X-ray focusing with lobster-eye optics: a comparison of theory with experiment

We report an experimental investigation and comparison with simulation of the x-ray focusing of a flat, square profile microchannel plate. We use x rays with an energy of ~1.5 keV from a laser-produced plasma. The images were recorded with x-ray film. We find the focal structure to be consistent with theoretical expectations. The angular resolution of the focus is 0.96 mrad, which is a major improvement over previous results. The measured peak intensity gain is 27 ± 4, which is ~33% of that for a perfect optic.     

Production issues for high aspect ratio Lobster-eye optics using LIGA

 A square packed array of square-channels with long channel axis aligned radially is a useful structure for condensing grazing incidence flux to a focus. These devices, known as Lobster-eye optics for their similarity to the eyes of the macruran crustaceans, show great promise as the focusing optic in the next generation of X-ray all-sky monitors. At X-ray wavelengths the optimal Lobster-eye structure requires an aspect ratio of channel length to width of greater than 30:1. Following recent success in fabricating a low aspect ratio Lobster-eye structure, we discuss some of the parameters for, and production issues involved in making, a useful Lobster-eye prototype using LIGA. We report on our initial attempts to produce high aspect ratio Lobster-eye optics using the LIGA process with a graphite substrate. Received: 10 August 2001/Accepted: 24 September 2001 AGP gratefully acknowledges receipt of an ARC post-doctoral fellowship. This work was supported by the Australian Synchrotron Research Program, which is funded by the Commonwealth of Australia under the Major National Research Facilities Program. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Energy Research, under Contract No. W-31-109-Eng-38. This paper was presented at the Fourth International Workshop on High Aspect Ratio Microstructure Technology HARMST 2001 in June 2001.     

Fabrication of support structures to prevent SU-8 stiction in high aspect ratio structures

We have previously demonstrated that it is possible to fabricate densely-packed high aspect ratio structures in SU-8 by means of a top-plate support member which stiffens the overall structure and prevents pattern collapse. In this work we have computed the tensile stresses induced in the top-plate structures due to the capillary forces that arise between the columns due to the surface tension of the drying liquid. We have further studied the dynamic behavior of the structure after an instantaneous force. Based on these results, we have shown that the predicted optimal thickness of the top-plate structure is sufficient to maintain structural integrity.     

Characterization of strong fiber Bragg gratings using an applied thermal chirp and iterative algorithm

Coupling coefficients of various grating types and strengths are calculated from measurements of the complex reflectivity using an applied thermal chirp and optical frequency domain reflectometry (OFDR). The complex reflectivity is then utilized by a layer peeling algorithm to determine the coupling coefficient of the thermally chirped grating. A guess of the temperature profile enables the coupling coefficient of the unchirped grating to be estimated. An iterative algorithm is then used to converge on the exact coupling coefficient, employing an error minimization method applied to the reflectivity spectra. This technique removes the need for a reference grating while preserving the spatial resolution obtained with the initial OFDR measurement. Successful reconstruction of gratings with integrated |κ|L ~ 9.0 are demonstrated with a spatial resolution of less than 100 μm.     

The cultural context of psychological approaches to alcoholism: Can we control the effects of alcohol?

Argues that the unique history of alcohol use in the US has led to the ascendance of disease theory as the dominant conception of alcoholism. Social-scientific research has consistently conflicted with disease theory, but psychological and other nondisease conceptions of alcoholism are not well-represented in the public consciousness, in treatment programs, or in policies for affecting nationwide drinking practices. Conflict in the field has intensified in the last decade, most notably surrounding the issue of controlled drinking in alcoholism treatment. It is suggested that the current cultural attitude toward alcoholism in the US, one strongly influenced by disease notions, has not led to an improvement in society's drinking problems and that there continues to be a need for psychologists to present alternative views of alcoholism. The concepts of dependence and addiction as related to alcohol and to drugs are discussed. (3 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Red clover isoflavonoids as anthocyanin color enhancing agents in muscadine wine and juice

Isoflavonoid extracts from red clover (Trifolium pratense) leaves were found to enhance overall color and stability of anthocyanin 3,5-diglucosides present in muscadine grape (Vitis rotundifolia) juice and wine through intermolecular copigmentation reactions. Predominant isoflavonoids present in red clover included formononetin, biochanin A, and prunetin and were the major polyphenolics identified to influence anthocyanin color and stability. Since red clover isoflavonoids have poor water solubility characteristics, this allowed for removal of extraneous non-isoflavonoid compounds using hot water and subsequent extraction with ethanol. Isoflavonoid solubility was evaluated as a function of ethanol concentration with recoveries up to 57% found in 20% solutions. Changes in maximum absorbance, total soluble phenolics, isoflavonoids, and anthocyanins were evaluated in muscadine juice and wine following the addition of isoflavonoid extracts with maximum color enhancement found at an anthocyanin to cofactor ratio of 1:8, after which their solubility was prohibitive. Additionally, dried leaves and ethanolic extracts of red clover were added prior to and following fermentation of muscadine wine (11% ethanol) stimulating the natural copigmentation that takes place during red wine fermentation and aging processes. Once fermentation was complete, finished wines were evaluated over a 9-week storage period at 20 and 37 °C. Despite low levels of isoflavonoids present, color improvement and anthocyanin stability was observed in the wines during storage. Little information is available on copigmentation reactions occurring in actual food systems, yet red clover isoflavonoids proved to be novel and effective color enhancing compounds when used in low concentrations in young muscadine wines.     

Dependence of YBaCuO Superconductor Properties on Constituent Oxide Preparation: I, CuO and BaCO3 Pretreatment

A systematic study has been made of the influence of different solid-state decomposition preparations of copper oxide and barium carbonate on the synthesis of YBa₂Cu₃O_7−x superconductor. Considerable morphological control on the end product can be achieved through a monitored calcining of starting materials. The ceramic particle size is found to be primarily dependent on initial CuO morphology, whereas uniformity of the ceramic and the occurrence of an intergranular phase is sensitive to the form of the BaO precursor. The use of accoustic testing for characterizing the ceramic quality is suggested.     

Lobster-eye x-ray optics: a rapid evaluation of the image distribution

A method for calculating the image distribution for one-dimensional lobster-eye optics is presented. This method gives the image distribution exactly for certain cases and offers improved speed over the method of ray tracing. Examples of the use of the algorithm are given. We show that the algorithm gives the same results as detailed ray-tracing codes. Extension of the method to the two-dimensional case is discussed.     

Metabolism of naturally occurring propenylbenzene derivatives. III. Allylbenzene, propenyl benzene, and related metabolic products

The acidic and neutral urinary metabolites of allylbenzene, propenylbenzene, 1'-hydroxyallylbenzene, and cynnamyl alcohol were identified and related through a common metabolic scheme. The rat metabolizes allylbenzene to 1'-hydroxyallylbenzene which can rearrange to yield cinnamyl alcohol whick is further metabolized. This mechanism is proposed to account for the appearance of "propenyl type" metabolites from allylbenzene compounds. Propenylbenzene is oxidized to cynnamyl alcohol. Both 1'-hydroxyallylbenzene and cunnamyl alcohol are excreted unchanged in the neutral extract when given to rats. Allylbenzene and 1'-hydroxyallylbenzene yield basic ninhydrin-positive metabolites. Allylbenzene is first oxidized on the benzylic carbon to form 1'-hydroxyallylbenzene, which is further oxidized to form phenyl vinyl ketone, which condenses with the secondary amines piperidine and dimethylamine to form tertiary aminopropiophenones (Mannich bases). Analogous compounds, cinnamyl alcohol and propenylbenzene, do not yield Mannich base metabolites. This proposed metabolic scheme is consistent with the chemical mechanism operative in the synthesis of Mannich base from allylbenzene via chromic acid oxidation followed by amine addition.     

Primacy of interresponse-time reinforcement in accounting for rate differences under variable-ratio and variable-interval schedules.

Pigeons' keypeck rates under VR schedules are typically higher than under VI schedules when between-schedule reinforcement rates are equated. Exp I, with 4 male White Carneaux pigeons, reproduced this between-schedule rate difference in a multiple VR-VI schedule. However, when the short interresponse times (IRTs) typically reinforced under VRs were required for VI reinforcement, between-component rate differences diminished. Exp II (4 Ss) replicated Exp I except that long IRTs reinforced under VI schedules were required for VR reinforcement. This manipulation eliminated between-schedule rate differences. In Exp III (4 Ss), VR/VI and VI/VR tandems had the same correlation between response and reinforcement rates. In a simulation, C. P. Shimp's (1969) IRT response rule was used as an algorithm to mimic between-schedule rate difference. Findings show that IRT reinforcement (a molecular factor), rather than the feedback function between response rate and reinforcement rate (a molar factor), accounts for the higher response rates under VR schedules. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)