Forward Modeling of Double Neutron Stars: Insights from Highly-Offset Short Gamma-Ray Bursts

We present a detailed analysis of two well-localized, highly offset short gamma-ray bursts---GRB~070809 and GRB~090515---investigating the kinematic evolution of their progenitors from compact object formation until merger. Calibrating to observations of their most probable host galaxies, we construct semi-analytic galactic models that account for star formation history and galaxy growth over time. We pair detailed kinematic evolution with compact binary population modeling to infer viable post-supernova velocities and inspiral times. By populating binary tracers according to the star formation history of the host and kinematically evolving their post-supernova trajectories through the time-dependent galactic potential, we find that systems matching the observed offsets of the bursts require post-supernova systemic velocities of hundreds of kilometers per second. Marginalizing over uncertainties in the stellar mass--halo mass relation, we find that the second-born neutron star in the GRB~070809 and GRB~090515 progenitor systems received a natal kick of $\gtrsim 200~\mathrm{km\,s}^{-1}$ at the 78\% and 91\% credible levels, respectively. Applying our analysis to the full catalog of localized short gamma-ray bursts will provide unique constraints on their progenitors and help unravel the selection effects inherent to observing transients that are highly offset with respect to their hosts.Comment: 18 pages, 7 figures, 1 table. ApJ, in pres

Water and Sewer Extension Policies as a Technique for Guiding Development

It would be difficult, no doubt, to find any relatively informed observer of urban affairs who would not decry the many undesirable aspects of urban sprawl. Planner and decision-maker alike are too well aware of the substantial costs associated with "leap frog" development on the urban fringe. Cities have grown and continue to grow in this extremely inefficient manner while possessing a potentially potent tool for regulating the location and timing of this development—the provision of municipal water and sewer services

Energy-Efficient Circuit Design

We initiate the theoretical investigation of energy-efficient circuit design. We assume that the circuit design specifies the circuit layout as well as the supply voltages for the gates. To obtain maximum energy efficiency, the circuit design must balance the conflicting demands of minimizing the energy used per gate, and minimizing the number of gates in the circuit; If the energy supplied to the gates is small, then functional failures are likely, necessitating a circuit layout that is more fault-tolerant, and thus that has more gates. By leveraging previous work on fault-tolerant circuit design, we show general upper and lower bounds on the amount of energy required by a circuit to compute a given relation. We show that some circuits would be asymptotically more energy-efficient if heterogeneous supply voltages were allowed, and show that for some circuits the most energy-efficient supply voltages are homogeneous over all gates. In the traditional approach to circuit design the supply voltages for each transistor/gate are set sufficiently high so that with sufficiently high probability no transistor fails. We show that if there is a better (in terms of worst-case relative error with respect to energy) method than the traditional approach then $P=NP$, and thus there is a complexity theoretic obstacle to achieving energy savings with Near-Threshold computing. We show that almost all Boolean functions require circuits that use exponential energy. This is not an immediate consequence of Shannon's classic result that most functions require exponential sized circuits of faultless gates because, as we show, the same circuit layout can compute many different functions, depending on the value of the supply voltage. If the error bound must vanish as the number of inputs increases, we show that a natural class of functions can be computed with asymptotically less energy using heterogeneous supply voltages than is possible using homogeneous supply voltages. We also prove upper bounds on the asymptotic energy savings achieved by using heterogeneous supply voltages over homogeneous supply voltages for a class of functions, and also show a relation that can bypass this bound

The laughter of inclusion

This study is concerned with school-children’s communication, behavioural, and emotional development, in which the first concern has been to focus on their laughter. Although commonly thought of as an integral component of childhood, children’s laughter seldom receives the attention it deserves. The significance of laughter’s correlation with children’s social connectivity remains largely undiscovered. Little account has been taken of laughter’s exclusive orientation, and the strain this may create in schools with an avowedly inclusive ethos. Teachers and pupils who agreed to take part in this study were recruited from two primary schools. Together, they formed the substantive part of a pair of ethnographic case-studies. Data obtained from a series of playground/classroom observations and informal interviews were framed around Robert Putnam’s theory of social capital, and its own inclusive-exclusive (bridging and bonding) dynamic. Findings indicate that our diminishing stocks of social capital may be directly correlated with our decline in laughter production. They also confirm the view that it is unhelpful to consider inclusive and exclusive entities in isolation. Exclusive laughter appears to be a fundamental condition of inclusive schooling, with pupils and their teachers apparently natural exponents of a form of behaviour that may be described as inclusive-exclusive