Starter Radio &amp; Video Project

Flannery, Michael

doi:10.1049/ee.1994.0084

Cited by 9 publications

(2 citation statements)

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“…As a physical process of great importance in astrophysical and laboratory sources, electron-ion recombination has been studied extensively [1][2][3]. Together with primary atomic processes such as photoionization and electron impact excitation and ionization, electron-ion recombination rates are needed to compute theoretical models for plasma diagnostics.…”

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confidence: 99%

Photorecombination Spectra of Highly Charged Ions

Zhang

Pradhan

1997

Phys. Rev. Lett.

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A general method for the theoretical calculation of relativistic photorecombination cross sections is employed to obtain detailed theoretical spectra for highly charged ions for the first time in an ab initio manner. The calculations are carried out using the relativistic Breit-Pauli R-matrix method. The theoretical cross sections incorporate total electron-ion recombination and correspond directly to that observed experimentally. In particular, the detailed resonance structures are found to be in good agreement with the experiment results for Fe XXV obtained from the electron-beam ion trap (EBIT) at Livermore, and with the absolute values for Ar XIV measured using the heavy-ion storage ring (CRYRING) at Stockholm. [S0031-9007(96)02066-2]

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confidence: 99%

Photorecombination Spectra of Highly Charged Ions

Zhang

Pradhan

1997

Phys. Rev. Lett.

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“…It is usually assumed [15,16] that the size of the total cross section can be predicted independent of the distribution of flux at the avoided crossings, the cross section being mainly determined by the overlap between the initial vibrational wave function and the vibrational continuum of the dissociative state, as well as by its autoionization probability. In particular, H 2 1 and HD 1 are textbook examples for DR since the reaction proceeds in the "crossing mode" [16] via only one doubly excited potential curve that connects to all final states accessible at moderate electron energies; thus a smooth variation of the DR cross section without any changes related to the opening of new dissociation channels is expected within this description. First experimental evidence is presented in this Letter that the opening of new channels does significantly influence the total recombination rate.…”

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Threshold Effects and Ion-Pair Production in the Dissociative Recombination ofHD+

et al. 1999

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Sharp thresholds are observed in the dissociative recombination cross section of vibrationally cold HD 1 in the energy range where new channels H͑1s͒ 1 D͑n͒ [or D͑1s͒ 1 H͑n͒] with n . 2 open. The occurrence of these thresholds, not predicted by current theoretical calculations, contradicts the current assumption that the size of the total cross section can be calculated without accounting for the detailed branching ratios. An indirect signature of ion pair production is also found in the data, suggesting a significant branching into that channel.

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The origins of agriculture in the Americas

Smith

1994

Evolutionary Anthropology

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Three independent centers of domestication and agricultural origin have been identified in the Americas: the south‐central Andes, Mexico, and most recently, eastern North America. Much of the evidence for early domesticates in these three regions has been excavated from higher elevation dry caves and rock shelters. These sites contain remarkably well preserved plant and animal remains, along with a record of short‐term occupation by small groups of hunter‐gatherers and early cultivators. As a result it has long been thought that plants and animals were brought under domestication in the Americas by small, seasonally mobile societies living in upland settings. The age of small seeds and other plant materials recovered from such dry caves and believed to represent early domesticates was, of necessity, determined indirectly, through conventional large‐sample radiocarbon dating of organic material thought to be contemporaneous. In each of the three regions, the earliest domesticates were believed to date between 7,000 and 10,000 B.P. The origin of agriculture in the Americas was thought to be roughly contemporary with the transition from foraging to farming in the Near East (Fertile Crescent, ca. 10,000 B.P.) and China (Yangtze Corridor, ca. 8,500 B.P.). Since the mid‐1980s, however, the age of many of the proposed early domesticates in the Americas, as well as their contexts of domestication, have been re‐examined, beginning in eastern North America. The excavation of larger and more sedentary river valley settlements in eastern North America has yielded ample evidence of the cultivation of domesticated seed plants. This evidence is as old as or older than that recovered from seasonally occupied upland caves and rock shelters. In addition, a new and more rigorous standard for evidence of domestication has been adopted in eastern North America. That standard, which requires direct dating of seeds and other plant parts that exhibit clear, unequivocal, and well‐documented morphological markers of domestication, is now being applied throughout the Americas, producing conservative timetables of domestication and agricultural origins that contradict alternative, more speculative chronological frameworks. Under the new standard of evidence, domestication of plants in all three independent centers (and in the Andes, domestication of animals) appears to have taken place between about 5,500 and 4,000 years ago, much more recently than previously was thought. Several lines of evidence also suggest that the Native American societies that first brought these species under domestication may not have been exclusively seasonally mobile hunter‐gatherers of higher‐elevation environments. In each of the three regions, domesticates recovered from upland caves may reflect a transition to a farming way of life accomplished by societies occupying more sedentary settlements in river valleys. In some cases, upland caves containing domesticates may represent one component in the seasonal round of early food production by societies o...

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Starter Radio & Video Project

Cited by 9 publications

References 0 publications

Photorecombination Spectra of Highly Charged Ions

Photorecombination Spectra of Highly Charged Ions

Threshold Effects and Ion-Pair Production in the Dissociative Recombination ofHD+

The origins of agriculture in the Americas

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