Mode conversion is an important feature of wave propagation used in ultrasonic nondestructive testing with Lamb waves. When a wave packet with a given central frequency, and a correspondent central wavenumber, impinges on the free edge of a plate, the reflected wave generally is a weighed combination of all the possible modes compatible with the given frequency. Under particular conditions, only one wave packet is reflected with a distinct central wavenumber compared to the incident one. In such a case, according to Snell's law, the reflection angle is different from the incident one (anomalous reflection). In this article, experimental results are presented on anomalous reflection on a free edge of a thin plate of a Lamb wave packet; moreover, experimental results are reported on a Lamb wave packet that is reflected at an angle lying on the same side, with respect to the normal direction, of the impinging wave (negative reflection). Negative reflection of Lamb waves has been obtained through mode conversion taking place at the free edge of a thin plate of constant thickness: More precisely, a symmetric S1 Lamb mode has been converted into the same mode but with phase velocity antiparallel to group velocity, so obtaining the so-called backward-propagating Lamb wave packet.

Evanescent waves are characterized by the exponential decay of the amplitude along the propagation direction, such that no phase velocity could be properly defined and the concept of propagation itself has to be properly redefined. However, evanescent waves can carry energy beyond a tunneling region where they are produced, and their effect in the forbidden region may be properly inferred by the outgoing wave. In the present paper, evidence of evanescent Lamb waves on a plate is given, as they are produced within a forbidden region where thickness is properly reduced and the acoustic modes are above threshold of propagation. However, the coupling of modes at each line boundary between different regions makes it difficult to single out the tunneling mode alone, since all modes share the same frequency. Therefore, we resort to the propagation of the backward S1 mode, that can be properly isolated from all the others. That makes the problem of refraction/reflection of backward propagating modes at a boundary, a problem by itself to be investigated and makes it worth to perform experiments on it. This is done in the present paper, as well, by detecting the acoustic field of a backward propagating Lamb mode reflected from the end boundary of a steel plate and the focusing effect from such a boundary is put in evidence in the case that a forward propagating mode is reflected as a backward propagating one.

Photoacoustics has emerged as a tool for the study of liquid gel suspension behavior and has been recently employed in a number of new biomedical applications. In this paper, a photoacoustic sensor is presented which was designed and realized for analyzing photothermal signals from solutions filled with microbubbles, commonly used as ultrasound contrast agents in echographic imaging techniques. It is a closed cell device, where photothermal volume variation of an aqueous solution produces the periodic deflection of a thin membrane closing the cell at the end of a short pipe. The cell then acts as a Helmholtz resonator, where the displacement of the membrane is measured through a laser probe interferometer, whereas photoacoustic signal is generated by a laser chopped light beam impinging onto the solution through a glass window. Particularly, the microbubble shell has been modeled through an effective surface tension parameter, which has been then evaluated from experimental data through the shift of the resonance frequencies of the photoacoustic sensor. This shift of the resonance frequencies of the photoacoustic sensor caused by microbubble solutions is high enough for making such a cell a reliable tool for testing ultrasound contrast agent, particularly for bubble shell characterization.

Water temperature dependence of single bubble sonoluminescence (SBSL) threshold has been experimentally measured to perform measurements at different temperatures on the very same bubble. Results show lower thresholds, i.e. an easier prime of mechanism, of sonoluminescence at lower water temperatures. Dependence is almost linear at lower temperatures while between 14 degrees C and about 20 degrees C the curve changes its slope reaching soon a virtual independence from water temperature above about 20 degrees C.

In the framework of the DS4 EUROFEL collaboration, a research work plan at the SPARC free-electron laser (FEL) test facility aiming at the investigation of seeded and cascaded FEL configurations is under implementation. The main goal of the collaboration is to study and test the amplification and the FEL harmonic generation process of an input seed signal obtained as higher-order harmonics generated both in crystals (400 and 266nm) and in gases (266, 160, 114nm). The SPARC FEL can be configured to test several cascaded FEL configurations. In this paper we introduce SPARC and its main parameters and we analyze the superradiant cascade and the harmonic cascade seeded with a signal with the typical time structure of the harmonics generated in gas.

In recent years there has been a significant growth of investment products aimed at attracting investors who are worried about the downside potential of the financial markets. This paper introduces a dynamic stochastic optimization model for the design of such products. The pricing of minimum guarantees as well as the valuation of a portfolio of bonds based on a three-factor term structure model are described in detail. This allows us to accurately price individual bonds, including the zero-coupon bonds used to provide risk management, rather than having to rely on a generalized bond index model.

In the present paper the nonlinear generation of harmonic vibrations is analysed in specific piezoelectric structure, shaped as hollow cylinders, excited at fundamental modes. The question rises of how the energy is distributed in space when second or higher harmonics are nonlinearly generated and different examples are produced when the generated second harmonic wave strictly follows the distribution of the second power of the fundamental mode or that of the linearly generated wave at twice the frequency of the fundamental wave. A simplified model is schematically introduced, that may give a justification of the experimental results.

Corporate sponsored defined benefit (DB) pension schemes have recently found themselves in hot water. Accounting practices that led to over-exposure to equity markets, increases in longevity of the scheme participants and low interest rates have all contributed to the majority of schemes in the EU and the UK finding themselves underfunded. In essence, a DB scheme promises to pay its participants an annuity at retirement that gives them a pension equal to a proportion of their final salary (the proportion depending on the number of years of service). Therefore the responsibility to meet these promises (liabilities) rests firmly with the scheme’s trustees and ultimately with the corporate sponsor. The management of these corporate schemes was greatly affected in the past by quarterly earnings reports which directly impacted stock prices in the quest for ‘shareholder value’. Consequently DB scheme sponsors resorted to a management style that was able to keep the liabilities, if not off the balance sheet, then at least to a minimum. One sanctioned tactic that achieved these aims was the ability to discount liabilities by the expected return of the constituent asset classes of the fund. In other words, by holding a large part of the fund in equities, the liabilities could be discounted away at over 10% p.a. The recent performance of the equity markets and the perception of equity as a long-horizon asset class assisted in justifying this asset-mix in the eyes of the scheme’s trustees. However, with the collapse of the equity-market bubble in 2001, many funds found their schemes grossly underfunded and were forced to crystallize their losses by panicked trustees. Consequent tightening of the regulations has made the situation even worse (e.g. all discounting must be done by the much lower AA credit quality bond yield rates in the UK FRS17 standard). As a result many DB schemes have closed and are now being replaced with defined contribution (DC) schemes.y In this world of corporate sponsored DC pension schemes the liability is separated from the sponsor and the market risk is placed on the shoulders of the participants. The scheme is likely to be overseen by an investment consultant and if the scheme invests in funds that perform badly over time a decision may be made by the consultant to move the capital to another fund. However, any losses to the fund will be borne by the participants in the scheme and not by the corporate sponsor. Since at retirement date scheme participants will wish to either purchase an annuity or invest their fund payout in a self-managed portfolio, an obvious need arises in the market place for real return guaranteed schemes which

Atomic force acoustic microscopy is a dynamical AFM-based technique developed for non-destructive characterization of elastic properties of materials at micrometrical and sub-micrometrical scale. A standard AFM apparatus is equipped with a piezoelectric transducer exciting longitudinal oscillations at ultrasonic frequencies in the sample under investigation. Tip–sample contact stiffness is obtained through the values of the measured resonance frequencies of the cantilever contacting the sample surface, thus allowing one to obtain the value of the sample indentation modulus. The paper describes a generalization of the technique: while performing topography, the first and the second contact resonance frequencies are acquired at each point of the scanned area. Data are then properly processed and acoustic images are obtained as a bi-dimensional pattern of the indentation modulus over the imaged samples area. The technique is illustrated in two different kinds of sample: a metallographic (110) GaAs sample, prepared by incorporating GaAs single crystals into an epoxy matrix, and a diamond-like carbon film, deposited on a Mo substrate by laser ablation from a glassy carbon target.

This communication describes the research work plan that is under implementation at the SPARC FEL facility in the framework of the DS4 EUROFEL programme. The main goal of the collaboration is to study and test the amplification and the FEL harmonic generation process of an input seed signal obtained as higher order harmonics generated both in crystals (400 nm and 266 nm) and in gases (266 nm, 160 nm, 114 nm). The SPARC FEL can be con-figured to test several cascaded FEL layouts that will be briefly analysed.

Migration of Kirschner (K) wires from the upper extremity joints has often been reported, but it is less common from the lower extremities. In this report, we describe an 85-year-old man treated, during a hip replacement procedure, with a K-wire because of a trochanteric fracture; after one year, the K-wire was found in the popliteal fossa. This report illustrates the first case of K-wire migration in the popliteal area of the knee and suggests avoiding the use of free K-wires without any tension banding.

The generation of harmonic and subharmonic vibrations is considered in a finite monodimensional structure, as it is produced by the nonlinear acoustic characteristics of the medium. The equation of motion is considered, where a general function of the displacement and its derivatives acts as the forcing term for (sub)harmonic generation and a series of 'selection rules' is found, depending on the sample constrains. The localization of the nonlinear term is also considered that mimics the presence of defects or cracks in the structure, together with the spatial distribution of subharmonic modes. Experimental evidence is given relative to the power law dependence of the harmonic modes vs. the fundamental mode displacement amplitude, and subharmonic mode distribution with hysteretic effects is also reported in a cylindrical sample of piezoelectric material.

We have seen in recent years a significant growth in investment products aimed at investors who are worried about downside potential in the financial markets. One response is a dynamic stochastic optimization model for managing products with nominal or real guarantees. An optimal dynamic portfolio allocation strategy combined with risk management allows an institution to provide the best possible portfolio returns commensurate with clients' risk aversion. Implementation of such an investment strategy is illustrated using real market data and backtested through 1999-2004.

Almost all photosystem I (PSI) complexes from oxygenic photosynthetic organisms contain chlorophylls that absorb at longer wavelength than that of the primary electron donor P700. We demonstrate here that the low-energy pool of chlorophylls in the PSI-LHCI complex from the green alga Chlamydomonas reinhardtii, containing five to six pigments, is significantly blue-shifted (A(max) at 700 nm at 4 K) compared to that in the PSI core preparations from several species of cyanobacteria and in PSI-LHCI particles from higher plants. This makes them almost isoenergetic with the primary donor. However, they keep the other characteristic features of "red" chlorophylls: clear spectral separation from the bulk chlorophylls, big Stokes shift revealing pronounced electron-phonon coupling, and large homogeneous and inhomogeneous broadening of approximately 170 and approximately 310 cm(-1), respectively.

Visible absorption spectra and circular dichroism (CD) of the red absorption band of isolated photosystem II reaction centers were measured at room temperature during progressive bleaching by electrochemical oxidation, in comparison with aerobic photochemical destruction, and with anaerobic photooxidation in the presence of the artificial electron acceptor silicomolybdate. Initially, selective bleaching of peripheral chlorophylls absorbing at 672 nm was obtained by electrochemical oxidation at +0.9 V, whereas little selectivity was observed at higher potentials. Illumination in the presence of silicomolybdate did not cause a bleaching but a spectral broadening of the 672-nm band was observed, apparently in response to the oxidation of carotene. The 672-nm absorption band is shown to exhibit a positive CD, which accounts for the 674-nm shoulder in CD spectra at low temperature. The origin of this CD is discussed in view of the observation that all CD disappears with the 680-nm absorption band during aerobic photodestruction.

Atomic force acoustic microscopy (AFAM) is a dynamical AFM-based technique very promising for nondestructive analysis of local elastic properties of materials. AFAM technique represents a powerful investigation tool in order to retrieve quantitative evaluations of the mechanical parameters, even at nanoscale. The quantitative determination of elastic properties by AFAM technique is strongly influenced by a number of experimental parameters that, at present, are not fully under control. One of such issues is that the quantitative evaluation require the knowledge of the tip geometry effectively contacting the surface during the measurements. We present and discuss an experimental approach able to determine, at first, tip geometry from contact stiffness measurements and, on the basis of the achieved information, to measure sample indentation modulus. The reliability and the accuracy of the technique has been successfully tested on samples (Si, GaAs, and InP) with very well known structural and morphological properties and with indentation modulus widely reported in literature.