1,721,275 research outputs found
Physical Apects of EEG.
No full textItem does not contain fulltextTU Twente, 11 november 1999Promotores : Rogalla, H., Oosterom, A. van Co-promotor : Peters, M.J.145 p
Recent progress in developing HTS quasi-particle injection devices
No full textIn recent years, there was some progress in developing HTS three-terminal devices based on quasi-particles injection with a current gain of up to 10. This is still one order less than already demonstrated for low-T-c junctions. The main obstacle for further progress is the unsolved problem of a suitable HTS barrier which allows for quasi-particle tunneling. If the preparation conditions for barrier materials such as natural YBa2Cu3O7-delta and SrTiO3 can be better controlled, as well as the quality of the YBa2Cu3O7-delta surface improved, this kind of device could be developed into a useful fast current switch or even implemented in superconducting digital electronics. We investigated the properties of planar injection devices with (001) YBa2Cu3O7-delta as HTS superconductor, a natural oxide, PTBa2Cu3O7-delta and PrBa2Cu3-xGaxO7-delta barriers with a normal conducting counter electrode. YBa2Cu3O7-delta films used showed an average surface roughness between 1 and 6 nm. The observed current gain for devices with a natural barrier was 6.2 at 40 K and for PBCO and PBCGO barrier less than one between T-c and 10 K
A new YBCO thin film patterning technique for use in multilayer structures
No full textA new patterning technique for YBa2Cu3O7-delta (YBCO) thin films has been developed. After deposition of the superconductor a thin (10-20 nm), patterned chromium layer is deposited. During a subsequent anneal step the chromium layer reacts locally with the YBCO to form an insulating Ba-Cr-O compound. By careful optimisation of the parameters during annealing, it is possible to obtain smooth and intrinsically planarised structures. This makes this technique very attractive for multilayer patterning
Terahertz response of high-Tc ramp-type junctions on MgO
Get PDFWe successfully fabricated the high-T-c ramp-type junctions with PrBa2Cu3-xGaxO7-delta (PBCGO:x=0.1, 0.4) barriers on MgO substrates. The junctions showed RSJ-like I-V curves with increased thermally and voltage activated conductivity. The IcRn products for these junctions scale very well with the Ga-doping. Using far infrared laser radiations, we confirmed terahertz (THz) responses of these junctions. The junction with PBCGO (x=0.4) had IcRn products of similar to 1mV at 4.2K and showed Shapiro steps with THz-wave irradiation, without any additional antenna structure
Integrated submm wave receiver with superconductive local oscillator
No full textA fully superconductive integrated receiver is very promising for submm space astronomy where low weight, low power consumption, and limited volume are required. The new versions of the integrated quasioptical submm wave receiver have been designed, fabricated and tested in the frequency range of 450-700 GHz. The integrated receiver chip comprises a planar double dipole antenna, SIS-mixer and on-chip superconductive Flux-Flow Oscillator (FFO) with matching circuits. The receiver noise temperature (DSB) as low as 140 K at 500 GHz has been obtained. A light-weight and low power consuming submm imaging array is under development. Each of 9 pixels of the array is realized by an all-Nb single-chip superconductive receiver, mounted on an elliptical silicon lens with anti-reflection coating. The experimental test results of one pixel receiver are presented. A computer based system is developed to control the operation of the integrated receiver
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
NbN-MgO-NbN tunnel junctions integrated in aluminum strip lines for terahertz quasiparticle mixers
No full textNbN tunnel junctions are of great interest for THz heterodyne receivers because their large gap voltage of V-gap approximate to 5 mV implies an upper frequency limit of 4 Delta/h approximate to 2.6 THz as compared to 1.4 THz of Nb. However, due to the high ac losses in NbN films for frequencies above the NbN gap frequency, 2 Delta/h approximate to 1.3 THz, NbN matching circuits cannot be used. Lower losses are achieved with normal metals such as Al. Both for waveguide mixers and quasioptical mixers, quartz substrates are preferred. We report on a room-temperature fabrication process for NbN-MgO-NbN junctions with surfaces below 1 mu m(2) integrated in Al strip lines on quartz substrates. Appropriate plasma conditions for NbN-film deposition are obtained through the use of a second Nb target which acts as a selective nitrogen pump. NbN films on quartz substrates with and without an intermediate layer of Al have T-c > 15 K and rho(N) = 100 - 130 mu Omega.cm. Nb buffers should prevent the possible formation of insulating AIN at the Al-NbN interfaces. We fabricated the first NbN junctions sandwiched between Al layers. Sputtered Al were employed. Critical-current densities of up to 60 kA/cm(2) and subgap resistances R-sg approximate to 5.R-N were achieved. The I-V curves show various structures below the gap voltage. We discuss here the observation of a distinct steep step at eV = 2 Delta/3
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