Logarithmic correction to the bekenstein-hawking entropy

The exact formula derived by us earlier for the entropy of a four dimensional nonrotating black hole within the quantum geometry formulation of the event horizon in terms of boundary states of a three dimensional Chern-Simons theory is reexamined for large horizon areas. In addition to the semiclassical Bekenstein-Hawking contribution proportional to the area obtained earlier, we find a contribution proportional to the logarithm of the area together with subleading corrections that constitute a series in inverse powers of the area.     

Vibrational dynamics of the organometallic compound triarylorganoantimony (V) SbPh<Subscript>3</Subscript>[O<Subscript>2</Subscript>CC(OH)Ph<Subscript>2</Subscript>]<Subscript>2</Subscript>

A complete normal coordinate analysis was performed for five-coordinate non-rigid triarylantimony diester SbPh₃(O₂CR)₂, known to be a bioactive molecule, using Wilson G-F matrix method and Urey Bradley force field. The study of vibrational dynamics was performed using the concept of group frequencies and band intensities.      

Kinetic effects in manganites La1 − x Ag y MnO3 (y ≤ x)

We have measured the resistivity, magnetoresistance, and thermopower of ceramic manganite samples La_{1 ? x} Ag _y MnO₃ (y ≤ x) doped with silver as functions of temperature (4.2–350 K) and magnetic field (up to 26 kOe). A metal-insulator phase transition is observed in all investigated samples at temperatures close to room temperature. The behavior of the resistivity and thermopower in the high-temperature paramagnetic region is interpreted using the concept of small radius polaron; the activation energy decreases with increasing doping level. The resistivity in the low-temperature ferromagnetic region is approximated by the expression ρ_FM(T) = ρ₀ + AT ² + BT ^4.5 presuming the existence of electron-electron and electron-magnon interactions. A resistivity minimum and a strong magnetoresistive effect are observed at low temperatures. The latter effect is associated with scattering of charge carriers at grain boundaries, which are antiferromagnetically ordered relative to one another. The temperature dependence of thermopower in the magnetically ordered phase is described in the framework of a model taking into account the drag of charge carriers by magnons.     

Structural, magnetotransport and morphological studies of Sb-doped La2/3Ba1/3MnO3 ceramic perovskites

We report here the structural, magnetotransport and morphological studies of Sb-doped La_2/3Ba_1/3Mn_1−xSb_xO₃ perovskite manganites. Pristine material La_2/3Ba_1/3MnO₃ (LBMO) shows two insulator-metal (I-M) transitions in the electrical resistivity-temperature (ρ-T) behavior. While the higher temperature transition (T_P1) at ∼340 K is reminiscent of the usual I-M transition in manganites, the lower temperature transition (T_P2) at ∼250 K has been ascribed to the grain boundary (GB) effects arising out of the ionic size mismatch between the ions present at the rare-earth site (La³⁺ and Ba²⁺). With Sb-doping T_P1 shifts to lower temperatures while T_P2 remains invariant up to 3% and shifts to lower temperature for 5%. Room temperature electrical resistivity and the peak values also increase successively with Sb-doping. Scanning electron micrographs of the samples exhibit a gradual increase in their grain sizes with Sb indicating a gradual decrease in the GB density. Shift of T_P1 with doping is explained on the basis of a competition between double-exchange and super-exchange mechanisms. The overall electrical resistivity increases and the shift in the electrical resistivity hump (T_P2) with Sb-doping is found related to be gradually decreasing GB density and the ensuing lattice strain increase at the GBs. The intrinsic magnetoresistance (MR) gets suppressed and extrinsic MR gets enhanced with Sb-doping. At T>T_P1, the electrical resistivity is found to follow the adiabatic polaron hopping model whereas the electron-magnon scattering is found to dominate in the metallic regime (T<T_P1).     

Search for anomalous interaction mean free paths of charge, 2≦Z≦18 projectile fragments in emulsions exposed to 1.8 A GeV40Ar ions

⁴⁰Ar-emulsion interactions are studied, to investigate the question of anomalons, in twoG- 5 emulsion stacks. In about 4600 primary interactions, projectile fragments of Z≧2 for all generations have been followed until they interact or leave the stack. After careful estimation of charges of these fragments, variation of their mean free paths is studied as a function of distance from the preceding interaction. Generation effect,N _h dependence and production angle effect are investigated. In addition multi-chain events are analysed separately. Our results do not show anomalons at the 6% level and are consistent with non-occurrence of anomalons. However, this experiment is not sensitive enough to rule out anomalons (with a mfp of the order of 2 to 3 cm) produced at about 1% (or less) level.     

Crystal and magnetic structure of the Sm0.55Sr0.45MnO3 and (Nd0.545Tb0.455)0.55Sr0.45MnO3 manganites

Neutron diffraction data are presented for the ¹⁵²Sm_0.55Sr_0.45MnO₃ (SSM) and (Nd_0.545Tb_0.455)_0.55Sr_0.45MnO₃ (NTSM) manganites. The Nd and Tb contents in the latter composition are such that the average radius of the A cation 〈r _A 〉 in these two compounds is the same. The difference in local tolerance factor fluctuations was about 10%. It was found that replacement of a rare-earth cation with leaving 〈r _A 〉 unchanged has practically no effect on the structural and transport properties; indeed, both compounds are metals at low temperatures, have the same crystal structure from liquid-helium to room temperature, and exhibit the same pattern of structural distortions at the onset of magnetic ordering. Magnetic moments of Mn ions in both compositions are ferromagnetically ordered at low temperatures, with T _C =122 and 90 K for the SSM and NTSM, respectively. Below 80 K, the rare-earth cation moments in NTSM undergo additional ordering. In contrast to compositions that are close in Sr concentration (x _Sr=0.4, 0.5), which feature a phase-separated state with a mixture of the ferromagnetic metallic and antiferromagnetic insulator phases, the ground state of both studied compositions with x _Sr=0.45 is uniformly ferromagnetic and metallic. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 9, 2004, pp. 1650–1656. Original Russian Text Copyright ? 2004 by Kurbakov, Trounov, Balagurov, Pomyakushin, Sheptyakov, Gorbenko, Kaul.     

First order transition to oscillation death through an environment

The emergence of dynamical abrupt transitions for the first time in an ensemble of identical limit-cycle and chaotic oscillators coupled via a common environment is reported. The transition from the oscillatory state to the death state and vice versa, in these networks of oscillators are found not only discontinuous as well as irreversible in the parameter space. This first order phase transition in these systems is termed as Explosive Death. The occurrence of such transition is studied in details by using an appropriate order parameter for both limit-cycle and chaotic oscillators, in particular, Stuart–Landau and Rössler oscillators. The backward transition point for this phenomenon is obtained analytically using linear stability analysis and is found to be consistent with the numerical results.     

Isotope effect for transport and magnetic properties of La 0.35 Pr 0.35 Ca 0.3 MnO 3 thin films

The effect of ¹⁶ O → ¹⁸ O isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La_0.35Pr_0.35Ca_0.3MnO₃ epitaxial thin films deposited onto LaAlO₃ and SrTiO₃ substrates. For the films on LaAlO₃, the isotope substitution resulted in the reversible transition from a metal-like to insulating state. The applied magnetic field ( H ≥ 2 T) transformed the sample with ¹⁸O back to the metallic state. The films on SrTiO₃ remained metallic at low temperatures for both ¹⁶O and ¹⁸O, but the shift of the resistivity peak corresponding to onset of metallic state exceeded 63 K after ¹⁶ O → ¹⁸ O substitution. The temperature dependence of both resistivity and magnetic susceptibility was characterized by hysteresis, especially pronounced in the case of the films on LaAlO₃. Such a behavior gives certain indications of the phase separation characteristic of interplay between ferromagnetism and charge ordering. Received 11 February 2000 and Received in final form 13 September 2000     

Competition between hydrogen bonding and dispersion interactions in the indole···pyridine dimer and (indole)2···pyridine trimer studied in a supersonic jet

Structures of the indole···pyridine dimer and (indole)2···pyridine trimer have been investigated in a supersonic jet using resonant two-photon ionization (R2PI) and IR-UV double resonance spectroscopic techniques combined with quantum chemistry calculations. R2PI spectra of the dimer and the trimer recorded by electronic excitation of the indole moiety show that the red-shift in the band origin of the dimer with respect to the 0(0)(0) band of the monomer is larger compared to that of the trimer. The presence of only one conformer in the case of both the dimer and the trimer has been confirmed from IR-UV hole-burning spectroscopy. The structures of the dimer and the trimer have been determined from resonant ion dip infrared (RIDIR) spectra combined with ab initio as well as DFT/M05-2X and DFT/M06-2X calculations. It has been found that the dimer, observed in the experiment, has a V-shaped geometry stabilized by N–H···N and C–H···N hydrogen bonding interactions, as well as C–H···π and π···π dispersion interactions. The geometry of the trimer has been found to be a cyclic one stabilized by N–H···N, N–H···π, C–H···π, and C–H···N interactions. The most important finding of this current study is the observation of the mixed dimer and trimer, which are stabilized by hydrogen bonding as well as dispersion interactions.     

Markovnikov addition of vinyl acetate with azoles catalyzed by potassium tert-butoxide

A simple and efficient methodology for Markovnikov addition of azoles with vinyl acetate catalyzed by potassium tert-butoxide is described.N-heterocyclic compounds are synthesized from simple and commercially available starting materials under mild conditions in high yields.