On “Radiating Vaidya metric imbedded in deSitter space”

Mallett has generalized the Vaidya metric as well as the deSitter metric to obtain what he called the Vaidya-Schwarzschild-deSitter metric and has obtained the condition under which this metric represents a pure radiation field. The present note obtains the complete first integral of that equation as well as well as some particular solutions.     

Simple leaky box model for cosmic-ray propagation, models for production of antiprotons at ultrahigh energies and the estimations of the [`(p)]/p\bar p/p ratiosratios

Summary Accepting the simple leaky box model as the basis for propagation of cosmic rays, the problematical ratio has been estimated theoretically by applying two versions of antiproton production models. The results have been compared with those from the experiments as well as from some other empirio-theoretical models. It has been emphatically pointed out that even within the premises of the simple leaky box model the discrepancies can be removed only by taking into account the contributions from the large-p _T antiproton production cross-sections and the role of theA-dependence of nuclear cross-sections in a much more pronounced way.

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Riassunto Accettando il modello semplice della scatola non isolata, è stato stimato il rapporto critico teoricamente applicando due versioni dei modelli di produzione degli antiprotoni. Sono stati confrontati i risultati con quelli degli esperimenti ed anche con quelli di altri modelli empirico-teorici. è stato evidenziato che anche nell’ambito delle premesse del modello semplice della scatola non isolata si possono eliminare le discrepanze tenendo maggiormente conto dei contributi delle sezioni d’urto di produzione di antiprotoni a grandep _T e del ruolo della dipendenza daA delle sezioni d’urto nucleare in modo molto più marcato.

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Простая модель распространения космических лучей, модели образования антипротонов при ультравысоких Энергиях и оценки отнощенийотнощений

Резюме Ha основе простой модели распространения космических лучей теоретически оценивается отнощение, используя две модели образования антипротонов. Полученные результаты сравниваются с результатами Экспериментов, а также с результатами других Эмпирико-теоретич еских моделей. Отмечается, что, используя только предположения простой модели, можно устранить расхождения, если учесть вклады поперечных сечений образования антипротонов с больщимир _T и более явно зависимость от А ядерных поперечных сечений.

     

On exact calculation of response properties of oscillators in static electric field: A Fourier grid Hamiltonian approach. I. One-dimensional systems

The Fourier grid Hamiltonian method is used to calculate the response properties of different types of 1-d (one-dimensional) quantum oscillators in a uniform static electric field. The calculations are potentially exact. Excepting the harmonic oscillator, the other model oscillators studied are seen to possess nonlinear polarizabilities. In general, the polarizabilities are not monotonic functions of appropriate vibrational quantum numbers. The exact nature of this vibrational-state dependence of polarizabilities is shown to depend on the type of mechanical anharmonicity in which the nuclei move and the nature of electrical anharmonicity characterizing the field–oscillator coupling. The large vibrational contribution to nonlinear polarizabilities often predicted for real diatomics could therefore originate from the mechanical and electrical anharmonicities of the potential in which the nuclei move when placed in a static electric field. © 1994 John Wiley & Sons, Inc.     

The effects of static quartic anharmonicity on the quantum dynamics of a linear oscillator with time-dependent harmonic frequency: Perturbative analysis and numerical calculations

The effects of quartic anharmonicity on the quantum dynamics of a linear oscillator with time-dependent force constant (K) or harmonic frequency (ω) are studied both perturbatively and numerically by the time-dependent Fourier grid Hamiltonian method. In the absence of anharmonicity, the ground-state population decreases and the population of an accessible excited state (k = 2, 4, 6…) increases with time. However, when anharmonicity is introduced, both the ground- and excited-state populations show typical oscillations. For weak coupling, the population of an accessible excited state at a certain instant of time (short) turns out to be a parabolic function of the anharmonic coupling constant (λ), when all other parameters of the system are kept fixed. This parabolic nature of the excited-state population vs. the λ profile is independent of the specific form of the time dependence of the force constant, K_t. However, it depends upon the rate at which K_t relaxes. For small anharmonic coupling strength and short time scales, the numerical results corroborate expectations based on the first-order time-dependent perturbative analysis, using a suitably repartitioned Hamiltonian that makes H₀ time-independent. Some of the possible experimental implications of our observations are analyzed, especially in relation to intensity oscillations observed in some charge-transfer spectra in systems in which the dephasing rates are comparable with the time scale of the electron transfer. © 1995 John Wiley & Sons, Inc.     

Reactions of hydroxyalkyl radicals with nickel(II) and copper (II) complexes of 2-methyl-5-nitro-1H-imidazole-1-ethanol: A steady-state gamma-radiolysis and flash photolysis study

The yields for the loss of chromophore of Ni(II) and Cu(II) complexes of metronidazole,G(-Ni(II)M) andG(-Cu(II)M), reached almost zero when their aqueous solutions were -irradiated in the presence, of 0.4 mol·dm^–3 of MeOH, EtOH,i-PrOH andt-BuOH in aerated medium. However, under N₂O saturated conditions, these yields attained limiting values which suggests that the hydroxyalkyl radicals, derived from the alcohols by reaction with OH, react with the complexes in deaerated medium. But in aerated medium they react preferentially with O₂. The rate constants for the reactions of the different hydroxyalkyl radicals with the complexes have been determined by the flash photolysis technique and the plausible mechanisms for the reactions have been suggested.     

Molecules in an electric field: Some structural and spectroscopic consequences

It is theoretically shown that under the influence of an appropriately directed external electric field (ε) in H₂CO or a similar molecule (of the XYC = O type), the barrier to planar inversion in the ³n π* state decreases as the field strength increases. The molecule assumes a forced planar geometry in the ³n π* state rather abruptly when ε_(applied) > ε_(critical). This phenomenon of field-induced change of structure of an isolated molecule has the attributes of a first order phase transition. The effects should be spectroscopically detectable in the inversion spectrum. The existence of another critical field strength at which the molecule makes a more or less continuous transition from the normal convalent to a purely ionic structure is demonstrated and rationalized through a simple model.     

The INDO/2-AHP (average hole potential) method for excited states: Comparison with the simple INDO/2-HP (hole potential) method

The INDO/2 version of the average hole potential (AHP) model is analyzed. The model is applied to study the geometric features, molecular inversion barriers, singlet-triplet splittings, etc., of a few small carbonyl molecules (H₂CO, HFCO, F₂CO) in the ^1,3nπ* states with partial as well as complete optimization of all geometric parameters in the excited states. The results are compared with those obtained by a simple hole-potential (HP) model.     

Chemistry of metal-bound anion radicals. A family of mono- and bis(azopyridine) chelates of bivalent ruthenium

The reaction of the dihydride [RuII(H)2(CO)(PPh3)3], 3, with excess azo-2,2'-bipyridine (abp) in boiling dry benzene has afforded the diradical bischelate [RuII(abp.-)2(CO)(PPh3)], 4, and the hydridic monochelate monoradical [RuII(abp.-)(H)(CO)(PPh3)2], 5. A similar reaction between 3 and 2-(p-chlorophenylazo)pyridine (Clpap) did not yield a bischelate, but the hydridic monoradical [RuII(Clpap.-)(H)(CO)(PPh3)2], 6, has been isolated. Upon treatment of 4-6 with NH4PF6 in a wet dichloromethane-acetonitrile medium, the one-electron-oxidized salts 4+PF6-, 5+PF6-, and 6+PF6- are isolated, H+ being the oxidizing agent. The X-ray structures of 4+PF6-.CH2Cl2, 5+PF6-.H2O, and 6+PF6- have been determined. In the monoradical 4+ the azo N-N bond lengths in the two chelate rings are 1.284(6) and 1.336(6) A, showing that the radical electron is localized in the latter ring. The half-filled extended Hückel HOMO is indeed found to be so localized, and it has a large azo character. Complexes 4-6 display radical redox couples with E1/2 in the range -0.5 to +0.10 V vs SCE. The E1/2 values qualitatively correlate with corresponding vco values (1900-2000 cm-1). The monoradicals (S = 1/2) 4+, 5, and 6 uniformly display a strong EPR signal near g = 2.00. Metal-mediated magnetic interaction makes the EPR-silent diradical 4 strongly antiferromagnetic with J = -299 cm-1. Crystal data are as follows: (4+PF6-.CH2Cl2, C40H33Cl2F6N8-OP2Ru) monoclinic, space group P2(1)/c (no. 14), a = 14.174(6) A, b = 16.451(4) A, c = 18.381(4) A, beta = 98.00(3) degrees, Z = 4; (5+PF6-.H2O, C47H41F6N4O2P3Ru) monoclinic, space group P2(1)/n (no. 14), a = 9.433(2) A, b = 38.914(17) A, c = 13.084(3) A, beta = 103.47(2) degrees, Z = 4; (6+PF6-, C48H39ClF6N3OP3Ru) monoclinic, space group P2(1)/n (no. 14), a = 10.496(5) A, b = 22.389(8) A, c = 19.720(6) A, beta = 90.53(3) degrees, Z = 4.     

Ab initio QM/MM study of excited state electron transfer between pyrene and 4,4′‐bis(dimethylamino)‐diphenylmethane with different solvent systems: Role of hydrogen bonding within solvent molecules

The exciplex is a charge transfer species formed in the process of electron transfer between an electron donor and an electron acceptor and hence is very sensitive to solvent polarity. In order to understand the role of solvent in exciplex formation between pyrene (PY) and 4,4′‐bis(dimethylamino)diphenylmethane (DMDPM), we used two types of solvent approximations: an implicit solvent model and an explicit solvent model. The difference in energies between the excited and the meta‐stable Frank–Condon state (ΔE) of the structures were assumed to correspond to the emission maximum of the exciplex in different solvents. The ΔE values show the trend of stabilization of the exciplex with an increase in solvent polarity. This trend in stabilization is substantially more prominent in the explicit solvent model than that with the implicit solvent model. The ΔE value obtained in methanol reflects equal stabilization compared to that in a more polar solvent, N,N‐dimethylformamide. This extra stabilization of the exciplex may be explained on the basis of the H‐bonding capability of the protic solvent, methanol. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Isoelectric focusing studies of concanavalin A and the lentil lectin

Isoelectric focusing (IEF) of metallized and demetallized preparations of concanavalin A (Con A) consisting of either intact or fragmented subunits shows different band patterns. Metallized Con A consisting of intact polypeptide chains (intact Con A) has an isoelectric point (pI) 8.35. Metallized preparations consisting of fragmented chains (fragmented Con A) show three bands with pI values 8.0, 7.8 and 7.7. Demetallized intact Con A (intact apoCon A) has a pI of 6.5, however, it undergoes pH dependent association during IEF under certain conditions, which gives rise to multiple bands. Ampholyte-mediated demetallization of intact and fragmented Con A and subsequent aggregation of the apoprotein results in multiple bands during IEF in the presence of the pH range 3 to 10 ampholytes. However, ampholytes of the pH range 7 to 9 do not demetallize the proteins and show a single band with intact Con A. The pI of intact Con A remains essentially the same in the presence of inhibitory sugar. Furthermore, different moleculars forms of Con A, including locked and unlocked conformers of intact apoCon A, and the dimeric and tetramic states of both intact Con A and intact apoCon A have been identified and their pI values determined. IEF of the lentil isoelectins, LcH-A and LcH-B, shows single bands of pI 8.5 and 9.0, respectively. However, the native lectin mixture gives rise to an additional band of pI 8.8 due to a hybrid protein formed by ampholyte-mediated subunit exchange between the isolectins.