a b s t r a c t We extend and improve two existing methods of generating random correlation matrices, the onion method of Ghosh and Henderson [S. Ghosh, S.G. Henderson, Behavior of the norta method for correlated random vector generation as the dimension increases, ACM Transactions on Modeling and Computer Simulation (TOMACS) 13 (3) (2003) 276-294] and the recently proposed method of Joe [H. Joe, Generating random correlation matrices based on partial correlations, Journal of Multivariate Analysis 97 (2006) 2177-2189] based on partial correlations. The latter is based on the so-called D-vine. We extend the methodology to any regular vine and study the relationship between the multiple correlation and partial correlations on a regular vine. We explain the onion method in terms of elliptical distributions and extend it to allow generating random correlation matrices from the same joint distribution as the vine method. The methods are compared in terms of time necessary to generate 5000 random correlation matrices of given dimensions.
In this paper the magnetomechanical properties of magnetorheological (MR) elastomers with isotropic and anisotropic structure are examined. A method for manufacturing magnetorheological elastomers (MRE) with thermoplastic elastomer matrix and 60 μm iron particles is presented. The influence of various chemical compositions on the material parameters is investigated. The properties of isotropic and anisotropic MR elastomers are examined in a wide range of mechanical and magnetic stimulations. Test samples are subjected to cyclic shearing with a constant frequency of 1 Hz. The change in magnetomechanical properties is expressed by the relative change of hysteresis loop area δW and stress amplitude δτ .
The aim of this work study was to evaluate the cytophysiological activity of equine adipose-derived stem cells (ASCs) cultured under conditions of static magnetic field. Investigated cells were exposed to a static magnetic field (MF) with the intensity of 0.5 T. In order to investigate the effects of magnetic field on stem cell signaling, the localization and density and content of microvesicles (MVs) as well as morphology, ultrastructure, and proliferation rate of equine ASCs were evaluated. Results showed that potential of equine adipose-derived mesenchymal stem cells was accelerated when magnetic field was applied. Resazurin-based assay indicated that the cells cultured in the magnetic field reached the population doubling time earlier and colony-forming potential of equine ASCs was higher when cells were cultured under magnetic field conditions. Morphological and ultrastructural examination of equine ASCs showed that the exposure to magnetic field did not cause any significant changes in cell morphology whereas the polarity of the cells was observed under the magnetic field conditions in ultrastructural examinations. Exposition to MF resulted in a considerable increase in the number of secreted MVs—we have clearly observed the differences between the numbers of MVs shed from the cells cultured under MF in comparison to the control culture and were rich in growth factors. Microvesicles derived from ASCs cultured in the MF condition might be utilized in the stem cell-based treatment of equine musculoskeletal disorders and tendon injuries.
This paper presents a procedure for manufacturing composites, a methodology for testing them and the cyclic properties of isotropic magnetorheological elastomers. The choice of a thermoplastic matrix and magnetically active iron powder as the filling (much larger than the carbonyl iron powder filling used so far) is expounded. A manufacturing technology has been developed. Possibilities for the experimental investigation of magnetomechanical properties have been created by building a measuring system enabling the testing of various elastomers in a wide range of mechanical and magnetic parameters. The effect of the magnetic field and that of the stress frequency on the damping properties of a selected elastomer (considered to be optimal) were examined.
Continuous hydrolysis of an active pharmaceutical ingredient intermediate, and subsequent liquid−liquid (L-L) separation of the resulting organic and aqueous phases, have been achieved using a simple PTFE tube reactor connected to a miniscale hydrophobic membrane separator. An alkoxide product, obtained in continuous mode by a Grignard reaction in THF, reacted with acidic water to produce partially miscible organic and aqueous phases containing Mg salts. Despite the partial THF− water miscibility, the two phases could be separated at total flow rates up to 40 mL/min at different flow ratios, using a PTFE membrane with 28 cm 2 of active area. A less challenging separation of water and toluene was achieved at total flow rates as high as 80 mL/min, with potential to achieve even higher flow rates. The operability and flexibility of the membrane separator and a plate coalescer were compared experimentally as well as from a physical viewpoint. Surface tension-driven L-L separation was analyzed in general terms, critically evaluating different designs. It was shown that microporous membrane L-L separation can offer very large operating windows compared to other separation devices thanks to a high capillary pressure (Laplace pressure) combined with a large number of pores per unit area offering low pressure drop. The separation device can easily be operated by means of a back-pressure regulator ensuring flow-independent separation efficiency. Simple monitoring and control strategies as well as scaling-up/out approaches are proposed, concluding that membrane-based L-L separation may become a standard unit operation for continuous pharmaceutical manufacturing.
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