Low-temperature Limit Research Articles

(Invited) The Behavior of High-Capacity Anodes at Low Temperature for Li-Ion Batteries

Lithium metal and alloy anodes offer the promise of improved capacity for Li-based batteries, and they could overcome low-temperature diffusion limitations associated with graphite. However, the electrochemical behavior of these materials at low temperatures has been seldom investigated, and most liquid electrolytes exhibit extremely low Coulombic efficiency (CE) for cycling of these high-capacity electrode materials at low temperatures. Here, we demonstrate an ether-based electrolyte system with carbonate additives that substantially improves the CE of lithium metal cycling down to -60 °C. Lithium metal deposited at low temperatures in this and other electrolytes shows a clear reduction in grain size with decreasing temperature, which is correlated with lower CE. Cryo-TEM and X-ray photoelectron spectroscopy investigation of the solid-electrolyte interphase (SEI) shows that this tailored electrolyte allows for greater inorganic content in the SEI at low temperatures, which enables a compact and conducting passivation layer. We further extend these studies to sodium metal anodes, which show improved CE at low temperatures compared to lithium. Finally, we investigate alloy anode materials and show that they can exhibit stable electrochemical cycling down to -40 °C, indicating the promise of these high-capacity materials for low-temperature batteries.

Advanced Design of Integrated Heat Recovery and Supply System Using Heated Water Storage for Textile Dyeing Process

Heat recovery from a high-temperature wastewater is the major concern in the conventional textile industry. However, limited space in the textile plant is an important constraint for the process enhancement. Therefore, an easily applicable heat recovery system with a small amount of additional equipment to the existing dyeing process is required. To meet the needs from the industry, this study suggests an integrated heat recovery and supply system consisting of single heat exchanger and single storage tank using freshwater as a thermal carrier to utilize the reusable heat in the wastewater. Freshwater is stored in a tank after direct heat exchange with wastewater and is supplied to the next dyeing process. Three different designs of the integrated system were compared based on the lower limit of the wastewater temperature: above 50 °C, 40 °C, and 30 °C for Cases 1, 2, and 3, respectively. The energy and energy flow analyses showed Case 2 to be well balanced between the quality and quantity of the recovered heat, and there was no heat loss via drainage. The heat demand for Case 2 was 795.5 kW, which was the lowest among all cases. Furthermore, an economic analysis showed that the total cost for Case 2 was reduced by 63.2% compared with the base case. Despite the use of an additional heat exchanger and water storage tank, the proposed system was more economical because of the reduced operating costs. Finally, a detailed analysis was conducted by determining the more efficient temperature for heat recovery and supply.

Scaled affine quantization of varphi ^4_4 in the low temperature limit

We prove through Monte Carlo analysis that the covariant Euclidean scalar field theory, varphi ^r_n, where r denotes the power of the interaction term and n = s + 1 where s is the spatial dimension and 1 adds imaginary time, such that r = n = 4 can be acceptably quantized using scaled affine quantization and the resulting theory is nontrivial and renormalizable even at low temperatures in the highly quantum regime.

Oxygen Vacancy-Induced Anomalous Hall Effect in a Nominally Non-magnetic Oxide

The anomalous Hall effect, a hallmark of broken time-reversal symmetry and spin-orbit coupling, is frequently observed in magnetically polarized systems. Its realization in non-magnetic systems, however, remains elusive. Here, we report on the observation of anomalous Hall effect in nominally non-magnetic KTaO3. Anomalous Hall effect emerges in reduced KTaO3 and shows an extrinsic to intrinsic crossover. A paramagnetic behavior is observed in reduced samples using first principles calculations and quantitative magnetometry. The observed anomalous Hall effect follows the oxygen vacancy-induced magnetization response, suggesting that the localized magnetic moments of the oxygen vacancies scatter conduction electrons asymmetrically and give rise to anomalous Hall effect. The anomalous Hall conductivity becomes insensitive to scattering rate in the low temperature limit (T<5 K), implying that the Berry curvature of the electrons on the Fermi surface controls the anomalous Hall effect. Our observations describe a detailed picture of many-body interactions, triggering anomalous Hall effect in a non-magnetic system.

Compression-induced buckling of a semiflexible filament in two and three dimensions.

The ability of biomolecules to exert forces on their surroundings or resist compression from the environment is essential in a variety of biologically relevant contexts. For filaments in the low-temperature limit and under a constant compressive force, Euler buckling theory predicts a sudden transition from a compressed state to a bent state in these slender rods. In this paper, we use a mean-field theory to show that if a semiflexible chain is compressed at a finite temperature with a fixed end-to-end distance (permitting fluctuations in the compressive forces), it exhibits a continuous phase transition to a buckled state at a critical level of compression. We determine a quantitatively accurate prediction of the transverse position distribution function of the midpoint of the chain that indicates this transition. We find that the mean compressive forces are non-monotonic as the extension of the filament varies, consistent with the observation that strongly buckled filaments are less able to bear an external load. We also find that for the fixed extension (isometric) ensemble, the buckling transition does not coincide with the local minimum of the mean force (in contrast to Euler buckling). We also show that the theory is highly sensitive to fluctuations in length in two dimensions and the buckling transition can still be accurately recovered by accounting for those fluctuations. These predictions may be useful in understanding the behavior of filamentous biomolecules compressed by fluctuating forces, relevant in a variety of biological contexts.

Quality factor for zero-bias conductance peaks in Majorana nanowire

Despite recent experimental progress towards observing large zero-bias conductance peaks (ZBCPs) as signatures of Majorana modes, confusion remains about whether Majorana modes have been observed. This is in part due to the theoretical prediction of fine-tuned trivial (i.e., non-topological) zero-bias peaks that occur because of uncontrolled quantum dots or disorder potentials. While many aspects of the topological phase can be somewhat fine-tuned because the topological phase space is often small, the quantized height of the ZBCP associated with a Majorana mode is known to be robust at sufficiently low temperatures even as the tunnel barrier is pinched off to vanishingly small normal-state conductance. The key shortcoming of the existing experimental works is an acute lack of stability of the putative Majorana mode features, indicating the probable absence of a topological phase, and the current paper suggests specific experimentally accessible measures for a careful quantitative analysis of the measured ZBCP stability. In this paper, we study how the counter-intuitive robustness of the ZBCP height to the tunnel barrier strength can be used to distinguish Majorana modes from non-topological ZBCPs. To this end, we introduce a dimensionless quality factor $F$ to quantify the robustness of the ZBCP height based on the range of normal-state (i.e. above-gap) conductance (which depends crucially on the tunnel barrier height) over which the ZBCP height remains within a pre-specified range of quantization. By computing this quality factor $F$ together with the topological characteristics for a wide range of models and parameters, we find that Majoranas are significantly more robust (i.e., have a higher value of $F$) compared with non-topological ZBCPs in the ideal low-temperature limit. Even at a temperature as high as the experimentally used $20$ mK, we find that we can set a threshold value of $F\sim 2.5$ (for $\epsilon=0.1$) so that ZBCPs associated with a quality factor $F>2.5$ are likely topological and $F\ll 2.5$ are topologically trivial. More precisely, the value of $F$ is operationally related to the degree of separation of the Majorana modes in the system, although $F$ uses only the experimentally measured tunnel conductance properties. Finally, we discuss how the quality factor $F$ measured in a transport setup can help estimate the quality of topological qubits made from Majorana modes. In particular, we show that if the induced gap can be enhanced somehow beyond the currently available $\sim 30$ $\mu$eV in InAs/Al samples, large (small) values of $F$ could easily distinguish between stable topological (unstable trivial) ZBCPs with the quantum dot induced quasi-Majorana bound states occasionally behaving similar to topological Majorana modes in short wires.

Thermal transport and nonmechanical forces in metals

We discuss contributions to the thermopower in an electron fluid. A simple argument based on Newton's second law with the pressure gradient as the force suggests that the thermopower is given by a thermodynamic derivative, viz., the entropy per particle, rather than being an independent transport coefficient. The resolution is the existence of an entropic force that results from a coupling between the mass current and the heat current in the fluid. We also discuss and clarify some aspects of a recent paper (Phys. Rev. B {\bf 102}, 214306 (2020)) that provided a method for exactly solving electronic transport equations in the low-temperature limit.

Thermal correction to entanglement spectrum for conformal field theories

We calculate the thermal correction to the entanglement spectrum for separating a single interval of two dimensional conformal field theories. Our derivation is a direct extension of the thermal correction to the Rényi entropy. Within a low-temperature expansion by including only the first excited state in the thermal density matrix, we approach analytical results of the thermal correction to the entanglement spectrum at both of the small and large interval limit. We find the temperature correction reduces the large eigenvalues in the entanglement spectrum while increases the small eigenvalues in the entanglement spectrum, leading to an overall crossover changing pattern of the entanglement spectrum. Crucially, at low-temperature limit, the thermal corrections are dominated by the first excited state and depend on its scaling dimension ∆ and degeneracy g. This opens an avenue to extract universal information of underlying conformal data via the thermal entanglement spectrum. All of these analytical computation is supported from numerical simulations using 1+1 dimensional free fermion. Finally, we extend our calculation to resolve the thermal correction to the symmetry-resolved entanglement spectrum.

Effect of valence state of cobalt in cobalt hexacyanoferrate coprecipitated at different temperatures on electrochemical behavior

Cobalt hexacyanoferrate (CoFe(CN)6; CoHCF) is coprecipitated as a cathode material in an Na-ion aqueous battery with varying solution temperatures of 5°C, 25°C, 50°C, and 70°C to tailor the particle size and defect content. At a low temperature, the small cubic particle is prepared with high Fe vacancies and low Na amounts. Conversely, an elevated temperature results in the enlarged particle with lower Fe vacancies and high Na amounts. Meanwhile, the lattice parameter is extended at a high temperature based on the Co2+ evolution with a larger ionic radius than that of the Co3+ ion at the Co site. Contrary with the expectations, a lower specific capacity is obtained for the highly crystalline structure at high temperature due to the evolution of the irreversible redox-inactive Co2+. The low temperature of 5°C confers an excellent rate capability, capacity retention of 89% at 20 times faster charging rate, based on the smaller particles and relieved distortion in cycling. The shorter diffusion path for Na intercalation due to the fine powder enables a faster charging process. Higher Fe vacancies induced at lower temperature limit Na accommodation, yielding a reduced distortion. The coprecipitation at low temperature enhances the rate performance and cyclability, sacrificing the capacity. Novelty Statement High temperature builds the large particle with low Fe vacancies and high Na amounts. High temperature derives the extended lattice constant due to Co2+ evolution in CoHCF. Evolution of the irreversible redox-inactive Co2+ degrades the specific capacity. Low temperature enhances rate performance due to small powder and relaxed distortion. High rate performance and cyclability at low temperature sacrifices the capacity.

The use of steam dryer with heat recovery to decrease the minimum exhaust flue gas temperature and increase the net efficiency of thermal power plant

Net power plant efficiency is the ratio of exportable electrical power output to the product of fuel consumption rate and fuel heating value. Conventionally, power plants are designed to attain the maximum net power plant efficiency by using regenerative feed water heating, in which extracted steam from steam turbine is used to increase feed water temperature. An important factor that determines the net power plant efficiency is the temperature of flue gas exhausted from the power plant. Decreasing this temperature increases the net power plant efficiency. However, exhaust flue gas temperature should not be lower than the lower limit in order to avoid the corrosion resulting from condensation of sulfuric acid vapor in flue gas on heat exchanger tubes. The lower limit can be raised by reducing fuel moisture content and raising air temperature at boiler inlet. In this paper, it is proposed that low-pressure extracted steam should be used for fuel drying in steam dryer, and vapor released from steam dryer should be used for air heating in heat recovery air preheater. By doing so, the lower limit of exhaust flue gas temperature is decreased, and the net efficiency of the power plant is increased. A case study of a 600-MW lignite-fired power plant is used to demonstrate that the integration of steam dryer and heat recovery air preheater is economically justified.

Temperature limits for storage of extended boar semen from the perspective of the sperm's energy status.

The optimum storage temperature for liquid-preserved boar semen has been empirically determined to be between 15 and 20°C. Lower temperatures provide an advantage to inhibit bacterial growth, but are regarded as critical due to the high sensitivity of boar spermatozoa to chilling injury. Higher storage temperatures are supposed to induce energy deficiency due to an insufficient depression of metabolic cell activity. However, experimental evidence for alterations of the sperm's energy status in relation to storage temperature and duration is missing. Therefore, we aimed to revisit the upper and lower storage temperature limits for liquid-preserved boar semen from the perspective of the sperm's energy metabolism. Ejaculates (n = 7 boars) were cooled down in Beltsville Thawing Solution (BTS) to 25, 17, 10, or 5°C and stored for up to 120 h. ATP and adenylate energy charge (EC) levels were assessed at storage temperature (24, 72, and 120 h storage) and after subsequent re-warming (38°C). Sperm quality and energy status remained at a stable level in samples stored at 25 and 17°C. Chilling to and storage at 10 or 5°C in BTS provoked cold shock in a subset of sperm as shown by a loss in viability and motility (P < 0.05), which was accompanied by a significant release of adenine nucleotides into the semen extender. Prolonged storage for 120 h resulted in significantly lower mean ATP concentrations in viable spermatozoa at 5 or 10°C compared to 17°C (P < 0.05). Cluster analysis revealed that the main sperm subpopulation, i.e., sperm with moderate speed and linearity, decreased from 50 to 30% (P < 0.05) in favor of slow-moving spermatozoa (5°C) or spermatozoa with a hyperactivation-like motility pattern (10°C). The results point to a sublethal imbalance in available ATP in a subset of the surviving sperm population, rather than a general decrease in available ATP in all spermatozoa. In conclusion, storing diluted boar semen at a stable temperature between 17 and 25°C is a safe procedure concerning the spermatozoa's energy status. Future concepts for hypothermic boar semen preservation below 17°C require measures which ameliorate the imbalanced energy status in viable spermatozoa.

Superdiffusive quantum work and adiabatic quantum evolution in finite temperature chaotic Fermi systems

We study the full distribution of quantum work in generic, noninteracting, disordered fermionic nanosystems at finite temperature. We derive an analytical determinant formula for the characteristic function of work statistics for quantum quenches starting from a thermal initial state. For work small compared to the thermal energy of the Fermi gas, work distribution is Gaussian, and the variance of work is proportional to the average work, while in the low-temperature or large-work limit, a non-Gaussian distribution with superdiffusive work fluctuations is observed. Similarly, the time dependence of the probability of adiabaticity crosses over from an exponential to a stretched exponential behavior. For large enough average work, the work distribution becomes universal, and depends only on the temperature and the mean work. Apart from initial low-temperature transients, work statistics are well captured by a Markovian energy-space diffusion process of hardcore particles, starting from a thermal initial state. Our findings can be verified by measurements on nanoscale circuits or via single qubit interferometry.

Revealing the Thermal Properties of Superconducting Magic-Angle Twisted Bilayer Graphene.

The allegedly unconventional superconducting phase of magic-angle twisted bilayer graphene (MATBG) has been predicted to possess extraordinary thermal properties, as it is formed from a highly diluted electron ensemble with a record-low carrier density (n) of ∼1011 cm-2 and electronic heat capacity (Ce) of <100kB. While these attributes position MATBG as a ground-breaking material platform for revolutionary calorimetric applications, these properties have so far not been experimentally shown. Here, we reveal the thermal properties of superconducting MATBG by monitoring its temperature dependent critical current (Ic) under continuous laser heating at 1550 nm. From the bolometric effect, we extract the temperature dependence of the electronic thermal conductance (Gth), which has a value of Gth = 0.2 pW/K at 35 mK and in the low temperature limit is consistent with a power law dependence, as expected for nodal superconductors. Our work lays the foundation for future thermal transport studies on this system.

Casimir self-entropy of nanoparticles with classical polarizabilities: Electromagnetic field fluctuations

Not only are Casimir interaction entropies not guaranteed to be positive, but also, more strikingly, Casimir self-entropies of bodies can be negative. Here, we attempt to interpret the physical origin and meaning of these negative self-entropies by investigating the Casimir self-entropy of a neutral spherical nanoparticle. After extracting the polarizabilities of such a particle by examining the asymptotic behavior of the scattering Green's function, we compute the corresponding free energy and entropy. Two models for the nanoparticle, namely a spherical plasma $\ensuremath{\delta}$-function shell and a homogeneous dielectric/diamagnetic ball, are considered at low temperature, because that is all that can be revealed from a nanoparticle perspective. The second model includes a contribution to the entropy from the bulk free energy, referring to the situation where the medium inside or outside the ball fills all space, which must be subtracted on physical grounds in order to maintain consistency with van der Waals interactions, corresponding to the self-entropy of each bulk. (The van der Waals calculation is described in Appendix A.) The entropies so calculated agree with known results in the low-temperature limit, appropriate for a small particle, and are negative. But we suggest that the negative self-entropy is simply an interaction entropy, the difference between the total entropy and the blackbody entropy of the two bulks, outside or inside of the nanosphere. The vacuum entropy is always positive and overwhelms the interaction entropy. Thus the interaction entropy can be negative, without contradicting the principles of statistical thermodynamics. Given the intrinsic electrical properties of the nanoparticle, the self-entropy arises from its interaction with the thermal vacuum permeating all space. Because the entropy of blackbody radiation by itself plays an important role, it is also discussed, including dispersive effects, in detail.

Emission detection of dark resonance in a dilute lithium atomic vapor

Dark resonance in coherent population trapping of lithium atoms in the ground state is measured by detecting atomic light emission. Compared to transmission detection, emission detection improves the signal-to-noise ratio of the resonance signal at low temperatures, extending the lower temperature limit to 220 ∘ C . This corresponds to an atomic density, 1 order of magnitude smaller than the saturated density required in transmission detection. In Ar gas, the resonance width at a low temperature is found to be decreased to 45 Hz, which is as narrow as in He and Ne gases.

A framework for rapid diagnosis of natural ventilation effect during early design stage using Thermal Autonomy

ABSTRACT Natural ventilation is one of the most important passive strategies for optimizing building energy saving and environmental performance. However, it is difficult for natural ventilation design to realize the utmost utilization of ambient energy based on the conventional design process due to the design performance of natural ventilation is significantly influenced by the schematic plan of a building. Therefore, this study introduces a design process using a concise model of Thermal Autonomy as an evaluation metric for the early design stage. To apply the proposed metric to modern office buildings, which are equipped with effective HVAC systems, a practical and common thermal comfort criterion of 21°C–27°C is adopted to replace the adaptive comfort standard in the original Thermal Autonomy quantification. The availability of the proposed metric for rapid diagnosis is evaluated through parametric simulation based on a typical office building in Shanghai. The evaluation result and the visual map of Thermal Autonomy are verified to determine the proper air change rate and to help architects to understand the design performance of their natural ventilation scheme. In the case study, the proper air change rate is estimated at 8 ac/h corresponding to a comfort hour of 1314 h. This comfort hour value accounts for the maximum value of 50% during the occupied hour. In addition, the effect of Thermal Autonomy in decision-making regarding envelope insulation and initial operation conditions is examined. It is beneficial to maintain the indoor thermal environment by setting the lower outdoor temperature limit for opening windows at 17°C under a higher feasible ventilation volume. A relatively high envelope insulation level with 50 mm or 75 mm insulation layer is advantageous for improving Thermal Autonomy under a larger ventilation volume condition. The method proposed in this study is practical for objectively evaluating the design performance of natural ventilation during the early design stage.

Overwinter survival of Corbicula fluminea in a central Minnesota lake.

Although Corbicula fluminea has been one of the more prolific freshwater invasive species in the world, previous studies have suggested a low probability for overwinter survival in northern latitudes without an artificially created thermal refuge. The discovery of live C. fluminea in a central Minnesota lake absent any known thermal refuge in 2020 presented an opportunity to further evaluate the overwinter survival and population structure of C. fluminea at the presumed edge of their potential range. The population was monitored from December 2020 through September 2021 alongside water temperature to better understand at which temperatures C. fluminea survived and if the population structure suggested reproduction occurring in the lake. We documented live C. fluminea in temperatures as low as 0.3°C. Shell size of recovered individuals suggested multiple cohorts, and the appearance of a new cohort at the end of the study, indicating active reproduction in the lake and suggesting the population had likely been present in the lake for at least two winters by the conclusion of the study period. Our findings provide evidence of the survival below historically documented lower lethal temperature limits and suggests adaptations to modeling predicting suitable habitat, both present and in a changing climate, are necessary to better assess risk of invasion by this species.

Fermion sign bounds theory in quantum Monte Carlo simulation

Sign problem in fermion quantum Monte Carlo (QMC) simulation appears to be an extremely hard problem. Traditional lore passing around for years tells people that when there is a sign problem, the average sign in QMC simulation approaches zero exponentially fast with the space-time volume of the configurational space. We, however, analytically show this is not always the case and manage to find physical bounds for the average sign. Our understanding is based on a direct connection between the sign bounds and a well-defined partition function of reference system and could distinguish when the bounds have the usual exponential scaling, and when they are bestowed on an algebraic scaling at low temperature limit. We analytically explain such algebraic sign problems found in flat band moir\'e lattice models at low temperature limit. At finite temperature, a domain size argument based on sign bounds also explains the connection between sign behavior and finite temperature phase transition. Sign bounds, as a well-defined observable, may have ability to ease or even make use of the sign problem.

Quantization of topological indices in critical chains at low temperatures

Various types of topological phenomena at criticality are currently under active research. In this paper we suggest to generalize the known topological quantities to finite temperatures, allowing us to consider gapped and critical (gapless) systems on the same footing. It is then discussed that the quantization of the topological indices, also at critically, is retrieved by taking the low-temperature limit. This idea is explicitly illustrated on a simple case study of chiral critical chains where the quantization is shown analytically and verified numerically. The formalism is also applied for studying robustness of the topological indices to various types of disordering perturbations.

Genome Functional Analysis of the Psychrotrophic Lignin-Degrading Bacterium Arthrobacter sp. C2 and the Role of DyP in Catalyzing Lignin Degradation.

In the cold regions of China, lignin-rich corn straw accumulates at high levels due to low temperatures. The application of psychrotrophic lignin-degrading bacteria should be an effective means of overcoming the low-temperature limit for lignin degradation and promoting the utilization of corn straw. However, this application is limited by the lack of suitable strains for decomposition of lignin; furthermore, the metabolic mechanism of psychrotrophic lignin-degrading bacteria is unclear. Here, the whole genome of the psychrotrophic lignin-degrading bacterium Arthrobacter sp. C2, isolated in our previous work, was sequenced. Comparative genomics revealed that C2 contained unique genes related to lignin degradation and low-temperature adaptability. DyP may participate in lignin degradation and may be a cold-adapted enzyme. Moreover, DyP was proven to catalyze lignin Cα-Cβ bond cleavage. Deletion and complementation of the DyP gene verified its ability to catalyze the first-step reaction of lignin degradation. Comparative transcriptomic analysis revealed that the transcriptional expression of the DyP gene was upregulated, and the genetic compensation mechanism allowed C2ΔDyP to degrade lignin, which provided novel insights into the survival strategy of the psychrotrophic mutant strain C2ΔdyP. This study improved our understanding of the metabolic mechanism of psychrotrophic lignin-degrading bacteria and provided potential application options for energy-saving production using cold-adapted lignin-degrading enzymes.