Home About us Contact
|
Home About us Contact | ||
|
|
||
Similar Systems (similar + system)
Selected AbstractsSunscreen protection in the ultraviolet A region: how to measure the effectivenessPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 1 2001C. Cole Products containing ultraviolet (UV) radiation absorbing or scattering ingredients provide varying degrees of protection from sunlight (or other UV sources), thus minimizing the deleterious effects on the skin. The "sun protection factor" (SPF) of sunscreen products has become a well recognized indicator of protection against sunburn induced predominantly by ultraviolet B radiation (UVB: 290,320 nm). A similar system of denoting sunscreen protection from ultraviolet A (UVA: 320,400 nm) radiation has not been universally recognized. A variety of test methods have been proposed, both in vitro and in vivo, each with specific virtues and shortcomings. Regulatory agencies and industry have been reviewing the available methods over the past decade in an effort to develop consumer meaningful claims and appropriate substantiation methods. This article reviews these test methodologies, in vitro and in vivo, as well as the biological background that establishes the need for UVA protection, and the UVA content of solar radiation and its variability. [source] Reviewing child deaths,learning from the American experience,CHILD ABUSE REVIEW, Issue 2 2005Lisa Bunting Abstract Current systems for investigating child deaths in England, Wales and Northern Ireland have come under intense scrutiny in recent years and questions have been raised about the accuracy of child death investigations and resulting statistics. Research has highlighted the ways in which multidisciplinary input can contribute to investigative and review processes, a perspective which is further supported by recent UK policy developments. The experience of creating multidisciplinary child death review teams (CDRTs) in America highlights the potential benefits the introduction of a similar system might have. These benefits include improved multi-agency working and communication, more effective identification of suspicious cases, a decrease in inadequate death certification and a broader and more in-depth understanding of the causes of child deaths through the systematic collection and analysis of data. While a lack of funding, regional coordination and evaluation limit the impact of American CDRTs, the positive aspects of this process make it worthwhile, and timely, to consider how such a model might fit within our own context. Current policy developments such as the Home Office review of coroner services, the Children Bill and related Department for Education and Skills (DfES) work on developing screening groups demonstrate that strides have been made in respect of introducing a multidisciplinary process. Similarly, the development of local protocols for the investigation and[sol ]or review of child deaths in England, Wales and Northern Ireland highlights an increased focus on multidisciplinary processes. However, key issues from the American experience, such as the remit of CDRTs[sol ]screening panels, the need for national coordination and the importance of rigorous evaluation, can inform the development of a similar process in the UK. Copyright © 2005 John Wiley & Sons, Ltd. [source] Modeling aspects of mechanisms for reactions catalyzed by metalloenzymesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2001P. E. M. Siegbahn Different models to treat metal-catalyzed enzyme reactions are investigated. The test case chosen is the recently suggested full catalytic cycle of manganese catalase including eight different steps. This cycle contains OO and OH activations, as well as electron transfer steps and redox active reactions, and is therefore believed to be representative of many similar systems. Questions concerning modeling of ligands and the accuracy of the computational model are studied. Imidazole modeling of histidines are compared to ammonia modeling, and formate modeling compared to acetate modeling of glutamates. The basis set size required for the geometry optimization and for the final energy evaluation is also investigated. The adequacy of the model is judged in relation to the inherent accuracy achievable with the hybrid DFT method B3LYP. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1634,1645, 2001 [source] Adaptation provisioning with respect to learning styles in a Web-based educational system: an experimental studyJOURNAL OF COMPUTER ASSISTED LEARNING, Issue 4 2010E. Popescu Abstract Personalized instruction is seen as a desideratum of today's e-learning systems. The focus of this paper is on those platforms that use learning styles as personalization criterion called learning style-based adaptive educational systems. The paper presents an innovative approach based on an integrative set of learning preferences that alleviates some of the limitations of similar systems. The adaptive methods used as well as their implementation in a dedicated system (WELSA) are presented, together with a thorough evaluation of the approach. The results of the experimental study involving 64 undergraduate students show that accommodating learning styles in WELSA has a beneficial effect on the learning process. [source] Solid-solid reactions in series: A modeling and experimental studyAICHE JOURNAL, Issue 9 2009A. K. Suresh Abstract Reactions among particulate solid phases are important and abundant in many materials, chemical, and metallurgical process industries. Many of these are reaction networks, and not single-step reactions as normally assumed. There is no theoretical framework available for the analysis of such systems, and single-reaction models derived from the gas,solid literature continue to be used. Formation of cement clinker in the rotary cement kiln is a prime example of the genre, in which mechanistic aspects play an important role in determining energy efficiency and the composition and nature of the phases that form. In the present study, we formulate a model within the ambit of the "shrinking core" class of models, for reactions in series among solid phases. The model shows the presence of one or two moving fronts in the reacting particle, depending on the relative rates of the processes involved. A single Thiele-type parameter controls the model behavior, at once describing the relative rates of the intermediate formation and consumption processes, and the diffusion-reaction competition for the product formation step. The model has been shown to reduce to the well known single reaction models at the limits of low and high values of the Thiele parameter. Experimental data have been obtained on the calcia-alumina system, an important one in cement manufacture, in the temperature range 1150,1250°C. The model has been fitted to these data and the kinetic parameters determined. The comparison bears out the salient features of the theory, and shows that a degree of diffusion limitation exists for the intermediate conversion step under these conditions. The diffusivity values estimated are in the range of 10,19 to 10,18 m2/s and agree with values found in the literature for similar systems. The rate constant for the intermediate conversion step is of the order of 10,6 s,1. This being among the first such determinations, this value awaits confirmation from other studies. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Novel experiments and a mechanistic model for macroinstabilities in stirred tanksAICHE JOURNAL, Issue 2 2006A. Paglianti Abstract In this work a new experimental technique and a simple model for the identification and the analysis of macro-instabilities (MIs) in stirred tanks are presented. A pressure transducer is proposed for detecting the MIs that can take place inside a stirred vessel; its main advantages are the non-intrusivity, cheapness, and simplicity of installation and operation. Moreover, it can be used for both laboratory and industrial scale stirred tanks. The experimental technique and the time series analysis method, based on Fast Fourier Transform (FFT), are shown to provide reliable information on the frequency of MIs, through the comparison of the present data with those, from literature, obtained in similar systems. Its applicability to solid-liquid systems is also assessed. Afterwards, the data collected in several conditions differing by geometric characteristics of the stirred tanks and by the physical properties of the systems are presented. Finally, a new simplified model, based on the theory of impinging jets,1 is suggested for predicting the MI frequency. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] Physical image vs structure relation: part 12 , structure of 2,2,5,5-tetramethyl-dihydro-furan-3-one oxime and its protonated forms through isomerization and NMR spectra,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2007Ryszard B. Nazarski Abstract The study of an isomeric A/B mixture of the title oxime 1, by photolytic or thermal E,Z -isomerization and NMR measurement including 1H{1H}-NOE difference spectra, led to assignment of the E configuration to its predominating form A. The 1H/13C data were interpreted in terms of steric overcrowding of both forms, especially of the thermolabile photoproduct B. Four classical (empirical) NMR methods of elucidating the oxime geometry were critically tested on these results. Unexpected vapor-phase photoconversion A,B in the window glass-filtered solar UV and spectroscopic findings on their protonated states were discussed, as well. The kinetically controlled formation of the N- protonated species (Z)- 5+ was proved experimentally. In addition, some 1H NMR assignments reported for structurally similar systems were rationalized (3 and 4) or revised (1 and 7,9) with the GIAO-DFT(B3LYP) and/or GIAO-HF calculational results. Copyright © 2007 John Wiley & Sons, Ltd. [source] FT-Raman, FTIR and density functional theory studies of a hydrogen-bonded formamide:pyridine complexJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2009Filipe S. F. Jacinto Abstract Raman and IR experiments have been carried out on formamide (FA) and pyridine (Py) mixtures at different compositions. The appearance of a new Raman band at 996 cm,1 (,1 region of Py), whose intensity depends on the FA concentration, is assigned to an FA:Py adduct and this result is in excellent agreement with those of other authors who employed noisy light-based coherent Raman scattering spectroscopy (I(2) CARS). Another band at 1587 cm,1 (,8 region of Py) has been observed for the first time by using Raman and IR spectroscopies. Its intensity shows the same dependence on the FA concentration and this fact allows us to also attribute it to an FA:Py adduct. The good relationship between the Raman and IR data demonstrates the potential of the vibrational spectroscopy for this kind of study. Owing to higher absolute Raman scattering cross section, the ,1 region of Py has been chosen for the quantitative analysis and a stoichiometry of 1:1 FA:Py is reported. The experimental data are very well supported by the density functional theory (DFT) calculation, which was employed for the first time to the present system. Furthermore, the actual investigation shows an excellent agreement with those reported from computational calculations for similar systems. A comparison with our previous studies confirms that the solvent dielectric constant determines the stoichiometry of a given Lewis acid,base adduct in the infinite dilution limit. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preface: phys. stat. sol. (b) 245/3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2008Christopher W. Smith This is the third Special Issue of physica status solidi (b) focusing on materials with a negative Poisson's ratio or other ,anomalous' physical properties. This issue contains selected papers from the First International Conference on Auxetics and Anomalous Systems held at the University of Exeter, UK, on 4,6 September 2006. Around 50 participants from all over the world as well as from a wide range of scientific and engineering disciplines contributed to what was a highly successful conference. This conference follows in the footsteps of two previous workshops held at the Mathematical Research and Conference Centre in B,dlewo near Pozna,, Poland, in 2004 and 2005 [1, 2]. The papers selected for this issue publish recent results obtained for ,anomalous systems' in experiment, theory and computer simulations. In the following we summarize very briefly their contents. Alderson and Coenen compare the performance of auxetic composites to similar systems with conventional positive Poisson's ratios. They find that there are indeed differences which appear to arise from the change of the overall Poisson's ratio of the composite, some beneficial like a rise in impact tolerance at low impact rates, and others deleterious such as the reduced tolerance at higher impact rates. This is one of the first investigations of possible applications for auxetic materials. The two papers by Gaspar and Koenders both examine the effects of disorder upon anomalous properties, especially negative Poisson's ratio. In the first one Gaspar demonstrates how a mean strain estimate fails to predict negative values of Poisson's ratio because of an inability to account for local fluctuations in elastic properties. For instance it is shown that the volume fraction of auxetic regions in an globally auxetic material (measured experimentally) are smaller than a mean strain homogenisation would require. Koenders and Gaspar explore the elastic properties, and especially Poisson's ratio, of a heterogeneous 2D network of bending beams. They predict auxetic behaviour arising from localised disorder in the packing, and therefore effective locally aggregated elastic properties of the beams. In the three articles by Gatt et al. and Grima et al. models based on simple geometry are used to explain the behaviour of seemingly disparate systems, i.e. 2D honeycombs systems and zeolite SiO2 networks. Two papers concerning honeycombs demonstrate relationships between elastic properties and structure and the bounds for auxetic behaviour. The paper concerning the zeolite Natrolite uses numerical force field based energy minimisation methods to simulate the response of this particular zeolite to applied forces and then simplifies the predicted properties even further by considering structural units as rigid 2D polyhedra linked by flexible hinges. In a similar vein, though using a different approach and concerning a very different form of matter, Heyes shows how the heterogeneity in an assembly of particles in a liquid can affect the elastic properties of a liquid and notably the infinite frequency Poisson's ratio. Heyes uses the Molecular Dynamics approach to simulate a Lennard,Jones fluid under various pressures, notably comparing behaviour under positive and negative pressures. In their first paper Jasiukiewicz and co-authors derive elastic constants of 2D crystals for all four classes of 2D crystalline solids: hexagonal (isotropic), quadratic, rectangular, and oblique systems. In their second paper they demonstrate conditions required for auxetic behaviour of 2D crystals. Auxetic solids are further divided into those with some negative Poisson's ratios (auxetic), all negative Poisson's ratios (completely auxetic) and no negative Poisson's ratios (non-auxetic). Lakes and Wojciechowski consider counterintuitive properties of matter, like negative compressibility, negative Poisson's ratio, negative thermal expansion, negative specific heat, and negative pressure. They present and interpret experimental observations of negative bulk modulus in pre-strained foams. They propose also a constrained microscopic model which exhibits negative compressibility. Finally, they solve a very simple thermodynamic model with negative thermal expansion. Martin et al. take a long stride toward a real world application of auxetic materials with a wide ranging study starting with numerical modelling of a wingbox section to experimental testing in a wind tunnel. They show that an auxetic core in a wing box section can allow a passive aero-elastic response which can be tailored by careful design of the core so that camber, and thus drag, is reduced with increasing airspeed but without sacrificing structural integrity. Miller et al. consider another anomalous physical property, negative thermal expansivity, and its application in the form of particulate composites for amelioration of stresses arising from thermal mismatch. They show via experiments that particles with a negative coefficient of thermal expansion may be used as a composite reinforcer to reduce overall thermal expansion and behave according to the standard volume fraction based models. Narojczyk and Wojciechowski examine the effects of disorder upon the bulk elastic properties of 3D fcc soft sphere systems in terms of particle size. Systems, such as colloids, can be thought of in such terms. The study shows that higher order moments of probability distribution do not influence the bulk elastic properties much, but that lower moments such as the standard deviation of particle size influence the elastic properties greatly. The "hardness" of the particle interaction potential is also important in this context. In general, it is shown that the effect of increasing polydispersity is to increase the Poisson's ratio, except the [110] [10] directions. Scarpa and Malischewsky in their paper on Rayleigh waves in auxetic materials show how the Rayleigh wave speed is affected by the Poisson's ratio. The behaviour is complex and depends upon the homogeneity within the material, for instance slowing with decreasing Poisson's ratio in isotropic solids, but showing the reverse trend and increased sensitivity to Poisson's ratio in laminate composites. Scarpa et al. explore the buckling behaviour of auxetic tubes via three types of model, a simple beam mechanics and Eulerian buckling model, a 3D linear elastic FE model and a bespoke non-linear continuum model. The more sophisticated models provide increasing insight into the buckling behaviour though the simple beam model predicts reasonably well in the pre-buckling linear region. Some unexpected and interesting behaviour is predicted by the continuum model as the Poisson's ratio approaches the isotropic limit of ,1, including increasing sensitivity to Poisson's ratio and rapid mode jumping between integer wave numbers. The paper by Shilko et al. presents an analysis of a particular kind of friction joint, a double lap joint, and explores the effects of altering the elastic properties of one component, in particular it's Poisson's ratio. The manuscript introduces the evolution of smart materials from monolithic materials, and the classification of composites exhibiting negative Poisson's ratios. The paper then presents the case of a double lap joint and performs a sensitivity type study, via a 2D FE model, of the effects of changing the elastic properties and degree of anisotropy of one section of the model on various parameters defining the limits of functionality of the joint. The main finding is that an enhanced shear modulus, via a negative Poisson's ratio, can endow such a friction joint with superior performance. Manufacturing of auxetic materials on a commercial scale has proved to be the largest obstacle to their fuller exploitation. The paper by Simkins et al. explores one route for post processing of auxetic polymers fibres produced by a conventional melt extrusion route. Simkins et al. showed that a post process thermal annealing treatment, with carefully optimised parameters, was able to even out otherwise inhomogenous auxetic properties, and moreover improve other elastic and fracture properties often sacrificed for auxetic behaviour. We gratefully acknowledge the support given by the sponsors of the conference, namely the EPSRC of the UK and Auxetic Technologies Ltd. (UK). We also thank the Scientific Committee, the Organising Committee, and all the participants of the conference. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phonon-assisted tunnelling in coupled quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003H. B. Sun Abstract We apply a quantum master equation approach to coupled quantum dot systems that involve inelastic transitions between the dots. The Hamiltonian we use to model the inelastic interaction between electrons and the phonon bath differs from those of other papers. The calculated current spectra as a function of temperature and the coherent tunnelling rate are consistent with experimental results. The model is applicable to similar systems involving interactions between electrons and different types of bosons. [source] Two cobalt(III) mono-dimethylglyoximates isolated from one reactionACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Agnieszka Czapik The reaction of cobalt(II) nitrate hexahydrate with dimethylglyoxime (DMGH2) and 1,10-phenanthroline (phen) in a 1:1:2 molar ratio results in two CoIII mono-dimethylglyoximates having two chelating phen ligands in cis positions and the CoIII atom coordinated by six N atoms in a distorted octahedral coordination geometry. The isolated products differ in the deprotonation state of the DMGH2 ligand. In [,-hydrogen bis(N,N,-dioxidobutane-2,3-diimine)]tetrakis(1,10-phenanthroline)cobalt(III) trinitrate ethanol disolvate 1.87-hydrate, [Co2(C4H6N2O2)(C4H7N2O2)(C12H8N2)4](NO3)3·2C2H6O·1.87H2O, (I), the C2 -symmetric cation is formed with the coordination [Co(DMG)(phen)2]+ cations aggregating via a very strong O,...H+...O, hydrogen bond with an O...O distance of 2.409,(4),Å. Crystals of (I) exhibit extensive disorder of the solvent molecules, the nitrate anions and one of the phen ligands. Compound (I) is a kinetic product, not isolated previously from similar systems, that transforms slowly into (N -hydroxy- N,-oxidobutane-2,3-diimine)bis(1,10-phenanthroline)cobalt(III) dinitrate ethanol monosolvate 0.4-hydrate, [Co(C4H7N2O2)(C12H8N2)2](NO3)2·C2H6O·0.40H2O, (II), with the DMGH, ligand hydrogen bonded to one of the nitrate anions. In (II), the solvent molecules and one of the nitrate anions are disordered. [source] | |||||||||||||