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Negative Values (negative + value)
Selected AbstractsNitrogen balance and seasonal fluctuations in soil nitrogen contents in a corn (Zea mays L)-rye (Secale cereale L) rotation fieldGRASSLAND SCIENCE, Issue 1 2005Yuzo Kurokawa Abstract In a corn (Zea mays L)-rye (Secale cereale L) rotation field, the N output (plant uptake) and N input (crop residue and fertilizer applied) were measured for two years in order to evaluate the N balance in a forage production field. The soil was Low-humic Andosol (mesic Typic Hapludand). The disappearance of crop residues on both a dry matter and N basis, and the seasonal fluctuations of total, inorganic, and available soil N content in the field were investigated. The interaction between the nitrogen balance and the soil N contents are discussed. The total plant N uptake of the corn and rye exceeded the sum of the N input of the fertilizer applied and the N from crop residues, so the N balance of the corn-rye rotation had a negative value (two year average: ,8.4 gN m,2). After the gradual disappearance of crop residue on the dry matter basis, rapid disappearance on the N basis was observed. At the same time, the C/N ratio decreased to less than 20. The soil available (38.4,55.3 mg kg,1) and inorganic (21.5,45.2 mg kg,1) N had their lowest values in spring. After they increased in early summer, they decreased in late summer and increased in autumn. The total N (0.5,0.7%) gradually decreased during the experimental period. The results indicated that the soil-available N and inorganic N in the present study were highly dependent on the fertilizer-applied N. The relation among management practices, N input and soil available N contents are discussed. It is suggested that the negative N balance is one of the causes for a decrease in soil total N. [source] The Impact of Airport Noise and Proximity on Residential Property ValuesGROWTH AND CHANGE, Issue 3 2000Molly Espey The hedonic price method is used to estimate the relationship between residential property values and airport noise and proximity to the airport in the Reno-Sparks area. Empirical results suggest there is a statistically significant negative relationship between airport noise and residential property values, with the average home in areas where noise levels are 65 decibels or high selling for about $2400 less than equivalent homes in quieter areas. However, in direct contrast to the study by Tomkins et al.(1998) who found proximity to the Manchester airport to be an amenity, this study finds proximity to the Reno-Sparks airport to have a significant negative value. [source] A new formulation of garnet,clinopyroxene geothermometer based on accumulation and statistical analysis of a large experimental data setJOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2009D. NAKAMURAArticle first published online: 13 JUL 200 Abstract Published experimental data including garnet and clinopyroxene as run products were used to develop a new formulation of the garnet,clinopyroxene geothermometer based on 333 garnet,clinopyroxene pairs. Only experiments with graphite capsules were selected because of difficulty in estimating the Fe3+ content of clinopyroxene. For the calibration, a published subregular-solution model was adopted to express the non-ideality of garnet. The magnitude of the Fe,Mg excess interaction parameter for clinopyroxene (WFeMgCpx), and differences in enthalpy and entropy of the Fe,Mg exchange reaction were regressed from the accumulated experimental data set. As a result, a markedly negative value was obtained for the Fe,Mg excess interaction parameter of clinopyroxene (WFeMgCpx = , 3843 J mol,1). The pressure correction is simply treated as linear, and the difference in volume of the Fe,Mg exchange reaction was calculated from a published thermodynamic data set and fixed to be ,120.72 (J kbar,1 mol,1). The regressed and obtained thermometer formulation is as follows: where T = temperature, P = pressure (kbar), A = 0.5 Xgrs (Xprp , Xalm , Xsps), B = 0.5 Xgrs (Xprp , Xalm + Xsps), C = 0.5 (Xgrs + Xsps) (Xprp , Xalm), Xprp = Mg/(Fe2+ + Mn + Mg + Ca)Grt, Xalm = Fe/(Fe2+ + Mn + Mg + Ca)Grt, Xsps = Mn/(Fe2+ + Mn + Mg + Ca)Grt, Xgrs = Ca/(Fe2+ + Mn + Mg + Ca)Grt, XMgCpx = Mg/(Al + Fetotal + Mg)Cpx, XFeCpx = Fe2+/(Al + Fetotal + Mg)Cpx, KD = (Fe2+/Mg)Grt/(Fe2+/Mg)Cpx, Grt = garnet, Cpx = clinopyroxene. A test of this new formulation to the accumulated data gave results that are concordant with the experimental temperatures over the whole range of the experimental temperatures (800,1820 °C), with a standard deviation (1 sigma) of 74 °C. Previous formulations of the thermometer are inconsistent with the accumulated data set; they underestimate temperatures by about 100 °C at >1300 °C and overestimate by 100,200 °C at <1300 °C. In addition, they tend to overestimate temperatures for high-Ca garnet (Xgrs , 0.30,0.50). This new formulation has been tested against previous formulations of the thermometer by application to natural eclogites. This gave temperatures some 20,100 °C lower than previous formulations. [source] Biochemical markers of liver fibrosis and lymphocytic piecemeal necrosis in UDCA-treated patients with primary biliary cirrhosisLIVER INTERNATIONAL, Issue 3 2004Christophe Corpechot Abstract: Background/Aim: We have previously shown that the histological stage and severity of lymphocytic piecemeal necrosis (LPN) are independent predictive factors of cirrhosis development in ursodeoxycholic acid (UDCA)-treated patients with primary biliary cirrhosis (PBC). Our aim during this study was to determine whether biochemical parameters classically used in PBC management and measured under UDCA could be considered as reliable surrogate markers for these histological prognostic indices in clinical practice. Method: The study included 153 patients with PBC who had undergone a control liver biopsy after 2 years of UDCA therapy. The relationships between histological and biological features were assessed by variance analysis and logistic regression. The diagnostic value of independent markers was assessed in terms of their sensitivity, specificity, positive predictive value (PPV) and negative value (NPV) and receiver-operating characteristic curves. Results: Two variables were independently associated with extensive fibrosis (i.e. advanced histological stages): serum levels of bilirubin and hyaluronic acid (HA). A fibrosis index ([bilirubin (,mol/l)/14]+[HA (,g/l)/143]) higher than 1.5 exhibited good PPV and specificity (>74%) but rather poor NPV and sensitivity (<64%) regarding a diagnosis of extensive fibrosis. The only independent marker of LPN was aspartate aminotransferase (AST) activity. AST activity of more than twice the upper limit of normal showed acceptable PPV (>70%) but very low sensitivity (<25%) for a diagnosis of LPN. Conclusions: Serum bilirubin and HA levels measured under UDCA therapy are of acceptable diagnostic value for extensive fibrosis, but none of the biochemical tests commonly employed in the management of PBC can be considered as surrogate markers of LPN. Taken together with our previous results, these findings suggest that liver biopsy may be necessary to screen UDCA-treated patients who might require additional therapies. [source] Miscibility in Blends of Isotactic/Syndiotactic Polystyrenes at Melt or Quenched Amorphous Solid StateMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2006Shu Hsien Li Abstract Summary: Miscibility in amorphous phase and behavior in a crystalline phase of blends of two semicrystalline and isomeric polymers, isotactic polystyrene (iPS) and syndiotactic polystyrene (sPS), was probed. Optical and scanning electron microscopy results indicate no discernible heterogeneity in iPS/sPS blends in either melt state or rapidly quenched amorphous super-cooled state, while the Tg behavior of the quenched amorphous blends shows an intimately mixed state of two polymer chains. The crystal forms of the blends were further analyzed to provide additional evidence of miscibility in the amorphous domain. The sPS in the iPS/sPS blends upon melt crystallization was found to predominantly exist as the more stable , -form (rather than mixed , -form and , -form in neat sPS), which also suggests evidence of miscibility in the iPS/sPS blends. The melting behavior of semicrystalline sPS in the iPS/sPS mixtures was analyzed using the Flory-Huggins approach for estimation of interactions. By measuring the equilibrium melting point of the higher-melting sPS species in the sPS/iPS blends, a small negative value, for the interaction parameter (,,,,,0.11) was found. Further, by introducing a third polymer, poly(2,6-dimethyl- p -phenylene oxide) (PPO), a ternary iPS/sPS/PPO blend system was also proven miscible, which constituted a further test for stable phase miscibility in the iPS/sPS blend. General nature of miscibility in blends composed of two crystalline isomeric polymers is discussed. Issues in dealing with blends of polymers of the same chemical repeat unit but different tacticities were addressed. X-ray diffractograms for neat sPS and iPS/sPS blends, each having been isothermally crystallized at 245,°C for 4 h. [source] PhadiatopTM compared to skin-prick test as a tool for diagnosing atopy in epidemiological studies in schoolchildrenPEDIATRIC ALLERGY AND IMMUNOLOGY, Issue 3 2007Luis Garcia-Marcos The validity of the PhadiatopTM test as compared to the skin-prick test (SPT) for diagnosing atopy in the epidemiological field has not been studied in schoolchildren. The aim of the present study was to evaluate its validity for classifying schoolchildren 9,12 yr old into atopics and non-atopics. A total of 621 children whose parents authorized both a SPT and a blood extraction from all children participating in the phase II of the International Study of Allergies in Children (ISAAC) in Cartagena (Spain) were included in the analysis. A positive SPT was that with at least a wheal having a maximum diameter of 3 mm, once the negative value had been subtracted. PhadiatopTM was performed according to the manufacturer instructions. Diagnostic tests using SPT as the gold standard were calculated for the whole group of children and also for those with asthma or rhinoconjunctivitis and for children without any of them. The results of the tests were: sensitivity 85.0% (95% CI 82.2,87.8%), specificity 85.5% (95%CI 82.7,88.3%), positive predictive value 72.7% (95%CI 69.0,76.1%), negative predictive value 92.7% (95%CI 90.6,94.7%) and accuracy 85.3% (95%CI 82.3,88.0%). The results improved among the symptomatic groups. PhadiatopTM can be used as a valid alternative to SPT in the epidemiological setting to diagnose atopy. [source] Dobutamine stress surface mapping of myocardial ischemia in Kawasaki diseasePEDIATRICS INTERNATIONAL, Issue 3 2001Nobuyuki Takechi Abstract Background: To detect and localize myocardial ischemia, a method that does not require physical exertion is sometimes needed in children with Kawasaki disease. Methods: Dobutamine stress body surface mapping was performed in 115 children with a history of Kawasaki disease (58 without coronary artery lesions, 40 who had coronary lesions without myocardial ischemia and 17 with myocardial ischemia). The maximum infusion rate of dobutamine was 30 ,g/kg per min. Myocardial ischemia was diagnosed by the presence of an area of hypoperfusion on scintigraphy at rest and/or an increase in hypoperfusion during a dobutamine stress test compared with resting scintigraphy. We studied the number of leads that showed significant ST depression on the isopotential map (nST), the number of the row containing the lead with the smallest negative value on the isointegral map (Imin), and the localization of myocardial ischemia on the isointegral map. Based on findings in patients without coronary artery lesions, we defined the criteria for detecting myocardial ischemia as nST , 1 and Imin, 4. Results: The sensitivity of detecting myocardial ischemia was 94.1% using nST and 41.7% using Imin, while the specificity of these methods was 98.9 and 96.9%, respectively. The localization of myocardial ischemia on stress body surface mapping was 100% concordant with that determined by stress myocardial scintigraphy. Conclusions: Dobutamine stress body surface mapping for the detection of myocardial ischemia is a non-invasive, more convenient and repeatable test compared with exercise myocardial scintigraphy and it is a more objective test compared with exercise echocardiography. Dobutamine stress body surface mapping is useful for the identification and localization of silent myocardial ischemia in pediatric patients with Kawasaki disease, especially those who cannot perform tests involving physical exercise. [source] Characterization of Fe 3d states in CuFeS2 by resonant X-ray emission spectroscopyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009Katsuaki Sato Abstract Resonant X-ray emission spectroscopy (RXES) experiments were carried out in a single crystal of chalcopyrite CuFeS2, an antiferromagnetic semiconductor with a golden lustre, to unravel the overlapping d,d and charge-transfer transitions extending well above the absorption edge, which cannot be observed by conventional optical absorption experiments. The observed RXES spectra have been analyzed by means of cluster-model calculation with configuration interaction, which leads to the conclusion that CuFeS2 is a Haldane,Anderson insulator with a negative value of charge transfer energy, , = ,3 eV. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of cooling field strength and ferromagnetic shell shape on exchange bias in nanoparticles with inverted ferromagnetic,antiferromagnetic core-shell morphologyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2010Yong Hu Abstract The dependence of exchange bias (EB) effects on cooling field strength and particle shape in nanoparticles with antiferromagnetic (AFM) interfacial coupling and inverted AFM core with a fixed radius and ferromagnetic (FM) shell with various thicknesses are investigated by using a modified Monte Carlo Metropolis method. It is found that with the increase of cooling field, field-cooled exchange bias field (HE) fluctuates in the range of negative values initially, and then has an abrupt jump from the negative value to the positive value, finally levels off. However, HE decreases as the FM shell shape varies from No. 1 to No. 13 regardless of the strength of cooling field. Coercivity is affected by cooling fields and shapes indicating distinct behaviors. Because the AFM core is almost unaffected by shape and frozen completely during measuring hysteresis loops, the effect of ferromagnets on EB, negligible in most of other systems, is ambiguously manifested in such an unconventionally structural system. Moreover, the phenomena are interpreted well by presenting the snapshots of microscopic spin energy distributions, which make us observe directly and vividly the movement of domains and the competition of energies. This work will shed new light into the microscopic origin of peculiar magnetic properties of nanoparticles with special structures. [source] The myth of the best argument: power, deliberation and reason1THE BRITISH JOURNAL OF SOCIOLOGY, Issue 1 2001Luigi Pellizzoni ABSTRACT Power in communication takes two main forms. As ,external' power, it consists in the ability to acknowledge or disregard a speaker or a discourse. As ,internal' power, it is the ability of an argument to eliminate other arguments by demonstrating its superiority. A positive or negative value may be ascribed to these forms of power. Four ideal-typical positions are discussed , strategy, technocracy, constructionism, and deliberation. Public deliberation has three virtues , civic virtue, governance virtue and cognitive virtue. Deliberation lowers the propensity to, and the benefit of, strategic behaviour. It also increases knowledge, enhancing the quality of decisions. For Habermas, the unity of reason is expressed in the possibility of agreement on the most convincing argument. However, sometimes conflicts are deeplying, principles and factual descriptions are profoundly different, and uncertainty is radical. The best argument cannot be found. There is no universal reason. The question is whether non-strategic agreement may spring from the incommensurability of languages. In search of an answer, Rawls's concept of overlapping consensus, the feminist theory of the public sphere, and the idea of deliberation as co-operation are discussed. The argument developed is that the approach to deliberative democracy may be renewed by rethinking its motivational and cognitive elements. Public deliberation is grounded on a pre-political level of co-operation. Intractable controversies may be faced at the level of practices, looking for local, contextual answers. [source] Oceanic influence on the precipitation of the south-east of VenezuelaENVIRONMETRICS, Issue 3 2002Lelys Guenni Abstract The Caroní catchment located in the south-east of Venezuela accounts for 70 per cent of the total hydropower energy of the country. On a year to year basis, it has been shown that low frequency large scale ocean-atmosphere phenomena are highly coupled to the hydroclimatology of the region, El Niño-Southern Oscillation (ENSO) being a major forcing mechanism of climatic and hydrological anomalies. Regional differences in amplitude and timing are due to complex orographic interactions, land surface-atmosphere feedback mechanisms and the evolution of dominant synoptic meteorological conditions. A detailed analysis of the relationship between rainfall and several large scale ocean-atmospheric variables was carried out to determine the potential use of large scale climatic information as predictors of the rainfall anomalies over the region. The problem was tackled in two ways: (a) first a seasonal dynamic rainfall model was fitted to monthly rainfall for different locations. In this case rainfall is assumed as a normal variate w which has been transformed to account for its departure from normality and truncated to account for the positive probability mass of zero values, which corresponds to negative values of the normal variable. The time series of the model parameters and the macroclimatic variables are inspected for their potential relationship with local rainfall via the stochastic model. (b) Second, dynamic linear regression models between the macroclimatic variables as predictors and the rainfall anomalies as predictant were fitted to evaluate and quantify the significance of these dependencies. Consistent patterns are observed with the Tropical Atlantic and Pacific ocean temperature anomalies, in which a significant negative relationship has been present since 1976, indicating an overall decrease (increase) in rainfall when the Pacific and the Tropical Atlantic are warmer (colder) than normal. In all cases the results suggest that the relationships between rainfall anomalies and the macroclimatic variables are not constant with time. Copyright © 2002 John Wiley & Sons, Ltd. [source] Measurement of respiratory function by impulse oscillometry in horsesEQUINE VETERINARY JOURNAL, Issue 1 2004E. Van Erck Reasons for performing study: Due to technical implementations and lack of sensitivity, pulmonary function tests are seldom used in clinical practice. Impulse oscillometry (IOS) could represent an alternative method. Objectives: To define feasibility, methodology and repeatability of IOS, a forced oscillation technique that measures respiratory resistance (Rrs) and reactance (Xrs) from 5 to 35 Hz during spontaneous breathing, in horses. Methods: Using 38 healthy horses, Rrs and Xrs reference values were defined and influence of individual biometrical parameters was investigated. In addition, IOS measurements of 6 horses showing clinical signs of heaves were compared to those of 6 healthy horses. Results: Airtightness and minimal dead space in the facemask were prerequisites to IOS testing and standardisation of head position was necessary to avoid variations in Rrs due to modified upper airway geometry. In both healthy and diseased animals, measurements were repeatable. In standard-type breeds, the influence of the horse's size on IOS parameters was negligible. An increase in R5Hz greater than 0.10 kPa/l/sec and R5Hz>R10Hz, combined with negative values of Xrs between 5 and 20 Hz, was indicative of heaves crisis. Conclusions: IOS is a quick, minimally invasive and informative method for pulmonary function testing in healthy and diseased horses. Potential relevance: IOS is a promising method for routine and/or field respiratory clinical testing in the equine species. [source] Structural and Electrochemical Studies of Dimerization and Rotational Isomerization in Multi-Iron SilicotungstatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2005Travis M. Anderson Abstract A structural and electrochemical investigation of dimerization and Baker,Figgis (rotational) isomerization in the tri-ferric-substituted silicotungstates has been undertaken because these phenomena are important in a large number of polyoxometalates. A single-crystal X-ray diffraction analysis of K4Na7[(,-SiFe3W9(OH)3O34)2(OH)3] (,1) has been carried out [a = 12.9709(7) Å, b = 38.720(2) Å, c = 21.4221(12) Å, orthorhombic, Pbcm, R1 = 8.48,%, based on 13809 independent reflections]. The complex is isostructural with [(,-SiFe3W9(OH)3O34)2(OH)3]11, (,1) except that the edge-shared W3O13 caps in each [SiFe3W9(OH)3O34]4, unit are rotated by 60°. Electrochemical measurements, performed in a pH 5 acetate buffer, indicate a positive shift in the FeIII -based peak potential (and no change for the WVI -based potential) upon going from ,1 to its monomeric derivative [(,-Si(FeOH2)3W9(OH)3O34)]4, (,2) (,0.484,±,0.005 V and ,0.474,±,0.005 V, respectively). In contrast, the peak potentials of the FeIII - and WVI -based redox processes of ,1 are both found at more negative values than its rotational isomer ,1. The absolute values of the reduction peak potential differences are 0.022 V for FeIII and 0.162 V for WVI. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] A slowly inactivating sodium current (INa2) in the plateau range in canine cardiac Purkinje single cellsEXPERIMENTAL PHYSIOLOGY, Issue 1 2007Mario Vassalle The action potential of Purkinje fibres is markedly shortened by tetrodotoxin, suggesting the possibility that a slowly inactivating sodium current might flow during the plateau. The aim of the present experiments was to investigate, in canine cardiac Purkinje single cells by means of a whole cell patch clamp technique, whether a sodium current slowly inactivates at less negative potentials and (if so) some of its distinctive characteristics. The results showed that a 500 ms depolarizing step from a holding potential of ,90 mV to ,50 mV induced the fast inward current INa (labelled here INa1). With steps to ,40 mV or less negative values, a slowly decaying component (tentatively labelled here INa2) appeared, which peaked at ,30 to ,20 mV and decayed slowly and incompletely during the 500 ms steps. The INa2 was present also during steps to ,10 mV, but then the transient outward current (Ito) appeared. When the holding potential (Vh) was decreased to ,60 to ,50 mV, INa2 disappeared even if a small INa1 might still be present. Tetrodotoxin (30 ,m), lignocaine (100 ,m) and cadmium (0.2 mm; but not manganese, 1 mm) blocked INa2. During fast depolarizing ramps, the rapid inactivation of INa1 was followed by a negative slope region. During repolarizing ramps, a region of positive slope was present, whereas INa1 was absent. At less negative values of Vh, the amplitude of the negative and positive slopes became gradually smaller. Gradually faster ramps increased the magnitude of the negative slope, and tetrodotoxin (30 ,m) reduced or abolished it. Thus, Purkinje cells have a slowly decaying inward current owing to Na+ entry (INa2) that is different in several ways from the fast INa1 and that appears important for the duration of the plateau. [source] Interaction of the alpha-helical H6 peptide from the pro-apoptotic protein tBid with cardiolipinFEBS JOURNAL, Issue 21 2009Patrice X. Petit BH3 interacting domain death agonist (Bid), a pro-apoptotic member of the Bcl-2 family of proteins, is activated through cleavage by caspase-8. The active C-terminal fragment of Bid (tBid) translocates to the mitochondria where it interacts with cardiolipins at contact sites and induces the release of cytochrome c by a mechanism that is not yet fully understood. It has been shown that the alpha-helices ,H6 and ,H7 (which create the hairpin-forming domain of tBid) mediate the insertion of Bid into mitochondrial membranes and are essential for the cytochrome c -releasing activity. In the present study, we focused on the interaction between the ,H6 and the mitochondrial membrane. By the use of single-cell electropermeabilization associated with flow cytometric analysis of intact cells, we demonstrated that H6 is able to induce cell death when used in the micromolar range. We also studied the interactions of the ,H6 with artificial monolayers. We showed that the presence of negatively charged cardiolipins greatly enhances the insertion of ,H6 into the phospholipid monolayer. The modification of two charged amino acid residues in ,H6 abolished its insertion and also its in vivo effects. Furthermore, the negative values of the excess areas of mixing indicate that attractive interactions between cardiolipins and ,H6 occur in the mixed monolayers. Fluorescence microscopy observations revealed that ,H6 significantly disrupts cardiolipin packing and stabilizes the fluid lipid phase. These results suggest that cardiolipins at the contact sites between the two mitochondrial membranes could mediate the binding of tBid via ,H6. [source] What makes biochemical networks tick?FEBS JOURNAL, Issue 19 2004A graphical tool for the identification of oscillophores In view of the increasing number of reported concentration oscillations in living cells, methods are needed that can identify the causes of these oscillations. These causes always derive from the influences that concentrations have on reaction rates. The influences reach over many molecular reaction steps and are defined by the detailed molecular topology of the network. So-called ,autoinfluence paths', which quantify the influence of one molecular species upon itself through a particular path through the network, can have positive or negative values. The former bring a tendency towards instability. In this molecular context a new graphical approach is presented that enables the classification of network topologies into oscillophoretic and nonoscillophoretic, i.e. into ones that can and ones that cannot induce concentration oscillations. The network topologies are formulated in terms of a set of uni-molecular and bi-molecular reactions, organized into branched cycles of directed reactions, and presented as graphs. Subgraphs of the network topologies are then classified as negative ones (which can) and positive ones (which cannot) give rise to oscillations. A subgraph is oscillophoretic (negative) when it contains more positive than negative autoinfluence paths. Whether the former generates oscillations depends on the values of the other subgraphs, which again depend on the kinetic parameters. An example shows how this can be established. By following the rules of our new approach, various oscillatory kinetic models can be constructed and analyzed, starting from the classified simplest topologies and then working towards desirable complications. Realistic biochemical examples are analyzed with the new method, illustrating two new main classes of oscillophore topologies. [source] Arbitrage and the Evaluation of Linear Factor Models in UK Stock ReturnsFINANCIAL REVIEW, Issue 2 2010Jonathan Fletcher G12 Abstract I examine the impact of the no arbitrage restriction on the estimation and evaluation of linear factor models in UK stock returns. The no arbitrage restriction reduces volatility and eliminates most of the negative values of the fitted stochastic discount factor models. All of the factor models are rejected and there are significant differences in the pricing performance between models under the no arbitrage restriction. The no arbitrage restriction can have a significant impact on both the parameter estimates and pricing errors for some models. [source] A laboratory study of seismic velocity and attenuation anisotropy in near-surface sedimentary rocksGEOPHYSICAL PROSPECTING, Issue 5 2007Angus I. Best ABSTRACT The laboratory ultrasonic pulse-echo method was used to collect accurate P- and S-wave velocity (±0.3%) and attenuation (±10%) data at differential pressures of 5,50 MPa on water-saturated core samples of sandstone, limestone and siltstone that were cut parallel and perpendicular to the vertical borehole axis. The results, when expressed in terms of the P- and S-wave velocity and attenuation anisotropy parameters for weakly transversely isotropic media (,, ,, ,Q, ,Q) show complex variations with pressure and lithology. In general, attenuation anisotropy is stronger and more sensitive to pressure changes than velocity anisotropy, regardless of lithology. Anisotropy is greatest (over 20% for velocity, over 70% for attenuation) in rocks with visible clay/organic matter laminations in hand specimens. Pressure sensitivities are attributed to the opening of microcracks with decreasing pressure. Changes in magnitude of velocity and attenuation anisotropy with effective pressure show similar trends, although they can show different signs (positive or negative values of ,, ,Q, ,, ,Q). We conclude that attenuation anisotropy in particular could prove useful to seismic monitoring of reservoir pressure changes if frequency-dependent effects can be quantified and modelled. [source] Seismic anisotropy of shalesGEOPHYSICAL PROSPECTING, Issue 5 2005C.M. Sayers ABSTRACT Shales are a major component of sedimentary basins, and they play a decisive role in fluid flow and seismic-wave propagation because of their low permeability and anisotropic microstructure. Shale anisotropy needs to be quantified to obtain reliable information on reservoir fluid, lithology and pore pressure from seismic data, and to understand time-to-depth conversion errors and non-hyperbolic moveout. A single anisotropy parameter, Thomsen's , parameter, is sufficient to explain the difference between the small-offset normal-moveout velocity and vertical velocity, and to interpret the small-offset AVO response. The sign of this parameter is poorly understood, with both positive and negative values having been reported in the literature. , is sensitive to the compliance of the contact regions between clay particles and to the degree of disorder in the orientation of clay particles. If the ratio of the normal to shear compliance of the contact regions exceeds a critical value, the presence of these regions acts to increase ,, and a change in the sign of ,, from the negative values characteristic of clay minerals to the positive values commonly reported for shales, may occur. Misalignment of the clay particles can also lead to a positive value of ,. For transverse isotropy, the elastic anisotropy parameters can be written in terms of the coefficients W200 and W400 in an expansion of the clay-particle orientation distribution function in generalized Legendre functions. For a given value of W200, decreasing W400 leads to an increase in ,, while for fixed W400, , increases with increasing W200. Perfect alignment of clay particles with normals along the symmetry axis corresponds to the maximum values of W200 and W400, given by and . A comparison of the predictions of the theory with laboratory measurements shows that most shales lie in a region of the (W200, W400)-plane defined by W400/W200,Wmax400/Wmax200. [source] Reassessing the impact of North Atlantic Oscillation on the sub-Saharan vegetation productivityGLOBAL CHANGE BIOLOGY, Issue 4 2003GUILING WANG Abstract The Northern Atlantic Oscillation (NAO) has been shown to have a significant impact on the terrestrial ecosystem in the Sahelian region of Africa during the 1980s, and it has been strongly suggested that NAO may be a reliable predictor for the response of the Sahelian ecosystem to global climate variability. Using data from an extended period, we provide a reassessment for the impact of NAO on the Sahelian climate and ecosystem, and show that there is no consistent relationship between NAO and the ecosystem over Sahel. Statistical analysis on the NAO, vegetation, and precipitation data indicates that NAO influences the Sahelian vegetation productivity exclusively through its impact on precipitation. However, the relationship between the NAO index and Sahelian precipitation varies substantially with time. The correlation coefficient fluctuates between positive and negative values, and does not pass the 5% significance test during most of the twentieth century. The NAO system, although documented to govern the ecosystem dynamics over many other regions, does not have a consistent impact on the ecosystem over the Sahel. Therefore, the NAO index cannot produce a useful prediction on the ecosystem variability and changes in this region. This study provides an example that correlations based on short climate and ecological records (less than 20 years in this case) can be spurious and potentially misleading. [source] Aminodiphenylphosphanes: Isotope-induced chemical shifts 1,14/15N(31P), coupling constants 1J(31P,15N), and chemical shifts ,15N and ,31PHETEROATOM CHEMISTRY, Issue 6 2001Rosalinda Contreras A series of aminodiphenylphosphanes 1 [Ph2P-N(H)tBu (a), -NEt2 (b), -NiPr2 (c)], 2 [Ph2P-NHPh (a), -NH-2-pyridine (b), -NH-3-pyridine (c), -NH-4-pyridine (d), NH-pyrimidine (e), NH-2,6-Me2 -C6H3 (f), NH-3-Me-2-pyridine (g)], 3 [Ph2P-N(Me)Ph (a), -NPh2 (b)], and N-pyrrolyldiphenylphosphane 4 (Ph2P-NC4H4) was prepared and studied by NMR (1H, 13C, 31P, 15N NMR) spectroscopy. The isotope-induced chemical shifts 1,14/15N(31P) were determined at natural abundance of 15N by using HEED INEPT experiments. A dependence of 1,14/15N(31P) on the substituents at nitrogen was found (alkyl < H < aryl; increasingly negative values). The magnitude and sign of the coupling constants 1J(31P,15N) (positive sign) are dominated by the presence of the lone pair of electrons at the phosphorus atom. The X-ray structural analysis of 2b is reported, showing the presence of dimers owing to intermolecular hydrogen bridges in the solid state. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:542,550, 2001 [source] Above-stream microclimate and stream surface energy exchanges in a wildfire-disturbed riparian zoneHYDROLOGICAL PROCESSES, Issue 17 2010J. A. Leach Abstract Stream temperature and riparian microclimate were characterized for a 1·5 km wildfire-disturbed reach of Fishtrap Creek, located north of Kamloops, British Columbia. A deterministic net radiation model was developed using hemispherical canopy images coupled with on-site microclimate measurements. Modelled net radiation agreed reasonably with measured net radiation. Air temperature and humidity measured at two locations above the stream, separated by 900 m, were generally similar, whereas wind speed was poorly correlated between the two sites. Modelled net radiation varied considerably along the reach, and measurements at a single location did not provide a reliable estimate of the modelled reach average. During summer, net radiation dominated the surface heat exchanges, particularly because the sensible and latent heat fluxes were normally of opposite sign and thus tended to cancel each other. All surface heat fluxes shifted to negative values in autumn and were of similar magnitude through winter. In March, net radiation became positive, but heat gains were cancelled by sensible and latent heat fluxes, which remained negative. A modelling exercise using three canopy cover scenarios (current, simulated pre-wildfire and simulated complete vegetation removal) showed that net radiation under the standing dead trees was double that modelled for the pre-fire canopy cover. However, post-disturbance standing dead trees reduce daytime net radiation reaching the stream surface by one-third compared with complete vegetation removal. The results of this study have highlighted the need to account for reach-scale spatial variability of energy exchange processes, especially net radiation, when modelling stream energy budgets. Copyright © 2010 John Wiley & Sons, Ltd. [source] Institutionalized Intolerance of ADHD: Sources and ConsequencesHYPATIA, Issue 3 2010SUSAN C. C. HAWTHORNE Diagnosable individuals, caregivers, and clinicians typically embrace a biological conception of attention-deficit/hyperactivity disorder (ADHD), finding that medical treatment is beneficial. Scientists study ADHD phenomenology, interventions to ease symptoms, and underlying mechanisms, often with an aim of helping diagnosed people. Yet current understanding of ADHD, jointly influenced by science and society, has an unintended downside. Scientific and social influences have embedded negative values in the ADHD concept, and have simultaneously dichotomized ADHD-diagnosable from non-diagnosable individuals. In social settings insistent on certain types of success, the negative values associated with the diagnostic category are attributed to people in the dichotomized "ADHD" group. Devaluation, institutional restrictions on "success" definitions and endpoints, and limited options for achieving success jointly constitute institutionalized intolerance of ADHD. [source] Continuous Tuning of Organic Transistor Operation from Enhancement to Depletion ModeADVANCED MATERIALS, Issue 3 2009Piero Cosseddu An organic field-effect transistor able to switch from depletion (normally on) to enhancement (normally off) mode was obtained thanks to the composition of the mixed semiconductor that forms the device channel. The threshold voltage of the device can be predictably tuned from positive to negative values by adjusting the composition of a mixture of sexithiophene derivatives that are able to achieve a perfect intercalation inside the thin film. [source] A conservative 2D model of inundation flow with solute transport over dry bedINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2006J. Murillo Abstract In this paper, a transient 2D coupled vertically averaged flow/transport model is presented. The model deals with all kind of bed geometries and guarantees global conservation and positive values of both water level and solute concentration in the transient solution. The model is based on an upwind finite volume method, using Roe's approximate Riemann solver. A specific modification of the Riemann solver is proposed to overcome the generation of negative values of depth and concentration, that can appear as a consequence of existing wetting/drying and solute advance fronts over variable bed levels, or by the generation of new ones when dry areas appear. The numerical stability constraints of the explicit model are stated incorporating the influence of the flow velocity, the bed variations and the possible appearance of dry cells. Faced to the important restriction that this new stability condition can impose on the time step size, a different strategy to allow stability using a maximum time step, and in consequence a minimum computational cost is presented. Copyright © 2006 John Wiley & Sons, Ltd. [source] Kinetics and mechanism of adducts formation of tetraaza cobalt(II) complexes with some organic bases in DMF solventINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2007Mozaffar Asadi The kinetics and mechanism of the adduct formation of two Co(II) tetraaza complexes, [Co(ampen)] {[(N,N,-ethylenebis-(o -amino-,-phenylbenzylideneiminato)cobalt(II)]} and [Co(campen)] {[(N,N,-ethylenebis-(5-chloro- o -amino-,-phenylbenzylideneiminato)cobalt(II)]}, with four organic bases, 4-nitro imidazole (4-NO2Imid), 4-methyl imidazole (4-MeImid), imidazole (Imid), and 1-methyl imidazole (1-MeImid), in DMF were studied spectrophotometrically. The kinetic parameters and the second-order k2 rate constants show the following nucleophilicity trend of the bases toward the given substrate: 4-NO2Imid > 4-MeImid > Imid > 1-MeImid. The linear plots of kobs vs. the molar concentration of the base, the high span of k2 values, and the large negative values of ,S, suggest an associative (A) mechanism. © 2007 Wiley Periodicals, Inc. 39: 137,144, 2007 [source] The annual cycle of heavy precipitation across the United Kingdom: a model based on extreme value statisticsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2009D. Maraun Abstract The annual cycle of extreme 1-day precipitation events across the UK is investigated by developing a statistical model and fitting it to data from 689 rain gauges. A generalized extreme-value distribution (GEV) is fit to the time series of monthly maxima, across all months of the year simultaneously, by approximating the annual cycles of the location and scale parameters by harmonic functions, while keeping the shape parameter constant throughout the year. We average the shape parameter of neighbouring rain gauges to decrease parameter uncertainties, and also interpolate values of all model parameters to give complete coverage of the UK. The model reveals distinct spatial patterns for the estimated parameters. The annual mean of the location and scale parameter is highly correlated with orography. The annual cycle of the location parameter is strong in the northwest UK (peaking in late autumn or winter) and in East Anglia (where it peaks in late summer), and low in the Midlands. The annual cycle of the scale parameter exhibits a similar pattern with strongest amplitudes in East Anglia. The spatial patterns of the annual cycle phase suggest that they are linked to the dominance of frontal precipitation for generating extreme precipitation in the west and convective precipitation in the southeast of the UK. The shape parameter shows a gradient from positive values in the east to negative values in some areas of the west. We also estimate 10-year and 100-year return levels at each rain gauge, and interpolated across the UK. Copyright © 2008 Royal Meteorological Society [source] Bound state spectra of the 3D rational potentialINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2008Amlan K. Roy Abstract We present bound state spectra of the 3D rational potential, V(r) = r2 + ,r2/(1 + gr2), g > 0, by means of the generalized pseudospectral method. All the 30 states corresponding to n = 0,9 are considered for the first time for a broad range of coupling parameters. These results surpass the accuracy of all other existing calculations published so far except the finite-difference method, which yields similar accuracy as ours. Variation of energies and radial distribution functions is followed with respect to the interaction parameters. Special emphasis has been laid on higher excitations and negative values of the interaction, where relatively less work has been reported. The energy sequence is found to be different for positive and negative interaction; numerically following a mirror-image relationship usually, if not always. Additionally, 20 energy splittings arising from certain levels belonging to n = 0,9 are systematically studied as functions of the potential parameters. Several new states (including the higher ones) are presented. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Computational characterization of nucleotide bases: Molecular surface electrostatic potentials and local ionization energies, and local polarization energiesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3-4 2001Jane S. Murray Abstract Electrostatic potentials and local ionization energies have been computed at the HF/6-31G* level on the molecular surfaces of the five nucleotide bases. The potentials are analyzed in terms of their most positive and negative values as well as several statistically defined quantities that reflect their patterns over the entire surface. Considerable charge separation and variability are found for all five molecules. The results are consistent with the base pairing that is known to occur. The observed reactive behavior toward electrophiles can be interpreted in terms of the complementary roles of the surface potential and the local electron lability. Local polarization energies, corresponding to a test charge being placed at specific points above the molecules, are also calculated (HF/6-31+G*), and their relationship to the local ionization energies is examined. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 245,254, 2001 [source] Effects of Water Shortage and Air Temperature on Seed Yield and Seed Performance of Lucerne (Medicago sativa L.) in a Mediterranean EnvironmentJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 6 2009A. J. Karamanos Abstract Seed production and performance of lucerne is characterized by fluctuating yields with often poor seed quality, and is dependent on environmental conditions, genetic characteristics and agronomic techniques applied during seed set, development, maturation and storage. A field experiment was carried out in two successive growing seasons at Kopais (southern Greece) to evaluate the effects of drought stress imposed by three irrigation treatments, and temperature during flowering and seed filling on lucerne seed yield and quality. Plant water status, expressed in terms of the water potential index (WPI), growth in leaf area and dry weight, seed yield and yield components, flowering and seed quality parameters were measured throughout the growing seasons. The adopted irrigation schemes produced a clear differentiation among treatments concerning their plant water status. Seed yield and leaf growth showed close positive correlations with WPI. An irrigation effect was also detected for the number of pods/plant, but not for the average weight of seeds/pod. Less negative values of WPI, and, especially, higher temperatures during flowering were also positively associated with a longer duration of flowering, as well as with higher total numbers of inflorescences. A very good description of the time course of seed germination was performed by fitting the Richards' function to the real data. By examining the germination parameters derived from this function it was found that final germination and germination rate were improved, while germination duration was shortened with more negative values of WPI. The effects of growing season and seeding period were occasionally equally or more important than irrigation effects. These results are also discussed in terms of their practical implications for seed producing lucerne crops. [source] | |||||||||||||||||||||||||||||||||||||