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Experimental Trends (experimental + trend)
Selected AbstractsThe Relevance of the Collaborative Effect in Determining the Performances of Photorefractive Polymer MaterialsCHEMPHYSCHEM, Issue 2 2010Rocco Angelone Dr. Abstract A derivative of 2-methylindole, 3-[2-(4-nitrophenyl)ethenyl]-1-allyl-2-methylindole, NPEMI-A, is studied for its photoconductivity and photorefractivity behaviour. Its blends with the organic polymer poly-(2,3-dimethyl- N -vinylindole), PVDMI, are also investigated. Due to the expected and devised mutual solubility of the two components of the blends, it is possible to carry out measurements with the weight percent of the chromophore NPEMI-A changing from zero to 100. Films were produced by a squeezing process between two ITO-covered glass sheets. No opacity phenomena, that are so common for many other organic blends due to the segregation of the dissolved chromophore, are observed. The photorefractive optical gain ,2 is obtained as a function of the chromophore content. Differential scanning calorimetry measurements (DSC) are also carried out to obtain the whole change of the glass transition temperature Tg as a function of the amount of chromophore contained in the blends. From the experimental trend of Tg a meaningful quantitative estimate of the value of the electrostatic interactions acting in the studied blends, is obtained. The importance of the value of Tg, and of the electrostatic interactions, in determining the extent of the photorefractivity is clearly evident. The results are compared for NPEMI-A (,2=210 cm,1) and for NPEMI-E (,2 , 2000 cm,1) that has a N-2-ethylhexyl group instead of a N-allyl group. The Pockels and Kerr contributions and,for the first time,a "collaborative effect" of the photorefractivity of NPEMI-A are distinguished and quantitatively evaluated. [source] Predicting HCl concentrations in fire enclosures using an HCl decay model coupled to a CFD-based fire field modelFIRE AND MATERIALS, Issue 7 2007Z. Wang Abstract The amount of atmospheric hydrogen chloride (HCl) within fire enclosures produced from the combustion of chloride-based materials tends to decay as the fire effluent is transported through the enclosure due to mixing with fresh air and absorption by solids. This paper describes an HCl decay model, typically used in zone models, which has been modified and applied to a computational fluid dynamics (CFD)-based fire field model. While the modified model still makes use of some empirical formulations to represent the deposition mechanisms, these have been reduced from the original three to two through the use of the CFD framework. Furthermore, the effect of HCl flow to the wall surfaces on the time to reach equilibrium between HCl in the boundary layer and on wall surfaces is addressed by the modified model. Simulation results using the modified HCl decay model are compared with data from three experiments. The model is found to be able to reproduce the experimental trends and the predicted HCl levels are in good agreement with measured values. Copyright © 2006 John Wiley & Sons, Ltd. [source] Load-displacement and bearing capacity of foundations on granular soils using a multi-surface kinematic constitutive soil modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2006M. Banimahd Abstract A finite element approach based on an advanced multi-surface kinematic constitutive model is used to evaluate the bearing capacity of footings resting on granular soils. Unlike simple elastic-perfectly plastic models, often applied to granular foundation problems, the present model realistically accounts for stress dependency of the friction angle, strain softening,hardening and non-associativity. After the model and its implementation into a finite element code are briefly discussed, the numerical difficulty due to the singularity at the footing edge is addressed. The bearing capacity factor N, is then calculated for different granular materials. The effect of footing size, shape, relative density and roughness on the ultimate bearing capacity are studied and the computed results compare very favourably with the general experimental trends. In addition, it is shown that the finite element solution can clearly represent counteracting mechanisms of progressive failure which have an important effect on the bearing capacity of granular foundations. Copyright © 2006 John Wiley & Sons, Ltd. [source] Electrothermal Model Evaluation of Grain Size and Disorder Effects on Pulsed Voltage Response of Microstructured ZnO VaristorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008Guogang Zhao Time-dependent, two-dimensional, electrothermal simulations based on random Voronoi networks have been developed to study the internal heating, current distributions and breakdown effects in ZnO varistors in response to high-voltage pulsing. The simulations allow for dynamic predictions of internal failures and to track the progression of hot-spots and thermal stresses. The focus is on internal grain-size variations and relative disorder including micropores. Our results predict that parameters such as the hold-off voltage, internal temperature, and average dissipated energy density would be higher with more uniform grains. This uniformity is also predicted to produce lower thermal stresses and to allow for the application of longer duration pulses. It is shown that the principal failure mechanism arises from internal localized melting, while thermal stresses are well below the thresholds for cracking. Finally, detrimental effects of micropores have been quantified and shown to be in agreement with experimental trends. [source] AIM and NBO analysisMAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2010In the series of diaminoenones, large high-frequency shifts of the 1H NMR of the NH group in the cis -position relative to the carbonyl group suggests strong NH···O intramolecular hydrogen bonding comprising a six-membered chelate ring. The NH···O hydrogen bond causes an increase of the 1J(N,H) coupling constant by 2,4 Hz and high-frequency shift of the 15N signal by 9,10 ppm despite of the lengthening of the relevant NH bond. These experimental trends are substantiated by gauge-independent atomic orbital and density functional theory calculations of the shielding and coupling constants in the 3,3-bis(isopropylamino)-1-(aryl)prop-2-en-1-one (12) for conformations with the Z - and E -orientations of the carbonyl group relative to the NH group. The effects of the NH···O hydrogen-bond on the NMR parameters are analyzed with the atoms-in-molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the NH···O hydrogen bond as compared with that of 1,1-di(pyrrol-2-yl)-2-formylethene (13) where NH···O hydrogen bridge establishes a seven-membered chelate ring, and the corresponding 1J(N,H) coupling constant decreases. The NBO method reveals that the LP(O) ,,*NH hyperconjugative interaction is weakened on going from the six-membered chelate ring to the seven-membered one due to a more bent hydrogen bond in the former case. A dominating effect of the NH bond rehybridization, owing to an electrostatic term in the hydrogen bonding, seems to provide an increase of the 1J(N,H) value as a consequence of the NH···O hydrogen bonding in the studied diaminoenones. Copyright © 2010 John Wiley & Sons, Ltd. [source] Life-cycle kinetic model for endospore-forming bacteria, including germination and sporulationBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009Seongjun Park Abstract We develop a mechanistic life-cycle model for endospore-forming bacteria (EFB) and test the model with experiments with a Bacillus mixed culture. The model integrates and quantifies how sporulation and germination are triggered by depletion or presence of a limiting substrate, while both substrates affect the rate of vegetative growth by a multiplicative model. Kinetic experiments show the accumulation of small spherical spores after the triggering substrate is depleted, substantially more rapid decay during sporulation than for normal decay of vegetative cells, and a higher specific substrate utilization rate for the germinating cells than that for growth of vegetative cells. Model simulations capture all of these experimental trends. According to model predictions, when a batch reactor is started, seeding with EFB spores instead of active EFB delays the onset of rapid chemical oxygen demand (COD) utilization and biomass growth, but the end points are the same. Simulated results with low aeration intensity show that germination can consume some substrate without dissolved oxygen (DO) depletion. Biotechnol. Bioeng. 2009; 104: 1012,1024. © 2009 Wiley Periodicals, Inc. [source] | |||||||||||||