Different nano-particles volume fraction and Hartmann number effects on flow and heat transfer of water-silver nanofluid under the variable heat flux

Nanofluid flow and heat transfer composed of water-silver nanoparticles is investigated numerically inside a microchannel. Finite volume approach (FVM) is applied and the effects of gravity are ignored. The whole length of Microchannel is considered in three sections as l₁=l₃=0.151 and l₂=0.71. The linear variable heat flux affects the microchannel wall in the length of l₂ while a magnetic field with strength of B₀ is considered over the whole domain of it. The influences of different values of Hartmann number (Ha=0, 10, 20), volume fraction of the nanoparticles (ɸ=0, 0.02, 0.04) and Reynolds number (Re=10, 50, 200) on the hydrodynamic and thermal properties of flow are reported. The investigation of slip velocity variations under the effects of a magnetic field are presented for the first time (to the best knowledge of author) while the non-dimensional slip coefficient are selected as B=0.01, 0.05, 0.1 at different states.     

大气可吸入肺纳米颗粒的SEM及X射线微分析研究

以大气中可吸入肺纳米颗粒为研究对象,利用场发射扫描电子显微镜(FSEM)和X射线能谱仪对其形态和常量组分进行了系统研究。研究结果表明：大气可吸入物中的纳米颗粒大多为类球与椭球形,表面较为光滑,结构紧密,较小的纳米颗粒聚集成团呈松散絮状,粒度大小约在30～100 nm之间,纳米颗粒物中含有的常量元素同大颗粒污染物基本一致,主要含有C,O,Al,Si,Na,Mg,K,Ca,Fe,S,Cl等元素,能量色谱仪(EDS)的点分析研究证实一些纳米颗粒物中Cl和S元素的含量明显增大,而另一些颗粒主要为C和O元素,分析其原因,认为主要是气溶胶在形成过程中,以纳米无机灰尘颗粒为中心表面吸附了大气污染物中的有机排放物所致,从而形成了具有核壳结构的纳米颗粒污染物。因此,减少人为有机污染物的排放,对于减少可吸入肺有害纳米颗粒的形成具有很大的影响。     

Electrodeposited metals at conducting polymer electrodes: I—Effect of particle size and film thickness on electrochemical response

Conducting polymers are electrochemically polymerized at platinum electrode substrates. The thickness, porosity and surface morphology of the resulting films are controlled by the charge passing during electropolymerization step and the synthesis conditions. The polymer films are modified by electrochemically depositing platinum particles. The technique of deposition depends on applying a programmed potential pulse at the polymer film from a solution containing platinum complex that resulted in the formation of platinum particles of controlled size and distribution. The effect of changing the size of platinum particles and polymer film thickness on the voltammetric behavior of the resulting hybrid material showed noticeable changes in the electro-catalytic current in acid medium. On the other hand, the electrochemical impedance spectroscopy experiments showed that diffusion and charge-transfer rate increased in the order: unmodified polymer films, thin polymer films containing small size/amount of platinum particles and relatively thick polymer films containing larger size/amount of platinum particles. The morphology of polymer films, size and distribution of platinum particles in the film were studied by scanning electron microscopy. The presence of platinum and its distribution over the film surface was confirmed from the X-ray dispersive analysis and surface mapping. The hybrid materials are good candidates for the application in devices for exchange of hydrogen ions.     

Theoretical study on the photoelectric emission spectra of a field-assisted Au-BaO thin film

The dependence of the spectral distribution of photoelectron emission from gold nano-particles embedded in BaO semiconductor thin film on applied voltage and surface plasmon resonance of gold nano-particles is predicted and investigated theoretically. The photoelectron emission response curves to light wavelength between 0.2 and are given. The dependence of the wavelength threshold on the size of gold nano-particles and external field strength is also shown. The reason that the theoretical photoelectron emission spectra is in the visible region is explained. The probabilities increased for photoexcited electrons to overcome the barrier and escape from the surface are discussed. This could be of importance in designing field-assisted thin film and finding their optimum operation conditions.     

Iron doping effect on superconducting properties of MgB2

Iron-doped MgB₂ bulks are prepared by hybridized diffusion method using nano-powder and macro-powder of pure iron as iron source. The doping effect on superconductivity transition temperature, T_c, and critical current J_c have been investigated. It is found that both T_c and J_c of MgB₂ show quite different features depending on the particle size of the dopant powders. It is demonstrated that different from iron bulk or large size powders, iron nano-powders are active dopant for MgB₂ which suppresses both T_c and J_c of MgB₂.     

Preparation and characterization of carbon paste micro-electrode based on carbon nanoparticles

The present paper demonstrates the preparation and characterization of micro-electrodes based on carbon paste which is composed of carbon nano-particles with an average diameter of 30 nm and binding oil. The carbon paste electrode material is encased in pulled glass capillaries ranging in diameter from several tens down to less than ten micro-meters (r = 4.5 μm). Manipulation of the carbon paste micro-electrode (CPME) was accomplished via newly developed piston-driven system which construction and related problems are presented. Several parameters influencing the CPME performance including carbon paste composition and its electrochemical activation/preconditioning were investigated. Basic electrochemical behavior and properties were examined using typical redox system, i.e. potassium hexacyanoferrate. Applicability of the proposed carbon paste micro-electrode is illustrated by measuring some potentially interesting organic and inorganic analytes such as dopamine, ascorbic acid and selected heavy metals.     

Magnetic behaviour of nano-particles of Fe<Subscript>2.8</Subscript>Zn<Subscript>0.2</Subscript>O<Subscript>4</Subscript>

Magnetization measurements are reported on a nano-particle sample of Znsubstituted spinel ferrite Fe_2.8Zn_0.2O₄ in the temperature range 20–300 K. Analysis of small-angle neutron scattering data shows the sample to have a log-normal particle size distribution of median diameter 64.4 Å and standard deviation 0.38. Magnetization evolves over a long period of timet going nearly linearly with logt. Magnetic anisotropy, estimated by fitting M-logt curve, shows many fold increase over that of bulk particle sample. Major enhancement owes to disordered moments in surface layer. In the nano-particle state as well increasing amount of Zn causes anisotropy to decrease.