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The study of flow dynamics in porous media or randomly packed beds is essential because these systems are commonly applied in a wide array of engineering applications, such as thermal energy storage, catalytic reactors for processing and distillation, oil recovery, fuel cells, and pebble bed nuclear reactor cores. The flow mixing and turbulence characteristics in pore-scale regions of an experimental facility composed of randomly packed spheres with an aspect ratio of 4.4 were experimentally investigated in this study. Velocity measurements at several pores in the test facility were conducted by combining the matched-index-of-refraction and time-resolved particle image velocimetry techniques, and these measurements were performed at Reynolds numbers of 490, 1023, and 1555. The results obtained from the velocity measurements in the pore regions revealed different and complex flow patterns depending on the pore geometries. In pore region 1, it was found that a strong axial flow entered the pore and impinged into the sphere’s surface when it encountered another flow entering laterally. These dynamic interactions created a high level of turbulent mixing, a recirculation flow region, and a shear layer, as observed in the computed statistical results for $$u^{\prime }_\mathrm{{rms}}$$ , $$v^{\prime }_\mathrm{{rms}}$$ , and $$u^{\prime }v^{\prime }$$ . In other pore regions, the flow field results exhibited complex interactions among jet flows discharging into the pores from various flow gaps created by neighboring spheres. These mutual interactions between the entering jet flows were found to create highly turbulent mixing regions at the pore’ centers and low-velocity or stagnation-flow regions in the vicinity of the sphere surfaces. Flapping shear layers were also observed when two jet flows with unequal strengths entered the pores. The characteristics of turbulent flow mixing in different pore regions were investigated via the spatiotemporal two-point correlation of fluctuating velocities along the velocity streamlines. This approach mitigated the constraints of the random geometries of pore regions on the extent of spatial separation lengths in the two-point velocity correlations. Using this approach, spatial distributions of integral length scales and convection velocities were estimated along the streamlines within the random geometries of pore regions. It was found that the estimated values of the integral length scales and convection velocities were spatially dependent on the localized flow characteristics within the pores. The integral length scales were found to be less than $$0.4D_\mathrm{{sp}}$$ , experimentally confirming the pore-scale prevalence hypothesis that turbulent structures in porous media are restricted by the pore sizes. In addition, the ratio of the convection velocity to the interstitial velocity (or local velocity magnitude) decreased as the Reynolds number increased.

This work experimentally investigated the flow characteristics in a facility with randomly packed spheres at a low-aspect ratio of 4.4. Velocity fields in the near-wall region and in the pores between spheres were obtained by employing the matched-index-of-refraction (MIR) and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of 340, 520, and 720. From the obtained TR-PIV velocity vector fields, flow characteristics including first- and second-order statistics, such as mean velocity, root-mean-square fluctuating velocity, and Reynolds stress profiles, were computed. The effects of the wall enclosure and Reynolds numbers on the flow patterns were investigated by comparing the computed flow statistics and evaluating two-point cross correlations of the velocities measured adjacent to and far from the wall. Comparisons of the mean velocities, root-mean-square fluctuating velocities, and Reynolds stress component showed an increase in flow mixing and turbulent intensity in the gaps between spheres in the packed bed. The re-circulation-region sizes, however, were found to be independent from an increase in Reynolds numbers. Finally, flow modal decompositions, such as the proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), were applied to the vorticity fields extracted from sub-regions located near and far from the wall to reveal the most dominant POD and DMD flow structures.

Flesh color of watermelon is an agronomically important trait that is predominantly determined by a network of the carotenoid biosynthetic pathway, which also contributes to the nutritional value of the fruit through the health-promoting function of carotenoids. We have identified a key gene, lycopene β-cyclase (LCYB) that may determine canary yellow and red flesh color of watermelon and developed a zero-distance molecular marker that identifies a critical single nucleotide polymorphism (SNP) that distinguishes different alleles of the LCYB gene. Analysis of the flesh color inheritance in segregating populations indicated that a single gene determines the color difference between canary yellow and red flesh in watermelon. The sequence comparison of full-length cDNA of LCYB, which was isolated using degenerate PCR and RACE, identified three SNPs in the coding region of LCYB between canary yellow and red. These SNPs showed perfect co-segregation with flesh color phenotypes. One of the SNPs introduces an amino acid replacement of evolutionarily conserved Phe226 to Val, which may impair the catalytic function of LCYB. This SNP was used to develop a cleaved amplified polymorphic sequence (CAPS) marker, which perfectly cosegregated with flesh color phenotype. Our results strongly suggest that LCYB may be the genetic determinant for canary yellow or red flesh color and our CAPS marker will allow breeders to economically distinguish between canary yellow and red watermelon fruit color at the seedling stage.

A normalized cDNA library was constructed using watermelon flesh mRNA from three distinct developmental time-points and was subtracted by hybridization with leaf cDNA. Random cDNA clones of the watermelon flesh subtraction library were sequenced from the 5' end in order to identify potentially informative genes associated with fruit setting, development, and ripening. One-thousand and forty-six 5'-end sequences (expressed sequence tags; ESTs) were assembled into 832 non-redundant sequences, designated as "EST-unigenes". Of these 832 "EST-unigenes", 254 ( approximately 30%) have no significant homology to sequences published so far for other plant species. Additionally, 168 "EST-unigenes" ( approximately 20%) correspond to genes with unknown function, whereas 410 "EST-unigenes" ( approximately 50%) correspond to genes with known function in other plant species. These "EST-unigenes" are mainly associated with metabolism, membrane transport, cytoskeleton synthesis and structure, cell wall formation and cell division, signal transduction, nucleic acid binding and transcription factors, defense and stress response, and secondary metabolism. This study provides the scientific community with novel genetic information for watermelon as well as an expanded pool of genes associated with fruit development in watermelon. These genes will be useful targets in future genetic and functional genomic studies of watermelon and its development.