Using adiabatic coupling techniques in atom-chip waveguide structures

Adiabatic techniques are well known tools in multi-level electron systems to transfer population between different states with high fidelity. Recently it has been realised that these ideas can also be used in ultra-cold atom systems to achieve coherent manipulation of the atomic centre-of-mass states. Here we present an investigation into a realistic setup using three atomic waveguides created on top of an atom chip and show that such systems hold large potential for the observation of adiabatic phenomena in experiments.Comment: 10 pages, 6 figures, accepted for publication in Physica Scripta for the CEWQO2009 proceeding

Persistent topographic development along a strike-slip fault system: The Mount McKinley restraining bend

The Denali Fault is a major strike-slip fault extending from British Colombia, into western Alaska. Mount McKinley, at 6,114 m, is the highest peak in North America and is located to the south of a bend in the Denali Fault (Fig.1). To the north, at the apex of the bend in the fault, Peters Dome (3,221 m) is the highest peak and north-side peak elevations rapidly decrease moving away from the bend’s apex

The transport of cosmic rays in self-excited magnetic turbulence

The process of diffusive shock acceleration relies on the efficacy with which hydromagnetic waves can scatter charged particles in the precursor of a shock. The growth of self-generated waves is driven by both resonant and non-resonant processes. We perform high-resolution magnetohydrodynamic simulations of the non-resonant cosmic-ray driven instability, in which the unstable waves are excited beyond the linear regime. In a snapshot of the resultant field, particle transport simulations are carried out. The use of a static snapshot of the field is reasonable given that the Larmor period for particles is typically very short relative to the instability growth time. The diffusion rate is found to be close to, or below, the Bohm limit for a range of energies. This provides the first explicit demonstration that self-excited turbulence reduces the diffusion coefficient and has important implications for cosmic ray transport and acceleration in supernova remnants.Comment: 8 pages, 8 figures, accepted for publication in MNRA

A direct comparison of 2D versus 3D diffusion analysis at nanowire electrodes: A finite element analysis and experimental study

In electroanalysis, the benefits accrued by miniaturisation are a key driver in sensor development. Finite element simulations of electrochemical processes occurring at ultramicro- and nano-electrodes are used to provide key insight into experimental design in relation to diffusion profiles and expected currents. The most commonly used method, the diffusion domain approach (DDA) offers a means of reducing a three dimensional design to two dimensions to ease computational demands. However, the DDA approach can be limited when using basic assumptions which can be incorrect, for example that all electrodes in an array are equivalent. Consequently, to get a more realistic view of molecular diffusion to nanoelectrodes, it is necessary to undertake simulations in 3D. In this work, two and three dimensional models of electrodes comprising of (i) single nanowires, (ii) arrays of nanowires and (iii) interdigitated arrays of nanowires operating in generator-collector mode, were undertaken and compared to experimental results obtained from fabricated devices. The 3D simulations predicted a higher extracted current for a single nanowires and diffusionally independent nanowire arrays when compared to 2D simulations since, unlike the 2D model, they take into account molecular diffusion to and from nanowire termini. These current differences were observed to increase with increasing electrode width and decrease with electrode length. When the nanowire arrays were diffusionally overlapped, they behaved as an electrode of larger width, and the divergence between both models increased further. By contrast, using interdigitated nanowire arrays in generator-collector mode, the differences between extracted current values obtained using the 2D and 3D models were significantly lower. Simulations indicated however, that a higher collection efficiency was predicted by the 2D model when compared to the 3D model. Electrochemical experiments were undertaken to confirm the simulation study and demonstrated that the extracted currents from 3D simulations more closely mapped onto experimentally measured currents

Observed Faraday Effects in Damped Lyman-Alpha Absorbers and Lyman Limit Systems: The Magnetised Environment of Galactic Building Blocks at Redshift=2

Protogalactic environments are typically identified using quasar absorption lines, and these galactic building blocks can manifest as Damped Lyman-Alpha Absorbers (DLAs) and Lyman Limit Systems (LLSs). We use radio observations of Faraday effects to test whether DLAs and LLSs host a magnetised medium, by combining DLA and LLS detections throughout the literature with 1.4 GHz polarization data from the NRAO VLA Sky Survey (NVSS). We obtain a control, a DLA, and a LLS sample consisting of 114, 19, and 27 lines-of-sight respectively - all of which are polarized at $\ge8\sigma$ to ensure Rician bias is negligible. Using a Bayesian framework, we are unable to detect either coherent or random magnetic fields in DLAs: the regular coherent magnetic fields within the DLAs must be $\le2.8$ $\mu$G, and the lack of depolarization is consistent with the weakly magnetised gas in DLAs being non-turbulent and quiescent. However, we find mild suggestive evidence that LLSs have coherent magnetic fields: after controlling for the redshift-distribution of our data, we find a 71.5% probability that LLSs have a higher RM than a control sample. We also find strong evidence that LLSs host random magnetic fields, with a 95.5% probability that LLS lines-of-sight have lower polarized fractions than a control sample. The regular coherent magnetic fields within the LLSs must be $\le2.4$ $\mu$G, and the magnetised gas must be highly turbulent with a typical scale on the order of $\approx5$-20 pc, which is similar to that of the Milky Way. This is consistent with the standard dynamo pedagogy, whereby magnetic fields in protogalaxies increase in coherence and strength as a function of cosmic time. Our results are consistent with a hierarchical galaxy formation scenario, with the DLAs, LLSs, and strong magnesium II (MgII) systems exploring three different stages of magnetic field evolution in galaxies.Comment: Submitted to Ap

Decision Support Systems For Disease Control in Winter Wheat.

End of Project ReportA leaf diagnostic test and a computer-based decision support system were evaluated for the control of diseases of winter wheat caused by Septoria spp. Fungicide programmes, as dictated by both methods, were compared with a standard routine programme, a reduced-rate programme and an unsprayed control from 1998 to 2000. In some instances fungicide programmes, dictated by leaf diagnostic tests, resulted in lower disease and higher yields than routine programmes but these were not consistent. Fungicide programmes, based on the computer-based decision support system, offered no advantages over routine programmes in terms of lower levels of disease, reduced numbers of fungicide applications or increased yields. Reduced-rate programmes, based on more frequent applications of low rates of fungicides, resulted in substantial savings of fungicides and in 1999 and 2000 better disease control and higher yields than routine programmes

Antigen-specific suppression of inflammatory arthritis by dendritic cells

Purpose Antigen-specific suppression of a previously primed immune response is a major challenge for immunotherapy of autoimmune disease. We have shown that NF-κB inactivation in dendritic cells (modified DC) converts them into cells that tolerize rather than immunize to specific antigen [1]. Antigen-exposed modified DC prevent priming of immunity, and they suppress previously primed immune responses. Regulatory CD4+ T cells, which can transfer antigen-specific tolerance in an IL-10-dependent fashion, mediate the tolerance. We hypothesized that modified DC exposed to arthritogenic antigen would suppress clinical arthritis after disease onset. Methods Antigen-induced arthritis was induced in C57/Bl6 mice by priming to methylated bovine serum albumin (mBSA) antigen followed by challenge injection of mBSA to one knee. Knee swelling was apparent within 2 days, with peak clinical signs apparent at 5 days. Mice were treated with antigen-exposed modified DC between 2 and 6 days after mBSA challenge to the knee joint. Results Clinical arthritis was suppressed in each group receiving mBSA-exposed modified DC within 4 days compared with mice that received either no DC or keyhole limpet hemocyanin-exposed modified DC. Clinical improvement was associated with mBSA-specific tolerance in mice receiving mBSA-exposed modified DC. Tolerance induction was not impaired by concomitant administration of anti-tumor necrosis factor alpha monoclonal antibody. Subsequent rechallenge with intra-articular IL-1 induced flare of arthritis in all groups, which could be effectively suppressed by a second administration of mBSA-exposed modified DC. Conclusions The data indicate that modified DC induce antigen-specific immune suppression in this model of inflammatory arthritis, even after full clinical expression of the disease. These observations have important implications for antigen-specific therapy of autoimmunity