| 1. |
|
|
| 2. |
- Andreozzi, Emilio, et al.
(författare)
-
Phenomenological models of Na(V)1.5. A side by side, procedural, hands-on comparison between Hodgkin-Huxley and kinetic formalisms
- 2019
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Computational models of ion channels represent the building blocks of conductance-based, biologically inspired models of neurons and neural networks. Ion channels are still widely modelled by means of the formalism developed by the seminal work of Hodgkin and Huxley (HH), although the electrophysiological features of the channels are currently known to be better fitted by means of kinetic Markov-type models. The present study is aimed at showing why simplified Markov-type kinetic models are more suitable for ion channels modelling as compared to HH ones, and how a manual optimization process can be rationally carried out for both. Previously published experimental data of an illustrative ion channel (Na(V)1.5) are exploited to develop a step by step optimization of the two models in close comparison. A conflicting practical limitation is recognized for the HH model, which only supplies one parameter to model two distinct electrophysiological behaviours. In addition, a step by step procedure is provided to correctly optimize the kinetic Markov-type model. Simplified Markov-type kinetic models are currently the best option to closely approximate the known complexity of the macroscopic currents of ion channels. Their optimization can be achieved through a rationally guided procedure, and allows to obtain models with a computational burden that is comparable with HH models one.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Bosi, Ferdinando, et al.
(författare)
-
Experimental evidence for partial Fe2+ disorder at the Y and Z sites of tourmaline: a combined EMP, SREF, MS, IR and OAS study of schorl
- 2015
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 79:3, s. 515-528
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental study of an Al-rich schorl sample from Cruzeiro mine (Minas Gerais, Brazil) was carried out using electron microprobe analysis, structural refinement and Mössbauer, infrared and optical absorption spectroscopy in order to explore the disordering of Fe2+ over the Y and Z sites of the tourmaline structure.A structural formula was obtained by merging chemical and structural data. The cation distribution at the two non-equivalent octahedrally coordinated sites (Y and Z) was obtained by two different optimization procedures which, minimizing the residuals between observed and calculated data, converged to the formula: X(Na0.65〈0.32Ca0.02K0.01)Σ1.00Y(Fe1.652+Al1.15Fe0.063+Mn0.052+Zn0.05Ti0.044+)Σ3.00Z(Al5.52Fe0.302+Mg0.18)Σ6.00[T(Si5.87Al0.13)Σ6.00O18](BBO3)3V(OH)3W[(OH)0.34F0.28O0.38]Σ1.00.This result shows a partial disordering of Fe2+ over the Y and Z sites which explains adequately the mean atomic number observed for the Z site (13.5±0.1). Such a disordering is also in line with the shoulder recorded in the Mössbauer spectrum (fitted by a doublet with isomer shift of 1.00 mm/s and quadrupole splitting of 1.38 mm/s) as well as with the asymmetric bands recorded in the optical absorption spectrum at ∼9000 and 14,500 cm–1 (modelled by four Gaussian bands, centred at 7677 and 9418 cm–1, and 13,154 and 14,994 cm–1, respectively).The high degree of consistency in the results obtained using the different methods suggests that the controversy over Fe2+ order can be ascribed to the failure to detect small amounts of Fe2+ at Z (typically <<10% atoms/site) rather than a steric effect of Fe2+ on the tourmaline structure.
|
|
| 7. |
- Bosi, Ferdinando, et al.
(författare)
-
Late magmatic controls on the origin of schorlitic and foititic tourmalines from late-Variscan peraluminous granites of the Arbus pluton (SW Sardinia, Italy) : Crystal-chemical study and petrological constraints
- 2018
-
Ingår i: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 308-309, s. 395-411
-
Tidskriftsartikel (refereegranskat)abstract
- Tourmalines from the late-Variscan Arbus pluton (SW Sardinia) and its metamorphic aureole were structurally and chemically characterized by single-crystal X-ray diffraction, electron and nuclear microprobe analysis, Mössbauer, infrared and optical absorption spectroscopy, to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages. The Arbus pluton represents a peculiar shallow magmatic system, characterized by sekaninaite (Fe-cordierite)-bearing peraluminous granitoids, linked via AFC processes to gabbroic mantle-derived magmas. The Fe2+-Al-dominant tourmalines occur in: a) pegmatitic layers and pods, as prismatic crystals; b) greisenized rocks and spotted granophyric dikes, as clots or nests of fine-grained crystals in small miaroles locally forming orbicules; c) pegmatitic veins and pods close to the contacts within the metamorphic aureole. Structural formulae indicate that tourmaline in pegmatitic layers is schorl, whereas in greisenized rocks it ranges from schorl to fluor-schorl. Tourmalines in thermometamorphosed contact aureole are schorl, foitite and Mg-rich oxy-schorl. The main substitution is Na + Fe2+ ↔ □ + Al, which relates schorl to foitite. The homovalent substitution (OH) ↔ F at the O1 crystallographic site relates schorl to fluor-schorl, while the heterovalent substitution Fe2+ + (OH, F) ↔ Al + O relates schorl/fluor-schorl to oxy-schorl. Tourmaline crystallization in the Arbus pluton was promoted by volatile (B, F and H2O) enrichment, low oxygen fugacity and Fe2+ activity. The mineralogical evolutive trend is driven by decreasing temperature, as follows: sekaninaite + quartz → schorl + quartz → fluor-schorl + quartz → foitite + quartz. The schorl → foitite evolution represents a distinct trend towards (Al + □) increase and unit-cell volume decrease. These trends are typical of granitic magmas and consistent with Li-poor granitic melts, as supported by the absence of elbaite and other Li-minerals in the Arbus pluton. Tourmaline-bearing rocks reflect the petrogenetic significance of contribution from a metapelitic crustal component during the evolution of magmas in the middle-upper crust.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
|
|
| 14. |
- D'Ippolito, Veronica, et al.
(författare)
-
Color mechanisms in spinel: cobalt and iron interplay for the blue color
- 2015
-
Ingår i: Physics and chemistry of minerals. - : Springer Science and Business Media LLC. - 0342-1791 .- 1432-2021. ; 42:6, s. 431-439
-
Tidskriftsartikel (refereegranskat)abstract
- Six natural, blue colored spinel crystals were studied chemically by electron microprobe and laser ablation inductively coupled plasma mass spectrometry (LAICP-MS) techniques and optically by UV–VIS–NIR–MIR spectroscopy in the range 30,000–2,000 cm−1 to investigate the causes of their blue color hues. The positions of the absorption bands vary only marginally with the principal composition of the samples (gahnite vs. spinel s.s .). Although blue colors in spinels are frequently the result of various electronic processes in Fe cations, we demonstrate by comparison with synthetic Co-bearing samplesthat Co acts as an important chromophore also in natural spinels. Already at concentration levels of a few ppm (e.g.,>10 ppm), cobalt gives rise to absorption bands at ~18,000, 17,000 and 16,000 cm−1 that result in distinct blue coloration. In spinels with insignificant Co contents, different shades of paler blue (from purplish to greenish blue) colors are caused by electronic transitions in TFe2+, MFe2+, MFe3+ and Fe2+–Fe3+ cation pairs.
|
|
| 15. |
- D'Ippolito, Veronica, et al.
(författare)
-
Crystallographic and spectroscopic characterisation of a natural Zn-rich spinel approaching the endmember gahnite (ZnAl2O4) composition
- 2013
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 77, s. 2941-2953
-
Tidskriftsartikel (refereegranskat)abstract
- The crystal chemistry of a natural, gem-quality, blue-grey Zn-rich spinel crystal from Jemaa, Kaduna State, Nigeria, was studied using electron microprobe, single-crystal X-ray diffraction, optical absorption and Raman spectroscopies. The composition of the crystal approaches the gahnite endmember (ZnAl2O4), ∼94 mol.%, with the remainder being dominated by a hercynite component (FeAl2O4). The unit-cell dimension is 8.0850(3) Å and the tetrahedral and octahedral bond distances are determined asT–O 1.9485(6) Å andM–O 1.9137(3) Å. Crystal chemical analysis resulted in the empirical structural formulaT(Zn0.94Fe2+0.03Al0.03)M(Al1.96Fe2+0.03Fe3+0.01)O4, which shows Zn and Al almost fully ordered in the tetrahedrally and octahedrally coordinatedTandMsites, respectively. Raman spectra obtained using the excitation of the blue 473.1 nm line of a Nd:YAG laser display three of the five Raman-active modes predicted for the general oxide spinel group of minerals. These are the Egmode at 420.6 cm–1and the T2gmodes at 510 cm–1and 661 cm–1, due to vibrations in the AlO6octahedra. Optical absorption spectra recorded in the UV/VIS-NIR-MIR range 2000 29000 cm–1show a dominant absorption band at ∼5000 cm–1which is caused by spin-allowed electronicd–dtransitions in Fe2+located at theTsites. The blue-grey hue exhibited by the sample is mainly due to spin-forbidden electronic transitions inTFe2+and toMFe2+↔MFe3+intervalence charge transfer, and the poor saturation of the colour is due to the small concentration of Fe2+and Fe3+.
|
|
| 16. |
|
|
| 17. |
|
|
