Analysis of NuSTAR and Suzaku observations of Cyg X-1 in the hard state: evidence for a truncated disc geometry

The geometry of the accretion flow in black-hole X-ray binaries in the hard state, in particular the position of the disc inner edge, has been a subject of intense debate in recent years. We address this issue by performing a spectral study of simultaneous observations of Cyg X-1 in the hard state by NuSTAR and Suzaku. The same data were analysed before, and modelled by a lamppost containing hybrid electrons and located very close to the horizon, which emission was incident on a surrounding disc extending almost to the innermost stable circular orbit. We re-analyse the incident continuum model and show that it suffers from the lack of physical self-consistency. Still, the good fit to the data provided by this model indicates that the real continuum has a similar shape. We find it features a strong soft X-ray excess below a few keV, which we model as a soft thermal-Comptonization component, in addition to the main hard thermal-Compton component. This continuum model with reflection of both components yields the overall lowest $\chi^2$ and has a geometry with a hot inner accretion flow and a disc truncated at $\simeq$13--20 gravitational radii. On the other hand, we have also found spectral solution with a lamppost at a large height and a disc that can extend to the innnermost stable circular orbit, though somewhat statistically worse. Overall, we find the fitted truncation radius depends on the assumed continuum and geometry.Comment: MNRAS, in pres

FutureGRID: A Program for long-term research into GRID systems architecture

Proceedings of the 2003 UK e-Science All Hands Meeting, 31st August - 3rd September, Nottingham UKThis is a project to carry out research into long-term GRID architecture, in the University of Cambridge Computer Laboratory and the Cambridge eScience Center, with support from the Microsoft Research Laboratory, Cambridge. It is part of a larger vision for future systems architectures for public computing platforms, including both scientitic GRID and commodity level computing such as games, peer2peer computing and storage services and so forth, based on work in the laboratories in recent years into massively scaleable distributed systems for storage, computation, content distribution and collaboration[26]

Valuation, Adverse Selection, and Market Collapses

We study a market for funding real investment where valuation—meaning investors devoting resources to acquiring information about future payoffs—creates an adverse selection problem. Unlike previous models, more valuation is associated with lower market prices and so greater returns to valuation. This strategic complementarity in the capacity to do valuation generates multiple equilibria. With multiple equilibria, the equilibrium without valuation is most efficient despite funding some unprofitable investments. Switches to valuation equilibria, valuation runs, look like credit crunches. A large investor can ensure the efficient equilibrium only if it can precommit to a price and potentially, only if subsidized

Homoiterons and expansion in ribosomal RNAs

AbstractRibosomal RNAs in both prokaryotes and eukaryotes feature numerous repeats of three or more nucleotides with the same nucleobase (homoiterons). In prokaryotes these repeats are much more frequent in thermophile compared to mesophile or psychrophile species, and have similar frequency in both large RNAs. These features point to use of prokaryotic homoiterons in stabilization of both ribosomal subunits. The two large RNAs of eukaryotic cytoplasmic ribosomes have expanded to a different degree across the evolutionary ladder. The big RNA of the larger subunit (60S LSU) evolved expansion segments of up to 2400 nucleotides, and the smaller subunit (40S SSU) RNA acquired expansion segments of not more than 700 nucleotides. In the examined eukaryotes abundance of rRNA homoiterons generally follows size and nucleotide bias of the expansion segments, and increases with GC content and especially with phylogenetic rank. Both the nucleotide bias and frequency of homoiterons are much larger in metazoan and angiosperm LSU compared to the respective SSU RNAs. This is especially pronounced in the tetrapod vertebrates and seems to culminate in the hominid mammals. The stability of secondary structure in polyribonucleotides would significantly connect to GC content, and should also relate to G and C homoiteron content. RNA modeling points to considerable presence of homoiteron-rich double-stranded segments especially in vertebrate LSU RNAs, and homoiterons with four or more nucleotides in the vertebrate and angiosperm LSU RNAs are largely confined to the expansion segments. These features could mainly relate to protein export function and attachment of LSU to endoplasmic reticulum and other subcellular networks

Determining SUSY model parameters and masses at the LHC using cross-sections, kinematic edges and other observables

We address the problem of mass measurements of supersymmetric particles\ud at the Large Hadron Collider, using the ATLAS detector as an example. By\ud using Markov Chain sampling techniques to combine standard measurements of kinematic\ud edges in the invariant mass distributions of decay products with a measurement\ud of a missing pT cross-section, we show that the precision of mass measurements at\ud the LHC can be dramatically improved, even when we do not assume that we have\ud measured the kinematic endpoints precisely, or that we have identified exactly which\ud particles are involved in the decay chain causing the endpoints. The generality of the\ud technique is demonstrated in a preliminary investigation of a non-universal SUGRA\ud model, in which we relax the requirements of mSUGRA by breaking the degeneracy\ud of the GUT scale gaugino masses. The model studied is compatible with the WMAP\ud limits on dark matter relic density

Three body kinematic endpoints in SUSY models with non-universal Higgs masses.

We derive and present expressions for the kinematic endpoints that arise in the invariant mass distributions of visible decay products of cascade decays featuring a two body decay followed by a three body decay. This is an extension of a current technique that addresses chains of successive two body decays. We then apply these to a supergravity model with Non-Universal Higgs Masses (NUHM), having simulated a data set using the ATLFAST detector simulation. We find that, should such a model be chosen by nature, the endpoints will be visible in ATLAS data, and we discuss the problems associated with mass reconstruction in models with a similar phenomenology