56,083 research outputs found
When is 0.999... equal to 1?
A doubly infinite sum, numerically evaluated at between 0.999 and 1.001,
turns out to have a nice value
Evaluation of atomic constants for optical radiation, volume 1
Atomic constants for optical radiation are discussed which include transition probabilities, line strengths, and oscillator strengths for both dipole and quadrupole transitions, as well as the associated matrix elements needed for line broadening calculations. Atomic constants were computed for a wide selection of elements and lines. An existing computer program was used, with modifications to include, in an approximate manner, the effect of equivalent electrons, and to enable reordering and restructuring of the output for publication. This program is suitable for fast, low cost computation of the optical constants, using the Coulomb approximation formalism for LS coupling
Finite-size and pressure effects in YBa_2Cu_4O_8 probed by magnetic field penetration depth measurements
We explore the combined pressure and finite-size effects on the in-plane
penetration depth \lambda_{ab} in YBa_2Cu_4O_8. Even though this cuprate is
stoichiometric the finite-size scaling analysis of \lambda_{ab}^{-2}(T)
uncovers the granular nature and reveals domains with nanoscale size L_{c}
along the c-axis. L_{c} ranges from 33.2 Angstrom to 28.9 Angstrom at pressures
from 0.5 to 11.5 kbar. These observations raise serious doubts on the existence
of a phase coherent macroscopic superconducting state in cuprate
superconductors.Comment: 7 pages, 6 figure
Current-induced magnetic vortex core switching in a Permalloy nanodisk
We report on the switching of a magnetic vortex core in a sub-micron
Permalloy disk, induced by a short current pulse applied in the film plane.
Micromagnetic simulations including the adiabatic and non-adiabatic spin-torque
terms are used to investigate the current-driven magnetization dynamics. We
predict that a core reversal can be triggered by current bursts a tenth of a
nanosecond long. The vortex core reversal process is found to be the same as
when an external field pulse is applied. The control of a vortex core's
orientation using current pulses introduces the technologically relevant
possibility to address individual nanomagnets within dense arrays.Comment: 3 pages, 3 figure
The Collapse of the Wien Tail in the Coldest Brown Dwarf? Hubble Space Telescope Near-Infrared Photometry of WISE J085510.83-071442.5
We present Hubble Space Telescope (HST) near-infrared photometry of the
coldest known brown dwarf, WISE J085510.83071442.5 (WISE 08550714). WISE
08550714 was observed with the Wide Field Camera 3 (WFC3) aboard HST using
the F105W, F125W, and F160W filters, which approximate the , , and
near-infrared bands. WISE 08550714 is undetected at F105W with a
corresponding 2 magnitude limit of 26.9. We marginally detect
WISE 08550714 in the F125W images (S/N 4), with a measured magnitude
of 26.41 0.27, more than a magnitude fainter than the band magnitude
reported by Faherty and coworkers. WISE J08550714 is clearly detected in the
F160W band, with a magnitude of 23.90 0.02, the first secure detection of
WISE 08550714 in the near-infrared. Based on these data, we find that WISE
08550714 has extremely red F105WF125W and F125WF160W colors relative
to other known Y dwarfs. We find that when compared to the models of Saumon et
al. and Morley et al., the F105WF125W and F125WF160W colors of WISE
08550714 cannot be accounted for simultaneously. These colors likely
indicate that we are seeing the collapse of flux on the Wien tail for this
extremely cold object.Comment: Accepted for publication in ApJ Letter
A Comparison of Phycocyanins from Three Different Species of Cyanobacteria Employing Resonance-Enhanced Coherent Anti-Stokes Raman Spectroscopy
Resonance-enhanced coherent anti-Stokes Raman spectra are recorded for monomers and trimers of phycocyanin from three different cyanobacteria: Westiellopsis prolifica, Mastigocladus laminosus and Spirulina platensis. It is shown that upon aggregation from monomer to trimer the electronic structures of both the α84 and β84 chromophores are changed. The spectra of the trimers originating from S. platensis and M. laminosus are very similar to each other, but distinctly different from the spectrum of W. prolifica
- …