Picophotonic localization metrology beyond thermal fluctuations.

Despite recent tremendous progress in optical imaging and metrology1-6, there remains a substantial resolution gap between atomic-scale transmission electron microscopy and optical techniques. Is optical imaging and metrology of nanostructures exhibiting Brownian motion possible with such resolution, beyond thermal fluctuations? Here we report on an experiment in which the average position of a nanowire with a thermal oscillation amplitude of ∼150 pm is resolved in single-shot measurements with subatomic precision of 92 pm, using light at a wavelength of λ = 488 nm, providing an example of such sub-Brownian metrology with ∼λ/5,300 precision. To localize the nanowire, we employ a deep-learning analysis of the scattering of topologically structured light, which is highly sensitive to the nanowire's position. This non-invasive metrology with absolute errors down to a fraction of the typical size of an atom, opens a range of opportunities to study picometre-scale phenomena with light.

Optical Control of Nanomechanical Brownian Motion Eigenfrequencies in Metamaterials.

Nanomechanical photonic metamaterials provide a wealth of active switching, nonlinear, and enhanced light-matter interaction functionalities by coupling optically and mechanically resonant subsystems. Thermal (Brownian) motion of the nanostructural components of such metamaterials leads to fluctuations in optical properties, which may manifest as noise, but which also present opportunity to characterize performance and thereby optimize design at the level of individual nanomechanical elements. We show that nanomechanical motion in an all-dielectric metamaterial ensemble of silicon-on-silicon-nitride nanowires can be controlled by light at sub-µW/µm2 intensities. Induced changes in nanowire temperature of just a few Kelvin and nonthermal optical forces generated within the structure change the few-MHz Eigenfrequencies and/or picometric displacement amplitudes of motion, and thereby metamaterial transmission. The tuning mechanism can provide active control of frequency response in photonic metadevices and may serve as a basis for bolometric, mass, and micro/nanostructural stress sensing.

Deep-Learning-Assisted Focused Ion Beam Nanofabrication.

Focused ion beam (FIB) milling is an important rapid prototyping tool for micro- and nanofabrication and device and materials characterization. It allows for the manufacturing of arbitrary structures in a wide variety of materials, but establishing the process parameters for a given task is a multidimensional optimization challenge, usually addressed through time-consuming, iterative trial-and-error. Here, we show that deep learning from prior experience of manufacturing can predict the postfabrication appearance of structures manufactured by focused ion beam (FIB) milling with >96% accuracy over a range of ion beam parameters, taking account of instrument- and target-specific artifacts. With predictions taking only a few milliseconds, the methodology may be deployed in near real time to expedite optimization and improve reproducibility in FIB processing.

Coherently switching the focusing characteristics of all-dielectric metalenses.

Flat, gradient index, metasurface optics - in particular all-dielectric metalenses - have emerged and evolved over recent years as compact, lightweight alternative to their conventional bulk glass/crystal counterparts. Here we show that the focal properties of all-dielectric metalenses can be switched via coherent control, which is to say by changing the local electromagnetic field in the metalens plane rather than any physical or geometric property of the nanostructure or surrounding medium. The selective excitation of predominantly electric or magnetic resonant modes in the constituent cells of the metalens provides for switching, by design, of its phase profile enabling binary switching of focal length for a given lens type and, uniquely, switching between different (spherical and axicon) lens types.

Visualization of Subatomic Movements in Nanostructures.

Electron microscopy, scanning probe, and optical super-resolution imaging techniques with nanometric resolution are now routinely available but cannot capture the characteristically fast (MHz-GHz frequency) movements of micro-/nano-objects. Meanwhile, optical interferometric techniques can detect high-frequency picometric displacements but only with diffraction-limited lateral resolution. Here, we introduce a motion visualization technique, based on the spectrally resolved detection of secondary electron emission from moving objects, that combines picometric displacement sensitivity with the nanometric spatial (positional/imaging) resolution of electron microscopy. The sensitivity of the technique is quantitatively validated against the thermodynamically defined amplitude of a nanocantilever's Brownian motion. It is further demonstrated in visualizing externally driven modes of cantilever, nanomechanical photonic metamaterial, and MEMS device structures. With a noise floor reaching ∼1 pm/Hz1/2, it can provide for the study of oscillatory movements with subatomic amplitudes, presenting new opportunities for the interrogation of motion in functional structures across the materials, bio- and nanosciences.

Artificial intelligence for photonics and photonic materials.

Artificial intelligence (AI) is the most important new methodology in scientific research since the adoption of quantum mechanics and it is providing exciting results in numerous fields of science and technology. In this review we summarize research and discuss future opportunities for AI in the domains of photonics, nanophotonics, plasmonics and photonic materials discovery, including metamaterials.

Continuous beam steering by coherent light-by-light control of dielectric metasurface phase gradient.

Continuous and reversible tuning of the properties of optical metasurfaces, as a functionality that would enable a range of device applications, has been a focus of the metasurface research field in recent years. Tuning mechanisms proposed and demonstrated so far have generally relied upon changing the morphology of a metasurface or the intrinsic properties of its constituent materials. Here we introduce, via numerical simulation, an alternative approach to achieve continuous tuning of gradient metasurface response, and illustrate its potential application to the challenge of continuous beam steering, as required for example in LIDAR and machine vision systems. It is based upon the coherent illumination of a silicon nano-pillar metasurface with two counter-propagating beams. Control of the input beams' relative phase and intensity enables tuning of the individual nano-pillars' electromagnetic response and thereby the phase gradient of the array, which in turn steers the direction of the output beam continuously over an angular range of approximately 9 degrees.

Reconfigurable Ultraviolet and High-Energy Visible Dielectric Metamaterials.

Photonic materials with tunable and switchable ultraviolet (UV) to high-energy visible (HEV) optical properties may benefit applications such as sensing, high-density optical memory, beam-steering, adaptive optics, and light modulation. Here, for the first time we demonstrate a nonvolatile switchable dielectric metamaterial operating in the UV-HEV spectral range. Nanograting metamaterials in a layered composite of low-loss ZnS/SiO2 and the chalcogenide phase-change medium germanium-antimony-telluride (Ge2Sb2Te5 or GST) exhibit reflection resonances at UV-HEV wavelengths that are substantially modified by light-induced (amorphous-crystalline) phase transitions in the chalcogenide layer. Despite the presence of the lossy GST, resonance quality factors up to Q ∼ 15 are ensured by the transparency (low losses) of ZnS/SiO2 in the UV-HEV spectral range and values of Q increase as the refractive index of Ge2Sb2Te5 decreases, upon crystallization. Notably, however, this switching leaves resonance spectral positions unchanged.

Changes in EEG multiscale entropy and power-law frequency scaling during the human sleep cycle.

We explored changes in multiscale brain signal complexity and power-law scaling exponents of electroencephalogram (EEG) frequency spectra across several distinct global states of consciousness induced in the natural physiological context of the human sleep cycle. We specifically aimed to link EEG complexity to a statistically unified representation of the neural power spectrum. Further, by utilizing surrogate-based tests of nonlinearity we also examined whether any of the sleep stage-dependent changes in entropy were separable from the linear stochastic effects contained in the power spectrum. Our results indicate that changes of brain signal entropy throughout the sleep cycle are strongly time-scale dependent. Slow wave sleep was characterized by reduced entropy at short time scales and increased entropy at long time scales. Temporal signal complexity (at short time scales) and the slope of EEG power spectra appear, to a large extent, to capture a common phenomenon of neuronal noise, putatively reflecting cortical balance between excitation and inhibition. Nonlinear dynamical properties of brain signals accounted for a smaller portion of entropy changes, especially in stage 2 sleep.

Sleep restriction alters reactive aggressive behavior and its relationship with sex hormones.

Few studies have experimentally manipulated sleep to study its effect on aggressive behavior. The current study examined how reactive aggression was affected by having sleep restricted to 4-hours on a single night, a level of disruption commonly experienced. Both rested and sleep-restricted participants completed the Point Subtraction Aggression Paradigm (PSAP), a laboratory task in which participants seek to earn points, are provoked by a fictitious opponent stealing their points, and may choose to steal points in response. Logistic mixed-effect models were used to investigate the effect of sleep restriction and the role of sex hormones on the odds of choosing to steal. For men, and women in the luteal phase of the menstrual cycle, sleep restriction did not result in significant changes reactive aggression, although the patterns of aggressive behavior appeared less reactive and retaliatory in nature. For women in the follicular phase of the menstrual cycle, sleep restriction was associated with higher levels of reactive aggression. For both men and women in the luteal phase, sleep restriction disrupted an association between hormone change over the task (testosterone and estradiol, respectively) and reactive aggression that was observed in their control participants. In addition, higher testosterone before the PSAP in men was associated with maintaining a high level of stealing over the task. These results indicate a complex dynamic in which sex hormones and sleep interact to predict aggressive behavior in response to provocation.

A daytime nap enhances visual working memory performance and alters event-related delay activity.

Working memory (WM) is impaired following sleep loss and may be improved after a nap. The goal of the current study was to better understand sleep-related WM enhancement by: (1) employing a WM task that assesses the ability to hold and report visual representations as well as the fidelity of the reports on a fine scale, (2) investigating neurophysiological properties of sleep and WM capacity as potential predictors or moderators of sleep-related enhancement, and (3) exploring frontal and occipital event-related delay activity to index the neural processing of stimuli in WM. In a within-subjects design, 36 young adults (Mage = 20, 20 men, 16 women) completed a 300-trial, continuous-report task of visual WM following a 90-min nap opportunity and an equivalent period of wakefulness. Mixed-effect models were used to estimate the odds of successful WM reports and the fidelity of those reports. The odds of a successful report were approximately equal between nap and wake conditions for the start of the task, but by the end, the odds of success were 1.26 times greater in the nap condition. Successful WM reports were more accurate after a nap, independent of the time on task. Neither WM capacity nor any of the sleep variables measured were found to significantly moderate the nap effect on WM. Lastly, napping resulted in amplitude changes for frontal and occipital delay activity relative to the wake condition. The findings are discussed in relation to contemporary models of visual WM and the role of sleep in sustained attention.

Coherent illumination spectroscopy of nanostructures and thin films on thick substrates.

Many nanophotonic and nanoelectronic devices contain nanostructures and ultrathin films on the surface of a thick, effectively semi-infinite, substrate. Here we consider a spectroscopic technique based upon coherent illumination, for characterising such samples. The method uses two counter-propagating light beams to generate specific field configurations at the substrate surface plane, which can be modulated, for example, to selectively excite and thereby discriminate between resonant modes of plasmonic nanostructures, or to measure thin films thickness with nanometre resolution. The technique offers a variety of practical applications for the coherent illumination in solid state physics, analytical chemistry, biochemistry, and nano-engineering.

Compositionally controlled plasmonics in amorphous semiconductor metasurfaces.

Amorphous bismuth telluride (Bi:Te) provides a composition-dependent, CMOS-compatible alternative material platform for plasmonics in the ultraviolet-visible spectral range. Thin films of the chalcogenide semiconductor are found, using high-throughput physical vapor deposition and characterization techniques, to exhibit a plasmonic response (a negative value of the real part of relative permittivity) over a band of wavelengths extending from ~250 nm to between 530 and 978 nm, depending on alloy composition (Bi:Te at% ratio). The plasmonic response is illustrated via the fabrication of subwavelength period nano-grating metasurfaces, which present strong, period-dependent plasmonic absorption resonances in the visible range, manifested in the perceived color of the nanostructured domains in reflection.

Functional characterization of a novel family of acetylcholine-gated chloride channels in Schistosoma mansoni.

Acetylcholine is the canonical excitatory neurotransmitter of the mammalian neuromuscular system. However, in the trematode parasite Schistosoma mansoni, cholinergic stimulation leads to muscle relaxation and a flaccid paralysis, suggesting an inhibitory mode of action. Information about the pharmacological mechanism of this inhibition is lacking. Here, we used a combination of techniques to assess the role of cholinergic receptors in schistosome motor function. The neuromuscular effects of acetylcholine are typically mediated by gated cation channels of the nicotinic receptor (nAChR) family. Bioinformatics analyses identified numerous nAChR subunits in the S. mansoni genome but, interestingly, nearly half of these subunits carried a motif normally associated with chloride-selectivity. These putative schistosome acetylcholine-gated chloride channels (SmACCs) are evolutionarily divergent from those of nematodes and form a unique clade within the larger family of nAChRs. Pharmacological and RNA interference (RNAi) behavioral screens were used to assess the role of the SmACCs in larval motor function. Treatment with antagonists produced the same effect as RNAi suppression of SmACCs; both led to a hypermotile phenotype consistent with abrogation of an inhibitory neuromuscular mediator. Antibodies were then generated against two of the SmACCs for use in immunolocalization studies. SmACC-1 and SmACC-2 localize to regions of the peripheral nervous system that innervate the body wall muscles, yet neither appears to be expressed directly on the musculature. One gene, SmACC-1, was expressed in HEK-293 cells and characterized using an iodide flux assay. The results indicate that SmACC-1 formed a functional homomeric chloride channel and was activated selectively by a panel of cholinergic agonists. The results described in this study identify a novel clade of nicotinic chloride channels that act as inhibitory modulators of schistosome neuromuscular function. Additionally, the iodide flux assay used to characterize SmACC-1 represents a new high-throughput tool for drug screening against these unique parasite ion channels.

Sleep physiology predicts memory retention after reactivation.

Both sleep and future relevance influence memory consolidation; however, limited research has investigated their role in memory reconsolidation. We manipulated the future relevance of both stable and labile memories in need of reconsolidation. Two groups learned two blocks of syllable pairs on one evening and were told they would be tested on one of the blocks later. On the second evening, one group (Labile) received reminders designed to return their memories of syllable pairs to a labile state, while a second group (Stable) received reminders designed to leave these memories in a stable state. No significant differences in memory retention were found between blocks or groups the following morning. Frontal delta (0.5-4 Hz) electroencephalographic power during Stage 2 sleep correlated positively with retention of future-relevant material exclusively in the Labile group. Central theta (4-8 Hz) electroencephalographic power during rapid eye movement (REM) sleep correlated positively with the extent to which the Labile group selectively retained future-relevant material. These relationships suggest that sleep-dependent processes are involved in an economical reprocessing of memories beyond the initial stages of consolidation.

What is the use of imaging before referral to an orthopaedic oncologist? A prospective, multicenter investigation.

BACKGROUND: Patients often receive advanced imaging before referral to an orthopaedic oncologist. The few studies that have evaluated the value of these tests have been single-center studies, and there were large discrepancies in the estimated frequencies of unnecessary use of diagnostic tests. QUESTIONS/PURPOSES: (1) Is there regional variation in the use of advanced imaging before referral to an orthopaedic oncologist? (2) Are these prereferral studies helpful to the treating orthopaedic oncologist in making a diagnosis or treatment plan? (3) Are orthopaedic surgeons less likely to order unhelpful studies than other specialties? (4) Are there any tumor or patient characteristics that are associated with the ordering of an unhelpful study? METHODS: We performed an eight-center prospective analysis of patients referred for evaluation by a fellowship-trained orthopaedic oncologist. We recorded patient factors, referral details, advanced imaging performed, and presumptive diagnosis. The treating orthopaedic oncologist determined whether each study was helpful in the diagnosis or treatment of the patient based on objective and subjective criteria used in prior investigations. We analyzed the data using bivariate methods and logistic regression to determine regional variation and risk factors predictive of unhelpful advanced imaging. Of the 371 participants available for analysis, 301 (81%) were referred with an MRI, CT scan, bone scan, ultrasound, or positron emission tomography scan. RESULTS: There were no regional differences in the use of advanced imaging (range of patients presenting with advanced imaging 66%-88% across centers, p = 0.164). One hundred thirteen patients (30%) had at least one unhelpful study; non-MRI advanced imaging was more likely to be unhelpful than MRIs (88 of 129 [68%] non-MRI imaging versus 46 of 263 [17%] MRIs [p < 0.001]). Orthopaedic surgeons were no less likely than nonorthopaedic surgeons to order unhelpful studies before referral to an orthopaedic oncologist (56 of 179 [31%] of patients referred by orthopaedic surgeons versus 35 of 119 [29%] referred by primary care providers and 22 of 73 [30%] referred by nonorthopaedic specialists, p = 0.940). After controlling for potential confounding variables, benign bone lesions had an increased odds of referral with an unhelpful study (59 of 145 [41%] of benign bone tumors versus 54 of 226 [24%] of soft tissue tumors and malignant bone tumors; odds ratio, 2.80; 95% confidence interval, 1.68-4.69, p < 0.001). CONCLUSIONS: We found no evidence that the proportion of patients referred with advanced imaging varied dramatically by region. Studies other than MRI were likely to be considered unhelpful and should not be routinely ordered by referring physicians. Diligent education of orthopaedic surgeons and primary care physicians in the judicious use of advanced imaging in benign bone tumors may help mitigate unnecessary imaging. LEVEL OF EVIDENCE: Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Reduced Length of Hospitalization in Primary Total Knee Arthroplasty Patients Using an Updated Enhanced Recovery After Orthopedic Surgery (ERAS) Pathway.

Decreasing hospital length of stay may attenuate costs associated with total knee arthroplasty. The purpose of this study was to determine if updates to an existing orthopedic enhanced recovery after surgery (ERAS) pathway would improve length of hospitalization. Clinical and demographic data were collected on 252 primary total knee arthroplasties between January 2012 and July 2013. Pre-updated and post-updated ERAS pathway cohorts were analyzed for length of stay, clinical outcomes, and re-admissions. The mean length of stay decreased from 76.6 hours to 56.1 hours after implementation of the evidence-based orthopedic enhanced recovery after surgery pathway (P<0.001). This improvement was possible without a concomitant increase in readmission rates.

Coherent control of Snell's law at metasurfaces.

It was recently demonstrated that the well-known Snell's law must be corrected for phase gradient metasurfaces to account for their spatially varying phase, leading to normal and anomalous transmission and reflection of light on such metasurfaces. Here we show that the efficiency of normal and anomalous transmission and reflection of light can be controlled by the intensity or phase of a second coherent wave. The phenomenon is illustrated using gradient metasurfaces based on V-shaped and rectangular apertures in a metal film. This coherent control effect can be exploited for wave front shaping and signal routing.

Giant optical forces in planar dielectric photonic metamaterials.

We demonstrate that resonant optical forces generated within all-dielectric planar photonic metamaterials at near-infrared illumination wavelengths can be an order of magnitude larger than in corresponding plasmonic metamaterials, reaching levels many tens of times greater than the force resulting from radiation pressure. This is made possible by the dielectric structures' freedom from Joule losses and the consequent ability to sustain Fano-resonances with high quality factors that are unachievable in plasmonic nanostructures. Dielectric nano-optomechanical metamaterials can thus provide a functional platform for a range of novel dynamically controlled and self-adaptive nonlinear, tunable/switchable photonic metamaterials.

Domain-general mechanisms: what they are, how they evolved, and how they interact with modular, domain-specific mechanisms to enable cohesive human groups.

Domain-general mechanisms are evolutionarily ancient, resulting from the evolution of affective cues signaling the attainment of evolutionary goals. Explicit processing is a particularly important set of domain-general mechanisms for constructing human groups - enabling ideologies specifying future goal states and rationalizing group aims, enabling knowledge of others' reputations essential to cooperation, understanding the rights and obligations of group membership, monitoring group members, and providing appropriate punishments to those who deviate from group aims.