1,721,071 research outputs found
Mixed mode excitation and low cost control IC for electronic ballast
No full textThis paper introduces a gate-driven mixed mode excitation that is applicable to dimmable electronic ballasts. The proposed approach combines the characteristics of self-oscillating mode and external excitation. In the mixed mode excitation, the metal oxide semiconductor field effect transistors in an electronic ballast are turned on by the resonant current and turned off by the gate driver, which is triggered by a low voltage control integrated circuit (IC). By adjusting this triggering point, the low voltage control IC controls the switching frequency of the electronic ballast. In the electronic ballast with mixed mode excitation, filament preheating, dimming, and protection are all implemented by the low voltage control IC, which is fabricated in a 3.3-V standard CMOS process. The proposed approach allows for the realization of a low cost and high performance electronic ballast
Adsorption and reaction of 4-nitrobenzoic acid on omega-functionalized alkanethiol monolayers on powdered silver: Infrared and Raman spectroscopy study
No full textWe have investigated the stability of w-functionalized alkanethiol monolayers anchored on 2 mu m-sized silver particles by means of infrared and Raman spectroscopy. Although the alkyl chains of dodecanethiol (DDT) monolayers were deduced to have a trans-zigzag conformation by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), those of 11-mercapto-1-undecanol (11-MUD) and 12-mercapto-1-dodecylamine (12-MDA) monolayers seemed to assume strongly disordered conformations on the powdered silver surface. We also found by DRIFTS that 4-nitrobenzoic acid (4-NBA) can be incorporated nearly equally into the hydrophilic(11-MUD and 12-MDA) and hydrophobic (DDT) group-terminated monolayers by forming Ag--COO- bond(s). This seemed to be best understood by presuming that the hydrophobic interchain interaction is less optimal on a microscopically rough surface than on a smooth surface when monolayers of 11-MUD and 12-MDA are assembled on Ag. It was also found by surface-enhanced Raman scattering (SERS) that photoreaction of 4-NBA more readily occurs at the 11-MUD-derivatized Ag particles than at the 12-MDA- and DDT- derivatized Ag particles. Invoking the role of water in such photoreactions, the hydroxyl-terminated monolayers appeared to be more labile to water than the amine-terminated monolayers. The present observations clearly illustrate that commercially available powdered silver is an efficient substrate for the characterization of self-assembled monolayers on silver substrates by the simultaneous use of DRIFTS and SERS
A low-cost high-efficiency CCFL inverter with new capacitive sensing and control
No full textA new low-cost and efficient cold cathode fluorescent lamp (CCFL) inverter for liquid crystal display (LCD) application is suggested in this paper. The topology of the inverter is derived from modified class E-type resonant electronic ballasts and has a dc-like input current. In addition, a new sensing circuit for lamp current and transformer voltage is proposed. A simple RC-network measures the voltage of a ballasting capacitor in series with the lamp instead of the lamp current itself while the lamp is floated. Utilizing the printed circuit board capacitors for the sensing capacitors and integrating small-valued sensing resistors into a control integrated circuit make the inverter very simple, efficient, and cost-effective. The new sensing circuit can solve many problems that arise when a terminal of the lamp is grounded to sense the lamp current. The control circuits for the prototype experiments are also described in detail. The frequency control scheme with a fixed off-time and a varying on-time was chosen to maintain the operation of zero-voltage switching in the entire dimming range and to reduce the complexity of the control circuits. The control circuits have an analog dimming function using a current control loop, a low frequency pulsewidth modulation dimming, open-lamp protection and voltage regulation, and soft-on/off functions
Detection and regulation of CCFL current and open-lamp voltage while keeping floating condition of the lamp
No full textA new simple balanced circuitry using four printed circuit board trace capacitors effectively detects the cold-cathode fluorescent lamp current and the transformer voltage of the inverter without grounding either side of the lamp. The inverter employing this circuit is free from the problems caused by grounding one side of the lamp, and it provides a stable and wide dimming control as well as an open-lamp voltage regulation with a better efficacy
Adsorption and stability of phthalic acid on a colloidal silver surface: surface-enhanced Raman scattering study
No full textThe adsorption characteristics of phthalic acid on a silver surface were investigated by means of surface-enhanced Raman scattering (SERS). For a reliable analysis of the SER spectrum, we also performed an ab initio vibrational wavenumber calculation, The SER spectral features dictated that the phthalic acid molecules should be bound to silver as dicarboxylate, but in contrast with earlier reports, with a strongly tilted orientation with respect to the surface normal. The degree of tilt appeared to increase with increase in the bulk pH, Such a tilted orientation was presumed to occur by the simultaneous sigma- and pi-type coordination of carboxylate groups to silver caused by the steric hindrance and electrostatic repulsion between the two carboxylate groups. Probably owing to the latter effects, phthalic acid on silver was easily displaced with aromatic mono-acids that could be bound to silver by forming only sigma-type coordination. A sigma-type coordination therefore seemed to be more important than a pi-type coordination for an aromatic carboxylic acid derivative to assemble a robust monolayer on a silver surface. Copyright (C) 2000 John Whey & Sons, Ltd.This work was supported by the Korea Science and Engineering Foundation(KOSEF) through the Center for Molecular Catalysis at Seoul
National University (SNU) and by the Korea Research Foundation through the Research Institute for Basic Sciences at SNU. S.W.J. thanks the KOSEF for an Intern Research Fellowship
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Coefficient determination related to optical gain in erbium-doped silicon-rich silicon oxide waveguide amplifier
No full textGain-determining coefficients in Er-doped, nanocrystal-Si (nc-Si) sensitized silica waveguide amplifiers are investigated. Single-mode, Er-doped silica waveguides with nc-Si embedded in them were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition of Er-doped a-Si:O-x (x<2) followed by a high-temperature anneal to precipitate nc-Si. Exciting the Er ions via nc-Si by pumping the waveguide from the top with the 477 nm line of an Ar laser resulted in an enhancement of the transmitted 1535 nm signal of up to 14 dB/cm, indicating a possible net gain of up to 7 dB/cm. From the dependence of the signal enhancement upon the pump power, an emission cross section of 2x10(-19) cm(2) at 1535 nm and an effective excitation cross section of greater than or equal to10(-17) cm(2) at 477 nm is obtained. (C) 2002 American Institute of Physics
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