Key synthesis of magnetic Janus nanoparticles using a modified facile method

Inorganic/organic poly（methylmethacrylate-acrylic acid-divinylbenzene） iron oxide Janus magnetic nanoparticles（P（MMA-AA-DVB）/Fe3O4） with strong magnetic domains and unique surface functionalities were prepared using a solvothermal process.The P（MMA-AA-DVB） nanoparticles were prepared via soapfree emulsion polymerization and used as a precursor for preparing Janus nanoparticles.The morphology and magnetic properties of the magnetic Janus nanoparticles formed were characterized using a laser particle size analyzer,transmission electron microscopy,Fourier transform infrared spectroscopy,vibrating sample magnetometry,and thermogravimetric analysis.The synthesized P（MMA-AA-DVB）/Fe3O4 magnetic Janus nanoparticles were characterized by a Janus structure and possessed a stable asymmetric morphology after being dually functionalized.The particle size,magnetic content,and magnetic domain of the P（MMA-AA-DVB）/Fe3O4 magnetic Janus nanoparticles were 200 nm,40%,and 25 emu/g,respectively.The formation mechanism of the Janus nanoparticles was also investigated,and the results revealed that the reduction of Fe3＋ ions and growth of Fe3O4 took place on the surface of the P（MMA-AA-DVB） polymeric precursor particles.The size of the Janus particles could be controlled by narrowing the size distribution of the P（MMA-AA-DVB） precursor nanoparticles.     

Biopolymer-assisted synthesis of yttrium oxide nanoparticles

Yttrium oxide nanopowder was prepared by a novel technique using an alginate biopolymer as a precursor. The technique is based on thermal decomposition of an yttrium alginate gel, which is produced in the form of beads by ionic gelation between the yttrium solution and sodium alginate. The effect of post-annealing temperature on the particle size of the nanocrystals was investigated at various tempera- tures. The products were characterized using X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The size of the nanocrystalline Y2O3 particles varied from 22.7 to 38.7 nm, depending on the annealing temperature and time. The grain size distribution （GSD） was also determined. The GSD became more non-symmetrical as the annealing temperature increased, and the width of the distributions for the powders produced using the alginate method was less affected by heat treatment. This alginate method was compared with the conventional glycine combustion method, on the basis of particle size. The particles obtained using the proposed technique were smaller than those obtained using the combustion method. Alginate-assisted thermal decomposition is therefore an easy and cost-effective method for preparing nanosized Y2O3 crystals.     

Ultrasonic cavitation assisted solvothermal synthesis of superparamagnetic zinc ferrite nanoparticles

Nanoparticles of cubic zinc ferrites(Fd3m,a= 8.41(3)-8.44(l)A) were synthesized as a single phase by an ultrasonic cavitation-assisted solvothermal technique using ethyl alcohol-water mixed solvents at temperatures of 150 C or higher for 18h or more.The influences of the ultrasonic cavitation and the use of C2H5OH-H2O mixed solvents in diminishing average particle size and in improving particle size uniformity were illustrated.The largest average size of nanoparticles obtained was 20 nm as measured from SEM photographs,with crystallite size of approximately 10nm as estimated from XRD results.The room-temperature field-dependent magnetization of the nanoparticles obtained showed a characteristic S feature with magnetization of 24.32 emu/g at 1 T.     

Model reduction using Dynamic Mode Decomposition

Dynamic Mode Decomposition (DMD) is a recent post-processing technique that extracts from snapshots dynamic relevant information for the flow. Without explicit knowledge of the dynamical operator, the DMD algorithm determines eigenvalues and eigenvectors of an approximate linear model. The ability of DMD to extract dynamically relevant features of the flow predispose it for building a representative reduced-order subspace from the data and for deriving a reduced-order model. The use of the DMD for reduced-order modelling will be investigated in this paper on experimental flow data of a cylinder wake.     

Bluff-body drag reduction using a deflector

A passive flow control on a generic car model was experimentally studied. This control consists of a deflector placed on the upper edge of the model rear window. The study was carried out in a wind tunnel at Reynolds numbers based on the model height of 3.1 × 10⁵ and 7.7 × 10⁵. The flow was investigated via standard and stereoscopic particle image velocimetry, Kiel pressure probes and surface flow visualization. The aerodynamic drag was measured using an external balance and calculated using a wake survey method. Drag reductions up to 9% were obtained depending on the deflector angle. The deflector increases the separated region on the rear window. The results show that when this separated region is wide enough, it disrupts the development of the counter-rotating longitudinal vortices appearing on the lateral edges of the rear window. The current study suggests that flow control on such geometries should consider all the flow structures that contribute to the model wake flow.     

A novel method of supporting gold nanoparticles on MWCNTs： Synchrotron X-ray reduction

Gold nanoparticles decorating the surface of multiwalled carbon nanotubes （MWCNTs） are prepared by photochemical reduction. The gold clusters form different interesting geometrical faceted shapes in accordance to time duration of synchrotron X-ray irradiation. The shape of nanogold could be spherical, rod-like, or triangular. Carbon nanotubes serve as optimal templates for the heterogeneous nucleation of gold nanocrystals. These nanocrystal structures are characterized by transmission electron microscope （TEM） and element analysis by energy dispersive spectroscopy （EDS）. 2007 Chinese Society of Particuology and Institute of Process Engineering,Chinese Academy of Sciences. Published by Elsevier B.V.     

Hydrothermal synthesis of star-like and dendritic PbS nanoparticles from new precursors

Lead sulfide (PbS) nanostructures with different morphologies and particle sizes were obtained via a simple hydrothermal reaction between lead (II) salicylate (Pb(Hsal)₂) and thiourea (tu). Reaction products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible (UV–vis) and Fourier transform infrared (FT-IR) spectroscopy. Morphology of the product, varying from star-like to dendritic, depends on the mole ratio of tu to (Pb(Hsal)₂), pH, and reaction time.     

Two photoviscoelasticity experiments using analog data reduction

A tensile analog may conveniently be used to determine the history of the principal-stress difference from the results of some photoviscoelastic model tests. With this method, the model test is run, and the fringe-order history at the point (s) of interest in the model is recorded. A tensile specimen of the same material is placed in a loading frame and loaded with a stress history which forces it through the fringe-order history observed in the model. This stress history is then the desired principal-stress-difference history occurring in the model. The stress history at points in two nonhomogeneous models was determined with a tensile analog. The uses and limitations of the analog technique are discussed.     

Turbulent wall pressure reduction using suction control

A study of the fluctuating wall pressure beneath a 2-d turbulent boundary layer was conducted in a water tunnel with Reynolds numbers, based on momentum thickness, ranging between 2,100 and 4,300. The boundary layer was perturbed with steady mild suction to assess the effect of upstream suction on the fluctuating wall pressure measured downstream of the suction slit. Wall pressure signatures were captured using a custom-fabricated piezo-ceramic array with d ⁺ values ranging between 64 and 107. Likewise, the velocity field was measured with a laser Doppler velocimeter with l ⁺ values ranging between 4.0 and 6.7 for the lowest and highest Re _θ investigated. Estimates of the wall pressure spectra revealed a noticeable hydrodynamic peak that scaled reasonably well with outer variables and with an average convective speed of 75 % of the free stream velocity (based on unconditionally sampled pressure time series). Two boundary layer suction control cases were studied corresponding to suction rates of less then 30 % of the boundary layer momentum. The findings reveal how only modest amounts of suction are needed to reduce upwards 50–60 % of the hydrodynamic ridge.     

Metallic iron nanoparticles: Flame synthesis,characterization and magnetic properties

Metallic iron (Fe) nanoparticles (NPs) with a typical core–shell structure have been prepared by a simple and continuous flame spray pyrolysis (FSP) method, which are stabilized by the corresponding Fe₃O₄ shell with a thickness of 4–6 nm. The size of metallic Fe cores is about 30–80 nm. The core–shell structured iron NPs show an air stability as long as one month as a result of the protection of oxide shell. Through the control of the residence time of materials in flame and flame atmosphere, metallic Fe and iron oxides are obtained, showing a better external magnetic field responsibility. It is concluded that the evolution of morphology and composition of flame-made magnetic NPs could be attributed to the competition mechanism between reduction and oxidation reactions of in situ flame combustion, which offers more choices and better effective design strategy for the synthesis of advanced functional materials via FSP techniques.     

Synthesis of powdered silver nanoparticles using hydrogen in aqueous medium

Environmentally benign one-pot protocol is used in the synthesis of silver nanoparticles (AgNPs) in powder form, involving the reduction of silver nitrate in the presence of fully hydrolyzed polyvinyl alcohol (PVA) as stabilizer by hydrogen (H₂) as reducing agent in aqueous medium. Fully hydrolyzed biodegradable PVA has extremely low cytotoxicity, making it a favorable stabilizer from green perspective. In the present methodology, essentially naked silver nanoparticles are obtained in good yield. The prepared silver nanoparticles were characterized by TEM, XRD, EDAX, UV–Vis spectroscopy and DLS histogram, and studied for its activity as a recyclable catalyst for synthesis of different enaminones.     

Optimized synthesis and photovoltaic performance of TiO2 nanoparticles for dye-sensitized solar cell

This paper presents response surface methodology （RSM） as an efficient approach for modeling and optimizing TiO2 nanoparticles preparation via co-precipitation for dye-sensitized solar cell （DSSC） perfor- mance. Titanium （IV） bis-（acetylacetonate） di-isopropoxide （DIPBAT）, isopropanol and water were used as precursor, solvent and co-solvent, respectively. Molar ratio of water, aging temperature and calcina- tion temperature as preparation factors with main and interaction effects on particle characteristics and performances were investigated, Particle characteristics in terms of primary and secondary sizes, crys- tal orientation and morphology were determined by X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. Band gap energy and power conversion efficiency of DSSCs were used for perfor- mance studies. According to analysis of variance （ANOVA） in response surface methodology （RSM）, all three independent parameters were statistically significant and the final model was accurate. The model predicted maximum power conversion efficiency （0.14%） under the optimal condition of molar ratio of DIPBAT-to-isopropanol-to-water of 1 ： 10：500, aging temperature of 36 C and calcination temperature of 400 ℃. A second set of data was adopted to validate the model at optimal conditions and was found to be 0.14 ± 0.015%, which was very close to the predicted value. This study proves the reliability of the model in identi（ving the optimal condition for maximum performance.     

Vibration reduction in a flexible-link mechanism through synthesis of an optimal controller

In this paper, reduction of vibration of a flexible planar mechanism is achieved through synthesis of an optimal controller. A finite element model, based on the equivalent rigid-link system theory, is used to accurately describe the dynamic behavior of the system. The model, which accounts for geometric and inertial nonlinearities of the mechanism, has been fully validated through experimental tests. In order to be able to employ the classical optimal control theory, a suitable linear model has been derived from the original one by means of a suitable linearization procedure. Vibration reduction can then be obtained by first defining an adequate performance index, which accounts for vibration amplitude, then by solving Riccati’s equation in order to find the controller that minimizes the performance index, i.e. the optimal controller. The results of several tests that have been carried out are also reported, to show the effectiveness of the synthesized control system.     

Invariant spectral foliations with applications to model order reduction and synthesis

Nonlinear Dynamics - The paper introduces a technique that decomposes the dynamics of a nonlinear system about an equilibrium into low-order components, which then can be used to reconstruct the...     

Temperature measurement of reflected shock wave by using chemical indicator

This report describes a new method for measuring the temperature of the gas behind the reflected shock wave in shock tube, corresponding to the reservoir temperature of a shock tunnel, based on the chemical reaction of small amount of CF₄ premixed in the test gas. The final product C₂F₄ is used as the temperature indicator, which is sampled and detected by a gas chromatography in the experiment. The detected concentration of C₂F₄ is correlated to the temperature of the reflected shock wave with the initial pressureP ₁ and test time τ as parameters in the temperature range 3 300 K<T<5 600 K, pressure range 5 kPa<P ₁<12 kPa and τ≅0.4 ms. The project supported by the China Aerodynamics Project for Basic Researches (J13.5.2 ZK04)     

Validation of hypersonic chemical equilibrium flow calculations using ballistic-range data

The hypersonic flow field over a sphere flying in a ballistic-range is numerically simulated for the purpose of validating a hypersonic chemical equilibrium flow solver. The numerical results obtained are compared with available experimental data on the stand-off distance and the shape of the detached bow shock wave. In the calculation, an adaptive mesh is employed for a crisp capturing of the shock wave. Comparison with the experimental data reveals that the equilibrium flow solver can yield a fairly accurate prediction of the flow field. Received 18 November 1997 / Accepted 10 November 1998     

Roles of polyacrylate dispersant in the synthesis of well-dispersed BaSO4 nanoparticles by simple precipitation

Well-dispersed BaSO4 nanoparticles were synthesized in the presence of sodium polyacrylate （PAAS） by a simple precipitation method, with BaCl2 and （NH4）2SO4 as reactants. The different roles performed by PAAS in the synthesis of BaSO4 nanoparticles were investigated using X-ray diffractometry, Fourier transform infrared spectroscopy, and transmission electron microscopy. The results indicate that the assynthesized BaSO4 nanoparticles were spheres with an average diameter of 30 nm and that their surfaces were affected by the PAAS. Under a typical procedure employed, PAAS reacted with BaCl2 to yield an intermediate, serving as a control releasing agent and separating the nucleation and crystal growth processes of the BaSO4 nuclei. During formation of the BaSO4 nanospheres, the intermediate slowly dissolved and released barium and polyacrylate ions, inhibiting the growth and aggregation of newly formed BaSO4 seeds and resulting in particles of narrow diameter distribution and improved dispersibility. Moreover, these polyacrylate ions further modified the surfaces of the BaSO4 nanoparticles.     

Analysis and handling of bio-nanoparticles and environmental nanoparticles using electrostatic aerosol mobility

The successful application of differential mobility analysis for the characterization and manipulation of nanoparticles at atmospheric pressure has given rise to further development of this technique.The parallel differential mobility analyzer provides the possibility to simultaneously measure a size spectrum of nanoparticles and select a particular set of nanoparticles with a defined size for collection(as well as enrichment) and further orthogonal analysis(as for example electron microscopy,atomic force microscopy or mass spectrometry).Performing a high resolution measurement of electrical mobility diameters allows molecular weight determination of species with ultrahigh molecular masses in the mega Dalton range(e.g.protein complexes).The precise size measurement of the human rhinovirus has confirmed the potential of this technique to analyze even intact infectious human-pathogenic viruses. Moreover,the real-time measurement of nanoparticle occurrence in an urban environment confirms the versatility of the method presented here and its applicability also in other areas of importance.