Influence of thermal boundary conditions on natural convection in a square enclosure partially heated from below

Natural convection in air-filled 2D square enclosure heated with a constant source from below and cooled from above is studied numerically for a variety of thermal boundary conditions at the top and sidewalls. Simulations are performed for two kinds of lengths of the heated source, i.e., a small and a large source corresponding to 20% and 80% of the total length of the bottom wall, respectively. The Rayleigh number varied from 10³ to 10⁷. Results are presented in the form of streamline and isotherm plots as well as the variation of the Nusselt number and maximum temperature at the heat source surface. Comparisons among the different thermal configurations considered are reported.     

Parametric estimation of change-points for actual event data in recurrent events models

Time to event data have long been important in many applied fields. Many models and analysis methods have been developed for this type of data in which each sample unit experiences at most a single end-of-life event.In contrast, many applications involve repeated events, where a subject or sampling unit experiences more than one event. There is growing interest in the analysis of recurrent events data, also called repeated events and recurrence data. This type of data arises in many fields. For example, the repair history of manufactured items can be modeled as recurrent events. In medical studies, the times of recurrent disease episodes in patients can also be modeled as recurrent events. In this paper we focus on medical applications (e.g. seizures, heart attacks, cancerous tumors, etc.). However, our proposed methodologies can be applied to other areas as well.For analyzing recurrence data, the first and perhaps most important step is to model the expected number of events, and sometimes this can be facilitated by modeling the cumulative intensity function or its derivative, the intensity rate function. One particular recurrent events scenario involves patients experiencing events according to a common intensity rate, and then a treatment may be applied. Assuming the treatment to be effective, the patients would be expected to follow a different intensity rate after receiving the treatment. Further, the treatment might be effective for a limited amount of time, so that a third rate would govern arrivals of the recurrent events after the effects of the treatment wore out. In this paper we model the intensity rate for such scenarios. In particular we allow models for the intensity rate, post-treatment, to be piecewise constant. Two estimators of the location of this change are proposed. Properties of the estimators are discussed. An example is studied for illustrative purposes.     

Thermal cracking and combustion kinetics of asphaltenes derived from Fosterton oil

Thermal behavior of crude oil (Fosterton) asphaltenes mixed with reservoir sand was investigated using thermogravimetric analysis (TGA), in nitrogen and air atmospheres for different heating rates up to 800 °C. In this study, four sets of TGA runs were performed to examine the thermal behavior of Fosterton asphaltenes and the coke derived from the asphaltenes. The parameters studied were heating rate (10, 15 and 20 °C min^− 1) and the type of purge gas (N₂ and air) employed for the process of thermal degradation of asphaltenes. Distributed activation energy model (DAEM) has been applied to study the asphaltene pyrolysis kinetics. It was observed that the activation energy was distributed from 46.16 to 72.17 kJ/mol, for the conversion range of 0.1 to 0.4. The general model for nth order reaction was used to obtain the kinetic parameters of coke oxidation reaction from the TGA data. From the model, the calculated activation energy, E, was 93.46 kJ/mol and the pre-exponential factor was 9.59 × 10⁵ min^− 1 for the coke combustion. The apparent order of combustion reaction gradually increased from 0.7 to 0.8 for different temperatures.     

Radar Scattering from a Diffuse Vegetation Layer over a Smooth Surface

A simple model is presented for the oblique backscatter and bistatic scatter from a smooth surface overlain by a diffuse layer. Only single scattering in the diffuse layer is taken into account. The model analysis shows that the combination of volume scattering and oblique reflection at the surface may increase appreciably the waves scattering. The scattering strongly depends on the properties of the smooth surface. These results support some of the observations made with the Seasat spaceborne imaging radar over flooded regions with heavy vegetation cover.     

Creeping flow relative to permeable spheres

The several possible solutions to the problem of creeping flow relative to an isolated permeable sphere are discussed and compared quantitatively. The most satisfactory solutions is that based upon Brinkman's extension of Darcy's Law. This solution is generalized, using Happel's free-surface model, to cover the practically important problem of flow relative to a swarm of permeable spheres. A physically realistic and mathematically consistent expression for the hydrodynamic resistance experienced by a typical sphere within such a system is derived. This expression is then used to predict the settling rate and the overall permeability of the swarm.     

High numerical aperture in multimode microstructured optical fibers

Microstructured or "air-clad" fibers, with air holes surrounding a large core, have recently demonstrated much wider light-acceptance angles than conventional fibers. An original and accurate method is presented for determining the numerical aperture of such fibers using leaky modes. The dependence on length, wavelength, and various microstructure dimensions are evaluated for the first time for a class of fibers that exhibit exceptionally high numerical apertures. These results show excellent agreement with published measurements on similar fibers and verify that bridge thicknesses much smaller than the wavelength are required for high numerical apertures.     

On Designing PAM Pulses Optimally Tolerant to Timing Jitter

This paper deals with the design of bandlimited baseband PAM pulses that are optimally tolerant to timing jitter in a maximally flat sense. In this design the bandwidth can be chosen arbitrarily. The resulting time responses are relatively insensitive to small amounts of timing jitter and so represent an optimal solution for this type of impairment. Analytic results are derived in the frequency domain after translating conditions on maximal flatness from the time domain into the frequency domain by means of the Poisson sum formula.     

Lesions of the lateral parabrachial nucleus block the aversive motivational effects of both morphine and morphine withdrawal but spare morphine's discrimination properties.

This study examined if the aversive properties of morphine, the aversive properties of morphine withdrawal, and the discriminative properties of morphine are mediated by common neurobiological substrates. Lesions of the lateral parabrachial nucleus, which blocked the aversive properties of morphine in the conditioned taste aversion paradigm, also blocked the acquisition of conditioned place aversions to environments paired with the aversive properties of morphine withdrawal in morphine-dependent rats. When morphine and saline were used as cues in a discrimination task, however, both sham-operated and lesioned rats were able to solve the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Robust image watermarking scheme using bit-plane of hadamard coefficients

Multimedia Tools and Applications - Nowadays, due to widespread usage of the Internet, digital contents are distributed quickly and inexpensively throughout the world. Watermarking techniques can...     

Enhancement of immune response in mice fed with Streptococcus thermophilus and Lactobacillus acidophilus

Swiss mice, fed for 8 consecutive d with 50 micrograms/d of viable cultures of Lactobacillus acidophilus and Streptococcus thermophilus, showed significant variation in their immune system. In order to study this phenomenon assays for macrophage and lymphocyte function were carried out. Both lactic acid bacteria enhanced significantly the enzymatic and phagocytic activity of peritoneal macrophages as checked against the controls and also accelerated the phagocytic function of the reticuloendothelial system as revealed by the carbon clearance test. On the 2nd d (100 micrograms), L. acidophilus reached a peak of K = .271, which remained high. Streptococcus thermophilus was effective only on the 2nd d and then decreased. The lymphocytic activity studied by immunoglobulin secreting cells was assayed by Jerne's method of plaque-forming cells (PFC). This activity also was increased by the two microorganisms. Streptococcus thermophilus proved more effective than L. acidophilus. Lactobacillus acidophilus and S. thermophilus activated macrophages and lymphocytes and produced the same increase in the immune response of mice whether administered orally or intraperitoneally.