Buckling analysis of functionally graded microbeams based on the strain gradient theory

The buckling behavior of size-dependent microbeams made of functionally graded materials (FGMs) for different boundary conditions is investigated on the basis of Bernoulli–Euler beam and modified strain gradient theory. The higher-order governing differential equation for buckling with all possible classical and non-classical boundary conditions is obtained by a variational statement. The effects of the power of the material property variation function, boundary conditions, slenderness ratio, ratio of additional material length scale parameters for two constituents, beam thickness-to-additional material length scale parameter ratio on the buckling response of FGM microbeams are investigated. Some comparative results are presented in tabular and graphical form in order to show the differences between the results obtained by the present model and those predicted by modified couple stress and classical continuum models.     

Rational Engineering of Hydratase from Lactobacillus acidophilus Reveals Critical Residues Directing Substrate Specificity and Regioselectivity

Enzymatic conversion of fatty acids (FAs) by fatty acid hydratases (FAHs) presents a green and efficient route for high-value hydroxy fatty acid (HFA) production. However, limited diversity was achieved among HFAs, to date, with respect to chain length and hydroxy position. In this study, two highly similar FAHs from Lactobacillus acidophilus were compared: FA-HY2 has a narrow substrate scope and strict regioselectivity, whereas FA-HY1 utilizes longer chain substrates and hydrates various double-bond positions. It is revealed that three active-site residues play a remarkable role in directing substrate specificity and regioselectivity of hydration. If these residues on FA-HY2 are mutated to the corresponding ones in FA-HY1, a significant expansion of substrate scope and a distinct enhancement in hydration of double bonds towards the ω-end of FAs is observed. A three-residue mutant of FA-HY2 (TM-FA-HY2) displayed an impressive reversal of regioselectivity towards linoleic acid, shifting the ratio of the HFA regioisomers (10-OH/13-OH) from 99:1 to 12:88. Notable changes in regioselectivity were also observed for arachidonic acid and for C₁₈ polyunsaturated fatty acid substrates. In addition, TM-FA-HY2 converted eicosapentaenoic acid into its 12-hydroxy product with high conversion at the preparative scale. Furthermore, it is demonstrated that microalgae are a source of diverse FAs for HFA production. This study paves the way for tailor-made FAH design to enable the production of diverse HFAs for various applications from the polymer industry to medical fields.     

Fatty acid hydratase for value-added biotransformation:A review

The synthesis of hydroxy fatty acids(HFAs) from renewable oil feedstock by addition of water onto C_C bonds has attracted great attention in recent years. Given that selective asymmetric hydration of non-activated C_C bonds has been proven difficult to achieve with chemical catalysts, enzymatic catalysis by fatty acid hydratases(FAHs) presents an attractive alternative approach to produce value-added HFAs with high regio-, enantioand stereospecificity, as well as excellent atom economy. Even though FAHs have just been investigated as a potential biocatalyst for a decade, remarkable information about FAHs in different aspects is available; however, a comprehensive review has not been archived. Herein, we summarize the research progresses on biochemical characterization, structural and mechanistic determination, enzyme engineering, as well as biotechnological application of FAHs. The current challenges and opportunities for an efficient utilization of FAHs in organic synthesis and industrial applications are critically discussed.     

Kraftschlüssigkeit in einfachen Getrieben

Zusammenfassung Beim übertragen der Bewegungen und der Kr?fte in den Getrieben wird stillschweigend eine stetige Kraftschlüssigkeit in den Gelenken des Getriebes vorausgesetzt. Für die einfachen Getriebe l?βt, sich mit Hilfe bequem anwendbarer Bedingungen feststellen, ob diese Voraussetzung erfüllt ist oder welche zus?tzliche Forderung diese Voraussetzung andernfalls gew?hrleistet. Insbesondere bei den schnellaufenden, ungleichf?rmig übersetzenden einfachen Getrieben kann man durch stetiges Erzwingen der Kraftschlüssigkeit in den Gelenken die nachteilige Wirkung des Gelenkspiels auf den Bewegungsvorgang und auf die Lebensdauer weitgehend ausschalten.     

Investigation of electrokinetic and electrorheological properties of polyindole prepared in the presence of a surfactant

In this study, synthesis of polyindole (PIN) was carried out without and with the presence of a sodium dodecyl sulfate (SDS) surfactant (SPIN), using FeCl₃ as an oxidizing agent. The synthesized materials were subjected to various characterizations techniques namely: particle size, magnetic susceptibility, elemental analysis, density, conductivity, dielectric constant, FTIR, ¹H NMR, TGA, XRD, and SEM. Characterization results revealed the successful preparation of the homopolymers of PIN and SPIN. Zeta (ζ)-potentials of the samples were measured in aqueous and non-aqueous (silicone oil, SO) media. Electrokinetic properties of PIN and SPIN in aqueous media were determined by ζ-potential measurements in the presence of various electrolytes (NaCl, BaCl₂, AlCl₃, Na₂SO₄) and surfactants (cetyltrimethyl ammonium bromide, SDS, and Triton X-100). Besides, the effect of pH onto ζ-potentials of the materials was also examined. The suspensions prepared in SO were subjected to external electric field strength and their electrorheological (ER) properties were investigated. Then the effects of shear rate, frequency, and temperature onto ER activities of the suspensions were examined. Further, creep and creep–recovery tests were applied to the PIN/SO and SPIN/SO suspension systems and reversible non-linear viscoelastic deformations observed under applied electric field.     

Magnetic Properties of Sm1?x Tb x Ni4B compounds

Physical properties of the Sm_1?x Tb _x Ni₄B (0??x??0.8) compounds have been investigated by means of the X-ray powder diffraction, AC-susceptibility and DC-magnetization techniques. All the compounds studied crystallize in CeCo₄B-type structure with P6/mmm space group. The substitution of Tb for Sm leads to a decrease of the unit-cell parameters a,c and the unit-cell volume V. The magnetic phase transition temperatures are found as 39, 30, 26, 22 and 15 K, for x=0, 0.2, 0.4, 0.6 and 0.8, respectively. In addition, we have seen the second magnetic phase transition around 230 K, at the ac-susceptibility results. We have concluded that this behavior may arise from the Tb?CTb interaction in crystal structure.     

Magnetic Characterizations of Cobalt Oxide Nanoparticles

Cobalt oxide (Co₃O₄) nanoparticles were synthesized by a novel microwave-assisted decomposition reaction of the cobalt nitrate hexahydrate, Co(NO₃)₂?6H₂O. While most of the traditional methods for the preparation of Co₃O₄ are at relatively high temperature, microwave-assisted decomposition was adapted to have better control in the production of Co₃O₄ nanoparticles. The temperature dependence of the magnetic properties for the Co₃O₄ was investigated by vibrating sample magnetometer (VSM) and electron spin resonance (ESR) techniques. VSM and ESR measurements have shown a phase transition occurring at around 31?K, as the antiferromagnetic transition temperature for the bulk Co₃O₄ crystal exhibits almost the same value. The average particle size of the sample at around the transition temperature is estimated as 2.015?nm. The title compound was characterized and identified by an x-ray powder diffraction (XRD).     

Chemical preparation of conducting polyfuran/poly(2‐chloroaniline) composites and their properties: A comparison of their components,polyfuran and poly(2‐chloroaniline)

Conductive homopolymers and composites of poly(2‐chloroaniline) (P2ClAn) and polyfuran (PFu) were synthesized chemically in hydrous and anhydrous media, and their properties were investigated. The polymers and composites were characterized by Fourier infrared spectroscopy, ultraviolet‐visible absorption spectroscopy, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, magnetic susceptibility, and conductivity measurements. It was found that the PFu/P2ClAn composite is thermally more stable than both the P2ClAn/PFu composite and the homopolymers. It was determined from Gouy scale measurements that conducting mechanisms of homopolymers and composites are polaron and bipolaron in nature. It was observed that the conductivity and magnetic susceptibility values changed with a changing amount of the guest polymer in the prepared composites. The conductivity (3.21 × 10^?2 S/cm) of the P2ClAn/PFu (55.8% m/m) composite was found to be higher than the conductivities of both homopolymers (σ_PFu = 1.44 × 10^?5 S/cm; σ_P2ClAn = 1.32 × 10^?3 S/cm). It was determined that the composites synthesized had different conductivities and morphological and thermal properties from changing synthesis order. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2924–2931, 2003     

Properties of concrete containing waste glass

In our study, in which waste glass (WG) is considered as coarse aggregates in the concrete, WG was used reduced to 4-16 mm in proportions of 0-60% in the production of PKÇ/B 32.5/R type cement. The effects of WG on workability and strength of the concrete with fresh and hardened concrete tests were analyzed. As a result of the study conducted, WG was determined not to have a significant effect upon the workability of the concrete and only slightly in the reduction of its strength. Waste glass cannot be used as aggregate without taking into account its ASR properties. As for cost analysis, it was determined to lower the cost of concrete productions. Our study was an environmental one in consideration to the fact that WG could be used in the concrete as coarse aggregates without the need for a high cost or rigorous energy.     

Properties of heavyweight concrete produced with barite

Heavyweight concrete has been used for the prevention of seepage from radioactive structures due to the harmful effect of radioactive rays to living bodies (i.e., carcinogenic, etc.). The most important point about heavyweight concrete is the determination of w/c ratio. Selected cement dosage should be both high enough to allow for radioactive impermeability and low enough to prevent splits originating from shrinkage. In this study, heavyweight concrete mixtures at different w/c ratios were prepared in order to determine the most favorable w/c ratio of heavyweight concrete produced with barite. Physical and mechanical experiments were first carried out, and then by comparison with the results of other related studies the findings of this study were obtained. At the end of the study, it was found that the most favorable w/c ratio for heavyweight concrete is 0.40 and the cement dosage should not be lower than 350 kg/m³.