665 research outputs found
Density-PDFs and Lagrangian Statistics of highly compressible Turbulence
We report on probability-density-functions (PDF) of the mass density in
numerical simulations of highly compressible hydrodynamic flows and the
corresponding structure formation of Lagrangian particles advected by the
flows. Numerical simulations were performed with collocation points and
2 million tracer particles integrated over several dynamical times. We propose
a connection between the PDF of the Lagrangian tracer particles and the
predicted log-normal distribution of the density fluctuations in isothermal
systems
Response of a ferrofluid to traveling-stripe forcing
We observe the dynamics of waves propagating on the surface of a ferrofluid
under the influence of a spatially and temporarily modulated field. In
particular, we excite plane waves by a travelling lamellar modulation of the
magnetization. By this external driving both the wavelength and the propagation
velocity of the waves can be controlled. The amplitude of the excited waves
exhibits a resonance phenomenon similar to that of a forced harmonic
oscillator. Its analysis reveals the dispersion relation of the free surface
waves, from which the critical magnetic field for the onset of the Rosensweig
instability can be extrapolated
Progress in Three-Dimensional Coherent X-Ray Diffraction Imaging
The Fourier inversion of phased coherent diffraction patterns offers images
without the resolution and depth-of-focus limitations of lens-based tomographic
systems. We report on our recent experimental images inverted using recent
developments in phase retrieval algorithms, and summarize efforts that led to
these accomplishments. These include ab-initio reconstruction of a
two-dimensional test pattern, infinite depth of focus image of a thick object,
and its high-resolution (~10 nm resolution) three-dimensional image.
Developments on the structural imaging of low density aerogel samples are
discussed.Comment: 5 pages, X-Ray Microscopy 2005, Himeji, Japa
The ionized and hot gas in M17 SW: SOFIA/GREAT THz observations of [C II] and 12CO J=13-12
With new THz maps that cover an area of ~3.3x2.1 pc^2 we probe the spatial
distribution and association of the ionized, neutral and molecular gas
components in the M17 SW nebula. We used the dual band receiver GREAT on board
the SOFIA airborne telescope to obtain a 5'.7x3'.7 map of the 12CO J=13-12
transition and the [C II] 158 um fine-structure line in M17 SW and compare the
spectroscopically resolved maps with corresponding ground-based data for low-
and mid-J CO and [C I] emission. For the first time SOFIA/GREAT allow us to
compare velocity-resolved [C II] emission maps with molecular tracers. We see a
large part of the [C II] emission, both spatially and in velocity, that is
completely non-associated with the other tracers of photon-dominated regions
(PDR). Only particular narrow channel maps of the velocity-resolved [C II]
spectra show a correlation between the different gas components, which is not
seen at all in the integrated intensity maps. These show different morphology
in all lines but give hardly any information on the origin of the emission. The
[C II] 158 um emission extends for more than 2 pc into the M17 SW molecular
cloud and its line profile covers a broader velocity range than the 12CO
J=13-12 and [C I] emissions, which we interpret as several clumps and layers of
ionized carbon gas within the telescope beam. The high-J CO emission emerges
from a dense region between the ionized and neutral carbon emissions,
indicating the presence of high-density clumps that allow the fast formation of
hot CO in the irradiated complex structure of M17 SW. The [C II] observations
in the southern PDR cannot be explained with stratified nor clumpy PDR models.Comment: 4 pages, 4 figures, letter accepted for the SOFIA/GREAT A&A 2012
special issu
Protostars and Outflows in the NGC7538 - IRS9 Cloud Core
New high resolution observations of HCO+ J=1-0, H13CN J=1-0, SO 2,2 - 1,1,
and continuum with BIMA at 3.4 mm show that the NGC7538 - IRS9 cloud core is a
site of active ongoing star formation. Our observations reveal at least three
young bipolar molecular outflows, all ~ 10,000 -- 20,000 years old. IRS9 drives
a bipolar, extreme high velocity outflow observed nearly pole on. South of IRS9
we find a cold, protostellar condensation with a size of ~ 14" x 6" with a mass
> 250 Msun. This is the center of one of the outflows and shows deep,
red-shifted self absorption in HCO+, suggesting that there is a protostar
embedded in the core, still in a phase of active accretion. This source is not
detected in the far infrared, suggesting that the luminosity < 10^4 Lsun; yet
the mass of the outflow is ~ 60 Msun. The red-shifted HCO+ self-absorption
profiles observed toward the southern protostar and IRS9 predict accretion
rates of a few times 10^-4 to 10^-3 Msun/yr. Deep VLA continuum observations at
3.6 cm show that IRS9 coincides with a faint thermal VLA source, but no other
young star in the IRS9 region has any detectable free-free emission at a level
of ~ 60 microJy at 3.6 cm. The HCO+ abundance is significantly enhanced in the
hot IRS9 outflow. A direct comparison of mass estimates from HCO+ and CO for
the well-characterized red-shifted IRS9 outflow predicts an HCO+ enhancement of
more than a factor of 30, or [HCO+/H2] >= 6 10^-8.Comment: 40 pages, 3 tables and 10 figures included; to appear in Ap
Coherent X-ray Diffractive Imaging; applications and limitations
The inversion of a diffraction pattern offers aberration-free
diffraction-limited 3D images without the resolution and depth-of-field
limitations of lens-based tomographic systems, the only limitation being
radiation damage. We review our experimental results, discuss the fundamental
limits of this technique and future plans.Comment: 7 pages, 8 figure
High-resolution ab initio three-dimensional X-ray diffraction microscopy
Coherent X-ray diffraction microscopy is a method of imaging non-periodic
isolated objects at resolutions only limited, in principle, by the largest
scattering angles recorded. We demonstrate X-ray diffraction imaging with high
resolution in all three dimensions, as determined by a quantitative analysis of
the reconstructed volume images. These images are retrieved from the 3D
diffraction data using no a priori knowledge about the shape or composition of
the object, which has never before been demonstrated on a non-periodic object.
We also construct 2D images of thick objects with infinite depth of focus
(without loss of transverse spatial resolution). These methods can be used to
image biological and materials science samples at high resolution using X-ray
undulator radiation, and establishes the techniques to be used in
atomic-resolution ultrafast imaging at X-ray free-electron laser sources.Comment: 22 pages, 11 figures, submitte
MED12 regulates a transcriptional network of calcium-handling genes in the heart
The Mediator complex regulates gene transcription by linking basal transcriptional machinery with DNA-bound transcription factors. The activity of the Mediator complex is mainly controlled by a kinase submodule that is composed of 4 proteins, including MED12. Although ubiquitously expressed, Mediator subunits can differentially regulate gene expression in a tissue-specific manner. Here, we report that MED12 is required for normal cardiac function, such that mice with conditional cardiac-specific deletion of MED12 display progressive dilated cardiomyopathy. Loss of MED12 perturbs expression of calcium-handling genes in the heart, consequently altering calcium cycling in cardiomyocytes and disrupting cardiac electrical activity. We identified transcription factors that regulate expression of calcium-handling genes that are downregulated in the heart in the absence of MED12, and we found that MED12 localizes to transcription factor consensus sequences within calcium-handling genes. We showed that MED12 interacts with one such transcription factor, MEF2, in cardiomyocytes and that MED12 and MEF2 co-occupy promoters of calcium-handling genes. Furthermore, we demonstrated that MED12 enhances MEF2 transcriptional activity and that overexpression of both increases expression of calcium-handling genes in cardiomyocytes. Our data support a role for MED12 as a coordinator of transcription through MEF2 and other transcription factors. We conclude that MED12 is a regulator of a network of calcium-handling genes, consequently mediating contractility in the mammalian heart
Interoperability for the design and construction industry through semantic web technology
The domain of architecture, engineering and construction (AEC) has experienced significant improvements with the advent of building information modelling (BIM) applications, which allow AEC specialists to model all information concerning a building design into one three-dimensional building model. Much of these improvements are however generated by the mere availability of such an environment, whereas many more improvements were expected by achieving an appropriate interoperability of information. We are investigating why such an interoperability is not reached fully and consider the semantic web as an alternative approach to reach the targeted interoperability. In this paper, an AEC description framework based on semantic web technology is presented and compared to the BIM approach, after which we indicate how it might solve the issue of interoperability more appropriately. Our evaluation of this investigation indicates the semantic web approach as a valid alternative approach, although considerably more research is needed to show it capable of providing the targeted interoperability of information in the AEC domain
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