Quantum memory on the basis of photon echo in three-level optically dense gaseous media with the Ξ-configuration of atomic transitions

A new variant of realization of quantum memory based on the use of a photon echo in an optically dense three-level gaseous medium is proposed. The use of a long-lived highly excited optical level as a storage of quantum information is the characteristic feature of the scheme proposed. This scheme of quantum memory is distinguished by reduced optical noises owing to the possibility of realizing temporal, spectral, and spatial selection of weak quantum radiation relative to the accompanying laser pulsed fields.     

A manifestation of magnetism of bismuth in iron garnet films

Bismuth iron garnet films prepared through electron-beam and laser-induced evaporation on (001)-oriented substrates of scandium gallium gadolinium garnet are investigated using ferromagnetic resonance. It is assumed that the additional minima observed in the angular dependence of the resonance field can be associated with the magnetic moment of bismuth ions.     

Domain wall dynamics in a two-layer uniaxial film

Numerical solution of the Slonczewski equations were used to study the motion of an individual domain wall in a two-layer uniaxial film in which the damping parameter and the gyromagnetic ratio depend on the specific layer.     

Survivable network design under optimal and heuristic interdiction scenarios

We examine the problem of building or fortifying a network to defend against enemy attacks in various scenarios. In particular, we examine the case in which an enemy can destroy any portion of any arc that a designer constructs on the network, subject to some interdiction budget. This problem takes the form of a three-level, two-player game, in which the designer acts first to construct a network and transmit an initial set of flows through the network. The enemy acts next to destroy a set of constructed arcs in the designer’s network, and the designer acts last to transmit a final set of flows in the network. Most studies of this nature assume that the enemy will act optimally; however, in real-world scenarios one cannot necessarily assume rationality on the part of the enemy. Hence, we prescribe optimal network design algorithms for three different profiles of enemy action: an enemy destroying arcs based on capacities, based on initial flows, or acting optimally to minimize our maximum profits obtained from transmitting flows.     

Ageing of wet-synthesized oxide powders

Wet chemical synthesis of precursor oxide ceramics is a method to obtain small particulate powders. Such powders are far more prone to ageing in air than more traditional precursors. Thermogravimetric analysis is used to highlight the species responsible for the ageing of ceramic precursors. Indeed water and carbon dioxide are observed to evolve from aged powders. Ceramics obtained from aged precursors can reach a very low final density with respect to the theoretical value. A large degree of the original sintering properties can be recovered after washing the aged powders with ethanol in a basic medium.     

Studies on the curing kinetics of epoxy resins using mixture of nadic/or maleic anhydride and 4,4′-diaminodiphenyl sulfone

Curing kinetics of diglycidyl ether of bisphenol-A (DGEBA) in the presence of maleic anhydride (MA)/or nadic anhydride (NA) or mixture of MA/NA: 4,4′-diaminodiphenyl sulfone (DDS) in varying molar ratios were investigated using differential scanning calorimetry. Curing behaviour of DGEBA in the presence of varying amounts of DDS:MA/NA was evaluated by recording DSC scans at heating rates of 5, 10, 15 and 20°C min⁻¹. The peak exotherm temperature depends on the heating rate, structure of the anhydride as well as on the ratio of anhydride: DDS. Thermal stability of the isothermally cured resins was evaluated by thermogravimetry. The char yield was highest in case of resins cured using mixture of DDS:MA (0.75:0.25; sample EM-1) and DDS:NA (0.75:0.25, sample EN-1).     

Organylthiochloroacetylenes: IX. Reactions with geminal and vicinal dithiols

Alkylthiochloroacetylenes react with geminal (in ether) and vicinal (in THF) dithiols to form, respectively, functional 1,3-dithiolenes (yield 43%) or 1,3-dithiolanes (yield 34%).     

Two-dimensional phased arrays for surgical applications: Multiple focus generation and scanning

A numerical simulation and a comparative analysis of the acoustic fields produced by two-dimensional phased arrays intended for ultrasonic surgery are performed for the case of a multiple focus (in particular, 25 foci) generation. The calculations were conducted for arrays (with an operating frequency of 1.5 MHz) consisting of 256 elements 5 mm in diameter, which were positioned on the array surface both regularly and randomly. The array foci can be formed simultaneously, but, in this case, the intensity levels of the secondary peaks in the ultrasonic field can exceed the values that guarantee the safe application of this method in surgery. A much safer way is to synthesize many foci with the use of several configurations, each of which contains a smaller number of foci. The number of foci in individual configurations must be approximately the same. It is demonstrated that randomization of the element distribution over the array surface provides an opportunity to improve the array performance, to reduce the intensity levels of secondary peaks in the acoustic field, and to increase the array capability for multiple focus scanning off the array axis.     

Measurement of the $b\overline{b}$ production cross section in 920 GeV fixed-target proton-nucleus collisions

Using the HERA - B detector, the production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The production was tagged via inclusive bottom quark decays into by exploiting the longitudinal separation of decay vertices from the primary proton-nucleus interaction. Both e ⁺ e ^- and channels have been reconstructed and the combined analysis yields the cross section . Received: 6 June 2002 / Revised version: 2 September 2002 / Published online: 8 November 2002