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Publication date: 10 August 2017

Kathryn Freeman Anderson

Scholarship has demonstrated important consequences of segregation on health and health care outcomes, yet the mechanisms behind this association remain poorly understood. Several…

Abstract

Scholarship has demonstrated important consequences of segregation on health and health care outcomes, yet the mechanisms behind this association remain poorly understood. Several recent studies have shown inequities in the distribution of a wide variety of health-related organizations across urban neighborhoods, which may account for some portion of this negative health association. Though, within this literature, relatively little attention has been given to the distribution of health care facilities in particular.

Here, I consider how segregation is related to the distribution of several auxiliary health care practitioners in a series of spatial regression models of zip codes across the United States using data from the 2010 US Census and County Business Patterns (CBP).

I find that both Black and Latino segregation is negatively related to the density of a number of auxiliary health care practitioners, including mental health providers, dentists, physical/occupational/speech therapists, chiropractors, optometrists, podiatrists, and miscellaneous health care practitioners. However, this association is reduced (in certain instances to non-significance) with the inclusion of socioeconomic indicators, chiefly the percent of college educated individuals and the unemployment rate of the zip code. This is association is reduced for both Black and Latino segregation, with a larger reduction in the size of the effects for Latino segregation.

This research suggests that segregation plays an important role in the distribution of health care facilities, but that policy and public health interventions should focus on the intersection between racial residential segregation and socioeconomic considerations.

Details

Health and Health Care Concerns Among Women and Racial and Ethnic Minorities
Type: Book
ISBN: 978-1-78743-150-8

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Article
Publication date: 20 March 2017

Recep M. Gorguluarslan, Umesh N. Gandhi, Yuyang Song and Seung-Kyum Choi

Methods to optimize lattice structure design, such as ground structure optimization, have been shown to be useful when generating efficient design concepts with complex truss-like…

1745

Abstract

Purpose

Methods to optimize lattice structure design, such as ground structure optimization, have been shown to be useful when generating efficient design concepts with complex truss-like cellular structures. Unfortunately, designs suggested by lattice structure optimization methods are often infeasible because the obtained cross-sectional parameter values cannot be fabricated by additive manufacturing (AM) processes, and it is often very difficult to transform a design proposal into one that can be additively designed. This paper aims to propose an improved, two-phase lattice structure optimization framework that considers manufacturing constraints for the AM process.

Design/methodology/approach

The proposed framework uses a conventional ground structure optimization method in the first phase. In the second phase, the results from the ground structure optimization are modified according to the pre-determined manufacturing constraints using a second optimization procedure. To decrease the computational cost of the optimization process, an efficient gradient-based optimization algorithm, namely, the method of feasible directions (MFDs), is integrated into this framework. The developed framework is applied to three different design examples. The efficacy of the framework is compared to that of existing lattice structure optimization methods.

Findings

The proposed optimization framework provided designs more efficiently and with better performance than the existing optimization methods.

Practical implications

The proposed framework can be used effectively for optimizing complex lattice-based structures.

Originality/value

An improved optimization framework that efficiently considers the AM constraints was reported for the design of lattice-based structures.

Details

Rapid Prototyping Journal, vol. 23 no. 2
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 15 June 2015

Wenchao Zhou, Drew Loney, Andrei G. Fedorov, F. Levent Degertekin and David W. Rosen

– The aim of this paper is to advance the understanding of the droplet deposition process to better predict and control the manufacturing results for ink-jet deposition.

798

Abstract

Purpose

The aim of this paper is to advance the understanding of the droplet deposition process to better predict and control the manufacturing results for ink-jet deposition.

Design/methodology/approach

As material interface has both geometric and physical significance to manufacturing, the approach the authors take is to study the interface evolution during the material joining process in ink-jet deposition using a novel shape metric and a previously developed powerful simulation tool. This tool is an experimentally validated numerical solver based on the combination of the lattice Boltzmann method and the phase-field model that enabled efficient simulation of multiple-droplet interactions in three dimensions.

Findings

The underlying physics of two-droplet interaction is carefully examined, which provides deep insights into the effects of the printing conditions on the interface evolution of multiple-droplet interaction. By studying line printing, it is found that increasing impact velocity or decreasing fluid viscosity can reduce manufacturing time. For array printing, the authors have found the issue of air bubble entrapment that can lead to voids in the manufactured parts.

Research limitations/implications

The array of droplets impinges simultaneously, in contrast to most ink-jet printers. Sequential impingement of lines of droplet needs to be studied. Also, impingement on non-planar surfaces has not been investigated yet, but is important for additive manufacturing. Finally, it is recognized that the droplet hardening mechanisms need to be incorporated in the simulation tool to predict and control the final shape and size of the arbitrary features and manufacturing time for ink-jet deposition.

Practical implications

The research findings in this paper imply opportunities for optimization of printing conditions and print head design. Furthermore, if precise droplet control can be achieved, it may be possible to eliminate the need for leveling roller in the current commercial printers to save machine and manufacturing cost.

Originality/value

This work represents one of the first attempts for a systematic study of the interface dynamics of multiple-droplet interaction in ink-jet deposition enabled by the novel shape metric proposed in the paper and a previously developed numerical solver. The findings in this paper advanced the understanding of the droplet deposition process. The physics-based approach of analyzing the simulation results of the interface dynamics provides deep insights into how to predict and control the manufacturing relevant outcomes, and optimization of the deposition parameters is made possible under the same framework.

Details

Rapid Prototyping Journal, vol. 21 no. 4
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 18 April 2016

Xiayun Zhao and David W. Rosen

Exposure controlled projection lithography (ECPL) is an additive manufacturing process based on controlled UV photopolymerization. This paper aims to explore an advanced…

516

Abstract

Purpose

Exposure controlled projection lithography (ECPL) is an additive manufacturing process based on controlled UV photopolymerization. This paper aims to explore an advanced closed-loop control methodology to ECPL.

Design/methodology/approach

This paper proposes an evolutionary cycle to cycle (EC2C) control method, and started with a reduced order EC2C time control to control only the exposure time for given DMD bitmaps, which correspond to target 3D part cross-sections. A preliminary EC2C time control scheme was developed and followed by two types of EC2C time controllers based on two different parameter estimation methods, recursive least squares and L1 norm minimization (L1Min). Both algorithms were in an exponential weighted form, resulting in EWRLS and EWL1Min, to weight more on recent data to reflect the current process dynamics.

Findings

EWRLS was found to outperform EWL1Min in terms of computation speed and stability. The simulation study demonstrated that the proposed EC2C time control method was capable of adaptively tracking the ECPL process dynamics and updating online the model parameters with real-time measurements. It could control perfectly the exposure time for each bitmap, achieving the desired height for each layer and resulting in a total cured height conforming to the target 3D part height.

Research limitations/implications

The accuracy of EC2C time control method relies heavily on fast and accurate measurement, and this research assumes availability of an adequate real-time metrology. Measurement errors are not considered in this paper and will be explored in future. Only simulation study was performed without physical experiments to verify the EC2C controller.

Practical implications

For implementation, a real-time measurement system needs to be developed and the EC2C control software needs to be programmed and interfaced with the physical system.

Originality/value

It concludes that EC2C control method is very promising for a physical implementation, and could be extended for the development of a more comprehensive closed-loop controller for both exposure time and intensity to improve the ECPL process precision and robustness.

Details

Rapid Prototyping Journal, vol. 22 no. 3
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 15 June 2010

Jane Chu, Sarah Engelbrecht, Gregory Graf and David W. Rosen

The purpose of this paper is to investigate design synthesis methods for designing lattice cellular structures to achieve desired stiffnesses. More generally, to find appropriate…

2512

Abstract

Purpose

The purpose of this paper is to investigate design synthesis methods for designing lattice cellular structures to achieve desired stiffnesses. More generally, to find appropriate design problem formulations and solution algorithms for searching the large, complex design spaces associated with cellular structures.

Design/methodology/approach

Two optimization algorithms were tested: particle swarm optimization (PSO) and Levenburg‐Marquardt (LM), based on a least‐squares minimization formulation. Two example problems of limited complexity, specifically a two‐dimensional cantilever beam and a two‐dimensional simply‐supported plate, were investigated. Computational characteristics of the algorithms were reported for design problems with hundreds of variables. Constraints from additive manufacturing processes were incorporated to ensure that resulting designs are realizable.

Findings

Both PSO and LM succeeded in searching the design spaces and finding good designs. LM is one to two orders of magnitude more efficient for this class of problems.

Research limitations/implications

Three‐dimensional problems are not investigated in this paper.

Practical implications

LM appears to be a viable algorithm for optimizing structures of complex geometry for minimum weight and desired stiffness.

Originality/value

The testing of design synthesis methods (problem formulations and algorithms) for lattice cellular structures, and the testing of PSO and LM algorithms, are of particular value.

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Rapid Prototyping Journal, vol. 16 no. 4
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 25 July 2008

Sungshik Yim and David W. Rosen

The purpose of this paper is to present an information model (ontology) for design‐for‐manufacturing (DFM) problems, where parts are to be manufactured using an additive…

525

Abstract

Purpose

The purpose of this paper is to present an information model (ontology) for design‐for‐manufacturing (DFM) problems, where parts are to be manufactured using an additive manufacturing process. DFM problem formulation is often challenging since the formulation step requires both design and manufacturing process knowledge. The ontology also captures some relationships that model how that manufacturing knowledge applies to part designs. The ontology is implemented and serves as a repository of DFM problems that are available for reuse.

Design/methodology/approach

The ontology is encoded using a description logic (DL) known as ALE. Using this ontology, a designer can retrieve archived DFM problems that are similar to a problem being formulated. DLs are a subset of first‐order logic that have been used for information modeling in several application areas, including engineering information management. They are used typically to construct classification hierarchies that can be efficiently searched.

Findings

The paper demonstrates that the DL model is correct by showing that the classification hierarchies that are computed match our DFM ontology. Retrieval of DFM problems is demonstrated using a prototype implementation of our ontology. Examples are taken from the area of design for manufacture using the stereolithography process.

Research limitations/implications

The domain of the ontology is limited to additive manufacturing processes. Only DFM problems related to the determination of design parameters (e.g. dimensions) were within the scope of this work.

Originality/value

No ontology for DFM problems has been presented previously. Implementation of the ontology using DL is also original.

Details

Journal of Manufacturing Technology Management, vol. 19 no. 6
Type: Research Article
ISSN: 1741-038X

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Article
Publication date: 1 August 2003

David W. Rosen, Yong Chen, Shiva Sambu, Janet K. Allen and Farrokh Mistree

A new design‐for‐manufacturing method, called the geometric tailoring (GT), and the associated digital interface concept have been developed that enable the design activities to…

1018

Abstract

A new design‐for‐manufacturing method, called the geometric tailoring (GT), and the associated digital interface concept have been developed that enable the design activities to be separated from the manufacturing activities. Conditions for the successful application of this method are investigated. The GT method is demonstrated for rapid prototyping and rapid tooling technologies, where prototype parts are required to match the production properties as closely as possible. This method is embodied in a system called the rapid tooling testbed (RTTB). Research work is presented on GT and the distributed computing environment underlying the RTTB. Examples are summarized from the usage of this method and testbed.

Details

Rapid Prototyping Journal, vol. 9 no. 3
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 26 April 2011

Amit S. Jariwala, Fei Ding, Aparna Boddapati, Victor Breedveld, Martha A. Grover, Clifford L. Henderson and David W. Rosen

The purpose of this paper is to present a model that can be used to simulate the photopolymerization process in micro‐stereolithography (SL) in order to predict the shape of the…

1436

Abstract

Purpose

The purpose of this paper is to present a model that can be used to simulate the photopolymerization process in micro‐stereolithography (SL) in order to predict the shape of the cured parts. SL is an additive manufacturing process in which liquid photopolymer resin is cross‐linked and converted to solid with a UV laser light source. Traditional models of SL processes do not consider the complex chemical reactions and species transport occurring during photopolymerization and, hence, are incapable of accurately predicting resin curing behavior. The model presented in this paper attempts to bridge this knowledge gap.

Design/methodology/approach

The chemical reactions involved in the photopolymerization of acrylate‐based monomers were modeled as ordinary differential equations (ODE). This model incorporated the effect of oxygen inhibition and diffusion on the polymerization reaction. The model was simulated in COMSOL and verified with experiments conducted on a mask‐based micro‐SL system. Parametric studies were conducted to investigate the possibilities to improve the accuracy of the model for predicting the edge curvature.

Findings

The proposed model predicts well the effect of oxygen inhibition and diffusion on photopolymerization, and the model accurately predicts the cured part height when compared to experiments conducted on a mask‐based SL system. The simulated results also show the characteristic edge curvature as seen in experiments.

Research limitations/implications

A triacrylate monomer was used in the experiments conducted, so results may be limited to acrylate monomers. Shrinkage was not considered when comparing cured part shapes to those predicted using COMSOL.

Originality/value

This paper presents a unique and a pioneering approach towards modeling of the photopolymerization reaction in micro‐SL process. This research furthers the development of patent pending film micro‐SL process which can be used for fabrication of custom micro‐optical components.

Details

Rapid Prototyping Journal, vol. 17 no. 3
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 1 August 2008

Benay Sager and David W. Rosen

The purpose of this paper is to demonstrate that significant surface finish improvements can be accomplished in stereolithography (SL) fabricated parts by applying a new process…

1236

Abstract

Purpose

The purpose of this paper is to demonstrate that significant surface finish improvements can be accomplished in stereolithography (SL) fabricated parts by applying a new process planning method based on parameter estimation (PE).

Design/methodology/approach

PE is a method that finds a set of parameter values that minimize a measure of deviation. In this work, the measure of deviation is the difference between the exposure received by points along down‐facing surfaces and the SL resin's critical exposure.

Findings

The surface finish of down‐facing surfaces can be improved by a factor of 2‐9, depending upon the surface angle, compared with parts prepared using commercially available software. Surface finishes less than 1 μm Ra have been demonstrated on a SLA‐250/50 machine.

Research limitations/implications

Only down‐facing surfaces can have their surface finish improved using this method.

Practical implications

Common form errors known as “stair‐stepping” can be diminished on parts fabricated using SL.

Originality/value

The usage of PE methods for process planning is a new approach.

Details

Rapid Prototyping Journal, vol. 14 no. 4
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 22 August 2017

Jikai Liu and Huangchao Yu

Structural performance of additively manufactured parts is deposition path-dependent because of the induced material anisotropy. Hence, this paper aims to contribute a novel idea…

1325

Abstract

Purpose

Structural performance of additively manufactured parts is deposition path-dependent because of the induced material anisotropy. Hence, this paper aims to contribute a novel idea of concurrently performing the deposition path planning and the structural topology optimization for additively manufactured parts.

Design/methodology/approach

The concurrent process is performed under a unified level set framework that: the deposition paths are calculated by extracting the iso-value level set contours, and the induced anisotropic material properties are accounted for by the level set topology optimization algorithm. In addition, the fixed-geometry deposition path optimization problem is studied. It is challenging because updating the zero-value level set contour cannot effectively achieve the global orientation control. To fix this problem, a level set-based multi-step method is proposed, and it is proved to be effective.

Findings

The proposed concurrent design method has been successfully applied to designing additively manufactured parts. The majority of the planned deposition paths well match the principle stress direction, which, to the largest extent, enhances the structural performance. For the fixed geometry problems, fast and smooth convergences have been observed.

Originality/value

The concurrent deposition path planning and structural topology optimization method is, for the first time, developed and effectively implemented. The fixed-geometry deposition path optimization problem is solved through a novel level set-based multi-step method.

Details

Rapid Prototyping Journal, vol. 23 no. 5
Type: Research Article
ISSN: 1355-2546

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