Exactly solved polymer models with conformational escape transitions of a coil-to-flower type

We analyze exact analytical partition functions for Gaussian chains near surfaces and interfaces. These partition functions contain the possibility of conformational first-order phase transitions. Such transitions occur when chains are tethered in space and exposed to a local perturbing field. Then the chain can partially escape from the field: the chain transforms from the confined coil to an inhomogeneous flower conformation. The flower consists of a strongly stretched stem and a very weakly deformed crown. A generic phase diagram including one binodal and two spinodal lines is found for three related systems. The height of the barrier between stable and metastable states as well as the dynamics of barrier crossings is discussed

Analytical theory of finite-size effects in mechanical desorption

We discuss a unique system that allows exact analytical investigation of first- and second-order transitions with finite-size effects: mechanical desorption of an ideal lattice polymer chain grafted with one end to a solid substrate with a pulling force applied to the other end. We exploit the analogy with a continuum model and use accurate mapping between the parameters in continuum and lattice descriptions, which leads to a fully analytical partition function as a function of chain length, temperature (or adsorption strength), and pulling force. The adsorption-desorption phase diagram, which gives the critical force as a function of temperature, is nonmonotonic and gives rise to re-entrance. We analyze the chain length dependence of several chain properties (bound fraction, chain extension, and heat capacity) for different cross sections of the phase diagram. Close to the transition a single parameter (the product of the chain length N and the deviation from the transition point) describes all thermodynamic properties. We discuss finite-size effects at the second-order transition (adsorption without force) and at the first-order transition (mechanical desorption). The first-order transition has some unusual features: The heat capacity in the transition region increases anomalously with temperature as a power law, metastable states are completely absent, and instead of a bimodal distribution there is a flat region that becomes more pronounced with increasing chain length. The reason for this anomaly is the absence of an excess surface energy for the boundary between adsorbed and stretched coexisting phases (this boundary is one segment only): The two states strongly fluctuate in the transition point. The relation between mechanical desorption and mechanical unzipping of DNA is discusse

Temperature effects in the mechanical desorption of an infinitely long lattice chain: Re-entrant phase diagrams

We consider the mechanical desorption of an infinitely long lattice polymer chain tethered at one end to an adsorbing surface. The external force is applied to the free end of the chain and is normal to the surface. There is a critical value of the desorption force ftr at which the chain desorbs in a first-order phase transition. We present the phase diagram for mechanical desorption with exact analytical solutions for the detachment curve: the dependence of ftr on the adsorption energy (at fixed temperature T) and on T (at fixed ). For most lattice models ftr(T) displays a maximum. This implies that at some given force the chain is adsorbed in a certain temperature window and desorbed outside it: the stretched state is re-entered at low temperature. We also discuss the energy and heat capacity as a function of T; these quantities display a jump at the transition(s). We analyze short-range and long-range excluded-volume effects on the detachment curve ftr(T). For short-range effects (local stiffness), the maximum value of ftr decreases with stiffness, and the force interval where re-entrance occurs become narrower for stiffer chains. For long-range excluded-volume effects we propose a scaling ftr~T1-(Tc-T)/ around the critical temperature Tc, where =0.588 is the Flory exponent and 0.5 the crossover exponent, and we estimated the amplitude. We compare our results for a model where immediate step reversals are forbidden with recent self-avoiding walk simulations. We conclude that re-entrance is the general situation for lattice models. Only for a zigzag lattice model (where both forward and back steps are forbidden) is the coexistence curve ftr(T) monotonic, so that there is no re-entranc

Application of Business Games in Training of Employees of Regional Executive Bodies and Local Self-Government Bodies

The author raises the issues of applying innovative approaches in the educational and methodological process of training personnel, whose competence includes the implementation of measures to prevention of terrorism. The article discusses the features of conducting practical exercises in the simulation games form, their part and positive experience in the provision of education organization, and advanced training of employees of the antiterrorism commission apparatus in the constituent entities of the Russian Federation, executive authorities, and local self-government bodies

Practice of Using a Training Session in the Form of a “Business Game” to Practice Actions When Establishing Levels of Terrorist Danger

This article informs of training as a form of «business game» for functioning regional contraterrorist commission of Russian Federation, as well estimation the certain level of terroristic threat for personal and authorities supposed to manage such a case. Some difficulties are being marked and ways to solve similar are shown. These training was used as an example in several regions of Russia and was a rather successful