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It has been established for a long time that the long range van der Waals or thermal Casimir interaction between two semi-infinite dielectrics separated by a distance $H$ is screened by an intervening electrolyte. Here we show how this interaction is modified when an electric field of strength $E$ is applied parallel to the dielectric boundaries, leading to a non-equilibrium steady state with a current. The presence of the field induces a long range thermal repulsive interaction, scaling just like the thermal Casimir interaction between dielectrics without the intervening electrolyte, {\em i.e.} as $1/H^3$. At small $E$ the effect is of order $E^2$ while at large fields it saturates to an $E$ independent value. We explain the results in terms of a decoupling mechanism between the charge density fluctuations of cations and anions at large applied fields., Comment: 6 pages, 2 figures

Odd viscosity can emerge in 3D hydrodynamics when the time reversal symmetry is broken and anisotropy is introduced. Its ramifications on the stability of the prototypical Taylor-Couette flow in curved geometries have remained unexplored. Here, we investigate the effects of odd viscosity on the stability of Taylor-Couette flow under axisymmetric perturbations both analytically and numerically, deriving analytically the critical Taylor number for different odd viscosities in the narrow gap case as well as fully numerically implementing the wide gap case. We find that the odd viscosity modifies the vortex pattern by creating secondary vortices, and exerts an intriguing ``lever'' effect in the stability diagram, completely suppressing the instability of Taylor-Couette flow under axisymmetric perturbations when the odd viscosity is large, irrespective of its sign. Our findings highlight the role of odd viscosity for the rich flow patterns of the Taylor-Couette geometry and provide guidance for viscometer experiments when odd viscosity is present.

A particle driven by active self-propulsion can be subject to inhomogeneous potential fields, steering its orientation and leading to confinement and eventual trapping. Analytical treatment of capture and/or release dynamics for general steering potentials presents a challenge due to its coupling between external potential fields and intrinsic active noise. By using the projection operator method we obtain the coarse-grained Dynkin equations with orientation integrated out in the large fluctuations limit, and derive explicit analytical solutions for the mean first passage time in radially symmetric point source trapping potentials. We analyze the ensuing trapping instabilities related to a critical value of the steering potential strength below which the particle either cannot be lured into the trap, or above which it is unable to leave the trap after being lured into it.

Locomotion in segmented animals, such as annelids and myriapods (centipedes and millipedes), is generated by a coordinated movement known as metameric locomotion, which can be also implemented in robots designed to perform specific tasks. We introduce a theoretical model, based on an active directional motion of the head segment and a passive trailing of the rest of the body segments, in order to formalize and study the metameric locomotion. The model is specifically formulated as a steered Ornstein-Uhlenbeck curvature process, preserving the continuity of the curvature along the whole body filament, and thus supersedes the simple active Brownian model, which would be inapplicable in this case. We obtain the probability density by analytically solving the Fokker-Planck equation pertinent to the model. We also calculate explicitly the correlators, such as the mean-square orientational fluctuations, the orientational correlation function and the mean-square separation between the head and tail segments, both analytically either via the Fokker-Planck equation or directly by either solving analytically or implementing it numerically from the Langevin equations. The analytical and numerical results coincide. Our theoretical model can help understand the locomotion of metameric animals and instruct the design of metameric robots., Comment: 11 pages, 4 figures

Artificial stock market simulation based on agent is an important means to study financial market. Based on the assumption that the investors are composed of a main fund, small trend and contrarian investors characterized by four parameters, we simulate and research a kind of financial phenomenon with the characteristics of pyramid schemes. Our simulation results and theoretical analysis reveal the relationships between the rate of return of the main fund and the proportion of the trend investors in all small investors, the small investors' parameters of taking profit and stopping loss, the order size of the main fund and the strategies adopted by the main fund. Our work are helpful to explain the financial phenomenon with the characteristics of pyramid schemes in financial markets, design trading rules for regulators and develop trading strategies for investors., Comment: 23 pages, 11 figures, in this version we have corrected some expression errors in the previous version

Micro-droplets of soft matter solutions have different morphologies upon drying, and can finally become wrinkled, buckled or cavitated particles. We investigate the morphology evolution of a drying soft matter droplet in this work: at the early stage of drying, wrinkling or cavitation instability can occur in the droplet, depending on the comparison between the critical wrinkling and cavitation pressure; at a later stage of drying, no wrinkle will appear if cavitation happens first, while there can still be cavitation if wrinkling happens first. A three-dimensional phase diagram in the space of elastic length, gel layer thickness and weight loss is provided for illustrating these drying pathways of a soft matter droplet, which can guide future fabrications of micro-particles with desired morphologies., Comment: 13 pages, 3 figures

Despite the wide use of networks as a versatile tool for exploring complex social systems, little is known about how to detect and forecast abrupt changes in social systems. In this report, we develop an early warning approach based on network properties to detect such changes. By analysing three collaborative social networks---one co-stardom, one patent and one scientific collaborative network, we discover that abrupt transitions inherent in these networks can serve as a good early warning signal, indicating, respectively, the dissolution of the Soviet Union, the emergence of the "soft matter" research field, and the merging of two scientific communities. We then develop a clique growth model that explains the universal properties of these real networks and find that they belong to a new universality class, described by the Gumbel distribution.

We point out that the electroweak fine-tuning problem in the supersymmetric Standard Models (SSMs) is mainly due to the high energy definition of the fine-tuning measure. We propose super-natural supersymmetry which has an order one high energy fine-tuning measure automatically. The key point is that all the mass parameters in the SSMs arise from a single supersymmetry breaking parameter. In this paper, we show that there is no supersymmetry electroweak fine-tuning problem explicitly in the Minimal SSM (MSSM) with no-scale supergravity and Giudice-Masiero (GM) mechanism. We demonstrate that the $Z$-boson mass, the supersymmteric Higgs mixing parameter $\mu$ at the unification scale, and the sparticle spectrum can be given as functions of the universal gaugino mass $M_{1/2}$. Because the light stau is the lightest supersymmetric particle (LSP) in the no-scale MSSM, to preserve $R$ parity, we introduce a non-thermally generated axino as the LSP dark matter candidate. We estimate the lifetime of the light stau by calculating its 2-body and 3-body decays to the LSP axino for several values of axion decay constant $f_a$, and find that the light stau has a lifetime $\tau_{\tilde \tau_1}$ in $[10^{-4},100]$ s for an $f_a$ range $[10^{9},10^{12}]$ GeV. We show that our next to the LSP stau solutions are consistent with all the current experimental constraints, including the sparticle mass bounds, B-physics bounds, Higgs mass, cosmological bounds, and the bounds on long-lived charge particles at the LHC., Comment: 32 pages,10 figures and 1 table