1,815 research outputs found
Cancellation of probe effects in measurements of spin polarized momentum density by electron positron annihilation
Measurements of the two dimensional angular correlation of the
electron-positron annihilation radiation have been done in the past to detect
the momentum spin density and the Fermi surface. We point out that the momentum
spin density and the Fermi Surface of ferromagnetic metals can be revealed
within great detail owing to the large cancellation of the electron-positron
matrix elements which in paramagnetic multiatomic systems plague the
interpretation of the experiments. We prove our conjecture by calculating the
momentum spin density and the Fermi surface of the half metal CrO2, who has
received large attention due to its possible applications as spintronics
material
Objective Function and Constraints for Robust Transonic Aerofoil Optimization
Construction of the aerodynamic optimization problem is considered within the context of robustness. The most common aerodynamic optimization problem considered is a lift-constrained drag minimization problem (also subject to geometric constraints), however, point-design at transonic flow conditions can produce shock-free solutions and therefore the result is highly localised, where the gains obtained at the design point are outweighed by the losses at off-design conditions. As such, a range optimization problem subject to a constraint on fixed non-dimensional lift with a varying design point is considered to mitigate this issue. It is shown, first from an analytical treatment of the problem, and second from inviscid optimizations, that more robust solutions are obtainable when considering range optimization against drag minimization. Furthermore, to effectively capture the trade-offs that exist in three-dimensional aircraft design between range, lift, drag and speed, it is shown that an induced drag factor is required and this is suffcient to produce optimal solutions exhibiting shocks
Fermi Surface as the Driving Mechanism for Helical Antiferromagnetic Ordering in Gd-Y Alloys
The first direct experimental evidence for the Fermi surface (FS) driving the
helical antiferromagnetic ordering in a gadolinium-yttrium alloy is reported.
The presence of a FS sheet capable of nesting is revealed, and the nesting
vector associated with the sheet is found to be in excellent agreement with the
periodicity of the helical ordering.Comment: 4 pages, 4 figure
Electron attachment to valence-excited CO
The possibility of electron attachment to the valence state of CO
is examined using an {\it ab initio} bound-state multireference configuration
interaction approach. The resulting resonance has symmetry;
the higher vibrational levels of this resonance state coincide with, or are
nearly coincident with, levels of the parent state. Collisional
relaxation to the lowest vibrational levels in hot plasma situations might
yield the possibility of a long-lived CO state.Comment: Revtex file + postscript file for one figur
Biopolitical precarity in the permeable body: the social lives of people, viruses and their medicines
This article is based on multi-sited ethnography that traced a dynamic network of actors (activists, policy-makers, health care systems, pharmaceutical companies) and actants (viruses and medicines) that shaped South African women’s access to, and embodiment of, antiretroviral therapies (ARVs). Using actor network theory and post-humanist performativity as conceptual tools, the article explores how bodies become the meeting place for HIV and ARVs, or non-human actants. The findings centre around two linked sets of narratives that draw the focus out from the body to situate the body in relation to South Africa’s shifting biopolitical landscape. The first set of narratives articulate how people perceive the intra-action of HIV and ARVs in their sustained vitality. The second set of narratives articulate the complex embodiment of these actants as a form biopolitical precarity. These narratives flow into each other and do not represent a totalising view of the effects of HIV and ARVs in the lives of the people with whom I worked. The positive effects of ARVs (as unequivocally essential for sustaining life) were implicit and the precarious vitality of the people in this ethnography was fundamental. However, a related and emergent set of struggles become salient during the study that complicate a view of ARVs as a ‘technofix’. These emergent struggles were biopolitical, and they related first to the intra-action of HIV and ARVs ‘within’ the body; and second, to the ‘outside’ socio-economic context in which people’s bodies were situated
Nesting properties and anisotropy of the Fermi surface of LuNiBC
The rare earth nickel borocarbides, with the generic formula
NiBC, have recently been shown to display a rich variety of
phenomena. Most striking has been the competition between, and even coexistence
of, antiferromagnetism and superconductivity. We have measured the Fermi
surface (FS) of LuNiBC, and shown that it possesses nesting
features capable of explaining some of the phenomena experimentally observed.
In particular, it had previously been conjectured that a particular sheet of FS
is responsible for the modulated magnetic structures manifest in some of the
series. We report the first direct experimental observation of this sheet.Comment: 4 pages, 4 PS figure
Integrating agriculture and health research for development: LCIRAH as an interdisciplinary programme to address a global challenge
The multiple burdens of persistent undernutrition and micronutrient deficiencies, along with the rapidly growing rates of overweight, obesity, and associated chronic diseases, are major challenges globally. The role of agriculture and the food system in meeting these challenges is very poorly understood. Achieving food security and addressing malnutrition in all its forms, a Sustainable Development Goal, requires an understanding of how changing food systems affect health outcomes and the development of new tools to design and evaluate interventions. An interinstitutional programme to address this interdisciplinary research challenge is described. Over the past seven years, the Leverhulme Centre for Integrative Research on Agriculture and Health has built a portfolio of successful and innovative research, trained a new cadre of interdisciplinary researchers in “Agri‐Health,” and built an international research community with a particular focus on strengthening research capacity in low‐ and middle‐income countries. The evolution of this programme is described, and key factors contributing to its success are discussed that may be of general value in designing interdisciplinary research programmes directed at supporting global development goals
Enhancing Optical Up-Conversion Through Electrodynamic Coupling with Ancillary Chromophores
In lanthanide-based optical materials, control over the relevant operating characteristics–for example transmission wavelength, phase and quantum efficiency–is generally achieved through the modification of parameters such as dopant/host combination, chromophore concentration and lattice structure. An alternative avenue for the control of optical response is through the introduction of secondary, codoped chromophores. Here, such secondary centers act as mediators, commonly bridging the transfer of energy between primary absorbers of externally sourced optical input and other sites of frequency-converted emission. Utilizing theoretical models based on experimentally feasible, three-dimensional crystal lattice structures; a fully quantized theoretical framework provides insights into the locally modified mechanisms that can be implemented within such systems. This leads to a discussion of how such effects might be deployed to either enhance, or potentially diminish, the efficiency of frequency up-conversion
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Analyzing food value chains for nutrition goals
First proposed in 2010, the use of ‘value chain analysis’ to identify opportunities for targeted nutrition interventions in food systems is still an emerging method. This review explores and summarizes the application of value chain analysis to nutrition and from this provides five insights into how to more effectively conduct value chain analysis for nutrition: 1) use a consumer perspective to inform selection of foods and chains; 2) consider the research question, available resources, and the type of chain; 3) situate consumer research at the center of the analysis; 4) assess economic trade-offs; and 5) pay attention to governance and stakeholders’ capacity for and incentives to change
On isovector meson exchange currents in the Bethe-Salpeter approach
We investigate the nonrelativistic reduction of the Bethe-Salpeter amplitude
for the deuteron electrodisintegration near threshold energies. To this end,
two assumptions have been used in the calculations: 1) the static approximation
and 2) the one iteration approximation. Within these assumptions it is possible
to recover the nonrelativistic result including a systematic extension to
relativistic corrections. We find that the so-called pair current term can be
constructed from the -wave contribution of the deuteron Bethe-Salpeter
amplitude. The form factor that enters into the calculation of the pair current
is constrained by the manifestly gauge independent matrix elements.Comment: 15 pages, incl. 3 figures, to be published Phys. Rev.
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