7,844 research outputs found
Few-body physics in effective field theory
Effective Field Theory (EFT) provides a powerful framework that exploits a
separation of scales in physical systems to perform systematically improvable,
model-independent calculations. Particularly interesting are few-body systems
with short-range interactions and large two-body scattering length. Such
systems display remarkable universal features. In systems with more than two
particles, a three-body force with limit cycle behavior is required for
consistent renormalization already at leading order. We will review this EFT
and some of its applications in the physics of cold atoms and nuclear physics.
In particular, we will discuss the possibility of an infrared limit cycle in
QCD. Recent extensions of the EFT approach to the four-body system and N-boson
droplets in two spatial dimensions will also be addressed.Comment: 10 pages, 5 figures, Proceedings of the INT Workshop on "Nuclear
Forces and the Quantum Many-Body Problem", Oct. 200
Universal Properties of Two-Dimensional Boson Droplets
We consider a system of N nonrelativistic bosons in two dimensions,
interacting weakly via a short-range attractive potential. We show that for N
large, but below some critical value, the properties of the N-boson bound state
are universal. In particular, the ratio of the binding energies of (N+1)- and
N-boson systems, B_{N+1}/B_N, approaches a finite limit, approximately 8.567,
at large N. We also confirm previous results that the three-body system has
exactly two bound states. We find for the ground state B_3^(0) = 16.522688(1)
B_2 and for the excited state B_3^(1) = 1.2704091(1) B_2.Comment: 4 pages, 2 figures, final versio
Star formation rates of distant luminous infrared galaxies derived from Halpha and IR luminosities
We present a study of the star formation rate (SFR) for a sample of 16
distant galaxies detected by ISOCAM at 15um in the CFRS0300+00 and CFRS1400+52
fields. Their high quality and intermediate resolution VLT/FORS spectra have
allowed a proper correction of the Balmer emission lines from the underlying
absorption. Extinction estimates using the Hbeta/Hgamma and the Halpha/Hbeta
Balmer decrement are in excellent agreement, providing a robust measurement of
the instantaneous SFR based on the extinction-corrected Halpha luminosity. Star
formation has also been estimated exploiting the correlations between IR
luminosity and those at MIR and radio wavelengths. Our study shows that the
relationship between the two SFR estimates follow two distinct regimes: (1) for
galaxies with SFRIR below ~ 100Msolar/yr, the SFR deduced from Halpha
measurements is a good approximation of the global SFR and (2) for galaxies
near of ULIRGs regime, corrected Halpha SFR understimated the SFR by a factor
of 1.5 to 2. Our analyses suggest that heavily extincted regions completely
hidden in optical bands (such as those found in Arp 220) contribute to less
than 20% of the global budget of star formation history up to z=1.Comment: (1) GEPI, Obs. Meudon, France ;(2) CEA-Saclay, France ;(3) ESO,
Gemany ;(4) IAC, Spain. To appear in A&
Deep UV Luminosity Functions at the Infall Region of the Coma Cluster
We have used deep GALEX observations at the infall region of the Coma cluster
to measure the faintest UV luminosity functions (LFs) presented for a rich
galaxy cluster thus far. The Coma UV LFs are measured to M_UV = -10.5 in the
GALEX FUV and NUV bands, or 3.5 mag fainter than previous studies, and reach
the dwarf early-type galaxy population in Coma for the first time. The
Schechter faint-end slopes (alpha = -1.39 in both GALEX bands) are shallower
than reported in previous Coma UV LF studies owing to a flatter LF at faint
magnitudes. A Gaussian-plus-Schechter model provides a slightly better
parametrization of the UV LFs resulting in a faint-end slope of ~ -1.15 in both
GALEX bands. The two-component model gives faint-end slopes shallower than -1
(a turnover) for the LFs constructed separately for passive and star forming
galaxies. The UV LFs for star forming galaxies show a turnover at M_UV ~ -14
owing to a deficit of dwarf star forming galaxies in Coma with stellar masses
below M*=10^8 Msun. A similar turnover is identified in recent UV LFs measured
for the Virgo cluster suggesting this may be a common feature of local galaxy
clusters, whereas the field UV LFs continue to rise at faint magnitudes. We did
not identify an excess of passive galaxies as would be expected if the missing
dwarf star forming galaxies were quenched inside the cluster. In fact, the LFs
for both dwarf passive and star forming galaxies show the same turnover at
faint magnitudes. We discuss the possible origin of the missing dwarf star
forming galaxies in Coma and their expected properties based on comparisons to
local field galaxies.Comment: accepted for publication in Ap
Multiwavelength Observations of one Galaxy in Marano Field
We report the multiwavelength observations of one intermediate redshift
(z=0.3884) galaxy in the Marano Field. These data include ISOCAM middle
infrared, VLT/FORS2 spectroscopic and photometric data, associated with the
ATCA 1.4 GHz radio and ROSAT PSPC X-ray observations from literature. The
Spectral Energy Distribution obtained by VLT spectroscopy exhibits its
early-type galaxy property, while, in the same time, it has obvious [OIII]5007
emission line. The diagnostic diagram from the optical emission line ratios
shows its Seyfert galaxy property. Its infrared-radio relation follows the
correlation of sources detected at 15 \mu and radio. It has a high X-ray
luminosity of 1.26*10^{43} ergs/s, which is much higher than the general
elliptical galaxies s with the similar B band luminosity, and is about 2 orders
of magnitude higher than the derived value from the star forming tracer, the
FIR luminosity. This means that the X-ray sources of this galaxy are not
stellar components, but the AGN is the dominant component.Comment: 6 pages, 1 PS figure and 4 tables. Publication in ChJAA, Suppl., the
Special Issue for The Fifth Microquasar Workshop 2004:
http://chjaa.bao.ac.cn/, 2005, Vol.5, 335-34
An optical fibre dynamic instrumented palpation sensor for the characterisation of biological tissue
AbstractThe diagnosis of prostate cancer using invasive techniques (such as biopsy and blood tests for prostate-specific antigen) and non-invasive techniques (such as digital rectal examination and trans-rectal ultrasonography) may be enhanced by using an additional dynamic instrumented palpation approach to prostate tissue classification. A dynamically actuated membrane sensor/actuator has been developed that incorporates an optical fibre Fabry–Pérot interferometer to record the displacement of the membrane when it is pressed on to different tissue samples. The membrane sensor was tested on a silicon elastomer prostate model with enlarged and stiffer material on one side to simulate early stage prostate cancer. The interferometer measurement was found to have high dynamic range and accuracy, with a minimum displacement resolution of ±0.4μm over a 721μm measurement range. The dynamic response of the membrane sensor when applied to different tissue types changed depending on the stiffness of the tissue being measured. This demonstrates the feasibility of an optically tracked dynamic palpation technique for classifying tissue type based on the dynamic response of the sensor/actuator
2D Multi-Angle, Multi-Group Neutrino Radiation-Hydrodynamic Simulations of Postbounce Supernova Cores
We perform axisymmetric (2D) multi-angle, multi-group neutrino
radiation-hydrodynamic calculations of the postbounce phase of core-collapse
supernovae using a genuinely 2D discrete-ordinate (S_n) method. We follow the
long-term postbounce evolution of the cores of one nonrotating and one
rapidly-rotating 20-solar-mass stellar model for ~400 milliseconds from 160 ms
to ~550 ms after bounce. We present a multi-D analysis of the multi-angle
neutrino radiation fields and compare in detail with counterpart simulations
carried out in the 2D multi-group flux-limited diffusion (MGFLD) approximation
to neutrino transport. We find that 2D multi-angle transport is superior in
capturing the global and local radiation-field variations associated with
rotation-induced and SASI-induced aspherical hydrodynamic configurations. In
the rotating model, multi-angle transport predicts much larger asymptotic
neutrino flux asymmetries with pole to equator ratios of up to ~2.5, while
MGFLD tends to sphericize the radiation fields already in the optically
semi-transparent postshock regions. Along the poles, the multi-angle
calculation predicts a dramatic enhancement of the neutrino heating by up to a
factor of 3, which alters the postbounce evolution and results in greater polar
shock radii and an earlier onset of the initially rotationally weakened SASI.
In the nonrotating model, differences between multi-angle and MGFLD
calculations remain small at early times when the postshock region does not
depart significantly from spherical symmetry. At later times, however, the
growing SASI leads to large-scale asymmetries and the multi-angle calculation
predicts up to 30% higher average integral neutrino energy deposition rates
than MGFLD.Comment: 20 pages, 21 figures. Minor revisions. Accepted for publication in
ApJ. A version with high-resolution figures may be obtained from
http://www.stellarcollapse.org/papers/Ott_et_al2008_multi_angle.pd
Nonuniversal Effects in the Homogeneous Bose Gas
Effective field theory predicts that the leading nonuniversal effects in the
homogeneous Bose gas arise from the effective range for S-wave scattering and
from an effective three-body contact interaction. We calculate the leading
nonuniversal contributions to the energy density and condensate fraction and
compare the predictions with results from diffusion Monte Carlo calculations by
Giorgini, Boronat, and Casulleras. We give a crude determination of the
strength of the three-body contact interaction for various model potentials.
Accurate determinations could be obtained from diffusion Monte Carlo
calculations of the energy density with higher statistics.Comment: 24 pages, RevTex, 5 ps figures, included with epsf.te
Understanding and Affecting Student Reasoning About Sound Waves
Student learning of sound waves can be helped through the creation of
group-learning classroom materials whose development and design rely on
explicit investigations into student understanding. We describe reasoning in
terms of sets of resources, i.e. grouped building blocks of thinking that are
commonly used in many different settings. Students in our university physics
classes often used sets of resources that were different from the ones we wish
them to use. By designing curriculum materials that ask students to think about
the physics from a different view, we bring about improvement in student
understanding of sound waves. Our curriculum modifications are specific to our
own classes, but our description of student learning is more generally useful
for teachers. We describe how students can use multiple sets of resources in
their thinking, and raise questions that should be considered by both
instructors and researchers.Comment: 23 pages, 4 figures, 3 tables, 28 references, 7 notes. Accepted for
publication in the International Journal of Science Educatio
Algorithmic statistics revisited
The mission of statistics is to provide adequate statistical hypotheses
(models) for observed data. But what is an "adequate" model? To answer this
question, one needs to use the notions of algorithmic information theory. It
turns out that for every data string one can naturally define
"stochasticity profile", a curve that represents a trade-off between complexity
of a model and its adequacy. This curve has four different equivalent
definitions in terms of (1)~randomness deficiency, (2)~minimal description
length, (3)~position in the lists of simple strings and (4)~Kolmogorov
complexity with decompression time bounded by busy beaver function. We present
a survey of the corresponding definitions and results relating them to each
other
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