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The Parenthood “Happiness Penalty”: The Effects of Social Policies in 22 Countries
A large body of research has established that parents are less happy than nonparents. But is it always true that parents are less happy than nonparents? This research brief, by PRC faculty research associate Jennifer Glass and colleagues, shows that the “happiness penalty” is entirely explained by the presence or absence of social policies that allow parents to better combine paid work with family obligations.Population Research Cente
Lifting a Weak Poisson Bracket to the Algebra of Forms
We detail the construction of a weak Poisson bracket over a submanifold of a
smooth manifold M with respect to a local foliation of this submanifold. Such a
bracket satisfies a weak type Jacobi identity but may be viewed as a usual
Poisson bracket on the space of leaves of the foliation. We then lift this weak
Poisson bracket to a weak odd Poisson bracket on the odd tangent bundle,
interpreted as a weak Koszul bracket on differential forms on M. This lift is
achieved by encoding the weak Poisson structure into a homotopy Poisson
structure on an extended manifold, and lifting the Hamiltonian function that
generates this structure. Such a construction has direct physical
interpretation. For a generic gauge system, the submanifold may be viewed as a
stationary surface or a constraint surface, with the foliation given by the
foliation of the gauge orbits. Through this interpretation, the lift of the
weak Poisson structure is simply a lift of the action generating the
corresponding BRST operator of the system
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
Trees of Unusual Size: Biased Inference of Early Bursts from Large Molecular Phylogenies
An early burst of speciation followed by a subsequent slowdown in the rate of
diversification is commonly inferred from molecular phylogenies. This pattern
is consistent with some verbal theory of ecological opportunity and adaptive
radiations. One often-overlooked source of bias in these studies is that of
sampling at the level of whole clades, as researchers tend to choose large,
speciose clades to study. In this paper, we investigate the performance of
common methods across the distribution of clade sizes that can be generated by
a constant-rate birth-death process. Clades which are larger than expected for
a given constant-rate branching process tend to show a pattern of an early
burst even when both speciation and extinction rates are constant through time.
All methods evaluated were susceptible to detecting this false signature when
extinction was low. Under moderate extinction, both the gamma-statistic and
diversity-dependent models did not detect such a slowdown but only because the
signature of a slowdown was masked by subsequent extinction. Some models which
estimate time-varying speciation rates are able to detect early bursts under
higher extinction rates, but are extremely prone to sampling bias. We suggest
that examining clades in isolation may result in spurious inferences that rates
of diversification have changed through time.Comment: 17 pages, 5 figure
BamView: visualizing and interpretation of next-generation sequencing read alignments.
So-called next-generation sequencing (NGS) has provided the ability to sequence on a massive scale at low cost, enabling biologists to perform powerful experiments and gain insight into biological processes. BamView has been developed to visualize and analyse sequence reads from NGS platforms, which have been aligned to a reference sequence. It is a desktop application for browsing the aligned or mapped reads [Ruffalo, M, LaFramboise, T, Koyutürk, M. Comparative analysis of algorithms for next-generation sequencing read alignment. Bioinformatics 2011;27:2790-6] at different levels of magnification, from nucleotide level, where the base qualities can be seen, to genome or chromosome level where overall coverage is shown. To enable in-depth investigation of NGS data, various views are provided that can be configured to highlight interesting aspects of the data. Multiple read alignment files can be overlaid to compare results from different experiments, and filters can be applied to facilitate the interpretation of the aligned reads. As well as being a standalone application it can be used as an integrated part of the Artemis genome browser, BamView allows the user to study NGS data in the context of the sequence and annotation of the reference genome. Single nucleotide polymorphism (SNP) density and candidate SNP sites can be highlighted and investigated, and read-pair information can be used to discover large structural insertions and deletions. The application will also calculate simple analyses of the read mapping, including reporting the read counts and reads per kilobase per million mapped reads (RPKM) for genes selected by the user
Potential Applications of Modularity to Enable a Deep Space Habitation Capability for Future Human Exploration Beyond Low-Earth Orbit
Evaluating preliminary concepts of a Deep Space Habitat (DSH) enabling long duration crewed exploration of asteroids, the Moon, and Mars is a technically challenging problem. Sufficient habitat volumes and equipment, necessary to ensure crew health and functionality, increase propellant requirements and decrease launch flexibility to deliver multiple elements on a single launch vehicle; both of which increase overall mission cost. Applying modularity in the design of the habitat structures and subsystems can alleviate these difficulties by spreading the build-up of the overall habitation capability across several smaller parts. This allows for a more flexible habitation approach that accommodates various crew mission durations and levels of functionality. This paper provides a technical analysis of how various modular habitation approaches can impact the parametric design of a DSH with potential benefits in mass, packaging volume, and architectural flexibility. This includes a description of the desired long duration habitation capability, the definition of a baseline model for comparison, a small trade study to investigate alternatives, and commentary on potentially advantageous configurations to enable different levels of habitability. The approaches investigated include modular pressure vessel strategies, modular subsystems, and modular manufacturing approaches to habitat structure. The paper also comments upon the possibility of an integrated habitation strategy using modular components to create all short and long duration habitation elements required in the current exploration architectures
A Tool for the Automated Design and Evaluation of Habitat Interior Layouts
The objective of space habitat design is to minimize mass and system size while providing adequate space for all necessary equipment and a functional layout that supports crew health and productivity. Unfortunately, development and evaluation of interior layouts is often ignored during conceptual design because of the subjectivity and long times required using current evaluation methods (e.g., human-in-the-loop mockup tests and in-depth CAD evaluations). Early, more objective assessment could prevent expensive design changes that may increase vehicle mass and compromise functionality. This paper describes a new interior design evaluation method to enable early, structured consideration of habitat interior layouts. This interior layout evaluation method features a comprehensive list of quantifiable habitat layout evaluation criteria, automatic methods to measure these criteria from a geometry model, and application of systems engineering tools and numerical methods to construct a multi-objective value function measuring the overall habitat layout performance. In addition to a detailed description of this method, a C++/OpenGL software tool which has been developed to implement this method is also discussed. This tool leverages geometry modeling coupled with collision detection techniques to identify favorable layouts subject to multiple constraints and objectives (e.g., minimize mass, maximize contiguous habitable volume, maximize task performance, and minimize crew safety risks). Finally, a few habitat layout evaluation examples are described to demonstrate the effectiveness of this method and tool to influence habitat design
Semiclassical limits to the linewidth of an atom laser
We investigate the linewidth of a quasi-continuous atom laser within a
semiclassical framework. In the high flux regime, the lasing mode can exhibit a
number of undesirable features such as density fluctuations. We show that the
output therefore has a complicated structure that can be somewhat simplified
using Raman outcoupling methods and energy-momentum selection rules. In the
weak outcoupling limit, we find that the linewidth of an atom laser is
instantaneously Fourier limited, but, due to the energy `chirp' associated with
the draining of a condensate, the long-term linewidth of an atom laser is
equivalent to the chemical potential of the condensate source. We show that
correctly sweeping the outcoupling frequency can recover the Fourier-limited
linewidth.Comment: 9 Figure
High time-resolution observations of the Vela pulsar
We present high time resolution observations of single pulses from the Vela
pulsar (PSR B0833-45) made with a baseband recording system at observing
frequencies of 660 and 1413 MHz. We have discovered two startling features in
the 1413 MHz single pulse data. The first is the presence of giant micro-pulses
which are confined to the leading edge of the pulse profile. One of these
pulses has a peak flux density in excess of 2500 Jy, more than 40 times the
integrated pulse peak. The second new result is the presence of a large
amplitude gaussian component on the trailing edge of the pulse profile. This
component can exceed the main pulse in intensity but is switched on only
relatively rarely. Fluctutation spectra reveal a possible periodicity in this
feature of 140 pulse periods. Unlike the rest of the profile, this component
has low net polarization and emits predominantly in the orthogonal mode. This
feature appears to be unique to the Vela pulsar. We have also detected
microstructure in the Vela pulsar for the first time. These same features are
present in the 660 MHz data. We suggest that the full width of the Vela pulse
profile might be as large as 10 ms but that the conal edges emit only rarely.Comment: 6 pages, 5 figures, In Press with ApJ Letter
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