Chaotic string-capture by black hole

We consider a macroscopic charge-current carrying (cosmic) string in the background of a Schwarzschild black hole. The string is taken to be circular and is allowed to oscillate and to propagate in the direction perpendicular to its plane (that is parallel to the equatorial plane of the black hole). Nurmerical investigations indicate that the system is non-integrable, but the interaction with the gravitational field of the black hole anyway gives rise to various qualitatively simple processes like "adiabatic capture" and "string transmutation".Comment: 13 pages Latex + 3 figures (not included), Nordita 93/55

Dynamics of cosmic strings and springs; a covariant formulation

A general family of charge-current carrying cosmic string models is investigated. In the special case of circular configurations in arbitrary axially symmetric gravitational and electromagnetic backgrounds the dynamics is determined by simple point particle Hamiltonians. A certain "duality" transformation relates our results to previous ones, obtained by Carter et. al., for an infinitely long open stationary string in an arbitrary stationary background.Comment: 11 pages, Latex, Nordita preprint 93/28

Structural basis for sequence specific DNA binding and protein dimerization of HOXA13.

The homeobox gene (HOXA13) codes for a transcription factor protein that binds to AT-rich DNA sequences and controls expression of genes during embryonic morphogenesis. Here we present the NMR structure of HOXA13 homeodomain (A13DBD) bound to an 11-mer DNA duplex. A13DBD forms a dimer that binds to DNA with a dissociation constant of 7.5 nM. The A13DBD/DNA complex has a molar mass of 35 kDa consistent with two molecules of DNA bound at both ends of the A13DBD dimer. A13DBD contains an N-terminal arm (residues 324 - 329) that binds in the DNA minor groove, and a C-terminal helix (residues 362 - 382) that contacts the ATAA nucleotide sequence in the major groove. The N370 side-chain forms hydrogen bonds with the purine base of A5* (base paired with T5). Side-chain methyl groups of V373 form hydrophobic contacts with the pyrimidine methyl groups of T5, T6* and T7*, responsible for recognition of TAA in the DNA core. I366 makes similar methyl contacts with T3* and T4*. Mutants (I366A, N370A and V373G) all have decreased DNA binding and transcriptional activity. Exposed protein residues (R337, K343, and F344) make intermolecular contacts at the protein dimer interface. The mutation F344A weakens protein dimerization and lowers transcriptional activity by 76%. We conclude that the non-conserved residue, V373 is critical for structurally recognizing TAA in the major groove, and that HOXA13 dimerization is required to activate transcription of target genes

A genome-wide association study reveals specific transferases as candidate loci for bovine milk oligosaccharides synthesis.

BackgroundHuman milk oligosaccharides (OS) play a key role in brain and gut microbiota development of the neonate, but the underlying biosynthetic steps of OS in the mammary gland are still largely unknown. As bovine milk contains OS with somewhat similar structures and functionalities there is increased interest in further understanding the genetic basis underlying the OS content of milk for eventual extraction and generation of value-added ingredients for infant formulas and nutraceuticals. The present study is the first to report on genetic parameter estimation as well as on a genome wide association study (GWAS) from the largest bovine milk OS dataset analyzed to date.ResultsIn total 15 different bovine milk OS were monitored. Heritabilities ranged from 0 to 0.68 in Danish Holstein and from 0 to 0.92 in Danish Jersey. The GWAS identified in total 1770 SNPs (FDR < 0.10) for five different OS in Danish Holstein and 6913 SNPs (FDR < 0.10) for 11 OS in Danish Jersey. In Danish Holstein, a major overlapping QTL was identified on BTA1 for LNH and LNT explaining 24% of the variation in these OS. The most significant SNPs were associated with B3GNT5, a gene encoding a glycosyltransferase involved in glycan synthesis. In Danish Jersey, a very strong QTL was detected for the OS with composition 2 Hex 1 HexNAc (isomer 1) on BTA11. The most significant SNP had -log10(P-value) of 52.88 (BOVINEHD1100030300) and was assigned to ABO, a gene encoding ABO blood group glycosyltransferases. This SNP has been reported to be a missense mutation and explains 56% of the OS variation. Other candidate genes of interest identified for milk OS were ALG3, B3GALNT2, LOC520336, PIGV, MAN1C1, ST6GALNAC6, GLT6D1, GALNT14, GALNT17, COLGALT2, LFNG and SIGLEC.ConclusionTo our knowledge, this is the first study documenting a solid breeding potential for bovine milk OS and a strong indication of specific candidate genes related to OS synthesis underlying this genetic influence. This new information has the potential to guide breeding strategies to achieve production of milk with higher diversity and concentration of OS and ultimately facilitate large-scale extraction of bovine milk OS

Stable and Unstable Circular Strings in Inflationary Universes

It was shown by Garriga and Vilenkin that the circular shape of nucleated cosmic strings, of zero loop-energy in de Sitter space, is stable in the sense that the ratio of the mean fluctuation amplitude to the loop radius is constant. This result can be generalized to all expanding strings (of non-zero loop-energy) in de Sitter space. In other curved spacetimes the situation, however, may be different. In this paper we develop a general formalism treating fluctuations around circular strings embedded in arbitrary spatially flat FRW spacetimes. As examples we consider Minkowski space, de Sitter space and power law expanding universes. In the special case of power law inflation we find that in certain cases the fluctuations grow much slower that the radius of the underlying unperturbed circular string. The inflation of the universe thus tends to wash out the fluctuations and to stabilize these strings.Comment: 15 pages Latex, NORDITA 94/14-

Second Order Perturbations of a Macroscopic String; Covariant Approach

Using a world-sheet covariant formalism, we derive the equations of motion for second order perturbations of a generic macroscopic string, thus generalizing previous results for first order perturbations. We give the explicit results for the first and second order perturbations of a contracting near-circular string; these results are relevant for the understanding of the possible outcome when a cosmic string contracts under its own tension, as discussed in a series of papers by Vilenkin and Garriga. In particular, second order perturbations are necessaary for a consistent computation of the energy. We also quantize the perturbations and derive the mass-formula up to second order in perturbations for an observer using world-sheet time $\tau$. The high frequency modes give the standard Minkowski result while, interestingly enough, the Hamiltonian turns out to be non-diagonal in oscillators for low-frequency modes. Using an alternative definition of the vacuum, it is possible to diagonalize the Hamiltonian, and the standard string mass-spectrum appears for all frequencies. We finally discuss how our results are also relevant for the problems concerning string-spreading near a black hole horizon, as originally discussed by Susskind.Comment: New discussion about the quantum mass-spectrum in chapter

First Starbursts at high redshift: Formation of globular clusters

Numerical simulations of a Milky Way-size galaxy demonstrate that globular clusters with the properties similar to observed can form naturally at z > 3 in the concordance Lambda-CDM cosmology. The clusters in our model form in the strongly baryon-dominated cores of supergiant molecular clouds. The first clusters form at z = 12, while the peak formation appears to be at z = 3-5. The zero-age mass function of globular clusters can be approximated by a power-law dN/dM ~ M^-2, in agreement with observations of young massive star clusters.Comment: 4 pages, proceedings of the "Multi-Wavelength Cosmology" meeting, June 200

Deformations of extended objects with edges

We present a manifestly gauge covariant description of fluctuations of a relativistic extended object described by the Dirac-Nambu-Goto action with Dirac-Nambu-Goto loaded edges about a given classical solution. Whereas physical fluctuations of the bulk lie normal to its worldsheet, those on the edge possess an additional component directed into the bulk. These fluctuations couple in a non-trivial way involving the underlying geometrical structures associated with the worldsheet of the object and of its edge. We illustrate the formalism using as an example a string with massive point particles attached to its ends.Comment: 17 pages, revtex, to appear in Phys. Rev. D5