Plasma polymerization‐modified bacterial polyhydroxybutyrate nanofibrillar scaffolds

The design and the development of novel scaffold materials for tissue engineering have attracted much interest in recent years. Especially, the prepared nanofibrillar scaffold materials from biocompatible and biodegradable polymers by electrospinning are promising materials to be used in biomedical applications. In this study, we propose to produce low‐cost and cell‐friendly bacterial electrospun PHB polymeric scaffolds by using Alcaligenes eutrophus DSM 545 strain to PHB production. The produced PHB was characterized by Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR). Nanofibrous scaffolds were fabricated via electrospinning method that has a fiber diameter approximately 700–800 nm. To investigate cell attachment, cell growth, and antioxidant enzyme activity on positively and negatively charged PHB scaffold, PHB surface was modified by plasma polymerization technique using polyethylene glycol (PEG) and ethylenediamine (EDA). According to the results of superoxide dismutase (SOD) activity study, PEG‐modified nanofibrillar scaffolds indicated more cellular resistance against oxidative stress compared to the EDA modification. As can be seen in cell proliferation results, EDA modification enhanced the cell proliferation more than PEG modification, while PEG modification is better as compared with nonmodified scaffolds. In general, through plasma polymerization technique, surface modified nanofibrillar structures are effective substrates for cell attachment and outgrowth. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Determination of the Junction Recombination Velocity Initiating the Short Circuit Situation Sfsc of a Bifacial Silicon Solar Cell Irradiated Under Magnetic Field in Dynamic Frequency Regime

The object of this work, a study of the junction recombination velocity limiting the short circuit (Sfsc) of a silicon solar cell under magnetic field in the dynamic frequency regime is presented. From the continuity equation, the density of minority Charge carrier’s in the base and the photocurrent are determined. The study of this photocurrent, according to the junction recombination velocity, allows us to determine the junction recombination velocity limiting the short circuit. The photocurrent density is studied as a function of the junction recombination velocity for different modulation frequencies. From the variation profile of the photocurrent density as a function of the junction recombination velocity, a technique for determining junction recombination velocity initiating the short-circuit situation is presented.

     

Synthesis,Characterization, and In Vitro Bioactivity of Sol‐Gel‐Derived Zn,Mg, and Zn‐Mg Co‐Doped Bioactive Glasses

Bioactive glasses in the systems CaO‐SiO₂‐P₂O₅‐ZnO, CaO‐SiO₂‐P₂O₅‐MgO, and CaO‐SiO₂‐P₂O₅‐MgO‐ZnO were prepared and characterized. Bioactive glass powders were produced by the sol‐gel method. The prepared bioactive glass powders were immersed in a simulated body fluid (SBF) for periods of up to 28 days at 310 K to investigate the bioactivity of the produced samples. Inductively coupled plasma (ICP) and ultraviolet (UV) spectroscopic techniques were used to detect changes in the SBF composition. X‐Ray diffraction (XRD) was utilized to recognize and confirm the formation of a hydroxyapatite (HA) layer on the bioactive glass powders. Microstructural characterizations of the bioactive glass samples were investigated by scanning electron microscopy (SEM) techniques. Density, porosity, and surface area values of bioactive glass powders were also determined in order to characterize the textural properties of the samples. The results revealed the growth of an HA layer on the surface of the bioactive glass samples. MgO in the glass sample increases the rate of formation of an HA layer while ZnO in the glass slows it down.     

Experimental determination of effective moisture diffusivities of whole- and cut-rosehips in convective drying

Average effective moisture diffusivities for both the whole- and cut-rosehips were obtained during convective drying. The effects of process variables such as air temperature, air velocity and air absolute humidity on effective moisture diffusivity were studied. The average effective moisture diffusivity in rosehip ranged between 1.45 × 10^?10 and 10.3 × 10^?10 m²/s for whole-rosehip and between 1.44 × 10^?9 and 5.13 × 10^?9 m²/s for cut-rosehip at the temperatures studied. Activation energies for convective drying were found to be 62 kJ/mol for whole-rosehips and 58 kJ/mol for cut-rosehips.     

Pre-service teachers' perspectives of the diffusion of information and communications technologies (ICTs) and the effect of case-based discussions (CBDs)

This study investigates pre-service teachers' perspectives of the diffusion of information and communication technologies (ICTs) in elementary education and the effect of case-based discussions (CBDs). The sample consisted of 170 first-year pre-service teachers from elementary teacher education programs of the largest teacher education college in Turkey. The cases used in the study were obtained from a case repository at http://ornekolay.org, indexing teaching cases from elementary classrooms of the capital city of Turkey. The cases were mainly text-based and presented stories of elementary teachers' in-class usage of ICTs. A quasi-experimental pretest-posttest design was executed to test the effect of pre-service teachers' perspectives on ICTs diffusion in elementary teaching. Three scales were developed based on Rogers' Diffusion of Innovation Theory (2003) to measure pre-service teachers' preferred innovativeness, innovation perceptions, and innovation decisions in the use of ICTs. The results showed that pre-service teachers had pre-established perspectives, mainly positive, about the diffusion of ICTs in elementary teaching; their perceptions about innovativeness and relative advantage were the main indicators of persuasion and decision; and CBDs positively affected their perceptions such that their computer-related persuasion and decisions positively increased.     

Thermodynamics and thermal stress analysis of thermoelectric power generator: Influence of pin geometry on device performance

Thermodynamics and thermal stress analysis of thermo-electric power generator is carried out. The influence of device geometry on thermal stress, thermal efficiency and output power is examined. The finite element method is incorporated to predict temperature and stress fields in the thermo electric device. It is found that thermal efficiency improves for certain geometric configuration of the device. In this case; the maximum thermal stress developed in the pin reduces slightly indicating improved life expectation of the device.     

Suppression of asymmetric flow behavior downstream of two side-by-side circular cylinders with a splitter plate in shallow water

The flow downstream of a pair of circular cylinder in a side-by-side arrangement normal to the free stream is known to exhibit intermittently bistable structure for the range of G/D = 1.2–2.2 where G is the center-to-center distance between the cylinders and D is the diameter of the cylinder. Eventually, the wake downstream of one of the two cylinders can be wider or narrower than the one downstream of the other cylinder depending on the direction of gap-flow deflection. In the present study, such an asymmetric flow behavior downstream of two side-by-side cylinders, which were vertically located in shallow water, was passively controlled with a splitter plate with a length of L   (1?L/D?5$1?L/D?5$). The center of splitter plate was just coincided with the mid-height of the gap between centers of the cylinders. The investigations were carried out in a water channel using dye visualization and particle image velocimetry, PIV for qualitative and quantitative measurements, respectively. The diameter of the cylinder, D was 40 mm while the depth of water was 20 mm so that the shallow flow condition was provided through the experiments. The Reynolds number, Re based on D was 5000 and the cylinder’s center to center spacing to the cylinder diameter ratio (G/D  ) was equal to 1.25. The results demonstrated that the deflection of the wake and thereby the bistability of the wake was considerably prevented with the presence of the splitter plate for L/D?3$L/D?3$ which resulted in two well symmetric, stable wakes having approximately the same order of magnitudes of vortex shedding frequencies around the cylinders.     

Comparison of tool life between ceramic and cubic boron nitride (CBN) cutting tools when machining hardened steels

This paper describes a comparison of tool life between ceramics and cubic boron nitride (CBN) cutting tools when machining hardened bearing steels using the Taguchi method. An orthogonal design, signal-to-noise ratio (S/N) and analysis of variance (ANOVA) were employed to determine the effective cutting parameters on the tool life. First order linear and exponential models were carried out to find out the correlation between cutting time and independent variables. Second order regression model was also extended from the first order model when considering the effect of cutting speed (V), feed rate (f), hardness of cutting tool (TH) and two-way of interactions amongst V, f, TH variables. The results indicated that the V was found to be a dominant factor on the tool life, followed by the TH, lastly the f. The CBN cutting tool showed the best performance than that of ceramic based cutting tool. In addition, optimal testing parameter for cutting times was determined. The confirmation of experiment was conducted to verify the optimal testing parameter. Furthermore, the second order regression model and exponential model supported the first order model regarding the prediction capability. Improvements of the S/N ratio from initial testing parameters to optimal cutting parameters or prediction capability depended on the S/N ratio and ANOVA results. Moreover, the ANOVA indicated that the cutting speed was a higher significant but other parameters were also significant effects on the tool lives at 90% confidence level. The percentage contributions of the cutting speed, tool’s hardness, and feed rate were about 41.63, 32.68, and 25.22 on the tool life, respectively.     

Pressure casting of a zirconia-toughened alumina fiber-reinforced NiAl composite

A pressure-cast NiAl composite reinforced with polycrystalline alumina (PRD-166) fibers containing 0.2 weight fraction of partially stabilized zirconia was examined by optical and transmission electron microscopy (TEM). Fibers in the preform used for casting were forced into contact, and fiber bonding occurred in a number of instances. Fiber volume fraction was increased from an initial value of 0.4 to 0.6 as a consequence of the applied pressure. An explanation is offered for the interaction of applied pressure, wetting angle, and the rigidity of the fiber preform on the final volume fraction of the fibers in the composite. At the fiber/matrix interface, the alumina was free of zirconia particles. It is proposed that alumina grain growth forced the zirconia into the molten NiAl, where it dissolved. As solidification took place, the concentration of zirconium in the molten NiAl increased to a point where zirconium reacted with alumina to form zirconia again.     

Vibration control of an elastic strip by a singular force

Vibration characteristics of an elastic plate in the shape of an infinite strip are changed by applying a lateral concentrated force to the plate. The homogeneous, isotropic, elastic plate is infinite in the x-direction and the sides are simply supported. The size of the force is changed in proportion to the displacement measured at a certain point of the plate. The proportionality constant serves as the control parameter. The mathematical formulation of this distributed control problem and its analytical solution in terms of the vibration frequencies of the plate are given. The vibration frequencies are plotted as a function of the control parameter.