cl,Br,I).

A consistent physical analysis of both elastic- and inelastic-neutron-scattering experiments as well as of specific-heat measurements in the temperature range from 7 mK to 295 K on polycrystalline samples of the 5${\mathit{f}}^{3}$ electron systems ${\mathrm{K}}_{2}$U${\mathit{X}}_{5}$ (X=Cl,Br,I) was performed on the basis of a two-dimensional Ising model. The orthorhombic structure of ${\mathrm{K}}_{2}$${\mathrm{PrCl}}_{5}$ type was refined in the paramagnetic state and turned out to be built up by well-separated chains of [U${\mathit{X}}_{3}$${\mathit{X}}_{4/2}$${]}^{2\mathrm{\ensuremath{-}}}$ polyhedra. ${\mathrm{K}}_{2}$${\mathrm{UCl}}_{5}$ and ${\mathrm{K}}_{2}$${\mathrm{UBr}}_{5}$ undergo a magnetic phase transition to a long-range antiferromagnetically ordered state corresponding to the Shubnikov space group Pn'm'a' with k=0 at N\'eel temperatures ${\mathit{T}}_{\mathit{N}}$=3.8(1) K and ${\mathit{T}}_{\mathit{N}}$=2.8(1) K, respectively. ${\mathrm{K}}_{2}$${\mathrm{Ul}}_{5}$ orders antiferromagnetically at ${\mathit{T}}_{\mathit{N}}$=1.45(3) K in the Shubnikov space group Pnm'a with k=0. The ordering temperatures, the dominant intrachain exchange interactions, as well as the magnitudes of the magnetic moments at saturation [${\mathrm{\ensuremath{\mu}}}_{\mathrm{U}}$=3.24(4)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, 2.31(4)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, and 1.80(4)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ for X=Cl, Br, and I, respectively] are strongly dependent on the intra- and interchain uranium distances.Specific-heat measurements showed large magnetic contributions at temperatures higher than ${\mathit{T}}_{\mathit{N}}$ for all compounds ${\mathrm{K}}_{2}$U${\mathit{X}}_{5}$ (X=Cl,Br,I). Analyzed in terms of the anisotropic two-dimensional Ising model, these measurements proved the existence of short-range magnetic ordering along the uranium chains above ${\mathit{T}}_{\mathit{N}}$, followed by the long-range ordered magnetic phase. By means of inelastic neutron scattering we determined the crystal-field splitting of the series ${\mathrm{K}}_{2}$U${\mathit{X}}_{5}$ (X=Cl,Br,I) from well-defined crystal-field peaks. Due to the low local symmetry at the uranium site (sevenfold coordination), the crystal-field level scheme was analyzed introducing geometrical dependences of crystal-field parameters which provide a good description of both crystal-field energy levels and transition probabilities.

Ab initio investigation of the vibronic structure of the C 2H spectrum: Calculation of the hyperfine coupling constants for the three lowest-lying electronic states

The hyperfine coupling constants (isotropic hfcc and four Cartesian components of the anisotropic tensor) are calculated for all three atoms of C 2H in its three lowest-lying electronic states at various molecular geometries by means of the ab initio configuration interaction (MRD-CI) method. The off-diagonal electronic matrix elements involving the two species of the A′ symmetry are also computed. A diabatic transformation is performed leading to simple geometrical dependences of the hyperfine coupling constants.

Origin of 1/f noise observed in Hg0.7Cd0.3Te variable area photodiode arrays

The origin of 1/f noise in Hg0.7Cd0.3Te photodiodes is investigated with variable area n+–p junction photodiode arrays. From the geometrical dependences, it is found that both G–R current and 1/f noise in these diodes originate dominantly at the surface depletion region. Also, the 1/f noise power is found to be proportional to the reverse bias voltage for 0.01<VR<0.1 V.