10760123
Static VAr power factor correction for the ISIS main magnet power supply
ISIS sited at the Rutherford Appleton Laboratory (RAL) is the worlds brightest pulsed neutron source. Intense pulses of neutrons are produced at 50 Hz when a heavy metal target is bombarded with a beam of high energy (800MeV) protons. Energy is imparted to the protons by accelerating them in a synchrotron, the magnets of which are connected in a configuration known as a "white circuit". This white circuit suffers from problems arising from drifting values of capacitance and inductance which affect the resonant frequency. This paper provides a review of Static VAr technology, and focuses on the design and simulation of the implementation of this technology to regulate the resonant frequency of the white circuit.
55130881
The Replacement of the ISIS White-Circuit Choke
The ISIS accelerator is based on an 800 MeV synchrotron arranged as a White-Circuit [1]. Key to its operation is a large storage choke with ten main, and ten auxiliary windings. The main windings resonate with the associated capacitor banks at 50 Hz and also provide a path for a DC bias current past the capacitors. The auxiliary windings provide for the AC excitation of the magnet circuit. Known as the “NINA” choke from its previous service on the NINA synchrotron at Daresbury Laboratory, it was built in 1963. The windings are built into a single frame and are therefore closely coupled by the magnetic circuit. In the event of a failure on any winding, the choke would have to be dismantled to replace the damaged parts. As it weighs about 90 tons without its cooling oil this would be a major task even if sufficient spare parts were available.
56124619
Cosmological Parameters from Galaxy Clustering in the SDSS
We present estimates of cosmological parameters from the application of the Karhunen-Loève transform to the analysis of the 3D power spectrum of density fluctuations using Sloan Digital Sky Survey galaxy redshifts. We use Ωmh and fb Ωb Ωm to describe the shape of the power spectrum, σ8g for the (linearly extrapolated) normalization, and β to parametrize linear theory redshift space distortions. On scales k 0 16hMpc 1, our maximum likelihood values are Ωmh 0 264 0 043, fb 0 286 0 065, σ8g 0 966 0 048, and β 0 45 0 12. When we take a prior on Ωb from WMAP, we find Ωmh 0 207 0 030, which is in excellent agreement with WMAP and 2dF. This indicates that we have reasonably measured the gross shape of the power spectrum but we have difficulty breaking the degeneracy between Ωmh and fb because the baryon oscillations are not resolved in the current spectroscopic survey window function.
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.
11407796
Flux, gaugino condensation, and antibranes in heterotic M theory
We present the potential energy due to flux and gaugino condensation in heterotic M theory compactifications with antibranes in the vacuum. For reasons which we explain in detail, the contributions to the potential due to flux are not modified from those in supersymmetric contexts. The discussion of gaugino condensation is, however, changed by the presence of antibranes. We show how a careful microscopic analysis of the system allows us to use standard results in supersymmetric gauge theory in describing such effects - despite the explicit supersymmetry breaking which is present. Not surprisingly, the significant effect of antibranes on the threshold corrections to the gauge kinetic functions greatly alters the potential energy terms arising from gaugino condensation.
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.
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