PengSheng Wei

The Physics of Weld Bead Defects

Productivity in different welding techniques can be improved by increasing welding speed and current. This strategy, however, is limited by the appearance of surface defects such as rippling, humping, undercutting, etc [1]. Weld ripples exhibit rather regular, arc-shaped topographic features on a solidified surface, for example, as shown in Figure 1 in EBW of Al 6061 [2]. The ripples slightly elevate above the surface. Figure 2 shows a rippling structure on silicon surface irradiated by a p-polarized laser beam, provided by Pedraza et al. [3]. Notice tiny little “fingers” in lower rim of fringes and asymmetry in fringe profile taken in downward direction.

Nugget shape control in resistance spot welding

In resistance spot welding (RSW) thin workpieces held by two electrodes are joined via solidification of the molten nugget induced by heat generation from electrical resistances in workpieces and at the faying surface. Solidification starts after welding current is turned off, and heat is then transferred through the electrode to the coolant hole. RSW has been used in electronic, optical and medical packaging technologies. For example, micro-resistance spot welding has been used to attach outer shield clips to the plated steel cores of a circuit board during manufacturing of Motorolas MicroTAC cellular telephones. Small-scale parallel gap welding has been used to join high temperature microelectronic interconnects, and micro-resistance seam welding has been used to hermetically seal plated microelectronic packages. This study theoretically shows that the workpiece surface suffered from the defect of melting if electrode face radius and welding current frequency reduce, and welding current, Curie temperature and magnetic permeability increase.

Dynamic electrical resistance effects in resistance spot welding

The effects of dynamic electrical resistance subject to AC on transport variables, cooling rate and nugget shape during resistance spot welding are realistically investigated. The model accounts for electromagnetic force, heat generations and contact resistances at the faying surface and electrode-workpiece interfaces and bulk resistance in workpieces. Contact resistances are comprised of constriction and film resistances, which are functions of hardness, temperature, electrode force and surface condition. Except for the early stage of film breakdown, it is found that the influences of film resistance on the variations of dynamic resistances, contact and bulk resistances as well as transport processes are insignificant. The computed nugget thickness versus AC agrees well with available experimental data.

Effects of Bubble Growth and Solidification Rate on Pore Formation in Solid

The shapes of a pore in solid resulted from entrapment of a tiny bubble by a solidification front are predicted in this work. Pore formation and its shape in solid are one of the most critical factors affecting properties and microstructure, in materials. For simplicity without loss of generality, the tiny bubble is considered to have a spherical cap. From a geometrical analysis, the contact angle of the bubble cap on the solidification front or the pore shape in solid is found to be governed by the Abel equation of the first kind. The pore becomes closed by imposing a finite bubble growth rate-to-solidification rate ratio which can produce a minimal bubble radius at the contact angle of 90 degrees. Closure of a pore resulted from a greater solidification rate than bubble growth rate, as accepted in the literature, is incorrect.© 2012 ASME

Analysis of defects encountered in resistance spot welding

M electrochemical conversion and storage devices, such as fuel cells and redox-flow batteries, rely on the amazing properties of ion conducting polymer membranes. The development of polymer electrolyte membranes (PEMs) combining high ion conductivity and durability is a major challenge for materials chemistry. Nafion® (DuPont) is state of the art membrane due to its good mechanical strength, excellent proton conductivity and stability, but its limitation to low temperature operation, high cost and fuel crossover are major obstacles that renders its usage in commercialization of fuel cell. Various polymers have been synthesized and explored as an alternative membrane material to reduce cost and improved proton conduction to Nafion but most of these showed trade off properties. The membranes showing good conduction may have poor stability or mechanical strength. This fact impedes the technology to achieve commercialization status. In present study, radiochemical pore filled membranes were prepared in which porous polyethylene (PPE) substrate was radio-chemically grafted and filled with styrene/acrylic acid copolymer. Proton Exchange Membranes prepared through radiochemical pore filling process exhibited high ionic conductivity. High conductivity is attributed to the formation of micro level confinement within the membranes for ion transport is reported for the first time. Despite their simple preparation method, consisting single radiochemical grafting and pore-filling step using commercially available porous substrate, involves least amount of chemical. The polymer provides PEMs which exhibited exceptional proton conductivity at good but relatively lower ion-exchange capacity, as well as a high swelling resistance. An unprecedented hydroxide conductivity of 274 mS cm-1 is obtained at an ion-exchange capacity of 2.85 meq g-1 under optimal operating conditions. The exceptional ion conductivity appears related to the intrinsic microporosity of the charged polymer matrix, which facilitates rapid cation transport.

Fabrication of porous materials

B molecules such as EGF, TGF-β, BMP-2, are very important and useful materials in medical field; regenerative medicine and pharmacy. Immobilization method is one of current researching to overcome low stability and high cost of bioactive molecules. Chemical methods have been used widely for immobilization of bioactive molecules. However, there are some of drawbacks with this method. For example, chemical method may produce potential toxic by-product, and, in case of physical method, low efficiency of immobilized bioactive material is observed. To solve these problems, recently, the immobilization by photo-immobilization has been researched widely. The advantages of photo-immobilization are 1) high selectivity of chemical reactions or processes under mild conditions (ambient temperature of also much below), 2) typically no need for added catalysts or special solvents, 3) spatially addressable effects (2D and 3D structuring possible) and 4) applicable to very small and (relatively) large scales. To use for photo-immobilization, various natural polymers, such as gelatin, chitosan, hyaluronic acid reacted by irradiation to UV or visible light can be applied for medical area to increase biocompatibility and functionality, for example, coating agent for bioinert devices like stent and implant, anti-adhesive agent, wound dressing and bio-adhesive.Statement of the Problem: The endoprosthetics of hipand knee-joint replacements is currently the most common and successful methods in advanced surgery to treat degenerative joint disease for relieving pain and for correcting deformities. While these surgeries have positive outcomes, approximately 10% of the implants fail prematurely. The most common causes for revision surgeries are aseptic loosening and implant infection.T shape of a pore, resulting from a bubble entrapped by a solidification front, is predicted in this work. Porosity influences not only microstructure of materials, but also contemporary issues of various sciences of biology, engineering, foods, geophysics and climate change, etc. In this presentation, pore shape is determined by accounting for mass and momentum transport of solute across a self-consistent shape of the cap, as proposed previously. This work finds that there exist three different mechanisms for pore formation, depending on different directions and magnitude of solute transfer across the cap. Case 1 is subject to solute transport from the pore into surrounding liquid as a result of the cap emerged from a thin concentration boundary layer on the solidification front in the early stage. An increase in initial solute concentration in liquid decreases pore radius and times for bubble entrapment. Opposite directions of solute transport across the cap submerged into a thick concentration boundary layer along the solidification front, however, cannot result in bubble entrapment, because solute increases and decreases rapidly in late stage in Cases 2 and 3, respectively. The predicted pore shape in solid agrees with experimental data. Numerical computations of development of the pore shape associated with transport processes of fluid flow, temperature and concentration are also presented in Fig. 1.

Mass transfer controlling of pore shapes in solid

T current treatment of diabetes disease relies on insulin subcutaneous injection [1]. Because of parenteral administration drawbacks, alternative administration routes have been investigated [2]. Among all, the oral administration may lead to a better glucose regulation exploiting the liver first-pass metabolism of insulin, thus preventing the risks of fluctuating glycaemia. However, the oral bioavailability of peptides is very low and several efforts have been attempted to promote insulin bowel absorption. Despite all, the oral delivery of insulin remains an unmet need [3]. The aim of work was to prepare, characterize and evaluate both in vitro and in vivo a novel nanoformulated multiple-unit colon delivery system, i.e. coated pellets, as a possible oral nanocarrier for insulin. Insulin-loaded polymeric nanoparticles (NPs) were synthesized according to previously published protocols with some improvements [4]. The driving force of NPs formation was the opposite charges of polyethyleneimine and dextran sulphate resulting in the insulin entrapment into the polymeric matrix. NPs were incorporated into cores that were subsequently coated with three overlapping layers, aiming to release insulin into the large intestine: this gastrointestinal site is indeed characterized by a relatively low proteolytic activity. The system was evaluated in vitro for its physico-technological characteristics, NPs dispersion, disintegration and release performance, showing delayed release behavior. Finally, the coated nano-formulation effect was tested in diabetic rats: a significant hypoglycaemic activity, due to the synergistic effect of NPs and colon delivery, was observed. In this study, a new approach for the oral administration of insulin is proposed. The synergistic effect due to the nano-formulation of insulin and the encapsulation in a triple-layer pellet system for colon-release delivery results in a significant and long-lasting hypoglycemic effect. The impact of our multitasking macromolecule delivery system for oral insulin in controlling diabetes is clinically appealing, since it represents an oral route for insulin administration, with a prolonged hypoglycemic activity and a more physiological insulin metabolism.

Mechanisms of mass transfer on porosity during solidification

T alpha (α)-hematite (Fe2O3) nanomaterial is attractive due to its band gap, chemical robustness, availability in the nature and excellent photoelectrochemical (PEC) properties to split water into oxygen and hydrogen. However, the α-Fe2O3 suffers from low conductivity, slow surface kinetic, low carrier diffusion and greater electron-hole combination. The electronic properties such as carrier mobility and diffusion of α-Fe2O3 can be improved through doping, synthesis of composite material or formation of structured films. Recently, 2D-molybdenum disulfide (MoS2) has shown interesting photocatalytic activity due to its bonding, chemical composition, doping and nanoparticles grown on other 2D-film. Recently, our group has studied photoelectrochemical properties of hybrid film of regioregular poly (3-hexylthiophene-2, 5-diyl) (P3HT) with nanodiamond as well as P3HT-MoS2. In the present study, we have studied photoelectrochemical properties of polyhexylthiophene (RRPHTh)-nanodiamond (ND) and α-Fe2O3-MoS2 nanocomposite based electrodes films. The photoelectrochemical properties of α-Fe2O3-MoS2 as n-type and ND-RRPHTh as p-type electrodes in photoelectrochemical cell in various electrodes have been studied. We have obtained 3 to 4 times higher photocurrent and energy conversion efficiencies than the parent electrode based photoelectrochemical cell. We have synthesized nanocomposite α-Fe2O3MoS2 using sol-gel technique. The nanocomposite α-Fe2O3-MoS2 as well as ND-RRPHTh films were characterized using SEM, X-ray diffraction, UV-vis, FTIR and Raman techniques. The electrochemical techniques were used to understand the photocurrent in electrode/electrolyte interface of α-Fe2O3-MoS2 as well as ND-RRPHTh films in both acid base based electrolyte. The α-Fe2O3-MoS2 and ND-RRPHTh electrodes reveal improved production of hydrogen compared to α-Fe2O3 and aluminum doped α-Fe2O3 and MoS2 doped α-Fe2O3 nanostructured films. The band structure has been used to understand the mechanism of photoelectrochemical water splitting in p-n types based photoelectrochemical cell.Thermal degradation of two tung oil based reactive diluents, linseed oil alkyd and different amounts of two reactive diluents having paint formulations were investigated using TGA and DSC under non-isothermal conditions and dynamic nitrogen atmosphere and air. Activation energies were obtanied from Freidman method and Freeman-Carroll method and subsequently the preexponential factor, A, and reaction order,n,for reactive diluents and alkyd were also determined according to general rate equation. From kinetic analysis of the thermal degradation of using TGA, it was founded that thermal degradation of two diluents and alkyd has taken place in one stage but thermal degradation of all paint formulations have taken place in more than two stages. As shown from Freidman method and Freeman-Carroll method, the chemical composition and atmosphere of reactive diluents influenced the thermal degradation. Increasing reactive diluents decreased slightly the thermal stability of linseed oil alkyd.

Pore shape affected by gravity

Introduction: Gliomas represent nearly 70% of the central nervous system tumors. Despite the progress of chemotherapy and radiotherapy, the median survival is around 12-17 months. Studies have shown that the use of new natural antineoplastic agents has been highly effective and offers a wide field of research. The aim of this study is to investigate the antitumor potential of M chamissois Naudin chloroform partition and fractions on glioma cell lines.T is no doubt that the treatment of malignant tumors by chemotherapeutic drugs has contributed directly to the reduction or elimination of some of diseases, but the side effects of such drugs still represent a real fear at the feasibility of their use. In spite of that companies supplying such drugs subject drugs to many repeated experiments before approval for use. People that deal with these drugs must be very careful so as not to cause adverse or side effects, for both patient and medical staff supervisor. Due to the principle of treatment which is designed to kill only cancer cells and not others, it remains harmful which includes the effect of it on the rest of the body’s cells, especially germline cells or any associated somatic cells. Gemcitabine is a modern chemical drug used against many serious diseases including advanced cancers such as lung cancer, bladder and ovarian cancers & several blood cancers. Gemcitabine is one of the preferred choices in the treatment of pancreatic cancer. Short-term tests were conducted and the drug showed rapid and strong ability to detect toxicity or distorting the material studied in the neighborhood cells. Results showed that there are some changes in cell parameters which can be determined by cellular examination accurately. Also, exposing male inbred line SWR/J of laboratory mice to low dose of the drug Gemcitabine individually and combined affected significantly mitotic divisions and chromosomal aberrations and abnormalities.

Scaling of thermocapillary molten pool shape during laser melting

I two-dimensional (2D) electron system, electrons can move in two dimensions but are confined in the third, pretty much like billiard balls. Low-disorder 2D electron systems are currently the focus of a great deal of attention, particularly for low electron densities, where the interactions between them dominate their behavior, theoretical methods are still poorly developed, and new experimental results are of great interest. Consistent with Fermi liquid theory at high electron densities, these 2D systems are expected to freeze into a Wigner crystal in the dilute, strongly-interacting limit. In the intermediate regime, where interactions are not yet strong enough to cause crystallization, the electrons behave like a strongly-correlated liquid. Our recent data show that the low-temperature (fractions of 1 kelvin) properties of this strongly correlated electron liquid are unusual and very interesting. For example, the spin susceptibility grows and seemingly diverges as the electrons become more dilute, which indicates transition to a new state of matter (Wigner crystal or a precursor). Moreover, I will report the observation of strongly nonlinear voltage-current characteristics that display two distinct thresholds and a dramatic increase in noise at the breakdown of the insulating state. With the roles of voltage and current interchanged, this behavior is strikingly like that observed for the depinning of the vortex lattice in Type-II superconductors. Adapting the model used for vortexes to the case of an electron solid yields good agreement with our experimental results. This strongly favors the formation of the electron solid in the insulating phase as the double threshold behavior cannot be described within existing alternative models.W use the SU(3) Schwingers boson theory to study the spin transport properties of two-dimensional anisotropic frustrated Heisenberg model at T=0. We have investigated the behavior of the spin conductivity in diferent frustrated spin systems that presents exchange interactions J1, J2 and J3. We have studied the spin transport in the Bose-Einstein condensation regime where the bosons tz are condensed. Our results show an influence of the quantum phase transition point on the spin conductivity behavior. We also have made a diagrammatic expansion for the green-function and do not have obtained any significative change on the results.N methods for differential equations are one of the notable glories of contemporary science. Coupled with much algorithmic ingenuity, numerical methods are widely applied across science and engineering fields. One of the most important numerical methods is the numerical integration which has been the focus of intense research since its development in 1915 by David Gibb. In this abstract, we present the study of numerical integrator based on Fer expansion in the integration of the time-dependent Schrodinger equation (TDSE) which is a central problem to nuclear magnetic resonance (NMR) in general and solid-state NMR in particular. Numerical simulations of NMR experiments are often required for the development of new techniques and for the extraction of structural and dynamic information from the spectra. The development and design of various pulse sequences and understanding of different NMR experiments are based on the form of effective Hamiltonian or effective propagator that satisfies the TDSE which is difficult to solve unless the Hamiltonian is time independent or commutes with itself at two different times. The evolution operator allows obtaining the density matrix of the spin system that has evolved from the equilibrium density matrix due to the application of RF irradiation. The signal intensity depends on the final density matrix of the spin system. For example, if the numerical model is implemented with the approximate solutions of Fer or Magnus, the results of the simulation will show incorrect or undesirable effects of finite pulses and ring-down mainly when dealing with quadrupolar nuclei (I>1/2). In this study we proposed an efficient numerical integrator based on Fer expansion for solving the TDSE to obtain an effective propagator that continually improves the detected NMR signal. We will also compare the performance of the numerical integrator based on Fer expansion with respect to other Lie-group solvers, namely Magnus and Cayley methods.