Intercellular Migration of Centrioles in the Germarium of \u3cem\u3eDrosophila melanogaster\u3c/em\u3e. An Electron Microscopic Study

A cluster of centrioles has been found in the early Drosophila oocyte. Since the oocyte is connected to 15 nurse cells by a system of intercellular bridges or ring canals, the possibility that the cluster of centrioles arose in the germarium from an intercellular migration of centrioles from the nurse cells to the oocyte was analyzed in serial sections for the electron microscope. Initially, all of the 16 cells of the future egg chambers possess centrioles, which are located in a juxtanuclear position. At the time the 16 cell cluster becomes arranged in a lens-shaped layer laterally across the germarium, the centrioles lose their juxtanuclear position and move towards the oocyte. By the time the 16 cell cluster of cells is surrounded by follicle cells (Stage 1), between 14 and 17 centrioles are found in the oocyte. Later, these centrioles become located between the oocyte nucleus and the follicle cell border and become aggregated into a cluster less than 1.5 µ in its largest dimension. The fate of these centrioles in the oocyte is not known. The fine structure of the germarium and the early oocyte is also described

Silicon retina with adaptive photoreceptors

The central problem faced by the retina is to encode reliably small local differences in image intensity over a several-decade range of background illumination. The distal layers of the retina adjust the transducing elements to make this encoding possible. Several generations of silicon retinae that integrate phototransducers and CMOS processing elements in the focal plane are modeled after the distal layers of the vertebrate retina. A silicon retina with an adaptive photoreceptor that responds with high gain to small spatial and temporal variations in light intensity is described. Comparison with a spatial and temporal average of receptor response extends the dynamic range of the receptor. Continuous, slow adaptation centers the operating point of the photoreceptor around its time-average intensity and compensates for static transistor mismatch

Global and regional importance of the direct dust-climate feedback.

Feedbacks between the global dust cycle and the climate system might have amplified past climate changes. Yet, it remains unclear what role the dust-climate feedback will play in future anthropogenic climate change. Here, we estimate the direct dust-climate feedback, arising from changes in the dust direct radiative effect (DRE), using a simple theoretical framework that combines constraints on the dust DRE with a series of climate model results. We find that the direct dust-climate feedback is likely in the range of -0.04 to +0.02 Wm -2 K-1, such that it could account for a substantial fraction of the total aerosol feedbacks in the climate system. On a regional scale, the direct dust-climate feedback is enhanced by approximately an order of magnitude close to major source regions. This suggests that it could play an important role in shaping the future climates of Northern Africa, the Sahel, the Mediterranean region, the Middle East, and Central Asia

The KO*-rings of BT^m, the Davis-Januszkiewicz Spaces and certain toric manifolds

This paper contains an explicit computation of the KO*-ring structure of an m-fold product of CP^{\infty}, the Davis-Januszkiewicz spaces and toric manifolds which have trivial Sq^2-homology.Comment: 34 page

Particulate absorption of solar radiation: anthropogenic aerosols vs. dust

Particulate solar absorption is a critical factor in determining the value and even sign of the direct radiative forcing of aerosols. The heating to the atmosphere and cooling to the Earth’s surface caused by this absorption are hypothesized to have significant climate impacts. We find that anthropogenic aerosols play an important role around the globe in total particulate absorption of solar radiation. The global-average anthropogenic fraction in total aerosol absorbing optical depth exceeds 65% in all seasons. Combining the potentially highest dust absorption with the lowest anthropogenic absorption within our model range, this fraction would still exceed 47% in most seasons except for boreal spring (36%) when dust abundance reaches its peak. Nevertheless, dust aerosol is still a critical absorbing constituent over places including North Africa, the entire tropical Atlantic, and during boreal spring in most part of Eurasian continent. The equality in absorbing solar radiation of dust and anthropogenic aerosols appears to be particularly important over Indian subcontinent and nearby regions as well as North Africa.National Science Foundation (U.S.) (ATM-0329759)United States. National Aeronautics and Space Administration (NNX07AI49G)Massachusetts Institute of Technology. Joint Program on the Science & Policy of Global Chang

Silicon retina with adaptive photoreceptors

The central problem faced by the retina is to encode reliably small local differences in image intensity over a several-decade range of background illumination. The distal layers of the retina adjust the transducing elements to make this encoding possible. Several generations of silicon retinae that integrate phototransducers and CMOS processing elements in the focal plane are modeled after the distal layers of the vertebrate retina. A silicon retina with an adaptive photoreceptor that responds with high gain to small spatial and temporal variations in light intensity is described. Comparison with a spatial and temporal average of receptor response extends the dynamic range of the receptor. Continuous, slow adaptation centers the operating point of the photoreceptor around its time-average intensity and compensates for static transistor mismatch