Prospects for spectroscopic reflected-light planet searches     

Christopher Leigh  rew Collier Cameron  Tristan Guillot 《Monthly notices of the Royal Astronomical Society》2003,346(3):890-896

High-resolution spectroscopic searches for the starlight reflected from close-in extrasolar giant planets have the capability of determining the optical albedo spectra and scattering properties of these objects. When combined with radial velocity measurements they also yield the true mass of the planet. To date, only two such planets have been targeted for reflected-light signals, yielding upper limits on the optical albedos of the planets. Here we examine the prospects for future searches of this kind. We present Monte Carlo estimates of prior probability distributions for the orbital velocity amplitudes and planet/star flux ratios of six bright stars known to harbour giant planets in orbits with periods of less than 5 d. Using these estimates, we assess the viability of these targets for future reflected-light searches using 4- and 8-m class telescopes.  相似文献   

Testing materials to mitigate terrestrial organic contamination of meteorites: Implications for collection,curation, and handling of astromaterials     

Libby D. Tunney  Patrick J. A. Hill  Christopher D. K. Herd  Robert W. Hilts 《Meteoritics & planetary science》2023,58(2):207-217

Organic matter in astromaterials can provide important information for understanding the chemistry of our solar system and the prebiotic conditions of the early Earth. However, once astromaterials reach the Earth's surface, they can be readily contaminated through contact with the Earth's surface as well as during processing and curation. Here, we investigate how typical handling and curation materials interact with meteorite specimens by documenting hydrophobic organic compound contamination in the laboratory environment and on materials that might be used for their collection and storage. We use gas chromatography–mass spectrometry analysis of soluble organic compounds in dichloromethane extracts of these materials to gain insights into what materials and methods are best for the collection and curation of astromaterials. Our results have implications for how extraterrestrial samples—especially those containing significant intrinsic organic matter—are handled and curated to preserve them in their most pristine states. Following recommendations of other researchers in the area of returned sample curation, we advocate for a thorough investigation into the materials used in handling and curation of meteorites to create a contamination baseline to inform soluble organic analyses on astromaterials and enable the discrimination of terrestrial and extraterrestrial compounds.  相似文献   

Effects of streamflow isotope sampling strategies on the calibration of a tracer-aided rainfall-runoff model     

Jamie Lee Stevenson  Christian Birkel  Aaron J. Neill  Doerthe Tetzlaff  Chris Soulsby 《水文研究》2021,35(6):e14223

Isotopes are increasingly used in rainfall-runoff models to constrain conceptualisations of internal catchment functioning and reduce model uncertainty. However, there is little guidance on how much tracer data is required to adequately do this, and different studies use data from different sampling strategies. Here, we used a 7-year time series of daily stable water isotope samples of precipitation and streamflow to derive a range of typical stream sampling regimes and investigate how this impacts calibration of a semi-distributed tracer-aided model in terms of flow, deuterium and flux age simulations. Over the 7 years weekly sampling facilitated an almost identical model performance as daily, and there were only slight deteriorations in performance for fortnightly sampling. Monthly sampling resulted in poorer deuterium simulations and greater uncertainty in the derived parameter sets ability to accurately represent catchment functioning, evidenced by unrealistic reductions in the volumes of water available for mixing in the saturation area causing simulated water age decreases. Reducing sampling effort and restricting data collection to 3 years caused reductions in the accuracy of deuterium simulation, though the deterioration did not occur if sampling continued for 5 years. Analysis was also undertaken to consider the effects of reduced sampling effort over the driest and wettest hydrological years to evaluate effects of more extreme conditions. This showed that the model was particularly sensitive to changes in sampling during dry conditions, when the catchment hydrological response is most non-linear. Across all dataset durations, sampling in relation to flow conditions, rather than time, revealed that samples collected at flows >Q50 could provide calibration results comparable to daily sampling. Targeting only extreme high flows resulted in poor deuterium and low flow simulations. This study suggests sufficient characterization of catchment functioning can be obtained through reduced sampling effort over longer timescales and the targeting of flows >Q50.  相似文献   

Biogeochemistry of sterols in plankton, settling particles and recent sediments in a cold ocean ecosystem (Trinity Bay, Newfoundland)     

Edward D. Hudson  Christopher C. Parrish  Robert J. Helleur 《Marine Chemistry》2001,76(4)

In the context of a multidisciplinary study to determine current and past ecosystem health and the relative contributions of sources of organic matter (marine vs. terrestrial and natural vs. anthropogenic input), sterols were determined in plankton, settling particles and sediments from Trinity Bay, Newfoundland, a sub-polar Atlantic Ocean ecosystem. The centric diatoms Chaetoceros spp., Thalassiosira spp. and Leptocylindrus danicus were all prominent in the plankton samples, and centric diatoms predominated in the settling particles. Plankton samples contained 0.4±0.4 mg/g dw (1995) or 1.4±1.3 mg/g dw (1996) total sterols, with cholesta-5,24-dien-3β-ol (mean 26% of total sterols), cholest-5-en-3β-ol (24%) and cholesta-5,22(E)-dien-3β-ol (13%) chief among these, denoting diatom and zooplankton sources. In settling particles, the prominence of cholesta-5,24-dien-3β-ol (24%), cholest-5-en-3β-ol (24%), cholesta-5,22(E)-dien-3β-ol (13%) and 24-methylcholesta-5,22(E)-dien-3β-ol (9%) again suggested mainly marine sources. The sterol composition of plankton and settling particles from different sampling periods showed a high degree of consistency. Higher plant C₂₉ sterols (notably 24-ethylcholest-5-en-3β-ol, 9–26%) were prominent in sediments from both inshore and offshore sites. No decreasing trend in total or individual sterols was observed down the 30-cm sediment cores, suggesting good overall preservation. No 5β-stanols such as 5β-cholestan-3β-ol (coprostanol) were detected in offshore sediments, plankton or settling particles, with only low levels (5β-cholestan-3β-ol max. 4.4%, 5β-cholestan-3α-ol max. 5.1%) in certain inshore sediments. This suggests that raw sewage discharges in rural Newfoundland are being efficiently degraded or dispersed, or that inputs are highly localized. Source apportionation of organic matter in the sediment samples based on sterol composition was attempted. This highlighted the large terrestrial contribution to the sterols in marine sediments (up to 58% of sterols inshore, 24% offshore) and suggests either degradation or effective recycling of marine sterols.  相似文献   

Raster voronoi tessellation and its application to emergency modeling     

Ickjai Lee  Kyungmi Lee  Christopher Torpelund-Bruin 《地球空间信息科学学报》2011,14(4):235-245

Due to the advances in Web technologies,various raster maps are available through Web Map Services such as Google maps and Yahoo maps.These online maps are used to visualize diverse types of disasters.Understanding disasters with these online maps has become an important research issue.In this article,we propose a map-based general-purpose emergency management support system based on a computational model of generalized(multiplicatively weighted,order-k,and Minkowski-metric)Voronoi diagrams.The proposed system tessellates Web maps and models disasters(or emergency response units)having different weights in the complete order from 1 to k-1 in the three popular Minkowski metrics(Euclidean,Manhattan,and Maximum distance)pro-vide insightful information for various what-if emergency scenarios.The proposed map-based emergency management support system systematically supports neighboring queries,districting queries,location optimization queries,and routing queries.We pro-vide specific examples to illustrate how our system supports these queries.  相似文献   

A complete dynamical ozone budget measured in the tropical marine boundary layer during PASE     

Stephen A. Conley  Ian C. Faloona  Donald H. Lenschow  Teresa Campos  Clifford Heizer  Andrew Weinheimer  Christopher A. Cantrell  Roy L. Mauldin III  Rebecca S. Hornbrook  Ilana Pollack  Alan Bandy 《Journal of Atmospheric Chemistry》2011,68(1):55-70

The Pacific Atmospheric Sulfur Experiment (PASE) was a field mission that took place aboard the NCAR C-130 airborne laboratory over the equatorial Pacific Ocean near Christmas Island (Kirimati, Republic of Kiribati) during August?CSeptember, 2007. Eddy covariance measurements of the ozone fluxes at various altitudes above the ocean surface, along with simultaneous mapping of the horizontal gradients provided a unique opportunity to observe all of the dynamical components of the ozone budget in this remote marine environment. The results of six daytime and two sunrise flights indicate that vertical transport into the marine boundary layer from above and horizontal advection by the tradewinds are both important source terms, while photochemical destruction consisting of 82% photolysis (leading to OH production), 11% reaction with HO₂, and 7% reaction with OH provides the main sink. The overall photochemical lifetime of ozone in the marine boundary layer was found to be 6.5 days. Ocean uptake of ozone was observed to be fairly slow (mean deposition velocity of 0.024?±?0.014 cm s^?1) accounting for a diurnally averaged loss rate that was ??30% as large as the net photochemical destruction. From the measurement of deposition velocity an ozone reactivity of ??50 s^?1 in seawater is inferred. Due to the unprecedented measurement accuracy of the dynamical budget terms, unobserved photochemistry was able to be deduced, leading to the conclusion that 3.9?±?3.0 ppt (parts per trillion by volume) of NO is present on average in the daytime tropical marine boundary layer, broadly consistent with several previous studies in similar environments. It is estimated, however, that each ppt of BrO hypothetically present would counter each ppt of NO above the requisite 3.9 ppt needed for budget closure. The long-term budget of ozone is further analyzed in the buffer layer, between the boundary layer and free troposphere, and used to derive an entrainment velocity across the trade wind inversion of 0.51 ± 0.38 cm s^?1.  相似文献   

Pacific Atmospheric Sulfur Experiment (PASE): dynamics and chemistry of the south Pacific tropical trade wind regime     

Alan Bandy  Ian C. Faloona  Byron W. Blomquist  Barry J. Huebert  Antony D. Clarke  Steven G. Howell  R. L. Mauldin  Christopher A. Cantrell  James G. Hudson  Brian G. Heikes  John T. Merrill  Yuhang Wang  Daniel W. O��Sullivan  Wolfgang Nadler  Douglas D. Davis 《Journal of Atmospheric Chemistry》2011,68(1):5-25

The Pacific Atmospheric Sulfur Experiment (PASE) was a comprehensive airborne study of the chemistry and dynamics of the tropical trade wind regime (TWR) east of the island of Kiritibati (Christmas Island, 157º, 20?? W, 2º 52?? N). Christmas Island is located due south of Hawaii. Geographically it is in the northern hemisphere yet it is 6?C12º south of the intertropical convergence zone (ITCZ) which places it in the southern hemisphere meteorologically. Christmas Island trade winds in August and September are from east south east at 3?C15 ms^?1. Clouds, if present, are fair weather cumulus located in the middle layer of the TWR which is frequently labeled the buffer layer (BuL). PASE provided clear support for the idea that small particles (80 nm) were subsiding into the tropical trade wind regime (TWR) where sulfur chemistry transformed them to larger particles. Sulfur chemistry promoted the growth of some of these particles until they were large enough to activate to cloud drops. This process, promoted by sulfur chemistry, can produce a cooling effect due to the increase in cloud droplet density and changes in cloud droplet size. These increases in particle size observed in PASE promote additional cooling due to direct scattering from the aerosol. These potential impacts on the radiation balance in the TWR are enhanced by the high solar irradiance and ocean albedo of the TWR. Finally because of the large area involved there is a large factional impact on earth??s radiation budget. The TWR region near Christmas Island appears to be similar to the TWR that persists in August and September, from southwest of the Galapagos to at least Christmas Island. Transport in the TWR between the Galapagos and Christmas involves very little precipitation which could have removed the aerosol thus explaining at least in part the high concentrations of CCN (??300 at 0.5% supersaturation) observed in PASE. As expected the chemistry of sulfur in the trade winds was found to be initiated by the emission of DMS into the convective boundary layer (BL, the lowest of three layers). However, the efficiency with which this DMS is converted to SO₂ has been brought into further question by this study. This unusual result has come about as result of our using two totally different approaches for addressing this long standing question. In the first approach, based on accepted kinetic rate constants and detailed steps for the oxidation of DMS reflecting detailed laboratory studies, a DMS to SO₂ conversion efficiency of 60?C73% was determined. This range of values lies well within the uncertainties of previous studies. However, using a completely different approach, involving a budget analysis, a conversion value of 100% was estimated. The latter value, to be consistent with all other sulfur studies, requires the existence of a completely independent sulfur source which would emit into the atmosphere at a source strength approximately half that measured for DMS under tropical Pacific conditions. At this time, however, there is no credible scientific observation that identifies what this source might be. Thus, the current study has opened for future scientific investigation the major question: is there yet another major tropical marine source of sulfur? Of equal importance, then, is the related question, is our global sulfur budget significantly in error due to the existence of an unknown marine source of sulfur? Pivotal to both questions may be gaining greater insight about the intermediate DMS oxidation species, DMSO, for which rather unusual measurements have been reported in previous marine sulfur studies. The 3 pptv bromine deficit observed in PASE must be lost over the lifetime of the aerosol which is a few days. This observation suggests that the primary BrO production rate is very small. However, considering the uncertainties in these observations and the possible importance of secondary production of bromine radicals through aerosol surface reactions, to completely rule out the importance of bromine chemistry under tropical conditions at this time cannot be justified. This point has been brought into focus from prior work that even at levels of 1 pptv, the effect of BrO oxidation on DMS can still be quite significant. Thus, as in the case of DMS conversion to SO₂, future studies will be needed. In the latter case there will need to be a specific focus on halogen chemistry. Such studies clearly must involve specific measurements of radical species such as BrO.  相似文献   

Long-term coexistence of non-indigenous species in aquaculture facilities     

Rius M  Heasman KG  McQuaid CD 《Marine pollution bulletin》2011,62(11):2395-2403

Non-indigenous species (NIS) are a growing problem globally and, in the sea, aquaculture activities are critical vectors for their introduction. Aquaculture introduces NIS, intentionally or unintentionally, and can provide substratum for the establishment of other NIS. Little is known about the co-occurrence of NIS over long periods and we document the coexistence over decades of a farmed NIS (a mussel) with an accidently introduced species (an ascidian). Both are widespread and cause serious fouling problems worldwide. We found partial habitat segregation across depth and the position of rafts within the studied farm, which suggests competitive exclusion of the mussel in dark, sheltered areas and physiological exclusion of the ascidian elsewhere. Both species exhibit massive self-recruitment, with negative effects on the industry, but critically the introduction of NIS through aquaculture facilities also has strong detrimental effects on the natural environment.  相似文献   

Field comparison of passive sampling and biological approaches for measuring exposure to PAH and alkylphenols from offshore produced water discharges     

Harman C  Brooks S  Sundt RC  Meier S  Grung M 《Marine pollution bulletin》2011,63(5-12):141-148

Polycyclic aromatic hydrocarbons (PAH) and alkylphenols (AP) that are present in routine discharges of produced water (PW) from the offshore industry continue to cause concern. The suitability of biological methods and chemical based passive samplers to determine exposure to these compounds was tested by deploying them around an oil installation and at reference locations in the North Sea. PAH and AP were analysed either as parent compounds in passive samplers and mussel tissue or as metabolites in fish bile. Generally the pattern of exposure relative to proximity to the discharge was represented by mussels, SPMDs and fish for PAH. Fish and SPMDs showed good correlation for PAH accumulations, whereas some differences were apparent between mussels and SPMDs. POCIS was the only technique tested that could accurately measure the most abundant AP in PW. The advantages of biologically independent measures of exposure for inclusion in discharge monitoring studies are outlined.  相似文献   

The Khao Yai Fault on the southern margin of the Khorat Plateau, and the pattern of faulting in Southeast Thailand     

Michael F. Ridd  Christopher K. Morley 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(1):143-156

A study of Google Earth images has revealed a hitherto-unrecorded gently curved lineament within the southern marginal zone of the Khorat Plateau in eastern Thailand. The lineament, confirmed by digital elevation model (DEM) images, is at least 130 km long and coincides with a dip reversal of the Mesozoic Khorat Group. It is interpreted here as a fault, named the Khao Yai Fault, and it has characteristics which make it unusual within the Khorat Plateau. The fault forms the northern boundary of a belt of several ENE-WSW trending fault splays which are thought to link with the Mae Ping Fault further south; this is interpreted as a left-stepping, sinistral strike-slip duplex about 50 km wide and 150 km long. Apatite fission track data indicate that exhumation began during the earliest Palaeogene.The Khao Yai Fault is considered in its regional context which includes the Cardamomes Mountains of Cambodia, the offshore Phuquoc-Kampot Basin, and the Khao Thalai Red-beds outlier of the Khorat Group in Southeast Thailand. The latter is interpreted as a down-faulted sliver of the Khorat Group in the Tha Mai Fault belt which is thought, in turn, to be a splay of Thailand's other major regional fault, the Three Pagodas Fault. Carboniferous, Permian and Triassic shallow-marine rocks with unusual faunas occur in a limited NNW-SSE trending zone to the west and NNW of the Tha Mai Fault and it is suggested that wrench movement on the fault played a part in the emplacement of these rocks.  相似文献