Homogeneous Volume Research Articles

Enabling Electric Field Model of Microscopically Realistic Brain.

Modeling brain stimulation at the microscopic scale may reveal new paradigms for a variety of stimulation modalities. We present the largest map of distributions of the extracellular electric field to date within a layer L2/L3 mouse primary visual cortex brain sample, which was enabled by automated analysis of serial section electron microscopy images with improved handling of image defects (250×140×90 μm 3 volume). We used the map to identify microscopic perturbations of the extracellular electric field and their effect on the activating thresholds of individual neurons. Previous relevant studies modeled a macroscopically homogeneous cortical volume. Result: Our immediate result is a reduction of the predicted stimulation field strength necessary for neuronal activation by a factor of approximately 0.7 (or by 30%) on average, due to microscopic perturbations of the extracellular electric field-an electric field "spatial noise" with a mean value of zero. Although this result is largely sample-specific, it aligns with experimental data indicating that existing macroscopic theories substantially overestimate the electric fields necessary for brain stimulation. Currently, there is a discrepancy between macroscopic volumetric brain modeling for brain stimulation and experimental results: experiments typically reveal lower electric intensities required for brain stimulation. This study is arguably the first attempt to model brain stimulation at the microscopic scale, enabled by automated analysis of modern scanning electron microscopy images of the brain. The immediate result is a prediction of lower electric field intensities necessary for brain stimulation, with an average reduction factor of 0.7.

Micromechanics modeling on the prediction of dielectric constant of polymer‐matrix composites considering inhomogeneity interaction

AbstractPredicting the dielectric constant of composites based on their component characteristics can accelerate the development of high‐energy storage dielectrics. In this work, to take into account the shape and interaction of randomly oriented inhomogeneities on the dielectric properties of composites, the orientation interaction model (OIM) initially used for composite stiffness prediction is adopted to predict the dielectric constant of composites. OIM applies to multi‐phase composites, and the inhomogeneities are approximated using ellipsoids in OIM. To verify the proposed model, some test data are adopted, and the model predictions match well with the test data. It is found that the inhomogeneity shape has a large influence on the dielectric constant of composites, and the influence increases with increase of the dielectric property difference between inhomogeneities and the matrix. The model captures that at the same inhomogeneity volume fraction, composites containing high aspect ratio inhomogeneities exhibit a high dielectric constant, and it shows penny‐shaped inhomogeneities perform better than cylindrical inhomogenities on increasing the dielectric constant of composites.Highlights The interaction among randomly oriented inhomogeneities is considered. Every parameter can be determined based on the microstructure of composites. The proposed model applies to multi‐phase composites.

3T sodium-MRI as predictor of neurocognition in nondemented older adults: a cross sectional study.

Dementia is a burgeoning global problem. Novel magnetic resonance imaging (MRI) metrics beyond volumetry may bring new insight and aid clinical trial evaluation of interventions early in the Alzheimer's disease course to complement existing imaging and clinical metrics. To determine whether: (i) normalized regional sodium-MRI values (Na-SI) are better predictors of neurocognitive status than volumetry (ii) cerebral amyloid PET status improves modelling. Nondemented older adult (>60 years) volunteers of known Alzheimer's Disease Assessment Scale (ADAS-Cog11), Mini-Mental State Examination (MMSE) and Consortium to Establish a Registry for Alzheimer's Disease (CERAD) neurocognitive test scores, ApolipoproteinE (APOE) e4 +/- cerebral amyloid PET status were prospectively recruited for 3T sodium-MRI brain scans. Left and right hippocampal, entorhinal and precuneus volumes and Na-SI (using the proportional intensity scaling normalization method with field inhomogeneity and partial volume corrections) were obtained after segmentation and co-registration of 3D-T1-weighted proton images. Descriptive statistics, correlation and best-subset regression analyses were performed. In our 76 nondemented participants (mean(standard deviation) age 75(5) years; woman 47(62%); cognitively unimpaired 54/76(71%), mildly cognitively impaired 22/76(29%)), left hippocampal Na-SI, not volume, was preferentially in the best models for predicting MMSE (Odds Ratio (OR) = 0.19(Confidence Interval (CI) = 0.07,0.53), P-value = 0.001) and ADAS-Cog11 (Beta(B) = 1.2(CI = 0.28,2.1), P-value = 0.01) scores. In the entorhinal analysis, right entorhinal Na-SI, not volume, was preferentially selected in the best model for predicting ADAS-Cog11 (B = 0.94(CI = 0.11,1.8), P-value = 0.03). While right entorhinal Na-SI and volume were both selected for MMSE modelling (Na-SI OR = 0.23(CI = 0.09,0.6), P-value = 0.003; volume OR = 2.6(CI = 1.0,6.6), P-value = 0.04), independently, Na-SI explained more of the variance (Na-SI R 2 = 10.3; volume R 2 = 7.5). No imaging variable was selected in the best CERAD models. Adding cerebral amyloid status improved model fit (Akaike Information Criterion increased 2.0 for all models, P-value < 0.001-0.045). Regional Na-SI were more predictive of MMSE and ADAS-Cog11 scores in our nondemented older adult cohort than volume, hippocampal more robust than entorhinal region of interest. Positive amyloid status slightly further improved model fit.

Optimized algorithm for speed-of-sound-based infant sulfur hexafluoride multiple-breath washout measurements.

Major methodological issues with the existing algorithm (WBreath) used for the analysis of speed-of-sound-based infant sulfur hexafluoride (SF6) multiple-breath washout (MBW) measurements lead to implausible results and complicate the comparison between different age groups and centers. We developed OASIS-a novel algorithm to analyze speed-of-sound-based infant SF6 MBW measurements. This algorithm uses known context of the measurements to replace the dependence of WBreath on model input parameters. We validated the functional residual capacity (FRC) measurement accuracy of this new algorithm in vitro, and investigated its use in existing infant MBW data sets from different infant cohorts from Switzerland and South Africa. In vitro, OASIS managed to outperform WBreath at FRC measurement accuracy, lowering mean (SD) absolute error from 5.1 (3.2) % to 2.1 (1.6) % across volumes relevant for the infant age range, in variable temperature, respiratory rate, tidal volume and ventilation inhomogeneity conditions. We showed that changes in the input parameters to WBreath had a major impact on MBW results, a methodological drawback which does not exist in the new algorithm. OASIS produced more plausible results than WBreath in longitudinal tracking of lung clearance index (LCI), provided improved measurement stability in LCI over time, and improved comparability between centers. This new algorithm represents a meaningful advance in obtaining results from a legacy system of lung function measurement by allowing a single method to analyze measurements from different age groups and centers.

Characterization of the BOLDPET optical prototype, an innovative Cherenkov detector for 511 keV γ radiation

In the present work we describe the design, construction, and testing of the optical prototype developed for the BOLDPET project, with the objective of creating a PET detection module with high spatial and time resolution. The BOLDPET technology uses an innovative detection liquid, trimethylbismuth, for detecting 511 keV γ-quanta resulting from positron annihilation. The optical signal is exclusively produced through the Cherenkov mechanism, and the produced photons are detected using Planacon microchannel-plate photomultiplier. We achieve an excellent time resolution of 150 ps (FWHM) within a sizable detection volume measuring 55 mm× 55 mm× 25 mm. Through detailed Geant4 simulations, we examine the limiting factors affecting time resolution and explore potential avenues for improvement. Furthermore, we demonstrate the feasibility of coarse 2D localization of interactions using the optical signal alone, achieving a precision of about 5–8 mm (FWHM) within the homogeneous detection volume.

The extended resonant modal theory and its applications

AbstractThe authors extend the resonant modal theory (RMT) developed previously for a metal object to an arbitrary source region consisting of metals, dielectrics, or a combination of both. The influences of dielectrics on the fields are replaced by equivalent volume sources through the use of the compensation theorem in electromagnetic theory. The resonant frequencies can be determined by finding the roots of the determinant of the matrix resulted from the discretisation of the real homogeneous volume–surface integral equation derived from the requirement that the difference of stored field energies in the source region vanishes. As applications of the extended RMT, three examples have been investigated. The first example is a dielectric resonator antenna and is designed by exciting the first resonant mode of the composite structure in which the dielectric cylinder is combined with a conformal metallic strip. The second example is a dual‐band dielectric‐coated metallic wire antenna. The third example studies the resonant modes of a rectangular patch antenna.

Analysis of the interaction of a landslide with viaduct foundations under static and dynamic conditions

The analysis of landslide movements and their consequences on infrastructure is of pivotal interest for social and economic reasons. This article investigates the interaction between bridges and landslides by evaluating the interaction of a landslide with the foundations of a viaduct located on a moderately inclined slope, both under static and dynamic conditions. By analyzing numerous case studies located in different parts of the world, it was possible to highlight the most common conditions and consequences occurring when a landslide interacts, partially or completely, with a viaduct. Based on these analyses, a three-dimensional finite element analysis was developed, considering an ideal complex topography, and simulating a rotational landslide that moves along the direction aligned with the viaduct axis. To model the homogeneous soil volume where the viaduct is founded and the landslide is triggered, an advanced constitutive model was employed, capable of reproducing hysteresis during cyclic loading conditions and the contextual attenuation of the soil dynamic stiffness. The results highlighted that, in seismic scenarios, the foundation piles of the viaduct play a crucial role in balancing the destabilizing actions exerted by the landslide, resulting in a significant reduction in horizontal displacements at the base and top of the pier.

Improvement of the technological scheme fan cotton sprayer OВХ-600 for biologically effective plant protection

The article presents the developed technological scheme of the ОВХ-600 fan cotton sprayer, to switch to a low-volume spraying method with flow rate of working fluid in the range of 50-100 liters per hectare. Conducted studies of the technological scheme sprayer show that to ensure agrotechnical requirements of the low-volume process spraying needs improvement system for supplying working fluid to the sprayer. That is, the supplied working fluid must be the most homogeneous and given volume. Solving these problems for installation on the sprayer flow diagram led installation of a self-cleaning filter and dispenser tap. For facilitating installation and dismantling of the sprayer, as well it is proposed to reduce non-operating costs completely mounted version of the fan sprayer, without special constructive changes.

Investigation of a thermomechanical improved tangential fan geometry

In convection-dominated thermoprocessing plants, the current state of the art is to use centrifugal and axial fans in conjunction with flow straighteners to ensure a homogeneous inflow of the fluid and thus a homogeneous temperature distribution. However, flow straighteners lead to an additional pressure loss in the system that must be overcome. Tangential fans can deliver a homogeneous volume flow over the entire width of the fan even without flow straighteners. Therefore, they offer a possibility to increase the energy efficiency of these systems. Based on this motivation, the possibilities of increasing the thermomechanical long-term stability of tangential fans are being evaluated as part of a current research and development project. To this end, the effects of design changes on the generated flow and the mechanical loads are being investigated with the help of FEM and CFD simulations. The aim is to design a tangential fan that can withstand the mechanical and dynamic loads and deliver a consistently high and homogenous fluid flow at the same time. A geometry based on the results of the simulations was manufactured as a functional sample. This sample was investigated at the hot test stand of the IOB and is compared to a reference tangential fan.

Experimental investigation on the surface and volume homogeneity of additive manufactured fused silica components in the Laser Glass Deposition process

Laser Glass Deposition is an additive manufacturing method to produce individualized structural components out of glass. A CO2 laser is utilized as a heat source to melt fused silica filaments and transform them into a formable viscous state. The fiber filament is fed laterally under a defined angle into the process zone. The viscous filament is deposited layer-by-layer using a 3-axis linear system with an integrated rotational axis. To investigate the surface and volume quality of the additively manufactured fused silica components, fully dense test specimens are analyzed in this paper. Quality characteristics such as surface roughness, formation of boundary layers and optical transparency constitute the focus of the investigations. Consequently, fully dense glass components with homogeneous volume structures without pores and boundary layers and a surface roughness of less than 30 nm were printed successfully.

SIMULATION OF PREMATURE VENTRICULAR CONTRACTIONS IN PATIENT SPECIFIC BIDOMAIN VENTRICULAR MODEL

The goal of the study was to simulate electrical activation of the heart ventricles and corresponding body surface potentials (BSPs) during premature ventricular contractions (PVC) using the patient specific realistic homogeneous model of cardiac ventricles and the torso. Real position of the initial ectopic activation during PVC was determined by intracardial measurement in the upper part of the right ventricle near the His bundle and confirmed by successful catheter ablation of the PVC origin. Simulated electrical activation in the ventricular model was started at the position of the initial ectopic activation as well as at several other sites at various distances from this position. The propagation of electrical activation in the ventricular model was modeled using bidomain reaction-diffusion (RD) equations with the ionic transmembrane current density defined by the modified FitzHugh-Nagumo (FHN) equations. The torso was modeled as a homogeneous passive volume conductor. The RD equations were numerically solved in the Comsol Multiphysics environment. Simulated ECG signals and BSPs were compared with those measured during PVC in a real patient. The polarity and shape of simulated and measured ECG leads as well as the BSP distribution during the PVC were in best agreement when the stimulated region was less than 10 mm from the position of the initial ectopic activation.

Middle-Class Housing Development in Thessaloniki, Greece

Middle-class housing in Greece developed rapidly after World War II (WWII). Across all Greek cities a multi-story building type, so-called “polykatoikia” emerged because before the war, in 1929, a social and legal contract was constituted, according to which each apartment could be owned by “micro-owners”. The applied General and Special Building Regulations envisioned a homogeneous city volume composed of these polykatoikias. On the other hand, the new ownership model invited a heterogeneous middle-class population to buy and reside in these apartments, in contrast to the previous homogenous one owner per building model. Thessaloniki developed differently than other cities, starting with homogeneous urban planning and city volume, but heterogeneous architectural styles that would evolve vice versa in the post-WWII era. The contemporary political–social–economic changes modified the city’s development vision and population’s needs related to the polykatoikia. Today, the matured state of the polykatoikias, the expected deterioration of the building stock and its environmental (in)efficiency troubles the micro-owners. The lack of common decision-making strategies to enforce building unity increases the entropy to a dysfunctional level. The paper’s main goal is to investigate whether the polykatoikia model is reaching a breaking point. Will the future of the polykatoikia return to homogeneity by relying on one investor per building and be leading a decrease of polykatoikia’s variety, or are there strategies that lead to the sustainability of the building type and its micro-owners? The research is based on the author’s Ph.D. thesis; recent literature on the topic and in-situ observations both support the objectives.

Removing the Two-Phase Region in Spinel LiMn2O4 Towards High-Rate, High-Energy Density Partially Disordered Spinels

Resource constraints have become critical for the Li-ion industry. Spinel LiMn2O4 presents a cheaper, more sustainable alternative to traditional layered Li-ion cathodes, but its capacity is constrained by a two-phase transition at ~3V associated with a large, inhomogeneous volume change that leads to particle cracking and poor cycling stability. In contrast, the partially disordered spinels (PDS) have more sloping, solid-solution-like behavior, resulting in better rate capability and more homogeneous volume change. In this talk, we demonstrate that PDS achieves this by introducing cation disorder, which can shrink, and even fully remove, the two-phase region. By analyzing samples from cluster expansion-based Monte Carlo simulations, we identify the mechanisms that increase Li solubility in the LiMn2O4 phase and lead to this shortened ~3V plateau. These results provide guidance on the optimal level of disorder in spinels to achieve both solid-solution behavior and good Li mobility and also highlight more generally how disorder can be utilized to reduce the effects of problematic phase transformations in ordered frameworks.

A portable primary-standard level graphite calorimeter for absolute dosimetry in clinical pencil beam scanning proton beams

Objective. To report the use of a portable primary standard level graphite calorimeter for direct dose determination in clinical pencil beam scanning proton beams, which forms part of the recommendations of the proposed Institute of Physics and Engineering in Medicine (IPEM) Code of Practice (CoP) for proton therapy dosimetry. Approach. The primary standard proton calorimeter (PSPC) was developed at the National Physical Laboratory (NPL) and measurements were performed at four clinical proton therapy facilities that use pencil beam scanning for beam delivery. Correction factors for the presence of impurities and vacuum gaps were calculated and applied, as well as dose conversion factors to obtain dose to water. Measurements were performed in the middle of 10 × 10 × 10 cm3 homogeneous dose volumes, centred at 10.0, 15.0 and 25.0 g·cm−2 depth in water. The absorbed dose to water determined with the calorimeter was compared to the dose obtained using PTW Roos-type ionisation chambers calibrated in terms of absorbed dose to water in 60Co applying the recommendations in the IAEA TRS-398 CoP. Main results. The relative dose difference between the two protocols varied between 0.4% and 2.1% depending on the facility. The reported overall uncertainty in the determination of absorbed dose to water using the calorimeter is 0.9% (k = 1), which corresponds to a significant reduction of uncertainty in comparison with the TRS-398 CoP (currently with an uncertainty equal or larger than 2.0% (k = 1) for proton beams). Significance. The establishment of a purpose-built primary standard and associated CoP will considerably reduce the uncertainty of the absorbed dose to water determination and ensure improved accuracy and consistency in the dose delivered to patients treated with proton therapy and bring proton reference dosimetry uncertainty in line with megavoltage photon radiotherapy.

Spatial-temporal tracking of molecular species in Geant4-DNA track structure simulations

Monte Carlo particle transport codes have been used to simulate the radiolysis of water and subsequent evolution of molecular species during the chemical stage. In Geant4, accounting of molecules is performed using a molecule counter which provides only a global molecule count. We developed a modular counter implementation that was used to perform spatial-temporal tracking of molecule counts. This custom counter was validated in homogeneous and simplistic split geometries for 1 MeV electrons and 50 MeV protons.Using a spherical cell with one nucleus and one hundred mitochondria as an example, the radiolytic yields in the cytoplasm, nucleus, and mitochondria were compared between targeted (electrons originating from within mitochondria) and unspecific (electrons originating from within cytoplasm) for (very) low energy electrons with kinetic energies of 100 eV to 1 keV.At short times radiolytic yields in source volumes were consistent with reference yields obtained in a large homogeneous volume. Past 1 ns diffusion out of the source volumes led to yield reductions. For volumes abutting the source volumes radiolytic yields at short times strongly depended on track end effects, most pronounced for 100 eV electrons. Similarly, diffusion out of the source volumes greatly increased yields in abutting volumes past 1 ns with magnitude decreasing and time of increase increasing with increasing electron energy. For higher energy electron beams (100 keV and 200 keV) radiolytic yields in all volumes were consistent with reference yields for large statistics.Thus, in cases where energy deposit sites are uniformly distributed in the volume of interest and energies of the charged particles are high to avoid track end effects reference yields may be used in place of resource intensive chemical stage simulations. Spatially heterogeneous energy deposits, as observed in targeted ɑ or β radiation therapy or with targeted nanoparticles, using a spatially sensitive molecule counter is suggested when estimating radiolytic yields outside of the source volumes or at distances that are within the diffusion range of the molecules of interest.

Three-Dimensional Printing Enabled Droplet Microfluidic Device for Real-Time Monitoring of Single-Cell Viability and Blebbing Activity.

Droplet-based microfluidics with the characteristics of high throughput, low sample consumption, increasing reaction speed, and homogeneous volume control have been demonstrated as a useful platform for biomedical research and applications. The traditional fabrication methods of droplet microfluidics largely rely on expensive instruments, sophisticated operations, and even the requirement of an ultraclean room. In this manuscript, we present a 3D printing-based droplet microfluidic system with a specifically designed microstructure for droplet generation aimed at developing a more accessible and cost-effective method. The performance of droplet generation and the encapsulation capacity of the setup were examined. The device was further applied to measure the variation in cell viability over time and monitor the cell's blebbing activity to investigate its potential ability and feasibility for single-cell analysis. The result demonstrated that the produced droplets remained stable enough to enable the long-time detection of cell viability. Additionally, cell membrane protrusions featuring the life cycle of bleb initiation, expansion, and retraction can be well-observed. Three-dimensional printing-based droplet microfluidics benefit from the ease of manufacture, which is expected to simplify the fabrication of microfluidics and expand the application of the droplet approach in biomedical fields.

New Probabilistic Seismic Hazard Model for Nepal Himalayas by Integrating Distributed Seismicity and Major Thrust Faults

Nepal is one of the most seismically active regions in the world, as highlighted by the recent devastating 2015, Mw~7.8 Gorkha earthquake, and a robust assessment of seismic hazard is paramount for the design of earthquake-resistant structures. In this study, we present a new probabilistic seismic hazard assessment (PSHA) for Nepal. We considered data and findings from recent scientific publications, which allowed us to develop a unified magnitude homogenized seismicity catalog and propose alternative seismic source characterization (SSC) models including up-to-date parameters of major thrust faults like main frontal thrust (MFT) and main boundary thrust (MBT), while also considering existing SSC models and various seismic hazard modeling strategies within a logic tree framework. The sensitivity analyses show the seismic hazard levels are generally higher for SSC models integrating the major thrust faults, followed by homogenous volume sources and smoothed seismicity approach. The seismic hazard maps covering the entirety of Nepal are presented as well as the uniform hazard spectra (UHS) for five selected locations (Kathmandu, Pokhara, Biratnagar, Nepalganj, and Dipayal) at return periods of 475- and 2475-years considering Vs,30 = 760 m/s. The results obtained are generally consistent with most recent studies. However, a notable variability in seismic hazard levels and several discrepancies with respect to the Nepal Building Building Code NBC105: 2020 and global hazard model, GEM are noted, and possible causes are discussed.

An advanced fuzzy C-Means algorithm for the tissue segmentation from brain magnetic resonance images in the presence of noise and intensity inhomogeneity

ABSTRACT Segmentation of brain Magnetic Resonance Images (MRIs) into various brain tissues such as white matter (WM), grey matter (GM), and cerebrospinal fluid (CSF) is very important to detect and diagnose different brain-related disorders at the primitive level. Accurate segmentation of brain MRIs is very difficult because of the intricate anatomical structure of the tissues, the existence of Intensity Inhomogeneity (IIH), noise, and Partial Volume Effects (PVE). Clustering-based methods are generally used to segment brain images. This work proposes a Chaotic based Enhanced Firefly Algorithm Integrated with Fuzzy C-Means (CEFAFCM) for the segmentation of brain tissues WM, GM, and CSF from brain MRIs. The proposed method can handle IIH, PVE, and noise. CEFAFCM is a spatially modified FCM algorithm combined with the Firefly Algorithm (FA) along with a chaotic map for the initialization of the population of fireflies. The algorithm is tested with brain MRIs acquired from the BrainWeb database. The experimental results demonstrate that the proposed technique is producing better results in comparison with some existing brain MRI segmentation methods such as FCM, BCFCM, FAFCM, and En-FAFCM.

Assessment of scale-adaptive turbulence modeling in coupled CFD-PBM 3D flow simulations of disperse liquid-liquid flow in a baffled stirred tank with particular emphasis on the dissipation rate

The effect of scale-adaptive simulations (SAS) on the droplet size distribution (DSD) is assessed in a baffled stirred tank and compared with a classical statistical turbulence model in terms of the widely used shear-stress transport (SST) eddy-viscosity model. DSD predictions are obtained by 3D multiphase flow simulations coupled with a population balance model. Inclusion of a turbulent dispersion model in the SST model simulations leads to a more homogeneous volume fraction field but has no visible effect on the DSD. On the one hand, enhanced mixing by the SAS shows a broader and more homogeneous DSD throughout the tank than predicted by the SST model, corresponding to experimental trends. On the other hand, turbulence energy dissipation rate ε is considerably underestimated by the SAS, leading to less breakup activity, while coalescence is essentially unaffected. It is suggested that SAS should be improved with regard to a sounder ε prediction in future studies.

Numerical study of inhibition mechanism of high-pressure hydrogen leakage self-ignition with the addition of ammonia

Hydrogen and ammonia have attracted increasing attention as carbon-free fuels. Ammonia is considered to be an effective energy storage and hydrogen storage medium. However, a small amount of unremoved NH3 is still present in the product during the decomposition of ammonia to produce hydrogen. Therefore, it is very essential to investigate the self-ignition of hydrogen-ammonia mixtures in order to accommodate the various scenarios of hydrogen energy applications. In this paper, the effect of NH3 addition on the self-ignition of high-pressure hydrogen release is numerically investigated. The RNG k-ε turbulence model, EDC combustion model, and 213-step detailed NH3/H2 combustion mechanism are used. CHEMKIN-Pro programs for zero-dimensional homogeneous and constant volume adiabatic reactor models are used for sensitivity analysis and ignition delay time of the chemical reaction mechanism. The results showed that the minimum burst pressure required for self-ignition increased significantly after the addition of ammonia. The maximum temperature and shock wave intensity inside the tube decreases with increasing ammonia concentration. The ignition delay time and H, HO2, and OH radicals reduce with increasing ammonia concentration. H and HO2 radicals are suggested as indicators for tracking the second and third flame branches, respectively.