Asters, vortices, and rotating spirals in active gels of polar filaments

We develop a general theory for active viscoelastic materials made of polar filaments. This theory is motivated by the dynamics of the cytoskeleton. The continuous consumption of a fuel generates a nonequilibrium state characterized by the generation of flows and stresses. Our theory applies to any polar system with internal energy consumption such as active chemical gels and cytoskeletal networks which are set in motion by active processes at work in cells.     

扬声器线阵列高频波导有效辐射率的测量方法

研究了一种获取扬声器线阵列高频波导有效辐射率的简单可靠的方法。利用乘积理论和菲涅尔原理,得出在副瓣角度处扬声器线阵列与单节高频波导的垂直指向性相等,且均与其有效辐射率呈sinc函数的简单关系。按照此理论,通过实验测量单节高频波导单元的指向性,得到线阵列的有效辐射率平均值为82.5%,并测量整个线阵列进行验证实验,计算均方误差为0.051。结果表明,该方法可以快速得到阵列的有效辐射率,且准确度高。      

Investigations of range accuracy for long-range three-dimensional active imaging

Distance resolutions and noises are analyzed experimentally for long-range three-dimensional (3D) active imaging systems that have signal-to-noise ratios (SNRs) more optimal than 30:1. Findings indicate that the photon shot noise primarily determines the SNR. However, the active imaging method, which has a relatively low SNR, generates a relatively high distance resolution. To explain this phenomenon, a theory in which the distance resolution of 3D active imaging systems is determined by both the photon shot noise and the subinterval width is developed. Theoretical and experimental results differ by less than 4%.     

Swimming in external fields

Microswimmers move autonomously but are subject to external fields, which influence their swimming path and their collective dynamics. With three concrete examples we illustrate swimming in external fields and explain the methodology to treat it. First, an active Brownian particle shows a conventional sedimentation profile in a gravitational field but with increased sedimentation length and some polar order along the vertical. Bottom-heavy swimmers are able to invert the sedimentation profile.Second, active Brownian particles interacting by hydrodynamic flow fields in a three-dimensional harmonic trap can spontaneously break the isotropic symmetry. They develop polar order, which one can describe by mean-field theory reminiscent to Weiss theory of ferromagnetism, and thereby pump fluid.Third, a single microswimmer shows interesting non-linear dynamics in Poiseuille flow including swinging and tumbling trajectories. For pushers, hydrodynamic interactions with bounding surfaces stabilize either straight swimming against the flow or tumbling close to the channel wall, while pushers always move on a swinging trajectory with a specific amplitude as limit cycle.     

Theory of collision effects on atomic and molecular line shapes

A review of recent developments in the theory of the effects of binary collisions on the spectral profiles associated with atomic and molecular systems is presented. To consistently account for collisional perturbations of both the internal energy levels and the velocity of active (emitting or absorbing) atoms or molecules, one must use a theory in which the center-of-mass motion of the active atoms has been quantized. Following this procedure general equations for absorption or emission line shapes are obtained. The line shapes may exhibit narrowing or broadening with increasing perturber pressure, depending upon the nature of the collision interaction. The physical significance of the collision mechanisms giving rise to such behavior is discussed, as is the experimental evidence in support of the theory. Various applications of the theory are presented.     

Waves in an active medium guided by a reactive surface with reactance of gain modulation

The characteristics of surface waves (i) in a passive medium supported by a passive surface with reactance modulation and an active surface with the modulation of either the reactance or the negative resistance, and (ii) in an active medium supported by a passive surface with a reactance modulation are investigated with emphasis on the band regions. The periodic variation is sinusoidal and is in the propagation direction. For a passive medium terminated by a passive surface with a reactance modulation, there are stop bands in frequency for the surface waves and the structure of the first two stop bands is analyzed. For a passive medium terminated by an active surface and for an active medium terminated by a reactance-modulated passive surface, the characteristics of the absolute instabilities occurring in the first-order band are examined. The nature of the convective instability taking place in the second-order band for an active medium terminated by a reactance-modulated surface is discussed. Analytical expressions for the frequency shift of the second-order band are deduced. The Floquet theory is used to obtain the exact dispersion relation in the form of a continued fraction which is analyzed by singular expansions.     

Accessing Active Inference Theory through Its Implicit and Deliberative Practice in Human Organizations

Active inference theory (AIT) is a corollary of the free-energy principle, which formalizes cognition of living system’s autopoietic organization. AIT comprises specialist terminology and mathematics used in theoretical neurobiology. Yet, active inference is common practice in human organizations, such as private companies, public institutions, and not-for-profits. Active inference encompasses three interrelated types of actions, which are carried out to minimize uncertainty about how organizations will survive. The three types of action are updating work beliefs, shifting work attention, and/or changing how work is performed. Accordingly, an alternative starting point for grasping active inference, rather than trying to understand AIT specialist terminology and mathematics, is to reflect upon lived experience. In other words, grasping active inference through autoethnographic research. In this short communication paper, accessing AIT through autoethnography is explained in terms of active inference in existing organizational practice (implicit active inference), new organizational methodologies that are informed by AIT (deliberative active inference), and combining implicit and deliberative active inference. In addition, these autoethnographic options for grasping AIT are related to generative learning.     

Overcoming the shot-noise limitation of three-dimensional active imaging

Depth resolution is limited by the photoelectron shot noise in conventional gain-modulated active three-dimensional (3D) imaging methods. A proposed method, which is based on photon intensity correlation, is presented to overcome the depth resolution limitation. The signal photons are amplified by an imaging intensifier, and are then divided into two beams by a beam splitter. The theory shows that the shot-noise limitation is broken using the strong intensity coherence between the two beams. The experiment results show that the depth resolution of the correlated active 3D imaging method is three times better than that of the shot-noise limitation.     

Multireference second-order Brillouin–Wigner perturbation theory§

The multireference, state-specific, second-order, Brillouin–Wigner perturbation theory (MR-BWPT2) is presented. A posteriori corrections are made which, in the case of a single reference function, recover the well-known formula of second-order many-body perturbation theory, i.e. Møller–Plesset ‘MP2’ theory, and in the multireference case suppress terms which scale non-linearly with the number of electrons in the system. Prototype calculations are reported for the (H₂)₄ model in which the degree of quasi-degeneracy can be varied by changing a single geometric parameter. The calculated total energies obtained by a second-order Brillouin–Wigner treatment are compared with those supported by CAS-MP2 (complete active space self-consistent field followed by second-order Møller–Plesset-like treatment of dynamic correlation effects), by MR-BWCC (multireference Brillouin–Wigner coupled cluster expansion), and by full configuration interaction. MR-BWPT2 provides a theoretical apparatus comparable to the widely used MP2 theory, but which can be applied to quantum chemical problems requiring a multireference formalism.     

The stochastic bifurcation behaviour of speculative financial markets

This paper establishes a continuous-time stochastic asset pricing model in a speculative financial market with fundamentalists and chartists by introducing a noisy fundamental price. By application of stochastic bifurcation theory, the limiting market equilibrium distribution is examined numerically. It is shown that speculative behaviour of chartists can cause the market price to display different forms of equilibrium distributions. In particular, when chartists are less active, there is a unique equilibrium distribution which is stable. However, when the chartists become more active, a new equilibrium distribution will be generated and become stable. The corresponding stationary density will change from a single peak to a crater-like density. The change of stationary distribution is characterized by a bimodal logarithm price distribution and fat tails. The paper demonstrates that stochastic bifurcation theory is a useful tool in providing insight into various types of financial market behaviour in a stochastic environment.     

Optical design and active optics methods in astronomy

Optical designs for astronomy involve implementation of active optics and adaptive optics from X-ray to the infrared. Developments and results of active optics methods for telescopes, spectrographs and coronagraph planet finders are presented. The high accuracy and remarkable smoothness of surfaces generated by active optics methods also allow elaborating new optical design types with high aspheric and/or non-axisymmetric surfaces. Depending on the goal and performance requested for a deformable optical surface analytical investigations are carried out with one of the various facets of elasticity theory: small deformation thin plate theory, large deformation thin plate theory, shallow spherical shell theory, weakly conical shell theory. The resulting thickness distribution and associated bending force boundaries can be refined further with finite element analysis.     

A theoretical study of the 21Ag ← 11Ag two-photon transition and its vibronic band in trans-stilbene

The two-photon spectrum of the 2¹A_g ← 1¹A_g transition in trans-stilbene has been calculated at the complete active space self-consistent field (CASSCF) level of theory. Energies were obtained at the complete active space second-order perturbation (CASPT2) level of theory, while the geometries of both the initial and final states were optimized at the CASSCF level. The energy and the geometry optimizations were performed using an active space of 14 electrons in 14 active π orbitals. The vibrational frequencies of both states and the two-photon transition (TPT) cross-section were calculated with a smaller active space where the two lowest π orbitals were kept inactive. A newly implemented algorithm, in the quantum chemical package Molcas was used to determine the two-photon transition intensity. This method requires only the linear response of the CASSCF wavefunction. Furthermore, the vibronic structure of this TPT was studied. The Franck-Condon factors were obtained by calculating the overlap between the vibrational states involved, which were determined from the force fields of both the initial and final states, at the CASSCF level of theory. The results are in agreement with experiment.     

The Markov blanket trick: On the scope of the free energy principle and active inference

The free energy principle (FEP) has been presented as a unified brain theory, as a general principle for the self-organization of biological systems, and most recently as a principle for a theory of every thing. Additionally, active inference has been proposed as the process theory entailed by FEP that is able to model the full range of biological and cognitive events. In this paper, we challenge these two claims. We argue that FEP is not the general principle it is claimed to be, and that active inference is not the all-encompassing process theory it is purported to be either. The core aspects of our argumentation are that (i) FEP is just a way to generalize Bayesian inference to all domains by the use of a Markov blanket formalism, a generalization we call the Markov blanket trick; and that (ii) active inference presupposes successful perception and action instead of explaining them.     

Stochastic resonance for adhesion of membranes with active stickers

The behavior of two membranes that interact by active adhesion molecules or stickers is studied theoretically using mean-field theory and Monte Carlo simulations. The stickers are anchored in one of the membranes and undergo conformational transitions between on and off states. In their on states, the stickers can bind to ligands that are anchored in the other membrane. The transitions between the on and off states arise from the coupling of the stickers to some active, energy-releasing process, which keeps the system out of equilibrium. As one varies the transition rates of this active process, the membrane separation undergoes a stochastic resonance: this separation is maximal at intermediate rates of the sticker transitions and considerably smaller both at high and at low transition rates. This implies that the effective, fluctuation-induced repulsion between the membranes contains a rate-dependent contribution that arises from the switching of the active stickers.     

实验室中傅里叶望远术频谱抽取方式

傅里叶望远术是一种主动式的高分辨率成像技术,它使用激光发射阵列产生的干涉条纹场去照射目标,然后用探测器接收回波信号,再对回波信号作相应处理重构出目标图像.在实验室验证实验中,抽取目标频谱的干涉条纹不是由发射阵列产生的,而是通过改变光束位置的方式获得.对直线干涉条纹抽取目标频谱的原理进行了论述,并提出了一种新的光束移动方...     

洛伦兹-哈肯激光混沌系统有限时间稳定主动控制方法研究

研究了洛伦兹-哈肯激光混沌系统基于主动控制方法的有限时间稳定问题. 在研究Terminal 吸引子的基础上, 考虑系统不确定性, 提出一种基于Terminal 吸引子且具有动态主动补偿特性的主动控制方法, 使受控洛伦兹-哈肯激光混沌系统近似实现有限时间稳定.同时, 为解决系统不确定性问题, 设计了一种新的观测器, 并使这种观测器能在很短时间内跟踪系统的不确定性.通过引入奇异扰动性理论, 详细地分析了闭环系统近似有限时间稳定性.仿真实验结果验证了该主动控制方法及观测器的有效性.     

Microscopic modelling of bulk and quantum-well GaAs-based semiconductor lasers

The dynamical behaviour of Fabry-Perot type semiconductor lasers is modelled, including the relevant many-body Coulomb effects of the excited carriers. Conditions are given under which a parametrization of the full model is possible, allowing simple analytic relations for local gain, refractive index and linewidth enhancement factor. The parameters of the simplified model are uniquely determined by the microscopic theory and have to be optimized for the respective operating conditions. The theory is evaluated for bulk and quantum-well GaAs active material and a variety of laser structures, including strongly and weakly index-guided structures, as well as purely guided single-and twin-stripe lasers.     

A new theory of the solid-state growth of embryos during nucleation: the fundamental role of interfacial mobility

One of the major challenges in nucleation theory is to explain the kinetic pathway allowing multicomponent precipitates to grow until they reach stability. This problem is particularly challenging when the supersaturation is low, so that the critical size of nucleation is large and requires the condensation of thousands of atoms. A new theory is proposed to explain the growth of embryos before they reach the critical size of nucleation. This theory is not a substitute of the classical nucleation theory, but a complement aiming to understand the kinetic pathway allowing unstable embryos to grow at the expense of their neighbours. The theory stands on the strong interactions between embryos. The latter may exchange atoms via impingement and coarsening, which are possible when there are no concentration gradients between the embryos. This condition is supposed to be met during the unstable growth regime of nucleation considering that the growth is limited by the interface during that period. Assuming that the embryos behave in a collective manner when they are grouped in a cloud, we show that the growth velocity of the most active embryos will be limited only by their interfacial mobility and the available driving force.     

Active Inference: Applicability to Different Types of Social Organization Explained through Reference to Industrial Engineering and Quality Management

Active inference is a physics of life process theory of perception, action and learning that is applicable to natural and artificial agents. In this paper, active inference theory is related to different types of practice in social organization. Here, the term social organization is used to clarify that this paper does not encompass organization in biological systems. Rather, the paper addresses active inference in social organization that utilizes industrial engineering, quality management, and artificial intelligence alongside human intelligence. Social organization referred to in this paper can be in private companies, public institutions, other for-profit or not-for-profit organizations, and any combination of them. The relevance of active inference theory is explained in terms of variational free energy, prediction errors, generative models, and Markov blankets. Active inference theory is most relevant to the social organization of work that is highly repetitive. By contrast, there are more challenges involved in applying active inference theory for social organization of less repetitive endeavors such as one-of-a-kind projects. These challenges need to be addressed in order for active inference to provide a unifying framework for different types of social organization employing human and artificial intelligence.     

Active turbulence in active nematics

Dense, active systems show active turbulence, a state characterised by flow fields that are chaotic, with continually changing velocity jets and swirls. Here we review our current understanding of active turbulence. The development is primarily based on the theory and simulations of active liquid crystals, but with accompanying summaries of related literature.