Machines Can Get the Job Done Faster

The Geneva International Centre for Humanitarian Demining (GICHD) published A Study of Mechanical Application in Demining in June 2004. The study looked at the most suitable roles for machines in demining, examined the potential for machines to be considered a primary clearance tool, explained factors involved in protecting operators and presented a software model to help programme managers understand the cost-effectiveness of their mechanical assets. In 2005, the GICHD plans to release six more sub-studies related to mechanical demining. The following article explains some aspects of the operational tasks where machines are currently employed

Tracing water masses and pollution in the Southern Ocean using neodymium and lead isotopes

Trace elements and their isotopes play a vital role in the ocean as participants in, and tracers of, processes of interest to climate change and environmental pollution. This thesis focuses on the use of isotopic variations in neodymium (Nd) and lead (Pb) to understand the cycling of these elements in the Southern Ocean. Neodymium isotopes have been used as a palaeo-proxy to understand changes in Antarctic Bottom Water (AABW) circulation through time. The biogeochemical processes controlling Nd in seawater, however, remain under-constrained due to a paucity of modern observations in the Southern Ocean. In chapter 2, Nd isotope and rare earth element (REE) data are presented for the Wilkes Land continental margin. In this region, AABW exhibits a distinct εNd signature that is intermediate between Atlantic and Pacific sector AABW. The REE data confirm that the εNd signature is not caused by distinct local continental inputs but by mixing of advected AABW with (modified) Circumpolar Deep Water (CDW). Anthropogenic emissions from mining, smelting and fossil fuel combustion are important sources of oceanic Pb contamination. Seawater Pb isotope data, however, is currently severely limited by analytical challenges such as sample contamination, time-consuming extraction procedures and insufficient instrumental detection limits. In chapter 3, a novel method is presented for the determination of seawater Pb isotope compositions and concentrations. The method encompasses solid-phase extraction of Pb from seawater with Nobias chelate PA-1 resin followed by multi-collector inductively coupled mass spectrometry (MC-ICP-MS) analyses using a 207Pb-204Pb double-spike to correct for instrumental mass discrimination. When compared to an established double-spike procedure that employs thermal ionisation mass spectrometry (TIMS), the results are unbiased by systematic error and demonstrates improved precision for the and the minor 204Pb ratios (by about a factor of 2). In chapter 4, the new method is applied to seawater samples from the Australian sector of the Southern Ocean to assess the sources and processes governing the distribution of Pb in this region. Surface waters exhibit a high fraction of anthropogenic Pb (~30–50%). Reversible scavenging and equilibrium exchange are the dominant processes responsible for the vertical transport of this anthropogenic Pb to deeper waters. These processes may account for ~80% of the observed dissolved Pb isotope in the intermediate depth waters at the Polar Front. Overall, the thesis highlights the essential role that isotope analyses play in deconvolving the processes responsible for the biogeochemical cycling of Nd and Pb in the ocean.Open Acces

PrAGMATiC: a Probabilistic and Generative Model of Areas Tiling the Cortex

Much of the human cortex seems to be organized into topographic cortical maps. Yet few quantitative methods exist for characterizing these maps. To address this issue we developed a modeling framework that can reveal group-level cortical maps based on neuroimaging data. PrAGMATiC, a probabilistic and generative model of areas tiling the cortex, is a hierarchical Bayesian generative model of cortical maps. This model assumes that the cortical map in each individual subject is a sample from a single underlying probability distribution. Learning the parameters of this distribution reveals the properties of a cortical map that are common across a group of subjects while avoiding the potentially lossy step of co-registering each subject into a group anatomical space. In this report we give a mathematical description of PrAGMATiC, describe approximations that make it practical to use, show preliminary results from its application to a real dataset, and describe a number of possible future extensions

Mechanical Application in Demining: Modernising Clearance Methods

Even as mechanical mine clearance systems are increasingly employed throughout the world, the full potential of these machines remains to be seen. Further study of the issue has prompted the Geneva International Center for Humanitarian Demining (GICHD) to release the “Study of Mechanical Application in Mine Action,” due in December 2003

Tax distortions from inflation: What are they? How to deal with them?

Inflation that is fully anticipated has few real effects in purely private market economies, but this need not be the case in the presence of taxation. In practice, tax systems are not neutral with respect to inflation – though some countries have attempted make their tax systems inflation-neutral in the past – and this paper provides a comprehensive overview of the most relevant non-neutralities, drawing on existing literature, but also supplying new illustrations and evidence of the effects. The paper shows, for example, how taxing inflationary gains can have a large impact on effective tax rates – even at relatively low rates of inflation. It also shows how partial coverage of protection against inflation – for some types of incomes only – can create additional distortions. A new empirical analysis reveals how the erosion of the value of depreciation allowances through inflation affects investment

Universality of modulation length (and time) exponents

We study systems with a crossover parameter lambda, such as the temperature T, which has a threshold value lambda* across which the correlation function changes from exhibiting fixed wavelength (or time period) modulations to continuously varying modulation lengths (or times). We report on a new exponent, nuL, characterizing the universal nature of this crossover. These exponents, similar to standard correlation length exponents, are obtained from motion of the poles of the momentum (or frequency) space correlation functions in the complex k-plane (or omega-plane) as the parameter lambda is varied. Near the crossover, the characteristic modulation wave-vector KR on the variable modulation length "phase" is related to that on the fixed modulation length side, q via |KR-q|\propto|T-T*|^{nuL}. We find, in general, that nuL=1/2. In some special instances, nuL may attain other rational values. We extend this result to general problems in which the eigenvalue of an operator or a pole characterizing general response functions may attain a constant real (or imaginary) part beyond a particular threshold value, lambda*. We discuss extensions of this result to multiple other arenas. These include the ANNNI model. By extending our considerations, we comment on relations pertaining not only to the modulation lengths (or times) but also to the standard correlation lengths (or times). We introduce the notion of a Josephson timescale. We comment on the presence of "chaotic" modulations in "soft-spin" and other systems. These relate to glass type features. We discuss applications to Fermi systems - with particular application to metal to band insulator transitions, change of Fermi surface topology, divergent effective masses, Dirac systems, and topological insulators. Both regular periodic and glassy (and spatially chaotic behavior) may be found in strongly correlated electronic systems.Comment: 22 pages, 15 figure

On quantization of singular varieties and applications to D-branes

We calculate the ring of differential operators on some singular affine varieties (intersecting stacks, a point on a singular curve or an orbifold). Our results support the proposed connection of the ring of differential operators with geometry of D-branes in (bosonic) string theory. In particular, the answer does know about the resolution of singularities in accordance with the string theory predictions.Comment: LaTeX2e, 17 pages, misprints correcte