Wall-crossing formulae and strong piecewise polynomiality for mixed Grothendieck dessins d'enfant, monotone, and double simple Hurwitz numbers

We derive explicit formulae for the generating series of mixed Grothendieck dessins d'enfant/monotone/simple Hurwitz numbers, via the semi-infinite wedge formalism. This reveals the strong piecewise polynomiality in the sense of Goulden–Jackson–Vakil, generalising a result of Johnson, and provides a new explicit proof of the piecewise polynomiality of the mixed case. Moreover, we derive wall-crossing formulae for the mixed case. These statements specialise to any of the three types of Hurwitz numbers, and to the mixed case of any pair

Angular distributions of γ rays from the 7Li(p,γ) reaction at low energies

Angular distributions of the 14–17 MeV γ rays from the 7Li(p,γ) reaction at Ep=450, 402, and 80 keV were measured at 0°≤θlab≤135°, using a BGO detector and a 28-μg/cm2 LiF target. The angular distributions at Ep=450 and 402 keV agree with the previous results by Mainsbridge; at Ep=80 keV the ground-state transition is anisotropic on the order of 20%, confirming recent results by Chasteler et al

Thermal transport in nanocrystalline graphene investigated by approach-to-equilibrium molecular dynamics simulations

Approach-to-equilibrium molecular dynamics simulations have been used to study thermal transport in nanocrystalline graphene sheets. Nanostructured graphene has been created using an iterative process for grain growth from initial seeds with random crystallographic orientations. The resulting cells have been characterized by the grain size distribution based on the radius of gyration, by the number of atoms in each grain and by the number of atoms in the grain boundary. Introduction of nanograins with a radius of gyration of 1 nm has led to a significant reduction in the thermal conductivity to 3% of the value in single crystalline graphene. Analysis of the vibrational density of states has revealed a general reduction of the vibrational intensities and broadening of the peaks when nanograins are introduced which can be attributed to phonon scattering in the boundary layer. The thermal conductivity has been evaluated as a function of the grain size with increasing size up to 14 nm and it has been shown to follow an inverse rational function. The grain size dependent thermal conductivity could be approximated well by a function where transport is described by a connection in series of conducting elements and resistances (at boundaries).Comment: 9 pages, 9 figure

A New Executive Order for Improving Federal Regulation' Deeper and Wider Cost-Benefit Analysis

An updated version of this article was published in the University of Pennyslvania Law Review .For over two decades, federal agencies have been required to analyze the benefits and costs of significant regulatory actions and to show that the benefits justify the costs. But the regulatory state continues to suffer from significant problems, including poor priority-setting, unintended adverse side-effects, and, on occasion, high costs for low benefits. In many cases, agencies do not offer an adequate account of either costs or benefits, and hence the commitment to cost-benefit balancing is not implemented in practice. A major current task is to ensure a deeper and wider commitment to cost-benefit analysis, properly understood. We explain how this task might be accomplished and offer a proposed executive order that would move regulation in better directions. In the course of the discussion, we explore a number of pertinent issues, including the actual record of the last two decades, the precautionary principle, the value of 'prompt letters', the role of distributional factors, and the need to incorporate independent agencies within the system of cost-benefit balancing.

Star Formation Quenching Timescale of Central Galaxies in a Hierarchical Universe

Central galaxies make up the majority of the galaxy population, including the majority of the quiescent population at $\mathcal{M}_* > 10^{10}\mathrm{M}_\odot$. Thus, the mechanism(s) responsible for quenching central galaxies plays a crucial role in galaxy evolution as whole. We combine a high resolution cosmological $N$-body simulation with observed evolutionary trends of the "star formation main sequence," quiescent fraction, and stellar mass function at $z < 1$ to construct a model that statistically tracks the star formation histories and quenching of central galaxies. Comparing this model to the distribution of central galaxy star formation rates in a group catalog of the SDSS Data Release 7, we constrain the timescales over which physical processes cease star formation in central galaxies. Over the stellar mass range $10^{9.5}$ to $10^{11} \mathrm{M}_\odot$ we infer quenching e-folding times that span $1.5$ to $0.5\; \mathrm{Gyr}$ with more massive central galaxies quenching faster. For $\mathcal{M}_* = 10^{10.5}\mathrm{M}_\odot$, this implies a total migration time of $\sim 4~\mathrm{Gyrs}$ from the star formation main sequence to quiescence. Compared to satellites, central galaxies take $\sim 2~\mathrm{Gyrs}$ longer to quench their star formation, suggesting that different mechanisms are responsible for quenching centrals versus satellites. Finally, the central galaxy quenching timescale we infer provides key constraints for proposed star formation quenching mechanisms. Our timescale is generally consistent with gas depletion timescales predicted by quenching through strangulation. However, the exact physical mechanism(s) responsible for this still remain unclear.Comment: 16 pages, 11 figure

Developing a Framework for Sensible Regulation: Lessons from OSHA's Proposed Ergonomics Rule

Injuries caused by workplace activities that involve repetitive motion, known as musculoskeletal disorders (MSDs), increasingly concern workers, employers, and regulators because of their frequency and high treatment costs. The Occupational Safety and Health Administration (OSHA) recently proposed a national rule designed to reduce the workplace risk of MSDs. OSHA estimates there were about 626,000 MSDs in 1997, representing about one-third of all serious nonfatal workplace injuries and illnesses. OSHA estimates the proposed rule will cost $4 billion per year and generate$9 billion per year in benefits. Yet, OSHA does not provide sufficient evidence that private markets are failing to reduce MSD risk without government intervention and does not convincingly demonstrate that the rule will result in more good than harm. Unless OSHA effectively addresses some of the more serious flaws in the proposed rule, OSHA should not proceed with the final regulation. OSHA should more carefully evaluate the nature and extent of MSDs in the workplace than it did in the proposed rule and use improved economic analysis to target serious MSDs that employers can reduce at low cost. Furthermore, OSHA should include new provisions to improve employer access to information about reducing workplace risk of MSDs. The rule's ergonomics program requirements should apply only to those MSDs which employers do not have sufficient incentive to reduce without government intervention.

A Solution to Concerns over Public Access to Scientific Data

To balance the public need for accountability and better policy decision making with concerns regarding burdens on scientists and scientific progress, the authors propose that increased access be limited to data relevant in analyzing regulations that would have an annual economic impact of at least $100 million. They also recommend establishing an agency to replicate key findings used to support regulations before they are finalized.Regulatory Reform