Strong polarization dependence is observed in the optical transmission through nanohole arrays in metals. It is shown that the degree of polarization is determined by the ellipticity and orientation of the holes; the polarization axis lies perpendicular to the broad edge of the ellipse. Furthermore, the depolarization ratio shows a squared dependence on the aspect ratio of the holes, which is discussed in terms of coupling into and out of the surface plasmon modes. The observed results will be useful for tailoring the polarization behavior of metallic nanophotonic elements in many applications, including surface plasmon enhanced optical sensing and ultrafast optical switching.

Numerical techniques for deconvolution are many, and have rarely been compared for ease of use, accuracy of results, and resilience to noisy data. In this paper we report extensive computational tests using various artificial and real data sets and conclude that (i) several methods are satisfactory provided the structure of the observed data is simple, i.e., the lamp used has a sharp cutoff or the sample luminescence decay is accurately described by a single exponential process; (ii) if the decay is more complicated or the lamp has a long tail, a direct method of iterative convolution is more effective than any other; and (iii) artificial data may be generated which are indistinguishable from real observations. The problem of establishing confidence limits for the various parameters is discussed.

Corticotropin-releasing hormone (CRH) is an important regulator of adrenocorticotropin (ACTH) secretion from pituitary corticotroph cells. The intracellular signaling system that underlies this process involves modulation of voltage-sensitive Ca2+ channel activity, which leads to the generation of Ca2+ action potentials and influx of Ca2+. However, the mechanisms by which Ca2+ channel activity is modulated in corticotrophs are not currently known. We investigated this process in a Hodgkin-Huxley-type mathematical model of corticotroph plasma membrane electrical responses. We found that an increase in the L-type Ca2+ current was sufficient to generate action potentials from a previously resting state of the model. The increase in the L-type current could be elicited by either a shift in the voltage dependence of the current toward more negative potentials, or by an increase in the conductance of the current. Although either of these mechanisms is potentially responsible for the generation of action potentials, previous experimental evidence favors the former mechanism, with the magnitude of the shift required being consistent with the experimental findings. The model also shows that the T-type Ca2+ current plays a role in setting the excitability of the plasma membrane, but does not appear to contribute in a dynamic manner to action potential generation. Inhibition of a K+ conductance that is active at rest also affects the excitability of the plasma membrane.

Mass spectrometers produce distorted measurements of gas concentrations because of the time delays and rise times inherent in their responses. Three techniques for numerically correcting such distortion were applied to the acetylene step responses of a Perkin-Elmer MGA1100 mass spectrometer and to simulated data. The techniques investigated were 1) a simple time-delay correction, 2) an exponential model method that assumes a biexponential form for the peak of the impulse response, and 3) a Fourier transform method of deconvolution known as Wiener filtering. The time-delay correction produced an order of magnitude reduction in measurement error. The exponential model method improved on the time-delay correction, and the Wiener filter gave the most accurate corrections in all cases examined.

This paper presents a technique to identify and measure the prominent sources of sensor noise in commercially available charge-coupled device (CCD) video cameras by analysis of the output images. Noise fundamentally limits the distinguishable content in an image and can significantly reduce the robustness of an image processing application. Although sources of image sensor noise are well documented, there has been little work on the development of techniques to identify and quantify the types of noise present in CCD video-camera images. A comprehensive noise model for CCD cameras was used to evaluate the technique on a commercially available CCD video camera.Index Terms-Charge-coupled devices (CCDs), image processing, noise measurement, video signal processing.