An automated calibration method for non-see-through head mounted displays

Accurate calibration of a head mounted display (HMD) is essential both for research on the visual system and for realistic interaction with virtual objects. Yet, existing calibration methods are time consuming and depend on human judgements, making them error prone. The methods are also limited to optical see-through HMDs. Building on our existing HMD calibration method [1], we show here how it is possible to calibrate a non-see-through HMD. A camera is placed inside an HMD displaying an image of a regular grid, which is captured by the camera. The HMD is then removed and the camera, which remains fixed in position, is used to capture images of a tracked calibration object in various positions. The locations of image features on the calibration object are then re-expressed in relation to the HMD grid. This allows established camera calibration techniques to be used to recover estimates of the display’s intrinsic parameters (width, height, focal length) and extrinsic parameters (optic centre and orientation of the principal ray). We calibrated a HMD in this manner in both see-through and in non-see-through modes and report the magnitude of the errors between real image features and reprojected features. Our calibration method produces low reprojection errors and involves no error-prone human measurements.

Pupal parasitoid attack influences the relative fitness of Drosophila that have encapsulated larval parasitoids

1. The evolution of host resistance to parasitoid attack will be constrained by two factors: the costs of the ability to defend against attack, and the costs of surviving actual attack. These factors have been investigated using Drosophila melanogaster and its parasitoids as a model system. The costs of defensive ability are expressed as a trade-off with larval competitive ability, whereas the costs of actual defence are exhibited in terms of reduced adult fecundity and size. 2. The costs of actual defence may be ameliorated by the host-choice decisions made by Pachycrepoideus vindemiae, a pupal parasitoid. If larvae that have successfully encapsulated a parasitoid develop into poorer quality hosts, then these may be rejected by ovipositing pupal parasitoids. 3. Pupae developing from larvae that have encapsulated the parasitoid Asobara tabida are smaller and have relatively thinner puparia. Thinner puparia are likely to be associated with a reduction in mechanical strength and possibly with a decrease in desiccation tolerance. 4. Pachycrepoideus vindemiae that develop in capsule-bearing pupae are smaller than those that emerge from previously unattacked hosts. This supports the prediction that ovipositing female P. vindemiae should avoid attacking capsule-bearing hosts. However, in choice experiments with 1-day-old pupae, P. vindemiae females oviposited preferentially in hosts containing a capsule, whereas there was no preference found with 4-day-old hosts. This appears to be a maladaptive host choice decision, as the female pupal parasitoids are preferentially attacking hosts that will result in a reduction of their own fitness. 5. The increased likelihood of attack by a pupal parasitoid is another cost of actual defence against larval parasitoid attack.

The relative fitness of Drosophila melanogaster (Diptera, Drosophilidae) that have successfully defended themselves against the parasitoid Asobara tabida (Hymenoptera, Braconidae)

Drosophila melanogaster larvae defend themselves against parasitoid attack via the process of encapsulation. However, flies that successfully defend them selves have reduced fitness as adults. Adults which carry an encapsulated parasitoid egg are smaller and females produce significantly fewer eggs than controls. Capsule-bearing males allowed repeated copulations with females do not show a reduction in their number of offspring, but those allowed to copulate only once did. No differences were found in time to first oviposition in females, or in time to first copulation in males. We interpret the results as arising from a trade-off between investing resources in factors promoting fecundity and mating success, and in defence against parasitism. The outcome of this investment decision influences the strength of selection for defence against parasitism.

Habitat associations and breeding bird community composition within the city of Bristol, UK

Capsule: Different urban breeding bird communities are associated with different habitat types, but, although community species diversity varies significantly, total bird density does not. Aims: To investigate the association between breeding bird communities and habitats within Bristol, UK and how these communities vary in terms of species diversity and total bird abundance. Methods: Breeding density data for 70 species in the metropolitan area of Bristol, UK were subjected to de-trended correspondence analysis to identify the number of different communities present and their indicator species. These data were then used to identify patterns of habitat association with each community and differences in species richness and total bird density. Results: Three communities were identified: a rural community associated with woodland, managed grassland and inland water; a suburban community associated with buildings and residential gardens; and an intermediate community that shared some of these habitat characteristics. Species richness, but not total bird abundance, was lowest in the suburban community. Conclusion: The diversity of species in urban areas appears to be most dependent upon the availability of patches of natural and semi-natural habitats. Residential gardens support fewer species, but those species that are present may be found at high densities.

Conserved hydrophobic clusters on the surface of the Caf1A usher C-terminal domain are important for F1 antigen assembly

The outer membrane usher protein Caf1A of the plague pathogen Yersinia pestis is responsible for the assembly of a major surface antigen, the F1 capsule. The F1 capsule is mainly formed by thin linear polymers of Caf1 (capsular antigen fraction 1) protein subunits. The Caf1A usher promotes polymerization of subunits and secretion of growing polymers to the cell surface. The usher monomer (811 aa, 90.5 kDa) consists of a large transmembrane β-barrel that forms a secretion channel and three soluble domains. The periplasmic N-terminal domain binds chaperone-subunit complexes supplying new subunits for the growing fiber. The middle domain, which is structurally similar to Caf1 and other fimbrial subunits, serves as a plug that regulates the permeability of the usher. Here we describe the identification, characterization, and crystal structure of the Caf1A usher C-terminal domain (Caf1A(C)). Caf1A(C) is shown to be a periplasmic domain with a seven-stranded β-barrel fold. Analysis of C-terminal truncation mutants of Caf1A demonstrated that the presence of Caf1A(C) is crucial for the function of the usher in vivo, but that it is not required for the initial binding of chaperone-subunit complexes to the usher. Two clusters of conserved hydrophobic residues on the surface of Caf1A(C) were found to be essential for the efficient assembly of surface polymers. These clusters are conserved between the FGL family and the FGS family of chaperone-usher systems.

An automated calibration method for non-see-through head mounted displays

Accurate calibration of a head mounted display (HMD) is essential both for research on the visual system and for realistic interaction with virtual objects. Yet, existing calibration methods are time consuming and depend on human judgements, making them error prone, and are often limited to optical see-through HMDs. Building on our existing approach to HMD calibration Gilson et al. (2008), we show here how it is possible to calibrate a non-see-through HMD. A camera is placed inside a HMD displaying an image of a regular grid, which is captured by the camera. The HMD is then removed and the camera, which remains fixed in position, is used to capture images of a tracked calibration object in multiple positions. The centroids of the markers on the calibration object are recovered and their locations re-expressed in relation to the HMD grid. This allows established camera calibration techniques to be used to recover estimates of the HMD display's intrinsic parameters (width, height, focal length) and extrinsic parameters (optic centre and orientation of the principal ray). We calibrated a HMD in this manner and report the magnitude of the errors between real image features and reprojected features. Our calibration method produces low reprojection errors without the need for error-prone human judgements.

On-line prediction of cheese making using backscatter of near infrared indices light

The potential of a fibre optic sensor, detecting light backscatter in a cheese vat during coagulation and syneresis, to predict curd moisture, fat loses and curd yield was examined. Temperature, cutting time and calcium levels were varied to assess the strength of the predictions over a range of processing conditions. Equations were developed using a combination of independent variables, milk compositional and light backscatter parameters. Fat losses, curd yield and curd moisture content were predicted with a standard error of prediction (SEP) of +/- 2.65 g 100 g(-1) (R-2 = 0.93), +/- 0.95% (R-2 = 0.90) and +/- 1.43% (R-2 = 0.94), respectively. These results were used to develop a model for predicting curd moisture as a function of time during syneresis (SEP = +/- 1.72%; R-2 = 0.95). By monitoring coagulation and syneresis, this sensor technology could be employed to control curd moisture content, thereby improving process control during cheese manufacture. (c) 2007 Elsevier Ltd. All rights reserved..

Influence of curd cutting programme and stirring speed on the prediction of syneresis indices in cheese-making using NIR light backscatter

An NIR reflectance sensor, with a large field of view and a fibre-optic connection to a spectrometer for measuring light backscatter at 980 nm, was used to monitor the syneresis process online during cheese-making with the goal of predicting syneresis indices (curd moisture content, yield of whey and fat losses to whey) over a range of curd cutting programmes and stirring speeds. A series of trials were carried out in an 11 L cheese vat using recombined whole milk. A factorial experimental design consisting of three curd stirring speeds and three cutting programmes, was undertaken. Milk was coagulated under constant conditions and the casein gel was cut when the elastic modulus reached 35 Pa. Among the syneresis indices investigated, the most accurate and most parsimonious multivariate model developed was for predicting yield of whey involving three terms, namely light backscatter, milk fat content and cutting intensity (R2 = 0.83, SEy = 6.13 g/100 g), while the best simple model also predicted this syneresis index using the light backscatter alone (R2 = 0.80, SEy = 6.53 g/100 g). In this model the main predictor was the light backscatter response from the NIR light back scatter sensor. The sensor also predicted curd moisture with a similar accuracy.

Svetlana

Svetlana is a series of photographs documenting rehearsals for an opera that was never performed. Written by Waw Pierogi, founder of the 1980s group Xex, little is known of the opera, only that it was inspired by Svetlana, a character from one of their songs and the daughter of Stalin, who defected from the Soviet Union twice. A fictional Svetlana and a bogus Leon Theremin - inventor of the eponymous hands-free electronic musical instrument who was later kidnapped by the KGB - inhabit an archive of photographs from a session of stage rehearsals and location shots. Combining Svetlana’s narrative with a conspiracy to create sound weapons, this documentation of theatre workshops, styled after Bauhaus drama class exercises, produces an entirely spurious story of espionage, sonic weaponry and the clash between love and ideology. The performers sport geometric military costumes, brandishing sculptural forms fashioned after the acoustic locators that preceded radar technology. These redundant locators were still kept in use as props, concealing the introduction of radar from the Germans. They perfectly capture the theatricality of military might and suggest the rhetorical force of sound or even the political power of art. Svetlana was originally produced as part of a residency at S1 Artspace, Sheffield, and was later shown at Tatty Devine, alongside a special capsule collection of jewellery made by Tatty Devine.

Diaspora return of transnational migrants to Trinidad and Tobago: the additional contributions of social remittances

Current enthusiasm among development stakeholders for the enticement and recruitment ‘back home’ of skilled Diaspora migrants has predominantly revolved around how human capital gains and transfers of capital, knowledge, technical skills and workplace entrepreneurialism and innovation can be facilitated. In this article, we widen the conceptual basis of this dimension of the migration–development nexus, by bringing the additional contributions of the social remittances that return migrants offer, and practice, into the mix. As evidence, the article examines how and why a sample of ‘middling’1 Trinidadian transnational professionals engage in social development activities and why experiences vary widely on their return. Their views are appraised through the verbal optic of their narratives, which they shared with us during in-depth interviews. Several among these Diaspora returnees appear to be agents for the diffusion and infusion of social capital and non-monetary, social remittances in the homeland to which they have returned in mid-life and mid-career. Others are disappointed, or frustrated, and have their hopes dashed, leading to thoughts of re-migration, or re-return. Despite such difficulties, we find that family belonging and national pride strengthens many of these return migrants’ development potential through their deeply felt commitments to local ‘capacity-building’.

Electro-optical properties of liquid crystal copolymers and their relationship to structural order

A range of side chain liquid crystal copolymers have been prepared using mesogenic and non-mesogenic units. It is found that high levels of the non-mesogenic moieties may be introduced without completely disrupting the organization of the liquid crystal phase. Incorporation of this comonomer causes a marked reduction in the glass transition temperature (Tg), presumably as a result of enhanced backbone mobility and a corresponding lowering of the nematic transition temperature, thereby restricting the temperature range for stability of the liquid crystal phase. The effect of the interactions between the various components of these side-chain polymers on their electro-optic responses is described. Infrared (i.r.) dichroism measurements have been made to determine the order parameters of the liquid crystalline side-chain polymers. By identifying a certain band (CN stretching) in the i.r. absorption spectrum, the order parameter of the mesogenic groups can be obtained. The temperature and composition dependence of the observed order parameter are related to the liquid crystal phase transitions and to the electro-optic response. It is found that the introduction of the non-mesogenic units into the polymer chain lowers the threshold voltage of the electro-optic response over and above that due to the reduction in the order parameter. The dynamic electro-optic responses are dominated by the temperature-dependent viscosity and evidence is presented for relaxation processes involving the polymer backbone which are on a time scale greater than that for the mesogenic side-chain units.

Cinnamate ester containing liquid crystalline side chain polymers

The synthesis of methacrylate esters of 4-cyanophenyl-(4-(ω-hydroxyalkyloxy)) cinnamates, with spacer lengths of 2 and 6 methylene units and the synthesis of the corresponding acrylate ester with a spacer of 2 methylene units are described. The methacrylate monomers were polymerized by free radical polymerization, both as homopolymers and as copolymers with the analogous benzoate monomer of spacer length 6. The acrylate ester could not be polymerized successfully under the same reaction conditions. Polymers were characterized by NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermo-optic observations. Of the monomers prepared, only the cinnamate with a hexamethylene spacer shows a mesophase, seen on supercooling of the melt. All of the polymers prepared were liquid crystalline, with smectic behavior predominating in the polymethacrylates with the longer spacer group. A narrow nematic region is seen just below the clearing temperature with a range of 3–9°C, nematic character is increased in the copolymer series with the degree of incorporation of the cinnamate monomer with the spacer group of length 2.

Extended Kalman filtering for robotic proximity sensing

The authors address the problems in using a fiber-optic proximity sensor to detect robot end-effector positioning errors in performing a contact task when uncertainties about target position exist. An extended Kalman filter approach is employed to solve the nonlinear filtering problem. Some experimental results are given.

Assessing and understanding the impact of stratospheric dynamics and variability on the earth system

Advances in weather and climate research have demonstrated the role of the stratosphere in the Earth system across a wide range of temporal and spatial scales. Stratospheric ozone loss has been identified as a key driver of Southern Hemisphere tropospheric circulation trends, affecting ocean currents and carbon uptake, sea ice, and possibly even the Antarctic ice sheets. Stratospheric variability has also been shown to affect short term and seasonal forecasts, connecting the tropics and midlatitudes and guiding storm track dynamics. The two-way interactions between the stratosphere and the Earth system have motivated the World Climate Research Programme's (WCRP) Stratospheric Processes and Their Role in Climate (SPARC) DynVar activity to investigate the impact of stratospheric dynamics and variability on climate. This assessment will be made possible by two new multi-model datasets. First, roughly 10 models with a well resolved stratosphere are participating in the Coupled Model Intercomparison Project 5 (CMIP5), providing the first multi-model ensemble of climate simulations coupled from the stratopause to the sea floor. Second, the Stratosphere Historical Forecasting Project (SHFP) of WCRP's Climate Variability and predictability (CLIVAR) program is forming a multi-model set of seasonal hindcasts with stratosphere resolving models, revealing the impact of both stratospheric initial conditions and dynamics on intraseasonal prediction. The CMIP5 and SHFP model-data sets will offer an unprecedented opportunity to understand the role of the stratosphere in the natural and forced variability of the Earth system and to determine whether incorporating knowledge of the middle atmosphere improves seasonal forecasts and climate projections. Capsule New modeling efforts will provide unprecedented opportunities to harness our knowledge of the stratosphere to improve weather and climate prediction.