1,126 research outputs found
Searching for Earth-mass planets around Centauri: precise radial velocities from contaminated spectra
This work is part of an ongoing project which aims to detect terrestrial
planets in our neighbouring star system Centauri using the Doppler
method. Owing to the small angular separation between the two components of the
Cen AB binary system, the observations will to some extent be
contaminated with light coming from the other star. We are accurately
determining the amount of contamination for every observation by measuring the
relative strengths of the H- and NaD lines. Furthermore, we have
developed a modified version of a well established Doppler code that is
modelling the observations using two stellar templates simultaneously. With
this method we can significantly reduce the scatter of the radial velocity
measurements due to spectral cross-contamination and hence increase our chances
of detecting the tiny signature caused by potential Earth-mass planets. After
correcting for the contamination we achieve radial velocity precision of for a given night of observations. We have also
applied this new Doppler code to four southern double-lined spectroscopic
binary systems (HR159, HR913, HR7578, HD181958) and have successfully recovered
radial velocities for both components simultaneously.Comment: accepted for publication in the International Journal of Astrobiology
(published by Cambridge University Press); will appear in a revised form,
subsequent to editorial input by Cambridge University Pres
Short-Timescale monitoring of the X-ray, UV and broad double-peak emission line of the nucleus of NGC 1097
Recent studies have suggested that the short-timescale ( days)
variability of the broad (10,000 km s) double-peaked H
profile of the LINER nucleus of NGC1097 could be driven by a variable X-ray
emission from a central radiatively inefficient accretion flow (RIAF). To test
this scenario, we have monitored the NGC1097 nucleus in X-ray and UV continuum
with Swift and the H flux and profile in the optical spectrum using
SOAR and Gemini-South from 2012 August to 2013 February. During the monitoring
campaign, the H flux remained at a very low level --- 3 times lower
than the maximum flux observed in previous campaigns and showing only limited
() variability. The X-ray variations were small, only
throughout the campaign, while the UV did not show significant variations. We
concluded that the timescale of the H profile variation is close to the
sampling interval of the optical observations, which results in only marginal
correlation between the X-ray and H fluxes. We have caught the AGN in
NGC1097 in a very low activity state, in which the ionizing source was very
weak and capable of ionizing just the innermost part of the gas in the disk.
Nonetheless, the data presented here still support the picture in which the gas
that emits the broad double-peaked Balmer lines is illuminated/ionized by a
source of high-energy photons which is located interior to the inner radius of
the line-emitting part of the disk.Comment: The paper contains 14 pages, 7 figures and is accepted for
publication at the Astrophysical Journa
Enhanced protein immobilization on polymers - a plasma surface activation study
Over the last years, polymers have gained great attention as substrate material, because of the possibility to produce low-cost sensors in a high-throughput manner or for rapid prototyping and the wide variety of polymeric materials available with different features (like transparency, flexibility, stretchability, etc.). For almost all biosensing applications, the interaction between biomolecules (for example, antibodies, proteins or enzymes) and the employed substrate surface is highly important. In order to realize an effective biomolecule immobilization on polymers, different surface activation techniques, including chemical and physical methods, exist. Among them, plasma treatment offers an easy, fast and effective activation of the surfaces by micro/nanotexturing and generating functional groups (including carboxylic acids, amines, esters, aldehydes or hydroxyl groups). Hence, here we present a systematic and comprehensive plasma activation study of various polymeric surfaces by optimizing different parameters, including power, time, substrate temperature and gas composition. Thereby, the highest immobilization efficiency along with a homogenous biomolecule distribution is achieved with a 5-min plasma treatment under a gas composition of 50% oxygen and nitrogen, at a power of 1000 W and a substrate temperature of 80 C. These results are also confirmed by different surface characterization methods, including SEM, XPS and contact angle measurements
Two-photon linewidth of light "stopping" via electromagnetically induced transparency
We analyze the two-photon linewidth of the recently proposed adiabatic
transfer technique for ``stopping'' of light using electromagnetically induced
transparency (EIT). We shown that a successful and reliable transfer of
excitation from light to atoms and back can be achieved if the spectrum of the
input probe pulse lies within the initial transparency window of EIT, and if
the two-photon detuning is less than the collective coupling strength
(collective vacuum Rabi-frequency) divided by ,
with being the radiative decay rate, the effective number of atoms
in the sample, and the pulse duration. Hence in an optically thick medium
light ``storage'' and retrieval is possible with high fidelity even for systems
with rather large two-photon detuning or inhomogeneous broadening.Comment: 2 figure
Zooming into local active galactic nuclei: The power of combining SDSS-IV MaNGA with higher resolution integral field unit observations
Ionised gas outflows driven by active galactic nuclei (AGN) are ubiquitous in
high luminosity AGN with outflow speeds apparently correlated with the total
bolometric luminosity of the AGN. This empirical relation and theoretical work
suggest that in the range L_bol ~ 10^43-45 erg/s there must exist a threshold
luminosity above which the AGN becomes powerful enough to launch winds that
will be able to escape the galaxy potential. In this paper, we present pilot
observations of two AGN in this transitional range that were taken with the
Gemini North Multi-Object Spectrograph Integral Field Unit (IFU). Both sources
have also previously been observed within the Sloan Digital Sky Survey-IV
(SDSS) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey.
While the MaNGA IFU maps probe the gas fields on galaxy-wide scales and show
that some regions are dominated by AGN ionization, the new Gemini IFU data zoom
into the centre with four times better spatial resolution. In the object with
the lower L_bol we find evidence of a young or stalled biconical AGN-driven
outflow where none was obvious at the MaNGA resolution. In the object with the
higher L_bol we trace the large-scale biconical outflow into the nuclear region
and connect the outflow from small to large scales. These observations suggest
that AGN luminosity and galaxy potential are crucial in shaping wind launching
and propagation in low-luminosity AGN. The transition from small and young
outflows to galaxy-wide feedback can only be understood by combining
large-scale IFU data that trace the galaxy velocity field with higher
resolution, small scale IFU maps.Comment: 14 pages, accepted for publication in MNRA
Electrochemical etching of AlGaN for the realization of thin-film devices
Heterogeneously integrated AlGaN epitaxial layers will be essential for future optical and electrical devices like thin-film flip-chip ultraviolet (UV) light-emitting diodes, UV vertical-cavity surface-emitting lasers, and high-electron mobility transistors on efficient heat sinks. Such AlGaN-membranes will also enable flexible and micromechanical devices. However, to develop a method to separate the AlGaN-device membranes from the substrate has proven to be challenging, in particular, for high-quality device materials, which require the use of a lattice-matched AlGaN sacrificial layer. We demonstrate an electrochemical etching method by which it is possible to achieve complete lateral etching of an AlGaN sacrificial layer with up to 50% Al-content. The influence of etching voltage and the Al-content of the sacrificial layer on the etching process is investigated. The etched N-polar surface shows the same macroscopic topography as that of the as-grown epitaxial structure, and the root-mean square roughness is 3.5 nm for 1 \ub5m x 1 \ub5m scan areas. Separated device layers have a well-defined thickness and smooth etched surfaces. Transferred multi-quantum-well structures were fabricated and investigated by time-resolved photoluminescence measurements. The quantum wells showed no sign of degradation caused by the thin-film process
Physical Conditions in the Seyfert Galaxy NGC 2992
This paper presents long slit spectral maps of the bi-cone shaped extended
narrow line region (ENLR) in the Seyfert galaxy NGC 2992. We investigate the
physical properties of the ENLR via emission line diagnostics, and compare the
observations to shock and photoionization models for the excitation mechanism
of the gas. The line ratios vary as a function of position in the ENLR, and the
loci of the observed points on line ratio diagrams are shown to be most
consistent with shock+precursor model grids. We consider the energetics of a
nuclear ionizing source for the ENLR, and perform the q-test in which the rate
of ionizing photons from the nucleus is inferred from measurements of the
density and ionization parameter. The q-test is shown to be invalid in the case
of NGC 2992 because of the limitations of the [S II]6717/6731 density
diagnostic. The excitation of the gas is shown to be broadly consistent with
the kinematics, with higher [N II]6583/H-alpha present in the more dynamically
active region. We also show that the pressure associated with the X-ray
emitting plasma may provide a large fraction of the pressure required to power
the ENLR via shocks.Comment: 55 pages, 49 figures, ApJ accepted September 9, 1998. Figures 1a-f
are provided in jpeg forma
Extended half-life target module for sustainable UniCAR T-cell treatment of STn-expressing cancers
Background: Adapter chimeric antigen receptor (CAR) approaches have emerged has promising strategies to increase clinical safety of CAR T-cell therapy. In the UniCAR system, the safety switch is controlled via a target module (TM) which is characterized by a small-size and short half-life. The rapid clearance of these TMs from the blood allows a quick steering and self-limiting safety switch of UniCAR T-cells by TM dosing. This is mainly important during onset of therapy when tumor burden and the risk for severe side effects are high. For long-term UniCAR therapy, the continuous infusion of TMs may not be an optimal setting for the patients. Thus, in later stages of treatment, single infusions of TMs with an increased half-life might play an important role in long-term surveillance and eradication of residual tumor cells. Given this, we aimed to develop and characterize a novel TM with extended half-life targeting the tumor-associated carbohydrate sialyl-Tn (STn). Methods: The extended half-life TM is composed of the STn-specific single-chain variable fragment (scFv) and the UniCAR epitope, fused to the hinge region and Fc domain of a human immunoglobulin 4 (IgG4) antibody. Specific binding and functionality of the αSTn-IgG4 TM as well as pharmacokinetic features were assessed using in vitro and in vivo assays and compared to the already established small-sized αSTn TM. Results: The novel αSTn-IgG4 TM efficiently activates and redirects UniCAR T-cells to STn-expressing tumors in a target-specific and TM-dependent manner, thereby promoting the secretion of proinflammatory cytokines and tumor cell lysis in vitro and in experimental mice. Moreover, PET-imaging results demonstrate the specific enrichment of the αSTn-IgG4 TM at the tumor site, while presenting a prolonged serum half-life compared to the short-lived αSTn TM. Conclusion: In a clinical setting, the combination of TMs with different formats and pharmacokinetics may represent a promising strategy for retargeting of UniCAR T-cells in a flexible, individualized and safe manner at particular stages of therapy. Furthermore, as these molecules can be used for in vivo imaging, they pose as attractive candidates for theranostic approaches.publishersversionpublishe
New physics searches at near detectors of neutrino oscillation experiments
We systematically investigate the prospects of testing new physics with tau
sensitive near detectors at neutrino oscillation facilities. For neutrino beams
from pion decay, from the decay of radiative ions, as well as from the decays
of muons in a storage ring at a neutrino factory, we discuss which effective
operators can lead to new physics effects. Furthermore, we discuss the present
bounds on such operators set by other experimental data currently available.
For operators with two leptons and two quarks we present the first complete
analysis including all relevant operators simultaneously and performing a
Markov Chain Monte Carlo fit to the data. We find that these effects can induce
tau neutrino appearance probabilities as large as O(10^{-4}), which are within
reach of forthcoming experiments. We highlight to which kind of new physics a
tau sensitive near detector would be most sensitive.Comment: 20 pages, 2 figures, REVTeX
Entanglement generation by adiabatic navigation in the space of symmetric multi-particle states
We propose a technique for robust and efficient navigation in the Hilbert
space of entangled symmetric states of a multiparticle system with externally
controllable linear and nonlinear collective interactions. A linearly changing
external field applied along the quantization axis creates a network of well
separated level crossings in the energy diagram of the collective states. One
or more transverse pulsed fields applied at the times of specific level
crossings induce adiabatic passage between these states. By choosing the timing
of the pulsed field appropriately, one can transfer an initial product state of
all N spins into (i) any symmetric state with n spin excitations and (ii) the
N-particle analog of the Greenberger-Horne-Zeilinger state. This technique,
unlike techniques using pulses of specific area, does not require precise
knowledge of the number of particles and is robust against variations in the
interaction parameters. We discuss potential applications in two-component Bose
condensates and ion-trap systems.Comment: 7 pages, 6 figure
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