X-ray film holder permits single continuous picture of tubing joint

X ray technique produces a clear continuous picture of a welded brazed tubing joint on a single film with one exposure. A stationary X ray source located in the plane of the joint to be inspected, a means of rotating the tube, and a unique internal film holder and positioning fixture are used

Structure of 10N in 9C+p resonance scattering

The structure of exotic nucleus 10N was studied using 9C+p resonance scattering. Two L=0 resonances were found to be the lowest states in 10N. The ground state of 10N is unbound with respect to proton decay by 2.2(2) or 1.9(2) MeV depending on the 2- or 1- spin-parity assignment, and the first excited state is unbound by 2.8(2) MeV.Comment: 6 pages, 4 figures, 1 table, submitted to Phys. Lett.

Cosmic Voids: structure, dynamics and galaxies

In this review we discuss several aspects of Cosmic Voids. Voids are a major component of the large scale distribution of matter and galaxies in the Universe. They are of instrumental importance for understanding the emergence of the Cosmic Web. Their relatively simple shape and structure makes them into useful tools for extracting the value of a variety cosmic parameters, possibly including even that of the influence of dark energy. Perhaps most promising and challenging is the issue of the galaxies found within their realm. Not only does the pristine environment of voids provide a promising testing ground for assessing the role of environment on the formation and evolution of galaxies, the dearth of dwarf galaxies may even represent a serious challenge to the standard view of cosmic structure formation.Comment: 29 pages, 12 figures, invited review COSPA2008, Pohang, Korea. Modern Physics Letters A, accepted. For high-res version see http://www.astro.rug.nl/~weygaert/voids.cospa2008.weygaert.pd

Implications of climate change for expanding cities worldwide

This paper analyses the trends of the changing environmental effects within growing megacities as their diameters exceed 50–100 km and their populations rise beyond 30 million people. The authors consider how these effects are influenced by climate change, to which urban areas themselves contribute, caused by their increasing greenhouse gas emissions associated with rapidly expanding energy use. Other environmental and social factors are assessed, quantitatively and qualitatively, using detailed modelling of urban mesoscale meteorology, which shows how these factors can lead to large conurbations becoming more vulnerable to climatic and environmental hazards. The paper discusses the likely changes in meteorological and hydrological hazards in urban areas, both as the climate changes and the sizes of urban areas grow. Examples are given of how these risks are being reduced through innovations in warning and response systems, planning and infrastructure design, which should include refuges against extreme natural disasters. Policies are shown to be more effective when they are integrated and based on substantial community involvement. Some conclusions are drawn regarding how policies for the natural and artificial environment and for reducing many kinds of climate and hazard risk are related to future designs and planning of infrastructure and open spaces

Dynamical Friction in a Gaseous Medium

Using time-dependent linear perturbation theory, we evaluate the dynamical friction force on a massive perturber M_p traveling at velocity V through a uniform gaseous medium of density rho_0 and sound speed c_s. This drag force acts in the direction -\hat V, and arises from the gravitational attraction between the perturber and its wake in the ambient medium. For supersonic motion (M=V/c_s>1), the enhanced-density wake is confined to the Mach cone trailing the perturber; for subsonic motion (M<1), the wake is confined to a sphere of radius c_s t centered a distance V t behind the perturber. Inside the wake, surfaces of constant density are hyperboloids or oblate spheroids for supersonic or subsonic perturbers, respectively, with the density maximal nearest the perturber. The dynamical drag force has the form F_df= - I 4\pi (G M_p)^2\rho_0/V^2. We evaluate I analytically; its limits are I\to M^3/3 for M>1. We compare our results to the Chandrasekhar formula for dynamical friction in a collisionless medium, noting that the gaseous drag is generally more efficient when M>1 but less efficient when M<1. To allow simple estimates of orbit evolution in a gaseous protogalaxy or proto-star cluster, we use our formulae to evaluate the decay times of a (supersonic) perturber on a near-circular orbit in an isothermal \rho\propto r^{-2} halo, and of a (subsonic) perturber on a near-circular orbit in a constant-density core. We also mention the relevance of our calculations to protoplanet migration in a circumstellar nebula.Comment: 17 pages, 5 postscript figures, to appear in ApJ 3/1/9

Evidence for a Superglass State in Solid 4He

Although solid helium-4 (4He) may be a supersolid it also exhibits many phenomena unexpected in that context. We studied relaxation dynamics in the resonance frequency f(T) and dissipation D(T) of a torsional oscillator containing solid 4He. With the appearance of the "supersolid" state, the relaxation times within f(T) and D(T) began to increase rapidly together. More importantly, the relaxation processes in both D(T) and a component of f(T) exhibited a complex synchronized ultraslow evolution towards equilibrium. Analysis using a generalized rotational susceptibility revealed that, while exhibiting these apparently glassy dynamics, the phenomena were quantitatively inconsistent with a simple excitation freeze-out transition because the variation in f was far too large. One possibility is that amorphous solid 4He represents a new form of supersolid in which dynamical excitations within the solid control the superfluid phase stiffness.Comment: 25 pages (12 main manuscript, 13 supporting material), 10 figures (4 main manuscript, 6 supporting material

On the structure of the energy distribution function in the hopping regime

The impact of the dispersion of the transport coefficients on the structure of the energy distribution function for charge carriers far from equilibrium has been investigated in effective-medium approximation for model densities of states. The investigations show that two regimes can be observed in energy relaxation processes. Below a characteristic temperature the structure of the energy distribution function is determined by the dispersion of the transport coefficients. Thermal energy diffusion is irrelevant in this regime. Above the characteristic temperature the structure of the energy distribution function is determined by energy diffusion. The characteristic temperature depends on the degree of disorder and increases with increasing disorder. Explicit expressions for the energy distribution function in both regimes are derived for a constant and an exponential density of states.Comment: 16 page

Molecular depletion times and the CO-to-H2 conversion factor in metal-poor galaxies

Tracing molecular hydrogen content with carbon monoxide in low-metallicity galaxies has been exceedingly difficult. Here we present a new effort, with IRAM 30-m observations of 12CO(1-0) of a sample of 8 dwarf galaxies having oxygen abundances ranging from 12+logO/H=7.7 to 8.4. CO emission is detected in all galaxies, including the most metal-poor galaxy of our sample (0.1 Zsun); to our knowledge this is the largest number of 12CO(1-0) detections ever reported for galaxies with 12+logO/H<=8 (0.2 Zsun) outside the Local Group. We calculate stellar masses (Mstar) and star-formation rates (SFRs), and analyze our results by combining our observations with galaxy samples from the literature. Extending previous results for a correlation of the molecular gas depletion time, tau(dep), with Mstar and specific SFR (sSFR), we find a variation in tau(dep) of a factor of 200 or more (from <50 Myr to 10 Gyr) over a spread of 1000 in sSFR and Mstar. We exploit the variation of tau(dep) to constrain the CO-to-H2 mass conversion factor alpha(CO) at low metallicity, and assuming a power-law variation find alpha(CO) \propto (Z/Zsun)^1.9, similar to results based on dust continuum measurements compared with gas mass. By including HI measurements, we show that the fraction of total gas mass relative to the baryonic mass is higher in galaxies that are metal poor, of low mass, and of high sSFR. Finally, comparisons of the data with star-formation models of the molecular gas phases suggest that, at metallicities Z/Zsun<=0.2, there are some discrepancies with model predictions.Comment: 18 pages, 15 figures, accepted for publication in A&

The use of ICT in the assessment of modern languages: the English context and European viewpoints

The ever increasing explosion of highly attractive multimedia resources on offer has boosted the use of information and communication technology (ICT) in the teaching and learning of modern languages. The use of ICT to assess languages is less frequent, however, although online testing is starting to develop. This paper examines the national context for the assessment of modern foreign language proficiency in England, outlines the kinds of assessment currently available and the development of electronic forms of assessment and compares the above with the survey results of a European Union (EU) funded project on current good practice in online assessment of languages in other European countries. The findings indicate that speaking is inadequately served by online testing as tests currently focus primarily on receptive language skills. The implications for future successful online testing include the incorporation of interactive skills and effective formative feedback