On the nonlinear dynamics of topological solitons in DNA

Dynamics of topological solitons describing open states in the DNA double helix are studied in the frameworks of the model which takes into account asymmetry of the helix. It is shown that three types of topological solitons can occur in the DNA double chain. Interaction between the solitons, their interactions with the chain inhomogeneities and stability of the solitons with respect to thermal oscillations are investigated.Comment: 16 pages, 16 figure

Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50K superconductor

We report an easy single step synthesis route of title compound NdFeAsO0.80F0.20 superconductor having bulk superconductivity below 50 K. The title compound is synthesized via solid-state reaction route by encapsulation in an evacuated (10-3 Torr) quartz tube. Rietveld analysis of powder X-ray diffraction data shows that compound crystallized in tetragonal structure with space group P4/nmm. R(T)H measurements showed superconductivity with Tc (R=0) at 48 K and a very high upper critical field (Hc2) of up to 345 Tesla. Magnetic measurements exhibited bulk superconductivity in terms of diamagnetic onset below 50 K. The lower critical field (Hc1) is around 1000 Oe at 5 K. In normal state i.e., above 60 K, the compound exhibited purely paramagnetic behavior and thus ruling out the presence of any ordered FeOx impurity in the matrix. In specific heat measurements a jump is observed in the vicinity of superconducting transition (Tc) along with an upturn at below T=4 K due to the AFM ordering of Nd+3 ions in the system. The Thermo-electric power (TEP) is negative down to Tc, thus indicating dominant carriers to be of n-type in NdFeAsO0.80F0.20 superconductor. The granularity of the bulk superconducting NdFeAsO0.8F0.2 sample is investigated and the intra and inter grain contributions have been individuated by looking at various amplitude and frequencies of the applied AC drive magnetic field.Comment: 26pages text + Figures: comments/suggestions welcome ([email protected] & http://www.freewebs.com/vpsawana

PHONONS IN THE DNA DOUBLE HELIX

We have calculated a model for the phonon modes of the DNA double helix. We have used these modes in a number of applications to biological problems which use lattice concepts such as soft modes, local modes and quasi-momentum

ELECTRICAL TRANSITIONS IN PURE AND DOPED V2O3

Nous avons mesuré les propriétés électriques et thermiques de (CrxV1-x)2O3, 0 < x < 0,03 et de (TixV1-x)2O3, 0 < x < 0,06. Le dopage au chrome (0 < x < 0,018) augmente la température de la transition basse température et augmente la résistivité de la phase métallique ; il rend la transition haute température mieux définie puis diminue l'amplitude de cette transition. Cette dernière transition dans V2O3 dopé à 1 % de chrome est caractérisée par des discontinuités en forme de marche de la résistivité et par des pics lors des balayages en analyse thermique différentielle. L'étude de V2O3 dopé au titane montre que l'amplitude de même que la température de la transition basse température (Tt) diminue énormément lorsque le dopage au Ti augmente. Pour 5,6 % de Ti, Tt décroît de façon abrupte de 35 K à ≈ 0 K. L'énergie d'activation de la phase semi-conductrice diminue exponentiellement et tend vers zéro dans cette gamme de concentration. En rapprochant ces résultats avec d'autres (résistivité et chaleur spécifique), on peut penser que la transition haute température de (CrxV1-x)2O3 n'est pas une transition de Mott mais est peut-être une phase C. D. W. De plus, (TixV1-x)2O3 dont la structure n'est pas altérée par le dopage au Ti est un matériau intéressant pour tester les théories sur la disparition brutale des transitions isolant métal.Extensive electrical and thermal studies on transitions in (CrxV1-x)2O3, 0 ⩽ x ⩽ 0.03, and in (TixV1-x)2O3, 0 ⩽ x ⩽ 0.06, have been undertaken. An increase in Cr-doping (0 ⩽ x ⩽ 0.018) raises the temperature of the low-temperature transition and elevates the resistivity of the metallic phase ; it first sharpens and later diminishes the high-temperature transition. The latter (transition) in 1 at. % of Cr-doped V2O3 is characterized by stepwise discontinuities in resistivity and by sharp spikes in DSC scans. Experimental work on Ti-doped V2O3 shows that the size and temperature of the low-temperature transition (Tt) diminish drastically with increasing Ti content. At a Ti concentration of ca. 5.6 at. %, Tt drops abruptly from 35 to (presumably) 0 K. The activation energy of the semiconducting phase diminishes nearly exponentially to zero in this composition range. The above findings, in conjunction with other evidence obtained from resistivity and heat capacity measurements, suggest that the high-temperature transition in (CrxV1-x)2O3 system is not readily compatible with the Mott transition model but is consistent with the existence of Overhauser charge density waves. Further, the (TixV1-x)2O3 system, whose structure is essentially unaltered by Ti doping, provides a testing ground for theories on the abrupt disappearance of metal-insulator transitions