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Search Results: 1 - 10 of 150974 matches for " B. Greg Brown "
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Probabilistic Algorithms, Integration, and Empirical Evaluation for Disambiguating Multiple Selections in Frustum-Based Pointing
Greg Schmidt,Dennis G. Brown,Erik B. Tomlin,J. Edward Swan II
Journal of Multimedia , 2006, DOI: 10.4304/jmm.1.3.1-12
Abstract: There are a few fundamental pointing-based user interface techniques for performing selections in 3D environments. One of these techniques is ray pointing, which makes selections by determining intersections of objects along a single ray cast from the user. This technique is susceptible to inaccuracy of the user interface tracking technology and user noise (e.g., jittery hand, see actual viewing ray in Figure 1 (bottom) and how it misses the object when error is factored in). Another technique is the frustum-based (or equivalent cone-based) approach which casts a frustum from the user into the 3D scene. Selections are made by performing intersections of objects with the frustum. This technique resolves the imprecision associated with the ray pointing technique (see how the lightly shaded cone in Figure 1 (bottom) still intersects the object), but may produce multiple ambiguous selections as shown in Figure 2. This paper presents probabilistic selection algorithms and integration schemes that address some of the ambiguities associated with the frustum-based selection technique. The selection algorithms assign probabilities that the user has selected particular objects using a set of low-level 3D intersection-based selection techniques and the relationship of the objects in a hierarchical database. Final selections are generated by integating the outputs from each selection algorithm using one of several weighting schemes. We implemented the selection algoithms and weighting schemes within our distributed augmented reality (AR) and virtual reality (VR) architecture. Next, we performed several experiments to empirically evaluate the probabilistic selection techniques and integration schemes. Our results show that the combined selection and integration algorithms are effective at disambiguating multiple selections. This paper thoroughly describes the architecture, experiments, and results.
Levels of Cholesterol in Small LDL Particles Predict Atherosclerosis Progression and Incident CHD in the HDL-Atherosclerosis Treatment Study (HATS)
Paul T. Williams, Xue-Qiao Zhao, Santica M. Marcovina, B. Greg Brown, Ronald M. Krauss
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0056782
Abstract: Objective Test whether angiographically-documented changes in percent stenosis and clinical endpoints (coronary-related deaths, myocardial infarctions, stroke, revascularization for worsening ischemia) in the HDL-Atherosclerosis Treatment Study (HATS) were attributable to specific LDL-subclasses. Methods Gradient gel electrophoresis of on-study LDL-subclass cholesterol concentrations were measured in 32 placebo, 33 simvastatin-niacin, 38 antioxidant, and 39 simvastatin-niacin & antioxidant treated participants. The prespecified primary end point was the mean change per patient from the initial arteriogram to the final arteriogram in the percent stenosis caused by the most severe lesion in each of the nine proximal coronary segments. Results The change in the percent stenosis of the most severe proximal lesions increased in association with higher concentrations of the small LDL subfractions LDL-IIIb (24.2–24.6 nm) and LDL-IVa (23.3–24.1 nm) before (both P = 0.002) and after (P = 0.01 and P = 0.03 respectively) adjustment for treatment group and on-study HDL-cholesterol, LDL-cholesterol, and triglyceride concentrations. The associations appeared specific to lesions with <30% baseline stenosis. When adjusted for age, sex, baseline BMI and cigarette use, the odds for primary clinical endpoints (death from coronary causes, nonfatal myocardial infarction, stroke, or revascularization for worsening ischemia) were significantly greater in subjects with higher on-study LDL-IIIb levels both before (P = 0.01) and after (P = 0.03) adjustment for treatment group and the standard lipid values. Conclusions Plasma LDL-IIIb cholesterol concentrations were related to changes in coronary artery stenosis and cardiovascular events in patients with coronary artery disease and low HDL-cholesterol. Trial Registration ClinicalTrials.gov NCT00000553
Constraints on the Steady-State R-mode Amplitude in Neutron Star Transients
Edward F. Brown,Greg Ushomirsky
Physics , 1999, DOI: 10.1086/308969
Abstract: Recent observations suggest that neutron stars in low-mass X-ray binaries rotate within a narrow range of spin frequencies clustered around 300 Hz. A proposed explanation for this remarkable fact is that gravitational radiation from a steady-state r-mode oscillation in the neutron star's core halts the spin-up due to accretion. For the neutron star transients, balancing the time-averaged accretion torque with gravitational wave emission from steady-state, constant amplitude r-mode pulsations implies a quiescent luminosity too bright to be consistent with observations (in particular of Aql X-1). The viscous dissipation (roughly 10 MeV per accreted nucleon for a spin of 300 Hz) from such an r-mode makes the core sufficiently hot to power a thermal luminosity of order 1e34 erg/s when accretion halts. This is the minimum quiescent luminosity that the neutron star must emit when viscous heating in the core is balanced by radiative cooling from the surface, as is the case when the core of the star is superfluid. We therefore conclude that either the accretion torque is much less than (dM/dt)(GMR)^{1/2}, or that a steady-state r-mode does not limit the spin rate of the neutron star transients. Future observations with AXAF and XMM promise to further constrain the amount of viscous dissipation in the neutron star core.
Point Mutation Analysis of PMP22 in Patients Referred for Hereditary Neuropathy with Liability to Pressure Palsies  [PDF]
Samuel B. Brown, David J. Bunyan
Open Journal of Genetics (OJGen) , 2014, DOI: 10.4236/ojgen.2014.46040
Abstract: A cohort of 404 patients referred for hereditary neuropathy with liability to pressure palsies was tested initially for the common PMP22 whole gene deletion. 94 whole gene deletions were detected, plus three partial gene deletions, and the remaining 307 patients were screened for PMP22 point mutations. Nine point mutations were identified (8.5% of all mutations), eight of which were in exon 5, suggesting a point mutation hotspot for individuals with this condition. Sequencing analysis of PMP22 exon 5 should therefore be included as a routine diagnostic test for gene deletion-negative patients.
Measurements of Accelerations of Large Neutrally-buoyant Particles in Intense Turbulence
Rachel D. Brown,Zellman Warhaft,Greg A. Voth
Physics , 2009,
Abstract: We measure acceleration statistics of neutrally buoyant spherical particles with diameter 0.4 < d/eta <27 in intense turbulence (400< R_lambda <815). High speed cameras image polystyrene tracer particles in a flow between counter-rotating disks. The measurements of acceleration variance, , clearly resolve the transition from the tracer like behavior of small particles to the much smaller accelerations of large particles. For d>5 eta, decreases with diameter as d^{-2/3} in agreement with inertial range scaling arguments. A model relating to the pressure structure functions matches the transition from small to large particle behavior if the particles respond to pressure differences over (1.7 +- 0.3) d. A model relating to the fluid acceleration averaged over the particle diameter predicts the transition with no free parameters, but does not show clean inertial range scaling in the size range studied. Consistent with earlier work, we find that the scaled acceleration probability density function shows very little dependence on particle size.
Lithium Depletion in Fully Convective Pre-Main Sequence Stars
Lars Bildsten,Edward F. Brown,Christopher D. Matzner,Greg Ushomirsky
Physics , 1996, DOI: 10.1086/304151
Abstract: We present an analytic calculation of the thermonuclear depletion of lithium in contracting, fully convective, pre-main sequence stars of mass M < 0.5 M_sun. Previous numerical work relies on still-uncertain physics (atmospheric opacities and convection, in particular) to calculate the effective temperature as a unique function of stellar mass. We assume that the star's effective temperature, T_eff, is fixed during Hayashi contraction and allow its actual value to be a free parameter constrained by observation. Using this approximation, we compute lithium burning analytically and explore the dependence of lithium depletion on T_eff, M, and composition. Our calculations yield the radius, age, and luminosity of a pre-main sequence star as a function of lithium depletion. This allows for more direct comparisons to observations of lithium depleted stars. Our results agree with those numerical calculations that explicitly determine stellar structure during Hayashi contraction. In agreement with Basri, Marcy, and Graham (1996), we show that the absence of lithium in the Pleiades star HHJ 3 implies that it is older than 100 Myr. We also suggest a generalized method for dating galactic clusters younger than 100 Myr (i.e., those with contracting stars of M > 0.08 M_sun) and for constraining the masses of lithium depleted stars.
Influence of the El Ni o - La Ni a cycle on satellite-derived primary production in the California Current
Mati Kahru,B. Greg Mitchell
Investigaciones Marinas , 2002,
Spasers, VCSELs, and Surface plasmon emitting diodes (SPED): their unique features and figures of merit
Jacob B Khurgin,Greg Sun
Physics , 2013,
Abstract: We compare fundamental characteristics of proposed electrically pumped subwavelength plasmonic lasers (spasers) with ubiquitous all-dielectric semiconductor micro-lasers (VCSEL) and indicate their close similarities as well as large differences in performance (threshold, efficiency, coherence and speed). These results should assist researchers in making informed choice of the emitter for each particular opto-electronic application.
Plasmonic enhancement of the third order nonlinear optical phenomena: figures of merit
Jacob B Khurgin,Greg Sun
Physics , 2013,
Abstract: Recent years have seen increased interest to plasmonic enhancement of nonlinear optical effects, yet there remains an uncertainty of what are the limits of this enhancement. We present a simple and physically transparent theory of plasmonic enhancement of third order nonlinear optical processes achieved in plasmonic structures and show that while huge enhancement of effective nonlinear index can be attained, the most relevant figure of merit, the of phase shift per one absorption length remains very low. This means that while on one hand nonlinear plasmonic materials are not well suitable for applications requiring high efficiency, e.g. all-optical switching and wavelength conversion, on the other hand they can be very useful for the applications where the overall high efficiency is not a must, such as sensing.
Scaling of losses with size and wavelength in nanoplasmonics and metamaterials
Jacob B Khurgin,Greg Sun
Physics , 2011, DOI: 10.1063/1.3664105
Abstract: We show that, for the resonant metal-dielectric structures with sub-wavelength confinement of light in all three dimensions, the loss cannot be reduced significantly below the loss of the metal itself unless one operates in the far IR and THz regions of the spectrum or below. Such high losses cannot be compensated by introducing gain due to Purcell-induced shortening of recombination times. The only way low loss optical metamaterials can be engineered is with as yet unknown low loss materials with negative permittivity.
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