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| 3. |
- da Silva, AF, et al.
(author)
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Impurity resistivity of the double-donor system Si : P,Bi
- 1999
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 60:23, s. 15824-15828
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Journal article (peer-reviewed)abstract
- The electrical resistivity of the shallow double-donor system Si:P,Bi, prepared by ion implantation, was investigated in the temperature range from 1.7 to 300 K. Good agreement was obtained between the measured resistivities and resistivities calculated by a generalized Drude approach for the same temperatures and dopant concentrations. The critical impurity concentration for the metal-nonmetal transition for the double-doped Si:P,Bi system was found to lie between the critical concentrations of the two single-doped systems, Si:P and Si:Bi. [S0163-1829(99)11747-8].
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- Da Silva, Fernando Luis Barroso
(author)
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Statistical Mechanical Studies of Aqueous solutions and Biomolecular Systems
- 1999
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Doctoral thesis (other academic/artistic)abstract
- This thesis is concerned with theoretical studies of aqueous solutions and biomolecular systems. Part of the present work is to understand equilibrium solvent and solute properties, while the other part is to study processes that occur in these solutions. Three points were focused: (a) the study of structure and dynamics of 1M aqueous NaCl electrolyte solution at a molecular level, which revealed particular features of these solutions such as the formation of large clusters; (b) the development of a new simulation algorithm for the Reverse Monte Carlo technique aimed to study aqueous solutions and disordered systems. Results for spherical molecules and liquid water are presented; (c) the study of binding small ions to macromolecules (proteins and micelles). The Tanford-Kirkwood model is critically analysed for models of biomolecules by means of Monte Carlo calculations. Anomalous behaviour found for the binding of ions to macromolecules in the presence of highly charged macroparticles is also reported. And, a titration study is performed to characterize interfacial properties of a prototropic molecule in self-assembled surfactant aggregates. The core of our discussion is based on electrostatic interactions and statistical mechanics. The studied systems were modeled by effective Hamiltonians within the Born-Oppenheimer and McMillan-Mayer model levels. These Hamiltonians were solved by computer simulations (Monte Carlo and Molecular Dynamics), and, in some cases, also by solving the Poisson-Boltzmann equation. Dielectric continuum models are largely used, and a discussion of uniform and non-uniform cases for studies with biomolecules and micellar systems is also included.
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- Fries, I, et al.
(author)
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Morphological and molecular characterization of Antonospora scoticae n. gen., n. sp (Protozoa, Microsporidia) a parasite of the communal bee, Andrena scotica Perkins, 1916 (Hymenoptera, Andrenidae)
- 1999
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In: EUROPEAN JOURNAL OF PROTISTOLOGY. - : GUSTAV FISCHER VERLAG. - 0932-4739. ; 35:2, s. 183-193
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Journal article (peer-reviewed)abstract
- The new microsporidium Antonospora scoticae n. gen., n. sp., a parasite of the communal bee Andrena scotica, is described based on light microscopy, ultrastructural characteristics and the nucleotide sequence of the small subunit ribosomal RNA coding regi
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- Roberto, Amilcar Eliseu Rato da Silva
(author)
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Interaction between chemicals and melanin : Role in the aetiology, diagnosis and treatment of melanoma
- 1998
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Doctoral thesis (other academic/artistic)abstract
- The incidence of malignant melanoma has continually increased over the past decades and the prognosisis poor after dissemination of metastases. A conspicuous feature of melanocytes and melanoma cells is the production of melanin. Many chemicals are interacting with melanin and melanogenesis in various ways; certain substances, mainly polycyclic amines, are adsorbed on the preformed melanin, while 2-thiouracil and related thioureylenes are incorporated into nascent melanin as false precursors. The present investigations were focused on the interaction between chemicals and melanin as a possible basis for the induction of malignant melanoma as well as the diagnosis and treatment of the disease. The melanin affinity of 50 carcinogenic substances was demonstrated in vitro. The technique used is straightforward and gives basic data on substances that may be involved in melanoma induction. Inadditional autoradiographic studies, the disposition of two of these substances, known to induce melanoma in experimental animals (dimethylbenz(a)anthracene and benzo(a)pyrene), were studied in pigmented mice and the melanin affinic properties were confirmed also in vivo. It is known that enzymes capable of bioactivating chemicals are present in melanocytes, and together with the melanin affinity this combination is apparently an aetiological factor behind malignant melanoma.The thioureylenes, which are selectively incorporated into melanin during its synthesis, might be used for the diagnosis and treatment of malignant melanoma. By autoradiography it was found that 14C- and 125I-labelled 2-thiouracil are strongly retained in melanoma metastases in mice, which is encouraging for possible clinical imaging of the disease.For treatment of malignant melanoma, studies were focused on the development of boronated thioureylenes for neutron capture therapy. A simple technique for the covalent linking of decaborane to thioureylenes was utilised, and the results from studies of such adducts, e.g. decaborane-bis-5-(diethylamino)methyl-2-thiouracil, on the incorporation into melanin in vitro and in melanoma-bearing mice by neutron capture radiography clearly demonstrated specific uptake in melanin and melanoma, with concentrations in the tumours of the order suitable for possible therapy. By double-isotope radiography it was demonstrated that the melanin synthesis, the target for the incorporation, mainly takes place in melanoma cells out of the S-phase of the cell cycle.
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