Additive Manufacturing of Metal Structures at the Micrometer Scale

Currently, the focus of additive manufacturing (AM) is shifting from simple prototyping to actual production. One driving factor of this process is the ability of AM to build geometries that are not accessible by subtractive fabrication techniques. While these techniques often call for a geometry that is easiest to manufacture, AM enables the geometry required for best performance to be built by freeing the design process from restrictions imposed by traditional machining. At the micrometer scale, the design limitations of standard fabrication techniques are even more severe. Microscale AM thus holds great potential, as confirmed by the rapid success of commercial micro‐stereolithography tools as an enabling technology for a broad range of scientific applications. For metals, however, there is still no established AM solution at small scales. To tackle the limited resolution of standard metal AM methods (a few tens of micrometers at best), various new techniques aimed at the micrometer scale and below are presently under development. Here, we review these recent efforts. Specifically, we feature the techniques of direct ink writing, electrohydrodynamic printing, laser‐assisted electrophoretic deposition, laser‐induced forward transfer, local electroplating methods, laser‐induced photoreduction and focused electron or ion beam induced deposition. Although these methods have proven to facilitate the AM of metals with feature sizes in the range of 0.1–10 µm, they are still in a prototype stage and their potential is not fully explored yet. For instance, comprehensive studies of material availability and material properties are often lacking, yet compulsory for actual applications. We address these items while critically discussing and comparing the potential of current microscale metal AM techniques.     

Realization of Epitaxial Thin Films of the Topological Crystalline Insulator Sr3SnO

Topological materials are derived from the interplay between symmetry and topology. Advances in topological band theories have led to the prediction that the antiperovskite oxide Sr₃SnO is a topological crystalline insulator, a new electronic phase of matter where the conductivity in its (001) crystallographic planes is protected by crystallographic point group symmetries. Realization of this material, however, is challenging. Guided by thermodynamic calculations, a deposition approach is designed and implemented to achieve the adsorption-controlled growth of epitaxial Sr₃SnO single-crystal films by molecular-beam epitaxy (MBE). In situ transport and angle-resolved photoemission spectroscopy measurements reveal the metallic and electronic structure of the as-grown samples. Compared with conventional MBE, the used synthesis route results in superior sample quality and is readily adapted to other topological systems with antiperovskite structures. The successful realization of thin films of Sr₃SnO opens opportunities to manipulate topological states by tuning symmetries via strain engineering and heterostructuring.     

Impact of dissolved organic matter on colloid transport in the vadose zone: deterministic approximation of transport deposition coefficients from polymeric coating characteristics

Although numerous studies have been conducted to discern colloid transport and stability processes, the mechanistic understanding of how dissolved organic matter (DOM) affects colloid fate in unsaturated soils (i.e., the vadose zone) remains unclear. This study aims to bridge the gap between the physicochemical responses of colloid complexes and porous media interfaces to solution chemistry, and the effect these changes have on colloid transport and fate. Measurements of adsorbed layer thickness, density, and charge of DOM-colloid complexes and transport experiments with tandem internal process visualization were conducted for key constituents of DOM, humic (HA) and fulvic acids (FA), at acidic, neutral and basic pH and two CaCl₂ concentrations. Polymeric characteristics reveal that, of the two tested DOM constituents, only HA electrosterically stabilizes colloids. This stabilization is highly dependent on solution pH which controls DOM polymer adsorption affinity, and on the presence of Ca⁺² which promotes charge neutralization and inter-particle bridging. Transport experiments indicate that HA improved colloid transport significantly, while FA only marginally affected transport despite having a large effect on particle charge. A transport model with deposition and pore-exclusion parameters fit experimental breakthrough curves well. Trends in deposition coefficients are correlated to the changes in colloid surface potential for bare colloids, but must include adsorbed layer thickness and density for sterically stabilized colloids. Additionally, internal process observations with bright field microscopy reveal that, under optimal conditions for retention, experiments with FA or no DOM promoted colloid retention at solid-water interfaces, while experiments with HA enhanced colloid retention at air-water interfaces, presumably due to partitioning of HA at the air-water interface and/or increased hydrophobic characteristics of HA-colloid complexes.     

Port Moresby

Port Moresby is the capital of Papua New Guinea. With a population of nearly 200 000 it is by far the largest city in the country. Officially called the National Capital District (NCD), it straddles a low range of coastal hills in the south-east corner of the New Guinea mainland. It is a city facing serious problems today. A narrow economic base, a lack of land suitable for development and a deteriorating law and order situation are compounded by very rapid growth. The proposed construction of a transisland highway this decade, connecting Port Moresby to the populous interior, would have a profound impact on the future of the city.     

Breathhold imaging of the upper abdomen using a circular polarized-array coil: comparison with standard body coil imaging

Current studies emphasize the use of array coils to decrease noise and increase the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). We applied Tl-weighted and T2-weighted standard nonbreathhold spin echo (SE) sequences and Tl-weighted FLASH, TurboFLASH, T2-weighted spin-echo time (TSE), and heavily T2-weighted half Fourier acquisition single-shot TSE (HASTE) sequences during breathhold for abdominal imaging in 15 normal volunteers. The breathhold scans were performed using both a standard coil and a circular polarized array coil. We analyzed the signal intensity (SI), SNR, and CNR of abdominal organs in all sequences. SNRs increased in all cases by an overall factor of 3 due to an 8% increase in overall Sis and a 50% decrease in noise when applying the array coil. Although the array-coil FLASH sequence performed at least as well as the respective SE sequence, the SNRs of the array-coil TurboFLASH, TSE breathhold, and HASTE sequences were generally lower. We conclude that array-coil imaging significantly improves fast imaging of the abdomen.     

Trauma exposure among children with oppositional defiant disorder and attention deficit–hyperactivity disorder.

Consecutive admissions to an outpatient child psychiatry clinic diagnosed with oppositional defiant disorder (ODD), attention deficit-hyperactivity disorder (ADHD), or adjustment disorder were assessed for trauma exposure by a structured clinical interview and parent report. Controlling for age, gender, severity of internalizing behavior problems, social competence, family psychopathology, and parent–child relationship quality (assessed by parent report), an ODD diagnosis, with or without comorbid ADHD, was associated with increased likelihood of prior victimization (but not nonvictimization) trauma. ADHD alone was not associated with an increased likelihood of a history of trauma exposure Traumatic victimization contributed uniquely to the prediction of ODD but not ADHD diagnoses. Children in psychiatric treatment who are diagnosed with ODD, but not those diagnosed solely with ADHD, may particularly require evaluation and care for posttraumatic sequelae. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Virological treatment failure of protease inhibitor therapy in an unselected cohort of HIV-infected patients

OBJECTIVE: To determine the rate of virological treatment failure with protease inhibitor therapy in unselected patients and to assess underlying risk factors. DESIGN AND SETTING: Retrospective study in two German tertiary care treatment centres. PATIENTS: A total of 198 HIV-infected patients treated with protease inhibitors in 1996. MAIN OUTCOME MEASURES: Levels of HIV RNA 1-6 months after start of treatment; definition of treatment failure of < 1 log10 reduction in plasma HIV RNA within 6 months after starting protease inhibitor therapy; multivariate analysis of risk factors for treatment failures. RESULTS: A total of 226 treatment episodes with protease inhibitors were evaluable (saquinavir, 83; ritonavir, 47; indinavir, 96). The rate of virological treatment failure was 44% (saquinavir, 64%; ritonavir, 38%; indinavir, 30%). In a multivariate analysis, the following independent risk factors for virological failure were found: CD4 cell count, pretreatment with antiretroviral drugs (number), and protease inhibitor (compound). The relative risk reduction for each CD4 cell count increase was 0.997 (P = 0.012), 2.64 for pretreatment with one or two drugs versus no drug (P = 0.05), 2.97 for pretreatment with more than two drugs versus no drug (P = 0.05), and 4.62 for treatment with saquinavir versus indinavir (P = 0.001). CONCLUSION: An unexpectedly high rate of virological treatment failure of protease inhibitor therapy was found in an unselected cohort of HIV-infected patients. Response to antiretroviral combination therapy in normal clinical practice may considerably differ from results of randomized clinical trials. Further studies are warranted to find optimal treatment strategies for both initial and salvage therapy.     

Further evidence for a deficit in switching attention in schizophrenia.

In this study, sustained, selective, divided, and switching attention, and reloading of working memory were investigated in schizophrenia by using a newly developed Visual Attention Battery (VAB). Twenty-four outpatients with schizophrenia and 24 control participants were studied using the VAB. Performance on VAB components was correlated with performance of standard tests. Patients with schizophrenia were significantly impaired on VAB tasks that required switching of attention and reloading of working memory but had normal performance on tasks involving sustained attention or attention to multiple stimulus features. Switching attention and reloading of working memory were highly correlated with Trails (B–A) score for patients. The decline in performance on the switching-attention task in patients with schizophrenia met criteria for a differential deficit in switching attention. Future research should examine the neurophysiological basis of the switching deficit and its sensitivity and specificity to schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)