Inexpensive synthesis of 1,4-bis(4-aminophenoxy)-2- (6-oxido-6H-dibenz <c,e> <1,2> oxaphosphorin-6-yl) phenylene and its oxygen-plasma resistant polyamides

Inexpensive synthesis of diamine, 1,4-bis(4-nitrophenoxy)-2-(6-oxido-6H-dibenz <c,e> <1,2> oxaphosphorin-6-yl) phenylene was revealed in this work. Based on the diamine, a series of organosoluble polyamides were prepared by direct polycondensation of the diamine with various aromatic diacids using triphenyl phosphite and pyridine as condensing agents. The number-average molecular weights of the resulting polyamides range from 4.2 × 10⁴ to 10.5 × 10⁴ g/mol, and the weight-average molecular weights are in the range of 7.5-28.2 × 10⁴ g/mol. The T_gs of these polyamides range from 210 to 255 °C by dynamic mechanical analysis. The resulting polyamides are tough and flexible with tensile strength, elongation at break and moduli range from 84 to 101 MPa, 4.8-7.0%, and 2.36-3.22 GPa, respectively. The degradation temperatures (T_d 5%) and char yields at 800 °C in nitrogen range from 460 to 486 °C and 59-68 wt%, respectively. The cutoff wavelength of these polyamides falls in the range of 345-366 nm, showing a very light color characteristic. In addition, these polyamides display good oxygen plasma resistance.     

A simple PWM method for improving lamp current crest factor of valley‐filled electronic ballast

In this paper, a PWM method to improve the lamp current crest factor (CCF) of the valley‐filled electronic ballast (VFEB) is presented. The VFEB has merits of high power factor, simple structure, and low cost. However, it results in an excessive CCF, which will shorten the lifetime of low‐pressure discharge lamp. The proposed method controls switching duty ratio by feeding forward the dc‐link voltage waveform of VFEB. It decreased the duty ratio with rising of dc‐link voltage. Therefore, the proposed method could restrain the lamp peak current and improve the lamp CCF. The control block diagram and basic theory are introduced to improve the CCF. The computer simulations verify the proposed method and derive a minimum lamp CCF. The experimental results demonstrate that the lamp CCF was reduced from 1.9 to 1.58, the ac line power factor is 96%, and the input current THD is 29.3%. The fixed switching frequency operation gains a satisfactory power quality. Copyright © 2008 John Wiley & Sons, Ltd.     

A module‐integrated isolated solar micro‐inverter without electrolytic capacitors

This paper presents a module‐integrated isolated solar micro‐inverter. The studied grid‐tied micro‐inverters can individually extract the maximum solar power from each photovoltaic (PV) panel and transfer to the AC utility system. A harmonic suppression technique is used to reduce the DC‐bus capacitance. Electrolytic capacitors are not needed in the studied solar micro‐inverter. High conversion efficiency, high maximum power point tracking accuracy and long lifespan can be achieved. The operation principles and design considerations of the studied PV inverter are analyzed and discussed. A laboratory prototype is implemented and tested to verify its feasibility. Copyright © 2012 John Wiley & Sons, Ltd.     

Real‐time calculation of power system bus voltage using a hybrid approach combining the Newton–Raphson method and dynamic programming

The calculation of the magnitudes and phase angles of the bus voltage is a challenging task in real‐time applications for power systems. Voltage profile, which denotes the present conditions of a power system, is determined by executing the traditional AC power flow program or by searching the supervisory control and data acquisition system. The AC power flow program is not suitable for several real‐time applications, such as contingency analysis and security control calculations, because of its complexity and convergence problems. Fast computation is the major concern in such applications. In this paper, a new method based on sensitivity factors, referred to as Jacobian‐based distribution factors (JBDFs), is proposed for calculating the magnitudes and phase angles of bus voltages. This method requires setting up JBDFs and deriving optimal solution paths of bus voltage for non‐swing buses through dynamic programming under base‐case loading conditions. Under real‐time conditions, the proposed method initially calculates real and reactive power line flows via JBDFs, and then computes the voltage magnitudes and phase angles of non‐swing buses through the derived optimal solution paths. The excellence of the proposed hybrid calculation method is verified by IEEE test systems. Simulation results demonstrate that the proposed method exhibits fast computation and high accuracy. Thus, the method is suitable for real‐time applications. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A novel active‐clamp zero‐voltage‐switching buck‐boost converter

An active‐clamp zero‐voltage‐switching (ZVS) buck‐boost converter is proposed in this paper to improve the performance of converter in light load condition. By employing a small resonant inductor, the ZVS range of switches could be adjusted to very light load condition. Moreover, 2 clamping capacitors are added in the converter to eliminate the voltage spike on the switches during transition. The operating principle of the proposed converter is analyzed, and the optimal design guide for full range ZVS is also provided. A 60‐W output prototype is experimentally built and tested in laboratory to verify the feasibility of proposed converter. The measured results show the critical ZVS operation of power switches at 1 and 0.7‐W output power for buck and boost mode, respectively. The peak conversion efficiency is up to 92.3%.     

Bioconversion of n−3 and n−6 PUFA by <Emphasis Type="Italic">Clavibacter</Emphasis> sp. ALA2

Clavibacter sp. ALA2 oxidized n−3 and n−6 PUFA into a variety of oxylipins. Structures of products converted from EPA and DHA were determined as 15,18-dihydroxy-14,17-epoxy-5(Z),8(Z),11(Z)-eicosatrienoic acid and 17,20-dihydroxy-16,19-epoxy-4(Z),7(Z),10(Z),13(Z)-docosatetraenoic acid by GC-MS and NMR analyses. In contrast, γ-linolenic acid and arachidonic acid were converted to diepoxy bicyclic FA, tetrahydrofuranyl monohydroxy FA, and trihydroxy FA. Thus, the structures of bioconversion products were different between n−3 and n−6 PUFA. Furthermore, strain ALA2 placed hydroxy groups and cyclic structures at the same position from the ω-terminal despite the number of carbons in the chain and the double bonds in the PUFA.     

Crystal Structure and Elastic Properties of Hypothesized MAX Phase‐Like Compound (Cr2Hf)2Al3C3

The term “MAX phase” refers to a very interesting and important class of layered ternary transition‐metal carbides and nitrides with a novel combination of both metal and ceramic‐like properties that have made these materials highly regarded candidates for numerous technological and engineering applications. Using (Cr₂Hf)₂Al₃C₃ as an example, we demonstrate the possibility of incorporating more types of elements into a MAX phase while maintaining the crystallinity, instead of creating solid solution phases. The crystal structure and elastic properties of MAX phase‐like (Cr₂Hf)₂Al₃C₃ are studied using the Vienna ab initio Simulation Package. Unlike MAX phases with a hexagonal symmetry (P6₃/mmc, #194), (Cr₂Hf)₂Al₃C₃ crystallizes in the monoclinic space group of P2₁/m (#11) with lattice parameters of a = 5.1739 Å, b = 5.1974 Å, c = 12.8019 Å; α = β = 90°, γ = 119.8509°. Its structure is found to be energetically much more favorable with an energy (per formula unit) of ?102.11 eV, significantly lower than those of the allotropic segregation (?100.05 eV) and solid solution (?100.13 eV) phases. Calculations using a stress versus strain approach and the VRH approximation for polycrystals also show that (Cr₂Hf)₂Al₃C₃ has outstanding elastic moduli.     

Characterization of biogenic hydroxyapatite derived from animal bones for biomedical applications

In this work, the viability of producing biogenic hydroxyapatite from bio-waste animal bones, namely bovine (cow), caprine (goat) and galline (chicken), through a heat treatment process has been investigated. The animal bones were locally sourced, cleaned to remove collagen and subsequently heat treated in air atmosphere at different temperatures ranging from 600?°C to 1000?°C. From the range of sintering temperatures investigated, it was found that hydroxyapatite derived from bovine bone showed good thermal stability while those produced from caprine and galline bones exhibited phase instability with traces of tri-calcium phosphate (TCP) being detected after heat treatment beyond 700?°C. The porous nature of the bone samples can be observed from the microstructures obtained and supported by low relative density. Heating the bovine and caprine bones at selected temperatures yielded porous HA body, having hardness values that are comparable with human cortical bone. However, the sintered galline bone sample showed higher porosity levels and low hardness when compared to the other two bone types.     

Natural Products from Diaporthe arecae with Anti‐Angiogenic Activity

A new indoleglycerol, designated as arecine ( 1 ), and twenty‐three known diketopiperazines 2 – 24 were isolated from the endophytic fungus Diaporthe arecae associated with mangrove Kandelia obovate. Structures of all secondary metabolites 1 – 24 were identified on the basis of their spectrometric data, especially the nuclear magnetic resonance, optical rotation, and mass data. The absolute stereochemistry of compound 1 was determined by comparing its experimental electronic circular dichroism spectrum to those of in silico generated. Moreover, the ¹H and ¹³C NMR spectroscopic data of isolated diketopiperazines 3 – 24 were measured in dimethyl sulfoxide‐d₆ and presented in Table 2 for a convenient comparison. Pharmacological study showed cordysinin A ( 2 ) possessed mild anti‐angiogenic activity, which suppressed tube formation with an IC₅₀ value of 15.1±0.2 μg/mL.     

Permeability measurements and flow simulation for polyaniline carbon nanofibers modified nanopaper on glass fiber preform

Carbon nanofibers (CNFs) nanopapers have shown great potential to improve the surface of fiber‐reinforced polymeric composites, including providing electromagnetic interference shielding and erosion resistance. During typical resin transfer molding (RTM) process, the CNF nanopaper is incorporated into the fiber preform as a surface layer. To learn how resin flows through the fiber preform and nanopaper layer, permeabilities of the fiber preform and nanopaper need to be measured. As is well known, measuring the permeability of fiber preforms is experimentally challenging. Results usually exhibit large experimental variability. Measuring permeability of nanopapers is even more complicated. To improve the accuracy of results, permeability of CNF‐based nanopapers was measured using different experimental setups. In‐plane permeability of nanopaper was measured by both unidirectional microslit flow and radial flow approaches. Trans‐plane permeability was measured as well, using a trans‐plane flow cell and a flow visualization mold. In this article, we discuss the methods used and provide experimental results. We also conducted computational fluid dynamics simulations to study the detailed flow patterns of the nanopaper/RTM process and compared the simulated effect of the nanopaper on retarding the flow (length of the lag) with respect to the glass preform with flow visualization results. POLYM. COMPOS., 37:435–445, 2016. © 2014 Society of Plastics Engineers