39 research outputs found
Magnetoelastic nonlinear metamaterials
We introduce the concept of magnetoelastic metamaterials with electromagnetic
properties depending on elastic deformation. We predict a strong nonlinear and
bistable response of such metamaterials caused by their structural reshaping in
response to the applied electromagnetic field. In addition, we demonstrate
experimentally the feasibility of the predicted effect.Comment: 4 pages, 5 figure
Nonlinear Localization in Metamaterials
Metamaterials, i.e., artificially structured ("synthetic") media comprising
weakly coupled discrete elements, exhibit extraordinary properties and they
hold a great promise for novel applications including super-resolution imaging,
cloaking, hyperlensing, and optical transformation. Nonlinearity adds a new
degree of freedom for metamaterial design that allows for tuneability and
multistability, properties that may offer altogether new functionalities and
electromagnetic characteristics. The combination of discreteness and
nonlinearity may lead to intrinsic localization of the type of discrete
breather in metallic, SQUID-based, and symmetric metamaterials. We
review recent results demonstrating the generic appearance of breather
excitations in these systems resulting from power-balance between intrinsic
losses and input power, either by proper initialization or by purely dynamical
procedures. Breather properties peculiar to each particular system are
identified and discussed. Recent progress in the fabrication of low-loss,
active and superconducting metamaterials, makes the experimental observation of
breathers in principle possible with the proposed dynamical procedures.Comment: 19 pages, 14 figures, Invited (Review) Chapte
Metadevice for intensity modulation with sub-wavelength spatial resolution
Effectively continuous control over propagation of a beam of light requires light modulation with pixelation that is smaller than the optical wavelength. Here we propose a spatial intensity modulator with sub-wavelength resolution in one dimension. The metadevice combines recent advances in reconfigurable nanomembrane metamaterials and coherent all-optical control of metasurfaces. It uses nanomechanical actuation of metasurface absorber strips placed near a mirror in order to control their interaction with light from perfect absorption to negligible loss, promising a path towards dynamic beam diffraction, light focusing and holography without unwanted diffraction artefacts
Child/Adolescent Anxiety Multimodal Study (CAMS): rationale, design, and methods
<p>Abstract</p> <p>Objective</p> <p>To present the design, methods, and rationale of the Child/Adolescent Anxiety Multimodal Study (CAMS), a recently completed federally-funded, multi-site, randomized placebo-controlled trial that examined the relative efficacy of cognitive-behavior therapy (CBT), sertraline (SRT), and their combination (COMB) against pill placebo (PBO) for the treatment of separation anxiety disorder (SAD), generalized anxiety disorder (GAD) and social phobia (SoP) in children and adolescents.</p> <p>Methods</p> <p>Following a brief review of the acute outcomes of the CAMS trial, as well as the psychosocial and pharmacologic treatment literature for pediatric anxiety disorders, the design and methods of the CAMS trial are described.</p> <p>Results</p> <p>CAMS was a six-year, six-site, randomized controlled trial. Four hundred eighty-eight (N = 488) children and adolescents (ages 7-17 years) with DSM-IV-TR diagnoses of SAD, GAD, or SoP were randomly assigned to one of four treatment conditions: CBT, SRT, COMB, or PBO. Assessments of anxiety symptoms, safety, and functional outcomes, as well as putative mediators and moderators of treatment response were completed in a multi-measure, multi-informant fashion. Manual-based therapies, trained clinicians and independent evaluators were used to ensure treatment and assessment fidelity. A multi-layered administrative structure with representation from all sites facilitated cross-site coordination of the entire trial, study protocols and quality assurance.</p> <p>Conclusions</p> <p>CAMS offers a model for clinical trials methods applicable to psychosocial and psychopharmacological comparative treatment trials by using state-of-the-art methods and rigorous cross-site quality controls. CAMS also provided a large-scale examination of the relative and combined efficacy and safety of the best evidenced-based psychosocial (CBT) and pharmacologic (SSRI) treatments to date for the most commonly occurring pediatric anxiety disorders. Primary and secondary results of CAMS will hold important implications for informing practice-relevant decisions regarding the initial treatment of youth with anxiety disorders.</p> <p>Trial registration</p> <p>ClinicalTrials.gov NCT00052078.</p
Coupled Electromagnetic and Elastic Dynamics in Metamaterials
Metamaterials are well established in the field of electromagnetism, where they have demonstrated a wide variety of exotic material properties. More recently, mechanical metamaterials have also been shown to be quite promising in achieving exotic properties for acoustic waves. Here we discuss an emerging class of metamaterials with both electromagnetic and elastic properties, which are coupled to each other, giving rise to a new range of metamaterial properties. In particular, this can yield a very strong nonlinear response, including bistable states and self-oscillations. We present several structures which exhibit these properties, and experimentally demonstrate their feasibility
Optically reconfigurable metasurfaces and photonic devices based on phase change materials
Photonic components with adjustable parameters, such as variable-focal-length lenses or spectral filters, which can change functionality upon optical stimulation, could offer numerous useful applications. Tuning of such components is conventionally achieved by either micro- or nanomechanical actuation of their constituent parts, by stretching or by heating. Here, we report a novel approach for making reconfigurable optical components that are created with light in a non-volatile and reversible fashion. Such components are written, erased and rewritten as two-dimensional binary or greyscale patterns into a nanoscale film of phase-change material by inducing a refractive-index-changing phase transition with tailored trains of femtosecond pulses. We combine germanium–antimony–tellurium-based films with a diffraction-limited resolution optical writing process to demonstrate a variety of devices: visible-range reconfigurable bichromatic and multi-focus Fresnel zone plates, a super-oscillatory lens with subwavelength focus, a greyscale hologram, and a dielectric metamaterial with on-demand reflection and transmission resonances