4,879 research outputs found
First principles studies of modulated Co/Cu superlattices with strongly and weakly exchange biased Co-monolayers
First-principles calculations have been performed in order to determine
effective exchange integrals between {\it strongly} and {\it weakly}
exchange-coupled Co monolayers in certain modulated periodic
-type superlattices with three non-equivalent Co planes, which
have not yet been studied hitherto. For we find that the two
non-equivalent exchange integrals have opposite signs, i.e.~the strong coupling
is antiferromagnetic and the weak coupling ferromagnetic, and differ for from each other by one order of magnitude. It is shown that the results
depend on the system as a whole and could not be obtained from separate parts.
Finally we suggest that ''spin valve'' systems of such kind should be
considered when trying to obtain good magneto-resistance together with low
switching-fields.Comment: LaTex, 9 pages, including two .eps-figure
Investigating the X-ray emission from the massive WR+O binary WR 22 using 3D hydrodynamical models
We examine the dependence of the wind-wind collision and subsequent X-ray
emission from the massive WR+O star binary WR~22 on the acceleration of the
stellar winds, radiative cooling, and orbital motion. Simulations were
performed with instantaneously accelerated and radiatively driven stellar
winds. Radiative transfer calculations were performed on the simulation output
to generate synthetic X-ray data, which are used to conduct a detailed
comparison against observations. When instantaneously accelerated stellar winds
are adopted in the simulation, a stable wind-wind collision region (WCR) is
established at all orbital phases. In contrast, when the stellar winds are
radiatively driven, and thus the acceleration regions of the winds are
accounted for, the WCR is far more unstable. As the stars approach periastron,
the ram pressure of the WR's wind overwhelms the O star's and, following a
significant disruption of the shocks by non-linear thin-shell instabilities
(NTSIs), the WCR collapses onto the O star. X-ray calculations reveal that when
a stable WCR exists the models over-predict the observed X-ray flux by more
than two orders of magnitude. The collapse of the WCR onto the O star
substantially reduces the discrepancy in the keV flux to a factor of
at . However, the observed spectrum is not well matched
by the models. We conclude that the agreement between the models and
observations could be improved by increasing the ratio of the mass-loss rates
in favour of the WR star to the extent that a normal wind ram pressure balance
does not occur at any orbital phase, potentially leading to a sustained
collapse of the WCR onto the O star. Radiative braking may then play a
significant r\^{o}le for the WCR dynamics and resulting X-ray emission.Comment: 16 pages, 11 figures, 2 tables. Accepted for publication in A&
Greater professional empathy leads to higher agreement about decisions made in the consultation
Effect of sputter gas on the physical and magnetic microstructure of Co/Cu multilayers
The physical structure of Co/Cu multilayers, sputtered in different gases (Ar, Kr, and Xe) together with the domain structures that these films support have been investigated using electron microscopy in an attempt to explain the differences in their measured magnetoresistance (MR). Both planar and cross‐sectional analyses were undertaken. Due to only partial antiferromagnetic coupling submicron domain structures were observed by Lorentz microscopy in all multilayers. The complex nature of these domain structures made classification difficult, although small magnetic field application allowed wall motion and nucleation to be observed. All films were polycrystalline in nature, although average grains sizes differed. However, smoother interfaces together with less well defined crystal boundaries were observed in the Kr and Xe sputtered films. This trend did not correlate with giant MR (GMR) measurements as the Xe sputtered films had the lowest GMR value of the three
MuMax: a new high-performance micromagnetic simulation tool
We present MuMax, a general-purpose micromagnetic simulation tool running on
Graphical Processing Units (GPUs). MuMax is designed for high performance
computations and specifically targets large simulations. In that case speedups
of over a factor 100x can easily be obtained compared to the CPU-based OOMMF
program developed at NIST. MuMax aims to be general and broadly applicable. It
solves the classical Landau-Lifshitz equation taking into account the
magnetostatic, exchange and anisotropy interactions, thermal effects and
spin-transfer torque. Periodic boundary conditions can optionally be imposed. A
spatial discretization using finite differences in 2 or 3 dimensions can be
employed. MuMax is publicly available as open source software. It can thus be
freely used and extended by community. Due to its high computational
performance, MuMax should open up the possibility of running extensive
simulations that would be nearly inaccessible with typical CPU-based
simulators.Comment: To be published in JMM
The 2.35 year itch of Cyg OB2 #9. II. Radio monitoring
Cyg OB2 #9 is one of a small set of non-thermal radio emitting massive O-star
binaries. The non-thermal radiation is due to synchrotron emission in the
colliding-wind region. Cyg OB2 #9 was only recently discovered to be a binary
system and a multi-wavelength campaign was organized to study its 2011
periastron passage. We report here on the results of the radio observations
obtained in this monitoring campaign. We used the Expanded Very Large Array
(EVLA) radio interferometer to obtain 6 and 20 cm continuum fluxes. The
observed radio light curve shows a steep drop in flux sometime before
periastron. The fluxes drop to a level that is comparable to the expected
free-free emission from the stellar winds, suggesting that the non-thermal
emitting region is completely hidden at that time. After periastron passage,
the fluxes slowly increase. We introduce a simple model to solve the radiative
transfer in the stellar winds and the colliding-wind region, and thus determine
the expected behaviour of the radio light curve. From the asymmetry of the
light curve, we show that the primary has the stronger wind. This is somewhat
unexpected if we use the astrophysical parameters based on theoretical
calibrations. But it becomes entirely feasible if we take into account that a
given spectral type - luminosity class combination covers a range of
astrophysical parameters. The colliding-wind region also contributes to the
free-free emission, which can help to explain the high values of the spectral
index seen after periastron passage. Combining our data with older Very Large
Array (VLA) data allows us to derive a period P = 860.0 +- 3.7 days for this
system. With this period, we update the orbital parameters that were derived in
the first paper of this series.Comment: 10 pages, 4 figures, accepted for publication in A&
Evaluation of radiography as a screening method for detection and characterisation of congenital vertebral malformations in dogs
Congenital vertebral malformations (CVM) are common in brachycephalic ‘screw-tailed’ dogs; they can be associated with neurological deficits and a genetic predisposition has been suggested. The purpose of this study was to evaluate radiography as a screening method for congenital thoracic vertebral malformations in brachycephalic ‘screw-tailed’ dogs by comparing it with CT. Forty-nine dogs that had both radiographic and CT evaluations of the thoracic vertebral column were included. Three observers retrospectively reviewed the images independently to detect CVMs. When identified, they were classified according to a previously published radiographic classification scheme. A CT consensus was then reached. All observers identified significantly more affected vertebrae when evaluating orthogonal radiographic views compared with lateral views alone; and more affected vertebrae with the CT consensus compared with orthogonal radiographic views. Given the high number of CVMs per dog, the number of dogs classified as being CVM free was not significantly different between CT and radiography. Significantly more midline closure defects were also identified with CT compared with radiography. Malformations classified as symmetrical or ventral hypoplasias on radiography were frequently classified as ventral and medial aplasias on CT images. Our results support that CT is better than radiography for the classification of CVMs and this will be important when further evidence of which are the most clinically relevant CVMs is identified. These findings are of particular importance for designing screening schemes of CVMs that could help selective breeding programmes based on phenotype and future studies
The kinematics and kinetics of riding a racehorse: A quantitative comparison of a training simulator and real horses
Human papillomavirus-associated increase in p16INK4A expression in penile lichen sclerosus and squamous cell carcinoma
Re-use of this article is permitted in accordance with the Creative Commons Deed, Attribution 2·5, which does not permit commercial exploitationBackground: Human papillomaviruses (HPVs) are sexually transmitted human carcinogens that may play a role in the oncogenesis of penile cancer. Objectives: To investigate the role of HPV infection and expression of the tumour suppressor protein p16INK4A in the pathogenesis of penile cancer. Methods: By means of polymerase chain reaction amplification and reverse hybridization line probe assay to detect HPV infection, and immunohistochemical staining for p16INK4A and Ki67, we analysed 26 penile squamous cell carcinomas (SCCs) and 20 independent penile lichen sclerosus (LS) lesions from 46 patients. Results: HPV DNA was found in 54% of penile SCCs and 33% of penile LS cases in single and multiple infections. High-risk HPV 16 was the predominant HPV type detected. No relationship between Ki67 expression and HPV infection was observed. Strong immunostaining for p16INK4A correlated with HPV 16/18 infection in both penile LS and penile SCC. In our penile SCC series the cancer margins were also associated with penile LS in 13 of 26 lesions, and HPV was detected in seven of the 13 SCC cases associated with LS and in six of the 11 SCC lesions not involving LS. Conclusions: Our study shows a high prevalence of HPV 16 and p16INK4A expression in penile lesions, consistent with an active role for HPV in interfering with the retinoblastoma pathway. High-risk HPV infection could be involved in the tumorigenic process in 50% of penile cancers, and the use of prophylactic HPV vaccines has the potential to prevent these cancers.Peer reviewedFinal Published versio
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