1,338 research outputs found
A 10-bit SAR ADC with an Ultra-Low Power Supply
This paper presents a successive approximation analog-to-digital converter (SAR ADC) design, which operates with a 0.2 V power supply. The design utilizes a dynamic bulk biasing scheme to dynamically adjust the relative NMOS and PMOS strengths, which are very sensitive to temperature, process, and mismatch variations at low supply voltages. The design achieves a very low power consumption due to the 0.2 V supply. Several circuits in the design are optimized for full functionality at 0.2 V. Extracted simulations show a total power consumption of 9 nW with a peak SNDR of 61.3 dB and a Walden Figure of Merit of 1.91 fJ/conversion-step
Ultra-Low Power ADCs for Space Sensors and Instruments
A 28nm 0.1V 10-bit 2kS/s Successive Approximation Register ADC design is proposed. This design opens the doors to both low supply and low power space sensors and instruments. Due to the stringent voltage supply unique challenges arise that are met with innovation in the sample switch and comparator design. These components of the ADC architecture are optimized to perform successfully at a 0.1V supply with a sample rate suitable for most sensor applications
The effect of scattering on the structure and SED of protoplanetary disks
In this paper we investigate how the inclusion of scattering of the stellar
radiation into a passive flaring disk model affects its structure and spectral
energy distribution, and whether neglecting it could significantly decrease the
model reliability. In order to address these questions we construct a detailed
1+1D vertical structure model in which the scattering properties of the dust
can be varied. Models are presented with and without dust scattering, and for
different albedos and phase functions. It is found that scattering has the
effect of reducing the disk temperature at all heights, so that the disk
"shrinks", i.e., the the density at all intermediate heights decreases.
However, this effect in most cases is more than compensated by the increase of
the total extinction (absorption + scattering) cross section, so that the
surface scale height increases, and images in scattered light will see a
slightly thicker disk. The integrated infrared emission decreases as the albedo
increases, because an increasing part of the flux captured by the disk is
reflected away instead of absorbed and reprocessed. The reduction of the
infrared thermal emission of the disk is stronger at short wavelengths (near
infrared) and practically negligible at millimeter wavelengths. For relatively
low albedo (alb <~ 0.5), or for strongly forward-peaked scattering (g roughly
>0.8), the infrared flux reduction is relatively small.Comment: Accepted for publication in Astronomy & Astrophysic
The Solar--Stellar Connection
Stars have proven to be surprisingly prolific radio sources and the added
sensitivity of the Square Kilometer Array will lead to advances in many
directions. This chapter discusses prospects for studying the physics of
stellar atmospheres and stellar winds across the HR diagram.Comment: to appear in "Science with the Square Kilometer Array," eds. C.
Carilli and S. Rawlings, New Astronomy Reviews (Elsevier: Amsterdam
Evolution of Young Brown Dwarf Disks in the Mid-Infrared
We have imaged two bona-fide brown dwarfs with TReCS/GEMINI-S and find
mid-infrared excess emission that can be explained by optically thick dust disk
models. In the case of the young (2Myr) Cha H1 we measure
fluxes at 10.4m and 12.3m that are fully consistent with a standard
flared disk model and prominent silicate emission. For the 10Myr old
brown dwarf 2MASS1207-3932 located in the TW Hydrae association we find excess
emission at 8.7m and 10.4m with respect to its photosphere, and
confirm disk accretion as likely cause of its strong activity. Disks around
brown dwarfs likely last at least as long as their low-mass stellar
counterparts in the T-Tauri phase. Grain growth, dust settling, and evolution
of the geometry of brown dwarfs disks may appear on a timescale of 10Myr and
can be witnessed by observations in the mid-infrared.Comment: 6 pages, 4 figure
Vertical structure of debris discs
The vertical thickness of debris discs is often used as a measure of these
systems' dynamical excitation and as clues to the presence of hidden massive
perturbers such as planetary embryos. However, this argument could be flawed
because the observed dust should be naturally placed on inclined orbits by the
combined effect of radiation pressure and mutual collisions. We critically
reinvestigate this issue and numerically estimate what the "natural" vertical
thickness of a collisionally evolving disc is, in the absence of any additional
perturbing body. We use a deterministic collisional code, following the
dynamical evolution of a population of indestructible test grains suffering
mutual inelastic impacts. Grain differential sizes as well as the effect of
radiation pressure are taken into account. We find that, under the coupled
effect of radiation pressure and collisions, grains naturally acquire
inclinations of a few degrees. The disc is stratified with respect to grain
sizes, with the smallest grains having the largest vertical dispersion and the
bigger ones clustered closer to the midplane. Debris discs should have a
minimum "natural" observed aspect ratio at visible to
mid-IR wavelengths where the flux is dominated by the smallest bound grains.
These values are comparable to the estimated thicknesses of many vertically
resolved debris discs, as is illustrated with the specific example of AU Mic.
For all systems with , the presence (or absence) of embedded
perturbing bodies cannot be inferred from the vertical dispersion of the discComment: accepted for publication in Astronomy and Astrophysics (full abstract
in the pdf file
A layered edge-on circumstellar disk around HK Tau B
We present the first high angular resolution 1.4mm and 2.7mm continuum maps
of the T Tauri binary system HK Tau obtained with the Plateau de Bure
Interferometer. The contributions of both components are well disentangled at
1.4mm and the star previously known to host an edge-on circumstellar disk, HK
Tau B, is elongated along the disk's major axis. The optically bright primary
dominates the thermal emission from the system at both wavelengths, confirming
that it also has its own circumstellar disk. Its non-detection in scattered
light images indicates that the two disks in this binary system are not
parallel. Our data further indicate that the circumprimary disk is probably
significantly smaller than the circumsecondary disk.
We model the millimeter thermal emission from the circumstellar disk
surrounding HK Tau B. We show that the disk mass derived from scattered light
images cannot reproduce the 1.4mm emission using opacities of the same
population of submicron dust grains. However, grain growth alone cannot match
all the observed properties of this disk. We propose that this disk contains
three separate layers: two thin outer surfaces which contain dust grains that
are very similar to those of the ISM, and a disk interior which is relatively
massive and/or has experienced limited grain growth with the largest grains
significantly smaller than 1mm. Such a structure could naturally result from
dust settling in a protoplanetary disk.Comment: Accepted fopr publication in A&A, 8 pages, 1 embedded figur
HOIL1 regulates group 2 innate lymphoid cell numbers and type 2 inflammation in the small intestine
Patients with mutations in HOIL1 experience a complex immune disorder including intestinal inflammation. To investigate the role of HOIL1 in regulating intestinal inflammation, we employed a mouse model of partial HOIL1 deficiency. The ileum of HOIL1-deficient mice displayed features of type 2 inflammation including tuft cell and goblet cell hyperplasia, and elevated expression of Il13, Il5 and Il25 mRNA. Inflammation persisted in the absence of T and B cells, and bone marrow chimeric mice revealed a requirement for HOIL1 expression in radiation-resistant cells to regulate inflammation. Although disruption of IL-4 receptor alpha (IL4Rα) signaling on intestinal epithelial cells ameliorated tuft and goblet cell hyperplasia, expression of Il5 and Il13 mRNA remained elevated. KLRG
The circumstellar disk of HH 30. Searching for signs of disk evolution with multi-wavelength modeling
Circumstellar disks are characteristic for star formation and vanish during
the first few Myr of stellar evolution. During this time planets are believed
to form in the dense midplane by growth, sedimentation and aggregation of dust.
Indicators of disk evolution, such as holes and gaps, can be traced in the
spectral energy distribution (SED) and spatially resolved images.
We aim to construct a self-consistent model of HH 30 by fitting all available
continuum observations simultaneously. New data sets not available in previous
studies, such as high-resolution interferometric imaging with the Plateau de
Bure Interferometer (PdBI) at lambda = 1.3 mm and SED measured with IRS on the
Spitzer Space Telescope in the mid-infrared, put strong constraints on
predictions and are likely to provide new insights into the evolutionary state
of this object.
A parameter study based on simulated annealing was performed to find unbiased
best-fit models for independent observations made in the wavelength domain
lambda ~ 1 micron ... 4 mm. The method essentially creates a Markov chain
through parameter space by comparing predictions generated by our
self-consistent continuum radiation transfer code MC3D with observations.
We present models of the edge-on circumstellar disk of HH 30 based on
observations from the near-infrared to mm-wavelengths that suggest the presence
of an inner depletion zone with about 45 AU radius and a steep decline of mm
opacity beyond 140 AU. Our modeling indicates that several modes of dust
evolution such as growth, settling, and radial migration are taking place in
this object.
High-resolution observations of HH 30 at different wavelengths with
next-generation observatories such as ALMA and JWST will enable the modeling of
inhomogeneous dust properties and significantly expand our understanding of
circumstellar disk evolution.Comment: Accepted for publication in Astronomy and Astrophysic
The 2D Continuum Radiative Transfer Problem: Benchmark Results for Disk Configurations
We present benchmark problems and solutions for the continuum radiative
transfer (RT) in a 2D disk configuration. The reliability of three Monte-Carlo
and two grid-based codes is tested by comparing their results for a set of
well-defined cases which differ for optical depth and viewing angle. For all
the configurations, the overall shape of the resulting temperature and spectral
energy distribution is well reproduced. The solutions we provide can be used
for the verification of other RT codes.We also point out the advantages and
disadvantages of the various numerical techniques applied to solve the RT
problem.Comment: 13 pages, 10 figures, To appear in Astronomy and Astrophysic
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