Search Menu
DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information
Search Scholarly Publications

6 Search Results

Sorted by Relevance
Save Results
...

  1. Partial wave analysis of the reaction γ p → p ω and the search for nucleon resonances

    Williams, M. ; Applegate, D. ; Bellis, M. ; ... - Physical Review C, Nuclear Physics
    We performed an event-based partial wave analysis (PWA) of the reaction γ p -> p ω on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high precision spin density matrix element measurements, available to the event-based PWA through the decay distribution of omega-> π+ π - π0. The data confirm the dominance of the t-channel π0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F[15](1680) and D[13](1700) near threshold, as wellmore » as the G[17](2190) at higher energies. Suggestive evidence for the presence of a J(P)=5/2+ state around 2 GeV, a "missing" state, has also been found. Evidence for other states is inconclusive.« less

  2. Structural Analysis of the SHMS Cosine Theta Superconducting Dipole Force Collar

    Lassiter, Steven ; Brindza, Paul ; Fowler, Mike ; ... - IEEE Transactions on Applied Superconductivity
    Jefferson Laboratory is developing a set of innovative superconducting magnets for the 12 GeV upgrade in JLAB Hall C. Here, we will report on the finite element analysis (FEA) of the force collar for the Super High Momentum Spectrometer Cosine Theta Dipole magnet. The force collar is designed with an interference fit and intended to provide enough pressure after cool down to operating temperature to counteract Lorentz forces acting on the dipole coil during operation. By counteracting the Lorentz forces and keeping the coil pack in overall compression, movement of the coils is expected to be minimized. The dimensional geometrymore » of the cold mass is maintained in the commercial solid modeling code UG/I-DEAS while the magnetic field design is maintained in the commercial TOSCA code from Vector Fields. The three dimensional FEA was conducted in the commercial codes ANSYS and IDEAS. The method for converting the models and calculating the loads transferred to the structure is discussed. The results show the cold mass response to: force collar assembly preload, differential thermal contraction, and operational Lorentz loads. Evaluations are made for two candidate force collar materials and two candidate force collar designs.« less

  3. Perturbation Techniques for Models of Bursting Electrical Activity in Pancreatic $$\beta $$-Cells

    Pernarowski, M. ; Miura, R. M. ; Kevorkian, J. - SIAM Journal of Applied Mathematics
    Pancreatic β-cells exhibit periodic bursting electrical activity consisting of active and silent phases. Experimentally, the ratio, ρf, of the active phase duration to the overall period is correlated to the insulin response of these cells to glucose concentration. Several different mathematical models of the β-cell have been developed to describe changes in the intracellular ionic concentrations and the ionic flow through the cellular membrane. The membrane potential in each of these models exhibits the same active and silent phase bursting patterns observed experimentally and, therefore, these models can be used to predict the value of the plateau fraction, ρf. Themore » Sherman-Rinzel-Keizer (SRK) model of this phenomenon consists of three coupled first-order nonlinear differential equations which describe the dynamics of the membrane potential, the activation parameter for the voltage-gated potassium channel, and the intracellular calcium concentration. These equations are transformed into a Lienard differential equation coupled to a single first-order differential equation for the slowly changing nondimensional calcium concentration. Leading-order perturbation problems for the silent phase and the transition regions are reduced to quadrature. The solution of the leading-order active phase problem is a limit cycle which depends on the value of the intracellular calcium concentration. Since the active phase equations exhibit weak damping, Melnikov's method can be applied to determine the bifurcation point of these equations. Thus, an explicit expression for the active phase duration is obtained. Together with the silent phase analysis, an approximation of the plateau fraction, ρf, is derived and its value compared to the plateau fraction numerically obtained from the SRK model.« less

  4. Outline for an acceptable nuclear future

    Weinberg, Alvin M. - Energy
    Nuclear energy is likely to develop in two phases. Phase I, based on burner reactors, is self-limiting because the reserve of uranium is limited. Phase II, based on breeders, might last for an extremely long time. It is suggested that opposition to Phase I of nuclear energy might be reduced if an acceptable Phase II can be constructed. Elements of an acceptable Phase II might include isolated and collocated energy centers with resident IAEA inspectors; heavier security; professionalization of the nuclear cadre; immortality of the operating entities; and separation of generation and distribution. Though these measures are aimed primarily atmore » increasing the safety and reliability of the nuclear system, it is suggested that the proposed siting policy, with IAEA resident inspection, might be more proliferation-resistant than is the current dispersed system.« less

  5. Separation Factor

    Weaver, Boyd - Analytical Chemistry
    It is suggested that, in reporting the results of research on fractional separation of a pair of similar elements, more use should he made of the "separation factor" as a criterion for determining the effectiveness of a single stage in a division of a mixture into two fractions. The "separation factor" is the ratio between two elements in one fraction divided by their ratio in the other fraction. It is independent of the original composition and of the extent of the separation process. The literature dealing with separation of the hafniumzirconium pair and the rare earth group has been surveyedmore » as a means of evaluating separation methods. Separation factors have been calculated and compiled from the small amount of useful data. This criterion has been applied usefully in development of a separation process by the author.« less

  6. Proton Bremsstrahlung at 140 Mev

    Wilson, Richard - Physical Review
    The high energy gamma-rays arising from 140-Mev proton bombardment of several elements has been studied using a scintillation counter telescope to detect secondary electrons. The angular distribution is consistent with an approximately isotropic distribution in the center-of-mass system if we assume the bremsstrahlung to come from $p-n$ collisions inside the nucleus. This is in disagreement with a phenomenological potential treatment of the $p-n$ force or the scalar-meson theory. The form of the spectrum is found to be consistent with the $$\frac{dv}{v}$$ shape and the dependence on $$Z$$ much as would be expected from an opaque nucleus with only the neutronmore » contributing to the bremsstrahlung.« less
...
Search for:
All Records
Subject
ELEMENTS
Refine by:
Article Type
Availability
Journal
more less
Creator / Author
more less
Publication Date
Research Organization
more less