bluuebunny/crossref_metadata_2025 huggingface dataset:
DARK ENERGY MODELS WITH A TIME-DEPENDENT GRAVITATIONAL CONSTANT
Authors: RAY SAIBAL , MUKHOPADHYAY UTPAL , CHOUDHURY S. B. DUTTA
Published: December 2007

Two phenomenological models of Λ, viz. [Formula: see text] and [Formula: see text], are studied under the assumption that G is a time-variable parameter. Both models show that G is inversely proportional to time, as suggested earlier by others, including Dirac. The models considered here can be matched with observational results by properly tuning the parameters of the models. Our analysis shows that the [Formula: see text] model corresponds to a repulsive situation and hence correlates with the present status of the accelerating Universe. The other model, [Formula: see text], is in general attractive in nature. Moreover, it is seen that due to the combined effect of time-variable Λ and G the Universe evolved with acceleration as well as deceleration. Deceleration indicates a "big crunch".
THERMODYNAMICS OF ROTATING BLACK BRANES IN GAUSS–BONNET–BORN–INFELD GRAVITY
Authors: DEHGHANI M. H. , HENDI S. H.
Published: December 2007

Considering both the Gauss–Bonnet and the Born–Infeld terms, which are on a similar footing with regard to the string corrections on the gravity and electrodynamics sides respectively, we present a new class of rotating solutions in Gauss–Bonnet–Born–Infeld gravity with k rotation parameters. Although these solutions are not real in the whole space–time, they can be made real by a suitable transformation. Depending on the metric parameters, these real solutions may be interpreted as black brane solutions with inner and outer event horizons, an extreme black brane or naked singularity. We calculate the finite action and conserved quantities of the solutions by using the counterterm method, and find that these quantities do not depend on the Gauss–Bonnet parameter. We also compute the temperature, the angular velocities, the electric charge and the electric potential. Then, we calculate the entropy of the black brane through the use of the Gibbs–Duhem relation and show that it obeys the area law of entropy. We obtain a Smarr-type formula for the mass as a function of the entropy, the angular momenta and the charge, and show that the conserved and thermodynamic quantities satisfy the first law of thermodynamics. Finally, we perform a stability analysis in both the canonical and the grand-canonical ensemble and show that the presence of a nonlinear electromagnetic field has no effect on the stability of the black branes, which are stable in the whole phase space.
THE BIANCHI TYPE I MODEL WITH TWO INTERACTING SCALAR FIELDS
Authors: FOLOMEEV VLADIMIR
Published: December 2007

The flat anisotropic model of the early Universe is considered. Two interacting scalar fields with a special form of potential energy are a source of matter fields. Analytic solutions for stages of inflation and preheating are found. It is shown that the solutions tend asymptotically to an isotropic Friedmann model.
MODELING SEMANTIC CONCEPTS AND USER PREFERENCES IN CONTENT-BASED VIDEO RETRIEVAL
Authors: CHEN SHU-CHING , ZHAO NA , SHYU MEI-LING
Published: December 2007

In this paper, a user-centered framework is proposed for video database modeling and retrieval to provide appealing multimedia experiences on the content-based video queries. By incorporating the Hierarchical Markov Model Mediator (HMMM) mechanism, the source videos, segmented video shots, visual/audio features, semantic events, and high-level user perceptions are seamlessly integrated in a video database. With the hierarchical and stochastic design for video databases and semantic concept modeling, the proposed framework supports the retrieval for not only single events but also temporal sequences with multiple events. Additionally, an innovative method is proposed to capture the individual user's preferences by considering both the low-level features and the semantic concepts. The retrieval and ranking of video events and the temporal patterns can be updated dynamically online to satisfy individual user's interest and information requirements. Moreover, the users' feedbacks are efficiently accumulated for the offline system training process such that the overall retrieval performance can be enhanced periodically and continuously. For the evaluation of the proposed approach, a soccer video retrieval system is developed, presented, and tested to demonstrate the overall retrieval performance improvement achieved by modeling and capturing the user preferences.
SPOKEN DOCUMENT SUMMARIZATION BASED ON DYNAMIC TIME WARPING AND WAVELETS
Authors: GUIDO RODRIGO CAPOBIANCO , JUNIOR SYLVIO BARBON , VIEIRA LUCIMAR SASSO , SANCHEZ FABRÍCIO LOPES , MACIEL CARLOS DIAS , SCALASSARA PAULO ROGÉRIO , PEREIRA JOSÉ CARLOS , PUIA VITOR MULLER
Published: December 2007

This work presents a spoken document summarization (SDS) scheme that is based on an improved version of the Dynamic Time Warping (DTW) algorithm, and on the Discrete Wavelet Transform (DWT). Tests and results with sentences extracted from TIMIT speech corpus show the efficacy of the proposed technique.
Thermochronological (
40
Ar/
39
Ar) evidence of Early Palaeozoic basin inversion within the southern Prince Charles Mountains, East Antarctica: implications for East Gondwana
Authors: Phillips Glen , Wilson Christopher J.L. , Phillips David , Szczepanski Stan K.
Published: December 2007

40
Ar/
39
Ar systematics within metasedimentary rocks exposed in the southern Prince Charles Mountains, East Antarctica, were thermally reset during a period of Early Palaeozoic (between 524 ± 1 Ma and 486 ± 2 Ma) orogenesis. This event affected three temporally distinct (Archaean to Neoproterozoic) stratigraphic levels that are now exposed in the upper crust. In the structural record, evidence of orogenesis during Early Palaeozoic times is preserved as late-stage, subvertical mylonite zones in the Archaean orthogneiss–metasedimentary basement and thin-skinned folding and thrusting of the overlying Neoproterozoic metasedimentary rocks. Synchronous cooling ages, contrasting structural styles and similar peak metamorphic conditions are interpreted as reflecting basement-involved thin-skinned deformation that was the result of inversion of a Neoproterozoic basin. The presence of pre-existing crustal heterogeneities is the mechanism that localized Early Palaeozoic orogenesis within the region. This interpretation differs from previous models that attribute Early Palaeozoic orogenesis within the southern Prince Charles Mountains to a collisional tectonic setting. An Early Palaeozoic intra-cratonic setting for the region suggests that amalgamation between India and Antarctica was likely to have occurred prior to the final construction of Gondwana.
Crustal melting and melt extraction, ascent and emplacement in orogens: mechanisms and consequences
Authors: Brown Michael
Published: December 2007

Significant volume of wet melting requires an influx of H
2
O-rich volatile phase. In hydrate-breakdown melting, initial melt accumulation is diffusion-controlled and melt accumulates around peritectic phases in low-pressure sites. As the melt-bearing rock weakens, it becomes porous at a few volume per cent melt, initiating an advective flow regime; as melt volume reaches the melt connectivity transition, melt may be lost from the system in the first of several melt-build-up–melt-loss events. Using mineral equilibria modelling, major and accessory phase controls on melt chemistry are evaluated. In residual migmatites and granulites, microstructures indicate the former presence of melt whereas leucosome networks record melt extraction pathways. Sites of initial melting nucleate shear instabilities; strain and anisotropy of permeability control the form of millimetre- to centimetre-scale inferred melt channels and strong anisotropy promotes high fluid focusing. Focused melt flow occurs by dilatant shear failure of low melt volume rocks, which leads to the formation of melt flow networks allowing accumulation and storage of melt, and forming the link for melt flow from grain boundaries to ascent conduits. Melt ascent is via ductile fractures, which may propagate from dilation or shear bands. Fractures are characterized by blunt tips; also they may exhibit zigzag geometry close to the tips and petrographic continuity between leucosome in the host and granite in the dyke. Horizontal tabular and wedge-shaped intrusions commonly are associated with the brittle–ductile transition zone. Vertical lozenge-shaped intrusions represent congelation of magma in ascent conduits and blobby plutons record lateral expansion localized by instability; these intrusion types characterize emplacement at deeper levels in the crust.
The Khaviz Anticline: an outcrop analogue to giant fractured Asmari Formation reservoirs in SW Iran
Authors: Wennberg O. P. , Azizzadeh M. , Aqrawi A. A. M. , Blanc E. , Brockbank P. , Lyslo K. B. , Pickard N. , Salem L. D. , Svånå T.
Published: December 2007

The carbonate reservoirs in the Late Oligocene—Early Miocene Asmari Formation in the Dezful Embayment of SW Iran are characterized by low matrix permeability, and effective drainage is dependent on the occurrence of open fractures. Limited information on fracture orientation and fracture density is available from core and borehole image data, and high-quality/high-resolution three-dimensional seismic is often lacking in this area. Well and core data do not contain information on important fracture parameters like length distribution, crosscutting relationships, fracture density v. lithology and bed thickness. The understanding of fracture distribution and formation in the region and their effects on fluid flow has been greatly improved by the use of outcrop analogue data. Exposures of the Asmari Formation in the Khaviz Anticline are in close vicinity to the giant hydrocarbon fields. The Khaviz Anticline has a similar geometry and structural history to the major hydrocarbon fields in the area, and represents an excellent analogue for these. Two types of fracture features were observed: diffuse fracturing and fracture swarms. The diffuse fractures form networks and comprise structures grouped into four fractures sets, which are the typical for this type of anticline. Two orthogonal fracture sets are oriented parallel and perpendicular to the fold axis, and two conjugate fracture sets are oblique to the fold axis with their obtuse angle intersecting the trend of the fold axis. The fractures are typically stratabound, sub-perpendicular to bedding and commonly about the bounding stratigraphic surfaces. To a large extent the density and height of fractures in the Asmari Formation are controlled by the mechanical stratigraphy, which is controlled by the depositional environment and cycles. These outcrop data have been essential in the generation of discrete fracture network (DFN) models and the population of the fracture properties in the reservoir models.
Using VSP surveys to bridge the scale gap between well and seismic data
Authors: Emsley S. J. , Shiner P. , Enescu N. , Beccacini A. , Cosma C.
Published: December 2007

This case study was undertaken for a low-porosity fractured carbonate reservoir with a complex fracture network resulting from several phases of tectonic activity. The integration of the image log and seismic-derived interpretations was problematic due to the complexity of the image log signature and the variable quality of the surface seismic data. Earlier experience indicated that VSPs may provide information on faulting and/or fracturing that may otherwise be difficult to determine with confidence from other data sources. Consequently, specialist VSP processing techniques were used to identify and map reflectors in three-dimensional space. Data acquired in two wells were reprocessed to interpret structural features and determine their geometries. The interpreted VSP reflectors were validated and integrated with the analyses of image logs and the interpretation of surface seismic data providing a constrained structural model that allowed the interpretation of seismic data away from well control and provided a starting point for seismic interpretation in areas where structural geometries were poorly imaged on surface seismic. It is shown that VSP, including vertical incidence, data can contribute to the understanding of reservoirs and enables well-derived information to be extrapolated away from the wells.
Study of fracture-induced anisotropy from discrete fracture network simulation of well test responses
Authors: Leckenby R. J. , Lonergan L. , Rogers S. F. , Sanderson D. J.
Published: December 2007

Different conceptualizations of fracture networks have been generated in order to simulate well tests in fractured reservoirs. These models have two purposes: firstly to investigate whether the behaviour of realistic fracture networks can be emulated with more simple models; and secondly to assess whether different sources of anisotropy have characteristic and recognizable influences on the pressure derivative. The anisotropy of the fracture networks was increased by decreasing the angle between two originally orthogonal fracture sets, and by increasing the permeability contrast between two orthogonal fracture sets. Results indicate that simple models can capture the first-order behaviour of more realistic examples. However because early time data are strongly influenced by the connectivity of the fracture network, the degree of anisotropy can only be assessed at later times in a test. Increasing anisotropy results in increasing heterogeneity and compartmentalization, and permeability anisotropy in an orthogonal system can only partially replicate the behaviour of a geometrically anisotropic system.
A surface-subsurface study of reservoir-scale fracture heterogeneities in Cretaceous carbonates, North Oman
Authors: De Keijzer M. , Hillgartner H. , Al Dhahab S. , Rawnsley K.
Published: December 2007

Reservoir-scale structural heterogeneity, especially in terms of mechanical layering and natural fracture systems, is often insufficiently constrained by subsurface data alone. In North Oman, a large dataset in Cretaceous carbonates comprises data from multiple subsurface reservoirs and analogue outcrops. This provides an ideal opportunity to integrate outcrop constraints into the subsurface, and to calibrate the resulting models dynamically. For this purpose, a reservoir-scale analogue outcrop fracture template was created for the Jebel Madmar anticline in the Oman Mountains foothills. The outcrop template provides improved conceptual and quantitative constraints on (i) fracture types and dimensions (e.g. of NE-trending fracture corridors), (ii) fracture heterogeneity, both aerially and stratigraphically, (iii) fracture properties (e.g. cementation evolution, variations due to preferential fault/fracture reactivation) and (iv) structural evolution and history of reactivation. Within a regionally consistent structural framework, the outcrop template has greatly assisted in the creation of geologically realistic models for one of the fractured carbonate reservoirs, complementing the subsurface dataset. Initial dynamic calibration indicates successful application of the outcrop template in that the spatial fracture heterogeneity was succesfuUy captured in the reservoir models and provides a history match to production data. The reduced range of possible fracture system geometries in turn has provided better constraints on the effective fracture properties.
The rediscovery of an ancient exploitation site of Piperno, a valuable historical stone from the Phlegraean Fields (Italy)
Authors: Calcaterra D. , Cappelletti P. , De' Gennaro M. , De Gennaro R. , De Sanctis F. , Flora A. , Langella A.
Published: December 2007

This paper reports the research results over several years on Piperno, the most important ornamental architectural stone of Naples. Particular attention is paid to the rediscovery of the old exploitation sites of this rock and to the survey of the last underground quarry site, still accessible, at the base of the Camaldoli Hill (western Naples) at Pianura. The conservation state was assessed by means of specific surveys in view of possible futu
re utilization. At present, the re-opening of abandoned quarries is not possible owing to unsafe site conditions. The cultural relevance of the Pianura quarry site could suggest its possible restoration as a museum of mining and a centre for teaching the working of ornamental stone within the Campania Region.
Post-depositional modification of atmospheric dust on a granite building in central Rio de Janeiro: implications for surface induration and subsequent stone decay
Authors: Smith B. J. , McAlister J. J. , Baptista Neto J. A. , Silva M. A. M.
Published: December 2007

Extensive contour scaling of a 200 year old granite church is associated with the breaching of an apparently iron-rich crust and the widespread deposition of atmospheric dust within the canyon-like streetscape of Rio de Janeiro. Contemporary dust, accumulated dust from within a depression on the building surface, the surface crust and the underlying granite are examined by a combination of total element analysis and sequential extraction, X-ray diffraction and energy dispersive X-ray fluorescence. Results indicate an increase in total organic carbon and marked decrease in pH within the accumulated dust, and a rapid mobilization of anions and cations from the water-soluble and carbonate phases. It is considered that the latter is linked to salt accumulation within and eventual salt weathering of the granite. Post-depositional alteration of the dust is also linked with the de-silicification of clay minerals (illite to kaolinite) and the loss of silica from the amorphous Fe/Mn phase of the accumulated dust under the initially saline and progressively more acidic conditions experienced at the stone-atmosphere interface. This mobilization of silica is associated with the formation of what is, in effect, a thin silica-rich surface crust or glaze. Within the glaze, accessory amounts of extractable iron are concentrated within the amorphous and crystalline Fe/Mn phases at levels that are significantly elevated with respect to the underlying granite, but much lower than in the equivalent phases of the accumulated dust from which it is principally assumed to derive. The protection afforded to the stonework by the crust is not, however, permanent and within the last 15 years it has been possible to observe a rapid increase in the surface delamination of the church close to street level.
Geomythology: geological origins of myths and legends
Authors: Vitaliano Dorothy B.
Published: December 2007

Myths and geology are related in several ways. Some myths are the result of man's attempts to explain noteworthy features of his environment, such as striking landforms or unusual smaller features, whereas others try to account for conspicuous natural processes, such as earthquakes, volcanic phenomena, and floods. Local myths have sometimes proved helpful in solving geological problems, and even the geological nomenclature is indebted to mythology. Examples of each kind of relationship are given.
Geo-mythology of India
Authors: Chandrasekharam D.
Published: December 2007

In all the Indian legends, whether it is the Ramayana or Mahabharata, one can find embedded elements of geological processes. Perhaps due to the lack of a sound scientific basis for recognizing geological processes in ancient Indian civilization, such processes were believed to be the acts of ‘Gods’ (Suras) and ‘Demons’ (Asuras) and hence they formed an integral part of these legends. Even in the present age where science is able to explain several geological processes, the Hindu faith is such that these myths and legends continue to be passed on to succeeding generations. The fact that these geological processes are contained in these epics helps to sustain truth (dharma) and maintain harmony. Ancient Indian civilization adopted this doctrine and its continuance will remain a fresh and vital part of future generations in India.
The Fenris Wolf in the Nordic Asa creed in the light of palaeoseismics
Authors: Mörner N.-A.
Published: December 2007

The Nordic Asa Creed talks about a giant wolf, ‘the Fenris Wolf’, that was trapped and chained deep in the mountains. When he howled, the ground trembled violently and fractured. With the discovery of frequent high-magnitude palaeoseismic events in Sweden not only in de-glacial time but also in Late Holocene time, it seems both natural and logical that the Fenris tale refers to frightening earthquake events in the past. Once again tales and sagas have been shown to be rooted in facts.
Sooty sweat stains or tourmaline spots? The Argonauts on the Island of Elba (Tuscany) and the spread of Greek trading in the Mediterranean Sea
Authors: Dini Andrea , Corretti Alessandro , Innocenti Fabrizio , Rocchi Sergio , Westerman David Scott
Published: December 2007

In various ancient authors (e.g. the ‘Argonautika’ of Apollonios Rhodios) curious news about the Island of Elba can be found, concerning the existence, somewhere on the shore near Portoferraio, of pebbles that are ‘dirty’ from the Argonauts' sweat. The Argonauts are said to have stopped on the island during their journey back from the looting of the ‘Golden Fleece’. These pebbles are found to be typical of the gravelly beaches below the Capo Bianco cliffs. Such walls are made up of a bony-white aplitic rock dotted with blue-black tourmaline spots. Capo Bianco aplite is the uncommon result of the solidification of a boron-rich magma in a subvolcanic setting. Here, the separation of a boron-rich fluid phase gave way to the crystallization of peculiar spherical dark tourmaline clots in a very fine-grained white groundmass. This rock was noted by Argonauts (i.e. the ancient travellers they represent) and used as a lighthouse to the harbour of Argoos limen (now Portoferraio). Also in the myth, the unique mottled pebbles were recorded as stained by the Argonauts' sweat. The occurrence, within the same, complex myth, of ‘data’ concerning navigation (the white cliffs) and geology (description of the spotted aplite) identify the Argonauts as a blending of mineral prospectors, explorers and early eighteenth century-like naturalists, legitimatizing the commercial/political presence of Greeks in the region.
On the discovery of the ice age: science and myth
Authors: Berger W. H.
Published: December 2007

The discovery of the ice ages began with the invention of the Great Ice Age by Louis Agassiz, in the first half of the nineteenth century. His ideas were shaped by the interpretation of skeletons and frozen remains of large mammals found in Siberia, at the beginning of the nineteenth century. The concept of the Great Ice Age stands in contrast to earlier notions emphasizing widespread flooding, notions that owed much to the Great Flood described in the Bible, and which gave rise to geological terms such as ‘diluvial deposits’ and ‘glacial drift’. Nordic myth as recorded in Iceland during the Middle Ages likewise contains observations and interpretations concerning the remains of giant animals emerging from frozen ground and makes reference to large-scale flooding. The ancient cosmogony related by Icelandic poets postulates the former existence of a kingdom of ice, represented by a primeval Ice Giant, whose rule is ended by the newly emerged gods. According to the myth, the melting of ice (the blood of the dying Giant) caused widespread flooding that killed the large creatures abundant during ice time.
Siluro-Devonian Alpine reefs and pavements
Authors: Hubmann Bernhard , Suttner Thomas
Published: December 2007

Palaeozoic sediments of Austria are separated by the Periadriatic Fault into Eastern Alpine (Upper, Middle and Lower Austroalpine) and Southern Alpine units. We herein present six case studies showing up the different development of shallow-marine communities with special regard to carbonate factories and shell pavements occurring in both regions during the Siluro-Devonian time span. Upper Silurian—Upper Devonian deposits of the Eastern Alps comprise accumulations of serpulid tubes (Southern Burgenland) and
Septatrypa
pavements,
Amphipora
mounds, coral-stromatoporoid—biostromes and
Stachyodes
—auloporoid beds regarded as pioneer reef communities (Graz Palaeozoic), respectively. Lower Silurian strata of the Southern Alps consist of pelagic sediments persisting to the Upper Silurian and therefore differ from contemporaneous successions in the Eastern Alps. Intercalated in Ludlow orthocerid limestone beds
Cardiola
pavements appear (Carnic Alps). Within the Lower Devonian sequence, mounds were built by baffling calcareous algae and tabulozoan communities. Coral-stromatoporoid patch reefs occur during the Pragian, Givetian and Frasnian stages.
Sedimentology and magnetic susceptibility of the Upper Eifelian-Lower Givetian (Middle Devonian) in SW Belgium: insights into carbonate platform initiation
Authors: Mabille Cédric , Boulvain Frédéric
Published: December 2007

The major part of the Hanonet Formation is deposited on a mixed siliciclastic—carbonate detrital ramp, whereas the top is dominated by carbonate-rimmed shelf-related sedimentation. The transition corresponds roughly to the Eifelian—Givetian boundary. This work is based on two stratigraphic sections located in the southern part of the Dinant Synclinorium. Petrographic study leads to the definition of 11 microfacies, which demonstrate important sedimentological differences existing between the sections. A curve showing microfacies evolution is interpreted in terms of changing bathymetry. An environmental model depicts the lateral transition from a multiclinal carbonate ramp (to the east) to a fore-reef setting (to the west). Magnetic susceptibility was used to establish accurate stratigraphic correlations between the two sections. It also leads to an appreciation of the relative importance of eustatic sea-level change and local sedimentation rate. The combined interpretation of the microfacies curves and the magnetic susceptibility provides a new view of the sedimentary dynamics of the studied sections and, in a more general way, a better understanding of the processes responsible for magnetic susceptibility variations in carbonate rocks.
Permian reef and shelf carbonates of the Arabian platform and Neo-Tethys as recorders of climatic and oceanographic changes
Authors: Weidlich Oliver
Published: December 2007

The present study provides an example of how Permian benthic carbonate production is controlled by oceanographic factors and climate. After the Permo-Carboniferous glaciation, shallow-marine benthic carbonate production exhibits strikingly different temporal and spatial patterns on the eastern Arabian plate and on isolated platforms of the SW Neo-Tethys. Close to the SE margin of the Arabian plate in the Haushi area, Cisuralian (late Sakmarian-early Artinskian) mixed carbonate-siliciclastic deposits of the Saiwan Formation and Guadalupian (Wordian) marl-carbonate alterations of the Khuff Formation are characterized by dominance of crinoids, brachiopods, bivalves and bryozoans. Scarcity of calcareous algae and zooxanthellate invertebrates indicate that members of the heterozoan association (bryonoderm facies) were responsible for carbonate production. Guadalupian carbonates of the Khuff Formation in the Haushi area show striking compositional differences to lateral equivalents in the subsurface where photozoan carbonates dominate. Contemporaneous carbonates of the Saiq Formation from the Saih Hatat (Oman Mountains) exhibit a twofold composition: siliciclastic sediments contain small tabulate corals of the heterozoan association. Most of the formation is carbonate of the photozoan association with fusulinaceans, smaller foraminifers, calcareous algae, rugose corals and aggregate grains. Lopingian carbonates of the Saiq Formation (Saih Hatat) are dominated by heterozoan carbonate production with crinoids, chaetetids, bryozoans and brachiopods, and resemble heterozoan bryonoderm carbonates. Shallow-water reef carbonates of the Neo-Tethys, preserved as blocks in the Ba'id area (Oman Mountains) and the Batain coast, are contrasting: in the Ba'id area Late Cisuralian-Early Lopingian blocks of photozoan carbonates have been found, containing calcareous sponges, rugose corals, richthofeniid brachiopods and calcareous algae. Cisuralian blocks from the Batain coast are very similar to the heterozoan bryonoderm facies, while Guadalupian reef blocks show striking similarities to photozoan chlorosponge associations.

Combining climate modelling data with outcrop data, dominance of heterozoan carbonate production along the rim of Arabian plate and the Neo-Tethys can be explained by cool water during the Cisuralian and local upweUing of nutrient-rich water during the Guadalupian. Formation of Lopingian heterozoan carbonates of the Saiq Formation is least understood but could be the consequence of upwelling of saline and nutrient-rich oceanic bottom water. Comparing the ecological complexity of reefs, chlorosponge reefs built complex frameworks with a variety of ecological niches, if encrusters are present, whereas heterozoan reef communities are comparatively simple in their structure.
North Atlantic contourite sand channels
Authors: Akhmetzhanov A. , Kenyon N. H. , Habgood E. , Van Der Mollen A. S. , Nielsen T. , Ivanov M. , Shashkin P.
Published: December 2007

Two sand-rich channelized depositional systems, formed by strong contour currents, were studied west of the Faeroe Bank Channel and in the Gulf of Cadiz. Both are areas beyond the exit of constrictions where water overflows from the Norwegian Sea and the Mediterranean Sea, respectively. West of the Faeroe Bank, newly mapped channels are developed mainly under the influence of a geostrophic current and are characterized by significant lateral migration, which determines the marked cross-sectional asymmetry and the architecture of the deposits. The pathways of the Mediterranean Undercurrent in the Gulf of Cadiz are complex, with the greater proportion flowing under geostrophic conditions along a terrace but with some of the denser water becoming ageostrophic and descending downslope owing to gravity. A series of ‘peel-off’ channels is formed, with the largest one, Gil Eanes, being about 40 km long. Most of the channel fills consist of medium-coarse sand. Levees are mainly silts with a higher sand content in the vicinity of the channel. Both depositional systems have a variety of contourite sand channels, which in most respects are remarkably similar. In both cases there are stretches where the flow is ageostrophic, with water descending downslope for as much as 400 m before resuming geostrophic flow at deeper levels. In each case the main pathway of the densest water is the shallowest and several branches turn off to the left of this main pathway before bending to the right under the influence of Coriolis forces. In both cases there are channel fills of medium-coarse sand, probably cross-bedded, and up to 200 ms thick. Sheets of sand with a thickness of a few metres to a few tens of metres are common. Similarities to turbidite channels are the aggradational nature of some channel floors and the flanking muddy or silty sediment waves. Contourite channel depositional complexes are distinguished from turbiditic ones by their coarsening-up rather than fining-up sand units, the asymmetry in channel architecture, the presence of regional unconformities, and the distribution pattern with well-marked boundaries of current-derived deposits.
Quaternary evolution of the contourite depositional system in the Gulf of Cadiz
Authors: Llave E. , Hernández-Molina F. J. , Somoza L. , Stow D. A. V. , Díaz Del Río V.
Published: December 2007

This paper provides for the first time a detailed vertical and spatial representation of Quaternary evolution of the contourite depositional system (CDS) in the Gulf of Cadiz, based on the results of careful morphological, structural and stratigraphic analyses using high-resolution seismic reflection profiles as well as oil company borehole data, and piston and gravity cores. Different drifts observed on the stratigraphic architecture allow us to propose a regional Quaternary evolution for the whole system, in which three major stages can be identified. (1) In the Early Pleistocene to Mid-Pleistocene, the CDS was mainly dominated by depositional processes, where the upper and lower cores of the Mediterranean Outflow Water (MOW) generated the mounded elongated Cadiz—Faro—Albufeira drift in the transition between the middle and upper slope, and the equivalent Huelva—Guadalquivir drift on the middle slope. During this stage the main erosive features were established close to the Strait of Gibraltar. (2) In the Mid-Pleistocene to Late Pleistocene, two important changes in the CDS took place. One occurred at the transition between the middle and upper slope, related to a change in the upper branch of the MOW, when a mixed drift began to develop, burying the eastern part of the Cadiz-Faro-Albufeira mounded elongated and separated drift. The second change is observed on the central area of the middle slope, related to the lower branch of the MOW, where a large contourite channel (the Guadalquivir channel) progressively eroded the western part of the mounded Huelva-Guadalquivir drift. Laterally an extensive sheeted drift buried the previous mounded deposits. (3) In the Late Pleistocene to Holocene, in the northern area of the CDS, a plastered drift started to be developed in the transitional zone between the upper and middle slope. On the middle slope, the mounded elongated Huelva-Guadalquivir drift was not developed and more erosive processes became dominant as the lower core of the MOW intensified. In the sector close to the Straits of Gibraltar, a field of broad seabed forms was generated. These three evolutionary stages have been controlled by tectonics, including recent diapiric movement, Guadalquivir Bank uplift, and reactivation along several fault systems and anticline-syncline structures. Tectonics has been a key factor in the sea-floor morphological changes, which has caused new pathways for the core and branches of the MOW, and consequently has produced the contourite stratigraphic and architectural changes. Superimposed on these tectonic changes, both climatic and eustatic changes during the Quaternary (but especially from the Mid-Pleistocene) have controlled the development of vertical contourite stratigraphy. The general conclusion of this study is that the contourite depositional system of the Gulf of Cadiz has changed from a dominantly depositional system to a dominantly erosive one during the Quaternary.
Ridge and valley systems in the Upper Cretaceous chalk of the Danish Basin: contourites in an epeiric sea
Authors: Esmerode E. V. , Lykke-Andersen H. , Surlyk F.
Published: December 2007

Extensive low-lying parts of the NW European craton were flooded during the Late Cretaceous transgression, creating a relatively deep epeiric sea with reduced supply of siliciclastic material and insignificant coastal upwelling. The chalk, essentially an oceanic sediment type, was deposited as a pelagic rain of mainly coccolith debris and with local redeposition along structural highs. The study area is located in the eastern part of the Danish Basin, where the bordering Ringkøbing-Fyn High and the inverted Sorgenfrei-Tornquist Zone converge. Multichannel seismic reflection lines show the Chalk Group to be far from the expected flat-lying pelagic succession. A multitude of features of considerable relief, comprising an extensive unconformity, sediment waves, drifts and moats, are recognized. At least two episodes of widespread drift deposition are identified, one in the Santonian-Late Campanian and one in the Maastrichtian, separated by a Top Campanian Unconformity. The structures were formed by strong bottom currents flowing northwestward through the basin parallel to bathymetric contours. A lateral northeastward change, from more depositional to more erosional architecture, indicates a positive current velocity gradient towards the inversion zone, probably as a result of the Coriolis force. The strong similarity between the chalk drifts and modem contourite deposits supports the proposal that the oceanographic conditions linked to continental margins were extended into the Late Cretaceous epeiric sea of NW Europe.
Are there Middle Jurassic contourites in the Tarnovo depression (Southern Moesian platform margin)?
Authors: Georgiev George , Botoucharov Nikola
Published: December 2007

The first boreholes in the Tarnovo depression, located in the central Southern Moesian platform margin zone (Bulgaria), drilled at the end of the 1970s, display intervals of unusually thin, irregular and lens-like interbedding of shales and siltstones in the Middle Jurassic succession. Their specific lithological, log and seismic features, which resemble or distinguish them from contourites, have been studied and described in detail. The depositional setting in the Tarnovo depression during the Late Aalenian-Early Bajocian was favourable for the accumulation of deeper-water sediments, influenced by bottom currents. These were deposited along the hanging walls of major growth faults, which have a decisive geodynamic importance for Early-Middle Jurassic basin evolution throughout the Southern Moesian platform margin zone. Some lithological characteristics of the studied sediments correspond to diagnostic criteria for contourites. However, some other features, such as tractive indications, thin fine-grained laminae and wavy facies alternation, are also indicative of fine-grained turbidites and/or reworked bottom-current deposits.
The Biology of Interleukin-2
Authors: Malek Thomas R.
Published: December 2007

Much data support an essential role for interleukin (IL)-2 in immune tolerance. This idea is much different from the early paradigm in which IL-2 is central for protective immune responses. This change in thinking occurred when a T regulatory cell defect was shown to be responsible for the lethal autoimmunity associated with IL-2/IL-2R deficiency. This realization allowed investigators to explore immune responses in IL-2-nonresponsive mice rendered autoimmune-free. Such studies established that IL-2 sometimes contributes to optimal primary immune responses, but it is not mandatory. Emerging findings, however, suggest an essential role for IL-2 in immune memory. Here, the current understanding of the dual role of IL-2 in maintaining tolerance and contributing to immunity in vivo is reviewed with some emphasis on T regulatory cell production and homeostasis. Also discussed are implications of this new appreciation concerning the immunobiology of IL-2 with respect to targeting IL-2 or its receptor in immunotherapy.
Does gender influence learning style preferences of first-year medical students?
Authors: Slater Jill A. , Lujan Heidi L. , DiCarlo Stephen E.
Published: December 2007

Students have specific learning style preferences, and these preferences may be different between male and female students. Understanding a student's learning style preference is an important consideration when designing classroom instruction. Therefore, we administered the visual, auditory, reading/writing, kinesthetic (VARK) learning preferences questionnaire to our first-year medical students; 38.8% (97 of 250 students) of the students returned the completed questionnaire. Both male (56.1%) and female (56.7%) students preferred multiple modes of information presentation, and the numbers and types of modality combinations were not significantly different between genders. Although not significantly different, the female student population tended to be more diverse than the male population, encompassing a broader range of sensory modality combinations within their preference profiles. Instructors need to be cognizant of these differences and broaden their range of presentation styles accordingly.
Using a classic paper by I. E. Lawton and N. B. Schwartz to consider the array of factors that control luteinizing hormone production
Authors: Bauer-Dantoin Angela C. , Hanke Craig J.
Published: December 2007

Two significant benefits derived from reading and discussing classic scientific papers in undergraduate biology courses are 1) providing students with the realistic perspective that science is an ongoing process (rather than a set of inarguable facts) and 2) deepening the students' understanding of physiological processes. A classic paper that is useful in both of these regards is by I. E. Lawton and N. B. Schwartz (A circadian rhythm of luteinizing hormone secretion in ovariectomized rats. Am J Physiol 214: 213–217, 1968). The primary objective of the study is to determine whether tonic (pulsatile) secretion of luteinizing hormone (LH) from the pituitary gland exhibits a circadian rhythm. While this hypothesis seems relatively straightforward, its in vivo investigation necessitates an awareness of the multitude of factors, in addition to the circadian clock, that can influence plasma LH levels (and a consideration of how to control for these factors in the experimental design). Furthermore, discussion of the historical context in which the study was conducted (i.e., before the pulsatile nature of LH secretion had been discovered) provides students with the realistic perspective that science is not a set of facts but rather a systematic series of attempts by scientists to understand reality (a perspective that is difficult to convey using a traditional textbook alone). A review of the historical context in which the study was conducted, and a series of discovery learning questions are included to facilitate classroom discussions and to help deepen students' understanding of the complex nature of pituitary hormone regulation.
Influence of microvascular endothelial cells on transcriptional regulation of proximal tubular epithelial cells
Authors: Aydin Sonia , Signorelli Sara , Lechleitner Thomas , Joannidis Michael , Pleban Clara , Perco Paul , Pfaller Walter , Jennings Paul
Published: December 2007

In the renal cortex the peritubular capillary network and the proximal tubular epithelium cooperate in solute and water reabsorption, secretion, and inflammation. However, the mechanisms by which these two cell types coordinate such diverse functions remain to be characterized. Here we investigated the influence of microvascular endothelial cells on proximal tubule cells, using a filter-based, noncontact, close-proximity coculture of the human microvascular endothelial cell line HMEC-1 and the human proximal tubular epithelial cell line HK-2. With the use of DNA microarrays the transcriptomes of HK-2 cells cultured in mono- and coculture were compared. HK-2 cells in coculture exhibited a differential expression of 99 genes involved in pathways such as extracellular matrix (e.g., lysyl oxidase), cell-cell communication (e.g., IL-6 and IL-1β), and transport (e.g., GLUT3 and lipocalin 2). HK-2 cells also exhibited an enhanced paracellular gating function in coculture, which was dependent on HMEC-1-derived extracellular matrix. We identified a number of HMEC-1-enriched genes that are potential regulators of epithelial cell function such as extracellular matrix proteins (e.g., collagen I, III, IV, and V, laminin-α IV) and cytokines/growth factors (e.g., hepatocyte growth factor, endothelin-1, VEGF-C). This study demonstrates a complex network of communication between microvascular endothelial cells and proximal tubular epithelial cells that ultimately affects proximal tubular cell function. This coculture model and the data described will be important in the further elucidation of microvascular endothelial and proximal tubular epithelial cross talk mechanisms.
Bistable MAP kinase activity: a plausible mechanism contributing to maintenance of late long-term potentiation
Authors: Smolen Paul , Baxter Douglas A. , Byrne John H.
Published: December 2007

Bistability of MAP kinase (MAPK) activity has been suggested to contribute to several cellular processes, including differentiation and long-term synaptic potentiation. A recent model (Markevich NI, Hoek JB, Kholodenko BN. J Cell Biol 164: 353–359, 2004) predicts bistability due to interactions of the kinases and phosphatases in the MAPK pathway, without feedback from MAPK to earlier reactions. Using this model and enzyme concentrations appropriate for neurons, we simulated bistable MAPK activity, but bistability was present only within a relatively narrow range of activity of Raf, the first pathway kinase. Stochastic fluctuations in molecule numbers eliminated bistability for small molecule numbers, such as are expected in the volume of a dendritic spine. However, positive-feedback loops have been posited from MAPK up to Raf activation. One proposed loop in which MAPK directly activates Raf was incorporated into the model. We found that such feedback greatly enhanced the robustness of both stable states of MAPK activity to stochastic fluctuations and to parameter variations. Bistability was robust for molecule numbers plausible for a dendritic spine volume. The upper state of MAPK activity was resistant to inhibition of MEK activation for >1 h, which suggests that inhibitor experiments have not sufficed to rule out a role for persistent MAPK activity in the maintenance of long-term potentiation (LTP). These simulations suggest that persistent MAPK activity and consequent upregulation of translation may contribute to LTP maintenance and to long-term memory. Experiments using a fluorescent MAPK substrate may further test this hypothesis.
Muscle metabolic responses to exercise above and below the “critical power” assessed using31P-MRS
Authors: Jones Andrew M. , Wilkerson Daryl P. , DiMenna Fred , Fulford Jonathan , Poole David C.
Published: December 2007

We tested the hypothesis that the asymptote of the hyperbolic relationship between work rate and time to exhaustion during muscular exercise, the “critical power” (CP), represents the highest constant work rate that can be sustained without a progressive loss of homeostasis [as assessed using31P magnetic resonance spectroscopy (MRS) measurements of muscle metabolites]. Six healthy male subjects initially completed single-leg knee-extension exercise at three to four different constant work rates to the limit of tolerance (range 3–18 min) for estimation of the CP (mean ± SD, 20 ± 2 W). Subsequently, the subjects exercised at work rates 10% below CP (CP) for as long as possible, while the metabolic responses in the contracting quadriceps muscle, i.e., phosphorylcreatine concentration ([PCr]), Piconcentration ([Pi]), and pH, were estimated using31P-MRS. All subjects completed 20 min of CP exercise was 14.7 ± 7.1 min. During <CP exercise, stable values for [PCr], [Pi], and pH were attained within 3 min after the onset of exercise, and there were no further significant changes in these variables (end-exercise values = 68 ± 11% of baseline [PCr], 314 ± 216% of baseline [Pi], and pH 7.01 ± 0.03). During >CP exercise, however, [PCr] continued to fall to the point of exhaustion and [Pi] and pH changed precipitously to values that are typically observed at the termination of high-intensity exhaustive exercise (end-exercise values = 26 ± 16% of baseline [PCr], 564 ± 167% of baseline [Pi], and pH 6.87 ± 0.10, all P < 0.05 vs. <CP exercise). These data support the hypothesis that the CP represents the highest constant work rate that can be sustained without a progressive depletion of muscle high-energy phosphates and a rapid accumulation of metabolites (i.e., H+concentration and [Pi]), which have been associated with the fatigue process.