One-pass separation of single-wall carbon nanotubes by gel chromatography with a gradient of surfactant concentration

We have investigated the diameter-selective separation of carbon nanotubes by one-pass gel chromatography with a gradient of surfactant concentration. The formation of surfactant gradient in a column was successfully measured and is explained by a simple diffusion process even in the gel. We found that the diameter of eluted nanotubes is inversely proportional to the surfactant concentration of eluate. The detailed analysis of the movement of the nanotubes in the gel revealed that the separation mechanism was qualitatively explained by a model based on the trapping and de-trapping events of the nanotube–surfactant micelle on the gel surface,where the probability of the trapping and de-trapping events is proportional to the product of the diameter of the nanotubes and the surfactant concentration.     

Effects of work overload and burnout on cholesterol and triglycerides levels: The moderating efffects of emotional reactivity among male and female employees.

The effects of objective and subjective overload, and of physical and emotional burnout, on cholesterol and triglycerides levels were studied in a quasiprospective design. The possible moderating effects of emotional reactivity on these relationships were also investigated. The study's hypotheses were tested separately for male and female employees. Time I (T1) data were collected from 665 healthy employees (30% women) while they were undergoing periodic health examinations in a health-screening center Time 2 (T2) measures of cholesterol and triglycerides were collected 2 to 3 years after T1. The hypotheses were tested by regressing each T2 criterion on its T1 level; the control variables of age, obesity, diet, alcohol consumption, and smoking; and the other predictors. For female employees, the T2-T1 changes in the serum lipids were positively predicted by emotional burnout, as expected, but negatively predicted by physical fatigue. For male employees, both types of T1 burnout were positive predictors of the T2-T1 change in total cholesterol. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Improved Algorithms for Some Competitive Location Centroid Problems on Paths, Trees and Graphs

We consider a common scenario in competitive location, where two competitors (providers) place their facilities (servers) on a network, and the users, which are modeled by the nodes of the network, can choose between the providers. We assume that each user has an inelastic demand, specified by a positive real weight. A user is fully served by a closest facility. The benefit (gain) of a competitor is his market share, i.e., the total weight (demand) of the users served at his facilities. In our scenario the two providers, called the leader and the follower, sequentially place p and r servers, respectively. After the leader selects the locations for his p servers, the follower will determine the optimal locations for his r servers, that maximize his benefit. An (r,p)-centroid is a set of locations for the p servers of the leader, that will minimize the maximum gain of the follower who can establish r servers. In this paper we focus mainly on the cases where either the leader or the follower can establish only one facility, i.e., either p=1, or r=1. We consider two versions of the model. In the discrete case the facilities can be established only at the nodes, while in the absolute case they can be established anywhere on the network. For the (r,1)-centroid problem, we show that it is strongly NP-hard for a general graph, but can be approximated within a factor e/(e?1). On the other hand, when the graph is a tree, we provide strongly polynomial algorithms for the (r,p)-centroid model, whenever p is fixed. For the (1,1)-centroid problem on a general graph, we improve upon known results, and give the first strongly polynomial algorithm. The discrete (1,p)-centroid problem has been known to be NP-hard even for a subclass of series-parallel graphs with pathwidth bounded by 6. In view of this result, we consider the discrete and absolute (1,p) centroid models on a tree, and present the first strongly polynomial algorithms. Further improvements are shown when the tree is a path.     

Template-Based Volume Viewing

We present an efficient three-phase algorithm for volume viewing that is based on exploiting coherency between rays in parallel projection. The algorithm starts by building a ray-template and determining a special plane for projection - the base-plane. Parallel rays are cast into the volume from within the projected region of the volume on the base-plane, by repeating the sequence of steps specified in the ray-template. We carefully choose the type of line to be employed and the way the template is being placed on the base-plane in order to assure uniform sampling of the volume by the discrete rays. We conclude by describing an optimized software implementation of our algorithm and reporting its performance.     

Normal estimation in 3 D discrete space

Three-dimensional voxel-based objects are inherently discrete and do not maintain any notion of a continuous surface or normal values, which are crucial for the simulation of light behavior. Thus, in volume rendering, the normal vector of the displayed surfaces must be estimated prior to rendering. We survey several methods for normal estimation and analyze their performance. One unique method, the context-sensitive approach, employs segmentation and segment-bounded operators that are based on object and slope discontinuities in order to achieve high fidelity normal estimation for rendering volumetric objects.     

Multiple-wavelength quasi-phase-matched nonlinear interactions

Quasi-phase-matching allows one to arbitrarily phase match a single interaction by periodic modulation of the material nonlinear coefficient. A partial extension is obtained by Fibonacci-based quasi-periodic modulation of the nonlinear coefficient. These Fibonacci-based structures allow for simultaneously phase matching two interactions, provided that their wavevector mismatch ratio obeys selection rules, which are governed by the golden ratio τ=(1+√5)/2. In this paper, we present a novel method for simultaneously phase matching any two nonlinear interactions by general quasi-periodic modulation of the nonlinear coefficient. These quasi-periodic structures, which also include the Fibonacci-based structures as a subgroup, provide greater design flexibility. Our method can be useful for various nonlinear devices, such as multiple-peak frequency doublers, frequency triplers, and frequency quadruplers. We show for two specific devices that similar efficiency, compared to a cascaded device, can be obtained. Furthermore, in contrast to some cascaded devices, these structures can be used in double-pass and standing-wave configurations, since they operate with the same efficiency in both directions of propagation     

Pros and cons of quitting, self-efficacy, and the stages of change in smoking cessation.

In The Netherlands, 34% of the population smoke, and 70% of these smokers are not planning to quit. The lower percentages in the U.S. population seem to reflect a difference in smoking culture. This study analyzes the pros and cons of quitting and self-efficacy expectation in the 5 stages of change in the Dutch population. The results are compared with the pattern of the pros and cons of smoking and self-efficacy expectations found in U.S. samples. The data show the hypothesized pattern: In the first 2 stages, the expected positive outcomes of quitting discriminated better between the stages than self-efficacy, whereas for later stages, self-efficacy was the better discriminator. This study shows that the stage typology is applicable to the Dutch population and that the pattern of the pros, cons, and self-efficacy is very similar to the pattern found in the U.S. populations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Determination of the reactive component of fly ashes for geopolymer production using XRF and XRD

Geopolymers are a class of versatile materials that have the potential for utilisation as a cement replacement, fireproof barriers, materials for high temperatures, and biological implant applications. This study investigated methods for determining the formulation for manufacturing geopolymers made with fly ash from coal-fired power stations. The accepted method of determining the formulation of geopolymers to get the desired matrix chemistry uses the bulk composition of the feedstock materials. This formulation method is widely used in investigations using feedstock materials that almost completely react during processing. It is widely considered that amorphous components of fly ash are the reactive components in the geopolymerisation reaction. However, quantification of the amorphous components is challenging and generally avoided with the concomitant problem that the formulation is far from optimum. For the work presented here, the composition of the amorphous part is determined accurately and this information utilised to synthesise geopolymers. The bulk composition is first determined using X-ray fluorescence spectroscopy (XRF) and then the amorphous composition determined using XRF and quantitative X-ray diffraction (QXRD). Formulating the mixture based on amorphous composition produced samples with a significantly higher compressive strength than those formulated using the bulk composition. Using the amorphous composition of fly ash produced geopolymers with similar physical properties to that of metakaolin geopolymers with the same targeted composition. We demonstrated a new quantitative formulation method that is superior to the accepted method.