534 research outputs found
Evidence for higher order QED in e+ e- pair production at RHIC
A new lowest order QED calculation for RHIC e+ e- pair production has been
carried out with a phenomenological treatment of the Coulomb dissociation of
the heavy ion nuclei observed in the STAR ZDC triggers. The lowest order QED
result for the experimental acceptance is nearly two standard deviations larger
than the STAR data. A corresponding higher order QED calculation is consistent
with the data.Comment: 4 pages, 4 figures, latex, revte
Inclusive and exclusive diffractive production of dilepton pairs in proton-proton collisions at high energies
We calculate for the first time cross sections for single and central
diffractive as well as exclusive diffractive production of dilepton pairs in
proton-proton collisions. Several differential distributions are shown. The
inclusive diffractive processes are calculated using diffractive parton
distributions extracted from the analysis of diffractive structure function and
dijet production at HERA. We find that the inclusive single-diffractive
Drell-Yan process is by about 2 orders of magnitude smaller than ordinary
Drell-Yan process. The central-diffractive processes are smaller by one order
of magnitude compared to single-diffractive ones. We consider also exclusive
production of dilepton pairs. The exclusive photon-pomeron (pomeron-photon)
process constitutes a background to the QED photon-photon process proposed to
be used for controlling luminosity at LHC. Both processes are compared then in
several differential distributions. We find a region of the phase space where
the photon-pomeron or pomeron-photon contributions can be larger than the
photon-photon one.Comment: 20 page, 19 figure
Modelling of Quench Limit for Steady State Heat Deposits in LHC Magnets
A quench, the transition of a conductor from the superconducting to the normal conducting state, occurs irreversibly in the accelerator magnets if one of the three parameters: temperature, magnetic field or current density exceeds a critical value. Energy deposited in the superconductor by the particle beams provokes quenches detrimental for the accelerator operation. In particular if particles impacting on the vacuum chamber and their secondary showers depose energy in the magnet coils. The Large Hadron Collider (LHC) nominal beam intensity is 3.2 ldr 10^14 protons. A quench occurs if a fraction of the order of 10^7 protons per second is lost locally. A network model is used to simulate the thermodynamic behaviour of the magnets. The heat flow in the network model was validated with measurements performed in the CERN magnet test facility. A steady state heat flow was introduced in the coil by using the quench heaters implemented in the LHC magnets. The value of the heat source current is determined by the network model and the magnet coil current which is required to quench the coil is predicted accordantly. The measured and predicted value comparison is regarded as a sensitive test of the method
Footbridge dynamic performance assessment using inertial measurement units
This is the author accepted manuscriptDynamic performance of footbridges is still a great concern to designers, operators and users, with many structures requiring investigation before, during and after construction to manage performance. We have been investigating the use of wireless inertial measurement units (IMUs) designed for biomechanics, health and sports science application for estimating human dynamic loads or ground reaction forces (GRFs) on structures. The aim has been to move from direct measurements using force plates and treadmills, via optical motion capture in the laboratory (with application of Newtonâs Second law), to unconstrained field conditions. Initially we used IMUs to evaluate pedestrian synchronisation, but we found that a single IMU attached to the C7 neck vertebra can provide a remarkably accurate estimate of vertical GRF. With an ability to communicate and synchronise within a group wirelessly, to identify orientation and transform accelerations into world coordinates, IMUs can identify both the GRF force vectors and their time varying location with a moving pedestrian. As a side-benefit, the signal to noise ratio and synchronisation accuracy are sufficient to enable low-cost wireless footbridge ambient vibration testing and monitoring. So far we have used IMUs for ambient and forced vibration testing (the latter using a human shaker), moving pedestrian load and response measurement and crowd tracking. There are many more possibilities
QUENCH LIMIT CALCULATION FOR STEADY STATE HEAT DEPOSITS IN LHC INNER TRIPLET QUADRUPOLE MAGNETS
Abstract In hadron colliders such as the LHC, the energy deposited in the superconductors by the particles lost from the beams or coming from the collision debris may provoke quenches detrimental to the accelerator operation. A Network Model is used to simulate the thermodynamic behavior of the superconducting magnets. In previous papers the validations of network model with measurements performed in the CERN and Fermilab magnet test facilities were presented. This model was subsequently used for thermal analysis of the current LHC inner triplet quadrupole magnets for beam energy of 3.5 TeV and 7.0 TeV. The detailed study of helium cooling channels efficiency for energy deposits simulated with FLUKA was performed. The expected LHC inner triplet magnets quench limit is presented
Salmonella contamination of pig farm environment, Poland, 2014
Although pork is considered an important source of Salmonella infections, the introduction of control programs in pig farms are not obligatory in the EU. To resolve current epidemiological situation, monitoring of pig farms was introduced in Poland in 2014. The paper reports the first year outputs of the survey
Beam losses from ultra-peripheral nuclear collisions between Pb ions in the Large Hadron Collider and their alleviation
Electromagnetic interactions between colliding heavy ions at the Large Hadron
Collider (LHC) at CERN will give rise to localized beam losses that may quench
superconducting magnets, apart from contributing significantly to the
luminosity decay. To quantify their impact on the operation of the collider, we
have used a three-step simulation approach, which consists of optical tracking,
a Monte-Carlo shower simulation and a thermal network model of the heat flow
inside a magnet. We present simulation results for the case of Pb ion operation
in the LHC, with focus on the ALICE interaction region, and show that the
expected heat load during nominal Pb operation is 40% above the quench level.
This limits the maximum achievable luminosity. Furthermore, we discuss methods
of monitoring the losses and possible ways to alleviate their effect.Comment: 17 pages, 20 figure
A framework for experimental determination of localised vertical pedestrian forces on full-scale structures using wireless attitude and heading reference systems
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.A major weakness among loading models for pedestrians walking on flexible structures proposed in
recent years is the various uncorroborated assumptions made in their development. This applies to spatio-
temporal characteristics of pedestrian loading and the nature of multi-object interactions. To alleviate this
problem, a framework for the determination of localised pedestrian forces on full-scale structures is
presented using a wireless attitude and heading reference systems (AHRS). An AHRS comprises a triad
of tri-axial accelerometers, gyroscopes and magnetometers managed by a dedicated data processing unit,
allowing motion in three-dimensional space to be reconstructed. A pedestrian loading model based on a
single point inertial measurement from an AHRS is derived and shown to perform well against
benchmark data collected on an instrumented treadmill. Unlike other models, the current model does not
take any predefined form nor does it require any extrapolations as to the timing and amplitude of
pedestrian loading. In order to assess correctly the influence of the moving pedestrian on behaviour of a
structure, an algorithm for tracking the point of application of pedestrian force is developed based on data
from a single AHRS attached to a foot. A set of controlled walking tests with a single pedestrian is
conducted on a real footbridge for validation purposes. A remarkably good match between the measured
and simulated bridge response is found, indeed confirming applicability of the proposed framework.The research presented here was funded by EPSRC (grant EP/I029567/2). Authors thank Devon County Council for permitting the experimental campaign to be conducted on Baker Bridge in Exeter, UK, and Dr Erfan Shahabpour (supported by EPSRC grant EP/K03877X/1) for providing access to and assisting with measurements on the ADAL-3D treadmill at the University of Sheffield (funded by EPSRC grant EP/E018734/1)
A framework for experimental determination of localised vertical pedestrian forces on full-scale structures using wireless attitude and heading reference systems
A major weakness among loading models for pedestrians walking on flexible structures proposed in recent years is the various uncorroborated assumptions made in their development. This applies to spatio-temporal characteristics of pedestrian loading and the nature of multi-object interactions. To alleviate this problem, a framework for the determination of localised pedestrian forces on full-scale structures is presented using a wireless attitude and heading reference systems (AHRS). An AHRS comprises a triad of tri-axial accelerometers, gyroscopes and magnetometers managed by a dedicated data processing unit, allowing motion in three-dimensional space to be reconstructed. A pedestrian loading model based on a single point inertial measurement from an AHRS is derived and shown to perform well against benchmark data collected on an instrumented treadmill. Unlike other models, the current model does not take any predefined form nor does it require any extrapolations as to the timing and amplitude of pedestrian loading. In order to assess correctly the influence of the moving pedestrian on behaviour of a structure, an algorithm for tracking the point of application of pedestrian force is developed based on data from a single AHRS attached to a foot. A set of controlled walking tests with a single pedestrian is conducted on a real footbridge for validation purposes. A remarkably good match between the measured and simulated bridge response is found, indeed confirming applicability of the proposed framework
Quenching Capabilities of Long-Chain Carotenoids in Light-Harvesting-2 Complexes from Rhodobacter sphaeroides with an Engineered Carotenoid Synthesis Pathway
Six light-harvesting-2 complexes (LH2) from genetically modified
strains of the purple photosynthetic bacterium Rhodobacter (Rb.) sphaeroides were
studied using static and ultrafast optical methods and resonance Raman
spectroscopy. These strains were engineered to incorporate carotenoids for
which the number of conjugated groups (N = NCC + NCO) varies from 9 to 15.
The Rb. sphaeroides strains incorporate their native carotenoids spheroidene (N =
10) and spheroidenone (N = 11), as well as longer-chain analogues including
spirilloxanthin (N = 13) and diketospirilloxantion (N = 15) normally found in
Rhodospirillum rubrum. Measurements of the properties of the carotenoid first
singlet excited state (S1) in antennas from the Rb. sphaeroides set show that
carotenoid-bacteriochlorophyll a (BChl a) interactions are similar to those in LH2 complexes from various other bacterial species
and thus are not significantly impacted by differences in polypeptide composition. Instead, variations in carotenoid-to-BChl a
energy transfer are primarily regulated by the N-determined energy of the carotenoid S1 excited state, which for long-chain (N â„
13) carotenoids is not involved in energy transfer. Furthermore, the role of the long-chain carotenoids switches from a lightharvesting
supporter (via energy transfer to BChl a) to a quencher of the BChl a S1 excited state B850*. This quenching is
manifested as a substantial (âŒ2-fold) reduction of the B850* lifetime and the B850* fluorescence quantum yield for LH2
housing the longest carotenoids
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