6,364 research outputs found
Multi-strange baryon production in Au+Au collisions at top RHIC energy as a probe of bulk properties
We report STAR preliminary results on multi-strange baryon production in
Au+Au collisions at sqrt(s_NN)=200 GeV at RHIC. Its implication for the
formation of a new state of matter is discussed. The system size dependence on
the production of strange baryons is investigated to study the onset of strange
quark equilibration in the medium. The nuclear modification factor of Lambda,
Xi and Omega is also presented. Its suppression at p_T>3 GeV/c supports the
formation of a dense interacting medium at RHIC. The spectra of multi-strange
baryons reveal that within a hydro-inspired model, they may decouple prior than
lighter particles and that their flow may be mostly developed at a partonic
level. This idea is emphasized by the measurement of the v_2 of Xi+AntiXi and
Omega+AntiOmega whose behaviour is close to the Lambda+AntiLambda baryon
elliptic flow in the intermediate p_T region where a constituent quark scaling
of v_2 is observed.Comment: 8 pages, 8 figures, Strange Quark Matter 2004 conference proceeding
Pygmies, Giants, and Skins
Understanding the equation of state (EOS) of neutron-rich matter is a central
goal of nuclear physics that cuts across a variety of disciplines. Indeed, the
limits of nuclear existence, the collision of energetic heavy ions, the
structure of neutron stars, and the dynamics of core-collapse supernova all
depend critically on the nuclear-matter EOS. In this contribution I focus on
the EOS of cold baryonic matter with special emphasis on its impact on the
structure, dynamics, and composition of neutron stars. In particular, I discuss
how laboratory experiments on neutron skins as well as on Pygmy and Giant
resonances can help us elucidate the structure of these fascinating objects.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
World-leading science with SPIRou - the nIR spectropolarimeter / high-precision velocimeter for CFHT
SPIRou is a near-infrared (nIR) spectropolarimeter / velocimeter proposed as
a new-generation instrument for CFHT. SPIRou aims in particular at becoming
world-leader on two forefront science topics, (i) the quest for habitable
Earth-like planets around very- low-mass stars, and (ii) the study of low-mass
star and planet formation in the presence of magnetic fields. In addition to
these two main goals, SPIRou will be able to tackle many key programs, from
weather patterns on brown dwarf to solar-system planet atmospheres, to dynamo
processes in fully-convective bodies and planet habitability. The science
programs that SPIRou proposes to tackle are forefront (identified as first
priorities by most research agencies worldwide), ambitious (competitive and
complementary with science programs carried out on much larger facilities, such
as ALMA and JWST) and timely (ideally phased with complementary space missions
like TESS and CHEOPS).
SPIRou is designed to carry out its science mission with maximum efficiency
and optimum precision. More specifically, SPIRou will be able to cover a very
wide single-shot nIR spectral domain (0.98-2.35 \mu m) at a resolving power of
73.5K, providing unpolarized and polarized spectra of low-mass stars with a
~15% average throughput and a radial velocity (RV) precision of 1 m/s.Comment: 12 pages, 5 figures, conference proceedings of the French Society of
Astronomy and Astrophysics meeting 201
Single ion implantation for single donor devices using Geiger mode detectors
Electronic devices that are designed to use the properties of single atoms
such as donors or defects have become a reality with recent demonstrations of
donor spectroscopy, single photon emission sources, and magnetic imaging using
defect centers in diamond. Improving single ion detector sensitivity is linked
to improving control over the straggle of the ion as well as providing more
flexibility in lay-out integration with the active region of the single donor
device construction zone by allowing ion sensing at potentially greater
distances. Using a remotely located passively gated single ion Geiger mode
avalanche diode (SIGMA) detector we have demonstrated 100% detection efficiency
at a distance of >75 um from the center of the collecting junction. This
detection efficiency is achieved with sensitivity to ~600 or fewer
electron-hole pairs produced by the implanted ion. Ion detectors with this
sensitivity and integrated with a thin dielectric, for example 5 nm gate oxide,
using low energy Sb implantation would have an end of range straggle of <2.5
nm. Significant reduction in false count probability is achieved by modifying
the ion beam set-up to allow for cryogenic operation of the SIGMA detector.
Using a detection window of 230 ns at 1 Hz, the probability of a false count
was measured as 1E-1 and 1E-4 for operation temperatures of 300K and 77K,
respectively. Low temperature operation and reduced false, dark, counts are
critical to achieving high confidence in single ion arrival. For the device
performance in this work, the confidence is calculated as a probability of >98%
for counting one and only one ion for a false count probability of 1E-4 at an
average ion number per gated window of 0.015.Comment: 10 pages, 5 figures, submitted to Nanotechnolog
Gyrokinetic analysis and simulation of pedestals, to identify the culprits for energy losses using fingerprints
Fusion performance in tokamaks hinges critically on the efficacy of the Edge
Transport Barrier (ETB) at suppressing energy losses. The new concept of
fingerprints is introduced to identify the instabilities that cause the
transport losses in the ETB of many of today's experiments, from widely posited
candidates. Analysis of the Gyrokinetic-Maxwell equations, and gyrokinetic
simulations of experiments, find that each mode type produces characteristic
ratios of transport in the various channels: density, heat and impurities.
This, together with experimental observations of transport in some channel, or,
of the relative size of the driving sources of channels, can identify or
determine the dominant modes causing energy transport. In multiple ELMy H-mode
cases that are examined, these fingerprints indicate that MHD-like modes are
apparently not the dominant agent of energy transport; rather, this role is
played by Micro-Tearing Modes (MTM) and Electron Temperature Gradient (ETG)
modes, and in addition, possibly Ion Temperature Gradient (ITG)/Trapped
Electron Modes (ITG/TEM) on JET. MHD-like modes may dominate the electron
particle losses. Fluctuation frequency can also be an important means of
identification, and is often closely related to the transport fingerprint. The
analytical arguments unify and explain previously disparate experimental
observations on multiple devices, including DIII-D, JET and ASDEX-U, and
detailed simulations of two DIII-D ETBs also demonstrate and corroborate this
Intelligent sampling for the measurement of structured surfaces
Uniform sampling in metrology has known drawbacks such as coherent spectral aliasing and a lack of efficiency in terms of measuring time and data storage. The requirement for intelligent sampling strategies has been outlined over recent years, particularly where the measurement of structured surfaces is concerned. Most of the present research on intelligent sampling has focused on dimensional metrology using coordinate-measuring machines with little reported on the area of surface metrology. In the research reported here, potential intelligent sampling strategies for surface topography measurement of structured surfaces are investigated by using numerical simulation and experimental verification. The methods include the jittered uniform method, low-discrepancy pattern sampling and several adaptive methods which originate from computer graphics, coordinate metrology and previous research by the authors. By combining the use of advanced reconstruction methods and feature-based characterization techniques, the measurement performance of the sampling methods is studied using case studies. The advantages, stability and feasibility of these techniques for practical measurements are discussed
Spin three gauge theory revisited
We study the problem of consistent interactions for spin-3 gauge fields in
flat spacetime of arbitrary dimension n>3. Under the sole assumptions of
Poincar\'e and parity invariance, local and perturbative deformation of the
free theory, we determine all nontrivial consistent deformations of the abelian
gauge algebra and classify the corresponding deformations of the quadratic
action, at first order in the deformation parameter. We prove that all such
vertices are cubic, contain a total of either three or five derivatives and are
uniquely characterized by a rank-three constant tensor (an internal algebra
structure constant). The covariant cubic vertex containing three derivatives is
the vertex discovered by Berends, Burgers and van Dam, which however leads to
inconsistencies at second order in the deformation parameter. In dimensions n>4
and for a completely antisymmetric structure constant tensor, another covariant
cubic vertex exists, which contains five derivatives and passes the consistency
test where the previous vertex failed.Comment: LaTeX, 37 pages. References and comments added. Published versio
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