Thermodynamic Observables Research Articles

Active Learning of Boltzmann Samplers and Potential Energies with Quantum Mechanical Accuracy.

Extracting consistent statistics between relevant free energy minima of a molecular system is essential for physics, chemistry, and biology. Molecular dynamics (MD) simulations can aid in this task but are computationally expensive, especially for systems that require quantum accuracy. To overcome this challenge, we developed an approach combining enhanced sampling with deep generative models and active learning of a machine learning potential (MLP). We introduce an adaptive Markov chain Monte Carlo framework that enables the training of one normalizing flow (NF) and one MLP per state, achieving rapid convergence toward the Boltzmann distribution. Leveraging the trained NF and MLP models, we compute thermodynamic observables such as free energy differences and optical spectra. We apply this method to study the isomerization of an ultrasmall silver nanocluster belonging to a set of systems with diverse applications in the fields of medicine and catalysis.

Pseudogap Effects in the Strongly Correlated Regime of the Two-Dimensional Fermi Gas.

The two-species Fermi gas with attractive short-range interactions in two spatial dimensions provides a paradigmatic system for the understanding of strongly correlated Fermi superfluids in two dimensions. It is known to exhibit a BEC to BCS crossover as a function of ln(k_{F}a), where a is the scattering length, and to undergo a Berezinskii-Kosterlitz-Thouless superfluid transition below a critical temperature T_{c}. However, the extent of a pseudogap regime in the strongly correlated regime of ln(k_{F}a)∼1, in which pairing correlations persist above T_{c}, remains largely unexplored with controlled theoretical methods. Here, we use finite-temperature auxiliary-field quantum MonteCarlo methods on discrete lattices in the canonical ensemble formalism to calculate thermodynamical observables in the strongly correlated regime. We extrapolate to continuous time and the continuum limit to eliminate systematic errors and present results for particle numbers ranging from N=42 to N=162. We estimate T_{c} by a finite-size scaling analysis, and observe clear pseudogap signatures above T_{c} and below a temperature T^{*} in both the spin susceptibility and free-energy gap. We also present results for the contact, a fundamental thermodynamic property of quantum many-body systems with short-range interactions.

Trade-offs and thermodynamics of energy-relay proofreading.

Biological processes that are able to discriminate between different molecules consume energy and dissipate heat, using a mechanism known as proofreading. In this work, we thoroughly analyse the thermodynamic properties of one of the most important proofreading mechanisms, namely Hopfield's energy-relay proofreading. We discover several trade-off relations and scaling laws between several kinetic and thermodynamic observables. These trade-off relations are obtained both analytically and numerically through Pareto optimal fronts. We show that the scheme is able to operate in three distinct regimes: an energy-relay regime, a mixed relay-Michaelis-Menten (MM) regime and a Michaelis-Menten regime, depending on the kinetic and energetic parameters that tune transitions between states. The mixed regime features a dynamical phase transition in the error-entropy production Pareto trade-off, while the pure energy-relay regime contains a region where this type of proofreading energetically outperforms standard kinetic proofreading.

Evidence for large thermodynamic signatures of in-gap fermionic quasiparticle states in a Kondo insulator

The mixed-valence compound YbB12 displays paradoxical quantum oscillations in electrical resistivity and magnetic torque in a regime with a well-developed insulating charge gap and in the absence of an electronic Fermi surface. However, signatures of such unusual fermionic quasiparticles in other bulk thermodynamic observables have been missing. Here we report the observation of a series of sharp double-peak features in the specific heat as a function of the magnetic field. The measured Hall resistivity evolves smoothly across the field values at which the characteristic anomalies appear in the thermodynamic response and rules out the possibility of conventional electrons as their origin. Our observations of thermodynamic anomalies in a bulk three-dimensional electrical insulator provide the evidence for the presence of emergent dispersing fermionic excitations within the insulating bulk, which sets the stage for further investigation of electron fractionalization in other correlated mixed-valence compounds.

First Results of Airborne GNSS Radio Occultation Sounding From Airbus Commercial Aircraft

AbstractThe lack of high vertical resolution atmospheric thermodynamic structure observations inside or near major weather events impedes our understanding of physical processes and their predictability in numerical weather prediction (NWP) models. Airborne Global Navigation Satellite System (GNSS) radio occultation (airborne radio occultation [ARO]) has proven to be a viable remote sensing option to offer dense soundings near flight tracks. The global fleet of commercial aircraft already equipped with GNSS receivers could be leveraged to produce an unprecedented number of ARO soundings along global flight paths. Eleven cases of atmospheric bending angle and refractivity profiles were successfully retrieved and compared with the colocated European Center for Medium‐Range Weather Forecasting global reanalysis data. Good quality measurements are obtained with median refractivity differences less than 1% in the middle and upper troposphere, between 5.5 and 11.5 km. Given the use of aircraft data (e.g., Aircraft Meteorological DAta Relay) for data assimilation, incorporating ARO profiles would be a valuable addition, further enhancing the accuracy of aviation and weather forecasts.

Study of Thermodynamic Observables in Oxygen+Oxygen Collisions at sNN = 7 TeV Using Color String Percolation Approach

Study of Thermodynamic Observables in Oxygen+Oxygen Collisions at sNN = 7 TeV Using Color String Percolation Approach

QCD equation of state and thermodynamic observables from computationally minimal Dyson-Schwinger equations

We study the QCD equation of state and other thermodynamic observables including the isentropic trajectories and the speed of sound. These observables are of eminent importance for the understanding of experimental results in heavy ion collisions and also provide a QCD input for studies of the timeline of heavy-ion-collisions with hydrodynamical simulations. They can be derived from the quark propagator whose gap equation is solved within a minimal approximation to the Dyson-Schwinger equations (DSEs) of QCD at finite temperature and density. This minimal approximation aims at a combination of computational efficiency and simplification of the truncation scheme while maintaining quantitative precision. This minimal DSE scheme is confronted and benchmarked with results for correlation functions and observables from lattice QCD at vanishing density and quantitative functional approaches at finite density. Published by the American Physical Society 2024

Manybody interferometry of quantum fluids.

Characterizing strongly correlated matter is an increasingly central challenge in quantum science, where structure is often obscured by massive entanglement. It is becoming clear that in the quantum regime, state preparation and characterization should not be treated separately-entangling the two processes provides a quantum advantage in information extraction. Here, we present an approach that we term "manybody Ramsey interferometry" that combines adiabatic state preparation and Ramsey spectroscopy: Leveraging our recently developed one-to-one mapping between computational-basis states and manybody eigenstates, we prepare a superposition of manybody eigenstates controlled by the state of an ancilla qubit, allow the superposition to evolve relative phase, and then reverse the preparation protocol to disentangle the ancilla while localizing phase information back into it. Ancilla tomography then extracts information about the manybody eigenstates, the associated excitation spectrum, and thermodynamic observables. This work illustrates the potential for using quantum computers to efficiently probe quantum matter.

Local thermodynamics and entropy for relativistic hydrostatic equilibrium

By refining the method proposed in Aoki et al. (2021) [5], entropy current and entropy density for a relativistic hydrostatic equilibrium system with spherical symmetry are constructed as a non-Nöther conserved charge in the Einstein gravity with cosmological constant. It is shown that the constructed entropy density satisfies both the local Euler relation and the first law of thermodynamics non-perturbatively with respect to the Newton constant. Finally the established relativistic thermodynamics is applied to one of the systems with uniform energy density as a crude model of a degenerate star and its local thermodynamic observables are determined analytically.

Bounds on the rates of statistical divergences and mutual information via stochastic thermodynamics.

Statistical divergences are important tools in data analysis, information theory, and statistical physics, and there exist well-known inequalities on their bounds. However, in many circumstances involving temporal evolution, one needs limitations on the rates of such quantities instead. Here, several general upper bounds on the rates of some f-divergences are derived, valid for any type of stochastic dynamics (both Markovian and non-Markovian), in terms of information-like and/or thermodynamic observables. As special cases, the analytical bounds on the rate of mutual information are obtained. The major role in all those limitations is played by temporal Fisher information, characterizing the speed of global system dynamics, and some of them contain entropy production, suggesting a link with stochastic thermodynamics. Indeed, the derived inequalities can be used for estimation of minimal dissipation and global speed in thermodynamic stochastic systems. Specific applications of these inequalities in physics and neuroscience are given, which include the bounds on the rates of free energy and work in nonequilibrium systems, limits on the speed of information gain in learning synapses, as well as the bounds on the speed of predictive inference and learning rate. Overall, the derived bounds can be applied to any complex network of interacting elements, where predictability and thermodynamics of network dynamics are of prime concern.

Improved Thermodynamic Descriptions of Carbides in Ni-Based Superalloys

The Ni-based superalloy René 41 has sparked recent interest for applications in next-generation aircraft engines due to its high-temperature strength that is superior to all similar grades. These desirable properties are achieved by careful control of the microstructure evolution during thermomechanical processing, and this is commonly informed by simulations. In particular, the grain boundary carbides M6C and M23C6 play an essential role in controlling the grain size and strength of the final product. Therefore, a solid understanding of the thermodynamic stability and thermokinetic evolution of these carbides is essential. However, thermokinetic simulations using existing thermodynamic databases have been demonstrated to have discrepancies between thermodynamic stabilities and experimental observations. Here, we collected a new experimental time–temperature–precipitation diagram. In conjunction with improved crystallographic descriptions, these experimental results are used to modify a CALPHAD database for M6C and M23C6. The modified database correctly identifies temperature regions with rapid carbide precipitation kinetics. Further, kinetic simulations and strengthening models successfully predict the hardness increase due to γ′ precipitation. The modified database has been applied to Udimet 700, Waspaloy, and Haynes 282, demonstrating improved results. These updates will facilitate more accurate simulations of the microstructure evolution during thermomechanical processing of advanced Ni-based superalloys for aerospace and other applications.

Investigating the Wound-Healing Potential of a Nanoemulsion-Gel Formulation of Pituranthos tortuosus Essential Oil.

This study explores a nanoemulsion (NE)-based gel incorporating Tunisian Pituranthos tortuosus essential oil, with a focus on its wound-healing potential. The essential oil, extracted via hydrodistillation, underwent GC-MS analysis for compositional verification. The physicochemical characterization included dynamic light scattering (DLS), transmission electron microscopy (TEM), zeta potential measurement, pH, and viscosity. The gelification of the NE facilitated topical application. The results revealed an average extraction yield of 0.45% and identified 38 compounds in the essential oil. The NE exhibited a particle size of 27 ± 0.4 nm, a polydispersity index (PDI) of 0.3, and a zeta potential of -22.8 ± 1.4 mV. The stability of the gelified preparation was confirmed through thermodynamic stability studies, TEM observations, and zeta and size results. In vivo experiments confirmed significant wound-healing effects, highlighting the promising role of the NE-based gel in healthcare advancements. This research underscores the potential of novel phyto-based delivery systems in wound care.

Role of Time-Varying Magnetic Field on QGP Equation of State

The phase diagram of quantum chromodynamics (QCD) and its associated thermodynamic properties of quark-gluon plasma (QGP) are studied in the presence of time-dependent magnetic field. The study plays a pivotal role in the field of cosmology, astrophysics, and heavy-ion collisions. In order to explore the structure of quark-gluon plasma to deal with the dynamics of quarks and gluons, we investigate the equation of state (EoS) not only in the environment of static magnetic field but also in the presence of time-varying magnetic fields. So, for determining the equation of state of QGP at nonzero magnetic fields, we revisited our earlier model where the effect of time-varying magnetic field was not taken into consideration. Using the phenomenological model, some appealing features are noticed depending upon the three different scales: effective mass of quark, temperature, and time-independent and time-dependent magnetic fields. Earlier the effective mass of quark was incorporated in our calculations, and in the current work, it is modified for static and time-varying magnetic fields. Thermodynamic observables including pressure, energy density, and entropy are calculated for a wide range of temperature- and time-dependent as well as time-independent magnetic fields. Finally, we claim that the EoS are highly affected in the presence of a magnetic field. Our results are notable compared to other approaches and found to be advantageous for the measurement of QGP equation of state. These crucial findings with and without time-varying magnetic field could have phenomenological implications in various sectors of high-energy physics.

Observing the universal screening of a Kondo impurity

The Kondo effect, deriving from a local magnetic impurity mediating electron-electron interactions, constitutes a flourishing basis for understanding a large variety of intricate many-body problems. Its experimental implementation in tunable circuits has made possible important advances through well-controlled investigations. However, these have mostly concerned transport properties, whereas thermodynamic observations - notably the fundamental measurement of the spin of the Kondo impurity - remain elusive in test-bed circuits. Here, with a novel combination of a ‘charge’ Kondo circuit with a charge sensor, we directly observe the state of the impurity and its progressive screening. We establish the universal renormalization flow from a single free spin to a screened singlet, the associated reduction in the magnetization, and the relationship between scaling Kondo temperature and microscopic parameters. In our device, a Kondo pseudospin is realized by two degenerate charge states of a metallic island, which we measure with a non-invasive, capacitively coupled charge sensor. Such pseudospin probe of an engineered Kondo system opens the way to the thermodynamic investigation of many exotic quantum states, including the clear observation of Majorana zero modes through their fractional entropy.

Assessment of the partial saddle point approximation in field-theoretic polymer simulations.

Field-theoretic simulations are numerical treatments of polymer field theory models that go beyond the mean-field self-consistent field theory level and have successfully captured a range of mesoscopic phenomena. Inherent in molecularly-based field theories is a "signproblem" associated with complex-valued Hamiltonian functionals. One route to field-theoretic simulations utilizes the complex Langevin (CL) method to importance sample complex-valued field configurations to bypass the signproblem. Although CL is exact in principle, it can be difficult to stabilize in strongly fluctuating systems. An alternate approach for blends or block copolymers with two segment species is to make a "partial saddle point approximation" (PSPA) in which the stiff pressure-like field is constrained to its mean-field value, eliminating the signproblem in the remaining field theory, allowing for traditional (real) sampling methods. The consequences of the PSPA are relatively unknown, and direct comparisons between the two methods are limited. Here, we quantitatively compare thermodynamic observables, order-disorder transitions, and periodic domain sizes predicted by the two approaches for a weakly compressible model of AB diblock copolymers. Using Gaussian fluctuation analysis, we validate our simulation observations, finding that the PSPA incorrectly captures trends in fluctuation corrections to certain thermodynamic observables, microdomain spacing, and location of order-disorder transitions. For incompressible models with contact interactions, we find similar discrepancies between the predictions of CL and PSPA, but these can be minimized by regularization procedures such as Morse calibration. These findings mandate caution in applying the PSPA to broader classes of soft-matter models and systems.

Differential scanning calorimetry of aluminium EN AB-42000 alloy rheocasting semi-solid in different stage heating rates

Differential scanning calorimetry (DSC) is used to identify the thermal histories of samples to analyse and diagnose production and quality concerns connected to industrial rheocasting semi-solid alloy, that had undergone different tempers of aluminium alloy EN AB-42000 alloy. In this study, the solidus temperatures of several alloy samples are investigated using thermodynamic calculations and DSC observations in this work. The balance of important characteristics, including pseudo-eutectic, thermal sensitivity, heat flow, and enthalpies behaviour, of Al alloys has been investigated using experimental data from DSC and solid fractions. In addition, the choice of heating rates is critical as high rates can blur the two peaks in the mushy zone, while low rates lead to slower measurements. Using smaller sample weights and slower rates is preferable to obtain more accurate results. Analysing the shape of the fs curve, exact composition, and a reference composition without contaminants is essential for understanding complex behaviours, including pseudo-eutectic phenomena. The thermal sensitivity of compositions also plays a crucial role in the analysis. Despite heat flow decreasing with decreased sample weight, the measurement limit can still be exceeded at high heating or cooling rates (20 °C/min) during the eutectic reaction. The eutectic reaction exhibits higher peaks with enthalpies ranging from 360 to 430 mJ/g. However, drawing conclusions regarding trends in heating versus cooling or comparing low-mass and higher-mass samples can be challenging. The non-equilibrium transformation of the eutectic occurs within a more confined temperature range. Increasing rates lead to overlapping reactions, resulting in complex thermal behaviour.

Non-normalizable quasiequilibrium states under fractional dynamics.

Particles anomalously diffusing in contact with a thermal bath are initially released from an asymptotically flat potential well. For temperatures that are sufficiently low compared to the potential depth, the dynamical and thermodynamical observables of the system remain almost constant for long times. We show how these stagnated states are characterized as non-normalizable quasiequilibrium (NNQE) states. We use the fractional-time Fokker-Planck equation(FTFPE) and continuous-time random walk approaches to calculate ensemble averages. We obtain analytical estimates of the durations of NNQE states, depending on the fractional order, from approximate theoretical solutions of the FTFPE. We study and compare two types of observables, the mean square displacement typically used to characterize diffusion, and the thermodynamic energy. We show that the typical timescales for transient stagnation depend exponentially on the value of the depth of the potential well, in units of temperature, multiplied by a function of the fractional exponent.

Accurate modelling of pyrrolidinium ionic liquids with charge and vdW scaling

Molecular simulation as a complementing tool to experimental measurements has grown to be an instrument with predictive power for ionic liquids (ILs) derivatives. The combination of molecule-specific atomic charges generated with ab initio calculations and bonded and vdW parameters extracted from pre-fitted transferable force fields serves as the common practice in this field. Charge scaling is often applied to account for charge transfer and polarization effects and the scaling factor 0.8 has been concluded as a near-optimal solution in many scientific reports based on detailed analyses of various structural and thermodynamic observables. However, for ILs from the pyrrolidinium family investigated in the current work, we show that the charge scaling treatment cannot really minimize the experiment-simulation deviations to an acceptable level, which calls for further parameter adjustment. Following the modelling protocol summarized in our previous works, we tune the vdW radius of ILs-forming ions with a 298 K density scan and secure a parameter set that satisfactorily reproduces not only the room-temperature properties but also the mass densities in a large temperature range from 288 K to 348 K. The slopes of the vdW-scaling profiles are between −1.9 g/cm3 and −1.6 g/cm3, which are similar to quinuclidinium ILs investigated in our previous work. This phenomenon suggests the similarity of responding behaviors of the two ILs family during vdW scaling, and this range of response strengths could possibly be representative for ILs vdW scaling. Aside from bulk solvents, we further consider the interaction of ILs with a series of external organic agents. Following the previously accumulated experience, a slightly modified vdW scaling factor is picked as an option balancing different interactions within the heterogeneous solution. Nonequilibrium alchemical free energy calculations are conducted to compute solvation free energies in ILs and also the distribution (partition) behaviors of solutes between aqueous and ILs phases. The computed physiochemical properties involving pyrrolidinium ILs agree well with the experimental reference. Another feature of the selected pyrrolidinium ILs is the systematic variation of the length of the alkyl substituting chain, which enables a direct investigation of the chain-length dependence of the prediction accuracies for both bulk density and solvation/partition thermodynamics. Interestingly, with the chain-length variation, the error of bulk density exhibits a monotonic response, while a fluctuating (non-monotonic) behavior is observed for prediction errors of solvation and partition thermodynamics, which is related to the diverse features of solute-solvent interactions. Therefore, the observed behaviors of the properties of bulk solvents cannot be generalized to the solvation/partition behaviors of the same solvent, and accurate reproductions of bulk behaviors do not guarantee accurate calculations of solvation and partition thermodynamics.

Molecular Latent Space Simulators for Distributed and Multimolecular Trajectories.

All atom molecular dynamics (MD) simulations offer a powerful tool for molecular modeling, but the short time steps required for numerical stability of the integrator place many interesting molecular events out of reach of unbiased simulations. The popular and powerful Markov state modeling (MSM) approach can extend these time scales by stitching together multiple short discontinuous trajectories into a single long-time kinetic model but necessitates a configurational coarse-graining of the phase space that entails a loss of spatial and temporal resolution and an exponential increase in complexity for multimolecular systems. Latent space simulators (LSS) present an alternative formalism that employs a dynamical, as opposed to configurational, coarse graining comprising three back-to-back learning problems to (i) identify the molecular system's slowest dynamical processes, (ii) propagate the microscopic system dynamics within this slow subspace, and (iii) generatively reconstruct the trajectory of the system within the molecular phase space. A trained LSS model can generate temporally and spatially continuous synthetic molecular trajectories at orders of magnitude lower cost than MD to improve sampling of rare transition events and metastable states to reduce statistical uncertainties in thermodynamic and kinetic observables. In this work, we extend the LSS formalism to short discontinuous training trajectories generated by distributed computing and to multimolecular systems without incurring exponential scaling in computational cost. First, we develop a distributed LSS model over thousands of short simulations of a 264-residue proteolysis-targeting chimera (PROTAC) complex to generate ultralong continuous trajectories that identify metastable states and collective variables to inform PROTAC therapeutic design and optimization. Second, we develop a multimolecular LSS architecture to generate physically realistic ultralong trajectories of DNA oligomers that can undergo both duplex hybridization and hairpin folding. These trajectories retain thermodynamic and kinetic characteristics of the training data while providing increased precision of folding populations and time scales across simulation temperature and ion concentration.

Relativistic modeling of stellar objects in a Schwarzschild’s coordinates with embedded class one spacetime

In this study, we investigate a new relativistic anisotropic Einstein field equations solution for compact stars under embedding class 1 conditions. In order to do this, we apply the Karmarkar condition and the embedding class one technique. By taking Buchdahl type metric potential g_{rr} into consideration, the precise analytical solution has been investigated. We have studied physical characteristics of various compact star using this analytical solution. Central singularities are absent from the solution. We have explored thermodynamic observables inside the stellar models, such as radial and tangential pressures, matter density, anisotropic factor, energy conditions, TOV, red-shift, and the speed of sound, etc., after establishing this space-time geometry for the stellar models. From the graphical representation of various physical characteristics, it is demonstrated that our model meets all the specification for ultra-high density compact bodies.