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The US Government is challenged to maintain pace as the world’s de facto provider of space object cataloging data. Augmenting capabilities with nontraditional sensors…
The US Government is challenged to maintain pace as the world’s de facto provider of space object cataloging data. Augmenting capabilities with nontraditional sensors present an expeditious and low-cost improvement. However, the large tradespace and unexplored system of systems performance requirements pose a challenge to successful capitalization. This paper aims to better define and assess the utility of augmentation via a multi-disiplinary study.
Hypothetical telescope architectures are modeled and simulated on two separate days, then evaluated against performance measures and constraints using multi-objective optimization in a heuristic algorithm. Decision analysis and Pareto optimality identifies a set of high-performing architectures while preserving decision-maker design flexibility.
Capacity, coverage and maximum time unobserved are recommended as key performance measures. A total of 187 out of 1017 architectures were identified as top performers. A total of 29% of the sensors considered are found in over 80% of the top architectures. Additional considerations further reduce the tradespace to 19 best choices which collect an average of 49–51 observations per space object with a 595–630 min average maximum time unobserved, providing redundant coverage of the Geosynchronous Orbit belt. This represents a three-fold increase in capacity and coverage and a 2 h (16%) decrease in the maximum time unobserved compared to the baseline government-only architecture as-modeled.
This study validates the utility of an augmented network concept using a physics-based model and modern analytical techniques. It objectively responds to policy mandating cataloging improvements without relying solely on expert-derived point solutions.
For many applications, including space applications, the usability and performance of a component is dependent on the surface topology of the additively manufactured part…
For many applications, including space applications, the usability and performance of a component is dependent on the surface topology of the additively manufactured part. The purpose of this paper is to present an investigation into minimizing the residual surface roughness of direct metal laser sintering (DMLS) samples by manipulating the input process parameters.
First, the ability to manipulate surface roughness by modifying processing parameters was explored. Next, the surface topography was characterized to quantify roughness. Finally, microthruster nozzles were created both additively and conventionally for flow testing and comparison.
Surface roughness of DMLS samples was found to be highly dependent on the laser power and scan speed. Because of unintended partially sintered particles adhering to the surface, a localized laser fluence mechanism was explored. Experimental results show that surface roughness is influenced by the varied parameters but is not a completely fluence driven process; therefore, a relationship between laser fluence and surface roughness can be incorporated but not completely assumed.
This paper serves as an aid in understanding the importance of surface roughness and the mechanisms associated with DMLS. Rather than exploring a more common global energy density, a localized laser fluence was initiated. Moreover, the methodology and conclusions can be used when optimizing parts via metal additive manufacturing.
American sociology has long been concerned with the social conditioning of American character, particularly with regard to caring for others. This interest can be traced…
American sociology has long been concerned with the social conditioning of American character, particularly with regard to caring for others. This interest can be traced to Alexis de Tocqueville's Democracy in America (1899) in which he reflected on how democratic participation in government and voluntary associations in the 1830s shaped the American character. Tocqueville believed that participation in social institutions, and especially voluntary societies, balanced the potentially excessive individualism he observed in the United States. David Riesman's The Lonely Crowd: A Study of Changing American Character (1950) picked up similar themes in an exploration of the isolation of the individual within modern society. These concerns reached a broad audience more recently in Robert N. Bellah, Richard Madsen, William M. Sullivan, Ann Swidler, and Steven M. Tipton's Habits of the Heart: Individualism and Commitment in American Life (1985) in which the authors argued that the scale had swung in favor of individualism at the expense of commitment to the social good. Robert Wuthnow (1991) addressed these issues again in Acts of Compassion: Caring for Others and Helping Ourselves, in which he explored how in volunteer work, Americans attempted to reconcile compassion with individualism. These studies, primarily focusing on white, middle‐class Americans, have laid the groundwork for an exploration of the social nature of the American character within the context of caring for others.
Melvin Seeman (1989) has recently stated that nowadays the concept of alienation carries an antiquated meaning which is quite in contrast to its importance in the 1960s. There seems to be much evidence for a fading romance with alienation in the social sciences. I have continued Seeman's search for articles that have appeared between 1978 and 1982 in leading social science journals until 1989. There was only one major reference, however, a quite important one by Kai T. Erikson in his presidential address to the American Sociological Association in 1985. Contrary to these disappointing observations Seeman suggests that alienation is leading an underground life in contemporary research and theory. According to his assessment this theme survives because the assumptions involved in the tradition of the alienation motif are indispensable for critical analysis in sociology and psychology.
Builds on previous research by the authors to establish a mathematical representation of the surface roughness of stereolithography (SL) parts. It is the intention of the…
Builds on previous research by the authors to establish a mathematical representation of the surface roughness of stereolithography (SL) parts. It is the intention of the research to use this modelling technique as a design tool for defining optimum build orientation and planning post‐process finishing operations. During the development of this model, a number of in‐process attributes inherent in SL were seen to affect surface deviation. Most notably the phenomenon known as “print‐through” on down‐facing planes produces a build orientation envelope of very smooth surfaces. Although capable of providing low roughness over some 50°, print‐through smoothing cannot easily be extended to other angles, hence complementary processes for surface smoothing must be developed. Discusses a number of possible solutions, showing how the generation of a meniscus between layers can prove beneficial in reducing SL surface roughness, hence reducing the need for lengthy manual finishing operations.
An integer multiple objective non‐linear mathematical programming formulation is developed for simultaneously forming part/machine cells. In the proposed model, generic…
An integer multiple objective non‐linear mathematical programming formulation is developed for simultaneously forming part/machine cells. In the proposed model, generic capability units which are termed as resource elements are used to define the processing requirements of parts and processing capabilities of machine tools. Machine capabilities are not generally taken into account in the previous cell formation procedures. Explicit consideration of unique and overlapping machine capabilities can result in better manufacturing cell designs with higher utilisation levels and less machine duplication. The proposed cell formation model has distinguishing features. Several important cell formation objectives, such as minimisation of part dissimilarity (based on production requirements and processing sequences of parts) in formed cells, minimisation of cell load imbalance, and minimisation of extra capacity requirements for cell formation, are considered. In order to solve the mathematical programming model, a simulated annealing algorithm is developed. Cooperative game theoretic approach is applied for evaluating multiple objectives.
Presents the background to and efforts being made to find a direct production route using rapid prototype (RP) parts as the electrodes for electrical discharge machining…
Presents the background to and efforts being made to find a direct production route using rapid prototype (RP) parts as the electrodes for electrical discharge machining (EDM). It would have the double effect of unlocking the potential of the EDM die sinking process and expanding the role of RP in the production environment. Thin coated stereolithography (SL) models have been used to erode hardened tool steel to a depth of 4mm. Machining efficiency of these copper coated RP models is not comparable to that of conventional machined solid copper electrodes. Parametric optimization has been applied, achieving substantial improvements in machining efficiency. At present these electrodes are suitable for semi‐roughing or finishing cuts in EDM die sinking. Electroforming copper into SL cavities shows potential for manufacture of electrodes with comparable performance to that of solid copper.
Structural explanations of racial stratification are weakened by a failure to in‐corporate attitudinal and ideological factors into their theories. But attitudinal…
Structural explanations of racial stratification are weakened by a failure to in‐corporate attitudinal and ideological factors into their theories. But attitudinal researchers have tended to focus on racial prejudice and tolerance and neglected non‐racially specific beliefs that support white dominance. This article reviews the limits of each approach, discusses the problem of ideology for race relations theory and explores how, through the analysis of ideology, attitudinal and structural analysis might be synthesised. Findings on the relation between adherence to individualist explanations of poverty, perceptions of racial discrimination in employment and attitudes toward affirmative action programs are used to exemplify the power of class ideologies in shaping beliefs about racial inequality and vice versa. An exploration of ideologies of local autonomy and attitudes toward public housing and residential desegregation might elicit similar findings.
Adapting to change is never easy, particularly when everything is moving so fast that one has less and less time to devote to thinking about the transition process. We are all rather like white water canoeists: carried on rapid waters in a small and fragile boat — in danger of being either sunk or left on the bank — and, with head over paddle, unable to see very far ahead. The change always seems to be external and it is difficult to answer such questions as what change and for what purpose and even if we knew the answers it is unclear to what extent we are capable of affecting the outcomes. What might be helpful is to examine some of the undercurrents that are propelling us forward, affecting our work and our perceptions of our professional role.