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 $\alpha$ covering several orders of magnitude, $10^{-4} \le \alpha \le 10^{8}$. We apply these results to the experimental determination of dichroism and birefringence of the suspension as a function of $\alpha$.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

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

Symmetry and Piezoelectricity: Evaluation of α\alpha-Quartz coefficients

Piezoelectric coefficients of $\alpha$-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

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: Static properties

Recent advances in high-density magnetic storage and spin electronics are based on the use of magnetic materials along with conventional microelectronic materials (metals, insulators and semiconductors). The unit information (bit) is stored as a magnetization state in some ferromagnetic ma rial (FM) and controlled with an external field altering the magnetization state. As device size is shrinking steadily toward the nanometer and the need to incr se its bandwidth prevails, racing toward higher frequencies is getting even more cha enging. In magnetic systems, denser storage leads to finer magnetic grains and small size leads to single magnetic domain physics. The Stoner-Wohlfarth model is the simplest model that describes adequately the physics of fine magnetic grains containing single domains and where magnetization state changes by rotation or switching (abrupt reversal). The SW model is reviewed and discussed with its consequences and potential app cations in the physics of magnetism and spin electronics.Comment: 12 pages, 12 figures, submitted to American Journal of physic