Sources Of Error Research Articles

Finite element analysis for the measurement error of electrostatic accelerometer due to the electrode misalignment

Abstract The electrostatic accelerometer is the key payload of many space missions, such as satellite gravity measurements, space gravitational experiments, with a typical precision requirement from nano-g to femto-g. The measurement error model analysis is an important issue for the electrostatic accelerometer with numerous error sources. The traditional method by theoretical analysis is complicated to evaluate the complete measurement error models quantitatively especially when the machining and assembly errors of the sensor head are considered. Limited by the earth gravity and seismic noise which is much higher than the intrinsic noise, the complete error model of electrostatic accelerometers can also hardly be tested on ground. In this paper, the method by using finite element analysis of the sensor head is studied. The simulation model for an electrostatic accelerometer sensor head is built, and the multi-conductor capacitance matrix data is simulated. The accuracy of the capacitance simulation is evaluated in three ways including the convergence check of the capacitance with the mesh size, the symmetry verification, and the sensitivity comparison with the theoretical model. Finally, the accelerometer measurement model is analyzed based on the simulation data, using the case of rotating installation misalignment of the upper electrode as an example. The measurement model and error items of one horizontal axis and one rotating axis are quantitatively evaluated. The method proposed in this paper provide a new effective approach to the measurement model analysis of the electrostatic accelerometers in complex working scenarios both in orbit and on ground, which could be helpful to enhance the performance and the efficiency of application.

Grammatical Errors in Students’ Recount Text Writing (A Case Study in The Third Grade of SMAN 22 Jakarta)

This study is aimed to find out grammatical errors and the sources of errors in students’ recount texts. The subject of this study is the third-grade students of SMAN 22 Jakarta in the academic year 2023/2024 which consists of 23 students. Specifically, their recount texts focused on recounting their vacation activities. From the entire third-grade class of 23 students, 16 students were selected as the study sample using the purposive sampling technique. This study used a qualitative approach to analyze and identify grammatical errors. The analysis was carried out by referring to Dulay, Burt & Krashen’s theory, a surface strategy taxonomy consisting of Omission, Addition, Misformation, and Misordering and the sources of errors based on Ellis’s theory are Interlingual Transfer and Intralingual Transfer. The result of this study showed that the total number of grammatical errors made by the students in their recount texts is 32 errors. Which consist of 4 omission errors, 7 addition errors, 8 misordering erros, and 13 misinformation errors. Accordingly, the most frequent error is misinformation error which corresponds to 13 (40,6%) of the total error. Furthermore, this study also revealed that most of the errors are caused by Intralingual Transfer (30 errors or 94% of the total error). Based on these findings, it concluded that the students had some difficulties in applying English grammar rules in their writings. Therefore, it is suggested to be aware and pay more attention to improve the English teaching and learning process.

Real-Time Dialysis Dose: Ionic Dialysis Versus Classical Urea Kinetic Modeling Indices.

Introduction Worldwide, over 850 million people need renal replacement therapy, and over 80% of them are on hemodialysis. The term "dialysis adequacy" is most often associated with the achievement of minimally acceptable indices - single pool Kt/V (spKt/V) and urea reduction ratio (URR%) and largely does not take into account other clinical indicators in patients. In addition, it should be taken into account that in the conditions of clinical practice, their measurement is carried out according to standards controlled by the regulatory structures and is carried out with a frequency between one and three months, and not during each dialysis procedure. Accordingly, based on the obtained value, we assume that it refers to the urea clearance of the entire dialysis prescription. A new methodology for measuring dialysis adequacy through ionic dialysis allows dose estimation in real time without the need for additional blood testsby recording the difference in sodium ion conductivity at the dialyzer inlet and outlet. The latter corresponds to the dialysis dose delivered and can be measured at each dialysis session, enabling timely therapeutic intervention at minimal cost to the community. The aim of this original article is to present ion dialysis to the community as a reliable and inexpensive alternative to classical urea kinetic modeling (UKM), evaluating the comparability of the two methods and the possible sources of error in the result. Material and methods This was a retrospective study of 32 patients undergoing hemodialysis at the Clinic of Nephrology and Dialysis at the University Hospital St. Marina (Varna, Bulgaria) for the period between January and December 2020.For each of the patients, four measurements (every three months) of the delivered dialysis dose were performed by ion dialysis and classical urea kinetic modeling in order to assess the comparability and reliability of the two methods. Results The analysis of the results proved a high correlation between the validated indicators of dialysis adequacy (spKt/V; URR) and those registered with online monitoring (online clearance monitor) by ionic dialysis - online Kt/V (onKt/V)while at the same time reporting a significant difference in the two methods - primarily based on the anthropometric formulas used to estimate the volume. The established regression models confirmed the high predictive value of ionic dialysis in relation to the actually delivered dose. Discussion Despite the high bond strength, our recorded values ​​for onKt/V are 8% lower compared to results using UKM. Therefore, onKt/V as an assessment metric has the ability to underestimate the dialysis dose received. Various factors as a possible source of error and its cause have been reported by some authors. Several studies have reported differences of 2-5% in instantaneous conductance measurements, which they associate mainly with differences in the diffusion coefficients of urea and sodium, as well as different effects of dialysis membrane charge or inadequate ultrafiltration correction. Conclusions Our study confirms that online clearance monitoring (OCM) is a practical non-invasive tool for daily use that complements the classic performance of OCM by helping to deliver an adequate dialysis dose with increased patient benefit and minimal cost of financial resources.

Exploring AI-chatbots’ capability to suggest surgical planning in ophthalmology: ChatGPT versus Google Gemini analysis of retinal detachment cases

BackgroundWe aimed to define the capability of three different publicly available large language models, Chat Generative Pretrained Transformer (ChatGPT-3.5), ChatGPT-4 and Google Gemini in analysing retinal detachment cases and suggesting...

Estimation and validation of elastic constants in fused filament fabrication 3D printing: From mesoscale to macroscale

Evaluating the mechanical properties of 3D-printed parts is a cumbersome task. This study poses an approach based on computational homogenization to estimate the elastic constants of fused filament fabrication 3D-printed parts. A whole methodology for characterization and experimental validation is necessary to improve finite element numerical models.Samples are characterized both mechanically and geometrically. To improve the characterization, novel algorithms based on micro-computed tomography images and image segmentation techniques are implemented. Thereafter, elastic constants are estimated, informed by the characterization results. The method’s effectiveness is assessed through a deep comparison, based on the digital image correlation technique, between different experimental samples and finite element models.Results show that the numerical estimation provided in this work is accurate enough to develop realistic finite element models, including anisotropy of the structures. However, defects and voids developed during 3D printing are an important source of error for these numerical models.This work provides an estimation and validation of elastic constants in 3D-printed parts, including geometrical characterization, numerical homogenization and experimental validation. The results of this work provide valuable information encompassing techniques to improve the characterization of 3D-printed parts, tendencies on elastic constants, and main sources of error.

Reducing Leakage of Single-Qubit Gates for Superconducting Quantum Processors Using Analytical Control Pulse Envelopes

Improving the speed and fidelity of quantum logic gates is essential to reach quantum advantage with future quantum computers. However, fast logic gates lead to increased leakage errors in superconducting quantum processors based on qubits with low anharmonicity, such as transmons. To reduce leakage errors, we propose and experimentally demonstrate two new analytical methods, Fourier ansatz spectrum tuning derivative removal by adiabatic gate (FAST DRAG) and higher-derivative (HD) DRAG, both of which enable shaping single-qubit control pulses in the frequency domain to achieve stronger suppression of leakage transitions compared to previously demonstrated pulse shapes. Using the new methods to suppress the ef transition of a transmon qubit with an anharmonicity of −212 MHz, we implement RX(π/2) gates achieving a leakage error below 3.0×10−5 down to a gate duration of 6.25 ns without the need for iterative closed-loop optimization. The obtained leakage error represents a 20-fold reduction in leakage compared to a conventional cosine DRAG pulse. Employing the FAST DRAG method, we further achieve an error per gate of (1.56±0.07)×10−4 at a 7.9-ns gate duration, outperforming conventional pulse shapes both in terms of error and gate speed. Furthermore, we study error-amplifying measurements for the characterization of temporal microwave control-pulse distortions, and demonstrate that non-Markovian coherent errors caused by such distortions may be a significant source of error for sub-10-ns single-qubit gates unless corrected using predistortion. Published by the American Physical Society 2024

Error analysis model-driven workflow for self-calibration stitching testing of X-ray flat surfaces

Self-calibration stitching test is widely utilized for testing X-ray flat surfaces. Various factors, including environment disturbances, motion errors, misalignments, overlapping ratios, and sub-aperture sizes can affect the accuracy. Previous studies have shown that motion errors can introduce slope errors in the test surface, and higher overlapping ratios can increase the test error. However, these error analyses have not been comprehensive or quantitatively sufficient for practical applications. For X-ray flat surfaces with specific accuracy requirements, the necessary control levels for error sources and the optimal test parameters remain unclear. To this end, an error analysis model-driven workflow for self-calibration stitching testing of X-ray flat surfaces is proposed. This model allows for the systematic evaluation of how different error sources and test parameters affect test accuracy. Further, it can guide the determination of the control levels of error sources and test parameters, moving beyond the reliance on empirical experience as seen in previous studies. A flat X-ray mirror with clear aperture of 250 mm × 30 mm and 0.2 nm (50 nrad) RMS accuracy requirement was utilized to demonstrate the procedures of the workflow. Verification experiments demonstrated that this workflow can serve as a standard model for evaluating test accuracy and guiding test procedures to achieve the desired accuracy in self-calibration stitching of X-ray flat mirrors.

Dynamic Characteristics of a 1950s Heritage Building: A Comparison of Original Design Methods and Modern Techniques

Research on design rules and methods for architectural heritage is an important aspect of conservation practice. Nevertheless, efforts to recover and divulge design methods for Modern Heritage remain limited. This paper is related to the recent structural assessment of a 15-storey heritage building built in 1950, during which a document describing the original seismic analysis of this structure was identified. The methodology employed is of particular interest, as it involves the application of pioneer concepts of dynamic analysis in the design of the first tall buildings in Mexico. The primary aim of this paper is to review the seismic design criteria for the case under study in order to contribute to the state of the art in Modern Heritage. The review includes a comparison between the dynamic characteristics estimated during the design and the results of recent ambient vibration tests and numerical modeling. Several sources of error among the design criteria were identified. Notably, the fundamental period estimated during the design was 38% larger than the experimental value due to an underestimation in stiffness, which introduces significant uncertainty into the design. Overall, the review shows the evolution of seismic analysis over time and provide valuable insights for the study of similar buildings.

Maternal effects and its importance in the genetic evaluations of preweaning live weight traits of beef cattle. A review.

Maternal effects in cattle genetics are defined as the causal influence of the phenotype or maternal genotype on the offspring's phenotype by effects occurring when the genetic and environmental characteristics of the mother influence the phenotype of the offspring beyond the direct inheritance of genes. Its relevance has been strongly described in genetic models focused on the genetic improvement of preweaning traits in cow-calf beef cattle production systems. Here, basic concepts and the importance of maternal effects when using linear and animal model procedures for genetic evaluations of growth and live-weight traits in beef cattle are reviewed and discussed. A brief history of estimation methods from classical studies to recent studies used for the development of animal models for studying maternal effects is also provided. Some important biometric concepts for maternal effect estimation are described, and the antagonism between direct genetic effects and maternal effects, its biological basis, and sources of error in the estimation of direct genetic and maternal covariance are discussed. Finally, some genomic perspectives are presented.

Optical actinometry for number density measurements in low-pressure plasmas: Advantages, error sources, and method validation

Number density of plasma-generated atoms or molecules is an important parameter for both fundamental research and applications. It can be measured in a straightforward manner, using vacuum-ultraviolet absorption spectroscopy, which is mainly possible in laboratory conditions as it may require bulky equipment, such as lasers. By contrast, optical actinometry is an alternative approach that only uses spontaneous emission from the plasma. This technique relies on the so-called corona excitation and uses emission line ratios between the gases with unknown and known concentrations (called actinometer in the last case). As a result of using line ratios, the additional density calibration is not required if the excitation cross sections are known. This study discusses Ar-based actinometry in low-pressure (roughly <1 kPa) plasma discharges with an emphasis on multiple line ratios. The work is particularly focused on the method’s applicability, the choice of Ar cross sections, and potential error sources. The influence of the additional excitation mechanisms is analyzed based on both experiments and modeling. The optical transitions for F, O, H, N, and P atoms along with expressions for their number density are presented, not requiring high optical resolution for measurements. For the sake of method validation, it is shown that in low-pressure radiofrequency discharges, a nearly excellent agreement between the actinometry data and the calibrated measurements can be achieved by careful selection of optical transitions.

Quantitative analysis of spectral properties and composition of primitive achondrites (acapulcoites, lodranites and winonaites)

The establishment of robust meteorite-asteroid links has been a major focus of planetary exploration, and a major driver of asteroid sample return missions. Reflectance spectroscopy has been shown to be a powerful tool for this purpose. For the meteorites dominated by silicate minerals, quantitative analysis of spectral absorption features caused by the Fe2+-bearing minerals (mainly olivine and pyroxene) is a common method to determine mafic silicate mineralogy and end member abundances, and establish the relationship between them and possible parent bodies. In this study, the reflectance spectra of 22 primitive achondrites (acapulcoites, lodranites and winonaites) from NASA RELAB database were analyzed to determine their positions in the plot of the band area ratio (BAR) and 1 μm band center (Band I center). We found that Band I center and BAR of acapulcoites and lodranites are in roughly the same range. Acapulcoite-lodranite partially overlap with the field of H chondrites in the plot of the BAR and Band I center. This overlap means that spectral calibrations (also referred to as mineralogical formulas) based on the two types of meteorites needs to be applied with caution. The 2 μm band center of acapulcoite–lodranite is significantly lower than that of H chondrites, which is consistent with the conclusion of previous studies and provides a means to separate these two groups. In addition, the choice of spectral parameter analysis techniques may be a potential error source in similar studies. We provide generalized spectral fields of primitive achondrites in the plot of the BAR and Band I center derived from two widely used technologies.

Toward a Mølmer Sørensen gate with .9999 fidelity

Abstract Realistic fault-tolerant quantum computing at reasonable overhead requires two-qubit gates with the highest possible fidelity. Typically, an infidelity of ≲ 10 − 4 is recommended in the literature. Focusing on the phase-sensitive architecture used in laboratories and by commercial companies to implement quantum computers, we show that even under noise-free, ideal conditions, neglecting the carrier term and linearizing the Lamb–Dicke term in the Hamiltonian used for control-pulse construction for generating Mølmer–Sørensen XX gates based on the Raman scheme are not justified if the goal is an infidelity target of < 10 − 4 . We obtain these results with a gate simulator code that, in addition to the computational space, explicitly takes the most relevant part of the phonon space into account. With the help of a Magnus expansion carried to the third order, keeping terms up to the fourth order in the Lamb–Dicke parameters, we identify the leading sources of coherent errors, which we show can be eliminated by adding a single linear equation to the phase-space closure conditions and subsequently adjusting the amplitude of the control pulse (calibration). This way, we obtain XX gates with infidelities < 10 − 4 .

Exploring Sources of Errors in L3 English Production of Natives of Moroccan Arabic

Language learners’ writing products can provide insights into how these learners acquire the target language through the analysis of the committed errors. Indeed, research has revealed that error analysis in writing essays is crucial for understanding and improving language acquisition by identifying common errors, and their sources, and informing teaching strategies to address these issues. The current paper aims to identify, describe and analyze errors committed by Moroccan secondary school students in writing. The study also attempts to determine some of the possible causes of the errors to offer an understanding of how linguistic interference influences the foreign language learning process. To this end, a sample of tasks written in English by a group of 20 secondary school students was collected. Then, an analysis procedure was conducted to analyze errors and explain their sources. Hence, this study adopts a mixed-method approach design to generate qualitative as well as quantitative data by identifying error categories and calculating the total number of error types and sources, respectively. The findings show that the errors are committed both at the word as well as the sentential level including lexical, grammatical, substance, and syntactic errors. Besides, the results indicate that learners commit errors in their English writings partly due to interference of Moroccan or Standard Arabic and French, but mostly due to other developmental sources within the scope of the target language. These findings offer valuable insights into how learners acquire a second or foreign language and what obstacles they encounter in the learning process and, thus, could suggest some implications to reduce the errors caused by negative language transfer and improve learners’ language proficiency.

Producing annual Australia-wide vegetation height images from GEDI and Landsat data

ABSTRACT Vegetation height, and its spatial and temporal changes, is an important environmental parameter required for understanding natural habitats, estimating carbon stores and monitoring forestry activities. Recent satellite LiDAR altimetry sensors have discontinuous spatial coverage but can be combined with spatially complete remote sensing data to extrapolate to large regions. Earlier studies have focused on producing a single spatially continuous vegetation height product. This research builds on past studies, using Landsat (annual surface reflectance and fractional cover products) and the Global Ecosystem Dynamics Investigation (GEDI) data to generate annual vegetation height layers from 1988 to 2022. GEDI data for 2019 were used to train and validate the model, resulting in a root mean square error (RMSE) of 5.45 m, mean absolute error (MAE) of 3.82 m, and coefficient of determination (R2) of 0.63. This accuracy reduces when the modelled height for 2020, 2021, and 2022 is compared to GEDI data for the same years (RMSE = 6.08–6.29 m, MAE = 4.36–4.73 m, and R2 = 0.48–0.54). Validation with independent field measurements across Australia from 2011 to 2021 shows an RMSE, MAE, and R2 of 8.2 m, 5.2 m, and 0.48, respectively. One source of error is the saturation of the Landsat signal in tall, closed canopy vegetation. While model accuracy is correlated with plot-based vegetation height measurements, results indicate that accuracy reduces for the years outside of the model calibration year (i.e. 2019). When compared to other vegetation height products (also produced using GEDI and spatial remote sensing data) from three independent published studies (one for 2009, one for 2019, and one for 2020), the model developed here tends to estimate 2–4 m taller than the first two studies and around 5 m shorter when compared to the third study. This investigation demonstrates the potential to produce multiyear vegetation height at a continental scale but also highlights the large uncertainty in modelled estimates especially when extrapolating to years other than the model calibration year.

Equivalent Error Based Modelling for Prediction and Analysis of Measuring Accuracy in 3-Axis FXYZ Coordinate Measuring Machines from Position, Repeatability and Reversibility Errors

AbstractThe measuring accuracy of coordinate measuring machines (CMMs) will be affected by the different geometrical and dynamic errors, including the deviations associated to the axis displacement, the working table and the part to be measured. This work is focused on the analysis of the influence of the position errors, repeatability errors and reversibility errors in 3-axis FXYZ coordinate measuring machines, and it will be developed by a numerical model that is known as EE-based stochastic model. This model implements a new error index that is named equivalent error (EE), which will integrate the totality of machine errors of the CMMs and will allow a global description of all these error sources by means of a unique error parameter. The results obtained by this numerical model have been compared with the application of a traditional method, and it was probed that the EE-based model makes possible an increase of a 13.29% in the linear modelling of the performance of CMMs from the machine errors considered in this work, which implies a relevant improvement for the analysis and description of the effect of the distinct error sources on the achievable measuring accuracy of CMMs. For this reason, the EE-based model will be of special interest for industrial applications such as the quality control to be applied inside the production systems dedicated to manufacture mechanical components of high dimensional accuracy.

Development of a method for assessing the degree of hydrogenation of titanium alloy VT1-0 by acoustic method

In this paper, the possibilities of using a non-destructive acoustic method to determine the degree of hydrogenation of titanium alloy VT1-0 are investigated. The features of the use of various acoustic parameters for the construction of engineering techniques for determining the structural state of a titanium alloy at various stages of its hydrogenation are analyzed. A number of computational and experimental methods for determining the mass fraction of hydrogen in a titanium alloy are proposed, based on the use of its acoustic characteristics, which increase the accuracy and stability of the algorithms underlying the calculation part of the methods. The sources of errors of the proposed methods, the limits of their applicability, as well as the requirements for hardware and software for their implementation are analyzed. The results of acoustic measurements carried out on samples from the VT1-0 alloy are compared with the ideas about the patterns of its structural changes during its hydrogenation. The possibility of creating engineering algorithms for assessing the state of the material of products subjected to hydrogenation on the basis of experimental data obtained in order to prevent dangerous degradation of its operational properties is shown.

How to teach students of medical and biological sciences electrophoresis in the spirit of physical chemistry - a laboratory exercise scenario.

Gel electrophoresis is one of the most important and most widely used tools in biomedical sciences. However, when students are acquainted with these techniques, information related to practical applications often neglects the physicochemical foundations of the occurring phenomena. The following article proposes a laboratory exercises scenario conducted in the problem-solving and decision-making strategies, which aims to familiarize beginner students with the physicochemical basis of electrophoresis in a simple and accessible way. By analyzing the scheme presented, students will gain knowledge of the basic sciences, as they will learn about the advantages and limitations of the method in addition to its applications. The experiments are designed in a way that allows students to draw conclusions about the parameters affecting the electrophoresis process and the sources of obvious errors. Moreover, the use of simple ionic dyes eliminates the need for complex apparatus and toxic reagents, which may be harmful. The main outcome of the class is to develop students' skill to design their own simple experiments using this commonly used technique.

Medication stewardship in the operating theatre in Malaysia: A quality improvement project.

A quality improvement project ('Safe Anaesthesia for ALL-SEAL') was implemented to reduce preventable medication errors and drug wastage in the operating theatre (OT) of a tertiary hospital. The primary objective of this quality improvement project was to prevent the incidence of medication errors, and the secondary objective was to reduce the wastage of unused drugs. A pre-intervention questionnaire and an audit survey were performed, and multidirectional interventions were designed post-survey. A post-intervention survey was conducted to evaluate effectiveness. The incidence of medication errors, including near misses, was assessed for root causes. Unused drugs drawn or diluted in syringes were recorded daily in each OT. The weekly drug orders and mid-week reordering frequency were also monitored. The data were reported as simple means and percentages. Ninety-eight anaesthesia care providers participated in the survey (72.4% doctors and 27.6% anaesthetic nurses). Pre-intervention, 76.1% of respondents had experienced medication errors during their practice. Common errors included misidentification of ampoules or vials (65.2%), miscalculation of dosages (65.2%), improper syringe labelling (56.5%), accidental drug omission (54.3%) and wrong prescriptions (39.1%). The main sources of errors were fatigue/overwork (80.4%) and a hectic OT environment (71.7%). Post-intervention, no incidents of medication errors were reported. In addition, there was a significant reduction in drug wastage. The SEAL project positively prevented medication errors and reduced drug wastage, which should be further validated in other clinical settings.

Why Students Cannot Easily Integrate Component Skills: An Investigation of the Composition Effect in Programming

Programming skills are increasingly important to the current digital economy, yet these skills have long been regarded as challenging to acquire. A central challenge in learning programming skills involves the simultaneous use of multiple component skills. This article investigates why students struggle with integrating component skills—a challenge called the composition effect. This effect was first studied in learning mathematics, and findings in that area have led to more effective instruction in mathematics. In the current work, we systematically investigate the nature of the composition effect in novice code tracing through a classroom study in a university-level introductory programming course. We designed a set of problems that require integrating component skills, along with matched problems that use the same component skills separately. The composition effect was defined as the performance difference between these two types of problems. We further singled out errors that were committed in integration problems but not in the matched problems and conducted qualitative coding to categorize these errors. Statistical analyses produced three main findings. First, we found a robust composition effect across problems and students, mostly with small or medium effect sizes. Second, we identified two potential sources of errors for this composition effect: conceptual misunderstandings of how to integrate component skills and process errors resulting from slips related to cognitive load challenges. In particular, additional conceptual knowledge often appears to be needed when component skills are integrated in specific ways. Moreover, the primary source appears to be misunderstandings of how skills integrate. Composition effects may not generalize across topics, which suggests that domain topics may serve as the conceptual basis for the composition effect. Third, we found stable individual differences in susceptibility to the composition effect in both overall and finer-grained levels. Our findings provide implications for building theories that may generally explain challenges in learning complex skills and may result in practical designs for skill integration enhanced curricula and instruction to foster student mastery in computing education.

Phylogenomic analysis of brachyuran crabs using transcriptome data reveals possible sources of conflicting phylogenetic relationships within the group

Despite extensive morphological and molecular studies, the phylogenetic interrelationships within the infraorder Brachyura and the phylogenetic positions of many taxa remain uncertain. Studies that used a limited number of molecular markers have often failed to provide sufficient resolution, and may be susceptible to stochastic errors and incomplete lineage sorting (ILS). Here we reconstructed the phylogenetic relationships within the Brachyura using transcriptome data of 56 brachyuran species, including 14 newly sequenced taxa. Five supermatrices were constructed in order to exclude different sources of systematic error. The results of the phylogenetic analyses indicate that Heterotremata is non-monophyletic, and that the two Old World primary freshwater crabs (Potamidae and Gecarcinucidae) and the Hymenosomatoidea form a clade that is sister to the Thoracotremata, and outside the Heterotremata. We also found that ILS is the main cause of the gene-tree discordance of these freshwater crabs. Divergence time estimations indicate that the Brachyura has an ancient origin, probably either in the Triassic or Jurassic, and that the majority of extant families and superfamilies first appeared during the Cretaceous, with a constant increase of diversity in Post-Cretaceous-Palaeogene times. The results support the hypothesis that the two Old World freshwater crab families included in this study (Potamidae and Gecarcinucidae) diverged from their marine ancestors around 120 Ma, in the Cretaceous. In addition, this work provides new insights that may aid in the reclassification of some of the more problematic brachyuran groups.