This work investigates the efficiency of mixed base isolation, combining passive isolation bearings with semi-active (SAC)
devices, to reduce the floor spectral acceleration in the vicinity of the non-isolated modes’ frequencies. Both analytical
and experimental studies have been carried out. Analytical results of the behaviour of a multiple degree of freedom base isolated
structure demonstrate the efficacy of the method. Though the considered controller is based on a reduced order model with
only two degrees of freedom (2 DOF) without spillover compensation, the results show that, for the type of structures studied
here, spillover effects are not considerable. An experimental study of a 2 DOF model of a base isolated structure equipped
with a semi-active magneto-rheological (MR) damper has been carried out. Due to limitations of the experimental set-up, it
has not been possible to obtain direct experimental evidence of the efficacy of SAC control to improve floor spectra. Nevertheless,
based on the good agreement between analytical and experimental results which validate the considered MR model and control
algorithm, numerical analyses of more relevant configurations illustrated the benefit of the utilization of such devices. 相似文献
Results of large-scale finite element computations are presented for the problem of borehole failure due to the high stresses at great depths. Rock is modelled by an extension of the Mohr–Coulomb flow theory of plasticity for material with Cosserat micro-structure. The introduction of internal length (grain size) improves the computational stability and allows for robust post-localization computations. The presented results show clearly a progressive failure mechanism and the computed failure modes are in a good qualitative agreement with laboratory and field observations. 相似文献
This paper attempts to present and discuss the geomorphological and spatial analyses of Hygassos in the middle Mediterranean (a demos in ancient Bozburun Peninsula) through the application of GIS and photogrammetry, where necessary. The contextual data is composed of the settlement features and humanly constructed terrace relics. In search of the spatial and social territoria, the research questions greatly lean on the present geographical attributes and, the results of a recent survey concerning the ruins situated along a narrow valley in modern Selimiye-K?z?lköy and the Acropolis rising beside. The physical scope encompasses the khora of the Acropolis whose spatial coverage applies to ca. 27.26 km2. As the results show, the socio-economic transformation of Hygassos, under the observance of a major stronghold (Kaletepe), must have been quite dependent on the interplay of the topographical and natural factors, as well as the likely shifts from or to the Acropolis over time. However, ambiguities remain for the resilient western half territory (near immediate Losta Bay) which perhaps encroaches on the frontiers of neighbouring Tymnos. Unfavourable but cultivable areas were preferably used for household construction and terracing whereas the land exposed to maximum erosion was refrained for settling purposes. 相似文献
Macroinvertebrates play a key role in freshwater lentic and lotic ecosystems. The macroinvertebrate benthic community of a shallow Mediterranean lake (Lake Pamvotis, NW Greece) was studied. The benthic assemblage was sampled monthly at five sites during a period of 1 year (Apr. 1998–Mar. 1999). In addition hypolimnetic water quality variables were monitored over the same period at each site.
The aim of the study was (a) to describe the intra-annual and spatial variability in benthic communities, (b) to relate possible community changes to environmental conditions and (c) to evaluate the responses of the lake's ecological status on community indices.
The benthic fauna of Lake Pamvotis was found to be very limited with a total of 10 species belonging to five taxonomic groups. The oligochaete community comprised 80% of the total benthic fauna with Potamothrix bavaricus as a new record for the Lake Pamvotis and Potamothrix hammoniensis, being the dominant benthic species represented more than 61% of the total benthic fauna. Chironomus plumosus was the most abundant chironomid species contributing with about 6% of the total benthic fauna, and Chaoborus flavicans with 19% was the important dipteran. Almost all benthic species showed the same intra-annual seasonal pattern, with peak population densities during spring and early summer except P. hammoniensis which predominated during the whole sampling period. Dissolved oxygen and temperature seemed to be the main environmental factors affecting community indices.
Benthic communities are affected by human disturbances in Lake Pamvotis shifting their composition to more tolerant taxa, reflecting also the eutrophic to hypertophic character of the lake. 相似文献
We use a non-singular potential that appears in the literature under the influence of which the Poynting-Robertson effect
is studied. For that, dust particles originating within the asteroid belt are used, in circular and elliptic orbits, and expressions
for the semimajor axis as a function of time are obtained. The derived expressions are written in terms of the two basic dust
particle parameters, namely the density and the diameter. In both cases, we obtain expressions for the time that the dust
particles take to reach the orbit of Earth under the action of the non-singular potential and solar radiation. For the non-singular
potential, dust particles of diameter 10−3 m in circular and elliptical orbits require times of the order of 4.058×107 and 2.823×107 y to reach the orbit of the Earth respectively. Finally, the derived expressions and numerical results are compared with
those of the Newtonian potential. 相似文献