Comparative Viability of Spray Dried Lactobacilli Affected by Different Protective Agents and Storage Conditions

Because of their health benefits, probiotics are a significant part of the functional food industry. Spray drying is reported as the most common method used in the food industry to encapsulate probiotics. The objectives of this study were to investigate the effects of protective agents on the viability of lactobacilli after spray drying and during storage at different conditions and to evaluate spray drying conditions to produce these probiotic powders. Lactobacillus plantarum NRRL B-4496 (LP) and Lactobacillus acidophilus NRRL B-4495 (LA) were separately grown (~109 CFU/ml) and suspended in a 200 g/L solution of high maize starch (HM); maltodextrin (MD); or gum arabic (GA). The solutions were separately spray dried at 140 °C to obtain LP and LA-powders: LPHM, LPMD, LPGA, LAHM, LAMD, and LAGA. The powders were separately placed in aluminum bags and separately packed under 97% and 10% vacuum. The powders were stored at refrigerated (4 °C) or at room (23 °C) temperature for 60 days. Physicochemical properties, energy and mass balances, and cell viability during storage were determined. Triplicate experiments were conducted and data were statistically analyzed (α=0.05). The actual production rate of powders ranged from 0.091 to 0.105 (kg dry solids/h). The energy used during spray drying was not significantly different for any of the powders. After 60 days, LPHM powders packed under 10% and 97% vacuum and stored at 4 °C had significantly higher cell viability than the other powder samples. The study demonstrated significantly improved on the viability of LP at 10% vacuum stored at refrigerated temperature for the HM treatment compared to those treated with MD and GA. The data obtained showed that high maize starch can be used as a protective agent to maintain the viability of L. plantarum powder at recommended levels for up to 60 days of storage

Self organized mode locking effect in superconductor / ferromagnet hybrids

The vortex dynamics in a low temperature superconductor deposited on top of a rectangular array of micrometer size permalloy triangles is investigated experimentally. The rectangular unit cell is such that neighboring triangles physically touch each other along one direction. This design stabilizes remanent states which differ from the magnetic vortex state typical of individual non-interacting triangles. Magnetic Force Microscopy images have revealed that the magnetic landscape of the template can be switched to an ordered configuration after magnetizing the sample with an in-plane field. The ordered phase exhibits a broad flux flow regime with relatively low critical current and a highly anisotropic response. This behavior is caused by the spontaneous formation of two separated rows of vortices and antivortices along each line of connected triangles. The existence of a clear flux flow regime even for zero external field supports this interpretation. The density of induced vortex-antivortex pairs is directly obtained using a high frequency measurement technique which allows us to resolve the discrete motion of vortices. Strikingly, the presence of vortex-antivortex rows gives rise to a self organized synchronized motion of vortices which manifests itself as field independent Shapiro steps in the current-voltage characteristics.Comment: 9 pages, 11 figure

Vortex rectification effects in films with periodic asymmetric pinning

We study the transport of vortices excited by an ac current in an Al film with an array of nanoengineered asymmetric antidots. The vortex response to the ac current is investigated by detailed measurements of the voltage output as a function of ac current amplitude, magnetic field and temperature. The measurements revealed pronounced voltage rectification effects which are mainly characterized by the two critical depinning forces of the asymmetric potential. The shape of the net dc voltage as a function of the excitation amplitude indicates that our vortex ratchet behaves in a way very different from standard overdamped models. Rather, as demonstrated by the observed output signal, the repinning force, necessary to stop vortex motion, is considerably smaller than the depinning force, resembling the behavior of the so-called inertia ratchets. Calculations based on an underdamped ratchet model provide a very good fit to the experimental data.Comment: 5 pages, 4 figure

The Socially Situated Dynamics of Children’s Learning Processes in Classrooms:What Do We Learn from a Complex Dynamic Systems Approach?

This article concentrates on the question what kind of model-conceptual and statistical -can serve as a good working model for the study of learning and teaching processes qua processes. We claim that a good way of answering this question is to begin by observing a teaching and learning process as, where, and when it occurs. In addition, a conceptual model of intertwined learning-teaching processes is discussed, and dynamic modeling as an approach to theory formation about teaching-learning processes. The focus lies on the evolution term, the timescale of interaction processes, state space as a perspective on teacher-student interaction dynamics, and the principle of agency. Finally, an empirical approach to studying teaching-learning processes is illustrated by means of a case study, focusing on the use of cluster analyses techniques. In the Conclusion and Discussion section, further perspectives on theory building and empirical research are discussed

Voltage rectification in two dimensional Josephson junction arrays

We study numerically the directed motion of vortices (antivortices) under an applied ac bias in two-dimensional Josephson junction arrays (JJA) with an asymmetrically modulated periodic vortex pinning potential. We find that the ratchet effect in large 2D JJA can be obtained using the RSJ model for the overdamped vortex dynamics. The rectification effect shows a strong dependence on vortex density as well as an inversion of the vortex flow direction with the ac amplitude, for a wide range of high magnetic field around f=1/2 (f being the vortex density). Our results are in good agreement with very recent experiments by D.E. Shalom and H. Pastoriza [Phys. Rev. Lett. 94, 177001, (2005)].Comment: 4 pages, 4 figures, Proceedings Vortex IV Conference, September 3-9, 2005, Crete, Greece. To appear in Physica

Dipole-induced vortex ratchets in superconducting films with arrays of micromagnets

We investigate the transport properties of superconducting films with periodic arrays of in-plane magnetized micromagnets. Two different magnetic textures are studied: a square array of magnetic bars and a close-packed array of triangular microrings. As confirmed by MFM imaging, the magnetic state of both systems can be adjusted to produce arrays of almost point-like magnetic dipoles. By carrying out transport measurements with ac drive, we observed experimentally a recently predicted ratchet effect induced by the interaction between superconducting vortices and the magnetic dipoles. Moreover, we find that these magnetic textures produce vortex-antivortex patterns, which have a crucial role on the transport properties of this hybrid system.Comment: 4 pages, 4 figure