20,143 research outputs found
Simulated single molecule microscopy with SMeagol
SMeagol is a software tool to simulate highly realistic microscopy data based
on spatial systems biology models, in order to facilitate development,
validation, and optimization of advanced analysis methods for live cell single
molecule microscopy data. Availability and Implementation: SMeagol runs on
Matlab R2014 and later, and uses compiled binaries in C for reaction-diffusion
simulations. Documentation, source code, and binaries for recent versions of
Mac OS, Windows, and Ubuntu Linux can be downloaded from
http://smeagol.sourceforge.net.Comment: v2: 14 pages including supplementary text. Pre-copyedited,
author-produced version of an application note published in Bioinformatics
following peer review. The version of record, and additional supplementary
material is available online at:
https://academic.oup.com/bioinformatics/article-lookup/doi/10.1093/bioinformatics/btw10
Turbulent Velocity Structure in Molecular Clouds
We compare velocity structure in the Polaris Flare molecular cloud at scales
ranging from 0.015 pc to 20 pc to simulations of supersonic hydrodynamic and
MHD turbulence computed with the ZEUS MHD code. We use several different
statistical methods to compare models and observations. The Delta-variance
wavelet transform is most sensitive to characteristic scales and scaling laws,
but is limited by a lack of intensity weighting. The scanning-beam
size-linewidth relation is more robust with respect to noisy data. Obtaining
the global velocity scaling behaviour requires that large-scale trends in the
maps not be removed but treated as part of the turbulent cascade. We compare
the true velocity PDF in our models to velocity centroids and average line
profiles in optically thin lines, and find that the line profiles reflect the
true PDF better unless the map size is comparable to the total line-of-sight
thickness of the cloud. Comparison of line profiles to velocity centroid PDFs
can thus be used to measure the line-of-sight depth of a cloud. The observed
density and velocity structure is consistent with supersonic turbulence with a
driving scale at or above the size of the molecular cloud and dissipative
processes below 0.05 pc. Ambipolar diffusion could explain the dissipation. The
velocity PDFs exclude small-scale driving such as that from stellar outflows as
a dominant process in the observed region. In the models, large-scale driving
is the only process that produces deviations from a Gaussian PDF shape
consistent with observations. Strong magnetic fields impose a clear anisotropy
on the velocity field, reducing the velocity variance in directions
perpendicular to the field. (abridged)Comment: 21 pages, 24 figures, accepted by A&A, with some modifications,
including change of claimed direct detection of dissipation scale to an upper
limi
Interactions among intermediate redshift galaxies. The case of SDSSJ134420.86+663717.8
We present the properties of the central supermassive black holes and the
host galaxies of the interacting object SDSSJ134420.86+663717.8. We obtained
optical long slit spectroscopy data from the Large Binocular Telescope (LBT)
using the Multi Object Double Spectrograph (MODS). Analysing the spectra
revealed several strong broad and narrow emission lines of ionised gas in the
nuclear region of one galaxy, whereas only narrow emission lines were visible
for the second galaxy. The optical spectra were used to plot diagnostic
diagrams, deduce rotation curves of the two galaxies, and calculate the masses
of the central supermassive black holes. We find that the galaxy with broad
emission line features has Seyfert~1 properties, while the galaxy with only
narrow emission line features seems to be star-forming in nature. Furthermore,
we find that the masses of the central supermassive black holes are almost
equal at a few times 10^7 solar mass. Additionally, we present a simple N-body
simulation to shed some light on the initial conditions of the progenitor
galaxies. We find that for an almost orthogonal approach of the two interacting
galaxies, the model resembles the optical image of the system
AMI-LA Observations of the SuperCLASS Super-cluster
We present a deep survey of the SuperCLASS super-cluster - a region of sky
known to contain five Abell clusters at redshift - performed using
the Arcminute Microkelvin Imager (AMI) Large Array (LA) at 15.5GHz. Our
survey covers an area of approximately 0.9 square degrees. We achieve a nominal
sensitivity of Jy beam toward the field centre, finding 80
sources above a threshold. We derive the radio colour-colour
distribution for sources common to three surveys that cover the field and
identify three sources with strongly curved spectra - a high-frequency-peaked
source and two GHz-peaked-spectrum sources. The differential source count (i)
agrees well with previous deep radio source count, (ii) exhibits no evidence of
an emerging population of star-forming galaxies, down to a limit of 0.24mJy,
and (iii) disagrees with some models of the 15GHz source population.
However, our source count is in agreement with recent work that provides an
analytical correction to the source count from the SKADS Simulated Sky,
supporting the suggestion that this discrepancy is caused by an abundance of
flat-spectrum galaxy cores as-yet not included in source population models.Comment: 17 pages, 14 figures, 3 tables. Accepted for publication in MNRA
Measuring Ages and Elemental Abundances from Unresolved Stellar Populations: Fe, Mg, C, N, and Ca
We present a method for determining mean light-weighted ages and abundances
of Fe, Mg, C, N, and Ca, from medium resolution spectroscopy of unresolved
stellar populations. The method, pioneered by Schiavon (2007), is implemented
in a publicly available code called EZ_Ages. The method and error estimation
are described, and the results tested for accuracy and consistency, by
application to integrated spectra of well-known Galactic globular and open
clusters. Ages and abundances from integrated light analysis agree with studies
of resolved stars to within +/-0.1 dex for most clusters, and to within +/-0.2
dex for nearly all cases. The results are robust to the choice of Lick indices
used in the fitting to within +/-0.1 dex, except for a few systematic
deviations which are clearly categorized. The realism of our error estimates is
checked through comparison with detailed Monte Carlo simulations. Finally, we
apply EZ_Ages to the sample of galaxies presented in Thomas et al. (2005) and
compare our derived values of age, [Fe/H], and [alpha/Fe] to their analysis. We
find that [alpha/Fe] is very consistent between the two analyses, that ages are
consistent for old (Age > 10 Gyr) populations, but show modest systematic
differences at younger ages, and that [Fe/H] is fairly consistent, with small
systematic differences related to the age systematics. Overall, EZ_Ages
provides accurate estimates of fundamental parameters from medium resolution
spectra of unresolved stellar populations in the old and intermediate-age
regime, for the first time allowing quantitative estimates of the abundances of
C, N, and Ca in these unresolved systems. The EZ_Ages code can be downloaded at
http://www.ucolick.org/~graves/EZ_Ages.htmlComment: Accepted to ApJ
Design of ultraprecision machine tools with application to manufacturing of miniature and micro components
Currently the underlying necessities for predictability, producibility and productivity remain big issues in ultraprecision machining of miniature/microproducts. The demand on rapid and economic fabrication of miniature/microproducts with complex shapes has also made new challenges for ultraprecision machine tool design. In this paper the design for an ultraprecision machine tool is introduced by describing its key machine elements and machine tool design procedures. The focus is on the review and assessment of the state-of-the-art ultraprecision machining tools. It also illustrates the application promise of miniature/microproducts. The trends on machine tool development, tooling, workpiece material and machining processes are pointed out
Expansion and Collapse in the Cosmic Web
We study the kinematics of the gaseous cosmic web at high redshift with Lyman
alpha forest absorption in multiple QSO sightlines. Using a simple analytic
model and a cosmological hydrodynamic simulation we constrain the underlying
three-dimensional distribution of velocities from the observed line-of-sight
distribution of velocity shear across the plane of the sky. The distribution is
found to be in good agreement with the intergalactic medium (IGM) undergoing
large scale motions dominated by the Hubble flow. Modeling the Lyman alpha
clouds analytically and with a hydrodynamics simulation, the average expansion
velocity of the gaseous structures causing the Lyman alpha forest in the lower
redshift (z = 2) sample appears about 20 percent lower than the local Hubble
expansion velocity. We interpret this as tentative evidence for some clouds
undergoing gravitational collapse. However, the distribution of velocities is
highly skewed, and the majority of clouds at redshifts from 2 to 3.8 expand
typically about 5 - 20 percent faster than the Hubble flow. This behavior is
explained if most absorbers in the column density range typically detectable
are expanding filaments that stretch and drain into more massive nodes. We find
no evidence for the observed distribution of velocity shear being significantly
influenced by processes other than Hubble expansion and gravitational
instability, like galactic winds. To avoid overly disturbing the IGM, winds may
be old and/or limp by the time we observe them in the Lyman alpha forest, or
they may occupy only an insignificant volume fraction of the IGM. (abridged)Comment: 63 pages, 26 figures, AAS Latex; ApJ, in pres
Atomic-scale confinement of optical fields
In the presence of matter there is no fundamental limit preventing
confinement of visible light even down to atomic scales. Achieving such
confinement and the corresponding intensity enhancement inevitably requires
simultaneous control over atomic-scale details of material structures and over
the optical modes that such structures support. By means of self-assembly we
have obtained side-by-side aligned gold nanorod dimers with robust
atomically-defined gaps reaching below 0.5 nm. The existence of
atomically-confined light fields in these gaps is demonstrated by observing
extreme Coulomb splitting of corresponding symmetric and anti-symmetric dimer
eigenmodes of more than 800 meV in white-light scattering experiments. Our
results open new perspectives for atomically-resolved spectroscopic imaging,
deeply nonlinear optics, ultra-sensing, cavity optomechanics as well as for the
realization of novel quantum-optical devices
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