7,419 research outputs found
Crossovers in the Two Dimensional Ising Spin Glass with ferromagnetic next-nearest-neighbor interactions
By means of extensive computer simulations we analyze in detail the two
dimensional Ising spin glass with ferromagnetic next-nearest-neighbor
interactions. We found a crossover from ferromagnetic to ``spin glass'' like
order both from numerical simulations and analytical arguments. We also present
evidences of a second crossover from the ``spin glass'' behavior to a
paramagnetic phase for the largest volume studied.Comment: 19 pages with 9 postscript figures also available at
http://chimera.roma1.infn.it/index_papers_complex.html. Some changes in
captions of figures 1 and
Evaluation of a microbial muramidase supplementation on growth performance, apparent ileal digestibility, and intestinal histology of broiler chickens
The current study evaluated the effects of different inclusion levels of microbial muramidase (Muramidase 007, DSM Nutritional Products) on gastrointestinal functionality by determination of apparent ileal digestibility (AID) of nutrients, investigation of intestinal histomorphology, and quantification of resulting growth performance. Four maize-wheat-soybean experimental diets were produced without (C) and with different dosages of muramidase: low (L, 25,000 LSU(F)/kg), medium (M, 35,000 LSU(F)/kg), and high (H, 45,000 LSU(F)/kg); diets were fed to broilers for 35 d. At the end of the experiment, AID of ether extract (EE), crude protein (CP), Ca, and P were determined and samples of the mid-jejunum and -ileum were collected for histomorphological observations. Data were subjected to ANOVA analysis using the GLM procedure. Orthogonal polynomial contrasts were used to assess linear and quadratic effects of different levels of the muramidase. At the end of the trial, Muramidase 007 supplementation linearly increased body weight gain and decreased feed conversion ratio (FCR) (P ≤ 0.05). Adding the muramidase to broiler diets also linearly increased the European poultry efficiency factor (P ≤ 0.05). Inclusion of the muramidase in broiler diets linearly increased AID of CP, EE, and P (P ≤ 0.05), and the H group had a higher AID of EE and CP compared to C group (P ≤ 0.05). Microbial muramidase supplementation linearly increased ileal villus length to crypt depth ratio and decreased the number of ileal CD45 cells (P ≤ 0.05). Broilers fed M and H diets had fewer number of CD45 cells in the ileum compared to those in C group (P ≤ 0.05). In conclusion, the results of the present study demonstrated that inclusion of the microbial muramidase in broiler diets could increase AID of key nutrients and improve growth performance in broilers. Adding microbial muramidase to broiler diets can therefore be considered as an interesting prospect to improve gastrointestinal functionality. Biological mechanisms causing these improvements need to be studied further
Off-Equilibrium Dynamics in Finite-Dimensional Spin Glass Models
The low temperature dynamics of the two- and three-dimensional Ising spin
glass model with Gaussian couplings is investigated via extensive Monte Carlo
simulations. We find an algebraic decay of the remanent magnetization. For the
autocorrelation function a typical
aging scenario with a scaling is established. Investigating spatial
correlations we find an algebraic growth law of
the average domain size. The spatial correlation function scales with . The sensitivity of the
correlations in the spin glass phase with respect to temperature changes is
examined by calculating a time dependent overlap length. In the two dimensional
model we examine domain growth with a new method: First we determine the exact
ground states of the various samples (of system sizes up to )
and then we calculate the correlations between this state and the states
generated during a Monte Carlo simulation.Comment: 38 pages, RevTeX, 14 postscript figure
The implications from CANGAROO-III observations of TeV blazar PKS 2155-304
We have observed the high-frequency-peaked BL Lacertae object PKS2155-304 in
2004, 2005 and 2006 with the CANGAROO-III imaging atmospheric Cherenkov
telescope, and have detected a signal above 660 GeV at the 4.8/sigma level
during the 2006 outburst period. Intranight flux variability on time scale of
half an hour is observed. From this variability time scale, the size of the TeV
gamma-ray emission region is restricted to 5x10^13\delta cm, and the super
massive black hole mass is estimated to be less than 1.9x10^8\delta M_{Solar},
where \delta is the beaming factor. The differential energy spectrum is
obtained, and an upper limit of the extragalactic infrared background light
(EBL) flux is derived under some assumption. We also fit a synchrotron self
Compton (SSC) model to the spectral energy distribution (SED) and derive the
beaming factor and magnetic field strength.Comment: 4 pages, 5 figures, proceedings of the "4th Heidelberg International
Symposium on High Energy Gamma-Ray Astronomy" July 7-11, 2008, Heidelberg,
German
Chaos in the Random Field Ising Model
The sensitivity of the random field Ising model to small random perturbations
of the quenched disorder is studied via exact ground states obtained with a
maximum-flow algorithm. In one and two space dimensions we find a mild form of
chaos, meaning that the overlap of the old, unperturbed ground state and the
new one is smaller than one, but extensive. In three dimensions the
rearrangements are marginal (concentrated in the well defined domain walls).
Implications for finite temperature variations and experiments are discussed.Comment: 4 pages RevTeX, 6 eps-figures include
Quantum and thermal fluctuations in the SU(N) Heisenberg spin-glass model near the quantum critical point
We solve for the SU(N) Heisenberg spin-glass in the limit of large N focusing
on small S and T. We study the effect of quantum and thermal fluctuations in
the frequency dependent response function and observed interesting transfers of
spectral weight. We compute the T-dependence of the order parameter and the
specific heat and find an unusual T^2 behavior for the latter at low
temperatures in the spin-glass phase. We find a remarkable qualitative
agreement with various experiments on the quantum frustrated magnet
SrCr_{9p}Ga_{12-9p}O_{19}.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let
Fluctuation Dissipation Ratio in Three-Dimensional Spin Glasses
We present an analysis of the data on aging in the three-dimensional Edwards
Anderson spin glass model with nearest neighbor interactions, which is well
suited for the comparison with a recently developed dynamical mean field
theory. We measure the parameter describing the violation of the
relation among correlation and response function implied by the fluctuation
dissipation theorem.Comment: LaTeX 10 pages + 4 figures (appended as uuencoded compressed
tar-file), THP81-9
Flow correlated percolation during vascular network formation in tumors
A theoretical model based on the molecular interactions between a growing
tumor and a dynamically evolving blood vessel network describes the
transformation of the regular vasculature in normal tissues into a highly
inhomogeneous tumor specific capillary network. The emerging morphology,
characterized by the compartmentalization of the tumor into several regions
differing in vessel density, diameter and necrosis, is in accordance with
experimental data for human melanoma. Vessel collapse due to a combination of
severely reduced blood flow and solid stress exerted by the tumor, leads to a
correlated percolation process that is driven towards criticality by the
mechanism of hydrodynamic vessel stabilization.Comment: 4 pages, 3 figures (higher resolution at
http://www.uni-saarland.de/fak7/rieger/HOMEPAGE/flow.eps
Helical motion and the origin of QPO in blazar-type sources
Recent observations and analysis of blazar sources provide strong evidence
for (i) the presence of significant periodicities in their lightcurves and (ii)
the occurrence of helical trajectories in their radio jets. In scenarios, where
the periodicity is caused by differential Doppler boosting effects along a
helical jet path, both of these facts may be naturally tied together. Here we
discuss four possible driving mechanisms for the occurrence of helical
trajectories: orbital motion in a binary system, Newtonian-driven jet
precession, internal jet rotation and motion along a global helical magnetic
field. We point out that for non-ballistic helical motion the observed period
may appear strongly shortened due to classical travel time effects. Finally,
the possible relevance of the above mentioned driving mechanisms is discussed
for Mkn~501, OJ 287 and AO 0235+16.Comment: 6 pages, 1 figure; presented at the 5th Microquasar Workshop,
Beijing, June 2004. Accepted for publication in the Chinese Journal of
Astronomy and Astrophysic
Domain Growth in Random Magnets
We study the kinetics of domain growth in ferromagnets with random exchange
interactions. We present detailed Monte Carlo results for the nonconserved
random-bond Ising model, which are consistent with power-law growth with a
variable exponent. These results are interpreted in the context of disorder
barriers with a logarithmic dependence on the domain size. Further, we clarify
the implications of logarithmic barriers for both nonconserved and conserved
domain growth.Comment: 7 pages, 4 figure
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