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Träfflista för sökning "WFRF:(Jenkins M) srt2:(2000-2004)"

Sökning: WFRF:(Jenkins M) > (2000-2004)

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1.
  • Kelsall, N. S., et al. (författare)
  • Testing mean-field models near the N=Z line : gamma-ray spectroscopy of the T-z=1/2 nucleus Kr-73
  • 2002
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 65:4
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Excited states in the N=Z+1 nucleus Kr-73 have been investigated using the Ca-40(Ar-36,2pn) and Ca-40(Ca-40,alpha2pn) reactions at 145 and 160 MeV, respectively. gamma rays were detected using the Gammasphere array and events were recorded in coincidence with charged-particle and neutron detectors. The three previously observed bands were extended to high spin, and a new unfavored positive-parity band has been observed. The alignment characteristics and decay properties of the bands are all consistent with large-deformation prolate rotation, with no clear evidence for oblate bands or shape coexistence. This is quite different from neighboring Kr-72,Kr-74, indicating a strong shape-stabilizing role for the valence neutron. The experimental results are compared to extended total Routhian surface, cranked Nilsson Strutinsky, and cranked relativistic mean-field calculations. The results suggest that the paired calculations lack some important physics. Neutron-proton correlations may be the missing ingredient. There is also evidence for an unusual band crossing in the negative-parity bands, which may indicate the presence of T=0 pairing correlations. At high spin all the models can reproduce the experimental data.</p>
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2.
  • Fischer, S. M., et al. (författare)
  • Alignment delays in the N = Z nuclei Kr-72, Sr-76, and Zr-80
  • 2001
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 8713:13
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The ground state rotational bands of the N = Z nuclei Kr-72, Sr-76, and Zr-80 have been extended into the angular momentum region where rotation alignment of particles is normally expected. By measuring the moments of inertia of these bands we have observed a consistent increase in the rotational frequency required to start pair breaking, when compared to neighboring nuclei. Kr-72 shows the most marked effect. It has been widely suggested that these delayed alignments arise from np-pairing correlations. However, alignment frequencies are very sensitive to shape degrees of freedom and normal pairing, so the new experimental observations are still open to interpretation.</p>
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3.
  • McDonald, C., et al. (författare)
  • ELMy H-modes in JET helium-4 plasmas
  • 2004
  • Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 46:3, s. 519-534
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>ELMy H-modes in helium-4 plasmas provide valuable information on ELMy H-mode physics as well as a possible early low activation operational phase for next-step tokamaks, such as ITER. With this in mind, a series of helium-4 H-mode experiments were performed on JET with pure helium-4 NBI auxiliary heating (up to 12 MW). A set of ELMy H-mode plasmas were produced, in both the Type I ELM regime and a second regime, which showed characteristics similar to the deuterium Type III regime, but with a reverse ELM frequency dependence on power. Sawteeth were also observed, and had similar behaviour to those seen in deuterium. Compared with deuterium plasmas, Type I ELMy H-mode confinement is seen to be 28 +/- 6% poorer in helium-4 plasmas and the L-H power threshold 42 +/- 10% larger. This is the opposite of the behaviour predicted by experimental isotope mass scalings from hydrogenic plasmas.Comparison with a wider hydrogenic database, enables the effects of isotopic charge and mass to be studied independently.</p>
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4.
  • Bäck, Torbjörn, et al. (författare)
  • First observation of gamma-rays from the proton emitter Au-171
  • 2003
  • Ingår i: European Physical Journal A. - 1434-6001 .- 1434-601X. ; 16:4, s. 489-494
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Gamma-rays from the alpha- and proton-unstable nuclide Au-171 have been observed for the first time. The gamma-rays were correlated with both a proton- and an alpha-particle decay branch, confirming that the nucleus decays by alpha and proton emission from a single (11/2(-)) state. The measurement confirms the previously determined half-lives for these particle decays but the present values are of higher precision. In addition, a longer half-life than determined in previous work was measured for the proton-unstable tentative ground state. The results are discussed in relation to structures in neighbouring nuclei and compared with a Strutinsky-type TRS calculation.</p>
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5.
  • Bäck, Torbjörn, et al. (författare)
  • Spectroscopy of the neutron-deficient nuclide Pt-171
  • 2003
  • Ingår i: European Physical Journal A. - 1434-6001 .- 1434-601X. ; 17:1, s. 1-5
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>A number of previously unobserved gamma-rays emitted from the neutron-deficient nuclide Pt-171 have been identified using the recoil decay tagging technique. The level scheme has been updated using information from gamma-gamma coincidences and angular distribution measurements. To further confirm the assignments of the gamma-rays to Pt-171, the events were correlated with the alpha-decay of the daughter nucleus Os-167.</p>
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6.
  • Diehl, S., et al. (författare)
  • Effects of multiple, predator-induced behaviors on short-term producer-grazer dynamics in open systems
  • 2000
  • Ingår i: American Naturalist. - 0003-0147 ; 156:3, s. 293-313
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We investigated the population consequences of multiple behavioral responses of grazers to a foraging return-predation risk trade-off in an open system consisting of primary producers, grazers, and predators. Using a dynamical model where grazers adjust their foraging activity and emigration rate to the densities of predators and producers, we explored how changes in control variables (predator density, grazer immigration, and producer immigration and carrying capacity) affect the dynamics of producers and grazers at temporal scales shorter than consumer and predator reproduction. The model predicts that producer biomass increases and that both the density of foraging grazers and the feeding rate of predators decrease with predator density. These predictions hold although total (foraging + nonforaging) grazer density may actually increase with predator density. The latter will occur whenever the benefit of higher resource density outweighs the increased risk of predation. In this case. per capita grazer emigration decreases with predator density, which might be misinterpreted as a direct "freezing" response to predators. Increased grazer immigration is predicted to result in decreased producer density and increased densities of both foraging and total grazers, as well as increased grazer emigration and predator feeding rates. Increased producer immigration or carrying capacity should increase producer and grazer densities and predator feeding rate but decrease per capita grazer emigration. Manipulation of predator (trout) densities in a set of nine large (50 m(2)) stream channels produced results in broad agreement with model predictions. Most notably, a positive effect of trout on benthic algal biomass was mainly mediated through grazer behavior (changes in the use of epibenthic surfaces and in emigration rare) rather than through consumptive reductions of grazer numbers by trout.</p>
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7.
  • Jenkins, S. R., et al. (författare)
  • Spatial and temporal variation in settlement and recruitment of the intertidal barnacle Semibalanus balanoides (L.) (Crustacea : Cirripedia) over a European scale
  • 2000
  • Ingår i: Journal of Experimental Marine Biology and Ecology. - 0022-0981. ; 243:2, s. 209-225
  • Tidskriftsartikel (refereegranskat)abstract
    • Variation in the level of settlement and recruitment in the intertidal barnacle Semibalanus balanoides was studied using a hierarchical sampling programme. The effect of three spatial scales, 10s of metres (sites), 1000s of metres (shores) and 100s of kilometres (locations), was determined. The largest spatial scale represented the distance between four widely separated locations, Sweden, the Isle of Man, SW Ireland and SW England, covering a. large part of the range of S. balanoides in Europe. Temporal variation was determined by comparison between two years, 1997 and 1998. The settlement period of S. balanoides varied in length and timing, being earlier and shorter at the most northerly location, Sweden. The duration of settlement showed little difference among shores within locations, but the pattern of settlement did vary. Estimates of total settlement throughout the settlement period and of recruitment at the end of this period both showed substantial variation among locations which was dependent on the year of study. There was little consistency in the ranking of locations between the two years. Recruitment showed significant variation I the lower spatial scales of shore and site. In addition, examination of variance components showed a high degree of variation between replicates within sites in 1997. There was a significant relationship between settlement and recruitment at three of the four locations. Across all locations variation in settlement explained between 29 and 99% of variation in recruitment. However, locations showed distinct differences in the level of post-settlement survival. (C) 2000 Elsevier Science B.V. All rights reserved.
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