909 resultados para Operant conditioning
Resumo:
Factors relating to identity and to economics have been shown to be important predictors of attitudes towards the European Union (EU). In this article, we show that the impact of identity is conditional on economic context. First, living in a member state that receives relatively high levels of EU funding acts as a 'buffer', diluting the impact of an exclusive national identity on Euroscepticism. Second, living in a relatively wealthy member state, with its associated attractiveness for economic migrants, increases the salience of economic xenophobia as a driver of sceptical attitudes. These results highlight the importance of seeing theories of attitude formation (such as economic and identity theories) not as competitors but rather as complementary, with the predictive strength of one theoretical approach (identity) being a function of system-level variation in factors relating to the other theoretical approach (macro-level economic conditions).
Resumo:
Belief revision characterizes the process of revising an agent’s beliefs when receiving new evidence. In the field of artificial intelligence, revision strategies have been extensively studied in the context of logic-based formalisms and probability kinematics. However, so far there is not much literature on this topic in evidence theory. In contrast, combination rules proposed so far in the theory of evidence, especially Dempster rule, are symmetric. They rely on a basic assumption, that is, pieces of evidence being combined are considered to be on a par, i.e. play the same role. When one source of evidence is less reliable than another, it is possible to discount it and then a symmetric combination operation
is still used. In the case of revision, the idea is to let prior knowledge of an agent be altered by some input information. The change problem is thus intrinsically asymmetric. Assuming the input information is reliable, it should be retained whilst the prior information should be changed minimally to that effect. To deal with this issue, this paper defines the notion of revision for the theory of evidence in such a way as to bring together probabilistic and logical views. Several revision rules previously proposed are reviewed and we advocate one of them as better corresponding to the idea of revision. It is extended to cope with inconsistency between prior and input information. It reduces to Dempster
rule of combination, just like revision in the sense of Alchourron, Gardenfors, and Makinson (AGM) reduces to expansion, when the input is strongly consistent with the prior belief function. Properties of this revision rule are also investigated and it is shown to generalize Jeffrey’s rule of updating, Dempster rule of conditioning and a form of AGM revision.
Resumo:
Various parameters of coagulation and fibrinolysis were measured in 13 men (aged 54 +/- 3 yr) with non-insulin-dependent diabetes mellitus (NIDDM) before and after 12-14 wk of exercise training. Subjects exercised for 30 min 3 times/wk at 70% of maximum O2 consumption (VO2max). Training increased VO2max by 12.5% but did not alter body weight, relative body fat, blood pressure, cholesterol, triglycerides, or high-density lipoprotein cholesterol. Slight downward trends were apparent for fasting glucose and insulin, but glycosylated hemoglobin was unchanged. There were no changes in coagulation parameters of plasminogen, hematocrit, or alpha 2-antiplasmin. Plasma fibrinogen (303 +/- 24.2 vs. 256 +/- 12.3 mg/dl) and fibronectin (380 +/- 41.9 vs. 301 +/- 22.2 micrograms/ml) were significantly reduced (P less than 0.02) by exercise conditioning. Three assays of fibrinolytic activity (tissue plasminogen activator, euglobulin lysis time, and an isotopic measure of fibrinolysis) confirmed that neither basal fibrinolysis nor the fibrinolytic responses to venous occlusion and maximal exercise were significantly altered. Exercise conditioning may have antithrombotic effects in NIDDM by reducing plasma fibrinogen and fibronectin. Although the significance of the fall in fibronectin awaits further studies, the reduction in plasma fibrinogen gives a rationale for the use of exercise training in men with NIDDM.
Resumo:
Nowadays, the Earth Pressure Balanced (EPB) shields are used more and more caused by both the mechanical development of the machines and the more effective use of additives such as foams and polymers. These additives are used to condition spoil in the screw conveyor. A crucial component of EPB tunnelling applications is ground conditioning. Thus, in order to permit quantitative measurements of the conditioned ground behavior, it is necessary to develop and use a test able to simulate the extraction of earth from the chamber with a screw conveyor. This reliable test procedure can provide quantitative parameters that can really describe the conditioned soil behavior.
Resumo:
The screw conveyor system plays a fundamental role during the EPB tunnelling operations for the tunnel face pressure control. On the other hand, the use of additives such chemical foams is even more applied in order to extend the EPB technology to the cohesionless soils. Despite the extensive use of the EPB technique in urban environment, little knowledge exists in the understanding of the behavior of such conditioned soil during the excavation operations. At the Turin University of Technology the Tunnelling and Underground Space Centre, in the mainframe of a wider research on soil conditioning, has developed an experimental apparatus that simulates the extraction phase with screw conveyor from a pressurized tank. In this paper the apparatus is presented and the results of a first series of tests carried out on sand are discussed. © 2007 Taylor & Francis Group.
Resumo:
EPB tunnelling requires the application of soil conditioning to increase its field of applicability particularly for cohesionless soils. Choosing the most suitable conditioning set for the various soils requires the use of a feasible laboratory test which can permit to define the characteristics of the conditioned soils and provide measurable data. A series of tests has been carried out using a laboratory screw conveyor device which was designed for this purpose and which simulates the extraction of the spoil from a pressure chamber in a similar way as in EPB tunnelling. The tested soils were medium-grain sands with varying amounts of silt and the tested conditioned mixtures were obtained with different water contents and amounts of foam. A simple slump test was also used to analyze the global characteristics of the conditioned soils. The test has shown that the proposed laboratory procedure permits a quantitative comparison to be made between different conditioning amounts and agents on the basis of measurable parameters. © 2007 Elsevier Ltd. All rights reserved.
Resumo:
Soil conditioning consists of mixing and remolding the natural material during the mechanical excavation of tunnels, generally at low depth, with additives, in order to obtain suitable properties of plasticity and consistency for the excavated material, so becoming able to apply a counterpressure against natural earth pressure and groundwater flow towards the excavation chamber. The assessment and the control of the soil parameters and of machine performance are fundamental for a regular and safe excavation, also with regards to surface stability. This paper mainly focus on testing approach aimed to the proper soil conditioning with EPB shields, whose results have been validated at real scale. The influence of the water content and the amount of conditioning foam has been studied by the Authors. A proper definition of conditioning parameters can allow to extend the application field of Earth Pressure Balance (EPB) tunnel machines to various grain soil distribution, even in weak rock formations (e.g. siltstone or flysch). Importance of conditioning is reflected also on the possibility of a proper spoil disposal or better for its reuse.