Survival, elongation, and elevated tolerance of Salmonella enterica serovar Enteritidis at reduced water activity

Growing microorganisms on dry surfaces, which results in exposure to low water activity (a(w)), may change their normal morphology and physiological activity. In this study, the morphological changes and cell viability of Salmonella enterica serovar Enteritidis challenged to low a(w) were analyzed. The results indicated that exposure to reduced a(w) induced filamentation of the cells. The amount of filamentous cells at a(w) 0.94 was up to 90% of the total number of cells. Surviving filamentous cells maintained their membrane integrity after exposure to low a(w) for 21 days. Furthermore, cells prechallenged to low a(w), obtained with an ionic humectant, demonstrated higher resistance to sodium hypochlorite than control cells. These resistant cells are able to survive disinfection more efficiently and can therefore cause contamination of foods coming in contact with surfaces. This points to the need for increased attention to cleaning of surfaces in household environments and disinfection procedures in processing plants.     

Evaluation of the influences of solution path length and additives concentrations on the solar photo-Fenton degradation of 4-chlorophenol using multivariate analysis

This study reports the photodegradation of 4-chlorophenol (4-CP) in aqueous solution by the photo-Fenton process using solar irradiation. The influence of solution path length, and Fe(NO(3))(3) and H(2)O(2) concentrations on the degradation of 4-CP is evaluated by response surface methodology. The degradation process was monitored by the removal of total organic carbon (TOC) and the release of chloride ion. The results showed a very important role of iron concentration either for TOC removal or dechlorination. On the other hand, a negative effect of increasing solution path length on mineralization was observed, which can be compensated by increasing the iron concentration. This permits an adjustment of the iron concentration according to the irradiation exposure area and path length (depth of a tank reactor). Under optimum conditions of 1.5 mM Fe(NO(3))(3), 20.0 mM H(2)O(2) and 4.5 cm solution path length, 17 min irradiation under solar light were sufficient to reduce a 72 mg CL(-1) solution of 4-CP by 91%.     

Dynamic imaging and tracer kinetic modeling for emission tomography using rotating detectors

When performing dynamic studies using emission tomography the tracer distribution changes during acquisition of a single set of projections. This is particularly true for some positron emission tomography (PET) systems which, like single photon emission computed tomography (SPECT), acquire data over a limited angle at any time, with full projections obtained by rotation of the detectors. In this paper, an approach is proposed for processing data from these systems, applicable to either PET or SPECT. A method of interpolation, based on overlapped parabolas, is used to obtain an estimate of the total counts in each pixel of the projections for each required frame-interval, which is the total time to acquire a single complete set of projections necessary for reconstruction. The resultant projections are reconstructed using traditional filtered backprojection (FBP) and tracer kinetic parameters are estimated using a method which relies on counts integrated over the frame-interval rather than instantaneous values. Simulated data were used to illustrate the technique's capabilities with noise levels typical of those encountered in either PET or SPECT. Dynamic datasets were constructed, based on kinetic parameters for fluoro-deoxy-glucose (FDG) and use of either a full ring detector or rotating detector acquisition. For the rotating detector, use of the interpolation scheme provided reconstructed dynamic images with reduced artefacts compared to unprocessed data or use of linear interpolation. Estimates for the metabolic rate of glucose had similar bias to those obtained from a full ring detector.     

Efficient polarization converter for projection displays

In the waveguiding limit, a twisted nematic liquid crystal cell behaves as an achromatic polarization rotator. We propose and demonstrate the application of such a polarization rotator to convert unpolarized light into linearly polarized light with almost 100% efficiency. This polarization converter has a 2:1 aspect ratio, which is close to the 16:9 ratio for modern televisions. It can be used therefore in a projection display with polarization-dependent light valves such as a liquid crystal light valve. Both transmittive and reflective light valves can be used. The temperature dependence of the achromatic polarization rotator is also studied.     

Performance of a prototype for a large-aperture multipass Nd:glass laser for inertial confinement fusion

The Beamlet is a single-beam prototype of future multibeam megajoule-class Nd:glass laser drivers for inertial confinement fusion. It uses a multipass main amplifier, adaptive optics, and efficient, high-fluence frequency conversion to the third harmonic. The Beamlet amplifier contains Brewster-angle glass slabs with a clear aperture of 39 cm x 39 cm and a full-aperture plasma-electrode Pockels cell switch. It has been successfully tested over a range of pulse lengths from 1-10 ns up to energies at 1.053 mum of 5.8 kJ at 1 ns and 17.3 kJ at 10 ns. A 39-actuator deformable mirror corrects the beam quality to a Strehl ratio of as much as 0.4. The 1.053-mum output has been converted to the third harmonic at efficiencies as high as 80% and fluences as high as 8.7 J/cm(2) for 3-ns pulses.     

Measurements of the phase shift on reflection for low-order infrared Fabry-Perot interferometer dielectric stack mirrors

A simple technique based on a Fizeau interferometer to measure the absolute phase shift on reflection for a Fabry-Perot interferometer dielectric stack mirror is described. Excellent agreement between the measured and predicted phase shift on reflection was found. Also described are the salient features of low-order Fabry-Perot interferometers and the demonstration of a near ideal low-order (1-10) Fabry-Perot interferometer through minimizing the phase dispersion on reflection of the dielectric stack. This near ideal performance of a low-order Fabry-Perot interferometer should enable several applications such as compact spectral imagers for solid and gas detection. The large free spectral range of such systems combined with an active control system will also allow simple interactive tuning of wavelength agile laser sources such as CO(2) lasers, external cavity diode lasers, and optical parametric oscillators.     

Lift-off patterning of thin Au films on Si surfaces with atomic force microscopy

We studied a new lift-off process of thin Au film on silicon surfaces in nanometer-scale, combining anodic oxidation patterning with AFM, deposition of Au thin film on the patterned substrate and chemical etching processes of the Si oxide underneath the Au film. For Au films of thickness of 2-5 nm, the Au films on the Si oxide patterns were left unbroken and bent down to stick to Si surface after the removal of the oxide by the chemical etching. For an Au film of 1 nm in thickness, it was possible to lift-off the Au film on oxide patterns of the lines and dots in nanometer-scale using Si oxide as a sacrificial mask.     

Biosorption of nickel, chromium and zinc by MerP-expressing recombinant Escherichia coli

Escherichia coli hosts able to over-express metal-binding proteins (MerP) originating from Gram-positive (Bacillus cereus RC607) and Gram-negative (Pseudomonas sp. K-62) bacterial strains were used to adsorb Ni(2+), Zn(2+) and Cr(3+) in aqueous solutions. The initial adsorption rate and adsorption capacity were determined to evaluate the performance of the biosorbents. With the expression of MerP protein, the metal adsorption capacity of the recombinant strains for Ni(2+), Zn(2+) and Cr(3+) significantly improved. The cells carrying Gram-positive merP gene (GB) adsorbed Zn(2+) and Cr(3+) at a capacity of 22.3 and 0.98 mmol/g biomass, which is 121% and 72% higher, respectively, over that of the MerP-free host cells. Adsorption capacity of the cells carrying Gram-negative merP gene (GP) also increased 144% and 126% for Zn(2+) and Cr(3+), respectively. Both recombinant strains also exhibited 24% and 5% enhancement in adsorption of Ni(2+) for GB and GP, respectively. The initial adsorption rate of the recombinant biosorbents was also higher than that of the MerP-free host, suggesting an increased metal-binding affinity with MerP expression. Severe cell damage on GB biosorbent was observed after Cr(3+) adsorption, probably due to the metal toxicity effect on the cells.     

Biodegradable quantum dot nanocomposites enable live cell labeling and imaging of cytoplasmic targets

Semiconductor quantum dots (QDs) offer great promise as the new generation of fluorescent probes to image and study biological processes. Despite their superior optical properties, QDs for live cell monitoring and tracking of cytoplasmic processes remain limited due to inefficient delivery methods available, altered state or function of cells during the delivery process and the requirement of surface-functionalized QDs for specific labeling of subcellular structures. Here, we present a noninvasive method to image subcellular structures in live cells using bioconjugated QD nanocomposites. By incorporating antibody-coated QDs within biodegradable polymeric nanospheres, we have designed a bioresponsive delivery system that undergoes endolysosomal to cytosolic translocation via pH-dependent reversal of nanocomposite surface charge polarity. Upon entering the cytosol, the polymer nanospheres undergo hydrolysis thus releasing the QD bioconjugates. This approach facilitates multiplexed labeling of subcellular structures inside live cells without the requirement of cell fixation or membrane permeabilization. As compared to conventional intracellular delivery techniques, this approach allows the high throughput cytoplasmic delivery of QDs with minimal toxicity to the cell. More importantly, this development demonstrates an important rational strategy for the design of a multifunctional nanosystem for biological applications.