Core Boundary Research Articles

Numerical study of tornado-borne debris on a low-rise building through large eddy simulation

Tornado-borne debris is considered as a major source of damage. However, effects of tornado-borne debris on buildings have been seldom investigated. This study performed large eddy simulation to reproduce a tornado and examined the characteristics of incident debris on building surfaces, considering two factors: debris diameter (d=2, 5, and 10 cm), and distance between tornado center and building (r). The debris was assumed to be wooden. It has been found that the probability of the debris hitting the building is the highest when d=5 cm, and the debris mainly hit the windward surface and the far-tornado lee-side wall of the building. The downward flying debris is the reason of relatively high intensities of the debris hitting the building roof when r=0. The highest speed of the debris hitting the building occurs when the building is mounted at the core boundary of the tornado, reaching 126 m/s. In addition, interaction between the tornado and building disturbs and accelerates the flying debris. The windward wall of the building experiences the strongest debris hit, with the maximum hitting speed of 102 m/s, 126 m/s, and 188 m/s, when the debris diameter is 2, 5, and 10 cm, respectively. The most dangerous region is identified as the near-core part of windward building surface.

SOLPS-ITER modeling of ASDEX Upgrade L-mode detachment states

SOLPS-ITER is used to model ASDEX Upgrade L-mode detachment states including the onset of detachment, the fluctuating detachment, and the complete detachment states, considering drifts and mimicking filamentary convective transport with a radial outward velocity in the low field side. The effect of drifts, perpendicular outward convection and core boundary conditions on the numerical solution is presented. The modeling results are validated against experimental data. We find a good agreement of particle flux at the inner target between modeling results and experimental data. On the opposite, at the outer target computations underestimate measured particle flux by a factor of about 2 ∼ 3 in the onset of detachment and the fluctuating detachment states.

Prior Probability Distributions of Neutron Star Crust Models

Abstract To make best use of multifaceted astronomical and nuclear data sets, probability distributions of neutron star models that can be used to propagate errors consistently from one domain to another are required. We take steps toward a consistent model for this purpose, highlight where model inconsistencies occur, and assess the resulting model uncertainty. Using two distributions of nuclear symmetry energy parameters—one uniform, the other based on pure neutron matter theory—we prepare two ensembles of neutron star inner crust models. We use an extended Skyrme energy density functional within a compressible liquid drop model (CLDM). We fit the surface parameters of the CLDM to quantum 3D Hartree–Fock calculations of crustal nuclei. All models predict that more than 50% of the crust by mass and 15% of the crust by thickness comprises pasta with medians of around 62% and 30%, respectively. We also present 68% and 95% ranges for the crust composition as a function of density. We examine the relationships between crust–core boundary and pasta transition properties, the thickness of the pasta layers, the symmetry energy at saturation and subsaturation densities, and the neutron skins of 208Pb and 48Ca. We quantify the correlations using the maximal information coefficient, which can effectively characterize nonlinear relationships. Future measurements of neutron skins, information from nuclear masses and giant resonances, and theoretical constraints on PNM will be able to place constraints on the location of the pasta and crust–core boundaries and the amount of pasta in the crust.

A free boundary problem for necrotic tumor growth with angiogenesis

This paper deals with a mathematical model for tumor growth with angiogenesis and a necrotic core. The problem is a nonlinear problem which has two free boundaries: the external boundary of the tumor and the external boundary of the internal necrotic core. Using the implicit function theorem, the relationship between the two free boundaries is studied. The asymptotic stability of the unique steady-state solution is proved. The effect of nutrient concentration on tumor growth is studied. The relationship between the stage with a necrotic core and the stage without necrotic core is also studied. The results show that whether the steady-state of tumor growth has a necrotic core or not is determined by the concentration of external nutrients. The stage of tumor with necrotic core and the stage without necrotic core could transform into each other by adjusting the concentration of external nutrients.

A NOVEL METHOD FOR EVALUATING SHALE LOST GAS AMOUNT AND DESORPTION GAS AMOUNT BASED ON SEGMENTED VARIABLE BOUNDARY MODEL

The accurate evaluation of gas content is significant for the efficient exploration of unconventional natural gas reservoir, direct method adopts lost gas model and combines with desorption curve to evaluate reservoir gas content. However, the classical lost gas model is derived from constant pressure condition and spherical particle assumption in the estimation of coal bed methane, such as USBM method proposed by US Bureau of Mine, it brings a lot of errors for the deep-depth shale gas reservoir in which core sample is cylindrical shape. Based on diffusion theory, this work used time-varying pressure condition and cylindrical coordinate to solve one-dimensional diffusion equation and obtained analytical solution, then proposed a novel lost gas model (segmented variable boundary model). This model is enabled to describe two processes, i.e., drifting process and desorption process, with different gas-diffusion features. The result of segmented variable boundary model shows that the pressure drop between core sample and boundary increases in the drifting process when core sample is drifted from bottom hole to ground, due to the decreases of boundary pressure, lead to that the diffusion rate is accelerating when gas is escaping from core sample to environment, thus the diffusion curve of drifting process is concave. In the desorption process, core sample is placed in desorption canister and boundary pressure is constant, pressure drop between core sample and boundary is decreasing along the gas escaping from core sample, the diffusion rate is moderative and thus the curve of desorption process is convex. For further validating this model, a lost gas-desorption gas simulating experiment system was set up in lab based on the principle of similitude, and we conducted simulating experiment using cylindrical shale samples to obtain the diffusion curve in drifting process and desorption process, through comparing the experimental data with segmented variable boundary model and USBM model, demonstrated the validation of segmented variable boundary model. Moreover, the segmented variable boundary model is applied to fit the experiment data from the Y151 well in South Sichuan Basin, the fitting results have good consistency with experimental data, which indicates that the segmented variable boundary model is suitable for practical engineering condition.

Reconstruction of numerical inlet boundary conditions using machine learning: Application to the swirling flow inside a conical diffuser

A new approach to determine proper mean and fluctuating inlet boundary conditions is proposed. It is based on data driven techniques, i.e., machine learning approach, and its goal is to use any known information about the downstream flow to reconstruct the unknown or incomplete inlet boundary conditions for a numerical simulation. The European Research Community On Flow, Turbulence And Combustion (ERCOFTAC) test case of the swirling flow inside a conical diffuser is investigated. Despite its relatively simple geometry, it constitutes a very challenging test case for numerical simulations due to incomplete experimental data and to the delicate balance between core flow recirculation and boundary layer separation. Simulations are performed using both Reynolds averaged Navier–Stokes (RANS) and large-eddy simulations (LES) turbulence methods. The mean velocity and turbulence kinetic energy profiles obtained with the machine learning approach in RANS are found to be in very good agreement with the experimental measurements and the numerical predictions are greatly improved as compared to the previous results using basic inlet boundary conditions. They are indeed comparable to the best previous RANS using empirical ad hoc inlet conditions to accurately simulate the downstream flow. In LES, in addition to the mean velocity profiles, the machine learning approach also allows us to properly reconstruct the fluctuating part of the turbulent field. In particular, the methodology allows us to circumvent the lack of turbulent correlations associated with classical inlet synthetic turbulence.

A framework for effective data management outsourcing in investment management

Investment firms have historically engaged in outsourcing a range of back, middle and front office functions to specialist providers. Anyway, operational data management, until recently, remained within the purview of the in-house data team and managed on-premises. This state of affairs is changing. Over the past decade, firms have attempted to centralise data governance — here defined as the process of managing the availability, usage and integrity of data through internal standards, policies and processes — in order to meet a range of data challenges including poor data visibility, rising data costs and regulatory requirements. While many of these attempts have resulted in expensive and inflexible enterprise data management systems, they have helped make the case for outsourcing data management. Firms are now in a position to draft appropriate service-level agreements (SLAs) for outsourced data management services, and many see the value that comes with outsourcers’ consumption-based models and agile approaches to data management. In most investment firms today, there is a recognition that there are various different types of data and various data processes, some of which are core and some of which are non-core. Firms are coming to realise that the foundational, but not differentiating, activities of operational data management is expensive and time-consuming and that by outsourcing it they can free up time and resources to focus on what is core and proprietary — data analysis, insight and using that data and insight as a factor in business decision-making. As firms set about migrating to managed data services, they need to consider the core boundaries of their business, the commercial models of available services and how they can best ensure oversight of their outsource partners. Those that get it right will form strategic partnerships that can unlock value from data.

Innovative Investigation of Reflector Options for the Control of a Chloride-Based Molten Salt Zero-Power Reactor

Molten salt reactors have gained substantial interest in the last years due to their flexibility and their potential for simplified closed fuel cycle operations for massive net-zero energy production. However, a zero-power reactor experiment will be an essential first step into the process delivering this technology. The choice of the optimal reflector material is one of the key issues for such experiments since, on the one hand, it offers huge cost savings potential due to reduced fuel demand; on the other hand, an improper choice of the reflector material can have negative effects on the quality of the experiments. The choice of the reflector material is, for the first time, introduced through a literature review and a discussion of potential roles of the reflector. The 2D study of different potential reflector materials has delivered a first down-selection with SS304 as the representative for stainless steel, lead, copper, graphite, and beryllium oxide. A deeper look identified, in addition, iron-based material with a high Si content. The following evaluation of the power distribution has shown the strong influence of the moderating reflectors, creating a massively disturbed power distribution with a peak at the core boundary. This effect has been confirmed through a deeper analysis of the 2D multi-group flux distribution, which led to the exclusion of the BeO and the graphite reflector. The most promising materials identified were SS304, lead, and copper. The final 3D Monte Carlo study demonstrated that all three materials have the potential to reduce the required amount of fuel by up to 60% compared with NaCl, which has been used in previous studies and is now taken as the reference. An initial cost analysis has identified the SS304 reflector as the most attractive solution. The results of the 2D multi-group deterministic study and the 3D multi-group Monte Carlo study have been confirmed through a continuous energy Monte Carlo reference calculation, showing only minor differences.

Confinement loss of anti-resonant capillaries with curved boundaries.

A systematic analysis of the dependence of the confinement loss of an anti-resonant capillary on the curvature of the core surround is presented. The core boundary is described by circular arcs and the construction allows for a wide range of core shapes to be considered. It is found that both negative and positive curvatures substantially reduce the confinement loss relative to that of a circular anti-resonant capillary and that this effect is insensitive to the size of the core relative to the wavelength and to the properties of the glass capillary wall. In contrast, for a solid core surround there is a small increase in the confinement loss with curvature. Results of scalar and vector calculations are shown to be similar. A qualitative explanation of the results is proposed based on azimuthal confinement of the wave fields generated by the curved boundaries.

Validation of Monte Carlo activation calculation for V1 NPP reactor concrete shaft

This work is aimed at developing an advanced model of the Slovak VVER-440/V-230, reactor in the MCNP code, to calculate induced activity in ex-vessel structural components and to validate obtained results to achieve an effective calculation tool for decommissioning purposes. A survey of the V1 NPP operating history revealed that after 12 fuel cycles the shielding assemblies were placed at the core boundary positions thereby reducing the core and decreasing the neutron flux on reactor pressure vessel as well as in adjacent ex-vessel components. Representative fuel cycles were selected for given periods. Model of the V1 reactor at the core level was developed, covering in-vessel and ex-vessel components. The activation calculation of the reactor concrete shaft at the sample volume location was performed using the MCNP5 code with the ENDF/B-VII cross-section library. Activities of selected radionuclides were determined and verified by measurements of samples at the Slovak University of Technology.

Asteroseismic analysis of variable hot subdwarf stars observed with TESS

Context. We present photometric and spectroscopic analyses of gravity (g-mode) long-period pulsating hot subdwarf B (sdB) stars, also called V1093 Her stars, observed by the TESS space telescope in both 120 s short-cadence and 20 s ultra-short-cadence mode during the survey observation and the extended mission of the southern ecliptic hemisphere. Aims. We performed a detailed asteroseismic and spectroscopic analysis of five pulsating sdB stars observed with TESS in order to compare the observations with model predictions based on our stellar evolution computations coupled with adiabatic pulsation computations. Methods. We processed and analyzed TESS observations of long-period pulsating hot subdwarf B stars. We used standard pre-whitening techniques on the datasets to extract the pulsation periods from the TESS light curves. We applied standard seismic tools for mode identification, including asymptotic period spacings and rotational frequency multiplets. Based on the values obtained from Kolmogorov-Smirnov and Inverse Variance tests, we searched for a constant period spacing for dipole (l = 1) and quadrupole (l = 2) modes. We calculated the mean period spacing for l = 1 and l = 2 modes and estimated the errors by means of a statistical resampling analysis. For all stars, atmospheric parameters were derived by fitting synthetic spectra to the newly obtained low-resolution spectra. We computed stellar evolution models using the LPCODE stellar evolution code, and computed l = 1 g-mode frequencies with the adiabatic nonradial pulsation code LP-PUL. Derived observational mean period spacings were then compared to the mean period spacings from detailed stellar evolution computations coupled with the adiabatic pulsation computations of g-modes. Results. We detect 73 frequencies, most of which are identified as dipole and quadrupole g-modes with periods spanning from ∼3000 s to ∼14 500 s. The derived mean period spacing of dipole modes is concentrated in a narrow region ranging from 251 s to 256 s, while the mean period spacing for quadrupole modes spans from 145 s to 154 s. The atmospheric parameters derived from spectroscopic data are typical of long-period pulsating sdB stars with an effective temperature ranging from 23 700 K to 27 600 K and surface gravity spanning from 5.3 dex to 5.5 dex. In agreement with the expectations from theoretical arguments and previous asteroseismological works, we find that the mean period spacings obtained for models with small convective cores, as predicted by a pure Schwarzschild criterion, are incompatible with the observations. We find that models with a standard, modest convective boundary mixing at the boundary of the convective core are in better agreement with the observed mean period spacings and are therefore more realistic. Conclusions. Using high-quality space-based photometry collected by the TESS mission coupled with low-resolution spectroscopy from the ground, we provide a global comparison of the observations with model predictions by means of a robust indicator such as the mean period spacing. All five objects that we analyze in this work show remarkable homogeneity in both seismic and spectroscopic properties.

Experimental and mixed analytical–numerical studies for free and forced vibrations of Z-reinforced sandwich plates stiffened by steel ribs

Free and forced vibrations of Z-reinforced sandwich plates stiffened by steel ribs are researched by experimental and mixed analytical–numerical techniques. A test sample of the plate is firstly manufactured and an underwater vibration test is conducted with a random white-noise force. Meanwhile, a mixed analytical–numerical method (MA-NM) is proposed, which uses an analytical homogenization for the Z-reinforced core and coupling finite element and boundary element (FE/BE) analyses for the plate. Natural frequencies given by the MA-NM are compared with ones from the detailed FE model. Forced vibration responses from the MA-NM are validated against the experimental data. Good agreements are obtained and the high accuracy of the MA-NM is demonstrated. Parameters influences are then analyzed through the MA-NM. The core material shows a larger effect on natural frequencies than the reinforcement material. Ribs at the orthotropic midlines greatly enhance the bend stiffness of the whole structure, and ribs at the surrounding sides mainly influence boundary conditions. When in-plane coordinates of the external force near the plate center, vibration responses have fewer resonance peaks and lower amplitudes, while the influence of the thickness direction coordinate could be ignored. The fluid loading reduces both natural frequencies and vibration responses.

On the linear and non-linear fluid response to the circular forcing in a rotating spherical shell

Fluid flow excited by a core oscillating in a rotating spherical cavity is experimentally investigated. Oscillations are set by an external inertial field so that in the reference frame of the cavity, the core moves along a circular trajectory around the rotation axis. Two situations are considered: when the core oscillations are co-directed or counter-directed with respect to the rotation of the cavity. The oscillating core is a source of non-axisymmetric inertial waves that form a system of cone-shaped shear layers in fluid bulk. Depending on the oscillation frequency, various inertial flow regimes arise, the spatial structure of which strongly depends on the sign of the oscillations. It is found that a strong non-linear response in the form of a steady zonal flow corresponds to each flow regime. The flow structure is a system of nested liquid geostrophic cylinders, one of which is associated with the critical latitude at the core boundary, where inertial waves are generated. The next one is associated with the wave reflection from the cavity boundary and is clearly manifested when they are focused on the wave attractor. The most intense zonal flow occurs when inertial waves are superposed and global vortex structures are resonantly excited.

On the Origin of Geostrophic Liquid Cylinders in Rotating Sphere with Oscillating Inner Core

The effect of non-axisymmetric inertial waves on the zonal flow structure in a rotating spherical shell is studied experimentally. The wave source is the inner core, which performs circular oscillations in the equatorial plane. The case of positive frequencies that corresponds to the advanced core motion is considered. As a result of non-linear effects, a quasi-two-dimensional axisymmetric steady flow with a complex distribution of angular velocity is generated. The extrema in the velocity profile are equivalent to the nested liquid geostrophic cylinders, which appearance is due to the interaction of the inertial waves within a viscous boundary layer. One of the extrema is associated with the critical latitude at the core boundary, where the inertial waves are excited. With an increase in the oscillation frequency, the position of this extremum gradually shifts to the rotation axis. Additional geostrophic circulation occurs close to the points where the inertial wave reflects from the cavity boundary.

Probing the temperature gradient in the core boundary layer of stars with gravito-inertial modes

Aims. We investigated the thermal and chemical structure in the near-core region of stars with a convective core by means of gravito-inertial modes. We determined the probing power of different asteroseismic observables and fitting methodologies. We focus on the case of the B-type star KIC 7760680, rotating at a quarter of its critical rotation velocity. Methods. We computed grids of 1D stellar structure and evolution models for two different prescriptions of the temperature gradient and mixing profile in the near-core region. We determined which of these prescriptions is preferred according to the prograde dipole modes detected in 4 yr Kepler photometry of KIC 7760680. We considered different sets of asteroseismic observables and compared the outcomes of the regression problem for a χ2 and a Mahalanobis distance merit function, where the latter takes into account realistic uncertainties for the theoretical predictions and the former does not. Results. Period spacings of modes with consecutive radial order offer a better diagnostic than mode periods or mode frequencies for asteroseismic modelling of stars revealing only high-order gravito-inertial modes. We find KIC 7760680 to reveal a radiative temperature gradient in models with convective boundary mixing, but less complex models without such mixing are statistically preferred for this rotating star, revealing extremely low vertical envelope mixing. Conclusions. Our results strongly suggest the use of measured individual period spacing values for modes of consecutive radial order as an asteroseismic diagnostic for stellar modelling of B-type pulsators with gravito-inertial modes.

Behaviour of eccentrically inclined loaded rectangular foundation on reinforced sand

Abstract This study presents the behaviour of model footing resting over unreinforced and reinforced sand bed under different loading conditions carried out experimentally. The parameters investigated in this study includes the number of reinforced layers (N = 0, 1, 2, 3, 4), embedment ratio (Df /B = 0, 0.5, 1.0), eccentric and inclined ratio (e/L, e/B = 0, 0.05, 0.10, 0.15) and (a = 0°, 7°, 14°). The test sand was reinforced with bi-axial geogrid (Bx20/20). The test results show that the ultimate bearing capacities decrease with axial eccentricity and inclination of applied loads. The test results also show that the depth of model footing increase zero to B (B = width of model footing), an increase of ultimate bearing capacity (UBC) approximated at 93%. Similarly, the multi-layered geogrid reinforced sand (N = 0 to 4) increases the UBC by about 75%. The bearing capacity ratio (BCR) of the model footing increases with an increasing load eccentricity to the core boundary of footing; if the load eccentricities increase continuity, the BCR decreases. The tilt of the model footing is increased by increasing the eccentricity and decreases with increasing the number of reinforcing layers.

Single-mode antiresonant terahertz fiber based on mode coupling between core and cladding* *Project supported by the National Natural Science Foundation of China (Grant No. 62075159), the National Key Research and Development Program of China (Grant No. 2017YFF0104603), the 111 Project of China (Grant No. B17031), and the Major Scientific and Technological Innovation Projects of Key Research and Development Plans in

Based on the index-induced mode coupling between the higher-order mode in core and the fundamental mode in cladding tubes, the single-mode operation can be realized in any antiresonant fibers (ARFs) when satisfying that the area ratio of cladding tube and core is about 0.46:1, and this area ratio also should be modified according to the shape and the number of cladding tubes. In the ARF with nodal core boundary, the mode in core also can couple with the mode in the wall of core boundary, which can further enhance the suppression of high-order mode. Accordingly, an ARF with conjoint semi-elliptical cladding tubes realizes a loss of higher-order mode larger than 30 dB/m; simultaneously, a loss of fundamental mode loss less than 0.4 dB/m.

Polarization-maintaining terahertz anti-resonant fibers based on mode couplings between core and cladding

This study numerically investigated the index-induced mode coupling between the fundamental mode in core and the fundamental mode in cladding tubes in THz anti-resonant fibers (ARFs), and then, this index-induced mode coupling was applied for designing polarization-maintaining ARFs. Simulated results indicate that in the polarization-maintaining ARFs based on index-induced mode coupling, when the core diameter approaches the diameter of cladding tubes, ARFs can realize a birefringence which maintaining the polarization of incident light. Besides, the birefringence property which is realized by deforming the core boundary or categorizing the core boundary into two orthometric anti-resonant boundaries can be enhanced by the index-induced mode coupling. Based on the index-induced mode coupling, this paper proposed three compact polarization-maintaining ARFs, and the highest birefringence index exceeded 4 × 10−4.

Field-enhanced polarization in polytype ferric oxides: confronting anisotropy in dielectric ellipsoid dispersion

An analytic dielectric introspection in two cardinal ferric oxide polymorphs, viz. hematite and maghemite, is conducted using a three-fold line of direction. Firstly, dc field-dependent radio/audio-frequency impedance and dielectric spectra of polycrystalline MIM pellets, comprising near-stoichiometric (meticulously characterized) Fe2O3 nanoparticles, are analysed by employing the Cole–Davidson model, Jonscher’s power law and equivalent circuitry to quantify non-Debye dipolar relaxations, small polaron hopping conduction, grain core–boundary resistivity correlations and field-driven delocalization/de-trapping of carriers. Bias-tuned low-frequency enhancement of the dielectric constant by augmenting Maxwell–Wagner polarization is demonstrated for both samples, a prerequisite for conquering classical energy-storage bottleneck. Secondly, the optical dielectric function and associated parameters are evaluated under a density functional theory + U framework, to physically designate particular resonant absorption, dissipation, electronic polarization and decay. In doing so, a new crystallographically consistent and energetically stable vacancy-ordered maghemite-type supercell is constructed to accomplish reasonable computational cost. Thirdly, intrinsic anisotropy in materials sensitive to photonic excitations is videographed by simulating energy-dispersive evolution of the quadric surface to project real/imaginary dielectric tensors. The authors anticipate that this intensive technique will pictorially demonstrate anisotropic deviations in the dielectric ellipsoid, fostering materials physics over linear and nonlinear dielectrics.

Predictive modeling of a lithium vapor box divertor in NSTX-U using SOLPS-ITER

Abstract The unmitigated heat flux in attached operation of a fusion power plant is predicted to be destructive to any solid divertor surface. Detachment, whereby the plasma pressure drops significantly before reaching the divertor target thus greatly reducing the heat flux and sputtering, will be necessary to ensure adequate lifetime of plasma facing components (PFCs). The lithium vapor box divertor aims to detach the divertor plasma via evaporating and condensing lithium surfaces. By evaporating lithium near or at the divertor plate and condensing it closer to the main chamber, a lithium vapor density gradient can be created. This density gradient ties energy losses to poloidal distance between the target and the detachment point. The radiation zone is then prevented from reaching the X-point as the lithium ionization rate decreases when the detachment front moves away from the divertor target. Here we present Scrape Off Layer Plasma Simulator (SOLPS) simulations of a lithium vapor box divertor using an NSTX-U equilibrium and PFC geometry. The parameters for the core boundary conditions, gas puff intensity, and heat and particle transport coefficients are chosen to match experimental values. Acceptable agreement with experimental Scrape-Off Layer (SOL) widths is found, indicating a reasonable choice of transport coefficients. In predictive simulations, lithium is added via evaporation at the target. Predictions for peak heat fluxes and upstream impurity concentration are given for a variety of evaporation rates. Target electron temperature is predicted to be able to be reduced to recombination levels (below 1 eV) for lithium evaporation rates of 1 ⋅ 1 0 23 Li/s, indicating detachment. Peak heat flux at the lower outer target could be reduced by as much as a factor of six while maintaining upstream lithium fractions below 2%. The prevention of lithium from reaching the midplane is shown to be due to an increase in frictional forces acting on the lithium from a deuterium gas puff. Lithium is also shown to be redeposited close to the evaporator which is favorable for initial tests and future capillary porous systems.