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  • 1
    Electronic Resource
    Electronic Resource
    Pattern formation and morphogenesis: A reaction-diffusion model (1986)
    Springer
    Bulletin of mathematical biology 48 (1986), S. 213-228 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The problem of cellular differentiation and consequent pattern generation during embryonic development has been mathematically investigated with the help of a reaction-diffusion model. It is by now a well-recognized fact that diffusion of micromolecules (through intercellular gap junctions), which is dependent on the spatial parameter (r), serve the purpose of ‘positional information’ for differentiation. Based on this principle the present model has been constructed by coupling the Goodwin-type equations for RNA and protein synthesis with the diffusion process. The homogeneous Goodwin system can exhibit stable periodic solution if the value of the cooperativity as measured by the Hill coefficient (ρ) is greater than 8, which is not biologically realistic. In the present work it has been observed that inclusion of a negative cross-diffusion can drive the system into local instability for any value of ρ and thus a time-periodic spatial solution is possible around the unstable local equilibrium, eventually leading to a definite pattern formation. Inclusion of a negative cross-diffusion thus makes the system biologically realistic. The cross-diffusion can also give rise to a stationary wave-like dissipative structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02460024
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  • 2
    Electronic Resource
    Electronic Resource
    Crystal and molecular structure of diaqua-bis-(3,5-dimethyl-1-guanyl pyrazole) nickel (II) nitrate, [Ni(C6N4H10)2(H2O)2](N03)2 (1989)
    Springer
    Journal of chemical crystallography 19 (1989), S. 71-76 
    Details
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in space groupP21/n witha=10.651(3),b=11.082(2),c=8.993(3) Å,β=106.79(3)°;R=0.064 andR w=0.074 for 3399 observed reflections (I≥3σ(I)) from 3674 measured. The structure was solved by direct methods and refined by least squares. The Ni atom of the complex is located at a center of inversion, and is surrounded by four nitrogen atoms of the two ligands in square-planar geometry. The oxygen atoms of the two centrosymmetrically related water molecules complete the coordination around the metal ion to form an elongated octahedron.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01160844
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  • 3
    Electronic Resource
    Electronic Resource
    Nuclear magnetic resonance VI. Some quantitative applications of carbon-13 NMR spectroscopy to phenylindoles (1996)
    Springer
    Monatshefte für Chemie 127 (1996), S. 111-116 
    Details
    ISSN: 1434-4475
    Keywords: Phenylindoles ; Quantitative13C NMR ; Chromium(III) acetylacetonate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Anzahl der durch jedes Signal der Phenylindole1,4 und5 repräsentierten Kohlenstoffatome wird durch Integration der nach Zusatz von Chrom(III)acetonylacetat als Relaxationsreagens aufgenommenen13C-NMR-Spektren bestimmt. Ihre chemischen Verschiebungen werden eindeutig zugeordnet; die Literaturwerte für4 werden bestätigt. Durch eine vergleichende Untersuchung der13C-chemischen Verschiebungen von1,4 und5 können jene von2 und3 ebenfalls zugeordnet werden. Dieortho-Kohlenstoffe der Phenylgruppe von4 sind gegenüber denpara-Kohlenstoffatomen zu höherem Feld verschoben. Für die 2- und 3-Phenyl-Substituenten von1–3 und5 kehren sich die Verhältnisse um, wahrscheinlich wegen sterischer und/oder elektronischer Effekte der benachbarten Phenylgruppe.
    Notes: Summary The number of carbons represented by each signal of the phenylindoles1,4, and5 is measured quantitatively by integration of their13C NMR spectra, recorded after adding chromium(III) acetylacetonate to the sample solutions as a paramagnetic relaxation agent. Their carbon chemical shifts are assigned unambiguously; the literature assignments of4 are confirmed. By a comparative study of the carbon chemical shifts of1,4, and5, those of2 and3 are also assigned. Theortho carbons of the phenyl group of4 resonate upfield with respect to thepara carbon. Theortho carbons of the 2- and 3-phenyl moieties of1–3 and5, however, are found to absorb downfield from the correspondingpara carbons, probably because of steric and/or electronic effects exerted by their neighbouring phenyl group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807416
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  • 4
    Electronic Resource
    Electronic Resource
    Experimental study of flow past a square cylinder at high Reynolds numbers (2000)
    Springer
    Experiments in fluids 29 (2000), S. 553-563 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Measurements of two-components of velocity in the wake of a square cylinder using a hot-wire anemometer are reported. Two Reynolds numbers, namely 8700 and 17,625, have been considered. The measurements were carried out in a low-speed, low-turbulence wind tunnel. Benchmark experiments at much lower Reynolds numbers show good agreement between the present experiments and published results. At higher Reynolds numbers, the experimental data reveal anticipated trends in terms of wake recovery and turbulence decay. Both velocity and velocity fluctuations show symmetry about the wake axis. The experimental data have been compared with the large eddy simulation (LES) calculation reported by Wang et al. [University of Illinois at Urbana – Champaign (1996) Report CFD 96-03] and LDV measurements of Lyn et al. [J Fluid Mech (1995) 304: 285–319]. The agreement among the three sets is generally acceptable in terms of the time-averaged velocity components, but not the velocity fluctuations. The turbulence fluctuations in the present experiments are seen to be lower than in the referred work. The differences have been traced to factors such as the aspect ratio, blockage ratio and upstream turbulence. Experiments with increased upstream turbulence did show a reduction in the discrepancy between the present experiments and the published data. An assessment of the experimental data in terms of physical mechanisms revealed that (a) streamwise normal stresses were correlated with the vortex centers, and (b) the turbulence kinetic energy profiles are similar to the turbulence shear stress. Spectral analysis of the velocity signals was carried out in the present work. Energy transfer from the mean flow to the streamwise velocity fluctuation was confirmed in the near wake. A redistribution of the kinetic energy between the streamwise and transverse components of velocity over a longer distance downstream was subsequently observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480000123
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  • 5
    Electronic Resource
    Electronic Resource
    Stability of metal ion complexes formed with methyl phosphate and hydrogen phosphate (1996)
    Springer
    JBIC 1 (1996), S. 231-238 
    Details
    ISSN: 1432-1327
    Keywords: Key words Equilibrium constants ; Hydrogen phosphate ; Metal ion complexes ; Methyl phosphate ; Phosphate monoesters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The acidity constants of methyl phosphoric acid, CH3OPO(OH)2, and orthophosphoric acid, HOPO(OH)2, and the stability constants of the 1 : 1 complexes formed between Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, or Cd2+ and methyl phosphate, CH3OPO3 2–, or hydrogen phosphate, HOPO3 2–, were determined by potentiometric pH titration in aqueous solution (25  °C;I = 0.1 M, NaNO3). On the basis of previously established log K versus pK a straight-line plots for the complexes of simple phosphate monoesters and phosphonate derivatives, R-PO3 2–, where R is a noncoordinating residue, it is shown that the stability of the M(CH3OPO3) complexes is solely determined (as one might expect) by the basicity of the –PO3 2– residue. It is emphasized that the mentioned reference lines may also be used to reveal increased complex stabilities, for example, for certain complexes formed with 8-quinolyl phosphate the occurrence of 7-membered chelates can be proven in this way; the same procedure is also applicable to complexes of nucleotides, etc. The M(HOPO3) complexes are slightly more stable (on average by 0.08 log unit) than it is expected from the basicity of HPO4 2–; this observation is attributed to a more effective solvation, including hydrogen bonding, than is possible with CH3OPO3 2– species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050048
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  • 6
    Electronic Resource
    Electronic Resource
    Some problems of interpreting the correlations between the modal variables in granitic rocks (1974)
    Springer
    Mathematical geology 6 (1974), S. 245-258 
    Details
    ISSN: 1573-8868
    Keywords: correlation between proportions ; petrology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Correlation coefficients of modal variables from several suites of granitic rocks have been calculated and tested for significance using the Chayes-Kruskal and Chayes methods. The results show that although Chayes' remaining-space transformation does, in general, weaken the original proportion correlations, the positive and low-negative original proportion correlations tend to increase in absolute value because of a tendency of positive increment of the covariance by such transformation. However, no satisfactory procedure for choosing the variable to be transformed (V2)could be determined, and testing of the significance of remaining-space correlations is found to be highly problematic. It is shown also that the Vistelius-Sarmanov procedure of calculation of correlation coefficients from closed-table data does not effectively eliminate the closure effect. It is concluded that assigning statistical significance to the correlation coefficients between modal variables is, in general, unsatisfactory, except where the number of variables ⩾8,the sample size is large (say, ⩾30),and there is no negative element in the variance vector of the corresponding open variables.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02082890
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  • 7
    Electronic Resource
    Electronic Resource
    Quantitative discrimination between magmatic units of the singhbhum granite (1971)
    Springer
    Mathematical geology 3 (1971), S. 123-133 
    Details
    ISSN: 1573-8868
    Keywords: cluster analysis ; distance functions ; mineralogy ; petrology ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The weight-percent values of four mineralogic variables (quartz, K feldspar, color index, and muscovite) for 10 sets of granitic rocks (20–50 samples in each set) from magmatic units of the Singhbhum granite were used for (1) computation of the Mahalanobis' generalized distance functions (D 2) between all pairs of the 10 sets, (2) testing significance of the difference between the multivariate means, and (3) computation of the linear discriminant functions between all possible pairs of the sets. The 10 data sets are for six magmatic units which belong to three successive but closely related phases of emplacement. The multivariate means for all sets are significantly different except for those between two of the sets of phase I. Cluster analysis on the basis of theD 2 values enables the 10 sets to be placed into four distinct groups. Group A includes two subgroups, one of which consists of two sets representing typical members of phase I; the other subgroup includes two sets which are typical of phase II. Group B includes two sets which are typical of phase III. The other four sets do not group with the typical representatives of the three phases, probably because of certain special conditions of their emplacement. A separate series ofD 2 computation from the same data, but excluding the color index, was unsuccessful in making the four aberrant sets group with the typical members of the respective phases. Efficient LDF's could be determined for discrimination between most pairs of the 10 sets of granite rocks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02045956
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  • 8
    Electronic Resource
    Electronic Resource
    A multivariate statistical study of copper mineralization in the central section of Mosaboni Mine, Eastern Singhbhum, India (1986)
    Springer
    Mathematical geology 18 (1986), S. 215-235 
    Details
    ISSN: 1573-8868
    Keywords: cluster analysis ; R-mode factor analysis ; copper mineralization ; Singhbhum Copper Belt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract A multivariate statistical analysis was carried out with log-transformed values of Cu, Ni, Co, Pb, Zn, Ag, Cr, Mn, Ca, and Sr in several sets of samples collected across the mineralized base metal zone in sheared soda granite, feldspathic schist, and chlorite schist from the central section of Mosaboni Mine of the famous Singhbhum Copper Belt of eastern India. Linear correlation coefficient matrices of two sets of ore samples (〉0.5% Cu)—one from levels 18 and 21 and the other from levels 25 and 28—indicate two well-defined and distinct clusters comprising Cu, Ni, Co, Pb, and Zn on one hand and Ca, Sr, and Mn on the other. Varimax-rotatedR-mode factor analysis of two above-noted sample sets, taken along with available geologic information, indicates that over 80% of the variability in data matrices for 9–10 elements can be accounted for by four distinct processes: (a) an early phase of copper mineralization which apparently replaced Mn, Ca, and Sr in the host rock; (b) a silicate-cum-oxide phase of crystallization/recrystallization of host rock; (c) remobilization of sulfide-forming ore elements (Cu, Ni, Co, Pb, and Zn); and (d) a phase of mineralization of Ag which appears to have replaced Cr, Ca and Cu. Process (c) was quantitatively most important. Factor score studies are suggestive of preferred introduction of Ni, Co, Pb, and Zn along central parts of preexisting copper-mineralized zones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00898284
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  • 9
    Electronic Resource
    Electronic Resource
    Tropospheric ozone profiles near equator and meteorological parameters (1987)
    Springer
    Journal of atmospheric chemistry 5 (1987), S. 243-253 
    Details
    ISSN: 1573-0662
    Keywords: Ozone profile ; tropospheric ; equatorial ; weather disturbances ; lightning ; water vapour incursion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract This is a study of ozone profile shapes in the 800 to 100 millibar range obtained with balloonsonde data over Trivandrum (8.5° N) during 1975–76 and possible associations of these shapes to some meteorological parameters. Whereas monotonic ozone profiles were noted with clear weather conditions, those associated with cloud cover show three basic anomalous features. Some bulges of increased values are observed in the range of 800 to 500 mb. In the 500–100 mb range, short range or localized cloud cover or passing weather disturbances are associated with fluctuation patterns in the ozone profile and an average depleted value of ozone. The fluctuations are also associated with changing wind speed and direction at these heights. Possible causative mechanisms are discussed. Lightning associated with thundestorm, producing additional CO and NO are sought to interpret the bulges at lower heights. The decrease in values as well as the fluctuation patterns are suggested as due to possible incursion of water vapour from troposphere to stratosphere in the tropical region and dynamical effects associated with it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00114105
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  • 10
    Electronic Resource
    Electronic Resource
    Strengthening of alumina by cerium-zirconate (Ce2Zr2O7) (2000)
    Springer
    Journal of materials science 35 (2000), S. 3931-3937 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Composite powders of Al2O3 and 0 to 30 vol% Ce2Zr2O7 are prepared by a hybrid sol-gel method using Al2O3 powders and a sol formed from Zr-alkoxide and cerium nitrate. All the Zr from the sol goes to form the cerium zirconate phase when the powders are calcined in N2. Pressureless sintering in air at 1500°C yields composites with high density (∼98%). Maximum values of fracture toughness and strength, 6.5 MPa $$\sqrt {\text{m}}$$ and 620 MPa respectively, (e.g. 3.5 MPa $$\sqrt {\text{m}}$$ and 350 MPa for pure Al2O3) are obtained in 10 vol% Ce2Zr2O7 composite sintered in air. The dominant mechanism for enhancement in K IC is believed to be crack bridging. Crack bridging activity in the 10 vol% composite is found to be maximum and extends upto ∼190 μm from the crack tip.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004849918509
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