Mixed Field Research Articles

The mixing field and flame structure near the reaction zone of turbulent planar flames at different levels of mixture inhomogeneity

Turbulent flames with compositionally inhomogeneous mixtures are commonly used in many combustion systems. In this work, turbulent planar jet flames issued from a concentric flow slot burner, CFSB, were used to study the impact of mixture inhomogeneity near the flame sheet. The CFSB burner can control the mixing inhomogeneity by changing the mixing length “L” between the concentric fuel and air slot nozzles. At various levels of mixture inhomogeneity, the mixing field, presented by mixture fraction, Z, distribution, and the flame structure was investigated via simultaneous Rayleigh and OH-PLIF imaging technique. Our previous study investigated the mixing field immediately downstream of the burner exit in non-reacting conditions. The PDFs of Z showed that the mixing field covered a wide range of mixture fractions, where the high flame stabilization occurred when a large portion of the PDF(Z) was located within the fuel flammability limits. This work showed that further downstream, the highly stabilized flames were also obtained when the range of fluctuations in the mixture fraction was close to the stoichiometric mixture fraction. Moreover, plotting the mixing field using the scatter plot within the mixing regime diagram for various flame conditions showed that the mixing field downstream of the burner exit consistently follows the mixing diagram classification. Moreover, a close inspection of the flame structure showed that the flame sheet varies from thick, and corrugated at a low and high levels of mixing to thin flame sheet but less corrugated and that at a particular mixing normalized length L/D = 7. The flame corrugation data showed that the flame stability occurs at a minimum corrugation factor.

Effectively modulating spatial vortex four-wave mixing in a diamond atomic system

Due to the spatial characteristics of orbital angular momentum, vortex fields can be applied in the fields of quantum storage and quantum information. We study the realization of spatially modulated vortex fields based on four-wave mixing in a four-level atomic system with a diamond structure. The intensity and spiral phase of the vortex field are effectively transferred to the generated four-wave mixing field. By changing the detuning of the probe field, the phase and intensity of the generated vertex four-wave mixing field can be changed. When the probe field takes a large detuning value, the spatial distribution of the intensity and phase of the vertex four-wave mixing field can be effectively tuned by adjusting the Rabi frequency or detuning value of the coupled field. At the same time, we also provide a detailed explanation based on the dispersion relationship, and the results agree well with our simulation results.

Harnessing Nuclear Energy to Gold Nanoparticles for the Concurrent Chemoradiotherapy of Glioblastoma

Nuclear fission reactions can release massive amounts of energy accompanied by neutrons and γ photons, which create a mixed radiation field and enable a series of reactions in nuclear reactors. This study demonstrates a one-pot/one-step approach to synthesizing radioactive gold nanoparticles (RGNP) without using radioactive precursors and reducing agents. Trivalent gold ions are reduced into gold nanoparticles (8.6–146 nm), and a particular portion of 197Au atoms is simultaneously converted to 198Au atoms, rendering the nanoparticles radioactive. We suggest that harnessing nuclear energy to gold nanoparticles is feasible in the interests of advancing nanotechnology for cancer therapy. A combination of RGNP applied through convection-enhanced delivery (CED) and temozolomide (TMZ) through oral administration demonstrates the synergistic effect in treating glioblastoma-bearing mice. The mean survival for RGNP/TMZ treatment was 68.9 ± 9.7 days compared to that for standalone RGNP (38.4 ± 2.2 days) or TMZ (42.8 ± 2.5 days) therapies. Based on the verification of bioluminescence images, positron emission tomography, and immunohistochemistry inspection, the combination treatment can inhibit the proliferation of glioblastoma, highlighting the niche of concurrent chemoradiotherapy (CCRT) attributed to RGNP and TMZ.

Experimental, analytical, and simulation studies of modified concrete mix for radiation shielding in a mixed radiation field

The current study assessed two concrete mixes prepared using dolomite and barite/limonite aggregates to shield against both energetic photons and neutrons. After that, a designed mix which comprised barite/goethite aggregates plus fine-powdered boron carbide additive, was proposed to improve the overall radiation shielding properties and in the same time, doesn’t compromise or even improve the physic-mechanical properties of the mature concrete. The assessment started first with intensive experimental investigations to investigate the prepared mixes’ shielding capabilities against both γ-rays and fast neutrons. Then, analytical computations were performed via number of reliable software programs such as; Phy-X, NXCom, MRCsC, JANIS-4, and MCNP5, in order to confirm the experimental results and to validate the created Monte-Carlo models. Finally, an intensive radiation shielding assessment for all concrete mixes understudy using, mainly, the validated MCNP models, was performed. The obtained results have revealed the superiority of barite mixes over the dolomite mix concerning attenuating photons moreover, the proposed designed mix has shown superiority over the other two prepared mixes considering shielding against; energetic photons, fast/thermal neutrons, and secondary emitted γ-rays, which nominates this mix to be a suitable universal shield that can be used even in mixed radiation fields.

Phase field method of multi-mode fracture propagation in transversely isotropic brittle rock

A phase field model (PFM) for simulating multi-mode brittle fractures in transversely isotropic rock is proposed. In the model, we employ a novel decomposition form of strain energy consisting of tensile, tensile–shear and compressive–shear components to improve the fracture driving force, and the positive–negative decomposition forms of elastic energy are considered as an approximate extension of the spectral decomposition method for transversely isotropic materials. We also introduce the tensor form of the critical energy release rate and Lamé constants, which breaks through the limitations of traditional PFMs that cannot well reproduce fracture anisotropy and multi-mode brittle fracture in transversely isotropic rock, i.e. the tensile, shear, and mixed-mode fractures. A new mixed phase field model is established, which is solved in COMSOL by employing a staggered scheme to solve the phase field, displacement field, and historical field independently. Subsequently, the accuracy and effectiveness of the proposed model are comprehensively verified by a series of 2D and 3D numerical examples. The results show that the proposed model agrees well with the existing model in capturing tensile and tensile–shear fractures. Compressive–shear fractures can be additionally captured well in the compressive state.

Measurements in pulsed neutron fields.

Dosimetry in pulsed and mixed radiation fields represents an important challenge in radiation measurements, because in several accelerator technologies, the acceleration occurs in bunches of particles with short time duration, producing intense radiation pulses spaced by a relatively long time of beam off. The stray mixed radiation field generated around these installations maintains the same time structure as the primary beam and causes a problem in workplace fields' monitoring. Active neutron detectors normally used in steady neutron fields, specifically REM-counters and Bonner sphere spectrometers, can suffer pulsed fields because of the high dead time losses during the bursts and are often inadequate for pulsed field monitoring. This work reviews the efforts of European Radiation Dosimetry Group (EURADOS), and in particular of the Working Group 11 'High Energy Radiation Fields', to define the problem, characterize instrumentation and to propose solutions to the issue of pulsed and mixed radiation fields. Despite the EURADOS initiative, several open issues still remain. A metrological traceability for pulsed neutron fields is missing. There is still room for the optimization and better characterization of available instruments. Initiatives of education and training are required.

EURADOS whole-body dosemeters intercomparisons: lessons learnt from individual results.

Every 2years since 2008, Eurados WG2 has organised a whole-body dosemeters intercomparison (IC) in photon and beta fields. This paper presents the information that individual participants can extract from their results. The irradiation plan of each IC was designed to allow participants check the performance of some important characteristics of their dosimetry systems, in particular: linearity, angular response, energy response and response to mixed fields. The analysis of anomalous responses indicates that many systems can reduce the number of outliers by improving their calibration procedures.

Large-eddy simulations of compressible Rayleigh–Taylor turbulence with miscible fluids using spatial gradient model

Large-eddy simulations (LES) and implicit LES (ILES) of three-dimensional compressible Rayleigh–Taylor turbulence with miscible fluids are performed and compared with direct numerical simulation (DNS) at the Atwood number At=0.5 and stratification parameters Sr = 1.0 and 4.0. Three sub-grid-scale (SGS) models including constant-coefficient spatial gradient model (CSGM), dynamic Smagorinsky model (DSM), and dynamic mixed model (DMM) are considered. The CSGM model achieves a high accuracy by using the velocity gradients at the neighboring LES grids. The a priori tests show that the CSGM model has significantly higher correlation coefficients and lower relative errors than traditional SGS models. In the a posteriori tests, the probability density functions of SGS terms predicted by the CSGM model are consistent with the filtered DNS results. The CSGM model can accurately predict the small bubble and spike structures, resulting in good predictions of mixing heights and concentration fields. The instantaneous structures, spectra, and statistics of velocity and vorticity fields are also examined, showing the excellent performance of the CSGM model compared to the ILES, DSM, and DMM models. Moreover, the predictions of the temperature and pressure fields by the CSGM model are significantly better than the traditional SGS models and ILES.

Sound field navigation with virtual higher-order sound sources using complex greedy pursuit algorithm

As the Virtual Reality (VR) and metaverse industries continue to expand rapidly, there is a growing need to capture and recreate real-world experiences in immersive audio-visual scenes. Sound field translation, which activates equivalent virtual sources to recreate spatial sound fields, enables users to navigate through these scenes seamlessly. However, combining recordings from different microphones and processing mixed fields of exterior and interior sources present significant challenges. This paper introduces a novel method for virtual navigation by sparsely decomposing complex sound fields using distributed virtual higher-order sound sources and an iterative complex greedy pursuit algorithm. By combining spatially separated microphone recordings, the technique identifies its sparse representation with several higher-order virtual sources. This process effectively decomposes the complex sound field into a grid of higher-order sources, leveraging the power of the complex greedy pursuit algorithm. Through extensive experimentation, we demonstrate the suitability of our method for applications such as VR navigation and sound field reproduction with binaural devices. The results showcase enhanced realism and accuracy, offering users a truly immersive audio experience in virtual environments. As the demand for realistic audio-visual scenes grows, this innovative approach holds promise for advancing VR technology and enriching user experiences in the metaverse.

Scaled boundary perfectly matched layer for wave propagation in a three-dimensional poroelastic medium

In this paper, we introduce a novel direct time-domain artificial boundary condition, called the scaled boundary perfectly matched layer, for wave problems in 3D unbounded fluid-saturated poroelastic medium. The poroelastic medium is conceptualized as a two-phase medium composed of a solid skeleton and an interstitial fluid based on the u-p formulation of Biot's theory. The scaled boundary perfectly matched layer proposed in this work originates from an extension of a recently developed perfectly matched layer for wave problems in a single-phase solid medium. The dependence of the conventional perfectly matched layer on the global coordinate system is overcome in the present method. As a result, this method permits the utilization of an artificial boundary with general geometry (not necessarily convex) and can consider planar physical surfaces and interfaces extending to infinity. The proposed method is formulated by a mixed unsplit-field form, which includes both the mixed displacement-stress field and pore pressure-relative displacement field. The resulting scaled boundary perfectly matched layer formulation can be directly described by a system of third-order ordinary differential equations in time, which can be easily integrated into the standard finite-element framework of poroelastic theory. Finally, numerical benchmark examples are presented to demonstrate the accuracy and robustness of the proposed scaled boundary perfectly matched layer, as well as the versatility in practical engineering problems.

Decomposition of Displacement Field into the Irrotational and Solenoidal Component Using Fast Fourier Transform

Purpose: A new code based on Helmholtz decomposition is presented to separate longitudinal (pressure) and transverse (shear) components of a mixed wave field. This algorithm will help isolate shear or pressure components of an elastic wave to further concentrate on each specific wave and its physical characteristics, particularly in medical imaging instrument development and image processing techniques.
 Materials and Methods: Using the combination of Fourier transform and Helmholtz decomposition, first, the mathematical basis of the work is prepared. After reaching a usable formula, this basis is embedded in the Code written in MATLAB program. Then, various test data containing shear and pressure waves were created and fed to the Code to evaluate its ability to decompose the displacements into the shear and pressure waves.
 Results: This new algorithm successfully isolated the transverse and longitudinal wavefront of the mixed wavefield. The Code demonstrated 100% accuracy for separating the shear wave and more than 99% for the pressure wave. Moreover, the background noise was kept under 0.03% in every step.
 Conclusion: The results show that using Helmholtz decomposition in Fourier space on 3D data can help decompose a displacement field into its irrotational and solenoidal components with high accuracy. A weak dependency on wave thickness and contrast was observed, but the algorithm's accuracy never fell below 99%.

Modelling the response of CLLBC(Ce) and TLYC(Ce) SiPM-based radiation detectors in mixed radiation fields with Geant4

CLLBC(Ce) and TLYC(Ce) are novel scintillation materials capable of measuring mixed gamma ray and neutron radiation fields that have gained significant interest in the areas of space and nuclear safety/security science. To date Geant4, the world’s most popular Monte Carlo radiation modelling toolkit, has yet to be effectively used to simulate the full response of these materials when coupled to near ultra-violet Silicon PhotoMultipliers (SiPMs). In this work an experimentally validated Geant4 application has been developed with optimised material composition, optical data tables, and physics transport settings that is able to accurately simulate the response of CLLBC(Ce) and TLYC(Ce) SiPM-based radiation detectors under both gamma ray and neutron irradiation. Experimental benchmarking for five different radioactive sources (Co-60, Cs-137, Eu-152, Am-241, and Cf-252) illustrated that this developed Geant4 application was able to reproduce the position and structure of all major spectral features (full energy gamma ray photo-/neutron capture peaks, X-ray escape photopeaks, Compton edge, Compton backscatter peaks, and Compton plateau) to high level of accuracy.

A new Multi Leaf Collimator for the fission neutron therapy facility at FRM II

As a part of the general upgrade program of the fission neutron therapy facility MEDAPP at the research reactor FRM II, a newly designed, electronically operated Multi Leaf Collimator (MLC) was introduced. The design of the new collimator was optimized in order to increase dose output and to allow patient positioning closer to the collimator. The new collimator allows divergent and convergent beam shaping in order to maximize the effective area of the fission source used for irradiation. In comparison to the old MLC, the radiation dose for the staff is reduced by the motorized operation of the new MLC. The advanced beam shaping abilities of the new collimator are investigated by a comparison with depth dose curves and beam profiles of the old MLC. For the separation of neutron and gamma dose deposition in water, the two chamber dosimetry method recommended for mixed field dosimetry was applied. A re-calibration of the set of ionization chambers used for dosimetry in mixed neutron-gamma radiation fields at FRM II was performed. The calibration was done in a reference neutron field from 3H(p,n)3He-reactions in a low scattering environment. An overall increased dose output as intended by the design of the new MLC was shown. Also, improved dosimetric characteristics of the treatment field due to the optimized beam shaping abilities of the new MLC were demonstrated. In the calibration measurements of the magnesium ionization chamber used in the two chamber method, an unexpected increase of the neutron sensitivity by a factor of 8 was measured. The new MLC will enable more conformal dose delivery to the target volume in patients and therefore help to reduce healthy tissue damage by the application of neutron radiation.

Characteristics of ammonia-hydrogen nonpremixed bluff-body-stabilized flames

The combustion of ammonia (NH3) has received much attention over the last few years due to challenges associated with its low reactivity and the emission of nitric oxides. One way to improve the reactivity of NH3 is to blend it with (H2/N2) mixture as the product of its dissociation, before introducing it into energy systems. In this study, experimental measurements were carried out on nonpremixed bluff-body stabilized flames to better understand the flame and emission characteristics of NH3/H2/N2 flames. Four fuel mixtures at different NH3 and (H2/N2) ratios were investigated to represent different levels of ammonia cracking. Photography, planar laser-induced fluorescence of OH, thermocouples, and gas analysis techniques were used to understand flame features, reaction zone characteristics, NO, and NH3 concentration within the flame and at the exhaust. It was observed that a decrease in NH3 ratio in the mixtures resulted in longer and more stable flame with reduced thermal radiation as compared to NH3-rich fuel blends. For the highest NH3 blend studied, the flames exhibit extinction and re-ignition in the neck zone, as evidenced by OH-planar images and temperature profiles. As the H2/N2 ratio in the fuel mixture is increased, while keeping the Re constant, the momentum flux ratio (jet/co-flow) also increased resulting in a fuel-lean recirculation zone (RZ), and a shift in the maximum temperature and OH region from the outer shear layer to the inner layer next to the central jet. At levels of NH3 in the fuel mixture above 50% by volume, unburned ammonia slips through the flame and into the exhaust, and the subsequent reburn mechanism resulted in reduced NO emission. CFD simulations using Reynolds-averaged Navier-Stokes (RANS) and the flamelet–progress-variable submodel were conducted and compared with the experimental results. The CFD results helped to qualitatively describe and further explain what was observed in the experiment including the flame appearance, mixing field, and the reaction zone location in the tested flames.

Investigation on the physical dose filtered by linear energy transfer for treatment plan evaluation in carbon ion therapy.

Large tumor size has been reported as a predicting factor for inferior clinical outcome in carbon ion radiotherapy (CIRT). Besides the clinical factors accompanied with such tumors, larger tumors receive typically more low linear energy transfer (LET) contributions than small ones which may be the underlying physical cause. Although dose averaged LET is often used as a single parameter descriptor to quantify the beam quality, there is no evidence that this parameter is the optimal clinical predictor for the complex mixed radiation fields in CIRT. Purpose of this study was to investigate on a novel dosimetric quantity, namely high-LET-dose ( , the physical dose filtered based on an LET threshold) as a single parameter estimator to differentiate between carbon ion treatment plans (cTP) with a small and large tumorvolume. Ten cTPs with a planning target volume, (large) and nine with a (small) were selected for this study. To find a reasonable LET threshold ( ) that results in a significant difference in terms of , the voxel based normalized high-LET-dose ( ) distribution in the clinical target volume (CTV) was studied on a subset (12 out of 19 cTPs) for 18 LET thresholds, using standard distribution descriptors (mean, variance and skewness). The classical dose volume histogram concept was used to evaluate the and distributions within the target of all 19 cTPs at the before determined . Statistical significance of the difference between the two groups in terms of mean and volume histogram parameters was evaluated by means of (two-sided) t-test or Mann-Whitney-U-test. In addition, the minimum target coverage at the above determined was compared and validated against three other thresholds to verify its potential in differentiation between small and large volumetumors. An of approximately was found to be a reasonable threshold to classify the two groups. At this threshold, the and were significantly larger ( ) in small CTVs. For the small tumor group, the near-minimum and median (and ) in the CTV were in average (0.31 ± 0.08) and (0.46 ± 0.06), respectively. For the large tumors, these parameters were (0.20 ± 0.01) and (0.28 ± 0.02). The difference between the two groups in terms of mean near-minimum and median ( ) was 2.7 Gy (11%) and 5.0 Gy (18%),respectively. The feasibility of high-LET-dose based evaluation was shown in this study where a lower was found in cTPs with a large tumor size. Further investigation is needed to draw clinical conclusions. The proposed methodology in this work can be utilized for future high-LET-dose basedstudies.

Review on research progress in liquid jet in crossflow

Liquid jet in crossflow (LJIC) is an important subject of fluid mechanics, which is considered as an effective method of fuel atomization in aircraft and widely used in gas turbine engine, sub combustion ramjet, and scramjet. The atomization of liquid jet directly affects the subsequent fuel combustion, which is one of the most important processes in the engine propulsion system. Therefore, how to recognize the evolution of LJIC, and how to promote two-phase mixing determine the combustion efficiency of the engine directly. A lot of researches on LJIC have been done and provide impetus for the development of scramjet. Based on the recent researches, subsonic LJIC is reviewed from breakup model and surface wave, influence of crossflow on atomization, and factors affecting atomization. And supersonic LJIC is reviewed from two-phase mixing and flow field characteristics, jet breakup and surface wave, and factors affecting atomization. At the same time, the shortcomings of current research and the prospect of future research are put forward, especially in the selection of the jet medium, the determination of the experimental conditions, the application of the numerical method, the vortex, the pulsed jet, and the atomization enhancement by multiple means.

Meshless Improved Algorithm for Ion Flow Field in Large-Span AC-DC Parallel Lines

Background: The research in this paper aims to address the effect of large-span AC lines on ion currents in parallel DC lines. This paper proposes an algorithm for solving mixed ion flow fields based on meshless radial point interpolation, which can accurately solve the ion flow field of large-span AC-DC parallel lines. Methods: The shape function of the traditional meshless method is modified by polynomial radial point interpolation so that the shape function can satisfy the Kronecker-δ function property at the point where the boundary constraints are to be imposed so as to meet the requirements of directly applying the boundary constraints; Combined with the influencing factors of the AC line on the mixed ion flow field, the mixed ion flow field and the ion current density value was obtained. Results: Using the proposed algorithm, the relative error of ion current density can be reduced to 4.5%, and the relative error of ion flow field can be reduced to 24%. Conclusion: The simulation results are consistent with the measurement results, which proves the correctness and practicability of the mixed ion flow field solution algorithm based on meshless radial point interpolation.

Strain‐Induced Toroidal Polar States in Wrinkled Ferroelectric Polymer by Phase‐Field Simulations

AbstractWrinkled ferroelectric polymer films with out‐of‐plane deformation exhibit exotic strain fields that differ from those of conventional epitaxial film systems, offering a new path toward manipulating electrical and mechanical behaviors in ferroelectrics. However, the direct observation of the domain structure evolution in ferroelectric polymer films during continuous deformation is challenging with current experimental approaches. In this study, the strain‐induced evolution of toroidal domain structures in organic poly(vinylidene fluoride‐ran‐trifluoroethylene) (P(VDF‐TrFE)) films with concentric toroidal wrinkle patterns is comprehensively investigated using phase‐field simulations. The results reveal morphology‐ and thickness‐dependent toroidal polar topology in wrinkled P(VDF‐TrFE) films. External strain loading can modulate this ferroelectric domain, which exhibits robust coupling behavior with a mixed strain field of periodic tensile and compressive strains. It is demonstrated that toroidal wrinkled ferroelectric films provide an effective and unique flexible platform for continuously controllable strain engineering in ferroelectrics and a theoretical framework with potential applications in flexible electronic devices.

Mixed field radiation measurement using MOSFET sensor

We report here a study performed on MOSFET (Metal Oxide Semiconductor Field Effect Transistor) sensor for the measurement of accumulated doses from a mixed field radiations (especially gamma and fast neutron) environment such as nuclear detonation. The MOSFET sensor has shown its capability towards fast neutron dose measurement along with its well known gamma dose measurement capabilities. The study results are helpful in the establishment of MOSFET as a Personal Dosimeter for mixed field radiation. The measured sensitivities for gamma and fast neutron dose measurements are 1.1 mV/cGy and 0.6 mV/cGy respectively.

Chance coincidence analysis for capture-gated neutron spectrometry with a composite scintillator

Neutron spectrometry is important for radiation metrology, radiation protection, accelerator physics etc. The spectral response of a capture-gated detector to mono-energetic neutrons contains a significant peak, making it easy to be analyzed. But this system output not only capture-gated events (CGE) but also chance coincidence events (CCE). It is critical to identify and eliminate CCE. However, chance coincidence has not been analyzed in detail before. This paper aims to find a way to eliminate CCE and get the spectrum of CGE. Thus, categories of CCE were analyzed and their probability equations were established. Then recorded pulses from a composite scintillator measured in mixed radiation fields were used to verify CCE and explore the influence of timing gate. Results show that n/γ discrimination is effective to distinguish CCE caused by γ-rays and calculate the amount of CCE caused by fast neutrons. Timing gate should be determined according to the different distributions of CGE and CCE. Spectrum of CGE can be acquired by subtracting that of fast neutron CCE from the fast neutron spectrum of coincidence events.