65,733 research outputs found
A Third Planet Orbiting HIP 14810
We present new precision radial velocities and a three-planet Keplerian orbit
fit for the V = 8.5, G5 V star HIP 14810. We began observing this star at Keck
Observatory as part of the N2K Planet Search Project. Wright et al. (2007)
announced the inner two planets to this system, and subsequent observations
have revealed the outer planet planet and the proper orbital solution for the
middle planet. The planets have minimum masses of 3.9, 1.3, and 0.6 M_Jup and
orbital periods of 6.67, 147.7, and 952 d, respectively. We have numerically
integrated the family of orbital solutions consistent with the data and find
that they are stable for at least 10^6 yr. Our photometric search shows that
the inner planet does not transit.Comment: ApJL, accepte
People and guns involved in denied and completed handgun sales
Objective: Denial of handgun purchases by prohibited people and knowledge of the structure of gun commerce have helped to deter and prevent firearm violence. The authors hypothesize that handguns involved in a denied purchase would more closely resemble those used in crime compared with handguns sold. Design: Cross sectional. Setting: Denied and completed handgun sales in California, 1998 -- 2000. Main outcome measures: Handgun and purchaser characteristics of denied and completed sales were compared. In particular, handgun characteristics most closely associated with crime guns (type, caliber, barrel length, price) were examined. Results: Compared with handguns sold, handguns in denied sales were somewhat more likely to be semiautomatic pistols (74.6% v 69.4%), to have short barrels (25.9% v 22.2%), and be of medium caliber (48.9% v 37.3%). Ten percent of the handguns in denied sales and 3.4% of handguns sold were identified as inexpensive. Conclusions: The characteristics of denied handguns are similar to those seen among crime guns. Both groups of guns may reflect the desirability for criminal purposes of pistols, which have larger ammunition capacities than other handguns, and short barrels, which increase their ability to be concealed
Neural-Attention-Based Deep Learning Architectures for Modeling Traffic Dynamics on Lane Graphs
Deep neural networks can be powerful tools, but require careful
application-specific design to ensure that the most informative relationships
in the data are learnable. In this paper, we apply deep neural networks to the
nonlinear spatiotemporal physics problem of vehicle traffic dynamics. We
consider problems of estimating macroscopic quantities (e.g., the queue at an
intersection) at a lane level. First-principles modeling at the lane scale has
been a challenge due to complexities in modeling social behaviors like lane
changes, and those behaviors' resultant macro-scale effects. Following domain
knowledge that upstream/downstream lanes and neighboring lanes affect each
others' traffic flows in distinct ways, we apply a form of neural attention
that allows the neural network layers to aggregate information from different
lanes in different manners. Using a microscopic traffic simulator as a testbed,
we obtain results showing that an attentional neural network model can use
information from nearby lanes to improve predictions, and, that explicitly
encoding the lane-to-lane relationship types significantly improves
performance. We also demonstrate the transfer of our learned neural network to
a more complex road network, discuss how its performance degradation may be
attributable to new traffic behaviors induced by increased topological
complexity, and motivate learning dynamics models from many road network
topologies.Comment: To appear at 2019 IEEE Conference on Intelligent Transportation
System
The Burundi Heart Centre: From concept to design.
Burundi is one of the worlds poorest nations, which is also reflected in its relative lack of cardiac facilities, particularly those catering to young children and adults. The authors discuss current efforts to build The Burundi Heart Centre to help address this challenge. In particular, they highlight how the project can act as a case study for a sustainable architecture that involves local people and uses locally available materials in a contemporary and innovative way
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Toward a Formalism for Conservative Claims about the Dependability of Software-Based Systems
In recent work, we have argued for a formal treatment of confidence about the claims made in dependability cases for software-based systems. The key idea underlying this work is "the inevitability of uncertainty": It is rarely possible to assert that a claim about safety or reliability is true with certainty. Much of this uncertainty is epistemic in nature, so it seems inevitable that expert judgment will continue to play an important role in dependability cases. Here, we consider a simple case where an expert makes a claim about the probability of failure on demand (pfd) of a subsystem of a wider system and is able to express his confidence about that claim probabilistically. An important, but difficult, problem then is how such subsystem (claim, confidence) pairs can be propagated through a dependability case for a wider system, of which the subsystems are components. An informal way forward is to justify, at high confidence, a strong claim, and then, conservatively, only claim something much weaker: "I'm 99 percent confident that the pfd is less than 10-5, so it's reasonable to be 100 percent confident that it is less than 10-3." These conservative pfds of subsystems can then be propagated simply through the dependability case of the wider system. In this paper, we provide formal support for such reasoning
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Effective Temperature Of Uranus
NASA NGR 09-015-047, NGR 22-007-270, NGR 44-012-152Astronom
Environmental protection of titanium alloys at high temperatures
Various concepts were evaluated for protecting titanium alloys from oxygen contamination at 922 K (1200 F) and from hot-salt stress-corrosion at 755 K (900 F). It is indicated that oxygen-contamination resistance can be provided by a number of systems, but for hot-salt stress-corrosion resistance, factors such as coating integrity become very important. Titanium aluminides resist oxygen ingress at 922 K through the formation of alumina (on TiAl3) or modified TiO2 (on Ti3Al, TiAl) scales. TiAl has some resistance to attack by hot salt, but has limited ductility. Ductile Ti-Ni and Ti-Nb-Cr-Al alloys provide limited resistance to oxygen ingress, but are not greatly susceptible to hot-salt stress-corrosion cracking
Development of high-emittance scales on thoriated nickel-chromium-aluminum-base alloys
The surface regions of a DSNiCrAl alloy have been doped, by a pack diffusion process, with small amounts of Mn, Fe, or Co, and the effect of these dopants on the total normal emissivity of the scales produced by subsequent high temperature oxidation has been measured. While all three elements lead to a modest increase in emissivity, (up to 23% greater than the undoped alloy) only the change caused by manganese is thermally stable. However, this increased emissivity is within 85 percent of that of TDNiCr oxidized to form a chromia scale. The maganese-doped alloy is some 50 percent weaker than undoped DSNiCrAl after the doping treatment, and approximately 30 percent weaker after oxidation
Rocket ozone sounding network data
During the period December 1976 through February 1977, three regular monthly ozone profiles were measured at Wallops Flight Center, two special soundings were taken at Antigua, West Indies, and at the Churchill Research Range, monthly activities were initiated to establish stratospheric ozone climatology. This report presents the data results and flight profiles for the period covered
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