379 research outputs found
Numerical Calculation of Coherent Synchrotron Radiation Effects Using TraFiC4
Coherent synchrotron radiation (CSR) occurs when short bunches travel on
strongly bent trajectories. Its effects on high-quality beams can be severe and
are well understood qualitatively. For quantitative results, however, one has
to rely on numerical methods. There exist several simulation codes utilizing
different approaches. We describe in some detail the code TraFiC4 developed at
DESY for design and analysis purposes, which approaches the problem from first
principles and solves the equations of motion either perturbatively or
self-consistently. We present some calculational results and comparison with
experimental data. Also, we give examples of how the code can be used to design
beamlines with minimal emittance growth due to CSR
Urban water systems under climate stress : An isotopic perspective from Berlin, Germany
ACKNOWLEDGMENTS This project was funded by the German Research Foundation (DFG) as part of the Research Training Group âUrban Water Interfaces (UWI)â (GRK 2032, Project W1: âEcohydrological controls on urban groundwater recharge: an isotopeâbased approachâ) and supported by the project âModelling surface and groundwater with isotopes in urban catchments (MOSAIC)â funded by the EinsteinâFoundation. We thank all colleagues involved in the sample collection (A. Smith, N. WeiĂ, L. Kleine, L. Lachmann, E. Brakkee, W. Lehmann, A. Douinot, K. Dyck, D. Dubbert, H. DĂ€mpfling, A. Wieland), D. Dubbert for support with the isotope analysis, our colleagues in the chemical analytics laboratory at IGB for their support with the chemical analysis, in particular T. Goldhammer, as well as T. Rossoll for help with the measurement equipment. We further thank the BWB and especially the Berlin Senate Department for the Environment, Transport and Climate Protection for the support in accessing groundwater wells and the provided data.Peer reviewedPublisher PDFPublisher PD
Observation of Target Electron Momentum Effects in Single-Arm M\o ller Polarimetry
In 1992, L.G. Levchuk noted that the asymmetries measured in M\o ller
scattering polarimeters could be significantly affected by the intrinsic
momenta of the target electrons. This effect is largest in devices with very
small acceptance or very high resolution in laboratory scattering angle. We use
a high resolution polarimeter in the linac of the polarized SLAC Linear
Collider to study this effect. We observe that the inclusion of the effect
alters the measured beam polarization by -14% of itself and produces a result
that is consistent with measurements from a Compton polarimeter. Additionally,
the inclusion of the effect is necessary to correctly simulate the observed
shape of the two-body elastic scattering peak.Comment: 29 pages, uuencoded gzip-compressed postscript (351 kb). Uncompressed
postscript file (898 kb) available to DECNET users as
SLC::USER_DISK_SLC1:[MORRIS]levpre.p
Preparation and Characterization of [Au(CF3)xF3âx(SIMes)] (x=1â3) Complexes
Trifluoromethylation of [AuF3(SIMes)] with the RuppertâPrakash reagent TMSCF3 in the presence of CsF yields the product series [Au(CF3)xF3âx(SIMes)] (x=1â3). The degree of trifluoromethylation is solvent dependent and the ratio of the species can be controlled by varying the stoichiometry of the reaction, as evidenced from the 19Fâ
NMR spectra of the corresponding reaction mixtures. The molecular structures in the solid state of transâ[Au(CF3)F2(SIMes)] and [Au(CF3)3(SIMes)] are presented, together with a selective route for the synthesis of the latter complex. Correlation of the calculated SIMes affinity with the carbene carbon chemical shift in the 13Câ
NMR spectrum reveals that transâ[Au(CF3)F2(SIMes)] and [Au(CF3)3(SIMes)] nicely follow the trend in Lewis acidities of related organo gold(III) complexes. Furthermore, a new correlation between the AuâCcarbene bond length of the molecular structure in the solid state and the chemical shift of the carbene carbon in the 13Câ
NMR spectrum is presented
Coherent Synchrotron Radiation Measurements in the CLIC Test Facility (CTF II)
Bunches of high charge (up to 10 nC) are compressed in length in the CTF II
magnetic chicane to less than 0.2 mm rms. The short bunches radiate coherently
in the chicane magnetic field, and the horizontal and longitudinal phase space
density distributions are affected. This paper reports the results of beam
emittance and momentum measurements. Horizontal and vertical emittances and
momentum spectra were measured for different bunch compression factors and
bunch charges. In particular, for 10 nC bunches, the mean beam momentum
decreased by about 5% while the FWHM momentum spread increased from 5% to 19%.
The experimental results are compared with simulations made with the code
TraFiC4.Comment: 5 pages, 6 figures, submitted to the LINAC 2000 Conferenc
Reactivity of [AuF3(SIMes)] â Pathway to Unprecedented Structural Motifs
We report on a comprehensive reactivity study starting from [AuF3(SIMes)] to synthesize different motifs of monomeric gold(III) fluorides. A plethora of different ligands has been introduced in a mono-substitution yielding trans-[AuF2X(SIMes)] including alkynido, cyanido, azido, and a set of perfluoroalkoxido complexes. The latter were better accomplished via use of perfluorinated carbonyl-bearing molecules, which is unprecedented in gold chemistry. In case of the cyanide and azide, triple substitution gave rise to the corresponding [AuX3(SIMes)] complexes. Comparison of the chemical shift of the carbene carbon atom in the 13C{1H} NMR spectrum, the calculated SIMes affinity and the AuâC bond length in the solid state with related literature-known complexes yields a classification of trans-influences for a variety of ligands attached to the gold center. Therein, the mixed fluorido perfluoroalkoxido complexes have a similar SIMes affinity to AuF3 with a very low Gibbs energy of formation when using the perfluoro carbonyl route
Gastric cancer and Helicobacter pylori: a combined analysis of 12 case control studies nested within prospective cohorts
BACKGROUND: The magnitude of the association
between Helicobacter pylori and
incidence of gastric cancer is unclear. H
pylori infection and the circulating antibody
response can be lost with development
of cancer; thus retrospective studies
are subject to bias resulting from classifi-
cation of cases as H pylori negative when
they were infected in the past.
AIMS: To combine data from all case control
studies nested within prospective
cohorts to assess more reliably the relative
risk of gastric cancer associated with H
pylori infection.To investigate variation in
relative risk by age, sex, cancer type and
subsite, and interval between blood sampling
and cancer diagnosis.
METHODS: Studies were eligible if blood
samples for H pylori serology were collected
before diagnosis of gastric cancer in
cases. Identified published studies and two
unpublished studies were included. Individual
subject data were obtained for
each. Matched odds ratios (ORs) and 95%
confidence intervals (95% CI) were calculated
for the association between H pylori
and gastric cancer.
RESULTS: Twelve studies with 1228 gastric
cancer cases were considered. The association
with H pylori was restricted to noncardia
cancers (OR 3.0; 95% CI 2.3â3.8)
and was stronger when blood samples for
H pylori serology were collected 10+ years
before cancer diagnosis (5.9; 3.4â10.3). H
pylori infection was not associated with an
altered overall risk of cardia cancer (1.0;
0.7â1.4).
CONCLUSIONS: These results suggest that
5.9 is the best estimate of the relative risk
of non-cardia cancer associated with H
pylori infection and that H pylori does not
increase the risk of cardia cancer. They
also support the idea that when H pylori
status is assessed close to cancer diagnosis,
the magnitude of the non-cardia
association may be underestimated
The DNA methylation landscape of the human oxytocin receptor gene (OXTR): data-driven clusters and their relation to gene expression and childhood adversity
The oxytocin receptor gene (OXTR) is of interest when investigating the effects of early adversity on DNA methylation. However, there is heterogeneity regarding the selection of the most promising CpG sites to target for analyses. The goal of this study was to determine functionally relevant clusters of CpG sites within the OXTR CpG island in 113 mother-infant dyads, with 58 of the mothers reporting childhood maltreatment (CM). OXTR DNA methylation was analyzed in peripheral/umbilical blood mononuclear cells. Different complexity reduction approaches were used to reduce the 188 CpG sites into clusters of co-methylated sites. Furthermore, associations between OXTR DNA methylation (cluster- and site-specific level) and OXTR gene expression and CM were investigated in mothers. Results showed that, first, CpG sections differed strongly regarding their statistical utility for research of individual differences in DNA methylation. Second, cluster analyses and Partial Least Squares (PLS) suggested two clusters consisting of intron1/exon2 and the protein-coding region of exon3, respectively, as most strongly associated with outcome measures. Third, cross-validated PLS regression explained 7% of variance in CM, with low cross-validated variance explained for the prediction of gene expression. Fourth, substantial mother-child correspondence was observed in correlation patterns within the identified clusters, but only modest correspondence outside these clusters. This study makes an important contribution to the mapping of the DNA methylation landscape of the OXTR CpG island by highlighting clusters of CpG sites that show desirable statistical properties and predictive value. We provide a Companion Web Application to facilitate the choice of CpG sites
Emittance Growth and Energy Loss due to Coherent Synchrotron Radiation in a bunch compressor
Bunches of high charge (10 nC) are compressed in length in the CTF II bunch compressor from 1.2 mm rms to less than 0.4 mm. The short bunches start to radiate coherently, thus affecting the horizontal and longitudinal phase spaces of the beam. This paper reports the results of measurements and simulations concerning the increase of the beam emittance and the impact on the energy distribution. Beam emittances were measured for different bunch compression factors and bunch charges. For each compressor setting, the energy spectrum of the beam was recorded in order to measure the energy loss due to coherent synchrotron radiation. For bunch charges of 10 nC a maximum increase of the horizontal emittance of 50% was observed at full compression, while the mean beam energy decreased by 5% from 39 MeV to 37 MeV. Both effects are correlated with an increase of the energy spread from 2.3% to 8.5% rms. The experimental results are compared with simulations
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