Improving the Gain-Frequency Performance of Cascaded Single-Stage Distributed Amplifiers with Bandpass Filter Structure

In this paper a bandpass filter structure is proposed for realizing the artificial transmission lines of cascaded single-stage distributed amplifiers (CSSDA) and the basic analysis and design of the bandpass structured CSSDA (BP-CSSDA) is demonstrated. Some of the lower frequency region in the gain-frequency band of the CSSDA is not utilized due to presence of the bias components in traditional design methods. By using the bandpass structure for the realization of artificial transmission lines, the unused portion of the gain-frequency band can be utilized. Therefore, one can obtain more bandwidth using the bandpass type artificial lines in the CSSDA than using the lowpass type lines. The gain of a CSSDA can be increased, by increasing the interstage termination impedance (Z _0int) without compromising the bandwidth. In this paper, a graphical method for determining the optimum Z _0int is introduced. Simulation results showing the advantage of using the BP structured artificial lines in the CSSDA is provided.     

Effect of solids on viability of acidophilic bacteria

The effect of solids (up to 30% w/w) on the viability of a mesophilic culture of acidophilic bacteria was investigated in stirred tank reactors (STRs) using the Rushton turbine (RT) and the pitched blade turbine impellers in a speed range of 2.01–3.35 m/s. The results showed that hydrodynamic shear alone as a characteristic function of impeller type and speed has a very limited effect on the bacterial cells during mixing in STRs, but mechanical damage to bacterial cells occurs, to a most significant extent, via the attrition by solid particles promoted by the intensity of agitation. Extent of the adverse effect on the bacterial cells was found to depend on impeller design/speed and solids density. The loss in the viability of bacterial population with a tendency to increase with agitation rate and solids density was more extensive with the RT than the PBT impellers under the same experimental conditions e.g. 72% loss in the viability c.f. 40% over 4 h of mixing at 20% w/w solids and 3.35 m/s impeller speed. The kinetic analysis of the experimental data suggest that the rate and extent of oxidation of a substrate in a given process would be controlled by the inoculum size and by the difference between the “normal” growth rate and the deactivation rate of bacterial cells incurred at a particular mixing condition (impeller type/speed and solids density) i.e. by the “actual” growth rate.     

Optimal Capital Structure Model for BOT Power Projects in Turkey

Interest in the Build/Operate/Transfer (BOT) scheme for infrastructure projects has been growing rapidly, and numerous projects have been implemented around the world. Through BOT projects, a government reallocates the risks and rewards in the development of large infrastructure projects to the private sector. One key aspect to the successful implementation of the BOT concept in any country is the raising of finance by project sponsors. Financial engineering techniques and capital structuring skills are required to find the proper mix of debt and equity and to achieve successful financing for the proposed project. The objective of this paper is to present a simplified model to determine the optimum equity level for decisionmakers at the evaluation stage of a BOT hydroelectric power plant (HEPP) project in Turkey, which takes place immediately after the completion of the feasibility study. The resulting model is the combination of a financial model and a linear programming model that incorporates an objective of maximizing the return of the project from the equity holder’s point of view. To show versatility of the model, a real case study is conducted. Thus, this research is concerned with the determination of an equity funding level in BOT project finance. There are different equity levels found in BOT HEPP projects, and there is a need for such a model to determine optimal capital structure, which would assist the project sponsors to ensure that the equity level necessary for optimal capital structure is available prior to the project implementation stage.     

Determination of fatty acids and some undesirable fatty acid isomers in selected Turkish margarines

The fatty acid composition and total trans fatty acid content in 10 margarines produced in Turkey were determined by capillary gas chromatography and Fourier transform‐infrared spectroscopy (FT‐IR) spectroscopy. The fatty acid composition ranged as follows: saturated fatty acids, C16:0 (palmitic) 11.3 to 31.8% and C18:0 (stearic) 5.7 to 8.7%, monounsaturated fatty acids, C18:1 (oleic) 21.8 to 35.7% and C18:1 trans isomers 0.4 to 27.4%, polyunsaturated fatty acid, C18:2 linoleic acid 5.2 to 40.2%. Some positional isomers of C18:1 as cis‐11‐octadecenoic acid varied from 0.7 to 4.6% and cis‐13 trace to 2.4%. The total trans fatty acid contents were between 0.9 and 32.0% when measured with capillary gas chromatography and between 0 and 30.2% with FT‐IR spectroscopy. Some of the margarines analyzed contained trace amount of trans fatty acids which could not be detected by FT‐IR spectroscopy.     

Vibration of multi-walled carbon nanotubes by generalized shear deformation theory

In this study, free vibration of simply supported multi-walled carbon nanotubes (CNTs) was investigated by using the generalized shear deformation-beam theory (GSDBT). Parabolic shear deformation theory (PSDT) is used in the specific solutions. Unlike Timoshenko beam theory present theory satisfies zero traction boundary conditions on the upper and lower surface of the structures so there is no need to use a shear correction factor. Free vibration frequencies and amplitude ratios were obtained and results are compared with previous studies. Results showed that significant difference exist between PSDT and Euler beam theory. Present results are slightly higher than the results of Timoshenko beam theory. Shear deformation effects are important especially for higher modes. It is obtained that van der Waals (vdW) forces should be considered for small inner radius.     

Layered clay/epoxy nanocomposites: Thermomechanical,flame retardancy,and optical properties

In this study, layered clay/polymer nanocomposites were developed based on epoxy resins and montmorillonite as the nanoplatelet reinforcement. Clay particles were treated with hexadecyltrimethylammonium chloride (HTCA) through an ion exchange reaction. In this way, Na⁺ interlayer cations of the clay is exchanged with onium cation of the surfactant that turns the hydrophilic clays (MMT) to organophilic (OMMT) characteristics. Thermal analysis results revealed that the glass transition temperature (T_g) and the dynamic mechanical properties including the storage and loss modulus of the neat epoxy resin increases by the incorporation of clay particles. It was also found that flame resistance of the polymer is improved by the addition of the clay particles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

MOS-only second order current-mode LP/BP filter

In this study, a current-mode dual output low-pass and band-pass filter is presented using only six MOSFET transistors in its core. Transconductances and gate-to-source capacitances of the MOS transistors are employed instead of passive resistors and capacitors. The proposed circuit exhibits important features such as simplicity, low-voltage/power operation, reduced chip area and wide frequency range compared to classical analog circuits that require active elements with large number of transistors. Simulations are performed to verify the theoretical results.     

Adsorption of hexavalent chromium from aqueous solutions by bio-chars obtained during biomass pyrolysis

In this study, bio-chars were evaluated as a potential adsorbent for the removal of Cr (VI) ions from aqueous solutions. The effects of some important parameters including initial pH (1.5–7), adsorbent dose (0.2–5 g/L), contact time (5–900 min) and initial Cr (VI) ion concentration (5–75 mg/L) were tested on the removal of Cr (VI) ions from aqueous solution in batch experiments. Maximum adsorption capacities of the tested bio-chars under the certain experimental conditions determined as optimal were 3.53 mg/g for NCBC, 3.97 mg/g for NZCBC and 6.08 mg/g for ACBC, respectively. Results of the kinetic and isotherm modeling studies revealed that the adsorption data fitted well with a pseudo-second order and Langmuir model. In among the tested bio-chars, the bio-char (ACBC) was largely equivalent to activated carbon: AC (9.97 mg/g) in terms of adsorption capacity. All results indicated that the bio-chars had higher adsorption capacity than some chars and activated carbons reported previously, and also that these bio-chars could be used successfully as low-cost adsorbents for the removal of chromium ions from aqueous solutions under the tested experimental conditions.     

Effects of minor Cu and Si additions on glass forming ability and mechanical properties of Co-Fe-Ta-B Bulk metallic glass

Effect of Cu and Si substitutions for Co and B on the glass forming ability (GFA) of Co_(43-x)Cu_xFe₂₀Ta_5.5B_(31.5-x)Si_y (x=0-1.5 and y=5-10) were systematically investigated by X-ray diffraction, optical microscopy, scanning electron microscopy, and differential scanning calorimetry. In order to evaluate the contribution of copper and silicon, appropriate amounts of copper and silicon were individually introduced to the base alloy composition. By using the effects of copper and silicon together, significant enhancement was obtained and the critical casting thickness (CCT) of the base alloy was increased three times from 2 mm to 6 mm. Moreover, mechanical properties of the alloys were examined by compression tests and Vickers hardness measurements. The compression test results revealed that the glassy alloys having enhanced GFA shows high strength of about 3500-4000 MPa. In addition, existence of (Co,Fe)₂B and (Co,Fe)_20.82Ta_2.18B₆ crystalline phases in glassy matrix influences the hardnesses of the alloys compared to monolitic glassy structure having hardness of about 1200 Hv.