Signature of twin planes in Mössbauer spectroscopy of cuprate superconductors

One of the four quadrupole doublets (A, B, C, and D) observed in Mössbauer spectra of orthorhombic (Y or RE)₁Ba₂(Cu_1-xFe_x)30_7-δ(δ≈0) samples is identified with Fe dopant replacing a Cu site in twin planes. The site in question, labelled as D, is characterized by a quadrupole splitting Δ_D in the range 1.6±0.1 mm/s. The D-site intensity is found to approach zero when the 1-2-3, material is driven tetragonal, either upon oxygen desorption, upon oxygen loading, or upon increasing the Fe-dopant concentration.     

Particle Production in Expanding Spacetime

The complex time WKB (CWKB) approximation has been an effective technique to study particle production in expanding space time. The success of the approximation technique both in time and space dependent gauge has motivated us to study the method in relation to the time dependent approximation. In this work we try to understand the adiabatic and non-adiabatic transition within the framework of complex time WKB approximation. We find that the emergence of thermal radiation is due to some topological characteristics of cosmological spacetime that separates the spacetime into Euclidean and non-Euclidean region. This applies also to blackhole spacetime. The complex WKB trajectory approach shows that the Euclidean vacuum fluctuation is root cause of thermal particle production and is basically a Hawking effect. We also study here the sensitivity of particle production on the rise of scale factor at early times. It is found that the tunneling paths are responsible for the origin of thermal radiation whereas the slope of the scale factor determines the magnitude of the temperature of the thermal particle production. We also substantiate Hu's assertion in this connection.     

On modelling and forecasting of vector stochastic processes

Some deterministic and multivariate stochastic model identification techniques for setting up a suitable dynamic model for an observed multivariate process are described. Results of a case study involving the problem of multinodal load forecasting are presented in order to illustrate the practical utility of the methods discussed.     

Gas-liquid phase transition II: The van der Waals’ models

On the basis of a recently proposed theory of first order phase transition we discuss (i) the exact equation of state in the critical region and (ii) examine the van der Waals’ gas model.     

Oberfl?chenpotentiale von gemischten Einzelschichten aus normalen langkettigen Alkoholen und normalen Alkoxy?thanolen

Ohne Zusammenfassung     

Multielement analysis of water residue: A PIXE measurement

Summary A multielement PIXE method has been developed to analyse water residue obtained by evaporation technique. In this analysis, 250 ml of water sample mixed with 200 mg of cellulose powder is evaporated on steam bath in a platinum dish. From the residue thus obtained standard pellets are made for proton irradiation to excite characteristic X-rays. Proton irradiations were performed with 2.5 MeV beams with 20 nA intensity and the characteristic X-rays were detected with a high resolution Si(Li) detector and processed by standard electronics. A synthetic standard of cellulose matrix for concentration calibration was prepared by adding different elements from atomic absorption standards and homogeneously mixing them with the matrix with methanol.Using the present methodology, for a 20 C irradiation, it is possible to analyse quantitatively 10–15 different elements (K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Sr, Pb, etc.) in water samples. The procedure thus developed has been applied to study the concentration profiles of heavy elements in the municipal water supplies in the city of Dhaka and the results are compared with recommended levels of heavy elements in drinking water. Various aspects of the method and the implications of the data reported here have been discussed.

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Multielement-Analyse von Wasserrückständen: PIXE-Messung

Zusammenfassung 250 ml des Wassers wurden mit 200 mg Cellulosepulver gemischt und eingedampft. Aus dem Rückstand wurden Tabletten für die Protonenbestrahlung gepreßt. Die Bestrahlung wurde mit 2,5 MeV und 20 nA durchgeführt; die charakteristischen Röntgenstrahlen wurden mit Hilfe eines hochauflösenden Si(Li)-Detektors gemessen und elektronisch aufgearbeitet. Synthetische Standards für die Cellulosematrix wurden aus AAS-Standards hergestellt (Mischung mit Methanol). Mit dem beschriebenen Verfahren konnten bei 20-C-Bestrahlung 10–15 verschiedene Elemente (K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Sr, Pb, u.a.) in Wasserproben bestimmt werden. Die Methode wurde zur Untersuchung der Konzentrationsprofile von Schwermetallen im Leitungswasser der Stadt Dhaka eingesetzt, die mit den für Trinkwasser empfohlenen Konzentrationen verglichen wurden. Verschiedene Gesichtspunkte des Verfahrens und der erhaltenen Resultate werden diskutiert.

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This research was supported in part by the International Atomic Energy Agency, Vienna, Austria     

Influence of inhomogeneous distribution of the minority carriers on the doping dependence of the threshold current in EBP lasers using n-type GaAs at 300°K

The influence of inhomogeneous distribution of the minority carriers on the doping dependence of the threshold current in electron-beam-pumped (EBP) lasers using n-type GaAs at 300°K is studied theoretically. It is found that when inhomogeneity exists, the threshold current is weakly dependent on the doping concentration in agreement with the experimental observation.     

Single mode multiline emission from a hybrid CO2 laser

A simple technique of obtaining single mode multiline emission from a hybrid CO₂ laser is described. This involves operation of its low pressure section below lasing threshold and a judicious positioning of the axial modes with respect to the corresponding rotational line centres. Emission with comparable intensities on up to four rotational lines in the P-branch of the 10 μm band has been achieved.     

Elastic scattering of electrons by atomic hydrogen at intermediate energies

The improved second Born computational method of Das has been used in computing the differential cross section for the elastic scattering of electrons by atomic hydrogen at intermediate energies (in the range 20–50eV). The results show that the method of Das works nicely down to energies of 20 eV.