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Eccentricity

Distribution by Scientific Domains

Medical Sciences	34%
Physics and Astronomy	30%
Engineering	18%
Chemistry	5%
Life Sciences	4%
Earth and Environmental Science	4%
2 Other Domains	5%

Selected Abstracts

Demonstration of Left Ventricular Outflow Tract Eccentricity by Real Time 3D Echocardiography: Implications for the Determination of Aortic Valve Area

ECHOCARDIOGRAPHY, Issue 8 2007
Sanjay Doddamani M.D.
Background: Determination of the left ventricular outflow tract cross-sectional area (ALVOT) is necessary for calculating aortic valve area (AVA) by echocardiography using the continuity equation (CE). In the commonly applied form of CE, ,r2 is used to estimate ALVOT utilizing the assumptions that LVOT is round and the parasternal long axis (PLAX) plane bisects LVOT. Imaging LVOT using real time 3D echocardiography (RT3DE) eliminates the need for these assumptions. We tested the hypothesis that LVOT is round based on a formula for eccentricity. Methods and Results: In 53 patients, 2D echocardiography (2DE) and RT3DE were acquired. ALVOT was calculated by 2DE using ,r2 (ALVOT-2D). Using RT3DE, ALVOT planimetry was performed immediately beneath the aortic valve (ALVOT-3Dplan). Eccentricity Index (EI) was calculated using the shortest and longest LVOT diameters. The long axis was measured to be larger by 0.53 cm ± 0.36 (P < 0.005). The median EI was 0.20 (0.00,0.54), indicating that half the subjects had at least a 20% difference between the major and minor diameters. ALVOT-3Dplan was larger than ALVOT-2D (3.73 ± 0.95 cm2 vs. 3.18 ± 0.73 cm2; P < 0.001) by paired analysis. Using the equation of an ellipse (,ab), ALVOT-3Dellip was 3.57 ± 0.95 resulting in improved agreement with ALVOT-3Dplan. Conclusions: In our small patient sample with normal aortic valves, we showed the LVOT shape is usually not round and frequently, elliptical. Incorrectly assuming a round LVOT underestimated the ALVOT-3Dplan and consequently the AVA by 15%. Investigating the LVOT in aortic stenosis is warranted to evaluate whether RT3DE may improve measurement of AVA. [source]

Effects of Screw Eccentricity on the Initial Stability of the Acetabular Cup in Artificial Foam Bone of Different Qualities

ARTIFICIAL ORGANS, Issue 1 2010
Jui-Ting Hsu
Abstract Acetabular cup loosening is one of the major failure models of total hip replacement (THR), which is mostly due to insufficient initial stability of the cup. Previous studies have demonstrated that cup stability is affected by the quality of the host bone and the surgical skill when inserting screws. The purpose of this study was to determine the effects on the initial stability of the acetabular cup of eccentric screws in bone of different qualities. In this study, hemispherical cups were fixed into bone specimens constructed from artificial foam with three elastic moduli using one to three screws. The effects of two types of screw eccentricity (offset and angular) on the stability of the acetabular cup were also evaluated. The experimental results indicate that in the presence of ideal screwing, the cup was stable in bone specimens constructed from foam with the highest elastic modulus. In addition, increasing the number of ideal screws enhanced the cup stability, especially in bone specimens constructed from soft foam. Moreover, the cup stability was most affected by offset eccentric screw(s) in the hard-foam bone specimens and by angular eccentric screw(s) in the soft-foam bone specimens. The reported results indicate that the presence of screw eccentricity affects the initial stability of the acetabular cup. Surgeons should keep this in mind when performing screw insertions in THR. However, care is necessary when translating these results to the intraoperative situation due to the experiments being conducted under laboratory conditions, and hence, future studies should attempt to replicate the results reported here in vivo. [source]

Laboratory tests of steel simple torsionally unbalanced models

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2007
Jaime De-la-Colina
Abstract The objective of this work is to obtain estimations of the amplification factors , and , used for torsion design of buildings, from experiments. For this study, simple one-storey torsionally unbalanced (TU) steel models were considered. Models consisted of a deck supported on four columns with a selected arrangement of hinges at column ends. Two theoretical structural eccentricities (e = 0.05 and 0.15) were considered. Models were excited with a simple long-period pendulum consisting of a hanging platform with a forced-vibration generator on it. Eight models were tested at several excitation levels (frequencies and force magnitudes) in both ranges of behaviour: elastic and inelastic. Experiments were conducted at three frequency ratios of excitation. Registered accelerations of the pendulum platform indicate that the experimental set-up leads to excitations that resemble narrow-band seismic ground motions. Frame shear force estimations, based on accelerations recorded at both deck sides, indicate that torsion design factors (, and ,) depend on eccentricity. Estimations of frame shears based on measurements indicate that for normalized eccentricities e , 0.025, the amplification , can be between 2 and 3; while , factor resulted between 0.0 and 1.6. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Natural and accidental torsion in one-storey structures on elastic foundation under non-vertically incident SH-waves

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2006
Javier Avilés
Abstract Factors , and , used in equivalent static analysis to account for natural and accidental torsion are evaluated with consideration of soil,structure interaction. The combined torsional effects of structural asymmetry and foundation rotation are examined with reference to a single monosymmetric structure placed on a rigid foundation that is embedded into an elastic half-space, under to the action of non-vertically incident SH waves. Dynamic and accidental eccentricities are developed such that when used together with the code-specified base shear, the resulting static displacement at the flexible edge of the building is identical to that computed from dynamic analysis. It is shown that these eccentricities do not have a unique definition because they depend on both the selection of the design base shear and the criterion used for separation of the torsional effects of foundation rotation from those of structural asymmetry. Selected numerical results are presented in terms of dimensionless parameters for their general application, using a set of appropriate earthquake motions for ensuring generality of conclusions. The practical significance of this information for code-designed buildings is elucidated. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Inelastic earthquake response of single-story asymmetric buildings: an assessment of simplified shear-beam models

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 12 2003
K. G. Stathopoulos
Abstract The inelastic seismic torsional response of simple structures is examined by means of shear-beam type models as well as with plastic hinge idealization of one-story buildings. Using mean values of ductility factors, obtained for groups of ten earthquake motions, as the basic index of post-elastic response, the following topics are examined with the shear-beam type model: mass eccentric versus stiffness eccentric systems, effects of different types of motions and effects of double eccentricities. Subsequently, comparisons are made with results obtained using a more realistic, plastic hinge type model of single-story reinforced concrete frame buildings designed according to a modern Code. The consequences of designing for different levels of accidental eccentricity are also examined for the aforementioned frame buildings. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Approximate analysis methods for asymmetric plan base-isolated buildings

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2002
Keri L. Ryan
Abstract An approximate method for linear analysis of asymmetric-plan, multistorey buildings is specialized for a single-storey, base-isolated structure. To find the mode shapes of the torsionally coupled system, the Rayleigh,Ritz procedure is applied using the torsionally uncoupled modes as Ritz vectors. This approach reduces to analysis of two single-storey systems, each with vibration properties and eccentricities (labelled ,effective eccentricities') similar to corresponding properties of the isolation system or the fixed-base structure. With certain assumptions, the vibration properties of the coupled system can be expressed explicitly in terms of these single-storey system properties. Three different methods are developed: the first is a direct application of the Rayleigh,Ritz procedure; the second and third use simplifications for the effective eccentricities, assuming a relatively stiff superstructure. The accuracy of these proposed methods and the rigid structure method in determining responses are assessed for a range of system parameters including eccentricity and structure flexibility. For a subset of systems with equal isolation and structural eccentricities, two of the methods are exact and the third is sufficiently accurate; all three are preferred to the rigid structure method. For systems with zero isolation eccentricity, however, all approximate methods considered are inconsistent and should be applied with caution, only to systems with small structural eccentricities or stiff structures. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Detection of animals in natural images using far peripheral vision

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2001
Simon J. Thorpe
Abstract It is generally believed that the acuity of the peripheral visual field is too poor to allow accurate object recognition and, that to be identified, most objects need to be brought into foveal vision by using saccadic eye movements. However, most measures of form vision in the periphery have been done at eccentricities below 10° and have used relatively artificial stimuli such as letters, digits and compound Gabor patterns. Little is known about how such data would apply in the case of more naturalistic stimuli. Here humans were required to categorize briefly flashed (28 ms) unmasked photographs of natural scenes (39° high, and 26° across) on the basis of whether or not they contained an animal. The photographs appeared randomly in nine locations across virtually the entire extent of the horizontal visual field. Accuracy was 93.3% for central vision and decreased almost linearly with increasing eccentricity (89.8% at 13°, 76.1% at 44.5° and 71.2% at 57.5°). Even at the most extreme eccentricity, where the images were centred at 70.5°, subjects scored 60.5% correct. No evidence was found for hemispheric specialization. This level of performance was achieved despite the fact that the position of the image was unpredictable, ruling out the use of precued attention to target locations. The results demonstrate that even high-level visual tasks involving object vision can be performed using the relatively coarse information provided by the peripheral retina. [source]

Conformational and tautomeric eccentricities of 2-acetyl-1,8-dihydroxynaphthalenes

MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2007
Poul Erik Hansen
Abstract Tautomerism in aromatic systems with oxygen substitutents is rare. This is investigated in 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (1) and in 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (2). The tautomeric nature of 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene is supported by long-range hydrogen,hydrogen coupling between the OH-1 and the OH-8 and by the isotope effects on 13C caused by deuteration at the CH3CO methyl group. Compound 2 participates in a degenerate equilibrium between two equivalent nonsymmetrical rotamers (2A and 2B), each having two intramolecular O···HO hydrogen bonds: one involving an acetyl oxygen and the neighboring hydroxyl group, and the other between the oxygen centers at positions 1 and 8. In addition, each rotamer is involved in a tautomeric equilibrium, with a structure having an OH-substituted exocyclic double bond (2AT or 2BT). DFT calculations for a large set of compounds highlight the factors controlling the unusual rotational and tautomeric behaviors. A very important factor seems to be the repulsive interaction between the O -1 and O -8 centers, which is modulated by formation of an OH-1···O-8 or OH-8···O1 hydrogen bond. Steric interactions, mesomeric release of electrons from the oxygen at position 8, and a strong OH···O···C hydrogen bond are other factors. Solid-state 13C NMR spectra of 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene at different temperatures demonstrated no averaging in the solid, whereas partially deuterated 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene showed an isotope effect at C-1 of 1.5 ppm, indicating tautomerism in the solid state. Copyright © 2006 John Wiley & Sons, Ltd. [source]

The effects of nebula surface density profile and giant-planet eccentricities on planetary accretion in the inner solar system

METEORITICS & PLANETARY SCIENCE, Issue 11 2002
J. E. CHAMBERS
Two surface density profiles are examined: a decaying profile with , , 1/a, where a is orbital semi-major axis, and a peaked profile in which , increases for a < 2 AU and decreases for a > 2 AU. The peaked profiles are generated by models of coagulation in an initially hot nebula. Models with initial ej,s = 0.05 (the current value) and 0.1 are considered. Simulations using the decaying profile with ej,s = 0.1 produce systems most like the observed planets in terms of mass-weighted mean a and the absence of a planet in the asteroid belt. Simulations with doubled , produce planets roughly twice as massive as the nominal case. Most initial embryos are removed in each simulation via ejection from the solar system or collision with the Sun. The asteroid belt is almost entirely cleared on a timescale of 10,100 Ma that depends sensitively on ej,s. Most initial mass with a < 2 AU survives, with the degree of mass loss increasing with a. Mass loss from the terrestrial region occurs on a timescale that is long compared to the mass loss time for the asteroid belt. Substantial radial mixing of material occurs in all simulations, but is greater in simulations with initital ej,s = 0.05. The degree of mixing is equivalent to a feeding zone of half width 1.5 and 0.9 AU for an Earth mass planet at 1 AU for the cases ej,s = 0.05 and 0.1, respectively. In simulations with ej,s = 0.05, roughly one-third and 5,10% of the mass contained in final terrestrial planets originated in the region a > 2.5 AU for the decaying and peaked profiles, respectively. In the case ej,s = 0.1, the median mass accreted from a > 2.5 AU is zero for both profiles. [source]

The determination of planetary structure in tidally relaxed inclined systems

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2010
Rosemary A. Mardling
ABSTRACT The recent discovery of a transiting short-period planet on a slightly non-circular orbit with a massive highly eccentric companion orbiting the star HAT-P-13 offers the possibility of probing the structure of the short-period planet. The ability to do this relies on the system being in a quasi-equilibrium state in the sense that the eccentricities are constant on the usual secular time-scale (typically, a few thousand years), and decay on a time-scale which is much longer than the age of the system. Since the equilibrium eccentricity is effectively a function only of observable system parameters and the unknown Love number of the short-period planet, the latter can be determined with accurate measurements of the planet's eccentricity and radius. However, this analysis relies on the assumption that the system is coplanar, a situation which seems unlikely given the high eccentricity of the outer planet. Here we generalize our recent analysis of this fixed-point phenomenon to mutually inclined systems in which the outer body dominates the total angular momentum, and show that (1) the fixed point of coplanar systems is replaced by a limit cycle in eb,, space, where eb is the eccentricity of the inner planet and , is the angle between the periapse lines, with the average value of eb, e(av)b, decreasing and its amplitude of variation increasing with increasing mutual inclination. This behaviour significantly reduces the ability to unambiguously determine the Love number of the short-period planet if the mutual inclination is higher than around 10°. (2) We show that for Q -values less than 106, the HAT-P-13 system cannot have a mutual inclination between 54° and 126° because Kozai oscillations coupled with tidal dissipation would act to quickly move the inclination outside this range, and (3) that the behaviour of retrograde systems is the mirror image of that for prograde systems in the sense that (almost) identical limit cycles exist for a given mutual inclination and , minus this value. (4) We derive a relationship between e(av)b, the equilibrium radius of the short-period planet, its Q -value and its core mass, and show that given current estimates of eb and the planet radius, as well as the lower bound placed on the Q -value by the decay rate of e(av)b, the HAT-P-13 system is likely to be close to prograde coplanar, or have a mutual inclination between 130° and 135°. Lower rather than higher core masses are favoured. (5) An expression for the time-scale for decay of the mutual inclination is derived, revealing that it evolves towards a non-zero value as long as eb > 0 on a time-scale which is much longer than the age of the system. (6) We conclude with a scattering scenario for the origin of the HAT-P-13 system and show that almost identical initial conditions can result in significantly different outer planet eccentricities, stellar obliquities and planet radii. The implications for systems with high stellar obliquities such as HAT-P-7 and WASP-17 are briefly discussed. [source]

Stable satellites around extrasolar giant planets

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
R. C. Domingos
ABSTRACT In this work, we study the stability of hypothetical satellites of extrasolar planets. Through numerical simulations of the restricted elliptic three-body problem we found the borders of the stable regions around the secondary body. From the empirical results, we derived analytical expressions of the critical semimajor axis beyond which the satellites would not remain stable. The expressions are given as a function of the eccentricities of the planet, eP, and of the satellite, esat. In the case of prograde satellites, the critical semimajor axis, in the units of Hill's radius, is given by aE, 0.4895 (1.0000 , 1.0305eP, 0.2738esat). In the case of retrograde satellites, it is given by aE, 0.9309 (1.0000 , 1.0764eP, 0.9812esat). We also computed the satellite stability region (aE) for a set of extrasolar planets. The results indicate that extrasolar planets in the habitable zone could harbour the Earth-like satellites. [source]

High-eccentricity planets from the Anglo-Australian Planet Search

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006
Hugh R. A. Jones
ABSTRACT We report Doppler measurements of the stars HD 187085 and HD 20782 which indicate two high eccentricity low-mass companions to the stars. We find HD 187085 has a Jupiter-mass companion with a ,1000-d orbit. Our formal ,best-fitting' solution suggests an eccentricity of 0.47, however, it does not sample the periastron passage of the companion and we find that orbital solutions with eccentricities between 0.1 and 0.8 give only slightly poorer fits (based on rms and ,2,) and are thus plausible. Observations made during periastron passage in 2007 June should allow for the reliable determination of the orbital eccentricity for the companion to HD 187085. Our data set for HD 20782 does sample periastron and so the orbit for its companion can be more reliably determined. We find the companion to HD 20782 has M sin i= 1.77 ± 0.22 MJup, an orbital period of 595.86 ± 0.03 d and an orbit with an eccentricity of 0.92 ± 0.03. The detection of such high-eccentricity (and relatively low-velocity amplitude) exoplanets appears to be facilitated by the long-term precision of the Anglo-Australian Planet Search. Looking at exoplanet detections as a whole, we find that those with higher eccentricity seem to have relatively higher velocity amplitudes indicating higher mass planets and/or an observational bias against the detection of high-eccentricity systems. [source]

Reversing type II migration: resonance trapping of a lighter giant protoplanet

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001
F. Masset
We present a mechanism related to the migration of giant protoplanets embedded in a protoplanetary disc whereby a giant protoplanet is caught up, before having migrated all the way to the central star, by a lighter outer giant protoplanet. This outer protoplanet may get captured into the 2:3 resonance with the more massive one, in which case the gaps that the two planets open in the disc overlap. Two effects arise, namely a squared mass-weighted torque imbalance and an increased mass flow through the overlapping gaps from the outer disc to the inner disc, which both play in favour of an outwards migration. Indeed, under the conditions presented here, which describe the evolution of a pair of protoplanets respectively Jupiter- and Saturn-sized, the migration is reversed, while the semimajor axis ratio of the planets is constant and the eccentricities are confined to small values by the disc material. The long-term behaviour of the system is briefly discussed, and could account for the high eccentricities observed for the extrasolar planets with semimajor axis [source]

Stellar dynamical evidence against a cold disc origin for stars in the Galactic Centre

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008
Jorge Cuadra
ABSTRACT Observations of massive stars within the central parsec of the Galaxy show that, while most stars orbit within a well-defined disc, a significant fraction have large eccentricities and/or inclinations with respect to the disc plane. Here, we investigate whether this dynamically hot component could have arisen via scattering from an initially cold disc , the expected initial condition if the stars formed from the fragmentation of an accretion disc. Using N -body methods, we evolve a variety of flat, cold, stellar systems, and study the effects of initial disc eccentricity, primordial binaries, very massive stars and intermediate mass black holes. We find, consistent with previous results, that a circular disc does not become eccentric enough unless there is a significant population of undetected 100,1000 M, objects. However, since fragmentation of an eccentric disc can readily yield eccentric stellar orbits, the strongest constraints come from inclinations. We show that none of our initial conditions yields the observed large inclinations, regardless of the initial disc eccentricity or the presence of massive objects. These results imply that the orbits of the young massive stars in the Galactic Centre are largely primordial, and that the stars are unlikely to have formed as a dynamically cold disc. [source]

Just how useless is an amblyopic eye?

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 1 2008
Eve Panesar
Purpose:, The extent to which individuals with amblyopia are visually disadvantaged has generated renewed research interest. Investigation of the contribution of the amblyopic eye to visual performance under habitual conditions is a key component of this issue. This study aims to evaluate the contribution of each eye to a simple light detection task when both eyes are open and in their habitual motor position. Methods:, A custom program on the Humphrey Field Analyzer (Carl Zeiss Meditec Inc., Dublin, CA, USA) was used to measure detection thresholds for a blue light on a yellow background along the horizontal meridian at two degree intervals to an eccentricity of 25 degrees either side of fixation. Three viewing conditions were used: (1) both eyes open, (2) a yellow filter in front of the amblyopic eye and (3) a yellow filter in front of the fellow eye. The purpose of the yellow filter was to produce minimal dissociation as it only prevented the eye behind the filter from seeing the blue stimulus; the fixation mark and the background remained visible to both eyes. Participants included 10 visual normals and 16 volunteers with amblyopia. Results:, Within the sample of amblyopes there were three basic patterns of results, and each applied to around one third of the group: (1) habitual sensitivity governed by the sensitivity of the fellow eye at each stimulus location, (2) habitual sensitivity exceeding the sensitivities of either eye at each stimulus location and (3) a pattern of contribution that varied across the range of eccentricities. Surprisingly, in one amblyope the habitual sensitivity appeared to be governed by the sensitivity of the amblyopic eye. The pattern of contribution of each eye to the habitual sensitivity did not vary in a manner that was predictable by the visual acuity deficit or the presumed aetiology of the amblyopia. The control sample showed either pattern 2 (70%) or pattern 3 (30%). Conclusions:, The amblyopic eye did not contribute to the habitual performance in approximately one-third of cases in this simple detection task. Thus, in many cases the amblyopic eye may be a useful contributor to visual performance in the binocular field. This challenges the traditional view that an amblyopic eye is useful only for peripheral vision. [source]

Compensation for light loss due to filtering by macular pigment: relation to hue cancellation

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 3 2007
James M. Stringham
Abstract Background:, A long-standing question in colour vision research is how the visual system is able to correct for the significant absorbance of short wave light by the crystalline lens and macular pigment (MP). Such compensation must be required in order to maintain colour constancy across the retina where MP levels are changing quickly and dramatically. Objective:, We studied this compensation mechanism by measuring MP spatial density profiles and hue cancellation functions across the central retina in a sample of six young healthy subjects. Method:, Yellow (Y, 575 nm)/blue (B, 440 nm) and red (R, 600 nm)/green (G, 501 nm) cancellation functions were obtained at 0, 1, 1.75, 3 and 7° eccentricity. The MP optical density at 460 nm was measured at these same eccentricities using heterochromatic flicker photometry. One subject was assessed repeatedly over a 4-month period during daily supplementation with 30 mg of lutein (L). Results:, Hue cancellation values for the Y/B system did not change across the retina (r = 0.09). In contrast, R/G sensitivity changed as a direct function of MP absorbance (r = 0.99). The Y/B values did not change in the one subject supplemented with 30 mg L daily, despite increases in MP of about 50% over 4 months. Conclusions:, Despite large variations in MP across the retina, hue cancellation values for the Y-B system across the central retina were constant. For example, one subject's MP density declined from a central peak of 0.99 to near zero at 7° (near 90% transmission difference) yet thresholds for the Y/B system were unaffected. In contrast, the G lobe of the R/G system was directly correlated with MP density. Taken together, these results confirm that the Y/B system compensates for MP density, but the R/G system does not. [source]

The detection of small simulated field defects using multifocal VEPs

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 3 2003
H. L. Chan
Abstract Introduction: The multifocal visual-evoked potential (mfVEP) has been widely investigated in the study of diseases of the visual system. However, the sensitivity of the mfVEP in objective detection of field defects has not been determined. This study investigates the variation of the mfVEP responses whilst simulating field defects by using different sizes of mask on the stimulus pattern. Methods: Simulated field defects of four different sizes (2, 3, 5, and 7 degrees) at two different eccentricities (10 and 16 degrees) were generated on a standard mfVEP dartboard stimulus using opaque masks. These masks were placed at the centre of each dartboard sector and the modified stimuli were used to elicit mfVEPs from 10 normal subjects. The response densities and latencies of N1, P1 of the mfVEP were compared, without and with small simulated field defects. Results: The minimum size of simulated field defect causing significant response density reduction in P1 and N1 was 5 degrees at both retinal eccentricities. N1 showed similar reduction in response density at both retinal eccentricities, but P1 showed larger reduction at the 10-degree location than at the 16-degree location. There was no change in latencies with simulated field defect at either location. Conclusions: The mfVEP is only sensitive to a simulated field defect equal to or larger than 5 degrees in diameter, and mfVEP has greater sensitivity at 10-degree eccentricity than at 16-degree eccentricity. [source]

2111: Adaptive optics imaging in hereditary macular diseases

ACTA OPHTHALMOLOGICA, Issue 2010
K NAKASHIMA
Purpose This research aimed at exploring and characterizing differences in vivo between healthy and pathology retinas, hereditary macular diseases at the microscopic scale using a compact adaptive optics (AO) retinal camera and high resolution OCT. Methods Seven RP patients, Cone-rod dystrophies (3), Stargardt diseases (5), Occult macular dystrophies (4) and indeterminate macular dystrophies (4) had undergone en face retinal imaging by AO camera "rtx1" (Imagine Eyes, France). AO images were taken at the eccentricities from 0 deg to 6 deg temporal and nasal from fovea. Each patient was examined using high resolution spectral domain (SD)-OCT and infrared SLO (Spectralis OCT). Results Cellular-resolution images could be obtained in most cases. In inherited retinal dystrophies, AO helped to better evaluate losses of cone cells across the retina. Other microstructures, slightly larger in size than cones, were also visible in several pathological retinas. Hereditary macular disease cases showed loss of cone mosaics. Some of these cases, there were patchy areas of increased reflectance. In Cone rod dystrophy and some other cases, the RPE mosaic was visible where cone had disappeared. Conclusion Cellular-resolution images could be obtained in most cases. In inherited retinal dystrophies, AO helped to better evaluate losses of cone cells across the retina. Other microstructures, slightly larger in size than cones, were also visible in several pathological retinas. Hereditary macular disease cases showed loss of cone mosaics. Some of these cases, there were patchy areas of increased reflectance. In Cone rod dystrophy and some other cases, the RPE mosaic was visible where cone had disappeared. [source]

Axonal loss occurs early in dominant optic atrophy

ACTA OPHTHALMOLOGICA, Issue 3 2010
Dan Milea
Abstract. Purpose:, This study set out to investigate retinal nerve fibre layer (RNFL) thickness and best corrected visual acuity (BCVA) in relation to age in healthy subjects and patients with OPA1 autosomal dominant optic atrophy (DOA). Methods:, We carried out a cross-sectional investigation of RNFL thickness and ganglion cell layer density in 30 healthy subjects and 10 patients with OPA1 DOA using optical coherence tomography (OCT). We then performed a regression analysis of RNFL thickness and BCVA versus age. Results:, Both healthy subjects and DOA patients demonstrated a gradual reduction in RNFL thickness with age; the relationship was best described statistically by a model that assumed a constant offset between the two groups. Best corrected VA decreased significantly with age in DOA patients, in whom BCVA was correlated with peripapillary RNFL thickness in the inferior and superior peripapillary quadrants and with total macular thickness at eccentricities of 500,3000 ,m. The observations were best described by a constant offset of 41.9 ,m separating the two groups and an annual decrease in RNFL thickness of 0.48 ,m (p < 0.0001). In patients with DOA, increasing age was associated with decreasing BCVA (p = 0.046). Conclusions:, This cross-sectional study found evidence of comparable age-related decreases in RNFL thickness in healthy subjects and in DOA patients, where the deficit in DOA patients is best described using a model that assumes the deficit between the groups does not vary with age. The gradual reduction of BCVA with age may be a consequence of a relative deficit in RNFL thickness that is established before the second decade of life. [source]

Approximate analysis methods for asymmetric plan base-isolated buildings

Development of multisensory spatial integration and perception in humans

DEVELOPMENTAL SCIENCE, Issue 5 2006
Patricia A. Neil
Previous studies have shown that adults respond faster and more reliably to bimodal compared to unimodal localization cues. The current study investigated for the first time the development of audiovisual (A-V) integration in spatial localization behavior in infants between 1 and 10 months of age. We observed infants' head and eye movements in response to auditory, visual, or both kinds of stimuli presented either 25° or 45° to the right or left of midline. Infants under 8 months of age intermittently showed response latencies significantly faster toward audiovisual targets than toward either auditory or visual targets alone They did so, however, without exhibiting a reliable violation of the Race Model, suggesting that probability summation alone could explain the faster bimodal response. In contrast, infants between 8 and 10 months of age exhibited bimodal response latencies significantly faster than unimodal latencies for both eccentricity conditions and their latencies violated the Race Model at 25° eccentricity. In addition to this main finding, we found age-dependent eccentricity and modality effects on response latencies. Together, these findings suggest that audiovisual integration emerges late in the first year of life and are consistent with neurophysiological findings from multisensory sites in the superior colliculus of infant monkeys showing that multisensory enhancement of responsiveness is not present at birth but emerges later in life. [source]

Low-grade urothelial carcinoma: Reappraisal of the cytologic criteria on ThinPrep®

DIAGNOSTIC CYTOPATHOLOGY, Issue 3 2003
Ph.D., Wei Xin M.D.
Abstract The diagnostic criteria for low-grade urothelial lesions that have been described in the past were based on urinary specimens prepared by the cytospin method. Recognizing the recent popularity of the ThinPrep® methodology and the cytologic alterations it introduces to the cellular features, we sought to evaluate the reproducibility of these criteria in ThinPrep urinary samples. One hundred twenty-six ThinPrep urinary specimens with a tissue diagnosis of low-grade urothelial carcinoma (LGUC) and 45 negative controls were evaluated. Three pathologists blindly reviewed the slides separately and the consensus on each feature was used in the study. Logistic regression analysis was used to determine which criteria in combination were most predictive of low-grade urothelial carcinoma. All specimens were evaluated for the following 18 features: nucleus/cytoplasm ratio, irregular nuclear border, cytoplasm homogeneity, cell clusters, high cellularity, prominent nucleoli, granular nuclear chromatin, hyperchromasia, acute inflammation, vesicular chromatin, nuclear molding, nuclear eccentricity, elongated nuclei, necrosis, anisonucleosis, irregular bordered fragments, absent cytoplasmic collar, and peripheral palisading. High nucleus-to-cytoplasm ratio, irregular nuclear borders, and homogeneous cytoplasm (combination sensitivity of 59% and specificity of 100%) were the best predictive features for LGUC. Minor predictive criteria were eccentric nuclei and nuclear molding. ThinPrep provides well preserved, cleaner specimens without significantly altering the morphology. The three key criteria applied in cytospin specimens to diagnose LGUC were reproducible in ThinPrep specimens. Diagn. Cytopathol. 2003;29:125,129. © 2003 Wiley-Liss, Inc. [source]

Evidence for repeated re-activation of old landslides under forest

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2009
M. Van Den Eeckhaut
Abstract Local reactivations of landslides in forests are rarely reported in landslide catalogues. The occurrence of hillslope sections with fresh morphological landslide features in forested old, deep-seated landslides, however, suggests that landslide reactivations are not restricted to residential areas. In this study, a dendrogeomorphological analysis of beech stands was used to investigate the periods of reactivation of a deep-seated rotational slide in the Koppenberg forest (Flemish Ardennes, Belgium). The relation to rainfall and the correspondence to landslide reactivations reported in a nearby built-up area were also analysed. A dendrometrical study preceding the dendrochronological analysis proved that, compared with the nearby reference site, trees on the Koppenberg forest landslide site were significantly more inclined and showed more knees, indicating that the landslide site has not stabilized yet. As the sampled trees are younger than the landslide, dendrochronology did not allow determination of the year in which the landslide was initiated, but analysis of two different tree ring width parameters (i.e. ring eccentricity and growth change) calculated for trees sampled on the Koppenberg landslide and the reference site proved to be of great help in determining the temporal sequence of landslide reactivation. During the past 80 years, several periods indicative of local reactivations (i.e. 1943,1945, 1949,1952, 1967,1970, 1972,1977, 1979,1981, 1988,1997) were found within the investigated landslide, but delineation of the spatial extent of the reactivations during these indicative periods was not straightforward. These periods generally correspond to years with above-average rainfall. Finally, the fact that at least 34% of the years indicative of reactivation of the Koppenberg forest landslide correspond to a year in which a landslide reactivation was reported in the Flemish Ardennes suggests that in built-up areas, apart from anthropogenic interventions, natural triggering factors remain very important. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Parameter identification of torsionally coupled shear buildings from earthquake response records

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2008
Ganesh Hegde
Abstract This paper presents an efficient procedure to determine the natural frequencies, modal damping ratios and mode shapes for torsionally coupled shear buildings using earthquake response records. It is shown that the responses recorded at the top and first floor levels are sufficient to identify the dominant modal properties of a multistoried torsionally coupled shear building with uniform mass and constant eccentricity even when the input excitation is not known. The procedure applies eigenrealization algorithm to generate the state-space model of the structure using the cross-correlations among the measured responses. The dynamic characteristics of the structure are determined from the state-space realization matrices. Since the mode shapes are obtained only at the instrumented floor (top and first floors) levels, a new mode shape interpolation technique has been proposed to estimate the mode shape coefficients at the remaining floor levels. The application of the procedure has been demonstrated through a numerical experiment on an eight-storied torsionally coupled shear building subjected to earthquake base excitation. The results show that the proposed parameter identification technique is capable of identifying dominant modal parameters and responses even with significant noise contamination of the response records. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Laboratory tests of steel simple torsionally unbalanced models

Inelastic earthquake response of single-story asymmetric buildings: an assessment of simplified shear-beam models

Shake table tests on a mass eccentric model with base isolation

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2003
Bijan Samali
Abstract A mass eccentric structure is usually more seismically vulnerable than its concentric counterpart because of the coupled torsional,translational response of such structures. In this work, dynamic characteristics and response of a five-storey benchmark model with moderate mass eccentricity were investigated using a shake table, simulating four different ground motions. The effectiveness of laminated rubber bearings (LRB) and lead-core rubber bearings (LCRB) in protecting eccentric structures was examined and evaluated in relation to translational and torsional responses of the benchmark model. It was observed that both translational and torsional responses were significantly reduced with the addition of either a LRB or LCRB isolated system regardless of the nature of ground motion input. The LRB were identified to be more effective than LCRB in reducing model relative displacements, the relative torsional angle as well as accelerations, and therefore provided a better protection of the superstructure and its contents. On the other hand, LCRB rendered a smaller torsional angle and absolute displacement of the base isolation system, hence a more stable structural system. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Torsional response of symmetric buildings to incoherent and phase-delayed earthquake ground motion

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2003
Ernesto Heredia-Zavoni
Abstract This paper studies the effect of coherency loss and wave passage on the seismic torsional response of three-dimensional, multi-storey, multi-span, symmetric, linear elastic buildings. A model calibrated against statistical analyses of ground motion records in Mexico City is used for the coherency function. The structural response is assessed in terms of shear forces in structural elements. Incoherence and wave passage effects are found to be significant only for columns in the ground level of stiff systems. The increase of column shears in the ground level is much higher for soft than for firm soil conditions. For the torsionally stiff systems considered, it is found that incoherent and phase-delayed ground motions do not induce a significant rotational response of the structure. The use of a code eccentricity to account for torsion due to ground motion spatial variation is assessed. On firm soil, the use of a base shear along with an accidental eccentricity results in highly overestimated shear forces; however, for soft soil conditions, code formulations may result in underestimated shear forces. Copyright © 2003 John Wiley & Sons, Ltd. [source]