A miniature prototype of a resonance photoacoustic cell for gas sensing

We present a miniature prototype of a resonance photoacoustic cell with a banana-shaped internal cavity with a volume of less than ～5 mm³. The cell design and the experimental setup used for testing operational characteristics of the prototype are described. The results of testing the prototype in the experiments on photoacoustic detection of radiation absorption by ammonia in a nitrogen flow by using a single-mode diode laser generating radiation near ～1.53 μm are presented. The amplitude-frequency characteristic of the photoacoustic response induced by absorption of radiation in the presence and absence of ammonia is analyzed. The experiment revealed that sensitivity of gas sensing is limited only by the microphone noise. The measured noise-limited minimal detectable absorption was found to be about 8.48 × 10^?8 cm^?1 W Hz^?1/2.     

Coincidence of Least Uniform Deviations of Functions from Polynomials and Rational Fractions

For a given nonincreasing vanishing sequence {a _n } _{n = 0} of nonnegative real numbers, we find necessary and sufficient conditions for a sequence {n _k } _{k = 0} to have the property that for this sequence there exists a function f continuous on the interval [0,1] and satisfying the condition that , k = 0,1,2,..., where E _n (f) and R _n,m (f) are the best uniform approximations to the function f by polynomials whose degree does not exceed n and by rational functions of the form r _n,m (x) = p _n (x)/q _m (x), respectively.     

Inverse diagnostic problems associated with image processing

Translated from Chislennye Metody Resheniya Obratnykh Zadach Matematicheskoi Fiziki, pp. 9–20.     

Study on low-energy positron polarimetry

A polarised positron source has been proposed for the design of the international linear collider (ILC). In order to optimise the positron beam, a measurement of its degree of polarisation close to the positron creation point is desired. In this contribution, methods for determining the positron polarisation at low energies are reviewed. A newly developed polarisation extension to GEANT4 will provide the basis for further polarimeter investigations.      

Elastoplastic bending of a sandwich bar on an elastic foundation

The elastoplastic bending of a sandwich bar with a stiff compressible core on an elastic foundation is studied. The kinematics of the bar, which is asymmetric across the thickness, is described adopting Bernoulli’s hypotheses for the face layers. The displacements of the core are assumed to vary linearly across the thickness. The foundation is described by the Winkler model. A system of equilibrium equations for displacements is derived and solved. Numerical results for a metal-polymer sandwich bar are presented __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 4, pp. 110–120, April 2007.     

Solvability of a nonstationary problem of a rigid body motion in the flow of a viscous incompressible fluid in a pipe of arbitrary cross-section

The existence of a generalized weak solution is proved for the nonstationary problem of motion of a rigid body in the flow of a viscous incompressible fluid filling a cylindrical pipe of arbitrary cross-section. The fluid flow conforms to the Navier–Stokes equations and tends to the Poiseuille flow at infinity. The body moves in accordance with the laws of classical mechanics under the influence of the surrounding fluid and the gravity force directed along the cylinder. Collisions of the body with the boundary of the flow domain are not admitted and, by this reason, the problem is considered until the body approaches the boundary.     

Synthesis of Condensed Nitrofuroxanes Using Hydroxylamine

The possibility of preparing condensed nitrofuroxanes using hydroxylamine was examined.     

Circular Sandwich Plates under Local Impulsive Loads

The axisymmetric transverse vibrations of a circular elastic sandwich plate under impulsive surface and linear loads are studied. To describe the kinematics of the asymmetric plate, the hypotheses of broken normal are adopted. The core is a lightweight material. Analytical solutions are obtained using Heaviside functions and Dirac delta-function. The solutions are analyzed numerically