3D modelling of LASER hardening and tempering of hypo-eutectoid steels

In this paper a mathematical model solved by means of the finite differences method (FDM) for laser surface hardening of complex geometries is presented. The 3-D transient model characterizes a software package named Laser Hardening Simulator (LHS), which makes it possible to predict the extension of the treated area into the mechanical components and thus the hardened depth into the bulk material. The obtained microstructures and the resulting hardness with respect to the laser parameters and to the laser beam path strategy can be determined by considering the quenching and the tempering effects due to the overlapping trajectories. The initial workpiece microstructure is taken into account in the simulation by a digitized photomicrograph of the ferrite-pearlite distribution before the thermal cycle. In order to show the accuracy of the model, experimental trials were conducted on the keyway for spline machined on a hub made of SAE 1043. The domain discretization for the solution of the heat flux problem into the workpiece and for the diffusion of the carbon is carried out by means of a mesh generator strategy implemented into the code

The influence of plasma plume in laser milling for mold manufacturing

The paper refers to the modeling of the plasma plume influence on the shape of the crater obtained by means of nanosecond pulsed laser milling. A transient model of the physical state of the plasma plume is developed according to the laser parameters. Two empirical coefficients are proposed in the model in order to evaluate the plasma plume self-emission energy lost towards the environment and the energy spread from the plasma towards the target surface. These two coefficients, directly correlated to the depth and to the width of the crater, can be experimentally determined, due to the difficulty of their analytical quantification, and they can be used for tuning a complete plasma plume software package for laser milling simulation named LAS (Laser Ablation Simulator) already developed by the authors. In this paper their influence on the crater shape will be proved by means of several simulation runs

Effects of anisotropic and isotropic LIPSS on polymer filling flow and wettability of micro injection molded parts

In micro injection molding, the specific cavity surface texture and roughness directly influence the polymer flow and the heat transfer between polymer melt and mold. In this work, two different types of laser-induced periodic surface structures, linear and hexagonal, were generated, and their impact on the flow length in micro injection molding was evaluated. A complete investigation of the surface treatment effect on the polymer flow was carried out, comparing the performance of an untreated cavity surface with surfaces modified by LIPSS. The phenomenon was examined by localizing the weld lines created by the polymer flowing in two parallel channels having different surface treatments. Several cavity inserts were treated by varying the LIPSS process parameters to generate surfaces with different micro-and nanostructures directions and periodicity. Furthermore, the paper addresses the hydro-phobicity achieved on the micro molded surfaces replicated from mold inserts with different LIPSS-based surface topography. Mold surfaces with linear and hexagonal LIPSS and the respective molded parts were analyzed by optical profilometry and scanning electron microscopy to characterize the cavity surfaces replication and localize the weld lines on the micro injection molded parts

An experimental and theoretical approach for an estimation of DKth

The existence of a fatigue threshold value may affect the design process when a damage-tolerant design is considered that uses non-destructive techniques for evaluating the shape and dimensions of the defects inside materials. Obviously it should be possible to estimate the stress field surrounding these defects and this is not generally a problem with modern numerical methods.Many factors are involved in determining the growth rate of a fatigue crack. Some of these are highly significant and it is possible to obtain the coefficients of a correlation function. Some others are not well defined and the only effect is to expand the scatter of experimental data.Consider the sigmoidal curve we obtain when plotting the crack growth rate versus the applied DK_I . A very difficult parameter to measure but very useful for fatigue design is the DK_Ith value, because below this value a crack may be forming, hence, here DK_Ith is defined by the transition between a normal (e.g. 10-10 m/cycle) and a very low range of crack growth rate (<10-10 m/cycle).The DgrKIth value is very difficult to obtain by experimental methods because the growth rate is of the order or less than the atomic lattice span (3 × 10-10 m/cycle), but we can correlate the transition value with the cyclic crack tip plastic zone size and other structural parameters of metallic materials.The aim of this work is to offer a contribution about the parameters which influence DK_Ith in stainless steels and welded joints based on the crack tip plastic zone radius

A randomized, double-blind, placebo-controlled study of permanent cardiac pacing for the treatment of recurrent tilt-induced vasovagal syncope. The vasovagal syncope and pacing trial (SYNPACE)

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Two-Center Black Holes Duality-Invariants for stu Model and its lower-rank Descendants

We classify 2-center extremal black hole charge configurations through duality-invariant homogeneous polynomials, which are the generalization of the unique invariant quartic polynomial for single-center black holes based on homogeneous symmetric cubic special Kaehler geometries. A crucial role is played by an horizontal SL(p,R) symmetry group, which classifies invariants for p-center black holes. For p = 2, a (spin 2) quintet of quartic invariants emerge. We provide the minimal set of independent invariants for the rank-3 N = 2, d = 4 stu model, and for its lower-rank descendants, namely the rank-2 st^2 and rank-1 t^3 models; these models respectively exhibit seven, six and five independent invariants. We also derive the polynomial relations among these and other duality invariants. In particular, the symplectic product of two charge vectors is not independent from the quartic quintet in the t^3 model, but rather it satisfies a degree-16 relation, corresponding to a quartic equation for the square of the symplectic product itself.Comment: 1+31 pages; v2: amendments in Sec. 9, App. C added, other minor refinements, Refs. added; v3: Ref. added, typos fixed. To appear on J.Math.Phy

Separation delay on thick airfoil using multiple synthetic jets

High momentum 2D synthetic jet actuators are tested experimentally focusing the investigation on the separation delay over the airfoil NACA 0024 at high angles of attack. Four slots are present on the suction side of the airfoil. The number of slots in the downstream direction, the position and the width of the active slots and the forcing frequency were varied to investigate on their effects produced. Pressure measurements and wake analysis were performed at Reynolds number equal to 106. A weak influence was observed at low and medium incidences on the lift and drag curves. Considerable increments of the lift coefficient also associated with drag reductions were obtained at high angles of attack according to the values of the forcing frequency and the slots configuration. The influence of the slot width does not highlight great differences on the lift and drag curves. The upstream location of the slots is more effective to delay separation compared with further downstream positioning. Two consecutive active slots were effective as a single one at the same frequency while the estimated comparison at constant momentum could allow better performances. The tests were carried out operating with forcing frequencies near the resonance conditions of the system synthetic jet- cavity-pneumatic line

Sistemi di trasmissione WiFi per il monitoraggio sismico del Vesuvio

First-year engineering students at the University of Queensland used an interactive webbook to acquire information skills. These helped them search information resources for their projects, which they are required to undertake as part of the subject Introduction to professional engineering. The information skills exercise was an integral part of the project and worth 10% of the overall assessment. The exercises were only available on the Web, allowing the students to enter their answers from home or wherever they had access to the Internet. All answers were marked automatically using a database of all possible answers. Students were able to go back to check their answers. Students were assessed on both their responses to the exercises and also their final bibliography which largely reflected the impact of the webbook. The entire process was evaluated. This paper presents the process and the outcomes of the first-year engineering project involving use of WWW for information skills instruction. The webbooks can be found at http://www.library.uq.edu.au/9e105/

Il Sito Web accessibile dell’Osservatorio Vesuviano

Il sito web dell’Osservatorio Vesuviano (OV) nasce nel 1997. Lo scopo era quello di fornire informazioni sullo stato di attività dei vulcani della Campania, per i quali l’Osservatorio Vesuviano gestisce le reti strumentali di monitoraggio, nonché di far conoscere le attività scientifiche e i dati prodotti dall’ente. Nel 2002 il sito ha subito una sostanziale riorganizzazione, a seguito di una ristrutturazione dell’Osservatorio Vesuviano, che insieme ad altri istituzioni scientifiche affini era confluito, all’inizio del 2001, nell’Istituto Nazionale di Geofisica e Vulcanologia (INGV) diventandone la Sezione di Napoli. La nuova versione ha tenuto conto della più complessa articolazione delle attività dell’Osservatorio Vesuviano, che negli anni aveva visto aumentare il numero dei propri ricercatori e tecnici e aveva ulteriormente differenziato e specializzato le proprie attività. Inoltre la nuova strutturazione come sezione dell’INGV consentiva un’organizzazione in Unità Funzionali e Servizi. In occasione della realizzazione della seconda versione del sito è stata effettuata un’analisi sistematica dell’utenza basata prevalentemente sulla posta elettronica ricevuta all’indirizzo dedicato alle richieste di informazioni da parte del pubblico. Questo ha consentito di individuare diverse tipologie di utenza. In funzione delle crescenti richieste di informazioni è stato inoltre organizzato un gruppo per curare il servizio “info”, basato su richieste di informazione via mail, che ha dato modo di meglio delineare gli argomenti di maggior interesse da parte dei visitatori (Giudicepietro et al., 2006). Questa attività ha fatto nascere anche una sezione dedicata alle domande frequenti che, soprattutto nei periodi di maggior attenzione per le tematiche del rischio vulcanico, è risultata un utile supporto alla richiesta di informazioni da parte del pubblico. Negli ultimi anni in Italia, come in molti altri paesi del mondo, si è sviluppata una normativa in materia di web che ha dettato le linee guida per lo sviluppo dei siti delle Pubbliche Amministrazioni (Circolare Funzione Pubblica 13 marzo 2001, n. 3/2001 “Linee guida per l'organizzazione, l'usabilità e l'accessibilità dei siti web delle pubbliche amministrazioni”) nonché ha richiamato l’attenzione sull’accessibilità. La normativa italiana relativa all’accessibilità ha lo scopo principale di garantire la fruizione delle informazioni diffuse sul web e dei relativi servizi informatici anche alle persone disabili in ottemperanza al principio di uguaglianza ai sensi dell'articolo 3 della Costituzione. In particolare la Legge del 9 gennaio 2004 n. 4 (pubblicata in G.U. 13 del 17.01.2004) definisce l’accessibilità delle fonti di informazione e servizi informatici come “la capacità dei sistemi informatici, nelle forme e nei limiti consentiti dalle conoscenze tecnologiche, di erogare servizi e fornire informazioni fruibili, senza discriminazioni, anche da parte di coloro che a causa di disabilità necessitano di tecnologie assistive o configurazioni particolari”. Le tecnologie assistive sono definite nella stessa legge come “gli strumenti e le soluzioni tecniche, hardware e software, che permettono alla persona disabile, superando o riducendo le condizioni di svantaggio, di accedere alle informazioni e ai servizi erogati dai sistemi informatici”. Un esempio di tecnologia 4 assistiva può essere uno screen reader, ovvero un lettore di schermo, strumento utilizzato dai non vedenti per usare il computer. In attuazione della legge del 9 gennaio 2004 n. 4, il Decreto Ministeriale dell'8 luglio 2005 "Requisiti tecnici e i diversi livelli per l'accessibilità agli strumenti informatici", definisce 22 requisiti per l’accessibilità che i siti delle Pubbliche Amministrazioni devono soddisfare. La seconda versione del sito dell’Osservatorio Vesuviano non era conforme ai requisiti richiesti da questo decreto, pertanto si è resa necessaria una nuova ristrutturazione del sito che consentisse l’adeguamento alla normativa vigente (www.w3.org, www.governo.it, www.pubbliaccesso.it, www.cnipa.gov.it)

The PAMELA Time-of-Flight system: status report

Abstract The PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) satellite-borne experiment, scheduled to be launched in 2003, aboard a Soyuz TM2 rocket, is designed to provide a better understanding of the antimatter component of cosmic rays. In the following we report on the features and performances of its scintillator telescope system which will provide the primary experimental trigger and time-of-flight particle identification