2,462 research outputs found
Phenolics, depsides and triterpenes from the chilean lichen pseudocyphellaria nudata (zahlbr.) D.J. Galloway
Indexación: ScieloThe lichen Pseudocyphellaria nudata is a species endemic to southern South América. From the lichen tallus, methyl orsellinate, 2-methoxy-3,6-dimethyl-4-hydroxybenzaldehyde, methyl-evernate, tenuiorin, hopan-6ß,22-diol and hopan-6α,76,22-triol were isolated and identified as the main lichen constituents. This is the first report of the occurrence of 2-methoxy-3,6-dimethyl-4-hydroxybenzaldehyde in lichens.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=s0717-97072008000300017&nrm=is
The enigmatic spin evolution of PSR J0537-6910: r-modes, gravitational waves and the case for continued timing
We discuss the unique spin evolution of the young X-ray pulsar PSR
J0537-6910, a system in which the regular spin down is interrupted by glitches
every few months. Drawing on the complete timing data from the Rossi X-ray
Timing Explorer (RXTE, from 1999-2011), we argue that a trend in the
inter-glitch behaviour points to an effective braking index close to ,
much larger than expected. This value is interesting because it would accord
with the neutron star spinning down due to gravitational waves from an unstable
r-mode. We discuss to what extent this, admittedly speculative, scenario may be
consistent and if the associated gravitational-wave signal would be within
reach of ground based detectors. Our estimates suggest that one may, indeed, be
able to use future observations to test the idea. Further precision timing
would help enhance the achievable sensitivity and we advocate a joint observing
campaign between the Neutron Star Interior Composition ExploreR (NICER) and the
LIGO-Virgo network.Comment: 10 pages, 4 figures, emulate ApJ forma
Neutron star glitches have a substantial minimum size
Glitches are sudden spin-up events that punctuate the steady spin down of
pulsars and are thought to be due to the presence of a superfluid component
within neutron stars. The precise glitch mechanism and its trigger, however,
remain unknown. The size of glitches is a key diagnostic for models of the
underlying physics. While the largest glitches have long been taken into
account by theoretical models, it has always been assumed that the minimum size
lay below the detectability limit of the measurements. In this paper we define
general glitch detectability limits and use them on 29 years of daily
observations of the Crab pulsar, carried out at Jodrell Bank Observatory. We
find that all glitches lie well above the detectability limits and by using an
automated method to search for small events we are able to uncover the full
glitch size distribution, with no biases. Contrary to the prediction of most
models, the distribution presents a rapid decrease of the number of glitches
below ~0.05 Hz. This substantial minimum size indicates that a glitch must
involve the motion of at least several billion superfluid vortices and provides
an extra observable which can greatly help the identification of the trigger
mechanism. Our study also shows that glitches are clearly separated from all
the other rotation irregularities. This supports the idea that the origin of
glitches is different to that of timing noise, which comprises the unmodelled
random fluctuations in the rotation rates of pulsars.Comment: 8 pages; 4 figures. Accepted for publication in MNRA
The glitch activity of neutron stars
We present a statistical study of the glitch population and the behaviour of
the glitch activity across the known population of neutron stars. An unbiased
glitch database was put together based on systematic searches of radio timing
data of 898 rotation-powered pulsars obtained with the Jodrell Bank and Parkes
observatories. Glitches identified in similar searches of 5 magnetars were also
included. The database contains 384 glitches found in the rotation of 141 of
these neutron stars. We confirm that the glitch size distribution is at least
bimodal, with one sharp peak at approximately , which we
call large glitches, and a broader distribution of smaller glitches. We also
explored how the glitch activity , defined as the mean
frequency increment per unit of time due to glitches, correlates with the spin
frequency , spin-down rate , and various combinations of
these, such as energy loss rate, magnetic field, and spin-down age. It is found
that the activity is insensitive to the magnetic field and that it correlates
strongly with the energy loss rate, though magnetars deviate from the trend
defined by the rotation-powered pulsars. However, we find that a constant ratio
is consistent with the behaviour
of all rotation-powered pulsars and magnetars. This relation is dominated by
large glitches, which occur at a rate directly proportional to .
The only exception are the rotation-powered pulsars with the highest values of
, such as the Crab pulsar and PSR B054069, which exhibit a much
smaller glitch activity, intrinsically different from each other and from the
rest of the population. The activity due to small glitches also shows an
increasing trend with , but this relation is biased by selection
effects.Comment: Accepted for publication in A&
Confidence via correction: The effect of judgment correction on consumer confidence
At times, consumers are motivated to reduce the influence of a product recommendation on their judgments. Based on previous research, it is unclear whether this correction process will increase or decrease consumers' confidence in their judgments. We find that source credibility moderates the effect of correction on confidence: correction decreases confidence when a product recommendation comes from a high credibility source but increases confidence when the same message comes from a low credibility source. As a result, correction increases the effectiveness of recommendations from low credibility sources on purchase intentions. Notably, this confidence via correction effect is further moderated by elaboration, such that the effect is attenuated for high elaboration consumers. Our results have implications for understanding consumers' reactions to persuasive messages and for both marketing practitioners and consumer protection agencies using correction cues to influence message persuasiveness
X-ray Observations of High-B Radio Pulsars
The study of high-magnetic-field pulsars is important for examining the
relationships between radio pulsars, magnetars, and X-ray-isolated neutron
stars (XINSs). Here we report on X-ray observations of three such
high-magnetic-field radio pulsars. We first present the results of a deep
XMM-Newton observation of PSR J1734-3333, taken to follow up on its initial
detection in 2009. The pulsar's spectrum is well fit by a blackbody with a
temperature of 300 +/- 60 eV, with bolometric luminosity L_bb = 2.0(+2.2
-0.7)e+32 erg/s = 0.0036E_dot for a distance of 6.1 kpc. We detect no X-ray
pulsations from the source, setting a 1 sigma upper limit on the pulsed
fraction of 60% in the 0.5-3 keV band. We compare PSR J1734-3333 to other
rotation-powered pulsars of similar age and find that it is significantly
hotter, supporting the hypothesis that the magnetic field affects the observed
thermal properties of pulsars. We also report on XMM-Newton and Chandra
observations of PSRs B1845-19 and J1001-5939. We do not detect either pulsar,
setting 3 sigma upper limits on their blackbody temperatures of 48 and 56 eV,
respectively. Despite the similarities in rotational properties, these sources
are significantly cooler than all but one of the XINSs, which we attribute to
the two groups having been born with different magnetic fields and hence
evolving differently.Comment: 18 pages, 2 tables, 5 figures, accepted for publication in the
Astrophysical Journa
New long-term braking index measurements for glitching pulsars using a glitch-template method
Braking index measurements offer the opportunity to explore the processes
affecting the long-term spin evolution of pulsars and possible evolutionary
connections between the various pulsar populations. For young pulsars the
long-term trends are generally obscured by short term phenomena such as timing
noise and the recoveries form large glitches. Here we present a new method to
overcome the latter and report on braking index measurements for the Vela-like
pulsars PSR B1800-21 and PSR B1823-13, an updated measurement for Vela and new
estimates for four more glitching pulsars observed at Jodrell Bank Observatory.
The values of braking indices describe the long-term evolution of the pulsars
across the P-P' diagram. Despite some measurements being affected by
considerable uncertainties, there is evidence for a common trend involving low
braking indices (n<=2) among young glitching pulsars. Such values introduce a
new variant in the evolution of young pulsars and their relationship with other
populations in the P-P' diagram. Low braking indices also imply that these
pulsars could be a few times older than their characteristic ages. We consider
PSR B1757-24 and conclude that the pulsar could be old enough to be related to
the supernova remnant G5.4-1.2. Between glitches, the short-term evolution of
Vela-like pulsars is characterised by large inter-glitch braking indices n_ig >
10. We interpret both short and long term trends as signatures of the large
glitch activity, and speculate that they are driven by short-term post-glitch
re-coupling and a cumulative long-term decoupling of superfluid to the rotation
of the star.Comment: 16 pages, 6 figures. Accepted for publication in MNRA
Topical treatment of actinic keratoses with potassium dobesilate 5% cream. A preliminary open-label study
<p>Abstract</p> <p>Background</p> <p>Fibroblast growth factor (FGF) is involved in skin tumorigenesis: it promotes cell viability, induces angiogenesis and stimulates invasiveness. Dobesilate is a drug that blocks the activity of FGF. The primary objective was to evaluate the efficacy and tolerability of potassium dobesilate 5% cream in the treatment of actinic keratoses.</p> <p>Methods</p> <p>Potassium dobesilate 5% cream was applied twice daily for 16 weeks to actinic keratosis lesions in 30 patients. The lesions were evaluated clinically at an initial baseline visit, at intermediate visits, and at 16 weeks of treatment.</p> <p>Results</p> <p>The use of potassium dobesilate 5% cream for 16 weeks induced complete regression in 70% of evaluated actinic keratoses, corresponding to grade I, II and III clinical variants, and a partial response (at least 75% reduction of lesions) in 20% of the cases.</p> <p>Conclusion</p> <p>Our preliminary trial shows that potassium dobesilate exerts anti-tumorigenic effects and may play a useful role in the chemoprevention of skin cancers.</p
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