481 research outputs found
Orientation control by flow: Exact results and Langevin simulations
Rod shaped objects suspended in a flowing liquid might be orientated by the
velocity, nature of the liquid, the flow and the geometry of the channel
containing the flow. Orientation settings might enhance or inhibit certain
chemical reactions between the objects, other chemicals or with the walls of
vessels holding the flowing suspension. The probability density function (PDF)
describing the orientations of rod shaped objects in a flowing liquid satisfies
a Fokker-Planck equation whose solution is obtained analytically as well as
numerically from Langevin simulations for different flow parameters. The
analytical and numerical methods developed in the present work enable us to
calculate accurately the PDF for a range of the Peclet number covering
several orders of magnitude, . We apply these
results to the experimental determination of dichroism and birefringence of the
suspension as a function of .Comment: 6 pages, 7 figures submitted to Phys. Rev.
Light production metrics of radiation sources
Light production by a radiation source is evaluated and reviewed as an
important concept of physics from the Black-Body point of view. The mechanical
equivalent of the lumen, the unit of perceived light, is explained and
evaluated using radiation physics arguments. The existence of an upper limit of
luminous efficacy is illustrated for various sources and implications are
highlighted.Comment: 7 pages, 7 figures, to submit to American Journal of Physic
Symmetry and Piezoelectricity: Evaluation of -Quartz coefficients
Piezoelectric coefficients of -Quartz are derived from symmetry
arguments based on Neumann's Principle with three different methods: Fumi,
Landau-Lifshitz and Royer-Dieulesaint. While Fumi method is tedious and
Landau-Lifshitz requires additional physical principles to evaluate the
piezoelectric coefficients, Royer-Dieulesaint is the most elegant and most
efficient of the three techniques.Comment: 12 pages, 5 figures, 1 Tabl
Frequency and Phase Noise in Non-Linear Microwave Oscillator Circuits
We have developed a new methodology and a time-domain software package for
the estimation of the oscillation frequency and the phase noise spectrum of
non-linear noisy microwave circuits based on the direct integration of the
system of stochastic differential equations representing the circuit. Our
theoretical evaluations can be used in order to make detailed comparisons with
the experimental measurements of phase noise spectra in selected oscillating
circuits.Comment: 18 pages and 6 figure
Static and Dynamic Regimes of Arbitrary Gain Compensation Single-Mode Laser Diodes
We report on a methodology for the evaluation of the DC characteristics,
small-signal frequency response and large-signal dynamic response of carrier
and photon density responses in semiconductor laser diodes. A single mode laser
is considered and described with a pair of rate equations containing a novel
non-linear gain compensation term depending on a single parameter that can be
chosen arbitrarily. This approach can be applied to any type of solid-state
laser as long as it is described by a set of rate equations.Comment: 20 pages including 9 figures. Submitted to Computational Materials
Scienc
Non-linear quantization for arbitrary distributions and applications to Medical Image Processing
We report the development of a scalar quantization approach that helps build
tables of decision and reconstruction levels for any probability density
function (pdf). Several example pdf's are used for illustration:
Uniform, Gaussian, Laplace, one-sided Rayleigh, and Gamma (One sided and
double-sided symmetrical). The main applications of the methodology are
principally aimed at Multiresolution Image compression where generally the
Stretched Exponential pdf is encountered. Specialising to this important case,
we perform quantization and information entropy calculations from selected
medical MRI (Magnetic Resonance Imaging) pictures of the human brain. The image
histograms are fitted to a Stretched exponential model and the corresponding
entropies are compared.Comment: 10 tables and 9 figure
Generalised Modal Analysis with the Pad\'e-Laplace transform
We present the G-MAPLE (Generalised Modal Analysis from the Poles of the
Laplace Expansion) software that allows decomposing data depending on a single
parameter (such as time series data) into a set of exponential functions having
complex amplitudes and arguments. The novelty is that G-MAPLE determines the
unknown number of exponentials in the data along with the corresponding complex
amplitudes and arguments.Comment: 3 sets of tables and 2 figure
The Karlqvist approximation revisited
The Karlqvist approximation signaling the historical beginning of magnetic
recording head theory is reviewed and compared to various approaches
progressing from Green, Fourier, Conformal mapping that obeys the Sommerfeld
edge condition at angular points and leads to exact results.Comment: 9 pages and 9 figures. To submit to American Journal of Physic
Direct Determination of Harmonic and Inter-modulation distortions with an application to Single Mode Laser Diodes
Harmonic and Intermodulation distortions occur when a physical system is
excited with a single or several frequencies and when the relationship between
the input and output is non-linear. Working with non-linearities in the
Frequency domain is not straightforward specially when the relationship between
the input and output is not trivial. We outline the complete derivation of the
Harmonic and Intermodulation distortions from basic principles to a general
physical system. For illustration, the procedure is applied to the Single Mode
laser diode where the relationship of input to output is non-trivial. The
distortions terms are extracted directly from the Laser Diode rate equations
and the method is tested by comparison to many results cited in the literature.
This methodology is general enough to be applied to the extraction of
distortion terms to any desired order in many physical systems in a general and
systematic way.Comment: 11 pages, no figures. Submitted to Phys. Rev. A (April 2001
The Stoner-Wohlfarth model of Ferromagnetism: Dynamic and Statistical properties
The physics of magnetic state change or reversal in single domain magnetic
grains (called Stoner particles) is interesting from the fundamental as well as
the applied points of view. A change in magnetization can be finely tuned with
a specific time variation o f an externally applied magnetic field. It may also
occur naturally (without application of a field) at very low tempe rature with
quantum tunneling and at higher temperature with thermal excitation. The
optimal (usually shortest) time altering the magn etisation along with the
smallest applied magnetic field are sought in technological applications s uch
as high-density reading or writing of information, spintronics, quantum inform
ation and quantum communication systems. This work reviews the magnetization
change with a time dependent field and tem perature and discusses the time it
takes to alter the magnetization as a function of the control parameter chosen,
temperature and material parameters.Comment: 12 pages, 11 figures, submitted to American Journal of physic
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