1,044 research outputs found
Empirical Evaluation of the Parallel Distribution Sweeping Framework on Multicore Architectures
In this paper, we perform an empirical evaluation of the Parallel External
Memory (PEM) model in the context of geometric problems. In particular, we
implement the parallel distribution sweeping framework of Ajwani, Sitchinava
and Zeh to solve batched 1-dimensional stabbing max problem. While modern
processors consist of sophisticated memory systems (multiple levels of caches,
set associativity, TLB, prefetching), we empirically show that algorithms
designed in simple models, that focus on minimizing the I/O transfers between
shared memory and single level cache, can lead to efficient software on current
multicore architectures. Our implementation exhibits significantly fewer
accesses to slow DRAM and, therefore, outperforms traditional approaches based
on plane sweep and two-way divide and conquer.Comment: Longer version of ESA'13 pape
Electron Exchange Coupling for Single Donor Solid-State Qubits
Inter-valley interference between degenerate conduction band minima has been
shown to lead to oscillations in the exchange energy between neighbouring
phosphorus donor electron states in silicon \cite{Koiller02,Koiller02A}. These
same effects lead to an extreme sensitivity of the exchange energy on the
relative orientation of the donor atoms, an issue of crucial importance in the
construction silicon-based spin quantum computers. In this article we calculate
the donor electron exchange coupling as a function of donor position
incorporating the full Bloch structure of the Kohn-Luttinger electron
wavefunctions. It is found that due to the rapidly oscillating nature of the
terms they produce, the periodic part of the Bloch functions can be safely
ignored in the Heitler-London integrals as was done by Koiller et. al. [Phys.
Rev. Lett. 88,027903(2002),Phys. Rev. B. 66,115201(2002)], significantly
reducing the complexity of calculations.
We address issues of fabrication and calculate the expected exchange coupling
between neighbouring donors that have been implanted into the silicon substrate
using an 15keV ion beam in the so-called 'top down' fabrication scheme for a
Kane solid-state quantum computer. In addition we calculate the exchange
coupling as a function of the voltage bias on control gates used to manipulate
the electron wavefunctions and implement quantum logic operations in the Kane
proposal, and find that these gate biases can be used to both increase and
decrease the magnitude of the exchange coupling between neighbouring donor
electrons. The zero-bias results reconfirm those previously obtained by
Koiller.Comment: 10 Pages, 8 Figures. To appear in Physical Review
Antiflow of Nucleons at the Softest Point of the EoS
We investigate flow in semi-peripheral nuclear collisions at AGS and SPS
energies within macroscopic as well as microscopic transport models. The hot
and dense zone assumes the shape of an ellipsoid which is tilted by an angle
Theta with respect to the beam axis. If matter is close to the softest point of
the equation of state, this ellipsoid expands predominantly orthogonal to the
direction given by Theta. This antiflow component is responsible for the
previously predicted reduction of the directed transverse momentum around the
softest point of the equation of state.Comment: 13 pages LaTeX, 8 PS figures. Higher-quality PS versions of figures 3
and 4 available at
http://www.th.physik.uni-frankfurt.de/~brachman/afl3f/afl3f.htm
Harmonisation, Mosaicing and Production of the Global Land Cover 2000 Database.
Abstract not availableJRC.H-Institute for environment and sustainability (Ispra
Climate adaptation and agriculture: Solutions to successful national adaptation plans
The purpose of this brief is to share insights on agriculture and NAPs with national-level decision makers in developing countries and Least Developed Countries (LDCs), multilateral agencies, UNFCCC negotiators and donors. This brief explores how countries are overcoming the biggest challenges in developing NAPs, outlines examples of successful cross-sector adaptation planning, explores influence and leverage necessary for successful NAP processes, and offers specific recommendations
Ist ein bisschen Deradikalisierung besser als keine? Zur Ausstiegsarbeit mit Rückkehrerinnen und Rückkehrern aus dschihadistischen Gruppen in Deutschland
Zwischen 2013 und 2019 verließen mehr als 1.000 zumeist junge Menschen Deutschland, um sich in Syrien und dem Irak dschihadistischen Gruppen anzuschließen. Die bekannteste von ihnen ist der sogenannte "Islamische Staat", auf dessen Konto in den Jahren 2015 und 2016 auch mehrere Anschläge in Europa gingen. An diesen Terrorakten beteiligten sich zurückgekehrte europäische Dschihadisten. Inzwischen gilt der "Islamische Staat" zwar als weitgehend besiegt und ein knappes Drittel der nach Syrien und Irak Ausgereisten ist wieder zurück in Deutschland. Doch nicht alle dieser Rückkehrerinnen und Rückkehrer sind desillusioniert. Einige hängen nach wie vor islamistischen Ideologien an, fast alle sind zudem traumatisiert. Ein nicht unerheblicher Teil befindet sich in Haft. Es stellt sich die Frage, wie der Sicherheitsbedrohung, die von diesen Rückkehrerinnen und Rückkehrern ausgeht, zu begegnen ist. Deutschland beschreitet dabei unter anderem den Weg der Resozialisierung: Ausstiegs- und Reintegrationsmaßnahmen sollen diesen Personen den Weg zurück in die Gesellschaft ermöglichen. Durchgeführt werden solche Maßnahmen sowohl von staatlichen Programmen, als auch von zivilgesellschaftlichen Trägern. Dieses BICC Working Paper untersucht, wie Fachkräfte solcher Träger dieser Aufgabe nachkommen und welchen Hindernissen sie dabei begegnen. Um dies zu erläutern, stellt das Paper den gesamten Komplex von der Rückreise ehemaliger Dschihadistinnen und Dschihadisten aus dem Konfliktgebiet, über ihre psychische und soziale Wiedereingliederung nach der Ankunft in Deutschland bis zum Abschluss des Ausstiegsprozesses dar und untersucht die Herausforderungen, die sich dabei für soziale Arbeit und Prävention ergeben. Hierzu gehören besondere Aspekte der Fallarbeit wie der Umgang mit Traumatisierungen, die Bedarfe minderjähriger Rückkehrerinnen und Rückkehrer, die Arbeit in Haftanstalten sowie die Aufarbeitung extremistischer Ideologien. Die Untersuchung zeigt, dass Fachkräfte sich ihrer Aufgabe zwar professionell gewachsen sehen, jedoch einigen strukturellen Herausforderungen gegenüberstehen. Diese umfassen etwa zeitlich und finanziell begrenzte Projektförderungen, einen Mangel an therapeutischen Kapazitäten sowie Abstimmungsprobleme mit den Justizbehörden bei der Arbeit mit inhaftierten Rückkehrerinnen und Rückkehrern
Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions
We review the most important experimental results from the first three years
of nucleus-nucleus collision studies at RHIC, with emphasis on results from the
STAR experiment, and we assess their interpretation and comparison to theory.
The theory-experiment comparison suggests that central Au+Au collisions at RHIC
produce dense, rapidly thermalizing matter characterized by: (1) initial energy
densities above the critical values predicted by lattice QCD for establishment
of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by
constituent interactions of very short mean free path, established most
probably at a stage preceding hadron formation; and (3) opacity to jets. Many
of the observations are consistent with models incorporating QGP formation in
the early collision stages, and have not found ready explanation in a hadronic
framework. However, the measurements themselves do not yet establish
unequivocal evidence for a transition to this new form of matter. The
theoretical treatment of the collision evolution, despite impressive successes,
invokes a suite of distinct models, degrees of freedom and assumptions of as
yet unknown quantitative consequence. We pose a set of important open
questions, and suggest additional measurements, at least some of which should
be addressed in order to establish a compelling basis to conclude definitively
that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.
Evolution of the differential transverse momentum correlation function with centrality in Au+Au collisions at GeV
We present first measurements of the evolution of the differential transverse
momentum correlation function, {\it C}, with collision centrality in Au+Au
interactions at GeV. {\it C} exhibits a strong dependence
on collision centrality that is qualitatively similar to that of number
correlations previously reported. We use the observed longitudinal broadening
of the near-side peak of {\it C} with increasing centrality to estimate the
ratio of the shear viscosity to entropy density, , of the matter formed
in central Au+Au interactions. We obtain an upper limit estimate of
that suggests that the produced medium has a small viscosity per unit entropy.Comment: 7 pages, 4 figures, STAR paper published in Phys. Lett.
Single Spin Asymmetry in Polarized Proton-Proton Elastic Scattering at GeV
We report a high precision measurement of the transverse single spin
asymmetry at the center of mass energy GeV in elastic
proton-proton scattering by the STAR experiment at RHIC. The was measured
in the four-momentum transfer squared range \GeVcSq, the region of a significant interference between the
electromagnetic and hadronic scattering amplitudes. The measured values of
and its -dependence are consistent with a vanishing hadronic spin-flip
amplitude, thus providing strong constraints on the ratio of the single
spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated
by the Pomeron amplitude at this , we conclude that this measurement
addresses the question about the presence of a hadronic spin flip due to the
Pomeron exchange in polarized proton-proton elastic scattering.Comment: 12 pages, 6 figure
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
- …