107 research outputs found
The Composition of Cosmic Rays at the Knee
The observation of a small change in spectral slope, or 'knee' in the fluxes
of cosmic rays near energies 10^15 eV has caused much speculation since its
discovery over 40 years ago. The origin of this feature remains unknown. A
small workshop to review some modern experimental measurements of this region
was held at the Adler Planetarium in Chicago, USA in June 2000. This paper
summarizes the results presented at this workshop and the discussion of their
interpretation in the context of hadronic models of atmospheric airshowers.Comment: 36 pages, 10 figure
Heterogeneity of genomic evolution and mutational profiles in multiple myeloma
Multiple myeloma is an incurable plasma cell malignancy with a complex and incompletely understood molecular pathogenesis. Here we use whole-exome sequencing, copy-number profiling and cytogenetics to analyse 84 myeloma samples. Most cases have a complex subclonal structure and show clusters of subclonal variants, including subclonal driver mutations. Serial sampling reveals diverse patterns of clonal evolution, including linear evolution, differential clonal response and branching evolution. Diverse processes contribute to the mutational repertoire, including kataegis and somatic hypermutation, and their relative contribution changes over time. We find heterogeneity of mutational spectrum across samples, with few recurrent genes. We identify new candidate genes, including truncations of SP140, LTB, ROBO1 and clustered missense mutations in EGR1. The myeloma genome is heterogeneous across the cohort, and exhibits diversity in clonal admixture and in dynamics of evolution, which may impact prognostic stratification, therapeutic approaches and assessment of disease response to treatment
Coherent π0 photoproduction on the deuteron up to 4 GeV
The differential cross section for 2H(γ,d)π0 has been measured at deuteron center-of-mass angles of 90° and 136°. This work reports the first data for this reaction above a photon energy of 1 GeV, and permits a test of the apparent constituent counting rule and reduced nuclear amplitude behavior as observed in elastic ed scattering. Measurements were performed up to a photon energy of 4.0 GeV, and are in good agreement with previous lower energy measurements. Overall, the data are inconsistent with both constituent-counting rule and reduced nuclear amplitude predictions
Quasielastic (e,e′p) reaction on 12C,56Fe, and 197Au
We report the results from a systematic study of the quasielastic (e,e′p) reaction on 12C, 56Fe, and 197Au performed at Jefferson Lab. We have measured nuclear transparency and extracted spectral functions (corrected for radiation) over a Q2 range of 0.64–3.25 (GeV∕c)2 for all three nuclei. In addition, we have extracted separated longitudinal and transverse spectral functions at Q2 of 0.64 and 1.8 (GeV∕c)2 for these three nuclei (except for 197Au at the higher Q2). The spectral functions are compared to a number of theoretical calculations. The measured spectral functions differ in detail but not in overall shape from most of the theoretical models. In all three targets the measured spectral functions show considerable excess transverse strength at Q2=0.64 (GeV∕c)2, which is much reduced at 1.8 (GeV∕c)2
Separation of the Longitudinal and Transverse Cross Sections in the p(e, e′K+)Λ and p(e, e′K+)Σ0 Reactions
We report measurements of cross sections for the reaction p(e,e′K+)Y, for both the Λ and Σ0 hyperon states, at an invariant mass of W =1.84 GeV and four-momentum transfers 0.5 < Q2 < 2 (GeV/c)2. Data were taken for three values of virtual photon polarization ε, allowing the decom- position of the cross sections into longitudinal and transverse components. The Λ data is a revised analysis of prior work, whereas the Σ0 results have not been previously reported
Separated spectral functions for the quasifree 12C(e,e′p) reaction
A separation of the longitudinal and transverse 12C(e,e′p) cross sections in the quasifree region has been performed in parallel kinematics at Q2 of 0.64 and 1.8 GeV2 for initial proton momentum <80 MeV. The separated transverse and longitudinal spectral functions at Q2=0.64GeV2 show significant differences for missing energy between 25 and 60 MeV indicating a breakdown in the single nucleon knockout picture. The transverse spectral functions exhibit definite momentum transfer dependence
Measurements of Deuteron Photodisintegration up to 4.0 GeV
The first measurements of the differential cross section for the d(γ,p)n reaction up to 4.0 GeV were performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson Laboratory. We report the cross sections at the proton center-of-mass angles of 36°, 52°, 69°, and 89°. These results are in reasonable agreement with previous measurements at lower energy. The 89° and 69° data show constituent-counting-rule behavior up to 4.0 GeV photon energy. The 52° and 36° data disagree with the counting-rule behavior. The quantum chromodynamics (QCD) model of nuclear reactions involving reduced amplitudes disagrees with the present data.U.S. Department of Energy, National Science Foundatio
Fatigue of Plates and Weldments in HY-100 and HY-130/150 Steels
An evaluation of the axial fatigue behavior of plain plates and full
penetration weldments in HY-lOO steel is presented. Transverse butt-welded specimens
welded with the MIL-11018 electrodes were found to contain minute internal
weld flaws which often serve as critical locations for fatigue crack initiation.
The weld flaws, although not detected by usual radiographic inspection, were
successfully located with the use of ul trasonic detection equipment. The ultrasonic
equipment was used also to study the initiation and propagation of fatigue
cracks in several test weldments, A preliminary investigation of the axial fatigue
behavior of HY-l30/l50 steel plain plates is reported.Bureau of Ships, U.S. Navy.Contract NObs 92226Project Series No. SR-007-01-01, Task 88
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