Frequency-domain hot-wire sensor and 3D model for thermal conductivity measurements of reactive and corrosive materials at high temperatures.

High temperature solids and liquids are becoming increasingly important in next-generation energy and manufacturing systems that seek higher efficiencies and lower emissions. Accurate measurements of thermal conductivity at high temperatures are required for the modeling and design of these systems, but commonly employed time-domain measurements can have errors from convection, corrosion, and ambient temperature fluctuations. Here, we describe the development of a frequency-domain hot-wire technique capable of accurately measuring the thermal conductivity of solid and molten compounds from room temperature up to 800 °C. By operating in the frequency-domain, we can lock into the harmonic thermal response of the material and reject the influence of ambient temperature fluctuations, and we can keep the probed volume below 1 µl to minimize convection. The design of the microfabricated hot-wire sensor, electrical systems, and insulating wire coating to protect against corrosion is covered in detail. Furthermore, we discuss the development of a full three-dimensional multilayer thermal model that accounts for both radial conduction into the sample and axial conduction along the wire and the effect of wire coatings. The 3D, multilayer model facilitates the measurement of small sample volumes important for material development. A sensitivity analysis and an error propagation calculation of the frequency-domain thermal model are performed to demonstrate what factors are most important for thermal conductivity measurements. Finally, we show thermal conductivity measurements including model data fitting on gas (argon), solid (sulfur), and molten substances over a range of temperatures.

Ultrafast laser welding of ceramics.

Welding of ceramics is a key missing component in modern manufacturing. Current methods cannot join ceramics in proximity to temperature-sensitive materials like polymers and electronic components. We introduce an ultrafast pulsed laser welding approach that relies on focusing light on interfaces to ensure an optical interaction volume in ceramics to stimulate nonlinear absorption processes, causing localized melting rather than ablation. The key is the interplay between linear and nonlinear optical properties and laser energy-material coupling. The welded ceramic assemblies hold high vacuum and have shear strengths comparable to metal-to-ceramic diffusion bonds. Laser welding can make ceramics integral components in devices for harsh environments as well as in optoelectronic and/or electronic packages needing visible-radio frequency transparency.

Analysis of a simplified concentration sputum smear technique for pulmonary tuberculosis diagnosis in rural hospitals.

Rural hospitals in Africa face the challenge of an increasing number of pulmonary tuberculosis (PTB) cases, much of it related with the AIDS pandemic. The main diagnostic tool in these hospitals is the direct sputum smears. Sensitivity of direct sputum smears is low, especially in cases of AIDS related PTB. Several concentration methods have been described but none is routinely used in Zimbabwe. Fluorescence microscopy of auramine stained samples increases sensitivity and saves laboratory time but it is not an appropriate technique for rural African hospitals. In a rural hospital of southwest Zimbabwe, we studied the sensitivity and appropriateness of a simplified concentration method. The sensitivity against culture was significantly higher with the concentration method (80%) than with the classical direct smear method (57%). However, when sputum is not adequate (with high number of squamous epithelial cells, meaning upper airway origin), the sensitivity of this method is low. A combination of both methods is proposed to increase the sensitivity of PTB diagnosis in rural hospitals.

Clinical presentation of pulmonary tuberculosis in under 10s and differences in AIDS-related cases: a cohort study of 115 patients.

One hundred and fifteen cases of pulmonary tuberculosis (PTB) in children under 10 were reviewed, including a case-control retrospective study between HIV positive (+ve) and HIV negative (-ve) children. Overall, respiratory symptoms not responding to acute respiratory infection (ARI) protocol and > 10% weight loss or failure to thrive during 3 months were the main presenting symptoms, but chronic fever alone is also common in HIV infected children with PTB. Hylar enlargement is the most frequent radiologic pattern, although lobar infiltrates are common when HIV infection coexists. Gastric lavage culture was an important diagnostic tool but Mantoux test, gastric lavage direct smear and erythrocyte sedimentation rate (ESR) levels, were not helpful in diagnosing PTB. Our findings suggest that when HIV infection is suspected or confirmed, chronic fever and lower lobe infiltrates should also be considered as PTB warning signs.