3,554 research outputs found
An experimental study of tomographic imaging in layered media
Ultrasonic tomography has found its applications in material evaluation since the later 70’s. However, the techniques in this field are far less developed compared to their x-ray counterparts, which have been widely used in the medical community. One of the practical problems in acoustic tomography is that acoustic waves will not necessarily propagate along straight paths in a nonhomogeneous medium. The situation will be more complicated when material inhomogeneities are coupled with anisotropy as the approach is applied to composite media. In order to resolve the situation, one has either to tolerate the consequence of using straight line ray paths or to seek a way to correct the errors due to ray bending. Indeed, most of the previous work in this area has been based on the straight path assumption. As pointed out by Dines and Lytle[1], if the material inhomogeneity is not serious, the errors caused by straight path assumption can be safely neglected. However, in practice, situations may arise where serious inhomogeneities exist. Even with small inhomogeneities correction is highly desirable when accuracy is of particular concern
Is the association between blood pressure and cognition in the oldest-old modified by physical, vascular or brain pathology markers? The EMIF-AD 90 + Study
BACKGROUND: Prior studies suggest a changing association between blood pressure (BP) and cognition with aging, however work in the oldest-old has yielded ambiguous results. Potentially, these mixed results can be explained by modifying factors. The aim of this study was to establish whether physical, vascular or brain pathology markers that describe a state of increased vulnerability, affect the association between BP and cognition in the oldest-old. Results may influence clinicians’ decisions regarding the use of antihypertensives in this age group. METHODS: We included 122 individuals (84 without cognitive impairment and 38 with cognitive impairment) from the EMIF-AD 90 + Study (mean age 92.4 years). First, we tested cross-sectional associations of systolic and diastolic BP with a cognitive composite score. Second, we tested whether these associations were modified by physical markers (waist circumference, muscle mass, gait speed and handgrip strength), vascular markers (history of cardiac disease, carotid intima media thickness as a proxy for atherosclerosis and carotid distensibility coefficient as a proxy for arterial stiffness) or brain pathology markers (white matter hyperintensities and cortical thickness). RESULTS: In the total sample, there was no association between BP and cognition, however, waist circumference modified this association (p-value for interaction with systolic BP: 0.03, with diastolic BP: 0.01). In individuals with a high waist circumference, higher systolic and diastolic BP tended to be associated with worse cognition, while in individuals with a low waist circumference, higher systolic BP was associated with better cognition. The others physical, vascular and brain pathology markers did not modify the association between BP and cognition. CONCLUSIONS: When examining various markers for physical, vascular and brain vulnerability, only waist circumference affected the association between BP and cognition. This warrants further research to evaluate whether waist circumference may be a marker in clinical practice influencing the use of antihypertensives in the oldest-old
Complete Next to Leading Order QCD Corrections to the Photon Structure Functions and
We present the complete NLO QCD analysis of the photon structure functions
and for a real photon target. In
particular we study the heavy flavor content of the structure functions which
is due to two different production mechanisms, namely collisions of a virtual
photon with a real photon, and with a parton. We observe that the charm
contributions are noticeable for as well as
in the x-region studied.Comment: Latex 34 pages, 24 figures, uuencoded, attached at end, ITP-SB-93-46,
FERMILAB-Pub-93/240-T, SMU HEP 93-1
CO(4-3) and dust emission in two powerful high-z radio galaxies, and CO lines at high redshifts
We report the detection of sub-mm emission from dust at 850 microns and of
the 12CO J=4-3 line in the two distant powerful radio galaxies 4C 60.07
(z=3.79) and 6C 1909+722 (z=3.53). In the case of 4C 60.07 the dust emission is
also detected at 1.25 mm. The estimated molecular gas masses are large, of the
order of ~(0.5-1)x10^{11} Solar. The large FIR luminosities (L_fir ~ 10^{13}
Solar) suggest that we are witnessing two major starburst phenomena, while the
observed large velocity widths (FWHM > 500 km/sec) are characteristic of
mergers. In the case of 4C 60.07 the CO emission extends over ~30 kpc and spans
a velocity range of >1000 km/sec. It consists of two distinct features with
FWHM of >= 550 km/sec and ~150 km/sec and line centers separated by >=700
km/sec The least massive of these components is probably very gas-rich with
potentially >=60% of its dynamical mass in the form of molecular gas. The
extraordinary morphology of the CO emission in this object suggests that it is
not just a scaled-up version of a local Ultra Luminous Infrared Galaxy, and it
may be a formative stage of the elliptical host of the residing radio-loud AGN.
Finally we briefly explore the effects of the wide range of gas excitation
conditions expected for starburst environments on the luminosity of high-J CO
lines. We conclude that in unlensed objects, CO (J+1-->J), J+1>3 lines can be
significantly weak with respect to CO J=1-0 and this can hinder their detection
even in the presence of substantial molecular gas masses.Comment: 34 pages, 5 figures, accepted for publication in The Astrophysical
Journa
Optical Trapping of an Ion
For several decades, ions have been trapped by radio frequency (RF) and
neutral particles by optical fields. We implement the experimental
proof-of-principle for trapping an ion in an optical dipole trap. While
loading, initialization and final detection are performed in a RF trap, in
between, this RF trap is completely disabled and substituted by the optical
trap. The measured lifetime of milliseconds allows for hundreds of oscillations
within the optical potential. It is mainly limited by heating due to photon
scattering. In future experiments the lifetime may be increased by further
detuning the laser and cooling the ion. We demonstrate the prerequisite to
merge both trapping techniques in hybrid setups to the point of trapping ions
and atoms in the same optical potential.Comment: 5 pages, 3 figure
Resonant radiation pressure on neutral particles in a waveguide
A theoretical analysis of electromagnetic forces on neutral particles in an
hollow waveguide is presented. We show that the effective scattering cross
section of a very small (Rayleigh) particle can be strongly modified inside a
waveguide. The coupling of the scattered dipolar field with the waveguide modes
induce a resonant enhanced backscattering state of the scatterer-guide system
close to the onset of new modes. The particle effective cross section can then
be as large as the wavelength even far from any transition resonance. As we
will show, a small particle can be strongly accelerated along the guide axis
while being highly confined in a narrow zone of the cross section of the guide.Comment: RevTeX,4 pages,3 PS figure
Aspects of Two-Photon Physics at Linear e+e- Colliders
We discuss various reactions at future e+e- and gamma-gamma colliders
involving real (beamstrahlung or backscattered laser) or quasi--real
(bremsstrahlung) photons in the initial state and hadrons in the final state.
The production of two central jets with large pT is described in some detail;
we give distributions for the rapidity and pT of the jets as well as the
di--jet invariant mass, and discuss the relative importance of various initial
state configurations and the uncertainties in our predictions. We also present
results for `mono--jet' production where one jet goes down a beam pipe, for the
production of charm, bottom and top quarks, and for single production of W and
Z bosons. Where appropriate, the two--photon processes are compared with
annihilation reactions leading to similar final states. We also argue that the
behaviour of the total inelastic gamma-gamma cross section at high energies
will probably have little impact on the severity of background problems caused
by soft and semi--hard (`minijet') two--photon reactions. We find very large
differences in cross sections for all two--photon processes between existing
designs for future e+e- colliders, due to the different beamstrahlung spectra;
in particular, both designs with >1 events per bunch crossing exist.Comment: 51 pages, 13 figures(not included
A New 5-Flavour LO Analysis and Parametrization of Parton Distributions in the Real Photon
New, radiatively generated, LO quark (u,d,s,c,b) and gluon densities in a
real, unpolarized photon are presented. We perform a global 3-parameter fit,
based on LO DGLAP evolution equations, to all available data for the structure
function F2^gamma(x,Q^2). We adopt a new theoretical approach called ACOT(chi),
originally introduced for the proton, to deal with the heavy-quark thresholds.
This defines our basic model (CJKL model), which gives a very good description
of the experimental data on F2^gamma(x,Q^2), for both Q^2 and x dependences.
For comparison we perform a standard fit using the Fixed Flavour-Number Scheme
(FFNS_CJKL model), updated with respect to the previous fits of this type. We
show the superiority of the CJKL fit over the FFNS_CJKL one and other LO fits
to the F2^gamma(x,Q^2) data. The CJKL model gives also the best description of
the LEP data on the Q^2 dependence of the F2^gamma, averaged over various
x-regions, and the F_2,c^gamma, which were not used directly in the fit.
Finally, a simple analytic parametrization of the resulting parton densities
obtained with the CJKL model is given.Comment: 43 pages, RevTeX4 using axodraw style, 3 tex and 12 postscript
figures, version submitted to Phys. Rev. D, small text changes, one reference
added, FORTRAN program available at http://www.fuw.edu.pl/~pjank/param.html
and at http://www-zeuthen.desy.de/~alorca/id4.htm
New Parton Distribution Functions for the Photon
We present new improved parton distributions for the photon. We fit {\bf all}
available data on the photon structure function, , with
GeV, in order to determine the quark distributions. We also pay
particular attention to the gluon distribution in the photon,
, which has been poorly constrained in earlier analyses
which only include structure function data. We use large jet production
in collisions from TRISTAN to constrain . We also
see what information can be gleaned from collisions at HERA on
and on the quark distributions at large , where there are no
structure function data. We review future prospects of elucidating the parton
distributions of the photon.Comment: 33 pages, 8 figures, uses eps
The Higgs boson in the MSSM in light of the LHC
We investigate the expectations for the light Higgs signal in the MSSM in
different search channels at the LHC. After taking into account dark matter and
flavor constraints in the MSSM with eleven free parameters, we show that the
light Higgs signal in the channel is expected to be at most at
the level of the SM Higgs, while the from W fusion
and/or the can be enhanced. For the main discovery
mode, we show that a strong suppression of the signal occurs in two different
cases: low or large invisible width. A more modest suppression is
associated with the effect of light supersymmetric particles. Looking for such
modification of the Higgs properties and searching for supersymmetric partners
and pseudoscalar Higgs offer two complementary probes of supersymmetry.Comment: 19 pages, 8 figure
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