75 research outputs found
Continuation-Passing C: compiling threads to events through continuations
In this paper, we introduce Continuation Passing C (CPC), a programming
language for concurrent systems in which native and cooperative threads are
unified and presented to the programmer as a single abstraction. The CPC
compiler uses a compilation technique, based on the CPS transform, that yields
efficient code and an extremely lightweight representation for contexts. We
provide a proof of the correctness of our compilation scheme. We show in
particular that lambda-lifting, a common compilation technique for functional
languages, is also correct in an imperative language like C, under some
conditions enforced by the CPC compiler. The current CPC compiler is mature
enough to write substantial programs such as Hekate, a highly concurrent
BitTorrent seeder. Our benchmark results show that CPC is as efficient, while
using significantly less space, as the most efficient thread libraries
available.Comment: Higher-Order and Symbolic Computation (2012). arXiv admin note:
substantial text overlap with arXiv:1202.324
Flux-rope twist in eruptive flares and CMEs : due to zipper and main-phase reconnection
Funding: UK Science and Technology Facilities CouncilThe nature of three-dimensional reconnection when a twisted flux tube erupts during an eruptive flare or coronal mass ejection is considered. The reconnection has two phases: first of all, 3D âzipper reconnectionâ propagates along the initial coronal arcade, parallel to the polarity inversion line (PIL); then subsequent quasi-2D âmain phase reconnectionâ in the low corona around a flux rope during its eruption produces coronal loops and chromospheric ribbons that propagate away from the PIL in a direction normal to it. One scenario starts with a sheared arcade: the zipper reconnection creates a twisted flux rope of roughly one turn (2Ï radians of twist), and then main phase reconnection builds up the bulk of the erupting flux rope with a relatively uniform twist of a few turns. A second scenario starts with a pre-existing flux rope under the arcade. Here the zipper phase can create a core with many turns that depend on the ratio of the magnetic fluxes in the newly formed flare ribbons and the new flux rope. Main phase reconnection then adds a layer of roughly uniform twist to the twisted central core. Both phases and scenarios are modeled in a simple way that assumes the initial magnetic flux is fragmented along the PIL. The model uses conservation of magnetic helicity and flux, together with equipartition of magnetic helicity, to deduce the twist of the erupting flux rope in terms the geometry of the initial configuration. Interplanetary observations show some flux ropes have a fairly uniform twist, which could be produced when the zipper phase and any pre-existing flux rope possess small or moderate twist (up to one or two turns). Other interplanetary flux ropes have highly twisted cores (up to five turns), which could be produced when there is a pre-existing flux rope and an active zipper phase that creates substantial extra twist.PostprintPublisher PDFPeer reviewe
First Observation of a Upsilon(1D) State
We present the first evidence for the production of Upsilon(1D) states in the
four-photon cascade, Upsilon(3S)-->gamma chib(2P), chib(2P)-->gamma
Upsilon(1D), Upsilon(1D)-->gamma chib(1P), chib(1P)-->gamma Upsilon(1S),
followed by the Upsilon(1S) annihilation into e+e- or mu+mu-. The signal has a
significance of 10.2 standard deviations. The measured product branching ratio
for these five decays, (2.5+-0.5+-0.5)x10^(-5), is consistent with the
theoretical estimates. The data are dominated by the production of one
Upsilon(1D) state consistent with the J=2 assignment. Its mass is determined to
be (10161.1+-0.6+-1.6) MeV, which is consistent with the predictions from
potential models and lattice QCD calculations.
We also searched for Upsilon(3S)-->gammachib(2P),
chib(2P)-->gammaUpsilon(1D), followed by either Upsilon(1D)-->eta Upsilon(1S)
or Upsilon(1D)-->pi+pi- Upsilon(1S). We find no evidence for such decays and
set upper limits on the product branching ratios.Comment: 12 pages postscript,also available through this
http://w4.lns.cornell.edu/public/CLNS/, submitted to PR
MHD activity on JET
Paper at Workshop on Magnetic Reconnection and Turbulence, Cargese (FR), 8-13 Jul 1985Available from British Library Document Supply Centre- DSC:4672.262(JET-P--85/11) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo
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