Two Triterpene Synthases from Imperata cylindrica Catalyzing the Formation of a Pair of Diastereoisomers through Boat or Chair Cyclization

Imperata cylindrica is known to produce a pair of triterpenes, isoarborinol and fernenol, that exhibit identical planar structures but possess opposite stereochemistry at six of the nine chiral centers. These differences arise from a boat or a chair cyclization of the B-ring of the substrate. Herein, we report the characterization of three OSC genes from I. cylindrica. IcOSC1 and IcOSC5 were identified as isoarborinol and fernenol synthases, respectively, while IcOSC3 was characterized as a multifunctional enzyme that produces glutinol and friedelin as its major products. Mutational studies of isoarborinol and fernenol synthases revealed that the residues surrounding the DCTAE motif partially affected the conformation of the B-ring during cyclization. Additionally, the IcOSC1-W255H mutant produced the rare triterpene boehmerol. The introduced histidine residue presumably abstracted a proton from the intermediary carbocation at C18 during the 1,2-rearrangement. Expression analysis indicated that all OSC genes were highly expressed in stems.     

Principal Component Clustered Factors for Determining Study Performance in Computer Programming Class

Wireless Personal Communications - Studying computer programming requires not only an understanding of theories and concepts, but also coding pragmatism. Success in studying or conducting such a...     

Analysis of thermal diffusivity of Ti thin film by thermoreflectance and periodic heating technique

Thermal diffusivity of Ti thin film with several hundred nanometers thickness has been measured by means of thermoreflectance (TR) technique and periodic heating using front heating and front detection configuration. Ti thin films were prepared on Si substrates by dc sputtering method. Then thin Mo layers as reflection layers were coated on Ti thin films. Surface of the Mo layer is irradiated by sinusoidally intensity modulated heating laser. Temperature response at the heated area is measured by a probe laser beam with constant intensity, as a TR signal. Phase lag between the phase of TR signal and that of heating laser beam was obtained from 100 kHz to 2.6 MHz. To analyze thermal diffusivity of Ti thin films using the phase lag data, we developed a three-layer analytical model such as Mo coating (100 nm)∕thin film∕semi-infinite substrate. The calculated phase lag using analytical model is in good agreement with the experimental data for the whole frequency range. The thermal diffusivity of two Ti thin films is determined to be 5 × 10(-6) m(2)∕s, which is 53% of the bulk one.     

An Investigation of Titanium Nitride Prepared by a DC Arc Plasma Jet

The properties of a titanium nitride film prepared by a DC arc plasma jet were investigated by microscopic observations, composition analysis, and hardness measurements. Scanning electron microscopy showed that the film was composed of three phases, designated the A, B, and C regions from the outer surface. The existence of three regions was also supported by composition analysis and hardness measurements on the cross section. XRD patterns showed the presence of -TiN in the A region. In the B region, a number of voids were observed, which have never been reported in previous papers. These were made up from specific crystallographic surfaces. The C region also had a few voids which were somewhat different from those in the B region. In the matrix, an acicular texture was found and identified as -Ti solid solution by XRD. The cross section of the film changed the color determined by the nitrogen content.     

Solution‐Processed Silicane Field‐Effect Transistor: Operation Due to Stacking Defects on the Channel

2D silicon nanomaterials have unique potential for use in applications owing to their many different exotic electronic properties. Field‐effect transistors are fabricated based on free‐standing silicanes through a solution process. Owing to the sensitive surface and the nanometer thickness, the devices require the use of fabrication conditions similar to those of lithium‐ion batteries to prevent oxidation of the sheets. Reliable transistor performance is observed at room temperature in a channel thinner than 3 nm, as drain voltage dependent transfer curves current modulation, depending on the edge effect of the silicane, although the transistor property is modest (hole mobility of 1.8 cm² V^?1 s^?1). The results suggest the feasibility of other air‐sensitive 2D nanomaterials for applications in nanoelectronic devices.     

Topology optimization of density type for a linear elastic body by using the second derivative of a KS function with respect to von Mises stress

This study demonstrates the use of Newton method to solve topology optimization problems of density type for linear elastic bodies to minimize the maximum von Mises stress. We use the Kreisselmeier–Steinhauser (KS) function with respect to von Mises stress as a cost function to avoid the non-differentiability of the maximum von Mises stress. For the design variable, we use a function defined in the domain of a linear elastic body with no restriction on the range and assume that a density is given by a sigmoid function of the function of design variable. The main aim of this study involves evaluating the second derivative of the KS function with respect to variation of the design variable and to propose an iterative scheme based on an H¹ Newton method as opposed to the H¹ gradient method that was presented in previous studies. The effectiveness of the scheme is demonstrated by numerical results for several linear elastic problems. The numerical results show that the speed of the proposed H¹ Newton method exceeds that of the H¹ gradient method.     

Pressure dependence of upper critical solution temperatures in the polystyrene - cyclohexane system

The pressure dependence of the upper critical solution temperature $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ in the polystyrene-cyclohexane system has been measured over the pressure range of 1 to 50 atm. The value of $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ determined over the molecular weight (M_w) range of 3.7 × 10⁴ to ～145 × 10⁴ greatly depends on the molecular weight of polystyrene. The value of $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ for a polystyrene solution of low molecular weight (M_w = 3.7 × 10⁴) is positive (3.14 × 10^?3 degree atm^?1), while the values are negative (?0.52 × 10^?3～?5.64 × 10^?3 degree atm^?) for solutions of polystyrene over the high molecular weight range of 11 × 10⁴ to ～145 × 10⁴. The Patterson-Delmas theory of the corresponding state and the newer Flory theory have been used to explain this behaviour.     

Electrical and Thermal Conductivity and Conduction Mechanism of Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript> Alloy

Ge₂Sb₂Te₅ alloy has drawn much attention due to its application in phase-change random-access memory and potential as a thermoelectric material. Electrical and thermal conductivity are important material properties in both applications. The aim of this work is to investigate the temperature dependence of the electrical and thermal conductivity of Ge₂Sb₂Te₅ alloy and discuss the thermal conduction mechanism. The electrical resistivity and thermal conductivity of Ge₂Sb₂Te₅ alloy were measured from room temperature to 823 K by four-terminal and hot-strip method, respectively. With increasing temperature, the electrical resistivity increased while the thermal conductivity first decreased up to about 600 K then increased. The electronic component of the thermal conductivity was calculated from the Wiedemann–Franz law using the resistivity results. At room temperature, Ge₂Sb₂Te₅ alloy has large electronic thermal conductivity and low lattice thermal conductivity. Bipolar diffusion contributes more to the thermal conductivity with increasing temperature. The special crystallographic structure of Ge₂Sb₂Te₅ alloy accounts for the thermal conduction mechanism.     

Reworkable adhesives composed of photoresponsive azobenzene polymer for glass substrates

ABSTRACT

A reversible isothermal phase transition between the liquid and solid states in response to light irradiation was achieved in side chain-type azobenzene polymers. These materials can be used as adhesives that are detachable without applying any mechanical and thermal stress but also repeatedly reworkable because of their photoinduced liquefaction and solidification properties. The adhesive strength to glass plates was more than 3 MPa in single lap shear tests. This value is three times higher than previously reported and is sufficiently strong for glass substrates.