2,474 research outputs found
DASCH Discovery of Large Amplitude ~10-100 Year Variability in K Giants
Here we present the discovery of three unusual long-term variables found in
the Digital Access to a Sky Century at Harvard (DASCH) project, with ~1
magnitude variations in their lightcurves on ~10-100 yr timescales. They are
all spectroscopically identified as K2III giant stars, probably in the thick
disk. Their lightcurves do not match any previously measured for known types of
variable stars, or any theoretical model reported for red giants, and instead
suggest a new dust formation mechanism or the first direct observation of
"short" timescale evolution-driven variability. More theoretical work on the
lithium flash near the Red Giant Branch (RGB) bump and the helium shell
ignition in the lower Asymptotic Giant Branch (AGB), as well as long term
monitoring of K2III thick disk stars is needed.Comment: 6 pages, 3 figures. Accepted for publication in ApJ Letters. Typo
correcte
The co-benefits of biodiversity conservation programmes on wider ecosystem services
While multiple ecosystem service benefits are increasingly emphasised in policy as an outcome for land management, most conservation management and legislation is currently focused on conserving specific species and habitats. These management interventions may provide multiple co-benefits for other ecosystem services but more information is needed on where these synergies occur in order to realise these benefits. In this paper, we use expert data obtained from structured interviews with key stakeholders to examine the perceived impacts of 11 species-specific conservation schemes on wider ecosystem services in Scotland, UK. With some exceptions, impacts were perceived to be mostly positive or neutral, suggesting that there are many potential opportunities when looking to manage for the delivery of multiple ecosystem services. Unsurprisingly, 'wild species diversity' and 'environmental settings' are the ecosystem services perceived to benefit the most from species conservation management. Despite the clear benefits of aligning biodiversity conservation and ecosystem service objectives, many challenges remain and future policy and associated management will need to tackle issues of scale as well as the distribution of costs and benefits
Preparation of Calibration Standards of N1-H Paralytic Shellfish Toxin Analogues by Large-Scale Culture of Cyanobacterium Anabaena circinalis (TA04)
Mouse bioassay is the official testing method to quantify paralytic shellfish toxins (PSTs) in bivalves. A number of alternative analytical methods have been reported. Some methods have been evaluated by a single laboratory validation. Among the different types of methods, chemical analyses are capable of identifying and quantifying the toxins, however a shortage of the necessary calibration standards hampers implementation of the chemical analyses in routine monitoring of PSTs in bivalves. In our present study, we studied preparation of major PST analogues as calibrants by large-scale cultivation of toxic freshwater cyanobacteria Anabaena circinalis TA04. The cells were steadily grown in 10 L bottle for 28 days. The primary N1-H toxins, C1/C2, were produced at a concentration of 1.3 ±0.1 μmol/L. The intracellular and extracellular toxins occupied 80% and 20%, respectively. Over 220 μmol of the toxins was obtained from approximately 200 L of the culture over six months, demonstrating that it is sufficient to prepare saxitoxin analogues. The toxins were chemically converted to six N1-H analogues. Preparation of the analogues was carried out at relatively high yields (50–90%). The results indicate that our preparation method is useful to produce N1-H toxins. In our present study, detailed conditions for preparation of one of the rare N1-H analogues, gonyautoxin-5, were investigated
Phase space geometry in scalar-tensor cosmology
We study the phase space of spatially homogeneous and isotropic cosmology in
general scalar-tensor theories. A reduction to a two-dimensional phase space is
performed when possible-in these situations the phase space is usually a
two-dimensional curved surface embedded in a three-dimensional space and
composed of two sheets attached to each other, possibly with complicated
topology. The results obtained are independent of the choice of the coupling
function of the theory and, in certain situations, also of the potential.Comment: 18 pages, 9 figures, latex, to appear in Ann. Phys. (NY
Orbital Period Determinations for Four SMC Be/X-ray Binaries
We present an optical and X-ray study of four Be/X-ray binaries located in
the Small Magellanic Cloud (SMC). OGLE I-band data of up to 11 years of
semi-continuous monitoring has been analysed for SMC X-2, SXP172 and SXP202B,
providing both a measurement of the orbital period (Porb = 18.62, 68.90, and
229.9 days for the pulsars respectively) and a detailed optical orbital profile
for each pulsar. For SXP172 this has allowed a direct comparison of the optical
and X-ray emission seen through regular RXTE monitoring, revealing that the
X-ray outbursts precede the optical by around 7 days. Recent X-ray studies by
XMM-Newton have identified a new source in the vicinity of SXP15.3 raising
doubt on the identification of the optical counterpart to this X-ray pulsar.
Here we present a discussion of the observations that led to the proposal of
the original counterpart and a detailed optical analysis of the counterpart to
the new X-ray source, identifying a 21.7 d periodicity in the OGLE I-band data.
The optical characteristics of this star are consistent with that of a SMC
Be/X-ray binary. However, this star was rejected as the counterpart to SXP15.3
in previous studies due to the lack of H{\alpha} emission.Comment: Accepted for publication in MNRAS, 11 pages, 17 figure
Highly absorbed X-ray binaries in the Small Magellanic Cloud
Many of the high mass X-ray binaries (HMXRBs) discovered in recent years in
our Galaxy are characterized by a high absorption, most likely intrinsic to the
system, which hampers their detection at the softest X-ray energies. We have
undertaken a search for highly-absorbed X-ray sources in the Small Magellanic
Cloud (SMC) with a systematic analysis of 62 XMM-Newton SMC observations. We
obtained a sample of 30 sources showing evidence for an equivalent hydrogen
column density larger than 3x10^23 cm^-2. Five of these sources are clearly
identified as HMXRBs: four were already known (including three X-ray pulsars)
and one, XMM J005605.8-720012, reported here for the first time. For the
latter, we present optical spectroscopy confirming the association with a Be
star in the SMC. The other sources in our sample have optical counterparts
fainter than magnitude ~16 in the V band, and many of them have possible NIR
counterparts consistent with highly reddened early type stars in the SMC. While
their number is broadly consistent with the expected population of background
highly-absorbed active galactic nuclei, a few of them could be HMXRBs in which
an early type companion is severely reddened by local material.Comment: 10 pages, 4 figures, 4 tables. Accepted for publication by Astronomy
& Astrophysic
Near-infrared counterparts to Chandra X-ray sources toward the Galactic Center. II. Discovery of Wolf-Rayet stars and O supergiants
We present new identifications of infrared counterparts to the population of
hard X-ray sources near the Galactic center detected by the Chandra X-ray
Observatory. We have confirmed 16 new massive stellar counterparts to the X-ray
population, including nitrogen-type (WN) and carbon-type (WC) Wolf-Rayet stars,
and O supergiants. For the majority of these sources, the X-ray photometry is
consistent with thermal emission from plasma having temperatures in the range
of kT=1-8 keV or non-thermal emission having power-law indices in the range of
-1<gamma<3, and X-ray luminosities in the range of Lx~1e32-1e34 erg/s. Several
sources have exhibited X-ray variability of several factors between separate
observations. The X-ray properties are not a ubiquitous feature of single
massive stars but are typical of massive binaries, in which the high-energy
emission is generated by the collision of supersonic winds, or by accretion
onto a compact companion. However, the possibility of intrinsic hard X-ray
generation from single stars cannot be completely ruled out. The spectral
energy distributions of these sources exhibit significant infrared excess,
attributable to free-free emission from ionized stellar winds, supplemented by
hot dust emission in the case of the WC stars. With the exception of one object
located near the outer regions of the Quintuplet cluster, most of the new stars
appear isolated or in loose associations. Seven hydrogen-rich WN and O stars
are concentrated near the Sagittarius B HII region, while other similar stars
and more highly evolved hydrogen-poor WN and WC stars lie scattered within ~50
pc, in projection, of Sagitarrius A West. We discuss various mechanisms capable
of generating the observed X-rays and the implications these stars have for
massive star formation in the Galaxy's Central Molecular Zone.Comment: Accepted to ApJ on December 5, 2009. 61 pages, including 17 figure
From presence to consciousness through virtual reality
Immersive virtual environments can break the deep, everyday connection between where our senses tell us we are and where we are actually located and whom we are with. The concept of 'presence' refers to the phenomenon of behaving and feeling as if we are in the virtual world created by computer displays. In this article, we argue that presence is worthy of study by neuroscientists, and that it might aid the study of perception and consciousness
False Vacuum Inflation with Einstein Gravity
We investigate chaotic inflation models with two scalar fields, such that one
field (the inflaton) rolls while the other is trapped in a false vacuum state.
The false vacuum becomes unstable when the inflaton field falls below some
critical value, and a first or second order transition to the true vacuum
ensues. Particular attention is paid to Linde's second-order `Hybrid
Inflation'; with the false vacuum dominating, inflation differs from the usual
true vacuum case both in its cosmology and in its relation to particle physics.
The spectral index of the adiabatic density perturbation can be very close to
1, or it can be around ten percent higher. The energy scale at the end of
inflation can be anywhere between \,GeV and \,GeV, though
reheating is prompt so the reheat temperature can't be far below
GeV. Topological defects are almost inevitably produced at the end
of inflation, and if the inflationary energy scale is near its upper limit they
can have significant effects.
Because false vacuum inflation occurs with the inflaton field far below the
Planck scale, it is easier to implement in the context of supergravity than
standard chaotic inflation. That the inflaton mass is small compared with the
inflationary Hubble parameter is still a problem for generic supergravity
theories, but remarkably this can be avoided in a natural way for a class of
supergravity models which follow from orbifold compactification of
superstrings. This opens up the prospect of a truly realistic, superstringComment: 37 pages, LaTeX (3 figures available as hard copies only), SUSSEX-AST
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A chronometric exploration of high-resolution ‘sensitive TMS masking’ effects on subjective and objective measures of vision
Transcranial magnetic stimulation (TMS) can induce masking by interfering with ongoing neural activity in early visual cortex. Previous work has explored the chronometry of occipital involvement in vision by using single pulses of TMS with high temporal resolution. However, conventionally TMS intensities have been high and the only measure used to evaluate masking was objective in nature. Recent studies have begun to incorporate subjective measures of vision, alongside objective ones. The current study goes beyond previous work in two regards. First, we explored both objective vision (an orientation discrimination task) and subjective vision (a stimulus visibility rating on a four-point scale), across a wide range of time windows with high temporal resolution. Second, we used a very sensitive TMS-masking paradigm: stimulation was at relatively low TMS intensities, with a figure-8 coil, and the small stimulus was difficult to discriminate already at baseline level. We hypothesized that this should increase the effective temporal resolution of our paradigm. Perhaps for this reason, we are able to report a rather interesting masking curve. Within the classical-masking time window, previously reported to encompass broad SOAs anywhere between 60 and 120 ms, we report not one, but at least two dips in objective performance, with no masking in-between. The subjective measure of vision did not mirror this pattern. These preliminary data from our exploratory design suggest that, with sensitive TMS masking, we might be able to reveal visual processes in early visual cortex previously unreported
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