3,425 research outputs found
Implementation and experience with luminosity levelling with offset beam
The practice of luminosity levelling with an offset beam has been used as a
routine operation in the LHC since 2011. This paper will describe how it has
been implemented and what has been the operational experience with the system.Comment: 5 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects
in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201
Controllability for chains of dynamical scatterers
In this paper, we consider a class of mechanical models which consists of a
linear chain of identical chaotic cells, each of which has two small lateral
holes and contains a rotating disk at its center. Particles are injected at
characteristic temperatures and rates from stochastic heat baths located at
both ends of the chain. Once in the system, the particles move freely within
the cells and will experience elastic collisions with the outer boundary of the
cells as well as with the disks. They do not interact with each other but can
transfer energy from one to another through collisions with the disks. The
state of the system is defined by the positions and velocities of the particles
and by the angular positions and angular velocities of the disks. We show that
each model in this class is controllable with respect to the baths, i.e. we
prove that the action of the baths can drive the system from any state to any
other state in a finite time. As a consequence, one obtains the existence of at
most one regular invariant measure characterizing its states (out of
equilibrium)
Mid-infrared sub-wavelength grating mirror design: tolerance and influence of technological constraints
High polarization selective Si/SiO2 mid-infrared sub-wavelength grating
mirrors with large bandwidth adapted to VCSEL integration are compared. These
mirrors have been automatically designed for operation at \lambda = 2.3 m
by an optimization algorithm which maximizes a specially defined quality
factor. Several technological constraints in relation with the grating
manufacturing process have been imposed within the optimization algorithm and
their impact on the optical properties of the mirror have been evaluated.
Furthermore, through the tolerance computation of the different dimensions of
the structure, the robustness with respect to fabrication errors has been
tested. Finally, it appears that the increase of the optical performances of
the mirror imposes a less tolerant design with severer technological
constraints resulting in a more stringent control of the manufacturing process.Comment: The final publication is available at
http://iopscience.iop.org/2040-8986/13/12/125502
Effect of Beam Dynamics Processes in the Low Energy Ring ThomX
As part of the R\&D for the 50 MeV ThomX Compton source project, we have
studied the effect of several beam dynamics processes on the evolution of the
beam in the ring. The processes studied include among others Compton
scattering, intrabeam scattering, coherent synchrotron radiation. We have
performed extensive simulations of a full injection/extraction cycle (400000
turns). We show how each of these processes degrades the flux of photons
produced and how a feedback system contributes to recovering most of the flux.Comment: Submitted to IPAC'14, WEPRO00
A neglected disease of humans: a new focus of visceral leishmaniasis in Bakool, Somalia.
Visceral leishmaniasis (VL) was observed in children in Bakool region, Somalia, an area where VL has not been reported before. We describe the extent of the problem in this war- and famine-stricken area. A retrospective analysis was done of all cases admitted to a VL treatment centre between July 2000 and August 2001. Patients with longstanding fever, splenomegaly and a positive direct agglutination test (DAT; titre > 1:3200) were treated as suspected VL cases. A rapid epidemiological and entomological assessment was performed in the area. Species identification was attempted from blood samples by polymerase chain reaction-restriction fragment length polymorphism analysis of cysteine proteinase B genes. In 1 year, 230 serologically-positive cases were diagnosed as VL, and response to therapy was good in 91.6% of the 225 treated with sodium stibogluconate. Parasitological confirmation was attempted and obtained in 2 cases. Parasites were found to be most similar to Sudanese and Ethiopian reference strains of the Leishmania donovani complex. In a serological survey of 161 healthy displaced persons, 15% were positive by the leishmanin skin test and 3 (2%) were positive by the DAT. The sandfly captures showed Phlebotomus martini and P. vansomerenae. VL seems to be a longstanding and serious health problem in Bakool region. Food insecurity might have contributed to the emergence and detection of VL in this area
Spin-polarized tunneling spectroscopy in tunnel junctions with half-metallic electrodes
We have studied the magnetoresistance (TMR) of tunnel junctions with
electrodes of La2/3Sr1/3MnO3 and we show how the variation of the conductance
and TMR with the bias voltage can be exploited to obtain a precise information
on the spin and energy dependence of the density of states. Our analysis leads
to a quantitative description of the band structure of La2/3Sr1/3MnO3 and
allows the determination of the gap delta between the Fermi level and the
bottom of the t2g minority spin band, in good agreement with data from
spin-polarized inverse photoemission experiments. This shows the potential of
magnetic tunnel junctions with half-metallic electrodes for spin-resolved
spectroscopic studies.Comment: To appear in Physical Review Letter
Discovery Of Bilaterian-Type Through-Guts In Cloudinomorphs From The Terminal Ediacaran Period
Discovery Of Bilaterian-Type Through-Guts In Cloudinomorphs From The Terminal Ediacaran Period
Picophytoplankton biomass distribution in the global ocean
The smallest marine phytoplankton, collectively termed picophytoplankton, have been routinely enumerated by flow cytometry since the late 1980s during cruises throughout most of the world ocean. We compiled a database of 40 946 data points, with separate abundance entries for Prochlorococcus, Synechococcus and picoeukaryotes. We use average conversion factors for each of the three groups to convert the abundance data to carbon biomass. After gridding with 1? spacing, the database covers 2.4% of the ocean surface area, with the best data coverage in the North Atlantic, the South Pacific and North Indian basins, and at least some data in all other basins. The average picophytoplankton biomass is 12 ± 22 µg Cl-1 or 1.9 g Cm-2. We estimate a total global picophytoplankton biomass of 0.53–1.32 Pg C (17–39% Prochlorococcus, 12–15% Synechococcus and 49–69% picoeukaryotes), with an intermediate/best estimate of 0.74 Pg C. Future efforts in this area of research should focus on reporting calibrated cell size and collecting data in undersampled regions
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