19,113 research outputs found
Anisotropic Dependence of Giant Magneto-Impedance of Amorphous Ferromagnetic Ribbon on Biasing Field
The magneto-impedance (MI) in amorphous ribbon of nominal composition
Fe73.5Nb3Cu1Si13.5B9 has been measured at 1MHz and at room temperature for
different configurations of exciting a.c and biasing d.c. fields. A large drop
in both resistance and reactance is observed as a function of d.c magnetic
field. When the d.c and a.c fields are parallel but normal to the axis of
ribbon, smaller magnetic field is needed to reduce the impedance to its small
saturated value compared to the situation when fields are along the axis of
ribbon. Larger d.c. field is required to lower the impedance when the d.c field
acts perpendicular to the plane of the ribbon. Such anisotropy in
magneto-impedance is related to the anisotropic response of the magnetization
of ribbon. The large change of impedance is attributed to large variation of
a.c permeability on the direction and magnitude of the dc biasing field.Comment: 12 pages, 7 figures, to be published in "International Journal of
Modern Physics B
Agent Based Models of Language Competition: Macroscopic descriptions and Order-Disorder transitions
We investigate the dynamics of two agent based models of language
competition. In the first model, each individual can be in one of two possible
states, either using language or language , while the second model
incorporates a third state XY, representing individuals that use both languages
(bilinguals). We analyze the models on complex networks and two-dimensional
square lattices by analytical and numerical methods, and show that they exhibit
a transition from one-language dominance to language coexistence. We find that
the coexistence of languages is more difficult to maintain in the Bilinguals
model, where the presence of bilinguals in use facilitates the ultimate
dominance of one of the two languages. A stability analysis reveals that the
coexistence is more unlikely to happen in poorly-connected than in fully
connected networks, and that the dominance of only one language is enhanced as
the connectivity decreases. This dominance effect is even stronger in a
two-dimensional space, where domain coarsening tends to drive the system
towards language consensus.Comment: 30 pages, 11 figure
Cooling Flows of Self-Gravitating, Rotating, Viscous Systems
We obtain self-similar solutions that describe the dynamics of a
self-gravitating, rotating, viscous system. We use simplifying assumptions; but
explicitly include viscosity and the cooling due to the dissipation of energy.
By assuming that the turbulent dissipation of energy is as power law of the
density and the speed v_{rms} and for a power-law dependence of viscosity on
the density, pressure, and rotational velocity, we investigate turbulent
cooling flows. It has been shown that for the cylindrically and the spherically
cooling flows the similarity indices are the same, and they depend only on the
exponents of the dissipation rate and the viscosity model. Depending on the
values of the exponents, which the mechanisms of the dissipation and viscosity
determine them, we may have solutions with different general physical
properties. The conservation of the total mass and the angular momentum of the
system strongly depends on the mechanisms of energy dissipation and the
viscosity model.Comment: 19 pages, 5 figures, To appear in ApJ (scheduled for the v574, July
20, 2002
Numerical Modelling of Industrial Induction
Induction heating is a physical process extensively used in the metallurgical industry for different applications involving metal melting. The main components of an induction heating
system are an induction coil connected to a power-supply providing an alternating electric
current and a conductive workpiece to be heated, placed inside the coil. The alternating
current traversing the coil generates eddy currents in the workpiece and by means of ohmic
losses the workpiece is heate
Characterization of femtosecond laser written waveguides for integrated biochemical sensing
Fluorescence detection is known to be one of the most sensitive among the different optical sensing techniques. This work focuses on excitation and detection of fluorescence emitted by DNA strands labeled with fluorescent dye molecules that can be excited at a specific wavelength. Excitation occurs via optical channel waveguides written with femtosecond laser pulses applied coplanar with a microfluidic channel on a glass chip. The waveguides are optically characterized in order to facilitate the design of sensing structures which can be applied for monitoring the spatial separation of biochemical\ud
species as a result of capillary electrophoresis
On the Maximum Expected Electric Field in Electrically Small, Undermoded Enclosures
This paper reports the experimental validation of an improved statistical model for the prediction of maximum expected electric field in electrically small and under-moded enclosures. The aerospace community is interested in application of Hills statistical models to design of avionics boxes for shielding effectiveness and for tailoring EMC test requirements for critical applications. However, it is observed that the probability distribution for mean-squared electric field (|E(sub x)|(exp 2)) in an electrically small enclosure differs from the exponential distribution which is widely used in reverberation chamber testing. It is postulated here that the difference is attributable to the under-moded character of the small enclosure. We will define under-moded as the condition where a single excitation frequency does not excite enough closely spaced resonant modes to achieve Hills assumption of an isotropic (or fully diffuse) plane wave field in the enclosure
Reinforcement-Driven Spread of Innovations and Fads
We propose kinetic models for the spread of permanent innovations and
transient fads by the mechanism of social reinforcement. Each individual can be
in one of M+1 states of awareness 0,1,2,...,M, with state M corresponding to
adopting an innovation. An individual with awareness k<M increases to k+1 by
interacting with an adopter. Starting with a single adopter, the time for an
initially unaware population of size N to adopt a permanent innovation grows as
ln(N) for M=1, and as N^{1-1/M} for M>1. The fraction of the population that
remains clueless about a transient fad after it has come and gone changes
discontinuously as a function of the fad abandonment rate lambda for M>1. The
fad dies out completely in a time that varies non-monotonically with lambda.Comment: 4 pages, 2 columns, 5 figures, revtex 4-1 format; revised version has
been expanded and put into iop format, with one figure adde
The Probability Distribution Function of Column Density in Molecular Clouds
(Abridged) We discuss the probability distribution function (PDF) of column
density resulting from density fields with lognormal PDFs, applicable to
isothermal gas (e.g., probably molecular clouds). We suggest that a
``decorrelation length'' can be defined as the distance over which the density
auto-correlation function has decayed to, for example, 10% of its zero-lag
value, so that the density ``events'' along a line of sight can be assumed to
be independent over distances larger than this, and the Central Limit Theorem
should be applicable. However, using random realizations of lognormal fields,
we show that the convergence to a Gaussian is extremely slow in the high-
density tail. Thus, the column density PDF is not expected to exhibit a unique
functional shape, but to transit instead from a lognormal to a Gaussian form as
the ratio of the column length to the decorrelation length increases.
Simultaneously, the PDF's variance decreases. For intermediate values of
, the column density PDF assumes a nearly exponential decay. We then
discuss the density power spectrum and the expected value of in actual
molecular clouds. Observationally, our results suggest that may be
inferred from the shape and width of the column density PDF in
optically-thin-line or extinction studies. Our results should also hold for gas
with finite-extent power-law underlying density PDFs, which should be
characteristic of the diffuse, non-isothermal neutral medium (temperatures
ranging from a few hundred to a few thousand degrees). Finally, we note that
for , the dynamic range in column density is small
( a factor of 10), but this is only an averaging effect, with no
implication on the dynamic range of the underlying density distribution.Comment: 13 pages, 7 figures (10 postscript files). Accepted in ApJ.
Eliminated implication that ratio of column length to correlation length
necessarily increases with resolution, and thus that 3D simulations are
unresolved. Added discussion of dependence of autocorrelation function with
parameters of the turbulenc
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