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To show how apertures affect measurements of the circularly polarized components of light scattered to a detector, we develop two methods of averaging the V and I Stokes parameters over a circular aperture that collects light scattered from an optically active sphere. One method uses a two-dimensional numerical integration that is appropriate for small apertures, and the other gives analytical expressions for scattering into a solid angle of any size. We identify the aperture locations that, independent of aperture size, give an average V (and an effective degree of circular polarization) of zero for scattering from an optically inactive sphere and of nonzero for scattering from an optically active sphere.

Secreted and transmembrane proteins play an essential role in intercellular communication during the development of multicellular organisms. Because only a small number of these genes have been characterized, we developed a screen for genes encoding extracellular proteins that are differentially expressed during Drosophila embryogenesis. Our approach utilizes a new method for screening large numbers of cDNAs by whole-embryo in situ hybridization. The cDNA library for the screen was prepared from rough endoplasmic reticulum-bound mRNA and is therefore enriched in clones encoding membrane and secreted proteins. To increase the prevalence of rare cDNAs in the library, the library was normalized using a method based on cDNA hybridization to genomic DNA-coated beads. In total, 2,518 individual cDNAs from the normalized library were screened by in situ hybridization, and 917 of these cDNAs represent genes differentially expressed during embryonic development. Sequence analysis of 1,001 cDNAs indicated that 811 represent genes not previously described in Drosophila. Expression pattern photographs and partial DNA sequences have been assembled in a database publicly available at the Berkeley Drosophila Genome Project website (). The identification of a large number of genes encoding proteins involved in cell-cell contact and signaling will advance our knowledge of the mechanisms by which multicellular organisms and their specialized organs develop.

We describe a method for integrating analytically, over a circular aperture, the emission from an oscillating dipole inside a dielectric sphere. The model is useful for investigating fluorescence, Raman, or other emission from molecules inside of spherical particles or droplets. The analysis is performed for two cases: (a) the dipole emits from a fixed orientation, and (b) the dipole emits from all orientations and the collected energy is summed. This second case models the collection of emission from a molecule that is excited repeatedly; after each excitation it rotates to a random orientation before emitting. These results are applicable to single-molecule detection techniques employing microdroplets and to other techniques for characterizing microparticles with luminescence or inelastic scattering.

Light scattered from optically active spheres was theoretically analyzed for biodetection. The circularly polarized signal of near-forward scattering from circularly dichroic spheres was calculated. Both remote and point biodetection were considered. The analysis included the effect of a circular aperture and beam block at the detector. If the incident light is linearly polarized, a false signal would limit the sensitivity of the biodetector. If the incident light is randomly polarized, shot noise would limit the sensitivity. Suggested improvements to current techniques include a beam block, precise angular measurements, randomly polarized light, index-matching fluid, and larger apertures for large particles.

Measurements of minimum CO(2) laser fluence required to explode or disintegrate 10-60 microm radius droplets of water, ethanol, diesel (hexadecane), CCl(4), bromoform, and ethyl bromide are reported. Threshold fluences range from 0.4 J cm(-2) for 10-microm radius ethanol drops to 20 J cm(-2) for 30microm bromoform drops. Threshold fluences for water droplets are ~3 J cm(-2) independent of drop size. Comparison of the measurements to calculations of laser fluence required for considered absorbing droplets to reach superheat temperature is in good agreement for cases where liquid material properties are known, suggesting that superheating of droplets is the dominant mechanism causing explosion/disintegration. Measured droplet-induced laser breakdown thresholds are considerably higher than explosion thresholds and have less dependence on droplet size and composition. The highest breakdown threshold values are for water drops, which range from 150 to 280 J cm(-2) (0.9-1.7 x 10(9)W cm(-2)) compared with 670 J cm(-2) (4.0 x 10(9) W cm(-2)) for clean air breakdown for the laser pulse length and spot size.

Using the notion of a source function, which describes the power deposited inside irradiated particles, we study the internal motion of irradiated water droplets by an intense laser pulse. The spatial distribution of the absorbed energy allows us to investigate 2-D hydrodynamic motion of the droplet. We find shock waves within the droplet and jets of vaporized material moving into the surrounding medium.