Optical Rectification and Field Enhancement in a Plasmonic Nanogap

Metal nanostructures act as powerful optical antennas[1, 2] because collective modes of the electron fluid in the metal are excited when light strikes the surface of the nanostructure. These excitations, known as plasmons, can have evanescent electromagnetic fields that are orders of magnitude larger than the incident electromagnetic field. The largest field enhancements often occur in nanogaps between plasmonically active nanostructures[3, 4], but it is extremely challenging to measure the fields in such gaps directly. These enhanced fields have applications in surface-enhanced spectroscopies[5-7], nonlinear optics[1, 8-10], and nanophotonics[11-15]. Here we show that nonlinear tunnelling conduction between gold electrodes separated by a subnanometre gap leads to optical rectification, producing a DC photocurrent when the gap is illuminated. Comparing this photocurrent with low frequency conduction measurements, we determine the optical frequency voltage across the tunnelling region of the nanogap, and also the enhancement of the electric field in the tunnelling region, as a function of gap size. The measured field enhancements exceed 1000, consistent with estimates from surface-enhanced Raman measurements[16-18]. Our results highlight the need for more realistic theoretical approaches that are able to model the electromagnetic response of metal nanostructures on scales ranging from the free space wavelength, $\lambda$, down to $\sim \lambda/1000$, and for experiments with new materials, different wavelengths, and different incident polarizations.Comment: 15 pages, 5 figures + 12 pages, 5 figures of supplemental informatio

Wildflower plantings have mixed effects on insect herbivores and their natural enemies

Flower strips are advocated as a strategy to promote beneficial insects as well as the services they deliver to adjacent crops. Flower strips have, however, often been developed separately for pollinators and natural enemies and, additionally, little consideration has been given to effects on insect herbivores. We sampled insect herbi-vores, their natural enemies and parasitism of pest eggs using vacuum sampling, sticky cards and egg cards in nine pairs of bee-attractive wildflower plantings and control field borders, as well as in adjacent tomato and watermelon crop fields in Yolo County, California 2015-2016. Control field borders had a higher total number of herbivores on sticky traps than did wildflower plantings, a pattern that was driven by more aphids, hoppers, psyllids and whiteflies, whereas wildflower plantings had more lace bugs and Lygus bugs. The total number of herbivores in the adjacent crop fields did not differ between treatments, but there were more leaf beetles near (at 10 m but not 50 m from) wildflower plantings. Control field borders had a higher total number of predators, driven by more big-eyed bugs, lady beetles and minute pirate bugs, whereas spiders were more common in wildflower plantings. The total number of predators in adjacent crop fields was, however, higher in those next to wildflower plantings, which was driven by more minute pirate bugs. Parasitoid wasps were more common in wildflower plantings and at 10 m but not 50 m into adjacent crop fields. Stink bug egg parasitism rate did not differ between treatments, either in the borders or in the crop fields. In conclusion, wildflower plantings clearly affect the insect herbivore and natural enemy community, but do so in a highly taxon-specific manner, which can lead to both positive and negative outcomes for pest control as a result

Model theoretic forcing in analysis

We present a framework for model theoretic forcing in a non-first-order context, and present some applications of this framework to Banach space theory

High Resolution X-Ray Imaging of the Center of IC342

We presented the result of a high resolution (FWHM~0.5'') 12 ks Chandra HRC-I observation of the starburst galaxy IC342 taken on 2 April 2006. We identified 23 X-ray sources within the central 30' x 30' region of IC342. Our HRC-I observation resolved the historical Ultraluminous X-ray sources (ULX), X3, near the nucleus into 2 sources, namely C12 and C13, for the first time. The brighter source C12, with L(0.08-10keV)=(6.66\pm0.45)\times10^{38}ergs^-1, was spatially extended (~82 pc x 127 pc). From the astrometric registration of the X-ray image, C12 was at R.A.=03h:46m:48.43s, decl.=+68d05m47.45s, and was closer to the nucleus than C13. Thus we concluded that source was not an ULX and must instead be associated with the nucleus. The fainter source C13, with L(0.08-10keV)=(5.1\pm1.4) x 10^{37}ergs^-1 was consistent with a point source and located $6.51'' at P.A. 240 degree of C12. We also analyzed astrometrically corrected optical Hubble Space Telescope and radio Very Large Array images, a comparison with the X-ray image showed similarities in their morphologies. Regions of star formation within the central region of IC342 were clearly visible in HST H alpha image and this was the region where 3 optical star clusters and correspondingly our detected X-ray source C12 were observed. We found that a predicted X-ray emission from starburst was very close to the observed X-ray luminosity of C12, suggesting that nuclear X-ray emission in IC342 was dominated by starburst. Furthermore, we discussed the possibility of AGN in the nucleus of IC342. Although our data was not enough to give a firm existence of an AGN, it could not be discarded.Comment: 29 page, 8 figures, accepted by Ap

A reflection origin for the soft and hard X-ray excess of Ark 120

Over the last few years several models have been proposed to interpret the widespread soft excess observed in the X-ray spectra of type 1 active galactic nuclei (AGN). In particular, reflection from the photoionized accretion disc blurred by relativistic effects has proven to be successful in reproducing both the spectral shape and the variability pattern of many sources. As a further test to this scenario we present the analysis of a recent ~100 ks long Suzaku observation of Arakelian 120, a prototypical 'bare' Seyfert 1 galaxy in which no complex absorption system is expected to mimic a soft excess or mask the intrinsic properties of this key component. We show that a reflection model allowing for both warm/blurred and cold/distant reprocessing provides a self-consistent and convincing interpretation of the broadband X-ray emission of Ark 120, also characterized by a structured iron feature and a high-energy hump. Although warm absorbers, winds/outflows and multiple Comptonizing regions may play significant roles in sources with more spectral complexity, this case study adds evidence to the presence of blurred disc reflection as a basic component of the X-ray spectra of type 1 AGN.Comment: 11 pages, 6 figures, accepted for publication in MNRA

Chimeric streptavidins as host proteins for artificial metalloenzymes

The streptavidin scaffold was expanded with well-structured naturally occurring motifs. These chimeric scaffolds were tested as hosts for biotinylated catalysts as artificial metalloenzymes (ArM) for asymmetric transfer hydrogenation, ring-closing metathesis and anion−π catalysis. The additional second coordination sphere elements significantly influence both the activity and the selectivity of the resulting hybrid catalysts. These findings lead to the identification of propitious chimeric streptavidins for future directed evolution efforts of artificial metalloenzymes

Recomendações da Sociedade Latino-Americana de Tireoide no manejo de nódulos tireoideos

Several guidelines on diagnosis and treatment of thyroid nodules and cancer have recently been published. However, recommended practices are not always appropriate to different settings or countries. The aim of this consensus was to develop Clinical Guidelines for evaluation and management of patients with thyroid nodules applicable to Latin American countries. The panel was composed by 13 members of the Latin American Thyroid Society involved with research and management of thyroid nodules and cancer from different medical centers in Latin America. The consensus was produced based on the expert opinion of the panel with use of principles of evidence-based medicine. Following a group meeting, a first draft based on the expert opinion of the panel was elaborated and later circulated among panel members for further revision. After revision, this document was submitted to all LATS members for commentaries and considerations and finally revised and refined by the authors. The final recommendations represent state of the art on management of thyroid nodules applied to all Latin American countries.Vários consensos têm sido publicados acerca do diagnóstico e do tratamento de nódulos e câncer da tireoide. Entretanto, as recentes recomendações nem sempre são apropriadas para diferentes regiões ou países. O objetivo deste trabalho foi oferecer uma série de recomendações para a avaliação e conduta de pacientes portadores de nódulos tireoideos aplicáveis a todos os países da América Latina. O trabalho foi realizado por um comitê composto por 13 membros da Sociedade Latino-Americana de Tireoide envolvidos com pesquisa e manejo de pacientes portadores de nódulos e carcinoma diferenciado da tireoide, de diferentes centros médicos da América Latina. As recomendações foram estabelecidas, após consenso, utilizando as opiniões especializadas de cada membro e os princípios da medicina baseada em evidência. Após a primeira reunião do grupo, um primeiro documento foi elaborado e encaminhado a todos os membros para revisão. Posteriormente, o documento foi enviado aos membros da Sociedade Latino-Americana de Tireoide para avaliação, sugestões e comentários. A versão final, elaborada após refinada revisão de todos os autores, representa o estado da arte no diagnóstico e na conduta de nódulos tireoideos, aplicáveis a todos os países da América Latina

Recomendações da sociedade Latino-Americana de tireoide no manejo de nódulos tireoideos

Several guidelines on diagnosis and treatment of thyroid nodules and cancer have recently been published. However, recommended practices are not always appropriate to different settings or countries. The aim of this consensus was to develop Clinical Guidelines for evaluation and management of patients with thyroid nodules applicable to Latin American countries. The panel was composed by 13 members of the Latin American Thyroid Society involved with research and management of thyroid nodules and cancer from different medical centers in Latin America. The consensus was produced based on the expert opinion of the panel with use of principles of evidence-based medicine. Following a group meeting, a first draft based on the expert opinion of the panel was elaborated and later circulated among panel members for further revision. After revision, this document was submitted to all LATS members for commentaries and considerations and finally revised and refined by the authors. The final recommendations represent state of the art on management of thyroid nodules applied to all Latin American countries539Vários consensos têm sido publicados acerca do diagnóstico e do tratamento de nódulos e câncer da tireoide. Entretanto, as recentes recomendações nem sempre são apropriadas para diferentes regiões ou países. O objetivo deste trabalho foi oferecer uma série de recomendações para a avaliação e conduta de pacientes portadores de nódulos tireoideos aplicáveis a todos os países da América Latina. O trabalho foi realizado por um comitê composto por 13 membros da Sociedade Latino-Americana de Tireoide envolvidos com pesquisa e manejo de pacientes portadores de nódulos e carcinoma diferenciado da tireoide, de diferentes centros médicos da América Latina. As recomendações foram estabelecidas, após consenso, utilizando as opiniões especializadas de cada membro e os princípios da medicina baseada em evidência. Após a primeira reunião do grupo, um primeiro documento foi elaborado e encaminhado a todos os membros para revisão. Posteriormente, o documento foi enviado aos membros da Sociedade Latino-Americana de Tireoide para avaliação, sugestões e comentários. A versão final, elaborada após refinada revisão de todos os autores, representa o estado da arte no diagnóstico e na conduta de nódulos tireoideos, aplicáveis a todos os países da América Latin

The complex radio and X-ray structure in the nuclear regions of the active galaxy NGC1365

We present a multiwavelength analysis of the prominent active galaxy NGC1365, in particular looking at the radio and X-ray properties of the central regions of the galaxy. We analyse ROSAT observations of NGC1365, and discuss recent ASCA results. In addition to a number of point sources in the vicinity of NGC1365, we find a region of X-ray emission extending along the central bar of the galaxy, combined with an emission peak near the centre of the galaxy. This X-ray emission is centred on the optical/radio nucleus, but is spatially extended. The X-ray spectrum can be well fitted by a thermal plasma model, with kT=0.6-0.8keV and a low local absorbing column. The thermal spectrum is suggestive of starburst emission rather than emission from a central black-hole. The ATCA radio observations show a number of hotspots, located in a ring around a weak radio nucleus. Synchrotron emission from electrons accelerated by supernovae and supernova remnants (SNRs) is the likely origin of these hotspots. The radio nucleus has a steep spectrum, indicative perhaps of an AGN or SNRs. The evidence for a jet emanating from the nucleus is at best marginal. The extent of the radio ring is comparable to the extended central X-ray source.Comment: 13 pages, 5 figures, to be published in MNRA