Local Radius Research Articles

Physically consistent metrics with independent parameters instead of standard metrics with unphysical consequences. 2. Rotating sources

The Kerr metric, the external metric for a rotating body, contains the equatorial gravitational radius implicitly depending on the specific angular momentum (SAM). Ignoring this dependence due to the formal mathematical approach without understanding the physical aspects led to absurd unphysical consequences in the black hole theory, in particular, that an increase in the rotational energy at increasing SAM weakens gravity, decreasing the gravitational radius at the pole and the effects of gravity (redshifts, mean radii of orbits and shadows). This shortcoming of the Kerr metric is improved in a new form of this metric with an independent parameter - the gravitational radius at the pole, determined by the mass of matter without rotational energy. The contributions of the energies of matter and rotation have the same sign and an increase in SAM strengthens gravity, increasing its effects (the equatorial gravitational radius, redshifts, mean radii of orbits and shadows). The modified form of the Kerr metric describes the gravitational field of a frozar having angular momentum, a star with frozen structure and the surface asymptotically tending to the local gravitational radius (minimal at pole and maximal at equator). The application of this method to the Kerr-Newman metric, including the charge, and to the NUT metric, gave modified forms of these metrics with independent parameters. In the frozar theory, particle energies are positive everywhere, and the theory is free from the non-physical effects of the former black hole theory (horizons, singularities, ergosphere and the extraction of energy from it, evaporation). Thermodynamics of frozars follows from the almost irreversible freezing, as the result of which, during accretion and other processes, the mass of neutral matter without rotational energy grows almost irreversibly.

The universal shear conductivity of Fermi liquids and spinon Fermi surface states and its detection via spin qubit noise magnetometry

We demonstrate a remarkable property of metallic Fermi liquids: the transverse conductivity assumes a universal value in the quasi-static (ω → 0) limit for wavevectors q in the regime , where l mfp is the mean free path and p F is the Fermi momentum. This value is in two dimensions (2D), where measures the local radius of curvature of the Fermi surface (FS) in momentum space. Even more surprisingly, we find that U(1) spin liquids with a spinon FS have the same universal transverse conductivity. This means such spin liquids behave effectively as metals in this regime, even though they appear insulating in standard transport experiments. Moreover, we show that transverse current fluctuations result in a universal low-frequency magnetic noise that can be directly probed by a spin qubit, such as a nitrogen-vacancy (NV) center in diamond, placed at a distance z above of the 2D metal or spin liquid. Specifically the magnetic noise is given by , where is the perimeter of the FS in momentum space and C is a combination of fundamental constants of nature. Therefore these observables are controlled purely by the geometry of the FS and are independent of kinematic details of the quasi-particles, such as their effective mass and interactions. This behavior can be used as a new technique to measure the size of the FS of metals and as a smoking gun probe to pinpoint the presence of the elusive spinon FS in two-dimensional systems. We estimate that this universal regime is within reach of current NV center spectroscopic techniques for several spinon FS candidate materials.

Assessment of fully automatic segmentation of pulmonary artery and aorta on noncontrast CT with optimal surface graph cuts.

PurposeAccurate segmentation of the pulmonary arteries and aorta is important due to the association of the diameter and the shape of these vessels with several cardiovascular diseases and with the risk of exacerbations and death in patients with chronic obstructive pulmonary disease. We propose a fully automatic method based on an optimal surface graph‐cut algorithm to quantify the full 3D shape and the diameters of the pulmonary arteries and aorta in noncontrast computed tomography (CT) scans.MethodsThe proposed algorithm first extracts seed points in the right and left pulmonary arteries, the pulmonary trunk, and the ascending and descending aorta by using multi‐atlas registration. Subsequently, the centerlines of the pulmonary arteries and aorta are extracted by a minimum cost path tracking between the extracted seed points, with a cost based on a combination of lumen intensity similarity and multiscale medialness in three planes. The centerlines are refined by applying the path tracking algorithm to curved multiplanar reformatted scans and are then smoothed and dilated nonuniformly according to the extracted local vessel radius from the medialness filter. The resulting coarse estimates of the vessels are used as initialization for a graph‐cut segmentation. Once the vessels are segmented, the diameters of the pulmonary artery (PA) and the ascending aorta (AA) and the PA:AA ratio are automatically calculated both in a single axial slice and in a 10 mm volume around the automatically extracted PA bifurcation level. The method is evaluated on noncontrast CT scans from the Danish Lung Cancer Screening Trial (DLCST). Segmentation accuracy is determined by comparing with manual annotations on 25 CT scans. Intraclass correlation (ICC) between manual and automatic diameters, both measured in axial slices at the PA bifurcation level, is computed on an additional 200 CT scans. Repeatability of the automated 3D volumetric diameter and PA:AA ratio calculations (perpendicular to the vessel axis) are evaluated on 118 scan–rescan pairs with an average in‐between time of 3 months.ResultsWe obtained a Dice segmentation overlap of 0.94 ± 0.02 for pulmonary arteries and 0.96 ± 0.01 for the aorta, with a mean surface distance of 0.62 ± 0.33 mm and 0.43 ± 0.07 mm, respectively. ICC between manual and automatic in‐slice diameter measures was 0.92 for PA, 0.97 for AA, and 0.90 for the PA:AA ratio, and for automatic diameters in 3D volumes around the PA bifurcation level between scan and rescan was 0.89, 0.95, and 0.86, respectively.ConclusionThe proposed automatic segmentation method can reliably extract diameters of the large arteries in non‐ECG‐gated noncontrast CT scans such as are acquired in lung cancer screening.

Differential evolution algorithm-based multiple-factor optimization methods for data assimilation

The methods of searching for optimized parameters have substantial effects on the forecast accuracy of ensemble data assimilation systems. The selection of these factors is usually performed using trial-and-error methods, and poor parameterizations may lead to filter divergence. Combined with the local ensemble transform Kalman filtering method (LETKF), a technique for an automated search of the best configuration (parameters) of a data assimilation system is proposed. To obtain better assimilation, a differential evolution (DE) algorithm-based multiple-factor parameterization method results in the corresponding circumstances. By combining with fast-searching DE algorithms, we may retrieve the most ideal parameter combinations. Several numerical experiments performed with the Lorenz-96 model show that new methods performed better than the original one-parameter optimization methods. As the basis of DE methods, the best combinations of the local radius and the covariance inflation parameter, which can guarantee the best DA performances in the corresponding circumstances, are retrieved. It is found that the new method is capable of outperforming previous search algorithms under both perfect and imperfect model scenarios, and the calculation cost in Lorenz-96 model is lower. However, how to apply the new proposed method to more complex atmospheric or land surface models requires further verification.

Automated in vivo detection and localization of posterior staphyloma in ultrasound b-modes

In high and pathologic myopia eyes, staphyloma, an outpouching of the eyewall, is associated with risks of permanent vision loss. Automated detection of staphyloma in ultrasound B-modes could assist clinicians in quickly identifying patients at risk. In this study, an algorithm to detect the presence of staphyloma and locate the staphyloma apex was developed. A 10 MHz ultrasound probe was used to acquire 127 B-modes, from 82 eyes and 52 patients. Sixty-one of the B-modes included staphyloma, as determined by an experienced ophthalmologist who also marked the staphyloma apex in each image where present. In each B-mode, the vitreoretinal boundary was automatically detected by a thresholding method. The local radius of curvature (K) was computed, and the ability of the standard deviation of K to detect staphyloma was evaluated by receiver-operating characteristic analysis. The staphyloma apex was automatically detected as the point on the vitreoretinal boundary furthest from the center of the transducer. The area under the curve using standard deviation of K for staphyloma detection was 0.927. The average error in detected staphyloma apex location was 1.34 ± 1.36 mm. These results demonstrate the potential of automated staphyloma detection and localization from ultrasound, which could assist in quick diagnosis of staphyloma.

An Aggregation-Free Local Volume Fraction Formulation for Topological Design of Porous Structure.

Cellular structure can possess superior mechanical properties and low density simultaneously. Additive manufacturing has experienced substantial progress in the past decades, which promotes the popularity of such bone-like structure. This paper proposes a methodology on the topological design of porous structure. For the typical technologies such as the p-norm aggregation and implicit porosity control, the violation of the maximum local volume constraint is inevitable. To this end, the primary optimization problem with bounds of local volume constraints is transformed into unconstrained programming by setting up a sequence of minimization sub-problems in terms of the augmented Lagrangian method. The approximation and algorithm using the concept of moving asymptotes is employed as the optimizer. Several numerical tests are provided to illustrate the effectiveness of the proposed approach in comparison with existing approaches. The effects of the global and local volume percentage, influence radius and mesh discretization on the final designs are investigated. In comparison to existing methods, the proposed method is capable of accurately limiting the upper bound of global and local volume fractions, which opens up new possibilities for additive manufacturing.

Three-dimensional optimization of La0.6Sr0.4Co0.2Fe0.8O3 cathode microstructure with particle radius constraint

A numerical model is developed to optimize the La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode porous microstructure of solid oxide fuel cell (SOFC), in which the local radius constraints are applied. During the optimization, the LSCF porous microstructure is deformed and the total reaction current is maximized. A level-set method is utilized to parametrize the 3D microstructure, and an adjoint method is applied for the sensitivity analysis. In addition, in order to improve the computational accuracy and to make the optimized microstructure manufacturable, a radius constraint is imposed to ensure that the local radii are above the target value, where the interface is updated only when the local radius value is larger than the target radius. Computational results show that the sphere-shaped LSCF solid particles are preferred in terms of performance improvement. In addition, the computational accuracy is improved with the imposed radius constraint, and the total electrochemical reaction current in the optimal microstructure is improved comparing with the experimentall fabricated microstructure obtained with 3D recontruction technique. Furthermore, the optimized microstructure and performance of the LSCF cathode are independent from the initial cathode structures. Finally, the relation between Thiele modulus and the optimal microstructure is investigated by varying the ionic conductivities and exchange current densities.

Balancing efficiency and homogeneity of biomaterial transport in networks

Transport of biomaterial in tubular networks is ubiquitous in nature, where examples include the endoplasmic reticulum, leaf venation or vessel networks in vertebrates. Flow feedback by adjustment of the local tube radius in response to a fluid flow is a pivotal mechanism to optimize the transport properties of a network. To describe liquid transport in tubular networks we develop a minimal mathematical model, which includes the interplay of the viscous flow feedback and the tubes elastic bending energy while conserving the network material. Flow feedback in pitted, branched and loopy networks is shown to lower their resistance, as compared to a feedback-free system, by local adaptations without the need for additional network material. Flow feedback in particular reduces the resistance in pitted and branched networks, directly linked with a reduction in the effective number of neighboring tubes. In loopy networks we find a direction-dependent flow resistance, with a prevailing transport direction set by the network geometry.

Cyclone‐Anticyclone Asymmetry of Eddy Detection on Gridded Altimetry Product in the Mediterranean Sea

AbstractWe perform an Observing System Simulation Experiment that simulates the satellite sampling and the mapping procedure on the sea surface of the high‐resolution model CROCO‐MED60v40, to investigate the reliability and the accuracy of the eddy detection. The main result of this study is a strong cyclone‐anticyclone asymmetry of the eddy detection on the altimetry products AVISO/CMEMS in the Mediterranean Sea. Large‐scale cyclones having a characteristic radius larger than the local deformation radius are much less reliable than large‐scale anticyclones. We estimate that less than 60% of these cyclones detected on gridded altimetry product are reliable, while more than 85% of mesoscale anticyclones are reliable. Besides, both the barycenter and the size of these mesoscale anticyclones are relatively accurate. This asymmetry comes from the difference of stability between cyclonic and anticyclonic eddies. Large mesoscale cyclones often split into smaller sub‐mesoscale structures having a rapid dynamical evolution. The numerical model CROCO‐MED60v40 shows that this complex dynamic is too fast and too small to be accurately captured by the gridded altimetry products. The spatio‐temporal interpolation smoothes out this sub‐mesoscale dynamics and tends to generate an excessive number of unrealistic mesoscale cyclones in comparison with the reference field. On the other hand, large mesoscale anticyclones, which are more robust and which evolve more slowly, can be accurately tracked by standard altimetry products. We also confirm that the AVISO/CMEMS products induce a bias on the eddy intensity. The azimuthal geostrophic velocities are always underestimated for large mesoscale anticyclones.

Improved neoclassical plasma confinement and turbulence suppression in a magnetic well in tokamak reactors

It has been known that the width of the trapped particles, i.e. bananas, is reduced or squeezed in a magnetic well in tokamaks. The magnetic squeezing factor S B depends on the energy and pitch angle of the particles. When ρ p/a ∼ 1, S B becomes appreciably larger than unity; it can be of the order of 2 for a parabolic well with B −1 d2 B/dr 2 ∼ 2a −2. Here, ρ p is the poloidal gyro-radius, B is the magnetic field strength, r is the local minor radius, and a is the minor radius. However, the real orbit width measured in terms of the poloidal magnetic flux is still less than a because of the magnetic squeezing; for S B = 2, it is a 30% reduction. The transport consequences of the squeezed bananas in a magnetic well are calculated by solving the drift kinetic equation utilizing the constants of motion in the large aspect ratio limit. Consequently, neoclassical ion heat conductivity χ h in the reactor relevant collisionality regime (i.e. banana regime) is reduced by a factor of ; for S B = 2, it is almost a factor of three reduction for the same temperature. The ion temperature scaling of χ h improves from the conventional, and weakly favorable scaling to the strongly favorable scaling for high temperature fusion grade tokamak plasmas; the scaling however does not take the temperature dependence of the magnetic well itself into account. Here, T i is the ion temperature. In addition, it is shown that plasma turbulence is suppressed in a magnetic well using the reduced decorrelation time argument and anomalous plasma confinement is improved. The combined improvements result in a favorable temperature scaling in the ion energy confinement time, and make burning aneutronic fuels feasible. The implications on a tokamak with a magnetic well as a fusion reactor are discussed.

Water-driven CsPbBr3 nanocrystals and poly(methyl methacrylate)-CsPbBr3 nanocrystal films with bending-endurable photoluminescence

Perovskite nanocrystals are regarded as next-generation functional materials for display applications, especially for flexible liquid crystal displays (LCDs). As a potential component of flexible LCD backlights, perovskite nanocrystal films are facing a challenge issue of deformation-induced shift of photoluminescence, leading to an image distortion. To date, most synthesis methods have involved the use of organic solvent in precursor solutions, such as N,N-dimethylformamide and dimethyl sulfoxide, which poses a potential threat to the environment, health and security. In this work, we demonstrate the feasibility to produce microsized CsPbBr3 crystals with deionized water as the precursor solvent via an environmental-friendly and cost-efficient approach and CsPbBr3 nanocrystals with green (~522 nm) and blue (~493 nm) emissions from the microsized CsPbBr3 crystals in toluene under sonication. The blue-emitting nanocrystals exhibit a photoluminescence (PL) quantum yield of 80%, much larger than 61.4% of the CsPbBr3 nanocrystals made by an anti-solvent method; the green-emitting nanocrystals exhibit better stability than those made by the antisolvent method over 9 days. Using the green-emitting CsPbBr3 nanocrystals, we prepare a bilayer structure with a poly(methyl methacrylate)-CsPbBr3 nanocrystal film on a polyethylene terephthalate plate. The films exhibit bending-endurable photoluminescence, i.e. the wavelength of the PL peak remains unchanged, for local radius of curvature of the bilayer up to 10.07 mm under bending. This study opens a new avenue to potentially produce microsized perovskite crystals without harmful organic solvents and bending-endurable backlight films for the applications in flexible display.

Influence of span-wise coherence on the acoustic radiation in a cylinder wake

The aim of this study is to detect and visualise the influence of span-wise coherence on propagating sound waves emanating from a flow around circular cylinders with span-wise variations of the local radius. Synchronous particle image velocimetry (PIV) and microphone measurements are performed in a circular wind tunnel with a nozzle size of 0.4 m×0.4 m at a maximum flow speed of U∞ = 43m s−1 . The test section is surrounded by a full anechoic chamber of approximately 9 m×9 m×5 m.

Radioscapholunate Arthrodesis and Distal Radioulnar Joint Arthroplasty for Rheumatoid Wrist Arthritis: A Surgical Technique

Introduction: We describe the treatment of rheumatoid radiocarpal joint and distal radioulnar joint (DRUJ) arthritis with radioscapholunate (RSL) arthrodesis and DRUJ arthroplasty in 2 patients with 2 years follow-up. The RSL arthrodesis utilizes nitinol staples and local distal radius autograft to fuse the scaphoid and lunate to the distal radius. Materials and Methods: One patient was treated in their nondominant extremity, and the other patient had bilateral procedures. A constrained endoprosthesis was used for the DRUJ arthroplasty portion, using the same dorsal approach to the wrist as the RSL arthrodesis. Results: Before his procedures, this first patient-reported a Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH) score of 66, which improved to 16 at 2 years postoperatively. He also reported a Visual Analog Scale score of 6/10 at rest in both wrists preoperatively. Following his procedures, Visual Analog Scale scores improved to 3/10 in the right wrist and 0/10 in the left wrist. Active wrist range of motion was measured to be a 60-degree arc on the right and a 47-degree arc on the left. Our second patient reported an improved QuickDASH score from 97 preoperatively to 68 at 2 years postoperatively and had a 70-degree arc of left wrist range of motion. No postoperative complications or reoperations were encountered in the cases. Discussion: The benefit of this technique is to allow simultaneous treatment of radiocarpal joint arthritis with RSL arthrodesis, permitting wrist flexion and extension through the midcarpal joints, and DRUJ arthritis with DRUJ arthroplasty, preserving pronation and supination.

Vortex Ring Theory—An Alternative to the Existing Actuator Disk and Rotating Annular Stream Tube Theories

Currently, the actuator disk theory (ADT) and the rotating annular stream-tube theory (RAST), both of which predicate on the axial momentum and generalized momentum theories, among others, are commonly used in investigating the aerodynamic characteristics of horizontal axis wind turbines (HAWTs). These theories, which are based on a rotor with an infinite number of blades, typically do not properly capture the flow physics of wind blowing past the rotors of HAWTs. A vortex ring theory (VRT) that analyzes HAWTs based solely on the characteristics of fluids flowing past obstructions is proposed. The VRT is not predicated on the assertion that the induced velocity in the wake is twice the induced velocity at the rotor. On the contrary, it splits the axial induction factor in the wake into two components, namely, the induction or interference factor due to the solidity of the rotor and the induction factor due to the wake of the rotor aw; aw and its azimuthal counterpart are determined using the Biot–Savart law. The pressure differences across the rotor segments of a HAWT are derived from the Bernoulli equation for all the three theories. Blade segment/local areas based on the blade sectional geometry of the rotor are used in the case of the VRT to estimate the local forces. All the calculations in this study are based on the design parameters of the 5 MW National Renewable Energy Laboratory’s reference offshore wind turbine. Pressure differences are plotted as functions of local radii using the calculated axial and azimuthal induction factors for each theory. The local power coefficient is plotted as a function of the local tip-speed ratio, while the local thrust coefficient is plotted as a function of the local radii for all the three theories. There is piece-wise agreement between the VRT, the ADT, the RAST and numerical and experimental data available in the literature.

A Study on the Failure Behavior of Sand Grain Contacts with Hertz Modeling, Image Processing, and Statistical Analysis.

The crushing behavior of particles is encountered in a large number of natural and engineering systems, and it is important for it to be examined in problems related to hydraulic fracturing, where proppant–proppant and proppant–rock interactions are essential to be modeled as well as geotechnical engineering problems, where grains may crush because the transmitted stresses at their contacts exceed their tensile strength. Despite the interest in the study of the crushing behavior of natural particles, most previous experimental works have examined the single-grain or multiple-grain crushing configurations, and less attention has been given in the laboratory investigation of the interactions of two grains in contact up to their failure as well as on the assessment of the methodology adopted to analyze the data. In the present study, a quartz sand of 1.18–2.36 mm in size was examined, performing a total of 244 grain-to-grain crushing tests at two different speeds, 0.01 and 1 mm/min. In order to calculate stresses from the measured forces, Hertz modeling was implemented to calculate an approximate contact area between the particles based on their local radii (i.e., the radius of the grains in the vicinity of their contact). Based on the results, three different modes of failure were distinguished as conservative, fragmentary, and destructive, corresponding to micro-scale, meso-scale, and macro-scale breakage, respectively. From the data, four different classes of curves could be identified. Class-A and class-B corresponded to an initially Hertzian behavior followed by a brittle failure with a distinctive (single) peak point. The occurrence of hardening prior to the failure point distinguished class-B from class-A. Two additional classes (termed as class-C and class-D) were observed having two or multiple peaks, and much larger displacements were necessary to mobilize the failure point. Hertz fitting, Weibull statistics, and clustering were further implemented to estimate the influence of local radius and elastic modulus values. One of the important observations was that the method of analysis adopted to estimate the local radius of the grains, based on manual assessment (i.e., eyeball fitting) or robust Matlab-based image processing, was a key factor influencing the resultant strength distribution and m-modulus, which are grain crushing strength characteristics. The results from the study were further compared with previously reported data on single- and multiple-grain crushing tests.

Local spectrum, local spectral radius, and growth conditions

Let X be a complex Banach space and \(x\in X.\) Assume that a bounded linear operator T on X satisfies the condition $$\begin{aligned} \left\| e^{tT}x\right\| \le C_{x}\left( 1+\left| t\right| \right) ^{\alpha }\quad \left( \alpha \ge 0\right) , \end{aligned}$$for all \(t\in {\mathbb {R}} \) and for some constant \(C_{x}>0.\) For the function f from the Beurling algebra \(L_{\omega }^{1}\left( {\mathbb {R}} \right) \) with the weight \(\omega \left( t\right) =\left( 1+\left| t\right| \right) ^{\alpha },\) we can define an element in X, denoted by \(x_{f}\), which integrates \(e^{tT}x\) with respect to f. We present a complete description of the elements \(x_{f}\) in the case when the local spectrum of T at x consists of one point. In the case \(0\le \alpha <1,\) some estimates for the norm of Tx via the local spectral radius of T at x are obtained. Some applications of these results are also given.

Application of Gaussian Weight to Improve Perturbation Features of Convection-Permitting Ensemble Forecast Based on Local Breeding of Growing Modes

The local breeding growth mode (LBGM) method does not consider the difference between the grid points within the local radius. To address this problem, Gaussian weights (GWs) were proposed, which cause the influence of each grid within a local radius to exert an increase in distance with Gaussian decay on the central grid. In this paper, the effects of two different LBGM methods under GWs and equal weights (EWs) in convection-permitting ensemble forecasting are compared and analyzed using two squall line examples. The results showed that the use of the GWs intensified the local characteristics of the initial condition perturbation (ICP) and made the distribution of the ICP more flow-dependent. The result of the kinetic energy spectrum of the ICP indicated that there could be more large-scale information in the ICP using the GWs. In addition, meso-scale information also improved slightly. For nonprecipitation variable forecasting, GWs improved the relationships between the root-mean-square error and the spread and contributed to the forecasting accuracy of wind, temperature, geopotential height, and humidity. For the precipitation forecast, GWs simulated the precipitation structure successfully and provided better probability forecasting during the evolution of two squall line processes than the EWs.

Local flame and flow properties of propagating premixed turbulent flames during light-round process in a MICCA-type annular combustor

In this paper, local flame and flow properties of propagating premixed turbulent propane/air flames were derived by two-dimensional time-resolved Mie scattering and PIV methodology in a MICCA-type annular combustor. The curvature of flame front, local flame speed and the evolution of leading points during the light-round process were analyzed in detail. All experiments were performed under a constant equivalence ratio of 0.67, with the bulk flow velocity set from 1.95 to 5.85 m/s in five cases to achieve different turbulent intensities. The instantaneous flame fronts and velocity fields of unburned gases were measured to investigate the flame-flow interactions corresponding to four regions of the annular combustor. The results indicate that the slight asymmetry of the propagation in two flame branches is mainly due to the competition between the local swirling injection and the overall circumferential flow along the inner or outer parts of the combustor. Based on the statistical analysis of the local radius of flame curvature, the whole flame front tends to be convex to the unburned mixture. As a characteristic length scale, the inner-cutoff scale εi of the flame front is about 2–3 times the flame thickness δL, which decreases with the increase of turbulent intensity. The value of fractal dimension increases with the increase of turbulence intensity, and its value is about 2.15–2.25 for all cases. Besides, in order to analyze the flame properties during the ignition process, the local flame speed wn was calculated using statistical method as well as the velocity of unburned mixture gas. Moreover, the experimental results (Ub=3.90 m/s) of the leading points’ trajectory were consistent with the large-eddy simulations at the height of h =25 mm, and the leading points of the flame fronts were generally concentrated near (about 5 mm away) the inner tube for both flame branches. The researches of ignition mechanisms in annular combustors have been carried out for almost ten years, but the quantitative measurements of flow and flame fronts are barely reported. Motivated by this, it will provide new insights into the ignition process in annular combustors from this work.

The Gas Content and Stripping of Local Group Dwarf Galaxies

Abstract The gas content of the complete compilation of Local Group dwarf galaxies (119 within 2 Mpc) is presented using H i survey data. Within the virial radius of the Milky Way (224 kpc here), 53 of 55 dwarf galaxies are devoid of gas to limits of M H i &lt; 104 M ⊙. Within the virial radius of M31 (266 kpc), 27 of 30 dwarf galaxies are devoid of gas (with limits typically &lt;105 M ⊙). Beyond the virial radii of the Milky Way and M31, the majority of the dwarf galaxies have detected H i gas and H i masses higher than the limits. When the relationship between gas content and distance is investigated using a Local Group virial radius, more of the nondetected dwarf galaxies are within this radius (85 ± 1 of the 93 nondetected dwarf galaxies) than within the virial radii of the Milky Way and M31. Using the Gaia proper-motion measurements available for 38 dwarf galaxies, the minimum gas density required to completely strip them of gas is calculated. Halo densities between 10−5 and 5 × 10−4 cm−3 are typically required for instantaneous stripping at perigalacticon. When compared to halo density with radius expectations from simulations and observations, 80% of the dwarf galaxies with proper motions are consistent with being stripped by ram pressure at Milky Way pericenter. The results suggest that a diffuse gaseous galactic halo medium is important in quenching dwarf galaxies, and that a Local Group medium also potentially plays a role.

Characterisation of actual weld geometry and stress concentration of butt welds exhibiting local undercuts

Nowadays automated welding processes produce high-quality welds with smooth and regular global weld geometry. However, the local geometry of the weld exhibits a certain amount of variance in its topography due to dynamic effects of the welding process itself. The subsequent change in local stress concentrations affects the fatigue behaviour of welded structures. In literature, numerous equations for the estimation of a weld’s stress concentration based on characteristic parameters of the weld geometry are available.Three-dimensional scans of ultra high-strength steel butt welds exhibiting local undercuts are processed with digital image acquisition to derive weld geometry parameters, which facilitate a subsequent statistical analysis. Hereby, a novel approach to estimate the local weld toe radius is presented. Furthermore, the derived values are utilized to calculate the respective stress concentration at various locations of the weld using state-of-the-art notch-factor approximation equations. For undercut-free samples, a comparison of the investigated notch stress concentration equations and the results of numerical simulations of the actual weld geometry show good accordance for all models. However, at locations with a distinct undercut, the stress concentration is consequentially underestimated. Therefore, an improved approach extending the existing notch-factor equations is presented. It enables the consideration of the stress concentrating effect of a local undercut at the weld toe.