Stability of Negative Image Equilibria in Spike-Timing Dependent Plasticity

We investigate the stability of negative image equilibria in mean synaptic weight dynamics governed by spike-timing dependent plasticity (STDP). The neural architecture of the model is based on the electrosensory lateral line lobe (ELL) of mormyrid electric fish, which forms a negative image of the reafferent signal from the fish's own electric discharge to optimize detection of external electric fields. We derive a necessary and sufficient condition for stability, for arbitrary postsynaptic potential functions and arbitrary learning rules. We then apply the general result to several examples of biological interest.Comment: 13 pages, revtex4; uses packages: graphicx, subfigure; 9 figures, 16 subfigure

Limb reconstruction in Ollier's disease.

We present our experience of lengthening and correction of complex deformities in the management of patients with Ollier's dysplasia (multiple enchondromatosis) from 1985 and 2002. All patients were under 18 years with a minimum follow-up time of 2 years (mean 9.6 years, range 2-15 years). There were a total of ten patients of which seven were male and three female. The mean age at presentation was 10.7 years (range 5-17 years; SD 3.7 years). The total length gain was 42.3 mm (range 30-110 mm; SD 28.9 mm). The number of days in external fixation was 164.8 days (range 76-244 days; SD 42.9 days). The bone healing index was 32.5 days/cm (18-50 days/cm; SD 10.3 days/cm). Patients with Ollier's disease have limb length inequality and angular deformities and require multiple reconstructive procedures owing to a high incidence of recurrence. We identified a tendency for the osteotomy to prematurely consolidate and advise the latency period after surgery to be 4-5 days and for distraction to proceed at a faster rate

Environmental and economic information for aggregates provision

This report describes a one-year research project entitled ‘Environmental and economic information systems for aggregates provision’. This project is an extension to previous research on Strategic Environmental Assessment (SEA) and future aggregates extraction, which was carried out by the British Geological Survey (BGS) and reported in early 2004 (Steadman, et al., 2004). Both phases of the research were co-funded by the BGS and the Mineral Industry Sustainable Technology Programme (MIST). Environmental, economic and social information are essential for sustainable planning for the provision of aggregates. There is a need to bring together disparate information relating to aggregate extraction. Datasets include the location of resources and their potential end-uses, as well as those on the environment and transport. Bringing this digital information together into one location or system will assist in supporting a more balanced and informed approach to the decision making process. A number of regulatory mechanisms are currently driving the gathering and compilation of relevant environmental, economic and social information. Current drivers for information relevant to aggregate provision include environmental appraisal of the provision of aggregates, SEA and Sustainability Appraisal (SA). The objective of this research was to provide an interactive ‘tool’ or information system for the minerals industry, land-use planners and other stakeholders to use when considering options for future aggregate provision. The study area for the research was the East Midlands Region of England. The project had three main deliverables: 1. To provide an online Geographic Information System (GIS) to access the ‘environmental sensitivity’ map which was developed for the East Midlands Region during the first phase of research; 2. to compile aggregate end-use suitability maps for the East Midland Region; and 3. to hold a stakeholder consultation exercise and dissemination seminars. Each of these was met within the agreed timeframe. The environmental sensitivity map information and associated attributes have been made available on the internet via the BGS ‘Minerals information online’ web GIS for the East Midlands Region (www.mineralsuk.com/web_gis). Accommodating these data in a web GIS environment has entailed some compromises on data resolution and system functionality. A methodology has been developed to integrate a range of aggregate technical property data. This can be used to summarise the distribution of aggregate resources suitable for particular end-uses. These summary technical data are useful in communicating issues of variable aggregate quality and economic value to non-technical stakeholders in the mineral planning process. Availability of appropriate technical property data for different aggregate resources across a wide geographical area is critical in developing these maps. Feedback from an extensive consultation and dissemination exercise has generally been very positive. Two critiques by independent consultants of the environmental sensitivity map were also undertaken. These were deemed an important aspect of the consultation process. Stakeholders raised several issues. There were some concerns about updating and maintenance of asset data and about the lack of social information. In addition, some fundamental issues of approach (particularly asset weighting) raised in the previous phase of this research resurfaced during this consultation. Environmental sensitivity mapping will be carried out for the whole of England by the BGS in the near future. The data will be made available online as each region becomes available. It is anticipated that the mineral GISs for all regions of England (except London) will be completed by December 2005. New datasets may be added to the environmental sensitivity layer as they become available. The research into end-use suitability maps will be carried on by the BGS under its Minerals Programme, with the support of co-funding where possible. The project team continue to welcome feedback and criticism of this research

HadISDH: an updateable land surface specific humidity product for climate monitoring

HadISDH is a near-global land surface specific humidity monitoring product providing monthly means from 1973 onwards over large-scale grids. Presented herein to 2012, annual updates are anticipated. HadISDH is an update to the land component of HadCRUH, utilising the global high-resolution land surface station product HadISD as a basis. HadISD, in turn, uses an updated version of NOAA's Integrated Surface Database. Intensive automated quality control has been undertaken at the individual observation level, as part of HadISD processing. The data have been subsequently run through the pairwise homogenisation algorithm developed for NCDC's US Historical Climatology Network monthly temperature product. For the first time, uncertainty estimates are provided at the grid-box spatial scale and monthly timescale. HadISDH is in good agreement with existing land surface humidity products in periods of overlap, and with both land air and sea surface temperature estimates. Widespread moistening is shown over the 1973–2012 period. The largest moistening signals are over the tropics with drying over the subtropics, supporting other evidence of an intensified hydrological cycle over recent years. Moistening is detectable with high (95%) confidence over large-scale averages for the globe, Northern Hemisphere and tropics, with trends of 0.089 (0.080 to 0.098) g kg−1 per decade, 0.086 (0.075 to 0.097) g kg−1 per decade and 0.133 (0.119 to 0.148) g kg−1 per decade, respectively. These changes are outside the uncertainty range for the large-scale average which is dominated by the spatial coverage component; station and grid-box sampling uncertainty is essentially negligible on large scales. A very small moistening (0.013 (−0.005 to 0.031) g kg−1 per decade) is found in the Southern Hemisphere, but it is not significantly different from zero and uncertainty is large. When globally averaged, 1998 is the moistest year since monitoring began in 1973, closely followed by 2010, two strong El Niño years. The period in between is relatively flat, concurring with previous findings of decreasing relative humidity over land

ALTERED PHOSPHORYLATION STATUS, PHOSPHOLIPID-METABOLISM AND GLUCONEOGENESIS IN THE HOST LIVER OF RATS WITH PROSTATE-CANCER - A P-31 MAGNETIC-RESONANCE SPECTROSCOPY STUDY

31P magnetic resonance spectroscopy (MRS) in vivo and in vitro was used to study modulation of host liver (HL) metabolism in rats bearing the MAT-LyLu variant of the Dunning prostate tumour. Animals were inoculated either with 10(6) or 10(7) MAT-LyLu cells, or with saline to serve as controls. Carcass weight in tumour-bearing (TB) animals decreased despite similar food and water intake in both groups. Absence of metastatic tumour cells from HL of all TB animals was confirmed by histological examination. Twenty-one days after inoculation, 31P MRS showed a 2.5-fold increase in [Pi]/[ATP] ratios in HL in vivo (P < 0.001) which was confirmed by 31P MRS of liver extracts in vitro (P < 0.005). Phosphodiester to ATP ratios were significantly increased (P < 0.05) in HL in vivo, but absolute PDE levels were similar in both groups. Phosphomonoester to ATP ratios did not change, although absolute phosphomonoester levels in HL were reduced by -41% (not significant). In HL extracts in vitro, sharp reductions in the levels of glucose-6-phosphate (P < 0.05), fructose-6-phosphate (P = 0.05), phosphocholine (P < 0.001), glycerophosphocholine (P < 0.001), and glycerophosphoethanolamine (P < 0.001) were observed. Electron microscopy revealed increased amounts and altered distribution of rough endoplasmic reticulum in HL. These findings show that experimental prostate cancer significantly affects hepatic phosphorylation status, phospholipid metabolism, and gluconeogenesis in the host animal, and demonstrate the value of combined MRS in vivo and in vitro in monitoring HL metabolism in cancer

A class of elementary particle models without any adjustable real parameters

Conventional particle theories such as the Standard Model have a number of freely adjustable coupling constants and mass parameters, depending on the symmetry algebra of the local gauge group and the representations chosen for the spinor and scalar fields. There seems to be no physical principle to determine these parameters as long as they stay within certain domains dictated by the renormalization group. Here however, reasons are given to demand that, when gravity is coupled to the system, local conformal invariance should be a spontaneously broken exact symmetry. The argument has to do with the requirement that black holes obey a complementarity principle relating ingoing observers to outside observers, or equivalently, initial states to final states. This condition fixes all parameters, including masses and the cosmological constant. We suspect that only examples can be found where these are all of order one in Planck units, but the values depend on the algebra chosen. This paper combines findings reported in two previous preprints, and puts these in a clearer perspective by shifting the emphasis towards the implications for particle models.Comment: 28 pages (incl. title page), no figure

Entanglement of two-mode Bose-Einstein condensates

We investigate the entaglement characteristics of two general bimodal Bose-Einstein condensates - a pair of tunnel-coupled Bose-Einstein condensates and the atom-molecule Bose-Einstein condensate. We argue that the entanglement is only physically meaningful if the system is viewed as a bipartite system, where the subsystems are the two modes. The indistinguishibility of the particles in the condensate means that the atomic constituents are physically inaccessible and thus the degree of entanglement between individual particles, unlike the entanglement between the modes, is not experimentally relevant so long as the particles remain in the condensed state. We calculate the entanglement between the modes for the exact ground state of the two bimodal condensates and consider the dynamics of the entanglement in the tunnel-coupled case.Comment: 11 pages, 8 figures, submitted to Physical Review A, to be presented at the third UQ Mathematical Physics workshop, Oct. 4-6; changes made in response to referee comment

The mass-to-light ratio of rich star clusters

We point out a strong time-evolution of the mass-to-light conversion factor eta commonly used to estimate masses of unresolved star clusters from observed cluster spectro-photometric measures. We present a series of gas-dynamical models coupled with the Cambridge stellar evolution tracks to compute line-of-sight velocity dispersions and half-light radii weighted by the luminosity. We explore a range of initial conditions, varying in turn the cluster mass and/or density, and the stellar population's IMF. We find that eta, and hence the estimated cluster mass, may increase by factors as large as 3 over time-scales of 50 million years. We apply these results to an hypothetic cluster mass distribution function (d.f.) and show that the d.f. shape may be strongly affected at the low-mass end by this effect. Fitting truncated isothermal (Michie-King) models to the projected light profile leads to over-estimates of the concentration parameter c of delta c ~ 0.3 compared to the same functional fit applied to the projected mass density.Comment: 6 pages, 2 figures, to appear in the proceedings of the "Young massive star clusters", Granada, Spain, September 200

Anisotropic distribution functions for spherical galaxies

A method is presented for finding anisotropic distribution functions for stellar systems with known, spherically symmetric, densities, which depends only on the two classical integrals of the energy and the magnitude of the angular momentum. It requires the density to be expressed as a sum of products of functions of the potential and of the radial coordinate. The solution corresponding to this type of density is in turn a sum of products of functions of the energy and of the magnitude of the angular momentum. The products of the density and its radial and transverse velocity dispersions can be also expressed as a sum of products of functions of the potential and of the radial coordinate. Several examples are given, including some of new anisotropic distribution functions. This device can be extended further to the related problem of finding two-integral distribution functions for axisymmetric galaxies.Comment: 5 figure

How spiking neurons give rise to a temporal-feature map

A temporal-feature map is a topographic neuronal representation of temporal attributes of phenomena or objects that occur in the outside world. We explain the evolution of such maps by means of a spike-based Hebbian learning rule in conjunction with a presynaptically unspecific contribution in that, if a synapse changes, then all other synapses connected to the same axon change by a small fraction as well. The learning equation is solved for the case of an array of Poisson neurons. We discuss the evolution of a temporal-feature map and the synchronization of the single cells’ synaptic structures, in dependence upon the strength of presynaptic unspecific learning. We also give an upper bound for the magnitude of the presynaptic interaction by estimating its impact on the noise level of synaptic growth. Finally, we compare the results with those obtained from a learning equation for nonlinear neurons and show that synaptic structure formation may profit from the nonlinearity