Multivariable spatial prediction     

Jay M. Ver Hoef  Noel Cressie 《Mathematical Geology》1994,26(2):273-275

  相似文献   

EURD: The Mission and the Stellar Absolute Fluxes of B-Type Stars     

Carmen Morales  Joaquín Trapero  José F. Gómez  Verónica Orozco  Alvaro Gimenez  Stuart Bowyer  Jerry Edelstein  Eric Korpela  Michael Lampton  Jeff Cobb 《Astrophysics and Space Science》2001,276(1):141-150

We present here stellar spectra of B stars obtained with the EURD spectrograph, one of the three instruments on board MINISAT-01. EURD is a spectrograph specially designed to detect diffuse radiation in thewavelength range between 350 and 1100 Å with 5 Å spectral resolution. EURD main scientific targets are: the spectrum of interstellar medium,atmospheric airglow, decaying neutrinos, Moon and early type stars.  相似文献   

Temperature effects on asexual reproduction of the scyphozoan Aurelia aurita s.l.: differences between exotic (Baltic and Red seas) and native (Mediterranean Sea) populations   总被引：1，自引：0，他引：1       下载免费PDF全文

Maria Pascual  Verónica Fuentes  Antonio Canepa  Dacha Atienza  Josep‐Maria Gili  Jennifer E. Purcell 《Marine Ecology》2015,36(4):994-1002

Massive occurrences of jellyfish can cause direct impacts on the economy, especially on tourism and commercial fisheries. Translocation of jellyfish species by humans has caused damaging blooms in new habitats. Aurelia aurita s.l. has been introduced in many locations around the world. To test the potential success of Au. aurita s.l. in various habitats, scyphistomae from different climatic locations (Mediterranean, Red and Baltic Seas) were cultured individually for 201 days at three temperatures (14, 21 and 28 °C) with the same salinity, food and light. We tested the null hypotheses that there were no differences in survival or asexual reproduction (budding and strobilation) amongst populations [native (Mediterranean) and exotic (Red and Baltic)]. Survival of the three scyphistoma populations did not differ significantly across temperatures; however, the Red Sea group had lower survival at all temperatures than did the other populations. Most individuals strobilated at 14 °C. Red Sea scyphistomae strobilated more quickly than Baltic and Mediterranean Sea scyphistomae and produced the fewest ephyrae, whereas Baltic Sea scyphistomae produced the most. Our results indicate that Au. aurita from the Baltic or Red Seas introduced into the Northwest Mediterranean Sea would potentially persist and successfully asexually reproduce there. A new invader could even have greater asexual production than the local Au. aurita s.l. Establishment of the invaders could increase genetic variation of subsequent generations and increase their adaptability to environmental changes. Our results suggest that introduction of exotic Au. aurita s.l. populations could increase jellyfish blooms in the Mediterranean Sea.  相似文献   

The sequential megafaunal collapse hypothesis: Testing with existing data   总被引：4，自引：1，他引：4  

Douglas P. DeMaster  Andrew W. Trites  Phillip Clapham  Sally Mizroch  Paul Wade  Robert J. Small  Jay Ver Hoef 《Progress in Oceanography》2006,68(2-4):329

Springer et al. [Springer, A.M., Estes, J.A., van Vliet, G.B., Williams, T.M., Doak, D.F., Danner, E.M., Forney, K.A., Pfister, B., 2003. Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling? Proceedings of the National Academy of Sciences 100 (21), 12,223–12,228] hypothesized that great whales were an important prey resource for killer whales, and that the removal of fin and sperm whales by commercial whaling in the region of the Bering Sea/Aleutian Islands (BSAI) in the late 1960s and 1970s led to cascading trophic interactions that caused the sequential decline of populations of harbor seal, northern fur seal, Steller sea lion and northern sea otter. This hypothesis, referred to as the Sequential Megafaunal Collapse (SMC), has stirred considerable interest because of its implication for ecosystem-based management. The SMC has the following assumptions: (1) fin whales and sperm whales were important as prey species in the Bering Sea; (2) the biomass of all large whale species (i.e., North Pacific right, fin, humpback, gray, sperm, minke and bowhead whales) was in decline in the Bering Sea in the 1960s and early 1970s; and (3) pinniped declines in the 1970s and 1980s were sequential. We concluded that the available data are not consistent with the first two assumptions of the SMC. Statistical tests of the timing of the declines do not support the assumption that pinniped declines were sequential. We propose two alternative hypotheses for the declines that are more consistent with the available data. While it is plausible, from energetic arguments, for predation by killer whales to have been an important factor in the declines of one or more of the three populations of pinnipeds and the sea otter population in the BSAI region over the last 30 years, we hypothesize that the declines in pinniped populations in the BSAI can best be understood by invoking a multiple factor hypothesis that includes both bottom–up forcing (as indicated by evidence of nutritional stress in the western Steller sea lion population) and top–down forcing (e.g., predation by killer whales, mortality incidental to commercial fishing, directed harvests). Our second hypothesis is a modification of the top–down forcing mechanism (i.e., killer whale predation on one or more of the pinniped populations and the sea otter population is mediated via the recovery of the eastern North Pacific population of the gray whale). We remain skeptical about the proposed link between commercial whaling on fin and sperm whales, which ended in the mid-1960s, and the observed decline of populations of northern fur seal, harbor seal, and Steller sea lion some 15 years later.  相似文献   

Hydrothermal alteration and magnetic properties of rocks in the Carolina de Michilla stratabound copper district,northern Chile     

Brian Townley  Pierrick Roperch  Verónica Oliveros  Andres Tassara  César Arriagada 《Mineralium Deposita》2007,42(7):771-789

In the Carolina de Michilla district, northern Chile, stratabound copper mineralization is hosted by Jurassic volcanic rocks along the trace of the Atacama fault system. In this study, we present the overall effects of hydrothermal alteration on the magnetic properties of rocks in this district. Two types of metasomatic alteration associations occur, one of regional extent and the other of local hydrothermal alteration associated with copper mineralization (e.g., Lince–Estefanía–Susana). Regional alteration is interpreted as a low-grade “propylitic association” characterized by an epidote–chlorite–smectite–titanite–albite–quartz–calcite association. The local hydrothermal alteration is characterized broadly by a quartz–albite–epidote–chlorite–calcite mineral assemblage. The most pervasive alteration mineral is albite, followed by epidote and, locally, actinolite. These minerals contrast sharply against host rock minerals such as chlorite, calcite, zeolite, prehnite, and pumpellyite, but alteration is constrained to mineralized bodies as narrow and low contrast alteration halos that go outwards from actinolite–albite to epidote–albite, to epidote–chlorite, and finally to chlorite. Hydrothermal alteration minerals, compared to regional alteration minerals, show iron-rich epidotes, a lower chlorite content of the chlorite–smectite series, and a nearly total albite replacement of plagioclase in the mineralized zones. Opaque minerals associated with regional alteration are magnetite and maghemite, and those associated to hydrothermal alteration are magnetite, hematite, and copper sulphides. We present paleomagnetic results from nine sites in the Michilla district and from drill cores from two mines. Local effects of hydrothermal alteration on the original magnetic mineralogy indicate similar characteristics and mineralogy, except for an increase of hematite that is spatially associated with the Cu–sulphide breccias with low magnetic susceptibilities. Results indicate that it is impossible to magnetically differentiate mineralized bodies from unmineralized lavas, except for pyrite-rich hydrothermal breccias. In conclusion, for stratabound copper deposits of the Michilla type, the overall effect of hydrothermal alteration on the paleomagnetic properties of rocks is of low contrast, not clearly discernable even at a small scale. From an exploration point of view, magnetic exploration surveys should not discern mineralized bodies of Cu–sulphide breccias except in detailed ground surveys due to the small size of contrasting bodies. Unoriented drill cores with primary ore mineralization record a characteristic remanent magnetization of reverse polarity. Taking into account the azimuth and dip of the drill cores, we were able to compare the magnetization of the mineralized bodies with the characteristic directions from sites drilled in situ from Late Jurassic–Early Cretaceous intrusives mostly. The characteristic direction recorded by the Pluton Viera is similar to the magnetization of the ore bodies of the Estefania mine. If copper mineralization mostly postdates the tilt of the volcanic flows, the low paleomagnetic inclinations suggest an age for the mineralization near 145 Ma, the time of the lowest paleolatitude for the South American plate during the Mesozoic.  相似文献   

Coupling of the Perturbed C–N–P Cycles in Industrial Time     

Abraham Lerman  Fred T. Mackenzie  L. May Ver 《Aquatic Geochemistry》2004,10(1-2):3-32

Coupling of the C–N–P biogeochemical cycles is effected by the dependence of the land and aquatic primary producers on the availability of N and P. In general, the Redfield ratios C:P and N:P in the reservoirs supplying nutrients for primary production on land, in the oceanic coastal zone, and in the surface ocean differ from these ratios in the land phytomass and aquatic plankton. When N:P in the source is higher than in primary producers, this results in a potential accumulation of some excess nitrogen in soil water and coastal water, and increased denitrification flux to the atmosphere. The oceanic coastal zone plays an important role in the coupled C–N–P cycles and their dynamics because of its intermediate position between the land and oceanic reservoirs. These coupled cycles were analyzed for the last 300 years of exposure to four human-generated forcings (fossil fuel emissions, land use change, chemical fertilization of land, and sewage discharge to the coastal zone) and global temperature rise. In the period from 1700 to 2000, there has been a net loss of C, N, and P primarily from the land phytomass and soil humus, despite the rise in atmospheric CO₂, increased recycling of nutrients from humus, chemical fertilization, and re-growth of forests on previously disturbed land. The main mechanisms responsible for the net loss were increased riverine transport to the coastal zone of dissolved and particulate materials and, for N, increased denitrification on land. The oceanic coastal zone gained N and P, resulting in their accumulation in the organic pool of living biomass and dissolved and reactive particulates, as well as in their accumulation in coastal sediments from land-derived and in situ produced organic matter. Pronounced shifts in the rates and directions of change in some of the major land reservoirs occurred near the mid-1900s. Denitrification removes N from the pool available for primary production. It is the strongest on land, accounting for 73–83% of N removal from land by the combined mechanisms of denitrification and riverine export.  相似文献   

L’anomalie régionale de la direction des courants telluriques du bassin des carpathes     

Antal Ádám  József Verö 《Studia Geophysica et Geodaetica》1968,12(4):412-414

  相似文献   

Petrogenesis of Quebrada de la Mina and Altar North porphyries (Cordillera of San Juan,Argentina): Crustal assimilation and metallogenic implications     

Laura Maydagán  Marta Franchini  Massimo Chiaradia  Verónica Bouhier  Noelia Di Giuseppe  Roger Rey  Luis Dimieri 《地学前缘(英文版)》2017,8(5):1135-1159

We investigate the geology of Altar North (Cu–Au) and Quebrada de la Mina (Au) porphyry deposits located in San Juan Province (Argentina), close to the large Altar porphyry copper deposit (995 Mt, 0.35% Cu, 0.083 g/t Au), to present constraints on the magmatic processes that occurred in the parental magma chambers of these magmatic-hydrothermal systems. Altar North deposit comprises a plagioclase-amphibole-phyric dacite intrusion (Altar North barren porphyry) and a plagioclase-amphibole-biotite-phyric dacite stock (Altar North mineralized porphyry, 11.98 ± 0.19 Ma). In Quebrada de la Mina, a plagioclase-amphibole-biotite-quartz-phyric dacite stock (QDM porphyry, 11.91 ± 0.33 Ma) crops out. High Sr/Y ratios (92–142) and amphibole compositions of Altar North barren and QDM porphyries reflect high magmatic oxidation states (fO₂ = NNO +1.1 to +1.6) and high fH₂O conditions in their magmas. Zones and rims enriched in anorthite (An_37–48), SrO (0.22–0.33 wt.%) and FeO (0.21–0.37 wt.%) in plagioclase phenocrysts are evidences of magmatic recharge processes in the magma chambers. Altar North and Quebrada de la Mina intrusions have relatively homogeneous isotopic compositions (⁸⁷Sr/⁸⁶Sr_(t) = 0.70450–0.70466, ε_Nd(t) = +0.2 to +1.2) consistent with mixed mantle and crust contributions in their magmas. Higher Pb isotopes ratios (²⁰⁷Pb/²⁰⁴Pb = 15.6276–15.6294) of these intrusions compared to other porphyries of the district, reflect an increase in the assimilation of high radiogenic Pb components in the magmas. Ages of zircon xenocrysts (297, 210, 204, 69 Ma) revealed that the magmas have experienced assimilation of Miocene, Cretaceous, Triassic and Carboniferous crustal rocks.Fluids that precipitated sulfides in the Altar deposit may have remobilized Pb from the host rocks, as indicated by the ore minerals being more radiogenic (²⁰⁷Pb/²⁰⁴Pb = 15.6243–15.6269) than their host intrusions. Au/Cu ratio in Altar porphyries (average Au/Cu ratio of 0.14 × 10^?4 by weight in Altar Central) is higher than in the giant Miocene porphyry deposits located to the south: Los Pelambres, Río Blanco and Los Bronces (Chile) and Pachón (Argentina). We suggest that the increase in Au content in the porphyries of this region could be linked to the assimilation of high radiogenic Pb components in the magmas within these long-lived maturation systems.  相似文献   

EURD Data Processing     

José F. Gómez  Joaquín Trapero  Carmen Morales  Verónica Orozco  Jerry Edelstein  Eric Korpela  Michael Lampton 《Astrophysics and Space Science》2001,276(1):233-238

EURD (EspectrógrafoUltravioleta extremo para la Radiación Difusa) is one of thescientific instruments on board MINISAT 01. EURD is a spectrograph withvery high sensitivity and spectral resolution ( 5 Å), designed to obtain extremeultraviolet ( 350-1100 Å) spectra of diffuse radiation.We outline the processing of EURD data, and how we obtain informationfrom these data on the scientific goals of the mission: hot interstellarmedium, neutrino decay line, nightglow emission, and early-type stars.  相似文献   

Nematode diversity in different microhabitats in a mangrove region     

Taciana K. Pinto  Melanie C. V. Austen  Richard M. Warwick  Paul J. Somerfield  André M. Esteves  Francisco J. V. Castro  Verônica G. Fonseca‐Genevois  Paulo J. P. Santos 《Marine Ecology》2013,34(3):257-268

Mangroves are highly productive environments that play important ecological and socioeconomic roles; however, they have been impacted to different degrees in most countries worldwide. The knowledge of which organisms inhabit this environment and their ecological interactions is the first step towards its conservation. The natural variability of environmental factors in mangroves provides numerous niches available to different species. Meiofauna have patchy patterns of distribution that are related to the availability of resources. Hence, meiofauna are expected to present a high diversity of different taxa occupying the different microhabitats offered by mangroves. This work aims to test the hypothesis that the assemblage structure of Nematoda varies significantly among mangrove microhabitats and to contribute knowledge on the meiofauna diversity in mangrove environments. This work was carried out in a mangrove region at Pernambuco state, Northeastern Brazil. Qualitative samples were collected in nine microhabitats which show different characteristics mainly in terms of presence of vegetation or another organism and sediment grain size. Univariate and multivariate analysis were applied to Nematoda genera abundance data. Our results demonstrate the existence of significant differences among microhabitats regarding nematode assemblage structure corroborating the hypothesis. Different Nematoda assemblages are present in at least seven microhabitats. These assemblages are composed of nematode genera with different trophic and morphological features, demonstrating a strong relationship between morphological diversity and ecological plasticity. Furthermore, this study also demonstrates the importance of the conservation of this ecosystem and its attributes.  相似文献