Maximum Distortion Research Articles

Hypergraph-Based Source Codes for Function Computation Under Maximal Distortion

This work investigates functional source coding problems with maximal distortion, motivated by approximate function computation in many modern applications. The maximal distortion treats imprecise reconstruction of a function value as good as perfect computation if it deviates less than a tolerance level, while treating reconstruction that differs by more than that level as a failure. Using a geometric understanding of the maximal distortion, we propose a hypergraph-based source coding scheme for function computation that is constructive in the sense that it gives an explicit procedure for finding optimal or good auxiliary random variables. Moreover, we find that the hypergraph-based coding scheme achieves the optimal rate-distortion function in the setting of coding for computing with side information and achieves the Berger-Tung sum-rate inner bound in the setting of distributed source coding for computing. It also achieves the El Gamal-Cover inner bound for multiple description coding for computing and is optimal for successive refinement and cascade multiple description problems for computing. Lastly, the benefit of complexity reduction of finding a forward test channel is shown for a class of Markov sources.

The Effect of Microchannel Cavity on the Bulk Acoustic Wave-Induced Acoustofluidics: Numerical Investigation

Acoustofluidics is emerging as an effective approach to manipulating microparticles and cells no matter their optical, electrical, and magnetic properties and no requirement of pre-processing. Standing field in a microfluidic channel produced by a bulk acoustic wave (BAW) could accumulate the microparticles at the plane of the pressure node. In order to further accumulate them from a plane (2D) to a line (1D), a new strategy without significant change of the systematic setup (i.e., adding another orthogonal standing field) was proposed and evaluated numerically in a full-sized model. Concave cavity on the conventional rectangular microchannel leads to a slight increase of the maximum acoustic pressure and distortion of the wavefront, but two more vortexes close to the edge of the bottom cavity and directional acoustic radiation forces in the middle line of the microchannel (the upper part pointing downwards while the lower part upwards). Subsequently, most of the microparticles are accumulated in a very small region in the middle line of the microchannel. The effect of the cavity geometry on such a novel phenomenon was investigated. With the increase of the diameter of the cavity from 170 μm to 260 μm, the resonant frequency of the microchannel, the maximum acoustic pressure, and the maximum acoustic streaming velocity increased by 13%, 78%, and 7.1 fold, respectively. When shifting the center of the cavity, the position of 1D accumulated microparticles could be changed correspondingly. In summary, the characteristics of acoustofluidics are highly dependent on the microchannel geometry. Microparticle accumulation with a significant reduction to one dimension using only one acoustic standing field is theoretically possible by introducing an appropriate concave cavity in the conventional rectangular microchannel.

Assessment of MRI image distortion based on 6 consecutive years of annual QAs and measurements on 14 MRI scanners used for radiation therapy.

To determine the magnitude of MRI image distortion based on 6 consecutive years of annual quality assurances/measurements on 14 MRI scanners used for radiation therapy and to provide evidence for the inclusion of additional margin for treatment planning. We used commercial MRI image phantoms to quantitatively study the MRI image distortion over period of 6 years for up to 14 1.5 and 3T MRI scanners that could potentially be used to provide MRI images for treatment planning. With the phantom images collected from 2016 to 2022, we investigated the MRI image distortion, the dependence of distortion on the distance from the imaging isocenter, and the possible causes of large distortion discovered. MRI image distortion increases with the distance from the imaging isocenter. For a region of interest (ROI) with a radius of 100 mm centered at the isocenter, the mean magnitude of distortion for all MRI scanners is , and the maximum distortion varies from depending on MRI scanners. For an ROI with a radius of 200 mm centered at the isocenter, the mean magnitude of distortion increases to , and the range of the maximum distortion increases to depending on MRI scanners. The distortion could reach 2mm at 150mm from the isocenter. An additional margin to accommodate image distortion should be considered for treatment planning. Imaging with proper patient alignment to the isocenter is vital to reducing image distortion. We recommend performing image distortion checks annually and after major upgrade on MRI scanners.

A novel gut inflammatory rat model by laparotomic injection of peptidoglycan from Staphylococcus aureus.

Inflammatory bowel disease includes ulcerative colitis and Crohn's disease, and is globally increasing. An appropriate model system is required to dissect the disease pathogenesis and drugs screening for adequate treatment. In the present study, we established a novel model of gut inflammation by injecting peptidoglycan from Staphylococcus aureus using laparotomic procedure. For this, three different doses of peptidoglycan, i.e., 2.5, 5 and 10mg/kg body weight were used. The treatment effect was evaluated by studying the macrophage phagocytic function, spleen lymphocytes' proliferation and qRT-PCR for the assessment of peritoneal cells' gene expression. In addition, histological analysis of gut sections, gastric acidity, immunoglobulins and cytokines were assessed. There was significant increase in phagocytic activity in 10mg/kg body weight PGN group. A dose dependent increase in spleen lymphocytes' proliferation and a significant increase in total acid secretion in 5 and 10mg/kg body weight PGN treated rats were observed. In addition, a significant increment in TLR-2 and CD-14 mRNA expression in peritoneal cells, TNF-α, IL-6 and IFN-γ level and maximum distortion of gut architecture was observed in 10mg/kg body weight PGN group. Hence, peptidoglycan from S. aureus can be used for establishing the screening model to study the action and mechanism of anti-inflammatory food products and drugs.

Cost-Effective Design of a Miniaturized Zoom Lens for a Capsule Endoscope.

This paper presents a miniaturized design of a 2× zoom lens for application to a one-megapixel image sensor in a capsule endoscope. The zoom lens is composed of four lenses, including three plastic aspheric lenses and one glass spherical lens, and adopts a three-lens group design. This capsule endoscope is mainly for observation of the small intestine, which has a radius of about 12.5 mm. The height of the object is thus set to 12.5 mm. The object surface is designed to be curved surface with a radius of curvature of 15 mm. The focal length of the zoom lens ranges from 1.064 mm to 2.039 mm, and the full angle of view ranges from 60° to 143°, the f-number is F/2.8-F/3.5, the zoom lens is 11.6 mm in length, and the maximum effective diameter of the zoom lens is 6 mm. The zoom lens design is divided into six segments, corresponding to the different magnifications from Zoom 1 to Zoom 6. The magnification ratios are -0.0845, -0.0984, -0.1150, -0.1317, -0.1482, and -0.1690, respectively. Comparing the positions from Zoom 1 to Zoom 6, the maximum optical distortion is -14.89% for the Zoom 1 and 1.45% for the Zoom 6. The maximum vertical video distortion is 8.19% for Zoom 1 and 1.00% for Zoom 6. At a 1.0 field of view, the minimum relative illuminance is 71.8% at a magnification of M = -0.1317. Finally, we perform the tolerance analysis and lens resolution analysis at different zooming positions. Our design can obtain high-quality images for capsule endoscope.

Application of Deep Learning Gated Recurrent Unit in Hybrid Shunt Active Power Filter for Power Quality Enhancement

This research work aims at providing power quality improvement for the nonlinear load to improve the system performance indices by eliminating maximum total harmonic distortion (THD) and reducing neutral wire current. The idea is to integrate a shunt hybrid active power filter (SHAPF) with the system using machine learning control techniques. The system proposed has been evaluated under an artificial neural network (ANN), gated recurrent unit, and long short-term memory for the optimization of the SHAPF. The method is based on the detection of harmonic presence in the power system by testing and comparison of traditional pq0 theory and deep learning neural networks. The results obtained through the proposed methodology meet all the suggested international standards of THD. The results also satisfy the current removal from the neutral wire and deal efficiently with minor DC voltage variations occurring in the voltage-regulating current. The proposed algorithms have been evaluated on the performance indices of accuracy and computational complexities, which show effective results in terms of 99% accuracy and computational complexities. deep learning-based findings are compared based on their root-mean-square error (RMSE) and loss function. The proposed system can be applied for domestic and industrial load conditions in a four-wire three-phase power distribution system for harmonic mitigation.

Complexity reduction of ordinary kriging algorithm for 3D REM design

This work has investigated the feasibility of using cluster ordinary kriging (OK) interpolation to speed up indoor three-dimensional (3D) radio environment map (REM) generation time than the conventional OK-based REM generation time in two-dimensional (2D) and 3D ways mainly. The REM has been generated on the real-time received signal strength (RSS) dataset of an ultra-high frequency active television (TV) channel to explore TV grey space (TVGS) volume for cognitive access inside a six-storied office building. It can support future home networks for high-speed data-based applications. The optimal number of clusters has been found at K=4 on both 3D and 2D ways through distortion % deviation analysis. The maximum distortion % deviation = 88.74%, has been found at K=4. The exponential semivariogram model has been selected as the best-fit model after a thorough cross-validated comparative analysis of the clustered and non-clustered OK algorithms separately on residual squared error (RSE), root mean square error (RMSE) and the ratio of expected variance (EV) and kriging variance (KV) results. The RSE and RMSE are minimum, and the EV: KV ratio is in between 0.95 to 1.05 for the exponential model. Significant observation of the analysis of the results shows that cluster OK algorithms outperform conventional OK algorithms of corresponding domains on time complexity. A comparative study on RMSE, correlation coefficient (CC), and relative recovery error (RRE) show that cluster OK improves the accuracy. Cluster 2D and 3D OK-based detected TVGS volume is 13450 m3, 5.634% of the whole building volume.

The separation performance of two-dimensional ZnPP-grid molecular sieve for C6 alkane molecules:A first-principles calculation

Membrane separation technology plays a vital role in producing high-octane gasoline field. Based on the first-principles calculation, ZnPP-Grid molecular sieve with uniform intrinsic pore is used to systematically evaluate the separation performance of hexane isomers and cyclohexane. The difference of energy barriers indicates that ZnPP-Grid membrane allows linear hexane molecule to pass through the pore, but block di-branched 2,2-dimethylbutane molecule. The analysis of geometric and energy variation reveals that during penetration processes, the effect of molecular changes on the penetration barrier is greater than the effect of ZnPP-Grid membrane deformation on barrier, which is related to the size and structural flexibility of molecules and ZnPP-Grid molecular pore. Especially, when cyclic cyclohexane molecule travels to the pore area, the maximum geometric distortion of pore-rimmed atoms have not caused higher energy barrier than mono-branched 3-methylpentane, which also proves the flexibility of ZnPP-Grid membrane. The molecular sieve exhibits superior hexane/cyclohexane, hexane/branched isomers separation performance with high selectivity of 108–1080 within 150 K–400 K. More importantly, the hexane isomers mono-branched 3-methylpentane/di-branched 2,2-dimethylbutane can be discriminated with high selectivity ∼1029 at 300 K, which helps to obtain high-octane gasoline. The results demonstrate that the ZnPP-Grid molecular sieve is probably an excellent molecular sieve in petrochemical industry.

Numerical and thermal analysis of mechanical properties degradations and distortions in steel weld joint

To quantify the degradation of mechanical properties and material distortion associated with steel weld. Twin mild steel plates each of dimension 20 mm × 100 mm × 6 mm were joined in butt configuration using the arc welding method. Thermal and mechanical analyses of the system were carried out using a numerical method and the associated heat transfer/stress distribution problems were formulated based on FEM. The thermal analysis involves numerical evaluation of the transient temperature distribution in the specimen. The effects of some operational parameters including welding speed and welding power on the temperature profile were studied independently. The results suggest that a good combination of these operational variables guarantees stable welding operation which in turn assists in achieving a quality welded joint. The numerical results were validated using experimental data and further applied to solve the prevailing mechanical problem. The maximum residual stress of 200 N/mm2 was recorded along the weld line while a maximum distortion of 15 mm was recorded numerically at the free end of the steel segment at the prevailing stress condition. Therefore it is recommended that maintaining low but sufficient high welding power helps to minimize excessive temperature rise in the base metal and improves stress distribution along the welding line, which in turn mitigates degradation of tensile strength and other mechanical properties.

Numerical Modeling of Distortion of Ti-6Al-4V Components Manufactured Using Laser Powder Bed Fusion

The laser powder bed fusion (L-PBF) process is a powder-based additive manufacturing process that can manufacture complex metallic components. However, when the metallic components are fabricated with the L-PBF process, they frequently encounter the residual stress and distortion that occurs due to the cyclic of rapid heating and cooling. The distortion detrimentally impacts the dimensional and geometrical accuracy of final built parts in the L-PBF process. The purpose of this research was to explore and predict the distortion of Ti-6Al-4V components manufactured using the L-PBF process by using numerical modeling in Simufact Additive 2020 FP1 software. Firstly, the numerical model validation was conducted with the twin-cantilever beam part. Later, studies were carried out to examine the effect of component sizes and support-structure designs on the distortion of tibial component produced by the L-PBF process. The results of this research revealed a good agreement between the numerical model and experiment data. In addition, the platform was extended to predict the distortion in the tibial component. Large distortion arose near the interface between the tibial tray and support structure due to the different stiffness between the solid bulk and support structure. The distortion of the tibial component increased with increasing component size according to the surface area of the tibial tray, and with increasing thickness of the tibial tray. Furthermore, the support-structure design plays an important role in distortion reduction in the L-PBF process. For example, the maximum distortion of the tibial component was minimized up to 44% when a block support-structure design with a height of 2.5 mm was used instead of the lattice-based support. The present study provides useful information to help the medical sector to manufacture effective medical components and reduce the chance of part failure from cracking in the L-PBF process.

Reduction of Deep Dielectric Charging of Polyimide by Incorporation of Glass Microsphere or Glass Fiber Reinforcement

In outer space’s extreme electron radiation environment, the insulating medium will experience a deep dielectric charging effect. As an excellent insulating medium, polyimide is widely used in spacecraft. In practical use, glass microspheres and glass fibers are often added to increase its mechanical strength. However, the influence of glass microspheres and glass fibers on deep dielectric charging effects has often been ignored in previous studies. Therefore, the work in this article established a 3-D deep dielectric charging model of glass microsphere and glass fiber reinforced polyimide. Using the model, the effects of glass microsphere and glass fiber volume fraction, glass microsphere spacing, glass fiber orientation, and 3-D glass fiber structure were investigated. The results show that the larger the volume fraction of glass fiber or glass microsphere, the more obvious the decrease of polyimide composite media’s average electric field strength. Under the same volume fraction, glass fibers are more favorable to reduce the average electric field strength than glass microspheres. The surface of glass microspheres will form charge accumulation, increasing local maximum electric field intensity, which is greater than the maximum electric field value of pure polyimide under electron radiation. When the spacing of glass microspheres decreases, the degree of electric field distortion increases, but the electric field value decreases when the microspheres contact each other. When the glass fiber orientation is perpendicular to the ground plane, it can better provide the electronic release channel, thereby reducing the deep dielectric charging effect. Using 3-D glass fiber structures can reduce the polyimide’s average electric field value and reduce the maximum local electric field distortion.

An equivalent beam approach for assessing tunnelling-induced distortions of frames with infills

This paper presents an approach to evaluate the response of low- and medium-rise frames with continuous foundations, either with or without infills, to tunnelling employing an equivalent beam with a behaviour dominated by shear deformations. Simplified soil-structure interaction models, consisting of a beam resting on an elastic continuum half-space, are compared against advanced three-dimensional analyses in which the tunnel, the soil, and the building are explicitly modelled. In the simplified approach, the frame is schematised as a Timoshenko beam and reliable procedures to estimate both bending and shear stiffness are discussed. In the refined modelling strategy, an advanced elastoplastic constitute law is employed, capable of reproducing fairly well the soil response to the excavation for increasing values of volume loss, while the full geometry of the structure is considered. First, the results of the proposed numerical approaches are compared in terms of tunnelling-induced foundation displacements, bay deformations and maximum tensile strains in the infills. Then, for the infill panels, the reliability of estimating the maximum tensile strain from the angular distortion of the frame bays is assessed. Finally, a meta-model is proposed to predict the maximum angular distortion based on greenfield settlements, eccentricity, and relative soil-structure stiffness.

Evaluation of the ability of the Brainlab Elements Cranial Distortion Correction algorithm to correct clinically relevant MRI distortions for cranial SRT.

Cranial stereotactic radiotherapy (SRT) requires highly accurate lesion delineation. However, MRI can have significant inherent geometric distortions. We investigated how well the Elements Cranial Distortion Correction algorithm of Brainlab (Munich, Germany) corrects the distortions in MR image-sets of aphantom and patients. Anon-distorted reference computed tomography image-set of aCIRS Model 603-GS (CIRS, Norfolk, VA, USA) phantom was acquired. Three-dimensional T1-weighted images were acquired with five MRI scanners and reconstructed with vendor-derived distortion correction. Some were reconstructed without correction to generate heavily distorted image-sets. All MR image-sets were corrected with the Brainlab algorithm relative to the computed tomography acquisition. CIRS Distortion Check software measured the distortion in each image-set. For all uncorrected and corrected image-sets, the control points that exceeded the 0.5-mm clinically relevant distortion threshold and the distortion maximum, mean, and standard deviation were recorded. Empirical cumulative distribution functions (eCDF) were plotted. Intraclass correlation coefficient (ICC) was calculated. The algorithm was evaluated with 10brain metastases using Dice similarity coefficients (DSC). The algorithm significantly reduced mean and standard deviation distortion in all image-sets. It reduced the maximum distortion in the heavily distorted image-sets from 2.072 to 1.059 mm and the control points with > 0.5-mm distortion fell from 50.2% to 4.0%. Before and especially after correction, the eCDFs of the four repeats were visually similar. ICC was 0.812 (excellent-good agreement). The algorithm increased the DSCs for all patients and image-sets. The Brainlab algorithm significantly and reproducibly ameliorated MRI distortion, even with heavily distorted images. Thus, it increases the accuracy of cranial SRT lesion delineation. After further testing, this tool may be suitable for SRT of small lesions.

Influence of Contact Surfaces’ Impact on the Gear Profile during Hobbing Process

This work is the result of research on the dynamic process that occurs during milling machining, namely, the influence of the contact surfaces’ impact on the gear and the hob and the influence of their displacements on the resulting profile of the tooth. An acquisition system was placed on the final elements of the milling machine chain to determine the torque moments and displacements during gear milling. The experimental analysis proves that the displacements are within admissible limits and have no major influence on the quality of the processing surfaces. A dynamic simulation of the hobbing process with the finite element method (ANSYS) was performed for a limited period of time, and the values of deformation, equivalent strain, and stress have been determined; the time at which the chips come off and the corresponding value of the equivalent stress that occurs at their break were determined based on the maximum distortion energy von Misses theory. It is required to simulate the entire hobbing process, even if it can be time-consuming to differentiate the influence of the dynamic behavior of the machine’s kinematic supplementary chains on the hob wear and the tooth profile. A modal analysis will be able to support the comparative study related to the obtained experimental data.

PLL Based Method for Supraharmonics Emission Assessment

Supraharmonic (SH) disturbances are generated mainly by power electronics whose usage has increased significantly in the last decades. Consequently, supraharmonics have increased as well. The SH frequency range from 2 kHz to 150 kHz still lacks a normative measurement method. Compatibility levels and emission limits of SH are commonly presented as quasi-peak (QP) detector values for a bandwidth (BW) of 200 Hz measured by CISPR 16 receivers. In this context, this paper proposes an optimized method emulating the CISPR 16 receiver with QP detector for measuring grid disturbance levels. It makes innovative use of PLL (Phase-Locked Loop) units for estimating the highest distortion levels in the SH frequency range of the test signal, and in sequence, the QP detector with the appropriate specifications in the CISPR 16 standard is applied. Different cases of both synthetic and real signals were applied to the proposed method, which showed to be efficient in evaluating SH levels for current and voltage signals. An analysis of maximum permissible distortion levels is performed considering an individual SH distortion. In addition, the proposed method presents a computational cost reduction of approximately 91% in relation to the CISPR 16 method considering a specific case of signal containing SH distortions used for power quality analysis.

Disturbances in the Ionosphere and Distortion of Radio Wave Characteristics That Accompanied the Super Typhoon Lekima Event of 4–12 August 2019

AbstractWe acquired measurements of four observable parameters of refracted signals received from the ionosphere (Doppler shift, Doppler spectrum, number of rays, and signal amplitude) with the oblique HF Doppler technique in the city of Harbin during the super typhoon Lekima event of 4–12 August 2019. The ionospheric response was observed by the Harbin Engineering University multifrequency multiple path coherent radio system in the People's Republic of China. The maximum distortion of radio‐wave characteristics and ionospheric disturbances were observed to occur during the day when the super typhoon Lekima energy gained a maximum value and when the super typhoon approached close to the ionospheric part of the radio‐wave propagation paths. The magnitude of the ionospheric disturbances decreased with the distance between the super typhoon and propagation path midpoints. Both aperiodic (chaotic) and quasi‐sinusoidal disturbances were observed to accompany the action of the super typhoon in the ionosphere. The action of the typhoon was often accompanied by up to ±1.5 Hz broadening of the Doppler spectra, 10–30 dBV variations in the signal amplitude, and quasi‐sinusoidal variations in the Doppler shift with 0.10‐ to 0.40‐Hz amplitudes and periods of 20–30 to 70–80 min. The quasi‐sinusoidal variations in the signal amplitude with a ∼24‐min period, T, are due to focusing and defocusing of rays by wavelike disturbances in the electron density. The periods of the quasi‐sinusoidal disturbances were observed to be ∼12–24 min. Such periods pertain to atmospheric gravity waves. The atmospheric gravity waves generated by the super typhoon gave rise to quasi‐sinusoidal variations in the electron density with relative amplitudes of ∼3%–∼19%.

Control of Grid-Tied Multiple Distributed Generation Systems With Cooperative Compensation Capabilities

This article deals with a cooperative controlof multiple distributed generation (DG) systems with power quality (PQ)-enhancing capabilities. This control algorithm is realized using an adaptive harmonic signals extraction method based on variable weight mixed norm least mean fourth–least mean square adaptive detection. This adaptive technique extracts all the necessary information required for the development of the proposed cooperative control algorithm. With this control algorithm, the voltage source inverters (VSIs) of the DG systems contribute to PQ improvement by mitigating harmonics and reactive currents in the distribution system. This algorithm operates the VSIs in maximum power generation and total harmonic distortion (THD) improvement modes. In maximum power generation mode, the algorithm utilizes the remaining capacity of the VSIs for compensation of nonactive currents drawn by the dedicated loads. Upon finishing the dedicated loads’ compensation, the remaining capacity is spent for compensation of the loads dedicated to other DG systems that are not in the position to render full compensation services. In THD improvement mode, the algorithm prioritizes compensation of harmonic currents generated by the loads. The efficacy of the proposed cooperative control algorithm for multiple DG systems is demonstrated via simulation and hardware-in-the-loop-based experimental results.

Development and Validation of a Novel Methodological Pipeline to Integrate Neuroimaging and Photogrammetry for Immersive 3D Cadaveric Neurosurgical Simulation.

BackgroundVisualizing and comprehending 3-dimensional (3D) neuroanatomy is challenging. Cadaver dissection is limited by low availability, high cost, and the need for specialized facilities. New technologies, including 3D rendering of neuroimaging, 3D pictures, and 3D videos, are filling this gap and facilitating learning, but they also have limitations. This proof-of-concept study explored the feasibility of combining the spatial accuracy of 3D reconstructed neuroimaging data with realistic texture and fine anatomical details from 3D photogrammetry to create high-fidelity cadaveric neurosurgical simulations.MethodsFour fixed and injected cadaver heads underwent neuroimaging. To create 3D virtual models, surfaces were rendered using magnetic resonance imaging (MRI) and computed tomography (CT) scans, and segmented anatomical structures were created. A stepwise pterional craniotomy procedure was performed with synchronous neuronavigation and photogrammetry data collection. All points acquired in 3D navigational space were imported and registered in a 3D virtual model space. A novel machine learning-assisted monocular-depth estimation tool was used to create 3D reconstructions of 2-dimensional (2D) photographs. Depth maps were converted into 3D mesh geometry, which was merged with the 3D virtual model’s brain surface anatomy to test its accuracy. Quantitative measurements were used to validate the spatial accuracy of 3D reconstructions of different techniques.ResultsSuccessful multilayered 3D virtual models were created using volumetric neuroimaging data. The monocular-depth estimation technique created qualitatively accurate 3D representations of photographs. When 2 models were merged, 63% of surface maps were perfectly matched (mean [SD] deviation 0.7 ± 1.9 mm; range −7 to 7 mm). Maximal distortions were observed at the epicenter and toward the edges of the imaged surfaces. Virtual 3D models provided accurate virtual measurements (margin of error <1.5 mm) as validated by cross-measurements performed in a real-world setting.ConclusionThe novel technique of co-registering neuroimaging and photogrammetry-based 3D models can (1) substantially supplement anatomical knowledge by adding detail and texture to 3D virtual models, (2) meaningfully improve the spatial accuracy of 3D photogrammetry, (3) allow for accurate quantitative measurements without the need for actual dissection, (4) digitalize the complete surface anatomy of a cadaver, and (5) be used in realistic surgical simulations to improve neurosurgical education.

MRI safety, imaging artefacts, and grid distortion evaluated for FFP3 respiratory masks worn throughout the COVID-19 pandemic

AIMTo determine which filtering face piece (FFP3) respirators worn throughout the COVID-19 pandemic are safe for magnetic resonance imaging (MRI).MATERIALS AND METHODSThree clinical MRI sequences were performed to assess imaging artefacts, grid distortion, and local heating for eight commercially available FFP3 respirators. All examinations were performed at Cardiff University Brain Research Imaging Centre using a 3 T Siemens Magnetom Prisma with a 64-channel head and neck coil. Each FFP3 mask was positioned on a custom-developed three-dimensional (3D) head phantom for testing.RESULTSFive of the eight FFP3 masks contained ferromagnetic components and were regarded as “MRI unsafe”. One mask was considered “MRI conditional” and only two masks were deemed “MRI safe” for both MRI staff and patients. Temperature strips positioned at the nasal bridge of the phantom did not exhibit local heating. A maximum grid distortion of 5 mm was seen in the anterior portion of the head of the ferromagnetic FFP3 masks.CONCLUSIONThis study has demonstrated the importance of assessing respiratory FFP3 masks for use in and around MRI machines. Future research involving FFP3 masks can be conducted safely by following the procedures laid out in this study.

Probabilistic seismic demand models for circular tunnels subjected to transversal seismic load

This paper proposes convenient probabilistic models to estimate the seismic demands of circular tunnels to transversal seismic load. The uncertainties in the earthquake intensity, seismic load, and calculation methods are fully considered. Peak ground velocity PGV is selected as an essential earthquake intensity parameter because it is more correlated with the earthquake damage of underground structures, and a probabilistic model of PGV is proposed. Because the seismic response of tunnel linings is highly correlated with the free-field ground deformation, the maximum free field shear strain gmax is selected as the seismic load parameter. A probabilistic model of gmax is developed based on a series of seismic site response analyses. PGV plays a key role in the estimation of gmax. The analytical methods have been proposed to estimate the seismic response of tunnels. However, the results are usually biased, and the underlying uncertainties have not been well studied. To obtained unbiased seismic response estimates and capture the uncertainties in the calculation methods, the probabilistic seismic demand models are constructed by developing correction terms to the analytical method. The maximum moment Mmax, thrust Tmax, and diametric distortion Δd/dmax of the tunnel lining are considered. A pseudo-static analysis approach is used to simulate the seismic response of tunnels, and Bayesian updating is used for the model optimization and parameter estimation. The results of this paper can be used in the seismic design and reliability analysis of circular tunnels.