16,213 research outputs found
Effect of delayed acquisition times on Gadolinium-enhanced MRI of the presumably normal canine brain
A delay in imaging following intravenous contrast medium administration has been recommended to reduce misdiagnoses. However, the normal variation of contrast enhancement in dogs following a delay has not been characterized. Contrast enhanced MR imaging of 22 dogs was assessed, in terms of identification of normal anatomic structures, to investigate the variation associated with 10 minute delay between contrast medium administration and imaging. All dogs had a normal brain MR imaging study and unremarkable CSF. Specific ROIs were assessed both objectively, using computer software, and subjectively using three observers. Mean contrast enhancement greater than 10% was seen in the pituitary gland, choroid plexus, meninges, temporal muscle, trigeminal nerve and the trigeminal nerve root. Structures with an active blood-brain-barrier had minimal contrast enhancement (<6%). Enhancing structures had significantly more contrast enhancement at t=1min versus t=10min, except in temporal muscle, the trigeminal nerve and the trigeminal nerve root. Inter-observer agreement was moderate to good in favor of the initial post contrast T1w sequence. The observers found either no difference or poor agreement in identification of the non-vascular structures. Intra-observer agreement was very good with all vascular structures and most non-vascular structures. A degree of meningeal enhancement was a consistent finding. The initial acquisition had higher enhancement characteristics and observer agreement for some structures; however, contrast-to-noise was comparable in the delayed phase or not significantly different. We provide baseline references and suggest that the initial T1w post contrast sequence is preferable but not essential should a delayed post contrast T1w sequence be performed
Growth of aerobic and anaerobic bacteria in agar subjected to freezing and diurnal freezing and thawing
Aerobic and anaerobic bacteria growth in agar after freezing and diurnal freezing and thawin
Fusion energy from the Moon for the twenty-first century
It is shown in this paper that the D-He-3 fusion fuel cycle is not only credible from a physics standpoint, but that its breakeven and ignition characteristics could be developed on roughly the same time schedule as the DT cycle. It was also shown that the extremely low fraction of power in neutrons, the lack of significant radioactivity in the reactants, and the potential for very high conversion efficiencies, can result in definite advantages for the D-He-3 cycle with respect to DT fusion and fission reactors in the twenty-first century. More specifically, the D-He-3 cycle can accomplish the following: (1) eliminate the need for deep geologic waste burial facilities and the wastes can qualify for Class A, near-surface land burial; (2) allow 'inherently safe' reactors to be built that, under the worst conceivable accident, cannot cause a civilian fatality or result in a significant (greater than 100 mrem) exposure to a member of the public; (3) reduce the radiation damage levels to a point where no scheduled replacement of reactor structural components is required, i.e., full reactor lifetimes (approximately 30 FPY) can be credibly claimed; (4) increase the reliability and availability of fusion reactors compared to DT systems because of the greatly reduced radioactivity, the low neutron damage, and the elimination of T breeding; and (5) greatly reduce the capital costs of fusion power plants (compared to DT systems) by as much as 50 percent and present the potential for a significant reduction on the COE. The concepts presented in this paper tie together two of the most ambitious high-technology endeavors of the twentieth century: the development of controlled thermonuclear fusion for civilian power applications and the utilization of outer space for the benefit of mankind on Earth
Modification of surface energy in nuclear multifragmentation
Within the statistical multifragmentation model we study modifications of the
surface and symmetry energy of primary fragments in the freeze-out volume. The
ALADIN experimental data on multifragmentation obtained in reactions induced by
high-energy projectiles with different neutron richness are analyzed. We have
extracted the isospin dependence of the surface energy coefficient at different
degrees of fragmentation. We conclude that the surface energy of hot fragments
produced in multifragmentation reactions differs from the values extracted for
isolated nuclei at low excitation. At high fragment multiplicity, it becomes
nearly independent of the neutron content of the fragments.Comment: 11 pages with 13 figure
RR Lyrae Stars In The GCVS Observed By The Qatar Exoplanet Survey
We used the light curve archive of the Qatar Exoplanet Survey (QES) to
investigate the RR Lyrae variable stars listed in the General Catalogue of
Variable Stars (GCVS). Of 588 variables studied, we reclassify 14 as eclipsing
binaries, one as an RS Canum Venaticorum-type variable, one as an irregular
variable, four as classical Cepheids, and one as a type II Cepheid, while also
improving their periods. We also report new RR Lyrae sub-type classifications
for 65 variables and improve on the GCVS period estimates for 135 RR Lyrae
variables. There are seven double-mode RR Lyrae stars in the sample for which
we measured their fundamental and first overtone periods. Finally, we detect
the Blazhko effect in 38 of the RR Lyrae stars for the first time and we
successfully measured the Blazhko period for 26 of them.Comment: Accepted IBV
The first magnetic maps of a pre-main sequence binary star system - HD 155555
We present the first maps of the surface magnetic fields of a pre-main
sequence binary system. Spectropolarimetric observations of the young, 18 Myr,
HD 155555 (V824 Ara, G5IV + K0IV) system were obtained at the Anglo-Australian
Telescope in 2004 and 2007. Both datasets are analysed using a new binary
Zeeman Doppler imaging (ZDI) code. This allows us to simultaneously model the
contribution of each component to the observed circularly polarised spectra.
Stellar brightness maps are also produced for HD 155555 and compared to
previous Doppler images. Our radial magnetic maps reveal a complex surface
magnetic topology with mixed polarities at all latitudes. We find rings of
azimuthal field on both stars, most of which are found to be non-axisymmetric
with the stellar rotational axis. We also examine the field strength and the
relative fraction of magnetic energy stored in the radial and azimuthal field
components at both epochs. A marked weakening of the field strength of the
secondary star is observed between the 2004 and 2007 epochs. This is
accompanied by an apparent shift in the location of magnetic energy from the
azimuthal to radial field. We suggest that this could be indicative of a
magnetic activity cycle. We use the radial magnetic maps to extrapolate the
coronal field (by assuming a potential field) for each star individually - at
present ignoring any possible interaction. The secondary star is found to
exhibit an extreme tilt (~75 deg) of its large scale magnetic field to that of
its rotation axis for both epochs. The field complexity that is apparent in the
surface maps persists out to a significant fraction of the binary separation.
Any interaction between the fields of the two stars is therefore likely to be
complex also. Modelling this would require a full binary field extrapolation.Comment: 17 pages, 12 figures, accepted for publication in MNRA
Velocity Dispersion of Dissolving OB Associations Affected by External Pressure of Formation Environment
This paper presents a possible way to understand dissolution of OB
associations (or groups). Assuming rapid escape of parental cloud gas from
associations, we show that the shadow of the formation environment for
associations can be partially imprinted on the velocity dispersion at their
dissolution. This conclusion is not surprising as long as associations are
formed in a multiphase interstellar medium, because the external pressure
should suppress expansion caused by the internal motion of the parental clouds.
Our model predicts a few km s as the internal velocity dispersion.
Observationally, the internal velocity dispersion is km s which
is smaller than our prediction. This suggests that the dissipation of internal
energy happens before the formation of OB associations.Comment: 6 pages. AJ accepte
Influence of Cytomatrix Proteins on Water and on Ions in Cells
This review concerns the influence that cytomatrix proteins have on the motional properties of water and on the major inorganic ions in cells. The techniques we used for study of water in cells and on the cytomatrix proteins include: pulsed NMR of water protons, quench cooled ice crystal imprint size, and osmotic behavior. The technique for study of ions involved use of electron-probe X-ray microanalysis of thin cryosections of cells. The cytomatrix was found to play the major role in determining the extent of hydration water in cells, The amount of hydration water varied greatly between cell types (e.g., lens fiber cells have no detectable bulk water) and varied in the same cell type studied under different states (e.g., unfertilized and fertilized sea urchin eggs). Aggregation of cytomatrix proteins (actin in particular) is a determinant of the extent of hydration water in cells. Hydration water appears not to participate in the ideal osmotic equation of van\u27t Hoff. The ionic content of cells does not accurately predict the chemical activity of the ions in cytoplasm. A major proportion of intracellular K+ and a substantial fraction of Cl- was found to be influenced by the cytomatrix such that their diffusion was impaired. The cytomatrix is responsible for the decreased motional properties of a substantial portion of cellular water and ions
- âŠ