Experimental Formation of Marine Abrasion on Bone and the Forensic Postmortem Submergence Interval

Human skeletal remains are frequently recovered from marine environments, where they have undergone months or years of immersion, and decomposition stage is no longer a possible method from which to estimate the postmortem submergence interval (PMSI). Over these longer PMSIs, a common taphonomic alteration that forms is the wearing and rounding of surfaces from marine abrasion, caused by repeated agitation in sediment or against rocks. Little is known about the timing of these changes and how to measure or score the degree of alteration. In a laboratory setting, multiple dry, defleshed bones of white-tailed deer (Odocoileus virginianus) were agitated in saltwater for varying intervals with abrasive sediment (1, 2, 4, 6, 8, and 10 days) and with rocks (5 and 12 days) using a laboratory tumbling device. These were compared to human remains cases from the Office of the Chief Medical Examiner, Boston, MA that had been in the Atlantic Ocean for known intervals. A five-stage (0–4) marine abrasion scoring system was devised for the taphonomic analysis of forensic cases from marine environments to allow for direct comparison among cases. A high degree of correlation between abrasion stage and known PMSI was detected.

Performance Assessment of Shockwaves of Chute Spillways in Large Dams

Spillways are the most important structures of large dams that are responsible for releasing the excessive flood discharge from the reservoir. Although many studies have been performed to determine the flow characteristics over these structures, however, the available information on the shockwaves’ characteristics for spillways’ design is limited. The supercritical flow below the chute piers generates an aerated flow known as shockwaves. Due to the flow interaction with the chute piers, three kinds of standing waves just downstream of the pier, in the middle of the chute, and on the sidewalls are generated. This phenomenon affects the flow domain and its hydraulic characteristics along the chute spillway. The height of the waves increases downstream, where they hit the chute walls and reflect again into the flow to interact together again. The process repeated and intensified downstream in a lozenge shape. The height of these waves can be more than twice the depth flow and thus run over the sidewalls. This is important for the design of chute walls in chute spillways with control gates. In this study, the experimental formation of the shockwaves and their behavior along the chute and their reduction measures are presented. Experiments were conducted on a scaled physical model (1/50) of Kheirabad Dam, Water Research Institute, Iran. It was realized that apart from the geometry of piers and chute spillway, Froude number of flow and gate opening are the main effective parameters on the hydraulic performance of shockwaves’ formation and their development on gated spillways.

Experimental formation of clay-coated sand grains using diatom biofilm exopolymers

In sedimentary environments, clay and sand are segregated by hydrodynamic processes. Yet, clay coats, thin clay envelopes lining sand grains, are abundant in modern and ancient coastal sedimentary deposits. Here, we present laboratory experiments in which we produced clay-coated quartz sands similar to those observed in modern and ancient estuarine sands. These coats were produced at ambient temperature by mixing exopolymeric substances (EPS) derived from intertidal diatom biofilms with clay minerals and quartz reference materials. The imaging of sediment-EPS mixes using cryo–scanning electron microscopy and atomic force microscopy demonstrated that EPS form organic bridges between clay and quartz. The physicochemical properties of the EPS were characterized independently through wet chemical assays and Fourier transform infrared spectroscopy. The results indicated that several EPS components (e.g., proteins, polysaccharides) had a potential to complex with quartz and clay. Our findings provide novel insights in the importance of biofilms in the aggregation of clay and sand. Detrital coats from ancient estuarine sandstones show textural similarities to the experimental clay-EPS complexes and could be considered as biosignatures of biofilm development and EPS production in past environments.

Supplemental Material: Experimental formation of clay-coated sand grains using diatom biofilm exopolymers

AFM and cryo-SEM images of clay-EPS experiments, FTIR spectra of clay-EPS experiments, physico-chemical properties of standard clay minerals, potential mechanisms of interaction between EPS and mineral surfaces, and a list of of FTIR absorption bands in Figure 2.<br>

Supplemental Material: Experimental formation of clay-coated sand grains using diatom biofilm exopolymers

AFM and cryo-SEM images of clay-EPS experiments, FTIR spectra of clay-EPS experiments, physico-chemical properties of standard clay minerals, potential mechanisms of interaction between EPS and mineral surfaces, and a list of of FTIR absorption bands in Figure 2.<br>