382 research outputs found
Freezing and pressure-driven flow of solid helium in Vycor
The recent torsional oscillator results of Kim and Chan suggest a supersolid
phase transition in solid He-4 confined in Vycor. We have used a capacitive
technique to directly monitor density changes for helium confined in Vycor at
low temperature and have used a piezoelectrically driven diaphragm to study the
pressure-induced flow of solid helium into the Vycor pores. Our measurements
showed no indication of a mass redistribution in the Vycor that could mimic
supersolid decoupling and put an upper limit of about 0.003 um/s on any
pressure-induced supersolid flow in the pores of Vycor.Comment: 5 pages, 4 figure
Deformation of Silica Aerogel During Fluid Adsorption
Aerogels are very compliant materials - even small stresses can lead to large
deformations. In this paper we present measurements of the linear deformation
of high porosity aerogels during adsorption of low surface tension fluids,
performed using a Linear Variable Differential Transformer (LVDT). We show that
the degree of deformation of the aerogel during capillary condensation scales
with the surface tension, and extract the bulk modulus of the gel from the
data. Furthermore we suggest limits on safe temperatures for filling and
emptying low density aerogels with helium.Comment: 8 pages, 5 figures, submitted to PR
An Improved Implementation and Abstract Interface for Hybrid
Hybrid is a formal theory implemented in Isabelle/HOL that provides an
interface for representing and reasoning about object languages using
higher-order abstract syntax (HOAS). This interface is built around an HOAS
variable-binding operator that is constructed definitionally from a de Bruijn
index representation. In this paper we make a variety of improvements to
Hybrid, culminating in an abstract interface that on one hand makes Hybrid a
more mathematically satisfactory theory, and on the other hand has important
practical benefits. We start with a modification of Hybrid's type of terms that
better hides its implementation in terms of de Bruijn indices, by excluding at
the type level terms with dangling indices. We present an improved set of
definitions, and a series of new lemmas that provide a complete
characterization of Hybrid's primitives in terms of properties stated at the
HOAS level. Benefits of this new package include a new proof of adequacy and
improvements to reasoning about object logics. Such proofs are carried out at
the higher level with no involvement of the lower level de Bruijn syntax.Comment: In Proceedings LFMTP 2011, arXiv:1110.668
Human Lin28 forms a high-affinity 1:1 complex with the 106~363 cluster miRNA miR-363
Lin28A is a post-transcriptional regulator of gene expression that interacts with and negatively regulates the biogenesis of let-7 family miRNAs. Recent data suggested that Lin28A also binds the putative tumour suppressor miR-363, a member of the 106~363 cluster of miRNAs. Affinity toward this miRNA and the stoichiometry of the protein-RNA complex are unknown. Characterisation of human Lin28's interaction with RNA has been complicated by difficulties in producing stable RNA-free protein. We have engineered a maltose binding protein fusion with Lin28, which binds let-7 miRNA with a Kd of 54.1 ± 4.2 nM, in agreement with previous data on a murine homologue. We show that human Lin28A binds miR-363 with 1:1 stoichiometry and with similar, if not higher, affinity (Kd = 16.6 ± 1.9 nM). Further analysis suggests that the interaction of the N-terminal cold shock domain of Lin28A with RNA is salt-dependent, supporting a model where the cold shock domain allows the protein to sample RNA substrates through transient electrostatic interactions
Libxc: a library of exchange and correlation functionals for density functional theory
The central quantity of density functional theory is the so-called
exchange-correlation functional. This quantity encompasses all non-trivial
many-body effects of the ground-state and has to be approximated in any
practical application of the theory. For the past 50 years, hundreds of such
approximations have appeared, with many successfully persisting in the
electronic structure community and literature. Here, we present a library that
contains routines to evaluate many of these functionals (around 180) and their
derivatives.Comment: 15 page
A tool to improve pre-selection for deep brain stimulation in patients with Parkinsonâs disease
Determining the eligibility of patients with Parkinsonâs disease (PD) for deep brain stimulation (DBS) can be challenging for general (non-specialised) neurologists. We evaluated the use of an online screening tool (Stimulus) that aims to support appropriate referral to a specialised centre for the further evaluation of DBS. Implementation of the tool took place via an ongoing European multicentre educational programme, currently completed in 15 DBS centres with 208 referring neurologists. Use of the tool in daily practice was monitored via an online data capture programme. Selection decisions of patients referred with the assistance of the Stimulus tool were compared to those of patients outside the screening programme. Three years after the start of the programme, 3,128 patient profiles had been entered. The intention for referral was made for 802 patients and referral intentions were largely in accordance with the tool recommendations. Follow-up at 6Â months showed that actual referral took place in only 28%, predominantly due to patientsâ reluctance to undergo brain surgery. In patients screened with the tool and referred to a DBS centre, the acceptance rate was 77%, significantly higher than that of the unscreened population (48%). The tool showed a sensitivity of 99% and a specificity of 12% with a positive and negative predictive value of 79 and 75%, respectively. The Stimulus tool is useful in assisting general neurologists to identify appropriate candidates for DBS consideration. The principal reason for not referring potentially eligible patients is their reluctance to undergo brain surgery
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