A nanoporous molecular magnet with reversible solvent-induced mechanical and magnetic properties

Interest in metal-organic open-framework structures has increased enormously in the past few years because of the potential benefits of using crystal engineering techniques to yield nanoporous materials with predictable structures and interesting properties. Here we report a new efficient methodology for the preparation of metal-organic open-framework magnetic structures based on the use of a persistent organic free radical (PTMTC), functionalized with three carboxylic groups. Using this approach, we create an open-framework structure Cu3(PTMTC)2(py)6(CH3CH2OH)2(H2O), which we call MOROF-1, combining very large pores (2.8-3.1 nm) with bulk magnetic ordering. MOROF-1 shows a reversible and highly selective solvent-induced 'shrinking-breathing' process involving large volume changes (25-35%) that strongly influence the magnetic properties of the material. This magnetic sponge-like behaviour could be the first stage of a new route towards magnetic solvent sensors.     

Effect of Magnetized Ethanol on the Shape Evolution of Zinc Oxide from Nanoparticles to Microrods: Experimental and Molecular Dynamic Simulation Study

In the current research, ethanol was exposed to an external magnetic field, called magnetized ethanol, and then, used as a solvent in the solvothermal method to synthesize various ZnO structures. Moreover, the morphologies of the synthesized structures are compared with those obtained using ordinary ethanol. The attained results evidently demonstrated the formation of ZnO nanoparticles and microrods by using ordinary and magnetized ethanol, respectively. Moreover, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized for characterizing the synthesized ZnO structures. The XRD results demonstrated that the synthesized products are in Zincite hexagonal phase. Besides, molecular dynamics simulation suggested that the molecular mobility is diminished upon using the magnetic field. It was found that the interactions among ZnO particles were enhanced by the slight increase in the magnetic field while the number of interactions between ZnO and solvent was reduced revealing the magnetic-field-induced particle growth from the molecular level insight.     

Differences of internal structures between amphiphilic and hydrophobic block-copolymer nanoparticles

In this report, we show a novel and simple preparation method for obtaining block-copolymer nanoparticles. Regular-sized polymer nanoparticles are formed after evaporation of a good solvent from a polymer solution containing a non-volatile poor solvent and the volatile good solvent. Nanoparticles of poly(styrene-b-sodium acrylate), poly(styrene-b-4-vinylpyridine), and poly(styreneb-isoprene) were prepared by using this method. We also discuss the difference of internal structures between amphiphilic and hydrophobic block-copolymer nanoparticles. From the results of scanning transmission electron microscope (STEM) imaging, the particles of amphiphilic block-copolymers have hollow structures were observed. On the other hand, the particles of a hydrophobic block-copolymer form lamellar micro-phase separation structures.     

Self-assembly of colloidal nanocrystals as route to novel classes of nanostructured materials

Colloidal crystallisation is the only way to obtain three-dimensional ordered materials in which semiconductor, metallic, and magnetic nanocrystals are in close contact. It is expected that the quantum mechanical and dipolar interactions between the nanocrystal units can lead to unseen physical phenomena and materials. Here we review the development of this new and exciting field. We first compare nanocrystal superlattices with regular atomic solids regarding their mechanical strength and opto-electronic properties. We describe how nanocrystal superlattices have been obtained from colloid suspensions in several ways. The thermodynamic driving force for colloidal crystallisation is discussed in terms of inter-particle interactions in a good solvent and entropy. We compare the binary superlattices that have been obtained by solvent evaporation with the predictions of the hard-sphere model and show that semiconductor nanocrystals in a good solvent can behave as hard spheres. Finally, we discuss the quantum mechanical and dipolar interactions in nanocrystal superlattices and review recent studies of the opto-electronic and magnetic properties of novel superlattice materials.     

Poly(vinylpyrrolidone) coated iron nanoparticles in polar aprotic solvent

Poly(vinylpyrrolidone) (PVP) coated iron nanoparticles which show well-defined core-shell structures have been successfully synthesized in a polar aprotic solvent. In this approach, PVP was employed not as capping agent, but as coating polymer directly applied to the metallic (iron) core nanoparticles. The morphologies, structures, compositions and magnetic properties of the products were investigated by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS), SQUID magnetometry and FTIR spectroscopy.     

Digital imaging-based three-dimensional characterization of flame front structures in a turbulent flame

This paper focuses on the application of a multicamera imaging system for three-dimensional (3-D) visualization and quantitative characterization of the flame front structures of a turbulent flame. The 2-D images of the flame front are captured simultaneously using identical monochromatic CCD cameras from three different directions around the flame. Dedicated computing algorithms have been developed to reconstruct the 3-D structures of the flame front using various image processing techniques such as edge detection, contour extraction, and mesh generation. A set of flame parameters, including ignition points, ignition volume, ignition surface area, and circularity, is determined from the models generated to characterize the flame front. Results obtained under a range of combustion conditions demonstrate the capability of the system for 3-D quantitative characterization of flame front structures.     

Occupational exposure to electromagnetic fields in physiotherapy departments

To assess occupational exposure to electromagnetic fields, 11 microwave (MW), 4 short-wave diathermy and 15 magneto therapy devices were analysed in eight physiotherapy departments. Measurements taken at consoles and environmental mapping showed values above European Directive 2004/40/EC and ACGIH exposure limits at approximately 50 cm from MW applicators (2.45 GHz) and above the Directive magnetic field limit near the diathermy unit (27.12 MHz). Levels in front of MW therapy applicators decreased rapidly with distance and reduction in power; this may not always occur in work environments where nearby metal structures (chairs, couches, etc.) may reflect or perturb electromagnetic fields. Large differences in stray field intensities were found for various MW applicators. Measurements of power density strength around MW electrodes confirmed radiation fields between 30 degrees and 150 degrees , with a peak at 90 degrees , in front of the cylindrical applicator and maximum values between 30 degrees and 150 degrees over the whole range of 180 degrees for the rectangular parabolic applicator. Our results reveal that although most areas show substantially low levels of occupational exposure to electromagnetic fields in physiotherapy units, certain cases of over-occupational exposure limits do exist.     

Self-assembly routes towards creating superconducting and magnetic arrays

Using self-assembly from colloidal suspensions of polystyrene latex spheres we prepared well-ordered templates. By electrochemical deposition of magnetic and superconducting metals in the pores of such templates highly ordered magnetic and superconducting anti-dot nano-structures with 3D architectures were created. Further developments of this template preparation method allow us to obtain dot arrays and even more complicated structures. In magnetic anti-dot arrays we observe a large increase in coercive field produced by nanoscale (50–1000nm) holes. We also find the coercive field to demonstrate an oscillatory dependence on film thickness. In magnetic dot arrays we have explored the genesis of 3D magnetic vortices and determined the critical dot size. Superconducting Pb anti-dot arrays show pronounced Little-Parks oscillations in T_c and matching effects in magnetization and magnetic susceptibility. The spherical shape of the holes results in significantly reduced pinning strength as compared to standard lithographic samples. Our results demonstrate that self-assembly template methods are emerging as a viable, low cost route to prepare sub-micron structures.     

Self-assembly Routes towards Creating Superconducting and Magnetic Arrays

No Heading Using self-assembly from colloidal suspensions of polystyrene latex spheres we prepared well-ordered templates. By electrochemical deposition of magnetic and superconducting metals in the pores of such templates highly ordered magnetic and superconducting anti-dot nano-structures with 3D architectures were created. Further developments of this template preparation method allow us to obtain dot arrays and even more complicated structures. In magnetic anti-dot arrays we observe a large increase in coercive field produced by nanoscale (50–1000nm) holes. We also find the coercive field to demonstrate an oscillatory dependence on film thickness. In magnetic dot arrays we have explored the genesis of 3D magnetic vortices and determined the critical dot size. Superconducting Pb anti-dot arrays show pronounced Little-Parks oscillations in Tc and matching effects in magnetization and magnetic susceptibility. The spherical shape of the holes results in significantly reduced pinning strength as compared to standard lithographic samples. Our results demonstrate that self-assembly template methods are emerging as a viable, low cost route to prepare sub-micron structures.PACS numbers: 74.25Ha, 75.75+a.     

Local Study of Magnetic Structures in High-Temperature Superconducting Composites

The results of magneto-optical investigations of the magnetization processes in high-temperature superconducting coated conductor composites are presented. The studies were performed in the temperature range of 4–80 K. It is shown that the re-magnetization of composites in external magnetic field is accompanied by formation and propagation of the magnetic flux annihilation waves (areas with zero magnetic induction). The relationship between penetration depth of annihilation front and the value of external magnetic field at different temperatures as well as temperature dependence of the rate of magnetic flux annihilation front motion are found. The experimental data agree qualitatively with the results of numerical calculations performed by using the Monte Carlo method.     

A geometric flow-based approach for diffusion tensor image segmentation

Diffusion tensor magnetic resonance imaging (DT-MRI, shortened as DTI) produces, from a set of diffusion-weighted magnetic resonance images, tensor-valued images where each voxel is assigned a 3x3 symmetric, positive-definite matrix. This tensor is simply the covariance matrix of a local Gaussian process with zero mean, modelling the average motion of water molecules. We propose a three-dimensional geometric flow-based model to segment the main core of cerebral white matter fibre tracts from DTI. The segmentation is carried out with a front propagation algorithm. The front is a three-dimensional surface that evolves along its normal direction with speed that is proportional to a linear combination of two measures: a similarity measure and a consistency measure. The similarity measure computes the similarity of the diffusion tensors at a voxel and its neighbouring voxels along the normal to the front; the consistency measure is able to speed up the propagation at locations where the evolving front is more consistent with the diffusion tensor field, to remove noise effect to some extent, and thus to improve results. We validate the proposed model and compare it with some other methods using synthetic and human brain DTI data; experimental results indicate that the proposed model improves the accuracy and efficiency in segmentation.     

Robust generation of high‐quality unstructured meshes on realistic biomedical geometry

In this paper, we propose efficient and robust unstructured mesh generation methods based on computed tomography (CT) and magnetic resonance imaging (MRI) data, in order to obtain a patient‐specific geometry for high‐fidelity numerical simulations. Surface extraction from medical images is carried out mainly using open source libraries, including the Insight Segmentation and Registration Toolkit and the Visualization Toolkit, into the form of facet surface representation. To create high‐quality surface meshes, we propose two approaches. One is a direct advancing front method, and the other is a modified decimation method. The former emphasizes the controllability of local mesh density, and the latter enables semi‐automated mesh generation from low‐quality discrete surfaces. An advancing‐front‐based volume meshing method is employed. Our approaches are demonstrated with high‐fidelity tetrahedral meshes around medical geometries extracted from CT/MRI data. Copyright © 2005 John Wiley & Sons, Ltd.     

新型长碳链半芳香尼龙的合成与表征

利用本体聚合方法制备了3种新型高分子量半芳香尼龙-聚联苯二甲酰十碳二胺(PA10B)、聚联苯二甲酰十二碳二胺(PA12B)和聚联苯二甲酰十三碳二胺(PA13B).用IR和1H-NMR表征此3种聚合物的结构;并用DSC、TG研究了聚合物的耐热性能;结果表明这3种新型的半芳香聚酰胺具有较高的熔融温度和热分解温度.同时合成的3种半芳香尼龙均具有良好的耐溶剂性能.     

Physical Simulation of Mold-Filling Processing of Thin-Walled Castings under Traveling Magnetic Field

Mold-filling process of thin-walled castings under the condition of traveling magnetic field has been studied by physical simulation method using gallium melt and fast speed photography. Flow morphology and its formation mechanism were obtained and discussed for thin-walled casting. The influences of magnetic field density on the filling ability, filling velocity and mold filling time have been studied. The differences in filling capability between gravity casting and casting under the traveling magnetic field have been compared. The results indicate that the mold filling ability of the gallium melt increases greatly under the condition of traveling magnetic field; the filling time is shortened from 18 s under gravity field to 3 s under the traveling magnetic field and average flow rate of the melt increases from 1.6 to 8.68 cm3/s; the change law of the cross-section morphology of the gallium melt during the mold filling is that at first, the cross-section area does not change, then it decreases gradual     

Structures and magnetic properties of ZnO nanoislands

Using first-principles calculations, we systematically study the atomic structures and electronic properties for two dimensional triangular ZnO nanoislands that are graphite-like with monolayer and bilayer thickness. We find that the monolayer ZnO nanoisland with oxygen-terminated zigzag-edges is magnetic at its ground state, and the magnetism comes from the oxygen-edge states. The other monolayer and bilayer ZnO nanoislands with different edge structures are all nonmagnetic at their ground states. It is further revealed that for different ZnO nanoislands, their magnetic properties are quite dependent on their sizes, with larger nanoislands having larger magnetic moments.     

Information rates of multidimensional front ends for digital storage channels with data-dependent transition noise

This paper presents a simulation-based method for the computation of the information rates of recently proposed multidimensional front ends for digital storage channels with transition noise. First, we propose an algorithm, based on linear prediction and state reduction techniques, that extends recent work on the information rates of magnetic recording channels affected by colored Gaussian thermal noise, intersymbol interference, and signal-dependent transition noise. Following a previous study on statistical sufficiency, we apply this algorithm to compute the information rates of digital storage systems featuring a multidimensional detection front end. The resulting information rates indicate that significant gains may be achievable by multidimensional signal processing techniques in transition-noise-limited digital storage channels.     

Resolving magnetic nanostructures in the 10-nm range using MFM at ambient conditions

Following the demand of the magnetic data storage industry, the magnetic structures in hard disk heads are continuously shrinking. This requires a powerful tool to investigate the magnetic properties of these elements in the range of about 10 nm. To achieve this goal, we prepared MFM tips using the electron-beam deposition (EBD) contamination technique, where carbon caps and needles are grown onto the micromachined Si cantilevers. For batch production of MFM tips, however, this technique is not suited well, so we employ the focussed ion-beam (FIB) technique to produce MFM tips with a high aspect ratio similar to those tips with carbon needles. We show that the use of these tips not only improves the lateral resolution, but also considerably reduces the disturbation effects of the weak magnetic structures due to the magnetic tips.     

Ice-Front Propagation Monitoring in Tissue by the use of Visible-Light Spectroscopy

For demonstrating that visible-light spectroscopy can be used for ice-front detection within freezing tissue, proton magnetic resonance images were correlated to time-evolving transmittance spectra as an ice front progressed across a tissue sample. The experimental apparatus was designed to be compatible with magnetic resonance imaging, to produce one-dimensional freezing, and to allow both reflectance and transillumination emitter-detector configurations about a normally progressing planar ice front in chicken muscle. This demonstration has potentially important medical applications in cryopreservation (freezing of biological materials for preservation) and cryosurgery (destruction of tissue by freezing).     

Investigation of the aqueous dissolution of semicrystalline poly(ethylene oxide) using infrared chemical imaging: the effects of molecular weight and crystallinity

Fourier transform infrared (FT-IR) imaging was used to successfully explore several factors influencing the dissolution of poly(ethylene oxide). The effect of the degree of crystallinity on the rate of dissolution of mid-range molecular weight PEO was negligible over the temperature ranges studied. The influence of molecular weight on polymer dissolution was found to be much greater than the changes in morphology. An examination of the polymer and solvent images and absorbance profiles, compared with the results of the bulk polymer/solvent boundary movement, confirmed this relationship. An investigation of the bulk polymer/solvent boundary using a crystalline-sensitive polymer band showed the crystalline to amorphous phase change occurred over a short distance. Moreover, solvent diffusion ahead of the bulk polymer/solvent front was minimal, most likely a result of the required phase change, which in turn regulated the degree of solvent ingress. Modeling of the dissolution was performed using the Peppas (power law) model. Physical parameters of the dissolution process were obtained from fitting the release profiles to the power law (fraction released = k x t(n), where k is the dissolution rate constant and n is the release exponent). Results indicated the model worked well to describe dissolution at all molecular weights. By varying the number of data points input to the model and then comparing the generated graphs, it becomes clear that not only does the dissolution slow down over the course of the experiment, but an increase in molecular weight enhances this effect. The effect of different types of drug on the rate of polymer dissolution was also studied. The dissolution of neat polymer was compared to the dissolution of polymer containing 10% (by weight) of theophylline, etophylline, or testosterone. The general trend of all the dissolution curves was the same, with the addition of etophylline and testosterone tracing almost the same route in terms of movement of the bulk polymer/solvent front.     

Parinaric acid methyl ester polymer films with hill-structured features: fabrication and different sensitivities to normal and tumor cells

Parinaric acid methyl ester (PnA-Me) polymer films with hill-structured features were fabricated by a solvent volatilization in situ cross-linking method. Moreover, nuclear magnetic resonance, Fourier transform infrared, and oxidation kinetic analyses were successfully applied to monitor the formation process of PnA-Me polymer films. The role of PnA-Me monomer concentrations for growth control of the hill structures on a glass matrix had also been investigated. Also, the results demonstrated that size control of the resulting hill structure ranging from 0.56 ± 0.18 to 19.6 ± 3.5 μm could be realized by varying the concentration of the PnA-Me monomer from 0.0117 to 1.5 mg/mL. Additionally, the effects of polymer films with different surface topographical structures on the behaviors of rat mesenchymal stem cells and human pheochromocytoma cells were measured by morphological and metabolic methods. The results revealed that the cell activity of PnA-Me films was topographical structure- and cell-type-dependent. Furthermore, the selective sensitivity of the PnA-Me films to normal and tumor cells supported the potential value as the coatings for the tissue engineering substitutes.