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71.
Trace metals, PCB congeners and DDT homologues were determined in composite sediment samples collected from 10 representative sites along the river Po in two separate seasons. The aim was to identify the most anthropogenically impacted areas for future monitoring programmes and to aid development of Italian sediment quality criteria. The surface samples were collected during low flow conditions. Trace metal concentrations were assayed by electrothermal (Cd, Co, Cr, Cu, Ni, Pb), flame (Fe, Mn, Zn) or hydride generation (As) atomic absorption spectrometry after microwave assisted acid digestion. Hg was determined on solid samples by automated analyser. Organic microcontaminants were determined by gas-chromatography with 63Ni electron capture detector after Soxhlet extraction. Concentrations of trace metals, total PCB and DDT homologues showed two distinct peaks at the sites immediately downstream of Turin and Milan, respectively, and in each case decreased progressively further downstream. Principal component analysis identified three major factors (from a multi-dimensional space of 35 variables) which explained 85-90% of the total observed variance. The first and second factors corresponded to anthropogenic inputs and geological factors on sediment quality; the third included seasonal processes of minor importance. Sediment quality assessment identified Cd, Cu, Hg, Pb, Zn and organic microcontaminants as posing the most serious threats to river sediment quality. A reference site within the Po basin provided useful background values. Moderate pollution by organochlorine compounds was ascribed both to local sources and to atmospheric deposition. 相似文献
72.
Can a Knowledge-Level layer be located in the Semantic Grid infrastructure? Is it possible to design an Agent Communication Language (ACL) which enables Knowledge-Level agents to cooperate in a geographically distributed Semantic Grid despite nodes’ failures or malfunctions? This paper tries to address the above Semantic Grid challenges presenting an agent-based Open Service Architecture which integrates geographically distributed agents in a Semantic Grid. The architecture is well integrated with standard Internet components and technologies and supports communication among Knowledge-Level agents. The role of agents is to retrieve, execute and compose available services providing more sophisticated instances of them. Inter-agent communication is realized by exploiting an advanced Agent Communication Language which supports a fault-tolerant anonymous interaction protocol and satisfies a set of well defined Knowledge-Level programming requirements. Here, we present the design of the architecture and of the Agent Communication Language as well as their implementation. The architecture is evaluated by means of several case studies which highlight the main feature of our proposal. The main advantage of our approach is to demonstrate that different issues, such as high level inter-agent communication and fault tolerance, can be successfully integrated in Grid infrastructures which provide Web Services maintaining a clean design of the architecture and a Knowledge-Level characterization. 相似文献
73.
Levi F Lorini L Calonico D Godone A 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2004,51(10):1216-1224
In this paper we report the accuracy evaluation of the Italian primary frequency standard IEN-CsF1. We discuss the shifts the frequency standard is corrected for and the procedure used for the accuracy evaluation. In the last section we report frequency comparisons of our fountain with those of remote laboratories and with International Atomic Time. 相似文献
74.
TETRA (TErrestrial Trunked RAdio) is a digital mobile radio standard for voice and data transmission. It aims at satisfying
the growing request of applications and facilities coming from professional users and emergency services. The system has been
standardized by ETSI (European Telecommunications Standards Institute) and is provided with an European harmonized frequency
band. The first TETRA networks appeared on the market in 1997. This paper reports TETRA radio performance evaluated via a
simulation software package, named TETRASIM, entirely developed at CSELT according to TETRA specifications. The simulation
results have been obtained for some of the traffic and control channels specified by the standard, in terms of BER (Bit Error
Rate) and MER (Message Erasure Rate). As far as the simulated receiver scheme is concerned, the characteristics of the equivalent
low-pass filters and the adopted synchronization technique are reported. The simulated demodulator uses a differential detection
scheme with soft decision outputs in the case of coded channels. Performance analyses and results comparison are provided
by taking into account the effects of signal-to-noise ratio, co-channel interference, adjacent channel interference, propagation
models defined in the standard and mobile unit speed. The simulation results reported in this work have been included in the
ETR (ETSI Technical Report) “TETRA Designers’ Guide Part 2: Radio and Traffic Performance”.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
75.
Unbundling dynamic capabilities: an exploratory study of continuous product innovation 总被引:12,自引:0,他引:12
In order to understand better the organizational sources ofcontinuous innovation, this paper provides an in-depth analysisof Oticon A/S, a leading company in the hearing-aid industry,which showed an impressive ability to develop new products inthe nineties. Findings highlight that dynamic capabilities aremade up of: knowledge creation and absorption, knowledge integrationand knowledge reconfiguration. Discussion links the findingsto previous literature and shows how these knowledge-based processesare all based on a coherent mix of organizational resources. 相似文献
76.
Massimo Brandolini Paolo Rossi Davide Sanzogni Francesco Svelto 《Analog Integrated Circuits and Signal Processing》2007,53(1):35-42
This paper presents the design of a high dynamic range direct down-converter for 3G cell-phone applications. The mechanisms
responsible for second-order intermodulation distortion are discussed in details, leading to the following design strategy:
the transconductor is degenerated by means of an RC filter, an LC network resonating at RF frequency loads the switching pair
and carefully matched resistors are used in the output load. Prototypes realized in 0.18 μm CMOS show: +78 dBm IIP2 minimum
among 40 samples, +10 dBm IIP3, 4 nV/√Hz input-referred noise density while burning only 4 mA from 1.8 V. 相似文献
77.
78.
Semantic web services are gaining more attention as an important element of the emerging semantic web. Therefore, testing semantic web services is becoming a key concern as an essential quality assurance measure. The objective of this systematic literature review is to summarize the current state of the art of functional testing of semantic web services by providing answers to a set of research questions. The review follows a predefined procedure that involves automatically searching 5 well-known digital libraries. After applying the selection criteria to the results, a total of 34 studies were identified as relevant. Required information was extracted from the studies and summarized. Our systematic literature review identified some approaches available for deriving test cases from the specifications of semantic web services. However, many of the approaches are either not validated or the validation done lacks credibility. We believe that a substantial amount of work remains to be done to improve the current state of research in the area of testing semantic web services. 相似文献
79.
Fabio Bovenga Davide Oscar Nitti Gianfranco Fornaro Fabio Radicioni Aurelio Stoppini Raffaella Brigante 《International journal of remote sensing》2013,34(11):4083-4104
This work presents an analysis of the applicability of synthetic aperture radar (SAR) interferometry to landslide monitoring. This analysis was carried out by using different interferometric approaches, different spaceborne SAR data (both in the C-band and in the X-band), and in situ global navigation satellite system (GNSS) measurements. In particular, we investigated both the reliability of displacement monitoring and the issues of the cross-comparison and validation of the interferometric synthetic aperture radar (InSAR) results. The work was focused on the slow-moving landslide that affects a relevant part of the urban area of the historical town of Assisi (Italy). A C-band ENVISAT advanced synthetic aperture radar (ENVISAT ASAR) dataset acquired between 2003 and 2010 was processed by using two different interferometric techniques, to allow cross-comparison of the obtained displacement maps. Good correspondence between the results was found, and a deeper analysis of the movement field was possible. Results were further compared to a set of GNSS measurements with a 7 year overlap with SAR data. A comparison was made for each GNSS marker with the surrounding SAR scatterers, trying to take into account local topological effects, when possible. Further, the high-resolution X-band acquired on both ascending and descending tracks by the COSMO-SkyMed (CSK) constellation was processed. The resultant displacement fields show good agreement with C-band and GNSS measurements and a sensible increase in the density of measurements. 相似文献
80.
Rosario G. Garroppo Stefano Giordano Davide Iacono Luca Tavanti 《Wireless Networks》2011,17(6):1441-1459
In WiMAX systems the Base Station scheduler plays a key role as it controls the sharing of the radio resources among the users.
The goal of the scheduler is multiple: achieve fair usage of the resources, satisfy the QoS requirements of the users, maximize
goodput, and minimize power consumption, and at the same time ensuring feasible algorithm complexity and system scalability.
Since most of these goals are contrasting, scheduler designers usually focus their attention on optimizing one aspect only.
In this scenario, we propose a scheduling algorithm (called GTSN\mathrm{GTS_N}) whose goal is to contemporaneously achieve efficiency and fairness, while also taking into account the QoS requirements
and the channel state. GTSN\mathrm{GTS_N} exploits the properties of Time Utility Functions (TUFs) and Game Theory. Simulations prove that the performance of GTSN,\mathrm{GTS_N}, when compared to that of several well-known schedulers, is remarkable. GTSN\mathrm{GTS_N} provides the best compromise between the two contrasting objectives of fairness and efficiency, while QoS requirements are
in most cases guaranteed. However, the exponential complexity introduced by the game theory technique makes it rather impractical
and not computationally scalable for a large number of users. Thus we developed a suboptimal version, named sub-GTSN.\mathrm{GTS_N}. We show that this version retains most of the features and performance figures of its brother, but its complexity is linear
with the number of users. 相似文献