431 research outputs found
One-dimentional magnonic crystal as a medium with magnetically tunable disorder on a periodical lattice
We show that periodic magnetic nanostructures (magnonic crystals) represent
an ideal system for studying excitations on disordered periodical lattices
because of the possibility of controlled variation of the degree of disorder by
varying the applied magnetic field. Ferromagnetic resonance (FMR) data
collected inside minor hysteresis loops for a periodic array of Permalloy
nanowires of alternating width and magnetic force microscopy images of the
array taken after running each of these loops were used to establish convincing
evidence that there is a strong correlation between the type of FMR response
and the degree of disorder of the magnetic ground state. We found two types of
dynamic responses: anti-ferromagnetic (AFM) and ferromagnetic (FM), which
represent collective spin wave modes or collective magnonic states. Depending
on the history of sample magnetization either AFM or FM state is either the
fundamental FMR mode or represents a state of a magnetic defect on the
artificial crystal. A fundamental state can be transformed into a defect one
and vice versa by controlled magnetization of the sample.Comment: 4 pages, 3 figures, Letter paper, already submitted to PR
Brillouin light scattering studies of planar metallic magnonic crystals
The application of Brillouin light scattering to the study of the spin-wave
spectrum of one- and two-dimensional planar magnonic crystals consisting of
arrays of interacting stripes, dots and antidots is reviewed. It is shown that
the discrete set of allowed frequencies of an isolated nanoelement becomes a
finite-width frequency band for an array of identical interacting elements. It
is possible to tune the permitted and forbidden frequency bands, modifying the
geometrical or the material magnetic parameters, as well as the external
magnetic field. From a technological point of view, the accurate fabrication of
planar magnonic crystals and a proper understanding of their magnetic
excitation spectrum in the GHz range is oriented to the design of filters and
waveguides for microwave communication systems
Collective spin waves in arrays of Permalloy nanowires with single-side periodically modulated width
We have experimentally and numerically investigated the dispersion of
collective spin waves prop-agating through arrays of longitudinally magnetized
nanowires with periodically modulated width. Two nanowire arrays with
single-side modulation and different periodicity of modulation were studied and
compared to the nanowires with homogeneous width. The spin-wave dispersion,
meas-ured up to the third Brillouin zone of the reciprocal space, revealed the
presence of two dispersive modes for the width-modulated NWs, whose amplitude
of magnonic band depends on the modula-tion periodicity, and a set of
nondispersive modes at higher frequency. These findings are different from
those observed in homogeneous width NWs where only the lowest mode exhibits
sizeable dis-persion. The measured spin-wave dispersion has been satisfactorily
reproduced by means of dynam-ical matrix method. Results presented in this work
are important in view of the possible realization of frequency tunable magnonic
device
Granite Dusts and Poultry Manure Effects on Growth Performance and Yield of Maize (Zea Mays L.)
Poultry manure is rich in organic manure since solid and liquid wastes are excreted together and there is no urine loss. Comparative studies of the effects of various rates of granite dust and poultry manure were tested on maize performance in field trials at Akure, Nigeria between 2011 and 2012 cropping seasons. The treatments involved were: Control(No treatment application), 2tha1 granite dust; 3tha1 poultry manure + 0.5tha1 granite dust; 2tha1 poultry manure + 1tha1 granite dust; 1tha1 poultry manure+ 1.5tha1 granite dust; 4tha1 poultry manure and 200kgha1 of NPK fertilizer. Agronomic parameters observed on maize at 2, 4, 6, 8, 10 and 12weeks after planting were plant height, stem girth, number of leaves. At harvest, cob weight, plant biomass, grains weight per cob and husk weight were also measured. Equally, the ratio of root to stem and leaf of maize were investigated. It was found out that application combined application of granite dust and poultry manure improved the growth and yield quality of maize compared with the control. Maize treated with 3tha1 poultry manure + 0.5tha1 granite dust promote the growth and yield parameter of maize to a level of the standard recommended fertilizer rate of 200kgha1 of NPK fertilizer in the ecological zone of the southwestern Nigeria. Keywords: Poultry manure, granite dusts, agronomic parameters, ratio, promote
Influence of Mycorrhizae and Rhizobium Inoculation on Growth, Nutrient Uptake and Proximate Composition of Upland Rice Cultivars
The activities of microbial rhizospheric organisms have been well documented in non-leguminous plants such as wheat, rice and maize. Such activities include nitrogen fixation, phosphate solubilization and mineralization that are beneficial for the overall growth and development of the plant. Field experiments were carried out in the early and late cropping season of 2013 in the tropical rainforest agro-ecology of southwest Nigeria to study the growth promotion, nutrient uptake, proximate composition of upland rice and harvested grains based on single inoculation of Mycorrhizae and Rhizobium. A 5 x 3 factorial experiment was conducted; five upland rice varieties selected with and without the application of mycorrhizae and rhizobium, laid out in split plot arrangement, with mycorrhizae and rhizobium in the main block, while variety was in the sub-plot. Each treatment was replicated three times. In both seasons, result show significant (P < 0.05) effect of single mycorrhizae and rhizobium inoculation on plant growth (plant height, numbers of tillers and leaves) and plant biomass except for shoot weight in the late season. Also, result show significant (P < 0.05) effect of single mycorrhizae and rhizobium inoculation on nutrient uptake in both seasons. Significant (P < 0.05) effect of single mycorrhizae and rhizobium inoculation was observed in proximate composition of rice grains in the early season, with rhizobium inoculated rice having the highest protein content. It was concluded that upland rice inoculation with mycorrhizae and rhizobium improved their nutrient uptake, proximate composition and growth. Keywords: Mycorrhizae, rhizobium, upland rice, nutrient uptake, growth, proximate compositio
Magnetotransport properties of lithographically defined lateral Co/Ni80Fe20 wires
In this article we have investigated the magnetization reversal process of laterally defined coupled magnetic structures consisting of micron-sized sputtered Co and Ni80Fe20 wires lying side by side at temperatures ranging from 3 to 300 K. We have used a microfabrication technique to create an array of planar, laterally coupled magnetic wires made of two ferromagnetic materials. We observed two distinct peaks in the magnetoresistance (MR) curves corresponding to the magnetization reversals of Co and Ni80Fe20 wires. Below a critical temperature of 20 K we observed an asymmetric shift in the Ni80Fe20 peak position for both forward and reverse field sweeps due to the exchange coupling between the ferromagnetic (Ni80Fe20) and antiferromagnetic (Co–oxide at the interface of Co and Ni80Fe20 formed during fabrication) parts. The Co peaks gradually disappeared as the temperature was reduced. At low temperature we also observed that the Ni80Fe20 peaks in the MR loops are considerably shifted to larger fields corresponding to the increase in coercivity
An Evaluation of Job Creation and Vocational Skills Development Programme of the National Directorate of Employment, In Lagos State of Nigeria
The purpose of the study is to critically analyse the Job Creation and Vocational Skills Development of the
National Directorate of Employment (NDE) in L~os State with particular reference to the National
Open Apprenticeship Scheme (NOAS). The descriptive survey approach was adopted for the study.
The sample used for the study was drawn from the trainees, trainers and the Operational and Support
Services staff of the NDE. The number was made up of seven hundred trainees, forty-two trainers and
twenty officials of the National Directorate of Employment, in Lagos State.
Three sets of questionnaires were the major research instruments used for gathering data. Records from the
NDE National Headquarters and the Lagos State office at Yaba, coupled with oral interview, conducted
on the beneficiaries of the NDE programme, complemented those data collec.ted through the
questionnaires. The data collected were statically determined through the use of measure of central
tendencies and chi-square (X' ) text. The study reveals that the objectives of the National Open
Apprenticeship Scheme upon which the evaluation was carried out were achieved. The recruitment of
trainees was carried out to adequately reflect the twenty local government areas of Lagos State. Thus,
there was wide coverage of the whole state under the scheme. The study also found out that the training
programme of NDE recognizes the training needs of the individual trainees. The study also revealed that
there is a significant difference between the graduate and the NDE training programme and their
counterparts in other vocational institutions. The study identifies some problems of NDE in the execution
of its programmes and made recommendations that could solve them
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