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

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

Nature of the constant factor in the relation between radial breathing mode frequency and tube diameter for single-wall carbon nanotubes

Resonance Raman scattering is used to determine the radial breathing mode (RBM) frequency (ωRBM) dependence on tube diameter (dt) for single-wall carbon nanotubes (SWNTs). We establish experimentally the ωRBM=227.0/dt as the fundamental relation for pristine SWNTs. All the other RBM values found in the literature can be explained by an upshift in frequency due mostly to van der Waals interaction between SWNTs and environment

Floristic Composition, Structural Analysis and Socio-economic Importance of Legume Flora of the Commune of Mayahi, Niger, West Africa

Floristic assessment plays a crucial role in managing and conserving phytodiversity. Thisstudy tried to determine the floristic composition, woody structure and socio-economic importance of the legume flora in the commune of Mayahi. We used plot method based on systematic sampling approach to inventory legume species within the parklands in September 2012. We recorded 55 legume species belonging to 24 genera in 56 relevés. Fabaceae is the dominant family among the legume botanical families in the parklands of the commune of Mayahi. The average woody legume density is 62 individuals per hectare in the commune of Mayahi. The woody legume species of highest average density are Faidherbia albida and Piliostigma reticulatum. While the total basal area of legumes of the commune is 1.12m2 / ha in the Mayahi commune. The crown cover varies according to the vegetation types but it is higher in the Goulbi N\u27kaba forest reserve. Legume flora provides a myriad of benefits to the people of Mayahi. The present study recommends furtherresearch that examines the impact of human activities on the legume flora of the parklands in the commune of Mayahi

Mycological Quality of Powdered Herbal Medicinal Preparations Packaged for Human Consumption in North Western Nigeria

The increase in the consumption of natural drugs have made their use a public health problem due to its poor quality, presence of  fungal contamination and the risk of the presence of mycotoxins. This investigation was designed to throw light on the mycological and aflatoxigenic status of powdered herbal medicinal products marketed in North Western Nigeria. A total of four hundred and thirty two(432) powdered herbal medicinal preparations consisting of twelve(12) each from six(6) localities in each of the six(6) states’ metropolis of the North Western Nigeria were obtained. These samples were subjected to various analyses. The parameters measured were grouped as follows: level of fungal contaminations of fungi; frequency of distribution of  fungi and  mycoflora type present in the herbal preparations. Results indicated that all the four hundred and thirty two herbal medicinal preparations assessed did not comply with the maximum acceptable limit of 2x102 cfu/g for fungal load. The study showed that samples from Kaduna and Kebbi  had  a significantly  higher  mean fungal count (1.09x105cfu/g and 1.05x105cfu/g respectively) that were not significantly different (p?0.05), hence suggesting higher contamination with fungi. The least was observed in Zamfara state with the lowest mean value of fungal load. The statistical analysis showed that fungal load in Katsina, Sokoto, Kano and  Zamfara  states were  not the same but not significantly different (p?0.05). This suggested low level of contamination with fungi when compared with samples from Kaduna and Kebbi state. In terms of fungal distribution in  herbal medicinal preparations, this study indicated that  fungi of the genus Aspergillus spp and Penicillus spp were the most frequently isolated and were found to be higher in frequency of occurrence. Out of one thousand and ninety five (1095)  total frequency of occurrence of fungi in the herbal medicinal preparations, the total frequency of occurrence of Aspergillus spp in this study is seven hundred and seventy five(70.77%), Penicillium spp (n=190;17.35%); Fusarium spp (n=86;7.85%)  and Rhizopus spp (n=44;4.02%). In this finding it could be suggested that Aspergillus spp and Penicillium spp are the major contaminant of herbal drugs. In all the samples screened from the six states, higher level of contamination with Aspergillus spp were found. Among  the Aspergillus spp observed,  A. flavus, A. paraceticus, A. niger were the most frequently occurred fungi in the herbal medicinal samples suggesting that these type of fungi are the major contaminant of the herbal medicinal products in all the six states of the North West of Nigeria. The highest frequency of occurrence of fungi observed in samples from Kaduna 151(69.59%), Kano139 (72.02%),sokoto135 (73.37%), Kebbi127 (66.49%), Kastina112 (70.89%) and Zamfara111 (68.52%)  may be as a result of poor harvesting, processing and storage practice of the handler of the herbal products. The  means of  frequency of occurrence of fungal isolates in herbal preparations from the North Western Nigeria also showed that incidence of  Aspergillus flavus, Aspergillus paraceticus, Aspergillus niger and Penicillium spp were not significantly  different at p<0.05 but significantly higher than Aspergillus ochraceus and Aspergillus versicolor. The result obtained also indicates that Fusarium spp and Rhizopus spp were significantly the lowest. This result suggests that the samples of herbal medicines obtained in the North Western Nigeria is heavily contaminated with the fungal species of Aspergillus spp and Penicillium spp. Keywords:  herbal medicines, fungal contamination, North Western Nigeri

Status of Muon Collider Research and Development and Future Plans

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides continued work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (CoM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay ($\pi \to \mu \nu_{\mu}$) channel, muon cooling, acceleration, storage in a collider ring and the collider detector. We also present theoretical and experimental R & D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the R & D since the Feasibility Study of Muon Colliders presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].Comment: 95 pages, 75 figures. Submitted to Physical Review Special Topics, Accelerators and Beam

Isolation and Characterization of some Hydrocarbon Utilizing bacteria from Refinery Effluents

The present work was undertaken to isolate and characterize the hydrocarbon degrading bacteria associated with effluent samples collected from Kaduna refinery and petrochemical company (KRPC). The samples were analyzed microbiologically using standard microbiological techniques. Bacillus cereus and Pseudomonas aeruginosa were successfully isolated from the refinery effluents. However, following treatment before the effluents are discharged, the levels of most parameters were brought within permissible limits. From the study, it was apparent that Bacillus cereus and Pseudomonas aeruginosa have the ability to grow and survive in refinery effluents