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851.
O. Manuel 《Physics of Atomic Nuclei》2004,67(11):1959-1962
Measurements are needed of low-energy antineutrinos generated by possible neutron decay at the core of the Sun. The measurement will test the validity of a proposal that solar luminosity, solar neutrinos, and the outpouring of H+ ions from the solar surface are the products of a chain of reactions triggered by neutron emission from the solar core. Inverse β decay of 87-d 35S, induced by capture of low-energy antineutrinos on 35Cl, is a likely candidate for this measurement. 相似文献
852.
Kitajima M Hashimoto K Sandoval M Aimi N Takayama H 《Chemical & pharmaceutical bulletin》2004,52(10):1258-1261
A new oleanan-type triterpene and three new cincholic acid glycosides were isolated from Peruvian "Una de Gato" (Cat's claw, plant of origin: Uncaria tomentosa), a traditional herbal medicine in Peru. Their structures were determined by spectroscopic analysis. 相似文献
853.
Rodríguez-Fernández J López-Fernández R Pereiro R Menéndez M Tejerina JM Sicilia A Sanz-Medel A 《Talanta》2004,62(2):421-426
Volatile sulphur compounds (VSCs) and particularly hydrogen sulphide are considered as the predominant gases causing oral malodour. In this paper, a simple alarm sensor has been developed for VSCs determination in mouth air. The device consists of a glass tube packed with a solid sensing phase. The VSCs react with the sensing phase to produce a change in the colour of the sensor visible with a naked eye.Different “reagents” were investigated to develop the sensing phase (neocuproine + Cu(II), bathocuproine + Cu(II), resazurin, 2,6-dichlorophenolindophenol and lead acetate), finding the neocuproine + Cu(II) as the best for our purposes. Also, different substrates such as Amberlite XAD-4 and XAD-7 and different trademarks of silica gel were tested as solid supports, being selected the silica gel.A device consisting of a glass tube packed with the sensing phase was optimized and tested with halitosis patients as a rapid illness test and the results compared with those obtained with a commercially available instrument, the Halimeter™, used for the determination of VSCs in mouth air. The results exhibited acceptable agreement between the proposed “qualitative” alarm sensor and a commercially available technique selected as reference, showing the possibility of using this “visual sensor” to control the halitosis and its evolution with an eventual treatment, by the own patient. 相似文献
854.
855.
Ribas X Dias JC Morgado J Wurst K Santos IC Almeida M Vidal-Gancedo J Veciana J Rovira C 《Inorganic chemistry》2004,43(12):3631-3641
The deprotonated form of the pyrazine-2,3-diselenol (pds) ligand, pds(2-), reacts with Ni(II) inorganic salts to form the nickel compounds [Ni(II)(pds)(2)](nBu(4)N)(2) (1), [Ni(II)(pds)(2)]Na(2).2H(2)O (2), and [Ni(III)(pds)(2)](2)Na(2).4H(2)O (3), depending on the reaction conditions. They are characterized by NMR, EPR, UV-vis, and IR spectroscopies, elemental analysis, cyclic voltammetry, and X-ray crystallography. The crystal structure of compound 3 shows the formation of segregated stacks of Ni(pds)(2-) units, with a strong dimerization along the stacks. The stacked fashion of the crystal packing was expected since the supramolecular forces of the alkaline side coordination to the pyrazine moieties dominate, as happens in the recently reported analogous copper system [Cu(III)(pds)(2)]Na.2H(2)O. The structure of 2 further emphasizes the alkaline coordination as the dominating supramolecular event, and an orthogonal array of 2D layers is observed. The absence of alkaline cations in complex 1 is reflected in a crystal packing with isolated complex Ni(pds)(2)(2-) units. The dimerization found in the paramagnetic Ni(III) complex 3 promotes a very strong antiferromagnetic interaction, leading to a singlet ground state. 相似文献
856.
Molecular dynamics simulations of room temperature molten salts (ionic liquids) containing imidazolium cations have been performed. Ten different systems were simulated at 323 K by using united atom force fields, in which the anion size (F-, Cl-, Br-, and PF6-) and the length of the alkyl chain of 1-alkyl-3-methylimidazolium cations (1-methyl-, 1-ethyl-, 1-butyl-, and 1-octyl-) were systematically varied. It is shown that the resulting equilibrium structures account for the observed features of experimental static structure factors when available. A detailed analysis of the simultaneous effect of changing the anion and the alkyl chain on the preferential location of nearest-neighbor anions around the cations is provided. It is shown that regions above and below the imidazolium ring are the preferential ones in case of large anions. By increasing the length of the alkyl chain, nearest-neighbor anions are pushed away from the volume occupied by the flexible alkyl chain. Partial structure factors of 1-butyl- and 1-octyl- derivatives display a peak at a wave vector smaller than the main peak, indicating the occurrence of an intermediate range order in these ionic liquids due to the presence of long alkyl chains. 相似文献
857.
Cristina López Moreno Pedro Cañada Rudner José Manuel Cano García José Manuel Cano Pavón 《Mikrochimica acta》2004,148(1-2):93-98
A sequential injection analysis method is developed for the determination of the total polyphenol index in wines. The determination is based on the Folin-Ciocalteu reaction, which is monitored spectrophotometrically. Interactions between experimental variables and their optimal levels were investigated using factorial designs. The proposed system is fully computerised and is able to monitor polyphenol index in real samples of white, sweet and red wines. The calibration graph is linear from 5 to 200mg·L–1 using Tannic acid as standard, with a detection limit of 3.2mg·L–1. Interferences are studied. For validation purposes the proposed methodology was applied to the determination of the total polyphenol index in different types of wines and compared with earlier alternatives in order to assess their performance. 相似文献
858.
The (C,F)-construction from a previous paper of the first authoris applied to produce a number of funny rank one infinite measurepreserving actions of discrete countable Abelian groups G withunusual multiple recurrence properties. In particular,the following are constructed for each p N{}:
- a p-recurrent actionT=(Tg)gG such that (if p) no one transformationTg is (p+1)-recurrentfor every element g of infinite order;
- an action T=(Tg)gGsuch that for every finite sequence g1,...,grGwithout torsionthe transformation Tg1x...x Tgr is ergodic,p-recurrent but(if p) not (p+1)-recurrent;
- a p-polynomially recurrent (C,F)-transformationwhich (if p)is not (p+1)-recurrent.
859.
David?EschwéEmail author Matthias?LangerEmail author 《Integral Equations and Operator Theory》2004,49(3):287-321
Variational principles for eigenvalues of certain functions whose values
are possibly unbounded self-adjoint operators T() are proved. A generalised
Rayleigh functional is used that assigns to a vector x a zero of the
function T()x, x), where it is assumed that there exists at most one zero.
Since there need not exist a zero for all x, an index shift may occur. Using
this variational principle, eigenvalues of linear and quadratic polynomials
and eigenvalues of block operator matrices in a gap of the essential spectrum
are characterised. Moreover, applications are given to an elliptic eigenvalue
problem with degenerate weight, Dirac operators, strings in a medium with a
viscous friction, and a Sturm-Liouville problem that is rational in the eigenvalue
parameter. 相似文献
860.
Ren C Tzoufras M Tsung FS Mori WB Amorini S Fonseca RA Silva LO Adam JC Heron A 《Physical review letters》2004,93(18):185004
A comprehensive examination of the interaction of a picosecond-long ignition pulse on high-density (40 times critical density) pellets using a two-dimensional particle-in-cell model is described. The global geometry consists of a 50 mum diameter pellet surrounded by a corona which is isolated by a vacuum region from the boundary. For cone-attached targets, as much as 67% of the incident laser energy is absorbed with 12% sent forward as fast electrons in a 23 degrees cone. The current filaments are driven by the Weibel instability of the forward-going fast electron flux and its return current with the ions playing an important role of neutralizing the space charge. No global current filament coalescence has been observed. The electron distribution function obeys a power law, which begins at E approximately 0.2 MeV and falls off as E-(2-3). 相似文献