38,442 research outputs found
Coherent manipulation of cold Rydberg atoms near the surface of an atom chip
Coherent superpositions of the 49s and 48s Rydberg states of cold Rb atoms
were studied near the surface of an atom chip. The superpositions were created
and manipulated using microwaves resonant with the two-photon 49s-48s
transition. Coherent behavior was observed using Rabi flopping, Ramsey
sequences, spin-echo and spin-locking. These results are discussed in the
context of Rydberg atoms as electric field noise sensors. We consider the
coherence of systems quadratically coupled to noise fields with 1/f^k power
spectral densities (k \approx 1).Comment: 11 pages, 7 figure
KIC 2856960: the impossible triple star
KIC 2856960 is a star in the Kepler field which was observed by Kepler for 4
years. It shows the primary and secondary eclipses of a close binary of 0.258d
as well as complex dipping events that last for about 1.5d at a time and recur
on a 204d period. The dips are thought to result when the close binary passes
across the face of a third star. In this paper we present an attempt to model
the dips. Despite the apparent simplicity of the system and strenuous efforts
to find a solution, we find that we cannot match the dips with a triple star
while satisfying Kepler's laws. The problem is that to match the dips the
separation of the close binary has to be larger than possible relative to the
outer orbit given the orbital periods. Quadruple star models can get round this
problem but require the addition of a so-far undetected intermediate period of
order 5 -- 20d that has be a near-perfect integer divisor of the outer 204d
period. Although we have no good explanation for KIC 2856960, using the full
set of Kepler data we are able to update several of its parameters. We also
present a spectrum showing that KIC 2856960 is dominated by light from a K3- or
K4-type star.Comment: 11 pages, 13 figures, accepted for publication in MNRAS August 21,
201
A rheological study of glass fibers in a Newtonian oil Semiannual status report, 1 Dec. 1966 - 31 May 1967
Rheological study of glass fibers in Newtonian oi
Resonant electric dipole-dipole interactions between cold Rydberg atoms in a magnetic field
Laser cooled Rb atoms were optically excited to 46d Rydberg states. A
microwave pulse transferred a fraction of the atoms to the 47p Rydberg state.
The resonant electric dipole-dipole interactions between atoms in these two
states were probed using the linewidth of the two-photon microwave transition
46d-47d. The presence of a weak magnetic field (approximately 0.5 G) reduced
the observed line broadening, indicating that the interaction is suppressed by
the field. The field removes some of the energy degeneracies responsible for
the resonant interaction, and this is the basis for a quantitative model of the
resulting suppression. A technique for the calibration of magnetic field
strengths using the 34s-34p one-photon transition is also presented.Comment: Accepted for publication in Physical Review
A new coordinate transformation for turbulent boundary layer flows
The transformation permits a uniform mesh to be used in the computational coordinate which extends across the layer. This coordinate transformation uses the local value of the skin friction coefficient to scale the thickness of the wall layer region, and the local maximum value of turbulent viscosity to scale the boundary-layer thickness. Results are presented for two dimensional boundary layers in both positive and negative pressure gradients and comparisons are made with experimental data and conventional variable-grid results for low speed turbulent boundary-layers. The cases chosen illustrate the capability of this new transformation to capture the boundary layer growth over the full extent of laminar, transitional, and turbulent flow with no grid adjustment as well as its ability to consistently enlarge the wall layer region for accurate shear stress representation. Results of mesh refinement studies using the new coordinate transformation are presented
B-R Colors of Globular Clusters in NGC 6166 (A2199)
We have analysed new R-band photometry of globular clusters in NGC 6166, the
cD galaxy in the cooling flow cluster A2199. In combination with the earlier B
photometry of Pritchet \& Harris (1990), we obtain BR colours for 40
globular clusters in NGC 6166. The mean BR is 1.26 0.11, corresponding
to a mean [Fe/H] = 1 0.4. Given that NGC 6166 is one of the most
luminous cD galaxies studied to date, our result implies significant scatter in
the relationship between mean cluster [Fe/H] and parent galaxy luminosity. We
obtain a globular cluster specific frequency of S 9, with a possible
range between 5 and 18. This value is inconsistent with the value of S
4 determined earlier by Pritchet \& Harris (1990) from B-band
photometry, and we discuss possible reasons for the discrepancy. Finally, we
reassess whether or not cooling flows are an important mechanism for forming
globular clusters in gE/cD galaxies.Comment: 8 pages, uuencoded, gzipped tar file with latex file, 6 figures (Fig
1 omitted because of size), and mn.sty file. Figures will be embedded into
the postscript file. Accepted (March 1996) for publication in MNRA
Southwest Research Institute assistance to NASA in biomedical areas of the technology utilization program
The activities are reported of the NASA Biomedical Applications Team at Southwest Research Institute between 25 August, 1972 and 15 November, 1973. The program background and methodology are discussed along with the technology applications, and biomedical community impacts
- …