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D. B. Saakian

Publications and source records attributed to D. B. Saakian.

At least 19 recordsLinked to original sources

Evolution models with base substitutions, insertions, deletions and selection

The evolution model with parallel mutation-selection scheme is solved for the case when selection is accompanied by base substitutions, insertions, and deletions. The fitness is assumed to be either a single-peak function (i.e., having one finite discontinuity) or a smooth function of the Hamming distance from the reference sequence. The mean fitness is exactly calculated in large-genome limit. In the case of insertions and deletions the evolution characteristics depend on the choice of reference sequence.

q-bio.PE↗

Thermodynamics of adiabatic feedback control

We study adaptive control of classical ergodic Hamiltonian systems, where the controlling parameter varies slowly in time and is influenced by system's state (feedback). An effective adiabatic description is obtained for slow variables of the system. A general limit on the feedback induced negative entropy production is uncovered. It relates the quickest negentropy production to fluctuations of the control Hamiltonian. The method deals efficiently with the entropy-information trade off.

cond-mat.stat-mech↗

Quasispecies Theory for Multiple-Peak Fitness Landscapes

We use a path integral representation to solve the Eigen and Crow-Kimura molecular evolution models for the case of multiple fitness peaks with arbitrary fitness and degradation functions. In the general case, we find that the solution to these molecular evolution models can be written as the optimum of a fitness function, with constraints enforced by Lagrange multipliers and with a term accounting for the entropy of the spreading population in sequence space. The results for the Eigen model are applied to consider virus or cancer proliferation under the control of drugs or the immune system.

q-bio.PE↗

Adiabatic feedback control of Hamiltonian systems

We study feedback control of classical Hamiltonian systems with the controlling parameter varying slowly in time. The control aims to change system's energy. We show that the control problems can be solved with help of an adiabatic invariant that generalizes the conservation of the phase-space volume to control situations. New mechanisms of control for achieving heating, cooling, entropy reduction and particle trapping are found. The feedback control of a many-body system via one of its coordinates is discussed. The results are illustrated by two basic models of non-linear physics.

cond-mat.other↗

Spin glasses at imaginary temperature

We consider spherical p-spin glass and p-spin glass models at imaginary temperatures. Imaginary temperatures are special case, when order parameters are real value numbers. Here there is a some antiferromagnetic like order.

cond-mat.dis-nn↗

Hierarchic trees with branching number close to one: noiseless KPZ equation with additional linear term for imitation of 2-d and 3-d phase transitions.

An imitation of 2d field theory is formulated by means of a model on the hierarhic tree (with branching number close to one) with the same potential and the free correlators identical to 2d correlators ones. Such a model carries on some features of the original model for certain scale invariant theories. For the case of 2d conformal models it is possible to derive exact results. The renormalization group equation for the free energy is noiseless KPZ equation with additional linear term.

cond-mat.dis-nn↗

Imitation of 2d quantum field theory by means of REM like models

An imitation of 2d field theory is formulated by means of a model on the hierarchic tree (with branching number close to one) with the same potential and the free correlators identical to those of 2d ones. Such a model possesses some features of original models for certain scale invariant theories. For the case of 2d conformal models it is possible to derive exact results. The renormalization group equation for the free energy is a reaction-diffusion equation, which is noise-free KPZ equation with an additional linear term. For the case of Liouville model and strings these models on trees may be naturally expressed via the Random Energy Model. This correspondence is used to identify the phase structure of strings for analytical continuation of DDK expressions. A phase transition is found for spherical strings a bit below three dimensions.

physics.gen-ph↗

The harmony, reflection and other principles of complex systems

A set of general physical principles is proposed as the structural basis for the theory of complex systems. First the concept of harmony is analyzed and its different aspects are uncovered. Then the concept of reflection is defined and illustrated by suggestive examples. Later we propose the principle of (random) projection of symmetrically expanded prereality as the main description method of complex systems.

cond-mat.dis-nn↗

8 levels of harmony and 8 concepts of Complex Systems

A set of general physical principles is proposed as the structural basis for the theory of complex systems. First the concept of harmony is analyzed and its different aspects are uncovered. Then the concept of reflection is defined and illustrated by suggestive examples. Later we propose the principle of (random) projection of symmetrically expanded prereality as the main description method of complex systems.

cond-mat.dis-nn↗

New type of extreme value statistics

We investigate the extreme value statistics connected with the dilute Random Energy Model with integer couplings. New universality class is found.

cond-mat.dis-nn↗

Multiscaling at ferromagnetic-spin glass transition point of Random Energy Model and complexity

We calculate moments of free energy's finite size correction for the transition point between ferromagnetic and spin glass phases. We find, that those moments scale with the number of spins with different critical indices, characteristic for the multiscaling. This critical point corresponds to threshold of errorless coding for a gaussian noisy channel. We are give the definition of statistical complexity using this free energy approach.

cond-mat.dis-nn↗

Ultrametric space cut instead of 2d one in 2d quantum field models

It is possible to formulate 2d field theory on the ultrametric space with the free correlators identical to 2d correlators and the same potential. Such model should carry some features of original model for scale invariant theories. For the case of strings and 2d conformal models it is possible to derive exact results. It is possible to investigate not only bulk structure (phase transition points) of theory, but sometimes also correlators. Such ultrametric models could be naturally expressed via Random energy model and directed polymer on Cayley tree.

cond-mat.dis-nn↗

Random Energy Model as a paradigm of complex systems

A quadratic extension of REM has been treated. Discussed here is the origin of relation of REM to strings and other complex physical phenomena. Two basic features of the REM class of complex phenomena were identified: the double thermodynamic reflection (a hierarchy of free energies) including the strong reflection at the upper level (the free energy on the order of a logarithm of the degrees of freedom) and the loss (complete or partial) of the local symmetry property. Two main classes of complex phenomena related to REM are seen: the spin glass phase of REM and the boundary the spin glass-ferromagnetic phases. Some examples of physics interest are analyzed from this viewpoint.

cond-mat.dis-nn↗

Simplified dynamics for glass model

In spin glass models one can remove minimization of free energy by some order parameter. One can consider hierarchy of order parameters. It is possible to divide energy among these parts. We can consider relaxation process in glass system phenomonologically, as exchange of energy between 2 parts. It is possible to identify trap points in phase space. We suggest some phenomonological approximation-truncated Langevine. The mean field statics is used to introduce a phenomenologic dynamics as its natural extension. Purely kinetical phase transitions are investigated..

cond-mat.dis-nn↗

Complex temperatures zeroes of partition function in spin-glass models

An approximate method is proposed for investigating complex-temperature properties of real-dimensional spin-glass models. The method uses the complex-temperature data of the ferromagnetic model on the same lattice. The universality line in the complex-temperature space is obtained.

cond-mat.stat-mech↗

Model glasses coupled to two different heat baths

In a $p$-spin interaction spherical spin-glass model both the spins and the couplings are allowed to change in the course of time. The spins are coupled to a heat bath with temperature $T$, while the coupling constants are coupled to a bath having temperature $T_{J}$. In an adiabatic limit (where relaxation time of the couplings is much larger that of the spins) we construct a generalized two-temperature thermodynamics. It involves entropies of the spins and the coupling constants. The application for spin-glass systems leads to a standard replica theory with a non-vanishing number of replicas, $n=T/T_J$. For $p>2$ there occur at low temperatures two different glassy phases, depending on the value of $n$. The obtained first-order transitions have positive latent heat, and positive discontinuity of the total entropy. This is the essentially non-equilibrium effect. The predictions of longtime dynamics and infinite-time statics differ only for $n<1$ and $p>2$. For $p=2$ correlation of the disorder (leading to a non-zero $n$) removes the known marginal stability of the spin glass phase. If the observation time is very large there occurs no finite-temperature spin glass phase. In this case there are analogies with the broken-ergodicity dynamics in the usual spin-glass models and non-equilibrium (aging) dynamics. A generalized fluctuation-dissipation relation is derived.

cond-mat.dis-nn↗

Random Energy Model at Complex Temperatures

The complete phase diagram of Random Energy Model (REM) is obtained for complex temperatures using the method proposed by Derrida. We find the density of zeroes for statistical sum. Then the method is applied to Generalized Random Energy Model (GREM). This allows us to propose new analytical method for investigating zeroes of statistical sum for finite-dimensional systems.

cond-mat.dis-nn↗