Microscopic theory of spin-orbit torques and skyrmion dynamics

We formulate a general microscopic approach to spin-orbit torques in thin ferromagnet/heavy-metal bilayers in linear response to electric current or electric field. The microscopic theory we develop avoids the notion of spin currents and spin-Hall effect. Instead, the torques are directly related to a local spin polarization of conduction electrons, which is computed from generalized Kubo-St\v{r}eda formulas. A symmetry analysis provides a one-to-one correspondence between polarization susceptibility tensor components and different torque terms in the Landau-Lifshitz-Gilbert equation for magnetization dynamics. The spin-orbit torques arising from Rashba or Dresselhaus type of spin-orbit interaction are shown to have different symmetries. We analyze these spin-orbit torques microscopically for a generic electron model in the presence of an arbitrary smooth magnetic texture. For a model with spin-independent disorder we find a major cancelation of the torques. In this case the only remaining torque corresponds to the magnetization-independent Edelstein effect. Furthermore, our results are applied to analyze the dynamics of a Skyrmion under the action of electric current.Comment: 13 pages, 4 figure

Assessment of Students Performances in Biology: Implication for Measurements and Evaluation of Learning

Scienceeducation is believed to be a vital tool for individual and societal development at large. The persistent low levels of students' achievement in sciences at the various public examinations in Nigeria have continued to draw the attention of major stakeholders in education. This study examined academic achievement of Senior Secondary School students in biology and gender difference in students' achievement was examined. Ex-post facto design of descriptive research was adopted for the study. A proforma was used to collect data from a sample of two hundred (200) students, selected using stratified random sampling procedure from the Science secondary schools in Kano state Nigeria. The data collected were the students' performances in biology achievement tests. The data were analysed using descriptive statistics and independent-sample t-test. Overall results showed that the test internal consistency reliability is low and unsatisfactory; the students performed below average (M=47.02, SD=16.493 (47%). Similarly, gender difference exists in biology performance with another significant difference between performance of urban and rural school students. The study concludes that, biology test used in Kano state qualifying examinations to assess students potential ability in biology is not a reliable measurement tool and that, academic performance of students in biology is unsatisfactory and evidence of differential performance between gender and schools locations. The implication for measurements and evaluation of learning as well as recommendations has been discussed

Theory of the Interfacial Dzyaloshinskii-Moriya Interaction in Rashba Antiferromagnets

In antiferromagnetic (AFM) thin films, broken inversion symmetry or coupling to adjacent heavy metals can induce Dzyaloshinskii-Moriya (DM) interactions. Knowledge of the DM parameters is essential for understanding and designing exotic spin structures, such as hedgehog Skyrmions and chiral N\'eel walls, which are attractive for use in novel information storage technologies. We introduce a framework for computing the DM interaction in two-dimensional Rashba antiferromagnets. Unlike in Rashba ferromagnets, the DM interaction is not suppressed even at low temperatures. The material parameters control both the strength and the sign of the interfacial DM interaction. Our results suggest a route toward controlling the DM interaction in AFM materials by means of doping and electric fields.Comment: 4.5 pages+references, 4 figure

Mycelial protein production by Aspergillus niger using banana peels

The ability of Aspergillus niger to produce mycelia protein from pretreated banana peels as substrate was studied with yeast nitrogen base glucose broth as control. Banana peels gave the highest yield of mycelia protein with optical density of 0.28 (O.D) compared to the yeast nitrogen base glucose broth 0.08 (O.D). The residual glucose content in the banana peel medium decreased from 1800 μg/ml on the first day to 320 μg/ml on the 7th day. In the yeast nitrogen base glucose broth, it decreased from 2440 μg/ml on day one to 420 μg/ml on the 7th day. The mycelia protein from banana peals had a crude content of 20.4% and a lipid content of 33.3%. The results indicate the possibility of using banana peels as substrates for mycelia protein production with A. niger. Keywords: Mycelial Protein, Banana Peels, A. niger

Web-based Billing and Collection System for a Municipal Water and Services Unit

Web-Based Billing and Collection System for a Municipal Water and Services Unit is a system that sought to address the problem of a municipal water unit. Using the technology, meter reading will be paperless. It can be accessible through the Internet; end-users and water consumers/customers could connect and performtransactions enabling them to become efficient on their daily tasks whether in the office or at home. The head of the unit can make overall viewing of the status of daily transactions and can be viewed using desktop, laptop computers and android mobile devices connected to the internet. The water consumers/customers mayreceive email and short messaging system showing their current water consumption and water bill. Added/unique features such as graphical chart showing regular water consumptions on the end-users and consumers/customers dashboard as well as on their billing statements are provided. On the level of satisfaction of the respondents on the features of the proposed billing and collection system; result show that efficiencyearned the highest weighted mean (4.43) interpreted as “satisfied”. Functionality posed weighted arithmetic mean (4.33) verbally interpreted as “satisfied”. Portability and reliability followed next. On the level of acceptance of the proposed billing and collection system; respondents’ acceptance according to consumer accounts updating gauged at 4.35 weighted arithmetic mean with verbal interpretation of “acceptable”.Auto-reminding the consumers for bills due for payment posed a 4.37 weighted arithmetic mean and was also “acceptable”. According to billing statement printing and free format report generation, respondents recorded 4.45 weighted arithmetic mean and interpreted as “acceptable”. Keywords: billing system, ewater, municipal water, web-based billing, collection system

Attitude of Students towards Teaching Practice Exercise in Nigerian University: A Case Study of University of Uyo, Uyo

This study assessed students teachers’ attitude towards teaching practice exercise in the faculty of Education, University of Uyo, Uyo, Akwa Ibom of Nigeria. The study was guided by three research questions and two hypotheses. The survey design was adopted for the study. A sample of 163 student teachers constituted the study. A questionnaire tagged Student Teachers Attitude Questionnaire (STAQ) was used to collect data on the attitude of student teachers while performance of student teachers were secondary data obtained from teaching practice coordinator of the Faculty of Education. The data collected were analysed using weighted mean, mean and standard deviation, analysis of variance (ANOVA) and t-test statistics. The result indicated that on the overall, student teachers had negative attitude towards teaching practice. The result also indicated a significant difference in performance of student teachers’ based on their attitude while a non significant difference existed between male and female student teachers given their attitude. Among others, it was recommended that the University of Uyo should ensure that all student teachers are properly groomed in all teaching and pedagogy courses before proceeding on teaching practice

Spin-torque resonance due to diffusive dynamics at a surface of topological insulator

We investigate spin-orbit torques on magnetization in an insulating ferromagnetic (FM) layer that is brought into a close proximity to a topological insulator (TI). In addition to the well-known field-like spin-orbit torque, we identify an anisotropic anti-damping-like spin-orbit torque that originates in a diffusive motion of conduction electrons. This diffusive torque is vanishing in the limit of zero momentum (i. e. for spatially homogeneous electric field or current), but may, nevertheless, have a strong effect on spin-torque resonance at finite frequency provided external field is neither parallel nor perpendicular to the TI surface. The required electric field configuration can be created by a grated top gate.Comment: 10 page main text, 3 figure