排序方式： 共有48条查询结果，搜索用时 109 毫秒
31.
Oya Algan M. Nam?k Yalç?n Yücel Y?lmaz Elmas K?rc?-Elmas Özlem Bulkan Cem Gazio?lu Mehmet Ali Polat 《Quaternary Research》2011,76(1):30-45
An extensive rescue excavation has been conducted in the ancient harbor of ?stanbul (Yenikap?) by the Sea of Marmara, revealing a depositional sequence displaying clear evidence of transgression and coastal progradation during the Holocene. The basal layer of this sequence lies at 6 m below the present sea level and contains remains of a Neolithic settlement known to have been present in the area, indicating that the sea level at ~ 8-9 cal ka BP was lower than 6 m below present. Sea level advanced to its maximum at ~ 6.8-7 cal ka BP, drowning Lykos Stream and forming an inlet at its mouth. After ~ 3 cal ka BP, coastal progradation became evident. Subsequent construction of the Byzantine Harbor (Theodosius; 4th century AD) created a restricted small basin and accumulation of fine-grained sediments. The sedimentation rate was increased due to coastal progradation and anthropogenic factors during the deposition of coarse-grained sediments at the upper parts of the sequence (7th-9th centuries AD). The harbor was probably abandoned after the 11th century AD by filling up with Lykos Stream detritus and continued seaward migration of the coastline. 相似文献
32.
A two‐phase research program has been undertaken to investigate fundamental natural periods of concentrically braced frames (CBFs) designed according to Eurocode 8 (EC8). In the first phase of the program, over 83,700 buildings were designed, and the accuracy of the lower bound expressions given in well‐known design specifications was evaluated. The results indicated that the lower bound expressions given in EC8 and National Building Code of Canada (NBCC) are acceptable. Although all structures had periods longer than the ones estimated by the EC8 expression, a few structures had shorter periods than the ones estimated by the NBCC expression. In general, the lower bound expressions given in EC8 and NBCC were found to provide over conservative estimates for most cases. In the second phase of the program, a simple hand method was developed to estimate the fundamental natural periods of CBFs designed to EC8. This method requires the use of inelastic top story drift ratio as a parameter to quantify stiffness characteristics. The drift ratios were extracted from the design pool developed as a part of the first phase and represented by simple mathematical relationships. Evaluation of the proposed method indicated that the method is accurate in providing estimates of the fundamental period. To safeguard against providing unconservative estimates, the method was modified to arrive at a new lower bound expression, which significantly improves the estimates compared with the ones provided by the existing expressions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
33.
Parameter Estimation for Step-Drawdown Tests 总被引：1，自引：0，他引：1
Cem B. Avci 《Ground water》1992,30(3):338-342
34.
Design recommendations for steel plate shear wall (SPSW) systems have recently been introduced into seismic provisions for steel buildings. Response modification (R), overstrength (Ωo), and displacement amplification (Cd) factors for SPSW systems presented in design codes were based on professional experience and judgment. A numerical study has been undertaken to evaluate these factors for SPSW systems. Forty‐four unstiffened SPSW possessing different geometrical characteristics were designed based on the recommendations given in the AISC Seismic Provisions. Bay width, number of stories, story mass, and steel plate thickness were considered as the prime variables that influence the response. Twenty records were selected to include the variability in ground motion characteristics. In order to provide a detailed analysis of the post‐buckling response, three‐dimensional finite element analyses were conducted for the 44 structures subjected to the selected suite of earthquake records. For each structure and earthquake record, two analyses were conducted in which the first includes geometrical nonlinearities and the other includes both geometrical and material nonlinearities, resulting in a total of 1760 time history analyses. In this paper, the details of the design and analysis methodology are given. Based on the analysis results, response modification (R), overstrength (Ωo), and displacement amplification (Cd) factors for SPSW systems are evaluated. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
35.
Dev K. Niyogi Janet M. Bandeff Cem Selman Drew E. Menke 《Aquatic Sciences - Research Across Boundaries》2010,72(2):203-212
We examined nutrient flux, uptake, and transformation along a spring-fed stream in the Ozark region of Missouri, USA, over
the year 2006. Water in Mill Creek originates from several springs, with a single spring contributing over 90% of the stream
discharge during much of the year of study. Soluble reactive phosphate concentrations were usually low (<10 μg L−1) along Mill Creek, but peaked during high discharge. Concentrations of dissolved inorganic nitrogen (DIN) were relatively
high in the spring water, mainly as nitrate, but usually declined across a small pond and the 10-km length of Mill Creek.
During low flows in summer and early autumn, the stream removed over 300 μg L−1 of DIN over its 10-km length, or about 80% of the initial amount. DIN retention along the stream, as a percentage of the
DIN upstream, was related mainly to discharge, with higher flows having much higher DIN concentrations. The net uptake rate
of DIN uptake was 0.91 μg m−2 s−1 in the stream during summer baseflow. The uptake rate declined downstream for different reaches and was closely related to
DIN concentration. In experimental channels, uptake by epilithic algae was one significant sink for nitrate-N in Mill Creek.
In 2006, inorganic nutrient export during a single day after a spring storm was similar to export during 40–100 days of low
flow conditions in summer and early autumn. Our results suggest that significant nutrient retention can occur during baseflow
periods via biological uptake, whereas substantial export occurs during high flow conditions. 相似文献
36.
We assessed the ambient noise level in the Aegean region and analyzed its diurnal variation and its relation to the earthquake detection capability of the Aegean Region Seismic Network (ARSN). We prepared probability density functions (PDFs) for 19 broadband stations in the Aegean region operated by the Earth and Marine Sciences Institute (EMSI) of the Marmara Research Center (MRC) of the Turkish Scientific Research Council (TÜB?TAK). The power spectral densities (PSDs) used to construct PDFs for each station were computed for the periods between ~?0.02 and 180 s. In addition, we generated noise map of the Aegean region for different periods using the PDFs to assess the origin of the noise. We analyzed earthquake activity in the region and found that there are more local events recorded at night than during the day for each station. This difference is strongly related to diurnal variation of background noise level for the period range mostly covering the frequency range for the local events. We observed daytime noise level ~?15 to 20 dB higher than that at the nighttime in high frequencies for almost all stations caused by its proximity to settled areas and roads. Additionally, we observed a splitting peak within the Double Frequency (DF) microseism band; it showed a clear noise increase around the short period DF band at all the stations, decreasing inland. This peak may be related to sea waves locally generated in the Aegean Sea. We also identified a prominent increase related to marble saw companies in some stations’ noise PDFs. 相似文献
37.
The standard practice for assessing aquifer parameters is to match groundwater drawdown data obtained during pumping tests against theoretical well function curves specific to the aquifer system being tested. The shape of the curve derived from the logarithmic time derivative of the drawdown data is also very frequently used as a diagnostic tool to identify the aquifer system in which the pumping test is being conducted. The present study investigates the incremental area method (IAM) to serve as an alternative diagnostic tool for the aquifer system identification as well as a supplement to the aquifer parameter estimation procedure. The IAM based diagnostic curves for ideal confined, leaky, bounded and unconfined aquifers have been derived as part of this study, and individual features of the plots have been identified. These features were noted to be unique to each aquifer setting, which could be used for rapid evaluation of the aquifer system. The effectiveness of the IAM methodology was investigated by analyzing field data for various aquifer settings including leaky, unconfined, bounded and heterogeneous conditions. The results showed that the proposed approach is a viable method for use as a diagnostic tool to identify the aquifer system characteristics as well as to support the estimation of the hydraulic parameters obtained from standard curve matching procedures. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
38.
Emre Aydınçakır Cem Yücel Gilles Ruffet Mehmet Ali Gücer Enver Akaryalı Abdullah Kaygusuz 《Chemie der Erde / Geochemistry》2022,82(2):125871
The debate about whether Eocene magmatism is considered to be post-collisional or subduction-related or not still continues. Here we offer new 40Ar-39Ar ad U-Pb zircon geochronology, mineral chemistry, bulk rock and Sr-Nd-Pb isotope geochemistry data obtained from the southern dike (SD) suite, in comparison with the northern dike (ND) suite, from the Eastern Pontides. The geochronological data indicate that the SD suite erupted between 45.89 and 45.10 Ma corresponding to the Lutetian (Middle Eocene). The magmas of the ND suite are characterised by slightly more alkaline affinity compared to the SD suite. The trace and rare earth element (REEs) content of the SD suite is characterised by large ion lithophile element (LILEs; Sr, K2O, Ba, Rb) enrichment and depletion of Nb, Ta, and TiO2 elements to different degree with high Th/Yb ratios, which indicate that the magmas forming the SD and ND suites were derived from lithospheric mantle sources enriched by mostly slab-derived fluids in the spinel stability field. The Sr, Nd and Pb radiogenic isotope ratios of the dikes support the view that the magma for the hydrous group (H-SD) was derived from a relatively more enriched mantle source than the other SD and ND suites. The ND suite and the anhydrous group (A-SD) display similar geochemical features characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios, while the H-SD group has respectively lower LREE/HREE ratios indicating higher melting degree. Detailed considerations of the alkalinity, enrichment and partial melting degree for the source of the studied volcanic rocks indicate that the magmas of the northern dike suite are characterised by slightly more alkaline affinity, whereas the magmas throughout the southern dike suite show increments in the enrichment rate and melting degree. In light of the obtained data and comparative interpretations, the geodynamic evolution and differences in petrogenetic character of the Lutetian magmas from both the northern and southern parts of the Eastern Pontides may be explained by different degrees of melting of a net veined mantle source initially metasomatized by mostly subduction fluids during asthenospheric upwelling due to fragmented asymmetric delamination in a post-collisional extensional tectonic environment. 相似文献
39.
Aquifer parameter estimation using an incremental area method 总被引：2，自引：0，他引：2
Theoretical well functions have been derived over the years to predict ground water level behaviour in aquifer systems under stress owing to groundwater extraction. The drawdown data collected during pump tests are typically analysed using graphical curve‐matching procedures to estimate aquifer parameters based on these well functions. Difficulty in aquifer characteristic identification and parameter estimation may arise when the field data do not perfectly match the drawdown curves obtained from the well functions. The present study provides a new method for the interpretation of aquifer pump tests which supplements the existing curve‐matching procedures in case ideal conditions do not exist; the proposed method provides a greater degree of flexibility in the data analysis for diagnostic tool purposes. The method, referred to as the Incremental Area Method (IAM) is based on integrating the logarithmic‐based drawdown curves within a discrete time and matching the results with a corresponding time integral of the Theis ( 1935 ) Well Function which governs ideal confined aquifers. The application of the proposed method to synthetically generated data and field data showed that IAM represents a viable method which yields information on potential non‐idealness of the aquifer and provides aquifer parameter estimates thus potentially overcoming drawdown data curve‐matching difficulties. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
40.
Mehmet Arslan İrfan Temizel Emel Abdioğlu Hasan Kolaylı Cem Yücel Durmuş Boztuğ Cüneyt Şen 《Contributions to Mineralogy and Petrology》2013,166(1):113-142
The Eocene volcano-sedimentary units in the southern part of the Eastern Pontides (NE Turkey) are confined within a narrow zone of east–west trending, semi-isolated basins in Bayburt, Gümü?hane, ?iran and Alucra areas. The volcanic rocks in these areas are mainly basalt and andesite through dacite, with a dominant calc-alkaline to rare tholeiitic tendency. 40Ar–39Ar dating of these volcanic rocks places them between 37.7 ± 0.2 and 44.5 ± 0.2 Ma (Middle Eocene). Differences in the major and trace element variations can be explained by the fractionation of clinopyroxene ± magnetite in basaltic rocks and that of hornblende + plagioclase ± magnetite ± apatite in andesitic rocks. Primitive mantle-normalized multi-element variations exhibit enrichment of large-ion lithophile elements and to a lesser extent, of light rare earth elements, as well as depletion of high field strength elements, thus revealing that volcanic rocks evolved from a parental magma derived from an enriched mantle source. Chondrite-normalized rare earth element patterns of the aforementioned volcanic rocks resemble each other and are spoon-shaped with low-to-medium enrichment (LaN/LuN = 2–14), indicating similar spinel lherzolitic mantle source(s). Sr, Nd and Pb isotopic systematics imply that the volcanic rocks are derived from a subduction-modified subcontinental lithospheric mantle. Furthermore, post-collisional thickened continental crust, lithospheric delamination and a subduction-imposed thermal structure are very important in generating Tertiary magma(s). The predominantly calc-alkaline nature of Eocene volcanic rocks is associated with increasing geodynamic regime-extension, whereas tholeiitic volcanism results from local variations in the stress regime of the ongoing extension and the thermal structure, as well as the thickness of the crust and the mantle-crust source regions. Based on volcanic variety and distribution, as well as on petrological data, Tertiary magmatic activity in Eastern Pontides is closely related to post-collisional thinning of the young lithosphere, which, in turn, is caused by extension and lithospheric delamination after collisional events between the Tauride–Anatolide Platform and the Eurasian Plate. 相似文献