| 51. |
- Hammarstrom, L., et al.
(författare)
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Mimicking photosystem II reactions in artificial photosynthesis : Ru(II)-polypyridine photosensitisers linked to tyrosine and manganese electron donors
- 2000
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Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 58:03-feb, s. 57-69
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Tidskriftsartikel (refereegranskat)abstract
- The paper describes a project aiming at constructing functional mimics of the oxygen evolving complex in photosystem II, coupled to photoinduced charge separation. Biomimetic electron donors, manganese complexes and tyrosine, have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photooxidised Ru(III) complex was demonstrated using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn(III,III)-->tyrosine-->Ru(III) was demonstrated, in analogy to the reaction on the donor side of photosystem II. Electron transfer from the tyrosine to Ru(III) was coupled to tyrosine deprotonation. This resulted in a large reorganisation energy and thus a slow reaction rate, unless the tyrosine was hydrogen bonded or already deprotonated. A comparison with analogous reaction in photosystem II is made. Finally, light-induced oxidation of a manganese dimer linked to a Ru(II)-photosensitiser was observed. Preliminary results suggest the possibility of photooxidising manganese dimers in several steps, which is an important step towards water oxidation,
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| 52. |
- Hanséus, Katarina, et al.
(författare)
-
Analysis of atrioventricular plane movements by Doppler tissue imaging and m-mode in children with atrial septal defects before and after surgical and device closure.
- 2002
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Ingår i: Pediatric Cardiology. - : Springer Science and Business Media LLC. - 0172-0643 .- 1432-1971. ; 23:2, s. 152-159
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Tidskriftsartikel (refereegranskat)abstract
- Our objective was to compare the effects of surgical and device closure of atrial septal defects (ASDs) on atrioventricular plane function. In healthy individuals, both short- and long-axis motion contribute to ventricular pump function. Short-axis function (i.e., the amplitude and velocity of atrioventricular plane movements) may be evaluated by M-mode and Doppler tissue imaging. The study group consisted of 19 children with ASD of the secundum type before and after surgical (n = 12) or device (n = 7) closure and 10 healthy controls. Surgical and device closures were uncomplicated and all defects were completely closed. Registrations of atrioventricular plane systolic and diastolic amplitude and velocity were made from the tricuspid and the mitral annulus and from the septum in the apical four-chamber view. Comparisons were made between examinations before and after closure, between the two subgroups of patients treated by surgical and device closure, respectively, and between the patient group and the control groups. Before ASD closure, all measurements were normal or near normal. After surgery, systolic amplitudes and velocities of the tricuspid annulus and in the septum decreased significantly, whereas no changes were seen in the device group. Less marked changes were seen in diastolic measurements. However, in the surgical group significant decrease to subnormal values were found in the tricuspid annulus and in the septum, which may indicate a decreased diastolic function postoperatively. Mitral valve annulus amplitude and velocity were not affected by the treatment. Atrioventricular function is normal in children with right ventricular volume overload. The decrease to subnormal values after open-heart surgery is not seen after device closure of the ASD, indicating that surgery affects right ventricular function.
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| 53. |
- Harnefors, Lennart, et al.
(författare)
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Torque-Maximizing Field-Weakening Control : Design, Analysis, and Parameter Selection
- 2001
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Ingår i: IEEE Transactions on Industrial Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0278-0046 .- 1557-9948. ; 48:1, s. 161-168
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Tidskriftsartikel (refereegranskat)abstract
- The torque-maximizing field-weakening controlscheme proposed by Kim and Sul is developed further. Theperformance under imperfect field orientation conditions isinvestigated, and it is shown that an overestimated—rather thanan underestimated—model leakage inductance should be used. Aslightly modified algorithm, which offers better robustness andreduced computational complexity, is presented. The importance,for good performance, of combining the scheme with currentand speed controllers featuring antiwindup and improved disturbancerejection is emphasized. The dynamics of the resultingclosed-loop system are analyzed. Obtained in the process are rulesfor selection of all controller parameters, allowing tuning withouttrial-and-error steps. Good performance of the resulting systemis verified experimentally.
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| 54. |
- Haussermann, U., et al.
(författare)
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FeGa3 and RuGa3 : Semiconducting intermetallic compounds
- 2002
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 165:1, s. 94-99
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Tidskriftsartikel (refereegranskat)abstract
- The intermetallic compounds FeGa3 and RuGa3 were prepared from the elements using a Ga flux and their structures were refined from single-crystal X-ray data. Both compounds crystallize with the FeGa3 structure type (tetragonal, space group P4(2)/mnm, Z=4). Electrical resistivity measurements revealed a semiconducting behavior for FeGa3 and RuGa3, which is in contrast to the good metallic conductivity observed for the isotypic compound CoGa3. The origin of the different electronic properties of these materials was investigated by first-principle calculations. It was found that in compounds adopting the FeGa3 structure type the transition metal atoms and Ga atoms interact strongly. This opens a d-p hybridization bandgap with a size of about 0.31 eV in the density of states at the Fermi level for 17-electron compounds (i.e., FeGa3 and RuGa3). The electronic structure of CoGa3 (an 18-electron compound) displays rigid band behavior with respect to FeGa3. As a consequence, the Fermi level in CoGa3 becomes located above the d-p hybridization gap which explains its metaltic conductivity.
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| 55. |
- He, Jianjun, et al.
(författare)
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Modified phthalocyanines for efficient near-IR sensitization of nanostructured TiO2 electrode
- 2002
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 124:17, s. 4922-4932
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Tidskriftsartikel (refereegranskat)abstract
- A zinc phthalocyanine with tyrosine substituents (ZnPcTyr), modified for efficient far-red/near-IR performance in dye-sensitized nanostructured TiO2 solar cells, and its reference, glycine-substituted zinc phthalocyanine, (ZnPcGly), were synthesized and characterized. The compounds were studied spectroscopically, electrochemically, and photoelectrochemically. Incorporating tyrosine groups into phthalocyanine makes the dye ethanol-soluble and reduces surface aggregation as a result of steric effects. The performance of a solar cell based on ZnPcTyr is much better than that based on ZnPcGly. Addition of 3alpha,7alpha-dihydroxy-5beta-cholic acid (cheno) and 4-tert-butylpyridine (TBP) to the dye solution when preparing a dye-sensitized TiO2 electrode diminishes significantly the surface aggregation and, therefore, improves the performance of solar cells based on these phthalocyanines. The highest monochromatic incident photo-to-current conversion efficiency (IPCE) of similar to24% at 690 nm and an overall conversion efficiency (eta) of 0.54% were achieved for a cell based on a ZnPcTyr-sensitized TiO2 electrode. Addition of TBP in the electrolyte decreases the IPCE and eta considerably, although it increases the open-circuit photovoltage. Time-resolved transient absorption measurements of interfacial electron-transfer kinetics in a ZnPoTyr-sensitized nanostructured 702 thin film show that electron injection from the excited state of the dye into the conduction band of TiO2 is completed in similar to500 fs and that more than half of the injected electrons recombines with the oxidized dye molecules in similar to300 ps. In addition to surface aggregation, the very fast electron recombination is most likely responsible for the low performance of the solar cell based on ZnPcTyr.
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| 56. |
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| 57. |
- Hedenmalm, Håkan, et al.
(författare)
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Carleson's convergence theorem for Dirichlet series
- 2003
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Ingår i: Pacific Journal of Mathematics. - : Mathematical Sciences Publishers. - 0030-8730 .- 1945-5844. ; 208:1, s. 85-109
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Tidskriftsartikel (refereegranskat)abstract
- A Hilbert space of Dirichlet series is obtained by considering the Dirichlet series f(s) = Sigma(n=1)(infinity) a(n)n(-s) that satisfy Sigma(n=0)(infinity) \a(n)\(2) < +&INFIN;. These series converge in the half plane Re s > 1/2 and define a functions that are locally L-2 on the boundary Re s > 1/2. An analog of Carleson's celebrated convergence theorem is obtained: Each such Dirichlet series converges almost everywhere on the critical line Re s = 1/2. To each Dirichlet series of the above type corresponds a trigonometric series Sigma(n=1)(infinity) a(n)chi(n), where chi is a multiplicative character from the positive integers to the unit circle. The space of characters is naturally identified with the infinite-dimensional torus T-infinity, where each dimension comes from a a prime number. The second analog of Carleson's theorem reads: The above trigonometric series converges for almost all characters chi.
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| 58. |
- Hedenmalm, Håkan, et al.
(författare)
-
Hele-Shaw flow on hyperbolic surfaces
- 2002
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Ingår i: Journal des Mathématiques Pures et Appliquées. - 0021-7824 .- 1776-3371. ; 81:3, s. 187-222
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Tidskriftsartikel (refereegranskat)abstract
- Consider a complete simply connected hyperbolic surface. The classical Hadamard theorem asserts that at each point of the surface, the exponential mapping from the tangent plane to the surface defines a global diffeomorphism. This can be interpreted as a statement relating the metric flow on the tangent plane with that of the surface. We find an analogue of Hadamard's theorem with metric flow replaced by Hele-Shaw flow, which models the injection of (two-dimensional) fluid into the surface. The Hele-Shaw flow domains are characterized implicitly by a mean value property on harmonic functions.
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| 59. |
- Hedenmalm, Håkan, et al.
(författare)
-
Mean value surfaces with prescribed curvature form
- 2004
-
Ingår i: Journal des Mathématiques Pures et Appliquées. - : Elsevier BV. - 0021-7824 .- 1776-3371. ; 83:9, s. 1075-1107
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Tidskriftsartikel (refereegranskat)abstract
- The Gaussian curvature of a two-dimensional Riemannian manifold is uniquely determined by the choice of the metric. The formulas for computing the curvature in terms of components of the metric, in isothermal coordinates, involve the Laplacian operator and therefore, the problem of finding a Riemannian metric for a given curvature form may be viewed as a potential theory problem. This problem has, generally speaking, a multitude of solutions. To specify the solution uniquely, we ask that the metric have the mean value property for harmonic functions with respect to some given point. This means that we assume that the surface is simply connected and that it has a smooth boundary. In terms of the so-called metric potential, we are looking for a unique smooth solution to a nonlinear fourth order elliptic partial differential equation with second order Cauchy data given on the boundary. We find a simple condition on the curvature form which ensures that there exists a smooth mean value surface solution. It reads: the curvature form plus half the curvature form for the hyperbolic plane (with the same coordinates) should be less than or equal to 0. The same analysis leads to results on the question of whether the canonical divisors in weighted Bergman spaces over the unit disk have extraneous zeros. Numerical work suggests that the above condition on the curvature form is essentially sharp. Our problem is in spirit analogous to the classical Minkowski problem, where the sphere supplies the chart coordinates via the Gauss map.
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| 60. |
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