Multimodal microscopy using 'half and half' contact mode and ultrasonic force microscopy.

Advances in the design and fabrication of multifunctional nanostructured materials require characterization techniques capable of simultaneously mapping multiple material properties with nanoscale resolution. We show that this can be achieved by combining nanomechanical information from ultrasonic force microscopy (UFM) with simultaneously acquired friction force and conductivity measurements from contact mode scanning. This utilizes a 'half and half' approach, where the AFM is operated alternatively in UFM and contact mode, with the switching rate sufficiently fast that simultaneous contact mode and UFM information is acquired at each pixel of an image. We demonstrate the potential of such a multimodal approach through its application to composite systems consisting of graphene islands on a copper surface, single-walled carbon nanotubes (SWNTs) on a silicon oxide substrate, and a graphene epoxy composite. The half and half approach enables the friction force to be measured without topographical cross-talk. Application to the SWNT sample reveals a further advantage; due to the superlubricity of UFM it enables standard contact mode imaging techniques to be applied to delicate samples.

Polymer-dispersed liquid-crystal coatings for ultrasound visualization: Experiment and theory.

Polymer dispersed liquid crystal (PDLC) films are formed of droplets of liquid crystal (LC) held in a polymer matrix. Similar to aligned LC films, PDLCs exhibit the acousto-optic (AO) effect when excited by acoustic waves of sufficient amplitude, whereby the PDLC film becomes transparent in the excited regions (acoustic clearing). Despite decades of research there is still debate over the mechanisms of the AO effect for the case of LC films, with several competing theories, and AO effects in PDLC have not been studied theoretically. This paper explores the AO effect in PDLC both experimentally and theoretically, and attempts a theoretical description of the observed phenomena based on the theoretical approach by Selinger et al. for aligned LC films. The acousto-optic effect in PDLC is shown to be due to direct interaction of acoustic waves with LC droplets, rather than due to compression of the droplet itself. Polarizing microscopy revealed changes in droplet shape at excited points. This is consistent with reorientation as a contributing factor, possibly coexisting with flows at higher excitation powers. In previous experimental studies PDLC films were prepared with cover slides, in the same way as LC AO cells, significantly limiting applications by adding complexity to the design. Also, to exhibit AO clearing it was considered that the PDLC needed to be prepared with high LC concentrations (over 75% by weight). We demonstrate that no cover slide is necessary, and that PDLC coatings without a cover have improved sensitivity to acoustic waves. We demonstrate the AO effect for LC concentrations as low as 40% by weight. The ability to use standard composition PDLC, with no top cover, is paving the way to paint-on visual ultrasound sensors.

Ultrasonic displacement measurements from local absorption of ultrasound in thermochromic liquid crystal sensors.

Wavefield imaging can be used for measuring the wavefield produced by an ultrasound transducer for medical and industrial applications, or for the detection and monitoring of defects in non-destructive testing. Typical wavefield imaging methods include interferometry/vibrometry, and the use of microphones and hydrophones. These involve scanning, making them time consuming, and microphones have limited resolution. An alternative method presented here uses thermochromic liquid crystal sensors which react to heat generated due to absorption of ultrasonic waves. The result is a colour scale that varies with temperature, with the temperature change dependent on ultrasonic displacement. Measurements of the resonant modes of a flexural ultrasonic transducer were taken between 320 kHz and 6.77 MHz. Temperature maps were obtained from photographs of the TLC sensor using the true-colour image processing method. The obtained temperature change across the transducer face was compared with displacement measurements taken using interferometry, showing excellent agreement in the position of the mode features and good resolution at lower frequencies. Thermal measurements were also taken to directly observe the heating of the transducer cap, showing the effect of the thermal conductivity of the transducer along with confirming the increased heat generated by the ultrasound absorption when a backing layer is used. The sensors show promise for fast transducer characterisation, with further potential applications in structural health monitoring and defect detection.

Acoustic field visualisation using local absorption of ultrasound and thermochromic liquid crystals.

Acoustic field and vibration visualisation is important in a wide range of applications. Laser vibrometry is often used for such visualisation, however, the equipment has a high cost and requires significant user expertise, and the method can be slow, as it requires scanning point by point. Here we suggest a different approach to visualisation of acoustic fields in the kHz - MHz range, using paint-on or removable film sensors, which produce a direct visual map of ultrasound displacement. The sensors are based on a film containing thermochromic liquid crystals (TLC), along with a backing/underlay layer which improves absorption of ultrasound. The absorption generates heat, which can be seen by a change in colour of the TLC film. A removable sensor is used to visualise the resonant modes of an air-coupled flexural transducer operated from 410 kHz to 7.23 MHz, and to visualise 40 kHz standing waves in a Perspex plate. The thermal basis of the visualisation is confirmed using thermal imaging. The speed and cost of visualisation makes the new sensor attractive for use in condition monitoring, for fast assessment of transducer quality, or for analysis of acoustic field distribution in power ultrasonic systems.

The effect of EMAT coil geometry on the Rayleigh wave frequency behaviour.

Understanding of optimal signal generation and frequency content for electromagnetic acoustic transducers (EMATs) is key to improving their design and signal to noise ratio. Linear and meander coil designs are fairly well understood, but other designs such as racetrack or focused coils have recently been proposed. Multiple transmission racetrack coil EMATs, with focused and unfocused designs, were constructed. The optimum driving frequency for maximum detected signal was found to range between 1.1 and 1.4 MHz on aluminium for a 1.5 mm width coil. A simple analytical model based on the instantaneous velocity of a wave predicts a maximum signal at 1.44 MHz. Modelling the detection coil as a spatial square wave agrees with this, and predicts a general relation of fP=0.761v/L between the optimum frequency fP, the wave velocity v, and the coil width L. A time domain model of the detection coil predicts a 1.4-1.5 MHz peak for continuous wave excitation, with a frequency that decreases as the length of the wavepacket is decreased, consistent with the experimental data. Linear coil modelling using the same technique is shown to be consistent with previous work, with improving detection at lower wave frequencies, and signal minima at every integer multiple of the wavelength. Finite Element Analysis (FEA) is used to model the effects of the spatial width of the racetrack generation coil and focused geometry, and no significant difference is found between the focused and the unfocused EMAT response. This highlights the importance of designing the EMAT coil for the correct lift-off and desired frequency of operation.

Depth gauging of defects using low frequency wideband Rayleigh waves.

In non-destructive testing for cracks it is not sufficient to simply detect the presence of a defect, but it is essential to have an accurate measure of the depth. Accurate calibration of the techniques used to gauge defect size is therefore necessary. Recent progress in the field of non-contact ultrasonic testing has led to the development of a practically viable system for generating and detecting wideband Rayleigh waves on electrically conducting or magnetic samples using electro-magnetic acoustic transducers (EMATs). This system has been used to gauge the depth and position of surface breaking defects, and has many applications including metal billet testing and detecting and sizing gauge corner cracking in rails. In this paper we report experiments calibrating the response of EMATs when a defect is present between the generator and receiver, using a calibration sample with slots machined perpendicular to the surface to simulate surface breaking cracks. The depth of the defect can be gauged in the time domain and frequency domain, with an accurate 'fingerprint' of the position given by an enhancement of the signal when the receiver is close to the defect. The best choice of EMAT design for different applications is discussed, as is the best position for the receive EMAT to avoid areas of interference between the Rayleigh wave and bulk waves diffracted from the crack tip.

Characterisation of hidden defects using the near-field ultrasonic enhancement of Lamb waves.

Defects that propagate from the inside of a structure can be difficult to detect by traditional non-destructive inspection methods. A non-contact inspection method is presented here that uses the near-field interactions of ultrasonic Lamb waves to detect defects propagating into a 1.5 mm thick aluminium sheet from the opposite side to that which is inspected. Near-field interactions of the S0 Lamb waves with the defects are shown to give rise to a characteristic increase in the wave magnitude, which is used to position and characterise these hidden defects. It is shown that such defects are difficult to detect from a study of their influence on ultrasonic transmission alone. Single defects of different depths, and systems of multiple defects with varying separations and relative depths, are successfully detected in both experimental trials and FEM simulations. Reliable single defect detection is achieved for defects with a minimum depth of 30% of the plate thickness, and resolution of multiple defects is achieved for defect separations of 5mm.

A comparative study of Ocusert Pilo 40, intensive pilocarpine and low-dose pilocarpine in the initial treatment of primary acute angle-closure glaucoma.

Acetazolamide and pilocarpine have a central role in the initial management of primary acute angle closure glaucoma (PACG), but there is no consensus concerning their mode of delivery, as borne out by a recent survey of senior UK ophthalmologists reported below. Ocusert Pilo 40 was developed to remain in situ releasing pilocarpine for up to one week. In view of its potential advantages, a trial of Ocusert Pilo 40's efficacy in PACG was conducted. In two separate controlled studies, eyes diagnosed with PACG were randomised to receive Ocusert Pilo 40, and either an intensive pilocarpine regimen or a low-dose pilocarpine treatment. All patients also received Diamox 500 mg i.v. Two hours after starting topical treatment, the study was terminated and ocular and systemic response to treatment and the eventual outcome were assessed. In both studies, intravenous Diamox caused a fall of intraocular pressure (IOP) within 30 min. Over the treatment period, a comparable reduction in IOP was seen in the Ocusert-treated, the intensive-pilocarpine-treated, and the low-dose-pilocarpine-treated groups. No damage to the corneas were observed.

Perceptual load in searching for sloping colored lines camouflaged by colored backgrounds: a separate-groups investigation.

Altogether 168 men searched briefly for colored sloping lines embedded in a background of random color. Using a separate-groups experimental design, search for six kinds of target was found to be less effective after practice than search for a single kind of target. Reducing the number of colors of targets from three to one was considerably more beneficial than reducing the number of main directions of slope from two to one. Reducing the number of kinds of target without reducing the number of relevant stimulus values was also found to improve the effectiveness of search, but search was even more effective when the number of relevant stimulus colors was reduced. The results can be predicted from the total number of selection operations required. However, a more precise fit needs to reflect the considerably greater difficulty of searching for a number of directions of slope. When targets were poorly camouflaged, search was equally effective whether there were four colors or only a single color of target to search for.

Behaviour of the fellow eye in acute angle-closure glaucoma.

A retrospective study of 245 fellow eyes of patients admitted in primary acute angle-closure glaucoma (ACG) is presented. Twenty-five (10.2%) had acute ACG in the fellow eye on presentation. Of the remaining 220, 33 (15%) subsequently developed acute ACG before prophylactic surgery was performed. Possible predisposing factors were analysed. The main findings were that acute ACG in the fellow eye occurred most frequently in hospital, or during the first month after discharge if prophylactic surgery was not performed. The instillation of mydriatics in the operated eye increased the risk to the fellow eye. Pilocarpine and carbonic anhydrase inhibitors confer the best protection on the fellow eye, but no medical regimen entirely prevented an attack of acute ACG in the fellow eye.

Trabeculectomy combined with cataract extraction: a follow-up study.

Fifty-nine eyes undergoing combined cataract extraction and trabeculectomy were studied. The follow-up period ranged from 6 months to 2 years. The visual outcome and postoperative control of intraocular pressure have been compared in chronic open-angle, chronic closed-angle, and secondary glaucoma. Good results were obtained in both primary open- and closed-angle glaucoma, but not in secondary glaucoma.

Ophthalmic emergencies in a district general hospital casualty department.

A survey of ophthalmic emergencies attending the casualty department of a district general hospital over a 12-month period is presented. The total number of new casualty attendances was 30,649 of which 1870 (6.1%) presented with an ophthalmic problem. There was a 3 to 1 male to female preponderance and a peak age of presentation between 20 and 30 years. The main aetiological factors were trauma 65.6% and inflammation 21.7%. Of the trauma patients 80% had sustained minor trauma (abrasions or foreign material to the cornea or conjunctiva) and of the patients with inflammation 71% had either conjunctivitis or blepharitis. There was a trend towards increased numbers in the summer months. The percentage of patients with inflammatory disease was higher in the early summer and the winter months. Nine of the 11 patients with acute angle closure glaucoma presented between November and February. All patients were initially seen by the accident and emergency medical staff, who were able to treat 69% without further consultation. No serious pathology was overlooked. It is suggested that, in the district general hospital setting, co-operation between the eye and the accident and emergency departments can be to their mutual benefit.

Superolateral dislocation of the condyle: report of a rare case.

Anterior dislocation of the mandibular condyle is commonly seen in patients with chronic dislocation of their temporomandibular joints. Posterior, superior and lateral dislocation is rare. Superolateral dislocation of an intact condyle, let alone intact mandible is uncommon, usually occurring after a traumatic insult to the mandible. The authors report on such a case, and its management.

Coupling mechanism of an EMAT.

Electro-magnetic acoustic transducers (EMATs) generate ultrasonic waves in metals through an electromagnetic coupling mechanism. A concept for EMAT generation, using a coil alone without a permanent magnet, but with a pulse generator and a sample, is introduced. A simplified equivalent coil circuit is given, and has been validated by experimental measurements. Such an equivalent circuit is useful for excitation current calculations, which have often been neglected in previous publications in this area but have proved to be of great importance in considering the efficiency and frequency characteristics of ultrasonic generation. Due to the coil sample coupling, the equivalent coil inductance is dependent on the electrical conductivity and magnetic permeability of the metal sample, the lift-off, the coil orientation relative to the metal sample and the coil configuration. The use of a coil alone to generate ultrasound has limited applications as a suitable ultrasonic detector must also be used, but where appropriate this type of generation source provides a robust, non-contact and inexpensive means of ultrasonic generation without worrying the permanent magnet attracting ferromagnetic particles that can prevent from practical on-line application of EMATs.

Pulsed Rayleigh wave scattered at a surface crack.

This paper investigates Rayleigh wave interaction with machined slots on flat aluminium blocks to simulate surface breaking cracks. Using a finite element method, Rayleigh wave scattering by narrow slots of varied depth ranging from 0.5 mm to 20 mm is calculated. Pulsed wideband Rayleigh waves with a centre frequency of 590 kHz and -6 dB bandwidth of 520 kHz is considered. Reflection and transmission coefficients are calculated and compare well with the published literature. We and other workers have reported enhancement of the measured amplitude or particle velocity of an apparent Rayleigh wave close to a surface defect. In this paper, it is found that the predicted enhancement of in-plane components of particle velocities close to a crack is significantly higher than that of the out-of-plane components of particle velocities which appears to be mainly due to the mode-converted surface skimming longitudinal wave from the crack that has mainly in-plane components near the sample surface. The enhancement of the in-plane particle velocity will be observed regardless of the type of in-plane sensitive ultrasonic detector used. The explanation of the discrepancy of the reflection and transmission coefficients obtained by pulsed and narrow band or pseudo continuous Rayleigh waves is discussed. The later-arriving Rayleigh waves from reverberation along the inside of the crack surface are observed, as has been previously reported by other workers, and this may also be used to gauge slot depth.

Retinal detachment in retinitis pigmentosa.

Three cases of retinal detachment occurring in patients with retinitis pigmentosa are presented and three previously reported cases reviewed. All the detachments were rhegmatogenous. One patient had a horseshoe tear, one had oral bay tears, two had dialyses, one a giant tear and in one case the break was not specified. Three patients were high myopes. All the patients were young males. The five operable cases all responded satisfactorily to conventional surgery. Histologically apparent adhesions between retinal pigment epithelium and neuroretina have been described in advanced cases of retinitis pigmentosa in older patients and may not be present in younger patients with less advanced disease. Until these adhesions occur patients with retinitis pigmentosa may have no additional protection against retinal detachment.

Definitive spectroscopic determination of the transverse interactions responsible for the magnetic quantum tunneling in Mn(12)-acetate.

We present detailed angle-dependent single crystal electron paramagnetic resonance (EPR) data for field rotations in the hard plane of the S=10 single molecule magnet Mn(12)-acetate. A clear fourfold variation in the resonance positions may be attributed to an intrinsic fourth-order transverse anisotropy (O(4)/(4)). Meanwhile, a fourfold variation of the EPR line shapes confirms a recently proposed model wherein disorder associated with the acetic acid of crystallization induces a locally varying quadratic (rhombic) transverse anisotropy [O (2)/(2) identical with E(S (2)/(x)-S(2)/(y))]. These findings explain most aspects of the magnetic quantum tunneling observed in Mn(12)-acetate.

Quantum coherence in an exchange-coupled dimer of single-molecule magnets.

A multi- high-frequency electron paramagnetic resonance method is used to probe the magnetic excitations of a dimer of single-molecule magnets. The measured spectra display well-resolved quantum transitions involving coherent superposition states of both molecules. The behavior may be understood in terms of an isotropic superexchange coupling between pairs of single-molecule magnets, in analogy with several recently proposed quantum devices based on artificially fabricated quantum dots or clusters. These findings highlight the potential utility of supramolecular chemistry in the design of future quantum devices based on molecular nanomagnets.