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Opposite Sign (opposite + sign)
Selected AbstractsAccumulation of heterocyclic nitrogen in humified organic matter: a 15N-NMR study of lowland rice soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2000N. Mahieu Summary Recent intensification of cropping and the attendant longer submergence of the soil for lowland rice in tropical Asia appear to have altered the nature of the soil organic matter, and perhaps also nutrient cycling. To identify the dominant forms of organic nitrogen in the soils we extracted the labile mobile humic acid (MHA) and the more recalcitrant calcium humate (CaHA) fractions from soils under several long-term field experiments in the Philippines and analysed them by 15N-nuclear magnetic resonance spectroscopy. Amide N dominated the spectra of all humic acid (HA) samples (60,80% of total peak area). Its proportion of total spectral area increased with increasing intensity of cropping and length of time during which the soil was flooded and was greater in the MHA fraction than in the CaHA fraction. Simultaneously the spectral proportion of free amino N and other chemical shift regions decreased slightly with increasing length of submergence. Heterocyclic N was detected at modest proportions (7,22%) and was more prevalent in more humified samples, especially in the CaHA of aerated soils. Correlations of spectral proportions of heterocyclic N with other properties of the HA, reported elsewhere, were highly significant. Correlations were positive with visible light absorption (r=,0.86) and concentration of free radicals (r=,0.85), both of which are indices of humification, and negative with concentration of H (r=,,0.86), a negative index of humification. Correlations of spectral proportions of amide N with these properties were also highly significant but in each case of opposite sign to that of heterocyclic N. Proportions of heterocyclic N declined with increasing duration of submergence. The results suggest that (i) 15N-NMR can reproducibly measure some portion of heterocyclic N, (ii) formation of heterocyclic N is associated solely with gradual humification occurring over many years, and (iii) the abundant phenols in the submerged rice soils did not promote formation of heterocyclic N, and hence some other process is responsible for a substantial decrease in the availability of native N associated with intensive rice cropping. [source] Integration of lakes and streams in a landscape perspective: the importance of material processing on spatial patterns and temporal coherenceFRESHWATER BIOLOGY, Issue 3 2000George W. Kling 1. We studied the spatial and temporal patterns of change in a suite of twenty-one chemical and biological variables in a lake district in arctic Alaska, U.S.A. The study included fourteen stream sites and ten lake sites, nine of which were in a direct series of surface drainage. All twenty-four sites were sampled between one and five times a year from 1991 to 1997. 2. Stream sites tended to have higher values of major anions and cations than the lake sites, while the lake sites had higher values of particulate carbon, nitrogen, phosphorous and chlorophyll a. There were consistent and statistically significant differences in concentrations of variables measured at the inlet versus the outlet of lakes, and in variables measured at upstream versus downstream sites in the stream reaches which connect the lakes. In-lake processing tended to consume alkalinity, conductivity, H+, DIC, Ca2+, Mg2+, CO2, CH4, and NO3,, and produce K+ and dissolved organic carbon (DOC). In-stream processing resulted in the opposite trends (e.g. consumption of K+ and DOC), and the magnitudes of change were often similar to those measured in the lakes but with the opposite sign. 3. Observed spatial patterns in the study lakes included mean concentrations of variables which increased, decreased or were constant along the lake chain from high to low altitude in the catchment (stream sites showed no spatial patterns with any variables). The strongest spatial patterns were of increasing conductivity, Ca2+, Mg2+, alkalinity, dissolved inorganic carbon and pH with lake chain number (high to low altitude in the basin). These patterns were partly determined by the effect of increasing catchment area feeding into lakes further downslope, and partly by the systematic processing of materials in lakes and in the stream segments between lakes. 4. Synchrony (the temporal coherence or correlation of response) of variables across all lakes ranged from 0.18 for particulate phosphorus to 0.90 for Mg2+ the average synchrony for all twenty-one variables was 0.50. The synchronous behaviour of lake pairs was primarily related to the spatial location or proximity of the lakes for all variables taken together and for many individual variables, and secondarily, to the catchment to lake area ratio and the water residence time. 5. These results illustrate that, over small geographic areas, and somewhat independent of lake or stream morphometry, the consistent and directional (downslope) processing of materials helps produce spatial patterns which are coherent over time for many limnological variables. We combine concepts from stream, lake and landscape ecology, and develop a conceptual view of landscape mass balance. This view highlights that the integration of material processing in both lakes and rivers is critical for understanding the structure and function of surface waters, especially from a landscape perspective. [source] Absolute Conformations of the (,)-[9](2,5)Pyridinophane MoleculeHELVETICA CHIMICA ACTA, Issue 8 2009Maxim Fedorovsky Abstract [9](2,5)Pyridinophane was first synthesized, and its enantiomers were separated, more than 40 years ago, but the molecule's absolute conformations could not be determined up to now. We show here, by the comparison of measured and computed vibrational optical activity (VOA), that the CIP descriptor (P) applies to the (,)-enantiomer. This assignment is based on the VOA of bands from vibrations localized on the pyridine ring bent by the tense (CH2)9 chain extending from position 2 to 5. The VOA of vibrations localized on the chain is in agreement with this assignment. Its behavior differs from the VOA of the bent pyridine ring, and conclusions drawn from the chain's VOA alone would not be sufficient, because the close-to-enantiomorphic geometries of the chain present in some of the 14 conformers of (,)-[9](2,5)pyridinophane lead to VOA with an opposite sign. Understanding of how VOA is generated is crucial for the unambiguous assignment of the molecule's absolute conformations. [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] Central suboptimal H, filter design for nonlinear polynomial systemsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 10 2009Michael Basin Abstract This paper presents the central finite-dimensional H, filter for nonlinear polynomial systems, which is suboptimal for a given threshold , with respect to a modified Bolza,Meyer quadratic criterion including the attenuation control term with the opposite sign. In contrast to the previously obtained results, the paper reduces the original H, filtering problem to the corresponding optimal H2 filtering problem, using the technique proposed in (IEEE Trans. Automat. Control 1989; 34:831,847). The paper presents the central suboptimal H, filter for the general case of nonlinear polynomial systems based on the optimal H2 filter given in (Int. J. Robust Nonlinear Control 2006; 16:287,298). The central suboptimal H, filter is also derived in a closed finite-dimensional form for third (and less) degree polynomial system states. Numerical simulations are conducted to verify performance of the designed central suboptimal filter for nonlinear polynomial systems against the central suboptimal H, filter available for the corresponding linearized system. Copyright © 2008 John Wiley & Sons, Ltd. [source] Complex dynamics in one-dimensional CNNsINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 1 2006István Petrás Abstract The effect of boundary conditions on the global dynamics of cellular neural networks (CNNs) is investigated. As a case study one-dimensional template CNNs are considered. It is shown that if the off-diagonal template elements have opposite sign, then the boundary conditions behave as bifurcation parameters and can give rise to a very rich and complex dynamic behaviour. In particular, they determine the equilibrium point patterns, the transition from stability to instability and the occurrence of several bifurcation phenomena leading to strange and/or chaotic attractors and to the coexistence of several attractors. Then the influence of the number of cells on the global dynamics is studied, with particular reference to the occurrence of hyperchaotic behaviour. Copyright © 2006 John Wiley & Sons, Ltd. [source] Uncertainties in central England temperature 1878,2003 and some improvements to the maximum and minimum seriesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2005David Parker Abstract We assess the random and systematic uncertainties affecting the central England temperature (CET) record since 1878 on daily, monthly and annual time scales. The largest contribution to uncertainty in CET on all these time scales arises from areal sampling, followed for annual and monthly CET by thermometer calibration. For the daily series, random thermometer precision and screen errors are the second largest source of uncertainty. Annual CETs are least uncertain, whereas daily CETs are most uncertain. Despite the uncertainties in annual mean CET, the trend of 0.077 °C per decade since 1900 is significant at the 1% level. In an additional investigation, we detect biases in the published series of central England maximum and minimum temperatures, and implement systematic adjustments of up to ±0.2 °C to the values up to 1921 and up to ±0.1 °C to the values since 1980. These adjustments are of opposite sign in maximum and minimum temperature, so they do not affect mean CET, but they improve the homogeneity of the diurnal temperature range, which then shows little trend before 1980 and a reduced rising trend thereafter. The uncertainties in maximum and minimum temperature make the data inadequate for the task of establishing the magnitude of the recent increase of diurnal range. © Crown Copyright 2005. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd. [source] The spatial and temporal behaviour of the lower stratospheric temperature over the Southern Hemisphere: the MSU view.INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2001Part II: spatial behaviour Abstract Monthly lower stratosphere temperature anomalies in a layer centred about 70 hPa, from the MSU data set are analysed for the period 1979,1997. T-mode approach principal component analysis (PCA) is used in order to obtain the leading spatial anomaly patterns and their sequences of occurrence throughout the period under study. Five principal components (PCs) are significantly different from the spatial distribution of noisy data. The patterns given by the PC scores represent ten typical spatial anomaly patterns: five correspond to the direct mode, that is to say anomaly fields with the same sign as the PC score patterns, and five have the opposite sign. The first three PCs represent simple spatial temperature anomaly distributions, with zonal wave 0 to wave 2 wave structures. The following significant PCs, orders four and five, display a more complex spatial behaviour, with wave 3 wave structures. The first two PC's frequency distribution in time, given by the PC loadings time series, do not show noticeable changes throughout the period analysed. The remaining three PCs show changes in their frequency of occurrence that might be associated with the negative trends in the lower stratosphere temperature, as well as to the other different features observed in the real temperature anomaly time series for the grid points in the Southern Hemisphere. The latter are studied with the PCA in the S-mode approach in the companion paper (Compagnucci et al., 2001. International Journal of Climatology21: 419,437). Copyright © 2001 Royal Meteorological Society [source] Census error and the detection of density dependenceJOURNAL OF ANIMAL ECOLOGY, Issue 4 2006ROBERT P. FRECKLETON Summary 1Studies aiming to identify the prevalence and nature of density dependence in ecological populations have often used statistical analysis of ecological time-series of population counts. Such time-series are also being used increasingly to parameterize models that may be used in population management. 2If time-series contain measurement errors, tests that rely on detecting a negative relationship between log population change and population size are biased and prone to spuriously detecting density dependence (Type I error). This is because the measurement error in density for a given year appears in the corresponding change in population density, with equal magnitude but opposite sign. 3This effect introduces bias that may invalidate comparisons of ecological data with density-independent time-series. Unless census error can be accounted for, time-series may appear to show strongly density-dependent dynamics, even though the density-dependent signal may in reality be weak or absent. 4We distinguish two forms of census error, both of which have serious consequences for detecting density dependence. 5First, estimates of population density are based rarely on exact counts, but on samples. Hence there exists sampling error, with the level of error depending on the method employed and the number of replicates on which the population estimate is based. 6Secondly, the group of organisms measured is often not a truly self-contained population, but part of a wider ecological population, defined in terms of location or behaviour. Consequently, the subpopulation studied may effectively be a sample of the population and spurious density dependence may be detected in the dynamics of a single subpopulation. In this case, density dependence is detected erroneously, even if numbers within the subpopulation are censused without sampling error. 7In order to illustrate how process variation and measurement error may be distinguished we review data sets (counts of numbers of birds by single observers) for which both census error and long-term variance in population density can be estimated. 8Tests for density dependence need to obviate the problem that measured population sizes are typically estimates rather than exact counts. It is possible that in some cases it may be possible to test for density dependence in the presence of unknown levels of census error, for example by uncovering nonlinearities in the density response. However, it seems likely that these may lack power compared with analyses that are able to explicitly include census error and we review some recently developed methods. [source] Chiral discrimination via nuclear magnetic shielding polarisabilities from NMR spectroscopy: Theoretical study of (Ra)-1,3-dimethylallene, (2R)-2-methyloxirane, and (2R)- N -methyloxaziridineJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2007R. Zanasi Abstract Three medium-size optically active molecules have been studied to make a guess at candidates suitable for chiral discrimination in an isotropic medium via nuclear magnetic resonance spectroscopy. The criterion for experimental detection is given by the magnitude of the isotropic part of nuclear magnetic shielding polarisability tensors, related to a pseudoscalar of opposite sign for the two enantiomers. The pseudoscalar shielding polarisability at the 17O nucleus in N -methyloxaziridine, calculated at the Hartree-Fock level, is ,7.8 ×10,17 mV,1. To obtain an experimentally observable magnetic field induced at the 17O nucleus in N -methyloxaziridine, electric fields as large as ,107,108 Vm,1 should be applied to the probe. The molecular electric dipole moment induced by precession of the magnetic dipole of the 17O nucleus in a magnetic field of 10 T is, in absolute value, ,8.8 × 10,42 Cm. The estimated rf-voltage at a resonance circuit is ,10 nV. Smaller values have been estimated for N, C, and H nuclei in 1,3-dimethylallene and 2-methyloxirane. © 2007 Wiley Periodicals, Inc. J Comput Chem 2007 [source] Enantioseparation of doubly functionalized polar norbornenes by HPLC and their ruthenium-catalyzed ring-opening metathesis polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2010Yasushi Nishihara Abstract Doubly fuctionalized polar norbornenes bearing the cyano and ester groups in 2,3-positions are synthesized and enantiomers are separated by high performance liquid chromatography (HPLC) with a chiral stationary phase. These optically active monomers are polymerized by ruthenium carbene catalysts, and high yields of the polymers were obtained. The chiral monomer bearing ethyl ester gave an optically active polymer of lower, but opposite sign of optical rotation (monomer [,]D = +61.0°, polymer [,]D = ,3.1°). The circular dichroism (CD) of the obtained chiral polymers gave a Cotton effect. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 485,491, 2010 [source] Propagation mechanisms for the Madden-Julian OscillationTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 569 2000Adrian J. Matthews Abstract The Madden-Julian Oscillation (MJO) is examined using 20-years of outgoing long-wave radiation and National Centers for Environmental Prediction/National Center for Atmospheric Research re-analysis data. Two mechanisms for the eastward propagation and regeneration of the convective anomalies are suggested. The first is a local mechanism operating over the warm-pool region. At the phase of the MJO with a dipole structure to the convection anomalies, there is enhanced tropical convection over the eastern Indian Ocean and reduced convection over the western Pacific. Over the equatorial western Indian Ocean, the equatorial Rossby wave response to the west of the enhanced convection includes a region of anomalous surface divergence associated with the anomalous surface westerlies and pressure ridge. This lends to suppress ascent in the boundary layer and shuts off the deep convection, eventually leading to a convective anomaly of the opposite sign. Over the Indonesian sector, the equatorial Kelvin wave response to the east of the enhanced convection includes a region of anomalous surface convergence into the anomalous equatorial surface easterlies and pressure trough, which will tend to favour convection in this region. The Indonesian sector is also influenced by an equatorial Rossby wave response (of opposite sign) to the west of die reduced convection over the western Pacific, which also has a region of anomalous surface convergence associated with its anomalous equatorial surface easterlies and pressure trough. Hence, convective anomalies of either sign tend to erode themselves from the west and initiate a convective anomaly of opposite sign via their equatorial Rossby wave response, and expand to the east via their equatorial Kelvin wave response. The second mechanism is global, involving an anomaly completing a circuit of the equator. Enhanced convection over the tropical western Pacific excites a negative mean-sea-level pressure (m.s.l.p.) anomaly which radiates rapidly eastward as a dry equatorial Kelvin wave at approximately 35 m s,1 over the eastern Pacific. It is blocked by the orographic barrier of the Andes and Central America for several days before propagating through the gap at Panama. After rapidly propagating as a dry equatorial Kelvin wave over the Atlantic, the m.s.l.p. anomaly is delayed further by the East African Highlands before it reaches the Indian Ocean and coincides with the development of enhanced convection at the start of the next MJO cycle. [source] Synthesis and characterization of novel chiral ionic liquids and investigation of their enantiomeric recognition propertiesCHIRALITY, Issue 2 2008David K. Bwambok Abstract We report the synthesis and characterization of amino acid ester based chiral ionic liquids, derived from L - and D -alanine tert butyl ester chloride. The synthesis was accomplished via an anion metathesis reaction between commercially available L - and D -alanine tert butyl ester chloride using a variety of counterions such as lithium bis (trifluoromethane) sulfonimide, silver nitrate, silver lactate, and silver tetrafluoroborate. Both enantiomeric forms were obtained as confirmed by bands of opposite sign in the circular dichroism spectra. The L - and D -alanine tert butyl ester bis (trifluoromethane) sulfonimide were obtained as liquids at room temperature and intriguingly exhibited the highest thermal stability (up to 263°C). In addition, the ionic liquids demonstrated enantiomeric recognition ability as evidenced by splitting of racemic Mosher's sodium salt signal using a liquid state 19F nuclear magnetic resonance (NMR) and fluorescence spectroscopy. The L - and D -alanine tert butyl ester chloride resulted in solid salts with nitrate, lactate, and tetrafluoroborate anions. This illustrates the previously observed tunability of ionic liquid synthesis, resulting in ionic liquids of varying properties as a function of varying the anion. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] Measurement of circular birefringence and circular dichroism of the single crystals of ,-(+)589 - and ,-(,)589 -tris(ethylenediamine)cobalt(III) triiodide monohydrate by the extended HAUP methodCHIRALITY, Issue 5 2004Ryo Matsuki Abstract We have achieved measuring four optical parameters simultaneously, namely, linear birefringence (LB), circular birefringence (CB), linear dichroism (LD), and circular dichroism (CD), of single crystals of ,-(+)589 - and ,-(,)589 -tris(ethylenediamine) cobalt(III) triiodide monohydrate (1) along the <001> plane at the fixed wavelength (514.5 nm). Such measurements are possible only when the High Accuracy Universal Polarimeter (HAUP) is employed; it is called the extended HAUP method. Our experimental results showed that both LB and LD of the ,-(+)589 -(1) crystal have the same magnitude as those of the ,-(,)589 -(1) crystal. It was also revealed for the first time that the CB data of crystals of ,-(+)589 -(1) and ,-(,)589 -(1) are almost of the same magnitude, but are of opposite sign, reflecting their opposite absolute configurations. On the other hand, although the CD data obtained for ,-(+)589 -(1) is almost three times larger than that for ,-(,)589 -(1,) these CD data are also opposite in sign, as expected from the opposite chirality of crystals. Chirality 16:286,293, 2004. © 2004 Wiley-Liss, Inc. [source] Spring phenology in boreal Eurasia over a nearly century time scaleGLOBAL CHANGE BIOLOGY, Issue 3 2008NICOLAS DELBART Abstract It has been widely reported that tree leaves have tended to appear earlier in many regions of the northern hemisphere in the last few decades, reflecting climate warming. Satellite observations revealed an 8-day advance in leaf appearance date between 1982 and 1991 in northern latitudes. In situ observations show that leaf appearance dates in Europe have advanced by an average of 6.3 days from 1959 to 1996. Modelling of leaf appearance on the basis of temperature also shows a marked advance in temperate and boreal regions from 1955 to 2002. However, before 1955, reported studies of phenological variations are restricted to local scale. Modelling, ground observations and satellite observations are here combined to analyse phenological variations in Eurasian taiga over nearly a century. The trend observed by remote sensing consists mainly in a shift at the end of the 1980s, reflecting a shift in winter and spring temperature. In western boreal Eurasia, a trend to earlier leaf appearance is evident since the mid-1930s, although it is discontinuous. In contrast, the strong advance in leaf appearance detected over Central Siberia using satellite data in 1982,1991 is strengthened by late springs in 1983,1984; moreover, in this region the green-up timing has displayed successive trends with opposite signs since 1920. Thus, such strong trend is not unusual if considered locally. However, the recent advance is unique in simultaneously affecting most of the Eurasian taiga, the leaf appearance dates after 1990 being the earliest in nearly a century in most of the area. [source] A comparison of tropical temperature trends with model predictionsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2008David H. Douglass Abstract We examine tropospheric temperature trends of 67 runs from 22 ,Climate of the 20th Century' model simulations and try to reconcile them with the best available updated observations (in the tropics during the satellite era). Model results and observed temperature trends are in disagreement in most of the tropical troposphere, being separated by more than twice the uncertainty of the model mean. In layers near 5 km, the modelled trend is 100 to 300% higher than observed, and, above 8 km, modelled and observed trends have opposite signs. These conclusions contrast strongly with those of recent publications based on essentially the same data. Copyright © 2007 Royal Meteorological Society [source] An improved method of constructing a database of monthly climate observations and associated high-resolution gridsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2005Timothy D. Mitchell Abstract A database of monthly climate observations from meteorological stations is constructed. The database includes six climate elements and extends over the global land surface. The database is checked for inhomogeneities in the station records using an automated method that refines previous methods by using incomplete and partially overlapping records and by detecting inhomogeneities with opposite signs in different seasons. The method includes the development of reference series using neighbouring stations. Information from different sources about a single station may be combined, even without an overlapping period, using a reference series. Thus, a longer station record may be obtained and fragmentation of records reduced. The reference series also enables 1961,90 normals to be calculated for a larger proportion of stations. The station anomalies are interpolated onto a 0.5° grid covering the global land surface (excluding Antarctica) and combined with a published normal from 1961,90. Thus, climate grids are constructed for nine climate variables (temperature, diurnal temperature range, daily minimum and maximum temperatures, precipitation, wet-day frequency, frost-day frequency, vapour pressure, and cloud cover) for the period 1901,2002. This dataset is known as CRU TS 2.1 and is publicly available (http://www.cru.uea.ac.uk/). Copyright © 2005 Royal Meteorological Society [source] Estimating Olympic-related investment and expenditureINTERNATIONAL JOURNAL OF TOURISM RESEARCH, Issue 4 2009ShiNa Li Abstract The analysis of the impact of mega events has included frameworks that evaluate different impacts under different criteria, for example, separating impacts according to whether they occur before, during or after the event itself. Analysis of the economic impacts of such events has shown that the distributional effects between the host city and the rest of an economy can be important, and can have opposite signs. This paper introduces frameworks to show the origin of the economic scale, that is, Olympic-related investment and expenditure, and shows how the frameworks can be used with reference to the Beijing 2008 Olympics. Copyright © 2008 John Wiley & Sons, Ltd. [source] Microwave Dielectric Properties of Ba3(VO4)2,Mg2SiO4 Composite CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Siqin Meng Novel Ba3(VO4)2,Mg2SiO4 microwave dielectric composite ceramics with compositions of (1,x)Ba3(VO4)2,xMg2SiO4 (x=0.50,0.65) have been prepared by firing mixtures of Ba3(VO4)2 and Mg2SiO4. X-ray diffraction and scanning electron microscopy analysis revealed that they coexist without forming secondary phases. Because their resonant frequency temperature coefficients (,f) have opposite signs, the ,f of the composite ceramic can be adjusted passing through zero by changing the relative content of the two phases. Dielectric property measurements were performed using the resonator method at around 11 GHz. Ceramics with Mg2SiO4 55 wt% sintered at 1175°C exhibited microwave dielectric properties of dielectric constant ,r=9.03, Q×f=52 500 GHz, and ,f=0.6 ppm/°C at 11.3 GHz. In this composite ceramic, we observed that the formation of the MgSiO3 secondary phase was suppressed. [source] Mode-locked Yb-doped large-mode-area photonic crystal fiber laser operating in the vicinity of zero cavity dispersionLASER PHYSICS LETTERS, Issue 3 2010Y.-J. Song Abstract A passively mode-locked ytterbium-doped largemode-area photonic crystal fiber oscillator operating in the vicinity of zero cavity dispersion is demonstrated. The self-starting mode-locking operation is achieved by a high contrast saturable absorber mirror. Two mode-locking regimes with opposite signs of net cavity dispersion are investigated. At a net cavity dispersion of ,0.0035 ps2, the fiber laser directly generates 10-nJ laser pulses with an average power of 630 mW at 65.3 MHz repetition rate. The pulses can be dechirped to 78 fs by extracavity dispersion compensation. The pulse energy is scaled up to 18 nJ, yielding an average power of 1.2 W, when the cavity dispersion is set at 0.0035 ps2. In this regime, the laser output can be extracavitydechirped to 120 fs. Dynamics of pulse evolution in the fiber laser is illustrated by numerical simulation, which agrees well with experimental results. (© 2010 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] NMR-based analysis of structure of heteroleptic triple-decker (phthalocyaninato) (porphyrinato) lanthanides in solutionsMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2010Kirill P. Birin Abstract A novel approach for the structural analysis of heteroleptic triple-decker (porphyrinato)(phthalocyaninato) lanthanides(III) in solutions is developed. The developed approach consists in molecular mechanics (MM+) optimization of the geometry of the complex taking into account the lanthanide-induced shift (LIS) datasets. LISs of the resonance peaks in 1H NMR spectra of a series of symmetric complexes [An4P]Ln[(15C5)4Pc]Ln[An4P], where An4P2, is 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrinato-dianion, [(15C5)4Pc]2, is 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninato-dianion and Ln = La, Ce, Pr, Nd, Sm, Eu, are analyzed. Analysis of LISs showed two sets of protons in the molecule with opposite signs of shift. Two-nuclei analysis of LISs testifies isostructurality of the whole series of investigated complexes in solution despite contraction of the lanthanide ions. Model-free separation of contact and dipolar contributions of LISs was performed with one-nucleus technique and did not show changes in contact and dipolar terms within the investigated series. MM+ optimization of the molecular structure allowed the interpretation of features of LIS for each particular group of protons. Parameterization of MM + -optimized model of molecule with values of structure-dependent dipolar contributions of LIS allows the development of the precise structural model of the triple-decker complex in solution. This approach allows the determination of the geometry and structure of the sandwich macrocyclic tetrapyrrolic complexes together with conformational analysis of flexible peripheral substituents in solutions. The developed method can be applied with minor modifications for the determination of structural parameters of other types of lanthanides(III) complexes with tetrapyrrolic ligands and also supramolecular systems based on them. Copyright © 2010 John Wiley & Sons, Ltd. [source] 29Si,13C spin,spin couplings over Si,O,Carom linkMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2006Jan Sýkora Abstract 29Si,13C couplings were measured in para substituted silylated phenols, XC6H4OSiR1R2R3(X 2, CF3, Cl, F, H, CH3, CH3O). The SiR1R2R3 silyl groups included trimethylsilyl (Si(CH3)3, TMS), tert- butyldimethylsilyl (Si(CH3)2C(CH3)3, TBDMS), dimethylsilyl (SiH(CH3)2, DMS), and tert- butyldiphenylsilyl (Si(C6H5)2C(CH3)3, TBDPS). Previously developed (Si,C,Si)gHMQC methods and narrow 29Si lines allowed the determination of coupling constants over up to five bonds. Besides the number of intervening bonds between the silicon and carbon atoms, all the measurable couplings depend also on the nature of the substituents on the silicon. The two- and three-bond couplings are not affected by ring substitution in the para position. These properties render the 29Si,13C couplings suitable for line assignment in the spectra of silylated polyphenols. The experimental results are in reasonable agreement with theoretical calculations. The calculations show, in agreement with the data reported in the literature for couplings between other nuclei, that the two-bond and three-bond couplings, which are of similar magnitudes, are of opposite signs. If the signs of these geminal and vicinal couplings could be determined experimentally, they would greatly facilitate the line assignment. The four- and five-bond couplings are affected by the substituent X in a nontrivial manner. Copyright © 2006 John Wiley & Sons, Ltd. [source] The impact of skewness in the hedging decisionTHE JOURNAL OF FUTURES MARKETS, Issue 5 2006Scott Gilbert The impact of skewness in the hedger's objective function is tested using a model of hedging derived from a third-order Taylor Series approximation of expected utility. To determine the effect of price skewness upon hedging and speculation, analytical results are derived using an example of cotton storage. Findings suggest that when forward risk premiums and price skewness in the spot asset have opposite signs, speculation increases relative to the mean-variance model. When the signs are identical, speculation will decrease, contradicting findings of mean-variance models. © 2006 Wiley Periodicals, Inc. Jrl Fut Mark 26:503,520, 2006 [source] Productivity Spillovers from FDI in Malaysian Manufacturing: Evidence from Micro-panel Data,ASIAN ECONOMIC JOURNAL, Issue 2 2009Noor Aini Khalifah C23; F23; L6 Using an establishment-level panel dataset for the Malaysian manufacturing industries for 2000,2004, we argue that differences in the proxies and degrees of foreign shareholdings in measuring foreign presence lead to opposite signs and/or significance of spillover effects. The results show significant evidence of positive productivity spillovers to local establishments in the same industry, based on a broad measure of foreign presence. However, there is no evidence of positive spillover when employment share is used as a proxy for foreign presence. Furthermore, significant negative spillover effects are related to higher employment shares of wholly foreign-owned establishments. Although there is no significant difference in labor productivity between wholly foreign-owned and locally-owned establishments, both majority and minority foreign-owned establishments have significantly lower levels of labor productivity than locally-owned establishments in Malaysia. [source] | |||||||||||||||||||||||||