Spin Coherence and 14^{14}N ESEEM Effects of Nitrogen-Vacancy Centers in Diamond with X-band Pulsed ESR

Pulsed ESR experiments are reported for ensembles of negatively-charged nitrogen-vacancy centers (NV$^-$) in diamonds at X-band magnetic fields (280-400 mT) and low temperatures (2-70 K). The NV$^-$ centers in synthetic type IIb diamonds (nitrogen impurity concentration $<1$~ppm) are prepared with bulk concentrations of $2\cdot 10^{13}$ cm$^{-3}$ to $4\cdot 10^{14}$ cm$^{-3}$ by high-energy electron irradiation and subsequent annealing. We find that a proper post-radiation anneal (1000$^\circ$C for 60 mins) is critically important to repair the radiation damage and to recover long electron spin coherence times for NV$^-$s. After the annealing, spin coherence times of T$_2 = 0.74$~ms at 5~K are achieved, being only limited by $^{13}$C nuclear spectral diffusion in natural abundance diamonds. At X-band magnetic fields, strong electron spin echo envelope modulation (ESEEM) is observed originating from the central $^{14}$N nucleus. The ESEEM spectral analysis allows for accurate determination of the $^{14}$N nuclear hypefine and quadrupole tensors. In addition, the ESEEM effects from two proximal $^{13}$C sites (second-nearest neighbor and fourth-nearest neighbor) are resolved and the respective $^{13}$C hyperfine coupling constants are extracted.Comment: 10 pages, 5 figure

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

Opening access to administrative data for evaluating public services: the case of the Justice Data Lab

As government administrative data sets are increasingly made available for new (non-administrative) purposes, there is a need to improve access to such resources for voluntary and community organizations, social enterprises and private businesses for statistical analysis and evaluation purposes. The Justice Data Lab set up by the Ministry of Justice in the UK presents an innovative case of how administrative data can be linked to other data held by organizations delivering public services. The establishment of a unit within a secure setting holding evaluation and statistical expertise has enabled providers of programmes aimed at reducing re-offending to obtain evidence on how the impact of their interventions differs from that of a matched comparison group. This article explores the development of the Justice Data Lab, the methodological and other challenges faced, and the experiences of user organizations. The article draws out implications for future development of Data Labs and the use of administrative data for the evaluation of public services

Interplay of structure and spin-orbit strength in magnetism of metal-benzene sandwiches: from single molecules to infinite wires

Based on first-principles density functional theory calculations we explore electronic and magnetic properties of experimentally producible sandwiches and infinite wires made of repeating benzene molecules and transition-metal atoms of V, Nb, and Ta. We describe the bonding mechanism in the molecules and in particular concentrate on the origin of magnetism in these structures. We find that all the considered systems have sizable magnetic moments and ferromagnetic spin-ordering, with the single exception of the V3-Bz4 molecule. By including the spin-orbit coupling into our calculations we determine the easy and hard axes of the magnetic moment, the strength of the uniaxial magnetic anisotropy energy (MAE), relevant for the thermal stability of magnetic orientation, and the change of the electronic structure with respect to the direction of the magnetic moment, important for spin-transport properties. While for the V-based compounds the values of the MAE are only of the order of 0.05-0.5 meV per metal atom, increasing the spin-orbit strength by substituting V with heavier Nb and Ta allows to achieve an increase in anisotropy values by one to two orders of magnitude. The rigid stability of magnetism in these compounds together with the strong ferromagnetic ordering makes them attractive candidates for spin-polarized transport applications. For a Nb-benzene infinite wire the occurrence of ballistic anisotropic magnetoresistance is demonstrated.Comment: 23 pages, 8 figure

Siting Transmission Lines in a Changed Milieu: Evolving Notions of the "Public Interest" In Balancing State and Regional Considerations

This Article discusses how state public utility law presents a barrier to the siting of new high voltage transmission lines to serve renewable resources, and how states could approach its evolution in order to preserve a role for state regulators in a new energy economy in which renewable energy will play a significant role. The traditional approach to determining the "public interest" in siting transmission lines is well on its way to obsolescence. Two developments over the past fifteen years have begun to challenge this paradigm. First, policies at the federal level and in many states have encouraged increased competition in generation, contributing to de-monopolization of the bulk power side of the industry. Second, the increased emphasis on environmental, energy independence, and other public policy objectives, has resulted in a dramatically increased demand for renewable energy, particularly given heightened attention to climate change. Given that wind power -- the most economically viable renewable resource on a bulk power basis -- is feasible predominantly in locations far removed from, load centers, the demand for new multistate transmission facilities has been brought clearly into focus. After an introduction in Part I, Part II describes the existing arrangements in several resource rich Western states for siting new transmission lines, and the coexistence of those arrangements with a conventional understanding of the public interest in determining need and addressing environmental concerns under traditional state transmission siting laws. Part III discusses transmission issues related to the competitive wholesale market and increased attention to climate change and highlights how federal law has expanded to accommodate some of these concerns. Part IV emphasizes the need for a new definition of the public interest which might better reflect these new market circumstances and opportunities, and highlights the two main barriers to this: 1) legislative and/or regulatory inertia and 2) an outdated cost-allocation model. The public interest under most state siting statutes is sufficiently capacious to give regulators some flexibility to evolve, but in other instances legislative action may be needed. In addition, the state cost-of-service ratemaking model must evolve to a more regional approach to allocating the costs of new transmission

Stark shift and field ionization of arsenic donors in 28^{28}Si-SOI structures

We develop an efficient back gate for silicon-on-insulator (SOI) devices operating at cryogenic temperatures, and measure the quadratic hyperfine Stark shift parameter of arsenic donors in isotopically purified $^{28}$Si-SOI layers using such structures. The back gate is implemented using MeV ion implantation through the SOI layer forming a metallic electrode in the handle wafer, enabling large and uniform electric fields up to $\sim$ 2 V/$\mu$m to be applied across the SOI layer. Utilizing this structure we measure the Stark shift parameters of arsenic donors embedded in the $^{28}$Si SOI layer and find a contact hyperfine Stark parameter of $\eta_a=-1.9\pm0.2\times10^{-3} \mu$m$^2$/V$^2$. We also demonstrate electric-field driven dopant ionization in the SOI device layer, measured by electron spin resonance.Comment: 5 pages, 3 figure

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

Time-resolved impulse response of the magnetoplasmon resonance in a two-dimensional electron gas

We have used optically excited ultrashort electrical pulses to measure the magnetoplasmon resonance of a two-dimensional electron gas formed in an AlGaAs/GaAs heterostructure at frequencies up to 200 gigahertz. This is accomplished by incorporating the sample into a guided wave probe operating in a pumped (^{3}He) system. We are able to detect the resonance by launching a stimulus pulse in the guide, and monitoring the system response in a time resolved pump-probe arrangement. Data obtained from measurements yield resonant frequencies that agree with the magnetoplasmon dispersion relation.Comment: 4 pages, 4 figure