Engineering of impact ionization characteristics in In0.53Ga0.47As/Al0.48In0.52As superlattice avalanche photodiodes on InP substrate.

We report on engineering impact ionization characteristics of In0.53Ga0.47As/Al0.48In0.52As superlattice avalanche photodiodes (InGaAs/AlInAs SL APDs) on InP substrate to design and demonstrate an APD with low k-value. We design InGaAs/AlInAs SL APDs with three different SL periods (4 ML, 6 ML, and 8 ML) to achieve the same composition as Al0.4Ga0.07In0.53As quaternary random alloy (RA). The simulated results of an RA and the three SLs predict that the SLs have lower k-values than the RA because the electrons can readily reach their threshold energy for impact ionization while the holes experience the multiple valence minibands scattering. The shorter period of SL shows the lower k-value. To support the theoretical prediction, the designed 6 ML and 8 ML SLs are experimentally demonstrated. The 8 ML SL shows k-value of 0.22, which is lower than the k-value of the RA. The 6 ML SL exhibits even lower k-value than the 8 ML SL, indicating that the shorter period of the SL, the lower k-value as predicted. This work is a theoretical modeling and experimental demonstration of engineering avalanche characteristics in InGaAs/AlInAs SLs and would assist one to design the SLs with improved performance for various SWIR APD application.

Determination of Debye temperatures and Lamb-Mössbauer factors for LnFeO3 orthoferrite perovskites (Ln = La, Nd, Sm, Eu, Gd).

Lanthanide orthoferrites have wide-ranging industrial uses including solar, catalytic and electronic applications. Here a series of lanthanide orthoferrite perovskites, LnFeO3 (Ln = La; Nd; Sm; Eu; Gd), prepared through a standard stoichiometric wet ball milling route using oxide precursors, has been studied. Characterisation through x-ray diffraction and x-ray fluorescence confirmed the synthesis of phase-pure or near-pure LnFeO3 compounds. 57Fe Mössbauer spectroscopy was performed over a temperature range of 10 K-293 K to observe hyperfine structure and to enable calculation of the recoil-free fraction and Debye temperature (θ D) of each orthoferrite. Debye temperatures (Ln = La 474 K; Nd 459 K; Sm 457 K; Eu 452 K; Gd 473 K) and recoil-free fractions (Ln = La 0.827; Nd 0.817; Sm 0.816; Eu 0.812; Gd 0.826) were approximated through minimising the difference in the temperature dependent experimental centre shift and theoretical isomer shift, by allowing the Debye temperature and isomer shift values to vary. This method of minimising the difference between theoretical and actual values yields Debye temperatures consistent with results from other studies determined through thermal analysis methods. This displays the ability of variable-temperature Mössbauer spectroscopy to approximate Debye temperatures and recoil-free fractions, whilst observing temperature induced transitions over the temperature range observed. X-ray diffraction and Rietveld refinement show an inverse relationship between FeO6 octahedral volume and approximated Debye temperatures. Raman spectroscopy show an increase in the band positions attributed to soft modes of Ag symmetry, Ag(3) and Ag(5) from La to GdFeO3 corresponding to octahedral rotations and tilts in the [0 1 0] and [1 0 1] planes respectively.

Prevalence of enteric infections among hospitalized patients in two referral hospitals in Ghana.

BACKGROUND: Diarrhea is an important cause of morbidity and mortality worldwide. In Africa and Ghana in particular, it is estimated to contribute directly to 19 and 25% of pediatric mortality among children under 5 years, respectively. METHODS: Surveillance for hospitalized acute diarrheal illness was initiated in November 2010 through October 2012 in a referral hospital in southern Ghana, and a teaching hospital in northern Ghana. Consenting hospitalized patients who met a standardized case definition for acute diarrheal illness provided demographic and epidemiologic data. Stool samples were collected and tested by culture for bacteria and by enzyme immunoassays for a panel of viruses and parasites. RESULTS: A total of 429 patients were enrolled; 216 (50.3%) were under 5 years, and 221 (51.5%) were females. Stool samples were received from 153 patients. Culture isolates included Shigella sp., Salmonella spp., Plesiomonas sp. and Vibrio cholerae. Of 147 samples tested for viruses, 41 (27.9%) were positive for rotaviruses, 11 (7.5%) for astroviruses, 10 (6.8%) for noroviruses, and 8 (5.4%) for adenoviruses. Of 116 samples tested for parasitic infections; 4 (3.4%) were positive for Cryptosporidium sp. and 3 (2.6%) for Giardia lamblia. Of the enrolled patients, 78.8% had taken antibiotics prior to sample collection. CONCLUSIONS: Diarrheal pathogens were identified across all ages, however, predominantly (81%) in the children under 5 years of age. This study also detected high antibiotic use which has the potential of increasing antibiotic resistance. The most common enteric pathogen detected (49.4%) was rotavirus.

The next step in infectious disease: taming bacteria.

Except for immunization programs our warfare with bacteria has always been a frontal assault with antibiotics. In this warfare we win battles, but with every new battle the enemy gets stronger. We need other options. Recent experience suggests two alternatives. First, public health measures designed to control the spread of infectious disease are associated with the selection of less virulent strains of microorganisms. Second, the same selection pressures obtained by public health measures outside the body are brought into play when we inhibit the adherence of bacteria within the body. Two recent studies using food sugars known to inhibit bacterial adherence show long-term benefits best explained by the previously observed decreases in bacterial virulence, following chronic exposure to the respective substances. Cranberry juice selects for less uropathogenic strains of Escherichia coli and xylitol for less caries producing Streptococcus mutans. The ability of these substances to reduce bacterial adherence in the human host has been known for some time, but poorly utilized. Their in vitro ability to decrease virulence has been reported but not clinically studied.

Why the increases in upper respiratory problems?

The incidence of ear infections has roughly tripled in the last 25 years. Sinus infections and allergies also have increased. Asthma, triggered by chronic sinus infections and allergies, has paralleled the increases of otitis. These increases began in the early 1970s when antihistamines, decongestants, and combinations thereof, became available without prescription and were heavily advertised in the growing media of television. These drugs are designed to block the immune system's attempts to wash pollutants and irritants from the nasopharynx. The alternative is helping the immune system with this washing. I have used such a technique in my office for the past three years. Its rationale is discussed as well as my own experience.

Microhardness of provisional fixed prosthodontic materials.

STATEMENT OF PROBLEM: Provisional restorations play a critical role in the success of restorative treatment. Thus, the provisional restoration must maintain its surface integrity throughout the restorative process. PURPOSE: This study evaluated the microhardness of 5 prosthodontic provisional materials. MATERIAL AND METHODS: Cylindrical samples of 3 bis-acryl resin composites (Integrity, Protemp Garant, Temphase) and 2 methyl methacrylate acrylic resins (Jet, Temporary Bridge) were fabricated (n = 5 per material). Specimens were wet-sanded through 600 grit abrasive and stored in artificial saliva at 37 degrees C for a total of 14 days. Baseline Knoop hardness (KHN) was measured 24 hours after specimen fabrication. Three microhardness measurements were obtained from each specimen. Knoop hardness was again recorded after 14 days of storage. RESULTS: ANOVA and Duncan's tests (P<.05) indicated a significant difference between the methyl methacrylate type resins and the bis-acryl resin composites at both time intervals. CONCLUSION: The hardness of most materials (Integrity, Protemp Garant, Jet) decreased over time. All of the bis-acryl resin composite materials exhibited superior microhardness over traditional methyl methacrylate (Jet, Temporary Bridge) resins.

Colorimetric assessment of laser and home bleaching techniques.

PURPOSE: This study recorded in vitro color change of three tooth bleaching techniques that included laser-activated hydrogen peroxide and two concentrations of carbamide peroxide. MATERIALS AND METHODS: Forty extracted human central incisors were exposed to argon laser-activated 35% H2O2, 10% carbamide peroxide, or 20% carbamide peroxide. A fourth group (control) did not receive any bleach treatment (n = 10/group). Commission International de l'Eclariage (CIE) L*a*b* coordinates were recorded prior to bleaching (baseline), at 1 week, and at 2 weeks. The color difference (delta E*ab) between baseline and subsequent measurements was calculated. RESULTS: The control group did not demonstrate significant color difference over time (p > .05). The laser group was not statistically different from the control group (p > .01). The color difference of the 10% and 20% carbamide peroxide groups was statistically different from the control group (p < .01). CLINICAL SIGNIFICANCE: Exposure to 20% carbamide peroxide produced the greatest perceivable change in color. The recommended one-time application of laser-activated hydrogen peroxide did not demonstrate any perceivable color change. The clinician should be aware that additional or longer applications may be required.

Biosafety and antibody responses of adult bison bulls after vaccination with Brucella abortus strain RB51.

OBJECTIVE: To evaluate clearance, antibody responses, potential shedding, and histologic lesions in reproductive tissues of adult bison bulls after vaccination with Brucella abortus strain RB51. ANIMALS: 61 two- and 3-year-old bison bulls. PROCEDURE: 12 bison bulls were vaccinated s.c. with B abortus strain RB51, 3 were inoculated s.c. with 0.15 M NaCl, and antibody responses were evaluated. Various specimens were obtained to evaluate bacterial shedding. Four vaccinates and 1 control were necropsied 10, 20, and 30 weeks after vaccination. In a separate experiment, bison bulls were vaccinated s.c. with 0.15 M NaCl, or by hand or ballistically with strain RB51. Antibody responses were monitored 6 weeks after vaccination and during necropsy 13 weeks after vaccination. Tissue specimens obtained during necropsy from both studies were evaluated bacteriologically and histologically. RESULTS: Strain RB51 was recovered at various times from semen of 3 of 12 vaccinated bison bulls in experiment 1. During necropsy, strain RB51 was recovered 10 and 20, but not 30, weeks after vaccination. In experiment 2, strain RB51 was recovered from lymphoid tissues of hand- and ballistic-vaccinated bison bulls during necropsy. In both experiments, microscopic lesions in testes, epididymis, and seminal vesicles were minimal and did not differ between strain RB51-vaccinated and saline-inoculated bison bulls. CONCLUSIONS AND CLINICAL RELEVANCE: Strain RB51 does not induce relevant inflammatory lesions in reproductive tissues of adult bison bulls. Shedding of strain RB51 in semen may be transient in some bison bulls; however, the importance of this observation is unknown.