Photoacoustic holographic imaging of absorbers embedded in silicone

Light absorbing objects embedded in silicone have been imaged using photoacoustic digital holography. The photoacoustic waves were generated using a pulsed Nd:YAG laser, λ=1064 nm, and pulse length=12 ns. When the waves reached the silicone surface, they were measured optically along a line using a scanning laser vibrometer. The acoustic waves were then digitally reconstructed using a holographic algorithm. The laser vibrometer is proven to be sensitive enough to measure the surface velocity due to photoacoustic waves generated from laser pulses with a fluence allowed for human tissue. It is also shown that combining digital holographic reconstructions for different acoustic wavelengths provides images with suppressed noise and improved depth resolution. The objects are imaged at a depth of 16.5 mm with a depth resolution of 0.5 mm.     

Comparison between infrared and Raman spectroscopic analysis of maturing rabbit cortical bone

The molecular composition of the organic and inorganic matrices of bone undergoes alterations during maturation. The aim of this study was to compare Fourier transform infrared (FT-IR) and near-infrared (NIR) Raman microspectroscopy techniques for characterization of the composition of growing and developing bone from young to skeletally mature rabbits. Moreover, the specificity and differences of the techniques for determining bone composition were clarified. The humeri of female New Zealand White rabbits, with age range from young to skeletally mature animals (four age groups, n = 7 per group), were studied. Spectral peak areas, intensities, and ratios related to organic and inorganic matrices of bone were analyzed and compared between the age groups and between FT-IR and Raman microspectroscopic techniques. Specifically, the degree of mineralization, type-B carbonate substitution, crystallinity of hydroxyapatite (HA), mineral content, and collagen maturity were examined. Significant changes during maturation were observed in various compositional parameters with one or both techniques. Overall, the compositional parameters calculated from the Raman spectra correlated with analogous parameters calculated from the IR spectra. Collagen cross-linking (XLR), as determined through peak fitting and directly from the IR spectra, were highly correlated. The mineral/matrix ratio in the Raman spectra was evaluated with multiple different peaks representing the organic matrix. The results showed high correlation with each other. After comparison with the bone mineral density (BMD) values from micro-computed tomography (micro-CT) imaging measurements and crystal size from XRD measurements, it is suggested that Raman microspectroscopy is more sensitive than FT-IR microspectroscopy for the inorganic matrix of the bone. In the literature, similar spectroscopic parameters obtained with FT-IR and NIR Raman microspectroscopic techniques are often compared. According to the present results, however, caution is required when performing this kind of comparison.     

Online and Offline Algorithms for the Time-Dependent TSP with Time Zones

The time-dependent traveling salesman problem (TDTSP) is a variant of TSP with time-dependent edge costs. We study some restrictions of TDTSP where the number of edge cost changes are limited. We find competitive ratios for online versions of TDTSP. From these we derive polynomial time approximation algorithms for graphs with edge costs one and two. In addition, we present an approximation algorithm for the orienteering problem with edge costs one and two.     

Time stepping finite element analysis of a variable speed synchronous generator with rectifier

Several applications for renewable energy conversion make use of variable speed generators. A conversion from variable frequency to grid frequency is therefore essential. One part of the converter is a rectifier. A rectifier model is presented, which is integrated in a time stepping finite element simulation environment where the generator and circuit equations are solved simultaneously. The model handles bidirectional alternator speeds as the application is a linear generator for ocean wave energy conversion. The rectifier model is extended with a load model, consisting of R, L and E, and simulations show what impact the rectifier has on the generator’s behaviour.     

Influence of molecular tilt angle on the SHG response of pyroelectric liquid crystal polymers

Second harmonic generation in novel pyroelectric liquid crystal polymers (PLCP) made from a series binary mixtures, was studied using 1100 nm as the fundamental wavelength. The PLCPs were prepared by photo-polymerization of binary mixtures of two monomers which exhibit a smectic C^* phase, A2c (4″-(R)-(−)-2-[(10-acrylo-yloxy)decyl]oxy-3-nitrophenyl 4-{4′-[(11-acryloyloxy)-undecyloxy]phenyl}benzoate) and Alb (4″-((R)-(+)-2-octyloxy)-3″-nitrophenyl 4-(4′-(11-acryloyloxy)undecyloxy)-phenyl)-benzoate). The highest d₁₆ and d₂₃ coefficients were found to be in the range 0.65–0.8 pm/V, and differed depending on the detailed preparation of the sample. All cases of polymers formed from the chiral smectic C* phase showed an SHG-signal with no external field present, indicating that polar order became fixed. The SHG-signal was found to increase with the tilt angle of the FLC molecules.     

Cluster formation as a tool for development in Medicon Valley.

Clusters are generally organized in order to stimulate the growth and competitiveness of a region in a particular technological area. They occur in many shapes and forms, and a specific cluster development is the product of a dynamic and interactive process among the key stakeholders in the specific region. Any region seeking to succeed in high-tech fields must have stakeholders that are able to collaborate and innovate across sectors. This approach is achieved by combining the scientific, entrepreneurial, financial, and structural elements into a globally viewed competitive approach that is focused on specific goals. The Medicon Valley, which covers the greater Copenhagen area and the southern tip of Sweden, is born with the task to promote research, innovation, and commercialization across the board and to enhance network formations and knowledge transfer among all the players of Medicon Valley.This paper discusses how cluster formation helped in the development of the medico/human life science research in Medicon Valley which has for its members biotech and medtech companies, major pharmaceutical companies, all the relevant university faculties, hospitals, service providers, and public organizations.     

Damped second-order Rayleigh-Timoshenko semi-infinite beam vibration—an exact complex dynamic member stiffness matrix

A uniform linear semi-infinite beam in a uniform linear ambient medium is studied. The beam performs stationary harmonic damped non-synchronous space vibration in simultaneous tension, torsion, bending and shear. Hysteretic and viscous dampings of the beam material and ambient medium are considered. Four new generalized complex Kolousek functions are derived. A 6 × 6 complex symmetric stiffness matrix is established for a semi-infinite beam member excited at its end by prescribed harmonic translations and rotations which have the same frequency but may be out of phase. This matrix extends the range of application of the so called ‘exact analysis’ of non-proportionally damped built-up beam structures as described in a previous paper by Lundén and Åkesson.¹ Numerical examples are given, including applications of the computer program SFVIBAT-DAMP. Power flows are studied.     

Real-time server-based communication with CAN

This paper investigates the concept of share-driven scheduling of networks using servers with real-time properties. Share-driven scheduling provides fairness and bandwidth isolation between predictable as well as unpredictable streams of messages on the network. The need for this kind of scheduled real-time communication network is high in applications that have requirements on flexibility, both during development for assigning communication bandwidth to different applications, and during run-time to facilitate dynamic addition and removal of system components. We illustrate the share-driven scheduling concept by applying it to the popular controller area network (CAN). We propose a scheduling mechanism that we call simple server-scheduled CAN (S/sup 3/-CAN), for which we also present an associated timing analysis. Additionally, we present a variant of S/sup 3/-CAN called periodic server-scheduled CAN (PS/sup 2/-CAN), which for some network configurations gives lower worst-case response-times than S/sup 3/-CAN. Also for this improvement, a timing analysis is presented. Moreover, we use simulation to evaluate the timing performance of both S/sup 3/-CAN and PS/sup 2/-CAN, comparing them with other scheduling mechanisms.     

Percussion hole drilling of metals with a fourth-harmonic Nd:YAG laser studied by defocused laser speckle correlation

Defocused speckle correlation is introduced as a tool for measuring the response in metal sheets during percussion laser drilling. For this procedure the fourth-harmonic Nd:YAG wavelength (266 nm) was used in pulsed mode. The method provides a cost-efficient and robust alternative to speckle interferometry for the study of the small deformations that appear during laser processing. The accuracy was shown to be of the order of a few tens of microradians for the tilt component that is measured, which translates to a few nanometers in deflection when the component is spatially integrated. In the measurements, deflections in the form of craters as large as 50 nm were detected on the back sides of silver and copper sheets. The diameters of the craters were 300 microm in the silver and 150 microm in the copper sheet; the output diameter of the hole was -5 microm.     

Characterization of micromachined ultrasonic transducers using light diffraction tomography

This paper demonstrates that light diffraction tomography can be used to measure the acoustic field of micromachined ultrasonic transducers (MUT) in cases in which standard methods like hydrophone and microphone measurements fail. Two types of MUTs have been characterized with the method, one air-coupled capacitive MUT (cMUT) and one waterloaded continuous wave (CW) miniature multilayer lead zirconate titanate (PZT) transducer. Light diffraction tomography is an ultrasound measurement method with some special characteristics. Based on the interaction of light and ultrasound, it combines light intensity measurements with tomography algorithms to produce a measurement system. The method offers nonperturbing pressure measurements with high spatial resolution. It has been shown that, under certain circumstances, light diffraction tomography can be used as an absolute pressure measurement method with accuracy in the order of 10% in water and 13% in air. The results show that air-coupled cMUTs in the frequency range of about 1 MHz as well as the extreme near field of a miniaturized CW 10 MHz water-loaded transducer were successfully characterized with light diffraction tomography.