Additivity of Entangled Channel Capacity for Quantum Input States

An elementary introduction into algebraic approach to unified quantum information theory and operational approach to quantum entanglement as generalized encoding is given. After introducing compound quantum state and two types of informational divergences, namely, Araki-Umegaki (a-type) and of Belavkin-Staszewski (b-type) quantum relative entropic information, this paper treats two types of quantum mutual information via entanglement and defines two types of corresponding quantum channel capacities as the supremum via the generalized encodings. It proves the additivity property of quantum channel capacities via entanglement, which extends the earlier results of V. P. Belavkin to products of arbitrary quantum channels for quantum relative entropy of any type.Comment: 17 pages. See the related papers at http://www.maths.nott.ac.uk/personal/vpb/research/ent_com.htm

X-Ray Flares from Postmerger Millisecond Pulsars

Recent observations support the suggestion that short-duration gamma-ray bursts are produced by compact star mergers. The X-ray flares discovered in two short gamma-ray bursts last much longer than the previously proposed postmerger energy release time scales. Here we show that they can be produced by differentially rotating, millisecond pulsars after the mergers of binary neutron stars. The differential rotation leads to windup of interior poloidal magnetic fields and the resulting toroidal fields are strong enough to float up and break through the stellar surface. Magnetic reconnection--driven explosive events then occur, leading to multiple X-ray flares minutes after the original gamma-ray burst.Comment: 10 pages, published in Scienc

Model checking a server - side micro payment protocol

Many virtual payment systems are available on the world wide web for micropayment, and as they deal with money, correctness is important. One such payment system is Netpay. This paper examines the server-side version of the Netpay protocol and provides its formalization as a CSP model. The PAT model checker is used to prove three properties essential for correctness: impossibility of double spending, validity of an ecoin during the execution and the absence of deadlock. We prove that the protocol is executing according to its description based on the assumption that the customers and vendors are cooperative. This is a very strong assumption for system built to prevent abuse, but further analysis suggests that without it the protocol does no longer guarantee all correctness properties

GRB 030226 in a Density-Jump Medium

We present an explanation for the unusual temporal feature of the GRB 030226 afterglow. The R-band afterglow of this burst faded as ~ t^{-1.2} in ~ 0.2 days after the burst, rebrightened during the period of ~ 0.2 - 0.5 days, and then declined with ~ t^{-2.0}. To fit such a light curve, we consider an ultrarelativistic jetted blast wave expanding in a density-jump medium. The interaction of the blast wave with a large density jump produces relativistic reverse and forward shocks. In this model, the observed rebrightening is due to emissions from these newly forming shocks, and the late-time afterglow is caused by sideways expansion of the jet. Our fitting implies that the progenitor star of GRB 030226 could have produced a stellar wind with a large density jump prior to the GRB onset.Comment: 9 pages, 1 figure, accepted for publication in ApJ Letter

The Chinese city Suzhou in seven hundred years: an investigation of the relationship between the changing functional pattern and its spatial structure in the urban transformation process

What is the relation between the changing functional pattern of a city and its spatial structure? And how might an understanding of this relation for a particular city improve our ability to plan its future? In this paper we ask this question of the Chinese city of Suzhou by analysing the changing spatial structure over 700 years against a background of what is known from urban historians of its morphological and functional changes, especially the growth and shift of its various centres. Over and above its main aims, this study raises four key theoretical issues: the difference between the changing functional pattern of the city in an incremental growth in the pre-1949 time and in a massive growth after 1949; the co-existence of a canal system alongside the road system and its meaning to the city’s spatial structure; the stability of the physical positions of historical urban elements against the shift of their syntactic context; and the special character of ‘interrupted’ as opposed to the more common ‘deformed’ grids. This study also explores the ability of space syntax to work in a social and cult ural context in which it has rarely been applied before. By the various spatial analyses carried out in this study, it proposed that it is very important to conduct the axial modelling in a flexible way according to the specific social context. E.g. the ve hicle models in the pre-1949 period are proved more powerful than the all-route model in terms of capturing the business centre; the Iida Syntaxa Model is suggested to be a better modelling to reflex the more complex spatial structure of the contemporary city

Interaction induced topological phase transition in Bernevig-Hughes-Zhang model

We study interaction induced topological phase transition in Bernevig-Hughes-Zhang model. Topological nature of the phase transition is revealed by directly calculating the Z2 index of the interacting system from the single-particle Green's function. The interacting Z2 index is also consistently checked through the edge spectra. Combined with ab initio methods, present approach is a useful tool searching for correlated topological insulating materials from the first-principle point of view.Comment: 4.5 pages, 4 figures, reference adde