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Model Regression (model + regression)
Selected AbstractsSynthesis and characterization of catalytic nanoporous carbon membranesAICHE JOURNAL, Issue 1 2001Michael S. Strano A method is reported for the synthesis of nobel catalyic nanoporous carbon membranes. Defect-free, nanoporous carbon films of 12.5,,m average thickness containing a dispersion of Ptx were synthesized on macroporous stainless-steel supports. Ideal gas selectivities for the catalytic membranes were simliar to those of inert nanoporous carbon membranes with He,N2=58.6 and O2N2=4.9. The selective hydrogenation of monoolefins (propylen, l-buiene, isobutylene) was used to probe the shape-selective catalytic proerties nad the transport selectivities of the membranes. The results were modeled using the linear regime of coupled sdsorption, transport and rection in the membrane. Model regression yielded 14.9, 19.7. and 18.4 kJ/mol for the activation energies of permeation for propylene, isobutylene, and l-butene, respectively. The system demonstrated selective reaction and transport favoring propane production with selectiveity ratios of 28.9:3.2.I for propane:n-butane:isobutane at 125°C. [source] Evaluation of mixed-conducting lanthanum-strontium-cobaltite ceramic membrane for oxygen separationAICHE JOURNAL, Issue 10 2009Lei Ge Abstract In this study, La0.4Sr0.6CoO3-, (LSC) oxide was synthesized via an EDTA-citrate complexing process and its application as a mixed-conducting ceramic membrane for oxygen separation was systematically investigated. The phase structure of the powder and microstructure of the membrane were characterized by XRD and SEM, respectively. The optimum condition for membrane sintering was developed based on SEM and four-probe DC electrical conductivity characterizations. The oxygen permeation fluxes at various temperatures and oxygen partial pressure gradients were measured by gas chromatography method. Fundamental equations of oxygen permeation and transport resistance through mixed conducting membrane were developed. The oxygen bulk diffusion coefficient (Dv) and surface exchange coefficient (Kex) for LSC membrane were derived by model regression. The importance of surface exchange kinetics at each side of the membrane on oxygen permeation flux under different oxygen partial pressure gradients and temperatures were quantitatively distinguished from the oxygen bulk diffusion. The maximum oxygen flux achieved based on 1.6-mm-thick La0.4Sr0.6CoO3-, membrane was ,4.0 × 10,7 mol cm,2 s,1at 950°C. However, calculation results show theoretical oxygen fluxes as high as 2.98 × 10,5 mol cm,2 s,1 through a 5-,m-thick LSC membrane with ideal surface modification when operating at 950°C for air separation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] P Wave Duration and Morphology Predict Atrial Fibrillation Recurrence in Patients with Sinus Node Dysfunction and Atrial-Based PacemakerPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 11 2002ANTONIO DE SISTI DE SISTI, A., et al.: P Wave Duration and Morphology Predict Atrial Fibrillation Recurrence in Patients with Sinus Node Dysfunction and Atrial-Based Pacemaker. P wave duration and morphology have never been systematically evaluated as markers of AF in patients with a conventional indication to pacing. This study correlated sinus P wave duration and morphology and the incidence of AF in patients with sinus node dysfunction (SND), previous history of AF before implant, and atrial-based pacemaker. Included were 140 patients (86 men, 54 women; mean age 71.8 ± 10.4 years) with recurrent paroxysmal AF and who received a DDD (128 patients) or AAI (12 patients) pacemaker for SND. Forty-nine patients had structural heart disease. Sinus P wave duration and morphology was evaluated in leads II, III. Twenty-two patients had an abnormal P wave morphology, diphasic (+/-) in 5 and notched (+/+) in 17. The basic pacemaker rate was programmed between 60 and 70 beats/min. Rate responsive function was activated in 65 patients. During a follow-up of 27.6 ± 17.8 months, AF was documented in 87 patients. Forty-four patients developed permanent AF, following at least one episode of paroxysmal AF in 26 cases. Statistical analysis used Cox model regression. Univariate predictors of AF (P < 0.10) were drugs (mean: 2 ± 1.4) and DC shock before pacing (16/140 patients), P wave duration (mean 112.5 ± 24.6 ms), basic pacemaker rate (mean 68 ± 5 beats/min), and drugs in the follow-up (mean 1.2 ± 0.94). Multivariate analysis showed that P wave duration (b = 0.013, s.e. = 0.004; P = 0.003), and drugs before pacing (b = 0.2; s.e.= 0.08; P < 0.01) resulted in a significant independent predictor of AF. Actuarial incidence of patients free of AF at 30 months was 35%: 56% in patients with a P wave < 120 ms, and 13% in those with P wave , 120 ms (P < 0.01 by Score test). Univariate predictors of permanent AF were drugs and DC shock before pacing, left atrial size (mean 39 ± 6 mm), P wave duration, abnormal P wave morphology (22/140 patients), and drugs in the follow-up. Multivariate analysis showed that P wave morphology was the most important predictor of permanent AF (b = - 0.56, s.e.= 0.2; P = 0.008). Incidence of patients free of permanent AF at 30 months was 69%: 74% in patients with normal P wave, compared to 28% in the case of abnormal P wave morphology (P < 0.01). P wave duration and morphology are good markers of postpacing AF recurrence in patients with SND and an atrial-based pacemaker. This observation suggests that intra- and interatrial conduction disturbances be extensively evaluated before implantation, and the indication for atrial resynchronization procedures be reevaluated. [source] Origins and characteristics of Nearctic landbirds in Britain and Ireland in autumn: a statistical analysisIBIS, Issue 4 2006IAN A. MCLAREN We used data from eastern North America in regressions to explain autumn frequencies of Nearctic landbird species in Britain and Ireland (UK-IR). The data were: day-counts of 16 August,15 November from Nova Scotia (NS) on Sable Island 1963,2000 and Seal Island (1963,2002), combined in half-monthly intervals to account for seasonality; published seasonal totals (10- to 11-day intervals, 20 August,10 November 1955,80) of birds killed at a Florida (FL) TV tower; and published counts following a ,Fallout', 11 October 1998, of unseasonal species and southern vagrants in NS, believed to have originated as migrants in the southeast USA that followed a cold front offshore into strong southwest flow beyond. We also used the following species variables: body mass and wing length for size; sd of mass as a proxy for lipid capacity; a five-level index of migratory span (1 for within North America to 5 for almost totally to South America); latitude of easternmost breeding, and distance to nearest normal range to indicate status in NS; a two-level index for day vs. night migrants; an index, where pertinent, of significant population change (0 and 2 for a decrease and increase, respectively, 1 for no change). We also used classification and regression trees to cluster the potential transatlantic vagrants into homogeneous groups based on the explanatory variables. Standard generalized linear model regressions using counts from NS islands and FL produced highly positively skewed residuals (many species too common in UK-IR), but robust regressions eliminated statistical problems, and strengthened effects of non-count variables. Results using Fallout records, representing a subset of longer-distance night migrants, were statistically acceptable. The Fallout list, when supplied with counts from the same species from the NS islands and FL, produced highly significant (R2 = 0.79,0.93) and statistically acceptable regressions that were not improved by robust versions. Overall, the results indicate that October counts, especially of generally larger, longer-distance migrants, best represented those reaching UK-IR. The effect of geographical remoteness was negative , vagrants in NS were less likely to appear in UK-IR. Population changes were important in predicting the 1956,2003 UK-IR counts from 1955,80 FL counts. The seasonal characteristics, high explanatory power of the Fallout list and over-representation of probable over-ocean migrants in the standard regressions all support suggestions by others that many Nearctic vagrants in UK-IR originate in flights off southeast USA and are displaced downwind across the North Atlantic. [source] Tree growth in an African woodland savanna affected by disturbanceJOURNAL OF VEGETATION SCIENCE, Issue 3 2006R.M. Holdo Abstract: Questions: How does tree growth in a tropical woodland savanna vary as a function of size, and how is it affected by competition from neighbours, site attributes, and damage caused by disturbance? Location: western Zimbabwe. Methods: Trees of common species were tagged, mapped, and measured annually between 2001 and 2003 in a Kalahari sand woodland savanna. Diameter increments were analysed with mixed model regressions for the largest ramet in each genet. Stem diameter and damage, soil texture, and indices of competition at multiple spatial scales were used as covariates. Results: Stem diameter increased initially and then declined as a function of size in undamaged trees, which grew faster than damaged trees. Growth in damaged trees declined with size. No site differences were detected, and there was evidence for between-tree competition on growth only in the fastest-growing species, Brachystegia spiciformis. In several species the growth rate of the largest ramet increased as a function of the basal area of secondary ramets, contrary to expectations. For many species, the growth models showed poor explanatory power. Conclusions: Growth in Kalahari sand savanna trees varies as a function of size and changes in tree architecture caused by disturbance agents such as fire, frost, and elephant browsing. Disturbance may thus play an important role on vegetation dynamics through its effects on growth in the post-disturbance phase. Growth is highly stochastic for some species in this system, and more deterministic in others. It is hypothesized that this dichotomy may be driven by differences in rooting depth among species. [source] ANNA: A new prediction method for bioassessment programsFRESHWATER BIOLOGY, Issue 1 2005Simon Linke Summary 1. Cluster analysis of reference sites with similar biota is the initial step in creating River Invertebrate Prediction and Classification System (RIVPACS) and similar river bioassessment models such as Australian River Assessment System (AUSRIVAS). This paper describes and tests an alternative prediction method, Assessment by Nearest Neighbour Analysis (ANNA), based on the same philosophy as RIVPACS and AUSRIVAS but without the grouping step that some people view as artificial. 2. The steps in creating ANNA models are: (i) weighting the predictor variables using a multivariate approach analogous to principal axis correlations, (ii) calculating the weighted Euclidian distance from a test site to the reference sites based on the environmental predictors, (iii) predicting the faunal composition based on the nearest reference sites and (iv) calculating an observed/expected (O/E) analogous to RIVPACS/AUSRIVAS. 3. The paper compares AUSRIVAS and ANNA models on 17 datasets representing a variety of habitats and seasons. First, it examines each model's regressions for Observed versus Expected number of taxa, including the r2, intercept and slope. Second, the two models' assessments of 79 test sites in New Zealand are compared. Third, the models are compared on test and presumed reference sites along a known trace metal gradient. Fourth, ANNA models are evaluated for western Australia, a geographically distinct region of Australia. The comparisons demonstrate that ANNA and AUSRIVAS are generally equivalent in performance, although ANNA turns out to be potentially more robust for the O versus E regressions and is potentially more accurate on the trace metal gradient sites. 4. The ANNA method is recommended for use in bioassessment of rivers, at least for corroborating the results of the well established AUSRIVAS- and RIVPACS-type models, if not to replace them. [source] | ||||||||||