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111.
There are currently a limited number of techniques to study nickel speciation in aqueous samples. This work reports on the use of the permeation liquid membrane (PLM) for that objective. In this paper, the composition of the organic phase was studied to maximize the Ni flux (thus the sensitivity of the device) over a wide Ni2+ concentration range (50 nM to 100 microM) in order to verify its ability to determine free Ni2+ in the presence of Ni complexes. A mixture containing 1,10-didecyl-1,10-diaza-18-crown-6 ether (22DD) and di(2-ethylhexyl)phosphoric acid (D2EHPA) in toluene/phenylhexane was selected as the optimized organic phase for the PLM. The PLM was shown to be a reliable tool to measure free nickel concentrations down to 10(-7) M. The effect of pH on Ni transport was also studied. Fluxes below pH 6 were reduced significantly, i.e. an order of magnitude smaller than fluxes above pH 7.8. Finally, as part of a broader study examining the ability of trace metals to induce antibiotic resistance in bacteria, we used the PLM to quantify the formation, at pH = 7.2, of a weak complex between Ni and Imipenem (a member of the carbapenem class of beta-lactam antibiotics) or its hydrolysis product(s). 相似文献
112.
A series of europium(III) complexes based on the macrocyclic azacarboxylate structure, DO3A, have been investigated, incorporating benzophenone appended at N10 of the macrocycle via linkers containing amide bonds (H3DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-tris-acetic acid). Complexes [EuL(1-3)] incorporate N10-CH2CONH-BP linkers (BP = benzophenone), which allow formation of a five-membered chelate ring containing the metal ion upon chelation of the amide oxygen; these three isomeric complexes differ from one another in the substitution position of the BP unit, namely para, meta, and ortho for L1, L2, and L3 respectively. The quantum yields of europium luminescence sensitized via the chromophore are found to be highly dependent upon the position of substitution, being 20 times smaller for the ortho compared to the para-substituted complex. A related para-substituted BP complex [EuL(4)], prepared by an unusual Michael reaction of the azamacrocycle with a BP-containing acrylamide, incorporates an additional methylene unit in the linker, namely N10-CH2CH2CONH-BP. Despite the longer linker, this complex equals the luminescence quantum yield achieved with [EuL(1)] (Phi(lum) = 0.097 and 0.095, respectively, in H2O at 298 K). Analysis of the pertinent kinetics reveals that the decreased energy transfer efficiency in this complex, arising from the longer donor-acceptor distance, is compensated by an increased radiative rate constant. Under basic conditions, the ortho-substituted complex [EuL(3)] undergoes an intramolecular rearrangement to generate an unprecedented complex [EuL(5)] incorporating a 4-phenyl-2-hydroxyquinoline unit directly bound to the ring nitrogen. Although this complex is a poor emitter, an analogous complex obtained from 2-amino-acetophenone, which generates 4-methyl-2-hydroxyquinoline during the corresponding rearrangement, is an order of magnitude more emissive while still benefiting from relatively long-wavelength absorption. The emission from this complex is pH sensitive, being dramatically quenched under mildly basic conditions. 相似文献
113.
C. R. Tench T. M. Fromhold P. B. Wilkinson M. J. Carter R. P. Taylor A. P. Micolich R. Newbury 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
We report quantum-mechanical calculations which replicate the self-similar magnetoconductance fluctuations observed in recent experiments on semiconductor Sinai billiards. We interpret these fluctuations by considering the mixed stable-chaotic classical dynamics of electrons in the billiard. In particular, we show that the fluctuation patterns are dominated by individual stable orbits. The scaling characteristics of the self-similar fluctuations depend on the geometry of the associated stable orbit. We find that our analysis is insensitive to the details of the potential landscape, and is applicable to real devices with a wide range of soft-wall profiles. We show that our analysis also provides a possible explanation for the distinct series of magnetoconductance fluctuations observed in recent experiments on carbon nanotubes. 相似文献
114.
KM Varier AM Vinodkumar NVSV Prasad PV Madhusudhana Rao DL Sastry Lagy T Baby MC Radhakrishna NG Puttaswamy JJ Das P Sugathan N Madhavan AK Sinha DO Kataria 《Pramana》1999,53(3):529-533
Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies.
Coupled channel calculations incorporating couplings to 2+ and 3− states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements
had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer
were carried out for 46,48Ti+61Ni systems. The present paper gives the results of these studies. 相似文献
115.
Permanent holographic recording in indium oxide thin films using 193 nm excimer laser radiation 总被引:2,自引:0,他引:2
S. Pissadakis S. Mailis L. Reekie J.S. Wilkinson R.W. Eason N.A. Vainos K. Moschovis G. Kiriakidis 《Applied Physics A: Materials Science & Processing》1999,69(3):333-336
Permanent holographic recording in sputtered indium oxide (InOx) thin films is demonstrated, using ultraviolet radiation at 193 nm emitted by an ArF excimer laser. Steady-state refractive
index changes of up to 5×10-3 are calculated from the measured diffraction efficiency of a HeNe laser probe beam. The recorded gratings exhibit a dynamic
behaviour that relaxes to a steady-state value that depends on the oxygen partial pressure used during growth and on the recording
beam intensity. The observed behaviour is explained in terms of laser-induced structural changes.
Received: 12 October 1998 / Accepted: 8 March 1999 / Published online: 4 August 1999 相似文献
116.
AymanA. Abdel‐Shafi PaulD. Beer RogerJ. Mortimer Francis Wilkinson 《Helvetica chimica acta》2001,84(9):2784-2795
Photophysical properties in dilute MeCN solution are reported for seven RuII complexes containing two 2,2′‐bipyridine (bpy) ligands and different third ligands, six of which contain a variety of 4,4′‐carboxamide‐disubstituted 2,2′‐bipyridines, for one complex containing no 2,2′‐bipyridine, but 2 of these different ligands, for three multinuclear RuII complexes containing 2 or 4 [Ru(bpy)2] moieties and also coordinated via 4,4′‐carboxamide‐disubstituted 2,2′‐bipyridine ligands, and for the complex [(Ru(bpy)2(L)]2+ where L is N,N′‐([2,2′‐bipyridine]‐4,4′‐diyl)bis[3‐methoxypropanamide]. Absorption maxima are red‐shifted with respect to [Ru(bpy)3]2+, as are phosphorescence maxima which vary from 622 to 656 nm. The lifetimes of the lowest excited triplet metal‐to‐ligand charge transfer states 3MLCT in de‐aerated MeCN are equal to or longer than for [Ru(bpy)3]2+ and vary considerably, i.e., from 0.86 to 1.71 μs. Rate constants kq for quenching by O2 of the 3MLCT states were measured and found to be well below diffusion‐controlled, ranging from 1.2 to 2.0⋅109 dm3 mol−1 s−1. The efficiencies f of singlet‐oxygen formation during oxygen quenching of these 3MLCT states are relatively high, namely 0.53 – 0.89. The product of kq and f gives the net rate constant k for quenching due to energy transfer to produce singlet oxygen, and kq−k equals k, the net rate constant for quenching due to energy dissipation of the excited 3MLCT states without energy transfer. The quenching rate constants were both found to correlate with ΔGCT, the free‐energy change for charge transfer from the excited Ru complex to oxygen, and the relative and absolute values of these rate constants are discussed. 相似文献
117.
Angus J. Wilkinson Graham Meaden David J. Dingley 《Superlattices and Microstructures》2009,45(4-5):285-294
In this paper, we describe the use of electron back scatter diffraction (EBSD) to study strain variations in crystalline samples at the nanoscale. The analysis relies on cross correlation measurements of small shifts in the EBSD pattern measured at many points dispersed across the pattern. The method allows the full strain tensor, and lattice rotations to be obtained at a sensitivity of ~10?4. The method is applied to study variations of strains and rotations near the surface of 200 nm thick epitaxial layers of Si0.85Ge0.15 grown on a Si substrate patterned with rectangular and square mesa. Linescans across rectangular mesas show that strain relaxation and accompanying lattice rotations are restricted to the edges of wide mesas but that the relaxation extends across the entirety of mesas narrower than ~6 μm. Two dimensional maps of the strain variation in a ~3 μm wide square mesa are also presented. 相似文献
118.
Christian Bonatti Sylvain Crovisier Amie Wilkinson 《Publications Mathématiques de L'IHéS》2009,109(1):185-244
Answering a question of Smale, we prove that the space of C
1 diffeomorphisms of a compact manifold contains a residual subset of diffeomorphisms whose centralizers are trivial. 相似文献
119.
A non-linear control method, known as Variable Structure Control (VSC), is employed to reduce the duration of ultrasonic (US) transducer transients. A physically realizable system using a simplified form of the VSC algorithm is proposed for standard piezoelectric transducers and simulated. Results indicate a VSC-controlled transmitter reduces the transient duration to less than a carrier wave cycle. Applications include high capacity ultrasound communication and localization systems. 相似文献
120.
Hojati Z Milne C Harvey B Gordon L Borg M Flett F Wilkinson B Sidebottom PJ Rudd BA Hayes MA Smith CP Micklefield J 《Chemistry & biology》2002,9(11):1175-1187
The calcium-dependent antibiotic (CDA), from Streptomyces coelicolor, is an acidic lipopeptide comprising an N-terminal 2,3-epoxyhexanoyl fatty acid side chain and several nonproteinogenic amino acid residues. S. coelicolor grown on solid media was shown to produce several previously uncharacterized peptides with C-terminal Z-dehydrotryptophan residues. The CDA biosynthetic gene cluster contains open reading frames encoding nonribosomal peptide synthetases, fatty acid synthases, and enzymes involved in precursor supply and tailoring of the nascent peptide. On the basis of protein sequence similarity and chemical reasoning, the biosynthesis of CDA is rationalized. Deletion of SCO3229 (hmaS), a putative 4-hydroxymandelic acid synthase-encoding gene, abolishes CDA production. The exogenous supply of 4-hydroxymandelate, 4-hydroxyphenylglyoxylate, or 4-hydroxyphenylglycine re-establishes CDA production by the DeltahmaS mutant. Feeding analogs of these precursors to the mutant resulted in the directed biosynthesis of novel lipopeptides with modified arylglycine residues. 相似文献