Piezoelectric Sensors Operating at Very High Temperatures and in Extreme Environments Made of Flexible Ultrawide-Bandgap Single-Crystalline AlN Thin Films

Extreme environments are often faced in energy, transportation, aerospace, and defense applications and pose a technical challenge in sensing. Piezoelectric sensor based on single-crystalline AlN transducers is developed to address this challenge. The pressure sensor shows high sensitivities of 0.4–0.5 mV per psi up to 900 °C and output voltages from 73.3 to 143.2 mV for input gas pressure range of 50 to 200 psi at 800 °C. The sensitivity and output voltage also exhibit the dependence on temperature due to two origins. A decrease in elastic modulus (Young's modulus) of the diaphragm slightly enhances the sensitivity and the generation of free carriers degrades the voltage output beyond 800 °C, which also matches with theoretical estimation. The performance characteristics of the sensor are also compared with polycrystalline AlN and single-crystalline GaN thin films to investigate the importance of single crystallinity on the piezoelectric effect and bandgap energy-related free carrier generation in piezoelectric devices for high-temperature operation. The operation of the sensor at 900 °C is amongst the highest for pressure sensors and the inherent properties of AlN including chemical and thermal stability and radiation resistance indicate this approach offers a new solution for sensing in extreme environments.     

Asymmetric Cyclic Phosphorothonamides Containing Substituted Pyridine

In order to find high-acitivity and low-toxicity pesticidal lead compounds, a type of novel, asymmetric cyclic phosphorothonamides containing substituted pyridine were synthesized via the condensation reactions of 2-chloro-4-substitutedphenyl-5,5-dimethyl-1,3,2-dioxaphosphinane 2-sulfide with 3-aminomethylpyridine. The cis and trans isomers of the products were isolated by column chromatography on silica gel. The structures of the products were characterized by ¹ H NMR, ³¹ P NMR, MS, and elemental analyses. The configuration of 3a was determined by X-ray diffraction analysis. The results of the preliminary bioassay showed that the new compounds possess potential fungicidal activities.     

A generalized modular redundancy scheme for enhancing fault tolerance of combinational circuits

Nano-scale devices are continuously shrinking, operating at lower voltages and higher frequencies. This makes them more susceptible to environmental perturbations and distinguished by their high dynamic fault rates. Redundancy techniques are widely used to increase the reliability of combinational logic circuits. In this work, soft error reliability is improved by using such techniques, and based on probability of occurrence for combinations at the outputs of circuits. A generalized modular redundancy scheme to enhance the reliability of combinational circuits is proposed. Additionally, several aspects regarding the application of this scheme are explored. This comprises types of redundant modules, complexity of voters and single versus multiple outputs protection. Also, a methodology for applying the generalized modular redundancy scheme is developed. Reliability analysis for various benchmarks from the LGSynth91 suite shows that the proposed methodology can achieve reliability figures higher than that of triple modular redundancy. In general, significant overhead savings are accomplished in addition to that superior reliability.     

Phytochemical study and cytotoxicity evaluation of Colchicum stevenii Kunth (Colchicaceae): a Jordanian meadow saffron

Isolation, characterization, and biological evaluation of active components of Colchicum stevenii Kunth (Colchicaceae) are described. Colchicum stevenii is an unexplored Jordanian specie with toxic reputation. Directed by brine shrimp lethality test (BST), methanolic extraction, liquid-liquid partition, preparative TLC, and semi-preparative HPLC, it resulted in the isolation of six cytotoxic compounds. The compounds, reported for the first time from this specie, are: (-)-colchicine (1), 2-demethyl-(-)-colchicine (2), (-)-cornigerine (3), beta-lumicolchicine (4), (-)-isoandrocymbine (5) and (-)-O-methylandrocymbine (6). A new, in-house developed, acidic-based reverse-phase gradient semi-preparative HPLC method for the separation of colchisides is presented here. Structural elucidation was based on spectroscopic techniques principally; 1H-NMR and low resolution EIMS. Based on BST results, reported as LC50 values in microg mL(-1) (ppm) with 95% confidence intervals, (-)-colchicine (2.5 ppm) and (-)-cornigerine (2.7 ppm) were the most potent.     

On the response of MEMS resonators under generic electrostatic loadings: experiments and applications

Nonlinear Dynamics - We present an investigation of the dynamic behavior of an electrostatically actuated clamped–clamped microbeam, under the simultaneous excitation of primary and...     

Novel photoinitiated cationic copolymerizations of 4-methylene-2-phenyl-1,3-dioxolane

Photoinitiated polymerization of 4-methylene-2-phenyl-1,3-dioxolane ( 1 ) was carried out using either tris (4-methylphenyl) sulfonium hexafluoroantimonate or 4-decyloxyphenyl phenyliodonium hexafluoroantimonate as initiators. ¹H-NMR analyses confirmed exclusive ring-opening while DSC and SEC were used to determine the glass transition temperatures (T_gs) and molecular weights, respectively. Photoinitiated cationic copolymerizations of 1 were investigated with several acyclic and cyclic monomers. Copolymerization of 1 with vinyl ethers and a spiroorthoester resulted in copolymers whose thermal properties were dependent on comonomer ratios. Copolymers of 1 and dihydrofuran or dihydropyran afforded soluble polymers with T_gs significantly higher than the homopolymer of 1 . © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2207–2219, 1997     

A validated HPLC determination of the flavone aglycone diosmetin in human plasma

Diosmetin, 3',5,7-trihydroxy-4'-methoxy flavone, is the aglycone of the flavonoid glycoside diosmin that occurs naturally in foods of plant origin. Diosmin exhibits antioxidant and anti-inflammatory activities, improves venous tone and it is used for the treatment of chronic venous insufficiency. Diosmin is hydrolyzed by enzymes of intestinal micro flora before absorption of its aglycone diosmetin. A specific, sensitive, precise, accurate and robust HPLC assay for the determination of diosmetin in human plasma was developed and validated. Diosmetin and the internal standard 7-ethoxycoumarin were isolated from plasma by liquid-liquid extraction and separated on a C8 reversed-phase column with methanol-water-acetic acid (55:43:2, v/v/v) as the mobile phase at 43 degrees C. Peaks were monitored at 344 nm. The method was linear in the 10-300 ng/mL concentration range (r > 0.999). Recovery for diosmetin and internal standard was greater than 89.7 and 86.8%, respectively. Intra-day and inter-day precision for diosmetin ranged from 1.6 to 4.6 and from 2.2 to 5.3%, respectively, and accuracy was better than 97.9%.     

An analytic solution of the static problem of inclined risers conveying fluid

Meccanica - We use the method of matched asymptotic expansion to develop an analytic solution to the static problem of clamped–clamped inclined risers conveying fluid. The inclined riser is...     

Determination of hypericin content in Hypericum triquetrifolium Turra (Hypericaceae) growing wild in Jordan

Hypericin content of methanolic extracts of dried flowers, leaves, stems, and roots of Hypericum triquetrifolium (Turra) were determined by HPLC. Conversion of protohypericin to hypericin was achieved by exposing samples to light for 30 min immediately before HPLC analysis. External standard calibration was used to quantify hypericin. Leaves showed the highest hypericin content of 0.36% w/w. Total aerial parts contained 0.43% w/w of hypericin. The relatively high hypericin content of the H. triquetrifolium in this study encourages the introduction, cultivation, and biological evaluation of hypericum specie in Jordan.     

Photocurrent generation in multilayer organic-inorganic thin films with cascade energy architectures

Zirconium organobisphosphonate multilayer thin films of viologen derivatives were grown on copper dithiolate multilayers of 5,15-di(p-thiolphenyl)-10,20-di(p-tolyl)porphyrin (POR) and 5,15-di(p-thiolphenyl)-10,20-di(p-tolyl)porphyrinzinc (ZOR) on a variety of substrates (e.g. Au, SiO(2)), using solution depositions methods. The multilayer structures were studied by atomic force microscopy, UV-vis spectroscopy, and ellipsometry. In the case of copper dithiolate thin films, layer-by-layer lamellar growth with low surface roughness resulted, while higher surface roughness was observed in the growth of Zr viologen bisphosphonate films. Gold electrodes modified with zirconium bisphosphonate multilayers of viologen on top of copper dithiolate multilayers of porphyrin derivatives (ZOR or POR) were photoelectroactive and produced efficient and stable photocurrents using visible light. By arranging the zinc-porphyrin (ZOR) and the free base porphyrin (POR) donors in an energetically favorable fashion, according to their redox potentials and optical energy gaps, the photoinduced charge separation was improved, and higher photocurrent quantum yields ( approximately 4%) and fill factor ( approximately 50%) of the photoelectrode were achieved.