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81.
Carlo Combi Giuseppe Pozzi 《The VLDB Journal The International Journal on Very Large Data Bases》2001,9(4):294-311
The granularity of given temporal information is the level of abstraction at which information is expressed. Different units of measure allow
one to represent different granularities. Indeterminacy is often present in temporal information given at different granularities:
temporal indeterminacy is related to incomplete knowledge of when the considered fact happened. Focusing on temporal databases, different granularities
and indeterminacy have to be considered in expressing valid time, i.e., the time at which the information is true in the modeled
reality. In this paper, we propose HMAP (The term is the transliteration of an ancient Greek poetical word meaning “day”.), a temporal data model extending the capability
of defining valid times with different granularity and/or with indeterminacy. In HMAP, absolute intervals are explicitly represented by their start,end, and duration: in this way, we can represent valid times as “in December 1998 for five hours”, “from July 1995, for 15 days”, “from March
1997 to October 15, 1997, between 6 and 6:30 p.m.”. HMAP is based on a three-valued logic, for managing uncertainty in temporal relationships. Formulas involving different temporal
relationships between intervals, instants, and durations can be defined, allowing one to query the database with different
granularities, not necessarily related to that of data. In this paper, we also discuss the complexity of algorithms, allowing
us to evaluate HMAP formulas, and show that the formulas can be expressed as constraint networks falling into the class of simple temporal problems,
which can be solved in polynomial time.
Received 6 August 1998 / Accepted 13 July 2000 Published online: 13 February 2001 相似文献
82.
Dynamic positioning of idle automated guided vehicles 总被引:2,自引:0,他引:2
Giuseppe Bruno Gianpaolo Ghiani Gennaro Improta 《Journal of Intelligent Manufacturing》2000,11(2):209-215
An automated guided vehicle (AGV) is a mobile robot commonly used to carry loads in material handling systems (MHS). Once a transfer is completed, an AGV stops at a home position, a point where it can park until it is assigned a new task. Determining the home positions is an important control problem with a direct influence on the overall performance of the MHS. The problem can be viewed as a location-allocation problem on a network. In this paper two fast and effective heuristics which dynamically determine the home positions are proposed. The methods were tested using two real-world instances. The obtained results are shown and discussed. 相似文献
83.
84.
Placidi G Franchi D Marsili L Gallo P 《Computer methods and programs in biomedicine》2007,88(2):144-151
Vascular catheterization is a common procedure in clinical medicine. It is normally performed by a specialist using an X-ray fluoroscopic guide and contrast-media. In the present paper, an image-guided navigation system which indicates a path providing guidance to the desired target inside the vascular tree is described with the aim of reducing the exposure of personnel and patients to X-rays during the catheterization procedure. A 3D model of the patient vascular tree, reconstructed with data collected by an angiography before starting the intervention, is used as a guide map instead of fluoroscopic scans. An accurate spatial correspondence between the body of the patient and the 3D reconstructed vascular model is established and, by means of a position indicator installed over the catheter tip, the real-time position/orientation of the tip is indicated correctly. This paper describes the system and the operational procedures necessary to use the proposed method efficiently during a catheter intervention. Preliminary experimental results on a phantom are also reported. 相似文献
85.
86.
Leonard Barolli Akio Koyama Arjan Durresi Giuseppe De Marco 《Information Systems Frontiers》2006,8(4):297-306
Due to the opportunities provided by the Internet, more and more people are taking advantage of distance learning courses
and during the last few years enormous research efforts have been dedicated to the development of distance learning systems.
So far, many e-learning systems are proposed and used practically. However, in these systems the e-learning completion rate
is about 30%. One of the reasons is the low study desire when the learner studies the learning materials. In this research,
we propose an interactive Web-based e-learning system. The purpose of our system is to increase the e-learning completion
rate by stimulating learner’s motivation. The proposed system has three subsystems: the learning subsystem, learner support
subsystem, and teacher support subsystem. The learning subsystem improves the learner’s study desire. The learner support
subsystem supports the learner during the study, and the teacher support subsystem supports the teacher to get the learner’s
study state. To evaluate the proposed system, we developed several experiments and surveys. By using new features such as:
display of learner’s study history, change of interface color, encourage function, ranking function, self-determination of
the study materials, and grouping of learners, the proposed system can increase the learning efficiency.
相似文献
Giuseppe De MarcoEmail: |
87.
88.
An alternative procedure for drought risk assessment and for the mitigation of drought risk is proposed in the paper. An analysis
of the relationship between failure of water supply systems and reservoir volumes for the urban area of Firenze in central
Tuscany, in central Italy, is performed. Long term simulations are carried out using the software package WEAP. A simplified
model of the water resources system is built to assess the threshold values and the management rules. The probability to have
definite degree of shortage in the water supply system is evaluated in function of the volume stored in the reservoir at the
beginning of the month with Monte Carlo simulations. The reservoir levels and volumes are simulated using time series of the
period 1970–2005. Four scenarios (i.e. normal, pre-alert, alert and emergency) associated with different levels of severity
of drought are defined. Threshold values are identified considering the probability to assure a given fraction of the demand
in a certain time horizon, and are calibrated with an optimization method, which try to minimize the water shortages, especially
the heavier. The critical situations are assessed month by month in order to evaluate optimal management rules during the
year and avoid conditions of total water shortage. 相似文献
89.
Armando Carravetta Giuseppe Del Giudice Oreste Fecarotta Helena M. Ramos 《Water Resources Management》2012,26(13):3947-3959
Pump operating as turbine (PAT) is an effective source of reducing the equipment cost in small hydropower plants. However, the manufacturers provide poor information on the PAT performance thus representing a limit for its wider diffusion. Additional implementation difficulties arise under variable operating conditions, characteristic of water distribution networks (WDNs). WDNs allow to obtain widespread and globally significant amount of produced energy by exploiting the head drop due to the network pressure control strategy for leak reductions. Thus a design procedure is proposed that couples a parallel hydraulic circuit with an overall plant efficiency criteria for the market pump selection within a WDN. The proposed design method allows to identify the performance curves of the PAT that maximizes the produced energy for an assigned flow and pressure-head distribution pattern. Finally, computational fluid dynamics (CFD) is shown as a suitable alternative for performance curve assessment covering the limited number of experimental data. 相似文献
90.
The Multiprocessor Bandwidth Inheritance (M-BWI) protocol is an extension of the Bandwidth Inheritance (BWI) protocol for symmetric multiprocessor systems. Similar to Priority Inheritance, M-BWI lets a task that has locked a resource execute in the resource reservations of the blocked tasks, thus reducing their blocking time. The protocol is particularly suitable for open systems where different kinds of tasks dynamically arrive and leave, because it guarantees temporal isolation among independent subsets of tasks without requiring any information on their temporal parameters. Additionally, if the temporal parameters of the interacting tasks are known, it is possible to compute an upper bound to the interference suffered by a task due to other interacting tasks. Thus, it is possible to provide timing guarantees for a subset of interacting hard real-time tasks. Finally, the M-BWI protocol is neutral to the underlying scheduling policy: it can be implemented in global, clustered and semi-partitioned scheduling. After introducing the M-BWI protocol, in this paper we formally prove its isolation properties, and propose an algorithm to compute an upper bound to the interference suffered by a task. Then, we describe our implementation of the protocol for the?LITMUS RT real-time testbed, and measure its overhead. Finally, we compare M-BWI against FMLP and OMLP, two other protocols for resource sharing in multiprocessor systems. 相似文献