bluuebunny/crossref_metadata_2025 huggingface dataset:
New Strong Cement Materials: Chemically Bonded Ceramics
Authors: Roy Della M.
Published: October 2006

New cements developed in recent years have strengths that are greater by an order of magnitude than those of conventional hydraulic cements. These low-temperature materials, whose strengths approach those of many traditional high-temperature ceramics, are termed chemically bonded ceramics. The different routes to generating strong cementitious materials, including warm pressing, chemical modification, high-shear mixing with polymer additions, and the making of fiber and particulate composites, are reviewed. Strength, toughness, durability, impermeability, and abrasion resistance of these new materials have been greatly improved, as have certain electrical and acoustical properties.
Problems in the Use of Survey Questions to Measure Public Opinion
Authors: Schuman Howard , Scott Jacqueline
Published: October 2006

Sample interview surveys are frequently proposed and sometimes used as a way of studying public choices among alternatives. Questions in such surveys may be either "open" or "closed." Two experiments are reported that demonstrate the difficulty of inferring not only absolute levels but even relative orderings of public choices from either type of question, although such questions can be used more successfully to study temporal change or variations across social categories.
Swept Away: Resuspension of Bacterial Mats Regulates Benthic-Pelagic Exchange of Sulfur
Authors: Grant Jonathan , Bathmann Ulrich V.
Published: October 2006

Filaments and extracellular material from colorless sulfur bacteria (
Beggiatoa
spp.) form extensive white sulfur mats on surface sediments of coastal, oceanic, and even deep-sea environments. These chemoautotrophic bacteria oxidize soluble reduced sulfur compounds and deposit elemental sulfur, enriching the sulfur content of surface sediment fivefold over that of deeper sediments. Laboratory flume experiments with
Beggiatoa
mats from an intertidal sandflat (Nova Scotia) demonstrated that even slight erosion of sediment causes a flux of 160 millimoles of sulfur per square meter per hour, two orders of magnitude greater than the flux produced by sulfur transformations involving either sulfate reduction or sulfide oxidation by benthic bacteria. These experiments indicate that resuspension of sulfur bacterial mats by waves and currents is a rapid mechanism by which sediment sulfur is recycled to the water column. Benthic communities thus lose an important storage intermediate for reduced sulfur as well as a high-quality bacterial food source for benthic grazers.
Demonstration of X-ray Holography with an X-ray Laser
Authors: Trebes James E. , Brown Steven B. , Campbell E. Michael , Matthews Dennis L. , Nilson David G. , Stone Gary F. , Whelan David A.
Published: October 2006

An x-ray hologram was made by means of an x-ray laser and a laser-quality near normal incidence x-ray mirror. The high brightness and large coherence lengths of x-ray lasers now offer the potential for in vitro three-dimensional high-resolution holographic images of dynamically varying biological microstructures.
Discovery of Transposable Element Activity Among Progeny of Tissue Culture—Derived Maize Plants
Authors: Peschke Virginia M. , Phillips Ronald L. , Gengenbach Burle G.
Published: October 2006

Tissue culture-derived plants of many species have often been observed to possess both genetic and cytogenetic abnormalities. A high frequency of structurally altered chromosomes in maize (
Zea mays
L.) plants regenerated from tissue culture led to the prediction that newly activated transposable elements could be detected in regenerated plants. Testcrosses of 1200 progeny from 301 regenerated maize plants confirmed that ten regenerated plants from two independent embryo cell lines contained an active
Ac
transposable element. No active
Ac
elements were present in the explant sources. Recovery of transposable element activity in regenerated plants indicates that some tissue culture—derived genetic variability may be the result of insertion or excision of transposable elements, or both.
Predominant Expression of T Cell Receptor V
α
7 in Tumor-Infiltrating Lymphocytes of Uveal Melanoma
Authors: Nitta Taizo , Oksenberg Jorge R. , Rao Narsing A. , Steinman Lawrence
Published: October 2006

Expression of T cell receptor (TCR) V
α
genes in tumor-infiltrating lymphocytes (TILs) within intraocular melanoma was studied. Primers for 18 different human TCR V
α
families were used to analyze TCR V
α
-C
α
gene rearrangements in TIL in these melanomas obtained at surgery. A limited number of TCR V
α
genes were expressed and rearranged in these tumors, and TILs expressing V
α
7 were found in seven of eight of these uveal melanomas. TCR gene usage is also restricted in experimental autoimmune disease, in T cells within organs like skin and other epithelial tissues, and in the brain of patients with multiple sclerosis (MS). The restricted usage of TCR genes in TIL may indicate that a specific antigen in these melanomas is targeted.
Recent Progress in the Direct Liquefaction of Coal
Authors: Lumpkin Robert E.
Published: October 2006

Interest in direct coal liquefaction steadily decreased during the 1980s as the price of crude oil dropped; there is now only one integrated coal liquefaction pilot plant active full time in the United States. The economics derived early in the decade established the price of transportation fuels from coal at $80 per barrel or higher. However, there have been dramatic improvements in the technology since 1983 that have not been widely appreciated. Recent designs and cost estimates show that a 60 percent decrease in the cost of liquid fuels from coal to an equivalent of $35 per barrel for crude oil. Although this cost is not low enough to justify immediate commercialization, additional improvements have been identified that could make direct liquefaction an attractive way to produce gasoline and other conventional fuels.
Slow Mortality Rate Accelerations During Aging in Some Animals Approximate That of Humans
Authors: Finch Caleb E. , Pike Malcolm C. , Witten Matthew
Published: October 2006

A general measure of the rate of senescence is the acceleration of mortality rate, represented here by the time required for the mortality rate to double (MRD). Rhesus monkeys have an MRD close to that of humans, about 8 years; their shorter life-span results mainly from higher mortality at all ages. In contrast, some groups with short life-spans (rodents and galliform birds) have shorter MRDs and faster senescence. On the basis of the Gompertz mortality rate model, one may estimate the MRD from the maximum life-span (
t
max
) and the overall population mortality rate. Such calculations show that certain birds have MRDs that are as long as that of humans. These results show that high overall mortality rates or small body sizes do not preclude slow rates of senescence.
Genome Size in Conodonts (Chordata): Inferred Variations During 270 Million Years
Authors: Morris S. Conway , Harper E.
Published: October 2006

DNA is too unstable to be preserved during fossilization, but it still seems possible to infer the genome content of fossils because in every group of organisms investigated cell size is proportional to quantity of DNA. Accordingly, information on macroevolutionary trends in genome size through millions of years is potentially available. This survey of inferred variation in genome content in fossils is based on measurements of epithelial cells in extinct conodonts over a period of 270 million years. Why genome size varies so widely amongst living organisms is a subject of continuing debate. Paleontology offers a distinct temporal perspective, but lack of data on conodont paleoecology make the proposed adaptive explanations for genome variation difficult to test.
Experimental Constraints on Theories of High-Transition Temperature Superconductors
Authors: Little W. A.
Published: October 2006

Recent experiments have revealed several key features of the unique nature of the new, high-transition temperature cuprate superconductors. These results provide an easily understandable, physical picture of the structure and behavior of the charge carriers in these materials, and point to the mechanism responsible for their existence. These experiments are now placing strong constraints on possible theoretical models of the phenomenon.
Isolation of a New Human Retrovirus from West African Patients with AIDS
Authors: Clavel François , Guétard Denise , Brun-Vézinet Françoise , Chamaret Sophie , Rey Marie-Anne , Santos-Ferreira M. O. , Laurent Anne G. , Dauguet Charles , Katlama Christine , Rouzioux Christine , Klatzmann David , Champalimaud J. L. , Montagnier Luc
Published: October 2006

The etiological agent of AIDS, LAV/HTLV-III, is common in Central Africa but is not endemic in other areas of that continent. A novel human retrovirus, distinct from LAV/HTLV-III, has now been isolated from two AIDS patients from West Africa. Partial characterization of this virus revealed that it has biological and morphological properties very similar to LAV but that it differs in some of its antigenic components. Although the core antigens may share some common epitopes, the West African AIDS retrovirus and LAV differ substantially in their envelope glycoproteins. The envelope antigen of the West African virus can be recognized by serum from a macaque with simian AIDS infected by the simian retrovirus termed STLV-III
mac
, suggesting that the West African AIDS virus may be more closely related to this simian virus than to LAV. Hybridization experiments with LAV subgenomic probes further established that this new retrovirus, here referred to as LAV-II, is distantly related to LAV and distinct from STLV-III
mac
.
Functional Differences Between Two Classes of Sodium Channels in Developing Rat Skeletal Muscle
Authors: Weiss Richard E. , Horn Richard
Published: October 2006

Excitability is generated in developing skeletal muscle by the incorporation of sodium-selective ion channels into the surface membrane. Whole-cell and patch voltage-clamp recording from myotubes and their embryologic precursors, myoblasts, indicated that voltage-activated sodium current in myoblasts was more resistant to block by tetrodotoxin (TTX) than that in myotubes. Single-channel recording from both cell types showed two classes of sodium channels. One class had a lower single-channel conductance, activated at more hyperpolarized voltages, and was more resistant to TTX than the other. The proportion of TTX-resistant to TTX-sensitive sodium channels was higher in myoblasts than in myotubes. Thus, the difference in TTX sensitivity between myoblasts and myotubes can be explained by a difference in the proportion of the two classes of sodium channels. In addition, the lower conductance of TTX-resistant channels provides insight into the relationship between the TTX binding site and the external mouth of the sodium channel.
Molecular Cloning of the Chicken Progesterone Receptor
Authors: Conneely Orla M. , Sullivan William P. , Toft David O. , Birnbaumer Mariel , Cook Richard G. , Maxwell Beth Lynn , Zarucki-Schulz Tanya , Greene Geoffrey L. , Schrader William T. , O'Malley Bert W.
Published: October 2006

To define the functional domains of the progesterone receptor required for gene regulation, complementary DNA (cDNA) clones encoding the chicken progesterone receptor have been isolated from a chicken oviduct λgt11 cDNA expression library. Positive clones expressed antigenic determinants that cross-reacted with six monospecific antibodies derived from two independent sources. A 36-amino acid peptide sequence obtained by microsequencing of purified progesterone receptor was encoded by nucleotide sequences in the longest cDNA clone. Analysis of the amino acid sequence of the progesterone receptor deduced from the cDNA clones revealed a cysteine-rich region that was homologous to a region found in the estrogen and glucocorticoid receptors and to the avian erythroblastosis virus
gag-erb
-A fusion protein. Northern blot analysis with chicken progesterone receptor cDNA's indicated the existence of at least three messenger RNA species. These messages were found only in oviduct and could be induced by estrogens.
Direct Activation of Mammalian Atrial Muscarinic Potassium Channels by GTP Regulatory Protein G
k
Authors: Yatani Atsuko , Codina Juan , Brown Arthur M. , Birnbaumer Lutz
Published: October 2006

The mammalian heart rate is regulated by the vagus nerve, which acts via muscarinic acetylcholine receptors to cause hyperpolarization of atrial pacemaker cells. The hyperpolarization is produced by the opening of potassium channels and involves an intermediary guanosine triphosphate-binding regulatory (G) protein. Potassium channels in isolated, inside-out patches of membranes from atrial cells now are shown to be activated by a purified pertussis toxin-sensitive G protein of subunit composition αβγ, with an α subunit of 40,000 daltons. Thus, mammalian atrial muscarinic potassium channels are activated directly by a G protein, not indirectly through a cascade of intermediary events. The G protein regulating these channels is identified as a potent G
k
; it is active at 0.2 to 1 p
M
. Thus, proteins other than enzymes can be under control of receptor coupling G proteins.
Chemical Identification of a Tumor-Derived Angiogenic Factor
Authors: Kull Frederick C. , Brent David A. , Parikh Indu , Cuatrecasas Pedro
Published: October 2006

Neoplasms produce substances that induce blood vessel formation (angiogenesis). Fractions from ethanol extracts of the Walker 256 carcinoma were isolated by silica column chromatography and C
18
reversed-phase high-performance liquid chromatography. Two of the isolated fractions induced neovascularization when tested in the rabbit corneal micropocket assay. One of the fractions was identified as nicotinamide by desorption-electron impact mass spectrometry, nuclear magnetic resonance spectroscopy, and gas chromatography-mass spectrometry. The second active fraction contained nicotinamide as part of a more complex, as yet unidentified, molecular arrangement. Microgram quantities of commercial nicotinamide induced neovascularization in the corneal micropocket assay and in the chick chorioallantoic membrane assay.
Thrombospondin Promotes Cell-Substratum Adhesion
Authors: Tuszynski George P. , Rothman Vicki , Murphy Andrew , Siegler Katherine , Smith Linda , Smith Sena , Karczewski Jerzy , Knudsen Karen A.
Published: October 2006

The physiological role of the platelet-secreted protein thrombospondin (TSP) is poorly understood, although it has been postulated to be involved in platelet aggregation and cellular adhesion. In this report, TSP isolated from human platelets was found to promote, in vitro, the cell-substratum adhesion of a variety of cells, including platelets, melanoma cells, muscle cells, endothelial cells, fibroblasts, and epithelial cells. The adhesion-promoting activity of TSP was species independent, specific, and not due to contamination by fibronectin, vitronectin, laminin, or platelet factor 4. The cell surface receptor for TSP is protein in nature and appears distinct from that for fibronectin.
Visual Detection of Transposition of the Maize Element
Activator (Ac)
in Tobacco Seedlings
Authors: Jones Jonathan D. G. , Carland Francine M. , Maliga Pal , Dooner Hugo K.
Published: October 2006

A bacterial streptomycin resistance gene (SPT) was engineered to make it possible to detect visually the transposition of the maize transposon
Activator (Ac)
in tobacco. In the presence of streptomycin, transgenic seedlings carrying the SPT gene appear green, whereas those carrying an SPT::
Ac
construct display clones of green cells on a white background. Fully green seedlings arise in the progeny of SPT::
Ac
transformants as a result of excision of
Ac
before fertilization. About half of these germinal revertants carry a transposed
Ac
element. Therefore, SPT::
Ac
constitutes an efficient marker for selecting plants that have undergone transposition. In maize, there is a negative effect of increasing
Ac
dosage on the frequency and timing of
Ac
transposition. This negative effect is not observed in tobacco with the streptomycin variegation assay.
Coulomb Explosion Imaging of Small Molecules
Authors: Vager Z. , Naaman R. , Kanter E. P.
Published: October 2006

Most of our knowledge of the structures of free molecules comes from indirect observations that focus on other properties (for example, energy or mass spectra) that depend on structure. Recently, a new method has been developed that instead yields geometrical images of individual molecules. This method takes advantage of the large Coulomb repulsion of the nuclei within molecules rapidly stripped of their electrons. The first experiments with this new technique have already revealed structural images of several important species, such as positively charged methane ions.
Ice Core Evidence for Extensive Melting of the Greenland Ice Sheet in the Last Interglacial
Authors: Koerner R. M.
Published: October 2006

Evidence from ice at the bottom of ice cores from the Canadian Arctic Islands and Camp Century and Dye-3 in Greenland suggests that the Greenland ice sheet melted extensively or completely during the last interglacial period more than 100 ka (thousand years ago), in contrast to earlier interpretations. The presence of dirt particles in the basal ice has previously been thought to indicate that the base of the ice sheets had melted and that the evidence for the time of original growth of these ice masses had been destroyed. However, the particles most likely blew onto the ice when the dimensions of the ice caps and ice sheets were much smaller. Ice texture, gas content, and other evidence also suggest that the basal ice at each drill site is superimposed ice, a type of ice typical of the early growth stages of an ice cap or ice sheet. If the present-day ice masses began their growth during the last interglacial, the ice sheet from the earlier (Illinoian) glacial period must have completely or largely melted during the early part of the same interglacial period. If such melting did occur, the 6-meter higher-than-present sea level during the Sangamon cannot be attributed to disintegration of the West Antarctic ice sheet, as has been suggested.
Genomic Organization and Deduced Amino Acid Sequence of a Putative Sodium Channel Gene in
Drosophila
Authors: Salkoff Lawrence , Butler Alice , Wei Aguan , Scavarda Nancy , Giffen Kelleen , Ifune Catherine , Goodman Richard , Mandel Gail
Published: October 2006

The deduced amino acid sequence of a
Drosophila
gene isolated with a vertebrate sodium channel complementary DNA probe revealed an organization virtually identical to the vertebrate sodium channel protein; four homologous domains containing all putative membrane-spanning regions are repeated in tandem with connecting linkers of various sizes. All areas of the protein presumed to be critical for channel function show high evolutionary conservation. These include those proposed to function in voltage-sensitive gating, inactivation, and ion selectivity. All 24 putative gating charges of the vertebrate protein are in identical positions in the
Drosophila
gene. Ten introns interrupt the coding regions of the four homology units; introns with positions conserved among homology units bracket a region hypothesized to be the selectivity filter for the channel. The
Drosophila
gene maps to the right arm of the second chromosome in region 60D-E. This position does not coincide with any known mutations that confer behavioral phenotypes, but is close to the
seizure
locus (60A-B), which has been hypothesized to code for a voltage-sensitive sodium channel.
Cloning of Genomic and Complementary DNA from
Shaker
, a Putative Potassium Channel Gene from
Drosophila
Authors: Papazian Diane M. , Schwarz Thomas L. , Tempel Bruce L. , Jan Yuh Nung , Jan Lily Yeh
Published: October 2006

On the basis of electrophysiological analysis of
Shaker
mutants, the
Shaker
locus of
Drosophila melanogaster
has been proposed to encode a structural component of a voltage-dependent potassium channel, the A channel. Unlike sodium channels, acetylcholine receptors, and calcium channels, K
+
channels have not been purified biochemically. To facilitate biochemical studies of a K
+
channel, genomic DNA from the
Shaker
locus has been cloned. Rearrangements in five
Shaker
mutants have been mapped to a 60-kilobase segment of the genome. Four complementary DNA clones have been analyzed. These clones indicate that the
Shaker
gene contains multiple exons distributed over at least 65 kilobases of genomic DNA in the region where the mutations mapped. Furthermore, the gene may produce several classes of alternatively spliced transcripts. Two of the complementary DNA clones have been sequenced and their sequences support the hypothesis that
Shaker
encodes a component of a K
+
channel.
A System for Rapid DNA Sequencing with Fluorescent Chain-Terminating Dideoxynucleotides
Authors: Prober James M. , Trainor George L. , Dam Rudy J. , Hobbs Frank W. , Robertson Charles W. , Zagursky Robert J. , Cocuzza Anthony J. , Jensen Mar A. , Baumeister Kirk
Published: October 2006

A DNA sequencing system based on the use of a novel set of four chain-terminating dideoxynucleotides, each carrying a different chemically tuned succinylfluorescein dye distinguished by its fluorescent emission is described. Avian myeloblastosis virus reverse transcriptase is used in a modified dideoxy DNA sequencing protocol to produce a complete set of fluorescence-tagged fragments in one reaction mixture. These DNA fragments are resolved by polyacrylamide gel electrophoresis in one sequencing lane and are identified by a fluorescence detection system specifically matched to the emission characteristics of this dye set. A scanning system allows multiple samples to be run simultaneously and computer-based automatic base sequence identifications to be made. The sequence analysis of M13 phage DNA made with this system is described.
Carbon-14 in Methane Sources and in Atmospheric Methane: The Contribution from Fossil Carbon
Authors: Wahlen M. , Tanaka N. , Henry R. , Deck B. , Zeglen J. , Vogel J. S. , Southon J. , Shemesh A. , Fairbanks R. , Broecker W.
Published: October 2006

Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in "clean air" samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, peat bogs, rice fields, and tundra is somewhat, depleted in carbon-14. Atmospheric
14
CH
4
seems to have increased from 1986 to 1987, and levels at the end of 1987 were 123.3 ± 0.8 percent modern carbon (pMC) in the Northern Hemisphere and 120.0 ± 0.7 pMC in the Southern Hemisphere. Model calculations of source partitioning based on the carbon-14 data, CH
4
concentrations, and δ
13
C in CH
4
indicate that 21 ± 3% of atmospheric CH
4
was derived from fossil carbon at the end of 1987. The data also indicate that pressurized water reactors are an increasingly important source of
14
CH
4
.
The Nature of the Near-Infrared Features on the Venus Night Side
Authors: Crisp D. , Sinton W. M. , Hodapp K.-W. , Ragent B. , Gerbault F. , Goebel J. H. , Probst R. G. , Allen D. A. , Pierce K. , Stapelfeldt K. R.
Published: October 2006

Near-infrared images of the Venus night side show bright contrast features that move from east to west, in the direction of the cloud-top atmospheric superrotation. Recently acquired images of the Venus night side along with earlier spectroscopic observations allow identification of the mechanisms that produce these features, their level of formation, and the wind velocities at those levels. The features are detectable only at wavelengths near 1.74 and 2.3 micrometers, in narrow atmospheric windows between the CO
2
and H
2
O bands. The brightest features have brightness temperatures near 480 Kelvin, whereas the darkest features are more than 50 Kelvin cooler. Several factors suggest that this radiation is emitted by hot gases at altitudes below 35 kilometers in the Venus atmosphere. The feature contrasts are produced as this thermal radiation passes through a higher, cooler, atmospheric layer that has horizontal variations in transparency. The 6.5-day east-west rotation period of the features indicates that equatorial wind speeds are near 70 meters per second in this upper layer. Similar wind speeds have been measured by entry probes and balloons at altitudes between 50 and 55 kilometers in the middle cloud layer. The bright features indicate that there are partial clearings in this cloud deck. The presence of these clearings could decrease the efficiency of the atmospheric greenhouse that maintains the high surface temperatures on Venus.
Reconstitution and Phosphorylation of Chloride Channels from Airway Epithelium Membranes
Authors: Valdivia Hector H. , Dubinsky William P. , Coronado Roberto
Published: October 2006

Airway epithelial chloride secretion is controlled by the apical-membrane chloride permeability. Purified apical-membrane vesicles from bovine tracheal epithelium have now been shown to contain functional chloride channels by using the planar-bilayer technique. Three types of chloride channels were observed; a voltage-dependent, calcium-independent, 71-picoSiemen (in 150 mM NaCl) channel accounted for more than 80 percent of the vesicular chloride conductance and was under strict control of phosphorylation. The channel underwent a fast rundown in less than 2 to 3 minutes of recording, and reactivation required in situ exposure to a phosphorylating "cocktail" containing the catalytic subunit of the adenosine 3′,5′-monophosphate (cAMP)-dependent protein kinase. Mean open time and open probability were increased after phosphorylation, whereas slope conductance remained unchanged. Thus, metabolic control of tracheal chloride single channels can now be studied in vitro.
A Regulatory Gene as a Novel Visible Marker for Maize Transformation
Authors: Ludwig Steven R. , Bowen Ben , Beach Larry , Wessler Susan R.
Published: October 2006

The temporal and spatial patterns of anthocyanin pigmentation in the maize plant are determined by the presence or absence of the
R
protein product, a presumed transcriptional activator. At least 50 unique patterns of pigmentation, conditioned by members of the
R
gene family, have been described. In this study, microprojectiles were used to introduce into maize cells a vector containing the transcription unit from one of these genes (
Lc
) fused to a constitutive promoter. This chimeric gene induces cell autonomous pigmentation in tissues that are not normally pigmented by the
Lc
gene. As a reporter for gene expression studies in maize,
R
is unique because it can be quantified in living tissue simply by counting the number of pigmented cells following bombardment.
R
may also be useful as a visible marker for selecting stably transformed cell lineages that can give rise to transgenic plants.
Imaging and Manipulating Molecules on a Zeolite Surface with an Atomic Force Microscope
Authors: Weisenhorn A. L. , Mac Dougall J. E. , Gould S. A. C. , Cox S. D. , Wise W. S. , Massie J. , Maivald P. , Elings V. B. , Stucky G. D. , Hansma P. K.
Published: October 2006

The adsorption of neutral molecules and ions on the surfaces of zeolites was observed in real time with an atomic force microscope (AFM). Direct imaging of the surface of the zeolite clinoptilolite was possible by using a diluted
tert
-butyl ammonium chloride solution as a medium. Images of the crystal in different liquids revealed that molecules could be bound to the surface in different ways; neutral molecules of
tert
-butanol formed an ordered array, whereas
tert
-butyl ammonium ions formed clusters. These absorbed molecules were not rearranged by the AFM tip when used in an imaging mode. However, when a sufficiently large force was applied, the tip of the AFM could rearrange the
tert
-butyl ammonium ions on the zeolite surface. This demonstration of molecular manipulation suggests new applications, including biosensors and lithography.
Ungrouped Iron Meteorites in Antarctica: Origin of Anomalously High Abundance
Authors: Wasson John T.
Published: October 2006

Eighty-five percent of the iron meteorites collected outside Antarctica are assigned to 13 compositionally and structurally defined groups; the remaining 15 percent are ungrouped. Of the 31 iron meteorites recovered from Antarctica, 39 percent are ungrouped. This major difference in the two sets is almost certainly not a stochastic variation, a latitudinal effect, or an effect associated with differences in terrestrial ages. It seems to be related to the median mass of Antarctic irons, which is about 1/100 that of non-Antarctic irons. During impacts on asteroids, smaller fragments tend to be ejected into space at higher velocities than larger fragments, and, on average, small meteoroids have undergone more changes in orbital velocity than large ones. As a result, the set of asteroids that contributes small meteoroids to Earth-crossing orbits is larger than the set that contributes large meteoroids. Most small iron meteorites may escape from the asteroid belt as a result of impact-induced changes in velocity that reduce their perihelia to values less than the aphelion of Mars.
Secretion of Activin by Interstitial Cells in the Testis
Authors: Lee Will , Mason Anthony J. , Schwall Ralph , Szonyi Eva , Mather Jennie P.
Published: October 2006

Activin, a dimer formed by the β subunits of inhibin, has an effect that is opposite to that of inhibin in a number of biological systems. Which cell types secrete activin in vivo is not known. TM3 cells, a Leydig-derived cell line, contained messenger RNAs that hybridized with human β
A
and β
B
complementary DNA probes and were similar in size to the porcine messenger RNA for the β subunits of inhibin. No hybridization to the inhibin α subunit was detectable in the TM3 cells. Conditioned medium from TM3 cells and from primary cultures of rat and porcine interstitial cells stimulated the release of follicle-stimulating hormone in a pituitary cell culture assay. It is likely that, in the testis, the Leydig cells secrete activin and the Sertoli cells produce inhibin, or a combination of both.
Finite Social Space, Evolutionary Pathways, and Reconstructing Hominid Behavior
Authors: Foley R. A. , Lee P. C.
Published: October 2006

Changes in social behavior were a key aspect of human evolution, and yet it is notoriously difficult for paleobiologists to determine patterns of social evolution. By defining the limited number of distributional strategies available to members of each sex of any species and investigating the conditions under which they may occur and change, the social behavior of different hominid taxa may be reconstructed.
Developmental Biology of a Plant-Prokaryote Symbiosis: The Legume Root Nodule
Authors: Nap Jan-Peter , Bisseling Ton
Published: October 2006

The development of nitrogen fixing root nodules on the roots of leguminous plants is induced by soil bacteria (for example, from the genus
Rhizobium
). The formation of this plant organ involves specific activation of genes in both plant and bacterium. Analysis of these genes gives insight into the way in which plant and bacterium succeed in coordinating plant development.
The Cauliflower Mosaic Virus 35
S
Promoter: Combinatorial Regulation of Transcription in Plants
Authors: Benfey Philip N. , Chua Nam-Hai
Published: October 2006

Appropriate regulation of transcription in higher plants requires specific cis elements in the regulatory regions of genes and their corresponding trans-acting proteins. Analysis of the cauliflower mosaic virus (CaMV) 35
S
promoter has contributed to the understanding of transcriptional regulatory mechanisms. The intact 35
S
promoter confers constitutive expression upon heterologous genes in most plants. Dissection into subdomains that are able to confer tissue-specific gene expression has demonstrated that the promoter has a modular organization. When selected subdomains are combined, they confer expression not detected from the isolated subdomains, suggesting that synergistic interactions occur among cis elements. The expression patterns conferred by specific combinations of 35
S
subdomains differ in tobacco and petunia. This indicates that a combinatorial code of cis-regulatory elements may be interpreted differently in different species.
Scaling Population Density to Body Size in Rocky Intertidal Communities
Authors: Marquet Pablo A. , Navarrete Sergio A. , Castilla Juan C.
Published: October 2006

Interspecific comparisons of animal population density to body size has been the subject of active research in the last decade, especially for terrestrial animals when considering particular taxa or taxonomic assemblages. Studies of rocky intertidal communities showed that animal population density scales with body size to the -0.77 power. This relation held within local communities representing a broad array of animal taxa and was not affected by a dramatic alteration in the network of between-species interactions, as revealed by two long-term human exclusion experiments.
Kinematics of Late Paleozoic Continental Collision Between Laurentia and Gondwana
Authors: Sacks Paul E. , Secor Donald T.
Published: October 2006

In the Appalachians, late Paleozoic Alleghanian orogenesis is widely regarded as resulting from dextral oblique collision between irregular margins of Gondwana and Laurentia. However, this relative plate motion cannot account for coeval convergence in the Ouachitas and Variscides and is incompatible with some tectonic transport indicators in the Appalachians. An alternative kinematic model is proposed in which early sinistral transpression in the Appalachians is followed by counterclockwise rotation of Gondwana and the development of a system of dextral strike-slip faults extending from southern Europe to Alabama.
Fibroblasts Transformed with v-
src
Show Enhanced Formation of an Inositol Tetrakisphosphate
Authors: Johnson R. M. , Wasilenko W. J. , Mattingly R. R. , Weber M. J. , Garrison J. C.
Published: October 2006

The tyrosine kinase pp60

v-
src

, encoded by the v-
src
oncogene, seems to regulate phosphatidylinositol metabolism. The effect of pp60

v-
src

on control points in inositol phosphate production was examined by measuring the amounts of inositol polyphosphates in Rat-1 cells expressing wild-type or mutant forms of the protein. Expression of v-
src
resulted in a five- to sevenfold elevation in the steady-state amount of an isomer of inositol tetrakisphosphate, whereas the concentrations of inositol trisphosphates or other inositol tetrakisphosphates were not affected. The activity of a key enzyme in the formation of inositol tetrakisphosphates, inositol (1,4,5)-trisphosphate 3-kinase, was increased six- to eightfold in cytosolic extracts prepared from the v-
src
-transformed cells, suggesting that this enzyme may be one target for the pp60

v-
src

kinase and that it may participate in the synthesis of novel, higher order inositol phosphates.
Hidden Fermi Surface Nesting and Charge Density Wave Instability in Low-Dimensional Metals
Authors: Whangbo M.-H. , Canadell E. , Foury P. , Pouget J. -P.
Published: October 2006

The concept of hidden Fermi surface nesting was introduced to explain the general observation that certain low-dimensional metals with several partially filled bands exhibit charge density wave (CDW) instabilities, although their individual Fermi surfaces do not reveal the observed nesting vectors. This concept was explored by considering the Fermi surfaces of the purple bronze AMo
6
O
17
(A = sodium or potassium) and then observing the CDW spatial fluctuations expected from its hidden nesting on the basis of diffuse x-ray scattering experiments. The concept of hidden Fermi surface nesting is essential for understanding the electronic instabilities of low-dimensional metals.
40
Ar/
39
Ar Age of Cretaceous-Tertiary Boundary Tektites from Haiti
Authors: Izett G. A. , Dalrymple G. B. , Snee L. W.
Published: October 2006

40
Ar/
39
Ar dating of tektites discovered recently in Cretaceous-Tertiary (K-T) boundary marine sedimentary rocks on Haiti indicates that the K-T boundary and impact event are coeval at 64.5 ± 0.1 million years ago. Sanidine from a bentonite that lies directly above the K-T boundary in continental, coal-bearing, sedimentary rocks of Montana was also dated and has a
40
Ar/
39
Ar age of 64.6 ± 0.2 million years ago, which is indistinguishable statistically from the age of the tektites.
Buckminsterfullerane: The Inside Story
Authors: Saunders Martin
Published: October 2006

The stereoisomers of fully reduced buckminsterfullerene C
60
H
60
have been investigated with the molecular mechanics program MM3. Although it might be expected that chemical reduction would deliver all of the hydrogens to the outside, the symmetric structure produced in this way is predicted to be highly strained. Moving just one hydrogen to the inside is predicted to decrease the energy by 53 kilocalories (kcal) per mole. Putting additional hydrogens on the inside further lowers the predicted energy (depending on the steric relations between them). The minimum energy isomer is predicted to have ten hydrogens inside with
C
1
symmetry and to have an energy 400 kcal/mol less than that of the all-outside isomer. These results suggest that a process which could achieve isomerization would produce a mixture of isomers, most of which with ten hydrogens on the inside.
Declining Amphibian Populations: The Problem of Separating Human Impacts from Natural Fluctuations
Authors: Pechmann Joseph H. K. , Scott David E. , Semlitsch Raymond D. , Caldwell Janalee P. , Vitt Laurie J. , Gibbons J. Whitfield
Published: October 2006

Reports of declining amphibian populations in many parts of the world are numerous, but supporting long-term census data are generally unavailable. Census data from 1979 to 1990 for three salamander species and one frog species at a breeding pond in South Carolina showed fluctuations of substantial magnitude in both the size of breeding populations and in recruitment of juveniles. Breeding population sizes exhibited no overall trend in three species and increased in the fourth. Recent droughts account satisfactorily for an increase in recruitment failures. These data illustrate that to distinguish between natural population fluctuations and declines with anthropogenic causes may require long-term studies.
Chromosomal Rearrangement Generating a Composite Gene for a Developmental Transcription Factor
Authors: Stragier Patrick , Kunkel Barbara , Kroos Lee , Losick Richard
Published: October 2006

Differential gene expression in the mother cell chamber of sporulating cells of
Bacillus subtilis
is determined in part by an RNA polymerase sigma factor called σ
K
(or σ
27
). The σ
K
factor was assigned as the product of the sporulation gene
spoIVCB
on the basis of the partial amino-terminal amino acid sequence of the purified protein. The
spoIVCB
gene is now shown to be a truncated gene capable of specifying only the amino terminal half of σ
K
. The carboxyl terminal half is specified by another sporulation gene,
spoIIIC
, to which
spoIVCB
becomes joined inframe at an intermediate stage of sporulation by site-specific recombination within a 5-base pair repeated sequence. Juxtaposition of
spoIVCB
and
spoIIIC
need not be reversible in that the mother cell and its chromosome are discarded at the end of the developmental cycle. The rearrangement of chromosomal DNA could account for the presence of σ
K
selectively in the mother cell and may be a precedent for the generation of cell type-specific regulatory proteins in other developmental systems where cells undergo terminal differentiation.
The Effect of GTPase Activating Protein Upon Ras Is Inhibited by Mitogenically Responsive Lipids
Authors: Tsai Men-Hwei , Yu Chun-Li , Wei Fu-Sheng , Stacey Dennis W.
Published: October 2006

Bacterially synthesized c-Ha-
ras
protein (Ras) was incubated with guanosine triphosphatase (GTPase) activating (GA) protein in the presence of various phospholipids. The stimulation of Ras GTPase activity by GA protein was inhibited in some cases. Among the lipids most active in blocking GA protein activity were lipids that show altered metabolism during mitogenic stimulation. These included phosphatidic acid (containing arachidonic acid), phosphatidylinositol phosphates, and arachidonic acid. Other lipids, including phosphatidic acid with long, saturated side chains, diacylglycerols, and many other common phospholipids, were unable to alter GA protein activity. The interaction of lipids with GA protein might be important in the regulation of Ras activity during mitogenic stimulation.
Cooperative Solution of Constraint Satisfaction Problems
Authors: Clearwater Scott H. , Huberman Bernardo A. , Hogg Tad
Published: October 2006

It is widely believed that a group of cooperating agents engaged in problem solving can solve a task faster than either a single agent or the same group of agents working in isolation from each other. Nevertheless, little is known about the quantitative improvements that result from cooperation. A number of experimental results are presented on constraint satisfaction that both test the predictions of a theory of cooperative problem solving and assess the value of cooperation for this class of problems. These experiments suggest an alternative methodology to existing techniques for solving constraint satisfaction problems in computer science and distributed artificial intelligence.
Systematic Inflation of Buckminsterfillerene C
60
: Synthesis of Diphenyl Fulleroids C
61
to C
66
Authors: Suzuki T. , Li Q. , Khemani K. C. , Wudl F. , Almarsson Ö.
Published: October 2006

The synthesis of a new family of spheroidal carbon molecules derived from the fullerenes is described. The fulleroids are produced by incremental addition of a divalent carbon equivalent that has two phenyl (Ph) rings to fullerene C
60
. The fulleroids Ph
2
C
61
, Ph
4
C
62
, Ph
6
C
63
, Ph
8
C
64
, Ph
10
C
65
, and Ph
12
C
66
have been prepared and characterized.
Physical Mapping of a Translocation Breakpoint in Neurofibromatosis
Authors: Fountain Jane W. , Wallace Margaret R. , Bruce Melissa A. , Seizinger Bernd R. , Menon Anil G. , Gusella James F. , Michels Virginia V. , Schmidt Michael A. , Dewald Gordon W , Collins Francis S.
Published: October 2006

The gene for von Recklinghausen neurofibromatosis (NF1), one of the most common autosomal-dominant disorders of humans, was recently mapped to chromosome 17 by linkage analysis. The identification of two NF1 patients with balanced translocations that involved chromosome 17q11.2 suggests that the disease can arise by gross rearrangement of the
NF1
locus, and that the NF1 gene might be identified by cloning the region around these translocation breakpoints. To further define the region of these translocations, a series of chromosome 17 Not I-linking clones has been mapped to proximal 17q and studied by pulsed-field gel electrophoresis. One clone, 17L1 (D17S133), clearly identifies the breakpoint in an NF1 patient with a t(1;17) translocation. A 2.3-megabase pulsed-field map of this region was constructed and indicates that the NF1 breakpoint is only 10 to 240 kilobases away from 17L1. This finding prepares the way for the cloning of
NF1
.
Inhibition of Postsynaptic PKC or CaMKII Blocks Induction But Not Expression of LTP
Authors: Malinow Roberto , Schulman Howard , Tsien Richard W.
Published: October 2006

Long-term potentiation (LTP) of synaptic transmission is a widely studied cellular example of synaptic plasticity. However, the identity, localization, and interplay among the biochemical signals underlying LTP remain unclear. Intracellular microelectrodes have been used to record synaptic potentials and deliver protein kinase inhibitors to postsynaptic CA1 pyramidal cells. Induction of LTP is blocked by intracellular delivery of H-7, a general protein kinase inhibitor, or PKC(19-31), a selective protein kinase C (PKC) inhibitor, or CaMKII(273-302), a selective inhibitor of the multifunctional Ca
2+
-calmodulin-dependent protein kinase (CaMKII). After its establishment, LTP appears unresponsive to postsynaptic H-7, although it remains sensitive to externally applied H-7. Thus both postsynaptic PKC and CaMKII are required for the induction of LTP and a presynaptic protein kinase appears to be necessary for the expression of LTP.
The Earth's Angular Momentum Budget on Subseasonal Time Scales
Authors: Dickey J. O. , Marcus S. L. , Steppe J. A. , Hide R.
Published: October 2006

Irregular length of day (
LOD
) fluctuations on time scales of less than a few years are largely produced by atmospheric torques on the underlying planet. Significant coherence is found between the respective time series of
LOD
and atmospheric angular momentum (
AAM
) determinations at periods down to 8 days, with lack of coherence at shorter periods caused by the declining signal-to-measurement noise ratios of both data types. Refinements to the currently accepted model of tidal Earth rotation variations are required, incorporating in particular the nonequilibrium effect of the oceans. The remaining discrepancies between
LOD
and
AAM
in the 100- to 10-day period range may be due to either a common error in the
AAM
data sets from different meteorological centers, or another component of the angular momentum budget.
The Widespread Distribution of a Novel Silica Polymorph in Microcrystalline Quartz Varieties
Authors: Heaney Peter J. , Post Jeffrey E.
Published: October 2006

An x-ray examination of more than 150 specimens of fine-grained quartz varieties from around the world has revealed that more than 10% and as much as 80% of the silica in many samples is actually moganite, a little-known silica polymorph. Rietveld refinements of 50 powder x-ray diffraction patterns produced by fibrous quartz (agate, chalcedony) and nonfibrous quartz (chert, flint) indicate that the concentrations of moganite within each subgroup are widely distributed. The large amount of moganite (>30%) found in cherts from arid, alkaline environments may resurrect length-slow silica as an indicator of evaporitic regimes, and the absence of moganite in weathered and hydrothermally altered silica samples may be a useful measure of fluid-rock interaction.
Structural Memory in Pressure-Amorphized AlPO
4
Authors: Tse John S. , Klug Dennis D.
Published: October 2006

Molecular dynamics simulations reveal the mechanism of the structural memory effect in α-berlinite (AlPO
4
), where a single crystal transforms to an amorphous solid by compression and then reverts to the original crystalline structure upon release of pressure. The enhanced oxygen coordination around the aluminum atoms in AlPO
4
at high pressure leads to a mechanical instability that causes the phase transformation. The difference in the structural memory behavior between AlPO
4
and isostructural α-quartz, for which the pressure-induced amorphized phase is recoverable, can be attributed to the presence of the PO
4
units, which remain essentially four-coordinated even when severely distorted.