gas density of the retained gas, kg/m 3 gf gas-free simulant density, kg/m 3 s dry density of the sediment particles, kg/m 3 w water density, kg/m 3 s undrained shear strength, Pa avg average retained gas fraction g retained gas fraction init initial retained gas fraction local local retained gas fraction
The low-frequency (100−1250 Hz) acoustic properties of metal− organic framework (MOF) materials were examined in impedance tube experiments. The anomalously high sound transmission loss of FeBTC, quantitatively demonstrated that these prototypical MOFs are absorptive acoustic metamaterials. To the best of our knowledge, this is the first example of MOFs that have been demonstrated to be acoustic metamaterials. Low-frequency acoustic dampening by subwavelength MOF metamaterials is likely due to sound dissipation and absorption facilitated by multiple internal reflections within the microporous framework structure. Modification of MIL-53(Al) with flexible organic linkers clarified that acoustic signatures of the MOFs may be tailored to add or alter certain diagnostic acoustic signatures. These results may be applied to the rational design of lightweight sound-insulating construction materials and acoustic contrast agents for subsurface mapping and monitoring applications at low frequency (100−1250 Hz).
The accumulation of bacteria in surface-attached biofilms can be detrimental to human health, dental hygiene, and many industrial processes. Natural biofilms are soft and often transparent, and they have heterogeneous biological composition and structure over micro- and macroscales. As a result, it is challenging to quantify the spatial distribution and overall intensity of biofilms. In this work, a new method was developed to enhance the visibility and quantification of bacterial biofilms. First, broad-spectrum biomolecular staining was used to enhance the visibility of the cells, nucleic acids, and proteins that make up biofilms. Then, an image analysis algorithm was developed to objectively and quantitatively measure biofilm accumulation from digital photographs and results were compared to independent measurements of cell density. This new method was used to quantify the growth intensity of Pseudomonas putida biofilms as they grew over time. This method is simple and fast, and can quantify biofilm growth over a large area with approximately the same precision as the more laborious cell counting method. Stained and processed images facilitate assessment of spatial heterogeneity of a biofilm across a surface. This new approach to biofilm analysis could be applied in studies of natural, industrial, and environmental biofilms.Graphical abstractA novel photographic method was developed to quantify bacterial biofilms. Broad spectrum biomolecular staining enhanced the visibility of the biofilms. Image analysis objectively and quantitatively measured biofilm accumulation from digital photographs. When compared to independent measurements of cell density the new method accurately quantified growth of Pseudomonas putida biofilms as they grew over time. The graph shows a comparison of biofilm quantification from cell density and image analysis. Error bars show standard deviation from three independent samples. Inset photographs show effect of stainingElectronic supplementary materialThe online version of this article (doi:10.1007/s00216-015-9195-z) contains supplementary material, which is available to authorized users.
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