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71.
MPOKOS J.Panagiotis YIAKOULAKI D.Maria PAPAZAFEIRIOU Z.Agapi SGARDELIS Stefanos ALIFRAGIS Dimitrios PAPANIKOLAOU Konstantinos 《山地科学学报》2014,(6):1579-1592
Several abiotic and biotic factors were investigated as possible predictors of local species richness in two sub-alpine grasslands of Jenna and Belles Mountains in Northern Greece.For species richness modelling a hierarchical modelling framework based on generalized additive models was adopted.The two sub-alpine grasslands differed in aspect,altitude and soil parent material(volcanic origin,mostly trachyte,and andesite(TA) for Jenna and metamorphic rocks,mostly gneiss(G) for Belles).12 fenced squared plots,16 m2 each,were used per grassland,where soil properties,herbage production,species presence and cover of grasses,legumes and forbs were estimated.Mean herbage production was significantly affected by slope and altitude,soil K content and floristic composition as expressed by an ordination axis.Soil p H,floristic composition and average herbage production were significant predictors of forbs and total species richness.For the former,soil N content and for the latter the occurrence of Agrostis capillaris,were also included as significant terms in the predictive model.Thepredictors for grasses species richness were N content,having a positive effect,and average herbage production.In all cases higher species richness was predicted for intermediate values of average herbage production.Differential responses were found between forbs and grasses.The predictors of their species richness were different while for the case of the common predictor(N) the responses of the two groups were also different(grasses species numbers increase and forbs species numbers decreased with increasing N).Maximum species richness of grasses was observed at relatively low production levels while forbs species richness maximized at relatively high production levels. 相似文献
72.
Christina Corbane Pesaresi Martino Politis Panagiotis Florczyk J. Aneta Melchiorri Michele Freire Sergio 《International Journal of Digital Earth》2020,13(1):101-118
ABSTRACTThe presence of green spaces within city centres has been recognized as a valuable component of the city landscape. Vegetation provides a variety of benefits including energy saving, improved air quality, reduced noise pollution, decreased ambient temperature and psychological restoration. Evidence also shows that the amount of vegetation, known as ‘greenness’, in densely populated areas, can also be an indicator of the relative wealth of a neighbourhood. The ‘grey-green divide’, the contrast between built-up areas with a dominant grey colour and green spaces, is taken as a proxy indicator of sustainable management of cities and planning of urban growth. Consistent and continuous assessment of greenness in cities is therefore essential for monitoring progress towards the United Nations Sustainable Development Goal 11. The availability of multi-temporal greenness information from Landsat data archives together with data derived from the city centres database of the Global Human Settlement Layer (GHSL) initiative, offers a unique perspective to quantify and analyse changes in greenness across 10,323 urban centres all around the globe. In this research, we assess differences between greenness within and outside the built-up area for all the urban centres described by the city centres database of the GHSL. We also analyse changes in the amount of green space over time considering changes in the built-up areas in the periods 1990, 2000 and 2014. The results show an overall trend of increased greenness between 1990 and 2014 in most cities. The effect of greening is observed also for most of the 32 world megacities. We conclude that using simple yet effective approaches exploiting open and free global data it is possible to provide quantitative information on the greenness of cities and its changes over time. This information is of direct interest for urban planners and decision-makers to mitigate urban related environmental and social impacts. 相似文献
73.
Structural identification of Egnatia Odos bridges based on ambient and earthquake induced vibrations
Evaggelos Ntotsios Christos Karakostas Vasilios Lekidis Panagiotis Panetsos Ioannis Nikolaou Costas Papadimitriou Thomas Salonikos 《Bulletin of Earthquake Engineering》2009,7(2):485-501
The dynamic characteristics of two representative R/C bridges on Egnatia Odos motorway in Greece are estimated based on low
amplitude ambient and earthquake-induced vibrations. The present work outlines the instrumentation details, algorithms for
computing modal characteristics (modal frequencies, damping ratios and modeshapes), modal-based finite element model (FEM)
updating methods for estimating structural parameters, and numerical results for the modal and structural dynamic characteristics
of the two bridges based on ambient and earthquake induced vibrations. Transverse, bending and longitudinal modes are reliably
identified and stiffness-related properties of the piers, deck and elastomeric bearings of the FEMs of the two bridges are
estimated. Results provide qualitative and quantitative information on the dynamic behavior of the bridge systems and their
components under low-amplitude vibrations. Modeling assumptions are discussed based on the differences in the characteristics
identified from ambient and earthquake vibration measurements. The sources of the differences observed between the identified
modal and structural characteristics of the bridges and those predicted by FEMs used for design are investigated and properly
justified. 相似文献
74.
Evaggelos Ntotsios Costas Papadimitriou Panagiotis Panetsos Grigorios Karaiskos Kyriakos Perros Philip C. Perdikaris 《Bulletin of Earthquake Engineering》2009,7(2):469-483
A bridge health monitoring system is presented based on vibration measurements collected from a network of acceleration sensors.
Sophisticated structural identification methods, combining information from the sensor network with the theoretical information
built into a finite element model for simulating bridge behavior, are incorporated into the system in order to monitor structural
condition, track structural changes and identify the location, type and extent of damage. This work starts with a brief overview
of the modal and model identification algorithms and software incorporated into the monitoring system and then presents details
on a Bayesian inference framework for the identification of the location and the severity of damage using measured modal characteristics.
The methodology for damage detection combines the information contained in a set of measurement modal data with the information
provided by a family of competitive, parameterized, finite element model classes simulating plausible damage scenarios in
the structure. The effectiveness of the damage detection algorithm is demonstrated and validated using simulated modal data
from an instrumented R/C bridge of the Egnatia Odos motorway, as well as using experimental vibration data from a laboratory
small-scaled bridge section. 相似文献
75.
An in vivo SCID mouse infectivity assay was used to determine its capacity to detect the infectivity of low concentrations of Cryptosporidium parvum oocysts in water. This biological test can be applied to demonstrate oocysts infectivity in water samples derived from drinking water supply and/or environmental sources. 相似文献
76.
Optimum seismic design of reinforced concrete frames according to Eurocode 8 and fib Model Code 2010
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Panagiotis E. Mergos 《地震工程与结构动力学》2017,46(7):1181-1201
Traditional seismic design, like the one adopted in Eurocode 8 (EC8), is force‐based and examining a single level of seismic action. In order to provide improved control of structural damage for different levels of seismic action, the new fib Model Code 2010 (MC2010) includes a fully fledged displacement‐based and performance‐based seismic design methodology. However, the level of complexity and computational effort of the MC2010 methodology is significantly increased. Hence, the use of automated optimization techniques for obtaining cost‐effective design solutions becomes appealing if not necessary. This study employs genetic algorithms to derive and compare optimum seismic design solutions of reinforced concrete frames according to EC8 and MC2010. This is important because MC2010 is meant to serve as a basis for future seismic design codes. It is found that MC2010 drives to more cost‐effective solutions than EC8 for regions of low seismicity and better or similar costs for regions of moderate seismicity. For high‐seismicity regions, MC2010 may yield similar or increased structural costs. This depends strongly on the provisions adopted for selecting the set of ground motions. In all cases, MC2010 provides enhanced control of structural damage. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
77.
Electrical resistivity tomography mapping of beachrocks: application to the island of Thassos (N. Greece) 总被引:1,自引:0,他引:1
Psomiadis David Tsourlos Panagiotis Albanakis Konstantinos 《Environmental Earth Sciences》2009,59(1):233-240
Electrical resistivity tomography (ERT) technique is widely used in mapping subsurface electrical properties. In this study,
ERT was used to map a beachrock outcrop, extended both inland, under beach sediments, and seawards, on and under seafloor
sediments. Mapping of beachrock is considered important because it can help evaluate the lateral and vertical extend of the
formation. Fast and reliable mapping of beachrocks may contribute in several applications like engineering and construction,
coastal management, recreational reformation as well as scientific approaches like coastal evolution research, and palaeo-environmental
studies. The outcome of the survey was the mapping of the formation with centimeter precision, especially towards the sea.
Special processing was applied to the data in order to constrain the inversion procedure to include the known sea water layer. 相似文献
78.
We present hereafter the formulation of a Timoshenko finite element straight beam with internal degrees of freedom, suitable for nonlinear material problems in geomechanics (e.g., beam type structures and deep pile foundations). Cubic shape functions are used for the transverse displacements and quadratic for the rotations. The element is free of shear locking, and we prove that one element is able to predict the exact tip displacements for any complex distributed loadings and any suitable boundary conditions. After the presentation of the virtual power and the weak form formulations, the construction of the elementary stiffness matrix is detailed. The analytical results of the static condensation method are provided. It is also proven that the element introduced by Friedman and Kosmatka in 1 , with shape functions depending on material properties, is derived from the new beam element. Validation is provided using linear and material nonlinear applications (reinforced concrete column under cyclic loading) in the context of a multifiber beam formulation. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
79.
Zenobia Jacobs Richard G. Roberts Terry J. Lachlan Panagiotis Karkanas Curtis W. Marean David L. Roberts 《Quaternary Geochronology》2011,6(5):491-513
Optically stimulated luminescence (OSL) dating is now commonly used to estimate the depositional age of Quaternary landforms along the southern Cape coast of South Africa. Due to the early onset of dose saturation in the quartz-rich sediments from this region, determining the age of deposits much older than the last three glacio-eustatic sea-level high stands has been a challenge. In this study, we explored the feasibility of using the thermally-transferred OSL (TT-OSL) dating method to obtain ages for aeolian and shallow marine deposits at three different localities that hold promise to further illuminate the long and complex Late Quaternary sea-level history of this region. The bleachability and behaviour of both the recuperated OSL (ReOSL) and the basic-transferred OSL (BT-OSL) signals were investigated, and used as independent chronometers to infer (a) the degree of bleaching of the sediments and (b) the stability of the ReOSL signal for dating of older samples. We examined the sensitivity of both signals to varying preheat temperatures and further developed the single-aliquot regenerative-dose procedure for TT-OSL dating of our samples. To verify our procedures, and to understand some of the underlying mechanisms responsible for the problems we observed, modern analogues and known-age Marine Isotope Sub-stage (MIS) 5e samples from the same localities were also measured. The Middle Pleistocene deposits investigated in this study produced statistically consistent ReOSL and BT-OSL ages compatible with sea-level high stands during Marine Isotope Stage 11. This result is of considerable significance, as it may yield new insights into maximum sea-level heights during this period, which is widely considered an appropriate analogue for future environmental conditions. 相似文献