A divide and conquer algorithm for medial surface calculation of planar polyhedra

The Medial Axis Transform surface, (or MAT or MS) is proving to be a useful tool for several applications and geometric reasoning tasks. However, calculation of the MAT is a time-consuming task and the benefits of the mathematical-based tool are offset by the cost of the calculation. This paper presents a method for medial surface calculation which uses subdivision to simplify the problem and hence speed up the calculation, a so-called ‘divide-and-conquer’ approach. The basis for this is a modification of the dual structure of the original object. As the calculation proceeds this structure is broken up into sub-pieces each representing a simpler sub-part of the MAT. Perhaps more importantly, this method creates a correct node decomposition of the dual structure. The paper goes on to demonstrate some applications of the results for geometric tasks, specifically offsetting and model subdivision, which are normally expensive but are simpler based on the MAT calculation results.     

Bureau of Mines Method of Calibrating a Primary Radon Measuring Apparatus

One important requirement for accurate monitoring of radon in working environments, dwellings, and outdoors is to ensure that the measurement instrumentation is properly calibrated against a recognized standard. To achieve this goal, the U.S. Department of Interior Bureau of Mines (BoM) Radiation Laboratory has participated since 1983 in a program to establish international radon measurement standards. Originally sponsored by the Organization for Economic Cooperation and Development (OECD), the program is also sponsored by the International Atomic Energy Agency. While the National Institute of Standards and Technology (NIST) radium solution ampules are acceptable to all participating laboratories as a primary standard, a method of transferring radon from the NIST source into each laboratory’s primary counting apparatus is a critical problem. The Bureau’s method transfers radon from the primary solution by bubbling 3 L of air through it into a steel cylinder. After homogenizing the radon concentrations in the cylinder, eight alpha-scintillation cells are filled consecutively and measured in a standard counting system. The resulting efficiency is 81.7±1.2%.     

Influence of a patient decision aid on decisional conflict related to PSA testing: A structural equation model.

Objective: To examine the impact of a decision aid (DA) designed to promote informed decision making for screening with the prostate-specific antigen (PSA) test and to test a theoretical model of factors influencing decisional conflict. Design: Structural equation modeling examined pathways between DA exposure, knowledge, schema, prostate cancer risk perceptions, decisional anxiety, and decisional conflict. Sample participants included 200 men from the general population (exclusive of African Americans) and 200 African American men. Half of the men in each subsample were randomly assigned to receive the DA. Main Outcome Measures: Decisional conflict regarding prostate cancer screening. Results: The DA influences level of decisional conflict by increasing patient knowledge. This effect of knowledge on decisional conflict is indirect, however, through an association with greater perceived risk and lower decisional anxiety. Also, positive PSA schema was associated with lower decisional anxiety and decisional conflict. It is important that exposure to the DA had no impact on PSA schema. Conclusion: Schemas about testing must be considered in developing messages about the risks and benefits of testing. If schemas are counter to message content, mechanisms for modifying schemas must be incorporated into interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Agreement of skinfold measurement and bioelectrical impedance analysis (BIA) methods with dual energy X-ray absorptiometry (DEXA) in estimating total body fat in Anglo-Celtic Australians

OBJECTIVE: To compare percentage total body fat (%BF) estimated by the four skinfold thickness measurement (SKF) and single-frequency bioelectrical impedance analysis (BIA) methods using three different sets of equations, to that assessed by the dual energy X-ray absorptiometric (DEXA) method using a Lunar DPX densitometer. DESIGN: Cross-sectional study. SUBJECTS: An Anglo-Celtic Australian population of 66 males and 130 females (age: 26-86 y). MEASUREMENTS: %BF by anthropometry, BIA using three different sets of equations and DEXA. RESULTS: Mean %BF assessed by DEXA (%BF(DEXA)) was similar to that estimated by SKF (%BF(SKF)) in males, while %BF(DEXA) was slightly higher in females. %BF estimated by BIA (%BF(BIA)) was significantly lower than %BF(DEXA) in females, regardless of equations used for calculation, while the level of agreement between BIA and DEXA in estimating %BF in males was dependent on prediction equations used for calculation of %BF(BIA). A better agreement was obtained from the use on the prediction equations of Segal et al (1988), compared to other two sets of equations. The agreement between SKF or BIA and DEXA declined with increasing %BF. CONCLUSIONS: There was a good agreement between DEXA and SKF, and slightly less so between DEXA and BIA, in estimating %BF in an Anglo-Celtic adult population. The agreement in most cases, however, was dependent on the degree of body fatness. In comparison to DEXA, both SKF and BIA, with the use of the equations of Segal et al (1988), are applicable to estimate %BF in an Anglo-Celtic Australian population.     

Posttraumatic stress disorder and late-onset smoking in the Vietnam era twin registry.

Epidemiological and clinical studies have consistently reported associations between smoking and posttraumatic stress disorder (PTSD). This study analyzed diagnostic interview data on 6,744 members of the Vietnam Era Twin Registry to clarify the PTSD-smoking relation and to examine whether genetic liability for smoking moderated this relation. Preexisting active (unremitted) PTSD increased risk of late-onset daily smoking. Remitted PTSD decreased risk. Active PTSD increased risk of smoking at all levels of genetic liability; the effect was strongest for those with least genetic liability. This suggests PTSD represents a nongenetic pathway to late-onset smoking among individuals who were nonsmokers prior to developing PTSD. If replicated, these results identify PTSD as a risk factor for smoking that should lead to early tobacco control treatment in this population. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dewey's integrated logic of science, ethics, and practice.

H. H. Kendler (see record 1994-09190-001), in his article on psychology and the ethics of social policy, argues in part that ethical imperatives cannot be inferred from empirical data. J. Dewey's (1929 [1958], 1938) instrumentalism and logic of inquiry are presented as solutions to the trifurcation of theoretical science, ethics, and practical science. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spectroscopic and microscopic characterizations of color lamellae in natural pink diamonds

Nineteen natural, untreated, type IaAB pink diamonds from various localities were studied. They display microscopic (～ 1 μm thick) pink lamellae along {111} in an otherwise colorless diamond. This coloration concentrated in lamellae is commonly referred to as “graining”. The diamonds were examined using high spatial resolution spectroscopic methods and transmission electron microscopy. TEM revealed that a pink lamella consists of a cluster of paired microtwins created under stress by plastic deformation. Raman line shift and broadening associated with the twinned pink lamellae indicate the presence of residual stress. Ultraviolet–visible absorption spectra from each of the samples showed a broad absorption band centered at ～ 550 nm, the source of the pink color. Cathodoluminescence spectra of the pink lamellae are different from those of the bulk, colorless diamond matrix. Within the lamellae only, the H3 center is observed along with a less intense N3 center. In some samples, instead of the N3 center a new center with a zero phonon line at 405.5 nm is observed. This previously unreported 405.5 nm center has phonon sidebands qualitatively identical to the N3 center, and may be an N3 center modified by a specific environment. These results suggest that lattice vacancies were created during twinning resulting from plastic deformation, and that impurity centers (such as those containing nitrogen) trap some of the diffusing vacancies. Since the pink lamellae are still under residual stress, new or modified defect centers are created, e.g. H3 and N3. The color center(s) responsible for the pink color (550 nm absorption) was not identified, but likely is only present in diamonds that experienced plastic deformation. Reported annealing of plastically deformed brown diamonds, which results in a residual pink color, suggests that the pink color is stable under these high pressure, high temperature conditions. The reported observations that annealing plastically deformed brown diamonds results in a residual pink color and that the pink color does not anneal out under similar high pressure, high temperature conditions, suggests that the deformation inducing pink color occurs inside the Earth's mantle, whereas brown coloration might be induced during a more recent event such as the ascent of the diamond to the surface in a kimberlitic/lamproitic eruption.