52,852 research outputs found
Calculations of Energy Losses due to Atomic Processes in Tokamaks with Applications to the ITER Divertor
Reduction of the peak heat loads on the plasma facing components is essential
for the success of the next generation of high fusion power tokamaks such as
the International Thermonuclear Experimental Reactor (ITER) 1 . Many present
concepts for accomplishing this involve the use of atomic processes to transfer
the heat from the plasma to the main chamber and divertor chamber walls and
much of the experimental and theoretical physics research in the fusion program
is directed toward this issue. The results of these experiments and
calculations are the result of a complex interplay of many processes. In order
to identify the key features of these experiments and calculations and the
relative role of the primary atomic processes, simple quasi-analytic models and
the latest atomic physics rate coefficients and cross sections have been used
to assess the relative roles of central radiation losses through
bremsstrahlung, impurity radiation losses from the plasma edge, charge exchange
and hydrogen radiation losses from the scrape-off layer and divertor plasma and
impurity radiation losses from the divertor plasma. This anaysis indicates that
bremsstrahlung from the plasma center and impurity radiation from the plasma
edge and divertor plasma can each play a significant role in reducing the power
to the divertor plates, and identifies many of the factors which determine the
relative role of each process. For instance, for radiation losses in the
divertor to be large enough to radiate the power in the divertor for high power
experiments, a neutral fraction of 10-3 to 10-2 and an impurity recycling rate
of netrecycle of ~ 10^16 s m^-3 will be required in the divertor.Comment: Preprint for the 1994 APSDPP meeting, uuencoded and gzipped
postscript with 22 figures, 40 pages
Phase separation in the Edwards model
The nature of charge transport within a correlated background medium can be
described by spinless fermions coupled to bosons in the model introduced by
Edwards. Combining numerical density matrix renormalization group and
analytical projector-based renormalization methods we explore the ground-state
phase diagram of the Edwards model in one dimension. Below a critical boson
frequency any long-range order disappears and the system becomes metallic. If
the charge carriers are coupled to slow quantum bosons the Tomonaga-Luttinger
liquid is attractive and finally makes room for a phase separated state, just
as in the t-J model. The phase boundary separating repulsive from the
attractive Tomonaga-Luttinger liquid is determined from long-wavelength charge
correlations, whereas fermion segregation is indicated by a vanishing inverse
compressibility. On approaching phase separation the photoemission spectra
develop strong anomalies.Comment: 6 pages, 5 figures, final versio
Use of ERTS-1 data in the educational and applied research programs of agricultural extension
There are no author-identified significant results in this report
Microsecond resolution of quasiparticle tunneling in the single-Cooper-pair-transistor
We present radio-frequency measurements on a single-Cooper-pair-transistor in
which individual quasiparticle poisoning events were observed with microsecond
temporal resolution. Thermal activation of the quasiparticle dynamics is
investigated, and consequently, we are able to determine energetics of the
poisoning and un-poisoning processes. In particular, we are able to assign an
effective quasiparticle temperature to parameterize the poisoning rate.Comment: 4 pages, 4 fig
An updated stellar census of the Quintuplet cluster
Context. Found within the central molecular zone, the Quintuplet is one of the most massive young clusters in the Galaxy. As a consequence it offers the prospect of constraining stellar formation and evolution in extreme environments. However, current observations suggest that it comprises a remarkably diverse stellar population that is difficult to reconcile with an instantaneous formation event.
Aims. To better understand the nature of the cluster our aim is to improve observational constraints on the constituent stars.
Methods. In order to accomplish this goal we present Hubble Space Telescope/NICMOS+WFC3 photometry and Very Large Telescope/SINFONI+KMOS spectroscopy for ∼100 and 71 cluster members, respectively.
Results. Spectroscopy of the cluster members reveals the Quintuplet to be far more homogeneous than previously expected. All supergiants are classified as either O7–8 Ia or O9–B0 Ia, with only one object of earlier (O5 I–III) spectral type. These stars form a smooth morphological sequence with a cohort of seven early-B hypergiants and six luminous blue variables and WN9-11h stars, which comprise the richest population of such stars of any stellar aggregate known. In parallel, we identify a smaller population of late-O hypergiants and spectroscopically similar WN8–9ha stars. No further H-free Wolf–Rayet (WR) stars are identified, leaving an unexpectedly extreme ratio of 13:1 for WC/WN stars. A subset of the O9–B0 supergiants are unexpectedly faint, suggesting they are both less massive and older than the greater cluster population. Finally, no main sequence objects were identifiable.
Conclusions. Due to uncertainties over which extinction law to apply, it was not possible to quantitatively determine a cluster age via isochrone fitting. Nevertheless, we find an impressive coincidence between the properties of cluster members preceding the H-free WR phase and the evolutionary predictions for a single, non-rotating 60 M⊙ star; in turn this implies an age of ∼3.0–3.6 Myr for the Quintuplet. Neither the late O-hypergiants nor the low luminosity supergiants are predicted by such a path; we suggest that the former either result from rapid rotators or are the products of binary driven mass-stripping, while the latter may be interlopers. The H-free WRs must evolve from stars with an initial mass in excess of 60 M⊙ but it appears difficult to reconcile their observational properties with theoretical expectations. This is important since one would expect the most massive stars within the Quintuplet to be undergoing core-collapse/SNe at this time; since the WRs represent an evolutionary phase directly preceding this event,their physical properties are crucial to understanding both this process and the nature of the resultant relativistic remnant. As such, the Quintuplet provides unique observational constraints on the evolution and death of the most massive stars forming in the local, high metallicity Universe
Space Station Facilities and Operations at the Kennedy Space Center
The Spaca Station Program potentially will a significant Impact on the Kennedy Space Canter Current and past programs have had their major Impact on KSC In the prelaunch and launch operations area with program support, subsequent to liftoff, generally performed at other locations. The Space Station Program also will Impact pre- launch and launch operations at KSC but, due to Its proposed 10-year operational lifetime, KSC also could have a significant role in support of the operational program. Support operations of the Space Station Program may be performed elsewhere; however, centralizing them at KSC has a number of attractive features which warrant study
Giant Relaxation Oscillations in a Very Strongly Hysteretic SQUID ring-Tank Circuit System
In this paper we show that the radio frequency (rf) dynamical characteristics
of a very strongly hysteretic SQUID ring, coupled to an rf tank circuit
resonator, display relaxation oscillations. We demonstrate that the the overall
form of these characteristics, together with the relaxation oscillations, can
be modelled accurately by solving the quasi-classical non-linear equations of
motion for the system. We suggest that in these very strongly hysteretic
regimes SQUID ring-resonator systems may find application in novel logic and
memory devices.Comment: 7 pages, 5 figures. Uploaded as implementing a policy of arXiving old
paper
The effect of 3He impurities on the nonclassical response to oscillation of solid 4He
We have investigated the influence of impurities on the possible supersolid
transition by systematically enriching isotopically-pure 4He (< 1 ppb of 3He)
with 3He. The onset of nonclassical rotational inertia is broadened and shifts
monotonically to higher temperature with increasing 3He concentration,
suggesting that the phenomenon is correlated to the condensation of 3He atoms
onto the dislocation network in solid 4He.Comment: 4 page
Design of a fault tolerant airborne digital computer. Volume 2: Computational requirements and technology
This final report summarizes the work on the design of a fault tolerant digital computer for aircraft. Volume 2 is composed of two parts. Part 1 is concerned with the computational requirements associated with an advanced commercial aircraft. Part 2 reviews the technology that will be available for the implementation of the computer in the 1975-1985 period. With regard to the computation task 26 computations have been categorized according to computational load, memory requirements, criticality, permitted down-time, and the need to save data in order to effect a roll-back. The technology part stresses the impact of large scale integration (LSI) on the realization of logic and memory. Also considered was module interconnection possibilities so as to minimize fault propagation
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