Fiber laser processing of amorphous rare earth NeFeB magnetic materials

Since the exchange coupling theory was proposed by Kneller and Hawig in 1991 there has been a significant effort within the magnetic materials community to enhance the performance of rare earth magnets by utilising nano-composite meta-materials. Inclusions of magnetically soft iron smaller than approximately 10 nm in diameter are exchange coupled to a surrounding magnetically hard Nd2Fe14B matrix and provide an enhanced saturisation magnetisation without reducing coercivity. For such a fine nanostructure to be produced, close control over the thermal history of the material is needed. A processing route which provides this is laser annealing from an amorphous alloy precursor. In the current work, relationships between laser parameters, thermal histories of laser processed amorphous stoichiometric NdFeB ribbons and the magnetic properties of the resulting nanocrystalline products have been determined with a view to applying the process to thick film nanocomposite magnet production.

In vitro osteoblast response to ferritic stainless steel fiber networks for magneto-active layers on implants

The use of a porous coating on prosthetic components to encourage bone ingrowth is an important way of improving uncemented implant fixation. Enhanced fixation may be achieved by the use of porous magneto-active layers on the surface of prosthetic implants, which would deform elastically on application of a magnetic field, generating internal stresses within the in-growing bone. This approach requires a ferromagnetic material able to support osteoblast attachment, proliferation, differentiation, and mineralization. In this study, the human osteoblast responses to ferromagnetic 444 stainless steel networks were considered alongside those to nonmagnetic 316L (medical grade) stainless steel networks. While both networks had similar porosities, 444 networks were made from coarser fibers, resulting in larger inter-fiber spaces. The networks were analyzed for cell morphology, distribution, proliferation, and differentiation, extracellular matrix production and the formation of mineralized nodules. Cell culture was performed in both the presence of osteogenic supplements, to encourage cell differentiation, and in their absence. It was found that fiber size affected osteoblast morphology, cytoskeleton organization and proliferation at the early stages of culture. The larger inter-fiber spaces in the 444 networks resulted in better spatial distribution of the extracellular matrix. The addition of osteogenic supplements enhanced cell differentiation and reduced cell proliferation thereby preventing the differences in proliferation observed in the absence of osteogenic supplements. The results demonstrated that 444 networks elicited favorable responses from human osteoblasts, and thus show potential for use as magnetically active porous coatings for advanced bone implant applications. © 2012 Wiley Periodicals, Inc.

Electrospun fiber - Hydrogel composites for nucleus pulposus tissue engineering

New materials are needed to replace degenerated intervertebral disc tissue and to provide longer-term solutions for chronic back-pain. Replacement tissue potentially could be engineered by seeding cells into a scaffold that mimics the architecture of natural tissue. Many natural tissues, including the nucleus pulposus (the central region of the intervertebral disc) consist of collagen nanofibers embedded in a gel-like matrix. Recently it was shown that electrospun micro- or nano-fiber structures of considerable thickness can be produced by collecting fibers in an ethanol bath. Here, randomly aligned polycaprolactone electrospun fiber structures up to 50 mm thick are backfilled with alginate hydrogels to form novel composite materials that mimic the fiber-reinforced structure of the nucleus pulposus. The composites are characterized using both indentation and tensile testing. The composites are mechanically robust, exhibiting substantial strain-to-failure. The method presented here provides a way to create large biomimetic scaffolds that more closely mimic the composite structure of natural tissue. © 2012 Materials Research Society.

A solid-phase microextraction fiber coated with diglycidyloxycalix[4]arene yields very high extraction selectivity and sensitivity during the analysis of chlorobenzenes in soil

A novel fiber coated with novel sol-gel (5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-diglycidyloxycalix[4]arene/hydroxy-terminated silicone oil; diglycidyloxy-C[4]/OH-TSO) was prepared for use with headspace solid-phase microextraction (HS-SPME) combined with gas chromatography (GC) and electron capture detection (ECD), which was applied in order to determine nine chlorobenzenes in soil matrices. Due to the improved fiber preparation, which increases the percentage of calixarene in the coating, the new calixarene fiber exhibits very high extraction selectivity and sensitivity to chlorine-substituted compounds. Various parameters affecting the extraction efficiency were optimized in order to maximize the sensitivity during the chlorobenzene analysis. Interferences from different soil matrices with different characteristics were investigated, and the amount extracted was strongly influenced by the matrix. Therefore, a standard addition protocol was performed on the real soil samples. The linear ranges of detection for the chlorobenzenes tested covered three orders of magnitude, and correlation coefficients > 0.9976 and relative standard deviations (RSD) < 8% were observed. The detection limits were found at sub-ng/g of soil levels, which were about an order of magnitude lower than those given by the commercial poly(dimethylsiloxane) (PDMS) coating for most of the compounds. The recoveries ranged from 64 to 109.6% for each analyte in the real kaleyard soil matrix when different concentration levels were determined over the linear range, which confirmed the reliability and feasibility of the HS-SPME/GC-ECD approach using the fiber coated with diglycidyloxy-C[4]/OH-TSO for the ultratrace analysis of chlorobenzenes in complex matrices.

Recent progresses of silicon-based optoelectronic devices for application in fiber communication

Si-based optoelectronic devices, including stimulated emission from Si diode, 1.3 and 1.5mum SiGe photodetector with quantum structures, 1GHz MOS optical modulator, SOI optical switch matrix and wavelength tunable filter are reviewed in the paper.

Impact of diode facet reflectivity on the fiber grating external cavity semiconductor laser

The scattering matrix method is used to analyze the multiple reflection effect between the laser diode facet and the fiber grating facet by considering the fiber grating external cavity laser diode (FGECL) as a four-mirror cavity laser. When neglecting other important parameters such as butt-coupling distance between the diode and the fiber facets, coupling efficiency, external cavity length, it is shown that low reflectivity is not a crucial factor for the laser characteristics such as SMSR. Experimentally high SMSR fiber grating external cavity laser is fabricated with a relatively large residual facet reflectivity (about 1%), which is coincident with our simulation results.

Optimization and comparison of single- and dual-pump fiber-optical parametric amplifiers with dispersion fluctuations

Solutions for fiber-optical parametric amplifiers (FOPAs) with dispersion fluctuations are derived using matrix operators. On the basis of the propagation matrix product and the hybrid genetic algorithm, we have optimized and compared single- and dual-pump FOPAs with zero-dispersion-wavelength variations. The simulations prove that the design of FOPAs involves multimodal function optimization problems. The numerical results show that dual-pump FOPAs are highly sensitive to dispersion fluctuations whereas dispersion variations have less impact on the gain of single-pump FOPAs. To increase signal gain and reduce ripple, dual-pump FOPAs, instead of single-pump FOPAs, have to be carefully optimized with a suitable multisegment fiber structure rather than a one-segment fiber structure. The different combinations of multisegment fibers can provide highly different gain properties. The increase in gain is at the cost of the ripple.

Sol-gel matrix modified microstructured optical fibre towards a fluoride sensitive optical probe

In this article, we report an optical fluoride probe based on microstructured polymer optical fibers (MPOFs) which is modified with morin-Al complex doped silica gel film. This probe is fabricated by sol-gel fluxion coating process. Sol solution doped with morin-Al is directly inhaled into array holes of MPOF and then forms morin-Al-gel matrix film in them. The sensing probe shows different fluorescence intensity to different fluoride ion concentrations in the aqueous solution. The range of response is 550 mmol/L, under the condition of pH 4.6. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

Theoretical Study on the Butt-coupling of Semiconductor Laser and Fiber Bragg Grating

The butt-coupling between a semiconductor laser diode and a fiber Bragg grating external cavity acts a key roll on the laser characteristics. The scatter matrix method considering the butt-coupling efficiency is used to analyze the butt-coupling between them. It is found that the butt-coupling distance and coupling efficiency determine the laser characteristics. For strong feedback, the single lasing wavelength changes in the reflection bandwidth of the effective reflectivity ( approximately the Bragg region of the fiber Bragg grating) as the distances change. For weak feedback condition, some different results are obtained. The SMSRs in the two conditions are presented and analyzed. These results can provide important design guidance of device parameters for the practical fabrication.

An eigenfunction expansion-variational method in prediction of the transverse thermal conductivity of fiber reinforced composites considering interfacial characteristics

An eigenfunction expansion-variational method based on a unit cell is developed to deal with the steady-state heat conduction problem of doubly-periodic fiber reinforced composites with interfacial thermal contact resistance or coating. The numerical results show a rapid convergence of the present method. The present solution provides a unified first-order approximation formula of the effective thermal conductivity for different interfacial characteristics and fiber distributions. A comparison with the present high-order results, available experimental data and micromechanical estimations demonstrates that the first-order approximation formula is a good engineering closed-form formula. An engineering equivalent parameter reflecting the overall influence of the thermal conductivities of the matrix and fibers and the interfacial characteristic on the effective thermal conductivity, is found. The equivalent parameter can greatly simplify the complicated relation of the effective thermal conductivity to the internal structure of a composite. (c) 2010 Elsevier Ltd. All rights reserved.

Explanation for Micromorphologies Around Broken Fibers in Fiber-Reinforced Composites

Experimental observations on micromorphologies around broken fibers in glass-fiber-reinforced epoxy matrix composites reveal different kinds of highly oriented patches at the circumambience of broken fibers, whereas the bulk of the matrix has been observed to be largely isotropic. These patches are interpreted to correlated areas where the stress gradients of the matrix are formed after fiber breaking, but the underlying cause for the orientation is still unknown. The authors have modified an embedded cell model to explain the experimental phenomena. The finite element simulation indicates that the surfaces around broken fibers display a change from an extension micromorphology to a mixed tension and shear micromorphology with the increase of applied strain.

Online study of the formation of PA6 droplets in PP matrix under shear flow

Breakup process of polyamide 6 (PA6) in polypropylene (PP) matrix under shear flow was online studied by using a Linkam CSS 450 stage equipped with optical microscopy. Both tip streaming and fracture breakup modes of PA6 droplets were observed in this study. It was reported that the droplet would break up by tip streaming model when the radio of the droplet phase viscosity to the matrix phase viscosity (n(r) = n(d)/n(m)) is smaller than 0.1 (Taylor, Proc R Soc London A 1934, 146, 501; Grace, Chem Eng Commun 1982, 14, 225; Bartok and Mason, J Colloid Sci 1959, 14, 13; Rumscheidt and Mason, J Colloid Sci 1961, 16, 238; de Bruijn, Chem Eng Sci 1993, 48, 277). However, the tip streaming model was observed even when the viscosity ratio was much greater than 0.1 (n(r) = 1.9). In this study for the tip streaming mode, small droplets were ruptured from the tip of the mother droplet. On the other hand, the mother droplet was broken into two or more daughter droplets with one or several satellite droplets between them for the fracture mode. It was found that PA6 droplet was much elongated at first, and then broke up via tip streaming or fracture to form daughter droplets or small satellite droplets with the shape of fiber or ellipse.

Co-electrospun poly(lactide-co-glycolide), gelatin, and elastin blends for tissue engineering scaffolds

In this study, we describe composite scaffolds composed of synthetic and natural materials with physicochemical properties suitable for tissue engineering applications. Fibrous scaffolds were co-electrospun from a blend of a synthetic biodegradable polymer (poly(lactic-co-glycolic acid), PLGA, 10% solution) and two natural proteins, gelatin (denatured collagen, 8% solution) and (x-elastin (20% solution) at ratios of 3:1:2 and 2:2:2 (v/v/v). The resulting PLGA-gelatin-elastin (PGE) fibers were homogeneous in appearance with an average diameter of 380 80 mn, which was considerably smaller than fibers made under identical conditions from the starting materials (PLGA, 780 +/- 200 nm; gelatin, 447 +/- 1.23 nm; elastin, 1060 170 nm). Upon hydration, PGE fibers swelled to an average fiber diameter of 963 +/- 132 nm, but did not disintegrate. Importantly, PGE scaffolds were stable in an aqueous environment without crosslinking, and were more elastic than those made of pure elastin fibers. To investigate the cytocompatibility of PGE, we cultured H9c2 rat cardiac myoblasts and rat bone marrow stromal cells (BMSCs) on fibrous PGE scaffolds. We found that myoblasts grew equally as well or slightly better on the scaffolds than on tissue-culture plastic. Microscopic evaluation confirmed that myoblasts reached confluence on the scaffold surfaces while simultaneously growing into the scaffolds.

Flexural fatigue behavior of injection-molded composites based on poly(phenylene ether ketone)

Flexural fatigue tests were conducted on injection-molded short fiber composites, carbon fiber/poly(phenylene ether ketone) (PEK-C) and glass fiber/PEK-C (with addition of polyphenylene sulfide for improving adhesion between matrix and fibers), using four-point bending at stress ratio of 0.1. The fatigue behavior of these materials was presented. By comparing the S-N curves and analyzing the fracture surfaces of the two materials, the similarity and difference of the failure mechanisms in the two materials were discussed. It is shown that the flexural fatigue failure of the studied materials is governed by their respective tensile properties. The matrix yielding is main failure mechanism at high stress, while at lower stress the fatigue properties appear fiber and interface dominated. (C) 1997 John Wiley & Sons, Inc.