arXiv subjects

Hiroshi Tamura

Publications and source records attributed to Hiroshi Tamura.

11 recordsLinked to original sources

arXiv2023

Spontaneous segregation of visual information between parallel streams of a multi-stream convolutional neural network

Visual information is processed in hierarchically organized parallel pathways in the primate brain. In lower cortical areas, color information and shape information are processed in a parallel manner, while in higher cortical areas, various types of visual information, such as color, face, animate/inanimate, are processed in a parallel manner. In the present study, the possibility of spontaneous segregation of visual information in parallel streams was examined by constructing a convolutional neural network with parallel architecture in all of the convolutional layers. The results revealed that color information was segregated from shape information in most model instances. Deletion of the color-related stream decreased recognition accuracy in the inanimate category, whereas deletion of the shape-related stream decreased recognition accuracy in the animate category. The results suggest that properties of filters and functions of a stream are spontaneously segregated in parallel streams of neural networks.

q-bio.NC↗

arXiv2023

Open Quadratic Fermion Systems and Algebras of Affine Transformations

We study evolution of open quadratic fermion systems in the framework of the quantum Markovian semigroup approach. We show that the algebra concerning commutators of Liouvillians for systems of quadratic interacting fermions of finite number, say $\mathcal{N}$, is isomorphic to that of certain affine transformations on the space of square matrices of size $\mathcal{N}$. By the use of this algebraic structure, we present a perspective method for solving master equations of quadratic fermion systems. Here, we mainly deal with gauge invariant quadratic interacting fermion systems. We briefly mention similar algebraic structures for general quadratic fermion systems and quadratic boson systems. Keywords : open quantum system, Markovian quantum dynamical system, quadratic interacting Fermion, affine transformation, asymptotic behavior, skin effect

math-ph↗

arXiv2020

On the open Dicke-type model generated by an infinite-component vector spin

We consider an open Dicke model comprising a single infinite-component vector spin and a single-mode harmonic oscillator which are connected by Jaynes--Cummings-type interaction between them. This open quantum model is referred to as the OISD (Open Infinite-component Spin Dicke) model. The algebraic structure of the OISD Liouvillian is studied in terms of superoperators acting on the space of density matrices. An explicit invertible superoperator (precisely, a completely positive trace-preserving map) is obtained that transforms the OISD Liouvillian into a sum of two independent Liouvillians, one generated by a dressed spin only, the other generated by a dressed harmonic oscillator only. The time evolution generated by the OISD Liouvillian is shown to be asymptotically equivalent to that generated by an adjusted decoupled Liouvillian with some synchronized frequencies of the spin and the harmonic oscillator. This asymptotic equivalence implies that the time evolution of the OISD model dissipates completely in the presence of any (tiny) dissipation.

quant-ph↗

arXiv2020

Deleting object selective units in a fully-connected layer of deep convolutional networks improves classification performance

Neurons in the primate visual cortices show a wide range of stimulus selectivity. Some neurons respond to only a small fraction of stimulus images, whereas others respond to many stimulus images in a non-selective manner. It is unclear how stimulus selective and non-selective neurons contribute to visual object recognition. Herein, we examined the relationship between stimulus selectivity and the effect of deletion of units on task performance using fully a connected layer of two types of deep convolutional neural networks (DCNNs). Deleting a stimulus selective unit caused slight improvements of task performance, whereas deleting stimulus non-selective units caused a significant decrease in task performance. However, these findings do not imply that stimulus selective units have no use for the task. Indeed, better performance was obtained when the networks consisted of both stimulus selective and non-selective units.

q-bio.NC↗

arXiv2015

Dynamical Semigroups for Unbounded Repeated Perturbation of Open System

We consider dynamical semigroups with unbounded Kossakowski-Lindblad-Davies generators which are related to evolution of an open system with a tuned repeated harmonic perturbation. Our main result is the proof of existence of uniquely determined minimal trace-preserving strongly continuous dynamical semigroups on the space of density matrices. The corresponding dual W *-dynamical system is shown to be unital quasi-free and completely positive automorphisms of the CCR-algebra. We also comment on the action of dynamical semigroups on quasi-free states.

math.OA↗

arXiv2015

Dynamics of an Open System for Repeated Harmonic Perturbation

We use the Kossakowski-Lindblad-Davies formalism to consider an open system defined as the Markovian extension of one-mode quantum oscillator S, perturbed by a piecewise stationary harmonic interaction with a chain of oscillators C. The long-time asymptotic behaviour of various subsystems of S+C are obtained in the framework of the dual W-dynamical system approach.

math-ph↗

arXiv2014

A Dynamics Driven by Repeated Harmonic Perturbations

We propose an exactly soluble W*-dynamical system generated by repeated harmonic perturbations of the one-mode quantum oscillator. In the present paper we deal with the case of isolated system. Although dynamics is Hamiltonian and quasi-free, it produces relaxation of initial state of the system to the steady state in the large-time limit. The relaxation is accompanied by the entropy production and we found explicitly the rate for it. Besides, we study evolution of subsystems to elucidate their eventual correlations and convergence to equilibrium state. Finally we prove a universality of the dynamics driven by repeated harmonic perturbations in a certain short-time interaction limit.

math.FA↗

arXiv2012

Random point field approach to analysis of anisotropic Bose-Einstein condensations

Position distributions of constituent particles of the perfect Bose-gas trapped in exponentially and polynomially anisotropic boxes are investigated by means of the boson random point fields (processes) and by the spatial random distribution of particle density. Our results include the case of \textit{generalised} Bose-Einstein Condensation. For exponentially anisotropic quasi two-dimensional system (SLAB), we obtain \textit{three} qualitatively different particle density distributions. They correspond to the \textit{normal} phase, the quasi-condensate phase (type III generalised condensation) and to the phase when the type III and the type I Bose condensations co-exist. An interesting feature is manifested by the type II generalised condensation in one-directional polynomially anisotropic system (BEAM). In this case the particle density distribution rests truly random even in the \textit{macroscopic} scaling limit.

math-ph↗

arXiv2009

Large Deviation Principle for Non-Interacting Boson Random Point Processes

Limit theorems, including the large deviation principle, are established for random point processes (fields), which describe the position distributions of the perfect boson gas in the regime of the Bose-Einstein condensation. We compare these results with those for the case of the normal phase.

math-ph↗

arXiv2008

Mean-Field Interacting Boson Random Point Fields in Weak Harmonic Traps

A model of the mean-field interacting boson gas trapped by a weak harmonic potential is considered by the \textit{boson random point fields} methods. We prove that in the Weak Harmonic Trap (WHT) limit there are two phases distinguished by the boson condensation and by a different behaviour of the local particle density. For chemical potentials less than a certain critical value, the resulting Random Point Field (RPF) coincides with the usual boson RPF, which corresponds to a non-interacting (ideal) boson gas. For the chemical potentials greater than the critical value, the boson RPF describes a divergent (local) density, which is due to \textit{localization} of the macroscopic number of condensed particles. Notice that it is this kind of transition that observed in experiments producing the Bose-Einstein Condensation in traps.

math-ph↗

arXiv2006

Random Point Fields for Para-Partcles of Any Order

Random point fields which describe gases consisting of para-particles of any order are given by means of the canonical ensemble approach. The analysis for the cases of the para-fermion gases are discussed in full detail.

math-ph↗