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31.
32.
It is well known that the inversion of populations in the ammonia maser leads to stimulated emission, and hence amplification, of microwaves. However, it is not well known that an inverted medium also leads to the superluminal propagation of off-resonance, finite-band-width wave packets, whose phase, group, energy, and signal velocities, as defined by Sommerfeld and Brillouin, all exceed the vacuum speed of lightc. Einstein causality is not violated, since the front velocity isc. The inversion of populations also implies a parelectric medium with negative electric susceptibility. (Parelectric media should not be confused withparaelectric media, which are ferroelectrics just above their Curie points.) The existence of a parelectric medium implies the possibility of the levitation of an electrical charge in the vacuum above this medium, as well as stable electrostatic configurations of charges placed inside an evacuated cavity surrounded by this medium. The apparent violation of Earn-shaw's theorem will be discussed. Numerical estimates for a proposed experiment to observe parelectricity will be given.Dedicated to Walther on the ocassion of his 60 birthday 相似文献
33.
The development of a mixed micellar electrokinetic capillary chromatography (MECC) method for the qualitative and quantitative determination of key components, including vanillin, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, vanillic acid and 3-methoxybenzaldehyde, that contribute to vanilla flavour was investigated. The micellar phase consisted of sodium dodecyl sulfate (SDS) and sodium cholate (SC). The percent relative standard deviation (R.S.D.%) for migration time was <1 over six runs. The R.S.D.% for peak areas ranged between 0.85-1.96% over six runs. Peak efficiencies were excellent with theoretical plate numbers typically in the range of 130,000-200,000 per column (52 cm effective length). The limits of detection (LOD) were between 5-10 μg/ml. The quantitative data was verified by high performance liquid chromatography (HPLC) and gas chromatography (GC). The mixed MECC method was successfully applied to a number of natural vanilla extracts, nature identical extracts and synthetic flavourings. 相似文献
34.
35.
Andrew G McDonald Sinéad Boyce Gerard P Moss Henry BF Dixon Keith F Tipton 《BMC biochemistry》2007,8(1):14
Background
We describe the database ExplorEnz, which is the primary repository for EC numbers and enzyme data that are being curated on behalf of the IUBMB. The enzyme nomenclature is incorporated into many other resources, including the ExPASy-ENZYME, BRENDA and KEGG bioinformatics databases. 相似文献36.
Available test time is an important issue for ground-based flow research, particularly for impulse facilities such as shock
tunnels, where test times of the order of several ms are typical. The early contamination of the test flow by the driver gas
in such tunnels restricts the test time. This paper reports measurements of the driver gas arrival time in the test section
of the T4 free-piston shock-tunnel over the total enthalpy range 3–17 MJ/kg, using a time-of-flight mass spectrometer. The
results confirm measurements made by previous investigators using a choked duct driver gas detector at these conditions, and
extend the range of previous mass spectrometer measurements to that of 3–20 MJ/kg. Comparisons of the contamination behaviour
of various piston-driven reflected shock tunnels are also made.
PACS 07.75.th; 47.40.-x 相似文献
37.
Parsons JG Stachurska-Buczek D Choi N Griffiths PG Huggins DA Krywult BM Marino ST Nguyen T Sheehan CS James IW Bray AM White JM Boyce RS 《Molecules (Basel, Switzerland)》2004,9(6):449-458
The synthesis of (2S)-2-benzyloxymethyl-3-(2-fluoro-4-methoxyphenyl)- propionic acid, (2S)-2-benzyloxymethyl-3-(2-fluoro-4-methylphenyl)propionic acid and (2S)-2-benzyl-oxymethyl-3-(2,4-dimethylphenyl)propionic acid has been achieved by TiCl4 mediated alkylation of the corresponding (4R)-4-benzyl-3-[3-(2-fluoro-4-methoxyphenyl-, 2-fluoro-4-methylphenyl-, 2,4- dimethylphenyl-)propionyl]-2-oxazolidinones, followed by hydrolysis of the chiral auxiliary. The stereochemistry of the alkylation reaction was confirmed by an X-ray crystal structure of (4R)-4-benzyl-3-[(2S)-2-benzyloxymethyl-3-(2- fluoro-4-methylphenyl)propionyl]-2-oxazolidinone. 相似文献
38.
Abstract— Photoaffinity labeling of synthetic DN As with ethidium monoazide was studied to determine if the efficiency of adduct formation was related to DNA sequence. Equilibrium drug binding to DNA homopolymers and copolymers was quanitified by phase partition techniques. The amount of drug bound to a deoxypolymer at equilibrium was then compared to the fraction of ethidium analog covalently-linked following photoactivation at the same drug/DNA input ratio. There were significant sequence-related differences in the ability of the photoaffinity probe to label DNA covalently. The efficiency of covalent-adduct formation decreased in the order poly(dG-dC). poly(dG-dC)> poly-(dG). poly(dC)poly(dA-dT). poly(dA-dT)poly(dA). poly(dT). Ethidium monoazide was about 2-fold more efficient in labeling deoxyhomopolymers and deoxycopolymers composed of G-C pairs than the A-T base counterparts. In low ionic buffers (0.015 M Na+), the efficiency of photoactivation decreased with increasing ethidium monoazide concentrations. However. the base sequence effect was observed over a 40-fold range of drug concentrations. Therefore, the amount of ethidium monoazide bound to a DNA site after irradiation does not appear to represent the true affinity of the drug for that site. 相似文献
39.
A. L. Boyce P. A. Sermon M. S. W. Vong M. A. Yates 《Reaction Kinetics and Catalysis Letters》1991,44(2):309-319
CO reduction of CuO in CuO/ZnO samples at 423 K isnot retarded by the support and occurs with no evidence of Cu2O formation as reported (Porta et al. 1989). The positive order with regard to CO concentration varies with the precise range of CO partial pressure.
CuO CO CuO/ZnO 423 Cu2O , (Porta etal Solid State Ionics 32–33, 1019, (1989)). CO CO.相似文献
40.
Annemè Boyce Thomas I. A. Gerber Eric C. Hosten 《Journal of chemical crystallography》2018,48(3):96-102
The reaction of the potentially bidentate ambidentate N,O-donor ligands 3-hydroxy-2-pyridinecarboxylic acid (Hhpc) and 3-hydroxy-2-(hydroxymethyl)pyridine (Hhhp) with trans-[ReOCl3(PPh3)2] led to the isolation of the products [ReOCl(hpc)2] (1) (from acetonitrile) and [ReOCl2(hhp)(PPh3)] (2) (from ethanol) respectively. In both complexes hpc and hhp are coordinated as bidentate N,O-donor chelates, rather than as O,O-donor ligands. From the reaction of [Re(CO)5Cl] and Hhhp·HCl in ethanol the neutral complex fac-[Re(CO)3Cl(Hhhp)] (3) was obtained, with N,O-coordination of Hhhp. Complex 1 crystallizes in the monoclinic space group P21/n with a?=?6.8782(3), b?=?20.0647(8), c?=?10.8692(4) Å, β?=?107.545(1)°, and Z?=?4. Complex 2 crystallizes in the triclinic space group P-1 with a?=?7.3523(4), b?=?8.1047(5), c?=?19.591(1) Å, α?=?91.133(2)°, β?=?93.656(2)°, γ?=?93.074(2)° and Z?=?2. Complex 3 has monoclinic P21/c symmetry with the cell parameters a?=?10.6452(5), b?=?11.1372(5), c?=?9.7229(5) Å, β?=?106.107(2)°, and Z?=?4. 相似文献