Department of Chemistry
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Item Magnetic resonance lineshapes in powdered and amorphous systems(IAS, 1986-04) Sivasubramanian, S.C.A survey is made of the theory and applications ofEPR andNMR absorption lineshapes observed in powdered and amorphous materials. The ‘spin Hamiltonian’ and ‘resonance condition’ formalisms are reviewed, andepr andnmr lineshapes are discussed which typify the singularity characteristics in powdered materials. In the amorphous or ‘glassy’ state, the measurable spin resonance parameters often have to be viewed as being ‘randomly distributed’ according to a probability density function. Several recent probability-theory based approaches to lineshape computation for modelling the amorphous state are discussed.Item X-ray diffraction, electron paramagnetic resonance, and electron spin echo modulation studies of the lead oxide-lead chloride-cupric chloride ternary glass system(ACS, 1991-08-01) Sivasubramanian, S.C.X-ray diffraction, EPR, and ESEM studies are reported for a novel ternary glass 43PbO-56PbCl2-1 CuCl2. The X-ray PDF data lead to a structural model in which octahedral building units of Cu04Cl2 are predominant. EPR spectra of the glass at X and Q bands have been fitted, by line shape simulation, to the distributed spin Hamiltonian parameters g^rnean) = 2.34, = 0.03, gx(mean) = 2.06, ± = 0.008, p = 0.95, /4,(mean) = 131.1 X 10"4 cm"1, and /4x(mean) = 5.8 X 10"4 cm"1. These data suggest a distribution of bonding geometries for Cu2+ in the glass structure, with the above-mentioned elongated octahedral Cu04Cl2 dominating. ESEM results suggest that Cu2+ may be surrounded by four Pb2+ in the second coordination shell at a distance of 3.8 Á.Item X-ray diffraction, electron paramagnetic resonance, and electron spin echo modulation studies of the lead oxide-lead chloride-cupric chloride ternary glass system(ACS, 1991-08-01) Sivasubramanian, S.C.X-ray diffraction, EPR, and ESEM studies are reported for a novel ternary glass 43PbO-56PbCl2-1 CuCl2. The X-ray PDF data lead to a structural model in which octahedral building units of Cu04Cl2 are predominant. EPR spectra of the glass at X and Q bands have been fitted, by line shape simulation, to the distributed spin Hamiltonian parameters g^rnean) = 2.34, = 0.03, gx(mean) = 2.06, ± = 0.008, p = 0.95, /4,(mean) = 131.1 X 10"4 cm"1, and /4x(mean) = 5.8 X 10"4 cm"1. These data suggest a distribution of bonding geometries for Cu2+ in the glass structure, with the above-mentioned elongated octahedral Cu04Cl2 dominating. ESEM results suggest that Cu2+ may be surrounded by four Pb2+ in the second coordination shell at a distance of 3.8 ÁItem Principle of maximum hardness: an accurate ab initio study(ACS, 1993) Roy, Ram KinkarIn this paper we test the principle of maximum hardness through an accurate quantum chemical calculation. Computations include extensive correlation and relaxation effects for the calculation of ionization potential and electron affinity. The molecule water has been chosen as a primary test case.Item Correlation of Polarizability, Hardness, and Electronegativity: Polyatomic Molecules(ACS, 1994) Roy, Ram KinkarIn this paper, for the first time we have correlated the hardness (η), softness (s), and polarizability (P) with the electronegativity and the distortion (ΔR) of a single bond in a complex polyatomic system. The study also shows some interesting: trends as different types of bonds are distorted. We have suggested a new concept, "local bond hardness", in a complex polyatomic system. The molecules H2O, CH4, CH3Cl, and CH3F are chosen as primary test cases.Item Change of Hardness and Chemical Potential in Chemical Binding: A Quantitative Model(ACS, 1994) Roy, Ram KinkarIn this paper we relate the change of chemical hardness and potential with the binding energies as the chemical binding takes place. We use a simple model to demonstrate that the hardness change is not only related to the binding energy of the molecule being formed, but also to the binding energies of the corresponding molecular cations and anions. Similar expressions are also derived for chemical potential. We have shown that our analysis can explain the existing data. The separated limit values of hardness and chemical potential are also derived. Two demonstrative calculations on the molecules H2 and HF are presented. The future potential of this model is discussed.chemical potentialItem Change of Hardness and Chemical Potential in Chemical Binding: A Quantitative Model(ACS, 1994) Roy, Ram KinkarItem Stationary multideterminantal coupled-cluster response(APS, 1994-03-01) Roy, Ram KinkarWe discuss a stationary version of the coupled-cluster response theory using multideterminantal model space. This brings in all the attendant advantages of a stationary theory for quasidegenerate cases.Item Chemical Potential and Hardness for Open Shell Radicals: Model for the Corresponding Anions(ACS, 1995) Roy, Ram KinkarIn this article, we have obtained theoretical values of chemical potential and hardness for open shell free radicals using a wave function approach. The calculated values of the hardness are useful particularly for rank ordering of the corresponding anions. A ΔSCF procedure is used to obtain these values, and the results are compared with corresponding experimental values. The procedure also leads us to the reliability of the ΔSCF procedure for these quantities.Item Hardness as a function of polarizability in a reaction profile(Elsiever, 1995-02-10) Roy, Ram KinkarIn this article, for the first time, we have correlated chemical hardness with polarizability when a single bond in a complex polyatomic molecule is distorted. A predominantly linear relation has been observed between the cube root of polarizability and hardness when various types of bonds are distorted. The molecules CH3Cl, CH3F and CH4 are chosen as typical example systems.Item Multilayer perceptron in damage detection of bridge structures(Elsiever, 1995-02-17) Barai, Sudhir KumarRecent developments in artificial neural networks (ANN) have opened up new possibilities in the domain of structural engineering. For inverse problems like structural identification of large civil engineering structures such as bridges and buildings where the in situ measured data are expected to be imprecise and often incomplete, the ANN holds greater promise. The detection of structural damage and identification of damaged element in a large complex structure is a challenging task indeed. This paper presents an application of multilayer perceptron in the damage detection of steel bridge structures. The issues relating to the design of network and learning paradigm are addressed and network architectures have been developed with reference to trussed bridge structures. The training patterns are generated for multiple damaged zones in a structure and performance of the networks with one and two hidden layers are examined. It has been observed that the performance of the network with two hidden layers was better than that of a single-layer architecture in general. The engineering importance of the whole exercise is demonstrated from the fact that measured input at only a few locations in the structure is needed in the identification process using the ANN.Item Vibration Signature Analysis Using Artificial Neural Networks(ASCE, 1995-10) Barai, Sudhir KumarDamage detection by measuring and analyzing vibration signals in a machine component is an established procedure in mechanical and aerospace engineering. This paper presents vibration signature analysis of steel bridge structures in a nonconventional way using artificial neural networks (ANN). Multilayer perceptrons have been adopted using the back-propagation algorithm for network training. The training patterns in terms of vibration signature are generated analytically for a moving load traveling on a trussed bridge structure at a constant speed to simulate the inspection vehicle. Using the finite-element technique, the moving forces are converted into stationary time-dependent force functions in order to generate vibration signals in the structure and the same is used to train the network. The performance of the trained networks is examined for their capability to detect damage from unknown signatures taken independently at one, three, and five nodes. It has been observed that the prediction using the trained network with single-node signature measurement at a suitability chosen location is even better than that of three-node and five-node measurement data.Item Reaction of Aryl and Heterocyclylhydrazines with 2-Methylchromone: Structural Investigation of the Products(Taylor & Francis, 1996) Kumar, DalipReaction of 2-methylchromone (2) with phenylhydrazine provides 3-methyl-5-(o-hydroxyphenyl)-1-phenylpyrazole (6) as a major product. In contrast under similar conditions, heterocyclylhydrazines (8a-c) yield exclusively 5-ethyl-3-(o-hydroxyphenyl)-1-heterocyclylpyrazoles (9a-c). The structural assignments are based on an unambiguous synthesis and an analysis of NMR (1H & 13C) spectral data.Item Conformation and ortho steric effects in a series of 2-(pyrazol-1-yl)quinolines(Wiley, 1996-04) Kumar, DalipNine 2-(pyrazol-1-yl)-4-methylquinolines bearing substituents on the pyrazole 3- or 5-positions (H, Me, Et, i-Pr, t-Bu) were regioselectively synthesized either using the direct condensation of 2-chloro-4-methylquinoline and sodium salt of 3(5)-substituted pyrazoles or by treatment of 2-hydrazino-4-methylquinoline with an appropriate β-ketoaldehyde. The 1H and 13C chemical shifts were discussed taking into account the preferred conformation about the C-2-N-1′ bond as calculated by the AM1 Hamiltonian. It appears that 5-ethyl and 5-isopropyl substituted derivatives present short C-H-N-1 interactions. Ortho steric effects appear to be responsible for these conformations.Item The Local Hard−Soft Acid−Base Principle: A Critical Study(ACS, 1997) Roy, Ram KinkarThe recently proposed local hard−soft acid−base principle characterizes the reactive centers of two systems on the basis of equal Fukui functions or/and equal local softnesses. We make a quantum chemical study of this principle using ab initio and density functional calculations in cases where the global softnesses of the reacting systems are different. We consider reactions of a dimer cluster model of faujasite X-type zeolite with the probe molecules CO, NH3, and H2O.Item Hypervalent Iodine Oxidation of 1, 3, 5-Trisubstituted Pyrazolines: A Facile Synthesis of 1,3,5-Trisubstituted Pyrazoles(Taylor & Francis, 1997) Kumar, Dalip1, 3, 5-Trisubstituted pyrazolines (1a–i) undergo facile oxidation to the corresponding pyrazoles (2a–i) in the presence of iodobenzene diacetate.Item A Facile Synthesis of 5-Methyl-1-(phenyl/heterocyclyl)-4-trifluoroacetylpyrazoles(RSC, 1997) Kumar, DalipTreatment of substituted hydrazines (2a–d) with 3-acetyl-4-ethoxy-1,1,1-trifluorobut-3-en-2-one (1) yields the title compounds (3a–d) whereas methylhydrazine on similar treatment gives 4-acetyl-1-methyl-3-trifluoromethylpyrazoleItem Structural Sensitivity as a Measure of Redundancy(ASCE, 1997) Barai, Sudhir KumarThe conventional definition of redundancy is applicable to skeletal structural systems only, whereas the concept of redundancy has never been discussed in the context of a continuum. Generally, structures in civil engineering constitute a combination of both skeletal and continuum segments. Hence, this paper presents a generalized definition of redundancy that has been defined in terms of structural response sensitivity, which is applicable to both continuum and discrete structures. In contrast to the conventional definition of redundancy, which is assumed to be fixed for a given structure and is believed to be independent of loading and material properties, the new definition would depend on strength and response of the structure at a given stage of its service life. The redundancy measure proposed in this paper is linked to the structural response sensitivities. Thus, the structure can have different degrees of redundancy during its lifetime, depending on the response sensitivity under consideration. It is believed that this new redundancy measure would be more relevant in structural evaluation, damage assessment, and reliability analysis of structures at large.Item Time-delay neural networks in damage detection of railway bridges(Elsiever, 1997-01) Barai, Sudhir KumarThe recent developments in multilayer perceptron using the backpropagation algorithm, has opened up new possibilities in structural identification. Limitation of traditional neural networks (TNN) in dealing with patterns that may vary in time domain has given birth to time-delay neural networks (TDNN). In the present paper the TNN and the TDNN have been implemented in detecting the damage in bridge structure using vibration signature analysis. A comparative study has been carried out for the various cases of complete as well as incomplete measurement data. It has been observed that TDNNs have performed better than TNNs in this application.Item Synthesis and Single-Crystal Structure of an Unusual Heptacoordinate Cadmium(II) Complex, [Cd(medien)(NO3)2] (medien = bis(2-aminoethyl)methylamine).(ACTA, 1998) Laskar, Inamur RahamanMolecular geometry and coordination number play the key role in exploring the chemistry of a coordination compound.