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In this research, we have developed a computational method for droplet sorting using a non-uniform electric field. The method is based on a three-dimensional level-set method and the leaky-dielectric electrohydrodynamics (EHD) model. Level-set method is used for modeling the interface of the two-phase flow system. The electrostatic phenomenon is dealt with the leaky dielectric-leaky dielectric fluid system. At first, we validated our developed model for a classical flow case: a droplet subjected to a uniform electric field. The results obtained from the present computational method show good agreement with the existing results from the literature. After validation, we implemented the developed code in a practical application of droplet sorting using a non-uniform electric field (known as dielectrophoresis) in a rectangular microchannel with an orthogonal side channel. We mainly focus on the sorting of the droplet without and with the electric field effect as a function of different parameters of the problem. Depending on the intensity of the physical parameters, the droplet can flow into either the downstream main channel or it can sort into the orthogonal side branch. The sorting of a droplet is characterized by the critical branch ratio, qc above which the droplet enters the side branch. The results and conclusions from the present thesis facilitate the understanding of the fundamental principles and mechanisms of electrohydrodynamics (EHD)-based droplet sorting using dielectrophoresis in microfluidic channels. Therefore, present results can have potential usefulness toward the design and development of droplet-based microfluidic devices. [ABSTRACT FROM AUTHOR]

Hexagonal Ba(Ti1-xFex)O3-δ (x = 1/6, 1/3) ceramics treated with post annealing are specifically synthesized to explore the origin mechanism of the unusual ferromagnetism in the doped system. X-ray diffraction refinements and transmission electron microscope experiments reveal that their structures are incommensurately modulated owing to simultaneous oxygen vacancies at both O1 and O2 sites. Consequently, coexisting weak ferrielectricity and weak ferromagnetism are presented at room temperature. Analysis on their leakage current plot reveals that their conduction follows trap-filled limit model. In combination with the magnetism studies on 5 mol% Fe-doped crystals [Phys. Rev. B 83, 144407 (2011)], the reduction of ferromagnetism with an increase of conductivity suggests that dynamic exchanges of trapped electrons among the bound magnetic polarons attribute to the intrinsic ferromagnetism. [ABSTRACT FROM AUTHOR]

Presents an electron spin resonance study of NiFe[sub2]O[sub4] nanosolids compacted under high pressure. Experimental procedures; Results and discussion; Conclusions.

The structure and magnetic properties of multilayer magnets with a hard phase (HP1=Nd13.5Dy1.5Fe68Co10B7 or HP2=Nd14Dy1Fe68Co10B7) and soft phase Fe, prepared by sputtering and subsequent heat treatment, have been investigated. For Si/Ti(20 nm)/[HP1(2.0 nm)/Fe(0.5 nm)]×200/Ti(10 nm) multilayer film, transmission electron microscopy results show that Fe disperses in amorphous NdDyFeCoB alloy. After annealing at 575 °C for 5 min, the hard Nd2Fe14B phase typically with grains of about 50 nm and some amount of α-Fe coexist in the film. The grain size of the hard and soft phases can be controlled by the proper thickness of the layer and the period. A coercivity of 7.7 kOe and a ratio Mr/Ms of 0.74 are achieved in the multilayer Si/Ti(20 nm)/[HP2(2 nm)/Fe(0.5 nm)]×200/Ti(10 nm). A good squareness of the hysteresis loop (measured even at 200 K) is observed, due to the effective exchange coupling between the magnetically soft and hard nanograins in the film. A pinning-type mechanism dominates the magnetization reversal process. In addition, the effect of the effective anisotropy, the grain size, and interfaces between the magnetically hard and soft phases on the exchange coupling is discussed. [ABSTRACT FROM AUTHOR]

A simple synthetic procedure involving the pyrolysis of Fe and Pt acetylacetonates mixed in trioctylamine results in the formation of alloy clusters with an average cluster around 4.2 nm and narrow size distribution. When the clusters are dispersed onto silicon wafers and heated under the protection of forming gas or nitrogen, the fcc structured clusters transform into hard magnetic FePt clusters with L10 chemical order. Coercivity values as high as 23 kOe are reached after rapid thermal annealing at 750 °C for 5 min. [ABSTRACT FROM AUTHOR]

Dy1-xPrx(Fe0.35Co0.55B0.1)2 (0<=x<=1) Laves compounds with a cubic MgCu2-type structure were synthesized by arc melting and subsequent annealing. The lattice parameter of the Laves compounds linearly increases, while the Curie temperature TC decreases with increasing Pr content. The saturation magnetization Ms at 5 K or 295 K for the Dy1-xPrx(Fe0.35Co0.55B0.1)2 alloys decreases to reach a minimum, then increases with increasing Pr content. The composition for magnetic moment compensation is about x=0.55 at 295 K and x=0.65 at 5 K, respectively. The magnetostriction λ∥ or λ⊥ at room temperature was investigated either parallel or perpendicular to the applied field using a standard strain gauge technique. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of multilayer magnets containing a hard phase [HP≡;(Nd0.95Dy0.05)(Fe,Co,Nb,B)5.5] and a soft phase (SP≡Fe and Fe65Co35) have been investigated. For the nanocomposite multilayer of Si(substrate)/Ti(30 nm)/ [HP(x nm)/SP(y nm)]n/Ti(30 nm), the remanence enhancement has been observed at different thickness and volume fractions of hard- and soft-phase layers. The remanence increases and the coercivity decreases with the addition of soft phase, in comparison with the results of the single-layer film. For the multilayer of Si(substrate)/Ti(30 nm)/[HP(15 nm)/Fe(5 nm)]n/Ti(30 nm) annealed at 575 °C for 30 min, the coercivity of the multilayer reaches a maximum at n=20. Effects of the layer thickness and volume fraction of hard- and soft-phase layers on magnetic properties and exchange coupling in the multilayer films have been observed. [ABSTRACT FROM AUTHOR]

FePt L10-structured clusters were synthesized by hydrogen reduction of FesNO3d3.9H2O and H2PtCl6.6H2O mixtures within the pores of alumina. They were released by dissolving the alumina matrix and capped with organic surfactants. After a series of chemical treatments, clusters with an average diameter of about 11 nm were precipitated. The clusters were drop casted onto ordered nanoporous arrays. Clusters reaching the bottom of the pores formed an ordered magnetic array. The corresponding magnetic film exhibits distinct anisotropic behavior caused by the external magnetic field. [ABSTRACT FROM AUTHOR]

In exchange-coupled two-phase permanent magnets, the length scale of soft phase is limited to about twice of the domain-wall width of the hard phase. To optimize the energy product, it is important to realize this length experimentally. In this work, we investigate the Sm-Co/Co hard/ soft multilayers with varying thickness of soft phase layers. On rapidly annealing, the multilayered hard-soft structure forms. Transmission electron microscopy micrography confirms that the multilayer structure is retained after the annealing. Single-phase-like hysteresis loops are obtained for samples with Co layers up to 13 nm thick. This behavior indicates that the soft phase is well exchange coupled to the neighboring SmCoz hard phase. An optimal energy product of 16.6 MGOe has been obtained. Longer annealing time results in more diffusion at the interface and yields two-phase-like hysteresis behavior. Direct current demagnetization measurement shows exchange-spring behavior of the samples annealed for longer time. Micromagnetic simulations with varying interface exchange coupling have been performed to compare with the experimental results. [ABSTRACT FROM AUTHOR]

FePt and Fe3O4 nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction, and superconducting quantum interference device magnetometry. Loading the templates with an Fe chloride and Pt chloride mixture, followed by hydrogen reduction at 560 °C, leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. An Fe nitrate solution, thermally decomposed at 250 °C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe3O4 tubes. The versatility of the method indicates that materials with a wide range of parameters can be produced. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nanochannels of porous alumina films were used as nanoreactors for the reaction of hydrogen gas with a mixture of Fe nitrate and Pt chloride. This results in the formation of of FePt clusters within the nanochannels. Both the sizes of the clusters and the coercivity the cluster assembly increase with the increase of annealing temperature. In order to reduce excessive agglomeration at high temperature, carbon was introduced by chemical vapor deposition and FePt:C composites in nanoscale channels were created. When FePt clusters were synthesized with carbon and heat treated at high temperatures, cluster sizes were much smaller than those without carbon, suggesting that the introduced carbon serves effectively to block the agglomeration of clusters. The coercivity of the FePt:C composite containing the smaller clusters is as high as 29.0 kOe. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The synthesis of hard-magnetic CoPt nanoparticle films by hydrogen reduction of Co nitride and Pt chloride mixture is reported. Thin porous alumina films are adopted as the carrier of the initial aqueous solution and of the final reducing products of CoPt nanoparticles. It is found that chemical ordering of L1[SUB0]-CoPt occurs above 400 °C. Partial phase transformation occurs in the alumina substrate when the treatment temperature is higher than 600 °C. The film coercivity increases with increasing annealing temperature and reaches a maximum value of 24.2 kOe when the reduction is carried out at 700 °C for 2 h. [ABSTRACT FROM AUTHOR]

The relationship between the phase evolution, nanostructure, exchange coupling, and magnetic properties of Nd[sub 8.4]Fe[sub 86]Mo[sub l.1]B[sub 4.5] magnets prepared by melt spinning (MS) and mechanical milling (MM) are studied by x-ray diffraction, Mössbauer spectroscopy, positron lifetime measurements, high resolution transmission electron microscopy observations, and magnetization measurements. The maximum magnetic energy product (BH)[sub max] for MM magnets annealed at 650 °C or below are notably higher than those of the corresponding MS samples due to the larger amount of the Nd(Fe,Mo)[sub 7] present in the MS samples. [ABSTRACT FROM AUTHOR]

Presents a study that examined the structure and magnetic properties of neodymium-iron-titanium alloys and their nitrides. Methodology; Analysis of the magnetic coercivities of the samples; Examination of the dependence of the magnetic properties on the composition of the samples.

We analyzed the protective ability of chemical vapor deposition (CVD) graphene domains against corrosion of Cu surfaces. Fresh graphene domains of various shapes were ideal corrosion-inhibiting layers. However, obvious corrosion was found within graphene domains exposed to the air for over a week. Our work demonstrates that the opportunities for corrosion of CVD graphene were provided by wrinkles but not others, such as Cu grain boundaries and graphene domain boundaries, which are always believed the primary factor for inferior quality of the CVD graphene at present. [ABSTRACT FROM AUTHOR]

A three-dimensional numerical model is proposed to simulate the dynamic motion of red blood cells (RBCs) in simple shear flow. The RBCs are approximated by ghost cells consisting of Newtonian liquid drops enclosed by Skalak membranes which take into account the membrane shear elasticity and the membrane area incompressibility. The RBCs have an initially biconcave discoid resting shape, and the internal liquid is assumed to have the same physical properties as the matrix fluid. The simulation is based on a hybrid method, in which the immersed boundary concept is introduced into the framework of the lattice Boltzmann method, and a finite element model is incorporated to obtain the forces acting on the nodes of the cell membrane which is discretized into flat triangular elements. The dynamic motion of RBCs is investigated in simple shear flow under a broad range of shear rates. At large shear rates, the cells are found to carry out a swinging motion, in which periodic inclination oscillation and shape deformation superimpose on the membrane tank treading motion. With the shear rate decreasing, the swinging amplitude of the cell increases, and finally triggers a transition to tumbling motion. This is the first direct numerical simulation that predicts both the swinging motion of the RBCs and the shear rate induced transition, which have been observed in a recent experiment. It is also found that as the mode changes from swinging to tumbling, the apparent viscosity of the suspension increases monotonically. [ABSTRACT FROM AUTHOR]

Presents a study that examined iron/copper, silver, gold/iron sandwiches by ion beam sputtering and interlayer coupling behavior by ferromagnetic resonance technique. Methods; Results; Discussion.

Top-gated, few-layer graphene field-effect transistors (FETs) fabricated on thermally decomposed semi-insulating 4H-SiC substrates are demonstrated. Physical vapor deposited SiO2 is used as the gate dielectric. A two-dimensional hexagonal arrangement of carbon atoms with the correct lattice vectors, observed by high-resolution scanning tunneling microscopy, confirms the formation of multiple graphene layers on top of the SiC substrates. The observation of n-type and p-type transition further verifies Dirac Fermions’ unique transport properties in graphene layers. The measured electron and hole mobilities on these fabricated graphene FETs are as high as 5400 and 4400 cm2/V s, respectively, which are much larger than the corresponding values from conventional SiC or silicon. [ABSTRACT FROM AUTHOR]

Polycrystalline Sr2Fe1-xAlxMoO6 compounds with x=0, 0.05, 0.10, 0.15, and 0.30 were fabricated and their low-field magnetoresistance (LFMR) performance studied. The LFMR was greatly enhanced as x increased from nil to 0.15, and its origin was found to be intragranular spin-dependent scattering. The replacement of Fe by Al weakened the antiferromagnetic exchange in the antiphase boundary arising from the antisite defect and acted as a barrier for electron transport along the Mo–O–Fe–O–Mo–O–Fe chain in the ferromagnetic segregation and weakened the ferromagnetic exchange. When the external magnetic field was applied, the spin in the antiphase boundary appeared to align more easily to the external field after Al doping and the transport of the electron was easier due to the weakening of the double exchange barrier. [ABSTRACT FROM AUTHOR]

Results from a new series of experiments on flows generated by localized heating in the presence of a background zonal current on the polar β-plane are presented. The flow induced by a heater without the background zonal flow is in the form of a β-plume. Zonal jets of alternating directions are formed within the plume. The westward transport velocity in the plume is proportional to the upwelling velocity above the heater in agreement with linear theory. When the background flow in the form of the eastward zonal current is present, the β-plume can be overwhelmed by the eastward current. The main control parameters of the experiment are the strength of the heater and strength of the sink which is used to create the background flow. The regime diagram shows the area where a β-plume can exist in the parameter space. The critical value of the velocity of the zonal flow below which the β-plume can exist is obtained by considering barotropic Rossby waves emitted by the baroclinic eddies in the heated area. [ABSTRACT FROM AUTHOR]

Multi-degree of freedom piezoelectric actuators are strongly needed for industrial applications, especially when manipulating a large and heavy mirror or lens in an optical system. A novel three-degree-of-freedom piezoelectric actuator, which is driven by two pairs of piezo-stack actuator with spatial compliant mechanisms designed to guide the motion and preload the piezo-stack actuators, is herein proposed. The structure and working principle of the proposed actuator are illustrated and its kinematic characteristic is analyzed. The stiffness of the spatial compliant mechanisms is modeled, and the dynamic characteristics are analyzed, Finite Element method is utilized to validate the correctness of the stiffness modeling and the free vibration analysis of the proposed actuator. A prototype actuator is fabricated and its output performances have been tested. Working space of X ranging from -7.1 to 5.6 μm, Y ranging from -6.2 to 8.2 μm and Z ranging from -2.3 to 2.1 μm, displacement resolutions of 15/16/21 nm along X-/Y-/Z-axis and average velocities of 52.3, 82.8 and 29.5 µm/s along X-axis, Y-axis, and Z-axis with carrying load up to 2 kg and driving frequency of 500 Hz have been achieved by the prototype actuator. The method of waveform generating for the proposed actuator has been developed with the inverse hysteresis compensation, and test results indicate that the positioning accuracy of the prototype actuator in the open loop has been improved from 0.94 to 0.23 μm for a circular trajectory tracking, from 0.48 to 0.29 μmm for an elliptical trajectory tracking, and from 0.61 to 0.32 μm for a rectangular trajectory tracking with the compensated waveform of driving voltage.

The magnetic tensor gradiometer, which is used for measuring the spatial derivatives of three orthogonal magnetic field components, is an important magnetic field characterization tool. Here, the construction of a magnetic full-tensor gradiometer is described, which utilizes four fluxgates arranged on a planar cross structure, and a single, triaxial, spherical feedback coil assembly. In this arrangement, one of the fluxgates is used as a reference, controlling the currents through the feedback coils. Since the fluxgates are working in the near-zero magnetic field environment, the magnetic tensor gradiometer is stable and of an improved accuracy. This design avoids the crosstalk normally caused by individual feedback coils for each fluxgate, and reduces the orthogonality and orientation errors. Moreover, the calibration parameters can be directly inferred using the spherical feedback coil. The measured gradient tensor magnitude can reach 0.52 nT/m/Hz(1/2) @ 1 Hz in unshielded laboratory conditions, while exhibiting good noise immunity. The functionality of the system is verified by locating a small, single, permanent, and dipole magnet in space. The gradiometer is compact, while employing global feedback, and therefore it is especially suitable for deployment on space-constrained moving platforms.