327 research outputs found
Dynamical spin-flip susceptibility for a strongly interacting ultracold Fermi gas
The Stoner model predicts that a two-component Fermi gas at increasing
repulsive interactions undergoes a ferromagnetic transition. Using the
random-phase approximation we study the dynamical properties of the interacting
Fermi gas. For an atomic Fermi gas under harmonic confinement we show that the
transverse (spin-flip) dynamical susceptibility displays a clear signature of
the ferromagnetic phase in a magnon peak emerging from the Stoner particle-hole
continuum. The dynamical spin susceptibilities could be experimentally explored
via spin-dependent Bragg spectroscopy.Comment: 4 pages, 3 figure
Disorder-induced magnetic memory: Experiments and theories
Beautiful theories of magnetic hysteresis based on random microscopic
disorder have been developed over the past ten years. Our goal was to directly
compare these theories with precise experiments. We first developed and then
applied coherent x-ray speckle metrology to a series of thin multilayer
perpendicular magnetic materials. To directly observe the effects of disorder,
we deliberately introduced increasing degrees of disorder into our films. We
used coherent x-rays to generate highly speckled magnetic scattering patterns.
The apparently random arrangement of the speckles is due to the exact
configuration of the magnetic domains in the sample. In effect, each speckle
pattern acts as a unique fingerprint for the magnetic domain configuration.
Small changes in the domain structure change the speckles, and comparison of
the different speckle patterns provides a quantitative determination of how
much the domain structure has changed. How is the magnetic domain configuration
at one point on the major hysteresis loop related to the configurations at the
same point on the loop during subsequent cycles? The microscopic return-point
memory(RPM) is partial and imperfect in the disordered samples, and completely
absent when the disorder was not present. We found the complementary-point
memory(CPM) is also partial and imperfect in the disordered samples and
completely absent when the disorder was not present. We found that the RPM is
always a little larger than the CPM. We also studied the correlations between
the domains within a single ascending or descending loop. We developed new
theoretical models that do fit our experiments.Comment: 26 pages, 25 figures, Accepted by Physical Review B 01/25/0
Lattice Matrix Elements and CP Violation in B and K Physics: Status and Outlook
Status of lattice calculations of hadron matrix elements along with CP
violation in B and in K systems is reviewed. Lattice has provided useful input
which, in conjunction with experimenatl data, leads to the conclusion that
CP-odd phase in the CKM matrix plays the dominant role in the observed
asymmetry in . It is now quite likely that any beyond the SM,
CP-odd, phase will cause only small deviations in B-physics. Search for the
effects of the new phase(s) will consequently require very large data samples
as well as very precise theoretical predictions. Clean determination of {\it
all} the angles of the unitarity triangle therefore becomes essential. In this
regard processes play a unique role. Regarding K-decays,
remarkable progress made by theory with regard to maintenance of chiral
symmetry on the lattice is briefly discussed. First application already provide
quantitaive information on and the rule. The enhancement
in appears to arise solely from tree operators, esp. ; penguin
contribution to appears to be very small. However, improved
calculations are necessary for \epsilon^'/epsilon as there the contributions
of QCD penguins and electroweak penguins largely seem to cancel. There are good
reasons, though, to believe that these cancellations will not survive
improvements that are now underway. Importance of determining the unitarity
triangle purely from K-decays is also emphasized.Comment: Invited talk at the 9th International Symposium on Particles, Strings
and Cosmology (PASCOS 03), Mumbai (Bombay) India,3-8 Jan 200
Pion photoproduction on the nucleon in the quark model
We present a detailed quark-model study of pion photoproduction within the
effective Lagrangian approach. Cross sections and single-polarization
observables are investigated for the four charge channels, , , , and .
Leaving the coupling strength to be a free parameter, we obtain a
reasonably consistent description of these four channels from threshold to the
first resonance region. Within this effective Lagrangian approach, strongly
constrainted by the quark model, we consider the issue of double-counting which
may occur if additional {\it t}-channel contributions are included.Comment: Revtex, 35 pages, 16 eps figures; version to appear on PR
Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma)
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma
and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a
centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The
value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08
^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical,
the second systematic and the third is associated to the ratio of fragmentation
fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/-
0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be
(3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.Comment: 15 pages, 1 figure, 2 table
Photoproduction of pions and properties of baryon resonances from a Bonn-Gatchina partial wave analysis
Masses, widths and photocouplings of baryon resonances are determined in a
coupled-channel partial wave analysis of a large variety of data. The
Bonn-Gatchina partial wave formalism is extended to include a decomposition of
t- and u-exchange amplitudes into individual partial waves. The multipole
transition amplitudes for and are
given and compared to results from other analyses.Comment: 18 pages, 14 figure
Agricultura orgĂąnica em ĂĄreas urbanas e periurbanas com base na agroecologia.
A agricultura orgĂąnica com base na agroecologia Ă© o mote tecnolĂłgico adequado Ă realidade dos agroecossistemas urbanos. Este artigo ressalta a necessidade de se desenvolver tecnologias e insumos especĂficos. A partir de experiĂȘncias com agricultura urbana em diferentes paĂses em desenvolvimento, evidencia-se a necessidade de se buscar capacidades locais e apoio do poder pĂșblico, especialmente nas iniciativas da sociedade organizada e mobilizada para a produção agrĂcola urbana
P-wave excited baryons from pion- and photo-induced hyperon production
We report evidence for , , ,
, , and , and find
indications that might have a companion state at 1970\,MeV. The
controversial is not seen. The evidence is derived from a
study of data on pion- and photo-induced hyperon production, but other data are
included as well. Most of the resonances reported here were found in the
Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were
challenged recently by the Data Analysis Center at GWU. Our analysis is
constrained by the energy independent scattering amplitudes from either
KH84 or GWU. The two amplitudes from KH84 or GWU, respectively, lead to
slightly different branching ratios of contributing resonances but the
debated resonances are required in both series of fits.Comment: 22 pages, 28 figures. Some additional sets of data are adde
Definition and classification of chyle leak after pancreatic operation: A consensus statement by the International Study Group on Pancreatic Surgery
Recent literature suggests that chyle leak may complicate up to 10% of pancreatic resections. Treatment depends on its severity, which may include chylous ascites. No international consensus definition or grading system of chyle leak currently is available. The International Study Group on Pancreatic Surgery, an international panel of pancreatic surgeons working in well-known, high-volume centers, reviewed the literature and worked together to establish a consensus on the definition and classification of chyle leak after pancreatic operation. Chyle leak was defined as output of milky-colored fluid from a drain, drain site, or wound on or after postoperative day 3, with a triglyceride content â„110 mg/dL (â„1.2 mmol/L). Three different grades of severity were defined according to the management needed: grade A, no specific intervention other than oral dietary restrictions; grade B, prolongation of hospital stay, nasoenteral nutrition with dietary restriction, total parenteral nutrition, octreotide, maintenance of surgical drains, or placement of new percutaneous drains; and grade C, need for other more invasive in-hospital treatment, intensive care unit admission, or mortality. This classification and grading system for chyle leak after pancreatic resection allows for comparison of outcomes between series. As with the other the International Study Group on Pancreatic Surgery consensus statements, this classification should facilitate communication and evaluation of different approaches to the prevention and treatment of this complicatio
Determination of the E2/M1 Ratio in the \gamma N \to \Delta(1232) Transition from a Simultaneous Measurement of p(\vec{\gamma},p)\pi^0 and p(\vec{\gamma},\pi^+)n
Tagged linearly polarized photons have been used at the Mainz Microtron MAMI
for simultaneous measurements of the p(\vec{\gamma},p)\pi^0 and
p(\vec{\gamma},\pi^+)n reaction channels to study the \gamma N \to \Delta(1232)
transition. The energy dependence of the magnetic dipole M_{1+}^{3/2} and
electric quadrupole E_{1+}^{3/2} amplitudes have been extracted from these data
in the photon energy range from 270 to 420 MeV. The E2/M1 ratio for the \gamma
N \to \Delta(1232) transition has been determined to be -
(2.5+-0.1_{stat}+-0.2_{sys}) % at the resonance position delta_{33}=90^0.Comment: 25 pages Latex including 13 postscript figures submitted for
publication in Phys. Rev.
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