An All-Dielectric Polaritonic Metasurface with a Giant Nonlinear Optical Response.

Enhancing the efficiency of second-harmonic generation using all-dielectric metasurfaces to date has mostly focused on electromagnetic engineering of optical modes in the meta-atom. Further advances in nonlinear conversion efficiencies can be gained by engineering the material nonlinearities at the nanoscale, however this cannot be achieved using conventional materials. Semiconductor heterostructures that support resonant nonlinearities using quantum engineered intersubband transitions can provide this new degree of freedom. By simultaneously optimizing the heterostructures and meta-atoms, we experimentally realize an all-dielectric polaritonic metasurface with a maximum second-harmonic generation power conversion factor of 0.5 mW/W2 and power conversion efficiencies of 0.015% at nominal pump intensities of 11 kW/cm2. These conversion efficiencies are higher than the record values reported to date in all-dielectric nonlinear metasurfaces but with 3 orders of magnitude lower pump power. Our results therefore open a new direction for designing efficient nonlinear all-dielectric metasurfaces for new classical and quantum light sources.

Sequence Ontology terminology for gene regulation.

The Sequence Ontology (SO) is a structured, controlled vocabulary that provides terms and definitions for genomic annotation. The Gene Regulation Ensemble Effort for the Knowledge Commons (GREEKC) initiative has gathered input from many groups of researchers, including the SO, the Gene Ontology (GO), and gene regulation experts, with the goal of curating information about how gene expression is regulated at the molecular level. Here we discuss recent updates to the SO reflecting current knowledge. We have developed more accurate human-readable terms (also known as classes), including new definitions, and relationships related to the expression of genes. New findings continue to give us insight into the biology of gene regulation, including the order of events, and participants in those events. These updates to the SO support logical reasoning with the current understanding of gene expression regulation at the molecular level.

Manipulation of quantum dot emission with semiconductor metasurfaces exhibiting magnetic quadrupole resonances.

Optical metasurfaces were suggested as a route for engineering advanced light sources with tailored emission properties. In particular, they provide a control over the emission directionality, which is essential for single-photon sources and LED applications. Here, we experimentally study light emission from a metasurface composed of III-V semiconductor Mie-resonant nanocylinders with integrated quantum dots (QDs). Specifically, we focus on the manipulation of the directionality of spontaneous emission from the QDs due to excitation of different magnetic quadrupole resonances in the nanocylinders. To this end, we perform both back focal plane imaging and momentum-resolved spectroscopy measurements of the emission. This allows for a comprehensive analysis of the effect of the different resonant nanocylinder modes on the emission characteristics of the metasurface. Our results show that the emission directionality can be manipulated by an interplay of the excited quadrupolar nanocylinder modes with the metasurface lattice modes and provide important insights for the design of novel smart light sources and new display concepts.

Strong Coupling in All-Dielectric Intersubband Polaritonic Metasurfaces.

Mie-resonant dielectric metasurfaces are excellent candidates for both fundamental studies related to light-matter interactions and for numerous applications ranging from holography to sensing to nonlinear optics. To date, however, most applications using Mie metasurfaces utilize only weak light-matter interaction. Here, we go beyond the weak coupling regime and demonstrate for the first time strong polaritonic coupling between Mie photonic modes and intersubband (ISB) transitions in semiconductor heterostructures. Furthermore, along with demonstrating ISB polaritons with Rabi splitting as large as 10%, we also demonstrate the ability to tailor the strength of strong coupling by engineering either the semiconductor heterostructure or the photonic mode of the resonators. Unlike previous plasmonic-based works, our new all-dielectric metasurface approach to generate ISB polaritons is free from ohmic losses and has high optical damage thresholds, thereby making it ideal for creating novel and compact mid-infrared light sources based on nonlinear optics.

Adverse and benevolent childhood experiences in Posttraumatic Stress Disorder (PTSD) and Complex PTSD (CPTSD): implications for trauma-focused therapies.

BACKGROUND: There is very little work on the role of positive or benevolent childhood experiences and how such events might offer protection from the insidious effects of adverse experiences in childhood or later in life. OBJECTIVES: We set out to test, using latent variable modelling, whether adverse and benevolent childhood experiences could be best described as a single continuum or two correlated constructs. We also modelled the relationship between adverse and benevolent childhood experiences and ICD-11 PTSD and Complex PTSD (CPTSD) symptoms and explored if these associations were indirect via psychological trauma. METHODS: Data were collected from a trauma-exposed sample (N = 275) attending a specialist trauma care centre in the UK. Participants completed measures of childhood adverse and benevolent experiences, traumatic exposure, and PTSD and CPTSD symptoms. RESULTS: Findings suggested that adverse childhood experiences operate only indirectly on PTSD and CPTSD symptoms through lifetime trauma exposure, and with a stronger effect for PTSD. Benevolent childhood experiences directly predicted only CPTSD symptoms. CONCLUSIONS: Benevolent and traumatic experiences seem to form unique associations with PTSD and CPTSD symptoms. Future research is needed to explore how benevolent experiences can be integrated within existing psychological interventions to maximise recovery from traumatic stress.

Objetivos: Nos propusimos evaluar, usando un modelo de variables latentes, si experiencias adversas y benignas en la infancia podrían ser mejor descritas como un continuo simple o bien como dos constructos correlacionados. También modelamos la relación entre experiencias adversas y benignas en la infancia y síntomas de TEPT y TEPT complejo (TEPTc) según la CIE-11 y exploramos si estas asociaciones eran indirectas a través del trauma psicológico.Métodos: Los datos fueron obtenidos de una muestra expuesta a trauma (N=275) que acudía a un centro especializado en trauma en el Reino Unido. Los participantes completaron mediciones sobre experiencias adversas y benignas en la infancia, exposición a trauma, y síntomas de TEPT y TEPTc.Resultados: Los hallazgos sugirieron que las experiencias adversas en la infancia operan sólo indirectamente en síntomas de TEPT y TEPTc a lo largo de exposición a trauma en la vida, con un importante efecto para TEPT. Las experiencias benignas en la infancia predijeron directamente sólo síntomas de TEPTc.Conclusiones: Las experiencias adversas y benignas parecen formar asociaciones particulares con síntomas de TEPT y TEPTc. Se requieren investigaciones futuras para explorar cómo las experiencias benignas pueden ser integradas en intervenciones psicológicas existentes para optimizar la recuperación de estrés traumático.

Frequency Conversion in a Time-Variant Dielectric Metasurface.

The color of light is a fundamental property of electromagnetic radiation; as such, control of the frequency is a cornerstone of modern optics. Nonlinear materials are typically used to generate new frequencies, however the use of time-variant systems provides an alternative approach. Utilizing a metasurface that supports a high-quality factor resonance, we demonstrate that a rapidly shifting refractive index will induce frequency conversion of light that is confined in the nanoresonator meta-atoms. We experimentally observe this frequency conversion and develop a time-dependent coupled mode theory model that well describes the system. The intersection of high quality-factor resonances, active materials, and ultrafast transient spectroscopy leads to the demonstration of metasurfaces operating in a time-variant regime that enables enhanced control over light-matter interaction.

Using social media to estimate visitor provenance and patterns of recreation in Germany's national parks.

Social media data are increasingly utilised as a low-cost alternative to visitor surveys in characterising nature-based recreation. However, the information available on individual users is limited and typically does not include provenance, restricting the potential applications and impact of the data. Here we investigate a methodology to estimate social media visitors' home locations at various spatial scales and apply it to the entire network of national parks in Germany. We compare predicted visitor provenance to representative onsite survey data and explore group-specific spatial and temporal patterns of recreation as characterised by users' geotagged photographs. Results show that photograph metadata can be used to assign home locations with accuracies between 62 and 89% depending on spatial scale implemented. Said social media-based predictions are reasonably well representative of the surveyed visitor structure in German national parks with Flickr visitor-days composed of 19% local, 62% non-local German and 19% international visits.

Coupling between plasmonic and photonic crystal modes in suspended three-dimensional meta-films.

A complementary metal oxide semiconductor (CMOS) compatible fabrication method for creating three-dimensional (3D) meta-films is presented. In contrast to metasurfaces, meta-films possess structural variation throughout the thickness of the film and can possess a sub-wavelength scale structure in all three dimensions. Here we use this approach to create 2D arrays of cubic silicon nitride unit cells with plasmonic inclusions of elliptical metallic disks in horizontal and vertical orientations with lateral array-dimensions on the order of millimeters. Fourier transform infrared (FTIR) spectroscopy is used to measure the infrared transmission of meta-films with either horizontally or vertically oriented ellipses with varying eccentricity. Shape effects due to the ellipse eccentricity, as well as localized surface plasmon resonance (LSPR) effects due to the effective plasmonic wavelength are observed in the scattering response. The structures were modeled using rigorous coupled wave analysis (RCWA), finite difference time domain (Lumerical), and frequency domain finite element (COMSOL). The silicon nitride support structure possesses a complex in-plane photonic crystal slab band structure due to the periodicity of the unit cells. We show that adjustments to the physical dimensions of the ellipses can be used to control the coupling to this band structure. The horizontally oriented ellipses show narrow, distinct plasmonic resonances while the vertically oriented ellipses possess broader resonances, with lower overall transmission amplitude for a given ellipse geometry. We attribute this difference in resonance behavior to retardation effects. The ability to couple photonic slab modes with plasmonic inclusions enables a richer space of optical functionality for design of metamaterial-inspired optical components.

Using STADIA to quantify dynamic instability in microtubules.

Quantification of microtubule (MT) dynamic instability (DI) is essential to mechanistic dissection of MT assembly and the activities of MT binding proteins. Typical methods for quantifying MT dynamics assume that MT behavior consists of growth and shortening phases, with instantaneous transitions (rescues and catastrophes) in between. However, examination of DI data at high temporal and spatial resolution reveals the presence of ambiguous behaviors that cannot easily fit into these categories. Failure to objectively recognize and quantify these behaviors could reduce the reproducibility of DI data and impact attempts to dissect mechanisms. To address these problems, we recently developed STADIA (Statistical Tool for Automated Dynamic Instability Analysis), a MT analysis software package that uses length-history data as input and is (presently) implemented in MATLAB. STADIA uses machine learning methods to objectively analyze and quantify macro-level DI behaviors exhibited by MTs, including variable rates of growth and shortening and a newly quantified DI phase: stutter. Here we overview the process of using STADIA to quantify MT dynamics and provide a set of concrete protocols for using STADIA to process and analyze MT length history data.

Semiconductor Hyperbolic Metamaterials at the Quantum Limit.

We study semiconductor hyperbolic metamaterials (SHMs) at the quantum limit experimentally using spectroscopic ellipsometry as well as theoretically using a new microscopic theory. The theory is a combination of microscopic density matrix approach for the material response and Green's function approach for the propagating electric field. Our approach predicts absorptivity of the full multilayer system and for the first time allows the prediction of in-plane and out-of-plane dielectric functions for every individual layer constructing the SHM as well as effective dielectric functions that can be used to describe a homogenized SHM.

Light-Emitting Metasurfaces: Simultaneous Control of Spontaneous Emission and Far-Field Radiation.

Light-emitting sources and devices permeate every aspect of our lives and are used in lighting, communications, transportation, computing, and medicine. Advances in multifunctional and "smart lighting" would require revolutionary concepts in the control of emission spectra and directionality. Such control might be possible with new schemes and regimes of light-matter interaction paired with developments in light-emitting materials. Here we show that all-dielectric metasurfaces made from III-V semiconductors with embedded emitters have the potential to provide revolutionary lighting concepts and devices, with new functionality that goes far beyond what is available in existing technologies. Specifically, we use Mie-resonant metasurfaces made from semiconductor heterostructures containing epitaxial quantum dots. By controlling the symmetry of the resonant modes, their overlap with the emission spectra, and other structural parameters, we can enhance the brightness by 2 orders of magnitude, as well as reduce its far-field divergence significantly.

An all-dielectric metasurface as a broadband optical frequency mixer.

A frequency mixer is a nonlinear device that combines electromagnetic waves to create waves at new frequencies. Mixers are ubiquitous components in modern radio-frequency technology and microwave signal processing. The development of versatile frequency mixers for optical frequencies remains challenging: such devices generally rely on weak nonlinear optical processes and, thus, must satisfy phase-matching conditions. Here we utilize a GaAs-based dielectric metasurface to demonstrate an optical frequency mixer that concurrently generates eleven new frequencies spanning the ultraviolet to near-infrared. The even and odd order nonlinearities of GaAs enable our observation of second-harmonic, third-harmonic, and fourth-harmonic generation, sum-frequency generation, two-photon absorption-induced photoluminescence, four-wave mixing and six-wave mixing. The simultaneous occurrence of these seven nonlinear processes is assisted by the combined effects of strong intrinsic material nonlinearities, enhanced electromagnetic fields, and relaxed phase-matching requirements. Such ultracompact optical mixers may enable a plethora of applications in biology, chemistry, sensing, communications, and quantum optics.

A crowdsourced valuation of recreational ecosystem services using social media data: An application to a tropical wetland in India.

Online social media represent an extensive, opportunistic source of behavioral data and revealed preferences for ecosystem services (ES) analysis. Such data may allow to advance the approach, scale and timespan to which ES are assessed, mapping and valued. This is especially relevant in the context of developing regions whose decision support tools are often limited by a lack of resources and funding. This research presents an economic valuation tool for recreational ES, suitable at wide spatial scales, relying on crowdsourced metadata from social media with a proof of concept tested on an Indian tropical Ramsar wetland. We demonstrate how geotagged photographs from Flickr can be used in the context of a developing country to (i) map nature-based recreation patterns, (ii) value recreational ecosystem services, and (iii) investigate how recreational benefits are affected by changes in ecosystem quality. The case-study application is the Vembanad Lake in Kerala, India, and the adjacent backwaters. Geographic Information Systems are implemented to extract 4328 Flickr photographs that are used to map hot spots of recreation and infer the home location of wetland visitors from within Kerala state with good accuracy. An individual, single-site travel cost demand function is generated and estimated using both Poisson and Negative Binomial regressions, which results in mean consumer surplus estimates between Rs. 2227-3953 ($34-$62) per visit and annual domestic recreation benefits of Rs. 7.53-13.37 billion ($115.5-$205 million) in the investigated wetlands. Improvement in water quality to a level that supports wildlife and fisheries is projected to result in a Rs. 260 million ($4 million) annual increase in recreational benefits, while restoring previously encroached lake area would result in almost Rs. 50 million ($760,000) in yearly value increase.

Tunable dual-band graphene-based infrared reflectance filter.

We experimentally demonstrated an actively tunable optical filter that controls the amplitude of reflected long-wave-infrared light in two separate spectral regions concurrently. Our device exploits the dependence of the excitation energy of plasmons in a continuous and unpatterned sheet of graphene on the Fermi-level, which can be controlled via conventional electrostatic gating. The filter enables simultaneous modification of two distinct spectral bands whose positions are dictated by the device geometry and graphene plasmon dispersion. Within these bands, the reflected amplitude can be varied by over 15% and resonance positions can be shifted by over 90 cm-1. Electromagnetic simulations verify that tuning arises through coupling of incident light to graphene plasmons by a grating structure. Importantly, the tunable range is determined by a combination of graphene properties, device structure, and the surrounding dielectrics, which dictate the plasmon dispersion. Thus, the underlying design shown here is applicable across a broad range of infrared frequencies.

Takeoff orientation of the major aortic arch branches irrespective of arch type: Ramifications for brachiocephalic interventions including carotid stenting.

BACKGROUND: Our previous work demonstrating great ease and predictability of cannulation of the major aortic arch branches with an upwardly pointing 3DR catheter, irrespective of aortic arch type, led us to hypothesize that centering or "cresting" of these vessels must occur along the superior most aspect of the aortic arch in a curvilinear fashion. METHODS: We retrospectively analyzed 111 computed tomographic scans of the chest and thoracic aorta with intravenous contrast performed at our hospital between April 2011 and May 2012 utilizing TeraRecon image reconstruction software. Four studies were excluded due to poor image quality and/or surgical changes to native aortic architecture. RESULTS: Of the 107 studies included, 104 (97.2%) demonstrated centering of the major aortic arch branches on a curvilinear line "cresting" the superior most aspect of the aortic arch irrespective of arch type. Of the three studies that did not demonstrate this "cresting," two were found to have aberrant right subclavian arteries associated with a type I aortic arch, and one had an aberrant right common carotid associated with a type II aortic arch. CONCLUSION: Operators engaging major aortic arch branches need to be mindful of the fact that these vessels are indeed centered on a line "cresting" along the superior most aspect of the aortic arch, and any algorithm that, by taking this information into account, reduces catheter manipulation in the aortic arch could potentially result in a reduction in distal atheroembolic events.

Suggested Bony Landmarks for Safe Axillary Artery Access.

OBJECTIVE: To identify a fluoroscopic bony landmark for safe percutaneous axillary artery cannulation. BACKGROUND: No bony landmarks exist to guide safe percutaneous axillary artery cannulation, which is an important alternate access site for catheter-based procedures in selected patients. METHODS: We retrospectively analyzed 51 consecutive percutaneous axillary artery sheath angiograms and attempted to correlate a fixed bony landmark to the proximal end of the third part of the artery. Proximal to this site, no cords of the brachial plexus traverse the anterior aspect of the vessel. Moreover, this site is proximal to the subscapular branch of the axillary artery, the first branch of its third part, and a sentinel component of the scapular anastomosis responsible for collateral blood flow to the arm. RESULTS: With the arm abducted at 135°, the subscapular artery originated at, or distal to, the inferior border of the glenoid cavity, as seen on fluoroscopy in the anterior-posterior projection, in all patients. The origin was within 5 mm distal to the inferior border of the glenoid cavity in 17 patients (46%), 5-10 mm in 13 patients (35%), and between 10 mm and 20 mm in 7 patients (19%). CONCLUSIONS: With the arm abducted, the origin of the subscapular artery correlates well with the inferior-most aspect of the glenoid cavity of the scapula under fluoroscopy. Axillary artery cannulation medial to this bony landmark typically lands the sheath in the second part or proximal end of the third part of the artery, thereby theoretically sparing injury to the brachial plexus and the subscapular artery.