Perfect partial reconstructions for multiple simultaneous sources

A major focus of research in the seismic industry of the past two decades has been the acquisition and subsequent separation of seismic data using multiple sources fired simultaneously. The recently introduced method of signal apparition provides a new take on the problem by replacing the random time-shifts usually employed to encode the different sources by fully deterministic periodic time-shifts. In this paper, we give a mathematical proof showing that the signal apparition method results in optimally large regions in the frequency–wavenumber space where exact separation of sources is achieved. These regions are diamond shaped and we prove that using any other method of source encoding results in strictly smaller regions of exact separation. The results are valid for arbitrary number of sources. Numerical examples for different number of sources (three, respectively, four sources) demonstrate the exact recovery of these diamond-shaped regions. The implementation of the theoretical proofs in the field is illustrated by the results of a conducted field test.     

New insights from low-temperature thermochronology into the tectonic and geomorphologic evolution of the south-eastern Brazilian highlands and passive margin

The South Atlantic passive margin along the south-eastern Brazilian highlands exhibits a complex landscape,including a northern inselberg area and a southern elevated plateau,separated by the Doce River valley.This landscape is set on the Proterozoic to early Paleozoic rocks of the region that once was the hot core of the Aracuai orogen,in Ediacaran to Ordovician times.Due to the break-up of Gondwana and consequently the opening of the South Atlantic during the Early Cretaceous,those rocks of the Araquai orogen became the basement of a portion of the South Atlantic passive margin and related southeastern Brazilian highlands.Our goal is to provide a new set of constraints on the thermo-tectonic history of this portion of the south-eastern Brazilian margin and related surface processes,and to provide a hypothesis on the geodynamic context since break-up.To this end,we combine the apatite fission track(AFT)and apatite(U-Th)/He(AHe)methods as input for inverse thermal history modelling.All our AFT and AHe central ages are Late Cretaceous to early Paleogene.The AFT ages vary between 62 Ma and90 Ma,with mean track lengths between 12.2μm and 13.6μm.AHe ages are found to be equivalent to AFT ages within uncertainty,albeit with the former exhibiting a lesser degree of confidence.We relate this Late Cretaceous-Paleocene basement cooling to uplift with accelerated denudation at this time.Spatial variation of the denudation time can be linked to differential reactivation of the Precambrian structural network and differential erosion due to a complex interplay with the drainage system.We argue that posterior large-scale sedimentation in the offshore basins may be a result of flexural isostasy combined with an expansion of the drainage network.We put forward the combined compression of the Mid-Atlantic ridge and the Peruvian phase of the Andean orogeny,potentially augmented through the thermal weakening of the lower crust by the Trindade thermal anomaly,as a probable cause for the uplift.     

Acidification at the Surface in the East Sea: A Coupled Climate-carbon Cycle Model Study

This modeling study investigates the impacts of increasing atmospheric CO₂ concentration on acidification in the East Sea. A historical simulation for the past three decades (1980 to 2010) was performed using the Hadley Centre Global Environmental Model (version 2), a coupled climate model with atmospheric, terrestrial and ocean cycles. As the atmospheric CO₂ concentration increased, acidification progressed in the surface waters of the marginal sea. The acidification was similar in magnitude to observations and models of acidification in the global ocean. However, in the global ocean, the acidification appears to be due to increased in-situ oceanic CO₂ uptake, whereas local processes had stronger effects in the East Sea. pH was lowered by surface warming and by the influx of water with higher dissolved inorganic carbon (DIC) from the northwestern Pacific. Due to the enhanced advection of DIC, the partial pressure of CO₂ increased faster than in the overlying air; consequently, the in-situ oceanic uptake of CO₂ decreased.     

The importance of wind forcing in fjord wave modelling

Ocean Dynamics - Accurate predictions of surface ocean waves in coastal areas are important for a number of marine activities. In complex coastlines with islands and fjords, the quality of wind...     

Waulsortian buildups of Waulsort,Belgium

The biostratigraphy and sedimentology of the late Tournaisian, Waulsortian buildups of the type area, at Waulsort (Belgium), are examined in detail. Four buildups are present. Overall, they span the stratigraphic interval from the base of the Ivorian stage to the lower part of the Moliniacian stage, ending just below the base of the Viséan. Petrographic study shows that all Waulsortian Phases are represented, the older buildups being of Phases A and B, whereas the youngest ranges through Phases A to D. The relatively crude Phase classification is refined by correspondence analysis, which shows that the grain types present in the Waulsortian and associated limestones conform closely to the relay (systematic shift of relative importance of grain types) described from other Waulsortian buildups in Belgium. A Relay Index, derived from the correspondence analysis and defining the position of each sample in the compositional relay, is plotted on stratigraphic logs of the sections studied to allow detailed comparison with other Waulsortian and peri-Waulsortian sections in the Dinant area for which similar curves already exist. The Waulsort buildups are found to fit closely into the depositional and palaeobathymetric patterns established or suspected in the area. Two shallowing upward sequences seem to be present, separated by an abrupt deepening. The earlier, relatively minor shallowing trend, in the Polygnathus communis carina Zone, is here recorded in buildup facies for the first time: previous evidence had come from the laterally equivalent facies. The other shallowing trend, which extends through the Scaliognathus anchoralis Zone and culminates near the base of the Moliniacian stage, is the regional, late Tournaisian regression which had a major influence on the biota of the Waulsortian banks in Belgium and was probably largely responsible for cessation of bank growth over most of the area.     

The Scale Expanding Cosmos

The Big Bang model assumes that the Universe expands by continuously changing the relationship between the metrics of space and time. However, the relationship between space and time could remain constant during the cosmological expansion and all cosmological locations in time and space could be equivalent, if the metrics of both space and time expand. The Scale Expanding Cosmos theory accurately models the universe we observe and offers simple and direct explanations for several cosmological enigmas. This revised version was published online in July 2006 with corrections to the Cover Date.     

UV-B induced immunomodulation: a health risk

The depletion in stratospheric ozone and changes in life-styles are likely to lead to an increased exposure to sunlight, including the UV-B waveband. Such irradiation may induce immunomodulation and therefore have adverse effects on human health. Alterations in immune responses could affect not only photocarcinogenesis but also resistance to infections, certain allergies and autoimmunity, and vaccination efficacy. In the present study, the risk of increased UV-B exposure has been estimated with respect to the resistance to a bacterial ( Listeria monocytogenes ) and a viral (herpes simplex virus) infection. The data indicate that suberythemal UV-B irradiation can have significant effects on immune responses to certain infectious diseases in human subjects.     

高铁铁橄榄石的新研究——兼论铁橄榄石的氧化作用

本文综合应用微束分析技术,包括扫描电镜、电子探针、电子显微镜和激光喇曼探针等多种分析技术,对国内外许多学者感兴趣的高铁铁橄榄石进行了系统深入的研究,发现高铁铁橄榄石通常是铁橄榄石和一系列氧化程度不等的氧化铁橄榄石及其他一些氧化产物的总和,并对高铁铁橄榄石和铁橄榄石的氧化作用提出了一些新认识:(1)铁橄榄石在其形成后至少受到两次蚀变;(2)铁橄榄石氧化的最终产物是玻璃;(3)原先关于高铁铁橄榄石的结构分析、反相畴、超结构和假双晶等问题尚待进一步研究;(4)将高铁铁橄榄石看成是新矿物实属疑问。     

A possible Caledonide arm through the Barents Sea imaged by OBS data

The assembly of the crystalline basement of the western Barents Sea is related to the Caledonian orogeny during the Silurian. However, the development southeast of Svalbard is not well understood, as conventional seismic reflection data does not provide reliable mapping below the Permian sequence. A wide-angle seismic survey from 1998, conducted with ocean bottom seismometers in the northwestern Barents Sea, provides data that enables the identification and mapping of the depths to crystalline basement and Moho by ray tracing and inversion. The four profiles modeled show pre-Permian basins and highs with a configuration distinct from later Mesozoic structural elements. Several strong reflections from within the crystalline crust indicate an inhomogeneous basement terrain. Refractions from the top of the basement together with reflections from the Moho constrain the basement velocity to increase from 6.3 km s⁻¹ at the top to 6.6 km s⁻¹ at the base of the crust. On two profiles, the Moho deepens locally into root structures, which are associated with high top mantle velocities of 8.5 km s⁻¹. Combined P- and S-wave data indicate a mixed sand/clay/carbonate lithology for the sedimentary section, and a predominantly felsic to intermediate crystalline crust. In general, the top basement and Moho surfaces exhibit poor correlation with the observed gravity field, and the gravity models required high-density bodies in the basement and upper mantle to account for the positive gravity anomalies in the area. Comparisons with the Ural suture zone suggest that the Barents Sea data may be interpreted in terms of a proto-Caledonian subduction zone dipping to the southeast, with a crustal root representing remnant of the continental collision, and high mantle velocities and densities representing eclogitized oceanic crust. High-density bodies within the crystalline crust may be accreted island arc or oceanic terrain. The mapped trend of the suture resembles a previously published model of the Caledonian orogeny. This model postulates a separate branch extending into central parts of the Barents Sea coupled with the northerly trending Svalbard Caledonides, and a microcontinent consisting of Svalbard and northern parts of the Barents Sea independent of Laurentia and Baltica at the time. Later, compressional faulting within the suture zone apparently formed the Sentralbanken High.     

Volcanic lake systematics I. Physical constraints

 Volcanic lakes have a wide range of characteristics, and we make an attempt to delineate the limiting physical conditions for several lake classes. The ratio between heat input and heat dissipation capacity of a lake constrains the temperature for perfectly mixed steady-state volcanic lakes. Poorly mixed lakes are also conditioned by this ratio, but their temperature structure is also strongly influenced by the hydrodynamics resulting from different mechanisms of heat transfer. The steady-state temperatures of volcanic lakes are largely determined by the magnitude of the volcanic heat influx relative to the surface area of the lake. Small lakes have only a small capacity for heat dissipation and their temperature rises quickly with only small heat inputs; large lakes are buffered against variations in heat input. Both the heat dissipation and meteoric water input into a lake are functions of lake surface area and therefore each lake water temperature demands a certain precipitation rate for mass conservation, independent of lake size. The results of energy/mass-balance modeling shows that under common atmospheric conditions, most steady-state volcanic lakes are unlikely to maintain a temperature in excess of 45–50  °C. Validation of the volcanic lake model was performed using published data from Yugama Lake (Japan) and the Keli Mutu lakes (Indonesia). Also, the model was applied to 24 natural systems to provide a baseline assessment of energy fluxes under the model assumptions so future work on those systems can identify nuances in individual systems that deviate from the simple model conditions. We recommend the model for use in assessing temperature variations and volcanic lake stability in settings with known physical and atmospheric conditions. Application of the energy/mass balance calculations of model lakes provides a genetic classification scheme largely based on physical process parameters. Received: 28 February 1996 / Accepted: 23 November 1996