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81.
Persistent Scatterers Interferometry detects and measures ground subsidence in Lisbon 总被引:1,自引:0,他引:1
Sandra I.N. Heleno Luís G.S. Oliveira Maria J. Henriques 《Remote sensing of environment》2011,115(8):2152-2167
Results from the application of Persistent Scatterers Interferometry in Lisbon Metropolitan Area revealed two previously unknown subsiding urban areas: one (Laranjeiras) is located in the center of Lisbon; another (Vialonga) is to be found toward the North, in an industrial region crossed by Lisbon's main highway and railway lines. The two subsiding sectors are bordered by sharp velocity gradients, and the subsidence pattern appears partially delimited by mapped geologic faults. Surface geology and urbanization alone are unable to explain the phenomena. In the Vialonga area, the historical record of water pore pressure shows a clear decline of the levels (up to 65 m in 27 years), providing evidence of over-exploitation of groundwater resources. Limited information from wells drilled inside and outside the subsidence area points to a spatial correlation between the subsidence and the water pressure levels, and suggests that faults could be acting as hydraulic barriers in the aquifer system. The surface subsidence detected is probably caused by compaction of a clay-rich Oligocene-aged aquitard, led by over-exploitation of adjacent aquifers. The same Oligocene aquitard layer is present in the Laranjeiras area, immediately bellow a multi-layered sand-clay-limestone Miocene aquifer, but further work is needed to diagnose the possibility of over-exploitation of groundwater here. In this work we were able to independently confirm the PSI results, by comparing autonomous PSI results processed for the same geographical areas, and by comparing PSI with leveling and continuous GPS derived subsidence velocities, whose close match provided further ground validation of the space-borne PSI technique. 相似文献
82.
TinyPBC: Pairings for authenticated identity-based non-interactive key distribution in sensor networks 总被引:2,自引:0,他引:2
Key distribution in Wireless Sensor Networks (WSNs) is challenging. Symmetric cryptosystems can perform it efficiently, but they often do not provide a perfect trade-off between resilience and storage. Further, even though conventional public key and elliptic curve cryptosystems are computationally feasible on sensor nodes, protocols based on them are not, as they require the exchange and storage of large keys and certificates, which is expensive.Using Pairing-Based Cryptography (PBC) protocols parties can agree on keys without any interaction. In this work, we (i) show how security in WSNs can be bootstrapped using an authenticated identity-based non-interactive protocol and (ii) present TinyPBC, to our knowledge, the most efficient implementation of PBC primitives for 8, 16 and 32-bit processors commonly found in sensor nodes. TinyPBC is able to compute pairings, the most expensive primitive of PBC, in 1.90 s on ATmega128L, 1.27 s on MSP430 and 0.14 s on PXA27x. 相似文献
83.
Simulations of extensional flow in microrheometric devices 总被引:1,自引:0,他引:1
Mónica S. N. Oliveira Lucy E. Rodd Gareth H. McKinley Manuel A. Alves 《Microfluidics and nanofluidics》2008,5(6):809-826
We present a detailed numerical study of the flow of a Newtonian fluid through microrheometric devices featuring a sudden
contraction–expansion. This flow configuration is typically used to generate extensional deformations and high strain rates.
The excess pressure drop resulting from the converging and diverging flow is an important dynamic measure to quantify if the
device is intended to be used as a microfluidic extensional rheometer. To explore this idea, we examine the effect of the
contraction length, aspect ratio and Reynolds number on the flow kinematics and resulting pressure field. Analysis of the
computed velocity and pressure fields show that, for typical experimental conditions used in microfluidic devices, the steady
flow is highly three-dimensional with open spiraling vortical structures in the stagnant corner regions. The numerical simulations
of the local kinematics and global pressure drop are in good agreement with experimental results. The device aspect ratio
is shown to have a strong impact on the flow and consequently on the excess pressure drop, which is quantified in terms of
the dimensionless Couette and Bagley correction factors. We suggest an approach for calculating the Bagley correction which
may be especially appropriate for planar microchannels.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
84.
Digital Butterworth filter for subtracting noise from low magnitude surface electromyogram 总被引:1,自引:0,他引:1
This work presents a digital filter designed to delimitate the frequency band of surface electromyograms (EMG) and remove the mains noise and its harmonics, focusing the signal analysis during reduced muscle activity. A Butterworth filter was designed as the frequency-domain product of a second order, high-pass filter with cutoff frequency 10 Hz, an eighth order low-pass filter, with cutoff at 400 Hz and six stop-band filters, second order, centered at the 60 Hz mains noise and its harmonics until 360 Hz. The resulting filter was applied in both direct and reverse directions of the signals to avoid phase distortions. The performance was evaluated with a simulated EMG signal with additive noise in multiples of 60 Hz. A qualitative assessment was made with real EMG data, acquired from 16 subjects, with age from 20 to 32 years. Subjects were positioned in orthostatic position during 21s, being only the last second analyzed to assure stationarity. EMG were collected by Ag/AgCl electrodes on right lateral gastrocnemius, amplified with gain 5000, filtered in the band from 10 Hz to 1 kHz, and thus digitized with 2ksamples/s. The filter effectively removed the mains noise components, with attenuations greater than 96.6%. The attenuation of the simulated signal at frequencies below 15 Hz and at 60 Hz caused only a small reduction of total power, preserving the original spectrum. Thus, the filter resulted suitable to the proposed application. 相似文献
85.
Clarisse Sieckenius de Souza Simone Diniz Junqueira Barbosa Raquel Oliveira Prates 《Knowledge》2001,14(8):461-465
Designing software involves good perception, good reasoning, and a talent to express oneself effectively through programming and interactive languages. Semiotic theories can help HCI designers increase their power to perceive, reason and communicate. By presenting some of the results we have reached with semiotic engineering over the last few years, we suggest that the main contributions of semiotic theory in supporting HCI design are: to provide designers with new perceptions on the process and product of HCI design; to bind together all the stages of software development and use, giving them a unique homogeneous treatment; and to pose innovative questions that extend the frontiers of HCI investigations. 相似文献
86.
BM Mytskan BV Shchutka VA Shakhlamov MA Mytskan 《Canadian Metallurgical Quarterly》1993,116(8):208-210
Under increased muscular activity in some muscular fibers disintegration areas of myofibrillar apparatus has been revealed. Migration of myonuclei into these microregions starts the mechanism of their segregation due to plasmolemma produced from the reticulum sarcoplasmaticum and triad systems surface. After plasmolemma production in "sarcocytes" intensive development and differentiation of organellae occur. As a result of differentiation "sarcocytes" transform in to myosatellitocytes of type-2 and migrate under lamina externa muscular fibers. So, a hypothesis about formation of myogenic tissue's cellular phase from the myosymplastic one has been confirmed. 相似文献
87.
Oliveira David 《矿业科学技术学报(英文版)》2012,22(5):639-643
Accurate modelling of the potential failure modes in the rock mass is an essential task towards a robust design of roof support systems in coal mines. The use of generalised rock mass properties based on averaged properties (e.g. Hoek–Brown model) has been found to limit the capability to reproduce the actual rock mass behaviour which may include a wide range of interacting and complex failure mechanisms such as shear and tension fracturing of the intact rock and shear and separation of pre-existing discontinuities, including re-activation. Recent studies have also shown that traditional models, such as the Mohr–Coulomb, may not accurately describe the behaviour of the intact rock, particularly for stress induced failures where spalling and slabbing are observed. This is mainly due to the cohesion and friction components of the shear strength of the intact rock not being mobilised at the same rate with strain-softening of the former component playing an essential role in the post peak behaviour. In addition, coal measure rocks are often transversely isotropic, both by way of the preferred orientation of clay particles within the finer grained lithology and by bedding textures and bedding partings, and this is often ignored in computer simulations. A newly developed transversely isotropic brittle rock mass model is applied in the simulation of a hypothetical and simple roadway development. A Cohesion Weakening-Friction Strengthening (CWFS) approach is adopted to describe the intact rock where the mobilisation and strain-softening of the two shear strength components are linked to plastic deformation. The impacts of anisotropy and brittle rock on the development of the excavation disturbed zone or height of softening, as often referred to, are investigated and their implication in the roof support design discussed. 相似文献
88.
This article presents an extensive study to select the theoretical probability distribution that represents the concentrations of major constituents from 35 wastewater treatment plants located in Brazil, as well as to verify the influence of the adopted treatment technology on the data distributions. Due to the lack of a solid basis for selecting the distributions that best fit the data, various distributions had to be tried and the choice was based on statistical tests and visual techniques, comprising a total of 3,444 tests undertaken. While comparing suitability of five distributions (normal, lognormal, gamma, exponential and rectangular) for analysis of data (influent and effluent biochemical oxygen demand, chemical oxygen demand, suspended solids, nitrogen, phosphorus, thermotolerant coliforms and flow), it was observed that the lognormal distribution was the most suitable, which is in agreement with the findings from other research studies. This conclusion requires a different position from the one currently adopted when analysing plant performance, in which symmetry of the data is generally implied, which has been shown not to be the case with the large array of data sets investigated. 相似文献
89.
Synchronized world embedding in virtual environments 总被引:1,自引:0,他引:1
We introduce a novel distributed approach that lets users copy a given CVE section and keep it consistent with all its other copies and its original CVE area. Although 3D world modeling tools such as Alias' Maya and Discreet's 3DS Max already use object embedding, our method is the first to introduce it in a functioning CVE system. We also expand the traditional object-embedding concept by introducing a mutual synchronization function between the source and destination worlds. The mutual synchronization scheme propagates events $such as changes in an object's color, shape, or position - to other copies of a world. This synchronized world embedding thus offers a new way to expand worlds. Our method is built on existing CVE functionality, which lets us deploy it without significantly interfering with existing CVE designs. We've also altered the method so that it's usable when consistency needs are more relaxed. 相似文献
90.
J.C Oliveira A Cavaleiro M.T Vieira L Bigot C Garapon J Mugnier B Jacquier 《Thin solid films》2004,446(2):264-270
Room-temperature photoluminescence (PL) measurements were performed on erbium-doped AlN thin films deposited by r.f. reactive magnetron sputtering on steel and amorphous quartz substrates. The Al/(N+Al) ratio in the as-deposited films varies in the range from 0.48 to 0.51, while erbium content ranges from 0.2 to 3.5 at.%. X-ray diffraction showed that the AlN(Er) films with erbium contents up to 1.4 at.% have the hexagonal AlN crystalline structure and a preferential orientation following the [0 0 1] direction. However, as a consequence of lattice distortion and/or defect generation originated by the incorporation of erbium atoms in the AlN structure, the films became amorphous for higher erbium contents. All the as-deposited films exhibited room-temperature PL at 1.54 μm, indicating that at least part of the erbium species are optically active in the as-grown samples. Subsequent annealing of the films led to an intensification of the PL signal up to a factor of 6 for the films heat-treated at 1075 K. Within the range of chemical compositions studied in this work, the PL signal increased with increasing erbium content. A weak green visible PL was also detected for the samples doped with the highest erbium contents when annealed at high temperatures. 相似文献