The Neoproterozoic-age Mali Group of the southwestern Taoudeni Basin, NW Africa, represents, in the Walidiala Valley, a glaciogenic and post-glacial succession that brackets the Cryogenian-Ediacaran ...period boundary. At its base, debris flows and turbidite-like, sandy units of the Pelel Member pass upward into siltstone and shale of the Diagoma Member. These two units represent the progressive evolution from some portion of a fan delta fed by a nearby ice shelf to a more distal environment disturbed only by the occasional fallout from passing icebergs. The appearance of coarse-grained, cross-bedded sandstone beds and gravels of the overlying Tanague Member heralds a return to a shallower, fluvially influenced environment before abrupt transgression caps the glaciogenic succession. The transgressive unit consists of a regionally extensive, 2-7 m-thick, silty dolostone, the Bowal Member, which is isotopically and petrographically indistinguishable from ca. 635-Ma cap dolostone units elsewhere in NW Africa and worldwide. The Bowal Member comprises microcrystalline dolomite in turbidite-like depositional sheets disrupted by internal brecciation, fracturing and cementation by first chert and then dolomite. The stratigraphic succession in the Walidiala Valley closely resembles facies models relating to glacial retreat in a proximal glaciomarine environment affected by glacioeustasy. A large volcaniclastic debris flow has caused slumping and soft-sediment deformation within the cap dolostone of the Bowal Member. The widespread association of pyroclastic deposits with cap dolostone throughout the Taoudeni Basin implies that volcanism and deglaciation were roughly contemporaneous across a huge area. We consider that the volcaniclastic debris flow and soft-sediment deformation within the underlying Tanague Member were possibly triggered by seismic activity during deglaciation, caused by isostatic relaxation of the lithosphere. However, fitted brecciation of cap dolostone beds here and elsewhere in the world is more consistent with pervasive dolomite cementation.Original Abstract: Dans la vallee de Walidiala, au sud-ouest du bassin de Taoudeni, le groupe du Mali comprend une succession glaciaire et postglaciaire neoproterozoique se rapportant a la limite Cryogenien-Edicarien. Cette succession debute par des coulees de debris et turbidites sableuses formant l'unite de Pelel, laquelle passe vers le haut a des siltstones et argilites a blocs laches de l'unite de Diagoma. Ces deux unites marquent le passage d'un environnement de type lobe deltaique, proche d'une marge glaciaire, a un environnement plus distal, alimente notamment par des icebergs. Au-dessus, la presence de gres grossiers a stratifications obliques de l'unite de Tanague marque le retour a un environnement moins profond et sous influence fluviatile, avant la grande transgression regionale representee par un banc de 2 a 7 m de dolomies silteuses formant l'unite de Bowal. La composition isotopique et petrographique de cette unite carbonatee est identique a celle des cap dolostones qui coiffent les depots glaciaires neoproterozoiques ( 635 Ma) en Afrique de l'Ouest et ailleurs dans le monde. Il s'agit de dolomie microcristalline formant des lits turbiditiques localement brechifies, fractures, avec un ciment siliceux puis dolomitique. La succession stratigraphique de la vallee de Walidiala est tres proche des modeles proposes pour illustrer un retrait glaciaire en milieu marin proximal affecte par la glacio-isostasie. Un important ecoulement de debris volcanoclastiques a provoque glissements et deformations souples dans les bancs dolomitiques de l'unite de Bowal. L'association generalisee de depots pyroclastiques avec le depot des cap dolostones sur l'ensemble du bassin de Taoudeni suggere que les deux phenomenes sont contemporains et en relation avec les evenements tectoniques panafricains. On considere que l'ecoulement de debris et la brechification de l'unite de Bowal, ainsi que les deformations souples dans les gres de Tanague sous-jacents, ont pour origine une activite sismique liee a la relaxation isostatique de la lithosphere lors de la deglaciation
The boundaries of the West African Craton mark the location of a continuous suture zone that records Neoproterozoic to Early Cambrian oceanic closure. The western part of the circum-West African ...suture zone extends through the line of outcrop of the Mauritanide, Bassaride and Rokelide mountain belts. Our geochemical analyses are consistent with the idea that igneous and metamorphic rocks of the Rokelide and Southern Mauritanide mountain belts of West Africa occupy a suture zone that records the closing of a Neoproterozoic to Early Cambrian ocean basin during the Pan-African orogeny and final assembly of Gondwana. The closing of that basin was marked by the collision between Archean rocks of the Leo massif of the West African Craton and reactivated Archean and Paleoproterozoic rocks that now outcrop nearer to the coast of Africa in Sierra Leone and Liberia. Within the Rokelides, the geochemistry of the Kasewe Hills volcanic rocks and Marampa amphibolite indicate that remnants of an arc system are caught up in the suture zone. The geochemistry of Guingan schists that outcrop along strike of the Rokelides is compatible with the idea that the metamorphosed equivalents of the Marampa and Kasewe Hills arc volcanic rocks extend through the Bassarides and into the Southern Mauritanides.
Cognitive radio (CR) is a novel approach to improving the spectral efficiency of licensed radio frequency bands by opportunistically accessing unused portions of the band without introducing ...interference to a licensed user. To reliably identify unused portions in a dynamic environment, a collaborative spectrum sensing (CSS) approach is known to be advantageous. In this article we will consider a weighted energy fusion scheme for secondary users with different sensing channel conditions and to analyze the performance we suggest a numerical approach by utilizing a result from probability density function of the weighted sum of noncentral chi-square random variables are used. Simulation experiments are provided to confirm the viability of the proposed numerical approach.
The classic papers of Phleger Phleger, F.B, 1951. Foraminifera Distribution, Part I. Geological Society of America Memoir 46, 1–88. and Parker Parker, F.L., 1954. Distribtuion of the foraminifera in ...the Northeastern Gulf of Mexico. Bulletin of the Museum of Comparative Zoology 111, 453–588, 13 plates. form the benchmark foraminiferal data sets for the northwestern and northeastern Gulf of Mexico, respectively. These pioneer researchers occupied stations from shelf to abyssal depths. SHE analysis, a method examining the distribution of cumulative sample values of species richness (
S), the information function (
H) and evenness (
E) with increasing number of individuals (
N), was used to establish 18 foraminiferal communities and evaluate their community structure. Regression analyses, as well as plots of ln
S,
H and ln
E versus ln
N (Biodiversitygrams, BDGs), indicate that the majority of the communities exhibit a log series pattern. Theoretical log series values of
S,
H and
E are similar to the regression estimates from observed values in the northeastern Gulf. In the northwestern Gulf, however, observed values of species richness are lower and evenness higher than those expected for a log series, indicating a dramatic difference in community structure between east and west. Since the sampling time of Phleger, subsequent workers have found higher values of species richness and lower values of evenness in the northwestern Gulf. Either biodiversity values have changed since Phleger's 1947 (1951) sampling suggesting a fundamental change in the environmental regime of the northwestern Gulf of Mexico or, as has been suggested, Phleger's data are incorrect due to some sampling methodology. A comprehensive study with suitable experimental design including downcore samples will be required to resolve this dichotomy.
The increasing prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with the ability to escape existing humoral protection conferred by previous infection and/or ...immunization necessitates the discovery of broadly reactive neutralizing antibodies (nAbs). Utilizing mRNA display, we identify a set of antibodies against SARS-CoV-2 spike (S) proteins and characterize the structures of nAbs that recognize epitopes in the S1 subunit of the S glycoprotein. These structural studies reveal distinct binding modes for several antibodies, including the targeting of rare cryptic epitopes in the receptor-binding domain (RBD) of S that interact with angiotensin-converting enzyme 2 (ACE2) to initiate infection, as well as the S1 subdomain 1. Further, we engineer a potent ACE2-blocking nAb to sustain binding to S RBD with the E484K and L452R substitutions found in multiple SARS-CoV-2 variants. We demonstrate that mRNA display is an approach for the rapid identification of nAbs that can be used in combination to combat emerging SARS-CoV-2 variants.
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•Broadly reactive neutralizing antibodies (nAbs) may overcome SARS-CoV-2 variant escape•mRNA display is used to rapidly identify SARS-CoV-2 spike (S)-protein-directed nAbs•Structural studies reveal distinct binding modes for several identified antibodies•An engineered nAb sustains binding to variant Gamma E484K and Delta L452R spikes
Tanaka et al. identify a set of SARS-CoV-2 spike (S)-targeted potentially neutralizing antibodies (nAbs) by mRNA display. Structural analyses reveal distinct binding modes, including the targeting of rare cryptic S receptor-binding domain epitopes. A further engineered ACE2-blocking nAb shows sustained binding to S RBD with the E484K and L452R substitutions.
Foraminifera have a fundamental role in the trophic structure of marine communities and may be used to assess primary stresses affecting environmental quality. In coastal barrier lagoons their ...distribution can provide a framework for future assessment of environmental quality. To establish a baseline for the barrier-lagoon system of the southern Delmarva Peninsula, 20 subenvironments were sampled and proved to contain 44 species of living benthic foraminifera. Densities of species were related to variations in substratum, salinity and organic-matter content. Not all of the 20 subenvironments could be recognised based on variations in foraminiferal community composition; only seven subenvironments were distinguished on the basis of the distribution of dominant living species. Foraminiferal community composition appeared to be closely tied to the natural variations of physical stresses produced by the inter- relationship of landscape and flow dynamics.
Racial/ethnic variations in clinical and service delivery characteristics among youth in public outpatient mental health services were examined using data from San Diego County mental health service ...programs for fiscal year 1996 to 1997 (N = 3,962). Differences in referral sources, primary diagnoses, and service types were investigated for three racial/ethnic groups (African Americans, Asian/Pacific Islander Americans, and Latinos) compared to non-Hispanic whites. Controlling for age, gender, functional impairment, and prior service use, significant differences by race/ethnicity were found for all three variables studied. Possible explanations for these variations and future directions for research are discussed.
Foraminiferal and sedimentary data, supplemented with geochemical dating and ground-penetrating radar transects, show that the barrier island at Pea Island National Wildlife Refuge just north of ...Rodanthe, North Carolina, has been dominated by a combination of inlet and overwash processes for at least 1000 years. The stratigraphic record of several vibracores does not preserve every, or even many, overwash events but, instead, is characterized by three to four fining-upward sequences. The last three commence with overwash sand or gravel that is overlain by a variety of finer-grained estuarine, inlet, and marsh deposits. The dynamic nature of this segment of the Outer Banks was muted in the late 1930s by construction of artificial barrier dune ridges, extensive planting of grass and shrubs, and construction of Highway 12 in 1953. Subsequently, the road and barrier dune ridge were rebuilt and relocated several times following storm events.
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Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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