FAST BOLOMETRIC RESPONSE OF BULK La0.7 Sr0.3
MnO3 ELECTROCERAMIC STRUCTURES
Yu.M. Nikolaenkoa, I.S. Maksimova,
Yu.V. Medvedeva, A.N. Ulyanova
and A.M. Grishinb
a Donetsk Physico-Technical Institute of the National Academy of Sciences of
the Ukraine 72 R. Luxemburg, Donetsk, 340114, Ukraine
b Dept. of Condensed
Matter Physics, Royal Institute of Technology 100 44, Stockholm, Sweden
Received: July 22, 1999; revised version December 10, 1999
We report on the performance of a microwave electroceramic bolometer
of
hybrid La0.7 Sr0.3
MnO3/Al2O3 (0.2×2×4 mm3)
structure. The
estimated thermal resistance of the bulk ceramic manganite film-single
crystal sapphire interface is about 500 K/W at room temperature. This
resistance is the main thermal barrier in the heat sink system and has been
found to be slightly dependent on temperature. When compared with the
high-Tc superconducting bolometers, the La0.7
Sr0.3 MnO3 microwave
electroceramic bolometer works in a more wide temperature range, from 77 K
to
330 K, excluding the narrow temperature interval at the metal-insulator
phase transition (T=230 K). The microwave electroceramic bolometer
sensitivity and the time constant at room temperature have been found to be
0.1 V/W and 100 ms, respectively. To improve the bolometer performance the
point contact has been fabricated by a break junction technique. The
optimization of a microwave electroceramic bolometer design brought to a
considerable improvement of basic bolometer characteristics. The microwave
sensitivity was about 0.3 V/W and the time constant was less than 100 ns.
PACS numbers: 07.57.Kp, 85.60.Gz, 72.15.Gd
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THE HARD ELLIPSOID POTENTIAL MODEL FOR THE ROTATIONAL ENERGY TRANSFER
AND ITS REGION IN MOLECULAR SYSTEMS
K. Agrawala, S. Tilwankarb and P. Dashorac
a Department of Physics, Government Polytechnic, Ajmer (Raj.), 305 002,
India
b Department of Physics, Government Polytechnic, Dhar (M.P.), 454 001,
India
c Department of Physics, University of Rajasthan, Jaipur (Raj.), 302
001, India
Received: November 9, 1999; in final form March 14, 2000
The hard ellipsoid potential model for understanding the mechanism of
the rotational energy transfer in a diatomic molecule due to collisions with
an atom was explored by performing quasi-classical trajectory calculations
on
N2-He and N2- Ne systems governed by a sum of pairwise
atom-atom Morse
interactions. It is found that the conversion of the orbital angular
momentum
into the angular momentum of the molecule takes place when the colliding
atom
is very close to the classical turning point ellipsoid. The quantitative
measures to define such closeness were introduced. Further, it is observed
that nearly 50% of the total angular momentum transfer takes place when the
colliding atom approaches the classical turning point ellipsoid and the
remaining 50% transfer takes place while the atom bounces back.
PACS numbers: 34.50.Ez
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PRESSURE BROADENING AND SHIFT OF THE 326.1 nm Cd LINE PERTURBED BY H2
AND D2
A. Bielski, R. Ciurylo, J. Domyslawska, D. Lisak, R.S. Trawiñski and
J. Wolnikowski
Institute of Physics, Nicholas Copernicus University Grudziadzka 5/7,
87-100 Toruñ, Poland
Received: December 13, 1999: in final form February 3, 2000
The experimental values of pressure broadening and shift coefficients
of the 114Cd 326.1 nm line perturbed by H2
and D2 are determined using
a LIF technique and compared with theoretical values calculated from the
impact theory.
PACS numbers: 32.70.-n, 33.70.-w, 34.20.-b
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SUPERCONDUCTING PROPERTIES OF THE CHARGED WEAKLY INTERACTING BOSE GAS
(``d'' SYMMETRY)
Z.M. Galasiewicz
Institute of Physics, Wroclaw University of Technology Wybrzeze
Wyspiañskiego 27, 50-370 Wroclaw, Poland
Received: February 2, 2000
A system of charged weakly interacting bosons with ``d'' symmetry is
considered. The interaction U(d) = U(s) f(theta)
contains the angle
dependence f(theta) ~ |Y2,1|2 consistent
with ``d'' symmetry. This
system resembles much more free bosons than the system with ``s'' symmetry
(interaction U(s)). For example at T=0, n approx nc(d),
where n, nc(d) are the densities of particles and condensate respectively.
PACS numbers: 67.40.-w, 74.20.-z
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TREATMENT OF THE PERIODICALLY INHOMOGENEOUS SURFACE: MULTIPLE BOUNDARY
CONDITION
H. Puszkarski and M. Krawczyk
Surface Physics Division, Faculty of Physics, Adam Mickiewicz University
Umultowska 85, 61-614 Poznañ, Poland
Received: March 14, 2000
We deal with the following question: how can the composite nature of a
boundary condition formulated for a periodically inhomogeneous surface and
involving the composite surface parameter, be treated analytically? We show
that when the appropriate Fourier transformation is applied, the composite
boundary condition reduces to a specific eigenproblem condition, which
constitutes the spectrum of eigenvalues of an ``effective'' surface
parameter, a novel quantity we introduced to account for the nonhomogeneity
of the surface.
PACS numbers: 68.35.-p, 02.60.Lj
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GROUND-STATE STRUCTURE OF A TWO-ELECTRON QUANTUM DOT
M. El-Said
Department of Physics, Eastern Mediterranean University Gazi Magusa, Mersin
10, Turkey
Received: July 20, 1999; revised version February 8, 2000
The energy spectrum of two interacting electrons, confined in a
parabolic quantum dot, presented in a magnetic field is obtained. We have
analyzed the energy level crossings between spin-singlet and spin-triplet
states. The influence of the quantum dot size on these crossings is also
shown. The results of our calculations seem to be in good agreement with
analytical and exact numerical data.
PACS numbers: 73.20.Dx
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THICKNESS DEPENDENCE OF EFFECTIVE CRITICAL EXPONENTS IN
THREE-DIMENSIONAL ISING PLATES
M.I. Marqués and J.A. Gonzalo
Departamento de Fisica de Materiales, C-IV Universidad Autónoma de
Madrid, 28049 Madrid, Spain
Received: October 20, 1999; revised version January 17, 2000
Phase transitions in Ising plates of equal area and different
thicknesses have been studied by the Monte Carlo approach. The evolution of
the critical temperature and of the effective critical exponents with the
thickness of the lattice has been numerically determined. The thickness
dependence of the maximum value of the effective critical exponents is well
described by an exponential decay towards the respective three-dimensional
value.
PACS numbers: 75.10.Hk, 64.60.Fr, 75.70.-i, 02.50.Ng
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THE FORM OF ENERGY GAP AND CRITICAL TEMPERATURE OF SUPERCONDUCTOR
IMPLIED
BY FLUCTUATIONS OF DENSITY OF STATES
M. Gladysiewicz, R. Gonczarek and M. Mulak
Institute of Physics, Wroclaw University of Technology Wybrzeze
Wyspiañskiego 27, 50-370 Wroclaw, Poland
Received: October 21, 1999; revised version February 8, 2000
The s-paired BCS superconductor with the electron density of states
depending on energy in the vicinity of Fermi level is considered. The
existence of such fluctuations of electron density of states may be referred
to Van Hove singularities widely discussed in the literature. In the paper
three types of small fluctuations of the electron density of states
introduced about its average background's value are analysed: Lorentzian,
triangle, and logarithmic ones. In order to calculate numerically the energy
gap and critical temperature, the formalism of parametric BCS gap equations
is applied. The positive fluctuations (peaks) correspond to the increase in
occupied states number inducing a higher critical temperature. On the other
hand, negative fluctuations, which decrease the number of occupied states,
lead to a lower critical temperature. Such decrease in critical temperature
can lead, at a specific choice of parameters, to the decease in
superconductivity. The presence of fluctuations finds reflection in the
shape
of energy gap as a function of temperature. In the vicinity of T=0 an abrupt
decrease or increase in the energy gap to the original BCS value, according
to the sign of the fluctuation, is observed. In turn, the fluctuations do
not
change the behaviour of the energy gap near Tc.
PACS numbers: 74.20.-z
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ON THE TRANSMISSION COEFFICIENT FOR THE DOUBLE delta' -FUNCTION
POTENTIAL
I. Yanetka
Department of Physics, Faculty of Civil Engineering, Slovak University of
Technology Radlinskèho 11, 813 68 Bratislava, Slovakia
Received: December 7, 1999
The unbound-state solution of the Schrödinger equation is examined
for the potential that is defined as the sum of two delta'-functions of
non-equal strengths. The analytical expression for the transmission
coefficient is derived from the solution. The transmission coefficient has
an
absolute maximum at the zero wave number. Further, the transmission
coefficient is shown to exhibit relative maxima and minima. Moreover, it is
proved that the transmission coefficient in its relative maxima is larger
and
in its relative minima is smaller than the transmission coefficient for the
corresponding single delta'-function potential.
PACS numbers: 73.40.Gk, 73.20.Dx
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DIELECTRIC PROPERTIES OF TRIGLYCINE SULPHATE CRYSTALS ADMIXTURED WITH D-
AND DL-PHENYLALANINE
J. Stankowskaa, E. Petera and M. Trybulab
a Institute of Physics, A. Mickiewicz University Umultowska 85, 61-614
Poznañ, Poland
b Institute of Molecular Physics, Polish Academy of
Sciences
Smoluchowskiego
17, 60-179 Poznañ, Poland
Received: January 3, 2000; revised version March 14, 2000
The paper reports studies on the effect of D-phenylalanine and
DL-phenylalanine admixtures on dielectric properties and domain structure
of triglycine sulphate crystals. Permittivity varepsilon and loss tangent
tgdelta were measured in a wide range of temperatures (10-340 K) as a
function of measuring field varied from 1 to 10000 kHz, for samples cut out
from two growth pyramids (001) and (110) from triglycine sulphate crystals
containing different concentrations of admixtures. A comparison of the
effects of D-phenylalanine and DL-phenylalanine admixtures on dielectric
properties of triglycine sulphate crystals was made. With increasing
concentrations of admixtures in the crystals, the values of varepsilonmax
decreased while Ec and Eb (bias field) increased, and Ps
and Tc showed
insignificant changes. Observations of the domain structure of the
admixtured
crystals by the liquid crystal method proved its refinement and
irregularity.
Changes in the domain structure of the crystals occurring in the process of
spontaneous ageing were analysed.
PACS numbers: 77.22.-d
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PHOTOACOUSTIC STUDY OF THE INTERACTION BETWEEN THIN OIL LAYERS WITH
WATER
J. Szurkowskia, I. Pawelskaa,
S. Wartewigb and S. Pogorzelskia
a Institute of Experimental Physics, University
of Gdañsk Wita Stwosza 57,
80-952 Gdañsk, Poland
b Martin-Luther-Universität Halle-Wittenberg
Fachbereich Pharmazie, Hoher Weg 7, 06099 Halle, Germany
Received: November 30, 1999; revised version March 24, 2000
In the presented paper the structural changes in thin olive oil layers
taking place as a result of interaction with water using a photoacoustic
technique were studied. The oil layers were spread from a solution in a
volatile solvent (ethyl ether) on the water and copper surface. These
studies
are a natural continuation of the previous work on a layered system
performed
within the light range (680 nm), which pointed to the irregularities of oil
layers related to their thickness is now expanded to the infrared band. A
structural irregularity was observed for a layer thickness of 100 µm, but
it did not appear for the one of pure bulk oil. Signatures of irregularity
were clearly observed in the phase plots whereas the amplitude dependences
were not sensitive to them. The performed studies allowed one to relate the
diversity of thermal parameters in the samples with structural changes found
in oil layers originated from oil-water interactions.
PACS numbers: 81.70.Cv, 36.20.Ng, 68.15.+e
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