6,541 research outputs found
The Mass of the Candidate Exoplanet Companion to HD136118 from Hubble Space Telescope Astrometry and High-Precision Radial Velocities
We use Hubble Space Telescope Fine Guidance Sensor astrometry and
high-cadence radial velocities for HD136118 from the HET with archival data
from Lick to determine the complete set of orbital parameters for HD136118b. We
find an orbital inclination for the candidate exoplanet of i_{b} = 163.1 +- 3.0
deg. This establishes the actual mass of the object, M_{b} = 42^{+11}_{-18}
MJup, in contrast to the minimum mass determined from the radial velocity data
only, M_{b}sin{i} ~ 12 MJup. Therefore, the low-mass companion to HD 136118 is
now identified as a likely brown dwarf residing in the "brown dwarf desert".Comment: 35 pages, 12 figures, 10 tables. Accepted for publication in
Astrophysical Journa
Dynamical Instabilities in a two-component Bose condensate in a 1d optical lattice
In this paper we carry out a stability analysis of the Bloch states of a
two-component Bose-Einstein condensate confined to a 1d optical lattice. We
consider two concrete systems: a mixture of two hyperfine states of Rubidium-87
and a mixture of Sodium-23 and Rubidium-87. The former is seen to exhibit
similar phenomena to a single component condensate while the latter also
suffers an instability to phase separation at small Bloch wave vectors. It is
shown that sufficiently deep optical lattices can remove this latter
instability, potentially allowing imiscible cold atoms species to be held in
intimate contact and transported within an experimental system.Comment: 14 Pages, 9 figure
The \u3cem\u3emir-51\u3c/em\u3e Family of MicroRNAs Functions in Diverse Regulatory Pathways in \u3cem\u3eCaenorhbditis elegans\u3c/em\u3e
The mir-51 family of microRNAs (miRNAs) in C. elegans are part of the deeply conserved miR-99/100 family. While loss of all six family members (mir-51-56) in C. elegans results in embryonic lethality, loss of individual mir-51 family members results in a suppression of retarded developmental timing defects associated with the loss of alg-1. The mechanism of this suppression of developmental timing defects is unknown. To address this, we characterized the function of the mir-51 family in the developmental timing pathway. We performed genetic analysis and determined that mir-51 family members regulate the developmental timing pathway in the L2 stage upstream of hbl-1. Loss of the mir-51 family member, mir-52, suppressed retarded developmental timing defects associated with the loss of let-7 family members and lin-46. Enhancement of precocious defects was observed for mutations in lin-14, hbl-1, and mir-48(ve33), but not later acting developmental timing genes. Interestingly, mir-51 family members showed genetic interactions with additional miRNA-regulated pathways, which are regulated by the let-7 and mir-35 family miRNAs, lsy-6, miR-240/786, and miR-1. Loss of mir-52 likely does not suppress miRNA-regulated pathways through an increase in miRNA biogenesis or miRNA activity. We found no increase in the levels of four mature miRNAs, let-7, miR-58, miR-62 or miR-244, in mir-52 or mir-52/53/54/55/56 mutant worms. In addition, we observed no increase in the activity of ectopic lsy-6 in the repression of a downstream target in uterine cells in worms that lack mir-52. We propose that the mir-51 family functions broadly through the regulation of multiple targets, which have not yet been identified, in diverse regulatory pathways in C. elegans
Quantitative test of a quantum theory for the resistive transition in a superconducting single-walled carbon nanotube bundle
The phenomenon of superconductivity depends on the coherence of the phase of
the superconducting order parameter. The resistive transition in
quasi-one-dimensional (quasi-1D) superconductors is broad because of a large
phase fluctuation. We show that the resistive transition of a superconducting
single-walled carbon nanotube bundle is in quantitative agreement with the
Langer-Ambegaokar-McCumber-Halperin (LAMH) theory. We also demonstrate that the
resistive transition below T^*_c = 0.89T_c0 is simply proportional to exp
[-(3\beta T^*_c/T)(1-T/T^*_c)^3/2], where the barrier height has the same form
as that predicted by the LAMH theory and T_c0 is the mean field superconducting
transition temperature.Comment: 4 pages, 3 figure
Simulating quantum transport for a quasi-one-dimensional Bose gas in an optical lattice: the choice of fluctuation modes in the truncated Wigner approximation
We study the effect of quantum fluctuations on the dynamics of a
quasi-one-dimensional Bose gas in an optical lattice at zero-temperature using
the truncated Wigner approximation with a variety of basis sets for the initial
fluctuation modes. The initial spatial distributions of the quantum
fluctuations are very different when using a limited number of plane-wave (PW),
simple-harmonic-oscillator (SHO) and self-consistently determined Bogoliubov
(SCB) modes. The short-time transport properties of the Bose gas, characterized
by the phase coherence in the PW basis are distinct from those gained using the
SHO and SCB basis. The calculations using the SCB modes predict greater phase
decoherence and stronger number fluctuations than the other choices.
Furthermore, we observe that the use of PW modes overestimates the extent to
which atoms are expelled from the core of the cloud, while the use of the other
modes only breaks the cloud structure slightly which is in agreement with the
experimental observations [1].Comment: 12 pages, 5 figure
The Mass of HD 38529 c from Hubble Space Telescope Astrometry and High-Precision Radial Velocities
(Abridged) Hubble Space Telescope (HST) Fine Guidance Sensor astrometric
observations of the G4 IV star HD 38529 are combined with the results of the
analysis of extensive ground-based radial velocity data to determine the mass
of the outermost of two previously known companions. Our new radial velocities
obtained with the Hobby-Eberly Telescope and velocities from the
Carnegie-California group now span over eleven years. With these data we obtain
improved RV orbital elements for both the inner companion, HD 38529 b and the
outer companion, HD 38529 c. We identify a rotational period of HD 38529
(P_{rot}=31.65 +/- 0.17 d) with FGS photometry. We model the combined
astrometric and RV measurements to obtain the parallax, proper motion,
perturbation period, perturbation inclination, and perturbation size due to HD
38529 c. For HD 38529 c we find P = 2136.1 +/- 0.3 d, perturbation semi-major
axis \alpha =1.05 +/-0.06i_{Jup}) companion at
P~194 days. Additional observations (radial velocities and/or Gaia astrometry)
are required to validate an interpretation of HD 38529 d as a planetary-mass
companion. If confirmed, the resulting HD 38529 planetary system may be an
example of a "Packed Planetary System".Comment: Accepted by The Astronomical Journa
Loss of Individual MicroRNAs Causes Mutant Phenotypes in Sensitized Genetic Backgrounds in \u3cem\u3eC. elegans\u3c/em\u3e
MicroRNAs (miRNAs) are small, noncoding RNAs that regulate the translation and/or stability of their mRNA targets. Previous work showed that for most miRNA genes of C. elegans, single-gene knockouts did not result in detectable mutant phenotypes. This may be due, in part, to functional redundancy between miRNAs. However, in most cases, worms carrying deletions of all members of a miRNA family do not display strong mutant phenotypes. They may function together with unrelated miRNAs or with non-miRNA genes in regulatory networks, possibly to ensure the robustness of developmental mechanisms. To test this, we examined worms lacking individual miRNAs in genetically sensitized backgrounds. These include genetic backgrounds with reduced processing and activity of all miRNAs or with reduced activity of a wide array of regulatory pathways. With these two approaches, we identified mutant phenotypes for 25 out of 31 miRNAs included in this analysis. Our findings describe biological roles for individual miRNAs and suggest that the use of sensitized genetic backgrounds provides an efficient approach for miRNA functional analysis
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