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21.
C McConville RM Kalin D Flood 《Rapid communications in mass spectrometry : RCM》1999,13(13):1339-1345
Current methods for stable oxygen isotopic (delta (18)O) analysis of soil water rely on separation of water from the soil matrix before analysis. These separation procedures are not only time consuming and require relatively large samples of soil, but also have been shown to introduce a large potential source of error. Current research at Queen's University Belfast is focused on using direct equilibration of CO(2) with the pore water to eliminate this extraction step using the automated Multiprep system and a Micromass Prism III isotope ratio mass spectrometer (IRMS). The findings of this research indicate the method is less time consuming, more reliable, and reproducible to within accepted limits (+/-0.1% per thousand delta (18)O). In this study the direct equilibration method is used to analyse delta (18)O tracer profiles in the unsaturated zone of field soils, concurrently with chloride tracer profiles, which can be used to assess infiltration rates and mechanisms through the unsaturated zone. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
22.
In this article we discuss the state of the art in the field of second‐order non‐linear optical polymers. More specifically, we highlight those results that we think made an important contribution to the field, combined with some of our own results. We start with a general overview of all the aspects involved in characterizing second‐order non‐linear optical polymers, from thin film formation and poling to second‐harmonic generation and electro‐optic measurements on such systems. Next, we review the second‐order non‐linear optical properties of selected polymer systems such as poly(vinyl ether)s, polystyrenes, polymethacrylates, main‐chain polymers and high Tg polymers like polyimides and polymaleimides. Finally, we discuss some new polymer systems that might become important in the field of non‐linear optics in the near future. 相似文献
23.
V. Vijayasundaram V. Ramasamy PL. RM. Palaniappan 《Journal of Thermal Analysis and Calorimetry》2009,98(1):183-188
The paper presents the changes in the thermal properties of control, arsenic exposed and DMSA treated Labeo rohita bones by using thermo analytical techniques. The result shows that the mass loss due to the thermal decomposition occurs
in three distinct steps due to loss of water, organic and inorganic materials. The arsenic exposed bones present a different
thermal behaviour compared to the control bones. The residue masses are increased due to arsenic exposure, while the DMSA
treatment reduces the residue mass level. These thermal characteristics can be used as a qualitative method to check the metal
accumulation in samples. 相似文献
24.
Guy Koeckelberghs Marnix Vangheluwe Kim Van Doorsselaere Elke Robijns Andr Persoons Thierry Verbiest 《Macromolecular rapid communications》2006,27(22):1920-1925
Summary: Poly(3‐alkoxythiophene)s with different degrees of regioregularity were prepared using three different methodologies. It is shown that their Faraday rotation is highly dependent on the degree of regioregularity. The origin of the differences in regiospecificity of the methodologies is discussed.
25.
Stefano Maiorana Antonio PapagniEmanuela Licandro Rita AnnunziataPiero Paravidino Dario PerdicchiaClelia Giannini Marco BenciniKoen Clays André Persoons 《Tetrahedron》2003,59(34):6481-6488
This paper describes a convenient preparation of tetrathia-[7]-helicene (TH[7]), the generation of the α-anion on the terminal thiophene ring, and the synthesis of the 2-formyl-tetrathia-[7]-helicene (2-CHO-TH[7]). The key intermediate trans-1,2-dibenzodithiophene-ethene, prepared in 97% yield by McMurry coupling of the 2-formyl-benzo[1,2-b;4,3-b′]dithiophene, was transformed into TH[7] using a known procedure. The described method affords TH[7] in 46% overall yield, which is more than four times the yield previously reported in the literature. The α-anion of TH[7], which is easily generated on the α-position of one of the terminal thiophene rings, reacts with electrophilic reagents such as D2O and DMF. The latter reaction proved to be the best way to prepare 2-CHO-TH[7], a key intermediate for the preparation of new substituted heterohelicenes. 相似文献
26.
Coe BJ Chamberlain MC Essex-Lopresti JP Gaines S Jeffery JC Houbrechts S Persoons A 《Inorganic chemistry》1997,36(15):3284-3292
A series of new Ru(II) complex salts trans-[Ru(NH(3))(4)(L(1))(L(2))](PF(6))(n) [n = 2, L(1) = 4-acetylpyridine (4-acpy) and L(2) = 4-(dimethylamino)pyridine (dmap) (1), 4-(dimethylamino)benzonitrile (dmabn) (2), 4-picoline (4-pic) (3), or 1-methylimidazole (1-MeIm) (4); n = 3, L(1) = N-methyl-4,4'-bipyridinium (MeQ(+)) and L(2) = dmap (6), dmabn (7), 1-MeIm (8), 4-acpy (9), or phenothiazine (PTZ) (10); n = 2, L(1) = dmap and L(2) = 4-pyridinecarboxaldehyde (pyca) (12) or ethyl isonicotinate (isne) (13)] have been synthesized and fully characterized. These complexes display intense, visible metal-to-ligand charge-transfer (MLCT) absorptions which are highly solvatochromic. An X-ray crystal structure determination has been carried out for trans-[Ru(NH(3))(4)(MeQ(+))(PTZ)](PF(6))(3).Me(2)CO (10.Me(2)CO). This salt, empirical formula C(26)H(38)F(18)N(7)OP(3)RuS, crystallizes in the hexagonal system, space group P6(3), with a = b = 17.853(4) ?, c = 21.514(6) ?, and Z = 6. The MeQ(+) ligand adopts an almost planar conformation, with a torsion angle of 9.6 degrees between the two pyridyl rings. The dipolar cations exhibit a strong projected component along the z axis, but crystal twinning precludes second-harmonic generation. Measurements of the first hyperpolarizability beta by using the hyper-Rayleigh scattering technique at 1064 nm yield very large values in the range (232-621) x 10(-30) esu, the largest being for trans-[Ru(NH(3))(4)(MeQ(+))(dmabn)](PF(6))(3) (7). These beta values are resonance enhanced via the MLCT excitations. A correlation between beta and the MLCT absorption energy confirms that this excitation is the primary contributor to beta. The two-level model yields static hyperpolarizabilities beta(0) in the range (10-130) x 10(-30) esu, with trans-[Ru(NH(3))(4)(MeQ(+))(dmap)](PF(6))(3) (6) having the largest. The beta(0) values of the complexes of the bipyridyl ligand MeQ(+) are larger than those of their analogues containing monopyridyl ligands because of extended conjugation. beta(0) correlates with the MLCT energy only when the MLCT absorption is sufficiently far from the second harmonic at 532 nm. 相似文献
27.
Alexander V. Yakimansky Stanislav V. Bushin Marina A. Bezrukova Alexey A. Lezov Alexander S. Gubarev Elena V. Lebedeva Lilija I. Akhmadeeva Anna N. Podseval'nikova Nikolaj V. Tsvetkov Guy Koeckelberghs Andre Persoons 《Journal of Polymer Science.Polymer Physics》2016,54(9):875-883
Conducting polymers demonstrate low solubility in organic solvents. Introducing aliphatic substituents into polymer chains improves their solubility, but may also lead to changes in conformational characteristics of macromolecules. In the present work, the studies of hydrodynamic properties and conformational characteristics of comb‐shaped poly(3‐hexylthiophene) with aliphatic side substituents were carried out in chloroform solutions. Conformational analysis of the studied macromolecules was performed for the first time using homologous series with a wide range of molecular weights of the polymers in dilute solutions. The hydrodynamic properties of these macromolecules were interpreted using the worm‐like spherocylinder model and the straight spherocylinder model. The projection of the monomer unit in the direction of the main polymer chain λ = 0.37 nm was determined experimentally. The following parameters of poly(3‐hexylthiophene) were characterized and quantified: equilibrium rigidity (Kuhn segment length) А = 6.7 nm and hydrodynamic diameter of a polymer chain d = 0.6 nm. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 875–883 相似文献
28.
Two samples of-FeOOH with different particle sizes have been studied in an external field of 4 T and as a function of temperature. They were found to have a ferrimagnetic structure due to an unequal occupancy of antiferromagnetically coupled octahedral ferric ions. The large surface contribution, which is characterized by a canted spin structure and by highly deformed Fe3+ co-ordinations, strongly influences the magnetic properties observed with Mössbauer spectroscopy. 相似文献
29.
Hennrich G Murillo MT Prados P Song K Asselberghs I Clays K Persoons A Benet-Buchholz J de Mendoza J 《Chemical communications (Cambridge, England)》2005,(21):2747-2749
Rigid, highly conjugated tetraalkynyl-calix[4]arenes synthesised via Sonogashira coupling give rise to improved second-order hyperpolarizability values as determined by hyper-Rayleigh scattering--a technique that in addition to X-ray crystallography also allows for the conformational analysis of the calixarene structures in solution. 相似文献
30.
MK Bhide RM Kadam MD Sastry Ajay Singh Shashwati Sen Manmeet Kaur DK Aswal SK Gupta VC Sahni 《Pramana》2002,58(5-6):799-802
Microwave absorption studies have been carried out on MgB2 superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for
polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave
absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime. 相似文献