19,427 research outputs found
2D-3D registration of CT vertebra volume to fluoroscopy projection: A calibration model assessment (doi:10.1155/2010/806094)
This study extends a previous research concerning intervertebral motion registration by means of 2D dynamic fluoroscopy to obtain a more comprehensive 3D description of vertebral kinematics. The problem of estimating the 3D rigid pose of a CT volume of a vertebra from its 2D X-ray fluoroscopy projection is addressed. 2D-3D registration is obtained maximising a measure of similarity between Digitally Reconstructed Radiographs (obtained from the CT volume) and real fluoroscopic projection. X-ray energy correction was performed. To assess the method a calibration model was realised a sheep dry vertebra was rigidly fixed to a frame of reference including metallic markers. Accurate measurement of 3D orientation was obtained via single-camera calibration of the markers and held as true 3D vertebra position; then, vertebra 3D pose was estimated and results compared. Error analysis revealed accuracy of the order of 0.1 degree for the rotation angles of about 1?mm for displacements parallel to the fluoroscopic plane, and of order of 10?mm for the orthogonal displacement.<br/
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Improving Visual Field Examination of the Macula Using Structural Information
Purpose: To investigate a novel approach for structure-function modeling in glaucoma to improve visual field testing in the macula.
Methods: We acquired data from the macular region in 20 healthy eyes and 31 with central glaucomatous damage. Optical coherence tomography (OCT) scans were used to estimate the local macular ganglion cell density. Perimetry was performed with a fundus-tracking device using a 10-2 grid. OCT scans were matched to the retinal image from the fundus perimeter to accurately map the tested locations onto the structural damage. Binary responses from the subjects to all presented stimuli were used to calculate the structure-function model used to generate prior distributions for a ZEST (Zippy Estimation by Sequential Testing) Bayesian strategy. We used simulations based on structural and functional data acquired from an independent dataset of 20 glaucoma patients to compare the performance of this new strategy, structural macular ZEST (MacS-ZEST), with a standard ZEST.
Results: Compared to the standard ZEST, MacS-ZEST reduced the number of presentations by 13% in reliable simulated subjects and 14% with higher rates (≥20%) of false positive or false negative errors. Reduction in mean absolute error was not present for reliable subjects but was gradually more important with unreliable responses (≥10% at 30% error rate).
Conclusions: Binary responses can be modeled to incorporate detailed structural information from macular OCT into visual field testing, improving overall speed and accuracy in poor responders.
Translational Relevance: Structural information can improve speed and reliability for macular testing in glaucoma practice
Propagation of perturbations and meandering in a free surface shallow water jet
A shallow water free-surface turbulent jet is investigated at Froude numbers variable between about 0.15 and 0.6 and a Reynolds number equal to 5000, with a jet height-to-width aspect ratio variable from 0.5 to 1.1. In these experimental conditions, the flow is unstable and develops local transverse instabilities, which are amplified to a global meandering motion, forcing the jet to oscillate orthogonally to its axis. Instantaneous and averaged velocity fields are obtained by means of high-density, correlation-based time-resolved Particle Tracking Velocimetry. From the average point of view, the present jet configuration resembles a confined jet condition similar to that of wall jets, but with additional relevant three-dimensional effects, retaining self-similar properties, with a net co-flow and some ambient fluid entrainment. For increasing Froude numbers, such configuration is moved downstream and the jet spreading is delayed. The high resolution in space and time of present measurements allows to locally detect and following perturbed patterns and to derive amplitude and frequency of oscillation of the global meandering motion, the former increasing with axial distance and decreasing with Froude number, the latter doing just the opposite. The velocity of propagation of perturbed patterns is also investigated in comparison to the jet mean velocity, the local celerity of propagation of fluctuating velocity fields being derived. Results indicate that axial fluctuations propagate downstream similarly to transverse fluctuations along the orthogonal direction, thus showing a close coupling among the two motions and the onset of a self-sustained mechanism driven by the mean flow, responsible for the generation of the macroscopic meandering motion. This effect is in agreement with numerical predictions and is emphasised as the Froude number increases
Resonating bipolarons
Electrons coupled to local lattice deformations end up in selftrapped
localized molecular states involving their binding into bipolarons when the
coupling is stronger than a certain critical value. Below that value they exist
as essentially itinerant electrons. We propose that the abrupt crossover
between the two regimes can be described by resonant pairing similar to the
Feshbach resonance in binary atomic collision processes. Given the
intrinsically local nature of the exchange of pairs of itinerant electrons and
localized bipolarons, we demonstrate the occurrence of such a resonance on a
finite-size cluster made out of metallic atoms surrounding a polaronic ligand
center.Comment: 7 pages, 4 figures, to be published in Europhysics Letter
A possible new phase of antagonistic nematogens in a disorienting field
A simple model is proposed for nematogenic molecules that favor perpendicular
orientations as well as parallel ones. (Charged rods, for example, show this
antagonistic tendency.) When a small disorienting field is applied along , a
low density phase of nematic order parameter coexists with a
dense biaxial nematic . (At zero field, becomes isotropic and
uniaxial.) But at stronger fields, a new phase , invariant under
rotations around the field axis, appears in between and .
Prospects for finding the phase experimentally are briefly discussed.Comment: 4 pages, 2 figures. Accepted for publication in PR
Effect of Ferric Sodium EDTA administration, in combination with vitamin C, folic acid, copper gluconate, zinc gluconate and selenomethionine, on cardiovascular risk evaluation: exploration of the HRV frequency domain
diseases. Using the Heart Rate Variability (HRV) analysis is possible to provide an evaluation of the safety and the
effectiveness of intervention.
Objective: To evaluate the efficacy and safety of Ferric Sodium EDTA in combination with vitamin C, folic acid, copper
gluconate, zinc gluconate and selenomethionine (Ferachel forte®) 2 tabs/day for 24 days in elderly patients with secondary
anaemia, by exploring the HRV frequency domain.
Methods: In 45 elderly patients with secondary anaemia and/or low-moderate kidney failure, laboratory values after
administration of Ferric Sodium EDTA, 2 tabs a day, in combination with vitamin C, folic acid, copper gluconate, zinc
gluconate and selenomethionine (Ferachel forte®) for 24 days (N=16 patients) or ferrous gluconate 63 mg/day added to
saline solution, administered using intravenous access during the hospitalization period of 15 ± 5 days (N=29 patients)
were evaluated. Also, ECG signals and bioelectrical impedance (BIA) were measured.
Results: Oral iron supplementation with Ferric Sodium EDTA, in combination with vitamin C, folic acid, copper gluconate,
zinc gluconate and selenomethionine (Ferachel forte®) confirmed to be effective and safe about the cardiovascular risk
in old patients. This study showed the real superiority of the oral administration about the cardiovascular risk in elderly
patients in comparison with intravenous administration of ferrous gluconate.
Conclusion: This study confirms that Ferric Sodium EDTA combination (Ferachel forte®) can be a valid alternative to ferrous
gluconate intravenous therapy (gold standard) in the treatment of secondary anaemia in elderly patients. In fact, during
the treatment, efficacy results have been maintained without statistically significant variations about cardiovascular risk,
evaluated by exploring the HRV frequency domain
Project Manager and Systems Engineer: a literature rich reflection on roles and responsibilities
There are several definitions of Systems Engineering (SE) in the literature, each with different definitions of its relationship with Project Management (PM), causing a great deal of misunderstanding. The paper offers a broad and critical discussion of the relevant literature with a deep reflection concerning the historical evolution and state-of-the-art of both the definition of SE and its relationship with PM. This endeavor provides two main results: (i) a conceptual framework to define SE in a project based environment and (ii) a model to identify the best formal interaction between the Project Manager and System Engineer based on the project characteristics
Status of Salerno Laboratory (Measurements in Nuclear Emulsion)
A report on the analysis work in the Salerno Emulsion Laboratory is
presented. It is related to the search for nu_mu->nu_tau oscillations in CHORUS
experiment, the calibrations in the WANF (West Area Neutrino Facility) at Cern
and tests and preparation for new experiments.Comment: Proc. The First International Workshop of Nuclear Emulsion Techniques
(12-24 June 1998, Nagoya, Japan), 15 pages, 11 figure
Evolution of Phase-Space Density in Dark Matter Halos
The evolution of the phase-space density profile in dark matter (DM) halos is
investigated by means of constrained simulations, designed to control the
merging history of a given DM halo. Halos evolve through a series of quiescent
phases of a slow accretion intermitted by violent events of major mergers. In
the quiescent phases the density of the halo closely follows the NFW profile
and the phase-space density profile, Q(r), is given by the Taylor & Navarro
power law, r^{-beta}, where beta ~ 1.9 and stays remarkably stable over the
Hubble time. Expressing the phase-space density by the NFW parameters, Q(r)=Qs
(r/Rs)^{-beta}, the evolution of Q is determined by Qs. We have found that the
effective mass surface density within Rs, Sigma_s = rhos Rs, remains constant
throughout the evolution of a given DM halo along the main branch of its
merging tree. This invariance entails that Qs ~ Rs^{-5/2} and Q(r) ~
Sigma_s^{-1/2} Rs^{-5/2} (r/ Rs)^{-beta}. It follows that the phase-space
density remains constant, in the sense of Qs=const., in the quiescent phases
and it decreases as Rs^{-5/2} in the violent ones. The physical origin of the
NFW density profile and the phase-space density power law is still unknown.
Yet, the numerical experiments show that halos recover these relations after
the violent phases. The major mergers drive Rs to increase and Qs to decrease
discontinuously while keeping Qs Rs^{5/2} = const. The virial equilibrium in
the quiescent phases implies that a DM halos evolves along a sequence of NFW
profiles with constant energy per unit volume (i.e., pressure) within Rs.Comment: 7 pages, 5 figures, accepted by the Astrophysical Journal. Revised, 2
figures adde
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