196 research outputs found
Simplified exponential approximation for thermodynamics of a hard-core repulsive Yukawa fluid
Exponential approximation based on the first order mean spherical
approximation (FMSA) is applied to the study of the structure and
thermodynamics of hard-core repulsive Yukawa fluids. The proposed theory
utilizes an exponential enhancement of the analytical solution of the FMSA due
to Tang and Lu [J. Chem. Phys., 1993, 99, 9828] for the radial distribution
function. From comparison with computer simulation data we have shown that at
low density and low temperature conditions, where original FMSA theory fails,
the FMSA-based exponential theory predicts a significant improvement.Comment: 14 pages, 6 figure
Improved first order mean spherical approximation for simple fluids
A perturbation approach based on the first-order mean spherical approximation
(FMSA) is proposed. It consists in adopting a hard-sphere plus short-range
attractive Yukawa fluid as the novel reference system, over which the
perturbative solution of the Ornstein-Zernike equation is performed. A choice
of the optimal range of the reference attraction is discussed. The results are
compared against conventional FMSA/HS theory and Monte-Carlo simulation data
for compressibility factor and vapor-liquid phase diagrams of the medium-ranged
Yukawa fluid. Proposed theory keeps the same level of simplicity and
transparency, as the conventional FMSA/HS approach does, but shows to be more
accurate.Comment: 8 pages, 3 figure
Results of application of modular artificial neural networks for intelligent data analysis (data mining) and forecasting processes in the field of ecology and environment protection
The aim of this work is the use of modular artificial neural networks (ANN) for data mining (Data Mining) and forecasting of various processes in the field of ecology and environmental protection, as well as the comparison of the results of the proposed model with the results of other data analysis methods (the methods of mathematical modeling and mathematical statistics).Метою даної роботи є використання модульних штучних нейронних мереж для виведення даних та прогнозування різних процесів у галузі екології та охорони навколишнього середовища, а також порівняння результатів запропонованої моделі з результатами інших методів аналізу даних (методи математичного моделювання та математичної статистики)
Towards frustration of freezing transition in a binary hard-disk mixture
The freezing mechanism, recently suggested for a monodisperse hard-disk fluid
[Huerta et al., Phys. Rev. E, 2006, 74, 061106] is extended here to an
equimolar binary hard-disk mixtures. We are showing that for diameter ratios,
smaller than 1.15 the global orientational order parameter of the binary
mixture behaves like in the case of a monodisperse fluid. Namely, by increasing
the disk number density there is a tendency to form a crystalline-like phase.
However, for diameter ratios larger than 1.15 the binary mixtures behave like a
disordered fluid. We use some of the structural and thermodynamic properties to
compare and discuss the behavior as a function of diameter ratio and packing
fraction.Comment: 9 pages, 4 figure
Virial expansions and augmented van der Waals approach: Application to Lennard-Jones-like Yukawa fluid
We argue that recently proposed [Melnyk et al., Fluid Phase Equilibr., 2009,
Vol. 279, 1] a criterion to split the pair interaction energy into two parts,
one of which is forced to be responsible the most accurate as possible for
excluded volume energy in the system, results in expressions for the virial
coefficients that improve the performance of the virial equation of state in
general, and at subcritical temperatures, in particular. As an example,
application to the Lennard-Jones-like hard-core attractive Yukawa fluid is
discussed.Comment: 12 pages, 6 figure
Mean spherical approximation for the Lennard-Jones-like two Yukawa model: Comparison against Monte Carlo data
Monte Carlo simulation studies are performed for the Lennard-Jones like two
Yukawa (LJ2Y) potential to show how properties of this model fluid depend on
the replacement of the soft repulsion by the hard-core repulsion. Different
distances for the positioning of hard core have been explored. We have found,
that for temperatures that are slightly lower and slightly higher of the
critical point temperature for the Lennard-Jones fluid, placing the hard core
at distances that are shorter than zero-potential energy is well justified by
thermodynamic properties that are practically the same as in original LJ2Y
model without hard core. However, going to extreme conditions with the high
temperature one should be careful since presence of the hard core provokes
changes in the properties of the system. The later is extremely important when
the mean spherical approximation (MSA) theory is applied to treat the
Lennard-Jones-like fluid.Comment: 11 pages, 13 figure
Marian Smoluchowski: A story behind one photograph
We discuss the photograph procured from the archives of the V. Stefanyk Lviv
National Scientific Library of Ukraine dated by 1904 which shows Marian
Smoluchowski together with professors and graduate students of the Philosophy
department of the Lviv University. The personalia includes both the professors
and the graduates depicted on the photograph with the emphasis on the graduates
as being much less known and studied. The photograph originates from the
collection of the Shevchenko Scientific Society, therefore a brief historical
background on the activities of physicists in this society around that period
of time is provided as well.Comment: 8 pages, 1 photograp
Frustration of freezing in a two dimensional hard-core fluid due to particle shape anisotropy
The freezing mechanism suggested for a fluid composed of hard disks [Huerta
et al., Phys. Rev. E, 2006, 74, 061106] is used here to probe the
fluid-to-solid transition in a hard-dumbbell fluid composed of overlapping hard
disks with a variable length between disk centers. Analyzing the trends in the
shape of second maximum of the radial distribution function of the planar
hard-dumbbell fluid it has been found that the type of transition could be
sensitive to the length of hard-dumbbell molecules. From the Monte
Carlo simulations data we show that if a hard-dumbbell length does not exceed
15% of the disk diameter, the fluid-to-solid transition scenario follows the
case of a hard-disk fluid, i.e., the isotropic hard-dumbbell fluid experiences
freezing. However, for a hard-dumbbell length larger than 15% of disk diameter,
there is evidence that fluid-to-solid transition may change to continuous
transition, i.e., such an isotropic hard-dumbbell fluid will avoid freezing.Comment: 9 pages, 7 figure
Bacterial levels in Saskatchewan retail ground beef
This thesis describes the results of three studies that used different measures of bacterial numbers in retail ground beef (n=309) collected across different locations in Saskatchewan within a one-year period (May 2011 – May 2012). The measurements were compared among three sample categories: 1 - ground beef displaying government inspection information on the label legend (n=126), 2 - originating from facilities licensed by local health regions and thus not subjected to government inspection (n=80), or 3 - processed and repackaged at the retail level thus carrying no government inspection information on the label (n=103).
The first study reports baseline levels of bacteria in Saskatchewan retail ground beef as measured by traditional (total aerobic plate count (TAPC) and total E. coli plate count (TEPC)) and culture-independent methods (estimate of total bacterial load (TBL) by real-time quantitative polymerase chain reaction). After accounting for season and whether the samples were fresh or frozen at purchase, the lowest TAPC (log10 4.9 culture forming units per gram (cfu/g); 95% CI log10 4.7 to log10 5.1 cfu/g), TEPC (log10 0.58 cfu/g; 95% CI log10 0.39 to log10 0.77 cfu/g), and TBL in frozen ground beef (log10 4.5 target copies per gram (tc/g); 95% CI log10 4.0 to log10 4.9 tc/g) were observed in samples originating from federally regulated or provincially licensed facilities.
In the second study, presence of known Enterobacteriaceae virulence factors (stx1, stx2, and eae) was detected by polymerase chain reaction (PCR) and compared between samples originating from three different regulatory and inspection environments as well as collected during different seasons of the year, and purchased fresh or frozen. One hundred and twelve out of all tested samples (n=308) were positive for the presence of at least one virulence marker with stx1 identified in 107 samples, stx2 - in 8, and eae - in 26. No significant associations were found between the virulence markers presence and sample category, state or season of purchase.
The third study investigates the presence and diversity of Campylobacter spp. organisms in the same pool of 309 retail beef samples as detected by molecular methods. Fifty samples (16.2%) tested positive for Campylobacter genus-specific DNA in conventional PCR and 49 samples (15.9%) tested positive for at least one Campylobacter species DNA presence in real-time qPCR, but the crude agreement between the two methods was less than 50%. C. coli DNA presence was observed in 14 samples (4.5%), C. curvus – in 11 (3.6%), C. fetus – in 6 (1.9%), C. hyointestinalis – in 24 (7.8%), C. jejuni – in 12 (3.9%), C. rectus – in 6 (1.9%), and C. upsaliensis – in 9 (2.9%). There was no difference in the frequency of Campylobacter identified among the three sample categories, fresh and frozen, or samples purchased during the cold or warm season.
These studies provide data on prevalence of bacteria in retail ground beef offered for sale in Saskatchewan and compare differences between samples presented to the consumer as originating from federally regulated or provincially licensed facilities, locally licensed facilities, or repackaged and processed directly at a retail outlet. The information on baseline levels of bacteria in retail ground beef and the comparisons among different categories can be used in prioritising food safety improvement efforts in Saskatchewan
- …