MSM Actuators: Design Rules and Control Strategies

Magnetic shape memory (MSM) alloys are comparatively new active materials which can be used for several industrial applications, ranging from precise positioning systems to advanced robotics. Beyond the material research, which deals with the basic thermo‐magneto‐mechanical properties of the crystals, the design as well as the control of the actuators displacement is an essential challenge. This paper addresses those two topics, trying to give to the reader a useful overview of existing results, but also presents new ideas. First, it introduces and discusses in details some possible designs, with a special emphasis on innovative actuator design concepts which are able to exploit the particular potentialities of MSM elements. The second focus of the paper is on the problem of designing a controller, i.e., an algorithm that allows to obtain a required performance from the actuator. The proposed control strategies try to take into account two main characteristics of MSM elements: the hysteresis and the temperature dependence. The effectiveness of the strategies is emphasized by experimental results performed on a commercially available MSM actuator demonstrator.     

A precise positioning actuator based on feedback-controlled magnetic shape memory alloys

This paper describes a precise positioning system based on magnetic shape memory alloys (MSMAs). This new type of material shows an interesting potential in the area of mechatronics due to its outstanding magnetically-induced strain, which is significantly larger than the one exhibited by other common active materials such as piezoelectric ceramics. However, MSMAs still have not found their way into industrial applications mainly due to their high hysteretic behavior and the strong sensitivity to temperature changes. The aim of this paper is to present the main challenges of using MSMAs for precise positioning systems by means of a simple yet effective experimental prototype. In particular, this paper examines the problem of effectively controlling the device in closed-loop. The performance of an adaptive hysteresis compensator based on the Preisach-like Krasnosel’skii–Pokrovskii model is analyzed and evaluated in the presence of temperature changes. Experiments confirm that the undesirable effects of temperature on the precision of the device can be partially addressed with an adaptive model-based algorithm devised to cope with time-varying nonlinearities.     

The Ketogenic Diet Reduces the Harmful Effects of Stress on Gut Mitochondrial Biogenesis in a Rat Model of Irritable Bowel Syndrome

Functional alterations in irritable bowel syndrome have been associated with defects in bioenergetics and the mitochondrial network. Effects of high fat, adequate-protein, low carbohydrate ketogenic diet (KD) involve oxidative stress, inflammation, mitochondrial function, and biogenesis. The aim was to evaluate the KD efficacy in reducing the effects of stress on gut mitochondria. Newborn Wistar rats were exposed to maternal deprivation to induce IBS in adulthood. Intestinal inflammation (COX-2 and TRL-4); cellular redox status (SOD 1, SOD 2, PrxIII, mtDNA oxidatively modified purines); mitochondrial biogenesis (PPAR-γ, PGC-1α, COX-4, mtDNA content); and autophagy (Beclin-1, LC3 II) were evaluated in the colon of exposed rats fed with KD (IBD-KD) or standard diet (IBS-Std), and in unexposed controls (Ctrl). IBS-Std rats showed dysfunctional mitochondrial biogenesis (PPAR-γ, PGC-1α, COX-4, and mtDNA contents lower than in Ctrl) associated with inflammation and increased oxidative stress (higher levels of COX-2 and TLR-4, SOD 1, SOD 2, PrxIII, and oxidatively modified purines than in Ctrl). Loss of autophagy efficacy appeared from reduced levels of Beclin-1 and LC3 II. Feeding of animals with KD elicited compensatory mechanisms able to reduce inflammation, oxidative stress, restore mitochondrial function, and baseline autophagy, possibly via the upregulation of the PPAR-γ/PGC-1α axis.     

ITER tungsten divertor design development and qualification program

In November 2011, the ITER Council has endorsed the recommendation that a period of up to 2 years be set to develop a full-tungsten divertor design and accelerate technology qualification in view of a possible decision to start operation with a divertor having a full-tungsten plasma-facing surface. To ensure a solid foundation for such a decision, a full tungsten divertor design, together with a demonstration of the necessary high performance tungsten monoblock technology should be completed within the required timescale. The status of both the design and technology R&D activity is summarized in this paper.     

Cure kinetics of diglycidylether of bisphenol A– ethylenediamine revisited using a mechanistic model

The polymerization kinetics of the reaction between diglycidylether of bisphenol A (DGEBA) and ethylenediamine (EDA) was analyzed, using dynamic scanning calorimetry, in both isothermal and programmed heating‐rate modes. A simple mechanistic model, consisting of an equilibrium reaction generating an epoxy–hydroxyl complex, and including two possible mechanisms for the consumption of amine hydrogens [(1) with free epoxy groups, (2) with the epoxy–hydroxyl complex], provided a reasonable fitting of the whole set of experimental results. It was found that the equilibrium constant decreased with temperature, making less important the reaction mechanism involving the epoxy–hydroxyl complex. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2319–2325, 2001     

A generalized self-consistent method for solids containing randomly oriented spheroidal inclusions

Summary In this paper, a generalized self-consistent method is proposed to predict the effective moduli of a material containing single-phase and randomly oriented spheroidal inclusions, with same aspect ratios. This is achieved by using an energy equivalence framework, associated with a generalization of the classical three phase model to spheroidal inclusions. The localization problem (spheroidal duplex inclusion problem) is formulated with the Papkovitch-Neuber approach; this requires expansion formulae for the spheroidal potentials, which are derived in the Appendix. Finally, the determination of the effective moduli is equivalent to solving a system of nonlinear equations. Effective moduli are presented for various types of inclusions, and comparisons are made with the estimations obtained from the self-consistent and Mori-Tanaka methods. Moreover, the effects of inclusion geometry and spatial distribution of inclusions on the effective moduli are investigated and compared to each other.     

Morphology profiles generated by temperature gradient in PMMA modified epoxy system

A diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin was modified with 15 wt% of poly(methylmethacrylate) (PMMA) and cured with a stoichiometric amount of 4,4′‐diamino diphenyl methane (DDM). The reactive mixture was cured in a heated mold with different gradients of temperature. Temperature profiles in the mold were imposed by generation of a heat flux from the base, supported on a hot plate, and the top, cooled with water; they were measured along the mold. Depending on the thermal history in each position of the mold, the competition between the phase‐separation process and reaction kinetics produces opaque or transparent zones. Phase separation can also occur in the postcure process while the gelation does not take place before. Therefore, a thermoset plate with gradient of morphology and properties was obtained. Mass fractions of PMMA dissolved in the matrix were calculated with the Fox equation from glass transition temperatures measured along the mold. They were related to morphologies developed during curing. The superposition of the phase diagrams with the conversion‐temperature trajectories during cure permitted an explanation of the morphology gradients generated.     

Comparison between beryllium and diamond-backing plates in diamond-anvil cells: application to single-crystal x-ray diffraction high-pressure data

A direct comparison between two complete intensity datasets, collected on the same sample loaded in two identical diamond-anvil pressure cells equipped, respectively, with beryllium and diamond-backing plates was performed. The results clearly demonstrate that the use of diamond-backing plates significantly improves the quality of crystal structure data. There is a decrease in the internal R factor for averaging, structure refinement agreement factors, and in the errors and uncertainties of the atomic coordinates, atomic displacement parameters, and individual bond lengths.     

OPERA: a novel method to reduce ghost and aliasing artifacts

Objective

A method for Orthogonal Phase Encoding Reduction of Artifact (OPERA) was developed and tested.

Materials and methods

Because the position of ghosts and aliasing artifacts is predictable along columns or rows, OPERA combines the intensity values of two images acquired using the same parameters, but with swapped phase-encoding directions, to correct the artifacts. Simulations and phantom experiments were conducted to define the efficacy, robustness, and reproducibility. Clinical validation was performed on a total of 1003 images by comparing the OPERA-corrected images and the corresponding image standard in terms of Signal-to-Noise Ratio (SNR) and Contrast-to-Noise Ratio (CNR). The method efficacy was also rated using a Likert-type scale response by two experienced independent radiologists using a single-blinded procedure.

Results

Simulations and phantom experiments demonstrated the robustness and effectiveness of OPERA in reducing artifacts strength. OPERA application did not significantly change the SNR [+?4.16%; inter-quartile range (IQR): 2.72–5.01%] and CNR (+?4.30%; IQR: 2.86–6.04%) values. The two radiologists observed a total of 893 original images with artifacts (89.03% of the total images), a reduction in the perceived artifacts of 82.0% and 83.9% (p?<?0.0001), and an improvement in the perceived SNR (82.8% and 88.5%; K?=?0.714) and perceived CNR (86.9–88.9%; K?=?0.722).

Discussion

The study demonstrated that OPERA reduces MR artifacts and improves the perceived image quality.