Agent mediation and management of virtual communities: a redefinition of the traditional community concept

The paper explores the evolution of the concept of community in the light of computer mediated immersive virtual environments. The traditional concept of community has become strained in its attempts to capture the evolving virtual community. We believe the concept of the virtual community is of paramount importance and examine the extent to which this is being redefined to cater for it. We examine the management and mediation of such an environment and specifically the social process associated with the cohabited users. We advocate the use of multi-agent systems in delivering this functionalit

The micro-optical ring electrode Part 2 : theory for the transport limited, steady-state photocurrent.

The micro-optical ring electrode (MORE) is a photoelectrochemical device based on a ring microelectrode that uses the insulating material interior to the ring electrode as a light guide. In this paper, we derive asymptotic analytical expressions for the steady-state, transport limited photocurrent generated at MOREs with thin microrings ((ring inner radius)/(ring outer radius) values > 0.99) for two general types of photoelectrochemical system (a) the PE (photophysical-electrochemical) system, wherein the photoexcited species itself is directly detected on the ring; and (b) the PCE (photophysical-chemical-electrochemical) system, wherein the photoexcited species undergoes a homogeneous electron transfer reaction prior to electrochemical detection. The expressions are generated by exploiting the properties of discontinuous integrals of Bessel functions to solve the diffusion equation for the photogenerated electroactive species both inside and outside the beam. The resultant solutions are then matched at the beam surface. The expressions themselves are used to design experimental protocols that allow for the complete characterization of the photoelectrochemical kinetics of a system and are tested by using them to interpret the results of a MORE study of the photoelectrochemical behaviour of the Ru(bipy)(3)(2+)/Fe3+ photosensitiser/ quenching agent system. The value of the Stern-Volmer constant for the quenching of photoexcited Ru(bipy)(3)(2+) by Fe obtained (0.36 m(3) mol(-1)) compares favourably with the value obtained from fluorescence measurements (0.9 m(3) mol(-1)). (c) 2006 Elsevier B.V. All rights reserved

AMPHIBIAN DISTRIBUTION IN THE GEORGIA SEA ISLANDS: IMPLICATIONS FROM THE PAST AND FOR THE FUTURE

We summarized amphibian distributions for 12 coastal islands in Georgia, USA. Occurrence among islands was correlated with life history traits, habitats, island size, distance to other islands, and island geological age. Species’ distributions were determined from published literature. Island sizes and vegetation types were derived from 2011 Georgia Department of Natural Resources habitat maps, which included both federal and state vegetation classification systems. Species occurring on more islands tended to have greater total reproductive output (i.e., life span >4 years, and annual egg production >1,000 eggs) and adults had tolerance of brackish environs. Larger islands had great­er area of freshwater wetlands, predominantly short hydroperiod (<6 months). Species tied to long hydroperiod wetlands (>6 months) were more restricted in their distribution across islands. Overall, larger islands supported more species, but the correlation was weaker for geologically younger Ho­locene islands (age <11,000 years). While Euclidean distance between islands does not necessarily preclude inter-island dispersal, inhospitable habitat for amphibians (brackish tidal marshes and creeks interspersed with wide rivers) suggests that inter-island dispersal is very limited. The paucity of recent occurrence data for amphibians in this dynamic coastal region, let alone standardized annual moni­toring data, hinders efforts to model species’ vulnerability in a region susceptible to sea level rise and development pressure. The most common survey method, standardized amphibian vocal surveys, will detect Anuran reproductive efforts, but is unlikely to ascertain if breeding was successful or to detect salamanders. While it will not replace actual population data, consideration of critical life-history traits and breeding habitat availability can be used to direct management to support long-term species per­sistence in changing environs. Even common amphibians in coastal conservation areas of Georgia are vulnerable to increasing population isolation caused by unsuitable habitat

Stellar kinematics from the symmetron fifth force in the Milky Way disk

It has been shown that the presence of nonminimally coupled scalar fields giving rise to a fifth force can noticeably alter dynamics on galactic scales. Such a fifth force must be screened in the Solar System but if unscreened it can have similar observational effects as a component of nonbaryonic matter. We consider this possibility in the context of the vertical motions of local stars in the Milky Way disk by reframing a methodology used to measure the local density of dark matter. By attempting to measure the properties of the symmetron field required to support vertical velocities we can test it as a theory of modified gravity and understand the behavior of screened scalar fields in galaxies. In particular, this relatively simple setup allows the symmetron field profile to be solved for model parameters where the equation of motion becomes highly nonlinear and difficult to solve in other contexts. We update the existing Solar System constraints for this scenario and find a region of parameter space not already excluded that can explain the vertical motions of local stars out to heights of 1 kpc. At larger heights the force due to the symmetron field profile exhibits a characteristic turn over which would allow the model to be distinguished from a dark matter halo

Respiratory challenge MRI: practical aspects

Respiratory challenge MRI is the modification of arterial oxygen (PaO2) and/or carbon dioxide (PaCO2) concentration to induce a change in cerebral function or metabolism which is then measured by MRI. Alterations in arterial gas concentrations can lead to profound changes in cerebral haemodynamics which can be studied using a variety of MRI sequences. Whilst such experiments may provide a wealth of information, conducting them can be complex and challenging. In this paper we review the rationale for respiratory challenge MRI including the effects of oxygen and carbon dioxide on the cerebral circulation. We also discuss the planning, equipment, monitoring and techniques that have been used to undertake these experiments. We finally propose some recommendations in this evolving area for conducting these experiments to enhance data quality and comparison between techniques

Refinement of the standard halo model for dark matter searches in light of the Gaia Sausage

Predicting signals in experiments to directly detect dark matter (DM) requires a form for the local DM velocity distribution. Hitherto, the standard halo model (SHM), in which velocities are isotropic and follow a truncated Gaussian law, has performed this job. New data, however, suggest that a substantial fraction of our stellar halo lies in a strongly radially anisotropic population, the "Gaia sausage." Inspired by this recent discovery, we introduce an updated DM halo model, the SHM++, which includes a "sausage" component, thus better describing the known features of our Galaxy. The SHM++ is a simple analytic model with five parameters: the circular speed, local escape speed, and local DM density, which we update to be consistent with the latest data, and two new parameters: the anisotropy and the density of DM in the sausage. The impact of the SHM++ on signal models for weakly interacting massive particles (WIMPs) and axions is rather modest since the multiple changes and updates have competing effects. In particular, this means that the older exclusion limits derived for WIMPS are still reasonably accurate. However, changes do occur for directional detectors, which have sensitivity to the full three-dimensional velocity distribution

Spatial and temporal resolution of global protein synthesis during HSV infection using bioorthogonal precursors and click chemistry

We used pulse-labeling with the methionine analogue homopropargylglycine (HPG) to investigate spatiotemporal aspects of protein synthesis during herpes simplex virus (HSV) infection. In vivo incorporation of HPG enables subsequent selective coupling of fluorochrome-capture reagents to newly synthesised proteins. We demonstrate that HPG labeling had no effect on cell viability, on accumulation of test early or late viral proteins, or on overall virus yields. HPG pulse-labeling followed by SDS-PAGE analysis confirmed incorporation into newly synthesised proteins, while parallel processing by in situ cycloaddition revealed new insight into spatiotemporal aspects of protein localisation during infection. A striking feature was the rapid accumulation of newly synthesised proteins not only in a general nuclear pattern but additionally in newly forming sub-compartments represented by small discrete foci. These newly synthesised protein domains (NPDs) were similar in size and morphology to PML domains but were more numerous, and whereas PML domains were progressively disrupted, NPDs were progressively induced and persisted. Immediate-early proteins ICP4 and ICP0 were excluded from NPDs, but using an ICP0 mutant defective in PML disruption, we show a clear spatial relationship between NPDs and PML domains with NPDs frequently forming immediately adjacent and co-joining persisting PML domains. Further analysis of location of the chaperone Hsc70 demonstrated that while NPDs formed early in infection without overt Hsc70 recruitment, later in infection Hsc70 showed pronounced recruitment frequently in a coat-like fashion around NPDs. Moreover, while ICP4 and ICP0 were excluded from NPDs, ICP22 showed selective recruitment. Our data indicate that NPDs represent early recruitment of host and viral de novo translated protein to distinct structural entities which are precursors to the previously described VICE domains involved in protein quality control in the nucleus, and reveal new features from which we propose spatially linked platforms of newly synthesised protein processing after nuclear import