20,080 research outputs found
Preparations of methoxynitrophenazines and their photoconductivities
Eight methoxynitrophenazines with a methoxy group at the 1 or 2 position and a nitro group at the 6-, 7-, 8- or 9-position of the phenazine ring 1,6, 1,7. 1,8, 1,9, 2,6, 2,7, 2,8 and 2,9 were prepared and their photocurrents were measured by illuminating the surface-type cell with white light from a W lamp under a N atmosphere at room temp. The photocurrents of 1-nitrophenazine 6 and 2-nitrophenazine 7 are compared with those of the methoxynitrophenazines. The photocurrent (i sub p) increases with increasing light intensity (I), thus satisfying log i varies as n log I. The n values are 0.5-1.0. When the nitro group is located at the beta-position of the phenazine ring, the photocurrent becomes larger owing to the electron withdrawing property of the nitro group. On the other hand, the photocurrents of phenazines with the nitro group at the Alpha-position are extremely small. The photoconductivities of methoxynitrophenazines are lower in air
Pattern-recalling processes in quantum Hopfield networks far from saturation
As a mathematical model of associative memories, the Hopfield model was now
well-established and a lot of studies to reveal the pattern-recalling process
have been done from various different approaches. As well-known, a single
neuron is itself an uncertain, noisy unit with a finite unnegligible error in
the input-output relation. To model the situation artificially, a kind of 'heat
bath' that surrounds neurons is introduced. The heat bath, which is a source of
noise, is specified by the 'temperature'. Several studies concerning the
pattern-recalling processes of the Hopfield model governed by the
Glauber-dynamics at finite temperature were already reported. However, we might
extend the 'thermal noise' to the quantum-mechanical variant. In this paper, in
terms of the stochastic process of quantum-mechanical Markov chain Monte Carlo
method (the quantum MCMC), we analytically derive macroscopically deterministic
equations of order parameters such as 'overlap' in a quantum-mechanical variant
of the Hopfield neural networks (let us call "quantum Hopfield model" or
"quantum Hopfield networks"). For the case in which non-extensive number of
patterns are embedded via asymmetric Hebbian connections, namely,
for the number of neuron ('far from saturation'), we evaluate
the recalling processes for one of the built-in patterns under the influence of
quantum-mechanical noise.Comment: 10 pages, 3 figures, using jpconf.cls, Proc. of Statphys-Kolkata VI
eta nucleus optical potential in a chiral unitary approach
The self-energy of an eta in a nuclear medium is calculated in a chiral
unitary model, and applied to eta states in nuclei. Our calculation predicts an
attractive eta nucleus optical potential which can accommodate many eta bound
states in different nuclei.Comment: 4 pages, 2 figures, Talk given at the XVI International Conference on
Particles and Nucle
Magnetic moments of S-shell pentaquarks in the constituent quark model
We discuss the magnetic moments of the recently discovered exotic baryons
Theta(+) and Xi(--) and their multiplet partners in the framework of a naive
additive quark model. These baryons are set up as pentaquark states where four
quarks and a single antiquark are located in their ground state orbit. The
pentaquark states are classified as members of the flavor SU(3) octet and
antidecuplet with spin-parity J^P = (1/2)^- and (3/2)^-, where we determine the
magnetic moments of these pentaquark states.Comment: 13 pages, 2 figures, elsart; publication version, 8 pages, 1 figure,
ptptex; upload miss correcte
Toward Understanding the Origin of Turbulence in Molecular Clouds: Small Scale Structures as Units of Dynamical Multi-Phase Interstellar Medium
In order to investigate the origin of the interstellar turbulence, detailed
observations in the CO J=1--0 and 3--2 lines have been carried out in an
interacting region of a molecular cloud with an HII region. As a result,
several 1,000 to 10,000 AU scale cloudlets with small velocity dispersion are
detected, whose systemic velocities have a relatively large scatter of a few
km/s. It is suggested that the cloud is composed of small-scale dense and cold
structures and their overlapping effect makes it appear to be a turbulent
entity as a whole. This picture strongly supports the two-phase model of
turbulent medium driven by thermal instability proposed previously. On the
surface of the present cloud, the turbulence is likely to be driven by thermal
instability following ionization shock compression and UV irradiation. Those
small scale structures with line width of ~ 0.6 km/s have a relatively high CO
line ratio of J=3--2 to 1--0, 1 < R(3-2/1-0) < 2. The large velocity gradient
analysis implies that the 0.6 km/s width component cloudlets have an average
density of 10^{3-4} cm^{-3}, which is relatively high at cloud edges, but their
masses are only < 0.05 M_{sun}.Comment: 12 pages, 9 figures. To be published in the Astrophysical Journa
Tunnel magnetoresistance and interfacial electronic state
We study the relation between tunnel magnetoresistance (TMR) and interfacial
electronic states modified by magnetic impurities introduced at the interface
of the ferromagnetic tunnel junctions, by making use of the periodic Anderson
model and the linear response theory. It is indicated that the TMR ratio is
strongly reduced depending on the position of the -levels of impurities,
based on reduction in the spin-dependent -electron tunneling in the majority
spin state. The results are compared with experimental results for Cr-dusted
ferromagnetic tunnel junctions, and also with results for metallic multilayers
for which similar reduction in giant magnetoresistance has been reported.Comment: 5 pages, 4 figures, 2 column revtex4 format, ICMFS 2002 (Kyoto
Studies on organic semiconductors. 15: Effects of the substituents on the photoconductivities of substituted anthracenes
The photocurrents of the substituted anthracenes, 1,5-diacetylanthracene (2), 1-acetylanthracene (3), 9-acetylanthracene (4), 1,5-dichloroanthracene (5), 1,5-diethylanthracene (6), 1,5-dimethoxyanthracene (7), 9-cyanoanthracene (8), and anthracene (1) were measured by using their surface type cells in nitrogen. The compounds of (1), (5), (6), (7), and (8) showed the photocurrent spectra which corresponded to the absorption spectra of their evaporated films. In the cases of (2) and (3), however, the anomalous photocurrent appeared in the threshold region of their absorption spectra. The appearance of the anomalous photocurrent was characteristic of anthracenes having the acetyl group at 1- and/or 5-position. The magnitude of the photocurrents of the 1,5-disubstituted anthracenes was similar to that of (1). The photocurrents of the monosubstituted anthracenes were smaller than that of (1). Among the monosubstituted anthracenes, the compound (4) showed no photocurrent under the same conditions. Contrary to the results obtained in the cases of phenazines, the photoconductivities of the anthracene derivatives became better in air
Substituent effects on the electrical conductivities of the phenazine derivatives
The and/or photoconductivities of 16 substituted phenazines having methoxy, hydroxy, chloro, nitro, amino or t-butyl group at 1-, 2-, 1, 6- or 2,7- positions of the phenazine ring measured by using the surface type cells. The energy gaps of the dark conductivities in the range 2.0 to 2.3 were independent of the kinds and the positions of the substituent groups, although the photo-absorption wavelength of the evaporated films changed with them. No correlation between photoconductivity and fluorescence was observed. The photocurrent was affected by the position of the substituents; namely, the photocurrents of the 1,6-di-substituted phenazines. When the substituent at 1,6-positions was hydroxy or amino group, however, the photocurrents decreased. The photocurrents decreased drastically in the presence of oxygen
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