1,096 research outputs found
Project PROMETHEUS: Design and Construction of a Radio Frequency Quadrupole at TAEK
The PROMETHEUS Project is ongoing for the design and development of a 4-vane
radio frequency quadrupole (RFQ) together with its H+ ion source, a low energy
beam transport (LEBT) line and diagnostics section. The main goal of the
project is to achieve the acceleration of the low energy ions up to 1.5 MeV by
an RFQ (352 MHz) shorter than 2 meter. A plasma ion source is being developed
to produce a 20 keV, 1 mA H+ beam. Simulation results for ion source,
transmission and beam dynamics are presented together with analytical studies
performed with newly developed RFQ design code DEMIRCI. Simulation results
shows that a beam transmission 99% could be achieved at 1.7 m downstream
reaching an energy of 1.5 MeV. As the first phase an Aluminum RFQ prototype,
the so-called cold model, will be built for low power RF characterization. In
this contribution the status of the project, design considerations, simulation
results, the various diagnostics techniques and RFQ manufacturing issues are
discussed.Comment: 4 pages, 8 figures, Proceedings of the 2nd International Beam
Instrumentation Conference 2013 (IBIC'13), 16-19 Sep 2013, WEPC02, p. 65
Geometric deep learning
The goal of these course notes is to describe the main mathematical ideas behind geometric deep learning and to provide implementation details for several applications in shape analysis and synthesis, computer vision and computer graphics. The text in the course materials is primarily based on previously published work. With these notes we gather and provide a clear picture of the key concepts and techniques that fall under the umbrella of geometric deep learning, and illustrate the applications they enable. We also aim to provide practical implementation details for the methods presented in these works, as well as suggest further readings and extensions of these ideas
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The interplay between learner beliefs and foreign language anxiety: insights from the Turkish EFL context
Foreign language learning in classroom settings has long been found to be associated with anxiety (Horwitz, 1986). Though it is known that sources of foreign language anxiety are varied (Young, 1991), whether anxiety is related to learnersâ inherent beliefs about language learning is understudied. To this end, the present study examines the possible relationship between learner beliefs and language anxiety in the under-researched Turkish EFL context. A population of university-level Turkish EFL learners (n=153) completed the Beliefs about Language Learning Inventory (BALLI) and the Foreign Language Classroom Anxiety scale (FLCAS). The underlying constructs in both instruments were explored using an Exploratory Factor Analysis (EFA). A series of Pearson Product-Moment Correlation Coefficient (PPMCC) tests were performed on the factor scores from both instruments. The findings revealed that fear of ambiguity was positively linked to classroom performance anxiety and negative feelings towards English. In addition, the more confident learners feel themselves using English, the more desire they seem to have to interact with native speakers. Overall, positive beliefs about language learning may be helpful in reducing anxiety and boosting confidence in language learning. These findings not only enhance our understanding of the complex psychology of language learning but also have important implications for instructed EFL/ESL settings
decays in SUSY models without R-parity
Being strictly forbidden in the standard model, experimental detection of the
lepton flavor violating decays and would constitute an unmistakable indication of new physics. We
study these decays in supersymmetric models without R-parity and without lepton
number. In order to derive order of magnitude predictions for the branching
ratios, we assume a horizontal U(1) symmetry with horizontal charges chosen to
explain the magnitude of fermion masses and quark mixing angles. We find that
the branching ratios for decays with a pair in the final state are
not particularly suppressed with respect to the lepton flavor conserving
channels. In general in these models {\rm B}[b\to\mu^+\mu^-(X)]\lsim {\rm
B}[b(\bar b)\to\tau^+\mu^-(X)] \lsim {\rm B}[b\to\tau^+\tau^-(X)]. While in
some cases the rates for final states can be up to one order of
magnitude larger than the lepton flavor violating channel, due to better
efficiencies for muon detection and to the absence of standard model
contributions, decays into final states appear to be better suited to
reveal this kind of new physics.Comment: 15 pages, LaTeX, 3 ps-figures (uses epsfig.sty) Minor typos
corrected, one normalization factor added to Eq. (3.11). To be published on
Phys. Rev.
Adolescent brain maturation and cortical folding: evidence for reductions in gyrification
Evidence from anatomical and functional imaging studies have highlighted major modifications of cortical circuits during adolescence. These include reductions of gray matter (GM), increases in the myelination of cortico-cortical connections and changes in the architecture of large-scale cortical networks. It is currently unclear, however, how the ongoing developmental processes impact upon the folding of the cerebral cortex and how changes in gyrification relate to maturation of GM/WM-volume, thickness and surface area. In the current study, we acquired high-resolution (3 Tesla) magnetic resonance imaging (MRI) data from 79 healthy subjects (34 males and 45 females) between the ages of 12 and 23 years and performed whole brain analysis of cortical folding patterns with the gyrification index (GI). In addition to GI-values, we obtained estimates of cortical thickness, surface area, GM and white matter (WM) volume which permitted correlations with changes in gyrification. Our data show pronounced and widespread reductions in GI-values during adolescence in several cortical regions which include precentral, temporal and frontal areas. Decreases in gyrification overlap only partially with changes in the thickness, volume and surface of GM and were characterized overall by a linear developmental trajectory. Our data suggest that the observed reductions in GI-values represent an additional, important modification of the cerebral cortex during late brain maturation which may be related to cognitive development
Inclusive Production Cross Sections from 920 GeV Fixed Target Proton-Nucleus Collisions
Inclusive differential cross sections and
for the production of \kzeros, \lambdazero, and
\antilambda particles are measured at HERA in proton-induced reactions on C,
Al, Ti, and W targets. The incident beam energy is 920 GeV, corresponding to
GeV in the proton-nucleon system. The ratios of differential
cross sections \rklpa and \rllpa are measured to be and , respectively, for \xf . No significant dependence upon the
target material is observed. Within errors, the slopes of the transverse
momentum distributions also show no significant
dependence upon the target material. The dependence of the extrapolated total
cross sections on the atomic mass of the target material is
discussed, and the deduced cross sections per nucleon are
compared with results obtained at other energies.Comment: 17 pages, 7 figures, 5 table
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV
The t t-bar production cross section (sigma[t t-bar]) is measured in
proton-proton collisions at sqrt(s) = 7 TeV in data collected by the CMS
experiment, corresponding to an integrated luminosity of 2.3 inverse
femtobarns. The measurement is performed in events with two leptons (electrons
or muons) in the final state, at least two jets identified as jets originating
from b quarks, and the presence of an imbalance in transverse momentum. The
measured value of sigma[t t-bar] for a top-quark mass of 172.5 GeV is 161.9 +/-
2.5 (stat.) +5.1/-5.0 (syst.) +/- 3.6(lumi.) pb, consistent with the prediction
of the standard model.Comment: Replaced with published version. Included journal reference and DO
Search for anomalous t t-bar production in the highly-boosted all-hadronic final state
A search is presented for a massive particle, generically referred to as a
Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are
sufficiently massive to produce highly Lorentz-boosted top quarks, which yield
collimated decay products that are partially or fully merged into single jets.
The analysis uses new methods to analyze jet substructure, providing
suppression of the non-top multijet backgrounds. The analysis is based on a
data sample of proton-proton collisions at a center-of-mass energy of 7 TeV,
corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits
in the range of 1 pb are set on the product of the production cross section and
branching fraction for a topcolor Z' modeled for several widths, as well as for
a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any
enhancement in t t-bar production beyond expectations of the standard model for
t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version
includes a minor typo correction that will be submitted as an erratu
Combined search for the quarks of a sequential fourth generation
Results are presented from a search for a fourth generation of quarks
produced singly or in pairs in a data set corresponding to an integrated
luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in
2011. A novel strategy has been developed for a combined search for quarks of
the up and down type in decay channels with at least one isolated muon or
electron. Limits on the mass of the fourth-generation quarks and the relevant
Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a
simple extension of the standard model with a sequential fourth generation of
fermions. The existence of mass-degenerate fourth-generation quarks with masses
below 685 GeV is excluded at 95% confidence level for minimal off-diagonal
mixing between the third- and the fourth-generation quarks. With a mass
difference of 25 GeV between the quark masses, the obtained limit on the masses
of the fourth-generation quarks shifts by about +/- 20 GeV. These results
significantly reduce the allowed parameter space for a fourth generation of
fermions.Comment: Replaced with published version. Added journal reference and DO
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