1,870 research outputs found
Effect of changing the fine particle mass of inhaled beclomethasone dipropionate on intrapulmonary deposition and pharmacokinetics
AbstractReformulation of beclomethasone dipropionate (BDP) in the chlorofluorocarbon (CFC)-free propellant hydrofluoroalkane-134a (HFA) gave the opportunity to produce a solution formulation that provides a greater total mass of fine drug particles than the current CFC suspension metered dose inhaler (MDI). The HFA-BDP MDI was studied in three pharmacokinetic trials in asthmatic patients. Serum levels of BDP plus metabolites [total beclomethasone (total BOH) assay] were used to test whether the increased fine particle mass of HFA-BDP would result in improved intrapulmonary deposition and subsequent differences in serum profiles. Serum levels, maximum serum concentrations and area under the serum concentration-time curves of total BOH following both single and multiple doses of HFA-BDP were similar to those obtained with approximately twice the dose of CFC-BDP. The observed lower bioavailability of CFC-BDP compared with HFA-BDP could be explained if most of each inhaled dose from the CFC-BDP MDI was swallowed and absorbed from the gastrointestinal tract, while most of each inhaled dose from the HFA-BDP MDI was absorbed from the lungs. Deposition studies have confirmed this explanation. These results suggest that asthmatic patients can be treated with lower total daily doses of drug from HFA-BDP extrafine aerosol than from CFC-BDP
Comparative study of density functional theories of the exchange-correlation hole and energy in silicon
We present a detailed study of the exchange-correlation hole and
exchange-correlation energy per particle in the Si crystal as calculated by the
Variational Monte Carlo method and predicted by various density functional
models. Nonlocal density averaging methods prove to be successful in correcting
severe errors in the local density approximation (LDA) at low densities where
the density changes dramatically over the correlation length of the LDA hole,
but fail to provide systematic improvements at higher densities where the
effects of density inhomogeneity are more subtle. Exchange and correlation
considered separately show a sensitivity to the nonlocal semiconductor crystal
environment, particularly within the Si bond, which is not predicted by the
nonlocal approaches based on density averaging. The exchange hole is well
described by a bonding orbital picture, while the correlation hole has a
significant component due to the polarization of the nearby bonds, which
partially screens out the anisotropy in the exchange hole.Comment: 16 pages, 5 figures, RevTeX, added conten
Hybrid poplar plantation establishment in Saskatchewan: first year results
Non-Peer ReviewedThe production of Short-Rotation Woody Crops (SRWC) has been growing steadily throughout
North America. In Saskatchewan, interest is focused on developing hybrid poplar (var.
âWalkerâ) plantations for an expanding fibre industry, and as a means to diversify farm income
and possibly to increase sequestered carbon. Preliminary results from a small 6 year-old
plantation suggest that there is good potential for operational-scale hybrid poplar production over
a 15 to 20 year rotation period. Larger-scale field trials were established in the spring of 2002 on
two sites in the Meadow Lake region, to assess and compare select silvicultural practices that are
regarded to enhance the growth of hybrid poplars. After one growing season, both types of
rooted stock (cuttings and plugs) showed superior survivability (~92 %) compared to non-rooted
cuttings (~40 %), underscoring the reduced risk in planting rooted stock, especially during dry
years. Measurements of tree growth (tree height, stem volume, total plant biomass and root
production) all indicated a noticeable advantage of rooted versus non-rooted stock.
Observational data pointed to the necessity of thorough site preparation, adherence to proper
planting techniques, and mechanical or chemical weed control for successful plantation
establishment
Electronic and thermal sequential transport in metallic and superconducting two-junction arrays
The description of transport phenomena in devices consisting of arrays of
tunnel junctions, and the experimental confirmation of these predictions is one
of the great successes of mesoscopic physics. The aim of this paper is to give
a self-consistent review of sequential transport processes in such devices,
based on the so-called "orthodox" model. We calculate numerically the
current-voltage (I-V) curves, the conductance versus bias voltage (G-V) curves,
and the associated thermal transport in symmetric and asymmetric two-junction
arrays such as Coulomb-blockade thermometers (CBTs),
superconducting-insulator-normal-insulator-superconducting (SINIS) structures,
and superconducting single-electron transistors (SETs). We investigate the
behavior of these systems at the singularity-matching bias points, the
dependence of microrefrigeration effects on the charging energy of the island,
and the effect of a finite superconducting gap on Coulomb-blockade thermometry.Comment: 23 pages, 12 figures; Berlin (ISBN: 978-3-642-12069-5
Non-destructive characterization of thin layer resonant tunnelling diodes
We present an advanced nondestructive characterization scheme for high current density AlAs/InGaAs resonant tunneling diodes pseudomorphically grown on InP substrates. We show how low-temperature photoluminescence spectroscopy (LT-PL) and high-resolution X-ray diffractometry (HR-XRD) are complementary techniques to increase the confidence of the characterized structure. The lattice-matched InGaAs is characterized and found to be of high quality. We discuss the inclusion of an undoped âcopyâ well (C-well) in terms of enhancements to HR-XRD and LT-PL characterization and quantify the improved precision in determining the structure. As a consequence of this enhanced precision in the determination of physical structure, the AlAs barriers and quantum well (QW) system are found to contain nonideal material interfaces. Their roughness is characterized in terms of the full width to half-maximum of the split LT-PL emission peaks, revealing a Âą1 atomic sheet variance to the QW width. We show how barrier asymmetry can be detected through fitting of both optical spectra and HR-XRD rocking curves
Identifying and prioritising services in European terrestrial and freshwater ecosystems
Ecosystems are multifunctional and provide humanity with a broad array of vital services. Effective management of services requires an improved evidence base, identifying the role of ecosystems in delivering multiple services, which can assist policy-makers in maintaining them. Here, information from the literature and scientific experts was used to systematically document the importance of services and identify trends in their use and status over time for the main terrestrial and freshwater ecosystems in Europe. The results from this review show that intensively managed ecosystems contribute mostly to vital provisioning services (e.g. agro-ecosystems provide food via crops and livestock, and forests provide wood), while semi-natural ecosystems (e.g. grasslands and mountains) are key contributors of genetic resources and cultural services (e.g. aesthetic values and sense of place). The most recent European trends in human use of services show increases in demand for crops from agro-ecosystems, timber from forests, water flow regulation from rivers, wetlands and mountains, and recreation and ecotourism in most ecosystems, but decreases in livestock production, freshwater capture fisheries, wild foods and virtually all services associated with ecosystems which have considerably decreased in area (e.g. semi-natural grasslands). The condition of the majority of services show either a degraded or mixed status across Europe with the exception of recent enhancements in timber production in forests and mountains, freshwater provision, water/erosion/natural hazard regulation and recreation/ecotourism in mountains, and climate regulation in forests. Key gaps in knowledge were evident for certain services across all ecosystems, including the provision of biochemicals and natural medicines, genetic resources and the regulating services of seed dispersal, pest/disease regulation and invasion resistance
A quantum mechanical relation connecting time, temperature, and cosmological constant of the universe: Gamow's relation revisited as a special case
Considering our expanding universe as made up of gravitationally interacting
particles which describe particles of luminous matter and dark matter and dark
energy which is described by a repulsive harmonic potential among the points in
the flat 3-space, we derive a quantum mechanical relation connecting,
temperature of the cosmic microwave background radiation, age, and cosmological
constant of the universe. When the cosmological constant is zero, we get back
the Gamow's relation with a much better coefficient. Otherwise, our theory
predicts a value of the cosmological constant
when the present values of cosmic microwave background temperature of 2.728 K
and age of the universe 14 billion years are taken as input.Comment: 4 pages, 1 figure, Study of the Universe from a condensed matter
point of view, section III corrected with a single body potentia
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