1,671 research outputs found
A Variational Approach for Minimizing Lennard-Jones Energies
A variational method for computing conformational properties of molecules
with Lennard-Jones potentials for the monomer-monomer interactions is
presented. The approach is tailored to deal with angular degrees of freedom,
{\it rotors}, and consists in the iterative solution of a set of deterministic
equations with annealing in temperature. The singular short-distance behaviour
of the Lennard-Jones potential is adiabatically switched on in order to obtain
stable convergence. As testbeds for the approach two distinct ensembles of
molecules are used, characterized by a roughly dense-packed ore a more
elongated ground state. For the latter, problems are generated from natural
frequencies of occurrence of amino acids and phenomenologically determined
potential parameters; they seem to represent less disorder than was previously
assumed in synthetic protein studies. For the dense-packed problems in
particular, the variational algorithm clearly outperforms a gradient descent
method in terms of minimal energies. Although it cannot compete with a careful
simulating annealing algorithm, the variational approach requires only a tiny
fraction of the computer time. Issues and results when applying the method to
polyelectrolytes at a finite temperature are also briefly discussed.Comment: 14 pages, uuencoded compressed postscript fil
Work-related airway symptoms, nasal reactivity and health-related quality of life in female hairdressers: a follow-up study during exposure.
OBJECTIVES: Hairdressers often complain of work-related rhinitis (WR). They are infrequently sensitized to persulphates. The cause and mechanism of the symptoms and the effects on their health-related quality of life (HRQoL) remains unclear. The objectives were to follow female hairdressers with WR mainly from bleaching powder regarding nasal reactivity to persulphate and to evaluate symptoms, HRQoL and inflammatory markers in nasal lavage during a working period after vacation and compared with hairdressers without symptoms and pollen allergic women. METHODS: Skin prick tests to persulphate were performed in the hairdressers. Participants kept a diary of symptoms and of work tasks (hairdressers only). They completed HRQoL questionnaires. Eosinophil cationic protein (ECP) in nasal lavage fluid was examined. The symptomatic hairdressers performed nasal challenges with persulphate before and after the exposure. RESULTS: Skin prick tests were negative. Although the nasal reactivity to persulphate did not change a steady increase in nasal symptoms, especially blockage, and in ECP was noticed in the symptomatic hairdressers. The HRQoL deteriorated in the symptomatic hairdressers indicating an effect on their working situation and daily life. The atopics had more, but varying symptoms (itching, sneezing and secretion). CONCLUSIONS: The difference in the clinical picture between the symptomatic hairdressers and the pollen allergic women, the increase in symptoms and ECP in the nasal lavage support the view that a sensitization to hairdresser chemicals by a mechanism not yet understood is operating. The deterioration of the HRQoL in the symptomatic hairdressers indicates a considerable effect on their life
Incorporation of excluded volume correlations into Poisson-Boltzmann theory
We investigate the effect of excluded volume interactions on the electrolyte
distribution around a charged macroion. First, we introduce a criterion for
determining when hard-core effects should be taken into account beyond standard
mean field Poisson-Boltzmann (PB) theory. Next, we demonstrate that several
commonly proposed local density functional approaches for excluded volume
interactions cannot be used for this purpose. Instead, we employ a non-local
excess free energy by using a simple constant weight approach. We compare the
ion distribution and osmotic pressure predicted by this theory with Monte Carlo
simulations. They agree very well for weakly developed correlations and give
the correct layering effect for stronger ones. In all investigated cases our
simple weighted density theory yields more realistic results than the standard
PB approach, whereas all local density theories do not improve on the PB
density profiles but on the contrary, deviate even more from the simulation
results.Comment: 23 pages, 7 figures, 1 tabl
Advanced therapy medicinal products and health technology assessment principles and practices for value-based and sustainable healthcare
Background
Advanced therapy medicinal products (ATMPs) are beginning to reach European markets, and questions are being asked about their value for patients and how healthcare systems should pay for them.
Objectives
To identify and discuss potential challenges of ATMPs in view of current health technology assessment (HTA) methodology—specifically economic evaluation methods—in Europe as it relates to ATMPs, and to suggest potential solutions to these challenges.
Methods
An Expert Panel reviewed current HTA principles and practices in relation to the specific characteristics of ATMPs.
Results
Three key topics were identified and prioritised for discussion—uncertainty, discounting, and health outcomes and value. The panel discussed that evidence challenges linked to increased uncertainty may be mitigated by collection of follow-on data, use of value of information analysis, and/or outcomes-based contracts. For discount rates, an international, multi-disciplinary forum should be established to consider the economic, social and ethical implications of the choice of rate. Finally, consideration of the feasibility of assessing the value of ATMPs beyond health gain may also be key for decision-making.
Conclusions
ATMPs face a challenge in demonstrating their value within current HTA frameworks. Consideration of current HTA principles and practices with regards to the specific characteristics of ATMPs and continued dialogue will be key to ensuring appropriate market access.
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Exploring Biorthonormal Transformations of Pair-Correlation Functions in Atomic Structure Variational Calculations
Multiconfiguration expansions frequently target valence correlation and
correlation between valence electrons and the outermost core electrons.
Correlation within the core is often neglected. A large orbital basis is needed
to saturate both the valence and core-valence correlation effects. This in turn
leads to huge numbers of CSFs, many of which are unimportant. To avoid the
problems inherent to the use of a single common orthonormal orbital basis for
all correlation effects in the MCHF method, we propose to optimize independent
MCHF pair-correlation functions (PCFs), bringing their own orthonormal
one-electron basis. Each PCF is generated by allowing single- and double-
excitations from a multireference (MR) function. This computational scheme has
the advantage of using targeted and optimally localized orbital sets for each
PCF. These pair-correlation functions are coupled together and with each
component of the MR space through a low dimension generalized eigenvalue
problem. Nonorthogonal orbital sets being involved, the interaction and overlap
matrices are built using biorthonormal transformation of the coupled basis sets
followed by a counter-transformation of the PCF expansions.
Applied to the ground state of beryllium, the new method gives total energies
that are lower than the ones from traditional CAS-MCHF calculations using large
orbital active sets. It is fair to say that we now have the possibility to
account for, in a balanced way, correlation deep down in the atomic core in
variational calculations
Monoamine related functional gene variants and relationships to monoamine metabolite concentrations in CSF of healthy volunteers
BACKGROUND: Concentrations of monoamine metabolites in human cerebrospinal fluid (CSF) have been used extensively as indirect estimates of monoamine turnover in the brain. CSF monoamine metabolite concentrations are partly determined by genetic influences. METHODS: We investigated possible relationships between DNA polymorphisms in the serotonin 2C receptor (HTR2C), the serotonin 3A receptor (HTR3A), the dopamine D(4 )receptor (DRD4), and the dopamine β-hydroxylase (DBH) genes and CSF concentrations of 5-hydroxyindolacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) in healthy volunteers (n = 90). RESULTS: The HTR3A 178 C/T variant was associated with 5-HIAA levels (p = 0.02). The DBH-1021 heterozygote genotype was associated with 5-HIAA (p = 0.0005) and HVA (p = 0.009) concentrations. Neither the HTR2C Cys23Ser variant, nor the DRD4 -521 C/T variant were significantly associated with any of the monoamine metabolites. CONCLUSIONS: The present results suggest that the HTR3A and DBH genes may participate in the regulation of dopamine and serotonin turnover rates in the central nervous system
Thin superconducting disk with B-dependent Jc: Flux and current distributions
The critical state in a superconducting thin circular disk with an arbitrary
magnetic field dependence of the critical sheet current, Jc(B), is analyzed.
With an applied field Ba perpendicular to the disk, a set of coupled integral
equations for the flux and current distributions is derived. The equations are
solved numerically, and flux and current profiles are presented graphically for
several commonly used Jc(B) dependences. It is shown that for small Ba the flux
penetration depth can be described by an effective Bean model with a
renormalized Jc entering the leading term. We argue that these results are
qualitatively correct for thin superconductors of any shape. The results
contrast the parallel geometry behavior, where at small Ba the B-dependence of
the critical current can be ignored.Comment: RevTeX, 7 pages including 8 figure
Optogalvanic Spectroscopy of Metastable States in Yb^{+}
The metastable ^{2}F_{7/2} and ^{2}D_{3/2} states of Yb^{+} are of interest
for applications in metrology and quantum information and also act as dark
states in laser cooling. These metastable states are commonly repumped to the
ground state via the 638.6 nm ^{2}F_{7/2} -- ^{1}D[5/2]_{5/2} and 935.2 nm
^{2}D_{3/2} -- ^{3}D[3/2]_{1/2} transitions. We have performed optogalvanic
spectroscopy of these transitions in Yb^{+} ions generated in a discharge. We
measure the pressure broadening coefficient for the 638.6 nm transition to be
70 \pm 10 MHz mbar^{-1}. We place an upper bound of 375 MHz/nucleon on the
638.6 nm isotope splitting and show that our observations are consistent with
theory for the hyperfine splitting. Our measurements of the 935.2 nm transition
extend those made by Sugiyama et al, showing well-resolved isotope and
hyperfine splitting. We obtain high signal to noise, sufficient for laser
stabilisation applications.Comment: 8 pages, 5 figure
A comprehensive comparison between APOGEE and LAMOST: Radial Velocities and Atmospheric Stellar Parameters
We undertake a critical and comprehensive comparison of the radial velocities
and the main stellar atmospheric parameters for stars in common between the
latest data releases from the APOGEE and the LAMOST surveys. There is a total
of 42,420 dwarfs/giants stars in common between the APOGEE DR14 - LAMOST DR3
stellar catalogs. A comparison between the RVs shows an offset of 4.54
0.03 km/s, with a dispersion of 5.8 km/s, in the sense that APOGEE RVs are
larger. We observe a small offset in the Teff of about 13 K, with a scatter of
155 K. Small offset in [Fe/H] of about 0.06 dex together with a scatter of 0.13
dex is also observed. We notice that the largest offset between the surveys
occurs in the surface gravities. Using only surface gravities in calibrated red
giants from APOGEE DR14, where there are 24,074 stars in common, a deviation of
0.14 dex is found with substantial scatter. There are 17,482 red giant stars in
common between APOGEE DR14 and those in LAMOST tied to APOGEE DR12 via the
Cannon. There is generally good agreement between the two data-sets. However,
we find dependencies of the differences of the stellar parameters on effective
temperature. For metal-rich stars, a different trend for the [Fe/H]
discrepancies is found. Surprisingly, we see no correlation between the
internal APOGEE DR14 - DR12 differences in Teff and those in DR14 - LAMOST tied
to DR12, where a correlation should be expected since LAMOST has been
calibrated to APOGEE DR12. We also find no correlation between the [Fe/H]
discrepancies, suggesting that LAMOST/Cannon is not well coupled to the APOGEE
DR12 stellar parameters scale. A [Fe/H] dependence between the stellar
parameters in APOGEE DR12 and those in DR14 is reported. We find a weak
correlation in the differences between APOGEE DR14 - DR12 and LAMOST on DR12
surface gravity for stars hotter than 4800 K and in the log g range between 2.0
and 2.8.Comment: 14 pages, 20 figures. Accepted for publication in Astronomy &
Astrophysics (A&A
Natural history of Arabidopsis thaliana and oomycete symbioses
Molecular ecology of plant–microbe interactions has immediate significance for filling a gap in knowledge between the laboratory discipline of molecular biology and the largely theoretical discipline of evolutionary ecology. Somewhere in between lies conservation biology, aimed at protection of habitats and the diversity of species housed within them. A seemingly insignificant wildflower called Arabidopsis thaliana has an important contribution to make in this endeavour. It has already transformed botanical research with deepening understanding of molecular processes within the species and across the Plant Kingdom; and has begun to revolutionize plant breeding by providing an invaluable catalogue of gene sequences that can be used to design the most precise molecular markers attainable for marker-assisted selection of valued traits. This review describes how A. thaliana and two of its natural biotrophic parasites could be seminal as a model for exploring the biogeography and molecular ecology of plant–microbe interactions, and specifically, for testing hypotheses proposed from the geographic mosaic theory of co-evolution
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