Low Temperature Regime Research Articles

Eelgrass (Zostera marina) Trait Variation Across Varying Temperature-Light Regimes

Seagrass trait variation, which results from both local genetic adaptation and phenotypic plasticity, has important effects on ecosystems. Physical drivers underlie these processes and are important determinants of trait variation. Despite this, few studies examine multivariate predictive relationships between sets of physical drivers and sets of seagrass traits. Here, we use redundancy analysis to define this relationship for eelgrass Zostera marina, using traits that represent bed structure, morphology, and physiology and physical drivers that emphasize light conditions and temperature variability on different time scales. We found a relationship between plant size (i.e., leaf length and width, rhizome width, number of leaves) and shoot density that dominated the trait variation. Specifically, as temperatures became warmer, more variable, and light was less limiting, plants became smaller (shorter, narrower, and fewer leaves, thinner rhizomes) but beds became denser. Plant biomass (leaf area index), which increased with decreasing temperature variability and bottom light, further refined this relationship. Overall, temperature variability (i.e., daily temperature range, heat accumulation, time in the optimal temperature range, and tidal and meteorological variability), as well as bottom light, were important predictors of eelgrass traits. We further identified three distinct temperature-light regimes across which traits differed; these included the cool low variability temperature regime with low light, the warm high variability temperature regime with high light, and the intermediate case between these endpoints. Our study identifies specific temperature and light drivers that define certain eelgrass traits and provides a multivariate statistical model that can be used to predict eelgrass trait values from known physical conditions.

Krylov complexity of fermion chain in double-scaled SYK and power spectrum perspective

We investigate Krylov complexity of the fermion chain operator which consists of multiple Majorana fermions in the double-scaled SYK (DSSYK) model with finite temperature. Using the fact that Krylov complexity is computable from two-point functions, the analysis is performed in the limit where the two-point function becomes simple and we compare the results with those of other previous studies. We confirm the exponential growth of Krylov complexity in the very low temperature regime. In general, Krylov complexity grows at most linearly at very late times in any system with a bounded energy spectrum. Therefore, we have to focus on the initial growth to see differences in the behaviors of systems or operators. Since the DSSYK model is such a bounded system, its chaotic nature can be expected to appear as the initial exponential growth of the Krylov complexity. In particular, the time at which the initial exponential growth of Krylov complexity terminates is independent of the number of degrees of freedom. More generally, and not limited to the DSSYK model, we systematically and specifically study the Lanczos coefficients and Krylov complexity using a toy power spectrum and deepen our understanding of those initial behaviors. In particular, we confirm that the overall sech-like behavior of the power spectrum shows the initial linear growth of the Lanczos coefficient, even when the energy spectrum is bounded.

Wilson Lines in the Abelian Lattice Higgs Model

AbstractLattice gauge theories are lattice approximations of the Yang–Mills theory in physics. The abelian lattice Higgs model is one of the simplest examples of a lattice gauge theory interacting with an external field. In a previous paper (Forsström et al. in Math Phys 4(2):257–329, 2023), we calculated the leading order term of the expected value of Wilson loop observables in the low-temperature regime of the abelian lattice Higgs model on $${\mathbb {Z}}^4,$$ Z 4 , with structure group $$G = {\mathbb {Z}}_n$$ G = Z n for some $$n \ge 2.$$ n ≥ 2 . In the absence of a Higgs field, these are important observables since they exhibit a phase transition which can be interpreted as distinguishing between regions with and without quark confinement. However, in the presence of a Higgs field, this is no longer the case, and a more relevant family of observables are so-called open Wilson lines. In this paper, we extend and refine the ideas introduced in Forsström et al. (Math Phys 4(2):257–329, 2023) to calculate the leading order term of the expected value of the more general Wilson line observables. Using our main result, we then calculate the leading order term of several natural ratios of expected values and confirm the behavior predicted by physicists.

Interlayer Hydrogen Recombination from Hydrogen Boride Nanosheets Elucidated by Isotope Labeling.

In this study, deuterium boride (DB) nanosheets were synthesized as deuterated borophane through the ion exchange of magnesium cations in magnesium diboride with deuterons from a deuterium-type ion-exchange resin in acetonitrile. The Fourier-transform infrared absorption spectrum of DB exhibited clear isotope effects, namely the shift in the absorption peak of the B-H stretching vibrational mode to a lower wavenumber. Temperature-programmed desorption (TPD) from a mixture of DB and hydrogen boride (HB) nanosheets yielded a more intense hydrogen-deuterium (HD) signal compared to the H2 and D2 signals. This indicates that the release of hydrogen molecules from the HB nanosheets upon heating originated from interlayer hydrogen recombination rather than intralayer hydrogen recombination. TPD analysis of HB with graphene in different mixing ratios confirmed that the interlayer reaction is predominant in the lower-temperature (<623 K) regime. Meanwhile, the intralayer reaction could proceed in the higher-temperature (>623 K) regime, where hydrogen recombination occurs following H migration on the HB nanosheets.

Quantum gravity phenomenology and the blackbody radiation

Abstract We analyze the blackbody radiation problem in the presence of quantum gravity effects encoded in modified dispersion relations. The spectral radiance and the generalized Stefan-Boltzmann law are studied in this context. Furthermore, the regime of low temperatures is also contemplated, where features related to the blackbody thermal laws and the thermodynamic quantities such as energy, pressure, entropy, and specific heat are obtained. Possible implications in compact objects such as neutron stars are also discussed.

Ozone Doping and Negative Temperature Response in the Explosion Limits of Ethylene-Oxygen Mixtures.

In this work, effects of ozone (O3) addition on ethylene-oxygen (C2H4-O2) mixtures are computationally studied through the explosion limit profiles. The results show that the addition of minute quantities of ozone (with a mole fraction of 0.06% in the oxidizer) shifts the explosion limit of the C2H4-O3-O2 mixtures to the low-temperature regime. Further increases in the ozone concentration gradually strengthen the negative temperature coefficient (NTC) behavior at the second limit. That is because the explosion limit is primarily controlled by the ethylene ozonolysis reaction, and both the sensitivity analysis and chemical reaction rate perturbation method reveal specific kinetic reasons. Furthermore, it is shown that with the increasing equivalence ratio, the explosion limit curve with minute ozone addition rotates counterclockwise around a crossover point, while the explosion limit curve becomes complicated and the NTC behavior appears on the second limit with larger quantities of ozone addition. Furthermore, the effects of dilutions of nitrogen (N2), argon (Ar), carbon dioxide (CO2), and water (H2O) on the explosion limits are also studied. To elucidate the different wall elimination effects of different explosion limit regimes, the impacts of surface reactions of six radicals (H, O, OH, HO2, H2O2, and HCO) have been examined and the dominant radicals are found to be H and HO2. The H radicals significantly influence the first explosion limit, while the HO2 radicals impact the entire explosion limit.

Sintering of Copper Nanoparticles using Intense Pulsed Light for screen-printed films on flexible substrate

Abstract Rapid growth in applications involving large area flexible electronics has led to wide adoption of the technique of sintering printed films using intense pulsed light (IPL) due to its pulse mode operation and ability to reach high sintering temperatures without affecting the underlying substrate significantly. We study sintering mechanisms of screen-printed thin films of copper nanoparticles on polyethylene terephthalate (PET) plastic substrate by varying irradiance energy over a wide range to monitor conductivity and associated microstructure changes. We obtain optimized parameters which indicate existence of a sharp threshold irradiance energy to kickstart sintering, and two distinct regimes beyond that. The low temperature regime has a high energy barrier while the high temperature regime has a substantially reduced energy barrier with change of phase due to local melting.

Exploring the soft pinning effect in the dynamics and the structure-dynamics correlation in multicomponent supercooled liquids.

We study multicomponent liquids by increasing the mass of 15% of the particles in a binary Kob-Andersen model. We find that the heavy particles have dual effects on the lighter particles. At higher temperatures, there is a significant decoupling of the dynamics between heavier and lighter particles, with the former resembling a pinned particle to the latter. The dynamics of the lighter particles slow down due to the excluded volume around the nearly immobile heavier particles. Conversely, at lower temperatures, there is a coupling between the dynamics of the heavier and lighter particles. The heavier particles' mass slows down the dynamics of both types of particles. This makes the soft pinning effect of the heavy particles questionable in this regime. We demonstrate that as the mass of the heavy particles increases, the coupling of the dynamics between the lighter and heavier particles weakens. Consequently, the heavier the mass of the heavy particles, the more effectively they act as soft pinning centers in both high and low-temperature regimes. A key finding is that akin to the pinned system, the self-dynamics and collective dynamics of the lighter particles decouple from each other as the mass of the heavy particles has a more pronounced impact on the latter. We analyze the structure-dynamics correlation by considering the system under the binary and modified quaternary framework, the latter describing the pinned system. Our findings indicate that whenever the heavy mass particles function as soft pinning centers, the modified quaternary framework predicts a higher correlation.

Consolidated Description of Explosion Limits and Ignition Delays: Hydrogen and C1-C7 N-Alkanes

ABSTRACT This study computationally investigates the auto-ignition delay times and explosion limits of H2/O2 and C1-C7 n-alkanes/O2 mixtures based on detailed chemical kinetics. Comprehensive ignition responses are consolidated through three-dimensional response surfaces of the ignition delay time as function of the system temperature and pressure, yielding the essential kinetic characteristics governing ignition. The intersection curves of the ignition surface with the cross-section perpendicular to the three coordinate axes are the characteristic response curves of the ignition delay time and explosion limit. Therefore, the ignition delay time and explosion limit are the changing characteristics of the three-dimensional ignition surface observed from different perspectives. Sensitivity analysis demonstrates that while the significant variations of the reaction pathways among different fuels are the primary reason of the wide spreading of the explosion limits curves for the various fuels in the low-temperature regime, their chain branching reactions tend to be similar in the intermediate temperature regime such that the explosion limit curves of different fuels are closely coalesced. Furthermore, in the high-temperature regime, the chain branching reactions of alkanes are primarily governed by small radicals, such as CH3, while it is still dominated by the H+O2=OH+O for H2.

Anomalous behaviour of transport properties in a supercooled water–glycerol mixture

Glycerol acts as a natural cryoprotectant by depressing the temperature of ice nucleation and slowing down the dynamics of water mixtures. In this work, we characterise dynamics – diffusion, viscosity and hydrogen bond dynamics – as well as density anomaly and structure of water mixtures with 1%–50% (w/w) glycerol at low temperatures via molecular dynamics simulations using all-atom and coarse-grained models. Simulations reveal distinct violations of the Stokes–Einstein relation in the low-temperature regime for water and glycerol. Deviations are positive for water at all concentrations, and positive for glycerol in very dilute solutions but turning negative in concentrated ones. The all-atom and coarse-grained models reveal an unexpected crossover in the dynamics of the 1% and 10 % (w/w) glycerol at the lowest simulated temperatures. This crossover manifests in the diffusion coefficients of water and glycerol, as well as in the viscosity and lifetime of hydrogen bonds in water. We interpret that the crossover originates on the opposing dependence with glycerol concentration of the two factors controlling the solutions' slow down: the increase in tetrahedrally coordinated water and the dynamics and clustering of the glycerol molecules. We anticipate that this dynamic crossover will also occur for solution of water with other polyols.

Path-integral calculation of the third dielectric virial coefficient of helium based on abinitio three-body polarizability and dipole surfaces.

We develop a surface for the electric dipole moment of three interacting helium atoms and use it with state-of-the-art potential and polarizability surfaces to compute the third dielectric virial coefficient, Cɛ, for both 4He and 3He isotopes. Our results agree with previously published data computed using an approximated form for the three-body polarizability and are extended to the low-temperature regime by including exchange effects. In addition, the uncertainty of Cɛ is rigorously determined for the first time by propagating the uncertainties of the potential and polarizability surfaces; this uncertainty is much larger than the contribution from the dipole-moment surface to Cɛ. Our results compare reasonably well with the limited experimental data. The first-principles values of Cϵ computed in this work will enhance the accuracy of primary temperature and pressure metrology based on measurements of the dielectric constant of helium.

Thermo-Magnetic properties of non-relativistic particles under the effect of energy-dependent Hellmann potential

This manuscript presents an analysis of the thermal and magnetic properties of particles moving in two dimensions under the influence of an external magnetic field and Aharanov-Bohm flux, considering an energy-dependent Hellmann potential. The energy eigenvalue is obtained using the asymptotic iteration method. Next, we model the system as a canonical ensemble and derive the partition function to acquire analytical expressions for the Helmholtz free energy, entropy, mean energy, and specific heat. We observe that an increase in the external magnetic field and AB flux generally increases the energy eigenvalues, with a stronger effect at lower flux values, while energy eigenvalues decrease with an increase in the screening parameter. Additionally, Helmholtz free energy and entropy functions are sensitive to temperature, particularly in the low-temperature regime, while specific heat exhibits a Schottky anomaly. We also compute the magnetisation and susceptibility functions, finding that both magnetisation and susceptibility increase with the external magnetic field strength and the AB flux.

Including detailed chemistry features in the modeling of emerging low-temperature reactive flows: A review on the application to diluted and MILD combustion systems

Developing and optimizing new reactive systems with carbon-neutral fuels like biofuels, e-fuel, hydrogen, or ammonia is crucial for sustainable energy. This requires advanced technologies capable of fuel flexibility, high efficiency, and minimal pollutant emissions. However, these energy carriers still produce pollutants, especially NOx. To address this, engineers aim to lower combustion process temperatures by adopting different strategies such as burned gas recirculation, staging or increasing the air-to-fuel ratio. Yet, lean flames, though effective at emission reduction, are prone to instability and extinction, posing safety and mechanical risks. Emerging technologies like MILD Combustion, based on burned gas recirculation and reactant dilutions offer interesting solutions. The review article begins by synthesizing experimental studies and numerical simulations of MILD turbulent combustion. It then explores fundamental phenomena specific to diluted combustion (where MILD regimes are included as sub-sets), including autoignition and flame propagation. Using high-fidelity simulations and advanced experiments, it examines flow and mixing roles in reactive zones stabilization. Moving forward, the review paper addresses the inclusion of detailed chemical properties in modeling turbulent combustion systems. Scientific challenges revolve around modeling the intricate interactions between combustion chemistry and flow turbulence while maintaining computational efficiency compatible with industrial constraints. To address this, various simplified chemistry methods – such as reduced, tabulated, or optimized chemistry – have been developed. Additionally, turbulence/chemistry coupling modeling remains unresolved in simulations, with three main routes – geometrical, statistical, or reactor-based approaches – available for turbulent combustion modeling. The state-of-the-art in simplified chemistry and turbulent combustion modeling for low-temperature regimes is then focused on capturing MILD regimes, where there is a crucial impact of dilution by burnt gases, heat transfer, and turbulence mixing on the chemical flame structure. Recent advancements enabled by machine learning and deep learning algorithms are also highlighted. Lastly, the article underscores the critical need for data to validate models, emphasizing the importance of scale-bridging experiments.

Real diffusion with complex spectral gap

The low-lying eigenvalues of the generator of a Langevin process are known to satisfy the Eyring–Kramers law in the low temperature regime under suitable assumptions. These eigenvalues are generically real. We construct generators whose spectral gap is given by non-real eigenvalues or by a real eigenvalue having a Jordan block.

Crystallization-Based Modification of Ammonium Perchlorate Heat Release.

Composite propellants use the decomposition of crystalline oxidizers, such as ammonium perchlorate (AP), to produce oxidizing species that can combust with fuels. Controlled crystal microstructure must be leveraged to tailor reactivity to minimize the use of exotic energetic materials. This work uses meniscus-guided coating (MGC) to fabricate films of AP with a high degree of control over the AP crystal microstructure. Exploring a wide range of crystallization parameters resulted in film thickness ranging from 200 nm to 14 μm, particle size ranging from 18 to 110 μm, variable preferential orientation with respect to the substrate, and relative defect density ranging from 2.74 × 105 to 6.78 × 105 μm-3. Increasing coating blade speed and substrate temperature within the MGC process shifts the preferential orientation of the AP crystals from predominantly exhibiting (002) and (210) crystal planes parallel to the substrate to (200)/(011) crystal planes parallel to the substrate. This shift in orientation is accompanied by an increase in defect density, which is shown to increase the heat release from the low-temperature decomposition regime and decrease the heat release from the high temperature regime. These results demonstrate the ability to use recrystallization, defect density control, and orientation control to tune the heat release profiles of energetic materials to augment propellant performance.

Thermodynamics and dynamics of coupled complex SYK models.

It has been known that the large-q complex SYK model falls under the same universality class as that of van der Waals (mean-field) and saturates the Maldacena-Shenker-Stanford bound, both features shared by various black holes. This makes the SYK model a useful tool in probing the fundamental nature of quantum chaos and holographic duality. This work establishes the robustness of this shared universality class and chaotic properties for SYK-like models by extending to a system of coupled large-q complex SYK models of different orders. We provide a detailed derivation of thermodynamic properties, specifically the critical exponents for an observed phase transition, as well as dynamical properties, in particular the Lyapunov exponent, via the out-of-time correlator calculations. Our analysis reveals that, despite the introduction of an additional scaling parameter through interaction strength ratios, the system undergoes a continuous phase transition at low temperatures, similar to that of the single SYK model. The critical exponents align with the Landau-Ginzburg (mean-field) universality class, shared with van der Waals gases and various AdS black holes. Furthermore, we demonstrate that the coupled SYK system remains maximally chaotic in the large-q limit at low temperatures, adhering to the Maldacena-Shenker-Stanford bound, a feature consistent with the single SYK model. These findings establish robustness and open avenues for broader inquiries into the universality and chaos in complex quantum systems. We provide a detailed outlook for future work by considering the ``very" low-temperature regime, where we discuss relations with the Hawking-Page phase transition observed in the holographic dual black holes. We present preliminary calculations and discuss the possible follow-ups that might be be taken to make the connection robust.

Phase transitions and thermodynamic cycles in the broken PT-regime

We propose a new type of quantum thermodynamic cycle whose efficiency is greater than the one of the classical Carnot cycle for the same conditions for a system when viewed as homogeneous. In our model, this type of cycle only exists in the low-temperature regime in the spontaneously broken parity-time-reversal (PT) symmetry regime of a non-Hermitian quantum theory and does not manifest in the PT-symmetric regime. We discuss this effect for an ensemble based on a model of a single boson coupled in a non-Hermitian way to a bath of different types of bosons with and without a time-dependent boundary. The cycle cannot be set up when considering our system as heterogeneous, i.e. undergoing a first-order phase transition. Within that interpretation, we find that the entropy is vanishing throughout the spontaneously broken PT-regime.

Influence of perturbative intertube interactions on ballistic and quasi-ballistic phonon transports in double-walled carbon nanotubes

Assembling single-walled carbon nanotubes (SWCNT) into multiwalled carbon nanotubes (MWCNT) reduces the intrinsically high thermal conductivity of individual SWCNTs. Typically, this reduction can be explained by structural imperfections, e.g., defects, and van der Waals (vdW) intertube interactions between the constituent SWCNTs are considered to have negligible impacts on the reduction. However, intertube interactions should alter the transport characteristics of low-frequency phonons responsible for heat conduction, which implies that intertube interactions may also reduce the thermal conductivity of MWCNTs when low-frequency phonons modulated by intertube interactions participate in the overall heat conduction. In this study, by applying a combination of the atomistic Green's function method and nonequilibrium molecular dynamics simulation to double-walled carbon nanotubes (DWCNT) with different chiral configurations of SWCNTs and various lengths, we investigated the length scale and chiral configuration where perturbative intertube interactions can suppress phonon transports. We found that thermal resistance attributed to intertube interactions manifests in the low-temperature ballistic regime and quasi-ballistic regime for DWCNT lengths greater than 1 μm. Revisiting the influence of the intertube interactions helps comprehend the intrinsic origin of the reduced thermal conductivity of MWCNTs. In addition, the reported findings are beneficial for the thermal engineering of SWCNT-assembled materials, including emerging one-dimensional vdW heterostructures.

Melt growth of crystalline α-SrSi2 by the vertical Bridgman method and its thermoelectric characteristics

As a candidate thermoelectric material operating in the low-temperature regime (room temperature to 473 K), we have examined α-SrSi2: a narrow bandgap semiconductor material, which is composed of environmentally benign elements. We are able to report the successful production of single-crystalline-like α-SrSi2 with clear semiconducting properties by melting synthesis, a thermodynamically stable and thermally equilibrium process that reduces unexpected process contamination and improves crystallinity.The crystals up to 20 × 20 × 5 mm3 have been obtained for a solid–liquid phase reaction temperature of 1308 K for 10 h with a growth rate averaging at 0.617 K/h in the temperature range from 1403 K to 1373 K. The band gap of this material was measured at 48 meV, which is higher than the values previously reported. The power factor was measured at 2.9 mW/mK2 at 300 K, which is the highest value ever reported for undoped α-SrSi2.Based on the experimental bandgap values, the hybrid functional was used to correct the first-principles calculation method, and the Seebeck coefficient obtained from the first-principles calculation was compared with experimental values. Which values showed good agreement with experimental values.

Effect of A-site disorder and reduced grain size on low temperature resistivity minima and magnetoresistance behaviour in Nd0.7-xGdxSr0.3MnO3 (0 ≤ x ≤ 0.3)

ABSTRACT The present work provides a detailed investigation of the electronic- and magneto-transport properties of bulk and nanostructured Nd0.7-xGdxSr0.3MnO3 (x = 0, 0.1, 0.2 and 0.3) polycrystalline manganites. We have specially addressed the issue of the observed minimum in the temperature dependent resistivity of these manganites in the low temperature regime (<50 K). It is observed that increase of A-site disorder due to progressive substitution of Gd and decrease of grain size enhances the observed resistivity minima. Different theoretical models have been employed to analyze the resistivity data in the low temperature regime. It has been established that the quantum interference effect due to electron–electron interaction, most likely, is the dominant factor of the observed resistivity minimum and upturn in resistivity in the lower temperature regime. The effect of phase separation is also found to play a key role in the electronic-transport of the materials. Further the magnetoresistance is found to increase with the increase of Gd concentration as well as with the decrease of grain size in the low temperature regime. The origin of magnetoresistance has been critically analyzed.