Now showing 1 - 10 of 16
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    Computational chemical studies on thermochemistry and ring strains in cyclic [ n ]Metaphenyleneacetylenes, butadiyne-bridged [4n] Metacyclophynes, and butadiyne-bridged [4n]paracyclophynes
    (03-09-2010)
    Ali, Mohamad Akbar
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    The thermochemical properties and ring strains in cyclic [n]metaphenyleneacetylenes ([n]CMPAs), butadiyne-bridged [4n] metacyclophynes (B-B[4n]MCs), and butadiyne-bridged [4 n]paracyclophynes (B-B[4n]PCs) were studied using a homodesmotic reaction scheme coupled with density functional theory (B3LYP/6-31G, mPW1PW91/6-31G, and M06-2X/6-31+G//B3LYP/6-31G). Strain energies of [n]CMPAs and B-B[4n]MCs decrease first from very high values for small rings to become zero when n becomes 6, then increase with n, and finally decrease as n becomes larger than 8. In the case of B-B[4n]PCs, strain energies decrease with increasing n. Heats of formation of [n]CMPAs, B-B[4n]MCs, and B-B[4n]PCs increase steadily with increasing numbers of phenylacetylene and 1-(buta-1,3-diynyl)benzene to reach a near-constant value per unit monomer as n increases. The geometries and (vibrational and nuclear magnetic resonance) spectroscopic properties of [n]CMPAs, B-B[4n]MCs, and B-B[4n]PCs were also studied. Geometrical parameters, Raman frequencies, and 1H NMR chemical shifts of [3]CMPA and [4]CMPA are found to be in good agreement with compounds for which there are experimentally available values at the B3LYP/6-31G* level of theory. In addition, electronic structure calculations were carried out for [n]CMPAs, B-B[4n]MCs, and B-B[4n]PCs. Ring diameters were also calculated for B-B[4n]PCs. © 2010 American Chemical Society.
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    Effective Floquet Hamiltonian for spin I = 1 in magie angle spinning NMR using contact transformation
    Contact transformation is an operator transformation method in time-independent perturbation theory which is used successfully in molecular spectroscopy to obtain an effective Hamiltonian. FIoquet theory is used to transform the periodic time-dependent Hamiltonian, to a time-independent Floquet Hamiltonian. In this article contact transformation method has been used to get the analytical representation of Floquet Hamiltonian for quadrupolar nuclei with spin I = 1 in the presence of an RF field and first order quadrupolar interaction in magic angle spinning NMR experiments. The eigenvalues of contact transformed Hamiltonian as well as Floquet Hamiltonian have been calculated and a comparison is made between the eigenvalues obtained using the two Hamiltonians. © Indian Academy of Sciences.
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    Quantum entanglement and teleportation using statistical correlations
    (01-01-2009)
    Kumar, Atul
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    A study of quantum teleportation using two and three-particle correlated density matrix is presented. A criterion based on standard quantum statistical correlations employed in the many-body virial expansion is used to determine the extent of entanglement for a 2N-particle system. A relation between the probability and statistical parameters is established using the correlated density matrices for the particles. © Indian Academy of Sciences.
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    Effective Floquet Hamiltonians for dipolar and quadrupolar coupled N-spin systems in solid state nuclear magnetic resonance under magic angle spinning
    Spin dynamics under magic angle spinning has been studied using different theoretical approaches and also by extensive numerical simulation programs. In this article we present a general theoretical approach that leads to analytic forms for effective Hamiltonians for an N-spin dipolar and quadrupolar coupled system under magic angle spinning (MAS) conditions, using a combination of Floquet theory and van Vleck (contact) transformation. The analytic forms presented are shown to be useful for the study of MAS spin dynamics in solids with the help of a number of simulations in two, three, and four coupled, spin-1/2 systems as well as spins in which quadrupolar interactions are also present. © 2010 American Institute of Physics.
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    T4E 2011
    (28-09-2011) ;
    Sampson, Demetrios G.
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    Perceived Challenge in E-Learning and Its Causes
    (29-01-2016)
    Ravi, Adit
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    Ravi, Jayanti
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    Jani, Haresh
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    Patel, Tushar
    This paper presents the results of a study on the perceived challenge of e-learning with special reference to the National Program for Technology Enhanced Learning (NPTEL) offered by the Indian Institutes of Technology (IITs) and Indian Institute of Science (IISc)jointly. The programme has been used to model learner requirement and expectations through technology enhanced and online learning worldwide. Survey data collected from across India is used to identify the predominant sections of users that feel "e-learning is challenging" and hence aren't able to engage fully in the e-learning process. Such findings will also have direct bearing on future design of all online learning processes worldwide through Massive Open Online Courses (MOOCs). An attempt is also made to identify the causes of this perception and corroborate the same with an analysis of the survey data. Finally, along with the results of the analysis, some suggestions for NPTEL and other online content providers worldwide, following the movement by UNESCO to create Open Educational Resources (OERs), are also given to help them chart their future courses of action. On the user side, some of these suggestions may also be helpful for overcoming this perception by addressing the roots of similar problems.
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    Chemical Education in India: Addressing Current Challenges and Optimizing Opportunities
    (11-10-2016) ;
    Brakaspathy, R.
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    Arunan, E.
    This article gives a brief introduction to the structure of higher education programs in chemical and general sciences in India. The lack of high-quality chemical education in India in the past is traced back to the economic and social developments of the past. Remedial measures undertaken recently to improve the overall quality of chemical education and research are indicated. For the chemical education community worldwide, opportunities in India for enhancing chemistry education quality through collaborations in technical and commercial undertakings are indicated.
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    Rotational spectra of mono-substituted asymmetric C6H 6-H2O dimers
    (01-08-2005)
    Prasad, B. Ram
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    Arunan, E.
    This paper reports the assignment of the rotational spectra of the m = 0 and 1 states of 13CC5H6-H2O and C6H5D-H2O dimers. The m = 1 progression was not identified or assigned for both 13CC5H 6-H2O and C6H5D-H2O in the earlier work, though for the symmetric isotopomers (C6H 6-H2O/D2O/H218O), they were identified [H.S. Gutowsky, T. Emilsson, E. Arunan, J. Chem. Phys. 99 (1993) 4883]. The m = 1 transitions for 13CC5H 6-H2O and C6H5D-H2O were split into two, unlike that of the parent C6H6-H 2O isotopomer. The splitting varied, somewhat randomly, with quantum numbers J and K. The m = 0 lines of 13CC5H 6-H2O had significant overlap with the m = 1 lines of the parent isotopomer, clouding proper assignment, and leading to an rms deviation of about 200 kHz in the earlier work. The general semi-rigid molecular Hamiltonian coupled to an internal rotor, described recently by Duan et al. [Y.B. Duan, H.M. Zhang, K. Takagi, J. Chem. Phys. 104 (1996) 3914], is used in this work to assign both m = 0 and 1 states of 13CC5H 6-H2O and C6H5D-H2O dimers. Consequently, the m = 0 fits for 13CC5H 6-H2O/D2O have an rms deviation of only 4/7 kHz, comparable to experimental uncertainties. The fits for m = 1 transitions for 13CC5H6-H2O and C 6H5D-H2O dimers have an rms deviation of about 200 kHz. However, it is of the same order of magnitude as that of the m = 1 state of the parent C6H6-H2O dimer. The A rotational constants determined from the m = 0 fits for both 13CC5H6-H2O and 13CC 5H6-D2O isotopomers are identical and very close to the C rotational constant for 13CC5H 6. This provides a direct experimental determination for the C rotational constant of 13CC5H6, which has a negligible dipole moment. © 2005 Elsevier Inc. All rights reserved.
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    Effective Hamiltonians in Floquet theory of magic angle spinning using van Vleck transformation
    (08-04-2001)
    Ramesh, R.
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    An overview is given on the use of the method of contact transformation for doing perturbation theory calculations on MAS Hamiltonians. The method can provide effective Hamiltonians and thus simplify the calculations of eigenvalues of Floquet-Hamiltonian.
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    Uncoupled effective Hamiltonians for molecules with several vibrational modes coupled by Coriolis and centrifugal terms
    (15-06-1997) ;
    Carrington, Tucker
    In this paper we extend methods we have developed [J. Chem. Phys. 94 (1991) 461; 98 (1993) 83] for studying the spectra of molecules with two modes coupled by Coriolis and centrifugal terms. Combining a transformation method due to Bogoliubov and Tyablikov (BT) and perturbation theory we calculate ro-vibrational energy levels of molecules (formal-dehyde and thioformaldehyde) with three coupled modes and a molecule (trans-d2 ethylene) with several coupled pairs of modes. The BT transformation is used to compute "vibrational" basis functions which include some of the rotational-vibrational coupling. © 1997 Published by Elsevier Science B.V.