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Understanding the engineering properties of hydrate-bearing sands (HBS) is the key to assessing the safety during the exploitation of natural gas hydrates. The formation and presence of hydrates in pore spaces are complicated, yet the HBS specimens with different hydrate morphologies have not been precisely tested due to the difficulty in controlling the hydrate formation in the laboratory. In this study, the discrete element method (DEM) is used to create HBS models containing pore-filling, cementing, load-bearing, grain-coating, and patchy hydrates. A series of HBS specimens with different hydrate morphologies and hydrate saturations ranging from 0 to 40% are tested by simulating biaxial compression tests. The numerical results show that the shear strength is slightly but the secant modulus is significantly influenced by the hydrate morphology. The shear strength and secant modulus of HBS increase with hydrate saturation regardless of the hydrate morphology. Further relationships are established between the micro mechanical analyses of the evolution of bonds and contact-type-related contributions and the macro mechanical properties of HBS. These DEM results can provide lower and upper limits for HBS, which are beneficial for further understanding the mechanical responses of HBS with complex hydrate morphologies. [ABSTRACT FROM AUTHOR]

Aim: Prolonged postoperative ileus (PPOI) occurs in around 15% of patients after major abdominal surgery, posing a significant clinical and economic burden. Significant fluid and electrolyte changes may occur peri‐operatively, potentially contributing to PPOI; however, this association has not been clearly elucidated. A joint clinical‐theoretical study was undertaken to evaluate peri‐operative electrolyte concentration trends, their association with ileus, and predicted impact on bioelectrical slow waves in interstitial cells of Cajal (ICC) and smooth muscle cells (SMC). Methods: Data were prospectively collected from 327 patients undergoing elective colorectal surgery. Analyses were performed to determine associations between peri‐operative electrolyte concentrations and prolonged ileus. Biophysically based ICC and SMC mathematical models were adapted to evaluate the theoretical impacts of extracellular electrolyte concentrations on cellular function. Results: Postoperative day (POD) 1 calcium and POD 3 chloride, sodium were lower in the PPOI group (p < 0.05), and POD3 potassium was higher in the PPOI group (p < 0.05). Deficits beyond the reference range in PPOI patients were most notable for sodium (Day 3: 29.5% ileus vs. 18.5% no ileus, p = 0.04). Models demonstrated an 8.6% reduction in slow‐wave frequency following the measured reduction in extracellular NaCl on POD5, with associated changes in cellular slow‐wave morphology and amplitude. Conclusion: Low serum sodium and chloride concentrations are associated with PPOI. Electrolyte abnormalities are unlikely to be a primary mechanism of ileus, but their pronounced effects on cellular electrophysiology predicted by modeling suggest these abnormalities may adversely impact motility recovery. Resolution and correction of electrolyte abnormalities in ileus may be clinically relevant. [ABSTRACT FROM AUTHOR]

Motility of the gastrointestinal (GI) tract is governed by a number of physiological mechanisms, including the bioelectrical slow-wave generated by the interstitial cells of Cajal, and innervation provided by the enteric nerves. Multi-channel mapping techniques involve the recording of both the temporal and spatial profiles of the physiological activities of the GI tract. The techniques have generated considerable evidence demonstrating the associations between slow-wave dysrhythmias, calcium transients, dysmotility and loss of digestive functions. This review highlights notable recent developments in GI multi-channel mapping techniques. [ABSTRACT FROM AUTHOR]