Optical radiation background from ^{40}K decays in undersea neutrino telescopes

The photon flux produced by light sources uniformly distributed in an infinite homogeneous medium is calculated on the basis of a known property of light propagation, taking into account the contribution of both absorption and scattering processes. The results are applied to the issue of the decays of K content in sea salt and then to the rates detected by photomultipliers deployed in the deep sea. Numerical calculations are in agreement with the recent measurements performed in the Mediterranean Sea by the ANTARES and NEMO Collaborations. Received: 29 August 2001 / Revised version: 25 October 2001 / Published online: 14 December 2001     

基于双光路原理的海水IOPs高光谱测量仪方案

设计了基于双光路原理的海水固有光学参数测量仪。该仪器可同步测量水体光谱吸收系数a、光束衰减系数c和体散射系数b。其中吸收系数a采用反射式吸收管测量,光束衰减系数c采用全吸收式样品池测量,体散射系数b根据c=a+b计算。光信号由光纤收集、光谱仪分光后用CCD探测器测量。光谱分辨率为4nm,灵敏度为0 001m-1。该仪器直接在水下工作,由水泵抽取被测海水,水下最大工作深度为200m。测量数据可以自动记录,同时也可以通过水下电缆实时传输到调查船实验室。     

Time-resolved Monte Carlo Simulation of Propagation of Photons Through Layered Tissues

The propagation of photons through layered tissues is discussed using time resolved Monte Carlo method. The effects of the absorption coefficient, scattering coefficient and anisotropy coefficient on the shape of time resolved transmission are investigated. The energy attenuation of light in layered tissues is also achieved for the infinitesimal-width light and infinite-width light, respectively.     

Time-resolved Monte Carlo Simulation of Propagation of Photons Through Layered Tissues

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｉｎｒｅｃｅｎｔｙｅａｒｓ ,ｒｅｓｅａｒｃｈｏｎｔｉｍｅ ｒｅｓｏｌｖｅｄｐｒｏｐａｇａｔｉｏｎｏｆｐｕｌｓｅｄｌｉｇｈｔｉｎｔｉｓｓｕｅｓｈａｓｂｅｃｏｍｅａｎｉｎｃｒｅａｓｉｎｇｉｎｔｅｒｅｓｔ[1～ 6] .Ｔｈｅｉｎｃｒｅａｓｉｎｇｕｓｅｏｆｔｈｅｌｉｇｈｔｉｎｄｉａｇｎｏｓｔｉｃａｎｄｔｈｅｒａｐｅｕｔｉｃｍｅｄｉｃｉｎｅｈａｓｃｒｅａｔｅｄｔｈｅｎｅｅｄｔｏｄｅｔｅｒｍｉｎｅｎｏｎｉｎｖａｓｉｖｅｌｙｔｈｅｏｐｔｉｃａｌｐｒｏｐｅｒｔｉｅｓｏｆｌｉｖｉｎｇｔｉ…     

Hybrid LD and LED-based underwater optical communication: state-of-the-art,opportunities,challenges,and trends [Invited]

In this paper, the current research of an underwater optical wireless communication(UWOC) network is reviewed first. A hybrid laser diode(LD) and light-emitting diode(LED)-based UWOC system is then proposed and investigated, in which hybrid cluster-based networking with mobility restricted nodes is utilized to improve both the life cycle and throughput of the UWOC network. Moreover, the LEDs are utilized for the coarse alignment, while the LDs are used for high-precision positioning to reduce the difficulty of optical alignment. Finally, challenges and trends for UWOC are pointed out to provide some insight for potential future work of researchers.     

Two-wavelength transmission: a rapid and precise method for measuring the light absorption in semiconductors

By means of two-wavelength transmission the reflection and scattering losses at surfaces are canceled out experimentally. A signal which is directly proportional to the light absorption is derived and measured in real time. The performance of the method for measuring the concentrations of EL2 in GaAs, of Fe in InP and of the thicknesses of InGaAsP/InP layers is demonstrated.     

Security Simulation of Continuous-Variable Quantum Key Distribution over Air-to-Water Channel Using Monte Carlo Method

Considering the ocean water's optical attenuation and the roughness of the sea surface, we analyze the security of continuous-variable(CV) quantum key distribution(QKD) based air-to-water channel. The effects of the absorption and scattering on the transmittance of underwater quantum channel and the maximum secure transmission distance are studied. Considering the roughness of the sea surface, we simulate the performance bounds of CV QKD with different wind speeds using the Monte Carlo method. The results show that even if the secret key rate gradually reduces as the wind speed increases, the maximum transmission distance will not be affected obviously.Compared to the works regarding short-distance underwater optical communication, our research represents a significant step towards establishing secure communication between air platform and submarine vehicle.     

Low-frequency sound absorption and attenuation in marine medium

Original experimental data are analyzed on the low-frequency sound attenuation in the Mediterranean, Black, and Baltic Seas, Sea of Japan, and the north-western region of the Pacific Ocean. In these regions, waters significantly differ in their temperatures and salinities. The analysis is aimed at obtaining an expression for calculating the low-frequency absorption coefficient in sea water. The analysis uses the previously published data on the measured (by the temperature discontinuity method) low-frequency relaxation times associated with boron present in sea water. The dependence of the absorption on the pH value (which was revealed in the 1970s) and the experimental data on sound absorption at frequencies higher than 5–10 kHz are also taken into account. As a result of the analysis based on the assumption that low-frequency relaxation takes place, an expression is proposed that relates the low-frequency absorption to the temperature, salinity, and pH value and equally well describes the experimental frequency dependences of attenuation for the four regions at hand (except for the Baltic Sea). Increased attenuation coefficients are noticed for shallow seas and deep-water regions where waters are influenced by intense currents, strait zones, and zones of mixing waters of different origin, i.e., for the ocean areas where, in addition to the attenuation, sound scattering by inhomogeneities of the marine medium and sound energy leakage into the sea floor are significant.     

Theoretical and experimental study of the ultrasonic attenuation in bovine cancellous bone

In this study a theoretical approach for the estimation of ultrasonic attenuation is proposed. The approach combines two models which take into account both absorption and scattering. Attenuation due to absorption is studied by using the Biot’s analytical model whereas that due to scattering is described by means of a generalized weak scattering model which is formulated for binary mixtures. The scattering model takes account of the density fluctuation of the porous medium in addition to the propagation velocity fluctuation. For the calculation of the attenuation coefficient due to absorption, experimental values have been used to link size of pores to porosity. The theoretical results have been compared with experimental data obtained on bovine cancellous bone samples filled with water. Using an immersion acoustic transmission method, the ultrasonic attenuation has been measured at a frequency range between 0.1 and 1.0 MHz for 12 bovine cancellous bone samples with a porosity range between 40% and 70%. The prediction of attenuation with this model appears to correspond more closely to its experimentally observed behavior. This study indicates that scattering is the predominant mechanism which is responsible for attenuation in trabecular bone. Furthermore, it shows that the density fluctuations contribute significantly to the phenomenon of attenuation and cannot thus be neglected.     

An integrated submersible fluorometer/nephelometer/ transmissometer: design and testing at sea

This paper describes a new submersible instrument which makes simultaneous measurements of chlorophyll fluorescence, beam attenuation and wide-angle scattering using a single xenon flashlamp as the light source. Cross-calibration against single-parameter commercial instruments shows satisfactory linear correlations, comparable resolution and enhanced dynamic range. The instrument package includes microprocessor control of data acquisition and a rechargeable battery pack. It is capable of acquiring high-resolution vertical profiles when deployed from a ship, or bio-optical time series from moorings. Results are presented here from initial deployments in inshore waters and in a deck tank at sea.     

多重散射方法研究轴对称空腔覆盖层的声学特性

发展了一种多重散射方法研究声学覆盖层的半数值半解析模型,分析了影响轴对称空腔结构声学性能的主要能量耗散机制。在球坐标条件下推导出轴对称空腔结构的位移和应力场基函数,通过对空腔表面基函数的数值积分,得到散射波和入射波之间的传输矩阵方程,结合分层介质声传播理论计算了周期性空腔结构覆盖层的反射、透射和吸声性能。研究结果表明;空腔共振是低频能量耗散的主要形式,边界条件对材料空腔结构的谐振特性影响很大,利用双空腔耦合共振可以拓宽材料的低频吸声频带;背衬对材料的高频吸声影响较小,材料的高频能量损耗取决于空腔的散射和波型转换特性。      

Utilization of light scattering in transmission laser welding of medical devices

This paper reports on optimization of material parameters in transmission laser welding of polymers including light absorption, light scattering and the thermal properties of the polymers. A criterion for making an optimized transmission laser weld between a transparent polymer part and an absorbing and scattering polymer part is formulated as a required thickness of the melt-zone in the transparent part with a corresponding minimum-line-energy-for-welding (MLEW). Experimental data of MLEW are presented for a medical device application involving joining polyethylene-octene parts for various concentrations of near-infrared absorber and titanium dioxide light scattering particles. Numerical and analytical models yield good agreement to the experimental data and enable optimization of the transmission laser welding process. By utilization of light scattering, the laser line-energy required for joining two polymer parts can be reduced by a factor up to three, enabling a corresponding reduction of the cycle time in the manufacturing process.     

Invalidity of the beam volume attenuation coefficient α

In considering the transmission of light in an isotropic, optically homogeneous medium such as the atmosphere or the ocean, it is current practice, without apparent exception, to add the beam volume absorption coefficient, a, to the beam volume scattering coeffient, s, to obtain the total beam volume attenuation or extinction coefficient α.     

Concentrated suspension theory of sound attenuation in marine sediments—linear dependence of absorption coefficient on frequency

Statistical averages of acoustic scattering and attenuation in sea bed sediments, and of the corresponding sea bed absorption coefficients, are obtained. The multiple scattering interactions among the particles in concentrated suspension are taken into account. The suspensions are assumed to be a collection of spherical particles of various sizes, and for which the masses corresponding to various radii follow a normal distribution. The numerical results obtained show that the absorption coefficient has a linear dependence on frequency if there is a sufficiently broad distribution of the particle radii. However, if βR ? 1, where R is particle radius and β is the viscous wavenumber, the absorption may be proportional to the frequency raised to a power higher than unity. Comparisons of results with some published experimental data are presented.     

浅海起伏海面下气泡层对声传播的影响

分析了起伏海面下风浪引起的气泡层对海面反射损失和对声传播的影响.一方面,气泡层会改变原来水中的声速剖面;另一方面,气泡层会对声波产生散射和吸收作用.考虑以上两方面的因素,分析了不同风速下气泡层对海面反射损失和声传播损失的影响,仿真发现,在风速大于10 m/s时,对于2 k Hz以上频率时气泡层对小掠射角下海面反射损失的影响不可忽视.在给定的水声环境中,当声源深度和接收深度都为7 m时,风速为16 m/s的风浪下生成的气泡层,在10 km处对3 k Hz的声传播损失的影响达到8.1 d B.当声源深度和接收深度都为18 m时,风速为16 m/s的风浪下生成的气泡层,在10 km处对3 k Hz的声传播损失的影响达到4 d B.     

沙尘信道下激光通信系统的性能分析

沙尘对激光信号的散射和吸收作用会引起激光信号的严重衰减,本文结合我国沙尘粒子的半径分布特征,在考虑含水影响的基础上,研究了沙尘对激光信号衰减特性的影响,得到了接收端信噪比的表达式;同时针对OOK调制,推导了沙尘天气下激光通信系统的误码率和信道容量。仿真分析了能见度、传输距离、含水量以及激光波长等因素对误码率和信道容量的影响。结果表明:随着含水量和传输距离的增大以及大气能见度的减小,系统的误码率会呈现出不断增大的趋势,而信道容量则呈现减小的趋势。在能见度为4 km的情况下,波长为1 550 nm、传输距离为1 km时系统的误码率可达10~(-2)数量级,且归一化信道容量为8.48 bps/Hz。     

An experimental evaluation of noise reduction by scattering in low velocity ducts

This paper presents the results of an experimental assessment of both conventional absorption and Bragg scattering techniques for the reduction of noise transmission by a fan in a short, low velocity duct connecting two reverberant rooms. There are several advantages of using the scattering technique; for example, the saving of space and the facts that the device can be tuned to a particular frequency and that it is not necessary to use materials such as absorbent foams which can be a health hazard. The system appears to work equally well with externally generated sources of sound but the maximum attenuation with eight scatterers is found to be about 12 dB at the Bragg frequency.     

An indirect hybrid sound transmission loss controller

The control of sound transmission through panels is an important noise control problem in the aerospace, aeronautical, and automotive industries. The trend towards using lightweight composite materials that have lower sound insulation performance is a negative factor regarding low frequency transmission loss. Double-panel partitions with the gap filled with sound absorption materials are often employed to improve the sound insulation performance with reduced added weight penalty. However, in the low frequency range, the strong coupling between the panels through the air cavity and mechanical paths may greatly reduce the sound transmission performance, making it even lower than the performance of a single panel in some frequency ranges. In this work, an experimental investigation of a new kind of hybrid (active/passive) acoustic actuator is presented. The idea consists of replacing the acoustic absorption material by a hybrid actuator aiming at improving the transmission loss at low frequencies without altering the passive attenuation. A prototype of the system is tested in a plane wave acoustic tube setup. Different kinds of SISO feedforward control implementations were used to attenuate the sound power transmitted through the hybrid active–passive panel using an error microphone or a particle velocity sensor placed downstream with respect to the sample panel. Measurement results of the transmission loss with active and hybrid attenuation are presented and discussed.     

海洋混合悬浮颗粒对蓝绿激光的散射特性研究

激光在水下的传输很大程度上会受到海水中悬浮颗粒物的影响,而目前对于海洋中悬浮颗粒物光散射的理论研究大多是针对单一成分的悬浮粒子而进行的,但是在真实海洋中悬浮颗粒物都是以多种成分混合的颗粒群形式而存在的,因此研究真实海洋中混合悬浮颗粒物对蓝绿激光的散射特性具有重要意义。该研究选取了对蓝绿激光传输产生较大影响的浮游藻类植物、悬浮泥沙、碎屑、悬浮气泡和矿物质这五种常见的悬浮颗粒物作为研究对象,充分考虑真实海况中这五种悬浮颗粒物的不同混合情况,构建了海水中混合球形悬浮颗粒物对蓝绿激光的散射特性模型。数值计算了海水中五种物质混合的球形悬浮颗粒物对532 nm蓝绿激光的统计平均光散射参量和平均散射相函数,分析不同混合悬浮颗粒物的混合比对平均散射、吸收和消光系数以及单次反照率随着粒子有效半径和粒子数浓度变化的影响,同时分析了不同粒子尺寸下的不同混合比对混合悬浮颗粒物的平均散射相函数随着角度变化的影响。数值结果表明,当悬浮泥沙在整个混合模型中占比越大时,平均散射系数越大,而当悬浮藻类粒子在整个混合模型中占比增大时,平均吸收系数增大,由此可知海洋中对光造成主要影响的五种常见悬浮颗粒物中,悬浮泥沙对光散射作用影响最大,悬浮藻类粒子对光吸收作用影响最大。随着悬浮颗粒物浓度的增大,混合粒子的单次反照率保持不变,由此可知混合悬浮颗粒物的平均光散射参量随着粒子浓度的增长速率是一致的。海洋中混合悬浮颗粒物的平均散射相函数随着粒子的有效半径的增大而增大,散射作用最大的混合比下的悬浮颗粒物其平均散射相函数最大,悬浮颗粒物的前向散射较强。该工作对蓝绿激光在海水中传输、信道建模,水下无线光通信的研究以及激光探测都具有重要的理论指导意义。