130,486 research outputs found
Vibrational cooling of cesium molecules using noncoherent broadband light
No full textWe demonstrate selective vibrational population transfer in cold cesium dimers using a simple approach based on the use of a shaped incoherent broadband diode laser near threshold. Optical pumping into a single vibrational level is accomplished with an incoherent light source by eliminating transitions from the targeted vibrational level. The broadband spectrum of the laser is wide enough to electronically excite several vibrational states of the molecule simultaneously. This method is relatively inexpensive, simple, and flexible to allow for development of new applications, in particular, the preparation of optically closed molecular system, opening the way to direct laser cooling of molecules
Broadband lasers to detect and cool the vibration of cold molecules
No full textBy using broadband lasers, we demonstrate the possibilities for control of cold molecules formed via photoassociation. Firstly, we present a detection REMPI scheme (M. Viteau et al., Phys. Rev. A, 2009, 79, 021402) to systematically investigate the mechanisms of formation of ultracold Cs(2) molecules in deeply bound levels of their electronic ground state X(1)Sigma(+)(g). This broadband detection scheme could be generalized to other molecular species. Then we report a vibrational cooling technique (M. Viteau et al., Science, 2008, 321, 232) through optical pumping obtained by using a shaped mode locked femtosecond laser. The broadband femtosecond laser excites the molecules electronically, leading to a redistribution of the vibrational population in the ground state via a few absorption-spontaneous emission cycles. By removing the laser frequencies corresponding to the excitation of the v = 0 level, we realize a dark state for the so-shaped femtosecond laser, leading, with the successive laser pulses, to an accumulation of the molecules in the v = 0 level, i.e. a laser cooling of the vibration. The simulation of the vibrational laser cooling allows us to characterize the criteria to extend the mechanism to other molecular species (R. V. Krems, Int. Rev. Phys. Chem., 2005, 24, 99). We finally discuss the generalization of the technique to laser cooling of the rotation of the molecule
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Varicocele at a prepubertal age. Adolescent varicocele.
No full textVaricocele is a dilatation of the spermatic veins, particularly on the left side, and represents one of the most frequent causes of male infertility. Its frequency in pre-adolescence varies from 10% to 15%. Even today varicocele pathogenesis is not clear. In the period from August 1990 to August 1999, 35 males between 10 and 16 years of age were treated surgically in our Institution via interruption of the internal spermatic vein using Palomo's technique. Patients that reached the age of 18 after surgery have had a spermiogramm. The problem of varicocele therapy in pre-adolescence has not yet been resolved with regard to surgical therapy and follow-up
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Cold cesium molecules: from formation to cooling RID E-9057-2011
No full textRecent experiments on formation of translationally cold ground state molecules, their subsequent broadband vibrational cooling and study of rotations are presented together with the related modeling. We produce cold molecules by photoassociating pairs of cold cesium atoms that can decay into ground state molecules in different vibrational levels. Then we laser cool the vibrational degree of freedom by selecting a single target vibrational level. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. Results for vibrational cooling into the nu = 0, nu = 1, nu = 2 and nu = 7 level of the singlet X(1)Sigma(g) ground electronic state are presented. Depletion spectroscopy is performed to study the rotational distribution of the created molecules. In the theoretical modeling of the process we are able to reproduce our results and investigate the prospects for a 'complete' cooling of molecules, including also their rotational degree of freedom
Broadband Vibrational Cooling of Cold Cesium Molecules: Theory and Experiments RID E-9057-2011
No full textThe use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample of cold molecules, initially distributed over several vibrational levels, has thus been transfered into a single selected vibrational level of the singlet. X(1)Sigma(g) ground electronic state. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. In this paper we briefly report the main experimental results and then address, in a detailed way by computer simulations, the perspectives for a "complete" cooling of the molecules, including also the rotational degree of freedom. Since the pumping process strongly depends on the relative shape of the ground and excited potential curves, ro-vibrational cooling through different excited states is theoretically compared
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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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