University of St Andrews

About: University of St Andrews is a education organization based out in St Andrews, Fife, United Kingdom. It is known for research contribution in the topics: Population & Laser. The organization has 16260 authors who have published 43364 publications receiving 1636072 citations. The organization is also known as: St Andrews University & University of St. Andrews.

Similarity of Scattering Rates in Metals Showing T-Linear Resistivity

Abstract: Many exotic compounds, such as cuprate superconductors and heavy fermion materials, exhibit a linear in temperature (T) resistivity, the origin of which is not well understood. We found that the resistivity of the quantum critical metal Sr(3)Ru(2)O(7) is also T-linear at the critical magnetic field of 7.9 T. Using the precise existing data for the Fermi surface topography and quasiparticle velocities of Sr(3)Ru(2)O(7), we show that in the region of the T-linear resistivity, the scattering rate per kelvin is well approximated by the ratio of the Boltzmann constant to the Planck constant divided by 2π. Extending the analysis to a number of other materials reveals similar results in the T-linear region, in spite of large differences in the microscopic origins of the scattering.

Territorial Behaviour of Juvenile Atlantic Salmon (Salmo Salar L.)

Abstract: 1. The territorial behaviour of young Atlantic salmon is described from observations made in the field and the laboratory. Six agonistic activities occur during the defence of territories; these are charging, nipping, chasing, frontal display, lateral display and fleeing. Certain colour changes of the fish are associated with extremes of aggression and submission. 2. The causation of the six agonistic acts is discussed. Charging, nipping and chasing result from high attack tendencies; fleeing is a result of high escape tendencies. Frontal and lateral displays occur as a result of conflict between attack and escape and are most common during fights between two aggressive fish when conflict is presumed to be high. Frontal display indicates relatively high levels of the tendency to attack; lateral display of the tendency to escape. 3. Agonistic behaviour among aquarium-held fish fluctuates with several factors. Territories are not defended actively until after a period of adaptation to new surroundings, particularly if the fish have been kept in crowded holding tanks for some time. Agonistic encounters increase with more frequent feeding, due probably to better condition and greater activity of the fish, resulting in more frequent infringements of territories. Gradual increase in numbers of fish in an aquarium leads first to an increase, then to a falling off in agonistic activity, as the non-territory-holding fish, which are moderately active with small numbers of fish present, form a closely-knit, stabilized group as the aquarium becomes crowded. 4. The territories of young salmon appear to be primarily feeding territories. The behaviour associated with their maintenance is important for optimum growth and survival and for maintaining position for long periods in fast flowing streams. The fate of hatchery-reared fish planted in rivers may be related to their ability to secure and maintain territories in competition with wild fish.

Assessing the impact of climate variation on survival in vertebrate populations

Abstract: The impact of the ongoing rapid climate change on natural systems is a major issue for human societies. An important challenge for ecologists is to identify the climatic factors that drive temporal variation in demographic parameters, and, ultimately, the dynamics of natural populations. The analysis of long-term monitoring data at the individual scale is often the only available approach to estimate reliably demographic parameters of vertebrate populations. We review statistical procedures used in these analyses to study links between climatic factors and survival variation in vertebrate populations. We evaluated the efficiency of various statistical procedures from an analysis of survival in a population of white stork, Ciconia ciconia, a simulation study and a critical review of 78 papers published in the ecological literature. We identified six potential methodological problems: (i) the use of statistical models that are not wellsuited to the analysis of long-term monitoring data collected at the individual scale; (ii) low ratios of number of statistical units to number of candidate climatic covariates; (iii) collinearity among candidate climatic covariates; (iv) the use of statistics, to assess statistical support for climatic covariates effects, that deal poorly with unexplained variation in survival; (v) spurious detection of effects due to the co-occurrence of trends in survival and the climatic covariate time series; and (vi) assessment of the magnitude of climatic effects on survival using measures that cannot be compared across case studies. The critical review of the ecological literature revealed that five of these six methodological problems were often poorly tackled. As a consequence we concluded that many of these studies generated hypotheses but only few provided solid evidence for impacts of climatic factors on survival or reliable measures of the magnitude of such impacts. We provide practical advice to solve efficiently most of the methodological problems identified. The only frequent issue that still lacks a straightforward solution was the low ratio of the number of statistical units to the number of candidate climatic covariates. In the perspective of increasing this ratio and therefore of producing more robust analyses of the links between climate and demography, we suggest leads to improve the procedures for designing field protocols and selecting a set of candidate climatic covariates. Finally, we present recent statistical methods with potential interest for assessing the impact of climatic factors on demographic parameters.

Eddington-limited Accretion and the Black Hole Mass Function at Redshift 6

Abstract: We present discovery observations of a quasar in the Canada-France High-z Quasar Survey (CFHQS) at redshift z = 6.44. We also use near-infrared spectroscopy of nine CFHQS quasars at z ~ 6 to determine black hole masses. These are compared with similar estimates for more luminous Sloan Digital Sky Survey quasars to investigate the relationship between black hole mass and quasar luminosity. We find a strong correlation between Mg II FWHM and UV luminosity and that most quasars at this early epoch are accreting close to the Eddington limit. Thus, these quasars appear to be in an early stage of their life cycle where they are building up their black hole mass exponentially. Combining these results with the quasar luminosity function, we derive the black hole mass function at z = 6. Our black hole mass function is ~104 times lower than at z = 0 and substantially below estimates from previous studies. The main uncertainties which could increase the black hole mass function are a larger population of obscured quasars at high redshift than is observed at low redshift and/or a low quasar duty cycle at z = 6. In comparison, the global stellar mass function is only ~102 times lower at z = 6 than at z = 0. The difference between the black hole and stellar mass function evolution is due to either rapid early star formation which is not limited by radiation pressure as is the case for black hole growth or inefficient black hole seeding. Our work predicts that the black hole mass-stellar mass relation for a volume-limited sample of galaxies declines rapidly at very high redshift. This is in contrast to the observed increase at 4 < z < 6 from the local relation if one just studies the most massive black holes.

Kink instability of solar coronal loops as the cause of solar flares

Abstract: Solar coronal loops are observed to be remarkably stable structures. A magnetohydrodynamic stability analysis of a model loop by the energy method suggests that the main reason for stability is the fact that the ends of the loop are anchored in the dense photosphere. In addition to such line-tying, the effect of a radial pressure gradient is incorporated in the analysis.