10,330 research outputs found
The sensitivity of saccharomyces mutants to palmitoleic acid may provide a means to study the controls of membrane fluidity in eukaryotes
The mechanisms which control the fluidity of eukaryotic membranes are unknown. We have identified S. cerevisiae deletion strains whose growth is impaired by palmitoleic (PO; C16:1) but not oleic (C18:1) acid. PO-sensitivity is suppressed by oleate thus perhaps identifying a signaling pathway that controls the ratio of these fatty acids in membrane phospholipid. Growth of these mutants is also inhibited by a known fluidizer, benzyl alcohol, thus indicating that PO has a fluidizing effect. Removal of Pkc1, known to play a key role in cell wall integrity control, leads to acute PO-sensitivity. Removal of Bck1, Mkk1, Mkk2, Slt2, or Swi6 downstream components of the cell wall integrity pathway, cause modest POsensitivity.
Suppression by 1M sorbitol of the PO-sensitivity of these four mutants implies that PO/oleate ratio influences the cell wall. Acute PO-sensitivity of the pkc1Δ strain, even in the presence of 1M sorbitol, suggests the cell wall to be more severely compromised by PO addition to this strain.
Alternatively, the failure to control the PO/oleate ratio could have an additional effect on the pkc1 strain, perhaps by disabling a 2nd pathway downstream of Pkc1 thus allowing PO addition to cause excess membrane fluidity. We are attempting to distinguish these two models by a variety of genetic, biochemical, and physical methods. Most notably, the effect of PO on the fluidity of the plasma membrane is being examined by measuring the depolarization of laurdan fluorescence
No news for Kerr-Schild fields
Algebraically special fields with no gravitational radiation are described.
Kerr-Schild fields, which include as a concrete case the Kinnersley photon
rocket, form an important subclass of them.Comment: 4 pages, Revtex
Amorphization induced by pressure: results for zeolites and general implications
We report an {\sl ab initio} study of pressure-induced amorphization (PIA) in
zeolites, which are model systems for this phenomenon. We confirm the
occurrence of low-density amorphous phases like the one reported by Greaves
{\sl et al.} [Science {\bf 308}, 1299 (2005)], which preserves the crystalline
topology and might constitute a new type of glass. The role of the zeolite
composition regarding PIA is explained. Our results support the correctness of
existing models for the basic PIA mechanim, but suggest that energetic, rather
than kinetic, factors determine the irreversibility of the transition.Comment: 4 pages with 3 figures embedded. More information at
http://www.icmab.es/dmmis/leem/jorg
Detection of radio emission from the gamma-ray pulsar J1732-3131 at 327 MHz
Although originally discovered as a radio-quiet gamma-ray pulsar, J1732-3131
has exhibited intriguing detections at decameter wavelengths. We report an
extensive follow-up of the pulsar at 327 MHz with the Ooty radio telescope.
Using the previously observed radio characteristics, and with an effective
integration time of 60 hrs, we present a detection of the pulsar at a
confidence level of 99.82%. The 327 MHz mean flux density is estimated to be
0.5-0.8 mJy, which establishes the pulsar to be a steep spectrum source and one
of the least-luminous pulsars known to date. We also phase-aligned the radio
and gamma-ray profiles of the pulsar, and measured the phase-offset between the
main peaks in the two profiles to be 0.240.06. We discuss the observed
phase-offset in the context of various trends exhibited by the radio-loud
gamma-ray pulsar population, and suggest that the gamma-ray emission from
J1732-3131 is best explained by outer magnetosphere models. Details of our
analysis leading to the pulsar detection, and measurements of various
parameters and their implications relevant to the pulsar's emission mechanism
are presented.Comment: 8 pages, 6 figures; Accepted for publication in MNRA
Spectral Energy Distributions for Disk and Halo M--Dwarfs
We have obtained infrared (1 to 2.5 micron) spectroscopy for 42 halo and disk
dwarfs with spectral type M1 to M6.5. These data are compared to synthetic
spectra generated by the latest model atmospheres of Allard & Hauschildt.
Photospheric parameters metallicity, effective temperature and radius are
determined for the sample. We find good agreement between observation and
theory except for known problems due to incomplete molecular data for metal
hydrides and water. The metal-poor M subdwarfs are well matched by the models
as oxide opacity sources are less important in this case. The derived effective
temperatures for the sample range from 3600K to 2600K; at these temperatures
grain formation and extinction are not significant in the photosphere. The
derived metallicities range from solar to one-tenth solar. The radii and
effective temperatures derived agree well with recent models of low mass stars.Comment: 24 pages including 13 figures, 4 Tables; accepted by Ap
Light-curve modelling constraints on the obliquities and aspect angles of the young Fermi pulsars
In more than four years of observation the Large Area Telescope on board the
Fermi satellite has identified pulsed -ray emission from more than 80
young pulsars, providing light curves with high statistics. Fitting the
observations with geometrical models can provide estimates of the magnetic
obliquity and aspect angle , yielding estimates of the
radiation beaming factor and luminosity. Using -ray emission geometries
(Polar Cap, Slot Gap, Outer Gap, One Pole Caustic) and radio emission geometry,
we fit -ray light curves for 76 young pulsars and we jointly fit their
-ray plus radio light curves when possible. We find that a joint radio
plus -ray fit strategy is important to obtain (, )
estimates that can explain simultaneous radio and -ray emission. The
intermediate-to-high altitude magnetosphere models, Slot Gap, Outer Gap, and
One pole Caustic, are favoured in explaining the observations. We find no
evolution of on a time scale of a million years. For all emission
geometries our derived -ray beaming factors are generally less than one
and do not significantly evolve with the spin-down power. A more pronounced
beaming factor vs. spin-down power correlation is observed for Slot Gap model
and radio-quiet pulsars and for the Outer Gap model and radio-loud pulsars. For
all models, the correlation between -ray luminosity and spin-down power
is consistent with a square root dependence. The -ray luminosities
obtained by using our beaming factors not exceed the spin-down power. This
suggests that assuming a beaming factor of one for all objects, as done in
other studies, likely overestimates the real values. The data show a relation
between the pulsar spectral characteristics and the width of the accelerator
gap that is consistent with the theoretical prediction for the Slot Gap model.Comment: 90 pages, 80 figures (63 in Appendices), accepted for publication in
Astronomy and Astrophysic
A Simple Family of Analytical Trumpet Slices of the Schwarzschild Spacetime
We describe a simple family of analytical coordinate systems for the
Schwarzschild spacetime. The coordinates penetrate the horizon smoothly and are
spatially isotropic. Spatial slices of constant coordinate time feature a
trumpet geometry with an asymptotically cylindrical end inside the horizon at a
prescribed areal radius (with ) that serves as the free
parameter for the family. The slices also have an asymptotically flat end at
spatial infinity. In the limit the spatial slices lose their trumpet
geometry and become flat -- in this limit, our coordinates reduce to
Painlev\'e-Gullstrand coordinates.Comment: 7 pages, 3 figure
Rates, determinants and success of implementing deprescribing in people with type 2 diabetes:A scoping review
Background Individualizing goals for people with type 2 diabetes may result in deintensification of medication, but a comprehensive picture of deprescribing practices is lacking. Aims To conduct a scoping review in order to assess the rates, determinants and success of implementing deprescribing of glucose-, blood pressure- or lipid-lowering medications in people with diabetes. Methods A systematic search on MEDLINE and Embase between January 2007 and January 2019 was carried out for deprescribing studies among people with diabetes. Outcomes were rates of deprescribing related to participant characteristics, the determinants and success of deprescribing, and its implementation. Critical appraisal was conducted using predefined tools. Results Fourteen studies were included; eight reported on rates, nine on determinants and six on success and implementation. Bias was high for studies on success of deprescribing. Deprescribing rates ranged from 14% to 27% in older people with low HbA(1c)levels, and from 16% to 19% in older people with low systolic blood pressure. Rates were not much affected by age, gender, frailty or life expectancy. Rates were higher when a reminder system was used to identify people with hypoglycaemia, which led to less overtreatment and fewer hypoglycaemic events. Most healthcare professionals accepted the concept of deprescribing but differed on when to conduct it. Deprescribing glucose-lowering medications could be successfully conducted in 62% to 75% of participants with small rises in HbA(1c). Conclusions Deprescribing of glucose-lowering medications seems feasible and acceptable, but was not widely implemented in the covered period. Support systems may enhance deprescribing. More studies on deprescribing blood pressure- and lipid-lowering medications in people with diabetes are needed
Modeling the non-recycled Fermi gamma-ray pulsar population
We use Fermi Gamma-ray Space Telescope detections and upper limits on
non-recycled pulsars obtained from the Large Area Telescope (LAT) to constrain
how the gamma-ray luminosity L depends on the period P and the period
derivative \dot{P}. We use a Bayesian analysis to calculate a best-fit
luminosity law, or dependence of L on P and \dot{P}, including different
methods for modeling the beaming factor. An outer gap (OG) magnetosphere
geometry provides the best-fit model, which is L \propto P^{-a} \dot{P}^{b}
where a=1.36\pm0.03 and b=0.44\pm0.02, similar to but not identical to the
commonly assumed L \propto \sqrt{\dot{E}} \propto P^{-1.5} \dot{P}^{0.5}. Given
upper limits on gamma-ray fluxes of currently known radio pulsars and using the
OG model, we find that about 92% of the radio-detected pulsars have gamma-ray
beams that intersect our line of sight. By modeling the misalignment of radio
and gamma-ray beams of these pulsars, we find an average gamma-ray beaming
solid angle of about 3.7{\pi} for the OG model, assuming a uniform beam. Using
LAT-measured diffuse fluxes, we place a 2{\sigma} upper limit on the average
braking index and a 2{\sigma} lower limit on the average surface magnetic field
strength of the pulsar population of 3.8 and 3.2 X 10^{10} G, respectively. We
then predict the number of non-recycled pulsars detectable by the LAT based on
our population model. Using the two-year sensitivity, we find that the LAT is
capable of detecting emission from about 380 non-recycled pulsars, including
150 currently identified radio pulsars. Using the expected five-year
sensitivity, about 620 non-recycled pulsars are detectable, including about 220
currently identified radio pulsars. We note that these predictions
significantly depend on our model assumptions.Comment: 26 pages, 10 figures, Accepted by ApJ on 8 September 201
Errors in kinematic distances and our image of the Milky Way Galaxy
Errors in the kinematic distances, under the assumption of circular gas
orbits, were estimated by performing synthetic observations of a model disk
galaxy. It was found that the error is < 0.5 kpc for most of the disk when the
measured rotation curve was used, but larger if the real rotation curve is
applied. In both cases, the error is significantly larger at the positions of
the spiral arms. The error structure is such that, when kinematic distances are
used to develope a picture of the large scale density distribution, the most
significant features of the numerical model are significantly distorted or
absent, while spurious structure appears. By considering the full velocity
field in the calculation of the kinematic distances, most of the original
density structures can be recovered.Comment: Accepted for publication in A
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