Critical Bed Research Articles

An Investigation of Silty Sediment Erodibility Considering the Effects of Upward Seepage and Slope Gradient

The phenomenon of extensive erosion of silty submarine slopes in the Yellow River delta has been well documented in numerous studies. Due to poor drainage and high compressibility, silty sediments are particularly prone to pore pressure buildup and accumulated seepage under wave and current action, which can influence sediment erodibility (e.g., the critical bed shear stress and the erosion rate under various bed shear stresses). To date, there remains a lack of parametric formulation to quantitatively characterize the erodibility of silty sediments with the coupled effects of the hydraulic gradient of upward seepage and the slope gradient. In this study, a series of laboratory experiments were conducted to explore the erodibility of silt sediments from the Yellow River delta under varying hydraulic gradients of upward seepage and slope gradients. The results reveal that both upward seepage and increased slope gradients can enhance the erodibility of silty sediments. Specifically, as the seepage gradient increases from 0.1 to 0.8, the critical Shields parameter required for initiating silty particle motion decreases linearly, with a reduction rate of 0.01 per 0.1 increase in the seepage gradient, independently of changes in slope gradient. Additionally, the erosion coefficient of silty sediments grows exponentially with rising seepage gradients, with its average growth rate accelerating with increasing slope inclination. For flat sediment beds, the erosion coefficient influenced by upward seepage can be up to five times that in the absence of seepage. An empirical formula for calculating the critical Shields parameter and an erosion model incorporating upward seepage gradient and slope effects were developed through multiple regression analysis, providing an experimental basis for numerical simulations of scour in silty submarine slopes under combined waves and currents.

Design of a Thermal Performance Test Equipment for a High-Temperature and High-Pressure Heat Exchanger in an Aero-Engine

For next-generation power systems, particularly aero-gas turbine engines, ultra-light and highly efficient heat exchangers are considered key enabling technologies for realizing advanced cycles. Consequently, the development of efficient and accurate aero-engine heat exchanger test equipment is essential to support future gas turbine heat exchanger advancements. This paper presents the development of a high-pressure and high-temperature (HPHT) heat exchanger test facility designed for aero-engine heat exchangers. The maximum temperature and pressure of the test facility were configured to simulate the conditions of the last-stage compressor of a large civil engine, specifically 1000 K and 5.5 MPa. These conditions were achieved using multiple electric heater systems in conjunction with an air compression system consisting of three turbo compressor units and a reciprocating compressor unit. A commissioning test was conducted using a compact tubular heat exchanger, and the results indicate that the test facility operates stably and that the measured data closely align with the predicted performance of the heat exchanger. A commissioning test of the tubular heat exchanger showed a thermal imbalance of 1.02% between the high-pressure (HP) and low-pressure (LP) lines. This level of imbalance is consistent with the ISO standard uncertainty of ±2.3% for heat dissipation. In addition, CFD simulation results indicated an average deviation of approximately 1.4% in the low-pressure outlet temperature. The close alignment between experimental and CFD results confirms the theoretical reliability of the test bench. The HPHT thermal performance test facility will be expected to serve as a critical test bed for evaluating heat exchangers for current and future gas turbine applications.

Managing Patients With COVID-19 in Armenia Using a Remote Monitoring System: Descriptive Study.

The COVID-19 pandemic has imposed immense stress on global health care systems, especially in low- and middle-income countries (LMICs). Armenia, a middle-income country in the Caucasus region, contended with the pandemic and a concurrent war, resulting in significant demand on its already strained health care infrastructure. The COVID@home program was a multi-institution, international collaboration to address critical hospital bed shortages by implementing a home-based oxygen therapy and remote monitoring program. The objective of this study was to describe the program protocol and clinical outcomes of implementing an early discharge program in Armenia through a collaboration of partner institutions, which can inform the future implementation of COVID-19 remote home monitoring programs, particularly in LMICs or low-resource settings. Seven hospitals in Yerevan participated in the COVID@home program. A web app based on OpenMRS was developed to facilitate data capture and care coordination. Patients meeting eligibility criteria were enrolled during hospitalization and monitored daily while on oxygen at home. Program evaluation relied on data extraction from (1) eligibility and enrollment forms, (2) daily monitoring forms, and (3) discharge forms. Over 11 months, 439 patients were screened, and 221 patients were managed and discharged. Around 94% (n=208) of participants safely discontinued oxygen therapy at home, with a median home monitoring duration of 26 (IQR 15-45 days; mean 32.33, SD 25.29) days. Women (median 28.5, mean 35.25 days) had similar length of stay to men (median 26, mean 32.21 days; P=.75). Despite challenges in data collection and entry, the program demonstrated feasibility and safety, with a mortality rate below 1% and low re-admission rate. Opportunities for operational and data quality improvements were identified. This study contributes practical evidence on the implementation and outcomes of a remote monitoring program in Armenia, offering insights into managing patients with COVID-19 in resource-constrained settings. The COVID@home program's success provides a model for remote patient care, potentially alleviating strain on health care resources in LMICs. Policymakers can draw from these findings to inform the development of adaptable health care solutions during public health crises, emphasizing the need for innovative approaches in resource-limited environments.

Critical care unit bed availability and postoperative outcomes: a multinational cohort study.

Critical care beds are a limited resource, yet research indicates that recommendations for postoperative critical care admission based on patient-level risk stratification are not followed. It is unclear how prioritisation decisions are made in real-world settings and the effect of this prioritisation on outcomes. This was a prespecified analysis of an observational cohort study of adult patients undergoing inpatient surgery, conducted in 274 hospitals across the UK and Australasia during 2017. The primary outcome was postoperative morbidity at day 7. Logistic regression models were used to evaluate the relationship between critical care admission and patient and health system factors. The causal effect of critical care admission on outcome was estimated using variation in critical care occupancy as a natural experiment in an instrumental variable analysis. A total of 19,491 patients from 248 hospitals were eligible for analysis, of whom 2107 were directly admitted to critical care postoperatively. Postoperative morbidity occurred in 2829/19,491 (15%) patients. Increasing surgical risk was associated with critical care admission, as was increased availability of critical care beds (odds ratio (95%CI) 1.04 (1.01-1.06), p = 0.002) per available bed; however, the probability of admission varied significantly between hospitals (median odds ratio 3.05). There was no evidence of a difference in postoperative morbidity with critical care admission (odds ratio (95%CI) 0.91 (0.57-1.45), p = 0.710). Postoperative critical care admission is variable and related to bed availability. Statistical methods that adjust for unobserved confounding lowered the estimates of harm previously reported to have been associated with postoperative critical care admission. Our findings provide a rationale for a clinical trial which would evaluate any potential benefits for postoperative critical care admission for patients in whom there is no absolute indication for admission.

A CFD-DEM investigation into hydraulic transport and retardation response characteristics of drainage pipeline siltation using intelligent model

Siltation of drainage pipelines is a major disaster-causing factor in urban flooding. Owing to critical bed shear stress and the possibility of settlement at the bottom of pipes, there are significant nonlinear differences in the hydraulic transport and retardation response characteristics of siltation particles under different initial flow velocities, siltation degrees, and siltation lengths. Studies on siltation in drainage pipelines lack a comprehensive understanding of the intricate coupling dynamics between siltation particles and water flow, and the regularity governing the siltation transport behaviour under varying water flow conditions remains unclear. To solve these problems, this study constructs computational fluid dynamics and discrete element (CFD-DEM) coupling method and adaptive penalty model for pipeline deposition based on probabilistic settlement function, adaptive genetic algorithm, and bidirectional long short-term memory neural network (PSF-AGA-BLSTM). A three-dimensional transient hydraulic model of pipeline siltation was adopted to clarify the critical bed shear stress of the silt particles, after which an adaptive genetic algorithm with a probability settlement function as fitness was constructed to generate a numerous silt particle sample sets with settlement result labels. Adaptive genetic algorithms were combined with bidirectional long short-term memory neural networks to establish a spatiotemporal adaptive penalisation mechanism for pipeline silt particle transport. The simulation model based on PSF-AGA-BLSTM and CFD-DEM was analysed using simulation and scale tests and was found to have strong robustness and reliability. The results showed that the effects of siltation degree, flow rate, and siltation length on the transport of silt particles were all non-negligible; when the siltation degree exceeded 0.2, the siltation degree had a more significant effect on particle transport than siltation length and flow rate. The transport of silt particles occurred in two phases, rapid growth and steady growth under erosion by water flow. The rate of change in silt length accounted for up to 45% of the reason for silt nudging and silt spreading. The study clarified the hydraulic transport law of silt particles and analyzed the effect of different influencing factors. These efforts provide technical support for subsequent pipe cleaning and maintenance as well as flood prevention and mitigation.

The influence of activated carbon fiber paper structure on adsorption performance of cyclohexane

Activated carbon fibers paper (ACFP), made through wet-laid technology, had exhibited promising adsorption performance compared with granular and powdered activated carbon. This study prepared activated carbon fibers papers with different fibrous structures and investigated the dynamic adsorption performance of thin-layered ACFP against cyclohexane gas. The effects of inter-fiber pore size, dilution degree of activated carbon fibers, and porosity of the paper sheet on the adsorption performance were explored. The Bed Depth Service Time (BDST) model was employed for fitting and calculation, and the Flowdict module in Geodict software was used to analyze the flow field within the paper sheet. The results indicated that the inter-fiber pore size variation of ACFP had no significant effect on its adsorption breakthrough curve against cyclohexane gas. However, as the dilution degree of activated carbon fibers in the ACFP increased, the breakthrough time prolonged, and the adsorption utilization efficiency of activated carbon fibers continuously improved. Furthermore, decrease of ACFP porosity significantly impaired the adsorption performance. When the porosity decreased from 95.4 % to 91.4 %, the breakthrough adsorption capacity decreased from 134 mg/g to 95 mg/g, and the critical bed thickness increased from 0.029 cm to 0.044 cm.

The Removal of As(III) Using a Natural Laterite Fixed-Bed Column Intercalated with Activated Carbon: Solving the Clogging Problem to Achieve Better Performance

Natural laterite fixed-bed columns intercalated with two types of layers (inert materials, such as fine sand and gravel, and adsorbent materials, such as activated carbon prepared from Balanites aegyptiaca (BA-AC)) were used for As(III) removal from an aqueous solution. Investigations were carried out to solve the problem of column clogging, which appears during the percolation of water through a natural laterite fixed-bed column. Experimental tests were conducted to evaluate the hydraulic conductivities of several fixed-bed column configurations and the effects of various parameters, such as the grain size, bed height, and initial As(III) concentration. The permeability data show that, among the different types of fixed-bed columns investigated, the one filled with repeating layers of laterite and activated carbon is more suitable for As(III) adsorption, in terms of performance and cost, than the others (i.e., non-intercalated laterite; non-intercalated activated carbon, repeating layers of laterite and fine sand; and repeating layers of laterite and gravel). A study was carried out to determine the most efficient column using breakthrough curves. The breakthrough increased from 15 to 85 h with an increase in the bed height from 20 to 40 cm and decreased from 247 to 32 h with an increase in the initial As(III) concentration from 0.5 to 2 mg/L. The Bohart–Adams model results show that increasing the bed height induced a decrease in the kAB and N0 values. The critical bed depths determined using the bed depth service time (BDST) model for As(III) removal were 15.23 and 7.98 cm for 1 and 20% breakthroughs, respectively. The results show that the new low-cost adsorptive porous system based on laterite layers with alternating BA-AC layers can be used for the treatment of arsenic-contaminated water.

Mechanism of rapid accretion-erosion transition in a complex hydrodynamic environment based on refined in-situ data

Morphological changes in estuaries are typically discussed on decadal time scales, with reported changes often exceed several decimeters. In our study, we utilized refined in-situ data to investigate bed-level changes and rapid accretion-erosion transitions during tidal cycles off the Changjiang Estuary. A field study employing a high-resolution bottom tripod system was conducted, measuring various parameters such as water level, waves, velocity profiles, near-bottom suspended sediment concentration (SSC), and bed level changes over ten tidal cycles. Our findings reveal significant and intense bed level changes occurring at the scale of tidal cycles. The data suggests that downward sediment transport plays a dominant role in the overall accretion tendency throughout the study period. Additionally, our research introduces a dynamic critical bed shear stress that increases during tidal cycles, deviating from fixed values. We also present a new quadrant analysis method to elucidate the primary processes controlling near-bed sediment transport. The results highlight the importance of horizontal advective sediment transport in frequent accretion-erosion transitions at tidal-cycle timescales. This implies a frequent exchange of sediment between adjacent shoals and channels in the seaward region of the North Channel in the Changjiang Estuary, which holds significance for future navigation and construction management.

Asymmetrical fixed-bed breakthrough curve modelling: Comparing simplistic, log-modified, fractal-like, and probability distribution function models

Column adsorption studies frequently adopt classical breakthrough curve models such as semi-mechanistic Bohart-Adams and Thomas models. They are logistic functions which simulate symmetrically sigmoidal curves centrosymmetric at 50% breakthrough; consequently, they fail and estimate erroneous results when dealing with asymmetric breakthrough curves. This work analyses and compares the trend of how log-modified, fractal-like modified, and probability distribution function models simulate asymmetric breakthrough curves with varied extents of tailing. We generated the asymmetric breakthrough curves by varying the bed depth: 6 mm, 9 mm, and 12 mm on a glass microcolumn of 100 mm length and 5.5 mm inner diameter at a fixed flow rate of 1 mL/min using 10 mg/L bisphenol-A as adsorbate and polyaniline as adsorbent. The asymmetrical curves were a consequence of polyaniline’s low specific surface area of 6.96 m²/g, heterogeneous particle size distribution, slow intraparticle and surface diffusion. The log-Bohart-Adams and fractal-like Bohart-Adams models perfectly fit the curves regardless of symmetry although log-Bohart-Adams performed subpar with increased tailing. The fractal-like Bohart-Adams model accurately estimated the breakthrough times of 13 min, 26 min, and 90 min for the 6 mm, 9 mm, and 12 mm bed depths with a critical bed depth of 5.65 mm. The normal and Gompertz probability distribution functions were unable to adapt to asymmetry of the curves owing to their fixed inflection points at c/cc = 0.5 and 0.37 respectively. Although the Weibull, log-normal, and log-Gompertz functions have floating inflection points, only log-Gompertz function had a satisfactory fit (Radj2>0.98) regardless of symmetry.

Sediment incipient motion on sandy seabed considering relative density effect: Laboratory experiments and mathematical analysis

The threshold of the sediment initial movement is closely related to marine structure scour. In complex marine environment, the relative density of seabed is usually changed by liquefaction and scour that is caused by currents and waves. It affects the scour depth and scour time scale which have been noted recently. However, the effect of relative density on sediment movement was mostly ignored in previous studies. In this paper, a series of tests were conducted to investigate the incipient motion under different relative density conditions on different seabeds. Subsequently, the internal friction force was introduced to describe the relative density effect, and an incipient motion model was built. Accordingly, a unified sediment incipient motion velocity function that considers relative density is proposed. Based on this function, the critical bed shear stress was assessed. A new theory was then evaluated in terms of the critical bed shear stress. Finally, the percentage of internal friction force to the whole resistance was discussed. Results indicated the significance of considering the relative density effect in predicting small-sized sediment movement. The new function provides better prediction accuracy with an acceptable error of 20%. Additionally, the discussion of the internal friction force gives a potential avenue to quantify interparticle force.

Subaqueous silt ripples measured by an echo sounder: Implications for bed roughness, bed shear stress and erosion threshold

Bedforms like ripples are widely distributed in the coastal zone. They influence the bed roughness thus the estimation of bed shear stress and associated sediment transport. An echo sounder was mounted on a bottom-supported tripod intended to measure the erosion and deposition of seabed in the subaqueous Yellow River Delta, China. However, variations in bed elevation are found to be not the net erosion or deposition at the observation site, but the migration of silt ripples which were generated by waves and pushed back and forth or flattened off by the tidal currents. Ripple heights were observed to be within 0.1–0.7 cm and were used for testing the model of Nielsen (1981). The model overestimated the height of silt ripples as it was developed for sands, but the deviation can be well addressed by incorporating a linear modification (R2 = 0.79). Alternatively, a new model specifically for silt ripple height was regressed from the field data with R2 up to 0.78. The existence of silt ripples increases the bed shear stress by 4 times due to the additional bed roughness. A “fluffy layer” overlies the consolidated seabed, therefore, net seabed erosion occurs after the “fluffy layer” is resuspended. A representative critical bed shear stress for net seabed erosion in the study area was found to be 0.8 Pa. The echo sounder can be an alternative tool for observing silt ripples in coastal regions like the Yellow River Delta where the water is too turbid for underwater videos. The proposed model infers silt-ripple features from bed grain size and flow condition and provides a quick estimate for bed roughness improving the understanding on sediment transport.

Analysis of Variables Influencing Scour on Large Sand-Bed Rivers Conducted Using Field Data

Throughout the lifespan of a bridge, morphological changes in the riverbed affect the variable action-imposed loads on the structure. This emphasizes the need for accurate and reliable data that can be used in model-based projections targeted for the identification of risk associated with bridge failure induced by scour. The aim of this paper is to provide an analysis of scour depth estimation on large sand-bed rivers under the clear water regime, detect the most influential (i.e., explanatory) variables, and examine the relationship between them and scour depth as a response variable. A dataset used for the analysis was obtained from the United States Geological Survey’s extensive field database of local scour at bridge piers, i.e., the Pier-Scour Database (PSDB-2014). The original database was filtered to exclude the data that did not reflect large sand-bed rivers, and several influential variables were omitted by using the principal component analysis. This reduction process resulted in 10 influential variables that were used in multiple non-linear regression scour modeling (MNLR). Two MNLR models (i.e., non-dimensional and dimensional models) were prepared for scour estimation; however, the dimensional model slightly overperformed the other one. According to the Pearson correlation coefficients (r), the most influential variables for estimating scour depth were as follows: Effective pier width (r = 0.625), flow depth (r = 0.492), and critical and local velocity (r = 0.474 and r = 0.436), respectively. In the compounded hydraulic-sediment category, critical velocity had the greatest impact (i.e., the highest correlation coefficient) on scour depth in comparison to densimetric Froude and critical Froude numbers that were characterized by correlation coefficients of r = 0.427 and r = 0.323, respectively. The remaining four variables (local and critical bed shear stress, Froude number, and particle Reynolds number) exhibited a very weak correlation with scour depth, with r < 0.3.

3D CFD Study of Scour in Combined Wave–Current Flows around Rectangular Piles with Varying Aspect Ratios

This study utilizes three-dimensional simulations to investigate scour in combined wave–current flows around rectangular piles with various aspect ratios. The simulation model solves the Reynolds-averaged Navier–Stokes (RANS) equations using the k–ω turbulence model, and couples the Exner equation to compute bed elevation changes. The model also employs the level-set approach to realistically capture the free surface, and couples a hydrodynamic module with a morphological module to simulate the scour process. The morphological module employs a modified critical bed shear stress formula on a sloping bed and a sand-slide algorithm for erosion and deposition calculations in the sediment bed. To validate the numerical model, simulations are conducted in a truncated numerical wave tank with the Dirichlet boundary condition and active wave absorption method. After validation, the numerical model is used to investigate the effect of aspect ratio and the Keulegan–Carpenter (KC) number on scour depth in a combined wave–current environment. The study finds that the normalized scour depth is highest for a rectangular pile with an aspect ratio of 2:1 and lowest for an aspect ratio of 1:2. The maximum normalized scour depth (S/D) for aspect ratios of 2:1 are 0.151, 0.218, and 0.323 for KC numbers 3.9, 5.75, and 10, respectively, whereas the minimum normalized scour depth (S/D) for aspect ratios of 1:2 are 0.132, 0.172, and 0.279. Additionally, the research demonstrates that the normalized scour depth increases with an increase in the KC number for a fixed wave–current parameter (Ucw).

Effect of complex hydraulic variables and physicochemical factors on freshwater mussel density in the largest floodplain lake, China

BackgroundHabitat degradation and flow regime alterations are two of the most prominent and common impact factors to freshwater mussel populations. Knowledge of the correlation between freshwater mussel distribution, density and habitat characteristics is important for maintaining and restoring their biodiversity and ecological functions. Information on predicting habitat suitability of freshwater mussels is lacking in China. Here, we aimed to analyze the correlation between freshwater mussel density and complex hydraulic and physicochemical variables to predict habitat suitability.ResultsThe results showed that four complex hydraulic variables (boundary Reynolds number, critical shear stress, bed roughness and mean sediment particle size) and four physicochemical variables (water temperature, chlorophyll-a, transparency and pH) were key factors for predicting habitat suitability of freshwater mussels. Freshwater mussel density was significantly correlated with Froude number, water temperature and chlorophyll-a.ConclusionsOur results confirmed that higher freshwater mussel density would be associated with areas that are stable in complex hydraulic and physicochemical variables. These results provide an important insight into the conservation of freshwater mussel diversity and their habitat restoration in China and globally.

Effects of Mud Supply and Hydrodynamic Conditions on the Sedimentary Distribution of Estuaries: Insights from Sediment Dynamic Numerical Simulation

Estuaries are important sediment facies in the fluvial-to-marine transition zone, are strongly controlled by dynamic interactions of tides, waves, and fluvial flows, and show various changes in depositional processes and sediment distribution. Deep investigations on the sediment dynamic processes of the sand component of estuaries have been conducted; however, the understanding of how mud supply affects estuaries’ sedimentary characteristics and morphology is still in vague. Herein, the effects of mud concentration, mud transport properties, fluvial discharge, and tidal amplitude on the sedimentary characteristics of an estuary were systematically analyzed using sedimentary dynamic numerical simulation. The results show that the mud concentration has significant effects on the morphology of tidal channels in estuaries, which become more braided with a lower mud concentration, and straighter, with reduced channel migration, with a higher mud concentration. The mud transport properties, namely, setting velocity, critical bed shear stress for sedimentation, and erosion, mostly affect the ratio between the length and width (RLW) of the sand bar; a sheet-like sand bar with a lower RLW value develops in the lower settling velocity, while there are obvious strip shaped bars with a high RLW value in the higher settling velocity case. Moreover, the effects of hydrodynamic conditions on sedimentary distribution were analyzed by changing the tidal amplitudes and fluvial discharges. The results show that a higher tidal amplitude is often accompanied by a stronger tidal energy, which induces a more obvious seaward progradation, while a higher fluvial discharge usually yields a higher deposition rate and yields a greater deposition thickness. From the above numerical simulations, the statistical characteristics of tidal bars and mud interlayers were further obtained, which show good agreement with modern sedimentary characteristics. This study suggests that sedimentary dynamic numerical simulation can provide insights into an efficient quantitative method for analyzing the effects of mud components on the sediment processes of estuaries.

1002. Complex Outpatient Antimicrobial Therapy (COpAT) Program at a Rural Academic Medical Center: Evaluation of First 100 Patients

Abstract Background Literature shows early intravenous (IV) to oral (PO) antimicrobial transition for infective endocarditis (IE) and bone and joint infection (BJI) is noninferior to prolonged IV antimicrobial therapy. COVID-19 pandemic peaks resulted in critical shortages of staffed hospital beds spurring innovation. Outpatient parenteral antimicrobial therapy (OPAT), a well-established program using prolonged IV antimicrobials, faces challenges such as infusion resource needs and social circumstance limitations. Complex outpatient antimicrobial therapy (COpAT) uses PO in place of IV antimicrobials. We hypothesized rapid adoption of COpAT would decrease hospital length of stay and open beds while retaining satisfactory clinical outcomes. Methods COpAT protocols (Image 1) and guidelines by infection type and isolated organism (Image 2) were created. Hospitalized patients including persons who inject drugs (PWID) were evaluated for IV to PO antimicrobial transition by an infectious diseases (ID) physician and then followed by an ID physician-pharmacist team. Demographic, ID, and clinical outcome data for the first 100 COpAT patients between December 2020 and February 2022 were obtained by retrospective chart review. Image 1.COpAT Inpatient and Outpatient Protocols Image 2. COpAT Guidelines by Infection Type and Isolated Organism MSSA = methicillin-susceptible Staphylococcus aureus; MRSA = methicillin-resistant Staphylococcus aureus; spp. = species; TMP/SMX = trimethoprim-sulfamethoxazole; DS = double strength; SSTI = skin and soft tissue infection; CAP = community-acquired pneumonia Results PWID accounted for 78% of COpAT patients. BJI followed by mixed infection (IE and BJI) was most prevalent (Image 3) with bacteremia in 53% of cases. Staphylococcus aureus was most frequently isolated (Image 4). Oral linezolid and fluoroquinolones, often in combination, were most commonly used. IV and PO antimicrobials were taken for a median 28 and 14 days, respectively. The COpAT program saved 1425 IV antimicrobial and 1363 hospital days. Assuming daily inpatient cost of $2050, cost avoided was $2,794,150. COpAT patients participated in ID follow-up and adhered to PO antimicrobials with low 30-day readmission rates (Image 5). Image 3.Infection TypeImage 4.Isolated Organism CoNS = coagulase-negative staphylococci Image 5.Clinical Outcomes Conclusion In a sample of 100 COpAT patients including PWID, IV to PO antimicrobial transition safely saved hospital days and mitigated critical bed shortages during pandemic peaks. A successful COpAT program requires a multidisciplinary group: close ID physician-pharmacist collaboration extending to OPAT and antimicrobial stewardship teams. With a COpAT program in place, even earlier IV to PO antimicrobial transitions should be studied. Disclosures All Authors: No reported disclosures.

EGS P17 No beds available for transfer! Experience of life saving pancreatic necrosectomies at a non-pancreatic upper GI unit

Abstract Background Infected necrotising pancreatitis (NP) has a high mortality. NICE recommends necrotising pancreatitis be managed at specialist pancreatic centres due to its challenging nature. However, timely transfer of patients from non-specialist centres to tertiary pancreatic units can be limited by critical bed availability. This problem is further compounded by the staffing issues and constraints on critical care facilities since the COVID19 pandemic. This situation places patients at high risk of mortality and poses the question as to whether lifesaving intervention can be offered within appropriate local upper GI non pancreatic units. We present our data from emergent pancreatic necrosectomies in a sub-set of critically ill patients for whom transfer to specialist care was not possible due to lack of availability of critical care beds. Methods A retrospective case series is presented over a two-year period at a non-pancreatic upper GI centre. Patients over a two-year period (2020–2022) were identified using clinical coding and operation note records. Data was collected on patient characteristics such as age, gender, and co-morbidities, as well as on their inflammatory markers on presentation, imaging modality used, nutritional status and duration of care in a high dependency unit. Complications, including death following pancreatic necrosectomy were also recorded. Only descriptive statistics were used in this audit. No advanced statistics were required. Data standards were assessed using fractions and then percentages for ease of understanding. Results A total of six patients were identified as having undergone emergency pancreatic necrosectomies. Patients included were all male with a mean age of 48 and an average BMI of 25.6. The mean number of days patients were in hospital prior to their necrosectomy was 42.6. On average patients had 5.5 CT scans prior to their necrosectomy. 50% of patients had organ failure requiring ventilatory support and/or hemofiltration. Comorbidities included diabetes mellitus, rheumatoid arthritis and Covid-19. Social factors such as excess alcohol consumption and cigarette smoking were also present. As per NICE guidance, 100% of patients were administered enteral nutrition through a nasojejunal tube during their admission. 50% of patients received parenteral nutrition after failure of enteral nutrition, in keeping with best practice. 100% underwent a pancreatic necrosectomy and 50% had further operations. The mean number of re-operations per patient was 2.3. The average number of days between admission and pancreatic necrosectomy was 42 days. 100% of patients had complications with 50% suffering from AKI and 33% patients were readmitted with pancreatitis related complications. One death was from post operative haemorrhage. Overall survival rate at this tertiary care centre was 83.3%. These patients are currently still being followed up. Conclusions The results of our audit have shown that necrotising pancreatitis can be managed outside of a specialist pancreatic centre providing there are appropriately skilled surgeons and critical care staff employed, who are confident in managing the condition. Complications at the centre, including death rates, were no higher than reported in the literature, suggesting patient safety was not adversely affected. Ideally, further audits will need to be carried out on a larger scale, potentially with multiple trusts involved, comparing specialist pancreatic centres to non-specialist facilities to ensure that the results of our audit are not limited to this tertiary care centre alone. The data in this audit stems from during the Covid-19 pandemic and therefore additional auditing will need to be done in case the pressures of the pandemic on healthcare services has impacted upon the results and findings, as well as the patient cohort.

Continuous successive cycles of biosorption and desorption of acid red 27 dye using water hyacinth leaves as an effective, economic, and ecofriendly biosorbent

We investigated the capacity of water hyacinth leaves (LEC) to biosorb 75 mg/L acid red 27 (AR27) in a continuous system comprising 30 successive biosorption/desorption cycles in a packed-bed column at pH 2.0 and 56.5 L/m2·h volumetric flux. Using 0.025 M NaHCO3 eluent at 113 L/m2·h volumetric flux, all the dye was desorbed (100% desorption efficiency) from the loaded LEC biomass within 5–6 h. The same biosorbent was used for 147.5 consecutive days. The AR27 biosorption capacity, breakthrough time, and exhaustion time decreased from 69.4 to 34.5 mg/g, 74.81 to 14.1 h, and 101.1 to 34.1 h, respectively, and the critical bed height increased from 1.04 to 2.35 cm, as the number of biosorption/desorption cycles increased from 1 to 30. LEC life factor based on biosorption capacity predicted that the packed bed would be exhausted after 51.95 cycles. LEC is a promising biosorbent for bioremediation of AR27-laden wastewaters.

Erosion Behavior of Sand‐Silt Mixtures: Revisiting the Erosion Threshold

AbstractThe erosion threshold, beyond which bed sediments start to move, is a key parameter describing sediment transport processes. For silt‐dominated mixtures, in which the grain size is between sand and clay, existing experimental studies exhibit contradictory observations. That is, the erosion was either sand‐like or clay‐like, suggesting transitional erosion behavior. To explore the underlying mechanism of the transitional erosion behavior of silt‐sized sediment, we revisited the topic of the erosion threshold of sand‐silt mixtures by carrying out a series of erosion experiments for different bed compositions. The results suggest that there exists a critical silt content of approximately 35%, separating two domains. Below this critical value, the critical bed shear stress follows the Shields criterion, whereas above this value, the erosion threshold of a mixed bed increases abruptly and remains relatively constant with a further increase in silt content. By combining with existing data, we found that the proposed critical silt content acts as a tipping point, beyond which the mixed bed shifts from a sand‐dominated to a silt‐dominated domain. For the silt‐dominated domain, a stable silt skeleton can be formed by attraction forces that resist erosion. However, the attraction forces are too weak to form a stable silt skeleton when the silt content is too small. Based on this finding, a modified critical bed shear stress formula is proposed for silt‐dominated mixtures, which results in a better agreement with experimental data (an averaged bias of 10%), performing better than existing formulas (larger than 30%).

Numerical analysis of die filling with a forced feeder using GPU-enhanced discrete element methods

Understanding die filling behaviour of powders is critical in developing optimal formulation and processes in various industries, such as pharmaceuticals and fine chemicals. In this paper, forced die filling is analysed using a graphics processing unit (GPU) based discrete element method (DEM), for which a powder feeder equipped with a wired stirrer is considered. The influences of operating parameters, such as the initial powder bed height, the filling speed, and the stirrer speed, on the die filling performance are systematically explored. It is shown that a larger initial powder bed height leads to a higher filling ratio, which can be attributed to a higher filling intensity; while the deposited particle mass in the die is almost independent of the powder bed height, when the initial fill level is larger than a critical bed height. Additionally, the filling ratio slightly increases with the increase of stirrer speed for cases with a stirrer, while the filling ratios are lower than that without a stirrer, which is attributed to the stirrer occupying some space above the die and reducing the effective discharge area. The obtained results can provide useful information for optimising the feeder system design and the operating condition.