14,462 research outputs found
The role of long-range forces in the phase behavior of colloids and proteins
The phase behavior of colloid-polymer mixtures, and of solutions of globular
proteins, is often interpreted in terms of a simple model of hard spheres with
short-ranged attraction. While such a model yields a qualitative understanding
of the generic phase diagrams of both colloids and proteins, it fails to
capture one important difference: the model predicts fluid-fluid phase
separation in the metastable regime below the freezing curve. Such demixing has
been observed for globular proteins, but for colloids it appears to be
pre-empted by the appearance of a gel. In this paper, we study the effect of
additional long-range attractions on the phase behavior of spheres with
short-ranged attraction. We find that such attractions can shift the
(metastable) fluid-fluid critical point out of the gel region. As this
metastable critical point may be important for crystal nucleation, our results
suggest that long-ranged attractive forces may play an important role in the
crystallization of globular proteins. However, in colloids, where refractive
index matching is often used to switch off long-ranged dispersion forces,
gelation is likely to inhibit phase separation.Comment: EURO-LATEX, 6 pages, 2 figure
Shuttle payload bay dynamic environments: Summary and conclusion report for STS flights 1-5 and 9
The vibration, acoustic and low frequency loads data from the first 5 shuttle flights are presented. The engineering analysis of that data is also presented. Vibroacoustic data from STS-9 are also presented because they represent the only data taken on a large payload. Payload dynamic environment predictions developed by the participation of various NASA and industrial centers are presented along with a comparison of analytical loads methodology predictions with flight data, including a brief description of the methodologies employed in developing those predictions for payloads. The review of prediction methodologies illustrates how different centers have approached the problems of developing shuttle dynamic environmental predictions and criteria. Ongoing research activities related to the shuttle dynamic environments are also described. Analytical software recently developed for the prediction of payload acoustic and vibration environments are also described
Correction: Limit theorems for coupled continuous time random walks
Correction to "Limit theorems for coupled continuous time random walks" (Ann.
Probab. 32 (2004) 730-756).Comment: Published in at http://dx.doi.org/10.1214/10-AOP635 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Recommended from our members
Cryo-EM structure of the potassium-chloride cotransporter KCC4 in lipid nanodiscs.
Cation-chloride-cotransporters (CCCs) catalyze transport of Cl- with K+ and/or Na+across cellular membranes. CCCs play roles in cellular volume regulation, neural development and function, audition, regulation of blood pressure, and renal function. CCCs are targets of clinically important drugs including loop diuretics and their disruption has been implicated in pathophysiology including epilepsy, hearing loss, and the genetic disorders Andermann, Gitelman, and Bartter syndromes. Here we present the structure of a CCC, the Mus musculus K+-Cl- cotransporter (KCC) KCC4, in lipid nanodiscs determined by cryo-EM. The structure, captured in an inside-open conformation, reveals the architecture of KCCs including an extracellular domain poised to regulate transport activity through an outer gate. We identify binding sites for substrate K+ and Cl- ions, demonstrate the importance of key coordinating residues for transporter activity, and provide a structural explanation for varied substrate specificity and ion transport ratio among CCCs. These results provide mechanistic insight into the function and regulation of a physiologically important transporter family
Local pressure-induced metallization of a semiconducting carbon nanotube in a crossed junction
The electronic and vibrational density of states of a semiconducting carbon
nanotube in a crossed junction was investigated by elastic and inelastic
scanning tunneling spectroscopy. The strong radial compression of the nanotube
at the junction induces local metallization spatially confined to a few nm. The
local electronic modifications are correlated with the observed changes in the
radial breathing and G-band phonon modes, which react very sensitively to local
mechanical deformation. In addition, the experiments reveal the crucial
contribution of the image charges to the contact potential at nanotube-metal
interfaces
Aging Dynamics of a Fractal Model Gel
Using molecular dynamics computer simulations we investigate the aging
dynamics of a gel. We start from a fractal structure generated by the DLCA-DEF
algorithm, onto which we then impose an interaction potential consisting of a
short-range attraction as well as a long-range repulsion. After relaxing the
system at T=0, we let it evolve at a fixed finite temperature. Depending on the
temperature T we find different scenarios for the aging behavior. For T>0.2 the
fractal structure is unstable and breaks up into small clusters which relax to
equilibrium. For T<0.2 the structure is stable and the dynamics slows down with
increasing waiting time. At intermediate and low T the mean squared
displacement scales as t^{2/3} and we discuss several mechanisms for this
anomalous time dependence. For intermediate T, the self-intermediate scattering
function is given by a compressed exponential at small wave-vectors and by a
stretched exponential at large wave-vectors. In contrast, for low T it is a
stretched exponential for all wave-vectors. This behavior can be traced back to
a subtle interplay between elastic rearrangements, fluctuations of chain-like
filaments, and heterogeneity.Comment: 30 pages, 25 figure
Intranasal insulin to improve developmental delay in children with 22q13 deletion syndrome: an exploratory clinical trial
Background: The 22q13 deletion syndrome (Phelan–
McDermid syndrome) is characterised by a global
developmental delay, absent or delayed speech, generalised
hypotonia, autistic behaviour and characteristic
phenotypic features. Intranasal insulin has been shown to
improve declarative memory in healthy adult subjects and
in patients with Alzheimer disease.
Aims: To assess if intranasal insulin is also able to
improve the developmental delay in children with 22q13
deletion syndrome.
Methods: We performed exploratory clinical trials in six
children with 22q13 deletion syndrome who received
intranasal insulin over a period of 1 year. Short-term
(during the first 6 weeks) and long-term effects (after
12 months of treatment) on motor skills, cognitive
functions, or autonomous functions, speech and communication,
emotional state, social behaviour, behavioural
disorders, independence in daily living and education were
assessed.
Results: The children showed marked short-term
improvements in gross and fine motor activities, cognitive
functions and educational level. Positive long-term effects
were found for fine and gross motor activities, nonverbal
communication, cognitive functions and autonomy.
Possible side effects were found in one patient who
displayed changes in balance, extreme sensitivity to touch
and general loss of interest. One patient complained of
intermittent nose bleeding.
Conclusions: We conclude that long-term administration
of intranasal insulin may benefit motor development,
cognitive functions and spontaneous activity in children
with 22q13 deletion syndrome
Recommended from our members
Towards the spatial resolution of metalloprotein charge states by detailed modeling of XFEL crystallographic diffraction.
Oxidation states of individual metal atoms within a metalloprotein can be assigned by examining X-ray absorption edges, which shift to higher energy for progressively more positive valence numbers. Indeed, X-ray crystallography is well suited for such a measurement, owing to its ability to spatially resolve the scattering contributions of individual metal atoms that have distinct electronic environments contributing to protein function. However, as the magnitude of the shift is quite small, about +2 eV per valence state for iron, it has only been possible to measure the effect when performed with monochromated X-ray sources at synchrotron facilities with energy resolutions in the range 2-3 × 10-4 (ΔE/E). This paper tests whether X-ray free-electron laser (XFEL) pulses, which have a broader bandpass (ΔE/E = 3 × 10-3) when used without a monochromator, might also be useful for such studies. The program nanoBragg is used to simulate serial femtosecond crystallography (SFX) diffraction images with sufficient granularity to model the XFEL spectrum, the crystal mosaicity and the wavelength-dependent anomalous scattering factors contributed by two differently charged iron centers in the 110-amino-acid protein, ferredoxin. Bayesian methods are then used to deduce, from the simulated data, the most likely X-ray absorption curves for each metal atom in the protein, which agree well with the curves chosen for the simulation. The data analysis relies critically on the ability to measure the incident spectrum for each pulse, and also on the nanoBragg simulator to predict the size, shape and intensity profile of Bragg spots based on an underlying physical model that includes the absorption curves, which are then modified to produce the best agreement with the simulated data. This inference methodology potentially enables the use of SFX diffraction for the study of metalloenzyme mechanisms and, in general, offers a more detailed approach to Bragg spot data reduction
- …