1,509 research outputs found
Effects of cryoprotectant concentration and cooling rate on vitrification of aqueous solutions
Vitrification of aqueous cryoprotectant mixtures is essential in
cryopreservation of proteins and other biological samples. We report systematic
measurements of critical cryoprotective agent (CPA) concentrations required for
vitrification during plunge cooling from T=295 K to T=77 K in liquid nitrogen.
Measurements on fourteen common CPAs including alcohols (glycerol, methanol,
isopropanol), sugars (sucrose, xylitol, dextrose, trehalose), PEGs (ethylene
glycol, PEG 200, PEG 2 000, PEG 20 000), glycols (DMSO, MPD), and salt (NaCl)
were performed for volumes ranging over four orders of magnitude from ~nL to 20
mkL, and covering the range of interest in protein crystallography. X-ray
diffraction measurements on aqueous glycerol mixtures confirm that the
polycrystalline-to-vitreous transition occurs within a span of less than 2% w/v
in CPA concentration, and that the form of polycrystalline ice (hexagonal or
cubic) depends on CPA concentration and cooling rate. For most of the studied
cryoprotectants, the critical concentration decreases strongly with volume in
the range from ~5 mkL to ~0.1 mkL, typically by a factor of two. By combining
measurements of the critical concentration versus volume with cooling time
versus volume, we obtain the function of greatest intrinsic physical interest:
the critical CPA concentration versus cooling rate during flash cooling. These
results provide a basis for more rational design of cryoprotective protocols,
and should yield insight into the physics of glass formation in aqueous
mixtures.Comment: 8 pages, 6 jpg figure, 2 table
Wigner-Crystal Formulation of Strong-Coupling Theory for Counter-ions Near Planar Charged Interfaces
We present a new analytical approach to the strong electrostatic coupling
regime (SC), that can be achieved equivalently at low temperatures, high
charges, low dielectric permittivity etc. Two geometries are analyzed in
detail: one charged wall first, and then, two parallel walls at small
distances, that can be likely or oppositely charged. In all cases, one type of
mobile counter-ions only is present, and ensures electroneutrality (salt free
case). The method is based on a systematic expansion around the ground state
formed by the two-dimensional Wigner crystal(s) of counter-ions at the
plate(s). The leading SC order stems from a single-particle theory, and
coincides with the virial SC approach that has been much studied in the last 10
years. The first correction has the functional form of the virial SC
prediction, but the prefactor is different. The present theory is free of
divergences and the obtained results, both for symmetrically and asymmetrically
charged plates, are in excellent agreement with available data of Monte-Carlo
simulations under strong and intermediate Coulombic couplings. All results
obtained represent relevant improvements over the virial SC estimates. The
present SC theory starting from the Wigner crystal and therefore coined Wigner
SC, sheds light on anomalous phenomena like the counter-ion mediated
like-charge attraction, and the opposite-charge repulsion
Counterions at Charged Cylinders: Criticality and universality beyond mean-field
The counterion-condensation transition at charged cylinders is studied using
Monte-Carlo simulation methods. Employing logarithmically rescaled radial
coordinates, large system sizes are tractable and the critical behavior is
determined by a combined finite-size and finite-ion-number analysis. Critical
counterion localization exponents are introduced and found to be in accord with
mean-field theory both in 2 and 3 dimensions. In 3D the heat capacity shows a
universal jump at the transition, while in 2D, it consists of discrete peaks
where single counterions successively condense.Comment: 4 pages, 3 figures; submitted to Phys. Rev. Lett. (2005
Overscreening in 1D lattice Coulomb gas model of ionic liquids
Overscreening in the charge distribution of ionic liquids at electrified
interfaces is shown to proceed from purely electrostatic and steric
interactions in an exactly soluble one dimensional lattice Coulomb gas model.
Being not a mean-field effect, our results suggest that even in higher
dimensional systems the overscreening could be accounted for by a more accurate
treatment of the basic lattice Coulomb gas model, that goes beyond the mean
field level of approximation, without any additional interactions.Comment: 4 pages 5 .eps figure
The Dynamics of Stage Structured Prey-Predator Model Involving Parasitic Infectious Disease
In this paper a prey-predator model involving parasitic infectious disease is proposed and analyzed. It is assumed that the life cycle of predator species is divided into two stages immature and mature. The analysis of local and global stability of all possible subsystems is carried out. The dynamical behaviors of the model system around biologically feasible equilibria are studied. The global dynamics of the model are investigated with the help of Suitable Lyapunov functions. Conditions for which the model persists are established. Finally, to nationalize our analytical results, numerical simulations are worked out for a hypothetical set of parameter values
Counterion-Mediated Weak and Strong Coupling Electrostatic Interaction between Like-Charged Cylindrical Dielectrics
We examine the effective counterion-mediated electrostatic interaction
between two like-charged dielectric cylinders immersed in a continuous
dielectric medium containing neutralizing mobile counterions. We focus on the
effects of image charges induced as a result of the dielectric mismatch between
the cylindrical cores and the surrounding dielectric medium and investigate the
counterion-mediated electrostatic interaction between the cylinders in both
limits of weak and strong electrostatic couplings (corresponding, e.g., to
systems with monovalent and multivalent counterions, respectively). The results
are compared with extensive Monte-Carlo simulations exhibiting good agreement
with the limiting weak and strong coupling results in their respective regime
of validity.Comment: 19 pages, 10 figure
Effect of consumption supplemented strained yoghurt with vegetables on reducing weight of obese women samples
Obesity during adulthood is a public health problem in modern society, and increasingly universal disease that is turning into an epidemic one. The main cause of the excessive deposition of fat is the destruction of the systems controlling the expenditure of energy. Pathological increase of mass fat leads to disorders of the body, and lipid-carbohydrate parameters, raise the development of vascular diseases and increases the risk of morbidity and mortality. A substantial body of data has elicited over the last five years to show that dairy foods especially low-fat yogurt modulate weight loss and has some unique properties that may enhance its role in maintenance of healthy weight. Regular physical activity is an important as what we eat for losing, maintains weight and keeping our heart healthy. Being active helps burn calories, tone our muscles and control our appetite. The aim of this study is to demonstrate the impact of diet which was restricted in its energy by consuming concentrated yogurt daily and physical activity changes in the body weight, body mass index, and in the parameters lipid- cholesterol of women's adulthood. Low-fat yogurt, restricted energy consumption with at least three times exercises weekly inversely associated with body weight, BMI, and WC (all p< 0.05). Also, consumption of low-fat yogurt and exercising daily was associated inversely with blood glucose, cholesterol and lipid parameter (all p< 0.05). Within a sample of obese adults women, consumption of low-fat dairy product and increases the physical activity with restricted energy ingestion was associated with more favorable body composition. Keywords: Obesity, diet-yogurt, physical activity, BMI-blood lipid, parameter
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