Breakdown Coefficients Research Articles

Low excess noise and high quantum efficiency avalanche photodiodes for beyond 2 µm wavelength detection

The rising concentration of greenhouse gases, especially methane and carbon dioxide, is driving global temperature increases and exacerbating the climate crisis. Monitoring these gases requires detectors that operate in the extended short-wavelength infrared range (~2.4 µm), covering methane (1.65 µm) and carbon dioxide (2.05 µm) wavelengths. Here, we present a high-performance linear mode avalanche photodetector (APD) with an InGaAs/GaAsSb type-II superlattice absorber and an AlGaAsSb multiplier, matched to InP substrates. This APD achieves a room temperature gain of 178, an external quantum efficiency of 3560% at 2 µm, low excess noise (less than 2 at gains below 20), and a small temperature coefficient of breakdown (7.58 mV/K·µm). These results indicate that a manufacturable semiconductor material-based APD could significantly advance high-sensitivity receivers for greenhouse gas monitoring, potentially enabling their commercial production and widespread use.

Direct observation of radio-frequency negative differential resistance in GaN-based single drift region IMPATT diodes

We report the direct observation of radio-frequency negative differential resistance, via on-wafer S-parameter measurements, in GaN-based impact ionization avalanche transit time (IMPATT) diodes. Clear signatures of reflection gain are observed from 18.7 to 30.6 GHz. These observations have been made possible by suppressing the reverse leakage current (and thereby parasitic shunt conductance) by optimization of the fabrication process, in conjunction with the use of pulsed measurements to suppress device self-heating. Consistent with avalanche-dominated behavior, the measured DC reverse bias current–voltage measurements show a positive temperature coefficient of breakdown. For the high-frequency on-wafer characterization, pulsed-bias S-parameter measurements with low (0.0067%) duty cycle were used to mitigate thermal effects. The measured avalanche frequency aligns closely with theoretical predictions based on Gilden and Hines' small signal model [Gilden and Hines, IEEE Trans. Electron Devices ED-13(1), 169–175 (1966)], measured impact ionization coefficients [Cao et al., Appl. Phys. Lett. 112(26), 262103 (2018)], and experimental saturation velocity measurements [Bajaj et al., Appl. Phys. Lett. 107(15), 153504 (2015)]; this excellent agreement confirms IMPATT operation and provides insights needed to further optimize device performance.

Stability analysis of a loess landslide considering rainfall patterns and spatial variability of soil

Accurate analysis of the stability of rainfall-induced landslides is an important and urgent task. Under complex geological conditions, traditional stability analysis methods cannot meet stability evaluation requirements. To study the impact of the rainfall pattern on the probability of instability of loess slopes, the intensity-frequency-duration curve and breakdown coefficient methods were introduced to analyse the effects of the rainfall extremum distribution and time scale, and bounded random cascade simulation were used to generate random rainfall patterns (RRPs). The obtained RRPs under several classical rainfall patterns were compared in terms of the safety factor, rainfall threshold (IaS/IaF), and annual failure probability (AFP) of loess slopes. Finally, soil preferential flow and spatial variability combined with the RRPs were introduced to analyse the change in the stability of rainfall-induced loess landslides under different theoretical frameworks. It was revealed that the use of a uniform rainfall pattern produced conservative stability evaluation results. Considering the RRPs, the calculation of IaS/IaF and AFP should include the common characteristics of various rainfall patterns. By comprehensively evaluating slope stability considering soil spatial variability and rainfall pattern variability, this study revealed that neglecting certain factors may result in incorrect slope stability estimates. Incorporating multiple assumptions in failure probability evaluation could provide more comprehensive slope safety assessment.

Time-dependent rheological behavior of pineapple pulp foam and its relationship with foaming properties and quality attributes of dried powder

The time-dependent rheological characteristics of pineapple pulp foam (PPF), prepared by whipping the pulp with varying concentrations (2–6%) of skim milk powder (SMP), were investigated at different shear rates (1, 10, and 50 s−1). The PPF showed time-dependent shear-thinning behavior that could be explained by the Hahn and Figoni-Shoemaker models (|r|≤0.997). The time and shear-rate-dependent structural breakdown coefficients (B- and M-values) varied due to foam properties (stability, expansion, and drainage volume) and SMP concentration. These coefficients could be suitable indices to judge the stability of the foam. The effective moisture diffusivity during foam drying increased significantly with SMP (p ≤ 0.05); the physical properties of powder were also influenced. A strong correlation existed between SMP, foaming, and rheological properties. The principal component analysis (PCA) indicated a good interrelation among rheological properties, foam, and powder characteristics.

Breakdown coefficient statistics in binary multiplicative cascades

Given the use of multiplicative cascades for the construction of multifractal measures, combined with the difficulty of obtaining the probability distribution function of a cascade generator from a realization thereof, it becomes important to develop mathematical tools to estimate the generator distributions. We are herein devising a method of obtaining the probability distribution of weights in a one-dimensional, binary multiplicative cascade, using its binary breakdown coefficients. Confirmation is provided by numerical simulations, and the method is applied to rainfall intensity time series.

Avalanche Multiplication Noise in GaN p–n Junctions Grown on Native GaN Substrates

GaN p–n junction diodes grown on native GaN substrates have been fabricated and characterized. The devices exhibit a positive temperature coefficient of breakdown obtained from variable temperature current–voltage measurements, confirming the impact ionization avalanche. The low‐frequency noise characteristics of these devices have been measured under forward and reverse bias conditions. The forward bias noise spectra are dominated by the 1/f noise, and the current spectral density is proportional to I1.6. Under reverse bias, the noise spectra show 1/f noise at reverse biases below the avalanche threshold. However, at reverse biases in the avalanche regime, the multiplication noise overwhelms the 1/f noise, resulting in a white noise spectrum. To further characterize the avalanche process, the excess noise factor, F, is obtained from the measured noise spectra of diodes biased in reverse avalanche. For the case of pure hole injection (achieved by incorporating a thin pseudomorphic In0.07Ga0.93N layer at the cathode of the device and illuminating with 390 nm UV light), a low excess noise factor is achieved. The impact ionization ratio α/β extracted from the multiplication noise ranges from 0.07 to 0.38 over the electric field ranging from 2.8 to 3.7 MV cm−1, consistent with the impact ionization coefficients reported previously using the photomultiplication method.

Rheological behavior of well-dispersed polypropylene/halloysite nanotube composites prepared by water-assisted mixing extrusion

Composites of polypropylene (PP) with 5 wt% halloysite nanotubes (HNTs) were prepared by conventional extrusion and water-assisted mixing extrusion, respectively. Transmission electron microscopy showed reduced aggregation of the HNTs in the composites prepared by injection of water during extrusion, with more efficient dispersion of the HNTs. The shear rheological behavior was systematically investigated to understand the effect of the HNT dispersion on the structure of nanocomposites prepared with water injection. The application of small amplitude oscillation shear at different temperatures led to an obvious increase in the storage modulus and complex viscosity of the composites prepared with water injection; and the viscoelastic properties were not affected by temperature. In using the modified Krieger–Dougherty model, the enhanced shear viscosity was correlated with the absorption of more polymer layers on the surface of the HNTs. Furthermore, the results of start-up flow tests showed that the PP/HNT nanocomposites prepared with water injection exhibited larger overshoots at various applied shear rates. Finally, the reversal flow responses of the nanocomposites were interpreted in terms of evolution of the microstructure during the rest period through a dynamic model. In this study, two competitive kinetic constants, namely, the build-up and breakdown coefficients in the dynamic model, were considered to be related to the interaction of PP-HNTs. Thus, it could be deduced from the model that due to the increased build-up coefficient of the composites with water injection, the structural parameter was more rapidly recovered to its initial state.

Comparing biotic drivers of litter breakdown across stream compartments

Litter breakdown in the streambed is an important pathway in organic carbon cycling and energy transfer in the biosphere that is mediated by a wide range of streambed organisms. However, most research on litter breakdown to date has focused on a small fraction of the taxa that drive it (e.g. microbial vs. macroinvertebrate‐mediated breakdown) and has been limited to the benthic zone (BZ). Despite the importance of the hyporheic zone (HZ) as a bioreactor, little is known about what, or who, mediates litter breakdown in this compartment and whether breakdown rates differ between the BZ and HZ.Here, we explore the relationship between litter breakdown and the variation in community structure of benthic and hyporheic communities by deploying two standardized bioassays (cotton strips and two types of commercially available tea bags) in 30 UK streams that encompass a range of environmental conditions. Then, we modelled these assays as a response of the streambed compartment and the biological features of the streambed assemblage (Prokaryota, Protozoa and Eumetazoa invertebrates) to understand the generality and efficiency of litter processing across communities.Litter breakdown was much faster in the BZ compared with the HZ (around 5 times higher for cotton strips and 1.5 times faster for the tea leaves). However, differences in litter breakdown between the BZ and the HZ were mediated by the biological features of the benthos and the hyporheos. Biomass of all the studied biotic groups, α‐diversity of Eumetazoa invertebrates and metabolic diversity of Prokaryota were important predictors that were positively related to breakdown coefficients demonstrating their importance in the functioning of the streambed ecosystem.Our study uses a novel multimetric bioassay that is able to disentangle the contribution by Prokaryota, Protozoa and Eumetazoa invertebrates to litter breakdown. In doing so, our study reveals new insights into how organic matter decomposition is partitioned across biota and streambed compartments.

Surface finish effect on dry sliding wear behavior of thermally oxidized commercially pure zirconium

Abstract The effect of surface polishing on the wear behavior of thermally oxidized commercial pure zirconium (CP-Zr) under dry sliding conditions was investigated. Surface ground CP-Zr with a roughness of 0.21 μm (Ra) was thermally oxidized (TO) at 650 °C for 6 h. After TO, some samples were polished to smoothen the surface with a finish of 0.04 μm (Ra). The response of the polished and unpolished TO samples to dry sliding wear was investigated under unidirectional sliding conditions. The results show that surface polishing after TO affects the dry sliding wear behavior of TO CP-Zr in several aspects, including coefficient of friction, wear rate, crack formation and oxide layer breakdown. In particular, it is found that smoothening the TO surface favors the formation of semi-circular cracks in the wear track and accelerates oxide layer breakdown during dry sliding. A slightly rough TO surface helps to reduce the tendency of the oxide layer towards cracking and to increase the wear resistance at high contact loads. The mechanisms involved are discussed in terms of asperity contacts, crack formation, propagation and final fracture.

Investigation of avalanche ruggedness of 650 V Schottky-barrier rectifiers

Avalanche breakdown of novel 650 V SiC Schottky-barrier rectifiers is investigated. The rectifier diode has low leakage current for the temperatures up to 300 °C. Thermal coefficient of avalanche breakdown increases with the temperature to around 0.009%/K at 200 °C. Near-uniform avalanche breakdown is verified using emission imaging, and maximum specific avalanche energy of 20.7 J/cm2 is achieved. The critical temperature for stability in unclamped inductive switching (UIS) is above 520 °C as estimated through thermal simulation. Long-term walkout of breakdown voltage at 176 °C is less than 0.02%.

Rheological, physical and sensory characteristics of light ice cream as affected by selected fat replacers

In this study, some rheological, physical and sensory properties of light (5% fat) ice cream in comparison with the control sample (10% fat) were investigated as functions of fat replacer type [guar gum (GG), basil seed gum (BSG) and their mixture (MGB, 50:50)] and concentration (0.35, 0.45, 0.50 and 0.55%). All samples exhibited shear-thinning and thixotropic behaviors. The fat reduction resulted in higher melting rate and lower breakdown coefficient, but a contrary trend was observed by increasing fat replacer concentration. Generally, BSG and MGB represented a more shear-sensitive thixotropic nature and melting resistance than GG samples. Regarding the first dripping time, GG light ice creams started dripping first, followed by MGB, then BSG light samples at the same gum concentration. The existence of synergistic relationship for consistency coefficient and plastic viscosity of light mixes was explored by MGB. A synergistic effect was observed for all rheological properties of MGB control sample, with exception of pseudoplasticity. At lower gum concentrations, there were not any significant differences found between the creaminess of samples at the same concentrations, but at 0.55% gum, BSG sample showed the highest value for this property. BSG was found to decrease coarseness, coldness, and meltdown of light ice creams more effectively than GG. Principal components analysis (PCA) revealed that the sensory properties had an inter-dependent with each other. Moreover, PCA scores divided the samples into three groups: full fat ice creams, light samples with 0.35 and 0.45% BSG and MGB, and light ice creams with 0.5 and 0.55% BSG and MGB.

Precipitation variability within an urban monitoring network via microcanonical cascade generators

Abstract. Understanding the variability of precipitation at small scales is fundamental in urban hydrology. Here we consider the case study of Warsaw, Poland, characterized by a precipitation-monitoring network of 25 gauges and microcanonical cascade models as the instrument of investigation. We address the following issues partially investigated in literature: (1) the calibration of microcanonical cascade model generators in conditions of short time series (i.e., 2.5–5 years), (2) the identification of the probability distribution of breakdown coefficients (BDCs) through ranking criteria and (3) the variability among the gauges of the monitoring network of the empirical distribution of BDCs. In particular, (1) we introduce an overlapping moving window algorithm to determine the histogram of BDCs and compare it with the classic non-overlapping moving window algorithm; (2) we compare the 2N–B distribution, a mixed distribution composed of two normal (N) and one beta (B), with the classic B distribution to represent the BDCs using the Akaike information criterion; and (3) we use the cluster analysis to identify patterns of BDC histograms among gauges and timescales. The scarce representation of the BDCs at large timescales, due to the short period of observation (~ 2.5 years), is solved through the overlapping moving window algorithm. BDC histograms are described by a 2N–B distribution. A clear evolution of this distribution is observed, in all gauges, from 2N–B for small timescales, N–B for intermediate timescales and B distribution for large timescales. The performance of the microcanonical cascades is evaluated for the considered gauges. Synthetic time series are analyzed with respect to the intermittency and the variability of intensity and compared to observed series. BDC histograms for each timescale are compared with the 25 gauges in Warsaw and with other gauges located in Poland and Germany.

Magnetic breakdown in an array of overlapping Fermi surfaces

We develop a theoretical framework for a magnetic breakdown in an array of circular two-dimensional bands with a finite overlap of neighboring Fermi surfaces due to the presence of a presumably weak periodic potential, and apply the obtained results to the electron bands in carbon honeycomb structures of doped graphene and intercalated graphite compounds. In contrast to the standard treatment, inaugurated more than fifty years ago by Slutskin and Kadigrobov, with electron semiclassical trajectories encircling significantly overlapping Fermi surfaces, we examine a configuration in which bands are related in a way that the Fermi surfaces only slightly overlap, forming internal band pockets with areas of the size comparable to the area of the quantum magnetic flux for a given external magnetic field. Such band configuration has to be treated quantum mechanically. The calculation leads to the results for magnetic breakdown coefficients comprising an additional large factor with respect to the standard results, proportional to the ratio of the Fermi energy and the cyclotron energy. Also, these coefficients show oscillating dependence on energy, as well as on the wave number of periodic potential. Both mentioned elements enable the adjustment of the preferred wave vector of possible magnetic breakdown induced density wave instability at the highest possible critical temperature.

Small leaf breakdown in a Savannah headwater stream

The chemical nature and nutritional quality of leaves influence microbial colonization, microbial activity and consequently leaf breakdown rates. In the present study, we compared the decomposition of Baccharis concinna and Baccharis dracunculifolia leaves and the influence of leaf quality on the microbial activity during the decomposition process. This investigation was conducted in a Brazilian savanna headwater stream with a riparian zone composed predominantly of herbaceous and shrubs. The breakdown coefficient was higher in B. dracunculifolia than in B. concinna ; for both species, increases in leaf mass were observed after the 60th day. The secondary compounds were quickly leached in the first seven days, but the structural compounds persisted longer and served as the main carbon source for the detritus-associated microorganisms. The highest values of ergosterol were observed in the final stages of leaf breakdown and indicated the difficulty of colonization on the detritus; these values were related to the increase in leaf mass. The ATP content increased without corresponding increase in ergosterol content, suggesting a biofilm formation during leaf breakdown. These results indicated that the total microbial biomass can assimilate organic compounds released from detritus by the enzymatic action of fungi, demonstrating the importance of this group for releasing the energy stored in small leaves.

Leaf breakdown in a natural open tropical stream

Leaf breakdown is a primary process of nutrient cycling and energy flow, contributing to the functioning of aquatic ecosystems. In the present study, leaves of Baccharis platypoda and Coccoloba cereifera were incubated in a high-altitude stream in a rupestrian field. Two hypotheses were tested: i) intrinsic factors (quality of detritus) are more important than extrinsic factors (decomposer communities) in decomposition; and ii) low detritus quality hinders microbial colonization, thereby altering the composition and structure of the associated invertebrate community and slowing leaf breakdown. The breakdown coefficients of B. platypoda and C. cereifera leaves were low (k = -0.0019 day -1 and k = -0.0008 day -1 , respectively) and the proportions of structural compounds were high, delaying the remobilization of energy and nutrients into the aquatic ecosystem. Fungal biomass was higher at the end of the experiment, suggesting favorable conditions for colonization. The densities of invertebrates associated with the detritus increased coincident with the peak concentration of ergosterol, with the trophic groups collector-gatherer and scraper having the highest densities. The distribution of these groups was likely related to the growth of biofilm on the surface of the litters. As described for tropical streams, shredders had the lowest densities of any invertebrate group, suggesting a reduced participation of these invertebrates in leaf processing. The results suggest that slow decomposing species are important to both invertebrates and microorganisms as substrates and sources of particulate organic matter. The low palatability and nutritional quality of the detritus in the present study, associated with low dissolved nutrient concentrations in water, delayed the leaf conditioning process by microorganisms. Decomposition rates and invertebrate participation were reduced as a result, leading to major physical decomposition. Headwater tropical streams have chemically diverse detrital resources, and the intrinsic factors of litter may play key roles in the decomposition process.

Finite element electro‐thermal modelling of nanocrystalline phase change elements using mesh‐based crystallinity approach

Phase change memory cells composed of nanocrystalline Ge2Sb2Te5 with a heater diameter of 10 nm and Ge2Sb2Te5 thickness of 100 nm are studied by using two-dimensional finite element simulations with COMSOL Multiphysics. The nanocrystalline Ge2Sb2Te5 is emulated by using a mesh-based model incorporating crystalline grains of random size and location embedded in the amorphous media. The material parameters are modelled with temperature dependency from 300 to 1000 K, including electrical resistivity, thermal conductivity, electric field breakdown and Seebeck coefficient. This model is shown to capture the cycle-to-cycle and device-to-device variability in phase change memory cells.

Study on the Regularity of the Influence of Wind Pressure on the Properties of Concrete Carbonation

The distribution of surface pressure of columns in concrete bridge with the effect of wind load has been simulated by Ansys software. Carbonation model of concrete in windy environment has been established by analyzing the relationship between the wind pressure, carbonization time and carbonation depth. Furthermore, by Taking air pressure of concrete surface into the carbonation model, there is a good consistency between the test value and the measured value of the actual place. At last, the design method of the durability of concrete structures under wind loads, which is based on concrete durability limit state, has been putted forward to determine the expression of the breakdown coefficient.

The rotational spectra, potential function, Born–Oppenheimer breakdown, and hyperfine structure of GeSe and GeTe

The pure rotational spectra of 18 and 21 isotopic species of GeSe and GeTe have been measured in the frequency range 5-24 GHz using a Fabry-Pérot-type resonator pulsed-jet Fourier-transform microwave spectrometer. Gaseous samples of both chalcogenides were prepared by a combined dc discharge/laser ablation technique and stabilized in supersonic jets of Ne. Global multi-isotopologue analyses of the derived rotational data, together with literature high-resolution infrared data, produced very precise Dunham parameters, as well as rotational constant Born-Oppenheimer breakdown (BOB) coefficients (δ(01)) for Ge, Se, and Te. A direct fit of the same datasets to an appropriate radial Hamiltonian yielded analytic potential-energy functions and BOB radial functions for the X(1)Σ(+) electronic state of both GeSe and GeTe. Additionally, the electric quadrupole and magnetic hyperfine interactions produced by the nuclei (73)Ge, (77)Se, and (125)Te were observed, yielding much improved quadrupole coupling constants and first determinations of the spin-rotation parameters.

Distributions of microcanonical cascade weights of rainfall at small timescales

Empirical frequency distributions of multiplicative cascade weights, or breakdown coefficients, at small timescales are analyzed for 5-min precipitation time series from four gauges in Germany. It is shown that histograms of the weights, W, are strongly deformed by the recording precision of rainfall amounts. A randomization procedure is proposed to statistically remove the artifacts due to precision errors in the original series. Evolution of the probability distributions of W from beta-like for large timescales to combined beta-normal distribution with a pronounced peak at W ≈ 0.5 for small timescales is observed. A new 3N-B distribution built from 3 separate normal, N, distributions and one beta, B, distribution is proposed for reproduction of the empirical histograms of W at small timescales. Parameters of the 3N-B distributions are fitted for all gauges and analyzed timescales. Microcanonical cascades models with a generator based on 3N-B distributions are developed and their performance at disaggregating precipitation at 1280-min intervals down to 5-min intervals is evaluated.

Random cascade driven rainfall disaggregation for urban hydrology: An evaluation of six models and a new generator

Six variations of multiplicative random cascade models for generating fine-resolution (i.e., 5-minute interval) rainfall time series were evaluated for rainfall in Wroclaw, Poland. Of these variations, one included a new beta-normal generator for a microcanonical cascade. This newly proposed model successfully reproduces the statistical behavior of local 5-minute rainfalls, in terms of intermittency as well as variability. In contrast, both the canonical cascade models with either constant or time-scaled parameters and a microcanonical cascade model with a beta generator substantially underestimate 5-minute maximum rainfall intensities. The canonical models also fail to properly reproduce the intermittency of the rainfall process across a range of timescales. New observations are also made concerning the histograms of the breakdown coefficients (BDC). The tendency of the BDC histograms to have values exactly equal to 0.5 is identified and explained by the quality of pluviograph records. Moreover, the hierarchical evolution of BDC histograms from beta-like for long time steps to beta-normal histograms for short time steps is observed for the first time. The potential advantage is shown of synthetic high resolution rainfall time series generated by the revised microcanonical model for use in hydrology, especially hydrodynamic modelling of urban drainage networks.