1,720,975 research outputs found
Laser cooling of solids to cryogenic temperatures
No full textLaser radiation has been used to cool matter ranging from dilute gases to micromechanical oscillators. In Doppler cooling of gases, the translational energy of atoms is lowered through interaction with a laser field(1,2). Recently, cooling of a high-density gas through collisional redistribution of radiation has been demonstrated(3). In laser cooling of solids, heat is removed through the annihilation of lattice vibrations in the process of anti-Stokes fluorescence(4-6). Since its initial observation in 1995, research(7-15) has led to achieving a temperature of 208 K in ytterbium-doped glass(16). In this Letter, we report laser cooling of ytterbium-doped LiYF(4) crystal to a temperature of similar to 155 K starting from ambient, with a cooling power of 90 mW. This is achieved by making use of the Stark manifold resonance in a crystalline host, and demonstrates the lowest temperature achieved to date without the use of cryogens or mechanical refrigeration. Optical refrigeration has entered the cryogenic regime, surpassing the performance of multi-stage Peltier coolers
Laser cooling of a semiconductor load to 165 K
No full textWe demonstrate cooling of a 2 micron thick GaAs/InGaP double-heterostructure to 165 K from ambient using an all-solid-state optical refrigerator. Cooler is comprised of Yb(3+)-doped YLF crystal, utilizing 3.5 Watts of absorbed power near the E4-E5 Stark manifold transition. (C) 2010 Optical Society of Americ
Local laser cooling of Yb:YLF to 110 K
No full textMinimum achievable temperature of similar to 110 K is measured in a 5% doped Yb:YLF crystal at lambda = 1020 nm, corresponding to E4-E5 resonance of Stark manifold. This measurement is in excellent agreement with the laser cooling model and was made possible by employing a novel and sensitive implementation of differential luminescence thermometry using balanced photo-detectors. (C) 2011 Optical Society of Americ
Optical refrigeration to 119 K, below National Institute of Standards and Technology cryogenic temperature
No full textWe report on bulk optical refrigeration of Yb:YLF crystal to a temperature of ∼124 K, starting from the ambient. This
is achieved by pumping the E4-E5 Stark multiplet transition at ∼1020 nm. A lower temperature of 119 +/- 1 K
(∼ − 154C) with available cooling power of 18 mW is attained when the temperature of the surrounding crystal
is reduced to 210 K. This result is within only a few degrees of the minimum achievable temperature of our crystal
and signifies the bulk solid-state laser cooling below the National Institute of Standards and Technology (NIST)-
defined cryogenic temperature of 123 K. © 2013 Optical Society of Americ
Optical refrigeration progress: Cooling below NIST cryogenic temperature of 123K
No full textWe have achieved cryogenic optical refrigeration with a record low temperature in optical refrigeration by cooling 5% wt.Yb:YLF crystal to 119K ± 1K (∼-154 C) at l=1020 nm corresponding to its E4-E5 Stark manifold resonance with an estimated cooling power of 18 mW. This demonstration confirms the predicted minimum achievable temperature (MAT). Further cooling is achievable as shown by measurements of a doping study where a 10% wt. Yb:YLF crystal with reduced parasitic heating has predicted cooling below 100K (∼-173K). © 2013 SPIE
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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