321 research outputs found
The role of the spin in quasiparticle interference
Quasiparticle interference patterns measured by scanning tunneling microscopy
(STM) can be used to study the local electronic structure of metal surfaces and
high temperature superconductors. Here, we show that even in non-magnetic
systems the spin of the quasiparticles can have a profound effect on the
interference patterns. On Bi(110), where the surface state bands are not
spin-degenerate, the patterns are not related to the dispersion of the
electronic states in a simple way. In fact, the features which are expected for
the spin-independent situation are absent and the observed interference
patterns can only be interpreted by taking spin-conserving scattering events
into account.Comment: 4 pages, 2 figure
Backflow in a Fermi Liquid
We calculate the backflow current around a fixed impurity in a Fermi liquid.
The leading contribution at long distances is radial and proportional to 1/r^2.
It is caused by the current induced density modulation first discussed by
Landauer. The familiar 1/r^3 dipolar backflow obtained in linear response by
Pines and Nozieres is only the next to leading term, whose strength is
calculated here to all orders in the scattering. In the charged case the
condition of perfect screening gives rise to a novel sum rule for the phase
shifts. Similar to the behavior in a classical viscous liquid, the friction
force is due only to the leading contribution in the backflow while the dipolar
term does not contribute.Comment: 4 pages, 1 postscript figure, uses ReVTeX and epsfig macro, submitted
to Physical Review Letter
Nanoscopic Tunneling Contacts on Mesoscopic Multiprobe Conductors
We derive Bardeen-like expressions for the transmission probabilities between
two multi-probe mesoscopic conductors coupled by a weak tunneling contact. We
emphasize especially the dual role of a weak coupling contact as a current
source and sink and analyze the magnetic field symmetry. In the limit of a
point-like tunneling contact the transmission probability becomes a product of
local, partial density of states of the two mesoscopic conductors. We present
expressions for the partial density of states in terms of functional
derivatives of the scattering matrix with respect to the local potential and in
terms of wave functions. We discuss voltage measurements and resistance
measurements in the transport state of conductors. We illustrate the theory for
the simple case of a scatterer in an otherwise perfect wire. In particular, we
investigate the development of the Hall-resistance as measured with weak
coupling probes.Comment: 10 pages, 5 figures, revte
How to detect fluctuating order in the high-temperature superconductors
We discuss fluctuating order in a quantum disordered phase proximate to a
quantum critical point, with particular emphasis on fluctuating stripe order.
Optimal strategies for extracting information concerning such local order from
experiments are derived with emphasis on neutron scattering and scanning
tunneling microscopy. These ideas are tested by application to two model
systems - the exactly solvable one dimensional electron gas with an impurity,
and a weakly-interacting 2D electron gas. We extensively review experiments on
the cuprate high-temperature superconductors which can be analyzed using these
strategies. We adduce evidence that stripe correlations are widespread in the
cuprates. Finally, we compare and contrast the advantages of two limiting
perspectives on the high-temperature superconductor: weak coupling, in which
correlation effects are treated as a perturbation on an underlying metallic
(although renormalized) Fermi liquid state, and strong coupling, in which the
magnetism is associated with well defined localized spins, and stripes are
viewed as a form of micro-phase separation. We present quantitative indicators
that the latter view better accounts for the observed stripe phenomena in the
cuprates.Comment: 43 pages, 11 figures, submitted to RMP; extensively revised and
greatly improved text; one new figure, one new section, two new appendices
and more reference
Project manager-to-project allocations in practice: an empirical study of the decision-making practices of a multi-project based organization
Empirical studies that examine how managers make project manager-to-project (PM2P) allocation decisions in multi-project settings are currently limited. Such decisions are crucial to organizational success. An empirical study of the PM2P practice, conducted in the context of Botswana, revealed ineffective processes in terms of optimality in decision-making. A conceptual model to guide effective PM2P practices was developed. The focus of this study is on deploying the model as a lens to study the PM2P practices of a large organization, with a view to identify and illustrate strengths and weaknesses. A case study was undertaken in the mining industry, where core activities in terms of projects are underground mineral explorations at identified geographical regions. A semi-structured interview protocol was used to collect data from 15 informants, using an enumeration. Integrated analysis of both data types (using univariate descriptive analysis for the quantitative data, content and thematic analysis for the qualitative data) revealed strengths in PM2P practices, demonstrated by informants’ recognition of some important criteria to be considered. The key weaknesses were exemplified by a lack of effective management tools and techniques to match project managers to projects. The findings provide a novel perspective through which improvements in working practices can be made
Teaching evidence-based management with a focus on producing local evidence
We present an approach to teaching evidence-based management (EBMgt) that trains future managers how to produce local evidence. Local evidence is causally interpretable data, collected on-site in companies to address a specific business problem. Our teaching method is a variant of problem-based learning, a method originally developed to teach evidence-based medicine. Following this method, students learn an evidence-based problem-solving cycle for addressing actual business cases. Executing this cycle, students use and produce scientific evidence through literature searches and the design of local, experimental tests of causal hypotheses. We argue the value of teaching EBMgt with a focus on producing local evidence, how it can be taught, and what can be taught. We conclude by outlining our contribution to the literature on teaching EBMgt and by discussing limitations of our approach
Análise da aptidão física, da antropometria e da prevalência de sintomas osteomusculares na categoria infanto-juvenil do voleibol
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