1,721,119 research outputs found
Subdiffraction resolution microscopy methods for analyzing centrosomes organization
No full textIn this chapter, we describe the current methods of examining the structure of centrosomes by fluorescence subdiffraction microscopy. By using recently developed microscopy techniques, centrosomal proteins can now be examined in cells with a resolution of only a few nanometers, a level of molecular detail beyond the reach of traditional cell biology methods as confocal and widefield microscopy. We emphasize imaging by three-dimensional structured illumination microscopy, stochastic optical reconstruction microscopy, and quantitative approaches to image data analysis. </p
Dehydrogenation study of cosmic-dust analogue grains
No full textNew infrared and optical-absorption measurements performed on hydrogenated amorphous-carbon grains are presented. In particular, the spectral modifications produced by dehydrogenation of the samples are analysed. We interpret the observed variations in terms of an increasing dimension of the graphitic clusters disordely arranged to form carbon grains. The results support the hypothesis that the behaviour of the interstellar extinction in the ultraviolet can be attributed to dehydrogenated amorphous-carbon grains. © 1993 Società Italiana di Fisica
Simulation of the cometary 10 Î1⁄4m band by laboratory data. II. Extension to spectra available for different comets
No full textRecent observations have shown that the presence of emission bands at 9.8 and 11.3 Î1⁄4m is a characteristic of many comets. Although their attribution to silicates is commonly accepted, a wide debate is open to identify the actual species responsible for the two bands. In a previous paper (Colangeli et al. 1995a) we fitted emission spectra from comets P/Halley 1986 III and Levy 1990 XX in the 10 Î1⁄4m band region by using spectroscopic data obtained in our laboratory on various silicate samples. In the present work we extend the simulation to available cometary spectra showing similar bands. We show that combinations of pyroxene-type and olivine-type submicron grains produce satisfactory fits. Despite the limited number of observational data available in the literature, our results evidence that spectral variations can be interpreted in terms of intrinsic and/or evolutionary differences among the comets
Interstellar extinction: a parametrical study by using laboratory data
No full textIn this paper we present a comparative study between laboratory data, astronomical observations and theoretical models in order to provide a contribution to the characterization of cosmic-dust properties. In particular, we propose a parametrization of the amorphous-carbon extinction curve. The laboratory extinction measurements, performed in the extreme ultraviolet spectral region, are compared to the UV interstellar extinction curves provided by the IUE satellite. The aim of our work was to define a model that could describe both observational and laboratory data. To this purpose we referred to the model developed by Fitzpatrick and Massa. The second step of the study was the determination of extinction coefficients, for two different size distributions of amorphous-carbon grains, by means of the optical constants, n and k, derived by Rouleau and Martin. © 1993 Società Italiana di Fisica
Amorphous no more: subdiffraction view of the pericentriolar material architecture
Full text linkThe centrosome influences the shape, orientation and activity of the microtubule cytoskeleton. The pericentriolar material (PCM), determines this functionality by providing a dynamic platform for nucleating microtubules and acts as a nexus for molecular signaling. Although great strides have been made in understanding PCM activity, its diffraction-limited size and amorphous appearance on electron microscopy (EM) have limited analysis of its high-order organization. Here, we outline current knowledge of PCM architecture and assembly, emphasizing recent super-resolution imaging studies that revealed the PCM has a layered structure made of fibers and matrices conserved from flies to humans. Notably, these studies debunk the long-standing view of an amorphous PCM and provide a paradigm to dissect the supramolecular organization of organelles in cells. </p
KLP10A and KLP59C: the dynamic duo of microtubule depolymerization
No full textKinesin-13s are important effectors of microtubule depolymerization in cells. In a recent series of studies, we examined the roles played by kinesin-13s throughout the cell cycle in Drosophila. Our findings have revealed remarkable coordination between two family members, KLP10A and KLP59C, in which alterations in the relative targeting of these proteins allows them to participate in markedly different tasks at distinct points in the cell cycle. During mitosis, KLP10A and KLP59C function in parallel by targeting to and depolymerizing the opposite ends of kinetochore-associated microtubules, thereby driving poleward chromatid motility by a Pacman-Flux mechanism. Alternatively, during interphase, both proteins target to the same end of the microtubule but act in series to divide the labor of microtubule depolymerization. KLP10A initiates depolymerization while KLP59C perpetuates depolymerization after its initiation. Below, we detail these findings and examine some of their implications.</p
Simulation of the dust flux on the ROSETTA probe during the orbiting phase around comet 46P/Wirtanen
Full text linkWe present a probabilistic model of the dust mass, flux and fluence which will be collected by the ROSETTA probe while orbiting around comet 46P/Wirtanen. The dust environment of the target comet is simulated according to the most recent data available in the literature. Best fits of the DIDSY-GIOTTO data collected during the fly-by of comet 1P/Halley have shown that the probabilistic properties of dust ejection from the inner coma are crucial (Fulle et al. 1995). Therefore, we pay particular attention to the dust ejection velocity, which is assumed to have a wide distribution around the most probable values, and the dust ejection distribution, which is assumed to have a strong anisotropy peaked towards the sun. To compute the impact velocity in the probe reference frame, the rigorous keplerian orbit of each grain is considered taking into account aberrations due to the probe orbital velocity. We analyse the dependence of the results on the probe orbit parameters, such as true anomaly, probe-nucleus distance, orbit node and inclination. Computations are performed for the six main directions of the probe reference frame and for different values of the acceptance angle. The only way to collect direct grains is to point towards the nucleus; the mass collected in this direction is almost independent of the acceptance angle and of the time evolution of dust loss rate. A strong dependence of the collected dust mass on node and inclination is evidenced. By assuming an acceptance angle of 40°, the flux of reflected grains received in the two directions perpendicular to the probe orbit is higher than that in the nucleus direction, for 42% of randomly oriented probe orbits. The value increases up to 56% when the acceptance angle in the directions perpendicular to the probe orbit is increased up to 80°. The dust ejection anisotropy produces a strong dependence of the fluxes on the probe anomaly. For reflected grains, the fluences show relevant depletions at the largest masses, due to dust orbital effects, and the collected masses strongly depend on the acceptance angle and on the time evolution of the dust loss rate. The total dust fluxes are evaluated by assuming a half sphere field of view (corresponding to an acceptance angle of 180°)
Interstellar-dust properties as deduced from FIR and millimetric observations
No full textWe have considered some millimetric observations of our Galaxy and of the Large Magellanic Cloud (LMC) taken at the Italian Base in Antarctica. Using other submm data and fitting all the observations with a modified Planck curve, we have obtained useful information about the temperaure T and the spectral index α of the dust grains both for the Galaxy and the LMC. For the galactic spectrum two different couples of T and α match the detected fluxes:a)T=7K, α=2;b)T=15K, α=1.1. We have tried to identify the nature of the dust grains responsible for the submm and mm emission by comparing these results with the spectral trend of some cosmic analogues studied in laboratory. © 1993 Società Italiana di Fisica
Super-resolution microscopy: from single molecules to supramolecular assemblies
No full textSuper-resolution microscopy (SRM) methods have allowed scientists to exceed the diffraction limit of light, enabling the discovery and investigation of cellular structures at the nanometer scale, from individual proteins to entire organelles. In this review we survey the application of SRM in elucidating the structure of macromolecules in the native cellular environment. We emphasize how SRM can generate molecular maps of protein complexes and extract quantitative information on the number, size, distribution, and spatial organization of macromolecules. We discuss both the novel information that can be generated through SRM as well as the experimental considerations to examine while conducting such studies. With the increasing popularity of SRM in the biological sciences, this review will serve as a tool to navigate the range of applications and harness the power of SRM to elucidate biological structures.</p
Extinction signatures of amorphous carbon grains from the vacuum UV to the far-IR
Full text linkAmong the various components of cosmic dust, amorphous carbon grains play a relevant role. Together with other carbon-based materials. they have been invoked to interpret a number of spectral features observed in the interstellar and circumstellar environments. In order to validate, on a more quantitative basis, the reliability of such hypotheses. it is necessary to analyse in detail the optical properties of "analogue" grains produced in the laboratory. In the present paper, we report, for the first time, a complete spectral analysis of the extinction properties measured on various kinds of amorphous carbon grains, from the vacuum UV to the far-IR. These data can be complemented with other experimental results obtained on the same samples by means of different analytical techniques. This approach allows us to propose a self-consistent interpretation about the actual physico-chemical properties of our cosmic dust analogues. The resulting scenario provides a powerful tool to interpret astronomical observations concerning cosmic dust. © 1995
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