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981.
A Kalman filter-based method combining the energy of both L1 C/A and L2C GPS signals in a combined tracking loop method to
enhance performance under adverse conditions is developed. Standard tracking methods and the ionospheric effect on GPS signals
are reviewed and compared to a new Kalman filter that simultaneously estimates delay, phase and total electron content by
combining L1 C/A and L2C code and phase discriminator outputs. The new filter is tested and compared to standard methods for
tracking L1 C/A and L2C using both simulated and real data. The new method is found to have improved sensitivity of 3 dB compared
to standard L1 tracking and 4.5 dB compared to standard L2C tracking while at the same time providing an accurate estimate
of the total electron content along the signal path. 相似文献
982.
Suzanne?E.?HollinsEmail author Jennifer?J.?Harrison Brian?G.?Jones Atun?Zawadzki Henk?Heijnis Stuart?Hankin 《Journal of Paleolimnology》2011,46(4):579-596
In this study, we combined grain size and geochemical analyses with radioisotope analysis of lead-210 (210Pb), caesium-137 (137Cs) and radiocarbon (14C) ages to reconstruct the sedimentation history of two urbanised coastal lagoons in south-east Australia. Towradgi and Fairy
Lagoons were both found to exhibit slow initial sedimentation of less than 1 mm year−1 prior to anthropogenic influences. Land clearing in the catchments increased runoff and erosion in the creeks feeding into
the estuaries, and has resulted in progradation of fluvial material into the estuarine systems with a marked increase in sedimentation
to between 2 and 7 mm year−1. The upper 20–50 cm of the sediment column in both lagoons contained elevated concentrations of heavy metals such as Pb,
Cu, Ni and Zn. This pollution trend was found to be consistent with the history of industrialisation and urbanisation in the
region, which expanded rapidly post World War 2. The total metal concentrations were consistent with other urbanised/industrialised
estuaries around the world. Despite the fairly disturbed nature of these coastal lagoons, the use of 210Pb, 137Cs and 14C dating in combination with bulk geochemical analyses allowed detailed reconstruction of sedimentation history. 相似文献
983.
Paulo?J.?HidalgoEmail author Tyrone?O.?Rooney 《Contributions to Mineralogy and Petrology》2014,168(3):1011
The origin of adakite magmas remains controversial because initially the term adakite had petrogenetic significance implying an origin by direct melting of the eclogitized subducting oceanic crust. Many models have been produced for their origin, and until now there has not been a straightforward method to discriminate between these models in a given adakite suite. Here, we use detailed chronological and geochemical studies of selected adakitic edifices that allows for the determination of the magmatic output rate parameter (Qe), which has been correlated with the rates of magma generation deep within subduction zones. By providing temporal and eruption rate estimates, we provide constraints on the possible petrogenetic processes involved in the generation of adakite-like signatures. Adakite magmas derived from the melting of the subducting slab should be volumetrically insignificant when compared to the adakite-like magmas produced by typical arc magma generation processes. In this study, we use this observation and the extraordinary stratigraphic exposure from Miocene to present in an adakitic volcano in Panama and to study the temporal and chemical variation in erupted magmas to estimate rates of magma generation. Detailed chemical and geochronological analyses of Baru volcano indicate that the volcanic edifice was constructed in its entirety during the Quaternary and magmas display adakite-like features such as steep rare earth elements patterns, pronounced depletions in the heavy rare earth elements, low Y, high Sr, and high Sr/Y. The magmatic output rates (Qe) that we have calculated show that compared to other typical adakitic volcanoes, most of the volcanic edifice of Baru volcano was constructed extremely rapidly (<~213 k.a.) and in time frames that are similar to typical arc volcanoes. The observed chemical and mineralogical variation, coupled with the high magma production rates, indicate that Baru volcano is more representative of a typical arc volcano than a small-volume melt of the subducting oceanic crust. The technique we outline may have broader application in determining the petrogenetic conditions of other adakite suites. 相似文献
984.
Arkadiusz?M.?TomczykEmail author Piotr?Piotrowski Ewa?Bednorz 《Theoretical and Applied Climatology》2017,128(3-4):623-634
This study describes warm spells in Northern Europe and determines the synoptic situations that cause their occurrence. In this article, a relatively warm day was defined as a day when the maximum temperature exceeded the 95th annual percentile, and a warm spell (WS) was considered to be a sequence of at least five relatively warm days. In the analysed multiannual period and within the investigated area, 24 (Kallax) to 53 (Oslo) WSs were observed. The occurrence of WSs was mainly connected with positive anomalies of sea level pressure and a 500-hPa isobaric surface, displaying the presence of high-pressure systems. This occurrence was also accompanied by positive T850 anomalies. 相似文献
985.
Recently it has been shown that for finite and small values of the electron Debye length, the ion polytropic coefficient is approached to some constant value in the plasma sheath region by decreasing the plasma density. In this paper, using a plasma multi fluid model, the effect of ion polytropic coefficient γ i on the plasma sheath structure have been examined. The numerical calculations of the basic equation of the model show that the polytropic coefficient strongly affects on the plasma sheath characteristics. The results show that by transition from an isothermal flow (γ i =1) to an adiabatic flow (γ i =3), the net current to the wall and the electric potential distribution increase and the sheath width decreases in a thermal plasma sheath. 相似文献
986.
Cosmic-ray exposure histories of two Antarctic meteorites from Chinese collections and the Guangmingshan and Zhuanghe chondrites 总被引:5,自引:0,他引:5
In this paper, we report cosmic-ray exposure ages (3He, 21Ne, 38Ar) and gas retention ages (4He, 40Ar) of two Antarctic meteorites, and the Guangmingshan and Zhuanghe ordinary chondrites. The Antarctic meteorites (GRV98002 and GRV98004) were collected on … 相似文献
987.
Application of multiple sublethal stress indicators to assess the health of fish in Pamlico Sound following extensive flooding 总被引:1,自引:0,他引:1
S.?Marshall?AdamsEmail author Mark?S.?Greeley J.?McHugh?Law Edward?J.?Noga Judith?T.?Zelikoff 《Estuaries and Coasts》2003,26(5):1365-1382
Multiple indicators of sublethal stress (bioindicators) were used to assess the health and condition of two important estuarine fish species in the Pamlico Sound estuary following extensive flooding from three sequential hurricanes that occurred during early fall 1999. Bioindicators ranging from the biochemical to the reproductive and organism-level were used to assess the health of southern flounder and spot in Pamlico Sound compared to the health of these same species sampled from a relatively unaffected references site in lower Core Sound. Many of the physiological, reproductive, immunological, histopathological, and general condition indices suggested that both species, and particularly spot, in Pamlico Sound were sublethally stressed and in poorer condition than fish sampled from Core Sound. The major environmental stressors causing these sublethal stress responses in Pamlico Sound fish appears to be those related to episodic hypoxic exposure or a combination of effects associated with hypoxic conditions such as alterations in preferred habitat and food availability. Although fish populations in Pamlico Sound do not appear to be severely damaged or impaired at this time, organisms that are sublethally stressed can incur increased vulnerability to additional or future stressors such as modified physicochemical regimes, changes in food and habitat availability, and increases in infectious pathogens. Because of the low flushing rate (~1 yr) of Pamlico Sound, recovery rate may be exceptionally slow, prolonging any adverse effects of altered nutrient regimes (such as hypoxia) on the health and fitness of resident fish populations. Flooding from the 1999 hurricanes may have contributed to the short-term health and condition of finfish species in Pamlico Sound and also influenced longer-term recovery and ecological status of this system. Longer-term manifestation of effects from flooding may be of particular concern as the frequency of hurricanes is expected to increase over the next few years and the accelerated uses of the coastal zone places further stress on estuarine resources. 相似文献
988.
Sebastian?WetterichEmail author Lutz?Schirrmeister Hanno?Meyer Finn?Andreas?Viehberg Andreas?Mackensen 《Journal of Paleolimnology》2008,39(4):427-449
The aim of this study is to describe ostracods from freshwater habitats in the Siberian Arctic in order to estimate the present-day
relationships between the environmental setting and the geochemical properties of ostracod calcite. A special focus is on
the element ratios (Mg/Ca, Sr/Ca), and the stable isotope composition (δ18O, δ13C), in both ambient waters and ostracod calcite. The most common species are Fabaeformiscandona pedata and F. harmsworthi with the highest frequency in all studied waters. Average partition coefficients D(Sr) of F. pedata are 0.33 ± 0.06 (1σ) in females, and 0.32 ± 0.06 (1σ) in males. A near 1:1 relationship of δ18O was found, with a mean shift of Δmean = 2.2‰ ± 0.5 (1σ) to heavier values in ostracod calcite of F. pedata as compared to ambient waters. The shift is not dependent on δ18Owater, and is caused by metabolic (vital) and temperature effects. Temperature-dependence is reflected in the variations of this
shift. For ostracod calcite of F. pedata a vital effect as compared to inorganic calcite in equilibrium was quantified with 1.4‰. Results of this study are valuable
for the palaeoenvironmental interpretation of geochemical data of fossil ostracods from permafrost deposits. 相似文献
989.
潘集煤矿二叠纪主采煤层中微量元素亲和性研究 总被引:5,自引:0,他引:5
安徽淮南煤田位于华北地台南端 ,发育了华北地区二叠纪含煤岩系中层位最高的可采煤层。采用仪器中子活化分析法 (INAA)测试了淮南煤田潘集煤矿二叠纪主采煤层 13个样品的 36个微量元素的浓度分布 ,并对其共生组合特点、地球化学特征及稀土元素配比模式作了初步分析 ,结果表明 ,煤中不同微量元素显示出不同的亲和性质。元素Br,As ,Sb ,Ni和Co等趋于在煤中富集 ,其中Br的有机亲和性最大。元素Na ,K ,Rb ,Th ,Hf,Zr ,Ta和REE则在煤层与顶底板接触带的碳质泥岩中富集 ,表现出与细粒陆源碎屑物更强的亲和性。其它元素倾向性不甚明显 ,但Fe ,Ca ,Sr ,HREE等元素在海水影响强度增大的煤层中含量增加。元素As,Cs,Ni,Fe和Ca在煤层中含量变化较大 ,其变异系数大于 1,其它元素则相对稳定 ,表明同一矿区煤层中微量元素含量在不受其它地质作用明显叠加影响时具有一定的稳定性。本区煤层稀土元素配比模式与华北其它地区C—P纪煤基本类似 ,普遍存在Eu亏损现象。 ∑REE在煤中分布范围为30× 10 -6~ 95× 10 -6,在顶板泥岩中超过 2 0 0× 10 -6。煤层中部 ∑REE降低 ,HREE相对富集。聚类分析表明 ,元素As ,Se ,Ag和Fe关系密切 ,这与煤中黄铁矿等成岩矿物有直接关系 ,泥炭沼泽演化期间或之后海水的直接或间接影响会促使这 相似文献
990.
Scott?K.?RowlandEmail author Andrew?J.?L.?Harris Martin?J.?Wooster Falk?Amelung Harold?Garbeil Lionel?Wilson Peter?J.?Mouginis-Mark 《Bulletin of Volcanology》2003,65(5):311-330
We have used a suite of remotely sensed data, numerical lava flow modeling, and field observations to determine quantitative characteristics of the 1995 Fernandina and 1998 Cerro Azul eruptions in the western Galápagos Islands. Flank lava flow areas, volumes, instantaneous effusion rates, and average effusion rates were all determined for these two eruptions, for which only limited syn-eruptive field observations are available. Using data from SPOT, TOPSAR, ERS-1, and ERS-2, we determined that the 1995 Fernandina flow covers a subaerial area of 6.5×106 m2 and has a subaerial dense rock equivalent (DRE) volume of 42×106 m3. Field observations, ATSR satellite data, and the FLOWGO numerical model allow us to determine that the effusion rate declined exponentially from a high of ~60–200 m3 s-1 during the first few hours to <5 m3 s-1 prior to ceasing after 73 days, with a mean effusion rate of 4–16 m3 s-1. Integrating the ATSR-derived, exponentially declining effusion rate over the eruption duration produces a total (subaerial + submarine) DRE volume of between 27 and 100×106 m3, the range in values being due to differing assumptions about heat loss characteristics; only values in the higher part of this range are consistent with the independently derived subaerial volume. Using SPOT, TOPSAR, ERS-1, and ERS-2 data, we determine that the 1998 Cerro Azul flow is 16 km long, covers 16 km2, and has a DRE volume of 54×106 m3. FLOWGO produces at-vent velocity and effusion rate values of 11 m s-1 and ~600 m3 s-1, respectively. The velocity value agrees well with the 12 m s-1 estimated in the field. The mean effusion rate (total DRE volume/duration) was 7–47 m3 s-1. Dike dimensions, fissure lengths, and pressure gradients along the conduit based on magma chamber depth estimates of 3–5 km produce mean effusion rates for the two eruptions that range over nearly four orders of magnitude, the range being due to uncertainty in the magma viscosity, dike dimensions, and pressure gradient between magma chamber and vent. Although somewhat consistent with mean effusion rates from other techniques, their wide range makes them less useful. The exponentially declining effusion rates during both eruptions are consistent with release of elastic strain being the driving mechanism of the eruptions. Our results provide independent input parameters for previously published theoretical relationships between magma chamber pressurization and eruption rates that constrain chamber volumes and increases in volume prior to eruption, as well as time constants of exponential decay during the eruption. The results and theoretical relationships combine to indicate that at both volcanoes probably 25–30% of the volumetric increase in the magma chamber erupted as lava onto the surface. In both eruptions the lava flow volumes are less than 1% of the magma chamber volume. 相似文献