Barkhausen jumps and related magnetic properties of iron nanowires encapsulated in aligned carbon nanotube bundles

Iron nanowires encapsulated in aligned carbon nanotube bundles show interesting magnetic properties. Besides the increased coercivity, Barkhausen jumps with 5 emu/g steps in magnetization are observed due to magnetization reversal or depinning of domains. (C) 2002 Elsevier Science B.V. All rights reserved.

Hydrothermal synthesis and structure of organically templated one-dimensional and three-dimensional iron fluorophosphate

Two new open-framework iron fluorophosphates, [C(4)N(2)H(12)](0.5) [FeF(HPO(4))(H(2)PO(4))] (I) and [C(4)N(2)H(12)][Fe(4)F(2)(H(2)O)(4)(PO(4))(4)]. 0.5H(2)O (II), were synthesized hydrothermally using piperazine as a templating agent. The structures were determined by single-crystal X-ray diffraction. Compound I crystallizes in the orthorhombic space group Pbca, a = 7.2126(2) Angstrom, b = 14.2071(4) Angstrom, c = 17.1338(2) Angstrom, Z = 8. The structure is composed of infinite anionic chains of [FeF(HPO(4))(H(2)PO(4))](n)(-) built by trans-fluorine sharing FeF(2)O(4) octahedra. These chains are similar to those found in tancoite-type minerals. Compound II crystallizes in the monoclinic space group P2(1)/n, a = 9.9045(3) Angstrom, b = 12.3011(3) Angstrom, c = 17.3220(4) Angstrom, beta = 103.7010(10)degrees, Z = 4. The structure of compound II has a three-dimensional (3D) architecture with an eight-membered channel along the b axis, in which protonoted piperazine molecules reside. The complex framework is built from two types of secondary building unit (SBU): one hexamer [Fe(3)F(2)(H(2)O)(2)(PO(4))(3)] (SBU6), and one dimer [FeO(4)(H(2)O)(2)PO(4)] (SBU2). The vertex sharing between these SBUs create the 3D structure.

Axially homogeneous, zero mean flow buoyancy-driven turbulence in a vertical pipe

We report an experimental study of a new type of turbulent flow that is driven purely by buoyancy. The flow is due to an unstable density difference, created using brine and water, across the ends of a long (length/diameter=9) vertical pipe. The Schmidt number Sc is 670, and the Rayleigh number (Ra) based on the density gradient and diameter is about 108. Under these conditions the convection is turbulent, and the time-averaged velocity at any point is ‘zero’. The Reynolds number based on the Taylor microscale, Reλ, is about 65. The pipe is long enough for there to be an axially homogeneous region, with a linear density gradient, about 6–7 diameters long in the midlength of the pipe. In the absence of a mean flow and, therefore, mean shear, turbulence is sustained just by buoyancy. The flow can be thus considered to be an axially homogeneous turbulent natural convection driven by a constant (unstable) density gradient. We characterize the flow using flow visualization and particle image velocimetry (PIV). Measurements show that the mean velocities and the Reynolds shear stresses are zero across the cross-section; the root mean squared (r.m.s.) of the vertical velocity is larger than those of the lateral velocities (by about one and half times at the pipe axis). We identify some features of the turbulent flow using velocity correlation maps and the probability density functions of velocities and velocity differences. The flow away from the wall, affected mainly by buoyancy, consists of vertically moving fluid masses continually colliding and interacting, while the flow near the wall appears similar to that in wall-bound shear-free turbulence. The turbulence is anisotropic, with the anisotropy increasing to large values as the wall is approached. A mixing length model with the diameter of the pipe as the length scale predicts well the scalings for velocity fluctuations and the flux. This model implies that the Nusselt number would scale as Ra1/2Sc1/2, and the Reynolds number would scale as Ra1/2Sc−1/2. The velocity and the flux measurements appear to be consistent with the Ra1/2 scaling, although it must be pointed out that the Rayleigh number range was less than 10. The Schmidt number was not varied to check the Sc scaling. The fluxes and the Reynolds numbers obtained in the present configuration are much higher compared to what would be obtained in Rayleigh–Bénard (R–B) convection for similar density differences.

An Improved Compact Compliant Mechanism for an External Pipe-Crawler

An external pipe-crawling device presented in this paper aids the inspection of pipes in hazardous environments and areas inaccessible to humans. The principal component of our design, which uses inchworm type motion, is a compliant ring mechanism actuated using shape memory alloy (SMA) wire. It was fabricated and tested and was reported in our earlier work. But this device had a drawback of low crawling speed (about 1 mm/min) owing to the delay in heating and cooling of the SMA strips in the linear actuation. Additionally, that design also had the difficulties of mounting on pipes with closed ends, large radial span, and the need for housing for electrical insulation and guiding of the SMA wire. In this paper we present a compact design that overcomes the difficulties of the earlier design. In particular, we present a compact compliant mechanism with two halves so as to enable mounting and un-mounting on any closed or open pipe. Another feature is the presence of insulation and guiding of the SMA wire without housing. This design results in a reduction of the radial span of the ring from 22 mm to 12 mm, and the stiffness of the mechanism and the SMA wire are matched. An SMA helical spring is to used in the place of an SMA strip to increase the crawling speed of the device. A microcontroller-based circuitry is also fitted to cyclically.activate the SMA wires and springs.

Influence of homogenization on the processing map for hot working of as-cast Mg-2Zn-1Mn alloy

Processing maps have been developed for hot deformation of Mg-2Zn-1Mn alloy in as-cast condition and after homogenization with a view to evaluate the influence of homogenization. Hot compression data in the temperature range 300-500degreesC and strain rate range 0.001-100 s(-1) were used for generating the processing map. In the map for the as-cast alloy the domain of dynamic recrystallization occurring, at 450degreesC and 0.1 s(-1) has merged with another domain occurring at 500degreesC and 0.001 s(-1) representing grain boundary cracking. The latter domain is eliminated by homogenization and the dynamic recrystallization domain expanded with a higher peak efficiency occurring at 500 degreesC and 0.05 s(-1). The flow localization occurring at strain rates higher than 5 s(-1) is unaffected by homogenization.

Studies of the wetting characteristics of liquid iron on dense alumina by the X-ray sessile drop technique

In the present work, the reaction between a molten iron drop and dense alumina was studied using the X-ray sessile-drop method under different oxygen partial pressures in the gas atmosphere. The changes in contact angles between the iron drop and the alumina substrate were followed as functions of temperature and varying partial pressures of oxygen in the temperature range 1823 to 1873 K both in static and dynamic modes. The results of the contact angle measurements with pure iron in contact with dense alumina in extremely well-purified argon as well as under different oxygen partial pressures in the gas atmosphere showed good agreement with earlier measurements reported in the literature. In the dynamic mode, when argon was replaced by a CO-CO2-Ar mixture with a well-defined PO, in the gas, the contact angle showed an initial decrease followed by a period of nearly constant contact angle. At the end of this period, the length of which was a function of the P-O2 imposed, a further steep decrease in the contact angle was noticed. An intermediate layer of FeAl2O4 was detected in the scanning electron microscope (SEM) analysis of the reacted substrates. An interesting observation in the present experiments is that the iron drop moved away from the site of the reaction once the product layer covered the interface. The results are analyzed on the basis of the various forces acting on the drop.

Rule-based modelling of iron homeostasis in tuberculosis

To establish itself within the host system, Mycobacterium tuberculosis (Mtb) has formulated various means of attacking the host system. One such crucial strategy is the exploitation of the iron resources of the host system. Obtaining and maintaining the required concentration of iron becomes a matter of contest between the host and the pathogen, both trying to achieve this through complex molecular networks. The extent of complexity makes it important to obtain a systems perspective of the interplay between the host and the pathogen with respect to iron homeostasis. We have reconstructed a systems model comprising 92 components and 85 protein-protein or protein-metabolite interactions, which have been captured as a set of 194 rules. Apart from the interactions, these rules also account for protein synthesis and decay, RBC circulation and bacterial production and death rates. We have used a rule-based modelling approach, Kappa, to simulate the system separately under infection and non-infection conditions. Various perturbations including knock-outs and dual perturbation were also carried out to monitor the behavioral change of important proteins and metabolites. From this, key components as well as the required controlling factors in the model that are critical for maintaining iron homeostasis were identified. The model is able to re-establish the importance of iron-dependent regulator (ideR) in Mtb and transferrin (Tf) in the host. Perturbations, where iron storage is increased, appear to enhance nutritional immunity and the analysis indicates how they can be harmful for the host. Instead, decreasing the rate of iron uptake by Tf may prove to be helpful. Simulation and perturbation studies help in identifying Tf as a possible drug target. Regulating the mycobactin (myB) concentration was also identified as a possible strategy to control bacterial growth. The simulations thus provide significant insight into iron homeostasis and also for identifying possible drug targets for tuberculosis.

Form, Content, and Magnetism in Iron Oxide Nanocrystals

Monodisperse iron oxide nanocrystals with spherical and cubic morphologies, of comparable dimensions, have been prepared by the thermal decomposition of FeOOH. The lattice spacings of both forms agree with that of magnetite, Fe(3)O(4). The two, however, exhibit very different blocking temperatures. Nanocrystals of cubic morphology are superparamagnetic above 190 K while the spherical nanocrystals at a lower temperature, 142 K. The higher blocking temperatures in particles of cubic morphology are shown to be a consequence of exchange bias fields. We show that in the present iron oxide nanocrystals the exchange bias fields originate from the presence of trace amounts of wustite, FeO. A Reitveld refinement analysis of the X-ray diffraction patterns shows that nanocrystals of cubic morphology have a higher FeO content. The higher FeO content is responsible for the larger exchange bias fields that in turn lead to a higher blocking temperature for nanocrystals with cubic morphology.

Threshold-like features in the magnetic response of iron-filled multi-walled carbon nanotube and polymer composite

The magnetic properties of iron-filled multi-walled carbon nanotubes dispersed in polystyrene (Fe-MWNT/PS) have been investigated as a function of Fe-MWNT concentration (0.1-15 wt%) from 300 to 10 K. Electron microscopy studies indicate that Fe nanorods (aspect ratio similar to 5) remain trapped at various lengths of MWNT and are thus, prevented from oxidation as well as aggregation. The magnetization versus applied field (M-H loop) data of 0.1 wt% of Fe-MWNTs in PS show an anomalous narrowing at low temperatures which is due to the significant contribution from shape anisotropy of Fe nanorods. The remanence shows a threshold feature at 1 wt%. The enhanced coercivity shows a maximum at 1 wt% due to the dominant dipolar interactions among Fe nanorods. Also the squareness ratio shows a maximum at 1 wt%.