Event-by-event fluctuations of the Kaon-to-Pion ratio in central Pb+Pb collisions at 158 GeV per nucleon

We present the first measurement of fluctuations from event to event in the production of strange particles in collisions of heavy nuclei. The ratio of charged kaons to charged pions is determined for individual central Pb+Pb collisions. After accounting for the fluctuations due to detector resolution and finite number statistics we derive an upper limit on genuine nonstatistical fluctuations, which could be related to a first- or second-order QCD phase transition. Such fluctuations are shown to be very small.     

Strong binding in the DNA minor groove by an aromatic diamidine with a shape that does not match the curvature of the groove

A combination of biophysical techniques has been used to characterize the interaction of an antitrypanosomal agent, CGP 40215A, with DNA. The results from a broad array of methods (DNase I footprinting, surface plasmon resonance, X-ray crystallography, and molecular dynamics) indicate that this compound binds to the minor groove of AT DNA sequences. Despite its unusual linear shape that is not complementary to that of the DNA groove, a high binding affinity was observed in comparison with other similar but more curved diamidine compounds. The amidine groups at both ends of the ligand and the -NH groups on the linker are involved in extensive and dynamic H-bonds to the DNA bases. Complementary and consistent results were obtained from both the X-ray and molecular dynamics studies; both of these methods reveal direct and water-mediated H-bonds between the ligand and the DNA.     

Jozimine A2: The First Dimeric Dioncophyllaceae‐Type Naphthylisoquinoline Alkaloid,with Three Chiral Axes and High Antiplasmodial Activity

A new dimeric naphthylisoquinoline alkaloid, jozimine A₂ ( 2 ), was isolated from the root bark of an Ancistrocladus species from the Democratic Republic of Congo. Its absolute stereostructure was determined by chemical, spectroscopic, and chiroptical methods, and confirmed by X‐ray crystallography. Jozimine A₂ ( 2 ) is one of the as yet very rare naphthylisoquinoline dimers whose central biaryl axis is rotationally hindered. Moreover, it is the first natural dimer of a Dioncophyllaceae‐type alkaloid, that is, lacking oxygen functions at C6, and bearing R configurations at C3 in its two isoquinoline portions. Despite this decreased steric hindrance, the outer biaryl axes are chiral, too, so that jozimine A₂ ( 2 ) has three consecutive stereogenic axes and, together with the four stereogenic centers, seven elements of chirality and is C₂‐symmetric. The new dimer exhibits excellent, and specific, antiplasmodial activity. To further confirm its stereostructure and for likewise testing the bioactivities of its (unnatural) atropo‐diastereomer, compound 2 was prepared by semi‐synthesis from the co‐occurring (and likewise synthetically available) dioncophylline A ( 5 ), along with its atropo‐diastereomer, 3′‐epi‐ 2 .     

Simulations of Closed Timelike Curves

Proposed models of closed timelike curves (CTCs) have been shown to enable powerful information-processing protocols. We examine the simulation of models of CTCs both by other models of CTCs and by physical systems without access to CTCs. We prove that the recently proposed transition probability CTCs (T-CTCs) are physically equivalent to postselection CTCs (P-CTCs), in the sense that one model can simulate the other with reasonable overhead. As a consequence, their information-processing capabilities are equivalent. We also describe a method for quantum computers to simulate Deutschian CTCs (but with a reasonable overhead only in some cases). In cases for which the overhead is reasonable, it might be possible to perform the simulation in a table-top experiment. This approach has the benefit of resolving some ambiguities associated with the equivalent circuit model of Ralph et al. Furthermore, we provide an explicit form for the state of the CTC system such that it is a maximum-entropy state, as prescribed by Deutsch.     

A local level-set method using a hash table data structure

We present a local level-set method based on the hash table data structure, which allows the storage of only a band of grid points adjacent to the interface while providing an O(1) access to the data. We discuss the details of the construction of the hash table data structure as well as the advection and reinitialization schemes used for our implementation of the level-set method. We propose two dimensional numerical examples and compare the results to those obtained with a quadtree data structure. Our study indicates that the method is straightforward to implement but suffers from limitations that make it less efficient than the quadtree data structure.