Investigation of the reversibility of deformation in silicon sheets

We have investigated the degree to which plastic deformation is reversible in silicon by bending and re-flattening initially defect-free single-crystal Czochralski silicon samples using four-point bending to simulate the deformation experienced during ribbon crystal growth. Optical and scanning electron microscopy of etched sample cross-sections after single bending and bending and re-flattening at 1100° C and 1200° C revealed that the dislocation densities in the re-flattened samples were lower than in singly-bent samples by 60–90%, indicating that dislocations are either being annihilated within the silicon bulk or are exiting the silicon at the free surfaces. There was little evidence of dislocation interaction in the singly-bent single-crystal samples investigated with transmission electron microscopy, so the latter mechanism is more likely. Although the re-flattened specimens have a lower dislocation density, there is little improvement in the minority-carrier diffusion length, measured by electron-beam induced current, which in all cases ranged from 10–20 μm. Since the minority-carrier diffusion length changed little, even with a change in dislocation density from 10⁶ dislocations/cm²–10⁸ dislocations/cm², other defects must be controlling the diffusion length. There is some correlation between dislocation density and minority-carrier diffusion length within a given sample, but this may be due to indirect effects such as generation of point defects by moving dislocations.     

Detection of <Emphasis Type="Italic">Campylobacter</Emphasis> colonies using hyperspectral imaging

The presence of Campylobacter in foods of animal origin is the leading cause of bacterially induced human gastroenteritis. Isolation and detection of Campylobacter in foods via direct plating involves lengthy laboratory procedures including enrichments and microaerobic incubations, which take several days to a week. The incubation time for growing Campylobacter colonies in agar media usually takes 24–48 h. Oftentimes the problem is the difficulty of visually differentiating Campylobacter colonies from non-Campylobacter contaminants that frequently grow together with Campylobacter on many existing agars. In this study, a new screening technique using non-destructive and non-contact hyperspectral imaging was developed to detect Campylobacter colonies in Petri dishes. A reflectance spectral library of Campylobacter and non-Campylobacter contaminants was constructed for characterization of absorption features in wavelengths from 400 to 900 nm and for developing classification methods. Blood agar and Campy-Cefex agar were used as culture media. The study found that blood agar was the better culture medium than Campy-Cefex agar in terms of Campylobacter detection accuracy. Classification algorithms including single-band thresholding, band-ratio thresholding and spectral feature fitting were developed for detection of Campylobacter colonies as early as 24 h of incubation time. A band ratio algorithm using two bands at 426 and 458 nm chosen from continuum-removed spectra of the blood agar bacterial cultures achieved 97–99% of detection accuracy. This research has profound implications for early detection of Campylobacter colonies with high accuracy. Also, the developed hyperspectral reflectance imaging protocol is applicable to other pathogen detection studies.     

Preparation of a hydrophobic recycled jute-based nonwoven using a titanium dioxide/stearic acid coating

This work aims at developing a hydrophobic treatment for jute fiber-based nonwovens. Three solutions of titanium dioxide (TiO₂) nanoparticles were prepared through a sol–gel method by varying the molar ratio of the various constituents. The nonwoven was pretreated with these solutions before being impregnated with different concentrations of stearic acid. The TiO₂ nanoparticles synthesized are amorphous; their size varies with the concentration of ethanol used as a solvent in the sol–gel method. The nanoparticle coating produced on the jute fibers is uniform. The nonwoven wettability was evaluated by measuring its water contact angle and retention time; the nonwoven became hydrophobic at the lowest fatty acid concentration tested. An increase in the stability of the hydrophobicity was observed when the TiO₂ nanoparticle pretreatment was used compared to the application of the stearic acid treatment only. No detrimental effect of the hydrophobic treatment on the nonwoven mechanical performance and thermal stability was observed. These results demonstrate the potential of the TiO₂ nanoparticle/stearic acid treatment as a fast method to provide a stable hydrophobicity to recycled jute-based nonwovens.     

Accumulation of magnetic iron oxide nanoparticles coated with variably sized polyethylene glycol in murine tumors

Iron oxide nanoparticles have found widespread applications in different areas including cell separation, drug delivery and as contrast agents. Due to water insolubility and stability issues, nanoparticles utilized for biological applications require coatings such as the commonly employed polyethylene glycol (PEG). Despite its frequent use, the influence of PEG coatings on the physicochemical and biological properties of iron nanoparticles has hitherto not been studied in detail. To address this, we studied the effect of 333-20,000 Da PEG coatings that resulted in larger hydrodynamic size, lower surface charge, longer circulation half-life, and lower uptake in macrophage cells when the particles were coated with high molecular weight (M(w)) PEG molecules. By use of magnetic resonance imaging, we show coating-dependent in vivo uptake in murine tumors with an optimal coating M(w) of 10,000 Da.     

Development of a selective broth medium for the detection of injured Campylobacter jejuni by capacitance monitoring

The purpose of these studies was to develop a conductimetric method for the rapid detection of Campylobacter jejuni. Numerous basal medium components were analyzed to develop a growth-enhancing broth medium for detection of freeze-injured Campylobacter cells using a conductimetric system. The final medium was composed of a modified Campy-Line agar from which the agar and triphenyltetrazolium chloride were removed and the amino acid, L-arginine was added. Pure isolates of C. jejuni. (frozen and thawed to produce stressed cells) were utilized to test the detection methodology. Monitoring of significant changes in the capacitance signal was found suitable for detection of Campylobacter proliferation. Using stressed pure cultures, Campylobacter growth was repeatedly detected at very low inoculum levels (about one cell per well). There was a direct linear relationship between detection times (DTs) and the initial inoculum level. For example, using a single strain, the mean DT (n = 20) at the 10 CFU/ml inoculum level was 28.6 h, with 100% of the inoculated wells detecting. The mean DTs at the 100, 1,000, and 10,000 CFU/ml inoculum levels were 24.9, 21.4, and 17.0 h, respectively. This study demonstrates that conductimetric methods can be utilized for the rapid detection of C. jejuni.     

Cyclic durability of D16T alloy covered with anodic and microplasmous coatings

Corrosion-protective properties of the anodic and microplasmous D16T alloy coatings obtained according to the previously developed techniques in two variants, namely, with and without the addition of polyurethane filler, which was saturated with a metallic powder, are studied. The effect of the coatings on the cyclic durability of the alloy is estimated. Microplasmous coatings with or without the filler are found to be effective on items made of D16T alloy because they increase the cyclic durability and the corrosion resistance of the alloy.     

Lichen Compounds Restrain Lichen Feeding by Bank Voles <Emphasis Type=Italic>(Myodes glareolus</Emphasis>)

Some lichen compounds are known to deter feeding by invertebrate herbivores. We attempted to quantify the deterring efficiency of lichen compounds against a generalist vertebrate, the bank vole (Myodes glareolus). In two separate experiments, caged bank voles had the choice to feed on lichens with natural or reduced concentrations of secondary compounds. We rinsed air-dry intact lichens in 100% acetone to remove extracellular compounds non-destructively. In the first experiment, pairs of control and rinsed lichen thalli were hydrated and offered to the bank voles. Because the lichens desiccated fast, we ran a second experiment with pairs of ground control and compound-deficient thalli, each mixed with water to porridge. Eight and six lichen species were tested in the first and second experiment, respectively. In the first, bank voles preferred compound-deficient thalli of Cladonia stellaris and Lobaria pulmonaria, but did not discriminate between the other thallus pairs. This was likely a result of deterring levels of usnic and stictic acid in the control thalli. When lichens were served as porridge, significant preference was found for acetone-rinsed pieces of Cladonia arbuscula, C. rangiferina, Platismatia glauca, and Evernia prunastri. The increased preference was caused mainly by lower consumption of control thalli. Grinding and mixing of thallus structures prevented bank voles from selecting thallus parts with lower concentration of secondary compounds and/or strengthened their deterring capacity. We conclude that some lichen secondary compounds deter feeding by bank voles.