615 research outputs found
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,
, down to , and for experiments with new materials,
different wavelengths, and different incident polarizations.Comment: 15 pages, 5 figures + 12 pages, 5 figures of supplemental informatio
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 paÃses. 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 paÃses 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 princÃpios 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 paÃses 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 paÃses. 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 paÃses 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 princÃpios 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 paÃses da América Latin
Patterns of subnet usage reveal distinct scales of regulation in the transcriptional regulatory network of Escherichia coli
The set of regulatory interactions between genes, mediated by transcription
factors, forms a species' transcriptional regulatory network (TRN). By
comparing this network with measured gene expression data one can identify
functional properties of the TRN and gain general insight into transcriptional
control. We define the subnet of a node as the subgraph consisting of all nodes
topologically downstream of the node, including itself. Using a large set of
microarray expression data of the bacterium Escherichia coli, we find that the
gene expression in different subnets exhibits a structured pattern in response
to environmental changes and genotypic mutation. Subnets with less changes in
their expression pattern have a higher fraction of feed-forward loop motifs and
a lower fraction of small RNA targets within them. Our study implies that the
TRN consists of several scales of regulatory organization: 1) subnets with more
varying gene expression controlled by both transcription factors and
post-transcriptional RNA regulation, and 2) subnets with less varying gene
expression having more feed-forward loops and less post-transcriptional RNA
regulation.Comment: 14 pages, 8 figures, to be published in PLoS Computational Biolog
Searching for Compton-thick active galactic nuclei at z~0.1
Using a suite of X-ray, mid-IR and optical active galactic nuclei (AGN)
luminosity indicators, we search for Compton-thick (CT) AGNs with intrinsic
L_X>10^42erg/s at z~0.03-0.2, a region of parameter space which is currently
poorly constrained by deep narrow-field and high-energy (E>10keV) all-sky X-ray
surveys. We have used the widest XMM-Newton survey (the serendipitous source
catalogue) to select a representative sub-sample (14; ~10%) of the 147 X-ray
undetected candidate CT AGNs in the Sloan Digital Sky Survey (SDSS) with
f_X/f_[OIII]<1; the 147 sources account for ~50% of the overall Type-2 AGN
population in the SDSS-XMM overlap region. We use mid-IR spectral decomposition
analyses and emission-line diagnostics, determined from pointed Spitzer-IRS
spectroscopic observations of these candidate CT AGNs, to estimate the
intrinsic AGN emission (predicted L_X,2-10keV (0.2-30)x10^42erg/s). On the
basis of the optical [OIII], mid-IR [OIV] and 6um AGN continuum luminosities we
conservatively find that the X-ray emission in at least 6/14 (>43%) of our
sample appear to be obscured by CT material with N_H>1.5x10^24cm^-2. Under the
reasonable assumption that our 14 AGNs are representative of the overall X-ray
undetected AGN population in the SDSS-XMM parent sample, we find that >20% of
the optical Type-2 AGN population are likely to be obscured by CT material.
This implies a space-density of log(Phi) >-4.9Mpc^-3 for CT AGNs with
L_X>10^42erg/s at z~0.1, which we suggest may be consistent with that predicted
by X-ray background synthesis models. Furthermore, using the 6um continuum
luminosity to infer the intrinsic AGN luminosity and the stellar velocity
dispersion to estimate M_BH, we find that the most conservatively identified CT
AGNs in this sample may harbour some of the most rapidly growing black holes
(median M_BH~3x10^7M_o) in the nearby Universe, with a median Eddington ratio
of ~0.2.Comment: 16 pages, 2 tables, 6 figures. Accepted for publication in MNRA
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