540 research outputs found
Probabilistic Models of Motor Production
N. Bernstein defined the ability of the central neural system (CNS) to control many degrees of freedom of a physical body with all its redundancy and flexibility as the main problem in motor control. He pointed at that man-made mechanisms usually have one, sometimes two degrees of freedom (DOF); when the number of DOF increases further, it becomes prohibitively hard to control them. The brain, however, seems to perform such control effortlessly. He suggested the way the brain might deal with it: when a motor skill is being acquired, the brain artificially limits the degrees of freedoms, leaving only one or two. As the skill level increases, the brain gradually "frees" the previously fixed DOF, applying control when needed and in directions which have to be corrected, eventually arriving to the control scheme where all the DOF are "free". This approach of reducing the dimensionality of motor control remains relevant even today.
One the possibles solutions of the Bernstetin's problem is the hypothesis of motor primitives (MPs) - small building blocks that constitute complex movements and facilitite motor learnirng and task completion. Just like in the visual system, having a homogenious hierarchical architecture built of similar computational elements may be beneficial.
Studying such a complicated object as brain, it is important to define at which level of details one works and which questions one aims to answer. David Marr suggested three levels of analysis: 1. computational, analysing which problem the system solves; 2. algorithmic, questioning which representation the system uses and which computations it performs; 3. implementational, finding how such computations are performed by neurons in the brain. In this thesis we stay at the first two levels, seeking for the basic representation of motor output.
In this work we present a new model of motor primitives that comprises multiple interacting latent dynamical systems, and give it a full Bayesian treatment. Modelling within the Bayesian framework, in my opinion, must become the new standard in hypothesis testing in neuroscience. Only the Bayesian framework gives us guarantees when dealing with the inevitable plethora of hidden variables and uncertainty.
The special type of coupling of dynamical systems we proposed, based on the Product of Experts, has many natural interpretations in the Bayesian framework. If the dynamical systems run in parallel, it yields Bayesian cue integration. If they are organized hierarchically due to serial coupling, we get hierarchical priors over the dynamics. If one of the dynamical systems represents sensory state, we arrive to the sensory-motor primitives. The compact representation that follows from the variational treatment allows learning of a motor primitives library. Learned separately, combined motion can be represented as a matrix of coupling values.
We performed a set of experiments to compare different models of motor primitives. In a series of 2-alternative forced choice (2AFC) experiments participants were discriminating natural and synthesised movements, thus running a graphics Turing test. When available, Bayesian model score predicted the naturalness of the perceived movements. For simple movements, like walking, Bayesian model comparison and psychophysics tests indicate that one dynamical system is sufficient to describe the data. For more complex movements, like walking and waving, motion can be better represented as a set of coupled dynamical systems. We also experimentally confirmed that Bayesian treatment of model learning on motion data is superior to the simple point estimate of latent parameters. Experiments with non-periodic movements show that they do not benefit from more complex latent dynamics, despite having high kinematic complexity.
By having a fully Bayesian models, we could quantitatively disentangle the influence of motion dynamics and pose on the perception of naturalness. We confirmed that rich and correct dynamics is more important than the kinematic representation.
There are numerous further directions of research. In the models we devised, for multiple parts, even though the latent dynamics was factorized on a set of interacting systems, the kinematic parts were completely independent. Thus, interaction between the kinematic parts could be mediated only by the latent dynamics interactions. A more flexible model would allow a dense interaction on the kinematic level too.
Another important problem relates to the representation of time in Markov chains. Discrete time Markov chains form an approximation to continuous dynamics. As time step is assumed to be fixed, we face with the problem of time step selection. Time is also not a explicit parameter in Markov chains. This also prohibits explicit optimization of time as parameter and reasoning (inference) about it. For example, in optimal control boundary conditions are usually set at exact time points, which is not an ecological scenario, where time is usually a parameter of optimization. Making time an explicit parameter in dynamics may alleviate this
Bose-Einstein condensation and/or modulation of "displacements" in the two-state Bose-Hubbard model
Instabilities resulting in Bose-Einstein condensation and/or modulation of
"displacements" in a system of quantum particles described by a two-state
Bose-Hubbard model (with an allowance for the interaction between particle
displacements on different lattice sites) are investigated. A possibility of
modulation, which doubles the lattice constant, as well as the uniform
displacement of particles from equilibrium positions are studied. Conditions
for realization of the mentioned instabilities and phase transitions into the
SF phase and into the "ordered" phase with frozen displacements are analyzed.
The behaviour of order parameters is investigated and phase diagrams of the
system are calculated both analytically (ground state) and numerically (at
non-zero temperatures). It is revealed that the SF phase can appear as an
intermediate one between the normal and "ordered" phases, while a supersolid
phase is thermodynamically unstable and does not appear. The relation of the
obtained results to the lattices with the double-well local potentials is
discussed.Comment: 17 pages, 11 figure
Two-state Bose-Hubbard model in the hard-core boson limit
Phase transition into the phase with Bose-Einstein (BE) condensate in the
two-band Bose-Hubbard model with the particle hopping in the excited band only
is investigated. Instability connected with such a transition (which appears at
excitation energies , where is
the particle hopping parameter) is considered. The re-entrant behaviour of
spinodales is revealed in the hard-core boson limit in the region of positive
values of chemical potential. It is found that the order of the phase
transition undergoes a change in this case and becomes the first one; the
re-entrant transition into the normal phase does not take place in reality.
First order phase transitions also exist at negative values of (under
the condition ).
At the phase transition mostly remains to be of the second order. The
behaviour of the BE-condensate order parameter is analyzed, the
and phase diagrams are built and localizations of
tricritical points are established. The conditions are found at which the
separation on the normal phase and the phase with the BE condensate takes
place.Comment: 14 pages, 12 figure
Phase separation in lithium intercalated anatase: A theory
Lithium intercalated anatase used in Li-ion batteries has some special
features: coexistence of Li-rich and Li-poor phases as well as two possible
positions for Li ions in the oxygen tetrahedron. A theoretical description of
the compound considering those peculiarities is presented. As shown by the
performed symmetry analysis, the intercalation induced lattice deformation can
be accompanied by the ordering of antiferroelectric type (internal
piezoeffect). In the following step, a qualitative illustration of the phase
separation in the lithiated anatase is given within the Landau expansion at the
proper choice of coefficients. A microscopic model for description of the
compound is also proposed which combines features of the Mitsui and
Blume-Emery-Griffits models and utilizes the symmetry analysis results. Various
ground state and temperature-dependent phase diagrams of the model are studied
to find a set of model parameters corresponding to the lithiated anatase. A
phase separation into the empty and half-filled phases in a wide temperature
range has been found closely resembling the phase coexistence in the
intercalated crystal. In the framework of the model, the two-position Li
subsystem could have the ordering of ferro- or antiferroelectric types which,
however, has not been yet observed by the experiment.Comment: 19 pages, Reported at the Conference "Statistical Physics: Modern
Trends and Applications" dedicated to the 100-th anniversary of N.N.
Bogolyubov (June 23--25, 2009 Lviv, Ukraine
Research and Development Workstation Environment: the new class of Current Research Information Systems
Against the backdrop of the development of modern technologies in the field
of scientific research the new class of Current Research Information Systems
(CRIS) and related intelligent information technologies has arisen. It was
called - Research and Development Workstation Environment (RDWE) - the
comprehensive problem-oriented information systems for scientific research and
development lifecycle support. The given paper describes design and development
fundamentals of the RDWE class systems. The RDWE class system's generalized
information model is represented in the article as a three-tuple composite web
service that include: a set of atomic web services, each of them can be
designed and developed as a microservice or a desktop application, that allows
them to be used as an independent software separately; a set of functions, the
functional filling-up of the Research and Development Workstation Environment;
a subset of atomic web services that are required to implement function of
composite web service. In accordance with the fundamental information model of
the RDWE class the system for supporting research in the field of ontology
engineering - the automated building of applied ontology in an arbitrary domain
area, scientific and technical creativity - the automated preparation of
application documents for patenting inventions in Ukraine was developed. It was
called - Personal Research Information System. A distinctive feature of such
systems is the possibility of their problematic orientation to various types of
scientific activities by combining on a variety of functional services and
adding new ones within the cloud integrated environment. The main results of
our work are focused on enhancing the effectiveness of the scientist's research
and development lifecycle in the arbitrary domain area.Comment: In English, 13 pages, 1 figure, 1 table, added references in Russian.
Published. Prepared for special issue (UkrPROG 2018 conference) of the
scientific journal "Problems of programming" (Founder: National Academy of
Sciences of Ukraine, Institute of Software Systems of NAS Ukraine
Інноваційний розвиток у логістиці та його зв’язок з логістичним управлінням і управлінням логістикою
У статті наведено авторську класифікацію та тлумачення основних видів (напрямів) інноваційного розвитку логістики. Установлено основні відмінності між процесами логістичного управління та управлінням логістикою, а також визначено їхній зв’язок з основними видами (напрямами) інноваційного логістичного розвитку.
При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/30376В статье представлена авторская классификация и толкование основных видов (направлений) инновационного развития логистики. Установлены основные отличия между процессами логистического управления и управлением логистикой, а также определенна их связь с основными видами (направлениями) инновационного логистического развития.
При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/30376In the article author’s classification and grounding of main kinds (directions) of innovative development in logistics have been revealed. Basic differences between processes of logistical management and management of logistics have been defined and their connection with main kinds (directions) of innovative development in logistics has been determined.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3037
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