Preparation and Characterization of Novel Polyimides from 2,6-bis[1-(p-dimethylaminophenylimino)ethyl] pyridine for the Selective Extraction of some Metals

Summary A group of new polyimides has been prepared by solution condensation of 2,6-bis[1-(p-dimethylaminophenylimino)ethyl] pyridine containing pendant NMe₂ units and various dianhyrides in N-methylpyrrolidone (NMP). The tridentate (N-N′-N) pydim ligands were prepared by Schiff-base condensation of 2,6-diacetylpyridine and 4-dimethylaminoaniline in the presence of formic acid as catalyst. These polymers were investigated for their extraction capabilities for Zn(II), Mn(II), Cu(II), Cd (II) and Ni(II) and at different pH. Under different conditions enhanced selectivity was observed. Up to 98% quantitative recoveries were observed for all metals.     

Estimation of Peak Flood Discharges at Ungauged Sites Across Turkey

The reliable forecasting of the peak flood discharge at river basins is a common problem, and it becomes more complicated when there is inadequate recorded data. The statistical methods commonly used for the estimation of peak flood discharges are generally considered to be inadequate because of the complexity of this problem. Recently, genetic programming (GP) which is a branch of soft computing methods has attracted the attention of the hydrologists. In this study, gene-expression programming (GEP) and linear genetic programming (LGP), which are extensions to GP, in addition to logistic regression (LR) were employed in order to forecast peak flood discharges. The study covered 543 ungauged sites across Turkey. Drainage area, elevation, latitude, longitude, and return period were used as the inputs while the peak flood discharge was the output. Model comparison results revealed that GEP predicted the peak flood discharges with R ²?=?57.4?% correlation, LGP with 56?% and LR model with 42.3?%, respectively. The peak flood discharges in all river basins can now be determined using the single equation provided by the GEP model.     

Frequency and Voltage Dependence of Dielectric Loss of MgB2 Composites at Different Temperatures

The dielectric loss (ε″) properties of MgB₂ composites were investigated by using the conductance–voltage (G/w–V) measurements in the wide frequency and applied bias voltage range at four different temperature levels. Experimental results show that both G/w and ε″ are found strong functions of frequency and applied bias voltage for each temperature level. These changes in G/w and ε″ are considerably high especially at low frequencies and temperatures. The values of ε″ decrease exponentially with increasing frequency until 100 kHz and then become almost constant. Such behavior of G/w and ε″ shows that interfacial polarization is more effective especially at low frequencies. In addition, the current–voltage (I–V) characteristics were also evaluated for 100, 200, and 300 K, and the I–V curves for each temperature show linear behavior. Results indicate that the G/w–V measurements may be a useful tool to characterize the dielectric properties and conductivity of MgB₂.     

Photoinduced electron transfer mechanism between green fluorescent protein molecules and metal oxide nanoparticles

Green fluorescent protein (GFP) molecules are attached to titanium dioxide and cadmium oxide nanoparticles via sol–gel method and fluorescence dynamics of such a protein–metal oxide assembly is investigated with a conventional time correlated single photon counting technique. As compared to free fluorescent protein molecules, time-resolved experiments show that the fluorescence lifetime of GFP molecules bound to these metal oxide nanoparticles gets shortened dramatically. Such a decrease in the lifetime is measured to be 22 and 43 percent for cadmium oxide and titanium dioxide respectively, which is due to photoinduced electron transfer mechanism caused by the interaction of GFP molecules (donor) and metal oxide nanoparticles (acceptor). Our results yield electron transfer rates of 3.139×10⁸ s⁻¹ and 1.182×10⁸ s⁻¹ from the GFP molecules to titanium dioxide and cadmium oxide nanoparticles, respectively. The electron transfer rates show a marked decrease with increasing driving force energy. This effect represents a clear example of the Marcus inverted region electron transfer process.     

Safety evaluation of a timber Warren truss hangar

This paper presents the preliminary test results of a destructive testing of a full-size wooden Warren truss hangar located at Canadian Forces Base Greenwood, Nova Scotia, Canada. A total of 16 Warren trusses were tested to failure (1) to determine the structural safety of the damaged and repaired timber structure, (2) to evaluate the effectiveness of the repair scheme and (3) to investigate the proposed repair scheme and reinforcement needed to restore the damaged members or joints and thus the structure to full capacity. Test results, based on load carrying performance, showed that the average failure load of the trusses was greater than the design ultimate load and that serviceability requirements were adequate and acceptable for all but one truss tested. While experimental evidence did not verify the significance of the influence of the post-tensioning process, it was found that gusset plate reinforcement at the joints had beneficial effects by increasing the load carrying capacities of the trusses by a marked margin.     

The effects of temperature,radiation, and illumination on current–voltage characteristics of Au/PVA(Co,Zn-doped)/n-Si Schottky diodes

Polyvinyl alcohol (PVA)/(Co-Ni) nanofiber film was fabricated on silicon wafer using electrospinning technique. The topography of the produced PVA/(Co-Ni) nanofiber film was examined by scanning electron microscopy (SEM). The Au/Poly (vinyl alcohol) (Co, Ni-doped)/n-Si Schottky diode (SD) was thermally formed in evaporating system after the spinning process. At first, the current–voltage (I–V) characteristics of Au/PVA (Co, Zn-doped)/n-Si SD was measured at the room temperature (300 K). For the investigating the effect of temperature, illumination and radiation on Au/PVA (Co, Zn-doped)/n-Si SD comparatively, the measurement was performed under the illumination intensity of 200 W, at 380K, and finally the radiation dose of 22 kGy respectively. The diode characteristics such as the zero-bias barrier height (ϕ_Bo), ideality factor (n) and series resistance (R_s) were calculated at room temperature and under the condition of high temperature, illumination, and radiation. It was found that these characteristics were affected by the illumination and radiation as well as the temperature. The density of interface states (N_ss) distribution profiles as a function of (E_c - E_ss) extracted from the forward I–V measurements were also affected by illumination and radiation even if just a bit. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Resonant frequency of an air gap tuned circular disc microstrip antenna

In this study, the formulation and the computation of the resonant frequency of an air gap tuned circular disc microstrip antenna are simplified, with improved accuracy, by using a new and very simple effective permittivity expression which is valid for thin and thick gaps. Very good agreement between the theoretical and the experimental resonant frequency values is obtained for the various structural parameters and operational modes.     

A new approach for the computation of design shear force in reinforced concrete walls subjected to seismic loads

This paper investigates the dynamic shear amplification in reinforced concrete shear walls designed according to the seismic provisions of the current Turkish Building Earthquake Code (TBEC-2018). Shear walls with a high ductility level and different aspect ratios are examined to evaluate the design shear force calculated by using the dynamic amplification factor (β_v) and overstrength factor (D) defined in TBEC-2018. For this purpose, response spectrum analyses (RSAs) are first carried out on two-dimensional cantilever shear walls with heights of 30, 45, and 60 m and with lengths of 1.5, 3, and 4.5 m in the plan. Then, a total of 198 nonlinear time history analyses (NLTHAs) are performed with real and simulated ground motions matched to the elastic design spectrum defined in TBEC-2018. The comparison of the design shear forces obtained from RSA and the shear demands obtained from NLTHA along the heights of the walls reveals that the design shear forces calculated according to TBEC-2018 may underestimate the actual shear demands from studied ground motions. Moreover, the applicability of the updates proposed to TBEC-2018 for the design shear force and shear force diagram along the wall height in reinforced concrete shear wall-frame systems to cantilever shear walls is also examined.     

Electrical and dielectric characteristics of Al/polyindole Schottky barrier diodes. II. Frequency dependence

The dielectric properties and ac electrical conductivity of Al/polyindole (Al/PIN) Schottky barrier diodes (SBDs) were investigated by using admittance spectroscopy (capacitance–voltage [C‐V] and conductance–voltage [G/ω‐V]) method. These C‐V and G/ω‐V characterizations were performed in the frequency range of 1 kHz to 10 MHz by applying a small ac signal of 40 mV amplitude from the external pulse generator, whereas the dc bias voltage was swept from (−10 V) to (+10 V) at room temperature. The values of dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tanδ), real and imaginary part of electrical modulus (M′ and M″), ac electrical conductivity (σ_ac), and series resistance (R_s) of the Al/PIN SBDs were found to be quite sensitive to frequency and applied bias voltage at relatively low frequencies. Although the values of the ε′, ε″, tanδ, and R_s of the device were observed to decrease with increasing frequencies, the electric modulus and σ_ac increased with increasing frequency for the high forward bias voltages. These results revealed that the interfacial polarization can more easily occur at low frequencies and that the majority of interface states (N_ss) between Al and PIN, consequently, contribute to deviation of dielectric properties of the Al/PIN SBDs. Furthermore, the voltage‐dependent profile of both R_s and N_ss were obtained from the C‐V and G/ω‐V characteristics of the Al/PIN SBDs at room temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011