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In many swimming and flying animals, propulsion emerges from the interplay of active muscle contraction, passive body elasticity and fluid–body interaction. Changes in the active and passive body properties can influence performance and cost of transport across a broad range of scales; they specifically affect the vortex generation that is crucial for effective swimming at higher Reynolds numbers. Theoretical models that account for both active contraction and passive elasticity are needed to understand how animals tune both their active and passive properties to move efficiently through fluids. This is particularly significant when one considers the phylogenetic constraints on the jellyfish mechanospace, such as the presence of relatively weak muscles that are only one cell layer thick. In this work, we develop an actively deforming model of a jellyfish immersed in a viscous fluid and use numerical simulations to study the role of active muscle contraction, passive body elasticity and fluid forces in the medusan mechanospace. By varying the strength of contraction and the flexibility of the bell margin, we quantify how these active and passive properties affect swimming speed and cost of transport. We find that for fixed bell elasticity, swimming speed increases with the strength of contraction. For fixed force of contractility, swimming speed increases as margin elasticity decreases. Varying the strength of activation in proportion to the elasticity of the bell margin yields similar swimming speeds, with a cost of transport is substantially reduced for more flexible margins. A scaling study reveals that performance declines as the Reynolds number decreases. Circulation analysis of the starting and stopping vortex rings showed that their strengths were dependent on the relative strength of activation with respect to the bell margin flexibility. This work yields a computational framework for developing a quantitative understanding of the roles of active and passive body properties in swimming.
Preliminary results are reported from an OH mainline absorption study of the galactic centre. The molecular clouds form a well-defined structure 2 kpc in projected diameter, which is warped in its outer regions. The distribution of molecular clouds is highly organised. There are places where the line-widths are anomalously high. The possible nature of these broad-line clouds is briefly discussed.
Since the last General Assembly in Patras, Greece, we have held three meetings of the Working Group. The 10th Meeting was held in Mzkheta, the ancient capital of Georgia, USSR, hosted by their Academy of Sciences on April 3-7, 1984. All members except one, who was represented by a member of his Task Group, were present at the very productive meeting.
Four working groups and three task groups of IAU Commission 5 deal specifically with information handling, technical aspects of collection, archiving, storage and dissemination of data, with designations and classification of astronomical objects, with library services, editorial policies, computer communications, ad hoc methodologies, and with various standards, reference frames etc. Information about Commission 5 working and task groups and their activities may be found in http://nut.inasan.rssi.ru/IAU/.
It is with great sadness that we have to report the death on 24 August 1990 of the WG’s President, Harold Masursky, at the age of 66. Dr. Masursky is known for his many contributions in planetary science and for his many years of dedicated work in planetary nomenclature. During the interim until the next IAU General Assembly the IAU Executive Committee has appointed K. Aksnes as Acting President of the WG.
A multi-faceted, multi-institutional laboratory astrophysics program is carried out at the Livermore electron beam ion trap facility, which is a mature spectroscopic source with unsurpassed controls and capabilities, and an unparalleled assortment of spectroscopic equipment, including a full complement of grating and crystal spectrometers and a 6x6 micro-calorimeter array. Recent results range from the calibration of x-ray diagnostics, including the Fe XVII and Fe XXV emission lines, extensive lists of L-shell ions, the first laboratory simulation and fit of a cometary x-ray emission spectrum, and the discovery of new spectral diagnostics for measuring magnetic field strengths.
Toxoplasma gondii is a globally distributed parasite infecting humans and warm-blooded animals. Although many surveys have been conducted for T. gondii infection in mammals, little is known about the detailed distribution in localized natural populations. In this study, host genotype and spatial location were investigated in relation to T. gondii infection. Wood mice (Apodemus sylvaticus) were collected from 4 sampling sites within a localized peri-aquatic woodland ecosystem. Mice were genotyped using standard A. sylvaticus microsatellite markers and T. gondii was detected using 4 specific PCR-based markers: SAG1, SAG2, SAG3 and GRA6 directly from infected tissue. Of 126 wood mice collected, 44 samples were positive giving an infection rate of 34·92% (95% CI: 27·14–43·59%). Juvenile, young adults and adults were infected at a similar prevalence, respectively, 7/17 (41·18%), 27/65 (41·54%) and 10/44 (22·72%) with no significant age-prevalence effect (P = 0·23). Results of genetic analysis of the mice showed that the collection consists of 4 genetically distinct populations. There was a significant difference in T. gondii prevalence in the different genotypically derived mouse populations (P = 0·035) but not between geographically defined populations (P = 0·29). These data point to either a host genetic/family influence on parasite infection or to parasite vertical transmission.
We report on a preliminary analysis of a 5600 sec per point survey of 32 square degrees in Centaurus, carried out with the Parkes 13-beam system. The signal-to-noise ratio is found to improve as for the whole integration. We have detected 102 HI sources between +250 and +12,700 km s−1 either by eye or by using the new galaxy-finding algorithm PICASSO. Over half of these are new HI detections. Around a dozen of these are not associated with catalogued galaxies and, in two of these cases, we have not identified an optical counterpart on the Digitized Sky Survey. Arguments are put forward to explain why deep integrations are needed to find low surface brightness objects.
Notocotylus malhamensis n. sp. is described from the caecum of the bank vole (Myodes glareolus) and the field vole (Microtus agrestis) from Malham Tarn Nature Reserve in North Yorkshire, UK. In total, 581 specimens were collected from rodents trapped at a wetland site (Tarn Fen) between July 2010 and October 2011 with a prevalence of 66·7% and mean intensity of 94·6 in the bank vole and 50% prevalence and a mean intensity of 4·3 in the field vole. This species appears to be most closely related to other previously described Notocotylus species infecting rodents in Europe but differs principally by the metraterm to cirrus sac ratio (1:1·5–1:1·2) in combination with a densely spinulated cirrus, simple caeca and a greater number of ventral glands in the lateral rows (14–17). The use of molecular differentiation was of limited use in this study due to a paucity of relevant information in the DNA sequence databases. However, the complete ITS1-5.8S rDNA-ITS2 and partial 28S gene sequences have been generated to provide a definitive tool for identification of this species in future studies. As far as we know this is the first report of a notocotylid infection in M. glareolus in the UK.
The objective of this research was to assess current patterns of hospital antibiotic prescribing in Northern Ireland and to determine targets for improving the quality of antibiotic prescribing. A point prevalence survey was conducted in four acute teaching hospitals. The most commonly used antibiotics were combinations of penicillins including β-lactamase inhibitors (33·6%), metronidazole (9·1%), and macrolides (8·1%). The indication for treatment was recorded in 84·3% of the prescribing episodes. A small fraction (3·9%) of the surgical prophylactic antibiotic prescriptions was for >24 h. The results showed that overall 52·4% of the prescribed antibiotics were in compliance with the hospital antibiotic guidelines. The findings identified the following indicators as targets for quality improvement: indication recorded in patient notes, the duration of surgical prophylaxis and compliance with hospital antibiotic guidelines. The results strongly suggest that antibiotic use could be improved by taking steps to address the identified targets for quality improvement.
The protozoan parasite Toxoplasma gondii is prevalent worldwide and can infect a remarkably wide range of hosts despite felids being the only definitive host. As cats play a major role in transmission to secondary mammalian hosts, the interaction between cats and these hosts should be a major factor determining final prevalence in the secondary host. This study investigates the prevalence of T. gondii in a natural population of Apodemus sylvaticus collected from an area with low cat density (<2·5 cats/km2). A surprisingly high prevalence of 40·78% (95% CI: 34·07%–47·79%) was observed despite this. A comparable level of prevalence was observed in a previously published study using the same approaches where a prevalence of 59% (95% CI: 50·13%–67·87%) was observed in a natural population of Mus domesticus from an area with high cat density (>500 cats/km2). Detection of infected foetuses from pregnant dams in both populations suggests that congenital transmission may enable persistence of infection in the absence of cats. The prevalences of the related parasite, Neospora caninum were found to be low in both populations (A. sylvaticus: 3·39% (95% CI: 0·12%–6·66%); M. domesticus: 3·08% (95% CI: 0·11%–6·05%)). These results suggest that cat density may have a lower than expected effect on final prevalence in these ecosystems.
Proton NMR and proton-29Si double resonance NMR have been performed on hot wire a-Si:H films deposited from SiH4. Results are compared with those from conventional plasma enhanced chemical vapor deposition a-Si:H. Proton nutational angle studies and proton-29Si spin-echo double resonance (SEDOR) signals at 80 and 294 K indicate that a significant proton resonance population arises from T-site-trapped molecular H2. The hot wire films also display a ≥80 kHz FWHM uperbroad proton line and a sharp feature diamagnetically shifted by 25 ppm.
Four series of samples, prepared at 250° C by decomposition of a mixture of silane and argon in a radio frequency powered deposition systems (rf-PECVD), have been studied. The dilution rates were 1 %, 1.5 %, 5 % and 10 % of silane in argon and the total pressure was 0.5 Torr for the first series and 0.2 Torr for the others. Structural and transport properties of the materials have been studied as function of power density. Structural studies show the transition from purely amorphous material towards microcrystalline material with increasing rf power density. The transport parameters were measured in the as-deposited, light-soaked and annealed states and compared to those obtained on state of the art material. The best material obtained is clearly device grade material. This study shows that argon dilution allows to tailor the material for a given application.
For many years it has been assumed widely that hydrogen is involved in some way in the formation of light induced defects. However recently some doubt has been cast on this because of experimental evidence that there is little H near light induced dangling bonds. In this paper we present a number of model calculations comparing ESR spectra of dangling bonds with and without correlations with H positions. The above models include different distributions of H and correlations or anti correlations of nearby H. In all cases the spectra are compared to those with no correlations or clustering. Our results coupled with published experimental data strongly suggest that dangling bonds are not correlated positively with the presence of nearby H and, in fact, it appears that light induced dangling bonds are negatively correlated with nearby H.
We find that hydrogen diffuses as H+, H0, or H- in hydrogenated amorphous silicon depending on its location within the i-layer of a p-i-n device. We annealed a set of five p-i-n devices, each with a thin deuterium-doped layer at a different location in the i-layer, and observed the D-diffusion using secondary ionmass spectrometry (SIMS). When H-diffuses in a charged state, electric fields in the device strongly influence the direction and distance of diffusion. When D is incorporated into a device near the p-layer, almost all of the D-diffusion occurs as D+, and when the D is incorporated near the n-layer, most of the D-diffusion occurs as D-. We correlate the preferential direction of D-motion at given depth within the i-layer, with the local Fermi level (as calculated by solar cell simulations), to empirically determine an effective correlation energy for mobile-H electronic transitions of 0.39 ± 0.1 eV. Using this procedure, the best fit to the data produces a disorder broadening of the transition levels of ∼0.25 eV. The midpoint between the H0/+ and the H0/- transition levels is ∼0.20 ± 0.05 eV above midgap.