Five-dimensional quasispin toward a complete classification of the isospin characteristics of shell-model states in the seniority scheme

A solution is proposed for the inner multiplicity problem associated with the five-dimensional quasispin description of shell-model states. A classification scheme, in terms of an orthonormal basis, leads to tractable results with definite symmetry properties under particle-hole conjugation. Explicit constructions are given for the R(5) irreducible representations for which the inner multiplicities are never greater than two. For states of seniority v = 2, reduced isospin t = 1, of a configuration jn general expressions are given for the matrix elements of an arbitrary two-body interaction, to determine their n, T dependence, and to isolate those features of the actual interaction among nucleons which are most effective in splitting the isospin degeneracy of such states.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32767/1/0000138.pd

Role of Spherical Aberration in Contrast Sensitivity Loss with Radial Keratotomy

A technique is described to determine the change in image contrast as a result of the spherical aberration induced by the radial keratotomy procedure. The hypothesis that the loss in contrast sensitivity of the RK eye is due to the change in spherical aberration postsurgically, is found to be acceptable for some patients. However, this is not a sufficient explanation in all cases. This conclusion may be due to assumptions inherent in the technique derived for calculating spherical aberration or to other factors of importance in the post-RK eye. Invest Ophthalmol Vis Sci 30: [1997][1998][1999][2000][2001]1989 It has been reported by several investigators 1 9 that some subjects show a measurable change in contrast sensitivity (CS) following radial keratotomy (RK). In some cases the losses reported appear transitory. In a recent study by Tomlinson and Caroline 1 CS was measured 1 year postoperatively on six subjects who had undergone RK on one eye only. In three of these subjects it was found that the CS of the maximally corrected, operated eye was significantly reduced compared to that of the maximally corrected, unoperated eye. Assuming that the CS of the unoperated eye is similar to the preoperative CS of the fellow eye this implies a reduction in visual performance as a consequence of RK. The losses in contrast sensitivity noted in this study 1 are not found in all patients undergoing the procedure. It is of interest to discover the source of the visual loss found in some patients since this might allow anticipation of such consequences of RK. Several possibilities have been considered including increased glare, 3 changes in corneal thickness 4 and change in retinal image size. 5 Another possibility, the one to be considered in this paper, is the loss of retinal image quality as a result of the change in spherical aberration of the post-RK cornea. Since we have pre-and 1 year postoperative photokeratoscopic data on each of the eyes which underwent RK in the previous study, it is possible to esti- mate the visual effects of increased spherical aberration resulting from change in corneal shape. We have carried out such a calculation and have compared our results to the measured differences in CS for each of the subjects. Technique of Calculation of Spherical Aberration with the Post-RK Eye Typical photokeratoscopic 10 data are shown in (1) and have used a least squares method to find the "best" values for the coefficients in Equation (1) by fitting Equation (1) to the nine data points. Typical pre-and postoperative results are shown i

The spectral, spatial and contrast sensitivity of human polarization pattern perception

It is generally believed that humans perceive linear polarized light following its conversion into a luminance signal by diattenuating macular structures. Measures of polarization sensitivity may therefore allow a targeted assessment of macular function. Our aim here was to quantify psychophysical characteristics of human polarization perception using grating and optotype stimuli defined solely by their state of linear polarization. We show: (i) sensitivity to polarization patterns follows the spectral sensitivity of macular pigment; (ii) the change in sensitivity across the central field follows macular pigment density; (iii) polarization patterns are identifiable across a range of contrasts and scales, and can be resolved with an acuity of 15.4 cycles/degree (0.29 logMAR); and (iv) the human eye can discriminate between areas of linear polarization differing in electric field vector orientation by as little as 4.4°. These findings, which support the macular diattenuator model of polarization sensitivity, are unique for vertebrates and approach those of some invertebrates with a well-developed polarization sense. We conclude that this sensory modality extends beyond Haidinger's brushes to the recognition of quantifiable spatial polarization-modulated patterns. Furthermore, the macular origin and sensitivity of human polarization pattern perception makes it potentially suitable for the detection and quantification of macular dysfunction

Understanding disability glare: light scatter and retinal illuminance as predictors of sensitivity to contrast

The presence of a bright light in the visual field has two main effects on the retinal image: reduced contrast and increased retinal illuminance due to scattered light; the latter can, under some conditions, lead to an improvement in retinal sensitivity. The combined effect remains poorly understood, particularly at low light levels. A psychophysical flicker-cancellation test was used to measure the amount and angular distribution of scattered light in the eye for 40 observers. Contrast thresholds were measured using a functional contrast sensitivity test. Pupil-plane glare-source illuminances (i.e. 0, 1.35, 19.21 lm/m2), eccentricities (5°, 10°, 15°), and background luminances (1, 2.6, 26 cd/m2) were investigated. Visual performance was better than predicted, based on loss of retinal image contrast caused by scattered light, particularly in the mesopic range. Prediction accuracy improved significantly when the expected increase in retinal sensitivity in the presence of scattered light was also incorporated in the model

Five Dimensional Quasispin Classification Of Shell Model States In The Seniority Scheme.

PhDNuclear physicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/187393/2/6912128.pd