External Radius Research Articles

Spacetime Metrics and Ringdown Waveforms for Galactic Black Holes Surrounded by a Dark Matter Spike

Theoretical models suggest the existence of a dark matter spike surrounding the supermassive black holes at the core of galaxies. The spike density is thought to obey a power law that starts at a few times the black hole horizon radius and extends to a distance, R sp, of the order of a kiloparsec. We use the Tolman–Oppenheimer–Volkoff equations to construct the spacetime metric representing a black hole surrounded by such a dark matter spike. We consider the dark matter to be a perfect fluid, but make no other assumption about its nature. The assumed power-law density provides in principle three parameters with which to work: the power-law exponent γ sp, the external radius R sp, and the spike density at R sp. These in turn determine the total mass of the spike. We focus on Sagittarius A* and M87 for which some theoretical and observational bounds exist on the spike parameters. Using these bounds in conjunction with the metric obtained from the Tolman–Oppenheimer–Volkoff equations, we investigate the possibility of detecting the dark matter spikes surrounding these black holes via the gravitational waves emitted at the ringdown phase of black hole perturbations. Our results suggest that if the spike to black hole mass ratio is roughly constant, greater mass black holes require relatively smaller spike densities to yield potentially observable signals. We find that is unlikely for the spike in M87 to be detected via the ringdown waveform with currently available techniques unless its mass is roughly an order of magnitude larger than existing observational estimates. However, given that the signal increases with black hole mass, dark matter spikes might be observable for more massive galactic black holes in the not too distant future.

Rotating-Coil Measurement System for Small-Bore-Diameter Magnet Characterization

Rotating-coil measurement systems are widely used to measure the multipolar fields of particle accelerator magnets. This paper presents a rotating-coil measurement system that aims at providing a complete data set for the characterization of quadrupole magnets with small bore diameters (26 mm). The PCB magnetometer design represents a challenging goal for this type of transducer. It is characterized by an aspect ratio 30% higher than the state of the art, imposed by the reduced dimension of the external radius of the rotating shaft and the necessity of covering the entire magnet effective length (500 mm or higher). The system design required a novel design for the mechanical asset, also considering the innovation represented by the commercial carbon fiber tube, housing the PCB magnetometer. Moreover, the measurement system is based primarily on standard and commercially available components, with simplified control and post-processing software applications. The system and its components are cross-calibrated using a stretched-wire system and another rotating-coil system. The measurement precision is established in a measurement campaign performed on a quadrupole magnet characterized by an inner bore diameter of 45 mm.

Individualized dosimetry in Ru-106 ophthalmic brachytherapy based on MRI-derived ocular anatomical parameters

PurposeTo estimate ocular geometry-related inaccuracies of the dosimetric plan in Ru-106 ophthalmic brachytherapy. Methods and MaterialsThirty patients with intraocular lesions were treated with brachytherapy using a Ru-106 plaque-shell of inner radius of 12 mm. Magnetic resonance imaging was employed to determine the external scleral radius at tumor site and the tumor margins. A mathematical model was developed to determine the distance between the external sclera and the internal surface of the plaque associated with the tangential application of the plaque on the treated eye. Differences in delivered dose to the tumor apex, sclera and tumor margins as derived by considering the default eye-globe of standard size (external sclera radius = 12 mm) against the individual-specific eye globe were determined. ResultsThe radius of external sclera at the tumor site was found to range between 10.90 and 13.05 mm for the patient cohort studied. When the patient specific eye-globe/tumor geometry is not taken into account, the delivered dose was found to be overestimated by 8.1% ± 4.1% (max = 15.3%) at tumor apex, by 1.5% ± 2.8% (max = 5.7%) at anterior tumor margin, by 16.6% ± 7.5% (max = 36.4%) at posterior tumor margin and 8.1% ± 3.8% (max = 13.2%) at central sclera of eyes with lower than the default radius. The corresponding dose overestimations for eyes with higher than the default radius was 13.5% ± 4.3% (max = 22.3%), 1.5% ± 2.8% (max = 5.7%), 12.6% ± 4.5% (max = 20.0%), and 15.1% ± 5.0% (max = 24.4%). ConclusionsThe proposed patient-specific approach for Ru-106 brachytherapy treatment planning may improve dosimetric accuracy. Individualized treatment planning dosimetry may prevent undertreatment of intraocular tumors especially for highly myopic or hyperopic eyes.

Enhancing the Thermal Conductivity of Amorphous Carbon with Nanowires and Nanotubes.

The thermal conductivity of nanostructures can be obtained using atomistic classical Molecular Dynamics (MD) simulations, particularly for semiconductors where there is no significant contribution from electrons to thermal conduction. In this work, we obtain and analyze the thermal conductivity of amorphous carbon (aC) nanowires (NW) with a 2 nm radius and aC nanotubes (NT) with 0.5, 1 and 1.3 nm internal radii and a 2 nm external radius. The behavior of thermal conductivity with internal radii, temperature and density (related to different levels of hybridization), is compared with experimental results from the literature. Reasonable agreement is found between our modeling results and the experiments for aC films. In addition, in our simulations, the bulk conductivity is lower than the NW conductivity, which in turn is lower than the NT conductivity. NTs thermal conductivity can be tailored as a function of the wall thickness, which surprisingly increases when the wall thickness decreases. While the vibrational density of states (VDOS) is similar for bulk, NW and NT, the elastic modulus is sensitive to the geometrical parameters, which can explain the enhanced thermal conductivity observed for the simulated nanostructures.

Nonlinear optical rectification of tuned quantum dots under the action of a vertical magnetic field

The changes of optical rectification (OR) coefficient in tuned quantum dots under the action of the external magnetic field, hydrostatic pressure, temperature and quantum dot radius are theoretically studied in detail. The tuned quantum dots are subjected to a uniform magnetic field perpendicular to the structural plane. Within the framework of effective mass approximation and parabolic band approximation, the energy level and wave function are derived, and the nonlinear OR coefficient is calculated by compact density matrix theory and iterative method. Numerical results show that the resonance peak of the OR coefficient moves in the direction of high energy or low energy under different constraint parameters, that is, red shift or blue shift. At the same time, the peak value of the OR coefficient will increase or decrease with the change of the parameters.

Theoretical and experimental study on a compound insulation system for high temperature applications

• Designed a test setup for determining high temperature thermal performance of CFMLI. • Measured the temperature profile and effective thermal conductivity of CFMLI at 800–1325 K. • Discussed CFMLI thermal performance with gas pressure, spacing materials and foil numbers. • Validated the accuracy of experimental data by comparison with theoretical predictions. High temperature thermal insulation performance plays a crucial role in the application of thermal contact resistance precision measurement to reduce systematic heat loss and ensure 1D axial heat flow. In this paper, a compound insulation system composed of carbon fibrous materials and multilayer insulation (CFMLI) with non-interlayer-contact space was proposed in terms of high temperature sustainability, low thermal conductivity and thermal performance stability. An experimental set-up was designed and fabricated to measure the temperature distribution and the effective thermal conductivity of CFMLI as a function of temperature (800 K−1325 K). The experimental results showed that the temperature gradually decreases from inner to external radius of CFMLI, and a temperature jump of 40 K−80 K appears at the interface between two segments under vacuum conditions. It also reveals that the thermal performance of CFMLI is strongly dependent on the gas pressure and the number of reflective layers, while it is hardly affected by the filling materials when the temperature is above 1050 K. Meanwhile, the effective thermal conductivity of CFMLI varies around 0.2 W/m/K for two levels of pressure (10 -4 Pa and 0.1 MPa), and it decreases by 14.7% when the number of reflective layers increases from 6 to 21 at 1325 K. Additionally, a theoretical model with thermal resistance network was developed for heat transfer analysis of CFMLI. The model could predict the external temperature of CFMLI with high accuracy so that the difference between the theoretical results and experimental data was less than 2.61%.

Buoyant flow instability induced by a uniform internal heat source in a vertical annular porous layer

The buoyancy–induced parallel flow in a vertical cylindrical porous layer with annular cross–section is analysed. A radial thermal gradient caused by a uniformly distributed heat source is assumed to induce the buoyant flow. The layer boundaries are modelled as isothermal and permeable to an external fluid reservoir. The onset of the convective instability is analysed by linearising the governing equations for the perturbations. The governing parameters driving the instability are the heat–source Rayleigh number and the ratio between the internal radius and the external radius. Neutral stability curves and the critical values of the Rayleigh number, the perturbation wave number and the angular frequency are computed numerically. It is shown that axisymmetric modes form the most dangerous type of instability.

Effects of hydrostatic pressure and temperature on refractive index changes in tuned quantum dots under magnetic field

The effects of external magnetic field, hydrostatic pressure, temperature and radius of the quantum dots (QDs) on refractive index changes (RICs) of tuned QDs are studied in detail theoretically. In the framework of effective mass approximation, energy levels and wave functions are derived. Simultaneously, the nonlinear RICs are obtained by compact-density-matrix approach and iterative method. Then, the numerical simulations show that under various constraint factors, the resonant peak position of RICs moves to high energy or low energy, that is, blue shift or red shift, and the peak value of RICs will also alter with the change of parameters.

Predicting horizontal well flow rates under the geological conditions of Western Siberia fields

Research relevance. The determination of the expected well flow rate is a key problem in designing the development of oil fields with horizontal wells. In industrial practice, actual and real flow rates of horizontal wells usually differ significantly. Research objective. The algorithms for horizontal well potential flow rates determination have been studied extensively. However, the issues of choosing a methodology for determining the flow rate in relation to particular geological conditions remain unresolved. It is necessary to compare the actual and design rates of horizontal wells and identify the most representative methods for flow rates determination for the geological conditions of Western Siberia fields. Methods of research. A single horizontal well draining a semi-infinite reservoir is considered in the absence of hydrodynamically isolated and poorly drained zones within the radius of the well external boundary. The Giger, Joshi, Janar, and Renard–Dupuy methods were used to determine the expected flow rates of horizontal wells only under the following conditions: a homogeneous reservoir and a near-rectilinear horizontal section of the well in the reservoir interval. As an example, the calculation of the expected flow rate of a horizontal well with the following initial data is given: the horizontal section length is 700 m, the net oil thickness is 7.8 m; the permeability coefficient is 127 · 10–15 m2 , oil viscosity is 1.24 MPa ∙ s, the drawdown is 3 MPa, the external boundary radius is 1000 m, and the volume factor is 1.08. Results. Quite significant discrepancies between the actual and design data are recorded for wells with arbitrary numbers 4, 7, 8, 10, 15, 18 and 20. All the methods used for calculations provided comparable results. For all other wells, the calculation results have a high convergence with field data. Conclusions. The Giger, Joshi, Janar, and Renard–Dupuy methods may be recommended for horizontal wells expected flow rates determination only under the following conditions: a homogeneous reservoir and a near-rectilinear horizontal section of the well in the reservoir interval.

Structural properties of humeral diaphyses of East Asian modern humans from the Late Pleistocene to Early Holocene

AbstractObjectivesThis study aims to explore the structural properties along entire humeral diaphyses of Late Pleistocene and Early Holocene East Asian modern humans relative to the contemporaneous Neandertal specimen Regourdou 1 to provide insight into adaptive behaviors within temporal and regional hominin contexts.Materials and methodsThe humeri of three individuals from East Asia securely dated from the Late Pleistocene to Early Holocene were selected: Tianyuan 1, Zhaoguo M1, and Qihe M2. These specimens were scanned using microcomputed tomography to evaluate structural properties: cortical bone thickness (CBT), second moment of area (SMA), external radius (ER), and polar moment of area (J).ResultsThe distribution patterns of CBT, ER, and J were similar across all specimens. However, the magnitude of these variables was notably large in Regourdou 1 right humerus. The SMA, ER, and J of left humerus of Tianyuan 1 were less than that of other East Asian specimens, whereas those from the right humerus of the Qihe M2 individual were slightly larger than two other East Asian individuals. Additionally, the humeral asymmetry of Tianyuan 1 was greater than that of Zhaoguo M1 and Qihe M2.DiscussionCompared to Regourdou 1, East Asian specimens had reduced humeral robusticity. Within East Asia, the Late Pleistocene modern humans exhibit greater humeral asymmetry than the Early Holocene humans, indicating a universal reduction of humeral asymmetry related to technological changes across Eurasia during this time. The current study contributes to developing a more thorough understanding of intergroup humeral structural variation across Eurasia during the Late Pleistocene and Early Holocene.

Optical response of dielectric&metal-core/metal-shell nanoparticles: Near electromagnetic field and resonance frequencies

We study the diffraction of a monochromatic electromagnetic plane wave by a dielectric&metal-core/metal-shell nanoparticle surrounded by a dielectric medium. This problem was solved by using generalized Mie’s theory and both the scattering cross section and the square module of the electric field were calculated as a function of shell thickness. Numerically, the first particles studied were gold-core/silver-shell nanoparticles and their inverse configuration. The gold-core/silver-shell particle presented more variation of their optical properties. The second particles were vacuum-core/metal-shell surrounded by vacuum, symmetric configurations. In this case, the dispersive Drude dielectric function for the metal was used, and a comparative study between the positions of the resonance frequencies obtained from quasi-static limit and electrodynamic theory was performed. Thus, consequently the formula obtained from the quasi-static limit can be used to calculate the positions of the resonance frequencies instead of the electrodynamic theory, when the external radius is smaller than 20 nm.

Numerical Investigation On Thermal Behaviours Of Latent Thermal Energy Storages With Pcm Partially Filled With Aluminum Foam

In this paper a numerical investigation on the effects of the metal foam into the Latent Heat Thermal Energy Storage System, based on a phase change material, is accomplished. The geometry of the system is a vertical shell and tube LHTESS made with two concentric aluminum tubes. The internal surface of the hollow cylinder is assumed at a constant temperature above the melting temperature of the PCM to simulate the heat transfer from a hot fluid. The other external surfaces are assumed adiabatic. The PCM is completely embedded in the volume between the two coaxial cylinders, it is pure paraffin wax with a low value of thermal conductivity and it melts in a range of temperatures. The metal foam is made of aluminum and it partially fills the volume starting from the internal cylinder with a thickness lower the differences between the external cylinder radius and internal one. The enthalpy-porosity theory is employed to simulate the phase change of the PCM and the metal foam is modelled as a porous media that follow the Brinkman-extended Darcy model. The governing equations are solved employing the Ansys-Fluent code. The results are shown in term of melting time, temperature and energy at varying of time and at varying the filling ratio.

Manipulating the shape of flexible magnetic nanodisks with meronlike magnetic states

The control of the magnetic properties of shapeable devices and the manipulation of flexible structures by external magnetic fields is a keystone of future magnetoelectronics-based devices. This work studies the elastic properties of a magnetoelastic nanodisc that hosts a meron as the magnetic state and can be deformed from structures with positive to negative Gaussian curvature. We show that the winding number of the hosted meron is crucial to determine the curvature sign of the stable obtained shape. Additionally, we show that the optimum curvature reached by the nanodisc depends on geometrical and mechanical parameters. It is shown that an increase in the external radius, thickness, and Young's modulus lead to a decrease in the optimum curvature absolute value. Finally, it is shown that the nanodisc's shape also depends on the connection between the polarity and chirality of the vortex-like meron.

External fixation in distal radius fractures

Background: Distal radius fractures are frequent in emergency departments, treatment is generally conservative, but there are patients who meet certain criteria of instability who need surgical treatment, including external fixation. Aim: To update on the most important elements regarding the use of external fixation in unstable fractures of the distal radius. Methods: The search and analysis of the information was carried out in a period of 30 days (from April 1 to April 30, 2021) and the following words were used: distal radius fractures, distal radius fractures and external fixation and unstable radius fractures from the information obtained, a bibliographic review of a total of 809 articles published in the PubMed databases, Hinari, SciELO and Medline was carried out using the search manager and EndNote reference manager, of which 44 selected citations were used to perform the review, 37 from the last five years. Development: The criteria to be taken into account for the instability described by various authors are indicated, as well as the imaging parameters. The two most used classification systems are mentioned. Reference is made to general surgical indications, external fixation, and placement of additional wires. Complications are discussed and a comparison is made between external fixation and blocked volar plates.

Design of the CAREM nuclear reactor core with dual cooled annular fuel and optimizing the thermal-hydraulic, natural circulation, and neutronics parameters

The small modular nuclear reactor (SMR) with annular fuel which is cooled internally and externally has the potential to maintain high power density with a sufficient safety margin. The benefit of the dual cooled annular fuel design is that heat can be transferred to the coolant from both the outer and inner surfaces.In this paper, design of the Argentina small modular reactor (CAREM) core with hexagonal assemblies using dual-cooled annular fuels with internal and external cooling is presented. Neutronics and thermal-hydraulic parameters are evaluated and analyzed by changing internal fuel radius. For this purpose, at the first, the dual-cooled annular fuel under clean and cold conditions is modeled and the effective multiplication factor has been calculated for different inner clad diameter. Indeed, the internal and external radius have been changed in such a way to maintain the reactor under moderated.Then, these annular fuels under full power conditions are modeled and power peaking factor has been calculated. Finally, natural circulation parameters are performed for a simulated fuel rod in the hot channel using computational fluid dynamics (CFD) simulation codes. These results are compared with the conventional CAREM reactor. One of the most prominent advantages of the annular fuels is the ability to make softer neutrons in which reduce maximum power peaking factor and improves fuel management and safety parameters in the reactor core.For data fitting, an artificial neural network is trained using the observed data. The input consists of different internal and external radiuses and output consists of fuel rods’ pitch, thermal-hydraulic and neutronic parameters. Finally, the optimal geometry of fuels is determined using the neural network by implementing the genetic algorithms.Indeed, developed Artificial Neural Network (ANN) utilizing the obtained data, predicts the thermal-hydraulic and neutronic parameters of the CAREM reactor core with dual-cooled annular fuels. Presented optimization algorithm, which has a significant ability to attain the best solutions, also determines the optimal values of natural circulation parameters (Vmax/Vavg, Vout-Vin, and pressure drops), heat transfer coefficients, MDNBR, RPPF, and excess reactivity of the reactor. Also, the designed artificial neural network and genetic algorithm has been validated using neutronic and thermal hydraulic calculations. Results indicate that by using annular fuels, better reactor safety and thermal efficiency are achieved.

Conceptual design of a radial collimator for MIRACLES, the time-of-flight backscattering spectrometer at the European Spallation Source

A parametrized conceptual design for a radial collimator in a neutron backscattering instrument is presented, with application to the characteristic geometry of the MIRACLES spectrometer, that will be constructed at the European Spallation Source (ESS). The analytic development of this design has considered both the forward scattering (sample-analyzer) and backscattering (analyzer-detectors) pathways. All the characteristic dimensions (internal and external radii, slit angle) and figures of merit (such as transmission and estimated background reduction) of the device are calculated as a function of the focal points. Finally, the estimated performance of the final concept has been validated by Monte Carlo simulations.

Model of porosity evolution and its practical application for describing the process of hydrogen corrosion during heating (cooling) of a steel cylindrical tube under internal hydrogen pressure

The process of nucleation of main cracks in a cylindrical tube deformed by internal pressure of hydrogen has two features, which are determined by the possibility of chemical interaction of hydrogen with steel. In the absence of chemical interaction of hydrogen with the material, under creep conditions, the main crack originates at the outer boundary radius, at which the effective tangential stress reaches the strength ultimate for the first time. During the chemical interaction of diffusing hydrogen with steel, under conditions of high temperature heating, main cracks are generated in the vicinity of the internal boundary radius. To be able to describe these two features, a model of porosity evolution has proposed, in which the relative change in the area of a ring with an infinitesimal thickness have considered as a porosity characteristic. In the mathematical formulation of the problem, all the considered mechanical and physical quantities depend on an arbitrary radius and time, and do not depend on the longitudinal coordinate and angle (the problem with axial symmetry). For the first time in practice, the dependence on an arbitrary radius for large linear displacements has considered, the linearization of which leads to a well known hyperbolic dependence for small linear displacements. Three hypotheses have accepted in solving the problem. The process of formation and growth of micropores does not have a noticeable effect on one of the two boundary radii (in this paper, the external boundary radius is taken as such). The linear size of discontinuities in a material with micropores is taken as the difference between radial displacements in a material with micropores and an incompressible material. The product of porosity and tangential deformation at a point of an arbitrary radius is determined by the product of the corresponding integral characteristics. Taking into account these hypotheses, the dependence of porosity on an arbitrary radius, as well as its effect on radial displacement and strains in a material with micropores, has determined.

Exhaustive Optimization Method Applied on Electromagnetic Device

This paper presents the application of an exhaustive optimization method based on the design of experiments (DOE) and the finite element method (FEM), with the aim of improving the actuation force developed by a DC electromagnet. The optimization of this device has been the subject of several previous works, allowing comparisons between the optimization methods applied in terms of the obtained precision and the workload. According to previous studies, two geometric parameters (the angle ratio of the support tip and the coil shape ratio) are very influential on the force developed at the maximum air gap. Thus, the exhaustive optimization method took into account these two parameters for its maximization, having as constraints the maintenance of the global dimensions of the device (external radius, the height of carcass, height of the plunger with support) and of the cross-section of the winding. The optimization algorithm used the results of 2-D FEM numerical experiments carried out with the FEMM program in combination with the LUA language and is based on the response surface methodology (RSM) and analysis of variance (ANOVA). Second-order polynomial models of the objective function were calculated using full factorial designs with three levels per factor. After three iterations, a very good result was obtained, comparable to those obtained by other methods, but with a significant cost in terms of workload, the optimum obtained being a global one.

Characteristics of a novel cylindrical arm spiral spring for linear compressor

The spring system is the key component of linear compressor, which is attractive in the field of household refrigeration due to its high efficiency and compact structure. Inspired by the traditional flexure spring, we proposed a novel cylindrical arm spiral spring for linear compressor with a comprehensive consideration on the cost, compactness and performance requirements. The design method of spring was introduced and different performance can be obtained by adjusting the internal radius, external radius, number of turns and wire diameter. The static displacement of spring was modelled by using FEA (Finite Element Analysis) method for various axial and radial force. And a specific fixture was built to measure the spring stiffness to verify the results obtained from FEA simulation. At last, the dynamic test of the linear compressor equipped with the proposed spring was conducted. The experimental results showed that the resonant frequency of linear compressor can meet the design requirements of 78 Hz without gas compressor, indicating that the application of this type of spring in the linear compressor is feasible.

Numerical and Analytical Studies of Soret-Driven Convection Flow Inside an Annular Horizontal Porous Cavity

This paper studies the species separation of a binary fluid in a porous cavity between two horizontal concentric cylinders, submitted to a temperature gradient. The thickness of the cavity is e=Ro−Ri, where Ri and Ro are the internal and external radius, respectively. The numerous previous experiments performed in thermogravitational vertical columns (TGCs) showed that in order to obtain a significant separation, the thickness of the cell must be very small, compared with its height. Therefore, in our configuration, we considered e≪Ri. The solution is assumed to be axisymmetric. Under the assumptions of parallel flow and forgotten effect, an analytical solution is obtained using Maple software, and the results are compared with those found numerically using Comsol Multiphysics. In natural convection, our results are in very good agreement with those evaluated with a regular perturbation method in powers of the dimensionless gap width ε=eRi of order 15, and with the Galerkin method. The species separation calculated for our configuration is very close to the one obtained in a TGC column of height: H=πRi. One of the main interests of the analytical solution presented here is that it can be used as a basic solution for a stability study analysis.