1,018 research outputs found
Realizing orders as group rings
An order is a commutative ring that as an abelian group is finitely generated
and free. A commutative ring is reduced if it has no non-zero nilpotent
elements. In this paper we use a new tool, namely, the fact that every reduced
order has a universal grading, to answer questions about realizing orders as
group rings. In particular, we address the Isomorphism Problem for group rings
in the case where the ring is a reduced order. We prove that any non-zero
reduced order can be written as a group ring in a unique ``maximal'' way,
up to isomorphism. More precisely, there exist a ring and a finite abelian
group , both uniquely determined up to isomorphism, such that
as rings, and such that if is a ring and is a group, then
as rings if and only if there is a finite abelian group such that as rings and as groups. Computing and for
given can be done by means of an algorithm that is not quite
polynomial-time. We also give a description of the automorphism group of in
terms of and
Subsurface processes generated by bore-driven swash on coarse-grained beaches
Peer reviewedPublisher PD
On the photometric variability of blue supergiants in NGC 300 and its impact on the Flux-weighted Gravity-Luminosity Relationship
We present a study of the photometric variability of spectroscopically
confirmed supergiants in NGC 300, comprising 28 epochs extending over a period
of five months. We find 15 clearly photometrically variable blue supergiants in
a sample of nearly 70 such stars, showing maximum light amplitudes ranging from
0.08 to 0.23 magnitudes in the V band, and one variable red supergiant. We show
their light curves, and determine semi-periods for two A2 Ia stars. Assuming
that the observed changes correspond to similar variations in the bolometric
luminosity, we test for the influence of this variability on the Flux-weighted
Gravity--Luminosity Relationship and find a negligible effect, showing that the
calibration of this relationship, which has the potential to measure
extragalactic distances at the Cepheid accuracy level, is not affected by the
stellar photometric variability in any significant way.Comment: 9 pages, 3 figures, 3 tables. Accepted for publication in the
Astrophysical Journa
Intercomparison of Metop-A SO2 measurements during the 2010- 2011 Icelandic eruptions
The European Space Agency project Satellite Monitoring of Ash and Sulphur Dioxide for the mitigation of Aviation
Hazards, was introduced after the eruption of the Icelandic volcano Eyjafjallajökull in the spring of 2010
to facilitate the development of an optimal EndtoEnd
System for Volcanic Ash Plume Monitoring and Prediction.
The Eyjafjallajökull plume drifted towards Europe and caused major disruptions of European air traffic for
several weeks affecting the everyday life of millions of people. The limitations in volcanic plume monitoring and
prediction capabilities gave birth to this observational system which is based on comprehensive satellitederived
ash plume and sulphur dioxide [SO2] level estimates, as well as a widespread validation using supplementary
satellite, aircraft and groundbased
measurements. Intercomparison
of the volcanic total SO2 column and
plume height observed by GOME2/
MetopA
and IASI/MetopA
are shown before, during and after the Eyjafjallajökull
2010 eruptions as well as for the 2011 GrĂmsvötn eruption. Colocated
groundbased
Brewer Spectrophotometer
data extracted from the World Ozone and Ultraviolet Radiation Data Centre for de Bilt, the Netherlands,
are also compared to the different satellite estimates. Promising agreement is found for the two different
types of instrument for the SO2 columns with linear regression coefficients ranging around from 0.64 when
comparing the different instruments and 0.85 when comparing the two different IASI algorithms. The agreement
for the plume height is lower, possibly due to the major differences between the height retrieval part of the
GOME2 and IASI algorithms. The comparisons with the Brewer groundbased
station in de Bilt, The Netherlands
show good qualitative agreement for the peak of the event however stronger eruptive signals are required
for a longer quantitative comparison
Spitzer Space Telescope observations of magnetic cataclysmic variables: possibilities for the presence of dust in polars
We present Spitzer Space Telescope photometry of six short-period polars, EF
Eri, V347 Pav, VV Pup, V834 Cen, GG Leo, and MR Ser. We have combined the
Spitzer Infrared Array Camera (3.6 -8.0 microns) data with the 2MASS J, H, K_s
photometry to construct the spectral energy distributions of these systems from
the near- to mid-IR (1.235 - 8 microns). We find that five out of the six
polars have flux densities in the mid-IR that are substantially in excess of
the values expected from the stellar components alone. We have modeled the
observed SEDs with a combination of contributions from the white dwarf,
secondary star, and either cyclotron emission or a cool, circumbinary dust disk
to fill in the long-wavelength excess. We find that a circumbinary dust disk is
the most likely cause of the 8 micron excess in all cases, but we have been
unable to rule out the specific (but unlikely) case of completely optically
thin cyclotron emission as the source of the observed 8 micron flux density.
While both model components can generate enough flux at 8 microns, neither dust
nor cyclotron emission alone can match the excess above the stellar components
at all wavelengths. A model combining both cyclotron and dust contributions,
possibly with some accretion-generated flux in the near-IR, is probably
required, but our observed SEDs are not sufficiently well-sampled to constrain
such a complicated model. If the 8 micron flux density is caused by the
presence of a circumbinary dust disk, then our estimates of the masses of these
disks are many orders of magnitude below the mass required to affect CV
evolution.Comment: 58 pages, 14 figures, ApJ accepte
V2368 Oph: An eclipsing and double-lined spectroscopic binary used as a photometric comparison star for U Oph
The A-type star HR 6412 = V2368 Oph was used by several investigators as a
photometric comparison star for the known eclipsing binary U Oph but was found
to be variable by three independent groups, including us. By analysing series
of new spectral and photometric observations and a critical compilation of
available radial velocities, we were able to find the correct period of light
and radial-velocity variations and demonstrate that the object is an eclipsing
and double-lined spectroscopic binary moving in a highly eccentric orbit. We
derived a linear ephemeris T min.I = HJD (2454294.67 +/- 0.01) + (38.32712 +/-
0.00004)d x E and estimated preliminary basic physical properties of the
binary. The dereddened UBV magnitudes and effective temperatures of the primary
and secondary, based on our light- and velocity-curve solutions, led to
distance estimates that agree with the Hipparcos distance within the errors. We
find that the mass ratio must be close to one, but the limited number and
wavelength range of our current spectra does not allow a truly precise
determination of the binary masses. Nevertheless, our results show convincingly
that both binary components are evolved away from the main sequence, which
makes this system astrophysically very important. There are only a few
similarly evolved A-type stars among known eclipsing binaries. Future
systematic observations and careful analyses can provide very stringent tests
for the stellar evolutionary theory.Comment: 10 pages, 7 figs, in press 2011 A&
Cardiac safety of adjuvant pegylated liposomal doxorubicin with concurrent trastuzumab: a randomized phase II trial
Background The cardiac safety of trastuzumab concurrent with pegylated liposomal doxorubicin (PLD) in an adjuvant breast cancer treatment regimen is unknown. Patients and methods Women with resected node-positive or intermediate-risk node-negative HER2 overexpressing breast cancer and baseline left ventricular ejection fraction (LVEF) â„55% were randomized (1:2) to doxorubicin 60 mg/m2 (A)+cyclophosphamide 600 mg/m2 (C) every 21 days (q21d) for four cycles or PLD 35 mg/m2+C q21d+trastuzumab 2 mg/kg weekly (H) for 12 weeks. Both groups then received paclitaxel (Taxol, T) 80 mg/m2 with H for 12 weeks followed by H to complete 1 year. The primary end point was cardiac event rate or inability to administer 1 year of trastuzumab. Results Of 181 randomized patients, 179 underwent cardiac analysis. The incidence of cardiac toxicity or inability to administer trastuzumab due to cardiotoxicity was 18.6% [n=11; 95% confidence interval (CI) 9.7% to 30.9%] with A+C â T+H and 4.2% (n=5; 95% CI 1.4% to 9.5%) with PLD+C+H â T+H (P=0.0036). All events, except one, were asymptomatic systolic dysfunction or mildly symptomatic heart failure. Mean absolute LVEF reduction at cycle 8 was greater with doxorubicin (5.6% versus 2.1%; P=0.0014). Conclusion PLD+C+H â T+H is feasible and results in lower early cardiotoxicity rates compared with A+C â T+
Observations of the Magnetic Cataclysmic Variable VV Puppis with the Far Ultraviolet Spectroscopic Explorer
We present the first far-ultraviolet (FUV) observations of the magnetic
cataclysmic variable VV Puppis, obtained with the Far Ultraviolet Spectroscopic
Explorer satellite. In addition, we have obtained simultaneous ground-based
optical photometric observations of VV Pup during part of the FUV observation.
The shapes of the FUV and optical light curves are consistent with each other
and with those of past observations at optical, extreme-ultraviolet, and X-ray
wavelengths. Time-resolved FUV spectra during the portion of VV Pup's orbit
when the accreting magnetic pole of the white dwarf can be seen show an
increasing continuum level as the accretion spot becomes more directly visible.
The most prominent features in the spectrum are the O VI 1031.9A, 1037.6A
emission lines. We interpret the shape and velocity shift of these lines in the
context of an origin in the accretion funnel near the white dwarf surface. A
blackbody function with T > 90,000 K provides an adequate fit to the FUV
spectral energy distribution of VV Pup.Comment: 18 pages, 6 figures, 1 table; to be published in the Astronomical
Journa
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