55346862
The Sloan Digital Sky Survey Quasar Survey: Quasar Luminosity Function from Data Release 3
We determine the number counts and z = 0-5 luminosity function for a well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey (SDSS). We conservatively define the most uniform statistical sample possible, consisting of 15,343 quasars within an effective area of 1622 deg2 that was derived from a parent sample of 46,420 spectroscopically confirmed broad-line quasars in the 5282 deg2 of imaging data from SDSS Data Release 3. The sample extends from i = 15 to 19.1 at z 3 and to i = 20.2 for z 3. The number counts and luminosity function agree well with the results of the Two Degree Field QSO Redshift Survey (2QZ) at redshifts and luminosities at which the SDSS and 2QZ quasar samples overlap, but the SDSS data probe to much higher redshifts than does the 2QZ sample. The number density of luminous quasars peaks between redshifts 2 and 3, although uncertainties in the selection function in this range do not allow us to determine the peak redshift more precisely. Our best-fit model has a flatter bright-end slope at high redshift than at low redshift. For z < 2.4 the data are best fit by a redshift-independent slope of ? = -3.1 [?(L) ? L?]. Above z = 2.4 the slope flattens with redshift to ? -2.37 at z = 5. This slope change, which is significant at the 5 ? level, must be accounted for in models of the evolution of accretion onto supermassive black holes.
12139365
TeraScale SneakerNet: Using Inexpensive Disks for Backup, Archiving, and Data Exchange
Large datasets are most economically trnsmitted via parcel post given the current economics of wide-area networking. This article describes how the Sloan Digital Sky Survey ships terabyte scale datasets both within the US and to Europe and Asia. We 3GT storage bricks (Ghz processor, GB ram, GbpsEthernet, TB disk) for about 2k$ each. These bricks act as database servers on the LAN. They are loaded at one site and read at the second site. The paper describes the bricks, their economics, and some software issues that they raise.
2633090
Online scientific data curation, publication, and archiving
Science projects are data publishers. The scale and complexity of current and future science data changes the nature of the publication process. Publication is becoming a major project component. At a minimum, a project must preserve the ephemeral data it gathers. Derived data can be reconstructed from metadata, but metadata is ephemeral. Longer term, a project should expect some archive to preserve the data. We observe that published scientific data needs to be available forever -- this gives rise to the data pyramid of versions and to data inflation where the derived data volumes explode. As an example, this article describes the Sloan Digital Sky Survey (SDSS) strategies for data publication, data access, curation, and preservation.
3204824
Designing a multi-petabyte database for LSST
The 3.2 giga-pixel LSST camera will produce approximately half a petabyte of archive images every month. These data need to be reduced in under a minute to produce real-time transient alerts, and then added to the cumulative catalog for further analysis. The catalog is expected to grow about three hundred terabytes per year. The data volume, the real-time transient alerting requirements of the LSST, and its spatio-temporal aspects require innovative techniques to build an efficient data access system at reasonable cost. As currently envisioned, the system will rely on a database for catalogs and metadata. Several database systems are being evaluated to understand how they perform at these data rates, data volumes, and access patterns. This paper describes the LSST requirements, the challenges they impose, the data access philosophy, results to date from evaluating available database technologies against LSST requirements, and the proposed database architecture to meet the data challenges.
3264527
Designing and mining multi-terabyte astronomy archives: the Sloan Digital Sky Survey
The next-generation astronomy digital archives will cover most of the sky at fine resolution in many wavelengths, from X-rays, through ultraviolet, optical, and infrared. The archives will be stored at diverse geographical locations. One of the first of these projects, the Sloan Digital Sky Survey (SDSS) is creating a 5-wavelength catalog over 10,000 square degrees of the sky (see http://www.sdss.org/). The 200 million objects in the multi-terabyte database will have mostly numerical attributes in a 100+ dimensional space. Points in this space have highly correlated distributions.
The archive will enable astronomers to explore the data interactively. Data access will be aided by multidimensional spatial and attribute indices. The data will be partitioned in many ways. Small tag objects consisting of the most popular attributes will accelerate frequent searches. Splitting the data among multiple servers will allow parallel, scalable I/O and parallel data analysis. Hashing techniques will allow efficient clustering, and pair-wise comparison algorithms that should parallelize nicely. Randomly sampled subsets will allow de-bugging otherwise large queries at the desktop. Central servers will operate a data pump to support sweep searches touching most of the data. The anticipated queries will require special operators related to angular distances and complex similarity tests of object properties, like shapes, colors, velocity vectors, or temporal behaviors. These issues pose interesting data management challenges.
19318578
Extending the SDSS Batch Query System to the National Virtual Observatory Grid
The Sloan Digital Sky Survey science database is approaching 2TB. While the vast majority of queries normally execute in seconds or minutes, this interactive execution time can be disproportionately increased by a small fraction of queries that take hours or days to run; either because they require non-index scans of the largest tables or because they request very large result sets. In response to this, we added a multi-queue job submission and tracking system. The transfer of very large result sets from queries over the network is another serious problem. Statistics suggested that much of this data transfer is unnecessary; users would prefer to store results locally in order to allow further cross matching and filtering. To allow local analysis, we implemented a system that gives users their own personal database (MyDB) at the portal site. Users may transfer data to their MyDB, and then perform further analysis before extracting it to their own machine. 
We intend to extend the MyDB and asynchronous query ideas to multiple NVO nodes. This implies development, in a distributed manner, of several features, which have been demonstrated for a single node in the SDSS Batch Query System (CasJobs). The generalization of asynchronous queries necessitates some form of MyDB storage as well as workflow tracking services on each node and coordination strategies among nodes.
96427576
The Atiyah class and complex structure stabilization in heterotic Calabi-Yau compactifications
Holomorphic gauge fields in N = 1 supersymmetri cheterotic compactifications can constrain the complex structure moduli of a Calabi-Yau manifold. In this paper, the tools necessary to use holomorphic bundles as a mechanism for moduli stabilization are systematically developed. We review the requisite deformation theory — including the Atiyah class, which determines the deformations of the complex structure for which the gauge bundle becomes non-holomorphic and, hence, non-supersymmetric. In addition, two equivalent approaches to this mechanism of moduli stabilization are presented. The first isan efficient computational algorithm for determining the supersymmetric moduli space, while the second is an F-term potential in the four-dimensional theory associated with vector bundle holomorphy. These three methods are proven to be rigorously equivalent. We present explicit examples in which large numbers of complex structure moduli are stabilized. Finally, higher-order corrections to the moduli space are discussed.
119055256
An explicit example of a moduli driven phase transition in heterotic models
We present an explicit example of a gauge symmetry breaking phase transition in heterotic models, the dynamics of which are not thermal and can be described in a well controlled manner throughout. The phase transition is driven by the evolution of bundle moduli--moduli associated with gauge field vacuum expectation values in the hidden dimensions. We present the necessary parts of the four dimensional effective theory including moduli which describe the embedding of the gauge bundle within the gauge group. We then present exact cosmological solutions to the system before going on to use them to describe the phase transition. The explicit nature of our description enables us to plot how the gauge bosons associated with the symmetries which are broken in the transition gain masses with time. This is in contrast to the use, for example, of a brane collision as a modulus driven phase transition. In the course of this work we find a number of other interesting results. We observe that the Kaehler potential of the system is given by the logarithm of the volume of the compact space even when bundle moduli are included. We also note that the dynamics of the gauge bundle mean that smallmore » instanton transitions are classically forbidden for all but a set of measure zero of the initial conditions of the system. The paper is written in such a manner that the cosmological description of the phase transition can be read independently of the derivation of the four dimensional theory.« less
17764338
Yukawa Couplings in Heterotic Compactification
We present a practical, algebraic method for efficiently calculating the Yukawa couplings of a large class of heterotic compactifications on Calabi-Yau three-folds with non-standard embeddings. Our methodology covers all of, though is not restricted to, the recently classified positive monads over favourable complete intersection Calabi-Yau three-folds. Since the algorithm is based on manipulating polynomials it can be easily implemented on a computer. This makes the automated investigation of Yukawa couplings for large classes of smooth heterotic compactifications a viable possibility.
55531346
REDESIGN OF THE ISIS MAIN MAGNET POWER SUPPLY STORAGE CHOKE
The ISIS facility, based at the Rutherford Appleton Laboratory in the UK, provides intense pulsed neutron and muon beams for condensed matter studies. As part of the facilities upgrade and refurbishment program, the 1MJ storage choke which forms part of the main magnet power supply system, will be replaced with a number of smaller units. The present storage choke, which consists of a split secondary winding transformer, is incorporated into a series-parallel resonant circuit known as the 'White circuit' [1]. This circuit ensures that each magnet receives identical currents, but is not subjected to excessive voltages. Although the storage choke is essentially a transformer, its secondary magnetising inductance is relatively low and a precisely defined value. This paper discusses the design and development of ten smaller units which will eventually replace the present equipment, and the testing of a one fifth scale model, which will be used to prove the technology.
55416040
Algorithmic Algebraic Geometry and Flux Vacua
We develop a new and efficient method to systematically analyse four dimensional effective supergravities which descend from flux compactifications. The issue of finding vacua of such systems, both supersymmetric and non-supersymmetric, is mapped into a problem in computational algebraic geometry. Using recent developments in computer algebra, the problem can then be rapidly dealt with in a completely algorithmic fashion. Two main results are (1) a procedure for calculating constraints which the flux parameters must satisfy in these models if any given type of vacuum is to exist; (2) a stepwise process for finding all of the isolated vacua of such systems and their physical properties. We illustrate our discussion with several concrete examples, some of which have eluded conventional methods so far.