Phase diagram of multilayer magnetic structures

Multilayer ferromagnet-layered antiferromagnet (Fe/Cr) structures frustrated because of roughness of interlayer boundaries were studied by mathematical modeling methods. The phase diagram of a three-layer system (plotted as film thickness versus the degree of roughness of the interfaces) was obtained, and the order parameter distributions in each phase were determined. The character of phase transitions in this system was studied. The applicability range of the Slonczewski magnetic proximity model was determined.     

Optimal detection of visual evoked potentials

The authors consider the problem of detecting visual evoked potentials (VEP's). A matched subspace filter is applied to the detection of the VEP and is demonstrated to perform better than a number of other evoked potential detectors. Unlike single-harmonic detectors, the matched subspace filter (MSF) detector is suitable for detecting multiharmonic VEP's. Moreover, the MSF is optimal in the uniformly most powerful sense for multiharmonic signals with unknown noise variance     

Geometrical restrictions of water diffusion in aqueous protein systems. A study using NMR field-gradient techniques

Geometrical restrictions of water diffusion in different aqueous protein systems were studied using two versions of the NMR field gradient technique. The samples were aqueous systems of bovine serum albumin, gelatin and horse myoglobin at concentrations ranging from diluted solutions to almost dry powders being only partly hydrated. Hydrated protein aerogels were produced by the aid of a special preparation procedure and studied in addition. The experiments referred to the, temperature and concentration dependences of the water diffusion coefficient above and below the free-water freezing temperature. The diffusion coefficient within clusters of overlapping hydration shells is reduced by one order of magnitude compared with that of bulk water. Geometrical restrictions manifest themselves (a) by the obstruction effect observed at low protein concentrations, (b) by the topologically two-dimensional diffusion in the network of overlapping hydration shells, (c) by the percolation threshold appearing at about 15%_b.w. water and (d) by the anomalous diffusion behaviour concluded from the protein aerogel study.     

Threshold voltage-minimum gate length trade-off in buried channelPMOS devices for scaled supply voltage CMOS technologies

The trade-off between threshold voltage (V_th) and the minimum gate length (L_min) is discussed for optimizing the performance of buried channel PMOS transistors for low voltage/low power high-speed digital CMOS circuits. In a low supply voltage CMOS technology it is desirable to scale V_th and L_min for improved circuit performance. However, these two parameters cannot be scaled independently due to the channel punch-through effect. Statistical process/device modeling, split lot experiments, circuit simulations, and measurements are performed to optimize the PMOS transistor current drive and CMOS circuit speed. We show that trading PMOS transistor V_th for a smaller L_min results in faster circuits for low supply voltage (3.3 to 1.8 V) n⁺-polysilicon gate CMOS technology, Circuit simulation and measurements are performed in this study. Approximate empirical expressions are given for the optimum buried channel PMOS transistor V _th for minimizing CMOS circuit speed for cases involving: (1) constant capacitive load and (2) load capacitance proportional to MOS gate capacitance. The results of the numerical exercise are applied to the centering of device parameters of a 0.5 μm 3.3 V CMOS technology that (a) matches the speed of our 0.5 μm 5 V CMOS technology, and (b) achieves good performance down to 1.8 V power supply. For this process the optimum PMOS transistor V_th (absolute value) is approximately 0.85-0.90 V     

Regioorientation in the reaction of side chain activated alkylpyridines with electrophiles

X-ray structural data has shown that condensation of sym-3-nitrocollidine with benzaldehyde occurs at the 6-methyl group. The presence of an acceptor group in the side chain of 2,6-dimethyl-4-cyanomethyl-3-nitropyridine causes condensation to occur at the activated methylene group in the 4-position.M. V. Lomonosov State University, Moscow 119899. A. N. Nesmeyanov Institute of Organoelemental Compounds, Moscow 117813. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11. pp. 1543–1550, November, 1995. Original article submitted June 10, 1995.     

On the possibility of a unified approach to investigating the indicatrices of coherent wave scattering by different inhomogeneities of the medium

A general expression describing the coherent scattering indicatrix by arbitrary inhomogeneities of the medium is derived. It is shown that a universal program can be devised for calculation of such indicatrices to avoid difficulties in the analytical and experimental investigations of the media through the wave processes.Institute of Applied Geophysics, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 7, pp. 631–638, July, 1995.     

Coulomb blockade electrometer with a high-T c island

We report on a successful attempt to fabricate a Coulomb blockade electrometer consisting of an ultrasmall YBa₂Cu₃O_7−δ (YBCO) island coupled to two gold electrodes through a high-resistance native surface tunnel barrier. A third electrode placed near the island was used as an electrostatic gate. Spectra typical for tunneling into the YBCO superconductor were reproducibly measured. At temperatures below 0.5 K the low-bias conductance was suppressed by the Coulomb blockade. The blockade could be periodically varied by the gate potential. An external magnetic field of up to 5 T strongly influenced the transport via the island but without any change in the period of the Coulomb oscillations. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 112–117 (25 January 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Monte Carlo simulations in the vicinity of the critical point: Vapour-liquid coexistence curve

A generalized Gibbs-ensemble methodology with a fluctuating particle is used to determine the coexistence vapor-liquid densities for a square-well fluid. It is shown that the presence of the fluctuating particle in sub-states of the Markov chain of states supresses considerably density fluctuations which makes it possible to carry out simulations efficiently even for temperatures very close to the critical temperature.     

The Doppler Rayleigh lidar system at Arecibo

The instrument structure and the operation of a Doppler Rayleigh lidar located at the Arecibo Observatory in Puerto Rico are described. The device consists of an injection seeded, frequency doubled, Nd:YAG laser coupled with a small Newtonian telescope and a single etalon, Fabry-Perot interferometer in its receiver. With this combination of transmitter and receiver, observations of the Doppler spectral components of the Rayleigh backscattered signal from the atmosphere are possible. Neutral wind and temperature up to mesospheric heights are presented. The improvements to the instrument that are underway, which will allow an increase in the temporal and spectral sampling of the winds, are discussed