Width Of Transition Region Research Articles

Numerical and experimental study on mass transfer and performance of proton exchange membrane fuel cell with a gradient 3D flow field

The design of the fuel cell cathode flow field affects its internal heat and mass transfer, thus influencing the fuel cell performance. Building on previous research on 3D flow fields, this study analyzes the impact of the ratio of the main and sub channels width, the ratio of the main/sub channel length to the transition region width on mass transfer and performance. The study proposes a 3D flow field design with a gradual variation in the length of main/sub channels. Numerical and experimental analysis was carried out and results indicate that reducing the D/d ratio can better alleviate ohmic losses at medium and low current densities, while reducing the L/W ratio can better alleviate concentration losses at high current densities. Compared to traditional parallel straight flow field PEMFC, the power density of the gradient 3D flow field PEMFC could increase by 21.54% at 1.9 A·cm−2. The experimental result of the PEMFC is basically consistent with the numerical simulation.

Data processing of Langmuir probe I – V traces to obtain accurate electron temperature and density in Maxwellian plasmas

The standard procedure for obtaining accurate electron temperature (Te) from Langmuir probe I–V characteristics measured in Maxwellian plasmas is studied by comparing the results of Te determined via different data-processing methods. The comparison results show that the width and position of the fitting interval in the transition region of the I–V curve as well as whether the ion collection current deducted from the I–V curve can significantly influence the calculation of Te and afford uncertainties in the calculation of electron density. The reasonable width of the linear fitting interval should be 30%–50% of the transition region width, and the results of Te are the most reliable, which are determined by the linear fitting intervals optimally selected from the electron part of I–V curves. Based on the results, a rigorous data-processing method is proposed to provide a standard procedure for obtaining reliable plasma parameters, especially accurate Te from Maxwellian plasmas using a Langmuir probe.

Atomic-scale structures and dynamics at the growing calcite step edge investigated by high-speed frequency modulation atomic force microscopy.

We have investigated the calcite growth mechanism by directly imaging atomic-scale structural changes at the growing step edges with high-speed frequency modulation atomic force microscopy (HS-FM-AFM). We compared the results with those previously obtained during dissolution, where a transition region (TR) consisting of a Ca(OH)2 monolayer was found to be formed along the step edges as an intermediate state. We found that the TR is created not only during dissolution but also during the growth process. Steps with and without a TR coexist with a ratio of 7 : 3 in both dissolution and growth, implying that their primary reaction pathways should involve TR formation. While all the dissolving steps show a linear shape, the growing steps additionally present a complex non-linear shape with many kinks. The TRs formed along the linear steps present a fixed and uniform width, while those along the complex steps present a non-uniform and dynamically varying width. The acute and obtuse steps show similar TR formation probability, TR width, and step velocity during growth, while a TR is preferentially formed along an acute step during dissolution. For both step types, TRs during growth are wider than those during dissolution. Based on these findings, we present possible reaction pathways triggered by the adsorption of either CO2 or HCO3- for the elementary steps in calcite growth.

Long-wavelength pass filter using green CsPbBr3 quantum dots glass

Perovskite CsPbBr3 quantum dots (QDs) glasses have been investigated for long-wavelength pass filter operating in green light region. The broad absorption band with an absorption shoulder, symmetrical profile of photoluminescence (PL), narrow full width at half maximum (FWHM), broad excitation band, and independence of excitation wavelength show exciton absorption and emission characteristics of semiconductor QDs. Strong cut-off absorption with excellent steepness is determined by first exciton absorption. The long-wavelength pass filter property is evaluated for different preparation conditions. For samples treated at 490, 510, 530 and 550 °C for 3 h, transition wavelength (λtj) is 494, 511, 518 and 525 nm respectively. Maximum transmittance (Tm) is 84%, 80%, 76% and 64%. Transition region (TR) width is 49, 10, 11 and 58 nm. Optical density (OD) is 2–5 in broad cut-off band. For samples treated at 510 °C for 2 h, 3 h, 5 h and 12 h, the λtj is 511, 511, 513 and 511 nm respectively. The Tm is 76%, 80%, 80% and 76%. The TR width is 14, 10, 16 and 13 nm. The OD is 2–5 in broad cut-off band. The proposed perovskite QDs glass filter is suitable for long-wavelength pass filter application.

Characterizing interface structure between crystalline and ion bombarded silicon by transmission electron microscopy and molecular dynamics simulations

Application of ion beams in modern technology requires quantifying disorder induced by the collisions of energetic species and substrate atoms. For studying the structure of the transition region between crystalline silicon and amorphous layer Si(001) substrate was bombarded by gallium ions with the energy of 5 keV. The transition region width and amorphous layer thickness were evaluated using cross-correlation analysis of high- resolution electron microscopy (HRTEM) images taken from cross-section specimens. Performed molecular dynamics simulations allowed obtaining atom positions in amorphized material, which provided close agreement between the simulated and experimental HRTEM images. Analysis of calculated atomic arrangements realized by employing an introduced displacement order parameter enabled finding the interface transition region width and amorphous layer thickness which agreed satisfactorily with the values estimated from HRTEM images. This agreement gives evidence that MD simulation can be applied for reliable prediction and quantification of the disordered region extension in the ion bombarded material. The obtained amorphous layer thickness is also consistent with the results established utilizing the critical point defect density model applied to Monte Carlo simulations.

Chimera states in ring–star network of Chua circuits

We investigate the emergence of amplitude and frequency chimera states in ring–star networks consisting of identical Chua circuits connected via nonlocal diffusive, bidirectional coupling. We first identify single-well chimera patterns in a ring network under nonlocal coupling schemes. When a central node is added to the network, forming a ring–star network, the central node acts as the distributor of information, increasing the chances of synchronization. Numerical simulations show that the radial coupling strength k between the central and the peripheral nodes acts as an order parameter leading from a lower- to a higher-frequency domain. The transition between the domains takes place for intermediate coupling values, $$0.5<k< 2$$ , where the frequency chimera states prevail. The transition region (width and boundaries) depends on the Chua oscillator parameters and the network specifics. Potential applications of star connectivity can be found in the control of Chua networks and in other coupled chaotic dynamical systems. By adding one central node and without further modifications to the individual network parameters, it is possible to entrain the system to lower- or higher-frequency domains as desired by the particular applications.

Tuning the tricritical points of percolation transitions in random networks

Percolation transition in networks as edges are gradually added, can generate a variety of critical and supercritical behaviors. Here we report a percolation transition model with two parameters α and β, in which by decreasing the value of α from 1 to 0 the phase transition could change from continuous to multiple discontinuous and finally to discontinuous without supercritical region, and that the corresponding tricritical points could be tuned by changing the value of β. In order to find out the tricritical point from continuous to multiple discontinuous, by investigating the cluster merging dynamics we find that it belongs to an interval and becomes larger with increasing value of β, and this result is verified by the distinctly different relative variance behaviors of the order parameter at the two endpoints of the interval. On the other hand, the tricritical point from multiple discontinuous to discontinuous is β/(1 + β), which also becomes larger when increasing the value of β. Our results might be helpful in controlling the width of phase transition region in random networks.

Analytical study on phase transition of shape memory alloy wire under uniaxial tension

This paper considers the stress-induced phase transitions of shape memory alloy slender cylinder, and analytically studies the phase transition process and the associated instability. A three-dimensional (3D) phenomenological model with an internal variable is adopted, which is simplified to a 1D system of two strains in three regions (austenite, martensite and phase transition regions). Suitable boundary conditions and interface conditions are proposed. Theoretically, it is a free boundary problem, as the position and shape of phase interfaces are unknown. We then focus on planar interfaces (which are energetically favored), and a symmetric case when phase transition occurs in the middle. For given applied stress, two-region solutions, three-region solutions and the connecting solutions between them are obtained analytically or semi-analytically, including many period-k solutions. Two-region solutions show that phase transition does not take place at one point, but simultaneously in a small region. The width of phase transition region is found analytically, revealing the roles of the material and geometrical parameters. Three-region solutions represent localized inhomogeneous deformations in experiments, and capture that the stress stays almost at the Maxwell stress during propagation of transformation front. For displacement-controlled process, the transition process is demonstrated by the stress-strain curve, which captures the stress drop/rise and the transition from homogeneous deformations to period-1 localized inhomogeneous deformations. When the radius is smaller than a critical value (given by material constants), the stress drop is very sharp due to transition of solutions in a snap-back bifurcation. These features show good agreement with experimental observations and shed light on the difficulties of numerical simulations.

Theoretical and Experimental Study of 13.4 kV/55 A SiC PiN Diodes with an Improved Trade-Off between Blocking Voltage and Differential On-Resistance.

In this paper, a 13.4 kV/55 A 4H-silicon carbide (SiC) PiN diode with a better trade-off between blocking voltage, differential on-resistance, and technological process complexity has been successfully developed. A multiple zone gradient modulation field limiting ring (MGM-FLR) for extremely high-power handling applications was applied and investigated. The reverse blocking voltage of 13.4 kV, close to 95% of the theoretical value of parallel plane breakdown voltage, was obtained at a leakage current of 10 μA for a 100 μm thick, lightly doped, 5 × 1014 cm−3 n-type SiC epitaxial layer. Meanwhile, a fairly low differential on-resistance of 2.5 mΩ·cm2 at 55 A forward current (4.1 mΩ·cm2 at a current density of 100 A/cm2) was calculated for the fabricated SiC PiN with 0.1 cm2 active area. The highest Baliga’s figure-of-merit (BFOM) of 72 GW/cm2 was obtained for the fabricated SiC PiN diode. Additionally, the dependence of the breakdown voltage on transition region width, number of rings in each zone, as well as the junction-to-ring spacing of SiC PiN diodes is also discussed. Our findings indicate that this proposed device structure is one potential candidate for an ultra-high voltage power system, and it represents an option to maximize power density and reduce system complexity.

Transition width effect on optical characterizations of ZnO thin films deposited by spray ultrasonic

Ultrasonic spray deposition was successfully employed to the synthesis of ZnO thin films, then found that can be suitable for application as a transparent conducting electrode. The effects of substrate temperature with film deposition on structural, optical and electrical properties of very thin ZnO films were investigated. ZnO thin films were observed in high crystallinity with a hexagonal wurtzite structure with a strong preferential c-axis, the maximum value of crystallite size 44.53 nm is attained of deposit ZnO thin film at 420 °C. The optical transmission spectra showed all the sprayed ZnO thin films are transparency within the visible wavelength region. Found that the highest transition region (width) ΔE have a higher optical gap energy and smaller urbach energy, which it is 3.26 eV and 0.053 eV respectively. The electrical conductivity was varied in the range of 1 to 5 (Ω.cm)−1 as a function of deposition temperature.

Prediction of loss factor (tan δ) for polymer nanocomposites as a function of yield tress, relaxation time and the width of transition region between Newtonian and power-law behaviors

This article develops a simple model for loss or damping factor (tan δ) in polymer blends and nanocomposites as a function of yield tress, relaxation time, power-law index and the width of transition region between Newtonian and power-law behavior. The predictions of the developed model are compared to the experimental results of loss factor for the blends and nanocomposites containing poly (lactic acid) (PLA), poly (ethylene oxide) (PEO) and carbon nanotubes (CNT). Moreover, the significances of all parameters on the loss factor are justified to confirm the developed model. The calculations of developed model properly agree with the experimental results at all frequency ranges and the model's parameters reasonably change in blends and nanocomposites. A poor yield stress, short relaxation time, low power-law index and large transition region between Newtonian and power-law behavior grow the loss factor. The rational roles of these parameters in the loss factor validate the developed model.

Quantum Hall transitions in the presence of Landau levels mixing in n-InGaAs/InAlAs structures

We provide a systematic measurement of the longitudinal ρxx and Hall ρxy resistivities of quantum Hall transition in a two-dimensional electron system In0.9Ga0.1As/In0.81Al0.19As with strong spin-orbit coupling. For half-integer filling factors the linear temperature dependence of the effective quantum Hall effect plateau-to-plateau transition width ΔB(T) is observed in contrast to scaling behavior for systems with short-range disorder. The recent prediction that the width of transition region remains finite when extrapolated to zero temperature, resulting from Landau level mixing, is more preferable. The shift of the transition point in magnetic field with the temperature is found to originate from the mixing between Landau levels due to the inelastic scattering.

The electric conductivity of composites based on various carbonaceous fillers and estimation of their percolation model parameters

We have studied the electric conductivity of composites with various carbonaceous fillers (multiwalled carbon nanotubes, colloidal graphite, and amorphous carbon) as a function of the filler content. The widths of critical regions of the percolation transition to the conducting state are determined and the percolation critical exponents are estimated. It is established that there is a tendency to increase in the width of transition region and values of critical exponents when the filler is varied in the following order: carbon nanotubes–colloidal graphite–amorphous carbon.

Perfect Separation of Hybrid Orientation Structure of CeO2(100) and (110) Regions Grown on SOI Substrates with Lithographically Formed Trenches

Using magnetron sputtering with low energy electron beam irradiation, epitaxial growth of CeO2 layers on Si(100) substrates has been studied for the application to microelectronics. We have found that orientation selective epitaxial (OSE) growth of CeO2(100) and (110) layers on Si(100) is capable by controlling surface potential distribution. With the aim of application to hybrid orientation technology for higher speed CMOS devices, we are studying the hybrid orientation structure of the CeO2(100) and (110) regions on Si(100) substrates using electron beam-induced OSE growth by reactive magnetron sputtering. Two separate areas of growth are seen, with CeO2(100) layers found to grow in areas irradiated by electrons during the growth process, and the CeO2(110) layers growing in the areas without irradiation. The lateral orientation mapping by X-ray diffraction measurements reveal the existence of transition regions between these two orientation areas. The width of the transition region is found to be considerably large and decrease proportionally as the logarithm of the underlying Si substrate resistivity. To make a breakthrough in the limitation in reduction of the transition region width, we propose a new method of OSE growth on silicon on insulator (SOI) substrates with lithographically formed trenches. The trenches prevent spread of the potential distribution to the neighboring Si islands. We report the experimental results showing perfect isolation between OSE grown regions having different crystallographic orientations, optimizing the Si layer thickness of SOI and the cross-sectional geometry of the trenches. Figure 1

Discrimination between Intact and Decayed Pulp Regions in Carious Teeth by ADC Mapping

The aim of this study was to evaluate an advanced magnetic resonance imaging (MRI) method, apparent diffusion coefficient (ADC) mapping, in the functional assessment of carious teeth. 38 extracted human teeth with scores of 0, 3 and 6 according to International Caries Detection and Assessment System (ICDAS) criteria were screened and subsequently analyzed by MRI at 2.35 T. Histology sectioning of teeth was used for the gold standard by analyzing two extreme cases (intact and severely decayed). ADC maps of the same teeth were calculated from corresponding diffusion-weighted images and used to obtain ADC distributions along dental pulp as functions of the relative pulp length measured from the occlusal pulp side. The measured distributions were analyzed for the best fit by a four-parameter three-segment linear regression model for ADC distribution along the pulp. MRI results were in good agreement with findings in histological sections of identical teeth. The best fit model parameters, relative decayed region depth, relative transition region width and ADC values of intact and decayed pulp tissue, showed statistically significant differences between the ADC values of intact and decayed pulp tissue (1.0 × 10^-9 m²/s vs. 0.74-0.89 × 10^-9 m²/s) and the relative decayed region depth progressing with ICDAS score (3 vs. 46% with ICDAS 3 vs. ICDAS 6). The results of this feasibility study confirmed relevance of ADC mapping for the discrimination and localization of intact and decayed regions in dental pulps of carious teeth.

Microstructure and composition of the grain/binder interface in WC–Ni3Al composites

The microstructure and composition of WC/Ni3Al interface were studied. An orientation relationship of [100]WC//[110]Ni3Al and (001)WC//(001)Ni3Al with a good coherence, besides many random orientation relationships between WC and Ni3Al, has been repetitively found by selected area electron diffraction and high resolution TEM observations. The XRD pattern of WC–Ni3Al composites indicated that the major binder phase was Ni3Al and showed possibility of coherence between WC and Ni3Al as common interplanar spacings existed. Electron probe microanalysis results revealed that the atomic ratio of Al:Ni is close to 1:3 in binder phase and WC/Ni3Al interface in the WC–Ni3Al composites has a sharper compositional gradient and a smaller width of transition region than the WC/Co interface in WC–Co composites.

On the effect of electron-phonon interaction on the temperature dependences of magnetotransport in quantum hall systems

The effect of electron-phonon interaction on the temperature dependences of conductivity is studied in the mode of the integer quantum Hall effect. It is shown that electron-phonon interaction leads to the possibility of transport in the region of localized states, thus forming the shape of magnetotransport curves at a given temperature. The relation between scaling indices in the power laws describing the dependences of the widths of transition regions between successive plateaus of the quantum Hall effect on the temperature and localization length is determined within an analytical model as a function of the energy measured from a certain Landau-level center. Direct numerical calculations of the magnetotransport curves are performed at various temperatures. The results are in good agreement with theory and experimental data on the integer quantum Hall effect.

WIDTH OF QUANTUM HALL TRANSITION REGION IN THE PRESENCE OF LANDAU LEVEL MIXING

In this paper, we have provided a systematic measurement of the longitudinal resistance Rxx of quantum Hall transition in a two-subband two-dimensional electron system. The data shows that the standard scaling behavior with single critical point remains unchanged even with strong Landau level degeneracy. There is no definite evidence to support the recent prediction that the width of transition region becomes finite when extrapolated to zero temperature, resulting from Landau level mixing.

Characterization of dynamics in complex lyophilized formulations: I. Comparison of relaxation times measured by isothermal calorimetry with data estimated from the width of the glass transition temperature region

The purposes of this study are to characterize the relaxation dynamics in complex freeze dried formulations and to investigate the quantitative relationship between the structural relaxation time as measured by thermal activity monitor (TAM) and that estimated from the width of the glass transition temperature (ΔTg). The latter method has advantages over TAM because it is simple and quick. As part of this objective, we evaluate the accuracy in estimating relaxation time data at higher temperatures (50°C and 60°C) from TAM data at lower temperature (40°C) and glass transition region width (ΔTg) data obtained by differential scanning calorimetry. Formulations studied here were hydroxyethyl starch (HES)–disaccharide, HES–polyol, and HES–disaccharide–polyol at various ratios. We also re-examine, using TAM derived relaxation times, the correlation between protein stability (human growth hormone, hGH) and relaxation times explored in a previous report, which employed relaxation time data obtained from ΔTg. Results show that most of the freeze dried formulations exist in single amorphous phase, and structural relaxation times were successfully measured for these systems. We find a reasonably good correlation between TAM measured relaxation times and corresponding data obtained from estimates based on ΔTg, but the agreement is only qualitative. The comparison plot showed that TAM data are directly proportional to the 1/3 power of ΔTg data, after correcting for an offset. Nevertheless, the correlation between hGH stability and relaxation time remained qualitatively the same as found with using ΔTg derived relaxation data, and it was found that the modest extrapolation of TAM data to higher temperatures using ΔTg method and TAM data at 40°C resulted in quantitative agreement with TAM measurements made at 50°C and 60°C, provided the TAM experiment temperature, is well below the Tg of the sample.

Multilayer La/B4C mirrors in the spectral region near 6.7 nm

The results from measuring reflection factors are presented for multilayer La/B4/C mirrors with barrier layers of carbon and scandium. It is shown that a higher reflection factor is obtained by depositing a layer of carbon onto a surface of boron carbide. This effect is caused by diminishing absorption in the structure and the reduced width of transition regions.