Conservative Forces Research Articles

Unified theory of thermodynamics and stochastic thermodynamics for nonlinear Langevin systems driven by non-conservative forces

We construct a unified theory of thermodynamics and stochastic thermodynamics for classical nonequilibrium systems driven by non-conservative forces, using the recently developed covariant Ito-Langevin theory. The thermodynamic forces are split into a conservative part and a non-conservative part. Thermodynamic functions are defined using the reference conservative system. Work and heat are partitioned into excess parts and house-keeping parts, which are due to, respectively, conservative forces and non-conservative forces. Excess entropy production (EP) and house-keeping EP are analogously defined. The splitting of thermodynamic forces is subjected to an arbitrariness resembling a gauge symmetry, with each gauge defining a reference conservative Langevin system. In the special Gibbs gauge, the nonequilibrium steady state (NESS) is characterized by Gibbs canonical distribution, the excess heat agrees with that defined by Hatano and Sasa, and the excess EP agrees with that of Glansdorff and Prigogine, i.e., it is the time rate of the second-order variation of system entropy near the NESS. Adopting the Gibbs gauge, and focusing on the excess parts of thermodynamic quantities, a complete analogy between thermodynamics of non-conservative systems and that of conservative systems is established. One important consequence of this analogy is that both the free energy and excess EP are minimized at NESS. Our theory therefore constitutes a statistical foundation both for the steady-state thermodynamics theory due to Sasa and Tasaki and for the stability theory of NESS due to Glansdorff and Prigogine. These results are valid even if the system is far from equilibrium. By studying detailed fluctuation theorem, we find striking differences between systems with symmetric kinetic matrices and those with asymmetric kinetic matrices. For systems with asymmetric kinetic matrices, the total EP is the sum of house-keeping EP, excess EP, and pumped entropy. Entropy pumping is an exchange of entropy between the system and environment without necessarily involving dissipation. In the presence of entropy pumping, the system may behave as either a demon or an antidemon. Fluctuation theorems and work relations are derived both for total work and for excess work. For systems with symmetric kinetic matrices, there is no entropy pumping, yet in the Gibbs gauge, the excess work and house-keeping work each satisfies a separate fluctuation theorem. We illustrate our theory using many concrete examples.

Emergence of negative viscosities and colored noise under current-driven Ehrenfest molecular dynamics

Molecules in molecular junctions are subject to current-induced forces that can break chemical bonds, induce reactions, destabilize molecular geometry, and halt the operation of the junction. Theories behind current-driven molecular dynamics simulations rely on a perturbative time-scale separation within the system with subsequent use of nonequilibrium Green's functions (NEGF) to compute conservative, non-conservative, and stochastic forces exerted by electrons on nuclear degrees of freedom. We analyze the effectiveness of this approximation, paying particular attention to the phenomenon of negative viscosities. The perturbative approximation is directly compared to the nonequilibrium Ehrenfest approach. We introduce a novel time-stepping approach to calculate the forces present in the Ehrenfest method via exact integration of the equations of motion for the nonequilibrium Green's functions, which does not necessitate a time-scale separation within the system and provides an exact description for the corresponding classical dynamics. We observe that negative viscosities are not artifacts of a perturbative treatment but also emerge in Ehrenfest dynamics. However, the effects of negative viscosity have the possibility of being overwhelmed by the predominantly positive dissipation due to the higher-order forces unaccounted for by the perturbative approach. Additionally, we assess the validity of the white-noise approximation for the stochastic forces, finding that it is justifiable in the presence of a clear time-scale separation and is more applicable when the current-carrying molecular orbital is moved outside of the voltage window. Finally, we demonstrate the method for molecular junction models consisting of one and two classical degrees of freedom.

“Oops, I didn’t know we couldn’t talk about sex”: Sex researchers talking back to the erotophobic academy using the researcher’s erotic subjectivitiesGuest editorial themed section ‘the researcher’s erotic subjectivities’

A proliferation of research outputs in recent years that takes into account the erotic subjectivities of the researcher seems to suggest that both research on sexuality and the inclusion of the desiring researcher’s body in academic writings have become accepted as valuable and relevant academic research topics and methods. Yet, the often animated and at times uncomfortable discussions these academic interventions generate—also beyond academic settings—attest to the enduring sensitivity that comes with (discussing) the researcher’s sex and sexuality. This special section aims to provide a space to explore the methodological, ethical, and epistemological implications of (i) the researcher’s immersion in or withdrawal from sexual/ized interactions, and (ii) reflexively reporting about the researcher’s erotic subjectivities in scholarly outputs such as journal articles or conference presentations. In doing so, it not only critiques current academic structures and a masculinist politics of science that are at best not equipped to take into account the complexities of (auto-)ethnographic sex research. It also turns a critical eye towards the blind spots we might have as sex researchers towards the differential power relations with different actors involved in (auto-) ethnographic research that explicitly deals with the researcher’s erotic subjectivities. Reducing those blind spots will make us less vulnerable to gratuitous comments by the erotophobic academy as well as the increasing conservative societal forces who are all too eager to delegitimize our academic writings, while exploring the complexities of (auto-) ethnographic sex research aims to increase the rigour of our work. By talking back, we aim to advance conversations on the methodological, ethical and epistemological implications of taking seriously the researcher’s erotic subjectivities in our research endeavours.

Unified theory of spin and charge in a ferromagnet

We derive a unified theory of spin and charge degrees of freedom in a ferromagnet. The spin-transfer torque and spin electromotive force are examined from the coarse-grained perspective of collective coordinates. The resulting equations of motion reflect a balance of conservative, gyroscopic (Berry-phase), and dissipative forces. We then expand the space of collective coordinates by adding the electric charge. The adiabatic spin-transfer torque and spin electromotive force (emf) turn out to be a gyroscopic force; their nonadiabatic counterparts are a dissipative force.

Hybrid mode atomic force microscopy of phase modulation and frequency modulation.

We propose hybrid phase modulation (PM)/frequency modulation (FM) atomic force microscopy (AFM) to increase the imaging speed of AFM in high-Q environments. We derive the relationship between the phase shift, the frequency shift and the tip-sample interaction force from the equation of motion for the cantilever in high-Q environments. The tip-sample conservative force is approximately given by the sum of the conservative force with respect to the phase shift in the PM mode and that with respect to the frequency shift in the FM mode. We preliminarily demonstrate that the hybrid PM/FM-AFM is a new and very promising AFM operation mode that can increase imaging speed.

Социально-политическая повестка итальянских правых – «Братья Италии»: между консерватизмом и популизмом

The article analyzes the political agenda of one of the fast growing political parties in Italy – «Fratelli d'Italia». The migration crisis in Europe in 2015–2016, climate change, the so-called Arab Spring and regime change in Libya have sharply raised the issue of regulating migration flows to Europe, actualized the issue of finding consensus among the countries of the European Union on the issue of accepting refugees. The main consequence is changes in the political field and the increasing influence of right-wingers and conservative political forces and movements. Anti-immigration rhetoric is used both by right wing parties and movements, and is partially intercepted by the ruling parties, as it was in Germany, Austria, France, and to the full extent in Italy. Italy has the most difficult situation with migration and reception of refugees. In the 2018 elections, the largest result was obtained by a coalition of center-right parties, including the «League» (formerly – «League of the North»), «Forward, Italy!» by former Italian Prime Minister Silvio Berlusconi and the ultra-right party «Brothers of Italy», which received a rather modest result of 4–5% of the vote. The coalition owes much of its electoral result to the «League» with its flamboyant anti-migrant and Eurosceptic rhetoric. In 2019–2020, the rhetoric of the «League» began to seem more moderate, and after the reformation of the Italian government, the «Brothers of Italy» did not join the new coalition, remaining in opposition, continuing its policy, including sharp anti-immigration. Currently, according to opinion polls, the rating of «Brothers of Italy» has begun to grow significantly, showing results of 18%–20%, which makes it an object of research for scientists interested in political movements, parties and political science in general.

Moving to the Right? How the Conservative Movement Has Shaped American Legal Education

The American legal academy has witnessed intense ideological assaults in recent decades, as political conservatives have sought to recast legal education and produce a different kind of legal professional. However, the paths by which conservatives have approached the law schools differ. Some conservative campaigns to remake American legal education have highlighted their ideological agenda, whereas other campaigns have taken steps to keep their ideological goals hidden. This review illustrates both strategies but dedicates special attention to conservative forces that have pursued the latter strategy of ideological concealment.

การสร้างแบบทดสอบวินิจฉัยมโนทัศน์ที่คลาดเคลื่อนแบบสี่ชั้นวิชาฟิสิกส์ เรื่อง งานและพลังงานสำหรับนักเรียนระดับชั้นมัธยมศึกษาปีที่ 4 สำนักงานเขตพื้นที่การศึกษามัธยมศึกษาเขต 18

This research aimed to 1) construct the four-tier diagnostic test for detecting the physics Misconceptions on work and energy of motion for the  grade students, 2) to validate the difficulty, the discrimination, the validity and the reliability of the test, 3) detecting physics misconceptions, and 4) to create the teacher manual of the test. The sample of the research was selected by stratified random sampling technique. The sample consisted of 701 students who studied in  and  grade of schools under Chon Buri–Rayong Secondary Educational Service Area Office. The research instrument was a 20-item of four–tier diagnostic test for detecting the physics misconceptions in work and energy.The research findings revealed that diagnostic test met the requirements of content validity with IOC indices which ranged between 0.80 and 1.00. The construct validity was between 0.72 and 0.95. The difficulty of all items ranged between 0.38 and 0.44. The discrimination index was calculated by Whitney and Sabers which ranged between 0.50 and 0.63. The reliability of the test according to Livingston Method ranged from 0.91 to 0.97. The cutting score calculated by Angoff Methed was 13 points from 20 points. The diagnostic test results showed that all most of the students had correct conception in power, did not understand the concept in meaning of kinetic energy, misconceived in power transform of the law of conservation and error in the meaning of conservation forces.

Stochastic motion in phase space on a surface of constant energy.

We study closed systems of particles that are subject to stochastic forces in addition to the conservative forces. The stochastic equationsof motion are set up in such a way that the energy is strictly conserved at all times. To ensure this conservation law, the evolution equation for the probability density is derived using an appropriate interpretation of the stochastic equationof motion that is not the Itô nor the Stratonovic interpretation. The trajectories in phase space are restricted to the surface of constant energy. Despite this restriction, the entropy is shown to increase with time, expressing irreversible behavior and relaxation to equilibrium. This main result of the present approach contrasts with that given by the Liouville equation, which also describes closed systems, but does not show irreversibility.

Eigenvalue analysis of planar linear multibody system under conservative force based on the transfer matrix method

AbstractThe linear multibody system transfer matrix method (LMSTMM) provides a powerful tool for analyzing the vibration characteristics of a mechanical system. However, the original LMSTMM cannot resolve the eigenvalues of the systems with ideal hinges (i.e., revolute hinge, sliding hinge, spherical hinge, cylindrical hinge, etc.) or bodies under conservative forces due to the lack of the corresponding transfer matrices. This paper enables the LMSTMM to solve the eigenvalues of the planar multibody systems with ideal hinges or rigid bodies under conservative forces. For a rigid body, the transfer matrix can now consider coupling terms between forces and kinematic state perturbations. Also, conservative forces that contribute to the eigenvalues can be considered. Meanwhile, ideal hinges are introduced to LMSTMM, which enables the treatment of eigenvalues of general multibody systems using LMSTMM. Finally, the comparative analysis with ADAMS software and analytical solutions verifies the effectiveness of the proposed approach in this paper.

Structural lubricity of physisorbed gold clusters on graphite and its breakdown: Role of boundary conditions and contact lines.

The sliding motion of gold slabs adsorbed on a graphite substrate is simulated using molecular dynamics. The central quantity of interest is the mean lateral force, that is, the kinetic friction rather than the maximum lateral forces, which correlates with the static friction. For most setups, we find Stokesian damping to resist sliding. However, velocity-insensitive (Coulomb) friction is observed for finite-width slabs sliding parallel to the armchair direction if the bottom-most layer of the three graphite layers is kept at zero stress rather than at zero displacement. Although the resulting kinetic friction remains much below the noise produced by the erratic fluctuations of (conservative) forces typical for structurally lubric contacts, the nature of the instabilities leading to Coulomb friction could be characterized as quasi-discontinuous dynamics of the Moiré patterns formed by the normal displacements near a propagating contact line. It appears that the interaction of graphite with the second gold layer is responsible for the symmetry break occurring at the interface when a contact line moves parallel to the armchair rather than to the zigzag direction.

Tunable light-induced dipole-dipole interaction between optically levitated nanoparticles.

Arrays of optically trapped nanoparticles have emerged as a platform for the study of complex nonequilibrium phenomena. Analogous to atomic many-body systems, one of the crucial ingredients is the ability to precisely control the interactions between particles. However, the optical interactions studied thus far only provide conservative optical binding forces of limited tunability. In this work, we exploit the phase coherence between the optical fields that drive the light-induced dipole-dipole interaction to couple two nanoparticles. In addition, we effectively switch off the optical interaction and observe electrostatic coupling between charged particles. Our results provide a route to developing fully programmable many-body systems of interacting nanoparticles with tunable nonreciprocal interactions, which are instrumental for exploring entanglement and topological phases in arrays of levitated nanoparticles.

Philanthropy and the sustaining of global elite university domination

How is it that global elite universities operating in a hyper-competitive world replete with aspirational challengers maintain positions of dominance within the field of higher education decade after decade? Taking a Bourdieusian approach, we argue that the highest-ranking universities strategically leverage pronounced philanthropic advantages to differentiate themselves from would-be challengers. Philanthropy is a critical differentiator because it enables elite universities to sustain privileges that attract highly qualified students, faculty and powerful supporters, who in turn boost their competitive positions through acquisition of valuable cultural, social and symbolic resources. Elite universities co-create with stakeholders strong bonds of identification, honing the disposition to give back philanthropically and complete the socially reproductive cycle of elite domination. At a time of increasing concern about social inequalities, our contribution is to uncover how higher education philanthropy – an essentially conservative force – operates to entrench privilege and magnify social differences while purporting to do the opposite.

Women, Peace and Security National Action Plans in anti-gender governments: The cases of Brazil and Poland

AbstractIn recent years, Brazil and Poland have elected governments that are sceptical of both the liberal international order and gender. In both cases, contemporary administrations have bolstered the pre-existing anti-gender offensive of religious and secular conservative forces and converted this into legislation and public policy. Yet, at the same time, both have also created National Action Plans around the UN's Women, Peace and Security agenda. Why is this the case? Why do two governments that see gender as an ‘ideology’ continue to work on WPS? Using a feminist institutionalist framework, this article draws on content analysis of the NAPs and semi-structured in-depth interviews with stakeholders in Brazil and Poland to explore this puzzle. We argue that the WPS agenda has survived in these political contexts due the presence of key ‘femocrats’ within the state; the influence of international institutions; and the symbolic power that the WPS agenda gives to these countries on the world stage. As such, the article makes a key contribution to the literature on the WPS agenda and also bolsters the argument for a complication of the idea of gender ‘backlash’ – in domestic and international audiences, states are willing to adopt different attitudes to gender if it furthers their interests.

Linear stochastic thermodynamics

We study the thermodynamics of open systems weakly driven out-of-equilibrium by nonconservative and time-dependent forces using the linear regime of stochastic thermodynamics. We make use of conservation laws to identify the potential and nonconservative components of the forces. This allows us to formulate a unified near-equilibrium thermodynamics. For nonequilibrium steady states, we obtain an Onsager theory ensuring nonsingular response matrices that is consistent with phenomenological linear irreversible thermodynamics. For time-dependent driving protocols that do not produce nonconservative forces, we identify the equilibrium ensemble from which Green–Kubo relations are recovered. For arbitrary periodic drivings, the averaged entropy production (EP) is expressed as an independent sum over each driving frequency of non-negative contributions. These contributions are bilinear in the nonconservative and conservative forces and involve a novel generalized Onsager matrix that is symmetric. In the most general case of arbitrary time-dependent drivings, we advance a novel decomposition of the EP rate into two non-negative contributions—one solely due to nonconservative forces and the other solely due to deviation from the instantaneous steady-state—directly implying a minimum EP principle close to equilibrium. This setting reveals the geometric structure of near-equilibrium thermodynamics and generalizes previous approaches to cases with nonconservative forces.

Robotic swimming in curved space via geometric phase

Locomotion by shape changes or gas expulsion is assumed to require environmental interaction, due to conservation of momentum. However, as first noted in [J. Wisdom, Science 299, 1865-1869 (2003)] and later in [E. Guéron, Sci. Am. 301, 38-45 (2009)] and [J. Avron, O. Kenneth, New J. Phys, 8, 68 (2006)], the noncommutativity of translations permits translation without momentum exchange in either gravitationally curved spacetime or the curved surfaces encountered by locomotors in real-world environments. To realize this idea which remained unvalidated in experiments for almost 20 y, we show that a precision robophysical apparatus consisting of motors driven on curved tracks (and thereby confined to a spherical surface without a solid substrate) can self-propel without environmental momentum exchange. It produces shape changes comparable to the environment's inverse curvatures and generates movement of [Formula: see text]cm per gait. While this simple geometric effect predominates over short time, eventually the dissipative (frictional) and conservative forces, ubiquitous in real systems, couple to it to generate an emergent dynamics in which the swimming motion produces a force that is counter-balanced against residual gravitational forces. In this way, the robot both swims forward without momentum and becomes fixed in place with a finite momentum that can be released by ceasing the swimming motion. We envision that our work will be of use in a broad variety of contexts, such as active matter in curved space and robots navigating real-world environments with curved surfaces.

A Multiresolution Discrete Element Method for Triangulated Objects with Implicit Time stepping

Simulations of many rigid bodies colliding with each other sometimes yield particularly interesting results if the colliding objects differ significantly in size and are non-spherical. The most expensive part within such a simulation code is the collision detection. We propose a family of novel multiscale collision detection algorithms that can be applied to triangulated objects within explicit and implicit time stepping methods. They are well-suited to handle objects that cannot be represented by analytical shapes or assemblies of analytical objects. Inspired by multigrid methods and adaptive mesh refinement, we determine collision points iteratively over a resolution hierarchy, and combine a functional minimisation plus penalty parameters with the actual comparision-based geometric distance calculation. Coarse surrogate geometry representations identify "no collision" scenarios early on and otherwise yield an educated guess which triangle subsets of the next finer level potentially yield collisions. They prune the search tree, and furthermore feed conservative contact force estimates into the iterative solve behind an implicit time stepping. Implicit time stepping and non-analytical shapes often yield prohibitive high compute cost for rigid body simulations. Our approach reduces these cost algorithmically by one to two orders of magnitude. It also exhibits high vectorisation efficiency due to its iterative nature.

A numerical investigation of 3D structural behaviour for steel-composite structures under various travelling fire scenarios

In performance-based structural fire engineering, “travelling fires” is being gradually accepted as an important fire boundary condition. However, its application is still limited by uncertainties in the selection of different design travelling fire parameters, resulting from the lack of relevant experimental data and corresponding validated structural finite element models which can be used with advanced travelling fire methodologies, e.g. the Extended Travelling Fire Methodology (ETFM) framework. This paper aims to fill this gap through modelling a prototype steel-composite floor structure (representing a “slice” of a large open-plan office), to investigate its true structural response under a wide range of travelling fire scenarios, with an emphasis on considering the effect of concrete slab in a 3D finite element model, using LS-DYNA. To ensure the credibility of this numerical study, the model was first validated against the experimental data of the structural response from the Veselí Travelling Fire Test. In the parametric studies, 32 cases were examined to investigate the thermal and structural response, related to the selection of key design parameters for travelling fires (i.e. fire spread rates, fuel load densities and inverse opening factors (IOF)); fire protection (i.e. different fire protection schemes and required fire resistance rating (FRR)), and the effect of slab specification (i.e. thicknesses and steel reinforcements).It was found that solely satisfying the critical temperature and deflection criteria for the structural members might not guarantee a sufficient structural design for travelling fire scenarios, and it is suggested that the steel stress utilisation should also be examined. Compared with the IOF, it appears that the selection of fire spread rates and fuel load densities are likely to be more critical in identifying the worst travelling fire scenario for the structural response with fire protection. Moreover, the global structural response under travelling fire is also affected by the combination of fire protection (i.e. equivalent FRR in this paper) and fire spread rate. Under a “slow” travelling fire (e.g. 0.5 mm/s) with increasing FRR, the failure of structural elements during the cooling phase was prevented effectively; however, under a relatively “fast” travelling fire (e.g. 2.5 mm/s, 12.5 mm/s), increasing FRR may not always improve the fire performance of the structure. This work also indicates that steel reinforcement ratio has a greater influence on structural response than slab thickness under travelling fires. Furthermore, the 3D finite element model is very important for structural fire analysis, not only due to the more conservative internal force captured by the 3D model (i.e. reduced by over 80 % on the 2D model in our case) thereby reproducing the collapse triggered by the failure of the connection under fire in general, but also the 3D model was able to better represent the deflection and the “internal force reversal” caused by travelling fires.

Dynamical analog spacetimes in nonrelativistic flows

Analogue gravity models describe linear fluctuations of fluids as a massless scalar field propagating on stationary acoustic spacetimes constructed from the background flow. In this paper, we establish that this paradigm generalizes to arbitrary order nonlinear perturbations propagating on dynamical analogue spacetimes. Our results hold for all inviscid, spherically symmetric and barotropic non-relativistic flows in the presence of an external conservative force. We demonstrate that such fluids always admit a dynamical description governed by a coupled pair of wave and continuity equations. We provide an iterative approach to solve these equations about any known stationary solution to all orders in perturbation. In the process, we reveal that there exists a dynamical acoustic spacetime on which fluctuations of the mass accretion rate propagate. The dynamical acoustic spacetime is shown to have a well defined causal structure and curvature. In addition, we find a classical fluctuation relation for the acoustic horizon of the spacetime that admit scenarios wherein the horizon can grow as well as recede, with the latter being a result with no known analogue in black holes. As an example, we numerically investigate the Bondi flow accreting solution subject to exponentially damped time dependent perturbations. We find that second and higher order classical perturbations possess an acoustic horizon that oscillates and changes to a new stable size at late times. In particular, the case of a receding acoustic horizon is realized through `low frequency' perturbations. We discuss our results in the context of more general analogue models and its potential implications on astrophysical accretion flows.

The impact of green credit policy on enterprise risk-taking: an empirical test based on DID

Green finance is a driving force for energy conservation and green development. Based on the "Green Credit Guidelines" policy issued by China Banking Regulatory Commission (CBRC) in 2012 as a quasi-natural experiment, combined with the financial data of Chinese listed companies from 2008 to 2016, we constructed a DID model to study the impact of green credit as a financial instrument on enterprise risk taking. The results show that green credit can significantly improve enterprise risk taking level. This effect is more effective for state-owned enterprises, enterprises with flexible strategies and enterprises with high information transparency. Furthermore, mechanism analysis indicates that green credit can increase enterprise risk taking level by restraining the inefficient investment behavior and stimulating the endogenous power of enterprises' innovation.