106 research outputs found
\u3csup\u3e12\u3c/sup\u3eC/\u3csup\u3e13\u3c/sup\u3eC Ratio in Planetary Nebulae from the \u3cem\u3eIUE\u3c/em\u3e Archives
We investigated the abundance ratio of 12C/13C in planetary nebulae by examining emission lines arising from C III 2s2p3Po2,1,0 â 2s21S0. Spectra were retrieved from the International Ultraviolet Explorer archives, and multiple spectra of the same object were co-added to achieve improved signal-to-noise ratio. The 13C hyperfine structure line at 1909.6 Ă
was detected in NGC 2440. The 12C/13C ratio was found to be ~4.4+/-1.2. In all other objects, we provide an upper limit for the flux of the 1910 Ă
line. For 23 of these sources, a lower limit for the 12C/13C ratio was established. The impact on our current understanding of stellar evolution is discussed. The resulting high-signal-to-noise ratio C III spectrum helps constrain the atomic physics of the line formation process. Some objects have the measured 1907/1909 Ă
flux ratio outside the low-electron density theoretical limit for 12C. A mixture of 13C with 12C helps to close the gap somewhat. Nevertheless, some observed 1907/1909 Ă
flux ratios still appear too high to conform to the currently predicted limits. It is shown that this limit, as well as the 1910/1909 Ă
flux ratio, are predominantly influenced by using the standard partitioning among the collision strengths for the multiplet 1S0-3PoJ according to the statistical weights. A detailed calculation for the fine-structure collision strengths between these individual levels would be valuable
C/C ratio in planetary nebulae from the IUE archives
We investigated the abundance ratio of C/C in planetary nebulae
by examining emission lines arising from \ion{C}{3} 2s2p ^3P_{2,1,0} \to 2s^2
^1S_0. Spectra were retrieved from the International Ultraviolet Explorer
archives, and multiple spectra of the same object were coadded to achieve
improved signal-to-noise. The C hyperfine structure line at 1909.6 \AA
was detected in NGC 2440. The C/C ratio was found to be
1.2. In all other objects, we provide an upper limit for the flux
of the 1910 \AA line. For 23 of these sources, a lower limit for the
C/C ratio was established. The impact on our current
understanding of stellar evolution is discussed.
The resulting high signal-to-noise \ion{C}{3} spectrum helps constrain the
atomic physics of the line formation process. Some objects have the measured
1907/1909 flux ratio outside the low-electron density theoretical limit for
C. A mixture of C with C helps to close the gap somewhat.
Nevertheless, some observed 1907/1909 flux ratios still appear too high to
conform to the presently predicted limits. It is shown that this limit, as well
as the 1910/1909 flux ratio, are predominantly influenced by using the standard
partitioning among the collision strengths for the multiplet --
according to the statistical weights. A detailed calculation for the fine
structure collision strengths between these individual levels would be
valuable.Comment: ApJ accepted: 19 pages, 3 Figures, 2 Table
Fourier ptychography: current applications and future promises
Traditional imaging systems exhibit a well-known trade-off between the resolution and the field of view of their captured images. Typical cameras and microscopes can either âzoom inâ and image at high-resolution, or they can âzoom outâ to see a larger area at lower resolution, but can rarely achieve both effects simultaneously. In this review, we present details about a relatively new procedure termed Fourier ptychography (FP), which addresses the above trade-off to produce gigapixel-scale images without requiring any moving parts. To accomplish this, FP captures multiple low-resolution, large field-of-view images and computationally combines them in the Fourier domain into a high-resolution, large field-of-view result. Here, we present details about the various implementations of FP and highlight its demonstrated advantages to date, such as aberration recovery, phase imaging, and 3D tomographic reconstruction, to name a few. After providing some basics about FP, we list important details for successful experimental implementation, discuss its relationship with other computational imaging techniques, and point to the latest advances in the field while highlighting persisting challenges
Super Weyl invariance: BPS equations from heterotic worldsheets
It is well-known that the beta functions on a string worldsheet correspond to
the target space equations of motion, e.g. the Einstein equations. We show that
the BPS equations, i.e. the conditions of vanishing supersymmetry variations of
the space-time fermions, can be directly derived from the worldsheet. To this
end we consider the RNS-formulation of the heterotic string with (2,0)
supersymmetry, which describes a complex torsion target space that supports a
holomorphic vector bundle. After a detailed account of its quantization and
renormalization, we establish that the cancellation of the Weyl anomaly
combined with (2,0) finiteness implies the heterotic BPS conditions: At the one
loop level the geometry is required to be conformally balanced and the gauge
background has to satisfy the Hermitean Yang-Mills equations.Comment: 1+31 pages LaTeX, 5 figures; final version, discussion relation Weyl
invariance and (2,0) finiteness extended, typos correcte
Translation correlations in anisotropically scattering media
Controlling light propagation across scattering media by wavefront shaping
holds great promise for a wide range of communications and imaging
applications. However, finding the right wavefront to shape is a challenge when
the mapping between input and output scattered wavefronts (i.e. the
transmission matrix) is not known. Correlations in transmission matrices,
especially the so-called memory-effect, have been exploited to address this
limitation. However, the traditional memory-effect applies to thin scattering
layers at a distance from the target, which precludes its use within thick
scattering media, such as fog and biological tissue. Here, we theoretically
predict and experimentally verify new transmission matrix correlations within
thick anisotropically scattering media, with important implications for
biomedical imaging and adaptive optics.Comment: main article (18 pages) and appendices (6 pages
Generalized Fano lineshapes reveal exceptional points in photonic molecules
The optical behavior of coupled systems, in which the breaking of parity and time-reversal symmetry occurs, is drawing increasing attention to address the physics of the exceptional point singularity, i.e., when the real and imaginary parts of the normal-mode eigenfrequencies coincide. At this stage, fascinating phenomena are predicted, including electromagnetic-induced transparency and phase transitions. To experimentally observe the exceptional points, the near-field coupling to waveguide proposed so far was proved to work only in peculiar cases. Here, we extend the interference detection scheme, which lies at the heart of the Fano lineshape, by introducing generalized Fano lineshapes as a signature of the exceptional point occurrence in resonant-scattering experiments. We investigate photonic molecules and necklace states in disordered media by means of a near-field hyperspectral mapping. Generalized Fano profiles in material science could extend the characterization of composite nanoresonators, semiconductor nanostructures, and plasmonic and metamaterial devices
Optical imaging and spectroscopy for the study of the human brain: status report
This report is the second part of a comprehensive two-part series aimed at reviewing an extensive and diverse toolkit of novel methods to explore brain health and function. While the first report focused on neurophotonic tools mostly applicable to animal studies, here, we highlight optical spectroscopy and imaging methods relevant to noninvasive human brain studies. We outline current state-of-the-art technologies and software advances, explore the most recent impact of these technologies on neuroscience and clinical applications, identify the areas where innovation is needed, and provide an outlook for the future directions
Mechanical Tension Increases CCN2/CTGF Expression and Proliferation in Gingival Fibroblasts via a TGFÎČ-Dependent Mechanism
Unlike skin, oral gingival do not scar in response to tissue injury. Fibroblasts,
the cell type responsible for connective tissue repair and scarring, are exposed
to mechanical tension during normal and pathological conditions including wound
healing and fibrogenesis. Understanding how human gingival fibroblasts respond
to mechanical tension is likely to yield valuable insights not only into
gingival function but also into the molecular basis of scarless repair.
CCN2/connective tissue growth factor is potently induced in fibroblasts during
tissue repair and fibrogenesis. We subjected gingival fibroblasts to cyclical
strain (up to 72 hours) using the Flexercell system and showed that CCN2 mRNA
and protein was induced by strain. Strain caused the rapid activation of latent
TGFÎČ, in a fashion that was reduced by blebbistatin and FAK/src inhibition,
and the induction of endothelin (ET-1) mRNA and protein expression. Strain did
not cause induction of α-smooth muscle actin or collagen type I mRNAs
(proteins promoting scarring); but induced a cohort of pro-proliferative mRNAs
and cell proliferation. Compared to dermal fibroblasts, gingival fibroblasts
showed reduced ability to respond to TGFÎČ by inducing fibrogenic mRNAs;
addition of ET-1 rescued this phenotype. Pharmacological inhibition of the
TGFÎČ type I (ALK5) receptor, the endothelin A/B receptors and FAK/src
significantly reduced the induction of CCN2 and pro-proliferative mRNAs and cell
proliferation. Controlling TGFÎČ, ET-1 and FAK/src activity may be useful in
controlling responses to mechanical strain in the gingiva and may be of value in
controlling fibroproliferative conditions such as gingival hyperplasia;
controlling ET-1 may be of benefit in controlling scarring in response to injury
in the skin
Wavefront shaping with disorder-engineered metasurfaces
Recently, wavefront shaping with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics, including extended volume, aberration-free focusing and subwavelength focusing. However, translating these capabilities to useful applications has remained challenging as the inputâoutput characteristics of the disordered media (P variables) need to be exhaustively determined via O(P) measurements. Here, we propose a paradigm shift where the disorder is specifically designed so its exact inputâoutput characteristics are known a priori and can be used with only a few alignment steps. We implement this concept with a disorder-engineered metasurface, which exhibits additional unique features for wavefront shaping such as a large optical memory effect range in combination with a wide angular scattering range, excellent stability, and a tailorable angular scattering profile. Using this designed metasurface with wavefront shaping, we demonstrate high numerical aperture (NAâ>â0.5) focusing and fluorescence imaging with an estimated ~2.2âĂâ10^8 addressable points in an ~8âmm field of view
- âŠ