bluuebunny/crossref_metadata_2025 huggingface dataset:
Underplating and Partial Melting: Implications for Melt Generation and Extraction
Authors: Bergantz George W.
Published: October 2006

The quantitative assessment of underplating and concomitant partial melting of continental crust requires the use of geologically reasonable melt fraction distributions as a function of temperature. Conductive modeling indicates that simple underplating of metapelite by basalt can yield magma bodies with melt fractions above the rheological limit of extraction for almost any reasonable geotherm. Convection and subsequent homogenization are likely in these bodies. Granitic and tonalitic protoliths do not appear to yield substantial amounts of extractable magma. These results indicate that underplating involves repeated intrusion or occurs in deep crust.
Interdecadal Variation in an Antarctic Sponge and Its Predators from Oceanographic Climate Shifts
Authors: Dayton Paul K.
Published: October 2006

During the 1960s there was extensive formation of anchor ice to depths of 30 meters at McMurdo Station, Antarctica. During this period the sponge
Homaxinella balfourensis
was rare, as were its predators in that depth zone. Most of the existing sponges were killed by anchor ice. During the 1970s, anchor ice formation was reduced, and there was a massive recruitment of
Homaxinella
, which covered as much as 80 percent of the substrata in that zone. Many predators appeared but did not control the sponge population, and it continued to grow through that decade. The early 1980s were characterized by ice formation and almost all of the
Homaxinella
were eliminated, leaving an order of magnitude more predators in that zone. The interdecadal increases in anchor ice probably result from local upwelling of extremely cold deep water, possibly in response to shifts in the strengths of regional currents.
Sequence and Expression of mRNAs Encoding the α
1
and α
2
Subunits of a DHP-Sensitive Calcium Channel
Authors: Ellis Steven B. , Williams Mark E. , Ways Nancy R. , Brenner Robert , Sharp Alan H. , Leung Albert T. , Campbell Kevin P. , McKenna Edward , Koch Walter J. , Hui Anna , Schwartz Arnold , Harpold Michael M.
Published: October 2006

Complementary DNAs were isolated and used to deduce the primary structures of the α
1
and α
2
subunits of the dihydropyridine-sensitive, voltage-dependent calcium channel from rabbit skeletal muscle. The α
1
subunit, which contains putative binding sites for calcium antagonists, is a hydrophobic protein with a sequence that is consistent with multiple transmembrane domains and shows structural and sequence homology with other voltage-dependent ion channels. In contrast, the α
2
subunit is a hydrophilic protein without homology to other known protein sequences. Nucleic acid hybridization studies suggest that the α
1
and α
2
subunit mRNAs are expressed differentially in a tissue-specific manner and that there is a family of genes encoding additional calcium channel subtypes.
Flood Basalts and Hot-Spot Tracks: Plume Heads and Tails
Authors: Richards Mark A. , Duncan Robert A. , Courtillot Vincent E.
Published: October 2006

Continental flood basalt eruptions have resulted in sudden and massive accumulations of basaltic lavas in excess of any contemporary volcanic processes. The largest flood basalt events mark the earliest volcanic activity of many major hot spots, which are thought to result from deep mantle plumes. The relative volumes of melt and eruption rates of flood basalts and hot spots as well as their temporal and spatial relations can be explained by a model of mantle plume initiation: Flood basalts represent plume "heads" and hot spots represent continuing magmatism associated with the remaining plume conduit or "tail." Continental rifting is not required, although it commonly follows flood basalt volcanism, and flood basalt provinces may occur as a natural consequence of the initiation of hot-spot activity in ocean basins as well as on continents.
Voyager 2 at Neptune: Imaging Science Results
Authors: Smith B. A. , Soderblom L. A. , Banfield D. , Barnet c. , Basilevsky A. T. , Beebe R. F. , Bollinger K. , Boyce J. M. , Brahic A. , Briggs G. A. , Brown R. H. , Chyba c. , Collins s. A. , Colvin T. , Cook A. F. , Crisp D. , Croft S. K. , Cruikshank D. , Cuzzi J. N. , Danielson G. E. , Davies M. E. , De Jong E. , Dones L. , Godfrey D. , Goguen J. , Grenier I. , Haemmerle V. R. , Hammel H. , Hansen c. J. , Helfenstein c. P. , Howell C. , Hunt G. E. , Ingersoll A. P. , Johnson T. V. , Kargel J. , Kirk R. , Kuehn D. I. , Limaye S. , Masursky H. , McEwen A. , Morrison D. , Owen T. , Owen W. , Pollack J. B. , Porco c. c. , Rages K. , Rogers P. , Rudy D. , Sagan C. , Schwartz J. , Shoemaker E. M. , Showalter M. , Sicardy B. , Simonelli D. , Spencer J. , Sromovsky L. A. , Stoker C. , Strom R. G. , Suomi V. E. , Synott S. P. , Terrile R. J. , Thomas P. , Thompson W. R. , Verbiscer A. , Veverka J.
Published: October 2006

Voyager 2 images of Neptune reveal a windy planet characterized by bright clouds of methane ice suspended in an exceptionally clear atmosphere above a lower deck of hydrogen sulfide or ammonia ices. Neptune's atmosphere is dominated by a large anticyclonic storm system that has been named the Great Dark Spot (GDS). About the same size as Earth in extent, the GDS bears both many similarities and some differences to the Great Red Spot of Jupiter. Neptune's zonal wind profile is remarkably similar to that of Uranus. Neptune has three major rings at radii of 42,000, 53,000, and 63,000 kilometers. The outer ring contains three higher density arc-like segments that were apparently responsible for most of the ground-based occultation events observed during the current decade. Like the rings of Uranus, the Neptune rings are composed of very dark material; unlike that of Uranus, the Neptune system is very dusty. Six new regular satellites were found, with dark surfaces and radii ranging from 200 to 25 kilometers. All lie inside the orbit of Triton and the inner four are located within the ring system. Triton is seen to be a differentiated body, with a radius of 1350 kilometers and a density of 2.1 grams per cubic centimeter; it exhibits clear evidence of early episodes of surface melting. A now rigid crust of what is probably water ice is overlain with a brilliant coating of nitrogen frost, slightly darkened and reddened with organic polymer material. Streaks of organic polymer suggest seasonal winds strong enough to move particles of micrometer size or larger, once they become airborne. At least two active plumes were seen, carrying dark material 8 kilometers above the surface before being transported downstream by high level winds. The plumes may be driven by solar heating and the subsequent violent vaporization of subsurface nitrogen.
Fidelity of HIV-1 Reverse Transcriptase
Authors: Preston Bradley D. , Poiesz Bernard J. , Loeb Lawrence A.
Published: October 2006

The human immunodeficiency virus type 1 (HIV-1) shows extensive genetic variation and undergoes rapid evolution. The fidelity of purified HIV-1 reverse transcriptase was measured during DNA polymerization in vitro by means of three different assays. Reverse transcriptase from HIV-1 introduced base-substitution errors in DNA from the bacteriophage φX174
amber
3 at estimated frequencies of 1/2000 to 1/4000. Analyses of misincorporation rates opposite a single template adenine residue showed that HIV-1 reverse transcriptase catalyzed nucleotide mismatches with a specificity of A:C >> A:G > A:A. The high error rate of HIV-1 reverse transcriptase in vitro translates to approximately five to ten errors per HIV-1 genome per round of replication in vivo. This high error rate suggests that misincorporation by HIV-1 reverse transcriptase is, at least in part, responsible for the hypermutability of the AIDS virus. The specificity of misincorporation may provide a basis for the systematic construction of antiviral nucleosides.
Protein Design, a Minimalist Approach
Authors: DeGrado William F. , Wasserman Zelda R. , Lear James D.
Published: October 2006

The question of how the amino acid sequence of a protein specifies its three-dimensional structure remains to be answered. Proteins are so large and complex that it is difficult to discern the features in their sequences that contribute to their structural stability and function. One approach to this problem is de novo design of model proteins, much simpler than their natural counterparts, yet containing sufficient information in their sequences to specify a given function (for example, folding in aqueous solution, folding in membranes, or formation of ion channels). Designed proteins provide simple model systems for understanding protein structure and function.
Ethanol Inhibits NMDA-Activated Ion Current in Hippocampal Neurons
Authors: Lovinger David M. , White Geoffrey , Weight Forrest F.
Published: October 2006

The ion current induced by the glutamate receptor agonist
N
-methyl-D-aspartate (NMDA) in voltage-clamped hippocampal neurons was inhibited by ethanol (EtOH). Inhibition increased in a concentration-dependent manner over the range 5 to 50 m
M
, a range that also produces intoxication. The amplitude of the NMDA-activated current was reduced 61 percent by 50 m
M
EtOH; in contrast, this concentration of EtOH reduced the amplitude of current activated by the glutamate receptor agonists kainate and quisqualate by only 18 and 15 percent, respectively. The potency for inhibition of the NMDA-activated current by several alcohols is linearly related to their intoxicating potency, suggesting that alcohol-induced inhibition of responses to NMDA receptor activation may contribute to the neural and cognitive impairments associated with intoxication.
Studies of the HER-2/
neu
Proto-Oncogene in Human Breast and Ovarian Cancer
Authors: Slamon Dennis J. , Godolphin William , Jones Lovell A. , Holt John A. , Wong Steven G. , Keith Duane E. , Levin Wendy J. , Stuart Susan G. , Udove Judy , Ullrich Axel , Press Michael F.
Published: October 2006

Carcinoma of the breast and ovary account for one-third of all cancers occurring in women and together are responsible for approximately one-quarter of cancer-related deaths in females. The HER-2/
neu
proto-oncogene is amplified in 25 to 30 percent of human primary breast cancers and this alteration is associated with disease behavior. In this report, several similarities were found in the biology of HER-2/
neu
in breast and ovarian cancer, including a similar incidence of amplification, a direct correlation between amplification and over-expression, evidence of tumors in which overexpression occurs without amplification, and the association between gene alteration and clinical outcome. A comprehensive study of the gene and its products (RNA and protein) was simultaneously performed on a large number of both tumor types. This analysis identified several potential shortcomings of the various methods used to evaluate HER-2/
neu
in these diseases (Southern, Northern, and Western blots, and immunohistochemistry) and provided information regarding considerations that should be addressed when studying a gene or gene product in human tissue. The data presented further support the concept that the HER-2/
neu
gene may be involved in the pathogenesis of some human cancers.
Control of Experimental Autoimmune Encephalomyelitis by T Cells Responding to Activated T Cells
Authors: Lohse Ansgar W. , Mor Felix , Karin Nathan , Cohen Irun R.
Published: October 2006

T cell vaccination against experimental autoimmune disease is herein shown to be mediated in part by anti-ergotypic T cells, T cells that recognize and respond to the state of activation of other T cells. The anti-ergotypic response thus combines with the previously shown anti-idiotypic T cell response to regulate autoimmunity.
The Product of the
mos
Proto-Oncogene as a Candidate "Initiator" for Oocyte Maturation
Authors: Sagata Noriyuki , Daar Ira , Oskarsson Marianne , Showalter Stephen D. , Vande Woude George F.
Published: October 2006

The endogenous c-
mos
product, pp39

mos

, is required for progesterone-induced meiotic maturation in
Xenopus
oocytes. Treatment of oocytes with progesterone induced a rapid increase in pp39

mos

that preceded both the activation of maturation promoting factor (MPF) and germinal vesicle breakdown (GVBD). Microinjection of synthetic
mos
RNA into oocytes activated MPF and induced GVBD in the absence of progesterone. Thus, the
mos
proto-oncogene product may qualify as a candidate "initiator" protein of MPF and is at least one of the "triggers" for G
2
to M transition.
Mantle Oxidation State and Its Relationship to Tectonic Environment and Fluid Speciation
Authors: Wood Bernard J. , Bryndzia L. Taras , Johnson Kathleen E.
Published: October 2006

The earth's mantle is degassed along mid-ocean ridges, while rehydration and possibly recarbonation occurs at subduction zones. These processes and the speciation of C-H-O fluids in the mantle are related to the oxidation state of mantle peridotite. Peridotite xenoliths from continental localities exhibit an oxygen fugacity (ƒ

O
2

) range from -1.5 to +1.5 log units relative to the FMQ (fayalite-magnetite-quartz) buffer. The lowest values are from zones of continental extension. Highly oxidized xenoliths (ƒ

O
2

greater than FMQ) come from regions of recent or active subduction (for example, Ichinomegata, Japan), are commonly amphibole-bearing, and show trace element and isotopic evidence of fluid-rock interaction. Peridotites from ocean ridges are reduced and have an average ƒ

O
2

of about -0.9 log units relative to FMQ, virtually coincident with values obtained from mid-ocean ridge basalt (MORB) glasses. These data are further evidence of the genetic link between MORB liquids and residual peridotite and indicate that the asthenosphere, although reducing, has CO
2
and H
2
O as its major fluid species. Incorporation of oxidized material from subduction zones into the continental lithosphere produces xenoliths that have both asthenospheric and subduction signatures. Fluids in the lithosphere are also dominated by CO
2
and H
2
O, and native C is generally unstable. Although the occurrence of native C (diamond) in deep-seated garnetiferous xenoliths and kimberlites does not require reducing conditions, calculations indicate that high Fe
3+
contents are stabilized in the garnet structure and that ƒ

O
2

deareases with increasing depth.
Seismic-Wave Attenuation Associated with Crustal Faults in the New Madrid Seismic Zone
Authors: Hamilton R. M. , Mooney W. D.
Published: October 2006

The attenuation of upper crustal seismic waves that are refracted with a velocity of about 6 kilometers per second varies greatly among profiles in the area of the New Madrid seismic zone in the central Mississippi Valley. The waves that have the strongest attenuation pass through the seismic trend along the axis of the Reelfoot rift in the area of the Blytheville arch. Defocusing of the waves in a low-velocity zone and/or seismic scattering and absorption could cause the attenuation; these effects are most likely associated with the highly deformed rocks along the arch. Consequently, strong seismic-wave attenuation may be a useful criterion for identifying seismogenic fault zones.
Proximal Cretaceous-Tertiary Boundary Impact Deposits in the Caribbean
Authors: Hildebrand Alan R. , Boynton William V.
Published: October 2006

Trace element, isotopic, and mineralogic studies indicate that the proposed impact at the Cretaceous-Tertiary (K-T) boundary occurred in an ocean basin, although a minor component of continental material is required. The size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact-wave deposits suggest an impact between the Americas. Coarse boundary sediments at sites 151 and 153 in the Colombian Basin and 5- to 450-meter-thick boundary sediments in Cuba may be deposits of a giant wave produced by a nearby oceanic impact. On the southern peninsula of Haiti, a ∼50-centimeter-thick ejecta layer occurs at the K-T boundary. This ejecta layer is ∼25 times as thick as that at any known K-T site and suggests an impact site within ∼1000 kilometers. Seismic reflection profiles suggest that a buried ∼300-km-diameter candidate structure occurs in the Colombian Basin.
Television Image of a Large Upward Electrical Discharge Above a Thunderstorm System
Authors: Franz R. C. , Nemzek R. J. , Winckler J. R.
Published: October 2006

An image of an unusual luminous electrical discharge over a thunderstorm 250 kilometers from the observing site has been obtained with a low-light-level television camera. The discharge began at the cloud tops at 14 kilometers and extended into the clear air 20 kilometers higher. The image, which had a duration of less than 30 milliseconds, resembled two jets or fountains and was probably caused by two localized electric charge concentrations at the cloud tops. Large upward discharges may create a hazard for aircraft and rocket launches and, by penetrating into the ionosphere, may initiate whistler waves and other effects on a magnetospheric scale. Such upward electrical discharges may account for unexplained photometric observations of distant lightning events that showed a low rise rate of the luminous pulse and no electromagnetic sferic pulse of the type that accompanies cloud-to-earth lightning strokes. An unusually high rate of such photometric events was recorded during the night of 22 to 23 September 1989 during a storm associated with hurricane Hugo.
Adaptive Optics Revisited
Authors: Babcock Horace W.
Published: October 2006

From the earliest days and nights of telescopic astronomy, atmospheric turbulence has been a serious detriment to optical performance. The new technology of adaptive optics can overcome this problem by compensating for the wavefront distortion that results from turbulence. The result will be large gains in resolving power and limiting magnitude, closely approaching the theoretical limit. In other words, telescopic images will be very significantly sharpened. Rapid and accelerating progress is being made today by several groups. Adaptive optics, together with the closely related technology of active optics, seems certain to be utilized in large astronomical telescopes of the future. This may entail significant changes in telescope design.
Single-Crystal
40
Ar/
39
Ar Dating of the Eocene-Oligocene Transition in North America
Authors: Swisher Carl C. , Prothero D. R.
Published: October 2006

Explanations for the causes of climatic changes and associated faunal and floral extinctions at the close of the Eocene Epoch have long been controversial because of, in part, uncertainties in correlation and dating of global events. New single-crystal laser fusion (SCLF)
40
Ar/
39
Ar dates on tephra from key magnetostratigraphic and fossil-bearing sections necessitate significant revision in North American late Paleogene chronology. The Chadronian-Orellan North American Land Mammal "Age" boundary, as a result, is shifted from 32.4 to 34.0 Ma (million years ago), the Orellan-Whitneyan boundary is shifted from 30.8 to 32.0 Ma, and the Whitneyan-Arikareean boundary is now approximately 29.0 Ma. The new dates shift the correlation of Chron C12R from the Chadronian to within the Orellan-Whitneyan interval, the Chadronian becomes late Eocene in age, and the North American Oligocene is restricted to the Orellan, Whitneyan, and early Arikareean. The Eocene-Oligocene boundary, and its associated climate change and extinction events, as a result, correlates with the Chadronian-Orellan boundary, not the Duchesnean-Chadronian boundary.
Fire-Southern Oscillation Relations in the Southwestern United States
Authors: Swetnam Thomas W. , Betancourt Julio L.
Published: October 2006

Fire scar and tree growth chronologies (1700 to 1905) and fire statistics (since 1905) from Arizona and New Mexico show that small areas burn after wet springs associated with the low phase of the Southern Oscillation (SO), whereas large areas burn after dry springs associated with the high phase of the SO. Through its synergistic influence on spring weather and fuel conditions, climatic variability in the tropical Pacific significantly influences vegetation dynamics in the southwestern United States. Synchrony of fire-free and severe fire years across diverse southwestern forests implies that climate forces fire regimes on a subcontinental scale; it also underscores the importance of exogenous factors in ecosystem dynamics.
An Assay for Circulating Antibodies to a Major Etiologic Virus of Human Non-A, Non-B Hepatitis
Authors: Kuo G. , Choo Q.-L. , Alter H.J. , Gitnick G.L. , Redeker A.G. , Purcell R.H. , Miyamura T. , Dienstag J.L. , Alter M.J. , Stevens C.E. , Tegtmeier G. E. , Bonino F. , Colombo M. , Lee W.-S. , Kuo C. , Berger K. , Shuster J. R. , Overby L. R. , Bradley D. W. , Houghton M.
Published: October 2006

A specific assay has been developed for a blood-borne non-A, non-B hepatitis (NANBH) virus in which a polypeptide synthesized in recombinant yeast clones of the hepatitis C virus (HCV) is used to capture circulating viral antibodies. HCV antibodies were detected in six of seven human sera that were shown previously to transmit NANBH to chimpanzees. Assays of ten blood transfusions in the United States that resulted in chronic NANBH revealed that there was at least one positive blood donor in nine of these cases and that all ten recipients seroconverted during their illnesses. About 80 percent of chronic, post-transfusion NANBH (PT-NANBH) patients from Italy and Japan had circulating HCV antibody; a much lower frequency (15 percent) was observed in acute, resolving infections. In addition, 58 percent of NANBH patients from the United States with no identifiable source of parenteral exposure to the virus were also positive for HCV antibody. These data indicate that HCV is a major cause of NANBH throughout the world.
Land Animals in the Silurian: Arachnids and Myriapods from Shropshire, England
Authors: Jeram Andrew J. , Selden Paul A. , Edwards Dianne
Published: October 2006

A new assemblage of arthropod cuticles from Upper Silurian rocks in Shropshire, England, includes at least two centipedes and a trigonotarbid arachnid. This unequivocal terrestrial fauna from the Silurian constitutes the earliest direct record of land animals. The presence of predatory arthropods suggests that complex terrestrial ecosystems were in place by the late Silurian (414 × 10
6
years before present) and that the animal invasion of the land occurred earlier than was previously thought.
Increase in Salicylic Acid at the Onset of Systemic Acquired Resistance in Cucumber
Authors: Métraux J. P. , Signer H. , Ryals J. , Ward E. , Wyss-Benz M. , Gaudin J. , Raschdorf K. , Schmid E. , Blum W. , Inverardi B.
Published: October 2006

In an effort to identify the signal compound that mediates systemic acquired resistance (SAR), changes in the content of phloem sap were monitored in cucumber plants inoculated with either tobacco necrosis virus or the fungal pathogen
Colletotrichum lagenarium
. The concentration of a fluorescent metabolite was observed to increase transiently after inoculation, with a peak reached before SAR was detected. The compound was purified and identified by gas chromatography-mass spectrometry as salicylic acid, a known exogenous inducer of resistance. The data suggest that salicylic acid could function as the endogenous signal in the transmission of SAR in cucumber.
Stable Isotopic Evidence for a Pedogenic Origin of Carbonates in Trench 14 near Yucca Mountain, Nevada
Authors: Quade Jay , Cerling Thure E.
Published: October 2006

Layered carbonate and silica encrust fault fractures exposed in Trench 14 near Yucca Mountain, site of the proposed high-level nuclear waste repository in southern Nevada. Comparison of the stable carbon and oxygen isotopic compositions of the fracture carbonates with those of modern soil carbonates in the area shows that the fracture carbonates are pedogenic in origin and that they likely formed in the presence of vegetation and rainfall typical of a glacial climate. Their isotopic composition differs markedly from that of carbonate associated with nearby springs. The regional water table therefore remained below the level of Trench 14 during the time that the carbonates and silica precipitated, a period probably covering parts of at least the last 300,000 years.
The Kangmar Dome: A Metamorphic Core Complex in Southern Xizang (Tibet)
Authors: Chen Z. , Liu Y. , Hodges K. V. , Burchfiel B. C. , Royden L. H. , Deng C.
Published: October 2006

The Kangmar metamorphic-igneous complex is one of the most accessible examples of an enigmatic group of gneiss domes (the North Himalayan belt) that lies midway between the Greater Himalaya and the Indus-Tsangpo suture in southern Tibet. Structural analysis suggests that the domal structure formed as a consequence of extensional deformation, much like the Tertiary metamorphic core complexes in the North American Cordillera. Unlike its North American counterparts, the Kangmar dome developed in an entirely convergent tectonic setting. The documentation of metamorphic core complexes in the Himalayan orogen supports the emerging concept that extensional processes may play an important role in the evolution of compressional mountain belts.
Chemistry of Excited Electronic States
Authors: Armentrout P. B.
Published: October 2006

Atomic and molecular orbitals are among the tools used by chemists to view the world. The validity of this view for reaction systems can be experimentally probed by examination of the chemistry of electronically excited states and, in particular, by comparison of the reactivities of states having different orbital occupations (electron configurations). Reactivity changes associated with electron configuration are instructive with regard to chemists' views of molecular orbital interactions, but electronic excitation can also influence the course of a chemical reaction by increasing the energy content of the system or by affecting access to different potential energy surfaces by changing spin, orbital symmetry, or spin-orbit level. These various effects are illustrated by studies of gas-phase transition metal—mediated H—H and C—H bond-activation processes.
Arctic Lakes and Streams as Gas Conduits to the Atmosphere: Implications for Tundra Carbon Budgets
Authors: Kling George W. , Kipphut George W. , Miller Michael C.
Published: October 2006

Arctic tundra has large amounts of stored carbon and is thought to be a sink for atmospheric carbon dioxide (CO
2
) (0.1 to 0.3 petagram of carbon per year) (1 petagram = 10
15
grams). But this estimate of carbon balance is only for terrestrial ecosystems. Measurements of the partial pressure of CO
2
in 29 aquatic ecosystems across arctic Alaska showed that in most cases (27 of 29) CO
2
was released to the atmosphere. This CO
2
probably originates in terrestrial environments; erosion of particulate carbon plus ground-water transport of dissolved carbon from tundra contribute to the CO
2
flux from surface waters to the atmosphere. If this mechanism is typical of that of other tundra areas, then current estimates of the arctic terrestrial sink for atmospheric CO
2
may be 20 percent too high.
Ultrafast X-ray Pulses from Laser-Produced Plasmas
Authors: Murnane Margaret M. , Kapteyn Henry C. , Rosen Mordecai D. , Falcone Roger W.
Published: October 2006

A high-temperature plasma is created when an intense laser pulse is focused onto the surface of a solid. An ultrafast pulse of x-ray radiation is emitted from such a plasma when the laser pulse length is less than a picosecond. A high-speed streak camera detector was used to determine the duration of these x-ray pulses, and computer simulations of the plasmas agree with the experimental results. Scaling laws predict that brighter and more efficient x-ray sources will be obtained by the use of more intense laser pulses. These sources can be used for time-resolved x-ray scattering studies and for the development of x-ray lasers.
The Assimilation of Elements Ingested by Marine Copepods
Authors: Reinfelder John R. , Fisher Nicholas S.
Published: October 2006

The efficiency with which a variety of ingested elements (Ag, Am, C, Cd, P, S, Se, and Zn) were assimilated in marine calanoid copepods fed uniformly radiolabeled diatoms ranged from 0.9% for Am to 97.1% for Se. Assimilation efficiencies were directly related to the cytoplasmic content of the diatoms. This relation indicates that the animals obtained nearly all their nutrition from this source. The results suggest that these zooplankton, which have short gut residence times, have developed a gut lining and digestive strategy that provides for assimilation of only soluble material. Because the fraction of total cellular protein in the cytoplasm of the diatoms increased markedly with culture age, copepods feeding on senescent cells should obtain more protein than those feeding on rapidly dividing cells. Elements that are appreciably incorporated into algal cytoplasm and assimilated in zooplankton should be recycled in surface waters and have longer oceanic residence times than elements bound to cell surfaces.
Cosmology in the Laboratory: Defect Dynamics in Liquid Crystals
Authors: Chuang Isaac , Durrer Ruth , Turok Neil , Yurke Bernard
Published: October 2006

Liquid crystals are remarkably useful for laboratory exploration of the dynamics of cosmologically relevant defects. They are convenient to work with, they allow the direct study of the "scaling solution" for a network of strings, and they provide a model for the evolution of monopoles and texture. Experiments described here support the simple "one-scale" model for cosmic string evolution, as well as some qualitative predictions of string statistical mechanics. The structure of monopoles and their apparent cylindrical but not spherical symmetry is discussed. A particular kind of defect known as texture is described and is shown to have a dynamical instability—it can decay into a monopole-antimonopole pair. This decay process has been observed occurring in the liquid crystal, and studied with numerical simulations.
Self-Arrangement of Molybdenum Particles into Cubes
Authors: Edelstein A. S. , Chow G. M. , Altman E. I. , Colton R. J. , Hwang D. M.
Published: October 2006

An unusual distribution of particle sizes has been observed following the formation of molybdenum particles by argon ion sputtering. Many of the molybdenum particles produced by sputtering at the threshold pressure for particle formation in the vapor appear to be single crystalline cubes. There are two prominent peaks in the edge length distribution of the cubes, one centered at 4.8 nanometers with a halfwidth of approximately 1.3 nanometers and the other at 17.5 nanometers. The peak for the larger cubes is approximately square and has a total width of 7.0 nanometers. Evidence is presented that the larger cubes are formed by a 3 by 3 by 3 self-arrangement of the smaller cubes, which contain approximately 7000 atoms. Self-arrangement in inorganic structures is normally only observed when the building blocks are atoms, molecules, or clusters of less than 100 atoms.
The Higher Fullerenes: Isolation and Characterization of C
76
, C
84
, C
90
, C
94
, and C
70
O, an Oxide of D
5h
-C
70
Authors: Diederich François , Ettl Roland , Rubin Yves , Whetten Robert L. , Beck Rainer , Alvare Marcos , Anz Samir , Sensharma Dilip , Wudl Fred , Khemani Kishan C. , Koch Andrew
Published: October 2006

The toluene extract of the fluffy carbon material produced by resistive heating of graphite contains a variety of molecules larger than C
60
and C
70
in a total amount of 3 to 4% by weight. Repeated chromatography of this material on neutral alumina has led to the isolation of stable solid samples of C
76
, C
84
, C
90
, and C
94
. The characterization, which includes mass spectrometry,
13
C nuclear magnetic resonance, electronic absorption (ultraviolet/visible) and vibrational (infrared) spectroscopy identifies these all-carbon molecules as higher fullerenes. In addition, C
70
O, a stable oxide, has been isolated that is structurally and electronically closely related to
D

5
h

-C
70
. This compound forms during the resistive heating process and probably has an oxygen atom inserted between two carbon atoms on the convex external surface of the C
70
skeleton.
Ultradeep (>300 Kilometers) Ultramafic Xenoliths: Petrological Evidence from the Transition Zone
Authors: Sautter Violaine , Haggerty Stephen E. , Field Stephen
Published: October 2006

The seismologically delineated transition zone, at depths between 400 and 670 kilometers, is a fundamental discontinuity in the earth that separates the upper mantle from the lower mantle. Xenoliths from within or close to the transition zone are dominated by pyropic garnet and associated pyroxene or mineralogically heterogeneous garnet lherzolite. These xenoliths show evidence for the high-pressure (90 to 120 kilobars) transformation of pyroxene to a solid solution of pyroxene in garnet (majorite) and silicon in octahedral coordination; low-pressure (less than 80 kilobars) exsolution of clinopyroxene or orthopyroxene from the original majorite is preserved. Although mineral modes and rock proportions below the transition zone and the relative amount of eclogite present cannot be accurately assessed from the xenoliths, it is likely that both majorite and β-spinel help produce the observed seismic gradient of the transition zone.
Instability of a 550-Base Pair DNA Segment and Abnormal Methylation in Fragile X Syndrome
Authors: Oberlé I. , Rousseau F. , Heitz D. , Kretz C. , Devys D. , Hanauer A. , Boué J. , Bertheas M. F. , Mandel J. L.
Published: October 2006

The fragile X syndrome, a common cause of inherited mental retardation, is characterized by an unusual mode of inheritance. Phenotypic expression has been linked to abnormal cytosine methylation of a single CpG island, at or very near the fragile site. Probes adjacent to this island detected very localized DNA rearrangements that constituted the fragile X mutations, and whose target was a 550-base pair GC-rich fragment. Normal transmitting males had a 150- to 400-base pair insertion that was inherited by their daughters either unchanged, or with small differences in size. Fragile X-positive individuals in the next generation had much larger fragments that differed among siblings and showed a generally heterogeneous pattern indicating somatic mutation. The mutated allele appeared unmethylated in normal transmitting males, methylated only on the inactive X chromosome in their daughters, and totally methylated in most fragile X males. However, some males had a mosaic pattern. Expression of the fragile X syndrome thus appears to result from a two-step mutation as well as a highly localized methylation. Carriers of the fragile X mutation can easily be detected regardless of sex or phenotypic expression, and rare apparent false negatives may result from genetic heterogeneity or misdiagnosis.
Predicting Coiled Coils from Protein Sequences
Authors: Lupas Andrei , Van Dyke Marc , Stock Jeff
Published: October 2006

The probability that a residue in a protein is part of a coiled-coil structure was assessed by comparison of its flanking sequences with sequences of known coiled-coil proteins. This method was used to delineate coiled-coil domains in otherwise globular proteins, such as the leucine zipper domains in transcriptional regulators, and to predict regions of discontinuity within coiled-coil structures, such as the hinge region in myosin. More than 200 proteins that probably have coiled-coil domains were identified in GenBank, including α- and β-tubulins, flagellins, G protein β subunits, some bacterial transfer RNA synthetases, and members of the heat shock protein (Hsp70) family.
Fragile X Genotype Characterized by an Unstable Region of DNA
Authors: Yu S. , Pritchard M. , Kremer E. , Lynch M. , Nancarrow J. , Baker E. , Holman K. , Mulley J. C. , Warren S. T. , Schlessinger D. , Sutherland G. R. , Richards R. I.
Published: October 2006

DNA sequences have been located at the fragile X site by in situ hybridization and by the mapping of breakpoints in two somatic cell hybrids that were constructed to break at the fragile site. These hybrids were found to have breakpoints in a common 5-kilobase Eco RI restriction fragment. When this fragment was used as a probe on the chromosomal DNA of normal and fragile X genotype individuals, alterations in the mobility of the sequences detected by the probe were found only in fragile X genotype DNA. These sequences were of an increased size in all fragile X individuals and varied within families, indicating that the region was unstable. This probe provides a means with which to analyze fragile X pedigrees and is a diagnostic reagent for the fragile X genotype.
Rapid Eruption of the Siberian Traps Flood Basalts at the Permo-Triassic Boundary
Authors: Renne Paul R. , Basu Asish R.
Published: October 2006

The Siberian Traps represent one of the most voluminous flood basalt provinces on Earth. Laser-heating
40
Ar/
39
Ar data indicate that the bulk of these basalts was erupted over an extremely short time interval (900,000 ± 800,000 years) beginning at about 248 million years ago at mean eruption rates of greater than 1.3 cubic kilometers per year. Such rates are consistent with a mantle plume origin. Magmatism was not associated with significant lithospheric rifting; thus, mantle decompression resulting from rifting was probably not the primary cause of widespread melting. Inception of Siberian Traps volcanism coincided (within uncertainty) with a profound faunal mass extinction at the Permo-Triassic boundary 249 ± 4 million years ago; these data thus leave open the question of a genetic relation between the two events.
Organic Molecular Soft Ferromagnetism in a Fullerene C
60
Authors: Allemand Pierre-Marc , Khemani Kishan C. , Koch Andrew , Wudl Fred , Holczer Karoly , Donovan Steven , Grüner George , Thompson Joe D.
Published: October 2006

The properties of an organic molecular ferromagnet [C
60
TDAE
0.86
; TDAE is tetrakis(dimethylamino)ethylene] with a Curie temperature
T
c
= 16.1 kelvin are described. The ferromagnetic state shows no remanence, and the temperature dependence of the magnetization below
T
c
does not follow the behavior expected of a conventional ferromagnet. These results are interpreted as a reflection of a three-dimensional system leading to a soft ferromagnet.
Earth's Variable Rotation
Authors: Hide Raymond , Dickey Jean O.
Published: October 2006

Recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the Earth's rotation. The interpretation of these fluctuations is inextricably linked with studies of the dynamics of the Earth-moon system and dynamical processes in the liquid metallic core of the Earth (where the geomagnetic field originates), other parts of the Earth's interior, and the hydrosphere and atmosphere. Fluctuations in the length of the day occurring on decadal time scales have implications for the topography of the core-mantle boundary and the electrical, magnetic, and other properties of the core and lower mantle. Investigations of more rapid fluctuations bear on meteorological studies of interannual, seasonal, and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations.
Interior Structure of Neptune: Comparison with Uranus
Authors: Hubbard W. B. , Nellis W. J. , Mitchell A. C. , Holmes N. C. , Limaye S. S. , McCandless P. C.
Published: October 2006

Measurements of rotation rates and gravitational harmonics of Neptune made with the Voyager 2 spacecraft allow tighter constraints on models of the planet's interior. Shock measurements of material that may match the composition of Neptune, the so-called planetary "ice," have been carried out to pressures exceeding 200 gigapascals (2 megabars). Comparison of shock data with inferred pressure-density profiles for both Uranus and Neptune shows substantial similarity through most of the mass of both planets. Analysis of the effect of Neptune's strong differential rotation on its gravitational harmonics indicates that differential rotation involves only the outermost few percent of Neptune's mass.
Biodiversity Studies: Science and Policy
Authors: Ehrlich Paul R. , Wilson Edward O.
Published: October 2006

Biodiversity studies comprise the systematic examination of the full array of different kinds of organisms together with the technology by which the diversity can be maintained and used for the benefit of humanity. Current basic research at the species level focuses on the process of species formation, the standing levels of species numbers in various higher taxonomic categories, and the phenomena of hyperdiversity and extinction proneness. The major practical concern is the massive extinction rate now caused by human activity, which threatens losses in the esthetic quality of the world, in economic opportunity, and in vital ecosystem services.
Motions and Relaxations of Confined Liquids
Authors: Granick Steve
Published: October 2006

When a liquid is confined in a narrow gap (as near a cell membrane, in a lubricated contact between solids, or in a porous medium), new dynamic behavior emerges. The effective shear viscosity is enhanced compared to the bulk, relaxation times are prolonged, and nonlinear responses set in at lower shear rates. These effects are more prominent, the thinner the liquid film. They appear to be the manifestation of collective motions. The flow of liquids under extreme confinement cannot be understood simply by intuitive extrapolation of bulk properties. Practical consequences are possible in areas from tribology and materials processing to membrane physics.
A Mantle Plume Initiation Model for the Wrangellia Flood Basalt and Other Oceanic Plateaus
Authors: RICHARDS MARK A. , JONES DAVID L. , DUNCAN ROBERT A. , DEPAOLO DONALD J.
Published: October 2006

The vast Wrangellia terrane of Alaska and British Columbia is an accreted oceanic plateau with Triassic strata that contain a 3- to 6-kilometers thick flood basalt, bounded above and below by marine sedimentary rocks. This enormous outpouring of basalt was preceded by rapid uplift and was followed by gradual subsidence of the plateau. The uplift and basalt eruptions occurred in less than ∼5 million years, and were not accompanied by significant extension or rifting of the lithosphere. This sequence of events is predicted by a mantle plume initiation, or plume head, model that has recently been developed to explain continental flood volcanism. Evidence suggests that other large oceanic basalt plateaus, such as the Ontong-Java, Kerguelen, and Caribbean, were formed as the initial outbursts of the Louisville Ridge, Kerguelen, and Galapagos hot spots, respectively. Such events may play an important role in the creation and development of both oceanic and continental crust.
The Structure of the C
60
Molecule: X-Ray Crystal Structure Determination of a Twin at 110 K
Authors: Liu Shengzhong , Lu Ying-Jie , Kappes Manfred M. , Ibers James A.
Published: October 2006

Single-crystal x-ray diffraction methods were used to determine the crystal and molecular structure of C
60
buckminsterfullerene. At 110 kelvin C
60
is cubic, apparent Laue symmetry
m
3
m
, but it exhibits noncrystallographic systematic extinctions indicative of a twin in which
I
(
hkl
) and
I
(
khl
) are superimposed. In fact, C
60
crystallizes with four molecules in space group
T

H

6
-Pa
3̅ of the cubic system (Laue symmetry
m
3) with lattice constant
a
= 14.052(5) angstroms (Å) at 110 kelvin. The twin components are equal. A given component, which has crystallographically imposed symmetry 3̅ (
C

3
i

), displays an ordered structure of a truncated icosahedron. The five independent C=C bonds that join C
6
rings average 1.355(9) Å; the ten independent C—C bonds that join C
6
and C
5
rings average 1.467(21) Å. The mean atom-to-atom diameter of the C
60
molecule is 7.065(3) Å. The molecules are very tightly packed in the crystal structure, with intermolecular C⋅⋅⋅C distances as short as 3.131(7) Å.
Length of the Solar Cycle: An Indicator of Solar Activity Closely Associated with Climate
Authors: Friis-Christensen E. , Lassen K.
Published: October 2006

It has recently been suggested that the solar irradiance has varied in phase with the 80- to 90-year period represented by the envelope of the 11-year sunspot cycle and that this variation is causing a significant part of the changes in the global temperature. This interpretation has been criticized for statistical reasons and because there are no observations that indicate significant changes in the solar irradiance. A set of data that supports the suggestion of a direct influence of solar activity on global climate is the variation of the solar cycle length. This record closely matches the long-term variations of the Northern Hemisphere land air temperature during the past 130 years.
Tuning High-
T
c
Superconductors via Multistage Intercalation
Authors: Xiang X. -D. , Vareka W. A. , Zettl A. , Corkill J. L. , Barbee T. W. , Cohen Marvin L. , Kijima N. , Gronsky R.
Published: October 2006

Multistage intercalation has been used to tune the interaction between adjacent blocks of CuO
2
sheets in the high-
T
c
(high superconducting transition temperature) superconductor Bi
2
Sr
2
CaCu
2
O

x

. As revealed by atomic-resolution transmission electron microscopy images, foreign iodine atoms are intercalated into every
n
th BiO bilayer of the host crystal, resulting in structures of stoichiometry IBi

2
n

Sr

2
n

Ca

n

Cu

2
n

O

x

with stage index
n
up to 4. An expansion of 3.6 angstroms for each intercalated BiO bilayer decouples the CuO
2
sheets in adjacent blocks. A comparison of the superconducting transition temperatures of the pristine host material and intercalated compounds of different stages suggests that the coupling between each pair of adjacent blocks contributes ∼5 K to
T
c
in Bi
2
Sr
2
CaCu
2
O

x

.
Localization and Mobility of ω-Conotoxin-Sensitive Ca
2+
Channels in Hippocampal CA1 Neurons
Authors: Jones Owen T. , Kunze Diana L. , Angelides Kimon J.
Published: October 2006

Voltage-dependent Ca
2+
channels (VDCCs) are modulators of synaptic plasticity, oscillatory behavior, and rhythmic firing in brain regions such as the hippocampus. The distribution and lateral mobility of VDCCs on CA1 hippocampal neurons have been determined with biologically active fluorescent and biotinylated derivatives of the selective probe ω-conotoxin in conjunction with circular dityndallism, digital fluorescence imaging, and photobleach recovery microscopy. On noninnervated cell bodies, VDCCs were found to be organized in multiple clusters, whereas after innervation the VDCCs were concentrated and immobilized at synaptic contact sites. On dendrites, VDCC distribution was punctate and was interrupted by extensive bare regions or abruptly terminated. More than 85% of the dendritic VDCCs were found to be immobile by fluorescence photobleach recovery. Thus, before synaptic contact, specific mechanisms target, segregate, and immobilize VDCCs to neuronal cell bodies and to specialized dendritic sites. Regulation of this distribution may be critical in determining the firing activity and integrative properties of hippocampal CA1 neurons.