Co‐operative cross‐platform courseware development

The UKMCC (UK Mathematics Courseware Consortium) is a Consortium funded under TLTP (Training and Learning Technology Programme) to produce courseware for service mathematics teaching, using the SEFI (Société Européenne pour la Formation des Ingénieurs) syllabus. There are agreed courseware design guidelines and a simple courseware management system which allows cross‐referencing. Courseware is divided into modules, with an author as implementer for each. On any one hardware platform, a variety of authoring languages is possible. Across hardware platforms, the design guidelines ensure that conversion is possible, and will preserve look and feel. We argue here that these arrangements provide a basis for continued co‐operation between authors and future development as the technology changes

Kinetics of natural aging in Al-Mg-Si alloys studied by positron annihilation lifetime spectroscopy

The process of natural aging in pure ternary Al-Mg-Si alloys was studied by positron annihilation lifetime spectroscopy in real time in order to clarify the sequence and kinetics of clustering and precipitation. It was found that natural aging takes place in at least five stages in these alloys, four of which were directly observed. This is interpreted as the result of complex interactions between vacancies and solute atoms or clusters. One of the early stages of positron lifetime evolution coincides with a clustering process observed by differential scanning calorimetry (DSC) and involves the formation of a positron trap with \sim 0.200 ns lifetime. In later stages, a positron trap with a higher lifetime develops in coincidence with the DSC signal of a second clustering reaction. Mg governs both the kinetics and the lifetime change in this stage. Within the first 10 min after quenching, a period of nearly constant positron lifetime was found for those Mg-rich alloys that later show an insufficient hardness response to artificial aging, the so-called "negative effect." The various processes observed could be described by two effective activation energies that were found by varying the aging temperature from 10 to 37\degree C.Comment: arXiv admin note: same as v2, to correct mistaken v

The law relating to activities of man in space, appendices A-D Final report

Jurisdiction over acts in outer space, domestic use of communication satellites, UN and other international agencies in controlling space, and bibliography on space law

Finite Temperature Behavior of the ν=1\nu=1 Quantum Hall Effect in Bilayer Electron Systems

An effective field theoretic description of $\nu=1$ bilayer electron systems stabilized by Coulomb repulsion in a single wide quantum well is examined using renormalization group techniques. The system is found to undergo a crossover from a low temperature strongly correlated quantum Hall state to a high temperature compressible state. This picture is used to account for the recent experimental observation of an anomalous transition in bilayer electron systems (T. S. Lay, {\em et al.} Phys. Rev. B {\bf 50}, 17725 (1994)). An estimate for the crossover temperature is provided, and it is shown that its dependence on electron density is in reasonable agreement with i the experiment.Comment: Corrected typos, and changed content, 5 pages and 2 figures, accepted in Phys. Rev.

Density of states and electron concentration of double heterojunctions subjected to an in-plane magnetic field

We calculate the electronic states of Al$_x$Ga$_{1-x}$As/GaAs/Al$_x$Ga$_{1-x}$As double heterojunctions subjected to a magnetic field parallel to the quasi two-dimensional electron gas. We study the energy dispersion curves, the density of states, the electron concentration and the distribution of the electrons in the subbands. The parallel magnetic field induces severe changes in the density of states, which are of crucial importance for the explanation of the magnetoconductivity in these structures. However, to our knowledge, there is no systematic study of the density of states under these circumstances. We attempt a contribution in this direction. For symmetric heterostructures, the depopulation of the higher subbands, the transition from a single to a bilayer electron system and the domination of the bulk Landau levels in the centre the wide quantum well, as the magnetic field is continuously increased, are presented in the ``energy dispersion picture'' as well as in the ``electron concentration picture'' and in the ``density of states picture''.Comment: J. Phys.: Condens. Matter 11 No 26 (5 July 1999) 5131-5141 Figures (three) embedde

Magnetic Anisotropy in Quantum Hall Ferromagnets

We show that the sign of magnetic anisotropy energy in quantum Hall ferromagnets is determined by a competition between electrostatic and exchange energies. Easy-axis ferromagnets tend to occur when Landau levels whose states have similar spatial profiles cross. We report measurements of integer QHE evolution with magnetic-field tilt. Reentrant behavior observed for the $\nu = 4$ QHE at high tilt angles is attributed to easy-axis anisotropy. This interpretation is supported by a detailed calculation of the magnetic anisotropy energy.Comment: 12 pages, 3 figures, submitted to Phys. Rev. Let

Probing beta decay matrix elements through heavy ion charge exchange reactions

To access information on neutrinoless double beta decay (0νββ) nuclear matrix elements, it has been proposed by the NUMEN collaboration to exploit the analogies between double beta decay processes and double charge exchange (DCE) nuclear reactions, looking in particular at the conditions where the corresponding cross section can be factorized into nuclear reaction and nuclear structure terms. DCE reactions can be treated as a convolution of two correlated or uncorrelated single charge exchange (SCE) processes, resembling 0νββ and 2νββ, respectively. Thus it is important to model first SCE processes, to get a deeper insight into the possibility to factorize the corresponding cross section, so one can gain a better understanding of DCE cross section factorization. In this contribution, DCE reactions are discussed in terms of the convolution of two uncorrelated SCE processes, which should allow one to extract information on 2νββ nuclear matrix elements. These theoretical investigations are performed in close synergy with the experimental activity running at INFN-LNS within the NUMEN project

Macrophage migration inhibitory factor downregulation: a novel mechanism of resistance to anti-angiogenic therapy.

Anti-angiogenic therapies for cancer such as VEGF neutralizing antibody bevacizumab have limited durability. While mechanisms of resistance remain undefined, it is likely that acquired resistance to anti-angiogenic therapy will involve alterations of the tumor microenvironment. We confirmed increased tumor-associated macrophages in bevacizumab-resistant glioblastoma patient specimens and two novel glioblastoma xenograft models of bevacizumab resistance. Microarray analysis suggested downregulated macrophage migration inhibitory factor (MIF) to be the most pertinent mediator of increased macrophages. Bevacizumab-resistant patient glioblastomas and both novel xenograft models of resistance had less MIF than bevacizumab-naive tumors, and harbored more M2/protumoral macrophages that specifically localized to the tumor edge. Xenografts expressing MIF-shRNA grew more rapidly with greater angiogenesis and had macrophages localizing to the tumor edge which were more prevalent and proliferative, and displayed M2 polarization, whereas bevacizumab-resistant xenografts transduced to upregulate MIF exhibited the opposite changes. Bone marrow-derived macrophage were polarized to an M2 phenotype in the presence of condition-media derived from bevacizumab-resistant xenograft-derived cells, while recombinant MIF drove M1 polarization. Media from macrophages exposed to bevacizumab-resistant tumor cell conditioned media increased glioma cell proliferation compared with media from macrophages exposed to bevacizumab-responsive tumor cell media, suggesting that macrophage polarization in bevacizumab-resistant xenografts is the source of their aggressive biology and results from a secreted factor. Two mechanisms of bevacizumab-induced MIF reduction were identified: (1) bevacizumab bound MIF and blocked MIF-induced M1 polarization of macrophages; and (2) VEGF increased glioma MIF production in a VEGFR2-dependent manner, suggesting that bevacizumab-induced VEGF depletion would downregulate MIF. Site-directed biopsies revealed enriched MIF and VEGF at the enhancing edge in bevacizumab-naive patients. This MIF enrichment was lost in bevacizumab-resistant glioblastomas, driving a tumor edge M1-to-M2 transition. Thus, bevacizumab resistance is driven by reduced MIF at the tumor edge causing proliferative expansion of M2 macrophages, which in turn promotes tumor growth