4,024 research outputs found
A note on the calculation of the effective range
The closed form of the first order non-linear differential equation that is
satisfied by the effective range within the variable phase formulation of
scattering theory is discussed. It is shown that the conventional method of
determining the effective range, by fitting a numerical solution of the
Schr\"odinger equation to known asymptotic boundary conditions, can be modified
to include the first order contribution of a long range interaction.Comment: 4 page
The variable phase method used to calculate and correct scattering lengths
It is shown that the scattering length can be obtained by solving a Riccati
equation derived from variable phase theory. Two methods of solving it are
presented. The equation is used to predict how long-range interactions
influence the scattering length, and upper and lower bounds on the scattering
length are determined. The predictions are compared with others and it is shown
how they may be obtained from secular perturbation theory.Comment: 7 pages including 3 figure
Formation of atomic tritium clusters and condensates
We present an extensive study of the static and dynamic properties of systems
of spin-polarized tritium atoms. In particular, we calculate the two-body
|F,m_F>=|0,0> s-wave scattering length and show that it can be manipulated via
a Feshbach resonance at a field strength of about 870G. Such a resonance might
be exploited to make and control a Bose-Einstein condensate of tritium in the
|0,0> state. It is further shown that the quartet tritium trimer is the only
bound hydrogen isotope and that its single vibrational bound state is a
Borromean state. The ground state properties of larger spin-polarized tritium
clusters are also presented and compared with those of helium clusters.Comment: 5 pages, 3 figure
Controlled single electron transfer between Si:P dots
We demonstrate electrical control of Si:P double dots in which the potential
is defined by nanoscale phosphorus doped regions. Each dot contains
approximately 600 phosphorus atoms and has a diameter close to 30 nm. On
application of a differential bias across the dots, electron transfer is
observed, using single electron transistors in both dc- and rf-mode as charge
detectors. With the possibility to scale the dots down to few and even single
atoms these results open the way to a new class of precision-doped quantum dots
in silicon.Comment: 3 figures, 3 page
1S-2S Spectrum of a Hydrogen Bose-Einstein Condensate
We calculate the two-photon 1S-2S spectrum of an atomic hydrogen
Bose-Einstein condensate in the regime where the cold collision frequency shift
dominates the lineshape. WKB and static phase approximations are made to find
the intensities for transitions from the condensate to motional eigenstates for
2S atoms. The excited state wave functions are found using a mean field
potential which includes the effects of collisions with condensate atoms.
Results agree well with experimental data. This formalism can be used to find
condensate spectra for a wide range of excitation schemes.Comment: 13 pages, 4 figure
Seasonal abundance of small cladocerans in Lake Mangakaware, Waikato, New Zealand
The seasonal changes in the dynamics and life histories of the Cladocera in Lake Mangakaware, North Island, New Zealand, were studied over 19 months by sampling at weekly or 2-weekly intervals. Lake Mangakaware is a 13.3 ha polymictic lake with high nutrient status, low Secchi disc transparencies, and an unstable thermal regime. The four planktonic cladoceran species (Bosmina longirostris, B. meridionalis, Ceriodaphnia pulchella, and C. dubia) exhibited disjunct population maxima. Only B. longirostris was perennially present. All species exhibited low fecundities and low lipid content, indicating that food resources were limited and that competitive interactions and resistance to starvation were probably important in determining species success. Increases in body size in cooler seasons were unrelated to clutch size, giving further support for the view that available food was limited. These results are consistent with previous experimental findings that subtle differences in life history can determine seasonal success and the outcome of competition between similar species
Cold Collision Frequency Shift of the 1S-2S Transition in Hydrogen
We have observed the cold collision frequency shift of the 1S-2S transition
in trapped spin-polarized atomic hydrogen. We find , where is the sample density. From this
we derive the 1S-2S s-wave triplet scattering length, nm,
which is in fair agreement with a recent calculation. The shift provides a
valuable probe of the distribution of densities in a trapped sample.Comment: Accepted for publication in PRL, 9 pages, 4 PostScript figures,
ReVTeX. Updated connection of our measurement to theoretical wor
Pressure-induced metallization in solid boron
Different phases of solid boron under high pressure are studied by first
principles calculations. The -B structure is found to be stable
up to 270 GPa. Its semiconductor band gap (1.72 eV) decreases continuously to
zero around 160 GPa, where the material transforms to a weak metal. The
metallicity, as measured by the density of states at the Fermi level, enhances
as the pressure is further increased. The pressure-induced metallization can be
attributed to the enhanced boron-boron interactions that cause bands overlap.
These results are consist with the recently observed metallization and the
associated superconductivity of bulk boron under high pressure (M.I.Eremets et
al, Science{\bf 293}, 272(2001)).Comment: 14 pages, 5 figure
Dealing with metaphysical evil : the Banker as evil genius in the British game show 'Deal or no deal?'
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