A Flexible Design Space Exploration Platform for Wireless Sensor Networks

My dissertation presents a flexible design space exploration platform for wireless sensor networks and an extensible design flow. The conceived platform enables the fast creation and evaluation of custom sensor node hard- and software architectures without developing custom hardware. One important feature of my platform is that it allows the evaluation of the computational- and communication domain of a sensor node in respect to power consumption

Reconstruction of ice-sheet changes in the Antarctic Peninsula since the Last Glacial Maximum

This paper compiles and reviews marine and terrestrial data constraining the dimensions and configuration of the Antarctic Peninsula Ice Sheet (APIS) from the Last Glacial Maximum (LGM) through deglaciation to the present day. These data are used to reconstruct grounding-line retreat in 5ka time-steps from 25kaBP to present. Glacial landforms and subglacial tills on the eastern and western Antarctic Peninsula (AP) shelf indicate that the APIS was grounded to the outer shelf/shelf edge at the LGM and contained a series of fast-flowing ice streams that drained along cross-shelf bathymetric troughs. The ice sheet was grounded at the shelf edge until ~20calkaBP. Chronological control on retreat is provided by radiocarbon dates on glacimarine sediments from the shelf troughs and on lacustrine and terrestrial organic remains, as well as cosmogenic nuclide dates on erratics and ice moulded bedrock. Retreat in the east was underway by about 18calkaBP. The earliest dates on recession in the west are from Bransfield Basin where recession was underway by 17.5calkaBP. Ice streams were active during deglaciation at least until the ice sheet had pulled back to the mid-shelf. The timing of initial retreat decreased progressively southwards along the western AP shelf; the large ice stream in Marguerite Trough may have remained grounded at the shelf edge until about 14calkaBP, although terrestrial cosmogenic nuclide ages indicate that thinning had commenced by 18kaBP. Between 15 and 10calkaBP the APIS underwent significant recession along the western AP margin, although retreat between individual troughs was asynchronous. Ice in Marguerite Trough may have still been grounded on the mid-shelf at 10calkaBP. In the Larsen-A region the transition from grounded to floating ice was established by 10.7-10.6calkaBP. The APIS had retreated towards its present configuration in the western AP by the mid-Holocene but on the eastern peninsula may have approached its present configuration several thousand years earlier, by the start of the Holocene. Mid to late-Holocene retreat was diachronous with stillstands, re-advances and changes in ice-shelf configuration being recorded in most places. Subglacial topography exerted a major control on grounding-line retreat with grounding-zone wedges, and thus by inference slow-downs or stillstands in the retreat of the grounding line, occurring in some cases on reverse bed slopes

The Space Infrared Interferometric Telescope (SPIRIT): High-resolution imaging and spectroscopy in the far-infrared

We report results of a recently-completed pre-Formulation Phase study of SPIRIT, a candidate NASA Origins Probe mission. SPIRIT is a spatial and spectral interferometer with an operating wavelength range 25 - 400 microns. SPIRIT will provide sub-arcsecond resolution images and spectra with resolution R = 3000 in a 1 arcmin field of view to accomplish three primary scientific objectives: (1) Learn how planetary systems form from protostellar disks, and how they acquire their inhomogeneous composition; (2) characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets of different types form; and (3) learn how high-redshift galaxies formed and merged to form the present-day population of galaxies. Observations with SPIRIT will be complementary to those of the James Webb Space Telescope and the ground-based Atacama Large Millimeter Array. All three observatories could be operational contemporaneously.Comment: 20 pages, 12 figures, accepted for publication in J. Adv. Space Res. on 26 May 200

A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20ka, 15ka, 10ka and 5ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorit. © 2014 The Authors

Modelling Nanoplasmonic Device Based on an Off-shelf Hybrid Desktop Supercomputing Platform

Designing nanoplasmonic devices presents a number of unique challenges. The time domain modelling and simulation of electromagnetic (EM) wave interaction with nanoplasmonic devices, at high spatial and time resolution, requires high computational power. Recent advances in commodity hardware technologies, particularly multi-core CPU, field-programmable gate arrays (FPGAs) and graphic processing units (GPUs) have allowed the creation of desktop-style devices to be powerful and capable high performance computers systems. In this paper, we propose an OpenCL framework with the support of modelling and simulation of nanoplamonic devices and demonstrate the key programming skills required to design customised high-speed hardware resources

Testing the Extent and Timing of Past Glaciations Offshore of the Sub-Antarctic Island of South Georgia

There has been a long history of debate over the extent and timing of past glaciations on the small but climatically-sensitive islands of the sub-Antarctic. The largest of these islands, South Georgia, has been the focus of contention with two conflicting models proposed for the peak of the last glaciation (the Last Glacial Maximum, c. 21 k yrs B.P.): one suggesting an ice cap of restricted extent that saw tidewater outlets limited to the coastal basins of radial fjords; the other proposing an extensive shelf-wide ice cap based on well-preserved though as yet un-dated or un-sampled sea-bed geomorphology. It has been suggested that these two models form comparative end-members of 'South American‘ (restricted) and 'Antarctic‘ (extensive) modes of glaciation, and thus establishing whether the pattern of glaciation on sub- Antarctic islands follows one of these modes, or is in itself entirely different, can provide potentially important insight into past climate forcing of an otherwise poorly-constrained Southern Ocean region. The extent of island glaciation can also provide valuable far-field constraint for Antarctic ice sheet models, and forms vital information for biologists seeking to understand benthic marine communities around South Georgia, whose evolution and structure are intimately linked to the long-term history of ice advance and retreat. Here we investigate the geological record offshore of South Georgia to improve understanding of the extent and timing of past glaciation. Marine geophysical data from new and previous research cruises have been compiled and analysed to advance knowledge of palaeo-ice cap dynamics on the island‘s submerged sea bed and subsurface. We have also sought an independent verification of the glacial history of the island by linking new geomorphological analyses with dated marine sedimentary records recovered by coring, for the first time, on the continental shelf. We present results of new landform mapping on the sea-bed of the South Georgia block. Mapped moraine belts demarcate a minimum of three shelf limits of former glaciation: (1) a shelf edge maximum, (2) an outer basin/fjord mouth limit, and (3) an inner basin moraine position. In addition, numerous spatially-discontinuous moraines must represent further intermediary ice-marginal extents. Geomorphological observations are consistent with the larger configurations of the palaeo-ice cap being highly dynamic, reflected in the pattern, geometry, and sedimentary sequences of cross-shelf glacial troughs, extensive depositional moraine systems, subglacially-generated bedforms, and meltwater-carved channels mapped from multibeam bathymetric survey and sub-bottom echo-sounder data. Reconstructed limits suggest a complex offshore glacial history, and provide hitherto unrivalled insight into the spatial configurations of past sub-Antarctic ice caps. A key question is whether the most prominent moraines were formed during successive Cenozoic glaciations or during retreat and readvance(s) since the last glaciation. We present preliminary chronological investigations of marine gravity cores from the Cumberland Bay and Royal Bay areas of the north-eastern shelf that provide tests of the restricted vs extensive ice-cap hypotheses. We show additional sedimentological and physical properties data from the suite of sediment cores that give insight into fjord and shelf depositional environments, patterns of Holocene glacier behaviour, and contribute more broadly towards a better characterisation of South Georgia‘s long-term marine environmental history

Exploring biological constraints on the glacial history of Antarctica

The evolutionary and biogeographic history of the contemporary Antarctic terrestrial and marine biotas reveals many components of ancient origin. For large elements of the terrestrial biota, long-term isolation over timescales from hundreds of thousands to tens of millions of years, and thus persistence through multiple glacial cycles, now appears to be the norm rather than the exception. For the marine biota there are some parallels with benthic communities also including ancient components, together with an incidence of species-level endemism indicating long-term isolation on the Antarctic continental shelf Although it has long been known that a few ice-free terrestrial locations have existed in Antarctica for up to 10-12 million years, particularly in the Dry Valleys of Victoria Land along with certain nunataks and higher regions of large mountain ranges, these do not provide potential refugia for the majority of terrestrial biota, which occur mainly in coastal and/or low-lying locations and exhibit considerable biogeographic regionalisation within the continent. Current glacial models and reconstructions do not have the spatial resolution to detect unequivocally either the number or geographical distribution of these glacial refugia, or areas of the continental shelf that have remained periodically free from ice scouring, but do provide limits for their maximum spatial extent. Recent work on the evolution of the terrestrial biota indicates that refugia were much more widespread than has been recognised and it is now clear that terrestrial biology provides novel constraints for reconstructing the past glacial history of Antarctica, and new marine biological investigations of the Antarctic shelf are starting to do likewise. (C) 2009 Elsevier Ltd. All rights reserved

Major Advance of South Georgia Glaciers during the Antarctic Cold Reversal Following Extensive Sub-Antarctic Glaciation

The history of glaciations on Southern Hemisphere sub-polar islands is unclear. Debate surrounds the extent and timing of the last glacial advance and termination on sub-Antarctic South Georgia in particular. Here, using sea-floor geophysical data and marine sediment cores, we resolve the record of glaciation offshore of South Georgia through the transition from the Last Glacial Maximum to Holocene. We show a sea-bed landform imprint of a shelf-wide last glacial advance and progressive deglaciation. Renewed glacier resurgence in the fjords between c. 15,170 and 13,340 yr ago coincided with a period of cooler, wetter climate known as the Antarctic Cold Reversal, revealing a cryospheric response to an Antarctic climate pattern extending into the Atlantic sector of the Southern Ocean. We conclude that the last glaciation of South Georgia was extensive, and the sensitivity of its glaciers to climate variability during the last termination more significant than implied by previous studies. The glaciated history of South Georgia is debated, with many suggesting a coastal limit to the island’s ice cap during the last glaciation. Here, the authors show extensive ice-cap cover of the continental block during this time and a readvance of glaciers to fjord mouths during the Antarctic Cold Reversal

New Data Constraints on Past Antarctic Ice Sheet Extent and Retreat in the Weddell Sea Embayment

The glacial history of the Antarctic Ice Sheet in the Weddell Sea embayment during the Last Glacial Maximum (LGM; 23-19 ka) is a matter of debate. Existing onshore and offshore data suggest two alternative reconstructions for the LGM ice sheet extent. One scenario shows an ice sheet grounding line that had advanced to (or at least close to) the shelf edge throughout the Weddell Sea, embayment. The other reconstruction concludes that the grounding line in the two main cross shelf troughs was located only slightly farther offshore than today. Here we present new data from multibeam swath bathymetry surveys, acoustic sub-bottom profiles and sediment cores collected during recent and past British and German marine expeditions. These data provide new constraints on the glacial history of the eastern part of the Weddell Sea embayment. A previously unknown, stacked grounding zone wedge discovered in the outer shelf part of Filchner Trough possibly marks the northernmost position of the LGM grounding line within this palaeo-ice stream trough. Crescentic moraines and a predominantly smooth seabed morphology mapped north of the Brunt Ice Shelf reveal a complex glacial history with repeated advances of grounded ice or episodic retreats, controlled by a hard seafloor substrate. We will compare new radiocarbon dates obtained from the sediment cores to existing chronologies and use them to reconstruct the timing of the last maximum ice sheet advance and post-LGM retreat. Finally, we will set our new findings into context with results from ice sheet models and discuss their implications for Antarctica's contribution to global meltwater pulses during the last deglaciation