4,093 research outputs found
Research in interactive scene analysis
An interactive scene interpretation system (ISIS) was developed as a tool for constructing and experimenting with man-machine and automatic scene analysis methods tailored for particular image domains. A recently developed region analysis subsystem based on the paradigm of Brice and Fennema is described. Using this subsystem a series of experiments was conducted to determine good criteria for initially partitioning a scene into atomic regions and for merging these regions into a final partition of the scene along object boundaries. Semantic (problem-dependent) knowledge is essential for complete, correct partitions of complex real-world scenes. An interactive approach to semantic scene segmentation was developed and demonstrated on both landscape and indoor scenes. This approach provides a reasonable methodology for segmenting scenes that cannot be processed completely automatically, and is a promising basis for a future automatic system. A program is described that can automatically generate strategies for finding specific objects in a scene based on manually designated pictorial examples
Probing Nucleon Strangeness with Neutrinos: Nuclear Model Dependences
The extraction of the nucleon's strangeness axial charge, Delta_s, from
inclusive, quasielastic neutral current neutrino cross sections is studied
within the framework of the plane-wave impulse approximation. We find that the
value of Delta_s can depend significantly on the choice of nuclear model used
in analyzing the quasielastic cross section. This model-dependence may be
reduced by one order of magnitude when Delta_s is extracted from the ratio of
total proton to neutron yields. We apply this analysis to the interpretation of
low-energy neutrino cross sections and arrive at a nuclear theory uncertainty
of plus/minus 0.03 on the value of Delta_s expected to be determined from the
ratio of proton and neutron yields measured by the LSND collaboration. This
error compares favorably with estimates of the SU(3)-breaking uncertainty in
the value of Delta_s extracted from inclusive, polarized deep-inelastic
structure function measurements. We also point out several general features of
the quasielastic neutral current neutrino cross section and compare them with
the analogous features in inclusive, quasielastic electron scattering.Comment: 40 pages (including 11 postscript figures), uses REVTeX and
epsfig.st
The Angular Correlations in the Decay of Excited States in 8Be
Motivated by the recent observation of anomalous electron-positron angular
correlations in the decay of the 18.15 MeV 1+ excited states in 8Be, we
reexamine in detail the Standard Model expectations for these angular
correlations. The 18.15 MeV state is above particle threshold, and several
multipoles can contribute to its decay. We present the general
theoretical expressions for angular distributions for nuclear decay by
C0, C1, C2 M1, E1, and E2 multipoles, and we examine their relative
contribution to the decay of 8Be at 18.15 MeV. We find that this
resonance is dominated by M1 and E1 decay, and that the ratio of M1 to E1
strength is a strong function of energy. This is in contract to the original
analysis of the angular distributions, where the M1/E1 ratio was
assumed to be a constant over the energy region Ep = 0:8-1:2 MeV. We find that
the existence of a `bump' in the measured angular distribution is strongly
dependent on the assumed M1/E1 ratio, with the present analysis finding the
measured large-angle contributions to the angular distribution to be
lower than expectation. Thus, in the current analysis we find no evidence for
axion decay in the 18.15 MeV resonance region of 8Be
A polarised QCD condensate: nu p elastic scattering as a probe of U_A(1) dynamics
U_A(1) dynamics have the potential to induce a polarised condensate inside a
nucleon. The formation of this condensate is related to the realisation of
U_A(1) symmetry breaking by tunneling processes such as instantons. If it is
present, the polarised condensate induces a term in g_1 which has support only
at x=0. Tunneling processes then induce a net transfer of ``spin'' from finite
x to x=0. The polarised condensate may be measured by comparing the
flavour-singlet axial charges which are extracted from polarised deep inelastic
and nu p elastic scattering experiments.Comment: 13 pages LaTeX, Section 3 improved to include discussion of the 3
flavour quark instanton interaction; to appear in Mod. Phys. Lett.
Malignant Fibrous Histiocytoma of The Pancreas
A case of fibrous histiocytoma of low grade malignancy arising from the uncinate lobe of the pancreas is
reported. This is an unusual site for these extremely rare tumours. Survival up to 4 years has been achieved
in our patient following surgical resection
Community action on natural flood management and the governance of a catchment-based approach in the UK
There is increasing interest in natural flood management (NFM) and the delivery of public environmental goods. Yet the implementation of NFM can be ad-hoc and is regionally diverse. Communities often play a role in NFM and thus we assess NFM governance in the UK and communities' position within it. We develop a theoretical framework using the concepts of public goods, social capital, collective action and polycentrism and use it to examine the governance of the design and implementation of NFM in Pickering and Calderdale in Yorkshire, to contribute to a debate on how NFM should be managed, by whom, and under what governance arrangements. Drawing on stakeholder interviews, we find that the participation of community flood groups (CFGs) in NFM improved community access to strategic conversations on flood risk management (FRM). In turn CFGs raised the public profile of NFM, enabled the deployment of NFM measures, and helped to generate the evidence base on them. We conclude that there is a need for a polycentric community and catchment-based approach to better coordinate NFM governance across and between scales, to support community access and contribution to flood risk strategy, and to foster sustainable flood risk management
On the Flavor Structure of the Constituent Quark
We discuss the dressing of constituent quarks with a pseudoscalar meson cloud
within the effective chiral quark model. SU(3) flavor symmetry breaking effects
are included explicitly. Our results are compared with those of the traditional
meson cloud approach in which pions are coupled to the nucleon. The pionic
dressing of the constituent quarks explains the experimentally observed
violation of the Gottfried Sum Rule and leads to an enhanced nonperturbative
sea of quark-antiquark pairs in the constituent quark and consequently in the
nucleon. We find 2.5 times more pions and 10-15 times more kaons in the nucleon
than in the traditional picture.Comment: 7 pages, LaTeX, 4 Postscript figures, to appear in J. Phys.
Spleen stiffness measurements using point shear wave elastography detects noncirrhotic portal hypertension in human immunodeficiency virus
Objectives:To assess the utility of spleen stiffness as a diagnostic tool inindividuals withHIV andnon-cirrhotic portal hypertension(NCPH).Design:The Philips EPIQ7TM, a newpoint shearwave elastography (pSWE) technique, was used to assess liver and spleen stiffnessin3 patient groups. Group1:HIV and NCPH(n=11); Group 2: HIV withpast didanosine(ddI) exposure without known liver disease or NCPH(n=5), Group 3: HIV without known liver disease or ddI exposure(n=9). Methods:Groups were matched for age, HIV chronicity and antiretroviral treatment (including cumulative ddI exposure in Groups 1 and 2). Differences in liver and spleen stiffness (in kPa) between groups were analysed using the Mann-Whiney U test.Results:Liver and spleen stiffness were both significantly higher in NCPH vs ddI-exposed (p=0.019 and p=0.006) and ddI-unexposed controls (p=0.038 and p<0.001). Spleen stiffness was more effective than liver stiffness at predicting NCPH, AUROC 0.812 vs 0.948. Combining the two variables improved the diagnostic performance, AUROC 0.961. The optimal cut-off for predicting NCPH using splenic stiffness was 25.4kPa, with sensitivity 91%, specificity 93%, PPV 91%, NPV 93%, positive likelihood ratio 12.73, negative likelihood ratio 0.10. Spleen and liver stiffness scores were strongly correlated (p=0.0004 95%CI 18,59). Conclusions:Elevated spleen stiffness is observed in HIV with NCPH and can be quantified easily using pSWE with high diagnostic accuracy. Novel strategies such as pSWE for longitudinal monitoring of patients with HIV and NCPH should be considered
Garvey-Kelson Relations for Nuclear Charge Radii
The Garvey-Kelson relations (GKRs) are algebraic expressions originally
developed to predict nuclear masses. In this letter we show that the GKRs
provide a fruitful framework for the prediction of other physical observables
that also display a slowly-varying dynamics. Based on this concept, we extend
the GKRs to the study of nuclear charge radii. The GKRs are tested on 455 out
of the approximately 800 nuclei whose charge radius is experimentally known. We
find a rms deviation between the GK predictions and the experimental values of
only 0.01 fm. This should be contrasted against some of the most successful
microscopic models that yield rms deviations almost three times as large.
Predictions - with reliable uncertainties - are provided for 116 nuclei whose
charge radius is presently unknown.Comment: 4 pages and 3 figure
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