1,715 research outputs found
Nucleocytoplasmic transport: taking an inventory
In eukaryotic cells, the enclosure of the genetic information in the nucleus allows the spatial and temporal separation of DNA replication and transcription from cytoplasmic protein synthesis. This compartmentalization not only permits a high level of regulation of these processes but at the same time necessitates a system of selective macromolecular transport between the nucleus and the cytoplasm. Transfer of macromolecules between both compartments is mediated by soluble receptors that interact with components of nuclear pore complexes (NPCs) to move their specific cargos. Transport occurs by way of a great variety of different pathways defined by individual receptors and accessory factors. Often, processes in substrate biogenesis that precede transport concurrently recruit transport factors to substrates, thus making transport responsive to correct and orderly synthesis of substrates. Some current challenges are to understand how transport factor-substrate interactions are controlled and integrated with sequential steps in substrate biogenesis, how large macromolecular complexes are restructured to fit through the NPC channel and to understand how transport factor-NPC interactions lead to actual translocation through the NP
High Frame-rate Imaging Based Photometry, Photometric Reduction of Data from Electron-multiplying Charge Coupled Devices (EMCCDs)
The EMCCD is a type of CCD that delivers fast readout times and negligible
readout noise, making it an ideal detector for high frame rate applications
which improve resolution, like lucky imaging or shift-and-add. This improvement
in resolution can potentially improve the photometry of faint stars in
extremely crowded fields significantly by alleviating crowding. Alleviating
crowding is a prerequisite for observing gravitational microlensing in main
sequence stars towards the galactic bulge. However, the photometric stability
of this device has not been assessed. The EMCCD has sources of noise not found
in conventional CCDs, and new methods for handling these must be developed.
We aim to investigate how the normal photometric reduction steps from
conventional CCDs should be adjusted to be applicable to EMCCD data. One
complication is that a bias frame cannot be obtained conventionally, as the
output from an EMCCD is not normally distributed. Also, the readout process
generates spurious charges in any CCD, but in EMCCD data, these charges are
visible as opposed to the conventional CCD. Furthermore we aim to eliminate the
photon waste associated with lucky imaging by combining this method with
shift-and-add.
A simple probabilistic model for the dark output of an EMCCD is developed.
Fitting this model with the expectation-maximization algorithm allows us to
estimate the bias, readout noise, amplification, and spurious charge rate per
pixel and thus correct for these phenomena. To investigate the stability of the
photometry, corrected frames of a crowded field are reduced with a PSF fitting
photometry package, where a lucky image is used as a reference.
We find that it is possible to develop an algorithm that elegantly reduces
EMCCD data and produces stable photometry at the 1% level in an extremely
crowded field.Comment: Submitted to Astronomy and Astrophysic
Stellar Dynamics and the implications on the merger evolution in NGC6240
We report near-infrared integral field spectroscopy of the luminous merging
galaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by
1.6arcsec are the central parts of inclined, rotating disk galaxies with equal
mass bulges. The dynamical masses of the nuclei are much larger than the
stellar mass derived from the K-band light, implying that the progenitor
galaxies were galaxies with massive bulges. The K-band light is dominated by
red supergiants formed in the two nuclei in starbursts, triggered ~2x10^7 years
ago, possibly by the most recent perigalactic approach. Strong feedback effects
of a superwind and supernovae are responsible for a short duration burst
(~5x10^6 years) which is already decaying. The two galaxies form a
prograde-retrograde rotating system and from the stellar velocity field it
seems that one of the two interacting galaxies is subject to a prograde
encounter. Between the stellar nuclei is a prominent peak of molecular gas
(H_2, CO). The stellar velocity dispersion peaks there indicating that the gas
has formed a local, self-gravitating concentration decoupled from the stellar
gravitational potential. NGC 6240 has previously been reported to fit the
paradigm of an elliptical galaxy formed through the merger of two galaxies.
This was based on the near-infrared light distribution which follows a
r^1/4-law. Our data cast strong doubt on this conclusion: the system is by far
not relaxed, rotation plays an important role, as does self-gravitating gas,
and the near-infrared light is dominated by young stars.Comment: 34 pages, 11 figures, using AASTEX 5.0rc3.1, paper submitted to the
Astrophysical Journal, revised versio
Methods and Algorithms for Robust Filtering
We discuss filtering procedures for robust extraction of a signal from noisy time series. Moving averages and running medians are standard methods for this, but they have shortcomings when large spikes (outliers) respectively trends occur. Modified trimmed means and linear median hybrid filters combine advantages of both approaches, but they do not completely overcome the difficulties. Improvements can be achieved by using robust regression methods, which work even in real time because of increased computational power and faster algorithms. Extending recent work we present filters for robust online signal extraction and discuss their merits for preserving trends, abrupt shifts and extremes and for the removal of spikes
On the thermodynamics of the SwiftâHohenberg theory
We present the microbalance including the microforces, the first- and second-order microstresses for the SwiftâHohenberg equation concomitantly with their constitutive equations, which are consistent with the free-energy imbalance. We provide an explicit form for the microstress structure for a free-energy functional endowed with second-order spatial derivatives. Additionally, we generalize the SwiftâHohenberg theory via a proper constitutive process. Finally, we present one highly resolved three-dimensional numerical simulation to demonstrate the particular form of the resulting microstresses and their interactions in the evolution of the SwiftâHohenberg equation
PKS 0537-441: extended [O II] emission and a binary QSO?
We present high-resolution imaging and low-resolution spectroscopy of the BL
Lac object PKS 0537-441 (z = 0.893) and its environment. The observations were
designed to clarify, whether the properties of PKS 0537-441 are affected by
gravitational microlensing, or whether PKS 0537-441 and its environment act as
a lensing system itself. Our observations show that neither case seems to be
likely. We did not find a galaxy along the line-of-sight to the BL Lac as
claimed previously, our spectroscopy shows that none of the four closest
companion galaxies is at high redshift. Two of the four nearby companion
galaxies to PKS 0537-441 are within 200 km/s of the systemic velocity of the BL
Lac (z = 0.892 and 0.895, respectively). The third companion galaxy is at
higher redshift (z = 0.947). The fourth companion galaxy shows evidence of Mg
II absorption redwards of its systemic velocity and is perhaps a mini low
ionization BAL QSO at z = 0.885. If the latter can be confirmed, PKS 0537-441
is the first BL Lacertae object being a member of a binary Quasar. We also
detected extended [O II] emission in the off-nuclear spectrum of PKS 05371-441,
which is most likely due to photoionization from the active nucleus.
Alternatively, the extended [O II] emission is due to jet-cloud interaction
with the counterjet of PKS 0537-441. Our clustering analysis indicates that PKS
0537-441 is located in a cluster environment as rich as Abell type 0-1. This is
supported by the detection of four galaxies in the field with similar redshifts
as the BL Lac (Delta z < 0.002). We found serendipitously even more galaxies at
somewhat higher redshifts (z = 0.9-1). Thus, PKS0537-441 might be located in
front of a galaxy cluster at somewhat higher redshift or even be part of a
large-scale structure with an extension towards the BL Lac.Comment: 13 pages, 9 figures, accepted for publication in A&
PANIC: the new panoramic NIR camera for Calar Alto
PANIC is a wide-field NIR camera, which is currently under development for
the Calar Alto observatory (CAHA) in Spain. It uses a mosaic of four Hawaii-2RG
detectors and covers the spectral range from 0.8-2.5 micron(z to K-band). The
field-of-view is 30x30 arcmin. This instrument can be used at the 2.2m
telescope (0.45arcsec/pixel, 0.5x0.5 degree FOV) and at the 3.5m telescope
(0.23arcsec/pixel, 0.25x0.25 degree FOV). The operating temperature is about
77K, achieved by liquid Nitrogen cooling. The cryogenic optics has three flat
folding mirrors with diameters up to 282 mm and nine lenses with diameters
between 130 mm and 255 mm. A compact filter unit can carry up to 19 filters
distributed over four filter wheels. Narrow band (1%) filters can be used. The
instrument has a diameter of 1.1 m and it is about 1 m long. The weight limit
of 400 kg at the 2.2m telescope requires a light-weight cryostat design. The
aluminium vacuum vessel and radiation shield have wall thicknesses of only 6 mm
and 3 mm respectively.Comment: This paper has been presented in the SPIE of Astronomical Telescopes
and Instrumentation 2008 in Marseille (France
Liver-Targeting of Interferon-Alpha with Tissue-Specific Domain Antibodies
PMCID: PMC3581439This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
New Measurements of the Motion of the Zodiacal Dust
Using the Wisconsin H-Alpha Mapper (WHAM), we have measured at high spectral
resolution and high signal-to-noise the profile of the scattered solar Mg I
5184 absorption line in the zodiacal light. The observations were carried out
toward 49 directions that sampled the ecliptic equator from solar elongations
of 48\dg (evening sky) to 334\dg (morning sky) plus observations near +47\dg
and +90\dg ecliptic latitude. The spectra show a clear prograde kinematic
signature that is inconsistent with dust confined to the ecliptic plane and in
circular orbits influenced only by the sun's gravity. In particular, the
broadened widths of the profiles, together with large amplitude variations in
the centroid velocity with elongation angle, indicate that a significant
population of dust is on eccentric orbits. In addition, the wide, flat-bottomed
line profile toward the ecliptic pole indicates a broad distribution of orbital
inclinations extending up to about 30\dg - 40\dg with respect to the ecliptic
plane. The absence of pronounced asymmetries in the shape of the profiles
limits the retrograde population to less than 10% of the prograde population
and also places constraints on the scattering phase function of the particles.
These results do not show the radial outflow or evening--morning velocity
amplitude asymmetry reported in some earlier investigations. The reduction of
the spectra included the discovery and removal of extremely faint, unidentified
terrestrial emission lines that contaminate and distort the underlying Mg I
profile. This atmospheric emission is too weak to have been seen in earlier,
lower signal-to-noise observations, but it probably affected the line centroid
measurements of previous investigations.Comment: 24 pages, 8 figures, 1 table, to appear in ApJ v612; figures appear
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