Localization of actin in Dictyostelium amebas by immunofluorescence

Antibody prepared against avian smooth muscle actin has been used to localize actin in the slime mold, Dictyostelium discoideum. The distribution of actin in migrating cells is different from that in feeding cells. Migrating amebas display fluorescence primarily in advancing regions whereas feeding amebas show uniform fluorescence throughout. The reaction is specific for actin since the fluorescence observed is blocked when the antibody is absorbed by actin purified from avian skeletal muscle, human platelets, and Dictyostelium. These results, in addition to describing the distribution of actin in D. discoideum, demonstrate that actins from these diverse sources share at least one common antigenic determinant

Understanding the relationship between design margins and trade-offs

To achieve an objective designers often need to make trade-offs between multiple parameters. In incremental design or during the design process an additional objective is often to minimise the changes they need to make to meet the objective. This is in particular an issue for systems with product platforms, over individual components are over-designed. This paper argues that designers can think about this problem in terms of the margins on the objective parameters as well as the parameters that are traded-off. This is illustrated with the case study of an engineering cooling system

Determination of Caries Lesion Activity: Reflection and Roughness for Characterization of Caries Progression

Used by permission. © Operative Dentistry, Inc. Transmission or reproduction of protected items beyond that allowed by fair use requires the written permission of Operative Dentistry, Inc.Caries lesion progression is difficult to determine with visual and tactile examinations. The hypothesis of this study was that reflection and roughness measurements could determine caries progression. Ground/polished sound human enamel specimens were analyzed at baseline (sound) and after two four-day demineralization periods for reflection using optical reflectometry (ORef) and for roughness using optical surface profilometry (SPro). Specimens were demineralized using a microbial–Streptococcus mutans aries model. Comparisons among the periods for ORef and SPro were performed using repeated measures analysis of variance. Two-sample t-tests were used for differences in transverse microradiography. The integrated mineral loss and depth of the four-day demineralization period were significantly smaller than those for the eight-day demineralization period (p<0.01). With increased demineralization time, reflection was significantly decreased and roughness was significantly increased (p<0.01). Correlation between ORef and SPro was moderate (r=−0.63). Both reflection and roughness can be characterized for nondestructive longitudinal assessment of caries lesion progression

Strategic, tactical decisions and information in Rapid Manufacturing supply chain

The efficiency and agility of its supply chain is vital to the commercial success of any product. Sharing strategic and tactical information effectively within the supply chain is often a key factor in achieving this goal. This paper proposes a framework to identify strategic, tactical decisions and information. The framework is used to conduct a sector based analysis of the Rapid Manufacturing (RM) industry. The decisions and information identified include amongst others various supply chain strategies and technical information

Properties of gas clumps and gas clumping factor in the intra cluster medium

The spatial distribution of gas matter inside galaxy clusters is not completely smooth, but may host gas clumps associated with substructures. These overdense gas substructures are generally a source of unresolved bias of X-ray observations towards high density gas, but their bright luminosity peaks may be resolved sources within the ICM, that deep X-ray exposures may be (already) capable to detect. In this paper we aim at investigating both features, using a set of high-resolution cosmological simulations with ENZO. First, we monitor how the bias by unresolved gas clumping may yield incorrect estimates of global cluster parameters and affects the measurements of baryon fractions by X-ray observations. We find that based on X-ray observations of narrow radial strips, it is difficult to recover the real baryon fraction to better than 10 - 20 percent uncertainty. Second, we investigated the possibility of observing bright X-ray clumps in the nearby Universe (z<=0.3). We produced simple mock X-ray observations for several instruments (XMM, Suzaku and ROSAT) and extracted the statistics of potentially detectable bright clumps. Some of the brightest clumps predicted by simulations may already have been already detected in X- ray images with a large field of view. However, their small projected size makes it difficult to prove their existence based on X-ray morphology only. Preheating, AGN feedback and cosmic rays are found to have little impact on the statistical properties of gas clumps.Comment: 17 pages, 11 figures. MNRAS accepte

Back and forth from cool core to non-cool core: clues from radio-halos

X-ray astronomers often divide galaxy clusters into two classes: "cool core" (CC) and "non-cool core" (NCC) objects. The origin of this dichotomy has been the subject of debate in recent years, between "evolutionary" models (where clusters can evolve from CC to NCC, mainly through mergers) and "primordial" models (where the state of the cluster is fixed "ab initio" by early mergers or pre-heating). We found that in a well-defined sample (clusters in the GMRT Radio halo survey with available Chandra or XMM-Newton data), none of the objects hosting a giant radio halo can be classified as a cool core. This result suggests that the main mechanisms which can start a large scale synchrotron emission (most likely mergers) are the same that can destroy CC and therefore strongly supports "evolutionary" models of the CC-NCC dichotomy. Moreover combining the number of objects in the CC and NCC state with the number of objects with and without a radio-halo, we estimated that the time scale over which a NCC cluster relaxes to the CC state, should be larger than the typical life-time of radio-halos and likely shorter than about 3 Gyr. This suggests that NCC transform into CC more rapidly than predicted from the cooling time, which is about 10 Gyr in NCC systems, allowing the possibility of a cyclical evolution between the CC and NCC states.Comment: Accepted for publication in A&

Gas clumping in galaxy clusters

The reconstruction of galaxy cluster's gas density profiles is usually performed by assuming spherical symmetry and averaging the observed X-ray emission in circular annuli. In the case of a very inhomogeneous and asymmetric gas distribution, this method has been shown to return biased results in numerical simulations because of the $n^2$ dependence of the X-ray emissivity. We propose a method to recover the true density profiles in the presence of inhomogeneities, based on the derivation of the azimuthal median of the surface brightness in concentric annuli. We demonstrate the performance of this method with numerical simulations, and apply it to a sample of 31 galaxy clusters in the redshift range 0.04-0.2 observed with ROSAT/PSPC. The clumping factors recovered by comparing the mean and the median are mild and show a slight trend of increasing bias with radius. For $R<R_{500}$, we measure a clumping factor $\sqrt{C}<1.1$, which indicates that the thermodynamic properties and hydrostatic masses measured in this radial range are only mildly affected by this effect. Comparing our results with three sets of hydrodynamical numerical simulations, we found that non-radiative simulations significantly overestimate the level of inhomogeneities in the ICM, while the runs including cooling, star formation, and AGN feedback reproduce the observed trends closely. Our results indicate that most of the accretion of X-ray emitting gas is taking place in the diffuse, large-scale accretion patterns rather than in compact structures.Comment: 12 pages, 11 figures, accepted for publication in MNRAS. Largely-improved version compared to v1, method and comparison with simulations update

On the connection between turbulent motions and particle acceleration in galaxy clusters

Giant radio halos are Mpc-scale diffuse radio sources associated with the central regions of galaxy clusters. The most promising scenario to explain the origin of these sources is that of turbulent re-acceleration, in which MeV electrons injected throughout the formation history of galaxy clusters are accelerated to higher energies by turbulent motions mostly induced by cluster mergers. In this Letter, we use the amplitude of density fluctuations in the intracluster medium as a proxy for the turbulent velocity and apply this technique to a sample of 51 clusters with available radio data. Our results indicate a segregation in the turbulent velocity of radio halo and radio quiet clusters, with the turbulent velocity of the former being on average higher by about a factor of two. The velocity dispersion recovered with this technique correlates with the measured radio power through the relation $P_{\rm radio}\propto\sigma_v^{3.3\pm0.7}$, which implies that the radio power is nearly proportional to the turbulent energy rate. Our results provide an observational confirmation of a key prediction of the turbulent re-acceleration model and possibly shed light on the origin of radio halos.Comment: Submitted to ApJ Letter