Design of solar -powered grass trimmer

Common grass-cutter machines are operated by fuel and electrical energy, which are expensive, and need high maintenance. To keep environment clean and reduce use of fuel a solar powered grass trimmer has been designed in this research work. The purpose of this study is to design and fabricate a solar-powered grass trimmer which is affordable, easy to operate and environment friendly. The grass trimmer uses a 12V, - 100AH battery to power a 12V DC motor of 180W. A solar panel 1 000V system voltage is used to charge the battery. A solar charge controller of 20A is used to control the energy into the battery. The machine uses sheet metal blade to cut the grass. It can run for almost two hours when fully charged and there is no sun. It is easy to tell if the battery is fully charged or flat.Mechanical and Industrial Engineerin

First-principles calculation of positron lifetimes and affinities in perfect and imperfect transition-metal carbides and nitrides

First-principles electronic structure and positron-state calculations for transition-metal carbides and nitrides are performed. Perfect NaCl structures as well as structures with metal or carbon/nitrogen vacancies are considered. The positron affinities and lifetimes are determined. The trends are discussed and the results are compared with recent positron lifetime measurements for group-IV and -V refractory metal carbides. The present analysis suggests, contradictory to an earlier interpretation, that positrons are trapped and annihilated at both carbon and metal vacancies. The concentration of metal vacancies detected by positron annihilation methods is probably very low, below the sensitivity limit of other experimental methods.Peer reviewe

Vacancies and vacancy-oxygen complexes in silicon: Positron annihilation with core electrons

ABSTRACT: Various point defects in silicon are studied theoretically from the point view of positron annihilation spectroscopy. Properties of a positron trapped at a single vacancy, divacancy, vacancy-oxygen complexes (VOn), and divacancy-oxygen complex are investigated. In addition to the positron lifetime and positron binding energy to defects, we also calculate the momentum distribution of annihilation photons (MDAP) for high momenta, which has been recently shown to be a useful quantity for defect identification in semiconductors. The influence of atomic relaxations around defects on positron properties is also examined. Mutual differences among the high momentum parts of the MDAP for various defects studied are mostly considerable, which can be used for the experimental defect determination

Ab-initio investigation of phonon dispersion and anomalies in palladium

In recent years, palladium has proven to be a crucial component for devices ranging from nanotube field effect transistors to advanced hydrogen storage devices. In this work, I examine the phonon dispersion of fcc Pd using first principle calculations based on density functional perturbation theory. While several groups in the past have studied the acoustic properties of palladium, this is the first study to reproduce the phonon dispersion and associated anomaly with high accuracy and no adjustable parameters. In particular, I focus on the Kohn anomaly in the [110] direction.Comment: 19 pages, preprint format, 7 figures, added new figures and discussio

Evaluation of some basic positron-related characteristics of SiC

First-principles electronic structure and positron-state calculations for perfect and defected 3C- and 6H-SiC polytypes of SiC have been performed. Monovacancies and divacancies have been treated; the influence of lattice position and nitrogen impurities have been considered in the former case. Positron affinities and binding energies have been calculated; trends are discussed, and the results compared with recent atomic superposition method calculations. Experimental determination of the electron and positron work functions of the same 6H-SiC allows an assessment of the accuracy of the present first-principles calculations, and to suggest further improvements. © 1996 The American Physical Society.Peer reviewe

Morphometric characterisation of indigenous taurine cattle in their natural environment in Cameroon

The morphometric characterisation of indigenous taurine breeds of cattle in their natural environment was undertaken in three agroecological zones of Cameroon. Descriptive traits for 97 animals, such as sex, age, coat colour, skin pigmentation, ear shape, and temperament, were observed visually and recorded for each breed identified. Biometric information was got by measuring body parts such as live weight (LW), body length (BoL), ear length (EL), head length (HL), heart girth (HG), neck length (NL), horn length (HoL), height at wither (HW) and thigh diameter (TD). There was a strong association (P0.0001) between the breed and the localities. Bakossi breed were dominated by a black/white coat colour while Namchi and Kapsiki breed demonstrated a high coat colour polymorphism. All the taurine had dark skin pigmentation, and 60.83% were docile. Their LW ranged from 199.9 kg (Namchi) to 229.9 kg (Kapsiki), BoL from 116.6 cm (Namchi) to 121.4 cm (Kapsiki), tail length (TL) from 11.1 cm (Kapsiki) to 17.4 cm (Bakossi), HG from 134.4 cm (Namchi) to 142.7 cm (Kapsiki), HoL from 21.4 cm (Bakosi) to 27.3cm (Kapsiki), and HW from 105.0 cm (Namchi) to 116.9 cm (Kapsiki). Apart from LW, BoL, and shoulder length, the other linear body measurements presented significant differences between breeds (0.05, 0.01). This study provides new information regarding the qualitative and quantitative traits of taurine breeds in Cameroon. Therefore, deep molecular characterisation should be carried out to confirm the breed’s types and possible admixtur

Phase stability and elasticity of C15 transition-metal intermetallic compounds

First-principle quantum mechanical calculations based on the local-density-functional theory have been performed to study the electronic, physical and metallurgical properties of C15 intermetallics MV{sub 2} (M = Zr, Hf, or Ta). The elastic constants of C15 HfV{sub 2} + Nb were measured by the resonant ultrasound spectroscopy technique. The phase stability of C15 HfV{sub 2} + Nb was studied by specific heat measurements and by transmission electron microscopy in a low temperature specimen holder. The total energies and their lattice volume dependence were used to obtain the equilibrium lattice constants and bulk modulus. The band structures at the X-point near the Fermi level were employed to understand the anomalous temperature dependence of shear modulus of the C15 intermetallics. It was found that the double degeneracy with a linear dispersion relation of electronic levels at the X-point near the Fermi surface is mainly responsible for the C15 anomalous elasticity. The density of states at the Fermi level, N(E{sub F}), and the Fermi surface geometry were obtained to understand the low temperature phase instability of C15 HfV{sub 2} and ZrV{sub 2} and the stability of C15 TaV{sub 2}. It was proposed that the large N(E{sub F}) and Fermi surface nesting are the physical reasons for the structural instability of the C15 HfV{sub 2} and ZrV{sub 2} at low temperatures. The relation between anomalous elasticity and structural instability of C15 HfV{sub 2} and ZrV{sub 2} is also discussed

Ab initio Investigation of Elasticity and Stability of Metal Aluminum

On the basis of the pseudopotential plane-wave(PP-PW) method in combination with the local-density-functional theory(LDFT), complete stress-strain curves for the uniaxial loading and uniaxial deformation along the [001] and [111] directions, and the biaxial proportional extension along [010] and [001] of aluminium are obtained. During the uniaxial loading, certain general behaviors of energy versus stretch and the load versus the stretch are confirmed; in each acse, there exist three special unstressed structures: f.c.c., b.c.c. and f.c.t. for [001]; f.c.c., s.c. and b.c.c. for [111]. Using stability criteria, we find that all of these state are unstable, and always occur together with shear instability, except the natural f.c.c. structure. A Bain transformation from the stable f.c.c. structure to the stable b.c.c. configuration cannot be obtained by uniaxial compression along any equivalent [001] and [111] direction. The tensile strength are similar for the two directions. For the higher energy barrier of [111] direction, the compressive strength is greater than that for the [001] direction. With increase in the ratio of the biaxial proportional extension, the stress and tensile strength increase; however, the critical strain does not change significantly. Our results add to the existing ab initio database for use in fitting and testing interatomic potentials.Comment: 9 Pages in Revtex and 11 Eps figure

Many-body aspects of positron annihilation in the electron gas

We investigate positron annihilation in electron liquid as a case study for many-body theory, in particular the optimized Fermi Hypernetted Chain (FHNC-EL) method. We examine several approximation schemes and show that one has to go up to the most sophisticated implementation of the theory available at the moment in order to get annihilation rates that agree reasonably well with experimental data. Even though there is basically just one number to look at, the electron-positron pair distribution function at zero distance, it is exactly this number that dictates how the full pair distribution behaves: In most cases, it falls off monotonously towards unity as the distance increases. Cases where the electron-positron pair distribution exhibits a dip are precursors to the formation of bound electron--positron pairs. The formation of electron-positron pairs is indicated by a divergence of the FHNC-EL equations, from this we can estimate the density regime where positrons must be localized. This occurs in our calculations in the range 9.4 <= r_s <=10, where r_s is the dimensionless density parameter of the electron liquid.Comment: To appear in Phys. Rev. B (2003

Effects of anharmonic strain on phase stability of epitaxial films and superlattices: applications to noble metals

Epitaxial strain energies of epitaxial films and bulk superlattices are studied via first-principles total energy calculations using the local-density approximation. Anharmonic effects due to large lattice mismatch, beyond the reach of the harmonic elasticity theory, are found to be very important in Cu/Au (lattice mismatch 12%), Cu/Ag (12%) and Ni/Au (15%). We find that is the elastically soft direction for biaxial expansion of Cu and Ni, but it is for large biaxial compression of Cu, Ag, and Au. The stability of superlattices is discussed in terms of the coherency strain and interfacial energies. We find that in phase-separating systems such as Cu-Ag the superlattice formation energies decrease with superlattice period, and the interfacial energy is positive. Superlattices are formed easiest on (001) and hardest on (111) substrates. For ordering systems, such as Cu-Au and Ag-Au, the formation energy of superlattices increases with period, and interfacial energies are negative. These superlattices are formed easiest on (001) or (110) and hardest on (111) substrates. For Ni-Au we find a hybrid behavior: superlattices along and like in phase-separating systems, while for they behave like in ordering systems. Finally, recent experimental results on epitaxial stabilization of disordered Ni-Au and Cu-Ag alloys, immiscible in the bulk form, are explained in terms of destabilization of the phase separated state due to lattice mismatch between the substrate and constituents.Comment: RevTeX galley format, 16 pages, includes 9 EPS figures, to appear in Physical Review