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Heat is transferred by radiation between two well-separated bodies at temperatures of finite difference in vacuum. At large distances the heat transfer can be described by black body radiation, at shorter distances evanescent modes start to contribute, and at separations comparable to inter-atomic spacing the transition to heat conduction should take place. We report on quantitative measurements of the near-field mediated heat flux between a gold coated near-field scanning thermal microscope tip and a planar gold sample at nanometre distances of 0.2–7 nm. We find an extraordinary large heat flux which is more than five orders of magnitude larger than black body radiation and four orders of magnitude larger than the values predicted by conventional theory of fluctuational electrodynamics. Different theories of phonon tunnelling are not able to describe the observations in a satisfactory way. The findings demand modified or even new models of heat transfer across vacuum gaps at nanometre distances. Kloppstechet al. report experimental observations of the heat transfer between a gold tip and an atomically flat gold sample in the 0.2–7 nm regime. The observed flux rates are four orders of magnitude larger than expected from theory, suggesting the possibility of additional heat transfer mechanisms.

We describe a recently developed formulation of coupled conductive and radiative heat transfer (RHT) between objects separated by nanometric, vacuum gaps. Our results rely on analytical formulas of RHT between planar slabs (based on the scattering-matrix method) as well as a general formulation of RHT between arbitrarily shaped bodies (based on the fluctuating–volume current method), which fully captures the existence of temperature inhomogeneities. In particular, the impact of RHT on conduction, and vice versa, is obtained via self-consistent solutions of the Fourier heat equation and Maxwell’s equations. We show that in materials with low thermal conductivities (e.g. zinc oxides and glasses), the interplay of conduction and RHT can strongly modify heat exchange, exemplified for instance by the presence of large temperature gradients and saturating flux rates at short (nanometric) distances. More generally, we show that the ability to tailor the temperature distribution of an object can modify the behaviour of RHT with respect to gap separations, e.g. qualitatively changing the asymptotic scaling at short separations from quadratic to linear or logarithmic. Our results could be relevant to the interpretation of both past and future experimental measurements of RHT at nanometric distances.

The first γ-ray spectroscopy of ^{52}Ar, with the neutron number N=34, was measured using the ^{53}K(p,2p) one-proton removal reaction at ∼210 MeV/u at the RIBF facility. The 2_{1}^{+} excitation energy is found at 1656(18) keV, the highest among the Ar isotopes with N>20. This result is the first experimental signature of the persistence of the N=34 subshell closure beyond ^{54}Ca, i.e., below the magic proton number Z=20. Shell-model calculations with phenomenological and chiral-effective-field-theory interactions both reproduce the measured 2_{1}^{+} systematics of neutron-rich Ar isotopes, and support a N=34 subshell closure in ^{52}Ar.

7 pags., 7 figs. -- XXIII International School on Nuclear Physics, Neutron Physics and Applications 22-28 September 2019, Varna, Bulgaria, Within the SEASTAR III campaign at the Radioactive Isotope Beam Factory, at the RIKEN Nishina Center, neutron-rich isotopes in the vicinity of 53K were produced from the fragmentation of the primary 70Zn beam on a 9Be target. After nucleon knockout reactions on the secondary liquid hydrogen MINOS target the known γ rays of the neutron-rich 55Sc isotope were observed (shown in this proceedings) and γ rays from 57,59Sc isotopes have been identified for the first time. The evolution of the occupied nucleon orbitals of these nuclei in the ground and excited state is investigated under the prism of the tensor force., We are grateful to the RIKEN Nishina Center accelerator staff for their work in the primary beam delivery and the BigRIPS team for preparing the secondary beams. This work was supported by the cooperation between TU Darmstadt and the GSI Helmholtz Center for Heavy Ion Research, by the Helmholtz Graduate School for Hadron and Ion Research for FAIR and its abroad program and the BMBF under grant No. 05P19RDFN1. D.S. was supported by projects No. GINOP2.3.3-15-2016-00034 and No. K128947.

Objective To generate normative data for the verbal fluency tests (VFT-letter M, fruits, and occupations categories) in Spanish-speaking adult populations, with country-specific adjustments for age, education, and sex when appropriate. Method The sample consisted of 3,977 healthy adults from 11 countries in Latin America (Argentina, Bolivia, Chile, Cuba, El Salvador, Guatemala, Honduras, Mexico, Paraguay, Peru, and Puerto Rico; sample size per country ranged between n = 184 and n = 1,300). Each participant was administered the VFT as part of a larger neuropsychological battery. Scores for letter M, fruits, and occupations categories were normed using multiple linear regressions. The country-specific regression models included age, age2, education, education2, and sex as predictors. Results The final multiple linear regression models showed that age affected the performance on these tests but not uniformly. For example, M letter scores decrease linearly with age except for Argentina, Guatemala, and Mexico, in which quadratic age effect was found. Scores also increase linearly as a function of education but not in all countries. For example, a quadratic education effect was found for the fruits category in Bolivia, Honduras, and Paraguay. Sex had a significant impact on the M letter category fluency in Guatemala, fruits category in Guatemala and Peru, and occupations' category in Mexico. Conclusions This study presents verbal fluency test normative data across 11 countries in Latin America. These norms are expected to be useful for neuropsychologists of these countries. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The super-Planckian features of radiative heat transfer in the near-field are known to depend strongly on both material and geometric design properties. However, the relative importance and interplay of these two facets, and the degree to which they can be used to ultimately control energy flow, remains an open question. Recently derived bounds suggest that enhancements as large as $|\chi|^4 \lambda^{2} / \left(\left(4\pi\right)^{2} \Im\left[\chi\right]^{2} d^{2}\right)$ are possible between extended structures (compared to blackbody); but neither geometries reaching this bound, nor designs revealing the predicted material ($\chi$) scaling, have been previously reported. Here, exploiting inverse techniques, in combination with fast computational approaches enabled by the low-rank properties of elliptic operators for disjoint bodies, we investigate this relation between material and geometry on an enlarged space structures. Crucially, we find that the material proportionality given above does indeed emerge in realistic structures. In reaching this result, we also show that (in two dimensions) lossy metals such as tungsten, typically considered to be poor candidate materials for strongly enhancing heat transfer in the near infrared, can be structured to selectively realize flux rates that come within $50\%$ of those exhibited by an ideal pair of resonant lossless metals for separations as small as $2\%$ of a tunable design wavelength., Comment: 6 pages, 2 figures

Hepatitis-C Virus (HCV) sequences are often used to establish networks of people who inject drugs (PWID). However, the degree to which within-host evolutionary dynamics affect those inferences has not been carefully studied. Here, we analyzed 702 longitudinally-sampled HCV E1 sequences from 88 HCV+ people who inject drugs (PWID) in the Baltimore Before and After Acute Study of Hepatitis (BBAASH) cohort. Individuals were tested for HCV RNA over multiple visits to the clinic, and the HCV E1 gene was sequenced for HCV+ samples. Genetic clustering was performed on the full set of sequences using a 3% genetic distance threshold to define epidemiological linkage. Maximum-likelihood (ML) phylogenies were inferred to assess evolutionary relationships. We found 22 clusters containing sequences sampled over five or more years (long-term clusters, LTC), of which 17 had >1 subject. In six of the multi-subject LTC, one subject had a sequence sampled >3 years earlier or later than the next-closest subject in the cluster (time-gap LTC). ML trees showed that, in three of the time-gap LTC, two subjects had identical sequences despite 7–10 years separating the sampling times. In four of the time-gap LTC for whom additional data were available, the subject with the later detected shared variant had both different variants and visits with no detectable HCV RNA (RNA-) prior to the appearance of the shared variant. In the subject with the earlier detection of the shared variant, different variants and RNA- visits were also detected in multiple cases subsequent to appearance of the shared variant. Complex patterns of shared viral variation among PWID reflect on-going re-infection, multiple transmission partners, and/or inconsistent detection of viral variants. Our results suggest that transmission events are currently underestimated by analysis of sequences at a single point in time.

Second harmonic conversion from 1550~nm to 775~nm with an efficiency of 400% W$^{-1}$ is demonstrated in a gallium phosphide (GaP) on oxide integrated photonic platform. The platform consists of doubly-resonant, phase-matched ring resonators with quality factors $Q \sim 10^4$, low mode volumes $V \sim 30 (\lambda/n)^3$, and high nonlinear mode overlaps. Measurements and simulations indicate that conversion efficiencies can be increased by a factor of 20 by improving the waveguide-cavity coupling to achieve critical coupling in current devices., Comment: 13 pages, 6 figures

Radiative emission experienced by a subwavelength particle near a resonant cavity is typically characterized by the well-known Purcell factor figure of merit. In recent work, we presented a generalization of Purcell enhancement that applies to situations involving exceptional points (EP)---spectral singularities in non-Hermitian systems where two or more eigenvectors and their corresponding complex eigenvalues coalesce, leading to a non-diagonalizable, defective Hamiltonian. EPs are attended by many intriguing physical effects and have been studied in various contexts, including lasers, atomic and molecular systems, photonic crystals, parity-time symmetric lattices, and optomechanical resonators. Thus far, the main focus of these works has been on analyzing the impact of second-order exceptional points on scattering from eternally incident light, e.g. for unidirectional transmission. An important but little explored property of EPs related to light-matter interactions is their ability to modify and enhance the local density of states (LDOS). Recently, we showed that EPs can modify the spontaneous emission rate or Purcell factor of narrow-band emitters embedded in resonant cavities. In this talk, we show that EPs can have an even greater impact on nonlinear optical processes like frequency conversion. In particular, we derive a general formula quantifying radiative emission from a subwavelength emitter in the vicinity of a triply resonant χ(2) cavity that supports an EP near the emission frequency and a bright mode at the second harmonic. We show that the resulting frequency up-conversion process can be enhanced by up to two orders of magnitude compared to nondegenerate scenarios and that, in contrast to the recently predicted spontaneous-emission enhancements, nonlinear EP enhancements can persist even when considering spatial distributions of broadband emitters, provided that the cavity satisfies special nonlinear selection rules. This is demonstrated via a two-dimensional proof-of-concept PhC designed to partially fulfill the various criteria needed to approach the derived bounds on the maximum achievable up-conversion efficiencies. Along these lines, we show that similar enhancements can arise in quantum systems consisting of single and multi-level atoms embedded in photonic cavities. Our predictions suggest an indirect but practically relevant route to experimentally observe the impact of EPs on spontaneous emission and related light–matter interactions, with implications to quantum information science.

Van der Waals (vdW) forces play an integral role in the binding and interaction energies of molecules in condensed phases; their long-range, many-body nature can modify phonons in molecular crystals and thereby impact thermodynamic stability. Typical macroscopic descriptions of such optical forces tend to ignore important atomistic effects arising at short (nanometric) scales, while microscopic treatments tend to ignore long-range, geometry-dependent electromagnetic effects. We describe an ab-initio approach to model such fluctuation-induced forces in mesoscopic systems comprising large molecules in the vicinity of macroscopic bodies, conjoining atomistic treatments of electronic and vibrational fluctuations derived from density functional theory in the former, with continuum descriptions of electromagnetic response in the latter, thereby accounting for many-body and multiple scattering effects to all orders. Such long-range electromagnetic effects become particularly important in situations where the finite sizes and shapes of the molecules and continuum bodies combine to create phonon polaritons with highly delocalized (nonlocal) charge distributions. We find that even in small molecules, but especially in elongated low-dimensional molecular systems, these effects modify van der Waals forces by orders of magnitude and produce qualitatively different behavior compared to predictions based on simple dipolar or pairwise approximations, valid only in atomically small or dilute molecular systems. In particular, we focus on the interactions of fullerenes, carbyne wires, and graphene sheets with one another and with a gold surface. We compare forces with and without phonon and at multiple temperatures, and compare our predictions to those obtained from commonly used dipolar and continuum treatments. In particular, we show that phonons can delocalize molecular charge distributions from a few angstroms to several nanometers, in ways that depend strongly on the shape of the molecules and their proximity to the surface. Even for small fullerenes, phonons can lead to force deviations at tens of nanometer separations from the surface compared to treatments lacking phononic effects, while for higher dimensional molecules such as elongated carbyne wires and graphene sheets, the nonlocality of these interactions produces nonmonotonic power laws that cannot be qualitatively captured by dipolar and/or continuum models.

We study a cavity-QED setup consisting of a two-level system coupled to a single cavity mode with two-photon relaxation. The system dynamics is modeled via a Lindblad master equation consisting of the Rabi Hamiltonian and a two-photon dissipator. We show that an even-photon relaxation preserves the $Z_2$ symmetry of the Rabi model, and provide a framework to study the corresponding non-Hermitian dynamics in the number-parity basis. We discuss the role of different terms in the two-photon dissipator and show how one can extend existing results for the closed Rabi spectrum to the open case. Furthermore, we characterize the role of the $Z_2$ symmetry in the excitation-relaxation dynamics of the system as a function of light-matter coupling. Importantly, we observe that initial states with even-odd parity manifest qualitatively distinct transient and steady state behaviors, contrary to the Hermitian dynamics that is only sensitive to whether the initial state is parity-invariant. Moreover, the parity-sensitive dynamical behavior is not a creature of ultrastrong coupling and is present even at weak coupling values., 14 pages, 8 figures and 1 table

The galactomannan extracted from Delonix regia (DRGM) seeds was hydrolyzed at different enzyme dosages and reaction times. A linear relation between inverse Molecular weight (Mn) and hydrolysis time was obtained, and the Mn reduction was controlled from 4.86 × 105 to 1.95 × 105 Da. The hydrolysis does not affect galactomannan structure as observed by FT-IR and DRX, maintaining an amorphous structure with only a slight increase in galactose:mannose relationship as observed by 1H NMR. A rheological behavior shift was observed below Mn = 4.15 × 105 Da when viscoelastic behavior changes from a weak gel to a macromolecular solution in a 3% (w/v) galactomannan hydrolysate. Shear viscosity of 3% (w/v) galactomannan dispersion in water follows closely a power law equation where the consistency index decreased, and the flow behavior index increased with increasing hydrolysis degree. These results indicate the conditions for obtaining specific viscoelastic properties of DRGM dispersions for specific applications by a careful control of the enzymatic hydrolysis process.

Nature Communications 8: Article number: 14475 (2017); Published: 15 February 2017, Updated: 25 June 2018 The original HTML version of this Article omitted the article number; it should have been ‘14475’. This has now been corrected in the HTML version of the Article. The PDF version was correct from the time of publication.

Nutrigenomics is the study of the effects of food and food constituents on gene expression. The study of nutrigenomics may have a major impact in the development of tailor-made food, supplements and beverage products in the near future. The “genetic nutritioneering” concept summarizes the information on how diet, supplements, lifestyle and environmental factors influence gene expression. In order to overcome their particular genetic pre-disposition that can lead to serious diseases, people may be able to choose customized diets, supplements and make lifestyle modifications, which would optimize their metabolic status. Nutrient intake for each person varies according to their unique genetic make-up and individual lifestyle choices. Therefore, it may be possible to “correct” physiological disruptions by implementing “Metabolic Correction” principles. To completely accomplish these goals of optimal health, new international alliances and policies need to be developed and implemented and more sound, evidence-based research needs to be conducted.

This essay considers the pedagogical legacies of ethnomusicologist Mantle Hood and jazz saxophonist Ornette Coleman, both of whom began their careers studying musical improvisation in Los Angeles in the 1950s. Drawing from a contemporary pedagogical case study that draws from those legacies, The Omni-Musicality Group at UCLA, the article posits four ethical standards that can guide music teachers in jazz studies and ethnomusicology alike towards cultivating ethical dispositions that are relevant to twenty first-century challenges. This is framed in terms of Aristotelian virtue ethics, which leads to a discussion of the relevance of musical universals not as ontological or aesthetic questions, but as ethical ones.84

Thermal radiative phenomena can be strongly influenced by the coupling of phonons and long-range electromagnetic fields at infrared frequencies. Typically employed macroscopic descriptions of thermal fluctuations tend to ignore atomistic effects that become relevant at nanometric scales, whereas purely microscopic treatments ignore long-range, geometry-dependent electromagnetic effects. We describe a mesoscopic framework for modeling thermal fluctuation phenomena among molecules in the vicinity of macroscopic bodies, conjoining atomistic treatments of electronic and vibrational fluctuations obtained from ab-initio density functional theory in the former with continuum descriptions of electromagnetic scattering in the latter. The interplay of these effects becomes particularly important at mesoscopic scales, where phonon polaritons can be strongly influenced by the finite sizes, shapes, and non-local/many-body response of the bodies to electromagnetic fluctuations. We show that even in small but especially in elongated low-dimensional molecular systems, such effects can modify thermal emission and heat transfer by orders of magnitude and produce qualitatively different behavior compared to predictions based on local, dipolar, or pairwise approximations valid only in dilute media., 7 pages, 2 figures, includes supplement as appendix

HIV-1 Nef is a flexible, multifunctional protein with several cellular targets that is required for pathogenicity of the virus. This protein maintains a high degree of genetic variation among intra- and inter-host isolates. HIV Nef is relevant to HIV-associated neurological diseases (HAND) in patients treated with combined anti-retroviral therapy because of the protein’s role in promoting survival and migration of infected brain macrophages. In this study, we analyzed 2,020 HIV Nef sequences derived from 22 different tissues and 31 subjects using a novel computational approach. This approach combines statistical regression and evolved neural networks (ENNs) to classify brain sequences based on the physical and chemical characteristics of functional Nef domains. Based on training, testing, and validation data, the method successfully classified brain Nef sequences at 84.5% and provided informative features for further examination. These included physicochemical features associated with the Src-homology-3 binding domain, the Nef loop (including the AP-2 Binding region), and a cytokine binding domain. Non-brain sequences from patients with HIV-associated neurological disease were frequently classified as brain, suggesting that the approach could indicate neurological-risk using blood-derived virus or for the development of biomarkers for use in assay systems aimed at drug efficacy studies for the treatment of HIV-associated neurological diseases.

Radiative heat-transport mediated by near-field interactions is known to be superdiffusive in dilute, many-body systems. In this Letter we use a generalized Landauer theory of radiative heat transfer in many-body planar systems to demonstrate a nonmonotonic transition from superdiffusive to ballistic transport in dense systems. We show that such a transition is associated to a change of the polarization of dominant modes, leading to dramatically different thermal relaxation dynamics spanning over three orders of magnitude. This result could have important consequences on thermal management at nanoscale of many-body systems., 5 pages, 4 figures

Few preclinical studies have compared the relative therapeutic efficacy of medications used to treat opiate addiction in relation to neuroAIDS. Here we compare the ability of methadone and buprenorphine, and the prototypic opiate morphine, to potentiate the neurotoxic and proinflammatory ([Ca2+] i , ROS, H 2 O 2 , chemokines) effects of HIV-1 Tat in neuronal and/or mixedglial co-cultures. Repeated observations of neurons during 48 h exposure to combinations of Tat, equimolar concentrations (500 nM) of morphine, methadone, or buprenorphine exacerbated neurotoxicity significantly above levels seen with Tat alone. Buprenorphine alone displayed marked neurotoxicity at 500 nM, prompting additional studies of its neurotoxic effects at 5 nM and 50 nM concentrations ± Tat. In combination with Tat, buprenorphine displayed paradoxical, concentrationdependent, neurotoxic and neuroprotective actions. Buprenorphine neurotoxicity coincided with marked elevations in [Ca 2+ ] i , but not increases in glial ROS or chemokine release. Tat by itself elevated the production of CCL5/RANTES, CCL4/MIP-1β, and CCL2/MCP-1. Methadone and buprenorphine alone had no effect, but methadone interacted with Tat to further increase production of CCL5/RANTES. In combination with Tat, all drugs significantly increased glial [Ca 2+ ] i , but ROS was only significantly increased by co-exposure with morphine. Taken together, the increases in glial [Ca 2+ ] i , ROS, and neuroinflammatory chemokines were not especially accurate predictors of neurotoxicity. Despite similarities, opiates displayed differences in their neurotoxic and neuroinflammatory interactions with Tat. Buprenorphine, in particular, was partially neuroprotective at a low concentration, which may result from its unique pharmacological profile at multiple opioid receptors. Overall, the results reveal differences among addiction medications that may impact neuroAIDS.

Objective To generate normative data for the Stroop Word-Color Interference test in Spanish-speaking pediatric populations. Method The sample consisted of 4,373 healthy children from nine countries in Latin America (Chile, Cuba, Ecuador, Guatemala, Honduras, Mexico, Paraguay, Peru, and Puerto Rico) and Spain. Each participant was administered the Stroop Word-Color Interference test as part of a larger neuropsychological battery. The Stroop Word, Stroop Color, Stroop Word-Color, and Stroop Interference scores were normed using multiple linear regressions and standard deviations of residual values. Age, age2, sex, and mean level of parental education (MLPE) were included as predictors in the analyses. Results The final multiple linear regression models showed main effects for age on all scores, except on Stroop Interference for Guatemala, such that scores increased linearly as a function of age. Age2 affected Stroop Word scores for all countries, Stroop Color scores for Ecuador, Mexico, Peru, and Spain; Stroop Word-Color scores for Ecuador, Mexico, and Paraguay; and Stroop Interference scores for Cuba, Guatemala, and Spain. MLPE affected Stroop Word scores for Chile, Mexico, and Puerto Rico; Stroop Color scores for Mexico, Puerto Rico, and Spain; Stroop Word-Color scores for Ecuador, Guatemala, Mexico, Puerto Rico and Spain; and Stroop-Interference scores for Ecuador, Mexico, and Spain. Sex affected Stroop Word scores for Spain, Stroop Color scores for Mexico, and Stroop Interference for Honduras. Conclusions This is the largest Spanish-speaking pediatric normative study in the world, and it will allow neuropsychologists from these countries to have a more accurate approach to interpret the Stroop Word-Color Interference test in pediatric populations.

Radiative heat transfer between uniform plates is bounded by the narrow range and limited contribution of surface waves. Using a combination of analytical calculations and numerical gradient-based optimization, we show that such a limitation can be overcome in complicated multilayer geometries, allowing the scattering and coupling rates of slab resonances to be altered over a broad range of evanescent wavevectors. We conclude that while the radiative flux between two inhomogeneous slabs can only be weakly enhanced, the flux between a dipolar particle and an inhomogeneous slab---proportional to the local density of states---can be orders of magnitude larger, albeit at the expense of increased frequency selectivity. A brief discussion of hyperbolic metamaterials shows that they provide far less enhancement than optimized inhomogeneous slabs., 9 pages, 3 figures

We present an approach for computing long-range van der Waals (vdW) interactions between complex molecular systems and arbitrarily shaped macroscopic bodies, melding atomistic treatments of electronic fluctuations based on density functional theory in the former, with continuum descriptions of strongly shape-dependent electromagnetic fields in the latter, thus capturing many-body and multiple scattering effects to all orders. Such a theory is especially important when considering vdW interactions at mesoscopic scales, i.e. between molecules and structured surfaces with features on the scale of molecular sizes, in which case the finite sizes, complex shapes, and resulting nonlocal electronic excitations of molecules are strongly influenced by electromagnetic retardation and wave effects that depend crucially on the shapes of surrounding macroscopic bodies. We show that these effects together can modify vdW interactions by orders of magnitude compared to previous treatments based on Casimir--Polder or non-retarded approximations, which are valid only at macroscopically large or atomic-scale separations, respectively., 6 pages (including abstract, appendices, and references), 4 figures

In this study, we employed proteomics to identify mechanisms of posttranslational regulation on cell survival signaling proteins. We focused on Cu-Zn superoxide dismutase (SOD1), which protects cells from oxidative stress. We found that acylation of K122 on SOD1, while not impacting SOD1 catalytic activity, suppressed the ability of SOD1 to inhibit mitochondrial metabolism at respiratory complex I. We found that deacylase depletion increased K122 acylation on SOD1, which blocked the suppression of respiration in a K122-dependent manner. In addition, we found that acyl-mimicking mutations at K122 decreased SOD1 accumulation in mitochondria, initially hinting that SOD1 may inhibit respiration directly within the intermembrane space (IMS). However, surprisingly, we found that forcing the K122 acyl mutants into the mitochondria with an IMS-targeting tag did not recover their ability to suppress respiration. Moreover, we found that suppressing or boosting respiration levels toggled SOD1 in or out of the mitochondria, respectively. These findings place SOD1-mediated inhibition of respiration upstream of its mitochondrial localization. Lastly, deletion-rescue experiments show that a respiration-defective mutant of SOD1 is also impaired in its ability to rescue cells from toxicity caused by SOD1 deletion. Together, these data suggest a previously unknown interplay between SOD1 acylation, metabolic regulation, and SOD1-mediated cell survival.

Compact metasurface devices herald an exciting revolution in optics technology. Their design complexity and functionality has been restricted to intuitive by-hand designs for single-layered devices. This study proposes a large-scale approach known as topology optimization, applied to multiple, closely spaced device layers, which greatly expands the scope and functionality of metadevices. In particular, the authors demonstrate angular phase control, the ability to encode arbitrary information using different angles of incidence, which enables $e.g.$ the design of a one-piece, aberration-corrected metalens, and of an angle-convergent metalens.

We apply a large-scale computational technique, known as topology optimization, to the inverse design of photonic Dirac cones. In particular, we report on a variety of photonic crystal geometries, realizable in simple isotropic dielectric materials, which exhibit dual-polarization and dual-wavelength Dirac cones. We demonstrate the flexibility of this technique by designing photonic crystals of different symmetry types, such as ones with four-fold and six-fold rotational symmetry, which possess Dirac cones at different points within the Brillouin zone. The demonstrated and related optimization techniques could open new avenues to band-structure engineering and manipulating the propagation of light in periodic media, with possible applications in exotic optical phenomena such as effective zero-index media and topological photonics.

This dialogue with physicist Alejandro W. Rodríguez is in two parts. The first part, which took place in the MIT campus, reflects on how theory has been overtaking experimentation in recent developments in science. It also addresses the subject of the Casimir forces and their effects by using devices which benefit from them in everyday life. Later, Alejandro explains why the vacuum is not empty; and, what are the "virtual photons". In the second part, Alejandro explains his current research in the Department of Electrical Engineering of Princeton University, focusing on the black body; and quantum and thermal processes of electromagnetic fluctuations at the nanoscale, where the rules of quantum mechanics now hold sway. He is now studying quantum fluctuations and how the forces and energy exchanged between objects work. This all-important area is the current driving force for development in the field of thermovoltaic energy and thermal panels for capturing light; an area with a revolutionary potential capable of changing the existing relationship of humans with energy, technology and the environment, in other words, with the planet.

Whether intentionally introduced to exert control over particles and macroscopic objects, such as for trapping or cooling, or whether arising from the quantum and thermal fluctuations of charges in otherwise neutral bodies, leading to unwanted stiction between nearby mechanical parts, electromagnetic interactions play a fundamental role in many naturally occurring processes and technologies. In this review, we survey recent progress in the understanding and experimental observation of optomechanical and quantum-fluctuation forces. Although both of these effects arise from exchange of electromagnetic momentum, their dramatically different origins, involving either real or virtual photons, lead to different physical manifestations and design principles. Specifically, we describe recent predictions and measurements of attractive and repulsive optomechanical forces, based on the bonding and antibonding interactions of evanescent waves, as well as predictions of modified and even repulsive Casimir forces between nanostructured bodies. Finally, we discuss the potential impact and interplay of these forces in emerging experimental regimes of micromechanical devices.

The Spallation Neutron Source (SNS) was designed and constructed by a collaboration of six U.S. Department of Energy national laboratories. The SNS accelerator system consists of a 1 GeV linear accelerator and an accumulator ring providing 1.4 MW of proton beam power in microsecond-long beam pulses to a liquid mercury target for neutron production. The accelerator complex consists of a front-end negative hydrogen-ion injector system, an 87 MeV drift tube linear accelerator, a 186 MeV side-coupled linear accelerator, a 1 GeV superconducting linear accelerator, a 248-m circumference accumulator ring and associated beam transport lines. The accelerator complex is supported by ~100 high-power RF power systems, a 2 K cryogenic plant, ~400 DC and pulsed power supply systems, ~400 beam diagnostic devices and a distributed control system handling ~100,000 I/O signals. The beam dynamics design of the SNS accelerator is presented, as is the engineering design of the major accelerator subsystems.

Growing populations and food demand in the tropics are leading to increased environmental pressures on wetland ecosystems, including a greater reliance on natural wetlands for water quality improvement. Effective assessment of wetland treatment potential requires an improved understanding of the hydraulic and biogeochemical factors that govern contaminant behavior, however detailed studies of flow through natural, tropical wetlands are scarce. We performed a tracer study using a conservative salt (potassium bromide) to examine the hydraulic behavior of a small, natural wetland in the Costa Rican humid tropics and modeled observed breakthrough curves using the 1-D advection–dispersion equation. Velocities in the wetland were extremely slow, from less than 4 m day−1 to a maximum of ~30 m day−1, and were distributed across several flowpaths, illustrating a spatial heterogeneity of flow and velocities. Modeled dispersion coefficients were also low (33 ± 33 m2 day−1). Estimated residence times suggested high potential pollutant removal capacity over a range of influent concentrations, reinforcing the environmental services provided by this and other small tropical wetlands. The study also highlighted how small variations in wetland topography and vegetation yield strong differences in transport patterns that affect transport and mixing in densely vegetated, heterogeneous wetland systems. Empirical data on the hydraulics, and resulting ecosystem functions, of small, distributed wetlands may provide support for improved conservation and management of these important ecosystems.

As a number of articles in this journal demonstrate, the recent trend in jazz scholarship towards transnational studies has brought with it a host of fascinating new questions. Two recent monograph...

We demonstrate concentration-dependent Forster-type energy transfer in a luminescent solar concentrator (LSC) material containing two high quantum yield laser dyes in a PMMA matrix. FRET heterotransfer is shown to be approximately 50% efficient in the regime of 2×10 −3 molal acceptor dye by weight in the host polymer. The two dyes used have been well studied for solar concentrator applications: BASF's Lumogen Red 305, and Exciton Chemical Company's DCM both demonstrate desirable stability, quantum yield, and complementary absorption spectra. We demonstrate how multiple-dye LSC devices employing FRET increase the absorption of air mass 1.5 solar irradiance without affecting the self-absorption properties of the film. Color tunability may be achieved through the addition of additional absorbers while minimizing the impact on waveguide efficiency.

Let D be a division ring, T be a variable over D, σ be an endomorphism of D, δ be a σ-derivation on D and R = D[T; σ, δ] the left skew polynomial ring over D. We show that the set \((Val_\nu(R),\preceq)\) of σ-compatible real valuations which extend to R a fixed proper real valuation ν on D has a natural structure of parameterized complete non-metric tree, where \(\preceq \) is the partial order given by \(\mu \preceq \widetilde{\mu}\) if and only if \(\mu (f)\leq \widetilde{\mu}(f)\) for all f ∈ R and \(\mu, \widetilde{\mu} \in Val_\nu (R)\). Furthermore and as a consequence, we also prove a criterion of irreducibility for left skew polynomials that includes as a particular case an Eisenstein valuation criterion which generalizes a similar one of Churchill and Zhang (J Algebra 322:3797–3822, 2009).

The nature of light interaction with matter can be dramatically altered in optical cavities, often inducing nonclassical behavior. In solid-state systems, excitons need to be spatially incorporated within nanostructured cavities to achieve such behavior. Although fascinating phenomena have been observed with inorganic nanostructures, the incorporation of organic molecules into the typically inorganic cavity is more challenging. Here, we present a unique optofluidic platform comprising organic molecules in solution suspended on a photonic crystal surface, which supports macroscopic Fano resonances and allows strong and tunable interactions with the molecules anywhere along the surface. We develop a theoretical framework of this system and present a rigorous comparison with experimental measurements, showing dramatic spectral and angular enhancement of emission. We then demonstrate that these enhancement mechanisms enable lasing of only a 100-nm thin layer of diluted solution of organic molecules with substantially reduced threshold intensity, which has important implications for organic light-emitting devices and molecular sensing.

We exploit recently developed topology-optimization techniques to design complex, wavelength-scale resonators for enhancing various nonlinear $\chi^{(2)}$ and $\chi^{(3)}$ frequency conversion processes. In particular, we demonstrate aperiodic, multi-track ring resonators and 2D slab microcavities exhibiting long lifetimes $Q \gtrsim 10^4$, small modal volumes $V \gtrsim (\lambda/2n)^3$, and among the largest nonlinear overlaps (a generalization of phase matching in large-etalon waveguides) possible, paving the way for efficient, compact, and wide-bandwdith integrated nonlinear devices.

Casimir forces are of fundamental interest because they originate from quantum fluctuations of the electromagnetic field. Apart from controlling the Casimir force via the optical properties of the materials, a number of novel geometries have been proposed to generate repulsive and/or non-monotonic Casimir forces between bodies separated by vacuum gaps. Experimental realization of these geometries, however, is hindered by the difficulties in alignment when the bodies are brought into close proximity. Here, using an on-chip platform with integrated force sensors and actuators, we circumvent the alignment problem and measure the Casimir force between two surfaces with nanoscale protrusions. We demonstrate that the Casimir force depends non-monotonically on the displacement. At some displacements, the Casimir force leads to an effective stiffening of the nanomechanical spring. Our findings pave the way for exploiting the Casimir force in nanomechanical systems using structures of complex and non-conventional shapes., 26 pages, 13 figures

OBJECTIVE: To generate normative data for the Modified Wisconsin Card Sorting Test (M-WCST) in Spanish-speaking pediatric populations. METHOD: The sample consisted of 4,373 healthy children from nine countries in Latin America (Chile, Cuba, Ecuador, Guatemala, Honduras, Mexico, Paraguay, Peru, and Puerto Rico) and Spain. Each participant was administered the M-WCST as part of a larger neuropsychological battery. Number of categories, perseverative errors, and total error scores were normed using multiple linear regressions and standard deviations of residual values. Age, age2, sex, and mean level of parental education (MLPE) were included as predictors in the analyses. RESULTS: The final multiple linear regression models indicated main effects for age on all scores, such that the number of categories correct increased and total number of perseverative errors and total number of errors decrease linearly as a function of age. Age2 had a significant effect in Chile, Cuba, Ecuador, and Spain for numbers of categories; a significant effect for number of perseverative errors in Chile, Cuba, Mexico, and Spain; and a significant effect for number of total errors in Chile, Cuba, Peru, and Spain. Models showed an effect for MLPE in Cuba (total errors), Ecuador (categories and total errors), Mexico (all scores), Paraguay (perseverative errors and total error), and Spain (categories and total errors). Sex affected number of total errors for Ecuador. CONCLUSIONS: This is the largest Spanish-speaking pediatric normative study in the world, and it will allow neuropsychologists from these countries to have a more accurate way to interpret the M-WCST with pediatric populations.

Objective To generate normative data for the Symbol Digit Modalities Test (SDMT) in Spanish-speaking pediatric populations. Method The sample consisted of 4,373 healthy children from nine countries in Latin America (Chile, Cuba, Ecuador, Guatemala, Honduras, Mexico, Paraguay, Peru, and Puerto Rico) and Spain. Each participant was administered the SDMT as part of a larger neuropsychological battery. SDMT scores were normed using multiple linear regressions and standard deviations of residual values. Age, age2, sex, and mean level of parental education (MLPE) were included as predictors in the analyses. Results The final multiple linear regression models showed main effects for age in all countries, such that score increased linearly as a function of age. In addition, age2 had a significant effect in all countries, except in Honduras and Puerto Rico. Models indicated that children whose parent(s) had a MLPE >12 years of education obtained higher score compared to children whose parent(s) had a MLPE ≤12 years for Chile, Guatemala, Mexico, and Spain. Sex affected SDMT score for Paraguay and Spain. Conclusions This is the largest Spanish-speaking pediatric normative study in the world, and it will allow neuropsychologists from these countries to have a more accurate interpretation of the SDMT with pediatric populations.

We apply a large-scale inverse design strategy based on topology optimization (TO) toward the automatic discovery of complex nanophotonic structures-new kinds of micropillars, photonic-cyrstal slabs, and waveguides comprising complicated arrangements of subwavelength dielectrics-exhibiting unusual nonlinear and spectral properties. The structures support multiple, tightly confined resonances at far-away wavelengths and exhibit the largest nonlinear confinement factors predicted thus far (oders of magnitude larger than state-of-the-art ring resonators or PhC cavities), leading to highly efficient nonlinear frequency conversion (NFC). The same TO approach can be exploited to design PhCs supporting dual-polarization, dual-wavelength, or highly degenerate Dirac cones, with implications to zero-index metamaterials, topological photonics, and exceptional points (EP).

Exceptional points (EPs) were recently predicted to modify the spontaneous emission rate or Purcell factor of narrow-band emitters embedded in resonant cavities. We demonstrate that EPs can have an even greater impact on nonlinear optical processes like frequency conversion by deriving a general formula quantifying radiative emission from a subwavelength emitter in the vicinity of a triply resonant ${\ensuremath{\chi}}^{(2)}$ cavity that supports an EP near the emission frequency and a bright mode at the second harmonic. We show that the resulting frequency up-conversion process can be enhanced by up to two orders of magnitude compared to nondegenerate scenarios and that, in contrast to the recently predicted spontaneous-emission enhancements, nonlinear EP enhancements can persist even when considering spatial distributions of broadband emitters, provided that the cavity satisfies special nonlinear selection rules. This is demonstrated via a two-dimensional proof-of-concept PhC designed to partially fulfill the various criteria needed to approach the derived bounds on the maximum achievable up-conversion efficiencies. Our predictions suggest an indirect but practically relevant route to experimentally observe the impact of EPs on spontaneous emission, with implications to quantum information science.

For 75 years it has been known that radiative heat transfer can exceed far-field blackbody rates when two bodies are separated by less than a thermal wavelength. Yet an open question has remained: what is the maximum achievable radiative transfer rate? Here we describe basic energy-conservation principles that answer this question, yielding upper bounds that depend on the temperatures, material susceptibilities, and separation distance, but which encompass all geometries. The simple structures studied to date fall far short of the bounds, offering the possibility for significant future enhancement, with ramifications for experimental studies as well as thermophotovoltaic applications.

We study the interplay of conductive and radiative heat transfer (RHT) in planar geometries and predict that temperature gradients induced by radiation can play a significant role on the behavior of RHT with respect to gap sizes, depending largely on geometric and material parameters and not so crucially on operating temperatures. Our findings exploit rigorous calculations based on a closed-form expression for the heat flux between two plates separated by vacuum gaps $d$ and subject to arbitrary temperature profiles, along with an approximate but accurate analytical treatment of coupled conduction--radiation in this geometry. We find that these effects can be prominent in typical materials (e.g. silica and sapphire) at separations of tens of nanometers, and can play an even larger role in metal oxides, which exhibit moderate conductivities and enhanced radiative properties. Broadly speaking, these predictions suggest that the impact of RHT on thermal conduction, and vice versa, could manifest itself as a limit on the possible magnitude of RHT at the nanoscale, which asymptotes to a constant (the conductive transfer rate when the gap is closed) instead of diverging at short separations., 5 pages, 3 figures. arXiv admin note: text overlap with arXiv:1605.05708

We apply a fluctuation electrodynamics framework in combination with semianalytical (dipolar) approximations to study amplified spontaneous energy transfer (ASET) between active and passive bodies. We consider near-field energy transfer between semi-infinite planar media and spherical structures (dimers and lattices) subject to gain, and show that the combination of loss compensation and near-field enhancement (achieved by the proximity, enhanced interactions, and tuning of subwavelength resonances) in these structures can result in orders of magnitude ASET enhancements below the lasing threshold. We examine various possible geometric configurations, including realistic materials, and describe optimal conditions for enhancing ASET, showing that the latter depends sensitively on both geometry and gain, enabling efficient and tunable gain-assisted energy extraction from structured surfaces.

We formulate and exploit a computational inverse-design method based on topology optimization to demonstrate photonic crystal structures supporting complex spectral degeneracies. In particular, we discover photonic crystals exhibiting third-order Dirac points formed by the accidental degeneracy of monopolar, dipolar, and quadrupolar modes. We show that, under suitable conditions, these modes can coalesce and form a third-order exceptional point, leading to strong modifications in the spontaneous emission (SE) of emitters, related to the local density of states. We find that SE can be enhanced by a factor of 8 in passive structures, with larger enhancements ∼sqrt[n^{3}] possible at exceptional points of higher order n.

We report on quantitative measurements of the absolute heat flux between a gold coated near-field scanning thermal microscope (NSThM) [2] tip and a planar gold sample at nanometer distances of 0.2 nm–7 nm. After a precise calibration procedure we are able to measure the local heat transfer in a quantitative way [1]. We find an extraordinary large heat flux which is more than five orders of magnitude larger than black-body radiation and three orders of magnitude larger than the values predicted by conventional theory of fluctuational electrodynamics [3–10]. Furthermore, we have investigated the influence of thin films of a dielectric material on the near-field mediated heat transfer at the fundamental limit of single monolayer islands on a metallic substrate. Spatially resolved measurements by Near-Field Scanning Thermal Microscopy are presented which are showing a distinct enhancement in heat transfer above NaCl islands compared to the bare Au(111) film [11]. Experiments at this sub-nanometer scale call for a microscopic theory beyond the macroscopic fluctuational electrodynamics used to describe near-field heat transfer today. The method facilitates the possibility to develop designs of nanostructured surfaces with respect to specific requirements in heat transfer down to a single atomic layer. These findings open up the possibility for a local surface modification by means of local heating, e.g., chemical modification and heat assisted magnetic recording, on a scale of a few nanometers.