Realistic Margins Research Articles

Estimation of the displacement of soil nailing vertical face structures intended for building undergrounds

ABSTRACT This study proposes a methodology for estimating horizontal displacements in vertical face soil-nailing structures in urban areas, analyzing 20 projects in São Paulo, Brazil. To minimize displacements, post-grouting sectorized injections through polyethylene tubes was used, a methodology routinely adopted in Brazil which gives the soil mass a significant increase in strength and stiffness.To study the effect of the sectorized injections on soil treatment, a three-dimensional computational model using Plaxis 3D software and calibrated through back-analysis according to the displacements of the structures. Additionally, 11 models were tested with variations in nail length, mesh configuration, and geotechnical parameters, considering injection effects. The study provides design and execution guidelines to optimize this technique. Equations derived from the study predict horizontal displacements, which will be used to assess the technical feasibility of the projects in advance and, when they are being executed, to provide performance control within a more precise and realistic margin.

Variation-learning high-resolution network for capsulorhexis recognition of cataract surgery

In cataract surgery, capsulorhexis is the first, one of the most critical steps. However, recognizing the margin of rhexis during capsulorhexis is challenging and has rarely been studied due to its intraoperative invisibility, variable shape, and lack of a proprietary labeled dataset. Capsulorhexis margin recognition is essential for robot-assisted surgery, surgical assessment, and intraoperative reference. To solve the problem, this paper proposes a creative dynamic margin recognition structure called THRC, which includes a novel segmentation network, THRNet, and a compensation block. First, the dilated HRNet is designed to expand the receptive field while maintaining high-resolution representation for better detail preservation. Second, cascaded transformer blocks are proposed. The channel transformer block (CTB) is developed to include fixed and dynamic weights while generating global context dependency for nonrigid tissue variation pattern learning. The layer transformer block (LTB) with redistributed transformer variables is then developed to fuse multi-resolution features effectively for better multi-scale semantic segmentation. Moreover, the compensation block compensates for inter-frame movement by key-point registration and recovers a more realistic margin by a smoothing process. Finally, to evaluate the proposed structure, we establish the capsulorhexis dataset CapsSeg. The THRNet achieves 78.24% mean intersection over union (mIoU) and 86.59% mean Dice (mDice), making it equivalent in performance to state-of-the-art networks, but with a lower computational cost. The feasibility of the compensation block is also visualized.

VAET-STT: Variation Aware STT-MRAM Analysis and Design Space Exploration Tool

Spin transfer torque magnetic random access memory is a promising candidate to replace CMOS based on-chip memories due to its advantages, such as nonvolatility, high density, and scalability. However, its stochastic switching and higher sensitivity to process variation compared to CMOS memories can significantly affect its performance, energy, and reliability. Although a few works exist which analyze the impact of process variation at the bit-cell level, such analysis at the system-level is missing. We have bridged this gap by developing a tool which can quantify the effect of stochasticity and process variations from the cell level to the overall memory system. The tool can perform a variation-aware design space exploration and memory configuration optimization for energy or performance while meeting reliability constraints. It also reports various failure rates and can evaluate the effectiveness of different error correcting code schemes. The results show that our framework can provide more realistic margins and the optimized variation-aware memory configuration could be significantly different from the conventional framework.

Molecular Modelling of the Hydrolysis of Tantalum and Niobium Pentafluoride

<span><p><span style="font-family: Times New Roman;" face="Times New Roman"><span style="font-size: medium;" size="3">Tantalum </span><span style="font-size: medium;" size="3">(Ta) and niobium (Nb) are two metals with similar chemical and physical properties and are found together in nature. One form of Ta is tantalum pentafluoride, which is stable in reducing environments, is corrosive resistant and stable under harsh conditions</span><span style="font-size: medium;" size="3">.</span><span style="font-size: medium;" size="3"> Ta is currently used in nuclear reactors with a wide variety of uses and advantages. </span></span><span style="font-family: Times New Roman;" face="Times New Roman"><span style="font-size: medium;" size="3">For these applications, pure Ta is needed to insure high value catalysts, contrary the higher the purity grade the more expensive the production of these high value catalysts. One way of ensuring an economic viable process for the production of high purity Ta, is to find a cost effective way to separate Ta from Nb. </span><span style="font-size: medium;" size="3">Ungerer </span><span style="font-size: medium;" size="3">et al</span><span style="font-size: medium;" size="3">. studied the separation of Ta and Nb, using safer chemicals and techniques for the environment in a solvent extraction (SX) process. During this study, separation was achieved in a sulphuric acid (H</span><span style="font-size: small;" size="2">2</span><span style="font-size: medium;" size="3">SO</span><span style="font-size: small;" size="2">4</span><span style="font-size: medium;" size="3">) medium with the extractants diiso-octyl phosphinic acid (PA) and di-(2-ethylhexyl) phosphoric acid (D2EHPA). The main obstacle during this study was the speciation of Ta and Nb, springing the question of why separation occurred with some extractants and not with the others. </span></span><span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3">One method for determining the speciation of the compounds in a reaction mixture is by using computational techniques for molecular modelling. Several molecular modelling programs are available which uses various mathematical equations and approximations. Progress in computational chemistry over the last 20 years has made quantum mechanical calculations on large molecules, chemical systems as well as on macromolecule reactions possible. Calculations based on the density-functional theory (DFT) are now, not only used on light elements and small molecules, but also on metal complexes, heavy metals and especially on metal separation in SX. </span><span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3">With these models at hand, SX processes were modelled within realistic margins to fit the experimental setup in a small scale laboratory. It is anticipated that the advances from this work will provide the possibility to determine, with good approximation, the outcome not only of the proposed Ta SX experiments, but also SX in general, before embarking on expensive, time consuming experiments and environmental unfriendly waste generation. </span><span style="font-family: Times New Roman;" face="Times New Roman"><span style="font-size: medium;" size="3">In this paper molecular modelling was used to compile a partial energy profile for a proposed reaction mechanism for the reaction of tantalum- and niobium pentafluoride (TaF</span><span style="font-size: small;" size="2">5</span><span style="font-size: medium;" size="3">, NbF</span><span style="font-size: small;" size="2">5</span><span style="font-size: medium;" size="3">) with water to form tantalum- and niobium hydroxides. In the process, possible species that may form during the reaction were identified and evaluated.</span></span></p>

Existence and stability of steady-state solutions of the shallow-ice-sheet equation by an energy-minimization approach

AbstractThe existence of solutions of the non-sliding shallow-ice-sheet equation on a flat horizontal bed with a mass balance linearly depending on altitude is proven for fixed margins. Free-margin solutions for the same mass balance do not exist. Fixed-margin solutions show unbounded shear stress and nonzero mass flux at the margin. Steady-state solutions with realistic margins, vanishing ice flux and vanishing shear stress are found numerically for ice sheets with Weertman-type sliding.

Demonstrating the robustness of population surveillance data: implications of error rates on demographic and mortality estimates

BackgroundAs in any measurement process, a certain amount of error may be expected in routine population surveillance operations such as those in demographic surveillance sites (DSSs). Vital events are likely to be missed and errors made no matter what method of data capture is used or what quality control procedures are in place. The extent to which random errors in large, longitudinal datasets affect overall health and demographic profiles has important implications for the role of DSSs as platforms for public health research and clinical trials. Such knowledge is also of particular importance if the outputs of DSSs are to be extrapolated and aggregated with realistic margins of error and validity.MethodsThis study uses the first 10-year dataset from the Butajira Rural Health Project (BRHP) DSS, Ethiopia, covering approximately 336,000 person-years of data. Simple programmes were written to introduce random errors and omissions into new versions of the definitive 10-year Butajira dataset. Key parameters of sex, age, death, literacy and roof material (an indicator of poverty) were selected for the introduction of errors based on their obvious importance in demographic and health surveillance and their established significant associations with mortality.Defining the original 10-year dataset as the 'gold standard' for the purposes of this investigation, population, age and sex compositions and Poisson regression models of mortality rate ratios were compared between each of the intentionally erroneous datasets and the original 'gold standard' 10-year data.ResultsThe composition of the Butajira population was well represented despite introducing random errors, and differences between population pyramids based on the derived datasets were subtle. Regression analyses of well-established mortality risk factors were largely unaffected even by relatively high levels of random errors in the data.ConclusionThe low sensitivity of parameter estimates and regression analyses to significant amounts of randomly introduced errors indicates a high level of robustness of the dataset. This apparent inertia of population parameter estimates to simulated errors is largely due to the size of the dataset. Tolerable margins of random error in DSS data may exceed 20%. While this is not an argument in favour of poor quality data, reducing the time and valuable resources spent on detecting and correcting random errors in routine DSS operations may be justifiable as the returns from such procedures diminish with increasing overall accuracy. The money and effort currently spent on endlessly correcting DSS datasets would perhaps be better spent on increasing the surveillance population size and geographic spread of DSSs and analysing and disseminating research findings.

Strategy for Online Correction of Rotational Organ Motion for Intensity-Modulated Radiotherapy of Prostate Cancer

To develop and evaluate a correction strategy for prostate rotation using gantry and collimator angle adjustments. Gantry and collimator angle adjustments were used to correct for prostate rotation without rotating the table. A formula to partially correct for left-right (LR) rotations was derived through geometric analysis of rotation-induced clinical target volume (CTV) beam's-eye-view shape changes. For 10 prostate patients, intensity-modulated radiotherapy (IMRT) plans with different margins were created. Simulating CTV LR rotation and correcting each beam by a collimator rotation, the corrected CTV dose was compared with the original and uncorrected dose. Effects of residual geometric uncertainties were assessed using a Monte Carlo technique. A large number of treatments representative for prostate patients were simulated. Dose probability histograms of the minimum CTV dose (D min) were derived, with and without online correction, resulting in a more realistic margin estimate. Dosimetric analysis of all IMRT plans showed that, with rotational correction and a 2-mm margin, D min was constant to within 3% for LR rotations up to +/-15 degrees . The Monte Carlo dose probability histograms showed that, with correction, a margin of 4 mm ensured that 90% of patients received a D min >or=95% of the prescribed dose. Without correction a margin of 6 mm was required. We developed and tested a practical method for (online) correction of prostate rotation, allowing safe and straightforward implementation of margin reduction and dose escalation.

Maximal dismounts from high bar

In men's artistic gymnastics the triple straight somersault dismount from the high bar has yet to be performed in competition. The present study used a simulation model of a gymnast and the high bar apparatus (J. Appl. Biomech. 19(2003a) 119) to determine whether a gymnast could produce the required angular momentum and flight to complete a triple straight somersault dismount. Optimisations were carried out to maximise the margin for error in timing the bar release for a given number of straight somersaults in flight. The amount of rotation potential (number of straight somersaults) the model could produce whilst maintaining a realistic margin for error was determined. A simulation model of aerial movement (J. Biomech.23 (1990) 85) was used to find what would be possible with this amount of rotation potential. The model was able to produce sufficient angular momentum and time in the air to complete a triple straight somersault dismount. The margin for error when releasing the bar using the optimum technique was 28 ms, which is small when compared with the mean margin for error determined for high bar finalists at the 2000 Sydney Olympic Games (55 ms). Although the triple straight somersault dismount is theoretically possible, it would require close to maximum effort and precise timing of the release from the bar. However, when the model was required to have a realistic margin for error, it was able to produce sufficient angular momentum for a double twisting triple somersault dismount.

Regulation of carbon monoxide: Are current standards safe?

Carbon monoxide regulation as mandated under the National Ambient Air Quality Standards (NAAQS) has not effectively protected the health of this country's citizens. The direct cause-and-effect relationships between carbon monoxide and cardiac dysfunction indicate a clear and urgent need for the reevaluation of carbon monoxide standards in order to protect the health of urban Americans. Failure to take effective action now will result in the severe impairment of individuals who are compromised by pathological conditions limiting their ability to live safely amidst rising CO levels. The NAAQS should be revised to ensure that CO emission source levels reflect a realistic margin of safety for individuals whose preexisting health conditions place them within the defined sensitive population.