Correlation between flexural strength and denture base acrylic thickness overlaying implant stud attachments

Objectives. To investigate the effect of acrylic resin thickness and the stud attachment housings on the maximum breaking load, flexural strength and flexural modulus of denture base acrylic resins overlying implant overdenture attachments.;Methods. Fifty-two rectangular specimens were fabricated from high impact denture acrylic resin (Lucitone 199). Forty specimens contain 2.00 mm height Locator attachment titanium denture caps with black processing males, 12 specimens did not include the denture cap. All specimens were fabricated according to ANSI/ADA SPECIFICATION NO. 12-2002 for testing denture base resin with constant measurements of 64 mm in length, 10 mm in width, and variable testing thickness. The specimens were divided into four testing groups according to different thickness of 3, 4, 5, and 6 mm. Each group had 10 specimens with denture cap and 3 specimens without denture cap. Specimens were subjected to 3-point-bending flexural test till fracture using the Instron Universal testing machine. After data collection, mean values and standard deviations were calculated and a two-way analysis of variance (ANOVA) was used to evaluate the effect of denture base thickness, on the flexural strength and modulus of the control and Locator testing specimens.;Results. The data collected showed a positive effect with the use of Locators caps in test specimens on the flexural modulus and maximum displacement. Results showed a positive relationship between maximum load, maximum displacement at break and acrylic thickness. There was no significant effect of different acrylic thicknesses on the flexural strength or flexural modulus.;Conclusions. Evaluation of the available interarch distance, proper diagnosis, and treatment planning is of critical importance to minimize prosthesis complications and failure. Implant-retained overdentures utilizing a low profile stud attachment (Locators by Zest) is a recommended treatment option for patients with compromised interarch space. Implant stud attachment components integrated in denture resin has a positive effect on the flexural modulus. The stiffness of the denture resin increased when Locator caps were contained in the specimens compared to specimens with no caps. There was a positive effect of acrylic thickness on the maximum load at break and maximum displacement. Increase acrylic thickness will lead to higher maximum load and decreased incidence of overdenture fractures

Inhibition of weld corrosion in flowing brines containing carbon dioxide

The aim of this research was to study the effectiveness of a typical oilfield corrosion inhibitor, which is considered to be a green inhibitor (non toxic to the environment) in controlling internal corrosion of welded X65 pipeline steel in brines saturated with carbon dioxide at one bar pressure, under dynamic flowing conditions, over a range of temperatures. Several experimental configurations were used ranging from a simple flat plate design to a novel rotating cylinder electrode, to allow high shear stress to be achieved. The rotating cylinder electrode (RCE) apparatus was designed to allow steel from the weld metal, heat affected zone (HAZ) and parent material to be galvanically coupled and tested in high shear stress conditions. In producing the RCE, the three regions of the weld were identified by optical metallography and samples of each were machined to produce cylindrical electrodes, which were mounted on a motor driven shaft. Electrical connections were made to the three electrodes via a high quality slip-ring assembly. The galvanic currents flowing between the regions of the weld were recorded using zero-resistance ammeters and their self-corrosion rates were found by uncoupling the electrodes and performing polarization resistance measurements. For static conditions the inhibitor had an effective performance and after a short initial period during which film formation took place, at longer exposure times a dramatic reduction of corrosion rate was obtained. Under flowing conditions, both the galvanic currents and the self-corrosion rates were found to increase with the shear stress, as the rotational speed of the RCE was increased. The total corrosion rate of each weld region was assessed from the sum of the self-corrosion and galvanic contributions. In most cases, the weld metal and HAZ were shown to be cathodic to the parent material and this was considered to be a desirable situation as localised corrosion of the weld was minimised. However, in some circumstances, including inhibition of pre-corroded steel surfaces, a current reversal took place, which resulted in accelerated corrosion of the weld. These findings are explained in terms of the protective nature of the films that form on each region of the weld.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Global overview of the management of acute cholecystitis during the COVID-19 pandemic (CHOLECOVID study)

Background: This study provides a global overview of the management of patients with acute cholecystitis during the initial phase of the COVID-19 pandemic. Methods: CHOLECOVID is an international, multicentre, observational comparative study of patients admitted to hospital with acute cholecystitis during the COVID-19 pandemic. Data on management were collected for a 2-month study interval coincident with the WHO declaration of the SARS-CoV-2 pandemic and compared with an equivalent pre-pandemic time interval. Mediation analysis examined the influence of SARS-COV-2 infection on 30-day mortality. Results: This study collected data on 9783 patients with acute cholecystitis admitted to 247 hospitals across the world. The pandemic was associated with reduced availability of surgical workforce and operating facilities globally, a significant shift to worse severity of disease, and increased use of conservative management. There was a reduction (both absolute and proportionate) in the number of patients undergoing cholecystectomy from 3095 patients (56.2 per cent) pre-pandemic to 1998 patients (46.2 per cent) during the pandemic but there was no difference in 30-day all-cause mortality after cholecystectomy comparing the pre-pandemic interval with the pandemic (13 patients (0.4 per cent) pre-pandemic to 13 patients (0.6 per cent) pandemic; P = 0.355). In mediation analysis, an admission with acute cholecystitis during the pandemic was associated with a non-significant increased risk of death (OR 1.29, 95 per cent c.i. 0.93 to 1.79, P = 0.121). Conclusion: CHOLECOVID provides a unique overview of the treatment of patients with cholecystitis across the globe during the first months of the SARS-CoV-2 pandemic. The study highlights the need for system resilience in retention of elective surgical activity. Cholecystectomy was associated with a low risk of mortality and deferral of treatment results in an increase in avoidable morbidity that represents the non-COVID cost of this pandemic

Inhibition of Weld Corrosion in Flowing Brines Containing Carbon Dioxide

The aim of this research was to study the effectiveness of a typical oilfield corrosion inhibitor, which is considered to be a green inhibitor (non toxic to the environment) in controlling internal corrosion of welded X65 pipeline steel in brines saturated with carbon dioxide at one bar pressure, under dynamic flowing conditions, over a range of temperatures. Several experimental configurations were used ranging from a simple flat plate design to a novel rotating cylinder electrode, to allow high shear stress to be achieved. The rotating cylinder electrode (RCE) apparatus was designed to allow steel from the weld metal, heat affected zone (HAZ) and parent material to be galvanically coupled and tested in high shear stress conditions. In producing the RCE, the three regions of the weld were identified by optical metallography and samples of each were machined to produce cylindrical electrodes, which were mounted on a motor driven shaft. Electrical connections were made to the three electrodes via a high quality slip-ring assembly. The galvanic currents flowing between the regions of the weld were recorded using zero-resistance ammeters and their self-corrosion rates were found by uncoupling the electrodes and performing polarization resistance measurements. For static conditions the inhibitor had an effective performance and after a short initial period during which film formation took place, at longer exposure times a dramatic reduction of corrosion rate was obtained. Under flowing conditions, both the galvanic currents and the self-corrosion rates were found to increase with the shear stress, as the rotational speed of the RCE was increased. The total corrosion rate of each weld region was assessed from the sum of the self-corrosion and galvanic contributions. In most cases, the weld metal and HAZ were shown to be cathodic to the parent material and this was considered to be a desirable situation as localised corrosion of the weld was minimised. However, in some circumstances, including inhibition of pre-corroded steel surfaces, a current reversal took place, which resulted in accelerated corrosion of the weld. These findings are explained in terms of the protective nature of the films that form on each region of the weld

An Optimization Study to Evaluate the Impact of the Supercritical CO2 Brayton Cycle’s Components on Its Overall Performance

The rising environmental problems due to fossil fuels’ consumption have pushed researchers and technologists to develop sustainable power systems. Due to properties such as abundance and nontoxicity of the working fluid, the supercritical carbon (sCO2) dioxide Brayton cycle is considered one of the most promising technologies among the various sustainable power systems. In the current study, a mathematical model has been developed and coded in Matlab for the recompression of the supercritical carbon dioxide Brayton cycle sCO2-BC. The real gas properties of supercritical carbon dioxide (sCO2) were incorporated into the program by pairing the NIST’s Refporp with Matlab© through a subroutine. The impacts of the various designs of the cycle’s individual components have been investigated on the performance of sCO2−BC. The impact of various sedative cycle parameters, i.e., compressor’s inlet temperature (T1), and pressure (P1), cycle pressure ratio (Pr), and split mass fraction (x), on the cycle’s performance (ηcyc) were studied and highlighted. Moreover, an optimization study using the genetic algorithm was carried out to find the abovementioned cycle’s optimized values that maximize the cycle’s per-formance under provided design constraints and boundaries

Evaluation of the Erosion Characteristics for a Marine Pump Using 3D RANS Simulations

In the present study, an erosion analysis of an industrial pump’s casing and impeller blades has been performed computationally. Effects of various critical parameters, i.e., the concentration and size of solid particles, exit pressure head, and cavitation on the erosion rate density of the casing and blade have been investigated. Commercial codes CFX, ICEM-CFD, and ANSYS Turbogrid are employed to solve the model, mesh generation for the casing, and mesh generation of the impeller, respectively. The Eulerian-Eulerian method is employed to model the pump domain’s flow to solve the two phases (water and solid particles) and the interaction between the phases. Published experimental data was utilized to validate the employed computational model. Later, a parametric study was conducted to evaluate the effects of the parameters mentioned above on the erosion characteristics of the pump’s casing and impeller’s blade. The results show that the concentration of the solid particles significantly affects the pump’s erosion characteristics, followed by the particle size and distribution of the particle size. On the other hand, the exit pressure head and cavitation do not affect the erosion rates considerably but significantly influence the regions of high erosion rate densities

Design and Optimization of a Radial Turbine to Be Used in a Rankine Cycle Operating with an OTEC System

Design and optimization of a radial turbine for a Rankine cycle were accomplished ensuring higher thermal efficiency of the system despite the low turbine inlet temperature. A turbine design code (TDC) based on the meanline design methodology was developed to construct the base design of the turbine rotor. Best design practices for the base design were discussed and adopted to initiate a robust optimization procedure. The baseline design was optimized using the response surface methodology and by coupling it with the genetic algorithm. The design variables considered for the study are rotational speed, total to static speed ratio, hub radius ratio, shroud radius ration, and number of blades. Various designs of the turbine were constructed based on the Central Composite Design (CCD) while performance variables were computed using the in-house turbine design code (TDC) in the MATLAB environment. The TDC can access the properties of the working fluid through a subroutine that links NIST’s REFPROP to the design code through a subroutine. The finalization of the geometry was made through an iterative process between 3D-Reynolds-Averaged Navier-Stokes (RANS) simulations and the one-dimensional optimization procedure. 3D RANS simulations were also conducted to analyze the optimized geometry of the turbine rotor for off-design conditions. For computational fluid dynamics (CFD) simulation, a commercial code ANSYS-CFX was employed. 3D geometry was constructed using ASYS Bladegen while structured mesh was generated using ANSYS Turbogrid. Fluid properties were supplied to the CFD solver through a real gas property (RGP) file that was constructed in MATLAB by linking it to REFPROP. Computed results show that an initial good design can reduce the time and computational efforts necessary to reach an optimal design successfully. Furthermore, it can be inferred from the CFD calculation that Response Surface Methodology (RSM) employing CFD as a model evaluation tool can be highly effective for the design and optimization of turbomachinery