Design of an anidolic concentrator and evaluation of daylight enhancement under an overcast sky

This paper discusses the performance evaluation of anidolic concentrators in an overcast sky condition. The concentrators were designed, with acceptance angles of 60°, 70° and 80°, first by maintaining the profile of the concentrator’s uniform and secondly by keeping the height uniform. Studies were done using these concentrators with a model light pipe and the performance was compared with that of an acrylic dome and a profiled Fresnel collector. For a given condition, the illuminance ratio (ratio of illuminance measured at the base of the pipe to external illumination) increased with the acceptance angle. For a given acceptance angle, the concentrator with uniform height and variation of entrance aperture, performed better than a concentrator having a uniform profile.

Sensitivity of instrumental line shape with respect to different optical attenuators and resulting error propagation into atmospheric trace gas retrievals

The TCCON (Total Carbon Column Observing Network) and most NDACC (Network for Detection of Atmospheric Composition Change) assume an ideal ILS (Instrumental line shape) in spectra retrieval and insert an attenuator or select a smaller entrance aperture to take some intensities away if incident radiation is too strong. These processes may alter the alignment of a high resolution FTIR (Fourier transform infrared) spectrometer and may result in biases due to ILS drift. In this paper, we first investigated the sensitivity of ILS monitoring with respect to various typical optical attenuators for ground-based high resolution FTIR spectrometers within the TCCON and NDACC networks. Both lamp and sun cell measurements were conducted in this analysis via the insertion of five different attenuators before and behind the interferometer. We compared the HCl profile retrievals using an ideal ILS with those using an actual measured ILS. The results showed that the total column amounts were under-estimated by about 0.4 % if the ME (modulation efficiency) amplitude deviates by about –3.5 %. Furthermore, the retrieval errors increased and the obvious profile deviations are shown in a height range with a high retrieval sensitivity. ILSs deduced from all scenarios of lamp cell measurements were compared, and were further used to derive the HCl profile from the same spectrum. As a result, the disturbances to the ILS of a high resolution FTIR spectrometer with respect to inserting different attenuators before and behind the interferometer are quantified. The resulting ILS errors propagation into gas retrievals were also analyzed. In conclusion, the alignment of the optical parts before the interferometer is more critical than those behind the interferometer, and the entrance aperture (the focus of the entrance parabolic/spherical mirror) exhibited the most critical influence. An optimum method to adapt the incident intensity of a detector was finally deduced.

Development of the lateral eye of American horseshoe crabs: Visual field and dioptric array

We used a precision two-circle goniometer mounted to the stage of a compound microscope to determine the optical alignment and to measure the entrance aperture diameter of individual cuticular cones in the dioptric array of the lateral eye of juvenile horseshoe crabs in order to learn about the development of the visual field. Our results show that the extent of the visual field of juvenile horseshoe crabs with prosomal lengths about 20% ofadult size (14–21 mm) is about 70% that of the visual field of adult horseshoe crabs (prosomal lengths: 100+ mm). The visual field of such juvenile animals covers between 77 and 85 deg vertically and 140 and 145 deg horizontally. Assuming that the dioptric array is uniform and square packed, the average interommatidial angle of the juvenile animals is between 5.6 and 6.0 deg as compared to 4.6 deg for an adult animal. The diameter of the entrance aperture of individual cuticular cones increases markedly with increasing animal size. In addition, we noted a statistically significant trend for entrance aperture diameters to increase from anterior to posterior within the eye for animals of all sizes. There may be a slight trend for entrance aperture diameters to increase from dorsal to ventral within the eye. Our results indicate that the extent of the visual field and the resolution of the lateral eye approach adult values in advance of animals' reaching sexual maturity.

Design and applications of a post-column imaging filter

We have designed and built an imaging filter which can can be attached to most standard TEMs, and is capable of operating at primary energies of up to 400 keV. The column-mounted hardware consists of 8 principal parts (Fig. 1): 1) entrance aperture, 2) pre-prism focussing and alignment coils, 3) magnetic prism, 4) spectrum-magnifying quadrupoles, 5) pneumatically retractable energy-selecting slit, 6) quadrupole-sextupole imaging assembly, 7) pneumatically retractable TV-rate CCD camera, and 8) slowscan CCD (SSC) camera. In normal operation, the entrance aperture selects a part of an image (or a diffraction pattern) that is projected by the microscope into the viewing chamber, and a doubly-focused spectrum is produced at the energy selecting slit (with a dispersion of 6 μm / eV at 200 keV). The slit width is piezoelectrically adjustable, and the whole slit assembly can be withdrawn pneumatically from the electron beam. Similar to the TEM column which can either produce an image or a diffraction pattern, the post-slit quadrupole-sextupole assembly can produce either a focussed spectrum at the SSC (or the TV), or a magnified image of the specimen.