Two-stage anaerobic digestion enables heavy metal removal.

To fully exploit the environmental benefits of the biogas process, the digestate should be recycled as biofertiliser to agriculture. This practice can however be jeopardized by the presence of unwanted compounds such as heavy metals in the digestate. By using two-stage digestion, where the first stage includes hydrolysis/acidification and liquefaction of the substrate, heavy metals can be transferred to the leachate. From the leachate, metals can then be removed by adsorption. In this study, up to 70% of the Ni, 40% of the Zn and 25% of the Cd present in maize was removed when the leachate from hydrolysis was circulated over a macroporous polyacrylamide column for 6 days. For Cu and Pb, the mobilization in the hydrolytic stage was lower which resulted in a low removal. A more efficient two-stage process with improved substrate hydrolysis would give lower pH and/or longer periods with low pH in the hydrolytic stage. This is likely to increase metal mobilisation, and would open up for an excellent opportunity of heavy metal removal.     

The Rician inverse Gaussian distribution: a new model for non-Rayleigh signal amplitude statistics.

In this paper, we introduce a new statistical distribution for modeling non-Rayleigh amplitude statistics, which we have called the Rician inverse Gaussian (RiIG) distribution. It is a mixture of the Rice distribution and the inverse Gaussian distribution. The probability density function (pdf) is given in closed form as a function of three parameters. This makes the pdf very flexible in the sense that it may be fitted to a variety of shapes, ranging from the Rayleigh-shaped pdf to a noncentral chi2-shaped pdf. The theoretical basis of the new model is quite thoroughly discussed, and we also give two iterative algorithms for estimating its parameters from data. Finally, we include some modeling examples, where we have tested the ability of the distribution to represent locale amplitude histograms of linear medical ultrasound data and single-look synthetic aperture radar data. We compare the goodness of fit of the RiIG model with that of the K model, and, in most cases, the new model turns out as a better statistical model for the data. We also include a series of log-likelihood tests to evaluate the predictive performance of the proposed model.     

Successful adaptive control of paper machines

The papermaking process can be viewed as a time-varying stochastic system. The purpose of the control is to minimize the variance of moisture and basis weight of the manufactured paper. In the framework of stochastic theory and recently published papers on adaptive control an algorithm has been developed to cover the above-mentioned purpose. The strategy which hardly requires any a priori knowledge about the process is, in fact, a self-adjusting regulator. The central part of the algorithm is a compact identification scheme which gives directly the optimal control action. It is notable that contrary to normal identification and control methods the process dynamics never need to be calculated. The algorithm has been applied to several real-time computer control systems for paper machines. Up to now medium-scale computers have been used, but as the control program is powerful and short, some hundred words in length, it is in fact sufficient to perform the control with a mini-computer. Before the implementation of the algorithm for the above processes, the control system was built around digitalized PI-controllers, the parameters of which were carefully chosen and constant. A great number of comparative tests have been made in order to evaluate the efficiency of the adaptive regulator. The results were so successful that the algorithm has been permanently installed in the systems. The algorithm has not only decreased the output variance but also reduced the losses at quality changes and mill set-ups. Finally, it should be mentioned that the general nature of the algorithm permits application to many other types of processes.     

Carbon fiber reinforced root canal posts. Mechanical and cytotoxic properties

The aim of this study was to compare the mechanical properties of a prefabricated root canal post made of carbon fiber reinforced composites (CFRC) with metal posts and to assess the cytotoxic effects elicited. Flexural modulus and ultimate flexural strength was determined by 3 point loading after CRFC posts had been stored either dry or in water. The bending test was carried out with and without preceding thermocycling of the CFRC posts. The cytotoxicity was evaluated by an agar overlay method after dry and wet storage. The values of flexural modulus and ultimate flexural strength were for dry stored CFRC post 82 +/- 6 GPa and 1154 +/- 65 MPa respectively. The flexural values decreased significantly after water storage and after thermocycling. No cytotoxic effects were observed adjacent to any CFRC post. Although fiber reinforced composites may have the potential to replace metals in many clinical situations, additional research is needed to ensure a satisfying life-span.     

Characterization of iron(III) in organic soils using extended X-ray absorption fine structure spectroscopy

The distribution of different iron (Fe) species in soils, sediments, and surface waters has a large influence on the mobility and availability of Fe, other nutrients, and potentially toxic trace elements. However, the knowledge about the specific forms of Fe that occurs in these systems is limited, especially regarding associations of Fe with natural organic matter (NOM). In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to characterize Fe(III) in organic soils (pH 4.6-6.0) with varying natural Fe content. The EXAFS data were subjected to wavelet transform analysis, to facilitate the identification of the nature of backscattering atoms, and to conventional EXAFS data fitting. The collective results showed the existence of two pools of iron: mononuclear Fe(III)-NOM complexes and precipitated Fe(III) (hydr)oxides. In the soil with lowest pH (4.6) and Fe content mononuclear organic complexes were the completely dominating fraction whereas in soils with higher pH and Fe content increasing amounts of Fe (hydr)oxides were detected. These results are of environmental importance, as the different iron pools most likely have markedly different reactivities.     

Biotic and abiotic determinants of the ascent behaviour of adult Atlantic salmon transiting passable waterfalls

The spawning migration of Atlantic salmon has been characterized by tracking salmon carrying electronic tags as they ascend rivers, but still little is known about how natural obstacles such as waterfalls influence migratory behaviour and how such behaviours are mediated by various biotic (e.g., fish size) and abiotic (e.g., discharge, water temperature, and barometric pressure) factors. The Norwegian river Numedalslågen is interrupted by natural waterfalls ranging in height from 2 to 6 m. We tagged 113 Atlantic salmon with radio transmitters in the estuary and used stationary radio telemetry stations to track fish. Ninety‐one salmon were recorded in Numedalslågen, 39 of which remained in the river for spawning. Large salmon moved farther and faster upriver but also delayed longer and had lower daily probability to pass the second waterfall. Delay below and passage probability at the final, largest waterfall was affected by water discharge, wherein passage occurred when discharge was declining. Barometric pressure also influenced daily probability of ascent, albeit in opposite directions for each waterfall. Importantly, we also found that salmon with surgically implanted radio transmitters moved farther upriver on average and delayed less time below one of the waterfalls than those with externally attached transmitters. Although there is variance in timing arising from individual decision‐making, we showed that natural waterfalls delay progress of Atlantic salmon on their spawning migration and that both biotic (i.e., size) and abiotic (i.e., barometric pressure and discharge) factors influenced the salmon's decisions to pass waterfalls that they encounter.     

Quantifying Effects of Incentives in a Rail Maintenance Performance-Based Contract

Methods to quantify and evaluate quality become important when lump sum and performance contracts replace traditional unit-price or cost-plus contracts. Here, a combined graphical and mathematical method is described along with its results when applied on a Swedish rail maintenance contract with incentives. The regression analysis tools in the Excel software were used. The result of the incentives was that train delay decreased about 10% and the number of technical errors decreased about 20%. The improved quality took place without cost increase. The good relation between the owner and the contractor did not suffer from the rise of efficiency. On the contrary, it was improved. With minor modifications and clarifications the owner now intends to use it for in-house contracting, as the case studied, as well as when outsourcing to private companies. With other performance indicators, the elaborated method and lessons learned should be applicable also for other sectors, where a contractor assuring a specified service level during a period of time is paid a bonus depending on degree of fulfillment.     

Critical success factors for implementing lean production: the effect of contingencies

To facilitate the implementation of lean production, practitioners and researchers have suggested an array of critical success factors (CSFs). However, despite a broad consensus about what needs to be done, companies still struggle to implement lean. Contingency theory posits the explanation that the common advice is not universal but is instead contingent on the situation. This paper investigates how contingency variables influence what practitioners see as success factors for implementing lean. A survey asked 432 practitioners from 83 factories belonging to two multinational companies for their opinions about what managers should do to ensure the success of the factory-level implementation of lean production. The survey responses were grouped into general success factors, which were then tested for differences across four contingency variables: corporation, factory size, stage of lean implementation and national culture. In general, the analysis supports a generic list of CSFs, but with some minor exceptions. For example, the stage of lean implementation in a factory influences to a slight extent which factors are perceived as more effectual than others. The paper contributes to the literature on lean production and offers several recommendations for managers striving to implement lean in their firms.     

Multivariate methods in the development of a new tablet formulation: excipient mixtures and principal properties

A tablet formulation for direct compression has previously been studied using multivariate design. An optimization study of one of the most important tablet properties, disintegration time, revealed that excipients with Principal Properties (PP's) that were predicted as suitable by the model were not represented within the studied material. The feasibility of using mixtures of excipients in the multivariate approach to tablet formulation to solve this problem has been investigated in the present study. By mixing different excipients of the same excipient class, it should be possible to obtain mixtures with the predicted PP's, which in turn should give a formulation with the desired properties. In order to investigate the utility of this approach, separate mixture designs were applied to both binders and fillers (diluents). As reported here, the Partial Least Squares Projections to Latent Structures (PLS) model developed in the previously published screening study has been validated in the sense that the interesting region of the PP space identified in it has been shown to contain excipients, pure or mixed, that give the formulation suitable properties. Formulations with suitable properties were found with the mixture experiments. The local models also offer several alternatives for the composition of the formulation that yield the desired disintegration time.     

Fault handling for a wind farm with an internal DC collection grid

As a result of the increased wind power penetration, there are increased requirements for robustness of the wind farms during disturbances and faults. The wind farms are required to stay connected during short grid faults, and also, the disturbances as a result of internal faults should be minimized. In this paper, the fault ride‐through properties during external faults for a wind farm with an internal direct current (DC) grid are investigated. A safe detection of the fault is derived, as well as the reconnection procedure after the fault has been cleared. Also, the operation during internal faults has been investigated, focusing on the faults in the DC bus. It has been shown that the wind farm with an internal DC grid can operate through faults in the external grid and reconnect well within the requirements stated in the grid codes. Further, methods for detection of internal faults are derived, and it was shown that a faulted part can be disconnected and the non‐faulted parts can be back in operation within 100 ms using a DC breaker in each radial and within 300 ms without DC breakers. Copyright © 2011 John Wiley & Sons, Ltd.