Projected changes in tropical cyclones over Vietnam and the South China Sea using a 25 km regional climate model perturbed physics ensemble     

Grace Redmond  Kevin I. Hodges  Carol Mcsweeney  Richard Jones  David Hein 《Climate Dynamics》2015,45(7-8):1983-2000

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A Paleoecological History of the Late Precolonial and Postcolonial Mesohaline Chesapeake Bay Food Web     

Angela A. Sowers  Grace S. Brush 《Estuaries and Coasts》2014,37(6):1506-1515

Geochemical (total nitrogen, total organic carbon, total phosphorus, total sulfur, and carbon and nitrogen stable isotopes) and selected biotic (diatom, foraminifera, polychaete) indicators preserved in two estuarine sediment cores from the mesohaline Chesapeake Bay provide a history of alterations in the food web associated with land-use change. One core from the mouth of the Chester River (CR) (collected in 2000) represents a 1,000-year record. The second core (collected in 1999), from the Chesapeake Bay’s main stem opposite the Choptank River (MD), represents a 500-year record. As European settlers converted a primarily forested landscape to agriculture, sedimentation rates increased, water clarity decreased, salinity decreased in some areas, and the estuarine food web changed into a predominantly planktonic system. Representatives of the benthic macrofaunal community (foraminifera and the polychaetes Nereis spp.) were affected by local changes before there were widespread landscape alterations. Nitrogen stable isotope records indicated that land-use changes affected nitrogen cycling beginning in the early 1700s. Extreme changes were evident in the mid-nineteenth century following widespread deforestation and since the mid-twentieth century reflecting heightened eutrophication as development increased in the Chesapeake Bay watershed. Results also demonstrate how paleoecological records vary due to the degree of terrestrial inputs of freshwater runoff and nutrients at core locations within the Chesapeake Bay.  相似文献   

Interpreting velocities from heat-based flow sensors by numerical simulation   总被引：1，自引：0，他引：1  

Su GW  Freifeld BM  Oldenburg CM  Jordan PD  Daley PF 《Ground water》2006,44(3):386-393

We have carried out numerical simulations of three-dimensional nonisothermal flow around an in situ heat-based flow sensor to investigate how formation heterogeneities can affect the interpretation of ground water flow velocities from this instrument. The flow sensor operates by constant heating of a 0.75-m-long, 5-cm-diameter cylindrical probe, which contains 30 thermistors in contact with the formation. The temperature evolution at each thermistor can be inverted to obtain an estimate of the ground water flow velocity vector using the standard interpretive method, which assumes that the formation is homogeneous. Analysis of data from heat-based flow sensors installed in a sand aquifer at the Former Fort Ord Army Base near Monterey, California, suggested an unexpected component of downward flow. The magnitudes of the vertical velocities were expected to be much less than those of the horizontal velocities at this site because the sensors were installed just above a clay aquitard. Numerical simulations were conducted to examine how differences in thermal conductivities may lead to spurious indications of vertical flow velocities. We found that a decrease in the thermal conductivity near the bottom of the sensor can perturb the temperature profiles along the instrument in such a manner that analyses assuming homogeneous thermal conductivity could indicate a vertical flow component even though flow is actually horizontal. This work demonstrates how modeling can be used to simulate instrument response to formation heterogeneity and shows that caution must be used in interpreting data from such devices.  相似文献   

Miniaturization of the flowing fluid electric conductivity logging technique     

Su GW  Quinn NW  Cook PJ  Shipp W 《Ground water》2006,44(5):754-757

An understanding of the hydraulic properties of the aquifer and the depth distribution of salts is critical for evaluating the potential of ground water for conjunctive water use and for maintaining suitable ground water quality in agricultural regions where ground water is used extensively for irrigation and drinking water. The electrical conductivity profiles recorded in a well using the flowing fluid electric conductivity (FEC) logging method can be analyzed to estimate interval-specific hydraulic conductivity and estimates of the salinity concentration with depth. However, operating irrigation wells commonly allow limited access, and the traditional equipment used for FEC logging cannot fit through the small access pipe intersecting the well. A modified, miniaturized FEC logging technique was developed for use in wells with limited access. In addition, a new method for injecting water over the entire screened interval of the well reduces the time required to perform FEC logging.  相似文献   

Red Mangrove Seedling Survival, Growth, and Reproduction: Effects of Environment and Maternal Genotype     

Charles Edward Proffitt  Steven E. Travis 《Estuaries and Coasts》2010,33(4):890-901

An adequate understanding of the nature and extent of response to stressors and resources by marine foundation plant species requires study of local adaptation and plasticity in traits. Analyses of variation among genotypes in growth and morphology and genotype × environment interactions are necessary for restoration in, for example, different combinations of tide, soil, and salinity regimes, and for assessing how foundation plant species will respond to global climate change. We conducted a field experiment to assess differences in responses among 86 half-sibling (same maternal tree) seedling families of the red mangrove (Rhizophora mangle) to different environmental conditions of hydrology imposed at low- and high-intertidal settings. At 3 years, Rhizophora survival and growth varied with maternal tree genotype, elevation, and genotype × elevation. This effect was independent of size of propagules at planting. Growth also differed among the five islands planted, a main effect that is a composite of a number of microenvironmental differences stemming from island size and shape, proximity to passes (and thus fetch), and island slope. Significant genotype × island interactions for some response variables further support the hypothesis that seedlings of different maternal genotypes can perform very differently under various suites of environmental conditions. Planted seedlings reproduced at an early age, and at 3 years there were differences in reproductive output among genotypes but not an overall mean difference between plants at low or high elevation. Whether our results show adaptation to local conditions or differences in plasticity among genotypes will require further study as the plants mature further to demonstrate fitness differences. However, either adaptation or plasticity provides a basis for maintenance of Rhizophora dominance over a wider range of environmental conditions and may be important for adaptation to conditions that will vary with global climate change.  相似文献   

Modeling the dynamics of spring-driven oscillating-foil propulsion     

Harper  K.A. Berkemeier  M.D. Grace  S. 《Oceanic Engineering, IEEE Journal of》1998,23(3):285-296

In this paper we present a model for oscillating-foil propulsion in which springs are used to transmit forces from the actuators to the foil. The expressions for hydrodynamic force and moment on the foil come from classical, linear, unsteady aerodynamics, and these are coupled to linearized rigid-body mechanics to obtain the complete model for swimming. The model is presented as a low-order set of ordinary differential equations, which makes it suitable for the application of techniques from systems and control theory. The springs serve to reduce energy costs, and we derive explicit expressions for spring constants which are optimal in this sense. However, the use of springs can potentially lead to unstable dynamics. Therefore, we also derive a set of necessary and sufficient conditions for stability. A detailed example is presented in which energy costs for one actuator are reduced by 33%  相似文献   

Investigation of star formation toward the Sharpless 155 H II region     

Ya-Fang Huang  Jin-Zeng Li  Travis A.Rector  Zhou Fan 《中国天文和天体物理学报》2014,(10)

We present a comprehensive study of star formation toward the H II region Sharpless 155(S155).Star-formation activities therein were investigated based on multi-wavelength data from optical to the far-infrared.The surface density distribution of selected 2MASS sources toward S155 indicates the existence of a compact cluster,which is spatially consistent with the position of the exciting source of the H II region,HD 217086.A sample of more than 200 sources with excessive emission in the infrared were selected based on their 2MASS color indices.The spatial distribution of the sample sources reveals the existence of three young subclusters in this region,among which subcluster A is spatially coincident with the bright rim of the H II region.In addition,photometric data from the WISE survey were used to identify and classify young stellar objects(YSOs).To further explore the evolutionary stages of the candidate YSOs,we fit the spectral energy distributions of 44 sources,which led to the identification of 14 Class I,27 Class II and 3 Class HI YSOs.The spatial distribution of the classified YSOs at different evolutionary stages presents a spatiotemporal gradient,which is consistent with a scenario of sequential star formation.On the other hand,Herschel PACS observations toward the interface between S155 and the ambient molecular cloud disclose an arc-shaped dust layer,the origin of which could be attributed to the UV dissipation from early type stars,e.g.HD 217061,in S155.Four dusty cores were revealed by the Herschel data,which hints at new generations of star formation.  相似文献   

Evaluation of In Situ Heterogeneity of Elements in Solids: Implications for Analytical Geochemistry     

Michael H. Ramsey  Grace Solomon‐Wisdom  Ariadne Argyraki 《Geostandards and Geoanalytical Research》2013,37(4):379-391

A general method for the evaluation of in situ heterogeneity of geochemical materials is described and the significance of the results discussed, by using three case studies and earlier data sets. The heterogeneity of Pb in soil (expressed as RSD due to sampling, RSD_samp) varies from < 5 to > 100% between different sites, in a way that relates to the mode of deposition of the element. The heterogeneity of an element also varies systematically as a function of the distance scale at some sites. This variation can be modelled using linear regression, accounting for over 90% of the experimental variance, at seven scales over three orders of magnitude. Variation in heterogeneity between elements at the same site, seems to be somewhat diagnostic of the origin of the element, lithogenic being less than anthropogenic, although the later is also being modified by the mode of deposition. Where the heterogeneity is large (RSD > 30%), it is proposed that it can be expressed more accurately as a heterogeneity factor (10^GSDsamp), to reflect its frequency distribution, which is positively skewed towards higher concentration values.  相似文献   

Fall,classification, and exposure history of the Mifflin L5 chondrite     

Noriko T. Kita  Kees C. Welten  John W. Valley  Michael J. Spicuzza  Daisuke Nakashima  Travis J. Tenner  Takayuki Ushikubo  Glenn J. MacPherson  Linda Welzenbach  Philipp R. Heck  Andrew M. Davis  Matthias M. M. Meier  Rainer Wieler  Marc W. Caffee  Matthias Laubenstein  Kunihiko Nishiizumi 《Meteoritics & planetary science》2013,48(4):641-655

The Mifflin meteorite fell on the night of April 14, 2010, in southwestern Wisconsin. A bright fireball was observed throughout a wide area of the midwestern United States. The petrography, mineral compositions, and oxygen isotope ratios indicate that the meteorite is a L5 chondrite fragmental breccia with light/dark structure. The meteorite shows a low shock stage of S2, although some shock‐melted veins are present. The U,Th‐He age is 0.7 Ga, and the K‐Ar age is 1.8 Ga, indicating that Mifflin might have been heated at the time of the 470 Ma L‐chondrite parent body breakup and that U, Th‐He, and K‐Ar ages were partially reset. The cosmogenic radionuclide data indicate that Mifflin was exposed to cosmic rays while its radius was 30–65 cm. Assuming this exposure geometry, a cosmic‐ray exposure age of 25 ± 3 Ma is calculated from cosmogenic noble gas concentrations. The low ²²Ne/²¹Ne ratio may, however, indicate a two‐stage exposure with a longer first‐stage exposure at high shielding. Mifflin is unusual in having a low radiogenic gas content combined with a low shock stage and no evidence of late stage annealing; this inconsistency remains unexplained.  相似文献   

DME/TACAN interference mitigation for GNSS: algorithms and flight test results     

Grace Xingxin Gao  Liang Heng  Achim Hornbostel  Holmer Denks  Michael Meurer  Todd Walter  Per Enge 《GPS Solutions》2013,17(4):561-573

The Galileo E5a/E5b signals and the Global Positioning System (GPS) L5 signal lie within the aeronautical radionavigation services (ARNS) band. They suffer interference from the services in this frequency band, in particular, pulsed signals from distance measuring equipment (DME) and tactical air navigation (TACAN) systems. To maintain system accuracy and integrity, interference mitigation is beneficial and necessary. We first present the real DME/TACAN environment at Stanford, CA as an example to illustrate the need for mitigating DME/TACAN interference. We then propose a time and frequency joint mitigation algorithm—Hybrid Blanking and its simplified version, frequency domain adaptive filtering (FDAF) for hardware implementation. Finally, a flight measurements campaign was performed over a European DME/TACAN hotspot near Frankfurt, Germany, to record a worst-case DME interference environment. Recorded data from the flight tests mixed with injected GNSS signals verify the effectiveness of the proposed mitigation algorithm.  相似文献