The study of underwater acoustic communication technology based-on the acoustic vector sensor

Underwater acoustic (UWA) communication based on an acoustic vector sensor is studied. The method of joint weighted sound pressure and velocity processing is used in phase modulation high-speed UWA communication system combined with coherent demodulation and adaptive equalization algorithm to demodulate and decode. Whereas the sound intensity could be used instead of pressure for frequency decoding in frequency modulation UWA communication system. The results of theory analysis, simulation calculations and lake trials have shown that either in phase modulation or in frequency modulation UWA communication system, the processing gain can be evidently increased, so that the BER (bit error rate) can be effectively reduced and the telemetry distance can be enlarged by using the acoustic vector sensor.     

Experimental study of the acoustic characteristics of micro-perforated functional absorbers

Micro-perforated panels have been widely used as fiber-free acoustical material for decades in the form of wall or ceiling covering with some air space behind. This paper presents the test study on the acoustical characteristics of two different types of functional absorbers, panel type and tube type, constructed with micro-perforated metal or PVC (polyvinyl chloride) sheets. Acoustical measurements of such functional absorbers in reverberation chamber demonstrate the merit of good absorption as expected. They are not only cost effective in construction and installation, but also appealing esthetically for architectural interior design.     

Modeling of acoustic wave propagation in time-domain using the discontinuous Galerkin method – A comparison with measurements

Simulations of acoustic wave propagation in time-domain are presented. In the simulations, the discontinuous Galerkin method for spatial derivatives and the low-storage Runge–Kutta approach for time derivatives are used. Three different simulation cases are studied. First, the directivity of loudspeaker is simulated. In the second case, acoustic wave propagation in free space is studied using a short pulse. In the last case, acoustic wave scattering from a metallic cylinder is simulated. All simulation results are compared with measurement results. The measurements for the acoustic wave scattering from the metallic cylinder are made in 2D planes using an automated measurement system. Comparison between the simulation and measurement results are made both temporally and spatially and a good agreement between the simulation and measurement results is found. The results suggest that the discontinuous Galerkin method coupled with the low-storage Runge–Kutta approach is a viable tool for modeling acoustic wave propagation in the time-domain.     

Effects of ultrasound frequency and acoustic amplitude on the size of sonochemically active bubbles – Theoretical study

Numerical simulation of chemical reactions inside an isolated spherical bubble of oxygen has been performed for various ambient bubble radii at different frequencies and acoustic amplitudes to study the effects of these two parameters on the range of ambient radius for an active bubble in sonochemical reactions. The employed model combines the dynamic of bubble collapse with the chemical kinetics of single cavitation bubble. Results from this model were compared with some experimental results presented in the literature and good apparent trends between them were observed. The numerical calculations of this study showed that there always exists an optimal ambient bubble radius at which the production of oxidizing species at the end of the bubble collapse attained their upper limit. It was shown that the range of ambient radius for an active bubble increased with increasing acoustic amplitude and decreased with increasing ultrasound frequency. The optimal ambient radius decreased with increasing frequency. Analysis of curves showing optimal ambient radius versus acoustic amplitude for different ultrasonic frequencies indicated that for 200 and 300 kHz, the optimal ambient radius increased linearly with increasing acoustic amplitude up to 3 atm. However, slight minima of optimal radius were observed for the curves obtained at 500 and 1000 kHz.     

Long term study of Harshaw TLD LiF – LLD and uncertainty

Long term study of Harshaw TLD LiF has been performed in this work. The study is carried out over a period of 24 months at storage temperatures of 0 °C, 20 °C and 40 °C using more than 3500 dosimeters. The length and variations of this study may be the most comprehensive study published to date. The dosimeters are HarshawTLD LiF based cards and extremity dosimeters, which include LiF:Mg,Ti and LiF:Mg,Cu,P materials in their different isotopes, sizes and forms. There are three parts in this study: material fade in sensitivity and in signal; lower limit of detection (LLD) and uncertainty; and glow curve peaks and sensitivity change over 24 months. Part I was presented at the SSD15 (15th International Conference on Solid State Dosimetry) in Delft. This paper is the continuous work focused on Part II – the lower limit of detection and uncertainty analysis. The detailed results of each case are provided.     

Numerical study of friction-induced instability and acoustic radiation – Effect of ramp loading on the squeal propensity for a simplified brake model

This paper presents a numerical study of the influence of loading conditions on the vibrational and acoustic responses of a disc brake system subjected to squeal. A simplified model composed of a circular disc and a pad is proposed. Nonlinear effects of contact and friction over the frictional interface are modelled with a cubic law and a classical Coulomb?s law with a constant friction coefficient. The stability analysis of this system shows the presence of two instabilities with one and two unstable modes that lead to friction-induced nonlinear vibrations and squeal noise. Nonlinear time analysis by temporal integration is conducted for two cases of loadings and initial conditions: a static load near the associated sliding equilibrium and a slow and a fast ramp loading. The analysis of the time responses shows that a sufficiently fast ramp loading can destabilize a stable configuration and generate nonlinear vibrations. Moreover, the fast ramp loading applied for the two unstable cases generates higher amplitudes of velocity than for the static load cases. The frequency analysis shows that the fast ramp loading generates a more complex spectrum than for the static load with the appearance of new resonance peaks. The acoustic responses for these cases are estimated by applying the multi-frequency acoustic calculation method based on the Fourier series decomposition of the velocity and the Boundary Element Method. Squeal noise emissions for the fast ramp loading present lower or higher levels than for the static load due to the different amplitudes of velocities. Moreover, the directivity is more complex for the fast ramp loading due to the appearance of new harmonic components in the velocity spectrum. Finally, the sound pressure convergence study shows that only the first harmonic components are sufficient to well describe the acoustic response.     

Delayed gadolinium-enhanced MRI of the fibrocartilage disc of the temporomandibular joint – a feasibility study

Objective

To 1) test the feasibility of delayed Gadolinium-Enhanced Magnetic Resonance Imaging of Cartilage (dGEMRIC) at 3 T in the temporomandibular joint (TMJ) and 2) to determine the optimal delay for measurements of the TMJ disc after i.v. contrast agent (CA) administration.

Design

MRI of the right and left TMJ of six asymptomatic volunteers was performed at 3 T using a dedicated coil. 2D inversion recovery (2D-IR) sequences were performed at 4 time points covering 120 minutes and 3D gradient-echo (3D GRE) dual flip-angle sequences were performed at 14 time points covering 130 minutes after the administration of 0.2 mmol/kg of Gd-diethylenetriamine pentaacetic acid ion (Gd-DTPA)^2-, i.e., 0.4 mL of Magnevist™ per kg body weight. Pair-wise tests were used to assess differences between pre-and post-contrast T1 values.

Results

2D-IR sequences showed a statistically significant drop (p < 0.001) in T1 values after i.v. CA administration. The T1 drop of 50% was reached 60 minutes after bolus injection in the TMJ disc. The 3D GRE dual flip-angle sequences confirmed these results and show plateau of T1 after 60 minutes.

Conclusions

T1(Gd) maps calculated from dGEMRIC data allow in vivo assessment of the fibrocartilage disc of the TMJ. The recommended measurement time for dGEMRIC in the TMJ after i.v. CA administration is from 60 to 120 minutes.     

On Segal-Wilson's construction for the τ-functions of the constrained KP hierarchies

In this Letter, we study the constrained KP hierarchies by employing Segal-Wilson's theory on the -functions of the KP hierarchy. We first describe the elements of the Grassmannian which correspond to solutions of the constrained KP hierarchy, and then we show how to construct its rational and soliton solutions from these elements of the Grassmannian.     

On the phase uncertainty of Fock states and “nonlocal realism”

Based on the study of the effects of the suppression of cross-correlation of photons on a beam splitter and preparation of squeezed states, an experimental proof is proposed for the lack of determinate values of the phase and phase difference of photons in Fock states. It is shown that this conclusion unveils the intrinsic inconsistency of interpreting quantum mechanics on the basis of the nonlocal theory of hidden variables and proves the inadequacy of the latter.     

On the application of wavelet transform to the solution of integral equations for acoustic radiation and scattering

1 IlltroductionIt is well Anown that Boundary Element Method (BEM), based on boundary integralequation, leads the reduction of the dimensionallty of the problem by one because the prob1emis formulated in terms of the flelds on botmdary ouly BEM, hOWver, generates algebraicequations with full matrices, whose solutions are moe eapensive than that of the bandedmatrices of FEM[1'2]. On the other hand, in boundary integral forInulations, an integral operatorhas the global behavior, that can b…     

A prediction of the acoustic field of a vibrating box by FEM-BEM

I.Mathematicalmodelofacousticfie1dByapplyingtheSommerfeldradiationcondihonThus,anacousticfic1disdescribcdbyHelmholtzformula.Byconsideringaficldpointinthearea,Helmholtzformulaisgivenbythefollowingthreeintegra1equations:(1)Theexternalintcgra1fOrmu1a'(2)Thcintcrnalintegralformu1af(3)Thesurfaceintegralformu1afwhcreP.isthesoundpressureonthcSsurface;rthedistancefrompointqtothee1ementsurfacedSiqtheficldpoint,tuthefrcqucncyoftheacousticradiation;pthedensityofthesurroundingmedium,vsthenormalvibrati…     

Calculation of acoustic scattering of a nonrigid surface using physical acoustic method

In this paper the physical acoustic method or the Kirchhoff approxima-tion is extended to treat the scattering of a nonrigid surface in order to estimatethe target strength of targets with absorbing coatings.By using the locally planewave approximation,the relationship between the sound pressure and its normalderivative on the surface can be represented by the plane wave reflectioncoefficient and the acoustic impedance of the surface.The resulting modifiedKirchhoff approximation involves the plane wave reflection coefficient.For aimpedance sphere,a comparison between the physical acoustic method and theexact solution shows that the physical acoustic method still is a good approxima-tion at higher κα values.     

On the effect of backscattering of γ quanta and statistics in positron-annihilation lifetime measurements

The contribution of backscattered, 1.27-MeV quanta to the coincidence counts in positron-annihilation lifetime measurements has been investigated. Depending on the energy window settings and geometry, as much as 20% of the coincidence counts was found to arise from backscattered events. Computer analysis of such spectra leads to erroneous results. Analysis of computer-generated lifetime spectra shows that good statistics is more important than good resolution power for the quality of the analysis.On leave of absence at Danfoss, DK-6430 Nordborg, Denmark     

On the dynamics and optimization of a non-smooth bistable oscillator – Application to energy harvesting

Bistable nonlinear oscillators can transform slow sinusoidal excitations into higher frequency periodic or quasi-periodic oscillations. This behaviour can be exploited to efficiently convert mechanical oscillations into electrical power, but being nonlinear, their dynamical behaviour is relatively complicated. In order to better understand the dynamics of bistable oscillators, an approximate bilinear analytical model, which is valid for narrow potential barriers, is developed. This model is expanded to the case of wider potential with experimental verification. Indeed, the model is verified by numerical simulations and a suitable Poincaré section that the analytical model captures most of bifurcations for large amplitude vibrations and can be used to optimize the harvested power of such devices. The method of Shaw and Holmes [1] is enhanced by exploiting symmetry to obtain closed form expressions of the Poincaré section and mapping.     

On study of the theory and algorithm of the three dimensional coupled mode-parabolic equation

A fast algorithm of sound propagation in three dimensional underwater environments is presented. On the basis of the generalized phase integral (WKBZ) theory and the beam displacement ray mode (BDRM) theory, the coupled mode parabolic equation (CMPE) theory of sound propagation in range dependent underwater environment is extended for three dimensional (3D) problems. The CMPE3D solution is expressed in terms of the normal modes     

A multidisciplinary approach for the conservation of a building of the seventeenth century

A long-term multidisciplinary conservation study is actually in progress inside the Villa della Regina, a prestigious Savoy residence built in the seventeenth century and recently restored. The walls of some rooms of the Villa are decorated with precious tin–mercury mirrors, that are baked with a reflective coating constituted of a tin–mercury compound surrounded by liquid mercury. The reflective layer is very soft, thus any restoration is difficult to be performed and can lead to a complete destruction of the artifact. Amalgam corrosion is a very slow process and, although there is no way to prevent the oxidation of the reflective layer, the conservation state of the artifacts may be improved by keeping them in a controlled environment. For this reason, a monitoring system has been designed and installed that is based on a wireless network of extremely compact sensors, for temperature and relative humidity measurements. The sensors have been specifically designed to satisfy the requirements for use in cultural heritage field and the system allows one to automatically collect the data that can be analyzed with the final aim to establish a correlation between the environmental conditions and the conservation state of the artifacts. A restoration has been carried out by producing in situ an amalgam inlay on the corroded area to slow down the release of liquid mercury in order to avoid also possible unsafe conditions for staff and visitors. In addition, a sensor has been developed which is based on a prototypical plastic optical fiber for the detection of low concentration Hg vapors to ensure the safe conditions in the Villa rooms. The sensor is being tested in laboratory.     

Hybrid acoustic synthesis – Assessment of rear final drives in an early stage of development,on the basis of transfer path analyses and test bench measurements

In order to be able to assess the acoustic characteristics of new rear axles respectively rear final drives at an early stage of development, a hybrid evaluation procedure was developed: this makes it possible to compare various construction stages on the basis of vehicle and test bench measurements. Transfer path analyses are used to calculate what contribution of the sound pressure on the driver’s ear is made up of structure-borne sound from the rear final drive (based on operational acceleration measured on the test bench and the bodywork’s transmission characteristics measured on the vehicle), which is used to classify the various construction stages. To use the test bench measurements for forecasting, the test object must have vibration characteristics that are as close as possible to those of the vehicle. In view of the above, comprehensive comparative measurements were taken with the help of artificial excitation and operational excitation. The measurement positions identified in the process were used to validate the calculation method by operating the very same rear final drive on the test bench and in a vehicle. In both cases, the rear final drive’s contribution of the total vehicle interior noise level was calculated, in one case on the basis of excitation from the vehicle measurement and in the other case on the basis of excitation from the test bench measurement. The good correlation between the vehicle-based and test bench-based calculations confirmed the applicability of the method. The “virtual” installation of the rear final drive enables faster construction stage comparisons because there is no need for alteration work on the vehicle and the rear final drive that is to be compared can simply be integrated into the existing test bench environment.     

On adaptation – a secondary concern?

The climate problem has many facets. Whether or not humans are capable of significantly changing climate is no longer a scientific question – they are in fact capable of doing so. However, only partly solved is the question what is happening here and now and how far future anthropogenic climate change will or may possibly go. The most important issue, namely how humankind can or should deal with this change, is a political issue, which needs more debate. Adaptation is a key element in this context. These issues are addressed in a non-technical manner here – from a deliberately broad range of perspectives, from both natural and social sciences. This paper is not a review; it is certainly biased in presenting the author’s views, analyses and conclusions. According to these views, adaptation is not a secondary concern.     

On a q-analog of the Wallach–Okounkov Formula

We obtain a q-analog of the well-known result on a joint spectrum of invariant differential operators with polynomial coefficients on a prehomogeneous vector space of complex n × n-matrices. We are motivated by applications to the problems of harmonic analysis in the quantum matrix ball: our main theorem can be used to prove the Plancherel formula (to be published).