Novel CMM-based implementation of the multi-step method for the separation of machine and probe errors

Coordinate measuring machines (CMMs) are subject to periodic verification to ensure measurement capability. However, users also need to rapidly diagnose the source of accuracy degradation to guide corrective actions. This paper presents a novel CMM-based implementation of the multi-step method for the separation of machine and reference sphere errors on one side and triggering probe and probe tip errors on the other. The procedure uses multiple redundancy probing of the machine's own reference sphere and result in a mathematical system similar to that of the multi-step method. The procedure's effectiveness is demonstrated for a variety of stylus lengths and shows its ability to detect changes in lobing errors. A metrological validation is conducted by measuring the errors of the probe and errors of the machine using independent methods.     

Ethanol-sensing properties of potassium bromide/multi-walled carbon nanotube composites

The work reported in this paper is related to the fabrication and electrical characterization of multi-walled carbon nanotubes (MWNT)-based solid composites pellets with potential application as gas sensor at room temperature, using potassium bromide as supporting material. Results show an electrical conductivity of the composites as a function of the MWNT loading following a power law associated with a percolation phenomenon. A variation of the electrical resistance of the composites as a function of ethanol concentration in a nitrogen atmosphere has also been observed, allowing detection of ethanol from about hundred of ppm. It is also shown the existence of an optimal MWNT loading for which the composite reaches its best ethanol-sensing performances.     

Use of Photothermally Generated Seebeck Voltage for Thermal Characterization of Thermoelectric Materials

A simple and accurate experimental procedure to measure simultaneously the thermal properties (conductivity, diffusivity, and effusivity) of thermoelectric (TE) materials using their Seebeck voltage is proposed. The technique is based on analysis of a periodically oscillating thermoelectric signal generated from a TE material when it is thermally excited using an intensity-modulated laser source. A self-normalization procedure is implemented in the presented method using TE signals generated by changing the laser heating from one side to another of the TE material. Experiments are done on a polyaniline carbon nanohybrid (6.6 wt.% carbon nanotubes), yielding a thermal conductivity of 1.106 ± 0.001 W/m-K. The results are compared with the results from photothermal infrared radiometry experiments.     

Integrating WordNet knowledge to supplement training data in semi-supervised agglomerative hierarchical clustering for text categorization

The text categorization (TC) is the automated assignment of text documents to predefined categories based on document contents. TC has been an application for many learning approaches, which proved effective. Nevertheless, TC provides many challenges to machine learning. In this paper, we suggest, for text categorization, the integration of external WordNet lexical information to supplement training data for a semi-supervised clustering algorithm which (i) uses a finite design set of labeled data to (ii) help agglomerative hierarchical clustering algorithms (AHC) partition a finite set of unlabeled data and then (iii) terminates without the capacity to classify other objects. This algorithm is the “semi-supervised agglomerative hierarchical clustering algorithm” (ssAHC). Our experiments use Reuters 21578 database and consist of binary classifications for categories selected from the 89 TOPICS classes of the Reuters collection. Using the vector space model (VSM), each document is represented by its original feature vector augmented with external feature vector generated using WordNet. We verify experimentally that the integration of WordNet helps ssAHC improve its performance, effectively addresses the classification of documents into categories with few training documents, and does not interfere with the use of training data. © 2001 John Wiley & Sons, Inc.     

ALADIN and WRF forecasting evaluation using satellite imagery

Simulated satellite images are a good indicator of the state of the atmosphere described by the fields predicted by numerical weather prediction (NWP) models. Therefore, in order to control NWP operational models used by the Algerian meteorological service, especially over the desert region, Meteosat Second Generation (MSG) simulated images of brightness temperature (BT) were generated from ALADIN (Aire Limitée Adaptation Dynamique Development International) and WRF (Weather and Research Forecasting) outputs using the Radiative Transfer for TIROS Television and Infrared Observation Satellite Operational Vertical Sounder (RTTOV9) model. As reference data, MSG images were used to compute certain deterministic and probabilistic statistical parameters. This version of the RTTOV model assimilates cumuliform clouds, stratiform clouds and those of upper levels, such as cirrus. This comparative study shows that WRF reproduces BTs well where they exist, but raises too many false alarms for very cold BTs with values of bias around 1. The number of false alarms greatly affects the quality of Heidke skill scores (HSS), unlike the ALADIN model, which reveals fewer false alarms but detects events less well. With low values of bias for the lowest temperatures, ALADIN HSS scores are better than those of WRF for the lowest BTs. The double-penalty impact is slightly lessened for local and convective cloud by about 10% with WRF compared with ALADIN.     

Modeling and control of a permanent magnet synchronous generator dedicated to standalone wind energy conversion system

The interest for the use of renewable energies has increased, because of the increasing concerns of the environmental problems. Among renewable energies, wind energy is now widely used. Wind turbines based on an asynchronous generator with a wound rotor present the inconvenience of requiring a system of rings and brooms and a multiplier, inferring significant costs of maintenance. To limit these inconveniences, certain manufacturers developed wind turbines based on synchronous machines with large number of pairs of poles coupled directly with the turbine, avoiding using the multiplier. If the generator is equipped with permanent magnets, the system of rings and brooms is eliminated. The control of the permanent magnet synchronous generator (PMSG) can be affected with the implementation of various techniques of control. This paper presented a new approach mainly based on the control strategy of power production system based on the PMSG. In fact, a mathematical model that simulates the Matlab chain was established with the introduction of control techniques, such as direct control of the torque (DTC) to control the load side converter (LSC), the control of the speed of the turbine and the DC-bus voltage ensured by PI regulators. To show the performance of the correctors used, some simulation results of the system were presented and analyzed.     

Maximum Shear Strength of RC Beams Retrofitted in Shear with FRP Composites

In reinforced concrete (RC) beams strengthened in shear with fiber-reinforced polymer (FRP), crushing of the web can be a potential mode of failure. The guidelines provided by codes and standards for the design of structures strengthened with externally bonded FRP recommend limiting the maximum shear strength to avoid such an undesirable failure scenario. However, these limitation provisions are not based on specific research studies performed on beams strengthened in shear with FRP. Rather, they simply duplicate provisions used in conventional concrete codes and standards. The main objective of this research study is to assess the suitability of the limits specified by the guidelines, and propose, if necessary, an alternative equation as an upper limit for shear strength against web crushing failure in such structures. To this end, an analytical approach was developed based on the static theorem of the theory of plasticity. The predictions of the equations resulting from this approach were compared with those obtained from tests reported in the literature and with those predicted by ACI Committee 440-02, Canadian Standard S6-06, and the European recommendations fib TG 9.3. The study shows that the current ACI Committee 440-02 and Canadian Standards provisions are overly conservative and therefore need to be reviewed.     

Fatigue Performance of RC Beams Strengthened in Shear with CFRP Fabrics

In recent years, a tremendous effort has been directed toward understanding and promoting the use of externally bonded fiber-reinforced polymer (FRP) composites to strengthen concrete structures. Despite this research effort, studies on the behavior of beams strengthened with FRP under fatigue loading are relatively few, especially with regard to its shear-strengthening aspect. This study aims to examine the fatigue performance of RC beams strengthened in shear using carbon FRP (CFRP) sheets. It involves six laboratory tests performed on full-size T-beams, where the following parameters are investigated: (1) the FRP ratio and (2) the internal transverse-steel reinforcement ratio. The major finding of this study is that specimens strengthened with one layer of CFRP survived 5 million cycles, some of them with no apparent signs of damage, demonstrating thereby the effectiveness of FRP strengthening systems on extending the fatigue life of structures. Specimens strengthened with two layers of CFRP failed in fatigue well below 5 million cycles. The failure mode observed for these specimens was a combination of crushing of the concrete struts, local debonding of CFRP, and yielding of steel stirrups. This failure may be attributed to the higher load amplitude and also to the greater stiffness of the FRP which may have changed the stress distribution among the different components coming into play. Finally, comparison between the performance of specimens with transverse steel and without seems to indicate that the addition of transverse steel extends the fatigue life of RC beams.     

State of Research on Seismic Retrofit of RC Beam-Column Joints with Externally Bonded FRP

A considerable amount of research has been directed recently toward understanding and promoting the use of externally applied fiber-reinforced polymer (FRP) for the seismic retrofit of reinforced concrete (RC) structures. In this paper, a comprehensive review and synthesis of published experimental studies on the seismic rehabilitation of RC frame beam-column joints with FRP is presented, and the issues that need to be addressed for further research are discussed. In addition, the paper presents a simple design model for predicting the contribution of the FRP to the shear strength of retrofitted joints. The key element in the model is the derivation of an expression for the effective FRP strain, based on the calibration of test data reported in the literature. A total of 54 tests carried out worldwide were considered in the review, and a database of the published studies, encompassing all relevant design parameters, was assembled. The reported test results confirm the structural effectiveness of the FRP strengthening technique for the seismic retrofit of RC joints. However, there are some gaps which need to be addressed. For instance, there is a lack of a rationale explanation of the resistance mechanisms involved in the beam-column joints retrofitted with FRP. Such a rational explanation is a prerequisite for the development of more comprehensive and rigorous design procedure.     

Nucleation and formation of oxide film with the magnetic field on dry sliding contact of ferromagnetic steel

The nucleation and formation of oxide film in unidirectional dry sliding contact has been studied in a vacuum chamber with and without the application of a magnetic field in the intention of identifying the role of magnetic intensity on the oxidation wear. The wear tests of the steel AISI 1045/steel AISI 1045 couple are investigated on a pin‐disc configuration under three various gas environments: in ambient air, under oxygen at 10⁵ Pa and in vacuum at 5.10⁻⁵ Pa. The formation of oxide layer strongly depends on oxygen partial pressure and magnetic field intensity. These took the form of protective raised ‘islands’ of compacted debris which is developed gradually but rapidly increased as the oxygen partial pressure is increased and which could persist for extended periods during subsequent evacuation. Evidence from various experimental techniques indicates that the compacted debris is a mixture of iron oxides in the form of oxide‐covered particles, although the depth of oxide film has not yet been fully elucidated. Copyright © 2010 John Wiley & Sons, Ltd.