4,891 research outputs found
Synthesis of non-linear protein dimers through a genetically encoded thiol-ene reaction
Site-specific incorporation of bioorthogonal unnatural amino acids into proteins provides a useful tool for the installation of specific functionalities that will allow for the labeling of proteins with virtually any probe. We demonstrate the genetic encoding of a set of alkene lysines using the orthogonal PylRS/PylTCUA pair in Escherichia coli. The installed double bond functionality was then applied in a photoinitiated thiol-ene reaction of the protein with a fluorescent thiol-bearing probe, as well as a cysteine residue of a second protein, showing the applicability of this approach in the formation of heterogeneous non-linear fused proteins. © 2014 Torres-Kolbus et al
On the Mass of Dense Star Clusters in Starburst Galaxies from Spectro-Photometry
The mass of unresolved young star clusters derived from spectro-photometric
data may well be off by a factor of 2 or more once the migration of massive
stars driven by mass segregation is accounted for. We quantify this effect for
a large set of cluster parameters, including variations in the stellar IMF, the
intrinsic cluster mass, and mean mass density. Gas-dynamical models coupled
with the Cambridge stellar evolution tracks allow us to derive a scheme to
recover the real cluster mass given measured half-light radius, one-dimensional
velocity dispersion and age. We monitor the evolution with time of the ratio of
real to apparent mass through the parameter eta. When we compute eta for rich
star clusters, we find non-monotonic evolution in time when the IMF stretches
beyond a critical cutoff mass of 25.5 solar mass. We also monitor the rise of
color gradients between the inner and outer volume of clusters: we find trends
in time of the stellar IMF power indices overlapping well with those derived
for the LMC cluster NGC 1818 at an age of 30 Myr. We argue that the core region
of massive Antennae clusters should have suffered from much segregation despite
their low ages. We apply these results to a cluster mass function, and find
that the peak of the mass distribution would appear to observers shifted to
lower masses by as much as 0.2 dex. The star formation rate (SFR) derived for
the cluster population is then underestimated by from 20 to 50 per cent.Comment: 20 pages, 16 figures, accepted for publication in MNRA
Modest-2: A Summary
This is a summary paper of MODEST-2, a workshop held at the Astronomical
Institute ``Anton Pannekoek'' in Amsterdam, 16-17 December 2002. MODEST is a
loose collaboration of people interested in MOdelling DEnse STellar systems,
particularly those interested in modelling these systems using all the
available physics (stellar dynamics, stellar evolution, hydrodynamics and the
interplay between the three) by defining interfaces between different codes. In
this paper, we summarize 1) the main advances in this endeavour since MODEST-1;
2) the main science goals which can be and should be addressed by these types
of simulations; and 3) the most pressing theoretical and modelling advances
that we identified.Comment: Accepted by New Astronom
Measurement of the Fermi Constant by FAST
An initial measurement of the lifetime of the positive muon to a precision of
16 parts per million (ppm) has been performed with the FAST detector at the
Paul Scherrer Institute. The result is tau_mu = 2.197083 (32) (15) microsec,
where the first error is statistical and the second is systematic. The muon
lifetime determines the Fermi constant, G_F = 1.166353 (9) x 10^-5 GeV^-2 (8
ppm).Comment: 15 pages, 6 figure
The M/L ratio of massive young clusters
We point out a strong time-evolution of the mass-to-light conversion factor
\eta commonly used to estimate masses of dense star clusters from observed
cluster radii and stellar velocity dispersions. We use a gas-dynamical model
coupled with the Cambridge stellar evolution tracks to compute line-of-sight
velocity dispersions and half-light radii weighted by the luminosity. Stars at
birth are assumed to follow the Salpeter mass function in the range [0.15--17
M_\sun]. We find that , and hence the estimated cluster mass, increases
by factors as large as 3 over time-scales of 20 million years. Increasing the
upper mass limit to 50 M_\sun leads to a sharp rise of similar amplitude but
in as little as 10 million years.
Fitting truncated isothermal (Michie-King) models to the projected light
profile leads to over-estimates of the concentration par ameter c of compared to the same functional fit applied to the proj ected
mass density.Comment: Draft version of an ApJ lette
Dynamical Processes in Globular Clusters
Globular clusters are among the most congested stellar systems in the
Universe. Internal dynamical evolution drives them toward states of high
central density, while simultaneously concentrating the most massive stars and
binary systems in their cores. As a result, these clusters are expected to be
sites of frequent close encounters and physical collisions between stars and
binaries, making them efficient factories for the production of interesting and
observable astrophysical exotica. I describe some elements of the competition
among stellar dynamics, stellar evolution, and other processes that control
globular cluster dynamics, with particular emphasis on pathways that may lead
to the formation of blue stragglers.Comment: Chapter 10, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
A rule driven approach for developing adaptive service oriented business collaboration
Current composite web service development and management solutions, e.g. BPEL, do not cater for flexible and adaptive business collaborations due to their pre-defined and inflexible nature that precludes them accommodating business dynamics. In this paper we propose a rule driven approach for adaptive business collaboration development in which rules drive and govern the development process. We introduce the Business Collaboration Development Framework (BCDF), which provides enterprizes with the context to define their capabilities and business collaboration agreements. Subsequently, we explain how rules can drive and control the business collaboration development process to develop complete, correct and consistent business collaboration agreements that are conform the conditions under which parties wish to cooperate.12 page(s
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