20,854 research outputs found
Anomalous microwave response of high-temperature superconducting thin-film microstrip resonator in weak dc magnetic fields
We have studied an anomalous microwave (mw) response of superconducting
YBa_{2}Cu_{3}O_{7-delta} (YBCO) microstrip resonators in the presence of a weak
dc magnetic field, H_{dc}. The surface resistance (R_{s}) and reactance (X_{s})
show a correlated non-monotonic behaviour as a function of H_{dc}. R_{s} and
X_{s} were found to initially decrease with elevated H_{dc} and then increase
after H_{dc} reaches a crossover field, H_{c}, which is independent of the
amplitude and frequency of the input mw signal within the measurements. The
frequency dependence of R_{s} is almost linear at fixed H_{dc} with different
magnitudes (H_{c}). The impedance plane analysis
demonstrates that r_{H}, which is defined as the ratio of the change in
R_{s}(H_{dc}) and that in X_{s}(H_{dc}), is about 0.6 at H_{dc}<H_{c} and 0.1
at H_{dc}>H_{c}. The H_{dc} dependence of the surface impedance is
qualitatively independent of the orientation of H_{dc}.Comment: REVTex 3.1, 5 pages, 6 EPS figures, submitted to Physica
Qualitative and quantitative phytochemical screening and in vitro anti oxidant and anti microbial activities of Elephantopus scaber Linn.
Preliminary phytochemical analysis and quantification of total phenols, In-vitro antioxidant and anti microbial activities of the different fractions (hydro alcoholic, hexane, ethyl acetate and methanol) of Elephantopus scaber were carried out against five selected pathogenic bacteria and three fungal species. The plant fraction possesses steroids, triterpinoids, saponins, flavonoides, carbohydrates, glycosides and oils. For total phenolic content gallic acid was taken as a standard, the ethyl acetate fraction contains rich phenolic content than other fractions and the methanol fraction shows more DPPH, superoxide and hydroxyl radical scavenging activity. In Anti-microbial activity study all fractions showed good inhibition zone against three organisms i.e., Escherichia coli, Staphylococcus aureus Klebsiella pneumonia among the other test organisms along with Candida spp (fungal organism)
Comment on ''the controlled charge ordering and evidence of the metallic state in PrCaMnO films''
In a recent paper (2000 \QTR{it}{J. Phys.: Condens. Matter} \QTR{bf}{12}
L133) Lee \QTR{it}{et al.} have studied the transport properties of
PrCaMnO thin films. They claimed that they are able to
controlled the charge-ordered (CO) state by the lattice strains. We propose
herein another alternative since another indexation of the orientation of the
film can be found leading to almost no distortion of the cell, as compared to
the bulk compound.Comment: 2 page
A dynamics-driven approach to precision machines design for micro-manufacturing and its implementation perspectives
Precision machines are essential elements in fabricating high quality micro products or micro features and directly affect the machining accuracy, repeatability and efficiency. There are a number of literatures on the design of industrial machine elements and a couple of precision machines commercially available. However, few researchers have systematically addressed the design of precision machines from the dynamics point of view. In this paper, the design issues of precision machines are presented with particular emphasis on the dynamics aspects as the major factors affecting the performance of the precision machines and machining processes. This paper begins with a brief review of the design principles of precision machines with emphasis on machining dynamics. Then design processes of precision machines are discussed, and followed by a practical modelling and simulation approaches. Two case studies are provided including the design and analysis of a fast tool servo system and a 5-axis bench-top micro-milling machine respectively. The design and analysis used in the two case studies are formulated based on the design methodology and guidelines
Nonequilibrium Phase Transition in the Kinetic Ising model: Critical Slowing Down and Specific-heat Singularity
The nonequilibrium dynamic phase transition, in the kinetic Ising model in
presence of an oscillating magnetic field, has been studied both by Monte Carlo
simulation and by solving numerically the mean field dynamic equation of motion
for the average magnetisation. In both the cases, the Debye 'relaxation'
behaviour of the dynamic order parameter has been observed and the 'relaxation
time' is found to diverge near the dynamic transition point. The Debye
relaxation of the dynamic order parameter and the power law divergence of the
relaxation time have been obtained from a very approximate solution of the mean
field dynamic equation. The temperature variation of appropiately defined
'specific-heat' is studied by Monte Carlo simulation near the transition point.
The specific-heat has been observed to diverge near the dynamic transition
point.Comment: Revtex, Five encapsulated postscript files, submitted to Phys. Rev.
Shielding Effectiveness of Laminated Shields
Shielding prevents coupling of undesired radiated electromagnetic energy into equipment otherwise susceptible to it. In view of this, some studies on shielding effectiveness of laminated shields with conductors and conductive polymers using plane-wave theory are carried out in this paper. The plane wave shielding effectiveness of new combination of these materials is evaluated as a function of frequency and thickness of material. Conductivity of the polymers, measured in previous investigations by the cavity perturbation technique, is used to compute the overall reflection and transmission coefficients of single and multiple layers of the polymers. With recent advances in synthesizing stable highly conductive polymers these lightweight mechanically strong materials appear to be viable alternatives to metals for EM1 shielding
Dynamics of Magnetized Bulk Viscous Strings in Brans-Dicke Gravity
We explore locally rotationally symmetric Bianchi I universe in Brans-Dicke
gravity with self-interacting potential by using charged viscous cosmological
string fluid. We use a relationship between the shear and expansion scalars and
also take the power law for scalar field as well as self-interacting potential.
It is found that the resulting universe model maintains its anisotropic nature
at all times due to the proportionality relationship between expansion and
shear scalars. The physical implications of this model are discussed by using
different parameters and their graphs. We conclude that this model corresponds
to an accelerated expanding universe for particular values of the parameters.Comment: 17 pages, 6 figure
Renormalization group study of the Kondo problem at a junction of several Luttinger wires
We study a system consisting of a junction of N quantum wires, where the
junction is characterized by a scalar S-matrix, and an impurity spin is coupled
to the electrons close to the junction. The wires are modeled as weakly
interacting Tomonaga-Luttinger liquids. We derive the renormalization group
equations for the Kondo couplings of the spin to the electronic modes on
different wires, and analyze the renormalization group flows and fixed points
for different values of the initial Kondo couplings and of the junction
S-matrix (such as the decoupled S-matrix and the Griffiths S-matrix). We
generally find that the Kondo couplings flow towards large and
antiferromagnetic values in one of two possible ways. For the Griffiths
S-matrix, we study one of the strong coupling flows by a perturbative expansion
in the inverse of the Kondo coupling; we find that at large distances, the
system approaches the ferromagnetic fixed point of the decoupled S-matrix. For
the decoupled S-matrix with antiferromagnetic Kondo couplings and weak
inter-electron interactions, the flows are to one of two strong coupling fixed
points in which all the channels are strongly coupled to each other through the
impurity spin. But strong inter-electron interactions, with K_\rho < N/(N+2),
stabilize a multi-channel fixed point in which the coupling between different
channels goes to zero. We have also studied the temperature dependence of the
conductance at the decoupled and Griffiths S-matrices.Comment: Revtex4, 16 pages including 6 figure
Transport in quantum wires
With a brief introduction to one-dimensional channels and conductance
quantisation in mesoscopic systems, we discuss some recent experimental puzzles
in these systems, which include reduction of quantised conductances and an
interesting {\it odd-even} effect in the presence of an in-plane magnetic
field. We then discuss a recent non-homogeneous Luttinger liquid model proposed
by us, which addresses and gives an explanation for the reduced conductances
and the {\it odd-even} effect. We end with a brief summary and discussion of
future projects.Comment: Talk presented at the International Discussion Meeting on Mesoscopic
and Disordered systems, December, 2000, 16 pages, 2 figure
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