35,836 research outputs found
The Double-Lined Spectroscopic Binary Haro 1-14c
We report detection of the low-mass secondary in the spectroscopic binary
Haro 1-14c in the Ophiuchus star forming region. The secondary/primary mass
ratio is . With an estimated photometric primary mass of 1.2
, the secondary mass is and the projected
semi-major axis is AU. The system is well-suited for astrometric
mapping of its orbit with the current generation of ground-based IR
interferometers. This could yield precision values of the system's component
masses and distance.Comment: Accepted by ApJ Letter
Cloning of the C-terminal cytoplasmic fragment of the tar protein and effects of the fragment on chemotaxis of Escherichia coli
A gene encoding only the C-terminal portion of the receptor-transducer protein Tar of Escherichia coli was constructed. The gene product was detected and localized in the cytoplasmic fraction of the cell by immunoblotting with anti-Tar antibodies. The C-terminal fragments from wild-type and mutant tar genes were characterized in vivo. The C-terminal fragment generated from tar-526, a mutation that results in a dominant "tumble" phenotype, was found to be deamidated and methylated by the CheB and CheR proteins, respectively. The C-terminal fragment derived from a wild-type gene was poorly deamidated, and the C-terminal fragment derived from tar-529, a dominant mutant with a "smooth swimming" phenotype, was not apparently modified. Cells carrying the C-terminal fragment with the tar-526 mutation as the sole receptor-transducer protein showed a high frequency of tumbling and chemotaxis responses to changes in intracellular pH. These results suggest that the cytoplasmic C-terminal fragment of Tar retains some of the functions of the whole protein in vivo
The G alpha q and G alpha 11 proteins couple the thyrotropin-releasing hormone receptor to phospholipase C in GH3 rat pituitary cells
Thyrotropin-releasing hormone stimulates the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) in GH3 cell membranes. The stimulation of the phosphoinositide phospholipase C (PI/PLC) activity can be blocked by incubation of GH3 membranes with polyclonal antibodies directed against a peptide derived from the C-terminal region of G alpha q and G alpha 11. Antibodies directed against the C- terminal region of other G alpha-subunits had no detectable effect. The inhibition was specific since addition of the peptide that was used to prepare the antibody completely reversed the inhibition. Further evidence for the coupling of the TRH receptor to G alpha q or G alpha 11 comes from a reconstitution experiment in which human embryonic kidney cells were transiently transfected with cDNAs corresponding to the TRH receptor, G alpha q or G alpha 11. The PIP2 hydrolysis detected with membranes from cells that over-expressed the TRH receptor alone was low, however, co-expression with the G alpha q or G alpha 11 subunits produced a synergistic stimulation of PI-PLC activity. In contrast, co-expression of these alpha-subunits with the M2 muscarinic acetylcholine receptor induced a weak stimulation of PIP2 hydrolysis. The results presented here suggest that the TRH-dependent stimulation of PI-PLC in GH3 cells is mediated through the G-protein alpha- subunits, G alpha q and/or G alpha 11
Medicaid Expansions and Fertility in the United States
Beginning in the mid 1980s and extending through the early to mid 1990s, a substantial number of women and children gained eligibility for Medicaid through a series of income-based expansions. Using natality data from the National Center for Health Statistics, we estimate fertility responses to these eligibility expansions. We measure changes in state Medicaid eligibility policy by simulating the fraction of a standard population that would qualify for benefits. From 1985 to 1996, the fraction of women aged 15 to 44 who were eligible for Medicaid coverage for a pregnancy increased on average by 24 percentage points. However, contrary to findings in the extant literature, our results do not indicate that this expansion in coverage had a statistically discernible effect on fertility.
A quantum Mermin--Wagner theorem for quantum rotators on two--dimensional graphs
This is the first of a series of papers considering symmetry properties of
quantum systems over 2D graphs or manifolds, with continuous spins, in the
spirit of the Mermin--Wagner theorem. In the model considered here (quantum
rotators) the phase space of a single spin is a dimensional torus, and
spins (or particles) are attached to sites of a graph satisfying a special
bi-dimensionality property. The kinetic energy part of the Hamiltonian is minus
a half of the Laplace operator. We assume that the interaction potential is
C-smooth and invariant under the action of a connected Lie group {\ttG}.
A part of our approach is to give a definition (and a construction) of a class
of infinite-volume Gibbs states for the systems under consideration (the class
\fG). This class contains the so-called limit Gibbs states, with or without
boundary conditions. We use ideas and techniques originated from various past
papers, in combination with the Feynman--Kac representation, to prove that any
state lying in the class \fG (defined in the text) is {\ttG}-invariant. An
example is given where the interaction potential is singular and there exists a
Gibbs state which is not {\ttG}-invariant.
In the next paper under the same title we establish a similar result for a
bosonic model where particles can jump from a vertex of the graph to one of its
neighbors (a generalized Hubbard model).Comment: 27 page
Response Function of the Fractional Quantized Hall State on a Sphere II: Exact Diagonalization
We study the excitation spectra and the dynamical structure factor of quantum
Hall states in a finite size system through exact diagonalization. Comparison
is made between the numerical results so obtained and the analytic results
obtained from a modified RPA in the preceding companion paper. We find good
agreement between the results at low energies.Comment: 22 pages (REVTeX 3.0). 10 figures available on request. Complete
postscript file (including figures) for this paper are available on the World
Wide Web at http://cmtw.harvard.edu/~simon/ ; Preprint number HU-CMT-94S0
Novel form of adaptation in mouse retinal rods speeds recovery of phototransduction
Photoreceptors of the retina adapt to ambient light in a manner that allows them to detect changes in illumination over an enormous range of intensities. We have discovered a novel form of adaptation in mouse rods that persists long after the light has been extinguished and the rod's circulating dark current has returned. Electrophysiological recordings from individual rods showed that the time that a bright flash response remained in saturation was significantly shorter if the rod had been previously exposed to bright light. This persistent adaptation did not decrease the rate of rise of the response and therefore cannot be attributed to a decrease in the gain of transduction. Instead, this adaptation was accompanied by a marked speeding of the recovery of the response, suggesting that the step that rate-limits recovery had been accelerated. Experiments on knockout rods in which the identity of the rate-limiting step is known suggest that this adaptive acceleration results from a speeding of G protein/effector deactivation
The GL 569 Multiple System
We report the results of high spectral and angular resolution infrared
observations of the multiple system GL 569 A and B that were intended to
measure the dynamical masses of the brown dwarf binary believed to comprise GL
569 B. Our analysis did not yield this result but, instead, revealed two
surprises. First, at age ~100 Myr, the system is younger than had been reported
earlier. Second, our spectroscopic and photometric results provide support for
earlier indications that GL 569 B is actually a hierarchical brown dwarf triple
rather than a binary. Our results suggest that the three components of GL 569 B
have roughly equal mass, ~0.04 Msun.Comment: 29 pages, 10 figures, accepted for publication in the Astrophysical
Journal; minor corrections to Section 5.1; changed typo in 6.
Spinful Composite Fermions in a Negative Effective Field
In this paper we study fractional quantum Hall composite fermion
wavefunctions at filling fractions \nu = 2/3, 3/5, and 4/7. At each of these
filling fractions, there are several possible wavefunctions with different spin
polarizations, depending on how many spin-up or spin-down composite fermion
Landau levels are occupied. We calculate the energy of the possible composite
fermion wavefunctions and we predict transitions between ground states of
different spin polarizations as the ratio of Zeeman energy to Coulomb energy is
varied. Previously, several experiments have observed such transitions between
states of differing spin polarization and we make direct comparison of our
predictions to these experiments. For more detailed comparison between theory
and experiment, we also include finite-thickness effects in our calculations.
We find reasonable qualitative agreement between the experiments and composite
fermion theory. Finally, we consider composite fermion states at filling
factors \nu = 2+2/3, 2+3/5, and 2+4/7. The latter two cases we predict to be
spin polarized even at zero Zeeman energy.Comment: 17 pages, 5 figures, 4 tables. (revision: incorporated referee
suggestions, note added, updated references
Probing the Superfluid to Mott Insulator Transition at the Single Atom Level
Quantum gases in optical lattices offer an opportunity to experimentally
realize and explore condensed matter models in a clean, tunable system. We
investigate the Bose-Hubbard model on a microscopic level using single
atom-single lattice site imaging; our technique enables space- and
time-resolved characterization of the number statistics across the
superfluid-Mott insulator quantum phase transition. Site-resolved probing of
fluctuations provides us with a sensitive local thermometer, allows us to
identify microscopic heterostructures of low entropy Mott domains, and enables
us to measure local quantum dynamics, revealing surprisingly fast transition
timescales. Our results may serve as a benchmark for theoretical studies of
quantum dynamics, and may guide the engineering of low entropy phases in a
lattice
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