Spherical Absorber Research Articles

Contemporary Impact Analysis Methodology for Planetary Sample Return Missions

Development of an Earth entry vehicle and the methodology created to evaluate the vehicle’s impact landing response when returning to Earth is reported. NASA’s future Mars Sample Return Mission requires a robust vehicle to return Martian samples back to Earth for analysis. The Earth entry vehicle is a proposed solution to this Mars mission requirement. During Earth reentry, the vehicle slows within the atmosphere and then impacts the ground at its terminal velocity. To protect the Martian samples, a spherical energy absorber called an impact sphere is under development. The impact sphere is composed of hybrid composite and crushable foam elements that endure large plastic deformations during impact and cause a highly nonlinear vehicle response. The developed analysis methodology captures a range of complex structural interactions and much of the failure physics that occurs during impact. Numerical models were created and benchmarked against experimental tests conducted at NASA Langley Research Center. The postimpact structural damage assessment showed close correlation between simulation predictions and experimental results. Acceleration, velocity, displacement, damage modes, and failure mechanisms were all effectively captured. These investigations demonstrate that the Earth entry vehicle has great potential in facilitating future sample return missions.

A simulation study on the quantitative assessment of tissue microstructure with photoacoustics.

A detailed derivation of a quantity, defined as the acoustic power per unit solid angle far from the illuminated volume divided by the intensity of the incident light beam and termed as differential photoacoustic (PA) cross section, is presented. The expression for the differential PA cross section per unit absorbing volume retains two terms, namely, the coherent and the incoherent parts. The second part based on a correlation model can be employed to analyze the PA signal power spectrum for tissue characterization. The performances of the fluid sphere, Gaussian, and exponential correlation models in assessing the mean size and the variance in the optical absorption coefficients of absorbers were investigated by performing in silico experiments. It was possible to evaluate diameters of solid spherical absorbers with radii ≥ 20 μm with an accuracy of 10% for an analysis bandwidth of 5 to 50 MHz using the first two correlation models. The accuracy of estimation was about 22% for fluid spheres mimicking erythrocytes for the third correlation model for an analysis bandwidth of 5 to 100 MHz. The extracted values of average variance in the optical absorption coefficients demonstrated good correlation with the nominal values. This study suggests that the method presented here may be developed as a potential tissue characterization tool.

Full absorption statistics of diffusing particles with exclusion

Suppose that an infinite lattice gas of constant density n0, whose dynamics are described by the symmetric simple exclusion process, is brought in contact with a spherical absorber of radius R. Employing the macroscopic fluctuation theory and assuming the additivity principle, we evaluate the probability distribution that N particles are absorbed during a long time T. The limit of N = 0 corresponds to the survival problem, whereas describes the opposite extreme. Here is the average number of absorbed particles (in three dimensions), and D0 is the gas diffusivity. For n0 ≪ 1 the exclusion effects are negligible, and can be approximated, for not too large N, by the Poisson distribution with mean . For finite n0, is non-Poissonian. We show that at . At sufficiently large N and n0 < 1/2 the most likely density profile of the gas, conditional on the absorption of N particles, is non-monotonic in space. We also establish a close connection between this problem and that of statistics of current in finite open systems.

Design and optimize spherical particle absorber by Fe-rich hollow cenosphere of fly-ash for broadband electromagnetic wave absorbing wall

Design and optimize spherical particle absorber by Fe-rich hollow cenosphere of fly-ash for broadband electromagnetic wave absorbing wall

ENERGY-DEPENDENT EVOLUTION IN IC10 X-1: HARD EVIDENCE FOR AN EXTENDED CORONA AND IMPLICATIONS

We have analyzed a ~130 ks XMM-Newton observation of the dynamically confirmed black hole + Wolf-Rayet (BH+WR) X-ray binary (XB) IC10 X-1, covering ~1 orbital cycle. This system experiences periodic intensity dips every ~35 hours. We find that energy-independent evolution is rejected at a >5 sigma level. The spectral and timing evolution of IC10 X-1 are best explained by a compact disk blackbody and an extended Comptonized component, where the thermal component is completely absorbed and the Comptonized component is partially covered during the dip. We consider three possibilities for the absorber: cold material in the outer accretion disk, as is well documented for Galactic neutron star (NS) XBs at high inclination; a stream of stellar wind that is enhanced by traveling through the L1 point; and a spherical wind. We estimated the corona radius (r_ADC) for IC10 X-1 from the dip ingress to be ~1 E+6 km, assuming absorption from the outer disk, and found it to be consistent with the relation between r_m ADC and 1--30 keV luminosity observed in Galactic NS XBs that spans 2 orders of magnitude. For the other two scenarios, the corona would be larger. Prior BH mass (M_BH) estimates range over 23--38 M_Sun, depending on the inclination and WR mass. For disk absorption, the inclination, i, is likely to be ~60--80 degrees, with M_BH ~24--41 M_Sun. Alternatively, the L1-enhanced wind requires i ~80 degrees, suggesting ~24--33 M_Sun. For a spherical absorber, i ~ 40 degrees, and M_BH ~50--65 M_Sun.

Survival of a static target in a gas of diffusing particles with exclusion.

Let a lattice gas of constant density, described by the symmetric simple exclusion process, be brought in contact with a "target": a spherical absorber of radius R. Employing the macroscopic fluctuation theory (MFT), we evaluate the probability P(T) that no gas particle hits the target until a long but finite time T. We also find the most likely gas density history conditional on the nonhitting. The results depend on the dimension of space d and on the rescaled parameter ℓ=R/√[D(0)T], where D(0) is the gas diffusivity. For small ℓ and d>2, P(T) is determined by an exact stationary solution of the MFT equations that we find. For large ℓ, and for any ℓ in one dimension, the relevant MFT solutions are nonstationary. In this case, lnP(T) scales differently with relevant parameters, and it also depends on whether the initial condition is random or deterministic. The latter effects also occur if the lattice gas is composed of noninteracting random walkers. Finally, we extend the formalism to a whole class of diffusive gases of interacting particles.

First invader dynamics in diffusion-controlled absorption

.We investigate the average time for the earliest particle to hit a spherical absorber when a homogeneous gas of freely diffusing particles with density ρ and diffusivity D is prepared in a deterministic state and is initially separated by a minimum distance ℓ from this absorber. In the high-density limit, this first absorption time scales as in one dimension; a similar scaling behavior occurs in greater than one dimension. In one dimension, we also determine the probability that the kth-closest particle is the first one to hit the absorber. At large k, this probability decays as k1/3exp(−Ak2/3), with A = 1.932 99… analytically calculable. As a corollary, the characteristic hitting time Tk for the kth-closest particle scales as k4/3; this corresponds to superdiffusive but still subballistic motion.

Validation of novel calibration scheme with traceable point-like 22Na sources on six types of PET scanners

To improve the reliability and convenience of the calibration procedure of positron emission tomography (PET) scanners, we have been developing a novel calibration path based on traceable point-like sources. When using (22)Na sources, special care should be taken to avoid the effects of 1.275-MeV γ rays accompanying β (+) decays. The purpose of this study is to validate this new calibration scheme with traceable point-like (22)Na sources on various types of PET scanners. Traceable point-like (22)Na sources with a spherical absorber design that assures uniform angular distribution of the emitted annihilation photons were used. The tested PET scanners included a clinical whole-body PET scanner, four types of clinical PET/CT scanners from different manufacturers, and a small-animal PET scanner. The region of interest (ROI) diameter dependence of ROI values was represented with a fitting function, which was assumed to consist of a recovery part due to spatial resolution and a quadratic background part originating from the scattered γ rays. The observed ROI radius dependence was well represented with the assumed fitting function (R (2) > 0.994). The calibration factors determined using the point-like sources were consistent with those by the standard cross-calibration method within an uncertainty of ±4 %, which was reasonable considering the uncertainty in the standard cross-calibration method. This novel calibration scheme based on the use of traceable (22)Na point-like sources was successfully validated for six types of commercial PET scanners.

Shock Absorber Design and Analysis of a Catapult-Spherical Reconnaissance Robot

Aim at the shock absorber general weak of spherical robot, design of a new shock absorber structure of the spherical detection robot, the robot have two shock absorption system include rubber with metal bonding reticulated spherical shell and telescopic shock absorber spring, at same time contact the internal parts with soft material. All these measures are to protect the internal parts in robot dropping or throwing process from bigger impact. Derivation it with kinematics and dynamics formula, simulate and experiment proved shock absorber mechanism has a good shock absorber performance. This design can effectively protect the internal parts of the spherical robot.

Novel Point-Like $^{68}{\rm Ge}/^{68}{\rm Ga}$ Radioactive Source With Spherical Positron Absorber

Purpose: In the conventional techniques for determining the calibration factors of positron emission tomography (PET) scanners, cylindrical water and resin phantoms with radioisotope 18F or 68Ge/68Ga are used. In these methods, however, the results depend on attenuation and scatter correction. The purpose of this study is to develop a point-like 68Ge/68Ga radioactive source that can be used to determine the calibration factors of PET scanners without the uncertainty of attenuation and scatter correction. Methods: A spherical absorber design was employed to realize a symmetric angular distribution of emitted annihilation photons. A Geant4-based Monte Carlo simulation code was used to compare physics characteristics of point-like sources with various absorber materials. On the basis of this simulation, a point-like 68Ge/68Ga source with a spherical aluminum absorber was manufactured. Its radioactivity was calibrated at an accredited national calibration facility. A calibration factor of a clinical PET scanner was then obtained with a point-like source and compared with that obtained by a standard cross-calibration method. Results: The emission probability of 0.511 MeV annihilation photon pairs per positron decay was typically 0.6-0.8. The fraction of background photon pairs was 6-8% in the energy region of 0.4-0.6 MeV. Considering these two figures, lower density materials such as aluminum and pol(ymethyl methacrylate) (PMMA) were preferable. For the aluminum absorber, a diameter of 8 mm was suitable to prevent positrons from escaping. The calibration factor obtained with the point-like source agreed with that obtained by the standard method within 2-3%. Conclusion: A point-like 68Ge/68Ga radioactive source was successfully designed, manufactured, and used for determining a calibration factor of a PET scanner. It can be considered a practical tool for calibrating and evaluating the quantitative aspects of PET scanners.

Modeling of adsorption–reaction–desorption in granular media

The scope of this work is to model the mass transport process from a moving Newtonian fluid to an assemblage of spherical solid absorbers. The flow field for laminar flow was obtained by numerically solving the Navier–Stokes equation in the pore space of a stochastically constructed three-dimensional assemblage of spherical particles, where the convective/diffusive transport is simulated by involving an adsorption/reaction/desorption mechanism as an appropriate boundary condition. The spatial/volume-averaging technique was used here for up-scaling, where the simplified boundary-value problems have been described and numerically solved for the velocity field and concentration. Macroscopic mass transfer coefficient was then calculated and compared with other approaches. The process was found to be controlled by the Peclet number as well as the porosity of the porous structure. Through model validation, the sorption mechanism considered here proved to provide a reasonable estimation of the mass transfer.

Design and Optimize Spherical Particle Absorber for Broadband Electromagnetic Wave Absorption Wall

In this paper, a method to simulate the absorbing effectiveness of spherical particle absorber is presented and the effect of the diameter of spheres, the number of layer and the stack modes of sphere particle to the absorbing effectiveness were also researched. Basing on the simulation results, an optimal spherical particle absorber was designed. The absorber has 3 layers with 1 mm, 2 mm and 4 mm spheres stacked on each layer respectively. Simulation result shows that the optimal absorber achieves a maximum reflection loss of -15 dB and the bandwidth being lower than -5 dB is more than 16 GHz in 1~18 GHz.

A practical method of determining cross-calibration factors of PET scanners by moving a point-like 22Na radioactive source

Thus far, cylindrical phantoms with (18)F or (68)Ge/(68)Ga have been used in the standard techniques for determining the cross-calibration factors (CCFs) of PET scanners. This paper describes a new practical method that uses a point-like (22)Na radioactive source for determining CCFs. A point-like (22)Na radioactive source (about 700kBq) was equipped with a spherical aluminium absorber capsule to ensure the symmetry of the emitted photons. During measurements, the source was moved in the axial direction to cover the whole axial field of view (FOV) of a clinical PET scanner, SET-2400W. The region-of-interest (ROI) values obtained in reconstructed images without scatter and attenuation corrections were used to calculate the CCFs of the PET scanner. The CCFs obtained by the proposed method agreed with those obtained by the standard cross-calibration (CC) method within a precision of 1.5% (σ). The temporal variations in the CCFs by the standard CC method were reproduced by the proposed method with a precision better than 1%. The CC method with a moving (22)Na point-like radioactive source is practically useful for determining the CCFs of PET scanners and monitoring their variations.

Optical and thermal performance of a three-dimensional compound parabolic concentrator for spherical absorber

For medium range temperature applications, focusing type collectors like Compound Parabolic Concentrator (CPC) are most commonly used. Considerable research work has been carried out to improve the performance of the two-dimensional compound parabolic concentrator (2D CPC). The three-dimensional compound parabolic concentrator (3D CPC) was found to be more efficient than 2D CPC because of the higher concentration ratio. In the present work a 3D CPC was fabricated with a half acceptance angle of 4° for a spherical absorber of radius 100 mm. UV stabilized aluminized polyester foil having high reflectivity (0·85) was pasted on the reflector for a total height of 441mm and an aperture width of 540 mm. The optical efficiency was estimated theoretically and compared with the experimental value. Experimentally determined values of optical and thermal efficiencies were in good agreement with theoretically predicted value. The experimental results shown that the optical efficiency obtained from the 3D CPC (0·626) was significantly higher than that of the 2D CPC (0·570) of similar dimensions. Since the optical efficiency of the 3D CPC was increased, the thermal efficiency of the collector was also increased. In addition to that, time constant of the concentrator was also calculated. The time constant of the 3D CPC (431 s) was fairly high when compared with the 2D CPC (110 s). An attempt was made to generate low pressure steam using 3D CPC in the in situ steam generation mode. The efficiency of the steam generation was about 38%, which was one of the possible applications of 3D CPC module.

Influence of plasma treatment on laser-induced damage characters of HfO_2 thin films at 355nm

HfO(2) thin films were deposited by e-beam evaporation, and were post-treated with plasma under different flow rate ratios of argon to oxygen. By measuring the surface defect density, weak absorption, laser-induced damage threshold (LIDT) and damage morphology, the influence of the flow rate ratio of argon to oxygen on the laser-induced damage characters of HfO(2) thin films were analyzed. The experimental results show that plasma treatment is effective in reducing the surface defect density of thin films. Compared with the as-grown sample, the absorption reduction is obvious after plasma treatment when argon and oxygen flow rate ratio is 5:25, but the absorption increases gradually with the continued increase of argon and oxygen flow rate ratio. LIDT measurements in 1-on-1 mode demonstrate that plasma treatment is not effective in improving LIDT of the samples at 355 nm. Damage morphologies reveal that the LIDT is dominated by nanoscale absorbing defects in subsurface layers, which agrees well with our numerical simulation result based on a spherical absorber model.

Acoustical resonant absorption of pulsed laser radiation by a spherical absorber

We investigate the thermomechanical response of a spherical absorber to pulsed laser radiation and the potential for causing damage to the absorber and the surrounding material due to shockwave and bubble formation. We calculate the expected response of a spherical absorber to a series of laser pulses as a function of the gap duration between the pulses. We model two common absorbers that have different characteristics: a 1 μm melanosome found in the retina, and a 100 nm gold particle. We find that the thermomechanical response strongly depends on the duration between pulses and displays resonant effects with a characteristic period that depends on the absorber properties. This allows tuning the duration between pulses to channel a greater or lesser fraction of the absorbed energy into shockfront and bubble production, presenting various possibilities such as delivering large amounts of laser energy to produce strong thermal effects while suppressing unwanted pressure effects in the surrounding material. Resonance can also be used to target absorbers of a specific size, allowing generation of shockfronts in localized target regions to destroy specific cells. This specificity can also be used to sort particles by size.

Spherical Perfectly Matched Absorber for Finite-Volume 3-D Domain Truncation

The theory of 2-D radial perfectly matched Maxwellian absorber is extended to 3-D domain truncation problems using a generalized approximate formulation of a spherical finite-volume absorber. The mathematical modeling of the spherical absorber is presented and update equations are derived. The performance of the absorber is characterized with numerical experiments. As practical application of the technique, a complex problem considering the coupling between two spiral antennas is simulated using the finite-volume time-domain method. The comparison of the results to measured data demonstrates the excellent performance of the spherical absorber.

Application of Synthetic Kernel ( SK N) method to participating linearly anisotropically scattering solid spherical medium

The Synthetic Kernel ( SK N ) method is applied to a solid spherical absorbing, emitting and linearly anisotropically scattering homogeneous and inhomogeneous medium. The SK N method relies on approximating the integral transfer kernels by Synthetic Kernels. The radiative integral transfer equation is then reducible to a set of coupled second-order differential equations. The SK N method, which uses Gauss quadratures, is tested against integral equation and the discrete-ordinates S 8 solutions for various optical radius and scattering albedo variations.

VALIDATION OF ACOUSTIC MODELS FOR TIME-HARMONIC DISSIPATIVE SCATTERING PROBLEMS

The aim of this paper is to study the time-harmonic scattering problem in a coupled fluid-porous medium system. We consider two different models for the treatment of porous materials: the Allard–Champoux equations and an approximate model based on a wall impedance condition. Both models are compared by computing analytically their respective solutions for unbounded planar obstacles, considering successively plane and spherical waves. A numerical method combining an optimal bounded PML and finite elements is also introduced to compute the solutions of both problems for more general axisymmetric geometries. This method is used to compare the solutions for a spherical absorber.

The emergence of chaos in a laser irradiated spherical absorber

We show in this paper that the simple system of a spherical absorber immersed in water can exhibit complex and chaotic behavior upon absorption of laser energy. We report on computer experiments performed on this simple system. We present power spectra and calculate Lyapunov exponents that show that for increasing laser pulse durations and increasing laser energy the pressure response of the system changes from periodic to a regime displaying spatiotemporal chaos. This is important from a theoretical point of view because the complex behavior displayed in this simple system makes it an excellent choice for investigations into the nonlinear dynamics of fluids and the complicated transition to turbulence. This is also important for people using these systems for various applications in material science and biomedicine.