100 research outputs found
Lower Bounds to Quality Factor of Small Radiators through Quasistatic Scattering Modes
The problem of finding the optimal current distribution supported by a small
radiator yielding the minimum quality () factor is a fundamental problem in
electromagnetism. factor bounds constrain the maximum operational bandwidth
of devices including antennas, metamaterials, and open optical resonators. In
this manuscript, a representation of the optimal current distribution in terms
of quasistatic scattering modes is introduced. Quasi-electrostatic and
quasi-magnetostatic modes describe the resonances of small plasmonic and
high-permittivity particles, respectively. The introduced representation leads
to analytical and closed form expressions of the electric and magnetic
polarizability tensors of arbitrarily shaped objects, whose eigenvalues are
known to be linked to the minimum . Hence, the minimum and the
corresponding optimal current are determined from the sole knowledge of the
eigenvalues and the dipole moments associated with the quasistatic modes. It is
found that, when the radiator exhibits two orthogonal reflection symmetries,
its minimum factor can be simply obtained from the factors of its
quasistatic modes, through a parallel formula. When an electric type radiator
supports a spatially uniform quasistatic resonance mode, or when a magnetic
type resonator supports a mode of curl type, then these modes are guaranteed to
have the minimum factor
Resonances On-Demand for Plasmonic Nano-Particles
A method for designing plasmonic particles with desired resonance spectra is
presented. The method is based on repetitive perturbations of an initial
particle shape while calculating the eigenvalues of the various quasistatic
resonances. The method is rigorously proved, assuring a solution exists for any
required spectral resonance location. Resonances spanning the visible and the
near-infrared regimes, as designed by our method, are verified using
finite-difference time-domain simulations. A novel family of particles with
collocated dipole-quadrupole resonances is designed, demonstrating the unique
power of the method. Such on-demand engineering enables strict realization of
nano-antennas and metamaterials for various applications requiring specific
spectral functions
Discourses of conflict and collaboration and institutional context in the implementation of forest conservation policies in Soria, Spain
This article examines the emergence of conflict and collaboration in the implementation of forest conservation policies in Soria, Spain. We draw insights from discursive institutionalism and use a comparative case study approach to analyse and compare a situation of social conflict over the Natural Park declaration in the Sierra de Urbión, and a civil society led collaborative process to develop management plans for the “Sierra de Cabrejas” in Soria. The implementation of the EU Habitats Directive generated different outcomes in these two cases, which unfolded in the context of the same nature conservation legislation and national and provincial administrative structures but differed in terms of types of forests involved, property rights arrangements and forest use histories. We critically examine the influence of the institutional context and dominant discourses on the emergence of outcomes: conflict emerged where local institutions and discourses were threatened by the EU directive, while collaboration was possible where local institutions and counter-discourses were weak. We find that the institutional context plays an important part in determining local discourses in the implementation of forest conservation policies. Yet local counter-discourses have limited influence in the implementation and policy processes in the face of contestation by the discourses of regional civil servants conservation activists
Theoretical Criteria for Scattering Dark States in Nanostructured Particles
Nanostructures with multiple resonances can exhibit a suppressed or even completely eliminated scattering of light, called a scattering dark state. We describe this phenomenon with a general treatment of light scattering from a multiresonant nanostructure that is spherical or nonspherical but subwavelength in size. With multiple resonances in the same channel (i.e., same angular momentum and polarization), coherent interference always leads to scattering dark states in the low-absorption limit, regardless of the system details. The coupling between resonances is inevitable and can be interpreted as arising from far-field or near-field. This is a realization of coupled-resonator-induced transparency in the context of light scattering, which is related to but different from Fano resonances. Explicit examples are given to illustrate these concepts.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001)National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Grant DMR-0819762
Knowledge and health care resource allocation: CME/CPD course guidelines-based efficacy.
BACKGROUND: Most health care systems consider continuing medical education a potential tool to improve quality of care and reduce disease management costs. Its efficacy in general practitioners needs to be further explored.
OBJECTIVE: This study assesses the effectiveness of a one-year continuing medical education/continuing professional development course for general practitioners, regarding the improvement in knowledge of ARIA and GINA guidelines and compliance with them in asthma management.
METHODS: Sixty general practitioners, covering 68,146 inhabitants, were randomly allocated to continuing medical education/continuing professional development (five residential events +four short distance-learning refresher courses over one year) or no training. Participants completed a questionnaire after each continuing medical education event; key questions were repeated at least twice. The Local Health Unit prescription database was used to verify prescription habits (diagnostic investigations and pharmacological therapy) and hospitalizations over one year before and after training.
RESULTS: Fourteen general practitioners (46.7%) reached the cut-off of 50% attendance of the training courses. Knowledge improved significantly after training (p < 0.001, correct answers to key questions +13%). Training resulted in pharmaceutical cost containment (trained general practitioners +0.5% vs. controls +18.8%) and greater attention to diagnosis and monitoring (increase in spirometry +63.4%, p < 0.01).
CONCLUSION: This study revealed an encouraging impact of educational events on improvement in general practitioner knowledge of guidelines and daily practice behavioral changes. Long-term studies of large populations are required to assess the effectiveness of education on the behavior of physicians in asthma management, and to establish the best format for educational events
Exploring the Pathologies of One-Party-Dominance on Third Sector Public Policy Engagement in Liberal Democracies: Evidence from Meso-Government in the UK
A generalized model for the signal propagation along single- and multi-walled carbon nanotubes with arbitrary chirality
The paper presents a self-consistent semi-classical model describing the electrical behavior of carbon nanotube interconnects. The model deals with the general case of arbitrary chirality and takes rigorously into account the effects of nanotube size and chirality on its electrical parameters. The general model includes as particular cases the models currently used in literature to describe metallic carbon nanotubes with small radius. The analysis of bundles of single-walled and multi-walled carbon nanotubes is carried-out. The model is also used to derive a semi-analytical approximation for the number of equivalent conduction channels in a multi-walled carbon nanotube shell
Hydrodynamic model for the signal propagation along carbon nanotubes
We formulated a hydrodynamic model in order to describe the dynamical behavior of the pi-electrons in single carbon nanotube shells of arbitrary chirality, either metallic or semiconducting, below terahertz frequencies, as long as only intraband transitions of the pi-electrons are allowed. The hydrodynamic equations were derived in a self-consistent way from the semiclassical Boltzmann equation. The electron fluid was taken to comprise many electron species, each characterized by a different effective mass, which takes into account the interaction with the nanotube ion lattice. A linear transport model for the pi-electrons was derived from the hydrodynamic equations. A transmission line model was eventually formulated to describe the propagation of an electric signal along a single-wall carbon nanotube of arbitrary chirality. The transport model formulated can be also used for analyzing electromagnetic propagation in complex structures composed of single carbon-nanotube shells with different chirality, such as bundles of single wall carbon nanotubes and multi-wall carbon nanotubes, provided that the tunneling between adjacent shells may be disregarded
Nouvelles technologies IFP pour la reformulation des essences Ifp's New Technologies for Reformulated Gasoline
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