2,711 research outputs found
Tracer Measurements in Growing Sea Ice Support Convective Gravity Drainage Parameterizations
Gravity drainage is the dominant process redistributing solutes in growing sea ice. Modeling gravity drainage is therefore necessary to predict physical and biogeochemical variables in sea ice. We evaluate seven gravity drainage parameterizations, spanning the range of approaches in the literature, using tracer measurements in a sea ice growth experiment. Artificial sea ice is grown to around 17 cm thickness in a new experimental facility, the Roland von Glasow airâseaâice chamber. We use NaCl (present in the water initially) and rhodamine (injected into the water after 10 cm of sea ice growth) as independent tracers of brine dynamics. We measure vertical profiles of bulk salinity in situ, as well as bulk salinity and rhodamine in discrete samples taken at the end of the experiment. Convective parameterizations that diagnose gravity drainage using Rayleigh numbers outperform a simpler convective parameterization and diffusive parameterizations when compared to observations. This study is the first to numerically model solutes decoupled from salinity using convective gravity drainage parameterizations. Our results show that (1) convective, Rayleigh numberâbased parameterizations are our most accurate and precise tool for predicting sea ice bulk salinity; and (2) these parameterizations can be generalized to brine dynamics parameterizations, and hence can predict the dynamics of any solute in growing sea ic
A physically motivated and empirically calibrated method to measure effective temperature, metallicity, and Ti abundance of M dwarfs
The ability to perform detailed chemical analysis of Sun-like F-, G-, and
K-type stars is a powerful tool with many applications including studying the
chemical evolution of the Galaxy and constraining planet formation theories.
Unfortunately, complications in modeling cooler stellar atmospheres hinders
similar analysis of M-dwarf stars. Empirically-calibrated methods to measure M
dwarf metallicity from moderate-resolution spectra are currently limited to
measuring overall metallicity and rely on astrophysical abundance correlations
in stellar populations. We present a new, empirical calibration of synthetic M
dwarf spectra that can be used to infer effective temperature, Fe abundance,
and Ti abundance. We obtained high-resolution (R~25,000), Y-band (~1 micron)
spectra of 29 M dwarfs with NIRSPEC on Keck II. Using the PHOENIX stellar
atmosphere modeling code (version 15.5), we generated a grid of synthetic
spectra covering a range of temperatures, metallicities, and
alpha-enhancements. From our observed and synthetic spectra, we measured the
equivalent widths of multiple Fe I and Ti I lines and a temperature-sensitive
index based on the FeH bandhead. We used abundances measured from
widely-separated solar-type companions to empirically calibrate transformations
to the observed indices and equivalent widths that force agreement with the
models. Our calibration achieves precisions in Teff, [Fe/H], and [Ti/Fe] of 60
K, 0.1 dex, and 0.05 dex, respectively and is calibrated for 3200 K < Teff <
4100 K, -0.7 < [Fe/H] < +0.3, and -0.05 < [Ti/Fe] < +0.3. This work is a step
toward detailed chemical analysis of M dwarfs at a similar precision achieved
for FGK stars.Comment: accepted for publication in ApJ, all synthetic spectra available at
http://people.bu.edu/mveyette/phoenix
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High-Throughput Drug Screening Identifies a Potent Wnt Inhibitor that Promotes Airway Basal Stem Cell Homeostasis.
Mechanisms underpinning airway epithelial homeostatic maintenance and ways to prevent its dysregulation remain elusive. Herein, we identify that ÎČ-catenin phosphorylated at Y489 (p-ÎČ-cateninY489) emerges during human squamous lung cancer progression. This led us to develop a model of airway basal stem cell (ABSC) hyperproliferation by driving Wnt/ÎČ-catenin signaling, resulting in a morphology that resembles premalignant lesions and loss of ciliated cell differentiation. To identify small molecules that could reverse this process, we performed a high-throughput drug screen for inhibitors of Wnt/ÎČ-catenin signaling. Our studies unveil Wnt inhibitor compound 1 (WIC1), which suppresses T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) activity, reduces ABSC proliferation, induces ciliated cell differentiation, and decreases nuclear p-ÎČ-cateninY489. Collectively, our work elucidates a dysregulated Wnt/p-ÎČ-cateninY489 axis in lung premalignancy that can be modeled in vitro and identifies a Wnt/ÎČ-catenin inhibitor that promotes airway homeostasis. WIC1 may therefore serve as a tool compound in regenerative medicine studies with implications for restoring normal airway homeostasis after injury
Radio Observations of HD 80606 Near Planetary Periastron
This paper reports Very Large Array observations at 325 and 1425 MHz (90cm
and 20cm) during and near the periastron passage of HD 80606b on 2007 November
20. We obtain flux density limits (3-sigma) of 1.7 mJy and 48 microJy at 325
and 1425 MHz, respectively, equivalent to planetary luminosity limits of 2.3 x
10^{24} erg/s and 2.7 x 10^{23} erg/s. These are well above the Jovian value
(at 40 MHz) of 2 x 10^{18} erg/s. The motivation for these observations was
that the planetary magnetospheric emission is driven by a stellar
wind-planetary magnetosphere interaction so that the planetary luminosity would
be elevated. Near periastron, HD 80606b might be as much as 3000 times more
luminous than Jupiter. Recent transit observations of HD 80606b provide
stringent constraints on the planetary mass and radius, and, because of the
planet's highly eccentric orbit, its rotation period is likely to be
"pseudo-synchronized" to its orbital period, allowing a robust estimate of the
former. We are able to make robust estimates of the emission frequency of the
planetary magnetospheric emission and find it to be around 60--90 MHz. We
compare HD 80606b to other high-eccentricity systems and assess the detection
possibilities for both near-term and more distant future systems. Of the known
high eccentricity planets, only HD 80606b is likely to be detectable, as HD
20782B b and HD 4113b are both likely to have weaker magnetic field strengths.
Both the forthcoming "EVLA low band" system and the Low Frequency Array may be
able to improve upon our limits for HD 80606b, and do so at a more optimum
frequency. If the low-frequency component of the Square Kilometre Array
(SKA-lo) and a future lunar radio array are able to approach their thermal
noise limits, they should be able to detect an HD 80606b-like planet, unless
the planet's luminosity increases by substantially less than a factor of 3000.Comment: 9 pages; accepted for publication in A
The spatial organization of multinational firms
Using six years of firm-level data covering 224 regions of the enlarged European Union, we evaluate the importance to a firm of locating its activities (production, headquarters, R&D, logistics and sales) close together. We find that, after controlling for regional characteristics, being closely located to a previous investment positively affects firm location choice. However, the impact of distance is dependent on the type of investment (production or service). The impact dies out faster for service activities. Finally, we show that a surprisingly positive effect comes from locating a new production plant close to an existing production investment, but in another country
On the discovery of doubly-magic Ni
The paper reports on the first observation of doubly-magic Nickel-48 in an
experimental at the SISSI/LISE3 facility of GANIL. Four Nickel-48 isotopes were
identified. In addition, roughly 100 Nickel-49, 50 Iron-45, and 290 Chromium-42
isotopes were observed. This opens the possibility to search for two-proton
emission from these nuclei.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. Let
Lifetime measurements in Co and Co
Lifetimes of the and states in Co and the
state in Co were measured using the recoil distance Doppler
shift and the differential decay curve methods. The nuclei were populated by
multi-nucleon transfer reactions in inverse kinematics. Gamma rays were
measured with the EXOGAM Ge array and the recoiling fragments were fully
identified using the large-acceptance VAMOS spectrometer. The E2 transition
probabilities from the and states to the ground
state could be extracted in Co as well as an upper limit for the
(E2) value in Co. The experimental
results were compared to large-scale shell-model calculations in the and
model spaces, allowing to draw conclusions on the single-particle
or collective nature of the various states.Comment: 8 pages, 8 figures, 1 table, accepted for publication in Physical
Review
L-Arginine promotes gut hormone release and reduces food intake in rodents
Aims: To investigate the anorectic effect of Lâarginine (LâArg) in rodents.
Methods: We investigated the effects of LâArg on food intake, and the role of the anorectic gut hormones glucagonâlike peptideâ1 (GLPâ1) and peptide YY (PYY), the Gâproteinâcoupled receptor family C group 6 member A (GPRC6A) and the vagus nerve in mediating these effects in rodents.
Results: Oral gavage of LâArg reduced food intake in rodents, and chronically reduced cumulative food intake in dietâinduced obese mice. Lack of the GPRC6A in mice and subdiaphragmatic vagal deafferentation in rats did not influence these anorectic effects. LâArg stimulated GLPâ1 and PYY release in vitro and in vivo. Pharmacological blockade of GLPâ1 and PYY receptors did not influence the anorectic effect of LâArg. LâArgâmediated PYY release modulated net ion transport across the gut mucosa. Intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) administration of LâArg suppressed food intake in rats.
Conclusions: LâArg reduced food intake and stimulated gut hormone release in rodents. The anorectic effect of LâArg is unlikely to be mediated by GLPâ1 and PYY, does not require GPRC6A signalling and is not mediated via the vagus. I.c.v. and i.p. administration of LâArg suppressed food intake in rats, suggesting that LâArg may act on the brain to influence food intake. Further work is required to determine the mechanisms by which LâArg suppresses food intake and its utility in the treatment of obesity
Low Temperature Opacities
Previous computations of low temperature Rosseland and Planck mean opacities
from Alexander & Ferguson (1994) are updated and expanded. The new computations
include a more complete equation of state with more grain species and updated
optical constants. Grains are now explicitly included in thermal equilibrium in
the equation of state calculation, which allows for a much wider range of grain
compositions to be accurately included than was previously the case. The
inclusion of high temperature condensates such as AlO and CaTiO
significantly affects the total opacity over a narrow range of temperatures
before the appearance of the first silicate grains.
The new opacity tables are tabulated for temperatures ranging from 30000 K to
500 K with gas densities from 10 g cm to 10 g cm.
Comparisons with previous Rosseland mean opacity calculations are discussed. At
high temperatures, the agreement with OPAL and Opacity Project is quite good.
Comparisons at lower temperatures are more divergent as a result of differences
in molecular and grain physics included in different calculations. The
computation of Planck mean opacities performed with the opacity sampling method
are shown to require a very large number of opacity sampling wavelength points;
previously published results obtained with fewer wavelength points are shown to
be significantly in error. Methods for requesting or obtaining the new tables
are provided.Comment: 39 pages with 12 figures. To be published in ApJ, April 200
Enabling the Reuse of Stored Model Transformations Through Annotations
International audienceWith the increasing adoption of MDE, model transformations , one of its core concepts together with metamodeling, stand out as a valuable asset. Therefore, a mechanism to annotate and store existing model transformations appears as a critical need for their efficient exploitation and reuse. Unfortunately, although several reuse mechanisms have been proposed for software artifacts in general and models in particular , none of them is specially tailored to the domain of model transformations. In order to fill this gap, we present here such a mechanism. Our approach is composed by two elements 1) a new DSL specially conceived for describing model transformations in terms of their functional and non-functional properties 2) a semi-automatic process for annotating and querying (repositories of) model transformations using as criteria the properties of our DSL. We validate the feasibility of our approach through a prototype implementation that integrates our approach in a GitHub repository
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