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Selected AbstractsSubstituent effects in solvolysis of 1,1-diphenylethyl p -nitrobenzoates.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2002Symmetrically disubstituted, monosubstituted systems Abstract The rates of solvolysis of 1,1-diarylethyl p -nitrobenzoates and chlorides were determined conductimetrically at 25,°C in 80% (v/v) aqueous acetone. Applying the Yukawa,Tsuno (Y,T) equation, the symmetrical (X,=,Y) subseries gave a precise additivity relationship for the whole substituent range with a ,sym value of ,3.78 and an rsym value of 0.77. While any Y subsets gave statistically less reliable Y,T correlations, the apparent , value changed significantly depending on the fixed Y substituents; the , value decreases with the more electron-donating fixed substituents Y, which is compatible with the Hammond shift of the transition state coordinate. Nevertheless, the concave correlations of the More O'Ferrall non-linearity relationship for any Y subsets are not in line with what is expected from the reactivity,selectivity relationship suggesting an anti-Hammond shift of transition state. However, we found a precise extended Brønsted relationship between the pK values of 1,1-diarylethylenes and solvolysis rate process with a constant slope of ,,=,1.03,±,0.03. This is direct evidence indicating that there is no significant shift of the transition-state coordinate over the whole range of substituent change. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of Molecular Weight on Photoinduced Birefringence in a Chiral Liquid Crystalline Azodye PolymerMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2006Mikhail Kozlovsky Abstract Summary: The evolution of the photoinduced birefringence in thin films of narrow polymer fractions is studied and compared with the behavior of the non-fractionated polymer. The ,nind value decreases by increasing the degree of polymerization () within the oligomeric range but becomes independent of molecular weight starting from a of ,70. Thermal pretreatment of the films results in higher photoinduced birefringence. The films show good stability of the photorecording. Birefringence induced after 10 min, ,nind(600) and its growth rate at the same moment versus molecular weight. [source] Establishing pediatric immune response zones using the Cylex® ImmuKnowTM assayCLINICAL TRANSPLANTATION, Issue 6 2005E Hooper Abstract:, For all transplant patients, the transplant physician must balance the risk of rejection caused by under-immunosuppression against the risk of drug toxicity, secondary infections and post-transplant lymphoproliferative disorder with over-immunosuppression. A Food and Drug Administration (FDA)-approved in vitro assay, the Cylex® ImmuKnowTM assay, provides a global assessment of cellular immune function to help monitor the immune status of immunosuppressed patients. This assay uses the plant lectin phytohemagglutinin to stimulate lymphocytes; an ATP assay is then used to measure the degree of activation of CD4+ T cells. However, the normal values for this assay were developed with healthy adult patients. In this study, we determined the normal ranges for the ImmuKnowTM assay in healthy children and compared those values to levels obtained in healthy adults and in stable pediatric renal transplant patients. We found that healthy children 12 yr of age and older showed immune function levels indistinguishable from adults, while healthy children under 12 had significantly lower immune function levels than adults. For adults, the ImmuKnowTM assay zones (in ng/mL ATP) of strong, moderate and low immune function correspond to >525, 225 to 525, and <225. In children under 12, we found the corresponding zones to be >395, 175,395 and <175 ng/mL. The median value for normal adults is 415, whereas it is only 295 for children <12 yr of age and this value decreases to 165 in stable renal transplant patients <12 yr of age (compared with 258 for stable adult renal transplant patients). Thus, this study provides critical information necessary to utilize the ImmuKnowTM assay with pediatric patients. In adults, the degree of immune function as assessed by the ImmuKnowTM assay helps to predict patients at risk for infection or rejection. If further studies in pediatric patients document the same and is true for children, then the ImmuKnowTM assay will provide a useful adjunct tool to prevent over- or under-immunosuppression as newly developed drugs are utilized or drug treatment is altered because of drug side effects, toxicity, concurrent illnesses or rejection. [source] Repeatability of dispersal behaviour in a common dwarf spider: evidence for different mechanisms behind short- and long-distance dispersalECOLOGICAL ENTOMOLOGY, Issue 2 2009DRIES BONTE Abstract 1.,The response of dispersal towards evolution largely depends on its heritability for which upper limits are determined by the trait's repeatability. 2.,In the Linyphiid spider E. atra, we were able to separate long- and short-distance dispersal behaviours (respectively ballooning and rappelling) under laboratory conditions. By performing repeated behavioural trials for females, we show that average dispersal trait values decrease with increasing testing days. By comparing mated and unmated individuals during two periods (before and after mating for the mated group, and the same two periods for the unmated group), we show that mating has no effect on the mean displayed dispersal behaviour or its within-individual variation. Repeatabilities were high and consistent for ballooning motivation, but not for rappelling. 3.,Ballooning motivation can be regarded as highly individual-specific behaviour, while general pre-dispersal and rappelling behaviours showed more individual variation. Such difference in repeatability between long- and short-distance dispersal suggests that short- and long-distance dispersal events are triggered by different ecological and evolutionary mechanisms. [source] Electrical Percolation Behavior in Silver Nanowire,Polystyrene Composites: Simulation and ExperimentADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Sadie I. White Abstract The design and preparation of isotropic silver nanowire-polystyrene composites is described, in which the nanowires have finite L/D (< 35) and narrow L/D distribution. These model composites allow the L/D dependence of the electrical percolation threshold, ,c, to be isolated for finite- L/D particles. Experimental ,c values decrease with increasing L/D, as predicted qualitatively by analytical percolation models. However, quantitative agreement between experimental data and both soft-core and core,shell analytical models is not achieved, because both models are strictly accurate only in the infinite- L/D limit. To address this analytical limitation, a soft-core simulation method to calculate ,c and network conductivity for cylinders with finite L/D are developed. Our simulated ,c results agree strongly with our experimental data, suggesting i) that the infinite-aspect-ratio assumption cannot safely be made for experimental networks of particles with L/D < 35 and ii) in predicting ,c, the soft-core model makes a less significant assumption than the infinite- L/D models do. The demonstrated capability of the simulations to predict ,c in the finite- L/D regime will allow researchers to optimize the electrical properties of polymer nanocomposites of finite- L/D particles. [source] An empirical approach to study the occurrence of ion exchange in the ionic micellar-mediated semi-ionic reactions: Kinetics of the rate of reaction of piperidine with ionized phenyl salicylate in the presence of cationic micellesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2001M. Niyaz Khan Pseudo-first-order rate constants (kobs),obtained for the cleavage of ionized phenyl salicylate (PS,) at constant [NaOH], [MeCN], [CTAZ]T (total concentration of cetyltrimethylammonium chloride and bromide), [Pip]T (total concentration of piperidine), and varying concentrations of sodium cinnamate, acetate, and butanoate ([NaX]),follow the relationship: kobs = (k0 + , K[NaX])/(1 + K[NaX]), where , and K are empirical parameters. The values of , are almost independent of [CTAZ]T, while K values decrease with the increase in [CTAZ]T within its range 0.006,0.020 M. The values of , and K are explained in terms of pseudophase model of micelle coupled with an empirical relationship: KS = KS0/(1 + ,X/S [NaX]), where KS is the CTAZ micellar binding constant of PS, in the presence of NaX. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 288,294, 2001 [source] Studying the effects of Mahonia aquifolium populations on small-scale mountain agro-ecosystems in Hungary with the view to minimise land degradationLAND DEGRADATION AND DEVELOPMENT, Issue 3 2009C. Hudek Abstract After the political changeover in Hungary in 1989, many farm owners faced problems typical of a small sized farm (<1,ha) as well as a lack of various resources. This led to many farms with great horticultural backgrounds being abandoned, especially in mountainous areas where erosion control is essential for soil conservation. Severe changes can occur on soil through property abandonment. The local socio-economic aspects must be taken into consideration as well as the problem of soil degradation as this will be a motivating factor in preservation initiatives. Under horticultural management, Mahonia aquifolium was tested to determine its efficiency in water erosion control in mountainous conditions in Hungary. Soil loss and water runoff were measured after every rainfall event at six different plots: four cultivated M. aquifolium populations with different ages (4, 12, 20 and 25 years old) and two control plots. A bare soil field and a grass field represented the control plots. The results show that as the age of the M. aquifolium populations increase, the cumulative runoff and sediment values decrease. It also showed that 2 years after setting up a new M. aquifolium plantation, the cumulative runoff decreased by 69 per cent and the cumulative soil loss decreased by 74 per cent. This indicates that a M. aquifolium population could play a significant role in erosion control within a short period of time. Copyright © 2009 John Wiley & Sons, Ltd. [source] Termination in Dilute-Solution Free-Radical Polymerization: A Composite ModelMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2003Gregory B. Smith Abstract Literature data are summarized for the chain-length-dependence of the termination rate coefficient in dilute solution free-radical polymerizations. In essence such experiments have yielded two parameter values: the rate coefficient for termination between monomeric free radicals, k, and a power-law exponent e quantifying how kt values decrease with increasing chain length. All indications are that the value e,,,0.16 in good solvent is accurate, however the values of k which have been deduced are considerably lower than well-established values for small molecule radicals. This seeming impasse is resolved by putting forward a ,composite' model of termination: it is proposed that the value e,,,0.16 holds only for long chains, with e being higher for small chains , the value 0.5 is used in this paper, although it is not held to dogmatically. It is then investigated whether this model is consistent with experimental data. This is a non-trivial task, because although the experiments themselves and the ways in which they are analyzed are elegant and not too complicated, the underlying theory is sophisticated, as is outlined. Simulations of steady-state polymerization experiments are first of all carried out, and it is shown that the composite model of termination both recovers the e values which have been found and beautifully explains why these experiments considerably underestimate the true value of k. Simulations of pulsed-laser polymerizations find the same, although not quite so strikingly. It is therefore concluded that our new termination model, which retains the virtue of simplicity and in which all parameter values are physically reasonable, is consistent with experimental data. Taking a wider view, it seems likely that the situation of the exponent e varying with chain length will not just be the case in dilute solution, but will be the norm for all conditions, which would give our model and our work a general relevance. Normalized chain length distributions from PLP simulations. [source] Fast transient fluorescence technique for studying swelling of gels made at various crosslinker contents and exposed to organic vapourPOLYMER INTERNATIONAL, Issue 9 2002M Erdo Abstract Fast transient fluorescence technique (FTRF) was employed for studying swelling of disc-shaped poly(methyl methacrylate) (PMMA) gels, which were prepared by free radical copolymerization of methyl methacrylate (MMA) using various ethylene glycol dimethacrylate (EGDM) contents at 60,°C. Pyrene (P) was introduced as a fluorescence probe during polymerization. Swelling experiments were performed by using P-doped PMMA gels under chloroform vapor. Decay curves of P were measured during in situ swelling experiments. Exponential fits were performed to measure pyrene lifetimes, ,, inside the PMMA gels. It was observed that , values decreased as swelling proceeded. An equation is derived for low quenching efficiencies to interpret the behaviour of P lifetimes during swelling. The Li,Tanaka equation was used to determine the cooperative diffusion coefficients, Dc, for the gels made at various crosslinker contents. It is observed that Dc values decrease as the crosslinker content is increased. © 2002 Society of Chemical Industry [source] Stable carbon and nitrogen isotope values of bone and teeth reflect weaning age at the Medieval Wharram Percy site, Yorkshire, UKAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2002M.P. Richards Abstract We report on the measurements of carbon and nitrogen stable isotopes of both bone and teeth from a single site and population (Medieval Wharram Percy), undertaken to explore variations due to weaning in a past population. There have been a number of recent studies of weaning using ,15N values of ribs, and we indicate a number of assumptions that must be met before the results of such studies can be correctly interpreted. We found that rib collagen ,15N values decrease to adult levels after age 2 years, indicating that weaning occurred at or before this age. Rib collagen ,13C values are also more enriched than adult ,13C values before age 2 years, and we argue that this is due to the so-called "carnivore" effect in ,13C. We measured teeth and rib ,15N values from the same individuals and found that for individuals up to age 11 years, tooth dentine ,15N is higher than adult rib ,15N values, indicating that the dentine was formed during breast-feeding and that there was almost no turnover of dentine since. We observed some decrease in ,13C and ,15N rib values, compared to adult rib and teeth values, for the few years after weaning that may relate to a theoretically predicted physiological nitrogen imbalance during this period of rapid growth, but this is more likely due to a childhood diet (up to age 9) which was isotopically different from later diet, possibly consisting of a greater proportion of plant foods. Am J Phys Anthropol 119:205,210, 2002. © 2002 Wiley-Liss, Inc. [source] A zero ODP replacement for R12 in a centrifugal compressor: an experimental study using R134aINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2002C. Aprea Abstract It is well believed that the hydrofluorocarbons (HFCs) and their mixtures are the most promising candidates to substitute the conventional refrigerants, chlorofluorocarbons (CFCs) and HCFCs which contain chlorine atoms in the molecule. This substitution is necessary for the harmful action of CFCs and of HCFCs toward atmospheric ozone layer damage because the disruption of ozone has been attributed to chlorine. For this reason they must be replaced by more environment-friendly refrigerants, as the new family, designated as HFCs, that are chlorine free. Centrifugal compressors differ from positive displacement compressors in two major respects: high vapour volume flow for a given physical size and lower pressure ratio. They are particularly suited to applications where differences between evaporator and condenser temperatures are low. The preferred properties for fluids used in centrifugal compressors differ in certain important aspects from those preferred for fluids used in positive displacement units. In particular centrifugal compressors typically utilize fluids such as CFC114, CFC113, CFC12 and CFC11 for which many potential candidate replacements exist; however, for CFC12, HFC134a is the most suitable replacement. A comparison of the refrigerants HFC134a and CFC12 has been carried out and the results from the tests, using data from a refrigerating plant operating with a centrifugal compressor are reported. The chilled water cooling plant, with a refrigerating capacity of 6500 kW is made up of a centrifugal two-stage compressor, a condenser linked to a cooling tower, an economizer and a flooded evaporator. Experimental results show that a lower coefficient of performance is found when R134a is used as substitute for R12; the difference between the COP values decreases rising the compression ratio. Copyright © 2002 John Wiley & Sons, Ltd. [source] A choice prediction competition: Choices from experience and from descriptionJOURNAL OF BEHAVIORAL DECISION MAKING, Issue 1 2010Ido Erev Abstract Erev, Ert, and Roth organized three choice prediction competitions focused on three related choice tasks: One shot decisions from description (decisions under risk), one shot decisions from experience, and repeated decisions from experience. Each competition was based on two experimental datasets: An estimation dataset, and a competition dataset. The studies that generated the two datasets used the same methods and subject pool, and examined decision problems randomly selected from the same distribution. After collecting the experimental data to be used for estimation, the organizers posted them on the Web, together with their fit with several baseline models, and challenged other researchers to compete to predict the results of the second (competition) set of experimental sessions. Fourteen teams responded to the challenge: The last seven authors of this paper are members of the winning teams. The results highlight the robustness of the difference between decisions from description and decisions from experience. The best predictions of decisions from descriptions were obtained with a stochastic variant of prospect theory assuming that the sensitivity to the weighted values decreases with the distance between the cumulative payoff functions. The best predictions of decisions from experience were obtained with models that assume reliance on small samples. Merits and limitations of the competition method are discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||