6,187 research outputs found
The Chiral Condensate of Strongly Coupled QCD in the 't Hooft Limit
Using the recently proposed generalization to an arbitrary number of colors
of the strong coupling approach to lattice gauge
theories\cite{Grignani:2003uv}, we compute the chiral condensate of massless
QCD in the 't Hooft limit.Comment: 12 pages, revtex
Investigation of the Domain Wall Fermion Approach to Chiral Gauge Theories on the Lattice
We investigate a recent proposal to construct chiral gauge theories on the
lattice using domain wall fermions. We restrict ourselves to the finite volume
case, in which two domain walls are present, with modes of opposite chirality
on each of them. We couple the chiral fermions on only one of the domain walls
to a gauge field. In order to preserve gauge invariance, we have to add a
scalar field, which gives rise to additional light mirror fermion and scalar
modes. We argue that in an anomaly free model these extra modes would decouple
if our model possesses a so-called strong coupling symmetric phase. However,
our numerical results indicate that such a phase most probably does not exist.
---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.Comment: 27p. Latex; UCSD/PTH 93-28, Wash. U. HEP/93-6
Spin Disorder and Magnetic Anisotropy in Fe3O4 Nanoparticles
We have studied the magnetic behavior of dextran-coated magnetite
(FeO) nanoparticles with median particle size \left=8 .
Magnetization curves and in-field M\"ossbauer spectroscopy measurements showed
that the magnetic moment of the particles was much smaller than the bulk
material. However, we found no evidence of magnetic irreversibility or
non-saturating behavior at high fields, usually associated to spin canting. The
values of magnetic anisotropy from different techniques indicate that
surface or shape contributions are negligible. It is proposed that these
particles have bulk-like ferrimagnetic structure with ordered A and B
sublattices, but nearly compensated magnetic moments. The dependence of the
blocking temperature with frequency and applied fields, ,
suggests that the observed non-monotonic behavior is governed by the strength
of interparticle interactions.Comment: 11 pages, 7 figures, 3 Table
Steady-state spin densities and currents
This article reviews steady-state spin densities and spin currents in
materials with strong spin-orbit interactions. These phenomena are intimately
related to spin precession due to spin-orbit coupling which has no equivalent
in the steady state of charge distributions. The focus will be initially on
effects originating from the band structure. In this case spin densities arise
in an electric field because a component of each spin is conserved during
precession. Spin currents arise because a component of each spin is continually
precessing. These two phenomena are due to independent contributions to the
steady-state density matrix, and scattering between the conserved and
precessing spin distributions has important consequences for spin dynamics and
spin-related effects in general. In the latter part of the article extrinsic
effects such as skew scattering and side jump will be discussed, and it will be
shown that these effects are also modified considerably by spin precession.
Theoretical and experimental progress in all areas will be reviewed
Remote sensing and hydrologic models for performance assessment in Sirsa Irrigation Circle, India
Irrigation management / Irrigation systems / Irrigation canals / Performance evaluation / Remote sensing / GIS / Models / Irrigated farming / Hydrology / Satellite surveys / Irrigation scheduling / Evapotranspiration / India
Grazing Impacts on Rangeland Condition in Semi-Arid South-Western Africa
The savannah biome, consisting of a dense herbaceous layer and a relatively open woody layer in competitive balance, constitutes 64% of the land surface of Namibia, an arid country in south-western Africa, and is used mainly for extensive cattle and sheep ranching. About half of the savannah area is affected by dense to moderately dense bush-thickening, resulting in a ten-fold decrease in the rangeland’s grass-based carrying capacity and a concomitant loss in meat production of about US$115 million per year (De Klerk, 2004). Bushencroached areas typically have densities \u3e 2 000 bushes/ha with \u3e 90% belonging to a single species. High grazing pressure by specialist grazers, such as domestic cattle, is often blamed for rangeland degradation. There is an urgent need to understand the dynamics of bush encroachment and devise grazing strategies to contain it
Asynchronous event driven distributed energy management using profile steering
Distributed Energy Management methodologies with a scheduling approach based on predictions require means to avoid problems related to prediction errors. Various approaches deal with such prediction errors by applying a different online control mechanism, such as a double-sided auction. However, this results in two separate control mechanisms for the planning phase and the real-time control phase. In this paper, we present a two-phase approach with profile steering based control in both phases. The first phase is synchronous and uses predictions to create a planning. The second phase uses profile steering to schedule individual devices in an event driven and asynchronous manner. Simulation results show that this methodology results in an improved power quality and follows the planning better with a RMSE reduction of up to 34%. In addition, it provides more robustness to failure of connection and improves transparency of its actions to prosumers
The Bright End of the z~9 and z~10 UV Luminosity Functions using all five CANDELS Fields
The deep, wide-area (~800-900 arcmin**2) near-infrared/WFC3/IR + Spitzer/IRAC
observations over the CANDELS fields have been a remarkable resource for
constraining the bright end of high redshift UV luminosity functions (LFs).
However, the lack of HST 1.05-micron observations over the CANDELS fields has
made it difficult to identify z~9-10 sources robustly, since such data are
needed to confirm the presence of an abrupt Lyman break at 1.2 microns. We
report here on the successful identification of many such z~9-10 sources from a
new HST program (z9-CANDELS) that targets the highest-probability z~9-10 galaxy
candidates with observations at 1.05 microns, to search for a robust
Lyman-break at 1.2 microns. The potential z~9-10 candidates are preselected
from the full HST, Spitzer/IRAC S-CANDELS observations, and the
deepest-available ground-based optical+near-infrared observations. We
identified 15 credible z~9-10 galaxies over the CANDELS fields. Nine of these
galaxies lie at z~9 and 5 are new identifications. Our targeted follow-up
strategy has proven to be very efficient in making use of scarce HST time to
secure a reliable sample of z~9-10 galaxies. Through extensive simulations, we
replicate the selection process for our sample (both the preselection and
follow-up) and use it to improve current estimates for the volume density of
bright z~9 and z~10 galaxies. The volume densities we find are 5(-2)(+3)x and
8(-3)(+9)x lower, respectively, than found at z~8. When compared with the
best-fit evolution (i.e., dlog_{10} rho(UV)/dz=-0.29+/-0.02) in the UV
luminosities densities from z~8 to z~4 integrated to 0.3L*(z=3) (-20 mag),
these luminosity densities are 2.6(-0.9)(+1.5)x and 2.2(-1.1)(+2.0)x lower,
respectively, than the extrapolated trends. Our new results are broadly
consistent with the "accelerated evolution" scenario at z>8, as seen in many
theoretical models.Comment: 23 pages, 15 figures, 7 tables, updated to match the version in
press, including some minor textual corrections identified at the proof stag
Current-driven vortex oscillations in metallic nanocontacts
We present experimental evidence of sub-GHz spin-transfer oscillations in
metallic nano-contacts that are due to the translational motion of a magnetic
vortex. The vortex is shown to execute large-amplitude orbital motion outside
the contact region. Good agreement with analytical theory and micromagnetics
simulations is found.Comment: 4 pages, 3 figure
Photometric Constraints on the Redshift of z~10 candidate UDFj-39546284 from deeper WFC3/IR+ACS+IRAC observations over the HUDF
Ultra-deep WFC3/IR observations on the HUDF from the HUDF09 program revealed
just one plausible z~10 candidate UDFj-39546284. UDFj-39546284 had all the
properties expected of a galaxy at z~10 showing (1) no detection in the deep
ACS+WFC3 imaging data blueward of the F160W band, exhibiting (2) a blue
spectral slope redward of the break, and showing (3) no prominent detection in
deep IRAC observations. The new, similarly deep WFC3/IR HUDF12 F160W
observations over the HUDF09/XDF allow us to further assess this candidate.
These observations show that this candidate, previously only detected at ~5.9
sigma in a single band, clearly corresponds to a real source. It is detected at
~5.3 sigma in the new H-band data and at ~7.8 sigma in the full 85-orbit H-band
stack. Interestingly, the non-detection of the source (<1 sigma) in the new
F140W observations suggests a higher redshift. Formally, the best-fit redshift
of the source utilizing all the WFC3+ACS (and IRAC+K-band) observations is
11.8+/-0.3. However, we consider the z~12 interpretation somewhat unlikely,
since the source would either need to be ~20x more luminous than expected or
show very high-EW Ly-alpha emission (which seems improbable given the extensive
neutral gas prevalent early in the reionization epoch). Lower-redshift
solutions fail if only continuum models are allowed. Plausible lower-redshift
solutions require that the H-band flux be dominated by line emission such as
Halpha or [OIII] with extreme EWs. The tentative detection of line emission at
1.6 microns in UDFj-39546284 in a companion paper suggests that such emission
may have already been found.Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ Letters,
updated to match the version in pres
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