800 research outputs found
On the number of minimal completely separating systems and antichains in a Boolean lattice
An (n)completely separating system C ((n)CSS) is a collection of blocks of [n] = {1,..., n} such that for all distinct a, b ∈ [n] there are blocks A, B ∈C with a ∈ A \ B and b ∈ B \ A. An (n)CSS is minimal if it contains the minimum possible number of blocks for a CSS on [n]. The number of non-isomorphic minimal (n)CSSs is determined for 11 ≤ n ≤ 35. This also provides an enumeration of a natural class of antichains
Momumentum Analyticity and Finiteness of Compactified String Amplitudes, Part I: Tori
We generalize to the case of compactified superstrings a construction given
previously for critical superstrings of finite one loop amplitudes that are
well-defined for all external momenta. The novel issues that arise for
compactified strings are the appearance of infrared divergences from the
propagation of massless strings in four dimensions and, in the case of orbifold
schemes, the contribution of tachyons in partial amplitudes with given spin
structure and twist sectors. Methods are presented for the resolution of these
problems and expressions for finite amplitudes are given in terms of double and
single dispersion relations, with explicit spectral densities.Comment: 18 pages, te
Observation of coasting beam at the HERA Proton--Ring
We present data collected with the HERA-B wire target which prove the
existence of coasting beam at the HERA proton storage ring. The coasting beam
is inherently produced by the proton machine operation and is not dominated by
target effects.Comment: 17 pages (Latex), 12 figures (Enc. Postscript
Applications of Small Satellites for Defense Space Communication Systems and Technology Development: Pegasus Flight-2 and the Launch of Microsat
DARPA\u27s seven Microsats were placed into orbit on the second flight of the Pegasus. The Microsat program objective is to assess the tactical utility of small, low-cost communications satellites. This paper describes the changes made to the Pegasus since its first flight, provides an overview of the Microsat demonstration program, and outlines the preliminary results of the Pegasus launch. Finally, the near-term Army and Navy demonstration plans for Microsat are discussed
Facilities for the Energy Frontier of Nuclear Physics
The Relativistic Heavy Ion Collider at BNL has been exploring the energy
frontier of nuclear physics since 2001. Its performance, flexibility and
continued innovative upgrading can sustain its physics output for years to
come. Now, the Large Hadron Collider at CERN is about to extend the frontier
energy of laboratory nuclear collisions by more than an order of magnitude. In
the coming years, its physics reach will evolve towards still higher energy,
luminosity and varying collision species, within performance bounds set by
accelerator technology and by nuclear physics itself. Complementary high-energy
facilities will include fixed-target collisions at the CERN SPS, the FAIR
complex at GSI and possible electron-ion colliders based on CEBAF at JLAB, RHIC
at BNL or the LHC at CERN.Comment: Invited talk at the International Nuclear Physics Conference,
Vancouver, Canada, 4-9 July 2010, to be published in Journal of Physics:
Conference Series. http://inpc2010.triumf.ca
High energy Coulomb-scattered electrons for relativistic particle beam diagnostics
A new system used for monitoring energetic Coulomb-scattered electrons as the
main diagnostic for accurately aligning the electron and ion beams in the new
Relativistic Heavy Ion Collider (RHIC) electron lenses is described in detail.
The theory of electron scattering from relativistic ions is developed and
applied to the design and implementation of the system used to achieve and
maintain the alignment. Commissioning with gold and 3He beams is then described
as well as the successful utilization of the new system during the 2015 RHIC
polarized proton run. Systematic errors of the new method are then estimated.
Finally, some possible future applications of Coulomb-scattered electrons for
beam diagnostics are briefly discussed.Comment: 16 pages, 23 figure
Rearrangement of cluster structure during fission processes
Results of molecular dynamics simulations of fission reactions and are presented. Dependence
of the fission barriers on isomer structure of the parent cluster is analyzed.
It is demonstrated that the energy necessary for removing homothetic groups of
atoms from the parent cluster is largely independent of the isomer form of the
parent cluster. Importance of rearrangement of the cluster structure during the
fission process is elucidated. This rearrangement may include transition to
another isomer state of the parent cluster before actual separation of the
daughter fragments begins and/or forming a "neck" between the separating
fragments
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Operational experience with a near-integer working point at RHIC.
During the RHIC polarized proton run in N 2006 it became evident that the luminosity performance is limited by the beam-beam effect. With a working point between 213 and 7/10, and the necessity to mirror the tunes of the two RHIC rings at the diagonal, the beam with a horizontal tune closest to 213 showed poor lifetime. To overcome this limitation, a near-integer working point has been proposed. Tracking studies performed at both working points showed a larger dynamic aperture near the integer tune than above 2/3. In Run-8, this new working point was commissioned in one ring of RHIC, while the other ring was operated at the same working point as in Run-6. In this paper we report the commissioning process and operational experience with this new working point
Ionic and electronic structure of sodium clusters up to N=59
We determined the ionic and electronic structure of sodium clusters with even
electron numbers and 2 to 59 atoms in axially averaged and three-dimensional
density functional calculations. A local, phenomenological pseudopotential that
reproduces important bulk and atomic properties and facilitates structure
calculations has been developed. Photoabsorption spectra have been calculated
for , , and to
. The consistent inclusion of ionic structure considerably
improves agreement with experiment. An icosahedral growth pattern is observed
for to . This finding is supported by
photoabsorption data.Comment: To appear in Phys. Rev. B 62. Version with figures in better quality
can be requested from the author
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