High Energy Gamma-rays from Globular Clusters

It is expected that specific globular clusters can contain up to a hundred of millisecond pulsars. These pulsars can accelerate leptons at the shock waves originated in collisions of the pulsar winds and/or inside the pulsar magnetospheres. Energetic leptons diffuse gradually through the globular cluster comptonizing stellar and microwave background radiation. We calculate the GeV-TeV $\gamma$-ray spectra for different models of injection of leptons and parameters of the globular clusters assuming reasonable, of the order of 1%, efficiency of energy conversion from the pulsar winds into the relativistic leptons. It is concluded that leptons accelerated in the globular cluster cores should produce well localized $\gamma$-ray sources which are concentric with these globular clusters. The results are shown for four specific globular clusters (47 Tuc, Ter 5, M13, and M15), in which significant population of millisecond pulsars have been already discovered. We argue that the best candidates, which might be potentially detected by the present Cherenkov telescopes and the planned satellite telescopes (AGILE, GLAST), are 47 Tuc on the southern hemisphere, and M13 on the northern hemisphere. We conclude that detection (or non-detection) of GeV-TeV $\gamma$-ray emission from GCs by these instruments put important constraints on the models of acceleration of leptons by millisecond pulsars.Comment: 12 pages, 10 figures, 1 table, accepted to MNRA

On the interpretation of responses from hydrogel based distributed microbend fibre optic sensors

This contribution discuses the physicochemical aspects associated with the response of hydrogel based distributed fibre optic microbend sensors to different humidity conditions. We explain that the swelling of the hydrogel which leads to the observed change in the OTDR signal should be attributed to a change in the water potential of the hydrogel being at an equilibrium with the water potential of its immediate physicochemical environment. Since the water potential in the hydrogel matrix is the result of several equilibration processes from multiple species that are interacting in the immediate environment surrounding the sensor, the observed fibre deformation should be attributed to all of the components of the chemical potential. The work draws attention to the necessity to fully characterize the hydrogel system used in each sensing application. The analysis is of relevance to all types of fibre optic biosensors that utilize hydrogels in the measurement process

On the interpretation of responses from hydrogel based distributed microbend fibre optic sensors

This contribution discuses the physicochemical aspects associated with the response of hydrogel based distributed fibre optic microbend sensors to different humidity conditions. We explain that the swelling of the hydrogel which leads to the observed change in the OTDR signal should be attributed to a change in the water potential of the hydrogel being at an equilibrium with the water potential of its immediate physicochemical environment. Since the water potential in the hydrogel matrix is the result of several equilibration processes from multiple species that are interacting in the immediate environment surrounding the sensor, the observed fibre deformation should be attributed to all of the components of the chemical potential. The work draws attention to the necessity to fully characterize the hydrogel system used in each sensing application. The analysis is of relevance to all types of fibre optic biosensors that utilize hydrogels in the measurement process

The formation of ultra-compact dwarf galaxies and nucleated dwarf galaxies

Ultra compact dwarf galaxies (UCDs) have similar properties as massive globular clusters or the nuclei of nucleated galaxies. Recent observations suggesting a high dark matter content and a steep spatial distribution within groups and clusters provide new clues as to their origins. We perform high-resolution N-body / smoothed particle hydrodynamics simulations designed to elucidate two possible formation mechanisms for these systems: the merging of globular clusters in the centre of a dark matter halo, or the massively stripped remnant of a nucleated galaxy. Both models produce density profiles as well as the half light radii that can fit the observational constraints. However, we show that the first scenario results to UCDs that are underluminous and contain no dark matter. This is because the sinking process ejects most of the dark matter particles from the halo centre. Stripped nuclei give a more promising explanation, especially if the nuclei form via the sinking of gas, funneled down inner galactic bars, since this process enhances the central dark matter content. Even when the entire disk is tidally stripped away, the nucleus stays intact and can remain dark matter dominated even after severe stripping. Total galaxy disruption beyond the nuclei only occurs on certain orbits and depends on the amount of dissipation during nuclei formation. By comparing the total disruption of CDM subhaloes in a cluster potential we demonstrate that this model also leads to the observed spatial distribution of UCDs which can be tested in more detail with larger data sets.Comment: 8 pages, 8 figures, final version accepted for publication in MNRA

Detection of solvents using a distributed fibre optic sensor

A fibre optic sensor that is capable of distributed detection of liquid solvents is presented. Sensor interrogation using optical time domain reflectometry (OTDR) provides the capability of locating solvent spills to a precision of ±2 m over a total sensor length that may extend to 20 km

Modeling the disruption of the globular cluster Pal5 by Galactic tides

In order to understand the extended massive tidal tails of the globular cluster Pal5, its very low mass and velocity dispersion, and its size, which is much larger than the theoretical tidal radius, we performed more than 1000 N-body simulations. Tidal shocks at disk crossings near perigalacticon dominate the evolution of extended low-concentration clusters, resulting in massive tidal tails and often in a quick destruction of the cluster. The overlarge size of Pal5 can be explained as the result of an expansion following the heating induced by the last strong disk shock ~150Myr ago. The models can reproduce the low observed velocity dispersion and the relative fractions of stars in the tails and between the inner and outer parts of the tails. The tidal tails of Pal5 show substantial structure not seen in our simulations. We argue that this structure is probably caused by Galactic substructure, such as giant molecular clouds, spiral arms, and dark-matter clumps. Clusters initially larger than their theoretical tidal limit remain so, because, after being shocked, they settle into a new equilibrium near apogalacticon, where they are unaffected by the perigalactic tidal field. This implies that, contrary to previous wisdom, globular clusters on eccentric orbits may well remain super-tidally limited and hence vulnerable to strong disk shocks, which dominate their evolution until destruction. Our simulations unambiguously predict the destruction of Pal5 at its next disk crossing in \~110Myr. This corresponds to only 1% of the cluster lifetime, suggesting that many more similar systems could once have populated the inner parts of the Milky Way, but have been transformed into debris streams by the Galactic tidal field. (Abridged)Comment: accepted for publication in The Astronomical Journa

Robert Hadow : a case study of an appeaser

Historians differ over the origins of Britain's policy of appeasement, and many analyses concentrate on the objectives of policy using the growth of overseas obligations or more recent historical markers such as the Japanese invasion of Manchuria. The approach of this thesis involves relating appeasement to the personal beliefs and decisions of those responsible for foreign policy. By pin-pointing Robert Hadow, a First Secretary in the Foreign Office, as an example of an appeaser, such an approach demonstrates how intelligent and capable men in Britain fell victim to a policy which, in retrospect, appears blind and irrational. An examination of Hadow's fear of war, bias against bolshevism, and sympathy for the German minority in Czechoslovakia is made in this thesis through detailed research of Foreign Office despatches and Hadow's reports, memoranda, and personal correspondence. Much of this hitherto unpublished material sheds new light on the course of events from the collapse of the Kredit Anstalt in Austria to the outbreak of World War II. By following the course of Hadow's career during this period, this thesis seeks to explain the mentality that produced the foreign policy followed by Britain in the 1930s

Subcellular fractionation of primary chronic lymphocytic leukemia cells to monitor nuclear/ cytoplasmic protein trafficking

Nuclear export of macromolecules is often deregulated in cancer cells. Tumor suppressor proteins, such as p53, can be rendered inactive due to aberrant cellular localization disrupting their mechanism of action. The survival of chronic lymphocytic leukaemia (CLL) cells, among other cancer cells, is assisted by the deregulation of nuclear to cytoplasmic shuttling, at least in part through deregulation of the transport receptor XPO1 and the constitutive activation of PI3K-mediated signaling pathways. It is essential to understand the role of individual proteins in the context of their intracellular location to gain a deeper understanding of the role of such proteins in the pathobiology of the disease. Furthermore, identifying processes that underlie cell stimulation and the mechanism of action of specific pharmacological inhibitors, in the context of subcellular protein trafficking, will provide a more comprehensive understanding of the mechanism of action. The protocol described here enables the optimization and subsequent efficient generation of nuclear and cytoplasmic fractions from primary chronic lymphocytic leukemia cells. These fractions can be used to determine changes in protein trafficking between the nuclear and cytoplasmic fractions upon cell stimulation and drug treatment. The data can be quantified and presented in parallel with immunofluorescent images, thus providing robust and quantifiable data

Is the Fast Evolution Scenario for Virialized Compact Groups Really Compelling? The Role of a Dark Massive Group Halo

We report on results of N-body simulations aimed at testing the hypothesis that galaxies in X-ray emitting (i.e., virialized) Compact Groups are not tidally stripped when they are embedded in a common, massive, quiescent dark matter halo. To disentangle the effects of interactions from spurious effects due to an incorrect choice of the initial galaxy model configurations, these have been chosen to be tidally-limited King spheres, representing systems in quasi-equilibrium within the tidal field of the halo. The potential of the halo has been assumed to be frozen and the braking due to dynamical friction neglected. Our results confirm the hypothesis of low rates of tidal stripping and suggest a scenario for virialized Compact Group evolution in their quiescent phases with only very moderate tidally induced galaxy evolution can be generally expected. This implies the group stability, provided that the dynamical friction timescales in these systems are not much shorter than the Hubble time. We discuss briefly this possibility, in particular taking account of the similarity between the velocity dispersions of a typical virialized Compact Groups and the internal velocity dispersion of typical member galaxies. A number of puzzling observational data on Compact Groups can be easily explained in this framework. Other observations would be better understood as the result of enhanced merging activity in the proto-group environment, leading to virialized Compact Group formation through mergers of lower mass halos, as predicted by hierarchical scenarios of structure formation.Comment: 18 pages, 1 postscript file, 2 tables, to be published in ApJLet