| 901. |
- He, Jianjun, et al.
(författare)
-
Modified phthalocyanines for efficient near-IR sensitization of nanostructured TiO2 electrode
- 2002
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 124:17, s. 4922-4932
-
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.
|
|
| 902. |
- He, Wang, et al.
(författare)
-
RF Compliance Study of Temperature Elevation in Human Head Model Around 28 GHz for 5G User Equipment Application : Simulation Analysis
- 2018
-
Ingår i: IEEE Access. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2169-3536. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- The crowdedness of current cellular bands and the demand for higher transmission speed prompt the use of the millimeter-wave spectrum for the next-generation mobile communication. In the millimeter-wave frequencies, the dosimetric quantity for human exposure to electromagnetic fields changes from the specific absorption rate to incident power density. In this paper, we used 28-GHz beam-steering patch arrays, a dipole antenna, and plane waves to investigate the temperature elevation in a multi-layer model of human head and its correlation with power density metrics. The power density averaged over one square-centimeter in free space and the peak temperature elevation in tissue at 28 GHz have good correlation. The peak temperature elevation indicated by the power density averaged one square-centimeter also agrees well with the peak temperature elevation induced by the plane waves. The results show that the averaging area of a few square-centimeters may be a good candidate for the spatial-average power density. The findings provide valuable input to the ongoing revision and updating of relevant safety standards and guidelines.
|
|
| 903. |
- Hebert, Hans, et al.
(författare)
-
Two-dimensional crystallization and electron crystallography of MAPEG proteins.
- 2005
-
Ingår i: Methods in Enzymology. - 0076-6879 .- 1557-7988. ; 401, s. 161-8
-
Tidskriftsartikel (refereegranskat)abstract
- Members of the membrane-associated proteins in the eicosanoid and glutathione metabolism (MAPEG) superfamily have been subjected to two-dimensional crystallization experiments. A common denominator for successful attempts has been the use of a low lipid/protein ratio in the range of 1-9 (mol/mol). Electron crystallography demonstrated either hexagonal or orthorhombic packing of trimeric protein units. Three-dimensional structure analysis of the MAPEG member microsomal glutathione transferase 1 has shown that the monomer for this protein contains a left-handed bundle of four transmembrane helices. It is likely that this is a common structural motif for MAPEG proteins, because projection maps of all structurally characterized members are very similar.
|
|
| 904. |
- Hedberg, Jonas, 1979-, et al.
(författare)
-
Tungsten carbide nanoparticles in simulated surface water with natural organic matter : dissolution, agglomeration, sedimentation and interaction with Daphnia magna
- 2017
-
Ingår i: Environmental Science: Nano. - : Royal Society of Chemistry. - 2051-8153 .- 2051-8161. ; 4:4, s. 886-894
-
Tidskriftsartikel (refereegranskat)abstract
- Even though anthropogenic nano-sized tungsten carbide nanoparticles (WC NPs) have been found in the environment, there are currently no investigations on their environmental fate. This work studies the interaction between natural organic matter (NOM) and WC NPs, as well as the potential uptake by the aquatic model organism Daphnia magna. We here show that the affinity between WC NPs and humic acid or dihydroxybenzoic acid (DHBA), which are model molecules of NOM, is very low with no observed surface adsorption. The lack of a stabilizing effect of these organic molecules, in combination with a relatively high effective density of WC NP agglomerates in humic acid, resulted in the substantial agglomeration and sedimentation of the WC NPs. A higher stability of the smaller sized WC NP agglomerates (<150 nm) means that this fraction is mobile and can be transported to other settings, suggesting that this particle fraction should be considered in further studies. The dissolution of tungsten from WC NPs was continuous and the relatively slow dissolution rate (on the order of 0.03 mg m-2 h-1) implies that particle transport will not be severely limited from a dissolution perspective. Uptake of tungsten (dissolved tungsten and WC particles) by D. magna was observed although this did not induce any acute toxic effects.
|
|
| 905. |
|
|
| 906. |
- Hedenmalm, Håkan, et al.
(författare)
-
Carleson's convergence theorem for Dirichlet series
- 2003
-
Ingår i: Pacific Journal of Mathematics. - : Mathematical Sciences Publishers. - 0030-8730 .- 1945-5844. ; 208:1, s. 85-109
-
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.
|
|
| 907. |
- Hedenmalm, Håkan, et al.
(författare)
-
Hele-Shaw flow on hyperbolic surfaces
- 2002
-
Ingår i: Journal des Mathématiques Pures et Appliquées. - 0021-7824 .- 1776-3371. ; 81:3, s. 187-222
-
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.
|
|
| 908. |
- 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
-
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.
|
|
| 909. |
|
|
| 910. |
- Hedlund, Artur, et al.
(författare)
-
Microstructures of cellulose coagulated in water and alcohols from 1-ethyl-3-methylimidazolium acetate : contrasting coagulation mechanisms
- 2019
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 26:3, s. 1545-1563
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract: Coagulation of cellulose solutions is a process whereby many useful materials with variable microstructures and properties can be produced. This study investigates the complexity of the phase separation that generates the structural heterogeneity of such materials. The ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), and a co-solvent, dimethylsulfoxide (DMSO), are used to dissolve microcrystalline cellulose in concentrations from 5 to 25 wt%. The solutions are coagulated in water or 2-propanol (2PrOH). The coagulated material is then washed and solvent exchanged (water → 2PrOH → butanone → cyclohexane) in order to preserve the generated microstructures upon subsequent drying before analysis. Sweep electron microscopy images of 50 k magnification reveal open-pore fibrillar structures. The crystalline constituents of those fibrils are estimated using wide-angle X-ray spectroscopy and specific surface area data. It is found that the crystalline order or crystallite size is reduced by an increase in cellulose concentration, by the use of the co-solvent DMSO, or by the use of 2PrOH instead of water as the coagulant. Because previous theories cannot explain these trends, an alternative explanation is presented here focused on solid–liquid versus liquid–liquid phase separations. Graphical abstract: [Figure not available: see fulltext.].
|
|
