Global noise characteristics of a laser Doppler vibrometer-II. Experiments using beam dynamics

The use of a laser Doppler vibrometer to obtain velocity information from vibrating structures has gained wide acceptance in recent years. Although use of such an instrument can yield a spatially dense matrix of velocity information, several users have noted ‘noise’ at certain points in the spatial field. The technique by which the SLDV system operates results in occasional velocity ‘drop-outs’ which are unidirectional, always estimating the velocity response closer to zero than reality. These ‘drop-out’ areas occur more predominately at points of maximum velocity response with small rotational components. Alternatively, points exhibiting minimum velocity response with large rotational components are less susceptible to the ‘noise’. In this paper, an experiment to visualize the speckle pattern motions received by the photo-detectors during these vibration conditions is presented. Theories regarding the source(s) of the ‘noise’ are developed.     

An unusual phenomenon observed when anodising CP titanium to produce coloured surfaces for jewellery and other decorative uses

The unpredictability of the evenness of colour developed on titanium surfaces for use in jewellery has led to a research project at Central Saint Martin's College of Art and Design (CSM) to investigate the detailed structure of the thin oxide films that produce the interference colours.In the course of some initial investigations an unusual phenomenon was observed when a specific material was anodised. Examination of the anodised surface by scanning electron microscopy (SEM) showed a profusion of flower-like ‘oxide growths’ developed in random orientations from about 30 V with increasing density up to 110 V.In honour of the late Professor Harvey Flower these features are currently referred to as ‘Flower oxides’ or ‘flowers’.Further work is continuing to clarify the nature of these growth features and their structure and composition.     

A spatial filtering technique for improved holographic character recognition

Conventional holographic pattern recognition systems suffer from the disadvantage that, in dealing with highly ordered patterns such as Arabic numerals or the letters of the Roman alphabet it is sometimes impossible to distinguish between patterns with a high degree of similarity (eg the capital letters ‘E’ and ‘F’ or ‘B’ and ‘P’).The present paper analyzes a simple case and shows how the insertion of a suitable spatial filter in the Fourier transform plane can reduce the unwanted cross-correlation signal between dissimilar patterns to zero, without removing the desired auto-correlation signal between similar patterns. Although no attempt is made to generalize the analysis, it seems probable that in cases involving the recognition of a small number of patterns with a strong ‘family resemblance’ a compromise filtering arrangement could be developed which would lead to a substantially improved performance.     

CO2 laser treatment system of tinea pedis

The CO₂ laser treatment system ‘Melase 1000’ has been developed for the treatment of Tinea pedis and the efficacy of the treatment using the system and its optimum irradiation condition are studied. The present system enables us to make the healing time of Tinea pedis treatment far shorter than conventional pharmaceuticals. This is in spite of using heat levels low enough for patients not to feel discomfort. Features offered by the system are a safe-and-easy operation and a stable laser power for a prolonged use. The efficacy of the present therapy is excellent; only two treatments a week for three weeks, i.e. six consecutive treatments, attained an improvement rate of 71.8% in the skin findings and a ‘usefulness’ of 66.2% determined from cases rated as ‘useful’ or ‘better’. The optimum laser irradiation condition for a single treatment found in this experiment is a light fluence of about 3 J/cm² and four laser pulses with a time interval between pulses of 1 s for a typical horny layer thinner than 0.5 mm.     

Progress in neutron diagnostics at JET

In the ITER tokamak, diagnosing the plasma neutron emission will be essential to characterise fusion burning process and determine the performance of the machine. JET, currently the world largest tokamak, is the most suitable test bed for development of the fusion-relevant neutron diagnostics due to its plasma parameters and unique tritium operation capability. Current works aim at improving the spatial and spectral characteristics of the neutron measurements at JET, as well as on technological tasks. The present enhancements of neutron diagnostics and data analyses at JET make-together with new fast particle measuring techniques and tritium retention studies-part of the “burning plasma” diagnostic developments towards reactor-grade fusion facilities.     

Predicting ‘lifetime’ of fibre optics exposed to radiation

Fibre optics communications systems are rapidly replacing ‘wired’ links in a variety of applications. The fibre links have proven to be smaller and lighter than either simple wire or coaxial lines. In addition, the fibre systems are immune to all forms of electrical interference (RFI; EMI; static electricity, etc.). Because of the very nature of the passive fibre lines, electrical disturbances may be considered as part of a benign environment, as contrasted with a hostile counterpart, such as high-energy particle fields which are prevalent in a nuclear reactor or other radiation-producing machine. It is known that nuclear radiation may damage the optical transmission properties of fibre optics waveguides. Described herein is the relationship between radiation flux and subsequent damage to the fibre waveguides. Some data, curves and calculations and supporting references are presented. And, finally, a procedure is given as an aid to predicting the ‘lifetime’ of a fibre optics link when it is exposed to the damaging effects of radiation.     

Linear and nonlinear optical properties of CdSexS1−x microcrystallites

Microcrystals of CdSe_xS_1−x (x≈0.6) with nanometer dimensions have been investigated experimentally by a range of optical techniques. This system of ‘quantum dot’ consists of nanometer sized semiconductor particles embedded within an insulating glass matrix. The existence of microscopic CdSeS crystals within the glass matrix is demonstrated by the observation of Raman scattering from the ‘CdSe-like’ and ‘CdS-like’ LO phonons. The nature of the electronic states within these three dimensionally confined systems is investigated by linear absorption and photoluminescence spectroscopy. The photoluminescence spectra show features which are attributed to direct electron-hole recombination and recombination via states within the ‘blue shifted’ energy gap (which are possibly surface related). Carrier relaxation is also investigated by a pump-probe experiment whereby the absorption is partially bleached by a short pump pulse then probed some variable time later by a delayed probe pulse of much lower intensity. Fast and slow components in the carrier relaxation process are identified, and a relationship is suggested between the carrier relaxation and the features observed in the photoluminescence spectra. The well known ‘photodarkening’ properties of such materials are also investigated by the above techniques.     

Coupling of one-dimensionally confined optical modes in porous silicon: Spectral observation and photonic-quantum-well description

Single and double photonic-quantum-wells (PQWs) have been fabricated, using refractive-index-modulated porous silicon multilayer structures. The one-dimensionally confined optical modes observed are consistent with those calculated using the transfer matrix method. While single PQWs exhibit atom-like discrete spectral features, molecule-like energy level splitting is accessible by combining two single PQWs into a double PQW structure. Similar to an electron in a double-quantum-well structure, the energy separation between the split ‘anti-bonding’ and ‘bonding’ photonic states can be ‘tuned’ by changing the strength of inter-well coupling.     

Red in Estonian popular belief and folk costume

A visit by one of the authors to Estonia, and the discovery that the term ‘red’ was used locally for the colour ‘orange’, led to a detailed study of the colour red in Estonian belief and culture. The study is reported here, together with an interpretation of the red/orange substitution based on Berlin and Kay's model of colour term development in language.     

JET: Preparing the future in fusion

JET (Joint European Torus) is the largest tokamak in the world and the only fusion facility able to operate with Tritium, the fusion fuel, and Beryllium, the ITER first wall material. JET also features the most complete remote handling equipment for invessel maintenance. As a multinational research center, JET provides logistic experience in preparing for operation of the global facility, tokamak ITER.Experiments on JET are focused on ITER-relevant studies, in particular on detailing the operational scenarios (EL My H-modes and advanced regimes), on enhancing the heating systems, on developing diagnostics for burning plasmas etc. Pioneering real-time control techniques have been implemented that maximize performance and minimize internal disturbances of JET plasmas. In helium plasmas, ion cyclotron heating (ICRH) created fast α-particles, mimicking their populations in future burning plasmas. The recent successful Trace Tritium campaign provided important new data on fuel transport. Current enhancements on JET include a new ITER-like ELM-resilient high power ICRH antenna (7 MW) and over twenty new diagnostics that will further extend the JET scientific capabilities and push the facility even closer to the ITER parameters.A special mention is given to the involvement of the fusion experts from Association EURATOM-IPP.CR, who have been actively participating in the collective use of JET facility for more than three years.     

New Developments in the Eight Vertex Model II. Chains of Odd Length

We study the transfer matrix of the 8 vertex model with an odd number of lattice sites N. For systems at the root of unity pointsη=mK/L with m odd the transfer matrix is known to satisfy the famous ‘‘TQ’’ equation where Q(υ) is a specifically known matrix. We demonstrate that the location of the zeroes of this Q(υ) matrix is qualitatively different from the case of evenN and in particular they satisfy a previously unknown equation which is more general than what is often called ‘‘Bethe’s equation.’’ For the case of even m where no Q(υ) matrix is known we demonstrate that there are many states which are not obtained from the formalism of the SOS model but which do satisfy the TQ equation. The ground state for the particular case of η=2K/3 and N odd is investigated in detail.     

Critical ray-like propagation modes along graded-index planar optical waveguides

Graded-index planar optical waveguides and surface compression layers were formed simultaneously in the surface layer of glass plates by ion exchange. A change in the refractometer patterns was observed. Before ion exchange, only a critical ray fringe was observed, but with ion exchange a guided wave fringe appeared on the high effective refractive index side of the ‘critical ray’ fringe, and the number of guided wave fringes increased. The guided wave fringe or fringes were birefringent, whereas the ‘critical ray’ fringe was kept nonbirefringent. It was concluded that the ‘critical ray’ propagated along the bottom of a waveguide, ie at the foot of the refractive index distribution.     

On the environmental decoherence and spin interference in mesoscopic loop structures

Mechanisms of ‘environmental decoherence’ such as surface scattering, Elliot–Yafet process and precession mechanisms, as well as their influence on the spin phase relaxation are considered and compared. It is shown that the ‘spin ballistic’ regime is possible, when the phase relaxation length for the spin part of the wave function (L^(s)) is much greater than the phase relaxation length for the ‘orbital part’ (L^(e)). In the presence of an additional magnetic field, the spin part of the electron's wave function (WF) acquires a phase shift due to additional spin precession about that field. If the structure length L is chosen to be L^(s)>L>L^(e), it is possible to ‘wash out’ the quantum interference related to the phase coherence of the ‘orbital part’ of the WF, retaining at the same time that related to the phase coherence of the spin part and, hence, to reveal corresponding conductance oscillations.     

Optimization of type-II frequency doubling of spatial and temporal limited laser light in nonlinear crystals

Type-II frequency doubling of short Gaussian laser pulses is studied theoretically. The situation is analysed when the group velocity mismatch and the walk-off angle of the interacting waves limit the frequency conversion efficiency. It is shown that with collinear ‘o’ and ‘e’ polarized fundamental waves a temporal and spatial separation of the fundamental beams is necessary to compensate for both effects. Results of the presented model are discussed for KDP crystals.     

The use and misuse of coloured light in the urban environment

The last few years have seen a huge increase in the transfer of coloured architectural lighting, derived from entertainment and theatre, into the urban and exterior environment. Part of the reason for this is that in the last 15 yr or so, there have been a number of important introductions in coloured lighting technology. These have transformed lighting practice, and while their widespread introduction is seen by some as an enrichment of the urban fabric, others see it as presenting considerable dangers, in terms of aesthetics, perception and in terms of civic identity. Its negative effects on the urban environment have been termed ‘colour blight’.In this paper, the range of coloured lighting technologies is surveyed and other causes for the increase in coloured lighting are also discussed, together with the problems and benefits involved. Finally, some tentative means are put forward for resolving the problems caused by ‘colour blight’. Current good practice is illustrated by the author's own experience, including his consultancy's participation in a number of urban lighting strategies in the UK and elsewhere. This work involves implementation of a comprehensive lighting plan for the historic city of York, as part of the Urban Lighting Group consortium of three lighting design practices.     

Interferometric testing of optical aspherical surfaces

This paper explains theoretically the principle of the Talbot interferometer using two ‘Fourier images’. The experimental results show that video techniques are more useful for superimposing two ‘Fourier images’ than photographic techniques.     

Modelling resonances of the standing body exposed to vertical whole-body vibration: Effects of posture

Lumped parameter mathematical models representing anatomical parts of the human body have been developed to represent body motions associated with resonances of the vertical apparent mass and the fore-and-aft cross-axis apparent mass of the human body standing in five different postures: ‘upright’, ‘lordotic’, ‘anterior lean’, ‘knees bent’, and ‘knees more bent’. The inertial and geometric parameters of the models were determined from published anthropometric data. Stiffness and damping parameters were obtained by comparing model responses with experimental data obtained previously.The principal resonance of the vertical apparent mass, and the first peak in the fore-and-aft cross-axis apparent mass, of the standing body in an upright posture (at 5–6 Hz) corresponded to vertical motion of the viscera in phase with the vertical motion of the entire body due to deformation of the tissues at the soles of the feet, with pitch motion of the pelvis out of phase with pitch motion of the upper body above the pelvis. Upward motion of the body was in phase with the forward pitch motion of the pelvis. Changing the posture of the upper body had minor effects on the mode associated with the principal resonances of the apparent mass and cross-axis apparent mass, but the mode changed significantly with bending of the legs. In legs-bent postures, the principal resonance (at about 3 Hz) was attributed to bending of the legs coupled with pitch motion of the pelvis in phase with pitch motion of the upper body. In this mode, extension of the legs was in phase with the forward pitch motion of the upper body and the upward vertical motion of the viscera.     

Radiation effects in concentrated alloys and compounds: equilibrium and kinetics of driven systems

What organization of condensed matter does resist irradiation, as a function of irradiation conditions? How to characterize the latter? We survey the advances in the field during the past three decades, when irradiation effects reduce to nuclear collisions. While in simple cases (structure defined by a scalar order parameter) one may define a stochastic potential, which yields the stationary states of the compounds under irradiation and their respective stability, in more general cases, we are left with brute force atomistic simulations to explore materials' behaviour as a function of irradiation conditions. Special attention is given to the kinetics of concentration fields under irradiation, a question with several practical implications. We conclude that irradiation conditions are best defined by three parameters: the cascade features (number of displacements and replacements, length of replacement sequences, …), the frequency of cascade occurrence, and the cumulated dose. We suggest cascade features be named ‘(elementary) dose’ and the cascade occurrence frequency ‘dose rate’. To cite this article: G. Martin, P. Bellon, C. R. Physique 9 (2008).