165 research outputs found
The Chemical Origin of SEY at Technical Surfaces
The secondary emission yield (SEY) properties of colaminated Cu samples for
LHC beam screens are correlated to the surface chemical composition determined
by X-ray photoelectron spectroscopy. The surface of the "as received" samples
is characterized by the presence of significant quantities of contaminating
adsorbates and by the maximum of the SEY curve (dmax) being as high as 2.2.
After extended electron scrubbing at kinetic energy of 10 and 500 eV, the dmax
value drops to the ultimate values of 1.35 and 1.1, respectively. In both cases
the surface oxidized phases are significantly reduced, whereas only in the
sample scrubbed at 500 eV the formation of a graphitic-like C layer is
observed. We find that the electron scrubbing of technical Cu surfaces can be
described as occurring in two steps, where the first step consists in the
electron induced desorption of weakly bound contaminants that occurs
indifferently at 10 and at 500 eV and corresponds to a partial decrease of
dmax, and the second step, activated by more energetic electrons and becoming
evident at high doses, which increases the number of graphitic-like C-C bonds
via the dissociation of adsorbates already contaminating the "as received"
surface or accumulating on this surface during irradiation. Our results
demonstrate how the kinetic energy of impinging electrons is a crucial
parameter when conditioning technical surfaces of Cu and other metals by means
of electron induced chemical processing.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,
Italy; CERN Yellow Report CERN-2013-002, pp.99-10
Electric fields in plasmas under pulsed currents
Electric fields in a plasma that conducts a high-current pulse are measured
as a function of time and space. The experiment is performed using a coaxial
configuration, in which a current rising to 160 kA in 100 ns is conducted
through a plasma that prefills the region between two coaxial electrodes. The
electric field is determined using laser spectroscopy and line-shape analysis.
Plasma doping allows for 3D spatially resolved measurements. The measured peak
magnitude and propagation velocity of the electric field is found to match
those of the Hall electric field, inferred from the magnetic-field front
propagation measured previously.Comment: 13 pages, 13 figures, submitted to PR
Status of COLDDIAG: A Cold Vacuum Chamber for Diagnostics
One of the still open issues for the development of superconducting insertion
devices is the understanding of the beam heat load. With the aim of measuring
the beam heat load to a cold bore and the hope to gain a deeper understanding
in the beam heat load mechanisms, a cold vacuum chamber for diagnostics is
under construction. The following diagnostics will be implemented: i) retarding
field analyzers to measure the electron energy and flux, ii) temperature
sensors to measure the total heat load, iii) pressure gauges, iv) and mass
spectrometers to measure the gas content. The inner vacuum chamber will be
removable in order to test different geometries and materials. This will allow
the installation of the cryostat in different synchrotron light sources.
COLDDIAG will be built to fit in a short straight section at ANKA. A first
installation at the synchrotron light source Diamond is foreseen in June 2011.
Here we describe the technical design report of this device and the planned
measurements with beam.Comment: Presented at First International Particle Accelerator Conference,
IPAC'10, Kyoto, Japan, from 23 to 28 May 201
One-carbon metabolism in cancer
Cells require one-carbon units for nucleotide synthesis, methylation and reductive metabolism, and these pathways support the high proliferative rate of cancer cells. As such, anti-folates, drugs that target one-carbon metabolism, have long been used in the treatment of cancer. Amino acids, such as serine are a major one-carbon source, and cancer cells are particularly susceptible to deprivation of one-carbon units by serine restriction or inhibition of de novo serine synthesis. Recent work has also begun to decipher the specific pathways and sub-cellular compartments that are important for one-carbon metabolism in cancer cells. In this review we summarise the historical understanding of one-carbon metabolism in cancer, describe the recent findings regarding the generation and usage of one-carbon units and explore possible future therapeutics that could exploit the dependency of cancer cells on one-carbon metabolism
Recoil Polarization Measurements of the Proton Electromagnetic Form Factor Ratio to Q^2 = 8.5 GeV^2
Among the most fundamental observables of nucleon structure, electromagnetic
form factors are a crucial benchmark for modern calculations describing the
strong interaction dynamics of the nucleon's quark constituents; indeed, recent
proton data have attracted intense theoretical interest. In this letter, we
report new measurements of the proton electromagnetic form factor ratio using
the recoil polarization method, at momentum transfers Q2=5.2, 6.7, and 8.5
GeV2. By extending the range of Q2 for which GEp is accurately determined by
more than 50%, these measurements will provide significant constraints on
models of nucleon structure in the non-perturbative regime
Non-typeable Haemophilus influenzae and Streptococcus pneumoniae as primary causes of acute otitis media in colombian children: a prospective study
<p>Abstract</p> <p>Background</p> <p>Acute otitis media (AOM) is one of the most frequently encountered bacterial infections in children aged < 5 years; <it>Streptococcus pneumoniae </it>(<it>S. pneumoniae</it>) and non-typeable <it>Haemophilus influenzae </it>(NTHi) are historically identified as primary AOM causes. Nevertheless, recent data on bacterial pathogens causing AOM in Latin America are limited. This prospective study aimed to identify and characterize bacterial etiology and serotypes of AOM cases including antimicrobial susceptibility in < 5 year old Colombian children.</p> <p>Methods</p> <p>From February 2008 to January 2009, children ≥3 months and < 5 years of age presenting with AOM and for whom a middle ear fluid (MEF) sample was available were enrolled in two medical centers in Cali, Colombia. MEF samples were collected either by tympanocentesis procedure or spontaneous otorrhea swab sampling. Bacteria were identified using standard laboratory methods, and antimicrobial resistance testing was performed based on the 2009 Clinical and Laboratory Standards Institute (CLSI) criteria. Most of the cases included in the study were sporadic in nature.</p> <p>Results</p> <p>Of the 106 enrolled children, 99 were included in the analysis. Bacteria were cultured from 62/99 (63%) of samples with <it>S. pneumoniae, H. influenzae, or S. pyogenes</it>. The most commonly isolated bacteria were <it>H. influenzae </it>in 31/99 (31%) and <it>S. pneumoniae </it>in 30/99 (30%) of samples. The majority of <it>H. influenzae </it>episodes were NTHi (27/31; 87%). 19F was the most frequently isolated pneumococcal serotype (10/30; 33%). Of the 30 <it>S. pneumoniae </it>positive samples, 8/30 (27%) were resistant to tetracycline, 5/30 (17%) to erythromycin and 8/30 (27%) had intermediate resistance to penicillin. All <it>H. influenzae </it>isolates tested were negative to beta-lactamase.</p> <p>Conclusions</p> <p>NTHi and <it>S. pneumoniae </it>are the leading causes of AOM in Colombian children. A pneumococcal conjugate vaccine that prevents both pathogens could be useful in maximizing protection against AOM.</p
An Obligatory Role of Mind Bomb-1 in Notch Signaling of Mammalian Development
Background. The Notch signaling pathway is an evolutionarily conserved intercellular signaling module essential for cell fate specification that requires endocytosis of Notch ligands. Structurally distinct E3 ubiquitin ligases, Neuralized (Neur) and Mind bomb (Mib), cooperatively regulate the endocytosis of Notch ligands in Drosophila. However, the respective roles of the mammalian E3 ubiquitin ligases, Neur1, Neur2, Mib1, and Mib2, in mammalian development are poorly understood. Methodology/Principal Findings. Through extensive use of mammalian genetics, here we show that Neur1 and Neur2 double mutants and Mib2-1- mice were viable and grossly normal. In contrast, conditional inactivation of MW in various tissues revealed the representative Notch phenotypes: defects of arterial specification as deltalike4 mutants, abnormal cerebellum and skin development as jagged1 conditional mutants, and syndactylism as jagged2 mutants. Conclusions/Significance. Our data provide the first evidence that Mib1 is essential for Jagged as well as Deltalike ligand-mediated Notch signaling in mammalian development, while Neur1, Neur2, and Mib2 are dispensable.open504
Measurements of Non-Singlet Moments of the Nucleon Structure Functions and Comparison to Predictions from Lattice QCD for
We present extractions of the nucleon non-singlet moments utilizing new
precision data on the deuteron structure function at large Bjorken-
determined via the Rosenbluth separation technique at Jefferson Lab
Experimental Hall C. These new data are combined with a complementary set of
data on the proton previously measured in Hall C at similar kinematics and
world data sets on the proton and deuteron at lower measured at SLAC and
CERN. The new Jefferson Lab data provide coverage of the upper third of the
range, crucial for precision determination of the higher moments. In contrast
to previous extractions, these moments have been corrected for nuclear effects
in the deuteron using a new global fit to the deuteron and proton data. The
obtained experimental moments represent an order of magnitude improvement in
precision over previous extractions using high data. Moreover, recent
exciting developments in Lattice QCD calculations provide a first ever
comparison of these new experimental results with calculations of moments
carried out at the physical pion mass, as well as a new approach which first
calculates the quark distributions directly before determining moments
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