3,085 research outputs found
Robust Foregrounds Removal for 21-cm Experiments
Direct detection of the Epoch of Reionization via the redshifted 21-cm line
will have unprecedented implications on the study of structure formation in the
early Universe. To fulfill this promise current and future 21-cm experiments
will need to detect the weak 21-cm signal over foregrounds several order of
magnitude greater. This requires accurate modeling of the galactic and
extragalactic emission and of its contaminants due to instrument chromaticity,
ionosphere and imperfect calibration. To solve for this complex modeling, we
propose a new method based on Gaussian Process Regression (GPR) which is able
to cleanly separate the cosmological signal from most of the foregrounds
contaminants. We also propose a new imaging method based on a maximum
likelihood framework which solves for the interferometric equation directly on
the sphere. Using this method, chromatic effects causing the so-called "wedge"
are effectively eliminated (i.e. deconvolved) in the cylindrical () power spectrum.Comment: Subbmited to the Proceedings of the IAUS333, Peering Towards Cosmic
Dawn, 4 pages, 2 figure
Gravitational Lensing & Stellar Dynamics
Strong gravitational lensing and stellar dynamics provide two complementary
and orthogonal constraints on the density profiles of galaxies. Based on
spherically symmetric, scale-free, mass models, it is shown that the
combination of both techniques is powerful in breaking the mass-sheet and
mass-anisotropy degeneracies. Second, observational results are presented from
the Lenses Structure & Dynamics (LSD) Survey and the Sloan Lens ACS (SLACS)
Survey collaborations to illustrate this new methodology in constraining the
dark and stellar density profiles, and mass structure, of early-type galaxies
to redshifts of unity.Comment: 6 pages, 2 figures; Invited contribution in the Proceedings of XXIst
IAP Colloquium, "Mass Profiles & Shapes of Cosmological Structures" (Paris,
4-9 July 2005), eds G. A. Mamon, F. Combes, C. Deffayet, B. Fort (Paris: EDP
Sciences
Optimizing propagating spin wave spectroscopy
The frequency difference between two oppositely propagating spin waves can be
used to probe several interesting magnetic properties, such as the
Dzyaloshinkii-Moriya interaction (DMI). Propagating spin wave spectroscopy is a
technique that is very sensitive to this frequency difference. Here we show
several elements that are important to optimize devices for such a measurement.
We demonstrate that for wide magnetic strips there is a need for de-embedding.
Additionally, for these wide strips there is a large parasitic antenna-antenna
coupling that obfuscates any spin wave transmission signal, which is remedied
by moving to smaller strips. The conventional antenna design excites spin waves
with two different wave vectors. As the magnetic layers become thinner, the
resulting resonances move closer together and become very difficult to
disentangle. In the last part we therefore propose and verify a new antenna
design that excites spin waves with only one wave vector. We suggest to use
this antenna design to measure the DMI in thin magnetic layers.Comment: 12 pages, 4 figure
Metagenomic sequencing for surveillance of food- and waterborne viral diseases
A plethora of viruses can be transmitted by the food- and waterborne route. However, their recognition is challenging because of the variety of viruses, heterogeneity of symptoms, the lack of awareness of clinicians, and limited surveillance efforts. Classical food- and waterborne viral disease outbreaks are mainly caused by caliciviruses, but the source of the virus is often not known and the foodborne mode of transmission is difficult to discriminate from human-to-human transmission. Atypical food- and waterborne viral disease can be caused by viruses such as hepatitis A and hepatitis E. In addition, a source of novel emerging viruses with a potential to spread via the food- and waterborne route is the repeated interaction of humans with wildlife. Wildlife-to-human adaptation may give rise to self- limiting outbreaks in some cases, but when fully adjusted to the human host can be devastating. Metagenomic sequencing has been investigated as a promising solution for surveillance purposes as it detects all viruses in a single protocol, delivers additional genomic information for outbreak tracing, and detects novel unknown viruses. Nevertheless, several issues must be addressed to apply metagenomic sequencing in surveillance. First, sample preparation is difficult since the genomic material of viruses is genera
Correlation between magnetism and spin-dependent transport in CoFeB alloys
We report a correlation between the spin polarization of the tunneling
electrons (TSP) and the magnetic moment of amorphous CoFeB alloys. Such a
correlation is surprising since the TSP involves s-like electrons close to the
Fermi level (EF), while the magnetic moment mainly arises due to all
d-electrons below EF. We show that probing the s and d-bands individually
provides clear and crucial evidence for such a correlation to exist through s-d
hybridization, and demonstrate the tuneability of the electronic and magnetic
properties of CoFeB alloys.Comment: Accepted for publication in Physical Review Letters. Letter (4 pages)
and Supplementary material (4 pages
Spin motive forces due to magnetic vortices and domain walls
We study spin motive forces, i.e, spin-dependent forces, and voltages induced
by time-dependent magnetization textures, for moving magnetic vortices and
domain walls. First, we consider the voltage generated by a one-dimensional
field-driven domain wall. Next, we perform detailed calculations on
field-driven vortex domain walls. We find that the results for the voltage as a
function of magnetic field differ between the one-dimensional and vortex domain
wall. For the experimentally relevant case of a vortex domain wall, the
dependence of voltage on field around Walker breakdown depends qualitatively on
the ratio of the so-called -parameter to the Gilbert damping constant,
and thus provides a way to determine this ratio experimentally. We also
consider vortices on a magnetic disk in the presence of an AC magnetic field.
In this case, the phase difference between field and voltage on the edge is
determined by the parameter, providing another experimental method to
determine this quantity.Comment: 8 pages, 9 figures, submitted to PR
Precession-torque-driven domain-wall motion in out-of-plane materials
Domain-wall (DW) motion in magnetic nanostrips is intensively studied, in
particular because of the possible applications in data storage. In this work,
we will investigate a novel method of DW motion using magnetic field pulses,
with the precession torque as the driving mechanism. We use a one dimensional
(1D) model to show that it is possible to drive DWs in out-of-plane materials
using the precession torque, and we identify the key parameters that influence
this motion. Because the DW moves back to its initial position at the end of
the field pulse, thereby severely complicating direct detection of the DW
motion, depinning experiments are used to indirectly observe the effect of the
precession torque. The 1D model is extended to include an energy landscape in
order to predict the influence of the precession torque in the depinning
experiments. Although preliminary experiments did not yet show an effect of the
precession torque, our calculations indicate that depinning experiments can be
used to demonstrate this novel method of DW motion in out-of-plane materials,
which even allows for coherent motion of multiple domains when the
Dzyaloshinskii-Moriya interaction is taken into account
A new method for the estimate of H_0 from quadruply imaged gravitational lens systems
We present a new method to estimate the Hubble constant H_0 from the measured
time delays in quadruply imaged gravitational lens systems. We show how it is
possible to get an estimate of H_0 without the need to completely reconstruct
the lensing potential thus avoiding any a priori hypotheses on the expression
of the galaxy lens model. Our method only needs to assume that the lens
potential may be expressed as r^{\alpha} F(\theta), whatever the shape function
F(\theta) is, and it is thus able to fully explore the degeneracy in the mass
models taking also into account the presence of an external shear. We test the
method on simulated cases and show that it does work well in recovering the
correct value of the slope \alpha of the radial profile and of the Hubble
constant H_0. Then, we apply the same method to the real quadruple lenses
PG1115+080 and B1422+231 obtaining H_0 = 58_{-15}^{+17} km/s/Mpc (68% CL).Comment: 12 pages, 5 figures, accepted for publication on Astronomy &
Astrophysic
Statistical 21-cm signal separation via Gaussian Process Regression analysis
Detecting and characterizing the Epoch of Reionization (EoR) and Cosmic Dawn via the redshifted 21-cm hyperfine line of neutral hydrogen will revolutionize the study of the formation of the first stars, galaxies, black holes, and intergalactic gas in the infant Universe. The wealth of information encoded in this signal is, however, buried under foregrounds that are many orders of magnitude brighter. These must be removed accurately and precisely in order to reveal the feeble 21-cm signal. This requires not only the modelling of the Galactic and extragalactic emission, but also of the often stochastic residuals due to imperfect calibration of the data caused by ionospheric and instrumental distortions. To stochastically model these effects, we introduce a new method based on ` Gaussian Process Regression' (GPR) which is able to statistically separate the 21-cm signal from most of the foregrounds and other contaminants. Using simulated LOFAR-EoR data that include strong instrumental mode mixing, we show that this method is capable of recovering the 21-cm signal power spectrum across the entire range k = 0.07 - 0.3 h cMpc (1). The GPR method is most optimal, having minimal and controllable impact on the 21-cm signal, when the foregrounds are correlated on frequency scales greater than or similar to 3 MHz and the rms of the signal has sigma(21cm) greater than or similar to 0.1 sigma(noise). This signal separation improves the 21-cm power-spectrum sensitivity by a factor greater than or similar to 3 compared to foreground avoidance strategies and enables the sensitivity of current and future 21-cm instruments such as the Square Kilometre Array to be fully exploited
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