Compositionally graded metals: A new frontier of additive manufacturing

The current work provides an overview of the state-of-the-art in polymer and metal additive manufacturing and provides a progress report on the science and technology behind gradient metal alloys produced through laser deposition. The research discusses a road map for creating gradient metals using additive manufacturing, demonstrates basic science results obtainable through the methodology, shows examples of prototype gradient hardware, and suggests that Compositionally Graded Metals is an emerging field of metallurgy research

Developing Gradient Metal Alloys through Radial Deposition Additive Manufacturing

Interest in additive manufacturing (AM) has dramatically expanded in the last several years, owing to the paradigm shift that the process provides over conventional manufacturing. Although the vast majority of recent work in AM has focused on three-dimensional printing in polymers, AM techniques for fabricating metal alloys have been available for more than a decade. Here, laser deposition (LD) is used to fabricate multifunctional metal alloys that have a strategically graded composition to alter their mechanical and physical properties. Using the technique in combination with rotational deposition enables fabrication of compositional gradients radially from the center of a sample. A roadmap for developing gradient alloys is presented that uses multi-component phase diagrams as maps for composition selection so as to avoid unwanted phases. Practical applications for the new technology are demonstrated in low-coefficient of thermal expansion radially graded metal inserts for carbon-fiber spacecraft panels

Abstraction and Identity

In this paper we outline and discuss various solutions to a restricted, but we think, more interesting version of the infamous Caesar Problem . This restricted version, labelled the C-R Problem , occurs in contexts where we have two distinct abstraction principles: and want to settle cross-sortal identity claims of the form: Both abstraction principles, however, are silent with regard to this identity -a special instance of the Caesar Problem . In what follows, we outline two distinct strategies to resolve the C-R problem . The first strategy decides such cross-abstraction identities in terms of whether or not the equivalence relations appearing on the right hand side of the abstraction principles are identical, while the second strategy settles such identities by appeal to the relevant equivalence classes. We then focus our discussion on the latter approach and offer three ways of implementing this strategy. Ultimately, we argue that this strategy fails, as each attempt to appeal to equivalence classes faces unsurmountable difficulties

Castable Bulk Metallic Glass Strain Wave Gears: Towards Decreasing the Cost of High-Performance Robotics

The use of bulk metallic glasses (BMGs) as the flexspline in strain wave gears (SWGs), also known as harmonic drives, is presented. SWGs are unique, ultra-precision gearboxes that function through the elastic flexing of a thin-walled cup, called a flexspline. The current research demonstrates that BMGs can be cast at extremely low cost relative to machining and can be implemented into SWGs as an alternative to steel. This approach may significantly reduce the cost of SWGs, enabling lower-cost robotics. The attractive properties of BMGs, such as hardness, elastic limit and yield strength, may also be suitable for extreme environment applications in spacecraft

A systematic review and meta-analysis of F-18-fluoro-D-deoxyglucose positron emission tomography interpretation methods in vascular graft and endograft infection

OBJECTIVE: Vascular graft and endograft infection (VGEI) has high morbidity and mortality rates. Diagnosis is complicated since symptoms vary and can be non-specific. A recent meta-analysis identified the use of 18F-fluoro-D-deoxyglucose positron emission tomography-computed tomography (18F-FDG PET(/CT)) as the most valuable tool for diagnosing VGEI and favorable to computed tomography as the current standard. However, the availability and varied use of several interpretation methods, without consensus on which interpretation method is best, complicates clinical use. The aim of this study was to evaluate the diagnostic performance of different interpretation methods of 18F-FDG PET(/CT) in diagnosing VGEI. METHODS: A systematic review was performed according to the PRISMA guidelines. Data sources included PubMed/Medline, Embase, and Cochrane. A meta-analysis was conducted on the different interpretation methods for 18F-FDG PET(/CT) in diagnosing VGEI, including visual FDG uptake intensity, visual FDG uptake pattern, and quantitative SUVmax. RESULTS: Out of 613 articles, 13 were included-10 prospective and 3 retrospective articles. The FDG uptake pattern method (I2 26.2%) showed negligible heterogeneity, while the FDG uptake intensity (I2 42.2%) and SUVmax (I2 42.1%) methods both showed moderate heterogeneity. The pooled sensitivity for FDG uptake intensity was 0.90 (95% CI: 0.79-0.96), for uptake pattern 0.94 (95% CI: 0.89-0.97), and for the SUVmax method 0.95 (95% CI: 0.76-0.99). The pooled specificity for FDG uptake intensity was 0.59 (95% CI: 0.38-0.78), whereas for FDG uptake pattern it was 0.81 (95% CI: 0.71-0.88) and for SUVmax it was 0.77 (95% CI: 0.63-0.87). The uptake pattern interpretation method demonstrated the best positive and negative post-test probability-82% and 10%, respectively. CONCLUSION: This meta-analysis identified the FDG uptake pattern as the most accurate assessment method of 18F-FDG PET(/CT) for diagnosing VGEI. The optimal SUVmax cutoff, depending on the vendor, demonstrated strong sensitivity and moderate specificity

Bacterial infections in Lilongwe, Malawi: aetiology and antibiotic resistance

<p>Abstract</p> <p>Background</p> <p>Life-threatening infections present major challenges for health systems in Malawi and the developing world because routine microbiologic culture and sensitivity testing are not performed due to lack of capacity. Use of empirical antimicrobial therapy without regular microbiologic surveillance is unable to provide adequate treatment in the face of emerging antimicrobial resistance. This study was conducted to determine antimicrobial susceptibility patterns in order to inform treatment choices and generate hospital-wide baseline data.</p> <p>Methods</p> <p>Culture and susceptibility testing was performed on various specimens from patients presenting with possible infectious diseases at Kamuzu Central Hospital, Lilongwe, Malawi.</p> <p>Results</p> <p>Between July 2006 and December 2007 3104 specimens from 2458 patients were evaluated, with 60.1% from the adult medical service. Common presentations were sepsis, meningitis, pneumonia and abscess. An etiologic agent was detected in 13% of patients. The most common organisms detected from blood cultures were <it>Staphylococcus aureus</it>, <it>Escherichia </it><it>coli</it>, Salmonella species and <it>Streptococcus pneumoniae</it>, whereas <it>Streptococcus pneumoniae </it>and <it>Cryptococcus neoformans </it>were most frequently detected from cerebrospinal fluid. <it>Haemophilus influenzae </it>was rarely isolated. Resistance to commonly used antibiotics was observed in up to 80% of the isolates while antibiotics that were not commonly in use maintained susceptibility.</p> <p>Conclusions</p> <p>There is widespread resistance to almost all of the antibiotics that are empirically used in Malawi. Antibiotics that have not been widely introduced in Malawi show better laboratory performance. Choices for empirical therapy in Malawi should be revised accordingly. A microbiologic surveillance system should be established and prudent use of antimicrobials promoted to improve patient care.</p

Castable Bulk Metallic Glass Strain Wave Gears: Towards Decreasing the Cost of High-Performance Robotics

The use of bulk metallic glasses (BMGs) as the flexspline in strain wave gears (SWGs), also known as harmonic drives, is presented. SWGs are unique, ultra-precision gearboxes that function through the elastic flexing of a thin-walled cup, called a flexspline. The current research demonstrates that BMGs can be cast at extremely low cost relative to machining and can be implemented into SWGs as an alternative to steel. This approach may significantly reduce the cost of SWGs, enabling lower-cost robotics. The attractive properties of BMGs, such as hardness, elastic limit and yield strength, may also be suitable for extreme environment applications in spacecraft