Analysis of voltage and frequency-dependent series resistance and interface states of Al/ZnCo2O4: Gelatin/n-Si diode

Journal of Materials Science: Materials in Electronics - In this work, which aims to investigate the capacitance and conductance properties of ZnCo2O4-doped Gelatin, 5% ZnCo2O4-doped Gelatin film...     

Quantifying selected growth parameters of Leptothrix discophora SP-6 in biofilms from oxygen concentration profiles

It is a dubious but common practice to use growth parameters measured in suspended cultures to predict substrate concentration profiles in biofilms. To obtain biofilm biokinetic parameters that apply to biofilms, a reliable method is needed that allows the computation of biokinetic parameters from substrate concentration profiles measured directly in biofilms. We have developed such a method and demonstrated its utility by evaluating biokinetic parameters from oxygen concentration profiles measured in biofilms of Leptothrix discophora SP-6 grown on a membrane, which was placed on top of an agar plate by fitting the data to Monod or Tessier growth kinetics, including maintenance substrate consumptions. We found that the Monod model represented the growth of L. discophora SP-6 biofilms marginally better than the Tessier model. The Monod half saturation coefficient was .     

Shape memory response of porous NiTi shape memory alloys fabricated by selective laser melting

Porous NiTi scaffolds display unique bone-like properties including low stiffness and superelastic behavior which makes them promising for biomedical applications. The present article focuses on the techniques to enhance superelasticity of porous NiTi structures. Selective Laser Melting (SLM) method was employed to fabricate the dense and porous (32–58%) NiTi parts. The fabricated samples were subsequently heat-treated (solution annealing?+?aging at 350?°C for 15?min) and their thermo-mechanical properties were determined as functions of temperature and stress. Additionally, the mechanical behaviors of the samples were simulated and compared to the experimental results. It is shown that SLM NiTi with up to 58% porosity can display shape memory effect with full recovery under 100?MPa nominal stress. Dense SLM NiTi could show almost perfect superelasticity with strain recovery of 5.65 after 6% deformation at body temperatures. The strain recoveries were 3.5, 3.6, and 2.7% for samples with porosity levels of 32%, 45%, and 58%, respectively. Furthermore, it was shown that Young’s modulus (i.e., stiffness) of NiTi parts can be tuned by adjusting the porosity levels to match the properties of the bones.

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The effects of conceptual change texts accompanied with animations on overcoming 11th grade students’ alternative conceptions of chemical bonding

This paper aims to determine the effect of conceptual change texts accompanied with computer animations on 11th grade students’ understanding and alternative conceptions related to chemical bonding. One experimental group (EG; N = 28) and one comparison group (CG; N = 30) were used in the study. While the comparison group taught traditional instruction, the experimental group received conceptual change text accompanied with computer animations instruction. Chemical bonding achievement test was applied as pre-test, post-test and delayed test to collect data. The results of the study indicated that while there is no statistically significant difference between groups in pre-test, performance of EG students is greater than the CG ones in post-test and delayed test. And also, the EG students are better in remediating their alternative conceptions related to chemical bonding. Based on the study, it is concluded that conceptual change texts combined with computer animations can be effective instructional tools to improve students’ conceptual understanding of chemical concepts.     

Optimum shape design of die and preform for improved hardness distribution in cold forged parts

Hardness of a cold formed part increases due to plastic deformation induced during the forming process. Hardness affects forgability of the part as well as its mechanical performance in use. In this study, a method was proposed to optimize the shape of preform and die to minimize variation in hardness distribution. The method was applied to backward extrusion. A finite element model of the mechanical behavior of the material during processing was developed to predict the effective strain distribution in the part. The hardness distribution was determined using an analytical relation between effective strain and hardness. An optimization code based on the Nelder-Mead search algorithm was developed and integrated with the finite element model. The results showed the effectiveness of the proposed method.     

Measurement of thermal neutron cross section and resonance integral for (n,γ) reaction in Sm

This study implies that ⁵⁵Mn(n,γ)⁵⁵Mn monitor reaction may be a convenient alternative comparator for the activation method and thus, it was used for the determination of thermal neutron cross section (TNX) and the resonance integral (RI) of the reaction ¹⁵²Sm(n,γ)¹⁵³Sm. The samples of MnO₂ and Sm₂O₃ diluted with Al₂O₃ powder were irradiated within and without a cylindrical 1 mm-Cd shield case in an isotropic neutron field obtained from the ²⁴¹Am–Be neutron sources. The γ-ray spectra from the irradiated samples were measured by high resolution γ-ray spectrometry with a calibrated n-type Ge detector. The correction factors for γ-ray attenuation, thermal neutron and resonance neutron self-shielding effects and epithermal neutron spectrum shape factor (α) were taken into account in the determinations. The thermal neutron cross section for ¹⁵²Sm(n,γ)¹⁵³Sm reaction has been determined to be 204.8 ± 7.9 b at 0.025 eV. This result has been obtained relative to the reference thermal neutron cross section value of 13.3 ± 0.1 b for the ⁵⁵Mn(n,γ)⁵⁶Mn reaction. For the TNX, most of the experimental data and evaluated one in JEFF-3.1, ENDF/B-VI, JENDL 3.3 and BROND 2.0, in general, agree well with the present result. The RI value for ¹⁵²Sm(n,γ)¹⁵³Sm reaction has also been determined to be 3038 ± 214 b, relative to the reference value of 14.0 ± 0.3 b for the ⁵⁵Mn(n,γ)⁵⁶Mn monitor reaction, using a 1/E^1+α epithermal neutron spectrum and assuming Cd cut-off energy of 0.55 eV. In surveying literature, the existing experimental and evaluated data for the RI values are distributed from 1715 to 3462 b. However, when the Cd cut-off energy is defined as 0.55 eV, the present RI value agrees with some previously reported RI values, 3020 ± 163 b by Simonits et al., 3141 ± 157 by Van Der Linden et al., and 2962 ± 54 b by Kafala et al., within the limits of error.     

New computation method for characteristic modes

To compute the characteristic modes of a perfectly conducting object a new weighted eigenvalue equation is derived, using the magnetic-field integral equation. The method of moments is used to solve this eigenvalue equation, and a number of bodies of revolution are examined. The results are presented and compared with those of previous methods.     

Shock tube coupled to the time-of-flight mass spectrometer via a molecular beam sampling system

A method for continuous mass spectrometric analysis of high-temperature reacting gas mixtures is described. The apparatus consists of a unique combination of three devices: the shock tube, the time-of-flight mass spectrometer, and the supersonic molecular beam. The driven section of the shock tube constitutes the reservoir of a supersonic molecular beam by which gas is continuously extracted from the reaction zone and introduced through a two-stage high-capacity vacuum system into the ionization region of the mass spectrometer. The shock tube and the mass spectrometer are coupled at right angles to one another. This configuration avoids excessive pressure buildup in the mass spectrometer system. The apparatus has an estimated mass resolution of 100 amu, a frequency range of 10-100 kHz, and can be operated over a wide range of shock conditions during the complete high-temperature pulse.     

Measurement of thermal neutron cross-section and resonance integral for the Yb(n,γ)Yb reaction by the cadmium ratio method

The thermal-neutron cross-section and the resonance integral for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction were measured by the activation method using a ⁵⁵Mn monitor as single comparator. Analytical grade MnO₂ and Yb₂O₃ powder samples with and without a cylindrical 1 mm Cd shield box were irradiated in an isotropic neutron field obtained from three ²⁴¹Am-Be neutron sources. The gamma-ray spectra from the activated samples were measured with a calibrated n-type high-purity Ge detector. The experimental results were corrected for the correction factors calculated for thermal and epithermal neutron self-shielding effects, epithermal neutron spectrum shape and gamma-ray self attenuation. Thus, the thermal neutron cross-section for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction is found to be 126.5 ± 6.6 b, relative to that of the ⁵⁵Mn monitor. The resonance integral value for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction is found to be 59.6 ± 8.5 b, at cadmium cut-off energy of a 0.55 eV. Using the measured cadmium ratios of ⁵⁵Mn and ¹⁷⁴Yb, the result for resonance integral of the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction has also been obtained relative to the reference value of the ⁵⁵Mn monitor. The present results for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction agree well only with the recent experimental ones obtained by Kafala et al. [1] and De Corte and Simonits [2] within uncertainty limits. However, the previously reported experimental data for the thermal neutron cross-section for this reaction are distributed between 24 and 141 b, and similarly the experimental values for the resonance integral value also show a large scatter in the range of 30-69 b.