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1

P-odd, P-even, and T-odd asymmetries in true quaternary fission of nuclei  

SciTech Connect

The coefficients of P-odd, P-even, and T -odd asymmetries for a third and a fourth prescission particle emitted in the true quaternary fission of nuclei that was induced by polarized cold neutrons were studied on the basis of quantum-mechanical fission theory. By using non-evaporation (nonadiabatic) mechanisms of light-particle emission, these coefficients were compared with the analogous coefficients for prescission third particles emitted in the ternary fission of nuclei.

Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru; Titova, L. V. [Voronezh State University (Russian Federation)] [Voronezh State University (Russian Federation)

2013-04-15

2

Probabilities for the emission of light particles and their energy and angular distributions for true quaternary nuclear fission  

SciTech Connect

On the basis of quantum-mechanical fission theory, the features of true quaternary nuclear fission are studied by treating this fission process as a sequence of three processes following one another in the course of time. The first two processes are the escape of the first and then the second of the two light particles emitted from the neck of a fissioning nucleus because of a nonadiabatic character of the collective deformation motion of this nucleus. Finally, the third process is the separation of the fissioning nucleus into two rather heavy fission fragments. The differences that arise in the emission probabilities and in the angular and energy distributions upon going over from the first emitted to the second emitted prescission third and fourth particles are analyzed by invoking experimental data on the spontaneous and thermalneutron-induced fission of nuclei, and it is shown that these differences are caused by the changes both in the geometric configuration of the fissioning nucleus and in the shell structure of its neck after the first prescission particle is emitted from it.

Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru; Titova, L. V. [Voronezh State University (Russian Federation)] [Voronezh State University (Russian Federation)

2013-01-15

3

New experimental studies on the quaternary fission of 233, 235U(nth, f ) and 252Cf (sf )  

NASA Astrophysics Data System (ADS)

Experiments have been performed for studying quaternary fission (QF) in spontaneous fission of 252Cf, on the one hand, and for the neutron-induced fission reactions 233, 235U(nth, f ), on the other hand. In this higher-multiplicity fission mode, by definition, four charged products appear in the final state. In other words, as a generalization of the ternary-fission process, not only one but two light charged particles (LCPs) are accompanying the splitting of an actinide nucleus into the customary pair of fission fragments. In the two sets of measurements, which have used quite different approaches, the yields of several QF reactions with ?-particles and tritons as the LCPs have been determined and the corresponding kinetic-energy distributions of the ?-particles measured. The QF process can appear in two basically different ways: i) the simultaneous creation of two LCPs in the act of fission (“true” QF) and ii) via a fast sequential decay of a single but particle-unstable LCP in common ternary fission (“pseudo” QF). Experimentally the two varieties of QF have been distinguished by exploiting the different patterns of angular correlations between the two outgoing LCPs. The experiments described in the present paper are the first to demonstrate that both types of reactions, true and pseudo QF, occur with quite comparable probabilities. As a new result also, the kinetic-energy distributions related to the two processes have been shown to be significantly different. For all QF reactions which could be explored, the yields for 252Cf(sf) were found to be roughly by an order of magnitude larger than the yields found in the 233U(nth, f ) and 235U(nth, f ) reactions. An interesting by-product has been the measurement of yields of excited LCPs which allows to deduce nuclear temperatures at scission by comparison to the respective yields in the ground state.

Jesinger, P.; Kopatch, Yu. N.; Mutterer, M.; Gönnenwein, F.; Gagarski, A. M.; v. Kalben, J.; Nesvizhevsky, V.; Petrov, G. A.; Trzaska, W. H.; Wollersheim, H.-J.

2005-06-01

4

The occurrence and fission-track ages of late neogene and quaternary volcanic sediments, Siwalik group, Northern Pakistan  

USGS Publications Warehouse

Volcanic sediments, now mostly bentonites and bentonitic mudstones, occur throughout the Late Neogene and Quaternary Siwalik Group of northern Pakistan. A number of these deposits have been dated by the fission-track method, utilizing zircon phenocrysts from these deposits, and provide the chronometric constraints upon which a paleomagnetic stratigraphy is developed for the Siwalik Group. Notable in the occurrence of these altered tuff horizons is an apparent mode in their stratigraphic development from approximately 3.0 to 1.5 m.y. B.P. which coincides with the period of activity of the Dacht-e-Nawar volcanic complex of east-central Afghanistan. Fission-track ages of certain tuffs for critical areas of northern Pakistan are reported herein. ?? 1982.

Johnson, G.D.; Zeitler, P.; Naeser, C.W.; Johnson, N.M.; Summers, D.M.; Frost, C.D.; Opdyke, N.D.; Tahirkheli, R.A.K.

1982-01-01

5

Nuclear Fission  

Microsoft Academic Search

The probability of nuclear fission is reviewed relative to spontaneous ; fission half lives, penetration of the fission barrier, fission with siow ; neutrons, fission at inoderate and high excitation energies. fission cross ; sections near the threshold, and the fission of elements lighter than thorium. ; The energy available for fission and the kinetic and excitation energies of ;

I. Halpern

1959-01-01

6

Quaternary Research Center  

NSDL National Science Digital Library

"The Quaternary Research Center (QRC) fosters interdisciplinary research on the last two million years of the global environment: a time which encompasses massive, abrupt changes of climate, sea level, global biota and ice extent, as well the evolution of humans and the advent of civilization." Divided into six laboratories, the University of Washington's Center studies Cosmogenic Isotopes, Stable Isotopes, Old Quaternary Isotopes, Periglacial environments, quaternary ecology, paleoecology, and remote sensing. Researchers can find a tremendous amount of isotope, carbon dioxide, and chemistry data on the Taylor Dome, a part of the East Antarctic ice sheet. Students and educators can read papers by the center covering topics such as interactions among climate, surface, and tectonics; and glaciations and climate variations in the Pacific Northwest.

7

Quaternary Faunal Environments  

NSDL National Science Digital Library

Students collect information the environments associated with a list of presently living mammals. Students use FAUNMAP to explore the spatial patterns associated with these living mammals during the late Quaternary. They compare these distributions for living mammals to the distribution patterns for a set of extinct mammals. Students answer a set of questions that provide a basis for a summary report.

Hill, Christopher

8

Nuclear Fission  

Microsoft Academic Search

Nuclear fission is a process in which a heavy nucleus splits into two much lighter nuclei. For some very unstable nuclei fission\\u000a can happen spontaneously, but that is a very rare event. Usually, the process is induced by the excitation of the nuclei by\\u000a bombarding them with particles or with gamma rays. Heavy nuclei have a greater neutron\\/proton ratio than

Hanne Andersen

9

Quaternary Research Association Educational Resources  

NSDL National Science Digital Library

The Quaternary Research Association (QRA) is an organization comprising archaeologists, botanists, civil engineers, geographers, geologists, soil scientists, zoologists and others interested in research into the problems of the Quaternary. This site describes their activities and organization. This direct link to the educational teaching resources provides access to glacier and glaciation resources.

10

Nuclear Fission  

Microsoft Academic Search

The potential role of nuclear fission to meet increased future energy demand while reducing greenhouse gas emissions and controlling nuclear proliferation is assessed. The World Energy Council projection for an environmentally driven future is used, which projects deployment of nearly 3 TW(e) of nuclear generation by 2100, with concurrent reduction of global CO2 emissions to one-third of present levels. We

ERICH SCHNEIDER; WILLIAM C. SAILOR

2006-01-01

11

Quaternary GIS Laboratory  

NSDL National Science Digital Library

This is the home page of the Quaternary Geographic Information System (GIS) Laboratory at the Institute of Arctic and Alpine Research (INSTAAR) at the University of Colorado. The laboratory supports quantitative spatial analysis of glacier, climate, coastal, and other environmental relationships at high latitudes. Users can access a collection of climate animations for the State of Alaska which show seasonal variation in monthly temperature and precipitation. There is also a set of high-resolution imagery and terrain models for Barrow, Alaska, an animation of the land bridge between Asia and North America, an atlas of paleoglaciation for the state, and links to a variety of other projects involving climatology, paleoclimatology, and glacial geomorphology in the Sate of Alaska.

2007-02-27

12

Synthesis of Quaternary Heterocyclic Salts  

PubMed Central

The microwave synthesis of twenty quaternary ammonium salts is described. The syntheses feature comparable yields to conventional synthetic methods reported in the current literature with reduced reaction times and the absence of solvent or minimal solvent. PMID:24256924

Winstead, Angela J.; Nyambura, Grace; Matthews, Rachael; Toney, Deveine; Oyaghire, Stanley

2014-01-01

13

Isomers in Fission Fragments  

Microsoft Academic Search

The structure of neutron-rich nuclei produced as secondary fission fragments was investigated using the EUROGAM and GAMMASPHERE ACS arrays, the LOHENGRIN fission-fragment mass separator and the FIFI fission-fragment identifier. Fission products were populated in spontaneous fission of 248Cm and 252Cf and in thermal neutron-induced fission of 233U, 235U and 241Pu at ILL Grenoble. Particularly useful in such studies are isomeric

W. Urban; H. Faust; M. Jentschel; U. Koester; J. Krempel; Th. Materna; P. Mutti; T. Soldner; J. Genevey; J. A. Pinston; G. Simpson; T. RzaCa-Urban; A. Zlomaniec; M. Lukasiewicz; K. Sieja; F. Nowacki; O. Dorvaux; B. J. P. Gall; B. Roux; J. A. Dare; J. L. Durell; A. G. Smith; B. J. Varley; I. Tsekhanovich; J. Jolie; A. Linnemann; A. Scherillo; R. Orlandi; J. F. Smith; I. Ahmad

2009-01-01

14

Fission in Stellar Plasma  

Microsoft Academic Search

The fission of heavy nuclides is examined in a dense stellar plasma. The correction in the Coulomb energy due to the interaction between the ion and the induced-electron charge density affects the process of fission and reduces the fission barrier depending upon the physical situation. Shell- and surface-symmetry effects are included in the calculation of the fission barrier as a

K. Duorah; H. L. Duorah

1973-01-01

15

The Quaternary History of Scandinavia  

NASA Astrophysics Data System (ADS)

During the Quaternary Period, Scandinavia's mountains were the source for repeated glaciation that covered much of eastern, central and western Europe. With a particular emphasis on Denmark, Norway, Sweden and Finland, this text describes how these glaciations, and their intervening warmer stages, affected Scandinavia and the surrounding areas. In particular, this account focuses on the last cold stage, the Weichselian, with its extensive Late Weichselian glaciation and the subsequent deglaciation, and on the last 10,000 years, the Holocene, with its well documented environmental changes. The Quaternary History of Scandinavia provides a cross-frontier synthesis of how the glaciation affected this vast region.

Donner, Joakim

2005-08-01

16

Quaternary alkaloids of Argemone mexicana.  

PubMed

Four quaternary isoquinoline alkaloids, dehydrocorydalmine, jatrorrhizine, columbamine, and oxyberberine, have been isolated from the whole plant of Argemone mexicana Linn. (Papaveraceae) and their structures established by spectral evidence. This is the first report of these alkaloids (dehydrocorydalmine, jatrorrhizine, columbamine, and oxyberberine) from Argemone mexicana and the Argemone genus. PMID:20645832

Singh, Sarita; Singh, Tryambak Deo; Singh, Virendra Pratap; Pandey, Vidya Bhushan

2010-02-01

17

Quaternary uplift of southern Italy  

Microsoft Academic Search

Dramatic coastline changes demonstrate rapid Quaternary uplift of Calabria in southern Italy. Because most of the west (Tyrrhenian Sea) coast is normal fault bounded, previous work has asserted that its uplift is local footwall uplift related to extension. However, the east (Ionian Sea) coast is also uplifting but is not normal fault bounded. This reanalysis, based on original field work

Rob Westaway

1993-01-01

18

Andrei Sher and Quaternary science  

NASA Astrophysics Data System (ADS)

Andrei Sher (1939-2008) was a key individual in Beringian studies who made substantial and original contributions, but also, importantly, built bridges between western and eastern Beringian scientists spanning some five decades of research. He is perhaps best known as a Quaternary palaeontologist, specializing in large mammals, and mammoths in particular, but his field of his scientific research was much broader, encompassing Quaternary geology, stratigraphy, geocryology, and paleoenvironmental reconstructions. He worked mainly in Siberia, in the Kolyma and Indigirka lowlands, and Chukotka, but also completed fieldwork in Alaska and Yukon through joint projects with American and Canadian scientists. Andrei was an active scientist until the last days of his life. He was involved in many different research projects ranging from mammoth evolution, fossil insects and environmental changes and ancient DNA. Without Andrei's connections between researchers, many unique discoveries would likely be unknown.

Kuzmina, Svetlana; Lister, Adrian M.; Edwards, Mary E.

2011-08-01

19

Quaternary ecology: A paleoecological perspective  

SciTech Connect

This book considers issues and problems in ecology which may be illuminated, if not solved, by considering paleoecology. The five central chapters include a discussion of application of Quaternary ecology to future global climate change, including global warming. Other areas presented include: population dispersal, invasions, expansions, and migrations; plant successions; ecotones; factors in community structure; ecosystem patterns and processes. Published case studies are numerous. The role played by continuing climatic change in vegetation change is acknowledged but not stressed.

Delcourt, H.R.; Delcourt, P.A.

1991-01-01

20

Quaternary glaciation of Mount Everest  

Microsoft Academic Search

The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and 10Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330ka (Tingri moraine), >41ka (Dzakar moraine), 24–27ka (Jilong

Lewis A. Owen; Ruth Robinson; Douglas I. Benn; Robert C. Finkel; Nicole K. Davis; Chaolu Yi; Jaakko Putkonen; Dewen Li; Andrew S. Murray

2009-01-01

21

Determinants of quaternary association in legume lectins  

PubMed Central

It is well known that the sequence of amino acids in proteins code for its tertiary structure. It is also known that there exists a relationship between sequence and the quaternary structure of proteins. The question addressed here is whether the nature of quaternary association can be predicted from the sequence, similar to the three-dimensional structure prediction from the sequence. The class of proteins called legume lectins is an interesting model system to investigate this problem, because they have very high sequence and tertiary structure homology, with diverse forms of quaternary association. Hence, we have used legume lectins as a probe in this paper to (1) gain novel insights about the relationship between sequence and quaternary structure; (2) identify the sequence motifs that are characteristic of a given type of quaternary association; and (3) predict the quaternary association from the sequence motif. PMID:15215518

Brinda, K.V.; Mitra, Nivedita; Surolia, Avadhesha; Vishveshwara, Saraswathi

2004-01-01

22

Ancient biomolecules in Quaternary palaeoecology  

NASA Astrophysics Data System (ADS)

The last few years have seen an enormous proliferation of ancient biomolecules research, especially in the field of ancient DNA. Ancient DNA studies have been transformed by the advent of next generation sequencing, with the first Pleistocene sample being analysed in 2005, and several complete and draft genomes that have been compiled from ancient DNA to date. At the same time, although less conspicuous, research on ancient proteins has also seen advances, with the time limit for research on ancient biomolecules now extending to over 1 million years. Here we review which effects these developments have on research in Quaternary science. We identify several lines of research that have the potential to profit substantially from these recent developments in ancient biomolecules research. First, the identification of taxa can be made using ancient biomolecules, and in the case of ancient DNA, specimens can even be assigned to specific populations within a species. Second, increasingly large DNA data sets from Pleistocene animals allow the elucidation of ever more precise pictures of the population dynamic processes whereby organisms respond to climate and environmental change. With the accompanying better understanding of process in the Quaternary, past ecologies can also more realistically be interpreted from proxy data sets. The dominant message from this research so far is that the Quaternary saw a great deal more dynamism in populations than had been forecast by conventional palaeoecology. This suggests that reconstructions of past environmental conditions need to be done with caution. Third, ancient DNA can also now be obtained directly from sediments to elucidate the presence of both plant and animal species in an area even in the absence of identifiable fossils, be it macro- or micro-fossils. Finally, the analysis of proteins enables the identification of bone remains to genus and sometimes species level far beyond the survival time of DNA, at least in temperate regions, illustrating that precise data is now forthcoming from seemingly unlikely sources. Together, these approaches allow the study of environmental dynamics throughout a substantial part, and perhaps even the entire Quaternary (the last 2.6 million years).

Hofreiter, Michael; Collins, Matthew; Stewart, John R.

2012-02-01

23

Stereoselective Synthesis of Quaternary Proline Analogues  

PubMed Central

This review describes available methods for the diastereoselective and asymmetric synthesis of quaternary prolines. The focus is on the preparation of ?-functionalized prolines with the pyrrolidine moiety not embedded in a polycyclic frame. The diverse synthetic approaches are classified according to the bond which is formed to complete the quaternary skeleton. PMID:19655047

Calaza, M. Isabel

2009-01-01

24

Quaternary glaciation of the Himalayan-Tibetan  

Microsoft Academic Search

Glacial geological evidence from throughout the Himalayan-Tibetan orogen is examined to determine the timing and extent of late Quaternary glaciation in this region and its relation to similar changes on a global scale. The evidence summarised here supports the existence of expanded ice caps and extensive valley glacier systems throughout the region during the late Quaternary. However, it cannot yet

LEWIS A. OWEN; MARC W. CAFFEE; ROBERT C. FINKEL; YEONG BAE SEONG

25

Relativistic Coulomb Fission  

NASA Technical Reports Server (NTRS)

Nuclear fission reactions induced by the electromagnetic field of relativistic nuclei are studied for energies relevant to present and future relativistic heavy ion accelerators. Cross sections are calculated for U-238 and Pu-239 fission induced by C-12, Si-28, Au-197, and U-238 projectiles. It is found that some of the cross sections can exceed 10 b.

Norbury, John W.

1992-01-01

26

Enantioselective Construction of Remote Quaternary Stereocenters  

PubMed Central

Summary Molecules containing all-carbon quaternary stereocenters – carbon atoms bonded to four distinct carbon substituents – are prevalent in Nature. However, the construction of such compounds in an enantioselective fashion remains a long-standing challenge to synthetic organic chemists. In particular, methods for forging quaternary stereocenters that are remote from other functional groups are underdeveloped. Herein we report a catalytic and enantioselective intermolecular Heck-type reaction of trisubstituted-alkenyl alcohols with aryl boronic acids. The reported method allows direct access to quaternary all-carbon-substituted ?-, ?-, ?-, ?- or ? aryl carbonyl compounds, as the unsaturation of the alkene is relayed to the alcohol resulting in the formation of a carbonyl group. The scope of the process also includes incorporation of pre-existing stereocenters along the alkyl chain, which links the alkene and the alcohol, wherein the stereocenter is preserved. The described method is flexible, allowing access to diverse building blocks containing an enantiomerically enriched, quaternary center. PMID:24717439

Mei, Tian-Sheng; Patel, Harshkumar H.; Sigman, Matthew S.

2014-01-01

27

Nuclear Fission Fuel is Inexhaustible  

Microsoft Academic Search

Nuclear fission energy is as inexhaustible as those energies usually termed ldquorenewablerdquo, such as hydro, wind, solar, and biomass. But, unlike the sum of these energies, nuclear fission energy has sufficient capacity to replace fossil fuels as they become scarce. Replacement of the current thermal variety of nuclear fission reactors with nuclear fission fast reactors, which are 100 times more

H. D. Lightfoot; W. Manheimer; D. A. Meneley; D. Pendergast; G. S. Stanford

2006-01-01

28

Singlet fission photovoltaics  

E-print Network

The efficiency of a solar cell is restricted by the "single junction limit," whereby photons with energy higher than the bandgap lose energy by thermalization. Singlet exciton fission splits a high-energy molecular excitation ...

Lee, Jiye

2013-01-01

29

Fission Systems for Mars Exploration  

NASA Technical Reports Server (NTRS)

Fission systems are used extensively on earth, and 34 such systems have flown in space. The energy density of fission is over 10 million times that of chemical reactions, giving fission the potential to eliminate energy density constraints for many space missions. Potential safety and operational concerns with fission systems are well understood, and strategies exist for affordably developing such systems. By enabling a power-rich environment and highly efficient propulsion, fission systems could enable affordable, sustainable exploration of Mars.

Houts, Michael G.; Kim, T.; Dorney, D. J.; Swint, Marion Shayne

2012-01-01

30

Quaternary geologic map of Minnesota  

NASA Technical Reports Server (NTRS)

The Quaternary Geologic Map of Minnesota is a compilation based both on the unique characteristics of satellite imagery and on the results of previous field investigations, both published and unpublished. The use of satellite imagery has made possible the timely and economical construction of this map. LANDSAT imagery interpretation proved more useful than expected. Most of the geologic units could be identified by extrapolating from specific sites where the geology had been investigated into areas where little was known. The excellent geographic registry coupled with the multi-spectral record of these images served to identify places where the geologic materials responded to their ecological environment and where the ecology responded to the geologic materials. Units were well located on the map at the scale selected for the study. Contacts between till units could be placed with reasonable accuracy. The reference points that were used to project delineations between units (rivers, lakes, hills, roads and other features), which had not been accurately located on early maps, could be accurately located with the help of the imagery. The tonal and color contrasts, the patterns reflecting geologic change and the resolution of the images permitted focusing attention on features which could be represented at the final scale of the map without distraction by other interesting but site-specific details.

Goebel, J. E.

1977-01-01

31

Quaternary glaciation of Mount Everest  

NASA Astrophysics Data System (ADS)

The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and 10Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24-27 ka (Jilong moraine), 14-17 ka (Rongbuk moraine), 8-2 ka (Samdupo moraines) and ˜1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8-7.7 ka) and Samdupo II (˜2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation.

Owen, Lewis A.; Robinson, Ruth; Benn, Douglas I.; Finkel, Robert C.; Davis, Nicole K.; Yi, Chaolu; Putkonen, Jaakko; Li, Dewen; Murray, Andrew S.

2009-07-01

32

Ice Age refugia and Quaternary extinctions: An issue of Quaternary evolutionary palaeoecology  

NASA Astrophysics Data System (ADS)

Quaternary palaeoecology, as a discipline, involves the analysis of a large range of fossil organisms from the last ca. 2 million years. This paper considers the role that these Quaternary records can take in better understanding the evolution of those organisms. We also discuss the surprisingly low uptake of evolutionary biology in Quaternary palaeoecological studies. This leads us to encourage an advance on both these fronts with a greater degree of collaboration with phylogeographic and ancient DNA researchers. These discussions accompany a summary of a special issue of Quaternary Science Reviews representing the proceedings of the XVII INQUA held in Cairns Australia in 2007. This special issue includes papers on a wide variety of Quaternary evolutionary palaeoecological and population dynamic subjects including extinct Pacific Island palm trees, Beringian beetles, Scandinavian trees, and the effects on human and animal populations of an extraterrestrial impact event in the Late Glacial of North America.

Stewart, John R.; Cooper, Alan

2008-12-01

33

Major Quaternary uplift along the northernmost San Andreas fault, King Range, northwestern California  

SciTech Connect

The King Range is a rugged coastal mountain range that parallels the San Andreas transform fault system just south of the Mendocino triple junction. Point Delgada is a small coastal headland that projects into the Pacific Ocean just southwest of the King Range. Apatite fission-track ages from parts of the King Range are remarkably young, averaging 1.2 Ma, indicating that a minimum of 2-5 km of uplift and unroofing have occured in the past 1.2 m.y. In contrast, ages from Point Delgada are about 12 Ma, and fission-track length data indicate that rocks there have resided at low temperatures ({le}50{degree}C) and thus at shallow depths since soon after 12 Ma. Therefore Point Delgada has experienced relative vertical stability. The contrast in uplift histories indicates that the two areas are separated by a major fault with a minimum of {approximately}1 km of Quaternary vertical offset. The fault is probably part of the San Andreas system and so may also have undergone major Quaternary strike-slip offset. The uplift in the King Range seems too great and too localized to have resulted from isostatic effects accompanying passage of the Mendocino triple junction and development of a slab-free window; rather, it is probably a local response to space problems among the various moving crustal blocks around the triple junction and San Andreas fault.

Dumitru, T.A. (La Trobe Univ., Bundoora, Victoria (Australia))

1991-05-01

34

Fission in Spallation Reactions  

NASA Astrophysics Data System (ADS)

Some properties of fission in spallation reactions in the GeV range are examined. It is shown on theoretical grounds that the charge, mass and excitation energy are strongly fluctuating. The range of accessible excitation energies is determined. The ability of a particular intranuclear plus evaporation model, namely the INCL4+ABLA model to describe the existing data is demonstrated. In view of the numerous parameters used in the fission model, the sensitivity of the results to these parameters is investigated. It is shown that, due to the complexity of the fission modeling, it is hard to get reliable information on the level density parameters at high excitation energy. Finally the influence of the nature of the incident projectile is shortly discussed.

Cugnon, J.; Aoust, Th.; Boudard, A.

2008-04-01

35

A Quaternary volcanic ash deposit in western Missouri  

SciTech Connect

Quaternary volcanic ash has been found in more than fifty localities in the midwest. The most widespread deposits originated from the Long Valley caldera, California; the Jemez calderas, New Mexico; or the Yellowstone caldera, Wyoming. Fission track dating has grouped the deposits into six separate ash falls ranging from 700,000--2,000,000 years old. A small volcanic ash deposit in western Missouri may be correlative with those found along the Kansas and Marais de Cygnes rivers in eastern Kansas. The ash deposit is in Northwest Bates County Missouri, exposed along a tributary to Miami Creek, four miles east of the Kansas state line. The ash layer is interbedded with alluvial terrace deposits and ranges from fifteen to thirty inches in thickness. It is inferred to have been deposited in a pond or oxbow lake. The color is white with a pale yellow tinge (Munsell 10YR 8/2). Shard examination shows that about 70% are flat bubble-wall types, about 20% have straight ridges, less than 10% are bubble-junction, and only a trace are vesicular. The closest known volcanic ash occurrence is an ash outcropping in a Kansas river terrace near DeSoto, KS, forty-five miles to the northwest. The DeSoto deposit has been identified as the .62 m.y. Lava Creek B ash from the Yellowstone caldera. A preliminary correlation of the Missouri ash with the DeSoto ash is based on similar shard morphology and color.

Emerson, J.W. (Central Missouri State Univ., Warrensburg, MO (United States))

1993-03-01

36

Process for treating fission waste  

DOEpatents

A method is described for the treatment of fission waste. A glass forming agent, a metal oxide, and a reducing agent are mixed with the fission waste and the mixture is heated. After melting, the mixture separates into a glass phase and a metal phase. The glass phase may be used to safely store the fission waste, while the metal phase contains noble metals recovered from the fission waste.

Rohrmann, Charles A. (Kennewick, WA); Wick, Oswald J. (Richland, WA)

1983-01-01

37

Late Quaternary history of Washington Land, North Greenland OLE BENNIKE  

E-print Network

Late Quaternary history of Washington Land, North Greenland OLE BENNIKE Bennike, O. 2002 (September): Late Quaternary history of Washington Land, North Greenland. Boreas, Vol. 31, 260­272. Oslo. ISSN 0300 Quaternary history of the region. The lack of data re ects the inaccessibility of this remote region

Ingólfsson, �lafur

38

Student Experiments in Spontaneous Fission.  

ERIC Educational Resources Information Center

Advanced undergraduate experiments utilizing a commercially available, thin spontaneous fission source are described, including studies of the energy and mass distribution of the fission fragments and their energy and angular correlation. The experiments provide a useful introduction to fission, nuclear mass equations, heavy-ion physics, and…

Becchetti, F. D.; Ying, J. S.

1981-01-01

39

Pulsed Fission Propulsion Concept  

NASA Technical Reports Server (NTRS)

In the 1960's U.S. Government laboratories, under Project Orion, investigated a pulsed nuclear fission propulsion system. Small nuclear pulse units would be sequentially discharged from the aft end of the vehicle. A blast shield and shock absorber system would protect the crew and convert the shock loads into a continuous propusive force.

1999-01-01

40

Pulsed Fission Propulsion Concept  

NASA Technical Reports Server (NTRS)

In the 1960's U.S. Government laboratories, under Project Orion, investigated a pulsed nuclear fission propulsion system. Small nuclear pulse units would be sequentially discharged from the aft end of the vehicle. A blast shield and shock absorber system would protect the crew and convert the shock loads into a continuous propulsive force.

1999-01-01

41

Enantioselective construction of remote quaternary stereocentres  

NASA Astrophysics Data System (ADS)

Small molecules that contain all-carbon quaternary stereocentres--carbon atoms bonded to four distinct carbon substituents--are found in many secondary metabolites and some pharmaceutical agents. The construction of such compounds in an enantioselective fashion remains a long-standing challenge to synthetic organic chemists. In particular, methods for synthesizing quaternary stereocentres that are remote from other functional groups are underdeveloped. Here we report a catalytic and enantioselective intermolecular Heck-type reaction of trisubstituted-alkenyl alcohols with aryl boronic acids. This method provides direct access to quaternary all-carbon-substituted ?-, ?-, ?-, ?- or ?-aryl carbonyl compounds, because the unsaturation of the alkene is relayed to the alcohol, resulting in the formation of a carbonyl group. The scope of the process also includes incorporation of pre-existing stereocentres along the alkyl chain, which links the alkene and the alcohol, in which the stereocentre is preserved. The method described allows access to diverse molecular building blocks containing an enantiomerically enriched quaternary centre.

Mei, Tian-Sheng; Patel, Harshkumar H.; Sigman, Matthew S.

2014-04-01

42

Quaternary deformation mapping with ground penetrating radar  

Microsoft Academic Search

Ground penetrating radar (GPR) was used in a programme of geological and hydrogeological investigations into the Quaternary of west Cumbria, UK. The investigations were part of an extensive programme to determine the suitability of the area for a deep radioactive waste repository. The hydrogeological characteristics of the drift deposits are important since they affect both recharge and discharge. The glacially

J. P Busby; J. W Merritt

1999-01-01

43

Quaternary International 138139 (2005) 14 In Memorium  

E-print Network

awards include being named a fellow of the Geological Society of America in 2004. Geoff's major galvanizing efforts to apply surface exposure dating methods to date moraines in Peru and Bolivia. Results, Geology, Quaternary Research, and GSA Bulletin. Geoff was blessed with a combination of keen intellectual

Howat, Ian M.

44

Late Quaternary fire regimes of Australasia  

Microsoft Academic Search

We have compiled 223 sedimentary charcoal records from Australasia in order to examine the temporal and spatial variability of fire regimes during the Late Quaternary. While some of these records cover more than a full glacial cycle, here we focus on the last 70,000 years when the number of individual records in the compilation allows more robust conclusions. On orbital

S. D. Mooney; S. P. Harrison; P. J. Bartlein; A.-L. Daniau; J. Stevenson; K. C. Brownlie; S. Buckman; M. Cupper; J. Luly; M. Black; E. Colhoun; D. D’Costa; J. Dodson; S. Haberle; G. S. Hope; P. Kershaw; C. Kenyon; M. McKenzie; N. Williams

2011-01-01

45

Dynamics of nuclear fission  

Microsoft Academic Search

The most interesting process of collective flow of nuclear matter is the fission process. The time-scale of this process at moderate to high excitation energies is reviewed. Various methods to measure the time associated with large scale collective flow of nuclei in the range of 10^(-21) to 10^(-17) s are compared. Pre- and post-scission multiplicities of light particles in particular

D. Hilscher; H. Rossner

1992-01-01

46

Neogene and Quaternary development of the Western Carpathian lithosphere: impact on georelief and geohazards  

NASA Astrophysics Data System (ADS)

Some essential features of the Western Carpathian (and adjacent regions) lithosphere and land surface were created simultaneously in the Neogene and Quaternary. Synthesis of published as well as new geophysical, sedimentological, thermochronological and geomorphological data provide following results: Our newest morphostructural division and modelling of the crustal thickness fit together very well. Newly identified distinct core root under central part of the Western Carpatians explains rise of the annular morphostructural regions. Despite of variant possible reasons of creation of the isostatic disequilibrium, coupled morphological features suggest neotectonic (post Miocene) age. Re-evaluation of geophysical and geological data from the northern Danube Basin and Turiec Basin, together with new field-work and laboratory results formed the ground-work for a new determination of particular sedimentary facies and their changes in time and space. The results enable a better correlation of depositional and denudational history including formation of the system of planation surfaces. Apatite fission track data reflects mainly older Alpine orogenetic phases. However, the last uplift connected with the rise of modern topography is reflected by newest low-temperature termochronology data from the central part of the Western Carpathians. They specify the last stages of exhumation in the Pliocene and Pleistocene and define maximum age of preserved remnants of planation surfaces. A cosmogenic nuclide dating of deglaciation of the highest mountain (Tatras) suggests their quick Quaternary uplift, too. The Neogene and Quaternary development of the Western Carpathians projects onto distribution and intensity of recent geodynamic processes and subsequently natural hazards and risks. As an example the Quaternary development of the northernmost part of the Danubian Basin is presented (including changes of tectonic regime and river network as well as estimation of the erosion and deposition budged). Finally, an explanation of distribution of synthetic hazardous regions of the Western Carpathians in terms of their Neogene and Quaternary development is presented. Acknowledgments: This work was financially supported by the Slovak Research and Development Agency APVV under contract No. ESF—EC—0006—07.

Minár, J.; Ková?, M.; Bielik, M.; Hók, J.; Králiková, S.; Smetanová, A.; Šabo, M.; Vojtko, R.

2012-04-01

47

Late quaternary sequence stratigraphy, South Florida margin  

SciTech Connect

Late Quaternary sea-level change and the Florida Current have combined to produce a progradational shelf-slope margin along the western portion of the south Florida Platform facing the Straits of Florida. Analysis of high resolution seismic reflection profiles suggest at least eight 5th order late Quaternary sequences downlap onto the Pourtales Terrace at 250 m water depth. Along most of the south Florida margin, this Late Quaternary section is very thin, and only where significant accumulations occur can the stratigraphic patterns produced by sea-level change be clearly observed. Recognition of systems tracts and their boundaries from high-resolution seismic data is important for prediction of sedimentary facies and stratigraphic development of margins. Many south Florida seismic boundaries can be fit to the Exxon sequence stratigraphy model. Others appear to reflect the added effect of bottom-current erosion that complicates the signal produced by sea-level change. Overall, the sea-level signal appears to dominate the stratigraphic record, especially from the 2-dimensional perspective of dip-oriented seismic profiles. However, the 3-dimensional geometry of deposits are strongly influenced by along slope accumulation patterns controlled by the Florida Current. This study provides new insight on the importance of both geostrophic boundary currents and sea-level change in controlling stratigraphic development of a carbonate platform margin. Similar anomalously thick slope deposits in ancient sequences may indicate similar controls on accumulation and could lend to predictions of related paleo-platform configurations.

Locker, S.D.; Hine, A.C. [Univ. of South Florida, St. Petersburg, FL (United States). Dept. of Marine Science

1995-12-01

48

Call Title: Nuclear Fission and Radiation Protection Call Identifier: FP7-Fission-2009  

E-print Network

Call Title: Nuclear Fission and Radiation Protection · Call Identifier: FP7-Fission-2009 · Date and competitiveness of existing and future nuclear installations Fission-2009-2.1.2: RPV irradiation effects in sustainable nuclear fission energy Coordination and Support Action (coordinating action) Fission-2.3 Fission

De Cindio, Fiorella

49

Fission and confusion.  

PubMed

Catholic opponents of abortion and embryonic stem cell research usually base their position on a hylomorphic account of ensoulment at fertilization. They maintain that we each started out as one-cell ensouled organisms. Critics of this position argue that it is plagued by a number of intractable problems due to fission (twinning) and fusion. We're unconvinced that such objections to early ensoulment provide any reason to doubt the coherence of the hylomorphic account. However, we do maintain that a defense of ensoulment at fertilization must deny that we're essentially organisms. PMID:17162672

Hershenov, David; Koch-Hershenov, Rose J

2006-12-01

50

Quaternary Geologic Map of Connecticut and Long Island Sound Basin  

USGS Publications Warehouse

The Quaternary geologic map (sheet 1) and explanatory figures and cross sections (sheet 2) portray the geologic features formed in Connecticut during the Quaternary Period, which includes the Pleistocene (glacial) and Holocene (postglacial) Epochs. The Quaternary Period has been a time of development of many details of the landscape and of all the surficial deposits. At least twice in the late Pleistocene, continental ice sheets swept across Connecticut. Their effects are of pervasive importance to the present occupants of the land. The Quaternary geologic map illustrates the geologic history and the distribution of depositional environments during the emplacement of glacial and postglacial surficial deposits and the landforms resulting from those events.

Stone, Janet Radway; Schafer, John P.; London, Elizabeth Haley; DiGiacomo-Cohen, Mary L.; Lewis, Ralph S.; Thompson, Woodrow B.

2005-01-01

51

Fission throughout the periodic table  

SciTech Connect

The dualistic view of fission and evaporation as two distinct compound nucleus processes is substituted with a unified view in which fission, complex fragment emission, and light particle evaporation are seen as different aspects of a single process. 47 refs., 22 figs.

Moretto, L.G.; Wozniak, G.J.

1989-04-01

52

Modern Pulsed Fission Propulsion Concept  

NASA Technical Reports Server (NTRS)

In the 1960's U.S. Government laboratories, under Project Orion, investigated a pulsed nuclear fission propulsion system. Based on Project Orion, an interplanetary vehicle using pulsed fission propulsion would incorporate modern technologies for momentum transfer, thermal management, and habitation design.

1999-01-01

53

40 CFR 721.9075 - Quaternary ammonium salt of fluorinated alkylaryl amide.  

Code of Federal Regulations, 2012 CFR

... false Quaternary ammonium salt of fluorinated alkylaryl amide...9075 Quaternary ammonium salt of fluorinated alkylaryl amide...generically as quaternary ammonium salt of fluorinated alkylaryl...f). (ii) Release to water. Requirements as...

2012-07-01

54

40 CFR 721.9075 - Quaternary ammonium salt of fluorinated alkylaryl amide.  

Code of Federal Regulations, 2013 CFR

... false Quaternary ammonium salt of fluorinated alkylaryl amide...9075 Quaternary ammonium salt of fluorinated alkylaryl amide...generically as quaternary ammonium salt of fluorinated alkylaryl...f). (ii) Release to water. Requirements as...

2013-07-01

55

Fifty years with nuclear fission  

SciTech Connect

The news of the discovery of nuclear fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fifieth anniversary of its discovery by holding a topical meeting entitled, Fifty Years with Nuclear Fission,'' in the United States during the year 1989. The objective of the meeting was to bring together pioneers of the nuclear industry and other scientists and engineers to report on reminiscences of the past and on the more recent development in fission science and technology. The conference highlighted the early pioneers of the nuclear industry by dedicated a full day (April 26), consisting of two plenary sessions, at the National Academy of Sciences (NAS) in Washington, DC. More recent developments in fission science and technology in addition to historical reflections were topics for two fully days of sessions (April 27 and 28) at the main site of the NIST in Gaithersburg, Maryland. The wide range of topics covered in this Volume 1 by this topical meeting included plenary invited, and contributed sessions entitled: Preclude to the First Chain Reaction -- 1932 to 1942; Early Fission Research -- Nuclear Structure and Spontaneous Fission; 50 Years of Fission, Science, and Technology; Nuclear Reactors, Secure Energy for the Future; Reactors 1; Fission Science 1; Safeguards and Space Applications; Fission Data; Nuclear Fission -- Its Various Aspects; Theory and Experiments in Support of Theory; Reactors and Safeguards; and General Research, Instrumentation, and By-Product. The individual papers have been cataloged separately.

Behrens, J.W.; Carlson, A.D. (eds.) (National Institute of Standards and Technology, Gaithersburg, MD (United States))

1989-01-01

56

Antibacterial activity of gemini quaternary ammonium salts.  

PubMed

A series of gemini quaternary ammonium salts (chlorides and bromides), with various hydrocarbon chain and spacer lengths, were tested. These compounds exhibited antibacterial activity against both Gram-positive and Gram-negative bacteria and were not mutagenic. The strongest antibacterial effect was observed for TMPG-10 Cl (against Pseudomonas aeruginosa ATCC 27853) and TMPG-12 Br (against Staphylococcus aureus ATCC 6538 and Escherichia coli ATCC 11229 and clinical ESBL(+) isolate 434) surfactants. These compounds inhibited the adhesion of Staphylococcus epidermidis ATCC 35984 to a polystyrene surface and eradicated biofilm formed by P. aeruginosa PAO1. The activity of studied compounds was dependent on hydrocarbon chain length. PMID:24236547

Ob??k, Ewa; Piecuch, Agata; Guz-Regner, Katarzyna; Dworniczek, Ewa

2014-01-01

57

The Fission Vision  

NSDL National Science Digital Library

Leo Szilard, a Hungarian physicist, imagined the two steps needed to free the energy in an atom's nucleus: one, a nuclear chain reaction, and two, a critical mass of the right element to set off and sustain it. Does he envision the process we now call "fission," the splitting of nuclei? Yes, he seems to, but Szilard's ideas are not yet clearly expressed. And he doesn't know which element will provide nuclei that can be easily split. This chapter describes his quest and that of his contemporaries, to identify this missing element--which ultimately unleashed nuclear energy into the world. In addition, this compelling chapter clearly illustrates the nature of science and science as a human endeavor as recommended in the National Science Education Standards.

Hakim, Joy

2007-08-17

58

Dynamical Aspects of Nuclear Fission  

NASA Astrophysics Data System (ADS)

Fission dynamics. Dependence of scission-neutron yield on light-fragment mass for [symbol]=1/2 [et al.]. Dynamics of capture quasifission and fusion-fission competition / L. Stuttgé ... [et al.] -- Fission-fission. The processes of fusion-fission and quasi-fission of superheavy nuclei / M. G. Itkis ... [et al.]. Fission and quasifission in the reactions [symbol]Ca+[symbol]Pb and [symbol]Ni+[symbol]W / G. N. Knyazheva ... [et al.]. Mass-energy characteristics of reactions [symbol]Fe+[symbol][symbol][symbol]266Hs and [symbol]Mg+[symbol]Cm[symbol][symbol]Hs at Coulomb barrier / L. Krupa ... [et al.]. Fusion of heavy ions at extreme sub-barrier energies / ?. Mi?icu and H. Esbensen. Fusion and fission dynamics of heavy nuclear system / V. Zagrebaev and W. Greiner. Time-dependent potential energy for fusion and fission processes / A. V. Karpov ... [et al.] -- Superheavy elements. Advances in the understanding of structure and production mechanisms for superheavy elements / W. Greiner and V. Zagrebaev. Fission barriers of heaviest nuclei / A. Sobiczewski ... [et al.]. Possibility of synthesizing doubly magic superheavy nuclei / Y Aritomo ... [et al.]. Synthesis of superheavy nuclei in [symbol]Ca-induced reactions / V. K. Utyonkov ... [et al.] -- Fragmentation. Production of neutron-rich nuclei in the nucleus-nucleus collisions around the Fermi energy / M. Veselský. Signals of enlarged core in [symbol]Al / Y. G. Ma ... [et al.] -- Exotic modes. New insight into the fission process from experiments with relativistic heavy-ion beams / K.-H. Schmidt ... [et al.]. New results for the intensity of bimodal fission in binary and ternary spontaneous fission of [symbol]Cf / C. Goodin ... [et al.]. Rare fission modes: study of multi-cluster decays of actinide nuclei / D. V. Kamanin ... [et al.]. Energy distribution of ternary [symbol]-particles in [symbol]Cf(sf) / M. Mutterer ... [et al.]. Preliminary results of experiment aimed at searching for collinear cluster tripartition of [symbol]Pu / Y. V. Pyatkov. Comparative study of the ternary particle emission in [symbol] and [symbol]Cm(SF) / S. Vermote ... [et al.] -- Structure of fission fragments and neurton rich nuclei / manifestation of average y-ray multiplicity in the fission modes of [symbol]Cf(sf) and the proton-induced fission of [symbol]Pa, [symbol]Np, and [symbol]Am / M. Berešová ... [et al.]. Yields of correlated fragment pairs and average gamma-ray multiplicities and energies in [symbol]Pb([symbol]O, f) / A. Bogachev ... [et al.]. Recent experiments at gammasphere intended to the study of [symbol]Cf spontaneous fission / A. V. Daniel ... [et al.]. Nuclear structure studies of microsecond isomers near A =100 / J. Genevey ... [et al.]. Covariant density functional theory: isospin properties of nuclei far from stability / G. A. Lalazisis. Relativistic mean-field description of light nuclei / J. Leja and Š. Gmuca. Energy nucleon spectra from reactions at intermediate energies / O. Grudzevich ... [et al.] -- Developments in experimental techniques. Analysis, processing and visualization of multidimensional data using DaqProVis system / M. Morhá? ... [et al.].

Kliman, J.; Itkis, M. G.; Gmuca, Š.

2008-11-01

59

Quaternary glacial and climate history of Antarctica lafur Inglfsson  

E-print Network

climate changes. A good un- derstanding of the Late Quaternary glacial and climate history of AntarcticaQuaternary glacial and climate history of Antarctica �lafur Ingólfsson University of Iceland, and is important for understanding the relative timing of climate changes between the polar hemispheres (Denton et

Ingólfsson, �lafur

60

Fifty years with nuclear fission  

SciTech Connect

The news of the discovery of nucler fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fiftieth anniversary of its discovery by holding a topical meeting entitled, Fifty years with nuclear fission,'' in the United States during the year 1989. The objective of the meeting was to bring together pioneers of the nuclear industry and other scientists and engineers to report on reminiscences of the past and on the more recent developments in fission science and technology. The conference highlighted the early pioneers of the nuclear industry by dedicating a full day (April 26), consisting of two plenary sessions, at the National Academy of Sciences (NAS) in Washington, DC. More recent developments in fission science and technology in addition to historical reflections were topics for two full days of sessions (April 27 and 28) at the main sites of the NIST in Gaithersburg, Maryland. The wide range of topics covered by Volume 2 of this topical meeting included plenary invited, and contributed sessions entitled, Nuclear fission -- a prospective; reactors II; fission science II; medical and industrial applications by by-products; reactors and safeguards; general research, instrumentation, and by-products; and fission data, astrophysics, and space applications. The individual papers have been cataloged separately.

Behrens, J.W.; Carlson, A.D. (eds.) (National Institute of Standards and Technology, Gaithersburg, MD (United States))

1989-01-01

61

Fission at intermediate nucleon energies  

NASA Astrophysics Data System (ADS)

In the present work Monte Carlo calculations of fission of actinides and pre- actinides induced by protons and neutrons in the energy range from 100 MeV to 1 GeV are carried out by means of a recent version of the Liège Intranuclear Cascade Model, INCL++, coupled with different evaporation-fission codes, in particular GEMINI++ and ABLA07. Fission model parameters are adjusted on experimental (p, f) cross sections and used to predict (n, f) cross sections, in order to provide a theoretical support to the campaign of neutron cross section measurements at the n_TOF facility at CERN.

Lo Meo, S.; Mancusi, D.; Massimi, C.; Vannini, G.; Ventura, A.

2014-07-01

62

?-delayed fission of 180Tl  

NASA Astrophysics Data System (ADS)

The detailed analysis of the ?-delayed fission data of 180Tl is presented. The experiment was performed by producing a pure beam of 180Tl by means of highly selective resonance laser ionization followed by mass separation with the ISOLDE (CERN, Geneva) isotope separator. A surprising asymmetric mass distribution of fission fragments from 180Hg, the daughter of 180Tl ? decays, was observed. Here, the energy calibration of the silicon detectors, which is crucial for a proper determination of the fission fragments’ energy and mass split, is presented and the total kinetic energy and its dependence on the mass split ratio is discussed. A more precise ?-delayed fission probability P?DF(180Tl)=3.2(2)×10-3% was deduced.

Elseviers, J.; Andreyev, A. N.; Huyse, M.; Van Duppen, P.; Antalic, S.; Barzakh, A.; Bree, N.; Cocolios, T. E.; Comas, V. F.; Diriken, J.; Fedorov, D.; Fedosseev, V. N.; Franchoo, S.; Ghys, L.; Heredia, J. A.; Ivanov, O.; Köster, U.; Marsh, B. A.; Nishio, K.; Page, R. D.; Patronis, N.; Seliverstov, M. D.; Tsekhanovich, I.; Van den Bergh, P.; Van De Walle, J.; Venhart, M.; Vermote, S.; Veselský, M.; Wagemans, C.

2013-10-01

63

Background radiation from fission pulses  

SciTech Connect

Extensive source terms for beta, gamma, and neutrons following fission pulses are presented in various tabular and graphical forms. Neutron results from a wide range of fissioning nuclides (42) are examined and detailed information is provided for four fuels: /sup 235/U, /sup 238/U, /sup 232/Th, and /sup 239/Pu; these bracket the range of the delayed spectra. Results at several cooling (decay) times are presented. For ..beta../sup -/ and ..gamma.. spectra, only /sup 235/U and /sup 239/Pu results are given; fission-product data are currently inadequate for other fuels. The data base consists of all known measured data for individual fission products extensively supplemented with nuclear model results. The process is evolutionary, and therefore, the current base is summarized in sufficient detail for users to judge its quality. Comparisons with recent delayed neutron experiments and total ..beta../sup -/ and ..gamma.. decay energies are included. 27 refs., 47 figs., 9 tabs.

England, T.R.; Arthur, E.D.; Brady, M.C.; LaBauve, R.J.

1988-05-01

64

Advanced Space Fission Propulsion Systems  

NASA Technical Reports Server (NTRS)

Fission has been considered for in-space propulsion since the 1940s. Nuclear Thermal Propulsion (NTP) systems underwent extensive development from 1955-1973, completing 20 full power ground tests and achieving specific impulses nearly twice that of the best chemical propulsion systems. Space fission power systems (which may eventually enable Nuclear Electric Propulsion) have been flown in space by both the United States and the Former Soviet Union. Fission is the most developed and understood of the nuclear propulsion options (e.g. fission, fusion, antimatter, etc.), and fission has enjoyed tremendous terrestrial success for nearly 7 decades. Current space nuclear research and technology efforts are focused on devising and developing first generation systems that are safe, reliable and affordable. For propulsion, the focus is on nuclear thermal rockets that build on technologies and systems developed and tested under the Rover/NERVA and related programs from the Apollo era. NTP Affordability is achieved through use of previously developed fuels and materials, modern analytical techniques and test strategies, and development of a small engine for ground and flight technology demonstration. Initial NTP systems will be capable of achieving an Isp of 900 s at a relatively high thrust-to-weight ratio. The development and use of first generation space fission power and propulsion systems will provide new, game changing capabilities for NASA. In addition, development and use of these systems will provide the foundation for developing extremely advanced power and propulsion systems capable of routinely and affordably accessing any point in the solar system. The energy density of fissile fuel (8 x 10(exp 13) Joules/kg) is more than adequate for enabling extensive exploration and utilization of the solar system. For space fission propulsion systems, the key is converting the virtually unlimited energy of fission into thrust at the desired specific impulse and thrust-to-weight ratio. This presentation will discuss potential space fission propulsion options ranging from first generation systems to highly advanced systems. Ongoing research that shows promise for enabling second generation NTP systems with Isp greater than 1000 s will be discussed, as will the potential for liquid, gas, or plasma core systems. Space fission propulsion systems could also be used in conjunction with simple (water-based) propellant depots to enable routine, affordable missions to various destinations (e.g. moon, Mars, asteroids) once in-space infrastructure is sufficiently developed. As fuel and material technologies advance, very high performance Nuclear Electric Propulsion (NEP) systems may also become viable. These systems could enable sophisticated science missions, highly efficient cargo delivery, and human missions to numerous destinations. Commonalities between NTP, fission power systems, and NEP will be discussed.

Houts, Michael G.; Borowski, Stanley K.

2010-01-01

65

Nuclear fission with inertial confinement  

Microsoft Academic Search

The possibility of inducing an explosive fission reaction in a small amount of fissionable material by a heavy-ion beam from\\u000a a high-power accelerator driver developed for bringing about fusion in deuterium-tritium cylindrical targets with direct burning\\u000a is analyzed. The consequences of the use of this method in the nuclear power industry are discussed.

D. G. Koshkarev; B. Yu Sharkov

2002-01-01

66

Nuclear dissipation from fission time  

Microsoft Academic Search

Fission times, pre-scission neutron multiplicities and GDR pre-scission gamma-ray multiplicities measured for uranium or thorium nuclei formed with temperatures T ~ 1.8 MeV have been compared with calculations performed with CDSM2, a two-dimensional dynamical model combined with a statistical one. Among the three experimental approaches considered, fission times give access to the most precise pieces of information on nuclear dissipation

I. Gontchar; M. Morjean; S. Basnary

2002-01-01

67

The role of Quaternary environmental change in plant macroevolution: the exception or the rule?  

Microsoft Academic Search

The Quaternary has been described as an important time for genetic diversification and speciation. This is based on the premise that Quaternary climatic conditions fostered the isolation of populations and, in some instances, allopatric speciation. However, the 'Quaternary Ice-Age speciation model' rests on two key assumptions: (i) that biotic responses to climate change during the Quaternary were significantly different from

Katherine J. Willis; Karl J. Niklas

2004-01-01

68

Antifungal activity of gemini quaternary ammonium salts.  

PubMed

A series of gemini quaternary ammonium chlorides and bromides with various alkyl chain and spacer lengths was synthesized. The most active compounds against fungi were chlorides with 10 carbon atoms within the hydrophobic chain. Among these compounds were few with no hemolytic activity at minimal inhibitory concentrations. None of the tested compounds were cytotoxic and mutagenic. Cationic gemini surfactants poorly reduced the adhesion of microorganisms to the polystyrene plate, but inhibited the filamentation of Candida albicans. One of the tested compounds eradicated C. albicans and Rodotorula mucilaginosa biofilm, what could be important in overcoming catheter-associated infections. It was also shown that gemini surfactants enhanced the sensitivity of C. albicans to azoles and polyenes, thus they might be potentially used in combined therapy against fungi. PMID:23827647

Ob??k, Ewa; Piecuch, Agata; Krasowska, Anna; Luczy?ski, Jacek

2013-12-14

69

Symmetric and asymmetric fission of Ac isotopes near the fission threshold  

Microsoft Academic Search

Fission probabilities and fragment anisotropies were investigated for fission of 227Ac and 228Ac by means of direct reactions with a 3He beam on a 226Ra target. Triple-humped mass distributions are found also for excitation energies where second-chance fission is excluded. The fission barrier is higher for symmetric fission compared to that for asymmetric fission by 1.2 and 2.0 MeV, respectively,

E. Konecky; H. J. Specht; J. Weber

1973-01-01

70

Late Quaternary temperature change velocity in Mesoamerica  

NASA Astrophysics Data System (ADS)

Quaternary climate has been highly variable, and yet few quantitative continental reconstructions are available for tropical areas. Quantitative records of temperature change during the Quaternary are especially relevant for putting modern climate change into a historic context. Within this perspective, two aspects are of singular relevance: i) Identifying and quantifying past climatic variability, and ii) Providing a means to estimate the seed at which climate change happened in the past. Here we show temperature reconstructions and temperature change velocity calculations for two locations in northern tropical America. Temperature reconstruction was based on two sedimentary records form Lake Chalco (30,000 years), central Mexican highlands, and Lake Petén-Itzá, Guatemalan lowlands (86,000 years). Temperature reconstruction was based on the analysis of fossil pollen on the light of pollen-temperature transfer functions. These functions were calibrated through an extensive survey of modern pollen samples covering an elevational gradient from 0 to 4,218 m asl. Derived temperature profiles show a parallel long-term trend and a similar cooling of approximately 5 oC during the Last Glacial Maximum in the lowlands and highlands of Mexico and Guatemala. Using a digital elevation model, we ere able to reconstruct the velocity at which isotherms displaced to produce the observed temperature anomalies. Spatial velocities of temperature change in the studied areas were at least four times slower than values reported for the last 50 years, but also at least twice as fast as those obtained from recent models. This study demonstrates that modern temperature change has no precedent within the last 86,000 years, but also that tropical climate has been more variable than it has been assumed to date.

Correa-Metrio, A.; Lozano, S.; Sosa-Nájera, S.; Bush, M. B.

2013-05-01

71

A quaternary temperament model and defense cluster preferences.  

PubMed

A quaternary model of temperament constructed from orthogonal axes defined by Extraversion-Introversion and Thinking-Feeling resulted in four groups: Introverted Thinking, Introverted Feeling, Extraverted Thinking, and Extraverted Feeling. Hypothesized relationships between quaternary groups and defense cluster preferences were tested by giving 158 female college students the Myers-Briggs Type Indicator and the Defense Mechanisms Inventory. There was little support for hypothesized relationships between the quaternary model and defense preferences. The only hypothesized significant group difference showed the Extraverted Feeling group recording a greater preference for the Reversal defense cluster than the Introverted Feeling group. PMID:14650666

Kelly, Kathryn E; Tobacyk, Jerome J

2003-10-01

72

Compact fission counter for DANCE  

SciTech Connect

The Detector for Advanced Neutron Capture Experiments (DANCE) consists of 160 BF{sub 2} crystals with equal solid-angle coverage. DANCE is a 4{pi} {gamma}-ray calorimeter and designed to study the neutron-capture reactions on small quantities of radioactive and rare stable nuclei. These reactions are important for the radiochemistry applications and modeling the element production in stars. The recognition of capture event is made by the summed {gamma}-ray energy which is equivalent of the reaction Q-value and unique for a given capture reaction. For a selective group of actinides, where the neutron-induced fission reaction competes favorably with the neutron capture reaction, additional signature is needed to distinguish between fission and capture {gamma} rays for the DANCE measurement. This can be accomplished by introducing a detector system to tag fission fragments and thus establish a unique signature for the fission event. Once this system is implemented, one has the opportunity to study not only the capture but also fission reactions. A parallel-plate avalanche counter (PPAC) has many advantages for the detection of heavy charged particles such as fission fragments. These include fast timing, resistance to radiation damage, and tolerance of high counting rate. A PPAC also can be tuned to be insensitive to {alpha} particles, which is important for experiments with {alpha}-emitting actinides. Therefore, a PPAC is an ideal detector for experiments requiring a fast and clean trigger for fission. A PPAC with an ingenious design was fabricated in 2006 by integrating amplifiers into the target assembly. However, this counter was proved to be unsuitable for this application because of issues related to the stability of amplifiers and the ability to separate fission fragments from {alpha}'s. Therefore, a new design is needed. A LLNL proposal to develop a new PPAC for DANCE was funded by NA22 in FY09. The design goal is to minimize the mass for the proposed counter and still be able to maintain a stable operation under extreme radioactivity and the ability to separate fission fragments from {alpha}'s. In the following sections, the description is given for the design and performance of this new compact PPAC, for studying the neutron-induced reactions on actinides using DANCE at LANL.

Wu, C Y; Chyzh, A; Kwan, E; Henderson, R; Gostic, J; Carter, D; Bredeweg, T; Couture, A; Jandel, M; Ullmann, J

2010-11-06

73

Energy production using fission fragment rockets  

NASA Astrophysics Data System (ADS)

Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the following advantages: approximately twice the efficiency if the fission fragment energy can be directly converted into electricity; reduction of the buildup of a fission fragment inventory in the reactor could avoid a Chernobyl type disaster; and collection of the fission fragments outside the reactor could simplify the waste disposal problem.

Chapline, G.; Matsuda, Y.

1991-08-01

74

Energy production using fission fragment rockets  

SciTech Connect

Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the following advantages: Approximately twice as efficient if one can directly convert the fission fragment energy into electricity; by reducing the buildup of a fission fragment inventory in the reactor one could avoid a Chernobyl type disaster; and collecting the fission fragments outside the reactor could simplify the waste disposal problem. 6 refs., 4 figs., 2 tabs.

Chapline, G.; Matsuda, Y.

1991-08-01

75

The newsletter of the CAMBRIDGE QUATERNARY ISSUE 36 LENT 2007  

E-print Network

entitled `The History of Quaternary Glaciations'. The work is also available online via ScienceDirect. #12 enjoys sport, especially floorball (which is played in Cambridge!) and ice hockey. Seminar Dates QDG

de Gispert, Adrià

76

Quaternary extension in southern Tibet: Field observations and tectonic implications  

Microsoft Academic Search

We summarize evidence for Quaternary and active faulting collected in the field during three Sino-French expeditions to southeastern Tibet (1980-1982). Detailed mapping of Quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the Himalayas in the last 2+\\/-0.5 m.y. The maximum horizontal principal stress in south Tibet appears

Rolando Armijo; Paul Tapponnier; J. L. Mercier; Han Tong-Lin

1986-01-01

77

The tempo of avian diversification during the Quaternary  

Microsoft Academic Search

It is generally assumed that the Quaternary was a period of heightened diversification in temperate ver- tebrate organisms. Previous molecular systematics studies have challenged this assertion. We re-examined this issue in north temperate birds using log-lineage plots and distributions of sister-taxon distances. Log- lineage plots support earlier conclusions that avian diversification slowed during the Quaternary. To test plots of empirical

Robert M. Zink; John Klicka; Brian R. Barber

2004-01-01

78

Late Quaternary geotechnical stratigraphy of North Texas continental shelf  

E-print Network

LATE QUATERNARY GEOTECHNICAL STRATIGRAPHY OF NORTH TEXAS CONTINENTAL SHELF A Thesis by JOHN SAL MUNSEY Submitted to the Graduate College of Texas Algi University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE... December 1985 Major Subject: Geology LATE QUATERNARY GEOTECHNICAL STRATIGRAPHY OF NORTH TEXAS CONTINENTAL SHELF A Thesis by JOHN SAL MUNSEY Approved as to style and content by: br' sto er . Mathewson (Cha&r of Committee) Norman R . ' ord (Memb...

Munsey, John Sal

2012-06-07

79

A Quaternary Geomagnetic Instability Time Scale  

NASA Astrophysics Data System (ADS)

Reversals and excursions of Earth's geomagnetic field create marker horizons that are readily detected in sedimentary and volcanic rocks worldwide. An accurate and precise chronology of these geomagnetic field instabilities is fundamental to understanding several aspects of Quaternary climate, dynamo processes, and surface processes. For example, stratigraphic correlation between marine sediment and polar ice records of climate change across the cryospheres benefits from a highly resolved record of reversals and excursions. The temporal patterns of dynamo behavior may reflect physical interactions between the molten outer core and the solid inner core or lowermost mantle. These interactions may control reversal frequency and shape the weak magnetic fields that arise during successive dynamo instabilities. Moreover, weakening of the axial dipole during reversals and excursions enhances the production of cosmogenic isotopes that are used in sediment and ice core stratigraphy and surface exposure dating. The Geomagnetic Instability Time Scale (GITS) is based on the direct dating of transitional polarity states recorded by lava flows using the 40Ar/39Ar method, in parallel with astrochronologic age models of marine sediments in which O isotope and magnetic records have been obtained. A review of data from Quaternary lava flows and sediments yields a GITS comprising 10 polarity reversals and 27 excursions during the past 2.6 million years. Nine of the ten reversals bounding chrons and subchrons are associated with 40Ar/39Ar ages of transitionally-magnetized lava flows. The tenth, the Guass-Matuyama chron boundary, is tightly bracketed by 40Ar/39Ar dated ash deposits. Of the 27 well-documented excursions, 14 occurred during the Matuyama chron and 13 during the Brunhes chron; 19 have been dated directly using the 40Ar/39Ar method on transitionally-magnetized volcanic rocks and form the backbone of the GITS. Excursions are clearly not the rare phenomena once thought. Rather, during the Quaternary period, they occur nearly three times as often as full polarity reversals. I will address analytical issues, including the size and consistency of system blanks, that have led to the recognition of minor (1%) discrepencies between the 40Ar/39Ar age for a particular reversal or excursion and the best astrochronologic estimates from ODP sediment cores. For example, re-analysis of lava flows from Haleakala volcano, Maui that record in detail the Matuyama-Brunhes polarity reversal have been undertaken with blanks an order of magntitude smaller and more stable than was common a decade ago. Using the modern astrochronologic calibration of 28.201 Ma for the age of the Fish Canyon sanidine standard, results thus far yield an 40Ar/39Ar age of 772 × 11 ka for the reversal that is identical to the most precise and accurate astrochronologic age of 773 × 2 ka for this reversal from ODP cores. Similarly, new dating of sanidine in the Cerro Santa Rosa I rhyolite dome, New Mexico reveals an age of 932 × 5 ka for the excursion it records, in perfect agreement with astrochronologically dated ODP core records. Work underway aims at refining the 40Ar/39Ar ages that underpin the entire GITS by further eliminating the bias between the radioisotopic and astrochronologically determined ages for several reversals and excursions.

Singer, B. S.

2013-12-01

80

Neck Influence on Fission Paths  

SciTech Connect

The neck region generates a microscopic potential, derived in correlation with the necking region within the fission-like shape on the potential theory basis. The whole microscopic potential is of the two-center type, yielding the evolution of proton and neutron level schemes from one parent to two completely separated fragment nuclei. The shell corrections are calculated using the neck in single-particle levels. The total deformation energy is obtained from the macroscopic-microscopic method. As an application, dynamic calculation is performed for the fission of {sup 236}Pu, using the multidimensional minimization within the total space of deformation of two spheroids joined by a smoothed necking region.

Gherghescu, Radu A.; Poenaru, D. N. [Horia Hulubei National Institute of Physics and Nuclear Engineering (IFIN-HH), P O Box MG-6, RO 077125 Bucharest-Magurele (Romania)

2008-01-24

81

Fission at intermediate neutron energies  

NASA Astrophysics Data System (ADS)

In the present work, as a theoretical support to the campaign of neutron cross section measurements at the n_TOF facility at CERN[1], Monte Carlo calculations of fission induced by neutrons in the energy range from 100 MeV to 1 GeV are carried out by means of a recent version of the Liege Intranuclear Cascade Model, INCL++[6], coupled with different evaporation-fission codes, such as Gemini++[7] and ABLA07[8]. Theoretical cross sections are compared with experimental data obtained by the n_TOF collaboration and perspectives for future theoretical work are outlined.

Lo Meo, S.; Mancusi, D.; Massimi, C.; Vannini, G.; Ventura, A.

2014-09-01

82

Neutronics for critical fission reactors and subcritical fission in hybrids  

SciTech Connect

The requirements of future innovative nuclear fuel cycles will focus on safety, sustainability and radioactive waste minimization. Critical fast neutron reactors and sub-critical, external source driven systems (accelerator driven and fusion-fission hybrids) have a potential role to meet these requirements in view of their physics characteristics. This paper provides a short introduction to these features.

Salvatores, Massimo [CEA-Cadarache, DEN-Dir, Bat. 101, St-Paul-Lez-Durance 13108 (France)

2012-06-19

83

Neutronics for critical fission reactors and subcritical fission in hybrids  

NASA Astrophysics Data System (ADS)

The requirements of future innovative nuclear fuel cycles will focus on safety, sustainability and radioactive waste minimization. Critical fast neutron reactors and sub-critical, external source driven systems (accelerator driven and fusion-fission hybrids) have a potential role to meet these requirements in view of their physics characteristics. This paper provides a short introduction to these features.

Salvatores, Massimo

2012-06-01

84

Nuclear fission in covariant density functional theory  

E-print Network

The current status of the application of covariant density functional theory to microscopic description of nuclear fission with main emphasis on superheavy nuclei (SHN) is reviewed. The softness of SHN in the triaxial plane leads to an emergence of several competing fission pathes in the region of the inner fission barrier in some of these nuclei. The outer fission barriers of SHN are considerably affected both by triaxiality and octupole deformation.

A. V. Afanasjev; H. Abusara; P. Ring

2013-09-12

85

Cold (neutronless) ? ternary fission of 252Cf  

NASA Astrophysics Data System (ADS)

The phenomenon of cold (neutronless) alpha ternary fission in spontaneous fission of 252Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Correlated pairs of 36Kr-60Nd, 38Sr-58Ce, 40Zr-56Ba, 42Mo-54Xe, 44Ru-52Te, and 46Pd-50Sn were observed to be associated with ? ternary fission of 252Cf. Yields of cold ? ternary fission were extracted.

Ramayya, A. V.; Hamilton, J. H.; Hwang, J. K.; Peker, L. K.; Kormicki, J.; Babu, B. R.; Ginter, T. N.; Sandulescu, A.; Florescu, A.; Carstoiu, F.; Greiner, W.; Ter-Akopian, G. M.; Oganessian, Yu. Ts.; Daniel, A. V.; Ma, W. C.; Varmette, P. G.; Rasmussen, J. O.; Asztalos, S. J.; Chu, S. Y.; Gregorich, K. E.; Macchiavelli, A. O.; MacLeod, R. W.; Cole, J. D.; Aryaeinejad, R.; Butler-Moore, K.; Drigert, M. W.; Stoyer, M. A.; Bernstein, L. A.; Lougheed, R. W.; Moody, K. J.; Prussin, S. G.; Zhu, S. J.; Griffin, H. C.; Donangelo, R.

1998-05-01

86

Induced nuclear fission viewed as a diffusion process: Transients  

Microsoft Academic Search

Induced nuclear fission is viewed as a diffusion process of the fission degree of freedom over the fission barrier. We describe this process in terms of a Fokker-Planck equation which contains the fission variable and its canonically conjugate momentum. We solve this equation numerically for several energies (temperatures) of the fissioning nucleus neglecting changes of the fission barrier due to

P. Grangé; Li Jun-Qing; H. A. Weidenmueller

1983-01-01

87

Origin of empirical threshold for dissipative fission  

NASA Astrophysics Data System (ADS)

The recent observation that the empirical threshold for fission hindrance correlates with the ratio of the threshold temperature to the temperature dependent fission barrier height is interpreted in terms of Bohr-Wheeler theory. A total fission delay of (2-4) times 10 sup -2- s is deduced from the empirical value of this ratio.

Vandenbosch, Robert

1994-11-01

88

Theoretical Description of the Fission Process  

Microsoft Academic Search

Advanced theoretical methods and high-performance computers may finally unlock the secrets of nuclear fission, a fundamental nuclear decay that is of great relevance to society. In this work, we studied the phenomenon of spontaneous fission using the symmetry-unrestricted nuclear density functional theory (DFT). Our results show that many observed properties of fissioning nuclei can be explained in terms of pathways

Witold Nazarewicz

2009-01-01

89

Budding and fission of vesicles.  

PubMed Central

We report on budding and fission of protein-free vesicles swollen from a natural lipid mixture of bovine brain sphingomyelins. Budding was induced by increasing the area-to-volume ratio through heating. Morphological changes were monitored by phase contrast microscopy and correlated with the thermal behavior of the bilayer by differential scanning calorimetry. Freeze fracture electron microscopy revealed that budding and fission are not restricted to giant vesicles but also occur on length scales relevant for cellular processes. We also observed osmotically induced budding and fission in mixtures of dimyristoyl phosphatidylcholine with cholesterol. We find that these shape transitions are driven by liquid/gel domain formation and/or coupling of the spontaneous curvature of the membrane to the local lipid composition. Our results provide evidence that coat proteins are not necessary for budding and fission of vesicles. The physics of the lipid bilayer is rich enough to explain the observed behavior. Images FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 PMID:8274633

Dobereiner, H G; Kas, J; Noppl, D; Sprenger, I; Sackmann, E

1993-01-01

90

Fluidized bed nuclear fission reactor  

Microsoft Academic Search

For the further development of nuclear fission reactors, the feasibility of a new concept is evaluated. It concerns a fluidized bed reactor in which carbon particles with a uranium core are fluidized and cooled by a high velocity pressurized helium flow. Nuclear reaction takes place if the bed is in fluidized conditions at a void fraction above 80% and it

T. H. J. J. Van Der Hagen; H. Van Dam

1996-01-01

91

Brownian motion and fission rate  

SciTech Connect

In this paper, the Fokker-Planck equation for two-dimensional Brownian motion is solved in the quasistationary approximation to study the dependence of the fission rate on the viscosity coefficient and nuclear temperature based on the liquid-drop--model parameters.

Wu, X.Z.; Zhuo, Y.Z.

1981-07-01

92

Brownian motion model of the fission process  

SciTech Connect

Fission process is considered as a multi-dimensional Brownian motion. The Fokker-Planck equation is solved and the fission probability in the steady state approximation is calculated. The results are compared with Bohr--Wheeler theory. A numerical calculation for the fission of /sup 236/U shows the capability of the model in taking the effect of viscosity into account. From the available estimate of the fission viscosity, it is estimated that such effects can reduce the fission probability by 20% to 40%.

Hu, J.; Zhong, Y.

1982-01-01

93

Space Fission Propulsion System Development Status  

NASA Technical Reports Server (NTRS)

The world's first man-made self-sustaining fission reaction was achieved in 1942. Since then fission has been used to propel submarines, generate tremendous amounts of electricity, produce medical isotopes, and provide numerous other benefits to society. Fission systems operate independently of solar proximity or orientation, and are thus well suited for deep spare or planetary surface missions. In addition, the fuel for fission systems (enriched uranium) is virtually non-radioactive. The primary safety issue with fission systems is avoiding inadvertent system start - addressing this issue through proper system design is straightforward. Despite the relative simplicity and tremendous potential of space fission systems, the development and utilization of these systems has proven elusive. The first use of fission technology in space occurred 3 April 1965 with the US launch of the SNAP-10A reactor. There have been no additional US uses of space fission system. While space fission system were used extensively by the former Soviet Union, their application was limited to earth-orbital missions. Early space fission systems must be safely and affordably utilized if Ae are to reap the benefits of advanced space fission systems.

Houts, Mike; VanDyke, Melissa; Godfroy, Tom; Pedersen, Kevin; Martin, James; Dickens, Ricky; Williams, Eric; Harper, Roger; Salvail, Pat; Hrbud, Ivana; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

94

Polygenetic Quaternary volcanism at Crater Flat, Nevada  

NASA Astrophysics Data System (ADS)

Alkali basalts erupted during the Quaternary at Crater Flat, Nevada, record a complex history of polycyclic and polygenetic volcanism. Magmas from the two main centers (Black Cone and Red Cone) are petrographically and geochemically similar, although field evidence suggests a number of separate eruptive events. High incompatible element concentrations, low Nb/La and high Zr/Y indicate that the magmas were derived by small degrees of partial melting from the lithospheric mantle. At Red Cone, a significant range of Sr, La, Ce, Ba and Th concentrations is observed with time (e.g., Sr range 1308-1848 ppm): the youngest samples having the more elevated values. However, there is only limited variation in the compatible trace elements (e.g., Sc and Ni). The array of compositions at Red Cone could not have been produced by changes in the degree of partial melting, or by fractional crystallization. Rather, a model of magma mixing is proposed between relatively enriched and depleted end-members. The cluster of Black Cone data falls consistently at the least-enriched end of the Red Cone sample arrays, suggesting that the Black Cone magma represents one of the mixing end-members. The modeling indicates that the magmatic plumbing systems of the two centers were linked, at least during the early stages of volcanism. Moreover, volcanic activity may have occurred at a number of sites along the length of the magmatic feeder zone during a single eruptive phase. This could have significant implications for volcanic hazard assessment in the region around Yucca Mountain, and the proposed nuclear waste repository.

Bradshaw, T. K.; Smith, Eugene I.

1994-11-01

95

Microscopic Description of Nuclear Fission Dynamics  

E-print Network

We discuss possible avenues to study fission dynamics starting from a time-dependent mean-field approach. Previous attempts to study fission dynamics using the time-dependent Hartree-Fock (TDHF) theory are analyzed. We argue that different initial conditions may be needed to describe fission dynamics depending on the specifics of the fission phenomenon and propose various approaches towards this goal. In particular, we provide preliminary calculations for studying fission following a heavy-ion reaction using TDHF with a density contraint. Regarding prompt muon-induced fission, we also suggest a new approach for combining the time-evolution of the muonic wave function with a microscopic treatment of fission dynamics via TDHF.

A. S. Umar; V. E. Oberacker; J. A. Maruhn; P. -G. Reinhard

2010-03-22

96

A fission fragment detector for correlated fission output studies  

NASA Astrophysics Data System (ADS)

A digital data acquisition system has been combined with a double Frisch gridded ionization chamber for use at both moderated and unmoderated neutron sources at the Los Alamos Neutron Science (LANSCE) facility. The high efficiency of the instrument combined with intense LANSCE beams and new acquisition system permits fission output measurements across 11 orders of magnitude incident neutron energy. The acquisition and analysis system is presented along with the first in-beam performance tests of the setup.

Mosby, S.; Tovesson, F.; Couture, A.; Duke, D. L.; Kleinrath, V.; Meharchand, R.; Meierbachtol, K.; O'Donnell, J. M.; Perdue, B.; Richman, D.; Shields, D.

2014-09-01

97

Space Fission Propulsion System Development Status  

NASA Technical Reports Server (NTRS)

The world's first man-made self-sustaining fission reaction was achieved in 1942. Since then fission has been used to propel submarines, generate tremendous amounts of electricity, produce medical isotopes, and provide numerous other benefits to society. Fission systems operate independently of solar proximity or orientation, and are thus well suited for deep space or planetary surface missions. In addition, the fuel for fission systems (enriched uranium) is virtually non-radioactive. The primary safety issue with fission systems is avoiding inadvertent system start. Addressing this issue through proper system design is straight-forward. Despite the relative simplicity and tremendous potential of space fission systems, the development and utilization of these systems has proven elusive. The first use of fission technology in space occurred 3 April 1965 with the US launch of the SNAP-10A reactor. There have been no additional US uses of space fission systems. While space fission systems were used extensively by the former Soviet Union, their application was limited to earth-orbital missions. Early space fission systems must be safely and affordably utilized if we are to reap the benefits of advanced space fission systems. NASA's Marshall Space Flight Center, working with Los Alamos National Laboratory (LANL), Sandia National Laboratories, and others, has conducted preliminary research related to a Safe Affordable Fission Engine (SAFE). An unfueled core has been fabricated by LANL, and resistance heaters used to verify predicted core thermal performance by closely mimicking heat from fission. The core is designed to use only established nuclear technology and be highly testable. In FY01 an energy conversion system and thruster will be coupled to the core, resulting in an 'end-to-end' nuclear electric propulsion demonstrator being tested using resistance heaters to closely mimic heat from fission. Results of the SAFE test program will be presented. The applicability of a SAFE-powered electric propulsion system to outer planet science missions will also be discussed.

Houts, M.; Van Dyke, M. K.; Godfroy, T. J.; Pedersen, K. W.; Martin, J. J.; Dickens, R.; Williams, E.; Harper, R.; Salvail, P.; Hrbud, I.

2001-01-01

98

Carbohydrate Binding, Quaternary Structure and a Novel Hydrophobic Binding Site in Two Legume  

E-print Network

Carbohydrate Binding, Quaternary Structure and a Novel Hydrophobic Binding Site in Two Legume to four. # 1999 Academic Press Keywords: protein-carbohydrate interactions; quaternary structure; legume carbohydrates in a reversible fashion, without showing enzymatic activity towards these carbohydrates. Lectins

Hamelryck, Thomas

99

The tempo of avian diversification during the Quaternary.  

PubMed Central

It is generally assumed that the Quaternary was a period of heightened diversification in temperate vertebrate organisms. Previous molecular systematics studies have challenged this assertion. We re-examined this issue in north temperate birds using log-lineage plots and distributions of sister-taxon distances. Log-lineage plots support earlier conclusions that avian diversification slowed during the Quaternary. To test plots of empirical sister-taxon distances we simulated three sets of phylogenies: constant speciation and extinction, a pulse of recent speciation, and a pulse of recent extinction. Previous opinions favour the model of recent speciation although our empirical dataset on 74 avian comparisons failed to reject a distribution derived from the constant and extinction models. Hence, it does not appear that the Quaternary was a period of exceptional rates of diversification, relative to the background rate. PMID:15101578

Zink, Robert M; Klicka, John; Barber, Brian R

2004-01-01

100

Tertiary and Quaternary Research with Remote Sensing Methods  

NASA Technical Reports Server (NTRS)

Problems encountered in mapping the Quaternary section of the Wind River Region using remote sensing methods are discussed. Analysis of the stratigraphic section is a fundamental aspect of the geologic study of sedimentary basins. Stratigraphic analysis of post-Cretaceous rocks in the Wind River Basin encounters problems of a distinctly different character from those involved in studying the pre-Cretaceous section. The interior of the basin is predominantly covered by Tertiary and Quaternary sediments. These rocks, except on the basin margin to the north, are mostly flat lying or gently dipping. The Tertiary section consists of sandstones, siltstones, and tuffaceous sediments, some variegated, but in general poorly bedded and of great lithologic similarity. The Quaternary sediments consist of terrace, fan, and debris tongue deposits, unconsolidated alluvium occupying the bottoms of modern watercourses, deposits of eolian origin and tufa. Terrace and fan deposits are compositionally diverse and reflect the lithologic diversity of the source terranes.

Conel, J. E.

1985-01-01

101

Quaternary naltrexone reverses radiogenic and morphine-induced locomotor hyperactivity  

SciTech Connect

The present study attempted to determine the relative role of the peripheral and central nervous system in the production of morphine-induced or radiation-induced locomotor hyperactivity of the mouse. Toward this end, we used a quaternary derivative of an opiate antagonist (naltrexone methobromide), which presumably does not cross the blood-brain barrier. Quaternary naltrexone was used to challenge the stereotypic locomotor response observed in these mice after either an i.p. injection of morphine or exposure to 1500 rads /sup 60/Co. The quaternary derivative of naltrexone reversed the locomotor hyperactivity normally observed in the C57BL/6J mouse after an injection of morphine. It also significantly attenuated radiation-induced locomotion. The data reported here support the hypothesis of endorphin involvement in radiation-induced and radiogenic behaviors. However, these conclusions are contingent upon further research which more fully evaluates naltrexone methobromide's capacity to cross the blood-brain barrier.

Mickley, G.A.; Stevens, K.E.; Galbraith, J.A.; White, G.A.; Gibbs, G.L.

1984-04-01

102

Characterization of Quaternary and suspected Quaternary faults, Amargosa area, Nevada and California  

SciTech Connect

This report presents the results of geologic studies that help define the Quaternary history of selected faults in the region around Yucca Mountain, Nevada. These results are relevant to the seismic-design basis of a potential nuclear waste repository at Yucca Mountain. The relevancy is based, in part, on a need for additional geologic data that became apparent in ongoing studies by S. Pezzopane (written commun., 1995) that resulted in the identification of 51 relevant and potentially relevant (see appendix A for definitions) individual and compound faults and fault zones in the 100-km-radius region around the Yucca Mountain site. These structures were divided into local and regional categories by Pezzopane (1995); this report deals with selected regional structures. In this introduction, the authors outline the scope and strategy of the studies and the tectonic environment of the studied structures.

Anderson, R.E.; Crone, A.J.; Machette, M.N.; Bradley, L.A.; Diehl, S.F.

1995-12-31

103

Nuclear-fission studies with relativistic secondary beams: analysis of fission channels  

E-print Network

Nuclear fission of several neutron-deficient actinides and pre-actinides from excitation energies around 11 MeV was studied at GSI Darmstadt by use of relativistic secondary beams. The characteristics of multimodal fission of nuclei around 226Th are systematically investigated and interpreted as the superposition of three fission channels. Properties of these fission channels have been determined for 15 systems. A global view on the properties of fission channels including previous results is presented. The positions of the asymmetric fission channels are found to be constant in element number over the whole range of systems investigated.

C. Boeckstiegel; S. Steinhaeuser; K. -H. Schmidt; H. -G. Clerc; A. Grewe; A. Heinz; M. de Jong; A. R. Junghans; J. Mueller; B. Voss

2007-12-21

104

Energy partition in nuclear fission  

Microsoft Academic Search

A scission point model (two spheroid model TSM) including semi-empirical, temperature-dependent shell correction energies for deformed fragments at scission is presented. It has been used to describe the mass-asymmetry-dependent partition of the total energy release on both fragments from spontaneous and induced fission. Characteristic trends of experimental fragment energy and neutron multiplicity data as function of incidence energy in the

A. Ruben; H. Märten; D. Seeliger

1991-01-01

105

Fission fusion hybrids- recent progress  

NASA Astrophysics Data System (ADS)

Fission-fusion hybrids enjoy unique advantages for addressing long standing societal acceptability issues of nuclear fission power, and can do this at a much lower level of technical development than a competitive fusion power plant- so it could be a nearer term application. For waste incineration, hybrids can burn intransigent transuranic residues (with the long lived biohazard) from light water reactors (LWRs) with far fewer hybrid reactors than a comparable system within the realm of fission alone. For fuel production, hybrids can produce fuel for ˜4 times as many LWRs with NO fuel reprocessing. For both waste incineration or fuel production, the most severe kind of nuclear accident- runaway criticality- can be excluded, unlike either fast reactors or typical accelerator based reactors. The proliferation risks for hybrid fuel production are, we strongly believe, far less than any other fuel production method, including today's gas centrifuges. US Thorium reserves could supply the entire US electricity supply for centuries. The centerpiece of the fuel cycle is a high power density Compact Fusion Neutron Source (major+minor radius ˜ 2.5-3.5 m), which is made feasible by the super-X divertor.

Kotschenreuther, M.; Valanju, P.; Mahajan, S.; Covele, B.

2012-03-01

106

Ice Age Earth: Late Quaternary geology and climate  

SciTech Connect

This book is a concise and readable account of the most important geologic records of the late Quaternary. It provides a synopsis of the major environmental changes that took place from approximately 13,000 to 7,000 years ago, highlighting the complexity and rapidity of past climate changes and the environmental responses they produced. The text is well illustrated, though some figures are rough and need more explanation. Also needed is a critical appraisal of the geochronology which places the paleoenvironmental records into the temporal domain. However, as a whole the book reaches its objective of summarizing the most important scientific findings about the nature of the late Quaternary climate changes.

Dawson, A.G.

1992-01-01

107

Quaternary glaciation of the Himalayan-Tibetan orogen  

Microsoft Academic Search

ABSTRACT: Glacial geological,evidence,from,throughout,the,Himalayan–Tibetan,orogen,is examined,to determine,the timing and,extent of late Quaternary,glaciation in this region and,its relation to similar changes,on a global scale. The evidence,summarised,here supports the existence of expanded,ice caps,and,extensive,valley glacier systems,throughout,the region,during,the late Quaternary. However, it cannot yet be determined whether the timing of the extent of maximum glaciation was synchronous,throughout,the entire region or whether,the response was more,varied. The lack

Lewis A. Owen; Marc W. Caffee; Robert C. Finkel; Yeong Bae Seong

2008-01-01

108

40 CFR 721.8658 - Modified polymer of vinyl acetate and quaternary ammonium compound (generic).  

Code of Federal Regulations, 2011 CFR

...2011-07-01 2011-07-01 false Modified polymer of vinyl acetate and quaternary ammonium...Chemical Substances § 721.8658 Modified polymer of vinyl acetate and quaternary ammonium...substance identified generically as modified polymer of vinyl acetate and quaternary...

2011-07-01

109

40 CFR 721.8658 - Modified polymer of vinyl acetate and quaternary ammonium compound (generic).  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Modified polymer of vinyl acetate and quaternary ammonium...Chemical Substances § 721.8658 Modified polymer of vinyl acetate and quaternary ammonium...substance identified generically as modified polymer of vinyl acetate and quaternary...

2010-07-01

110

Comparative evaluation of solar, fission, fusion, and fossil energy resources. Part 2: Power from nuclear fission  

NASA Technical Reports Server (NTRS)

Different types of nuclear fission reactors and fissionable materials are compared. Special emphasis is placed upon the environmental impact of such reactors. Graphs and charts comparing reactor facilities in the U. S. are presented.

Clement, J. D.

1973-01-01

111

Considerations on the Probability of Nuclear Fission  

Microsoft Academic Search

A semiempirical equation for fission thresholds has been extended to include the effects of unpaired nucleons on the rate of spontaneous fission. Excitation functions for the (alpha, 4n) reactions of Ra226, Th230, and U236 have been measured. These results and reported cross sections for other (alpha, 4n) reactions in the heaviest elements have been analyzed in terms of fission and

Robert Vandenbosch; Glenn T. Seaborg

1958-01-01

112

Possibility of optically induced nuclear fission  

Microsoft Academic Search

The process of nuclear fission induced by nonlinear radiative coupling to atomic electrons is considered. For 248-nm radiation at an intensity of approx. =10²¹ W\\/cm², highly relativistic currents are produced which can couple to the fission mode of nuclear decay. With irradiation for a time of approx. =100 fs the results indicate a fission probability of approx. =10⁻⁵ for \\/sub

K. Boyer; T. S. Luk; C. K. Rhodes

1988-01-01

113

Community inertia of Quaternary small mammal assemblages in North America  

E-print Network

Community inertia of Quaternary small mammal assemblages in North America Brian J. Mc is often studied by looking for the presence or absence of community inertia (lack of change) over time reference points for the amount of inertia in random biological systems, and (iii) using a robust approach

Hadly, Elizabeth

114

Impact of Quaternary Structure Dynamics on Allosteric Drug Discovery  

PubMed Central

The morpheein model of allosteric regulation draws attention to proteins that can exist as an equilibrium of functionally distinct assemblies where: one subunit conformation assembles into one multimer; a different subunit conformation assembles into a different multimer; and the various multimers are in a dynamic equilibrium whose position can be modulated by ligands that bind to a multimer-specific ligand binding site. The case study of porphobilinogen synthase (PBGS) illustrates how such an equilibrium holds lessons for disease mechanisms, drug discovery, understanding drug side effects, and identifying proteins wherein drug discovery efforts might focus on quaternary structure dynamics. The morpheein model of allostery has been proposed as applicable for a wide assortment of disease-associated proteins (Selwood, T., Jaffe, E., (2012) Arch. Bioch. Biophys, 519:131–143). Herein we discuss quaternary structure dynamics aspects to drug discovery for the disease-associated putative morpheeins phenylalanine hydroxylase, HIV integrase, pyruvate kinase, and tumor necrosis factor ?. Also highlighted is the quaternary structure equilibrium of transthyretin and successful drug discovery efforts focused on controlling its quaternary structure dynamics. PMID:23409765

Jaffe, Eileen K.

2013-01-01

115

Quantitation and Purification of Quaternary Ammonium Compounds From Halophyte Tissue  

PubMed Central

A simple and sensitive spectrophotometric assay for quaternary ammonium compounds (QACs) based on Dragendorff's reagent is described. Although not specific for a particular QAC, the assay allows for rapid survey of tissue for QAC content. A separation method for QACs in halophyte tissue containing high levels of cations was developed using ion exchange resins and ninhydrin to remove the amino acid fraction. PMID:16663593

Stumpf, David K.

1984-01-01

116

Synthesis and immobilization of quaternary ammonium cations in acidic zeolites  

Microsoft Academic Search

A general method for the synthesis of quaternary ammo- nium cations in acidic zeolites by a direct reaction of tertiary amines and alcohols is described. Zeolites and zeolite-related porous solids are ideal inorganic hosts for accommodating a large variety of guest species. 1 Bulky carbon-centered ionic intermediates, such as triar- ylmethyl cations, can be encapsulated within zeolite supercages via a

Wei Wang; Andreas Buchholz; Irina I. Ivanova; Jens Weitkampa; Michael Hunger

2003-01-01

117

Pliocene - Quaternary Faults and Potential Seismic Hazards in Southern Nevada  

Microsoft Academic Search

Known Quaternary faults in the Central Basin & Range Province (CBR) have a southern limit at about 35 degrees 30' N latitude, south of Las Vegas, NV. The boundary is generally aligned with the southern end of the Sierra Nevada and strike-slip faults, such as those in Death Valley, that accommodate the right-lateral motion transferred from the plate boundary to

W. J. Taylor; J. Wagoner; C. M. Depolo; B. Luke; J. Louie

2005-01-01

118

The newsletter of the CAMBRIDGE QUATERNARY ISSUE 32 MICHAELMAS 2005  

E-print Network

Research Institute and the British Antarctic Survey. The research environment at all levels is fostered in a wide range of Quaternary fields. This environment is unique in Britain, offering opportunities Antarctic Survey and Geography), Professor Roy Switsur (Godwin Lab), Professor Martin Jones (Archaeology

de Gispert, Adrià

119

Quaternary Paleoecology and Climate Change, Bladen County, NC  

NSDL National Science Digital Library

Students analyze a Quaternary pollen diagram from lakes in Bladen County, NC. This diagram contains (from the top down) the current deglaciation, the last glacial, and the previous interglacial. Students These lakes occur in Carolina Bays and students also evaluate a proposal that meteorite impact created the Bays.

Farley, Martin

120

The Quaternary Structure of the Saccharomyces cerevisiae Succinate Dehydrogenase  

Microsoft Academic Search

Succinate dehydrogenases and fumarate reductases are complex mitochondrial or bacterial respiratory chain proteins with remarkably similar structures and functions. Succinate dehydrogenase oxidizes succinate and reduces ubiquinone using a flavin adenine dinucle- otide cofactor and iron-sulfur clusters to transport elec- trons. A model of the quaternary structure of the tetrameric Saccharomyces cerevisiae succinate dehydrogenase was constructed based on the crystal structures

Kayode S. Oyedotun; Bernard D. Lemire

121

Quaternary fossil fish from the Kibish Formation, Omo Valley, Ethiopia  

Microsoft Academic Search

The late Quaternary Kibish Formation of the Omo Valley, southwestern Ethiopia, preserves environments reflecting a history of fluctuations in the level of nearby Lake Turkana over the past 200,000 years. The Kibish Formation has yielded a diverse mammalian fauna (as well as birds and crocodiles), stone tools, and the oldest anatomically modern Homo sapiens. Fish, the most common vertebrate fossils

Josh Trapani

2008-01-01

122

Recent dolomitization of quaternary biocalcarenites from fuerteventura (Canary Islands)  

Microsoft Academic Search

Quaternary marine and eolian biocalcarenites in the supratidal breaker and spray zone along the Barlovento coast of the peninsula Jandía, Fuerteventura (Canary Islands) are dolomitized by percolating brines with a high Mg\\/Ca ratio resulting from evaporation of seawater on the sediment's surface. Only fragments of calcareous algae primarily consisting of high-magnesian calcite are replaced by a cryptocrystalline variety of dolomite.

German Müller; Rerd Tietz

1966-01-01

123

Lignin biogeochemistry: from modern processes to Quaternary archives  

NASA Astrophysics Data System (ADS)

Lignin has been analysed as a proxy for vegetation change in the Quaternary science literature since the early 1990s in archives such as peat, lakes, and intertidal and marine sediment cores. Historically, it has been regarded as comparatively resistant to various types of degradation in comparison to other plant components. However, studies of modern biogeochemical processes affecting organic carbon have demonstrated significant degradation and alteration of lignin as it is transported through the terrestrial biosphere, including phase changes from particulate to dissolved organic matter, mineral binding and decay due to biotic and abiotic processes. The literature of such topics is vast, however it is not particularly useful to Quaternary research without a comprehensive review to link our understanding of modern processes involving lignin to Quaternary environments. This review will outline the current state of the art in lignin phenol research that is relevant to the Quaternary scientist, and highlight the potential future applications for this important biomarker for vegetation change and terrestrial organic carbon cycling.

Jex, Catherine N.; Pate, Gary H.; Blyth, Alison J.; Spencer, Robert G. M.; Hernes, Peter J.; Khan, Stuart J.; Baker, Andy

2014-03-01

124

Quaternary ammonium N,N-dichloroamines as topical, antimicrobial agents.  

PubMed

A series of backbone modified and sulfonic acid replacement analogs of our topical, clinical candidate (iii) were synthesized. Their antimicrobial activities and aqueous stabilities at pH 4 and pH 7 were determined, and has led us to identify quaternary ammonium N,N-dichloroamines as a new class of topical antimicrobial agents. PMID:19362467

Francavilla, Charles; Low, Eddy; Nair, Satheesh; Kim, Bum; Shiau, Timothy P; Debabov, Dmitri; Celeri, Chris; Alvarez, Nichole; Houchin, Ashley; Xu, Ping; Najafi, Ron; Jain, Rakesh

2009-05-15

125

Quaternary glaciation in Africa: key chronologies and climatic implications  

Microsoft Academic Search

Multiple episodes of Quaternary glaciation are evidenced on >10 distinct mountain localities throughout Africa, with the best dated sites from Kilimanjaro and Mt Kenya in equatorial East Africa. A general paucity of radiogenic dates constrains the glacial chronology, and regional sequences have largely been based on correlations by relative weathering of features. Excellent glacial moraine preservation and other features of

Bryan G. Mark; Henry A. Osmaston

2008-01-01

126

Singlet exciton fission in solution  

E-print Network

(Fig. 2c). These triplet features grow, and the singlet decays, with a characteristic time of 530 ps (Supplementary Fig. S7). This kinetic is equivalent to a triplet formation rate of 1.7 x 10-6 mol L-1 ps-1, with a bimolecular rate constant of 2.2 x... . & Nozik, A. J. Solar conversion efficiency of photovoltaic and photoelectrolysis cells with carrier multiplication absorbers. Journal of Applied Physics 100, 074510 (2006). 13. Jadhav, P. J. et al. Triplet exciton dissociation in singlet exciton fission...

Walker, Brian J.; Musser, Andrew J.; Beljonne, David; Friend, Richard H.

2013-11-17

127

Characterization of Quaternary and suspected Quaternary faults, regional studies, Nevada and California  

SciTech Connect

This report presents the results of geologic studies that help define the Quaternary history of selected faults in the region around Yucca Mountain, Nevada. These results are relevant to the seismic-design basis of a potential nuclear waste repository at Yucca Mountain. The relevancy is based, in part, on a need for additional geologic data that became apparent in ongoing studies that resulted in the identification of 51 relevant and potentially relevant individual and compound faults and fault zones in the 100-km-radius region around the Yucca Mountain site. Geologic data used to characterize the regional faults and fault zones as relevant or potentially relevant seismic sources includes age and displacement information, maximum fault lengths, and minimum distances between the fault and the Yucca Mountain site. For many of the regional faults, no paleoseismic field studies have previously been conducted, and age and displacement data are sparse to nonexistent. In November 1994, the Branch of Earthquake and Landslide Hazards entered into two Memoranda of Agreement with the Yucca Mountain Project Branch to conduct field reconnaissance, analysis, and interpretation of six relevant and six potentially relevant regional faults. This report describes the results of study of those faults exclusive of those in the Pahrump-Stewart Valley-Ash Meadows-Amargosa Valley areas. We also include results of a cursory study of faults on the west flank of the Specter Range and in the northern part of the Last Chance Range. A four-phase strategy was implemented for the field study.

Anderson, R.E.; Bucknam, R.C.; Crone, A.J.; Haller, K.M.; Machette, M.N.; Personius, S.F.; Barnhard, T.P.; Cecil, M.J.; Dart, R.L.

1995-12-31

128

Quaternary and pre-Quaternary( ) materials and processes of southeast Ohio: Overview, speculations, and recommendations  

SciTech Connect

Investigations and mapping of surficial deposits in Ohio have focused largely on the glacial deposits which cover nearly two-thirds of the state. Research on Quaternary deposits beyond the glacial border has been done by Foster, Hildreth, Andrews, Leverett, Tight, Stout, Goldthwait, Forsyth, Lessig, White, Totten, Hoyer, and Noltimier. However, growing human interaction with surficial materials of southeast Ohio now requires much more detailed mapping and characterization of these deposits. Recognition of periglacial, proglacial, and preglacial processes and materials in eastern and southern states has led to the search for similar processes and materials in southeast Ohio. Evidence for gelifraction, gelifluction, cryoturbation, and considerable periglacial colluviation is more extensive than previously thought. Proglacial deposits are also much more extensive, outwash and glaciolacustrine deposits cover large areas in southeast Ohio and are poorly mapped and characterized, or not mapped at all. Preglacial processes including a long span of profound weathering and formation of saprolite have been given little or no attention in southeast Ohio. The signature of protracted preglacial weathering still remains in this part of the state, and should change prevailing views of the terrain upon which periglacial processes worked. Mapping and characterization of these materials are urgently needed as citizens make important land-use decisions such as locating landfills and new developments.

Berg, T.M. (Ohio Geological Survey, Columbus, OH (United States))

1992-01-01

129

Nuclear fission with a Langevin equation  

Microsoft Academic Search

A microscopically derived Langevin equation is applied to thermally induced nuclear fission. An important memory effect is pointed out and discussed. A strong friction coefficient, estimated from microscopic quantities, tends to decrease the stationary limit of the fission rate and to increase the transient time. The calculations are performed with a collective mass depending on the collective variable and with

David Boilley; Eric Suraud; Abe Yasuhisa; Sakir Ayik

1993-01-01

130

Nuclear fission sustainability with hybrid nuclear cycles  

Microsoft Academic Search

An analysis is presented on the main requirements to develop nuclear fission in the context of social, economic and environmental sustainability. This analysis is mainly focused on maximizing the energy actually generated from the potential contents of fissionable natural resources. The role of fertile to fissile breeding is highlighted, as well as the need of attaining a very high safety

José M. Martínez-Val; Mireia Piera

2007-01-01

131

Options for Affordable Fission Surface Power Systems  

NASA Technical Reports Server (NTRS)

Fission surface power systems could provide abundant power anywhere on free surface of the moon or Mars. Locations could include permanently shaded regions on the moon and high latitudes on Mars. To be fully utilized; however, fission surface power systems must be safe, have adequate performance, and be affordable. This paper discusses options for the design and development of such systems.

Houts, Mike; Gaddis, Steve; Porter, Ron; VanDyke, Melissa; Martin Jim; Godfroy, Tom; Bragg-Sitton, Shannon; Garber, Anne; Pearson, Boise

2006-01-01

132

Fission reactor experiments for solid breeder blankets  

Microsoft Academic Search

The testing needs for solid breeder blanket development are different from those for liquid breeder blankets. In particular, a reasonable number of moderate volume test sites in a neutron environment are needed. Existing fission reactors are shown to be able to provide this environment with reasonable simulation of many important blanket conditions. Three major additional fission reactor tests are identified

P. J. Gierszewski; M. A. Abdou; R. Puigh

1986-01-01

133

Rapid separation of fresh fission products (draft)  

Microsoft Academic Search

The fission of highly eruiched uranium by thermal neutrons creates dozens of isotopic products. The Isotope and Nuclear Chemistry Group participates in programs that involve analysis of 'fiesh' fission products by beta counting following radiochemical separations. This is a laborious and time-consuming process that can take several days to generate results. Gamma spectroscopy can provide a more immediate path to

D. E. Dry; E. Bauer; L. A. Petersen

2003-01-01

134

Induced-Fission Imaging of Nuclear Material  

SciTech Connect

This paper presents initial results from development of the induced-fission imaging technique, which can be used for the purpose of measuring or verifying the distribution of fissionable material in an unopened container. The technique is based on stimulating fissions in nuclear material with 14 MeV neutrons from an associated-particle deuterium-tritium (D-T) generator and counting the subsequent induced fast fission neutrons with an array of fast organic scintillation detectors. For each source neutron incident on the container, the neutron creation time and initial trajectory are known from detection of the associated alpha particle of the d + t {yields} {alpha} + n reaction. Many induced fissions will lie along (or near) the interrogating neutron path, allowing an image of the spatial distribution of prompt induced fissions, and thereby fissionable material, to be constructed. A variety of induced-fission imaging measurements have been performed at Oak Ridge National Laboratory with a portable, low-dose D-T generator, including single-view radiographic measurements and three-dimensional tomographic measurements. Results from these measurements will be presented along with the neutron transmission images that have been performed simultaneously. This new capability may have applications to a number of areas in which there may be a need to confirm the presence or configuration of nuclear materials, such as nuclear material control and accountability, quality assurance, treaty confirmation, or homeland security applications.

Hausladen, Paul [ORNL] [ORNL; Blackston, Matthew A [ORNL] [ORNL; Mullens, James Allen [ORNL] [ORNL; McConchie, Seth M [ORNL] [ORNL; Mihalczo, John T [ORNL] [ORNL; Bingham, Philip R [ORNL] [ORNL; Ericson, Milton Nance [ORNL] [ORNL; Fabris, Lorenzo [ORNL] [ORNL

2010-01-01

135

Independent Isotopic Fission Yield Studies with Jyfltrap  

NASA Astrophysics Data System (ADS)

A technique to determine the independent isotopic fission yields utilizing the ability of a Penning trap to unambiguously identify the isotopes based on their mass has recently been developed at the IGISOL facility in the University of Jyväskylä. The analysis of proton induced fission of 238U at 25 MeV energy has been finalized. The results will be compared with theoretical models.

Penttilä, H.; Elomaa, V.-V.; Eronen, T.; Gorelov, D.; Hakala, J.; Jokinen, A.; Kankainen, A.; Karvonen, P.; Kolhinen, V. S.; Moore, I. D.; Rahaman, S.; Rinta-Antila, S.; Rissanen, J.; Rubchenya, V.; Saastamoinen, A.; Sonoda, T.; Weber, C.; Äystö, J.

2014-09-01

136

Get Close to a Nuclear Fission Reaction!  

NSDL National Science Digital Library

This animation-enhanced essay from the FRONTLINE Web site details what happens inside a nuclear reactor core. Learn how engineers and technicians have designed nuclear facilities to control fission activity, regulate the tremendous heat released during fission, contain radiation, and process electricity.

2004-01-29

137

Fission dynamics at low excitation energy. 2  

E-print Network

The mass asymmetry in the fission of U-236 at low excitation energy is clarified by the analysis of the trajectories obtained by solving the Langevin equations for the shape degrees of freedom. It is demonstrated that the position of the peaks in the mass distribution of fission fragments is determined mainly by the saddle point configuration originating from the shell correction energy. The width of the peaks, on the other hand, results from the shape fluctuations close to the scission point caused by the random force in the Langevin equation. We have found out that the fluctuations between elongated and compact shapes are essential for the fission process. According to our results the fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup, but is accompanied by the fluctuations between elongated and compact shapes. This picture presents a new viewpoint of fission dynamics and the splitting mechanism.

Aritomo, Y; Ivanyuk, F A

2014-01-01

138

Los Alamos National Laboratory Fission Basis  

SciTech Connect

This report is an overview of two main publications that provide a comprehensive review of the Los Alamos National Laboratory (LANL) Fission Basis. The first is the experimental paper, {sup F}ission Product Data Measured at Los Alamos for Fission Spectrum and Thermal Neutrons on {sup 239}Pu, {sup 235}U, {sup 238}U, [Selby, H. D., et al., Nucl. Data Sheets, Vol. 111 2010, pp. 2891-2922] and the second is the theoretical paper, Fission Product Yields from Fission Spectrum n+ {sup 239}Pu for ENDF/B-VII.1, [Chadwick, M. B., et al., Nucl. Data Sheets, Vol. 111, 2010, pp. 2923-2964]. One important note is that none of this work would have been possible without the great documentation of the experimental details and results by G.W. Knobeloch, G. Butler, C.I. Browne, B. Erdal, B. Bayhurst, R. Prestwood, V. Armijo, J. Hasty and many others. (authors)

Keksis, A.L.; Chadwick, M.B.; Selby, H.D.; Mac Innes, M.R.; Barr, D.W.; Meade, R.A.; Burns, C.J.; Wallstrom, T.C. [Los Alamos National Laboratory, NM 87545 (United States)

2011-07-01

139

Fifty years with nuclear fission. Volume 1  

SciTech Connect

The news of the discovery of nuclear fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fifieth anniversary of its discovery by holding a topical meeting entitled, ``Fifty Years with Nuclear Fission,`` in the United States during the year 1989. The objective of the meeting was to bring together pioneers of the nuclear industry and other scientists and engineers to report on reminiscences of the past and on the more recent development in fission science and technology. The conference highlighted the early pioneers of the nuclear industry by dedicated a full day (April 26), consisting of two plenary sessions, at the National Academy of Sciences (NAS) in Washington, DC. More recent developments in fission science and technology in addition to historical reflections were topics for two fully days of sessions (April 27 and 28) at the main site of the NIST in Gaithersburg, Maryland. The wide range of topics covered in this Volume 1 by this topical meeting included plenary invited, and contributed sessions entitled: Preclude to the First Chain Reaction -- 1932 to 1942; Early Fission Research -- Nuclear Structure and Spontaneous Fission; 50 Years of Fission, Science, and Technology; Nuclear Reactors, Secure Energy for the Future; Reactors 1; Fission Science 1; Safeguards and Space Applications; Fission Data; Nuclear Fission -- Its Various Aspects; Theory and Experiments in Support of Theory; Reactors and Safeguards; and General Research, Instrumentation, and By-Product. The individual papers have been cataloged separately.

Behrens, J.W.; Carlson, A.D. [eds.] [National Institute of Standards and Technology, Gaithersburg, MD (United States)

1989-12-31

140

Unexpected primitive rodents in the Quaternary of Argentina  

NASA Astrophysics Data System (ADS)

This article describes the first fossils recorded in the Hernandarias Formation (Pleistocene) in Entre Ríos province (eastern Argentina). They are represented by three teeth assigned to the caviomorph rodents (Rodentia, Mammalia) Aenigmys diamantensis gen. et sp. nov. and Eumysops. To establish the phylogenetic affinities of the two most enigmatic teeth, their enamel microstructure was studied. Aenigmys diamantensis is considered the most primitive taxon of a clade formed by Dinomyidae-Neoepiblemidae-Heptaxodontidae. Evidence of the close relationships among these families also is presented herein. The new fossils reinforce previous hypotheses about the survival of primitive Brazilian taxa after their extinction in the Pampas and Patagonia of southern South America. They also show that the diversity of caviomorph rodents during the Quaternary was greater than supposed and that an important Quaternary extinction, not previously detected, affected several lineages. With the available evidence, it is not possible to determine if these rodents indicate a warm pulse or a particular biogeographic situation in Entre Ríos.

Vucetich, María G.; Vieytes, Emma C.; Verzi, Diego H.; Noriega, Jorge I.; Tonni, Eduardo P.

2005-10-01

141

Helix Bundle Quaternary Structure from [alpha]/[beta]-Peptide Foldamers  

SciTech Connect

The function of a protein generally depends on adoption of a specific folding pattern, which in turn is determined by the side chain sequence along the polypeptide backbone. Here we show that the sequence-encoded structural information in peptides derived from yeast transcriptional activator GCN4 can be used to prepare hybrid {alpha}/{beta}-peptide foldamers that adopt helix bundle quaternary structures. Crystal structures of two hybrid {alpha}/{beta}-peptides are reported along with detailed structural comparison to {alpha}-peptides of analogous side chain sequence. There is considerable homology between {alpha}- and {alpha}/{beta}-peptides at the level of helical secondary structure, with modest but significant differences in the association geometry of helices in the quaternary structure.

Horne, W. Seth; Price, Joshua L.; Keck, James L.; Gellman, Samuel H. (UW-MED)

2008-11-18

142

Quaternary fluvial archives: achievements of the Fluvial Archives Group  

NASA Astrophysics Data System (ADS)

In their geomorphological and sedimentary records, rivers provide valuable archives of environments and environmental change, at local to global scales. In particular, fluvial sediments represent databanks of palaeoenvironment and palaeoclimatic (for example) of fossils (micro- and macro-), sedimentary and post-depositional features and buried soils. Well-dated sequences are of the most value, with dating provided by a wide range of methods, from radiometric (numerical) techniques to included fossils (biostratigraphy) and/or archaeological material. Thus Quaternary fluvial archives can also provide important data for studies of Quaternary biotic evolution and early human occupation. In addition, the physical disposition of fluvial sequences, be it as fragmented terrace remnants or as stacked basin-fills, provides valuable information about geomorphological and crustal evolution. Since rivers are long-term persistent features in the landscape, their sedimentary archives can represent important frameworks for regional Quaternary stratigraphy. Fluvial archives are distributed globally, being represented on all continents and across all climatic zones, with the exception of the frozen polar regions and the driest deserts. In 1999 the Fluvial Archives Group (FLAG) was established, as a working group of the Quaternary Research Association (UK), aimed at bringing together those interested in such archives. This has evolved into an informal organization that has held regular biennial combined conference and field-trip meetings, has co-sponsored other meetings and conference sessions, and has presided over two International Geoscience Programme (IGCP) projects: IGCP 449 (2000-2004) 'Global Correlation of Late Cenozoic Fluvial Deposits' and IGCP 518 (2005-2007) 'Fluvial sequences as evidence for landscape and climatic evolution in the Late Cenozoic'. Through these various activities a sequence of FLAG publications has appeared, including special issues in a variety of journals, amassing a substantial volume of information on fluvial archives worldwide. This presentation will highlight some of these data and will describe important patterns observed and interpretations arising therefrom.

Bridgland, David; Cordier, Stephane; Herget, Juergen; Mather, Ann; Vandenberghe, Jef; Maddy, Darrel

2013-04-01

143

Activity of an insoluble antimicrobial quaternary amine complex in plastics  

Microsoft Academic Search

Summary Growth and survival ofStaphylococcus aureus, Pseudomonas aeruginosa., Klebsiella pneumoniae andAspergillus niger were reduced by a low-solubility polysubstituted.-quaternary amine complex (InterseptR) processed into the matrices of ethylene vinyl acetate, polystyrene and polyethylene., Recoveries of challenge microorganisms from agar film overlays and determination of the effects of the complex on radiolabelled-leucine transport by adhered cells and bacterial biofilms were more suitable

D. L. Price; A. D. Sawant; D. G. Ahearn

1991-01-01

144

The impact of Quaternary Ice Ages on mammalian evolution.  

PubMed Central

The Quaternary was a time of extensive evolution among mammals. Most living species arose at this time, and many of them show adaptations to peculiarly Quaternary environments. The latter include continental northern steppe and tundra, and the formation of lakes and offshore islands. Although some species evolved fixed adaptations to specialist habitats, others developed flexible adaptations enabling them to inhabit broad niches and to survive major environmental changes. Adaptation to short-term (migratory and seasonal) habitat change probably played a part in pre-adapting mammal species to the longer-term cyclical changes of the Quaternary. Fossil evidence indicates that environmental changes of the order of thousands of years have been sufficient to produce subspeciation, but speciation has typically required one hundred thousand to a few hundred thousand years, although there are both shorter and longer exceptions. The persistence of taxa in environments imposing strong selective regimes may have been important in forcing major adaptive change. Individual Milankovitch cycles are not necessarily implicated in this process, but nor did they generally inhibit evolutionary change among mammals: many evolutionary divergences built over multiple climatic cycles. Deduction of speciation timing requires input from fossils and modern phenotypic and breeding data, to complement and constrain mitochondrial DNA coalescence dates which appear commonly to overestimate taxic divergence dates and durations of speciation. Migrational and evolutionary responses to climate change are not mutually exclusive but, on the contrary, may be synergistic. Finally, preliminary analysis suggests that faunal turnover, including an important element of speciation, was elevated in the Quaternary compared with the Neogene, at least in some biomes. Macroevolutionary species selection or sorting has apparently resulted in a modern mammalian fauna enriched with fast-reproducing and/or adaptively generalist species. PMID:15101579

Lister, Adrian M

2004-01-01

145

Quaternary freshwater Ostracoda from the Great Salt Lake Basin  

E-print Network

THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS October 23, 1975 Paper 78 QUATERNARY FRESHWATER OSTRACODA FROM THE GREAT SALT LAKE BASIN, UTAH' KENNETH H. LISTER Department of Geology, The University of Kansas, Lawrence; present address: 317... Via Anita, Redondo Beach, California ABSTRACT Ostracodes are described from two cores, each more than 200 m long taken in Quater- nary sediments of the Great Salt Lake Basin, Utah. Thirty-one species of Ostracoda in thirteen genera have been identified...

Lister, K. H.

1975-10-23

146

Precise timing and rate of massive late Quaternary soil denudation  

Microsoft Academic Search

Strontium isotopes are a unique tool to study soil-erosion dynamics. Changes in Sr isotope ratios (87Sr\\/86Sr) provide a record of late Quaternary landscape denudation of the Edwards Plateau of central Texas, United States. The use of Sr isotopes as a tracer for soil erosion is based on the observation that, in central Texas, the 87Sr\\/86Sr ratio of soil correlates with

M. Jennifer Cooke; Libby A. Stern; Jay L. Banner; Lawrence E. Mack; Thomas W. Stafford; Rickard S. Toomey

2003-01-01

147

Composite aromatic boxes for enzymatic transformations of quaternary ammonium substrates.  

PubMed

Cation-? interactions to cognate ligands in enzymes have key roles in ligand binding and enzymatic catalysis. We have deciphered the key functional role of both charged and aromatic residues within the choline binding subsite of CTP:phosphocholine cytidylyltransferase and choline kinase from Plasmodium falciparum. Comparison of quaternary ammonium binding site structures revealed a general composite aromatic box pattern of enzyme recognition sites, well distinguished from the aromatic box recognition site of receptors. PMID:25283789

Nagy, Gergely N; Marton, Lívia; Contet, Alicia; Ozohanics, Olivér; Ardelean, Laura-Mihaela; Révész, Agnes; Vékey, Károly; Irimie, Florin Dan; Vial, Henri; Cerdan, Rachel; Vértessy, Beáta G

2014-12-01

148

Vegetation ecotone dynamics in Southwest Alaska during the Late Quaternary  

Microsoft Academic Search

To examine Late Quaternary vegetation change across the modern vegetation gradient from continuous boreal forest (central Alaska) to Betula shrub tundra (Bristol Bay region), pollen records from Idavain and Snipe Lakes are described and compared to those of four other sites in southwest Alaska. Major features of the vegetation history at Idavain Lake include herb-dominated tundra (ca 14–12kaBP), mixed herb\\/Betula

Linda B. Brubaker; Patricia M. Anderson; Feng Sheng Hu

2001-01-01

149

Fifty years with nuclear fission. Volume 2  

SciTech Connect

The news of the discovery of nucler fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fiftieth anniversary of its discovery by holding a topical meeting entitled, ``Fifty years with nuclear fission,`` in the United States during the year 1989. The objective of the meeting was to bring together pioneers of the nuclear industry and other scientists and engineers to report on reminiscences of the past and on the more recent developments in fission science and technology. The conference highlighted the early pioneers of the nuclear industry by dedicating a full day (April 26), consisting of two plenary sessions, at the National Academy of Sciences (NAS) in Washington, DC. More recent developments in fission science and technology in addition to historical reflections were topics for two full days of sessions (April 27 and 28) at the main sites of the NIST in Gaithersburg, Maryland. The wide range of topics covered by Volume 2 of this topical meeting included plenary invited, and contributed sessions entitled, Nuclear fission -- a prospective; reactors II; fission science II; medical and industrial applications by by-products; reactors and safeguards; general research, instrumentation, and by-products; and fission data, astrophysics, and space applications. The individual papers have been cataloged separately.

Behrens, J.W.; Carlson, A.D. [eds.] [National Institute of Standards and Technology, Gaithersburg, MD (United States)

1989-12-31

150

Multiple sources of alkanes in Quaternary oceanic sediment of Antarctica  

USGS Publications Warehouse

Normal alkanes (n-C13n-C36), isoprenoid hydrocarbons (i-C15, i-C16, i-C18, i-C19, and i-C20) triterpanes (C27C32), and (C27C29) are present in low concentrations offshore Antarctica in near-surface, Quaternary sediment of the Wilkes Land continental margin and of the western Ross Sea. The distributions of these hydrocarbons are interpreted relative to possible sources and processes. The hydrocarbons appear to be mixtures of primary and recycled material from marine and terrigenous sources. The n-alkanes are most abundant and are characterized by two distinct populations, one of probable marine origin and the other likely from terrigenous, vascular plant sources. Because the continent of Antarctica today is devoid of higher plants, the plant-derived hydrocarbons in these offshore sediments probably came from wind-blown material and recycled Antarctic sediment that contains land-plant remains from an earlier period of time. Isoprenoid hydrocarbons are partially recycled and mainly of marine origin; the dominance of pristane over phytane suggests oxic paleoenvironmental conditions. Both modern and ancient triterpanes and steranes are present, and the distribution of these indicates a mixture of primary and recycled bacterial, algal, and possible higher-plant materials. Although the sampled sediments were deposited during the Quaternary, they apparently contain a significant component of hydrocarbons of pre-Quaternary age. ?? 1987.

Kvenvolden, K.A.; Rapp, J.B.; Golan-Bac, M.; Hostettler, F.D.

1987-01-01

151

Ecological impacts of the late Quaternary megaherbivore extinctions.  

PubMed

As a result of the late Quaternary megafaunal extinctions (50,000-10,000 before present (BP)), most continents today are depauperate of megaherbivores. These extinctions were time-transgressive, size- and taxonomically selective, and were caused by climate change, human hunting, or both. The surviving megaherbivores often act as ecological keystones, which was likely true in the past. In spite of this and extensive research on the causes of the Late Quaternary Extinctions, the long-term ecological consequences of the loss of the Pleistocene megafauna remained unknown until recently, due to difficulties in linking changes in flora and fauna in paleorecords. The quantification of Sporormiella and other dung fungi have recently allowed for explicit tests of the ecological consequences of megafaunal extirpations in the fossil pollen record. In this paper, I review the impacts of the loss of keystone megaherbivores on vegetation in several paleorecords. A growing number of studies support the hypothesis that the loss of the Pleistocene megafauna resulted in cascading effects on plant community composition, vegetation structure and ecosystem function, including increased fire activity, novel communities and shifts in biomes. Holocene biota thus exist outside the broader evolutionary context of the Cenozoic, and the Late Quaternary Extinctions represent a regime shift for surviving plant and animal species. PMID:24649488

Gill, Jacquelyn L

2014-03-01

152

Simulation of Quaternary glacial cycles with fully interactive carbon cycle  

NASA Astrophysics Data System (ADS)

Although it is generally accepted that, as postulated by the Milankovitch theory, Earth's orbital variations play an important role in Quaternary climate dynamics, the mechanism of glacial cycles still not fully understood. Among major scientific challenges remains the understanding of the nature of 100 kyr cycles that dominated climate variability over the late part of Quaternary and a strong link between ice volume and atmospheric CO2 concentration. Here using the Earth system model of intermediate complexity CLIMBER-2 which includes all major components of the Earth system - atmosphere, ocean, land surface, northern hemisphere ice sheets, terrestrial biota and soil carbon, aeolian dust and marine biogeochemistry - we performed simulations of the Quaternary climate cycles using variations in the Earth's orbital parameters as the only prescribed climate forcing. Thanks to high computational efficiency of the CLIMBER-2 model we performed a large suite of model simulations aimed on better understanding the role of individual processes. We found that the main drivers of atmospheric CO2 evolve with time: changes in sea surface temperature and volume of bottom water of southern origin exert CO2 control during glacial inception and deglaciation, while changes in carbonate chemistry and marine biology are dominant during the first and second parts of the glacial cycles, respectively. Changes in terrestrial carbon pool play significant role during deglaciation. We also discus how paleoclimate records, such as atmospheric and deep oceanic d13C, can help to constrain model parameters and test hypotheses on the mechanism of glacial-interglacial CO2 variations.

Ganopolski, Andrey; Brovkin, Victor

2014-05-01

153

Genetic ages for Quaternary topographic evolution: A new dating tool  

NASA Astrophysics Data System (ADS)

All eukaryote populations accumulate mutations in their mitochondrialDNA (mtDNA) over time, so reproductively isolated populationsbecome characterized by distinct mtDNA lineages. In addition,the degree of genetic differentiation among distinct populationscan be used to estimate time elapsed since their isolation.We have identified an informative system for calibrating themtDNA "clock" by genetically comparing freshwater galaxiid fishpopulations isolated in different river drainages. Calibrationusing a range of Quaternary geological events in southern NewZealand shows that the mtDNA divergence rate in galaxiid fishesis between 1% and 2%/100 k.y. up to 250 k.y., with the ratedecreasing with increasing age. The estimated divergence rateslows to around 4%/m.y. for the middle Quaternary, althoughcalibration is poor. A calibration curve has been fitted toall data: divergence (%) = -2.2e-9t + 2.5t + 2.2,where t is isolation age (in m.y.). This molecular clock haspotential as a dating tool for glacially related and activetectonic events that have caused river drainage changes in thelate Quaternary in the Southern Hemisphere, where galaxiidsare widespread. An application of this dating tool to an examplein northern South Island uses three different species of freshwater-limitedfish, and all three data sets imply formation of a drainagedivide at 320 ± 110 ka, at about the time of a majorglacial advance though the divide (oxygen isotope stage 8).

Craw, Dave; Burridge, Chris; Norris, Richard; Waters, Jon

2008-01-01

154

Quaternary diversification in European alpine plants: pattern and process.  

PubMed Central

Molecular clock approaches applied previously to European alpine plants suggest that Primula sect. Auricula, Gentiana sect. Ciminalis and Soldanella diversified at the beginning of the Quaternary or well within this period, whereas Globularia had already started diversifying in the (Late-)Tertiary. In the first part of this paper we present evidence that, in contrast to Globularia and Soldanella, the branching patterns of the molecular internal transcribed spacer phylogenies of both Primula and Gentiana are incompatible with a constant-rates birth-death model. In both of these last two taxa, speciation probably decreased through Quaternary times, perhaps because of some niche-filling process and/or a decrease in specific range size. In the second part, we apply nonlinear regression analyses to the lineage-through-time plots of P. sect. Auricula to test a range of capacity-dependent models of diversification, and the effect of Quaternary climatic oscillations on diversification and extinction. At least for one major clade of sect. Auricula there is firm evidence that both diversification and extinction are a function of temperature. Intriguingly, temperature appears to be correlated positively with extinction, but negatively with diversification. This suggests that diversification did not take place, as previously assumed, in geographical isolation in high-altitude interglacial refugia, but rather at low altitudes in geographically isolated glacial refugia. PMID:15101582

Kadereit, Joachim W; Griebeler, Eva Maria; Comes, Hans Peter

2004-01-01

155

FISSION YIELDS OF Sr⁹°  

Microsoft Academic Search

Fission yields were determined from 14-Mev neutrons on U²³⁵ and U\\/;\\u000a sup 238\\/, thermal neutrons on U²³⁵, and fission spectrum neutrons on U\\/sup ;\\u000a 235\\/, U²³⁸, and Pu²³⁹. The number of fissions was determined for the ;\\u000a Mo⁹⁹ activity. The Sr⁹° was chemically separated and Y⁹° ;\\u000a allowed to reach equilibrium. The Y⁹° was separated and counted. ;\\u000a (W.D.M.)

Bayhurst

2009-01-01

156

Fission Matrix Capability for MCNP Monte Carlo  

SciTech Connect

In a Monte Carlo criticality calculation, before the tallying of quantities can begin, a converged fission source (the fundamental eigenvector of the fission kernel) is required. Tallies of interest may include powers, absorption rates, leakage rates, or the multiplication factor (the fundamental eigenvalue of the fission kernel, k{sub eff}). Just as in the power iteration method of linear algebra, if the dominance ratio (the ratio of the first and zeroth eigenvalues) is high, many iterations of neutron history simulations are required to isolate the fundamental mode of the problem. Optically large systems have large dominance ratios, and systems containing poor neutron communication between regions are also slow to converge. The fission matrix method, implemented into MCNP[1], addresses these problems. When Monte Carlo random walk from a source is executed, the fission kernel is stochastically applied to the source. Random numbers are used for: distances to collision, reaction types, scattering physics, fission reactions, etc. This method is used because the fission kernel is a complex, 7-dimensional operator that is not explicitly known. Deterministic methods use approximations/discretization in energy, space, and direction to the kernel. Consequently, they are faster. Monte Carlo directly simulates the physics, which necessitates the use of random sampling. Because of this statistical noise, common convergence acceleration methods used in deterministic methods do not work. In the fission matrix method, we are using the random walk information not only to build the next-iteration fission source, but also a spatially-averaged fission kernel. Just like in deterministic methods, this involves approximation and discretization. The approximation is the tallying of the spatially-discretized fission kernel with an incorrect fission source. We address this by making the spatial mesh fine enough that this error is negligible. As a consequence of discretization we get a spatially low-order kernel, the fundamental eigenvector of which should converge faster than that of continuous kernel. We can then redistribute the fission bank to match the fundamental fission matrix eigenvector, effectively eliminating all higher modes. For all computations here biasing is not used, with the intention of comparing the unaltered, conventional Monte Carlo process with the fission matrix results. The source convergence of standard Monte Carlo criticality calculations are, to some extent, always subject to the characteristics of the problem. This method seeks to partially eliminate this problem-dependence by directly calculating the spatial coupling. The primary cost of this, which has prevented widespread use since its inception [2,3,4], is the extra storage required. To account for the coupling of all N spatial regions to every other region requires storing N{sup 2} values. For realistic problems, where a fine resolution is required for the suppression of discretization error, the storage becomes inordinate. Two factors lead to a renewed interest here: the larger memory available on modern computers and the development of a better storage scheme based on physical intuition. When the distance between source and fission events is short compared with the size of the entire system, saving memory by accounting for only local coupling introduces little extra error. We can gain other information from directly tallying the fission kernel: higher eigenmodes and eigenvalues. Conventional Monte Carlo cannot calculate this data - here we have a way to get new information for multiplying systems. In Ref. [5], higher mode eigenfunctions are analyzed for a three-region 1-dimensional problem and 2-dimensional homogenous problem. We analyze higher modes for more realistic problems. There is also the question of practical use of this information; here we examine a way of using eigenmode information to address the negative confidence interval bias due to inter-cycle correlation. We apply this method mainly to four problems: 2D pressurized water reactor (PWR) [6],

Carney, Sean E. [Los Alamos National Laboratory; Brown, Forrest B. [Los Alamos National Laboratory; Kiedrowski, Brian C. [Los Alamos National Laboratory; Martin, William R. [Los Alamos National Laboratory

2012-09-05

157

Quaternary extension in southern Tibet: Field observations and tectonic implications  

NASA Astrophysics Data System (ADS)

We summarize evidence for Quaternary and active faulting collected in the field during three Sino-French expeditions to southeastern Tibet (1980-1982). Detailed mapping of Quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the Himalayas in the last 2 ± 0.5 m.y. The maximum horizontal principal stress in south Tibet appears to be only the intermediate principal stress ?2, ?1 being vertical. South of the "chord" joining the eastern and western syntaxes of the Himalayan arc, extensional strains are principally localized within seven regularly spaced rift zones, three of which have been studied in some detail. The extension direction is determined to be N96° E ± 7° mainly from statistical averaging of strikes of newly formed normal faults. Throw rates on normal faults are evaluated for different time spans (2 ± 0.5 m.y., 60 ± 40 kyr, and 10 ± 2 kyr B.P.), using structural and topographic reliefs, as well as synglacial and postglacial vertical offsets. The rate of Quaternary extension is about 1% m.y.-1 along an 1100-km-long ESE traverse across south Tibet. This corresponds to a "spreading" rate of 1 ± 0.6 cm/yr. This rate and the divergent horizontal projections of slip vectors of earthquakes along the Himalayan front constrain the rate at which rigid India underthrusts southern Tibet to be 2 ± 1 cm/yr. Although most of the normal faults appear to be independent of, and nearly orthogonal to, the ?E-W Mesozoic-Tertiary tectonic fabric, the Yadong-Gulu rift appears to be guided for over 130 km by the older, oblique (?NE-SW) Nyainqentanglha range and fault zones along it. This reactivated zone is the most prominent left-lateral strike-slip fault system in SE Tibet. Excepting this zone, and the vicinity of the SE extremity of the Karakorum fault, Quaternary strike-slip faulting is rare in south Tibet, i.e., south of the chord between the syntaxes of the Himalayan arc. North of the chord, the tectonic style is different. There minor conjugate strike-slip faulting is widespread and appears to control Quaternary normal faulting, which is more diffuse and subdued than in south Tibet. Along the chord, the presence of a major zone of active right-lateral, en échelon strike-slip faults (Karakorum-Jiali fault zone) probably reflects the greater facility of eastward extrusion in north central Tibet, in response to the northward push of India. The eastern Himalayan syntaxis may be an obstacle to such extrusion movements south of the chord.

Armijo, Rolando; Tapponnier, Paul; Mercier, J. L.; Han, Tong-Lin

1986-12-01

158

Future challenges for nuclear data research in fission (u)  

SciTech Connect

I describe some high priority research areas in nuclear fission, where applications in nuclear reactor technologies and in modeling criticality in general are demanding higher accuracies in our databases. We focus on fission cross sections, fission neutron spectra, and fission product data.

Chadwick, Mark B [Los Alamos National Laboratory

2010-01-01

159

Digital release of the Alaska Quaternary fault and fold database  

NASA Astrophysics Data System (ADS)

The Alaska Division of Geological & Geophysical Surveys (DGGS) has designed a Quaternary fault and fold database for Alaska in conformance with standards defined by the U.S. Geological Survey for the National Quaternary fault and fold database. Alaska is the most seismically active region of the United States, however little information exists on the location, style of deformation, and slip rates of Quaternary faults. Thus, to provide an accurate, user-friendly, reference-based fault inventory to the public, we are producing a digital GIS shapefile of Quaternary fault traces and compiling summary information on each fault. Here, we present relevant information pertaining to the digital GIS shape file and online access and availability of the Alaska database. This database will be useful for engineering geologic studies, geologic, geodetic, and seismic research, and policy planning. The data will also contribute to the fault source database being constructed by the Global Earthquake Model (GEM), Faulted Earth project, which is developing tools to better assess earthquake risk. We derived the initial list of Quaternary active structures from The Neotectonic Map of Alaska (Plafker et al., 1994) and supplemented it with more recent data where available. Due to the limited level of knowledge on Quaternary faults in Alaska, pre-Quaternary fault traces from the Plafker map are shown as a layer in our digital database so users may view a more accurate distribution of mapped faults and to suggest the possibility that some older traces may be active yet un-studied. The database will be updated as new information is developed. We selected each fault by reviewing the literature and georegistered the faults from 1:250,000-scale paper maps contained in 1970's vintage and earlier bedrock maps. However, paper map scales range from 1:20,000 to 1:500,000. Fault parameters in our GIS fault attribute tables include fault name, age, slip rate, slip sense, dip direction, fault line type (i.e., well constrained, moderately constrained, or inferred), and mapped scale. Each fault is assigned a three-integer CODE, based upon age, slip rate, and how well the fault is located. This CODE dictates the line-type for the GIS files. To host the database, we are developing an interactive web-map application with ArcGIS for Server and the ArcGIS API for JavaScript from Environmental Systems Research Institute, Inc. (Esri). The web-map application will present the database through a visible scale range with each fault displayed at the resolution of the original map. Application functionality includes: search by name or location, identification of fault by manual selection, and choice of base map. Base map options include topographic, satellite imagery, and digital elevation maps available from ArcGIS on-line. We anticipate that the database will be publically accessible from a portal embedded on the DGGS website by the end of 2011.

Koehler, R. D.; Farrell, R.; Burns, P.; Combellick, R. A.; Weakland, J. R.

2011-12-01

160

The primary charge of fission products from the thermal neutron fission of 235U  

Microsoft Academic Search

The average primary charge Zp of fission products from thermal neutron fission of 235U is determined by measuring the number of beta-decays suffered by the fission products, which are mass separated with the gas-filled mass separator of the research reactor FRJ-2. The measurement is performed with a 4pi plastic detector to avoid errors caused by conversion electrons and gamma-rays emitted

K. Sistemich; P. Armbruster; J. Eidens; E. Roeckl

1969-01-01

161

Database and Map of Quaternary Faults and Folds in Peru and its Offshore Region  

USGS Publications Warehouse

This publication consists of a main map of Quaternary faults and fiolds of Peru, a table of Quaternary fault data, a region inset map showing relative plate motion, and a second inset map of an enlarged area of interest in southern Peru. These maps and data compilation show evidence for activity of Quaternary faults and folds in Peru and its offshore regions of the Pacific Ocean. The maps show the locations, ages, and activity rates of major earthquake-related features such as faults and fault-related folds. These data are accompanied by text databases that describe these features and document current information on their activity in the Quaternary.

Machare, Jose; Fenton, Clark H.; Machette, Michael N.; Lavenu, Alain; Costa, Carlos; Dart, Richard L.

2003-01-01

162

QUATERNARY RESEARCH 29, 93-112 (1988) Lithospheric Thickness, Antarctic Deglaciation History, and Ocean  

E-print Network

QUATERNARY RESEARCH 29, 93- 112 (1988) Lithospheric Thickness, Antarctic Deglaciation History the delay of West Antarctic melting and the thickness of the lithosphere required to reconcile the observed

Peltier, W. Richard

163

Fission fragment angular distribution in heavy-ion-induced fission with anomalous behavior  

NASA Astrophysics Data System (ADS)

Fission fragment angular distribution in heavy-ion-induced fission reactions is of particular importance. Transition state theory is provided to determine the angular distribution of fission fragments which includes standard saddle-point statistical and standard scission-point statistical models. The standard saddle-point statistical model was not able to reproduce the experimental fission fragment angular anisotropies for several heavy-ion-induced fission systems. In contrast to the standard saddle-point model, the standard scission-point statistical model was fairly successful in the prediction of angular anisotropy in heavy-ion-induced fission reaction systems with an anomalous behavior in angular anisotropy of fission fragments, but this model is not widely used as the standard saddle-point statistical model. In this research, a generalized model is introduced for the prediction of fission fragments angular anisotropy in the heavy-ion-induced fission reaction systems having an anomalous behavior. For this purpose, we study the N14,O16,F19+Th232;O16,F19+U238;Mg24,Si28,S32+Pb208;S32+Au197; and O16+Cm248 reaction systems. Finally, it is shown that the presented model is much more successful than previous models.

Soheyli, S.; Feizi, B.

2014-08-01

164

Angular momenta of fission fragments in the ?-accompanied fission of 252Cf  

NASA Astrophysics Data System (ADS)

For the first time, average angular momenta of the ternary fission fragments 100, 102Zr, 106Mo, 144, 146Ba and 138, 140, 142Xe from the ?-accompanied fission of 252Cf were obtained from relative intensities of prompt ?-ray transitions with the use of the statistical model calculation. Average values of the angular momenta were compared with the corresponding values for the same fission fragments from the binary fission of 252Cf. Results indicate the presence of a decreasing trend in the average values of angular momenta induced in ternary fission fragments compared to the same binary fission fragments. On the average, the total angular momentum extracted for ternary fission fragments is ˜1.4 ? lower than in binary fission. Consequently, results indicate that the mechanism of the ternary ?-particles emission may directly effect an induction of angular momenta of fission fragments, and possible scenarios of such mechanisms are discussed. Further, the dependence of the angular momenta of 106Mo and 140Xe on the number of emitted neutrons from correlated pairs of primary fragments was obtained also showing a decreasing dependence of average angular momenta with increasing number of emitted neutrons. Consequences are briefly discussed.

Jandel, M.; Kliman, J.; Krupa, L.; Morhá?, M.; Hamilton, J. H.; Kormicki, J.; Ramayya, A. V.; Hwang, J. K.; Luo, Y. X.; Fong, D.; Gore, P.; Ter-Akopian, G. M.; Oganessian, Yu. Ts.; Rodin, A. M.; Fomichev, A. S.; Popeko, G. S.; Daniel, A. V.; Rasmussen, J. O.; Macchiavelli, A. O.; Stoyer, M. A.; Donangelo, R.; Cole, J. D.

2005-06-01

165

Measurement of Prompt Fission ?-ray Spectra in Fast Neutron-induced Fission  

NASA Astrophysics Data System (ADS)

Knowledge of prompt fission ?-ray emission has been of major interest in reactor physics for a few years. Since very few experimental spectra were ever published until now, new measurements would be also valuable to improve our understanding of the fission process. An experimental method is currently being developed to measure the prompt fission ?-ray spectrum from some tens keV up to 10 MeV at least. The mean multiplicity and total energy could be deduced. In this method, the ?-rays are measured with a bismuth germanate (BGO) detector which has the advantage to present a high P/T ratio and a high efficiency compared to other ?-ray detectors. The prompt fission neutrons are rejected by the time of flight technique between the BGO detector and a fission trigger given by a fission chamber or a scintillating active target. Energy and efficiency calibration of the BGO detector were carried out up to 10.76 MeV by means of the 27Al(p,?) reaction. First prompt fission ?-ray spectrum measurements performed for the spontaneous fission of 252Cf and for 1.7 and 15.6 MeV neutron-induced fission of 238U at the CEA, DAM, DIF Van de Graaff accelerator, will be presented.

Laborie, J.-M.; Belier, G.; Taieb, J.

166

Studies On Particle-Accompanied Fission Of 252Cf(sf) And 235U(nth,f)  

NASA Astrophysics Data System (ADS)

In recent multi-parameter studies of spontaneous and thermal neutron induced fission, 252Cf(sf) and 235U(nth,f) respectively, the energies and emission angles of fission fragments and light charged particles were measured. Fragments were detected by an energy and angle sensitive twin ionization chamber while the light charged particles were identified by a series of ?E-Erest telescopes. Up to Be the light particle isotopes could be disentangled. In addition, in the 252Cf(sf) experiment, gammas emitted by the fragments were analyzed by a pair of large-volume segmented clover Ge detectors. Here the main interest is to study the ?-decay and the anisotropy of gammas emitted by fragments and light particles. On the other hand, the high count rates achieved in the U-experiment performed at the high flux reactor of the ILL, Grenoble, should allow to explore fragment-particle correlations in very rare events like quaternary fission. At the present stage of data evaluation, yields and energy distributions of light particles are available. For the present contribution in particular the yields of Be-isotopes for the two reactions studied are compared and discussed. For 252Cf(sf) these isotopic yields were hitherto not known.

Kopatch, Yu N.; Tishchenko, V.; Speransky, M.; Mutterer, M.; Gönnenwein, F.; Jesinger, P.; Gagarski, A. M.; von Kalben, J.; Kojouharov, I.; Lubkiewics, E.; Mezentseva, Z.; Nezvishevsky, V.; Petrov, G. A.; Schaffner, H.; Scharma, H.; Trzaska, W. H.; Wollersheim, H.-J.

2005-11-01

167

A new neutron counter for fission research  

NASA Astrophysics Data System (ADS)

A new neutron counter for research experiments on nuclear fission has been developed. This instrument is designed for the detection of prompt fission neutrons within relatively high levels of gamma and neutron background. It is composed of a set of 3He proportional counters arranged within a block of polyethylene which serves as moderator. The detection properties have been studied by means of Monte Carlo simulations and experiments with radioactive sources. These properties are confirmed by an experiment on neutron-induced fission of 238U at the WNR facility of the Los Alamos Neutron Science Center during which the mean prompt fission neutron multiplicity, or ?¯ has been measured from 1 to 20 MeV of incident neutron energy.

Laurent, B.; Granier, T.; Bélier, G.; Chatillon, A.; Martin, J.-F.; Taieb, J.; Hambsch, F.-J.; Tovesson, F.; Laptev, A. B.; Haight, R. C.; Nelson, R. O.; O'Donnell, J. M.

2014-05-01

168

Nuclear fission as resonance-mediated conductance  

E-print Network

For 75 years the theory of nuclear fission has been based on the existence of a collective coordinate associated with the nuclear shape, an assumption required by the Bohr-Wheeler formula as well as by the R-matrix theory of fission. We show that it is also possible to formulate the theory without the help of collective coordinates. In the new formulation, fission is facilitated by individual states in the barrier region rather than channels over the barrier. In a certain limit the theory reduces to a formula closely related to the formula for electronic conductance through resonant tunneling states. In contrast, conduction through channels gives rise to a staircase excitation function that is well-known in nanoscale electronics but has never been seen in nuclear fission.

Bertsch, G F

2014-01-01

169

Comparative Functional Genomics of the Fission Yeasts  

E-print Network

The fission yeast clade—comprising Schizosaccharomyces pombe, S. octosporus, S. cryophilus, and S. japonicus—occupies the basal branch of Ascomycete fungi and is an important model of eukaryote biology. A comparative ...

Regev, Aviv

170

Aqueous cutting fluid for machining fissionable materials  

DOEpatents

The present invention is directed to a cutting fluid for machining fissionable material. The cutting fluid is formed of glycol, water and boron compound in an adequate concentration for effective neutron attenuation so as to inhibit criticality incidents during machining.

Duerksen, Walter K. (Norris, TN); Googin, John M. (Oak Ridge, TN); Napier, Jr., Bradley (Powell, TN)

1984-01-01

171

Nuclear fission as resonance-mediated conductance  

E-print Network

For 75 years the theory of nuclear fission has been based on the existence of a collective coordinate associated with the nuclear shape, an assumption required by the Bohr-Wheeler formula as well as by the R-matrix theory of fission. We show that it is also possible to formulate the theory without the help of collective coordinates. In the new formulation, fission is facilitated by individual states in the barrier region rather than channels over the barrier. In a certain limit the theory reduces to a formula closely related to the formula for electronic conductance through resonant tunneling states. In contrast, conduction through channels gives rise to a staircase excitation function that is well-known in nanoscale electronics but has never been seen in nuclear fission.

G. F. Bertsch

2014-07-07

172

Reactor power history from fission product signatures  

E-print Network

The purpose of this research was to identify fission product signatures that could be used to uniquely identify a specific spent fuel assembly in order to improve international safeguards. This capability would help prevent and deter potential...

Sweeney, David J.

2009-05-15

173

Hollow fission fragment tracks in fluorapatite  

NASA Astrophysics Data System (ADS)

Spontaneous fission of uranium in minerals creates a damaged "track" along the trajectory of the fission fragments. Fission tracks in fluorapatite, enlarged by chemical etching, are widely used in geologic age-dating and the reconstruction of the thermal history of Earth's crust. However, despite this wide spread application, there have been no systematic studies of the internal structure of unetched fission tracks or the atomic-scale process of track annealing. In this research, fission tracks in fluorapatite are demonstrated to be nano-channels instead of amorphous cores as had been assumed. The formation of hollow tracks is ascribed to the highly ionizing energy deposition of fission fragments inducing radiolytic decomposition of fluorapatite accompanied by the loss of volatile elements. The mechanism for thermal annealing of hollow tracks in fluorapatite is shown to be entirely different from that of amorphous tracks in zircon. The discontinuity of fission tracks, in addition to the shrinkage, prevents chemicals from entering into the hollow tracks for further etching, and then significantly reduces the etched length. The shrinkage of hollow fission tracks results from thermo-emission of vacancies or gaseous species from the cavities to surrounding solids instead of atomic-scale recovery of the amorphous core. The high diffusivity of atoms on the surface of hollow tracks causes the discontinuity of tracks either by Rayleigh instability, by Brownian motion, or by preferential motion of track segments. The preferential motion of atoms along c-axis causes more rapid annealing of fission tracks perpendicular to the c-axis. Under the electron beam, the hollow tracks segment into droplets and the track segments randomly move at room temperature or preferentially move along c-axis at high temperatures. The radiolytic annealing results from beam-enhanced diffusion, which is similar to thermally enhanced diffusion. The similarity in the morphology of fission tracks and electron beam-induced bubbles and their preferential elongation along c-axis at high temperatures further confirm that the tracks are actually hollow channels. The radius profile of fission track along its trajectory has been calculated. These data will be critical to developing an atomic-scale model of track fading as it applied to geologic age-dating.

Li, Weixing

174

Microscopic description of complex nuclear decay: multimodal fission  

E-print Network

Our understanding of nuclear fission, a fundamental nuclear decay, is still incomplete due to the complexity of the process. In this paper, we describe a study of spontaneous fission using the symmetry-unrestricted nuclear density functional theory. Our results show that the observed bimodal fission can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. We also predict a new phenomenon of trimodal spontaneous fission for some rutherfordium, seaborgium, and hassium isotopes.

A. Staszczak; A. Baran; J. Dobaczewski; W. Nazarewicz

2009-06-23

175

A new interpretation of asymmetric nuclear fission  

Microsoft Academic Search

Summary  Twelve arguments are presented in favour of an interpretation of asymmetric nuclear fission as a two-step process. In the\\u000a first step, a light cluster is formed within the nucleus from the valence nucleons of the fissioning nucleus. In the second\\u000a step, the whole subshell of the208Pb core, or the major part of this subshell, is transferred to free valence states

G. Mouze; C. Ythier

1990-01-01

176

MCNP6 Fission Multiplicity with FMULT Card  

SciTech Connect

With the merger of MCNPX and MCNP5 into MCNP6, MCNP6 now provides all the capabilities of both codes allowing the user to access all the fission multiplicity data sets. Detailed in this paper is: (1) the new FMULT card capabilities for accessing these different data sets; (2) benchmark calculations, as compared to experiment, detailing the results of selecting these separate data sets for thermal neutron induced fission on U-235.

Wilcox, Trevor [Los Alamos National Laboratory; Fensin, Michael Lorne [Los Alamos National Laboratory; Hendricks, John S. [Los Alamos National Laboratory; James, Michael R. [Los Alamos National Laboratory; McKinney, Gregg W. [Los Alamos National Laboratory

2012-06-18

177

I-NERI ANNUAL TECHNICAL PROGRESS REPORT: 2006-002-K, Separation of Fission Products from Molten LiCl-KCl Salt Used for Electrorefining of Metal Fuels  

SciTech Connect

An attractive alternative to the once-through disposal of electrorefiner salt is to selectively remove the active fission products from the salt and recycle the salt back to the electrorefiner (ER). This would allow salt reuse for some number of cycles before ultimate disposal of the salt in a ceramic waste form. Reuse of ER salt would, thus, greatly reduce the volume of ceramic waste produced during the pyroprocessing of spent nuclear fuel. This final portion of the joint I-NERI research project is to demonstrate the separation of fission products from molten ER salt by two methods previously selected during phase two (FY-08) of this project. The two methods selected were salt/zeolite contacting and rare-earth fission product precipitation by oxygen bubbling. The ER salt used in these tests came from the Mark-IV electrorefiner used to anodically dissolved driver fuel from the EBR-II reactor on the INL site. The tests were performed using the Hot Fuel Dissolution Apparatus (HFDA) located in the main cell of the Hot Fuels Examination Facility (HFEF) at the Materials and Fuels complex on the INL site. Results from these tests were evaluated during a joint meeting of KAERI and INL investigators to provide recommendations as to the future direction of fission product removal from electrorefiner salt that accumulate during spent fuel treatment. Additionally, work continued on kinetic measurements of surrogate quaternary salt systems to provide fundamental kinetics on the ion exchange system and to expand the equilibrium model system developed during the first two phases of this project. The specific objectives of the FY09 I-NERI research activities at the INL include the following: • Perform demonstration tests of the selected KAERI precipitation and INL salt/zeolite contacting processes for fission product removal using radioactive, fission product loaded ER salt • Continue kinetic studies of the quaternary Cs/Sr-LiCl-KCl system to determine the rate of ion exchange during the salt/zeolite contacting process • Compare the adsorption models to experimentally obtained, ER salt results • Evaluate results obtained from the oxygen precipitation and salt/zeolite ion exchange studies to determine the best processes for selective fission-product removal from electrorefiner salt.

S. Frank

2009-09-01

178

Accurate fission data for nuclear safety  

E-print Network

The Accurate fission data for nuclear safety (AlFONS) project aims at high precision measurements of fission yields, using the renewed IGISOL mass separator facility in combination with a new high current light ion cyclotron at the University of Jyvaskyla. The 30 MeV proton beam will be used to create fast and thermal neutron spectra for the study of neutron induced fission yields. Thanks to a series of mass separating elements, culminating with the JYFLTRAP Penning trap, it is possible to achieve a mass resolving power in the order of a few hundred thousands. In this paper we present the experimental setup and the design of a neutron converter target for IGISOL. The goal is to have a flexible design. For studies of exotic nuclei far from stability a high neutron flux (10^12 neutrons/s) at energies 1 - 30 MeV is desired while for reactor applications neutron spectra that resembles those of thermal and fast nuclear reactors are preferred. It is also desirable to be able to produce (semi-)monoenergetic neutrons for benchmarking and to study the energy dependence of fission yields. The scientific program is extensive and is planed to start in 2013 with a measurement of isomeric yield ratios of proton induced fission in uranium. This will be followed by studies of independent yields of thermal and fast neutron induced fission of various actinides.

A. Solders; D. Gorelov; A. Jokinen; V. S. Kolhinen; M. Lantz; A. Mattera; H. Penttila; S. Pomp; V. Rakopoulos; S. Rinta-Antila

2013-03-12

179

Anatomy of neck configuration in fission decay  

E-print Network

The anatomy of neck configuration in the fission decay of Uranium and Thorium isotopes is investigated in a microscopic study using Relativistic mean field theory. The study includes $^{236}U$ and $^{232}Th$ in the valley of stability and exotic neutron rich isotopes $^{250}U$, $^{256}U$, $^{260}U$, $^{240}Th$, $^{250}Th$, $^{256}Th$ likely to play important role in the r-process nucleosynthesis in stellar evolution. Following the static fission path, the neck configurations are generated and their composition in terms of the number of neutrons and protons are obtained showing the progressive rise in the neutron component with the increase of mass number. Strong correlation between the neutron multiplicity in the fission decay and the number of neutrons in the neck is seen. The maximum neutron-proton ratio is about 5 for $^{260}$U and $^{256}$Th suggestive of the break down of liquid-drop picture and inhibition of the fission decay in still heavier isotopes. Neck as precursor of a new mode of fission decay like multi-fragmentation fission may also be inferred from this study.

S. K. Patra; R. K. Choudhury; L. Satpathy

2010-05-10

180

Spontaneous fission of the heaviest elements  

SciTech Connect

Although spontaneous fission was discovered in /sup 238/U in 1940, detailed studies of the process were first made possible in the 1960's with the availability of milligram quantities of /sup 252/Cf. The advent of solid-state detectors made it possible to perform measurements of coincident fission fragments from even very short-lived spontaneous fission activities or those available in only very small quantities. Until 1971 it was believed that the main features of the mass and kinetic-energy distributions were essentially the same as those for thermal neutron-induced fission and that all low-energy fission proceeded via asymmetric mass division with total kinetic energies which could be derived by linear extrapolation from those of lighter elements. In 1971, measurements of /sup 257/Fm showed an increase in symmetric mass division with anomalously high TKE's. Subsequent experiments showed that in /sup 258/Fm and /sup 259/Fm, the most probable mass split was symmetric with very high total kinetic energy. Measurements for the heavier elements have shown symmetric mass distributions with both high and low total kinetic energies. Recent results for spontaneous fission properties of the heaviest elements are reviewed and compared with theory. 31 refs., 8 figs., 1 tab.

Hoffman, D.C.

1989-04-01

181

A search for inverse fission of uranium  

SciTech Connect

There is a long-term interest in running the fission reaction backward, i.e., studying the 'inverse fission' of uranium. The recent availability of beams of n-rich fission fragments has stimulated interest in this endeavor. The purpose is to search for inverse fission in the reactions {sup 124,132}Sn + {sup 100}Mo. In the {sup 124}Sn + {sup 100}Mo reaction, evaporation residues were searched for using in-beam detection of evaporation residues, in-beam {alpha} spectroscopy, and post-irradiation {alpha} spectroscopy, while in the {sup 132}Sn + {sup 100}Mo reaction, the evaporation residue {sup 230}U was searched for using post-irradiation {alpha} spectroscopy. No evidence for the occurrence of the inverse fission reactions was found. The upper-limit cross section for the latter reaction is {approx}550 {mu}b, while the experimental upper-limit cross section for the former reaction is about 21{sup -21}{sup +38} nb. The intensity of suitable radioactive beams is not high enough at present to detect inverse fission. For the {sup 124}Sn + {sup 100}Mo reaction, the observed upper limits are below the estimates of current models for these reactions, probably due to fusion hindrance.

Yanez, R [Oregon State University, Corvallis; Loveland, Walter [Oregon State University; Beckerman, J. [Oregon State University, Corvallis; Leonard, M. [Oregon State University, Corvallis; Pettersson, G. [Oregon State University, Corvallis; Gross, Carl J [ORNL; Shapira, Dan [ORNL; Liang, J Felix [ORNL; Kohley, Zachary W [ORNL; Varner Jr, Robert L [ORNL

2012-01-01

182

Accurate Fission Data for Nuclear Safety  

NASA Astrophysics Data System (ADS)

The Accurate fission data for nuclear safety (AlFONS) project aims at high precision measurements of fission yields, using the renewed IGISOL mass separator facility in combination with a new high current light ion cyclotron at the University of Jyväskylä. The 30 MeV proton beam will be used to create fast and thermal neutron spectra for the study of neutron induced fission yields. Thanks to a series of mass separating elements, culminating with the JYFLTRAP Penning trap, it is possible to achieve a mass resolving power in the order of a few hundred thousands. In this paper we present the experimental setup and the design of a neutron converter target for IGISOL. The goal is to have a flexible design. For studies of exotic nuclei far from stability a high neutron flux (1012 neutrons/s) at energies 1 - 30 MeV is desired while for reactor applications neutron spectra that resembles those of thermal and fast nuclear reactors are preferred. It is also desirable to be able to produce (semi-)monoenergetic neutrons for benchmarking and to study the energy dependence of fission yields. The scientific program is extensive and is planed to start in 2013 with a measurement of isomeric yield ratios of proton induced fission in uranium. This will be followed by studies of independent yields of thermal and fast neutron induced fission of various actinides.

Solders, A.; Gorelov, D.; Jokinen, A.; Kolhinen, V. S.; Lantz, M.; Mattera, A.; Penttilä, H.; Pomp, S.; Rakopoulos, V.; Rinta-Antila, S.

2014-05-01

183

Theoretical descriptions of neutron emission in fission  

SciTech Connect

Brief descriptions are given of the observables in neutron emission in fission together with early theoretical representations of two of these observables, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. This is followed by summaries, together with examples, of modern approaches to the calculation of these two quantities. Here, emphasis is placed upon the predictability and accuracy of the new approaches. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are discussed. Then, recent work in multiple-chance fission and other recent work involving new measurements are presented and discussed. Following this, some properties of fission fragments are mentioned that must be better known and better understood in order to calculate N(E) and {bar {nu}}{sub p} with higher accuracy than is currently possible. In conclusion, some measurements are recommended for the purpose of benchmarking simultaneous calculations of neutron emission and gamma emission in fission. 32 refs., 26 figs.

Madland, D.G.

1990-01-01

184

An aminostratigraphy for the British Quaternary based on Bithynia opercula  

PubMed Central

Aminostratigraphies of Quaternary non-marine deposits in Europe have been previously based on the racemization of a single amino acid in aragonitic shells from land and freshwater molluscs. The value of analysing multiple amino acids from the opercula of the freshwater gastropod Bithynia, which are composed of calcite, has been demonstrated. The protocol used for the isolation of intra-crystalline proteins from shells has been applied to these calcitic opercula, which have been shown to more closely approximate a closed system for indigenous protein residues. Original amino acids are even preserved in bithyniid opercula from the Eocene, showing persistence of indigenous organics for over 30 million years. Geochronological data from opercula are superior to those from shells in two respects: first, in showing less natural variability, and second, in the far better preservation of the intra-crystalline proteins, possibly resulting from the greater stability of calcite. These features allow greater temporal resolution and an extension of the dating range beyond the early Middle Pleistocene. Here we provide full details of the analyses for 480 samples from 100 horizons (75 sites), ranging from Late Pliocene to modern. These show that the dating technique is applicable to the entire Quaternary. Data are provided from all the stratotypes from British stages to have yielded opercula, which are shown to be clearly separable using this revised method. Further checks on the data are provided by reference to other type-sites for different stages (including some not formally defined). Additional tests are provided by sites with independent geochronology, or which can be associated with a terrace stratigraphy or biostratigraphy. This new aminostratigraphy for the non-marine Quaternary deposits of southern Britain provides a framework for understanding the regional geological and archaeological record. Comparison with reference to sites yielding independent geochronology, in combination with other lines of evidence, allows tentative correlation with the marine oxygen isotope record. PMID:23396683

Penkman, Kirsty E.H.; Preece, Richard C.; Bridgland, David R.; Keen, David H.; Meijer, Tom; Parfitt, Simon A.; White, Tom S.; Collins, Matthew J.

2013-01-01

185

Quaternary Fault and Fold Database for the United States: California  

NSDL National Science Digital Library

This interactive map shows the major fault systems of the Quaternary for the State of California. It is subdivided into 1x2 degree sheets, each of which is linked to a more detailed map. Users can select a sheet and see an enlargement of the area. Individual fault systems are numbered and keyed to a legend which provides a link to a written synopsis of information for the fault, including fault type and geologic history. Links are also provided to more extensive reports for the faults, including a "complete" report with references.

186

Arctic-alpine blockfields in northern Sweden: Quaternary not Neogene  

NASA Astrophysics Data System (ADS)

Slowly-eroding, blockfield-mantled, non-glacial surface remnants may serve as markers against which to determine Quaternary glacial erosion volumes in high latitude mountain settings. To investigate this potential utility of these surfaces, chemical weathering, erosion rates, and origins of mountain blockfields are investigated in northern Sweden. This is done, firstly, by assessing the intensity of regolith chemical weathering along altitudinal transects descending from three blockfield-mantled summits. Clay/silt ratios, secondary mineral assemblages determined through X-ray diffraction, and the presence of chemically weathered grains visible on scanning electron microscopy, in fine matrix samples collected from pits excavated along the transects are each used for this purpose. Secondly, erosion rates and total surface histories of two of the summits are inferred from concentrations of in situ-produced cosmogenic 10Be and 26Al in quartz at the blockfield surface. An interpretative model is adopted that includes temporal variations in nuclide production rates through surface burial by glacial ice and glacial isostasy-induced elevation changes of the blockfield surfaces. Together, our data indicate that these blockfields are not derived from remnants of intensely weathered Neogene weathering profiles, as is commonly considered. Evidence for this interpretation includes minor chemical weathering in each of the three examined blockfields, despite some differences according to slope position. In addition, average erosion rates of ∼16.2 mm ka-1 and ∼6.7 mm ka-1, calculated for two blockfield-mantled summits, are low but of sufficient magnitude to remove present blockfield mantles, of up to a few meters in thickness, within a late-Quaternary timeframe. Hence, blockfield mantles appear to be replenished by regolith formation through, primarily physical, weathering processes that have operated during the Quaternary. Erosion rates remain low enough, however, for blockfield-mantled, non-glacial surface remnants to provide reasonable landscape markers against which to contrast Quaternary erosion volumes in surrounding glacial landscape elements. The persistence of blockfield mantles over a number of glacial-interglacial cycles and an apparently low likelihood that they can re-establish on glacially eroded bedrock, also discounts the operation of a "glacial buzz-saw" on surface remnants that are presently perceived as non-glacial. These interpretations are tempered though by outstanding questions concerning the composition of preceding Neogene regoliths and why they have apparently been comprehensively removed from these remnant non-glacial surfaces. It remains possible that periglacial erosion of perhaps more intensely weathered Neogene regoliths was high during the Pliocene-Pleistocene transition to colder conditions and that periglacial processes reshaped non-glacial surface remnants largely before the formation of blockfield armours.

Goodfellow, B. W.; Stroeven, A. P.; Fabel, D.; Fredin, O.; Derron, M.-H.; Bintanja, R.; Caffee, M. W.

2014-02-01

187

Quaternary Faults and Folds by State and Region  

NSDL National Science Digital Library

This interactive map of the United states provides access to maps of Quaternary faults and folds by state or region (for example, the Gulf Coast). Clicking on the colored areas of the map links the user to state/regional maps and further, to 1x2 degree sheets for each area. On the sheets, users can find faults numbered and indexed to a legend. Links from the legend provide access to written information, where available, for each fault. There are three levels of written reports, ranging from a brief synopsis to a "complete" report that includes references.

188

Microscopic Description of Nuclear Fission: Fission Barrier Heights of Even-Even Actinides  

E-print Network

We evaluate the performance of modern nuclear energy density functionals for predicting inner and outer fission barrier heights and energies of fission isomers of even-even actinides. For isomer energies and outer barrier heights, we find that the self-consistent theory at the HFB level is capable of providing quantitative agreement with empirical data.

J. McDonnell; N. Schunck; W. Nazarewicz

2013-01-31

189

Fission-product yields for thermal-neutron fission of curium-243  

SciTech Connect

Cumulative fission yields for 25 gamma rays emitted during the decay of 23 fission products produced by thermal-neutron fission of /sup 243/Cm have been determined. Using Ge(Li) spectroscopy, 33 successive pulse-height spectra of gamma rays emitted from a 77-ng sample of /sup 243/Cm over a period of approximately two and one-half months were analyzed. Reduction of these spectra resulted in the identification and matching of gamma-ray energies and half-lives to specific radionuclides. Using these results, 23 cumulative fission-product yields were calculated. Only those radionuclides having half-lives between 6 hours and 65 days were observed. Prior to this experiment, no fission-product yields had been recorded for /sup 243/Cm.

Breederland, D. G.

1982-01-01

190

Late Quaternary incised-valley fill of the Yangtze delta (China): its stratigraphic framework and evolution  

Microsoft Academic Search

A Late Quaternary stratigraphic framework of the Yangtze delta, China, has been established based on the analysis and correlation of over 600 cores. Thirty cores were drilled and analyzed during this study, and the rest were collected from numerous publications. The Late Quaternary stratigraphic framework of the Yangtze delta consists of incised-valley fill and two interfluvial sequences. The incised valley

Congxian Li; Ping Wang; Heping Sun; Jiaqiang Zhang; Daidu Fan; Bing Deng

2002-01-01

191

Quaternary Diffusion Coefficients in a Protein-Polymer-Salt-Water System Determined by Rayleigh Interferometry  

E-print Network

Quaternary Diffusion Coefficients in a Protein-Polymer-Salt-Water System Determined by Rayleigh in a protein-polymer-salt-water quaternary system. Specifically, we have measured the nine multicomponent diffusion coefficients, Dij, for the lysozyme-poly(ethylene glycol)-NaCl-water system at pH 4.5 and 25 °C

Annunziata, Onofrio

192

Late Quaternary vegetation and climate history near Little Lake, central Coast Range, Oregon  

E-print Network

­25 000 yr B.P.), the Fraser glaciation (ca. 25 000­ 10 000 yr B.P.), and the Holocene. Little Lake (latLate Quaternary vegetation and climate history near Little Lake, central Coast Range, Oregon Marc A recovered from Little Lake, Oregon, provide the first record of late Quaternary climate and veg- etation

Whitlock, Cathy L.

193

Dating late Quaternary planktonic foraminifer Neogloboquadrina pachyderma from the Arctic Ocean by using amino acid racemization  

E-print Network

Dating late Quaternary planktonic foraminifer Neogloboquadrina pachyderma from the Arctic Ocean was determined by using independently dated sediment cores from the Arctic Ocean. The racemization rates calibrated for the last 150 ka using 14 C ages and the emerging Quaternary chronostratigraphy of Arctic Ocean

Howat, Ian M.

194

Late Quaternary slip rates across the central Tien Shan, Kyrgyzstan, central Asia  

Microsoft Academic Search

(1) Slip rates across active faults and folds show that late Quaternary faulting is distributed across the central Tien Shan, not concentrated at its margins. Nearly every intermontane basin contains Neogene and Quaternary syntectonic strata deformed by Holocene north-south shortening on thrust or reverse faults. In a region that spans two thirds of the north-south width of the central Tien

Stephen C. Thompson; Ray J. Weldon; Charles M. Rubin; Kanatbek Abdrakhmatov; Peter Molnar; Glenn W. Berger

2002-01-01

195

Quaternary history of sea ice in the western Arctic Ocean based on foraminifera  

E-print Network

Quaternary history of sea ice in the western Arctic Ocean based on foraminifera Leonid Polyak a 4 February 2013 Keywords: Western Arctic Ocean Foraminifers Quaternary Mid-Pleistocene Transition Sea ice history a b s t r a c t Sediment cores from the Northwind Ridge, western Arctic Ocean

St-Ong, Guillaume

196

Quaternary history of sea ice in the western Arctic Ocean based on foraminifera  

E-print Network

Quaternary history of sea ice in the western Arctic Ocean based on foraminifera Leonid Polyak a xxx Keywords: Western Arctic Ocean Foraminifers Quaternary Mid-Pleistocene Transition Sea ice history a b s t r a c t Sediment cores from the Northwind Ridge, western Arctic Ocean, including uniquely

Long, Bernard

197

Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean Leonid Polyak a,  

E-print Network

Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean Leonid Polyak a Article history: Accepted 17 March 2009 Available online xxxx Keywords: Arctic Ocean sediment stratigraphy sedimentary environments Late Quaternary glaciations Sediment cores from the western Arctic Ocean obtained

Howat, Ian M.

198

LATE-QUATERNARY VEGETATION DYNAMICS IN NORTH AMERICA: SCALING FROM TAXA TO BIOMES  

Microsoft Academic Search

This paper integrates recent efforts to map the distribution of biomes for the late Quaternary with the detailed evidence that plant species have responded individual- istically to climate change at millennial timescales. Using a fossil-pollen data set of over 700 sites, we review late-Quaternary vegetation history in northern and eastern North America across levels of ecological organization from individual taxa

John W. Williams; Bryan N. Shuman; Thompson Webb; Patrick J. Bartlein; Phillip L. Leduc

2004-01-01

199

Flightless ducks, giant mice and pygmy mammoths: Late Quaternary extinctions on California's Channel Islands  

Microsoft Academic Search

Explanations for the extinction of Late Quaternary megafauna are heavily debated, ranging from human overkill to climate change, disease and extraterrestrial impacts. Synthesis and analysis of Late Quaternary animal extinctions on California's Channel Islands suggest that, despite supporting Native American populations for some 13,000 years, few mammal, bird or other species are known to have gone extinct during the prehistoric

Torben C. Rick; Courtney A. Hofman; Todd J. Braje; Jesús E. Maldonado; T Scott Sillett; Kevin Danchisko; Jon M. Erlandson

2012-01-01

200

Diatoms from the Quaternary sediments of the Nile Delta, Egypt, and their palaeoecological significance  

Microsoft Academic Search

This study represents the first contribution describing diatom taxa from the Quaternary sediments of the Nile Delta, Egypt. A total of 99 diatom species and varieties belonging to 28 genera were identified. The palaeoecological conditions during the time of deposition (pH salinity, eutrophication and dissolved silica concentration) are discussed. Deposition of the Quaternary Nile Delta sediments occurred in slightly alkaline,

Abdelfattah A. Zalat

1995-01-01

201

Espizua, L. (2004). Pleistocene glaciations in the Mendoza Andes, Argentina. In Quaternary Glaciations Extent  

E-print Network

Quaternary glaciations of Ecuador, Peru and Bolivia. In Quaternary Glaciations ­ Extent and Chronology, Part III (J. Ehlers and P. Gibbard, Eds.), pp. 151­163. Elsevier. Meglioli, A. (1992). Glacial geology-Ar chronology of Pleistocene glaciations in Patagonia. Geological Society of America Bulletin 116, 434

Sheldon, Nathan D.

202

A comparison of lignin and stable carbon isotope compositions in quaternary marine sediments  

Microsoft Academic Search

Heges, J.I. and van Geen, A., 1982. A comparison of lignin and stable carbon isotope compositions in quaternary marine sediments. Mar. Chem., 11: 43--53. Organic matter in four Quaternary sediment cores from the Gulf of Mexico and one core from the Washington State coast have been analyzed for lignin and stable carbon isotope compositions. Holocene sequences of all five cores

JOHN I. HEDGES; ALEXANDER VAN GEEN

1982-01-01

203

Late Quaternary marginal marine deposits and palaeoenvironments from northeastern Buenos Aires Province, Argentina: A review  

Microsoft Academic Search

The late Quaternary marginal marine deposits along eastern Argentina (Southwestern Atlantic) are reviewed according to our present knowledge. In the northeastern coastal area of Buenos Aires Province they have been assigned to a series of transgressions and regressions ranging from the late Pliocene to the late Quaternary. The most widely accepted model is Frenguelli's (1957) classical chronostratigraphical scheme of: ‘Belgranense’,

M. L. Aguirre; R. C. Whatley

1995-01-01

204

Quaternary Addition Circuits Based on SUSLOC Voltage-Mode Cells and Modeling with SystemVerilog  

E-print Network

Quaternary Addition Circuits Based on SUSLOC Voltage-Mode Cells and Modeling with System] are modeled and used for our adder circuit structures. Several different adder configurations are designed offers efficient modeling capabilities to model and simulate large MVL circuits [3]. The quaternary

Thornton, Mitchell

205

Options For Development of Space Fission Propulsion Systems  

NASA Technical Reports Server (NTRS)

Fission technology can enable rapid, affordable access to any point in the solar system. Potential fission-based transportation options include high specific power continuous impulse propulsion systems and bimodal nuclear thermal rockets. Despite their tremendous potential for enhancing or enabling deep space and planetary missions, to date space fission system have only been used in Earth orbit. The first step towards utilizing advanced fission propulsion systems is development of a safe, near-term, affordable fission system that can enhance or enable near-term missions of interest. An evolutionary approach for developing space fission propulsion systems is proposed.

Houta, Mike; VanDyke, Melissa; Godfroy, Tom; Pedersen, Kevin; Martin, James; Dickens, Ricky; Salvail, Pat; Hrbud, Ivana; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

206

Anatomy of neck configuration in fission decay  

E-print Network

The anatomy of neck configuration in the fission decay of Uranium and Thorium isotopes is investigated in a microscopic study using Relativistic mean field theory. The study includes $^{236}U$ and $^{232}Th$ in the valley of stability and exotic neutron rich isotopes $^{250}U$, $^{256}U$, $^{260}U$, $^{240}Th$, $^{250}Th$, $^{256}Th$ likely to play important role in the r-process nucleosynthesis in stellar evolution. Following the static fission path, the neck configurations are generated and their composition in terms of the number of neutrons and protons are obtained showing the progressive rise in the neutron component with the increase of mass number. Strong correlation between the neutron multiplicity in the fission decay and the number of neutrons in the neck is seen. The maximum neutron-proton ratio is about 5 for $^{260}$U and $^{256}$Th suggestive of the break down of liquid-drop picture and inhibition of the fission decay in still heavier isotopes. Neck as precursor of a new mode of fission decay li...

Patra, S K; Satpathy, L

2010-01-01

207

Properties of prompt-fission ? rays  

NASA Astrophysics Data System (ADS)

In a Monte Carlo Hauser-Feshbach statistical framework, we describe spectra, average multiplicities, average energy, and multiplicity distributions of the prompt ? rays produced in the thermal neutron-induced fission of U235 and Pu239, and the spontaneous fission of Cf252. Comparisons against recent experimental data show reasonable agreement in all cases investigated, after adjustment of the initial spin distribution in the fission fragments. In particular, when we include in the calculation the Doppler broadening we obtain a qualitatively good description of the measured low-energy spectra, where contributions from collective discrete transitions in specific fragments can be identified. At higher energies, both the calculated neutron and ?-ray spectra are softer than experimental data. The impact of selected model parameters on the prompt neutron and ?-ray spectra is analyzed. Finally, we present the prompt ? spectrum and multiplicity distribution for the neutron-induced fission of U235 for 5.5 MeV neutron incident energy, just below the threshold for second-chance fission.

Stetcu, I.; Talou, P.; Kawano, T.; Jandel, M.

2014-08-01

208

Correlation of recent fission product release data  

SciTech Connect

For the calculation of source terms associated with severe accidents, it is necessary to model the release of fission products from fuel as it heats and melts. Perhaps the most definitive model for fission product release is that of the FASTGRASS computer code developed at Argonne National Laboratory. There is persuasive evidence that these processes, as well as additional chemical and gas phase mass transport processes, are important in the release of fission products from fuel. Nevertheless, it has been found convenient to have simplified fission product release correlations that may not be as definitive as models like FASTGRASS but which attempt in some simple way to capture the essence of the mechanisms. One of the most widely used such correlation is called CORSOR-M which is the present fission product/aerosol release model used in the NRC Source Term Code Package. CORSOR has been criticized as having too much uncertainty in the calculated releases and as not accurately reproducing some experimental data. It is currently believed that these discrepancies between CORSOR and the more recent data have resulted because of the better time resolution of the more recent data compared to the data base that went into the CORSOR correlation. This document discusses a simple correlational model for use in connection with NUREG risk uncertainty exercises. 8 refs., 4 figs., 1 tab.

Kress, T.S.; Lorenz, R.A.; Nakamura, T.; Osborne, M.F.

1989-01-01

209

Fission-fragment spikes in uranium dioxide  

NASA Astrophysics Data System (ADS)

The article deals with some fundamental aspects of the fission energy dispersion in nuclear reactor fuel. The analysis starts from the transmission electron microscope observation of tracks produced by energetic fission fragments in thin foils of UO2 single crystals. On the one hand, these tracks appear on the free surface as explosive material displacements. On the other, the passage of fission fragments in the bulk does not leave visible, continuous traces. Furthermore, irradiated U4O9, which consists of a UO2 lattice hosting a temperature sensitive superstructure of interstitial oxygen, persists after experiencing the near-field action of fission fragment thermal spikes. These seemingly inconsistent phenomena have been explained by showing that a large fraction of the fission fragment electronic losses is converted in strong shock waves whose passage in the solid is too fast for producing atomic displacements, but which can release high energies by unloading on free surfaces. The consequent matter displacements have been shown to have important effects on the structural properties of the nuclear fuel.

Ronchi, C.; Wiss, T.

2002-11-01

210

Morphological Change in Quaternary Mammals of North America  

NASA Astrophysics Data System (ADS)

This book examines case studies of North American Quaternary mammalian evolution within the larger domain of modern evolutionary theory. It presents previously unpublished studies of a variety of taxa (xenarthrans, rodents, carnivores, ungulates) examined over several temporal scales, from a few thousand years during the Holocene to millions of years of late Pliocene and Pleistocene time. Different organizational levels are represented, from mosaic population variation, to a synopsis of Quaternary evolution of an entire order (Rodentia). In addition to specific case histories, the book includes purely theoretical and methodological contributions, for example, on the statistical recognition of stasis in the fossil record, new ways to calculate evolutionary rates, and the use of digital image analysis in the study of dental ontogeny. Perhaps the most important aspect of the studies reported in this book is that they span the time between the "ecological moment" and "deep time". Modern taxa can be traced back into the fossil record, and variation among extant taxa can be used as a control against which variation in the extinct ones can be understood.

Martin, Robert A.; Barnosky, Anthony D.

1993-09-01

211

Late Quaternary Lacustrine Pollen Records from Southwestern Beringia  

NASA Astrophysics Data System (ADS)

Sediment cores from three lakes in the Upper Kolyma region, northeast Russia, provide the first well-dated continuous record of late Quaternary vegetation change from far southwestern Beringia. The oldest pollen zone, tentatively assigned to the Karginsk (mid-Wisconsinan) Interstade, indicates an Artemisia shrub tundra with Pinus pumila, Betula, and Alnus at mid- to low elevations. With the onset of the Sartan (late Wisconsinan) Stade, Pinus disappeared, probably indicating severely cold, dry winters and cool summers. As conditions deteriorated further, an Artemisia -Gramineae tundra developed. Selaginella rupestris and minor herb taxa indicate the presence of poor soils and disturbed ground. This herb tundra was replaced by a short-lived (< 1000 yr) Betula-Alnus shrub tundra followed by the rapid establishment of a Larix dahurica forest with a Betula exilis-ericales-lichen understory. Populus suaveolens and Chosenia may have formed limited hardwood gallery forests at this time. Modern vegetation associations probably developed during the early Holocene with the arrival of Pinus pumila ca. 9000 yr B.P. This shrub became important in the forest understory and, with B. exilis, formed a belt of shrub tundra beyond altitudinal treeline. Comparison of the Upper Kolyma and Alaskan pollen records indicates that important differences in vegetation types and timing of vegetation change occurred across Beringia during the late Quaternary.

Lozhkin, Anatoly V.; Anderson, Patricia M.; Eisner, Wendy R.; Ravako, Lilia G.; Hopkins, David M.; Brubaker, Linda B.; Colinvaux, Paul A.; Miller, Michael C.

1993-05-01

212

Late Quaternary sediment fluxes from tropical watersheds [review article  

NASA Astrophysics Data System (ADS)

Inherited saprolite stores and continued weathering in Quaternary time juxtapose abundant clay and fresh rock in tropical landscapes. This influences sediment fluxes and affects the interpretation of sediment sequences derived from tropical watersheds. Detrital kaolinites derive from inherited saprolite sources as well as from soil clays and appear in delta and ocean sediments. These sediments appear to correspond with sub-Milankovitch, millennial-scale cycles of climate change, but may also record century-scale episodes of rapid warming (Dansgaard-Oeschger events). Destabilisation of sediment sources and increased sediment fluxes in the Late Quaternary followed millennia of climatic deterioration (cooling/aridity) and vegetation change and led to altered patterns of sedimentation during the Last Glacial Maximum (LGM). Sediment yield from slopes increased 10× around the LGM, when rainfall was reduced by 30-60% and led to fan building and braided channels. Rainfall increased 40-80% from the LGM to the Early Holocene maximum and this led to channel cutting and major sediment fluxes to delta and ocean sinks. Vegetation recovery lagged the rapid warming by several millennia and was interrupted by (Younger Dryas) YD aridity, influencing slope and stream behaviour. Holocene sedimentation has been by both vertical and lateral accretion, increasing floodplain sediment stores.

Thomas, Michael F.

2003-11-01

213

Radiosensitization by quaternary salts of 5-nitroimidazole derivatives.  

PubMed

The radiosensitizing effects of five newly synthesized quaternary salts of 5-nitroimidazole derivatives on the survival of TC-SV40 mammalian cells have been measured. A toxicity study was carried out in order to determine the concentrations to be used in the radiosensitizing experiments. The oxygen enhancement ratio (OER) for TC-SV40 cells was 2.74. None of the five 5-nitroimidazole derivatives showed radiosensitizing activity in aerobic conditions, while in hypoxia their dose-modifying factors (DMF) at the concentration of 0.2 mmol dm-3 range from 1.52 to 1.03 in this order: unsubstituted pyridinium greater than carbamoyl pyridinium greater than trimethyl pyridinium greater than t-butyl pyridinium greater than imidazolium. This latter product at the concentration of 2 mmol dm-3 has a DMF of 1.64. As comparison, metronidazole was also tested on this cell line and its DMF at 0.2 mmol dm-3 was 1.35. The response-concentration dependences for the unsubstituted pyridinium 5-nitroimidazole derivative and for metronidazole (comparing charged and uncharged structures) showed the flattening response-concentration curve of quaternary compounds. The electron affinity was evaluated through the CNDO/S theoretical method, and an exponential relationship between these values and the DMFs of the pyridinium derivatives was demonstrated. PMID:2567335

Santos, L; Lopez Zumel, M C; Alvarez, M V; Izquierdo, M C

1989-06-01

214

Latest Quaternary stratigraphic framework of the Mississippi River delta region  

USGS Publications Warehouse

Previous researchers separated the uppermost Quaternary stratigraphy of the Mississippi River delta region into two major lithofacies. The stratigraphically lower of these, "substratum," primarily consists of coarse-grained sediment deposited within lowstand-incised stream valleys. Relatively finer-grained "topstratum" overlies substratum; above interfluves, topstratum directly overlies weathered late Pleistocene sediments. However, the onshore to offshore distribution and architecture of these lithofacies was not well constrained. This study integrates published and unpublished lithostratigraphic data with high-resolution seismic profiles from the continental shelf to aid in mapping the regional distribution of major substratum deposits and thickness of topstratum sediments. A transgressive sand sheet commonly marks the base of the topstratum deposits, providing a stratigraphic marker to aid in regional lithostratigraphic correlations. Radiocarbondated deposits and boreholes tied to oxygen isotope chronologies provide chronostratigraphic control. Excellent correlation between these multiple datasets has been found to exist, enabling construction of regional isopachous and structural elevation maps and cross sections detailing elements of the Late Quaternary stratigraphy.

Kulp, Mark; Howell, Paul; Adiau, Sandra; Penland, Shea; Kindinger, Jack; Williams, S. Jeffress

2002-01-01

215

Mass distribution in 11B induced fission of 232Th  

NASA Astrophysics Data System (ADS)

Formation cross sections of several fission products have been determined using recoil catcher technique followed by ?-ray spectrometry in 11B induced fission of 232Th at Elab=72, 60, and 55 MeV. The data show significant admixture of fission from compound nucleus formed by complete fusion as well as targetlike nuclei formed by transfer reaction. Mass distributions for both the fissioning systems have been obtained using the systematics of charge distribution in low and medium energy fission. The mass distribution for complete fusion fission is broad, Gaussian whereas it is asymmetric for transfer induced fission. The evaporation residue cross sections of targetlike nuclei formed in 232Th(11B, 10Be)233Pa reaction were also measured. The measured evaporation residue cross sections and the decay probabilities of targetlike nucleus 233Pa, calculated by the PACE2 code have been used to estimate the proton transfer fission cross sections which were found to be negligible compared to the total transfer cross section for all the projectile energies used. The transfer fission cross section is dominated by alpha transfer fission as inferred by measured forward to backward ratios for several fission products as well as Qgg systematics for the probable transfer reactions. The proportion of transfer fission cross section to the total fission cross section was 15, 17, and 22 % at projectile energies of 72, 60, and 55 MeV, respectively.

Gubbi, G. K.; Goswami, A.; Tomar, B. S.; Ramaswami, A.; Reddy, A. V. R.; Burte, P. P.; Manohar, S. B.; John, B.

1999-06-01

216

Prompt fission neutron emission: Problems and challenges  

NASA Astrophysics Data System (ADS)

This paper presents some of the challenges ahead of us even after 75 years of the discovery of the fission process and large progress made since then. The focus is on application orientation, which requires improved measurements on fission cross-sections and neutron and ?-ray multiplicities. Experimental possibilities have vastly improved the past decade leading to developments of highly sophisticated detector systems and the use of digital data acquisition and signal processing. The development of innovative fast nuclear reactor technology needs improved respective nuclear data. Advancements in theoretical modelling also require better experimental data. Theory has made progress in calculating fission fragment distributions (i.e. GEF code) as well as prompt neutron and ?-ray emission to catch up with the improved experiments.

Hambsch, F.-J.; Bry?, T.; Gamboni, T.; Geerts, W.; Göök, A.; Matei, C.; Oberstedt, S.; Vidali, M.

2013-12-01

217

Prompt Fission ?-rays Measured Using Liquid Scintillators  

NASA Astrophysics Data System (ADS)

The prompt ?-ray spectra from 235U(n,f) at incident energies of 1 to 20 MeV and for 235Cf(s.f.) were measured up to 4 MeV in coincidence with two parallel plate avalanche counters and the liquid scintillator array FIGARO. The unfolded ?-ray spectra from 1-4 MeV using the single value decomposition and iterative Bayesian techniques for the incident neutron energy regions corresponding to the first, second and third chance fissions were found to nearly identical and similar to the distribution from the spontaneous fission of 252Cf. General agreement with the ?-ray distributions from fission was also found with previous measurements.

Kwan, E.; Wu, C. Y.; Haight, R. C.; Lee, H. Y.; Bredeweg, T. A.; Chyzh, A.; Devlin, M.; Fotiades, N.; Gostic, J. M.; Henderson, R. A.; Jandel, M.; Laptev, A.; Nelson, R. O.; O'Donnell, J. M.; Perdue, B. A.; Taddeucci, T. N.; Ullmann, J. L.; Wender, S. A.

2014-05-01

218

?-delayed fission and ? decay of 178Tl  

NASA Astrophysics Data System (ADS)

A detailed nuclear-decay spectroscopy study of the neutron-deficient isotope 178Tl has been performed using the highly selective Resonance Ionization Laser Ion Source and ISOLDE mass separator (CERN), which allowed a unique isobarically pure beam of 178Tl to be produced. The first identification of the ?-delayed fission of this isotope was made and its probability P?DF(178Tl)=0.15(6)% was determined. An asymmetric fission fragment mass distribution of the daughter isotope 178Hg (populated by the ? decay of 178Tl) was deduced based on the measured fission fragment energies. The fine-structure ?-decay pattern of 178Tl allowed the low-energy states in the daughter nucleus 174Au to be studied.

Liberati, V.; Andreyev, A. N.; Antalic, S.; Barzakh, A.; Cocolios, T. E.; Elseviers, J.; Fedorov, D.; Fedoseeev, V. N.; Huyse, M.; Joss, D. T.; Kalaninová, Z.; Köster, U.; Lane, J. F. W.; Marsh, B.; Mengoni, D.; Molkanov, P.; Nishio, K.; Page, R. D.; Patronis, N.; Pauwels, D.; Radulov, D.; Seliverstov, M.; Sjödin, M.; Tsekhanovich, I.; Van den Bergh, P.; Van Duppen, P.; Venhart, M.; Veselský, M.

2013-10-01

219

Energy partition in low energy fission  

E-print Network

The intrinsic excitation energy of fission fragments is dynamically evaluated in terms of the time dependent pairing equations. These equations are corroborated with two conditions. One of them fixes the number of particles and the another separates the pairing active spaces associated to the two fragments in the vicinity of the scission configuration. The fission path is obtained in the frame of the macroscopic-microscopic model. The single particle level schemes are obtained within the two center Woods-Saxon shell model. It is shown that the available intrinsic dissipated energy is not shared proportionally to the masses of the two fission fragments. If the heavy fragment possesses nucleon numbers close to the magic ones, the accumulated intrinsic excitation energy is lower than that of the light fragment.

M. Mirea

2011-02-14

220

Final excitation energy of fission fragments  

SciTech Connect

We study how the excitation energy of the fully accelerated fission fragments is built up. It is stressed that only the intrinsic excitation energy available before scission can be exchanged between the fission fragments to achieve thermal equilibrium. This is in contradiction with most models used to calculate prompt neutron emission, where it is assumed that the total excitation energy of the final fragments is shared between the fragments by the condition of equal temperatures. We also study the intrinsic excitation-energy partition in statistical equilibrium for different level-density descriptions as a function of the total intrinsic excitation energy of the fissioning system. Excitation energies are found to be strongly enhanced in the heavy fragment, if the level density follows a constant-temperature behavior at low energies, e.g., in the composed Gilbert-Cameron description.

Schmidt, Karl-Heinz; Jurado, Beatriz [Centre d'Etudes Nucleaires de Bordeaux Gradignan (CENBG), CNRS/IN2P3, Chemin du Solarium, B.P. 120, F-33175 Gradignan (France)

2011-06-15

221

Fission enhanced diffusion of uranium in zirconia  

NASA Astrophysics Data System (ADS)

This paper deals with the comparison between thermal and Fission Enhanced Diffusion (FED) of uranium into zirconia, representative of the inner face of cladding tubes. The experiments under irradiation are performed at the Institut Laue Langevin (ILL) in Grenoble using the Lohengrin spectrometer. A thin 235UO 2 layer in direct contact with an oxidised zirconium foil is irradiated in the ILL high flux reactor. The fission product flux is about 10 11 ions cm -2 s -1 and the target temperature is measured by an IR pyrometer. A model is proposed to deduce an apparent uranium diffusion coefficient in zirconia from the energy distribution broadening of two selected fission products. It is found to be equal to 10 -15 cm 2 s -1 at 480 °C and compared to uranium thermal diffusion data in ZrO 2 in the same pressure and temperature conditions. The FED results are analysed in comparison with literature data.

Bérerd, N.; Chevarier, A.; Moncoffre, N.; Sainsot, Ph.; Faust, H.; Catalette, H.

2005-11-01

222

Fission Enhanced diffusion of uranium in zirconia  

E-print Network

This paper deals with the comparison between thermal and Fission Enhanced Diffusion (FED) of uranium into zirconia, representative of the inner face of cladding tubes. The experiments under irradiation are performed at the Institut Laue Langevin (ILL) in Grenoble using the Lohengrin spectrometer. A thin $^{235}UO\\_2$ layer in direct contact with an oxidized zirconium foil is irradiated in the ILL high flux reactor. The fission product flux is about 10$^{11}$ ions cm$^{-2}$ s$^{-1}$ and the target temperature is measured by an IR pyrometer. A model is proposed to deduce an apparent uranium diffusion coefficient in zirconia from the energy distribution broadening of two selected fission products. It is found to be equal to 10$^{-15}$ cm$^2$ s$^{-1}$ at 480$\\circ$C and compared to uranium thermal diffusion data in ZrO$\\_2$ in the same pressure and temperature conditions. The FED results are analysed in comparison with literature data.

Bérerd, N; Moncoffre, N; Sainsot, P; Faust, H; Catalette, H

2005-01-01

223

Fission barriers of compound superheavy nuclei.  

PubMed

The dependence of fission barriers on the excitation energy of the compound nucleus impacts the survival probability of superheavy nuclei synthesized in heavy-ion fusion reactions. In this work, we investigate the isentropic fission barriers by means of the self-consistent nuclear density functional theory. The relationship between isothermal and isentropic descriptions is demonstrated. Calculations have been carried out for 264Fm, 272Ds, ;{278}112, ;{292}114, and ;{312}124. For nuclei around ;{278}112 produced in "cold-fusion" reactions, we predict a more rapid decrease of fission barriers with excitation energy as compared to the nuclei around ;{292}114 synthesized in "hot-fusion" experiments. This is explained in terms of the difference between the ground-state and saddle-point temperatures. The effect of the particle gas is found to be negligible in the range of temperatures studied. PMID:19518948

Pei, J C; Nazarewicz, W; Sheikh, J A; Kerman, A K

2009-05-15

224

Study on fission blanket fuel cycling of a fusion-fission hybrid energy generation system  

NASA Astrophysics Data System (ADS)

This paper presents a preliminary study on neutron physics characteristics of a light water cooled fission blanket for a new type subcritical fusion-fission hybrid reactor aiming at electric power generation with low technical limits of fission fuel. The major objective is to study the fission fuel cycling performance in the blanket, which may possess significant impacts on the feasibility of the new concept of fusion-fission hybrid reactor with a high energy gain (M) and tritium breeding ratio (TBR). The COUPLE2 code developed by the Institute of Nuclear and New Energy Technology of Tsinghua University is employed to simulate the neutronic behaviour in the blanket. COUPLE2 combines the particle transport code MCNPX with the fuel depletion code ORIGEN2. The code calculation results show that soft neutron spectrum can yield M > 20 while maintaining TBR >1.15 and the conversion ratio of fissile materials CR > 1 in a reasonably long refuelling cycle (>five years). The preliminary results also indicate that it is rather promising to design a high-performance light water cooled fission blanket of fusion-fission hybrid reactor for electric power generation by directly loading natural or depleted uranium if an ITER-scale tokamak fusion neutron source is achievable.

Zhou, Z.; Yang, Y.; Xu, H.

2011-10-01

225

Low-mass fission detector for the fission neutron spectrum measurement  

SciTech Connect

For the fission neutron spectrum measurement, the neutron energy is determined in a time-of-flight experiment by the time difference between the fission event and detection of the neutron. Therefore, the neutron energy resolution is directly determined by the time resolution of both neutron and fission detectors. For the fission detection, the detector needs not only a good timing response but also the tolerance of radiation damage and high {alpha}-decay rate. A parallel-plate avalanche counter (PPAC) has many advantages for the detection of heavy charged particles such as fission fragments. These include fast timing, resistance to radiation damage, and tolerance of high counting rate. A PPAC also can be tuned to be insensitive to particles, which is important for experiments with - emitting actinides. Therefore, a PPAC is an ideal detector for experiments requiring a fast and clean trigger for fission. In the following sections, the description will be given for the design and performance of a new low-mass PPAC for the fission-neutron spectrum measurements at LANL.

Wu, C Y; Henderson, R; Gostic, J; Haight, R C; Lee, H Y

2010-10-20

226

In-beam Fission Study at JAEA  

NASA Astrophysics Data System (ADS)

Fission fragment mass distributions were measured in heavy-ion induced fissions using 238U target nucleus. The measured mass distributions changed drastically with incident energy. The results are explained by a change of the ratio between fusion and quasifission with nuclear orientation. A calculation based on a fluctuation dissipation model reproduced the mass distributions and their incident energy dependence. Fusion probability was determined in the analysis. Evaporation residue cross sections were calculated with a statistical model in the reactions of 30Si + 238U and 34S + 238U using the obtained fusion probability in the entrance channel. The results agree with the measured cross sections for seaborgium and hassium isotopes.

Nishio, Katsuhisa

2013-12-01

227

High performance, suppressed-fission ICF hybrid  

SciTech Connect

The neutronics aspects of an ICF hybrid concept are discussed. The breeding blanket consists of a beryllium neutron multiplier, metallic thorium fertile fuel and a liquid-lithium coolant. The fertile fuel fraction is 30 vol%, which is much higher than previous one-zone, suppressed-fission hybrid concepts. Fission in the bred /sup 233/U is suppressed by competition from tritium breeding reactions in /sup 6/Li. The total breeding ratio, T + F, is 2.05, and the total neutron energy deposited is 41.1 MeV per DT neutron. The 800-MW (fusion) hybrid produces approx. 3500 kg of /sup 233/U per full-power-year.

Meier, W.R.

1983-12-01

228

Angular Momentum Distribution of Fission Fragments  

NASA Astrophysics Data System (ADS)

Latest generation fission experiments provide an excellent testing ground for theoretical models. In this contribution we compare the measurements obtained with the DANCE calorimeter at LANSCE with our full-scale simulation of the primary fragment de-excitation, using the recently developed CGMF code, based on a Monte-Carlo implementation of the Hauser-Feshbach theoretical model. We compute the isomeric ratios as a function of the initial angular momentum of the fission fragments. Comparison with the available experimental data allows us to determine the initial spin distribution. Finally, we study the sensitivity to the discrete spectra input.

Stetcu, I.; Talou, P.; Kawano, T.; Jandel, M.

2014-04-01

229

Italian hybrid and fission reactors scenario analysis  

SciTech Connect

Italy is a country where a long tradition of studies both in the fission and fusion field is consolidated; nevertheless a strong public opinion concerned with the destination of the Spent Nuclear Fuel hinders the development of nuclear power. The possibility to a severe reduction of the NSF mass generated from a fleet of nuclear reactors employing an hypothetical fusionfission hybrid reactor has been investigated in the Italian framework. The possibility to produce nuclear fuel for the fission nuclear reactors with the hybrid reactor was analyzed too.

Ciotti, M.; Manzano, J.; Sepielli, M. [ENEA CR Frascati, Via Enrico Fermi, 45, 00044, Frascati, Roma (Italy); ENEA CR casaccia, Via Anguillarese, 301, 00123, Santa Maria di Galeria, Roma (Italy)

2012-06-19

230

Quaternary history and contemporary patterns in a currently expanding species  

PubMed Central

Background Quaternary climatic oscillations had dramatic effects on species evolution. In northern latitudes, populations had to survive the coldest periods in refugial areas and recurrently colonized northern regions during interglacials. Such a history usually results in a loss of genetic diversity. Populations that did not experience glaciations, in contrast, probably maintained most of their ancestral genetic diversity. These characteristics dramatically affected the present-day distribution of genetic diversity and may influence the ability of species to cope with the current global changes. We conducted a range-wide study of mitochondrial genetic diversity in the pine processionary moth (Thaumetopoea pityocampa/T. wilkinsoni complex, Notodontidae), a forest pest occurring around the Mediterranean Basin and in southern Europe. This species is responding to the current climate change by rapid natural range expansion and can also be accidentally transported by humans. Our aim was to assess if Quaternary climatic oscillations had a different effect across the species' range and to determine if genetic footprints of contemporary processes can be identified in areas of recent introduction. Results We identified three main clades that were spatially structured. In most of Europe, the genetic diversity pattern was typical for species that experienced marked glaciation cycles. Except in refugia, European populations were characterized by the occurrence of one main haplotype and by a strong reduction in genetic diversity, which is expected in regions that were rapidly re-colonized when climatic conditions improved. In contrast, all other sub-clades around the Mediterranean Basin occurred in limited parts of the range and were strongly structured in space, as is expected in regions in which the impact of glaciations was limited. In such places, genetic diversity was retained in most populations, and almost all haplotypes were endemic. This pattern was extreme on remote Mediterranean islands (Crete, Cyprus, Corsica) where highly differentiated, endemic haplotypes were found. Recent introductions were typified by the existence of closely-related haplotypes in geographically distant populations, which is difficult to detect in most of Europe because of a lack of overall genetic structure. Conclusion In regions that were not prone to marked glaciations, recent moth introductions/expansions could be detected due to the existence of a strong spatial genetic structure. In contrast, in regions that experienced the most intense Quaternary climatic oscillations, the natural populations are not genetically structured, and contemporary patterns of population expansion remain undetected. PMID:19732434

Kerdelhué, Carole; Zane, Lorenzo; Simonato, Mauro; Salvato, Paola; Rousselet, Jérôme; Roques, Alain; Battisti, Andrea

2009-01-01

231

Development and Utilization of Space Fission Power Systems  

NASA Technical Reports Server (NTRS)

Space fission power systems could enable advanced civilian space missions. Terrestrially, thousands of fission systems have been operated since 1942. In addition, the US flew a space fission system in 1965, and the former Soviet Union flew 33 such systems prior to the end of the Cold War. Modern design and development practices, coupled with 65 years of experience with terrestrial reactors, could enable the affordable development of space fission power systems for near-term planetary surface applications.

Houts, Michael; Mason, Lee S.; Palac, Donald T.; Harlow, Scott E.

2008-01-01

232

Development and Utilization of Space Fission Power Systems  

NASA Technical Reports Server (NTRS)

Space fission power systems could enable advanced civilian space missions. Terrestrially, thousands of fission systems have been operated since 1942. In addition, the US flew a space fission system in 1965, and the former Soviet Union flew 33 such systems prior to the end of the Cold War. Modern design and development practices, coupled with 65 years of experience with terrestrial reactors, could enable the affordable development of space fission power systems for near-term planetary surface applications.

Houts, Michael G.; Mason, Lee S.; Palac, Donald T.; Harlow, Scott E.

2009-01-01

233

Syntheses and structure-activity relationships in cytotoxicities of 13-substituted quaternary coptisine derivatives.  

PubMed

Twenty five 13-substituted quaternary coptisine derivatives were synthesized to test their cytotoxicities against several cancer cell-lines and on intestinal epithelial cell-6 (IEC-6) in vitro to evaluate structure-activity relationship (SAR). Introduction of the alkyl groups into the C-13 position of quaternary coptisine (1) led to significant increase of the cytotoxic activity, while the substitution of arylmethyl groups and others at the same position showed no effect on improving cytotoxicities against the same cancer cell-lines. The cytotoxicities of quaternary 13-alkylcoptisines was significantly reinforced as the length of the aliphatic chain increased, with quaternary 13-n-undecylcoptisine (4l) showing 7, 23, 12, and 9 times, respectively, more active than quaternary coptisine (1) against HCT, A549, Bel7402, and C33A, and being 4, 11, 2, and 3 times, respectively, more active than the positive control, fluorouracil (5-FU), against the same cell-lines, by IC50 values. In comparison to quaternary 13-n-undecylcoptisine (4l) and the above references, quaternary 13-n-dodecylcoptisine (4m) almost showed the same cytotoxicities. In contrast with the n-alkyl chains, the arylmethyl substituents at C-13 displayed low cytotoxicity, except for naphthyl rings or phenyl rings with CF3 or methyl substituents. However, their low cytotoxicity could make them useful as drug candidates for other diseases (bowel, etc). PMID:25203783

Zhang, Zhi-Hui; Deng, An-Jun; Wu, Lian-Qiu; Fang, Lian-Hua; Yu, Jin-Qian; Li, Zhi-Hong; Yuan, Tian-Yi; Wang, Wen-Jie; Du, Guan-Hua; Qin, Hai-Lin

2014-10-30

234

Focused Pliocene-Quaternary exhumation of the Eastern Pamir domes, western China  

NASA Astrophysics Data System (ADS)

The Kongur Shan and Muztagata domes are the most prominent topographic features in the Eastern Pamir indenter corner. In spite of several previous bedrock thermochronology studies, the extent, processes and mechanisms of dome exhumation remain unclear. We present 1158 detrital zircon fission-track (DZFT) ages from modern glacier and river sediments along the domes to better constrain the spatial distribution of exhumation. Our thermochronologic dataset from the Chakragil massif shows a sharp increase in the proportion of DZFT ages >10 Ma from basins that drain the peak region to those further to the north, which suggests that the Kalagile fault forms the northern boundary of the rapidly exhuming dome structure. A cluster of Middle Miocene DZFT ages in these samples documents pre-doming cooling, possibly associated with motion on the Main Pamir thrust and/or Oytag fault. Large fractions of DZFT grain ages <10 Ma in samples from catchments east of the divide likely originate from the Chakragil, Kongur Shan and Muztagata massifs, implying focused exhumation consistent with DZFT age distributions in samples from catchments draining the western flank of the range and bedrock geo- and thermochronologic data from the core of the domes. Furthermore, the majority of the samples contain two distinct DZFT age groups at ?6-4 Ma and ?3-1 Ma respectively. These ages are synchronous with major fluvial sedimentation phases at the outlets of the rivers draining northeastward into the Tarim Basin and suggest rapid Pliocene-Quaternary exhumation of the domes. We interpret the ?6-4 Ma age group to record the onset of extension along the entire Kongur Shan fault; its timing with respect to compressional deformation supports a model of gravitational collapse of over-thickened crust. The fraction of ?3-1 Ma DZFT ages is larger than what would be inferred from the bedrock data alone. We interpret this to reflect recent focused denudation in response to glaciation and fluvial incision of the domes and their possible feedback with extensional faulting.

Cao, Kai; Bernet, Matthias; Wang, Guo-Can; van der Beek, Peter; Wang, An; Zhang, Ke-Xin; Enkelmann, Eva

2013-02-01

235

Constraining the age and magnitude of uplift in the northern National Petroleum Reserve in Alaska (NPRA)-apatite fission-track analysis of samples from three wells  

USGS Publications Warehouse

A broad, post-mid-Cretaceous uplift is defined in the northern National Petroleum Reserve in Alaska (NPRA) by regional truncation of Cretaceous strata, thermal maturity patterns, and amounts of exhumation estimated from sonic logs. Apatite fission-track (AFT) analysis of samples from three wells (South Meade No. 1, Topagoruk No. 1, and Ikpikpuk No. 1) across the eastern flank of the uplift indicates Tertiary cooling followed by Quaternary heating. Results from all three wells indicate that cooling, presumably caused by uplift and erosion, started about 75-65 Ma (latest Cretaceous-earliest Tertiary) and continued through the Tertiary Period. Data from South Meade indicate more rapid cooling after about 35-15 Ma (latest Eocene-middle Miocene) followed by a significant increase in subsurface temperature during the Quaternary, probably the result of increased heat flow. Data from Topagoruk and Ikpikpuk include subtle evidence of accelerated cooling starting in the latest Eocene-middle Miocene and possible evidence of increased temperature during the Quaternary. Subsurface temperature perturbations related to the insulating effect of permafrost may have been responsible for the Quaternary temperature increase at Topagoruk and Ikpikpuk and may have been a contributing factor at South Meade. Multiple lines of geologic evidence suggest that the magnitude of exhumation resulting from uplift and erosion is 5,000-6,500 ft at South Meade, 4,000-5,500 ft at Topagoruk, and 2,500-4,000 ft at Ikpikpuk. The results from these wells help to define the broad geometry of the uplift, which increases in magnitude from less than 1,000 ft at the Colville River delta to perhaps more than 7,000 ft along the northwestern coast of NPRA, between Point Barrow and Peard Bay. Neither the origin nor the offshore extent of the uplift, west and north of the NPRA coast, have been determined.

Houseknecht, David W.; Bird, Kenneth J.; O'Sullivan, Paul

2011-01-01

236

Exhumation mechanisms of SE Carpathians assessed by detrital zircon fission-track thermochronology  

NASA Astrophysics Data System (ADS)

Radiometric dating of detrital minerals has been more and more used in the recent years to better understand the long-term evolution of mountain belts and their topography. Low temperature geochronology studies of European orogens such as Swiss and Western Alps, Apennines or Betics show an unusual exhumation history since the late Neogene. Most of the current research has inferred the coupling between tectonics, climate and surface processes as responsible for topographic changes. In the south-eastern part of Romanian Carpathians recent thermochronological studies revealed that up to 5 km of sediments were exhumed during the two post-collisional exhumation stages: first around 5 Ma and a second phase during Quaternary times. We aim to unravel the mechanism(s) and improve the temporal resolution controlling the exhumation by applying detrital zircon fission-track thermochronology (DZFT) to key stratigraphic layers of the foreland basin, archive of the long-term orogenic exhumation. A large data-set of DZFT ages have been obtained for samples along three river profiles perpendicular to the strike of the East Carpathian orogen. The full grain age spectrum have well defined components around 70, 100 and >134 Ma which correlates with Laramian and Austrian (in Romanian nomenclature) tectonic phases. All the youngest components (P1) of each sample are non-reset and preserve the source provenance as well as the recent exhumation history. We suggest a climatic control on the exhumation and erosion of the SE Carpathians since late Neogene time, with significant peak accelerations that are correlated in space and time with the Messinian Salinity Crisis event (~5 Ma) and with the Quaternary stages of enhanced exhumation. However, a striking feature is the presence of few thermochronological age components situated in the very close temporal proximity to the stratigraphic age which show inclusions, euhedral morphometry and zonations. They are likely derived from the Neogene volcanism situated in eastern margin of Transylvanian basin, and dated by K-Ar method as young as Quaternary up to 10.5 Ma. This has significant inferences for constraining the timing of basin connectivity within the Paratethys domains that have bordered the East Carpathians Mountains.

Trifan, C?t?lin; Andriessen, Paul; Ma?enco, Liviu

2013-04-01

237

Calculations on fission gas behaviour in the high burnup structure  

Microsoft Academic Search

The behaviour of fission gas in high burnup fuel during steady-state and transient conditions is of special interest for safety reasons. Despite this, mechanistic models that reflect the fission gas transport processes and reliably predict the evolution of the remaining fission gas in the high burnup structure (HBS) are largely missing today. We start to address this problem by developing

P. Blair; A. Romano; Ch. Hellwig; R. Chawla

2006-01-01

238

Some predictions of the cluster model of nuclear fission  

Microsoft Academic Search

The unified viewpoint provided by the cluster model of nuclear fission ; is used to predict mass distributions using the observed minima in the excitation ; energies of fragmerts and to calculate angular distributions from the mass yield ; curves. The mass distribution in thermal neutron induced fission of U²³⁵ ; is calculated, using certain assumptions for asymmetric fission, and

H. Faissner; K. Wildermuth

1962-01-01

239

General view on nuclear fission Karl-Heinz Schmidt  

E-print Network

General view on nuclear fission Karl-Heinz Schmidt Beatriz Jurado CENBG, CNRS/IN2 P3 Chemin du.amouroux@cea.fr 1 in2p3-00976648,version1-10Apr2014 #12;Abstract: A general approach to nuclear fission is described which ex- plains the complex appearance of fission observables by universal principles of theoretical

Paris-Sud XI, Université de

240

Boolean Network Model Predicts Cell Cycle Sequence of Fission Yeast  

E-print Network

Boolean Network Model Predicts Cell Cycle Sequence of Fission Yeast Maria I. Davidich, Stefan network model of the cell-cycle regulatory network of fission yeast (Schizosaccharomyces Pombe sequence being a strongly attractive trajectory. Comparing the fission yeast cell-cycle model to a similar

Bornholdt, Stefan

241

DATA FUSION VIA FISSION FOR THE ANALYSIS OF BRAIN DEATH  

E-print Network

10 DATA FUSION VIA FISSION FOR THE ANALYSIS OF BRAIN DEATH L. Li, Y. Saito, D. Looney, T. Tanaka, J nonlinear and nonstationary brain signal is decomposed into its oscillatory components (fission knowledge about a process in hand (fusion). This chapter illustrates how the fusion via fission methodology

Kent, University of

242

Enabling the Use of Space Fission Propulsion Systems  

SciTech Connect

This paper gives brief descriptions of advantages of fission technology for reaching any point in the solar system and of earlier efforts to develop space fission propulsion systems, and gives a more detailed description of the safe, affordable fission engine (SAFE) concept being pursued at the National Aeronautics and Space Administration's Marshall Space Flight Center.

Mike Houts; Melissa Van Dyke; Tom Godfroy; James Martin; Kevin Pedersen; Ricky Dickens; Ivana Hrbud; Leo Bitteker; Bruce Patton; Suman Chakrabarti; Joe Bonometti

2000-06-04

243

A brief history of the Delayed'' discovery of nuclear fission  

Microsoft Academic Search

This year marks the Fiftieth Anniversary of the discovery of Nuclear Fission. In the early 1930's, the neutron was discovered, followed by the discovery of artificial radioactivity and then the use of the neutron to produce artificial radioactivity. The first experiments resulting in the fission of uranium took place in 1934. A paper which speculated on fission as an explanation

1989-01-01

244

Mass distribution of fission products following photofission of uranium-238  

Microsoft Academic Search

The mass-yield distribution of fission products following photofission ; of ²³⁸U using bremsstrahlung energies of 22, 24, and 28 MeV were measured ; by radiochemically isolating the fission products belonging to 24 mass chains. ; The absolute activities of these nuclides were determined by BETA - and gamma ; counting techniques, and the cumulative fission yields were calculated relative ;

D. Swindle; R. Wright; K. Takahashi; W. H. Rivera; J. L. Meason

1973-01-01

245

FY04&05 LDRD Final Report Fission Fragment Sputtering  

Microsoft Academic Search

Fission fragments born within the first 7 μm of the surface of U metal can eject a thousand or more atoms per fission event. Existing data in the literature show that the sputtering yield ranges from 10 to 10,000 atoms per fission event near the surface, but nothing definitive is known about the energy of the sputtered clusters. Experimental packages

B Ebbinghaus; T Trelenberg; T Meier; T Felter; J Sturgeon; A Kuboda; B Wolfer

2006-01-01

246

Fission-suppressed blankets for fissile fuel breeding fusion reactors  

Microsoft Academic Search

Two blanket concepts for deuterium-tritium (DT) fusion reactors are presented which maximize fissile fuel production while at the same time suppress fission reactions. By suppressing fission reactions, the reactor will be less hazardous, and therefore easier to design, develop, and license. A fusion breeder operating a given nuclear power level can produce much more fissile fuel by suppressing fission reactions.

J. D. Lee; R. W. Moir

1981-01-01

247

Expanded record of Quaternary oceanographic change: Amerasian Arctic Ocean  

USGS Publications Warehouse

Four sediment cores collected from the Northwind and Mendeleyev ridges, Arctic Ocean, from 1089 m to 1909 m water depth, provide an oceanographic record extending back into the Matuyama reversed polarity chron. Benthic foraminiferal analyses show four prominent assemblage zones: Bolivina arctica, Cassidulina teretis, Bulimina aculeata, and Oridorsalis tener from the upper Matuyama reversed polarity chronozone through the Brunhes normal polarity chronozone. These assemblage zones represent depth-dependent benthic foraminiferal biofacies changes associated with oceanographic events that occurred in the Amerasian basin at ??? 780 and 300 ka, and indicate oceanographic influence from the North Atlantic. Recognition of these benthic assemblage zones in Arctic cores from the Alpha Ridge indicates that the benthic foraminiferal zonations in intermediate to deep water (>1000 m) Arctic cores may be more useful than preexisting lithostratigraphic zonations and should provide important information pertaining to the Quaternary paleoceanographic evolution of the Arctic Ocean.

Ishman, S. E.; Polyak, L. V.; Poore, R. Z.

1996-01-01

248

[Synthesis and biological evaluation of tetrahydrocoptisine quaternary ammonium compounds].  

PubMed

The goal of treatment of metabolic syndrome is the prevention of diabetes and cardiovascular events. A series of novel tetrahydrocoptisine quaternary ammonium compounds were prepared to evaluate their action of hypoglycemia and hypolipidemia for finding the therapeutic agents of metabolic syndrome. Starting from the coptisine hydrochloride (2), fifteen target compounds were synthesized by reduction and substitution of the 7-N position. All of the target compounds were characterized by 1H NMR and HR-MS. Their hypoglycemic activities were evaluated in HepG2 cell and hypolipidemic activities of compounds with better hypoglycemic activity were tested further in vivo. Results indicated that compounds 5, 7, 8 and 9 exhibited better hypoglycemic activities in vitro and compounds 5 and 8 exhibited good hypolipidemic activities in high-fat-diet (HFD) induced hyperlipidemia mice and (or) hamsters. However, the activity is not as good as simvastatin. PMID:23460970

Wang, Dong-Mei; Wei, Jin-Zhao; Fan, Bao-Yan; Liu, Quan; Zhu, Hai-Bo; Shen, Zhu-Fang; Wu, Song

2012-12-01

249

Prompt muon-induced fission: a sensitive probe for nuclear energy dissipation and fission dynamics  

E-print Network

Following the formation of an excited muonic atom, inner shell transitions may proceed without photon emission by inverse internal conversion, i.e. the muonic excitation energy is transferred to the nucleus. In actinides, the 2p -> 1s and the 3d -> 1s muonic transitions result in excitation of the nuclear giant dipole and giant quadrupole resonances, respectively, which act as doorway states for fission. The nuclear excitation energy is typically 6.5 - 10 MeV. Because the muon lifetime is long compared to the timescale of prompt nuclear fission, the motion of the muon in the Coulomb field of the fissioning nucleus may be utilized to learn about the dynamics of fission.

Volker E. Oberacker; A. Sait Umar; Feodor F. Karpeshin

2004-03-30

250

Search for other natural fission reactors  

Microsoft Academic Search

Precambrian uranium ores have been surveyed for evidence of other natural fission reactors. The requirements for formation of a natural reactor direct investigations to uranium deposits with large, high-grade ore zones. Massive zones with volumes approximately greater than 1 m³ and concentrations approximately greater than 20 percent uranium are likely places for a fossil reactor if they are approximately greater

K. E. Apt; J. P. Balagna; E. A. Bryant; G. A. Cowan; W. R. Daniels; R. J. Vidale

1977-01-01

251

Asymptotically Correct Shell Model for Nuclear Fission  

Microsoft Academic Search

A two-center shell model with oscillator potentials, l-->.s--> forces, and l-->2 terms is developed. The shell structures of the original spherical nucleus and those of the final fragments are reproduced. For small separation of the two centers the level structure resembles the Nilsson scheme. This two-center shell model might be of importance in problems of nuclear fission.

D. Scharnweber; U. Mosel; W. Greiner

1970-01-01

252

In the exit channel of nuclear fission  

Microsoft Academic Search

The final period of nuclear fission is discussed. We propose the following picture: Nuclear scission happens because of an hydrodynamic instability triggered by random surface vibrations. Thus the scissioning complex ruptures at random positions. Measured total kinetic energies point to the very relevance of the instability, while the randomness of rupture shows up in neutron emission data.

U. Brosa; S. Grossmann

1983-01-01

253

Transfer-induced fission of superheavy nuclei  

SciTech Connect

Possibilities of transfer-induced fission of new isotopes of superheavy nuclei with charge numbers 103-108 are studied for the first time in the reactions {sup 48}Ca+{sup 244,246,248}Cm at energies near the corresponding Coulomb barriers. The predicted cross sections are found to be measurable with the detection of three-body final states.

Adamian, G. G. [Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); Institute of Nuclear Physics, Tashkent, UZ-702132 Uzbekistan (Uzbekistan); Antonenko, N. V.; Zubov, A. S. [Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); Sargsyan, V. V. [Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); Yerevan State University, Yerevan (Armenia); Scheid, W. [Institut fuer Theoretische Physik der Justus-Liebig-Universitaet, D-35392 Giessen (Germany)

2010-07-15

254

Brownian Shape Dynamics in Nuclear Fission  

NASA Astrophysics Data System (ADS)

It was recently found that remarkably accurate fission-fragment mass distributions can be obtained by treating the nuclear shape evolution as a Metropolis walk on previously calculated five-dimensional potential-energy surfaces; this novel method is briefly reviewed here.

Randrup, Jørgen; Möller, Peter

2014-09-01

255

Liquid uranium alloy-helium fission reactor  

DOEpatents

This invention describes a nuclear fission reactor which has a core vessel and at least one tandem heat exchanger vessel coupled therewith across upper and lower passages to define a closed flow loop. Nuclear fuel such as a uranium alloy in its liquid phase fills these vessels and flow passages. Solid control elements in the reactor core vessel are adapted to be adjusted relative to one another to control fission reaction of the liquid fuel therein. Moderator elements in the other vessel and flow passages preclude fission reaction therein. An inert gas such as helium is bubbled upwardly through the heat exchanger vessel operable to move the liquid fuel upwardly therein and unidirectionally around the closed loop and downwardly through the core vessel. This helium gas is further directed to heat conversion means outside of the reactor vessels to utilize the heat from the fission reaction to generate useful output. The nuclear fuel operates in the 1200 to 1800/sup 0/C range, and even higher to 2500/sup 0/C.

Minkov, V.

1984-06-13

256

Overview of tritium fast-fission yields  

Microsoft Academic Search

Tritium production rates are very important to the development of fast reactors because tritium may be produced at a greater rate in fast reactors than in light water reactors. This report focuses on tritium production and does not evaluate the transport and eventual release of the tritium in a fast reactor system. However, if an order-of-magnitude increase in fast fission

1981-01-01

257

Liquid uranium alloy-helium fission reactor  

DOEpatents

This invention teaches a nuclear fission reactor having a core vessel and at least one tandem heat exchanger vessel coupled therewith across upper and lower passages to define a closed flow loop. Nuclear fuel such as a uranium alloy in its liquid phase fills these vessels and flow passages. Solid control elements in the reactor core vessel are adapted to be adjusted relative to one another to control fission reaction of the liquid fuel therein. Moderator elements in the other vessel and flow passages preclude fission reaction therein. An inert gas such as helium is bubbled upwardly through the heat exchanger vessel operable to move the liquid fuel upwardly therein and unidirectionally around the closed loop and downwardly through the core vessel. This helium gas is further directed to heat conversion means outside of the reactor vessels to utilize the heat from the fission reaction to generate useful output. The nuclear fuel operates in the 1200.degree.-1800.degree. C. range, and even higher to 2500.degree. C., limited only by the thermal effectiveness of the structural materials, increasing the efficiency of power generation from the normal 30-35% with 300.degree.-500.degree. C. upper limit temperature to 50-65%. Irradiation of the circulating liquid fuel, as contrasted to only localized irradiation of a solid fuel, provides improved fuel utilization.

Minkov, Vladimir (Skokie, IL)

1986-01-01

258

Mitochondrial fission in apoptosis, neurodegeneration and aging  

Microsoft Academic Search

A decline in mitochondrial function is well recognized in neurodegenerative diseases and aging, and is thought to play a causal role in their biology. Unfortunately, the molecular basis underlying this detrimental loss in mitochondrial function remains mysterious. Interestingly, mitochondria undergo frequent fission and fusion. This process is regulated by molecular machinery that has been highly conserved during evolution, including dynamin-related

Ella Bossy-Wetzel; Mark J Barsoum; Adam Godzik; Robert Schwarzenbacher; Stuart A Lipton

2003-01-01

259

Critical Temperature from the Fission Data  

SciTech Connect

Experimental and calculated data on the fission probability are compared for highly excited 188Os. The calculations have been made within the statistical model using the more reliable parameterizations for the temperature dependence or surface tension. It is concluded that the critical temperature for the nuclear liquid-gas phase transition is higher than 16 MeV.

Cherepanov, E. A.; Karnaukhov, V. A. [Joint Institute for Nuclear Research, 141980, Dubna (Russian Federation)

2007-05-22

260

Fission Detection Using the Associated Particle Technique  

SciTech Connect

A beam of tagged 14 MeV neutrons from the deuterium-tritium (DT) reaction is used to induce fission in a target composed of depleted uranium. The generator yield is 107 neutrons/second radiated into a 4? solid angle. Two 4 in.×4 in. NaI detectors are used for gamma-ray detection. The fission process is known to produce multiple gamma-rays and neutrons. Triple coincidences (?-?-?) are measured as a function of neutron flight time up to 90 ns after fission, where the ?-particle arises from the DT reaction. A sudden increase in the triple coincidence rate at the location of the material is used to localize and detect fission in the interrogated target. Comparisons are made with experiment runs where lead, tungsten, and iron were used as target materials. The triple coincidence response profile from depleted uranium is noted to be different to those observed from the other target materials. The response from interrogation targets composed of fissile material is anticipated to be even more unique than that observed from depleted uranium.

R.P. Keegan, J.P. Hurley, J.R. Tinsley, R. Trainham, S.C. Wilde

2008-09-18

261

Fission cycling in a supernova r process  

SciTech Connect

Recent halo star abundance observations exhibit an important feature of consequence to the r process: the presence of a main r process between the second and third peaks that is consistent among halo stars. We explore fission cycling and steady {beta} flow as the driving mechanisms behind this feature. The presence of fission cycling during the r process can account for nucleosynthesis yields between the second and third peaks, whereas the presence of steady {beta} flow can account for consistent r-process patterns, robust under small variations in astrophysical conditions. We employ the neutrino-driven wind of the core-collapse supernova to examine fission cycling and steady {beta} flow in the r process. As the traditional neutrino-driven wind model does not produce the required very neutron-rich conditions for these mechanisms, we examine changes to the neutrino physics necessary for fission cycling to occur in the neutrino-driven wind environment, and we explore under what conditions steady {beta} flow is obtained.

Beun, J.; McLaughlin, G. C.; Surman, R.; Hix, W. R. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27595-8202 (United States); Department of Physics, Union College, Schenectady, New York 12308 (United States); Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6374 (United States)

2008-03-15

262

Renew Workshop on Fusion-Fission Hybrids  

E-print Network

contributed Technical findings #12;7 Status of Nuclear Power Fission View Components of nuclear power Fuel (DOE) DOE NNSA perspective Kirk Levedahl (DOE) Nuclear industry perspective Adrian Heymer (NEI) Proliferation and reprocessing Bob Bari (BNL) Panel discussion Andy Kadak (MIT) Moderator #12;6 Structure

263

Droplet fission: A performance of surface tension  

Microsoft Academic Search

Long liquid jets are unstable against surface vibrations whose wavelength exceeds the circumference (Rayleigh). We show that this instability also governs droplet formation in finite liquid files even if they are homogeneously charged. Whenever the drop gets too long it fissions so that the fragments meet the proper bound for length\\/circumference depending on fissility. The arbitrary rupture position of infinite

Ulrich Brosa; Siegfried Grossmann

1983-01-01

264

Fission Energy and Other Sources of Energy  

ERIC Educational Resources Information Center

Discusses different forms of energy sources and basic reasons for the opposition to the use of atomic energy. Suggests that research efforts should also be aimed toward the fission technology to make it acceptable besides major research studies conducted in the development of alternative energy sources. (CC)

Alfven, Hannes

1974-01-01

265

DE LA FISSION A LA FUSION  

E-print Network

bas DE LA FISSION A LA FUSION Aspects historiques et perspectives 15 octobre 2008 Gen`eve, Uni en physique des plasmas) L'histoire de la fusion nucl´eaire par Guy Laval, physicien, directeur de recherches au CNRS, membre de l'Acad´emie des sciences, auteur de "L'´energie bleue, une histoire de la

Schibler, Ueli

266

Quaternary incised valleys in southern Brazil coastal zone  

NASA Astrophysics Data System (ADS)

High-resolution seismic records obtained in the Rio Grande do Sul coastal zone, southern Brazil, revealed that prominent valleys and channels developed in the area before the installation of actual coastal plain. Landwards, the paleoincisions can be linked with the present courses of the main river dissecting the area. Oceanwards, they can be linked with related features previously recognized in the continental shelf and slope by means of seismic and morphostructural studies. Based mainly on seismic, core data and geologic reasoning, it can be inferred that the coastal valleys were incised during forced regression events into the coastal prism deposited during previous sea level highstand events of the Quaternary. Seismic data has revealed paleovalleys up to 10 km wide and, in some places, infilled with up to 40 m thick of sediments. The results indicated two distinct periods of cut-and-fill events in the Patos Lagoon area. The filling of the younger incision system is mainly Holocene and its onset is related to the last main regressive event of the Pleistocene, when the sea level fell about 130 m below the actual position. The older incision and filling event is related to the previous regressive-transgressive events of the Middle and Late Pleistocene. The fluvial discharge fed delta systems on the shelf edge during the sea level lowstands. The subsequent transgressions drowned the incised drainage, infilling it and closing the inlets formerly connecting the coastal river to the ocean. The incised features may have played a significant role on the basin-margin architecture, facies distribution and accommodation space during the multitude of up and down sea level events of the Quaternary.

Weschenfelder, Jair; Baitelli, Ricardo; Corrêa, Iran C. S.; Bortolin, Eduardo C.; dos Santos, Cristiane B.

2014-11-01

267

Fission barrier properties, resonance fluctuations and isomer fission cross-sections.  

SciTech Connect

Although the main picture of fission bamer physics was established some time ago many of the details still have to be settled. Consequently, the application to evaluation of crosssections of unmeasurable or exotic nuclides and their excited states is still in its early stages. In this paper I consider some of these details and explore the possibility of quantitative estimation of fission cross-sections

Lynn, J. E. (J. Eric); Hayes, A. C. (Anna C.)

2002-11-27

268

Yields of fission products produced by thermal-neutron fission of 245Cm  

Microsoft Academic Search

Absolute yields have been determined for 105 gamma rays emitted in the decay of 95 fission products representing 54 mass chains created during thermal-neutron fission of 245Cm. These results include 17 mass chains for which no prior yield data exist. Using a Ge(Li) detector, spectra were obtained of gamma rays between 30 sec and 0.3 yr after very short irradiations

J. K. Dickens; J. W. McConnell

1981-01-01

269

Measurement\\/Evaluation Techniques and Nuclear Data Associated with Fission of 239Pu by Fission Spectrum Neutrons  

Microsoft Academic Search

This Panel was chartered to review and assess new evaluations of work on fission product data, as well as the evaluation process used by the two U.S. nuclear weapons physics laboratories. The work focuses on fission product yields resulting from fission spectrum neutrons incident on plutonium, and includes data from measurements that had not been previously published as well as

P Baisden; E Bauge; J Ferguson; D Gilliam; T Granier; R Jeanloz; C McMillan; D Robertson; P Thompson; C Verdon; C Wilkerson; P Young

2010-01-01

270

Fission Fragment Deformation and Dynamical Effects in Spontaneous Fission of 252CF and 248CM  

NASA Astrophysics Data System (ADS)

The number of prompt neutrons emitted in the fission event have been measured separately for each complementary fragment in coincidence with fragment mass and kinetic energies in spontaneous fission of 252Cf and 248Cm. Two high efficient Gd-loaded liquid scintillator tanks were used for the neutron registration. Approximately 3-106 fission events coincident with prompt neutron emission have been accumulated for each isotope. Neutron multiplicity distributions corrected for efficiency, background and pile-up have been obtained as a function of fission fragment mass and kinetic energy. Based on these unfolded multiplicity distributions fragment mass distributions for specific numbers of emitted neutrons have been obtained. These mass spectra demonstrates the presence of cold compact and deformed fission and the strong influence of deformed neutron shells in fragments at the descent to scission. Possible explanations for deformed cold fission are given on the basis of an analysis of the behavior of the moments of the multiplicity distributions on the fragment total kinetic energy.

Kalinin, V. A.; Dushin, V. N.; Petrov, B. F.; Yakovlev, V. A.; Vorobyev, A. S.; Laptev, A. B.; Shcherbakov, O. A.; Hambsch, F.-J.

2003-10-01

271

The Oklo natural reactor: Cumulative fission yields and retentivity of the symmetric mass region fission products  

NASA Astrophysics Data System (ADS)

Solid source mass spectrometry has been used to determine the relative cumulative fission yields of five elements in three samples of uranium ore from reactor zones in the Oklo mine site. Eighteen fission chains covering the mass range from 105 ? A ? 130 have been measured for Pd, Ag, Cd, Sn and Te. These measurements have enabled a number of nuclear parameters to be calculated including the relative proportions of 235U, 238U and 239Pu involved in the fission process. The concentration of the five elements in the Oklo samples have also been measured using the stable isotope dilution technique. These values have then been compared to the estimates of the amount of these elements produced by fission under the conditions that are appropriate to the three samples. This procedure enables the retentivity of the elements in the reactor zones to be evaluated. Our work confirms the fact that Pd and Te are retained almost in their entirety in the samples, whereas the other three elements have been partially lost from the reactor site. Almost all the Cd fission products have been lost, and more than 50% of the Ag and Sn fission-produced material has been removed.

De Laeter, J. R.; Rosman, K. J. R.; Smith, C. L.

1980-10-01

272

Rapid separation of fresh fission products (draft)  

SciTech Connect

The fission of highly eruiched uranium by thermal neutrons creates dozens of isotopic products. The Isotope and Nuclear Chemistry Group participates in programs that involve analysis of 'fiesh' fission products by beta counting following radiochemical separations. This is a laborious and time-consuming process that can take several days to generate results. Gamma spectroscopy can provide a more immediate path to isolopic activities, however short-lived, high-yield isotopes can swamp a gamma spectrum, making difficult the identification and quantification of isotopes on the wings and valley of the fission yield curve. The gamma spectrum of a sample of newly produced fission products is dominated by the many emissions of a very few high-yield isotopes. Specilkally, {sup 132}Te (3.2 d), its daughter, {sup 132}I(2 .28 h), {sup 140}Ba (12.75 d), and its daughter {sup 140}La (1.68 d) emit at least 18 gamma rays above 100 keV that are greater than 5% abundance. Additionally, the 1596 keV emission fiom I4'La imposes a Compton background that hinders the detection of isotopes that are neither subject to matrix dependent fractionation nor gaseous or volatile recursors. Some of these isotopes of interest are {sup 111}Ag, {sup 115}Cd, and the rare earths, {sup 153}Sm, {sup 154}Eu, {sup 156}Eu, and {sup 160}Tb. C-INC has performed an HEU irradiation and also 'cold' carrier analyses by ICP-AES to determine methods for rapid and reliable separations that may be used to detect and quantify low-yield fission products by gamma spectroscopy. Results and progress will be presented.

Dry, D. E. (Donald E.); Bauer, E. (Eve); Petersen, L. A. (Lisa A.)

2003-01-01

273

Fission track dating of kimberlitic zircons  

USGS Publications Warehouse

The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206Pb and 238U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0-1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.3 ?? 6.5 m.y.), Orapa (87.4 ?? 5.7 and 92.4 ?? 6.1 m.y.), Nzega (51.1 ?? 3.8 m.y.), Koffiefontein (90.0 ?? 8.2 m.y.), and Val do Queve (133.4 ?? 11.5 m.y.). In addition we report the first radiometric ages (707.9 ?? 59.6 and 705.5 ?? 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption. ?? 1983.

Haggerty, S.E.; Raber, E.; Naeser, C.W.

1983-01-01

274

Induction of nuclear fission by high-voltage application  

E-print Network

In nuclear power generation, fissile materials are mainly used. For example, $U^{235}$ is fissile and therefore quite essential for use of nuclear energy. However, the material $U^{235}$ has very small natural abundance less than 1 %. We should seek possibility of utilizing fissionable materials such as $U^{238}$ because natural abundance of such fissionable materials is generally much larger than fissile ones. In this paper, we show that thermal neutrons with vanishing kinetic energy can induce nuclear fission when high voltage is applied to fissionable materials. To obtain this result, we use the liquid-drop model for nuclei. Finally, we propose how fissionable materials can be utilized.

Hirokazu Maruyama

2007-11-20

275

Fission Yield Measurements by Inductively Coupled Plasma Mass-Spectrometry  

SciTech Connect

Correct prediction of the fission products inventory in irradiated nuclear fuels is essential for accurate estimation of fuel burnup, establishing proper requirements for spent fuel transportation and storage, materials accountability and nuclear forensics. Such prediction is impossible without accurate knowledge of neutron induced fission yields. Unfortunately, the accuracy of the fission yields reported in the ENDF/B-VII.0 library is not uniform across all of the data and much of the improvement is desired for certain isotopes and fission products. We discuss our measurements of cumulative fission yields in nuclear fuels irradiated in thermal and fast reactor spectra using Inductively Coupled Plasma Mass Spectrometry.

Irina Glagolenko; Bruce Hilton; Jeffrey Giglio; Daniel Cummings; Karl Grimm; Richard McKnight

2009-11-01

276

Fission Technology for Exploring and Utilizing the Solar System  

NASA Technical Reports Server (NTRS)

Fission technology can enable rapid, affordable access to any point in the solar system. Potential fission-based transportation options include bimodal nuclear thermal rockets, high specific energy propulsion systems, and pulsed fission propulsion systems. In-space propellant re-supply enhances the effective performance of all systems, but requires significant infrastructure development. Safe, timely, affordable utilization of first-generation space fission propulsion systems will enable the development of more advanced systems. First generation space systems will build on over 45 years of US and international space fission system technology development to minimize cost,

Houts, Mike; VanDyke, Melissa; Godfroy, Tom; Pedersen, Kevin; Martin, James; Dickens, Ricky; Salvail, Pat; Hrbub, Ivana; Schmidt, George R. (Technical Monitor)

2000-01-01

277

Conservation of Isospin in Neutron-Rich Fission Fragments  

E-print Network

On the occasion of the $75^{th}$ anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavy-ion reactions $^{238}$U($^{18}$O,f) and $^{208}$Pb($^{18}$O,f) as well as a thermal neutron fission reaction $^{245}$Cm(n$^{th}$,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

Ashok Kumar Jain; Deepika Choudhury; Bhoomika Maheshwari

2014-08-11

278

REFUGIA AND MIGRATION IN THE QUATERNARY HISTORY OF THE NEW ENGLAND FLORA  

E-print Network

REFUGIA AND MIGRATION IN THE QUATERNARY HISTORY OF THE NEW ENGLAND FLORA DAVID S. BARRINGTON, biogeography, genetic diversity, plant migration, refugia One of the prominent themes in the first century

Lintilhac, Philip M.

279

Enantioselective synthesis of benzazepinoindoles bearing trifluoromethylated quaternary stereocenters catalyzed by chiral spirocyclic phosphoric acids.  

PubMed

The first highly enantioselective iso-Pictet-Spengler reaction of C-2-linked o-aminobenzylindoles with trifluoromethyl ketones was developed using chiral spirocyclic phosphoric acids as organocatalysts, which afforded optically active benzazepinoindoles bearing trifluoromethylated quaternary stereocenters. PMID:24890313

Li, Xuejian; Chen, Di; Gu, Haorui; Lin, Xufeng

2014-07-18

280

A multiple quantum well integrated with a selectively grown quaternary layer  

NASA Astrophysics Data System (ADS)

The multiple quantum well is an important backbone to a number of advanced III-V optoelectronic devices. These include semiconductor lasers, detectors and modulators. Increased device functionality can be achieved by monolithically integrating a multiple quantum well with a selectively grown bulk quaternary. We report on a method for fabricating a selectively deposited quaternary film integrated with a multiple quantum well in an MOCVD reactor. Selective area epitaxy is known to cause a composition shift in the deposited quaternary. Quantitative modelling of the selective area epitaxy process is used to determine the nominal group-III composition required to deposit a quaternary film such that the peak strain induced by the composition shift is minimized. Measurements using spatially resolved photoluminescence and surface profiling are reported to demonstrate the validity and usefulness of the model.

Greenspan, J. E.; Campbell, S.; Shih, I.

2006-07-01

281

Quaternary Science Reviews 24 (2005) 23752391 Saginaw Lobe tunnel channels (Laurentide Ice Sheet) and  

E-print Network

Quaternary Science Reviews 24 (2005) 2375­2391 Saginaw Lobe tunnel channels (Laurentide Ice Sheet meltwater activity beneath the Saginaw Lobe of the Laurentide Ice Sheet. The channels are incompletely

Fisher, Timothy G.

282

OMVPE Growth of Quaternary (Al,Ga,In)N for UV Optoelectronics (title change from A)  

SciTech Connect

We report the growth and characterization of quaternary AlGaInN. A combination of photoluminescence (PL), high-resolution x-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) characterizations enables us to explore the contours of constant PL peak energy and lattice parameter as functions of the quaternary compositions. The observation of room temperature PL emission at 351nm (with 20% Al and 5% In) renders initial evidence that the quaternary could be used to provide confinement for GaInN (and possibly GaN). AlGaInN/GrdnN MQW heterostructures have been grown; both XRD and PL measurements suggest the possibility of incorporating this quaternary into optoelectronic devices.

HAN,JUNG; FIGIEL,JEFFREY J.; PETERSEN,GARY A.; MYERS JR.,SAMUEL M.; CRAWFORD,MARY H.; BANAS,MICHAEL ANTHONY; HEARNE,SEAN JOSEPH

2000-01-18

283

The late Quaternary limnological history of Lake Kinneret (Sea of Galilee), Israel  

E-print Network

The late Quaternary limnological history of Lake Kinneret (Sea of Galilee), Israel N. Hazana , M) during the Neogene­Quartenary periods. We reconstructed the limnological history (level and composition

Marco, Shmuel "Shmulik"

284

Distribution of Prompt Neutron Emission Probability for Fission Fragments in Spontaneous Fission of 252Cf and 244,248Cm  

NASA Astrophysics Data System (ADS)

Neutrons emitted in fission events were measured separately for each complementary fragment in correlation with fission fragment energies. Two high-efficiency Gd-loaded liquid scintillator tanks were used for neutron registration. Fission fragment energies were measured using a twin Frisch gridded ionization chamber with a pinhole collimator. The neutron multiplicity distributions were obtained for each value of the fission fragment mass and energy and corrected for neutron registration efficiency, background, and pile-up. The dependency of these distributions on fragment mass and energy for different energy and mass bins as well as mass and energy distribution of fission fragments are presented and discussed.

Vorobyev, A. S.; Dushin, V. N.; Hambsch, F.-J.; Jakovlev, V. A.; Kalinin, V. A.; Laptev, A. B.; Petrov, B. F.; Shcherbakov, O. A.

2005-05-01

285

The role of Quaternary environmental change in plant macroevolution: the exception or the rule?  

PubMed Central

The Quaternary has been described as an important time for genetic diversification and speciation. This is based on the premise that Quaternary climatic conditions fostered the isolation of populations and, in some instances, allopatric speciation. However, the 'Quaternary Ice-Age speciation model' rests on two key assumptions: (i) that biotic responses to climate change during the Quaternary were significantly different from those of other periods in Earth's history; and (ii) that the mechanisms of isolation during the Quaternary were sufficient in time and space for genetic diversification to foster speciation. These assumptions are addressed by examining the plant fossil record for the Quaternary (in detail) and for the past 410 Myr, which encompasses previous intervals of icehouse Earth. Our examination of the Quaternary record indicates that floristic responses to climate changes during the past 1.8 Myr were complex and that a distinction has to be made between those plants that were able to withstand the extremes of glacial conditions and those that could not. Generation times are also important as are different growth forms (e.g. herbaceous annuals and arborescent perennials), resulting in different responses in terms of genetic divergence rates during isolation. Because of these variations in the duration of isolation of populations and genomic diversification rates, no canonical statement about the predominant floristic response to climatic changes during the Quaternary (i.e. elevated rates of speciation or extinction, or stasis) is currently possible. This is especially true because of a sampling bias in terms of the fossil record of tree species over that of species with non-arborescent growth forms. Nevertheless, based on the available information, it appears that the dominant response of arborescent species during the Quaternary was extinction rather than speciation or stasis. By contrast, our examination of the fossil record of vascular plants for the past 410 Myr indicates that speciation rates often increased during long intervals of icehouse Earth (spanning up to 50 Myr). Therefore, longer periods of icehouse Earth than those occurring during the Quaternary may have isolated plant populations for sufficiently long periods of time to foster genomic diversification and allopatric speciation. Our results highlight the need for more detailed study of the fossil record in terms of finer temporal and spatial resolution than is currently available to examine the significance of intervals of icehouse Earth. It is equally clear that additional and detailed molecular studies of extant populations of Quaternary species are required in order to determine the extent to which these 'relic' species have genomically diversified across their current populations. PMID:15101573

Willis, Katherine J; Niklas, Karl J

2004-01-01

286

THE NORWEGIAN–GREENLAND SEA CONTINENTAL MARGINS: MORPHOLOGY AND LATE QUATERNARY SEDIMENTARY PROCESSES AND ENVIRONMENT  

Microsoft Academic Search

The continental margins surrounding the Norwegian–Greenland Sea are to a large degree shaped by processes during the late Quaternary. The paper gives an overview of the morphology and the processes responsible for the formation of three main groups of morphological features: slides, trough mouth fans and channels.Several large late Quaternary slides have been identified on the eastern Norwegian–Greenland Sea continental

TORE O. VORREN; JAN SVERRE LABERG; FRANK BLAUME; JULIAN A. DOWDESWELL; NEIL H. KENYON; JÜRGEN MIENERT; JAN RUMOHR; FRIEDRICH WERNER

1998-01-01

287

Effect of alkyl quaternary ammonium on processing discoloration of melt-intercalated PVC-montmorillonite composites  

Microsoft Academic Search

The effects of alkyl quaternary ammonium on the processing thermal stability of poly (vinyl chloride)\\/alkyl quaternary ammonium modified montmorillonite (PVC\\/OMMT) composites were investigated. PVC\\/sodium montmorillonite (MMT) composites were prepared for comparison. The intercalated PVC\\/OMMT composites exhibited a non-terminal rheological behavior, and showed better mechanical properties and higher thermal degradation stability than the PVC\\/MMT composites. However, under identical melt processing conditions,

Chaoying Wan; Yong Zhang; Yinxi Zhang

2004-01-01

288

Catalytic performance of quaternary ammonium salts in the reaction of butyl glycidyl ether and carbon dioxide  

Microsoft Academic Search

The synthesis of cyclic carbonate from butyl glycidyl ether (BGE) and carbon dioxide was performed in the presence of quaternary ammonium salt catalysts. Quaternary ammonium salts of different alkyl group (C3, C4, C6 and C8) and anions (Cl?, Br? and I?) were used for this reaction carried out in a batch autoclave reactor at 60–120°C. The catalytic activity increased with

Hye-Young Ju; Mamparambath-Dharman Manju; Kyung-Hoon Kim; Sang-Wook Park; Dae-Won Park

2008-01-01

289

Synergistic chiral ion pair catalysts for asymmetric catalytic synthesis of quaternary ?,?-diamino acids.  

PubMed

The combination of a chiral phosphate anion with a silver ion has been demonstrated as a powerful and synergistic ion pair catalyst for the aza-Mannich reaction. A series of valuable quaternary ?,?-diamino acid derivatives was obtained in high yield, and with excellent diastereo- (up to 25:1 dr) and enantioselectivity (up to 99% ee). The adducts can be smoothly transformed into the corresponding protected chiral quaternary ?,?-diamino acids by a one-pot hydrolysis reaction. PMID:22472066

Shi, Shi-Hui; Huang, Fu-Ping; Zhu, Ping; Dong, Zhen-Wen; Hui, Xin-Ping

2012-04-20

290

Band Edge Energies and Band Gaps of Quaternary GaInAsSb Alloys  

Microsoft Academic Search

Quaternary alloys without a common atom such as (Ga,In)-(As,Sb) pose a difficult combinatorially design problem in that there are many different atomic configurations even when the system is constrained to be lattice-matched on a substrate. Using an atomistic pseudopotential approach we have calculated the band edge energies of this quaternary random alloys as a function of Ga\\/In (x) and As\\/Sb

Rita Magri; Alex Zunger; Herbert Kroemer

2007-01-01

291

System Concepts for Affordable Fission Surface Power  

NASA Technical Reports Server (NTRS)

This paper presents an overview of an affordable Fission Surface Power (FSP) system that could be used for NASA applications on the Moon and Mars. The proposed FSP system uses a low temperature, uranium dioxide-fueled, liquid metal-cooled fission reactor coupled to free-piston Stirling converters. The concept was determined by a 12 month NASA/DOE study that examined design options and development strategies based on affordability and risk. The system is considered a low development risk based on the use of terrestrial-derived reactor technology, high efficiency power conversion, and conventional materials. The low-risk approach was selected over other options that could offer higher performance and/or lower mass.

Mason, Lee; Poston, David; Qualls, Louis

2008-01-01

292

True ternary fission of superheavy nuclei  

SciTech Connect

True ternary fission with formation of a heavy third fragment is quite possible for superheavy nuclei because of the strong shell effects leading to a three-body clusterization with the two doubly magic tinlike cores. The simplest way to discover this phenomenon in the decay of excited superheavy nuclei is a detection of two tinlike clusters with appropriate kinematics in low-energy collisions of medium-mass nuclei with actinide targets. The three-body quasi-fission process could be even more pronounced for giant nuclear systems formed in collisions of heavy actinide nuclei. In this case a three-body clusterization might be proved experimentally by the detection of two coincident leadlike fragments in low-energy U + U collisions.

Zagrebaev, V. I.; Karpov, A. V. [Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region (Russian Federation); Greiner, Walter [Frankfurt Institute for Advanced Studies, J.W. Goethe-Universitaet, D-60438 Frankfurt am Main (Germany)

2010-04-15

293

Nuclear Fission Investigation with Twin Ionization Chamber  

SciTech Connect

The purpose of the present paper was to report the recent results, obtained in development of digital pulse processing mathematics for prompt fission neutron (PFN) investigation using twin ionization chamber (TIC) along with fast neutron time-of-flight detector (ND). Due to well known ambiguities in literature (see refs. [4, 6, 9 and 11]), concerning a pulse induction on TIC electrodes by FF ionization, we first presented detailed mathematical analysis of fission fragment (FF) signal formation on TIC anode. The analysis was done using Ramo-Shockley theorem, which gives relation between charged particle motion between TIC electrodes and so called weighting potential. Weighting potential was calculated by direct numerical solution of Laplace equation (neglecting space charge) for the TIC geometry and ionization, caused by FF. Formulae for grid inefficiency (GI) correction and digital pulse processing algorithms for PFN time-of-flight measurements and pulse shape analysis are presented and discussed.

Zeynalova, O.; Zeynalov, Sh. [JINR-Joint Institute for Nuclear Research, Dubna, Moscow region (Russian Federation); Nazarenko, M. [Moscow State Institute of Radioengineering and Automation, 78 Vernadski Avenue, 119454 Moscow (Russian Federation); Hambsch, F.-J.; Oberstedt, S. [EC-JRC Institute for Reference Materials and Measurements, Retieseweg 111, 2440 Geel (Belgium)

2011-11-29

294

Hot Bimodal Ternary Fission in 252Cf  

NASA Astrophysics Data System (ADS)

Spontaneous fission of ^252Cf was studied with 8 light charged particle detectors in Gammasphere. With a 62 ?C source, 5.7x10^11 triple-coincidence events were recorded. In coincidence with LCP, the ?-? matrix was analyzed. We obtained the relative yields of fission fragment pairs as a function of the neutron number. In the Ba-?-Zr and Mo-?-Xe splits, the 6n-10n channels show enhanced neutron emissions, just as previously found for the hot bimodal Ba-Mo binary yield. Two Gaussian curves describe the data, centered on 3.5 and 7 neutrons. For Mo-?-Xe, the average neutron numbers are approximately 3 and 6, and for Ba-?-Zr, approximately 3 and 8.

Fong, Dennis; Jandel, M.; Hamilton, J.; Ramayya, Akunuri; Hwang, J. K.; Gore, P.; Kormicki, J.; Luo, Y. X.; Kliman, J.; Krupa, L.; Daniel, A. V.; Fomichev, A.; Popeko, G. S.; Rodin, A.; Ter-Akopian, G. M.; Oganessian, Y. T.; Rasmussen, J. O.; Macchiavelli, A. O.; Stoyer, M. A.; Donangelo, R.; Cole, J. D.

2002-10-01

295

Hot Bimodal Ternary Fission in 252CF  

NASA Astrophysics Data System (ADS)

Spontaneous fission of 252Cf was studied with 8 light charged particle detectors in Gammasphere. 9×105 alpha coincident events were recorded. In coincidence with LCP, the ?-? matrix was analyzed. We obtained the relative yields of fission fragment pairs as a function of the neutron number. In the Ba-?-Zr and Mo-?-Xe splits, the 6n-10n channels show enhanced neutron emissions, just as previously found for the hot bimodal Ba-Mo binary yield. Two Gaussian curves describe the data, centered on 3.5 and 7 neutrons. For Mo-?-Xe, the average neutron numbers are approximately 3 and 6, and for Ba-?-Zr, approximately 3 and 8.

Fong, D.; Jandel, M.; Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Gore, P.; Kormicki, J.; Luo, Y. X.; Kliman, J.; Krupa, L.; Daniel, A. V.; Fomichev, A.; Popeko, G. S.; Rodin, A.; Ter-Akopian, G. M.; Oganessian, Y. T.; Rasmussen, J. O.; Macchiavelli, A. O.; Lee, I. Y.; Stoyer, M. A.; Donangelo, R.; Cole, J. D.; Greiner, W.; Poenaru, D.

2003-10-01

296

Fusion-fission energy systems evaluation  

SciTech Connect

This report serves as the basis for comparing the fusion-fission (hybrid) energy system concept with other advanced technology fissile fuel breeding concepts evaluated in the Nonproliferation Alternative Systems Assessment Program (NASAP). As such, much of the information and data provided herein is in a form that meets the NASAP data requirements. Since the hybrid concept has not been studied as extensively as many of the other fission concepts being examined in NASAP, the provided data and information are sparse relative to these more developed concepts. Nevertheless, this report is intended to provide a perspective on hybrids and to summarize the findings of the rather limited analyses made to date on this concept.

Teofilo, V.L.; Aase, D.T.; Bickford, W.E.

1980-01-01

297

Fission Product Release from SLOWPOKE-2 Reactors  

NASA Astrophysics Data System (ADS)

Increasing radiation fields at several SLOWPOKE -2 reactors fuelled with highly enriched uranium aluminum alloy fuel have begun to interfere with the daily operation of these reactors. To investigate this phenomenon, samples of reactor container water and gas from the headspace above the reactor were obtained at four SLOWPOKE-2 reactor facilities and examined by gamma ray spectroscopy methods. These radiation fields are due to the circulation of fission products within the reactor container vessel. The most likely source of the fission product release is an area of uranium-bearing material exposed to the coolant at the end weld line which originated at the time of fuel fabrication. The results of this study are compared with observations from an underwater visual examination of one core and the metallographic examination of archived fuel elements.

Harnden, Anne M. C.

298

Microscopic Calculations of 240Pu Fission  

SciTech Connect

Hartree-Fock-Bogoliubov calculations have been performed with the Gogny finite-range effective interaction for {sup 240}Pu out to scission, using a new code developed at LLNL. A first set of calculations was performed with constrained quadrupole moment along the path of most probable fission, assuming axial symmetry but allowing for the spontaneous breaking of reflection symmetry of the nucleus. At a quadrupole moment of 345 b, the nucleus was found to spontaneously scission into two fragments. A second set of calculations, with all nuclear moments up to hexadecapole constrained, was performed to approach the scission configuration in a controlled manner. Calculated energies, moments, and representative plots of the total nuclear density are shown. The present calculations serve as a proof-of-principle, a blueprint, and starting-point solutions for a planned series of more comprehensive calculations to map out a large set of scission configurations, and the associated fission-fragment properties.

Younes, W; Gogny, D

2007-09-11

299

Pliocene - Quaternary Faults and Potential Seismic Hazards in Southern Nevada  

NASA Astrophysics Data System (ADS)

Known Quaternary faults in the Central Basin & Range Province (CBR) have a southern limit at about 35 degrees 30' N latitude, south of Las Vegas, NV. The boundary is generally aligned with the southern end of the Sierra Nevada and strike-slip faults, such as those in Death Valley, that accommodate the right-lateral motion transferred from the plate boundary to east of the Sierra Nevada. Between ~8-4 Ma, the time range when the right-lateral motion was transferred to the east, CBR tectonism changed from rapid extension, low-angle normal faulting, and strike-slip faulting in the center to strike-slip faulting in the west and slower extension along normal faults in the middle and eastern CBR. Timing data from known <6-4 Ma CBR normal faults near the southern limit of Quaternary faulting show synchronicity with strike-slip faults in the southern Walker Lane and Eastern California shear zone on the west. Excellent examples of young faults in southern Nevada lie in Las Vegas basin and eastward to Mesquite. Our detailed stratigraphic and fault model of Las Vegas basin combined with shear-wave data shows significant ground shaking would occur there as a result of large magnitude earthquakes on almost any CBR fault. Faults in southern Nevada with documented Holocene activity include the normal-slip California Wash and Black Hills faults, and the strike-slip Mead Slope, Rock Valley, Pahrump Valley and Amargosa Valley faults / fault zones. The latter two faults aid in accommodating the step-over of some plate boundary slip from the San Andreas fault to faults east of the Sierra Nevada. Potential earthquake magnitudes for these faults range from ~M6.5-7.2 based on surface rupture lengths and documented single-event offsets. The <6-4 Ma central CBR faults appear to accommodate a change in shape of the rock volume between the strike-slip faults on the west and the Colorado Plateau to the east. We suggest that the shape change results from NW-motion of strike-slip fault blocks in the west and deformation on long segmented normal faults in the east.

Taylor, W. J.; Wagoner, J.; Depolo, C. M.; Luke, B.; Louie, J.

2005-12-01

300

Late Quaternary carbonate deposition at the bottom of the world  

NASA Astrophysics Data System (ADS)

Carbonate sediments on polar shelves hold great potential for improving understanding of climate and oceanography in regions of the globe that are particularly sensitive to global change. Such deposits have, however, not received much attention from sedimentologists and thus remain poorly understood. This study investigates the distribution, composition, diagenesis, and stratigraphic context of Late Quaternary calcareous sediments recovered in 15 piston cores from the Ross Sea shelf, Antarctica. Results are used to develop a depositional model for carbonate deposition on glaciated, polar shelves. The utility of the deposits as analogs for the ancient record is explored. In the Ross Sea, carbonate-rich lithofacies, consisting of poorly sorted skeletal sand and gravel, are concentrated in the west and along the outer reaches of the continental shelf and upper slope. Analysis of fossil assemblages shows that deposits were produced by numerous low-diversity benthic communities dominated locally by stylasterine hydrocorals, barnacles, or bryozoans. Radiocarbon dating indicates that carbonate sedimentation was episodic, corresponding to times of reduced siliciclastic deposition. Most accumulation occurred during a time of glacial expansion in the lead-up to the Last Glacial Maximum. A more recent interval of carbonate accumulation postdates the early Holocene sea level rise and the establishment of the modern grounding line for the Ross Ice Shelf. When carbonate factories were inactive, fossil debris was subjected to infestation by bioeroders, dissolution, fragmentation, and physical reworking. This study reveals the episodic nature of carbonate deposition in polar settings and a reciprocal relationship with processes that deliver and redistribute siliciclastic debris. Carbonate production is most active during colder periods of the glacial-interglacial cycle, a potential new sedimentological paradigm for polar carbonate systems. Low accumulation rates and long residence times on the seafloor leave sediments vulnerable to significant post-depositional modification, processes that profoundly affect the appearance of deposits as they enter the rock record. Comparison with other examples of polar carbonates highlights the utility of these Late Quaternary deposits as a well-constrained analog that can aid in the recognition and interpretation of similar deposits from the ancient record.

Frank, Tracy D.; James, Noel P.; Bone, Yvonne; Malcolm, Isabelle; Bobak, Lindsey E.

2014-05-01

301

LONG-RANGE PARTICLES FROM NUCLEAR FISSION  

Microsoft Academic Search

A measurement of the probability of emission of longrange particles, ; which are known to be predominantly alpha particles, made with a multiple ; ionization chamber gave the following results for spontaneous fission: Cf²⁵²; , 299 plus or minus 18; Cm²⁴², 257 plus or minus 17; Cm²⁴⁴, 314 ; plus or minus 20; Pu²⁴°, 314 approximately 20; a nd Pu²⁴²,

Ralph Nobles

1962-01-01

302

Fusion, Fission, and Secretion During Phagocytosis  

NSDL National Science Digital Library

Phagocytosis is essential for the elimination of pathogens and for clearance of apoptotic bodies. The ingestion process entails extensive remodeling of the cellular membranes, particularly when large and/or multiple particles are engulfed. The membrane fusion and fission events that accompany phagocytosis are described. The coordinated sequence of membrane trafficking events required for phagocytosis involves multiple organelles and also serves other cellular functions, such as cytokine secretion.

2007-12-01

303

Observation of thermoluminescence induced by fission fragments  

Microsoft Academic Search

Thermoluminescence induced in CaF2 powder by fission fragments emanating from a uranium foil bombarded by fast neutrons has been measured as a function of neutron fluence. A linear relationship between the glow produced and the fast neutron fluence between 5 × 1010 and 6.5 × 1011 n\\/cm2 has been obtained, thus establishing the feasibility of the use of this method

K. V. Ettinger; S. A. Durrant; C. Christodoulides

1970-01-01

304

Fission fragment rockets: A new frontier  

SciTech Connect

A new reactor concept is described which would enable fission fragments to be continuously extracted from the reactor. Such a reactor has the potential of enabling extremely energetic and ambitious deep space missions. In this talk the basic physics issues involved in the operation of this type of reactor are outlined, and some possible applications to space exploration are described. 3 refs., 2 figs., 3 tabs.

Chapline, G.F.; Howard, W.M.; Schnitzler, B.G.

1989-04-01

305

Laser produced plasmas with fissionable material  

Microsoft Academic Search

The compression of a pellet consisting of fissionable material, such as U233, U235 or Pu239, to high densities by a laser- (or possibly relativistic electron-) beam induced implosion, will lead to very small critical masses. The critical mass can be furthermore substantially reduced by simultaneously compressing the pellet together with a neutron reflector. By this method microfission-explosions can be triggered

F. Winterberg

1974-01-01

306

Near Term Fission-Fusion Hybrids- Advantages for Fission and Fusion  

NASA Astrophysics Data System (ADS)

Fission-fusion hybrids are described with unique advantages relative to fission only systems, for different missions. Innovative designs allow hybrids to incinerate waste, or produce fuel, with far fewer hybrids than would be possible with fission-only fast reactors. In addition, hybrids can perform these missions while addressing concerns regarding proliferation, by using unique fuel cycles, not accessible to fission alone, that use no reprocessing, or greatly reduced reprocessing. These goals can be achieved using fusion devices in the range considered for fusion Component Test Facilities (CTF). The fusion physics and fusion engineering performance necessary for these missions is far less stringent than for a pure fusion power reactor. Unique designs aspects substantially separate the fission and fusion aspects, allowing much more independent development of each. Hence, a suitable hybrid can provide a nearer term, lower risk, application for fusion, and be an additional incentive to implement a fusion CTF device. The fuel cycle possibilities above are verified using Monte-Carlo neutron calculations. Fusion neutron sources with high power densities and modest power levels are sufficient and necessary.

Kotschenreuther, M.; Mahajan, S.; Valanju, P.

2010-11-01

307

Spontaneous fission half-lives and their systematics  

SciTech Connect

Spontaneous fission is a phenomenon exhibited by heavy nuclei, which can be a major mode of decay of nuclei of elements heavier than thorium and can be a determining factor in their stability. For purposes of this paper, spontaneous fission will be considered a process in which a nucleus breaks up into two approximately equal parts. The emission of light nuclei or heavy ions such as {sup 12}C, {sup 16}O, or {sup 32}S will not be considered. This radioactive decay mode is often much smaller than the spontaneous fission decay mode, although this is not true in all cases. Barwick noted that this might indicate that the assumed half-life for spontaneous fission of some older experiments might be partially due to heavy fragment radioactivity. Other than taking note of this potential correction to spontaneous fission half-lives, this decay mode of heavy fragment radioactivity will be ignored. Excited states of some heavy nuclei may decay via spontaneous fission. These so-called fission isomers will not be discussed here. Electron capture (EC) or beta-delayed fission is a process in which prompt fission of a sufficiently excited daughter state occurs following population by EC or beta decay. The fission activity will appear to decay with the half-life of the parent and was earlier confused in some cases with SF. This process has been discussed in detail in a review and will not be considered in this paper.

Holden, N.E.

1998-03-01

308

Undergraduate Measurements For Fission Reactor Applications  

SciTech Connect

Undergraduate students at the University of Dallas (UD) have investigated elastic and inelastic neutron scattering cross sections on structural materials important for criticality considerations in nuclear fission processes. Neutrons scattered off of {sup 23}Na and {sup Nat}Fe were detected using neutron time-of-flight techniques at the University of Kentucky Low-Energy Nuclear Accelerator Facility. These measurements are part of an effort to increase the efficiency of power generation from existing fission reactors in the US and in the design of new fission systems. Students have learned the basics of how to operate the Model CN Van de Graaff generator at the laboratory, setup detectors and electronics, use data acquisition systems, and they are currently analyzing the angular dependence of the scattered neutrons for incident neutron energies of 3.57 and 3.80 MeV. Most students participating in the project will use the research experience as the material for their undergraduate research thesis required for all Bachelor of Science students at the University of Dallas. The first student projects on this topic were completed during the summer of 2010; an overview of student participation in this investigation and their preliminary results will be presented.

Hicks, S. F.; Kersting, L. J.; Lueck, C. J.; McDonough, P. [Department of Physics, University of Dallas, Irving TX 75019 (United States); Crider, B. P.; McEllistrem, M. T.; Peters, E. E. [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States); Vanhoy, J. R. [Department of Physics, United States Naval Academy, Annapolis MD 21402 (United States)

2011-06-01

309

Time dependent particle emission from fission products  

SciTech Connect

Decay heating following nuclear fission is an important factor in the design of nuclear facilities; impacting a variety of aspects ranging from cooling requirements to shielding design. Calculations of decay heat, often assumed to be a simple product of activity and average decay product energy, are complicated by the so called 'pandemonium effect'. Elucidated in the 1970's this complication arises from beta-decays feeding high-energy nuclear levels; redistributing the available energy between betas and gammas. Increased interest in improving the theoretical predictions of decay probabilities has been, in part, motivated by the recent experimental effort utilizing the Total Absorption Gamma-ray Spectrometer (TAGS) to determine individual beta-decay transition probabilities to individual nuclear levels. Accurate predictions of decay heating require a detailed understanding of these transition probabilities, accurate representation of particle decays as well as reliable predictions of temporal inventories from fissioning systems. We will discuss a recent LANL effort to provide a time dependent study of particle emission from fission products through a combination of Quasiparticle Random Phase Approximation (QRPA) predictions of beta-decay probabilities, statistical Hauser-Feshbach techniques to obtain particle and gamma-ray emissions in statistical Hauser-Feshbach and the nuclear inventory code, CINDER.

Holloway, Shannon T [Los Alamos National Laboratory; Kawano, Toshihiko [Los Alamos National Laboratory; Moller, Peter [Los Alamos National Laboratory

2010-01-01

310

Fission Barriers of Compound Superheavy Nuclei  

NASA Astrophysics Data System (ADS)

The dependence of fission barriers on the excitation energy of the compound nucleus impacts the survival probability of superheavy nuclei synthesized in heavy-ion fusion reactions. In this work [1,2], we investigate the isentropic fission barriers by means of the self-consistent nuclear density functional theory. The relationship between isothermal and isentropic descriptions is demonstrated. Calculations have been carried out for ^264Fm, ^272Ds, ^278Cp, ^292114, and ^312124. For nuclei around ^278Cp produced in ``cold fusion" reactions, we predict a more rapid decrease of fission barriers with excitation energy as compared to the nuclei around ^292114 synthesized in ``hot fusion'' experiments. This is explained in terms of the difference between the ground-state and saddle-point temperatures. [4pt] [1] J.C. Pei, W. Nazarewicz, J.A. Sheikh and A.K. Kerman, Phys. Rev. Lett. 102, 192501 (2009).[0pt] [2] J.A. Sheikh, W. Nazarewicz, and J.C. Pei, Phys. Rev. C 80, 011302(R) (2009). )

Nazarewicz, Witold

2010-02-01

311

Quaternary heteroaromatic salts with prophylactic and antidotal activity towards soman  

SciTech Connect

A series of quaternary heteroaromatic salts has been prepared and evaluated for prophylactic and antidotal activity towards the lethal toxicity of soman. One series of compounds contains 2-, 3-, or 4-(dimethylaminocarbonyloxy)phenoxymethyl substituents at the 2 position of the following rings: 1,3-dimethylimidazolium, 1-methylpyridinium, 1-methylquinolinium, 1,3-dimethylbenzimidazolium and 1-methylimidazo1,2-Apyridinium. The compounds were evaluated both in vitro, by determining the IC50 for electric eel acetylcholinesterase, and in vivo, using both antidotal and prophylactic assays in mice. Compound 2b was most active in the in vitro assay (IC50 = 0.01 M). However, its toxicity is high and compound la is more effective in vivo with 80-100% protective activity against 2 LD50 of soman at 6.2 to 62.5 mg/kg. A second series of compounds consisted of 6-substituted 2'-, 3'-, and 4'-(dimethylaminocarbonyloxy) phenylimidazo (1,2-a) pyridinium salts (8).

Sundberg, R.J.; Dalvie, D.; Cordero, J.; Sabat, M.

1993-05-13

312

Latest quaternary volcanism in the St. George Basin, southwestern Utah  

SciTech Connect

The St. George Basin was the site of mafic volcanism from about 6 Ma to 1 ka. The nature of latest Quaternary volcanism is of interest because the Basin is recognized as a low temperature (< 90C) geothermal resource area and it is part of the transition zone between the Basin and Range Province and the Colorado Plateau. The authors have studied the geochemistry, mineralogy, and aerial distribution of two of the youngest eruptions centers: (1) Veyo Volcano; and (2) the Diamond Valley scoria cones (DVSC). Veyo Volcano erupted basaltic andesite, beginning with an explosive stage marked by a 0.5 m basal Plinian layer. Later eruptions alternated between quiescent and Strombolian-styles. Phenocrysts include clear plagioclase, sieve-texture plagioclase, olivine and rare augite. The DVSC and associated Santa Clara lava flow are tholeiitic basalt, consisting of olivine phenocrysts, and rare plagioclase phenocrysts. Based on preliminary geochemical data, Diamond Valley rocks exhibit lower incompatible element ratios compared to mafic rocks on the Markagunt Plateau and transition zone rocks. In contrast, Veyo Volcano rocks are similar to transition zone mafic rocks with regard to incompatible element abundances.

Millings, V.T. III; Green, J.D.; Nusbaum, R.L. (Coll. of Charleston, SC (United States). Dept. of Geology)

1993-03-01

313

Antibacterial nanocomposite with calcium phosphate and quaternary ammonium.  

PubMed

Secondary caries is a frequent reason for restoration failure, resulting from acidogenic bacteria and their biofilms. The objectives of this study were to: (1) develop a novel nanocomposite containing nanoparticles of amorphous calcium phosphate (NACP) and quaternary ammonium dimethacrylate (QADM); and (2) investigate its mechanical and antibacterial durability. A spray-drying technique yielded NACP with particle size of 116 nm. The nanocomposite contained NACP and reinforcement glass fillers, with QADM in the resin. Two commercial composites were tested as controls. Composites were inoculated with Streptococcus mutans. After 180-day water-aging, NACP+QADM nanocomposite had flexural strength and elastic modulus matching those of commercial controls (p > 0.1). NACP+QADM nanocomposite reduced the biofilm colony-forming units (CFU) by 3-fold, compared with commercial composites (p < 0.05). Metabolic activity and lactic acid production of biofilms on NACP+QADM were much less than those on commercial composites (p < 0.05). The antibacterial properties of NACP+QADM were maintained after water-aging for 30, 90, and 180 d (p > 0.05). In conclusion, the novel NACP-QADM nanocomposite greatly decreased biofilm metabolic activity, CFU, and lactic acid, while matching the load-bearing capability of commercial composites without antibacterial properties. The NACP-QADM nanocomposite with strong and durable antibacterial properties, together with its previously reported Ca-PO(4) release capability, may render it useful for caries-inhibiting restorations. PMID:22403412

Cheng, L; Weir, M D; Zhang, K; Xu, S M; Chen, Q; Zhou, X; Xu, H H K

2012-05-01

314

Mucoadhesive nanoparticles made of thiolated quaternary chitosan crosslinked with hyaluronan.  

PubMed

Mucoadhesive polymeric nanoparticles intended for drug transport across the gastrointestinal mucosa were prepared from quaternary ammonium-chitosan conjugates synthesised from reduced-MW chitosan (32 kDa). Conjugates contained pendant moieties of 2-4 adjacent diethyl-dimethylene-ammonium groups substituted on repeating units (26-55%). Conjugates were thiolated via amide bonds with thioglycolic acid to yield products with thiol content in the 35-87 ?mol/g range. Nanoparticles with mean size in the 270-370 nm range and positive zeta-potential (+3.7 to +12.5 mV) resulted from ionotropic gelation of the thiolated conjugates with de-polymerised hyaluronic acid (470 kDa). The nanoparticles were fairly stable in size and thiol content and showed a significant mucoadhesivity, matching and even exceeding that of the constituent polymers. Nanoparticles were internalised by endothelial progenitor cells in direct relation to their surface charge intensity. Nanoparticle uptake significantly improved cell viability and resistance to oxidation. The lyophilised nanoparticles were re-dispersible and could make a manageable formulation for oral use. PMID:23218262

Zambito, Ylenia; Felice, Francesca; Fabiano, Angela; Di Stefano, Rossella; Di Colo, Giacomo

2013-01-30

315

Effects of Quaternary Ammonium Chain Length on Antibacterial Bonding Agents  

PubMed Central

The objectives of this study were to synthesize new quaternary ammonium methacrylates (QAMs) with systematically varied alkyl chain lengths (CL) and to investigate, for the first time, the CL effects on antibacterial efficacy, cytotoxicity, and dentin bond strength of bonding agents. QAMs were synthesized with CL of 3 to 18 and incorporated into Scotchbond Multi-Purpose (SBMP) bonding agent. The cured resins were inoculated with Streptococcus mutans. Bacterial early attachment was investigated at 4 hrs. Biofilm colony-forming units (CFU) were measured after 2 days. With CL increasing from 3 to 16, the minimum inhibitory concentration and minimum bactericidal concentration were decreased by 5 orders of magnitude. Incorporating QAMs into SBMP reduced bacterial early attachment, with the least colonization at CL = 16. Biofilm CFU for CL = 16 was 4 log lower than SBMP control (p < .05). All groups had similar dentin bond strengths (p > .1). The new antibacterial materials had fibroblast/odontoblast viability similar to that of commercial controls. In conclusion, increasing the chain length of new QAMs in bonding agents greatly increased the antibacterial efficacy. A reduction in Streptococcus mutans biofilm CFU by 4 log could be achieved, without compromising bond strength and cytotoxicity. New QAM-containing bonding agents are promising for a wide range of restorations to inhibit biofilms. PMID:23958761

Li, F.; Weir, M.D.; Xu, H.H.K.

2013-01-01

316

Antibacterial Nanocomposite with Calcium Phosphate and Quaternary Ammonium  

PubMed Central

Secondary caries is a frequent reason for restoration failure, resulting from acidogenic bacteria and their biofilms. The objectives of this study were to: (1) develop a novel nanocomposite containing nanoparticles of amorphous calcium phosphate (NACP) and quaternary ammonium dimethacrylate (QADM); and (2) investigate its mechanical and antibacterial durability. A spray-drying technique yielded NACP with particle size of 116 nm. The nanocomposite contained NACP and reinforcement glass fillers, with QADM in the resin. Two commercial composites were tested as controls. Composites were inoculated with Streptococcus mutans. After 180-day water-aging, NACP+QADM nanocomposite had flexural strength and elastic modulus matching those of commercial controls (p > 0.1). NACP+QADM nanocomposite reduced the biofilm colony-forming units (CFU) by 3-fold, compared with commercial composites (p < 0.05). Metabolic activity and lactic acid production of biofilms on NACP+QADM were much less than those on commercial composites (p < 0.05). The antibacterial properties of NACP+QADM were maintained after water-aging for 30, 90, and 180 d (p > 0.05). In conclusion, the novel NACP-QADM nanocomposite greatly decreased biofilm metabolic activity, CFU, and lactic acid, while matching the load-bearing capability of commercial composites without antibacterial properties. The NACP-QADM nanocomposite with strong and durable antibacterial properties, together with its previously reported Ca-PO4 release capability, may render it useful for caries-inhibiting restorations. PMID:22403412

Cheng, L.; Weir, M.D.; Zhang, K.; Xu, S.M.; Chen, Q.; Zhou, X.; Xu, H.H.K.

2012-01-01

317

Facilitating Progress on the Quaternary History of Sea Level Change  

NASA Astrophysics Data System (ADS)

Understanding Future Sea Level Rise: The Challenges of Dating Past Interglacials; Woods Hole, Massachusetts, 20-25 September 2009; Substantial uncertainty exists in projections of future sea level rise, due primarily to a lack of understanding about ice sheet dynamics. Paleo Constraints on Sea Level Rise (PALSEA) is a working group of the Past Global Changes (PAGES) project and the International Marine Global Change Studies (IMAGES) program that aims to extract information about ice sheet response to temperature change by examining the history of sea level over the Quaternary (spanning the past ˜2.5 million years). In particular, PALSEA focuses on the past 800,000 years, particularly interglacial periods, with a range of temperatures bracketing the modern. PALSEA recently held a workshop at Woods Hole Oceanographic Institution (WHOI). Funded by IMAGES, PAGES, and WHOI's Ocean and Climate Change Institute, the workshop focused on challenges in uranium-thorium (U-Th) coral dating. The meeting also included a public outreach event, “Where land and sea meet: Managing shoreline change over the next 100 years,” funded by WHOI's Morss Colloquium.

Thompson, W. G.; Andersen, M. B.

2010-04-01

318

Effects of quaternary ammonium chain length on antibacterial bonding agents.  

PubMed

The objectives of this study were to synthesize new quaternary ammonium methacrylates (QAMs) with systematically varied alkyl chain lengths (CL) and to investigate, for the first time, the CL effects on antibacterial efficacy, cytotoxicity, and dentin bond strength of bonding agents. QAMs were synthesized with CL of 3 to 18 and incorporated into Scotchbond Multi-Purpose (SBMP) bonding agent. The cured resins were inoculated with Streptococcus mutans. Bacterial early attachment was investigated at 4 hrs. Biofilm colony-forming units (CFU) were measured after 2 days. With CL increasing from 3 to 16, the minimum inhibitory concentration and minimum bactericidal concentration were decreased by 5 orders of magnitude. Incorporating QAMs into SBMP reduced bacterial early attachment, with the least colonization at CL = 16. Biofilm CFU for CL = 16 was 4 log lower than SBMP control (p < .05). All groups had similar dentin bond strengths (p > .1). The new antibacterial materials had fibroblast/odontoblast viability similar to that of commercial controls. In conclusion, increasing the chain length of new QAMs in bonding agents greatly increased the antibacterial efficacy. A reduction in Streptococcus mutans biofilm CFU by 4 log could be achieved, without compromising bond strength and cytotoxicity. New QAM-containing bonding agents are promising for a wide range of restorations to inhibit biofilms. PMID:23958761

Li, F; Weir, M D; Xu, H H K

2013-10-01

319

Enhanced adsorption of quaternary amine using modified activated carbon.  

PubMed

This study examined different methodologies to modify activated carbon (AC) for the removal of quaternary amine, tetramethylammonium hydroxide (TMAH), from water. Commercial carbon (WAC) was treated by nitric acid oxidation (NA-WAC), silica impregnation (SM-WAC0.5), and oxygen plasma (P10-WAC), and their characteristics and adsorption capacity were compared. The Langmuir model fitted the equilibrium adsorption data well under different pH. The maximum adsorption capacity of WAC was 27.77 mg/g, while those of NA-WAC, SM-WAC 0.5, and P10-WAC were 37.46, 32.83 and 29.03 mg/g, respectively. Nitric acid oxidation was the most effective method for enhancing the adsorption capacity of TMAH. Higher pH was favorable for TMAH adsorption. Desorption study revealed that NA-WAC had no considerable reduction in performance even after five cycles of regeneration by 0.1 N hydrochloric acid. It was proposed that electrostatic interaction was the main mechanism of TMAH adsorption on activated carbon. PMID:24845325

Prahas, Devarly; Wang, M J; Ismadji, Suryadi; Liu, J C

2014-01-01

320

Quaternary modulation formats for 100-Gbps optical links  

NASA Astrophysics Data System (ADS)

The demand for 100 Gb/s optical links is rapidly spreading across all levels of the optical networking infrastructure. Many of the first deployments will be in the local area network (LAN) and metro-core and regional network environments. To address needs in LAN, the upcoming IEEE standard (IEEE P802.3ba) seeks 100 Gb/s over distances up to 40km. Furthermore metro-core/regional dense wavelength division multiplexing (DWDM) architectures require reach of several hundred km and the ability to pass through ten or more ROADMs. However, a number of fundamental challenges remain including the selection of appropriate modulation formats that are robust to a variety of nonlinearities, are sufficiently spectrally efficient, and able to withstand the strong optical filtering of cascaded ROADMs. Here we compare a variety of single-carrier quaternary modulation formats, each providing 2 bits/symbol/polarization and each likely to provide some advantages at 100Gb/s. Each format is presented with an appropriate MZM-based transmitter, and constrained by practical signal fidelity limitations that also enable comparison to experimental results from our 100G testbed. We primarily examine direct detection for cost-sensitive metro networks; however we also quantify the performance of coherent receivers, where applicable. Simulation results demonstrate the relative OSNR penalty (at a pre-FEC BER of 10-3) for a range of launch powers and adjacent channel formats.

Detwiler, Thomas F.; Searcy, Steven M.; Lingle, Robert, Jr.; Basch, E. Bert; Ralph, Stephen E.

2010-01-01

321

Late Quaternary tephrostratigraphy of southern Chile and Argentina  

NASA Astrophysics Data System (ADS)

The Southern and Austral Volcanic Zones of the Andes comprise 74 volcanic centres with known post-glacial activity. At least 21 of these have had one or more large explosive eruptions in the late Quaternary, dispersing tephra over vast areas. These tephra layers therefore have great potential as tephrochronological marker horizons in palaeoenvironmental studies in southern Chile and Argentina, a region that is particularly useful to study climate dynamics of the southern hemisphere. However, to date tephrochronology has rarely been fully utilised in this region as a correlation and dating tool. Here we review the existing post-glacial tephrostratigraphic record of the Southern and Austral Volcanic Zones, and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine, marine, peat, and cave sediment records. We address the inconsistencies in and revisions of the tephrostratigraphies presented in prior literature, and discuss the challenges in correlating tephras and the limitations of the tephrostratigraphic record in this area. This study highlights the many gaps that still exist in our knowledge of the eruptive histories of these volcanoes, but also reveals the largely under-utilised potential of tephra as a correlation tool in this region. This is exemplified by the severe lack of adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections, which are particularly important tephrostratigraphic records in southern Chile and Argentina due to the paucity of surface preservation.

Fontijn, Karen; Lachowycz, Stefan M.; Rawson, Harriet; Pyle, David M.; Mather, Tamsin A.; Naranjo, José A.; Moreno-Roa, Hugo

2014-04-01

322

Liquid chromatography of hydrocarbonaeous quaternary amines on cyclodextrin bonded silica  

USGS Publications Warehouse

Mixtures of n-alkylbenzyldimethylammonium chloride (ABDAC) were resolved into homologous components by high-performance liquid chromatography (HPLC) with a cyclodextrin-bonded silica stationary phase. With a few exceptions, results from this study are similar to those obtained from traditional reversed-phase HPLC. It was found that the presence of electrolytes in aqueous mobile phases is not a critical factor in determining the success of HPLC separation. Under normal HPLC conditions, a mobile phase consisting of either methanol–water (50:50) or acetonitrile–water (30:70) was employed for obtaining adequate resolution of the quaternary ammonium mixtures. Although the percent organic modifier–water profiles were similar to those in previous studies with these compounds, resolution (R) and selectivity (?) parameters were found to be quite susceptible to changes in the mobile phase solvent composition. The retention behavior of the cationic analytes in the homologous series is consistent with the hydrophobic-interaction concept proposed for the retention mechanism via dominant inclusion complex formation. Several electrolytes were chosen for a study of the counter ion effect on the chromatographic characteristics of ABDAC components. Among the electrolytes examined, the perchlorate ion was found most likely to act as an ion-pairing counter ion for ammonium cations in the HPLC system studied. A correlation study established linear relationships between the chain length of ABDAC and the logarithmic capacity factor (k2). The analytical utility of the HPLC method was demonstrated by the analysis of various unknown mixtures.

Abidi, S. L.

1986-01-01

323

Effects of late quaternary climate change on Palearctic shrews.  

PubMed

The Late Quaternary was a time of rapid climatic oscillations and drastic environmental changes. In general, species can respond to such changes by behavioral accommodation, distributional shifts, ecophenotypic modifications (nongenetic), evolution (genetic) or ultimately face local extinction. How those responses manifested in the past is essential for properly predicting future ones especially as the current warm phase is further intensified by rising levels of atmospheric carbon dioxide. Here, we use ancient DNA (aDNA) and morphological features in combination with ecological niche modeling (ENM) to investigate genetic and nongenetic responses of Central European Palearctic shrews to past climatic change. We show that a giant form of shrew, previously described as an extinct Pleistocene Sorex species, represents a large ecomorph of the common shrew (Sorex araneus), which was replaced by populations from a different gene-pool and with different morphology after the Pleistocene Holocene transition. We also report the presence of the cold-adapted tundra shrew (S. tundrensis) in Central Europe. This species is currently restricted to Siberia and was hitherto unknown as an element of the Pleistocene fauna of Europe. Finally, we show that there is no clear correlation between climatic oscillations within the last 50 000 years and body size in shrews and conclude that a special nonanalogous situation with regard to biodiversity and food supply in the Late Glacial may have caused the observed large body size. PMID:23505017

Prost, Stefan; Klietmann, Johannes; van Kolfschoten, Thijs; Guralnick, Robert P; Waltari, Eric; Vrieling, Klaas; Stiller, Mathias; Nagel, Doris; Rabeder, Gernot; Hofreiter, Michael; Sommer, Robert S

2013-06-01

324

Regulated assembly and disassembly of the yeast telomerase quaternary complex.  

PubMed

The enzyme telomerase, which elongates chromosome termini, is a critical factor in determining long-term cellular proliferation and tissue renewal. Hence, even small differences in telomerase levels can have substantial consequences for human health. In budding yeast, telomerase consists of the catalytic Est2 protein and two regulatory subunits (Est1 and Est3) in association with the TLC1 RNA, with each of the four subunits essential for in vivo telomerase function. We show here that a hierarchy of assembly and disassembly results in limiting amounts of the quaternary complex late in the cell cycle, following completion of DNA replication. The assembly pathway, which is driven by interaction of the Est3 telomerase subunit with a previously formed Est1-TLC1-Est2 preassembly complex, is highly regulated, involving Est3-binding sites on both Est2 and Est1 as well as an interface on Est3 itself that functions as a toggle switch. Telomerase subsequently disassembles by a mechanistically distinct pathway due to dissociation of the catalytic subunit from the complex in every cell cycle. The balance between the assembly and disassembly pathways, which dictate the levels of the active holoenzyme in the cell, reveals a novel mechanism by which telomerase (and hence telomere homeostasis) is regulated. PMID:25240060

Tucey, Timothy M; Lundblad, Victoria

2014-10-01

325

Quaternary glaciation of the Tashkurgan Valley, Southeast Pamir  

NASA Astrophysics Data System (ADS)

The Quaternary glacial history of Tashkurgan valley, in the transition between the Pamir and Karakoram, in Xinjiang Province, China was examined using remote sensing, field mapping, geomorphic analysis of landforms and sediments, and 10Be terrestrial cosmogenic nuclide dating. Moraines were assigned to four glacial stages: 1) the Dabudaer glacial stage that dates to the penultimate glacial cycle and/or earlier, and may represent one or more glaciations; 2) the Tashkurgan glacial stage that dates to early last glacial, most likely Marine Oxygen Isotope Stage (MIS) 4; 3) the Hangdi glacial stage that dates to MIS 2, possibly early MIS 2; and 4) the Kuzigun glacial stage that dates to the MIS 2, possibly the global Last Glacial Maximum, and is younger than the Hangdi glacial stage. Younger moraines and rock glaciers are present at the heads of tributary valleys; but these were inaccessible because they are located close to politically sensitive borders with Pakistan, Afghanistan and Tajikistan. Glaciers during the Dabudaer glacial stage advanced into the central part of the Tashkurgan valley. During the Tashkurgan glacial stages, glaciers advanced several kilometers beyond the mouths of the tributary valleys into the Tashkurgan valley. Glaciers during the Hangdi and Kuzigun glacial stages advanced just beyond the mouths of the tributary valleys. Glaciation in this part of the Himalayan-Tibetan orogen is likely strongly controlled by northern hemisphere climate oscillations, although a monsoonal influence on glaciation cannot be ruled out entirely.

Owen, Lewis A.; Chen, Jie; Hedrick, Kathyrn A.; Caffee, Marc W.; Robinson, Alexander C.; Schoenbohm, Lindsay M.; Yuan, Zhaode; Li, Wenqiao; Imrecke, Daniel B.; Liu, Jinfeng

2012-07-01

326

Micropaleontologic record of late Pliocene and Quaternary paleoenvironments in the northern Albemarle Embayment, North Carolina, U.S.A  

Microsoft Academic Search

Micropaleontological data provide a strong actualistic basis for detailed interpretations of Quaternary paleoenvironmental change. The 90 m-thick Quaternary record of the Albemarle Embayment in the mid-Atlantic coastal plain of the USA provides an excellent opportunity to use such an approach in a region where the details of Quaternary environmental change are poorly known.The foraminiferal record in nine cores from the northern

Stephen J. Culver; Kathleen M. Farrell; David J. Mallinson; Benjamin P. Horton; Debra A. Willard; E. Robert Thieler; Stanley R. Riggs; Scott W. Snyder; John F. Wehmiller; Christopher E. Bernhardt; Caroline Hillier

2008-01-01

327

Fission xenon from extinct Pu-244 in 14,301.  

NASA Technical Reports Server (NTRS)

Xenon extracted in step-wise heating of lunar breccia 14,301 contains a fission-like component in excess of that attributable to uranium decay during the age of the solar system. There seems to be no adequate source for this component other than Pu-244. Verification that this component is in fact due to the spontaneous fission of extinct Pu-244 comes from the derived spectrum which is similar to that observed from artificially produced Pu-244. It thus appears that Pu-244 was extant at the time lunar crustal material cooled sufficiently to arrest the thermal diffusion of xenon. Subsequent history has apparently maintained the isotopic integrity of plutonium fission xenon. Of major importance are details of the storage itself. Either the fission component is the result of in situ fission of Pu-244 and subsequent storage in 14,301 material, or the fission xenon was stored in an intermediate reservoir before incorporation into 14,301.

Drozd, R.; Hohenberg, C. M.; Ragan, D.

1972-01-01

328

Exotic fission properties of highly neutron-rich Uranium isotopes  

E-print Network

The series of Uranium isotopes with $N=154 \\sim 172$ around the magic number N=162/164 are identified to be thermally fissile. The thermal neutron fission of a typical representative $^{249}$U of this region amenable to synthesis in the radioactive ion beam facilities is considered here. Semiempirical study of fission barrier height and width shows this nucleus to be infinitely stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. Calculation of probability of fragment mass yields and microscopic study in relativistic mean field theory, show this nucleus to undergo a new mode of thermal fission decay termed {\\it multifragmentation fission} where a number of prompt scission neutrons are simultaneously released along with the two heavy fission fragments.

L. Satpathy; S. K. Patra; R. K. Choudhury

2007-03-05

329

Sharp change over from compound nuclear fission to shape dependent quasi fission  

E-print Network

Fission fragment mass distribution has been measured from the decay of $^{246}$Bk nucleus populating via two entrance channels with slight difference in mass asymmetries but belonging on either side of the Businaro Gallone mass asymmetry parameter. Both the target nuclei were deformed. Near the Coulomb barrier, at similar excitation energies the width of the fission fragment mass distribution was found to be drastically different for the $^{14}$N + $^{232}$Th reaction compared to the $^{11}$B + $^{235}$U reaction. The entrance channel mass asymmetry was found to affect the fusion process sharply.

T. K. Ghosh; K. Banerjee; C. Bhattacharya; S. Bhattacharya; S. Kundu; P. Mali; J. K. Meena; G. Mukherjee; S. Mukhopadhyay; T. K. Rana; P. Bhattacharya; K. S. Golda

2008-09-17

330

HEAVY-ION-INDUCED TERNARY FISSION AS A PROBE OF THE DYNAMICAL DECAY OF  

E-print Network

of Nuclear Fission Dynamics . . . . . . . . . . . . . . . . . . 5 1.2.1 Total Kinetic Energy of the Fission of Ternary Fission . . . . . . . . . . . . . . 11 1.4 Models of Nuclear FissionHEAVY-ION-INDUCED TERNARY FISSION AS A PROBE OF THE DYNAMICAL DECAY OF EXCITED NUCLEI Todd A

de Souza, Romualdo T.

331

On "Sub-Threshold" Reactions Involving Nuclear Fission  

E-print Network

We analyze reactions of several types that are naively below threshold but can proceed because of the release of binding energy from nuclear fission and occasionally the formation of Coulombic bound states. These reactions include (i) photofission with pion production and (ii) charged current neutrino-nucleus reactions that lead to fission and/or formation of a Coulomb bound state of a $\\mu^-$ with the nucleus of a fission fragment. We comment on the possible experimental observation of these reactions.

M. Goldhaber; R. Shrock

2000-11-29

332

Excitation-energy dependence of fission in the mercury region  

NASA Astrophysics Data System (ADS)

Background: Recent experiments on ?-delayed fission reported an asymmetric mass yield in the neutron-deficient nucleus Hg180. Earlier experiments in the mass region A =190-200 close to the ?-stability line, using the (p,f) and (?,f) reactions, observed a more symmetric distribution of fission fragments. While the ?-delayed fission of Hg180 can be associated with relatively low excitation energy, this is not the case for light-ion reactions, which result in warm compound nuclei. The low-energy fission of Hg180,198 has been successfully described by theory in terms of strong shell effects in pre-scission configurations associated with dinuclear structures. Purpose: To elucidate the roles of proton and neutron numbers and excitation energy in determining symmetric- and asymmetric-fission yields, we compute and analyze the isentropic potential energy surfaces of 174,180,198Hg and Po196,210. Methods: We use the finite-temperature superfluid nuclear density functional theory for excitation energies up to E*=30 MeV and zero angular momentum. For our theoretical framework, we consider the Skyrme energy density functional SkM* and a density-dependent pairing interaction. Results: For Hg174,180, we predict fission pathways consistent with asymmetric fission at low excitation energies, with the symmetric-fission pathway opening very gradually as excitation energy is increased. For Hg198 and Po196, we expect the nearly symmetric-fission channel to dominate. Po210 shows a preference for a slightly asymmetric pathway at low energies, and a preference for a symmetric pathway at high energies. Conclusions: Our self-consistent theory suggests that excitation energy weakly affects the fission pattern of the nuclei considered. The transition from the asymmetric fission in the proton-rich nuclei to a more symmetric fission in the heavier isotopes is governed by the shell structure of pre-scission configurations.

McDonnell, J. D.; Nazarewicz, W.; Sheikh, J. A.; Staszczak, A.; Warda, M.

2014-08-01

333

Proton induced fission of 181-Ta at relativistic energies  

E-print Network

Total fission cross sections of 181-Ta induced by protons at different relativistic energies have been measured at GSI, Darmstadt. The inverse kinematics technique used together with a dedicated set-up, made it possible to determine these cross sections with high accuracy. The new data obtained in this experiment will contribute to the understanding of the fission process at high excitation energies. The results are compared with data from previous experiments and systematics for proton-induced fission cross sections.

Y. Ayyad; J. Benlliure; E. Casarejos; H. Álvarez-Pol; A. Bacquias; A. Boudard; M. Caamaño; T. Enqvist; V. Föhr; A. Keli?-Heil; K. Kezzar; S. Leray; C. Paradela; D. Pérez-Loureiro; R. Pleska?; D. Tarrío

2012-03-07

334

Macroscopic Features of Light Heavy-Ion Fission Reactions  

E-print Network

Global macroscopic features observed in the fully-damped binary processes in light di-nuclear systems, such as limiting angular momenta, mean total kinetic energies and energy thresholds for fusion-fission processes (''fission thresholds") are presented. Their deduced systematics are consistent with that obtained for heavier systems and follow a fusion-fission picture which can be described by a realistic rotating liquid drop model considering diffuse-surface and finite-nuclear-range effects.

C. Beck; A. Szanto de Toledo

1995-12-19

335

ELSA: A simplified code for fission product release calculations  

SciTech Connect

During a light water reactor severe accident, fission products are released from the overheated core as it progressively degrades. A new computer module named ELSA is being developed to calculate fission product release. The authors approach is to model the key phenomena, as opposed to more complete mechanistic approaches. Here they present the main features of the module. Different release mechanisms have been identified and are modeled in ELSA, depending on fission product volatility: diffusion seems to govern the release of the highly volatile species if fuel oxidation is properly accounted for, whereas mass transport governs that of lower volatility fission products and fuel volatilization that of the practically involatile species.

Manenc, H. [Institut de Protection et de Surete Nucleaire, St. Paul-lez-Durance (France); Notley, M.J. [MJF International, Oundle (United Kingdom)

1996-12-31

336

Magnetic Materials Suitable for Fission Power Conversion in Space Missions  

NASA Technical Reports Server (NTRS)

Terrestrial fission reactors use combinations of shielding and distance to protect power conversion components from elevated temperature and radiation. Space mission systems are necessarily compact and must minimize shielding and distance to enhance system level efficiencies. Technology development efforts to support fission power generation scenarios for future space missions include studying the radiation tolerance of component materials. The fundamental principles of material magnetism are reviewed and used to interpret existing material radiation effects data for expected fission power conversion components for target space missions. Suitable materials for the Fission Power System (FPS) Project are available and guidelines are presented for bounding the elevated temperature/radiation tolerance envelope for candidate magnetic materials.

Bowman, Cheryl L.

2012-01-01

337

Summary of Quaternary Stratigraphy and history, Eastern Canada  

NASA Astrophysics Data System (ADS)

Deposits of three Wisconsinan substages, Sangamonian Stage, and older Quaternary stratigraphic units are recognized in Eastern Canada. The age assignment of these units is based on radiocarbon dating and correlation of events. Quaternary deposits older than Sangamonian are recognized locally in Eastern Canada. In southern Ontario glacial deposits directly underlie Sangamonian sediments and are referred to as Illinoian in age. In other areas the ages of older sediments are largely unknown. Offshore core stratigraphy suggests that a major glaciation took place about 436 ka and that the Illinoian (oxygen isotope stage 6) was also a time of extensive glaciation. In this report Sangamonian is used as the name for the chronostratigraphic stage that includes all of deep-sea oxygen isotope stage 5 and consequently, on a regional basis, it includes warm interglacial deposits, glacial deposits and cool interglacial deposits. In southern Ontario the warm interglacial deposits are represented by the Don Formation, the stadial deposits by the Scarborough Formation and the cool interglacial deposits by the Pottery Road Formation. Warm interglacial deposits have not been recognized in Quebec (unless they are part of the pre-Johnville Sediments); the Bécancour Till is included as glacial Sangamonian sediments, and the St. Pierre Sediments are recognized as cool interglacial sediments. The Early Wisconsinan appears to have been the time of maximum Wisconsinan glaciation in Eastern Canada with ice moving south of the International Boundary and well out onto the continental shelf. The Middle Wisconsinan was primarily a nonglacial period in southern Ontario and a glacial stade elsewhere in Eastern Canada. In southern Ontario the Middle Wisconsinan record has been subdivided into two interstades (Port Talbot and Plum Point), separated by a stade (Cherrytree). The Port Talbot Interstade began before the limit of radiocarbon dating (before 48 ka) and ended about 40 ka; glacial or near glacial conditions of the Cherrytree Stage lasted from about 40 to 35 ka ago, and the Plum Point Interstade was from about 35 to 23 ka ago. Central St. Lawrence Lowland was occupied by ice throughout the Middle Wisconsinan, but southeastern Quebec and the Montreal area were briefly deglaciated. Scattered evidence in Atlantic Canada suggests local deglaciation of coastal areas during Middle Wisconsinan but extensive ice remained on the continental shelf and ice from centres located on the shelf flowed onto land in at least two areas. Glacial conditions predominated throughout Eastern Canada during the Late Wisconsinan. At the Late Wisconsinan maximum, through-moving ice deposited the Catfish Creek Drift in southern Ontario but ice lobes, which developed in the basins of the Great Lakes after 15.5 ka, controlled ice flow during a period of ice margin oscillation and retreat. A calving bay developed in lower St. Lawrence valley, after the Late Wisconsinan maximum, causing a reversal of flow on the south shore of the St. Lawrence and replacing ice in the valley with the Champlain Sea about 12 ka. Late Wisconsinan glaciers were largely limited to land areas in Atlantic Canada. Local ice caps dominated with complicated patterns of flow and retreat developing as centres of accumulation shifted and competing ice centres achieved dominance. The period of Late Wisconsinan retreat in Atlantic Canada appears to have lasted from about 14 to 10 ka.

Fulton, R. J.; Karrow, P. F.; LaSalle, P.; Grant, D. R.

338

Mapping the late Quaternary evolution of the lower Mississippi Valley  

NASA Astrophysics Data System (ADS)

The lower Mississippi Valley (LMV) extends from Cape Girardeau to Natchez and from Little Rock to Memphis. Extensive Quaternary terraces within the LMV have been considered to reflect downstream changes in base level (global sea level) and (or) upstream changes in water and sediment input because of glaciation. We suggest that the first-order control on terrace development was glacial-isostatic adjustment (GIA). Observed variation in heights of Quaternary alluvial surfaces at Memphis is 50 m (Rittenour et al., 2007). GIA modeling by Clark et al. (1994) predicted vertical displacement of as much as 130 m at Memphis over the last 18,000 years. ICE-5G models predict smaller displacement and reinforce the viability of GIA as the primary cause of LMV aggradation and incision. Existing analyses of LMV terraces are built on geomorphic maps by Saucier and colleagues (1974, 1994; Autin et al., 1991) that were interpreted from aerial photographs and inch-to-the-mile contour maps. Geomorphic mapping from high-resolution DEMs is more accurate, more rapid, and more reproducible than mapping from aerial photography and intermediate-resolution contours. Working from lidar DEMs (1-5 m XY resolution) and the 10 m National Elevation Dataset (NED) DEM largely derived from 1:24,000 scale contours, Haugerud is mapping the geomorphology of the LMV at ~1:500,000 scale. Goals are to explore the GIA-terrace hypothesis and improve the geomorphic and stratigraphic context for studies of New Madrid seismicity. Mapping leads to several observations: 1. The Holocene floodplain of the Mississippi River onlaps older surfaces. The river appears to be filling a hole created by collapse of the Laurentide forebulge. Continued filling of this accommodation space will, barring human intervention, enable the river to abandon its course through Thebes Gap in favor of a lower-elevation route through Oran Gap. 2. Within Holocene meander belts, younger levee crests are higher than older levee crests. The belts are aggrading, their substrates are compacting, or both. 3. Pleistocene braid plains step downward and merge downstream. Evidently there was up-to-the-north tilting as the braid plains formed. 4. Anomalous landforms suggest Holocene faulting or folding. Greater sinuosity and more-extensive wetlands along the St Francis River immediately upstream of Crowleys Ridge and pronounced incision where the river crosses the ridge indicate uplift of the ridge relative to the Western Lowlands. Unusual inset terraces along the L'Anguille River south of Forrest City, AR may record local uplift. Ten km southeast of Monroe, LA, N-S scarps dissect a meander belt; to the east, a subtle NE-SW scarp truncates braid plain. These are probably fault scarps. 5. Much of the LMV has been surveyed with lidar. Surveys have been at the behest of NRCS, FEMA, USACE, state agencies, and USGS-NEHRP. Improved coordination among survey efforts would reduce overlap and costs, could ease data access, and might lead to greater use of the data.

Haugerud, R. A.; Simon, K. M.; James, T. S.

2013-12-01

339

Gamma-irradiation synthesis of quaternary phosphonium cationic starch flocculants.  

PubMed

Quaternary phosphonium cationic starch (St-g-AM/ATPPB) flocculant was synthesized by using corn starch and acrylamide (AM), allyl triphenyl phosphonium bromide binary (ATPPB) through simultaneous gamma-irradiation. The chemical structure of the copolymer was characterized by FTIR (Fourier transform infrared spectroscopy) and (1)H NMR (nuclear magnetic resonance) technologies. The effects of the absorbed dose in the range of 1 to 6 kGy, AM/ATPPB ratio and starch/(AM + ATPPB) ratio on grafting and flocculation were investigated. At a starch:AM:ATPPB wt ratio of 1:1.4:0.93, the graft ratio of AM/ATPPB reached maximum values at 3 and 6 kGy, and the cationic degree of St-g-AM/ATPPB increased with absorbed dose, while the turbidity reduction reached a maximum value at 5 kGy. At 3 kGy using a starch:(AM + ATPPB) wt. ratio of 1:2.33, the graft ratio of AM and ATPPB increased with AM/ATPPB ratio, while the cationic degree and turbidity reduction reached maximum values at AM:ATPPB wt. ratios of 1:0.67 and 1:0.5, respectively. At a constant AM:ATPPB wt. ratio of 1:0.67 and 3 kGy, the grafting ratio increased with starch/(AM + ATPPB), while the cationic degree and turbidity reduction simultaneously reached maximum values at a starch:(AM + ATPPB) wt. ratio of 1:2.67. Further study revealed that the higher the absorbed dose or the lower the starch/(AM + ATPPB) ratio, the lower the optimal flocculant concentration. PMID:24185060

Song, Weiqiang; Zhao, Zhiwei; Zheng, Hongjuan; Wang, Gaimin

2013-01-01

340

Late Quaternary land-sea correlations, northern Labrador, Canada  

SciTech Connect

Late Quaternary glacial and postglacial units in the Torngat Mountains, northern Labrador, are correlated with units identified on the adjacent continental shelf. The late Wisconsinan Laurentide Ice Sheet drained through major valleys of the Torngat Mountains as outlet glaciers, depositing the Saglek Moraines. These are of regional extent and have been mapped from Saglek Fiord north to Noodleook Fiord. A C-14 date of 18,210 +/- 1900 BP on total organic matter (TOM) from lake sediment dammed by a segment of the Saglek Moraines is interpreted as a maximum date for deposition of the Saglek Moraine system because of possible contamination. Glacial sediments comprising the Saglek Moraines are correlated with upper till mapped in troughs and saddles on the continental shelf. Outlet glaciers depositing a late Wisconsinan unit flowed through Labrador fiords and onto the shelf at low basal shear stresses, particularly on the shelf where, although grounded, they were hydrostatically buoyed up and moved principally by sliding. A glaciomarine unit conformably overlies late Wisconsinan till on the shelf and on the land. This unit is a gravelly clayey silt, contains abundant foraminifera, and has up to 60% limestone in the pebble fraction. C-14 dates suggest deposition of this unit began ca. 10,000 BP on the shelf and 9000 BP on the land, an ended by 8000 BP. Limestone pebbles in this unit suggest a source in part from sediment-laden icebergs and pack-ice from the north. Marine deposition from ca. 8000-0 BP is characterize by basinal sedimentation.

Clark, P.; Josenhans, H.

1985-01-01

341

Quaternary landscape evolution of the Turkey River Valley, northeastern Iowa  

SciTech Connect

The Turkey River Valley, a major Mississippi tributary in northeastern Iowa, provides a more complete and accessible Quaternary record than the Upper Mississippi Valley. This project, using 3-dimensional reconstructions of both valley and upland deposits, revealed at least 13 important depositional, erosional, and soil-forming events. From oldest to youngest these events are: (1) deposition of pre-Illinoian till; (2) erosion of till and bedrock as the Turkey River cut down; (3) deposition of fluvial and colluvial sediments in the valley; (4) development of a Sangamon soil(s) on both the pre-Illinoian (upland) till and valley sediments; (5) truncation of the Sangamon soil(s) relatively high in the valley as bedrock entrenchment proceeded to its deepest point; (6) deposition of coarse fluvial and colluvial sediments in the valley prior to 32,000 yr. B.P.; (7) aggradation of mostly loess-derived alluvium until approximately 16,000 yr. B.P.; (8) large-scale colluviation between approximately 32,000 and 13,000 yr., B.P.; (9) major downcutting between 16,000 and 14,000 yr. B.P.; (10) aggradation of coarse to medium alluvium from approximately 14,000 to 13,000 yr. B.P.; (11) overall downcutting during several intervals of the late Wisconsinan and early Holocene; (12) aggradation of mid to late Holocene alluvium starting by 5000 yr. B.P.; (13) lateral erosion and deposition during the past 200 yr. B.P. Turkey River Valley deposits previously interpreted as pre-Illinoian are now recognized as late Wisconsinan or early Holocene, as indicated by /sup 14/C dates and molluscan fossils. The Paleozoic Plateau landform region (formerly part of the Driftless Area) is herein interpreted as a rugged, although complex, extension of the Iowan Erosion Surface.

Hudak, C.M.

1987-01-01

342

Antiproton Powered Gas Core Fission Rocket  

SciTech Connect

Extensive research in recent years has demonstrated that 'at rest' annihilation of antiprotons in the uranium isotope U238 leads to fission at nearly 100% efficiency. The resulting highly-ionizing, energetic fission fragments can heat a suitable medium to very high temperatures, making such a process particularly suitable for space propulsion applications. Such an ionized medium, which would serve as a propellant, can be confined by a magnetic field during the heating process, and subsequently ejected through a magnetic nozzle to generate thrust. The gasdynamic mirror (GDM) magnetic configuration is especially suited for this application since the underlying confinement principle is that the plasma be of such density and temperature as to make the ion-ion collision mean free path shorter than the plasma length. Under these conditions the plasma behaves like a fluid, and its escape from the system is analogous to the flow of a gas into vacuum from a vessel with a hole. For the system we propose we envisage radially injecting atomic or U238 plasma beam at a pre-determined position and axially pulsing an antiproton beam which upon interaction with the uranium target gives rise to near isotropic ejection of fission fragments with a total mass of 212 amu and total energy of about 160 MeV. These particles, along with the annihilation products (i.e. pions and muons) will heat the background U238 gas - inserted into the chamber just prior to the release of the antiproton - to one keV temperature. Preliminary analysis reveals that such a propulsion system can produce a specific impulse of about 3000 seconds at a thrust of about 50 kN. When applied to a round trip Mars mission, we find that such a journey can be accomplished in about 142 days with 2 days of thrusting and requiring only one gram of antiprotons to achieve it.

Kammash, Terry [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Blvd, Ann Arbor, MI 48109 (United States)

2005-02-06

343

Deformation and Quaternary Faulting in Southeast Missouri across the Commerce Geophysical Lineament  

USGS Publications Warehouse

High-resolution seismic-reflection data acquired at three sites along the surface projection of the Commerce geophysical lineament in southeast Missouri reveal a complex history of post-Cretaceous faulting that has continued into the Quaternary. Near Qulin, Missouri, approximately 20 m of apparent vertical fault displacement has occurred in the Quaternary. Reflection data collected at Idalia Hill, about 45 km to the northeast, reveal a series of reverse and possibly right-lateral strike-slip faults with Quaternary displacement. In the Benton Hills, 45 km northeast of Idalia Hill, seismic data image a complicated series of anticlinal and synclinal fault-bounded blocks immediately north of the Commerce fault. We infer that most of the deformation imaged in the upper 400 m of these three data sets occurred since post-Cretaceous time, and a significant portion of it occurred during Quaternary time. Collectively, these seismic data along with geomorphic and surface-geologic evidence suggest (1) the existence of at least one potential seismogenic structure in southeastern Missouri outside the main zones of New Madrid seismicity, and (2) these structures have been active during the Quaternary. The geographic location of the imaged deformation suggests it is related to structures along with the Commerce geophysical lineament.

Stephenson, W. J.; Odum, J. K.; Williams, R. A.; Pratt, T. L.; Harrison, R. W.; Hoffman, D.

1999-01-01

344

Ceramics in fission and fusion technology  

SciTech Connect

The role of ceramic components in fission and fusion reactors is described. Almost all of the functions normally performed by ceramics, except mechanical, are required of nuclear ceramics. The oxides of uranium and plutonium are of predominant importance in nuclear applications, but a number of other ceramics play peripheral roles. The unique service conditions under which nuclear ceramics must operate include intense radiation fields, high temperatures and large temperature gradients, and aggressive chemical environments. Examples of laboratory research designed to broaden understanding of the behavior of uranium dioxide in such conditions are given. The programs described include high temperature vaporization, diffusional processes, and interaction with hydrogen.

Olander, D.R.

1986-04-01

345

Nuclear multifragmentation and fission: similarity and differences  

E-print Network

Thermal multifragmentation of hot nuclei is interpreted as the nuclear liquid--fog phase transition deep inside the spinodal region. The experimental data for p(8.1GeV) + Au collisions are analyzed. It is concluded that the decay process of hot nuclei is characterized by two size parameters: transition state and freeze-out volumes. The similarity between dynamics of fragmentation and ordinary fission is discussed. The IMF emission time is related to the mean rupture time at the multi-scission point, which corresponds to the kinetic freeze-out configuration.

V. Karnaukhov; H. Oeschler; S. Avdeyev; V. Rodionov; V. Kirakosyan; A. Simonenko; P. Rukoyatkin; A. Budzanowski; W. Karcz; I. Skwirczynska; B. Czech; L. Chulkov; E. Kuzmin; E. Norbeck; A. Botvina

2006-02-10

346

PhET Simulation: Nuclear Fission  

NSDL National Science Digital Library

This webpage contains a simulation that provides qualitative pictures of alpha radiation, fission of a Uranium 235 nucleus, and controlled and uncontrolled nuclear chain reactions. Evolution of the processes over time is shown. Variables such as the number of nuclei and the containment of reactions can be altered to demonstrate the statistical nature of the reactions. Sample learning goals as well as a teacher's guide for the simulation are available. This simulation is part of a large and growing collection. It has been designed using principles from physics education research and refined based on student interviews.

2006-10-21

347

Excitation energy dependence of fission in the mercury region  

E-print Network

Background: Recent experiments on beta-delayed fission reported an asymmetric mass yield in the neutron-deficient nucleus 180Hg. Earlier experiments in the mass region A=190-200 close to the beta-stability line, using the (p,f) and (\\alpha,f) reactions, observed a more symmetric distribution of fission fragments. While the beta-delayed fission of 180Hg can be associated with relatively low excitation energy, this is not the case for light-ion reactions, which result in warm compound nuclei. Purpose: To elucidate the roles of proton and neutron numbers and excitation energy in determining symmetric and asymmetric fission yields, we compute and analyze the isentropic potential energy surfaces of 174,180,198Hg and 196,210Po. Methods: We use the finite-temperature superfluid nuclear density functional theory, for excitation energies up to E*=30MeV and zero angular momentum. For our theoretical framework, we consider the Skyrme energy density functional SkM* and a density-dependent pairing interaction. Results: For 174,180Hg, we predict fission pathways consistent with asymmetric fission at low excitation energies, with the symmetric fission pathway opening very gradually as excitation energy is increased. For 198Hg and 196Po, we expect the nearly-symmetric fission channel to dominate. 210Po shows a preference for a slightly asymmetric pathway at low energies, and a preference for a symmetric pathway at high energies. Conclusions: Our self-consistent theory suggests that excitation energy weakly affects the fission pattern of the nuclei considered. The transition from the asymmetric fission in the proton-rich nuclei to a more symmetric fission in the heavier isotopes is governed by the shell structure of pre-scission configurations.

J. D. McDonnell; W. Nazarewicz; J. A. Sheikh; A. Staszczak; M. Warda

2014-06-26

348

Pairing-induced speedup of nuclear spontaneous fission  

E-print Network

Collective inertia is strongly influenced at the level crossing at which quantum system changes diabatically its microscopic configuration. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of those configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes. To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of $^{264}$Fm and $^{240}$Pu using the state-of-the-art self-consistent framework. We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM$^*$ and a density-dependent pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action principle in a four-dimensional collective space of shape and pairing coordinates. Pairing correlations are enhanced along the minimum-action fission path. For the symmetric fission of $^{264}$Fm, where the effect of triaxiality on the fission barrier is large, the geometry of fission pathway in the space of shape degrees of freedom is weakly impacted by pairing. This is not the case for $^{240}$Pu where pairing fluctuations restore the axial symmetry of the dynamic fission trajectory. The minimum-action fission path is strongly impacted by nucleonic pairing. In some cases, the dynamical coupling between shape and pairing degrees of freedom can lead to a dramatic departure from the static picture. Consequently, in the dynamical description of nuclear fission, particle-particle correlations should be considered on the same footing as those associated with shape degrees of freedom.

Jhilam Sadhukhan; J. Dobaczewski; W. Nazarewicz; J. A. Sheikh; A. Baran

2014-10-06

349

SOCIAL GROUP FISSION AND GENE DYNAMICS AMONG BLACK-TAILED PRAIRIE DOGS  

E-print Network

SOCIAL GROUP FISSION AND GENE DYNAMICS AMONG BLACK-TAILED PRAIRIE DOGS (CYNOMYS LUDOVICIANUS fission. Key words: coancestry, competition, cooperation, Cynomys ludovicianus, dispersal, fission, gene al. 1990). Black-tailed prairie dogs (Cynomys ludovicianus; hereafter, simply ``prairie dogs

Foltz, David W.

350

Characterisation of quaternary mixtures by the apparent content curves method: identification of tocopherols in vegetable oils.  

PubMed

A procedure for identification of the compounds in quaternary mixtures has been developed. The proposed procedure is based on the apparent content curves method. From these curves and using the Q parameter, work conditions are selected and quaternary mixtures treated as "pseudoternary" mixtures.A simple strategy to test matrix effects at working wavelengths has been developed, identification limits established and following the identification table quaternary mixtures were easily characterised. The procedure has been applied to the identification of phenols in mixtures by UV-visible spectrophotometry and tocopherols in edible oils by fluorimetry. Results obtained for edible oils are in agreement with the composition obtained by use of the reference method. PMID:12638048

Maurí-Aucejo, A R; Llobat-Estellés, M; Marín-Saez, R

2003-03-01

351

Quad-PRE: A Hybrid Method to Predict Protein Quaternary Structure Attributes  

PubMed Central

The protein quaternary structure is very important to the biological process. Predicting their attributes is an essential task in computational biology for the advancement of the proteomics. However, the existing methods did not consider sufficient properties of amino acid. To end this, we proposed a hybrid method Quad-PRE to predict protein quaternary structure attributes using the properties of amino acid, predicted secondary structure, predicted relative solvent accessibility, and position-specific scoring matrix profiles and motifs. Empirical evaluation on independent dataset shows that Quad-PRE achieved higher overall accuracy 81.7%, especially higher accuracy 92.8%, 93.3%, and 90.6% on discrimination for trimer, hexamer, and octamer, respectively. Our model also reveals that six features sets are all important to the prediction, and a hybrid method is an optimal strategy by now. The results indicate that the proposed method can classify protein quaternary structure attributes effectively. PMID:24963340

Sheng, Yajun; Qiu, Xingye; Zhang, Chen; Xu, Jun; Zhang, Yanping; Zheng, Wei; Chen, Ke

2014-01-01

352

Quad-PRE: a hybrid method to predict protein quaternary structure attributes.  

PubMed

The protein quaternary structure is very important to the biological process. Predicting their attributes is an essential task in computational biology for the advancement of the proteomics. However, the existing methods did not consider sufficient properties of amino acid. To end this, we proposed a hybrid method Quad-PRE to predict protein quaternary structure attributes using the properties of amino acid, predicted secondary structure, predicted relative solvent accessibility, and position-specific scoring matrix profiles and motifs. Empirical evaluation on independent dataset shows that Quad-PRE achieved higher overall accuracy 81.7%, especially higher accuracy 92.8%, 93.3%, and 90.6% on discrimination for trimer, hexamer, and octamer, respectively. Our model also reveals that six features sets are all important to the prediction, and a hybrid method is an optimal strategy by now. The results indicate that the proposed method can classify protein quaternary structure attributes effectively. PMID:24963340

Sheng, Yajun; Qiu, Xingye; Zhang, Chen; Xu, Jun; Zhang, Yanping; Zheng, Wei; Chen, Ke

2014-01-01

353

Magnetic Properties of Quaternary Deposits, Kenai Peninsula, Alaska -- Implications for Aeromagnetic Anomalies of Upper Cook Inlet  

USGS Publications Warehouse

We measured magnetic susceptibilities of exposed Quaternary deposits on several beach cliffs and river banks on the Kenai Peninsula near Soldotna, Alaska. Data, descriptions, and photos from nine sites are included in this report. The mean susceptibility for Quaternary materials in this region is approximately 2.5 x 10-3 SI units. This is sufficiently magnetic to produce subtle aeromagnetic anomalies such as those observed to correlate with topographic features in the region of the measurements. The highest susceptibilities measured (greater than 20 x 10-3 SI units) may help, at least in part, to explain moderate amplitude aeromagnetic anomalies observed elsewhere in Cook Inlet, particularly those relating to structures showing Quaternary movement. Comparison of measured beach cliff susceptibility and susceptibility predicted from idealized formulas and two-dimensional cliff models suggests that measured susceptibilies underestimate true bulk susceptibility by 20 percent to 50 percent in this region.

Saltus, R. W.; Haeussler, P. J.

2004-01-01

354

Nuclear fission with mean-field instantons  

SciTech Connect

We present a description of nuclear spontaneous fission, and generally of quantum tunneling, in terms of instantons, that is, periodic imaginary-time solutions to time-dependent mean-field equations. This description allows comparisons to be made with the more familiar generator coordinate (GCM) and adiabatic time-dependent Hartree-Fock (ATDHF) methods. It is shown that the action functional whose value for the instanton is the quasiclassical estimate of the decay exponent fulfills the minimum principle when additional constraints are imposed on trial fission paths. In analogy with mechanics, these are conditions of energy conservation and the velocity-momentum relations. In the adiabatic limit, the instanton method reduces to the time-odd ATDHF equation, with collective mass including the time-odd Thouless-Valatin term, while the GCM mass completely ignores velocity-momentum relations. This implies that GCM inertia generally overestimates the instanton-related decay rate. The very existence of the minimum principle offers hope for a variational search for instantons. After the inclusion of pairing, the instanton equations and the variational principle can be expressed in terms of the imaginary-time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory. The adiabatic limit of this theory reproduces ATDHFB inertia.

Skalski, Janusz [Soltan Institute for Nuclear Studies, ul. Hoz 69, PL-00681, Warsaw (Poland)

2008-06-15

355

A Fission-Powered Interstellar Precursor Mission  

SciTech Connect

An 'interstellar precursor mission' lays the groundwork for eventual interstellar exploration by studying the interstellar medium and by stretching technologies that have potential application for eventual interstellar exploration. The numerous scientific goals for such a mission include generating a 3-D stellar map of our galaxy, studying Kuiper-belt and Oort cloud objects, and observing distant objects using the sun's gravitational lens as the primary of an enormous telescope. System equations are developed for a space tug which propels a 2500-kg scientific payload to 550 astronomical units in about 20 years. The tug to transport this payload uses electric propulsion with an Isp of 15,000 seconds and a fission reactor with a closed Brayton cycle to genemte the electricity. The optimal configuration may be to thrust for only about 6 years and then coast for the remaining 14 pars. This spacecraft does not require any physics breakthroughs or major advances in technology. The fission power syslem can be engineered and built by drawing upon known technologies developed for relatgd systems over the past 40 years. The tug system would eventually reach 1000 a.u in 33 years, and would have adequate power to relay large amounts of data throughout its journey.

Lenard, R.X.; Lipinski, R.J.; West, J.L.; Wright, S.A.

1998-10-28

356

KNVK vacuum fission chambers for measuring neutron flux density  

Microsoft Academic Search

Vacuum fission chambers (VFC) are used to record the time dependence of the flux density of neutrons from nuclear reactors. Their comparatively high yield of slow secondary electrons (about 500 per fission fragment), large dynamic range, high temporal resolution, radiation resistance, and operating reliability make them superior to other detectors. However, the accuracy with which fast neutrons are recorded with

E. K. Malyshev; S. V. Chuklyaev; O. I. Shchetinin

1987-01-01

357

Electroplating method for producing ultralow-mass fissionable deposits  

DOEpatents

A method for producing ultralow-mass fissionable deposits for nuclear reactor dosimetry is described, including the steps of holding a radioactive parent until the radioactive parent reaches secular equilibrium with a daughter isotope, chemically separating the daughter from the parent, electroplating the daughter on a suitable substrate, and holding the electroplated daughter until the daughter decays to the fissionable deposit.

Ruddy, Francis H. (Monroeville, PA)

1989-01-01

358

Nuclear fission in heavy elements by high-energy particles  

Microsoft Academic Search

The results of a radiochemical investigation of nuclear fission in uranium, thorium, and bismuth by protons with an energy of 680 Mev are presented. Using an interpolation method a complete chart of the fission residue products is obtained. It is noted that there is a predominance in the production of nuclei with excess neutrons (58–64%); it is also shown that

A. K. Lavrukhina; L. D. Krasavina

1957-01-01

359

NUCLEAR FISSION IN THE EARLY HISTORY OF THE EARTH  

Microsoft Academic Search

Differences in the isotopic ratios of xenon in the Earth's atmosphere ; and in the Richardson meteorite are discussed. The differences indicate that at ; least 10% of the atmospheric xenon-138 is fissiogenic. This is much greater than ; that expected from the uranium-238 spontaneous fission alone but can be explained ; as due to the spontaneous fission of some

P. K. KURODA

1960-01-01

360

Semiclassical Interpretation of the Mass Asymmetry in Nuclear Fission  

Microsoft Academic Search

We give a semiclassical interpretation of the mass asymmetry in the fission of heavy nuclei. Using only a few classical periodic orbits and a cavity model for the nuclear mean field, we reproduce the onset of left-right asymmetric shapes at the fission isomer minimum and the correct topology of the deformation energy surface of 240Pu in the region of the

M. Brack; S. M. Reimann; M. Sieber

1997-01-01

361

Nuclear Thermal Rockets: The Physics of the Fission Reactor  

E-print Network

Nuclear Thermal Rockets: The Physics of the Fission Reactor Shane D. Ross Control and Dynamical combustion are those powered by nuclear fission. Comparison of Chemical and Nuclear Rockets. Most existent.g., hydrogen and oxygen). In a nuclear rocket, or more precisely, a nuclear thermal rocket, the propellant

Ross, Shane

362

Fusion-Fission Hybrids Driven By Heavy Ion Inertial Fusion  

Microsoft Academic Search

There is a desire to resolve fuel cycle issues for increasing the role of nuclear energy. The recent Laser Inertial Fusion-Fission Energy (LIFE) initiative that builds upon NIF ignition, is likely to rekindle national interest in developing intense, high power ion beam accelerators for fusion energy production and for fusion-fission hybrid concepts that combine an ion beam driven fusion neutron

P. A. Seidl

363

Fission product removal from molten salt using zeolite  

Microsoft Academic Search

Spent nuclear fuel (SNF) can be treated in a molten salt electrorefiner for conversion into metal and mineral waste forms for geologic disposal. The fuel is dissolved in molten chloride salt. Non-transuranic fission products in the molten salt are ion-exchanged into zeolite A, which is subsequently mixed with glass and consolidated. Zeolite was found to be effective in removing fission

C. Pereira; B. D. Babcock

1996-01-01

364

Addressing different active neutron interrogation signatures from fissionable material  

Microsoft Academic Search

In a continuing effort to examine portable methods for implementing active neutron interrogation for detecting shielded fissionable material research is underway to investigate the utility of analyzing multiple time-correlated signatures. Time correlation refers here to the existence of unique characteristics of the fission interrogation signature related to the start and end of an irradiation, as well as signatures present in

David L. Chichester; Edward H. Seabury

2009-01-01

365

Fission Fragment Damage in Semiconductors and Ionic Crystals  

Microsoft Academic Search

Electron microscopic observation is carried out on fission fragment irradiated germanium, silicon and magnesium oxide which have different grain size and thickness. Tracks of fission fragments are observed in evaporated films of germanium with about 10 Å grain size and of magnesium oxide with about 50 Å grain size, while no track is observed in other materials. A number of

Kazuhiko Izui

1965-01-01

366

GAMMA SPECTRA OF GROSS FISSION PRODUCTS FROM THERMAL REACTORS  

Microsoft Academic Search

Calculations of gamma spectra from products of thermal fission of U\\/sup ; 235\\/ are presented. The fission yield values and decay data used are taken from ; literature published up to April 1958. The calculations cover seven different ; irradiation times from one day to two years and continuous cooling times from one ; day to 1000 years. The gamma

J. Prawitz; K. Low; R. Bjornerstedt

1959-01-01

367

Mitochondrial Morphological Features Are Associated with Fission and Fusion Events  

PubMed Central

Mitochondria are dynamic organelles that undergo constant remodeling through the regulation of two opposing processes, mitochondrial fission and fusion. Although several key regulators and physiological stimuli have been identified to control mitochondrial fission and fusion, the role of mitochondrial morphology in the two processes remains to be determined. To address this knowledge gap, we investigated whether morphological features extracted from time-lapse live-cell images of mitochondria could be used to predict mitochondrial fate. That is, we asked if we could predict whether a mitochondrion is likely to participate in a fission or fusion event based on its current shape and local environment. Using live-cell microscopy, image analysis software, and supervised machine learning, we characterized mitochondrial dynamics with single-organelle resolution to identify features of mitochondria that are predictive of fission and fusion events. A random forest (RF) model was trained to correctly classify mitochondria poised for either fission or fusion based on a series of morphological and positional features for each organelle. Of the features we evaluated, mitochondrial perimeter positively correlated with mitochondria about to undergo a fission event. Similarly mitochondrial solidity (compact shape) positively correlated with mitochondria about to undergo a fusion event. Our results indicate that fission and fusion are positively correlated with mitochondrial morphological features; and therefore, mitochondrial fission and fusion may be influenced by the mechanical properties of mitochondrial membranes. PMID:24733410

Martin, Katie R.; Hlavacek, William S.; MacKeigan, Jeffrey P.

2014-01-01

368

Compound Nucleus Reactions in LENR, Analogy to Uranium Fission  

Microsoft Academic Search

The discovery of nuclear fission by Hahn and Strassmann was based on a very rare microanalytical result that could not initially indicate the very complicated details of this most important process. A similarity is discussed for the low energy nuclear reactions (LENRs) with analogies to the yield structure found in measurements of uranium fission. The LENR product distribution measured earlier

Heinrich Hora; George Miley; Karl Philberth

2008-01-01

369

Whole-rock uranium analysis by fission track activation  

NASA Technical Reports Server (NTRS)

We report a whole-rock uranium method in which the polished sample and track detector are separated in a vacuum chamber. Irradiation with thermal neutrons induces uranium fission in the sample, and the detector records the integrated fission track density. Detection efficiency and geometric factors are calculated and compared with calibration experiments.

Weiss, J. R.; Haines, E. L.

1974-01-01

370

The spectrum of nuclear energy levels during the fission process  

Microsoft Academic Search

Despite great success in explaining the fission process qualitatively, the liquid-drop model has failed to explain a number of important aspects of nuclear fission. Thus there has appeared a tendency to interpret experimental data by considering shell [1] and single-particle [2] effects. However, the authors of these and other works have confined themselves to a qualitative examination of the problem.

P. A. Cherdantsev; V. E. Marshalkin

1966-01-01

371

Development Progress in Phase 1 Fission Propulsion Systems  

NASA Technical Reports Server (NTRS)

Phase 1 fission propulsion systems are those fission propulsion systems that are highly testable and require no development of nuclear fuels or materials. The systems can be developed without new or significantly modified facilities, have adequate performance for numerous missions of interest, and demonstrate technologies and programmatics that are traceable to Phase 2 and Phase 3 systems. Phase 1 fission propulsion systems focus on safety, cost and schedule. Phase 1 flight units can be tested at full thrust using resistance heaters to simulate heat from fission. The development and use of Phase 1 systems will help enable Phase 2 or Phase 3 fission propulsion systems capable of giving rapid, affordable access to any point in the solar system. A Phase 1 fission propulsion system under development at the Marshall Space Flight Center (MSFC) in collaboration with individuals from Department of Energy Laboratories and industry is the Safe Affordable Fission Engine (SAFE). The propellant energy source of a 30 kW SAFE unit (SAFE-30) is being fabricated, and will begin testing at MSFC in FY00. The conceptual design of a 300 kW SAFE unit (SAFE-300)is nearing completion. Experiments have been performed on both SAFE-30 and SAFE-300 components. Module tests have confirmed the performance potential of the SAFE series of propulsion systems. This paper will report on the development status of the Phase 1 SAFE fission propulsion system.

Houts, Michael G.; VanDyke, Melissa; Godfroy, Tom; Martin, Jim; Dickens, Ricky; Pedersen, Kevin; Poston, David; Reid, Bob; Lipinski, Ron; Wright, Steve; Lenard, Roger

2000-01-01

372

Fission Limits for Bifurcated Asteroids: The Case of Kleopatra  

NASA Astrophysics Data System (ADS)

Based on radar and optical measurement of Kleopatra we show that it is spinning near, but less than, its fission limit. Our method is also applied to five other asteroids to map out their spin limits before they are susceptible to spin fission.

Hirabayashi, M.; Scheeres, D. J.

2012-03-01

373

Missing in Action? Evaluating the Putative Absence of Impacts by Large Asteroids and Comets during the Quaternary Period  

Microsoft Academic Search

The Quaternary period represents the interval of oscillating climatic extremes (glacial and interglacial periods) beginning about 2.6 million years ago to the present. Based on modeling by the Near Earth Object (NEO) community of planetary scientists, the known and validated record of Quaternary impact on Earth by comets and asteroids is seemingly depauperate in terms of larger impactors of 10,000+

W. Bruce Masse; Robert P. Weaver; Dallas H. Abbott; Viacheslav K. Gusiakov; Edward A. Bryant

2007-01-01

374

Environ. Sci. Technol. 1993, 27, 1625-1631 Sorptlon and Desorption of Quaternary Amine Cations on Clays  

E-print Network

that the nature of the sorption process was cation exchange, since washing the clay samples with water alone only 19714 We have studied the sorption and desorption of three quaternary amines, namely of the montmoril- lonite. Sorption of quaternary amine cations involves at least twotypes of reactions, namely

Sparks, Donald L.

375

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Simple formula for the thermal conductivity of a quaternary solid solution  

NASA Astrophysics Data System (ADS)

An analysis is made of the thermal conductivity of quaternary solid solutions (alloys) allowing for their disordered structure on the basis of a phenomenological analysis proposed by Abeles. This method is applied to a quaternary solid solution In1 - xGaxAsyP1 - y. A simple analytic expression is derived for the thermal conductivity of this material.

Nakwaski, W.

1988-11-01

376

Fission energy program of the US Department of Energy, FY 1981  

SciTech Connect

Information is presented concerning the National Energy Plan and fission energy policy; fission energy program management; converter reactor systems; breeder reactor systems; and special nuclear evaluations and systems.

Not Available

1980-03-01

377

Binary and ternary fission studies with 252Cf  

NASA Astrophysics Data System (ADS)

The spontaneous fission of 252Cf has been studied via ? ? ? ? ? coincidences and ? ? ?-light charged particle coincidences with Gammasphere. The yields of correlated Mo-Ba pairs in binary fission with 0-10 neutron emission have been remeasured with an uncompressed ????? coincidence data. The previous hot fission mode with 8-10 neutron emission seen in the Mo-Ba split is found to be smaller than earlier results but still present. New 0n binary SF yields are reported. By gating on the light charged particles detected in ?E-E Si detectors and ??? coincidences with Gammasphere, the relative yields of correlated pairs in alpha ternary fission with zero to 6n emission are observed for the first time. A number of correlated pairs are identified in ternary fission with 10Be as the LCP. We observed only cold, 0n 10Be and little, if any, hot, xn 10Be channel.

Ramayya, A. V.; Hamilton, J. H.; Hwang, J. K.; Beyer, C. J.; Ter Akopian, G. M.; Daniel, A. V.; Rasmussen, J. O.; Wu, S.-C.; Donangelo, R.; Kormicki, J.; Zhang, X. Q.; Rodin, A.; Formichev, A.; Kliman, J.; Krupa, L.; Oganessian, Yu. Ts.; Chubaryan, G.; Seweryniak, D.; Janssens, R. V. F.; Ma, W. C.; Piercey, R. B.; Cole, J. D.

2001-01-01

378

Fission matrix capability for MCNP, Part II - Applications  

SciTech Connect

This paper describes the initial experience and results from implementing a fission matrix capability into the MCNP Monte Carlo code. The fission matrix is obtained at essentially no cost during the normal simulation for criticality calculations. It can be used to provide estimates of the fundamental mode power distribution, the reactor dominance ratio, the eigenvalue spectrum, and higher mode spatial eigenfunctions. It can also be used to accelerate the convergence of the power method iterations. Past difficulties and limitations of the fission matrix approach are overcome with a new sparse representation of the matrix, permitting much larger and more accurate fission matrix representations. Numerous examples are presented. A companion paper (Part I - Theory) describes the theoretical basis for the fission matrix method. (authors)

Carney, S. E. [University of Michigan, NERS Department, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109 (United States); Brown, F. B. [Los Alamos National Laboratory, Monte Carlo Codes Group, MS A143, PO Box 1663, Los Alamos, NM 87545 (United States); Kiedrowski, B. C. [University of Michigan, NERS Department, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109 (United States); Martin, W. R. [Los Alamos National Laboratory, Monte Carlo Codes Group, MS A143, PO Box 1663, Los Alamos, NM 87545 (United States)

2013-07-01

379

Applications of Event-by-Event Fission Modeling with FREYA  

SciTech Connect

The recently developed code FREYA (Fission Reaction Event Yield Algorithm) generates large samples of complete fission events, consisting of two receding product nuclei as well as a number of neutrons and photons, all with complete kinematic information. Thus it is possible to calculate arbitrary correlation observables whose behavior may provide unique insight into the fission process. We first discuss the present status of FREYA, which has now been extended to include spontaneous fission. Concentrating on {sup 239}Pu(n{sub th},f), {sup 240}Pu(sf) and {sup 252}Cf(sf), we discuss the neutron multiplicity correlations, the dependence of the neutron energy spectrum on the neutron multiplicity, and the relationship between the fragment kinetic energy and the number of neutrons and their energies. We also suggest novel fission observables that could be measured with modern detectors.

Vogt, R; Randrup, J

2011-09-16

380

Double Glacier Volcano, a `new' Quaternary volcano in the eastern Aleutian volcanic arc  

NASA Astrophysics Data System (ADS)

The Double Glacier Volcano (DGV) is a small dome complex of porphyritic hornblende andesite and dacite that is part of the Cook Inlet segment of Quaternary volcanoes of the eastern Aleutian arc. Its discovery reduces the previously described large volcano gap in Cook Inlet segment to a distance similar to that between other volcanoes in the area. DGV lavas are medium-K, calcalkaline andesites and dacites with concentrations of major and minor elements similar to the other Quaternary volcanoes of the Cook Inlet segment. Available K-Ar ages indicate that DGV was active 600 900 ka.

Reed, Bruce L.; Lanphere, Marvin A.; Miller, Thomas P.

1992-10-01

381

Vegetation ecotone dynamics in Southwest Alaska during the Late Quaternary  

NASA Astrophysics Data System (ADS)

To examine Late Quaternary vegetation change across the modern vegetation gradient from continuous boreal forest (central Alaska) to Betula shrub tundra (Bristol Bay region), pollen records from Idavain and Snipe Lakes are described and compared to those of four other sites in southwest Alaska. Major features of the vegetation history at Idavain Lake include herb-dominated tundra (ca 14-12 ka BP), mixed herb/ Betula shrub tundra (ca 12-8 ka BP), and Alnus/Betula shrub tundra (8 ka BP to present). The Snipe Lake record reveals a brief period of herb tundra (>12 ka BP), Betula shrub tundra (ca 12-8.5 ka BP), and Picea forest mixed with Alnus/Betula shrub tundra (ca 8 ka BP to present). Comparisons with other pollen records indicate that southwest Alaska has been the location of major vegetation ecotones throughout the last 12 ka years. Northern areas have consistently been dominated by larger growth forms (shrubs or trees) than have southern areas. During the Betula period (12-8 ka BP), a dense Betula shrubland occupied central Alaska, changing to a mixed low- Betula shrub and herb tundra in the south. In the Alnus/Picea period (8 ka BP to present), Picea and Betula trees were more common to the north; Alnus and Betula shrubs more abundant to the south. Vegetation dynamics have been complex at individual sites and across the region. Each site shows both long- and short-term shifts in major taxa, but the magnitude of these changes varies across the transect. In addition, some pollen changes appear to be synchronous among sites (within the constraints of existing chronologies), whereas others are strikingly time transgressive across the region. Similar vegetation dynamics at all sites are: (1) long-term decreases in herb taxa during the Betula period, (2) short-term oscillations between Betula shrubs and herbs during the Betula period, and (3) major increase in Alnus shrubs ca 8 ka BP. Significant differences among sites include: (1) major expansion of Populus trees in northern but not southern areas during the Betula period, (2) progressively later expansion of P. glauca at northern sites than at southern sites (ca 9.5-4.5 ka BP), and (3) fluctuation of P. glauca populations in extreme northern areas during the early Alnus/Picea period.

Brubaker, Linda B.; Anderson, Patricia M.; Hu, Feng Sheng

2001-01-01

382

Quaternary Ammonium Salts From Hydrolysed Fatty Oil Based on Novel Tertiary Amines Used as Corrosion Inhibitors for Pipelines Carbon Steel at Acid Job in Petroleum Industry  

Microsoft Academic Search

Ten new quaternary ammonium salts were designed and synthesized from hydrolyzed fatty oils; the hydrolysed oils were used as a source of alkyl halides to prepare the quaternary ammonium salts by refluxing the fatty alkyl halide with ethoxylated amines as untraditional 3° amines in acetone. The structure of the prepared quaternary ammonium salts were characterized by FTIR and H NMR

A. M. Al-Sabagh; N. G. Kandile; Nahed Amer; Omaima Ramadan; E. A. Khamis

2011-01-01

383

Mass-Yield Curve of First-Chance Fission from Proton and Deuteron-Induced Fission of 226Ra  

Microsoft Academic Search

Information has been obtained on the mass distribution and kinetic energy release for fission of 226Ra induced by protons and deuterons at moderate bombarding energies (<20 MeV). The mass distribution, which is triple peaked, has previously been interpreted in terms of two separate fission \\

D. G. Perry; A. W. Fairhall

1971-01-01

384

Late Miocene extensional tectonics in the evolution of the eastern Betics and Neogene-Quaternary basins, an example from the Sorbas basin (SE Spain).  

NASA Astrophysics Data System (ADS)

Neogene to Quaternary basins in the eastern Betics occur in synclines among near E/W-elongated antiformal ridges where the metamorphic basement crops out. These antiforms are related to or cut by large-scale strike-slip faults, both developed in response of the NW-SE Africa-Iberia convergence. Most literature associated the origin and evolution of the Neogene-Quaternary eastern Betics basins with this transpressional strike-slip regime. However, recent work showed the great importance of extensional tectonics in the development and evolution of these basins during the middle to late Miocene. In order to define the role of Miocene extensional tectonics in the origin and evolution of Neogene - Quaternary basins, we have carefully mapped a key area in the southeastern Betics, the western termination of Sierra Cabrera. We analyzed the age and linking relationships between brittle fault segments, and finally we constructed a balanced cross section. We identified a NW-SE listric normal fault system that was active during the Tortonian producing southwestward hanging-wall displacement. These normal faults show hard linkage relationships with E-W to N70E vertical strike-slip and oblique-slip extensional transfer faults that show both dextral and sinistral kinematics. The balanced cross section shows that listric faults probably join together into a basal detachment (about 1 km depth) inside the metamorphic basement (Nevado-Filabride complex). The fault system influenced the Tortonian sedimentary evolution of the Sorbas Basin controlling the sediments thickness. The early Tortonian sedimentary unit is missed in the hangingwall of the fault system, meanwhile the thickness of late Tortonian sediments deposited between 11 and 8 Ma change across the main faults from approximately 200 m thick in the footwall of the system to up to 800 m in the main depocentre. Furthermore, the fault system controlled the Tortonian sedimentary facies shifting from continental and deltaic conglomerates in the footwall to silts and basin marls in the main depocentre. Finally, in the Tortonian sediments two main angular unconformities were recognized probably associated with two extensional pulses in the wider context of the late Miocene extension that affected most of the western Mediterranean region. The first unconformity occurred at approx. 10 Ma between early Tortonian continental conglomerates and the Tortonian marine Chozas formation, meanwhile the second one between the Chozas and Turre formations at approx. 8 Ma. These extensional pulses are supported by fission-track and U-He data available in the area that indicate ages approx. 12 Ma for zircon and 7-9 Ma for apatite grains and U-He corresponding with two exhumation events. Extensional tectonics represented the main control process in the origin and evolution of Neogene-Quaternary basins of the eastern Betics that were later inverted by the current NW-SE convergence between Africa and Europe. Many strike-slip faults interpreted as transcurrent in origin in the eastern Betics represent extensional transfer faults or folded extensional detachments produced during the middle to late Miocene extensional regime.

Giaconia, Flavio; Booth-Rea, Guillermo; Martínez-Martínez, José Miguel; Azañón, José Miguel

2013-04-01

385

Description of Induced Nuclear Fission with Skyrme Energy Functionals: I. Static Potential Energy Surfaces and Fission Fragment Properties  

E-print Network

Eighty years after its experimental discovery, a microscopic description of induced nuclear fission based solely on the interactions between neutrons and protons and quantum many-body methods still poses formidable challenges. The goal of this paper is to contribute to the development of a predictive microscopic framework for the accurate calculation of static properties of fission fragments for hot fission and thermal or slow neutrons. To this end, we focus on the 239Pu(n,f) reaction and employ nuclear density functional theory with Skyrme energy densities. Potential energy surfaces are computed at the Hartree-Fock-Bogoliubov approximation with up to five collective variables. We find that the triaxial degree of freedom plays an important role, both near the fission barrier and at scission. The impact of the parameterization of the Skyrme energy density on deformation properties from the ground-state up to scission is also quantified. We introduce a general template for the detailed description of fission fr...

Schunck, N; Carr, H; Knoll, A

2013-01-01

386

Heavy-ion versus 3He/4He fusion-fission reactions: Angular momentum dependence of dissipation in nuclear fission  

NASA Astrophysics Data System (ADS)

The stochastic Langevin model is employed to study dissipation properties in fission in the 16O + 181Ta ?197Tl system by analyzing prescission neutron yields measured in this reaction. It has been found that the 197Tl nuclei undergo fission that is not in accordance with the standard Bohr-Wheeler statistical theory. A detailed comparison with previously published work in which fission excitation functions measured in 3,4He + 197Au ?200,201Tl are shown to be in excellent agreement with the fission width formula predicted by the traditional models of nuclear fission suggests that nuclear dissipation strength may have an angular momentum dependence in addition to the known deformation and temperature dependence. Implications for the basic understanding of the observed abnormal rise in prescission particles at high energy and the need for further experimental confirmations are discussed.

Ye, W.

2011-09-01

387

Results of interlaboratory comparison of fission track ages for 1992 fission track workshop  

USGS Publications Warehouse

Two apatites and one sphene were made available to the fission track research community for analysis prior to the 1992 Fission Track Workshop held in Philadelphia, U.S.A., 13-17 July. Eighteen laboratories throughout the world received aliquots of apatite and sphene. To date, analyses by 33 different scientists have been representing 15 different laboratories. With respect to the previous two interlaboratory comparisons, there is a noticeable improvement in the accuracy of the age results (Naeser and Cebula, 1978; Naeser et al., 1981; Miller et al., 1985;Miller et al.1990). Ninety-four percent of the analysis used the external detector method (EDM) combined with the zeta technique while the remaining individuals used the population method (POP). Track length measurements (requested for the first time in the interlaboratory comparison studies) were in relatively good agreement. ?? 1993.

Miller, D.S.; Crowley, K.D.; Dokka, R.K.; Galbraith, R.F.; Kowallis, B.J.; Naeser, C.W.

1993-01-01

388

?-ray spectroscopy of fission fragments from the cold-neutron 235U induced fission with EXILL  

NASA Astrophysics Data System (ADS)

A cold neutron induced fission experiment recently took place at the Institute Laue-Langevin (ILL) in Grenoble. The neutron beam was provided by the nuclear reactor facility at ILL and the detector setup that was used for the ?-spectroscopy of the fission products consisted mainly of the detectors of the EXOGAM array [1], thereby the name of the campaign is EXILL. The main purpose of our measurement was to investigate the nuclei in the region with N = 50 close to 78Ni as well as the nuclei close to the N = 82 shell closure. In this paper, the motivation of the experiment is described as well as the experimental setup and the status of the ongoing data analysis.

Konstantinopoulos, T.; Astier, A.; Petrache, C.; Abudra, A.; Bontemps, R.; Deloncle, I.; Kaim, S.; Leguillon, R.; Petrache, C.; Porquet, M.-G.; Zerrouki, T.; Grente, L.; Salsac, M.-D.; Zielinska, M.; de France, G.; Janas, Z.; Karny, M.; Korgul, A.; Ramdhane, M.; Gey, G.; Simpson, G.; Vancraeyenest, A.; Blanc, A.; Jentschel, M.; Köster, U.; Mutti, P.; Soldner, T.; Urban, W.; Duchêne, G.; Lozeva, R.; Ibrahim, F.; Gargano, A.; Covello, A.; Mengoni, D.; Ur, C. A.; Sferrazza, M.; Melon, B.

2013-12-01

389

Fission Product Yield Study of 235U, 238U and 239Pu Using Dual-Fission Ionization Chambers  

NASA Astrophysics Data System (ADS)

To resolve long-standing differences between LANL and LLNL regarding the correct fission basis for analysis of nuclear test data [M.B. Chadwick et al., Nucl. Data Sheets 111, 2891 (2010); H. Selby et al., Nucl. Data Sheets 111, 2891 (2010)], a collaboration between TUNL/LANL/LLNL has been established to perform high-precision measurements of neutron induced fission product yields. The main goal is to make a definitive statement about the energy dependence of the fission yields to an accuracy better than 2-3% between 1 and 15 MeV, where experimental data are very scarce. At TUNL, we have completed the design, fabrication and testing of three dual-fission chambers dedicated to 235U, 238U, and 239Pu. The dual-fission chambers were used to make measurements of the fission product activity relative to the total fission rate, as well as for high-precision absolute fission yield measurements. The activation method was employed, utilizing the mono-energetic neutron beams available at TUNL. Neutrons of 4.6, 9.0, and 14.5 MeV were produced via the 2H(d,n)3He reaction, and for neutrons at 14.8 MeV, the 3H(d,n)4He reaction was used. After activation, the induced ?-ray activity of the fission products was measured for two months using high-resolution HPGe detectors in a low-background environment. Results for the yield of seven fission fragments of 235U, 238U, and 239Pu and a comparison to available data at other energies are reported. For the first time results are available for neutron energies between 2 and 14 MeV.

Bhatia, C.; Fallin, B.; Howell, C.; Tornow, W.; Gooden, M.; Kelley, J.; Arnold, C.; Bond, E.; Bredeweg, T.; Fowler, M.; Moody, W.; Rundberg, R.; Rusev, G.; Vieira, D.; Wilhelmy, J.; Becker, J.; Macri, R.; Ryan, C.; Sheets, S.; Stoyer, M.; Tonchev, A.

2014-05-01

390

Charge distributions in low-energy nuclear fission and their relevance to fission dynamics  

Microsoft Academic Search

Radiochemical and energy loss techniques have been used to measure fragment charge distributions in the systems 229Th(nth, f), 235U(n3 MeV, f) and 252Cf(s, f). Together with those previously obtained [233, 235U(nth, f) and 239, 241Pu(nth, f] the results show that these charge distributions depend very sensitively on both the fissioning species and the initial excitation energy. Very strong even-odd effects

G. Mariolopoulos; Ch. Hamelin; J. Blachot; J. P. Bocquet; R. Brissot; J. Crançon; H. Nifenecker; Ch. Ristori

1981-01-01

391

Anomalous anisotropies of fission fragments for sub-barrier fusion-fission reactions  

NASA Astrophysics Data System (ADS)

It is shown that preequilibrium fission can give rise to a large anisotropy at sub-barrier energies for the 16O+232Th and 12C+236U reactions, since the transmission coefficient is several times larger for target orientation angles around 180° in comparison with angles around 90°. At higher energies the effect dilutes, since the transition probability becomes of approximately equal magnitude for all orientations.

Vorkapi?, D.; Ivaniševi?, B.

1995-10-01

392

RADIOCHEMICAL STUDIES ON URANIUM MULTIPLE FISSION. 4. FISSION YIELD OF Cu⁶⁷  

Microsoft Academic Search

Uranium with various U²³⁵ contents was irradiated with neutrons, ; and the copper activity was separated from the fission products. After decay of ; the Cu⁶⁴ activity which could be limited by the small copper content of the ; sample, the Cu⁶⁷ could be detected and measured. (tr-auth) Natural neon ; was bombarded by alpha -particles with laboratory energies ranging

R. Muenze; O. Hladik

1963-01-01

393

Nuclear fission and the transuranium elements  

SciTech Connect

Many of the transuranium elements are produced and isolated in large quantities through the use of neutrons furnished by nuclear fission reactions: plutonium (atomic number 94) in ton quantities; neptunium (93), americium (95), and curium (96) in kilogram quantities; berkelium (97) in 100 milligram quantities; californium (98) in gram quantities; and einsteinium (99) in milligram quantities. Transuranium isotopes have found many practical applications---as nuclear fuel for the large-scale generation of electricity, as compact, long-lived power sources for use in space exploration, as means for diagnosis and treatment in the medical area, and as tools in numerous industrial processes. Of particular interest is the unusual chemistry and impact of these heaviest elements on the periodic table. This account will feature these aspects. 9 refs., 5 figs.

Seaborg, G.T.

1989-02-01

394

Prescission neutron multiplicity and fission probability from Langevin dynamics of nuclear fission  

E-print Network

A theoretical model of one-body nuclear friction which was developed earlier, namely the chaos-weighted wall formula, is applied to a dynamical description of compound nuclear decay in the framework of the Langevin equation coupled with statistical evaporation of light particles and photons. We have used both the usual wall formula friction and its chaos-weighted version in the Langevin equation to calculate the fission probability and prescission neutron multiplicity for the compound nuclei $^{178}$W, $^{188}$Pt, $^{200}$Pb, $^{213}$Fr, $^{224}$Th, and $^{251}$Es. We have also obtained the contributions of the presaddle and postsaddle neutrons to the total prescission multiplicity. A detailed analysis of our results leads us to conclude that the chaos-weighted wall formula friction can adequately describe the fission dynamics in the presaddle region. This friction, however, turns out to be too weak to describe the postsaddle dynamics properly. This points to the need for a suitable explanation for the enhanced neutron emission in the postsaddle stage of nuclear fission.

Gargi Chaudhuri; Santanu Pal

2001-05-04

395

Results of interlaboratory comparison of fission-track age standards: Fission-track workshop-1984  

USGS Publications Warehouse

Five samples were made available as standards for the 1984 Fission Track Workshop held in the summer of 1984 (Rensselaer Polytechnic Institute, Troy, New York). Two zircons, two apatites and a sphene were distributed prior to the meeting to 40 different laboratories. To date, 24 different analysts have reported results. The isotopic ages of the standards ranged from 16.8 to 98.7 Myr. Only the statement that the age of each sample was less than 200 Myr was provided with the set of standards distributed. Consequently, each laboratory was required to use their laboratory's accepted treatment (irradiation level, etching conditions, counting conditions, etc.) for these samples. The results show that some workers have serious problems in achieving accurate age determinations. This emphasizes the need to calibrate experimental techniques and counting procedures against age standards before unknown ages are determined. Any fission-track age determination published or submitted for publication can only be considered reliable if it is supported by evidence of consistent determinations on age standards. Only this can provide the scientific community with the background to build up confidence concerning the validity of the fission-track method. ?? 1985.

Miller, D.S.; Duddy, I.R.; Green, P.F.; Hurford, A.J.; Naeser, C.W.

1985-01-01

396

Suppressed-fission ICF hybrid reactor  

SciTech Connect

A suppressed-fission ICF hybrid reactor has been designed to maximize the production of /sup 233/U. In this design, Be is used as a neutron multiplier. An annular array of Be columns surrounds the fusion pulse inside the reaction chember. The Be columns consist of short cylinders of Be joined together with steel snap rings. Vertical holes in the Be carry liquid lithium coolant and steel-clad thorium fuel pins. The lithium coolant is supplied at the top of the chamber, traverses through the Be columns and exits at the bottom. The columns are attached to top and bottom plates in such a way as to tolerate radiation-induced swelling and the vibrations resulting from each fusion pulse. A thin (10 cm) liquid Li fall region protects the Be columns from direct exposure to the X-rays and debris emitted by the fuel capsule. A neutronics study of this design indicates that the specific production of /sup 233/U fuel is increased by operating at relatively large thorium volume fractions. A design at a fertile fuel fraction of 30 vol % produces a total breeding ratio of over 2.1. The /sup 6/Li to /sup 7/Li ratio is adjusted to keep the tritium breeding ratio at about 1.0. In such a reactor, about 3400 kg of /sup 233/U can be produced per full power year at a fusion power level of 800 MW. Reactor support ratios greater than 13 can be achieved, leading to beneficial results even if the fusion reactor cost is significantly greater than that of a fission reactor.

Hogan, W.J.; Meier, W.R.

1986-05-20

397

Feasibility of an antiproton catalyzed fission fragment rocket  

SciTech Connect

The purpose of this project was to investigate the feasibility of an antiproton catalyzed fission fragment rocket (FFR). The FFR is characterized by the extraction of fission fragments from the fissile fuel, and the utilization of their kinetic energy for thrust generation. A significant drawback to previous FFR designs was the requirement to maintain a critical nuclear pile as the fission fragment source. The author examined the possibility of replacing the critical pile with a sub-critical pile driven by antiprotons. Recent experiments have revealed that antiprotons stimulate highly energetic fissions in {sup 238}U, with a neutron multiplicity of 13.7 neutrons per fission. This interaction was used as a throttled neutron source. The pile consisted of layers of fissile coated fibers which are designed to allow fission fragments to escape them, where the fragments collide with a fluid. The heated fluid is then ejected from the rocket to provide thrust. The calculations performed indicate that each antiproton injected into the pile can stimulate 8 or more fissions while maintaining a neutron multiplication of less than 0.4. Based on the results seen, the engine design presented is inadequate. Limitations introduced by the reaction fluid far outweigh the simplicity-of-design gained. Despite this, the basic idea of using the antiproton-U interaction as a source of spacecraft propulsion warrants further study.

Hdinger, D.S.

1992-03-01

398

Fission-product SiC reaction in HTGR fuel  

SciTech Connect

The primary barrier to release of fission product from any of the fuel types into the primary circuit of the HTGR are the coatings on the fuel particles. Both pyrolytic carbon and silicon carbide coatings are very effective in retaining fission gases under normal operating conditions. One of the possible performance limitations which has been observed in irradiation tests of TRISO fuel is chemical interaction of the SiC layer with fission products. This reaction reduces the thickness of the SiC layer in TRISO particles and can lead to release of fission products from the particles if the SiC layer is completely penetrated. The experimental section of this report describes the results of work at General Atomic concerning the reaction of fission products with silicon carbide. The discussion section describes data obtained by various laboratories and includes (1) a description of the fission products which have been found to react with SiC; (2) a description of the kinetics of silicon carbide thinning caused by fission product reaction during out-of-pile thermal gradient heating and the application of these kinetics to in-pile irradiation; and (3) a comparison of silicon carbide thinning in LEU and HEU fuels.

Montgomery, F.

1981-07-13

399

Modelling Animal Group Fission Using Social Network Dynamics  

PubMed Central

Group life involves both advantages and disadvantages, meaning that individuals have to compromise between their nutritional needs and their social links. When a compromise is impossible, the group splits in order to reduce conflict of interests and favour positive social interactions between its members. In this study we built a dynamic model of social networks to represent a succession of temporary fissions involving a change in social relations that could potentially lead to irreversible group fission (i.e. no more group fusion). This is the first study that assesses how a social network changes according to group fission-fusion dynamics. We built a model that was based on different parameters: the group size, the influence of nutritional needs compared to social needs, and the changes in the social network after a temporary fission. The results obtained from this theoretical data indicate how the percentage of social relation transfer, the number of individuals and the relative importance of nutritional requirements and social links influence the average number of days before irreversible fission occurs. The greater the nutritional needs and the higher the transfer of social relations during temporary fission, the fewer days will be observed before an irreversible fission. It is crucial to bridge the gap between the individual and the population level if we hope to understand how simple, local interactions may drive ecological systems. PMID:24831471

Sueur, Cédric; Maire, Anaïs

2014-01-01

400

Neutron induced capture and fission discrimination using calorimetric shape decomposition  

NASA Astrophysics Data System (ADS)

The neutron capture and fission cross-sections of 233U have been measured at the neutron time-of-flight facility n_TOF at CERN in the energy range from 1 eV to 1 keV using a high performance 4? BaF2 Total Absorption Calorimeter (TAC) as a detection device. In order to separate the contributions of neutron capture and neutron induced fission in the TAC, a methodology called Calorimetric Shape Decomposition (CSD) was developed. The CSD methodology is based on the study of the TAC's energy response for all competing reactions, allowing to discriminate between ? s originating from neutron induced fission and those from neutron capture reactions without the need for fission tagging or any additional detection system. In this article, the concept behind the CSD is explained in detail together with the necessary analysis to obtain the TAC's response to neutron capture and neutron induced fission. The discrimination between capture and fission contributions is shown for several neutron energies. A comparison between the 233U neutron capture and fission yield extraction with ENDF/B-VII v1. library data is also provided.

Carrapiço, C.; Berthoumieux, E.; Dridi, W.; Gonçalves, I. F.; Gunsing, F.; Lampoudis, C.; Vaz, P.; n TOF Collaboration

401

Evaluation of the amino acid racemization reaction in studies of Quaternary marine sediments in South Australia  

Microsoft Academic Search

A preliminary assessment has been made of the application of amino acid racemization in molluscan fossils for chronostratigraphic studies of Late Quaternary coastal and marine sediments in South Australia. Evaluation of sources of amino acid D\\/L ratio variation provides a basis for interpreting the reliability of the technique. Several potential error sources have been recognized within the ambit of analytical

C. V. Murray-Wallace; R. W. L. Kimber

1987-01-01

402

Sulfated quaternary amine lipids: a new class of inverse charge zwitterlipids†  

PubMed Central

We describe a new class of charge inverted zwitterionic sulfated lipids (AS) with a cationic quaternary amine anchored at the membrane interface and an anionic sulfate moiety extended into the aqueous phase. These lipids have exceptionally high transition temperatures and assemble into lipid aggregates when dispersed in aqueous solutions. PMID:24984814

Venditto, Vincent J.; Dolor, Aaron; Kohli, Aditya; Salentinig, Stefan; Boyd, Ben J.

2014-01-01

403

Quaternary Science Reviews 24 (2005) 123140 The deforming bed characteristics of a stratified till assemblage in  

E-print Network

Quaternary Science Reviews 24 (2005) 123­140 The deforming bed characteristics of a stratified till) and laboratory (Iverson et al., 1997, 1998) based investigations of till deformation subscribe to a plastic rheological model for till behaviour however, and recent micromorphological studies point to the presence

Hart, Jane

404

Late Quaternary Morphological Changes of the Waipaoa River Outer Shelf and Upper Slope, New Zealand  

Microsoft Academic Search

The outer shelf and slope seaward of the Waipaoa River, New Zealand has experienced considerable morphological change in the late Quaternary. The complexion of the margin has evolved as a result of sedimentation affected by sea level, oceanographic, and tectonic forcings. Integration of seismic, core and multibeam data indicate that the modern seabed morphology along a 30-km stretch of the

J. P. Walsh; B. Sumners; C. Alexander; A. Orpin; T. Gerber; L. Pratson

2006-01-01

405

Late Quaternary paleoenvironmental records from the western Lena Delta, Arctic Siberia  

Microsoft Academic Search

The three main Lena Delta terraces were formed during different stages of the late Quaternary. While only the first floodplain terrace is connected with active deltaic processes, the second and third terraces, which dominate the western part of the delta, are erosional remnants of arctic paleolandscapes affected by periglacial processes. The landscape dynamics of the second and the third terraces,

Lutz Schirrmeister; Guido Grosse; Moritz Schnelle; Margret Fuchs; Matthias Krbetschek; Mathias Ulrich; Viktor Kunitsky; Mikhail Grigoriev; Andrei Andreev; Frank Kienast; Hanno Meyer; Olga Babiy; Irina Klimova; Anatoly Bobrov; Sebastian Wetterich; Georg Schwamborn

2011-01-01

406

Highly diastereoselective synthesis of quaternary ?-trifluoromethyl ?-amino acids from chiral imines of trifluoropyruvate.  

PubMed

An efficient method for highly diastereoselective synthesis of quaternary ?-trifluoromethyl ?-amino acids was developed via indium mediated allylation of (R)-phenylglycinol methyl ether based imines of trifluoropyruvate in good yields with high diastereoselectivities at room temperature; to illustrate the application of this method in organic synthesis, 2-allyl-2-(trifluoromethyl) aziridine was prepared in an efficient manner. PMID:20856962

Min, Qiao-Qiao; He, Chun-Yang; Zhou, Haibing; Zhang, Xingang

2010-11-14

407

Late Quaternary geomorphology and soils in Crater Flat, Yucca Mountain area, southern Nevada  

E-print Network

Late Quaternary geomorphology and soils in Crater Flat, Yucca Mountain area, southern Nevada indicate that six major allostratigraphic units occur in Cra- ter Flat, Nevada, adjacent to Yucca Moun for a Crater Flat cation-leaching curve. This curve differs somewhat from a previous Yucca Mountain curve

Dorn, Ron

408

Late Neogene to Quaternary environmental changes in the Antarctic Peninsula region: evidence from drift sediments  

Microsoft Academic Search

Clay-mineral composition and biogenic opal content in upper Miocene to Quaternary drift sediments recovered at two Ocean Drilling Program (ODP) sites from the continental rise in the Bellingshausen Sea had been analyzed in order to reconstruct the climatic and glacial history of the Antarctic Peninsula. The clay mineral composition at both sites is dominated by smectite, illite, and chlorite, and

Claus-Dieter Hillenbrand; Werner Ehrmann

2005-01-01

409

Prediction of Protein Quaternary Structural Type with Functional Domain and Pseudo Amino Acid Composition  

Microsoft Academic Search

In the protein universe, many proteins are composed of two or more polypeptide chains, generally referred to as subunits, which associate through noncovalent interactions and, occasionally, disulfide bonds. With the number of protein sequences entering into data banks rapidly increasing, we are confronted with a challenge: how to develop an automated method to identify the quaternary attribute for a new

Xuan Xiao; Pu Wang

2009-01-01

410

Caldera-forming eruptions of the Quaternary Kone Volcanic Complex, Ethiopia  

Microsoft Academic Search

Quaternary volcanism in the northern Main Ethiopian Rift is characterized by rift-axis eruptive centres with complicated collapse structures. Despite their association with major explosive eruptions, few modern studies have been carried out on them. We present the results of fieldwork and laboratory analyses of one of the largest of these centres, the Kone Volcanic Complex (KVC). It consists of nested

Michael L. Rampey; Clive Oppenheimer; David M. Pyle; Gezahegn Yirgu

2010-01-01

411

QUATERNARY RESEARCH 28,238-244 (1987) A Reexamination of Late-Pleistocene Boreal Forest Reconstructions  

E-print Network

-analytical episodes and the interpretations of boreal forest for the region, made in light of recent advancesQUATERNARY RESEARCH 28,238-244 (1987) A Reexamination of Late-Pleistocene Boreal Forest" and the proposal that boreal forest existed in the region in the late Pleistocene. These interpretations are now

Holliday, Vance T.

412

Quaternary Science Reviews 20 (2001) 15611576 Millennial scale climate variability of the northeast Pacific Ocean and  

E-print Network

Quaternary Science Reviews 20 (2001) 1561­1576 Millennial scale climate variability of the northeast Pacific to millennial scale climate changes is related to changes in atmospheric circulation elements. This finding suggests that, unlike longer-period millennial scale events, the propagation

Kurapov, Alexander

413

Quaternary Science Reviews 22 (2003) 16311646 Greenland--Antarctic phase relations and millennial time-scale  

E-print Network

Quaternary Science Reviews 22 (2003) 1631­1646 Greenland--Antarctic phase relations and millennial the south to north time lag. At higher frequencies, in the millennial band, there is no measurable average. All rights reserved. 1. Introduction Millennial time-scale signals in ice and seafloor cores have

Wunsch, Carl

414

JOURNAL OF QUATERNARY SCIENCE (2001) 16(7) 717726 Copyright 2001 John Wiley & Sons, Ltd.  

E-print Network

.1002/jqs.650 Holocene variations of sea-surface conditions in the southeastern Barents Sea, reconstructed Barents Sea reconstructed from dinoflagellate cyst assemblages. J. Quaternary Sci., Vol. 16 pp. 717: Palynomorphs were analysed in two sediment cores from the southeastern Barents Sea representing the past 8

Long, Bernard

415

Late Quaternary environmental history of central Prins Karls Forland, western Svalbard  

E-print Network

Quaternary ice-sheet and sea-level varia- tions in the Barents Sea area, principally to address the timing-sheet on the Barents Sea shelf in the Late Weichselian (Salvigsen 1981; Salvigsen & Nydal 1981; Solheim et al. 1990 reconstruct a 3200-m-thick central ice-dome in the Barents Sea with a parabolic-shaped ice-sheet margin over

Ingólfsson, �lafur

416

Late quaternary coseismic uplift history of Huon Peninsula, Papua New Guinea  

Microsoft Academic Search

Repeated episodic uplift at Huon Peninsula is represented by regressive terraces cut into raised late Quaternary reef tracts. Up to six regressive terraces occur on the Holocene reef tract and up to 15 occur on reef tracts II and III, which span the interval from 33 ka to 52 ka. The uplift events are believed to be coseismic. The uplift

John Chappell; Yoko Ota; Kelvin Berryman

1996-01-01

417

Quaternary Science Reviews 23 (2004) 14351454 Is the central Arctic Ocean a sediment starved basin?  

E-print Network

Quaternary Science Reviews 23 (2004) 1435­1454 Is the central Arctic Ocean a sediment starved basin sediment cores have been retrieved from the central Arctic Ocean, many of which have been assigned age, suggests that cm/ka-scale rates are pervasive in the central Arctic Ocean. This is not surprising

Jakobsson, Martin

418

Luminescence chronometry and Late Quaternary geomorphic history of the Ganga Plain, India  

Microsoft Academic Search

Flexing of the Indian lithosphere due to the continent–continent collision and thrust fold loading produced the Gangetic Foreland Basin during the Middle Miocene. The basin attained its present configuration during the Late Quaternary. Neotectonics and climate change since the last interglacial influenced the evolution of the present landscape of the Gangetic (Ganga) plains. The regional geomorphic surfaces in these plains

P Srivastava; I. B Singh; M Sharma; A. K Singhvi

2003-01-01

419

A New Genus and Species of Buteonine Hawk from Quaternary Deposits in Bermuda (Aves: Accipitridae)  

Microsoft Academic Search

Bermuteo avivorus, new genus and species, is described from rare Quaternary fossils from the island of Bermuda. Although clearly referable to the Buteoninae, its relationships within that group are difficult to assess. Considerable size variation may be attributable to sexual dimorphism associated with bird-catching behavior. It is uncertain if the species survived into the historic period. Factors contributing to the

Storrs L. Olson

2008-01-01

420

Stratigraphy of the late Quaternary deposits of the northern Canterbury Plains, New Zealand  

Microsoft Academic Search

Stratigraphic correlations of late Quaternary subsurface deposits of the Canterbury Plains, New Zealand, are revised and defined using well logs, radiocarbon dates, and pollen analyses. Three new members—Bleak House, Riverview, and Courtenay—are proposed for the postglacial fluvial Springston Formation. Riccarton Gravel (last glaciation) and Bromley Formation (last interglaciation) are revised. Five new formations are defined for coastal subsurface deposits to

L. J. Brown; D. D. Wilson; N. T. Moar; D. C. Mildenhall

1988-01-01

421

Hierarchical dynamic stratigraphy in various Quaternary gravel deposits, Rhine glacier area (SW Germany): implications for hydrostratigraphy  

Microsoft Academic Search

The approach of ‘dynamic stratigraphy’ aims to understand genetic processes that form stratigraphic units in a hierarchy of spatial and temporal scales. This approach was used to investigate Quaternary gravel deposits in terms of their sedimentology and in order to characterize the various sedimentary units in terms of their hydrogeological properties. Facies analysis within 62 gravel pits, laboratory permeability measurements

Jürgen Heinz; Thomas Aigner

2003-01-01

422

Late Quaternary vegetation history of Rough Canyon, south-central New Mexico, USA  

Microsoft Academic Search

South-central New Mexico, USA, at the junction of the Rocky Mountains, High Plains and Chihuahuan Desert, is one of the better known regions in the late Quaternary of North America. Plant macrofossils and pollen from a packrat midden series in Rough Canyon, New Mexico allows refinement of plant distributions and paleoclimates in this transitional area since full glacial times. From

Julio L. Betancourt; Kate Aasen Rylander; Cristina Peñalba; Janet L. McVickar

2001-01-01

423

Toward establishing a maritime proxy record of the East Asian summer monsoons for the late Quaternary  

E-print Network

Toward establishing a maritime proxy record of the East Asian summer monsoons for the late Accepted 19 June 2003 Abstract An astronomically tuned late Quaternary planktic foraminiferal N18 O record of this maritime proxy matches well with the summer monsoon index obtained from the terrestrial record of Louchuan

Wei, Kuo-Yen

424

Late Quaternary constructional development of the Axial Volcanic Zone, eastern Snake River Plain, Idaho  

E-print Network

Late Quaternary constructional development of the Axial Volcanic Zone, eastern Snake River Plain volcanic ridge that trends northeast across the middle of the eastern Snake River Plain, and acts, but overlying supergroups emplaced from 515 to 247 ka commonly exhibit a ponded morphology along a construct

Wetmore, Paul H.

425

Quaternary International 115116 (2004) 3945 An overview of coastal development in a  

E-print Network

probably conceal newly developed folds or faults where SW trending, paleo-incised valleys and domes of LateQuaternary International 115�116 (2004) 39�45 An overview of coastal development in a Young, Caltech, USA Abstract The coastal morphology of Taiwan exhibits characteristics of collisional tectonism

Lin, Andrew Tien-Shun

426

Late Quaternary hillslope evolution recorded in eastern South African colluvial badlands  

E-print Network

, South Africa c Council for Geoscience, P.O.Box 900, Pietermaritzburg 3200, South Africa d Institute Hillslopes in parts of Swaziland and the Kwa- Zulu^Natal province of South Africa are exten- sively blanketedLate Quaternary hillslope evolution recorded in eastern South African colluvial badlands M

Clarke, Michèle

427

Quaternary Science Reviews 23 (2004) 12851311 Middle Pleistocene glaciations of the Russian North  

E-print Network

Quaternary Science Reviews 23 (2004) 1285­1311 Middle Pleistocene glaciations of the Russian North the latest results by the Russian­Norwegian PECHORA project, are synthesized in order to present evidence history of the Russian North. Only a few sections of Middle Pleistocene drift have been studied by QUEEN

Ingólfsson, �lafur

428

Quaternary International 188 (2008) 3140 Associations of multi-decadal sea-surface temperature  

E-print Network

and North Atlantic Oceans on decadal to multidecadal (D2M) time scales. Results show that the Atlantic Multidecadal Oscillation (AMO) is the most consistent indicator of D2M drought variability in the conterminousQuaternary International 188 (2008) 31­40 Associations of multi-decadal sea-surface temperature

429

Phase Behavior of Bis(Quaternary Ammonium Bromide)\\/Sodium Cholate\\/H2O System  

Microsoft Academic Search

Interactions in an oppositely charged surfactant mixture composed of a gemini surfactant (bis(quaternary ammonium bromide)) and a bile salt (sodium cholate) in water were studied at 30°C. A combination of techniques was used including surface tension, conductometry, light scattering, light microscopy, and microelectrophoretic measurements. A strong dependence of the phase behavior on the molar ratio and actual concentration of surfactants

M. Jendric; M. Vincekovi?; M. Bujan; I. Primoži?

2005-01-01

430

Montane climate and vegetation dynamics in easternmost Beringia during the Late Quaternary  

Microsoft Academic Search

New and published palynological data are used to investigate the Quaternary vegetation history of high-elevation sites in the Mackenzie Mountains of easternmost Beringia (Northwest Territories, Canada). During some previous interglacials, sites that are presently treeless supported spruce forest, indicating conditions were warmer than present and possibly warmer than at any time in the Holocene. No information is available on vegetation

J. M Szeicz; G. M MacDonald

2001-01-01

431

Quaternary Science Reviews 23 (2004) 21132126 Sea surface temperatures and ice rafting in the Holocene North  

E-print Network

Quaternary Science Reviews 23 (2004) 2113­2126 Sea surface temperatures and ice rafting through analyses of sea surface temperature (SST; alkenone unsaturation ratios) and ice rafting were coupled to SST variability and ice rafting. The records outline four major climatic phases: (i

Born, Andreas

432

The Quaternary vegetation and landscape evolution of Novaya Zemlya in the light of palynological records  

Microsoft Academic Search

The paper presents the results of paleoenvironmental (pollen) investigations of Novaya Zemlya throughout all the Quaternary, including Eopleistocene, Pleistocene and Holocene. Clear evidence of continuity between the modern flora and paleofloras confirms the lack of sharp and continuous interruptions in the vegetation development in high latitudes as well as the absence of gigantic ice sheets in the Eastern Arctic. During

Leonid Serebryanny; Eugeniya Malyasova

1998-01-01

433

Seismicity characteristics of a potentially active Quaternary volcano: The Tatun Volcano Group, northern Taiwan  

E-print Network

Seismicity characteristics of a potentially active Quaternary volcano: The Tatun Volcano Group Volcano Group (TVG) is located at the northern tip of Taiwan, near the capital Taipei and close to two as an extinct volcano, even though more recent studies suggest that TVG might have been active during the last

Lin, Andrew Tien-Shun

434

Salt diapirs in the Dead Sea basin and their relationship to Quaternary extensional tectonics  

E-print Network

Salt diapirs in the Dead Sea basin and their relationship to Quaternary extensional tectonics, USA b US Geological survey, Woods Hole Field Center, 384 Woods Hole Road, Woods Hole, MA 02543, USA extension of a brittle overburden and underlying salt causes differential loading that is thought

ten Brink, Uri S.

435

Quaternary Science Reviews 25 (2006) 11471149 Running hot and cold in the eastern equatorial Pacific  

E-print Network

Quaternary Science Reviews 25 (2006) 1147­1149 Context Running hot and cold in the eastern models can shift the mass balance for northern hemisphere ice sheets from positive (ice growth remains enigmatic. Some have considered ice-age climate in the region to be similar to a warm ``El Nin~ o

Kurapov, Alexander

436

Geochemistry of Quaternary travertines in the region north of Rome (Italy): structural, hydrologic and paleoclimatic implications  

Microsoft Academic Search

In the Tyrrhenian region of central Italy, late Quaternary fossil travertines are widespread along two major regional structures: the Tiber Valley and the Ancona–Anzio line. The origin and transport of spring waters from which travertines precipitate are elucidated by chemical and isotopic studies of the travertines and associated thermal springs and gas vents. There are consistent differences in the geochemical

A. Minissale; D. M. Kerrick; G. Magro; M. T. Murrell; M. Paladini; S. Rihs; N. C. Sturchio; F. Tassi; O. Vaselli

2002-01-01

437

Late Quaternary paleoceanography of the South China Sea: surface circulation and carbonate cycles  

Microsoft Academic Search

Paleoceanographic information from 34 sediment cores is summarized to investigate the glacial-interglacial variations in sea surface circulation and late Quaternary carbonate cycles in the South China Sea. Judging from the distribution pattern of deposition rates, the enormous terrigenous supply by rivers is responsible for the high rate of hemipelagic sedimentation which was even higher during glacial periods.Paleotemperature maps based on

Pinxian Wang; Luejiang Wang; Yunhua Bian; Zhimi Jian

1995-01-01

438

The insect response to climate change: Perspectives from the Quaternary record  

SciTech Connect

Data based on museum collections of insects are generally inadequate to answer questions related to the response of insects to recent and potential changes in climate. The most important source of information for this purpose is the late Quaternary fossil record. Abundant, well-preserved, [sup 14]C-dated assemblages of insect fossils provide information with which to answer the following questions: (1) will climate change result in speciation--all evidence suggests that species are constant through the climate changes of the late Quaternary, future climate change would not be expected to result in accelerated rates of speciation; (2) will climate change result in extinction--few species became extinct as a result of the large-scale changes in climate and physical environment during the quaternary, although large-scale extirpation might occur, future climate change would not be expected to result in widespread extinction of species; (3) will climate change result in changes in geographic distribution--species survived late Quaternary climatic change through the ability of individuals to disperse into suitable habitats. The result was large changes in geographic distribution of species, as exemplified by the succession of faunal changes that occurred in response to the climatic changes of the late Wisconsinan in the midcontinent, future climate change would be expected to result in significant range changes of species.

Ashworth, A.C.; Schwert, D.P. (North Dakota State Univ., Fargo, ND (United States). Quaternary Entomology Lab.)

1993-03-01

439

Changes in deep Pacific temperature during the mid-Pleistocene transition and Quaternary  

E-print Network

Changes in deep Pacific temperature during the mid-Pleistocene transition and Quaternary Mark April 2009 Accepted 11 May 2009 Available online xxx a b s t r a c t An attempt is made to unravel of benthic foraminifers from the deep Pacific (d18 Ob). Our approach is to estimate a non-linear transfer

Siddall, Mark

440

Climatic imprints in Quaternary valley fill deposits of the middle Teesta valley, Sikkim Himalaya  

Microsoft Academic Search

Quaternary alluvial sediments occur as distinct terrace and fan deposits in the middle Teesta valley in the belt between the Main Central Thrust and the Main Boundary Thrust in the Sikkim Himalaya. These sequences are characterized by lithofacies deposited by braided river channels, debris flows and hyperconcentrated flows. The channel flow deposits constitute relatively well sorted, well imbricated and clast-supported

Lukram I. Meetei; Sanjaya K. Pattanayak; Arun Bhaskar; Maharaj K. Pandit; Sampat K. Tandon

2007-01-01

441

TOPOGRAPHIC SITE RESPONSE AT A QUATERNARY TERRACE IN HACHIOJI, JAPAN, OBSERVED IN STRONG MOTIONS AND MICROTREMORS  

Microsoft Academic Search

SUMMARY We investigated a topographic site effect of a Quaternary terrace in Hachioji, Japan, on ground-motion amplification. The terrace discussed herein is about 12-m high consisting of volcanic ash, clay, silt and sand. 7 accelerographs were deployed in the site: 6 on the crest and 1 on the base of the terrace. The maximum PGA and PGV ratios with respect

Takumi TOSHINAWA; Yoshiaki Hisada; Katsuaki KONNO; Akihiro SHIBAYAMA; Yuya HONKAWA; Hiromichi ONO

442

Megafauna biomass tradeoff as a driver of Quaternary and future extinctions  

E-print Network

Megafauna biomass tradeoff as a driver of Quaternary and future extinctions Anthony D. Barnosky,000 and 3,000 years ago. Estimates of megafauna biomass (including hu- mans as a megafauna species) for before, during, and after the extinction episode suggest that growth of human biomass largely matched

California at Berkeley, University of

443

A Structural and Kinetic Study into the Role of the Quaternary Shift in Bacillus stearothermophilus Phosphofructokinase  

E-print Network

represents the enzyme bound to the PEP analog, phosphoglycolate (PGA). When comparing the EA and the X'E structures, a 7° rotation about the substrate-binding interface is observed and is termed the quaternary shift. The current study uses methyl TROSY NMR...

Mosser, Rockann Elizabeth

2011-10-21

444

Utility of quercetin for determination of some tertiary amine and quaternary ammonium salts  

Microsoft Academic Search

A simple and sensitive spectrophotometric method for the assay of eight drugs containing quaternary ammonium or tertiary amine moieties is described. The method is based on the interaction of these drugs with quercetin after its oxidation with N-bromosuccinimide (as counter ion) to give highly colored ion-pairing complexes extractable with organic solvents. The absorbances of the colored complexes are measured in

Fardous A. Mohamed; Abdel-Maaboud I. Mohamed; Horria A. Mohamed; Samiha A. Hussein

1996-01-01

445

Continuing the debate on the role of Quaternary environmental change for macroevolution  

Microsoft Academic Search

The Quaternary has been a period of dramatic environmental change for the past 1.8 Myr, with major shifts in distributions and abundances of terrestrial and marine organisms. The evolutionary consequences of this have been debated since the nineteenth century. However, the lack of accurate relative and absolute time-scales for evolutions and environmental change inhibited progress. We do now have an

K. D. Bennett

2004-01-01

446

Synthesis of hierarchical zeolites using an inexpensive mono-quaternary ammonium surfactant as mesoporogen.  

PubMed

A simple amphiphilic surfactant containing a mono-quaternary ammonium head group (N-methylpiperidine) is effective in imparting substantial mesoporosity during synthesis of SSZ-13 and ZSM-5 zeolites. Highly mesoporous SSZ-13 prepared in this manner shows greatly improved catalytic performance in the methanol-to-olefins reaction compared to bulk SSZ-13. PMID:25316609

Zhu, Xiaochun; Rohling, Roderigh; Filonenko, Georgy; Mezari, Brahim; Hofmann, Jan P; Asahina, Shunsuke; Hensen, Emiel J M

2014-10-28

447

Quaternary Science Reviews 22 (2003) 209223 Investigation of the relationship between permafrost distribution in  

E-print Network

Quaternary Science Reviews 22 (2003) 209­223 Investigation of the relationship between permafrost with reconstructed European mean annual temperatures derived from permafrost indicators. Analysis of the results suggest that during cold phases of the Last Glacial, the southern margin of permafrost in western Europe

Renssen, Hans

448

Quaternary tectonic movements in the Argentine Puna, 24/sup 0/ to 27/sup 0/ s latitude  

SciTech Connect

The Puna of NW Argentina, one of the highest plateaus in the world, is the southern continuation of the Andean Altiplano geomorphic province of Peru and Bolivia. The region is not seismically active and reports of neotectonic movements are scarce. However, the areas of Salar de los Pastos Grandes, Salar del Hombre Muerto and Sierra Calalaste clearly have experienced Quaternary tectonic movements. At Salar de los Pastos Grandes, early Pleistocene lake sediments are offset by reverse faulting. At Salar del Hombre Muerto, Quaternary pyroclastic and debris-flow deposits are unconformable over sediments 5.86 m.y. old that were folded during the Pliocene-Pleistocene Diaguita deformation. Within the Quaternary sediments two separate deformational phases with reverse faulting and shallow thrusting are recognized. The timing of movement is well defined since the deformed strata are covered by a basalt flow 0.75 m.y. old. The flow in turn is affected by normal faulting. Similar normal faults associated with basalt flows were found at Sierra Calalaste. These observations are in accord with pronounced extensional movements and basaltic volcanism at the Calama-Olacapato-Toro Lineament (0.2 m.y. old flows) and might document the Quaternary transition from a compressive to an extensional tectonic regime in the southern Puna.

Strecker, M.R.; Alonso, R.; Rivelli, F.; Mon, R.

1985-01-01

449

A remarkable new species of small falcon from the Quaternary of Cuba (Aves: Falconidae: Falco)  

Microsoft Academic Search

An enigmatic small falcon. Falco kurochkini, new species, is de- scribed from postcranial bones from several Quaternary sites in western and central Cuba. It was approximately intermediate in size between F. sparverius and F. columbarius but had proportionately longer and more slender leg ele- ments than any living species of Falco. It is hypothesized that F. kurochkini may have been

William Suárez; Storrs L. Olson

2001-01-01

450

Different Virucidal Activities of Hyperbranched Quaternary Ammonium Coatings on Poliovirus and Influenza Virus  

PubMed Central

Virucidal activity of immobilized quaternary ammonium compounds (IQACs) coated onto glass and plastic surfaces was tested against enveloped influenza A (H1N1) virus and nonenveloped poliovirus Sabin1. The IQACs tested were virucidal against the influenza virus within 2 min, but no virucidal effect against poliovirus was found in 6 h. PMID:22287007

Tuladhar, Era; de Koning, Martijn C.; Fundeanu, Irina; Beumer, Rijkelt

2012-01-01

451

Quaternary epitopes of ?345(IV) collagen initiate Alport post-transplant anti-GBM nephritis.  

PubMed

Alport post-transplant nephritis (APTN) is an aggressive form of anti-glomerular basement membrane disease that targets the allograft in transplanted patients with X-linked Alport syndrome. Alloantibodies develop against the NC1 domain of ?5(IV) collagen, which occurs in normal kidneys, including renal allografts, forming distinct ?345(IV) and ?1256(IV) networks. Here, we studied the roles of these networks as antigens inciting alloimmunity and as targets of nephritogenic alloantibodies in APTN. We found that patients with APTN, but not those without nephritis, produce two kinds of alloantibodies against allogeneic collagen IV. Some alloantibodies targeted alloepitopes within ?5NC1 monomers, shared by ?345NC1 and ?1256NC1 hexamers. Other alloantibodies specifically targeted alloepitopes that depended on the quaternary structure of ?345NC1 hexamers. In Col4a5-null mice, immunization with native forms of allogeneic collagen IV exclusively elicited antibodies to quaternary ?345NC1 alloepitopes, whereas alloimmunogens lacking native quaternary structure elicited antibodies to shared ?5NC1 alloepitopes. These results imply that quaternary epitopes within ?345NC1 hexamers may initiate alloimmune responses after transplant in X-linked Alport patients. Thus, ?345NC1 hexamers are the culprit alloantigen and primary target of all alloantibodies mediating APTN, whereas ?1256NC1 hexamers become secondary targets of anti-?5NC1 alloantibodies. Reliable detection of alloantibodies by immunoassays using ?345NC1 hexamers may improve outcomes by facilitating early, accurate diagnosis. PMID:23620401

Olaru, Florina; Luo, Wentian; Wang, Xu-Ping; Ge, Linna; Hertz, Jens Michael; Kashtan, Clifford E; Sado, Yoshikazu; Segal, Yoav; Hudson, Billy G; Borza, Dorin-Bogdan

2013-05-01

452

Relative Age Dating Techniques and a Late Quaternary Chronology, Arikaree Cirque, Colorado  

Microsoft Academic Search

Late Quaternary deposits in Arikaree Cirque are re-examined, using eight relative age dating methods including lichenometry. If snowkill of lichens is unrecognized, an erroneously young age may be assigned to Neoglacial deposits if only lichenometric methods are employed. The data were entered into two clustering programs, which were used to group sample sites according to age. The results of this

Tom Carroll

1974-01-01

453

Highly enantio- and diastereoselective generation of two quaternary centers in spirocyclopropanation of oxindole derivatives.  

PubMed

Spirocyclopropanes: Only one out of eight possible stereoisomers was obtained in the asymmetric cascade cyclopropanation of alkylidene oxindoles with ethyl 2-chloroacetoacetate. Improved catalyst design ensured that spirocyclopropyl oxindoles featuring two quaternary centers were synthesized in high yield and high enantio- and diastereoselectivity (see scheme). PMID:23112107

Noole, Artur; Sucman, Natalia S; Kabeshov, Mikhail A; Kanger, Tõnis; Macaev, Fliur Z; Malkov, Andrei V

2012-11-19

454

Evolution of Quaternary Tholeiitic Basalt Eruptive Centers on the Eastern Snake River Plain, Idaho  

Microsoft Academic Search

The tectonic and magmatic evolution of Quaternary olivine tholeiites in the eastern Snake River Plain (SRP) are evaluated by their spatial distribution and geochemi- cal signatures. Individual lava-flow groups and their as- sociated shield-building eruptive centers are either ex- posed at the surface or inferred to exist beneath overly- ing volcanic layers. Stratigraphy and dimensions of over- lapping subsurface flow

Scott S. Hughes; Paul H. Wetmore; Jason L. Casper

2002-01-01

455

Late Quaternary Basin-Range faulting north of the eastern Snake River Plain, Idaho  

Microsoft Academic Search

In the decade since the Borah Peak earthquake, paleoseismic studies have elucidated details of the late Quaternary histories of the Lost River, Lemhi, and Beaverhead faults of eastern Idaho, which comprise part of the northward continuation of the Basin-Range province across the Eastern Snake River Plain (ESRP). The faults are segmented but have temporally and\\/or spatially clustered paleoseismic activity. Each

Knuepfer

1993-01-01

456

Quaternary faults of south-central Australia: Palaeoseismicity, slip rates and origin  

Microsoft Academic Search

Faults bounding the Flinders Ranges of South Australia and the Barrier Ranges of New South Wales display clear evidence of significant Quaternary displacements. Kinematic analysis of the Wilkatana, Burra and Mundi Mundi Faults indicates that reverse-oblique fault slip occurred in response to east - west compression, consistent with maximum compressive stress (SHMax) orientations derived from historical earthquake focal mechanisms. Surface-rupturing

M. C. Quigley; M. L. Cupper; M. Sandiford

2006-01-01

457

Miocene -Quaternary tectonic evolution of the northern eastern California shear zone  

E-print Network

in California and Nevada: tectonics, stratigraphy and hydrogeology: Pacific Section, SEPM (Society173 1 Miocene - Quaternary tectonic evolution of the northern eastern California shear zone Kurt L the eastern California shear zone. This field trip includes 12 stops focused on the active tectonics

Lee, Jeff

458

Influence of late Quaternary climate change on present patterns of genetic variation in valley oak,  

E-print Network

with large-scale range shifts for an eastern North American white oak (Quercus alba L.). Coast Range, Quercus lobata Nee PAUL F. GUGGER,* MAKIHIKO IKEGAMI1 and VICTORIA L. SORK* *Department of Ecology the effects of late Quaternary climate change on contemporary genetic variation of valley oak (Quercus lobata

Gugger, Paul F.

459

Late-Quaternary lowstands of Lake Titicaca: evidence from high-resolution seismic data  

Microsoft Academic Search

Approximately 600 km of high-resolution seismic reflection data were collected to investigate the late-Quaternary stratigraphic development of Lake Titicaca. The focus of this report is on two seismic sequence boundaries, which are interpreted as erosional surfaces formed at times of low lake level. The younger erosional surface occurs as much as 90 m below the present lake level and up

Karin D’Agostino; Geoffrey Seltzer; Paul Baker; Sherilyn Fritz; Robert Dunbar

2002-01-01

460

Quaternary International 117 (2004) 2734 Chemical weathering of the loess deposits in the lower  

E-print Network

the last decade, chemical weathering and paleoclimatic changes recorded in Chinese Loess deposits duringQuaternary International 117 (2004) 27­34 Chemical weathering of the loess deposits in the lower, and considerable weathering of some silicate minerals, especially plagioclase. Chemical mobility of Ca

Yang, Shouye

461

Quaternary Science Reviews 24 (2005) 22812300 Holocene fire and vegetation along environmental gradients  

E-print Network

Quaternary Science Reviews 24 (2005) 2281­2300 Holocene fire and vegetation along environmental, OR 97403-1251, USA c Laboratory of Tree-Ring Research, University of Arizona, PO Box 210058, Tucson, Arizona 85721, USA Received 6 February 2004; accepted 24 November 2004 Abstract Holocene records of fire

Whitlock, Cathy L.

462

The Late Quaternary Flow through the Bering Strait Has Been Forced by the Southern Ocean Winds  

E-print Network

The Late Quaternary Flow through the Bering Strait Has Been Forced by the Southern Ocean Winds Until fairly recently, investigators of the Bering Strait (BS) flow focused on the long-strait pressure. This idea has been expressed in several articles where a series of analytical models show that the Bering