High repetition rate sealed CO2 TEA lasers using heterogeneous catalysts

The significant operational advantages offered by CO2 lasers, operating in the 10.6 micron region of the spectrum, over current solid state lasers, emitting in the near IR region, have prompted increased interest in the development of compact, reliable, rugged CO2 laser sources. Perhaps the most critical aspect associated with achieving a laser compatible with military use is the development of lasers which require no gas replenishment. Sealed, single shot, CO2 TEA lasers have been available for a number of years. Stark et al were first to demonstrate reliable sealed operation in single shot CO2 TEA lasers in 1975 using gas catalysis. GEC Avionics reported the compact, environmentally qualified, MKIII CO2 TEA laser with a pulse life of greater than 10 to the 6th power pulses in 1980. A sealed laser lifetime of greater than 10 to the 6th power pulses is acceptable for single shot cases, such as direct detection rangefinders for tank laser sights. However, in many other applications, such as tracking of fast moving targets, it is essential that a repetition rate of typically 30Hz to 100Hz is employed. In such cases, a pulse lifetime of 10 to the 6th power pulses is no longer sufficient and a minimum pulse lifetime 10 to the 7th power pulses is essential to ensure a useful service life. In 1983 Stark el al described a sealed, 100Hz CO2 TEA laser, with a life of greater than 2.6 x 10 to the 6th power, which employed heterogeneous catalysis. Following this pioneering work, GEC Avionics has been engaged in the development of sealed high repetition rate lasers with a pulse lifetime of 20 million pulses

The shapes of the circumstellar silicate features

Around oxygen-rich stars the spectra of most long-period variables (LPV) show an excess infrared emission which is attributed to circumstellar silicate dust grains. It is known that the spectral energy distribution of the 10 micron emissions shows variations from star to star. With the availability of many Infrared Astronomy Satellite (IRAS) Low Resolution Spectra (LRS) in the 8 to 22 micron region, the 10 micron feature can be studied to determine its uniformity (or lack thereof). The excess silicate emissions (10 micron emission), divided into three groups characterized by similar spectral shapes, are discussed

Constrained hyperbolic divergence cleaning in smoothed particle magnetohydrodynamics with variable cleaning speeds

We present an updated constrained hyperbolic/parabolic divergence cleaning algorithm for smoothed particle magnetohydrodynamics (SPMHD) that remains conservative with wave cleaning speeds which vary in space and time. This is accomplished by evolving the quantity $\psi / c_h$ instead of $\psi$. Doing so allows each particle to carry an individual wave cleaning speed, $c_h$, that can evolve in time without needing an explicit prescription for how it should evolve, preventing circumstances which we demonstrate could lead to runaway energy growth related to variable wave cleaning speeds. This modification requires only a minor adjustment to the cleaning equations and is trivial to adopt in existing codes. Finally, we demonstrate that our constrained hyperbolic/parabolic divergence cleaning algorithm, run for a large number of iterations, can reduce the divergence of the field to an arbitrarily small value, achieving $\nabla \cdot B=0$ to machine precision.Comment: 23 pages, 16 figures, accepted for publication in Journal of Computational Physic

The role of right and left parietal lobes in the conceptual processing of numbers

Neuropsychological and functional imaging studies have associated the conceptual processing of numbers with bilateral parietal regions (including intraparietal sulcus). However, the processes driving these effects remain unclear because both left and right posterior parietal regions are activated by many other conceptual, perceptual, attention, and response-selection processes. To dissociate parietal activation that is number-selective from parietal activation related to other stimulus or response-selection processes, we used fMRI to compare numbers and object names during exactly the same conceptual and perceptual tasks while factoring out activations correlating with response times. We found that right parietal activation was higher for conceptual decisions on numbers relative to the same tasks on object names, even when response time effects were fully factored out. In contrast, left parietal activation for numbers was equally involved in conceptual processing of object names. We suggest that left parietal activation for numbers reflects a range of processes, including the retrieval of learnt facts that are also involved in conceptual decisions on object names. In contrast, number selectivity in right parietal cortex reflects processes that are more involved in conceptual decisions on numbers than object names. Our results generate a new set of hypotheses that have implications for the design of future behavioral and functional imaging studies of patients with left and right parietal damage

The Ladders Revolution: material struggle, social media and news coverage

This article, which focuses on a strike and ocupation that took place in Barcelona in May 2015, is part of a larger enquiry that attempts to locate public expressions of dissent in their sociopolitical, discursive and spatiotemporal context. The methods used to conduct this study include the standard collection of observational and media data, but also encompass an attempt to investigate the control of space by public and private authorities. Discursive manifestations of dissent and the arguments posed by social actors are therefore considered in conjunction with the physical impact and material setting within which goals are pursued. The case study used in this article is the workers’ occupation, in 2015, of the Telefónica building, the famous landmark identified in George Orwell's Homage to Catalonia as the epicentre of the internecine struggle that took place within the Republican camp in 1937

Investigating prescriptions for artificial resistivity in smoothed particle magnetohydrodynamics

In numerical simulations, artificial terms are applied to the evolution equations for stability. To prove their validity, these terms are thoroughly tested in test problems where the results are well known. However, they are seldom tested in production-quality simulations at high resolution where they interact with a plethora of physical and numerical algorithms. We test three artificial resistivities in both the Orszag-Tang vortex and in a star formation simulation. From the Orszag-Tang vortex, the Price et. al. (2017) artificial resistivity is the least dissipative thus captures the density and magnetic features; in the star formation algorithm, each artificial resistivity algorithm interacts differently with the sink particle to produce various results, including gas bubbles, dense discs, and migrating sink particles. The star formation simulations suggest that it is important to rely upon physical resistivity rather than artificial resistivity for convergence.Comment: 8 pages, 7 figures. Proceedings of the "12th international SPHERIC workshop", Ourense, Spain, 13-15 June 201

Embodiment and designing learning environments

There is increasing recognition amongst learning sciences researchers of the critical role that the body plays in thinking and reasoning across contexts and across disciplines. This workshop brings ideas of embodied learning and embodied cognition to the design of instructional environments that engage learners in new ways of moving within, and acting upon, the physical world. Using data and artifacts from participants' research and designs as a starting point, this workshop focuses on strategies for how to effectively leverage embodiment in learning activities in both technology and non-technology environments. Methodologies for studying/assessing the body's role in learning are also addressed

Collimated jets from the first core

We have performed Smoothed Particle Magnetohydrodynamics (SPMHD) simulations demonstrating the production of collimated jets during collapse of 1 solar mass molecular cloud cores to form the `first hydrostatic core' in low mass star formation. Recently a number of candidate first core objects have been observed, including L1448 IRS2E, L1451-mm and Per Bolo 58, although it is not yet clear that these are first hydrostatic cores. Recent observations of Per Bolo 58 in particular appear to show collimated, bipolar outflows which are inconsistent with previous theoretical expectations. We show that low mass first cores can indeed produce tightly collimated jets (opening angles <~ 10 degrees) with speeds of ~2-7 km/s, consistent with some of the observed candidates. We have also demonstrated, for the first time, that such phenomena can be successfully captured in SPMHD simulations.Comment: 5 pages, 4 figures, accepted to MNRAS Letters. Movies at http://users.monash.edu.au/~dprice/pubs/jet

Use of remote sensing techniques for geological hazard surveys in vegetated urban regions

The feasibility of using aerial photography for lithologic differentiation in a heavily vegetated region is investigated using multispectral imagery obtained from LANDSAT satellite and aircraft-borne photography. Delineating and mapping of localized vegetal zones can be accomplished by the use of remote sensing because a difference in morphology and physiology results in different natural reflectances or signatures. An investigation was made to show that these local plant zones are affected by altitude, topography, weathering, and gullying; but are controlled by lithology. Therefore, maps outlining local plant zones were used as a basis for lithologic map construction