2,130 research outputs found
Remarks on the stability of the Navier-Stokes equations supplemented with stress-free boundary conditions
The purpose of this note is to analyze the long term stability of the
Navier-Stokes equations supplemented with the Coriolis force and the
stress-free boundary condition. It is shown that, if the flow domain is
axisymmetric, spurious stability behaviors can occur depending whether the
Coriolis force is active or not
Low genetic diversity in Polish populations of sibling ant species: Lasius niger (L.) and Lasius platythorax Seifert (Hymenoptera, Formicidae)
We present preliminary data on mitochondrial DNA diversity within and among populations of the ants Lasius niger and Lasius platythorax in Poland. Phylogenetic analysis based on the mitochondrial DNA markers: cytochrome c oxidase subunit I (cox1) and 16S ribosomal RNA (16S rRNA) confirms the species status of L. niger and L. platythorax. Intraspecific variability is low in both species, which might be a result of severe bottlenecks and rapid postglacial expansion into Central Europe
Galaxies Probing Galaxies at High Resolution: Co-Rotating Gas Associated with a Milky Way Analog at z=0.4
We present results on gas flows in the halo of a Milky Way-like galaxy at
z=0.413 based on high-resolution spectroscopy of a background galaxy. This is
the first study of circumgalactic gas at high spectral resolution towards an
extended background source (i.e., a galaxy rather than a quasar). Using
longslit spectroscopy of the foreground galaxy, we observe spatially extended H
alpha emission with circular rotation velocity v=270 km/s. Using echelle
spectroscopy of the background galaxy, we detect Mg II and Fe II absorption
lines at impact parameter rho=27 kpc that are blueshifted from systemic in the
sense of the foreground galaxy's rotation. The strongest absorber EW(2796) =
0.90 A has an estimated column density (N_H>10^19 cm-2) and line-of-sight
velocity dispersion (sigma=17 km/s) that are consistent with the observed
properties of extended H I disks in the local universe. Our analysis of the
rotation curve also suggests that this r=30 kpc gaseous disk is warped with
respect to the stellar disk. In addition, we detect two weak Mg II absorbers in
the halo with small velocity dispersions (sigma<10 km/s). While the exact
geometry is unclear, one component is consistent with an extraplanar gas cloud
near the disk-halo interface that is co-rotating with the disk, and the other
is consistent with a tidal feature similar to the Magellanic Stream. We can
place lower limits on the cloud sizes (l>0.4 kpc) for these absorbers given the
extended nature of the background source. We discuss the implications of these
results for models of the geometry and kinematics of gas in the circumgalactic
medium.Comment: 14 pages, 6 figures, submitted to ApJ, comments welcom
Ultrahigh Bandwidth Spin Noise Spectroscopy: Detection of Large g-Factor Fluctuations in Highly n-Doped GaAs
We advance all optical spin noise spectroscopy (SNS) in semiconductors to
detection bandwidths of several hundred gigahertz by employing an ingenious
scheme of pulse trains from ultrafast laser oscillators as an optical probe.
The ultrafast SNS technique avoids the need for optical pumping and enables
nearly perturbation free measurements of extremely short spin dephasing times.
We employ the technique to highly n-doped bulk GaAs where magnetic field
dependent measurements show unexpected large g-factor fluctuations.
Calculations suggest that such large g-factor fluctuations do not necessarily
result from extrinsic sample variations but are intrinsically present in every
doped semiconductor due to the stochastic nature of the dopant distribution.Comment: 5 pages, 3 figure
Kick stability in groups and dynamical systems
We consider a general construction of ``kicked systems''. Let G be a group of
measure preserving transformations of a probability space. Given its
one-parameter/cyclic subgroup (the flow), and any sequence of elements (the
kicks) we define the kicked dynamics on the space by alternately flowing with
given period, then applying a kick. Our main finding is the following stability
phenomenon: the kicked system often inherits recurrence properties of the
original flow. We present three main examples. 1) G is the torus. We show that
for generic linear flows, and any sequence of kicks, the trajectories of the
kicked system are uniformly distributed for almost all periods. 2) G is a
discrete subgroup of PSL(2,R) acting on the unit tangent bundle of a Riemann
surface. The flow is generated by a single element of G, and we take any
bounded sequence of elements of G as our kicks. We prove that the kicked system
is mixing for all sufficiently large periods if and only if the generator is of
infinite order and is not conjugate to its inverse in G. 3) G is the group of
Hamiltonian diffeomorphisms of a closed symplectic manifold. We assume that the
flow is rapidly growing in the sense of Hofer's norm, and the kicks are
bounded. We prove that for a positive proportion of the periods the kicked
system inherits a kind of energy conservation law and is thus superrecurrent.
We use tools of geometric group theory and symplectic topology.Comment: Latex, 40 pages, revised versio
The Cleft Care UK study. Part 4:perceptual speech outcomes
OBJECTIVES: To describe the perceptual speech outcomes from the Cleft Care UK (CCUK) study and compare them to the 1998 Clinical Standards Advisory Group (CSAG) audit. SETTING AND SAMPLE POPULATION: A cross-sectional study of 248 children born with complete unilateral cleft lip and palate, between 1 April 2005 and 31 March 2007 who underwent speech assessment. MATERIALS AND METHODS: Centre-based specialist speech and language therapists (SLT) took speech audio–video recordings according to nationally agreed guidelines. Two independent listeners undertook the perceptual analysis using the CAPS-A Audit tool. Intra- and inter-rater reliability were tested. RESULTS: For each speech parameter of intelligibility/distinctiveness, hypernasality, palatal/palatalization, backed to velar/uvular, glottal, weak and nasalized consonants, and nasal realizations, there was strong evidence that speech outcomes were better in the CCUK children compared to CSAG children. The parameters which did not show improvement were nasal emission, nasal turbulence, hyponasality and lateral/lateralization. CONCLUSION: These results suggest that centralization of cleft care into high volume centres has resulted in improvements in UK speech outcomes in five-year-olds with unilateral cleft lip and palate. This may be associated with the development of a specialized workforce. Nevertheless, there still remains a group of children with significant difficulties at school entry
Impact of Six Genetic Modifications of Corn on Feed Cost and the Consumption of Traditional Feed Ingredients
There is excitement about the potential profit and economic development opportunities from genetic modifications of grain. This excitement is manifested in huge industry consolidations through buyouts, joint ventures, and mergers of chemical, seed and agribusiness companies. State and federal government agencies and private organizations have developed programs to encourage and facilitate the production, handling, processing, and marketing of genetically modified grains. Huge investments are being allocated to research and development of new commodities and specialty grains. A large share of these research and development funds are being invested in modifying com because of the large amount of com produced in the United States and its diversity of uses. About 80 percent of the U.S. corn crop is used in animal feeds domestically and abroad; therefore, genetic modifications of com for animal feed are believed to have major profit and development potential
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