ELECTRICAL RESISTANCE VARIATIONS ACROSS A GROWING FATIGUE CRACK AS A FUNCTION OF THE LOAD CYCLE

Greater understanding of fatigue crack growth requires detailed measurements of crack tip plastic flow. A high resolution crack length measurement system based on the electrical potential method has been used to measure the variations in electrical resistance of specimens containing growing fatigue cracks. Crack growth increments caused by individual load cycles could be resolved down to a size of 0.1 μm. The electrical resistance has been found to vary cyclically as a function of the applied load. These variations are consistent with Bowles' observations that the crack initially grows with a very sharp crack tip followed by plastic blunting which is resharpened during unloading. Crack closure effects could be observed in the results generated from tests conducted with stress ratios of 0 and 0.1, but not for a test with a stress ratio of 0.5.     

Platelet activation and clotting cascade activation by dialyzers designed for high volume online hemodiafiltration

Introduction: Hemodialysis patients are pro‐thrombotic. Higher volume online postdilutional hemodiafiltration (OL‐HDF), with increasing hematocrit increases the risk of clotting in the extracorporeal circuit (ECC). We wished to determine whether OL‐HDF increased platelet activation and ECC clotting. Methods: Coagulation parameters, platelet, white cell, and endothelial activation markers were measured at the start and end of dialysis sessions in 10 patients and also pre‐ and post‐dialyzer after 15 minutes using two different dialyzers designed for high volume OL‐HDF; cellulose triacetate (TAGP) and polysulphone (PS), and polyvinylpyrrolidone (PVP). Patients were anticoagulated with a heparin bolus. Findings: At the start of OL‐HDF, D dimers, thrombin antithrombin complexes (TATs), and soluble adhesions molecules (sICAM‐1 and sVCAM‐1) were increased. Post‐treatment soluble P selectin (PS/PVP 26.7 ± 7.1 versus 36.6 ± 9.9; TAGP 28.7 ± 7.2 versus 43.5 ± 8.4 ng/ml, P < 0.001), and soluble CD40 ligand (PS/PVP 297 ± 228 versus 552 ± 272, TAGP 245 ± 187 versus 390 ± 205 ng/ml, P < 0.05) increased. Post‐dialyzer concentrations increased versus pre‐dialyzer for tissue factor (PS/PVP 117 ± 12 versus 136 ± 16, TAGP 100 ± 25 versus 128 ± 40 ng/ml, P < 0.05), factor VIIIc (PS/PVP 174 ± 54 versus 237 ± 83, TAGP 163 ± 60 versus 247 ± 102 IU/ml, P < 0.01), sVCAM‐1 (PS/PVP 782 ± 64 versus 918 ± 140, TAGP 722 ± 121 versus 889 ± 168 ng/ml, P < 0.01), and D‐dimers (PS/PVP 292 ± 132 versus 355 ± 167, TAGP 300 ± 129 versus 391 ± 171 ng/ml, P < 0.001). There was no macroscopic thrombus noted in the ECC, and no increase in microparticles, platelet factor‐4, or TATs. Discussion: Despite being pro‐thrombotic, with activation of platelets, and lymphocytes during passage through ECC, no macroscopic clotting, or increased TATs were noted during OL‐HDF, and no major differences between cellulosic and polysulphone dialyzers.     

Evaluation of the effect on heart rate variability of some agents acting at the beta-adrenoceptor using nonlinear scatterplot and sequence methods

There is evidence that the processes regulating heart rate variability (HRV) reflect nonlinear complexity and show "chaotic" determinism. Data analyses using nonlinear methods may therefore reveal patterns not apparent with the standard methods for HRV analysis. We have consequently used two nonlinear methods, the Poincaré plot (scatterplot) and cardiac sequence (quadrant) analysis, in addition to the standard time-domain summary statistics, during a normal volunteer investigation of the effects on HRV of some agents acting at the cardiac beta-adrenoceptor. Under double-blind and randomized conditions (Latin square design), 25 normal volunteers received placebo, salbutamol 8 mg (beta 2-adrenoceptor partial agonist), pindolol 10 mg (beta 2-adrenoceptor partial agonist), or atenolol 50 mg (beta 1-adrenoceptor antagonist). Single oral doses of medication (at weekly intervals) were administered at 22:30 hours, with sleeping heart rates recorded overnight. The long-term (SDNN, SDANN) and short-term (rMSSD) time-domain summary statistics were reduced by salbutamol 8 mg and increased by atenolol 50 mg compared with placebo. The reductions in both SDNN and SDANN were greater after salbutamol 8 mg compared with pindolol 10 mg. The reduced HRV after pindolol 10 mg differed from the increased HRV following atenolol 50 mg. The Poincaré plot, constructed by plotting each RR interval against the preceding RR interval, was measured using a reproducible computerized method. Scatterplot length and area were reduced by salbutamol 8 mg and increased by atenolol 50 mg compared with placebo; scatterplot length and area were lower after pindolol 10 mg compared with atenolol 50 mg. Geometric analysis of the scatterplots allowed width assessment (i.e., dispersion) at fixed RR intervals. At the higher percentiles (i.e., 90% of scatterplot length: low HR), salbutamol 8 mg reduced and atenolol 50 mg increased dispersion; at lower percentiles (i.e., 10%, 25%, and 50% length), atenolol 50 mg and pindolol 10 mg increased dispersion compared with placebo and salbutamol 8 mg. Cardiac sequence analysis (differences between three adjacent beats; delta RR vs. delta RRn + 1) was used to assess the short-term patterns of cardiac acceleration and deceleration. Four patterns were identified: +/+ (a lengthening sequencing), +/- or -/+ (balanced sequences), and finally -/- (a shortening sequence). Cardiac acceleration episodes (i.e., number of times delta RR and delta RRn + 1 were both changed) were increased in quadrants -/- and +/+ following pindolol 10 mg and salbutamol 8 mg; the beat-to-beat difference (delta RRn + 1) was reduced after salbutamol 8 mg compared with the three other groups. These results demonstrated a shift towards sympathetic dominance (beta-adrenoceptor partial agonist salbutamol 8 mg) or parasympathetic dominance (beta 1-adrenoceptor antagonist atenolol 50 mg); pindolol 10 mg exhibited HR-dependent effects, reducing HRV at low but increasing variability at high prevailing heart rates. These nonlinear methods appear to be valuable tools to investigate HRV in health and to study the implications of perturbation of HRV with drug therapy in disease states.     

Bending the law: geometric tools for quantifying influence in the multinetwork of legal opinions

Legal reasoning requires identification through search of authoritative legal texts (such as statutes, constitutions, or prior judicial opinions) that apply to a given legal question. In this paper, using a network representation of US Supreme Court opinions that integrates citation connectivity and topical similarity, we model the activity of law search as an organizing principle in the evolution of the corpus of legal texts. The network model and (parametrized) probabilistic search behavior generates a Pagerank-style ranking of the texts that in turn gives rise to a natural geometry of the opinion corpus. This enables us to then measure the ways in which new judicial opinions affect the topography of the network and its future evolution. While we deploy it here on the US Supreme Court opinion corpus, there are obvious extensions to large evolving bodies of legal text (or text corpora in general). The model is a proxy for the way in which new opinions influence the search behavior of litigants and judges and thus affect the law. This type of “legal search effect” is a new legal consequence of research practice that has not been previously identified in jurisprudential thought and has never before been subject to empirical analysis. We quantitatively estimate the extent of this effect and find significant relationships between search-related network structures and propensity of future citation. This finding indicates that “search influence” is a pathway through which judicial opinions can affect future legal development.     

Cesium uptake studies on human erythrocytes

We compared the performance of second and third generation ELISA assays to detect antibodies to HIV-1 virus with conventional Western blotting (WB) and radioimmune Western blotting (RIWB). Both sera from commercial seroconversion panels and serial dilutions of a serum for HIV-1 antibodies were tested with Murex HIV Recombinant, Vidas bioMérieux HIV 1/2 (2nd generation ELISA) Murex HIV 1-2 (3rd generation ELISA), as well as with WB and RIWB. In seroconversion panels all ELISA assays were positive for the same serum with the exception of the first serum of Panel D which was negative with both sample Murex assays and borderline with Vidas assay. This serum was negative with WB but evidenced antibodies to gp160 p66, p51, p24 HIV-1 proteins when assayed by RIWB. In only two cases did WB reveal antibodies to HIV-1 proteins before ELISA assays (Panel A and E); not only did RIWB show the same sensitivity as WB in the two last panels, but it also detected antibodies to HIV-1 proteins earlier than WB, ranging from a few days (Panel C) to approximately 12 weeks (Panel D). The results obtained by testing the dilutions of the serum positive for anti HIV-1 antibodies showed the following degrees of sensitivity: Murex HIV 1-2 (the most sensitive), Murex HIV Recombinant and Vidas bioMérieux HIV 1/2. Although WB was more sensitive than the ELISA assays and picked out antibodies to gp160, gp120 and p24 HIV proteins at 1/4000 serum dilution, the most sensitive test was RIWB which at 1/20,000 serum dilution enabled detection of antibodies to gp160, p66 and p24 HIV proteins.     

Rectification for cone-beam projection and backprojection

The purpose of this paper is to derive a technique for accelerating the computation of cone-beam forward and backward projections that are the basic steps of tomographic reconstruction. The cone-beam geometry of C-arm systems is commonly described with projection matrices. Such matrices provide a continuous framework for analyzing the flow of operations needed to compute backprojection for analytical reconstruction, as well as the combination of forward and backward projections for iterative reconstruction. The proposed rectification technique resampies the original data to planes that are aligned with two of the reconstructed volume main axes, so that the original cone-beam geometry can be replaced by a simpler geometry, where succession of plane magnifications are involved only. Rectification generalizes previous independent results to the cone-beam backprojection of preprocessed data as well as to cone-beam iterative reconstruction. The memory access pattern of simple magnifications provides superior predictability and is, therefore, easier to optimize, independently of the choice of the interpolation technique. Rectification is also shown to provide control over interpolation errors through oversampling, allowing tradeoffs between computation speed and precision to be set. Experimental results are provided for linear and nearest neighbor interpolations, based on simulations, as well as phantom and patient data acquired on a digital C-arm system.     

Resin defect detection in appearance lumber using 2D NIR spectroscopy

Resinous defects incorporated into exterior, treated, appearance products, such as barge boards and weatherboards, can cause unsightly resin bleed and resin show-through, which is a discolouration of the paint layer above the resin feature. Manufacturers, therefore, go to great lengths to eliminate resinous wood via manual grading operations and also as part of automated grading systems. Images from resinous and non-resinous wood were acquired using a near-infrared (NIR) hyperspectral camera which produced spectral data for each pixel (0.94?×?1.00 mm). NIR data from these images in the range from 977 to 1565 nm were used to generate a partial least squares (PLS) model that was able to detect resin features reliably. Wavelength regions with peaks at 1180 and 1370 nm showed a distinct difference between non-resinous and resinous wood. Using a multi-step classification process, it was possible to filter out other wood features, such as sapstain or knots that might interfere with the correct identification of resinous areas. It was possible to average the spectral information of the PLS model to 18 wavelengths and the spatial information to 10 mm/data point without significant loss of resin-prediction ability. The optimised, reduced-information model predicted resin features in 24 out of 30 shooks correctly (80%). Solely shooks with small or narrow resin features or minor show-through were predicted incorrectly, i.e. they were typically predicted as rejects even though no resin show-through feature was apparent in the painted shook.     

Noninvasive estimation of the aorta input function for measurement of tumor blood flow with

Quantitative measurement of tumor blood flow with [15O]water can be used to evaluate the effects of tumor treatment over time. Since quantitative flow measurements require an input function, we developed the profile fitting method (PFM) to measure the input function from positron emission tomography images of the aorta. First, a [11C]CO scan was acquired and the aorta region was analyzed. The aorta diameter was determined by fitting the image data with a model that includes scanner resolution, the measured venous blood radioactivity concentration, and the spillover of counts from the background. The diameter was used in subsequent fitting of [15O]water dynamic images to estimate the aorta and background radioactivity concentrations. Phantom experiments were performed to test the model. Image quantification biases (up to 15%) were found for small objects, particularly for those in a large elliptical phantom. However, the bias in the PFM concentration estimates was much smaller (2%-6%). A simulation study showed that PFM had less bias and/or variability in flow parameter estimates than an ROI method. PFM was applied to human [11C]CO and [15O]water dynamic studies with left ventricle input functions used as the gold standard. PFM parameter estimates had higher variability than found in the simulation but with minimal bias. These studies suggest that PFM is a promising technique for the noninvasive measurement of the aorta [15O]water input function.     

A linear wavelet filter for parametric imaging with dynamic PET

This paper describes a new filter for parametric images obtained from dynamic positron emission tomography (PET) studies. The filter is based on the wavelet transform following the heuristics of a previously published method that are here developed into a rigorous theoretical framework. It is shown that the space-time problem of modeling a dynamic PET sequence reduces to the classical one of estimation of a normal multivariate vector of independent wavelet coefficients that, under least-squares risk, can be solved by straightforward application of well established theory. From the study of the distribution of wavelet coefficients of PET images, it is inferred that a James-Stein linear estimator is more suitable for the problem than traditional nonlinear procedures that are incorporated in standard wavelet filters. This is confirmed by the superior performance of the James-Stein filter in simulation studies compared to a state-of-the-art nonlinear wavelet filter and a nonstationary filter selected from literature. Finally, the formal framework is interpreted for the practitioner's point of view and advantages and limitations of the method are discussed.