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71.
Maciejewska Gabriela Cieślak-Golonka Maria Staszak Zbigniew Szeląg Adam 《Transition Metal Chemistry》2002,27(6):587-593
Six new heteropolynuclear chromium(III)/vanadium(V) complexes with natural ligands: glycine, glutaminic, nicotinic and asparginic acids, have been isolated and physicochemically characterised. The complexes have been analysed using spectroscopic (diffuse reflectance u.v.–vis., i.r.), magnetic methods and by FAB mass spectra. Spectral analyses with the digital filter and band deconvolution methods are presented. Additionally, preliminary toxicity studies have been performed. 相似文献
72.
Zgoła-Grześkowiak A Grześkowiak T Zembrzuska J Frańska M Frański R Lukaszewski Z 《Journal of chromatography. A》2005,1068(2):327-333
In the current study a method of isotachophoretic separation of selected carboxylic acids was developed. The method was used for the determination of carboxylated oligo(ethylene glycol)s and their degradation products in biodegradation tests of PEG 250 DA [a mixture of dicarboxylated oligo(ethylene glycol)s]. Two tests were performed in the studies: the Organization for Economic Cooperation and Development (OECD) screening test and the river water die-away test. Both the biodegradation tests proved relatively fast biodegradation of the studied compounds. In the OECD screening test the biodegradation was faster than in the river water die-away test which can be ascribed to a higher concentration of bacteria in the biodegradation liquor. The minimal sample pretreatment and relatively low cost of analysis by the isotachophoretic method used here make it a good alternative to existing methods of carboxylic acids analysis. 相似文献
73.
Marcin Marczak Lidia Wolska Wojciech Chrzanowski Jacek Namieśnik 《Mikrochimica acta》2006,155(3-4):331-348
Volatile organic compounds (VOCs), due to their toxicity and persistence in the environment, are particularly important pollutants.
Some of these compounds are mutagens, teratogens or carcinogens, while others are responsible for the degradation of organoleptic
parameters such as taste and odour of water. This review focuses on a number of key procedural steps in the analysis of volatile
organic compounds (VOCs) in water samples. A wide spectrum of techniques for the isolation and preconcentration of the aforementioned
pollutants for trace organic analysis by gas chromatography are presented and discussed. The advantages and disadvantages
of these techniques are discussed and novel developments are also taken into consideration. 相似文献
74.
Jan Kučera 《Czechoslovak Journal of Physics》1991,41(9):825-846
Three parts of the paper [Czech. J. Phys.41 (1991) 620,7 are focused on the Landauer-Büttiker approach to the study of transport in two-dimensional electron systems, with particular attention to the influence of an external magnetic field. In the previous parts the Landauer formalism was generalized for two-dimensional systems in quantizing magnetic fields. In the present part we applied the formalism to an analysis of magnetoresistance measurements. The two-dimensional electron gas preserved in the non-dissipative quantum Hall regime acts as the ideal leads necessary in the Landauer-Büttiker approach. The voltage, applied to the gate, forms a scattering region in the gated part of the sample, in between of its undisturbed parts (ideal leads). The dependence of the resistance on the gate voltage and the number of available channels within the ideal leads are discussed.The author wishes to thank to Professor P. Steda for cooperation and to Professor L. Smrka for his encouragement and support. Dr. R. J. Haug should be acknowledged for providing his experimental results. 相似文献
75.
Jan Kučera 《Czechoslovak Journal of Physics》1991,41(8):749-780
The paper of three parts is focused on the Landauer-Büttiker approach to the study of transport in two-dimensional electron systems, with particular attention to the influence of an external magnetic field. In the previous part the total conductance of such a system was shown to be proportional to the transmission current. In the present part we give a detailed proof, based on the linear response theory, to the last statement. The value of the magnetic field may be arbitrary and possible inhomogeneity of the electric field is also considered.The author wishes to thank to Professor P. Steda and Professor L. Smrka for discussions and encouragement. 相似文献
76.
Piotr Podleś 《Communications in Mathematical Physics》1992,150(1):167-179
Exterior algebras of differential forms on quantum 2-spheresS
qc
2
,q[–1, 1]/{0},c[0, ] (c=0 forq=±1), are classified. In the definition of exterior algebras we assume the invariance w.r.t. the action of the quantumSU(2) group and dimensionality conditions (which imply that we deal with two-dimensional manifolds). The exterior algebras exist only forc=0 and are unique in that case. The corresponding generalized directional derivatives are provided. 相似文献
77.
It is shown that generic small data Robinson-Trautman space-times cannot beC
123 extended beyond the r=2m Schwarzschild-like event horizon. This implies that an observer living in such a space-time can determine by local measurements whether or not he has crossed the event-horizon of the black-hole. 相似文献
78.
Self-diffusion coefficients of vanadium in the FeV -phase and in the corresponding -solid solution (Fe-47 wt.% V) measured in the temperature ranges 1002–1115 °C (-phase) and 1230–1320 °C are reported. The found results differ fundamentally and significantly from the relations in ordered and disordered solid solutions [9]. The diffusivity in -phase at the transition temperature (T
/=1200 °C) is cca 14 times lower than the diffusivity in the b.c.c. solid solution, the chemical composition of which is the same. The lowering is caused by the different values of frequency factors,D
O=0.11 cm2/s andD
O=45 cm2/s. The effect of the corresponding activation enthalpiesH
=252 kJ/mole andH
=293 kJ/mole is small and quite opposite. The occurence of higher activation enthalpyH
in the -solid solution at temperaturesT>T
/ may be attributed to a certain amount of the f.c.c. phase coexisting in the b.c.c. matrix at concentrationsc
v>27 wt.% at sufficiently high temperatures [7]. A comparison of vanadium self-diffusion characteristics measured in the -phase to the extrapolated values obtained on the basis of the previous measurements [1] in the Fe-V primary solid solutions 1 shows that the diffusivity ratioD
1/D
(1473 K)=33 and that the activation enthalpyH
is by about 3% higher than the valuesH
1 (eq. (5)) measured in the uniphase b.c.c. solid solutions. 相似文献
79.
Kim SY Augustine S Eo YJ Bae BS Woo SI Kang JK 《The journal of physical chemistry. B》2005,109(19):9397-9403
We use a first-principles calculation and small-angle neutron scattering (SANS) to investigate the mechanism and the nanosize products of the sol-gel reaction with diphenylsilanediol (DPD) and 3-methacryloxypropyltrimethoxysilane (MEMO) precursors in synthesizing a hybrid waveguide material. It is predicted that switching between a DPD hydroxyl and a MEMO methoxy with a reaction rate of 6.8 x 10(-6) s(-1) at 300 K is the fastest process for the first reaction step, thus generating diphenylmethoxysilanol (DPM) and 3-methacryloxypropyldimethoxysilanol (MEDO) as products. However, we determine that this reaction pathway could be modified by the presence of the H2O released from a catalyst such as Ba(OH)2.H2O. Next, switching between the DPM hydroxyl and the MEDO methoxy is followed to generate diphenyldimethoxysilane (DPDM) and 3-methacryloxypropylmethoxysilanediol (MEMDO). However, condensation between a MEMDO hydroxyl and a DPDM methoxy is found to be most favorable for the third reaction step, which generates the DPDM-MEMDO dimer and CH3OH molecule as products. In a similar fashion, a DPDM methoxy of the DPDM-MEMDO dimer can condense with a MEMDO hydroxyl of the second DPDM-MEMDO dimer to increase the chain, but its reaction rate of 2.8 x 10(-11) s(-1) is predicted to be about 5 times smaller than that between a DPDM methoxy and a MEMDO hydroxyl. This implies that the reaction rate for the larger nanostructures becomes smaller. Additionally, our SANS measurements determine that the final products from our sol-gel reaction are on the nanometer scale, at sizes from 1.76 to 2.36 nm. 相似文献
80.
A cluster of two atoms described by thes-f model with Coulomb repulsion has been considered. The interaction between localized 4f electrons (S=1/2) is taken in the molecular field approximation. The thermodynamic quantities like magnetization, specific heat and correlation functions n
, n
, S
z
n
, S
z
n
, S
z (n
–n
), n
n
and S
+
a
+
a
as functions of temperature are presented for different band fillingN=0, 0.5, 1, 1.5, 2. The dependence of Curie temperature onN is calculated. The phase diagram forN=1 (T=0K) shows the possibility of existence of two phases: paramagnetic and ferromagnetic.The Curie temperature and the specific heat as functions ofN exhibit similar trends as found in experiments on doped magnetic semiconductors. 相似文献