Thermoheliox: effect on the functional hemodynamics of the human brain

A kinetic study of the effect of thermoheliox (inhalation of a helium and oxygen mixture, 70 °C) on the functional hemodynamics of the human brain by functional magnetic resonance imaging was carried out. The dynamic responses of the BOLD signal were found to be biphasic. An empirical equation describing the first phase of the hemodynamic response to visual stimulus was proposed. It was shown that preliminary inhalation of thermoheliox stimulates the hemodynamic responses by slowing down the vasoconstriction.

     

Dependences of the Transport Scattering Time and Quantum Lifetime on the Two-Dimensional Electron Gas Density in Modulation-Doped Single GaAs Quantum Wells with AlAs/GaAs Short-Period Superlattice Barriers

JETP Letters - The dependences of the transport scattering time τt, quantum lifetime τq, and their ratio τt/τq on the density ne of the electron gas in modulation-doped single...     

Nonlinear AC and DC Conductivities in a Two-Subband n-GaAs/AlAs Heterostructure

JETP Letters - The DC and AC conductivities of the n-GaAs/AlAs heterostructure with two filled size quantization levels are studied within a wide magnetic field range. The electron spectrum of such...     

Identification of the Characteristics of Viscoelastic Materials during Repeated Compression after Unloading by the Numerical-Graphical Method

The problem of describing the behavior of a highly filled polymeric material under compression, which was preceded by preliminary compression and unloading, is considered. The peculiarity of the compression diagrams obtained in the experiment is the downward convexity of the curves of the stress modulus versus time. To solve this problem, a variant of the non-linear endochronic theory of aging viscoelastic materials with several aging and viscosity functions and a numerical-graphical method for identifying the properties of viscoelasticmaterials proposed by the authors earlier, suggesting comparison of the deformation diagrams of intact samples and those that received preliminary damage, are used.     

Sigma models as Gross–Neveu models

Theoretical and Mathematical Physics - We review the correspondence between integrable sigma models with complex homogeneous target spaces and the chiral bosonic (and possibly mixed...     

Use of structural components of specific work of internal forces for estimating the strength of viscoelastic structures in local stress concentration regions

Material fracture experiments on specimens and structures testify that materials can resist greater stresses in local stress concentration regions than in regions with a nearly homogeneous stress state. Taking this fact into account in design stress analysis permits one to reveal additional structure loading and/or service life margins. One approach aimed at taking into account the increased strength in local stress concentration regions is to use averaged limit characteristics parametrically depending on the characteristic size L of the averaging region. One version of this approach is the concept of “elementary block” of a material [1, 2]. The averaged limit characteristics are determined by an experiment-calculation method involving the analysis of the stress-strain state of a material specimen with a stress concentrator at the time when the specimen attains the limit state preceding macrofracture.In [3], the dependence of the averaged limit separation stresses on the size of the averaging region was determined on the basis of numerical analysis of the singular stress state of the specimen used to determine the standard characteristics of the adhesion strength of a filled polymer material. In the present paper, we generalize the above approach to the case of a viscoelastic material. For the limit characteristics of the material in the local stress concentration region we take the volume-averaged components of the specific work of internal forces [4, 5] (the averaged specific absorbed energy and the averaged specific instantaneously reversible energy). The introduction of two limit energies originates from the fact that, to initiate the process of macrofracture, it is necessary to satisfy the following two conditions simultaneously: the material must be “damaged” sufficiently strongly by the preceding loading, and the “damaged” material must be loaded sufficiently strongly. As an example of determining the material averaged limit energy characteristics in a local stress concentration region, we consider the problem about the strain of a viscoelastic specimen used to determine the standard adhesion strength characteristics. The problem is solved numerically under the following assumptions: the specimen material is assumed to be linearly viscoelastic, and the specific absorbed energy in the stress concentration region is assumed to coincide in magnitude with the specific scattered energy. To estimate the accuracy of the numerical method, we use the solution of the model problem about the action of a plane circular die on a half-space consisting of a linearly viscoelastic incompressible material.     

Efficient implementation of the analytic second derivatives of Hartree–Fock and hybrid DFT energies: a detailed analysis of different approximations

In this paper, various implementations of the analytic Hartree–Fock and hybrid density functional energy second derivatives are studied. An approximation-free four-centre implementation is presented, and its accuracy is rigorously analysed in terms of self-consistent field (SCF), coupled-perturbed SCF (CP-SCF) convergence and prescreening criteria. The CP-SCF residual norm convergence threshold turns out to be the most important of these. Final choices of convergence thresholds are made such that an accuracy of the vibrational frequencies of better than 5 cm^?1 compared to the numerical noise-free results is obtained, even for the highly sensitive low frequencies (<100–200 cm^?1). The effects of the choice of numerical grid for density functional exchange–correlation integrations are studied and various weight derivative schemes are analysed in detail. In the second step of the work, approximations are introduced in order to speed up the computation without compromising its accuracy. To this end, the accuracy and efficiency of the resolution of identity approximation for the Coulomb terms and the semi-numerical chain of spheres approximation to the exchange terms are carefully analysed. It is shown that the largest performance improvements are realised if either Hartree–Fock exchange is absent (pure density functionals) and otherwise, if the exchange terms in the CP-SCF step of the calculation are approximated by the COSX method in conjunction with a small integration grid. Default values for all the involved truncation parameters are suggested. For vancomycine (176 atoms and 3593 basis functions), the RIJCOSX Hessian calculation with the B3LYP functional and the def2-TZVP basis set takes ～3 days using 16 Intel® Xeon® 2.60GHz processors with the COSX algorithm having a net parallelisation scaling of 11.9 which is at least ～20 times faster than the calculation without the RIJCOSX approximation.     

Higher spin $${{\mathfrak {s}}}{{\mathfrak {l}}}_2$$ s l 2 R-matrix from equivariant (co)homology

Letters in Mathematical Physics - We compute the rational $${{\mathfrak {s}}}{{\mathfrak {l}}}_2$$ R-matrix acting in the product of two spin- $$\ell \over 2$$ ( $${\ell \in {\mathbb {N}}}$$ )...