Searcharxiv⌕ Search

arXiv subjects

Mesfin Taye

Publications and source records attributed to Mesfin Taye.

17 recordsLinked to original sources
arXiv2026

Thermodynamic optimization of thermal landscapes and energy barriers in a Brownian heat engine

Spatial temperature fields in Brownian heat engines are commonly prescribed \emph{a priori}, and the resulting transport and thermodynamic properties are then calculated. Here we formulate the complementary inverse-design problem: determining the temperature profile and barrier height that optimize a chosen thermodynamic objective. We consider an overdamped Brownian particle in a symmetric triangular periodic potential under a constant opposing load and derive the exact stationary current and probability density for an arbitrary bounded temperature field, $\Tc\le T(x)\le\Th$. In the quasistatic limit, the efficiency becomes an exact functional of two inverse-temperature integrals over the uphill and downhill branches. Its rigorous global maximum under the pointwise temperature bounds is $\eta_{\max}=1-\Tc/\Th$, attained uniquely, up to sets of measure zero, by the hot-uphill/cold-downhill piecewise-constant profile. At finite current, however, the optimization changes qualitatively because the current is determined jointly by the cycle affinity and a nonlocal transport resistance. We derive the exact functional gradient and the corresponding box-constrained optimality conditions, showing that the current- or power-maximizing profile generally differs from the quasistatic efficiency optimum. For any prescribed temperature field, the current-maximizing barrier satisfies an exact balance between the marginal gain in thermal rectification and the marginal increase in transport resistance, with the characteristic estimate $U_0^*\simeq T_{\rm act}$, where $T_{\rm act}^{-1}=(2/L)\int_0^{L/2}\dd x/T(x)$.

cond-mat.stat-mech↗
arXiv2026

Exact chemo--thermal Metropolis Brownian engine: chemical leverage, temperature-neutral stall, power optimization, and multicyclic dissipation

We develop an exactly solvable chemo--thermal extension of the three-state Metropolis Brownian heat engine. The particle moves through the periodic energy sequence $0\to E\to 2E\to0$, performs mechanical work against a load $f$ on every forward step, interacts with two cold links and one hot link, and consumes one fuel molecule of free-energy drop $\muu$ on the hot transition. Local detailed balance gives an exact cycle affinity \begin{equation*} \mathcal A=E\left(\Tc^{-1}-\Th^{-1}\right)+\muu/\Th-f\left(2/\Tc+1/\Th\right), \end{equation*} and the full stationary probabilities and current are obtained without linear-response, weak-driving, or high-barrier approximations. Several results follow. First, the exact stall force is \begin{equation*} \fs=\frac{E(\Th-\Tc)+\Tc\muu}{2\Th+\Tc}. \end{equation*} Second, there is a temperature-neutral chemical compensation point $\muu_*=3E/2$ at which $\fs=E/2$ for every $\Th>\Tc$ and the hot and cold heats both vanish at reversible stall. Third, in both Metropolis branches the stationary current is a strictly increasing function of $\muu$ at fixed mechanical parameters, but approac

cond-mat.stat-mech↗
arXiv2026

A Nonequilibrium Internal-Time Model of Aging: Entropy-Normalized Biological Proper Time and Repair Bifurcations

Chronological age is an incomplete coordinate for aging. Individuals and species sharing the same calendar time can differ substantially in physiological reserve, molecular damage, mortality hazard, and remaining lifespan. The Principle of Biological Time Equivalence (PBTE) offers a thermodynamic reformulation: biological aging is governed by the accumulation of \emph{internal} physiological time rather than chronological time alone. Building on prior PBTE work, this paper defines the internal-time coordinate $\theta(t)=\int_0^t f(s)\dd s$, where $t$ is chronological time and $f(s)$ is an instantaneous physiological frequency (for example heart rate or respiratory rate), so that $\theta$ is the accumulated count of physiological cycles. Its entropy-normalized extension is $\Tsig(t)=\int_0^t[\sigz(s)/\sref]f(s)\dd s$, where $\sigz(s)=\dd\Sigma/\dd\theta$ is the entropy produced per physiological cycle (the entropy cost per biological tick), $\Sigma$ is cumulative entropy production, and $\sref$ is a fixed reference entropy cost per cycle used as a normalizing unit. The normalized PBTE age $\APBTE(t)=\Tsig(t)/\Nref$ measures the fraction of a reference entropy--cycle budget consumed, where $\Nref$ is the reference number of entropy-weighted cycles available over a lifetime. The manuscript is explicitly theoretical: no empirical cohort is analyzed, and the numerical demonstrations are synthetic stress tests rather than validation.

physics.bio-ph↗
arXiv2026

Biological proper time and entropy-cost invariance in cardiac and respiratory lifespan scaling

Warm-blooded vertebrates accumulate approximately conserved numbers of physiological cycles over a natural lifetime: of order $10^9$ heartbeats and $10^8$--$3\times10^8$ breaths. These regularities are not exact constants, but their persistence across orders-of-magnitude variation in body mass, metabolic power, physiological frequency, and lifespan suggests that biological time is not measured by chronological duration alone. We develop the Principle of Biological Time Equivalence (PBTE), a thermodynamic framework in which lifetime cycle count is determined by the ratio between total lifetime entropy production and the entropy cost of one physiological cycle. Starting from the open-system entropy balance $\dot S=\dot e_p-\dot h_d$, we define the entropy cost per cycle as $\sigma_0=d\Sigma/dN$, where $d\Sigma$ is the entropy produced as the physiological clock advances by $dN$ cycles. For an adult homeostatic regime, this gives the cycle-count relation $N_\star=\Sigma/\langle\sigma_0\rangle$, with $\Sigma=\int_0^L \dot e_p(t)\,dt$, where $N_\star$ is the lifetime cycle count, $\Sigma$ is total lifetime entropy production, and $\langle\sigma_0\rangle$ is the lifetime-averaged entropy cost per cycle. In the homeostatic limit, $\dot e_p\simeq P/T$, so direct measurement of metabolic power $P$, body temperature $T$, and physiological frequency $f$ gives $\sigma_0\simeq P/(Tf)$. PBTE converts the empirical lifetime-cycle invariants into entropy-cost invariants. Under Kleiber metabolic scaling and quarter-power physiological-frequency scaling, the mass-specific entropy cost satisfies $\bar\sigma_0=P/(TfM)\propto M^{3/4+1/4-1}=M^0$, providing a thermodynamic interpretation of allometric mass cancellation.

q-bio.OT↗
arXiv2026

The Lifetime Cardiac-Cycle Invariant in Endothermic Vertebrates: A 230-Species Comparative Dataset, Statistical Validation, and Explicit Falsifiability Criteria

A pygmy shrew (\textit{Suncus etruscus}, ${\approx}2$\,g) sustains a resting heart rate near $1{,}000$\,beats\,min$^{-1}$ and dies within two years; an African elephant (${\approx}4{,}000$\,kg) beats at $28$\,beats\,min$^{-1}$ and lives seven decades. Their chronological lifespans differ by a factor of 35, yet each accumulates close to $10^9$ cardiac cycles before death -- a near-constancy first noted by Rubner~(1908) and quantified by Lindstedt and Calder~(1981)~\cite{lindstedt1981}, but never subjected to multi-clade statistical testing, phylogenetic correction, or explicit falsifiability criteria with a large modern dataset. We address this gap with a curated 230-species vertebrate dataset spanning non-primate placentals ($n=43$), primates ($n=18$), marsupials and monotremes ($n=19$), duty-cycle-corrected bats ($n=31$), dive-corrected cetaceans ($n=12$), birds ($n=78$), and Arrhenius-corrected ectotherms ($n=26$), and subject the log-invariant $\ell = \log_{10}(N^{\!\star})$ -- where $N^{\!\star} = f_H\,L\times 525{,}960$ cardiac cycles -- to four independent tests.

physics.bio-ph↗
arXiv2026

Neural Investment as an Entropy-Budget Strategy: A Thermodynamic Derivation of Primate Longevity from the Principle of Biological Time Equivalence

Primates exhibit a robust deviation from canonical allometric scaling: at fixed body mass, their lifespans exceed those of non-primate mammals by factors of two to three. A rhesus macaque (8 kg) lives 25-40 years, whereas a cat of similar mass rarely exceeds 18 years. This statistically significant clade-level excess cannot be explained by standard metabolic or ecological models. We provide a thermodynamic explanation within the Principle of Biological Time Equivalence (PBTE), where lifespan is determined by a finite cycle budget governed by entropy production. We show that primates reduce entropy production per physiological cycle through increased neural energy allocation. The neural power fraction acts as a control parameter, extending the effective lifetime cycle count. Three mechanisms, predictive regulation, enhanced repair, and behavioral buffering, jointly suppress dissipation. This yields a quantitative neuro-metabolic multiplier that explains primate longevity and provides testable predictions linking brain energetics, entropy production, and lifespan.

physics.bio-ph↗
arXiv2026

Thermodynamic Parametrisation of the Vertebrate Lifetime Cycle Invariant: Biological Proper Time, Allometric Mass-Cancellation, and Clade-Specific Predictions

Warm-blooded vertebrates accumulate approximately $\Nstar \approx 10^9$ cardiac cycles over a natural lifetime, a striking empirical regularity first quantified by Lindstedt and Calder yet lacking a physical interpretation. We propose that this invariance is consistent with a conserved thermodynamic budget, formulated here as the Principle of Biological Time Equivalence (PBTE). The framework rests on a constitutive closure $\dot{\Sigma} = \sigma_0 f$, which links the entropy production rate to the intrinsic physiological frequency; integration over the lifespan yields $\Sigma_{\mathrm{life}} = \sigma_0 \Nstar$, so that the observed constancy of $\Nstar$ corresponds to an approximately constant lifetime entropy budget. Algebraic exponent cancellation under Kleiber and Calder scaling laws, $\sigstar \propto M^{3/4+1/4-1}=M^0$, is consistent with mass-independence and reproduces the numerical value $N_0 \approx 1.52\times10^9$ without free parameters. The framework offers a thermodynamically consistent account of two outstanding problems: the origin of the numerical value of $\Nstar$ and the systematic deviations observed across clades. A multiplicative correction factor $\Phi_C$, constructed from physiological determinants -- activity allocation, body temperature, mitochondrial efficiency, and extrinsic hazard -- predicts long-lived clades as regimes of reduced effective entropy production per cardiac cycle.

cond-mat.stat-mech↗
arXiv2026

Biological Time Equivalence in Vertebrates: Thermodynamic Framework, Comparative Tests, and Clade-Specific Deviations

The product of resting heart rate and maximum lifespan is approximately constant across adult warm-blooded vertebrates, $N^\star = f_H L \approx 10^9$ cardiac cycles, a regularity documented since Rubner (1908) but lacking a thermodynamic derivation. We derive $N^\star$ from the non-equilibrium second law by treating the adult organism as a metabolic non-equilibrium steady state (NESS) and introducing the closure $\dot{e}_p = \sigma_0 f$, linking entropy production rate to heart rate via a mass-specific parameter $\sigma_0 \propto M^0$. Integration yields a finite dissipative budget $\Sigma = \sigma_0 N^\star$, identifying $N^\star = \Sigma/\sigma_0$ as the correct primitive conserved quantity; lifetime energy per unit mass is a derived consequence valid only under simultaneous constancy of body temperature and $\sigma_0$. Phylogenetically independent contrasts on 112 endotherm species yield a $\log f_H$--$\log L$ slope of $-0.99 \pm 0.04$ ($p=0.84$ against $-1$); the West--Brown--Enquist null of zero inter-clade variation is rejected ($F=12.7$, $p<0.001$). A factored multiplier $\Phi_C = \Phi_{\mathrm{duty}} \cdot \Phi_{\mathrm{thermal}} \cdot \Phi_{\mathrm{mito}} \cdot \Phi_{\mathrm{haz}}$, calibrated from independently measured physiology, accounts for longevity deviations across four warm-blooded clades. The integral of physiological frequency defines a biological proper time classifying longevity mechanisms as time dilation (reduce $f$) or budget expansion (reduce $\sigma_0$). The decisive test is calorimetric measurement of $\sigma_0 = P/(TfM)$ across three body-mass decades.

physics.bio-ph↗
arXiv2025

A Unified Nonequilibrium Framework: Thermodynamic Distance, Dissipation, and Stationary Laws via Effective State Count, Variational Stationarity, and Thermodynamic Bounds

We propose a variational framework for nonequilibrium thermodynamics built around the effective number of accessible state, a multiplicative count that ranges from for a uniform distribution to one under complete localization, and whose logarithm coincides with the Gibbs Shannon entropy. This gives a natural thermodynamic distance to equipartition that bounds statistical distinguishability and grows monotonically under doubly stochastic relaxation. The construction extends to arbitrary nonequilibrium steady states with a chosen reference distribution, where the Kullback Leibler divergence splits into an entropy deficit and a reference weight coupling, acts as a Lyapunov functional when the reference is fixed, and reduces to excess free energy in canonical settings. We connect these static notions to dynamics by decomposing entropy production into adiabatic (housekeeping) and nonadiabatic parts, identify the latter with the rate of decay of the divergence to the reference, and complement this with trajectory and activity-based potentials that yield fluctuation symmetries, thermodynamic uncertainty bounds, and activity-limited speed constraints on steady currents

cond-mat.stat-mech↗
arXiv2025

Noise-Activated Dopant Dynamics in Two-Dimensional Thermal Landscapes with Localized Cold Spots

Controlling dopant transport with high spatial precision is crucial for improving the semiconductor functionality, reliability, and scalability. Although prior models of noise-assisted diffusion have been largely confined to idealized one dimensional settings, we present a physically realistic two-dimensional theoretical framework that integrates anisotropic quartic confinement with localized thermal cold spots to direct impurity dynamics. Using a generalized Fokker Planck formalism, we show that the geometry of the thermal landscape, particularly the width and arrangement of cold spots, governs a noise induced transition between monostable and bistable effective potentials. This enables tunable noise activated hopping and supports conditions favorable for stochastic resonance (SR) if weak periodic driving is applied. Quantitative predictions are made for how impurity localization and effective barrier heights depend on the cold spot width and trap depth , offering experimentally testable signatures. We propose an experimental realization using optothermal techniques, such as dual beam optical tweezers and laser cooling, which can sculpt reconfigurable thermal profiles with sub micron resolution. This model establishes a versatile pathway for programmable impurity manipulation and noise sensitive control in semiconductor structures, bridging theoretical predictions with feasible experimental detection via photoluminescence mapping or lock in signal amplification.

cond-mat.stat-mech↗
arXiv2025

Thermodynamic Irreversibility in Underdamped Brownian Motion with Spatial Temperature Gradients

We analyze underdamped Brownian motion in non-isothermal media with quadratic, linear, and piecewise-constant temperature profiles. Exact identities for entropy production and entropy extraction are derived, addressing whether a vanishing rate implies equilibrium. For a free particle (no external forces or ratchets), the instantaneous entropy production and extraction rates decay to zero at long times despite a spatial temperature gradient. However, their time-integrated values remain finite, demonstrating intrinsic irreversibility arising from kinetic-energy-mediated heat flow from hot to cold regions. Hence, zero entropy-production rate does not certify equilibrium in non-isothermal underdamped systems. Without loads/potentials, most thermodynamic rates vanish asymptotically while irreversibility persists via cumulative heat transfer.

cond-mat.stat-mech↗
arXiv2025

A Universal Thermodynamic Inequality: Scaling Relations Between Current, Activity, and Entropy Production

We derive a universal thermodynamic bound constraining directional transport in both discrete and continuous nonequilibrium systems. For continuous-time Markov jump processes and overdamped diffusions governed by Fokker--Planck equations, we prove the inequality $ \frac{2 V(t)^2}{A(t)} \leq \dot{e}_p(t), $ linking the squared net velocity $V(t)$, entropy production rate $\dot{e}_p(t)$, and dynamical activity $A(t)$. This relation captures a fundamental trade-off between transport, dissipation, and fluctuation intensity, valid far from equilibrium and without detailed balance. In addition, we introduce dimensionless thermodynamic ratios that quantify dissipation asymmetry, entropy extraction, and relaxation. These scaling laws unify discrete and continuous stochastic thermodynamics and provide experimentally accessible constraints on transport efficiency in nanoscale machines and active systems.

cond-mat.stat-mech↗
arXiv2025

Thermodynamic Features of a Heat Engine Coupled with Exponentially Decreasing Temperature Across the Reaction Coordinate, as well as Perspectives on Nonequilibrium Thermodynamics

In this study, we advance the understanding of non-equilibrium systems by deriving thermodynamic relations for a heat engine operating under an exponentially decreasing temperature profile. Such thermal configurations closely mimic spatially localized heating such as laser-induced thermal gradients. Using exact analytical solutions, we show that this arrangement results in significantly higher velocity, entropy production, and extraction rates than piecewise thermal profiles, while exhibiting reduced irreversibility and complexity relative to linear or quadratic gradients. We further examine the thermodynamic behavior of the Brownian particles in the networks. Our study reveals that the velocity and entropy production rates remain independent of network size; on the contrary, extensive quantities such as total entropy depend on the number of microstates. Additionally, we show that a Brownian particle in a ratchet potential with spatially varying temperature achieves directed motion, even without external forces driven by solely thermal asymmetry. These findings highlight the critical role of temperature asymmetry in controlling the transport processes and optimizing the particle dynamics. This in turn will have promising applications in microfluidic devices and nanoscale sensors. Finally, we explore the influence of the system parameters on the efficiency and performance of the heat engine. The exponential temperature profiles enable faster velocities while simultaneously exhibiting higher efficiency compared with other thermal arrangements. Moreover, by addressing key questions on entropy production, we provide insights into the transition between nonequilibrium and equilibrium systems and contribute tools for optimizing energy-efficient systems in both natural and engineered settings.

cond-mat.stat-mech↗
arXiv2025

Entropy Production and Thermodynamic Dynamics in Active and Passive Brownian Systems Driven by Time Dependent Forces and Temperatures

In this work, we examine the impact of time-varying temperature and force on the thermodynamic features of active Brownian motor that moves with velocity against the force as well as passive Brownian motor. By deriving analytical expressions In this work, we examine the impact of time-varying temperature and force on the thermodynamic features of active Brownian motor that moves with velocity against the force as well as passive Brownian motor. By deriving analytical expressions for entropy production and entropy extraction rates, we extend the existing theoretical frameworks by considering a force or temperature that varies exponentially, linearly, and quadratically. By studying the system analytically, we investigate how thermal relaxation, steady-state conditions, and nonlinear dissipation effects are affected over time. We find that the total entropy depends only on temperature and viscous friction if the Brownian particle moves freely, while the entropy production and dissipation rates are strongly influenced by the external force.

cond-mat.stat-mech↗
arXiv2025

Drug Washout and Viral Rebound: Modeling HIV Reactivation Under ART Discontinuation

Due to the persistence of latently infected CD4$^+$ T cells, achieving a functional cure for HIV-1 remains a significant challenge since the viruses are able to evade immune clearance, which in turn enables post-treatment viral rebound. Because traditional deterministic models assume a constant reactivation rate, they fail to capture the stochastic nature of latency reversal influenced by immune perturbations and ART pharmacokinetics. Thus, in this study, by using a Poisson-driven stochastic framework that incorporates fluctuations in activation rates, we study viral rebound dynamics. Via an exponentially decreasing drug washout model, we accurately quantifies the nonlinear interplay between ART decay and stochastic reactivation, improving the theoretical estimates of post-treatment control. Beyond the introduction of stochasticity, our model establishes a time-dependent viral reactivation framework that integrates periodic and random perturbations in the activation rates. Unlike conventional models that assume uniform (temporally independent reactivation), we show that latency reversal follows structured oscillatory patterns modulated by immune cycles, circadian rhythms, and transient inflammatory episodes. This finding suggests that viral rebound risk is dynamically shaped by immune fluctuations, contrary to the assumption of a constant reactivation probability. We also study the model system by incorporating Gamma-distributed waiting times to account for heterogeneity in reactivation kinetics, which in turn provides a more flexible characterization of reservoir dynamics. We believe that these insights have critical implications for HIV cure strategies.

physics.bio-ph↗
arXiv2023

Dynamics of blood cells during a routine laboratory examination

Centrifugation is a commonly performed laboratory procedure that helps to separate blood cells such as $RBCs$, $WBCs$, and platelets from plasma or serum. Although centrifugation is a routine procedure in most medical laboratories, the factors that affect the efficacy of the centrifugation process have never been studied analytically. In this paper, we examine the effect of the centrifugation time on the efficacy of the centrifugation process by studying the dynamics of the blood cells via the well-known Langevin equation or equivalently, by solving the Fokker-Plank equation. Our result depicts that the speed of the centrifuge is one of the determinant factors concerning the efficacy of the centrifugation process. As the angular speed increases, the centrifugal force steps up and as result, the particles are forced to separate from the plasma or serum. The room temperature also considerably affects the dynamics of analyse during centrifugation. Most importantly, the generation of heat during centrifugation steps up the temperature within a centrifuge and as a result, not only the stability of the sample but also mobility of analyse is affected. We show that as the centrifuge temperature steps up, the velocity of the cells as well as the displacement of the cell in the fluid decreases. We then study the dynamics of the whole blood during capillary action where in this case the blood flows upward in a narrow space without the assistance of external forces. Previous investigations show that the height that the fluid rises increases as the surface tension steps up.

physics.bio-ph↗
arXiv2022

Exact time-dependent analytical solutions for entropy production rate for a system that operates in a heat bath where its temperature varies linearly in space

The nonequilibrium thermodynamics feature of a Brownian motor is investigated by obtaining exact time-dependent solutions. This in turn enables us to investigate not only the long time property (steady-state) but also the short time the behavior of the system. The general expressions for the free energy, entropy production ${\dot e}_{p}(t)$ as well as entropy extraction ${\dot h}_{d}(t)$ rates are derived for a system that is genuinely driven out of equilibrium by time-independent force as well as by spatially varying thermal background. We show that for a system that operates between hot and cold reservoirs, most of the thermodynamics quantities approach a non-equilibrium steady state in the long time limit. The change in free energy becomes minimal at a steady state. However for a system that operates in a heat bath where its temperature varies linearly in space, the entropy production and extraction rates approach a non-equilibrium steady state while the change in free energy varies linearly in space. This reveals that unlike systems at equilibrium, when systems are driven out of equilibrium, their free energy may not be minimized. The thermodynamic properties of a system that operates between the hot and cold baths are further compared and contrasted with a system that operates in a heat bath where its temperature varies linearly in space along with the reaction coordinate. We show that the entropy, entropy production, and extraction rates are considerably larger for linearly varying temperature case than a system that operates between the hot and cold baths revealing such systems are inherently irreversible. For both cases, in the presence of load or when a distinct temperature difference is retained, the entropy $S(t)$ monotonously increases with time and saturates to a constant value as $t$ further steps up.

cond-mat.stat-mech↗