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Good Models (good + models)
Selected AbstractsA Review on Residence Time Distribution (RTD) in Food Extruders and Study on the Potential of Neural Networks in RTD ModelingJOURNAL OF FOOD SCIENCE, Issue 6 2002G. Ganjyal ABSTRACT: Residence time distribution and mean residence time depend on process variables, namely feed rate, screw speed, feed moisture content, barrel temperature, die temperature and die diameter. Flow in an extruder has been modeled by simulating residence time distribution, assuming the extruder to be a series of continuous-stirred-tank or plug-flow reactors. Others have developed relationships for mean residence time as functions of process variables. Better models can be developed using neural networks. As an example, data from the literature were used to model mean residence time as a function of process variables using statistical regression and neural networks. Neural network models performed better than regression models. [source] Optical remote mapping of rivers at sub-meter resolutions and watershed extentsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2008W. Andrew Marcus Abstract At watershed extents, our understanding of river form, process and function is largely based on locally intensive mapping of river reaches, or on spatially extensive but low density data scattered throughout a watershed (e.g. cross sections). The net effect has been to characterize streams as discontinuous systems. Recent advances in optical remote sensing of rivers indicate that it should now be possible to generate accurate and continuous maps of in-stream habitats, depths, algae, wood, stream power and other features at sub-meter resolutions across entire watersheds so long as the water is clear and the aerial view is unobstructed. Such maps would transform river science and management by providing improved data, better models and explanation, and enhanced applications. Obstacles to achieving this vision include variations in optics associated with shadows, water clarity, variable substrates and target,sun angle geometry. Logistical obstacles are primarily due to the reliance of existing ground validation procedures on time-of-flight field measurements, which are impossible to accomplish at watershed extents, particularly in large and difficult to access river basins. Philosophical issues must also be addressed that relate to the expectations around accuracy assessment, the need for and utility of physically based models to evaluate remote sensing results and the ethics of revealing information about river resources at fine spatial resolutions. Despite these obstacles and issues, catchment extent remote river mapping is now feasible, as is demonstrated by a proof-of-concept example for the Nueces River, Texas, and examples of how different image types (radar, lidar, thermal) could be merged with optical imagery. The greatest obstacle to development and implementation of more remote sensing, catchment scale ,river observatories' is the absence of broadly based funding initiatives to support collaborative research by multiple investigators in different river settings. Copyright © 2007 John Wiley & Sons, Ltd. [source] Preferential flow and transport in soil: progress and prognosisEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2008B. E. Clothier Summary Soil is the first filter of the world's water; its buffering and filtering determine the quality and quantity of our reserves of subterranean and surface water. Preferential flow can either enhance, or curtail, the capacity of the soil to buffer and filter, and it can compromise, or boost, other ecosystem services. We ask ,when do preferential flow and transport matter?' We identify 12 of 17 ecosystem services that benefit from preferential flow and three that are affected detrimentally. We estimate by simple arithmetic the value of preferential flow to ecosystem services to be globally some US$304 billion (109) per year. We review the 1989 Monte Veritą meeting on preferential flow processes and summarize the 2006 presentations, some of which are published in this issue of the Journal. New technologies and innovative experiments have increased our understanding of the conditions that initiate and sustain preferential flows. We identify contemporary exigencies, and suggest avenues for their resolution. We are progressing through observation-led discovery. Our prognosis is that new data will enable us to develop better models, and more aptly to parameterize existing models, and thereby predict the impact, benefits and detriments of preferential flow in soil. [source] A general model of the public goods dilemmaJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2010S. A. Frank Abstract An individually costly act that benefits all group members is a public good. Natural selection favours individual contribution to public goods only when some benefit to the individual offsets the cost of contribution. Problems of sex ratio, parasite virulence, microbial metabolism, punishment of noncooperators, and nearly all aspects of sociality have been analysed as public goods shaped by kin and group selection. Here, I develop two general aspects of the public goods problem that have received relatively little attention. First, variation in individual resources favours selfish individuals to vary their allocation to public goods. Those individuals better endowed contribute their excess resources to public benefit, whereas those individuals with fewer resources contribute less to the public good. Thus, purely selfish behaviour causes individuals to stratify into upper classes that contribute greatly to public benefit and social cohesion and to lower classes that contribute little to the public good. Second, if group success absolutely requires production of the public good, then the pressure favouring production is relatively high. By contrast, if group success depends weakly on the public good, then the pressure favouring production is relatively weak. Stated in this way, it is obvious that the role of baseline success is important. However, discussions of public goods problems sometimes fail to emphasize this point sufficiently. The models here suggest simple tests for the roles of resource variation and baseline success. Given the widespread importance of public goods, better models and tests would greatly deepen our understanding of many processes in biology and sociality. [source] Virtuous Viragos: Female Heroism and Ethical Action in Shakespearean DramaLITERATURE COMPASS (ELECTRONIC), Issue 6 2010Unhae Langis Virtue, from the Latin vir for manly courage and strength, was the mark of male excellence in Renaissance culture. Embodying both physical and moral strength through the famous figure of Hercules, virtue took on other values of courtly gentility and political prudence as the medieval warrior society was gradually transformed into the modern state. In inverse proportion to the expansion of male virtue, the conception of the virago underwent a corresponding constriction and decline from a manlike, heroic woman to a scold. Encompassing both physical and moral excellence (OED 2a, 7), male virtue came to appropriate the heroic definition of virago, and female virtue, by Shakespeare's time, became confined to chastity (OED 2c). Challenging the traditions of male virtue and female monstrosity in Renaissance drama, this essay examines the virtuous viragos populating the Shakespearean canon, who present themselves as better models of ethical action than men, with whom virtue is etymologically and historically associated. This study examines two nuanced conceptions of female heroism and ethical action centering on the erotic and politic Cleopatra and the chaste, self-affirming Desdemona as virtuous viragos. Moreover, the notion of heroism, traditionally associated with tragedy, translates to the less exalted but more prudentially successful ethical action of viragos in Shakespeare's comedies such as The Taming of the Shrew. I argue that virtuous viragos attain their ethical stature against this male-inflected standard of tragic heroism even while calling for its dismantling and replacement with the more discerning framework of neo-Aristotelian virtue grounded on practical wisdom. [source] UV-induced immune suppression and sunscreenPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 3 2000E. M. Gil Sun protection factor (SPF) that measures sunscreen protection against erythema and edema may not be enough to measure a sunscreen's activity against many other biologic reactions induced by ultraviolet radiation (UV). It may be better to evaluate sunscreen efficacy using various tools including immune protection factor (IPF), mutation protection factor (MPF) and protection against photocarcinogenesis. In terms of immune protection, sunscreens protected against UV-induced immune suppression significantly. But protection in some cases was partial and often the IPF of sunscreens were less than the SPF. IPF may differ with various immunological endpoints, and it may be better to use a couple of different assays to measure sunscreen protection more objectively. Sunscreen use protects against most UV-induced non-melanoma skin cancers and actinic keratoses but its activity against melanoma is not clear. More studies with broad-spectrum stable sunscreens and better models for the investigation of malignant melanoma are required. [source] Worldwide allele frequencies of the human apolipoprotein E gene: Climate, local adaptations, and evolutionary historyAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010Dan T.A. Eisenberg Abstract The ,4 allele of the apolipoprotein E (APOE) gene is associated with increased cholesterol levels and heart disease. Population allele frequencies of APOE have previously been shown to vary, with ,4 frequencies generally increasing with latitude. We hypothesize that this trend resulted from natural selection protecting against low-cholesterol levels. In high-latitude cold environments and low-latitude hot environments, metabolic rate is elevated, which could require higher cholesterol levels. To explore this hypothesis, we compiled APOE allele frequencies, latitude, temperature, and elevation from populations around the world. ,4 allele frequencies show a curvilinear relationship with absolute latitude, with lowest frequencies found in the mid-latitudes where temperatures generally require less expenditure on cooling/thermogenesis. Controlling for population structure in a subset of populations did not appreciably change this pattern of association, consistent with selection pressures that vary by latitude shaping ,4 allele frequencies. Temperature records also predict APOE frequency in a curvilinear fashion, with lowest ,4 frequencies at moderate temperatures. The model fit between historical temperatures and ,4 is less than between latitude and ,4, but strengthened after correcting for estimated temperature differences during the Paleolithic. Contrary to our hypothesis, we find that elevation did not improve predictive power, and an integrated measure of the cholesterol effect of multiple APOE alleles was less related to latitude than was ,4 alone. Our results lend mixed support for a link between past temperature and human APOE allele distribution and point to the need to develop better models of past climate in future analyses. Am J Phys Anthropol 143:13,20, 2010. © 2010 Wiley-Liss, Inc. [source] Silica-Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 1.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Characterization, Synthesis Abstract Various silica-supported acetylacetonate and alkoxy zirconium(IV) complexes have been prepared and characterized by quantitative chemical measurements of the surface reaction products, quantitative surface microanalysis of the surface complexes, in situ infrared spectroscopy, CP-MAS 13C,NMR spectroscopy and EXAFS. The complex (SiO)Zr(acac)3 (acac=acetylacetonate ligand) (1) can be obtained by reaction of zirconium tetraacetylacetonate [Zr(acac)4] with a silica surface previously dehydroxylated at 500,°C. The complexes (SiO)3Zr(acac) (2) and (SiO)3Zr(O- n- Bu) (n- Bu=butyl ligand) (3) can be synthesized by reaction of (SiO)3ZrH with, respectively, acetylacetone and n -butanol at room temperature. The spectroscopic data, including EXAFS spectroscopy, confirm that in compound 1 the zirconium is linked to the surface by only one SiOZr bond whereas in the case of compounds 2 and 3 the zirconium is linked to 3 surface oxygen atoms which are sigma bonded. EXAFS data indicate also that the acetylacetonate ligands behave as chelating ligands leading to a hepta-coordination around the zirconium atom in 1 and a penta-coordination in 2. In order to provide a molecular analogue of 1, the synthesis of the following polyoligosilsesquioxane derivative (c -C5H9)7Si8O12(CH3)2Zr(acac)3 (1,) was achieved. The compound 1, is obtained by reacting (c -C5H9)7Si8O11(CH3)2(OH), 4, with an equimolecular amount of Zr(acac)4. In the same manner, syntheses of complexes (c -C5H9)7Si7O12Zr(acac) (2,) and of (c-C5H9)7Si7O12Zr(O- n- Bu) (3,) were achieved by reaction of the unmodified trisilanol, (c -C5H9)7Si7O9(OH)3, with respectively Zr(acac)4 and Zr(O- n- Bu)4 at 60,°C in tetrahydrofuran. Compounds 1,, 2, and 3, can be considered as good models of 1, 2 and 3 since their spectroscopic properties are comparable with those of the surface complexes. The synthetic results obtained will permit us to study the catalytic properties of these surface complexes and of their molecular analogues with the ultimate goal of delineating clear structure-activity relationships. [source] Selection of low investment in sex in a cyclically parthenogenetic rotiferJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 10 2009M. J. CARMONA Abstract Cyclical parthenogens, which combine asexual and sexual reproduction, are good models for research into the ecological and population processes affecting the evolutionary maintenance of sex. Sex in cyclically parthenogenetic rotifers is necessary for diapausing egg production, which is essential to survive adverse conditions between planktonic growing seasons. However, within a planktonic season sexual reproduction prevents clonal proliferation. Hence, clones with a low propensity for sex should be selected, becoming dominant in the population as the growing season progresses. In this context, we studied the dynamics of the heritable variation in propensity for sexual reproduction among clones of a Brachionus plicatilis rotifer population in a temporary Mediterranean pond during the period the species occurred in plankton. Clonal isolates displayed high heritable variation in their propensity for sex. Moreover, the frequency of clones with low propensity for sex increased during the growing season, which supports the hypothesized short-term selection for low investment in sex within a growing season. These results demonstrate (1) the inherent instability of the cyclical parthenogenetic life cycle, (2) the cost of sexual reproduction in cyclical parthenogens where sex produces diapausing eggs and (3) the role of the association between sexual reproduction and diapause in maintaining sex in these cyclical parthenogens. [source] Vertebrate limb development and possible clues to diversity in limb formJOURNAL OF MORPHOLOGY, Issue 1 2002Cheryll Tickle Abstract Chick embryos are good models for vertebrate development. The principles that underlie chick wing development have been discovered and there is increasing knowledge about the molecules involved. The importance of identifying molecules is that this provides a direct link to understanding the genetic basis of diversity in form. Chick wing development will be compared with limb development in other vertebrates. Possible mechanisms that could lead to variations in form, including limb reductions and limblessness, differences between fore- and hindlimbs, limb proportions, and interdigital webbing can be suggested. J. Morphol. 252:29,37, 2002. © 2002 Wiley-Liss, Inc. [source] The Use of Atomic Charges and Orbital Energies as Hydrogen-bonding-donor Parameters for QSAR Studies: Comparison of MNDO, AM1 and PM3 MethodsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 6 2000TARAVAT GHAFOURIAN Hydrogen-bonding, important in drug-receptor interactions, also determines the solubility and partitioning of drugs between phases. It is, therefore, important to incorporate the effects of hydrogen-bonding in studies of quantitative structure-activity relationships (QSAR). In this study the atomic charge on the most positively charged hydrogen atom in a molecule and the energy of the lowest unoccupied molecular orbital (LUMO) have been used as a measure of hydrogen-bond-donor capacity. For several hydrogen-bonding acids the Mulliken atomic charges and the energy of the LUMO produced by use of three semi-empirical methods, AM1, PM3 and MNDO, and MNDO electrostatic-potential-derived atomic charges, have been compared in correlations with solvatochromic hydrogen-bonding acidity (,,2H). Atomic charges and LUMO energies, particularly those calculated by use of the AM1 and MNDO methods, were found to correlate well with ,,2H. They were also found to be good models of hydrogen-bonding in QSAR correlations. [source] RELATIVE IMPORTANCE OF COHESION AND ADHESION FOR SENSORY STICKINESS OF SEMISOLID FOODSJOURNAL OF TEXTURE STUDIES, Issue 6 2004B. DUNNEWIND ABSTRACT Sensory stickiness (sticky mouthfeel) was hypothesized to result from the viscoelastic and adhesive properties of a foodstuff. The objective of the present study was to investigate the relative importance of these two properties. Measurements consisted of compression , decompression cycles on a texture analyzer, with product, type of surface, the presence or absence of saliva and compression regime as variables. Products included commercial mayonnaises, custard desserts and warm sauces, varying in apparent viscosity (at shear rate of 10 s,1) between 0.3 and 18.3 Pa.s. Fairly good models were obtained, predicting sensory stickiness with R2 = 0.85,0.92. The predictive value of the mathematical models did not increase when the surface characteristics approached those of the human tongue (use of porcine lingual mucosa). Different surfaces or the use of saliva resulted in differences in the absolute values of the parameters, but their relative values when comparing different products did not change. The parameters appearing in the predictive models represented product characteristics only. The type of surface was not an important factor in determining differences in sensory stickiness between these samples. For the products used in this study, adhesion was large enough to prevent detachment of the sample from the surfaces, i.e., adhesion was not limiting. Variations in perceived stickiness could be explained with R2 = 0.86, based on only two product characteristics: consistency and ,long behavior' (the extent to which necking occurs during decompression). This was better than the correlation between sensory stickiness and apparent viscosity (R2 = 0.77),, confirming, the relevance of ,long behavior' for sensory stickiness. [source] POM Forum: Transfer of Changing Production Know-HowPRODUCTION AND OPERATIONS MANAGEMENT, Issue 1 2006Kasra Ferdows Even with the rich literature on knowledge management, we still don't know enough about how the rate of change in production-know-how affects the choice of mechanisms for its transfer. Codifying tacit know-how helps, but codification becomes more challenging as the know-how changes more frequently. Transfer of tacit know-how becomes much more complicated when it changes often. We need more research in this area, particularly to help production and operations managers who must ultimately use the new know-how and change their companies' production processes. The paper suggests a framework as a step in that direction. The framework focuses on the interplay between the level of codification and the rate of change of production know-how, and identifies four zones for classifying production know-how: "slow and codified," "slow and tacit," "fast and codified," and "fast and tacit." Examples from McDonald,s, Club Med, Intel, and AOL are used to illustrate primary transfer mechanisms for each zone (manuals and systems, people, joint-development, and projects, respectively). Appropriate absorptive capacities in the production units for each zone are also identified. Since the ultimate responsibility of operations managers is to improve (i.e., change) their production know-how as fast as possible, they would be wise to adopt policies that are closer to those suited for the "fast and codified" zone. Intel and Toyota show good models. [source] Social enterprise for work integration in 12 european countries: a descriptive analysis,ANNALS OF PUBLIC AND COOPERATIVE ECONOMICS, Issue 2 2005by Roger Spear And one sector where they have found a particularly important place is in work integration, addressing some of the more difficult problems of social exclusion in labour markets. The study on which this paper is based was a large scale comparative analysis of developments of these social enterprise in 12 European countries While there are clear differences in national contexts, there are also similarities in the forms and characteristics of these social enterprise across Europe. It is argued that this form of social enterprise has proved effective and is an important innovation to address problems of more marginalised groups and individuals, but there remain issues about how to sustain and promote the good models and good practices developed. [source] Photosensitization and the Photocurrent Switching Effect in Nanocrystalline Titanium Dioxide Functionalized with Iron(II) Complexes: A Comparative StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2007Wojciech Macyk Dr. Abstract Selected iron(II) complexes (ferrocene, ferrocenylboronic acid, hexacyanoferrate(II)) have been used as photosensitizers of titanium dioxide. Various types of electronic interactions between the surface complex and the semiconducting support are reflected in different yields of photocurrent generated upon visible-light irradiation and different efficiencies of the photosensitization effect. The studied systems, showing the photocurrent switching upon changes of electrode potential and energy of photons (the PEPS effect), are good models of simple photoelectrochemical logic devices. The mechanism of photosensitization and photocurrent switching is discussed with respect to the type of surface-complex,support interaction. Quantum-mechanical calculations support the proposed mechanisms. Wybrane kompleksy ,elaza(II) (ferrocen, kwas ferrocenyloboronowy i heksacyjano,elazian(II)) zosta,y u,yte jako fotosensybilizatory dwutlenku tytanu. Ró,ne typy oddzia,ywa, elektronowych pomi,dzy kompleksami powierzchniowymi a pod,o,em pó,przewodnikowym znajduj, odbicie w ró,nych wydajno,ciach generacji fotopr,du i ró,nym stopniu fotosensybilizacji materia,ów na ,wiat,o widzialne. Wszystkie badane uk,ady wykazuj, efekt fotoelektrochemicznego prze,,czenia fotopr,du na skutek zmian potencja,u fotoelektrody i zmian d,ugo,ci fali ,wiat,a padaj,cego (efekt PEPS), dlatego te, stanowi, bardzo dobre modele prostych prze,,czników fotoelektrochemicznych. Niniejsza praca szczegó,owo okre,la mechanizm fotosensybilizacji i prze,,czenia fotopr,du na podstawie analizy oddzia,ywa, pomi,dzy kompleksem a powierzchni, pó,przewodnika. Obliczenia kwantowo-mechaniczne potwierdzaj, postulowany mechanizm. [source] | |||||||||||||||||||