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The precipitation of dusty material via unstable orbits on to Saturn from the ring plane is a phenomenon known as ring rain. A key open question for Saturn’s rings is whether silicates and organics rain out of the rings on to Saturn faster than water ice. Such preferential precipitation of dusty material would ‘clean’ the rings and make them appear youthful. In this paper, we investigate the stability of orbiting dust that is stochastically charged and may precipitate on to the planet, be ejected from the system, or remain stable over the duration of our numerical integrations. We find no clear relationship between dust particles’ launch locations in the main rings and their final deposition latitudes on the planet because the orbital motion is sensitive to initial conditions and the charging environment, but averaging over distributions of dust particle properties should lead to high-resolution stability maps for dust in the rings and deposition distributions on the planet, and hence predictions for the observable $\rm H_3^+$ emission strength.

We use deep follow-up XMM-Newton observations of 6 clusters discovered in the XXL Survey at $z>1$ to gain robust measurements of their X-ray properties and to investigate the extent to which scaling relations at low redshift are valid at $z>1$. This sample is unique as it has been investigated for AGN contamination, which ensures measurements are not undermined by systematic uncertainties, and pushes to lower mass at higher redshift than is usually possible, for example with Sunyaev-Zel'dovich (SZ) selected clusters. We determine the flux contribution of point sources to the XXL cluster flux in order to test for the presence of AGN in other high-redshift cluster candidates, and find 3XLSS J231626.8-533822 to be a point source misclassified as a cluster and 3XLSS J232737.3-541618 to be a genuine cluster. We present the first attempt to measure the hydrostatic masses in a bright subsample of $z>1$ X-ray selected galaxy clusters with a known selection function. Periods of high particle background significantly reduced the effective exposure times of observations (losing >50% in some cases) limiting the power of this study. When combined with complementary SZ selected cluster samples at higher masses, the data appear broadly consistent with the self-similar evolution of the low redshift scaling relations between ICM properties and cluster mass, suggesting that properties such as the X-ray temperature, gas mass and SZ signal remain reliable mass proxies even at high redshift., Comment: 13 pages, 7 figures, published in MNRAS

To realise an ISO standard for offshore structures account has to be taken of the differing engineering and safety demands of the participating bodies experienced in their analysis, design and construction. This process of harmonisation began with the strength requirements of tubular members and joints but now involves all platform components and systems. This paper concentrates on members. The competing documents are identified and briefly discussed. The basis of the formulations for the two most suitable candidates is reviewed. Strength formulations are compared and sensitivities to basic variables evaluated. Criteria for selection of the preferred formulations are presented. These are identified but are recommended for improvement. The effects of some of the improvements are examined. In one case, a difference in failure probability of one order of magnitude between competing designs is found. Notwithstanding, the selected formulations are judged to be suitable when implemented with the proposed improvements.

The XXL survey currently covers two 25 sq. deg. patches with XMM observations of ~10ks. We summarise the scientific results associated with the first release of the XXL data set, that occurred mid 2016. We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray (z 1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions.

Ambidexterity is widely understood to be critical for a firm’s sustained success and survival. Yet how exactly firms achieve ambidexterity is still not well understood. In particular, we lack a goo...

[Aims] X-ray sources at intermediate fluxes (a few x 10-14 erg cm-2 s-1) with a sky density of ~100 deg-2 are responsible for a significant fraction of the cosmic X-ray background at various energies below 10 keV. The aim of this paper is to provide an unbiased and quantitative description of the X-ray source population at these fluxes and in various X-ray energy bands., [Methods] We present the XMM-Newton Medium sensitivity Survey (XMS), including a total of 318 X-ray sources found among the serendipitous content of 25 XMM-Newton target fields. The XMS comprises four largely overlapping source samples selected at soft (0.5-2 keV), intermediate (0.5-4.5 keV), hard (2-10 keV) and ultra-hard (4.5-7.5 keV) bands, the first three of them being flux-limited., [Results] We report on the optical identification of the XMS samples, complete to 85-95%. At the flux levels sampled by the XMS we find that the X-ray sky is largely dominated by Active Galactic Nuclei. The fraction of stars in soft X-ray selected samples is below 10%, and only a few per cent for hard selected samples. We find that the fraction of optically obscured objects in the AGN population stays constant at around 15-20% for soft and intermediate band selected X-ray sources, over 2 decades of flux. The fraction of obscured objects amongst the AGN population is larger (~35-45%) in the hard or ultra-hard selected samples, and constant across a similarly wide flux range. The distribution in X-ray-to-optical flux ratio is a strong function of the selection band, with a larger fraction of sources with high values in hard selected samples. Sources with X-ray-to-optical flux ratios in excess of 10 are dominated by obscured AGN, but with a significant contribution from unobscured AGN., Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Based on observations made with the INT/WHT, TNG and NOT operated on the island of La Palma by the Isaac Newton Group, the Centro Galileo Galilei and ESA Member States and the USA (NASA). Based on observations made with the INT/WHT, TNG and NOT operated on the island of La Palma by the Isaac Newton Group, the Centro Galileo Galilei and the Nordic Optical Telescope Science Association respectively, in the Spanish Observatorio del Roque de los Muchachos. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). Based on observations collected at the European Southern Observatory, Paranal, Chile, as part of programme 75.A-0336.

We present Chandra X-ray results for the jet, nucleus, and gaseous atmosphere ofNGC315, a nearby radio galaxy whose jet kinematics are known through deep radio map-ping. Diffuse X-ray synchrotron emission is detected from the jet out to 30 arcsec from thenucleus, through regions both of fast bulk flow and decelerat ion. The X-ray to radio flux ra-tio drops considerably where the flow decelerates, but the X-ray and radio emissions showsimilar transverse extents throughout, requiring distributed particle acceleration to maintainthe supply of X-ray-emitting electrons. A remarkable knotty filament within the jet is seen inboth the radio and X-ray, contributing roughly 10 per cent ofthe diffuse emission along itsextent at both wavelengths. No completely satisfactory explanation for the filament is found,though its oscillatory appearance, roughly aligned magnetic field, and requirements for par-ticle acceleration, suggest that it is a magnetic strand within a shear layer between fast innerand slower outer flow.Keywords: galaxies:active– galaxies:individual:NGC315– galaxies :jets –radiationmech-anisms: non-thermal – radio continuum: general – X-rays: galaxies

We present results on the physical states of three high-redshift powerful radio galaxies (3C 292 at z=0.7, 3C 184 at z=1, and 3C322 at z=1.7). They were obtained by combining radio measurements with X-ray measurements from XMM-Newton that separate spectrally and/or spatially radio-related and hot-gas X-ray emission. Originally observed as part of a programme to trace clusters of galaxies at high redshift, none of the sources is found to lie in a rich X-ray-emitting environment similar to those of some powerful radio galaxies at low redshift, although the estimated gas pressures are sufficient to confine the radio lobes. The weak gas emission is a particularly interesting result for 3C 184, where a gravitational arc is seen, suggesting the presence of a very massive cluster. Here Chandra data complement the XMM-Newton measurements in spatially separating X-ray extended emission from that associated with the nucleus and rather small radio source. 3C 292 is the source for which the X-ray-emitting gas is measured with the greatest accuracy, and its temperature of 2 keV and luminosity of 6.5E43 erg/s are both characteristic of a poor cluster. This source allows the most accurate measurement of inverse-Compton X-ray emission associated with the radio lobes. In all structures where the magnetic-field strength can be estimated through combining measurements of radio-synchrotron and inverse-Compton-X-ray emission, the field strengths are consistent with sources being in a state of minimum total energy., Comment: 5 pages, 7 figures. To appear in "X-ray and Radio Connections", eds. Sjouwerman, L.O. & Dyer, K.K. (see http://www.aoc.nrao.edu/events/xraydio/)

This paper presents the methodology and key findings of a study aimed at comparing the reliability of a representative jacket platform with that of a representative jack-up unit. Both structures were assumed to operate at the same location under identical environmental conditions (typical of the North Sea). Each structure was designed to the limits of their relevant recommended practice (API RP2A LRFD and SNAME T&R Bulletin 5-5A for the jacket and jack-up, respectively) to ensure a consistent comparison. This was followed by component and system reliability analyses using detailed modelling for both structures. Initially, the foundation failure was suppressed to enable the structure response to be compared and then, in the final stage of the study, detailed foundation modelling was included to examine the effect of foundation reliability on the overall structural reliability. For the specific site and environmental conditions considered in the study, it is concluded that the structures do not realise substantially different structural system reliability levels when designed/assessed to their most recent practices.

We present new X-ray (Chandra) and radio (JVLA) observations of the nearby cluster Abell 3744. It hosts two prominent radio galaxies with powers in the range critical for radio-mode feedback. The radio emission from these galaxies terminates in buoyant tendrils reaching the cluster's outer edge, and the radio-emitting plasma clearly influences the cluster's X-ray-emitting atmosphere. The cluster's average gas temperature, of kT=3.5 keV, is high for its bolometric luminosity of 3.2 \times 10^{43} ergs s^{-1}, but the 100 kpc-scale cavity carved out by radio-emitting plasma shows evidence of less than 2 per cent of the excess enthalpy. We suggest instead that a high-velocity encounter with a galaxy group is responsible for dispersing and increasing the entropy of the gas in this non-cool-core cluster. We see no evidence for shocks, or established isobaric gas motions (sloshing), but there is much sub-structure associated with a dynamically active central region that encompasses the brightest radio emission. Gas heating is evident in directions perpendicular to the inferred line of encounter between the infalling group and cluster. The radio-emitting tendrils run along boundaries between gas of different temperature, apparently lubricating the gas flows and inhibiting heat transfer. The first stages of the encounter may have helped trigger the radio galaxies into their current phase of activity, where we see X-rays from the nuclei, jets, and hotspots., Accepted for publication in ApJ (13 pages, 17 figures)

This paper describes a comparitive study on the structural reliability of a sample jacket and a sample jack-up. The methodology adopted is outlined and results obtained presented with emphasis on the jack-up. Findings of relevance to the jack-up community are discussed and some comments on the SNAME RP are given. An approach for improved spudcan–soil interaction modelling to be used in the next phase of the study is presented.

The introduction of the fixed jacket Load and Resistance Factor Design code (API RP 2A-LRFD), and the Jack-up Site Assessment Recommended Practice (SNAME T&R Bulletin 5-5A), raises debates regarding differences in the reliability levels associated with the use of the two documents. In an effort to investigate whether substantial differences exist, and to understand the underlying causes of the differences, a major study has been initiated by the UK Health and Safety Executive to compare the reliabilities of these two structures when operating in similar weather conditions and in similar water depths, to the extreme weather hazard. To ensure the comparison is appropriate, both units will be assumed to be operating close to the limits of their relevant code. Both will be subject to the same analysis packages in respect to wave-current force determination, structural analysis, pushover analysis, and reliability analysis. Initially, foundation failure will be suppressed in order that structural reliabilities under extreme weather conditions can be directly compared. Foundation failure will then be introduced to quantify the effect this has on the structural safety levels. Reliabilities will be determined at both component and system level using the response surface reliability methodology. Component strength modelling will exploit the formulations currently being harmonised for the new ISO offshore code, whilst global strength will be evaluated using CAP/Seastar for both installation types, thus reducing the potential for modelling based differences occurring during the system analysis of the study.

A three-fold typology of subsidiary roles (world mandate, specialized contributor, local implementer) was induced from the literature and its empirical validity was confirmed. Adopting a configurational approach, we then explored the ways in which subsidiary ‘structural context’ varies across subsidiary role types. Structural context characteristics were determined through a discussion of the underlying principles of the ‘hierarchy’ and ‘heterarchy’ models of multinational organization. The key findings were: (a) higher strategic autonomy in world mandates than in local implementers; (b) a more internationally configured value-chain in world mandates and specialized contributors than local implementers; (c) lower levels of internal product flows in world mandates than the other two types; and (d) a significantly lower performance in specialized contributors. Implications for a configurational model of subsidiary management, and for heterarchy as a higher level conceptualization, are discussed.© 1995 JIBS. Journal of International Business Studies (1995) 26, 729–753

The first major offshore oil and gas production facility went into service in the North Sea over two decades ago. Offshore structures in hostile environments like the North Sea are subjected to time-dependent local damage such as corrosion and fatigue. To ensure safe operations, the integrity of these components needs to be maintained in service. This is achieved by carrying out planned non-destructive inspection coupled with structural integrity assessments. The inspections are not an entirely reliable process, however. There are also many uncertainties involved in the fatigue integrity calculations. In order to take these uncertainties into account, reliability-based assessment can be used. This paper summarizes the recent development of reliability-based fatigue initiation and fracture mechanics (crack growth) analyses for the in-service assessment of the integrity of offshore structural components. The techniques are illustrated with two specific forms of structural connection: welded tubular joints and threaded (screw type) joints. Related practical issues, including the reliability of non-destructive inspection (NDI) and the considerations of targeting maintenance resources, are also discussed.

The emission mechanisms in extragalactic jets include synchrotron and various inverse-Compton processes. At low (radio through infrared) energies, it is widely agreed that synchrotron emission dominates in both low-power (FR I) and high-power (FR II and quasar) jets, because of the power-law nature of the spectra observed and high polarizations. However, at higher energies, the emission mechanism for high-power jets at kpc scales is hotly debated. Two mechanisms have been proposed: either inverse-Compton of cosmic microwave background photons or synchrotron emission from a second, high-energy population of electrons. Here we discuss optical polarimetry as a method for diagnosing the mechanism for the high-energy emission in quasar jets, as well as revealing the jet's three-dimensional energetic and magnetic field structure. We then discuss high-energy emission mechanisms for powerful jets in the light of the HST polarimetry of PKS 1136-135., 4 pages, 1 figure. To appear in proceedings of "The Monster's Fiery Breath: Feedback in galaxies, groups, and clusters" meeting, June 1-5, 2009 held in Madison, WI, USA

We present a concept for the payload SAGACE, the Spectroscopic Active Galaxies And Cluster Explorer, devoted to study the evolution of Universe structures using different observables, all of them in the mm/submm wavelength. The SAGACE payload is made of a passively cooled 3 m telescope, a cryogenic Fourier Transform Spectrometer (FTS) and detector arrays to be operated at 0.3 K by a 3He fridge. The detectors are Ti/Au Transition Edge Sensor (TES) bolometers with a NEP

A massive object distorts the path of light passing near it. If the object's metric changes at a different rate than that of the Universe, then a monochromatic source behind the object will change in frequency and flux relative to a similar source elsewhere. Contracting lenses and large masses in the early Universe provide effects of this type, but an alternative mechanism for producing such an effect is motion of the lensing object. A lensing object moving across the line of sight should cause (a) a redshift difference between multiple images of a background object (e.g., a quasar lensed by a galaxy), and (b) a brightness anisotropy in the microwave background radiation. Effect (a) is unlikely to be measurable for the multiple images formed by ‘conventional’ astrophysical objects, although a string may produce a detectable effect if it has sufficient mass per unit length. Effect (b) should soon be detectable for clusters of galaxies with large peculiar velocities.

With many offshore installations in the UK sector of the North Sea now reaching or being in excess of their original anticipated design life, there is a particular need to evaluate approaches to structural integrity management by offshore operators. Ageing processes can affect the structural integrity of the installation and demonstration of adequate performance beyond its original design life is thus a necessary requirement. This paper addresses the issues relevant to the life extension of ageing installations.

With an ever-increasing population of ageing offshore installations in the North Sea, the Health and Safety Executive’s (HSE’s) Offshore Safety Division has focused its front-line operational activity in recent years on the structural integrity management process and establishing the extent of any deterioration in structural integrity. The current phase of work, the Structural Integrity Management Inspection Programme (SIMIP), is described and the findings to date are presented in this paper.Copyright © 2008 by British Crown

In recent years, a significant amount of effort has been expended by HSE and the offshore industry on the development of good practice for structural integrity management in the new code for offshore structures, ISO 19902. However, a review of the structural integrity management of fixed offshore installations operated on the UKCS has indicated that duty holders adopt varying approaches, in terms of both the methods used and effectiveness. The elements of a framework for the management of the structural integrity of fixed jacket structures are presented.Copyright © 2008 by British Crown

There is an increasing number of ageing installations in UK waters, many of which are being or will be operated beyond their original planned service life. This important trend, in combination with (a) the introduction of risk-based goal-setting regulations which require the maintenance of life cycle integrity as a key target, (b) the development of guidelines in the draft ISO standard for offshore structures, ISO 19902, and (c) significant technology advances in recent years (e.g. in loading, fatigue, fire and blast integrity and system integrity), makes reassessment an important consideration in the structural integrity management of offshore installations. The paper outlines procedures in place for reassessment, including those in the draft ISO standard, and reviews recent technical advances relevant to this area. The important role of inspection and maintenance for existing structures is assessed and related to both current practices and target requirements. The need for reliable and comprehensive inspection data is important for reassessment and the status of this is reviewed. An overall framework for reassessment is developed in the light of the above issues.Copyright © 2002 by ASME

If a galaxy cluster's X-ray gas distribution follows an isothermal polytropic β model, we may write the electron radial density distribution as; ne = ne0(1 + r2/rc2)–3/2β, rc being the core radius and ne0 the central electron density. This may be related to both an X-ray surface brightness distribution and a Sunyaev-Zel'dovich effect distribution (Sarazin 1986). Fitting to observational data then enables us to constrain the value of β. The normalisation value, ne0, to obtain a total mass estimate is calculated via the relationship between the X-ray and S-Z distribution normalisation constants, and the gas temperature and spectral emissivity parameters from fits to the X-ray spectrum. We are then in a position to evaluate ne(r) and its integral; the total electron gas mass. If we can further assume that there exists a simple ratio between the electron and proton number densities within the gas, we may straightforwardly posit a value for the total gas mass. An additional method of determining the polytropic gas index exists, with optical constraints on the galactic velocity dispersion, through the relation; β = μmHσz2/kBTe. Studies at optical, as well as X-ray and radio wavelengths are thus useful as a corroborative measure in determining the total gas mass.

We present 18 GHz Australia Telescope Compact Array imaging of the Mpc-scale quasar jet PKS 0637-752 with angular resolution ~0.58 arcseconds. We draw attention to a spectacular train of quasi-periodic knots along the inner 11 arcseconds of the jet, with average separation ~1.1 arcsec (7.6 kpc projected). We consider two classes of model to explain the periodic knots: those that involve a static pattern through which the jet plasma travels (e.g. stationary shocks); and those that involve modulation of the jet engine. Interpreting the knots as re-confinement shocks implies the jet kinetic power Q ~ 10^{46} erg/s, but the constant knot separation along the jet is not expected in a realistic external density profile. For models involving modulation of the jet engine, we find that the required modulation period is 2 x 10^3 yr < \tau < 3 x 10^5 yr. The lower end of this range is applicable if the jet remains highly relativistic on kpc-scales, as implied by the IC/CMB model of jet X-ray emission. We suggest that the quasi-periodic jet structure in PKS 0637-752 may be analogous to the quasi-periodic jet modulation seen in the microquasar GRS 1915+105, believed to result from limit cycle behaviour in an unstable accretion disk. If variations in the accretion rate are driven by a binary black hole, the predicted orbital radius is 0.7 < a < 30 pc, which corresponds to a maximum angular separation of ~0.1 - 5 mas.

One of ROSAT’s major achievements has been its ability to separate X‐ray emission components in many radio galaxies, where this was previously possible only for a very few well‐known sources, e.g.,M87 and Cen A. The dominant X‐ray emission mechanism in radio galaxies as a class was unclear, with correlations between the X‐ray and radio emissions used on one hand to argue for a nuclear origin for the X‐rays, and on the other hand for a thermal origin. Now, with ROSAT we find the presence of both resolved (thermal) and unresolved emission to be typical.Our results are illustrated with PSPC data from the first six radio galaxies in our study. Spectral and spatial measurements independently support the presence of multiple emission components. The resolved emission can be modeled as thermal radiation from gas of galaxy, group, or cluster dimension depending on object. The unresolved emission may be thermal or nonthermal. Evidence is presented to support a nonthermal origin for most of the unresolved emission:...

The ROSAT PSPC spectrum of NGC 6251 can be fitted with either a multiple‐component model obscured by the gas column within our Galaxy or by a single power‐law component obscured by this Galactic gas and an additional column N=1.3×1021 cm−2. We have used the VLA to search for the the HI line in absorption towards the radio core of NGC 6251 to set limits on the total X‐ray absorbing column. We find marginal evidence for a weak, broad, absorption feature associated with NGC 6251 which could provide the extra HI column suggested by the simpler X‐ray spectral fit.

The title of this keynote address is ‘Offshore Foundation Safety’. This is a wide subject and could be controversial, however nothing I am going to say is particularly new rather I am going to present old information with a new emphasis. I will be concentrating on the UK offshore sector but the principles that I will be elaborating on are the same worldwide.

Reliable detections of the Sunyaev-Zel’dovich effect exist for only a few clusters of galaxies although many observations exhibit random errors < 0.5 mK. Several observational techniques are in use and particular promise for future improvements in the measurements are shown by sub-millimetre work with single dishes and centimetre-wavelength observations with small, dedicated interferometers. The three best-observed clusters display effects which are clearly associated with the X-ray emitting intracluster gas, and which can be used to investigate the properties of this gas and to estimate the value of the Hubble constant.

Prior to ROSAT, separation of X-ray components in radio galaxies has been limited to a few well-known sources, e.g., M 87 and Cen A. Now, from ROSAT PSPC measurements of the first six objects in our study of low-power radio galaxies, we find that both resolved (thermal) and unresolved X-ray emission in a single source is typical (Worrall & Birkinshaw 1993; ApJ, submitted). The angular size of, and fraction of luminosity in, the resolved X-ray emission varies between objects. There is evidence to relate the unresolved X-ray emission with the inner radio jet.

Les densites de flux limites atteintes au centre de la region observee sont 12,9 et 1,4 mJy a 408 et 1407 MHz respectivement. On presente une liste des 222 sources detectees et de leurs identifications optiques

On derive une equation differentielle qui regit l'evolution des perturbations de pression de premier ordre d'un faisceau hydrodynamique relativiste et cylindrique avec une structure de densite et de vitesse. Les solutions pour le cas d'une couche a vortex simple sont utilisees pour etudier le probleme de la stabilite dans le cas de la nature convective d'instabilites de Kelvin-Helmholtz. Le domaine spatial et le domaine temporel conduisent a des resultats differents pour les longueurs de croissances des instabilites

An approach is described which was used to estimate the wave loading on a small offshore gas platform located at a shallow water site in the southern North Sea. Extreme kinematics were predicted to be due to spilling breakers and the resulting forces drag dominated. The design wave was modelled in a laboratory flume at Edinburgh University to a scale of 1:120, and the velocities and accelerations were measured using a novel laser Doppler system. These values were compared with numerical predictions obtained using the Dean's stream function theory, taking into account the appropriate Froude scaling. Measured velocities and accelerations were in general agreement with the computed values but were slightly higher in the crest region. On this basis, the grid of velocities derived from Dean's method was modified before being input to the design programme. The calculated loadings resulted in minimal structural changes for the particular design configuration.

Observational data on the Sunyaev-Zel'dovich effect for three clusters are used to obtain limits to the value of the Hubble constant. Only a wide bound on the value of H0, 10 km s−1 Mpc−1 < H0 < 160 km s−1 Mpc−1, can be derived, mostly because of the large uncertainty in the measured temperature of the intracluster medium in each cluster. Better information on this temperature and on the distribution of the intracluster medium are needed for this method to yield a good measurement of H0.

Results for the decrements in the microwave background radiation towards the centres of 13 clusters of galaxies are presented. It is shown that these data imply central gas densities of about 2 × 10−24 kg m−3 and cluster masses of about 5 × 1045 kg.

Recent data taken with the 40-m telescope of the Owens Valley Radio Observatory at 20 GHz have confirmed the detections of the Sunyaev-Zel’dovich effect towards three clusters of galaxies, 0016+16, Abell 665 and Abell 2218. Rough measurements of the angular scale of the effect have also been made, and a comparison of these with the X-ray observations supports an isothermal model for the cluster gas.