Friction of Polymers Sliding on Smooth Surfaces

Friction plots of polymers sliding on smooth metal surfaces are generally characterized by two regions of distinct dependency on the normal load, with low sensitivity at low stress levels followed by a sharp change in the rate of decrease of friction with increasing pressure at levels above the plastic flow limit of the polymer. A simplified model is proposed to describe this behavior which accounts for the effect of the normal load on the growth of the real contact area and the shear stress at the interface between the polymer and the mating surface. The model has a wide generality when expressed in terms of dimensionless variables, allowing to rationalize the friction behavior of different polymers within a single framework

Design of an innovative polymerase chain reaction device based on buoyancy driven flow

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Polymerase Chain Reaction (PCR) plays a central role in the field of molecular biology. The miniaturization of PCR systems is promising as it potentially minimizes costly reagent consumption and time required for analysis. In PCR microdevices a sample solution is usually handled by external pumps. An alternative solution relies on temperature-induced density difference in the presence of a body force to induce buoyancy driven flow. This alternative method is easy to be used and does not require expensive setup, but, to date, the thermo-fluid-dynamic field in the micro-channels still needs to be optimized. The present study focuses on the design of micro-channels, having innovative and optimized shapes to obtain proper fluid actuation and DNA sample amplification within buoyancy driven flow PCR devices. A parametric study is carried out by means of computational thermal fluid dynamic modeling: several channel geometry configurations were compared in terms of time required for analysis, temperature distribution and priming volume. The advantages and disadvantages of such configurations are discussed

Computational and experimental investigation of mixing in microchannels

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Mixing is a key process for the successful of all chemical or biochemical reactions, so effective micromixers represent essential components for micro total analysis systems (μTAS) or lab-on-a-chip. In the present study a combined computational and experimental approach was adopted to evaluate how the efficiency of a Y-mixer can be enhanced by modifying its downstream geometry. Three different geometries were studied and compared: Y-straight channel, Y-sine channel and Y-wrinkled wall channel. For each of them the influence of perfusing flow rates and channel cross section aspect ratio was investigated. Physical prototypes were built using a simple technique based on a xerographic process, and their mixing performance was experimentally evaluated. Computational models of the designed micromixers were generated: the Navier-Stokes equations for an incompressible Newtonian fluid and the advection-diffusion equation were solved with an uncoupled approach by means of the finite volume method. The computational and experimental results were critically compared, revealing Y-wrinkled wall mixer as the best performer among those considered and suggesting criteria of possible improvements and optimization

Numerical simulation of a deformable cell in microchannels

The main goal of this work is to numerically investigate the behavior of a cell flowing in a microfluidic system. In particular, we want to model flow-induced deformations of an isolated cell to quantitatively evaluate the cell response when subjected to a representative range of flow rates in a realistic geometry, with specific interest in the case of cell trapping. This research will help optimize operating conditions as well as the design of cell manipulation/culture micro-devices, so as to guarantee cell viability and ultimately improve high-throughput performance

Acerca del saber de los docentes: un aporte a la cuestión

There are diverse positions and theories about the knowledgeof teachers. This article intends to contribute to this debate through the presentation and development of a work hypothesis that sustains: teachers are capable of producing pedagogic knowledge beyond the explicit knowledge implied on their practices. There are diverse positions and theories about the knowledge of teachers. This article intends to contribute to this debate through the presentation and development of a work hypothesis that sustains: teachers are capable of producing pedagogic knowledge beyond the explicit knowledge implied on their practicesenable reflection and shared thought.The development of these ideas is articulated around a reflection on an experience shared with a group of teachers of an Educational Community Center of Buenos Aires City.Existen diversas posiciones y teorizaciones sobre el saber o los saberes de los enseñantes. Las reflexiones que contiene este escrito se proponen hacer un aporte más a este debate a través de la presentación y desarrollo de una hipótesis de trabajo que afirma que los educadores son capaces de producir un saber pedagógico que excede la explicitación de saberes implícitos en sus prácticas y que esa producción es posible cuando se brindan las condiciones  institucionales que habilitan espacios de reflexión y pensamiento compartido.El desarrollo de estas ideas se articula en torno a una reflexión sobre una experiencia compartida con un grupo de docentes de un Centro Educativo Comunitario de la Ciudad de Buenos Aires

IL GIUDIZIO CIVILE DI RINVIO A SEGUITO DI ANNULLAMENTO DELLA SENTENZA PENALE AI SOLI EFFETTI CIVILI

Il presente elaborato \ue8 dedicato allo studio del giudizio di rinvio che si svolge davanti al giudice civile a seguito dell\u2019annullamento della sentenza penale ai soli effetti civili, ai sensi dell\u2019art. 622 c.p.p. In particolare, l\u2019obiettivo del presente studio \ue8 quello di individuare - nel silenzio della legge - la disciplina propria di questo particolare giudizio, giudizio che costituisce un punto di contatto tra sistema processuale penale e sistema processuale civile. Premessi brevi cenni - nel primo capitolo - in merito all\u2019evoluzione della disciplina del rapporto tra azione civile e azione penale, al fine di inquadrare l\u2019istituto dell\u2019annullamento della sentenza penale ai soli effetti civili, l\u2019indagine si sofferma - nel secondo capitolo - sull\u2019individuazione delle ipotesi applicative dell\u2019art 622 c.p.p. Una volta chiariti ratio e oggetto del giudizio di rinvio in esame, l\u2019elaborato esamina le soluzioni proposte dalla dottrina e dalla giurisprudenza in merito a struttura, funzione, natura, caratteri, limiti e regole processuali, giungendo ad affermare che non possono essere applicate direttamente ed esclusivamente le norme del codice di procedura civile che disciplinano lo svolgimento del giudizio di rinvio. L\u2019analisi si occupa, quindi, di illustrare come, e in che termini, devono essere coordinate disciplina processuale penale e disciplina processuale civile.This paper addresses the proceedings called \u201cgiudizio di rinvio\u201d before the civil judge following the declaration of the judgment as null and void (\u201cannullamento\u201d) with respect to its civil effects only, ex Article 622 of the Italian Code of Criminal Procedure. In particular, this paper aims at identifying - in the absence of ad hoc law provisions - the proper rules for this peculiar proceedings, the latter being a point of contact between the criminal procedure system and the civil procedure system. In Section first, with the aim at framing the procedure relating to the declaration as null and void (\u201cannullamento\u201d) of the criminal judgement with respect to its civil effects only, this paper briefly addresses how the rules applicable to the relationship between civil action and criminal action have developed. In the Section second, this paper addresses the cases wherein Article 622 of the Italian Code of Criminal Procedure is applicable. Once the ratio and the scope of the \u201cgiudizio di rinvio\u201d has been addressed, this paper analyses the solutions proposed by the Italian Authors and case laws with respect to structure, purpose, nature, characters, limitations and procedural rules, concluding that the civil procedure rules governing the \u201cgiudizio di rinvio\u201d cannot be applied directly and exclusively. Accordingly, this paper illustrates how the applicable criminal procedure rules and civil procedure rules should be coordinated