979 resultados para grating lobes
Resumo:
This study of landscape evolution presents both new modern and palaeo process-landform data, and analyses the behaviour of the Antarctic Peninsula Ice Sheet through the Last Glacial Maximum (LGM), the Holocene and to the present day. Six sediment-landform assemblages are described and interpreted for Ulu Peninsula, James Ross Island, NE Antarctic Peninsula: (1) the Glacier Ice and Snow Assemblage; (2) the Glacigenic Assemblage, which relates to LGM sediments and comprises both erratic-poor and erratic-rich drift, deposited by cold-based and wet-based ice and ice streams respectively; (3) the Boulder Train Assemblage, deposited during a Mid-Holocene glacier readvance; (4) the Ice-cored Moraine Assemblage, found in front of small cirque glaciers; (5) the Paraglacial Assemblage including scree, pebble-boulder lags, and littoral and fluvial processes; and (6) the Periglacial Assemblage including rock glaciers, protalus ramparts, blockfields, solifluction lobes and extensive patterned ground. The interplay between glacial, paraglacial and periglacial processes in this semi-arid polar environment is important in understanding polygenetic landforms. Crucially, cold-based ice was capable of sediment and landform genesis and modification. This landsystem model can aid the interpretation of past environments, but also provides new data to aid the reconstruction of the last ice sheet to overrun James Ross Island.
Resumo:
At various times during the Quaternary, north-eastern England was a zone of confluence between dynamic ice lobes sourced from the Pennines, northern Scotland, the Cheviots, and Scandinavia. The region thus has some of the most complex exposures of Middle to Late Pleistocene sediments in Britain, with both interglacial and glacial sediments deposited in terrestrial and marine settings. We investigated sedimentary sequences exposed on the coastline of County Durham at Warren House Gill, and present a new model of British and Fennoscandian Ice Sheet interaction in the North Sea Basin during the Middle Pleistocene. The stratigraphy at Warren House Gill consists of a lower diamicton and upper estuarine sediments, both part of the Warren House Formation. They are separated from the overlying Weichselian Blackhall and Horden tills by a substantial unconformity. The lower diamicton of the Warren House Formation is re-interpreted here as an MIS 8 to 12 glaciomarine deposit containing ice-rafted lithics from north-eastern Scotland and the northeast North Sea, and is renamed the ‘Ash Gill Member’. It is dated by lithological comparison to the Easington Raised Beach, Middle Pleistocene Amino Acid Racemisation values, and indirectly by optically stimulated luminescence. The overlying shallow subaqueous sediments were deposited in an estuarine environment by suspension settling and bottom current activity. They are named the ‘Whitesides Member’, and form the uppermost member of the Warren House Formation. During glaciation, ice-rafted material was deposited in a marine embayment. There is no evidence of a grounded, onshore Scandinavian ice sheet in County Durham during MIS 6, which has long been held as the accepted stratigraphy. This has major implications for the currently accepted British Quaternary Stratigraphy. Combined with recent work on the Middle Pleistocene North Sea Drift from Norfolk, which is now suggested to have been deposited by a Scottish ice sheet, the presence of a Scandinavian ice sheet in eastern England at any time during the Quaternary is becoming increasingly doubtful.
Resumo:
In 1972, episodic and semantic memories were considered to reflect different types of knowledge (Tulving, 1972). However, these early definitions encountered many difficulties. Now, Episodic and semantic memories are discussed in terms of awareness associated with retrieval (Wheeler, Stuss, & Tulving, 1997): Autonoetic consciousness (i.e., feeling of remembering) is considered associated with retrieval from the episodic memory system, while noetic consciousness (i.e., feeling of knowing) is considered characterized by retrieval from the semantic memory system. The present article investigated determinants of autonoetic consciousness in order to clarify characteristics of perceptual knowledge that is being recalled, the more strongly the individual feels autonoetic consciousness during retrieval, and that autonoetic consciousness is based on rich sensory-perceptual knowledge. Furthermore, we suggested that the parietal and frontal lobes mediate the process of generating autonoetic consciousness. This suggested that sensory-perceptual knowledge, the parietal lobe and the frontal lobe are important factors for discriminating episodic memory afrom semantic memory.
Resumo:
During the substorm growth phase, magnetic reconnection extracts ~10^15 J from the solar wind through magnetic reconnection at the magnetopause, which is then stored in the magnetotail lobes. Plasma sheet pressure then increases to balance magnetic flux density increases in the lobes. We examine plasma sheet pressure, density and temperature during substorm growth phases using nine years of Cluster data (>316,000 data points). We show that plasma sheet pressure and temperature are higher during growth phases with higher solar wind driving whereas the density is approximately constant. We also show a weak correlation between plasma sheet temperature before onset and the minimum SuperMAG SML auroral index in the subsequent substorm. We discuss how energization of the plasma sheet before onset may result from thermodynamically adiabatic processes; how hotter plasma sheets may result in magnetotail instabilities and how this relates to the onset and size of the subsequent substorm expansion phase.
Resumo:
We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°-78°. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71° by the time of the expansion phase onset. A westward electrojet, centred at 65.4°, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1° at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the “distant” neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary.
Resumo:
A new dayside source of O+ ions for the polar magnetosphere is described, and a statistical survey presented of upward flows of O+ ions using 2 years of data from the retarding ion mass spectrometer (RIMS) experiment on board DE 1, at geocentric distances below 3 RE and invariant latitudes above 40°. The flows are classified according to their spin angle distributions. It is believed that the spacecraft potential near perigee is generally less than +2 V, in which case the entire O+ population at energies below about 60 eV is sampled. Examples are given of field-aligned flow and of transversely accelerated “core” O+ ions; in the latter events a large fraction of the total O+ ion population has been transversely accelerated, and in some extreme cases all the observed ions (of all ion species) have been accelerated, and no residual cold population is observed (“toroidal” distributions). However, by far the most common type of O+ upflow seen by DE RIMS lies near the dayside polar cap boundary (particularly in the prenoon sector) and displays an asymmetric spin angle distribution. In such events the ions carry an upward heat flux, and strong upflow of all species is present (H+, He+, O+, O++, and N+ have all been observed with energies up to about 30 eV, but with the majority of ions below about 2 eV); hence, these have been termed upwelling ion events. The upwelling ions are embedded in larger regions of classical light ion polar wind and are persistently found under the following conditions: at geocentric distances greater than 1.4 RE; at all Kp in summer, but only at high Kp in winter. Low-energy conical ions (<30 eV) are only found near the equatorial edge of the events, the latitude of which moves equatorward with increasing Kp and is highly correlated with the location of field-aligned currents. The RIMS data are fully consistent with a “mass spectrometer effect,” whereby light ions and the more energetic O+ ions flow into the lobes and mantle and hence the far-tail plasma sheet, but lower-energy O+ is swept across the polar cap by the convection electric field, potentially acting as a source for the nightside auroral acceleration regions. The occurrence probability of upwelling ion events, as compared to those of low-altitude transversely accelerated core ions and of field-aligned flow, suggests this could be the dominant mechanism for supplying the nightside auroral acceleration region, and subsequently the ring current and near-earth plasma sheet, with ionospheric O+ ions. It is shown that the total rate of O+ outflow in upwelling ion events (greater than 10^25 s^{−1}) is sufficient for the region near the dayside polar cap boundary to be an important ionospheric heavy ion source.
Resumo:
The retarding ion mass spectrometer on the Dynamics Explorer 1 spacecraft has generated a unique data set which documents, among other things, the occurrence of non-Maxwellian superthermal features in the auroral topside ionosphere distribution functions. In this paper, we provide a representative sampling of the observed features and their spatial morphology as observed at altitudes in the range from a few thousand kilometers to a few earth radii. At lower altitudes, these features appear at auroral latitudes separating regions of polar cap and subauroral light ion polar wind. The most common signature is the appearance of an upgoing energetic tail having conical lobes representing significant ion heat and number flux in all species, including O+. Transverse ion heating below the observation point at several thousand kilometers is clearly associated with O+ outflows. In some events observed, transverse acceleration apparently involves nearly the entire thermal plasma, the distribution function becomes highly anisotropic with T⊥ > T∥, and may actually develop a minimum at zero velocity, i.e., become a torus having as its axis the local magnetic field direction. At higher altitudes, the localized dayside source region appears as a field aligned flow which is dispersed tailward across the polar cap according to parallel velocity by antisunward convective flow, so that upflowing low energy O+ ions appear well within the polar cap region. While this flow can appear beamlike in a given location, the energy dispersion observed implies a very broad energy distribution at the source, extending from a few tenths of an eV to in excess of 50 eV. On the nightside, upgoing ion beams are found to be latitudinally bounded by regions of ion conics whose half angles increase with increasing separation from the beam region, indicating low altitude transverse acceleration in immediate proximity to, and below, the parallel acceleration region. These observations reveal a clear distinction between classical polar wind ion outflow and O+ enhanced superthermal flows, and confirm the importance of low altitude transverse acceleration in ionospheric plasma transport, as suggested by previous observations.
Resumo:
It has been postulated that autism spectrum disorder is underpinned by an ‘atypical connectivity’ involving higher-order association brain regions. To test this hypothesis in a large cohort of adults with autism spectrum disorder we compared the white matter networks of 61 adult males with autism spectrum disorder and 61 neurotypical controls, using two complementary approaches to diffusion tensor magnetic resonance imaging. First, we applied tract-based spatial statistics, a ‘whole brain’ non-hypothesis driven method, to identify differences in white matter networks in adults with autism spectrum disorder. Following this we used a tract-specific analysis, based on tractography, to carry out a more detailed analysis of individual tracts identified by tract-based spatial statistics. Finally, within the autism spectrum disorder group, we studied the relationship between diffusion measures and autistic symptom severity. Tract-based spatial statistics revealed that autism spectrum disorder was associated with significantly reduced fractional anisotropy in regions that included frontal lobe pathways. Tractography analysis of these specific pathways showed increased mean and perpendicular diffusivity, and reduced number of streamlines in the anterior and long segments of the arcuate fasciculus, cingulum and uncinate—predominantly in the left hemisphere. Abnormalities were also evident in the anterior portions of the corpus callosum connecting left and right frontal lobes. The degree of microstructural alteration of the arcuate and uncinate fasciculi was associated with severity of symptoms in language and social reciprocity in childhood. Our results indicated that autism spectrum disorder is a developmental condition associated with abnormal connectivity of the frontal lobes. Furthermore our findings showed that male adults with autism spectrum disorder have regional differences in brain anatomy, which correlate with specific aspects of autistic symptoms. Overall these results suggest that autism spectrum disorder is a condition linked to aberrant developmental trajectories of the frontal networks that persist in adult life.
Resumo:
We present here new results of two-dimensional hydrodynamical simulations of the eruptive events of the 1840s (the great) and the 1890s (the minor) eruptions suffered by the massive star eta Carinae (Car). The two bipolar nebulae commonly known as the Homunculus and the little Homunculus (LH) were formed from the interaction of these eruptive events with the underlying stellar wind. We assume here an interacting, non-spherical multiple-phase wind scenario to explain the shape and the kinematics of both Homunculi, but adopt a more realistic parametrization of the phases of the wind. During the 1890s eruptive event, the outflow speed decreased for a short period of time. This fact suggests that the LH is formed when the eruption ends, from the impact of the post-outburst eta Car wind (that follows the 1890s event) with the eruptive flow (rather than by the collision of the eruptive flow with the pre-outburst wind, as claimed in previous models; Gonzalez et al.). Our simulations reproduce quite well the shape and the observed expansion speed of the large Homunculus. The LH (which is embedded within the large Homunculus) becomes Rayleigh-Taylor unstable and develop filamentary structures that resemble the spatial features observed in the polar caps. In addition, we find that the interior cavity between the two Homunculi is partially filled by material that is expelled during the decades following the great eruption. This result may be connected with the observed double-shell structure in the polar lobes of the eta Car nebula. Finally, as in previous work, we find the formation of tenuous, equatorial, high-speed features that seem to be related to the observed equatorial skirt of eta Car.
Resumo:
The morphology of terebelliform polychaetes was investigated for a phylogenetic study focused on Terebellidae. For this study, specimens belonging to 147 taxa, preferably type material or specimens from type localities or areas close to them, were examined under stereo, light and scanning electron microscopes. The taxa examined were 1 Pectinariidae, 2 Ampharetidae, 2 Alvinellidae, 8 Trichobranchidae, and 134 Terebellidae, which included 8 Polycirrinae, 15 Thelepodinae, and 111 Terebellinae. A comparison of the morphology, including prostomium, peristomium, anterior segments and lobes, branchiae, glandular venter, nephridial and genital papillae, notopodia and notochaetae, neuropodia and neurochaetae, and posterior end, was made of all the currently recognized families of terebelliform polychaetes, with special emphasis on Terebellidae. A discussion of the characters useful to distinguish between genera is given. This character set will be used in a subsequent phylogenetic study (Nogueira & Hutchings in prep.)
Resumo:
Four taxa of terebellines with problematic taxonomic histories are redescribed. One is a new species that has been mis-identified for the last 37 years and one is allocated to a different genus from that to which it was previously assigned. Pista corrientis McIntosh, 1885 was described from Argentina and has been reported from several localities along the Brazilian coast. Examination of the holotype of P. corrientis revealed that the Brazilian specimens belong to a separate species, herein described as P. nonatoi sp. nov., and a redescription of the holotype of P. corrientis is provided. Pista sombreriana (McIntosh, 1885) was considered indeterminable due to the poor condition of the holotype. Our examination of the holotype showed that although it is poorly preserved most taxonomic characters are visible. The morphology of the lobes on anterior segments, especially those of segments 3-4, is closer to Lanicides than to Pista but considering that Lanicides is also poorly defined we redescribe P. sombreriana under its original designation. Finally, Eupolymnia turgidula (Ehlers, 1887) has been considered as a junior synonym of E. crassicornis (Schmarda, 1861) but a recent study resurrected it as a valid species of Terebella, which was the original generic designation. According to our examination of the holotype, E. turgidula does belong to Eupolymnia, but it is uncertain as to whether it is a valid species or a synonym of either E. crassicornis or E. magnifica (Webster, 1884).
Resumo:
Background and Aims The amount of data collected previously for Velloziaceae neither clarified relationships within the family nor helped determine an appropriate classification, which has led to huge discordance among treatment by different authors. To achieve an acceptable phylogenetic result and understand the evolution and roles of characters in supporting groups, a total evidence analysis was developed which included approx. 20 % of the species and all recognized genera and sections of Velloziaceae, plus outgroups representatives of related families within Pandanales. Methods Analyses were undertaken with 48 species of Velloziaceae, representing all ten genera, with DNA sequences from the atpB-rbcL spacer, trnL-trnF spacer, trnL intron, trnH-psbA spacer, ITS ribosomal DNA spacers and morphology. Key Results Four groups consistently emerge from the analyses. Persistent leaves, two phloem strands, stem cortex divided in three regions and violet tepals support Acanthochlamys as sister to Velloziaceae s. s., which are supported mainly by leaves with marginal bundles, transfusion tracheids and inflorescence without axis. Within Velloziaceae s. s., an African Xerophyta + Talbotia clade is uniquely supported by basal loculicidal capsules; an American clade, Barbacenia s. l. + Barbaceniopsis + Nanuza + Vellozia, is supported by only homoplastic characters. Barbacenia s. l. (Aylthonia + Barbacenia + Burlemarxia + Pleurostima) is supported by a double sheath in leaf vascular bundles and a corona; Barbaceniopsis + Nanuza + Vellozia is not supported by an unambiguous character, but Barbaceniopsis is supported by five characters, including diclinous flowers, Nanuza + Vellozia is supported mainly by horizontal stigma lobes and stem inner cortex cells with secondary walls, and Vellozia alone is supported mainly by pollen in tetrads. Conclusions The results imply recognition of five genera (Acanthochlamys (Xerophyta (Barbacenia (Barbaceniopsis, Vellozia)))), solving the long-standing controversies among recent classifications of the family. They also suggest a Gondwanan origin for Velloziaceae, with a vicariant pattern of distribution.
Resumo:
The crystal structures of an aspartic proteinase from Trichoderma reesei (TrAsP) and of its complex with a competitive inhibitor, pepstatin A, were solved and refined to crystallographic R-factors of 17.9% (R(free)=21.2%) at 1.70 angstrom resolution and 15.81% (R(free) = 19.2%) at 1.85 angstrom resolution, respectively. The three-dimensional structure of TrAsP is similar to structures of other members of the pepsin-like family of aspartic proteinases. Each molecule is folded in a predominantly beta-sheet bilobal structure with the N-terminal and C-terminal domains of about the same size. Structural comparison of the native structure and the TrAsP-pepstatin complex reveals that the enzyme undergoes an induced-fit, rigid-body movement upon inhibitor binding, with the N-terminal and C-terminal lobes tightly enclosing the inhibitor. Upon recognition and binding of pepstatin A, amino acid residues of the enzyme active site form a number of short hydrogen bonds to the inhibitor that may play an important role in the mechanism of catalysis and inhibition. The structures of TrAsP were used as a template for performing statistical coupling analysis of the aspartic protease family. This approach permitted, for the first time, the identification of a network of structurally linked residues putatively mediating conformational changes relevant to the function of this family of enzymes. Statistical coupling analysis reveals coevolved continuous clusters of amino acid residues that extend from the active site into the hydrophobic cores of each of the two domains and include amino acid residues from the flap regions, highlighting the importance of these parts of the protein for its enzymatic activity. (C) 2008 Elsevier Ltd. All rights reserved.
Resumo:
Middle to Late Holocene barriers are conspicuous landforms in southeastern and southern Brazilian regions. The barriers in the coastal zones of northern Santa Catarina, Parana and Sao Paulo states (27 degrees 19`-24 degrees 00`S) are formed mainly by beach ridge alignments and many barriers present foredune and blowout alignments in their seaward portion. The development of these eolian landforms appears to record a regional shift in coastal dynamics and barrier building. In this context, the Ilha Comprida barrier stands out for its well-developed and well-preserved foredunes and blowouts. Based on the presence or not and type of eolian landforms, the Ilha Comprida barrier can be divided seaward into inner, middle and outer units. The inner unit is formed entirely by beach ridges. The middle unit comprises a narrow belt of blowouts (up to 15 m high) aligned alongshore. Blowout lobes pointing NNW are indicative of their generation by southern winds. The outer unit is represented by low (<= 1 m high) active or stabilized foredunes and a small transgressive dunefield (similar to 1 km(2)). Twenty-seven luminescence ages (SAR protocol) obtained for the beach ridges, foredunes, and blowouts of these three units allow definition of a precise chronology of these landforms and calculation of rates of coastal progradation. The inner unit presents ages greater than 1004 +/- 88 years. The blowouts of the middle unit show ages from 575 +/- 47 to 172 +/- 18 years. The ages of the outer unit are less than 108 +/- 10 years. Rates of coastal progradation for the inner and outer units are 0.71-0.82 m/year and 0.86-2.23 m/year, respectively. The main phase of blowout development correlates well with the Little Ice Age (LIA) climatic event. These results indicate that southern winds in subtropical Brazil became increasingly more intense and/or frequent during the LIA. These conditions persist to the present and are responsible for the development of the eolian landforms in the outer unit. Thus, barrier geomorphology can record global climatic events. The sensitivity of barrier systems in subtropical Brazil to Late Holocene climate changes was favored by the relative sea level stillstand during this time. Luminescence dating makes it possible to analyze barrier geomorphology during Late Holocene climate changes operating on timescales of a hundred to thousand years. These results improve our knowledge of barrier building and will help in the evaluation of the impact of future climate changes on coastal settings. (C) 2008 Elsevier Ltd. All rights reserved.
Resumo:
O abscesso de pulmão continua sendo hoje, em plena era dos antibióticos, um importante problema médico. O presente trabalho se propõe mostrar aspectos diagnósticos e terapêuticos da doença em uma série de pacientes coletada nos últimos 34 anos em um hospital universitário especializado em doenças pulmonares. No período de 1968 a 2002 foram reunidos e estudados 241 casos de abscesso pulmonar de aspiração - 199 em homens e 42 em mulheres, com média de idade de 41,3 anos. Em 69,0% dos pacientes esteve presente a ingestão de álcool e em 64,0% o hábito tabágico. Tosse, expectoração, febre e comprometimento do estado geral foram os achados clínicos mais freqüentes, encontrados na quase totalidade dos casos; 62,5% tinham dor torácica e 30,0% hipocratismo digital. Verificaram-se dentes em mau estado de conservação em 81,7 % dos pacientes, episódio de perda de consciência em 78,0% e presença de odor fétido em 66,0%. Em 85,5% das vezes as lesões localizaram-se em segmento posterior de lobo superior ou segmento superior de lobo inferior, 97,1% delas unilaterais, ocorrendo com igual freqüência tanto no pulmão direito como no esquerdo. A maioria das lesões (66,0%) mediram entre 4,0 e 8,0 cm de diâmetro. Em 25 pacientes (10,4%) houve a associação de empiema pleural. Flora mista, indicativa da presença de germes anaeróbios, foi identificada em secreções broncopulmonares ou pleurais em 172 pacientes (71,4 %). Estreptococos e Gram negativos aeróbios foram também algumas vezes encontrados. Todos os pacientes foram inicialmente tratados com antibióticos (penicilina em 78,0% das vezes) e submetidos a sessões de drenagem postural. Em 51 (21,2%) acabou sendo necessário algum procedimento cirúrgico (24 drenagens de empiema, 21 ressecções pulmonares e 6 pneumostomias). Cura foi obtida em 231 pacientes (95,8%) e 10 (4,2%) foram ao óbito, estes em geral com grandes abscessos, três dos quais também com empiema.