2,533 research outputs found
Fundamental limits to optical response in absorptive systems
At visible and infrared frequencies, metals show tantalizing promise for
strong subwavelength resonances, but material loss typically dampens the
response. We derive fundamental limits to the optical response of absorptive
systems, bounding the largest enhancements possible given intrinsic material
losses. Through basic conservation-of-energy principles, we derive
geometry-independent limits to per-volume absorption and scattering rates, and
to local-density-of-states enhancements that represent the power radiated or
expended by a dipole near a material body. We provide examples of structures
that approach our absorption and scattering limits at any frequency, by
contrast, we find that common "antenna" structures fall far short of our
radiative LDOS bounds, suggesting the possibility for significant further
improvement. Underlying the limits is a simple metric, for a material with susceptibility , that enables
broad technological evaluation of lossy materials across optical frequencies.Comment: 21 pages and 6 figures (excluding appendices, references
Fluctuating surface-current formulation of radiative heat transfer for arbitrary geometries
We describe a fluctuating surface-current formulation of radiative heat
transfer, applicable to arbitrary geometries, that directly exploits standard,
efficient, and sophisticated techniques from the boundary-element method. We
validate as well as extend previous results for spheres and cylinders, and also
compute the heat transfer in a more complicated geometry consisting of two
interlocked rings. Finally, we demonstrate that the method can be readily
adapted to compute the spatial distribution of heat flux on the surface of the
interacting bodies
Anomalous near-field heat transfer between a cylinder and a perforated surface
We predict that the radiative heat-transfer rate between a cylinder and a
perforated surface depends non-monotonically on their separation. This
anomalous behavior, which arises due to near-field effects, is explained using
a heuristic model based on the interaction of a dipole with a plate. We show
that nonmonotonicity depends not only on geometry and temperature but also on
material dispersion - for micron and submicron objects, nonmonotonicity is
present in polar dielectrics but absent in metals with small skin depths
Calculation of nonzero-temperature Casimir forces in the time domain
We show how to compute Casimir forces at nonzero temperatures with
time-domain electromagnetic simulations, for example using a finite-difference
time-domain (FDTD) method. Compared to our previous zero-temperature
time-domain method, only a small modification is required, but we explain that
some care is required to properly capture the zero-frequency contribution. We
validate the method against analytical and numerical frequency-domain
calculations, and show a surprising high-temperature disappearance of a
non-monotonic behavior previously demonstrated in a piston-like geometry.Comment: 5 pages, 2 figures, submitted to Physical Review A Rapid
Communicatio
Characterization and application of artificial light sources for nighttime aerosol optical depth retrievals using the Visible Infrared Imager Radiometer Suite Day/Night Band
Using nighttime observations from Visible Infrared Imager Radiometer Suite (VIIRS) Day/Night band (DNB), the characteristics of artificial light sources are evaluated as functions of observation conditions, and incremental improvements are documented on nighttime aerosol retrievals using VIIRS DNB data on a regional scale. We find that the standard deviation of instantaneous radiance for a given artificial light source is strongly dependent upon the satellite viewing angle but is weakly dependent on lunar fraction and lunar angle. Retrieval of nighttime aerosol optical thickness (AOT) based on the novel use of these artificial light sources is demonstrated for three selected regions (United States, Middle East and India) during 2015. Reasonable agreement is found between nighttime AOTs from the VIIRS DNB and temporally adjacent daytime AOTs from the AErosol RObotic NETwork (AERONET) as well as from coincident nighttime AOT retrievals from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), indicating the potential of this method to begin filling critical gaps in diurnal AOT information at both regional and global scales. Issues related to cloud, snow and ice contamination during the winter season, as well as data loss due to the misclassification of thick aerosol plumes as clouds, must be addressed to make the algorithm operationally robust
Microstructure Effects for Casimir Forces in Chiral Metamaterials
We examine a recent prediction for the chirality-dependence of the Casimir
force in chiral metamaterials by numerical computation of the forces between
the exact microstructures, rather than homogeneous approximations. We compute
the exact force for a chiral bent-cross pattern, as well as forces for an
idealized "omega"-particle medium in the dilute approximation and identify the
effects of structural inhomogeneity (i.e. proximity forces and anisotropy). We
find that these microstructure effects dominate the force for separations where
chirality was predicted to have a strong influence. To get observations of
chirality free from microstructure effects, one must go to large separations
where the effect of chirality is at most of the total force.Comment: 5 pages, 4 figure
Computational inverse design of non-intuitive illumination patterns to maximize optical force or torque
This paper aims to maximize optical force or torque on arbitrary micro- and nanoscale objects using numerically optimized structured illumination. By developing a numerical framework for computer-automated design of 3d vector-field illumination, we demonstrate a 20-fold enhancement in optical torque per intensity over circularly polarized plane wave on a model plasmonic particle. The nonconvex optimization is efficiently performed by combining a compact cylindrical Bessel basis representation with a fast boundary element method and a standard derivative-free, local optimization algorithm. We analyze the optimization results for 2000 random initial configurations, discuss the tradeoff between robustness and enhancement, and compare the different effects of multipolar plasmon resonances on enhancing force or torque. All results are obtained using open-source computational software available online
Management of the airway and lung isolation for thoracic surgery during the COVID-19 pandemic
Intra-operative aerosol generating procedures are arguably unavoidable in the routine provision of thoracic anaesthesia. Airway management for such patients during the COVID-19 pandemic including tracheal intubation, lung isolation, one-lung ventilation and flexible bronchoscopy may pose a significant risk to healthcare professionals and patients. That said, there remains a need for timely thoracic surgery for patients with lung cancer or thoracic trauma. The thoracic anaesthetic community has been confronted with the need to modify existing techniques to maximise safety for patients and healthcare professionals. With appropriate modification, aerosol generation may be mitigated against in most circumstances. We developed a set of practice-based recommendations for airway management in thoracic surgical patients, which have been endorsed by the Association for Cardiothoracic Anaesthesia and Critical Care and the Society for Cardiothoracic Surgery in Great Britain and Ireland
Management of the airway and lung isolation for thoracic surgery during the COVID‐19 pandemic: a reply
No abstract available
Shaping the Supervision Narrative: Innovating Teaching and Leading to Improve STEM Instruction
This paper offers a model of supervisory collaboration that brings teacher and administrator programs together through a lens of formative evaluation. The roles of teacher and principal must be collaborative to sustain student success, yet the preparation models for those respective positions are often isolated from each other, as varying university departments and focus areas exist in silos. Preparation programs must maximize the clinical experiences of teacher education and administrator preparation programs, with a focus on practical teaching strategies and authentic feedback to pre-service educators and their instructors for reflection and change. This paper overviews a collaborative supervision model and incorporates case study vignettes focused on reflective supervisory practices in a STEM instructional environment
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