Two-color planar laser-induced fluorescence thermometry in aqueous solutions

We demonstrate a two-color planar laser-induced fluorescence technique for obtaining two-dimensional temperature images in water. For this method, a pulsed Nd:YAG laser at 532 nm excites a solution of temperature-sensitive rhodamine 560 and temperature-insensitive sulforhodamine 640. The resulting emissions are optically separated through filters and detected via a charged-couple device (CCD) camera system. A ratio of the two images yields temperature images independent of incident irradiance. An uncertainty in temperature of +/- 1.4 degrees C is established at the 95% confidence interval.     

Influence of virtual objects' shadows and lighting coherence on distance perception in optical see‐through augmented reality

This paper focuses on how virtual objects' shadows as well as differences in alignment between virtual and real lighting influence distance perception in optical see‐through (OST) augmented reality (AR). Four hypotheses are proposed: (H1) Participants underestimate distances in OST AR; (H2) Virtual objects' shadows improve distance judgment accuracy in OST AR; (H3) Shadows with different realism levels have different influence on distance perception in OST AR; (H4) Different levels of lighting misalignment between real and virtual lights have different influence on distance perception in OST AR scenes. Two experiments were designed with an OST head mounted display (HMD), the Microsoft HoloLens. Participants had to match the position of a virtual object displayed in the OST‐HMD with a real target. Distance judgment accuracy was recorded under the different shadows and lighting conditions. The results validate hypotheses H2 and H4 but surprisingly showed no impact of the shape of virtual shadows on distance judgment accuracy thus rejecting hypothesis H3. Regarding hypothesis H1, we detected a trend toward underestimation; given the high variance of the data, more experiments are needed to confirm this result. Moreover, the study also reveals that perceived distance errors and completion time of trials increase along with targets' distance.     

Dynamic experimentation on the confocal laser scanning microscope: application to soft-solid, composite food materials

Confocal laser scanning microscopy (CLSM) is used to follow the dynamic structural evolution of several phase-separated mixed biopolymer gel composites. Two protein/polysaccharide mixed gel systems were examined: gelatin/maltodextrin and gelatin/agarose. These materials exhibit 'emulsion-like' structures, with included spherical particles of one phase (i.e. polymer A) within a continuous matrix of the second (i.e. polymer B). Compositional control of these materials allows the phase order to be inverted (i.e. polymer B included and polymer A continuous), giving four basic variants for the present composites. Tension and compression mechanical tests were conducted dynamically on the CLSM, with crack/microstructure interactions investigated using a notched compact tension geometry. Gelatin/maltodextrin composites exhibit a 'pseudo-yielding' stress/strain response in both tension and compression, when the gelatin-rich phase is continuous, which was attributed to debonding of the particle/matrix interface. This behaviour is significantly less apparent for both the gelatin/agarose composites, and the maltodextrin continuous gelatin/maltodextrin composites, with these materials responding in a nominally linear elastic manner. Values of the interfacial fracture energy for selected compositions of the two biopolymer systems were determined by 90 degrees peel testing, where a gelatin layer was peeled from either a maltodextrin or agarose substrate. For biopolymer layers 'cast' together, a value of 0.2 +/- 0.2 J m-2 was obtained for the fracture energy of a gelatin/maltodextrin interface, while a significantly higher value of 6.5 +/- 0.2 J m-2 was determined for a gelatin/agarose interface. The interfacial fracture energy of the two mixed systems was also determined following an indirect elastomer composite debonding model. An interfacial fracture energy of approximately 0.25 J m-2 was determined using this approach for the gelatin continuous gelatin/maltodextrin composite, which compares favourably with the value calculated directly by peel testing (i.e. approximately 0.2 J m-2). A somewhat higher value was estimated for the gelatin continuous gelatin/agarose system (1.0-2.0 J m-2), using this model, although there are severe limitations to this approach for this mixed gel system. In the present case, it is believed that the differing mechanical response of the two mixed biopolymer systems, when the gelatin phase is continuous, arises from the order of magnitude difference in interfacial fracture energy. It is postulated that polymer interdiffusion may occur across the interface for the gelatin/agarose system, to a significantly greater extent than for interfaces between gelatin and maltodextrin, resulting in a higher interfacial fracture energy.     

Hybrid organic–inorganic materials for molecular proton memory devices

Molecular storage elements consisting of a stack of a proton conducting layer (PCL) and a proton trapping layer (PTL) are investigated in view of their perspective application to non-volatile proton memories. Experimental studies are conducted on PCL and PTL materials made of poly(methyl methacrylate) (PMMA) with embedded molecules of 12-tungstophosphoric acid (HPW) and 2-aminoanthracene (AA), respectively. Particular emphasis is placed on the thermal processing parameters (temperature and duration) used in material preparation and their optimization for circumventing undesirable phenomena, for the device stability and performance, like reactions between HPW and PMMA and inter-mixing of the PCL and PTL. Transient current measurements performed on metal–insulator–semiconductor devices containing an HPW/PMMA layer allowed the determination of both the concentration and mobility of the protons within this layer. Comparison of the extracted proton concentration (ca. 3.8 × 10¹⁷ protons/cm³) under full polarization conditions with the HPW concentration determined by UV spectroscopy indicates that only 2 protons per ～1000 HPW molecules are mobile and contribute to the current. Finally, the material features of a generic PCL/PTL stacked structure affecting the operation of a molecular proton memory device are examined from a theoretical point of view. Results indicate that the write characteristics of this type of memory such as the magnitude of the memory window and the write speed depend on the thickness, the proton mobility and the proton concentration of the PCL, while the write voltage is mainly determined by the thickness of the PTL. In light of these analyses, it appears that memory windows as large as 2.8 V might be obtained for a 1 ms/3 V write operation regime even in the case of PCL and PTL thicknesses as high as 175 nm. These observations suggest that a PTL/PCL storage element may be well suited in future low-cost, low-power, and non-volatile single-organic transistor memory applications.     

Long-term storage conditions for carriers with denitrifying biomass of the fluidized, methanol-fed denitrification reactor of the Montreal Biodome, and the impact on denitrifying activity and bacterial population

The Montreal Biodome has a denitrification system to stabilize the nitrate concentration in its 3 million liter seawater aquarium. However, this microbial process has failed periodically due to various technical problems. The system can take several weeks to recover its full denitrification capacity. In order to provide the denitrification system with a backup of active biomass, different freezing conditions for the denitrifying biomass were tested. The biomass was conserved for 1 week-17 months at -20 degrees C with and without glycerol or at -80 degrees C with and without glycerol, and the denitrifying activity was tested in batch culture for 140 h periods at various intervals. Our results showed that glycerol was required for fast recovery of the microbial community's denitrifying activity. The -20 degrees C and -80 degrees C conservation temperatures with glycerol gave similar results although there was a short period of nitrite accumulation in the -20 degrees C sample. There were no substantial changes in the microbial community of any of the frozen samples after 17 months of conservation as monitored by denaturing gradient gel electrophoresis. This is the first report on the long-term conservation of a complex denitrifying population by freezing.     

A study of the randomly fluctuating microbial counts in foods and water using the Expanded Fermi Solution as a model

Randomly fluctuating industrial microbial count records, with and without zero counts, were simulated with a version of the Expanded Fermi Solution, originally developed for risk assessment. The basic assumption has been that each individual count is determined by the multiplicative effect of several random factors, which augment or suppress the microbial population size, and in the case of sporadic pathogens, determine the probability of their initial presence too. Records were generated by a series of Monte Carlo simulations in which the factors were specified by ranges and their values chosen randomly within them. The process has been automated and posted as a freely downloadable Wolfram Demonstration on the Internet. The program allows the user to enter and alter the series length, parameters' ranges, and count level deemed dangerous with sliders on the screen. The display includes the chosen factors' ranges, the corresponding generated count record and its histogram, and an estimate of the risk of surpassing the dangerous threshold. Where the record contains no zero counts, the histogram is accompanied by the lognormal distribution, which naturally emerges from the fluctuations' mathematical model. Once the factors are identified and their ranges specified, the method could be used as a tool to analyze, compare, and quantify microbial risks in foods and water.     

Indirect Color Prediction of Amorphous Carbohydrate Melts as a Function of Thermal History

Glassy carbohydrate microcapsules are widely used for the encapsulation of flavors in food applications, and are made using various thermal processes (for example, extrusion). During manufacturing, these carbohydrate melts are held at elevated temperatures and color can form due to nonenzymatic browning reactions. These reactions can negatively or positively affect the color and flavor of microcapsules. The rate of color formation of maltodextrin and maltodextrin/sucrose melts at elevated temperatures was determined spectrophotometrically and was found to follow pseudo zero‐order kinetics. The effect of temperature was adequately modeled by an Arrhenius relationship. Reaction rate constants and Arrhenius parameters were determined for individual wavelengths in the visible range (360 to 700 nm at 1 nm intervals). Transient processes (temperature changes with time) were modeled as a sequence of small isothermal events, and the equivalent thermal history at a reference temperature calculated using the Arrhenius relationship. Therefore, spectral transmittance curves could be predicted with knowledge of the time/temperature relationship. Validation was conducted by subjecting both melts to a transient thermal history. Experimental transmittance spectrum compared favorably against predicted values. These spectra were optionally converted to any desirable color space (for example, CIELAB, XYZ, RGB) or derived parameter (for example, Browning Index). The tool could be used to better control nonenzymatic browning reactions in industrial food processes.     

Self-healing processes in coil-coated cladding studied by the scanning vibrating electrode

The ability of the zinc layer in coil-coated cladding to protect the underlying metal substrate exposed to the environment through a sub-centimeter circular defect was established by using the scanning vibrating electrode technique (SVET). The onset of electrochemical corrosion is observed through the development of local anodes and cathodes in the defective system, with the formation of soluble zinc species. The dissolution process is maintained until a sufficiently high concentration is attained by the metal ions, and their subsequent precipitation inside the holiday blocks the defect as to hinder further corrosion. A self-healing effect was thus observed. The role of zinc salts was confirmed by SEM and EDX observations.