Effect Of Thermal Fluctuations Research Articles

Life-stage related responses to combined effects of acclimation temperature and humidity on the thermal tolerance of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae)

Adaptive thermal plasticity plays a key role in mitigating the effects of seasonal and diurnal thermal fluctuations among ectotherms at various life-stages. While the role of thermal history in conferring such plasticity is widely documented, its interaction with relative humidity (RH), another important driver of ectotherm survival and activity, is relatively underexplored. Yet the potential responses to these combinational stressors across ontogeny remain largely neglected. Against this background, we used a full-factorial design to test the combined acclimation effects of RH (45%, 65% and 85%) and temperature (23, 28 and 33 °C) on various indices of thermal sensitivity of laboratory reared spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) following acclimation beginning at larval, pupal and adult life-stages. Traits measured included critical thermal limits (CTLs), supercooling points (SCPs), chill coma recovery time (CCRT) and heat knockdown time (HKDT). Larval acclimation at 23 °C; 85% RH recorded the lowest critical thermal minima (CTmin) whereas adult acclimation at 28 °C; 45% RH recorded the highest critical thermal maxima (CTmax). There were no significant differences (P > 0.05) in SCPs across all temperature × RH acclimations. Larval and pupal acclimations at 23 °C; 85% RH and adult acclimation at 23 °C; 45% RH significantly improved CCRT. Similarly, commencing acclimation at larval, pupal and adult stages at 28 °C; 85% RH improved HKDT whereas larval and pupal acclimations at 33 °C; 45% RH impaired it. Our results indicate that combinational interactions of temperature and RH have significant thermal fitness costs and benefits and are dependent on the life-stage acclimation timing. Results also imply that both the vulnerability and adaptive potential of C. partellus populations under rapid climate variability varies with ontogeny. This therefore calls for the consideration of the role of ontogeny and multi-factors in better understanding the impact of environmental stress on ectotherms.

Kibble-Zurek scaling of the one-dimensional Bose-Hubbard model at finite temperatures

We use tensor network methods - Matrix Product States, Tree Tensor Networks, and Locally Purified Tensor Networks - to simulate the one dimensional Bose-Hubbard model for zero and finite temperatures in experimentally accessible regimes. We first explore the effect of thermal fluctuations on the system ground state by characterizing its Mott and superfluid features. Then, we study the behavior of the out-of-equilibrium dynamics induced by quenches of the hopping parameter. We confirm a Kibble-Zurek scaling for zero temperature and characterize the finite temperature behavior, which we explain by means of a simple argument.

Evaluation of Operating Margin and Switching Probability of Voltage- Controlled Magnetic Anisotropy Magnetic Tunnel Junctions

Voltage-controlled magnetic anisotropy (VCMA) has attracted great attention as it allows faster switching and lower energy consumption compared to traditional spin-transfer torque-based magnetization switching. In this paper, we evaluate the operating margin and switching probability of VCMA-based magnetic tunnel junctions using realistic material and device parameters. For this paper, we developed a physics-based SPICE model that incorporates various VCMA parameters such as VCMA coefficient, energy barrier, time constant, and external magnetic field. Switching probability of a VCMA device was obtained by running Monte Carlo simulations including thermal fluctuation effects. A design space exploration was performed using the proposed simulation framework. The highest switching probabilities we were able to achieve were 94.9%, 84.8%, and 53.5%, for VCMA coefficient values of 33, 105, and 290 fJ · V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> · m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively. Our study shows that for VCMA devices to become viable, their switching probability must be improved significantly either through new physics or material innovation.

Effects of Thermal Fluctuations on Temperature Anisotropy Instabilities in the Solar Wind

AbstractThe proton temperature anisotropy in the solar wind, when plotted as a two‐dimensional histogram in (β∥,T⊥/T∥) phase space, shows that the bulk of the data are broadly distributed in quasi‐isotropic state, while the fringe of data distribution is apparently regulated by various marginal stability conditions. The physical origin of magnetic field fluctuations in the stable regime is an open question. Among plausible mechanisms is the spontaneous thermal emission process. Discrete particle effects are central to the theory of spontaneous emission and reabsorption of electromagnetic fluctuations in plasmas. The present paper formulates the quasi‐linear theory of temperature anisotropy‐driven instabilities in which discrete particle effects are taken into account. The hybrid simulation is also carried out with varying number of superparticles per cell in order to unveil the underlying relationship between the theoretical and simulated discrete particle effects. The present paper demonstrates that the inherent numerical noise in the particle simulation is not always undesirable but may actually be exploited in order to control the degree of particle discreteness. Such a finding may have a significant implication for simulating the solar wind plasmas.

Nuclear pairing fluctuations and angular momentum dependence of superconductivity in 94Mo nucleus

The effects of thermal fluctuations on pairing properties of nuclei with inclusion of angular momentum have been investigated. To treat nuclei at finite temperature and angular momentum, we have extended the formalism in which the mean value of the gap parameter is used to obtain thermal properties of nuclei based on the BCS scheme [Z. Kargar and V. Dehghani, J. Phys. G, Nucl. Part. Phys. 40 (2013) 045108] let us name it MEGBCS. The results obtained for [Formula: see text] nucleus show the appearance of thermally assisted pairing correlations with increasing angular momentum. Also, the [Formula: see text]-shaped heat capacity found experimentally [K. Kaneko et al., Phys. Rev. C 74 (2006) 024325] and theoretically, interpreted as the second phase transition in mesoscopic systems, disappears with increasing angular momentum above a critical value. The nuclear level density of [Formula: see text] is calculated versus excitation energy at various values of total angular momentum. The total level density matches the experimental data closely.

Thermal fluctuations in the conical state of monoaxial helimagnets

The effect of thermal fluctuations on the phase structure of monoaxial helimagnets with external magnetic field parallel to the chiral axis is analyzed by means of a saddle point expansion of the free energy. The phase transition that separates the conical and forced ferromagnetic phases is changed to first order by the thermal fluctuations. In a purely monoaxial system the pitch of the conical state remains independent of temperature and magnetic field, as in mean field theory, even when fluctuations are taken into account. However, in presence of weak Dzyaloshinskii-Moriya interactions in the plane perpendicular to the chiral axis, thermal fluctuations induce a dependence of the pitch on temperature and magnetic field. This may serve to determine the nature of magnetic interactions in such systems.

Persistence of pinning and creep beyond critical drive within the strong pinning paradigm

Pinning and thermal creep determine the response of numerous systems containing superstructures, e.g., vortices in type II superconductors, domain walls in ferroics, or dislocations in metals. The combination of drive and thermal fluctuations lead to the superstructure's depinning and its velocity $v$ determines the electric, magnetic, or mechanical response. It is commonly believed that pinning and creep collapse above the critical drive $F_c$, entailing a sharp rise in the velocity $v$. We challenge this perception by studying the effects of thermal fluctuations within the framework of strong vortex pinning in type-II superconductors. In fact, we show that pinning and thermal creep persist far beyond the critical force. The resulting force-velocity characteristic largely maintains its zero-temperature shape and thermal creep manifests itself by a downward renormalisation of the critical drive. Such characteristics is in agreement with Coulomb's law of dry friction and has been often observed in experiments.

Precisive calculation of specific heat in type-II superconductor under magnetic field

A precisive calculation of specific heat contributions of vortex liquids and solids in type-II superconductor is presented. We use the self-consistent method in the presence of magnetic field for the Ginzburg-Landau description of thermal fluctuations effects in the vortex liquids. Self-consistent calculation of the specific heat summing over all Landau levels is valid for arbitrary values of the magnetic field not too close to Hc1. Our results are in good agreement with the experimental data in a wide region around Tc, including both the vortex liquid below Tc and the normal state above Tc. Our calculation shows that the specific heat behaves as a long tail which persists far into the normal state, indicating the residual superconductivity above Tc.

Effects of thermal fluctuations in the fragmentation of a nanoligament

We study the effects of thermally induced capillary waves in the fragmentation of a liquid ligament into multiple nanodroplets. Our numerical implementation is based on a fluctuating lattice Boltzmann (LB) model for nonideal multicomponent fluids, including nonequilibrium stochastic fluxes mimicking the effects of molecular forces at the nanoscales. We quantitatively analyze the statistical distribution of the breakup times and the droplet volumes after the fragmentation process at changing the two relevant length scales of the problem, i.e., the thermal length scale and the ligament size. The robustness of the observed findings is also corroborated by quantitative comparisons with the predictions of sharp interface hydrodynamics. Beyond the practical importance of our findings for nanofluidic engineering devices, our study also explores a novel application of LB in the realm of nanofluidic phenomena.

Size- and temperature-dependent bending rigidity of graphene using modal analysis

The bending rigidity of two-dimensional (2D) materials is a key parameter for understanding the mechanics of 2D NEMS devices. The apparent bending rigidity of graphene membranes at macroscopic scale differs from theoretical predictions at micro-scale. This difference is believed to originate from thermally induced dynamic ripples in these atomically thin membranes. In this paper, we perform modal analysis to estimate the effective bending rigidity of graphene membranes from the frequency spectrum of their Brownian motion. Our method is based on fitting the resonance frequencies obtained from the Brownian motion in molecular dynamics simulations, to those obtained from a continuum mechanics model, with bending rigidity and pretension as the fit parameters. In this way, the effective bending rigidity of the membrane and its temperature and size dependence, are extracted, while including the effects of dynamic ripples and thermal fluctuations. The proposed method provides a framework for estimating the macroscopic mechanical properties in other 2D nanostructures at finite temperatures.

Universal stabilization of single-qubit states using a tunable coupler

We theoretically analyze a scheme for fast stabilization of arbitrary qubit states with high fidelities, extending a protocol recently demonstrated experimentally [Lu et al., Phys. Rev. Lett. 119, 150502 (2017)]. That experiment utilized red and blue sideband transitions in a system composed of a fluxonium qubit, a low-Q LC-oscillator, and a coupler enabling us to tune the interaction between them. Under parametric modulations of the coupling strength, the qubit can be steered into any desired pure or mixed single-qubit state. For realistic circuit parameters, we predict that stabilization can be achieved within 100 ns. By varying the ratio between the oscillator's damping rate and the effective qubit-oscillator coupling strength, we can switch between under-damped, critically-damped, and over-damped stabilization and find optimal working points. We further analyze the effect of thermal fluctuations and show that the stabilization scheme remains robust for realistic temperatures.

Compressive response and buckling of graphene nanoribbons

We examine the mechanical response of single layer graphene nanoribbons (GNR) under constant compressive loads through molecular dynamics simulations. Compressive stress-strain curves are presented for GNRs of various lengths and widths. The dependence of GNR’s buckling resistance on its size, aspect ratio, and chiral angle is discussed and approximate corresponding relations are provided. A single master curve describing the dependence of the critical buckling stress of GNRs on their aspect ratio is presented. Our findings were compared to the continuum elasticity theories for wide plates and wide columns. In the large width limit, the response of the GNRs agrees with the predictions of the wide plates theory and thus, with that of wide graphenes. In the small width limit, the behavior of graphene nanoribbons deviates from that of periodic graphenes due to various edge related effects which govern the stiffness and the stability of the graphene membranes, but it qualitatively agrees with the theory of wide columns. In order to assess the effect of thermal fluctuations on the critical buckling stress a wide range of temperatures is examined. The findings of the current study could provide important insights regarding the feasibility and the evaluation of the performance of graphene-based devices.

Thermodynamic variables of first-order entropy corrected Lovelock-AdS black holes: $$P{-}V$$ P - V criticality analysis

We investigate the effect of thermal fluctuations on the thermodynamics of a Lovelock-AdS black hole. Taking the first order logarithmic correction term in entropy we analyze the thermodynamic potentials like Helmholtz free energy, enthalpy and Gibbs free energy. We find that all the thermodynamic potentials are decreasing functions of correction coefficient $\alpha$. We also examined this correction coefficient tmust be positive by analysing $P-V$ diagram. Further we study the P-V criticality and stability and find that presence of logarithmic correction in it is necessary to have critical points and stable phases. When P-V criticality appears, we calculate the critical volume $V_c$, critical pressure $P_c$ and critical temperature $T_c$ using different equations and show that there is no critical point for this black hole without thermal fluctuations. We also study the geometrothermodynamics of this kind of black holes. The Ricci scalar of the Ruppeiner metric is graphically analysed.

Thermal noise in a boost-invariant matter expansion in relativistic heavy-ion collisions

We formulate a general theory of thermal fluctuations within causal second-order viscous hydrodynamic evolution of matter formed in relativistic heavy-ion collisions. The fluctuation is treated perturbatively on top of a boost-invariant longitudinal expansion. Numerical simulation of thermal noise is performed for a lattice QCD equation of state and for various second-order dissipative evolution equations. Phenomenological effects of thermal fluctuations on the two-particle rapidity correlations are studied.

Response of the Higgs amplitude mode of superfluid Bose gases in a three-dimensional optical lattice

We study the Higgs mode of superfluid Bose gases in a three dimensional optical lattice, which emerges near the quantum phase transition to the Mott insulator at commensurate fillings. Specifically, we consider responses of the Higgs mode to temporal modulations of the onsite interaction and the hopping energy. In order to calculate the response functions including the effects of quantum and thermal fluctuations, we map the Bose-Hubbard model onto an effective pseudospin-one model and use a perturbative expansion based on the imaginary-time Green's function theory. We also include the effects of an inhomogeneous trapping potential by means of a local density approximation. We find that the response function for the hopping modulation is equal to that for the interaction modulation within our approximation. At the unit filling rate and in the absence of a trapping potential, we show that the Higgs mode can exist as a sharp resonance peak in the dynamical susceptibilities at typical temperatures. However, the resonance peak is significantly broadened due to the trapping potential when the modulations are applied globally to the entire system. We suggest that the Higgs mode can be detected as a sharp resonance peak by partial modulations around the trap center.

Quantum and thermal fluctuations in two-component Bose gases

We study the effects of quantum and thermal fluctuations on Bose-Bose mixtures at finite temperature employing the time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory. The theory governs self-consistently the motion of the condensates, the noncondensates, and of the anomalous components on an equal footing. The finite temperature criterion for the phase separation is established. We numerically analyze the temperature dependence of different densities for both miscible and immiscible mixtures. We show that the degree of the overlap between the two condensates and the thermal clouds is lowered and the relative motion of the centers of mass of the condensed and thermal components is strongly damped due to the presence of the pair anomalous fluctuations. Our results are compared with previous theoretical and experimental findings. On the other hand, starting from our TDHFB equations, we develop a random-phase theory for the elementary excitations in a homogeneous mixture. We find that the normal and anomalous fluctuations may lead to enhance the excitations and the thermodynamics of the system.

The costs of living in a thermal fluctuating environment for the tropical haematophagous bug, Rhodnius prolixus

Environmental temperature is an abiotic factor with great influence on biological processes of living beings. Jensen's inequality states that for non-lineal processes, such as most biological phenomena, the effects of thermal fluctuations cannot be predicted from mean constant temperatures. We studied the effect of daily temperature fluctuation (DTF) on Rhodnius prolixus, a model organism in insect physiology, and an important vector of Chagas disease. We measured development time from egg to adult, fecundity, fertility, body mass reduction rate (indirect measurement of nutrient consumption rates) and survival after a single blood meal. Insects were reared at constant temperature (24 °C), or with a DTF (17–32 °C; mean = 24 °C). Taking into account Jensen's inequality as well as the species tropical distribution, we predict that living in a variable thermal environment will have higher costs than inhabiting a stable one. Development time and fertility were not affected by DTF. However, fecundity was lower in females reared at DTF than at constant temperature, and males had higher body mass reduction rate and lower survival in the DTF regime, suggesting higher costs associated to fluctuating thermal environments. At a population and epidemiological level, higher energetic costs would imply an increase in nutrient consumption rate, biting frequency, and, consequently increasing disease transmission from infected insects. On the contrary, lower fecundity could be associated with a decrease in population growth. This knowledge will not only provide basic information to the field of insect ecophysiology, but also could be a useful background to develop population and disease transmission models.

Phase transitions and spin excitations of spin-1 bosons in optical lattice

We investigate ground state properties of spin-1 bosonic system trapped in optical lattice with extended standard basis operator (SBO) method. For both ferromagnetic ($U_2<0$) and antiferromagnetic ($U_2>0$) systems, we analytically figure out the symmetry properties in Mott-insulator and superfluid phases, which would provide a deeper insight into the MI-SF phase transition process. Then by applying self-consistent approach to the method, we include the effect of quantum and thermal fluctuations and derive the MI-SF transition phase diagram, which is in quantitative agreement with recent Monte-Carlo simulation at zero temperature, and at finite temperature, we find the underestimation of finite-temperature-effect in the mean-field approximation method. If we further consider the spin excitations in the insulating states of spin-1 system in external field, distinct spin phases are expected. Therefore, in the Mott lobes with $n=1$ and $n=2$ atoms per site, we give analytical and numerical boundaries of the singlet, nematic, partially magnetic and ferromagnetic phases in the magnetic phase diagrams.

Superconductivity versus quantum criticality: Effects of thermal fluctuations

We study the interplay between superconductivity and non-Fermi liquid behavior of a Fermi surface coupled to a massless $\text{SU}(N)$ matrix boson near the quantum critical point. The presence of thermal infrared singularities in both the fermionic self-energy and the gap equation invalidates the Eliashberg approximation, and makes the quantum-critical pairing problem qualitatively different from that at zero temperature. Taking the large $N$ limit, we solve the gap equation beyond the Eliashberg approximation, and obtain the superconducting temperature ${T}_{c}$ as a function of $N$. Our results show an anomalous scaling between the zero-temperature gap and ${T}_{c}$. For $N$ greater than a critical value, we find that ${T}_{c}$ vanishes with a Berezinskii-Kosterlitz-Thouless scaling behavior, and the system retains non-Fermi liquid behavior down to zero temperature. This confirms and extends previous renormalization-group analyses done at $T=0$, and provides a controlled example of a naked quantum critical point. We discuss the crucial role of thermal fluctuations in relating our results with earlier work where superconductivity always develops due to the special role of the first Matsubara frequency.

Self-propelled colloidal particle near a planar wall: A Brownian dynamics study

Miniaturized, self-propelled locomotors use chemo-mechanical transduction mechanisms to convert fuel in the environment to autonomous motion. Recent experimental and theoretical studies demonstrate that these autonomous engines can passively follow the contours of solid boundaries they encounter. Boundary guidance, however, is not necessarily stable: Mechanical disturbances can cause the motor to hydrodynamically depart from the passively guided pathway. Furthermore, given the scaled-down size of micromotors (typically 100 nm -10 $\mu$m), Brownian thermal fluctuation forces are necessarily important and these stochastic forces can randomize passively-steered trajectories. Here we examine theoretically the stability of boundary guided motion of micromotors along infinite planar walls to mechanical disturbances and to Brownian forces. Our aim is to understand under what conditions this passively guided motion is stable. We choose a locomotor design in which spherical colloids are partially coated with a catalytic cap that reacts with solute to produce a product. The product is repelled from the particle surface, causing the particle to move with the inert face at the front (autonomous motion via self-diffusiophoresis). When propelled towards a planar wall, deterministic hydrodynamic studies demonstrate that these locomotors can exhibit, for large enough cap sizes, steady trajectories in which the particle either skims unidirectionally along the surface at a constant distance from the wall, or becomes stationary. We first investigate the linear hydrodynamic stability of these states by expanding the equations of motion about the states, and find that linear perturbations decay exponentially in time. We then study the effects of thermal fluctuations by formulating a Langevin equation for the particle motion which includes the Brownian stochastic force...