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981.
Tadeusz Wibig 《Central European Journal of Physics》2007,5(4):528-538
A new feature in the spectrum of ultra high energy cosmic rays (UHECR) has been announced in the paper by Berezinsky, Gazizov
and Kachelrieβ. The ratio of the solution of the exact transport equation to its solution in the continuous energy loss limit
shows intriguing features which, according to the Authors, are related to the very nature of the energy loss processes of
UHECR: the very sharp second dip predicted at 6.3 × 1019 eV can be used as an energy calibration point and also as the UHECR mass indicator for big future cosmic ray experiments.
In the present paper we would like to advocate that this statement is an overinterpretation. The second dip is a result of an inappropriate approximation used, and thus it cannot help to understand the nature of UHECR in any way.
相似文献
982.
Tadeusz M. Krygowski Marcin Palusiak Anna Płonka Joanna E. Zachara‐Horeglad 《Journal of Physical Organic Chemistry》2007,20(5):297-306
Molecular geometry of 10 isomeric nitronaphtholate ions (excluding peri‐ and ortho‐type substituted systems), 1‐ and 2‐naphtholate ions, 1‐ and 2‐nitronaphthalene, meta‐ and para‐nitrophenolate, phenolate, and nitrobenzene were optimized at B3LYP/6‐311G** level of approximation. Substituent effect stabilization energy (SESE), geometry‐based aromaticity index HOMA, magnetism‐based indices NICS, NICS(1), NICS(1)zz, and parameters characterizing Bond Critical Points (BCP) (ρ, ?2ρ, ellipticity, ion/cov) of the Bader AIM theory were used to characterize transmitting properties for substituent effect through the naphthalene moiety. It results from our study that the studied systems could be clearly divided into two groups, (i) a para‐type group, where the intramolecular charge transfer between the π‐electron donating and π‐electron accepting substituents can be described by canonical forms with charge separation (as in the case of para‐nitrophenolate) and (ii) a meta‐type group, where this transfer requires using canonical forms with double charge separation (as in the case of meta‐nitrophenolate). Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
983.
The geometry and electronic structure of the amino group in aniline and its derivatives are very sensitive to both intramolecular interactions such as substituent effects and intermolecular ones such as H-bonding. An analysis of experimental geometries retrieved from the CSD base and computational modeling of aniline and its derivatives and their H-bonded complexes by use of B3LYP/6-311+G** and MP2/aug-cc-pVDZ showed that the degree of pyramidalization of the amino group depends on H-bonding, which exists in two forms, (i) NH...B (base) and (ii) N...HB (Br?nsted acid), both of which affect the shape of the NH2 group. The effect may be significantly enhanced by a substituent through resonance interaction from electron-attracting substituents. The NH...B interactions lead to a substantial planarization of the group, whereas N...HB interactions do not. The natural bond orbital analysis allowed the authors to show that the changes in occupancy of the "lone pair" orbital and in geometry parameters describing pyramidalization of the group depend on the substituent constants. 相似文献
984.
The AIM parameters at the ring critical point (the electron density and its Laplacian, the total electron energy density and both its components, potential and kinetic electron energy densities), have been intercorrelated with aromaticity indices: the geometry-based HOMA and the magnetism-based NICS, NICS(1), and NICS(1)(zz). A set of 33 phenylic rings having possibly a diversified aromatic character, and a set of 20 quasi-rings formed by intramolecular hydrogen and lithium bonds, have been taken into consideration. It has been found that the density of total electron energy, H, may serve as a new quantitative characteristic of pi-electron delocalization. The dependences between H values and aromaticity indices are correlated (cc(H/HOMA)=0.99, cc(H/NICS(1)zz)=0.95). 相似文献
985.
The main advantage of the application of cyclic chronopotentiometry (CCP) in end-column CE detection arises from the fact that the detection parameters and the magnitude of the analytical signal are (in contrast with other electrochemical detection methods) independent of the ohmic polarization of the solution caused by the separation current at the detection end of the capillary. CCP was used to determine sugars on platinum and gold microelectrodes after separation by CE. The results obtained with a gold microelectrode were better. Subsequently this detection method was used for quantitative determination of sugars in honeys and for their authentication. 相似文献
986.
Silica xerogel-hydrogen peroxide composites: their morphology, stability, and antimicrobial activity
Zegliński J Cabaj A Strankowski M Czerniak J Haponiuk JT 《Colloids and surfaces. B, Biointerfaces》2007,54(2):165-172
Hydrogen peroxide was incorporated into silica xerogel matrix over the concentration range from 3.8 to 68.0 wt% via the sol–gel route. The obtained composites were characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The release rates of H2O2 from the composites into the aqueous phase were examined. In most cases, a 90% release was attained after ca. 10 min, and it was only slightly dependent on H2O2 concentration and particle size. The antimicrobial activity of the composite containing 3.59% H2O2 was evaluated against Escherichia coli and Micrococcus luteus. A comparative assay was carried out for aqueous solution of H2O2 of the same concentration. The results demonstrated a potent microbicidal efficacy of the composite. Furthermore, diffusion range of the hydrogen peroxide from the solid composite into an agar medium matched that of the H2O2 in aqueous solution. The stability tests with the xerogels containing 3.8, 26.4, and 68.0% of H2O2 showed that after 63 days respective losses of the H2O2 at 3 °C were 8.8, 9.7, and 6.2%. Both the DSC results and the stability tests have shown that the molecular water present in the pores stabilizes the composite, probably through improving the binding of the H2O2 molecules onto the silica surface. 相似文献
987.
Jaworska M Lodowski P Andruniów T Kozlowski PM 《The journal of physical chemistry. B》2007,111(10):2419-2422
The relevant excited states involved in the photolysis of methylcobalamin (MeCbl) have been examined by means of time-dependent density functional theory (TD-DFT). The low-lying singlet and triplet excited states have been calculated along the Co-C bond at the TD-DFT/BP86/6-31g(d) level of theory in order to investigate the dissociation process of MeCbl. These calculations have shown that the photodissociation is mediated by the repulsive 3(sigmaCo-C --> sigma*Co-C) triplet state. The key metastable photoproduct involved in Co-C bond photolysis was identified as an S1 state having predominantly dCo --> pi*corrin metal-ligand charge transfer (MLCT) character. 相似文献
988.
An unprecedented 24-N-imidazolyl steroidal alkaloid, amaranzole A, was isolated from a tropical sponge, Phorbas amaranthus. The structure was solved by interpretation of MS, NMR, including a novel exciton-coupled CD spectrum due to an allyl imidazole, and comparison with model compounds. 相似文献
989.
Dutka M Oleś T Mossakowski M Froncisz W 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,210(1):44-50
A modified rectangular loop-gap resonator for X-band electron paramagnetic resonance (EPR) studies of aqueous samples, enabling the light access, is described. Changes introduced into rectangular resonator geometry, previously presented in Piasecki et al. (1998) [1], and redesigned coupling structure lead to the better thermal and mechanical stability. The modified structure makes provision for the controlled light access to the sample placed in a flat cell during an EPR experiment. The sensitivity of the resonator for aqueous samples as well as an experimentally tested microwave magnetic field homogeneity are presented. Results of simulations and experimental tests indicate that the presence of light access holes in the resonator's front side does not disturb the uniformity of microwave magnetic field distribution in the nodal plane. The optimal flat cell thickness for unsaturable and saturable aqueous samples has been calculated for this new structure. A modified rectangular geometry of the loop-gap resonator ensures a good performance for aqueous samples allowing its convenient and efficient light illumination during EPR signal recording . 相似文献
990.
Jaroslava Maroszová Jan Moncol Zdeňka Padělková Reijo Sillanpää Tadeusz Lis Marian Koman 《Central European Journal of Chemistry》2011,9(3):453-459
The crystal and molecular structure of [Cu(nif)2(4-PM)2]·CH3OH (1) and [Cu(2-Clbz)2(4-PM)2(H2O)] (2), (where nif = niflumate anion, 2-Clbz = 2-chlorobenzoate anion and 4-PM is the 4-pyridylmethanol), have been determinated
by X-ray crystallography. The Cu2+ cation in (1), is coordinated by two pairs of oxygen atoms from asymmetric bidentate niflumate anions and by a pair of pyridine
nitrogen atoms from monodentate 4-pyridylmethanol ligands in trans position forming an extremely elongated bipyramid. The
Cu2+ cation in (2), is coordinated by a pair of oxygen atoms from monodentate 2-chlorobenzoate anions, further by a pair of pyridine
nitrogen atoms from monodentate 4-pyridylmethanol ligands and finally by a water oxygen atom forming a tetragonal-pyramidal
coordination polyhedron. The molecules of both complexes in crystal structures are linked by O-H…O hydrogen bonds, which created
a three-dimensional hydrogen-bonding networks. The Π-Π stacking interactions are also observed in crystal structures of complex
2. The spectral properties (IR and electronic spectra) of both complexes were also investigated. 相似文献