4,130 research outputs found
L1551NE - Discovery of a Binary Companion
L1551NE is a very young (class 0 or I) low-mass protostar located close to
the well-studied L1551 IRS5. We present here evidence, from 1.3mm continuum
interferometric observations at ~1'' resolution, for a binary companion to
L1551NE. The companion, whose 1.3mm flux density is ~1/3 that of the primary
component, is located 1.43'' (~230 A.U. at 160pc) to the southeast. The
millimeterwave emission from the primary component may have been just barely
resolved, with deconvolved size ~0.82"x0.70" (~131x112 A.U.). The companion
emission was unresolved (<100 A.U.). The pair is embedded within a flattened
circum-binary envelope of size ~5.4'' x 2.3'' (~860 x 370 A.U.). The masses of
the three components (i.e. from the cicumstellar material of the primary star
and its companion, and the envelope) are approximately 0.044, 0.014 and 0.023
Mo respectively.Comment: 8 pages, 1 figur
Decuplet Baryon Structure from Lattice QCD
The electromagnetic properties of the SU(3)-flavor baryon decuplet are
examined within a lattice simulation of quenched QCD. Electric charge radii,
magnetic moments, and magnetic radii are extracted from the E0 and M1 form
factors. Preliminary results for the E2 and M3 moments are presented giving the
first model independent insight to the shape of the quark distribution in the
baryon ground state. As in our octet baryon analysis, the lattice results give
evidence of spin-dependent forces and mass effects in the electromagnetic
properties. The quark charge distribution radii indicate these effects act in
opposing directions. Some baryon dependence of the effective quark magnetic
moments is seen. However, this dependence in decuplet baryons is more subtle
than that for octet baryons. Of particular interest are the lattice predictions
for the magnetic moments of and for which new recent
experimental measurements are available. The lattice prediction of the
ratio appears larger than the experimental ratio, while the
lattice prediction for the magnetic moment ratio is in good
agreement with the experimental ratio.Comment: RevTeX manuscript, 34 pages plus 21 figures (available upon request
Female Sex Development and Reproductive Duct Formation Depend on Wnt4a in Zebrafish.
In laboratory strains of zebrafish, sex determination occurs in the absence of a typical sex chromosome and it is not known what regulates the proportion of animals that develop as males or females. Many sex determination and gonad differentiation genes that act downstream of a sex chromosome are well conserved among vertebrates, but studies that test their contribution to this process have mostly been limited to mammalian models. In mammals, WNT4 is a signaling ligand that is essential for ovary and Müllerian duct development, where it antagonizes the male-promoting FGF9 signal. Wnt4 is well conserved across all vertebrates, but it is not known if Wnt4 plays a role in sex determination and/or the differentiation of sex organs in nonmammalian vertebrates. This question is especially interesting in teleosts, such as zebrafish, because they lack an Fgf9 ortholog. Here we show that wnt4a is the ortholog of mammalian Wnt4, and that wnt4b was present in the last common ancestor of humans and zebrafish, but was lost in mammals. We show that wnt4a loss-of-function mutants develop predominantly as males and conclude that wnt4a activity promotes female sex determination and/or differentiation in zebrafish. Additionally, both male and female wnt4a mutants are sterile due to defects in reproductive duct development. Together these results strongly argue that Wnt4a is a conserved regulator of female sex determination and reproductive duct development in mammalian and nonmammalian vertebrates
Baryon Octet to Decuplet Electromagnetic Transitions
The electromagnetic transition moments of the -flavor baryon octet to
decuplet are examined within a lattice simulation of quenched QCD. The magnetic
transition moment for the channel is found to be in
agreement with recent experimental analyses. The lattice results indicate
. In terms of the Particle Data Group
convention, GeV for
transitions. Lattice predictions for the hyperon transition moments agree
with those of a simple quark model. However the manner in which the quarks
contribute to the transition moments in the lattice simulation is different
from that anticipated by quark model calculations. The scalar quadrupole form
factor exhibits a behavior consistent with previous multipole analyses. The
multipole transition moment ratios are also determined. The lattice
results suggest \% for
transitions. Of particular interest are significant
nonvanishing signals for the ratio in and
electromagnetic transitions.Comment: PostScript file, 37 pages including figures. U. MD PP #93-085, U. KY
PP #UK/92-09, TRIUMF PP #TRI-PP-92-12
On the Effect of Quantum Interaction Distance on Quantum Addition Circuits
We investigate the theoretical limits of the effect of the quantum
interaction distance on the speed of exact quantum addition circuits. For this
study, we exploit graph embedding for quantum circuit analysis. We study a
logical mapping of qubits and gates of any -depth quantum adder
circuit for two -qubit registers onto a practical architecture, which limits
interaction distance to the nearest neighbors only and supports only one- and
two-qubit logical gates. Unfortunately, on the chosen -dimensional practical
architecture, we prove that the depth lower bound of any exact quantum addition
circuits is no longer , but . This
result, the first application of graph embedding to quantum circuits and
devices, provides a new tool for compiler development, emphasizes the impact of
quantum computer architecture on performance, and acts as a cautionary note
when evaluating the time performance of quantum algorithms.Comment: accepted for ACM Journal on Emerging Technologies in Computing
System
Effects of imperfections for Shor's factorization algorithm
We study effects of imperfections induced by residual couplings between
qubits on the accuracy of Shor's algorithm using numerical simulations of
realistic quantum computations with up to 30 qubits. The factoring of numbers
up to N=943 show that the width of peaks, which frequencies allow to determine
the factors, grow exponentially with the number of qubits. However, the
algorithm remains operational up to a critical coupling strength
which drops only polynomially with . The numerical dependence of
on is explained by analytical estimates that allows to
obtain the scaling for functionality of Shor's algorithm on realistic quantum
computers with a large number of qubits.Comment: 10 pages, 10 figures, 1 table. Added references and new data. Erratum
added as appendix. 1 Figure and 1 Table added. Research is available at
http://www.quantware.ups-tlse.fr
A Lattice Study of Quark and Glue Momenta and Angular Momenta in the Nucleon
We report a complete calculation of the quark and glue momenta and angular
momenta in the proton. These include the quark contributions from both the
connected and disconnected insertions. The quark disconnected insertion loops
are computed with noise, and the signal-to-noise is improved with
unbiased subtractions. The glue operator is comprised of gauge-field tensors
constructed from the overlap operator. The calculation is carried out on a
quenched lattice at for Wilson fermions with
, and which correspond to pion masses at , and ~MeV, respectively. The chirally extrapolated and quark
momentum/angular momentum fraction is found to be , the
strange momentum/angular momentum fraction is , and that of
the glue is . The previous study of quark spin on the same
lattice revealed that it carries a fraction of of proton spin. The
orbital angular momenta of the quarks are then obtained from subtracting the
spin from their corresponding angular momentum components. We find that the
quark orbital angular momentum constitutes of the proton spin with
almost all of it coming from the disconnected insertions.Comment: Renormalization section is expanded to include more details. There
are slight changes in the final numbers. A few modification and corrections
are made in the rest of the tex
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