131 research outputs found
The Similarity Hypothesis in General Relativity
Self-similar models are important in general relativity and other fundamental
theories. In this paper we shall discuss the ``similarity hypothesis'', which
asserts that under a variety of physical circumstances solutions of these
theories will naturally evolve to a self-similar form. We will find there is
good evidence for this in the context of both spatially homogenous and
inhomogeneous cosmological models, although in some cases the self-similar
model is only an intermediate attractor. There are also a wide variety of
situations, including critical pheneomena, in which spherically symmetric
models tend towards self-similarity. However, this does not happen in all cases
and it is it is important to understand the prerequisites for the conjecture.Comment: to be submitted to Gen. Rel. Gra
How reliable is pooled analysis in political economy? The globalization-welfare state nexus revisited
Efficiency and productivity growth comparisons of European and U.S. Air carriers: A first look at the data
In this paper we carry out technical efficiency and productivity growth comparisons among the four largest European carriers and eight of their American counterparts. The time period of our comparisons is 1976 through 1986. This is a particularly interesting period since it begins just after the informal steps toward deregulation in the United States and ends just prior to the introduction of the first wave of reforms by the Council of Ministers in Europe. We also identify the potential efficiency gains of the European liberalization by comparing efficiency differences between the two carrier groups. The reductions in inefficiency describe the amount that inputs can be decreased without altering output.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47558/1/11123_2005_Article_BF01073469.pd
Lichenometric dating (lichenometry) and the biology of the lichen genus rhizocarpon:challenges and future directions
Lichenometric dating (lichenometry) involves the use of lichen measurements to estimate the age of exposure of various substrata. Because of low radial growth rates and considerable longevity, species of the crustose lichen genus Rhizocarpon have been the most useful in lichenometry. The primary assumption of lichenometry is that colonization, growth and mortality of Rhizocarpon are similar on surfaces of known and unknown age so that the largest thalli present on the respective faces are of comparable age. This review describes the current state of knowledge regarding the biology of Rhizocarpon and considers two main questions: (1) to what extent does existing knowledge support this assumption; and (2) what further biological observations would be useful both to test its validity and to improve the accuracy of lichenometric dates? A review of the Rhizocarpon literature identified gaps in knowledge regarding early development, the growth rate/size curve, mortality, regeneration, competitive effects, colonization, and succession on rock surfaces. The data suggest that these processes may not be comparable on different rock surfaces, especially in regions where growth rates and thallus turnover are high. In addition, several variables could differ between rock surfaces and influence maximum thallus size, including rate and timing of colonization, radial growth rates, environmental differences, thallus fusion, allelopathy, thallus mortality, colonization and competition. Comparative measurements of these variables on surfaces of known and unknown age may help to determine whether the basic assumptions of lichenometry are valid. Ultimately, it may be possible to take these differences into account when interpreting estimated dates
Galaxy bulges and their massive black holes: a review
With references to both key and oft-forgotten pioneering works, this article
starts by presenting a review into how we came to believe in the existence of
massive black holes at the centres of galaxies. It then presents the historical
development of the near-linear (black hole)-(host spheroid) mass relation,
before explaining why this has recently been dramatically revised. Past
disagreement over the slope of the (black hole)-(velocity dispersion) relation
is also explained, and the discovery of sub-structure within the (black
hole)-(velocity dispersion) diagram is discussed. As the search for the
fundamental connection between massive black holes and their host galaxies
continues, the competing array of additional black hole mass scaling relations
for samples of predominantly inactive galaxies are presented.Comment: Invited (15 Feb. 2014) review article (submitted 16 Nov. 2014). 590
references, 9 figures, 25 pages in emulateApJ format. To appear in "Galactic
Bulges", E. Laurikainen, R.F. Peletier, and D.A. Gadotti (eds.), Springer
Publishin
Common Genetic Variants Associate with Serum Phosphorus Concentration
Phosphorus is an essential mineral that maintains cellular energy and mineralizes the skeleton. Because complex actions of ion transporters and regulatory hormones regulate serum phosphorus concentrations, genetic variation may determine interindividual variation in phosphorus metabolism. Here, we report a comprehensive genome-wide association study of serum phosphorus concentration. We evaluated 16,264 participants of European ancestry from the Cardiovascular Heath Study, Atherosclerosis Risk in Communities Study, Framingham Offspring Study, and the Rotterdam Study. We excluded participants with an estimated GFR <45 ml/min per 1.73 m(2) to focus on phosphorus metabolism under normal conditions. We imputed genotypes to approximately 2.5 million single-nucleotide polymorphisms in the HapMap and combined study-specific findings using meta-analysis. We tested top polymorphisms from discovery cohorts in a 5444-person replication sample. Polymorphisms in seven loci with minor allele frequencies 0.08 to 0.49 associate with serum phosphorus concentration (P = 3.5 x 10(-16) to 3.6 x 10(-7)). Three loci were near genes encoding the kidney-specific type IIa sodium phosphate co-transporter (SLC34A1), the calcium-sensing receptor (CASR), and fibroblast growth factor 23 (FGF23), proteins that contribute to phosphorus metabolism. We also identified genes encoding phosphatases, kinases, and phosphodiesterases that have yet-undetermined roles in phosphorus homeostasis. In the replication sample, five of seven top polymorphisms associate with serum phosphorous concentrations (P < 0.05 for each). In conclusion, common genetic variants associate with serum phosphorus in the general population. Further study of the loci identified in this study may help elucidate mechanisms of phosphorus regulation
Morning cortisol does not mediate the association of size at birth with blood pressure in children born from full-term pregnancies.
OBJECTIVE: It had been suggested that programming of the hypothalamo-pituitary-adrenal axis may underlie the associations of reduced size at birth with raised blood pressure in later life. We investigated whether morning salivary cortisol mediates the inverse association of birthweight with systolic blood pressure in children. DESIGN: Subjects and measurements--a historical cohort study involving 1152 Swedish children aged 5-14 years, who took part in a family study comprised of mother, father, and two full-sibs delivered in 1987-1995 after 38-41 weeks gestation within 36 months of each other. Birthweight and gestational age were available from obstetric records. Blood pressure, weight, height and puberty stage were measured at a clinic. Cortisol was measured by radioimmunoassay in morning salivary samples taken at home, within 30 min of waking. RESULTS: Morning cortisol showed a weak negative association with length of gestation in siblings, was not related to birthweight or to systolic or diastolic blood pressure. There was no change in the strength of the negative association between birthweight and systolic blood pressure on adjustment for cortisol (-1.4 mmHg/kg, 95% CI -2.7, -0.2; adjusted for age, sex, puberty stage, weight and height, and cortisol). CONCLUSIONS: Morning cortisol was not associated with size at birth, and did not mediate the birthweight-blood pressure association in children born from full-term pregnancies. It is possible that basal cortisol levels are of more importance in explaining associations of size at birth with later blood pressure in older subjects, or in populations with more varied length of gestation. Alternatively, our results may be caused by misclassification of the hypothalamo-pituitary-adrenal activity
Valuing Benefits of Tourism Activities in Nara Prefecture: An Application of the KuhnâTucker Model
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