Charge-remote fragmentation and the two-step elimination of alkanols from fast atom bombardment-desorbed (M + H)+, (M + Cat)+, and (M − H)− ions of aromatic β-hydroxyoximes

AbstractAromatic β-hydroxyoximes undergo unusual fragmentation reactions as protonated or cationized species, as radical cations, or as (M − H)− ions. As protonated species, they expel OH· from the oxime functionality in violation of the even electron rule. Parallel eliminations of alkyl radicals follow OH· loss when the aromatic ring is substituted with an alkyl chain. Alkyl radical losses appear to be characteristic of radical cations that can isomerize to ions in which the alkyl chain bears a radical site and the charged site is the conjugate acid of a basic functionality (e.g., oxime or imine). Evidence for the mechanisms was found in the ion chemistry of oxime and imine radical cations. The imine reference compounds were conveniently generated by fast atom bombardment-induced reduction of oximes, removing the requirement for using conventional chemical synthesis. Protonated imines and the (M − H)− ions of oximes fragment extensively via charge-remote processes to eliminate the elements of alkanes. This chemistry is not shared by the protonated oximes

Statistical Multifragmentation in Thermodynamic Limit

An exact analytical solution of the statistical multifragmentation model is found in thermodynamic limit. The model exhibits a 1-st order phase transition of the liquid-gas type. The mixed phase region of the phase diagram, where the gas of nuclear fragments coexists with the infinite liquid condensate, is unambiguously identified. The peculiar thermodynamic properties of the model near the boundary between the mixed phase and the pure gaseous phase are studied. The results for the caloric curve and specific heat are presented and a physical picture of the nuclear liquid-gas phase transition is clarified.Comment: 4 figure

Sol-Gel Synthesis and Characterization of Cerium Substituted Calcium Hydroxyapatite

In this study, an aqueous sol-gel chemistry route based on phosphoric acid as the phosphorus precursor, calcium acetate monohydrate and cerium (III) nitrate hexahydrate as source of calcium and cerium ions, respectively, have been used to prepare cerium-substituted calcium hydroxyapatite (CHAp) powders. The tartaric acid was used as complexing agent in the sol-gel processing. The final products were obtained by calcination of the dry precursor gels for 5 h at 1000 °C. The phase transformations, composition, and structural changes in the polycrystalline samples were studied by infrared spectroscopy (IR), X-ray powder diffraction analysis (XRD), scanning electron microscopy (SEM), UV-visible reflection spectroscopy and luminescence measurements. It was demonstrated, however, that the high substitution of calcium by cerium does not proceed in the CHAp. The reflectance spectra of Ce substituted CHAp show nearly 100% reflection in the wavelength range of 450-800 nm. The luminescent properties of these samples were also investigated. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3493

Schwinger type processes via branes and their gravity duals

We consider Schwinger type processes involving the creation of the charge and monopole pairs in the external fields and propose interpretation of these processes via corresponding brane configurations in Type IIB string theory. We suggest simple description of some new interesting nonperturbative processes like monopole/dyon transitions in the electric field and W-boson decay in the magnetic field using the brane language. Nonperturbative pair production in the strong coupling regime using the AdS/CFT correspondence is studied. The treatment of the similar processes in the noncommutative theories when noncommutativity is traded for the background fields is presented and the possible role of the critical magnetic field which is S-dual to the critical electric field is discussed.Comment: 29pp, LaTeX; v3. reference adde

Critical Exponents of the Statistical Multifragmentation Model

For the statistical multifragmentation model the critical indices $\alpha^\prime, \beta, \gamma^\prime, \delta$ are calculated as functions of the Fisher parameter $\tau$. It is found that these indices have different values than in Fisher's droplet model. Some peculiarities of the scaling relations are discussed. The basic model predicts for the index $\tau$ a narrow range of values, $1.799< \tau < 1.846$, which is consistent with two experiments on nuclear multifragmentation.Comment: minor changes of the text, four references adde

Model of multifragmentation, Equation of State and phase transition

We consider a soluble model of multifragmentation which is similar in spirit to many models which have been used to fit intermediate energy heavy ion collision data. We draw a p-V diagram for the model and compare with a p-V diagram obtained from a mean-field theory. We investigate the question of chemical instability in the multifragmentation model. Phase transitions in the model are discussed.Comment: Revtex, 9 pages including 6 figures: some change in the text and Fig.

Thermal one- and two-graviton Green's functions in the temporal gauge

The thermal one- and two-graviton Green's function are computed using a temporal gauge. In order to handle the extra poles which are present in the propagator, we employ an ambiguity-free technique in the imaginary-time formalism. For temperatures T high compared with the external momentum, we obtain the leading T^4 as well as the subleading T^2 and log(T) contributions to the graviton self-energy. The gauge fixing independence of the leading T^4 terms as well as the Ward identity relating the self-energy with the one-point function are explicitly verified. We also verify the 't Hooft identities for the subleading T^2 terms and show that the logarithmic part has the same structure as the residue of the ultraviolet pole of the zero temperature graviton self-energy. We explicitly compute the extra terms generated by the prescription poles and verify that they do not change the behavior of the leading and sub-leading contributions from the hard thermal loop region. We discuss the modification of the solutions of the dispersion relations in the graviton plasma induced by the subleading T^2 contributions.Comment: 17 pages, 5 figures. Revised version to be published in Phys. Rev.

Quenching 2D Quantum Gravity

We simulate the Ising model on a set of fixed random $\phi^3$ graphs, which corresponds to a {\it quenched} coupling to 2D gravity rather than the annealed coupling that is usually considered. We investigate the critical exponents in such a quenched ensemble and compare them with measurements on dynamical $\phi^3$ graphs, flat lattices and a single fixed $\phi^3$ graph.Comment: 8 page

Negative specific heat in a thermodynamic model of multifragmentation

We consider a soluble model of multifragmentation which is similar in spirit to many models which have been used to fit intermediate energy heavy ion collision data. In this model $c_v$ is always positive but for finite nuclei $c_p$ can be negative for some temperatures and pressures. Furthermore, negative values of $c_p$ can be obtained in canonical treatment. One does not need to use the microcanonical ensemble. Negative values for $c_p$ can persist for systems as large as 200 paticles but this depends upon parameters used in the model calculation. As expected, negative specific heats are absent in the thermodynamic limit.Comment: Revtex, 13 pages including 6 figure

Hadronic τ\tau decay, the renormalization group, analiticity of the polarization operators and QCD parameters

The ALEPH data on hadronic tau-decay is throughly analysed in the framework of QCD. The perturbative calculations are performed in 1-4-loop approximation. The analytical properties of the polarization operators are used in the whole complex q^2 plane. It is shown that the QCD prediction for R_{tau} agrees with the measured value R_{tau} not only for conventional Lambda^{conv}_3 = (618+-29) MeV but as well as for Lambda^{new}_3 = (1666+-7) MeV. The polarization operator calculated using the renormgroup has nonphysical cut [-Lambda^2_3, 0]. If Lambda_3 = Lambda^{conv}_3, the contribution of only physical cut is deficient in the explanation of the ALEPH experiment. If Lambda_3 = Lambda^{new}_3 the contribution of nonphysical cut is very small and only the physical cut explains the ALEPH experiment. The new sum rules which follow only from analytical properties of polarization operators are obtained. Basing on the sum rules obtained, it is shown that there is an essential disagreement between QCD perturbation theory and the tau-lepton hadronic decay experiment at conventional value Lambda_3. In the evolution upwards to larger energies the matching of r(q^2) (Eq.(12)) at the masses J/psi, Upsilon and 2m_t was performed. The obtained value alpha_s(-m^2_z) = 0.141+-0.004 (at Lambda_3 = Lambda^{new}_3) differs essentially from conventional value, but the calculation of the values R(s) = sigma(e+e- -> hadrons)/sigma(e+e- -> mu+mu-), R_l = Gamma(Z -> hadrons)/Gamma(Z -> leptons), alpha_s(-3 GeV^2), alpha_s(-2.5 GeV^2) does not contradict the experiments.Comment: 20 page