Spin resonance spectroscopy of grown-in defects in Ga(In)NP alloys

We employ the optically detected magnetic resonance (ODMR) technique to study and identify important grown-in defects in Ga(In)NP grown by molecular-beam epitaxy (MBE). Several types of defects were revealed from ODMR studies. The dominant defects were found to be related to Ga interstitials, evident form their characteristic hyperfine interaction arising from the spin interaction between the electron and the Ga nucleus. Some other as yet unidentified intrinsic defects were also found to be commonly present in the alloys. The effects of growth conditions (ion bombardment, N₂ gas flow, etc.) and post-growth rapid thermal annealing on the formation of these defects were studied in detail, shedding light on the formation mechanism of defects.     

Synthesis and spectroscopic investigation of π‐conjugated (E)‐enyne polycarbazole with different organo‐metallic catalysts from 3,6‐diethynyl‐9‐(2‐ethylhexyl)carbazole

In the present study, a new (E)‐rich‐enyne π‐conjugated polymer containing a carbazole was designed and synthesized. Two different synthesis methods of poly[N‐(2‐ethylhexyl)‐3,6‐carbazolyleneethynylene‐(E)‐vinylene] (PCZEV) have been prepared from 3,6‐diethynyl‐9(2‐ethylhexyl)carbazole by using the palladium‐carbene‐catalyzed reaction and/or by using the organolanthanide‐catalyzed reaction leading to well‐defined polymer, and their general properties were studied. Compared to poly[N‐(2‐ethylhexyl)‐3,6‐carbazolyleneethynylene] (PCE), the UV‐vis absorption and photoluminescence of the PCZEV was red‐shifted, which indicates the extension of conjugation length. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2434–2442, 2009     

Active feedback control of a beam subjected to a nonconservative force

This study examines the possibility of controlling through feedback a thin cantilevered beam subjected to a nonconservative follower force. A converging frequency flutter instability which occurs in this model is similar to classical bending-torsion flutter of an aircraft wing. Because of the similar nature of the instabilities, the beam under the follower force can be a useful vehicle for investigating the fundamental aspects of stabilization of wing flutter by feedback control. A modal approach is used for obtaining the mathematical model and control laws. A standard root locus technique for simple analytical models is also used to understand and explain the control of the beam. Experiments are carried out to verify the validity of this theoretical model. Good correlation is shown between theoretically and experimentally determined stability boundaries as well as for modal frequency and damping variation with follower force.     

First synthesis of 2′-oxabicyclo[3.1.0]hexyl nucleosides with a north conformation

The first synthesis of 2′-oxabicyclo[3.1.0]hexyl nucleosides, a novel class of bicyclonucleosides, with a north conformation was successfully accomplished starting from (S)-epichlorohydrin via a tandem alkylation-lactonization, a less steric hindrance-dependent silylation in equilibrium and a coupling reaction with nucleobases under Vorbruggen conditions. Addition of acetic acid prevented a benzoyl group from migrating during desilylation with TBAF. ¹H NMR and X-ray crystallographic analysis indicated that the anomeric effect worked on the β-2′-oxabicyclo[3.1.0]hexyl nucleosides.     

Enantioselective organocatalytic conjugate addition of α-nitroacetate to α,β-unsaturated ketones in water

The catalytic enantioselective conjugate addition reaction of α-nitroacetate to α,β-unsaturated ketones promoted by chiral bifunctional organocatalysts is described. The treatment of α-nitroacetate to α,β-unsaturated ketones under aqueous-phase reaction conditions afforded the corresponding Michael adducts with high enantioselectivity. The conjugate addition adducts are easily converted to chiral δ-keto nitroalkanes and δ-keto esters.     

Ketene functionalized polyethylene: control of cross-link density and material properties

The functionalization and cross-linking of polyethylene is synthetically challenging, commonly relying on highly optimized radical based postpolymerization strategies. To address these difficulties, a norbornene monomer containing Meldrum's acid is shown to be effectively copolymerized with polyethylene using a nickel α-iminocarbaxamidato complex, providing high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. Upon heating the copolymer to common polyethylene processing temperatures, the thermolysis of Meldrum's acid to ketene provides the desired reactive group. This simple and versatile methodology does not require small molecule radical sources or catalysts, and the dimerization of the in situ generated ketenes is shown to provide tunable cross-linking densities in polyethylene. Subsequent rheological and tensile experiments illustrate the ability to tune cross-linked polyethylene properties by comonomer incorporation and elucidate valuable structure/property relationships in these materials. This study illustrates the power of well-defined and synthetically accessible functional groups in polyolefin synthesis and functionalization.     

Thermodynamic Investigation of Molecular Interactions in 1,3-Dioxolane or 1,4-Dioxane+Benzene or Toluene+Formamide or +<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylformamide Ternary Mixtures at 308.15 K and Atmospheric Pressure

Excess molar volumes, V^E₁₂₃V^{\mathrm{E}}_{123} of 1,3-dioxolane or 1,4-dioxane (1) + benzene or toluene (2) + formamide or + N,N-dimethylformamide (3) ternary mixtures at 308.15 K and at atmospheric pressure have been determined dilatometrically over the entire composition range. The excess molar volumes data of these ternary systems were fitted to the Redlich–Kister equation. The data have been analyzed in terms of Graph theory (model) to understand the nature and strength of molecular interactions existing in these mixtures. It has been observed that V^E₁₂₃V^{\mathrm{E}}_{123} values predicted by Graph theory compare well with their corresponding experimental values.     

Surface molecular degradation of 3D glass polymer composite under low earth orbit simulated space environment

Epoxy resin reinforced with 3D parabeam glass fibre was subjected to low earth orbit (LEO) simulation conditions comprising ultra high vacuum, temperature cycling (TC), and ultraviolet (UV) radiation and atomic oxygen (AO) bombardment. Inspection of the same composite using only a selection of these hazardous conditions provided comparison measures to identify the effect of each condition on the surface degradation of the resin composite. Each of the individually selected conditions showed a different degradation mechanism that is accelerated by the presence of other conditions. X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy (SEM) were used to provide surface information. The resin composite samples suffered surface oxidation that increased the oxygen content to 17.24% in comparison with the untreated sample (only 14.2%). The samples that were treated with AO showed higher C-O and CO functional groups on the surface in comparison with the rest of the samples (as indicated by XPS). Molecular information (from ToF-SIMS) showed that surface oxidation differs with different conditions and in comparison with the use of all conditions. All treated samples were shown to suffer significant chain scission and loss of volatiles as a result of the LEO conditions. The extent of the chain scission reaction for each condition can be indicated by the extent of the reduction of the relative concentration of the aliphatic hydrocarbon ions. The relative intensity of the C₄H₁₁N₄O₂⁺ ion showed that AO bombardment accelerated the oxidation of the surface. The AO effect is doubled when UV and TC are also present. SEM results indicated that sample surfaces were eroded and roughened upon exposure to LEO conditions. Presence of AO and UV in the LEO conditions introduced white deposits onto the surface, believed to be crosslinked formations.     

Continuous Ethanol Production from Cassava Through Simultaneous Saccharification and Fermentation by Self-Flocculating Yeast Saccharomyces Cerevisiae CHFY0321

In this study, a fermentor consisting of four linked stirred towers that can be used for simultaneous saccharification and fermentation (SSF) and for the accumulation of cell mass was applied to the continuous production of ethanol using cassava as the starchy material. For the continuous process with SSF, the pretreated cassava liquor and saccharification enzyme at total sugar concentrations of 175 g/L and 195 g/L were continuously fed to the fermentor with dilution rates of 0.014, 0.021, 0.031, 0.042, and 0.05 h⁻¹. Considering the maximum saccharification time, the highest volumetric productivity and ethanol yield were observed at a dilution rate of 0.042 h⁻¹. At dilution rates in the range of 0.014 h⁻¹ to 0.042 h⁻¹, high production rates were observed, and the yeast in the first to fourth fermentor showed long-term stability for 2 months with good performance. Under the optimal culture conditions with a feed sugar concentration of 195 g/L and dilution rate of 0.042 h⁻¹, the ethanol volumetric productivity and ethanol yield were 3.58 g/L∙h and 86.2%, respectively. The cell concentrations in the first to fourth stirred tower fermentors were 74.3, 71.5, 71.2, and 70.1 g dry cell/L, respectively. The self-flocculating yeast, Saccharomyces cerevisiae CHFY0321, developed by our group showed excellent fermentation results under continuous ethanol production.