2,692 research outputs found
Spin Physics at COMPASS
The COMPASS experiment is a fixed target experiment at the CERN SPS using
muon and hadron beams for the investigation of the spin structure of the
nucleon and hadron spectroscopy. The main objective of the muon physics program
is the study of the spin of the nucleon in terms of its constituents, quarks
and gluons. COMPASS has accumulated data during 6 years scattering polarized
muons off a longitudinally or a transversely polarized deuteron (6LiD) or
proton (NH3) target. Results for the gluon polarization are obtained from
longitudinal double spin cross section asymmetries using two different
channels, open charm production and high transverse momentum hadron pairs, both
proceeding through the photon-gluon fusion process. Also, the longitudinal spin
structure functions of the proton and the deuteron were measured in parallel as
well as the helicity distributions for the three lightest quark flavors. With a
transversely polarized target, results were obtained with proton and deuteron
targets for the Collins and Sivers asymmetries for charged hadrons as well as
for identified kaons and pions. The Collins asymmetry is sensitive to the
transverse spin structure of the nucleon, while the Sivers asymmetry reflects
correlations between the quark transverse momentum and the nucleon spin.
Recently, a new proposal for the COMPASS II experiment was accepted by the CERN
SPS which includes two new topics: Exclusive reactions like DVCS and DVMP using
the muon beam and a hydrogen target to study generalized parton distributions
and Drell-Yan measurements using a pion beam and a polarized NH3 target to
study transverse momentum dependent distributions.Comment: Proceedings of the Rutherford conference, Manchester, August 2011.
Changes due to referees comments implemente
Finite-size effects in amorphous Fe90Zr10/Al75Zr25 multilayers
The thickness dependence of the magnetic properties of amorphous Fe90Zr10
layers has been explored using Fe90Zr10/Al75Zr25 multilayers. The Al75Zr25
layer thickness is kept at 40 \AA, while the thickness of the Fe90Zr10 layers
is varied between 5 and 20 \AA. The thickness of the Al75Zr25 layers is
sufficiently large to suppress any significant interlayer coupling. Both the
Curie temperature and the spontaneous magnetization decrease non-linearly with
decreasing thickness of the Fe90Zr10 layers. No ferromagnetic order is observed
in the multilayer with 5 {\AA} Fe90Zr10 layers. The variation of the Curie
temperature with the Fe90Zr10 layer thickness is fitted with a
finite-size scaling formula [1-\Tc(t)/\Tc(\infty)]=[(t-t')/t_0]^{-\lambda},
yielding , and a critical thickness \AA, below which the
Curie temperature is zero.Comment: 8 pages, 8 figure
A measurement of the cross-section ratios for flavour tagged events at energies of 183 and 189 GeV
Mechanical testing of copper and copper alloy micropillars containing a single twin boundary
Nanotwinned metals are a promising class of modern materials combining a very high strength with a high ductility and excellent electrical properties. This remarkable strength is believed to be connected to the good efficiency of twin boundaries as obstacles to dislocation motion. The present study aims at identifying and characterizing the possible interaction modes between dislocations and coherent twin boundaries. This is achieved by compressing micropillars containing a single twin boundary of a controlled orientation. The influence of the stacking fault energy on the intrinsic strength of the twin boundary is also investigated by varying the investigated material.
In detail, the micropillars are fabricated from recrystallized polycrystalline samples of copper and α-brass, which is a low stacking-fault energy alloy exhibiting a high density of recrystallization twins. Coherent twin boundaries are selected from an EBSD orientation mapping of the sample and oriented by means of a custom 3D-printed sample holder. FIB-milling at these interfaces yields micropillar specimens containing a single twin boundary. Single crystalline reference samples are obtained from the bulk of the grains located on both sides of the twin boundary. The microcompression tests allow quantifying the influence of the twin boundary barrier on the strength of the sample as a function of the stacking fault energy of the material. The activated glide systems are subsequently identified from slip trace analysis and STEM mapping of lamellas obtained by lift-off from the bulk of the tested micropillars. This allows identifying the different deformation modes, which will be discussed in the presentation
Cellular Automaton Study of Time-Dynamics of Avalanche Breakdown in IMPATT Diodes
Employing a recently developed efficient cellular automaton technique for solving
Boltzmann's transport equation for realistic devices, we present a detailed study of the
carrier dynamics in GaAs avalanche p-i-n (IMPATT) diodes. We find that the impact
ionization in reverse bias p-i-n diodes with ultrathin (less than 50 nm) intrinsic regions is
triggered by Zener tunneling rather than by thermal generation. The impact generation
of hot carriers occurs mainly in the low-field junction regions rather than in the high
field intrinsic zone. The calculations predict significantly more minority carriers on the
n-side than on the p-side
Photon reconstruction in the ATLAS inner detector and liquid argon barrel calorimeter at the 2004 combined test beam
De kast met draaibare ramen - die zaak is nog niet rond
Sinds 2003 worden er kasten met draaibare ramen gemaakt in Hongarije. Het stopt de varroamijt en het zwermen van de bijen. Het lijkt ook daadwerkelijk te helpen, maar de vraag is of het de hoge investering waard i
Simulator for Microlens Planet Surveys
We summarize the status of a computer simulator for microlens planet surveys.
The simulator generates synthetic light curves of microlensing events observed
with specified networks of telescopes over specified periods of time.
Particular attention is paid to models for sky brightness and seeing,
calibrated by fitting to data from the OGLE survey and RoboNet observations in
2011. Time intervals during which events are observable are identified by
accounting for positions of the Sun and the Moon, and other restrictions on
telescope pointing. Simulated observations are then generated for an algorithm
that adjusts target priorities in real time with the aim of maximizing planet
detection zone area summed over all the available events. The exoplanet
detection capability of observations was compared for several telescopes.Comment: Proc. IAU Symp. No. 293 "Formation, detection, and characterization
of extrasolar habitable planets", ed. by N. Haghighipour. 4 pages, in pres
Study of material homogeneity in the long fiber thermoset injection molding process by image texture analysis
To quantify the homogeneity of fiber dispersion in short fiber-reinforced polymer composites, a method for image texture analysis of 3-dimensional X-ray micro computed tomography (µCT) images is presented in this work. The adaption of the method to the specific requirements of the composite material is accomplished using a statistical region merging approach. Subsequently, the method is applied for evaluating the homogeneity of specimens from an intermediate step of the long fiber thermoset injection molding process as well as molded parts. This new injection molding process enables the manufacturing of parts with a flexible combination of short and long glass fibers. By using a newly developed screw element based on the Maddock mixing element design, the material homogeneity of parts molded in the long fiber injection molding process is improved
Field-Scale Soil Property Changes under Switchgrass Managed for Bioenergy
The capacity of perennial grasses to affect change in soil properties is well documented but information on switchgrass (Panicum virgatum L.) managed for bioenergy is limited. An on-farm study (10 fields) in North Dakota, South Dakota, and Nebraska was sampled before switchgrass establishment and after 5 years to determine changes in soil bulk density (SBD), pH, soil phosphorus (P), and equivalent mass soil organic carbon (SOC). Changes in SBD were largely constrained to near-surface depths (0–0.05 m). SBD increased (0–0.05 m) at the Nebraska locations (mean=0.16 Mgm-3), while most South Dakota and North Dakota locations showed declines in SBD (mean=-0.18 Mgm-3; range=-0.42–0.07 Mgm-3). Soil pH change was significant at five of the 10 locations at near surface depths (0–0.05 m), but absolute changes were modest (range=-0.67–0.44 pH units). Available P declined at all sites where it was measured (North Dakota and South Dakota locations). When summed across the surface 0.3 m depth, annual decreases in available P averaged 1.5 kg P ha-1 yr-1 (range=0.5–2.8 kg P ha-1 yr-1). Averaged across locations, equivalent mass SOC increased by 0.5 and 2.4 Mg Cha-1 yr-1 for the 2500 and 10 000 Mg ha-1 soil masses, respectively. Results from this study underscore the contribution of switchgrass to affect soil property changes, though considerable variation in soil properties exists within and across locations
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