Support-Free Infiltration of Selective Laser Sintered (SLS) Silicon Carbide Preforms

Non-metallic objects are often difficult to manufacture due to high melting temperatures, poor sinterability, limited ductility, and difficulty in machining. Freeform fabrication techniques coupled with liquid infiltration offer a cost-effective and rapid manufacturing mechanism for composite parts with complex geometry and adequate properties. Selective laser sintered (SLS) silicon carbide (SiC) preforms infiltrated with liquid silicon develop localized infiltrant overextrusions onto surfaces and at surface irregularities. Several shrinkage mechanisms including densification were studied as possible causes of these overfilling extrusions, and the results are discussed below. This research was supported by NSF Grant Number DMI-0522176.Mechanical Engineerin

Selective Laser Sintering of Quartz Powder

This research describes the feasibility of fusing quartz powder by Selective Laser Sintering (SLS). SLS is a method of rapid prototyping three-dimensional objects from a computer-aided design database. The effects of different processing parameters, including powder size, laser power and scan mte were explored. Single and multiple layer specimens have been made. The resulting structures were evaluated using SEM and the density of the multiple-layer structure was detected by a geometrical mass/volume technique. It was determined that particle size was the dominant variable affecting part quality. Smaller and spherical unifonn particles are preferred. Future work will concentrate on optimizing powder size and shape and higher laser power.Mechanical Engineerin

Effect of In-Plane Voiding on the Fracture Behavior of Laser Sintered Polyamide

The primary contributors to poor mechanical properties in polyamide materials used during Selective Laser Sintering® are qualified. Methods to quantify the decreased mechanical properties, including Scanning Electron Microscopy (SEM) of fracture surfaces, are compared against each other and against mechanical properties of components fabricated using multiple process parameters. Of primary interest are Ultimate Tensile Strength (UTS) and Elongation at Break (EOB) of tensile specimens fabricated under conditions that produce varying degrees of ductile and brittle fracture.Mechanical Engineerin

Multiple material systems for selective beam sintering

A method and apparatus for selectively sintering a layer of powder to produce a part comprising a plurality of sintered layers. The apparatus includes a computer controlling a laser to direct the laser energy onto the powder to produce a sintered mass. The computer either determines or is programmed with the boundaries of the desired cross-sectional regions of the part. For each cross-section, the aim of the laser beam is scanned over a layer of powder and the beam is switched on to sinter only the powder within the boundaries of the cross-section. Powder is applied and successive layers sintered until a completed part is formed. Preferably, the powder comprises a plurality of materials having different dissociation or bonding temperatures. The powder preferably comprises blended or coated materials.Board of Regents, University of Texas Syste

Preferences and skills of Indian public sector teachers

With a sample of 700 future public sector primary teachers in India, a Discrete Choice Experiment is used to measure job preferences, particularly regarding location. General skills are also tested. Urban origin teachers and women are more averse to remote locations than rural origin teachers and men respectively. Women would require a 26-73 percent increase in salary for moving to a remote location. The results suggest that existing caste and gender quotas can be detrimental for hiring skilled teachers willing to work in remote locations. The most preferred location is home, which supports decentralised hiring, although this could compromise skills

Abscess of adrenal gland caused by disseminated subacute Nocardia farcinica pneumonia. A case report and mini-review of the literature

<p>Abstract</p> <p>Background</p> <p>Infections caused by <it>Nocardia farcinica </it>are uncommon and show a great variety of clinical manifestations in immunocompetent and immunocompromised patients. Because of its unspecific symptoms and tendency to disseminate it may mimic the clinical symptoms and radiologic findings of a tumour disease and the diagnosis of nocardiosis can easily be missed, because there are no characteristic symptoms.</p> <p>Case presentation</p> <p>We present a case of an adrenal gland abscess caused by subacute disseminated <it>N. farcinica </it>pneumonia.</p> <p>Conclusion</p> <p>An infection with <it>N. farcinica </it>is potentially lethal because of its tendency to disseminate -particularly in the brain- and its high resistance to antibiotics. Awareness of this differential diagnosis allows early and appropriate treatment to be administered.</p

Over-expression of adenosine deaminase in mouse podocytes does not reverse puromycin aminonucleoside resistance

<p>Abstract</p> <p>Background</p> <p>Edema in nephrotic syndrome results from renal retention of sodium and alteration of the permeability properties of capillaries. Nephrotic syndrome induced by puromycin aminonucleoside (PAN) in rats reproduces the biological and clinical signs of the human disease, and has been widely used to identify the cellular mechanisms of sodium retention. Unfortunately, mice do not develop nephrotic syndrome in response to PAN, and we still lack a good mouse model of the disease in which the genetic tools necessary for further characterizing the pathophysiological pathway could be used. Mouse resistance to PAN has been attributed to a defect in glomerular adenosine deaminase (ADA), which metabolizes PAN. We therefore attempted to develop a mouse line sensitive to PAN through induction of normal adenosine metabolism in their podocytes.</p> <p>Methods</p> <p>A mouse line expressing functional ADA under the control of the podocyte-specific podocin promoter was generated by transgenesis. The effect of PAN on urinary excretion of sodium and proteins was compared in rats and in mice over-expressing ADA and in littermates.</p> <p>Results</p> <p>We confirmed that expression of ADA mRNAs was much lower in wild type mouse than in rat glomerulus. Transgenic mice expressed ADA specifically in the glomerulus, and their ADA activity was of the same order of magnitude as in rats. Nonetheless, ADA transgenic mice remained insensitive to PAN treatment in terms of both proteinuria and sodium retention.</p> <p>Conclusions</p> <p>Along with previous results, this study shows that adenosine deaminase is necessary but not sufficient to confer PAN sensitivity to podocytes. ADA transgenic mice could be used as a background strain for further transgenesis.</p