bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Quaternary Arthropod Remains from Sonoran Desert Packrat Middens, Southwestern Arizona and Northwestern Sonora
Authors: Hall W. Eugene , Van Devender Thomas R. , Olson Carl A.
Published: December 2004

A total of 50 arthropod taxa were identified from 41 fossil packrat (Neotomasp.) middens from 160 to 625 m elevation in three study areas in the Lower Colorado River Valley subdivision of the Sonoran Desert. Radiocarbon dates associated with the middens range from >43,200 to 610 yr B.P. The fauna in the Tinajas Altas Mountains, southwestern Arizona, was relatively modern by ca. 10,000 yr B.P. in the early Holocene although a California juniper woodland persisted in the area until 8970 yr B.P. In contrast the fauna of the Hornaday Mountains, northwestern Sonora, increased dramatically in species richness after 4000 yr B.P. Although we are limited by poor taxonomic resolution and by insufficient knowledge of current distributions, the arthropod fauna may have been much more conservative than the regional flora during the last glacial/interglacial climatic cycle. Decreasing differences between modern and glacial climates (both temperature and precipitation) at lower latitudes and elevations may have resulted in minimal changes in the arthropod fauna of the Sonoran Desert lowlands.
Climatostratigraphic Scheme of the Black Sea Pleistocene and its Correlation with the Oxygen-Isotope Scale and Glacial Events
Authors: Zubakov V.A.
Published: December 2004

New evidence from the Asov Sea-Black Sea region shows that after the Cobb Mountain magnetic event (1.1 myr) there were 8 saline water events, with Mediterranean molluscs penetrating into the Asov Sea (five times farther than the western Manych Strait), and 7 or 10 cold freshwater events. During the freshening phase, the Caspian Sea molluscan fauna penetrated into the Black Sea; each time the Caspian mollusc assemblage was characterized by a new species of Didacna. Thus, some 18–20 bioclimatostratigraphic units can be distinguished in the Asov Sea-Black Sea section for the last 1 myr. Their numerical age is estimated by some dozen thermoluminescence dates and 12 magnetic-polarity datum planes. The Karangatian s. lato corresponds to the interval 300,000–50,000 yr, the Uzunlarian to 580,000–300,000 yr, and the Chaudian to 1,100,000–600,000 yr. The Karangatian and Tyrrhenian marine terraces correspond to marine isotope stages 5 and 7, the Uzunlarian and Milazzian to stages 11–15, and the Chaudian and Sicilian to stages 16–28. The number and ages of glacial-interglacial cycles in continental Europe are identical to the climatic cycles in the Black Sea and Mediterranean.
The Kashiru Pollen Sequence (Burundi) Palaeoclimatic Implications for the Last 40,000 yr B.P. in Tropical Africa
Authors: Bonnefille Raymonde , Riollet Guy
Published: December 2004

A continuous pollen record from a central African highland site (3°28′S, 29°34′E) with 15 radio-carbon dates spans at least the last 40,000 yr. Both modern and fossil pollen have been investigated. A clear pattern of changes in vegetation and climate is suggested. Prior to 30,000 yr B.P., the occurrence of the montane conifer forest, including the upper forest limit, indicates climatic conditions colder and drier than now, but more humid than in late-glacial time. Between 30,000 and 15,000 yr B.P., grassland with afroalpine indicators expanded down to 2500-2000 m altitude as a result of dry, and most probably cool, climate; the montane forest persisted in refuges, although much reduced. Forest vegetation with the same floristic composition as today appeared after 13,250 ± 200 yr B.P., suggesting more humid conditions. The occurrence of a possible short-term humid episode about 21,500 yr B.P. is correlated with some high lake-level stages in East Africa and with organic deposits in deep-sea cores from the Mediterranean and the Atlantic Ocean.
Holocene Environmental Changes in Lily Lake, Minnesota Inferred from Fossil Diatom and Pollen Assemblages
Authors: Brugam Richard B. , Grimm Eric C. , Eyster-Smith Nancy M.
Published: December 2004

A postglacial core was taken from Lily Lake, a soft-water lake, located on carbonate-poor till in eastern Minnesota. Pollen analysis allowed the reconstruction of watershed vegetation change. Diatom assemblages from the core were compared with 255 surface sediment assemblages from Minnesota, Maine, Labrador, and the Canadian arctic. Late-glacial assemblages were similar to Canadian arctic lakes. During the mid-postglacial period of warmer and drier climate, fossil diatom assemblages at Lily Lake were similar to those in the surface sediment of modern eutrophic hardwater lakes in Central Minnesota. The shift to hardwater diatom assemblages coincided with a shift to prairie species in fossil pollen assemblages at about 8000 yr B.P. At about 3400 year B.P. the fossil diatom assemblage that characterized presettlement times was established.
Particle Motion and the Theory of Charcoal Analysis: Source Area, Transport, Deposition, and Sampling
Authors: Clark James S.
Published: December 2004

Principles from particle-motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data: (1) fires within catchments of lakes often produce no record in fossil-charcoal curves and (2) periods characterized by no local fire (e.g., 20th-century fire suppression) often display as much charcoal as times when local fire was frequent. Quantitative theory on source area, transport, deposition, and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis (pollen slides for particles 5–80 μm in diameter, petrographic thin sections for particles 50–10,000 μm diameter) and charcoal diagrams. The relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods. Charcoal recorded on pollen slides is of a size that is difficult to lift, but once entrained it remains in suspension. Thin-section charcoal is lifted at relatively low wind velocities, but it is not suspended at normal surface wind speeds. Thermal buoyancy during fire lofts charcoal above the forest canopy, depending on particle size and wind speed. Pollen-slide charcoal sizes are underrepresented near the fire, because they remain in suspension and are preferentially exported from the burn area. Thin-section charcoal is convected to lower heights on average and is deposited nearby. Following fire, thin-section charcoal is redistributed locally by wind and thus may enter lakes. Because of cohesive forces and aerodynamics, more pollen-slide charcoal remains on the ground, and less enters lakes. Source areas for pollen-slide charcoal are subcontinental to global, and diagrams of pollen-slide charcoal are biased toward nonlocal charcoal. They can be used to interpret importance of fire for broad spatial and temporal scales. Thin-section charcoal represents, the catchment fire regime. Simulation models that generate charcoal during fire, mix sediments, and then sample at specified intervals indicate that (1) in the absence of sediment mixing the pollen-slide method should consistently resolve individual fires that occur with an expectation of >30–50 yr, (2) unless samples are continuous, neither method will produce useful estimates of fire frequency, and (3) even a modest amount of sediment mixing will obscure the signal.
New Source of Dietary Data for Extinct Herbivores
Authors: Akersten William A. , Foppe Theresea M. , Jefferson George T.
Published: December 2004

The teeth of many large herbivores contain “pockets” (fossettes, fossettids, etc.) which entrap impacted samples of food (dental boluses) during mastication. These do not preserve well in most fossil deposits, but at Rancho La Brea, paleobotanical remains survive essentially intact and dental boluses from late Pleistocene forms are amenable to microhistological analysis. Of the identifiable bolus contents, those from Bison antiquus averaged 87% nonmonocotyledons; from Camelops hesternus, 90% nonmonocotyledons; and from Equus occidentalis (one specimen), 56% nonmonocotyledons. A control study on modern Bison bison shows that the boluses contain somewhat lower percentages of monocotyledons than do alimentary samples from the same individuals. However, this accounts for only a part of the very high percentage of nonmonocotyledons in the boluses of the extinct Bison. We conclude that the populations of B. antiquus and C. hesternus represented at Rancho La Brea probably fed little on grasses and that there is enough indirect evidence to suggest that the same may be true for other populations of these taxa. The Equus data are not sufficient to do more than question the usual assumption that Pleistocene horses were always obligate grass eaters.
Late Quaternary Ice-Surface Fluctuations of Hatherton Glacier, Transantarctic Mountains
Authors: Bockheim James G. , Wilson Scott C. , Denton George H. , Andersen Björn G. , Stuiver Minze
Published: December 2004

Former longitudinal profiles of Hatherton Glacier, an outlet through the Transantarctic Mountains, constrain nearby polar plateau elevations and ice-shelf grounding in the southwestern Ross Embayment. Four gravel drift sheets of late Quaternary age beside Hatherton Glacier are, from youngest to oldest, Hatherton, Britannia I, Britannia II, and Danum. The Hatherton drift limit is uniformly 20 to 70 m above the present ice surface. The Britannia II drift limit is within 100 m of the present surface of uppermost Hatherton Glacier but is 450 m above middle Hatherton Glacier. Extrapolation of this profile downglacier indicates a surface elevation 1100 m above the present Ross Ice Shelf. The Britannia I drift limit is parallel to, but 50–100 m below, Britannia II drift. The Danum drift limit is parallel to, but 50–100 m above, the Britannia II profile. From correlation with drifts near McMurdo Sound and from local 14C dates, we assign an early Holocene age to Hatherton drift, a late Wisconsin age to Britannia drifts, and an age of marine isotope Stage 6 to Danum drift. By our age model, the upper reaches of Hatherton Glacier (and presumably the adjacent polar plateau) have not exceeded their current elevations by more than 100–150 m during the last two complete global glacial-interglacial cycles, whereas the middle and lower reaches of Hatherton Glacier have thickened considerably during the last two global glaciations (late Wisconsin and marine isotope Stage 6). The effect of ice-shelf grounding probably was the major control of these changes of Hatherton Glacier. Holocene ice-surface lowering probably represents the last pulse of grounding-line recession in the southwestern Ross Embayment.
Glacial-Marine Sedimentation and Quaternary Glacial History of Marguerite Bay, Antarctic Peninsula
Authors: Kennedy Douglas S. , Anderson John B.
Published: December 2004

Marguerite Bay, situated between the subpolar glacial regime of the northern Antarctic Peninsula and the polar glacial regime of West Antarctica, is ideally located to test various models of glacial and glacial-marine sedimentation and specific scenarios of late Wisconsin ice sheet expansion. Piston cores and single-channel seismic reflection data were collected during the Deep Freeze 85 and 86 expeditions to determine the late Quaternary history of the area. Seismic data in the bay show a rugged seafloor, with numerous deep troughs and a very thin layer of sediment over crystalline basement or older sediments. Glacial erosion is important in modifying existing features, although the ultimate repository of the eroded material is not known; it is not found within the bay. The piston cores are topped by diatomaceous muds, which are underlain by terrigenous muds and muddy gravels that imply deposition beneath an ice shelf. Basal tills were penetrated at three sites, reflecting deposition by a grounded marine ice sheet. A reconstruction of the glacial history of Marguerite Bay since the last glacial maximum shows grounded ice filling the bay in late Wisconsin time. Rising sea level caused an uncoupling of the ice sheet and slow retreat of an ice shelf throughout the Holocene.
AMS-14C Ages Measured in Deep Sea Cores from the Southern Ocean: Implications for Sedimentation Rates during Isotope Stage 2
Authors: Bard Edouard , Labeyrie Laurent , Arnold Maurice , Labracherie Monique , Pichon Jean-Jacques , Duprat Josette , Duplessy Jean-Claude
Published: December 2004

14C dates obtained by accelerator mass spectrometry (AMS) on monospecific foraminiferal samples from two deep-sea sediment cores raised in the Indian sector of the Southern Ocean have been corrected for the difference in14C composition between atmosphere and sea surface by using a reconstruction of the latitudinal14C gradient which existed in the Southern Ocean prior to 1962. The corrected AMS-14C data show a reduced sedimentation rate in core MD 84-527 between 25,000 and 10,000 yr BP. For core MD 84-551 the available data suggest that the sedimentation rate was higher during the Holocene than during the glacial period. These changes in sedimentation rates may be attributed to an increased opal dissolution during the last glacial maximum.
Accelerator-Mass Spectrometer Ages for Late-Glacial Events at Ballybetagh, Ireland
Authors: Cwynar Les C. , Watts W. A.
Published: December 2004

Although the character of late-glacial vegetation development in Ireland is well known, the dating is weak for a number of reasons. We report six accelerator-mass spectrometer (AMS) 14C dates of hand-picked organic material from Ballybetagh. Several of the dates are based on terrestrial plant remains, thus eliminating the commonly encountered problem associated with Irish sites of errors due to the hard-water effect. The two most significant indicate that (1) the Rumex-Salix zone, which represents the initial establishment of vegetation following deglaciation, began about 12,600 yr B.P. and (2) the classic Younger Dryas began at 10,600 yr B.P., somewhat younger than the traditionally accepted age of 11,000 yr B.P.
Postglacial Vegetation and Climate in the Northwestern Great Plains of Montana
Authors: Barnosky Cathy W.
Published: December 2004

Two pollen records from the northern Great Plains of Montana portray vegetational and climatic changes during the last 12,200 yr in a region where few other data are available. A 6.4-m core from Guardipee Lake, east of the Rocky Mountains in the area formerly covered by the Two Medicine glacial lobe, contains the Glacier Peak G and Mt. St. Helens Jy volcanic ashes. Pollen percentage data are dominated byPinus, Poaceae,Artemisia, and Chenopodiaceae/Amaranthaceae. High nonarboreal percentages and small amounts ofJuniperus, Alnus, Salix, andPopuluspollen in sediments deposited between ca. 12,200 and ca. 9300 yr B.P. suggest a temperate grassland with shrubs growing locally in mesic settings. After ca. 9300 yr B.P. an increase in Chenopodiaceae/Amaranthaceae pollen and a concomitant decline inArtemisiaindicate the development of more xerophytic grassland and the beginning of the altithermal period. The lake probably was intermittently dry thoughout the Holocene. A high sedimentation rate and the presence of cereal taxa characterize the last ca. 100 yr of Euroamerican settlement. Lost Lake at the northern margin of the Highwood Mountains yielded a 16.94-m core with no volcanic ashes that spans the last 9400 yr. High amounts of Chenopodiaceae/Amaranthaceae,Artemisia, and Poaceae pollen, from ca. 9400 to ca. 6000 yr B.P., suggest the presence of xeric grassland and a climate drier than at present. After ca. 6000 yr B.P. Chenopodiaceae/Amaranthaceae values declined andArtemisia, Poaceae,Pinus, Picea, Salix, Alnus, andBetulaincreased. The inferred spread of shrubs in wet habitats at this time and the expansion of forest in nearby mountain ranges indicate the end of the altithermal period and the onset of cooler/moister conditions.
Middle Holocene Drought on the Southern High Plains
Authors: Holliday Vance T.
Published: December 2004

The climate of the Southern High Plains during the middle Holocene is indicated by data from a variety of sources. Stratigraphic, geomorphic, and pedologic research at six localities in draws, several dune sites, and one playa-lake basin show that widespread eolian erosion and sedimentation began in some areas by 9000 yr B.P. and culminated 6000-4500 yr B.P., probably because of warmer, drier conditions that reduced the vegetative cover. Archaeological investigations at three sites provide evidence for the excavation of wells at this time, apparently because of a declining water table. Studies of a few vertebrate and invertebrate faunas also indicate warming and drying in the middle Holocene. Climate models and very limited isotopic data fromBisonbone suggest that summers in the middle Holocene were warmer than present, with reduced effective precipitation. All lines of evidence indicate that the Southern High Plains was subjected to prolonged drought in the middle Holocene with a maximum between 6500 and 4500 yr B.P., conforming climatically and chronologically to the Altithermal.
A Review of Pedogenic Zonation in Well-Drained Soils of the Southern Circumpolar Region
Authors: Bockheim James G. , Ugolini Fiorenzo C.
Published: December 2004

The concept of zonality is used to link well-drained mineral soils and processes along a bioclimatic gradient extending from ca. 48° to 87° S, including southernmost Chile, the subantarctic islands, and maritime and continental Antarctica. The following environmental factors decline along this gradient: mean annual temperature and precipitation and the type and number of plant species. Six pedological zones (along with representative soils) are identified along the gradient: (1) Subantarctic Forest Zone (Podzol?), (2) Subantarctic Low Tundra zone, (3) Subantarctic High Tundra Zone (Subantarctic Brown soil, without permafrost), (4) Antarctic Sub-Polar Desert Zone (Subantarctic Brown soil, with permafrost), (5) Antarctic Polar Desert Zone (Red Ahumisol), and (6) Cold Desert Zone (Ahumisol). Zonal mineral soils in the Subantarctic Forest and Low Tundra Zones are rare, because large amounts of precipitation (≥2500 mm) and cool summers have led to thick accumulation of peat. Whereas the processes of rubification, melanization, and peat accumulation decline in relative magnitude southward, the processes of salinization and desert pavement formation increase in relative importance along this bioclimatic gradient. Carbonation and pervection (silt and clay migration) are maximized in the Subantarctic Tundra and Antarctic Polar Desert Zones. Because of the limited amount of land between 40° and 65° S and the presence of the Antarctic Convergence, comparable pedogenic zones occur at lower latitudes in the Southern than in the Northern Circumpolar Region.
Ferrimagnetic Sulfide Formation in Recent Sediments of Loch Ba, Scotland and Implications for Magnetostratigraphic Interpretation
Authors: Williams T. Martin
Published: December 2004

Magnetic and chemical analyses of 1-m piston cores from Loch Ba, Scotland illuminated the presence of a ferrimagnetic mineral which is sensitive to atmospheric oxidation and is soluble in H2O2. This phase, plausibly only an authigenic sulfide, is probably spinel Fe3S4 (greigite). Authigenesis of Fe3S4 requires reactive FeS and elemental S, the latter likely being derived from in situ oxidation of bisulfide near the sediment redoxycline. This is consistent with the observation of maximum “oxidation-sensitive” magnetic fractions around the oxic/anoxic sediment boundary at ca. 4–16 cm depth. Progressive pyritization of Fe3S4 during burial provides the most viable explanation for the loss of “oxidation-sensitive” phases at greater depth. The results extend the range of environments known to be subject to postdepositional magnetic enhancement to include oligotrophic lakes with relatively low productivity. This may have ramifications for magnetically based sediment-source linkage, core correlation, and pollution studies which fail to demonstrate that magnetostratigraphic profiles are solely reflectively of allogenic mineral presence.
14C Offsets and Apparently Non-Synchronous δ18O Stratigraphies between Nannofossil and Foraminiferal Pelagic Carbonates
Authors: Paull Charles K. , Hills Scott J. , Thierstein Hans R. , Bonani Georges , Wölfli Willi
Published: December 2004

Multiple stratigraphies of subtropical South Atlantic cores reveal significant stratigraphic discrepancies between the nannofossil and the foraminiferal carbonates. Variations in the stratigraphic signals carried in the nannofossil-dominated <38 μm fraction and foraminifera-dominated >38 μm fraction were measured with detailed stratigraphies of δ18O, δ13C,14C, grain size, percentage carbonate, percentage aragonite, and taxonomic composition across the last deglaciation in INMD box core 111 No. 9. Three other cores (INMD box cores 113 and 115, and V 22–174), also from the shallow flanks of the mid-Atlantic ridge in the South Atlantic (10°–17° S), contain similar stratigraphies indicating that these cores represent regional patterns. The onset of the deglacial δ18O shift in foraminiferal carbonate occurs 6 to 20 cm deeper than the δ18O shift in the nannofossil fraction. Nineteen accelerator mass spectrometer14C dates of various fractions (<38 μm, 38–62 μm, 62–150 μm, 150–250 μm, >355 μm, andG. ruber) from INMD Box 111 show that the components within an individual core slice may differ by up to 490014C years. Twelve traditional14C dates (determined by beta counting) of the >38 and <38 μm fractions from six levels in INMD Box 111 No. 6 confirm the large offsets. The observed isotopic offsets are not explained by an individual process, and suggest that multiple causes have left a lumpy stratigraphic record. However, the variability in the data illustrates the difficulty in accurately measuring the chronology of deglaciation, reopens the question of which components of pelagic sediment best monitor surface water conditions, and complicates the direct interpretation of benthic-planktonic age differences in terms of ocean ventilation changes.
Theoretical Correlations and Lateral Discontinuities in the Quaternary Aminostratigraphic Record of the U.S. Atlantic Coastal Plain
Authors: Wehmiller J. F. , York L. L. , Belknap D. F. , Snyder S. W.
Published: December 2004

Aminostratigraphic correlations of emergent Quaternary deposits along the U.S. Atlantic Coastal Plain have employed independent radiometric data, regional temperature history models, and assumptions regarding the nature of the preserved late Quaternary sea-level record on this passive margin. A substantial “aminostratigraphic offset” is required if regional aminozones are rigorously constrained by all available Th/U data. New insights regarding the relation of this offset to subsurface stratigraphy in the Cape Fear region of southeastern North Carolina can explain these conflicts as consequences of the highly incomplete post-Cretaceous depositional record of the region. Southward projection of theoretical aminostratigraphic correlation trends suggests that stage 5 correlative marine units are rarely preserved on the emergent portion of the Coastal Plain between Cape Lookout and central South Carolina and that samples of this age would be most frequently found in this region only as fragmentary (and/or reworked) deposits on the inner shelf or in the subsurface of modern barrier islands. If this hypothesis is correct, then the accuracy of several Th/U coral dates from the South Carolina Coastal Plain must be questioned, along with sea-level, tectonic, and paleoclimatic conclusions derived from these dates.
Reevaluation of the Lake-Sediment Chronology in the Dead Sea Basin, Israel, Based on New 230Th/U dates
Authors: Kaufman Aaron , Yechieli Yoseph , Gardosh Michael
Published: December 2004

The Dead Sea is surrounded by chemical and detrital sediments that were deposited in its larger precursor lakes, Lake Samra and Lake Lisan. The sedimentary history of these lakes was recon-structed by means of 230Th/234U ages of 30 samples, mostly of argonite laminae, from 8 columnar sections up to 110 km apart. The general validity of the ages was demonstrated by subjecting them to tests of internal isotopic consistency, agreement with stratigraphic order, and concordance with 14C ages. In the south, only the part of the Samra Formation older than 170,000 yr is exposed, while the aragonite-detritus rhythmites found in the central and northern region are generally younger than 120,000 yr. The Lisan Formation started accumulating about 63,000 yr B.P., with the clay and aragonite beds in the south-central area reflecting a rise in water level to at least −280 m. The upper part of the Lisan Formation, the aragonite-rich White Cliff Member, started accumulating about 36,000 yr B.P. The lake probably reached its highest level sometime after this, based on the ages of Lisan sediments preserved in the southernmost reaches of the basin.
Recent Dynamics of Subarctic Dunes as Determined by Tree-Ring Analysis of White Spruce, Hudson Bay, Québec
Authors: Marin Pierre , Filion Louise
Published: December 2004

The radial-growth patterns of white spruce were studied on a number of trees growing in subarctic dunes along the eastern coast of Hudson Bay to calculate the rates of accumulation, erosion, and migration of cold-climate sand dunes. The average rate of sand accumulation in sheltered dunes (forest sites) was 2.5 to 3.3 cm/yr, which is two to three times lower than in highly exposed dunes with a rate of sedimentation of 7.65 cm/yr. The average erosion rate was 1.4–1.7 cm/yr, about two times lower than the accumulation rate. The migration rate of sheltered dunes was 18 to 30 cm/yr, three to five times lower than for an exposed dune which advanced at a speed of 74 cm/yr. This migration rate established for highly exposed dunes in the Subarctic with tree-ring methods is about 10 times lower than that established for a barchan in the Sahara with other methods.
A Holocene Marine Climate Record in Mollusc Shells from the Southwest African Coast
Authors: Cohen Anne L. , Parkington John E. , Brundrit Geoff B. , van der Merwe Nikolaas J.
Published: December 2004

Details of short-term climatic variability are often lost from marine sediments through bioturbation in the upper, aerobic sediment layers. Alternatively, a high-resolution and dated record of climatic events may be obtained using material preserved in archaeological deposits. The Holocene history of the southern Benguela upwelling regime has been constructed from the oxygen isotope and mineral analysis of midden shells. Three discrete episodes of significant isotope enrichment corresponded to periods of glacial expansion in the northern hemisphere. Significant changes in shell mineralogy, which is a response to sea-surface temperatures, were also recorded. The timing and duration of these changes approximated those in the isotope record and may provide a link between events affecting the subcontinent and global temperature changes of the late Quaternary.
The N‐terminal rhodanese domain from Azotobacter vinelandii has a stable and folded structure independently of the C‐terminal domain
Authors: Melino Sonia , Cicero Daniel O. , Forlani Fabio , Pagani Silvia , Paci Maurizio
Published: December 2004

Sulfurtransferase are enzymes involved in the formation, conversion and transport of compounds containing sulfane‐sulfur atoms. Although the three‐dimensional structure of the rhodanese from the nitrogen‐fixing bacterium Azotobacter vinelandii is known, the role of its two domains in the protein conformational stability is still obscure. We have evaluated the susceptibility to proteolytic degradation of the two domains of the enzyme. The two domains show different resistance to the endoproteinases and, in particular, the N‐terminal domain shows to be more stable to digestion during time than the C‐terminal one. Cloning and overexpression of the N‐terminal domain of the protein was performed to better understand its functional and structural role. The recombinant N‐terminal domain of rhodanese A. vinelandii is soluble in water solution and the spectroscopic studies by circular dichroism and heteronuclear NMR spectroscopy indicate a stable fold of the protein with the expected α/β topology. The results indicate that this N‐terminal domain has already got all the elements necessary for an C‐terminal domain independent folding. Its solution structure by NMR, actually under course, will be a valid contribution to understand the role of this domain in the folding process of the sulfurtransferase.
Phorbol ester‐induced differentiation of L6 myogenic cells involves phospholipase D activation
Authors: Komati Hiba , Minasi Alessandra , Naro Fabio , Lagarde Michel , Prigent Annie-France , Adamo Sergio , Némoz Georges
Published: December 2004

TPA, a potent PKC activator, inhibits myogenic differentiation and activates phospholipase D (PLD). We evaluated the involvement of PLD in the TPA effects on L6 myoblasts differentiation. TPA, at concentrations inhibiting differentiation of L6 cells, induced a strong, though transient, PLD activation. Surprisingly, at nanomolar concentration, TPA induced both myogenic differentiation and sustained activation of PLD. Differential effect of TPA can be ascribed to PKC downregulation induced by highest TPA concentrations. TPA‐induced differentiation was inhibited by 1‐butanol, confirming the involvement of PLD in this effect. These data suggest that prolonged elevation of PLD activity is required for myogenic differentiation.
Low doses of reactive oxygen species protect endothelial cells from apoptosis by increasing thioredoxin‐1 expression
Authors: Haendeler Judith , Tischler Verena , Hoffmann Jörg , Zeiher Andreas M. , Dimmeler Stefanie
Published: December 2004

The redox regulator thioredoxin‐1 (Trx‐1) is required for the redox potential of the cell and exerts important functions in cell growth and apoptosis. Severe oxidative stress has been implicated in the oxidation of proteins and cell death. However, the role of low doses of reactive oxygen species (ROS) is poorly understood. Here, we show that 10 and 50 μM H2O2 and short‐term exposure to shear stress significantly increased Trx‐1 mRNA and protein levels in endothelial cells. Since it is known that Trx‐1 exerts anti‐apoptotic functions, we next investigated whether low doses of ROS can inhibit basal and serum‐depletion induced endothelial cell apoptosis. Indeed, treatment of endothelial cells with 10 and 50 μM H2O2 significantly reduced apoptosis induction. Reduction of Trx‐1 expression using an antisense oligonucleotide approach resulted in the induction of apoptosis and abolished the inhibitory effect of low doses of H2O2. Taken together, our results demonstrate that low doses of ROS act as signaling molecules and exert anti‐apoptotic functions in endothelial cells via upregulation of the redox‐regulator Trx‐1.
Hypoxia activates the capacity of tumor‐associated carbonic anhydrase IX to acidify extracellular pH
Authors: Švastová Eliška , Hulı́ková Alžbeta , Rafajová Monika , Zat'ovičová Miriam , Gibadulinová Adriana , Casini Angela , Cecchi Alessandro , Scozzafava Andrea , Supuran Claudiu T. , Pastorek Jaromı́r , Pastoreková Silvia
Published: December 2004

Acidic extracellular pH (pHe) is a typical attribute of a tumor microenviroment, which has an impact on cancer development and treatment outcome. It was believed to result from an accumulation of lactic acid excessively produced by glycolysis. However, metabolic profiles of glycolysis‐impaired tumors have revealed that CO2 is a significant source of acidity, thereby indicating a contribution of carbonic anhydrase (CA). The tumor‐associated CA IX isoform is the best candidate, because its extracellular enzyme domain is highly active, expression is induced by hypoxia and correlates with poor prognosis. This study provides the first evidence for the role of CA IX in the control of pHe. We show that CA IX can acidify the pH of the culture medium in hypoxia but not in normoxia. This acidification can be perturbed by deletion of the enzyme active site and inhibited by CA IX‐selective sulfonamides, which bind only to hypoxic cells containing CA IX. Our findings suggest that hypoxia regulates both expression and activity of CA IX in order to enhance the extracellular acidification, which may have important implications for tumor progression.
Stratum corneum‐derived caspase‐14 is catalytically active
Authors: Fischer Heinz , Stichenwirth Martin , Dockal Michael , Ghannadan Minoo , Buchberger Maria , Bach Juergen , Kapetanopoulos Andreas , Declercq Wim , Tschachler Erwin , Eckhart Leopold
Published: December 2004

Caspase‐14, a cysteine protease with restricted tissue distribution, is highly expressed in differentiated epidermal keratinocytes. Here, we extracted soluble proteins from stratum corneum (SC) of human epidermis and demonstrate that the extract cleaves tetrapeptide caspase substrates. The activity decreased to below 10% when caspase‐14 was removed by immunodepletion showing that caspase‐14 is the predominant caspase in SC. In contrast to normal SC, where caspase‐14 was present exclusively in its processed form, incompletely matured SC of parakeratotic skin from psoriasis and seborrheic dermatitis contained both procaspase‐14 and caspase‐14 subunits. Fractionation of extract from parakeratotic SC revealed that the peak caspase activity coeluted with processed caspase‐14 but not with procaspase‐14. Our results suggest that during regular terminal keratinocyte differentiation, endogenous procaspase‐14 is converted to caspase‐14 subunits that are catalytically active in the outermost layers of normal human skin.
Intégrer l’ELAO dans une classe de français,
deuxième langue étrangère, dans une université de province au Vietnam
Authors: TRÉPANIER JEAN-GUY , HUONG TRURONG LAN
Published: December 2004

Before implementing and/or adapting Computer Asisted Language Learning (CALL) materials, Vietnamese teachers of
French ought to examine the design (Warschauer & Healy) of whatever resources they are going to use in the classroom. But there
are certainly ways to test CALL documents with students, ahead of research results. We will suggest an avenue to introduce a CALL
model drawn from programs used in a western environment (Canada, France) which could be appropriately tailored to a regional
Vietnamese university, taking into account such constraints as program and facilities. We will present the outcomes of a
limited experimentation with students taking French for special purposes.
Mediating the digital divide in CALL classrooms: Promoting effective language
tasks in limited technology contexts
Authors: EGBERT JOY , YANG YU-FENG (DIANA)
Published: December 2004

This paper focuses on the divide at the classroom level in computer-assisted language learning (CALL)
that is centered on how those who have technology use it in the pursuit of effective language teaching and learning. This divide
is the result in part of the current emphasis on emerging technologies in the CALL literature and in CALL language teacher
development that seems to indicate that good CALL activities and lessons can only be carried out with the use of advanced
and cutting-edge technologies. The aim of this paper is twofold: (a) to argue that optimal language learning activities can
be supported by the use of ‘limited’ technologies, and (b) to present a framework for developing language
learning tasks in limited technology contexts. We do not suggest ways to bridge the digital divide that exists between
technology haves and have-nots. Instead, we focus on ways to provide effective language learning experiences in CALL
classrooms regardless of the technologies available. In doing so, we propose ways to work around the divide created by
the overemphasis on new technologies. We suggest that rather than lamenting the fact that our tools are not the latest and
greatest, we must pay attention to using the tools at hand to students’ best advantage while we look for ways to obtain
additional resources. We must also consider and collaborate with educators who have accepted the position that the use of
limited technology cannot be effective in supporting student learning or who do not know how to use their technology to present
students with effective opportunities. By addressing these issues in the literature and other forums, the digital divide in
CALL classrooms between good technology use and poor technology use can be bridged to the benefit of all.
Putting principles into practice
Authors: JAMIESON JOAN , CHAPELLE CAROL A. , PREISS SHERRY
Published: December 2004

CALL evaluation might ideally draw on principles from fields such as second language acquisition,
language pedagogy, instructional design, and testing and measurement in order to make judgments about criteria such as
elaborated input, feedback, collaborative learning, authentic tasks, navigation, screen design, reliability, validity,
impact, and practicality. In this study, a subset of criteria were used to evaluate the design of English as a second or
foreign language (ESL/EFL) online courses and assessments, Longman English Online. This article illustrates how a set of
principles suggested evaluation criteria which, in turn, suggested particular variables for the instructional design;
these variables, again in turn, suggested potential operationalizations which could be implemented as task features in
CALL materials. Results of the judgmental evaluation indicated that most of the criteria were met, although some better
than others.
Oral conversations online: Redefining oral competence in synchronous environments
Authors: LAMY MARIE-NOËLLE
Published: December 2004

In this article the focus is on methodology for analysing learner-learner oral conversations mediated by
computers. With the increasing availability of synchronous voice-based groupware and the additional facilities offered by
audio-graphic tools, language learners have opportunities for collaborating on oral tasks, supported by visual and textual
stimuli via computer-conferencing. Used synchronously with real-time voice-based work, these tools present learners with the
challenge of learning a new type of oral interaction, and researchers with the need for developing methodologies for redefining
L2 oral competence in these environments. In this paper we address the latter. We examine approaches from the interactionist
branch of Second Language Acquisition research, and we question the ability of this model of language learning to fully account
for the processes that take place when learners are interacting with machines while talking to each other. To complement the
socio-cognitive insights of that school, we look to interactional linguistics and to social semiotics. Building on findings
from these fields, we offer a qualitative discussion of the discourses evidenced in conversational data from two distance-learning
projects that use synchronous voice in conjunction with other stimuli, in an intermediate French programme at the UK Open
University. We then present detailed conclusions about the methodological challenges involved in analysing the oral
competence of students who use these tools.
Radial glia give rise to adult neural stem cells in the subventricular zone
Authors: Merkle Florian T. , Tramontin Anthony D. , García-Verdugo José Manuel , Alvarez-Buylla Arturo
Published: December 2004

Neural stem cells with the characteristics of astrocytes persist in the subventricular zone (SVZ) of the juvenile and adult brain. These cells generate large numbers of new neurons that migrate through the rostral migratory stream to the olfactory bulb. The developmental origin of adult neural stem cells is not known. Here, we describe a lox–Cre-based technique to specifically and permanently label a restricted population of striatal radial glia in newborn mice. Within the first few days after labeling, these radial glial cells gave rise to neurons, oligodendrocytes, and astrocytes, including astrocytes in the SVZ. Remarkably, the rostral migratory stream contained labeled migratory neuroblasts at all ages examined, including 150-day-old mice. Labeling dividing cells with the S-phase marker BrdUrd showed that new neurons continue to be produced in the adult by precursors ultimately derived from radial glia. Furthermore, both radial glia in neonates and radial glia-derived cells in the adult lateral ventricular wall generated self-renewing, multipotent neurospheres. These results demonstrate that radial glial cells not only serve as progenitors for many neurons and glial cells soon after birth but also give rise to adult SVZ stem cells that continue to produce neurons throughout adult life. This study identifies and provides a method to genetically modify the lineage that links neonatal and adult neural stem cells.
Structure of the streptococcal endopeptidase IdeS, a cysteine proteinase with strict specificity for IgG
Authors: Wenig Katja , Chatwell Lorenz , von Pawel-Rammingen Ulrich , Björck Lars , Huber Robert , Sondermann Peter
Published: December 2004

Pathogenic bacteria have developed complex and diverse virulence mechanisms that weaken or disable the host immune defense system. IdeS (IgG-degrading
e
nzyme of
Streptococcus pyogenes
) is a secreted cysteine endopeptidase from the human pathogen
S. pyogenes
with an extraordinarily high degree of substrate specificity, catalyzing a single proteolytic cleavage at the lower hinge of human IgG. This proteolytic degradation promotes inhibition of opsonophagocytosis and interferes with the killing of group A
Streptococcus
. We have determined the crystal structure of the catalytically inactive mutant IdeS-C94S by x-ray crystallography at 1.9-Å resolution. Despite negligible sequence homology to known proteinases, the core of the structure resembles the canonical papain fold although with major insertions and a distinct substrate-binding site. Therefore IdeS belongs to a unique family within the CA clan of cysteine proteinases. Based on analogy with inhibitor complexes of papain-like proteinases, we propose a model for substrate binding by IdeS.
Ultrarapid mixing experiments shed new light on the characteristics of the initial conformational ensemble during the folding of ribonuclease A
Authors: Welker Ervin , Maki Kosuke , Shastry M. C. Ramachandra , Juminaga Darmawi , Bhat Rajiv , Scheraga Harold A. , Roder Heinrich
Published: December 2004

The earliest folding events in single-tryptophan mutants of RNase A were investigated by fluorescence measurements by using a combination of stopped-flow and continuous-flow mixing experiments covering the time range from 70 μs to 10 s. An ultrarapid double-jump mixing protocol was used to study refolding from an unfolded ensemble containing only native proline isomers. The continuous-flow measurements revealed a series of kinetic events on the submillisecond time scale that account for the burst-phase signal observed in previous stopped-flow experiments. An initial increase in fluorescence within the 70-μs dead time of the continuous-flow experiment is consistent with a relatively nonspecific collapse of the polypeptide chain whereas a subsequent decrease in fluorescence with a time constant of ≈80 μs is indicative of a more specific structural event. These rapid conformational changes are not observed if RNase A is allowed to equilibrate under denaturing conditions, resulting in formation of nonnative proline isomers. Thus, contrary to previous expectations, the isomerization state of proline peptide bonds can have a major impact on the structural events during early stages of folding.
The bacteriophage T4 late-transcription coactivator gp33 binds the flap domain of
Escherichia coli
RNA polymerase
Authors: Nechaev Sergei , Kamali-Moghaddam Masood , André Estelle , Léonetti Jean-Paul , Geiduschek E. Peter
Published: December 2004

Transcription of bacteriophage T4 late genes requires concomitant DNA replication. T4 late promoters, which consist of a single 8-bp –10 motif, are recognized by a holoenzyme containing
Escherichia coli
RNA polymerase core and the T4-encoded promoter specificity subunit, gp55. Initiation of transcription at these promoters by gp55-holoenzyme is inefficient, but is greatly activated by the DNA-loaded DNA polymerase sliding clamp, gp45, and the coactivator, gp33. We report that gp33 attaches to the flap domain of the
Escherichia coli
RNA polymerase β-subunit and that this interaction is essential for activation. The β-flap also mediates recognition of –35 promoter motifs by binding to σ
70
domain 4. The results suggest that gp33 is an analogue of σ
70
domain 4 and that gp55 and gp33 together constitute two parts of the T4 late σ. We propose a model for the role of the gp45 sliding clamp in activation of T4 late-gene transcription.
Diffusion of nucleoside triphosphates and role of the entry site to the RNA polymerase II active center
Authors: Batada Nizar N. , Westover Kenneth D. , Bushnell David A. , Levitt Michael , Kornberg Roger D.
Published: December 2004

Nucleoside triphosphates (NTPs) diffuse to the active center of RNA polymerase II through a funnel-shaped opening that narrows to a negatively charged pore. Computer simulation shows that the funnel and pore reduce the rate of diffusion by a factor of ≈2 × 10
–7
. The resulting limitation on the rate of RNA synthesis under conditions of low NTP concentration may be overcome by NTP binding to an entry site adjacent to the active center. Binding to the entry site greatly enhances the lifetime of an NTP in the active center region, and it prevents “backtracking” and the consequent occlusion of the active site.
Pace and differentiation in the Literacy Hour: some outcomes of an analysis of transcripts
Authors: Eke Richard , Lee John
Published: December 2004

This article discusses the detailed analysis of utterances in two classes where the pedagogy enshrined in the UK government's Literacy Strategy was followed. The pedagogy is set out in The National Literacy Strategy: framework for teaching (DFEE, 1998) which provides termly objectives for each year for word, sentence level and text work. General evaluations of the strategy are discussed in the context of scrutiny, undertaken by researchers, of what was happening in classrooms. Following a brief discussion of methodological issues, a framework for the analysis of the pedagogic discourse of the Literacy Hour is outlined. This framework is applied to transcripts from two classrooms. A discussion of the data, focusing on issues of gender, of pupils with special educational needs, and of pace, offers tentative analysis of what is currently happening in English primary schools. The making of a 'reduced' curriculum experience for pupils with special educational needs and of the differentiated curriculum for boys and girls are illustrated. Issues of the pace of the lesson for different groups and implications for literacy teaching are discussed.
Curriculum reform in post‐Soviet Kyrgyzstan: indigenization of the history curriculum
Authors: Ismailova Baktygul
Published: December 2004

This article raises general questions regarding the relations between curriculum and ideology in reforming, specifically indigenizing the curriculum by focusing on the importance attached to the history curriculum under reform circumstances. Through an examination of indigenization of history curriculum in the context of Kyrgyzstan, a post‐Soviet republic in Central Asia, it offers a description and understanding of particular forces, interests and circumstances that surround the curriculum design process. It discusses indigenization as a political, social and cultural process, which emerges as a response to a long‐term domination, neglect and denigrtation by the colonial regimes and powerful groups of the culture, languages and traditions of the indigenous people. Based on the declonization experiences of other formerly colonized nations, the article explores the implications of indigenization of curriculum for learners. It also discusses the recent educational and pedagogical practices, which have emerged to address implications of indigenization for the curriculum users, resolve its limitations and to establish new, more inclusive visions for curriculum design. The analysis is constructed on the basis of the review of relevant theoretical literature, newspaper and journal articles, history textbooks and other learning materials used in schools and universities.