972 research outputs found
Accurate mass measurements of Ne, Na, Mg performed with the {\sc Mistral} spectrometer
The minuteness of the nuclear binding energy requires that mass measurements
be highly precise and accurate. Here we report on new measurements Mg
and Na performed with the {\sc Mistral} mass spectrometer at {\sc
Cern}'s {\sc Isolde} facility. Since mass measurements are prone to systematic
errors, considerable effort has been devoted to their evaluation and
elimination in order to achieve accuracy and not only precision. We have
therefore conducted a campaign of measurements for calibration and error
evaluation. As a result, we now have a satisfactory description of the {\sc
Mistral} calibration laws and error budget. We have applied our new
understanding to previous measurements of Ne, Na and
Mg for which re-evaluated values are reported.Comment: submitted to Nuclear Physics
National Space Transportation Systems Program mission report
The STS 41-C National Space Transportation Systems Program Mission Report contains a summary of the major activities and accomplishments of the eleventh Shuttle flight and fifth flight of the OV-099 vehicle, Challenger. Also summarized are the significant problems that occurred during STS 41-C, and a problem tracking list that is a complete list of all problems that occurred during the flight. The major objectives of flight STS 41-C were to successfully deploy the LDEF (long duration exposure facility) and retrieve, repair and redeploy the SMM (Solar Maximum Mission) spacecraft, and perform functions of IMAX and Cinema 360 cameras
Effects of excitonic diffusion on stimulated emission in nanocrystalline ZnO
We present optically-pumped emission data for ZnO, showing that high excitation effects and stimulated emission / lasing are observed in nanocrystalline ZnO thin films at room temperature, although such effects are not seen in bulk material of better optical quality. A simple model of exciton density profiles is developed which explains our results and those of other authors. Inhibition of exciton diffusion in nanocrystalline samples compared to bulk significantly increases exciton densities in the former, leading, via the nonlinear dependence of emission in the exciton bands on the pump intensity, to large increases in emission and to stimulated emission
Energy balance of a laser ablation plume expanding in a background gas
The energy balance of a laser ablation plume in an
ambient gas for nanosecond pulses has been investigated on
the basis of the model of Predtechensky and Mayorov (PM),
which provides a relatively simple and clear description of
the essential hydrodynamics. This approach also leads to an
insightful description in dimensionless units of how the initial
kinetic energy of the plume is dissipated into kinetic and
thermal energy of the background gas. Eventually when the
plume has stopped, the initial kinetic energy of the plume is
converted into thermal energy of the plume and background
gas
Search for supernova-produced 60Fe in a marine sediment
An 60Fe peak in a deep-sea FeMn crust has been interpreted as due to the
signature left by the ejecta of a supernova explosion close to the solar system
2.8 +/- 0.4 Myr ago [Knie et al., Phys. Rev. Lett. 93, 171103 (2004)]. To
confirm this interpretation with better time resolution and obtain a more
direct flux estimate, we measured 60Fe concentrations along a dated marine
sediment. We find no 60Fe peak at the expected level from 1.7 to 3.2 Myr ago.
However, applying the same chemistry used for the sediment, we confirm the 60Fe
signal in the FeMn crust. The cause of the discrepancy is discussed.Comment: 15 pages, 5 figures, submitted to PR
360-PLAYLEARN: GAMIFICATION AND GAME-BASED LEARNING FOR VIRTUAL LEARNING ENVIRONMENTS ON INTERACTIVE TELEVISION
Ferromagnetism in substituted zinc oxide
Room-temperature ferromagnetism is observed in (110) oriented ZnO films
containing 5 at % of Sc, Ti, V, Fe, Co or Ni, but not Cr, Mn or Cu ions. There
are large moments, 1.9 and 0.5 muB/atom for Co- and Ti-substituted oxides,
respectively. Sc-substituted ZnO shows also a moment of 0.3 muB/Sc.
Magnetization is very anisotropic, with variations of up to a factor three
depending on the orientation of the applied field relative to the R-cut
sapphire substrates. Results are interpreted in terms of a spin-split donor
impurity band model, which can account for ferromagnetism in insulating or
conducting high-k oxides with concentrations of magnetic ions that lie far
below the percolation threshold. The variation of the ferromagnetism with
oxygen pressure used during film growth is evidence of a link between
ferromagnetism and defect concentration.Comment: 15 pages, 4 figure
Quantum chaos and nuclear mass systematics
The presence of quantum chaos in nuclear mass systematics is analyzed by
considering the differences between measured and calculated nuclear masses as a
time series described by the power law 1/ f^alpha. While for the liquid droplet
model plus shell corrections a quantum chaotic behavior alpha approx 1 is
found, errors in the microscopic mass formula have alpha approx 0.5, closer to
white noise. The chaotic behavior seems to arise from many body effects not
included in the mass formula.Comment: 4 pages, 6 figures, replaced to match the published versio
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