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.

Environment and plasticity of myogenesis in teleost fish.

Abstract: Embryonic development in teleosts is profoundly affected by environmental conditions, particularly temperature and dissolved oxygen concentrations. The environment determines the rate of myogenesis, the composition of sub-cellular organelles, patterns of gene expression, and the number and size distribution of muscle fibres. During the embryonic and larval stages, muscle plasticity to the environment is usually irreversible due to the rapid pace of ontogenetic change. In the early life stages, muscle can affect locomotory performance and behaviour, with potential consequences for larval survival. Postembryonic growth involves myogenic progenitor cells (MPCs) that originate in the embryo. The embryonic temperature regime can have long-term consequences for the growth of skeletal muscle in some species, including the duration and intensity of myotube formation in adult stages. In juvenile and adult fish, abiotic (temperature, day-length, water flow characteristics, hypoxia) and biotic factors (food availability, parasitic infection) have complex effects on the signalling pathways regulating the proliferation and differentiation of MPCs, protein synthesis and degradation, and patterns of gene expression. The phenotypic responses observed to the environment frequently vary during ontogeny and are integrated with endogenous physiological rhythms, particularly sexual maturation. Studies with model teleosts provide opportunities for investigating the underlying genetic mechanisms of muscle plasticity that can subsequently be applied to non-model species of more ecological or commercial interest.

Time course of neural responses discriminating different views of the face and head.

Abstract: 1. Measurements of the magnitude and time course of response were made from 44 cells responsive to static head views at different levels of stimulus effectiveness. In this way responses to complex stimulus patterns evoking good, poor, and midrange responses could be compared across the cell population. 2. Cells exhibiting both good and poor initial discrimination between head views were found at short and long latencies; there was no correlation of any of the temporal response parameters measured with cell response latency. 3. The time course of the population response to the most effective stimuli showed a rapid increase to a peak firing rate (onset to peak, rise time, 58 ms) that was on average 115 spikes/s above spontaneous activity (S/A), followed by slower decay (decay time, 93 ms) to a maintained discharge rate (15% of the peak rate above S/A). 4. Discrimination between responses to different head views exhibited by the population showed a sharp rise and reached highly significant levels within 25 ms after the population's response onset. 5. On average, activity in a single neuron (the Average Cell) rises to 44% of its peak response rate within 5 ms of the response onset. 6. The Average Cell also showed exceptionally fast discrimination between views, significant within 5 ms of response onset. 7. It is argued that the fast rise in firing rate, followed by a decay to a lower rate and the very fast emergence of discrimination are features of pattern processing present in real neural systems that are lacking in many processing models based on artificial networks of neuronlike elements, particularly those where discrimination relies on top-down and/or lateral competitive inhibition. 8. It is concluded that the only way to account for the rapid discrimination is to consider a coding system in which the first spike from multiple sources is used to transmit information between stages of processing.

Tectonic setting of the South China Block in the early Paleozoic: Resolving intracontinental and ocean closure models from detrital zircon U‐Pb geochronology

Abstract: [1] Zircon U-Pb geochronological data on over 900 zircon grains for Cambrian to Silurian sandstone samples from the South China Block constrain the pre-Devonian tectonic setting of, and the interrelationships between, the constituent Cathaysia and Yangtze blocks. Zircons range in age from 3335 to 465 Ma. Analyses from the Cathaysia sandstone samples yield major age clusters at ∼2560, ∼1850, ∼1000, and 890–760 Ma. Zircons from the eastern and central Yangtze sandstone samples show a similar age distribution with clusters at ∼2550, ∼1860, ∼1100, and ∼860–780 Ma. A minor peak at around 1450 Ma is also observed in the Cathaysia and central Yangtze age spectra, and a peak at ∼490 Ma represents magmatic zircons from Middle Ordovician sandstone in the eastern Yangtze and Cathaysia blocks. The Cambrian and Ordovician strata show a transition from a carbonate-dominated succession in the central Yangtze Block, to an interstratified carbonate-siliciclastic succession in the eastern Yangtze Block, to a neritic siliciclastic succession in the Cathaysia Block. Paleocurrent data across this succession consistently indicate directions toward the W-NNW, from the Cathaysia Block to the Yangtze Block. Our data, together with other geological constraints, suggest that the Cathaysia Block constitutes a fragment on the northern margin of east Gondwana and both Cathaysia and east Gondwana constituted the source for the analyzed early Paleozoic samples. The similar age spectra for the Cambrian to Silurian sandstone samples from the Yangtze and Cathaysia blocks argue against the independent development and spatial separation of these blocks in the early Paleozoic but rather suggest that the sandstone units accumulated in an intracontinental basin that spanned both blocks. Subsequent basin inversion and Kwangsian orogenesis possibly at 400–430 Ma also occurred in an intracontinental setting probably in response to the interaction of the South China Block with the Australian-Indian margin of east Gondwana.

Transformation Optics and the Geometry of Light

Abstract: Metamaterials are beginning to transform optics and microwave technology thanks to their versatile properties that, in many cases, can be tailored according to practical needs and desires. Although metamaterials are surely not the answer to all engineering problems, they have inspired a series of significant technological developments and also some imaginative research, because they invite researchers and inventors to dream. Imagine there were no practical limits on the electromagnetic properties of materials. What is possible? And what is not? If there are no practical limits, what are the fundamental limits? Such questions inspire taking a fresh look at the foundations of optics and at connections between optics and other areas of physics. In this article we discuss such a connection, the relationship between optics and general relativity, or, expressed more precisely, between geometrical ideas normally applied in general relativity and the propagation of light, or electromagnetic waves in general, in materials. We also discuss how this connection is applied: in invisibility devices, perfect lenses, the optical Aharonov-Bohm effect of vortices and in analogues of the event horizon.