4,093 research outputs found
The age of the oldest Open Clusters
We determine ages of 71 old Open Clusters by a two-step method: we use
main-squence fitting to 10 selected clusters, in order to obtain their
distances, and derive their ages from comparison with our own isochrones used
before for Globular Clusters. We then calibrate the morphological age indicator
delta(V), which can be obtained for all remaining clusters, in terms of age and
metallicity. Particular care is taken to ensure consistency in the whole
procedure. The resulting Open Cluster ages connect well to our previous
Globular Cluster results. From the Open Cluster sample, as well as from the
combined sample, questions regarding the formation process of Galactic
components are addressed. The age of the oldest open clusters (NGC6791 and
Be17) is of the order of 10 Gyr. We determine a delay by 2.0+-1.5 Gyr between
the start of the halo and thin disk formation, whereas thin and thick disk
started to form approximately at the same time. We do not find any significant
age-metallicity relationship for the open cluster sample. The cumulative age
distribution of the whole open cluster sample shows a moderately significant
(~2sigma level) departure from the predictions for an exponentially declining
dissolution rate with timescale of 2.5 Gyr. The cumulative age distribution
does not show any trend with galactocentric distance, but the clusters with
larger height to the Galactic plane have an excess of objects between 2-4 and 6
Gyr with respect to their counterpart closer to the plane of the Galaxy.Comment: Astronomy & Astrophysics, in pres
The Housing and Support Needs of Older People with Visual Impairment
Visual impairment is one of the most prevalent anddisabling conditions among older people, and yet verylittle research has been conducted that could inform thedevelopment of appropriate public services. In order toaddress this deficiency, Thomas Pocklington Trust fundedresearch to examine the housing and support needs of 400visually impaired people aged over 55.The study found that:? There is little professional recognition, or offers of help andadvice for the anxiety, depression, and sense of profoundloss that people experience with late onset of visualimpairment.? Both blind and partially sighted people need timely andholistic assessment, rehabilitation, affordable equipment andregular review.? People with sight loss do not wish to leave their homes.Home is the epicentre of a mental map that assistsorientation and continuity following sight loss.? Social isolation and lack of human contact are majorproblems for people with sight loss.? People with sight loss have poor knowledge of supportgroups, community services and/or specialist housingoptions for older people with visual impairment. Visual impairment is one of the most prevalent anddisabling conditions among older people, and yet verylittle research has been conducted that could inform thedevelopment of appropriate public services. In order toaddress this deficiency, Thomas Pocklington Trust fundedresearch to examine the housing and support needs of 400visually impaired people aged over 55.The study found that:? There is little professional recognition, or offers of help andadvice for the anxiety, depression, and sense of profoundloss that people experience with late onset of visualimpairment.? Both blind and partially sighted people need timely andholistic assessment, rehabilitation, affordable equipment andregular review.? People with sight loss do not wish to leave their homes.Home is the epicentre of a mental map that assistsorientation and continuity following sight loss.? Social isolation and lack of human contact are majorproblems for people with sight loss.? People with sight loss have poor knowledge of supportgroups, community services and/or specialist housingoptions for older people with visual impairment
Selected topics in Planck-scale physics
We review a few topics in Planck-scale physics, with emphasis on possible
manifestations in relatively low energy. The selected topics include quantum
fluctuations of spacetime, their cumulative effects, uncertainties in
energy-momentum measurements, and low energy quantum-gravity phenomenology. The
focus is on quantum-gravity-induced uncertainties in some observable
quantities. We consider four possible ways to probe Planck-scale physics
experimentally: 1. looking for energy-dependent spreads in the arrival time of
photons of the same energy from GRBs; 2. examining spacetime
fluctuation-induced phase incoherence of light from extragalactic sources; 3.
detecting spacetime foam with laser-based interferometry techniques; 4.
understanding the threshold anomalies in high energy cosmic ray and gamma ray
events. Some other experiments are briefly discussed. We show how some physics
behind black holes, simple clocks, simple computers, and the holographic
principle is related to Planck-scale physics. We also discuss a formulation of
the Dirac equation as a difference equation on a discrete Planck-scale
spacetime lattice, and a possible interplay between Planck-scale and
Hubble-scale physics encoded in the cosmological constant (dark energy).Comment: 31 pages, 1 figure; minor changes; to appear in Mod. Phys. Lett. A as
a Brief Revie
A general computer program for the Bell detection loophole
The difference between ideal experiments to test Bell's weak nonlocality and
the real experiments leads to loopholes. Ideal experiments involve either
inequalities (Bell) or equalities (Greenberger, Horne, Zeilinger). Every real
experiment has its own critical inequalities, which are almost all more
complicated than the corresponding ideal inequalities and equalities. If one of
these critical inequalities is violated, then the detection loophole is closed,
with no further assumptions. If all the critical inequalities are satisfied,
then it remains open, unless further assumptions are made. The computer program
described here and published on the website
http://www.strings.ph.qmw.ac.uk/QI/main.htm obtains the critical inequalities
for any real experiment, given the number of allowed settings of the angles and
the corresponding possible output signals for a single run. Given all the
necessary conditional probabilities or rates, it tests whether all these
inequalities are satisfied.Comment: 10 pages, no figures. Revised version with additional reference to
Pitowski and Svozi
The impact of systematic uncertainties in stellar parameters on integrated spectra of stellar populations
In this paper we investigate a hitherto unexplored source of potentially
significant error in stellar population synthesis (SPS) models, caused by
systematic uncertainties associated with the three fundamental stellar
atmospheric parameters; effective temperature T_eff, surface gravity g, and
iron abundance [Fe/H]. All SPS models rely on calibrations of T_eff, logg and
[Fe/H] scales, which are implicit in stellar models, isochrones and synthetic
spectra, and are explicitly adopted for empirical spectral libraries. We assess
the effect of a mismatch in scales between isochrones and spectral libraries
(the two key components of SPS models) and quantify the effects on 23 commonly
used diagnostic line indices. We find that typical systematic offsets of 100K
in T_eff, 0.15 dex in [Fe/H] and/or 0.25 dex in logg significantly alter
inferred absolute ages of simple stellar populations (SSPs) and that in some
circumstances, relative ages also change. Offsets in T_eff, logg and [Fe/H]
scales for a scaled-solar SSP produce deviations from the model which can mimic
the effects of altering abundance ratios to non-scaled-solar chemical
compositions, and could also be spuriously interpreted as evidence for a more
complex population, especially when multiple-index or full-SED fitting methods
are used. We stress that the behavior we find can potentially affect any SPS
models, whether using full integrated spectra or fitting functions to determine
line strengths. We present measured offsets in 23 diagnostic line indices and
urge caution in the over-interpretation of line-index data for stellar
populations.Comment: 14 pages, including 4 figures and 3 tables. Accepted for publication
in Ap
Sea turtle nesting in the Ten Thousand Islands of Florida
Loggerhead sea turtles (Caretta caretta) nest in numerous substrate and beach
types within the Ten Thousand Islands (TTl) of southwest Florida. Nesting beach
selection was analyzed on 12 islands within this archipelago. Numerous physical
characteristics were recorded to identify the relatedness of these variables and determine
their importance for nesting beach selection in C. caretta. These variables were chosen
after evaluating the islands, conducting literature searches and soliciting personal
communications. Along transects, data were collected, on the following: height of
canopy, beach width, overall slope (beach slope and slope of offshore approach) and sand
samples analyzed for pH, percentage of water, percentage of organic content, percentage
of carbonate and particle size (8 size classes). Data on ordinal aspect of beaches and
beach length were also recorded and included in the analysis. All of the variables were
analyzed by tree regression, incorporating the nesting data into the analysis. In the TTl,
loggerheads appear to prefer wider beaches (p< 0.001; R2
= 0.56) that inherently have less
slope, and secondarily, wider beaches that have low amounts of carbonate (p< O.00 1). In
addition, C. caretta favors nest sites within or in close proximity to the supra-littoral
vegetation zone of beaches in the TTl (p< 0.001). (86 page document
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