The analysis of rigid polyurethanes by chemical ionization mass spectrometry

Methods for the elucidation of the chemical components of polyurethane foams are described. Foam samples of 50 mg were hydrolyzed in aqueous base and the resulting mixture of polyols and polyamines was analyzed by chemical ionization mass spectrometry (CI-MS) and high-pressure liquid chromatography (HPLC). The aromatic polyamines, which were separated by HPLC, produced few fragment ions under methane chemical ionization and were identified without difficulty. Each propoxylated homolog in the mixture of polyols was detected by CI-MS techniques, and approximate molecular weight profiles are presented for each polyol studied. Chemical ionization spectra are listed for samples of standard polyols and of base-hydrolyzed isocyanates. The hydrolysis products from urethane foam formulations were easily related to the standard compounds via CI-MS. These methods should be applicable to polymeric materials containing urethane, urea, and ester link-ages.     

Control of equine influenza: scenario testing using a realistic metapopulation model of spread

We present a metapopulation model of the spread of equine influenza among thoroughbred horses parametrized with data from a 2003 outbreak in Newmarket, UK. The number of horses initially susceptible is derived from a threshold theorem and a published statistical model. Two simulated likelihood-based methods are used to find the within- and between-yard transmissions using both exponential and empirical latent and infectious periods. We demonstrate that the 2003 outbreak was largely locally driven and use the parametrized model to address important questions of control. The chance of a large epidemic is shown to be largely dependent on the size of the index yard. The impact of poor responders to vaccination is estimated under different scenarios. A small proportion of poor responders strongly influences the efficiency of vaccine policies, which increases risk further when the vaccine and infecting strains differ following antigenic drift. Finally, the use of vaccinating in the face of an outbreak is evaluated at a global and individual management group level. The benefits for an individual horse trainer are found to be substantial, although this is influenced by the behaviour of other trainers.     

Volatiles Retention in the Drying of Skin Forming Materials PART 1: Materials Which Gelatinise at Moderately High Temperatures

ABSTRACT

Single droplets were dried whilst suspended from a rotating thermocouple in a horizontal wind tunnel, to study the effect of skin formation upon the retention of flavours. Native rice starch, wheat starch, or dextrin were used to encapsulate ethanol as a simulated flavour. The ethanol content of the dried droplets was measured using gas liquid chromatography and the crusts were examined using a scanning electron microecope. The effects of variations in encapsulant concentration, drying air temperature, and air flow rates upon flavour retention were determined.

With the rice starch, the ‘final retention’ of ethanol, defined as the ethanol content of the droplet after drying for ten minutes, was largely independent of initial solids     

The story of socio-technical design: reflections on its successes, failures and potential

Abstract.  This paper traces the history of socio-technical design, emphasizing the set of values it embraces, the people espousing its theory and the organizations that practise it. Its role in the implementation of computer systems and its impact in a number of different countries are stressed. It also shows its relationship with action research, as a humanistic set of principles aimed at increasing human knowledge while improving practice in work situations. Its evolution in the 1960s and 1970s evidencing improved working practices and joint agreements between workers and management are contrasted with the much harsher economic climate of the 1980s and 1990s when such principled practices, with one or two notable exceptions, gave way to lean production, downsizing and cost cutting in a global economy, partly reflecting the impact of information and communications technology. Different future scenarios are discussed where socio-technical principles might return in a different guise to humanize the potential impact of technology in a world of work where consistent organizational and economic change are the norm.     

Occlusion Models for Natural Images: A Statistical Study of a Scale-Invariant Dead Leaves Model

We develop a scale-invariant version of Matheron's dead leaves model for the statistics of natural images. The model takes occlusions into account and resembles the image formation process by randomly adding independent elementary shapes, such as disks, in layers. We compare the empirical statistics of two large databases of natural images with the statistics of the occlusion model, and find an excellent qualitative, and good quantitative agreement. At this point, this is the only image model which comes close to duplicating the simplest, elementary statistics of natural images—such as, the scale invariance property of marginal distributions of filter responses, the full co-occurrence statistics of two pixels, and the joint statistics of pairs of Haar wavelet responses.     

A radiomicroassay for cytotoxic antibody to human spermatozoa. Quantification by tritiated actinomycin d

A radiomicroassay for titration of spermocytotoxic antibody is described. The assay used [3H]AACTINOMYCIN D ([3H]Act D) to label damaged spermatozoa in a fashion analogous to penetration by vital dye. Optimal conditions for and some kinetics of the assay are presented. The assay is sensitive, reliable, simple to perform and uses only small amounts of serum and spermatozoa. Applied to sperm antibody positive human postvasectomy sera, the assay compared favourably in sensitivity eith vital dye microscopic observations and with parallel titration by the Isojima's immobilization tests.     

Hierarchical Bayesian inference in the visual cortex

Traditional views of visual processing suggest that early visual neurons in areas V1 and V2 are static spatiotemporal filters that extract local features from a visual scene. The extracted information is then channeled through a feedforward chain of modules in successively higher visual areas for further analysis. Recent electrophysiological recordings from early visual neurons in awake behaving monkeys reveal that there are many levels of complexity in the information processing of the early visual cortex, as seen in the long-latency responses of its neurons. These new findings suggest that activity in the early visual cortex is tightly coupled and highly interactive with the rest of the visual system. They lead us to propose a new theoretical setting based on the mathematical framework of hierarchical Bayesian inference for reasoning about the visual system. In this framework, the recurrent feedforward/feedback loops in the cortex serve to integrate top-down contextual priors and bottom-up observations so as to implement concurrent probabilistic inference along the visual hierarchy. We suggest that the algorithms of particle filtering and Bayesian-belief propagation might model these interactive cortical computations. We review some recent neurophysiological evidences that support the plausibility of these ideas.     

The Nonlinear Statistics of High-Contrast Patches in Natural Images

Recently, there has been a great deal of interest in modeling the non-Gaussian structures of natural images. However, despite the many advances in the direction of sparse coding and multi-resolution analysis, the full probability distribution of pixel values in a neighborhood has not yet been described. In this study, we explore the space of data points representing the values of 3 × 3 high-contrast patches from optical and 3D range images. We find that the distribution of data is extremely sparse with the majority of the data points concentrated in clusters and non-linear low-dimensional manifolds. Furthermore, a detailed study of probability densities allows us to systematically distinguish between images of different modalities (optical versus range), which otherwise display similar marginal distributions. Our work indicates the importance of studying the full probability distribution of natural images, not just marginals, and the need to understand the intrinsic dimensionality and nature of the data. We believe that object-like structures in the world and the sensor properties of the probing device generate observations that are concentrated along predictable shapes in state space. Our study of natural image statistics accounts for local geometries (such as edges) in natural scenes, but does not impose such strong assumptions on the data as independent components or sparse coding by linear change of bases.