197 research outputs found
Noncontact ultrasound imaging applied to cortical bone phantoms
Purpose: The purpose of this paper was to take the first steps toward applying noncontact ultrasound (NCU) to the tasks of monitoring osteoporosis and quantitative ultrasound imaging (QUS) of cortical bone. The authors also focused on the advantages of NCU, such as its lack of reliance on a technologist to apply transducers and a layer of acoustical coupling gel, the ability of the transducers to operate autonomously as specified by preprogrammed software, and the likely reduction in statistical and systematic errors associated with the variability in the pressure applied by the clinician to the transmitting transducer that NCU might provide. The authors also undertook this study in order to find additional applications of NCU beyond its past limited usage in assessing the severity of third degree burns. Methods: A noncontact ultrasound imaging system using a pair of specially designed broadband, 1.5 MHz noncontact piezoelectric transducers and cortical bone phantoms, were used to determine bone mineral density (BMD), speed of sound (SOS), integrated response (IR), and ultrasonic transmittance. Air gaps of greater than 3 cm, two transmission and two reflection paths, and a digital signal processor were also used in the collection of data from phantoms of nominal mass densities that varied from 1.17 to 2.25 g/cm3 and in bone mineral density from 0 to 1.7 g/cm3. Results: Good correlations between known BMD and measured SOS, IR, and transmittance were obtained for all 17 phantoms, and methods for quantifying and minimizing sources of systematic errors were outlined. The BMD of the phantom sets extended through most of the in vivo range found in cortical bone. A total of 16â20 repeated measurements of the SOS, thickness, and IR for the phantom set that were conducted over a period of several months showed a small variation in the range of measurements of ±1%â2%. These NCU data were shown to be in agreement with similar results using contact ultrasound to be within 1%â2%. Transmittance images of cortical bone phantoms showed differences in the nominal overall BMD values of the phantoms that were large enough to be distinguished by a visual examination. A list of possible sources of errors in quantitative NCU was also included in this study. Conclusions: The results of this paper suggest that NCU might find additional applications in medical imaging, beyond its original and only previous usage in assessing third degree burns. The fact that the authorsâ phantom measurements using conventional, gel coupled ultrasound are in agreement with those obtained with NCU demonstrates that in spite of large additional levels of attenuation of up to 150 dB and new error sources, NCU could have comparable levels of accuracy to those of conventional quantitative ultrasound, while providing the medical and patient comfort-related advantages of not involving direct contact
Proton Decay in Supersymmetric GUT Models
The instability of protons is a crucial prediction of supersymmetric GUTs. We
review the decay in minimal supersymmetric SU(5), which is dominated by
dimension-five operators, and discuss the implications of the failure of Yukawa
unification for the decay rate. In a consistent SU(5) model, where SU(5)
relations among Yukawa couplings hold, the proton decay rate can be several
orders of magnitude smaller than the present experimental bound. Finally, we
discuss orbifold GUTs, where proton decay via dimension-five operators is
absent. The branching ratios of dimension-six decay can significantly differ
from those in four dimensions.Comment: DESY report number correcte
Nuclear and nucleon transitions of the H di-baryon
We consider 3 types of processes pertinent to the phenomenology of an H
di-baryon: conversion of two 's in a doubly-strange hypernucleus to an
H, decay of the H to two baryons, and -- if the H is light enough -- conversion
of two nucleons in a nucleus to an H. We compute the spatial wavefunction
overlap using the Isgur-Karl and Bethe-Goldstone wavefunctions, and treat the
weak interactions phenomenologically. The observation of decays from
doubly-strange hypernuclei puts a constraint on the H wavefunction which is
plausibly satisfied. In this case the H is very long-lived as we calculate. An
absolutely stable H is not excluded at present. SuperK can provide valuable
limits
Solar neutrino measurements in Super-Kamiokande-I
The details of Super--Kamiokande--I's solar neutrino analysis are given.
Solar neutrino measurement in Super--Kamiokande is a high statistics collection
of B solar neutrinos via neutrino-electron scattering. The analysis method
and results of the 1496 day data sample are presented. The final oscillation
results for the data are also presented.Comment: 32pages, 57figures, submitted to Physical Review
Study of Non-Standard Neutrino Interactions with Atmospheric Neutrino Data in Super-Kamiokande I and II
In this paper we study non-standard neutrino interactions as an example of
physics beyond the standard model using atmospheric neutrino data collected
during the Super-Kamiokande I(1996-2001) and II(2003-2005) periods. We focus on
flavor-changing-neutral-currents (FCNC), which allow neutrino flavor
transitions via neutral current interactions, and effects which violate lepton
non-universality (NU) and give rise to different neutral-current
interaction-amplitudes for different neutrino flavors. We obtain a limit on the
FCNC coupling parameter, varepsilon_{mu tau}, |varepsilon_{mu tau}|<1.1 x
10^{-2} at 90%C.L. and various constraints on other FCNC parameters as a
function of the NU coupling, varepsilon_{e e}. We find no evidence of
non-standard neutrino interactions in the Super-Kamiokande atmospheric data.Comment: 12 Pages, 14 figures. To be submitted to Phys. Rev.
Evidence for the Appearance of Atmospheric Tau Neutrinos in Super-Kamiokande
Super-Kamiokande atmospheric neutrino data were fit with an unbinned maximum
likelihood method to search for the appearance of tau leptons resulting from
the interactions of oscillation-generated tau neutrinos in the detector.
Relative to the expectation of unity, the tau normalization is found to be
1.42 \pm 0.35 \ (stat) {\}^{+0.14}_{-0.12}\ (syst) excluding the
no-tau-appearance hypothesis, for which the normalization would be zero, at the
3.8 level. We estimate that 180.1 \pm 44.3\ (stat)
{\}^{+17.8}_{-15.2}\ (syst) tau leptons were produced in the 22.5 kton
fiducial volume of the detector by tau neutrinos during the 2806 day running
period. In future analyses, this large sample of selected tau events will allow
the study of charged current tau neutrino interaction physics with oscillation
produced tau neutrinos.Comment: 7 pages, 4 figures. This is the version as published in Physical
Review Letters including the supplemental figure. A typographical error in
the description of figure 3 is also correcte
Remarks on Limits on String Scale from Proton Decay and Low-Energy amplitudes in Braneworld Scenario
We discuss IR limit of four-fermion scattering amplitudes in braneworld
models including intersecting-branes and SUSY SU(5) GUT version of it. With
certain compactification where instanton effect is negligible, grand
unification condition in D6-D6 intersecting-branes scenario subject to
experimental constraint on proton decay provides possibility for upper limit on
the string scale, , through relationship between the string coupling,
, and the string scale. We discuss how IR divergence is related to number
of twisted fields we have to introduce into intersection region and how it can
change IR behaviour of tree-level amplitudes in various intersecting-branes
models. Using number of twisted fields, we identify some intersecting-branes
models whose tree-level amplitudes are purely stringy in nature and
automatically proportional to at low energy. They are
consequently suppressed by the string scale. For comparison, we also derive
limit on the lower bound of the string scale from experimental constraint on
proton decay induced from purely stringy contribution in the coincident-branes
model, the limit is about TeV.Comment: 14 page
Three flavor neutrino oscillation analysis of atmospheric neutrinos in Super-Kamiokande
We report on the results of a three-flavor oscillation analysis using
Super-Kamiokande~I atmospheric neutrino data, with the assumption of one mass
scale dominance (0). No significant flux change due to
matter effect, which occurs when neutrinos propagate inside the Earth for
0, has been seen either in a multi-GeV -rich sample
or in a -rich sample. Both normal and inverted mass hierarchy
hypotheses are tested and both are consistent with observation. Using
Super-Kamiokande data only, 2-dimensional 90 % confidence allowed regions are
obtained: mixing angles are constrained to and for the normal mass hierarchy. Weaker constraints,
and , are obtained
for the inverted mass hierarchy case.Comment: 7 figures, 3 table
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