5,115 research outputs found
Diffusion Monte Carlo study of two-dimensional liquid He
The ground-state properties of two-dimensional liquid He at zero
temperature are studied by means of a quadratic diffusion Monte Carlo method.
As interatomic potential we use a revised version of the HFDHE2 Aziz potential
which is expected to give a better description of the interaction between
helium atoms. The equation of state is determined with great accuracy over a
wide range of densities in the liquid phase from the spinodal point up to the
freezing density. The spinodal decomposition density is estimated and other
properties of the liquid, such as radial distribution function, static form
factor, momentum distribution and density dependence of the condensate fraction
are all presented.Comment: 19 pages, RevTex 3.0, 7 figures available upon reques
Quantum sticking, scattering and transmission of 4He atoms from superfluid 4He surfaces
We develop a microscopic theory of the scattering, transmission, and sticking
of 4He atoms impinging on a superfluid 4He slab at near normal incidence, and
inelastic neutron scattering from the slab. The theory includes coupling
between different modes and allows for inelastic processes. We find a number of
essential aspects that must be observed in a physically meaningful and reliable
theory of atom transmission and scattering; all are connected with
multiparticle scattering, particularly the possibility of energy loss. These
processes are (a) the coupling to low-lying (surface) excitations
(ripplons/third sound) which is manifested in a finite imaginary part of the
self energy, and (b) the reduction of the strength of the excitation in the
maxon/roton region
The Double Quasar Q2138-431: Lensing by a Dark Galaxy?
We report the discovery of a new gravitational lens candidate Q2138-431AB,
comprising two quasar images at a redshift of 1.641 separated by 4.5 arcsecs.
The spectra of the two images are very similar, and the redshifts agree to
better than 115 km.sec. The two images have magnitudes and
, and in spite of a deep search and image subtraction procedure, no
lensing galaxy has been found with . Modelling of the system
configuration implies that the mass-to-light ratio of any lensing galaxy is
likely to be around , with an absolute lower limit of
for an Einstein-de Sitter universe. We conclude that
the most likely explanation of the observations is gravitational lensing by a
dark galaxy, although it is possible we are seeing a binary quasar.Comment: 17 pages (Latex), 8 postscript figures included, accepted by MNRA
Dynamics of liquid He-4 in confined geometries from Time-Dependent Density Functional calculations
We present numerical results obtained from Time-Dependent Density Functional
calculations of the dynamics of liquid He-4 in different environments
characterized by geometrical confinement. The time-dependent density profile
and velocity field of He-4 are obtained by means of direct numerical
integration of the non-linear Schrodinger equation associated with a
phenomenological energy functional which describes accurately both the static
and dynamic properties of bulk liquid He-4. Our implementation allows for a
general solution in 3-D (i.e. no symmetries are assumed in order to simplify
the calculations). We apply our method to study the real-time dynamics of pure
and alkali-doped clusters, of a monolayer film on a weakly attractive surface
and a nano-droplet spreading on a solid surface.Comment: q 1 tex file + 9 Ps figure
Quantum Films Adsorbed on Graphite: Third and Fourth Helium Layers
Using a path-integral Monte Carlo method for simulating superfluid quantum
films, we investigate helium layers adsorbed on a substrate consisting of
graphite plus two solid helium layers. Our results for the promotion densities
and the dependence of the superfluid density on coverage are in agreement with
experiment. We can also explain certain features of the measured heat capacity
as a function of temperature and coverage.Comment: 13 pages in the Phys. Rev. two-column format, 16 Figure
Observation of Single Transits in Supercooled Monatomic Liquids
A transit is the motion of a system from one many-particle potential energy
valley to another. We report the observation of transits in molecular dynamics
(MD) calculations of supercooled liquid argon and sodium. Each transit is a
correlated simultaneous shift in the equilibrium positions of a small local
group of particles, as revealed in the fluctuating graphs of the particle
coordinates versus time. This is the first reported direct observation of
transit motion in a monatomic liquid in thermal equilibrium. We found transits
involving 2 to 11 particles, having mean shift in equilibrium position on the
order of 0.4 R_1 in argon and 0.25 R_1 in sodium, where R_1 is the nearest
neighbor distance. The time it takes for a transit to occur is approximately
one mean vibrational period, confirming that transits are fast.Comment: 19 pages, 8 figure
LuSIV Cells: A Reporter Cell Line for the Detection and Quantitation of a Single Cycle of HIV and SIV Replication
AbstractA single cycle of viral replication is the time required for a virus to enter the host cell, replicate its genome, and produce infectious progeny virions. The primate lentiviruses, human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV), require on average 24 h to complete one cycle of replication. We have now developed and characterized a reporter assay system in CEMx174 cells for the quantitative measurement of HIV/SIV infection within a single replication cycle. The SIVmac239 LTR (â225 â +149) was cloned upstream of the firefly luciferase reporter gene and this reporter plasmid is maintained in CEMx174 cells under stable selection. This cell line, designated LuSIV, is highly sensitive to infection by primary and laboratory strains of HIV/SIV, resulting in Tat-mediated expression of luciferase, which correlates with viral infectivity. Furthermore, manipulation of LuSIV cells for the detection of luciferase activity is easy to perform and requires a minimal amount of time as compared to current HIV/SIV detection systems. The LuSIV system is a powerful tool for the analysis of HIV/SIV infection that provides a unique assay system that can detect virus replication prior to 24 h and does not require virus to spread from cell to cell. Thus these cells can be used for the study of replication-deficient viruses and the high throughput screening of antivirals, or other inhibitors of infection
Structural and dynamical properties of superfluid helium: a density functional approach
We present a novel density functional for liquid 4He, properly accounting for
the static response function and the phonon-roton dispersion in the uniform
liquid. The functional is used to study both structural and dynamical
properties of superfluid helium in various geometries. The equilibrium
properties of the free surface, droplets and films at zero temperature are
calculated. Our predictions agree closely to the results of ab initio Monte
Carlo calculations, when available. The introduction of a phenomenological
velocity dependent interaction, which accounts for backflow effects, is
discussed. The spectrum of the elementary excitations of the free surface and
films is studied.Comment: 37 pages, REVTeX 3.0, figures on request at [email protected]
B-type natriuretic peptide-guided treatment for heart failure
Background
Heart failure is a condition in which the heart does not pump enough blood to meet all the needs of the body. Symptoms of heart failure include breathlessness, fatigue and fluid retention. Outcomes for patients with heart failure are highly variable; however on average, these patients have a poor prognosis. Prognosis can be improved with early diagnosis and appropriate use of medical treatment, use of devices and transplantation. Patients with heart failure are high users of healthcare resources, not only due to drug and device treatments, but due to high costs of hospitalisation care. Bâtype natriuretic peptide levels are already used as biomarkers for diagnosis and prognosis of heart failure, but could offer to clinicians a possible tool to guide drug treatment. This could optimise drug management in heart failure patients whilst allaying concerns over potential side effects due to drug intolerance.
Objectives
To assess whether treatment guided by serial BNP or NTâproBNP (collectively referred to as NP) monitoring improves outcomes compared with treatment guided by clinical assessment alone.
Search methods
Searches were conducted up to 15 March 2016 in the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library; MEDLINE (OVID), Embase (OVID), the Database of Abstracts of Reviews of Effects (DARE) and the NHS Economic Evaluation Database in the Cochrane Library. Searches were also conducted in the Science Citation Index Expanded, the Conference Proceedings Citation Index on Web of Science (Thomson Reuters), World Health Organization International Clinical Trials Registry and ClinicalTrials.gov. We applied no date or language restrictions.
Selection criteria
We included randomised controlled trials of NPâguided treatment of heart failure versus treatment guided by clinical assessment alone with no restriction on followâup. Adults treated for heart failure, in both inâhospital and outâofâhospital settings, and trials reporting a clinical outcome were included.
Data collection and analysis
Two review authors independently selected studies for inclusion, extracted data and evaluated risk of bias. Risk ratios (RR) were calculated for dichotomous data, and pooled mean differences (MD) (with 95% confidence intervals (CI)) were calculated for continuous data. We contacted trial authors to obtain missing data. Using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach, we assessed the quality of the evidence and GRADE profiler (GRADEPRO) was used to import data from Review Manager to create a 'Summary of findings' table.
Main results
We included 18 randomised controlled trials with 3660 participants (range of mean age: 57 to 80 years) comparing NPâguided treatment with clinical assessment alone. The evidence for allâcause mortality using NPâguided treatment showed uncertainty (RR 0.87, 95% CI 0.76 to 1.01; patients = 3169; studies = 15; low quality of the evidence), and for heart failure mortality (RR 0.84, 95% CI 0.54 to 1.30; patients = 853; studies = 6; low quality of evidence).
The evidence suggested heart failure admission was reduced by NPâguided treatment (38% versus 26%, RR 0.70, 95% CI 0.61 to 0.80; patients = 1928; studies = 10; low quality of evidence), but the evidence showed uncertainty for allâcause admission (57% versus 53%, RR 0.93, 95% CI 0.84 to 1.03; patients = 1142; studies = 6; low quality of evidence).
Six studies reported on adverse events, however the results could not be pooled (patients = 1144; low quality of evidence). Only four studies provided cost of treatment results, three of these studies reported a lower cost for NPâguided treatment, whilst one reported a higher cost (results were not pooled; patients = 931, low quality of evidence). The evidence showed uncertainty for quality of life data (MD â0.03, 95% CI â1.18 to 1.13; patients = 1812; studies = 8; very low quality of evidence).
We completed a 'Risk of bias' assessment for all studies. The impact of risk of bias from lack of blinding of outcome assessment and high attrition levels was examined by restricting analyses to only low 'Risk of bias' studies.
Authors' conclusions
In patients with heart failure lowâquality evidence showed a reduction in heart failure admission with NPâguided treatment while lowâquality evidence showed uncertainty in the effect of NPâguided treatment for allâcause mortality, heart failure mortality, and allâcause admission. Uncertainty in the effect was further shown by very lowâquality evidence for patient's quality of life. The evidence for adverse events and cost of treatment was low quality and we were unable to pool results.</p
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