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Temperature fluctuations during storage and distribution of frozen foods lead to ice recrystallization and microstructural modifications that can affect food quality. Low temperature transitions may occur in frozen foods due to temperature fluctuations, resulting in less viscous and partially melted food matrices. This study systematically investigated the influence of state/phase transitions and temperature fluctuations on ice recrystallization during the frozen storage of salmon fillets. Using a modulated differential scanning calorimeter, we identified the characteristics glass transition temperature (T g ′) of −27°C and the onset temperature for ice crystal melting (T m ′) of −17°C in salmon. The temperature of salmon fillets in sealed plastic trays was lowered to −35°C in a freezer to achieve the glassy state. The temperature (T) of frozen salmon fillets in sealed plastic trays was modulated to achieve a rubbery state (T>T m ′), a partially freeze-concentrated state (T g ′T m ′) due to the increased mobility of unfrozen water compared to the glassy state. The morphological/geometric parameters of ice crystals in frozen salmon stored for 1 month differed significantly from those in 0-day storage. These findings are important to the frozen food industry because they can help optimize storage and distribution conditions and minimize quality loss of frozen salmon due to recrystallization.

Natural and artificial gas hydrates with internal pores of nano to centimeters and weak graincementation have been widely reported, while the detailed formation process of grain-cementing hydrates remains poorly identified. Pore-scale morphology of carbon dioxide (CO 2 ) hydrate formed in a partially brine-saturated porous medium was investigated via X-ray computed microtomography (X-ray CMT). Emphasis is placed on the pore-scale growth patterns of gas hydrate, including the growth of dendritic hydrate crystals on preformed hydrate and water-wetted grains, porous nature of the hydrate phase, volume expansion of more than 200% during the water-to-hydrate phase transformation, preference of unfrozen water wetting hydrophilic minerals, and the relevance to a weak cementation effect on macroscale physical properties. The presented pore-scale morphology and growth patterns of gas hydrate are expected in natural sediment settings where free gas is available for hydrate formation, such as active gas vents, gas seeps, mud volcanoes, permafrost gas hydrate provinces, and CO 2 injected formation for the sake of geologic carbon storage; and in laboratory hydrate samples synthesized from partially brine-saturated sediments or formed from water-gas interfaces.

The concept of a representative elementary volume (REV) provides an effective means of developing macroscopic measures in the description of granular materials. However, due to the difficulties associated with the measurement and characterization of granular microstructure the existence and size of an REV has remained largely conjectural. This study presents a systematic method to examine the characteristics of the REV using X-ray computed tomography images. The 3-D images of spherical glass beads, Silica sand, and Ottawa sand have been characterized using advanced image processing techniques. An interactive computer program is developed to study porosity variation within a sphere with increasing radius from the images of these materials. The porosity variation of Silica sand and Ottawa sand showed three characteristic regions: an initial fluctuation region due to microscopic variations, a constant plateau region, and a region with a monotonic increase/decrease due to heterogeneity. The homogenous medium of glass beads did not show the last region. The results show that for a random packing of spherical glass beads the REV is about two to three times of the identical average diameter. The radius for Silica sand composed mainly of elongated particles is between 5 to 11 times of d50 and for Ottawa sand composed mainly of subrounded particles is between 9 to 16 times of d50.

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The performance of asphalt concrete (AC) mixtures is influenced by its internal structure, which refers to the arrangement of aggregates and their associated air voids. Currently, most of the discussion on the effects of internal structure on AC performance is qualitative. This study proposes computer-automated image analysis procedures to quantify the internal structure of AC. Internal structure is quantified in terms of aggregate orientation, aggregate contacts, and air void distribution. The new procedures are useful tools to describe and compare AC materials produced by different compaction methods and mix designs. The new procedures are used to study the difference in internal structure of AC specimens compacted with the Superpave gyratory compactor (SGC) and the linear kneading compactor (LKC). Specimens compacted with the SGC were found to have aggregates with more preferred orientation and fewer contacts than specimens compacted with the LKC. In addition, SGC specimens were found to have more air voids at the top and bottom, whereas air voids in LKC specimens were found to increase from the top to the bottom.