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Experimental Observations (experimental + observation)
Kinds of Experimental Observations Selected AbstractsExperimental observation of a strange temporal oscillation of X-ray Pendellösung fringesJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2009Jun-ichi Yoshimura As a strange property not explained by existing theories, it has been known from experiment that X-ray moiré and Pendellösung interference fringes show a small spatial oscillation in the beam path in free space that the diffraction image carrying those fringes is propagated after emerging from the crystal. In connection with the investigation into this strange fringe oscillation, it has been found, by an experiment successively recording Pendellösung-fringe topographs using an X-ray CCD camera, that X-ray Pendellösung fringes also show a small temporal oscillation. Characteristics of this temporal Pendellösung-fringe oscillation, namely irregularities in the fringe profile, the manner of fringe oscillation and a reciprocal correlation between oscillation amplitude and fringe contrast, are shown to be very similar to those of the previously reported spatial oscillation of moiré and Pendellösung fringes. Therefore this temporal oscillation is supposed to have the same origin as the spatial oscillation, revealing another section of the same phenomenon. This discovery of the temporal oscillation advances a step nearer to the full understanding of this strange phenomenon, while disclosing a new property of Pendellösung fringes. As well as the above, a three-dimensional profile representation (surface plot) is given of the image of Pendellösung fringes, to make it clear that unidentified fine intensity modulations, called subfringes in this paper, are produced superposed on the main fringe system. Overall inspection of the intensity profiles of the fringe-imaged topographs suggests that temporal intensity oscillations also occur on a more global scale than the extension of individual fringes, as an unidentified action of the wavefield. [source] Experimental observation of photo-excited electron depletion for stability improvement in a lithium niobate polarization converterMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2010Ruey-Ching Twu Abstract The relations between conversion stabilities and photo-excited electron-depletion effects have been experimentally evaluated in a Zn-indiffused lithium niobate polarization converter, for the first time. A simple method with a biased voltage and laser trimming was performed to observe these phenomena. The results show that the stable conversions for both polarities of applied polarization-conversion voltages are achievable due to the depletion of photo-excited electrons in the waveguides. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1937,1941, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25384 [source] Contribution to the stability analysis of the dewetted Bridgman growth under microgravity conditionsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2004L. Bizet Abstract Experimental observations show that the gap between the sample and the crucible, commonly obtained after solidification in microgravity, is remarkably stable. With the aim to understand the reason of this stability, the dewetting phenomenon is studied by Lyapunov's method. After a short review of the existing mechanisms leading to dewetting, the open smooth crucible configuration is chosen as the most representative. The analytical stability analysis, taking into account geometrical and thermal effects, performed under some boundary heat transfer approximations, shows that, in most cases, the dewetting process is intrinsically stable. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural Evolution and Copper-Ion Release Behavior of Cu-pHEMA Hybrids Synthesized In Situ,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Yen-Yu Liu Abstract A novel Cu-pHEMA hybrid was successfully prepared by in situ photopolymerization of 2-hydroxyethyl methacrylate (HEMA) monomer in the presence of Cu(II) copper ions, following an in situ chemical reduction. Experimental observations indicate that intermolecular interactions such as the coupling force and hydrogen bonding between the Cu and the hydroxyl groups further stabilize the hybrid structure to a considerable extent. Localization of the metallic copper particles within the pHEMA network structure as a result of those intermolecular interactions gives rise to the formation of discretely distributed nanocrystallites with particle sizes ranging from 5 to 25,nm in diameter. A crystallographic change of the Cu nanophase from an amorphous-like to a crystalline structure is observed as the H2O:HEMA molar ratio increases, upon synthesis, accompanied with an increase in the particle size. A relatively slow and sustained release of the Cu (in the form of cupric ions) from the hybrids was measured for a time period of about 10 days, which also illustrates a Cu(II)-induced proliferation of the endothelial cells over a relatively small range of release rate of the Cu from the hybrids. Such a new type of Cu-loaded hybrid hydrogel is expected to be compatible and may be considered as a candidate biomaterial for biomedical/therapeutic uses. [source] Importance of O(3P) atoms and OH radicals in hydrocarbon oxidation during the nonthermal plasma treatment of diesel exhaust inferred using relative-rate methods,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2003John Hoard The consumption of acetylene and propene during passage of simulated diesel exhaust through a nonthermal plasma at 453 K and atmospheric pressure was studied using experimental and computational techniques. Experimental observations of the relative decay rates of acetylene and propene and computer modeling of the chemical and physical processes in the plasma suggest that O(3P) atoms and, to a lesser extent, OH radicals are the dominant species responsible for initiating hydrocarbon oxidation in this system. Results are discussed in terms of the gas-phase chemistry occurring during the nonthermal plasma treatment of diesel exhaust. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 231,238, 2003 [source] The 1,3-Diaminobenzene-Derived Aminophosphine Palladium Pincer Complex {C6H3[NHP(piperidinyl)2]2Pd(Cl)} , A Highly Active Suzuki,Miyaura Catalyst with Excellent Functional Group ToleranceADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Jeanne Abstract The rapidly prepared 1,3-diaminobenzene-derived aminophosphine pincer complex {C6H3[NHP(piperidinyl)2]2Pd(Cl)} (1) is an effective Suzuki catalyst with excellent functional group tolerance. Side-product formations, such as homocoupling, debromation or protodeboration have only rarely been detected and if so, were in all cases below the 5% level. The presented reaction protocol is universally applicable. Experimental observations indicate that palladium nanoparticles are the catalytically active form of 1. [source] Highly Convenient, Clean, Fast, and Reliable Sonogashira Coupling Reactions Promoted by Aminophosphine-Based Pincer Complexes of Palladium Performed under Additive- and Amine-Free Reaction ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009Jeanne Abstract Sequential addition of 1,1,,1,,-phosphinetriyltripiperidine and 1,3-diaminobenzene or resorcinol to toluene solutions of (cyclooctadiene)palladium dichloride [Pd(cod)(Cl)2] under nitrogen in "one pot" almost quantitatively yielded the aminophosphine-based pincer complexes {[C6H3 -2,6-(XP{piperidinyl}2)2]Pd(Cl)} (X=NH 1; X=O 2). Complex 1 (and to a minor extent 2) proved to be efficient Sonogashira catalysts, which allow the quantitative coupling of various electronically deactivated and/or sterically hindered and functionalized aryl iodides and aryl bromides with several alkynes as coupling partners within very short reaction times and low catalyst loadings. Importantly, in contrast to most of the Sonogashira catalysts, which either are both air- and moisture-sensitive and/or require the addition of co-catalysts, such as copper(I) iodide [CuI], for example, or a large excess of an amine, the coupling reactions were carried out without the use of amines, co-catalysts or other aditives and without exclusion of air and moisture. Moreover, the desired products were exclusively formed (no side-products were detected) without employing an excess of one of the substrates. Ethylene glycol and potassium phosphate (K3PO4) were found to be the ideal solvent and base for this transformation. Experimental observations strongly indicate that palladium nanoparticles are not the catalytically active form of 1 and 2. On the other hand, their transformation into another homogeneous catalytically active species cannot be excluded. [source] Acupuncture in Polycystic Ovary Syndrome: Current Experimental and Clinical EvidenceJOURNAL OF NEUROENDOCRINOLOGY, Issue 3 2008E. Stener-Victorin This review describes the aetiology and pathogenesis of polycystic ovary syndrome (PCOS) and evaluates the use of acupuncture to prevent and reduce symptoms related with PCOS. PCOS is the most common female endocrine disorder and it is strongly associated with hyperandrogenism, ovulatory dysfunction and obesity. PCOS increases the risk for metabolic disturbances such as hyperinsulinaemia and insulin resistance, which can lead to type 2 diabetes, hypertension and an increased likelihood of developing cardiovascular risk factors and impaired mental health later in life. Despite extensive research, little is known about the aetiology of PCOS. The syndrome is associated with peripheral and central factors that influence sympathetic nerve activity. Thus, the sympathetic nervous system may be an important factor in the development and maintenance of PCOS. Many women with PCOS require prolonged treatment. Current pharmacological approaches are effective but have adverse effects. Therefore, nonpharmacological treatment strategies need to be evaluated. Clearly, acupuncture can affect PCOS via modulation of endogenous regulatory systems, including the sympathetic nervous system, the endocrine and the neuroendocrine system. Experimental observations in rat models of steroid-induced polycystic ovaries and clinical data from studies in women with PCOS suggest that acupuncture exert long-lasting beneficial effects on metabolic and endocrine systems and ovulation. [source] Theoretical Modeling of the Phase Separation Dynamics in Blends of Reactive MonomersMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2005Gregory R. Yandek Abstract Summary: Experimental observations of the dynamics of phase behavior for blends of reactive constituents, i.e. diglycidyl ether of bisphenol A (DGEBA), curing agent methylene dianiline (MDA), and a reactive liquid rubber (R45EPI), have been theoretically modeled by coupling system thermodynamics governed by a summation of the free energies of mixing and network elasticity with reaction kinetics and diffusion equations. Snap-shots of the temporal evolution of ternary phase diagrams have been established based on the self-condensation reactions of DGEBA-MDA and R45EPI as well as a cross-reaction between the two constituents forming a copolymer. Numerical solution of the proposed mean-field model provides good qualitative agreement with experimental results, namely, the observance of phase separation followed by a phase dissolution and subsequent secondary segregation in a 50/25.4/50 DGEBA/MDA/R45EPI mixture, as well as a single gradual phase separation in a 70/25.4/30 mixture. The phase separation dynamics are explained by a competition between the growth in molecular weights of the reactive species rendering the systems towards instability, and the formation of copolymer acting to compatibilize the mixtures. Theoretical phase diagram for a DGEBA/MDA/R45EPI system. [source] Experimental observations and numerical modelling of diffusion-driven crystallisation processesACTA CRYSTALLOGRAPHICA SECTION D, Issue 10-1 2002Luigi Carotenuto This paper reports experimental results and modelling on the crystallisation processes induced by counter diffusion method of a precipitant agent in a lysozyme protein solution. Comparison between experimental observations and numerical simulations in the presence of convection and sedimentation and without them (suppressed using gel) provides a validation of the model. Different values of the initial protein concentration are used, in order to investigate the effects of supersaturation conditions on the process, and in particular on nucleation. The model and the experimental approach may represent a useful methodology for the determination of the parameters and conditions that may lead to protein crystallisation. A Mach-Zehnder interferometer is used to monitor the transport dynamics insitu in the fluid phase by observing the compositional field. The effect of the solute transport gives rise to a "nucleation front" that propagates inside the protein solution. The crystal formation, caused by progressing of the front, results in a modulation in time and in space (similar to Liesegang patterns), due to the non-linear interplay among transport, crystal nucleation and growth. Both experimental observation and numerical modelling show spatial and size distributions of crystals that demonstrate comparable evidences of the phenomena. [source] Implications of a simple mathematical model to cancer cell population dynamicsCELL PROLIFERATION, Issue 1 2006A. L. Garner Many potential treatments preferentially interact with cells at certain stages of the cell cycle by either selective killing or halting the cell cycle, such as intense, nanosecond-duration pulsed electric fields (nsPEFs). Simple mathematical models of unfed cancer cell populations at the plateau of their growth characteristics may estimate the long-term consequences of these treatments on proliferating and quiescent cell populations. Applying such a model with no transition from the quiescent to proliferating state shows that it is possible for the proliferating cell population to fall below 1 if the quiescent cell population obtains a sufficient competitive advantage with respect to nutrient consumption and/or survival rate. Introducing small, realistic transition rates did not appreciably alter short-term or long-term population behaviour, indicating that the predicted small cell population behaviour (< 1 cell) is not an artefact of the simpler model. Experimental observations of nsPEF-induced effects on the cell cycle suggest that such a model may serve as a first step in assessing the viability of a given cancer treatment in vitro prior to clinical application. [source] Binuclear Mixed Valence Oxovanadium(IV/V) Complexes Containing a [OVIV(,-Ooxo)(,-Ophen)VVO]2+ Core: Synthesis, EPR Spectra, Molecular and Electronic StructureEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2006Amrita Mondal Abstract Binuclear mixed valence oxovanadium(IV/v) complexes of general formula [V2O3L] containing a [OVIV(,-Ooxo)(,-Ophen)VVO]2+ core have been synthesised using conformationally labile N4O3 -coordinating heptadentate ligands (H3L). The X-ray structure of one complex has been examined. Solution EPR spectra revealed that the unpaired electron of the complexes is delocalised between the two vanadium centres. The simulated EPR spectrum of one complex confirms this experimental observation. DFT studies have been performed using crystallographic coordinates in order to obtain further insight into the electronic structure of this type of molecule. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Plastic Dissipation Mechanisms in Periodic Microframe-Structured PolymersADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Lifeng Wang Abstract Novel lightweight micro- and nanostructured materials are being used as constituents in hierarchically structured composites for providing high stiffness, high strength, and energy absorbing capability at low weight. Three dimensional SU-8 periodic microframe materials with submicrometer elements exhibit unusual large plastic deformations. Here, the plastic dissipation and mechanical response of polymeric microframe structures is investigated using micromechanical modeling of large deformations. Finite element analysis shows that multiple deformation domains initiate, stabilize, and then spread plasticity through the structure; simulated deformation mechanisms and deformation progression are found to be in excellent agreement with experimental observation. Furthermore, the geometry can be used to tailor aspects of 3D behavior such as effective lateral contraction ratios (elastic and plastic) during tensile loading as well as negative normal stress during simple shear deformation. The effects of structural geometry on mechanical response are also studied to tailor and optimize mechanical performance at a given density. These quantitative investigations enable simulation-based design of optimal lightweight material microstructures for dissipating energy. [source] Enhancement of condensation on a vertical plate (2nd report, prediction of condensation on a dispersed finned surface)HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2010Rencai Chu Abstract In this study, a prediction model for condensation heat transfer on a vertical dispersed finned surface was proposed, utilizing the Adamek-Webb model for condensation heat transfer outside a horizontal finned tube. The prediction model was based on two main experimental observation results. One is the phenomena of the condensate retention at the bottom of each row of the dispersed fin. Another is the offset phenomena of the condensate flow between each row of the dispersed fin. Given the results by the present model, it is predicted that the dependence of the condensation heat transfer coefficient for the dispersed finned surface on the fin pitch is controlled mainly by the dispersed fin length, not the total fin length. On the contrary, for a different fin pitch, the effect to the condensation heat transfer by dispersing the fin is different. From comparison with the experiment results, it is confirmed that the present model was able to predict the condensation with extremely good precision when the fin pitch was larger. Further, when the fin pitch was smaller, the predicted values were higher than the experimental values, but the tendency of the condensation heat transfer with dispersing the fin was nearly predicted. In addition, this condensing model can predict the experimental values with an error of 25% at the maximum in a range of fin pitch 0.6 mm to 1 mm. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20288 [source] Resonant Tunneling Processes along Conjugated Molecular Wires: A Quantum-Chemical DescriptionADVANCED FUNCTIONAL MATERIALS, Issue 11-12 2002Y. Karzazi Abstract Molecular electronics research is a very active area in the field of nanotechnology. It is now well established that individual or self-assembled molecules can behave as nanoscopic switches in transistor and diode configurations. Molecular wires inserted into nanopores and contacted by two metallic electrodes can also be used as active elements for the fabrication of resonant tunneling diodes (RTDs). The RTD current/voltage (I/V) characteristics can display a negative differential resistance (NDR) behavior (i.e., a negative slope in the I/V curve) for reasons that are not yet fully understood. Here we describe a possible mechanism at the quantum-chemical level that is based on conformational effects and accounts for the experimental observation of strong NDR signatures in substituted phenylene ethynylene oligomers. The occurrence of a peak current in the I/V curves is rationalized by analyzing the evolution of the one-electron structure of the molecular wires upon application of a static electric field aligned along the molecular axis (the field simulates the driving voltage applied between the two electrodes in the RTD devices). The results of our calculations provide a general basis to develop strategies for the design of molecular wires displaying an NDR behavior. [source] Strain localization in soft rock,a typical rate-dependent solid: experimental and numerical studiesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2005A. R. Bhandari Abstract Strain localization developing inside soft rock specimens is examined through experimental observation and numerical simulation. In the experimental study, soft rock specimens are sheared at different strain rates under plane strain conditions and deformation and strain localization characteristics are analysed. Transition of localization mode from highly localized mode for higher strain rate to distributed and diffused mode of strain localization for lower strain rates was observed. In the numerical study, simulations of plane strain compression tests are carried out at different strain rates by using an overstressed-type elasto-viscoplastic model in finite element computations. The role of strain rates on setting gradients of strain fields across shear band is clarified. The probable mechanism for transition of localization mode is discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Theoretical studies on high-valent manganese porphyrins: Toward a deeper understanding of the energetics, electron distributions, and structural features of the reactive intermediates of enzymatic and synthetic manganese-catalyzed oxidative processesISRAEL JOURNAL OF CHEMISTRY, Issue 1 2000Abhik Ghosh We present here a relatively comprehensive theoretical study, based on nonlocal density functional theory calculations, of the energetics, electron distributions, and structural features of the low-lying electronic states of various high-valent intermediates of manganese porphyrins. Two classes of molecules have been examined: (a) compounds with the general formula [(P)MnX2]0 (P = porphyrin; X = F, Cl, PF6) and (b) high-valent manganese-oxo species. For [(P)Mn(PF6)2]0, the calculations reveal a number of nearly equienergetic quartet and sextet states as the lowest states, consistent with experimental results on a comparable species, [(TMP)Mn(ClO4)2]0 (TMP = tetramesitylporphyrin). In contrast, [(P)MnCl2]0 and [(P)MnF2]0 have a single well-defined S = 3/2 Mn(IV) ground state, again in agreement with experiment, with the three unpaired spins largely concentrated (>90%) on the manganese atom. Manganese(IV)-oxo porphyrins have an S = 3/2 ground state, with the three unpaired spins distributed approximately 2.3:0.7 between the manganese and oxygen atoms. The metal-to-oxygen spin delocalization, as measured by the oxygen spin population, for MnIV = O porphyrins is less than, but still qualitatively similar to, that in analogous iron(IV)-oxo intermediates, indicating that the MnIV = O bond is significantly weaker than the FeIV = O bond in an analogous molecule. Thus, the optimized metal,oxygen bond distances are 1.654 and 1.674 Ĺ for (P)FeIV(O)(Py) and (P)MnIV(O)(Py), respectively (Py = pyridine). This is consistent with the experimental observation that MnIV = O stretching frequencies are over 10% lower than FeIV = O stretching frequencies for analogous compounds. For [(P)Mn(O)(PF6)]0, [(P)Mn(O)(Py)]+, and [(P)Mn(O)(F)]0, the ground states clearly correspond to a (dxy)2 Mn(V) configuration and the short Mn,O distances of 1.541, 1.546, and 1.561 Ĺ for the three compounds, respectively, reflect the formal triple bond character of the Mn,O interaction. Interestingly, the corresponding Mn(IV)-oxo porphyrin cation radical states are calculated to be a few tenths of an electrovolt higher than the Mn(V) ground states, suggesting that the Mn(IV)-oxo porphyrin cation radicals are not likely to exist as ground-state species. [source] Reaction pathways of propene pyrolysisJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2010Yena Qu Abstract The gas-phase reaction pathways in preparing pyrolytic carbon with propene pyrolysis have been investigated in detail with a total number of 110 transition states and 50 intermediates. The structure of the species was determined with density functional theory at B3PW91/6-311G(d,p) level. The transition states and their linked intermediates were confirmed with frequency and the intrinsic reaction coordinates analyses. The elementary reactions were explored in the pathways of both direct and the radical attacking decompositions. The energy barriers and the reaction energies were determined with accurate model chemistry method at G3(MP2) level after an examination of the nondynamic electronic correlations. The heat capacities and entropies were obtained with statistical thermodynamics. The Gibbs free energies at 298.15 K for all the reaction steps were reported. Those at any temperature can be developed with classical thermodynamics by using the fitted (as a function of temperature) heat capacities. It was found that the most favorable paths are mainly in the radical attacking chain reactions. The chain was proposed with 26 reaction steps including two steps of the initialization of the chain to produce H and CH3 radicals. For a typical temperature (1200 K) adopted in the experiments, the highest energy barriers were found in the production of C3 to be 203.4 and 193.7 kJ/mol. The highest energy barriers for the production of C2 and C were found 174.1 and 181.4 kJ/mol, respectively. These results are comparable with the most recent experimental observation of the apparent activation energy 201.9 ± 0.6 or 137 ± 25 kJ/mol. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Gibbs energy of activation for thermal isomerization of (1Z)-acetaldehyde hydrazone and (1Z)-acetaldehyde N,N-dimethylhydrazone by Gaussian-4 theory and CCSD(T)/CBS computationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2009Shih-I Lu Abstract In this article, we examined the Gibbs energy of activation for the Z/E thermal isomerization reaction of (1Z)-acetaldehyde hydrazone and (1Z)-acetaldehyde N,N-dimethylhydrazone, at 298.15 K in the solvent of cyclohexane. We carried out computations employing both the Gaussian-4 (G4) theory and the coupled cluster method using both single and double substitutions and triple excitations noniteratively, CCSD(T). The CCSD(T) energy is extrapolated to the complete basis set (CBS). We compared the calculated results to the available experimental observation. It appeared that both G4 and CCSD(T)/CBS computations overestimated the experimental value by as much as about 6 and 12 kcal/mol in the present two cases. We discussed possible sources of error and proposed the experimental kinetic data could be questionable. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] On the possibility of self-induction of drug protein bindingJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2010Leonid M. Berezhkovskiy Abstract The equilibrium unbound drug fraction (fu) is an important pharmacokinetic parameter, which influences drug elimination and distribution in the body. Commonly the drug plasma concentration is substantially less then that of drug binding proteins, so that fu can be assumed constant independent of drug concentration. A general consideration of protein binding based on the mass-action law provides that the unbound drug fraction increases with the increase of drug concentration, which is also a usual experimental observation. For several drugs, though, a seemingly unusual sharp decrease of the unbound drug fraction with the increase of total drug concentration (Ro) in the interval 0,<,Ro,,,5,µM was experimentally observed. A possible explanation of this apparently strange phenomenon is presented. The explanation is based on the consideration of a two-step mechanism of drug protein binding. The first step occurs as a drug binding to the site with relatively low affinity. Consequently this binding leads to the activation of a high affinity site, which otherwise is not available for binding. The suggested binding scheme yields the curves for fu dependence on the total drug concentration that are in good agreement with experimental measurements. The interpretation of pharmacokinetic data for the drugs with such unusual concentration dependence of fu appears to be a formidable problem. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4400,4405, 2010 [source] Effect of Pressure on the Miscibility of Polyethylene/Poly(ethylene- alt -propylene) BlendsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2006Phillip Choi Abstract Summary: Effect of density, and hence pressure, on the miscibility of a 50:50 mol/mol PE/PEP blend was studied using a coarse-grained MC simulation approach on a high-coordination lattice, with the conformations of the coarse-grained chains constrained by the RIS model. Interchain pair correlation functions are used to assess the miscibility of the mixtures. Miscibility increases with increasing temperature over the range ,50,150,°C. It is rather insensitive to pressure at high temperatures, but at ,50,°C, the blend miscibility increases with decreasing pressure. The findings are consistent with the fact that the blend is an UCST blend and that the simulation temperatures used, except ,50,°C, were considerably higher than the UCST of the blend. The pressure dependence of the blend miscibility observed near ,50,°C is also in agreement with the experimental observation that the blend exhibits a negative volume change of mixing. The present work demonstrates that the coarse-grained MC approach, when it is used with periodic boundary cells of different sizes filled with the same number of chains, is capable of capturing the pressure dependence of UCST blends. In addition, such a simulation also provides us with insights about the molecular origin of the observed pressure dependence of miscibility. In the present case, the segregation of PE and PEP chains at low temperatures and high pressure simply originates from the fact that fully extended segments of PE chains tend to cluster so that their intermolecular interactions can be maximized. As the temperature increases, there is a decrease in the probability of a trans state at a CC bond in PE, and therefore the attraction between the PE chains is reduced at higher temperatures, promoting miscibility and the UCST behavior. Density (pressure) dependence of the 2nd shell pair correlation function values for a 50/50 PE/PEP blend at ,50,°C. [source] Self-induced transparency in InGaAs quantum dot waveguidesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2003S. Schneider Abstract We present the experimental observation and the theoretical modelling of self-induced transparency signatures such as nonlinear transmission, pulse retardation and reshaping for subpicosecond pulse propagation in a 2 mm-long InGaAs quantum-dot ridge waveguide at 10 K. The measurements were obtained using a cross-correlation frequency resolved optical gating technique which allows us to retrieve the field amplitude of the propagating pulses. [source] Theoretical and visual study of bubble dynamics in foam injection moldingPOLYMER ENGINEERING & SCIENCE, Issue 3 2010Mehdi Mahmoodi This article presents an experimental observation and a theoretical prediction of bubble dynamics in foam injection molding process with a main focus on the cell collapse phenomenon under pressure. Using a visualizing setup, cell growth behavior under a nonisothermal condition was monitored. In conjunction with the growth behavior, dynamics of cell collapse under different pressures and the effect of growing time on collapse behavior and final cell size were studied. Theoretical simulation of bubble behavior included power law model, which predicted bubble dynamics during foaming process. The results show that collapse phenomenon strongly depends on both exerted holding pressure and growth time. The presented model can also give a reasonable prediction of growth and collapse of cells and could give insight to control of cell size in injection foaming process. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Overcoming merohedral twinning in crystals of bacteriorhodopsin grown in lipidic mesophaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2010Valentin Borshchevskiy Twinning is one of the most common crystal-growth defects in protein crystallography. There are neither efficient rational approaches for the growth of nontwinned protein crystals nor are there examples of systematic studies of the dependence of the twinning-ratio distribution on crystallization conditions. The description of the twinning phenomenon has been covered even less for membrane-protein crystals and is non-existent for crystals grown using lipidic phases (in meso). In the present work, possibilities for overcoming merohedral twinning are investigated for crystals of the membrane protein bacteriorhodopsin (bR) grown in meso. It is shown that traditional crystallization additives are not effective in the case of the in meso crystallization of bR. The twinning ratio was determined for 310 crystals grown under different crystallization conditions. A correlation of the twinning ratio with the growth rate of the crystals was observed. Slow growth indicated that crystals had a noticeable chance of avoiding twinning. Model calculations were performed in order to rationalize this observation. The calculations confirmed the experimental observation that most crystals consist of two twin domains and showed that under this condition small changes in the probability of twin-domain formation lead to dramatic changes in the number of nontwinned crystals, which explains why slow crystal growth results in a considerable number of nontwinned crystals. [source] Experimental observations and numerical modelling of diffusion-driven crystallisation processesACTA CRYSTALLOGRAPHICA SECTION D, Issue 10-1 2002Luigi Carotenuto This paper reports experimental results and modelling on the crystallisation processes induced by counter diffusion method of a precipitant agent in a lysozyme protein solution. Comparison between experimental observations and numerical simulations in the presence of convection and sedimentation and without them (suppressed using gel) provides a validation of the model. Different values of the initial protein concentration are used, in order to investigate the effects of supersaturation conditions on the process, and in particular on nucleation. The model and the experimental approach may represent a useful methodology for the determination of the parameters and conditions that may lead to protein crystallisation. A Mach-Zehnder interferometer is used to monitor the transport dynamics insitu in the fluid phase by observing the compositional field. The effect of the solute transport gives rise to a "nucleation front" that propagates inside the protein solution. The crystal formation, caused by progressing of the front, results in a modulation in time and in space (similar to Liesegang patterns), due to the non-linear interplay among transport, crystal nucleation and growth. Both experimental observation and numerical modelling show spatial and size distributions of crystals that demonstrate comparable evidences of the phenomena. [source] Cybernetic Modeling and Regulation of Metabolic Pathways in Multiple Steady States of Hybridoma CellsBIOTECHNOLOGY PROGRESS, Issue 5 2000Maria Jesus Guardia Hybridoma cells utilize a pair of complementary and partially substitutable substrates, glucose and glutamine, for growth. It has been shown that cellular metabolism shifts under different culture conditions. When those cultures at different metabolic states are switched to a continuous mode, they reach different steady states under the same operating conditions. A cybernetic model was constructed to describe the complementary and partial substitutable nature of substrate utilization. The model successfully predicted the metabolic shift and multiple steady-state behavior. The results are consistent with the experimental observation that the history of the culture affects the resulting steady state. [source] Insight into the Metabolism Rate of Quinone Analogues from Molecular Dynamics Simulation and 3D-QSMR MethodsCHEMICAL BIOLOGY & DRUG DESIGN, Issue 4 2007Hai-Feng Chen Molecular dynamics simulation was applied to investigate the metabolism mechanism for quinone analogues. Favourable hydrogen bonds between ligand and NQO1, and parallel orientation between ligand and flavin adenine dinucleotide could explain the difference of metabolism rate (in ,mol/min/mg) for quinone analogues. This is consistent with the experimental observation (Structure 2001;9:659,667). Then Support Vector Machines was used to construct quantitative structure,metabolism rate model. The model was evaluated by 14 test set compounds. Some descriptors selected by Support Vector Machine, were introduced into standard fields of three-dimensional quantitative structure,metabolism relationship to improve the statistical parameters of three-dimensional quantitative structure,metabolism relationship models. The results show that the inclusion of highest occupied molecular orbital and lowest unoccupied molecular orbital is meaningful for three-dimensional quantitative structure,metabolism relationship models. These in silico absorption, distribution, metabolism and excretion models are helpful in making quantitative prediction of their metabolic rates for new lead compounds before resorting in vitro and in vivo experimentation. [source] Effect of the Nature of the Substituent in N -Alkylimidazole Ligands on the Outcome of Deprotonation: Ring Opening versus the Formation of N-Heterocyclic Carbene ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2010Miguel Abstract Complexes [Re(CO)3(N -RIm)3]OTf (N -RIm=N -alkylimidazole, OTf=trifluoromethanesulfonate; 1,a,d) have been straightforwardly synthesised from [Re(OTf)(CO)5] and the appropriate N -alkylimidazole. The reaction of compounds 1,a,d with the strong base KN(SiMe3)2 led to deprotonation of a central CH group of an imidazole ligand, thus affording very highly reactive derivatives. The latter can evolve through two different pathways, depending on the nature of the substituents of the imidazole ligands. Compound 1,a contains three N -MeIm ligands, and its product 2,a features a C-bound imidazol-2-yl ligand. When 2,a is treated with HOTf or MeOTf, rhenium N-heterocyclic carbenes (NHCs) 3,a or 4,a are afforded as a result of the protonation or methylation, respectively, of the non-coordinated N atom. The reaction of 2,a with [AuCl(PPh3)] led to the heterobimetallic compound 5, in which the N-heterocyclic ligand is once again N-bound to the Re atom and C-coordinated to the gold fragment. For compounds 1,b,d, with at least one N -arylimidazole ligand, deprotonation led to an unprecedented reactivity pattern: the carbanion generated by the deprotonation of the C2H group of an imidazole ligand attacks a central CH group of a neighbouring N -RIm ligand, thus affording the product of CC coupling and ring-opening of the imidazole moiety that has been attacked (2,c,,d). The new complexes featured an amido-type N atom that can be protonated or methylated, thus obtaining compounds 3,c,,d or 4,c,,d, respectively. The latter reaction forces a change in the disposition of the olefinic unit generated by the ring-opening of the N -RIm ligand from a cisoid to a transoid geometry. Theoretical calculations help to rationalise the experimental observation of ring-opening (when at least one of the substituents of the imidazole ligands is an aryl group) or tautomerisation of the N-heterocyclic ligand to afford the imidazol-2-yl product. [source] Theoretical Study of Catalytic Efficiency of a Diels,Alderase Catalytic Antibody: An Indirect Effect Produced During the Maturation ProcessCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2008Sergio Martí Dr. Abstract The Diels,Alder reaction is one of the most important and versatile transformations available to organic chemists for the construction of complex natural products, therapeutics agents, and synthetic materials. Given the lack of efficient enzymes capable of catalyzing this kind of reaction, it is of interest to ask whether a biological catalyst could be designed from an antibody-combining site. In the present work, a theoretical study of the different behavior of a germline catalytic antibody (CA) and its matured form, 39,A-11, that catalyze a Diels,Alder reaction has been carried out. A free-energy perturbation technique based on a hybrid quantum-mechanics/molecular-mechanics scheme, together with internal energy minimizations, has allowed free-energy profiles to be obtained for both CAs. The profiles show a smaller barrier for the matured form, which is in agreement with the experimental observation. Free-energy profiles were obtained with this methodology, thereby avoiding the much more demanding two-dimensional calculations of the energy surfaces that are normally required to study this kind of reaction. Structural analysis and energy evaluations of substrate,protein interactions have been performed from averaged structures, which allows understanding of how the single mutations carried out during the maturation process can be responsible for the observed fourfold enhancement of the catalytic rate constant. The conclusion is that the mutation effect in this studied germline CA produces a complex indirect effect through coupled movements of the backbone of the protein and the substrate. [source] Formation of Trichlorinated Dibenzo- p -dioxins from 2,4-Dichlorophenol and 2,4,5-Trichlorophenolate: A Theoretical StudyCHEMPHYSCHEM, Issue 11 2006Ernesto Suárez Abstract The reaction of the 2,4,5-trichlorophenolate anion with 2,4-dichlorophenol to afford trichlorinated dibenzo- p -dioxins (T3CDDs) is investigated at the B3LYP/6-31+G(d) and B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d)+ZPVE(B3LYP/6-31+G(d)) levels of theory. The first stage of the process corresponds to the formation of a predioxin, which can evolve through four different routes. Two of them lead directly to the products 2,3,7-T3CDD and 1,3,8-T3CDD, and the other two afford different predioxin-type intermediates, which in turn can evolve through all or some of the four routes to give new predioxins or T3CDD. Consequently, the theoretical results obtained show plainly the complex chemistry implied in the formation of dioxins from chlorophenols via anionic mechanisms by disclosing all the critical structures through which the system evolves, thus allowing assessment of the viability of the different mechanistic routes and the accessible products. The statistical thermodynamics treatment at 1 atm and 298.15, 600, 900, and 1200 K indicates that at higher temperatures, the Gibbs energy barrier for the formation of the initial predioxin is clearly the rate-determining step for the whole process, but at lower temperatures the Gibbs energy barrier for this step is similar to those for its evolution into 2,3,7-T3CDD. This result is in contrast with previous proposals that the closure of the central ring is the rate-limiting step. Finally, according to our results the rate constant for the formation of polychlorinated dibenzo- p -dioxins increases with the temperature, in agreement with the experimental observation that the conversion of trichlorophenols increases when going from 600 to 900 K in the gas phase in the absence of catalysts, and with DFT molecular dynamics results. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||