356 research outputs found
Mantle Degassing Lifetimes through Galactic Time and the Maximum Age Stagnant-lid Rocky Exoplanets can Support Temperate Climates
The ideal exoplanets to search for life are those within a star's habitable
zone. However, even within the habitable zone planets can still develop
uninhabitable climate states. Sustaining a temperate climate over geologic
(Gyr) timescales requires a planet contain sufficient internal energy to
power a planetary-scale carbon cycle. A major component of a rocky planet's
energy budget is the heat produced by the decay of radioactive elements,
especially K, Th, U and U. As the planet ages
and these elements decay, this radiogenic energy source dwindles. Here we
estimate the probability distribution of the amount of these heat producing
elements (HPEs) that enter into rocky exoplanets through Galactic history, by
combining the system-to-system variation seen in stellar abundance data with
the results from Galactic chemical evolution models. Using these distributions,
we perform Monte-Carlo thermal evolution models that maximize the mantle
cooling rate. This allows us to create a pessimistic estimate of lifetime a
rocky, stagnant-lid exoplanet can support a global carbon cycle and temperate
climate as a function of its mass and when it in Galactic history. We apply
this framework to a sample of 17 likely rocky exoplanets with measured ages, 7
of which we predict are likely to be actively degassing today despite our
pessimistic assumptions. For the remaining planets, including those orbiting
TRAPPIST-1, we cannot confidently assume they currently contain sufficient
internal heat to support mantle degassing at a rate sufficient to sustain a
global carbon cycle or temperate climate without additional tidal heating or
undergoing plate tectonics.Comment: Accepted to ApJ Letter
Wearable activity technology and action-planning (WATAAP) to promote physical activity in cancer survivors: Randomised controlled trial protocol
Background/Objective: Colorectal and gynecologic cancer survivors are at cardiovascular risk due to comorbidities and sedentary behaviour, warranting a feasible intervention to increase physical activity. The Health Action Process Approach (HAPA) is a promising theoretical frame-work for health behaviour change, and wearable physical activity trackers offer a novel means of self-monitoring physical activity for cancer survivors.
Method: Sixty-eight survivors of colorectal and gynecologic cancer will be randomised into 12- week intervention and control groups. Intervention group participants will receive: a Fitbit AltaTM to monitor physical activity, HAPA-based group sessions, booklet, and support phone-call. Participants in the control group will only receive the HAPA-based booklet. Physical activity (using accelerometers), blood pressure, BMI, and HAPA constructs will be assessed at baseline, 12-weeks (post-intervention) and 24-weeks (follow-up). Data analysis will use the Group x Time interaction from a General Linear Mixed Model analysis.
Conclusions: Physical activity interventions that are acceptable and have robust theoretical underpinnings show promise for improving the health of cancer survivors
Searching for a Light Stop at the Tevatron
We describe a method to help the search for a light stop squark [M(stop) +
M(LSP) < M(top)] at the Fermilab Tevatron. Traditional search methods rely upon
a series of stringent background-reducing cuts which, unfortunately, leave very
few signal events given the present data set. To avoid this difficulty, we
instead suggest using a milder set of cuts, combined with a "superweight,"
whose purpose is to discriminate between signal and background events. The
superweight consists of a sum of terms, each of which are either zero or one.
The terms are assigned event-by-event depending upon the values of various
observables. We suggest a method for choosing the observables as well as the
criteria used to assign the values such that the superweight is "large" for the
supersymmetric signal and "small" for the standard model background. For
illustration, we mainly consider the detection of stops coming from top decay,
making our analysis especially relevant to the W+2 jets top sample.Comment: 45 pages, revtex, 15 figures included. Final version, as will appear
in Phys. Rev. D. Contains an expanded introduction plus a few additional
reference
Protection against alcohol-induced neuronal and cognitive damage by the PPARγ receptor agonist pioglitazone
Binge alcohol drinking has emerged as a typical phenomenon in young people. This pattern of drinking, repeatedly leading to extremely high blood and brain alcohol levels and intoxication is associated with severe risks of neurodegeneration and cognitive damage. Mechanisms involved in excitotoxicity and neuroinflammation are pivotal elements in alcohol-induced neurotoxicity. Evidence has demonstrated that PPARγ receptor activation shows anti-inflammatory and neuroprotective properties. Here we examine whether treatment with the PPARγ agonist pioglitazone is beneficial in counteracting neurodegeneration, neuroinflammation and cognitive damage produced by binge alcohol intoxication. Adult Wistar rats were subjected to a 4-day binge intoxication procedure, which is commonly used to model excessive alcohol consumption in humans. Across the 4-day period, pioglitazone (0, 30, 60mg/kg) was administered orally twice daily at 12-h intervals. Degenerative cells were detected by fluoro-jade B (FJ-B) immunostaining in brain regions where expression of pro-inflammatory cytokines was also determined. The effects of pioglitazone on cognitive function were assessed in an operant reversal learning task and the Morris water maze task. Binge alcohol exposure produced selective neuronal degeneration in the hippocampal dentate gyrus and the adjacent entorhinal cortex. Pioglitazone reduced FJ-B positive cells in both regions and prevented alcohol-induced expression of pro-inflammatory cytokines. Pioglitazone also rescued alcohol-impaired reversal learning in the operant task and spatial learning deficits in the Morris water maze. These findings demonstrate that activation of PPARγ protects against neuronal and cognitive degeneration elicited by binge alcohol exposure. The protective effect of PPARγ agonist appears to be linked to inhibition of pro-inflammatory cytokines
The Transit Light Curve Project. X. A Christmas Transit of HD 17156b
Photometry is presented of the Dec. 25, 2007 transit of HD 17156b, which has
the longest orbital period and highest orbital eccentricity of all the known
transiting exoplanets. New measurements of the stellar radial velocity are also
presented. All the data are combined and integrated with stellar-evolutionary
modeling to derive refined system parameters. The planet's mass and radius are
found to be 3.212_{-0.082}^{+0.069} Jupiter masses and 1.023_{-0.055}^{+0.070}
Jupiter radii. The corresponding stellar properties are 1.263_{-0.047}^{+0.035}
solar masses and 1.446_{-0.067}^{+0.099} solar radii. The planet is smaller by
1 sigma than a theoretical solar-composition gas giant with the same mass and
equilibrium temperature, a possible indication of heavy-element enrichment. The
midtransit time is measured to within 1 min, and shows no deviation from a
linear ephemeris (and therefore no evidence for orbital perturbations from
other planets). We provide ephemerides for future transits and superior
conjunctions. There is an 18% chance that the orbital plane is oriented close
enough to edge-on for secondary eclipses to occur at superior conjunction.
Observations of secondary eclipses would reveal the thermal emission spectrum
of a planet that experiences unusually large tidal heating and insolation
variations.Comment: To appear in ApJ [26 pages
Spinons in a Crossed-Chains Model of a 2D Spin Liquid
Using Random Phase Approximation, we show that a crossed-chains model of a
spin-1/2 Heisenberg spins, with frustrated interchain couplings, has a
non-dimerized spin-liquid ground state in 2D, with deconfined spinons as the
elementary excitations. The results are confirmed by a bosonization study,
which shows that the system is an example of a `sliding Luttinger liquid'. In
an external field, the system develops an incommensurate field-induced long
range order with a finite transition temperature.Comment: 4 pages, 3 figures; added references; scaling analysis, preserving
spin rotational invariance, is extended to finite temperatur
Angular Correlations in Top Quark Pair Production and Decay at Hadron Colliders
We show how to observe sizable angular correlations between the decay
products of the top quark and those of the anti-top quark in top quark pair
production and decay at hadron colliders. These correlations result from the
large asymmetry in the rate for producing like-spin versus unlike-spin top
quark pairs provided the appropriate spin axes are used. The effects of new
physics at production or decay on these correlations are briefly discussed.Comment: 34 pages, revtex, including 12 uuencoded postscript figure
Diversity and specificity of orchid mycorrhizal fungi in a leafless epiphytic orchid, Dendrophylax lindenii and the potential role of fungi in shaping its fine-scale distribution
Orchids grow in diverse habitats worldwide with most (approximately 69%) growing on trees as epiphytes. Although orchid mycorrhizal fungi have been identified as potential drivers for terrestrial orchid distribution, the influence of these fungi on the fine-scale distribution of epiphytic orchids is poorly understood. In this study, we investigated the mycorrhizal fungal community and fine-scale distribution of Dendrophylax lindenii, a rare and endangered epiphytic orchid that is leafless when mature. We used amplicon sequencing to investigate the composition of orchid mycorrhizal fungi in the roots of 39 D. lindenii individuals in their natural habitat, the swamps of Florida. We compared the orchid mycorrhizal fungi of D. lindenii to those of co-occurring epiphytic orchids, as well as to the orchid mycorrhizal fungal communities of bark from potential host trees, with and without D. lindenii. Our results show that D. lindenii has a high specificity for a single Ceratobasidium species, which is widely distributed on phorophytes and detected in both wet and dry periods in the orchid’s habitat. This Ceratobasidium species was mostly absent or only recorded in low frequency in the roots of co-occurring epiphytic orchids. Phylogenetic analysis documented that this Ceratobasidium was conspecific with the strain that is used to germinate D. lindenii ex-situ. However, our findings suggest that laboratory germinated adult D. lindenii transplanted into the field had lower read abundances of this Ceratobasidium compared to naturally occurring plants. These findings suggest that this orchid mycorrhizal fungus may play a significant role in the fine-scale distribution of naturally occurring D. lindenii
The First Extrasolar Planet Discovered with a New Generation High Throughput Doppler Instrument
We report the detection of the first extrasolar planet, ET-1 (HD 102195b),
using the Exoplanet Tracker (ET), a new generation Doppler instrument. The
planet orbits HD 102195, a young star with solar metallicity that may be part
of the local association. The planet imparts radial velocity variability to the
star with a semiamplitude of m s and a period of 4.11 days.
The planetary minimum mass () is .Comment: 42 pages, 11 figures and 5 tables, Accepted for publication in Ap
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