Calculations of laser cavity dumping for optical communications

For deep-space pulse-position modulation (PPM) optical communication links using Nd:YAG lasers, two types of laser transmitter modulation techniques are available for efficiently producing laser pulses over a broad range of repetition rates: Q-switching and cavity dumping. The desired modulation scheme is dependent on the required pulse repetition frequency and link parameters. These two techniques are discussed, theoretical and numerical calculations of the internal energy of the laser cavity in cavity dumping are described, and an example of cavity dumping is applied to a link for a proposed experiment package on Cassini

"Talk" about male suicide? Learning from community programmes

Purpose – The purpose of this paper is to examine the contribution of public awareness campaigning in developing community capacity toward preventing male suicide and explores emerging considerations for suicide prevention programme development. Design/methodology/approach – The paper draws on campaign evaluation data, specifically qualitative discussion groups with the general public, to report results concerning campaign processes, and “interim” effectiveness in changing public awareness and attitudes, and then discusses how progress is to be lasting and transformational. Findings – The campaign raised the awareness of a substantial proportion of those targeted, and affected attitudes and behaviour of those who were highly aware. The community settings approach was effective in reaching younger men, but there were challenges targeting the public more selectively, and engaging communities in a sustained way. Practical implications – The paper discusses emerging considerations for suicide prevention, focusing on gender and approaches and materials for engaging with the public as “influencers”. There are challenges to target audiences more specifically, provide a clear call to action, and engage the public in a sustained way. Social implications – The paper discusses emerging considerations for suicide prevention, focusing on gender and approaches and materials for engaging with the public as “influencers”. There are challenges to target audiences more specifically, provide a clear call to action, and engage the public in a sustained way. Originality/value – The paper adds fresh evidence of gendered communication processes, including their effects on public awareness, attitudes and engagement. Application of a theory of change model leads to systems level findings for sustaining programme gains

Semiparametric Fractional Cointegration Analysis

Fractional cointegration is viewed from a semiparametric viewpoint as a narrow-band phenomenon at frequency zero. We study a narrow-band frequency domain least squares estimate of the cointegrating vector, and related semiparametric methods of inference for testing the memory of observables and the presence of fractional cointegration. These procedures are employed in analysing empirical macroeconomic series; their usefulness and feasibility in finite samples is supported by results of a Monte Carlo experiment.Semiparametric analysis, fractional cointegration.

Weak Convergence of Multivariate Fractional Processes - (Now published in Stochastic Processes and their Applications, 80 (1999), pp.103-120.)

Weak convergence to a form of fractional Brownian motion is established for a wide class of nonstationary fractionally integrated multivariate processes. Instrumental for the main argument is a result of some independent interest on approximations for partial sums of stationary linear vector sequences. A functional central limit theorem for smoothed processes is analyzed under more general assumptions.Nonstationary fractional integration, functional central limit theorem

Spatial frequency response of an optical heterodyne receiver

The principles of transfer function analysis are applied to a passive optical heterodyne receiver to obtain the modulation transfer function (MTF). MTF calculations are performed based on an optical platform which is imaging vertically varying profiles at worst case shuttle orbit altitudes. An analysis of the derogatory effects of sampling (aliasing) and central obscurations on both resolution and heterodyne efficiency is given. It is found that the cascading property of MTF analysis must be carefully applied since the coherent transfer function of the optical receiver and that due to the local oscillator-detector combination are not separable but are related by the convolution of their products. Application of these results to the specific case of a space-lab type optical heterodyne receiver shows that resolutions of the order of 1.5-2.0 Km are possible for worst-case type orbital scenarios. Further, comparison of obscured-type receivers (e.g., Cassegrains) with unobscured receivers shows that both resolution and efficiency are severely degraded in an obscured-type receiver and consequently should not be used for a passive heterodyne detection scheme

Effects of state recovery on creep buckling under variable loading

Structural alloys embody internal mechanisms that allow recovery of state with varying stress and elevated temperature, i.e., they can return to a softer state following periods of hardening. Such material behavior is known to strongly influence structural response under some important thermomechanical loadings, for example, that involving thermal ratchetting. The influence of dynamic and thermal recovery on the creep buckling of a column under variable loading is investigated. The column is taken as the idealized (Shanley) sandwich column. The constitutive model, unlike the commonly employed Norton creep model, incorporates a representation of both dynamic and thermal (state) recovery. The material parameters of the constitutive model are chosen to characterize Narloy Z, a representative copper alloy used in thrust nozzle liners of reusable rocket engines. Variable loading histories include rapid cyclic unloading/reloading sequences and intermittent reductions of load for extended periods of time; these are superimposed on a constant load. The calculated results show that state recovery significantly affects creep buckling under variable loading. Structural alloys embody internal mechanisms that allow recovery of state with varying stress and time

Design of a "Digital Atlas Vme Electronics" (DAVE) Module

ATLAS-SCT has developed a new ATLAS trigger card, 'Digital Atlas Vme Electronics' ("DAVE"). The unit is designed to provide a versatile array of interface and logic resources, including a large FPGA. It interfaces to both VME bus and USB hosts. DAVE aims to provide exact ATLAS CTP (ATLAS Central Trigger Processor) functionality, with random trigger, simple and complex deadtime, ECR (Event Counter Reset), BCR (Bunch Counter Reset) etc. being generated to give exactly the same conditions in standalone running as experienced in combined runs. DAVE provides additional hardware and a large amount of free firmware resource to allow users to add or change functionality. The combination of the large number of individually programmable inputs and outputs in various formats, with very large external RAM and other components all connected to the FPGA, also makes DAVE a powerful and versatile FPGA utility cardComment: 8 pages, 4 figures, TWEPP-2011; E-mail: [email protected]

Starburst and AGN activity in ultraluminous infrared galaxies

(Abridged) We examine the power source of 41 local Ultraluminous Infrared Galaxies using archival infrared and optical photometry. We fit the observed Spectral Energy Distributions (SEDs) with starburst and AGN components; each component being drawn from a family of templates. We find all of the sample require a starburst, whereas only half require an AGN. In 90% of the sample the starburst provides over half the IR emission, with a mean fractional luminosity of 82%. When combined with other galaxy samples we find that starburst and AGN luminosities correlate over 6 decades in IR luminosity suggesting that a common factor governs both luminosities, plausibly the gas masses in the nuclear regions. We find that the mid-IR 7.7 micron line-continuum ratio is no indication of the starburst luminosity, or the fractional AGN luminosity, and therefore that this ratio is not a reliable diagnostic of the power source in ULIRGs. We propose that the scatter in the radio-IR correlation in ULIRGs is due to a skewed starburst IMF and/or relic relativistic electrons from a previous starburst, rather than contamination from an obscured AGN. We show that most ULIRGs undergo multiple starbursts during their lifetime, and by inference that mergers between more than two galaxies may be common amongst ULIRGs. Our results support the evolutionary model for ULIRGs proposed by Farrah et al 2001, where they can follow many different evolutionary paths of starburst and AGN activity in transforming merging spiral galaxies into elliptical galaxies, but that most do not go through an optical QSO phase. The lower level of AGN activity in our local sample than in z~1 HLIRGs implies that the two samples are distinct populations. We postulate that different galaxy formation processes at high-z are responsible for this difference.Comment: 24 pages, 8 figures. Accepted for publication in MNRA