205 research outputs found
Edge- and Node-Disjoint Paths in P Systems
In this paper, we continue our development of algorithms used for topological
network discovery. We present native P system versions of two fundamental
problems in graph theory: finding the maximum number of edge- and node-disjoint
paths between a source node and target node. We start from the standard
depth-first-search maximum flow algorithms, but our approach is totally
distributed, when initially no structural information is available and each P
system cell has to even learn its immediate neighbors. For the node-disjoint
version, our P system rules are designed to enforce node weight capacities (of
one), in addition to edge capacities (of one), which are not readily available
in the standard network flow algorithms.Comment: In Proceedings MeCBIC 2010, arXiv:1011.005
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Laser/rf spectroscopic techniques in fast ion beams
The perturbation free environment and kinematically compressed velocity distribution of ion beams are ideal for high precision spectroscopic measurements using laser techniques. The limitations in the optical techniques are explored and the evolution to laser-rf double resonance techniques is described. Using the double resonance technique a 150-fold improvement in precision is achieved. Problems in applying the double resonance technique are encountered at low rf frequencies. A novel method based upon stimulated resonance Raman spectroscopy is described which circumvents these problems. 5 figs
Doppler cooling and trapping on forbidden transitions
Ultracold atoms at temperatures close to the recoil limit have been achieved
by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms
has been cooled and trapped to a temperature as low as 6 \mu K by operating a
magneto-optical trap on the spin-forbidden intercombination transition.
Quenching the long-lived excited state with an additional laser enhanced the
scattering rate by a factor of 15, while a high selectivity in velocity was
preserved. With this method more than 10% of pre-cooled atoms from a standard
magneto-optical trap have been transferred to the ultracold trap. Monte-Carlo
simulations of the cooling process are in good agreement with the experiments
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Capture from pair production as a beam loss mechanism for heavy ions at RHIC
Electron capture from electron-positron pair production is predicted to be a major source of beam loss for the heaviest ions at RHIC. Achieving the highest luminosity thus requires an understanding of the capture process. The authors report measurements of this process at Brookhaven National Laboratory`s AGS using 10.8 GeV/nucleon Au{sup 79+} projectiles on Au targets. Capture from pair production is a process in which the very high electromagnetic field involved in the collision of two relativistic heavy ions results in the production of an electron-positron pair with the capture of the electron by one of the ions. There are many theoretical papers published on capture from pair production with discrepancies between predicted cross sections. The experimental results are compared to theory and to previous experiments at 1 GeV/nucleon. The implications of extrapolations to RHIC energies are presented
On the feasibility of cooling and trapping metastable alkaline-earth atoms
Metastability and long-range interactions of Mg, Ca, and Sr in the
lowest-energy metastable state are investigated. The calculated
lifetimes are 38 minutes for Mg*, 118 minutes for Ca*, and 17 minutes for Sr*,
supporting feasibility of cooling and trapping experiments. The
quadrupole-quadrupole long-range interactions of two metastable atoms are
evaluated for various molecular symmetries. Hund's case (c) 4_g potential
possesses a large 100-1000 K potential barrier. Therefore magnetic trap losses
can possibly be reduced using cold metastable atoms in a stretched M=2 state.
Calculations were performed in the framework of ab initio relativistic
configuration interaction method coupled with the random-phase approximation.Comment: 8 pages, 2 figures; to appear in PR
Collisions of cold magnesium atoms in a weak laser field
We use quantum scattering methods to calculate the light-induced collisional
loss of laser-cooled and trapped magnesium atoms for detunings up to 30 atomic
linewidths to the red of the 1S_0-1P_1 cooling transition. Magnesium has no
hyperfine structure to complicate the theoretical studies. We evaluate both the
radiative and nonradiative mechanisms of trap loss. The radiative escape
mechanism via allowed 1Sigma_u excitation is dominant for more than about one
atomic linewidth detuning. Molecular vibrational structure due to
photoassociative transitions to bound states begins to appear beyond about ten
linewidths detuning.Comment: 4 pages with 3 embedded figure
Magnetic trapping of metastable atomic strontium
We report the magnetic trapping of metastable atomic strontium. Atoms
are cooled in a magneto-optical trap (MOT) operating on the dipole allowed
transition at 461 nm. Decay via
continuously loads a magnetic trap formed by the quadrupole magnetic field of
the MOT. Over atoms at a density of cm and
temperature of 1 mK are trapped. The atom temperature is significantly lower
than what would be expected from the kinetic and potential energy of atoms as
they are transferred from the MOT. This suggests that thermalization and
evaporative cooling are occurring in the magnetic trap.Comment: This paper has been accepted by PR
High-accuracy relativistic many-body calculations of van der Waals coefficients C_6 for alkaline-earth atoms
Relativistic many-body calculations of van der Waals coefficients C_6 for
dimers correlating to two ground state alkaline-earth atoms at large
internuclear separations are reported. The following values and uncertainties
were determined : C_6 = 214(3) for Be, 627(12) for Mg, 2221(15) for Ca,
3170(196) for Sr, and 5160(74) for Ba in atomic units.Comment: 5 pages, submitted to Phys. Rev.
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