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Dynamic Character (dynamic + character)
Selected AbstractsReconciling differences in trophic control in mid-latitude marine ecosystemsECOLOGY LETTERS, Issue 10 2006Kenneth T. Frank Abstract The dependence of long-term fishery yields on primary productivity, largely based on cross-system comparisons and without reference to the potential dynamic character of this relationship, has long been considered strong evidence for bottom-up control in marine systems. We examined time series of intensive empirical observations from nine heavily exploited regions in the western North Atlantic and find evidence of spatial variance of trophic control. Top-down control dominated in northern areas, the dynamics evolved from bottom-up to top-down in an intermediate region, and bottom-up control governed the southern areas. A simplified, trophic control diagram was developed accounting for top-down and bottom-up forcing within a larger region whose base state dynamics are bottom-up and can accommodate time-varying dynamics. Species diversity and ocean temperature co-varied, being relatively high in southern areas and lower in the north, mirroring the shifting pattern of trophic control. A combination of compensatory population dynamics and accelerated demographic rates in southern areas seems to account for the greater stability of the predator species complex in this region. [source] The transient nature of maximum maleic anhydride grafting of polypropylene: A mechanistic approach based on a consecutive reaction model.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Abstract This article compares the batch solution and molten state chemical modification of an atactic polypropylene to yield a grafted polypropylene. Short reaction times appear to be sufficient and indeed necessary for the highest graft yields to be obtained if degradative processes occurring in both reaction media are to be avoided. The consecutive reactions for the optimized grafting reaction pathway were proposed for the solution process in an earlier article. The present work attempts to correlate this pathway with that of the molten state process. Grafted succinic anhydride groups react with two resorcine molecules to yield grafted succinyl-fluorescein groups. This work considers the resorcine units as true molecular probes, to be able to stabilize and activate the complexes formed between the succinic anhydride groups and the propylene sequence. This work shows the unsteady and later dynamic character of the process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 345,351, 2007 [source] Mobility, Violence and the Gendering of HIV in Papua New GuineaTHE AUSTRALIAN JOURNAL OF ANTHROPOLOGY, Issue 2 2008Katherine Lepani The links between gender, sexuality and violence hold serious implications for HIV transmission and its social and economic effects. In Papua New Guinea, enduring and pervasive patterns of male sexual behaviour involving coercion, violence and gang rape are highly conducive to the transmission of HIV and other sexually transmitted infections and have a critical bearing on women's sexual autonomy and health. The realities of violence are intensified by the widespread view that women are responsible for the spread of the virus. This paper engages the theme of mobility to consider the fluid and dynamic character of gender relations and sexuality in contemporary Papua New Guinea, and to gain perspective on constructions of modern masculinity and the discursive representations of gender violence in the context of the escalating HIV epidemic. [source] Structural changes of hexamethylenetetramine and undecanedioic acid co-crystal (HMT-C11) as a function of the temperatureACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2003Carlos Basílio Pinheiro HMT-C11 belongs to the family of adducts formed by the co-crystallization of N4(CH2)6 molecules (hexamethylenetetramine or HMT) and aliphatic dicarboxylic acids HOOC(CH2)n, 2COOH with 5 ,n, 13 (Cn). The adducts exhibit a layered structure in which the packing between HMT and Cn is determined by strong hydrogen bonds. The compounds in this family studied so far present thermotropic structural phase transitions and, depending on the chain length, disordered, twinned and modulated phases. The structure refinement of HMT-C11 based on X-ray diffraction experiments indicates three distinct phases from the melting point down to liquid nitrogen temperature: phase I is not crystalline; phase II is disordered (stacking fault) and its average structure is described in space group Bmmb; phase III is partially disordered and its symmetry is P21/c. The systematic study of the structure evolution of phase III upon cooling revealed that the disorder has a dynamic character (anharmonicity). The main structural change observed from 293,K down to 93,K is the increase of the tilting angle of the C11 chains relative to the layer plane and the rotation of the HMT molecules. Both HMT and C11 behave like rigid bodies in the temperature range investigated. The quality of the refinements leads to a conclusive model for the O,H,N hydrogen bonds linking HMT and C11. [source] The early history of 32P as a radioactive tracer in biochemical research: A personal memoirBIOCHEMISTRY AND MOLECULAR BIOLOGY EDUCATION, Issue 3 2005Howard Gest The concept of using radioactive isotopes as "tracers" of chemical conversions was conceived and developed by inorganic chemist Georg de Hevesy (Nobel Laureate in Chemistry 1943). In 1935, he began to apply the technique to various biological processes using 32P, and his experiments revealed the dynamic character of physiology and metabolism. Following de Hevesy's lead, Samuel Ruben (University of California, Berkeley) exploited 32P in 1937,38 for investigation of phospholipid metabolism. Between 1937 and 1940, Ruben and colleague Martin Kamen spearheaded tracer studies in various biological systems using 32P, short-lived 11C, and other radioactive isotopes. During this period, Kamen was responsible for cyclotron-produced radioactive tracers and was able to sustain de Hevesy's research by supplying him with 32P. In 1940, Ruben and Kamen discovered long-lived 14C, which later proved to be a very powerful tool for analysis of complex biochemical processes, such as the path of carbon in photosynthesis. Between 1946 and 1950, 32P was used in studies of bacteriophage replication and photosynthetic metabolism. This memoir surveys the history of these early investigations. [source] Scanning beyond the limits of standard OCT: OCT scans of the peripheral retina and the anterior chamber angle with a slitlamp integtrated FD-OCT systemACTA OPHTHALMOLOGICA, Issue 2009M STEHOUWER Purpose Exploring the quality of OCT images of the peripheral retina and anterior chamber angle made through a 3-mirror contactlens and a new FD-OCT device integrated into a slit lamp. Methods Patients with peripheral lesions (n=10) and glaucoma (n=10), seen in the outpatient clinic of the Academic Medical Center, were scanned with a Fourier Domain OCT integrated into a common Topcon slitlamp (SLD light source, central wavelength 830 nm, bandwidth 30 nm, 1024 pixel CCD camera, scan speed 5k A-scans per second, up to 1024 A-scans per b-scan). For posterior segment scans a fast Z-tracking system in the reference arm compensates for the dynamic character (movements of patient, handheld lens, slitlamp) of the examination. Scans of peripheral lesions, and the anterior chamber angle were made with a 3-mirror lens, while simultaneously the lesions were observed with the slitlamp. Results Scans of the peripheral retina obtained with a 3-mirror lens with the FD-OCT integrated into the slitlamp were of reasonably good quality and lesions, like peripheral laser scars, could be clearly identified. Compared to stand alone OCT systems, the integrated OCT system reached more peripheral lesions. The anterior chamber angle scanned through a 3-mirror lens enabled scans of the angle structures. Conclusion It is possible to scan the peripheral retina and anterior chamber angle through a 3-mirror contact lens with the slitlamp with integrated OCT. These scans could be of clinical interest in patients with pathology in the peripheral retina pathology or the anterior chamber angle. [source] Direct Assignment of Enantiofacial Discrimination on Single Heterocyclic Substrates by Self-induced CDCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2005Carsten Siering Abstract The first direct assignment of highly dynamic enantiofacial discrimination acting on a single heterocyclic substrate has been achieved by a combination of experimental and theoretical CD spectroscopy. The interaction of chirally modified hosts based on triphenylene ketals with appropriate prochiral guests can lead to the preferential formation of one diastereomeric host,guest complex. This reversible stereoselective binding transmits the chiral information from remote chiral groups in the host to the strongly absorbing triphenylene chromophore, which gives rise to self-induced CD. This effect was exploited for the determination of the enantiofacial recognition in various host,guest systems. Inversion of the steric demand either of the chiral substituents at the host or of the prochiral guest leads to almost complete inversion of the resulting CD spectra. For the assignment of the absolute stereochemistry of the complexes, a combined molecular dynamics/quantum-chemical approach was successfully employed. Despite the size and the highly dynamic character of the supramolecular systems, fundamental properties of the systems and details of the spectra were simulated accurately, providing access to fast and reliable assignment of the enantiofacial preference. The results are highly consistent with available X-ray data. [source] | ||||||||||