4,847 research outputs found
High-fidelity simulation of an ultrasonic standing-wave thermoacoustic engine with bulk viscosity effects
We have carried out boundary-layer-resolved, unstructured fully-compressible
Navier--Stokes simulations of an ultrasonic standing-wave thermoacoustic engine
(TAE) model. The model is constructed as a quarter-wavelength engine,
approximately 4 mm by 4 mm in size and operating at 25 kHz, and comprises a
thermoacoustic stack and a coin-shaped cavity, a design inspired by Flitcroft
and Symko (2013). Thermal and viscous boundary layers (order of 10
m) are resolved. Vibrational and rotational molecular relaxation
are modeled with an effective bulk viscosity coefficient modifying the viscous
stress tensor. The effective bulk viscosity coefficient is estimated from the
difference between theoretical and semi-empirical attenuation curves.
Contributions to the effective bulk viscosity coefficient can be identified as
from vibrational and rotational molecular relaxation. The inclusion of the
coefficient captures acoustic absorption from infrasonic (10 Hz) to
ultrasonic (100 kHz) frequencies. The value of bulk viscosity depends on
pressure, temperature, and frequency, as well as the relative humidity of the
working fluid. Simulations of the TAE are carried out to the limit cycle, with
growth rates and limit-cycle amplitudes varying non-monotonically with the
magnitude of bulk viscosity, reaching a maximum for a relative humidity level
of 5%. A corresponding linear model with minor losses was developed; the linear
model overpredicts transient growth rate but gives an accurate estimate of
limit cycle behavior. An improved understanding of thermoacoustic energy
conversion in the ultrasonic regime based on a high-fidelity computational
framework will help to further improve the power density advantages of
small-scale thermoacoustic engines.Comment: 55th AIAA Aerospace Sciences Meeting, AIAA SciTech, 201
Gravitational Lensing Bound On The Average Redshift Of Gamma Ray Bursts In Models With Evolving Lenses
Identification of gravitationally lensed Gamma Ray Bursts (GRBs) in the BATSE
4B catalog can be used to constrain the average redshift of the GRBs.
In this paper we investigate the effect of evolving lenses on the of
GRBs in different cosmological models of universe. The cosmological parameters
$\Omega$ and $\Lambda$ have an effect on the of GRBs. The other factor
which can change the of GRBs is higher in evolving model of galaxies as compared to
non-evolving models of galaxies.Comment: 23 pages,one plain LaTeX file with three postscript figures This is
modified version with recent BATSE efficiency parameter and with the latest F
paramete
Synthesis, Characterization and Quantification of Simvastatin Metabolites and Impurities
Simvastatin is used in treatment of hypercholesterolemia because it regulates cholesterol synthesis as a result of its β-hydroxy acid acting as an inhibitor of 3-hydroxy-methylglutaryl coenzyme A (HMG-CoA). The present communication deals with synthesis, characterization and development of accurate, precise and sensitive Reverse Phase High Performance Liquid Chromatography (RP-HPLC) method for simultaneous estimation of simvastatin and its synthetic impurities. The impurities methyl ether and β-hydroxy acid of simvastatin were synthesized in the laboratory and characterized by MS, NMR and FT-IR spectroscopy. The separation of simvastatin and its impurities was carried out on an isocratic JASCO RP-HPLC system using KYA TECH HIQ SIL C18 column (150 × 4.6 mm internal diameter, particle size 5 μm) operating at ambient temperature using acetonitrile:water (80:20 v/v) with 0.1% orthophosphoric acid as mobile phase. The method developed for HPLC analysis of three impurities along with simvastatin was validated using ICH Q2B (R1) guidelines and it complied with these guidelines. The results of analysis were found to be in the range of 98.14% to 101.89% for all analytes with acceptable accuracy and precision. The method can be used for detection and quantification of synthetic impurities in bulk or formulations of simvastatin
Strange Quarks Nuggets in Space: Charges in Seven Settings
We have computed the charge that develops on an SQN in space as a result of
balance between the rates of ionization by ambient gammas and capture of
ambient electrons. We have also computed the times for achieving that
equilibrium and binding energy of the least bound SQN electrons. We have done
this for seven different settings. We sketch the calculations here and give
their results in the Figure and Table II; details are in the Physical Review
D.79.023513 (2009).Comment: Six pages, one figure. To appear in proceedings of the 2008 UCLA
coference on dark matter and dark energ
Linux kernel compaction through cold code swapping
There is a growing trend to use general-purpose operating systems like Linux in embedded systems. Previous research focused on using compaction and specialization techniques to adapt a general-purpose OS to the memory-constrained environment, presented by most, embedded systems. However, there is still room for improvement: it has been shown that even after application of the aforementioned techniques more than 50% of the kernel code remains unexecuted under normal system operation. We introduce a new technique that reduces the Linux kernel code memory footprint, through on-demand code loading of infrequently executed code, for systems that support virtual memory. In this paper, we describe our general approach, and we study code placement algorithms to minimize the performance impact of the code loading. A code, size reduction of 68% is achieved, with a 2.2% execution speedup of the system-mode execution time, for a case study based on the MediaBench II benchmark suite
Resonance Damping in Ferromagnets and Ferroelectrics
The phenomenological equations of motion for the relaxation of ordered phases
of magnetized and polarized crystal phases can be developed in close analogy
with one another. For the case of magnetized systems, the driving magnetic
field intensity toward relaxation was developed by Gilbert. For the case of
polarized systems, the driving electric field intensity toward relaxation was
developed by Khalatnikov. The transport times for relaxation into thermal
equilibrium can be attributed to viscous sound wave damping via
magnetostriction for the magnetic case and electrostriction for the
polarization case.Comment: 5 pages no figures ReVTeX
Novel Spectrophotometric Method for Estimation of Olmesartan Medoxomil from its Tablet Dosage Form Using Hydrotropic Solubilization
Aim: Quantitative estimation of poorly water-soluble drugs involves use of organic solvents. In the present investigation, hydrotropic solubilization is employed to enhance the aqueous solubilities of poorly water-soluble drugs like Olmesartan Medoxomil in tablet dosage forms.
Material and methods: This method utilizes 0.05 M Sodium acetate solution as hydrotropic solubilizing agent Where Olmesartan Medoxomil shows maximum absorbance at 256 nm. The 0.05 M Sodium acetate solution does not show any interference with the sampling wavelength. The hydrotropic agent and additives used in the manufacture of tablets did not interfere in the analysis.
Results and Conclusion: The drug obeys the Beer’s Law in the concentration range 2-14 μg/ml with correlation coefficient value of 0.9987. The developed reliable method was validated statistically following ICH Q2B (R1) guidelines. Statistical analysis proved that the method was simple and rapid for the estimation of Olmesartan Medoxomil and can be used for routine analysis of Olmesartan Medoxomil in quality control laboratories. The ex vivo mucoadhesion time of patches ranged between 109 min (FA10) to 126 min (FB14). The ex vivo mucoadhesive force was in the range of 0.278 to 0.479 Kg.m.s-2. The in vitro drug release studies revealed that formulation FA8 released 84% and FB16 released 99.01% of drug in 140 min.Objetivo: La estimación cuantitativa de fármacos poco solubles en agua implica el uso de disolventes orgánicos. En la presente investigación, se emplea la solubilización hidrotrópica para mejorar las solubilidades acuosas fármacos poco solubles en agua como el olmesartán medoxomilo dosificado en comprimido.
Material y Métodos: Este método emplea acetato sódico 0,05 M como agente solubilizante hidrotrópico, mostrando el olmesartán medoxomilo una absorbancia máxima a 256 nm. La solución de acetato 0.05 M no muestra ninguna interferencia con la longitud de onda de muestreo. El agente hidrotrópico y los aditivos utilizados en la elaboración de los comprimidos no interfieren en el análisis.
Resultados y conclusiones: El fármaco obedece a la Ley de Beer en el intervalo de concentraciones 2-14 mg / ml con un de coeficiente de correlación de 0,9987. El método desarrollado fue validado estadísticamente siguiendo las directrices ICH Q2B (R1) . El análisis estadístico demostró que el método era sencillo y rápido para la estimación de olmesartán medoxomilo y se puede utilizar para análisis de rutina de olmesartán medoxomilo en laboratorios de control de calidad
Detecting foraminiferal photosymbionts in the fossil record: a combined micropalaeontological and geochemical approach
Poster from International Conference on Paleoceanography 12 (ICP 12). See the above link for more information on the conference
Gravitational lensing constraint on the cosmic equation of state
Recent redshift-distance measurements of Type Ia supernovae (SNe Ia) at
cosmological distances suggest that two-third of the energy density of the
universe is dominated by dark energy component with an effective negative
pressure. This dark energy component is described by the equation of state
. We use gravitational lensing statistics to
constrain the equation of state of this dark energy. We use ,
image separation distribution function of lensed quasars, as a tool to probe
. We find that for the observed range of ,
should lie between in order to have five lensed quasars
in a sample of 867 optical quasars. This limit is highly sensitive to lens and
Schechter parameters and evolution of galaxies.Comment: Modified results and inclusion of calculations with new set of
parameter
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