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Individuals with developmental prosopagnosia (DP) have severe difficulties recognising familiar faces. A current debate is whether these face recognition impairments derive from problems with face perception and in particular whether individuals with DP cannot utilize holistic representations of individual faces. To assess this hypothesis, we recorded event-related potentials (ERPs) during a sequential face identity matching task where successively presented pairs of upright faces were either identical or differed with respect to their internal features, their external features, or both. Participants with DP and age-matched controls reported on each trial whether the face pair was identical or different. To track the activation of cortical visual face memory representations, we measured N250r components over posterior face-selective regions. N250r components to full face repetitions were strongly attenuated for DPs as compared to control participants, indicating impaired face identity matching processes in DP. In the Control group, the N250r to full face repetitions was superadditive (i.e., larger than the sum of the two N250r components to partial repetitions of external or internal features). This demonstrates that holistic face representations were involved in identity matching processes. In the DP group, N250r components to full and partial identity repetitions were strictly additive, indicating that the identity matching of external and internal features operated in an entirely part-based fashion, without any involvement of holistic representations. In line with this conclusion, DPs also made a disproportionate number of errors on partial repetition trials, where they often failed to report a change of internal facial features. This suggests an atypical strategy for encoding external features as cues to identity in DP. These results provide direct electrophysiological and behavioural evidence for qualitative differences in the representation of face identity in the occipital-temporal face processing system in developmental prosopagnosia.

International audience; We investigated selective impairments of visual identity discrimination in developmental prosopagnosia (DP), using a fast periodic identity oddball stimulation paradigm with electroencephalography (EEG). In Experiment 1, neural responses to unfamiliar face identity changes were strongly attenuated for individuals with DP as compared to Control participants, to the same extent for upright and inverted faces. This reduction of face identity discrimination responses, which was confirmed in Experiment 2, provides direct evidence for deficits in the visual processing of unfamiliar facial identity in DP. Importantly, Experiment 2 demonstrated that DPs showed attenuated neural responses to identity oddballs not only with face images, but also with non-face images (cars). This result strongly suggests that rapid identity-related visual processing impairments in DP are not restricted to faces, but also affect familiar classes of non-face stimuli. Visual discrimination deficits in DP do not appear to be face-specific. To account for these findings, we propose a new account of DP as a domain-general deficit in rapid visual discrimination.

Individuals with developmental prosopagnosia (DP) have severe face recognition deficits, but the mechanisms that are responsible for these deficits have not yet been fully identified. We assessed whether the activation of visual working memory for individual faces is selectively impaired in DP. Twelve DPs and twelve age-matched control participants were tested in a task where they reported whether successively presented faces showed the same or two different individuals, and another task where they judged whether the faces showed the same or different facial expressions. Repetitions versus changes of the other currently irrelevant attribute were varied independently. DPs showed impaired performance in the identity task, but performed at the same level as controls in the expression task. An electrophysiological marker for the activation of visual face memory by identity matches (N250r component) was strongly attenuated in the DP group, and the size of this attenuation was correlated with poor performance in a standardized face recognition test. Results demonstrate an identity-specific deficit of visual face memory in DPs. Their reduced sensitivity to identity matches in the presence of other image changes could result from earlier deficits in the perceptual extraction of image-invariant visual identity cues from face images.

Geskin & Behrmann provide an extensive and scholarly meta-analysis of the extant cases of developmental prosopagnosia (DP) in order to ascertain how often impairments in face recognition and object...

Developmental prosopagnosia (DP) is a severe impairment of visual face recognition in the absence of any apparent brain damage. The factors responsible for DP have not yet been fully identified. This article provides a selective review of recent studies investigating cognitive and neural processes that may contribute to the face recognition deficits in DP, focusing primarily on event-related brain potential (ERP) measures of face perception and recognition. Studies that measured the face-sensitive N170 component as a marker of perceptual face processing have shown that the perceptual discrimination between faces and non-face objects is intact in DP. Other N170 studies suggest that faces are not represented in the typical fashion in DP. Individuals with DP appear to have specific difficulties in processing spatial and contrast deviations from canonical upright visual–perceptual face templates. The rapid detection of emotional facial expressions appears to be unaffected in DP. ERP studies of the activation of visual memory for individual faces and of the explicit identification of particular individuals have revealed differences between DPs and controls in the timing of these processes and in the links between visual face memory and explicit face recognition. These observations suggest that the speed and efficiency of information propagation through the cortical face network is altered in DP. The nature of the perceptual impairments in DP suggests that atypical visual experience with the eye region of faces over development may be an important contributing factor to DP.

Three experiments are presented that investigate the two-dimensional valence/trustworthiness by dominance model of social inferences from faces (Oosterhof & Todorov, 2008). Experiment 1 used image averaging and morphing techniques to demonstrate that consistent facial cues subserve a range of social inferences, even in a highly variable sample of 1000 ambient images (images that are intended to be representative of those encountered in everyday life, see Jenkins, White, Van Montfort, & Burton, 2011). Experiment 2 then tested Oosterhof and Todorov’s two-dimensional model on this extensive sample of face images. The original two dimensions were replicated and a novel ‘youthful-attractiveness’ factor also emerged. Experiment 3 successfully cross-validated the three-dimensional model using face averages directly constructed from the factor scores. These findings highlight the utility of the original trustworthiness and dominance dimensions, but also underscore the need to utilise varied face stimuli: with a more realistically diverse set of face images, social inferences from faces show a more elaborate underlying structure than hitherto suggested.

It is often assumed that upright faces are represented in a holistic fashion, while representations of inverted faces are essentially part-based. To assess this hypothesis, we recorded event-related potentials (ERPs) during a sequential face identity matching task where successively presented pairs of upright or inverted faces were either identical or differed with respect to their internal features, their external features, or both. Participants' task was to report on each trial whether the face pair was identical or different. To track the activation of visual face memory representations, we measured N250r components that emerge over posterior face-selective regions during the activation of visual face memory representations by a successful identity match. N250r components to full identity repetitions were smaller and emerged later for inverted as compared to upright faces, demonstrating that image inversion impairs face identity matching processes. For upright faces, N250r components were also elicited by partial repetitions of external or internal features, which suggest that the underlying identity matching processes are not exclusively based on non-decomposable holistic representations. However, the N250r to full identity repetitions was super-additive (i.e., larger than the sum of the two N250r components to partial repetitions of external or internal features) for upright faces, demonstrating that holistic representations were involved in identity matching processes. For inverted faces, N250r components to full and partial identity repetitions were strictly additive, indicating that the identity matching of external and internal features operated in an entirely part-based fashion. These results provide new electrophysiological evidence for qualitative differences between representations of upright and inverted faces in the occipital-temporal face processing system.

Contrast-related signals from the eye region are known to be important for the processing of facial identity. Individuals with developmental prosopagnosia (DP) have severe face recognition problems, which may be linked to deficits in the perceptual processing of identity-related information from the eyes. We tested this hypothesis by measuring N170 components in DP participants and age-matched controls in response to face images where the contrast polarity of the eyes and of other face parts was independently manipulated. In different trials, participants fixated either the eye region or the lower part of a face. In the Control group, contrast-reversal of the eyes resulted in enhanced and delayed N170 components, irrespective of the contrast of other face parts and of gaze location. In the DP group, these effects of eye contrast on N170 amplitudes were strongly and significantly reduced, demonstrating that perceptual face processing in DP is less well tuned to contrast information from the eye region. Inverting the contrast of other parts of the face affected N170 amplitudes only when fixation was outside the eye region. This effect did not differ between the two groups, indicating that DPs are not generally insensitive to the contrast polarity of face images. These results provide new evidence that a selective deficit in detecting and analysing identity-related information provided by contrast signals from the eye region may contribute to the face recognition impairment in DP.

Based on a categorization of simulation and gaming barriers developed in a previous study, this work seeks to explore in greater depth the composition and nature of these obstacles. It examines the interrelationships between the barriers and the impact of other contextual factors in the pedagogic environment. A series of in-depth interviews were conducted with 11 staff involved in teaching with simulations and games within a UK higher education institution. The findings underline the significant linkages apparent between three broad barriers to teaching with simulations, games and role-play: suitability, resource and risk. Further analysis of the interview transcripts facilitated the identification of a range of mechanisms which may be employed to overcome the aforementioned barriers: freeing up academics’ time, providing training and development, enabling informal learning, providing resource support, facilitating access to networks and providing access to secondary information sources. These mechanisms are discussed and evaluated in relation to the broader educational context.

It is frequently assumed that facial identity and facial expression are analysed in functionally and anatomically distinct streams within the core visual face processing system. To investigate whether expression and identity interact during the visual processing of faces, we employed a sequential matching procedure where participants compared either the identity or the expression of two successively presented faces, and ignored the other irrelevant dimension. Repetitions versus changes of facial identity and expression were varied independently across trials, and event-related potentials (ERPs) were recorded during task performance. Irrelevant facial identity and irrelevant expression both interfered with performance in the expression and identity matching tasks. These symmetrical interference effects show that neither identity nor expression can be selectively ignored during face matching, and suggest that they are not processed independently. N250r components to identity repetitions that reflect identity matching mechanisms in face-selective visual cortex were delayed and attenuated when there was an expression change, demonstrating that facial expression interferes with visual identity matching. These findings provide new evidence for interactions between facial identity and expression within the core visual processing system, and question the hypothesis that these two attributes are processed independently.

Individuals with developmental prosopagnosia (DP) are strongly impaired in recognizing faces, but the causes of this deficit are not well understood. We employed event-related brain potentials (ERPs) to study the time-course of neural processes involved in the recognition of previously unfamiliar faces in DPs and in age-matched control participants with normal face recognition abilities. Faces of different individuals were presented sequentially in one of three possible views, and participants had to detect a specific Target Face (“Joe”). EEG was recorded during task performance to Target Faces, Nontarget Faces, or the participants' Own Face (which had to be ignored).\ud \ud The N250 component was measured as a marker of the match between a seen face and a stored representation in visual face memory. The subsequent P600f was measured as an index of attentional processes associated with the conscious awareness and recognition of a particular face. Target Faces elicited reliable N250 and P600f in the DP group, but both of these components emerged later in DPs than in control participants. This shows that the activation of visual face memory for previously unknown learned faces and the subsequent attentional processing and conscious recognition of these faces are delayed in DP. N250 and P600f components to Own Faces did not differ between the two groups, indicating that the processing of long-term familiar faces is less affected in DP. However, P600f components to Own Faces were absent in two participants with DP who failed to recognize their Own Face during the experiment. These results provide new evidence that face recognition deficits in DP may be linked to a delayed activation of visual face memory and explicit identity recognition mechanisms.

Misidentifications are a common phenomenon in unfamiliar face processing, but little is known about the underlying cognitive and neural mechanisms. We used the face identity-sensitive N250r component of the event-related brain potential as a measure of identity-sensitive face matching process in visual working memory. Two face images were presented in rapid succession, and participants had to judge whether they showed the same or two different individuals. Identity match and mismatch trials were presented in random sequence. On similar mismatch trials, perceptually similar faces of two different individuals were shown, while two physically distinct faces were presented on dissimilar mismatch trials. Misidentification errors occurred on 40% of all similar mismatch trials. N250r components were elicited not only in response to an identity match, but also on trials with misidentification errors. This misidentification N250r was smaller and emerged later than the N250r to correctly detected identity repetitions. Importantly, N250r components were entirely eliminated on similar mismatch trials where participants correctly reported two different facial identities. Results show that misidentification errors are not primarily a post-perceptual decision-related phenomenon, but are generated during early visual stages of identity-related face processing. Misidentification errors occur when stored representations of a particular individual face in visual working memory are incorrectly activated by a perceptual match with a different face.

Face recognition is known to be impaired when the contrast polarity of the eyes is inverted. We studied how contrast affects early perceptual face processing by measuring the face-sensitive N170 component to face images when the contrast of the eyes and of the rest of the face was independently manipulated. Fixation was either located on the eye region or on the lower part of a face. Contrast-reversal of the eyes triggered delayed and enhanced N170 components independently of the contrast of other face parts, and regardless of gaze location. Similar N170 modulations were observed when the rest of a face was contrast-inverted, but only when gaze was directed away from the eyes. Results demonstrate that the contrast of the eyes and of other face parts can both affect face perception, but that the contrast polarity of the eye region has a privileged role during early stages of face processing.

The capacity of visual working memory for faces is extremely limited, but the reasons for these limitations remain unknown. We employed event-related brain potential (ERP) measures to demonstrate that individual faces have to be focally attended in order to be maintained in working memory, and that attention is allocated to only a single face at a time. When two faces have to be memorized simultaneously in a face identity matching task, the focus of spatial attention during encoding predicts which of these faces can be successfully maintained in working memory and matched to a subsequent test face. We also show that memory representations of attended faces are maintained in a position-dependent fashion. These findings demonstrate that the limited capacity of face memory is directly linked to capacity limits of spatial attention during the encoding and maintenance of individual face representations. We suggest that the capacity and distribution of selective spatial attention is a dynamic resource that constrains the capacity and fidelity of working memory for faces.

Individuals with developmental prosopagnosia (DP) are strongly impaired in recognizing faces, but it is controversial whether this deficit is linked to atypical visual-perceptual face processing mechanisms. Previous behavioural studies have suggested that face perception in DP might be less sensitive to the canonical spatial configuration of face parts in upright faces. To test this prediction, we recorded event-related brain potentials (ERPs) to intact upright faces and to faces with spatially scrambled parts (eyes, nose, and mouth) in a group of ten participants with DP and a group of ten age-matched control participants with normal face recognition abilities. The face-sensitive N170 component and the vertex positive potential (VPP) were both enhanced and delayed for scrambled as compared to intact faces in the control group. In contrast, N170 and VPP amplitude enhancements to scrambled faces were absent in the DP group. For control participants, the N170 to scrambled faces was also sensitive to feature locations, with larger and delayed N170 components contralateral to the side where all features appeared in a non-canonical position. No such differences were present in the DP group. These findings suggest that spatial templates of the prototypical feature locations within an upright face are selectively impaired in DP.

High-level visual object processing is often assumed to be largely position-independent. Here we demonstrate that when faces and non-face objects simultaneously appear in opposite visual hemifields, the face-sensitive N170 component of the event-related brain potential (ERP) is exclusively generated in the contralateral hemisphere. The effects of face inversion on N170 amplitudes and latencies also show strong contralateral biases. These results reveal that retinotopic biases in low-level visual cortex extend well into category-selective high-level vision. We suggest that the contralateral organisation of face-sensitive visual processing results from generic competitive interactions between hemispheres during the simultaneous perception of visual objects.

This article explores the use of simulations and games in tertiary education. It examines the extent to which academics use different simulation-based teaching approaches and how they perceive the barriers to adopting such techniques. Following a review of the extant literature, a typology of simulations is constructed. A staff survey within a UK higher education (HE) institution is conducted to investigate the use of the different approaches identified within the typology. The findings show significant levels of use of both computer and non-computer-based simulations and games. The main barrier to teaching with simulations, as perceived by the respondents, is the availability of resources. However, further analysis indicates that use of simulations is not associated with perceptions of resource issues, but rather is influenced by views on the suitability of, and risk attached to, such learning methods. The study concludes by recommending improved promotion of simulation-based teaching through enhanced information provision on the various techniques available and their application across subject areas.

Low power, storage liquid crystal displays are of interest in the foreseeable future in portable applications. The use of a bistable twisted namatic (BTN) mode in a true storage device requires long term bistability of its operating states since it is intrinsically a metastable device. Two novel isolation techniques are described and demonstrated to isolate and stabilize the operating states in a BTN device. Existing limitations are highlighted and further areas for research suggested.

Earlier works have discussed addressing schemes for switching Bistable twisted nematic (BTN) liquid crystal displays (LCD) with continued refresh, for video rate displays. This paper presents a novel storage-addressing scheme for the BTN mode.

It is well known that the operating state (e.g. bend or V state) of a pi-cell must be nucleated prior to operation. For direct view liquid crystal display applications, such as direct view TV, low voltage nucleation of the operating state is necessary. A brief description of existing nucleation techniques is presented, followed by a detailed consideration of three low voltage nucleation techniques. The concept behind these techniques and their observed performance is described. Possible areas for further work are included.

Individuals with developmental prosopagnosia (DP) have a severe difficulty recognizing the faces of known individuals in the absence of any history of neurological damage. These recognition problems may be linked to selective deficits in the holistic/configural processing of faces. We used two-tone Mooney images to study the processing of faces versus non-face objects in DP when it is based on holistic information (or the facial gestalt) in the absence of obvious local cues about facial features. A rapid adaptation procedure was employed for a group of 16 DPs. Naturalistic photographs of upright faces were preceded by upright or inverted Mooney faces or by Mooney houses. DPs showed face-sensitive N170 components in response to Mooney faces versus houses, and N170 amplitude reductions for inverted as compared to upright Mooney faces. They also showed the typical pattern of N170 adaptation effects, with reduced N170 components when upright naturalistic test faces were preceded by upright Mooney faces, demonstrating that the perception of Mooney and naturalistic faces recruits shared neural populations. Our findings demonstrate that individuals with DP can utilize global information about face configurations for categorical discriminations between faces and non-face objects, and suggest that face processing deficits emerge primarily at more fine-grained higher level stages of face perception.

We discuss the role of the Miesowicz viscosities on director reorientation in pi-cells, showing that the symmetry of this system allows for a simplification of the dynamical equations. We consider practical aspects of material optimisation for increased pi-cell switching speed. We make an observation regarding the switching speeds of positive and negative dielectric anisotropy surface mode devices.

In this paper we present a theoretical analysis of shear induced melting in smectic A liquid crystals. We have performed a detailed numerical analysis and find that for a range of parameter values a first order transition, from a supersheared state to a more relaxed state, is periodically encountered as the total shear is increased. This first order transition involves the melting and reformation of the smectic layers. In this paper we present a summary of this analysis while a more detailed analysis, including analytic expressions for certain critical quantities, is presented elsewhere.

The role of surface tilt in the operation of pi-cells (OCB) is discussed. We show the effect of tilt on the relative stability of the H and V states, the switching characteristics and the domain growth speed. We further study the effects of temperature and cell thickness on the domain growth.

The influence of an asymmetric periodic grooved cell surface on the 2D static director configuration of a nematic liquid crystal has been investigated. The minimum in the Frank-Oseen free energy was solved numerically with the Rapini-Papoular form of the surface anchoring energy at the nematic-grating interface. Results are presented for the variation of pretilt angle in the tilted bulk director field as a function of the surface groove depth, pitch and asymmetry and the bulk parameters. The simulations demonstrate the existence of two energetically degenerate high and low pretilted bulk alignment configurations. The pretilt values in these two regimes and also for the low tilt regime with finite surface anchoring are consistent with experimental results. An effective increase in the resolution of the model is obtained by using an irregular grid to describe the surface profile.

Mukai and Nakagawa have predicted that hairpin and lightning defects correspond to compressive and dilative regions in the smetic C layer structure. Walton et al. have previously used the Helfrich-...

We consider a chiral smectic C liquid crystal confined between parallel plates in the bookshelf geometry. Using a recently proposed continuum theory for such materials the behaviour of the cell is discussed when an electric field is applied and subsequently removed from the cell. We examine both symmetric and asymmetric boundary conditions for the director.

A new method is proposed to assess the switching characteristics of chiral Smectic C mixtures. In this method the minimum in the τ-V curve (Vmin) is measured as a function of the stabilizing AC field and is fitted to an approximate analytical function derived from the uniform switching model of Towler et al. This procedure provides a value for Vmin at infinite AC field stabilization, which gives a cell-independent quantity, allowing improved comparison between materials.

A homeotropically aligned layer of smectic C liquid crystal has been studied using optical excitation of half leaky guided modes. Under the application of an AC voltage, the director configuration changes over a time-scale of the order of seconds. Fitting model results to the recorded angle dependent reflectivity data indicates firstly a change of tilt angle of the primary director, suggesting perhaps a layer tilt, and secondly a reduction of the imaginary part of the optical permittivity, implying a suppression of fluctuations. There is no evidence for a Helfrich-like deformation in the liquid crystal layer. Detailed analysis finally shows that the results are correctly interpreted as an increase in cone angle, not layer tilt, with field. Then from the fitted data, the change of tilt angle with field is obtained and hence information on the mean-field theory parameters.

Individuals with developmental prosopagnosia (DP) show severe face recognition deficits in the absence of any history of neurological damage. To examine the time-course of face processing in DP, we measured the face-sensitive N170 component of the event-related brain potential (ERP) in a group of 16 participants with DP and 16 age-matched control participants. Reliable enhancements of N170 amplitudes in response to upright faces relative to houses were found for the DP group. This effect was equivalent in size to the effect observed for controls, demonstrating normal face-sensitivity of the N170 component in DP. Face inversion enhanced N170 amplitudes in the control group, but not for DPs, suggesting that many DPs do not differentiate between upright and inverted faces in the typical manner. These N170 face inversion effects were present for younger but not older controls, while they were absent for both younger and older DPs. Results suggest that the early face-sensitivity of visual processing is preserved in most individuals with DP, but that the face processing system in many DPs is not selectively tuned to the canonical upright orientation of faces.

People with developmental prosopagnosia (DP) show severe face-recognition deficits that typically emerge during childhood without history of neurological damage. We review findings from recent event-related brain potential (ERP) studies of face perception and face recognition in DP. The generic face-sensitivity of the N170 component is present in most DPs, suggesting rapid category-selective streaming of facial information. In contrast, DPs show atypical N170 face inversion effects, indicative of impaired structural encoding, specifically for upright faces. In line with neurodevelopmental accounts of DP, these effects are similar to those observed for other developmental disorders, as well as for younger children and older adults. Identity-sensitive ERP components (N250, P600f) triggered during successful face recognition are similar for DPs and control participants, indicating that the same mechanisms are active in both groups. The presence of covert face-recognition effects for the N250 component suggests that visual face memory and semantic memory can become disconnected in some individuals with DP. The implications of these results for neuropsychological and neurodevelopmental perspectives on DP are discussed.

Neuropsychological and neuroimaging studies have demonstrated a role for the amygdala in processing the perceived trustworthiness of faces, but it remains uncertain whether its responses are linear (with the greatest response to the least trustworthy-looking faces), or quadratic (with increased fMRI signal for the dimension extremes). It is also unclear whether the trustworthiness of the stimuli is crucial or if the same response pattern can be found for faces varying along other dimensions. In addition, the responses to perceived trustworthiness of face-selective regions other than the amygdala are seldom reported. The present study addressed these issues using a novel set of stimuli created through computer image-manipulation both to maximise the presence of naturally occurring cues that underpin trustworthiness judgments and to allow systematic manipulation of these cues. With a block-design fMRI paradigm, we investigated neural responses to computer-manipulated trustworthiness in the amygdala and core face-selective regions in the occipital and temporal lobes. We asked whether the activation pattern is specific for differences in trustworthiness or whether it would also track variation along an orthogonal male-female gender dimension. The main findings were quadratic responses to changes in both trustworthiness and gender in all regions. These results are consistent with the idea that face-responsive brain regions are sensitive to face distinctiveness as well as the social meaning of the face features. © 2012 Elsevier Ltd.

The operation of ferroelectric liquid crystal displays depends strongly on the material properties and the electrical addressing method. Fast, high-contrast displays with high levels of multiplexing and wide operating ranges are possible using materials showing a minimum in their response time-voltage characteristic operated with JOERS/Alvety and related drive schemes. These utilize materials with significant dielectric biaxialities and relatively low values of the ferroelectric polarization so that a minimum is observed in the switching characteristic. The route for material improvement is explored.

Using a simple uniform switching model, we investigate the behaviour of the voltage dependent switching time of surface stabilized ferroelectric liquid crystals as a function of the biaxial permittivity tensor and the layer tilt angle. We show that the dielectric biaxiality can markedly effect the response time (τ) of the device and is the origin of the minimum in τ as a function of voltage (V) in tilted layer systems. The dielectric biaxiality should, therefore, be optimized for multiplexing schemes which use the τ—V minimum.

Ferroelectric liquid crystal displays offer an attractive matrix addressed alternative for complex displays. However, their potential can only be realised by using novel addressing schemes suitable for the fast responding, DC sensitive, ferroelectric electro-optic effect. Over a period of several years, a high performance, novel, ferroelectric drive scheme1 has been developed in a UK, JOERS/Alvey funded, collaborative programme. The JOERS/Alvey drive scheme is based on monopulse strobe waveforms2,3,4 and utilises the response time - voltage minimum5,6 found in certain materials. Using this novel drive scheme, complex ferroelectric displays with a high contrast ratio, wide operating range and fast addressing times have been made7,8,9,10 The JOERS/Alvey drive scheme is described, compared with other published drive schemes, and the operating principles discussed.

Surface stabilised ferroelectric liquid crystals (SSFLC) provide fast, bistable, optical modulators suitable for display and other applications. The effect of surface alignments and the resulting director profiles are not fully understood, but can be probed by studying the wavelength dependent optical transmission properties. 5° and 30° evaporated SiO alignments are investigated and it is shown that the surface pretilt affects markedly the director profile.

The dielectric biaxiality of SCE13, a commercially available ferroelectric liquid crystal (FLC) mixture, has been measured. The results have been used to compare theoretically predicted AC field stabilization effects and the voltages for response time minima with experiment.

In thin layers of aligned smectic C materials, the balance between surface and bulk elastic forces within the confine of the chevron layer geometry led to the proposal for a triangular director profile (TDP), and an understanding of the director profile in parallel aligned low tilt cells. We have measured the wavelength dependent extinction angles of high tilt cells fabricated using 5° SiO alignment, and offer a qualitative explanation based on the TDP. We conclude that the differences in the extinction angles at wavelengths around λ = Δd are a useful probe of the SC director profile.

AC field stabilisation of ferroelectric SC* liquid crystals with the chevron layer geometry requires that there is a significant dielectric biaxiality.1,2 To investigate this, the electric permittivities of an SC host mixture based on the phenyl pyrimidines and exhibiting an N-SA-SC phase sequence are reported. A large relaxation of e∥ occurred, which caused a sign reversal of the dielectric anisotropy with a crossover frequency of 25 kHz at 25°C. The host electro-optic behaviour was then characterised using extinction angle measurements as a function of applied voltage at frequencies corresponding to Δ≈ > 0, Δe ≈ 0 and δe < 0, and the results explained using a tilted layer model with a biaxial dielectric tensor. The magnitude of the SC dielectric biaxiality, the layer tilt angle in the planar homogeneous geometry and the cone angle are determined. Measurements for several other hosts commonly used in commercial FLC mixtures are reported and it is shown that in each case the dielectric biaxiality...

The optical behaviour of surface-stabilized ferroelectric liquid crystal samples cannot be described using a uniform director profile. The simplest model based on the chevron layer structure and the surface alignment is a triangular director profile. Analytical expressions for the resulting transmitted light were calculated using the Jones matrix formalism and fitted to experimental data results of a smectic-C host made using an optical multichannel analyser (OMA). This simple model gives an excellent fit, with results that are consistent with X-ray measurements of the chevron structure.

The ‘anomalous’ switching behaviour of Sc * liquid crystals has been reported both theoretically and experimentally. These FLCs show a minimum in switching time (τ) at sufficiently high fields. Although in many cases the simple uniform switching model successfully predicts the electric field for which τ attains a minimum, for other materials the switching time is found to decrease monotonically with increasing applied voltage. We discuss the inadequacies of the uniform switching model and then proceed to describe our early attempts to develop a non-uniform model. We consider the E-field variation through the cell and also the effect of introducing asymmetry into the system. At all times we use the bookshelf geometry.

This paper will describe areas where there has been government and industry cooperation in the development of new simulation modeling tools that are being applied in the development of flight procedures and airport standards. This paper will provide information on where there has been successful application of some of these tools to design problems that are international and domestic in scope and where there are needs for further development and application from the aerospace research community.

A mixture of a ferroelectric or anti-ferroelectric liquid crystal material and a monomer having a single photopolymeric functional group is injected in the space between two electrode substrates while heat is applied. After cooling of the mixture it is irradiated with ultraviolet light at a temperature at which the liquid crystal material remains in the smectic phase so as to polymerise the monomer. Areas of liquid crystal material requiring different threshold voltages for switching are thereby produced. Alternatively such areas can be produced by changing the conditions applied to a mixture of liquid crystal material with a suitable dopant so as to cause separation of the dopant out of the liquid crystal material in order to provide a polarity of nucleation points for controlling domain formation within the liquid crystal material. Such control of domain formation can be used to provide greyscale in a liquid crystal device.

A numerical and analytical analysis of shear-induced melting in smectic-A liquid crystals is presented. Based on a Landau expansion of the complex smectic order parameter, equations governing the phase and amplitude of the local density modulation are found. Numerically solving these equations indicates that for a range of parameter values a first-order transition, from a shear-stressed to a more relaxed state, is periodically encountered as the total shear is increased. Suitable approximations allow the analytic determination of certain characteristics of this first-order transition.