Pattern formation in the basilar papilla: evidence for cell rearrangement.

The avian basilar papilla is composed of hair and supporting cells arranged in a regular pattern in which the hair cells are surrounded and isolated from each other by supporting cell processes. This arrangement of cells, in which the apical borders of hair cells do not contact one another, may be generated by contact-mediated lateral inhibition. Little is known, however, about the way in which hair and supporting cells are organized during development. Whole mounts double-labeled with antibodies to the 275 kDa hair-cell antigen and the tight junction protein cingulin were therefore used to examine the development of cell patterns in the basilar papilla. Hair cells that contact each other at their apical borders are seen during early development, especially on embryonic days (E) 8 and 9, but are no longer observed after E12. Hair and supporting cell patterns were analyzed in three different areas of the papilla at E9 and E12. In two of these regions between E9 and E12, the ratio of supporting cells to hair cells does not change significantly, whereas there is an increase in both the number of supporting cells around each hair cell and the number of hair cells that each supporting cell contacts. In the third region examined, there is a dramatic rise in the number of supporting cells around each hair cell, which although accompanied by a small, significant increase in the ratio of supporting cells to hair cells cannot be accounted for by an increase in supporting cell numbers. These data show that a rearrangement of hair and supporting cells with respect to one another may be a fundamental process underlying the development of a regular pattern in the basilar papilla

A Novel Antigen Sensitive to Calcium Chelation That is Associated with the Tip Links and Kinocilial Links of Sensory Hair Bundles

Tip links are extracellular, cell-surface-associated filaments of unknown molecular composition that are thought to gate the mechanotransducer channel of the sensory hair cell. They disappear from the hair bundle in response to calcium chelation and lanthanum treatment and resist degradation by the protease subtilisin. A monoclonal antibody derived from a hybridoma screen identified a novel antigen associated with tip links, the tip-link antigen. The tip-link antigen is also associated with kinocilial links, subtilisin-resistant filaments that are sensitive to calcium chelation and connect the kinocilium to the tallest stereocilia of the hair bundle. Furthermore, the tip-link antigen is expressed in the retina, where it is associated with the ciliary calyx, a ring of microvilli that surrounds the outer segment of the photoreceptor. The tip-link antigen rapidly disappears from the surface of the hair bundle in response to calcium chelation. It is also subtilisin resistant, relative to the ankle-link antigen, an antigen associated with another type of hair bundle link. The tip-link antigen is lanthanum sensitive and, like tip links, reappears on the surface of the hair bundle after calcium chelation. The monoclonal antibody to the tip-link antigen immunoprecipitates two concanavalin A-reactive polypeptides with apparent molecular masses of 200 and 250 kDa from detergent extracts of the retina. These results provide the first identification of a cell surface antigen associated with tip links, indicate that tip links share properties in common with kinocilial links, and reveal a second epitope that, along with the ankle-link antigen, is common to both sensory hair bundles and the ciliary calyx of photoreceptors

Effect of Setup Configurations of Split Computer Keyboards on Wrist Angle

Alternative computer keyboards whose halves can be slanted toward each other can reduce a risk factor (ulnar deviation) for work-related musculoskeletal disorders (WMSDs) affecting the upper limbs. Two questions that computer keyboard operators face when using keyboards that can be separated into halves (split keyboards) are: (1) At what angle should the keyboard halves be opened? and (2) At what distance apart should the keyboard halves be placed? The objective of this study was to investigate the effects of the opening angle and separation distance between halves of a split keyboard on wrist ulnar deviation and typing efficiency. Methods. Eleven experienced computer keyboard operators participated in this study and used a split keyboard that was set up in a conventional (nonsplit) format and also in 3 alternative configurations: (1) centers of keyboard halves were separated at 20-cm distance, (2) keyboard halves were separated half of the distance of shoulder width, and (3) keyboard halves were separated at shoulder width distance. Results. The 3 alternative configurations resulted in ulnar deviation of both wrists that were less than ulnar deviation from typing on a conventional setup. There were no differences in ulnar deviations among the 3 alternative configurations. Discussion and Conclusion. The results of this research provide physical therapists and ergonomists with a set of configurations of a split keyboard that they can recommend to their patients or clients. All of the alternative configurations of the split keyboard are beneficial in promoting a neutral wrist position, which theoretically would decrease exposure to WMSDs such as tenosynovitis in the wrist and carpal tunnel syndrome. [Marklin RW, Simoneau GG. Effect of setup configurations of split computer keyboards on wrist angle. Phys Ther. 2001;81:1038 –1048.

Prolongation of Poisson 2-form on Weil bundles

In this paper, M denotes a smooth manifold of dimension n, A a Weil algebra and M^{A} the associated Weil bundle. When (M,_{M}) is a Poisson manifold with 2-form _{M}, we construct the 2-Poisson form _{M^{A}}^{A}, prolongation on M^{A} of the 2-Poisson form _{M}. We give a necessary and sufficent condition for that M^{A} be an A-Poisson manifold

Conway's subprime Fibonacci sequences

It's the age-old recurrence with a twist: sum the last two terms and if the result is composite, divide by its smallest prime divisor to get the next term (e.g., 0, 1, 1, 2, 3, 5, 4, 3, 7, ...). These sequences exhibit pseudo-random behaviour and generally terminate in a handful of cycles, properties reminiscent of 3x+1 and related sequences. We examine the elementary properties of these 'subprime' Fibonacci sequences.Comment: 18 pages, 5 figure

Extensive and Intensive Margins of Labour Supply: Working Hours in the US, UK and France

This paper documents the key stylised facts underlying the evolution of labour supply at the extensive and intensive margins in the last forty years in three countries: United-States, United-Kingdom and France. We develop a statistical decomposition that provides bounds on changes at the extensive and intensive margins. This decomposition is also shown to be coherent with the analysis of labour supply elasticities at these margins. We use detailed representative micro-datasets to examine the relative importance of the extensive and intensive margins in explaining the overall changes in total hours worked.labor supply, employment, hours of work

Does Relative Income Matter? Are the Critics Right?

Do other peoples' incomes reduce the happiness which people in advanced countries experience from any given income? And does this help to explain why in the U.S., Germany and some other advanced countries, happiness has been constant for many decades? The answer to both questions is 'Yes'. We provide 4 main pieces of evidence. 1) In the U.S. General Survey (repeated samples since 1972) comparator income has a negative effect on happiness equal in magnitude to the positive effect of own income. 2) In the West German Socio-Economic Panel since 1984 the same is true but with lifesatisfaction as the dependant variable. We also use the Panel to compare the effect of income comparisons and of adaptation as factors explaining the stable level of life-satisfaction: income comparisons emerge as much the more important. 3) When in our U.S. analysis we introduce "perceived" relative income as a potential explanatory variable, its effect is as large as the effect of actual relative income - further supporting the view that comparisons matter. 4) Finally, for a panel of European countries since 1973 we estimate the effect of average income upon average lifesatisfaction, splitting income into two components: trend and cycle. The effect of trend income is small and ill-defined. Our conclusions relate to time series and to advanced countries only. They differ from those drawn in recent studies by Deaton and Stevenson/Wolfers, but those studies are largely cross-sectional and mostly include non-advanced as well as advanced countries.Easterlin Paradox, happiness, relative income, growth