A multi-agent approach to process planning and fabrication in distributed manufacturing

In the paper a multi-agent approach to the development of a distributed manufacturing architecture is presented. An essential building block introduced here is the virtual work system (VWS) which represents a manufacturing work system in the information space. The VWS is structured as an autonomous agent and is a constituent entity of an agent network. In the network dynamic clusters of cooperating agents are solving manufacturing tasks. A machining work system and its VWS is demonstrated in a case study. Its role in the agent communication network is discussed in a process planning and fabrication domain.     

Tomographic Imaging of Dynamic Objects With the Ensemble Kalman Filter

We address the image formation of a dynamic object from projections by formulating it as a state estimation problem. The problem is solved with the ensemble Kalman filter (EnKF), a Monte Carlo algorithm that is computationally tractable when the state dimension is large. In this paper, we first rigorously address the convergence of the EnKF. Then, the effectiveness of the EnKF is demonstrated in a numerical experiment where a highly variable object is reconstructed from its projections, an imaging modality not yet explored with the EnKF. The results show that the EnKF can yield estimates of almost equal quality as the optimal Kalman filter but at a fraction of the computational effort. Further experiments explore the rate of convergence of the EnKF, its performance relative to an idealized particle filter, and implications of modeling the system dynamics as a random walk.     

Interlaboratory bias in the determination of mercury concentrations in commercially available fish utilizing thermal decomposition/amalgamation atomic absorption spectrophotometry

Four commercially available fish fillets were freeze-dried, homogenized, and analyzed for mercury by the Texas A&M Trace Element Research Laboratory and the Utah Public Health Laboratory (UPHL) utilizing thermal decomposition/amalgamation atomic absorption spectrophotometry. Two-way analysis of variance detected bias in the data between the two laboratories. Some of the bias could be attributed to different calibration curve quantitation and near detection limit quantitation, albeit causal explanations could be confounded with other effects. Knowledge of analytical bias will aid interpretation of interlaboratory data. The swordfish mercury content, as determined by both laboratories, was about 1 ppm, while mercury content found in the Atlantic salmon was about 0.021 ppm. For the Alaskan halibut, the Texas A&M measured a mercury concentration of 0.155 ppm, while the UPHL measured a mercury concentration of 0.181 ppm for the same fish. The Texas A&M determined that the Canadian-raised salmon contained about 0.019 ppm of mercury, while the UPHL determined a mercury content of about 0.025 ppm for the same fish. The mercury found within the fish fillets did not exceed nationwide mercury mean values determined by the U.S. Food and Drug Administration.     

Ring-shaped field emission patterns from carbon nanotube films

Highly symmetric ring-shaped field emission patterns were observed from broad-area flat cathodes prepared by growing a film of vertically aligned carbon nanotubes (CNTs) on TiN coated Si substrates. The images were obtained utilizing a luminescent screen of a specially designed triode cell composed of parallel electrodes. The emission rings sporadically appeared during voltage scans in which the emission patterns and cathode currents were recorded. The fine structure and stability of the rings suggests that their formation is due to an emission state of an individual CNT. The observed patterns are consistent with models that predict the formation of emission rings produced by the inhomogeneous electron emission from CNTs. The macroscopic value of the electric field when the rings were observed was between 0.7 and 2.5 V/μm, and the emission current corresponding to individual rings was estimated to be in the range of 2–4 μA. Numerical simulation of electron trajectories for sidewall emission from similar shaped metallic structures is in qualitative and quantitative agreement with the experimentally observed ring-shaped field emission patterns. The results also appear consistent with a recent model [Marchand M, Journet C, Adessi C, Purcell ST. Phys Rev B 2009;80:245425] based on thermal-field emission due to Joule heating.     

Modelling of grinding gap macro geometry and workpiece kinematics in throughfeed centreless grinding

The paper discusses the simulation of a throughfeed centreless grinding process in a virtual environment (VE). The developed simulations are based on an analytical grinding gap model describing the grinding gap macro geometry and workpiece kinematics. First of all, the model is embedded in a desktop application (Cegris), which facilitates regulating wheel truing and the determination of set-up variables, both of which yield an optimal grinding gap macro geometry in a reduced set-up time. Finally, the Cegris is ported to a CAVE (CAVE Automatic Virtual Environment) for an interactive visualisation of the process, an application used to train machine tool operators.     

Visualization of individual emission sites on flat broad-area field emission cathodes

We introduce a novel scanning projection field emission microscope (SPFEM) designed to study flat broad-area field emission cathodes. The instrument merges capabilities of measuring the electron field emission current from an individual emitting site and genuine projection of electrons onto a luminescent screen. This is achieved by an optimized shape of the anode probe having a 0.04 mm aperture which generates an uniform macroscopic electric field across the investigated area of the cathode. This fact also enables presentation of the relation between the current density and the applied electric field. The magnification of the electron-optical system alone was calculated by computational modeling for some cathode-probe distances and for some voltages. The unique SPFEM performance is demonstrated on smooth sulfur-doped nanodiamond films synthesized on molybdenum substrates.     

An overview of methods to suppress hydrogen outgassing rate from austenitic stainless steel with reference to UHV and EXV

The present review of methods reveals some new theoretical aspects and findings concerning suppression of the hydrogen outgassing rate q_out from austenitic stainless steels in relation to the ultrahigh vacuum and extreme high vacuum.The review includes work on thermal treatment and modelling, permeation rate and the role of surfaces, diffusion barriers and coatings.     

Incorporation of latent loads into the cooling degree days concept

The cooling degree days concept is a tool to estimate and analyze weather related energy consumption in buildings, i.e. the cooling system electric energy consumption. The main problem with applying this method is that it disregards latent cooling loads. This paper deals with an approach for monitoring electric energy consumption due to cooling in buildings based on cooling degree days, which allows an estimation of latent loads. In addition to applying methods for determining base temperature to base humidity, a new technique is introduced, which is based on a significance test of the enthalpy latent days partial regression coefficient. Analogous to the performance line concept, the influence of latent loads can be presented in the form of a “performance surface” graph. The performance surface is a plot of electric energy consumption as a function of cooling degree days and latent enthalpy days. The above methods are tested on data sets consisting of electric energy consumption data obtained from two buildings and hourly meteorological data.     

The influence of a hot cathode vacuum gauge on the residual gas composition

The residual atmosphere of an UHV chamber is known to be influenced by the hot cathode gauge (HCG) via processes on the hot cathode and by ionisation. In the presence of such a gauge, some gases are pumped while several residuals are generated, depending on the condition of the chamber's inner surface, gauge parameters and gases that are released spontaneously or introduced on purpose.We analysed the influence of the HCG in three different cases of gas accumulation lasting typically for 1 h: (1) in the leak tight vessel, where the background outgassing from the walls was the only inflow Q_backg=1.6×10⁻⁸ mbar l H₂ s⁻¹, (2) during the constant nitrogen inflow in the vessel and (3) during the constant deuterium inflow. Both inflow values were in the order of 1×10⁻⁶ mbar l s⁻¹. The absolute total pressure in the 13 l system was monitored by a capacitance manometer. After the accumulation, the composition of the accumulated gases was analysed by a quadrupole mass spectrometer (QMS), calibrated with the gases of interest. Regarding the operation of the HCG, an obvious difference is noted both in the pressure rise curves and QMS spectra. The generation of carbon-contained residuals by the HCG was evident, but the most unexpected was its pumping action: nitrogen content decreased from 99% (HCG off) to 62% (HCG on) and deuterium content decreased from 65% (HCG off) to only 2% (HCG on).