Remanence of Ni nanowire arrays: Influence of size and labyrinth magnetic structure

The influence of the macroscopic size of the Ni nanowire array system on their remanence state has been investigated. A simple magnetic phenomenological model has been developed to obtain the remanence as a function of the magnetostatic interactions in the array. We observe that, due to the long range of the dipolar interactions between the wires, the size of the sample strongly influence the remanence of the array. On the other hand, the magnetic state of nanowires has been studied by variable field magnetic force microscopy for different remanent states. The distribution of nanowires with the magnetization in up or down directions and the subsequent remanent magnetization has been deduced from the magnetic images. The existence of two short-range magnetic orderings with similar energies can explain the typical labyrinth pattern observed in magnetic force microscopy images of the nanowire arrays

Single magnetic molecule between conducting leads: Effect of mechanical rotations

We study spin-rotation effects in a magnetic molecule bridged between two conducting leads. Dynamics of the total angular momentum couples spin tunneling to the mechanical rotations. Landau-Zener spin transition produced by the time-dependent magnetic field generates a unique pattern of mechanical oscillations that can be detected by measuring the electronic tunneling current through the molecule.Comment: 5 pages, 2 figure

Measurement of streaming potential coupling coefficient in sandstones saturated with natural and artificial brines at high selenity

We report experimental measurements of the streaming potential coupling coefficient in sandstones saturated with NaCl-dominated artificial and natural brines up to 5.5 M (321.4 g L−1 of NaCl; electrical conductivity of 23 S m−1). We find that the magnitude of the coupling coefficient decreases with increasing brine salinity, as observed in previous experimental studies and predicted by models of the electrical double layer. However, the magnitude of the coupling coefficient remains greater than zero up to the saturated brine salinity. The magnitude of the zeta potential we interpret from our measurements also decreases with increasing brine salinity in the low-salinity domain (0.4 M). We hypothesize that the constant value of zeta potential observed at high salinity reflects the maximum packing of counterions in the diffuse part of the electrical double layer. Our hypothesis predicts that the zeta potential becomes independent of brine salinity when the diffuse layer thickness is similar to the diameter of the hydrated counterion. This prediction is confirmed by our experimental data and also by published measurements on alumina in KCl brine. At high salinity (>0.4 M), values of the streaming potential coupling coefficient and the corresponding zeta potential are the same within experimental error regardless of sample mineralogy and texture and the composition of the brine

Dynamics of Einstein - de Haas Effect: Application to Magnetic Cantilever

Local time-dependent theory of Einstein - de Haas effect is developed. We begin with microscopicinteractions and derive dynamical equations that couple elastic deformations with internal twists due to spins. The theory is applied to the description of the motion of a magnetic cantilever caused by the oscillation of the domain wall. Theoretical results are compared with a recent experiment on Einstein - de Haas effect in a microcantilever.Comment: 7 PR pages, 5 figures, submitted to PR

Tailoring the magnetic properties of Fe asymmetric nanodots

Asymmetric dots as a function of their geometry have been investigated using three-dimensional (3D) object oriented micromagnetic framework (OOMMF) code. The effect of shape asymmetry of the disk on coercivity and remanence is studied. Angular dependence of the remanence and coercivity is also addressed. Asymmetric dots are found to reverse their magnetization by nucleation and propagation of a vortex, when the field is applied parallel to the direction of asymmetry. However, complex reversal modes appear when the angle at which the external field is applied is varied, leading to a non monotonic behavior of the coercivity and remanence.Comment: 5 pages, 7 figure

Influence of torsion on the inelastic response of three-dimensional r.c. frames

A three-dimensional reinforced concrete framed building was modelled using finite element method. Two types of elements, the beam-column element and flat shell element were used for modelling the frame and floor slabs, respectively. A computer program has been developed for the analysis of 3D framed building by integrating the finite element and stiffness method. The lumped inelasticity model with three-dimensional point hinges at the ends of the beam-column element was implemented. A yield surface for a reinforced section of the member subjected to simultaneous actions of biaxial bending, torsion and axial forces was evolved. The developed yield surface integrated with the theory of plasticity was used to develop a suitable procedure for inelastic analysis of three-dimensional problems with the floor slab assumed to remain elastic throughout the analysis. The inelastic procedure is able to predict the sequential formation of plastic hinges in the frame members and the continuous deterioration of the stiffness of the frame. A single storey one bay reinforced concrete space frame was analysed for twist loading to study the inelastic response of the reinforced concrete frame. The results indicate that, the consideration of torsion in defining the yielding surface plays a significant role in the inelastic behaviour and estimation of failure load for reinforced concrete frames under torsional loading

Strength Estimation of Concrete in Different Environments Using UPV

Deterioration of concrete in a structure is a result of several internal and external degradation mechanisms which decrease the strength or the integrity of the structure. This paper presents results of use of non-destructive ultrasonic pulse velocity tests (UPV) to determine the strength of concrete in three different environments, namely oven-dry, air-dry and saturated conditions, as the full potential of UPV in different environments is still not fully explored. Moisture is known to have a significant effect on ultrasonic pulse velocity. In order to improve the efficiency of UPV in estimating the concrete strength, the degree of moisture present in the concrete i.e. the physical condition of the concrete is to be considered. Pulse velocity path in the different physical conditions of concrete also has to be examined. In the present investigations, four different grades of concrete in three different environments were considered. Extensive series of tests were carried out in the laboratory to obtain a correlation of the UPV test results with the actual compressive strength of concrete. A total of 108 cubes were cast. The cement used was the ordinary Portland cement and the coarse aggregate consisted of granite with the maximum aggregate size of 19mm as is generally used in conventional RC structures. The DOE-method of mix-design was used to design four different grades of concrete in order to simulate concrete strengths found in practice. Test results indicated that the presence of moisture in concrete changes the UPV values significantly. The UPV tests through the direct transmission measurements display better estimates compared to the indirect measurements. Exponential expressions have been proposed for the strength estimation of concrete under oven dry and air dry conditions

Development of an innovative interlocking load bearing hollow block system in Malaysia

The paper describes the development of a new interlocking hollow block masonry system appropriate for load bearing masonry wall construction. The developed system is an alternative to the traditional bonded masonry system where the blocks in the wall are integrated through mortar layers. In the system developed, the blocks are stacked on one another and three-dimensional interlocking protrusions are provided in the blocks to integrate the blocks into walls. This paper includes the background, concept and procedure used to develop an efficient interlocking hollow block system, which may be used in the construction of load bearing walls. Twenty-one different block models have been investigated and analysed with respect to weight, bearing and shear areas, shape, ease of production, ability to accommodate vertical and horizontal reinforcing stabilising ties and efficiency of the interlocking mechanism under imposed loads. The blocks, developed under the name ‘PUTRA BLOCK’, have been used to construct a single-storey house at Universiti Putra Malaysia. The system provides a fast, easy and an accurate building system