How do binary clusters form?

Approximately 10 per cent of star clusters are found in pairs, known as binary clusters. We propose a mechanism for binary cluster formation; we use N-body simulations to show that velocity substructure in a single (even fairly smooth) region can cause binary clusters to form. This process is highly stochastic and it is not obvious from a region's initial conditions whether a binary will form and, if it does, which stars will end up in which cluster. We find the probability that a region will divide is mainly determined by its virial ratio, and a virial ratio above 'equilibrium' is generally necessary for binary formation. We also find that the mass ratio of the two clusters is strongly influenced by the initial degree of spatial substructure in the region

Superfluid toroidal currents in atomic condensates

The dynamics of toroidal condensates in the presence of condensate flow and dipole perturbation have been investigated. The Bogoliubov spectrum of condensate is calculated for an oblate torus using a discrete-variable representation and a spectral method to high accuracy. The transition from spheroidal to toroidal geometry of the trap displaces the energy levels into narrow bands. The lowest-order acoustic modes are quantized with the dispersion relation $\omega \sim |m| \omega_s$ with $m=0,\pm 1,\pm 2, ...$. A condensate with toroidal current $\kappa$ splits the $|m|$ co-rotating and counter-rotating pair by the amount: $\Delta E \approx 2 |m|\hbar^2 \kappa < r^{-2}>$. Radial dipole excitations are the lowest energy dissipation modes. For highly occupied condensates the nonlinearity creates an asymmetric mix of dipole circulation and nonlinear shifts in the spectrum of excitations so that the center of mass circulates around the axis of symmetry of the trap. We outline an experimental method to study these excitations.Comment: 8 pages, 8 figure

Nonlinear Stability in the Generalised Photogravitational Restricted Three Body Problem with Poynting-Robertson Drag

The Nonlinear stability of triangular equilibrium points has been discussed in the generalised photogravitational restricted three body problem with Poynting-Robertson drag. The problem is generalised in the sense that smaller primary is supposed to be an oblate spheroid. The bigger primary is considered as radiating. We have performed first and second order normalization of the Hamiltonian of the problem. We have applied KAM theorem to examine the condition of non-linear stability. We have found three critical mass ratios. Finally we conclude that triangular points are stable in the nonlinear sense except three critical mass ratios at which KAM theorem fails.Comment: Including Poynting-Robertson Drag the triangular equilibrium points are stable in the nonlinear sense except three critical mass ratios at which KAM theorem fail

Poliovirus RNA-dependent RNA polymerase (3D(pol)): Structural, biochemical, and biological analysis of conserved structural motifs A and B

We have constructed a structural model for poliovirus RNA-dependent RNA polymerase (3D(pol)) in complex with a primer-template (sym/sub) and ATP. Residues found in conserved structural motifs A (Asp-238) and B (Asn-297) are involved in nucleotide selection. Asp-238 appears to couple binding of nucleotides with the correct sugar configuration to catalytic efficiency at the active site of the enzyme. Asn-297 is involved in selection of ribonucleoside triphosphates over 2'-dNTPs, a role mediated most likely via a hydrogen bond between the side chain of this residue and the 2'-OH of the ribonucleoside triphosphate. Substitutions at position 238 or 297 of 3D(pol) produced derivatives exhibiting a range of catalytic efficiencies when assayed in vitro for poly(rU) polymerase activity or sym/sub elongation activity. A direct correlation existed between activity on sym/sub and biological phenotypes; a 2.5-fold reduction in polymerase elongation rate produced virus with a temperature-sensitive growth phenotype. These data permit us to propose a detailed, structural model for nucleotide selection by 3D(pol), confirm the biological relevance of the sym/sub system, and provide additional evidence for kinetic coupling between RNA synthesis and subsequent steps in the virus life cycle

Problem detection in legislative oversight:An analysis of legislative committee agendas in the U.K. and U.S.

This paper outlines a dynamic problem-detection model of legislative oversight where legislative committees engage in information-gathering to identify emerging policy problems. It is argued that activities of legislative committees are responsive to indicators of problem status across a range of policy domains. This enables committees to react to problems before, or at least simultaneously to, citizens. Our analyses use a new dataset on the policy agenda of UK Parliamentary Select Committees in combination with directly comparable data on US Congressional hearings. Aggregate measures of problem status (e.g. GDP, crime rates) and public opinion on the �most important problem� facing the country are used as independent variables. The comparison between a well-established and developing committee system offers insights into common dynamics across institutional contexts. The findings show that committee agendas in both the UK and US are responsive to problem status for the majority of issues

New Fits for the Non-Perturbative Parameters in the CSS Resummation Formalism

We update the non-perturbative function of the Collins-Soper- Sterman resummation formalism in hadron collisions. Two functional forms in impact parameter space are considered, one with a pure Gaussian form with two parameters and the other with an additional linear term. The results for the two parameter fit are found to be g1=0.24+0.08-0.07 GeV^2, g2=0.34+0.07-0.08 GeV^2. The results for the three parameter fit are g1=0.15+004-0.03 GeV^2, g2=0.48+0.07-0.05 GeV^2, and g3=-0.58+0.26-0.20 GeV^-1. We discuss the potential for the full Tevatron Run I Z boson data for further testing of the universality of the non-perturbative function.Comment: 22 pages, 12 figures, LaTe

Structure-function relationships of the RNA-dependent RNA polymerase from poliovirus (3Dpol): A surface of the primary oligomerization domain functions in capsid precursor processing and VPg uridylylation

The primary oligomerization domain of poliovirus polymerase, 3Dpol, is stabilized by the interaction of the back of the thumb subdomain of one molecule with the back of the palm subdomain of a second molecule, thus permitting the head-to-tail assembly of 3Dpol monomers into long fibers. The interaction of Arg-455 and Arg-456 of the thumb with Asp-339, Ser-341, and Asp-349 of the palm is key to the stability of this interface. We show that mutations predicted to completely disrupt this interface do not produce equivalent growth phenotypes. Virus encoding a polymerase with changes of both residues of the thumb to alanine is not viable; however, virus encoding a polymerase with changes of all three residues of the palm to alanine is viable. Biochemical analysis of 3Dpol derivatives containing the thumb or palm substitutions revealed that these derivatives are both incapable of forming long fibers, suggesting that polymerase fibers are not essential for virus viability. The RNA binding activity, polymerase activity, and thermal stability of these derivatives were equivalent to that of the wild-type enzyme. The two significant differences observed for the thumb mutant were a modest reduction in the ability of the altered 3CD proteinase to process the VP0/VP3 capsid precursor and a substantial reduction in the ability of the altered 3Dpol to catalyze oriI-templated uridylylation of VPg. The defect to uridylylation was a result of the inability of 3CD to stimulate this reaction. Because 3C alone can substitute for 3CD in this reaction, we conclude that the lethal replication phenotype associated with the thumb mutant is caused, in part, by the disruption of an interaction between the back of the thumb of 3Dpol and some undefined domain of 3C. We speculate that this interaction may also be critical for assembly of other complexes required for poliovirus genome replication