1,088 research outputs found
Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
Brown dwarfs of a variety of spectral types have been observed to be
photometrically variable. Previous studies have focused on objects at the L/T
transition, where the iron and silicate clouds in L dwarfs break up or
dissipate. However, objects outside of this transitional effective temperature
regime also exhibit variability. Here, we present models for mid-late T dwarfs
and Y dwarfs. We present models that include patchy salt and sulfide clouds as
well as water clouds for the Y dwarfs. We find that for objects over 375 K,
patchy cloud opacity would generate the largest amplitude variability within
near-infrared spectral windows. For objects under 375 K, water clouds also
become important and generate larger amplitude variability in the mid-infrared.
We also present models in which we perturb the temperature structure at
different pressure levels of the atmosphere to simulate hot spots. These models
show the most variability in the absorption features between spectral windows.
The variability is strongest at wavelengths that probe pressure levels at which
the heating is the strongest. The most illustrative types of observations for
understanding the physical processes underlying brown dwarf variability are
simultaneous, multi-wavelength observations that probe both inside and outside
of molecular absorption features.Comment: 6 pages, 5 figures, Accepted for publication in ApJ Letter
Self-managed cells and their federation
Future e-Health systems will consist of low-power, on-body wireless sensors attached to mobile users that interact with a ubiquitous computing environment. This kind of system needs to be able to configure itself with little or no user input; more importantly, it is required to adapt autonomously to changes such as user movement, device failure, the addition or loss of services, and proximity to other such systems. This extended abstract describes the basic architecture of a Self-Managed Cell (SMC) to address these requirements, and discusses various forms of federation between/among SMCs. This structure is motivated by a typical e-Health scenario
Using 3D shadows to detect object hiding attacks on autonomous vehicle perception
Autonomous Vehicles (AVs) are mostly reliant on LiDAR sensors which enable spatial perception of their surroundings and help make driving decisions. Recent works demonstrated attacks that aim to hide objects from AV perception, which can result in severe consequences. 3D shadows, are regions void of measurements in 3D point clouds which arise from occlusions of objects in a scene. 3D shadows were proposed as a physical invariant valuable for detecting spoofed or fake objects. In this work, we leverage 3D shadows to locate obstacles that are hidden from object detectors. We achieve this by searching for void regions and locating the obstacles that cause these shadows. Our proposed methodology can be used to detect an object that has been hidden by an adversary as these objects, while hidden from 3D object detectors, still induce shadow artifacts in 3D point clouds, which we use for obstacle detection. We show that using 3D shadows for obstacle detection can achieve high accuracy in matching shadows to their object and provide precise prediction of an obstacle’s distance from the ego-vehicle
Judicial Competence and Fundamental Rights
In the April 1979 issue of the Michigan Law Review, Professor Ira Lupu added his valuable contribution to the continuing debate on the problem of defining the nature of fundamental rights under the Constitution. In many respects his article is a wholly admirable piece of scholarship, both well-researched and carefully reasoned. However, on one issue - the question of judicial competence to identify the values he defines as fundamental - Professor Lupu\u27s discussion is seriously deficient. This letter will examine the problem of judicial competence and conclude that it is fatal to Professor Lupu\u27s conception of the appropriate role of the Court under the due process and equal protection clauses
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Expressive Policy Analysis with Enhanced System Dynamicity
Despite several research studies, the effective analysis of policy based systems remains a significant challenge. Policy analysis should at least (i) be expressive (ii) take account of obligations and authorizations, (iii) include a dynamic system model, and (iv) give useful diagnostic information. We present a logic-based policy analysis framework which satisfies these requirements, showing how many significant policy-related properties can be analysed, and we give details of a prototype implementation. Copyright 2009 ACM
Water Clouds in Y Dwarfs and Exoplanets
The formation of clouds affects brown dwarf and planetary atmospheres of
nearly all effective temperatures. Iron and silicate condense in L dwarf
atmospheres and dissipate at the L/T transition. Minor species such as sulfides
and salts condense in mid-late T dwarfs. For brown dwarfs below Teff=450 K,
water condenses in the upper atmosphere to form ice clouds. Currently over a
dozen objects in this temperature range have been discovered, and few previous
theoretical studies have addressed the effect of water clouds on brown dwarf or
exoplanetary spectra. Here we present a new grid of models that include the
effect of water cloud opacity. We find that they become optically thick in
objects below Teff=350-375 K. Unlike refractory cloud materials, water ice
particles are significantly non-gray absorbers; they predominantly scatter at
optical wavelengths through J band and absorb in the infrared with prominent
features, the strongest of which is at 2.8 microns. H2O, NH3, CH4, and H2 CIA
are dominant opacity sources; less abundant species such as may also be
detectable, including the alkalis, H2S, and PH3. PH3, which has been detected
in Jupiter, is expected to have a strong signature in the mid-infrared at 4.3
microns in Y dwarfs around Teff=450 K; if disequilibrium chemistry increases
the abundance of PH3, it may be detectable over a wider effective temperature
range than models predict. We show results incorporating disequilibrium
nitrogen and carbon chemistry and predict signatures of low gravity in
planetary- mass objects. Lastly, we make predictions for the observability of Y
dwarfs and planets with existing and future instruments including the James
Webb Space Telescope and Gemini Planet Imager.Comment: 23 pages, 20 figures, Revised for Ap
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