Existence and stability of singularly perturbed standing pulse solutions of a three-component FitzHugh-Nagumo

In this article, a singularly perturbed three-component FitzHugh-Nagumo system, which is proposed in [2], is considered. As a simple localized pattern, the existence of standing pulse solutions with high accurate approximations for a small parameter and their stability are shown by using an analytic singular perturbation technique

Effect of high annealing temperature on giant tunnel magnetoresistance ratio of CoFeB/MgO/CoFeB magnetic tunnel junctions

We report tunnel magnetoresistance (TMR) ratios as high as 472% at room temperature and 804% at 5 K in pseudo-spin valve (SV) CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) annealed at 450oC, which is approaching the theoretically predicted value. By contrast, the TMR ratios for exchange-biased (EB) SV MTJs with a MnIr antiferromagnetic layer are found to drop when they are annealed at 450oC. Energy dispersive X-ray analysis shows that annealing at 450oC induces interdiffusion of Mn and Ru atoms into the MgO barrier and ferromagnetic layers in EB-SV MTJs. Mechanisms behind the different annealing behavior are discussed.Comment: 13 pages, 5 figure

Dependence of tunnel magnetoresistance on ferromagnetic electrode materials in MgO-barrier magnetic tunnel junctions

We investigated the relationship between the tunnel magnetoresistance (TMR) ratio and the electrode structure in MgO-barrier magnetic tunnel junctions (MTJs). The TMR ratio in a MTJ with Co40Fe40B20 reference and free layers reached 355% at the post-deposition annealing temperature of Ta=400 degree C. When Co50Fe50 or Co90Fe10 is used for the reference layer material, no high TMR ratio was observed. The key to have high TMR ratio is to have highly oriented (001) MgO barrier/CoFeB crystalline electrodes. The highest TMR ratio obtained so far is 450% at Ta = 450 degree C in a pseudo spin-valve MTJ.Comment: 6 pages, 2 figures, 1 table. to be published in J. Magn. Magn. Mate

Unfolding symmetric Bogdanov-Takens bifurcations for front dynamics in a reaction-diffusion system

This manuscript extends the analysis of a much studied singularly perturbed three-component reaction-diffusion system for front dynamics in the regime where the essential spectrum is close to the origin. We confirm a conjecture from a preceding paper by proving that the triple multiplicity of the zero eigenvalue gives a Jordan chain of length three. Moreover, we simplify the center manifold reduction and computation of the normal form coefficients by using the Evans function for the eigenvalues. Finally, we prove the unfolding of a Bogdanov-Takens bifurcation with symmetry in the model. This leads to stable periodic front motion, including stable traveling breathers, and these results are illustrated by numerical computations.Comment: 39 pages, 7 figure

Single Transition Layer in Mass-Conserving Reaction-Diffusion Systems with Bistable Nonlinearity

Mass-conserving reaction-diffusion systems with bistable nonlinearity are useful models for studying cell polarity formation, which is a key process in cell division and differentiation. We show the existence and stability of stationary solutions with a single internal transition layer in such reaction-diffusion systems under general assumptions by the singular perturbation theory.Comment: 35 pages, 2 figure

SCIENCE TALK IN THE SECONDARY CLASSROOMS: ANALYSIS OF TEACHERS’ FEEDBACK

Feedback, the third part of Initiation-Response-Feedback (IRF) structure in typical lesson discussion, is the most crucial part of teaching and science talk. Feedback constructs cognitive scaffolding as well as dialogical pattern of discussion in the classroom. Several studies analyzing teachers’ feedback types and wait time of effect have been reported. Owing to its tremendous effect on teaching and learning, as stated by Chin (2007), a fine grained analysis has been felt. Video recorded data of fourteen science lessons in secondary level (Grade VI-X) of Bangladesh used as data source of this study. Data were analyzed with coded category. Through video analysis, the nine categories of teachers’ feedback were emerged to students’ correct and incorrect or no response. The prevalent nature of feedback was evaluative and corrective. All the generated categories were illustrated with example taken from the real lesson and tried to explain the effect of each type of feedback on lesson discussion. The results of the study are illustrated vignettes of the teachers’ varieties of feedback and the role of the feedback at secondary science lessons, and would be helpful for teachers to think and frame their practices that make a science lesson into collaborative, dialogic and facilitative one

An Evaluation of the Effect of the Improvised Experiments on Student-teachers’ Conception of Static Electricity

This study is investigating the student-teachers’ conception of static  electricity in Rwandan teacher training colleges. The study used a preand post-intervention design, where two groups of students were randomly  assigned in two groups. Along a period of four weeks, one group was taught using the traditional method (TRAD) while another using improvised  experiment (IME) method. The student-teachers were given a test before teaching while after teaching the same test was administered to both groups. The study was not interested in testing student-teachers’  achievement rather the conception of static electricity. The test was composed of six item questions and their answers were coded as “out of the topic, unrelated information and opposite answers”. After performing pre-test, student-teachers showed confusions related to non-mastery of content and alternative conceptions related to static electricity and  magnetism. Though about 27 per cent and 17 per cent of student-teachers in TRAD and IME respectively, reduced the gaps in their confusion after getting teaching intervention, however, there was found to be no statistically significant difference (p>.05 at df=10) in all of the item questions between these teaching methods in favour of IME. Four item questions showed an improvement while student-teachers developed more conceptual confusions in other two item questions. Not only examining student-teachers’ conception in static electricity but also teachers were recommended to be aware of students’ ideas, opinions and confusions prior to their lesson planning, teaching materials preparation, as well as teaching implementation. Keywords: Conceptions, Static electricity, Improvised experiments, Student-teacher

Caffeic acid inhibits the formation of 1-hydroxyethyl radical in the reaction mixture of rat liver microsomes with ethanol partly through its metal chelating activity

Effect of caffeic acid on the formation of 1-hydroxyethyl radicals via the microsomal ethanol-oxidizing system pathway was examined. The electron spin resonance spin trapping showed that 1-hydroxyethyl radicals form in the control reaction mixture which contained 0.17 M ethanol, 1 mg protein/ml rat river microsomes, 0.1 M α-(4-pyridyl-1-oxide)-N-tert-butylnitrone, 5 mM nicotinamide adenine dinucleotide phosphate and 30 mM phosphate buffer (pH 7.4). When the electron spin resonance spectra of the control reaction mixtures with caffeic acid were measured, caffeic acid inhibited the formation of 1-hydroxyethyl radicals in a concentration dependent manner. Gallic acid, dopamine, l-dopa, chlorogenic acid and catechin also inhibited the formation of 1-hydroxyethyl radicals. Above results indicated that the catechol moiety is essential to the inhibitory effect. Caffeic acid seems to chelate of iron ion at the catechol moiety. Indeed, the inhibitory effect by caffeic acid was greatly diminished in the presence of desferrioxamine, a potent iron chelator which removes iron ion in the Fe (III)-caffeic acid complex. Since Fe (III)-desferrioxamine complex is active for the 1-hydroxyethyl radicals formation, caffeic acid inhibits the formation of 1-hydroxyethyl radicals in the reaction mixture partly through its metal chelating activity

Status of MSBS study at NAL

Two Magnetic Suspension and Balance Systems (MSBS) at the National Aerospace Laboratory (NAL) in Japan are introduced. They are the 10 cm MSBS and the 60 cm MSBS. They have 10 cm x 10 cm and 60 cm x 60 cm test sections. The control of suspending a model at the 10 cm MSBS is six degrees of freedom including the rolling moment control. The model for the rolling moment control has two pairs of small extra permanent magnets at both its ends plus a main cylindrical magnet. The rolling moment is generated by the magnetic forces acting on the extra magnets by controlled current passing through the four side coils independently. Test results show the roll angle of the model is controlled in this way. The dynamic calibration test was carried out at the MSBS in five degrees of freedom without the rolling moment control. The model is a simple cylindrical magnet magnetized along its axis. The obtained results show that the dynamic calibration with measured magnetic field intensity is much superior to that with the coil currents. The 60 cm MSBS was designed with some data obtained at the 10 cm one. It is fundamentally proportional to the 10 cm one in size and coil positions. The measured magnetic field intensity is not so strong as expected at design. It was operated first in 1993. The control is three degrees of freedom in the longitudinal direction