893 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
Electrostatic Disorder-Induced Interactions in Inhomogeneous Dielectrics
We investigate the effect of quenched surface charge disorder on
electrostatic interactions between two charged surfaces in the presence of
dielectric inhomogeneities and added salt. We show that in the linear
weak-coupling regime (i.e., by including mean-field and Gaussian-fluctuations
contributions), the image-charge effects lead to a non-zero disorder-induced
interaction free energy between two surfaces of equal mean charge that can be
repulsive or attractive depending on the dielectric mismatch across the
bounding surfaces and the exact location of the disordered charge distribution.Comment: 7 pages, 2 figure
Quenched Charge Disorder and Coulomb Interactions
We develop a general formalism to investigate the effect of quenched fixed
charge disorder on effective electrostatic interactions between charged
surfaces in a one-component (counterion-only) Coulomb fluid. Analytical results
are explicitly derived for two asymptotic and complementary cases: i)
mean-field or Poisson-Boltzmann limit (including Gaussian-fluctuations
correction), which is valid for small electrostatic coupling, and ii)
strong-coupling limit, where electrostatic correlations mediated by counterions
become significantly large as, for instance, realized in systems with
high-valency counterions. In the particular case of two apposed and ideally
polarizable planar surfaces with equal mean surface charge, we find that the
effect of the disorder is nil on the mean-field level and thus the plates
repel. In the strong-coupling limit, however, the effect of charge disorder
turns out to be additive in the free energy and leads to an enhanced long-range
attraction between the two surfaces. We show that the equilibrium inter-plate
distance between the surfaces decreases for elevated disorder strength (i.e.
for increasing mean-square deviation around the mean surface charge), and
eventually tends to zero, suggesting a disorder-driven collapse transition.Comment: 13 pages, 2 figure
Drag forces on inclusions in classical fields with dissipative dynamics
We study the drag force on uniformly moving inclusions which interact
linearly with dynamical free field theories commonly used to study soft
condensed matter systems. Drag forces are shown to be nonlinear functions of
the inclusion velocity and depend strongly on the field dynamics. The general
results obtained can be used to explain drag forces in Ising systems and also
predict the existence of drag forces on proteins in membranes due to couplings
to various physical parameters of the membrane such as composition, phase and
height fluctuations.Comment: 14 pages, 7 figure
Electromagnetic fluctuation-induced interactions in randomly charged slabs
Randomly charged net-neutral dielectric slabs are shown to interact across a
featureless dielectric continuum with long-range electrostatic forces that
scale with the statistical variance of their quenched random charge
distribution and inversely with the distance between their bounding surfaces.
By accounting for the whole spectrum of electromagnetic field fluctuations, we
show that this long-range disorder-generated interaction extends well into the
retarded regime where higher-order Matsubara frequencies contribute
significantly. This occurs even for highly clean samples with only a trace
amount of charge disorder and shows that disorder effects can be important down
to the nano scale. As a result, the previously predicted non-monotonic behavior
for the total force between dissimilar slabs as a function of their separation
distance is substantially modified by higher-order contributions, and in almost
all cases of interest, we find that the equilibrium inter-surface separation is
shifted to substantially larger values compared to predictions based solely on
the zero-frequency component. This suggests that the ensuing non-monotonic
interaction is more easily amenable to experimental detection. The presence of
charge disorder in the intervening dielectric medium between the two slabs is
shown to lead to an additional force that can be repulsive or attractive
depending on the system parameters and can, for instance, wash out the
non-monotonic behavior of the total force when the intervening slab contains a
sufficiently large amount of disorder charges.Comment: 9 pages, 5 figure
RAD Module Infrastructure of the Field-programmable Port eXtender (FPX) Version 2.0
The Field-programmable Port eXtender (FPX) provides dynamic, fast, and flexible mechanisms to process data streams at the ports of the Washington University Gigabit Switch (WUGS-20). In order to facilitate the design and implementation of portable hardware modules for the Reprogrammable Application Device (RAD) on the FPX board, infrastructure components have been developed. These components abstract application module designers from device-specific timing specifications of off-chip memory devices, as well as processing system-level control cells. This document describes the design and internal functionality of the infrastructure components and is intended as a reference for future component revisions and additions. Application module designers should refer to the Generalized RAD Module Interface Specification of the Field Programmable Port Extender (FPX), EUCS-TM-01-15
Comparative Study between Neopterin and Alvarado Score in the Diagnosis of Acute Appendicitis and Its Severity
BACKGROUND: Acute appendicitis (AA) remains a complex case even for experienced surgeons. Rate of negative appendectomy is 5–40% and delayed intervention result in perforated appendicitis in 5–30% of cases.
AIM: The aim of the study was to evaluate NPT as a marker for the diagnosis of AA concerning its severity. And compare the diagnostic value of it with the ALV scoring system.
METHODS: One hundred twenty patients presented with signs and symptoms of AA and underwent appendectomy, only 84 patients proved to be AA by histopathological examination, were included in the study. Blood samples for neopterin (NPT) estimation and Alvarado (ALV) score was calculated. Control group consists of 45 healthy individual.
RESULTS: NPT levels were significantly higher in patients’ group than control with p = 0.001 at a cutoff point 5.3 nmol/L. The diagnostic accuracy of NPT was higher than ALV score. NPT sensitivity, specificity, positive predictive value, and negative predictive value were 85.4%, 76.9%, 89%, and 70%, respectively.
CONCLUSION: NPT significantly elevated in patient with AA and has a high diagnostic accuracy, with correlation to clinical features and severity of the inflammation
Non-monotoic fluctuation-induced interactions between dielectric slabs carrying charge disorder
We investigate the effect of monopolar charge disorder on the classical
fluctuation-induced interactions between randomly charged net-neutral
dielectric slabs and discuss various generalizations of recent results (A. Naji
et al., Phys. Rev. Lett. 104, 060601 (2010)) to highly inhomogeneous dielectric
systems with and without statistical disorder correlations. We shall focus on
the specific case of two generally dissimilar plane-parallel slabs, which
interact across vacuum or an arbitrary intervening dielectric medium. Monopolar
charge disorder is considered to be present on the bounding surfaces and/or in
the bulk of the slabs, may be in general quenched or annealed and may possess a
finite lateral correlation length reflecting possible `patchiness' of the
random charge distribution. In the case of quenched disorder, the bulk disorder
is shown to give rise to an additive long-range contribution to the total
force, which decays as the inverse distance between the slabs and may be
attractive or repulsive depending on the dielectric constants of the slabs. We
show that in the case of two dissimilar slabs the net effect due to the
interplay between the disorder-induced and the pure van der Waals interactions
can lead to a variety of unusual non-monotonic interaction profiles between the
dielectric slabs. In particular, when the intervening medium has a larger
dielectric constant than the two slabs, we find that the net interaction can
become repulsive and exhibit a potential barrier, while the underlying van der
Waals force is attractive. On the contrary, when the intervening medium has a
dielectric constant in between that of the two slabs, the net interaction can
become attractive and exhibit a free energy minimum, while the pure van der
Waals force is repulsive. Therefore, the charge disorder, if present, can
drastically alter the effective interaction between net-neutral objects.Comment: 13 pages, 8 figure
Molecular Dynamics Simulation of Semiflexible Polyampholyte Brushes - The Effect of Charged Monomers Sequence
Planar brushes formed by end-grafted semiflexible polyampholyte chains, each
chain containing equal number of positively and negatively charged monomers is
studied using molecular dynamics simulations. Keeping the length of the chains
fixed, dependence of the average brush thickness and equilibrium statistics of
the brush conformations on the grafting density and the salt concentration are
obtained with various sequences of charged monomers. When similarly charged
monomers of the chains are arranged in longer blocks, the average brush
thickness is smaller and dependence of brush properties on the grafting density
and the salt concentration is stronger. With such long blocks of similarly
charged monomers, the anchored chains bond to each other in the vicinity of the
grafting surface at low grafting densities and buckle toward the grafting
surface at high grafting densities.Comment: 8 pages,7 figure
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