Seeding of Strange Matter with New Physics

At greater than nuclear densities, matter may convert into a mixture of nucleons, hyperons, dibaryons, and strangelets, thus facilitating the formation of strange matter even before the onset of the quark-matter phase transition. From a nonstrange dibaryon condensate, it may even be possible to leapfrog into strange matter with a certain new interaction, represented by an effective six-quark operator which is phenomenologically unconstrained.Comment: 7 pages, no figure (Talk given at SQM97

An open boundary condition for application in numerical coastal models

Open boundaries (OBs) are usually unavoidable in numerical coastal circulation simulations. At OBs, appropriate open boundary conditions (OBCs) are required and a good OBC should be able to let outgoing waves freely pass to the exterior of a computational domain without creating reflections at the OBs. In the present study, a methodology has been developed to predict two parameters, phase speed c_r and decay time T_f, in a standard OBC formulation, so that the OBC is significantly improved compared to commonly used existing OBCs with specified c_r and T_f. For the conditions where wave period is unknown, the OBC with approximated c_r and T_f may be applied and a test reveals that this OBC is able to yield good results in typical coastal flow conditions. In addition, a Swing-Door Boundary Condition (SDBC) is proposed and tested for application at an offshore open boundary where both incoming and outgoing waves exist.Singapore-MIT Alliance for Research and Technology Cente

Strangelets: Who is Looking, and How?

It has been over 30 years since the first suggestion that the true ground state of cold hadronic matter might be not nuclear matter but rather strange quark matter (SQM). Ever since, searches for stable SQM have been proceeding in various forms and have observed a handful of interesting events but have neither been able to find compelling evidence for stable strangelets nor to rule out their existence. I will survey the current status and near future of such searches with particular emphasis on the idea of SQM from strange star collisions as part of the cosmic ray flux.Comment: Talk given at International Conference on Strangeness in Quark Matter, 2006. 8 pages. 1 figur

Energy compensation and received echo level dynamics in constant-frequency bats during active target approaches

This work was supported by the Semper Arden Carlsberg grant to P.T.M., by a National Science Foundation grant [1658620] to R.M. and by a National Natural Science Foundation of China [11574183] to R.M.Bats have been reported to adjust the energy of their outgoing vocalizations to target range (R) in a logarithmic fashion close to 20log10R which has been interpreted as providing one-way compensation for increasing echo levels during target approaches. However, it remains unknown how species using high-frequency calls, which are strongly affected by absorption, adjust their vocal outputs during approaches to point targets. We hypothesized that such species should compensate less than the 20log10R model predicts at longer distances and more at shorter distances as a consequence of the significant influence of absorption at longer ranges. Using a microphone array and an acoustic recording tag, we show that the output adjustments of two Hipposideros pratti and one Hipposideros armiger do not decrease logarithmically during approaches to different-sized targets. Consequently, received echo levels increase dramatically early in the approach phase with near-constant output levels, but level off late in the approach phase as a result of substantial output reductions. To improve echo-to-noise ratio, we suggest that bats using higher frequency vocalizations compensate less at longer ranges, where they are strongly affected by absorption. Close to the target, they decrease their output levels dramatically to mitigate reception of very high echo levels. This strategy maintains received echo levels between 6 and 40 dB re. 20 µPa2 s across different target sizes. The bats partially compensated for target size, but not in a one-to-one dB fashion, showing that these bats do not seek to stabilize perceived echo levels, but may instead use them to gauge target size.Publisher PDFPeer reviewe

Genetic structure among the local chicken ecotypes of Tanzania based on microsatellite DNA typing

A study was conducted to evaluate the genetic structure of local chicken ecotypes of Tanzania using 20 polymorphic microsatellite DNA markers. A standard PCR was followed by manual genotyping (6% native polyacrylamide gel visualized by silver staining). Phylogenetic analysis of 13 individuals from each of the nine ecotypes named Ching'wekwe, Kuchi, Mbeya, Morogoro-medium, N'zenzegere, Pemba, Singamagazi, Unguja and a White Leghorn breed was performed. The ten populations assorted into nine clusters with chickens from the same ecotype often clustering together. It is concluded that there is high genetic relatedness within indigenous chicken ecotype than between ecotypes. This offers a basic step towards rational decision-making on the modalities of selective breeding without compromising the existence of each unique genetic resource.Key words: Local-chicken, ecotypes, microsatellites, DNA, PCR.African Journal of Biotechnology Vol. 4 (8), pp. 768-77

Quark matter in compact stars?

Ozel, in a recent reanalysis of EXO 0748-676 observational data (astro-ph/0605106), concluded that quark matter probably does not exist in the center of compact stars. We show that the data is actually consistent with the presence of quark matter in compact stars.Comment: 4 pages, LaTeX; New title and overall rewrite to reflect version published in Nature. Conclusions unchange

Practical use of variational principles for modeling water waves

This paper describes a method for deriving approximate equations for irrotational water waves. The method is based on a 'relaxed' variational principle, i.e., on a Lagrangian involving as many variables as possible. This formulation is particularly suitable for the construction of approximate water wave models, since it allows more freedom while preserving the variational structure. The advantages of this relaxed formulation are illustrated with various examples in shallow and deep waters, as well as arbitrary depths. Using subordinate constraints (e.g., irrotationality or free surface impermeability) in various combinations, several model equations are derived, some being well-known, other being new. The models obtained are studied analytically and exact travelling wave solutions are constructed when possible.Comment: 30 pages, 1 figure, 62 references. Other author's papers can be downloaded at http://www.denys-dutykh.com