The Photometry of Undersampled Point Spread Functions

An undersampled point spread function may interact with the microstructure of a solid-state detector such that the total flux detected can depend sensitively on where the PSF center falls within a pixel. Such intra-pixel sensitivity variations will not be corrected by flat field calibration and may limit the accuracy of stellar photometry conducted with undersampled images, as are typical for Hubble Space Telescope observations. The total flux in a stellar image can vary by up to 0.03 mag in F555W WFC images depending on how it is sampled, for example. For NIC3, these variations are especially strong, up to 0.39 mag, strongly limiting its use for stellar photometry. Intra-pixel sensitivity variations can be corrected for, however, by constructing a well-sampled PSF from a dithered data set. The reconstructed PSF is the convolution of the optical PSF with the pixel response. It can be evaluated at any desired fractional pixel location to generate a table of photometric corrections as a function of relative PSF centroid. A caveat is that the centroid of an undersampled PSF can also be affected by the pixel response function, thus sophisticated centroiding methods, such as cross-correlating the observed PSF with its fully-sampled counterpart, are required to derive the proper photometric correction.Comment: 20 pages, 14 postscript figures, submitted to the PAS

African and Non-African Time: To Contrast or not to Contrast? The Geo-political Convenience of Conceptual Dichotomization

This essay offers a critique of the controversial proposal that peculiarities in African thought concerning time have a negative impact upon African economic development. The proposal under scrutiny takes the form of two corollaries whose notoriety dates back to John S. Mbiti’s (1969) infamous claim that African cultures lack an indigenous concept of the distant future. It is shown that these joint hypotheses appear to be either self-refuting or false. In consequence, the proposal that a cross-cultural scrutiny of time will reveal defective concepts is reconsidered. It is proposed that deficiencies in the perception of time that bear a negative impact upon African economics are instead the cache of foreign experts who fail to appreciate conventional uses of time in Africa as rational strategies for risk avoidance, damage control, for resisting hegemonic authority, quelling foreign expropriation of African resources, and for maximizing efficiency given scarce capital and inadequate infrastructure. What begins as a deflationary dismissal of a long-standing debate over African indigenous thoughts about time concludes with a promising speculation about African idiosyncratic practices of time-management that are instrumental in negotiating the vicissitudes of spiralling underdevelopment.   Key Words African concepts of time, cultural relativism, economic development, John S. Mbiti, post-colonial hermeneutics, time managemen

Will a Private War on Poverty Succeed? The Case of the St. Louis Provident Association

In view of the current emphasis on private approaches to social problem resolution, it is instructive to look at private efforts of the past. The St. Louis Provident Association was a private effort to deal with poverty. It was organized in 1860 to provide relief for the needy and distressed. Data on the volunteer leaders of the association and on the people who were actually helped show a number of things about the 19th-century effort to deal with poverty. First, the volunteers were upwardly- mobile business and professional men who were concerned about the stability of their society. Second, the policies and practices of the Association reflected the social status and ideology of the volunteer directors. Third, the consequences for the poor were a limited amount of help and disproportionate help to particular groups of the impoverished

Effect of aluminum substitution on the reflectance spectra of hematite

Hematite and aluminous hematite were synthesized and the diffuse reflectance spectra were recorded for the region between 0.35 and 1.20 microns. Results show that the near-IR based minimum for the aluminous hematite is shifted longward by about 0.02 microns and is much more shallow. Also, the aluminous specimen is considerably more reflective shortward of approximately 0.55 microns where the ferritic specimen is strongly absorbing. This is noteworthy since the visible slope and the red shoulder are often used in the construction of false color and band ratio images

ADEPT - Next Generation Process Management Technology

In the ADEPT project we have been working on the design and implementation of a next generation process management technology for several years. Based on a conceptual framework for dynamic process changes, on innovative process support functions, and on advanced implementation concepts, the developed system enables the realization of adaptive, process-aware information systems (PAIS). Basically, process changes can take place at the process type as well as the process instance level: Changes of single process instances may have to be carried out in an ad-hoc manner (e.g., to deal with an exceptional situation) and must not affect system robustness and consistency. Process type changes, in turn, must be quickly accomplished in order to adapt the PAIS to business process changes. This may also include the migration of (thousands of) instances to the new process schema (if desired). Important requirements are to perform respective migrations on-the-fly, to preserve correctness, and to avoid performance penalties

General Hospitals, Specialty Hospitals and Financially Vulnerable Patients

Examines whether specialty hospitals draw well-insured patients away from general and safety-net hospitals, reducing their ability to cross-subsidize less profitable services and uncompensated care, in three cities. Notes challenges and implications

Bremsstrahlung in alpha-Decay Reexamined

A high-statistics measurement of bremsstrahlung emitted in the alpha decay of 210Po has been performed, which allows to follow the photon spectra up to energies of ~ 500 keV. The measured differential emission probability is in good agreement with our theoretical results obtained within the quasi classical approximation as well as with the exact quantum mechanical calculation. It is shown that due to the small effective electric dipole charge of the radiating system a significant interference between the electric dipole and quadrupole contributions occurs, which is altering substantially the angular correlation between the alpha particle and the emitted photon.Comment: 10 pages, 5 figures, v2: fix of small typo