110 research outputs found
Thermoacoustic effects in supercritical fluids near the critical point: Resonance, piston effect, and acoustic emission and reflection
We present a general theory of thermoacoustic phenomena in supercritical
fluids near the critical point in a one-dimensional cell. We take into account
the effects of the heat conduction in the boundary walls and the bulk viscosity
near the critical point. We introduce a coefficient characterizing
reflection of sound with frequency at the boundary. As applications,
we examine the acoustic eigenmodes in the cell, the response to time-dependent
perturbations, sound emission and reflection at the boundary. Resonance and
rapid adiabatic changes are noteworthy. In these processes, the role of the
thermal diffusion layers is enhanced near the critical point because of the
strong critical divergence of the thermal expansion.Comment: 15 pages, 7 figure
Evaluation of the Antioxidant Capacity of Fruit Juices by Two Original Analytical Methods
Two analytical methods previously developed by our groups were employed to estimate the antioxidant capacity of commercial fruit juices. The electrochemical method, which measures the scavenging activity of antioxidants towards OH radicals generated by both hydrogen peroxide photolysis and Fenton’s reaction, is based on the recovery of the cyclic voltametric response of the redox probe Ru(NH3)63+ at a Glassy Carbon electrode modified with a thin film of an insulating polyphenol, in the presence of compounds with antioxidant properties. The values of the antioxidant capacity of the fruit juices are expressed as vitamin C equivalents/L. The chromatographic method is based on the generation of OH radicals via Fenton’s reaction in order to test the inhibition of their formation in the presence of antioxidant compounds by monitoring salicylate aromatic hydroxylation derivatives as markers of •OH production, by means of HPLC coupled to coulometric detection. The results are expressed as the percentage of inhibition of •OH production in the presence of the tested juice compared to the control sample. When OH radicals are produced by Fenton’s reaction, the antioxidant capacity of the juices, estimated by both methods, displays an analogous trend, confirming that they can be considered an alternative for measuring the ability of antioxidants to block OH radical formation
Distributional map of the terminal and sub-terminal sugar residues of the glycoconjugates in the prepubertal and postpubertal testis of a subject affected by complete androgen insensitivity syndrome (Morris's syndrome): lectin histochemical study
Erratum to: The Italian Registry of Endovascular Treatment in Acute Stroke: rationale, design and baseline features of patients
Postural control and contingent negative variation during transient floor translation while standing with the ankle fixed
The Molecular Identification of Organic Compounds in the Atmosphere: State of the Art and Challenges
UN APPROCCIO COOPERATIVO ALL\u2019INSEGNAMENTO DELLA CHIMICA ANALITICA STRUMENTALE IN UN ISTITUTO DI SCUOLA SECONDARIA SUPERIORE. 2. Applicazione del modello logico R.A.Re.Co. allo studio della strumentazione gascromatografica
Evaluation rubrics: a tool for laboratory activities assessment in chemistry and physics
Rubrics are a powerful tool for the evaluation of complex activities or authentic tasks. In these situations the final score is best represented when the task is subdivided in well defined portions, each of them describing the elements concurring to the overall performance. In this communication a set of evaluation rubrics for the assessment of several laboratory activities is presented, together with a rubric for the evaluation of the final report of an experimental work. This latter rubric is centered on the problem/hypothesis couple: the students are firstly encouraged to formulate a \u201cproblem\u201d, arising from the observation of a physical phenomenon. After the \u201cproblem\u201d has been defined, the students must find out an interpretative \u201chypothesis\u201d to be tested by the experimental process. Such an approach agrees with the indication of the Rocard Report on Education Science to increase interest and attainments in science. The introduction to the use of rubrics was presented to the students by means of a cooperative activity, centered on the examination of laboratory reports of different qualitative levels made by students of previous course years. The described strategy has been practiced both at university and in a secondary school (ITIS). A first approach has been also attempted within the \u201cPhysics and Chemistry Laboratory\u201d at LST. The extensive use of report rubrics for the whole period of the courses has increased both the understanding of how a scientific report should be organized and the student ability in effective written skills
- …