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PubMedDate not supplied

Regression models for calculating gas fluxes measured with a closed chamber.

Portable closed chambers provide a valuable tool for measuring crop photosynthesis and evapotranspiration. Typically, the rates of change of CO2 and water vapor concentration are assumed to be constant in the short time required to make the closed-chamber measurement, and a linear regression model is used to estimate the CO2 and H2O fluxes. However, due to the physical and physiological effects the measurement system has on the measured process, assuming a constant rate and using a linear model may underestimate the flux. Our objective was to provide a model that estimates the CO2 and H20 exchange rates at the time of chamber closure. We compared the linear regression model with a quadratic regression model using field measurements from two studies. Generally, 60 to 100% of all chamber measurement data sets were significantly nonlinear, causing the quadratic model to yield fluxes 10 to 40% greater than those calculated with the linear regression model. The frequency and degree of nonlinearity were related to the measured rate and chamber volume. Closed-chamber data should be tested for nonlinearity and an appropriate model used to calculate flux. The quadratic model provides users of well-mixed closed chambers an alternative to a simple linear model for data sets with significant nonlinearity.

Carbon Dioxide↗

PubMed2004

Generalized additive models for cancer mapping with incomplete covariates.

Maps depicting cancer incidence rates have become useful tools in public health research, giving valuable information about the spatial variation in rates of disease. Typically, these maps are generated using count data aggregated over areas such as counties or census blocks. However, with the proliferation of geographic information systems and related databases, it is becoming easier to obtain exact spatial locations for the cancer cases and suitable control subjects. The use of such point data allows us to adjust for individual-level covariates, such as age and smoking status, when estimating the spatial variation in disease risk. Unfortunately, such covariate information is often subject to missingness. We propose a method for mapping cancer risk when covariates are not completely observed. We model these data using a logistic generalized additive model. Estimates of the linear and non-linear effects are obtained using a mixed effects model representation. We develop an EM algorithm to account for missing data and the random effects. Since the expectation step involves an intractable integral, we estimate the E-step with a Laplace approximation. This framework provides a general method for handling missing covariate values when fitting generalized additive models. We illustrate our method through an analysis of cancer incidence data from Cape Cod, Massachusetts. These analyses demonstrate that standard complete-case methods can yield biased estimates of the spatial variation of cancer risk.

Algorithms↗

PubMed2001

Linear solvation energy relationships of mixed micelles of sodium dodecyl sulfate and decanol: towards a better model of octanol/water partitioning.

We show that we can alter the mechanism of micelle/water partitioning by the addition of decanol as a co-surfactant to an SDS micellar solution. Linear solvation energy relationship (LSER) studies indicate that as we increase the amount of decanol added to sodium dodecyl sulfate solution, the hydrogen bond donating ability of the aqueous phase increases and the cavity term of the micellar phase increases. We obtain a better correlation with octanol/water partitioning using the mixed micelle system compared to normal micelle solution. Choosing the appropriate micelle marker is very important. Significant changes in the LSER equations can occur if a different compound is used as the micelle marker.

Fatty Alcohols↗

PubMed2005

Optimal fleetwide emissions reductions for passenger ferries: an application of a mixed-integer nonlinear programming model for the New York-New Jersey Harbor.

Emissions from passenger ferries operating in urban harbors may contribute significantly to emissions inventories and commuter exposure to air pollution. In particular, ferries are problematic because of high emissions of oxides of nitrogen (NOx) and particulate matter (PM) from primarily unregulated diesel engines. This paper explores technical solutions to reduce pollution from passenger ferries operating in the New York-New Jersey Harbor. The paper discusses and demonstrates a mixed-integer, non-linear programming model used to identify optimal control strategies for meeting NOx and PM reduction targets for 45 privately owned commuter ferries in the harbor. Results from the model can be used by policy-makers to craft programs aimed at achieving least-cost reduction targets.

Air Pollutants↗

PubMedDate not supplied

Optimal synthesis of protein purification processes.

There has been an increasing interest in the development of systematic methods for the synthesis of purification steps for biotechnological products, which are often the most difficult and costly stages in a biochemical process. Chromatographic processes are extensively used in the purification of multicomponent biotechnological systems. One of the main challenges in the synthesis of purification processes is the appropriate selection and sequencing of chromatographic steps that are capable of producing the desired product at an acceptable cost and quality. This paper describes mathematical models and solution strategies based on mixed integer linear programming (MILP) for the synthesis of multistep purification processes. First, an optimization model is proposed that uses physicochemical data on a protein mixture, which contains the desired product, to select a sequence of operations with the minimum number of steps from a set of candidate chromatographic techniques that must achieve a specified purity level. Since several sequences that have the minimum number of steps may satisfy the purity level, it is possible to obtain the one that maximizes final purity. Then, a second model that may use the total number of steps obtained in the first model generates a solution with the maximum purity of the product. Whenever the sequence does not affect the final purity or more generally does not impact the objective function, alternative models that are of smaller size are developed for the optimal selection of steps. The models are tested in several examples, containing up to 13 contaminants and a set of 22 candidate high-resolution steps, generating sequences of six operations, and are compared to the current synthesis approaches.

Biotechnology↗

PubMed2006

Software design to facilitate information transfer at hospital discharge.

Discharge communication between inpatient and outpatient physicians is often an inefficient and error-prone process. Adverse events result from poor communication at the time of discharge. The objective of this study was to describe development of discharge software to overcome communication barriers. The secondary objective was to assess factors that influence the time to complete tasks with the software. Methods were a performance improvement model and database analysis of 336 discharges. Software design specifications included computerised physician order entry, immediate utility, minimal development and deployment costs, acceptability to physician-users, and satisfaction of primary care physicians, patients and pharmacists. Design features included simple 'just-in-time' prompts and point-of-care prescribing resources. The dependent variable for analysis was physician time to complete discharge prescriptions and instructions while using the software. General linear and mixed-effects regression models adjusted for physician effects and other predictors. Results revealed that physician factors significantly affected the time to complete a discharge while using the software. As the number of accesses (log-ins) and free text typing increased, then time to complete the computerised discharge increased. Patient-related factors that increased physician time were discharge diagnoses, prescriptions and length of stay. In conclusion, discharge software can help inpatient physicians transfer timely, complete and legible information to outpatient physicians, pharmacists and patients. Physician and patient factors influence the time to complete discharges using the software.

Adolescent↗

PubMed1999

The pharmacokinetic modelling of GI198745 (dutasteride), a compound with parallel linear and nonlinear elimination.

AIMS: To characterize the pharmacokinetics of the dual 5alpha-reductase inhibitor GI198745 (dutasteride) to allow for more accurate predictions of GI198745 concentrations after different dosing schedules. METHODS: In this randomized, single-blind, parallel group study, 32 healthy male volunteers received single oral doses of GI198745 ranging from 0.01 to 40 mg. Data were analysed by nonlinear mixed effects modelling using NONMEM where both linear and nonlinear pharmacokinetic models were examined. RESULTS: The time course of GI198745 serum concentrations indicated concentration dependent elimination, with the apparent half-life increasing with dose. Data were best described by a two-compartment model with first order absorption and parallel linear and nonlinear elimination pathways. Drug absorption was rapid, and was followed by a short distribution phase. A high volume of distribution (511 l) and a low linear clearance (0.58 l h(-1)) combined to give a half-life of up to 5 (1-7) weeks at high concentrations. As concentrations declined towards Km (0.96 ng ml(-1)), the proportion eliminated by the relatively rapid saturable elimination pathway, with a maximum clearance of 6.2 l h(-1), increased and the half-life reduced to about 3 days. The estimated inter individual variability for the linear clearance was high (CV = 70%). CONCLUSIONS: G1198745 pharmacokinetics are well described by a pharmacokinetic model with parallel linear and nonlinear elimination. Simulations using this model show that at daily doses of 0.1 mg the steady state drug concentrations, and the rate at which these are achieved, are mainly influenced by the nonlinear pathway, while at daily doses above 1 mg they are almost entirely influenced by the linear pathway.

Adult↗

PubMed2000

Graphical approaches to support the analysis of linear-multilevel models of lamb pre-weaning growth in Kolda (Senegal).

Linear-multilevel models (LMM) are mixed-effects models in which several levels of grouping may be specified (village, herd, animal, ellipsis). This study highlighted the usefulness of graphical methods in their analysis through: (1) the choice of the fixed and random effects and their structure, (2) the assessment of goodness-of-fit and (3) distributional assumptions for random effects and residuals. An LMM was developed to study the effect of ewe deworming with morantel on lamb pre-weaning growth in a field experiment involving 182 lambs in 45 herds and 10 villages in Kolda, Senegal. Growth was described as a quadratic polynomial of age. Other covariates were sex, litter-size and treatment. The choice of fixed and random effects relied on three graphs: (1) a trellis display of mean live-weight vs. age, to select main effects and interactions (fixed effects); (2) a trellis display of individual growth curves, to decide which growth-curve terms should be included as random effects and (3) a scatter plot of parameters of lamb-specific regressions (live-weight vs. quadratic polynomial of age) to choose the random-effects covariance structure.Age, litter-size, agexlitter-size, litter-sizextreatment and agexlitter-sizextreatment were selected graphically as fixed effects and were significant (p<0.05) in subsequent statistical models. The selection of random-effect structures was guided by graphical assessment and comparison of the Akaike's information criterion for different models. The final random-effects selected included no random effect at the village level but intercept, age and squared-age at the herd and lamb levels. The structure of the random-effects variance-covariance matrices were blocked-diagonal at the herd level and unstructured at the lamb level. An order-1 autoregressive structure was retained to account for serial correlations of residuals. Smaller residual variance at 90 days than at younger ages was modeled with a dummy variable taking a value of 1 at 90 days and 0 elsewhere.Ewe-deworming with morantel during the rainy season lead to higher lamb live-weights (probably related to a better ewe-nutrition and -health status). A positive correlation was demonstrated between early weight and growth rate at the population level (with important lamb and herd-level random deviations). The persistence of this correlation at older ages should be checked to determine whether early weights are good predictors of mature weights and ewe-reproductive lifetime performance.

Animal Husbandry↗

PubMed2005

A population pharmacokinetic model for montelukast disposition in adults and children.

PURPOSE: The purpose was to develop a population pharmacokinetic model for montelukast after intravenous administration. Clinical trial simulations were conducted using the model developed to identify the lowest intravenous dose in 6- to 14-year-old children that would give montelukast systemic exposures that were comparable to those found to be associated with efficacy in adults. METHODS: Two clinical studies were conducted where montelukast was administered intravenously as a 7-mg dose to adults and as a 3.5-mg dose to children aged 6 to 14 years. Model development included defining the base pharmacostatistical model and investigating the effects of demographic variables [age and total body weight (TBW)] on the structural parameters, using a nonlinear mixed effect modeling approach. RESULTS: A linear three-compartment pharmacokinetic model was found to best describe the disposition of montelukast. Inclusion of TBW as a covariate caused a 35% and 63% decrease in the interindividual variabilities on clearance and central volume of distribution, respectively. Trial simulations suggested that a 5.25-mg intravenous dose of montelukast should be chosen in children aged 6 to 14 years. CONCLUSIONS: The model developed can adequately describe the intravenous pharmacokinetics of montelukast and can be used as a useful tool for dose selection in pediatric subpopulations.

Acetates↗

PubMed2026

Low-burden metrics for monitoring healthy diets among nonpregnant females aged 15 to 49 years: a multicountry validation analysis using quantitative 24-hour dietary intake data.

BACKGROUND: Limited nationally representative quantitative dietary intake data and a lack of consensus on lower-burden tools and metrics hinder high-frequency monitoring of healthy diets globally. OBJECTIVES: This study aimed to evaluate the comparative construct validity and potential complementarity of low-burden metrics of a healthy diet among nonpregnant females aged 15 to 49 y. METHODS: Quantitative 24-h dietary intake data collected from 77,118 adolescent and adult females across 27 countries were used to construct low-burden metrics and reference metrics of dietary intake. Associations between mean-standardized low-burden measures or indicators and reference metrics were assessed using linear and logistic mixed-effect models, with Spearman's ρ used for survey-level rank correlations. Test characteristics identified low-burden indicators best differentiated adherence to reference indicators. RESULTS: An indicator reflecting nonconsumption of sweet foods and/or sweet beverages was most robustly associated with greater adherence to <10% energy from free sugars in upper-middle-income countries {odds ratio [OR] [95% confidence interval (CI)]: 5.35 [5.05, 5.66]}. Food group diversity score (FGDS) was most strongly associated with and differentiated higher mean adequacy ratio of micronutrients [β of 1-standard deviation (SD) change: ∼11 percentage points (9, 12); ρ: 0.79], whereas noncommunicable disease-Protect score best reflected consumption of ≥400 g/d of fruits and vegetables [range OR of 1-SD changes (95% CI): 2.56-3.01 (2.40, 3.13) in lower-middle and high-income countries, respectively; ρ: 0.56]. FGDS and Global Diet Quality Score Positive were most consistently associated with achieving ≥25 g/d of fiber and ≥3510 mg/d of potassium across contexts. CONCLUSIONS: Low-burden data collection tools yield valid metrics, enabling high-frequency monitoring of healthy diets across contexts. Specifically, avoiding sweet foods and/or sweet beverages is an indicator for adherence to WHO free sugar guidelines among nonpregnant females in upper-middle-income countries, whereas metrics reflecting nutritious food group diversity strongly reflect better micronutrient adequacy and adherence to WHO guidelines for fruits and vegetables, fiber, and potassium intakes within and across contexts.

Humans↗

PubMed2006

Surveillance for transplant coronary artery disease in infant, child and adolescent heart transplant recipients: an intravascular ultrasound study.

BACKGROUND: Transplant coronary arteriopathy (TCAD) limits graft survival after heart transplantation in adult and pediatric heart transplant recipients. Intravascular ultrasound (IVUS) provides a highly sensitive technique to detect TCAD. However, its use to determine factors associated with TCAD in pediatric recipients has been limited and its utility in surveillance for symptomatic TCAD in this population is uncertain. METHODS: One hundred fifty-eight IVUS studies from 66 patients (27 <1 year and 39 >1 year at time of transplant) were performed 12 to 144 months after transplantation within the routine surveillance for TCAD. Maximal intimal thickness (MIT) and intimal index (II) were measured, and the Stanford classification was utilized to grade overall severity of disease. Mixed repeated-measures linear regression models were used to investigate the main and interaction effects of age at transplant, age at time of study, time since transplant and rejection events. RESULTS: Age at catheterization (p = 0.0002), transplantation at age >12 months (p = 0.014), increasing time after transplantation (p = 0.021) and the combination of late rejection and hemodynamic compromising rejection (p = 0.05) were significantly associated with increasing MIT. Age at catheterization (p = 0.0149), transplantation at age >12 months (p = 0.016), time from transplantation (p = 0.0076) and rejection with hemodynamic compromise (p = 0.01) were significantly associated with increased II. Nine patients developed evidence of severe (Stanford Class 4) TCAD by IVUS, but only 2 (22%) developed symptomatic TCAD, with a median follow-up of 44 months. Four of the 7 patients who developed symptomatic TCAD had no or minimal TCAD (Stanford Class 0 or 1) on a surveillance examination within 18 months of the onset of symptoms. CONCLUSIONS: Increasing time after transplantation, recipient age and age at transplantation as well as rejection history, especially rejection with hemodynamic compromise, are associated with the development of TCAD as detected by IVUS in pediatric heart transplant recipients. Severe TCAD detected by IVUS does not often rapidly progress to symptomatic TCAD. Symptomatic TCAD may develop rapidly even in patients with little or no TCAD detected by IVUS.

Adolescent↗

PubMed2005

Modeling cortisol rhythms in a population-based study.

The aim of these analyses was to develop and describe easily implementable, yet information rich, approaches for analysis of the temporal profile of cortisol in human populations. A typical waking profile of cortisol in a sample of women aged 15-44 was parameterized by a piecewise linear regression model, implemented as a mixed model to accommodate repeated observations among individuals. The model was extended to distinguish characteristic cortisol profiles of obese women from those of non-obese women. Sharp inflection points for the diurnal profile of cortisol were noted at 30 and 75 min past awakening. Obese women showed a slight tendency to have a less sharply rising and declining response to awakening than non-obese women.

Adolescent↗

PubMedDate not supplied

Effect of polysulfated glycosaminoglycan on DNA content and proteoglycan metabolism in normal and osteoarthritic canine articular cartilage explants.

OBJECTIVE: To study the effect of polysulfated glycosaminoglycan (PSGAG) on proteoglycan metabolism and DNA content of control and osteoarthritic (OA) cartilage. STUDY DESIGN: An in vitro study comparing the effects of PSGAG on articular cartilage explants from canine stifle joints with and without chronic OA after transection of the left cranial cruciate ligament. SAMPLE POPULATION: Five large cross-breed dogs. METHODS: Cartilage explants (6 to 13 per treatment group) from the medial side of the femoral trochlea and medial femoral condyle from both stifles of each dog were incubated in a defined medium containing 0, 0.05, 0.5, or 5 mg/mL of PSGAG. After 72 hours in culture, explants were pulsed for 6 hours with sodium [35S]sulfate. Aminophenylmercuric acetate (APMA) was used to activate endogenous neutral matrix metalloproteinases (MMPs) and induce proteoglycan degradation in the radiolabeled explants. DNA content and radioactivity were measured in papain-digested explants, and radioactivity was measured in the medium by liquid scintillation counting. Proteoglycan synthesis and degradation were calculated. Cartilage was examined histologically for signs of OA. A mixed model analysis of variance and linear contrasts were used to test for significant (P < .05) effects of OA and treatment with PSGAG. RESULTS: Transection of the cranial cruciate ligament produced OA in operated joints. DNA content and proteoglycan synthesis of OA cartilage were significantly lower than in cartilage from control joints. For both DNA content and proteoglycan synthesis, significant interactions occurred between the concentration of PSGAG and whether the articular cartilage was from OA or control joints. The two lower concentrations of PSGAG (0.05 and 0.5 mg/mL) predominantly increased DNA content in OA cartilage (7 and 18%, respectively, compared with 0 mg/mL PSGAG) while the highest concentration (5 mg/mL) predominantly increased DNA content in control cartilage (30% compared with 0 mg/mL PSGAG). PSGAG at .05 mg/mL predominantly decreased proteoglycan synthesis in OA cartilage (19% reduction compared with 0 mg/mL PSGAG) while PSGAG at .5 and 5 mg/mL predominantly decreased proteoglycan synthesis in control cartilage (17 and 55% reduction, respectively, compared with 0 mg/mL PSGAG). Following activation of MMPs, PSGAG caused a dose-dependent decrease in degradation of radiolabeled proteoglycan in both OA and control cartilage. CONCLUSIONS: OA cartilage was responsive to treatment with PSGAG at 100-fold lower concentration than control cartilage. When treated with PSGAG, articular cartilage explants maintained or increased DNA content at the expense of proteoglycan synthesis. Following MMP activation, proteoglycan degradation was inhibited in OA and control explants in a dose-dependent manner. CLINICAL RELEVANCE: If the results of this study extend to in vivo use, treatment with PSGAG may modify the progression of OA in articular cartilage by maintaining chondrocyte viability or stimulating chondrocyte division as well as protecting against extracellular matrix degradation.

Animals↗

PubMed1999

Time-on-task decrements in "steer clear" performance of patients with sleep apnea and narcolepsy.

Loss of attention with time-on-task reflects the increasing instability of the waking state during performance in experimentally induced sleepiness. To determine whether patients with disorders of excessive sleepiness also displayed time-on-task decrements indicative of wake state instability, visual sustained attention performance on "Steer Clear," a computerized simple RT driving simulation task, was compared among 31 patients with untreated sleep apnea, 16 patients with narcolepsy, and 14 healthy control subjects. Vigilance decrement functions were generated by analyzing the number of collisions in each of six four-minute periods of Steer Clear task performance in a mixed-model analysis of variance and linear regression equations. As expected, patients had more Steer Clear collisions than control subjects (p=0.006). However, the inter-subject variability in errors among the narcoleptic patients was four-fold that of the apnea patients, and 100-fold that of the controls volunteers; the variance in errors among untreated apnea patients was 27-times that of controls. The results of transformed collision data revealed main effects for group (p=0.006), time-on-task (p=0.001), and a significant interaction (p=0.022). Control subjects showed no clear evidence of increasing collision errors with time-on-task (adjusted R2=0.22), while apnea patients showed a trend toward vigilance decrement (adjusted R2=0.42, p=0.097), and narcolepsy patients evidenced a robust linear vigilance decrement (adjusted R2=0.87, p=0.004). The association of disorders of excessive somnolence with escalating time-on-task decrements makes it imperative that when assessment of neurobehavioral performance is conducted in patients, it involves task durations and analyses that will evaluate the underlying vulnerability of potentially sleepy patients to decrements over time in tasks that require sustained attention and timely responses, both of which are key components in safe driving performance.

Accidents, Traffic↗

PubMed1996

Population pharmacokinetic study of teicoplanin in severely neutropenic patients.

The teicoplanin pharmacokinetics (PK) of 30 febrile and severely neutropenic patients (polymorphonuclear count, < 500/mm3) with hematologic malignancies were compared with those determined for five healthy volunteers (HV). Neutropenic patients were given piperacillin combined with amikacin, and teicoplanin was added to the regimen the day fever developed in patients suspected of having a staphylococcal infection or 48 h later. Teicoplanin was given intravenously at a dosage of 6 mg/kg of body weight at 0, 12, and 24 h and once a day thereafter. Five to eleven blood samples per patient were collected. Teicoplanin concentrations were measured by liquid chromatography. A bicompartmental model was fitted to the data by a nonlinear mixed-effect-model approach. Multiple-linear regression analysis was applied in an attempt to correlate PK parameters to nine covariates. The mean trough concentrations of teicoplanin 48 h after the onset of treatment and 24 h after the last injection (last trough) +/- standard deviations were 8.8 +/- 4.1 and 17.5 +/- 13.5 mg/liter, respectively. A significant increase was noted in the mean rate of elimination clearance of teicoplanin in neutropenic patients compared with that of HV (0.86 versus 0.73 liter/h, P = 0.002), as was the case with rates of distribution clearance (5.89 versus 4.94 liter/h, P = 0.002); the mean half-life of distribution was significantly shorter in patients than in HV (0.43 versus 0.61 h, P = 0.002). In contrast, the volumes of the central compartment (ca. 5.8 liters for both groups), the volumes of distribution at steady state (HV, 37.6 liters; patients, 55.9 liters), and the elimination half-lives (HV, 39.6 h; patients, 52.7 h) were not significantly different between HV and neutropenic patients. Interindividual variabilities of rates of clearance (coefficient of variation [CV], 43%) and elimination half-lives (CV, 56%) were mainly explained by the variabilities among rates of creatinine clearance. Interindividual variabilities of the volumes of the central compartment (CV, 33%) and the volumes of distribution at steady state (CV = 51%) were correlated to interindividual variabilities among numbers of leukocytes and the ages of patients, respectively. On the basis of the population PK model of teicoplanin, simulations were made to optimize the dosing schedule. A supplemental 6 mg/kg dose of teicoplanin at 36 h resulted in a trough concentration at 48 h of 16.0 +/- 4.5 mg/liter, with only 7% of patients having a trough concentration of less than 10 mg/liter, compared with 46% of patients on the usual schedule.

Adult↗

PubMed1997

Effect of total allelic relationship on accuracy of evaluation and response to selection.

Total allelic relationship (TA) as a possible alternative to the pedigree-derived additive genetic relationship (RA) is defined. The TA measures the actual allelic identity between individuals for loci segregating for the trait concerned. Its value was studied by simulation in populations of different family structure, different numbers of loci, different numbers of alleles per locus, and different heritability levels. The alternative types of relationship matrices were used in mixed model equations to derive best linear unbiased prediction estimates (EBV) of breeding values (BV). Accuracies of evaluations were calculated as correlations of EBV with true breeding values. In populations with random selection and mating, EBVTA derived using TA had higher accuracies than EBVRA derived using RA. In populations with selection, EBVTA was more accurate and resulted in higher responses than selection on EBVRA. We conclude that not accounting for variation in average measures of relationship and identity in state can be important sources of variance of prediction error, and taking account of them increases the accuracy of selection.

Alleles↗

PubMedDate not supplied

Do social influences contribute to occupational differences in quitting smoking and attitudes toward quitting?

PURPOSE: To examine occupational differences in social influences supporting quitting smoking and their relationships to intentions and self-efficacy to quit smoking and to quitting. DESIGN: Data were collected as part of a large worksite cancer prevention intervention trial. SETTING: Forty-four worksites. SUBJECTS: Subjects included 2626 smokers from a total baseline survey sample of 11,456 employees (response rate = 63%). MEASURES: Differences by job category in social support for quitting, pressure to quit smoking, rewards for quitting, and nonacceptability of smoking were measured using mixed model analysis of variance and the Cochran-Mantel-Haenszel test. Their association to self-efficacy, intention to quit, and quitting smoking was assessed using mixed model analysis of variance and linear logistic regression modeling. RESULTS: Compared with other workers, blue-collar workers reported less pressure to quit (p = .0001), social support for quitting (p = .0001), and nonacceptability of smoking among their coworkers (p < .001). Intention to quit was associated with higher levels of social pressure to quit smoking (p = .0001) and social support for quitting (p = .002). Self-efficacy was associated with social pressure to quit (p = .0001), social support for quitting (p = .004), and perceiving greater rewards for quitting (p = .0001). CONCLUSIONS: Although these results are limited somewhat by response and attrition rates, these results suggest that differing social environments may contribute to the differences by occupational category in smoking prevalence and smoking cessation.

Adult↗

PubMed2006

Predictions of tensile strength of binary tablets using linear and power law mixing rules.

There has recently been an increased interest in predicting the tensile strength of binary tablets from the properties of the individual components. In this paper, measurements are reported for tensile strength of tablets compressed from single-component and binary powder mixtures of lactose with microcrystalline cellulose (MCC), and lactose with two types of silicified microcrystalline cellulose (SMCC and SMCC-HD), which are different in compressibility. Measurements show the tensile strength increases with the relative density for single powders, and both with the relative density and the mass fraction of cellulose in the mixtures. It was also observed, for binary mixtures compacted at 50 and 150 MPa, that there was a slight variation in porosity with the mass fraction of celluloses. The predictions of the tensile strength of binary tablets from the characteristics of the single-components was analysed with the extended Ryshkewitch-Duckworth model by assuming both linear and power law mixing rules for the determination of the parameters "tensile strength at zero porosity and bonding capacity constant". As consequence, four models were analysed and compared with measurements using criteria based on the standard deviation from the mean values. Results showed a good prediction using a linear mixing rule combined with the power law. However, as the predictions of these models depend on the powders and the porosity range for the characterization of single-components, none of them can be systematically considered as being the best to predict binary behaviour from data for individual powders.

Cellulose↗