178,521 research outputs found
Direct observation of Fermi-pressure-driven electron-hole plasma expansion in GaAs on a picosecond time scale
No full textApplying pump and probe differential reflection (Delta R) and transmission (Delta T) of femtosecond light pulses inr either co- or counterpropagating pump and probe geometries, a direct time of flight method with submicrometer resolution is presented. With this technique we study the density-dependent transport of photogenerated carrier plasmas perpendicular to the surface of GaAs samples for delay times 20 ps less than or equal to tau less than or equal to 1 ns. At a pump fluence of 800 mu J cm(-2) a relatively sharp charge-carrier front was observed, with high velocities of 14 x 10(5) cm/s at a delay time tau approximate to 20 ps, decreasing as v proportional to tau(-2/3) to 2 x 10(5) cm/s at tau approximate to 350 ps. The arrival times tau of the carriers at a fixed sample thickness depend on the fluence of the pump pulses F such as tau proportional to 1/F-0.45. The results are discussed in the framework of diffusive transport with a strongly density-dependent diffusivity D. The data can be described consistently with the assumption of Fermi pressure as the dominating driving force fur plasma expansion
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
Use of pyrethroid analogues to identify key structural features for enhanced esterase resistance in Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae)
No full textIt has been reported previously that the major resistance mechanism to pyrethroid insecticides by the cotton bollworm Helicoverpa armigera (Hubner) in Australia is a consequence of overproduction of esterase isoenzymes. This paper reports structure-activity relationships that support such a view, based on in vivo bioassays conducted with a range of pyrethroid structures containing a variety of acid and alcohol moieties and the correlation with in vitro esterase inhibition assays against the same structures, and identifies the critical regions of the molecule with regard to esterase inhibition, and hence resistance. The implications of this work in terms of possible resistance management are evaluated and discussed. (c) 2007 Society of Chemical Industry
Encapsulating reactive behaviour in goal-based plans for programming BDI agents
No full textReactive behaviour in Belief Desire Intention (BDI)-based models and architectures adopted in agent programming is typically specified in terms of reactive plans not bound to any specific goal. In this paper, we present and discuss an extension of the plan model used in BDI programming languages in which goal-based plans encapsulate both proactive and reactive behaviour. This brings important benefits both to the practice of agent programming and in supporting agent reasoning at runtime. The approach is evaluated through concrete implementations based on two existing agent programming platforms, namely Jason and ASTRA
Ultrafast spectroscopy with spin polarization
No full textA project for the design and r.alization of an experimental station dedicated to ultrafast spin polarization dynamics allowing for spin polarization measurements of photoelectron yield as excited by free electron laser pulses is presented
Histological study of SlNPV infection on body weight and peritrophic membrane damage of Spodoptera litura larvae
No full textSanjaya, Machmudin D, Kurniawati ND. 2010. Kajian histologis infeksi SlNPV terhadap berat badan dan kerusakan
membran peritrofik larva Spodoptera litura. Nusantara Bioscience 2: 135-140. Pengaruh infeksi SlNPV pada berat badan dan kerusakan
membran peritrofik larva Spodoptera litura Fab. telah dilakukan. Metode yang digunakan adalah analisis probit, dan berdasarkan LD 50
virus yang terinfeksi untuk mengetahui berat badan dan kerusakan pasca infeksi. Kerusakan struktur histologi yang disebabkan oleh
infeksi SlNPV (0, 315, 390, 465, 540 dan 615 PIB/mL) diamati setelah 0, 12, 24, 72 dan 96 jam pasca infeksi. Preparasi histologis
dibuat dengan metode parafin setelah fiksasi dengan larutan Bouin, kemudian diiris setebal 7 um dan diwarnai dengan Hematoxilin-
Eosin. Hasil penelitian menunjukkan bahwa paparan SlNPV menyebabkan penurunan konsumsi pangan terutama pada 540 PIB/mL
dengan rata-rata 0.1675 mg. Pengamatan deskriptif pada struktur histologi membran peritrophic yang terkena infeksi SlNPV
menunjukkan kecenderungan kerusakan, sementara pada kontrol tidak ada kerusakan sama sekali. Semakin lama paparan virion di
dalam lumen midgut maka semakin tinggi terjadinya kerusakan membran peritrofik. Kerusakan paling parah terjadi 96 jam setelah
infeksi. Hasilnya membuktikan bahwa virion haNPV dapat menghancurkan struktur histologi midgut.
Kata kunci: SlNPV, Spodoptera litura, LD50, tingkat konsumsi, membran peritrophic
"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.
The Exception That Proves the Rule: How Sodium Chelation Can Alter the Charge-Cell Binding Correlation of Fluorescein-Based Multimodal Imaging Agents
No full textIn the present study we describe and explain an aberrant behavior in terms of receptor binding profile of a fluorescein-based multimodal imaging agent for gastrin releasing peptide receptor (GRPR) visualization by elucidating a chelating mechanism on sodium ions of its fluorescent dye moiety. This hypothesis is supported by both biological results and spectroscopic analyses of different fluorescein-carrying conjugates and an equally charged set of analogous tartrazine-based GRPR-binding imaging agents. Fluorescein interacts with sodium which reduces the overall negative charge of the dye molecule by one. This reduction in apparent total net charge explains the exceptional behavior found for the fluorescein-based multimodal bioconjugate in the context of the charge-cell binding correlation hypothesis
The Missing Link in the Monogermanide Series: YbGe
No full textHigh-pressure, high-temperature synthesis at 12 GPa between 750 and 1000 °C for 30 to 300 min yields the last missing rare-earth metal monogermanide, YbGe. Powder and single-crystal X-ray diffraction measurements reveal that the compound crystallizes in a FeB-type structure (space group Pnma, a=7.901(2) Å, b=3.8981(9) Å, and c=5.873(2) Å). The results of the chemical bonding study, while supporting the presence of polyanionic Ge chains interacting with the surrounding Yb through multi-atomic polar bonds, suggest a transitional scenario between the monogermanides formed by alkaline-earth elements and those formed by trivalent rare-earth metals
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
- …
