Stereolithography Cure Process Modeling Using Acrylate Resin

In this paper, a complex stereolithography (SL) cure process model is presented that incorporates transient thermal and chemical effects which influence final part shape and properties. The model incorporates photopolymerization, mass diffusion, and heat transfer. Material properties are characterized and a comprehensive kinetic model parameterized for a model compound system. SL process simulations are performed using finite element methods with the software package FEMLAB, and validated by the capability of predicting the fabricated part dimensions. A degree of cure (DOC) threshold model is proposed which can predict the cure line size within 15% error, comparing with 30% prediction error by the exposure threshold model currently used in SL. Furthermore, through the sensitivity analysis conducted by the process model presented here, the sensitive parameters are identified and the SL bath temperature, photointiator absorptivity and concentration are found to be the most sensitive factors that affect the SL fabrication results. The sensitive variables will be the focus of further research meant to improve SL process speed and resolution.Mechanical Engineerin

Struggling to a monumental triumph : Re-assessing the final stages of the smallpox eradication program in India, 1960-1980

The global smallpox program is generally presented as the brainchild of a handful of actors from the WHO headquarters in Geneva and at the agency's regional offices. This article attempts to present a more complex description of the drive to eradicate smallpox. Based on the example of India, a major focus of the campaign, it is argued that historians and public health officials should recognize the varying roles played by a much wider range of participants. Highlighting the significance of both Indian and international field officials, the author shows how bureaucrats and politicians at different levels of administration and society managed to strengthen—yet sometimes weaken—important program components. Centrally dictated strategies developed at WHO offices in Geneva and New Delhi, often in association with Indian federal authorities, were reinterpreted by many actors and sometimes changed beyond recognition

Triple positive solutions for multipoint conjugate boundary value problems

For the nth order nonlinear differential equation y (n)(t)=f(y(t)), t [0,1], satisfying the multipoint conjugate boundary conditions, y (j)(ai) = 0,1 i k, 0 j n i - 1, 0 =a 1 a 2 a k = 1, and i=1 k n i =n, where f: [0, ) is continuous, growth condtions are imposed on f which yield the existence of at least three solutions that belong to a cone

Positive Solutions for a Singular Fourth Order Nonlocal Boundary Value Problem

Positive solutions are obtained for the fourth order nonlocal boundary value problem, u(4)=f(x,u), 0 \u3c x \u3c 1, u(0) = u\u27\u27(0) = u\u27(1) = u\u27\u27(1) - u\u27\u27(2/3)=0, where f(x,u) is singular at x = 0, x=1, y=0, and may be singular at y=∞. The solutions are shown to exist at fixed points for an operator that is decreasing with respect to a cone

The benefits of expediting government gold sales

Additional gold can be made available either by mining at high cost (approximately $250 per ounce in 1997 dollars) or by mobilizing government stocks at zero cost. Governments own massive above‐ground stocks but loan out only a small percentage of these stocks. Making all government gold available for private uses immediately through some combination of sales and loans maximizes total welfare from private uses, a consequence of the first welfare theorem. We simulate a calibrated version of our model to quantify the effects of liquidating government stocks on alternative dates. If governments sell immediately rather than never, total welfare increases by$340 billion; if they make an unanticipated sale in 20 years, $105 billion of that amount is lost. By depressing prices, such sales benefit depletion and service users but injure private owners of stocks above and below‐ground. However, the injury to above‐ground stock owners is more than offset by the benefits to service users—often the same individuals. Mine owners would be the principal losers; however, they could be compensated (twice over) from government sales revenue without any need for tax increases.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142282/1/rfe235.pd

Purification, growth, and characterization of Zn(x)Cd(1-x)Se crystals

The purification of starting materials which were used in the growth of Zn(x)Cd(1-x)Se (x = 0.2) single crystals using the traveling solution method (TSM) is reported. Up to 13 cm long single crystals and as grown resistivities of 6 x 10(exp 12) ohm/cm could be achieved. Infrared and Raman spectra of Zn(0.2)Cd(0.8)Se are also presented and discussed