A Fast,Sensitive and Validated Technique for Eurycomanone and Cordycepin Quantitation using UPLC‒MS/MS

Herbs and herbal based products have been widely used, but some products might contain no herbal ingredient as claimed in the product label. Therefore, it is crucial to develop a fast, sensitive and reliable method to analyze the herbs and their finished products. The roots of Eurycoma longifolia, and the health supplement of E. longifolia and Cordyceps were used as the sample matrices in this study. Sonication assisted extraction was applied to extract the marker compounds, namely eurycomanone and cordycepin from E. longifolia and Cordyceps, respectively. The presence of the marker compounds was established by high throughput ultra-performance liquid chromatography tandem mass spectrometry (UPLC?MS/MS) using a highly sensitive and selective technique of multiple reaction monitoring (MRM). The positive ion transitions in MRM for eurycomanone and cordycepin are m/z 409 → 391 and m/z 252 → 136, respectively. The test method was validated for its robustness, accuracy, precision, linearity, detection and quantitation limits, as well as estimated for its measurement uncertainty.     

On the rational cuspidal subgroup and the rational torsion points of

For two distinct prime numbers , , we compute the rational cuspidal subgroup of and determine the -primary part of the rational torsion subgroup of the old subvariety of for most primes . Some results of Berkovic on the nontriviality of the Mordell-Weil group of some Eisenstein factors of are also refined.

     

High-density arrays of InGaN nanorings, nanodots, and nanoarrows fabricated by a template-assisted approach

Dense, crystalline arrays of InGaN nanorings, nanodots, and nanoarrows have been fabricated on GaN substrates by template-assisted nano-area selective growth. To create the nanostructures, we have used nanoporous anodic alumina films as templates to pattern nanopores in an SiO2 transfer layer, and then used this patterned SiO2 layer as a template for nitride growth by metalorganic chemical vapor deposition. We have varied the diameter of the deposited nitride nanostructures from 35 to 250 nm by changing the initial anodic alumina template structure. In addition, by controlling the nitride growth time we have created various types of nanostructures, from nanorings to nanoarrows. This structural evolution begins with the nucleation and formation of a nanoring structure, followed by coalescence and growth to form faceted nanodots, and finally lateral overgrowth to form faceted nanoarrows.     

Stabilizing and Activating Nitrogen Catenates

The remarkably stable catenated hexa‐nitrogen chain in bis(benzotriazene‐4‐one) is structurally, theoretically, and spectroscopically characterized to illustrate the durability of the central N?N bond in this hexaazo chain. The reactions of this species illustrate the potential of these nitrogen catenates for the preparation of other condensed heterocycles, such as bispyrazolones, by thermal nitrogen exclusion or by trapping the single ring‐opened Dimroth intermediates. In these latter reactions, 2‐naphtholate anion condenses with bis(benzotriazene‐4‐one) to trap and retain a zwitterionic diazonium intermediate as an isolated diazo product, whereas transition metals ring effect ring‐extrusion of dinitrogen from the Dimroth intermediate to generate chelating σ‐aryls. The catenated nitrogen species can be stabilized by incorporating strong formal sp²?sp² N?N σ bonds with orthogonal orientations. Extending these stabilization and activation principles may allow these types of nitrogen catenates to be useful synthons for other polyaza species.     

Carbocatalysis: The State of “Metal‐Free” Catalysis

The rise in global demand for crucial chemical compounds has driven immense research in the fundamental science of catalysis. Graphene and its derivatives (chemically modified graphene, CMGs) have recently emerged as a new class of heterogeneous catalyst that promises economically viable and greener routes to these compounds. Although CMGs possess unique catalytic properties, the actual active sites are often points of discussion. Current minimal understanding on the possible effects of metallic impurities on the electrocatalytic performances of these CMGs calls forth the need to raise awareness on possible metallic impurities misrepresenting the actual chemical catalytic performances of the CMGs. This Minireview highlights the latest advances in the application of CMGs as catalysts, with an emphasis on the possible effects of metallic impurities on CMG catalysis.     

Chemical Preparation of Graphene Materials Results in Extensive Unintentional Doping with Heteroatoms and Metals

Chemical synthesis of graphene relies on the usage of various chemical reagents. The initial synthesis step, in which graphite is oxidized to graphite oxide, is achieved by a combination of chemical oxidants and acids. A subsequent chemical reduction step eliminates/reduces most oxygen functionalities to yield graphene. We demonstrate here that these chemical treatments significantly contaminate graphene with heteroatoms/metals, depending on the procedures followed. Contaminations with heteroatoms (N, B, Cl, S) or metals (Mn, Al) were present at relatively high concentrations (up to 3 at %), with their chemical states dependent on the procedures. Such unintentional contaminations (unwanted doping) during chemical synthesis are rarely anticipated and reported, although the heteroatoms/metals may alter the electronic and catalytic properties of graphene. In fact, the levels of unintentionally introduced contaminants on graphene are often higher than typical levels found on intentionally doped graphene. Our findings are important for scientists applying chemical methods to prepare graphene.     

Broad-band photoresponse from InAs quantum dots embedded into InGaAs graded well

A broad-band photoresponse is obtained from undoped InAs multiple quantum dots grown by the molecular beam epitaxy (MBE) technique on a (100) GaAs substrate. The quantum dots were embedded in an In/sub x/Ga/sub 1-x/As graded well where the In mole fraction is chosen in the range of 0.3 /spl ges/ x /spl ges/ 0.0. The photoresponse of the reversed biased device, obtained at 80.5 K and using the normal incident configuration, was found to span the spectral range of 3.5 - 9.5 /spl mu/m. While the photoresponse is significantly high under the influence of the reverse bias voltage, the forward bias photoresponse is found to be negligible.     

Connected sensor cover for area information coverage in wireless sensor networks

Coverage is an important issue in wireless sensor networks (WSNs) and is often used to measure how well a sensor field is monitored by the deployed sensors. If the area covered by a sensor can also be covered by some other sensors, this sensor can go into an energy‐saving sleep state without sacrificing the coverage requirement. In this paper, we study the problem of how to select active sensors with the constraints that the selected active sensors can provide complete field coverage and are completely connected. We propose to use the notion of information coverage, which is based on estimation theory to exploit the collaborative nature of WSNs, instead of using the conventional definition of coverage. Owing to the use of information coverage, a point that is not within the sensing disk of any sensor can still be considered to be covered without loss of estimation reliability. We propose a heuristic to approximately solve our problem. The basic idea is to grow a connected sensor tree to maximize the profit from the covered points of the selected sensors in each step. Simulations are used to validate the effectiveness of the proposed algorithm and the results illustrate that the number of active sensors to provide area coverage can be greatly reduced by using the notion of information coverage compared with that by using the conventional definition of coverage. Copyright © 2008 John Wiley & Sons, Ltd.     

Optimization of hydrothermal growth ZnO Nanorods for enhancement of light extraction from GaN blue LEDs

In this study, we report on the enhancement in the light extraction efficiency of GaN blue LEDs topped with ZnO nanorods. The ZnO nanorods were grown by a two-step hydrothermal synthesis with pre-coated ZnO nanoparticles under optimized condition to give the appropriate size and quality, giving an increase in the light output efficiency of 66%. This improvement is attributed to the optimal rod size and spacing with improved thermal dissipation as compared to light extraction from plain GaN surface. During the ZnO growth on the LEDs, 0.55 M of NH₃ was added and the ZnO sample was later annealed at 475 °C in N₂ ambient, to drive out interstitial oxygen atoms from the tetrahedral unstable site. As a result, a high ratio of UV to orange defect band emission was achieved. The two-step growth of ZnO nanorods on GaN LEDs was effective in generating array of ZnO nanorods which serve as reflector to enhance light extraction from LEDs.