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91.
Dominik P. J. Barz Peter Ehrhard 《Nanoscale and Microscale Thermophysical Engineering》2013,17(3):305-316
We have investigated the flow and mass transport within an electroosmotically pumped incompressible liquid through a meander microchannel system. We employ two-dimensional, time-dependent finite element simulations in conjunction with a matched asymptotic treatment of the electrical double layers. The electroosmotic pumping is realized for two idealized and two realistic electrical fields, while a pressure-driven flow is used for comparison. We focus on the aspects of the electroosmotic transport. We find for most of the electroosmotically driven cases rather complex flow fields, involving recirculation regions. These recirculation regions in all cases increase dispersion. (i) The least dispersion is associated with a plug-type velocity profile, which is obtained for an idealized purely wall-tangential orientation of the electrical field. (ii, iii) We find that both the idealized horizontal electrical field and the real electrical field between two vertical plates give considerably higher dispersion than the pressure-driven flow. Vertical plate electrodes, therefore, do not allow for a electrical field, which minimizes dispersion. (iv) The arrangement of two point electrodes at the in and out sections likewise proves to be no optimal means to reduce dispersion beyond the pressure-driven flow. Thus, meander geometries of channels, in general, cause severe problems if electroosmotic pumping needs to be achieved in combination with minimized dispersion. 相似文献
92.
Hannes Federrath Christoph Gerber Dominik Herrmann 《Datenschutz und Datensicherheit - DuD》2011,35(11):791-796
Die Analyse der Aktivit?ten eines Internet-Nutzers ist über l?ngere Zeit in der Regel nur mit Kenntnis der bei vielen Internet-Zugangsprovidern
mindestens einmal t?glich wechselnden IP-Adressen m?glich. Verwendet der Nutzer zudem einen Anonymisierungsdienst, sollte
eine Verkettung der Nutzer-Aktivit?ten auch für den Zugangsprovider unm?glich sein. Der Beitrag zeigt, dass eine verhaltensbasierte
Verkettung dennoch m?glich ist und verbreitete Anonymisierungsl?sungen in der Praxis einen deutlich geringeren Schutz vor
Beobachtung bieten, als bisher angenommen. 相似文献
93.
Dominik Benz Andreas Hotho Robert Jäschke Beate Krause Folke Mitzlaff Christoph Schmitz Gerd Stumme 《The VLDB Journal The International Journal on Very Large Data Bases》2010,19(6):849-875
Social resource sharing systems are central elements of the Web 2.0 and use the same kind of lightweight knowledge representation,
called folksonomy. Their large user communities and ever-growing networks of user-generated content have made them an attractive object of
investigation for researchers from different disciplines like Social Network Analysis, Data Mining, Information Retrieval
or Knowledge Discovery. In this paper, we summarize and extend our work on different aspects of this branch of Web 2.0 research,
demonstrated and evaluated within our own social bookmark and publication sharing system BibSonomy, which is currently among
the three most popular systems of its kind. We structure this presentation along the different interaction phases of a user
with our system, coupling the relevant research questions of each phase with the corresponding implementation issues. This
approach reveals in a systematic fashion important aspects and results of the broad bandwidth of folksonomy research like
capturing of emergent semantics, spam detection, ranking algorithms, analogies to search engine log data, personalized tag
recommendations and information extraction techniques. We conclude that when integrating a real-life application like BibSonomy
into research, certain constraints have to be considered; but in general, the tight interplay between our scientific work
and the running system has made BibSonomy a valuable platform for demonstrating and evaluating Web 2.0 research. 相似文献
94.
95.
Prof. Dr.-Ing. habil. Dominik Surek Dipl.-Ing. Hubertus Galinsky 《Forschung im Ingenieurwesen》1995,61(5):117-128
Zusammenfassung Seitenkanalverdichter unterliegen trotz ihrer geringen Druckverh?ltnisse im Teillastbereich erheblichen thermischen Belastungen.
Dadurch steigt nicht nur die Verdichtungsendtemperatur und die Maschinenbelastung, sondern mit steigender Maschinentemperatur
erfolgt auch eine erhebliche Aufheizung des Gases bereits im Eintrittsbereich, wodurch die Arbeitsübertragung beeinflu?t wird.
Die Resultate experimenteller Untersuchungen zeigen, da? die Aufheizung des Gases besonders im Eintrittsbereich des Seitenkanals
erfolgt und dadurch die Arbeitsübertragung im vorderen Bereich stark verlustbehaftet erfolgt. Die Folge davon sind sehr hohe
Polytropenexponenten bei gro?en Druckverh?ltnissen im Teillastbereich, die zu einer gro?en W?rmezufuhr an das Gas führen und
den Wirkungsgrad der Maschinen mindern. 相似文献
96.
Prof. Dr.-Ing habil. Dominik Surek Prof. Dr.-Ing. habil. Gerd Grabow Dr.-Ing. H. H. Henning 《Forschung im Ingenieurwesen》1995,61(9):233-240
Zusammenfassung Im Resonator von Laseranlagen werden ca. 20% der zugeführten Energie für den Laserstrahl genutzt. 80% der zugeführten Gesamtenergie
werden mit dem Lasergas ungenutzt aus dem Resonator in den nachfolgenden W?rmeübertrager abgeführt. Um den Anlagenwirkungsgrad
von Laseranlagen zu erh?hen, soll die ungenutzte Austrittsenergie aus dem Resonator in einer nachgeschalteten Entspannungsturbine
in mechanische Energie umgesetzt werden, die zum Antrieb des Lasergasverdichters genutzt wird. Dadurch kann der Verdichter
mit der vorhandenen Proze?energie angetrieben werden und der Anlagenwirkungsgrad vonη
A
bis 0,20 aufη
A
bis 0,34 erh?ht werden. Durch thermodynamische Proze?untersuchungen werden die erreichbaren Wirkungsgradsteigerungen von
Laseranlagen ausgewiesen und die optimalen Parameterbereiche für die Druck-und Temperaturverh?ltnisse ermittelt. Das Leistungsverh?ltnis
der gewonnenen Turbinenleistung zur notwendigen Verdichterleistung wird angegeben. 相似文献
97.
Shan Jiang Thammanoon Sreethawong Serina Siew Chen Lee Michelle Bee Jin Low Khin Yin Win Agata Maria Brzozowska Serena Lay‐Ming Teo G. Julius Vancso Dominik Jaczewski Ming‐Yong Han 《Advanced Materials Interfaces》2015,2(3)
With the ban of tributyltin, copper‐based biocides are now widely used in antifouling coatings as the major active ingredients. Given the past experience of heavy‐metal accumulation in harbors with limited water exchange, there is a significant interest in developing copper materials that greatly reduce the amount of copper ions released into marine surroundings. In this paper, copper nanowires (NWs) encapsulated in polymer matrices are investigated as the means to control the release of copper ions and to achieve a long‐lasting antifouling effect. Very long CuNWs with high aspect ratio in organic solution are drop‐coated onto substrates to fabricate uniform thin films. They are then incorporated into an elastomeric polydimethylsiloxane (PDMS) matrix. A small amount of CuNWs in PDMS can inhibit barnacle cyprid settlement, while it exhibits low mortality to cyprids and nauplii present in the surrounding seawater environment. The low levels of copper released after 50 days suggest that the intersecting and interconnected CuNWs embedded in PDMS could potentially release copper ions continuously over a few years in seawater. This approach provides a novel platform to use hybrid materials as effective marine antifouling coatings, and may be applied to fouling release materials to enhance their antifouling properties. 相似文献
98.
This paper describes the technological status of and some challenges in the manufacturing of Cu(In,Ga)Se2 (CIGS)-based solar cells on flexible polymer and metal substrates. Substrate characteristics such as thermal expansion properties and stability, surface roughness, or substrate composition, strongly influence growth and properties of the following layers. For example, adhesion failure, cracking, or contamination by diffusion of impurities from the substrate may occur with some substrates. Aspects of (external) sodium incorporation into CIGS are discussed for high and low CIGS deposition temperature. Low-temperature deposition processes are particularly important when polyimide substrates are used. The electrical insulation of metal foils by dielectric barriers (e.g. SiOx or Al2O3) allows the fabrication of monolithically integrated modules. A soft and selective patterning technique based on laser scribing and mask-free photolithography is described. Working modules as large as 20 cm × 30 cm were achieved with these methods. 相似文献
99.
A laser based process for the formation of a local back surface field for n-type silicon solar cells
We report on the development of a laser doping process for the formation of a local back surface field (LBSF) for n-type silicon solar cells. Local point contacts are formed by applying a laser process to a doped, passivating layer of amorphous silicon carbide (PassDop layer). The exposure to laser radiation results in local doping and opening of the passivation layer at the same time. By variation of the laser parameters and the dopant content in the layer, strength and depth of the doping can be controlled. Both parameters are varied and the formation of a LBSF structure on lifetime samples is investigated. High dopant content in the passivation layer and comparably low laser fluencies yield the best electrical results, evidencing the formation of an effective LBSF in combination with a restricted laser induced damage in the silicon crystal. 相似文献
100.