197 research outputs found

    Noncontact ultrasound imaging applied to cortical bone phantoms

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    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 16–20 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%–2%. These NCU data were shown to be in agreement with similar results using contact ultrasound to be within 1%–2%. 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 authors’ 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

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    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

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    We consider 3 types of processes pertinent to the phenomenology of an H di-baryon: conversion of two Λ\Lambda'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 Λ\Lambda 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

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    The details of Super--Kamiokande--I's solar neutrino analysis are given. Solar neutrino measurement in Super--Kamiokande is a high statistics collection of 8^8B 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

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    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

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    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 3.8σ\sigma 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

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    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, MSM_S, through relationship between the string coupling, gsg_s, 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 gs/MS2g_s/M^2_{S} 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 10510^5 TeV.Comment: 14 page

    Search for Nucleon Decay into Charged Anti-lepton plus Meson in Super-Kamiokande I and II

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    Searches for a nucleon decay into a charged anti-lepton (e^+ or {\mu}^+) plus a light meson ({\pi}^0, {\pi}^-, {\eta}, {\rho}^0, {\rho}^-, {\omega}) were performed using the Super-Kamiokande I and II data. Twelve nucleon decay modes were searched for. The total exposure is 140.9 kiloton \cdot years, which includes a 91.7 kiloton \cdot year exposure (1489.2 live days) of Super-Kamiokande-I and a 49.2 kiloton \cdot year exposure (798.6 live days) of Super-Kamiokande-II. The number of candidate events in the data was consistent with the atmospheric neutrino background expectation. No significant evidence for a nucleon decay was observed in the data. Thus, lower limits on the nucleon partial lifetime at 90% confidence level were obtained. The limits range from 3.6 \times 10^31 to 8.2 \times 10^33 years, depending on the decay modes.Comment: 25 pages, 18 figure
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