Arguments in favour of a program of seismic detection of gravity wave bursts

Summary The possibility is shown of selecting gravity wave perturbations in earth crust block in the seismic-noise background due to far local sources. It is shown that the utilization of different space-time ?colourations? of gravity wave and noise perturbations makes it possible, in principle, to extract the signal in the background of noise of exceeding intensity.     

Doped polysiloxane scintillators for thermal neutrons detection

Boron doped polysiloxane scintillators have been produced with different concentrations of boron and their scintillation yields have been studied as a function of the boron content under α, γ and fast and thermal neutrons irradiation. Their response has been compared with standard commercial plastic scintillators, namely EJ-212 as plastic scintillator and EJ-254 as boron doped scintillator. The produced samples exhibited a scintillation yield similar to EJ-212. The effect of boron on the energy transfer mechanism and on the polymer radiation hardness has been investigated by means of fluorescence and ion beam induced luminescence (IBIL) measurements. Detection efficiencies for thermal neutrons higher than commercial plastic scintillators have been attained with boron doped samples.     

The variational method in contact problems. The present state of the problem and trends in its development

Research on variational methods for solving problems on the contact of solid deformable bodies is reviewed and trends in the development of these researches at the present time are analysed. The Signorini problem and it generalizations, numerical methods, different models of friction, investigations into the problem of the existence and uniqueness of a solution, the problem of rolling motion, the problem of describing the boundary conditions, inelastic materials and problems of contact dynamics and electro-elastic contact are considered. The analysis shows that research on the problem of the contact of deformable bodies is being conducted over a broad front in different areas and the results are being applied in different areas of modern engineering and technology.     

X-ray fluorescence from the element with atomic number Z=120

An atomic clock based on x-ray fluorescence yields has been used to estimate the mean characteristic time for fusion followed by fission in reactions 238U + 64Ni at 6.6 MeV/A. Inner shell vacancies are created during the collisions in the electronic structure of the possibly formed Z=120 compound nuclei. The filling of these vacancies accompanied by a x-ray emission with energies characteristic of Z=120 can take place only if the atomic transitions occur before nuclear fission. Therefore, the x-ray yield characteristic of the united atom with 120 protons is strongly related to the fission time and to the vacancy lifetimes. K x rays from the element with Z=120 have been unambiguously identified from a coupled analysis of the involved nuclear reaction mechanisms and of the measured photon spectra. A minimum mean fission time τ(f)=2.5×10(-18) s has been deduced for Z=120 from the measured x-ray multiplicity.     

Time-projection chamber for the PEN experiment

The PEN collaboration carries out a precision measurement of the ??⁺ ?? e ⁺?? decay branching ratio at the Paul Scherrer Institute (PSI, Switzerland). A special mini time-projection chamber (mTPC) has been developed for registration of particles in the pion beam. The chamber contains 14 × 10^?3 g/cm² of matter on the particle path. The chamber was successfully used during one-year-long run. Design and characteristics of the mTPC are described.     

Identification of the Topology of Inhomogeneous Dynamical Systems

This paper considers identification problems arising in elasticity theory and methods for their solution; in particular, the impedance and diffraction tomography methods are considered. Some particular problems important in practice are also studied. __________ Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 16, Partial Differential Equations, 2004.     

Solution of sparse quasi-square rectangular systems by Gaussian elimination

We present a general method for the linear least-squares solutionof overdetermined and underdetermined systems. The method isparticularly efficient when the coefficient matrix is quasi-square,that is when the number of rows and number of columns is almostthe same. The numerical methods for linear least-squares problemsand minimum-norm solutions do not generally take account ofthis special characteristic. The proposed method is based onLU factorization of the original quasi-square matrix A, assumingthat A has full rank. In the overdetermined case, the LU factorsare used to compute a basis for the null space of A^T. The right-handside vector b is then projected onto this subspace and the least-squaressolution is obtained from the solution of this reduced problem.In the case of underdetermined systems, the desired solutionis again obtained through the solution of a reduced system.The use of this method may lead to important savings in computationaltime for both dense and sparse matrices. It is also shown inthe paper that, even in cases where the matrices are quite small,sparse solvers perform better than dense solvers. Some practicalexamples that illustrate the use of the method are included.     

Development of a solution method for frictional contact problems with complex loading

In this work, solution methods for frictional contact problems are extended to the case of moving punches and to the external loading history-dependent system states. To solve the frictional contact problems in the contact area, an iterative method is developed and implemented. Solutions of two-dimensional problems are constructed using the boundary element method. Numerical analysis is aimed at the quantitative study of effects such as the interaction of contact pressure and friction forces, estimates of the friction force differences due to the differences in the choice of local basis for the calculation of normal pressure and friction forces, and evaluation of the effects of complex loading (rotation of the rigid punch after its preliminary penetration into the solid). We find that, for the same definition of the friction force, different initial approximations lead to the same solution. At the same time, the friction forces defined either as projections onto the common tangent plane or as projections onto the plane tangent to the punch can differ quite substantially. Similar conclusions are derived for the solutions corresponding to single or multiple loading steps. The work relies on the variational principle for the solution of contact problems and numerical algorithms developed for the problems with one-sided constraints. The variational principle was first applied by Signorini [1] to the determination of the stress-strain state in a linearly deformed body in a rigid smooth shell. The modern view of the problem and its generalizations to the frictional problems and some other problems involving unilateral constraints in given in the monograph [2]. Finite difference and finite element methods in application to the problems with unilateral constraints are described in [3]. Analytical solution methods are developed in the monographs [4–6].