| 1. |
- Bermudez, V. D., et al.
(författare)
-
Eu3+ coordination in an organic/inorganic hybrid matrix with methyl end-capped short polyether chains
- 2005
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 109:15, s. 7110-7119
-
Tidskriftsartikel (refereegranskat)abstract
- Fourier Transform mid-infrared (FT-IR), Fourier Transform Raman (FT-Raman) and photoluminescence spectroscopies and Two-Dimensional (2D) Correlation Spectroscopic Analysis were employed to examine the anionic and cationic local environments in mono-urethanesils doped with europium triflate (Eu(CF 3-SO3)3). The hybrid host framework of these materials is composed of a siliceous backbone bonded through urethane linkages to CH3-terminated polymer chains containing about 7 OCH 2CH2 units. Samples with ∞ ≥ n (composition) ≥5 (where n = OCH2CH2/Eu3+) were studied. In terms of ionic association, the level of complexity of these xerogels is very high. In all the compounds the triflate ions exist "free", weakly coordinated and forming cross-link separated ion pairs. At 20 ≥ n ≥ 5, in addition to all these species contact ion pairs occur. In agreement with these conclusions, photoluminescence establishes the presence of three distinct cation local sites (Eu3+/O=C(urethane cross-links), Eu3+/O-C- C(polyether chains) and weakly coordinated Eu3+/CF3SO 3- ionic pairs).
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Carlos, L. D., et al.
(författare)
-
Nanoscopic photoluminescence memory as a fingerprint of complexity in self-assembled alkyl/siloxane hybrids
- 2007
-
Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 19:3, s. 341-348
-
Tidskriftsartikel (refereegranskat)abstract
- A thermally activated photoluminescence memory effect, induced by a reversible order-disorder phase transition of the alkyl chains, is reported for highly organized bilayer alkyl/siloxane hybrids (see figure; left at room temperature, right at 120 degrees C). The emission energy is sensitive to the annihilation/formation of the hydrogen-bonded amide-amide array displaying a unique nanoscopic sensitivity (ca. 150 nm).
|
|
| 5. |
- Etiene, Tiago, et al.
(författare)
-
Verifying Volume Rendering Using Discretization Error Analysis
- 2014
-
Ingår i: IEEE Transactions on Visualization and Computer Graphics. - : Institute of Electrical and Electronics Engineers (IEEE). - 1077-2626 .- 1941-0506. ; 20:1, s. 140-154
-
Tidskriftsartikel (refereegranskat)abstract
- We propose an approach for verification of volume rendering correctness based on an analysis of the volume rendering integral, the basis of most DVR algorithms. With respect to the most common discretization of this continuous model (Riemann summation), we make assumptions about the impact of parameter changes on the rendered results and derive convergence curves describing the expected behavior. Specifically, we progressively refine the number of samples along the ray, the grid size, and the pixel size, and evaluate how the errors observed during refinement compare against the expected approximation errors. We derive the theoretical foundations of our verification approach, explain how to realize it in practice, and discuss its limitations. We also report the errors identified by our approach when applied to two publicly available volume rendering packages.
|
|
| 6. |
- Goncalves, M. C., et al.
(författare)
-
Local structure and near-infrared emission features of neodymium-based amine functionalized organic/inorganic hybrids
- 2005
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 109:43, s. 20093-20104
-
Tidskriftsartikel (refereegranskat)abstract
- Nd3+-based organic/inorganic hybrids have potential application in the field of integrated optics. Attractive sol-gel derived di-urea and di-urethane cross-linked poly (oxyethylene) (POE)/siloxane hybrids (di-ureasils and di-urethanesils, respectively) doped with neodymium triflate (Nd(CF3SO3)(3)) were examined by Fourier transform mid-infrared (FT-IR), Raman (FT-Raman), Si-29 magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and photoluminescence spectroscopies, and small-angle X-ray scattering (SAXS). The goals of this work were to determine which cation coordinating site of the host matrix (ether oxygen atoms or carbonyl oxygen atoms) is active in each of the materials analyzed, its influence on the nanostructure of the samples and its relation with the photoluminescence properties. The main conclusion derived from this study is that the hydrogen-bonded associations formed throughout the materials play a major role in the hybrids nanostructure and photoluminescence properties.
|
|
| 7. |
- Gonçalves, Maria M., et al.
(författare)
-
Cationic and anionic environments in mono-urethanesil hybrids doped with magnesium triflate
- 2004
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 166:1-2, s. 103-114
-
Tidskriftsartikel (refereegranskat)abstract
- Sol–gel derived poly(oxyethylene), POE/siloxane hybrids (mono-urethanesils) with a wide range of magnesium triflate (Mg(CF3SO3)2) concentrations were analyzed by infrared and Raman spectroscopies with the goal of examining the cation/polymer, cation/cross-link, hydrogen bonding and cation/anion interactions. In the host matrix of these xerogels short CH3-terminated POE segments are covalently bonded to the siliceous backbone through urethane linkages. Samples with ∞>n≥6 (where n is the molar ratio of (OCH2CH2) moieties per Mg2+ ion) were synthesized.The spectral data obtained provided conclusive evidence that the ether oxygen atoms of the polymer chains of the host structure complex the alkaline-earth ions in materials with n≤60. "Free" triflate ions and weakly coordinated anions were detected over the whole range of salt concentration examined. The coordinated triflate species are formed in two different bonding environments. Contact ion pairs appear in materials with n≤60.This work confirms previous studies that suggested that the nature of the cations added to the mono-urethanesil-type framework plays a key-role in the properties of these composites.
|
|
| 8. |
- Murari, A., et al.
(författare)
-
A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
-
Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.
|
|
| 9. |
- Nunes, S. C., et al.
(författare)
-
Cation coordination and hydrogen bonding in potassium and magnesium based-di-amidosil hybrids
- 2008
-
Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860. ; 874:1-3, s. 128-137
-
Tidskriftsartikel (refereegranskat)abstract
- Fourier transform mid-infrared and Raman spectroscopies were employed to elucidate the cation/alkylene chains, cation/cross-link, cation/anion interactions and hydrogen bonding occurring in amorphous di-amide cross-linked alkylene/siloxane hybrid materials (diamidosils) doped with potassium and magnesium triflates (KCF3SO3 and Mg(CF3SO3)(2), respectively). Materials with compositions infinity > n >= 5 (where it expresses the molar ratio of carbonyl oxygen atoms per guest cation) were investigated. The conformations (gauche) of the alkylene chains of the host di-amidosil matrix are not affected by the presence of the guest salt in both doped di-amidosil families. The K+ and M2+ ions coordinate to the carbonyl oxygen atoms of the amide cross-links within the whole range of salt concentration considered, leading to the saturation of the cross-linkages, to a redistribution of the amide-amide hydrogen-bonded aggregates of the host matrix and, in the case of the K+-doped sample with n = 10, to the formation of a new type of aggregate, stronger and more ordered than those detected at lower salt content. In both di-amidosil systems guest salt addition leads to the increase of ionic associated species and to a concomitant decrease of the concentration of "free" anions. (c) 2007 Elsevier B.V. All rights reserved.
|
|
| 10. |
- Nunes, S. C., et al.
(författare)
-
Di-ureasil ormolytes doped with Mg2+ ions: Part 2. Cationic and anionic environments
- 2005
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 176:17-18, s. 1601-1611
-
Tidskriftsartikel (refereegranskat)abstract
- Fourier Transform mid-infrared and Raman (FT-IR and FT-Raman, respectively) spectroscopies were used to investigate the cation/polymer, cation/cross-link, cation/anion and hydrogen bonding interactions in sol-gel derived ormolytes doped with magnesium triflate (Mg(CF3SO3)2). The framework of these xerogels (di-ureasils) contains poly(oxyethylene) (POE) segments with about 40.5 repeat units bonded at both ends to a siliceous backbone through urea cross-links. Materials with compositions ∞ > n ≥ 1 (where n is the ratio of oxyethylene moieties per Mg2+ ion) were studied. FT-IR data revealed that, while the urea carbonyl oxygen atoms bond to the cations in all the compounds analyzed, the POE chains complex the Mg2+ ions only at high salt content. Although the beginning of the POE/Mg2+ interaction was detected spectroscopically at n = 10, thermal data obtained in Part 1 of this series of papers suggest that this threshold composition is probably located at lower salt content. Bonding of the Mg2+ ions to the ether oxygen atoms of the POE chains is accompanied by the destruction of the urea/POE hydrogen-bonded aggregates formed in the d-U(2000) medium. Proofs of the existence of a crystalline POE/Mg(CF 3SO3)2 complex in samples with n ≤ 10 were found. "Free" and weakly coordinated CF3SO3- ions, present in all the samples examined, appear to be the main charge carriers of the conductivity maximum of this family of ormolytes (i.e., d-U(2000)20Mg(CF3SO3)2). At n ≤ 40, along with those anionic species, another anionic configuration, attributed to contact ion pairs, emerges. Higher ionic aggregates are formed in di-ureasils with n ≤ 5.
|
|
