2,465 research outputs found
Renormalization of Massive Lattice Fermions
The renormalization of a general action for massive lattice fermions is
discussed. The analysis applies for all . Preliminary results for the
self energy at one loop in perturbation theory are presented.Comment: 3 pages (you guessed it: to appear in Lattice '93), uuencoded
PostScript file, FERMILAB-CONF-93/382-T and EFI 93-72. Regular PostScript
file by anonymous ftp to fnth06.fnal.gov as pub/Fermilab-Pub/93.38
The effect of metapopulation processes on the spatial scale of adaptation across an environmental gradient
We show that the butterfly Aricia agestis (Lycaenidae) is adapted to its
thermal environment in via integer changes in the numbers of generations per year
(voltinism): it has two generations per year in warm habitats and one generation per
year in cool habitats in north Wales (UK). Voltinism is an âadaptive peakâ since
individuals having an intermediate number of generations per year would fail to
survive the winter, and indeed no populations showed both voltinism types in nature.
In spite of this general pattern, 11% of populations apparently possess the âwrongâ
voltinism for their local environment, and population densities were lower in thermally
intermediate habitat patches. Population dynamic data and patterns of genetic
differentiation suggest that adaptation occurs at the metapopulation level, with local
populations possessing the voltinism type appropriate for the commonest habitat type
within each population network. When populations and groups of populations go
extinct, they tend to be replaced by colonists from the commonest thermal environment
nearby, even if this is the locally incorrect adaptation. Our results illustrate how
stochastic population turnover can impose a limit on local adaptation over distances
many times larger than predicted on the basis of normal dispersal movements
X-ray Emission Diagnostics from the M87 Jet
We use Chandra, HST and VLA observations of M87 to investigate the physics of
X-ray emission from AGN jets. We find that X-ray hotspots in the M87 jet occur
primarily in regions with hard optical-to-X-ray spectra and lower than average
polarization. Particle injection appears to be required both continuously in
the jet sheath as well as locally at X-ray hotspots.Comment: 4 pages, 2 figures, submitted to "The Physics of Relativistic Jets in
the CHANDRA and XMM Era", Bologna 200
Radio Source Heating in the ICM: The Example of Cygnus A
One of the most promising solutions for the cooling flow problem involves
energy injection from the central AGN. However it is still not clear how
collimated jets can heat the ICM at large scale, and very little is known
concerning the effect of radio lobe expansion as they enter into pressure
equilibrium with the surrounding cluster gas. Cygnus A is one of the best
examples of a nearby powerful radio galaxy for which the synchrotron emitting
plasma and thermal emitting intra-cluster medium can be mapped in fine detail,
and previous observations have inferred possible shock structure at the
location of the cocoon. We use new XMM-Newton observations of Cygnus A, in
combination with deep Chandra observations, to measure the temperature of the
intra-cluster medium around the expanding radio cavities. We investigate how
inflation of the cavities may relate to shock heating of the intra-cluster gas,
and whether such a mechanism is sufficient to provide enough energy to offset
cooling to the extent observed.Comment: To appear in the Proceedings of "Heating vs. Cooling in Galaxies and
Clusters of Galaxies", August 2006, Garching (Germany), Eds. H. Boehringer,
G.W. Pratt, A. Finoguenov, P. Schuecker, Springer-Verlag series "ESO
Astrophysics Symposia", p.101, in press. 8 pages, 3 multiple figure
A More Improved Lattice Action for Heavy Quarks
We extend the Fermilab formalism for heavy quarks to develop a more improved
action. We give results of matching calculations of the improvement couplings
at tree level. Finally, we estimate the discretization errors associated with
the new action.Comment: 3 pages, 1 figure, Lattice 2003 Tsukuba Japa
Jet confinement by magneto-torsional oscillations
Many quasars and active galactic nuclei (AGN) appear in radio, optical, and
X-ray maps, as a bright nuclear sources from which emerge single or double
long, thin jets. When observed with high angular resolution these jets show
structure with bright knots separated by relatively dark regions. Nonthermal
nature of a jet radiation is well explained as the synchrotron radiation of the
relativistic electrons in an ordered magnetic field. We consider magnetic
collimation, connected with torsional oscillations of a cylinder with elongated
magnetic field, and periodically distributed initial rotation around the
cylinder axis. The stabilizing azimuthal magnetic field is created here by
torsional oscillations, where charge separation is not necessary. Approximate
simplified model is developed. Ordinary differential equation is derived, and
solved numerically, what gives a possibility to estimate quantitatively the
range of parameters where jets may be stabilized by torsional oscillations.Comment: accepted for publication in Astrophysics and Space Scienc
Quantum-mechanical tunnelling and the renormalization group
We explore the applicability of the exact renormalization group to the study
of tunnelling phenomena. We investigate quantum-mechanical systems whose energy
eigenstates are affected significantly by tunnelling through a barrier in the
potential. Within the approximation of the derivative expansion, we find that
the exact renormalization group predicts the correct qualitative behaviour for
the lowest energy eigenvalues. However, quantitative accuracy is achieved only
for potentials with small barriers. For large barriers, the use of alternative
methods, such as saddle-point expansions, can provide quantitative accuracy.Comment: 9 pages, 5 figures, to appear in Phys. Lett.
Stoke-on-Trent: a geological background for planning and development
This study, carried out between 1988 and 1990, was commissioned by the Department of the Environment (DOE)
and funded jointly by the Department and the British
Geological Survey (BGS). Its main aim was to make a synthesis of geological data relevant to planning of land-use and development in the Stoke-on-Trent area. This report is specifically written for planners and there has been an
attempt to avoid complex geological terms. Besides text
illustrations the report includes ten thematic maps at a common scale of 1 :25 000. An additional volume concentrates
on engineering geology for site investigation companies.
Seven further short reports feature geological details of separate 1: 10 000 sheets, couched in more technical language
Differentiation of marrow stromal cells into photoreceptors in the rat eye
Retinal degenerations and dystrophies are the major causes of genetically inherited blindness that are characterized by the apoptotic death of the photoreceptor cell layer of the retina. To date, no treatment exists for these diseases and only recently have they been considered as candidates for gene and stem cell therapies. Here we report the ability of adult CD90+ marrow stromal cells (MSCs) to be induced by activin A, taurine, and EGF into cells (20-32%) expressing photoreceptor-specific markers rhodopsin, opsin, and recoverin in vitro. CD90+ cells were either transduced with recombinant adeno-associated virus expressing green fluorescent protein (GFP) or bromodeoxyuridine (BrdU) labeled and then injected into the subretinal space of adult Royal College of Surgeons rats. Fundus photography and angiography showed no adverse effects of CD90+ MSC transplantation. GFP-expressing cells or BrdU-positive cells covered âŒ30% of the entire retinal area. By 2 weeks after injection, CD90+ MSCs integrated into the host retina, forming structures similar to the photoreceptor layer and expressed a photoreceptor-specific marker. No teratoma formation was observed in the recipient retina. The subretinally delivered CD90+ MSCs did not stain for proliferating cell nuclear antigen, indicating that they primarily undergo differentiation rather than proliferation. In addition, we established that transplanted cells can attract synaptic vesicles and hence are potentially capable of signal transduction. This study demonstrates for the first time the partial differentiation of adult CD90+ MSCs into photoreceptors in vitro and in vivo. Our results establish a proof of concept for CD90+ MSC differentiation with autologous transplantation, which may provide a promising therapeutic strategy for the treatment of some forms of genetically inherited retinal degenerations
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Robust metastable skyrmions with tunable size in the chiral magnet FePtMo3 N
The synthesis of new materials that can host magnetic skyrmions and their thorough experimental and theoretical characterization are essential for future technological applications. The ÎČ-Mn-type compound FePtMo3N is one such novel material that belongs to the chiral space group P4132, where the antisymmetric Dzyaloshinskii-Moriya interaction is allowed due to the absence of inversion symmetry. We report the results of small-angle neutron scattering (SANS) measurements of FePtMo3N and demonstrate that its magnetic ground state is a long-period spin helix with a Curie temperature of 222 K. The magnetic field-induced redistribution of the SANS intensity showed that the helical structure transforms to a lattice of skyrmions at âŒ13 mT at temperatures just below TC. Our key observation is that the skyrmion state in FePtMo3N is robust against field cooling down to the lowest temperatures. Moreover, once the metastable state is prepared by field cooling, the skyrmion lattice exists even in zero field. Furthermore, we show that the skyrmion size in FePtMo3N exhibits high sensitivity to the sample temperature and can be continuously tuned between 120 and 210 nm. This offers different prospects in the control of topological properties of chiral magnets. © 2020 authors. Published by the American Physical Society
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