2,544 research outputs found
DNA conformational dynamics in the presence of catanionic mixtures
DNA conformational behavior in the presence of non-stoichiometric mixtures of two oppositely charged surfactants, cetyltrimethylammonium bromide and sodium octyl sulfate, was directly visualized in an aqueous solution with the use of a fluorescence microscopy technique. It was found that in the presence of cationic-rich catanionic mixtures, DNA molecules exhibit a conformational transition from elongated coil to compact globule states. Moreover, if the catanionic mixtures form positively charged vesicles, DNA is adsorbed onto the surface of the vesicles in a collapsed globular form. When anionic-rich catanionic mixtures are present in the solution, no change in the DNA conformational behavior was detected. Cryogenic transmission electron microscopy, as well as measurements of translational diffusion coefficients of individual DNA chains, supported our optical microscopy observations.http://www.sciencedirect.com/science/article/B6T36-3WRB313-V/1/07d45ede3443f93c49fe5d72c57fdfa
Radial Temperature Profiles of X-Ray--Emitting Gas Within Clusters of Galaxies
Previous analyses of ASCA data of clusters of galaxies have found conflicting
results regarding the slope of the temperature profile of the hot X-ray gas
within clusters, mainly because of the large, energy-dependent point spread
function (PSF) of the ASCA mirrors. We present a summary of all ASCA-determined
cluster temperature profiles found in the literature, and find a discrepancy in
the radial temperature trend of clusters based on which PSF-correction routine
is used. This uncertainty in the cluster temperature profile in turn can lead
to large uncertainties in the amount of dark matter in clusters. In this study,
we have used ROSAT PSPC data to obtain independent relative temperature
profiles for 26 clusters, most of which have had their temperature profiles
determined by ASCA. Our aim is not to measure the actual temperature values of
the clusters, but to use X-ray color profiles to search for a hardening or
softening of the spectra with radius for comparison to ASCA-derived profiles.
The radial color profiles indicate that outside of the cooling flow region, the
temperature profiles of clusters are in general constant. Within 35% of the
virial radius, we find a temperature drop of 20% at 10 keV and 12% at 5 keV can
be ruled out at the 99% confidence level. A subsample of non-cooling flow
clusters shows that the condition of isothermality applies at very small radii
too, although cooling gas complicates this determination in the cooling flow
subsample. The colors predicted from the temperature profiles of a series of
hydrodynamical cluster simulations match the data very well, although they
cannot be used to discriminate among different cosmologies. An additional
result is that the color profiles show evidence for a central peak in
metallicity in low temperature clusters.Comment: 39 pages, 15 embedded Postscript figures, uses aaspp4.sty, accepted
for publication in Astrophysical Journa
Automated face recognition using deep neural networks produces robust primate social networks and sociality measures
Longitudinal video archives of behaviour are crucial for examining how sociality shifts over the lifespan in wild animals. New approaches adopting computer vision technology hold serious potential to capture interactions and associations between individuals in video at large scale; however, such approaches need a priori validation, as methods of sampling and defining edges for social networks can substantially impact results.Here, we apply a deep learning face recognition model to generate association networks of wild chimpanzees using 17 years of a video archive from Bossou, Guinea. Using 7 million detections from 100 h of video footage, we examined how varying the size of fixed temporal windows (i.e. aggregation rates) for defining edges impact individual-level gregariousness scores.The highest and lowest aggregation rates produced divergent values, indicating that different rates of aggregation capture different association patterns. To avoid any potential bias from false positives and negatives from automated detection, an intermediate aggregation rate should be used to reduce error across multiple variables. Individual-level network-derived traits were highly repeatable, indicating strong inter-individual variation in association patterns across years and highlighting the reliability of the method to capture consistent individual-level patterns of sociality over time. We found no reliable effects of age and sex on social behaviour and despite a significant drop in population size over the study period, individual estimates of gregariousness remained stable over time.We believe that our automated framework will be of broad utility to ethology and conservation, enabling the investigation of animal social behaviour from video footage at large scale, low cost and high reproducibility. We explore the implications of our findings for understanding variation in sociality patterns in wild ape populations. Furthermore, we examine the trade-offs involved in using face recognition technology to generate social networks and sociality measures. Finally, we outline the steps for the broader deployment of this technology for analysis of large-scale datasets in ecology and evolution.info:eu-repo/semantics/publishedVersio
Step-Wise Computational Synthesis of Fullerene C60 derivatives. 1.Fluorinated Fullerenes C60F2k
The reactions of fullerene C60 with atomic fluorine have been studied by
unrestricted broken spin-symmetry Hartree-Fock (UBS HF) approach implemented in
semiempirical codes based on AM1 technique. The calculations were focused on a
sequential addition of fluorine atom to the fullerene cage following indication
of the cage atom highest chemical susceptibility that is calculated at each
step. The effectively-non-paired-electron concept of the fullerene atoms
chemical susceptibility lays the foundation of the suggested computational
synthesis. The obtained results are analyzed from energetic, symmetry, and the
composition abundance viewpoints. A good fitting of the data to experimental
findings proves a creative role of the suggested synthesis methodology.Comment: 33 pages, 11 figures, 2 tables, 2 chart
First GIS analysis of modern stone tools used by wild chimpanzees (Pan troglodytes verus) in Bossou, Guinea, West Africa
Stone tool use by wild chimpanzees of West Africa offers a unique opportunity to explore the evolutionary roots of technology during human evolution. However, detailed analyses of chimpanzee stone artifacts are still lacking, thus precluding a comparison with the earliest archaeological record. This paper presents the first systematic study of stone tools used by wild chimpanzees to crack open nuts in Bossou (Guinea-Conakry), and applies pioneering analytical techniques to such artifacts. Automatic morphometric GIS classification enabled to create maps of use wear over the stone tools (anvils, hammers, and hammers/anvils), which were blind tested with GIS spatial analysis of damage patterns identified visually. Our analysis shows that chimpanzee stone tool use wear can be systematized and specific damage patterns discerned, allowing to discriminate between active and passive pounders in lithic assemblages. In summary, our results demonstrate the heuristic potential of combined suites of GIS techniques for the analysis of battered artifacts, and have enabled creating a referential framework of analysis in which wild chimpanzee battered tools can for the first time be directly compared to the early archaeological record.Leverhulme Trust [IN-052]; MEXT [20002001, 24000001]; JSPS-U04-PWS; FCT-Portugal [SFRH/BD/36169/2007]; Wenner-Gren Foundation for Anthropological Researc
Spiral-like structure in nearby clusters of galaxies
X-ray data analysis have found that fairly complex structures at cluster
centres are more common than expected. Many of these structures have similar
morphologies, which exhibit spiral-like substructure. It is not yet well known
how these structures formed or are maintained. Understanding the origin of
these spiral-like features at the centre of some clusters is the major
motivation behind this work. We analyse deep \textit{Chandra} observations of
15 nearby galaxy clusters (0.01 0.06), and use X-ray temperature and
substructure maps to detect small features at the cores of the clusters. We
detect spiral-like features at the centre of 7 clusters: A85, A426, A496, Hydra
A cluster, Centaurus, Ophiuchus, and A4059. These patterns are similar to those
found in numerical hydrodynamic simulations of cluster mergers with non-zero
impact parameter. In some clusters of our sample, a strong radio source also
occupies the inner region of the cluster, which indicates a possible connection
between the two. Our investigation implies that these spiral-like structures
may be caused by off-axis minor mergers. Since these features occur in regions
of high density, they may confine radio emission from the central galaxy
producing, in some cases, unusual radio morphology.Comment: 14 pages, 3 figures, accepted for publication in A&A (Nov 17, 2009
CANGAROO-III Observation of TeV Gamma Rays from the vicinity of PSR B1 706-44
Observation by the CANGAROO-III stereoscopic system of the Imaging Cherenkov
Telescope has detected extended emission of TeV gamma rays in the vicinity of
the pulsar PSR B170644. The strength of the signal observed as
gamma-ray-like events varies when we apply different ways of emulating
background events. The reason for such uncertainties is argued in relevance to
gamma-rays embedded in the "off-source data", that is, unknown sources and
diffuse emission in the Galactic plane, namely, the existence of a complex
structure of TeV gamma-ray emission around PSR B170644.Comment: 10 pages, 13 figures, to be published in Ap
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