Modelling and validation of synthesis of poly lactic acid using an alternative energy source through a continuous reactive extrusion process

PLA is one of the most promising bio-compostable and bio-degradable thermoplastic polymers made from renewable sources. PLA is generally produced by ring opening polymerization (ROP) of lactide using the metallic/bimetallic catalyst (Sn, Zn, and Al) or other organic catalysts in a suitable solvent. In this work, reactive extrusion experiments using stannous octoate Sn(Oct)2 and tri-phenyl phosphine (PPh)3 were considered to perform ROP of lactide. Ultrasound energy source was used for activating and/or boosting the polymerization as an alternative energy (AE) source. Ludovic® software, designed for simulation of the extrusion process, had to be modified in order to simulate the reactive extrusion of lactide and for the application of an AE source in an extruder. A mathematical model for the ROP of lactide reaction was developed to estimate the kinetics of the polymerization process. The isothermal curves generated through this model were then used by Ludovic software to simulate the “reactive” extrusion process of ROP of lactide. Results from the experiments and simulations were compared to validate the simulation methodology. It was observed that the application of an AE source boosts the polymerization of lactide monomers. However, it was also observed that the predicted residence time was shorter than the experimental one. There is potentially a case for reducing the residence time distribution (RTD) in Ludovic® due to the ‘liquid’ monomer flow in the extruder. Although this change in parameters resulted in validation of the simulation, it was concluded that further research is needed to validate this assumption

Statistics of velocity gradients in wall-bounded shear flow turbulence

The statistical properties of velocity gradients in a wall-bounded turbulent channel flow are discussed on the basis of three-dimensional direct numerical simulations. Our analysis is concentrated on the trend of the statistical properties of the local enstrophy ${\bm \omega}^2({\bm x},t)$ and the energy dissipation rate $\epsilon({\bm x},t)$ with increasing distance from the wall. We detect a sensitive dependence of the largest amplitudes of both fields (which correspond with the tail of the distribution) on the spectral resolution. The probability density functions of each single field as well as their joint distribution vary significantly with increasing distance from the wall. The largest fluctuations of the velocity gradients are found in the logarithmic layer. This is in agreement with recent experiments which observe a bursting of hairpin vortex packets into the logarithmic region.Comment: 13 pages, 5 figure

The evaluation and calibration of pressure mapping system for the measurement of the pressure distribution of agricultural tyres

The accuracy of a commercial pressure mapping system was evaluated and a number of techniques for the improvement of pressure measurements were developed. These were required in order to use the pressure mapping system in a tyre/surface interaction study which involved determination of the tyre contact pressure distribution on, both, hard and soil surfaces. In the evaluation of the system, the effect of sensor calibration procedures on the accuracy of the system in measuring pressure was investigated. A purpose built pressure calibration chamber was used to calibrate the sensors, which enabled the proprietary built-in calibration system to be evaluated along with a novel calibration procedure employing, both, an individual and multi-point calibration of each sensing element and the rejection of sensing elements that did not conform to the sensitivity of the majority of the sensing elements. These measures reduced the uncertainty in pressure measurements from ±30% to ±4%. Further, evaluation of the compliance of the material was also conducted to enable the sensors to be used for interface pressure measurements between two different surface materials other than those used during sensor calibration. As a result, a procedure for normalising the recorded pressure by adjusting the recorded load output to equal the applied load was established. The improvement of the accuracy of the sensors made it possible for the system to be used to determine the pressure distribution resulting from a range of tyres on a hard surface and in the soil profile

In-channel 3D models of riverine environments for hydromorphological characterization

Recent legislative approaches to improve the quality of rivers have resulted in the design and implementation of extensive and intensive monitoring programmes that are costly and time consuming. An important component of assessing the ecological status of a water body as required by the Water Framework Directive is characterising the hydromorphology. Recent advances in autonomous operation and the spatial coverage of monitoring systems enables more rapid 3D models of the river environment to be produced. This study presents a Structure from Motion (SfM) semi-autonomous based framework for the estimation of key reach hydromorphological measures such as water surface area, wetted water width, bank height, bank slope and bank-full width, using in-channel stereo-imagery. The framework relies on a stereo-camera that could be positioned on an autonomous boat. The proposed approach is demonstrated along three 40 m long reaches with differing hydromorphological characteristics. Results indicated that optimal stereo-camera settings need to be selected based on the river appearance. Results also indicated that the characteristics of the reach have an impact on the estimation of the hydromorphological measures; densely vegetated banks, presence of debris and sinuosity along the reach increased the overall error in hydromorphological measure estimation. The results obtained highlight a potential way forward towards the autonomous monitoring of freshwater ecosystem

Development of CNC prototype for the characterization of the nanoparticle release during physical manipulation of nanocomposites

This work focuses on the release of nanoparticles from commercially used nanocomposites during machining operations. A reliable and repeatable method was developed to assess the intentionally exposure to nanoparticles, in particular during drilling. This article presents the description and validation of results obtained from a new prototype used for the measurement and monitoring of nanoparticles in a controlled environment. This methodology was compared with the methodologies applied in other studies. Also, some preliminary experiments on drilling nanocomposites are included. Size, shape and chemical composition of the released nanoparticles were investigated in order to understand their hazard potential. No significant differences were found in the amount of nanoparticles released between samples with and without nanoadditives. Also, no chemical alteration was observed between the dust generated and the bulk material. Finally, further developments of the prototype are proposed

Quantum plasticity and dislocation-induced supersolidity

We suggest that below a certain temperature T_k, the free energy for the creation of kinks-antikinks pairs in the dislocation network of solid He4 becomes negative. The underlying physical mechanism is the related liberation of vacancies which initiate Feynman's permutation cycles in the bulk. Consequently, dislocations should wander and sweep an increasingly larger volume at low temperatures. This phenomenon should lead both to a stiffening of the solid below T_k and to the appearance of a non zero superfluid fraction at a second temperature T_c < T_k.Comment: Longer revised version with more detailed discussion, submitted to EPJ

The Brera Multi-scale Wavelet Chandra Survey. I. Serendipitous source catalogue

We present the BMW-Chandra source catalogue drawn from essentially all Chandra ACIS-I pointed observations with an exposure time in excess of 10ks public as of March 2003 (136 observations). Using the wavelet detection algorithm developed by Lazzati et al. (1999) and Campana et al. (1999), which can characterise both point-like and extended sources, we identified 21325 sources. Among them, 16758 are serendipitous, i.e. not associated with the targets of the pointings, and do not require a non-automated analysis. This makes our catalogue the largest compilation of Chandra sources to date. The 0.5--10 keV absorption corrected fluxes of these sources range from ~3E-16 to 9E-12 erg cm^-2 s^-1 with a median of 7E-15 erg cm^-2 s^-1. The catalogue consists of count rates and relative errors in three energy bands (total, 0.5-7keV; soft, 0.5-2keV; and hard, 2-7keV), and source positions relative to the highest signal-to-noise detection among the three bands. The wavelet algorithm also provides an estimate of the extension of the source. We include information drawn from the headers of the original files, as well, and extracted source counts in four additional energy bands, SB1 (0.5-1keV), SB2 (1-2keV), HB1 (2-4keV), and HB2 (4-7keV). We computed the sky coverage for the full catalogue and for a subset at high Galactic latitude (|b|> 20deg). The complete catalogue provides a sky coverage in the soft band (0.5-2keV, S/N =3) of ~8 deg^2 at a limiting flux of 1E-13 erg cm^-2 s^-1, and ~2 deg^2 at a limiting flux of ~1E-15 erg cm^-2 s^-1.Comment: Accepted by A&A, Higher res. Figs 4 and 5 at http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f4.eps http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f5.eps, Catalog Web pages: http://www.brera.inaf.it/BMC/bmc_home.html http://www.ifc.inaf.it/~romano/BMC/bmc_home.html (Mirror

Low prevalence of valvular heart disease in 226 phentermine-fenfluramine protocol subjects prospectively followed for up to 30 months

AbstractOBJECTIVESThis investigation sought to determine the effect of phentermine-fenfluramine (phen-fen) on the prevalence of valvular heart disease in 226 obese subjects enrolled in a prospective, strict weight loss, research protocol.BACKGROUNDEarly reports have suggested that the use of phen-fen for weight loss may be associated with increased valvular heart disease. Such reports were based on small numbers of patients, limited data on dose and duration of phen-fen therapy, and no correlation with matched controls.METHODSAll subjects underwent transthoracic echocardiography for significant valvular lesions within a mean of 97 days from the manufacturer’s announcement of the voluntary withdrawal of fenfluramine and dexfenfluramine. All echocardiograms were interpreted by two independent readers.RESULTSThe study population included 183 women and 43 men with a mean age of 46.9 ± 8.9 years and mean starting body mass index of 39.8 ± 7.7 kg/m2. Using the Food and Drug Administration criteria, significant aortic regurgitation was detected in 15 subjects (6.6%) and mitral regurgitation in 3 subjects (1.3%). Only one patient had significant regurgitation of both aortic and mitral valves. No valves had severe regurgitation. Significant valvular disease did not correlate with the dose or duration of phen-fen therapy. Furthermore, the prevalence of valvular regurgitation is comparable to the normal offspring in the Framingham Heart Study, who are similar in age, gender, and geographical location.CONCLUSIONSPhen-fen therapy is associated with a low prevalence of significant valvular regurgitation. Valvular regurgitation in our subjects may reflect age-related degenerative changes

Comparative analysis of RANS and DDES methods for aerodynamic performance predictions for high performance vehicles at low ground clearances

Various assessments of RANS and Hybrid RANS-LES turbulence models have been conducted for automotive applications. However, their applicability for high performance vehicles which exhibit much more complex flow phenomena is not well studied yet. In this work, the predictive capabilities of RANS and DDES models are investigated through a comparative study on a high performance configuration of the DrivAer Fastback model at a low ground clearance in an open road computational domain. The results show much agreement in the general pressure distribution, except in areas of highly unsteady flow. Visualisation of the flow field depicts that the DDES simulation is able to capture a wider range of turbulent scales with a higher fidelity. Lastly, variation in the magnitude, distribution and decay of pressure losses in the wake are observed between both simulations. The presented results are used to illustrate the capabilities and limitations of these turbulence models for other academic or industrial users to make an informed decision on the turbulence model suited for their objectives