Main Source Of Inaccuracy Research Articles

Strained AlGaInAs on InP: Bandgap dependence on composition—Model benchmark and optimization

Influence of chemical composition on the bandgap of AlGaInAs deposited on InP is often calculated using models for unstrained composition and then corrected for strain-induced bandgap energy changes using deformation potentials. This method relies on up to 25 coefficients, many of which are burdened with large uncertainty. In this paper, a large set of experimental data is used to verify the accuracy of existing approaches and to search for optimal deformation potentials. It is shown that the main source of inaccuracy is not the deformation potentials, but the unstrained bandgap formulas. Additionally, a novel model is proposed, yielding the highest accuracy on our dataset. For the first time, composition determination of a quaternary alloy on InP is reported using inductively coupled plasma-optical emission spectrometry, which is used as a benchmark for modeling.

Effect of selected process parameters on dimensional accuracy in Arburg Plastic Freeforming

PurposeThe body of the literature on the Arburg Plastic Freeforming process is still very limited despite the increasing industrial importance of this technology. This paper aims to contribute to a better understanding of this technology by investigating relations between characteristic process parameters and part features. Particularly, the effects of nominal dimension, drop aspect ratio, build chamber temperature and part position on accuracy are investigated. The density of manufactured parts is also measured to understand its relation with dimensional error.Design/methodology/approachA benchmark part was designed and manufactured in Polycarbonate on an Arburg Plastic Freeformer 2K-3A. The process was repeated with two levels of drop aspect ratio (1.2125 and 1.2150) and two build chamber temperatures (90°C and 120°C). Each build job included five parts in different positions of the chamber. The dimensional accuracy of benchmarks was measured by using a digital caliper, while Archimede’s principle was used for density measurements. All the acquired results were processed through an analysis of variance to investigate the role of experimental factors.FindingsResults demonstrate that the linear shrinkage occurring at the end of the 3D printing process is the main source of inaccuracy. The higher the building chamber temperature, the most the part accuracy is influenced by the nominal dimension. The drop aspect ratio affects the dimensional error in the XY plane by increasing the overlap of adjacent droplets. On the other hand, this parameter does not influence the accuracy along the Z direction. The position of the parts inside the building chamber exhibited an influence on results, arguably due to the hot airflows.Research limitations/implicationsThis research did not allow for a complete understanding of the role of part positioning on part accuracy. Further study is needed to understand the detail of this phenomenon.Practical implicationsThe results of this study can aid the users of Arburg Plastic Freeforming technology by uncovering the role of the main process parameters.Originality/valueThis paper expands the body of knowledge on the Arburg Plastic Freeforming process by providing new information on the role of the main process parameters on dimensional accuracy and density. Particularly, the results answer a research question on the role of the drop aspect ratio, demonstrating that its main effect is to vary the droplets overlap, which, in turn, affects the thermal shrinkage.

Stencil Penalty approach based constraint immersed boundary method

The constraint-based immersed boundary (cIB) method has been shown to be accurate between low and moderate Reynolds number (Re) flows when the immersed body constraint is imposed as a volumetric constraint force. When the IB is modelled as a zero-thickness interface, where it is no longer possible to model a volumetric constraint force, we found that cIB is not able to produce accurate results. The main source of inaccuracies in the cIB method is the distribution of the pressure field around the IB surface. An IB surface results in a jump in the pressure field across the IB. Evaluation of the discrete gradient of pressure close to the IB leads to a pressure gradient that does not satisfy the Neumann boundary condition for pressure at the IB. Furthermore, a non-zero discrete pressure gradient on the IB results in spurious flow at grid points close to the IB. We present a novel numerical formulation which adapts the cIB formulation for ‘zero-thickness’ immersed bodies. To impose the Neumann boundary condition on pressure on the IB more accurately, we introduce an additional body force to the momentum equation. A WENO based stencil penalization technique is used to define the new force term. Due to the more accurate imposition on the Neumann pressure boundary condition on the IB, spurious flow is reduced and the accuracy of no penetration velocity boundary condition on the IB is improved.

Analysis of induced error by susceptibility effect in low-density gel dosimeters.

In low-density (LD) gel dosimeter, diffusive spin-spin relaxation rate (R2)-dispersion caused by susceptibility-induced internal gradient leads to a significant deviation in the measured R2 from the real value. In this study, the effect of induced internal gradient on R2 was visualized and quantified algebraically as an important cause of inaccuracy in LD gel dosimeters. In this method, two sets of LD and unit-density (UD) gel dosimeters were prepared. The LD gel was made by mixing the UD gel with expanded polystyrene spheres. The R2 was used to determine the spatially resolved decay rates due to diffusion in internal magnetic field. The internal gradient was calculated for a multiple spin-echo sequence. It is shown that in a LD gel, the internal gradient leads to overestimation of mean R2 value (R2mean). Pixel-by-pixel R2 measurements inside a LD gel showed significant deviation from R2 mapping in UD gel. It appears that significant differences between R2mean in a selected region of interest and pixel-by-pixel R2 values are the main source of inaccuracy in dose mapping of a LD gel.

Visible light spectroscopic analysis of Methylene Blue in water; the resonance virtual equilibrium hypothesis

After a critical approach to the centennial literature on Methylene Blue self-aggregation in water, accurate visible-light absorption spectra and thermodynamic equilibrium constants for the monomeric and dimeric forms of this dye in water at different temperatures were obtained by means of a novel procedure based on the Beer-Lambert equation. A thermo-solvatochromic effect was clearly detected in the monomer spectra, which we believe to be the main source of inaccuracy in all previous works. The only published explanation for this phenomenon, the existence of a colorless form of the monomer, is refuted here. Instead, a new notion has been introduced; the resonance virtual equilibrium hypothesis. According to this hypothesis the temperature-dependent absorption behavior of the monomer is provoked by the change in its electron charge distribution with the variation in the temperature-dependent dielectric constant of water. The monomer charge distribution stands between those of the virtual resonance forms, being the absorption spectrum of the monomer a composition of the theoretical spectra for the virtual mesomers, whose proportion is established by a temperature-dependent equilibrium constant. The application of this hypothesis allowed the virtual equilibrium constants and spectra for the mesomers to be evaluated with remarkable accuracy.

Digital image stabilization in mountain areas using complete ensemble empirical mode decomposition with adaptive noise and structural similarity

Cameras mounted on scouting vehicles frequently suffer from image shake because of unintentional motions. Image shake is a main source of inaccuracies that lead to bad scouting results, particularly in mountain areas with complicated terrains. To overcome this disadvantage, this study proposes a digital image stabilization method based on complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and structural similarity (SSIM) to generate a stable scouting video sequence. The proposed method first calculates the global motion vector (GMV) from a scouting video sequence using the bit-plane matching algorithm. To separate jitter motion from intentional motion, we decompose GMV into several modes using CEEMDAN. Then according to different structural characteristics, SSIM is used to draw a boundary among modes to separate jitter motion from intentional motion. To evaluate stabilization performance in complicated situations, several known methods and the proposed stabilization method are compared. Experimental results show that CEEMDAN outperforms the other stabilization methods under mountain area conditions.

Analysis of CAD Model-based Visual Tracking for Microassembly using a New Block Set for MATLAB/Simulink

Microassembly is an innovative alternative to the microfabrication process of MOEMS, which is quite complex. It usually implies the use of microrobots controlled by an operator. The reliability of this approach has been already confirmed for micro-optical technologies. However, the characterization of assemblies has shown that the operator is the main source of inaccuracies in the teleoperated microassembly. Therefore, there is great interest in automating the microassembly process. One of the constraints of automation in microscale is the lack of high precision sensors capable to provide the full information about the object position. Thus, the usage of visual-based feedback represents a very promising approach allowing to automate the microassembly process. The purpose of this article is to characterize the techniques of object position estimation based on the visual data, i.e., visual tracking techniques from the ViSP library. These algorithms enables a 3-D object pose using a single view of the scene and the CAD model of the object. The performance of three main types of model-based trackers is analyzed and quantified: edge-based, texture-based and hybrid tracker. The problems of visual tracking in microscale are discussed. The control of the micromanipulation station used in the framework of our project is performed using a new Simulink block set. Experimental results are shown and demonstrate the possibility to obtain the repeatability below 1 µm.

The Effective Thermal Conductivity Method in Continuous Casting of Steel

The main concept of the effective thermal conductivity method is to include the effect of fluid flow in the heat transfer modelling by modifying the thermal conductivity of steel by a coefficient A to enhance the heat transfer in the liquid pool and the mushy zone in continuous casting. In this work, a case study comparison was conducted by calculating the actual flow field, heat transfer and solidification with a CFD model and comparing it with a model using the effect thermal conductivity method with A values ranging from 1 to 18. The objective of the study was to find out if the effective thermal conductivity can be used accurately to describe the effect of fluid flow and if so, which A values correspond to the CFD models results. The results indicate that the effective thermal conductivity method cannot be used reliably with constant A values: the best match in this study between the CFD model and the effective thermal conductivity method was with A value of 1 in the end of the strand and with values 9-18 in the mould area. It was concluded that main sources of inaccuracy in the effective thermal conductivity method were the use of constant A and the model’s inability to take into account the increased heat transfer produced by the SEN. The authors suggest setting the coefficient A as a function of strand location in order to fix these inaccuracies in the effective thermal conductivity method for continuous casting of steel.

PROBABILISTIC TRANSFER MATRIX WITH MIXED BINARY-DECIMAL CODING FOR LOGIC CIRCUIT RELIABILITY ANALYSIS

Technology scale leads to increasing the vulnerability of new integrated logic circuits. The high-energy neutrons (present in terrestrial cosmic radiation) and alpha particles (that originate from impurities in the packaging materials) play important role in occurrence of transient faults which are effective factor for designing reliable integrated circuits. Thus, a fast and scalable method to obtain accurate reliability value is an issue to have a dependable logic circuit design. In this paper, a new fast and scalable method is proposed to calculate the circuit reliability in which the effects of nested reconvergent paths, as a main source of inaccuracy, is considered. In the presence of reconverging signals a binary probability matrix is used to resolve signals correlation problem and increase the accuracy of the obtained reliability. Also a new mixed binary-decimal code allocation is proposed to increase the scalability of the method and reduce the complexity of calculation. Simulation results show that our proposed solution is a fast method with less complexity and also gives an accurate reliability value in comparison with other methods.

Orthogonal polynomials-based thermally induced spindle and geometric error modeling and compensation

The spindle error and geometric error are the main sources of inaccuracy in CNC machining. With the rising of the machine tool parts' temperature, the spindle error and geometric error increase continually, and the error curves have a nonlinear distribution. To analyze the thermal effects on spindle error and geometric error, an experiment is carried out. To improve the machining accuracy of a CNC machine, an error model is proposed based on orthogonal polynomials. With the application of the orthogonal polynomials, the polynomial regression can be transformed into multiple linear regressions which are easier to calculate. In order to implement the real-time error compensation for the thermally induced spindle error and geometric error, an error compensation method is proposed based on the external coordinate offset. The thermally induced spindle and geometric error are compensated by 90 % compared with no compensation.

PSD를 이용한 초정밀소형공작기계의 기하학적 오차 측정

초정밀 소형공작기계는 초정밀가공분야에서 마이크로/메조 스케일 가공품의 정밀제조기술의 핵심으로 개발되어 왔다. 소형초정밀기계의 기하학적 오차는 가공품의 품질에 큰 영향을 미치기 때문에 반드시 분석 및 보정되어야 한다. 기존 소형공작기계의 기하학적 오차는 주로 레이저 간섭계로 측정되었으나 한번의 설치로 모든 기하학적 오차를 측정할 수 없고 까다로운 절차를 따라야 한다. 그 대안으로써 PSD 로 구성된 측정시스템이 개발되었으나 측정가능거리가 PSD 의 유효영역에 한정되었다. 본 논문에서는 측정가능거리를 확장시키고 설치오차를 최소화하여 6-자유도 기하학적 오차를 측정하는 시스템을 제안하고 민감도 해석과 실험을 통하여 이 측정 시스템의 정확도를 증명하였다.

Numerical Study of Aerodynamic Losses of Effusion Cooling Holes in Aero-Engine Combustor Liners

Due to the stringent cooling requirements of novel aero-engines combustor liners, a comprehensive understanding of the phenomena concerning the interaction of hot gases with typical coolant jets plays a major role in the design of efficient cooling systems. In this work, an aerodynamic analysis of the effusion cooling system of an aero-engine combustor liner was performed; the aim was the definition of a correlation for the discharge coefficient (CD) of the single effusion hole. The data were taken from a set of CFD RANS (Reynolds-averaged Navier-Stokes) simulations, in which the behavior of the effusion cooling system was investigated over a wide range of thermo/fluid-dynamics conditions. In some of these tests, the influence on the effusion flow of an additional air bleeding port was taken into account, making it possible to analyze its effects on effusion holes CD. An in depth analysis of the numerical data set has pointed out the opportunity of an efficient reduction through the ratio of the annulus and the hole Reynolds numbers: The dependence of the discharge coefficients from this parameter is roughly linear. The correlation was included in an in-house one-dimensional thermo/fluid network solver, and its results were compared with CFD data. An overall good agreement of pressure and mass flow rate distributions was observed. The main source of inaccuracy was observed in the case of relevant air bleed mass flow rates due to the inherent three-dimensional behavior of the flow close to bleed opening. An additional comparison with experimental data was performed in order to improve the confidence in the accuracy of the correlation: Within the validity range of pressure ratios in which the correlation is defined (>1.02), this comparison pointed out a good reliability in the prediction of discharge coefficients. An approach to model air bleeding was then proposed, with the assessment of its impact on liner wall temperature prediction.

Mapping the severity of fire using object-based classification of IKONOS imagery

Mapping fire severity is necessary in order (1) to locate areas in need of special or intense post-fire management; (2) to allow the study of fire impact and vegetation recovery; and (3) to validate fire risk and fire behaviour models. The present study aimed to develop a method to map the severity of fire by employing post-fire IKONOS imagery. The objective was to develop an object-oriented model that would distinguish between different degrees of fire severity and to assess the accuracy of the model by employing field-collected data. The work comprised five main consecutive steps, namely, field data collection, data preprocessing, image segmentation, image classification and accuracy assessment. An adapted version of the FIREMON (fire effects monitoring and inventory protocol) landscape assessment method was employed to quantitatively record fire severity in the field. As a result, two different datasets were used: one for training and developing the classification rules, and another one for assessing the accuracy of the classification. Separate and independent data were used for training and for accuracy assessment. Overall accuracy was estimated to be 83%, while the Kappa Index of Agreement obtained was 0.74. The main source of inaccuracy was the inability of IKONOS to penetrate the dense canopy of unburned vegetation. The main conclusion drawn from the present work was that object-based classification applied to IKONOS imagery has the potential to produce accurate maps of fire severity, especially in the case of the open Mediterranean forest.

Towards benchmark second-order correlation energies for large atoms. II. Angular extrapolation problems

We have studied the use of the asymptotic expansions (AEs) for the angular momentum extrapolation (to l --> infinity) of atomic second-order Moller-Plesset (MP2) correlation energies of symmetry-adapted pairs (SAPs). The AEs have been defined in terms of partial wave (PW) increments to the SAP correlation energies obtained with the finite element MP2 method (FEM-MP2), as well as with the variational perturbation method in a Slater-type orbital basis. The method employed to obtain AEs from PW increments is general in the sense that it can be applied to methods other than MP2 and, if modified, to molecular systems. Optimal AEs have been determined for all types of SAPs possible in large atoms using very accurate FEM PW increments up to lmax = 45. The impact of the error of the PW increments on the coefficients of the AEs is computed and taken into account in our procedure. The first AE coefficient is determined to a very high accuracy, whereas the second involves much larger errors. The optimum l values (lopt) for starting the extrapolation procedures are determined and their properties, interesting from the practical point of view, are discussed. It is found that the values of the first AE coefficients obey expressions of the type derived by Kutzelnigg and Morgan [J. Chem. Phys. 96, 4484 (1992); 97, 8821(E) (1992)] for He-type systems in the bare-nucleus case provided they are modified by fractional factors in the case of triplet and unnatural singlet SAPs. These expressions give extremely accurate values for the first AE coefficient both for the STO and the FEM Hartree-Fock orbitals. We have compared the performance of our angular momentum extrapolations with those of some of the principal expansion extrapolations performed with correlation consistent basis sets employed in the literature and indicated the main sources of inaccuracy.

Use of hand-held laser scanning in the assessment of facial swelling: a preliminary study

A new generation lightweight, hand-held, laser surface scanner (FastSCAN™) was validated and clinically evaluated for the assessment of postoperative facial swelling. The potential sources of error—scanner error, registration error, and repositioning and movement error were established for laser scans of a mannequin head and seven volunteers. For the mannequin head the mean (S.D.) volume of the simulated swelling was 12.5 (0.5) cm 3. The measurement error was therefore about 4%, and reflected the error in scanned data and in surface registration. Among the volunteers, repositioning of the head introduced additional errors of up to 7.6 cm 3 (mean 1.8 cm 3), illustrating the additional influence of variable positions. We then scanned 20 patients (9 women and 11 men, age range 18–26) before and 2 days after, third molar removal. The external, facial soft tissue volume changes were calculated for both left and right sides (range 0.2–64.3 cm 3). The main source of inaccuracy was again variability of position. Despite this, the FastSCAN™ proved to be a simple, accurate, and non-invasive method of measuring postoperative changes in volume in the external, soft tissues of the face. Minimising variability in position by using more precise positioning techniques will increase the accuracy of this technique and is a focus for future work.

CD45-assisted PanLeucogating for accurate, cost-effective dual-platform CD4+ T-cell enumeration.

North American and European guidelines for dual-platform (DP) flow cytometry recommend absolute CD4 T-cell counts to be calculated from two parameters: the absolute lymphocyte counts obtained on a hematology analyzer and the percentages of CD4+ cells among lymphocytes (CD4%/lympho) obtained by flow cytometry. Nevertheless, the identification of lymphocytes is error-prone: a poor match between these common denominators in the two systems is the main source of inaccuracy. In contrast, total leucocyte counts (white cell counts [WCC]) and CD4% among the gated CD45+ leucocytes (CD4%/leuco) can be determined with greater accuracy. We introduced "PanLeucogating," i.e., we used total leucocytes as the common denominator for improving the precision of DP absolute CD4 counting. Correlations and Bland-Altman tests were used for statistical analysis. First, 22 stabilized blood product samples were provided by U.K. National External Quality Assessment Scheme (NEQAS) and a higher accuracy and precision of CD4 counts were documented using PanLeucogating compared with lymphocyte gating. Next, 183 fresh and 112 fixed (TransFix) whole blood samples were used to compare DP methods and single-platform (SP) methodology, including both volumetric and bead-based techniques. A particularly high correlation and comparable precision of absolute CD4 counts were observed between the SP volumetric method and DP PanLeucogating (R(2) = 0.990; bias 6 +/- SD 17%). The SP volumetric method showed lower levels of agreement with the DP lymphocyte gating (R(2) = 0.758; bias 14 +/- SD 51%) and with the SP bead-based method (R(2) = 0.923; bias 4 +/-SD 31%). These observations show that DP leucocyte counts (WCC) should replace lymphocyte counts as the "common denominator" although CD4%/lympho values can, as an extra step, be also provided readily if requested. When coupled with quality control for WCC on hematology analyzers, the DP method with CD45 PanLeucogating represents a robust CD4 T-cell assay that is as accurate as the SP volumetric technique. This DP method uses only two, CD45 and CD4, antibody reagents and can be run on any pair of hematological analyzer plus flow cytometer.

Daily growth increments in the otoliths of the three‐spined stickleback, Gasterosteus aculeatus L.

Daily increment formation was demonstrated in the sagittae of the three‐spined stickleback, Gasterosieus aculeatus L., under both laboratory and field conditions. The onset of daily increment formation coincided with the day of hatching. The main sources of inaccuracy in age determination resulted from difficulties in resolving narrow increments in the sagittae of fish held at low temperatures and the increasing incidence of checks with age. The advantage of daily increments for investigating growth in this species was demonstrated from a comparison between increment‐derived age‐at‐length data and length‐at‐capture data, since the latter significantly under‐estimated early growth rate within a population.

On possible inaccuracy in quantification of chaotic motion

Several main sources of inaccuracy in computation of characteristics of chaotic motion are illustrated by simple examples. It is shown, that the insufficiency in the number of points used for computations, the weak coupling between the subsystems and other factors may result not only in under- or overestimation of characteristics, but may lead to qualitatively wrong conclusions about the investigated systems.

Metacarpophalangeal pattern profiles: Q‐score for ages from birth to 7 years

The metacarpophalangeal pattern profile (MCPP) analysis is a widely used method of standardization of bone length measurements to quantify congenital skeletal dysplasia of the hands. A main source of inaccuracy is the prominent scatter in the values of the standard deviation (S.D.) of the reference length, which is used in the calculation of the standardized values (Z-scores). Other sources of error, especially when bone length measurements of younger children are evaluated, are the rather large variability in the age of appearance of the epiphyses of the different bones, and the use of tabulated reference data which are available only at one-year intervals. We have devised another method of standardization of bone length measurements, by calculating the Q-score. Its advantages are that no S.D. values are needed and that more accurate results are obtained. Moreover the interpretation of the Q-scores is more straightforward than the interpretation of the Z-scores. Q-scores for 3 patients with Sotos syndrome are presented. Use of the MCPP in the form of the Q-score, will probably make it an even stronger tool than before.

MODELLING FOR FATIGUE CRACK GROWTH PREDICTION IN AIRCRAFT

AbstractFatigue crack growth models, having application to Mirage III0 aircraft, have been calibrated with test data. Of the four crack growth retardation models examined—Wheeler, Willenborg, modified Willenborg and Crack Closure—the Wheeler and modified Willenborg models are the most satisfactory but both require calibration by test. Even so, crack growth is not accurately predicted when the specimen geometry and the test sequence are varied from those used in calibrating the models.Apart from the crack growth models, the main sources of inaccuracy in predicting crack growth are the inadequacy of the growth rate basic data, incorrect assumptions of crack shape and uncertainty in stress history. Thus, crack growth life may not be confidently predicted to better than a factor of two on actual life and, in some cases, the factor may be as high as ten.