A Linearization Beam-Hardening Correction Method for X-Ray Computed Tomographic Imaging of Structural Ceramics

Computed tomographic (CT) imaging with both monochromatic and polychromatic x-ray sources can be a powerful NDE method for characterization (e. g., measurement of density gradients) as well as flaw detection (e. g., detection of cracks, voids, inclusions) in ceramics. However, the use of polychromatic x-ray sources can cause image artifacts and overall image degradation through beam hardening (BH) effects [1]. Beam hardening occurs because (i) x-ray attenuation in a given material is energy dependent and (ii) data collection in CT systems is not energy selective. Without an appropriate correction, the BH effect prevents the establishment of an absolute scale for density measurement. Thus, quantitative density comparisons between samples of the same material but of different geometrical shape becomes unreliable [2]

Testing the Hubble Law with the IRAS 1.2 Jy Redshift Survey

We test and reject the claim of Segal et al. (1993) that the correlation of redshifts and flux densities in a complete sample of IRAS galaxies favors a quadratic redshift-distance relation over the linear Hubble law. This is done, in effect, by treating the entire galaxy luminosity function as derived from the 60 micron 1.2 Jy IRAS redshift survey of Fisher et al. (1995) as a distance indicator; equivalently, we compare the flux density distribution of galaxies as a function of redshift with predictions under different redshift-distance cosmologies, under the assumption of a universal luminosity function. This method does not assume a uniform distribution of galaxies in space. We find that this test has rather weak discriminatory power, as argued by Petrosian (1993), and the differences between models are not as stark as one might expect a priori. Even so, we find that the Hubble law is indeed more strongly supported by the analysis than is the quadratic redshift-distance relation. We identify a bias in the the Segal et al. determination of the luminosity function, which could lead one to mistakenly favor the quadratic redshift-distance law. We also present several complementary analyses of the density field of the sample; the galaxy density field is found to be close to homogeneous on large scales if the Hubble law is assumed, while this is not the case with the quadratic redshift-distance relation.Comment: 27 pages Latex (w/figures), ApJ, in press. Uses AAS macros, postscript also available at http://www.astro.princeton.edu/~library/preprints/pop682.ps.g

On a notion of maps between orbifolds, I. function spaces

This is the first of a series of papers which are devoted to a comprehensive theory of maps between orbifolds. In this paper, we define the maps in the more general context of orbispaces, and establish several basic results concerning the topological structure of the space of such maps. In particular, we show that the space of such maps of C^r-class between smooth orbifolds has a natural Banach orbifold structure if the domain of the map is compact, generalizing the corresponding result in the manifold case. Motivations and applications of the theory come from string theory and the theory of pseudoholomorphic curves in symplectic orbifolds.Comment: Final version, 46 pages. Accepted for publication in Communications in Contemporary Mathematics. A preliminary version of this work is under a different title "A homotopy theory of orbispaces", arXiv: math. AT/010202

Sequential Posted Price Mechanisms with Correlated Valuations

We study the revenue performance of sequential posted price mechanisms and some natural extensions, for a general setting where the valuations of the buyers are drawn from a correlated distribution. Sequential posted price mechanisms are conceptually simple mechanisms that work by proposing a take-it-or-leave-it offer to each buyer. We apply sequential posted price mechanisms to single-parameter multi-unit settings in which each buyer demands only one item and the mechanism can assign the service to at most k of the buyers. For standard sequential posted price mechanisms, we prove that with the valuation distribution having finite support, no sequential posted price mechanism can extract a constant fraction of the optimal expected revenue, even with unlimited supply. We extend this result to the the case of a continuous valuation distribution when various standard assumptions hold simultaneously. In fact, it turns out that the best fraction of the optimal revenue that is extractable by a sequential posted price mechanism is proportional to ratio of the highest and lowest possible valuation. We prove that for two simple generalizations of these mechanisms, a better revenue performance can be achieved: if the sequential posted price mechanism has for each buyer the option of either proposing an offer or asking the buyer for its valuation, then a Omega(1/max{1,d}) fraction of the optimal revenue can be extracted, where d denotes the degree of dependence of the valuations, ranging from complete independence (d=0) to arbitrary dependence (d=n-1). Moreover, when we generalize the sequential posted price mechanisms further, such that the mechanism has the ability to make a take-it-or-leave-it offer to the i-th buyer that depends on the valuations of all buyers except i's, we prove that a constant fraction (2-sqrt{e})/4~0.088 of the optimal revenue can be always be extracted.Comment: 29 pages, To appear in WINE 201

Full density matrix dynamics for large quantum systems: Interactions, Decoherence and Inelastic effects

We develop analytical tools and numerical methods for time evolving the total density matrix of the finite-size Anderson model. The model is composed of two finite metal grains, each prepared in canonical states of differing chemical potential and connected through a single electronic level (quantum dot or impurity). Coulomb interactions are either excluded all together, or allowed on the dot only. We extend this basic model to emulate decoherring and inelastic scattering processes for the dot electrons with the probe technique. Three methods, originally developed to treat impurity dynamics, are augmented to yield global system dynamics: the quantum Langevin equation method, the well known fermionic trace formula, and an iterative path integral approach. The latter accommodates interactions on the dot in a numerically exact fashion. We apply the developed techniques to two open topics in nonequilibrium many-body physics: (i) We explore the role of many-body electron-electron repulsion effects on the dynamics of the system. Results, obtained using exact path integral simulations, are compared to mean-field quantum Langevin equation predictions. (ii) We analyze aspects of quantum equilibration and thermalization in large quantum systems using the probe technique, mimicking elastic-dephasing effects and inelastic interactions on the dot. Here, unitary simulations based on the fermionic trace formula are accompanied by quantum Langevin equation calculations

Initial KAATSU Cuff Tightness: Effect of Limb Anthropometrics on Blood Flow Restriction

abstractINTRODUCTION KAATSU training involves low load (20%1RM) resistance exercise combined with partial blood flow restriction (BFR). BFR is achieved by positioning a specially designed pneumatic cuff around the proximal aspect of the limb, cinching it to an initial cuff tightness (ICT), then inflating the cuff to a higher restrictive training pressure. ICTs can potentially impact the degree of BFR (%BFR) caused at the higher training pressures, yet many studies use the same ICTs for all subjects (1). Identifying that discrepancies in %BFR exist between subjects with different limb anthropometrics is an important step in moving toward standardization of BFR dose for KAATSU training prescription. The purpose of this study was to identify variation in %BFR between subjects experiencing the same ICT and what limb anthropometrics (circumference, muscle, and fat composition) may be determinants. METHODS Forty-two volunteers (26 men, 16 women) provided informed consent. Caliper skin folds, Gulick tape circumferences, and peripheral quantitative computed tomography (pQCT) scans were performed on the randomly assigned ipsilateral arm and leg at the level of the KAATSU cuff application. %BFR was measured via pulse-wave Doppler ultrasound at baseline (no cuff) and at an ICT of 30 mmHg. Variable relationships were assessed using Pearson correlations and stepwise linear regression. RESULTS The average %BFR (avg±st. dev.) for the arm and leg was 16.01±11.42% and 16.75±9.27% with a range of 46.66% and 36.41%, respectively. The dependent variable for regression analysis was %BFR. In the arm, pQCT-determined muscle (R2=0.614) and fat composition (R2=0.587) were significant (p<0.05) determinants of %BFR. Circumference was also a determinant (R2=0.163). There were no significant correlations between %BFR and the anthropometrics for the leg. pQCT fat composition and sum of skin folds correlated significantly (r=0.915, p<0.05). pQCT circumference and Gulick circumference measures correlated significantly (r=0.991, p<0.05). DISCUSSION Conflicting BFR training results have been reported in the literature. A potential cause could be universal ICT usage causing some individuals to receive an inadequate training stimulus. Individuals using a 30 mmHg ICT will experience different %BFR when limb anthropometrics vary. Thus a method of assigning ICTs specific to individuals’ anthropometric characteristics is needed to ensure equally potent stimuli. Skin fold measures and circumference measures were highly correlated with pQCT data. As a result, skin fold and Gulick circumference measures can be used to predict arm composition at the level of the cuff and may inform prescription of appropriate ICTs that result in more consistent initial %BFR across individuals

KAATSU Cuff Tightness and Limb Anthropometry: Effect on Blood Flow Restriction

abstractKAATSU resistance training involves low loads (20%1RM) and partial blood flow restriction (BFR). When applying a BFR cuff, the initial cuff tightness (ICT) is important. ICTs can potentially impact the degree of BFR (%BFR) caused by the subsequent inflation to the target training pressures. It’s known that limb anthropometrics can affect the amount of BFR that is produced at specific pressures. Understanding the interaction between limb anthropometrics and ICT is an important first step in standardizing BFR dose between individuals for KAATSU training prescription. Purpose: To determine what limb anthropometrics (circumference, muscle or fat composition) have the greatest effect on %BFR with various ICTs. Methods: Forty-two volunteers (26 men, 16 women) provided informed consent. Caliper skin folds (anterior and posterior), Gulick tape circumferences, and peripheral quantitative computed tomography (pQCT) scans were performed on the randomly assigned ipsilateral arm and leg at the level of the KAATSU cuff. %BFR was measured via pulse-wave Doppler ultrasound at baseline (no cuff) and at 5 ICT pressures (20, 30, 40, 50 and 60mmHg). Variable relationships were assessed using Pearson correlations and stepwise linear regression. Results: The dependent variable for regression analysis was %BFR at each ICT. pQCT-determined muscle (R2= .147, .614, .445, .360, & .232, respectively) and fat composition (R2= .138, .587, .429, .338, & .220, respectively) were significant (p<.05) determinants of BFR at all ICT pressures in the arm. At 30mmHg, circumference was also a determinant (R2=.163). There were no significant correlations between %BFR and any of the ICT pressures for the leg. pQCT fat composition and sum of skin folds correlated significantly (r=.915, p<.05). pQCT circumference and Gulick circumference measures correlated significantly (r=.991, p<.05). Conclusion: Arm anthropometrics impact the %BFR created by 5 ICTs in the arm. Skin fold measures and circumference measures were highly correlated with pQCT data. As a result, skin fold and Gulick circumference measures can be used to predict arm composition at the level of the cuff and may inform prescription of appropriate ICTs that result in more consistent initial %BFR across individuals

The binding of estradiol in the uterus: a mechanism for derepression of RNA synthesis

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Spectrum Generating Algebras for the free motion in S3S^3

We construct the spectrum generating algebra (SGA) for a free particle in the three dimensional sphere $S^3$ for both, classical and quantum descriptions. In the classical approach, the SGA supplies time-dependent constants of motion that allow to solve algebraically the motion. In the quantum case, the SGA include the ladder operators that give the eigenstates of the free Hamiltonian. We study this quantum case from two equivalent points of view.Comment: 29 pages, 1 figur