Key Engineering Materials Vols. 656-657

Abstract: A influence of friction on the deformation behavior and strain homogeneity during ECAP has been studied by conducting 2D and 3D finite element simulations for a range of friction conditions m = 0 – 0.2. The deformation was more uniform in central steady zone as compared to the ends of the sample. The calculated ram load was higher in 3D simulations than 2D simulations. For a frictionless condition, the ram load was similar in both 2D and 3D simulations. Keywords: ECAP, SPD, FEM, Coulomb friction model, friction condition, ram load.

Abstract: The finite volume simulation of equal channel angular pressing (ECAP) was realized using 3D commercial code MSC.SuperForge. The knowledge of stress and temperature during ECAP process is very important for forming a hard-to-deform as Ti under optimal thermo-mechanical conditions to achieve desired mechanical properties. In this work, the strain, stress and temperature fields of both the die and workpiece are studied. The resulted stress and temperature distributions showed maximal values in the region of corner and channel angles of the die. Also, the temperature increased during the processing, as a consequence of the deformation. The heating of the deformation system was calculated and analyzed for three different ram speeds (v = 1, 10 and 20 mm/s) at 400 °C. Keywords: ECAP, SPD, FEM, FVM, heat transfer analysis, titanium

Abstract: In this research study, a synthetic exhaust gas system is employed to simulate various exhaust conditions similar to those from conventional diesel and Dual Fuel-Premixed Charge Compression Ignition (DF-PCCI) combustion. OEM DOC is tested to compare the effectiveness of reducing CO from both exhaust characteristics. Variations of the temperature and the concentration of CO, THC, and O₂ are done to investigate DOC performance on CO reductions according to Design of Experiment (DOE) concept. The results showed that in DF-PCCI exhaust conditions, DOC requires higher exhaust gas temperature as well as O₂ concentration to reduce CO emissions.

Abstract: In this paper, the Taguchi method is employed to systematically optimize the operating parameters of an anode-supported SOFC cell. Effects of cell temperatures (650, 675, and 700°C), fuel flow rates (400, 500, and 600 sccm), and oxidant flow rates (1000, 1500, and 2000 sccm) on electrochemical performance, fuel utilization, and electrical efficiency are investigated. The L₂₇ orthogonal arrays of Taguchi experiments are designed and carried out. The signal-to-noise ratios (S/N) indicate that the electrical efficiency is majorly determined by the hydrogen and air flow rates, while the power output is significantly affected by the operating temperatures. The analysis of variance (ANOVA) reveals that, under the operating temperature at 675°C with hydrogen and air flow rates respectively of 500 and 1500 sccm, the maximum power density is 480 mW/cm², where the overall electrical efficiency and fuel utilization is 51.9% and 86.1%, respectively.

Abstract: Dielectrophoresis (DEP) force will arise when an inhomogeneous AC electric field with sinusoidal wave is applied to microelectrodes. By using DEP, we could distinguish between viable and non-viable cells by their movement through a non-uniform electric field. In this paper, we propose a yeast cell separation system, which utilizes an Au DEP chip and an optical tweezers. The Au DEP chip is planar quadrupole microelectrodes, which were fabricated by Au thin-film and a box cutter. This fabrication method is low cost and simpler than previous existing methods. The tip of the optical tweezers was fabricated by dynamic chemical etching in a mixture of hydrogen fluoride and toluene. The optical tweezers has the feature of high manipulation performance. That does not require objective lens for focusing light because the tip of optical tweezers has conical shape. By using both the Au DEP chip and optical tweezers, we could obtain three-dimensional manipulation of specific cells after viability separation.

Abstract: As the single molecules detection tool, nanopore is applied in more and more fields, such as medicine controlled delivery, ion conductance microscopes, nanosensors and DNA sequencing. When molecules pass through a nanopore, they will physically block the pore and produce measurable changes in ionic currents under an external electrical potential. Based on analyzing the resultant electrical signals, it is possible to detect various bio-molecules.Generally, the capturing ratio of nanopre for molecules is dependent on the intensity of electrical potential, to which the duration time of event is inversely proportional. It is difficult to analyze the too short duration time. Therefore, we investigate the study on concentration gradient of ionic solution effect on the capturing ratio of nanopore for DNA, which is in order to get the higher capturing ratio with the invariant duration time.In the experiments, we add different concentration solution in trans and cis parts of naopore separately to form the concentration gradient. We use three different types nanopore (α-hemolysin nanopore, Si3N4 membrane nanopore, glass capillary nanopore) to compare and get the similar results. The events of DNA translocating through nanopore are observed more compressed during the fixed time under the higher concentration gradient and there is no change to the duration time of DNA passing through the nanopore. It is demonstrated that concentration gradient could increase the capturing ratio of nanopore for DNA.

Abstract: Optical interferometry methods are widely used for measuring microdisplacement with nanometer accuracy. However, most commercially available optical interferometry systems are large and expensive for manufacturing applications. In this study, we report the development of a low-cost portable optical interferometry microscope for factory use. The light source was a tungsten–halogen white lamp with an optical filter. The microscope has an objective lens with a numerical aperture of 0.3, a magnifying power of 10, and field depth of 3.056 μm. Interference images were collected with an NTSC CCD-video camera. The resolution of the interference image is 320 × 240 pixels and stored in BMP format. To obtain phase shifted interferometry images, a piezoelectric actuator was used to monitor the table movement along the optical axis. The total cost of all system parts is approximately 7000 to 8000 US dollars. To evaluate the basic performance of the developed interferometry microscope, we measured a steel ball, the penetration mark of a Rockwell scale hardness indenter, and a gauge block surface with a bump. The developed interferometry microscope can measure continuous and gently sloping surfaces. The processing time is approximately 10–20 s.

Abstract: Nanopore based sensors have been widely spread utilized for detection and analysis of various single charged molecules. However, collision and trap events also block the ionic current that interferes recording the actually translocation events. In order to resolve the problem, we propose inducing a salt gradient to turn the pulse form negative to positive. And the salt gradients dependence of pulse signals ranging from 1 M (cis & trans) to 1 M (cis) - 4 M (trans) is mapped. Experiment results demonstrate that applying a high salt gradient prolong translocation time 1.5 times and increase molecule capture rate by a fact of 3. It is benefit for nanopore further application.

Abstract: Microwave vacuum drying is one of innovative drying techniques that is today used in drying of foods, medical products and other high quality products. In this drying technology, heat is generated by directly transforming the electromagnetic energy into kinetic molecular energy of water, thus the heat is produced deep within the material to be dried under vacuum environment. This paper presents the results of research on microwave vacuum drying of “Cat Chu” mango in Mekong Delta – Vietnam. “Cat Chu” mango, with moisture content of (80 ± 1) % (wet basis - wb), was sliced into 5 cm thickness, and was dried in mWaveVac0150-lc dryer (Püschner - Germany). The drying vacuum was from 60 to 120 mbar. Three levels of microwave power were established: the first phase from 600 to 800 W, the second phase from 300 to 500 W, the last one from 150 to 250 W. The control sample was dried by convective drying method at 60 °C; and vacuum drying at 70 mbar, 60 °C. The results of this research showed that high quality product in terms of color, surface shrinkage and structure was obtained by microwave vacuum drying. The drying time was about 45 min, 450 min and 870 min with microwave vacuum drying, vacuum drying and convective hot-air drying, respectively. In addition, Fick’s equation and Crank’s solution were applied to analyze and calculate the accessibility and diffusion coefficient of microwave vacuum drying process. Starting accessibility of process was significantly increased; the diffusivity obtained was within a range from 6.44*10^-10 m²/s to 16.16*10^-10 m²/s. The results also indicated that there was a higher exchange in surface and a greater internal diffusion of experimental microwave vacuum drying samples compared to the control vacuum and hot-air drying samples.

Abstract: Injuries or other ailments can cause swelling of tissues in the body, or of ligaments and tendons surrounding the bones. Such inflammation can lead to discomfort, pain, or even serious illness. Knowledge of the biomechanics of soft tissues is essential for correct prognosis and diagnosis. This requires good modeling and simulation of soft skeletal tissues, which cannot be carried out without experimental material characterization. Behavior of organic tissues is quite similar to that of elastomeric materials that swell when immersed in certain fluids. This work investigates the effect of swelling on compression and bulk properties and the polymeric structure of a water-based elastomer. A drastic change in mechanical and structural properties is observed during the initial swelling period. Elastic and shear moduli decrease by nearly 90% within a few days, and then exhibit almost no change. An opposite trend can be observed for Poisson’s ratio; dramatic increase in the beginning, then a near-constant behavior. Variation in bulk modulus is somewhat fluctuating, but the general trend is a decrease due to swelling. After ten days of swelling, value of Poisson’s ratio becomes approximately 0.5. A sharp decrease in the first week of swelling can be observed in chain density, while cross-link average molecular weight shows the opposite trend of an increase with swelling (with minor fluctuations). Results of this study can provide the material input values for modeling and simulation of the behavior of tissues and other soft biological materials. This, in turn, can form a basis for more detailed analytical and computational studies in biomechanics and biomedical engineering.