Home About us Contact
|
Home About us Contact | ||
|
|
||
Simple Scheme (simple + scheme)
Selected AbstractsHydrological regime analysis of the Selenge River basin, MongoliaHYDROLOGICAL PROCESSES, Issue 14 2003X. Ma Abstract Arid and semi-arid regions are very vulnerable to environmental changes. Climate change studies indicate that the environment in such areas will steadily deteriorate with global warming; inland lakes will shrink and desert areas will expand. Mongolia is a landlocked country in north-central Asia that contains a unique ecological system consisting of taiga, steppe, and desert from north to south. The Selenge River basin (280 000 km2) in northern Mongolia is a semi-arid region underlain by permafrost, between latitudes 46 and 52°N, and longitudes 96 and 109°E. The issue of sustainable development of the basin is very important owing to its limited natural resources, including fresh water, forest, and rangeland. To examine the water cycle processes in the basin, a hydrological analysis was carried out using a simple scheme for the interaction between the land surface and atmosphere (big-leaf model) coupled to a hydrological model for the period 1988,92 to estimate the hydrological regime of the basin. Annual precipitation in this period averaged 298 mm, ranging from 212 to 352 mm at a 1 ° × 1 ° resolution based on data from 10 gauges, and the estimated annual evapotranspiration averaged 241 mm, ranging between 153 and 300 mm. This indicates that evapotranspiration accounts for the overwhelming majority of the annual precipitation, averaging 81% and ranging between 64 and 96%. The annual potential evapotranspiration in the basin averaged 2009 mm; the ratio of evapotranspiration (actual to potential evapotranspiration) was 0·12 and the wetness index (annual precipitation to potential evapotranspiration) was 0·15. Copyright © 2003 John Wiley & Sons, Ltd. [source] Simulating pan-Arctic runoff with a macro-scale terrestrial water balance modelHYDROLOGICAL PROCESSES, Issue 13 2003Michael A. Rawlins Abstract A terrestrial hydrological model, developed to simulate the high-latitude water cycle, is described, along with comparisons with observed data across the pan-Arctic drainage basin. Gridded fields of plant rooting depth, soil characteristics (texture, organic content), vegetation, and daily time series of precipitation and air temperature provide the primary inputs used to derive simulated runoff at a grid resolution of 25 km across the pan-Arctic. The pan-Arctic water balance model (P/WBM) includes a simple scheme for simulating daily changes in soil frozen and liquid water amounts, with the thaw,freeze model (TFM) driven by air temperature, modelled soil moisture content, and physiographic data. Climate time series (precipitation and air temperature) are from the National Centers for Environmental Prediction (NCEP) reanalysis project for the period 1980,2001. P/WBM-generated maximum summer active-layer thickness estimates differ from a set of observed data by an average of 12 cm at 27 sites in Alaska, with many of the differences within the variability (1,) seen in field samples. Simulated long-term annual runoffs are in the range 100 to 400 mm year,1. The highest runoffs are found across northeastern Canada, southern Alaska, and Norway, and lower estimates are noted along the highest latitudes of the terrestrial Arctic in North America and Asia. Good agreement exists between simulated and observed long-term seasonal (winter, spring, summer,fall) runoff to the ten Arctic sea basins (r = 0·84). Model water budgets are most sensitive to changes in precipitation and air temperature, whereas less affect is noted when other model parameters are altered. Increasing daily precipitation by 25% amplifies annual runoff by 50 to 80% for the largest Arctic drainage basins. Ignoring soil ice by eliminating the TFM sub-model leads to runoffs that are 7 to 27% lower than the control run. The results of these model sensitivity experiments, along with other uncertainties in both observed validation data and model inputs, emphasize the need to develop improved spatial data sets of key geophysical quantities (particularly climate time series) to estimate terrestrial Arctic hydrological budgets better. Copyright © 2003 John Wiley & Sons, Ltd. [source] The direct simulation Monte Carlo method using unstructured adaptive mesh and its applicationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2002J.-S. Wu Abstract The implementation of an adaptive mesh-embedding (h-refinement) scheme using unstructured grid in two-dimensional direct simulation Monte Carlo (DSMC) method is reported. In this technique, local isotropic refinement is used to introduce new mesh where the local cell Knudsen number is less than some preset value. This simple scheme, however, has several severe consequences affecting the performance of the DSMC method. Thus, we have applied a technique to remove the hanging node, by introducing the an-isotropic refinement in the interfacial cells between refined and non-refined cells. Not only does this remedy increase a negligible amount of work, but it also removes all the difficulties presented in the originals scheme. We have tested the proposed scheme for argon gas in a high-speed driven cavity flow. The results show an improved flow resolution as compared with that of un-adaptive mesh. Finally, we have used triangular adaptive mesh to compute a near-continuum gas flow, a hypersonic flow over a cylinder. The results show fairly good agreement with previous studies. In summary, the proposed simple mesh adaptation is very useful in computing rarefied gas flows, which involve both complicated geometry and highly non-uniform density variations throughout the flow field. Copyright © 2002 John Wiley & Sons, Ltd. [source] Comparative study of unscreened and screened molecular static linear polarizability in the Hartree,Fock, hybrid-density functional, and density functional modelsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2008Rajendra R. Zope Abstract The sum-over-states (SOS) polarizabilities are calculated within approximate mean-field electron theories such as the Hartree,Fock approximation and density functional models using the eigenvalues and orbitals obtained from the self-consistent solution of the single-particle equations. The SOS polarizabilities are then compared with those calculated using the finite-field (FF) method. Three widely used mean-field models are as follows: (1) the Hartree,Fock (HF) method, (2) the three parameter hybrid generalized gradient approximation (GGA) (B3LYP), and (3) the parameter-free generalized gradient approximation due to Perdew,Burke,Ernzerhof (PBE). The comparison is carried out for polarizabilities of 142 molecules calculated using the 6-311++G(d,p) basis set at the geometries optimized at the B3LYP/6-311G** level. The results show that the SOS method almost always overestimates the FF polarizabilities in the PBE and B3LYP models. This trend is reversed in the HF method. A few exceptions to these trends are found. The mean absolute errors (MAE) in the screened (FF) and unscreened (SOS) polarizability are 0.78, 1.87, and 3.44 Å3 for the HF, B3LYP, and PBE-GGA methods, respectively. Finally, a simple scheme is devised to obtain FF quality polarizability from the SOS polarizability. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Integrated polymerase chain reaction-based procedures for the detection and identification of species and subspecies of the Gram-positive bacterial genus LactococcusJOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2002Z.Y. Pu Aims:,Five species of the Gram-positive bacterial genus Lactococcus (Lactococcus lactis, L. garvieae, L. plantarum, L. piscium and L. raffinolactis) are currently recognized. The aim of this work was to develop a simple approach for the identification of these species, as well as to differentiate the industrially important dairy subspecies L. lactis subsp. lactis and L. lactis subsp. cremoris. Methods and Results:,Methods were devised based on specific polymerase chain reaction (PCR) amplifications that exploit differences in the sequences of the 16S ribosomal RNA genes of each species, followed by restriction enzyme cleavage of the PCR products. The techniques developed were used to characterize industrial cheese starter strains of L. lactis and the results were compared with biochemical phenotype and DNA sequence data. Conclusions:,The PCR primers designed can be used simultaneously, providing a simple scheme for screening unknown isolates. Strains of L. lactis show heterogeneity in the 16S ribosomal RNA gene sequence. Significance and Impact of the Study:,This work provides an integrated set of methods for differentiation and identification of lactococcal species associated with agricultural, veterinary, medical and processed food industries. [source] A unified model for the evolution of galaxies and quasarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2000Guinevere Kauffmann We incorporate a simple scheme for the growth of supermassive black holes into semi-analytic models that follow the formation and evolution of galaxies in a cold dark matter-dominated Universe. We assume that supermassive black holes are formed and fuelled during major mergers. If two galaxies of comparable mass merge, their central black holes coalesce and a few per cent of the gas in the merger remnant is accreted by the new black hole over a time-scale of a few times 107 yr. With these simple assumptions, our model not only fits many aspects of the observed evolution of galaxies, but also reproduces quantitatively the observed relation between bulge luminosity and black hole mass in nearby galaxies, the strong evolution of the quasar population with redshift, and the relation between the luminosities of nearby quasars and those of their host galaxies. The strong decline in the number density of quasars from z,2 to z=0 is a result of the combination of three effects: (i) a decrease in the merging rate; (ii) a decrease in the amount of cold gas available to fuel black holes, and (iii) an increase in the time-scale for gas accretion. The predicted decline in the total content of cold gas in galaxies is consistent with that inferred from observations of damped Ly, systems. Our results strongly suggest that the evolution of supermassive black holes, quasars and starburst galaxies is inextricably linked to the hierarchical build-up of galaxies. [source] Anionic and ionic coordinative polymerization of ,-caprolactonePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2001Dr Cristina Stere Abstract The polymerization of ,-caprolactone initiated by two catalyst systems was studied: (1) carbazole-potassium in the presence of 18-crown-6 ether and (2) NdCl3/TBP/TIBA (neodymiumtrichloride/tri-n-butyl-phosphate/triisobutylaluminium) at the molar ratio 1/3/1. For both initiator systems conversion/time plots were determined and the polymers were characterized by IR, GPC and by 1H - and 13C,NMR spectroscopy. Polyesters with the highest molecular weight (Mn,44 000 g/mol) were obtained for the polymerizations initiated by the carbazole-potassium/18-crown-6 ether system. The features of the polymerization initiated by the carbazole-potassium/18-crown-6 ether system are discussed on the basis of a simple scheme. The nature of this polymerization is non-living. Copyright © 2000 John Wiley & Sons, Ltd. [source] Mountain torques and synoptic systems in the MediterraneanTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 634 2008Joseph Egger Abstract The mountains surrounding the Mediterranean exert torques T during the passage of North Atlantic systems which affect the angular momentum of the airflow passing over and around the massifs. The Alps, the Atlas range and the orographic block of Asia Minor are selected to investigate the typical flow conditions during torque events. These mountain ranges are small enough to justify a local angular momentum analysis. Both the zonal and the meridional components of a mountain's torque (T, and T,) are used as stratification parameters in a statistical investigation of the interaction of large-scale perturbations with this mountain. How are these flows affected by the obstacle? A simple scheme is tested which attempts to interpret results. The torque analysis singles out eastward-moving large-scale systems. Their isobars are oriented from southwest (northwest) to northeast (southeast) near the mountain in zonal torque T, (T,) cases. The massifs tend to generate a low-level distortion of the pressure field such that the angular momentum of the flow over the mountain is reduced. These results can be explained within the framework of the scheme. The influence of the mountains on the pressure field is seen only at heights ,4000 m. The low-level distortions of the pressure field contribute positively to the total torque for lags ,,0 in the Alps and for all lags , 2,,,2 days in Asia Minor, where only T, is evaluated. The impact of the Atlas mountains is seen only at , = 0. Copyright © 2008 Royal Meteorological Society [source] Two Typical Examples of Scaling Ionic Partition Scheme for Estimating Correlation Energy of A2 Type MoleculesCHINESE JOURNAL OF CHEMISTRY, Issue 4 2004Shu-Ping Zhuo Abstract Based on the calculation results of pair correlation energy contributions of the various electron pairs in Naz and H2NNH2 systems and the application of the scaling ionic partition scheme for symmetrical A2 type systems, the total correlation energies of Na2 and H2NNH2 have been reproduced by using this simple scheme. The two results show that the absolute deviations are within an acceptable range of mr, however, in this way, more than 90% of computational work can be. saved. The most attractive result in present paper is that, in these two molecules the coefficients c1 and c2 in the estimation equation can be obtained by the proportion of correlation energy of A, to that of A+ singlet system. Therefore, it is believed that the proposed ionic partition scheme for symmetrical A2 molecules would be very useful to estimate the correlation energies of large symmetrical molecules. [source] | |||||||||||||