Testing hypotheses of the cause of peripheral thinning of the Greenland Ice Sheet: is land-terminating ice thinning at anomalously high rates?

Recent observations have shown that the periphery of the Greenland ice sheet (GrIS) is thinning rapidly and that this thinning is greatest around marine-terminating outlet glaciers. Several theories have been proposed which provide a link between climate and ice thinning. We present surface elevation change (<i>dh/dt</i>) data from NASA's Program for Arctic Regional Climate Assessment (PARCA) laser altimetry surveys for fourteen and eleven of the largest outlet glaciers in Southern Greenland from 1993 to 1998 and 1998 to 2006 respectively to test the applicability of these theories to the GrIS. <br><br> Initially, outlet glacier <i>dh/dt</i> data are compared with data from concurrent surveys over inland ice (slow flowing ice that is not obviously draining into an outlet glacier) to confirm the effect of ice flow on surface thinning rates. Land-terminating and marine-terminating outlet glacier <i>dh/dt</i> data are then compared from 1993 to 1998 and from 1998 to 2006. Finally, ablation anomalies (the difference between the "normal" ablation rate from 1970 to 2000 and the ablation rate in the time period of interest) calculated with a positive degree day model are compared to both marine-terminating and land-terminating outlet glacier <i>dh/dt</i> data. <br><br> Our results support earlier conclusions that certain marine-terminating outlet glaciers have thinned much more than land-terminating outlet glaciers during both time periods. Furthermore we show that these differences are not limited to the largest, fastest-flowing outlet glaciers – almost all marine-terminating outlet glaciers are thinning more than land-terminating outlet glaciers. There was a four fold increase in mean marine-terminating outlet glacier thinning rates below 1000 m elevation between the periods 1993 to 1998 and 1998 to 2006, while thinning rates of land-terminating outlet glaciers remained statistically unchanged. This suggests that a change in a controlling mechanism specific to the thinning rates of marine-terminating outlet glaciers occurred in the late 1990s and that this change did not affect thinning rates of land-terminating outlet glaciers. <br><br> Thinning rates of land-terminating outlet glaciers are statistically the same as ablation anomalies, while thinning rates of marine-terminating outlet glaciers are not. Thinning of land-terminating outlet glaciers therefore seems to be a response to changes in local mass balance (principally increases in air temperature) while thinning of marine-terminating outlet glaciers is principally controlled by ice dynamics. The mechanism by which this dynamic thinning occurs is still not clear although its association with marine-terminating outlet glaciers suggests perturbations at marine termini (calving) as the likely cause

Fabrication and evaluation of advanced titanium and composite structural panels

Advanced manufacturing methods for titanium and composite material structures are being developed and evaluated. The focus for the manufacturing effort is the fabrication of full-scale structural panels which replace an existing shear panel on the upper wing surface of the NASA YF-12 aircraft. The program involves design, fabrication, ground testing, and Mach 3 flight service of full-scale structural panels and laboratory testing of representative structural element specimens

Numerical investigation into the influence of cubicle positioning in large-scale explosive arena trials

In arena blast testing, a common and economical practice employed is to distribute several targets radially around a central charge. However, if these targets are positioned too proximally, reflections and diffractions of blast waves off neighbouring cubicles can affect the nature of expected blast loading. Computational fluid dynamics software has been used through an extensive series of simulations to identify the levels of interference in incident pressure–time histories with and without an obstructing target present. The data were post-processed to identify the Cartesian co-ordinates in which different levels of interference in peak incident overpressure and incident positive phase impulse were achieved. The results indicated that in all cases, there was a greater interference in peak incident overpressure than incident positive phase impulse values directly proximal to the target but, at greater separations, significant differences in incident positive phase impulse existed where peak incident overpressure had returned to free-field equivalent magnitudes. When compared with the established ‘rules of thumb’ for cubicle placement, for targets at different stand-off ranges, an angle of 45° to the rear cubicle still holds some practical relevance, although it is too acute to cover all interference effects. For targets positioned at the same stand-off range, a separation distance of two cubicle widths is generally too conservative and, in many cases, more cubicles can be positioned around the charge. A bespoke recommendation table has been presented for targets at stand-off ranges between 15 and 50 m to allow users to identify the minimum distance from a target at which obstructed-field peak incident overpressure and incident positive phase impulse values differ negligibly from free-field equivalents

Recommendations for cubicle separation in large-scale explosive arena trials

In large-scale arena blast testing, a common and economical practice undertaken is to position several cubicle targets radially around a central charge. To gain maximal benefit from this, targets should be positioned at their minimum permissible separation at which no blast wave interference is sustained from neighbouring obstructions. This interference typically occurs either when targets positioned at the same stand-off range are too close creating an amplification effect where a superposition forms between the incident blast wave and the reflected wave off the cubicle, or, where a target is positioned in the region behind another target, which causes a shadowing effect with decreased magnitudes of pressure and impulse. A comprehensive computational modelling study was undertaken using the hydrocode Air3D to examine the influence of cubicle positioning at different ranges on the surrounding blast wave pressure-time fields. A systematic series of simulations were conducted to show the differences in incident peak overpressure and positive phase impulse between free-field and obstructed-field simulation configurations. The predictions from the modelling study indicated that the presence of cubicle target obstructions resulted in differences in peak incident overpressure and positive phase impulse in nearby pressure waves. In all cases, at close separation distances, there were greater differences in peak pressure than positive phase impulse. However, with increased separation, peak pressure returned to free-field conditions sooner whilst differences in impulse remained significant, thus governing separation distance recommendations. The simulations showed that, for targets at the same stand-off range, clear separations of between 3.88 m and 6.92 m were required to achieve free-field equivalency, depending on the distance from the charge to the target. For targets at different stand-off ranges an angle greater than 54.2° from the front corner of the cubicle has been shown to ensure free-field equivalent conditions. A bespoke recommendation table has been generated to provide precise positioning for cubicles at different stand-off ranges in a look-up matrix format that can be readily used by engineers in the field

General implementation of all possible positive-operator-value measurements of single photon polarization states

Positive Operator Value Measures (POVMs) are the most general class of quantum measurements. We propose a setup in which all possible POVMs of a single photon polarization state (corresponding to all possible sets of two-dimensional Kraus operators) can be implemented easily using linear optics elements. This method makes it possible to experimentally realize any projective orthogonal, projective non-orthogonal or non-projective sets of any number of POVM operators. Furthermore our implementation only requires vacuum ancillas, and is deterministic rather than probabilistic. Thus it realizes every POVM with the correct set of output states. We give the settings required to implement two different well-known non-orthogonal projective POVMs.Comment: 5 pages, newer version with minor addition

Smartphone Based E-Learning

Children often attend schools intermittently in rural areas in Africa and India due to socio-economic conditions which make pupils augment their family income by working. An e-Learning solution could aid in raising the level of education by making it easier for children to fit schoolwork into the day, acting as a complement to when they are able to attend school. Traditional distance learning solutions based on computers are not suitable due to lack of infrastructure support. In this paper, we evaluate both text and voice based smartphone prototype environments which could provide the tools and services for pupils to download educational content, interact with teachers as well as other pupils to discuss topics. These have been implemented as a proof-of- concept and the initial evaluation feedback, although not from target users, was very promising. We intend to re-implement the prototype and do a proper evaluation with rural-area school children.Accepted versio