Transport in two dimensional electronic micro-emulsions

In two dimensional electron systems with Coulomb or dipolar interactions, a direct transition, whether first or second order, from a liquid to a crystalline state is forbidden. As a result, between these phases there must be other (micro-emulsion) phases which can be viewed as a meso-scale mixture of the liquid and crystalline phases. We investigate the transport properties of these new electronic phases and present arguments that they are responsible for the various transport anomalies that have been seen in experiments on the strongly correlated 2DEG in high mobility semiconductor devices with low electron densities.     

Structure and superconductivity in FexCu1−xBa2YCu2O7+y superconductors synthesized by high pressure

Comprehensive studies of X-ray diffraction, oxygen content, superconductivity and Mössbauer effect have been made on Fe_xCu_1−xBa₂YCu₂O_7+y superconductors (0.00≤x≤0.70) synthesized by ambient (AM) and high pressure (HP). Results indicate that all the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples. The studies of oxygen content, and Mössbauer spectroscopy indicate that the HP-samples have higher oxygen content, carrier concentration and average valence of Fe than the AM-samples. Moreover, for the HP-samples more Fe atoms located in CuO_x chains have fivefold-oxygen coordination. These are important reasons for the enhancement of T_c in the HP-samples.     

Investigations of low- and high-spin states of <Superscript>132</Superscript>La

The fusion evaporation reaction ¹²²Sn(¹⁴N, 4n)¹³²La was used to populate the high-spin states of ¹³²La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2^- and the isomeric state 6^-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh _11/2 ⊗ νh _11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies in the spin assignment of the band head. Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003     

On dimensional rigidity of bar-and-joint frameworks

Let V={1,2,…,n}. A mapping p:V→R^r, where p¹,…,pⁿ are not contained in a proper hyper-plane is called an r-configuration. Let G=(V,E) be a simple connected graph on n vertices. Then an r-configuration p together with graph G, where adjacent vertices of G are constrained to stay the same distance apart, is called a bar-and-joint framework (or a framework) in R^r, and is denoted by G(p). In this paper we introduce the notion of dimensional rigidity of frameworks, and we study the problem of determining whether or not a given G(p) is dimensionally rigid. A given framework G(p) in R^r is said to be dimensionally rigid iff there does not exist a framework G(q) in R^s for s?r+1, such that ∥qⁱ-q^j∥²=∥pⁱ-p^j∥² for all (i,j)∈E. We present necessary and sufficient conditions for G(p) to be dimensionally rigid, and we formulate the problem of checking the validity of these conditions as a semidefinite programming (SDP) problem. The case where the points p¹,…,pⁿ of the given r-configuration are in general position, is also investigated.     

Property changes of electroplated Cu/Co alloys and multilayers by organic additives

We investigated the change of magnetic properties of the electroplated Cu/Co alloys and multilayers caused by organic additives and high temperature annealing. When plated with a pure Cu/Co electrolyte, the alloy contained ∼25% of Cu and ∼75% of Co. The alloy was made of hcp-Co, fcc-Co and Cu(1 1 1) and was super-paramagnetic at room temperature. As we add a few organic additives in the plating electrolyte, the hcp-Co of the films disappeared. The organic additives contained in the electrolytes changed paramagnetic Cu/Co multilayers to ferromagnets. High-temperature thermal annealing increased coercivity due to the growth of the Co grains.     

Lifetime study of high-spin states in 104,105In

In the neutron deficient isotopes _104,105In lifetimes of high spin states in the range from 0.5 ps to 600 ps have been measured in a coincidence recoil distance Doppler shift (RDDS) experiment. By combining the Doppler shift attenuation (DSA) and RDDS methods at few μm flight distances, the problem of delayed feeding has been avoided and very short lifetimes in the range 0.5–0.8 ps have been determined. Shell model calculations with strong restrictions for the neutron orbitals reveal good agreement with experimental level energies and still fair agreement for most measured B(M1) and B(E2) values. Received: 30 June 1998     

Exact solutions to linear programming problems

The use of floating-point calculations limits the accuracy of solutions obtained by standard LP software. We present a simplex-based algorithm that returns exact rational solutions, taking advantage of the speed of floating-point calculations and attempting to minimize the operations performed in rational arithmetic. Extensive computational results are presented.     

External influence on magnetic properties of Fe-based nanocrystalline alloys

Amorphous and nanocrystalline ribbons of NANOPERM, FINEMET and HITPERM were studied by Mössbauer spectroscopy (MS) after the influence of external factors: different annealing atmospheres, tensile stress and several kinds of corrosion. MS is a suitable tool for such studies because the spectral parameters are very sensitive to changes in the vicinity of the probe — ⁵⁷Fe nuclei. The most sensitive parameters were hyperfine magnetic field in crystalline component, average hyperfine field in amorphous component and direction of net magnetic moments. Influence of external factors modified also the structure of the alloys, i.e. new or modified phases were identified by MS phase analysis.