63 research outputs found
EQCM study of redox properties of PEDOT/MnO2 composite films in aqueous electrolytes
Electrochemical behavior of poly-3,4-ethylenedioxythiophene composites with manganese dioxide (PEDOT/MnO2) has been investigated by cyclic voltammetry and electrochemical quartz crystal microbalance at various component ratios and in different electrolyte solutions. The electrochemical formation of PEDOT film on the electrode surface and PEDOT/MnO2 composite film during the electrochemical deposition of manganese dioxide into the polymer matrix was gravimetrically monitored. The mass of manganese dioxide deposited into PEDOT at different time of electrodeposition and apparent molar mass values of species involved into mass transfer during redox cycling of PEDOT/MnO2 composites were evaluated. It was found that during the redox cycling of PEDOT/MnO2 composite films with various MnO2 content, the oppositely directed fluxes of counterions (anions and cations) occur, resulting in a change of the slope of linear parts of the Delta f-E plots with changing the mass fraction of MnO2 in the composite film. Rectangular shape of cyclic voltammograms of PEDOT/MnO2 composites with different loadings of manganese dioxide was observed, which is characteristic of the pseudocapacitive behavior of the composite material. Specific capacity values of PEDOT/MnO2 composites obtained from cyclic voltammograms were about 169 F g(-1). The specific capacity, related to the contribution of manganese dioxide component, was about 240 F g(-1)
A mathematical and computational review of Hartree-Fock SCF methods in Quantum Chemistry
We present here a review of the fundamental topics of Hartree-Fock theory in
Quantum Chemistry. From the molecular Hamiltonian, using and discussing the
Born-Oppenheimer approximation, we arrive to the Hartree and Hartree-Fock
equations for the electronic problem. Special emphasis is placed in the most
relevant mathematical aspects of the theoretical derivation of the final
equations, as well as in the results regarding the existence and uniqueness of
their solutions. All Hartree-Fock versions with different spin restrictions are
systematically extracted from the general case, thus providing a unifying
framework. Then, the discretization of the one-electron orbitals space is
reviewed and the Roothaan-Hall formalism introduced. This leads to a exposition
of the basic underlying concepts related to the construction and selection of
Gaussian basis sets, focusing in algorithmic efficiency issues. Finally, we
close the review with a section in which the most relevant modern developments
(specially those related to the design of linear-scaling methods) are commented
and linked to the issues discussed. The whole work is intentionally
introductory and rather self-contained, so that it may be useful for non
experts that aim to use quantum chemical methods in interdisciplinary
applications. Moreover, much material that is found scattered in the literature
has been put together here to facilitate comprehension and to serve as a handy
reference.Comment: 64 pages, 3 figures, tMPH2e.cls style file, doublesp, mathbbol and
subeqn package
A globális éghajlatváltozás: hazai hatások és válaszok. A magyarországi klímapolitika alapjai.
Arbuscular mycorrhizal colonisation of roots of grass species differing in invasiveness
Recent research indicates that the soil microbial community, particularly arbuscular mycorrhizal
fungi (AMF), can influence plant invasion in several ways. We tested if 1) invasive species are
colonised by AMF to a lower degree than resident native species, and 2) AMF colonisation of native
plants is lower in a community inhabited by an invasive species than in an uninvaded resident
community. The two tests were run in semiarid temperate grasslands on grass (Poaceae) species,
and the frequency and intensity of mycorrhizal colonisation, and the proportion of arbuscules and
vesicles in plant roots have been measured. In the first test, grasses representing three classes of
invasiveness were included: invasive species, resident species becoming abundant upon
disturbance, and non-invasive native species. Each class contained one C3 and one C4 species. The
AMF colonisation of the invasive Calamagrostis epigejos and Cynodon dactylon was consistently
lower than that of the non-invasive native Chrysopogon gryllus and Bromus inermis, and contained
fewer arbuscules than the post-disturbance dominant resident grasses Bothriochloa ischaemum and
Brachypodium pinnatum. The C3 and C4 grasses behaved alike despite their displaced phenologies
in these habitats. The second test compared AMF colonisation for sand grassland dominant grasses
Festuca vaginata and Stipa borysthenica in stands invaded by either C. epigejos or C. dactylon, and
in the uninvaded natural community. Resident grasses showed lower degree of AMF colonisation in the invaded stand compared to the uninvaded natural community with F. vaginata responding so to
both invaders, while S. borysthenica responding to C. dactylon only. These results indicate that
invasive grasses supposedly less reliant on AMF symbionts have the capacity of altering the soil
mycorrhizal community in such a way that resident native species can establish a considerably
reduced extent of the beneficial AMF associations, hence their growth, reproduction and ultimately
abundance may decline. Accumulating evidence suggests that such indirect influences of invasive
alien plants on resident native species mediated by AMF or other members of the soil biota is probably more the rule than the exception
Long-term weather sensitivity of open sand grasslands of the Kiskunság Sand Ridge forest-steppe mosaic after wildfires
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