414 research outputs found
Electron cloud in the CERN accelerators (PS, SPS, LHC)
Several indicators have pointed to the presence of an Electron Cloud (EC) in
some of the CERN accelerators, when operating with closely spaced bunched
beams. In particular, spurious signals on the pick ups used for beam detection,
pressure rise and beam instabilities were observed at the Proton Synchrotron
(PS) during the last stage of preparation of the beams for the Large Hadron
Collider (LHC), as well as at the Super Proton Synchrotron (SPS). Since the LHC
has started operation in 2009, typical electron cloud phenomena have appeared
also in this machine, when running with trains of closely packed bunches (i.e.
with spacings below 150ns). Beside the above mentioned indicators, other
typical signatures were seen in this machine (due to its operation mode and/or
more refined detection possibilities), like heat load in the cold dipoles,
bunch dependent emittance growth and degraded lifetime in store and
bunch-by-bunch stable phase shift to compensate for the energy loss due to the
electron cloud. An overview of the electron cloud status in the different CERN
machines (PS, SPS, LHC) will be presented in this paper, with a special
emphasis on the dangers for future operation with more intense beams and the
necessary countermeasures to mitigate or suppress the effect.Comment: 8 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
PyECLOUD and build-up simulations at CERN
PyECLOUD is a newly developed code for the simulation of the electron cloud
(EC) build-up in particle accelerators. Almost entirely written in Python, it
is mostly based on the physical models already used in the ECLOUD code but,
thanks to the implementation of new optimized algorithms, it exhibits a
significantly improved performance in accuracy, speed, reliability and
flexibility. Such new features of PyECLOUD have been already broadly exploited
to study EC observations in the Large Hadron Collider (LHC) and its injector
chain as well as for the extrapolation to high luminosity upgrade scenarios.Comment: 6 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
Benchmarking headtail with electron cloud instabilities observed in the LHC
After a successful scrubbing run in the beginning of 2011, the LHC can be
presently operated with high intensity proton beams with 50 ns bunch spacing.
However, strong electron cloud effects were observed during machine studies
with the nominal beam with 25 ns bunch spacing. In particular, fast transverse
instabilities were observed when attempting to inject trains of 48 bunches into
the LHC for the first time. An analysis of the turn-by-turn bunch-bybunch data
from the transverse damper pick-ups during these injection studies is
presented, showing a clear signature of the electron cloud effect. These
experimental observations are reproduced using numerical simulations: the
electron distribution before each bunch passage is generated with PyECLOUD and
used as input for a set of HEADTAIL simulations. This paper describes the
simulation method as well as the sensitivity of the results to the initial
conditions for the electron build-up. The potential of this type of simulations
and their clear limitations on the other hand are discussed.Comment: 7 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
Synchronous Phase Shift at LHC
The electron cloud in vacuum pipes of accelerators of positively charged
particle beams causes a beam energy loss which could be estimated from the
synchronous phase. Measurements done with beams of 75 ns, 50 ns, and 25 ns
bunch spacing in the LHC for some fills in 2010 and 2011 show that the average
energy loss depends on the total beam intensity in the ring. Later measurements
during the scrubbing run with 50 ns beams show the reduction of the electron
cloud due to scrubbing. Finally, measurements of the individual bunch phase
give us information about the electron cloud build-up inside the batch and from
batch to batch.Comment: Presented at ECLOUD'12: Joint INFN-CERN-EuCARD-AccNet Workshop on
Electron-Cloud Effects, La Biodola, Isola d'Elba, Italy, 5-9 June 201
The molecular defect of albumin Tagliacozzo: 313 Lys → Asn
AbstractAlbumin Tagliacozzo is a fast-moving genetic variant of human serum albumin found in 19 unrelated families. The protein was isolated from the serum of a heterozygous healthy subject. Analysis of CNBr fragments by isoelectric focusing allowed us to localize the mutation to CNBr fragment IV (residues 299–329). This fragment was isolated on a preparative scale and subjected to tryptic digestion. Sequential analysis of the abnormal tryptic peptide, purified by RP-HPLC, revealed the variant was caused by 313 Lys → Asn substitution, probably due to a point mutation in the structural gene. The lack of a lysine residue accounts for the electrophoretic behavior of albumin Tagliacozzo
Driver Drowsiness Detection: A Machine Learning Approach on Skin Conductance
The majority of car accidents worldwide are caused by drowsy drivers. Therefore, it is important to be able to detect when a driver is starting to feel drowsy in order to warn them before a serious accident occurs. Sometimes, drivers are not aware of their own drowsiness, but changes in their body signals can indicate that they are getting tired. Previous studies have used large and intrusive sensor systems that can be worn by the driver or placed in the vehicle to collect information about the driver’s physical status from a variety of signals that are either physiological or vehicle-related. This study focuses on the use of a single wrist device that is comfortable for the driver to wear and appropriate signal processing to detect drowsiness by analyzing only the physiological skin conductance (SC) signal. To determine whether the driver is drowsy, the study tests three ensemble algorithms and finds that the Boosting algorithm is the most effective in detecting drowsiness with an accuracy of 89.4%. The results of this study show that it is possible to identify when a driver is drowsy using only signals from the skin on the wrist, and this encourages further research to develop a real-time warning system for early detection of drowsiness
Dependence of e-cloud on the longitudinal bunch profile: studies in the PS & extension to the HL-LHC
Recent studies have shown that the prospects for significantly increasing
bunch intensities in the LHC for the luminosity upgrade (HL-LHC) may be
severely limited by the available cryogenic cooling capacity and the
electron-cloud (EC) driven beam instability. However, it is planned that during
the HL-LHC era the bunch intensities in the LHC will go up by nearly a factor
of two compared to the LHC-design values. This motivates the exploration of
additional EC mitigation techniques that can be adopted in addition to those
already in place. Preliminary simulations indicated that long flat bunches can
be beneficial over Gaussian bunches to reduce the EC build up. Rigorous studies
using realistic bunch profiles have never been done. Therefore, we have
undertaken an in-depth investigation in the CERN 26 GeV PS to see if we can
validate the previous findings and, in particular, if flattening the bunch can
mitigate the EC. Here we present the results from dedicated EC measurements in
the PS using a variety of bunch shapes and a comparison with simulations.
Finally, we investigate if reshaping the bunch profiles using a 2nd harmonic rf
cavity can mitigate EC in the HL-LHC
Production of serine chymotrypsin - like elastase by aspergillus fumigatus strains
Thirty-four Aspergillus fumigatus strains isolated from air, horse-hair; agricultural soil and human samples were screened to evaluate the production of elastase. Aspergillus fumigatus strains were grown in elastin solid medium, showing a widespread elastin solubilization. However, isolates from human and agricultural soil samples were found to be the highest elastase producers. Then, eight out of 34 strains were grown in four different liquid media, on wich we investigated total and specific proteolytic activity. Results from this experiments suggest that the elastase production is induced by the presence of elastin as a substrate and that the elastase is a chymotrypsin like enzyme. Inhibitory profile showed that the A.fumigatus elastase is a serine proteinase
Progress with the Upgrade of the SPS for the HL-LHC Era
The demanding beam performance requirements of the High Luminosity (HL-) LHC
project translate into a set of requirements and upgrade paths for the LHC
injector complex. In this paper the performance requirements for the SPS and
the known limitations are reviewed in the light of the 2012 operational
experience. The various SPS upgrades in progress and still under consideration
are described, in addition to the machine studies and simulations performed in
2012. The expected machine performance reach is estimated on the basis of the
present knowledge, and the remaining decisions that still need to be made
concerning upgrade options are detailed.Comment: 3 p. Presented at 4th International Particle Accelerator Conference
(IPAC 2013
An isoform of the giant protein titin is a master regulator of human T lymphocyte trafficking
Response to multiple microenvironmental cues and resilience to mechanical stress are essential features of trafficking leukocytes. Here, we describe unexpected role of titin (TTN), the largest protein encoded by the human genome, in the regulation of mechanisms of lymphocyte trafficking. Human T and B lymphocytes ex-press five TTN isoforms, exhibiting cell-specific expression, distinct localization to plasma membrane micro -domains, and different distribution to cytosolic versus nuclear compartments. In T lymphocytes, the LTTN1 isoform governs the morphogenesis of plasma membrane microvilli independently of ERM protein phosphor-ylation status, thus allowing selectin-mediated capturing and rolling adhesions. Likewise, LTTN1 controls chemokine-triggered integrin activation. Accordingly, LTTN1 mediates rho and rap small GTPases activation, but not actin polymerization. In contrast, chemotaxis is facilitated by LTTN1 degradation. Finally, LTTN1 con-trols resilience to passive cell deformation and ensures T lymphocyte survival in the blood stream. LTTN1 is, thus, a critical and versatile housekeeping regulator of T lymphocyte trafficking
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