6,025 research outputs found
A Gaussian approximation of the distributed computing process
Get PDFThe authors propose a refinement of the stochastic model describing the dynamics of the Desktop Grid (DG) project with many hosts and many workunits to be performed, originally proposed by Morozov et al. in 2017. The target performance measure is the mean duration of the runtime of the project. To this end, the authors derive an asymptotic expression for the amount of the accumulated work to be done by means of limit theorems for superposed on-off sources that lead to a Gaussian approximation. In more detail, depending on the distribution of active and idle periods, Brownian or fractional Brownian processes are obtained. The authors present the analytic results related to the hitting time of the considered processes (including the case in which the overall amount of work is only known in a probabilistic way), and highlight how the runtime tail distribution could be estimated by simulation. Taking advantage of the properties of Gaussian processes and the Conditional Monte-Carlo (CMC) approach, the authors present a theoretical framework for evaluating the runtime tail distribution
The effective stiffness of a nanoporous rod
No full textA study was conducted to analyze the influence of surface effects on the elastic characteristics of nanoporous materials. Two models were considered, such as one based on taking into account the surface stresses and the other using the approach of the theory of composite materials. This approach involved taking into account the surface effects due to the surface layer of finite thickness with elastic moduli differing from those of the basic material. The increase or decrease in the rod stiffness depended the relation between the elastic moduli of the surface layer and the matrix. The effective stiffness decreased and increased with decreasing pore radius. A complex model combining both the presence of surface stresses and the surface layer with the properties that differ from those of the matrix was proposed on the basis of these two approaches
Modeling of spiral nanofilms with piezoelectric properties
No full textA modal analysis of a two-layer nanofilm with piezoelectric properties was performed. Eigenfrequencies were determined and eigenmodes corresponding to them were constructed. The effect of the surroundings on the eigenfrequencies was analyzed
Some problems of nanomechanics
No full textThe paper presents a selection of simulation results obtained for nanosized objects in continuum and structural mechanics. Eigenfrequency measurements as a tool to study nanostructures composed of a multitude of like nanoelements are discussed. The structures under consideration are ordered arrays of nanoobjects (nanocrystals, nanoshells) fixed on an elastic substrate. It is shown that from the eigenfrequency spectrum of this type of mechanical systems one can determine several eigenfrequencies of a single nanoobject. Also considered in the paper is accounting for surface stress and associated modification of effective properties of nanomaterials
On free oscillations of an elastic solids with ordered arrays of nano-sized objects
No full textWe discuss free oscillations of some elastic structures consisting of an elastic substrate and an ordered array of aligned nano-sized objects. Considering various shapes of nano-objects such as beams, tubes, and spheres, we investigate the spectrum of eigenfrequencies of these structures in comparison with the spectra of one nano-object and of the substrate. As a result, we find the correspondence between the spectrum of whole structure and the spectrum of one nano-object, which gives the possibility to determine few first eigenfrequencies of nano-sized objects
Mechanical properties of materials considering surface effects
No full textWe discuss the influence of surface effects on the effective properties of materials such as the effective bending stiffness of plates or the stiffness of rods. The interest to the investigation of the surface effects is recently grown with respect to nanomechanics. The surface effects play an important role for such nanosized materials as films, nanoporous materials, etc. We consider two models of surface effects. The first one is based on the concept of surface stresses which are the generalization of the surface tension for solids. The second one (more classical approach) is based on the consideration of the thin surface layer with mechanical properties different from the bulk material. Within the framework of these models we present the effective stiffness properties of plates, shells, and nanoporous rods
Linear theory of shells taking into account surface stresses
No full textA study was conducted to obtain the equations of equilibrium and constitutive equations for the stress resultants and couples tensors while taking into account the surface stresses acting on the shell surfaces. The equations were obtained generalizing the results to the case of the linear theory of elastic shells taking into account the transverse shear. The effective shell stiffness, specifically the bending stiffness Deff depended on the surface elastic moduli, which is substantial for nanodimensional thicknesses. The variational method was used for the formulation of boundary-value problems of the theory of elasticity with surface stresses. Constitutive equations also made it possible to write the equilibrium equations for the shell and plate with taking into account surface stresses in terms of displacements and rotations
The influence of surface tension on the effective stiffness of nanosize plates
No full textThe problem of bending of a nanosize plate, taking into account the action of the surface effects, is considered, and the influence of surface tension on the effective stiffness of nanosize plates is found. The deformation of a linearly elastic body is considered and the action of the surface effects on the upper and lower surfaces are taken into account. An approximation for the field of displacements that is linear in thickness is assumed to describe the deformations of the plates. The equations of state allows the determination of the equilibrium equations for the plate, with the surface tension being taken into account, in terms of the displacements and rotations. The dependence of the transverse shear forces and momentum tensors on deformations is defined by the four elastic constant
Osmotic Pressure Induced Coupling between Cooperativity and Stability of a Helix-Coil Transition
No full textMost helix-coil transition theories can be characterized by three parameters: energetic, describing the (free) energy cost of forming a helical state in one repeating unit; entropic, accounting for the decrease of entropy due to formation of the helical state; and geometric, indicating how many repeating units are affected by the formation of one helical state. Depending on their effect on the helix-coil transition, solvents or cosolutes can be classified with respect to their action on these parameters. Solvent interactions that alter the entropic cost of helix formation by their osmotic action can affect both the stability (transition temperature) and the cooperativity (transition interval) of the helix-coil transition. Consistent inclusion of osmotic pressure effects in a description of helix-coil transition, for poly(L-glutamic acid) in solution with polyethylene glycol, can offer an explanation of the experimentally observed linear dependence of transition temperature on osmotic pressure as well as the concurrent changes in the cooperativity of the transition
Fatkullina imitata n. sp., second species of a unique cheilostome bryozoan genus with reversed-polarity zooidal budding, and new family Fatkullinidae
No full textGrischenko, Andrei V., Gordon, Dennis P., Morozov, Taras B. (2018): Fatkullina imitata n. sp., second species of a unique cheilostome bryozoan genus with reversed-polarity zooidal budding, and new family Fatkullinidae. Zootaxa 4508 (1), DOI: 10.11646/zootaxa.4508.1.
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