Sostanzialismo e relazionalismo dello spaziotempo alla luce della relatività generale

Until recently the debate on the ontology of spacetime had only a philosophical significance, since, from a physical point of view, General Relativity has been made "immune" to the consequences of the "Hole Argument" simply by reducing the subject to the assertion that solutions of Einstein equations which are mathematically different and related by an active diffeomorfism are physically equivalent. From a technical point of view, the natural reading of the consequences of the "Hole Argument” has always been to go further and say that the mathematical representation of spacetime in General Relativity inevitably contains a “superfluous structure” brought to light by the gauge freedom of the theory. This position of apparent split between the philosophical outcome and the physical one has been corrected thanks to a meticulous and complicated formal analysis of the theory in a fundamental and recent (2006) work by Luca Lusanna and Massimo Pauri entitled “Explaining Leibniz equivalence as difference of non-inertial appearances: dis-solution of the Hole Argument and physical individuation of point-events”. The main result of this article is that of having shown how, from a physical point of view, point-events of Einstein empty spacetime, in a particular class of models considered by them, are literally identifiable with the autonomous degrees of freedom of the gravitational field (the Dirac observables, DO). In the light of philosophical considerations based on realism assumptions of the theories and entities, the two authors then conclude by saying that spacetime point-events have a degree of "weak objectivity", since they, depending on a NIF (non-inertial frame), unlike the points of the homogeneous newtonian space, are plunged in a rich and complex non-local holistic structure provided by the “ontic part” of the metric field. Therefore according to the complex structure of spacetime that General Relativity highlights and within the declared limits of a methodology based on a Galilean scientific representation, we can certainly assert that spacetime has got "elements of reality", but the inevitably relational elements that are in the physical detection of point-events in the vacuum of matter (highlighted by the “ontic part” of the metric field, the DO) are closely dependent on the choice of the global spatiotemporal laboratory where the dynamics is expressed (NIF). According to the two authors, a peculiar kind of structuralism takes shape: the point structuralism, with common features both of the absolutist and substantival tradition and of the relationalist one. The intention of this thesis is that of proposing a method of approaching the problem that is, at least at the beginning, independent from the previous ones, that is to propose an approach based on the possibility of describing the gravitational field at three distinct levels. In other words, keeping the results achieved by the work of Lusanna and Pauri in mind and following their underlying philosophical assumptions, we intend to partially converge to their structuralist approach, but starting from what we believe is the "foundational peculiarity" of General Relativity, which is that characteristic inherent in the elements that constitute its formal structure: its essentially geometric nature as a theory considered regardless of the empirical necessity of the measure theory. Observing the theory of General Relativity from this perspective, we can find a "triple modality" for describing the gravitational field that is essentially based on a geometric interpretation of the spacetime structure. The gravitational field is now "visible" no longer in terms of its autonomous degrees of freedom (the DO), which, in fact, do not have a tensorial and, therefore, nor geometric nature, but it is analyzable through three levels: a first one, called the potential level (which the theory identifies with the components of the metric tensor), a second one, known as the connections level (which in the theory determine the forces acting on the mass and, as such, offer a level of description related to the one that the newtonian gravitation provides in terms of components of the gravitational field) and, finally, a third level, that of the Riemann tensor, which is peculiar to General Relativity only. Focusing from the beginning on what is called the "third level" seems to present immediately a first advantage: to lead directly to a description of spacetime properties in terms of gauge-invariant quantites, which allows to "short circuit" the long path that, in the treatises analyzed, leads to identify the "ontic part” of the metric field. It is then shown how to this last level it is possible to establish a “primitive level of objectivity” of spacetime in terms of the effects that matter exercises in extended domains of spacetime geometrical structure; these effects are described by invariants of the Riemann tensor, in particular of its irreducible part: the Weyl tensor. The convergence towards the affirmation by Lusanna and Pauri that the existence of a holistic, non-local and relational structure from which the properties quantitatively identified of point-events depend (in addition to their own intrinsic detection), even if it is obtained from different considerations, is realized, in our opinion, in the assignment of a crucial role to the degree of curvature of spacetime that is defined by the Weyl tensor even in the case of empty spacetimes (as in the analysis conducted by Lusanna and Pauri). In the end, matter, regarded as the physical counterpart of spacetime curvature, whose expression is the Weyl tensor, changes the value of this tensor even in spacetimes without matter. In this way, going back to the approach of Lusanna and Pauri, it affects the DOs evolution and, consequently, the physical identification of point-events (as our authors claim). In conclusion, we think that it is possible to see the holistic, relational, and non-local structure of spacetime also through the "behavior" of the Weyl tensor in terms of the Riemann tensor. This "behavior" that leads to geometrical effects of curvature is characterized from the beginning by the fact that it concerns extensive domains of the manifold (although it should be pointed out that the values of the Weyl tensor change from point to point) by virtue of the fact that the action of matter elsewhere indefinitely acts. Finally, we think that the characteristic relationality of spacetime structure should be identified in this "primitive level of organization" of spacetime.

Adding regional analgesia to general anaesthesia: increase of risk or improved outcome?

Although it is clear that regional analgesia in association with general anaesthesia substantially reduces postoperative pain, the benefits in terms of overall perioperative outcome are less evident. The aim of this nonsystematic review was to evaluate the effect on middle and long-term postoperative outcomes of adding regional perioperative analgesia to general anaesthesia. This study is based mostly on systematic reviews, large epidemiological studies and large or high-quality randomized controlled trials that were selected and evaluated by the author. The endpoints that are discussed are perioperative morbidity, cancer recurrence, chronic postoperative pain, postoperative rehabilitation and risk of neurologic damage. Epidural analgesia may have a favourable but very small effect on perioperative morbidity. The influence of other regional anaesthetic techniques on perioperative morbidity is unclear. Preliminary data suggest that regional analgesia might reduce the incidence of cancer recurrence. However, adequately powered randomized controlled trials are lacking. The sparse literature available suggests that regional analgesia may prevent the development of chronic postoperative pain. Rehabilitation in the immediate postoperative period is possibly improved, but the advantages in the long term remain unclear. Permanent neurological damage is extremely rare. In conclusion, while the risk of permanent neurologic damage remains extremely low, evidence suggests that regional analgesia may improve relevant outcomes in the long term. The effect size is mostly small or the number-needed-to-treat is high. However, considering the importance of the outcomes of interest, even minor improvement probably has substantial clinical relevance.

Using Blackboard Administered Precourse and Post course Tests to Assess Student Readiness to Learn and Change in Knowledge

Students arrive at classes with a varying social situations and course subject knowledge. Blackboard is a web based course delivery program that permits testing of students before arriving at the first class. A pretest was used to assess preexisting subject knowledge(S) and a survey was used to assess non-subject (N) factors that might impact the student’s final grade. A posttest was administered after all content was delivered and used to access change in S. [See PDF for complete abstract]

Approximation to earth material from international normative

For centuries, earth has been used as a construction material. Nevertheless, the normative in this matter is very scattered, and the most developed countries, to carry out a construction with this material implies a variety of technical and legal problems. In this paper we review, in an international level, the normative panorama about earth constructions. It analyzes ninety one standards and regulations of countries all around the five continents. These standards represent the state of art that normalizes the earth as a construction material. In this research we analyze the international standards to earth construction, focusing on durability test (spray and drip erosion tests). It analyzes the differences between methods of test. Also we show all results about these tests in two types of compressed earth block.

Quasi-cylindrical approximation to the swirling flow in an atomizer chamber

A quasi-cylindrical approximation is used to analyse the axisymmetric swirling flow of a liquid with a hollow air core in the chamber of a pressure swirl atomizer. The liquid is injected into the chamber with an azimuthal velocity component through a number of slots at the periphery of one end of the chamber, and flows out as an anular sheet through a central orifice at the other end, following a conical convergence of the chamber wall. An effective inlet condition is used to model the effects of the slots and the boundary layer that develops at the nearby endwall of the chamber. An analysis is presented of the structure of the liquid sheet at the end of the exit orifice, where the flow becomes critical in the sense that upstream propagation of long-wave perturbations ceases to be possible. This nalysis leads to a boundary condition at the end of the orifice that is an extension of the condition of maximum flux used with irrotational models of the flow. As is well known, the radial pressure gradient induced by the swirling flow in the bulk of the chamber causes the overpressure that drives the liquid towards the exit orifice, and also leads to Ekman pumping in the boundary layers of reduced azimuthal velocity at the convergent wall of the chamber and at the wall opposite to the exit orifice. The numerical results confirm the important role played by the boundary layers. They make the thickness of the liquid sheet at the end of the orifice larger than predicted by rrotational models, and at the same time tend to decrease the overpressure required to pass a given flow rate through the chamber, because the large axial velocity in the boundary layers takes care of part of the flow rate. The thickness of the boundary layers increases when the atomizer constant (the inverse of a swirl number, proportional to the flow rate scaled with the radius of the exit orifice and the circulation around the air core) decreases. A minimum value of this parameter is found below which the layer of reduced azimuthal velocity around the air core prevents the pressure from increasing and steadily driving the flow through the exit orifice. The effects of other parameters not accounted for by irrotational models are also analysed in terms of their influence on the boundary layers.

Identifying asthma and chronic obstructive pulmonary disease in patients with persistent cough presenting to general practitioners: descriptive study

Objective: To determine the prevalence of asthma and chronic obstructive pulmonary disease in patients not known to have these disorders, who present in general practice with persistent cough, and to ascertain criteria to help general practitioners in diagnosis.

Approximation to EU Technical Standards with and without the Promise of Membership: the Cases of Slovakia and Ukraine. EU Diplomacy Paper 02/2013

This paper aims to identify the extent to which the non-promise of membership of the European Union (EU) precludes the motivation of Ukraine as European Neighbourhood Policy country to adopt EU policies in the field of market access, namely technical standards and regulations. Its approximation approach is compared to the fast-tracked accession of Slovakia, which was driven by a clear-cut membership promise. Furthermore, the paper elaborates whether the conclusion of an Association Agreement between the EU and Ukraine, including a Deep and Comprehensive Free Trade Agreement, provides sufficient incentives for Ukraine to continue reforming its quality infrastructure in order to gain access to the Single European Market. Finally, scenarios of possible developments of EU-Ukraine relations are deliberated in the context of the EU-Ukraine-Russia triangle. The paper argues that market access provides sufficient stimulus for third countries to adhere to EU technical standards – even in the absence of a clear and credible promise of future EU membership. Yet, in the case of Ukraine, the country’s relations with Russia appear to compete with its EU approximation process, resulting for the time being in Ukraine attempting to pursue a balanced dual cooperation with both the EU and Russia.

Conservation laws and variational principles in general relativity /

"April 23, 1962."

Epistemology, or the theory of knowledge; an introduction to general metaphysics, by P. Coffey ...

First published, 1917; reprinted 1958."