Modeling of Free Chlorine Consumption and Escherichia coli O157:H7 Cross‐Contamination During Fresh‐Cut Produce Wash Cycles

Controlling the free chlorine (FC) availability in wash water during sanitization of fresh produce enhances our ability to reduce microbial levels and prevent cross‐contamination. However, maintaining an ideal concentration of FC that could prevent the risk of contamination within the wash system is still a technical challenge in the industry, indicating the need to better understand wash water chemistry dynamics. Using bench‐scale experiments and modeling approaches, we developed a comprehensive mathematical model to predict the FC concentration during fresh‐cut produce wash processes for different lettuce types (romaine, iceberg, green leaf, and red leaf), carrots, and green cabbage as well as Escherichia coli O157:H7 cross‐contamination during fresh‐cut iceberg lettuce washing. Fresh‐cut produce exudates, as measured by chemical oxygen demand (COD) levels, appear to be the primary source of consumption of FC in wash water, with an apparent reaction rate ranging from L/mg·min for all produce types tested, at stable pH levels (6.5 to 7.0) in the wash water. COD levels increased over time as more produce was washed and the lettuce type impacted the rate of increase in organic load. The model parameters from our experimental data were compared to those obtained from a pilot‐plant scale study for lettuce, and similar reaction rate constant (5.38 × 10^-4 L/mg·min) was noted, supporting our hypothesis that rise in COD is the main cause of consumption of FC levels in the wash water. We also identified that the bacterial transfer mechanism described by our model is robust relative to experimental scale and pathogen levels in the wash water. Finally, we proposed functions that quantify an upper bound on pathogen levels in the water and on cross‐contaminated lettuce, indicating the maximum potential of water‐mediated cross‐contamination. Our model results could help indicate the limits of FC control to prevent cross‐contamination during lettuce washing.     

Thermopower of Mesoscopic Normal-metal/Superconductor Heterostructures

Measurements of micron-size doubly connected normal-Metal/superconductor (NS) heterostructures show athermoelectric response which oscillates as a function ofmagnetic field, with a fundamental period corresponding to oneflux quantum h/2e through the area of the loop. Theoscillations of the thermopower are either symmetric orantisymmetric with respect to magnetic field, depending on thetopology of the sample. The temperature dependence of theamplitude of the oscillations shows a minimum at a temperatureof 0.14 K, although this nonmonotonic behavior doesnot appear to be related to the reentrance effect recentlyobserved in the electrical transport properties of NSstructures.     

Altering the ordering and disordering of a triangular nanographene at room temperature

Molecular self-organization has the potential to serve as an efficient and versatile tool for the spontaneous creation of low-dimensional nanostructures on surfaces. We demonstrate how the subtle balance between intermolecular interactions and molecule-surface interactions can be altered by modifying the environment or through manipulation by means of the tip in a scanning tunnelling microscope (STM) at room temperature. We show how this leads to the distinctive ordering and disordering of a triangular nanographene molecule, the trizigzag-hexa-peri-hexabenzocoronenes-phenyl-6 (trizigzagHBC-Ph6), on two different surfaces: graphite and Au(111). The assembly of submonolayer films on graphite reveals a sixfold packing symmetry under UHV conditions, whereas at the graphite-phenyloctane interface, they reorganize into a fourfold packing symmetry, mediated by the solvent molecules. On Au(111) under UHV conditions in the multilayer films we investigated, although disorder prevails with the molecules being randomly distributed, their packing behaviour can be altered by the scanning motion of the tip. The asymmetric diode-like current-voltage characteristics of the molecules are retained when deposited on both substrates. This paper highlights the importance of the surrounding medium and any external stimulus in influencing the molecular organization process, and offers a unique approach for controlling the assembly of molecules at a desired location on a substrate.     

Photoinducible Oncometabolite Detection

Dysregulated metabolism can fuel cancer by altering the production of bioenergetic building blocks and directly stimulating oncogenic gene-expression programs. However, relatively few optical methods for the direct study of metabolites in cells exist. To address this need and facilitate new approaches to cancer treatment and diagnosis, herein we report an optimized chemical approach to detect the oncometabolite fumarate. Our strategy employs diaryl tetrazoles as cell-permeable photoinducible precursors to nitrileimines. Uncaging these species in cells and cell extracts enables them to undergo 1,3-dipolar cycloadditions with endogenous dipolarophile metabolites such as fumarate to form pyrazoline cycloadducts that can be readily detected by their intrinsic fluorescence. The ability to photolytically uncage diaryl tetrazoles provides greatly improved sensitivity relative to previous methods, and enables the facile detection of dysregulated fumarate metabolism through biochemical activity assays, intracellular imaging, and flow cytometry. Our studies showcase an intersection of bioorthogonal chemistry and metabolite reactivity that can be applied for biological profiling, imaging, and diagnostics.     

Dimensionless Empirical Model to Correlate Pharmaceutical Compound Solubility in Supercritical Carbon Dioxide

The accurate experimental determination of pharmaceutical compound solubilities at various temperature and pressure ranges in supercritical carbon dioxide (ScCO₂) is a challenging and time‐consuming task. Therefore, prediction or correlations of solute solubilities are essential for implementation of ScCO₂ technologies to pharmaceutical industries. Solubilities of 41 pharmaceutical compounds in ScCO₂ are correlated by an empirical model, which is developed based on the degree of freedom analysis. Its correlating ability is compared with existing solubility models elaborated by other authors and evaluated in terms of global mean absolute relative deviation, sum of squares due to error, root mean square deviation, R², and Adj. R². The proposed model is found to correlate better than existing models.     

Proton‐exchange membranes via the grafting of styrene and acrylic acid onto fluorinated ethylene propylene copolymer by a preirradiation technique. III. Thermal and mechanical properties of the membranes and their sulfonated derivatives

Polymer electrolyte membranes were prepared via the grafting of styrene and acrylic acid onto fluorinated ethylene propylene copolymer with a preirradiation technique and subsequent sulfonation. The thermal and mechanical properties of the grafted membranes and their sulfonated derivatives were dependent on the degree of grafting. The grafted membranes showed a two‐step degradation pattern, whereas their sulfonated derivatives showed a three‐step degradation pattern. The glass‐transition temperature and crystallinity percentage of the membranes were determined with differential scanning calorimetry. With an increase in the degree of grafting and sulfonation, the glass‐transition temperature increased, whereas the crystallinity percentage decreased. The tensile strength and elongation decreased with the degree of grafting and sulfonation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1418–1425, 2005     

Regulation of Charge Carrier Dynamics in ZnO Microarchitecture‐Based UV/Visible Photodetector via Photonic‐Strain Induced Effects

A feasible, morphological influence on photoresponse behavior of ZnO microarchitectures such as microwire (MW), coral‐like microstrip (CMS), fibril‐like clustered microwire (F‐MW) grown by one‐step carrier gas/metal catalyst “free” vapor transport technique is reported. Among them, ZnO F‐MW exhibits higher photocurrent (I_Ph) response, i.e., I_{Ph/ZnO F‐MW} > I_{Ph/ZnO CMS} > I_{Ph/ZnO MW}. The unique structural alignment of ZnO F‐MW has enhanced the I_Ph from 14.2 to 186, 221, 290 µA upon various light intensities such as 0 to 6, 11, 17 mW cm^?2 at λ_{405 nm}. Herein, the nature of the as‐fabricated ZnO photodetector (PD) is also demonstrated modulated by tuning the inner crystals piezoelectric potential through the piezo‐phototronic effect. The I_Ph response of PD decreases monotonically by introducing compressive strain along the length of the device, which is due to the synergistic effect between the induced piezoelectric polarization and photogenerated charge carriers across the metal–semiconductor interface. The current behavior observed at the two interfaces acting as the source (S) and drain (D) is carefully investigated by analyzing the Schottky barrier heights (Φ_SB). This work can pave the way for the development of geometrically modified strain induced performances of PD to promote next generation self‐powered optoelectronic integrated devices and switches.     

Optimization of hybrid laser–TIG welding of 316LN stainless steel using genetic algorithm

Determination of optimum hybrid laser–TIG welding process variables for achieving the maximum depth of penetration (DOP) in type 316LN stainless steel has been carried out using a genetic algorithm (GA). Nd:YAG pulsed laser and the TIG heat source were coupled at the weld pool to carry out hybrid welding. Design of experiments approach was used to generate the experimental design matrix. Bead-on-plate welds were carried out based on the design matrix. The input variables considered were laser power, pulse frequency, pulse duration, and TIG current. The response variable considered was the DOP. Multiple-regression model was developed correlating the process variables with the DOP using the generated data. The regression model was used for evaluating the objective function in GA. GA-based model was developed and it produced a set of solutions. Tournament and roulette wheel selection methods were used during the execution of GA. It was found that both the selection methods identified similar welding process parameters for achieving the maximum DOP. Excellent agreement was observed between the target DOP and the DOP values obtained in the validation experiments during hybrid laser–TIG welding.