Showing papers by "University of Cambridge published in 1995"

Mindblindness : An Essay on Autism and Theory of Mind

Abstract: Mindblindness and mindreading evolutionary psychology and social chess mindreading - nature's choice developing mindreading - the four steps autism and mindblindness how brains read minds the language of the eyes mindreading - back to the future.

Performance measurement system design: A literature review and research agenda

Abstract: The importance of performance measurement has long been recognized by academics and practitioners from a variety of functional disciplines. Seeks to bring together this diverse body of knowledge into a coherent whole. To ensure that the key issues are identified, focuses on the process of performance measurement system design, rather than the detail of specific measures. Following a comprehensive review of the literature, proposes a research agenda.

Efficient photodiodes from interpenetrating polymer networks

Abstract: THE photovoltaic effect involves the production of electrons and holes in a semiconductor device under illumination, and their subsequent collection at opposite electrodes. In many inorganic semiconductors, photon absorption produces free electrons and holes directly1. But in molecular semiconductors, absorption creates electrona¤-hole pairs (excitons) which are bound at room temperature2, so that charge collection requires their dissociation. Exciton dissociation is known to be efficient at interfaces between materials with different electron affinities and ionization potentials, where the electron is accepted by the material with larger electron affinity and the hole by the material with lower ionization potential3. A two-layer diode structure can thus be used, in which excitons generated in either layer diffuse towards the interface between the layers. However, the exciton diffusion range is typically at least a factor of 10 smaller than the optical absorption depth, thus limiting the efficiency of charge collection3. Here we show that the interpenetrating network formed from a phase-segregated mixture of two semiconducting polymers provides both the spatially distributed interfaces necessary for efficient charge photo-generation, and the means for separately collecting the electrons and holes. Devices using thin films of these polymer mixtures show promise for large-area photodetectors.

Costs of a predictible switch between simple cognitive tasks.

Abstract: In an investigation of task-set reconfiguration, participants switched between 2 tasks on every 2nd trial in 5 experiments and on every 4th trial in a final experiment. The tasks were to classify either the digit member of a pair of characters as even/odd or the letter member as consonant/vowel. As the response-stimulus interval increased up to 0.6 s, the substantial cost to performance of this predictable task-switch fell: Participants could partially reconfigure in advance of the stimulus. However, even with 1.2 s available for preparation, a large asymptotic reaction time (RT) cost remained, but only on the 1st trial of the new task. This is attributed to a component of reconfiguration triggered exogenously, i. e., only by a task-relevant stimulus. That stimuli evoke associated task-sets also explains why RT and switch costs increased when the stimulus included a character associated with the currently irrelevant task. © 1995 American Psychological Association.

Statistical Mechanics of Dissipative Particle Dynamics.

Abstract: The stochastic differential equations corresponding to the updating algorithm of Dissipative Particle Dynamics (DPD), and the corresponding Fokker-Planck equation are derived. It is shown that a slight modification to the algorithm is required before the Gibbs distribution is recovered as the stationary solution to the Fokker-Planck equation. The temperature of the system is then directly related to the noise amplitude by means of a fluctuation-dissipation theorem. However, the correspondingly modified, discrete DPD algorithm is only found to obey these predictions if the length of the time step is sufficiently reduced. This indicates the importance of time discretisation in DPD.

Remembering: A Study in Experimental and Social Psychology

Abstract: Part I. Experimental Studies: 2. Experiment in psychology 3. Experiments on perceiving III Experiments on imaging 4-8. Experiments on remembering: (a) The method of description (b) The method of repeated reproduction (c) The method of picture writing (d) The method of serial reproduction (e) The method of serial reproduction picture material 9. Perceiving, recognizing, remembering 10. A theory of remembering 11. Images and their functions 12. Meaning Part II. Remembering as a Study in Social Psychology: 13. Social psychology 14. Social psychology and the matter of recall 15. Social psychology and the manner of recall 16. Conventionalism 17. The notion of a collective unconscious 18. The basis of social recall 19. A summary and some conclusions.

Hilbert space representation of the minimal length uncertainty relation.

Abstract: The existence of a minimal observable length has long been suggested in quantum gravity as well as in string theory. In this context a generalized uncertainty relation has been derived which quantum theoretically describes the minimal length as a minimal uncertainty in position measurements. Here we study in full detail the quantum mechanical structure which underlies this uncertainty relation. DAMTP/94-105, hep-th/9412167, and Phys.Rev.D52:1108 (1995)

Economic growth, carrying capacity, and the environment.

Abstract: National and international economic policy has usually ignored the environment. In areas where the environment is beginning to impinge on policy, as in the General Agreement on Tariffs and Trade (GATT) and the North American Free Trade Agreement (NAFTA), it remains a tangential concern, and the presumption is often made that economic growth and economic liberalization (including the liberalization of international trade) are, in some sense, good for the environment. This notion has meant that economy-wide policy reforms designed to promote growth and liberalization have been encouraged with little regard to their environmental consequences, presumably on the assumption that these consequences would either take care of themselves or could be dealt with separately. In this article, we discuss the relation between economic growth and environmental quality, and the link between economic activity and the carrying capacity and resilience of the environment.

On quantum noise

Abstract: We discuss the distribution function for the current noise in Quantum point contacts. Special interest is paid to contact of a superconductor with a normal metal. A new derivation of the Lesovik-Levitov formulae is suggested. It is shown, for the SN point contacts, that the distribution of the noise describes independent processes when charge ±e 0 or ±2e 0 passes through the contact. At low temperature and voltage only processes with double charge transfer are relevant. At zero temperature and low voltage the distribution has a binomial form.

Capacitative calcium entry.

Abstract: The original idea that calcium might enter cells through a capacitative mechanism was first introduced by Jim Putney [1]. The somewhat surprising hypothesis was that calcium entry was regulated by the state of filling of the calcium stores. By analogy with a capacitor in an electrical circuit, the calcium stores prevent entry when they are charged up but immediately begin to promote entry as soon as stored calcium is discharged. This capacitative entry mechanism is present in many cells and has properties which are very similar from one cell to the next [2-6]. Capacitative calcium entry can be switched on by a great variety of stimuli such as normal agonists or pharmacological agents all of which share a common property of releasing stored calcium. Examples include calcium-mobilizing agonists [7-13], the calcium-mobilizing second messenger inositol 1,4,5trisphosphate (InsP3) [11,12,14-18], the calcium ionophore ionomycin [14,19], inhibitors of the endoplasmic reticulum (ER) pumps such as thapsigargin [8,10,12,20] and cyclopiazonic acid [20,21] or simply by incubating cells in Ca2+-free conditions [12,14,15]. All this evidence indicates that the entry of external calcium is somehow controlled by the calcium content of the ER. This review is focused primarily on the mechanism ofcapacitative Ca2+ entry.

Simulations of X-ray clusters

Abstract: We present simulations of the formation and evolution of galaxy clusters in the Cold Dark Matter cosmogony. Clusters with a wide range of mass were selected from previous N-body models, and were resimulated at higher resolution using a combined N-body/Smooth Particle Hydrodynamics code. The effects of radiative cooling on the gas are neglected. While many present-day clusters are predicted to be undergoing mergers, the density profiles of those that are approximately in equilibrium are all very similar, both for the gas and for the dark matter. These profiles show no sign of a uniform density core and steepen gradually from the centre outwards. The standard $\beta$-model is a reasonable fit over most of the radius range observable in real clusters. However, the value obtained for the slope parameter $\beta_f$ increases with the outermost radius of the fit. Temperature profiles of different simulated clusters are also similar. Typically the temperature is almost uniform in the regions which emit most of the X-ray flux but drops at larger radii. The gas temperature and dark matter velocity dispersion in equilibrium clusters give values of $\beta_T\equiv \mu m_p\sigma_{DM}^2/kT$ which are consistent with unity provided an X-ray emission-weighted temperature is used. Larger values of $\beta_T$ are found in merging objects where there is a transient boost in the velocity dispersion of the system. Thus $\beta_T >1$ may be an observational indicator of merging in real clusters. The similar structure of clusters of differing mass results in scaling relations between the X-ray and dynamical properties of clusters identified at

Gravitationally redshifted emission implying an accretion disk and massive black hole in the active galaxy MCG-6-30-15

Abstract: ACTIVE galactic nuclei and quasars are probably powered by the accretion of gas onto a supermassive black hole at the centre of the host galaxy1, but direct confirmation of the presence of a black hole is hard to obtain. As the gas nears the event horizon, its velocity should approach the speed of light; the resulting relativistic effects, and a gravitational redshift arising from the proximity to the black hole, should be observable, allowing us to test specific predictions of the models with the observations. Here we report the detection of these relativistic effects in an X-ray emission line (the Kα line) from ionized iron in the galaxy MCG–6–30–15. The line is extremely broad, corresponding to a velocity of ∼100,000 km s−1, and asymmetric, with most of the line flux being redshifted. These features indicate that the line most probably arises in a region between three and ten Schwarzschild radii from the centre, so that we are observing the innermost region of the accretion disk.

Catalytic specificity of protein-tyrosine kinases is critical for selective signalling

Abstract: HOW do distinct protein-tyrosine kinases activate specific downstream events? Src-homology-2 (SH2) domains on tyrosine kinases or targets of tyrosine kinases recognize phosphotyrosine in a specific sequence context and thereby provide some specificity1–3. The role of the catalytic site of tyrosine kinases in determining target specificity has not been fully investigated. Here we use a degenerate peptide library to show that each of nine tyrosine kinases investigated has a unique optimal peptide substrate. We find that the cytosolic tyrosine kinases preferentially phosphorylate peptides recognized by their own SH2 domains or closely related SH2 domains (group I; ref. 3), whereas receptor tyrosine kinases preferentially phosphorylate peptides recognized by subsets of group III SH2 domains3. The importance of these findings for human disease is underscored by our observation that a point mutation in the RET receptor-type tyrosine kinase, which causes multiple endocrine neoplasia type 2B, results in a shift in peptide substrate specificity.

Probable networks and plausible predictions - a review of practical Bayesian methods for supervised neural networks

Abstract: Bayesian probability theory provides a unifying framework for data modelling. In this framework the overall aims are to find models that are well-matched to the data, and to use these models to make optimal predictions. Neural network learning is interpreted as an inference of the most probable parameters for the model, given the training data. The search in model space (i.e., the space of architectures, noise models, preprocessings, regularizers and weight decay constants) can then also be treated as an inference problem, in which we infer the relative probability of alternative models, given the data. This review describes practical techniques based on Gaussian approximations for implementation of these powerful methods for controlling, comparing and using adaptive networks.

Punishment in animal societies.

Abstract: Although positive reciprocity (reciprocal altruism) has been a focus of interest in evolutionary biology, negative reciprocity (retaliatory infliction of fitness reduction) has been largely ignored. In social animals, retaliatory aggression is common, individuals often punish other group members that infringe their interests, and punishment can cause subordinates to desist from behaviour likely to reduce the fitness of dominant animals. Punishing strategies are used to establish and maintain dominance relationships, to discourage parasites and cheats, to discipline offspring or prospective sexual partners and to maintain cooperative behaviour.

The stone skeleton

Abstract: The mode of action of masonry construction is investigated, using the principles of plastic design developed originally for steel frames. These principles are applied to the analysis of the structural system of the Gothic cathedral; the flying buttress and the nave vault are treated in some detail.

Modelling accretion in protobinary systems

Abstract: A method for following fragmentation simulations further in time using smoothed particle hydrodynamics (SPH) is presented In a normal SPH simulation of the collapse and fragmentation of a molecular cloud, high-density regions of gas that form protostars are represented by many particles with small separations These high-density regions require small time steps, limiting the time for which the simulation can be followed Thus, the end result of the fragmentation can never be definitively ascertained, and comparisons between cloud fragmentation calculations and the observed characteristics of stellar systems cannot be made In this paper, each high-density region is replaced by a single, non-gaseous particle, with appropriate boundary conditions, which contains all the mass in the region and accretes any infalling mass This enables the evolution of the cloud and the resulting protostars to be followed for many orbits or until most of the original cloud mass has been accreted

Neural computation of log likelihood in control of saccadic eye movements

Abstract: The latency between the appearance of a visual target and the start of the saccadic eye movement made to look at it varies from trial to trial to an extent that is inexplicable in terms of ordinary 'physiological' processes such as synaptic delays and conduction velocities. An alternative interpretation is that it represents the time needed to decide whether a target is in fact present: decision processes are necessarily stochastic, because they depend on extracting information from noisy sensory signals. In one such model, the presence of a target causes a signal in a decision unit to rise linearly at a rate r from its initial value s0 until it reaches a fixed threshold theta, when a saccade is initiated. One can regard this decision signal as a neural estimate of the log likelihood of the hypothesis that the target is present, the threshold being the significance criterion or likelihood level at which the target is presumed to be present. Experiments manipulating the prior probability of the target's appearing confirm this notion: the latency distribution then changes in the way expected if s0 simply reflects the prior log likelihood of the stimulus.

Patterns of gene action in plant development revealed by enhancer trap and gene trap transposable elements.

Abstract: The crucifer Arabidopsis thaliana has been used widely as a model organism for the study of plant development. We describe here the development of an efficient insertional mutagenesis system in Arabidopsis that permits identification of genes by their patterns of expression during development. Transposable elements of the Ac/Ds system carrying the GUS reporter gene have been designed to act as enhancer traps or gene traps. A novel selection scheme maximizes recovery of unlinked transposition events. In this study 491 plants carrying independent transposon insertions were generated and screened for expression patterns. One-half of the enhancer trap insertions and one-quarter of the gene trap insertions displayed GUS expression in seedlings or flowers, including expression patterns specific to organs, tissues, cell types, or developmental stages. The patterns identify genes that act during organogenesis, pattern formation, or cell differentiation. Transposon insertion lines with specific GUS expression patterns provide valuable markers for studies of Arabidopsis development and identify new cell types or subtypes in plants. The diversity of gene expression patterns generated suggests that the identification and cloning of Arabidopsis genes expressed in any developmental process is feasible using this system.

Residual symptoms after partial remission: an important outcome in depression

Abstract: This paper draws attention to an important adverse outcome in depression, the occurrence of residual symptoms after partial remission. Among patients with definite major depression followed every 3 months to remission and thereafter, residual symptoms reaching 8 or more on the Hamilton Depression Scale 17-item total were present in 32% (19) of the 60 who remitted below major depression by 15 months. The pattern was of mild but typical depressive symptoms. Residual symptoms were more common in subjects with more severe initial illness, but were not related to any other predictors, including longer prior illness, dysthymia, or lower dose of drug treatment during the illness episode. There were weak associations with personality that might have been consequences of symptom presence. Residual symptoms were very strong predictors of subsequent early relapse, which occurred in 76% (13/17) of those with residual symptoms and 25% (10/40) of those without.