Oscillation frequency dependence of nonclassical rotation inertia of solid 4He

The nonclassical rotational inertia fraction of the identical cylindrical solid 4He below 300 mK is studied at 496 and 1173 Hz by a double resonance torsional oscillator. Below 35 mK, the fractions are the same at sufficiently low rim velocities. Above 35 mK, the fraction is greater for the higher than the lower mode. The dissipation peak of the lower mode occurs at a temperature approximately 4 mK lower than that of the higher mode. The drive dependence of the two modes shows that the reduction of the fraction is characterized by critical velocity, not amplitude or acceleration.     

Calories from carbohydrates: energetic contribution of the carbohydrate moiety of rebeccamycin to DNA binding and the effect of its orientation on topoisomerase I inhibition.

BACKGROUND: Only a few antitumor drugs inhibit the DNA breakage-reunion reaction catalyzed by topoisomerase. One is the camptothecin derivative topotecan that has recently been used clinically. Others are the glycosylated antibiotic rebeccamycin and its synthetic analog NB-506, which is presently in phase I of clinical trials. Unlike the camptothecins, rebeccamycin-type compounds bind to DNA. We set out to elucidate the molecular basis of their interaction with duplex DNA, with particular emphasis on the role of the carbohydrate residue. RESULTS: We compared the DNA-binding and topoisomerase-I-inhibition activities of two isomers of rebeccamycin that contain a galactose residue attached to the indolocarbazole chromophore via an alpha (axial) or a beta (equatorial) glycosidic linkage. The modification of the stereochemistry of the chromophore-sugar linkage results in a marked change of the DNA-binding and topoisomerase-I- poisoning activities. The inverted configuration at the C-1' of the carbohydrate residue abolishes intercalative binding of the drug to DNA thereby drastically reducing the binding affinity. Consequently, the alpha isomer has lost the capacity to induce topoisomerase-I-mediated cleavage of DNA. Comparison with the aglycone allowed us to determine the energetic contribution of the sugar residue. CONCLUSIONS: The optimal interaction of rebeccamycin analogs with DNA is controlled to a large extent by the stereochemistry of the sugar residue. The results clarify the role of carbohydrates in stereospecific drug-DNA interactions and provide valuable information for the rational design of new rebeccamycin-type antitumor agents.     

Magnetic reconnection triggering magnetohydrodynamic instabilities during a sawtooth crash in a Tokamak plasma

Thomson scattering measurements with subcentimeter spatial resolution have been made during a sawtooth crash in a Mega Ampere Spherical Tokamak fusion plasma. The unparalleled resolution of the temperature profile has shed new light on the mechanisms that underlie the sawtooth. As magnetic reconnection occurs, the temperature gradient at the island boundary increases. The increased local temperature gradient is sufficient to make the helical core unstable to ideal magnetohydrodynamic instabilities, thought to be responsible for the rapidity of the collapse.     

Kernel-based fuzzy clustering and fuzzy clustering: A comparative experimental study

In this study, we present a comprehensive comparative analysis of kernel-based fuzzy clustering and fuzzy clustering. Kernel based clustering has emerged as an interesting and quite visible alternative in fuzzy clustering, however, the effectiveness of this extension vis-à-vis some generic methods of fuzzy clustering has neither been discussed in a complete manner nor the performance of clustering quantified through a convincing comparative analysis. Our focal objective is to understand the performance gains and the importance of parameter selection for kernelized fuzzy clustering. Generic Fuzzy C-Means (FCM) and Gustafson–Kessel (GK) FCM are compared with two typical generalizations of kernel-based fuzzy clustering: one with prototypes located in the feature space (KFCM-F) and the other where the prototypes are distributed in the kernel space (KFCM-K). Both generalizations are studied when dealing with the Gaussian kernel while KFCM-K is also studied with the polynomial kernel. Two criteria are used in evaluating the performance of the clustering method and the resulting clusters, namely classification rate and reconstruction error. Through carefully selected experiments involving synthetic and Machine Learning repository (http://archive.ics.uci.edu/beta/) data sets, we demonstrate that the kernel-based FCM algorithms produce a marginal improvement over standard FCM and GK for most of the analyzed data sets. It has been observed that the kernel-based FCM algorithms are in a number of cases highly sensitive to the selection of specific values of the kernel parameters.     

Generalized double exponential potential functions for diatomic molecules

Two variants of the double exponential potential function and their virial modifications are proposed and tested. The first in reduced variables is F(t)=e^−mt{[m(m²−1)^−1/2−1]exp[−(m²−1)^1/2t]−[m(m²−1)^−1/2+1]exp[(m²−1)^1/2t]} where t=κs=κ(R−R_e))/R_e, κ is a scaling constant, and m is a parameter. The second is G(t)=e^−mt{e^−mt−exp[(m²−1)^1/2t]+exp[−(m²−1)^1/2t]}. For m<1, F(t) and G(t) are expressible in terms of trigonometric functions. A new procedure [multiplication by e^s/(1+s)] is illustrated that modifies potential functions so that they necessarily satisfy the molecular virial theorem. The generalized double exponential functions generate scaled first and second Dunham coefficients that well describe the experimental results for both ground and excited states. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 1–8, 1997     

Cohomology of incidence coalgebras

The cohomology groups Hⁿ(M, C) are studied, where C is the incidence coalgebra of a locally finite partially ordered set P and where M is a C-C comodule depending on a convex coarsening of the given partial order on P. The case where P is a geometric lattice and the convex coarsening is just the equality relation is emphasized.     

Charge asymmetry in inelastic π−p interactions at 205 GeV/c for particles with transverse momentum > 1.0 GeVc

In 205 GeV/cπ^?p inelastic interactions, negative particles with transverse momentum greater than 1.0 GeV/c moving forward in the center of mass outnumber similar positive particles by a factor of 3.7 to 1, greatly in excess of the corresponding ratio for small transverse momentum. The asymmetry is reversed in the backward direction. The forward asymmetry is most prominent in 2-, 4-, and 6-prong interactions, but both forward and backward asymmetries are also substantial for higher multiplicity interactions.