338 research outputs found
The density and pressure of helium nano-bubbles encapsulated in silicon
The excitation in confined and compressed helium atoms in
either the bulk material or encapsulated in a bubble is shifted to energies
higher than that in the free atom. For bulk helium, the energy shifts predicted
from non-empirical electronic structure computations are in excellent agreement
with the experimentally determined values. However, there are significant
discrepancies both between the results of experiments on different bubbles and
between these and the well established descriptions of the bulk. A critique is
presented of previous attempts to determine the densities in bubbles by
measuring the intensities of the electrons inelastically scattered in STEM
experiments. The reported densities are untrustworthy because it was assumed
that the cross section for inelastic electron scattering was the same as that
of a free atom whilst it is now known that this property is greatly enhanced
for atoms confined at significant pressures.
It is shown how experimental measurements of bubbles can be combined with
data on the bulk using a graphical method to determine whether the behavior of
an encapsulated guest differs from that in the bulk material. Experimental
electron energy loss data from an earlier study of helium encapsulated in
silicon is reanalyzed using this new method to show that the properties of the
helium in these bubbles do not differ significantly from those in the bulk
thereby enabling the densities in the bubbles to be determined. These enable
the bubble pressures to be deduced from a well established experimentally
derived equation of state. It is shown that the errors of up to 80% in the
incorrectly determined densities are greatly magnified in the predicted
pressures which can be too large by factors of over seven. This has major
practical implications for the study of radiation damage of materials exposed
to particle bombardment
Symmetry Breaking of Relativistic Multiconfiguration Methods in the Nonrelativistic Limit
The multiconfiguration Dirac-Fock method allows to calculate the state of
relativistic electrons in atoms or molecules. This method has been known for a
long time to provide certain wrong predictions in the nonrelativistic limit. We
study in full mathematical details the nonlinear model obtained in the
nonrelativistic limit for Be-like atoms. We show that the method with sp+pd
configurations in the J=1 sector leads to a symmetry breaking phenomenon in the
sense that the ground state is never an eigenvector of L^2 or S^2. We thereby
complement and clarify some previous studies.Comment: Final version, to appear in Nonlinearity. Nonlinearity (2010) in
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Surprising variations in the rotation of the chemically peculiar stars CU Virginis and V901 Orionis
CU Vir and V901 Ori belong among these few magnetic chemically peculiar stars
whose rotation periods vary on timescales of decades. We aim to study the
stability of the periods in CU Vir and V901 Ori using all accessible
observational data containing phase information. We collected all available
relevant archived observations supplemented with our new measurements of these
stars and analysed the period variations of the stars using a novel method that
allows for the combination of data of diverse sorts. We found that the shapes
of their phase curves were constant, while the periods were changing. Both
stars exhibit alternating intervals of rotational braking and acceleration. The
rotation period of CU Vir was gradually shortening until the year 1968, when it
reached its local minimum of 0.52067198 d. The period then started increasing,
reaching its local maximum of 0.5207163 d in the year 2005. Since that time the
rotation has begun to accelerate again. We also found much smaller period
changes in CU Vir on a timescale of several years. The rotation period of V901
Ori was increasing for the past quarter-century, reaching a maximum of 1.538771
d in the year 2003, when the rotation period began to decrease. A theoretically
unexpected alternating variability of rotation periods in these stars would
remove the spin-down time paradox and brings a new insight into structure and
evolution of magnetic upper-main-sequence stars.Comment: 5 pages, 3 figure
The radio lighthouse CU Virginis: the spindown of a single main sequence star
The fast rotating star CU Virginis is a magnetic chemically peculiar star
with an oblique dipolar magnetic field. The continuum radio emission has been
interpreted as gyrosyncrotron emission arising from a thin magnetospheric
layer. Previous radio observations at 1.4 GHz showed that a 100% circular
polarized and highly directive emission component overlaps to the continuum
emission two times per rotation, when the magnetic axis lies in the plane of
the sky. This sort of radio lighthouse has been proposed to be due to cyclotron
maser emission generated above the magnetic pole and propagating
perpendicularly to the magnetic axis. Observations carried out with the
Australia Telescope Compact Array at 1.4 and 2.5 GHz one year after this
discovery show that this radio emission is still present, meaning that the
phenomenon responsible for this process is steady on a timescale of years. The
emitted radiation spans at least 1 GHz, being observed from 1.4 to 2.5 GHz. On
the light of recent results on the physics of the magnetosphere of this star,
the possibility of plasma radiation is ruled out. The characteristics of this
radio lighthouse provides us a good marker of the rotation period, since the
peaks are visible at particular rotational phases. After one year, they show a
delay of about 15 minutes. This is interpreted as a new abrupt spinning down of
the star. Among several possibilities, a quick emptying of the equatorial
magnetic belt after reaching the maximum density can account for the magnitude
of the breaking. The study of the coherent emission in stars like CU Vir, as
well as in pre main sequence stars, can give important insight into the angular
momentum evolution in young stars. This is a promising field of investigation
that high sensitivity radio interferometers such as SKA can exploit.Comment: Accepted to MNRAS, 8 pages, 7 figures, updated versio
Multidimensional analysis of human intestinal fluid composition
The oral administration of solid dosage forms is the commonest method to achieve systemic therapy and relies on the drug’s solubility in human intestinal fluid (HIF), a key factor that influences bioavailability and biopharmaceutical classification. However, HIF is difficult to obtain and is known to be variable, which has led to the development of a range of simulated intestinal fluid (SIF) systems to determine drug solubility in vitro. In this study we have applied a novel multidimensional approach to analyse and characterise HIF composition using a published data set in both fasted and fed states with a view to refining the existing SIF approaches. The data set provided 152 and 172 measurements of five variables (total bile salt, phospholipid, total free fatty acid, cholesterol and pH) in time-dependent HIF samples from 20 volunteers in the fasted and fed state, respectively. The variable data sets for both fasted state and fed state are complex, do not follow normal distributions but the amphiphilic variable concentrations are correlated. When plotted 2-dimensionally a generally ellipsoid shaped data cloud with a positive slope is revealed with boundaries that enclose published fasted or fed HIF compositions. The data cloud also encloses the majority of fasted state and fed state SIF recipes and illustrates that the structured nature of design of experiment (DoE) approaches does not optimally cover the variable space and may examine media compositions that are not biorelevant. A principal component analysis in either fasted or fed state in combination with fitting an ellipsoid shape to enclose the data results in 8 points that capture over 95% of the compositional variability of HIF. The variable’s average rate of concentration change in both fasted state and fed state over a short time scale (10 min) is zero and a Euclidean analysis highlights differences between the fasted and fed states and among individual volunteers. The results indicate that a 9-point DoE (8 + 1 central point) could be applied to investigate drug solubility in vitro and provide statistical solubility limits. In addition, a single point could provide a worst-case solubility measurement to define the lowest biopharmaceutical classification boundary or for use during drug development. This study has provided a novel description of HIF composition. The approach could be expanded in multiple ways by incorporation of further data sets to improve the statistical coverage or to cover specific patient groups (e.g., paediatric). Further development might also be possible to analyse information on the time dependent behaviour of HIF and to guide HIF sampling and analysis protocols
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Kootenai River Fisheries Investigation; Stock Status of Burbot, 2003-2004 Annual Report.
The main objective of this investigation was to monitor movement and spawning activity of burbot Lota lota in the Kootenai River, Idaho and British Columbia, Canada during the winter of 2003-2004. Due to low precipitation and snow pack, as well as low levels of Lake Koocanusa, the U.S. Army Corps of Engineers refrained from releasing discharges >113 m{sup 3}/s from Libby Dam for most of the winter. This situation provided suitable conditions for burbot migration and spawning in the mainstem river. Hoop nets captured 19 burbot, which ranged from 447 mm to 760 mm TL (mean = 630 mm) and weighed from 420 g to 4,032 g (mean = 1,937 g) with a mean W{sub r} of 99. One burbot (burbot 214) was captured for the fifth time since its first capture in 2000, and each capture was near Ambush Rock (rkm 244.4-244.8). Eleven burbot were tagged with five-month duration external sonic transmitters, and a 12th burbot, tagged with a 14-month transmitter, has been monitored since 2001. During the post-spawn period, three sonic-tagged burbot exhibited downstream and sedentary movement patterns, while five remained at Ambush Rock. Concentrations of tagged burbot near Ambush Rock (rkm 244.5) during January and February 2004 (eight tagged fish) may suggest that this area is critical spawning habitat. The appearance of burbot at Ambush Rock during the spawning period and upstream movements of tagged fish (PIT and sonic tagged) in previous years during the low discharges help validate results suggesting that discharges <113 m{sup 3}/s will permit burbot migration and may increase spawning habitat. Though it seems apparent that the Ambush Rock area is an important burbot spawning ground, no adult burbot were recaptured after the spawning period and no burbot larva were caught, despite considerable sampling efforts during the winter of 2003-2004
Hospital usage of TOXBASE in Great Britain:Temporal trends in accesses 2008 to 2015
Aim: Examining temporal trends in accesses to the UK's National Poison Information Service's TOXBASE database in Britain. Methods: Generalised additive models were used to examine trends in daily numbers of accesses to TOXBASE from British emergency departments between January 2008 and December 2015. Day-of-the-week, seasonality and long term trends were analysed at national and regional levels (Wales, Scotland and the 9 English Government Office Regions). Results: The long-term trend in daily accesses increases from 2.8 (95% CI:2.6, 3.0) per user on 1st January 2008 to 4.6 (95% CI:4.3, 4.9) on 31st December 2015, with small but significant differences in population-corrected accesses by region (p<0.001). There are statistically significant seasonal and day of the week patterns (p<0.001) across all regions. Accesses are 18 % (95% CI:14%, 22%) higher in summer than in January and at the weekend compared to weekdays in all regions; there is a 7.5% (95% CI:6.1%, 8.9%) increase between Friday and Sunday. Conclusions: There are consistent in-year patterns in access to TOXBASE indicating potential seasonal patterns in poisonings in Britain, with location-dependant rates of usage. This novel descriptive work lays the basis for future work on the interaction of TOXBASE use with emergency admission of patients into hospital
Revisiting the Rigidly Rotating Magnetosphere model for sigma Ori E. I. Observations and Data Analysis
We have obtained 18 new high-resolution spectropolarimetric observations of
the B2Vp star sigma Ori E with both the Narval and ESPaDOnS
spectropolarimeters. The aim of these observations is to test, with modern
data, the assumptions of the Rigidly Rotating Magnetosphere (RRM) model of
Townsend & Owocki (2005), applied to the specific case of sigma Ori E by
Townsend et al. (2005). This model includes a substantially offset dipole
magnetic field configuration, and approximately reproduces previous
observational variations in longitudinal field strength, photometric
brightness, and Halpha emission. We analyze new spectroscopy, including H I, He
I, C II, Si III and Fe III lines, confirming the diversity of variability in
photospheric lines, as well as the double S-wave variation of circumstellar
hydrogen. Using the multiline analysis method of Least-Squares Deconvolution
(LSD), new, more precise longitudinal magnetic field measurements reveal a
substantial variance between the shapes of the observed and RRM model
time-varying field. The phase resolved Stokes V profiles of He I 5876 A and
6678 A lines are fit poorly by synthetic profiles computed from the magnetic
topology assumed by Townsend et al. (2005). These results challenge the offset
dipole field configuration assumed in the application of the RRM model to sigma
Ori E, and indicate that future models of its magnetic field should also
include complex, higher-order components.Comment: 13 pages, 8 figures. Accepted for publication in MNRA
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