On transitive orientations with restricted covering graphs

We consider the problem of finding a transitive orientation of a comparability graph, such that the edge set of its covering graph contains a given subset of edges. We propose a solution which employs the classical technique of modular tree decomposition. The method leads to a polynomial time algorithm to construct such an orientation or report that it does not exist.     

An improved kinetic model for the peroxide initiated modification of polyethylene

We propose a generalized kinetic model for the peroxide initiated modification of polyethylene. It takes into account not only combination reactions but also transfer to polymer and scission. The model describes the length of the polymer chain and the concentration of vinyl groups simultaneously. Any number of vinyl groups per molecule is allowed. The resulting infinite system of mass balance equations is solved using a double moment technique. The model calculates number, weight and z-average molecular weights and the average concentration of vinyl groups as functions of time. The kinetic constants and the initiation efficiency were estimated through a nonlinear regression using experimental data. The relevance of each one of the reactions included in the mechanism was assessed. By means of the model we studied the influence of temperature and initial peroxide concentration on the modified polymer properties. It follows well the observed experimental trends and gives good estimates of both average molecular weights and average vinyl content, within experimental error.     

Crystallization of Stoichiometric SbSI Glass

Congruent crystallization of antimony sulphoiodide (SbSI) glass of stoichiometric composition, which is prepared successfully for the first time using rapid melt‐quenching, has been investigated using differential scanning calorimetry (DSC). The results for glass powder show a glass transition at 127°C and two separate exothermal peaks with maxima around 140°C and 190°C. The ratio of the intensities of the exothermal peak at ~190°C to the peak at ~140°C increases as the particle size and heating rate are increased, but their total enthalpy remains constant at 62 ± 2 J/g for all DSC runs. Surface heating of the glass induced by a 520 nm CW laser shows two contracted regions: needle‐like crystalline formations at low temperature and bulk crystallization at high temperature. The observed phenomena and DSC results suggest two different kinds of crystallization of the SbSI phase: one‐dimensional crystallization at low temperature which starts from the sample surface and three‐dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The origin of the two different crystallizations can be traced to the strong anisotropy of the SbSI crystal structure due to the weak van der Waals interaction between covalent‐ionic chains (Sb₂S₂I₂)_n.     

High‐Pressure High‐Temperature Transparent Fixed‐Bed Reactor for Operando Gas‐Liquid Reaction Follow‐up

A 3‐MPa, 350 °C fixed‐bed reactor was designed to follow‐up gas‐liquid‐solid reactions on a millimetric size heterogeneous catalyst with Raman spectroscopy. The transparent reactor is a quartz cylinder enclosed in a Joule effect heated stainless‐steel tube. A methodology to determine how to focus the microscope for liquid and solid phase characterization is presented. The setup was validated by performing diesel hydrodesulfurization on a CoMo/alumina extrudate catalyst with a conversion very close to expected values along with the acquisition of Raman spectra of the solid catalyst showing an evolution of the catalyst phase during sulfidation.     

Mechanisms of call note-type perception in black-capped chickadees (Poecile atricapillus): Peak shift in a note-type continuum.

We report on operant conditioning and artificial neural network (ANN) simulations aimed at further elucidating mechanisms of black-capped chickadee chick-a-dee call note category perception. Specifically, we tested for differences in the speed of acquisition among different discrimination tasks and, in two selected discrimination groups, searched for evidence of peak shift. Earlier, unreported ANN data were instrumental in providing the motivation for the current set of studies with chickadees and are provided here. The ANNs revealed differences in the speed of learning among note-type discrimination groups that is related to the degree of perceptual similarity among the three note types tested (i.e., A, B, and C notes). In many respects, bird and network results were in agreement (i.e., in the observation of peak shift in the same group), but they also differed in important ways (i.e., all discrimination groups showed differences in speed of learning in simulations but not in chickadees). We suggest that the start, peak and end frequency of the chick-a portion of chick-a-dee call notes, which form a graded but overlapping continuum, may drive the peak shift observed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The temporal dynamics of visual search: Evidence for parallel processing in feature and conjunction searches.

Feature and conjunction searches have been argued to delineate parallel and serial operations in visual processing. The authors evaluated this claim by examining the temporal dynamics of the detection of features and conjunctions. The 1st experiment used a reaction time (RT) task to replicate standard mean RT patterns and to examine the shapes of the RT distributions. The 2nd experiment used the response-signal speed-accuracy trade-off (SAT) procedure to measure discrimination (asymptotic detection accuracy) and detection speed (processing dynamics). Set size affected discrimination in both feature and conjunction searches but affected detection speed only in the latter. Fits of models to the SAT data that included a serial component overpredicted the magnitude of the observed dynamics differences. The authors concluded that both features and conjunctions are detected in parallel. Implications for the role of attention in visual processing are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Investigation on the biomimetic influence of biopolymers on calcium phosphate precipitation-part 2: Chitosan

A better understanding of how macromolecules act in the precipitation of inorganic phases is the key to designing biomimetic routes for producing self-organized materials with remarkable properties. The role of small amounts of biopolymers (ppm) in the precipitation of calcium phosphate was studied: chitosan and alginate were chosen to be explored in our group studies since they are polysaccharides that present, respectively, amino and carboxyl groups, the most common functions in biopolymers. The effect of chitosan was found to be more intense than that of alginate in terms of influence (compared to blank samples) and also in orientation of the inorganic phase that was obtained. These results may indicate that polymers have interactions, but just enough to conduct ions for molecular recognition and correct epitaxy to orient crystals. Strong interactions would lead to the binding of the species, making them unavailable for further oriented growth.     

The emotional harbinger effect: Poor context memory for cues that previously predicted something arousing.

A key function of memory is to use past experience to predict when something important might happen next. Indeed, cues that previously predicted arousing events (emotional harbingers) garner more attention than other cues. However, the current series of five experiments demonstrates that people have poorer memory for the context of emotional harbinger cues than of neutral harbinger cues. Participants first learned that some harbinger cues (neutral tones or faces) predicted emotionally arousing pictures and others predicted neutral pictures. Then they studied associations between the harbinger cues and new contextual details. They were worse at remembering associations with emotional harbingers than with neutral harbingers. Memory was impaired not only for the association between emotional harbingers and nearby digits, but also for contextual details that overlapped with or were intrinsic to the emotional harbingers. However, new cues that were inherently emotionally arousing did not yield the same memory impairments as the emotional harbingers. Thus, emotional harbinger cues seem to suffer more from proactive interference than do neutral harbinger cues, impairing formation of new associations with cues that previously predicted something arousing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exposure to information technology and its relation to burnout

This paper investigates - in a sample of 202 Spanish employees - the hypothesis that the impact of the exposure to technology on burnout is mediated by the appraisal of technology. In addition, the factorial validity of the Maslach Burnout Inventory-General Survey (MGI-GS) is studied. The hypothesized three-factor-model of the MBI-GS (i.e. exhaustion, cynicism and professional efficacy) was not replicated; instead a four-factor model (i.e. exhaustion, cynicism, selfconfidence and goal-attainment) fitted better to the data. Results from Structural Equation Modelling confirmed the hypothesis that the impact on burnout of the exposure to technology (in terms of time and frequency of use of computer aided technology) is mediated by the appraisal of technology. The higher the exposure, the more positive the appraisal and the lower the burnout levels (i.e. less cynicism, more selfconfidence and a greater sense of goal attainment). No such effect was demonstrated for exhaustion. Limitations of the study and future research directions are discussed.