1,244 research outputs found
Securing a Healthy Future: The Commonwealth Fund State Scorecard on Child Health System Performance, 2011
Ranks states on twenty indicators of healthcare access, affordability, prevention and treatment, potential for healthy lives, and health system equity for children. Examines the need for targeted initiatives and policy implications for better performance
S-matrix approach to quantum gases in the unitary limit II: the three-dimensional case
A new analytic treatment of three-dimensional homogeneous Bose and Fermi
gases in the unitary limit of negative infinite scattering length is presented,
based on the S-matrix approach to statistical mechanics we recently developed.
The unitary limit occurs at a fixed point of the renormalization group with
dynamical exponent z=2 where the S-matrix equals -1. For fermions we find T_c
/T_F is approximately 0.1. For bosons we present evidence that the gas does not
collapse, but rather has a critical point that is a strongly interacting form
of Bose-Einstein condensation. This bosonic critical point occurs at n lambda^3
approximately 1.3 where n is the density and lambda the thermal wavelength,
which is lower than the ideal gas value of 2.61.Comment: 26 pages, 16 figure
Wide-Area Geolocalization with a Limited Field of View Camera in Challenging Urban Environments
Cross-view geolocalization, a supplement or replacement for GPS, localizes an
agent within a search area by matching ground-view images to overhead images.
Significant progress has been made assuming a panoramic ground camera.
Panoramic cameras' high complexity and cost make non-panoramic cameras more
widely applicable, but also more challenging since they yield less scene
overlap between ground and overhead images. This paper presents Restricted FOV
Wide-Area Geolocalization (ReWAG), a cross-view geolocalization approach that
combines a neural network and particle filter to globally localize a mobile
agent with only odometry and a non-panoramic camera. ReWAG creates pose-aware
embeddings and provides a strategy to incorporate particle pose into the
Siamese network, improving localization accuracy by a factor of 100 compared to
a vision transformer baseline. This extended work also presents ReWAG*, which
improves upon ReWAG's generalization ability in previously unseen environments.
ReWAG* repeatedly converges accurately on a dataset of images we have collected
in Boston with a 72 degree field of view (FOV) camera, a location and FOV that
ReWAG* was not trained on.Comment: 10 pages, 16 figures. Extension of ICRA 2023 paper arXiv:2209.1185
Virial expansion coefficients in the harmonic approximation
The virial expansion method is applied within a harmonic approximation to an
interacting N-body system of identical fermions. We compute the canonical
partition functions for two and three particles to get the two lowest orders in
the expansion. The energy spectrum is carefully interpolated to reproduce
ground state properties at low temperature and the non-interacting large
temperature limit of constant virial coefficients. This resembles the smearing
of shell effects in finite systems with increasing temperature. Numerical
results are discussed for the second and third virial coefficients as function
of dimension, temperature, interaction, and the transition temperature between
low and high energy limits.Comment: 11 pages, 7 figures, published versio
MAR-CPS: Measurable Augmented Reality for Prototyping Cyber-Physical Systems
Cyber-Physical Systems (CPSs) refer to engineering platforms that rely on the inte- gration of physical systems with control, computation, and communication technologies. Autonomous vehicles are instances of CPSs that are rapidly growing with applications in many domains. Due to the integration of physical systems with computational sens- ing, planning, and learning in CPSs, hardware-in-the-loop experiments are an essential step for transitioning from simulations to real-world experiments. This paper proposes an architecture for rapid prototyping of CPSs that has been developed in the Aerospace Controls Laboratory at the Massachusetts Institute of Technology. This system, referred to as MAR-CPS (Measurable Augmented Reality for Prototyping Cyber-Physical Systems), includes physical vehicles and sensors, a motion capture technology, a projection system, and a communication network. The role of the projection system is to augment a physical laboratory space with 1) autonomous vehicles' beliefs and 2) a simulated mission environ- ment, which in turn will be measured by physical sensors on the vehicles. The main focus of this method is on rapid design of planning, perception, and learning algorithms for au- tonomous single-agent or multi-agent systems. Moreover, the proposed architecture allows researchers to project a simulated counterpart of outdoor environments in a controlled, indoor space, which can be crucial when testing in outdoor environments is disfavored due to safety, regulatory, or monetary concerns. We discuss the issues related to the design and implementation of MAR-CPS and demonstrate its real-time behavior in a variety of problems in autonomy, such as motion planning, multi-robot coordination, and learning spatio-temporal fields.Boeing Compan
Organic chloramines in drinking water: An assessment of formation, stability, reactivity and risk
© 2016 Elsevier Ltd. Although organic chloramines are known to form during the disinfection of drinking water with chlorine, little information is currently available on their occurrence or toxicity. In a recent in vitro study, some organic chloramines (e.g. N-chloroglycine) were found to be cytotoxic and genotoxic even at micromolar concentrations. In this paper, the formation and stability of 21 different organic chloramines, from chlorination of simple amines and amino acids, were studied, and the competition between 20 amino acids during chlorination was also investigated. For comparison, chlorination of two amides was also conducted. The formation and degradation of selected organic chloramines were measured using either direct UV spectroscopic or colorimetric detection. Although cysteine, methionine and tryptophan were the most reactive amino acids towards chlorination, they did not form organic chloramines at the chlorine to precursor molar ratios that were tested. Only 6 out of the 21 organic chloramines formed had a half-life of more than 3 h, although this group included all organic chloramines formed from amines. A health risk assessment relating stability and reactivity data from this study to toxicity and precursor abundance data from the literature indicated that only N-chloroglycine is likely to be of concern due to its stability, toxicity and abundance in water. However, given the stability of organic chloramines formed from amines, more information about the toxicity and precursor abundance for these chloramines is desirable
A Detailed Study of Spitzer-IRAC Emission in Herbig-Haro Objects (I): Morphology and Flux Ratios of Shocked Emission
We present a detailed analysis of Spitzer-IRAC images obtained toward six
Herbig-Haro objects (HH 54/211/212, L 1157/1448, BHR 71). Our analysis
includes: (1) comparisons in morphology between the four IRAC bands (3.6, 4.5,
5.8 and 8.0 um), and H2 1-0 S(1) at 2.12 um for three out of six objects; (2)
measurements of spectral energy distributions (SEDs) at selected positions; and
(3) comparisons of these results with calculations of thermal H2 emission at
LTE (207 lines in four bands) and non-LTE (32-45 lines, depending on particle
for collisions). We show that the morphologies observed at 3.6 and 4.5 um are
similar to each other, and to H2 1-0 S(1). This is well explained by thermal H2
emission at non-LTE if the dissociation rate is significantly larger than
0.002-0.02, allowing thermal collisions to be dominated by atomic hydrogen. In
contrast, the 5.8 and 8.0 um emission shows different morphologies from the
others in some regions. This emission appears to be more enhanced at the wakes
in bow shocks, or less enhanced in patchy structures in the jet. These
tendencies are explained by the fact that thermal H2 emission in the 5.8 and
8.0 um band is enhanced in regions at lower densities and temperatures.
Throughout, the observed similarities and differences in morphology between
four bands and 1-0 S(1) are well explained by thermal H2 emission. The observed
SEDs are categorized into:- (A) those in which the flux monotonically increases
with wavelength; and (B) those with excess emission at 4.5-um. The type-A SEDs
are explained by thermal H2 emission, in particular with simple shock models
with a power-law cooling function. Our calculations suggest that the type-B
SEDs require extra contaminating emission in the 4.5-um band. The CO
vibrational emission is the most promising candidate, and the other
contaminants discussed to date are not likely to explain the observed SEDs.Comment: 35 pages, 21 figures, 6 tables, accepted by Astrophysical Journa
A Forward Reachability Perspective on Robust Control Invariance and Discount Factors in Reachability Analysis
Control invariant sets are crucial for various methods that aim to design
safe control policies for systems whose state constraints must be satisfied
over an indefinite time horizon. In this article, we explore the connections
among reachability, control invariance, and Control Barrier Functions (CBFs) by
examining the forward reachability problem associated with control invariant
sets. We present the notion of an "inevitable Forward Reachable Tube" (FRT) as
a tool for analyzing control invariant sets. Our findings show that the
inevitable FRT of a robust control invariant set with a differentiable boundary
is the set itself. We highlight the role of the differentiability of the
boundary in shaping the FRTs of the sets through numerical examples. We also
formulate a zero-sum differential game between the control and disturbance,
where the inevitable FRT is characterized by the zero-superlevel set of the
value function. By incorporating a discount factor in the cost function of the
game, the barrier constraint of the CBF naturally arises as the constraint that
is imposed on the optimal control policy. As a result, the value function of
our FRT formulation serves as a CBF-like function, which has not been
previously realized in reachability studies. Conversely, any valid CBF is also
a forward reachability value function inside the control invariant set, thereby
revealing the inverse optimality of the CBF. As such, our work establishes a
strong link between reachability, control invariance, and CBFs, filling a gap
that prior formulations based on backward reachability were unable to bridge.Comment: The first two authors contributed equally to this wor
- …