177,559 research outputs found
Editorial
No full textThis issue of Quaternary Geochronology is the last one where I am the Editor-in-Chief. Quaternary Geochronology(QG) was born during a conversation when Giff Miller, John Chappell and John Magee and I were sitting around a camp fire in the Simpson Desert in Australia. I took the idea to David Bowen, the Editor-in-Chief of Quaternary Science Reviews (QSR) and Peter Henn, the Production Manager of QSR at Pergamon Press. Both agreed that it was a good idea, however, rather than starting a new journal it was decided to have special issues in QSR. The first issue of Quaternary Geochronology was published in 1994 as QSR 13 (2). In the early 2000s, Jim Rose, then the Editor-in-Chief of QSR, suggested that QG should become a stand-alone-journal. I have to admit that I was quite reluctant to go alone. QSR had impact factors of more than 4, and I thought that QG would struggle to reach 1. Jim suggested to start with a special issue on Cosmogenic Isotopes, as these papers did well in QSR. This was brilliant advice, as QG published some of the most influential papers on this topic over the years. The dreaded impact factor of less than 1 never materialised. QG did much better. The factor has been oscillating widely in a range between 2 and 4, which is typical for a relatively small journal.Full Tex
Fatigue behaviour of bonded anchors subjected to tensile loads
No full textFollowing recent studies on the fatigue behaviour of noise barriers for high speed railways for train transits, threaded rods bonded with epoxy resin for column base plate anchorage had to be qualified. A fatigue test campaign was carried out at Fischer Laboratories in Denzlingen (Germany) on M20 and M30 (8.8 Grade) threaded rod samples embedded in concrete by means of FIS EM epoxy resin. The tests considered also threaded rods (M16 and M30, 8.8 Grade) not directly embedded in concrete, but in pre-cast corrugated pipes having a diameter constant and equal to 40 mm.
The results were found to be very satisfactory as far as the resin performance was concerned. In fact, under tensile loads carried out under a nominal load ratio R 0, all fatigue failures took place in the threaded rods, under the nut, notwithstanding the embedment length was that suggested by technical manuals for static loading. Some typical fracture surfaces relating to medium and high cycle fatigue regime are documented.
A statistical re-analysis has been carried out considering also other data, either obtained at Fischer laboratories from analogous threaded applications or taken from the literature. A new scatterband is provided for threaded rods with diameter equal to or less than 20 mm
On a fourth-order degenerate parabolic equation: global entropy estimates, existence, and qualitative behavior of solutions
No full textBy means of energy and entropy estimates, we prove existence and positivity results in higher space dimensions for degenerate parabolic equations of fourth order with nonnegative initial values. We discuss their asymptotic behavior for t --> infinity and give a counterexample to uniqueness
Editorial-LED 2017
No full textThis special Quaternary Geochronology volume of the Proceedings of the 15th International Conference on Luminescence and Electron Spin Resonance Dating is dedicated to the memory of Martin Aitken, one of the great pioneers in luminescence dating, who passed away on 13 June 2017, aged 95. We are pleased that Ann Wintle, herself the great Dame of luminescence dating, wrote a fitting tribute to Martin, which follows this editorial.Full Tex
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Quinazolin-4-one derivatives from Streptomyces isolates
No full textFrom the ethyl acetate extract of the strain Streptomyces sp. isolate GW23/1540, besides 16 known products, several 1H-quinazolin-4-one derivatives were isolated. (S R )-2-(1-Hydroxyethyl)-2-methyl-2,3-dihydro-1H-quinazolin-4-one (4) and (R R )-2-(1-hydroxyethyl)-2-methyl-2,3-dihydro-1H-quinazolin-4-one (5) are new natural products. 2-Methyl-3H-quinazolin-4-one (2) and 1H-quinazoline-2,4-dione (3) are known from other bacteria and plants, respectively. From another Streptomyces sp., GW2/577, 5-methyl-1H-quinazoline-2,4-dione (6) was isolated and the structure proven by comparison with the isomeric 7. The new natural products showed no activity against the microalgae Chlorella vulgaris, Chlorella sorokiniana, and Scenedesmus subspicatus, the fungus Mucor miehei, the yeast Candida albicans, and the bacteria Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Streptomyces viridochromogenes
"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.
Assessment of potential advantages of relevant ions for particle therapy: A model based study
No full textPurpose: Different ion types offer different physical and biological advantages for therapeutic applications. The purpose of this work is to assess the advantages of the most commonly used ions in particle therapy, i.e., carbon (12C), helium (4He), and protons (1H) for different treatment scenarios. Methods: A treatment planning analysis based on idealized target geometries was performed using the treatment planning software TRiP98. For the prediction of the relative biological effectiveness (RBE) that is required for biological optimization in treatment planning the local effect model (LEM IV) was used. To compare the three ion types, the peak-to-entrance ratio (PER) was determined for the physical dose (PERPHYS), the RBE (PERRBE), and the RBE-weighted dose (PERBIO) resulting for different dose-levels, field configurations, and tissue types. Further, the dose contribution to artificial organs at risk (OAR) was assessed and a comparison of the dose distribution for the different ion types was performed for a patient with chordoma of the skull base. Results: The study showed that the advantages of the ions depend on the physical and biological properties and the interplay of both. In the case of protons, the consideration of a variable RBE instead of the clinically applied generic RBE of 1.1 indicates an advantage in terms of an increased PERRBE for the analyzed configurations. Due to the fact that protons show a somewhat better PERPHYS compared to helium and carbon ions whereas helium shows a higher PERRBE compared to protons, both protons and helium ions show a similar RBE-weighted dose distribution. Carbon ions show the largest variation of the PERRBE with tissue type and a benefit for radioresistant tumor types due to their higher LET. Furthermore, in the case of a two-field irradiation, an additional gain in terms of PERBIO is observed when using an orthogonal field configuration for carbon ions as compared to opposing fields. In contrast, for protons, the PERBIO is almost independent on the field configuration. Concerning the artificial lateral OAR, the volume receiving 20% of the prescribed RBE-weighted dose (V20) was reduced by over 35% using helium ions and by over 40% using carbon ions compared to protons. The analysis of the patient plan showed that protons, helium, and carbon ions are similar in terms of target coverage whereas the dose to the surrounding tissue is increasing from carbon ions toward protons. The mean dose to the brain stem can be reduced by more than 55% when using helium ions and by further 25% when using carbon ions instead of protons. Conclusions: The comparison of the PERRBE and PERPHYS of the three ion types suggests a strong dependence of the advantages of the three ions on the dose-level, tissue type, and field configuration. In terms of conformity, i.e., dose to the normal tissue, a clear gain is expected using carbon or helium ions compared to protons
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
Physical and biological factors determining the effective proton range
No full textPurpose: Proton radiotherapy is rapidly becoming a standard treatment option for cancer. However, even though experimental data show an increase of the relative biological effectiveness (RBE) with depth, particularly at the distal end of the treatment field, a generic RBE of 1.1 is currently used in proton radiotherapy. This discrepancy might affect the effective penetration depth of the proton beam and thus the dose to the surrounding tissue and organs at risk. The purpose of this study was thus to analyze the impact of a tissue and dose dependent RBE of protons on the effective range of the proton beam in comparison to the range based on a generic RBE of 1.1. Methods: Factors influencing the biologically effective proton range were systematically analyzed by means of treatment planning studies using the Local Effect Model (LEM IV) and the treatment planning software TRiP98. Special emphasis was put on the comparison of passive and active range modulation techniques. Results: Beam energy, tissue type, and dose level significantly affected the biological extension of the treatment field at the distal edge. Up to 4 mm increased penetration depth as compared to the depth based on a constant RBE of 1.1. The extension of the biologically effective range strongly depends on the initial proton energy used for the most distal layer of the field and correlates with the width of the distal penumbra. Thus, the range extension, in general, was more pronounced for passive as compared to active range modulation systems, whereas the maximum RBE was higher for active systems. Conclusions: The analysis showed that the physical characteristics of the proton beam in terms of the width of the distal penumbra have a great impact on the RBE gradient and thus also the biologically effective penetration depth of the beam. © 2013 American Association of Physicists in Medicine
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