699 research outputs found
The Disks of Galaxies with Seyfert and Starburst Nuclei: II. Near-Infrared Structural Properties
We have derived the near-infrared structural components of a sample of
Seyfert and starburst (SBN) host galaxies by fitting the images of Hunt et al.
(1997,ApJS,108,229) with a new two-dimensional decomposition algorithm. An
analysis of the fitted parameters shows that Seyfert 1 and SBN bulges resemble
normal early-type bulges in structure and color, with (J-K)^c_b about 0.1 mag
redder than disk (J-K)^c_d. Seyfert 2 bulges, instead, are bluer than normal
with (J-K)^c_b ~ (J-K)^c_d. Seyfert disks (especially Type 1), but not those of
SBNs, are abnormally bright (in surface brightness), significantly more so than
even the brightest normal disks. Seyfert disks are also compact, but similar to
those in normal early-type spirals. For a given mass, Seyferts and especially
SBNs are abnormally rich in neutral hydrogen, and there is strong, albeit
indirect, evidence for lower mass-to-light (M/L) ratios in Seyfert and SBN
disks, but for normal M/Ls in their bulges. In Seyferts and SBNs, HI mass
fractions and M/L ratios are anticorrelated, and we attribute the high gas mass
fractions and low M/Ls in SBNs and several Seyferts to ongoing star formation.
Such abundant gas in Seyferts would be expected to inhibit bar formation, which
may explain why active galaxies are not always barred.Comment: 25 pgs (two-column, single-spaced) including 8 incorporated figures
and 2 tables (aas2pp4, amssym, epsfig). Accepted for publication in Ap
Does the Radiative Avalanche Fueling Work in Any Active Galactic Nuclei ?
Recently Umemura, Fukue, & Mineshige (1997) proposed the radiative avalanche
fueling to active galactic nuclei; gas accretion is driven by radiation drag
exerted by stellar radiation from circumnuclear starburst regions. This
mechanism is also interesting in terms of starburst-AGN connections. We
therefore present observational tests for the radiative avalanche fueling. Our
tests, however, show that gas accretion rates driven by the radiative avalanche
are significantly lower than those expected from the standard accretion theory
applied for typical active galactic nuclei with the circumnuclear starburst
regions. Instead we propose an alternative, possible starburst-AGN connection;
a minor merger with a nucleated satellite drives circumnuclear starbursts and
then leads to gas fueling onto the central engine as the merger proceeds.Comment: 12 page
Controlling Cherenkov angles with resonance transition radiation
Cherenkov radiation provides a valuable way to identify high energy particles
in a wide momentum range, through the relation between the particle velocity
and the Cherenkov angle. However, since the Cherenkov angle depends only on
material's permittivity, the material unavoidably sets a fundamental limit to
the momentum coverage and sensitivity of Cherenkov detectors. For example, Ring
Imaging Cherenkov detectors must employ materials transparent to the frequency
of interest as well as possessing permittivities close to unity to identify
particles in the multi GeV range, and thus are often limited to large gas
chambers. It would be extremely important albeit challenging to lift this
fundamental limit and control Cherenkov angles as preferred. Here we propose a
new mechanism that uses constructive interference of resonance transition
radiation from photonic crystals to generate both forward and backward
Cherenkov radiation. This mechanism can control Cherenkov angles in a flexible
way with high sensitivity to any desired range of velocities. Photonic crystals
thus overcome the severe material limit for Cherenkov detectors, enabling the
use of transparent materials with arbitrary values of permittivity, and provide
a promising option suited for identification of particles at high energy with
enhanced sensitivity.Comment: There are 16 pages and 4 figures for the manuscript. Supplementary
information with 18 pages and 5 figures, appended at the end of the file with
the manuscript. Source files in Word format converted to PDF. Submitted to
Nature Physic
Tunable anisotropy in inverse opals and emerging optical properties
Using self-assembly, nanoscale materials can be fabricated from the bottom up. Opals and inverse opals are examples of self-assembled nanomaterials made from crystallizing colloidal particles. As self-assembly requires a high level of control, it is challenging to use building blocks with anisotropic geometry to form complex opals, which limits the realizable structures. Typically, spherical colloids are employed as building blocks, leading to symmetric, isotropic superstructures. However, a significantly richer palette of directionally dependent properties are expected if less symmetric, anisotropic structures can be created, especially originating from the assembly of regular, spherical particles. Here we show a simple method to introduce anisotropy into inverse opals by subjecting them to a post-assembly thermal treatment that results in directional shrinkage of the silica matrix caused by condensation of partially hydrated sol-gel silica structures. In this way, we can tailor the shape of the pores, and the anisotropy of the final inverse opal preserves the order and uniformity of the self-assembled structure, while completely avoiding the need to synthesize complex oval-shaped particles and crystallize them into such target geometries. Detailed X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy studies clearly identify increasing degrees of sol-gel condensation in confinement as a mechanism for the structure change. A computer simulation of structure changes resulting from the condensation-induced shrinkage further confirmed this mechanism. As an example of property changes induced by the introduction of anisotropy, we characterized the optical spectra of the anisotropic inverse opals and found that the optical properties can be controlled in a precise way using calcination temperature
Unanticipated Insights into Biomedicine from the Study of Acupuncture
Research into acupuncture has had ripple effects beyond the field of acupuncture. This paper identifies five exemplars to illustrate that there is tangible evidence of the way insights gleaned from acupuncture research have informed biomedical research, practice, or policy. The first exemplar documents how early research into acupuncture analgesia has expanded into neuroimaging research, broadening physiologic understanding and treatment of chronic pain. The second describes how the acupuncture needle has become a tool to enhance biomedical knowledge of connective tissue. The third exemplar, which illustrates use of a modified acupuncture needle as a sham device, focuses on emergent understanding of placebo effects and, in turn, on insights into therapeutic encounters in treatments unrelated to acupuncture. The fourth exemplar documents that two medical devices now in widespread use were inspired by acupuncture: transcutaneous electrical nerve stimulators for pain control and antinausea wrist bands. The final exemplar describes how pragmatic clinical trial designs applied in acupuncture research have informed current general interest in comparative effectiveness research. In conclusion, these exemplars of unanticipated outcomes of acupuncture research comprise an additional rationale for continued support of basic and clinical research evaluating acupuncture and other under-researched therapies
Ultra-fast responsive colloidal-polymer composite-based volatile organic compounds (VOC) sensor using nanoscale easy tear process
There is an immense need for developing a simple, rapid, and inexpensive detection assay for health-care applications or monitoring environments. To address this need, a photonic crystal (PC)-based sensor has been extensively studied due to its numerous advantages such as colorimetric measurement, high sensitivity, and low cost. However, the response time of a typical PC-based sensor is relatively slow due to the presence of the inevitable upper residual layer in colloidal structures. Hence, we propose an ultra-fast responsive PC-based volatile organic compound (VOC) sensor by using a "nanoscale easy tear (NET) process" inspired by commercially available "easy tear package". A colloidal crystal-polydimethylsiloxane (PDMS) composite can be successfully realized through nanoscale tear propagation along the interface between the outer surface of crystallized nanoparticles and bulk PDMS. The response time for VOC detection exhibits a significant decrease by allowing the direct contact with VOCs, because of perfect removal of the residual on the colloidal crystals. Moreover, vapor-phase VOCs can be monitored, which had been previously impossible. High-throughput production of the patterned colloidal crystal-polymer composite through the NET process can be applied to other multiplexed selective sensing applications or may be used for nanomolding templates
Inkjet Printing Based Mono-layered Photonic Crystal Patterning for Anti-counterfeiting Structural Colors
Photonic crystal structures can be created to manipulate electromagnetic waves so that many studies have focused on designing photonic band-gaps for various applications including sensors, LEDs, lasers, and optical fibers. Here, we show that mono-layered, self-assembled photonic crystals (SAPCs) fabricated by using an inkjet printer exhibit extremely weak structural colors and multiple colorful holograms so that they can be utilized in anti-counterfeit measures. We demonstrate that SAPC patterns on a white background are covert under daylight, such that pattern detection can be avoided, but they become overt in a simple manner under strong illumination with smartphone flash light and/or on a black background, showing remarkable potential for anti-counterfeit techniques. Besides, we demonstrate that SAPCs yield different RGB histograms that depend on viewing angles and pattern densities, thus enhancing their cryptographic capabilities. Hence, the structural colorations designed by inkjet printers would not only produce optical holograms for the simple authentication of many items and products but also enable a high-secure anti-counterfeit techniqueope
Hot Very Small dust Grains in NGC 1068 seen in jet induced structures thanks to VLT/NACO adaptive optics
We present K, L and M diffraction-limited images of NGC 1068 obtained with
NAOS+CONICA at VLT/YEPUN over a 3.5" field around the central engine. Hot dust
(Tcol = 550-650 K) is found in three different regions : (a) in the true
nucleus, seen as a slightly NS elongated, core of extremely hot dust,
"resolved" in K and L with respective diameters of ~5 pc and 8.5 pc ; (b) along
the NS direction, as a "spiral arm" and a southern tongue ; (c) as a set of
parallel elongated nodules ("wave-like") bracketting the jet. Several
structures observed on radio maps, mid-IR or HST UV-visible maps are seen, so
that a precise registration can be done from UV to 6 cm. These results do
support the current interpretion that source (a) corresponds to emission from
dust near sublimation temperature delimiting the walls of the cavity in the
central obscuring torus. Structure (b) is thought to be a mixture of hot dust
and active star forming regions along a micro spiral structure that could trace
the tidal mechanism bringing matter to the central engine. Structure c)which
was not known, exhibits too high a temperature for "classical'' grains ; it is
most probably the signature of transiently heated very small dust grains (VSG)
: "nano-diamonds", which are resistant and can form in strong UV field or in
shocks, are very attractive candidates. The "waves'' can be condensations
triggered by jet induced shocks, as predicted by recent models. First
estimates, based on a simple VSG model and on a detailed radiative transfer
model, do agree with those interpretations, both qualitatively and
quantitatively.Comment: Submitted : 15 March 2003 ; accepted : 15 May 200
Analysis of ground reaction force and electromyographic activity of the gastrocnemius muscle during double support
O documento em anexo encontra-se na versão post-print (versão corrigida pelo editor).Purpose: Mechanisms associated with energy expenditure during gait have been extensively researched and studied. According to the double-inverted pendulum model energy expenditure is higher during double support, as lower limbs need to work to redirect the centre of mass velocity. This study looks into how the ground reaction force (GRF) of one limb affects the muscle activity required by the medial gastrocnemius (MG) of the contralateral limb during step-to-step transition. Methods: Thirty-five subjects were monitored as to the MG electromyographic activity (EMGa) of one limb and the GRF of the contralateral limb during double support. Results: After determination of the Pearson correlation coefficient (r), a moderate correlation was observed between the MG EMGa of the dominant leg and the vertical (Fz) and anteroposterior (Fy) components of GRF of the non-dominant leg (r=0.797, p<0.0001; r=-0.807, p<0.0001) and a weak and moderate correlation was observed between the MG EMGa of the non-dominant leg and the Fz and Fy of the dominant leg, respectively (r=0.442, p=0.018; r=-0.684 p<0.0001). Conclusions: The results obtained suggest that during double support, GRF is
associated with the EMGa of the contralateral MG and that there is an increased dependence between the GRF of the non-dominant leg and the EMGa of the dominant MG
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