607 research outputs found
Developmental pharmacokinetics of morphine and its metabolites in neonates, infants and young children
BACKGROUND: Descriptions of the pharmacokinetics and metabolism of
morphine and its metabolites in young children are scant. Previous studies
have not differentiated the effects of size from those related to age
during infancy. METHODS: Postoperative children 0-3 yr old were given an
intravenous loading dose of morphine hydrochloride (100 micro g kg(-1) in
2 min) followed by either an intravenous morphine infusion of 10 micro g
h(-1) kg(-1) (n=92) or 3-hourly intravenous morphine boluses of 30 micro g
kg(-1) (n=92). Additional morphine (5 micro g kg(-1)) every 10 min was
given if the visual analogue (VAS, 0-10) pain score was >/=4. Arterial
blood (1.4 ml) was sampled within 5 min of the loading dose and at 6, 12
and 24 h for morphine, morphine-3-glucuronide (M3G) and
morphine-6-glucuronide (M6G). The disposition of morphine and formation
clearances of morphine base to its glucuronide metabolites and their
elimination clearances were estimated using non-linear mixed effects
models. RESULTS: The analysis used 1856 concentration observations from
184 subjects. Population parameter estimates and their variability (%) for
a one-compartment, first-order elimination model were as follows: volume
of distribution 136 (59.3) litres, formation clearance to M3G 64.3 (58.8)
litres h(-1), formation clearance to M6G 3.63 (82.2) litres h(-1),
morphine clearance by other routes 3.12 litres h(-1) per 70 kg,
elimination clearance of M3G 17.4 (43.0) litres h(-1), elimination
clearance of M6G 5.8 (73.8) litres h(-1). All parameters are standardized
to a 70 kg person using allometric 3/4 power models and reflect fully
mature adult values. The volume of distribution increased exponentially
with a maturation half-life of 26 days from 83 litres per 70 kg at birth;
formation clearance to M3G and M6G increased with a maturation half-life
of 88.3 days from 10.8 and 0.61 litres h(-1) per 70 kg respectively at
birth. Metabolite formation decreased with increased serum bilirubin
concentration. Metabolite clearance increased with age (maturation
half-life 129 days), and appeared to be similar to that described for
glomerular filtration rate maturation in infants. CONCLUSION: M3G is the
predominant metabolite of morphine in young children and total body
morphine clearance is 80% that of adult values by 6 months. A mean
steady-state serum concentration of 10 ng ml(-1) can be achieved in
children after non-cardiac surgery in an intensive care unit with a
morphine hydrochloride infusion of 5 micro g h(-1) kg(-1) at birth (term
neonates), 8.5 micro g h(-1) kg(-1) at 1 month, 13.5 micro g h(-1) kg(-1)
at 3 months and 18 micro g h(-1) kg(-1) at 1 year and 16 micro g h(-1)
kg(-1) for 1- to 3-yr-old children
Flux Creep and Flux Jumping
We consider the flux jump instability of the Bean's critical state arising in
the flux creep regime in type-II superconductors. We find the flux jump field,
, that determines the superconducting state stability criterion. We
calculate the dependence of on the external magnetic field ramp rate,
. We demonstrate that under the conditions typical for most of the
magnetization experiments the slope of the current-voltage curve in the flux
creep regime determines the stability of the Bean's critical state, {\it i.e.},
the value of . We show that a flux jump can be preceded by the
magneto-thermal oscillations and find the frequency of these oscillations as a
function of .Comment: 7 pages, ReVTeX, 2 figures attached as postscript file
Understorey plant community and light availability in conifer plantations and natural hardwood forests in Taiwan
Questions: What are the effects of replacing mixed species natural forests with Cryptomeria japonica plantations on understorey plant functional and species diversity? What is the role of the understorey light environment in determining understorey diversity and community in the two types of forest?
Location: Subtropical northeast Taiwan.
Methods: We examined light environments using hemispherical photography, and diversity and composition of understorey plants of a 35âyr C. japonica plantation and an adjacent natural hardwood forest.
Results: Understorey plant species richness was similar in the two forests, but the communities were different; only 18 of the 91 recorded understorey plant species occurred in both forests. Relative abundance of plants among different functional groups differed between the two forests. Relative numbers of shadeâtolerant and shadeâintolerant seedling individuals were also different between the two forest types with only one shadeâintolerant seedling in the plantation compared to 23 seedlings belonging to two species in the natural forest. In the natural forest 11 species of tree seedling were found, while in the plantation only five were found, and the seedling density was only one third of that in the natural forest. Across plots in both forests, understorey plant richness and diversity were negatively correlated with direct sunlight but not indirect sunlight, possibly because direct light plays a more important role in understorey plant growth.
Conclusions: We report lower species and functional diversity and higher light availability in a natural hardwood forest than an adjacent 30âyr C. japonica plantation, possibly due to the increased dominance of shadeâintolerant species associated with higher light availability. To maintain plant diversity, management efforts must be made to prevent localized losses of shadeâadapted understorey plants
Momentum flux density, kinetic energy density and their fluctuations for one-dimensional confined gases of non-interacting fermions
We present a Green's function method for the evaluation of the particle
density profile and of the higher moments of the one-body density matrix in a
mesoscopic system of N Fermi particles moving independently in a linear
potential. The usefulness of the method is illustrated by applications to a
Fermi gas confined in a harmonic potential well, for which we evaluate the
momentum flux and kinetic energy densities as well as their quantal mean-square
fluctuations. We also study some properties of the kinetic energy functional
E_{kin}[n(x)] in the same system. Whereas a local approximation to the kinetic
energy density yields a multi-valued function, an exact single-valued
relationship between the density derivative of E_{kin}[n(x)] and the particle
density n(x) is demonstrated and evaluated for various values of the number of
particles in the system.Comment: 10 pages, 5 figure
Surface Effects in Magnetic Microtraps
We have investigated Bose-Einstein condensates and ultra cold atoms in the
vicinity of a surface of a magnetic microtrap. The atoms are prepared along
copper conductors at distances to the surface between 300 um and 20 um. In this
range, the lifetime decreases from 20 s to 0.7 s showing a linear dependence on
the distance to the surface. The atoms manifest a weak thermal coupling to the
surface, with measured heating rates remaining below 500 nK/s. In addition, we
observe a periodic fragmentation of the condensate and thermal clouds when the
surface is approached.Comment: 4 pages, 4 figures; v2: corrected references; v3: final versio
Stability of Repulsive Bose-Einstein Condensates in a Periodic Potential
The cubic nonlinear Schr\"odinger equation with repulsive nonlinearity and an
elliptic function potential models a quasi-one-dimensional repulsive dilute gas
Bose-Einstein condensate trapped in a standing light wave. New families of
stationary solutions are presented. Some of these solutions have neither an
analog in the linear Schr\"odinger equation nor in the integrable nonlinear
Schr\"odinger equation. Their stability is examined using analytic and
numerical methods. All trivial-phase stable solutions are deformations of the
ground state of the linear Schr\"odinger equation. Our results show that a
large number of condensed atoms is sufficient to form a stable, periodic
condensate. Physically, this implies stability of states near the Thomas-Fermi
limit.Comment: 12 pages, 17 figure
Highly anisotropic Bose-Einstein condensates: crossover to lower dimensionality
We develop a simple analytical model based on a variational method to explain
the properties of trapped cylindrically symmetric Bose-Einstein condensates
(BEC) of varying degrees of anisotropy well into regimes of effective one
dimension (1D) and effective two dimension (2D). Our results are accurate in
regimes where the Thomas-Fermi approximation breaks down and they are shown to
be in agreement with recent experimental data.Comment: 4 pages, 2 figures; significantly more new material added; title and
author-list changed due to changes in conten
The Low Energy Amplitude to One and Two Loops
The low-energy amplitude is computed explicitly to two-loop accuracy
in the chiral expansion. It depends only on six independent (combinations of)
low-energy constants which are not fixed by chiral symmetry. Four of these
constants are determined {\it via} sum rules which are evaluated using
scattering data at higher energies. Dependence of the low-energy phase shifts
and of the threshold parameters on the remaining two constants (called
and ) are discussed and compared to the existing data from
experiments. Using generalised PT, the constants and are
related to fundamental QCD parameters such as the quark condensate and the quark mass ratio . It is shown
that forthcoming accurate low-energy data can be used to provide, for
the first time, experimental evidence in favour of or against the existence of
a large quark-antiquark condensate in the QCD vacuum.Comment: 61 pages, LaTeX, 10 figures in separate tarred, compressed and
uuencoded Postscript fil
The Aharonov-Bohm effect for an exciton
We study theoretically the exciton absorption on a ring shreded by a magnetic
flux. For the case when the attraction between electron and hole is
short-ranged we get an exact solution of the problem. We demonstrate that,
despite the electrical neutrality of the exciton, both the spectral position of
the exciton peak in the absorption, and the corresponding oscillator strength
oscillate with magnetic flux with a period ---the universal flux
quantum. The origin of the effect is the finite probability for electron and
hole, created by a photon at the same point, to tunnel in the opposite
directions and meet each other on the opposite side of the ring.Comment: 13 RevTeX 3.0 pages plus 4 EPS-figures, changes include updated
references and an improved chapter on possible experimental realization
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