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81.
82.
We consider five different peer-to-peer file-sharing systems with two chunks, assuming non-altruistic peers who leave the
system immediately after downloading the second chunk. Our aim is to find chunk selection algorithms that have provably stable
performance with any input rate. We show that many algorithms that first looked promising lead to unstable or oscillating
behaviour. However, we end up with a system with desirable properties. Most of our rigorous results concern the corresponding
deterministic large system limits, but in the two simplest cases we provide proofs for the stochastic systems also. 相似文献
83.
Katja Vähävihu Lasse Ylianttila Hannu Kautiainen Pentti Tuohimaa Timo Reunala Erna Snellman 《Photochemistry and photobiology》2010,86(5):1174-1178
The objective of the study was to compare Bacillus subtilis spore film dosimeters with a Robertson Berger UV meter (RB meter) and diary records for assessing personal UV-B doses during a 13-day heliotherapy (HT) for atopic dermatitis (AD). In addition, the relationship between the personal UV-B dose and change in serum 25-hydroxyvitamin D (25(OH)D) was studied. Altogether 21 adult patients with AD completed the study arranged in the Canary Islands, either in January or March 2005. The spore film dosimeters were used throughout the day during the HT. Serum 25(OH)D was analyzed using radioimmunoassay. The mean personal UV-B dose measured with the dosimeters was 75 SED in January and 131 SED in March. The respective results gained from the RB meter combined with diary records were 63 SED and 119 SED showing a close correlation with the dosimeter results. Serum 25(OH)D concentration increased by 9.7 nmol L−1 in January and by 26.0 7 nmol L−1 in March. The increase in serum 25(OH)D correlated with the UV-B dose received. The patients complied well to use the dosimeters. We conclude spore films to be a feasible and reliable personal UV dosimeter in vivo in field conditions. 相似文献
84.
Kubicka D Kumar N Venäläinen T Karhu H Kubicková I Osterholm H Murzin DY 《The journal of physical chemistry. B》2006,110(10):4937-4946
The metal-support interactions on a series of catalysts of different acidities, including platinum-modified zeolites and H-MCM-41, are investigated by means of XPS, CO and pyridine adsorption, and a model reaction (ring opening of decalin). The electronic properties of Pt are influenced by the acidity of the support, and the alteration of Pt properties increases with increasing acidity of the support, as can be seen from the changes in the Pt binding energy and stretching frequency of adsorbed CO. At the same time, the presence of platinum affects the acidic properties of the supports by reducing the strength of the acid sites. This is observed directly as the changes in desorption of pyridine from the acid sites and indirectly as the suppression of cracking reactions during the ring opening of decalin on the Pt-modified catalysts. The observed results are discussed in terms of the interatomic potential model. 相似文献
85.
86.
Haiyan Qu Hannu Alatalo Henry Hatakka Jarno Kohonen Marjatta Louhi-Kultanen Satu-Pia Reinikainen Juha Kallas 《Journal of Crystal Growth》2009,311(13):3466-3475
Batch-reactive crystallization of the two polymorphs of l-glutamic acid was studied using in-line Raman and ATR FTIR spectroscopy. It was observed that the barrier to the nucleation of the stable β-form was higher, and thus the occurrence of β-form nucleation requires a higher supersaturation level. The local supersaturation level inside the reactive crystallizer is significantly affected by the feeding manner of the reactant. When the reactant was fed to a poorly mixed zone, such as the surface of the liquid, a high local supersaturation level was generated near the feeding point. This high local supersaturation level drastically increased with the increase in the concentrations of the reactants. As a consequence, the fraction of the β-form increased with the increase in reactants concentrations. On the other hand, feeding the reactant to a well-mixed zone near the impeller can avoid the occurrence of high local supersaturation, and therefore the dependence of the polymorphic composition of the final product on the concentration of the reactants can be reduced. The information obtained from the spectroscopy leads to improved understanding of the precipitation process and offers great potential for process optimization and control of crystalline quality. 相似文献
87.
Kasper S. Pedersen Marc Sigrist Mikkel A. Sørensen Dr. Anne‐Laure Barra Dr. Thomas Weyhermüller Dr. Stergios Piligkos Dr. Christian Aa. Thuesen Morten G. Vinum Hannu Mutka Dr. Høgni Weihe Dr. Rodolphe Clérac Prof. Dr. Jesper Bendix 《Angewandte Chemie (International ed. in English)》2014,53(5):1351-1354
A facile synthesis of the [ReF6]2? ion and its use as a building block to synthesize magnetic systems are reported. Using dc and ac magnetic susceptibility measurements, INS and EPR spectroscopies, the magnetic properties of the isolated [ReF6]2? unit in (PPh4)2[ReF6]?2 H2O ( 1 ) have been fully studied including the slow relaxation of the magnetization observed below ca. 4 K. This slow dynamic is preserved for the one‐dimensional coordination polymer [Zn(viz)4(ReF6)]∞ ( 2 , viz=1‐vinylimidazole), demonstrating the irrelevance of low symmetry for such magnetization dynamics in systems with easy‐plane‐type anisotropy. The ability of fluoride to mediate significant exchange interactions is exemplified by the isostructural [Ni(viz)4(ReF6)]∞ ( 3 ) analogue in which the ferromagnetic NiII–ReIV interaction (+10.8 cm?1) dwarfs the coupling present in related cyanide‐bridged systems. These results reveal [ReF6]2? to be an unique new module for the design of molecule‐based magnetic materials. 相似文献
88.
89.
Comprehensive self-assembly studies for nine bile acid amides of amino acid esters are reported. The number of the hydroxyl groups attached to the steroidal skeleton and the character of the amino acid ester moiety were used as variables when examining the self-assembly properties of the compounds. Two of the compounds were shown to undergo self-assembly leading to organogelation. In addition, preliminary self-assembly studies in aqueous mixtures of polar organic solvents were conducted. Microscopic methods (optical microscopy and scanning electron microscopy) were utilised in order to gain a deeper insight into the self-assembled structures. Furthermore, single-crystal X-ray structures for three of the compounds were solved. 相似文献
90.
Hannu Honkasalo 《Topology and its Applications》1998,90(1-3):11-19
E.H. Spanier (1992) has constructed, for a cohomology theory defined on a triangulated space and locally constant on each open simplex, a spectral sequence whose E2-term consists of certain simplicial cohomology groups, converging to the cohomology of the space. In this paper we study a closed G-fibration ƒ: Y → X, where G is a finite group. We show that if the base-G-spaceX is equivariantly triangulated and Y is paracompact, then Spanier's spectral sequence yields an equivariant Serre spectral sequence for ƒ. The main point here is to identify the equivariant singular cohomology groups of X with appropriate simplicial cohomology groups of the orbit space X/G. 相似文献