131,902 research outputs found
Uitbesteding in de financiële sector. In het bijzonder van vermogensbeheer door pensioenfondsen
No full textContains fulltext :
151628.pdf (Publisher’s version ) (Open Access)Radboud Universiteit Nijmegen, 14 december 2015Promotores : Busch, D., Grundmann-van de Krol, C.M.XXVI, 431 p
Studies on the expression of plasmid-borne genes in the endosymbiotic state of Rhizobium leguminosarum
No full textThe subject matter of the research reported in this thesis is the role of plasmid-borne genes of Rhizobium in symbiosis and nitrogen fixation. Plasmid DNA was isolated from Rhizobium leguminosarum strain PRE and the expression of plasmid DNA in nitrogen fixing nodules was investigated by hybridization with RNA from bacteroids. These experiments are described in Chapters 3 and 4. From these experiments it is concluded that only one of the two plasmids present in PRE is strongly expressed in the symbiotic state. On this plasmid also the nitrogenase genes are located. Hooykaas et al . (1981) showed with genetic techniques that a large number, if not all, of the rhizobial genes involved in nodule formation and nitrogen fixation are carried on only one of the plasmids occurring in R. leguminosarum . Therefore they proposed to call such plasmids Sym plasmids, since obviously these plasmids are essential for the development of the symbiotic state. Our results which indicate that only one of the plasmids of R. leguminosarum is strongly expressed in the symbiotic state are in good agreement with the results of Hooykaas et al . (1981). Sym plasmids from different isolates of R. leguminosarum vary remarkably in size, as shows in Chapter 4. The reason why some Sym plasmids contain much more DNA then other Sym plasmids is still unknown. Besides the Sym plasmid a large number of R.leguminosarum strains contain at least one other plasmid, and many strains even more. No function has till now been allocated to these plasmids.For comparison with the hybridizations of plasmid DNA with RNA from bacteroids, plasmid DNA was hybridized with RNA from free living bacteria. No plasmid specific hybridization with RNA from free living bacteria was detectable, as is shown in Chapter 3. A similar result was obtained by Prakash (1981), who could not detect hybridization of plasmid DNA with RNA from exponentially growing bacteria. However, with RNA from stationary bacteria he found hybridization with some restriction fragments of the plasmid. On the physical map of a Sym plasmid which he constructed the part which is expressed in stationary bacteria differs from the parts which are expressed in bacteroids (Prakash, 1981). Both his results and ours indicate that a number of plasmid-borne genes are only expressed in the symbiotic state, and that plasmid-borne genes in exponentially growing bacteria are not expressed, or at the most at a level below detection. It is possible that in exponentially growing bacteria messenger RNA is more rapidly degraded than in bacteroids or in stationary phase bacteria. This could make the detection of specific expression of genes more difficult in exponentially growing bacteria. Rhizobia without Sym plasmids are still viable (Hooykaas et al . , 1981) so expression of this plasmid DNA is not necessary for growth of free living bacteria.Among the plasmid-borne genes which are strongly expressed in the symbiotic state are the nitrogenase genes. This was demonstrated by hybridization of plasmid DNA with plasmid pSA30. Plasmid pSA30 is a recombinant plasmid containing the nitrogenase operon of Klebsiella pneumoniae (Cannon et al ., 1979). pSA30 is only homologous to the part of Rhizobium nif H, coding for the subunits of component II of nitrogenase, and to a part of nif D, coding for the αsubunits of component I (Ruvkun and Ausubel, 1980). It is therefore not possible to determine with pSA30 as a probe in hybridizations with Rhizobium DNA whether nif K, coding for the βsubunits of component I of nitrogenase, constitutes in a single operon together with nif D and nif H, as is the case in Klebsiella pneumoniae (MacNeal et al ., 1978). A decisive answer might be obtained if it would be possible to detect intact messenger RNA from the nitrogenase operon of Rhizobium . As described in Chapter 5 it is possible to isolate large messenger RNAs from bacteroids. Based on the molecular weight of the RNA and on hybridizations with fragments of pSA30 coding for nif H and nif D respectively it is concluded that in Rhizobium nif H, coding for the subunits of component II, is located in a single operon together with nif D and nif K, coding respectively for the αand βsubunits of component I. Bisseling (1980) studied the regulation of the synthesis of the nitrogenase components I and II of R. leguminosarum in pea root nodules. It was shown by radioimmunoassays that component I could be detected 1 or 2 days before component II during the development of the root nodules. During waterlogging component I was still synthesized, whereas the synthesis of component II was repressed. These results indicate that the synthesis of component I and component II of nitrogenase of R. leguminosarum can be regulated rather independently. if the genes for the subunits of the components I and II are transcribed in a single messenger RNA, a regulation on the level of translation of this messenger has to be postulated to explain the different rates of synthesis of component 1 and component II during nodule formation or in waterlogging root nodules. Whether this difference in regulation of the synthesis of component I and component II is on the level of transcription or translation cannot be concluded from our experiments. For that the synthesis of nitrogenase messenger RNA has to be examined under conditions which result in different rates of synthesis of component I and component II. Now the analytical devices are available isolated nitrogen fixing bacteroids may have good potentialities in further study of the mechanism of the regulation of the nitrogenase genes in Rhizobium.</em
Optical Properties of CdSe Nanoparticle Assemblies
No full textLeon FR, Zaitseva N, Gerion D, Huser T, Krol DM. Optical Properties of CdSe Nanoparticle Assemblies. In: Proceedings of the MRS. 2004
What can 14 CO measurements tell us about OH?
No full textThe possible use of 14CO measurements to constrain hydroxyl radical (OH) concentrations in the atmosphere is investigated. 14CO is mainly produced in the upper atmosphere from cosmic radiation. Measurements of 14CO at the surface show lower concentrations compared to the upper atmospheric source region, which is the result of oxidation by OH. In this paper, the sensitivity of 14CO mixing ratio surface measurements to the 3-D OH distribution is assessed with the TM5 model. Simulated 14CO mixing ratios agree within a few molecules 14CO cm¿3 (STP) with existing measurements at five locations worldwide. The simulated cosmogenic 14CO distribution appears mainly sensitive to the assumed upper atmospheric 14C source function, and to a lesser extend to model resolution. As a next step, the sensitivity of 14CO measurements to OH is calculated with the adjoint TM5 model. The results indicate that 14CO measurements taken in the tropics are sensitive to OH in a spatially confined region that varies strongly over time due to meteorological variability. Given measurements with an accuracy of 0.5 molecules 14CO cm¿3 STP, a good characterization of the cosmogenic 14CO fraction, and assuming perfect transport modeling, a single 14CO measurement may constrain OH to 0.2¿0.3×106 molecules OH cm¿3 on time scales of 6 months and spatial scales of 70×70 degrees (latitude×longitude) between the surface and 500 hPa. The sensitivity of 14CO measurements to high latitude OH is about a factor of five higher. This is in contrast with methyl chloroform (MCF) measurements, which show the highest sensitivity to tropical OH, mainly due to the temperature dependent rate constant of the MCF¿OH reaction. A logical next step will be the analysis of existing 14CO measurements in an inverse modeling framework. This paper presents the required mathematical framework for such an analysis
Leptogyra bujnitzkii Krol & Nekhaev 2020
No full textLeptogyra bujnitzkii (Gorbunov, 1946) (Figure 1) Ganesa bujnitzkii Gorbunov, 1946b: p. 309, pl. 1, fig. 1a–b, v. Skenea bujnitzkii: Kantor & Sysoev 2006: p. 40, pl. 18D. Type material. 2 syntypes, R / V Sadko, det. Gorbunov, 24.07.1938, sta. 101, trawl, Zoological Institute of Russian Academy of Sciences No 1908/1. Type locality. Arctic Ocean, slope of Lomonosov Ridge, 81°50’N, 136°14’E, 3,700–3,800 m. Diagnosis. Leptogyra Bush, 1897 with skeneiform shell, thin sigmoidal growth lines, wide spiral wrinkles, wide, deep umbilicus. Central tooth of radula wide, rectangular, first three lateral teeth similar, fourth lateral tooth rather large, numerous filamentous marginal teeth. Description. Shell small (maximal shell width 3.15 mm), skeneiform, light brownish with convex rounded whorls, suture deep, periphery of penultimate whorl rounded, convex. Teleoconch surface with thin numerous sigmoidal growth lines, spiral sculpture consists of wide wrinkles (Fig. 1A, E). Almost whole surface of embryonic shell covered with irregular network sculpture, only narrow part near protoconch border smooth (Fig. 1 C–D). Aperture rhomboid with rounded angles. Umbilicus wide, deep. Periostracum, operculum and soft body unknown. According to original description operculum consist of four whorls in larger specimen, of three whorls in smaller specimen (Gorbunov 1946b). Radula (Fig. 1 F–G). n -4-1-4- n. Central tooth poorly visible on preparation, wide, rectangular, with thin cutting edge without distinct cusps. Three inner lateral teeth uniform, narrow, with small triangular cutting edge, outer lateral large, with single relatively small triangular cutting edge. Marginal teeth numerous, thin, filamentous. Measurements of syntype 1: shell height 2.45 mm, body whorl height 2.20 mm, aperture height 1.45 mm, shell width 3.15 mm, aperture width 1.65 mm, diameter of protoconch 308 µm, diameter of the initial part of protoconch 67 µm, number of whorls 3.4, number of protoconch whorls 0.7. Measurements of syntype 2: shell height 2.30 mm, body whorl height 2.05 mm, aperture height 1.35 mm, shell width 2.95 mm, aperture width 1.50 mm, diameter of protoconch 300 µm, diameter of the initial part of protoconch 67 µm, number of whorls 3.5, number of protoconch whorls 0.7. Distribution. Known only from the type locality. Remarks. We suggest that Ganesa bujnitzkii Gorbunov, 1946 actually belongs to the genus Leptogyra. The representatives of this genus have the same pattern of protoconch sculpture, consisting of an irregular network vanishing towards adult whorls (Marshall 1988). The teleoconch sculpture of Leptogyra bujnitzkii resembles that of Leptogyra by the presence of prosocline sigmoidal growth lines and spirally arranged wrinkles or riblets (Bouchet & Warén 1993; Marshall 1988; Warén & Bouchet 2009). The radular morphology of Leptogyra bujnitzkii is the same as in the majority of Leptogyra species (see Marshall 1988). The irregular network sculpture on the protoconch and the sigmoidal growth lines are also present in Xyleptogyra Marshall, 1988 and Leptogyropsis Marshall, 1988. However, both genera differ from Leptogyra bujnitzkii in radular morphology (Marshall 1988). Leptogyropsis has three curved lateral teeth and a deeply medially split central tooth that is curved laterally. Xyleptogyra has three strongly curved lateral teeth and a wide laterally curved central tooth (Marshall 1988). Marshall (1988) recognized that Leptogyra constricta Marshall, 1988 and Leptogyra patula Marshall, 1988 have only three lateral teeth. However, he mistakenly interpreted the fourth rather large lateral tooth as innermost marginal. Leptogyra inflata Warén & Bouchet, 1993 has five lateral teeth according to Warén & Bouchet (1993), however, only four laterals can be recognized on the figures provided by these authors. In accordance with Hess et al. (2008), we consider the presence of four lateral teeth as a diagnostic feature of Leptogyra. Leptogyra bujnitzkii was described in a book presenting results of Soviet studies in the Siberian seas and the Arctic Ocean during the 1930s. The name Ganesa bujnitzkii (like other newly-introduced species names) was first mentioned in the first chapter of this book summarizing ecological, distributional, and biogeographical data for all sea floor fauna known for this region (Gorbunov 1946a). This publication also contains information about the collection site for G. bujnitzkii. However, the morphological description is given in another chapter (Gorbunov 1946b), which constitutes the valid description of this taxon according to the article 13.1 of the International Code of the Zoological Nomenclature. The coordinates of the type locality given by Gorbunov (1946a) (82°51’ N, 137°23’ E) (Fig. 2B, red star) are different from those on the label of the type lot (81°50’ N, 136°14’ E) (Fig. 2, green star); however, other information, such as depth (3,700 –3,800 m), date of collection (July 24, 1938), and station number (st. 101), is the same in both sources. The sample with Leptogyra bujnitzkii was collected during the forced drift of r/v Sadko, which was blocked by ice together with two ice-breakers, i/b Georgiy Sedov and i/b Malygin (Zubov 1940). The captain of the i/b Georgiy Sedov (Badygin 1950) gives coordinates of the convoy for July 23 and 25, 1938 in his memories (81°50.8’ N, 136°11’ E and 81°51.5’ N, 135°40’ E, respectively), which are very close to the location indicated on the label (Fig. 2C). Therefore, we conclude that they are correctly indicating type locality of this species. Leptogyra bujnitzkii is the first representative of the gastropod subclass Neomphaliones known from the Arctic Ocean. Representatives of the genus Leptogyra, like other members of the subclass, are known exclusively from habitats such as sunken wood or hydrothermal vents (Hess et al. 2008). Unfortunately, there is no information about the habitat of Leptogyra bujnitzkii. The collection site is located on the way of “transpolar drift stream”: a route of travel of Siberian wood to Greenland and the American continent (Dyke et al. 1997). Bottom communities associated with sunken wood are known from several deep water regions of the extreme North of the Atlantic Ocean, such as from the deep water off Northern Iceland (Warén 1996; Ockelmann & Dinesen 2011) and eastern Greenland (Schulz et al. 2010), but there is no direct evidence about the presence of such biocoenoses from the high Arctic Basin, which remains poorly studied. As there are no known geothermal areas around the type locality of Leptogyra bujnitzkii, we hypothesize that sunken wood is the most probable habitat for this species. *mean values **measured from published picture “-” – no data based on Marshall 1988, Warén & Bouchet, 1993, 2009 and original dataPublished as part of Krol, Ekaterina N. & Nekhaev, Ivan O., 2020, Redescription of Leptogyra bujnitzkii (Gorbunov, 1946) comb. nov., the first representative of the gastropod subclass Neomphaliones from the high Arctic, pp. 446-450 in Zootaxa 4759 (3) on pages 446-449, DOI: 10.11646/zootaxa.4759.3.13, http://zenodo.org/record/374115
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
"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.
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