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Systematic Trends (systematic + trend)
Selected AbstractsThe Branchiopoda (Crustacea: Anomopoda, Ctenopoda and Cyclestherida) of the rain forests of Cameroon, West Africa: low abundances, few endemics and a boreal,tropical disjunctionJOURNAL OF BIOGEOGRAPHY, Issue 9 2005George Y. Chiambeng Abstract Aim, We provide the first in-depth study of the Branchiopoda of the rain forests of Cameroon and also of the African continent. Location, Surface water environments, Cameroon. Methods, Qualitative plankton samples were collected in all types of surface water environments present, ranging from big lakes to water collected in rock crevices or fallen fruit cavities. A tow or hand-held plankton net of mesh size 100 ,m was used, and water volumes filtered were at least several m3 in large water bodies, or half to whole water volume in small water bodies. Results, We recorded 61 species (53 first records for the country), based on 700+ samples collected between September 1998 and March 2002. Anomopoda (92%) was the dominant order, followed by Ctenopoda (6.5%) and Cyclestherida (1.5%). Chydoridae (67%) was the most speciose family followed by Macrothricidae (6.5%) and Daphniidae (5%). Alona (11%) was the dominant genus followed by Chydorus (10%) and Pleuroxus (8%). Several species of Chydorinae, especially of the genus Pleuroxus, are shared with continental Eurasia,North America, but are absent from the Mediterranean and desert,steppe,savanna zones of Africa (boreal,tropical disjunction). Daphnia was absent, as in most tropical lowlands. No single species was really abundant, and a majority were rare to very rare, and of restricted occurrence within the rain forest patches. Comparing Africa, South America and Southeast Asia, we found a current total of 196 species for the combined rain forest areas, out of a world total of 500+ species. Systematic trends in richness at three taxonomic levels were the same for all continents: Anomopoda,Ctenopoda,Cyclestherida at ordinal level, Chydoridae,Daphniidae,Macrothricidae,Sididae at family level and Alona,Chydorus,Macrothrix,Diaphanosoma at genus level. Southeast Asia was richest (111 species, 14 endemics) with South America a close second (110 species, 27 endemics). Africa was the most species-poor (95 species, of which only 5 are endemics). Main conclusions, We hypothesize that the post-Miocene cooling and aridization of the world climate hit the freshwater biota of Africa particularly hard, with more extinction here than elsewhere, and little recolonization. Most extinction occurred in the savanna-desert belt, and eight disjunct boreal species (four Pleuroxus, Picripleuroxus laevis, Kurzia latissima, Alonella exigua, and Monospilus dispar) survive morphologically unchanged since pre-Pleistocene times in the Cameroon rain forest. Slow evolution thus appears typical of these cyclic parthenogenetic branchiopods in which sexual recombination occurs only at intervals. Illustrative of the same slow evolution is the fact that the two endemic cladocerans of Cameroon (Nicsmirnovius camerounensis and Bryospilus africanus) belong to tropicopolitan genera of Gondwanan age. [source] On the Effect of Tether Composition on cis/trans Selectivity in Intramolecular Diels,Alder ReactionsCHEMISTRY - AN ASIAN JOURNAL, Issue 1 2009Michael Abstract Intramolecular Diels,Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6-31+G(d) and CBS-QB3 levels of theory for a series of 1,3,8-nonatrienes, H2CCHCHCHCH2XZCHCH2 [XZ=CH2CH2 (1); OC(O) (2); CH2C(O) (3); OCH2 (4); NHC(O) (5); SC(O) (6); OC(S) (7); NHC(S) (8); SC(S) (9)]. For each system studied (1,9), cis - and trans -TS isomers, corresponding, respectively, to endo - and exo -positioning of the CXZ tether with respect to the diene, have been located and their relative energies (ErelTS) employed to predict the cis/trans IMDA product ratio. Although the ErelTS values are modest (typically <3,kJ,mol,1), they follow a clear and systematic trend. Specifically, as the electronegativity of the tether group X is reduced (XO,NH or S), the IMDA cis stereoselectivity diminishes. The predicted stereochemical reaction preferences are explained in terms of two opposing effects operating in the cis -TS, namely (1),unfavorable torsional (eclipsing) strain about the C4C5 bond, that is caused by the CXC(Y) group's strong tendency to maintain local planarity; and (2),attractive electrostatic and secondary orbital interactions between the endo -(thio)carbonyl group, CY, and the diene. The former interaction predominates when X is weakly electronegative (XN, S), while the latter is dominant when X is more strongly electronegative (XO), or a methylene group (XCH2) which increases tether flexibility. These predictions hold up to experimental scrutiny, with synthetic IMDA reactions of 1, 2, 3, and 4 (published work) and 5, 6, and 8 (this work) delivering ratios close to those calculated. The reactions of thiolacrylate 5 and thioamide 8 represent the first examples of IMDA reactions with tethers of these types. Our results point to strategies for designing tethers, which lead to improved cis/trans -selectivities in IMDAs that are normally only weakly selective. Experimental verification of the validity of this claim comes in the form of fumaramide 14, which undergoes a more trans -selective IMDA reaction than the corresponding ester tethered precursor 13. [source] Calculated Electron Impact Ionization Cross Sections of Excited Ne Atoms Using the DM FormalismCONTRIBUTIONS TO PLASMA PHYSICS, Issue 7 2005H. Deutsch Abstract We used the semi-classical Deutsch-Märk (DM) formalism to calculate absolute electron-impact ionization cross sections of excited Ne atoms from threshold to 1000 eV. Excited states of Ne where the outermost valence electron is excited to states with principal quantum numbers up to n = 7 and orbital angular momentum quantum numbers up to l = 2 have been considered and systematic trends in the calculated cross section data are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Numerical simulation of overbank processes in topographically complex floodplain environmentsHYDROLOGICAL PROCESSES, Issue 4 2003A. P. Nicholas Abstract This article presents results from an investigation of the hydraulic characteristics of overbank flows on topographically-complex natural river floodplains. A two-dimensional hydraulic model that solves the depth-averaged shallow water form of the Navier,Stokes equations is used to simulate an overbank flow event within a multiple channel reach of the River Culm, Devon, UK. Parameterization of channel and floodplain roughness by the model is evaluated using monitored records of main channel water level and point measurements of floodplain flow depth and unit discharge. Modelled inundation extents and sequences are assessed using maps of actual inundation patterns obtained using a Global Positioning System, observational evidence and ground photographs. Simulation results suggest a two-phase model of flooding at the site, which seems likely to be representative of natural floodplains in general. Comparison of these results with previous research demonstrates the complexity of overbank flows on natural river floodplains and highlights the limitations of laboratory flumes as an analogue for these environments. Despite this complexity, frequency distributions of simulated depth, velocity and unit discharge data closely follow a simple gamma distribution model, and are described by a shape parameter (,) that exhibits clear systematic trends with changing discharge and floodplain roughness. Such statistical approaches have the potential to provide the basis for computationally efficient flood routing and overbank sedimentation models. Copyright © 2002 John Wiley & Sons, Ltd. [source] Asteroid photometric and polarimetric phase curves: Joint linear-exponential modelingMETEORITICS & PLANETARY SCIENCE, Issue 12 2009K. Muinonen Here we model the two phase curves jointly at phase angles ,25° using a linear-exponential model, accounting for the opposition effect in disk-integrated brightness and the negative branch in the degree of linear polarization. We apply the MCMC methods to V-band phase curves of asteroids 419 Aurelia (taxonomic class F), 24 Themis (C), 1 Ceres (G), 20 Massalia (S), 55 Pandora (M), and 64 Angelina (E). We show that the photometric and polarimetric phase curves can be described using a common nonlinear parameter for the angular widths of the opposition effect and negative-polarization branch, thus supporting the hypothesis of common physical mechanisms being responsible for the phenomena. Furthermore, incorporating polarimetric observations removes the indeterminacy of the opposition effect for 1 Ceres. We unveil a trend in the interrelation between the enhancement factor of the opposition effect and the angular width: the enhancement factor decreases with decreasing angular width. The minimum polarization and the polarimetric slope at the inversion angle show systematic trends when plotted against the angular width and the normalized photometric slope parameter. Our new approach allows improved analyses of possible similarities and differences among asteroidal surfaces. [source] Evolution of the winonaite parent body: Clues from silicate mineral trace element distributionsMETEORITICS & PLANETARY SCIENCE, Issue 4 2008Christine FLOSS Textural evidence in these meteorites, including the presence of a plagioclase/clinopyroxene-rich lithology and coarse-grained olivine lithologies, suggests that they may have experienced some silicate partial melting. However, trace element distributions in these lithologies do not show any clear signatures for such an event. Pyroxene trace element compositions do exhibit systematic trends, with abundances generally lowest in Pontlyfni and highest in Winona. The fact that the same trends are present for both incompatible and compatible trace elements suggests, however, that the systematics are more likely the result of equilibration of minerals with initially heterogeneous and distinct compositions, rather than partial melting of a compositionally homogeneous precursor. The winonaites have experienced brecciation and mixing of lithologies, followed by varying degrees of thermal metamorphism on their parent body. These factors probably account for the variable bulk rare earth element (REE) patterns noted for these meteorites and may have led to re-equilibration of trace elements in different lithologies. [source] Chemical variation within fragments of Australasian tektitesMETEORITICS & PLANETARY SCIENCE, Issue 6 2005Trinh Hai SON No data for intra-sample trace element variations existed. Thus, we sectioned a Muong Nong-type tektite fragment from Vietnam and a splash-form tektite fragment from the Philippines into eleven and six pieces, respectively, and analyzed the individual fragments for major and trace element contents. The compositions obtained agree well with those found in previous studies, supporting argument that tektites have been derived from terrestrial upper crustal sediments. Chemical variations within the tektite fragments are present, but do not show any systematic trends, probably reflecting incomplete mixing of parent rocks. The intra-sample heterogeneity of the Muong Nong-type tektite is more pronounced than that in the philippinite. For the Muong Nong-type tektite, the intra-sample variation in the trace element contents is higher than that for the major elements, again reflecting target rock properties. For the philippinite the intra-sample variations mostly do not exceed the limits imposed by the precision of the analytical data, confirming that the splash form tektites are indeed well homogenized. [source] Dust emission in the far-infrared as a star formation tracer at z= 0: systematic trends with luminosityMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003D. Pierini ABSTRACT We investigate whether dust emission in the far-infrared (far-IR) continuum provides a robust estimate of the star formation rate (SFR) for a nearby, normal late-type galaxy. We focus on the ratio of the 40,1000 ,m luminosity (Ldust) to the far-ultraviolet (far-UV) (0.165 ,m) luminosity, which is connected to recent episodes of star formation. Available total photometry at 0.165, 60, 100 and 170 ,m limits the statistics to 30 galaxies, which, however, span a large range in observed (and, thus, attenuated by dust) K -band (2.2 ,m) luminosity, morphology and inclination (i). This sample shows that the ratio of Ldust to the observed far-UV luminosity depends not only on i, as expected, but also on morphology and, in a tighter way, on observed K -band luminosity. We find that Ldust/LFUV, eLK0.62, where LFUV and LK are the unattenuated stellar luminosities in far-UV and K, respectively, and , is the ratio of the attenuation optical depths at 0.165 ,m (,FUV) and 2.2 ,m (,K). This relation is to zeroth order independent of i and morphology. It may be further expressed as Ldust/LFUV,L,K, where ,= 0.61 , 0.02,, under the observationally motivated assumption that, for an average inclination, e,L,0.02K. We adopt calculations of two different models of attenuation of stellar light by internal dust to derive solid-angle-averaged values of ,. We find that , is positive and decreases towards 0 from the more luminous to the less luminous galaxies. This means that there is no universal ratio of far-IR luminosity to unattenuated far-UV luminosity for nearby, normal late-type galaxies. The far-IR luminosity systematically overestimates SFR in more luminous, earlier-type spirals, owing to the increased fractional contribution to dust heating of optical/near-IR photons in these objects. Conversely, it systematically underestimates SFR in fainter, later-type galaxies, the ,FUV of which is reduced. The limited statistics and the uncertainty affecting the previous scaling relations do not allow us to establish quantitative conclusions, but an analogous analysis making use of larger data sets, available in the near future (e.g. from GALEX, ASTRO-F and SIRTF), and of more advanced models will allow a quantitative test of our conclusions. [source] The Relative (Un)Importance of Rehnquist Court DecisionsPOLITICS & POLICY, Issue 5 2010ROBERT ROBINSON The Rehnquist Court took conservative positions more often than its immediate predecessors. Less clear, however, is the degree to which its decisions actually impacted the legal framework. Given studies that suggest that ideological heterogeneity within Supreme Court majority coalitions and systematic trends of "institutional thickening" hinder the creation of legally important decisions, I hypothesize that the decisions of the Rehnquist Court should be less legally important relative to prior courts, and should create more important liberal legal decisions than expected. Employing measures of legal importance developed through the network analysis of Supreme Court precedent, I find that Rehnquist Court decisions are less legally important than decisions from prior eras. Furthermore, I find that in the most salient legal subject areas, the Rehnquist Court's liberal and conservative decisions are of roughly equal importance. Given these findings, the Rehnquist Court's ideological impact on precedent is more modest than its critics charge. La Corte de Rehnquist tomó posiciones conservadoras más a menudo que sus predecesores inmediatos. Sin embargo, el grado en el que sus decisiones en realidad impactaron el marco legal es menos claro. Determinados estudios que sugieren que la heterogeneidad ideológica dentro de las coaliciones de mayoría de la Suprema Corte y las tendencias sistemáticas de "robustecimiento institucional" dificultan la formulación de decisiones legalmente importantes, planteo que las decisiones de la Corte de Rehnquist serán legalmente menos importantes en comparación con cortes previas, y formularán decisiones legales liberales más importantes de lo esperado. Utilizando medidas de la importancia legal desarrolladas a través del análisis de red de los precedentes de la Suprema Corte, descubro que las decisiones de la Corte de Rehnquist son legalmente menos importantes que las decisiones de las eras previas. Además, encuentro que en las áreas legales más importantes, las decisiones liberales y conservadoras de la Corte de Rehnquist son aproximadamente de una importancia similar. Dado estos hallazgos, el impacto ideológico de la Corte de Rehnquist sobre precedente es mucho más modesto de lo que sus críticos la acusan. [source] Industrialization, class structure, and social mobility in postwar Japan 1THE BRITISH JOURNAL OF SOCIOLOGY, Issue 4 2001Hiroshi Ishida ABSTRACT This study examines intergenerational class mobility in Japan using cross-national comparisons with Western nations and cross-temporal comparisons of five national surveys conducted in postwar Japan. Cross-national comparisons highlight the similarity in relative mobility pattern between Japan and Western nations and at the same time the Japanese distinctiveness in absolute mobility rates especially regarding the demographic character of the Japanese manual working class. The results of cross-temporal comparisons of mobility pattern report some systematic trends in total mobility, inflow and outflow rates, reflecting the Japanese experience of late but rapid industrialization. The pattern of association between class origin and class destination, however, was stable in postwar Japan. It is therefore the combination of distinctive absolute mobility rates and similar relative mobility rates that characterizes the Japanese mobility pattern in comparison with the Western experience. Furthermore, Japan's distinctive pattern of postwar social mobility is characterized by a combination of rapidly changing absolute mobility rates and comparatively stable relative mobility rates. [source] Measuring temporal variability in residential magnetic field exposuresBIOELECTROMAGNETICS, Issue 4 2001W.T. Kaune Abstract Considerable interest has developed during the past ten years regarding the hypothesis that living organisms may respond to temporal variability in ELF magnetic fields to which they are exposed. Consequently, methods to measure various aspects of temporal variability are of interest. In this paper, five measures of temporal variability were examined: Arithmetic means (Dmean) and rms values (Drms) of the first differences (i.e., absolute value of the difference between consecutive measurements) of magnetic field recordings; "standardized" forms of Drms, denoted RCMS, obtained by dividing Drms by the standard deviations of the magnetic field data; and mean (Fmean) and rms (Frms) values of fractional first differences. Theoretical investigations showed that Dmean and Drms are virtually unaffected by long-term systematic trends (changes) in exposure. These measures thus provide rather specific measures of short-term temporal variability. This was also true to a lesser extent for Fmean and Frms. In contrast, the RCMS metric was affected by both short-term and long-term exposure variabilities. The metrics were also investigated using a data set consisting of twice-repeated two-calendar-day recordings of bedroom magnetic fields and personal exposures of 203 women residing in the western portion of Washington State. The predominant source of short-term temporal variability in magnetic field exposures arose from the movement of subjects through spatially varying magnetic fields. Spearman correlations between TWA bedroom magnetic fields or TWA personal exposures and five measures of temporal variability were relatively low. Weak to moderate levels of correlation were observed between temporal variability measured during two different sessions separated in time by 3 or 6 months. We conclude that first difference and fractional difference metrics provide specific and fairly independent measures of short-term temporal variability. The RCMS metric does not provide an easily interpreted measure of short-term or long-term temporal variability. This last result raises uncertainties about the interpretation of published studies that use the RCMS metric. Bioelectromagnetics 22:232,245, 2001. © 2001 Wiley-Liss, Inc. [source] | |||||||||||||