1,387 research outputs found
Diffusion and Correlations in Lattice Gas Automata
We present an analysis of diffusion in terms of the spontaneous density
fluctuations in a non-thermal two-species fluid modeled by a lattice gas
automaton. The power spectrum of the density correlation function is computed
with statistical mechanical methods, analytically in the hydrodynamic limit,
and numerically from a Boltzmann expression for shorter time and space scales.
In particular we define an observable -- the weighted difference of the species
densities -- whose fluctuation correlations yield the diffusive mode
independently of the other modes so that the corresponding power spectrum
provides a measure of diffusion dynamics solely. Automaton simulations are
performed to obtain measurements of the spectral density over the complete
range of wavelengths (from the microscopic scale to the macroscopic scale of
the automaton universe). Comparison of the theoretical results with the
numerical experiments data yields the following results: (i) the spectral
functions of the lattice gas fluctuations are in accordance with those of a
classical `non-thermal' fluid; (ii) the Landau-Placzek theory, obtained as the
hydrodynamic limit of the Boltzmann theory, describes the spectra correctly in
the long wavelength limit; (iii) at shorter wavelengths and at moderate
densities the complete Boltzmann theory provides good agreement with the
simulation data. These results offer convincing validation of lattice gas
automata as a microscopic approach to diffusion phenomena in fluid systems.Comment: 9 pages (revtex source), 12 Postscript figure
Lattice gas automaton approach to "Turbulent Diffusion"
A periodic Kolmogorov type flow is implemented in a lattice gas automaton.
For given aspect ratios of the automaton universe and within a range of
Reynolds number values, the averaged flow evolves towards a stationary
two-dimensional type flow. We show the analogy between the streamlines of
the flow in the automaton and the phase plane trajectories of a dynamical
system. In practice flows are commonly studied by seeding the fluid with
suspended particles which play the role of passive tracers. Since an actual
flow is time-dependent and has fluctuations, the tracers exhibit interesting
intrinsic dynamics. When tracers are implemented in the automaton and their
trajectories are followed, we find that the tracers displacements obey a
diffusion law, with ``super-diffusion'' in the direction orthogonal to the
direction of the initial forcing.Comment: 7 revtex4 pages including 3 figure
Statutory protection of freshwater flora and fauna
The aim of this paper is to summarize the present legislation aimed at protecting freshwater species in Britain, and briefly to review its effectiveness. Some areas have been deliberately omitted, such as fisheries legislation designed to conserve stocks, and the statutory protection of birds associated with fresh waters which forms a large subject area in its own right
The effect of different frequencies of ultrasound on the activity of horseradish peroxidase
Ultrasound technology has been studied by food researchers as an alternative method for thermal processing. The use of ultrasound as a way to inactivate and/or activate enzymes has been widely studied at low frequencies (20â40 kHz), however, little research on the effect of high frequencies has been reported. Thus, the effect of high and low frequency ultrasound on commercial horseradish peroxidase with a concentration of 0.005 mg mLâ1 is described. Experiments were performed for 60 min using 20, 378, 583, 862, 995, 1144 and 1175 kHz ultrasound at power levels (acoustic energy) between 2.1 and 64 W. Residual activity was monitored using a spectrophotometric method and data analysis was performed using ANOVA. A significant enhancement of enzyme inactivation (p < 0.05) was observed at each frequency with an increase of sonication time and power. Inactivation of peroxidase by ultrasound followed first order kinetics and an increase of the rate constant with the power applied was observed for all the frequencies studied. Overall, low frequency (20 kHz) and low power are not effective on the enzyme inactivation and the level of residual activity remained high. The use of 378 and 583 kHz (48 W) is particularly effective for complete enzyme inactivation
Metabolomics on integrated circuit
We have demonstrated a chip-based diagnostics tool for the quantification of metabolites, using specific enzymes, to study enzyme kinetics and calculate the Michaelis-Menten constant. An array of 256Ă256 ion-sensitive field effect transistors (ISFETs) fabricated in a complementary metal oxide semiconductor (CMOS) process is used for this prototype. We have used hexokinase enzyme reaction on the ISFET CMOS chip with glucose concentration in the physiological range of 0.05 mM â 231 mM and successfully studied the enzyme kinetics of hexokinase in detail. This will promote future research towards multiplexing enzyme-based metabolite quantification on a single chip, ultimately opening a pathway towards a personal metabolome machine
Time-resolved fluorescence observation of di-tyrosine formation in horseradish peroxidase upon ultrasound treatment leading to enzyme inactivation
The application of ultrasound to a solution can induce cavitional phenomena and generate high localised temperatures and pressures. These are dependent of the frequency used and have enabled ultrasound application in areas such as synthetic, green and food chemistry. High frequency (100 kHz to 1 MHz) in particular is promising in food chemistry as a means to inactivate enzymes, replacing the need to use periods of high temperature. A plant enzyme, horseradish peroxidase, was studied using time-resolved fluorescence techniques as a means to assess the effect of high frequency (378 kHz and 583 kHz) ultrasound treatment at equivalent acoustic powers. This uncovered the fluorescence emission from a newly formed species, attributed to the formation of di-tyrosine within the horseradish peroxidase structure caused by auto-oxidation, and linked to enzyme inactivation
Hybrid dual mode sensor for simultaneous detection of two serum metabolites
Metabolites are the ultimate readout of disease phenotype that plays a significant role in the study of human disease. Multiple metabolites sometimes serve as biomarkers for a single metabolic disease. Therefore, simultaneous detection and analysis of those metabolites facilitate early diagnostics of the disease. Conventional approaches to detect and quantify metabolites include mass spectrometry and nuclear magnetic resonance that require bulky and expensive equipment. Here, we present a disposable sensing platform that is based on complementary metalâoxideâsemiconductor process. It contains two sensors: an ion sensitive field-effect transistor and photodiode that can work independently for detection of pH and color change produced during the metabolite-enzyme reaction. Serum glucose and cholesterol have been detected and quantified simultaneously with the new platform, which shows good sensitivity within the physiological range. Low cost and easy manipulation make our device a prime candidate for personal metabolome sensing diagnostics
Distributions of Triplets in Genetic Sequences
Distributions of triplets in some genetic sequences are examined and found to
be well described by a 2-parameter Markov process with a sparse transition
matrix. The variances of all the relevant parameters are not large, indicating
that most sequences gather in a small region in the parameter space. Different
sequences have very near values of the entropy calculated directly from the
data and the two parameters characterizing the Markov process fitting the
sequence. No relevance with taxonomy or coding/noncoding is clearly observed.Comment: revtex, 17pages, 8 figures, submitted to Physica
Curiosity-Driven Study: A Paradigm Revisited
Research has undergone tremendous changes over the years, as technology grows more sophisticated and definitions of what research is continues to evolve. Despite the number of paradigms being developed to address different needs and wants, curiosity has been surprisingly overlooked in recent years. This article will revisit some of the major objectives of conducting research, which is followed by a discussion on the limitations of the paradigms available at present. The article will then discuss the âforgottenâ drive in research â curiosity â and argues for a recalibration to place curiosity as the primary drive of research, as oppose to solely focusing on problem-solving, filling gap in literature, giving voice and fulfilling industrial demands. A research framework is then proposed, along with the potential outcomes of the paradigm in social and educational settings. Lastly, the article calls for more studies revisiting the potential advantages of curiosity-oriented research, and how future researchers can benefit from this shift in perspective
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