38,246 research outputs found
Beam-beam observations in the RHIC
The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory
has been in operation since 2000. Over the past decade, the luminosity in the
polarized proton (p-p) operations has increased by more than one order of
magnitude. The maximum total beam-beam tune shift with two collisions has
reached 0.018. The beam-beam interaction leads to large tune spread, emittance
growth, and short beam and luminosity lifetimes. In this article, we review the
beam-beam observations during the previous RHIC p-p runs. The mechanism for
particle loss is presented. The intra-beam scattering (IBS) contributions to
emittance and bunch length growths are calculated and compared with the
measurements. Finally, we will discuss current limits in the RHIC p-p
operations and their solutions.Comment: 7 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects
in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201
Scanning Tunneling Spectroscopy of Bi2Sr2CuO6+d: New Evidence for the Common Origin of the Pseudogap and Superconductivity
Using scanning tunneling spectroscopy, we investigated the temperature dependence of the quasiparticle density of states of overdoped Bi2Sr2CuO6+δ between 275 mK and 82 K. Below Tc = 10 K, the spectra show a gap with well-defined coherence peaks at ±Δp≃12 meV, which disappear at Tc. Above Tc, the spectra display a clear pseudogap of the same magnitude, gradually filling up and vanishing at T*≃68 K. The comparison with Bi2Sr2CaCu2O8+δ demonstrates that the pseudogap and the superconducting gap scale with each other, providing strong evidence that they have a common origin
Six-dimensional weak-strong simulations of head-on beam-beam compensation in RHIC
To compensate the large beam-beam tune spread and beam-beam resonance driving
terms in the polarized proton operation in the Relativistic Heavy Ion Collider
(RHIC), we will introduce a low-energy DC electron beam into each ring to
collide head-on with the opposing proton beam. The device to provide the
electron beam is called an electron lens. In this article, using a 6-D
weak-strong-beam-beam interaction simulation model, we investigate the effects
of head-on beam-beam compensation with electron lenses on the proton beam
dynamics in the RHIC 250 GeV polarized proton operation. This article is
abridged from the published article [1].Comment: 5 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects
in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201
A New Digital Georeferenced Database of Grassland in China
Grassland covers some 40 percent of China's territory and constitutes an important territorial resource serving critical economic and environmental functions. Pastoralism has been an important pillar of the rural economies in the dry and cold areas of the plateau region, Nei Mongol and north-western China. Grass cover plays also an important environmental role in the protection of highly erodible soils of sloped land, and in arresting sand in areas prone to wind erosion and desertification.
In the 1980s and the early 1990s, Chinese institutions have undertaken detailed county-level surveys of grassland resources, and compiled maps and databases of grassland distribution and productivity.
The "Map of Grassland in China" at the scale of 1:4M was recently completed and implemented as a digital database of 17 grassland types on GIS. This report describes the features of the database and summarizes the extents geographical distribution of grassland in China
Local quasiparticle density of states of superconducting SmFeAsOF single crystals: Evidence for spin-mediated pairing
We probe the local quasiparticles density-of-states in micron-sized
SmFeAsOF single-crystals by means of Scanning Tunnelling
Spectroscopy. Spectral features resemble those of cuprates, particularly a
dip-hump-like structure developed at energies larger than the gap that can be
ascribed to the coupling of quasiparticles to a collective mode, quite likely a
resonant spin mode. The energy of the collective mode revealed in our study
decreases when the pairing strength increases. Our findings support
spin-fluctuation-mediated pairing in pnictides.Comment: 11 pages, 4 figure
Computational challenges for beam-beam simulation for RHIC
In this article we will review the computational challenges in the beam-beam simulation for the polarized proton run of the Relativistic Heavy Ion Collider (RHIC). The difficulties in our multi-particle and million turn tracking to calculate the proton beam lifetime and proton beam emittance growth due to head-on beam-beam interaction and head-on beam-beam compensation are presented and discussed. Solutions to obtain meaningful physics results from these trackings are proposed and tested. In the end we will present the progress in the benchmarking of the RHIC operational proton beam lifetime
Anisotropic magnetic diffuse scattering in an easy-plane type antiferromagnet ErNiGe
We report on neutron scattering studies of a rare earth intermetallic
compound ErNiGe. Polarized neutron scattering experiments revealed
that the magnetic ordered moment lies in ab-plane. Taking account of
a lack of the third higher harmonic reflection, ErNiGe is
considered to have a helical magnetic structure. The magnetic scattering
profiles along the - and the -directions are well
described by the sum of Gaussian and modified-Lorentzian terms, even far below
, indicating that short-range orders coexist with a
long-range order. Interestingly, the modified-Lorentzian-type diffuse
scattering is not present in the profiles along the -direction.
The anisotropy of the diffuse scattering suggests that the short-range-order
consists of one dimensional long-range helices along the c-axis.Comment: 4 pages, to be published in J. Phys.: Condens. Matter (HFM2008
Four-point measurements of n- and p-type two-dimensional systems fabricated with cleaved-edge overgrowth
We demonstrate a contact design that allows four-terminal magnetotransport
measurements of cleaved-edge overgrown two-dimensional electron and hole
systems. By lithographically patterning and etching a bulk-doped surface layer,
finger-shaped leads are fabricated, which contact the two-dimensional systems
on the cleave facet. Both n- and p-type two-dimensional systems are
demonstrated at the cleaved edge, using Si as either donor or acceptor,
dependent on the growth conditions. Four-point measurements of both gated and
modulation-doped samples yield fractional quantum Hall features for both n- and
p-type, with several higher-order fractions evident in n-type modulation-doped
samples.Comment: 3 pages, 3 figure
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