The Xpress Transfer Protocol (XTP): A tutorial (expanded version)

The Xpress Transfer Protocol (XTP) is a reliable, real-time, light weight transfer layer protocol. Current transport layer protocols such as DoD's Transmission Control Protocol (TCP) and ISO's Transport Protocol (TP) were not designed for the next generation of high speed, interconnected reliable networks such as fiber distributed data interface (FDDI) and the gigabit/second wide area networks. Unlike all previous transport layer protocols, XTP is being designed to be implemented in hardware as a VLSI chip set. By streamlining the protocol, combining the transport and network layers and utilizing the increased speed and parallelization possible with a VLSI implementation, XTP will be able to provide the end-to-end data transmission rates demanded in high speed networks without compromising reliability and functionality. This paper describes the operation of the XTP protocol and in particular, its error, flow and rate control; inter-networking addressing mechanisms; and multicast support features, as defined in the XTP Protocol Definition Revision 3.4

Finite-mass helium atoms. ii- the 23p state plus

Energy states of helium isoelectronic series investigated by 50-term variational wave function with two nonlinear parameter

Major Galaxy Mergers and the Growth of Supermassive Black Holes in Quasars

Despite observed strong correlations between central supermassive black holes (SMBHs) and star-formation in galactic nuclei, uncertainties exist in our understanding of their coupling. We present observations of the ratio of heavily-obscured to unobscured quasars as a function of cosmic epoch up to z~3, and show that a simple physical model describing mergers of massive, gas-rich galaxies matches these observations. In the context of this model, every obscured and unobscured quasar represent two distinct phases that result from a massive galaxy merger event. Much of the mass growth of the SMBH occurs during the heavily-obscured phase. These observations provide additional evidence for a causal link between gas-rich galaxy mergers, accretion onto the nuclear SMBH and coeval star formation.Comment: Accepted for publication in Science. Published by Science Express on March 25th. 17 pages, 5 figures, including supplemental online materia

Two-Color Terawatt Laser System For High-Intensity Laser-Plasma Experiments

We report a two-color terawatt laser system for use in controlling laser-plasma instabilities. The system includes a commercial 45 TW Ti:Sapphire laser system at 800 nm, temporally synchronized with a 1 TW CPA Raman-Ti:Sapphire hybrid laser centered at 873nm that we designed and built to complement the 800 nm system. The two-color system will be used to seed, enhance, suppress, or otherwise control a variety of instabilities which arise in laser-plasma interactions.Physic

Optimal states and almost optimal adaptive measurements for quantum interferometry

We derive the optimal N-photon two-mode input state for obtaining an estimate \phi of the phase difference between two arms of an interferometer. For an optimal measurement [B. C. Sanders and G. J. Milburn, Phys. Rev. Lett. 75, 2944 (1995)], it yields a variance (\Delta \phi)^2 \simeq \pi^2/N^2, compared to O(N^{-1}) or O(N^{-1/2}) for states considered by previous authors. Such a measurement cannot be realized by counting photons in the interferometer outputs. However, we introduce an adaptive measurement scheme that can be thus realized, and show that it yields a variance in \phi very close to that from an optimal measurement.Comment: 4 pages, 4 figures, journal versio

X-ray emission from the Ultramassive Black Hole candidate NGC1277: implications and speculation on its origin

We study the X-ray emission from NGC1277, a galaxy in the core of the Perseus cluster, for which van den Bosch et al. have recently claimed the presence of an UltraMassive Black Hole (UMBH) of mass 1.7 times 10^10 Msun, unless the IMF of the stars in the stellar bulge is extremely bottom heavy. The X-rays originate in a power-law component of luminosity 1.3 times 10^40 erg/s embedded in a 1 keV thermal minicorona which has a half-light radius of about 360 pc, typical of many early-type galaxies in rich clusters of galaxies. If Bondi accretion operated onto the UMBH from the minicorona with a radiative efficiency of 10 per cent, then the object would appear as a quasar with luminosity 10^46 erg/s, a factor of almost 10^6 times higher than observed. The accretion flow must be highly radiatively inefficient, similar to past results on M87 and NGC3115. The UMBH in NGC1277 is definitely not undergoing any significant growth at the present epoch. We note that there are 3 UMBH candidates in the Perseus cluster and that the inferred present mean mass density in UMBH could be 10^5 Msun/Mpc^3, which is 20 to 30 per cent of the estimated mean mass density of all black holes. We speculate on the implied growth of UMBH and their hosts, and discuss the possibiity that extreme AGN feedback could make all UMBH host galaxies have low stellar masses at redshifts around 3. Only those which end up at the centres of groups and clusters later accrete large stellar envelopes and become Brightest Cluster Galaxies. NGC1277 and the other Perseus core UMBH, NGC1270, have not however been able to gather more stars or gas owing to their rapid orbital motion in the cluster core.Comment: 5 pages, 4 figures, MNRAS in pres

A Modelling Approach for Evaluating Agri-Environmental Policies at Sector Level

This paper presents a new approach to evaluate the cost effectiveness of agri-environmental policies at sector level. Policy uptake, cumulative environmental effects and public expenditure are identified as the main determinants of cost-effectiveness. On the basis of the sector-consistent, comparative-static, farm group model FARMIS, the determinants of policy cost-effectiveness at sector level are addressed. Firstly, intensity levels for the FARMIS activities are defined in order to model uptake of agri-environmental policies with FARMIS, secondly, life-cycle assessment data is attached to these intensity levels to determine environmental effects of the policies and thirdly, public expenditure is calculated under consideration of transaction costs. This paper concludes delineating the strengths and limitations of the approach

Modified gravity without dark matter

On an empirical level, the most successful alternative to dark matter in bound gravitational systems is the modified Newtonian dynamics, or MOND, proposed by Milgrom. Here I discuss the attempts to formulate MOND as a modification of General Relativity. I begin with a summary of the phenomenological successes of MOND and then discuss the various covariant theories that have been proposed as a basis for the idea. I show why these proposals have led inevitably to a multi-field theory. I describe in some detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and discuss its successes and shortcomings. This lecture is primarily pedagogical and directed to those with some, but not a deep, background in General RelativityComment: 28 pages, 10 figures, lecture given at Third Aegean Summer School, The Invisible Universe: Dark Matter and Dark Energy, minor errors corrected, references update