A Process Planning Method and Data Format for Achieving Tolerances in Stereolithography

When building parts in a stereolithography apparatus (SLA), the user is faced with many decis!ons regarding the setting of process variables. To 'achieve a set of tolera~ces as closely as pOSSIble, relationships between part geometry, tolerances, and process v~nables ~ust be understood quantitatively. This paper presents a method for SLA process plannIng that IS based on response surface methodology and multi-objective optimization, where the response surfaces capture these relationships. These response surfaces were generated by extensive design-of-experiment studies for a variety of geometries. An annotated STL data format is also presented that enables the inclusion of tolerance and surface information in fatetted representations. Application of the data format and process planning method is illustrated on one part.Mechanical Engineerin

Accelerating Certifiable Estimation with Preconditioned Eigensolvers

Convex (specifically semidefinite) relaxation provides a powerful approach to constructing robust machine perception systems, enabling the recovery of certifiably globally optimal solutions of challenging estimation problems in many practical settings. However, solving the large-scale semidefinite relaxations underpinning this approach remains a formidable computational challenge. A dominant cost in many state-of-the-art (Burer-Monteiro factorization-based) certifiable estimation methods is solution verification (testing the global optimality of a given candidate solution), which entails computing a minimum eigenpair of a certain symmetric certificate matrix. In this paper, we show how to significantly accelerate this verification step, and thereby the overall speed of certifiable estimation methods. First, we show that the certificate matrices arising in the Burer-Monteiro approach generically possess spectra that make the verification problem expensive to solve using standard iterative eigenvalue methods. We then show how to address this challenge using preconditioned eigensolvers; specifically, we design a specialized solution verification algorithm based upon the locally optimal block preconditioned conjugate gradient (LOBPCG) method together with a simple yet highly effective algebraic preconditioner. Experimental evaluation on a variety of simulated and real-world examples shows that our proposed verification scheme is very effective in practice, accelerating solution verification by up to 280x, and the overall Burer-Monteiro method by up to 16x, versus the standard Lanczos method when applied to relaxations derived from large-scale SLAM benchmarks.Comment: 8 pages, 6 figure

Is the US Population Behaving Healthier?

In the past few decades, some measures of population risk have improved, while others have deteriorated. Understanding the health of the population requires integrating these different trends. We compare the risk factor profile of the population in the early 1970s with that of the population in the early 2000s and consider the impact of a continuation of recent trends. Despite substantial increases in obesity in the past three decades, the overall population risk profile is healthier now than it was formerly. For the population aged 25-74, the 10 year probability of death fell from 9.8 percent in 1971-75 to 8.4 percent in 1999-2002. Among the population aged 55-74, the 10 year risk of death fell from 25.7 percent to 21.7 percent. The largest contributors to these changes were the reduction in smoking and better control of blood pressure. Increased obesity increased risk, but not by as large a quantitative amount. In the future, however, increased obesity may play a larger role than continued reductions in smoking. We estimate that a continuation of trends over the past three decades to the next three decades might offset about a third of the behavioral improvements witnessed in recent years.

Financial Aid Packages and College Enrollment Decisions: An Econometric Case Study

We study the effects of a change in financial aid policy introduced by a Northeastern university in 1998. Prior to that time, the university's financial aid packages for low-income students consisted of grants, loans, and campus jobs. After the change, the entire loan portion of the package for low-income students was replaced with grants. We find the program increased the likelihood of matriculation by low-income students by about 3 percentage points, although the effect is not statistically significant. The effect among low-income minority students was between 8 and 10 percentage points and statistically significant at the 10 percent level.

Whole-genome sequencing of Klebsiella pneumoniae isolates to track strain progression in a single patient with recurrent urinary tract infection

Klebsiella pneumoniae is an important uropathogen that increasingly harbors broad-spectrum antibiotic resistance determinants. Evidence suggests that some same-strain recurrences in women with frequent urinary tract infections (UTIs) may emanate from a persistent intravesicular reservoir. Our objective was to analyze K. pneumoniae isolates collected over weeks from multiple body sites of a single patient with recurrent UTI in order to track ordered strain progression across body sites, as has been employed across patients in outbreak settings. Whole-genome sequencing of 26 K. pneumoniae isolates was performed utilizing the Illumina platform. PacBio sequencing was used to create a refined reference genome of the original urinary isolate (TOP52). Sequence variation was evaluated by comparing the 26 isolate sequences to the reference genome sequence. Whole-genome sequencing of the K. pneumoniae isolates from six different body sites of this patient with recurrent UTI demonstrated 100% chromosomal sequence identity of the isolates, with only a small P2 plasmid deletion in a minority of isolates. No single nucleotide variants were detected. The complete absence of single-nucleotide variants from 26 K. pneumoniae isolates from multiple body sites collected over weeks from a patient with recurrent UTI suggests that, unlike in an outbreak situation with strains collected from numerous patients, other methods are necessary to discern strain progression within a single host over a relatively short time frame.</p

A Proposed Method for Monitoring U.S. Population Health: Linking Symptoms, Impairments, and Health Ratings

We propose a method of quantifying non-fatal health on a 0-1 QALY scale that details the impact of specific symptoms and impairments and is not based on ratings of counterfactual scenarios. Measures of general health status are regressed on health impairments and symptoms in different domains, using ordered probit and ordinary least squares regression. This yields estimates of their effects analogous to disutility weights, and accounts for complex non-additive relationships. Health measures used include self-rated health status on a 5-point scale, EuroQol 5D (EQ-5D) scores, and ratings of current health using a 0-100 rating scale and a time-tradeoff. Data are from the nationally representative Medical Expenditure Panel Survey (MEPS) year 2002 (N=34,615), with validation in an independent sample from MEPS 2000 (N=21,067) and among 1420 adults age 45-89 in the Beaver Dam Health Outcomes Study. Decrement weights for symptoms and impairments are used to derive estimates of overall health-related quality of life, laying the groundwork for a detailed national summary measure of health. To purchase a copy of the earlier version of this paper, please contact the Working Papers department directly at (617) 588 1405.

Measuring Health Care Costs of Individuals with Employer-Sponsored Health Insurance in the U.S.: A Comparison of Survey and Claims Data

As the core nationally representative health expenditure survey in the United States, the Medical Expenditure Panel Survey (MEPS) is increasingly being used by statistical agencies to track expenditures by disease. However, while MEPS provides a wealth of data, its small sample size precludes examination of spending on all but the most prevalent health conditions. To overcome this issue, statistical agencies have turned to other public data sources, such as Medicare and Medicaid claims data, when available. No comparable publicly available data exist for those with employer-sponsored insurance. While large proprietary claims databases may be an option, the relative accuracy of their spending estimates is not known. This study compared MEPS and MarketScan estimates of annual per person health care spending on individuals with employer-sponsored insurance coverage. Both total spending and the distribution of annual per person spending differed across the two data sources, with MEPS estimates 10 percent lower on average than estimates from MarketScan. These differences appeared to be a function of both underrepresentation of high expenditure cases and underestimation across the remaining distribution of spending.