Showing papers by "Indian Association for the Cultivation of Science published in 1986"
TL;DR: The linked-cluster theorem (LCT) holds for incomplete model spaces as discussed by the authors, provided the intermediate normalization condition (IN) for the eigenfunctions is abandoned.
198 citations
TL;DR: In this article, it is shown that if only excitation energies, rather than the full wave-operator Ω, are desired, then no theoretical error is made, and the theoretical status of earlier applications which had used formulae appropriate to IN, yet ignored disconnected diagrams, is analyzed.
151 citations
TL;DR: Semiconducting vanadium-bismuth oxide glasses have been prepared in the composition range 80-95 mol% V2O5 and the DC conductivity of the annealed glasses has been measured in the temperature range 80 −480 K and compared with those of phosphate and tellurite glasses as discussed by the authors.
Abstract: Semiconducting vanadium-bismuth oxide glasses have been prepared in the composition range 80–95 mol% V2O5 The DC conductivity of the annealed glasses has been measured in the temperature range 80–480 K and compared with those of phosphate and tellurite glasses The conductivity is sensitive to microstructure The data have been analysed in the light of models of polaronic hopping conduction Hopping of the polaron is shown to be adiabatic in nature Mott's T 1 4 analysis is made at low temperature
124 citations
TL;DR: In this article, a method of generating separable forms of the wave operator for incomplete model spaces is discussed, which can be viewed as a Fock-space realization of the intermediate Hamiltonian approach.
Abstract: In this paper, a method of generating separable forms of the wave-operator for incomplete model spaces is discussed. With a time-dependent access to the many-body perturbation and coupled-cluster theories, it is shown how one can extract the regular part of the wave-operator which consists of linked cluster-operators only in the adiabatic limit. The procedure naturally suggests a hierarchy of lower valence model spaces P (k) . once a particular m-valence incomplete model space P (m) is specified. The wave-operator Ω and the effective Hamiltonian H eff are linked in this development and are valence-universal in the sense of being valid for all P (k)' s. 0 k m. We have derived two distinct forms for Ω: (i) Ω = {exp(S)}, with { } as normal order with respect to suitable vacuum, where S are open operators inducing transitions from P (m) to outside it; (ii) Ω N = {exp(S + X)}, where X are additional closed operators which are introduced to maintain isometry of Ω N : P (k) Ω N + Ω N P (k) = P (k) . In neither of these choices do we have intermediate normalization. It is also possible to develop an alternative strategy with the complete model spaces, such that an effective valence-universal operator H may be found which generates roots, only a subset of which are equal to the eigenvalues of H. These subsets are the ones that H eff would have furnished. This may thus be viewed as a Fock-space realization of the intermediate Hamiltonian approach.
89 citations
TL;DR: In this article, the authors used X-ray diffraction and transmission electron microscopy to characterize the resistivity, Hall effect, transmittance and optical band gap of ITO films.
54 citations
TL;DR: The first ab initio molecular applications of the open-shell coupled cluster (CC) method for direct calculation of energy differences are reported in this article, starting from the zero-valence ground-state problem, various one-, two-, ⋯ m -valence problems are hierarchically generated.
42 citations
TL;DR: In this article, it was shown that the open-shell coupled cluster (CC) theory is not inconsistent with the assumption of intermediate normalization, and that all the discussions on the appearance of unlinked diagrams based on the implicit use of normalization are invalid.
Abstract: In this paper we have demonstrated the following aspects of the open-shell coupled cluster (CC) theory when the model space consists ofmp-mh determinants: (I) If no other subsidiary conditions (besides the ‘minimality’ requirementPSP=0) on the normalization of the wave functions are imposed, then the demand that the wave operator admits of the corevalence separation of energy is inconsistent with the assumption of intermediate normalization. Thus all the discussions on the appearance of unlinked diagrams based on the implicit use of intermediate normalization are invalid. (ii) The open-shell CC developments of Mukherjeeet al are independent: of the normalization of the wavefunctions and the linked cluster theorems and the core-valence separation derived by them are valid formp-mh model space functions. In particular it has been shown that there are two different cluster ansatz for which the aspect (iii) above is valid. For a valence-universal wave operator ω admitting of a corevalence separation, it has been proved that the CC equations are linked as a consequence of the multicommutator nature of the expressions. There is a choice between two alternative schemes: one in whichS operators connecting all thekp-kh determinants withk m are retained, and another in which transitions fork
31 citations
TL;DR: To study the chemical transformations of these components as a function of time and environment, fingerprint residues from four males and four females were analysed by thin-layer chromatography and high performance liquid chromatography.
30 citations
TL;DR: Using Faddeev's three-body scattering formalism for positron--hydrogen-atom collisions, an amplitude is obtained for the forward scattering angle which shows a cusp due to the effect of positronium formation to the continuum and heretofore has not been predicted.
Abstract: Depending on the distribution of energy between the scattered positron and the ejected electron in the final channel, two competing processes are involved in positron-impact ionization of atoms, namely (a) direct head-on ionization of an electron and (b) positronium formation to the continuum. Using Faddeev's three-body scattering formalism for positron--hydrogen-atom collisions, we get an amplitude which takes account of both these processes. The doubly differential cross section thus obtained for the forward scattering angle shows a cusp when plotted against the emission energy. The cusp is due to the effect of positronium formation to the continuum and heretofore has not been predicted.
30 citations
TL;DR: Dynamic dipole polarizabilities [alpha][sub [ital d]]([omega]) have been calculated within and beyond the normal-dispersion region for the isoelectronic members of argon up to Mn[sup 7+] using time-dependent coupled Hartree-Fock theory.
Abstract: The frequency-dependent dipole polarizabilities ${\ensuremath{\alpha}}_{d}$(\ensuremath{\omega}) of the sodium isoelectronic sequence (Z=11,...,18) have been calculated within linear-response theory using the time-dependent coupled Hartree-Fock scheme. The excitation energies for the transitions 3 ${\mathrm{}}^{2}$S\ensuremath{\rightarrow}n ${\mathrm{}}^{2}$P (n=3,...,7) have been estimated from the position of the poles of a frequency-dependent functional, and analytic representations of the excited Rydberg p-state wave functions have been obtained. The extrapolated polarizability values ${\ensuremath{\alpha}}_{d}$(\ensuremath{\omega}${)}_{\ensuremath{\omega}\ensuremath{\rightarrow}0}$ are compared with the available static data. The transition energies compared well with spectroscopic data. The oscillator strengths have been estimated in length form and the quantum defect values have been calculated using complete screening. They all compare favorably with data currently available.
28 citations
TL;DR: Calculations, complete through second order in the collision potentials, are presented for 1s-italic-1s-ITALic capture by positrons, finding that the total cross sections for capture bypositrons are larger than those for captured protons at the same velocity because of a kinematical effect.
Abstract: Calculations, complete through second order in the collision potentials, are presented for 1s-italic-1s-italic capture by positrons. Some new destructive interference between second-order amplitudes is evident. This destruction interference was not important in capture by protons where one Thomas amplitude is dominant. Nevertheless, the total cross sections for capture by positrons are larger than those for capture by protons at the same velocity because of a kinematical effect.
TL;DR: The room temperature and low temperature absorption and emission spectra corresponding to the relaxed and unrelaxed excited states of benzil are reported in this article, showing that the relaxed state has a transplanar geometry with a zero dipole moment, while the unrelaxed form must be skew in both singlet and triplet excited states.
TL;DR: In this paper, NiL2X2 has been synthesized and their thermal studies carried out and their probable mechanisms are described, and they have been made in solid state by temperature arrest technique from [NiL2(CX3CO2)2] (X = Cl− and Br−).
Abstract: [NiL2X2] (L =N,N′-dimethyl-1,2-ethanediamine; X = Cl−, CF3CO2−, CC13CO2− and CBr3CO2−), [NiL2C2O4] · H2O and [NiL2X2] · 2 H2O (X = Br−, 0.5 SO42− and 0.5 SeO4−) have been synthesised and their thermal studies carried out. Thermally induced phase transition phenomena are noticed in [NiL2X2] (X = CF3CO2− and CCl3CO2−) and their probable mechanisms are described. [NiL2X2] (X = Br−, 0.5 SO42− and 0.5 SeO42−) and [NiLX2] (X = Cl−, 0.5 C2O42− and 0.5 SO42−) have been prepared by solid state pyrolysis from the respective parent diamine complexes. [NiL2X2] have been made in solid state by temperature arrest technique from [NiL2(CX3CO2)2] (X = Cl− and Br−).
TL;DR: The effect of boron doping on light-induced effects has also been studied in this paper, where it was found that the light induced effects decreased with an increase in hydrogen concentration, which may be due to the removal of weak bonds contributing to the Staebler-Wronski effect.
Abstract: Light-induced effects on the dark conductivity, photoconductivity, spectral responses and band gap of hydrogenated amorphous silicon thin films have been studied. The a-Si:H films were prepared by the r.f. glow-discharge decomposition of silane gas in a capacitatively coupled plasma-reactor system. Undoped a-Si:H films were prepared from a mixture of silane and hydrogen with the proportion of hydrogen varying from 0 to 80%. It was found that the magnitude of light-induced effects decreased with an increase in hydrogen concentration, which may be due to the removal of weak bonds contributing to the Staebler-Wronski effect. The effect of boron doping on light-induced effects has also been studied. For nearly compensated films at low boron concentrations the light-induced effects are small. As the boron doping is increased, the dark conductivity increases on light exposure and reaches a maximum which is the reverse of the normal Staebler–Wronski effect. It has been suggested that this effect is due ...
TL;DR: A 2 MBr 4 undergoes endothermic reversible phase transitions at subambient and above ambient temperatures as discussed by the authors, and the cooling curve of A 2 Mbr 4 (M = Cu and Ni) above 400 K is split compared to the corresponding heating curve and the nature of splitting appears to be dependent on time.
TL;DR: In this paper, an algorithm based on a "constrained variational principle" is proposed for the direct determination of constrained one-electron density matrices in a self-consistent manner.
TL;DR: In this article, the usefulness of circular dichroism (CD) studies in the assignment of lanthanide Δ J = 0, ± 1 transitions with two chiral single crystals, Tm 2 Ge 2 O 7 (Tm-PG) and Tb 2 Ge O 7(Tb-PG), was explored.
TL;DR: In this paper, a large number of studies have been made on the crystal l izat ion processes which may occur in a m o r p h o u s selenium films.
Abstract: In recent years quite a large number o f exper imenta l studies have been made on the crystal l izat ion processes which may occur in a m o r p h o u s selenium films [1-15] and these were under t aken to predic t the g rowth s t ructure o f the a m o r p h o u s phase o f the films. I t m a y be noted that a con t roversy still exists as to whether the shor t range s t ructure o f a m o r p h o u s selenium is compr i sed o f hexagona l chains or e igh t -a tom rings or a mixture of both . As there are few deta i led and conclusive studies [1] on the crys ta l l iza t ion processes (by thermal t r ea tment a t different t empera tures ) in relat ively thin selenium films, the present work a ims to repor t the findings f rom micros t ructura l invest igat ions with Xray diffract ion and scanning e lect ron microscopy (SEM) a long with the measurements o f da rk conduct iv i ty and pho toconduc t iv i ty . This has been under taken in cont inuat ion o f our present exper imenta l p r o g r a m m e of mic ros t ruc tu ra l studies on semiconduct ing thin films [16-18]. Selenium films o f thicknesses 545, 1245, 3000 and 5900 nm were depos i ted by vacuum e v a p o r a t i o n (normal incidence o f v a p o u r beam) at a pressure o f 5 × 10 6 to r t on clean glass substrates at r oom tempera ture (298 K) with a depos i t ion rate o f 5 _+ 1.5 nm sec ~. A m a x i m u m o f four films was depos i ted at the same t ime which were then annea led separa te ly at different tempera tures for subsequent studies at r o o m tempera ture . Tables I and II record the detai ls o f the exper imenta l condi t ions as well as the obse rva t ions made. The m a x i m u m anneal ing t ime was 5 h and the m a x i m u m anneal ing t empera tu re was 358 K. X r a y dif f ract ion pa t te rns were ob ta ined with L i F m o n o c h r o m a t e d MoK~ rad ia t ion in a Phil ips P W 1050/51 counte r diff rac tometer coupled to a Phil ips P W 1130, 3 k W X r a y genera tor . Da rk -conduc t iv i t y and p h o t o c o n d u c t i v i t y measurements were done on a p p r o x i m a t e l y 3000 to 3200-rimthick films annealed at 338,348 and 358 K, respectively, and depos i ted under ident ical condi t ions . S E M studies were carr ied out on a lmos t ident ica l samples as above with a Hi tach i S-415 e lec t ron microscope . Conduct ivi ty measurements were m a d e be tween two par allel surface e lect rodes (with a s epa ra t i on o f 0.003 m) o f e va po ra t e d silver which was depos i t ed on the films. The cur ren t and 200 V d.c. supply were measu red by a Kie th ley 610C e lec t rometer and a Kie th ley D M M 177 vol tmeter , respectively. A 200 W m 2 l ight source was used for the pho toc onduc t i v i t y measurements . A n a t t empt was also made to depos i t the selenium films on the p rehea ted substra tes . F i lms with a maxim u m thickness o f a pp rox ima te ly 1200 nm could be depos i ted wi thou t being peeled off a t subs t ra te tempera tures o f 358 and 398 K, respectively. A t the h igher t empera tu re o f 398K, the film was d i scon t inuous
TL;DR: Using variable atmospheric eddy diffusivities, it is possible to obtain a theoretical explanation of observations concerning the increase of cell flatness in cellular cloud patterns as mentioned in this paper, which suggests that it may be useful to rethink our ideas about the existence of spatial variations in the eddy transfer coefficients in atmospheric convection.
Abstract: Using variable atmospheric eddy diffusivities, it is possible to obtain a theoretical explanation of observations concerning the increase of cell flatness in cellular cloud patterns The inclusion of a horizontal variation of eddy size as proposed by Ray (1965) and supported by Agee (1973) has a large influence on theoretical Rayleigh number and cell shape, the degree of cell flatness being principally controlled by the degree of horizontal variation of the eddies It is also shown that observations regarding the reversal of the circulation pattern could be interpreted on the basis of eddy diffusivities that change sign along the reference directions This suggests that it may be useful to rethink our ideas about the existence of spatial variations in the eddy transfer coefficients in atmospheric convection
TL;DR: In this article, the interactions of the synergistic pair of accelerators comprising of thiocarbamyl sulfenamide and 2-(iminodithio)benzothiazole have been carried out through hplc. The OTCS-PDB system was found to yield vulcanizates which exhibit the greatest crosslink density, scorch safety, and highest modulus and tensile strength.
Abstract: Investigations on the interactions of the synergistic pair of accelerators comprising of thiocarbamyl sulfenamide and 2-(iminodithio)benzothiazole have been carried out through hplc. N-cyclopentamethylene thiocarbamyl-N'-oxydiethylene sulfenamide, N-oxydiethylenethiocarbamyl-N'-cyclopentamethylene sulfenamide (OTCS), 2-morpholinodithiobenzothiazole, and 2-piperidinodithiobenzothiazole (PDB) have been selected as the reactants which, when suitably combined, provide most effective accelerator systems capable of generating heat and age resistant vulcanizates. The OTCS–PDB system has been found to yield vulcanizates which exhibit the greatest crosslink density, scorch safety, and highest modulus and tensile strength. An attempt has been made to explain the higher activity of the binary systems studied as compared to that obtained from comparable thiocarbamyl sulfenamide plus dibenzothiazyl disulfide system. Zin–dithiocarbamates have been found to influence the curing reactions depending upon the composition of the mixed accelerators. Cyclohexyl thiophthalimide, a versatile cure retarder, reacts with the accelerators to yield cyclohexyl thiomorpholine and cyclohexyl thiopiperidine, as the case may, which also have a profound effect upon cure retardation as noticed in the present investigation.
TL;DR: Spergulagenin-A-3-O(α-L -rhamnopyranosyl-(1 → 2) as discussed by the authors is a triterpenoid saponin derived from Mollugo spergula.
TL;DR: In this paper, the rigid polycylic β,γ-unsaturated diazomethyl ketones (1a and b ) and ( 2a, b ) promoted by Cu(acac)2, Cu(OTf)2 and Ni(acAC)2 or silver benzoatetriethylamine in the presence of methanol are shown to give the respective rearranged γ,δ-uns saturated angularly substituted esters ( 3a andb ) and 6a and B ) along with other products.
TL;DR: In this paper, the authors used the hplc studies with all their limitations to obtain information regarding the vulcanization of rubber accelerated by CTOS and MBTS in the early part of the reaction.
Abstract: The hplc studies with all their limitations have been employed to obtain information regarding the vulcanization of rubber accelerated by CTOS and MBTS in the early part of the reaction. It is noticed that even in the initial part of the induction period (the scorch safety, t2, of the recipe is 10.5 min), CTOS and MBTS react so rapidly with each other and also with rubber that at the end of 10 min we could detect only MBT, while the concentration of the other components formed in the reaction—namely, CTOS, OBTS, CPTD, BPTD, PMTU, CPTM, BPTM, etc.—decreased to an extremely low level. We noticed that under the experimental conditions, OBTS and CPTU have the same retention time. This naturally obscures the path for understanding the individual effect of these accelerators. The sharp disappearance of OBTS, associated with the abundant formation of MBT and nonavailability of CPTU (from CPTD, Figure 11b), gives testimony to the fact that the unsymmetrical thiourea (PMTU) rather than the symmetrical one...
TL;DR: The hexasaccharide structure 1 has been assigned to the repeating unit of the K-10 polysaccharide, and the anomeric configurations of the sugar residues were determined by oxidation of the acetylated native and carboxyl-reducedpolysaccharides with chromium trioxide.
TL;DR: In this article, the optical properties of indium tin oxide (ITO) films in the range of photon energies 0.7 to 4.5 eV were studied in the light of existing theories indicating Burstein- Moss shift.
Abstract: Optical properties of de sputtered indium tin oxide (ITO) films are studied in the range of photon energies 0.7 to 4.5 eV. The data are analysed in the light of existing theories indicating Burstein- Moss shift. Correlation among carrier concentration, plasma frequency, and optical band gap indicates an effective mass me* = 0.56me, me being the free electron mass. Structural details of ITO films deposited on glass substrates are analysed by X-ray diffraction pattern.
TL;DR: In this article, structural features of a series of tetraatomic carbonyls in the 1,3 nπ ∗ states were studied by using a recently proposed MCSCF algorithm at the INDO/2 level.
Abstract: Structural features of a series of tetraatomic carbonyls in the 1,3 nπ ∗ states are studied by using a recently proposed MCSCF algorithm at the INDO/2 level. The computed geometrical parameters and the inversion barrier heights agree quite well with the available experimental or ab initio theoretical data. The calculated transition energies turn out to be somewhat lower than the experimental counterparts. The specific MCSCF algorithm used is found to have excellent convergence properties.
TL;DR: In this paper, the effect of CTP on thiocarbamyl sulfenamides, either alone or in combination with MBTS, in the vulcanization of NR was investigated.
Abstract: Investigations have been carried out on the effect of CTP on thiocarbamyl sulfenamides, either alone or in combination with MBTS, in the vulcanization of NR. It has been observed that CM, CP, CPTCD, OTCD, and CDB formed from various thiocarbamyl sulfenamides like OTOS, OTCS, and CTOS in the presence of CTP play a vital role in cure retardation. CM and CDB under the experimental conditions have been found to prolong the onset of cure, while CP, CPTCD, and OTCD reduce scorch time. The presence of a substituent on the carbamate N-atom of thiocarbamyl sulfenamides greatly influences cure retardation. OTOS and CTOS give rise to CM and CP respectively in the presence of CTP. OTCS, however, generates both CM and CP under the identical conditions and thus differs from OTOS and CTOS. CPTCD and OTCD formed from thiuramdisulfides have been shown to be poor and scorchy accelerators, and these, like CM and CP, play a significant role in cure retardation.
TL;DR: It is found that at low laser intensities the spontaneous decay of the intermediate resonant state can modify the PE angular distribution significantly, whereas at higher intensities, this effect is washed out by the other intensity-dependent competing channels.
Abstract: The photoelectron (PE) angular distribution for the resonant two-photon autoionization of H/sub 2/ through the lowest autoionizing state of /sup 1/..sigma../sub g/(1sigma/sub u//sup 2/) symmetry has been studied. It is found that at low laser intensities the spontaneous decay of the intermediate resonant state (different vibrational levels of the B/sup 1/..sigma../sub u/ state) can modify the PE angular distribution significantly, whereas at higher intensities, this effect is washed out by the other intensity-dependent competing channels.
TL;DR: In this paper, a method based on the direct inversion in the iterative subspace (DIIS) in accelerating the approach to self consistency in the calculation of the MCSCF wavefunction using a novel algorithm developed earlier, is compared with that of a simple damping technique.
Abstract: The efficacy of a method based on the direct inversion in the iterative subspace (DIIS) in accelerating the approach to self consistency in the calculation of theMCSCF wavefunction using a novel algorithm developed earlier, is compared with that of a simple damping technique. Although the ‘damping’ turns out to be ineffective in the ‘quadratic region’, it accelerates remarkably in the rate of descent on the energy hypersurface in the early stages of the iterative process which leads to an impressive overall increase in the rate of approach to self consistency. TheDIIS based procedure turns out to be ineffective when coupled to the present method and is plagued by ill conditioning problems. Calculations are done to compute the equilibrium geometrical parameter, charge density on different atoms, and dipole moment of HNO molecule in the lowest1,3
nπ* states at theINDO/2-MCSCF level.