The relative effects of particles and turbulence on acoustic scattering from deep-sea hydrothermal vent plumes

Acoustic methods are applied to the investigation and monitoring of a vigorous hydrothermal plume within the Main Endeavor vent field at the Endeavor segment of the Juan de Fuca Ridge. Forward propagation and scattering from suspended particulates using Rayleigh scattering theory is shown to be negligible (log-amplitude variance σ(χ) (2)~10(-7)) compared to turbulence induced by temperature fluctuations (σ(χ) (2)~0.1). The backscattering from turbulence is then quantified using the forward scattering derived turbulence level, which gives a volume backscattering strength of s(V)=6.5 × 10(-8) m(-1). The volume backscattering cross section from particulates can range from s(V)=3.3 × 10(-6) to 7.2 × 10(-10) m(-1) depending on the particle size. These results show that forward scatter acoustic methods in hydrothermal vent applications can be used to quantify turbulence and its effect on backscatter measurements, which can be a dominant factor depending on the particle size and its location within the plume.     

The contribution of bubbles to high-frequency sea surface backscatter: a 24-h time series of field measurements

Measurements of acoustic sea surface backscattering, wind speed, and surface wave spectra were made continually over a 24-h period in an experiment conducted in 26 m of water near the Dry Tortugus collection of islands off south Florida in February 1995. The backscattering measurements were made at a frequency of 30 kHz and a sea surface grazing angle of 20 degrees; a time series of the decibel equivalent of this variable, called SS20, was studied in terms of its dependence on environmental variables. On occasion reliable estimates of scattering in the grazing range 15 degrees-27 degrees were also obtained during the 24 hours. The scattering data exhibited evidence, in terms of scattering level and grazing angle dependence, of scattering from near-surface bubbles rather than scattering from the rough air-sea interface. The scattering data were compared with a model for sigma(b), the apparent backscattering cross section per unit area due to bubble scattering, that is driven by a parameter, beta1, equal to the depth-integrated extinction cross section per unit volume. Using an empirical model for beta1 based on data from a 1977 experiment conducted in pelagic waters, model predictions agreed reasonably well with the 1995 measurements presented here. Additional model-data comparisons were made using four measurements from a 1992 experiment conducted in pelagic waters. Finally, the 24-h time series of acoustic scattering exhibited a hysteresis effect, wherein for a given wind speed, there was a tendency for the scattering level to be higher if prior winds had been falling. A better understanding of this effect is essential to reduce uncertainty in model predictions.     

Acoustic scattering from a submerged cylindrical shell coated with locally resonant acoustic metamaterials

Using the multilayered cylinder model, we study acoustic scattering from a submerged cylindrical shell coated with locally resonant acoustic metamaterials, which exhibit locally negative effective mass densities. A spring model is introduced to replace the traditional transfer matrix, which may be singular in the negative mass region. The backscattering form function and the scattering cross section are calculated to discuss the acoustic properties of the coated submerged cylindrical shell.     

Anisotropy in high-frequency broadband acoustic backscattering in the presence of turbulent microstructure and zooplankton

High-frequency broadband (120-600 kHz) acoustic backscattering measurements have been made in the vicinity of energetic internal waves. The transducers on the backscattering system could be adjusted so as to insonify the water-column either vertically or horizontally. The broadband capabilities of the system allowed spectral classification of the backscattering. The distribution of spectral shapes is significantly different for scattering measurements made with the transducers oriented horizontally versus vertically, indicating that scattering anisotropy is present. However, the scattering anisotropy could not be unequivocally explained by either turbulent microstructure or zooplankton, the two primary sources of scattering expected in internal waves. Daytime net samples indicate a predominance of short-aspect-ratio zooplankton. Using zooplankton acoustic scattering models, a preferential orientation of the observed zooplankton cannot explain the measured anisotropy. Yet model predictions of scattering from anisotropic turbulent microstructure, with inputs from coincident microstructure measurements, were not consistent with the observations. Possible explanations include bandwidth limitations that result in many spectra that cannot be unambiguously attributed to turbulence or zooplankton based on spectral shape. Extending the acoustic bandwidth to cover the range from 50?kHz to 2?MHz could help improve identification of the dominant sources of backscattering anisotropy.     

Helium ion stopping cross sections in gold

The stopping cross section of He ions in gold has been measured at incident energies from 0.4 MeV–1.9 MeV. A backscattering technique was used to measure the energy loss in gold films which had been vacuum evaporated on sapphire substrates. The stopping cross section results are compared with the previous data of Wilcox, Gobeli and Nakata. Brice's semi-empirical formula has been fit to the data with a resultant root-mean-square percentage deviation of 0.6 per cent.     

MMW-Band Backscattering Cross Sections from Typical Clouds over Xi''an

In this paper, macro- and micro-physical properties of clouds over Xi'an region are discussed based on meteorologic observation data. The theory and mechanism of backscattering for clouds are analyzed. The quantity calculations of the backscattering cross sections for various reflection mechanism of clouds are dealt with at 1100GHz. The results calculated show that the major contributions for the backscattering cross section come possibly from clear-air and humidity turbulence, and also from distributions of cloud particles, especially, at higher frequencies. These numerical calculation results on the basis of Xi'an typical clouds properties confirm previous results and it is significance for millimeter wave communication, active and passive remote sensing, and low availability satellite links.     

AL L CORE EDGE FINE STRUCTURE IN Al,AlN AND α-Al2O3：A COMPARISON OF MICROELECTRON ENERGY LOSS SPECTRA WITH THEORY

The Al L near-edge fine structures of aluminum and its compounds with nitrogen and oxygen are studied using electron energy loss microspectroscopy in a transmission electron microscope. These edges are normalized to the same scattering cross section per Al atom per electronvolt. The cross section is calculated by using the Born approximation. The contributions to the cross section are from the valence shell crystal states obtained by using the extended Hückel band calculation and the ionization states obtained by using the electron gas model. The chemical effects in the ionization region are taken into account by in cluding the contributions from the elastic backscattering of outgoing plane waves by the atoms that neighbor the excited atoms. The results by theoretical calculation agree semiquantitatively with experimental results.     

AL L CORE EDGE FINE STRUCTURE IN Al, AlN AND α-Al2O3：A COMPARISON OF MICROELECTRON ENERGY LOSS SPECTRA WITH THEORY

The Al L near-edge fine structures of aluminum and its compounds with nitrogen and oxygen are studied using electron energy loss microspectroscopy in a transmission electron microscope. These edges are normalized to the same scattering cross section per Al atom per electronvolt. The cross section is calculated by using the Born approximation. The contributions to the cross section are from the valence shell crystal states obtained by using the extended Hückel band calculation and the ionization states obtained by using the electron gas model. The chemical effects in the ionization region are taken into account by in cluding the contributions from the elastic backscattering of outgoing plane waves by the atoms that neighbor the excited atoms. The results by theoretical calculation agree semiquantitatively with experimental results.     

High-frequency ultrasound backscattering by blood: analytical and semianalytical models of the erythrocyte cross section

This paper proposes analytical and semianalytical models of the ultrasonic backscattering cross section (BCS) of various geometrical shapes mimicking a red blood cell (RBC) for frequencies varying from 0 to 90 MHz. By assuming the first-order Born approximation and by modeling the shape of a RBC by a realistic biconcave volume, different scattering behaviors were identified for increasing frequencies. For frequencies below 18 MHz, a RBC can be considered a Rayleigh scatterer. For frequencies less than 39 MHz, the general concept of acoustic inertia tensor is introduced to describe the variation of the BCS with the frequency and the incidence direction. For frequencies below 90 MHz, ultrasound backscattering by a RBC is equivalent to backscattering by a cylinder of height 2 microm and diameter 7.8 microm. These results lay the basis of ultrasonic characterization of RBC aggregation by proposing a method that distinguishes the contribution of the individual RBC acoustical characteristics from collective effects, on the global blood backscattering coefficient. A new method of data reduction that models the frequency dependence of the ultrasonic BCS of micron-sized weak scatterers is also proposed. Applications of this method are in tissue characterization as well as in hematology.     

核子-核子碰撞截面的参数化公式

核子-核子碰撞截面(σ_NN)是描述原子核反应模型中的重要物理量。 核子-核子碰撞截面包括质子-质子碰撞截面（σ_pp）、中子-中子碰撞截面（σ_NN）和中子 质子碰撞截面（σ_np）, 它们随着核子能量与核物质密度的改变而变化。人们在目前研究中提出了多种核子-核子碰撞截面关于能量和核物质密度的参数化公式,通过计算12C+12C的完全反应截面,比较了不同入射能量下使用各种核子-核子碰撞截面参数化公式对12C完全反应截面的影响。 The nucleus-nucleus cross sections(σ_NN) include the proton-proton cross section, neutron-neutron cross section, and neutron-proton cross section. σ_NN change with the variations of the incident energies and the densities. Some parameterizations of σ_NNas a function of incident energy and density have been proposed in the theoretical and experimental study of nuclear reactions. Through the calculation of reaction cross sections of 12C+12C at different energies, the effect of different σ_NN parameterizations in the reaction cross sections of 12 are studied.      

The total photon deuteron hadronic cross section in the energy range 0.265–4.215 GeV

The total cross section for photoproduction of hadrons on the deutron, σ_T^d, has been measured for photon energies in the range 0.265–40215 GeV. From this, using results for the photon total cross section, obtained previously with the same apparatus, the neutron total cross section has been determined in the resonance region. The resonant structure is found to be quite different from that for the proton. Thereafter the neutron cross section falls off steadily with energy, and the values obtained are consistently lower than those for the proton. Forward scattering amplitudes have been evaluated for the deuteron.     

THE STUDIES OF NON-RUTHERFORD BACKSCATTERING CROSS SECTIONS OF 4He FROM 16O

In this article, we report the 170° backscattering cross sections of ⁴He from ¹⁶O in the energy range of 2.0-9.0 MeV. Our measurements show that the alpha-oxygen scattering remains Rutherford scattering up to E_α=2.35 MeV, and there exist two energy regions, namely 5.55-5.85MeV and 8.50-8.80MeV, where the cross sections are enhanced and show a smooth variation. The measured laboratory cross sections are 9.50-9.97 and 35.0-33.0 times greater than the Rutherford values, respectively. In the 8.50-8.80MeV region, the cross sections at scattering angles of 160°, 165°, 170° and 175° were measured and found to be strongly angle-dependent. A most strong resonance occurred at 7.60 MeV, where the cross section is 200 times of its Rutherford value. This resonance has been used to measure the ¹⁶O concentration on a Cu surface, with a sensitivity of 1×10¹⁵ oxygen atoms/cm², Besides, we have studied the backscattering angle dependence of the threshold energy, i.e., the energy at which the elastic cross section begins to deviate from its Rutherford value. The experimental result seems not in agreement with the prediction made from the analytical formula developed by Bozoian et al.     

Measurement of the ZZ production cross section and limits on anomalous neutral triple gauge couplings in proton-proton collisions at sqrt[s] = 7 TeV with the ATLAS detector

A measurement of the ZZ production cross section in proton-proton collisions at sqrt[s] = 7 TeV using data corresponding to an integrated luminosity of 1.02 fb(-1) recorded by the ATLAS experiment at the LHC is presented. Twelve events containing two Z boson candidates decaying to electrons and/or muons are observed, with an expected background of 0.3 ± 0.3(stat)(-0.3)(+0.4)(syst) events. The cross section measured in a phase-space region with good detector acceptance and for dilepton masses within the range 66 to 116 GeV is σ(ZZ → ?+ ?- ?+ ?-)(fid) = 19.4(-5.2)(+6.3)(stat)(-0.7)(+0.9)(syst) ± 0.7(lumi) fb. The resulting total cross section for on-shell ZZ production, σ(ZZ)(tot) = 8.5(-2.3)(+2.7)(stat)(-0.3)(+0.4)(syst) ± 0.3(lumi) pb, is consistent with the standard model expectation of 6.5(-0.2)(+0.3) pb calculated at the next-to-leading order in QCD. Limits on anomalous neutral triple gauge boson couplings are derived.     

Measurement of Reaction Cross Section for 17C and Finite-Range Glauber Model Analysis

We have measured the reaction cross section σ_R of ¹⁷C on the carbon target at the intermediate energy of 97A MeV by using transmission method.finite-range Glauber model has been employed to investigate the density distribution of ¹⁷C by fitting the present result and the previous result of interaction cross section σ_I.By contrast with the result from the analysis of σ_I,a tail in the neutron density distribution of ¹⁷C is found necessary to interpret the present result.Considering the configuration of the valence neutron,a dominant 1d_5/2(77±21%)occupancy is found,which is in agreement with results of momentum distribution measurements.     

Fe2O3纳米微粒溶胶非线性光学特性的Z-扫描研究

利用Z扫描技术在透明区域研究了Fe₂O₃纳米微粒水溶胶和表面包覆有机溶胶的非线性光学特性，给出了非线性折射率γ、双光子吸收系数β、自由载流子折射系数σ_r和自由载流子吸收截面σ_ab等重要物理参数，讨论了自由载流子效应对Fe₂O₃纳米微粒非线性特性的影响 关键词：     

Rheo-acoustical study of the shear disruption of reversible aggregates. Ultrasound scattering from concentrated suspensions of red cell aggregates

Shear-induced disruption of reversible aggregates or clusters in a concentrated suspension is investigated by ultrasound backscattering in the low shear regime. Fractal aggregates are considered as non-Brownian scatterers much smaller than the wavelength with acoustic properties close to those of the surrounding liquid, so that the attenuation of the coherent field is weak and multiple scattering can be neglected. The concept of variance in local particle volume fraction is used to deduce a first-order expression of the ultrasound scattering cross section per unit volume for Rayleigh scatterers in a dense suspension. On the basis of a scaling law for the shear-induced disruption of aggregates, the shear stress dependence of the ultrasonic scattered intensity from a dense suspension of clusters is derived. In a second part, the shear breakup of hardened red blood cell aggregates is investigated in plane-plane flow geometry by ultrasound scattering. Rheo-acoustical experiments are analyzed within the framework of the self-consistent field approximation and the scaling laws currently used in microrheological models. Finally, the ability of ultrasonic, light reflectometry and viscometry methods to provide quantitative information about red blood cell aggregation and membrane adhesiveness is discussed.     

Optical design of retro-reflectors by coordinate transformation

Transformation optics based on the form-invariant coordinate transformation of Maxwell’s equations offers an unconventional approach for designing devices with unprecedented electromagnetic (EM) behaviors. In this paper, we expand the coordinate transformation method to design omni-directional (OD) retro-reflectors by extending the conventional Luneberg lens reflectors to work in a much wider angular width. The constitutive medium tensors of the transformation devices are derived. Based on full wave simulations combined with Huygen’s principle, the flat and efficient backscattering responses of the resultant devices have been evaluated quantitatively. We confirm that the proposed structures are highly visible to incident EM waves from all directions, and they can be used as good OD radar cross section (RCS) enhancers in radar applications, such as the reference target for RCS measurements, range finding and position identification.     

Measurements of near-surface bubble plumes in the open ocean with implications for high-frequency sonar performance

This study examines near-surface bubble data obtained with a self-contained 200-kHz inverted echo-sounder deployed at Ocean Station Papa (NE Pacific, 1400 km west of Vancouver Is.) over an 81-day period in the spring of 1996. The instrument operated continuously, recording calibrated volume scattering profiles from near-surface bubbles with 3-s and 30-cm resolution. The data show the frequent occurrence of bubbles organized into vertical, plume-like structures, presumably drawn downwards by turbulence and other near-surface circulations. Average bubble plume penetrations of up to 15 m were observed, with maximum penetrations up to 25 m. Within the plumes, the backscatter cross section exhibited an exponential decay with depth, with e-folding scale in the range 0.5 to 3 m, increasing proportionally to the square of average plume depth. Using standard models for bubble scattering, and incorporating recent acoustic resonator measurements of bubble-size distributions along with actual bubble plume data, high-frequency near-surface sonar performance models were developed. These models show that on a ping-to-ping basis the bubble plume structures can induce significant spatial variations in the reverberation level and path-integrated extinction losses to near-surface targets.     

Experimental demonstration of a three-dimensional omnidirectional and broadband acoustic concentrator using an anisotropic metamaterial

We report the theoretical design and experimental demonstration of a three-dimensional(3D)omnidirectional and broadband metamaterial-based concentrator for airborne sound.The proposed mechanism uses a homogeneous anisotropic acoustic metamaterial with an ellipsoidal equifrequency contour to efficiently redirect the acoustic energy impinging on its outer surface into the central region,regardless of the incident direction.A design of the metamaterial unit cell is proposed as a practical implementation of our strategy,which is simply realized by perforating a solid spherical shell with a linearly shrinking cross section in the radial direction.We analytically and numerically prove that the non-resonant anisotropic effective acoustic parameters required for building the concentrator are produced with such a design.Good agreement is observed between the theoretical predictions and experimental measurements.An effective concentration of the incident acoustic energy is observed within a broadband that ranges 1000-1600 Hz.The experimental realization of this 3D acoustic concentrator with a simple design,low energy loss,replaceable constituent material,and omnidirectional and broadband functionality offers new possibilities for acoustic manipulations and may have important applications in a plethora of scenarios ranging from energy harvesting to noise mitigation.     

Size,Shape, and Wavelength Effect on Photothermal Heat Elevation of Gold Nanoparticles: Absorption Coefficient Experimental Measurement

Complex-shaped nanoparticles as gold nanourchins (GNU) and nanorods (GNR) are very suitable agents in the case of photothermal therapy due to their photon-heat conversion ability in the red and near-infrared region (NIR). The quantification in heat generation of complex shaped nanostructures is an important key to predict the therapeutic effect of these nanoparticles. For that, the determination of the nanoparticles absorption cross section (σ_Abs) responsible for the heat generation is one of the important steps before any application. Although it is obvious to determine σ_Abs for spheres via Mie's theory, in the case of complex structures like GNU or GNR, this parameter is difficult to model. In this work, a new methodology is used to determine experimentally σ_Abs for both GNU and GNR. Experimental measurements of the photothermal properties of 100 nm size GNU and two different sizes of GNRs are studied regarding different parameters such as concentration, laser excitation wavelength, and exposure time. By using the heat transfer theory, the temperature elevation in the nanoparticles solutions is converted to temperature elevation at the nanoparticles surface and σ_Abs values are then calculated for both GNU and GNR in the NIR spectral region.