Inferring the eccentricity distribution

Standard maximum-likelihood estimators for binary-star and exoplanet eccentricities are biased high, in the sense that the estimated eccentricity tends to be larger than the true eccentricity. As with most non-trivial observables, a simple histogram of estimated eccentricities is not a good estimate of the true eccentricity distribution. Here we develop and test a hierarchical probabilistic method for performing the relevant meta-analysis, that is, inferring the true eccentricity distribution, taking as input the likelihood functions for the individual-star eccentricities, or samplings of the posterior probability distributions for the eccentricities (under a given, uninformative prior). The method is a simple implementation of a hierarchical Bayesian model; it can also be seen as a kind of heteroscedastic deconvolution. It can be applied to any quantity measured with finite precision--other orbital parameters, or indeed any astronomical measurements of any kind, including magnitudes, parallaxes, or photometric redshifts--so long as the measurements have been communicated as a likelihood function or a posterior sampling.Comment: Ap

Does Medicaid Make a Difference? Findings from the Commonwealth Fund Biennial Health Insurance Survey, 2014

As millions of Americans gain Medicaid coverage under the Affordable Care Act, attention has focused on the access to care, quality of care, and financial protection that coverage provides. This analysis uses the Commonwealth Fund Biennial Health Insurance Survey, 2014, to explore these questions by comparing the experiences of working-age adults with private insurance who were insured all year, Medicaid beneficiaries with a full year of coverage, and those who were uninsured for some time during the year. The survey findings suggest that Medicaid coverage provides access to care that in most aspects is comparable to private insurance. Adults with Medicaid coverage reported better care experiences on most measures than those who had been uninsured during the year. Medicaid beneficiaries also seem better protected from the cost of illness than do uninsured adults, as well as those with private coverage

Experimental Investigation of the Effect of Screw Fastener Spacing on the Local and Distortional Buckling Behavior of Built-Up Cold-Formed Steel Columns

This paper addresses an ongoing experimental and computational effort on the buckling and strength of built-up cold-formed steel (CFS) columns. Specifically, two 6 in. (152 mm) deep lipped channel sections (i.e. the 600S137-54 and 600S162-54 using AISI S200-12 nomenclature) are studied here in a back-to-back, screw-connected form and were chosen for their local and distortional slenderness to study the effect of fastener spacing and layout on local and distortional buckling and collapse behavior. Thirty column tests are completed with concentric loading. The screw spacing is varied from L to L/6, where L is the column length, with and without varying lengths of End Fastener Groups (EFG), which are a prescriptive layout of fasteners at the ends of built-up columns that is required by AISI S100-12 and is intended to insure end rigidity and increase composite action. Results yield two general types of deformation modes: compatible (where the connected webs conform to the same buckling shape) and isolated stud buckling. Buckling loads and half-wavelengths of deformation are shown to be affected by the tighter screw spacings. EFGs increase compatibility of buckling, but prove to be an inefficient (costly) method of fastening studs together. Future work includes expanding the design methods for built-up CFS columns to explicitly account for local and distortional buckling behavior of the built-up section, and to develop efficient numerical tools supporting a new design method under development

Experimental Investigation of the Effect of Screw Fastener Spacing on the Local and Distortional Buckling Behavior of Built-Up Cold-Formed Steel Columns

This paper addresses an ongoing experimental and computational effort on the buckling and strength of built-up cold-formed steel (CFS) columns. Specifically, two 6 in. (152 mm) deep lipped channel sections (i.e. the 600S137-54 and 600S162-54 using AISI S200-12 nomenclature) are studied here in a back-to-back, screw-connected form and were chosen for their local and distortional slenderness to study the effect of fastener spacing and layout on local and distortional buckling and collapse behavior. Thirty column tests are completed with concentric loading. The screw spacing is varied from L to L/6, where L is the column length, with and without varying lengths of End Fastener Groups (EFG), which are a prescriptive layout of fasteners at the ends of built-up columns that is required by AISI S100-12 and is intended to insure end rigidity and increase composite action. Results yield two general types of deformation modes: compatible (where the connected webs conform to the same buckling shape) and isolated stud buckling. Buckling loads and half-wavelengths of deformation are shown to be affected by the tighter screw spacings. EFGs increase compatibility of buckling, but prove to be an inefficient (costly) method of fastening studs together. Future work includes expanding the design methods for built-up CFS columns to explicitly account for local and distortional buckling behavior of the built-up section, and to develop efficient numerical tools supporting a new design method under development

Americans' Experiences in the Health Insurance Marketplaces: Results from The First Three Months

Conducted December 11–29, 2013, The Commonwealth Fund's second Affordable Care Act Tracking Survey interviewed a nationally representative sample of adults who are potentially eligible for the health reform law's new insurance options, whether private plans or Medicaid. Results show that by the end of December, 24 percent of potentially eligible adults had visited a marketplace to find a plan. The first survey, conducted in October, had found that 17 percent of people potentially eligible for coverage had visited the marketplaces during the first month of open enrollment. By the end of December, 41 percent of visitors were ages 19 to 34, and 77 percent reported being in good health. People's ability to compare benefits and premiums improved between October and December, but many reported challenges in plan selection. A majority of respondents say they are determined to gain coverage by the end of this year's open enrollment period

Verifying RISC-V Physical Memory Protection

We formally verify an open-source hardware implementation of physical memory protection (PMP) in RISC-V, which is a standard feature used for memory isolation in security critical systems such as the Keystone trusted execution environment. PMP provides per-hardware-thread machine-mode control registers that specify the access privileges for physical memory regions. We first formalize the functional property of the PMP rules based on the RISC-V ISA manual. Then, we use the LIME tool to translate an open-source implementation of the PMP hardware module written in Chisel to the UCLID5 formal verification language. We encode the formal specification in UCLID5 and verify the functional correctness of the hardware. This is an initial effort towards verifying the Keystone framework, where the trusted computing base (TCB) relies on PMP to provide security guarantees such as integrity and confidentiality.Comment: SECRISC-V 2019 Worksho

Dynamical inference from a kinematic snapshot: The force law in the Solar System

If a dynamical system is long-lived and non-resonant (that is, if there is a set of tracers that have evolved independently through many orbital times), and if the system is observed at any non-special time, it is possible to infer the dynamical properties of the system (such as the gravitational force or acceleration law) from a snapshot of the positions and velocities of the tracer population at a single moment in time. In this paper we describe a general inference technique that solves this problem while allowing (1) the unknown distribution function of the tracer population to be simultaneously inferred and marginalized over, and (2) prior information about the gravitational field and distribution function to be taken into account. As an example, we consider the simplest problem of this kind: We infer the force law in the Solar System using only an instantaneous kinematic snapshot (valid at 2009 April 1.0) for the eight major planets. We consider purely radial acceleration laws of the form a_r = -A [r/r_0]^{-\alpha}, where r is the distance from the Sun. Using a probabilistic inference technique, we infer 1.989 < \alpha < 2.052 (95 percent interval), largely independent of any assumptions about the distribution of energies and eccentricities in the system beyond the assumption that the system is phase-mixed. Generalizations of the methods used here will permit, among other things, inference of Milky Way dynamics from Gaia-like observations