Solid Freeform Fabrication An Advanced Manufacturing Approach

Solid freeform fabrication (SFF) is the production of freeform solid objects directly from a computer model without part-specific tooling or human intervention. SFF has been realized in the last ten years through the merging of several previously distinct technologies: computer science, mechanical design, controls, high-energy beam technology and materials science and engineering. Their combination has produced over a relatively short time..frame numerous SFF methods. The value of SFF to the commercial sector is usually articulated in terms of reduced time to market (prototyping), low production "one-of-a-kind" parts and patterns for casting. The purpose of this introductory paper is to describe briefly some of the approaches to SFF as a background for the articles included in this proceedings.Mechanical Engineerin

Densification Behavior of SLS Processed Al2O3/Al Composite

Production of structurally sound parts by any rapid prototype technique is essential, because fully functional features are necessary where application testing is required. In the present work, a powder blend of A1203/AI (3:1 by weight) was mixed with ammonium dihydrogen phosphate and subjected to selective laser sintering (SLS) using a C02 laser. An attempt has been made to increase the powder bed density by introducing vibration to the part cylinder. These SLS processed preforms were then subj ected to a secondary heat treatment in a hydrogen atmosphere and to hot isostatic pressing. Densification behavior of these Al20 3/Al composite preforms is discussed.Mechanical Engineerin

Fundamentals of Liquid Phase Sintering During Selective Laser Sintering

One of the advantages of the Selective Laser Sintering (SLS) process is that a variety of materials can be processed. However, the goal of being able to produce fully dense metal parts with no post processing has been elusive. Using Selective Laser Sintering to produce metal parts with full density without post processing poses a challenge since both the processing conditions and the metal system must be controlled. This article describes two metallurgical mechanisms by which loose metal powder beds could be sintered to nearly full density using a scanning laser beam. The mechanisms are particle rearrangement during liquid phase sintering (LPS) and in-situ infiltration. Some of the particles, when heated by the laser radiation, melt and form a liquid. Ifthis liquid has certain physical properties (e.g., low viscosity and high surface tension) and wets the other solid particles, then the SLS process can in theory produce dense layers by either mechanism. The purpose of this study is to determine the process and material selection parameters required to achieve fully dense parts during direct Selective Laser Sintering of metal.Mechanical Engineerin

Relaxation spectra of surface waves

A new method is described for computing free surface flows. The method allows for arbitrary wind profiles to be imposed above the surface as well as arbitrary subsurface current and density profiles. The method combines recent advances in projection methods for stratified flows with level set strategies for computing the motion of a distinguished interface. High resolution discretization. schemes provide robust and accurate treatment of advection, even for singular initial data and in the limit of vanishing viscosity. The method is applied to the modulation of a nonlinear Stokes wave by wind applied at the surface. Speeds of 4,6, and 8 m/s relative to the rest frame are considered. The initial relaxation rate, {beta}, is calculated. The phase and phase speeds of the complex Fourier coefficient of the fundamental are found to increase with wind speed

Collective dynamics of colloids at fluid interfaces

The evolution of an initially prepared distribution of micron sized colloidal particles, trapped at a fluid interface and under the action of their mutual capillary attraction, is analyzed by using Brownian dynamics simulations. At a separation \lambda\ given by the capillary length of typically 1 mm, the distance dependence of this attraction exhibits a crossover from a logarithmic decay, formally analogous to two-dimensional gravity, to an exponential decay. We discuss in detail the adaption of a particle-mesh algorithm, as used in cosmological simulations to study structure formation due to gravitational collapse, to the present colloidal problem. These simulations confirm the predictions, as far as available, of a mean-field theory developed previously for this problem. The evolution is monitored by quantitative characteristics which are particularly sensitive to the formation of highly inhomogeneous structures. Upon increasing \lambda\ the dynamics show a smooth transition from the spinodal decomposition expected for a simple fluid with short-ranged attraction to the self-gravitational collapse scenario.Comment: 13 pages, 12 figures, revised, matches version accepted for publication in the European Physical Journal

Perceptions of trekking tourism and social and environmental change in Nepal's Himalayas

The Himalayas are among the world’s youngest mountain ranges. In addition to the geologic processes of mountain building and erosion, they are also highly vulnerable to human influenced change, occurring at local, national, regional, and international scales. A photo-elicitation methodology is employed to show how residents perceive those changes from historical perspectives, as well as their current conditions and impacts on their daily lives. Nepal’s Khumbu region has undergone major social and environmental transformations since the 1960s when international trekking first began to influence the area's economy. The current perceptions of Khumbu residents of these changes is assessed through photo-elicitation interviews. Their responses are placed in the historical context of: (i) institutional and political changes, much of which have been driven by national government policies; (ii) social and economic changes, for which the tourism economy has been central; and (iii) environmental changes, reflecting the impacts of resource management and climate change. The mostly positive perceptions of Khumbu residents toward how their region has changed reflects general improvements in the physical and cultural landscapes of the Khumbu over time, as well as its continuing geographic isolation, which has helped to slow the rate of globalization, while also keeping the region a dynamic and popular tourist destination

Radioimmunotherapy of B-cell lymphoma with radiolabelled anti-CD20 monoclonal antibodies

CD20 has proven to be an excellent target for the treatment of B-cell lymphoma, first for the chimeric monoclonal antibody rituximab (Rituxan™), and more recently for the radiolabelled antibodies Y-90 ibritumomab tiuxetan (Zevalin™) and I-131 tositumomab (Bexxar™). Radiation therapy effects are due to beta emissions with path lengths of 1–5 mm; gamma radiation emitted by I-131 is the only radiation safety issue for either product. Dose-limiting toxicity for both radiolabelled antibodies is reversible bone marrow suppression. They produce response rates of 70%–90% in low-grade and follicular lymphoma and 40%–50% in transformed low-grade or intermediate-grade lymphomas. Both products produce higher response rates than related unlabelled antibodies, and both are highly active in patients who are relatively resistant to rituximab-based therapy. Median duration of response to a single course of treatment is about 1 year with complete remission rates that last 2 years or longer in about 25% of patients. Clinical trials suggest that anti- CD20 radioimmunotherapy is superior to total body irradiation in patients undergoing stem cell supported therapy for B-cell lymphoma, and that it is a safe and efficacious modality when used as consolidation therapy following chemotherapy. Among cytotoxic treatment options, current evidence suggests that one course of anti-CD20 radioimmunotherapy is as efficacious as six to eight cycles of combination chemotherapy. A major question that persists is how effective these agents are in the setting of rituximab- refractory lymphoma. These products have been underutilised because of the complexity of treatment coordination and concerns regarding reimbursement

The evolution of language: a comparative review

For many years the evolution of language has been seen as a disreputable topic, mired in fanciful "just so stories" about language origins. However, in the last decade a new synthesis of modern linguistics, cognitive neuroscience and neo-Darwinian evolutionary theory has begun to make important contributions to our understanding of the biology and evolution of language. I review some of this recent progress, focusing on the value of the comparative method, which uses data from animal species to draw inferences about language evolution. Discussing speech first, I show how data concerning a wide variety of species, from monkeys to birds, can increase our understanding of the anatomical and neural mechanisms underlying human spoken language, and how bird and whale song provide insights into the ultimate evolutionary function of language. I discuss the ‘‘descended larynx’ ’ of humans, a peculiar adaptation for speech that has received much attention in the past, which despite earlier claims is not uniquely human. Then I will turn to the neural mechanisms underlying spoken language, pointing out the difficulties animals apparently experience in perceiving hierarchical structure in sounds, and stressing the importance of vocal imitation in the evolution of a spoken language. Turning to ultimate function, I suggest that communication among kin (especially between parents and offspring) played a crucial but neglected role in driving language evolution. Finally, I briefly discuss phylogeny, discussing hypotheses that offer plausible routes to human language from a non-linguistic chimp-like ancestor. I conclude that comparative data from living animals will be key to developing a richer, more interdisciplinary understanding of our most distinctively human trait: language

Amyloid and tau pathology associations with personality traits, neuropsychiatric symptoms, and cognitive lifestyle in the preclinical phases of sporadic and autosomal dominant Alzheimer’s disease

Background Major prevention trials for Alzheimer’s disease (AD) are now focusing on multidomain lifestyle interventions. However, the exact combination of behavioral factors related to AD pathology remains unclear. In 2 cohorts of cognitively unimpaired individuals at risk of AD, we examined which combinations of personality traits, neuropsychiatric symptoms, and cognitive lifestyle (years of education or lifetime cognitive activity) related to the pathological hallmarks of AD, amyloid-β, and tau deposits. Methods A total of 115 older adults with a parental or multiple-sibling family history of sporadic AD (PREVENT-AD [PRe-symptomatic EValuation of Experimental or Novel Treatments for AD] cohort) underwent amyloid and tau positron emission tomography and answered several questionnaires related to behavioral attributes. Separately, we studied 117 mutation carriers from the DIAN (Dominant Inherited Alzheimer Network) study group cohort with amyloid positron emission tomography and behavioral data. Using partial least squares analysis, we identified latent variables relating amyloid or tau pathology with combinations of personality traits, neuropsychiatric symptoms, and cognitive lifestyle. Results In PREVENT-AD, lower neuroticism, neuropsychiatric burden, and higher education were associated with less amyloid deposition (p = .014). Lower neuroticism and neuropsychiatric features, along with higher measures of openness and extraversion, were related to less tau deposition (p = .006). In DIAN, lower neuropsychiatric burden and higher education were also associated with less amyloid (p = .005). The combination of these factors accounted for up to 14% of AD pathology. Conclusions In the preclinical phase of both sporadic and autosomal dominant AD, multiple behavioral features were associated with AD pathology. These results may suggest potential pathways by which multidomain interventions might help delay AD onset or progression