503 research outputs found
The Distribution and Excitation of CH₃CN in a Solar Nebula Analog
Cometary studies suggest that the organic composition of the early Solar Nebula was rich in complex nitrile species such CH3CN. Recent ALMA detections in protoplanetary disks suggest that these species may be common during planet and comet formation, but connecting gas-phase measurements to cometary abundances first requires constraints on formation chemistry and distributions of these species. We present here the detection of seven spatially resolved transitions of CH3CN in the protoplanetary disk around the T-Tauri star TW Hya. Using a rotational diagram analysis, we find a disk-averaged column density of cm−2 and a rotational temperature of K. A radially resolved rotational diagram shows the rotational temperature to be constant across the disk, suggesting that the CH3CN emission originates from a layer at z/r ~ 0.3. Through comparison of the observations with predictions from a disk chemistry model, we find that grain-surface reactions likely dominate CH3CN formation and that in situ disk chemistry is sufficient to explain the observed CH3CN column density profile without invoking inheritance from the protostellar phase. However, the same model fails to reproduce a solar system cometary abundance of CH3CN relative to H2O in the midplane, suggesting that either vigorous vertical mixing or some degree of inheritance from interstellar ices occurred in the Solar Nebula
Compactified N = 1 supersymmetric Yang-Mills theory on the lattice: continuity and the disappearance of the deconfinement transition
Dressing Up the Kink
Many quantum field theoretical models possess non-trivial solutions which are
stable for topological reasons. We construct a self-consistent example for a
self-interacting scalar field--the quantum (or dressed) kink--using a two
particle irreducible effective action in the Hartree approximation. This new
solution includes quantum fluctuations determined self-consistently and
nonperturbatively at the 1-loop resummed level and allowed to backreact on the
classical mean-field profile. This dressed kink is static under the familiar
Hartree equations for the time evolution of quantum fields. Because the quantum
fluctuation spectrum is lower lying in the presence of the defect, the quantum
kink has a lower rest energy than its classical counterpart. However its energy
is higher than well-known strict 1-loop results, where backreaction and
fluctuation self-interactions are omitted. We also show that the quantum kink
exists at finite temperature and that its profile broadens as temperature is
increased until it eventually disappears.Comment: 13 pages, latex, 3 eps figures; revised with yet additional
references, minor rewordin
Locus coeruleus integrity is related to tau burden and memory loss in autosomal-dominant Alzheimer’s disease (Version posted online February 2, 2021)
Influence of electron correlations on ground-state properties of III-V semiconductors
Lattice constants and bulk moduli of eleven cubic III-V semiconductors are
calculated using an ab initio scheme. Correlation contributions of the valence
electrons, in particular, are determined using increments for localized bonds
and for pairs and triples of such bonds; individual increments, in turn, are
evaluated using the coupled cluster approach with single and double
excitations. Core-valence correlation is taken into account by means of a core
polarization potential. Combining the results at the correlated level with
corresponding Hartree-Fock data, we obtain lattice constants which agree with
experiment within an average error of -0.2%; bulk moduli are accurate to +4%.
We discuss in detail the influence of the various correlation contributions on
lattice constants and bulk moduli.Comment: 4 pages, Latex, no figures, Phys. Rev. B, accepte
Electron correlations for ground state properties of group IV semiconductors
Valence energies for crystalline C, Si, Ge, and Sn with diamond structure
have been determined using an ab-initio approach based on information from
cluster calculations. Correlation contributions, in particular, have been
evaluated in the coupled electron pair approximation (CEPA), by means of
increments obtained for localized bond orbitals and for pairs and triples of
such bonds. Combining these results with corresponding Hartree-Fock (HF) data,
we recover about 95 % of the experimental cohesive energies. Lattice constants
are overestimated at the HF level by about 1.5 %; correlation effects reduce
these deviations to values which are within the error bounds of this method. A
similar behavior is found for the bulk modulus: the HF values which are
significantly too high are reduced by correlation effects to about 97 % of the
experimental values.Comment: 22 pages, latex, 2 figure
Endoplasmic reticulum Ca2+-homeostasis is altered in small and non-small cell lung cancer cell lines
<p>Abstract</p> <p>Background</p> <p>Knowledge of differences in the cellular physiology of malignant and non-malignant cells is a prerequisite for the development of cancer treatments that effectively kill cancer without damaging normal cells. Calcium is a ubiquitous signal molecule that is involved in the control of proliferation and apoptosis. We aimed to investigate if the endoplasmic reticulum (ER) Ca<sup>2+</sup>-homeostasis is different in lung cancer and normal human bronchial epithelial (NHBE) cells.</p> <p>Methods</p> <p>The intracellular Ca<sup>2+</sup>-signaling was investigated using fluorescence microscopy and the expression of Ca<sup>2+</sup>-regulating proteins was assessed using Western Blot analysis.</p> <p>Results</p> <p>In a Small Cell Lung Cancer (H1339) and an Adeno Carcinoma Lung Cancer (HCC) cell line but not in a Squamous Cell Lung Cancer (EPLC) and a Large Cell Lung Cancer (LCLC) cell line the ER Ca<sup>2+</sup>-content was reduced compared to NHBE. The reduced Ca<sup>2+</sup>-content correlated with a reduced expression of SERCA 2 pumping calcium into the ER, an increased expression of IP<sub>3</sub>R releasing calcium from the ER, and a reduced expression of calreticulin buffering calcium within the ER. Lowering the ER Ca<sup>2+</sup>-content with CPA led to increased proliferation NHBE and lung cancer cells.</p> <p>Conclusion</p> <p>The significant differences in Ca<sup>2+</sup>-homeostasis between lung cancer and NHBE cells could represent a new target for cancer treatments.</p
The edge-on protoplanetary disk HH 48 NE I. Modeling the geometry and stellar parameters
Context. Observations of edge-on disks are an important tool for constraining
general protoplanetary disk properties that cannot be determined in any other
way. However, most radiative transfer models cannot simultaneously reproduce
the spectral energy distributions (SEDs) and resolved scattered light and
submillimeter observations of these systems, due to the differences in geometry
and dust properties at different wavelengths. Aims. We simultaneously constrain
the geometry of the edge-on protoplanetary disk HH 48 NE and the
characteristics of the host star. HH 48 NE is part of the JWST early release
science program Ice Age. This work serves as a stepping stone towards a better
understanding of the disk physical structure and icy chemistry in this
particular source. This kind of modeling lays the groundwork for studying other
edge-on sources to be observed with the JWST. Methods. We fit a parameterized
dust model to HH 48 NE by coupling the radiative transfer code RADMC-3D and an
MCMC framework. The dust structure was fitted independently to a compiled SED,
a scattered light image at 0.8 m and an ALMA dust continuum observation
at 890 m. Results. We find that 90% of the dust mass in HH 48 NE is
settled to the disk midplane, less than in average disks, and that the
atmospheric layers of the disk contain exclusively large grains (0.3-10
m). The exclusion of small grains in the upper atmosphere likely has
important consequences for the chemistry due to the deep penetration of
high-energy photons. The addition of a relatively large cavity (ca. 50 au in
radius) is necessary to explain the strong mid-infrared emission, and to fit
the scattered light and continuum observations simultaneously.Comment: 16 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
Optical Spectroscopic Observations of CI Camelopardalis
We present the results of optical spectroscopic observations of CI Cam.
Double-peaked profiles were simultaneously observed for the first time in the
hydrogen Balmer, He {\small I} 6678 and Fe {\small II} lines during an
observational run in 2001 September. An intermediate viewing angle of the
circumstellar disk around the B[e] star is consistent with our data. A
significant decrease in the intensity of the H and He {\small I} lines
in our 2004 September observations might have been the precursor of a line
outburst at the end of 2004. The remarkable increase in the intensity of all
lines and the decrease in visual brightness in 2005 might be due to the
environment filling with new material ejected during the outburst. The
environment of CI Cam is influenced by mass loss from the B[e] star and the
outburst of its compact companion.Comment: 18 pages, 4 figures, 1 tabl
Visual parameter optimisation for biomedical image processing
Background: Biomedical image processing methods require users to optimise input parameters to ensure high quality
output. This presents two challenges. First, it is difficult to optimise multiple input parameters for multiple
input images. Second, it is difficult to achieve an understanding of underlying algorithms, in particular, relationships
between input and output.
Results: We present a visualisation method that transforms users’ ability to understand algorithm behaviour by
integrating input and output, and by supporting exploration of their relationships. We discuss its application to a
colour deconvolution technique for stained histology images and show how it enabled a domain expert to
identify suitable parameter values for the deconvolution of two types of images, and metrics to quantify
deconvolution performance. It also enabled a breakthrough in understanding by invalidating an underlying
assumption about the algorithm.
Conclusions: The visualisation method presented here provides analysis capability for multiple inputs and outputs
in biomedical image processing that is not supported by previous analysis software. The analysis supported by our
method is not feasible with conventional trial-and-error approaches
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