Cargo navigation across 3D microtubule intersections Bergman, Jared P.; Bovyn, Matthew J.; Doval, Florence F. ...
Proceedings of the National Academy of Sciences - PNAS,
01/2018, Letnik:
115, Številka:
3
Journal Article
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The eukaryotic cell’s microtubule cytoskeleton is a complex 3D filament network. Microtubules cross at a wide variety of separation distances and angles. Prior studies in vivo and in vitro suggest ...that cargo transport is affected by intersection geometry. However, geometric complexity is not yet widely appreciated as a regulatory factor in its own right, and mechanisms that underlie this mode of regulation are not well understood. We have used our recently reported 3D microtubule manipulation system to build filament crossings de novo in a purified in vitro environment and used them to assay kinesin-1–driven model cargo navigation. We found that 3D microtubule network geometry indeed significantly influences cargo routing, and in particular that it is possible to bias a cargo to pass or switch just by changing either filament spacing or angle. Furthermore, we captured our experimental results in a model which accounts for full 3D geometry, stochastic motion of the cargo and associated motors, as well as motor force production and force-dependent behavior. We used a combination of experimental and theoretical analysis to establish the detailed mechanisms underlying cargo navigation at microtubule crossings.
Metallicity of M dwarfs Neves, V; Bonfils, X; Santos, N C ...
Astronomy and astrophysics (Berlin),
03/2013, Letnik:
551
Journal Article
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Aims. The aim of this work is the study of the planet-metallicity and the planet-stellar mass correlations for M dwarfs from the HARPS GTO M dwarf subsample. Methods. We use a new method that takes ...advantage of the HARPS high-resolution spectra to increase the precision of metallicity, using previous photometric calibrations of Fe/H and effective temperature as starting values. Results. In this work we use our new calibration (rms = 0.08 dex) to study the planet-metallicity relation of our sample. The wellknown correlation for giant planet FGKM hosts with metallicity is present. Regarding Neptunians and smaller hosts no correlation is found but there is a hint that an anti-correlation with Fe/H may exist. We combined our sample with the California Planet Survey late-K and M-type dwarf sample to increase our statistics but found no new trends. We fitted a power law to the frequency histogram of the Jovian hosts for our sample and for the combined sample, f sub(p)= C10 super( alpha Fe/H), using two different approaches: a direct bin fitting and a Bayesian fitting procedure. We obtained a value for C between 0.02 and 0.04 and for alpha between 1.26 and 2.94. Regarding stellar mass, an hypothetical correlation with planets was discovered, but was found to be the result of a detection bias.
Metal-polluted white dwarfs (DZ stars) are characterized by a helium-rich atmosphere contaminated by heavy elements traces originating from accreted rocky planetesimals. As a detailed spectroscopic ...analysis of those objects can reveal the composition of the accreted debris, there is a great interest in developing accurate DZ atmosphere models. However, the coolest DZ white dwarfs are challenging to model due to the fluidlike density of their atmospheres. Under such extreme conditions, spectral absorption lines are heavily broadened by interactions with neutral helium, and it is no longer justified to use the conventional Lorentzian profiles. In this work, we determine the theoretical profiles of the Ca i resonance line (the most prominent spectral line for the coolest DZ white dwarfs) in the dense atmospheres of cool DZ white dwarfs. To do so, we use a unified theory of collisional line profiles and accurate ab initio potential energies and transition dipole moments for the CaHe molecule. We present the resulting profiles for the full range of temperatures and helium densities relevant for the modeling of cool, metal-polluted white dwarfs (from 3000 to 6000 K and from 1021 to 1023 cm−3). We also implement these new profiles in our atmosphere models and show that they lead to improved fits to the Ca i resonance line of the coolest DZ white dwarfs.
Context. In June 2010, we confirmed the existence of a giant planet in the disk of the young star βPictoris located between 8 AU and 15 AU from the star. This young planet offers the rare ...opportunity to monitor a large fraction of the orbit using the imaging technique over a reasonably short timescale. It also offers the opportunity to study its atmospheric properties using spectroscopy and multi-band photometry, and possibly derive its dynamical mass by combining imaging with radial velocity data to set tight constraints on giant planet formation theories. Aims. We aim to measure the evolution of the planet’s position relative to the star βPictoris to determine the planetary orbital properties. Our ultimate goal is to relate both the planetary orbital configuration and physical properties to either the disk structure or the cometary activity observed for decades in the βPictoris system. Methods. Using the NAOS-CONICA adaptive-optics instrument (NACO) at the Very Large Telescope (VLT), we obtained repeated follow-up images of the βPictoris system in the Ks and L′ filters at four new epochs in 2010 and 2011. Complementing these data with previous measurements, we conduct a homogeneous analysis, which covers more than eight yrs, to accurately monitor the βPictoris b position relative to the star. We then carefully consider the various sources of uncertainties that may affect the orbital parameter determination. Results. On the basis of the evolution of the planet’s relative position with time, we derive the best-fit orbital solutions for our measurements using two fitting methods, a least squares Levenberg-Marquardt algorithm and a Markov-chain Monte Carlo approach. More reliable results are found with the second approach as our measurements do not cover the complete planetary orbit, and are biased toward the most recent epochs since the planet recovery. The solutions favor a low-eccentricity orbit e ≲ 0.17, with semi-major axis in the range 8–9 AU corresponding to orbital periods of 17–21 yrs. Our solutions favor a highly inclined solution with a peak around i = 88.5 ± 1.7°, and a longitude of ascending node tightly constrained at Ω = −147.5 ± 1.5°. These results indicate that the orbital plane of the planet is likely to be above the midplane of the main disk, and compatible with the warp component of the disk being tilted between 3.5 deg and 4.0 deg. This suggests that the planet plays a key role in the origin of the inner warped-disk morphology of the β Pic disk. Finally, these orbital parameters are consistent with the hypothesis that the planet is responsible for the transit-like event observed in November 1981, and also linked to the cometary activity observed in the β Pic system.
VOSA: virtual observatory SED analyzer Bayo, A.; Rodrigo, C.; Barrado y Navascués, D. ...
Astronomy and astrophysics (Berlin),
12/2008, Letnik:
492, Številka:
1
Journal Article
Recenzirano
Context. The physical properties of almost any kind of astronomical object can be derived by fitting synthetic spectra or photometry extracted from theoretical models to observational data. Aims. We ...want to develop an automatic procedure to perform this kind of fitting to a relatively large sample of members of a stellar association and apply this methodology to the case of Collinder 69. Methods. We combine the multiwavelength data of our sources and follow a work-flow to derive the physical parameters of the sources. The key step of the work-flow is performed by a new VO-tool, VOSA. All the steps in this process are done in a VO environment. Results. We present this new tool, and provide physical parameters such as T_{eff}, gravity, luminosity, etc. for similar to 170 candidate members of Collinder 69, and an upper-limit for the age of this stellar association. Conclusions. This kind of study of star forming regions, clusters, etc. produces a huge amount of data, very tedious to analyse using the traditional methodology. Thus, they are excellent examples of where to apply the VO techniques.
The analysis of the far wings of resonance lines of alkali elements in brown dwarf spectra requires their accurate determination. A unified theory of collisional line profiles has been applied for ...the evaluation of absorption profiles of alkalis perturbed by helium and molecular hydrogen. The study of the dependence on temperature of the far wings of Li–He and Li–H2 collisional profiles is reported.
ABSTRACT
Mt Abu Faint Object Spectrograph and Camera (MFOSC-P) is an in-house-developed instrument for the Physical Research Laboratory (PRL) 1.2 m telescope at Mt Abu, India, commissioned in 2019 ...February. Here we present the first science results derived from the low-resolution spectroscopy programme of a sample of M dwarfs carried out during the commissioning run of MFOSC-P between 2019 February and June. M dwarfs carry great significance for exoplanet searches in the habitable zone and are among the promising candidates for the observatory’s several ongoing observational campaigns. Determination of their accurate atmospheric properties and fundamental parameters is essential to constrain both their atmospheric and evolutionary models. In this study, we provide a low-resolution (R ∼ 500) spectroscopic catalogue of 80 bright M dwarfs (J < 10) and classify them using their optical spectra. We have also performed spectral synthesis and χ2 minimization techniques to determine their fundamental parameters regarding effective temperature and surface gravity by comparing the observed spectra with the most recent BT-Settl synthetic spectra. The spectral type of M dwarfs in our sample ranges from M0 to M5. The derived effective temperature and surface gravity range from 4000–3000 K and 4.5–5.5 dex, respectively. In most of the cases, the derived spectral types are in good agreement with previously assigned photometric classifications.
Context: Since the discovery of its dusty disk in 1984, β Pictoris has become the prototype of young early-type planetary systems, and there are now various indications that a massive Jovian planet ...is orbiting the star at ~10 AU. However, no planets have been detected around this star so far. Aims: Our goal was to investigate the close environment of β Pic, searching for planetary companion(s). Methods: Deep adaptive-optics L'-band images of β Pic were recorded using the NaCo instrument at the Very Large Telescope. Results: A faint point-like signal is detected at a projected distance of ≃8 AU from the star, within the northeastern extension of the dust disk. Various tests were made to rule out possible instrumental or atmospheric artefacts at a good confidence level. The probability of a foreground or background contaminant is extremely low, based in addition on the analysis of previous deep HST images. Its L'=11.2 apparent magnitude would indicate a typical temperature of ~1500 K and a mass of ~8 M_Jup. If confirmed, it could explain the main morphological and dynamical peculiarities of the β Pic system. The present detection is unique among A-stars by the proximity of the resolved planet to its parent star. Its closeness and location inside the β Pic disk suggest a formation process by core accretion or disk instabilities rather than binary-like formation processes. Based on observations collected at the European Southern Observatory, Chile, ESO (runs 072.C-0624(B) and 60.A-9026(A)) and on observations made with the Space Telescope Imaging Spectrograph onboard the NASA/ESA Hubble Space Telescope.
Au/TiO2 catalysts used in the water−gas shift (WGS) reaction at 120 °C, 7% CO, 22% H2O, 9% CO2, and 37% H2 had rates up to 0.1 moles of CO converted per mole of Au per second. However, the rate per ...mole of Au depends strongly on the Au particle size. The use of a nonporous, model support allowed for imaging of the active catalyst and a precise determination of the gold size distribution using transmission electron microscopy (TEM) because all the gold is exposed on the surface. A physical model of Au/TiO2 is used to show that corner atoms with fewer than seven neighboring gold atoms are the dominant active sites. The number of corner sites does not vary as particle size increases above 1 nm, giving the surprising result that the rate per gold cluster is independent of size.
To investigate the efficacy of adding supplemental fusion or arthroplasty after cervical anterior discectomy for symptomatic mono-level cervical degenerative disease (radiculopathy), which has not ...been substantiated in controlled trials until now.
A randomized controlled trial is reported with 9 years follow up comparing anterior cervical anterior discectomy without fusion, with fusion by cage standalone, or with disc prosthesis. Patients suffering from symptomatic cervical disk degeneration at one level referred to spinal sections of department of neurosurgery or orthopedic surgery of a large general hospital with educational facilities were eligible. Neck Disability Index (NDI), McGill Pain Questionnaire Dutch language version (MPQ-DLV), physical-component summary (PCS), and mental-component summary (MCS) of the 36-item Short-Form Health Survey (SF-36), and re operation rate were evaluated.
142 patients between 18 and 55 years were allocated. The median follow-up was 8.9±1.9 years (5.6 to 12.2 years). The response rate at last follow-up was 98.5%. NDI at the last follow-up did not differ between the three treatment groups, nor did the secondary outcomes as MPQ-DLV and PCS or MCS from SF-36. The major improvement occurred within the first 6 weeks after surgery. Afterward, it remained stable. Eleven patients underwent surgery for recurrent symptoms and signs due to nerve root compression at the index or adjacent level.
This randomized trial could not detect a difference between three surgical modalities for treating a single-level degenerative disk disease. Anterior cervical discectomy without implant seems to be similar to anterior cervical discectomy with fusion by cage stand-alone or with disk prosthesis. Due to the small study sample size, this statement should be considered as inconclusive so far.
ISRCTN41681847.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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