206 research outputs found
Estimating Spectroscopic Redshifts by Using k Nearest Neighbors Regression I. Description of Method and Analysis
Context: In astronomy, new approaches to process and analyze the
exponentially increasing amount of data are inevitable. While classical
approaches (e.g. template fitting) are fine for objects of well-known classes,
alternative techniques have to be developed to determine those that do not fit.
Therefore a classification scheme should be based on individual properties
instead of fitting to a global model and therefore loose valuable information.
An important issue when dealing with large data sets is the outlier detection
which at the moment is often treated problem-orientated. Aims: In this paper we
present a method to statistically estimate the redshift z based on a similarity
approach. This allows us to determine redshifts in spectra in emission as well
as in absorption without using any predefined model. Additionally we show how
an estimate of the redshift based on single features is possible. As a
consequence we are e.g. able to filter objects which show multiple redshift
components. We propose to apply this general method to all similar problems in
order to identify objects where traditional approaches fail. Methods: The
redshift estimation is performed by comparing predefined regions in the spectra
and applying a k nearest neighbor regression model for every predefined
emission and absorption region, individually. Results: We estimated a redshift
for more than 50% of the analyzed 16,000 spectra of our reference and test
sample. The redshift estimate yields a precision for every individually tested
feature that is comparable with the overall precision of the redshifts of SDSS.
In 14 spectra we find a significant shift between emission and absorption or
emission and emission lines. The results show already the immense power of this
simple machine learning approach for investigating huge databases such as the
SDSS.Comment: accepted for publication in A&
Properties of optically selected BL Lac candidates from the SDSS
\textbf{Context.} Deep optical surveys open the avenue for find large numbers
of BL Lac objects that are hard to identify because they lack the unique
properties classifying them as such. While radio or X-ray surveys typically
reveal dozens of sources, recent compilations based on optical criteria alone
have increased the number of BL Lac candidates considerably. However, these
compilations are subject to biases and may contain a substantial number of
contaminating sources. \textbf{Aims.} In this paper we extend our analysis of
182 optically selected BL Lac object candidates from the SDSS with respect to
an earlier study. The main goal is to determine the number of bona fide BL Lac
objects in this sample. \textbf{Methods.} We examine their variability
characteristics, determine their broad-band radio-UV SEDs, and search for the
presence of a host galaxy. In addition we present new optical spectra for 27
targets with improved S/N with respect to the SDSS spectra. \textbf{Results.}
At least 59% of our targets have shown variability between SDSS DR2 and our
observations by more than 0.1-0.27 mag de- pending on the telescope used. A
host galaxy was detected in 36% of our targets. The host galaxy type and
luminosities are consistent with earlier studies of BL Lac host galaxies.
Simple fits to broad-band SEDS for 104 targets of our sample derived
synchrotron peak frequencies between with a peak at
. Our new optical spectra do not reveal any new
redshift for any of our objects. Thus the sample contains a large number of
bona fide BL Lac objects and seems to contain a substantial fraction of
intermediate-frequency peaked BL Lacs.Comment: Accepted for publication in A\&
Bose-Einstein condensation in a circular waveguide
We have produced Bose-Einstein condensates in a ring-shaped magnetic
waveguide. The few-millimeter diameter non-zero bias ring is formed from a
time-averaged quadrupole ring. Condensates which propagate around the ring make
several revolutions within the time it takes for them to expand to fill the
ring. The ring shape is ideally suited for studies of vorticity in a
multiply-connected geometry and is promising as a rotation sensor.Comment: 4 pages, 4 figure
Bound States and Threshold Resonances in Quantum Wires with Circular Bends
We study the solutions to the wave equation in a two-dimensional tube of unit
width comprised of two straight regions connected by a region of constant
curvature. We introduce a numerical method which permits high accuracy at high
curvature. We determine the bound state energies as well as the transmission
and reflection matrices, and and focus on the nature of
the resonances which occur in the vicinity of channel thresholds. We explore
the dependence of these solutions on the curvature of the tube and angle of the
bend and discuss several limiting cases where our numerical results confirm
analytic predictions.Comment: 24 pages, revtex file, one style file and 17 PostScript figures
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Correction to: Ret is essential to mediate GDNF’s neuroprotective and neuroregenerative effect in a Parkinson disease mouse model
Correction to: Cell Death Dis. (2016) 7, e2359; https://doi.org/10.1038/cddis.2016.263; published online 08 September 2016</jats:p
Stabilization and humanization of a single-chain Fv antibody fragment specific for human lymphocyte antigen CD19 by designed point mutations and CDR-grafting onto a human framework
A single-chain Fv (scFv) fragment derived from the murine antibody 4G7, specific for human lymphocyte CD19, was engineered for stability and expression in Escherichia coli in view of future use as a therapeutic protein. We compared two orthogonal knowledge-based procedures. In one approach, we designed a mutant with 14 single amino-acid substitutions predicted to correct destabilizing residues in the 4G7-wt sequence to create 4G7-mut. In the second variant, the murine CDRs were grafted to the human acceptor framework huVκ3-huVH3, with 11 additional point mutations introduced to obtain a better match between CDR graft and acceptor framework, to arrive at 4G7-graft. Compared to 4G7-wt, 4G7-mut showed greater thermodynamic stability in guanidinium chloride-induced equilibrium denaturation experiments and somewhat greater stability in human serum. The loop graft maintained the comparatively high stability of the murine loop donor, but did not improve it further. Our analysis indicates that this is due to subtle strain introduced between CDRs and framework, mitigating the otherwise highly favorable properties of the human acceptor framework. This slight strain in the loop graft is also reflected in the binding affinities for CD19 on leukemic cells of 8.4 nM for 4G7-wt, 16.4 nM for 4G7-mut and 30.0 nM for 4G7-graft. This comparison of knowledge-based mutation and loop-grafting-based approaches will be important, when moving molecules forward to therapeutic application
AAV-Tau Mediates Pyramidal Neurodegeneration by Cell-Cycle Re-Entry without Neurofibrillary Tangle Formation in Wild-Type Mice
In Alzheimer's disease tauopathy is considered secondary to amyloid, and the duality obscures their relation and the definition of their respective contributions
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