The mass spectra of some O-methyloximes of aliphatic aldehydes and ketones

The mass spectra of O-methyloximes of fifteen aliphatic aldehydes and ketones of various molecular weights and degrees of branching have been examined. All give molecular ions, and many of the fragmentations parallel those of aldoximes and ketoximes. The formation of some ions is better explained by the initial production of a novel substituted cyclopropene ion. O-Methyloximes of of the long-chain aldehydes and methyl ketones are readily distinguished by the masses of abundant products of McLafferty rearrangement at m/e 73 and 87, repectively.     

Deep-levels in silicon waveguides: a route to high yield fabrication

In this paper we outline two recent results which demonstrate the utility of deep-level engineering in silicon photonics. We describe the integration of silicon waveguide p-i-n photo-detectors in a ring (or race-track) resonator structure. The detectors are made sensitive to wavelengths around 1,550?nm via the introduction of deep-levels into the intrinsic volume of the waveguide detector. By exploiting the multiple-pass of the optical signal through the detector, we are able to significantly decrease the size of the detector structure (relative to straight waveguide detectors) while maintaining excellent responsivity on resonance. We also describe the use of deep-levels for optical modulation. Preliminary results show that thallium doped silicon waveguides may be switched between a dark and transparent condition through the variation of phosphorus doping. It is suggested that active devices may be fabricated in such a way as to vary the occupancy of the thallium level through field mediated modulation. The straightforward fabrication methods described lend themselves to a high-volume, high yield manufacturing process which should find general applicability in wavelength division multiplexing systems.     

Polymer supported chromium porphyrin as catalyst for polycarbonate formation in supercritical carbon dioxide

A new polymer-supported chromium porphyrin has been prepared and fully characterised; its catalytic activity and recyclability were investigated for the ring-opening copolymerisation of 1,2-cyclohexene oxide (CHO) and carbon dioxide (CO2).     

Nitrogen doping effects on the structure of graphene

Graphene and nitrogen doped graphene have been prepared by modified Hummers’ method and the following ammonia heat-treatment process, respectively. The effects of N-doping on the structure of graphene have been systematically investigated by various characterization techniques. SEM, TEM, BET, Raman and XRD analysis were used to distinguish the difference of the microstructures; and FT-IR, XPS, especially XANES were performed to elucidate the bonding information such as C-N. The effect of nitrogen doping on the structure of graphene has been obtained. More defects are present on nitrogen doped graphene as elucidated by BET, XRD, Raman, and XANES characterizations. XANES analysis also indicates that the N-doping decreases the surface oxygen-containing groups.     

Optically induced electron spin resonance in doped amorphous silicon

We report the first observations of optically induced electron spin resonance signals in doped and undoped amorphous silicon. We also report the observation of equilibrium surface or interface spin densities ～ 10¹³cm^?2 and volume spin densities ～ 6 × 10¹⁵ cm^?3. The small number of spins observed in equilibrium compared to the large optically induced spin density shows that most electrons are spin paired in equilibrium. We conclude that this implies a very small mean effective correlation energy, U ～ kT.     

Photogeneration of charge carriers in amorphous selenium

A model is proposed to explain the outstanding features of the free-carrier photogeneration process in amorphous selenium. The excitation of an electron-hole pair and the subsequent separation or recombination are considered as a function of photon energy, applied electric field and temperature. The results of the model are compared in detail with new experimental data and also with published results from a number of sources.     

Precise mass measurement of a double-stranded 500 base-pair (309 kDa) polymerase chain reaction product by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd.     

Determination of gas-phase ozonolysis rate coefficients of a number of sesquiterpenes at elevated temperatures using the relative rate method

The rates of ozonolysis of four sesquiterpenes, β-caryophyllene, α-humulene, isolongifolene and α-cedrene, are determined in the gas phase at an elevated temperature of 366 ± 3 K and a pressure of ~780 Torr using the EXTreme RAnge chamber (EXTRA). The experimentally obtained rate coefficients agree with extrapolated room temperature rate coefficients for isolongifolene and α-cedrene but not for β-caryophyllene and α-humulene, which were found to be three orders of magnitude slower than this in the literature. These new measurements support the hypothesis that operating under ambient conditions, kinetic measurements of condensable species can be influenced adversely by heterogeneous processes and should therefore be treated with caution.     

Enhanced stability of Pt electrocatalysts by nitrogen doping in CNTs for PEM fuel cells

Electrochemical stabilities of Pt deposited on carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (CN_x) of different nitrogen contents are compared with accelerated durability tests (ADT) for the first time. Transmission electron microscopy (TEM) images reveal the different structures of CNTs and CN_x, and the decrease of Pt particle size with the nitrogen incorporation into CNTs. Based on the loss of electrochemical surface area (ESA) and TEM images, Pt/CN_x exhibited much higher stability than Pt/CNTs, and the Pt stability increases with the increase of nitrogen contents in the CN_x supports.