4,948 research outputs found
X-ray and optical observations of three clusters of galaxies: Abell 901, Abell 1437, and Abell 3570
We analyse three clusters of galaxies, Abell 901 (z=0.17), Abell 1437
(z=0.13) and Abell 3570 (z=0.037). They have low to intermediate X-ray fluxes
and an irregular morphology in the ROSAT All-Sky Survey (RASS). These clusters
are chosen to test the abilities and limitations of the RASS in terms of
cluster fluxes and cluster morphologies. Therefore some ``worst'' cases are
used here. X-ray observations with the ROSAT/HRI and optical spectroscopic
observations are carried out. The ROSAT/HRI observations, which have a much
better spatial resolution than the RASS, reveal in two of the three cases a
significantly different morphology than seen in the RASS. The reasons are point
sources which could not be resolved in the RASS and were therefore confused
with the cluster emission. For A3570 we could confirm the relaxed state of the
cluster by the optical determination of a small velocity dispersion. In the
cluster with the lowest flux (Abell 901) the countrate measurement is strongly
affected by point sources, in the two other cases the countrate measurements of
the RASS are reliable, i.e. they are reproduced by the ROSAT/HRI measurement.
We conclude that for clusters with a flux of a few times 10^{-12} erg/cm^2/s or
smaller, which show at the same time a non-relaxed morphology, the flux
measurement of the RASS can be seriously affected by fore- or background
sources. We point out that an all-sky survey of a second ABRIXAS mission would
provide a much clearer source distinction for low-flux clusters and thus a much
improved countrate determination.Comment: 8 pages (incl. 6 figures), accepted for publication in A&A (Suppl.
Chaos in the thermodynamic limit
We study chaos in the Hamiltonian Mean Field model (HMF), a system with many
degrees of freedom in which classical rotators are fully coupled. We review
the most important results on the dynamics and the thermodynamics of the HMF,
and in particular we focus on the chaotic properties.We study the Lyapunov
exponents and the Kolmogorov--Sinai entropy, namely their dependence on the
number of degrees of freedom and on energy density, both for the ferromagnetic
and the antiferromagnetic case.Comment: 10 pages, Latex, 4 figures included, invited talk to the Int.
school/Conf. on "Let's face Chaos Through Nonlinear Dynamics" Maribor
(Slovenia) 27 june - 11 july 1999, submitted to Prog. Theor. Physics supp
Challenging the empire
This paper considers how Paul Gilroy transformed hitherto dominant understandings of the relationship between race and class by developing an innovative account that foregrounded questions of racist oppression and collective resistance amid the organic crisis of British capitalism. The returns from this rethinking were profound in that he was able to make transparent both the structuring power of racism within the working class, and the necessity for autonomous black resistance. At the same time, significant lacunae in his account are identified, including the neglect of the episodic emergence of working-class anti-racism and the part played by socialists, particularly those of racialized minority descent in fashioning a major anti-racist social movement. The paper concludes with a lament for the disappearance of such work informed by a ‘Marxism without guarantees’ in the contemporary field of racism studies, and asks readers to consider the gains to be derived from such a re-engagement
Suppression of weak localization effects in low-density metallic 2D holes
We have measured the conductivity in a gated high-mobility GaAs two
dimensional hole sample with densities in the range (7-17)x10^9 cm^-2 and at
hole temperatures down to 5x10^-3 E_F. We measure the weak localization
corrections to the conductivity g=G/(e^2/h) as a function of magnetic field
(Delta g=0.019 +/- 0.006 at g=1.5 and T=9 mK) and temperature (d ln g/dT<0.0058
and 0.0084 at g=1.56 and 2.8). These values are less than a few percent of the
value 1/pi predicted by standard weak localization theory for a disordered 2D
Fermi liqui
Headache and pregnancy. a systematic review
This systematic review summarizes the existing data on headache and pregnancy with a scope on clinical headache phenotypes, treatment of headaches in pregnancy and effects of headache medications on the child during pregnancy and breastfeeding, headache related complications, and diagnostics of headache in pregnancy. Headache during pregnancy can be both primary and secondary, and in the last case can be a symptom of a life-threatening condition. The most common secondary headaches are stroke, cerebral venous thrombosis, subarachnoid hemorrhage, pituitary tumor, choriocarcinoma, eclampsia, preeclampsia, idiopathic intracranial hypertension, and reversible cerebral vasoconstriction syndrome. Migraine is a risk factor for pregnancy complications, particularly vascular events. Data regarding other primary headache conditions are still scarce. Early diagnostics of the disease manifested by headache is important for mother and fetus life. It is especially important to identify "red flag symptoms" suggesting that headache is a symptom of a serious disease. In order to exclude a secondary headache additional studies can be necessary: electroencephalography, ultrasound of the vessels of the head and neck, brain MRI and MR angiography with contrast ophthalmoscopy and lumbar puncture. During pregnancy and breastfeeding the preferred therapeutic strategy for the treatment of primary headaches should always be a non-pharmacological one. Treatment should not be postponed as an undermanaged headache can lead to stress, sleep deprivation, depression and poor nutritional intake that in turn can have negative consequences for both mother and baby. Therefore, if non-pharmacological interventions seem inadequate, a well-considered choice should be made concerning the use of medication, taking into account all the benefits and possible risks
The information sources and journals consulted or read by UK paediatricians to inform their clinical practice and those which they consider important: a questionnaire survey
Background: Implementation of health research findings is important for medicine to be
evidence-based. Previous studies have found variation in the information sources thought to be of greatest importance to clinicians but publication in peer-reviewed journals is the traditional route for dissemination of research findings. There is debate about whether the impact made on clinicians should be considered as part of the evaluation of research outputs. We aimed to determine first which information sources are generally most consulted by paediatricians to inform their clinical practice, and which sources they considered most important, and second, how many and which peer-reviewed journals they read.
Methods: We enquired, by questionnaire survey, about the information sources and academic
journals that UK medical paediatric specialists generally consulted, attended or read and
considered important to their clinical practice.
Results: The same three information sources – professional meetings & conferences, peerreviewed
journals and medical colleagues – were, overall, the most consulted or attended and ranked the most important. No one information source was found to be of greatest importance to all groups of paediatricians. Journals were widely read by all groups, but the proportion ranking them first in importance as an information source ranged from 10% to 46%. The number of journals read varied between the groups, but Archives of Disease in Childhood and BMJ were the most read
journals in all groups. Six out of the seven journals previously identified as containing best paediatric evidence are the most widely read overall by UK paediatricians, however, only the two most prominent are widely read by those based in the community.
Conclusion: No one information source is dominant, therefore a variety of approaches to
Continuing Professional Development and the dissemination of research findings to paediatricians should be used. Journals are an important information source. A small number of key ones can be identified and such analysis could provide valuable additional input into the evaluation of clinical research outputs
A Contingent Claim Analysis of Suicide
çµŒæ¸ˆå¦ / EconomicsAn option-theoretic model of suicide in the continuous time framework is proposed. Given completeness of the financial market and the associated contingent claim argument, the value of human capital consistent with the no-arbitrage principle is determined as the expected, discounted, present value of the future wage stream under the risk-neutral probability measure. The suicide option ? the right but not the obligation to commit suicide ? is modelled as an American put option with this human capital stock and a certain reference level of human capital as the underlier and strike price, respectively. The value of underlier falling short of the srtike price doet not induce the option holder\u27s immediate suicide because of the option value to postpone such a fatal and irreversible decision. This value, the delayed exercise premium, is given in a near closed form up to a deterministic exercise boundary. The nearly closed-form nature of this boundry allows one to calibrate the model to the real suicide rates among Japanese male workers from 1998 to 2009. The calibrated value of the strike price roughly amounts to the perpetual annuity value of the 90 percentage of the initial wage earned as of the new entry into the labor market, with the coupon rate given by the spread in market prices of risk between financial and labor market.JEL Classification Codes: D91, G13, J24http://www.grips.ac.jp/list/jp/facultyinfo/ikeda_shinsuke
Graphical analyses of occupation-wise suicide risk in Japan
I construct data on the numbers of workers and suicide victims in their working ages in Japan from 1980 to 2010 for each of 10 occupation classes and for males and females separately. I document a complex transition of the job profiles of occupation classes, and establish a correspondence between Japanese and international job classifications. Four general characteristics of occupation-wise suicide risk in Japan emerge from graphical analyses of constructed data. First, heterogeneous aging patterns of suicide deaths and numbers of workers create complex aging patterns of suicide rates. Second, the age-adjustment and stabilizations of suicide rates are crucial for an accurate measurement and a fair comparison of suicide risk for workers in each occupation or over the entire economy. Third, the surge of overall suicide risk in Japan since 1998 might be driven by that in few occupations for each gender. Particularly, (a) a high suicide-risk profiles for male workers in agricultural, forestry and fishery and jobless categories has been stable over time, hence not a main culprit of such surge, and (b) less informative patterns of female suicide rates may be a consequence of the cancellations of higher suicide risk in some occupations and lower suicide risk in any other occupations during such surge. Fourth, gender- and occupation-wise pattern of suicide risk is further confounded with heterogeneity across regions.http://www.grips.ac.jp/list/jp/facultyinfo/ikeda_shinsuke
- …