6,108 research outputs found
Hiding the complexity: building a distributed ATLAS Tier-2 with a single resource interface using ARC middleware
Since their inception, Grids for high energy physics have found management of data to be the most challenging aspect of operations. This problem has generally been tackled by the experiment's data management framework controlling in fine detail the distribution of data around the grid and the careful brokering of jobs to sites with co-located data. This approach, however, presents experiments with a difficult and complex system to manage as well as introducing a rigidity into the framework which is very far from the original conception of the grid.<p></p>
In this paper we describe how the ScotGrid distributed Tier-2, which has sites in Glasgow, Edinburgh and Durham, was presented to ATLAS as a single, unified resource using the ARC middleware stack. In this model the ScotGrid 'data store' is hosted at Glasgow and presented as a single ATLAS storage resource. As jobs are taken from the ATLAS PanDA framework, they are dispatched to the computing cluster with the fastest response time. An ARC compute element at each site then asynchronously stages the data from the data store into a local cache hosted at each site. The job is then launched in the batch system and accesses data locally.<p></p>
We discuss the merits of this system compared to other operational models and consider, from the point of view of the resource providers (sites), and from the resource consumers (experiments); and consider issues involved in transitions to this model
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Electrospray synthesis of PLGA TIPS microspheres
We successfully demonstrate the synthesis of polymer microspheres using a single electrospray source, and show their physical characterisation. Electrospray has proven to be a versatile method to manufacture particles, giving tight control over size with quasi-monodisperse size distributions. It is a liquid atomisation technique that generates a monodisperse population of highly charged liquid droplets over a broad size range (nanometres to tens of microns). The droplets contain liquid precursors for the in-flight synthesis of particles, and control over the trajectory of these droplets can be precisely manipulated with the use of electric fields to drive them to a grounded substrate. This study reports a method to synthesize poly(lactic-co-glycolic) acid (PLGA) microspheres using the electrospray and thermally induced phase separation (TIPS) techniques, followed by subsequent freeze-drying, for particle production. These microspheres are of interest as vehicles for controlled drug release systems
A New Gravitational Wave Verification Source
We report the discovery of a detached 20 min orbital period binary white
dwarf. WD0931+444 (SDSS J093506.93+441106.9) was previously classified as a WD
+ M dwarf system based on its optical spectrum. Our time-resolved optical
spectroscopy observations obtained at the 8m Gemini and 6.5m MMT reveal
peak-to-peak radial velocity variations of 400 km/s every 20 min for the WD,
but no velocity variations for the M dwarf. In addition, high-speed photometry
from the McDonald 2.1m telescope shows no evidence of variability nor evidence
of a reflection effect. An M dwarf companion is physically too large to fit
into a 20 min orbit. Thus, the orbital motion of the WD is almost certainly due
to an invisible WD companion. The M dwarf must be either an unrelated
background object or the tertiary component of a hiearchical triple system.
WD0931+444 contains a pair of WDs, a 0.32 Msol primary and a >0.14 Msol
secondary, at a separation of >0.19 Rsol. After J0651+2844, WD0931+444 becomes
the second-shortest period detached binary WD currently known. The two WDs will
lose angular momentum through gravitational wave radiation and merge in <9 Myr.
The log h ~ -22 gravitational wave strain from WD0931+444 is strong enough to
make it a verification source for gravitational wave missions in the
milli-Hertz frequency range, e.g. the evolved Laser Interferometer Space
Antenna (eLISA), bringing the total number of known eLISA verification sources
to nine.Comment: MNRAS Letters, in pres
Combined ultraviolet studies of astronomical sources
Topics addressed include: Cygnus Loop; P Cygni profiles in dwarf novae; YY Gem; nova shells; HZ Herculis; activity cycles in cluster giants; Alpha Ori; metal deficient giant stars; ultraviolet spectra of symbiotic stars detected by the Very Large Array; time variability in symbiotic stars; blue galaxies; and quasistellar objects with X-ray spectra
A note on dimer models and McKay quivers
We give one formulation of an algorithm of Hanany and Vegh which takes a
lattice polygon as an input and produces a set of isoradial dimer models. We
study the case of lattice triangles in detail and discuss the relation with
coamoebas following Feng, He, Kennaway and Vafa.Comment: 25 pages, 35 figures. v3:completely rewritte
Discrete complex analysis on planar quad-graphs
We develop a linear theory of discrete complex analysis on general
quad-graphs, continuing and extending previous work of Duffin, Mercat, Kenyon,
Chelkak and Smirnov on discrete complex analysis on rhombic quad-graphs. Our
approach based on the medial graph yields more instructive proofs of discrete
analogs of several classical theorems and even new results. We provide discrete
counterparts of fundamental concepts in complex analysis such as holomorphic
functions, derivatives, the Laplacian, and exterior calculus. Also, we discuss
discrete versions of important basic theorems such as Green's identities and
Cauchy's integral formulae. For the first time, we discretize Green's first
identity and Cauchy's integral formula for the derivative of a holomorphic
function. In this paper, we focus on planar quad-graphs, but we would like to
mention that many notions and theorems can be adapted to discrete Riemann
surfaces in a straightforward way.
In the case of planar parallelogram-graphs with bounded interior angles and
bounded ratio of side lengths, we construct a discrete Green's function and
discrete Cauchy's kernels with asymptotics comparable to the smooth case.
Further restricting to the integer lattice of a two-dimensional skew coordinate
system yields appropriate discrete Cauchy's integral formulae for higher order
derivatives.Comment: 49 pages, 8 figure
Quivers, Tilings, Branes and Rhombi
We describe a simple algorithm that computes the recently discovered brane
tilings for a given generic toric singular Calabi-Yau threefold. This therefore
gives AdS/CFT dual quiver gauge theories for D3-branes probing the given
non-compact manifold. The algorithm solves a longstanding problem by computing
superpotentials for these theories directly from the toric diagram of the
singularity. We study the parameter space of a-maximization; this study is made
possible by identifying the R-charges of bifundamental fields as angles in the
brane tiling. We also study Seiberg duality from a new perspective.Comment: 36 pages, 40 figures, JHEP
The Size Distribution of Kuiper Belt Objects
We describe analytical and numerical collisional evolution calculations for
the size distribution of icy bodies in the Kuiper Belt. For a wide range of
bulk properties, initial masses, and orbital parameters, our results yield
power-law cumulative size distributions, N_C propto r^{-q}, with q_L = 3.5 for
large bodies with radii of 10-100 km, and q_s = 2.5-3 for small bodies with
radii lesss than 0.1-1 km. The transition between the two power laws occurs at
a break radius of 1-30 km. The break radius is more sensitive to the initial
mass in the Kuiper Belt and the amount of stirring by Neptune than the bulk
properties of individual Kuiper Belt objects (KBOs). Comparisons with
observations indicate that most models can explain the observed sky surface
density of KBOs for red magnitudes, R = 22-27. For R 28, the model
surface density is sensitive to the amount of stirring by Neptune, suggesting
that the size distribution of icy planets in the outer solar system provides
independent constraints on the formation of Neptune.Comment: 24 pages of text, 12 figures; to appear in the Astronomical Journal,
October 200
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