On the determination of the equinox and equator of the new fundamental reference coordinate system,the FK5     

W. Fricke 《Celestial Mechanics and Dynamical Astronomy》1980,22(2):113-125

According to IAU recommendations for the improvement of the specification of the fundamental reference system, the positions and centennial variations in the FK5 shall correspond as closely as possible to the dynamical reference frame. Described here is the status of work on the determination of a correction to the FK4 equinox and a correction to the proper motions in right ascension of the FK4 such that the equinox of the FK5 corresponds at all times as closely as possible to the dynamical equinox. Evidence is presented for a correction to the right ascensions of the FK4 (equinox correction) of aboutE=+0^s.050 at 1960, and for a correction to the FK4 proper motions of about = É = +1.25 per century. This investigation has given new findings on the deficiencies of older equinox determinations that have given rise to confusion for a long time. Concerning the determination of the equator point of the FK5 it appears that available new data do not support a significant correction to the FK4.Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978.  相似文献   

Seasonal,tidal, and geomorphic controls on sediment export to Amazon River tidal floodplains     

Daniel J. Nowacki  Andrea S. Ogston  Charles A. Nittrouer  Aaron T. Fricke  Nils E. Asp  Pedro Walfir M. Souza Filho 《地球表面变化过程与地形》2019,44(9):1846-1859

Mainstem–floodplain material exchange in the tidal freshwater reach of major rivers may lead to significant sequestration of riverine sediment, but this zone remains understudied compared to adjacent fluvial and marine environments. This knowledge gap prompts investigation of floodplain-incising tidal channels found along the banks of tidal rivers and their role in facilitating water and suspended-sediment fluxes between mainstem and floodplain. To evaluate this role, and how it evolves along the tidal river and with time, we measured water level, flow velocity, temperature, and suspended-sediment concentration (SSC) in four tidal channels along the tidal Amazon River, Brazil. Eleven deployments were made during low, rising, high, and falling seasonal Amazon discharge. Generally, channels export high-SSC water from the mainstem to the tidal floodplain on flood tides and transfer low-SSC water back to the mainstem on ebbs. Along the length of the tidal river, the interaction between tidal and seasonal water-level variations and channel–floodplain morphology is a primary control on tidal-channel sediment dynamics. Close to the river mouth, where tides are large, this interaction produces transient flow features and current-induced sediment resuspension, but the importance of these processes decreases with distance upstream. Although the magnitude of the exchange of water and sediment between mainstem and floodplain via tidal channels is a small percentage of the total mainstem discharge in this large tidal-river system, tidal channels are important conduits for material flux between these two environments. This flux is critical to resisting floodplain submergence during times of rising sea level. © 2019 John Wiley & Sons, Ltd.  相似文献   

Morphological evolution of a macrotidal back-barrier environment: The Amazon Coast     

Robin L. McLachlan  Andrea S. Ogston  Nils E. Asp  Aaron T. Fricke  Charles A. Nittrouer  Carlos A. F. Schettini 《Sedimentology》2020,67(7):3492-3512

Coastal barriers provide sheltered, low-energy settings for fine-grained sediment deposition and retention, although the process of back-barrier infilling and how tidal-channel connectivity impacts this process is not well-understood. Understanding how back-barrier environments infill and evolve is necessary to predict how they will respond to future changes in sea-level and sediment supply. With this motivation, in situ observations and sedimentary signatures from an Amazonian tidal-channel system are interpreted to create a conceptual model of morphological evolution in a macrotidal back-barrier environment that is rich in fine-grained sediment, vegetated by mangroves and incised by tidal channels with multiple outlets. Results indicate that within a high-connectivity back-barrier channel, tidal processes dominate sedimentation and morphological development. Sediment cores (<60 cm) exhibited millimetre-scale tidalites composed of sand and mud. High-connectivity channels allow tidal propagation from multiple inlets, and in this case, the converging flood waves promote delivery of sediment fluxing through the system to the mangrove flats in the convergence zone. Sediment preferentially deposits in regions with adequate accommodation space and dense vegetation, and in these zones, sediment grain size is slightly finer than that transiting through the system. The greatest sediment-accumulation rates (3 to 4 cm yr⁻¹), calculated from steady-state ²¹⁰Pb profiles, were found in the convergence zone near the mangrove-channel edge. As tidal flats aggrade vertically and prograde into the channels, accommodation space diminishes. In effect, the channel’s narrowest stretch is expected to migrate along the path of net-sediment flux towards regions with more accommodation space until it reaches the tidal-convergence zone. The location of recent preferential infilling is evidenced by relatively rapid sediment-accumulation rates, finer sediment and significant clustering of small secondary tidal channels. These findings shed light on how sediment transported through vegetated back-barrier environments is ultimately preserved and how evidence preserved in surface morphology and the geological record can be interpreted.  相似文献   

In Situ Destruction of Perchlorate and Nitrate Using Gaseous Electron Donor Injection Technology     

Patrick J. Evans  Rodney A. Fricke  Karl Hopfensperger  Tom Titus 《Ground Water Monitoring & Remediation》2011,31(4):103-112

Perchlorate and nitrate in vadose‐zone soil can be continuing sources of groundwater contamination and technologies for remediation of these sources are limited. Gaseous electron donor injection technology (GEDIT) is an in situ approach that was demonstrated at a site in California. A mixture of hydrogen, carbon dioxide, liquefied petroleum gas (LPG), and nitrogen was injected into the vadose zone over a period of 5 months followed by 3 months of LPG alone. Perchlorate and nitrate plus nitrite nitrogen concentrations were reduced by over 90% and both were capable of being reduced to nondetectable concentrations. Hydrogen was required for perchlorate destruction, although concentrations as low as 0.5% were effective. Hydrogen was not required for nitrate destruction. Contaminant destruction was observed in both fine‐grained and coarse‐grained soils ranging from clay to gravel. Hydrogen was an effective electron donor because of its low molecular weight and high diffusivity which likely promoted its penetration into low‐permeability formations. Contaminant destruction was also observed in moisture contents ranging from 6.8% to 36% demonstrating that GEDIT was effective in low‐ and high‐moisture soils. The radius of influence (ROI) for perchlorate destruction was approximately 3.0 to 4.6 m while that for nitrate was greater than 17 m. The ROI was limited by use of a single injection location. Use of a grid injection system is anticipated to greatly increase efficiency. This research represents the first demonstration of GEDIT for treatment of contaminants in the vadose zone.  相似文献   

New insights into the photometric structure of Blue Compact Dwarf Galaxies from a deep Near-Infrared study     

K.G. Noeske  P. Papaderos  L.M. Cairós  K.J. Fricke 《Astrophysics and Space Science》2003,284(2):615-618

We present deep Near-Infrared (NIR) imaging of Blue Compact Dwarf Galaxies (BCDs), allowing for the first time to derive and systematize the NIR structural properties of their stellar low-surface brightness (LSB) host galaxies. Compared to optical data, NIR images, being less contamined by the extended stellar and ionized gas emission from the starburst, permit to study the LSB host galaxy closer to its center. We find that radial surface brightness profiles (SBPs) of the LSB hosts show at large radii a mostly exponential intensity distribution, in agreement with previous optical studies. At small to intermediate radii, however, the NIR data reveal an inwards flattening with respect to the outer exponential slope (`type V SBPs', Binggeli and Cameron, 1991) in the LSB component of more than one half of the sample BCDs. This result may constitute an important observational constraint to the dynamics and evolution of BCDs. We apply a modified exponential fitting function (Papaderos et al., 1996a) to parametrize and systematically study type V profiles in BCDs. A Sérsic law is found to be less suitable for studying the LSB component of BCDs, since it yields very uncertain solutions. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Evolutionary synthesis models for galaxy transformation in clusters     

Jens Bicker  U. Fritze-von Alvensleben  K.J. Fricke 《Astrophysics and Space Science》2003,284(2):463-466

The galaxy population in rich local galaxy clusters shows a ratio of one quarter elliptical galaxies, two quarters S0 galaxies, and one quarter spiral galaxies. Observations of clusters at redshift 0.5 show a perspicuously different ratio, the dominant galaxy type are spiral galaxies with a fraction of two quarters while the number of S0 galaxies decreases to a fraction of one quarter (Dressler et al. 1997). This shows an evolution of the galaxy population in clusters since redshift 0.5 and it has been suspected that galaxy transformation processes during the infall into a cluster are responsible for this change. These could be merging, starburst or ram-pressure stripping. We use our evolutionary synthesis models to describe various possible effects of those interactions on the star formation of spiral galaxies infalling into clusters. We study the effects of starbursts of various strengths as well as of the truncation of star formation at various epochs on the color and luminosity evolution of model galaxies of various spectral types. As a first application we present the comparison of our models with observed properties of the local S0 galaxy population to constrain possible S0 formation mechanisms in clusters. Application to other types of galaxies is planned for the future. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Numerical Simulations of Interacting Gas-Rich Barred Galaxies     

I. Berentzen  C.H. Heller  K.J. Fricke  E. Athanassoula 《Astrophysics and Space Science》2001,276(2-4):699-706

Using an N-body + SPH code, we have performed numerical simulations to investigate the dynamical effects of an interaction between an initially barred galaxy and a small spherical companion. In the models described here the small companion passes through the disc of the larger galaxy perpendicularly to its plane. The impact positions and times are varied with respect to the evolutionary phase of the bar and disc. The interactions produce expanding ring structures, offset bars, spokes and other asymmetries in the stars and gas. They also affect the strength and pattern speed of the bar. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Changes in Coastal Benthic Algae Succession Trajectories and Assemblages Under Contrasting Nutrient and Grazer Loads     

A. Fricke  G. A. Kopprio  D. Alemany  M. Gastaldi  M. Narvarte  E. R. Parodi  R. J. Lara  F. Hidalgo  A. Martínez  E. A. Sar  O. Iribarne  P. Martinetto 《Estuaries and Coasts》2016,39(2):462-477

Eutrophication plays a crucial role in coastal systems, driving changes in the composition and abundance of flora and fauna with consequent effects for the entire ecosystem. Sensitive to nutrient levels, micro- and macroalgal blooms serve as valuable indicators of eutrophication. The San Antonio Bay (Northern Argentinean Patagonia, 40° 43′ S, 64° 56′ W) provides an appropriate system to study in situ eutrophication processes on coastal communities. In a multi-scale approach, using two different kind of settlement substrates (micro: polyethylene terephthalate, and macro: ceramic), the present study followed benthic algal dynamics over one year, distinguishing changes in natural succession and seasonality. Strong differences were found in the biofilm assemblages after three days, marked by tube dwelling diatoms and Cocconeis spp. under high nutrient-grazer conditions and needle like diatoms (e.g. Nitzschia spp., Tabularia spp.) under lower nutrient-grazer loads. The succession continued by the colonization of macroalgae, with a higher recruitment rate in the nutrient and grazer rich environment with a concomitant higher diversity. Our results show that under higher nutrient-grazer conditions natural benthic succession not only differs in trajectory but in its final taxa composition promoting higher biodiversity and biomass accumulation. In addition, taxa specific substrate preferences interfere with the observed eutrophication pattern, suggesting substrate dependant interrelations between the bloom forming taxa. These findings provide evidence that nutrient enrichment can not only affect an established assemblage but also affect the early succession stages, changing the succession trajectory and thus the final assemblage.  相似文献   

Pathways for sediment transport and retention in a vegetated,mid-channel island: Connecting sediment dynamics to morphology in Meinmahla Island,Ayeyarwady Delta,Myanmar     

Hannah E. Glover  Andrea S. Ogston  Aaron T. Fricke  Chuck A. Nittrouer  Cherry Aung  Thet Naing  Evan J. Lahr 《Sedimentology》2023,70(1):214-234

Vegetated mid-channel islands play an important though poorly understood role in the sediment dynamics and morphology of tide-dominated deltas. Meinmahla Island is a mangrove-forest preserve at the mouth of the Bogale distributary channel, in the Ayeyarwady Delta, Myanmar. In this relatively unaltered mid-channel island, sediment dynamics can be directly connected to morphology. Field measurements from 2017 to 2019 provide insight into the pathways for sediment transport and resulting morphological evolution. Water depth, salinity and turbidity were monitored semi-continuously, and velocity profilers with turbidity and salinity sensors were deployed seasonally in single-entrance (dead-end/blind) and multi-entrance tidal channels of the island. The morphological evolution was evaluated using grain size, ²¹⁰Pb geochronology, remote sensing and channel surveys. The data show that ebb-dominant, single-entrance channels along the island exterior import sediment year-round to the land surface. However, these exterior channels do not deliver enough sediment to maintain the observed ca 0.8 cm/yr accretion rate, and most of the sediment import occurs via interior, multi-entrance channels. Interior channels retain water masses that are physically distinct from the water in the Bogale distributary, and estuarine processes at the tidal-channel mouths import sediment into the island. Sediment is sourced to the island from upriver in the wet season and from the Gulf of Mottoma in the dry season, as the location of the estuary shifts seasonally within the Bogale distributary. The salinity and biogeochemistry of the distributary water are affected by interactions with sediment and groundwater in the island interior. The largest interior channels have remained remarkably stable while the island has aggraded and prograded over decadal timescales. However, the studied multi-entrance channel is responding to a drainage-network change by narrowing and shoaling. Overall, mid-channel islands trap sediment and associated nutrients at the river–ocean interface, and these resilient landscape features evolve in response to changes in drainage-network connectivity.  相似文献   

Mineralogical and chemical variations in hypogene and supergene kaolin deposits in a mobile fold belt the Central Andes of northwestern Peru   总被引：1，自引：0，他引：1  

H. G. Dill  H.-R. Bosse  K.-H. Henning  A. Fricke  H. Ahrendt 《Mineralium Deposita》1997,32(2):149-163

In western Peru kaolin-alunite deposits occur in Lower Cretaceous and Tertiary clastic, volcaniclastic and volcanic, mostly rhyolitic, rocks. Alunites from␣hypogene kaolin deposits yield  K /Ar ages of 11.5 ±␣0.7␣Ma and 13.3 ± 0.4 Ma. In addition to kaolin and alunite, the following minerals are present: white mica, smectite, barite, pyrophyllite, tridymite, cristobalite, α- and β-quartz, chamosite, gibbsite, and aluminum-phosphate-sulphate minerals (APS). APS mineralizations with REE-bearing svanbergite and florencite originate from supergene alteration. Woodhouseite, goyazite, crandallite and pure svanbergite develop in hypogene and supergene kaolin deposits. The distinction between hypogene and supergene kaolinization can be made using various element ratios in kaolin (P vs. S, Zr vs. Ti, Cr + Nb vs. Ti + Fe, and Ce + Y + La vs. Ba + Sr). S,␣Ba, and Sr are considerably enriched in kaolin during hydrothermal alteration, whereas Cr, Nb, Ti and lanthanide elements are concentrated mainly during weathering. Au and Ag become enriched during hypogene kaolinization (advanced argillitization). Kaolinization is associated with the evolution of the Central Andes as follows: (1) during the Lower Cretaceous kaolinization characterizes phases of relative tectonic quiescence during mountain building and took place in a miogeosynclinal back-arc basin. The kaolin-bearing sediments were laid down in flood plain to delta plain environments; (2) in the magmatic arc/back-arc basin (eugeosyncline) kaolinization was mainly associated with uplift and peneplanation; (3) in the magmatic arc proper, late Miocene kaolinization of volcanic and volcaniclastic rocks has many features in common with the high sulphidation epithermal Au deposits. Received: 11 August 1995 / Accepted: 8 May 1996  相似文献