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  • American Society of Hematology  (4)
  • American Institute of Physics (AIP)  (3)
  • American Association for the Advancement of Science (AAAS)
  • 2005-2009
  • 1990-1994  (8)
  • 1980-1984
  • 1965-1969
  • 1991  (8)
  • 1
    Electronic Resource
    Electronic Resource
    High-purity ion beam production at high current densities with a liquid-helium-cooled series-field-coil extraction ion diode (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2926-2938 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments are described in which a high-purity, high-power (0.15 TW, 1 MeV) proton beam is generated from an ion source consisting of H2 gas frozen onto a liquid-helium-cooled copper anode at 4.2 K in a series-field-coil extraction diode on the 0.7 TW HydraMITE-II accelerator. Peak anode proton current densities of 2 kA/cm2 were measured. This current density is a factor of 100 higher than those obtained in previous liquid-helium-cooled cryogenic diode experiments on small accelerators and is in the range required for high-power ion beam applications. Thomson parabola, Faraday cup, and carbon activation measurements indicate an ion beam proton fraction close to 100% for the cryogenic source, compared to 50–70% for the standard hydrocarbon anode tested. The cryogenic proton source is believed to consist of no more than a few monolayers of molecular hydrogen. The hydrogen-coated cryogenic anode shows a faster initial anode turn-on than other materials. However, source-limited emission from the thin hydrogen layer results in a somewhat longer current risetime, reduced ion diode efficiency, lower proton current enhancement over the Child–Langmuir limit, and a proton spectrum of lower average energy than for the hydrocarbon anode. Techniques to overcome these limitations are discussed. Cryogenic ion sources consisting of frozen N2, CH4, and Ne have also been studied. In each case, high intensity beams consisting predominantly of components of the refrigerated gas were produced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349317
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Twistor representation of Yang–Mills fields on Minkowski space (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 259-265 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A correspondence between (not necessarily self-dual nor anti-self-dual) Yang–Mills fields on Minkowski space, and pairs of cohomology classes γ, φ, on null twistor space PN(large-closed-square) is established; γ∈H1CR (PN(large-closed-square),@sg) defines a deformed Cauchy–Riemman (C–R)(γ) structure on a principal bundle over PN, and φ∈H1CR(γ) (PN(large-closed-square),O(−4)⊗@sg). The correspondence depends on the choice of a spacelike hyperplane in Minkowski space. Here, γ and φ provide initial values in the spin bundle over this hyperplane for a system of evolution equations, along the null geodesic spray congruence in the spin bundle over Minkowski space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529129
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  • 3
    Electronic Resource
    Electronic Resource
    An experimental study of the molecular mixing process in an axisymmetric laminar vortex ring (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1385-1392 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are presented from an experimental study of the molecular mixing of a dynamically passive conserved scalar quantity in an axisymmetric laminar vortex ring. The experiments are based on highly resolved laser-induced fluorescence imaging measurements of the scalar field ζ(x,t) in the diametral plane of the ring, from which the evolution of the molecular mixing rate field ∇ζ⋅∇ζ(x,t) can be directly examined. In particular, the structure and dynamics of the mixing process are addressed during the three characteristic stages in the ring evolution, namely, (i) the ring generation stage, (ii) the ring pinch-off stage, and (iii) the asymptotic stage of the ring. Results show a layering of the mixing process in which the diffusional cancellation term ∇(∇ζ):∇(∇ζ) plays a major role in setting the overall mixing rate achieved. The scalar field measurements are also used to extract detailed information about the underlying velocity field in the ring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858069
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  • 4
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    Evidence for biased gene conversion in concerted evolution of ribosomal DNA (1991)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1991-01-18
    Description: Concerted evolution is the production and maintenance of homogeneity within repeated families of DNA. Two mechanisms--unequal crossing over and biased gene conversion--have been the principal explanations of concerted evolution. Concerted evolution of ribosomal DNA (rDNA) arrays is thought to be largely the result of unequal crossing over. However, concerted evolution of rDNA in parthenogenetic lizards of hybrid origin is strongly biased toward one of two parental sequences, which is consistent with biased gene conversion as the operative mechanism. The apparent gene conversions are independent of initial genome dosage and result in homogenization of rDNA arrays across all nucleolar organizer regions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hillis, D M -- Moritz, C -- Porter, C A -- Baker, R J -- New York, N.Y. -- Science. 1991 Jan 18;251(4991):308-10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Zoology, University of Texas, Austin 78712.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1987647" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biological Evolution ; Blotting, Southern ; DNA, Ribosomal/*genetics ; Gene Conversion ; Karyotyping ; Lizards ; Nucleic Acid Hybridization ; Parthenogenesis ; Restriction Mapping
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Detection of lymphomatous bone marrow involvement with magnetic resonance imaging [see comments] (1991)
    American Society of Hematology
    Details
    Publication Date: 1991-08-01
    Description: We reviewed magnetic resonance (MR) staging examinations of 98 patients with malignant lymphoma who failed other therapy and were under evaluation for bone marrow transplantation. MR scan results were compared with blind posterior iliac crest aspirations and biopsies. Images of vertebral, pelvic, and femoral marrow were obtained using a standard T1-weighted, short repetition time (TR), short time to echo (TE) (TR700/TE22), spin-echo (T1-SE) method in 92 patients and short TI inversion recovery (STIR) technique (TR1,500/TE36/TI100) in all. On standard T1-SE sequence, normal marrow is bright due to the predominance of marrow fat, and tumor is dark. With STIR images, water containing tumor has a very high signal intensity in a dark (fat suppressed) background. Thirteen patients had positive MR scans and marrow biopsies, whereas 49 had negative MR scans and biopsies. Of 36 discordant MR/histology results, 10 had positive biopsies and negative MR exams; eight of these had microscopic infiltration (less than or equal to 5%) with tumor. MR detected marrow tumor either in the crests or elsewhere in 25 of 75 (33%) patients with negative study biopsies. We could confirm marrow involvement in 15 of these 25 (60%) by clinical methods. Therefore, up to one third of the patients evaluated with routine biopsies may have occult marrow tumor detectable by MR exam. In patients with negative marrow biopsies, especially those with Hodgkin's disease or intermediate to high-grade non-Hodgkin's lymphomas, MR scans found focal lesions distant from the crests. Biopsy better detected lower grade microscopic involvement. We conclude that optimal marrow staging of lymphoma patients incorporates both biopsy and MR imaging.
    Print ISSN: 0006-4971
    Electronic ISSN: 1528-0020
    Topics: Biology , Medicine
    Published by American Society of Hematology
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  • 6
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    Comparison of the subacute toxicity and efficacy of 3-hydroxypyridin-4- one iron chelators in overloaded and nonoverloaded mice (1991)
    American Society of Hematology
    Details
    Publication Date: 1991-11-15
    Description: Five orally effective iron chelators of the 3-hydroxypyridin-4-one series have been administered intraperitoneally to iron-overloaded and nonoverloaded male mice at a dose of 200 mg/kg/24 h for a total of 60 days to investigate the effect on iron loading and toxicity. There was a significant reduction in hepatic iron at the end of the study in the iron-overloaded mice with all compounds studied using chemical iron quantitation (P less than .001) and with Perls' stain (P less than .01). Liver iron removal with the hydroxypyridinones ranged from 37% with CP20 to 63% with CP51, compared with 46% removal for desferrioxamine (DFO). There was no significant reduction in splenic or cardiac iron with any chelator. There were no deaths in iron-overloaded animals receiving any of the hydroxypyridin-4-ones, but significantly more deaths in the nonoverloaded groups as a whole (P less than .03). No weight loss was observed with any chelator. Significant reductions in hemoglobin and white cell count were observed with CP20(L1). No histologic abnormalities of kidney, spleen, bone marrow, or stifle joints were observed. Intracytoplasmic inclusion bodies were observed in the centrilobular hepatocytes of animals administered each of the hydroxypyridin-4-ones, while the DFO-treated and control groups showed no such changes.
    Print ISSN: 0006-4971
    Electronic ISSN: 1528-0020
    Topics: Biology , Medicine
    Published by American Society of Hematology
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  • 7
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    Detection of lymphomatous bone marrow involvement with magnetic resonance imaging [see comments] (1991)
    American Society of Hematology
    Details
    Publication Date: 1991-08-01
    Description: We reviewed magnetic resonance (MR) staging examinations of 98 patients with malignant lymphoma who failed other therapy and were under evaluation for bone marrow transplantation. MR scan results were compared with blind posterior iliac crest aspirations and biopsies. Images of vertebral, pelvic, and femoral marrow were obtained using a standard T1-weighted, short repetition time (TR), short time to echo (TE) (TR700/TE22), spin-echo (T1-SE) method in 92 patients and short TI inversion recovery (STIR) technique (TR1,500/TE36/TI100) in all. On standard T1-SE sequence, normal marrow is bright due to the predominance of marrow fat, and tumor is dark. With STIR images, water containing tumor has a very high signal intensity in a dark (fat suppressed) background. Thirteen patients had positive MR scans and marrow biopsies, whereas 49 had negative MR scans and biopsies. Of 36 discordant MR/histology results, 10 had positive biopsies and negative MR exams; eight of these had microscopic infiltration (less than or equal to 5%) with tumor. MR detected marrow tumor either in the crests or elsewhere in 25 of 75 (33%) patients with negative study biopsies. We could confirm marrow involvement in 15 of these 25 (60%) by clinical methods. Therefore, up to one third of the patients evaluated with routine biopsies may have occult marrow tumor detectable by MR exam. In patients with negative marrow biopsies, especially those with Hodgkin's disease or intermediate to high-grade non-Hodgkin's lymphomas, MR scans found focal lesions distant from the crests. Biopsy better detected lower grade microscopic involvement. We conclude that optimal marrow staging of lymphoma patients incorporates both biopsy and MR imaging.
    Print ISSN: 0006-4971
    Electronic ISSN: 1528-0020
    Topics: Biology , Medicine
    Published by American Society of Hematology
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  • 8
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    Comparison of the subacute toxicity and efficacy of 3-hydroxypyridin-4- one iron chelators in overloaded and nonoverloaded mice (1991)
    American Society of Hematology
    Details
    Publication Date: 1991-11-15
    Description: Five orally effective iron chelators of the 3-hydroxypyridin-4-one series have been administered intraperitoneally to iron-overloaded and nonoverloaded male mice at a dose of 200 mg/kg/24 h for a total of 60 days to investigate the effect on iron loading and toxicity. There was a significant reduction in hepatic iron at the end of the study in the iron-overloaded mice with all compounds studied using chemical iron quantitation (P less than .001) and with Perls' stain (P less than .01). Liver iron removal with the hydroxypyridinones ranged from 37% with CP20 to 63% with CP51, compared with 46% removal for desferrioxamine (DFO). There was no significant reduction in splenic or cardiac iron with any chelator. There were no deaths in iron-overloaded animals receiving any of the hydroxypyridin-4-ones, but significantly more deaths in the nonoverloaded groups as a whole (P less than .03). No weight loss was observed with any chelator. Significant reductions in hemoglobin and white cell count were observed with CP20(L1). No histologic abnormalities of kidney, spleen, bone marrow, or stifle joints were observed. Intracytoplasmic inclusion bodies were observed in the centrilobular hepatocytes of animals administered each of the hydroxypyridin-4-ones, while the DFO-treated and control groups showed no such changes.
    Print ISSN: 0006-4971
    Electronic ISSN: 1528-0020
    Topics: Biology , Medicine
    Published by American Society of Hematology
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