FIR and millimetric measurements from a pulsed emission

Frequency mixing of two pulsed CO₂ lasers in a AsGa crystal induces a very low frequency emission (between 40 and 4 cm^–1).Using these emissions for spectroscopic measurements is very interesting, due to the spectral range covered in this way. However the shortness of the pulses does not allow the transposition of the classical method used with continuous emitting pumped lasers.In this paper are studied different experimental methods used to obtain absorption measurements of a given substance, with the best possible accuracy.     

Coronal holes with a saddle structure as deduced from Yohkoh observations

Saddle structures are seen in some images of the Sun in the soft X-rays obtained by Yohkoh mission. At the center of any such structure, there is a small coronal hole having the outlines of an astroid or a cross. The coronal saddles occur in magnetic configurations with a high degree of symmetry (quadrupoles). Comparison with the models shows that open field lines cannot be modeled using only the source surface.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 10, pp. 1275–1279, October, 1996.This work was supported in part by the Russian Foundation for Fundamental Research under Grant No. 93-02-15112.     

Cold sources observations in the millimetric region from the TIRGO telescope

Summary We describe a photometer which uses a³He-cooled bolometer working in the millimetric atmospheric window, aimed at a program of observations of galactic and extra-galactic sources. We also give an account of the results obtained during the January 1988 run at the TIRGO telescope. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Mechanism of spherulitic crystallization as deduced from observations of partially crystallized glassy polystyrene

Thin films of isotactic polystyrene partially crystallized from the glassy state were studied in detail by means of transmission electron microscopy and electron diffraction. Initial nucleation and growth stages of spherulitic fibrils (or lamellae) were illustrated clearly by using novel techniques, such as Au decoration, and novel specimens such as thin films containing holes.

Spherulitic nucleation begins with the crystallization of a liquid-crystal-like nodule or a group of these nodules merging to form a spherulitic center. Fibrils or lamellae grow and fan out from the nucleus by additional incorporation of maturing nodules. Proliferation of fibrils is essentially a space-filling process through the crystallization of uncrystallized nodules or nodules that were left behind by growing fibrils which had initiated earlier. The deduced mechanism of spherulitic crystallization leads directly to the formation of interlamellar links between neighboring fibrils. However, no extended-chain-type interlamellar links were revealed by Au decoration.

The application of the mechanism of spherulitic crystallization from the glass to that from the melt is also suggested; it is based primarily on recent studies which show remarkable similarities between structures existing in the glassy and the melt states prior to crystallization.     

Clusterization of water molecules as deduced from statistical mechanical approach

Using the methods of statistical mechanics we have shown that a homogeneous water network is unstable and spontaneously disintegrates to the nonhomogeneous state (i.e. peculiar clusters), which can be treated as an ordinary state of liquid water. The major peculiarity of the concept is that it separates the paired potential into two independent components—the attractive potential and the repulsive one, which in turn should feature a very different dependence on the distance from the particle (a water molecule in the present case). We choose the interaction potential as a combination of the ionic crystal potential and the vibratory potential associated with the elastic properties of the water system as a whole. The number ℵ of water molecules that enters a cluster is calculated as a function of several parameters, such as the dielectric constant, the mass of a water molecule, the distance between nearest molecules, and the vibrations of nearest molecules in their nodes. The number of H₂O molecules that comprise a cluster is estimated as about ℵ ≈ 900, which agrees with the available experimental data. Presented at the 2nd International Conference “Physics of Liquid Matter: Modern Problems” (September 2003, Kyiv, Ukraine)     

Grain boundary behavior in metallic solid solutions as deduced from diffusion and segregation experiments

Grain boundary diffusion and segregation experiments have been carried out in the same metallic solid solutions by means of radio-isotopes and Auger techniques. It was shown that the mass transport parameters could only be understood by assuming the formation of “2D phases” in “segregated grain boundaries” where the main bonds between atoms were identical to those which limit the bulk solid solubility of the solutes.     

Structure-property relationships in major ampullate spider silk as deduced from polarized FTIR spectroscopy

Polarized Fourier Transform Infrared (FTIR) spectroscopy is employed to study structure-property relationships in major ampullate spider silk being exposed to an external mechanical strain. From the measured infrared dichroism of aminoacid-residue - specific bands the molecular order parameter, the frequency width at half-maximum (FWHM) and the spectral position of the absorption maximum are determined in dependence on the external strain. For the highly ordered alanine-rich β sheets a change in the vibrational potential is found for macroscopic strains as low as a few percent. It can be quantitatively described by a quantum-mechanical approach in which the mechanical strain is treated as a weak external perturbation. The immediate microscopic response to the external field proves that β -sheeted crystals are tightly interconnected by pre-stretched chains as suggested recently (Y. Liu et al., Nat. Mater. 4, 901 (2005)).     

General properties of the effective conductivity tensor of inhomogeneous media deduced from variational principles

It is shown that the effective conductivity tensor of an inhomogeneous sample of finite size is not determined uniquely. Boundary conditions corresponding to extremal values of this tensor are found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 58–61, December, 1980.     

New FIR laser lines from hydrazine and assignments

Our new waveguide pulsed CO₂ laser, with peak powers above 1 kW, has allowed us to observe 24 new far-infrared laser lines emitted by hydrazine. Each of them is characterized in wavelength, relative polarization, intensity, optimum operating pressure and pump offset from the center of the exciting CO₂ line. These new laser emissions either form pairs sharing the same pump line, or complete such pairs with lines known from the literature. In the latter case, we have measured the relative polarization and offset of the partner lines whenever they were not reported in the literature. The availability of laser systems with two emission lines orthogonally polarized and sharing the same upper level is expected to facilitate the assignment work. We present complete assignments for four FIR laser emissions, and we propose J and K values for 12 further laser systems. PACS 42.55.Lt; 42.62.Fi     

Cygnus X-3: Six years of observations atE0≥50 TeV from the Plateau Rosa array

Summary Cygnus X-3 has been observed from 1982 to 1987 at primary energyE ₀≃10¹⁴ eV from the Plateau Rosa array. The absolute excess in the counting rate from the source region amounts to 0.15%, mostly concentrated in 1982 and 1986. The effect is observed in two classes of events although with small significance (2 and 1.4 s.d.). The 1986 data are consistent with observations of other arrays. The study of the 4.8 h time periodicity over a long observation time does not show any significant structure (2.5 s.d. excess at phase 0.2÷0.5). In 1982 and 1986 the light curves show respectively a wide excess between phases 0.60 and 0.85 and a 2.7 s.d. excess at phase 0.2÷0.25. The analysis of daily excesses from the source shows a good agreement with the expectations from pure statistical fluctuations, and no significant evidence of burst activity. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

The FIR optical properties of GaAs at 6 and 300 K

The amplitude and phase reflection spectra of GaAs have been determined in the FIR at 6 and 300 K by dispersive FTS and used to calculate values of the optical constants and dielectric parameters in the region of the fundamental lattice resonance.     

On the moment of inertia in deformed Ba-Xe nuclei as deduced from gamma-gamma energy correlation experiments

The γ-rays following reactions induced by bombarding targets of ^{114, 116, 118, 120, 122}Sn with 118 MeV ¹²C ions were investigated using six NaI(Tl) detectors in a two-dimensional coincidence arrangement. Experimental energy-correlation spectra were extracted from the original coincidence matrices. The energy-correlation spectra exhibit the features expected for rotational nuclei and were used to deduce information on the moment of inertia $\text{I}{}^{\mathrm{(2)}}\text{= ΔI/Δω}$. The gross properties of the behaviour of $\text{I}$⁽²⁾ in the Ba-Xe region are discussed together with their interpretation within the cranked shell model (CSM).     

Mechanism of charging of the pyrite/aqueous interface as deduced from the surface potential measurements

Surface potential of pyrite in an aqueous environment was measured by means of a single crystal pyrite electrode. The effect of the activity of S²⁻ and Fe²⁺ ions as well as of pH, was examined. The results show that S²⁻ and Fe²⁺ ions are the dominant potential determining ions. These ions are bound to surface sites with the extent depending on their activity in the bulk of the solution. Adsorption affinity of S²⁻ ions is significantly higher than that of Fe²⁺ ions so that in most cases the pyrite surface is negatively charged. The results were explained on the basis of the surface complexation model. It was found that the surface potential depends also on pH.     

Oscillator strengths for SiH and SiH deduced from the solar spectrum

Recent identifications of SiH (A²Δ-X²Π) and SiH⁺ (A¹Π-X¹Σ⁺) in the solar photospheric spectrum have enabled us to derive absolute oscillator strengths for the (0, 0) bands of these transitions: f₀₀(SiH) = 0.0033 and f₀₀(SiH⁺) = 0.0005. Our result for SiH is compared with other values.     

A Note on CH3OD Spectra, Ground-State Energies and FIR Laser Assignments

Literature data on the CO-stretching and the ground-state torsion-rotation spectra of the CH₃OD isotopic species of methanol have been exploited to extrapolate the ground-state energies to higher J through use of ground-state combination differences derived from the CO-stretching wavenumbers. In particular, the J-dependence has been extended and better defined for the difficult |K| = 0 to 2 E energy level sequences, which are strongly affected by molecular asymmetry. The pattern of the J-dependence is found to be qualitatively well reproduced by a simple 11 × 11 Hamiltonian model incorporating K = ±1 and ±2 off-diagonal asymmetry matrix elements. The results suggest partial reassignment of certain CO-stretching subbands, and the K = 8 and 9 A subbands have been newly identified through clues from reported far-infrared laser (FIRL) emission. Transition combination loops support a number of FIRL line assignments previously proposed, but show that the FIRL system pumped by the 9R(4) CO₂ line must be reassigned.     

On the role of anisotropic turbomachinery flow structures in inter-scale turbulence energy flux as deduced from SPIV measurements

The present study uses stereoscopic particle image velocimetry in the rotor exit of a centrifugal turbomachine to analyse anisotropy and geometrical characteristics of tensorial flow quantities. The purpose is to identify dominant topologies of turbulence stress tensor and principal directions of flow structures. The misalignment between principal directions of strain and turbulence stress tensors is more evident in the jet–wake interaction regions and questions the eddy-viscosity models which assume an exact alignment between stress/strain eigenvectors. Anisotropy analysis based on the barycentric approach shows that the disk-like structure and/or the rod-like structure limiting states of turbulence are the most frequent topologies of turbulence stress. Additionally, planar straining is the dominant deformation characteristic in the measurement area. These anisotropic behaviours considerably attribute to the turbulence energy cascade. Conditional isolation of flow structures based on inter-scale energy flux shows that a larger extent of turbulence stress anisotropy results in a larger energy flux and therefore significantly affects the dynamics of turbulent flow structures.     

Properties of8Be and12C deduced from the folding-potential model

Theα-α differential cross sections are analyzed in the optical model using a double-folded potential. With the knowledge of this potential bound and resonance-state properties ofα-cluster states in⁸Be and¹²C as well as astrophysical S-factors of⁴He(α,γ)⁸Be and⁸Be(α,γ)¹²C are calculated. Γ_γ-widths and B(E2)-values are deduced.