CFD aided design and experimental validation of an innovative Air Assisted Pure Water Jet cutting system

Water jet cutting has always been a promising technology because of its extreme simplicity and flexibility, even if it often suffers a lack of control on its process parameters, especially if compared to technologies such as laser cutting or electro-discharge machining. Recent studies have showed how the presence of water inside the orifice causes disturbances and instabilities which systematically affect the jet structure, both during the jet formation and the cutting process. These disturbances can be neglected in industrial applications, but they can play a relevant role in case of high-precision water jet machining. The aim of the research presented in this paper is to develop an innovative system able to modify the orifice flow field by means of a simple modification of the standard cutting head geometry; the system allows the controlled injection of air inside the primary orifice to prevent the jet instabilities and to adapt the level of jet coherence to the specific machining operation. The fluid dynamics aspects of the outflow process are investigated by means of a 3D numerical simulation with the Ansys Fluent CFD solver, while considerable experimental efforts are provided in order to validate the numerical model and finally evaluate the system performances on real case studies

Influence of machining parameters on part geometrical error in abrasive waterjet offset-mode turning

Geometrical error in abrasive waterjet turned parts is an important challenge toward the commercialization of abrasive waterjet turning process. A systematic study has not been done yet to investigate the effects of process parameters on geometrical error in abrasive waterjet offset-mode turning. In this article, a comprehensive study has been performed to investigate the influence of several machining parameters on the geometrical error (part diameter percent error) in turning AA2011-T4 aluminum alloy round bars. Water pressure, cutting head traverse speed, workpiece rotational speed, abrasive mass flow rate and depth of cut were considered as the main machining parameters in a five-level statistical experimental design. Based on central composite rotatable design, a total of 52 experiments were carried out. The main effects of the parameters and interactions among them were analyzed based on the analysis of variance technique, and the response contours for the part geometrical error were obtained using a quadratic regression model (i.e. response surface methodology). The model predictions were found to be in good agreement with experimental data. Furthermore, among the significant parameters, water pressure, depth of cut and traverse speed are the most influential parameters, with percent contribution of almost 25% each. Abrasive mass flow rate is the least influential parameter with a percent contribution of 4%

Applicability of abrasive waterjet cutting to irradiated graphite decommissioning

Characterization, dismantling and pre-disposal management of irradiated graphite (i-graphite) have an important role in safe decommissioning of several nuclear facilities which used this material as moderator and reflector. In addition to common radiation protection issues, easily volatizing long-lived radionuclides and stored Wigner energy could be released during imprudent retrieval and processing of i-graphite. With this regard, among all cutting technologies, abrasive waterjet (AWJ) can successfully achieve all of the thermo-mechanical and radiation protection objectives. In this work, factorial experiments were designed and systematically conducted to characterize the AWJ processing parameters and the machining capability. Moreover, the limitation of dust production and secondary waste generation has been addressed since they are important aspects for radiation protection and radioactive waste management. The promising results obtained on non-irradiated nuclear graphite blocks demonstrate the applicability of AWJ as a valid technology for optimizing the retrieval, storage, and disposal of such radioactive waste. These activities would benefit from the points of view of safety, management, and costs

On the temperature behavior of shunt-leakage currents in Cu(In,Ga)Se2 solar cells: The role of grain boundaries and rear Schottky contact

By comparing simulated and measured dark current-voltage (I-V) characteristics of CIGS cells at different temperatures, we investigate the temperature behavior of the shunt leakage current, and find that it can be explained by large donor trap concentrations at grain boundaries (GBs), and by a Schottky barrier at the backside contact where the GBs meets the anode metallization. We studied the I-V characteristics in the temperature range 280 K - 160 K achieving good fits of the measured I-V curves, especially for reverse bias and low forward bias, where the shunt leakage current dominates. The most important parameters determining the shunt leakage current value and its temperature dependence are the peak energy and density of the GB donor distribution, which control the inversion of GBs and the pinning of Fermi level at the anode/GB contact

The Agile Alert System For Gamma-Ray Transients

In recent years, a new generation of space missions offered great opportunities of discovery in high-energy astrophysics. In this article we focus on the scientific operations of the Gamma-Ray Imaging Detector (GRID) onboard the AGILE space mission. The AGILE-GRID, sensitive in the energy range of 30 MeV-30 GeV, has detected many gamma-ray transients of galactic and extragalactic origins. This work presents the AGILE innovative approach to fast gamma-ray transient detection, which is a challenging task and a crucial part of the AGILE scientific program. The goals are to describe: (1) the AGILE Gamma-Ray Alert System, (2) a new algorithm for blind search identification of transients within a short processing time, (3) the AGILE procedure for gamma-ray transient alert management, and (4) the likelihood of ratio tests that are necessary to evaluate the post-trial statistical significance of the results. Special algorithms and an optimized sequence of tasks are necessary to reach our goal. Data are automatically analyzed at every orbital downlink by an alert pipeline operating on different timescales. As proper flux thresholds are exceeded, alerts are automatically generated and sent as SMS messages to cellular telephones, e-mails, and push notifications of an application for smartphones and tablets. These alerts are crosschecked with the results of two pipelines, and a manual analysis is performed. Being a small scientific-class mission, AGILE is characterized by optimization of both scientific analysis and ground-segment resources. The system is capable of generating alerts within two to three hours of a data downlink, an unprecedented reaction time in gamma-ray astrophysics.Comment: 34 pages, 9 figures, 5 table

Frequency, characterisation and therapies of fatigue after stroke.

Post-stroke objective or subjective fatigue occurs in around 50% of patients and is frequent (30%) even after minor strokes. It can last more than one year after the event, and is characterised by a different quality from usual fatigue and good response to rest. Associated risk factors include age, single patients, female, disability, depression, attentional impairment and sometimes posterior strokes, but also inactivity, overweight, alcohol and sleep apnoea syndrome. There are few therapy studies, but treatment may include low-intensity training, cognitive therapy, treatment of associated depression, wakefulness-promoting agents like modafinil, correction of risk factors and adaptation of activities

Unscrambling Light Automatically on a Photonic Chip

Light beams can get mixed by transmission through a scattering system like a multimode channel. Separating beams of the same wavelength and polarization would appear to be very hard. Although the information carried by the beams is not fundamentally lost, its recovery requires a coherent interferometric reconstruction of the original signals, which have been scrambled among the modes of the system. In principle, a reconfigurable mesh of 2×2 interferometers could perform the necessary unitary mathematical operation.1 In practice, however, use of such photonic meshes—the size of which scales up quadratically with the number of modes— has been hindered by the need for complex, time-consuming procedures for calibration, control and configuration. Setting up and stabilizing a complex network of interferometers can be challenging, especially for interferometers buried inside the mesh. In work this year, we constructed a silicon photonics integrated mesh that can self-configure automatically to unscramble arbitrarily mixed optical beams, without any advance knowledge of the scattering system.2 Our architecture integrates six thermally controlled Mach-Zehnder interferometers that are sequentially and automatically adjusted, without calculations, to simultaneously reconstruct, separate (with a residual crosstalk of less than –20 dB), and sort out four optical beams that have been completely mixed in a multimode waveguide. By keying each signal with a different pilot tone, built-in transparent detectors3 monitor the evolution of each mode along the mesh, allowing tuning and adaptive individual feedback control of each interferometer with a simple, progressive algorithm.4 The entire mesh, controlled by custom-designed electronics, resets itself automatically after the mode mixing is significantly perturbed, can completely reconfigure on a time scale of a few seconds, and can track modes undergoing time-varying mixing on a time scale of a few hundred milliseconds. Our calibration and control strategy enables scalability to larger meshes (that is, to higher number of modes) without substantially increasing control complexity. Further, the principle of a self-configuring, self-resetting mesh can be extended to different mesh topologies to implement nonunitary linear operations4 and emerging programmable photonic processors,5 for applications in fields such as telecommunications, imaging, sensing, secrecy and quantum information processing. This work demonstrates that, despite the apparent challenges of undoing complicated scattering and interferometric mixing of optical beams, self-configuring and self-stabilizing optics systems can automatically unscramble light in real time

Workpiece surface flatness improvement by tool length compensation in micromilling

Micromilling quality improvement requires an accurate management of all the involved resources (machine tool, tool, fixture, workpiece). Specific attention has to be paid, comparing to macro operations, also to machining strategies and tool and workpiece measuring strategies. The extreme workpiece accuracy requires to reinterpret some procedures, already applied in the macro world, with the purpose to minimize errors. It is the case of the tool length compensation, which plays a strong role on the micromilling overall performance. In order to demonstrate the importance of factors affecting tool length, as machine spindle thermal transients and tool wear assessment, the present paper takes the workpiece flatness deviation as a case study and presents a manufacturing and measuring strategy able to meet a challenging flatness constraint

Study about the Influence of Powder Mixed Water Based Fluid on Micro-EDM Process

This paper discusses the performance of micro-electro-discharge machining (micro-EDM) process using different flushing media. Several tests have been performed considering a hardened steel thin workpiece machined via micro-EDM drilling and through-trench and different flushing fluids: deionized water, tap water, deionized water with Garnet, tap water with Garnet. Garnet is the abrasive material exploited in the micro-AWJ and the concentration per liter of water considered in micro-EDM experiments is the same as required in micro-abrasive water jet (micro-AWJ) machining. A customized system has been built on micro-EDM Sarix SX 200 HP machine to allow the water-based fluid refill and liquid level monitoring during the experiments. The micro-EDM trials have been carried out considering two machining regimes, roughing and semi finishing. The different water-based fluids have different electrical conductivities, which lead to different machining performance. Material removal rate (MRR) and tool wear ratio (TWR) have been estimated in terms of average and standard deviation. The results show that the presence of Garnet does not affect MRR consistently, since the particles do not play an active role in the erosion process but affect surface quality, as proved by the inspection of crater morphology and dimensions estimation performed via confocal microscope. For the considered experiments, MRR is generally increased as the conductivity decreases, in particular when semi-finishing regime is used. Also TWR decreases dramatically with the use of water-based fluids, since a protective recast layer is also deposited on the tool tip preventing wearing. Our analysis shows that micro-EDM can be successfully performed using the same liquid (water and abrasive) used in micro-AWJ, and so paves the way towards the implementation of a hybrid process based on micro-AWJ and micro-EDM technologies

Language Control and Lexical Competition in Bilinguals: An Event-Related fMRI Study

Language selection (or control) refers to the cognitive mechanism that controls which language to use at a given moment and context. It allows bilinguals to selectively communicate in one target language while minimizing the interferences from the nontarget language. Previous studies have suggested the participation in language control of different brain areas. However, the question remains whether the selection of one language among others relies on a language-specific neural module or general executive regions that also allow switching between different competing behavioral responses including the switching between various linguistic registers. In this functional magnetic resonance imaging study, we investigated the neural correlates of language selection processes in German-French bilingual subjects during picture naming in different monolingual and bilingual selection contexts. We show that naming in the first language in the bilingual context (compared with monolingual contexts) increased activation in the left caudate and anterior cingulate cortex. Furthermore, the activation of these areas is even more extended when the subjects are using a second weaker language. These findings show that language control processes engaged in contexts during which both languages must remain active recruit the left caudate and the anterior cingulate cortex (ACC) in a manner that can be distinguished from areas engaged in intralanguage task switchin