The Use of the Statistical Entropy in Some New Approaches for the Description of Biosystems

Some problems of describing biological systems with the use of entropy as a measure of the complexity of these systems are considered. Entropy is studied both for the organism as a whole and for its parts down to the molecular level. Correlation of actions of various parts of the whole organism, intercellular interactions and control, as well as cooperativity on the microlevel lead to a more complex structure and lower statistical entropy. For a multicellular organism, entropy is much lower than entropy for the same mass of a colony of unicellular organisms. Cooperativity always reduces the entropy of the system; a simple example of ligand binding to a macromolecule carrying two reaction centers shows how entropy is consistent with the ambiguity of the result in the Bernoulli test scheme. Particular attention is paid to the qualitative and quantitative relationship between the entropy of the system and the cooperativity of ligand binding to macromolecules. A kinetic model of metabolism. corresponding to Schrödinger’s concept of the maintenance biosystems by “negentropy feeding”, is proposed. This model allows calculating the nonequilibrium local entropy and comparing it with the local equilibrium entropy inherent in non-living matter.     

Stability analysis of nonautonomous difference systems with delaying arguments

We present sufficient conditions for the stability of the nonautonomous difference system , k∈Z⁺, with m?1, when the (n×n)-matrices Aj(⋅) are slowly varying coefficients. The proposed approach is based on the generalization of the “freezing” method for ordinary differential equations. The stability conditions are formulated in terms of the corresponding Cauchy's function.     

Memory Effects in High-Dimensional Systems Faithfully Identified by Hilbert–Schmidt Speed-Based Witness

A witness of non-Markovianity based on the Hilbert–Schmidt speed (HSS), a special type of quantum statistical speed, has been recently introduced for low-dimensional quantum systems. Such a non-Markovianity witness is particularly useful, being easily computable since no diagonalization of the system density matrix is required. We investigate the sensitivity of this HSS-based witness to detect non-Markovianity in various high-dimensional and multipartite open quantum systems with finite Hilbert spaces. We find that the time behaviors of the HSS-based witness are always in agreement with those of quantum negativity or quantum correlation measure. These results show that the HSS-based witness is a faithful identifier of the memory effects appearing in the quantum evolution of a high-dimensional system with a finite Hilbert space.     

Effects of the Low Frequencies of Noise on On–Off Intermittency

A bifurcating system subject to multiplicative noise can exhibit on–off intermittency close to the instability threshold. For a canonical system, we discuss the dependence of this intermittency on the Power Spectrum Density (PSD) of the noise. Our study is based on the calculation of the Probability Density Function (PDF) of the unstable variable. We derive analytical results for some particular types of noises and interpret them in the framework of on-off intermittency. Besides, we perform a cumulant expansion (N. G. van Kampen, 24, 171 (1976).) for a random noise with arbitrary power spectrum density and we show that the intermittent regime is controlled by the ratio between the departure from the threshold and the value of the PSD of the noise at zero frequency. Our results are in agreement with numerical simulations performed with two types of random perturbations: colored Gaussian noise and deterministic fluctuations of a chaotic variable. Extensions of this study to another, more complex, system are presented and the underlying mechanisms are discussed. PACS Number: 05.40.-a, 05.45.-a, 91.25.-r     

Yield drag in a two-dimensional foam flow around a circular obstacle: Effect of liquid fraction

We study the two-dimensional flow of foams around a circular obstacle within a long channel. In experiments, we confine the foam between liquid and glass surfaces. In simulations, we use a deterministic software, the Surface Evolver, for bubble details and a stochastic one, the extended Potts model, for statistics. We adopt a coherent definition of liquid fraction for all studied systems. We vary it in both experiments and simulations, and determine the yield drag of the foam, that is, the force exerted on the obstacle by the foam flowing at very low velocity. We find that the yield drag is linear over a large range of the ratio of obstacle to bubble size, and is independent of the channel width over a large range. Decreasing the liquid fraction, however, strongly increases the yield drag; we discuss and interpret this dependence.     

Adiabatic dynamics of one-dimensional classical Hamiltonian dissipative systems

A linearized plane pendulum with the slowly varying mass and length of string and the suspension point moving at a slowly varying speed is presented as an example of a simple 1D mechanical system described by the generalized harmonic oscillator equation, which is a basic model in discussion of the adiabatic dynamics and geometric phase. The expression for the pendulum geometric phase is obtained by three different methods. The pendulum is shown to be canonically equivalent to the damped harmonic oscillator. This supports the mathematical conclusion, not widely accepted in physical community, of no difference between the dissipative and Hamiltonian 1D systems.     

Complete and Nondestructive Atomic Bell‐State Analysis Assisted by Inverse Engineering

A protocol for complete and nondestructive atomic Bell‐state analysis by using inverse engineering is presented. The setups for the Bell‐state analysis contain four atoms trapped in four separated cavities, respectively. The laser pulses designed by inverse engineering help in the manipulation of the transitions of atoms in a robust manner. By using the protocol, the information for distinguishing four Bell states of two information‐carrying atoms is encoded on two auxiliary atoms. Therefore, the four Bell states can be distinguished without being destroyed by detecting the states of the two auxiliary atoms. Moreover, as shown by the numerical simulations, the protocol has high successful probabilities to distinguish four Bell states when decoherence is considered. Thus, the protocol may provide some helpful perspectives for the quantum information tasks based on Bell states.     

Collective current rectification

We consider a set of coupled underdamped ac-driven dynamical units exposed to a heat bath. The coupling scheme defines the absence/presence of certain symmetries, which in turn cause a nonzero/zero value of a mean dc-output. We discuss dynamical mechanisms of a dc-current appearance and identify current reversals with synchronization/desynchronization transitions in the collective ratchet's dynamics.     

低场磁共振系统的低噪声前置放大器研究设计

噪声前置放大器是磁共振射频接收子系统中的重要组件,它的性能优劣直接决定了最终磁共振图像的好坏.目前市场上的低噪声前置放大器大多基于中高场磁共振系统开发,而针对低场磁共振系统的很少;另外,商用低场磁共振系统的低噪声前置放大器价格相对较贵,并且多采用两级放大结构,结构复杂、调试难度大、成本相对较高.在此背景下,针对0.5 T低场磁共振设备利用Keysight公司的先进设计系统（ADS）软件对低噪声前置放大器进行研究设计,采用一级放大结构,探索电路设计与布局对放大器性能的影响.实测结果表明自主设计的低噪声前置放大器在21 MHz共振频率附近噪声系数为0.5 dB左右,增益达到了30 dB,能够满足低场磁共振应用的要求.