Theoretical and experimental investigation of pulsed laser grooving process

A theoretical model has been developed for simulating the laser grooving process. It takes into account the interaction among subsequent pulses, the required time for the melting temperature to be reached and the subsequent removal of a finite volume of material during each laser pulse. The model predicts the maximum groove depth that can be achieved for a specified set of process parameters, such as laser power, pulsing frequency, and scanning velocity. The theoretical predictions have been experimentally tested with a medium-power laser beam.     

Testing and applications of a process model in the metallurgical production practice of ferronickel from laterites

A mathematical model of the electro-reduction furnace process (ERF process), for the production of ferronickel from laterite ores, has been tested at Larco's metallurgical plant at Larymna Greece. The theoretical predictions for the progress of the nickel reduction have been compared with the operational results. The tests were carried out in the ERF no. 2 of Larco's plant. The influence of the main process variables on the nickel recovery and nickel losses in the ERF slags have been investigated in conjunction with the variation of the analysis of the feed and the nickel content of the metal bath. The further application of the model to the metallurgical practice is discussed. According to the predictions of the model the further development of the process in the direction of the production of low-nickel ferronickel (Ni < 15%) is analyzed. The advantages of the production of low-nickel ferronickel are presented and the possibility of its straight conversion to nickel-bearing steel-grades is discussed.     

Lignite industry in Greece within a world context: Mining,energy supply and environment

Today coal covers 38% of global production and roughly 30% of the EU-25 power output.     

Reliability assessment of the rotation algorithm for earthquake damage estimation

A rotation algorithm was developed that computes the slope of permanently deformed columns subjected to earthquake ground motion using micro-electro-mechanical system accelerometers. Previous studies by the authors have shown that the algorithm can provide estimates of the residual displacement in the column, and thus the story drift can be evaluated. The algorithm was validated through applications to columns that deflect in single and double curvature. Information from tests on such columns conducted at various laboratories was used to conduct the study. The optimal number of sensors and their placement on the test columns were determined through a series of numerical analyses. The accuracy of the rotation and displacement estimates is assessed under the assumptions of zero-noise sensors and perfect measurements. In this paper, the effect of measurement error and sensor noise on the predicted rotations and corresponding deformations is studied in order to provide bounds on the accuracy of the rotation algorithm and on the allowable sensor noise. The same test columns are used for the purposes of these analyses.     

Hydrolytic Depolymerization of PET in a Microwave Reactor

Recycling of PET was examined using hydrolytic depolymerization in an alkaline solution under microwave irradiation. The reaction was carried out in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. The main products were the monomers TPA and EG. The effect of reaction temperature, time, amount of PET and alkaline concentration on the degree of PET depolymerization and TPA recovery was investigated. Microwave irradiation was found to reduce the time needed to achieve a specific degradation of PET significantly, with almost complete depolymerization occurring in 30 min at 180 °C and only 46 W of microwave power. Using a phase transfer catalyst (TOMAB) resulted in the same amount of unreacted PET but at significantly lower depolymerization temperatures.

     

Laser Melting of Spark Plasma-Sintered Zirconium Carbide: Thermophysical Properties of a Generation IV Very High-Temperature Reactor Material

Melting temperatures of zirconium carbide were investigated in validating a novel thermal analysis technique for refractory materials. Commercial ZrC_0.96 powder was densified by spark plasma sintering to >96% relative density after 6–30 min at 2173–2453 K under 40–100 MPa. Sintered ceramics were heated to >4000 K via pulsed laser heating. Mean values for solidus and liquidus transitions were 3451 and 3608 K, respectively, in fair agreement with the present phase diagram. Postmelting analysis revealed dendritic microstructure and composition consistent with single-phase ZrC. Subsurface gas porosity and ZrC–C eutectic indicate complex processes occurring during melting and freezing.     

Algorithmic Exploration and Implementation of a MIMO-OFDM Equalizer

In this paper we explore algorithms and architectures for the implementation of a MIMO OFDM Equalizer for high speed wireless communications. The algorithmic exploration is based on matrix computations and factorizations. A scalable computational methodology and architecture is proposed for the implementation of a 4×4 MIMO OFDM. A 2×3 Equalizer supporting Maximum Ratio Combining and Zero Forcing equalization for 20/40 MHz 64-QAM OFDM modulation has been implemented in 150 nm technology. The Equalizer area is 133k gates and the maximum throughput achieved is 480Mbits/s. The system described in this paper is compliant with the latest IEEE standard for MIMO wireless communications (802.11n)     

Lead contamination and associated disease in captive and reintroduced red kites Milvus milvus in England

Since 1989, a red kite Milvus milvus reintroduction programme has been underway in the United Kingdom, with 4-6 week old nestlings brought into captivity and held for 6-8 weeks before reintroduction. As scavengers, red kites may consume unretrieved game, and ingest shot or lead (Pb) fragments in their prey's flesh. We evaluated exposure to Pb in captive and wild red kites by taking blood samples from 125 captive young red kites prior to release, through analysing 264 pellets (regurgitated by wild birds) collected from under a roost site, and analysing Pb concentrations in livers and/or bones of 87 red kites found dead between 1995 and 2003. Lead isotope analyses of livers were also conducted in an effort to identify Pb exposure routes. Forty-six (36.8%) kites sampled prior to release had elevated blood Pb concentrations (201-3340 microg l(-1)). The source of this Pb was probably small fragments of lead ammunition in the carcasses of birds or mammals either fed to the nestlings by their parents or, more likely, subsequently whilst in captivity. Once released, kites were also exposed to lead shot in their food, and a minimum of 1.5-2.3% of regurgitated pellets contained Pb gunshot. Seven of 44 red kites found dead or that were captured sick and died within a few days had elevated (>6 mg kg(-1) dry weight [d.w.]) liver Pb concentrations, and six of these (14%) had concentrations of >15 mg kg(-1) d.w., compatible with fatal Pb poisoning. Post-mortem analyses indicated that two of these birds had died of other causes (poisoning by rodenticide and a banned agricultural pesticide); the remaining four (9%) probably died of Pb poisoning. Bone samples from 86 red kites showed a skewed distribution of Pb concentration, and 18 samples (21%) had Pb concentrations >20 mg kg(-1) d.w., indicating elevated exposure to Pb at some stage in the birds' life. Lead isotopic signatures (Pb (208/206); Pb (206/207)) in liver samples of the majority of kites were compatible with those found in lead shot extracted from regurgitated pellets. Lead isotope ratios found in the livers of kites with very low Pb concentrations were distinct from UK petrol Pb isotopic signatures, indicating that birds were exposed to little residual petrol Pb. We conclude that the primary source of Pb to which red kites are exposed is lead ammunition (shotgun pellets or rifle bullets), or fragments thereof, in their food sources; in some cases exposure appears sufficient to be fatal. We make recommendations to reduce Pb poisoning in both captive and wild red kites and other scavenging species.     

Reliability assessment of cutting tool life based on surrogate approximation methods

A novel reliability estimation approach to the cutting tools based on advanced approximation methods is proposed. Methods such as the stochastic response surface and surrogate modeling are tested, starting from a few sample points obtained through fundamental experiments and extending them to models able to estimate the tool wear as a function of the key process parameters. Subsequently, different reliability analysis methods are employed such as Monte Carlo simulations and first- and second-order reliability methods. In the present study, these reliability analysis methods are assessed for estimating the reliability of cutting tools. The results show that the proposed method is an efficient method for assessing the reliability of the cutting tool based on the minimum number of experimental results. Experimental verification for the case of high-speed turning confirms the findings of the present study for cutting tools under flank wear.