443 research outputs found
CDM, Feedback and the Hubble Sequence
We have performed TreeSPH simulations of galaxy formation in a standard LCDM
cosmology, including effects of star formation, energetic stellar feedback
processes and a meta-galactic UV field, and obtain a mix of disk, lenticular
and elliptical galaxies. The disk galaxies are deficient in angular momentum by
only about a factor of two compared to observed disk galaxies. The stellar
disks have approximately exponential surface density profiles, and those of the
bulges range from exponential to r^{1/4}, as observed. The bulge-to-disk ratios
of the disk galaxies are consistent with observations and likewise are their
integrated B-V colours, which have been calculated using stellar population
synthesis techniques. Furthermore, we can match the observed I-band
Tully-Fisher (TF) relation, provided that the mass-to-light ratio of disk
galaxies, (M/L_I), is about 0.8. The ellipticals and lenticulars have
approximately r^{1/4} stellar surface density profiles, are dominated by
non-disklike kinematics and flattened due to non-isotropic stellar velocity
distributions, again consistent with observations.Comment: 6 pages, incl. 4 figs. To appear in the proceedings of the
EuroConference "The Evolution of Galaxies: II - Basic Building Blocks", Ile
de La Reunion (France), 16-21 October 2001 (Slightly updated version). A much
more comprehensive paper about this work with links to pictures of some of
the galaxies can be found at http://babbage.sissa.it/abs/astro-ph/020436
Chemical Blocking of Zinc Ions in CNS Increases Neuronal Damage Following Traumatic Brain Injury (TBI) in Mice
Traumatic brain injury (TBI) is one of the leading causes of disability and death among young people. Although much is already known about secondary brain damage the full range of brain tissue responses to TBI remains to be elucidated. A population of neurons located in cerebral areas associated with higher cognitive functions harbours a vesicular zinc pool co-localized with glutamate. This zinc enriched pool of synaptic vesicles has been hypothesized to take part in the injurious signalling cascade that follows pathological conditions such as seizures, ischemia and traumatic brain injury. Pathological release of excess zinc ions from pre-synaptic vesicles has been suggested to mediate cell damage/death to postsynaptic neurons.In order to substantiate the influence of vesicular zinc ions on TBI, we designed a study in which damage and zinc movements were analysed in several different ways. Twenty-four hours after TBI ZnT3-KO mice (mice without vesicular zinc) were compared to littermate Wild Type (WT) mice (mice with vesicular zinc) with regard to histopathology. Furthermore, in order to evaluate a possible neuro-protective dimension of chemical blocking of vesicular zinc, we treated lesioned mice with either DEDTC or selenite. Our study revealed that chemical blocking of vesicular zinc ions, either by chelation with DEDTC or accumulation in zinc-selenium nanocrystals, worsened the effects on the aftermath of TBI in the WT mice by increasing the number of necrotic and apoptotic cells within the first 24 hours after TBI, when compared to those of chemically untreated WT mice.ZnT3-KO mice revealed more damage after TBI compared to WT controls. Following treatment with DEDTC or selenium an increase in the number of both dead and apoptotic cells were seen in the controls within the first 24 hours after TBI while the degree of damage in the ZnT3-KO mice remained largely unchanged. Further analyses revealed that the damage development in the two mouse strains was almost identical after either zinc chelation or zinc complexion therapy
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EML Surface Air Sampling Program, 1990--1993 data
Measurements of the concentrations of specific atmospheric radionuclides in air filter samples collected for the Environmental Measurements Laboratory`s Surface Air Sampling Program (SASP) during 1990--1993, with the exception of April 1993, indicate that anthropogenic radionuclides, in both hemispheres, were at or below the lower limits of detection for the sampling and analytical techniques that were used to collect and measure them. The occasional detection of {sup 137}Cs in some air filter samples may have resulted from resuspension of previously deposited debris. Following the April 6, 1993 accident and release of radionuclides into the atmosphere at a reprocessing plant in the Tomsk-7 military nuclear complex located 16 km north of the Siberian city of Tomsk, Russia, weekly air filter samples from Barrow, Alaska; Thule, Greenland and Moosonee, Canada were selected for special analyses. The naturally occurring radioisotopes that the authors measure, {sup 7}Be and {sup 210}Pb, continue to be detected in most air filter samples. Variations in the annual mean concentrations of {sup 7}Be at many of the sites appear to result primarily from changes in the atmospheric production rate of this cosmogenic radionuclide. Short-term variations in the concentrations of {sup 7}Be and {sup 210}Pb continued to be observed at many sites at which weekly air filter samples were analyzed. The monthly gross gamma-ray activity and the monthly mean surface air concentrations of {sup 7}Be, {sup 95}Zr, {sup 137}Cs, {sup 144}Ce, and {sup 210}Pb measured at sampling sites in SASP during 1990--1993 are presented. The weekly mean surface air concentrations of {sup 7}Be, {sup 95}Zr, {sup 137}Cs, {sup 144}Ce, and {sup 210}Pb for samples collected during 1990--1993 are given for 17 sites
Distances for Weighted Transition Systems: Games and Properties
We develop a general framework for reasoning about distances between
transition systems with quantitative information. Taking as starting point an
arbitrary distance on system traces, we show how this leads to natural
definitions of a linear and a branching distance on states of such a transition
system. We show that our framework generalizes and unifies a large variety of
previously considered system distances, and we develop some general properties
of our distances. We also show that if the trace distance admits a recursive
characterization, then the corresponding branching distance can be obtained as
a least fixed point to a similar recursive characterization. The central tool
in our work is a theory of infinite path-building games with quantitative
objectives.Comment: In Proceedings QAPL 2011, arXiv:1107.074
Non-Thermal Dark Matter, High Energy Cosmic Rays and Late-Decaying Particles From Inflationary Quantum Fluctuations
It has been suggested that the origin of cosmic rays above the GZK limit
might be explained by the decay of particles, X, with mass of the order of
10^{12} GeV. Generation of heavy particles from inflationary quantum
fluctuations is a prime candidate for the origin of the decaying X particles.
It has also been suggested that the problem of non-singular galactic halos
might be explained if dark matter originates non-thermally from the decay of
particles, Y, such that there is a free-streaming length of the order of
0.1Mpc. Here we explore the possibility that quantum fluctuations might account
for the Y particles as well as the X particles. For the case of non-thermal
WIMP dark matter with unsuppressed weak interactions we find that there is a
general problem with deuterium photo-dissociation, disfavouring WIMP dark
matter candidates. For the case of more general dark matter particles, which
may have little or no interaction with conventional matter, we discuss the
conditions under which X and Y scalars or fermions can account for non-thermal
dark matter and cosmic rays. For the case where X and Y scalars are
simultaneously produced, we show that galactic halos are likely to have a
dynamically significant component of X scalar cold dark matter in addition to
the dominant non-thermal dark matter component.Comment: 18 Pages, LaTeX. Substantially revised with corrected WIMP
cross-section
Sparse Decomposition and Modeling of Anatomical Shape Variation
Recent advances in statistics have spawned powerful methods for regression and data decomposition that promote sparsity, a property that facilitates interpretation of the results. Sparse models use a small subset of the available variables and may perform as well or better than their full counterparts if constructed carefully. In most medical applications, models are required to have both good statistical performance and a relevant clinical interpretation to be of value. Morphometry of the corpus callosum is one illustrative example. This paper presents a method for relating spatial features to clinical outcome data. A set of parsimonious variables is extracted using sparse principal component analysis, producing simple yet characteristic features. The relation of these variables with clinical data is then established using a regression model. The result may be visualized as patterns of anatomical variation related to clinical outcome. In the present application, landmark-based shape data of the corpus callosum is analyzed in relation to age, gender, and clinical tests of walking speed and verbal fluency. To put the data-driven sparse principal component method into perspective, we consider two alternative techniques, one where features are derived using a model-based wavelet approach, and one where the original variables are regressed directly on the outcome
Merger Histories in Warm Dark Matter Structure Formation Scenario
Observations on galactic scales seem to be in contradiction with recent high
resolution N-body simulations. This so-called cold dark matter (CDM) crisis has
been addressed in several ways, ranging from a change in fundamental physics by
introducing self-interacting cold dark matter particles to a tuning of complex
astrophysical processes such as global and/or local feedback. All these efforts
attempt to soften density profiles and reduce the abundance of satellites in
simulated galaxy halos. In this paper, we explore a somewhat different approach
which consists of filtering the dark matter power spectrum on small scales,
thereby altering the formation history of low mass objects. The physical
motivation for damping these fluctuations lies in the possibility that the dark
matter particles have a different nature i.e. are warm (WDM) rather than cold.
We show that this leads to some interesting new results in terms of the merger
history and large-scale distribution of low mass halos, as compared to the
standard CDM scenario. However, WDM does not appear to be the ultimate
solution, in the sense that it is not able to fully solve the CDM crisis, even
though one of the main drawbacks, namely the abundance of satellites, can be
remedied. Indeed, the cuspiness of the halo profiles still persists, at all
redshifts, and for all halos and sub-halos that we investigated. Despite the
persistence of the cuspiness problem of DM halos, WDM seems to be still worth
taking seriously, as it alleviates the problems of overabundant sub-structures
in galactic halos and possibly the lack of angular momentum of simulated disk
galaxies. WDM also lessens the need to invoke strong feedback to solve these
problems, and may provide a natural explanation of the clustering properties
and ages of dwarfs.Comment: 11 pages, 17 figures, MNRAS submitted, high-res figures can be found
at http://www-thphys.physics.ox.ac.uk/users/AlexanderKnebe/publications.html,
replaced with accepted version (warmon masses corrected!
The UK market for energy service contracts in 2014â2015
This paper provides an overview of the UK market for energy service contracts in 2014 and highlights the growing role of intermediaries. Using information from secondary literature and interviews, it identifies the businesses offering energy service contracts, the sectors and organisations that are purchasing those contracts, the types of contract that are available, the areas of market growth and the reasons for that growth. The paper finds that the UK market is relatively large, highly diverse, concentrated in particular sectors and types of site and overwhelmingly focused upon established technologies with high rates of return. A major driver is the emergence of procurement frameworks for energy service contracts in the public sector. These act as intermediaries between clients and contractors, thereby lowering transaction costs and facilitating learning. The market is struggling to become established in commercial offices, largely as a result of split incentives, and is unlikely to develop further in this sector without different business models, tenancy arrangements and policy initiatives. Overall, the paper concludes that energy service contracts can play an important role in the transition to a low-carbon economy, especially when supported by intermediaries, but their potential is still limited by high transaction costs
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