EFFECTS OF BINARY MIXTURE CONDENSATION ON TURBULENT MIXED CONVECTION HEAT AND MASS TRANSFER IN A VERTICAL CHANNEL

Abstract

A numerical analysis was carried out to study the detailed heat and mass transfer processes between a condensation liquid film and mixed turbulent moist airflow. Results show that the condensation latent heat transfer is more important for a system with higher inlet relative humidity or lower inlet Reynolds number of a moist airstream. The heat and mass transfer coefficients are higher for a system with higher inlet relative humidity and inlet Reynolds number of moist air. In addition, the aiding-buoyancy forces cause diminution in heat and mass transfer results compared with the corresponding results of forced convection.     

Effects of interfacial structure on the magnetic properties of ultrathin Fe/Pt(111) films with Ag buffer layer

For Fe/Pt(111) grown at 180 K, the easy axis of magnetization changes from out-of-plane to in-plane while the surface structure changes from fcc(111) to bcc(110). The Curie temperature for 1 ML Fe/Pt(111) is close to room temperature. After insertion of submonolayer Ag, no significant change for the Curie temperature is observed. By thermally annealing Ag/Pt(111) at 550 K to form a Ag-Pt surface alloy, we demonstrate that the Curie temperature of the deposited Fe films is elevated to be higher than room temperature. For an ultrathin Fe/Ag/Fe/Pt(111) sandwich system, the strong interaction between the two Fe layers is superior due to the effect of the double Fe/Ag interfaces. This causes that the easy axis of the magnetization switches back to the in-plane direction during the deposition of Fe overlayer on the surface of a Ag/Fe/Pt(111) film.     

Structures and magnetic properties of Co and CoFe films prepared by magnetron sputtering

Structures and magnetic properties of Co and CoFe films on Si(100) have been investigated by employing scanning tunneling microscopy, atomic force microscopy, and magneto-optic Kerr effect techniques. As the film thickness increases, Co or CoFe clusters with different sizes are observed. As the film thickness increases below 20 nm, the size of the metal clusters decreases. For thicker films, the surface roughness increases monotonously by increasing the thickness. The easy axis of magnetization for both Co/Si(100) and CoFe/Si(100) prefers to be in the surface plane. By deposition of the Co or CoFe overlayers, the evolution of the longitudinal coercive force shows similar trend to the surface roughness. Minimum coercive force coincides with the smallest roughness of the film. For a film with greater roughness, the observation of larger coercive force could be explained by the impediment of the propagation of domain wall motion by defects of the films. At a higher deposition rate, Co islands in triangle shapes with an edge length around 100 nm are observed. This nanostructure shows an hcp-Co with the c axis parallel to the surface plane and is observed to be able to stabilize the coercive force for Co/Si(100) films.     

Variance and Covariance Computations for 2-D ARMA Processes

An algorithm is presented to compute the variance of the output of a two-dimensional (2-D) stable auto-regressive moving-average (ARMA) process driven by a white noise bi-sequence with unity variance. Actually, the algorithm is dedicated to the evaluation of a complex integral of the form , where and G(z₁,z₂) = B(z₁, z₂) / A(z₁, z₂) is stable (z₁,z₂)-transferfunction. Like other existing methods, the proposed algorithmis based on the partial-fraction decomposition G(z₁,z₂)G(z ₁ ^-1 , z ₂ ^-1 ) = X(z₁, z₁) / A(z₁,z₂)+ X(z ₁ ^-1 , z ₂ ^-1 ) / A(z ₁ ^-1 , z ₂ ^-1 ). However,the general and systematic partial-fraction decomposition schemeof Gorecki and Popek [1] is extended to determine X(z₁,z₂).The key to the extension is that of bilinearly transforming thediscrete (z₁, z₂)-transfer function G(z₁,z₂)into a mixed continuous-discrete (s₁, z₂)-transferfunction . As a result, the partial-fraction decomposition involves only efficient DFT computations for the inversion of a matrix polynomial, and the value of I is finally determined by the residue method with finding the roots of a 1-D polynomial. The algorithm is very easy to implement and it can be extended to the covariance computation for two 2-D ARMA processes.     

A study of multi-angles knife-edge method applied to digital modulation transfer function measurement

Microsystem Technologies - The objective of this study was to propose a newly-developed method to calculate digital modulation transfer function (DMTF) of digital image system which integrates with...     

Optimization of the hydrogen evolution activity on zinc-nickel deposits using experimental strategies

The experimental strategies including the fractional factorial design (FFD), path of the steepest ascent study, and the central composite design (CCD) coupled with the response surface methodology (RSM) was adopted to optimize the hydrogen evolution activity of Zn-Ni deposits. The key deposition variables, pH, the Zn/Ni ionic ratio and the TEPA concentration in the plating solutions, influencing the hydrogen evolution activity of Zn-Ni cathodes were found in the FFD investigation. These variables were subjected to the steepest ascent study to approach the vicinity of the optimal deposition conditions for plating the Zn-Ni deposits with the highest hydrogen evolution activity. In the CCD investigation, the optimal deposition settings, where the temperature of 50 °C, the current density of 2500 A m⁻², pH of 13.0, the Zn/Ni ionic ratio of 0.89 and the TEPA concentration of 0.58 M, were obtained by means of a regression model. This highest activity of the Zn-Ni deposits mainly consisting of the γ phase structure for hydrogen evolution is due to a combination of their good electrocatalytic activity and relatively high surface area. The electrocatalytic activity of these cathodes mainly composed of the γ phase Zn-Ni alloy was damaged by the selective dissolution of Zn from the deposits in 5 M KOH.     

ASSISTED CRACK GROWTH IN MARAGING STEEL WELDS BY GASEOUS HYDROGEN

Abstract— The effects of environmental hydrogen content on fatigue crack growth rates (FCGRs) in T-250 maraging steel plates and laser welds were investigated. The influence of ageing treatments on fatigue characteristics of the alloy was also studied. Experimental results revealed that the accelerated FCGRs in the presence of hydrogen were always associated with changes in fracture modes that appear in compact-tension specimens. Even for overaged specimens with excellent resistance to gaseous hydrogen embrittlement, such an acceleration of crack growth in hydrogen could not be avoided. The crack path of underaged specimens in hydrogen was found mainly along prior austenite boundaries for steel plates and along coarse columnar boundaries for welds. In gaseous hydrogen, peak-aged welds exhibited intergranular and quasi-cleavage mixed fracture modes, compared to mainly quasi-clevage for similar aged steel plates. Hence, the enhancement of crack growth in hydrogen was more pronounced for the welds. Overaged welds showed higher FCGRs than the same aged steel plates only in hydrogen and for Δ K values greater than 20MPa√m.     

Behavioristic image-based pose control of mobile manipulators using an uncalibrated eye-in-hand vision system

In the execution of material handling, the mobile manipulator is controlled to reach a station by its mobile base. This study adopts an uncalibrated eye-in-hand vision system to provide visual information for the manipulator to pick up a workpiece on the station. A novel vision-guided control strategy with a behavior-based look-and-move structure is proposed. This strategy is based on six image features, predefined by image moment method. In the designed neural-fuzzy controllers with varying learning rate, each image feature error is taken to generate intuitively one DOF motion command relative to the camera coordinate frame using fuzzy rules, which define a particular visual behavior. These behaviors are then fused to produce a final command action to perform grasping tasks using the proposed behavior fusion scheme. Finally, the proposed control strategy is experimentally applied to control the end-effector to approach and grasp a workpiece in various locations on a station.     

FIUT: A new method for mining frequent itemsets

This paper proposes an efficient method, the frequent items ultrametric trees (FIUT), for mining frequent itemsets in a database. FIUT uses a special frequent items ultrametric tree (FIU-tree) structure to enhance its efficiency in obtaining frequent itemsets. Compared to related work, FIUT has four major advantages. First, it minimizes I/O overhead by scanning the database only twice. Second, the FIU-tree is an improved way to partition a database, which results from clustering transactions, and significantly reduces the search space. Third, only frequent items in each transaction are inserted as nodes into the FIU-tree for compressed storage. Finally, all frequent itemsets are generated by checking the leaves of each FIU-tree, without traversing the tree recursively, which significantly reduces computing time. FIUT was compared with FP-growth, a well-known and widely used algorithm, and the simulation results showed that the FIUT outperforms the FP-growth. In addition, further extensions of this approach and their implications are discussed.