Optically Transparent Lead Halide Perovskite Polycrystalline Ceramics

We utilize room-temperature uniaxial pressing at applied loads achievable with low-cost, laboratory-scale presses to fabricate freestanding CH3NH3PbX3 (X- = Br-, Cl-) polycrystalline ceramics with millimeter thicknesses and optical transparency up to ∼70% in the infrared. As-fabricated perovskite ceramics can be produced with desirable form factors (i.e., size, shape, and thickness) and high-quality surfaces without any postprocessing (e.g., cutting or polishing). This method should be broadly applicable to a large swath of metal halide perovskites, not just the compositions shown here. In addition to fabrication, we analyze microstructure-optical property relationships through detailed experiments (e.g., transmission measurements, electron microscopy, X-ray tomography, optical profilometry, etc.) as well as modeling based on Mie theory. The optical, electrical, and mechanical properties of perovskite polycrystalline ceramics are benchmarked against those of single-crystalline analogues through spectroscopic ellipsometry, Hall measurements, and nanoindentation. Finally, γ-ray scintillation from a transparent MAPbBr3 ceramic is demonstrated under irradiation from a 137Cs source. From a broader perspective, scalable methods to produce freestanding polycrystalline lead halide perovskites with comparable properties to their single-crystal counterparts could enable key advancements in the commercial production of perovskite-based technologies (e.g., direct X-ray/γ-ray detectors, scintillators, and nonlinear optics).

Photothermal Optical Beam Steering Using Large Deformation Multi-Layer Thin Film Structures

Photothermal actuation of microstructures remains an active area of research for microsystems that demand electrically isolated, remote, on-chip manipulation. In this study, large-deformation structures constructed from thin films traditional to microsystems were explored through both simulation and experiment as a rudimentary means to both steer and shape an incident light beam through photothermal actuation. A series of unit step infrared laser exposures were applied at increasing power levels to both uniformly symmetric and deliberately asymmetric absorptive structures with the intent of characterizing the photothermal tilt response. The results indicate that a small angle (<4° at ~74 W/cm²) mechanical tilt can be instantiated through central placement of an infrared beam, although directional control appears highly sensitive to initial beam placement. Greater responsivity (up to ~9° mechanical tilt at ~54 W/cm²) and gross directional control was demonstrated with an asymmetrical absorptive design, although this response was accompanied by a large amount (~5–10°) of mechanical tilt burn-in and drift. Rigorous device cycling remains to be explored, but the results suggest that these structures, and those similar in construction, can be further matured to achieve controllable photoactuation suitable for optical beam control or other applications.

Large arrays and properties of 3-terminal graphene nanoelectromechanical switches

Large arrays of 3-terminal nanoelectromechanical graphene switches are fabricated. The switch is designed with a novel geometry that leads to low actuation voltages and improved mechanical integrity, while reducing adhesion forces, which improves the reliability of the switch. A finite element model including non-linear electromechanics is used to simulate the switching behavior and to deduce a scaling relation between the switching voltage and device dimensions.

Detection of antibodies to Trypanosoma cruzi among blood donors in the southwestern and western United States. II. Evaluation of a supplemental enzyme immunoassay and radioimmunoprecipitation assay for confirmation of seroreactivity

BACKGROUND

Chagas' disease, caused by the protozoan parasite Trypanosoma cruzi, is endemic to Latin America and may be transmitted in the United States via blood donated by infected immigrants. Blood-borne pathogens such as T. cruzi require supplemental testing for confirmation of seroreactivity.

STUDY DESIGN AND METHODS

A study was undertaken to determine an optimal scheme for confirmation of seroreactivity in repeatedly reactive samples identified by the Chagas antibody enzyme immunoassay (EIA). The procedure for initial confirmation involves three purified antigens coated onto three separate polystyrene beads and uses an EIA format. If the sample is reactive with two of three or three of three antigens, it is confirmed as seroreactive. If none or one of three beads is reactive, the sample is indeterminate and subjected to a radioimmunoprecipitation assay (RIPA). The RIPA must demonstrate characteristic bands at 32, 34, and 90 kDa.

RESULTS

When tested with sera from persons with potentially cross-reactive diseases (n = 39) or against a presumed negative population from southeast Wisconsin (n = 289), the confirmatory EIA had a specificity of 100 percent. Sensitivity was 100 percent (28/28) with xenodiagnosis-positive sera and 97.6 percent (80/82) with chagasic sera from Latin America. The RIPA showed a specificity of 100 percent in EIA-nonreactive samples (n = 100) and a sensitivity of 100 percent with both xenodiagnosis-positive (28/28) and chagasic (82/82) sera.

CONCLUSION

The confirmatory EIA and the RIPA together provide a highly specific and sensitive means of confirming seroreactivity for antibodies to T. cruzi.

Detection of antibodies to Trypanosoma cruzi among blood donors in the southwestern and western United States. I. Evaluation of the sensitivity and specificity of an enzyme immunoassay for detecting antibodies to T. cruzi

BACKGROUND

Chagas' disease or American trypanosomiasis, caused by infection with Trypanosoma cruzi, is a significant health problem in Latin America. In the United States, transfusions of T. cruzi-contaminated blood from Latin American immigrants may represent the major source of Chagas' disease.

STUDY DESIGN AND METHODS

A new enzyme immunoassay (EIA) for the detection of antibody to T. cruzi was evaluated in the sera of blood donors from the southwestern and western regions of the United States. Serum samples had been screened and were negative for all tests required. Specimens that were repeatedly reactive in the Chagas antibody EIA were analyzed for seroreactivity by a confirmatory EIA and by radioimmunoprecipitation assay.

RESULTS

Fourteen of the 13,309 donor samples (0.105%) were confirmed as being positive for antibody to T. cruzi. The Chagas antibody EIA showed improved sensitivity over the Chagas IgG enzyme-linked immunosorbent assay and two indirect hemagglutination assays. The Chagas antibody EIA had a specificity of 99.98 percent with negative samples. The sensitivity of the Chagas antibody EIA was 100 percent (80/80) in xenodiagnosed specimens and 100 percent (50/50) in specimens positive by consensus (i.e., reactive in EIA, indirect hemagglutination assay, and immunofluorescence assays).

CONCLUSION

This Chagas antibody EIA meets the need for accurate and rapid identification of seroreactive samples in low-prevalence or endemic populations.

Comparison of aztreonam and tobramycin in the treatment of lower respiratory tract infections caused by gram-negative bacilli

A comparison of aztreonam and tobramycin was carried out in 49 hospitalized patients with lower respiratory tract infections caused by gram-negative bacilli. Patients were randomly assigned to the treatment drug. Clindamycin was given concomitantly until the pathogen was identified and the presence of a gram-positive microorganism was ruled out. Samples of sputum were obtained for culture from the lung parenchyma by deep expectoration or transtracheal aspiration. A pathogen was defined as an organism that showed heavy growth and predominated in the culture. Pseudomonas aeruginosa was the most frequently isolated pathogen, followed by Haemophilus influenzae and Proteus mirabilis. A variety of less common pathogens were represented. Thirty-five patients were treated with intravenous aztreonam (1-2 g every 8 hr) and 14 with intravenous tobramycin (3-5 mg/kg per day) until they were afebrile and sputum cultures had been free of the pathogen for 48 hr. The minimum duration of treatment was five days. In the aztreonam group, only two (5%) of the 37 gram-negative pathogens--one P. aeruginosa and one Escherichia coli--persisted. In the tobramycin group, seven (50%) of the 14 pathogens persisted. Clinical response paralleled microbiologic response. Adverse effects in both treatment groups were minor and transient. In this trial aztreonam was effective and safe for treatment of lower respiratory tract infections caused by P. aeruginosa and a variety of other gram-negative bacilli.

Clinical evaluation of cefotetan in the treatment of lower respiratory tract infections

Cefotetan, a new cephamycin antibiotic, was evaluated for the treatment of lower respiratory tract infections. Intravenous cefotetan (2 g every 12 h) was administered for 4 to 8 days (mean, 5.8 days) to 56 hospitalized adult patients. Of the 41 evaluable patients, the clinical response was satisfactory in 38 (93%) and the bacteriological response was satisfactory in 36 (88%). The drug was well tolerated, and there were minimal complaints or changes in clinical laboratory values. From these preliminary results, cefotetan appears to be safe and effective for the treatment of lower respiratory tract infections.