4,143 research outputs found
Factors affecting protein synthesis in vitro in rabbit reticulocytes
Rabbit reticulocytes in vitro rapidly incorporate labeled amino acids into their proteins. The process is accelerated by the plasma of every mammal investigated and also by extracts of normal erythrocytes, rabbit reticulocytes, liver, spleen, and yeast (1). We have described two sets of stimulating factors: one of these sets consists of certain amino acids (1), the other of fructose-amino acids in liver (2-4). The latter set is ineffective without the addition of iron to the reaction medium. The effect of iron has been referred to in preceding publications (2-5), but without detail. After the necessity of adding iron was recognized, in order to obtain a maximal rate of protein synthesis the reaction mixture was improved further by adding to it certain substances which depend upon added iron for their effect. These increased the effect of plasma. Eventually the total (potential as well as actual) accelerating effects of plasma and liver extract were accounted for by known substances. This led to the devising of a reaction mixture formula in which the amino acid incorporation is about five times as fast as that observed when the cells are incubated in saline
Two Jovian-Mass Planets in Earthlike Orbits
We report the discovery of two new planets: a 1.94 M_Jup planet in a 1.8-year
orbit of HD 5319, and a 2.51 M_Jup planet in a 1.1-year orbit of HD 75898. The
measured eccentricities are 0.12 for HD 5319 b and 0.10 for HD 75898 b, and
Markov Chain Monte Carlo simulations based on derived orbital parameters
indicate that the radial velocities of both stars are consistent with circular
planet orbits. With low eccentricity and 1 < a < 2 AU, our new planets have
orbits similar to terrestrial planets in the solar system. The radial velocity
residuals of both stars have significant trends, likely arising from substellar
or low-mass stellar companions.Comment: 32 pages, including 11 figures and 5 tables. Accepted by Ap
A Hot Uranus Orbiting the Super Metal-rich Star HD77338 and the Metallicity - Mass Connection
We announce the discovery of a low-mass planet orbiting the super metal-rich
K0V star HD77338 as part of our on-going Calan-Hertfordshire Extrasolar Planet
Search. The best fit planet solution has an orbital period of 5.7361\pm0.0015
days and with a radial velocity semi-amplitude of only 5.96\pm1.74 m/s, we find
a minimum mass of 15.9+4.7-5.3 Me. The best fit eccentricity from this solution
is 0.09+0.25-0.09, and we find agreement for this data set using a Bayesian
analysis and a periodogram analysis. We measure a metallicity for the star of
+0.35\pm0.06 dex, whereas another recent work (Trevisan et al. 2011) finds
+0.47\pm0.05 dex. Thus HD77338b is one of the most metal-rich planet host stars
known and the most metal-rich star hosting a sub-Neptune mass planet. We
searched for a transit signature of HD77338b but none was detected. We also
highlight an emerging trend where metallicity and mass seem to correlate at
very low masses, a discovery that would be in agreement with the core accretion
model of planet formation. The trend appears to show that for Neptune-mass
planets and below, higher masses are preferred when the host star is more
metal-rich. Also a lower boundary is apparent in the super metal-rich regime
where there are no very low-mass planets yet discovered in comparison to the
sub-solar metallicity regime. A Monte Carlo analysis shows that this, low-mass
planet desert, is statistically significant with the current sample of 36
planets at around the 4.5\sigma\ level. In addition, results from Kepler
strengthen the claim for this paucity of the lowest-mass planets in super
metal-rich systems. Finally, this discovery adds to the growing population of
low-mass planets around low-mass and metal-rich stars and shows that very
low-mass planets can now be discovered with a relatively small number of data
points using stable instrumentation.Comment: 25 pages, 15 figures, 5 tables, accepted for publication in Ap
A phytolith supported biosphere-hydrosphere predictive model for Southern Ethiopia:Insights into paleoenvironmental changes and human landscape preferences since the last glacial maximum
During the past 25 ka, southern Ethiopia has undergone tremendous climatic changes, from dry and relatively cold during the Last Glacial Maximum (LGM, 25–18 ka) to the African Humid Period (AHP, 15–5 ka), and back to present-day dry conditions. As a contribution to better understand the effects of climate change on vegetation and lakes, we here present a new Predictive Vegetation Model that is linked with a Lake Balance Model and available vegetation-proxy records from southern Ethiopia including a new phytolith record from the Chew Bahir basin. We constructed a detailed paleo-landcover map of southern Ethiopia during the LGM, AHP (with and without influence of the Congo Air Boundary) and the modern-day potential natural landcover. Compared to today, we observe a 15–20% reduction in moisture availability during the LGM with widespread open landscapes and only few remaining forest refugia. We identify 25–40% increased moisture availability during the AHP with prevailing forests in the mid-altitudes and indications that modern anthropogenic landcover change has affected the water balance. In comparison with existing archaeological records, we find that human occupations tend to correspond with open landscapes during the late Pleistocene and Holocene in southern Ethiopia
The ground state of the carbon atom in strong magnetic fields
The ground and a few excited states of the carbon atom in external uniform
magnetic fields are calculated by means of our 2D mesh Hartree-Fock method for
field strengths ranging from zero up to 2.35 10^9 T. With increasing field
strength the ground state undergoes six transitions involving seven different
electronic configurations which belong to three groups with different spin
projections S_z=-1,-2,-3. For weak fields the ground state configuration arises
from the field-free 1s^2 2s^2 2p_0 2p_{-1}, S_z=-1 configuration. With
increasing field strength the ground state involves the four S_z=-2
configurations 1s^22s2p_0 2p_{-1}2p_{+1}, 1s^22s2p_0 2p_{-1}3d_{-2}, 1s^22p_0
2p_{-1}3d_{-2}4f_{-3} and 1s^22p_{-1}3d_{-2}4f_{-3}5g_{-4}, followed by the two
fully spin polarized S_z=-3 configurations 1s2p_02p_{-1}3d_{-2}4f_{-3}5g_{-4}
and 1s2p_{-1}3d_{-2}4f_{-3}5g_{-4}6h_{-5}. The last configuration forms the
ground state of the carbon atom in the high field regime \gamma>18.664. The
above series of ground state configurations is extracted from the results of
numerical calculations for more than twenty electronic configurations selected
due to some general energetical arguments.Comment: 6 figures,acc. Phys.Rev.
EXPRES. II. Searching for Planets Around Active Stars: A Case Study of HD 101501
By controlling instrumental errors to below 10 cm/s, the EXtreme PREcision
Spectrograph (EXPRES) allows for a more insightful study of photospheric
velocities that can mask weak Keplerian signals. Gaussian Processes (GP) have
become a standard tool for modeling correlated noise in radial velocity
datasets. While GPs are constrained and motivated by physical properties of the
star, in some cases they are still flexible enough to absorb unresolved
Keplerian signals. We apply GP regression to EXPRES radial velocity
measurements of the 3.5 Gyr old chromospherically active Sun-like star, HD
101501. We obtain tight constraints on the stellar rotation period and the
evolution of spot distributions using 28 seasons of ground-based photometry, as
well as recent data. Light curve inversion was carried out on both
photometry datasets to reveal the spot distribution and spot evolution
timescales on the star. We find that the m/s rms radial velocity
variations in HD 101501 are well-modeled with a GP stellar activity model
without planets, yielding a residual rms scatter of 45 cm/s. We carry out
simulations, injecting and recovering signals with the GP framework, to
demonstrate that high-cadence observations are required to use GPs most
efficiently to detect low-mass planets around active stars like HD 101501.
Sparse sampling prevents GPs from learning the correlated noise structure and
can allow it to absorb prospective Keplerian signals. We quantify the moderate
to high-cadence monitoring that provides the necessary information to
disentangle photospheric features using GPs and to detect planets around active
stars.Comment: 25 pages, 16 figures, accepted to A
EXPRES IV: Two Additional Planets Orbiting Coronae Borealis Reveal Uncommon System Architecture
Thousands of exoplanet detections have been made over the last twenty-five
years using Doppler observations, transit photometry, direct imaging, and
astrometry. Each of these methods is sensitive to different ranges of orbital
separations and planetary radii (or masses). This makes it difficult to fully
characterize exoplanet architectures and to place our solar system in context
with the wealth of discoveries that have been made. Here, we use the EXtreme
PREcision Spectrograph (EXPRES) to reveal planets in previously undetectable
regions of the mass-period parameter space for the star Coronae
Borealis. We add two new planets to the previously known system with one hot
Jupiter in a 39-day orbit and a warm super-Neptune in a 102-day orbit. The new
detections include a temperate Neptune planet ( M)
in a 281.4-day orbit and a hot super-Earth ( M) in a
12.95-day orbit. This result shows that details of planetary system
architectures have been hiding just below our previous detection limits; this
signals an exciting era for the next generation of extreme precision
spectrographs.Comment: Accepted to AJ; 20 pages, 13 figures, 5 Table
The N2K Consortium. II. A Transiting Hot Saturn Around HD 149026 With a Large Dense Core
Doppler measurements from Subaru and Keck have revealed radial velocity
variations in the V=8.15, G0IV star HD 149026 consistent with a Saturn-Mass
planet in a 2.8766 day orbit. Photometric observations at Fairborn Observatory
have detected three complete transit events with depths of 0.003 mag at the
predicted times of conjunction. HD 149026 is now the second brightest star with
a transiting extrasolar planet. The mass of the star, based on interpolation of
stellar evolutionary models, is 1.3 +/- 0.1 solar masses; together with the
Doppler amplitude, K=43.3 m s^-1, we derive a planet mass Msin(i)=0.36 Mjup,
and orbital radius of 0.042 AU. HD 149026 is chromospherically inactive and
metal-rich with spectroscopically derived [Fe/H]=+0.36, Teff=6147 K, log g=4.26
and vsin(i)=6.0 km s^-1. Based on Teff and the stellar luminosity of 2.72 Lsun,
we derive a stellar radius of 1.45 Rsun. Modeling of the three photometric
transits provides an orbital inclination of 85.3 +/- 1.0 degrees and (including
the uncertainty in the stellar radius) a planet radius of 0.725 +/- 0.05 Rjup.
Models for this planet mass and radius suggest the presence of a ~67 Mearth
core composed of elements heavier than hydrogen and helium. This substantial
planet core would be difficult to construct by gravitational instability.Comment: 25 pages, 5 figures, accepted by the Astrophysical Journa
HAT-P-11b: A Super-Neptune Planet Transiting a Bright K Star in the Kepler Field
We report on the discovery of HAT-P-11b, the smallest radius transiting
extrasolar planet (TEP) discovered from the ground, and the first hot Neptune
discovered to date by transit searches. HAT-P-11b orbits the bright (V=9.587)
and metal rich ([Fe=H] = +0.31 +/- 0.05) K4 dwarf star GSC 03561-02092 with P =
4.8878162 +/- 0.0000071 days and produces a transit signal with depth of 4.2
mmag. We present a global analysis of the available photometric and
radial-velocity data that result in stellar and planetary parameters, with
simultaneous treatment of systematic variations. The planet, like its near-twin
GJ 436b, is somewhat larger than Neptune (17Mearth, 3.8Rearth) both in mass Mp
= 0.081 +/- 0.009 MJ (25.8 +/- 2.9 Mearth) and radius Rp = 0.422 +/- 0.014 RJ
(4.73 +/- 0.16 Rearth). HAT-P-11b orbits in an eccentric orbit with e = 0.198
+/- 0.046 and omega = 355.2 +/- 17.3, causing a reflex motion of its parent
star with amplitude 11.6 +/- 1.2 m/s, a challenging detection due to the high
level of chromospheric activity of the parent star. Our ephemeris for the
transit events is Tc = 2454605.89132 +/- 0.00032 (BJD), with duration 0.0957
+/- 0.0012 d, and secondary eclipse epoch of 2454608.96 +/- 0.15 d (BJD). The
basic stellar parameters of the host star are M* = 0.809+0.020-0.027 Msun, R* =
0.752 +/- 0.021 Rsun and Teff = 4780 +/- 50 K. Importantly, HAT-P-11 will lie
on one of the detectors of the forthcoming Kepler mission. We discuss an
interesting constraint on the eccentricity of the system by the transit light
curve and stellar parameters. We also present a blend analysis, that for the
first time treats the case of a blended transiting hot Jupiter mimicing a
transiting hot Neptune, and proves that HAT-P-11b is not such a blend.Comment: Accepted for publication in ApJ, 24 pages, 14 figures, 6 tables. All
RV data presented in this versio
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