Low-temperature Breakdown Research Articles

RealTimeTransport: An open-source C++ library for quantum transport simulations in the strong coupling regime.

The description of quantum transport in the strong system-reservoir coupling regime poses a significant theoretical and computational challenge that demands specialized tools for accurate analysis. RealTimeTransport is a new open-source C++ library that enables the computation of both stationary and transient transport observables for generic quantum systems connected to metallic reservoirs. It computes the Nakajima-Zwanzig memory kernels for both dynamics and transport in real-time, going beyond traditional expansions in the bare system-reservoir couplings. Currently, several methods are available as follows: (i) A renormalized perturbation theory in leading and next-to-leading order, which avoids the low-temperature breakdown that limits the traditional theory. (ii) Starting from this well-behaved reference solution, a two- and three-loop, self-consistent renormalization-group transformation of the memory kernels is implemented. This allows refined quantitative predictions even in the presence of many body resonances, such as the Kondo enhancement of cotunneling. This paper provides an overview of the theory, the architecture of RealTimeTransport, and practical demonstrations of the currently implemented methods. In particular, we analyze the stationary transport through a serial double quantum dot and showcase for the T = 0 interacting Anderson model the complete time-development of single-electron tunneling (SET), cotunneling-assisted SET, and inelastic cotunneling resonances throughout the entire gate-bias stability diagram. We discuss the range of applicability of the implemented methods and benchmark them against other advanced approaches.

Giant electrocaloric effect and breakdown field strength in ferroelectric terpolymer nanocomposites by morphologically diverse nanostructures

Electrocaloric cooling is a method for flexible electronics and compact chips with a promising ability to subvert traditional vapor compression refrigeration technology. Nevertheless, most reported EC materials exhibit relatively low adiabatic temperature (ΔT) and low breakdown field strength (Eb) at room temperature, limiting their further applications. Here, we develop a ferroelectric nanocomposite, composed of relaxor terpolymer poly(vinylidene fluoride-trifluoroethylen-chlorofluoroethylene) (PVTC), ceramic nanofillers [0.68(BaZr0.2Ti0.8O3)-0.32(Ba0.7Ca0.3TiO3)] (BCZT), boron nitride nanosheets (BNNSs), and BiFeO3 nanofibers (BFO NFs) with different morphologies and vary components ratios. The most optimal 12BBBP nanocomposite demonstrates gigantic ECE values including an isothermal entropy change (ΔS) of 94.5 J·kg−1·K−1 and a ΔT of 13.5 K under 220 MV/m electric field at 303 K, ΔS and ΔT are 3.5 times and 2.2 times larger than PVTC under 100 MV/m. It also exhibits an excellent Eb with a value of 290 MV/m. The phase-field simulation is used to simulate Eb behavior of nanocomposites with fillers of different nano-morphologies under an electrostatic field. Simultaneously, the interfacial coupling and ferroelectric domain structures are also simulated based on the time-dependent Landau-Ginzburg-Devonshire (TLGD) theory through finite element analysis (FEA) to present a better explanation for ECE performance. The experimental and simulation results simultaneously denote the ferroelectric nanocomposite possesses outstanding ECE and high Eb performance, laying foundation for the ferroelectrics in fields of flexible electronics and compact chip cooling. Coupled with the facile processability of terpolymer and lead-free nature of electroactive ceramics, this work paves a new way to develop a scalable, environmentally friendly and high-performance EC materials for next generation of refrigeration.

AC-DC breakdown characteristics of oil-paper insulation at low temperature

New energy sources such as wind energy are mainly distributed in low temperature areas such as high altitude and high dimensionality in inland China, which has higher requirements for the low-temperature insulation characteristics of power equipment. This poses higher demands for the low-temperature insulation capabilities of power equipment. However, the existing research on the low temperature breakdown characteristics of oil-impregnated paper is limited. In this study, the authors constructed an AC-DC combined power supply and a specialized low-temperature breakdown testing platform. Various oil-impregnated paper samples with different moisture contents were prepared. The paper investigated the AC-DC breakdown characteristics of these samples under low-temperature conditions, focusing on the effects of temperature, moisture content, and DC component on the breakdown strength. The findings serve as a valuable design reference for the application of oil-impregnated power equipment in low-temperature environments.

Ta/Al/CuW low temperature ohmic contacts for GaN-on-Si HEMT

We proposed a low temperature Au-free ohmic contacts of GaN-on-Si HEMT with the Ta/Al/CuW metal stack. The CuW was deposited by using the dual-target magnetron sputter deposition method. The annealing conditions and recess depth of ohmic area were systematically investigated. By utilizing the Ta/Al/CuW structure, an improved contact characteristic (0.49 Ω·mm) is obtained following annealing at 550 °C for 10 min in vacuum, with the recess depth of 30 nm(±2 nm). This performance surpasses that of Ta/Al/W Au-free contacts (1.07 Ω·mm). Furthermore, both the Ta/Al/CuW ohmic contacts (RMS = 6.3 nm) and the Ta/Al/W ohmic contacts (RMS = 6.0 nm) exhibit smooth surface morphology. Compared to Ti contact layer, Ta demonstrates superior performance in low temperature contact and breakdown test. Amorphous Ta layer can effectively suppress Cu diffusion. The GaN-on-Si HEMT was also fabricated based on Ta/Al/CuW Au-free ohmic contacts, exhibiting excellent DC characteristics.

Design and thermal study of a test device for breakdown characteristics of insulation materials in low temperature vacuum environment

With the application and development of low-temperature superconductivity technology, the research on electrical properties of insulating materials under different low-temperature conditions has attracted more and more attention. According to the breakdown characteristics of materials in low-temperature environments, a test device for the discharge breakdown characteristics of insulating materials in vacuum low-temperature environments is designed. This device can meet test of the gaseous and solid insulating materials in different low temperature and vacuum conditions. Compared with the traditional low temperature electrical test device, it has the advantages of convenient replacement, short test cycle and multi-functional testing. The finite element simulation software is used to simulate the performance of the cooling device of gas and solid insulating materials, and the effects of liquid helium cooling and refrigerator cooling on the temperature distribution of the device are analyzed and compared. Finally, the flow field analysis of the cooling system defines the internal flow characteristics of liquid helium under liquid helium cooling, which provides theoretical guidance for the design of the low-temperature breakdown test device.

Influence of growing regions on losses from physiological diseases of fruits cv. Honeycrisp

The work was carried out at the Federal Research Center named after I.V. Michurin (Tambov region, Russia) in 2019, using fruits cv. Honeycrisp with a high susceptibility to bitter pit (BP), low temperature breakdown (LTB) and soft scald (SS). Studied fruits were grown at commercial orchards from 6 regions of the Central Federal District (Moscow, Tula, Lipetsk, Kursk, Belgorod, Voronezh). The aim of the research was to assess the influence of meteorological factors of different growing regions on the susceptibility of fruits to physiological diseases during storage. The maximum susceptibility to BP is observed for fruits from the Southern region of the Central Federal District (Kursk, Voronezh, Belgorod regions) with high air temperatures (> 25 °C) and moisture deficit (HTC <0.7) during the growing season. The fruits from the Northern region of the Central Federal District (Moscow, Tula regions) with low air temperatures (minimum temperatures <10 °C) and sufficient moisture supply during the growing season (HTC > 1) are characterized by the maximum susceptibility to SS and LTB. An intermediate position is occupied by the Lipetsk region, where the risks of BP, SS and LTB development are quite high. Stressful agronomic factors such as young age of plantations (1-2 years of fruiting), low yield, strong pruning, etc. can cause the development of BP regardless of growing region, with higher risks of disease development under stressful meteorological conditions.

Some indicators of the quality and cold storage of the fruit of new scab immune columnar apple cultivars

The qualitative indicators of the fruits of new scab-immune columnar apple cultivars selected by VNIISPK (‘Vostorg’, ‘Zvezda’, ‘Poezia’, ‘Priokskoe’ and ‘Sozvezdie’) were analyzed at the beginning and end of storage in the +2°C mode with parallel monitoring of weather conditions for 4 years of the research. The influence of meteorological conditions of the growing season on some components of the commercial quality of fruits and their storage life was noted. The most favorable conditions were formed in the years with optimal moisture of the growing season (hydrothermal coefficient (HTC) at the level of 1.0). The longest storage life was observed in ‘Zvezda Efira’–135 days, the shortest storage life was in ‘Poetry’–102 days. The yield of commercial fruits at the end of storage varied between 76.2% (‘Vostorg’) and 92.1% (‘Sozvezdie’). In 2018, anthracnose of fruits was recorded for the first time in ‘Vostorg’, ‘Poezia’ and ‘Priokskoye’. The genotypic resistance of fruits was observed to bitter pit (excluding ‘Zvezda Efira’), low-temperature breakdown of the pulp, in ‘Zvezda Efira’ and ‘Poezia’–to scald. The susceptibility to senescent breakdown of fruits was observed in all of the cultivars. ‘Sozvezdie’ was resistant to physiological disorders. There was a decrease in the content of sugars and organic acids and an increase in the value of the sugar-acid index in fruits at the end of storage.

Low-temperature breakdown of many-body perturbation theory for thermodynamics

It is shown analytically and numerically that the finite-temperature many-body perturbation theory in the grand canonical ensemble has zero radius of convergence at zero temperature when the energy ordering or degree of degeneracy for the ground state changes with the perturbation strength. When the degeneracy of the reference state is partially or fully lifted at the first-order Hirschfelder-Certain degenerate perturbation theory, the grand potential and internal energy diverge as $T \to 0$. Contrary to earlier suggestions of renormalizability by the chemical potential $\mu$, this nonconvergence, first suspected by W. Kohn and J. M. Luttinger, is caused by the nonanalytic nature of the Boltzmann factor $e^{-E/k_\text{B}T}$ at $T=0$, also plaguing the canonical ensemble, which does not involve $\mu$. The finding reveals a fundamental flaw in perturbation theory, which is deeply rooted in the mathematical limitation of power-series expansions and is unlikely to be removed within its framework.

Electrocaloric refrigeration capacity in BNT-based ferroelectrics benefiting from low depolarization temperature and high breakdown electric field

High electrocaloric performance around room temperature is achieved in lead-free (Bi0.5Na0.5)TiO3-based ceramicsviaenhancing the breakthrough electric field and lower depolarization temperature.

Low temperature breakdown behavior analysis of natural esters from the perspective of molecular structure

To better promote and apply natural esters safely in cold area transformers, it is very important to master its low temperature insulation performance. Low temperature breakdown properties of two kinds of the most widely used natural esters named soybean oil and palm oil were tested and analyzed from the perspective of molecular structure. Results show that the AC breakdown voltage of the two natural esters first decrease and then increase, showing the shape of U from −20 °C to 20 °C. Based on the molecular dynamic simulation and first principle of density functional theory, it was found that the physical and chemical properties, like free volume, interaction energy, water form and hydrogen bond, are mainly related to the low temperature breakdown behavior of natural esters. The electrical properties, such as molecule orbital, band structure and density of states, are secondary factors. From −20 °C to −5 °C, the viscosity, the interaction energy between natural ester and water are the main influencing factors where the breakdown voltage declines with the increase of temperature. From 5 °C to 20 °C, the ability of natural esters to dissolve water becomes stronger and hydrogen bonds formed by moisture and natural esters decline, which play a major role in process of breakdown voltage rising with temperature. When the temperature is between −5 °C and 5 °C, all the factors work together to breakdown performance. Compared with soybean oil, palm oil has a greater free volume, a weaker ability of gain and lose electrons, and a wider band gap and forbidden band. The difference of breakdown voltage between soybean oil and palm oil at low temperature is mainly caused by these diversities of electrical characteristics. Therefore, the breakdown behavior of natural esters at low temperature is a complex phenomenon, which is closely related to the molecular structure.

Comparative metabolomics of temperature sensitive resistance to wheat streak mosaic virus (WSMV) in resistant and susceptible wheat cultivars

In order to evaluate wheat resistance to wheat streak mosaic virus (WSMV) at low temperature and resistance breakdown at high temperature, metabolic profile of WSMV-resistant (R) and susceptible (S) wheat cultivars were analyzed. Metabolites were detected by UPLC-QTOF/MS in leaves of R and S plants challenged with WSMV at 20 °C and 32 °C, 24, 48 and 72 h post inoculation (hpi). WSMV and mock inoculated plants were used for discriminating the most significant metabolites and metabolic pathways affected at those temperatures. At 24 hpi/20 °C and 48 hpi/20 °C, the most important metabolites in R plants were coumarins, a limited number of lipids, and unknown compounds, while at 72 hpi/20 °C, in addition to coumarins, alkaloids and several amino acids were increased. Compared to 24 and 48 hpi, at 72hpi, in R plants most metabolic pathways were up-regulated at 20 °C. These resistance-related specific pathways included amino acid metabolism, lipid metabolism and alkaloids pathways. Also, several pathways were up-regulated at 32 °C.These combined heat stress and pathogen related pathways, included lipid metabolism and amino acid metabolism. Some carbohydrate metabolism pathways were considered as heat stress related pathways and could be associated with resistance breakdown. On the other hand, the increased expression of lipid compounds, especially 24 hpi at 32 °C in R plant, can be attributed to plant adaptation to combined stressors such as pathogen and high temperature. Increased susceptibility of R plants at 32 °C coincided with a down-regulated expression of components of signal transduction pathways or in a decreased level of metabolites related to this pathway, especially at a later time after infection, leading to decreased metabolite signaling. Decrease of signaling compounds under combined stress is a possible outcome of deactivating WSMV specific signaling networks leading to compatible response in R plants. The significance of these findings considering the recent increase of global temperature and the challenge of breakdown of temperature sensitive resistance to some plant viruses is discussed.

What happens in a full-scale kiwifruit curing stack?

Curing of kiwifruit occurs immediately after harvest, where the fruit are placed in picking bins in a shaded region for a few days. This procedure was originally developed in order to reduce subsequent Botrytis rots in storage, but now is also used as a logistical tool to enable accumulation of fruit at the packhouse in front of the grading system. Rates of cooling to storage temperature have been identified as influencing long-term storage outcomes (firmness and low-temperature breakdown development) for kiwifruit. Consequently, given that curing is the process immediately prior to packing and cooling, questions now exist about how curing is influencing long-term storage outcomes. In order to be able to simulate and understand the curing process, more knowledge on what occurs within a commercial-scale curing stack is required. In this work, temperature, humidity and weight loss of more than 200 full-scale commercial bins of fruit from a block of orchard were monitored from harvest to packing over a three-day period. The resulting data provide an example of the potential for positional and temporal variability that is created during the curing process, within a typical batch of kiwifruit destined for long-term storage.

Effect of Temperature on Breakdown Characteristics of Propylene Carbonate Under Microsecond Pulse

Propylene carbonate (PC) has a good application prospect in compact pulsed power source as the energy storage medium of pulse forming line. However, its insulation strength is susceptible to impurities, temperature, pressure, and other factors. Hence, it is of great significance to study the effect of temperature on breakdown characteristics of propylene carbonate. In this paper, the effect of temperature on breakdown characteristics of PC was carried out under microsecond pulse. First, pulsed breakdown setup was built. The temperature of PC varied from −50 °C to 50 °C. Breakdown voltages were captured with a capacitive voltage divider and streamer patterns are obtained by ultrahigh-speed cameras. Second, the experimental results are obtained. The breakdown strength of PC increases with increasing temperature. It is 239 kV/cm at −50 °C and rises to 407 kV/cm at 50 °C. At low-temperature breakdown, electron current is more concentrated and breakdown voltage is more stable. Moreover, the energy release for streamer at low temperature is more concentrated, but it is more dispersed for streamer at high temperature. At last, considering the CO2 solubility in PC, PC generates more bubbles and the increase of temperature benefits the release of bubbles at low temperature, resulting in lower breakdown strength. Because of the moisture in PC, breakdown strength of PC falls slightly near 0 °C. Thus, the experimental results are explained by use of stream theory and bubble breakdown theory. PC can adapt to wide-range temperatures, effectively expanding practical applications of the PC in pulsed power source.

Nonlinear and Quantum Optics on the Nature of Sugar Emission Excited by the First Harmonic of a Nd Laser

The physical nature of emissions excited in pressed-sugar samples by the first harmonic of a neodymium laser (1064 nm, 12 ns) is studied. The spectral, kinetic, spatial, and amplitude characteristics of emissions upon single- and multipulse irradiation with energy densities of 0.012–3.2 J/cm2 are measured. It is found that excitation of a sample by the first pulse causes two emission types, namely, emission of the second harmonic of a Nd laser (532 nm) and glowing of dense low-temperature plasma formed as a result of a low-temperature optical breakdown on absorbing inhomogeneities. Multipulse excitation leads to annealing of absorbing inhomogeneities and to an increase in the optical breakdown threshold.

Probing Magnetism in the Vortex Phase of PuCoGa_{5} by X-Ray Magnetic Circular Dichroism.

We measure x-ray magnetic circular dichroism (XMCD) spectra at the Pu M_{4,5} absorption edges from a newly prepared high-quality single crystal of the heavy-fermion superconductor ^{242}PuCoGa_{5}, exhibiting a critical temperature T_{c}=18.7 K. The experiment probes the vortex phase below T_{c} and shows that an external magnetic field induces a Pu 5f magnetic moment at 2K equal to the temperature-independent moment measured in the normal phase up to 300K by a superconducting quantum interference device. This observation is in agreement with theoretical models claiming that the Pu atoms in PuCoGa_{5} have a nonmagnetic singlet ground state resulting from the hybridization of the conduction electrons with the intermediate-valence 5f electronic shell. Unexpectedly, XMCD spectra show that the orbital component of the 5f magnetic moment increases significantly between 30 and 2K; the antiparallel spin component increases as well, leaving the total moment practically constant. We suggest that this indicates a low-temperature breakdown of the complete Kondo-like screening of the local 5f moment.

Detecting magma-poor orogens in the detrital record

Abstract The clastic record is commonly interrogated by analysis of detrital heavy mineral assemblages, with the bulk of modern detrital geochronological studies employing U-Pb dating of detrital zircon. However, the bias of zircon toward felsic igneous sources, and the limited ability of the U-Pb system in zircon to record low- to medium-grade metamorphic events, means that the U-Pb detrital zircon record is largely insensitive to magma-poor orogens. In this study, U-Pb ages were obtained by laser ablation–inductively coupled plasma–mass spectrometry for apatite and rutile extracted from alluvium of the French Broad River (FBR) in the southern Appalachians (southeastern United States). In contrast to previously published FBR U-Pb zircon data sets, which yield essentially no record of the most recent Appalachian metamorphic events (ca. 320 Ma) associated with assembly of Pangea, the U-Pb detrital rutile and especially the U-Pb apatite systems together provide a complete record of complex polyphase Appalachian orogenesis. It is unexpected that the apatite and rutile U-Pb Appalachian age populations differ significantly, with probable low-temperature breakdown of rutile biasing the rutile data set toward the most recent (Alleghanian) metamorphic event. These data make the FBR one of the most intensely studied river systems globally for multiproxy single-grain U-Pb analysis, clearly demonstrate dependence of provenance information on mineral proxy choice, and emphasize the resolving power of multiproxy provenance studies.

Quantifying the ethylene induced softening and low temperature breakdown of ‘Hayward’ kiwifruit in storage

Kiwifruit are considered highly sensitive to exogenous ethylene during refrigerated storage (0°C). This study aimed to quantifiably describe the effect of continuous application of exogenous ethylene (0.001, 0.01, 0.1 and 1μLL−1) in the storage environment (0°C, 95% RH) on quality (softening and low temperature breakdown; LTB) of ‘Hayward’ kiwifruit when exposed either after harvest or after 10 weeks of storage. For both ethylene application times fruit exposed to 1 and 0.1μLL−1 ethylene exhibited significant loss of firmness compared to control (0.001μLL−1) after 2 weeks of application. Fruit exposed to 0.01μLL−1 ethylene also softened rapidly compared to control fruit (0.001μLL−1) when ethylene was applied at-harvest, but no substantial difference in softening was observed when applied after 10 weeks of storage. Most of the softening differentiation occurred in the first 4 weeks of exposure, after which the rates of softening returned to being relatively constant irrespective of the ethylene environment. Along with rapid softening, fruit exposed to 1μLL−1 ethylene were higher in incidence of LTB, irrespective of exposure timing. This study demonstrates that ethylene concentrations as low as 0.01μLL−1 can influence softening of ‘Hayward’ kiwifruit in a commercial cool storage environment. As the differentiation of treatments occurs solely in the initial period of ethylene exposure, more research is required to understand the impact of small exposure occasions, which are more likely to occur in real supply chain scenarios.

Thermal stability of active/inactive nanocomposite anodes based on Cu2Sb in lithium-ion batteries

Various active/inactive nanocomposites of Cu2Sb–Al2O3@C, Cu2Sb–TiC, and Cu2Sb–TiC@C have been synthesized by high energy mechanical milling and investigated by differential scanning calorimetry (DSC) to determine the lithiated phase stability and heat generation arising from these electrodes. The milling process reduces the Li3Sb phase stability, relative to the un-milled samples, to below ∼200 °C. However, the incorporation of the reinforcing, inactive phases Al2O3, TiC, and carbon black offer a slight improvement. DSC curves also show that the low-temperature heat generation in the SEI-layer reaction range is not noticeably altered by either the milling process or the addition of the inactive phases. A strong exothermic peak is observed at ∼200 °C for the 0% state of charge electrodes of Cu2Sb–Al2O3@C and Cu2Sb–TiC@C that was caused by the incorporation of carbon black into the composite. This peak was not present in the electrodes of milled Cu2Sb or Cu2Sb–TiC, suggesting that efforts to extend the cycle life of alloy anodes should avoid carbon black due to its destabilizing effects on delithiated electrodes. Fourier Transform infrared spectroscopy analysis indicates that the reaction arising from the incorporation of carbon black is tied to a low-temperature breakdown of the lithium salt LiPF6.

Electrical breakdown in nominally undoped n-Ge and p-Ge samples under interband photoexcitation

The results of studying low-temperature impurity-related electrical breakdown Ethr in nominally undoped n-Ge and p-Ge samples subjected to intrinsic photoexcitation are reported. It was expected that, on the basis of the model of the recombination of free charge carriers via deep impurity centers, the value of Ethr under these conditions would be bound to be the same for samples with different conductivity types and be independent of the degree of compensation in the samples. However, the experiments show that the breakdown field does not depend on the illumination intensity and is equal to its value in the absence of illumination. A qualitative explanation to the observed effect is suggested.

Non-ohmic hopping conduction of a diode base extracted from the diode current-voltage characteristics

Using the method of extracting a series resistance from a p- n diode current-voltage characteristics developed earlier, parameters of low-temperature non-ohmic conduction in bases of two types of silicon diodes have been studied. In the diode of the first type, with finite value of impurity ionization energy, low-temperature impurity breakdown in the diode base is accompanied by hysteresis of its conduction; in the diode of the second type, the impurity breakdown occurs in soft form. In the pre-breakdown region, the results obtained for the diodes of both types, agree completely with existing picture of non-ohmic hopping conduction in spite of significant space inhomogeneity of the diode structures and non-equilibrium character of the transport in them. In the post-breakdown region, the certain peculiarities are available. For the first time the activationless hopping conduction has been revealed in crystalline silicon.