The ranges of great camas (Camassia leichtlinii) and small camas (C. quamash) overlap extensively in the western United States. Previous systematic treatments of the genus are inconclusive, as a ...recent flora classifies C. leichtlinii as a subspecies of C. quamash. We investigated species boundaries and putative hybrid zones at multiple sites in the Willamette Valley of Oregon and in allopatric populations ranging as far north as British Columbia. Genotypic inferences from allozyme electrophoresis of 218 individuals yielded 12 resolvable loci across three buffer systems. Lower mean Nei's genetic identity (I) in interspecific pairwise comparisons (0.76) than in intraspecific comparisons (0.91 for C. quamash and 0.89 for C. leichtlinii) indicates that these taxa are readily distinguishable using allozymes. Furthermore, four alleles uniquely characterize either C. leichtlinii or C. quamash and five additional alleles are common in one species but rare in the other. In different, sympatric populations, C. quamash and C. leichtlinii also varied in interspecific genetic identity (Nei's I = 0.66-0.87), and in the additivity of allozyme patterns for plants identified as putative hybrids based on morphology. Principal Component Analysis (PCA), hybrid indices, and the relatively large interspecific Nei's I suggest that hybrid formation and introgression are discontinuous, occurring extensively only at one site. For all populations, allozyme data support species-level distinction of C. quamash and C. leichtlinii.
R&D of Nb/sub 3/Sn accelerator magnets at Fermilab Zlobin, A.V.; Ambrosio, G.; Andreev, N. ...
IEEE transactions on applied superconductivity,
2005-June, 20050601, Letnik:
15, Številka:
2
Journal Article
Recenzirano
Fermilab is developing and investigating different high-field magnets (HFM) for present and future accelerators. The HFM R&D program focused on the 10-12 T magnets based on Nb/sub 3/Sn superconductor ...and explored both basic magnet technologies for brittle superconductors-wind-and-react and react-and-wind. Magnet design studies in support of LHC upgrades and VLHC were conducted. A series of 1-m long cos-theta dipole models based on the wind-and-react technique was fabricated and tested. Three 1-m long flat racetracks and the common coil dipole model, based on a single-layer coil and react-and-wind technique, were also fabricated and tested. Extensive theoretical and experimental studies of electro-magnetic instabilities in Nb/sub 3/Sn strands, cables and magnets were performed and led to a successful 10 T dipole model. This paper presents the details of Fermilab's HFM program, reports its status and major results, and formulates the next steps for the program.
Current lithium-oxygen (Li-O2) batteries suffer from large charge overpotentials related to electronic resistivity of the insulating lithium peroxide (Li2O2) discharge product. One potential solution ...to this challenge is the stabilization of the lithium superoxide (LiO2) discharge intermediate, which has much higher electronic conductivity compared to Li2O2. Cathodes based on small iridium (Ir) nanoparticles have been recently used in a Li-O2 battery to successfully stabilize the LiO2 product, however, the LiO2 had a short lifetime. In the previous study, researchers found that the LiO2 was stabilized on Ir3Li surfaces which were formed from Ir nanoparticles during battery operation. Little is known about the electronic properties of Ir3Li and its role in stabilizing LiO2 product formation. This work provides the first study of the electronic properties of Ir3Li, which was thermally synthesized in bulk prior to implementation on the reduced graphene oxide (rGO) cathode of a Li-O2 cell. The bulk Ir3Li was found to have comparable electrical conductivity to Ir metal, possess metal-like magnetic properties, and has an affinity towards O2 adsorption. The LiO2 discharge product formed from the Li-O2 battery discharge was characterized using Raman spectroscopy, titration, along with a comprehensive transmission electron microscopy (TEM) study. This analysis revealed the formation of ultra-nanocrystalline LiO2 particles greater than 200 nm. This result was attributed to the use of large micron sized Ir3Li particles, which could stabilize larger LiO2 particles compared to previous cathodes that utilized Ir nanoparticles that partially converted to Ir3Li during cycling. These results demonstrate that cathode properties can be modified to stabilize the bulk LiO2 discharge product, which can be useful for the further development of LiO2-based Li-O2 batteries.
Display omitted
•Bulk synthesis and characterization of Ir3Li as Li-O2 battery cathode material.•Reduced Li-O2 battery charge overpotentials using Ir3Li-rGO cathodes.•Formation of stable, > 200 nm particles of lithium superoxide as discharge product.
Design and performance tests of the CDF time-of-flight system Paus, Ch; Grozis, C.; Kephart, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2001, Letnik:
461, Številka:
1
Journal Article
Recenzirano
The CDF
II detector contains a time-of-flight detector consisting of 216 scintillator bars of 279
cm length and 4×4
cm
2 cross-section located at a radius of 138
cm from the beam axis. The bars are ...installed on the inner surface of the CDF solenoid, which produces an axial field of 1.4
T. Nineteen-stage fine-mesh photomultiplier tubes are attached at both ends of the scintillator bars. Photostatistics limit the time-of-flight resolution, which is expected to be 100
ps. The primary physics motivation is K
± identification for improved neutral B meson flavor determination.
This study investigates the extent of pollinator sharing and specialization of three co—occurring species of milkweed (Asclepias) in experimental plantings. The potential for competition among plants ...for pollinators was also assessed from observed levels of pollinator constancy, interspecific pollination, and seed set in experimental populations. All three species (A. incarnata, A. syriaca, and A. verticillata) were visited by a wide variety of Hymenoptera and Lepidoptera. Niche breadth estimates for populations of A. syriaca were comparatively low (.09—.27); Bombus griseocollis and the introduced honeybee, Apis mellifera, were clearly the most common visitors to this species. Niche breadths were greater, implying less specialization, for A. incarnata (x = .30) and A. verticillata (x = .39). Paper wasps (Polistes) and digger wasps (Sphex) were numerous and effective pollinators of A. verticillata, but bumblebees comprised the largest proportion (27%) of the pollinators at some sites. Similarly, utilization of pollinators A. incarnata was highly dependent on the locality of the population studied, with Sphex pennsylvanicus, Apis mellifera, Bombus griseocollis, and Xylocopa virginica constituting the most abundant pollinators. Intraspecific comparisons of the similarity of pollinators among populations of A. syriaca gave values that were higher than corresponding values for different species within a locality, implying possible niche differentiation with respect to this species. However, a hypothesis of pollinator partitioning among species was not accepted for A. incarnata and A. verticillata because estimates of niche overlap between these species were as great as those involving populations of either species alone. Both the timing and amount of flowering, as well as the degree of interplanting of A. verticillata and A. incarnata, affected the abundance and constancy of pollinators on these species in experimental plots. Interspecific flights or pollinators and interspecific insertion of pollinia for A. incarnata were much higher in 1978 when flowering of A. verticillata was earlier and more extensive. During that same year, interspecific pollination of A. verticillata was lower. In addition, the abundance of Bombus griseocollis on this species declined rapidly as A. incarnata came into flower, even though peak flowering of A. verticillata had not been reached. Mixed plantings of these species gave higher levels of interspecific pollination and lower seed set than unispecific plantings at the same density. The lack of specialization in pollination of A. incarnata and A. verticillata is not surprising since these species typically occupy different habitats and have nectar that is readily accessible. However, the current proliferation of disturbed environments where species occur in close proximity provides the potential for exploitative competition between them when pollinators are a scarce or limiting resource. The presence of pollen from other species may also interfere with intraspecific pollination, reducing seed set. The fitness reduction may be small, however, in view of the perennial habit and abundant seed produced by plants of these species.
This paper reports on a test time-of-flight (TOF) system that operated in the Collider Detector at Fermilab (CDF) during
p
p
̄
Tevatron collider operation at
s
=1.8
TeV in the fall 1995 running ...period. The TOF system consisted of 20
130×4×4
cm
3
long Bicron BC408 scintillator bars, with each end of the bars fitted with a small compound parabolic concentrator and a 16-stage R5946 Hamamatsu fine-mesh photomultiplier. The electronics chain consisted of a custom designed preamplifier, constant fraction discriminator, and commercial TDC and ADC FASTBUS modules read out with the CDF data acquisition system. The counters were installed between the Central Tracking Chamber and the 1.4 T superconducting solenoid at a mean radius of 140 cm. We report a procedure for calculating the
t
0 time from all tracks in an event, the timing resolution, and the particle identification performance of this system.
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