Emissivity of CO2-H2O mixtures at temperatures up to 1000° K

The emissivity in the 2.7 m range is examined with a spectrometer having 25 cm^–1 for 2.5, ,7.5 cm·atm,4 8cm·atm, 400T1000° K; 150P730 mm Hg. It is found that relation (1) is obeyed to within /0.1, though the calculated transmission is usually less than the measured value. It is shown that the relation is obeyed on account of the mutual position of the CO₂ and H₂O lines in the band, i.e., one gas may be considered as unselective relative to the other.     

Mössbauer study of the perovskite series Sr(Fe1−xTix)Oy

⁵⁷Fe Mssbauer effect in the perovskite series Sr(Fe_1–xTi_x)O_y (0.0x0.99; y3) at RT and 78K has been analyzed. The influences of the Ti composition on the coexitence of Fe⁴⁺ and Fe³⁺, the ratio of Fe⁴⁺ to the total Fe, and the Y value have been studied. When 0x0.6 the ratio of Fe³⁺ (II) doublet to the total Fe increases as the final firing temperature increases, agreeing with the result obtained from the positron lifetime measurements. When x0.7, the Fe³⁺ (II) doublet disappears. In the range of x=0.9 and x=0.99, there still exists a considerable content of Fe⁴⁺ in samples, disagreeing with the result obtained from the chemical analysis by Clevenger. The relations between the electrical resistivity and the thermistor material constant B of negative temperature characteristic varying with Ti composition have been discussed.     

Mössbauer studies on the series La1-xSrxFeO3

Mössbauer spectra have been recorded at 4.2 and 300 K on the series La_1–x Sr _x FeO₃, wherex varies from 0 to 1.0 in steps of 0.1. Neutron diffraction experiments have shown that the crystal structure is orthorhombic for 0x<0.3, rhombohedral for 0.4x0.7, and cubic for 0.8<x1.0. Mössbauer spectra at 4.2 K are composed of magnetic sextet components arising from different charge states of iron ions. In the orthorhombic and rhombohedral phases, the charge states Fe³⁺ and Fe⁵⁺ coexist. In the cubic phase, iron is present as Fe³⁺ and Fe⁴⁺ states. At 300 K, the samples are magnetically ordered in the range 0 x0.3 and the coexistence of Fe³⁺ and Fe⁵⁺ remains. For samples 0.4x1.0, the samples are paramagnetic. Fits to these spectra require two components, one corresponding to an Fe⁴⁺ state, the other being best described as an Fe³⁺ ion forx0.7 but forx>0.7 having a mean charge state which increases to 3.5 forx=1.0.     

Mössbauer study of mixed valent silicides Eu(Ir1−x Pd x )2Si2

The solid solutions Eu(Ir_1–x Pd _x )₂Si₂, which exist for 0x0.125 and 0.75x1. cristallize with the tetragonal ThCr₂Si₂-type structure. The variation of the europium valence with composition has been thoroughly studied at temperatures 4.2T293 K by¹⁵¹Eu Mössbauer resonance. For 0x0.125 the europium valence at room temperature decreases asx increases. For 0.75x1 the valence transition temperature Eu³⁺Eu²⁺ increases asx increases.     

Electronic structure of amorphous Nb1-x Si x films studied by X-ray emission and X-ray photoelectron spectroscopy

We present valence band spectra of the amorphous system Nb_1–x Si _x (0.2x0.8), of bcc-Nb and of a-Si obtained by X-ray photoelectron spectroscopy (XPS, Al K) and X-ray emission spectroscopy (XES, Si K-emission bands). The samples were prepared as thin films by sputtering. The origin of all prominent spectral features was identified and consistently correlated to Si 3s-, Si 3p-and Nb 4d-derived states. The Nb4d-Si3p coupling is stable in binding energy over a wide concentration range. There is strong experimental evidence that the short range order changes considerably within the concentration interval 0.4x0.7, whereas the partial density of states of the Si 3p-electrons is clearly altered in the small concentration range 0.50x0.57.     

Zeros of the finite-size scaling region partition function for a model with a wetting transition

We derive a finite-size scaling representation for the partition function for an Onsager-Temperley string model with a wetting transition, and analyze the zeros of this partition function in the complex scaled coupling parameter of relevance. The system models the one-dimensional interface between two phases in a rectangular two-dimensional region (x, y) ²,–L yL,oxN. The two phases are at coexistence. The string or interface has a surface tension 2KkT per unit length and an extra Boltzmann weighta per unit length if it touches the surfaces aty=±L. There is a critical valuea _c=1/2K and fora>a _c the string is confined to one of the surfaces, while fora a _c the string moves roughly in the rectangular region. The finite-size scaling parameters are =a _c ² N/L ² and =L(a–a _c)/a _c ² . We find that for || large, the zeros of the scaled partition function lie close to the lines arg()=±/4 with re()>0. We discuss the motion of all the zeros as changes by both analytic and numerical arguments.     

Influence of manganese admixture on the magnetic properties of CdHgSe

The magnetic susceptibility of Cd_x-Hg_1–x–yMn_ySe(x 0.1, 0 y 0.1) in the temperature range 77–300 K is investigated. According to the usual model, the dependence Mn^–1=f(T) is due to clusters in the form of closely spaced Mn atoms, between which there may be both direct and indirect (through a nonmagnetic atom) exchange interaction, leading to antiferromagnetic ordering.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 65–67, August, 1991.     

Evidence of Hg-chain formation in Hg x TiS2: a199mHg-TDPAC study

We determined the^199mHg nuclear quadrupole interaction in the misfit or superstoichiometric compound Hg _x TiS₂ by time differential perturbed angular correlation. A unique Hg-site withv _Q =511(1) MHz and =0.410(4) was observed, irrespective of the Hg-uptake (2/3x4/3). We propose a model of Hg-Hg zig-zag chains which accounts for these observations as well as for the X-ray diffraction data.     

Investigation of conductivity in the Sr(Fe1−xTix)Oy system by iron-57 Mössbauer spectroscopy

On the basis of our previous work electrical conductivity in the Sr(Fe_1–xTi_x)O_y system (0.0x0.9,y3) has been further studied by means of Mössbauer spectroscopy. When 0.0x0.6, the concentration of Fe³⁺ (II) doublet relates to the final firing temperature and electrical conductivity of the materials is sensitive to the concentration of Fe³⁺ (II). Atx=0.25, the curve of the resistivity versus Ti contentx shows a local minimum which is observed for the first time. The results indicate that the coexistence of Fe⁴⁺ and Fe³⁺ in the same lattice leads to high conductivity; the conductivity increases when the Fe⁴ concentration approaches to that of the Fe³⁺ one. When the temperature is at 260 K and 230 K, the presence of the intermediate state showing quadrupole splitting has an effect on the conductivity of the materials.     

Properties of theL p -solutions of linear impulsive equations in a banach space

Conditions for the existence ofL _p-solutions (1p) of linear impulsive equations in a Banach space are found.     

Invariants of linear combinations of transpositions

It is shown that for a one-parameter set H _N of linear combinations of N(N–1)/2 elementary transpositions {P _jk } (1j at arbitrary natural N3, one can construct a variety {I _m } (3mN) of operators which commute with H _N . Being applied to SU(n) spin representations of the permutation group, this proves the integrability of 1D periodic spin chains with elliptic short-range interaction.     

Temperature dependence of the electric field gradient in Er metal

The method of perturbed angular distributions was used to measure the temperature dependence of the electric field gradient in Er single crystal for 98 KT156 K. The I=11^– isomer in Er¹⁵⁴) was used as a probe. ₀ increases monotonically for 98 KT259 K and then decreases. A possible cause for this effect may be short range interactions between the f electrons above the Neel point.Visitor from the Weizmann Institute, Rehovoth, Israel.     

Recent results from the TCV tokamak

During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0B _tor1.46T,I _p800kA,k2.05, –0.71. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000s^–1 have been stabilized using the external coil system. Ohmic H-modes with Troyon factors ( _tor aB/I _p) up to two and densities up to 2.25×10²⁰m^–3, corresponding to the Greenwald limit, have been obtained in diverted discharges. Limiter H-modes with line averaged electron densities up to 1.7×10²⁰m^–3 have been obtained in elongated D-shaped plasmas with 360 kAI _P600 kA.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was partly supported by the Fonds National Suisse de la Recherche Scientifique.     

Schrödinger Operators with Empty Singularly Continuous Spectra

Let H be a semibounded perturbation of the Laplacian H ₀ in L ²( ^d ). For an admissible function sufficient conditions are given for the completeness of the scattering system (H), (H ₀). If is the exponential function and if e^{– H} is an integral operator we denote the kernel of the difference D = e^{– H} – e^{– H} ₀ by D (x, y), > 0. The singularly continuous spectrum of H is empty if^d dx ^d dy |D(x,y)| (1 + |y|²)< for some > 1. This result is applied to potential perturbations and to perturbations by imposing Dirichlet boundary conditions.     

Vibrational property of the slow N 2 + ions deposited SiNx films

We have investigated vibrational properties of silicon-nitride films, SiN_x (0.3×1.33), produced by a non-thermal method using high-resolution electron energy loss spectroscopy. The results, based on a continuous random network model assuming a planar XY₃ vibrational bond unit, show that the Si-N bonds in the films closely resemble those in typical thermal silicon nitride although nitrogens occupy some metastable binding sites. We estimate force constants of the restoring forces for a Si₃N bond unit, which tend to increase gradually with increasing nitrogen content x. In particular, the central force constant k₁ for the in-plane stretching mode of silicon atoms varies with x in the range 297k331 N/M, larger than the theoretical value for a nitrogen atom imbedded in a pure Si crystal.     

Cation distribution and entropic disordering in mixed spinel ferrite Ga0.4Fe0.6NiCr1−yAlyO4

Mössbauer measurements (4.2T298°K) indicate the presence of entropic disordering in (Ga _0.4 ³⁺ Fe _0.6 ³⁺ Al _p ³⁺ )[Ni²⁺Cr _1–y ³⁺ Al _y-p ³⁺ Fe _p ³⁺ ]O₄ and a linear increase in p with y between 0(y=0) and 0.11(y=1). Entropic spins are located only on A-sites indicating relatively large A-sublattice frustration. Weak A-B coupling could explain this separate sublattice behaviour. Magneton number, alongwith Mössbauer p values, shows B-site canting which increases with y revealing weakness of A-B interaction. Present system can be called a frustrated ferrimagnet or entropie ferrimagnet where ferrimagnetic and frustrated (entropie) spins are coexisting.     

Measurement of the refractive index and optical absorption spectra of epitaxial bismuth substituted yttrium iron garnet films at uv to near-ir wavelengths

Refractive-index and optical-absorption spectra of Bi-substituted yttrium iron garnet films, epitaxially grown by liquid-phase epitaxy, have been measured in the spectral regime 0.26 m1.9 m by thin-film interference for 0.52 m and by ellipsometry for0.52 m. The Y_3–x–y Bi _x Pb _y Fe_5–z Pt _z O₁₂ films contain bismuth in the range Ox 1.42, lead in the range 0.01 y0.08 and platinum in the range 0.005<=z0.03. There is satisfactory coincidence between the results from ellipsometry and thin-film interference in the overlapping wavelength region. The materials investigated are the same as reported earlier from this laboratory in ter mof their magnetic and magnetooptic properties.     

Operator product expansions on the vacuum in conformal quantum field theory in two spacetime dimensions

Let ₁(x) and ₂(y) be two local fields in a conformal quantum field theory (CQFT) in two dimensional spacetime. It is then shown that the vector-valued distribution ₁(x)₂(y)|0 is a boundary value of a vectorvalued holomorphic function which is defined on a large conformally invariant domain. By group theoretical arguments alone it is proved that ₁(x)₂(y)|0 can be expanded into conformal partial waves. These have all the properties of a global version of Wilson's operator product expansions when applied to the vacuum state |0. Finally, the corresponding calculations are carried out more explicitly in the Thirring model. Here, a complete set of local conformally covariant fields is found, which is closed under vacuum expansion of any two it its elements (a vacuum expansion is an operator product expansion applied to the vacuum).Work supported by Deutsche Forschungsgemeinschaft     

From ferromagnetic to non-magnetic singlet ground state in CePd1-x Ni x

Magnetic, resistivity and specific heat measurements were performed on the CePd_1-x Ni _x system, which ranges between a ferromagnetic (CePd) and non-magnetic (CeNi) singlet ground state. The Curie temperature (T _c ) grows with Ni concentration, reaching a maximum value ofT _c =(10.5±0.1) K for 0.5x0.8. Both, the concentration dependence ofT _c and the Curie-Weiss temperature ( _P ) follow the predicted competition between the magnetic exchange interactions and the Kondo effect. In the crossover region (x0.9) the entropy gain shows that only the doublet crystal field ground state is involved in the singlet ground state formation.Partially supported by the Direction de la Coopération Scientifique et Technique du Ministère des Relations Extérieures of France     

An approximation method to solve Einstein's field equations on a curved background metric

An approximation method is developed to calculate the gravitational field of a matter sourceT moving on a curved background metric that is an exact solution of the field equations and deviates only weakly from flat space-time. The fieldh of the sourceT is supposed to be much smaller than the curved part of the background, so that in the series expansion ofh each order can be expanded in powers of the background.