Market institutions and urban food supply in West and Southern Africa: a review

As the urban share of Africa‟s population increases, the importance of understanding how food supply is shaped by market institutions has grown. However, this topic has received little attention from policy makers and researchers despite the implications of market institutions and regulatory systems for livelihoods and poverty. This paper reviews the existing literature on market intermediaries, access to selling spaces, finance for traders and sources of information on prices and supplies. The gaps in research are identified and a set of key research issues in this crucial, yet under-researched, area are articulated

Improving market institutions and urban food supplies for the urban poor: a comparative study of Nigeria and Zambia.

This study examines the systems which govern the marketing opportunities for informal urban and peri-urban cultivators, and for rural producers, in our two study countries, Nigeria and Zambia and it explores the mechanisms of marketing food in urban areas. Our literature review illustrates how little is known about how these formal and informal regulatory systems currently operate. For example, the positive contribution of both urban-based and rural-based traders in providing an essential service to urban consumers has not been adequately analysed

Oxygen isotopes implanted in the LDEF spacecraft

Secondary ion mass spectrometry was used to study oxygen implanted in the surface of copper from the Long Duration Exposure Facility (LDEF). Oxidation that occurred in orbit shows a characteristic oxygen isotope composition, depleted in O-18. The measured depletion is comparable to the predicted depletion (45 percent) based on a model of the gravitational separation of the oxygen isotopes. The anomalous oxygen was contained within 10nm of the surface. Tray E10 was calculated to have received 5.14 x 10(exp 21) atoms of oxygen cm(sup -2) during the LDEF mission and so there is sufficient anomalous implanted oxygen present in the surface to obtain a reliable isotopic profile

Electron spin relaxation of N@C60 in CS2

We examine the temperature dependence of the relaxation times of the molecules N@C60 and N@C70 (which comprise atomic nitrogen trapped within a carbon cage) in liquid CS2 solution. The results are inconsistent with the fluctuating zero field splitting (ZFS) mechanism, which is commonly invoked to explain electron spin relaxation for S > 1/2 spins in liquid solution, and is the mechanism postulated in the literature for these systems. Instead, we find a clear Arrhenius temperature dependence for N@C60, indicating the spin relaxation is driven primarily by an Orbach process. For the asymmetric N@C70 molecule, which has a permanent non-zero ZFS, we resolve an additional relaxation mechanism caused by the rapid reorientation of its ZFS. We also report the longest coherence time (T2) ever observed for a molecular electron spin, being 0.25 ms at 170K.Comment: 6 pages, 6 figures V2: Updated to published versio

A low power photoemission source for electrons on liquid helium

Electrons on the surface of liquid helium are a widely studied system that may also provide a promising method to implement a quantum computer. One experimental challenge in these studies is to generate electrons on the helium surface in a reliable manner without heating the cryo-system. An electron source relying on photoemission from a zinc film has been previously described using a high power continuous light source that heated the low temperature system. This work has been reproduced more compactly by using a low power pulsed lamp that avoids any heating. About 5e3 electrons are collected on 1 cm^2 of helium surface for every pulse of light. A time-resolved experiment suggests that electrons are either emitted over or tunnel through the 1eV barrier formed by the thin superfluid helium film on the zinc surface. No evidence of trapping or bubble formation is seen.Comment: 9 pages, 3 figures, submitted to J. Low Temp. Phy

Environmental effects on electron spin relaxation in N@C60

We examine environmental effects of surrounding nuclear spins on the electron spin relaxation of the N@C60 molecule (which consists of a nitrogen atom at the centre of a fullerene cage). Using dilute solutions of N@C60 in regular and deuterated toluene, we observe and model the effect of translational diffusion of nuclear spins of the solvent molecules on the N@C60 electron spin relaxation times. We also study spin relaxation in frozen solutions of N@C60 in CS2, to which small quantities of a glassing agent, S2Cl2 are added. At low temperatures, spin relaxation is caused by spectral diffusion of surrounding nuclear 35Cl and 37Cl spins in the S2Cl2, but nevertheless, at 20 K, T2 times as long as 0.23 ms are observed.Comment: 7 pages, 6 figure

Coherence of Spin Qubits in Silicon

Given the effectiveness of semiconductor devices for classical computation one is naturally led to consider semiconductor systems for solid state quantum information processing. Semiconductors are particularly suitable where local control of electric fields and charge transport are required. Conventional semiconductor electronics is built upon these capabilities and has demonstrated scaling to large complicated arrays of interconnected devices. However, the requirements for a quantum computer are very different from those for classical computation, and it is not immediately obvious how best to build one in a semiconductor. One possible approach is to use spins as qubits: of nuclei, of electrons, or both in combination. Long qubit coherence times are a prerequisite for quantum computing, and in this paper we will discuss measurements of spin coherence in silicon. The results are encouraging - both electrons bound to donors and the donor nuclei exhibit low decoherence under the right circumstances. Doped silicon thus appears to pass the first test on the road to a quantum computer.Comment: Submitted to J Cond Matter on Nov 15th, 200

An Iterative and Toolchain-Based Approach to Automate Scanning and Mapping Computer Networks

As today's organizational computer networks are ever evolving and becoming more and more complex, finding potential vulnerabilities and conducting security audits has become a crucial element in securing these networks. The first step in auditing a network is reconnaissance by mapping it to get a comprehensive overview over its structure. The growing complexity, however, makes this task increasingly effortful, even more as mapping (instead of plain scanning), presently, still involves a lot of manual work. Therefore, the concept proposed in this paper automates the scanning and mapping of unknown and non-cooperative computer networks in order to find security weaknesses or verify access controls. It further helps to conduct audits by allowing comparing documented with actual networks and finding unauthorized network devices, as well as evaluating access control methods by conducting delta scans. It uses a novel approach of augmenting data from iteratively chained existing scanning tools with context, using genuine analytics modules to allow assessing a network's topology instead of just generating a list of scanned devices. It further contains a visualization model that provides a clear, lucid topology map and a special graph for comparative analysis. The goal is to provide maximum insight with a minimum of a priori knowledge.Comment: 7 pages, 6 figure

Young Lives and Imagined Futures: Insights from Archived Data

On 15th November 2010, Timescapes and the UK Data Archive (UKDA) hosted a seminar ‘Young Lives and Imagined Futures: Analysing and Re-Analysing Narrative Data on Young Lives.’ The seminar investigated data on young people’s orientationto their future lives. In addition to engaging with time and young lives, the seminar also explored methodologies for primary and secondary analysis of historical and contemporary datasets. In this working paper we bring together two papers from this event: Graham Crow and Dawn Lyon’s ‘Turning points in work and family life in the imagined futures of young people on Sheppey in 1978’ and Mandy Winterton and Sarah Irwin’s ‘Youngsters’ expectations and context: secondary analysis and interpretation’. These papers are significant together because they both draw on secondary analysis projects, constructing new insight from archived data collected by others and for other purposes. These two papers draw heavily on similar kinds of data to explore young people’s lives and imagined futures, although in very different ways. Yet it is worth noting that they were never pre-designed to sit so readily side by side. There was no discussion between the authors at any point. It was entirely fortuitous that they offered, by the extent of their similarities and difference, stimulating insight about the possibilities of qualitative secondary analysis when placed side by side. Before introducing these two papers, we provide some insight into the context of the day. We can only map below the nature and diversity of the research that was presented and cannot do justice here to the complexity and richness of the research that was offered