Variable Rate Working Memories for Phonetic Categorization and Invariant Speech Perception

Speech can be understood at widely varying production rates. A working memory is described for short-term storage of temporal lists of input items. The working memory is a cooperative-competitive neural network that automatically adjusts its integration rate, or gain, to generate a short-term memory code for a list that is independent of item presentation rate. Such an invariant working memory model is used to simulate data of Repp (1980) concerning the changes of phonetic category boundaries as a function of their presentation rate. Thus the variability of categorical boundaries can be traced to the temporal in variance of the working memory code.Air Force Office of Scientific Research (F49620-92-J-0225, 90-0128); Defense Advanced Research Projects Agency (ONR N00014-92-J-4015); Office of Naval Research (N00014-91-J-4100

Neural Dynamics of Phonetic Trading Relations for Variable-Rate CV Syllables

The perception of CV syllables exhibits a trading relationship between voice onset time (VOT) of a consonant and duration of a vowel. Percepts of [ba] and [wa] can, for example, depend on the durations of the consonant and vowel segments, with an increase in the duration of the subsequent vowel switching the percept of the preceding consonant from [w] to [b]. A neural model, called PHONET, is proposed to account for these findings. In the model, C and V inputs are filtered by parallel auditory streams that respond preferentially to transient and sustained properties of the acoustic signal, as in vision. These streams are represented by working memories that adjust their processing rates to cope with variable acoustic input rates. More rapid transient inputs can cause greater activation of the transient stream which, in turn, can automatically gain control the processing rate in the sustained stream. An invariant percept obtains when the relative activations of C and V representations in the two streams remain uncha.nged. The trading relation may be simulated as a result of how different experimental manipulations affect this ratio. It is suggested that the brain can use duration of a subsequent vowel to make the [b]/[w] distinction because the speech code is a resonant event that emerges between working mernory activation patterns and the nodes that categorize them.Advanced Research Projects Agency (90-0083); Air Force Office of Scientific Reseearch (F19620-92-J-0225); Pacific Sierra Research Corporation (91-6075-2

Enzymatic transhalogenation of dendritic RGD peptide constructs with the fluorinase

We thank EPSRC and the Scottish Imaging Network (SINAPSE) for grants. DO’H thanks the Royal Society for a Wolfson Research Merit Award and ST is grateful to the John and Kathleen Watson Scholarship for financial support. We are grateful to Dr Catherine Botting and Dr Sally Shirran of the St Andrews Mass Spectrometry Service for MALDI-MS acquisitions. We also thank Dr Sally Pimlott of the University of Glasgow for the use of radiochemistry facilities. Open access via RSC Gold for Gold.Peer reviewedPublisher PD

A compiler approach to scalable concurrent program design

The programmer's most powerful tool for controlling complexity in program design is abstraction. We seek to use abstraction in the design of concurrent programs, so as to separate design decisions concerned with decomposition, communication, synchronization, mapping, granularity, and load balancing. This paper describes programming and compiler techniques intended to facilitate this design strategy. The programming techniques are based on a core programming notation with two important properties: the ability to separate concurrent programming concerns, and extensibility with reusable programmer-defined abstractions. The compiler techniques are based on a simple transformation system together with a set of compilation transformations and portable run-time support. The transformation system allows programmer-defined abstractions to be defined as source-to-source transformations that convert abstractions into the core notation. The same transformation system is used to apply compilation transformations that incrementally transform the core notation toward an abstract concurrent machine. This machine can be implemented on a variety of concurrent architectures using simple run-time support. The transformation, compilation, and run-time system techniques have been implemented and are incorporated in a public-domain program development toolkit. This toolkit operates on a wide variety of networked workstations, multicomputers, and shared-memory multiprocessors. It includes a program transformer, concurrent compiler, syntax checker, debugger, performance analyzer, and execution animator. A variety of substantial applications have been developed using the toolkit, in areas such as climate modeling and fluid dynamics

Neutron-Capture Nucleosynthesis in the First Stars

Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly-rotating massive stars and pair instability supernovae did not contribute substantial amounts of neutron-capture elements to the regions where the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor stars with low levels of neutron-capture elements were enriched by products of zero-metallicity supernovae only, then the presence of these heavy elements indicates that at least one form of neutron-capture reaction operated in some of the first stars.Comment: Accepted for publication in the Astrophysical Journal (36 pages, 26 figures

Comment on the Nature of the Ds1∗(2710)D_{s1}^*(2710) and DsJ∗(2860)D_{sJ}^*(2860) Mesons

Two charm-strange mesons, the $D_{s1}^*(2710)$ and the $D_{sJ}^*(2860)$, have recently been observed by several experiments. There has been speculation in the literature that the $D_{s1}^*(2710)$ is the $2^3S_1(c\bar{s})$ state and the $D_{sJ}^*(2860)$ is the $1^3D_1(c\bar{s})$ state. In this paper we explore this and other explanations in the context of the relativized quark model and the pseudoscalar emission decay model. We conclude that the $D_{s1}^*(2710)$ is most likely the $1^3D_1 (c\bar{s})$ state and the $D_{sJ}^*(2860)$ is most likely the $1^3D_3 (c\bar{s})$ state with the $1D_2$ resonances also contributing to the observed signals and explaining the observed ratios of branching ratios to $D^*K$ and $DK$ final states. We point out that measuring the $D_{sJ}^*(2860)$ spin can support or eliminate this explanation and that there are six excited $D_s$ states in this mass region; the $2^3S_1$, $2^1S_0$, $1^3D_1$, $1^3D_3$ and two $1D_2$ states. Observing some of the missing states would help confirm the nature of the $D_{s1}^*(2710)$ and the $D_{sJ}^*(2860)$ states.Comment: 8 pages, 2 figure

An influenza pandemic : what it could mean for Scottish tourism

There is a growing unease among World Health Organisation (WHO) officials and other global disease surveillance organisations that Avian Flu will mutate into a human influenza pandemic. Such is the concern that the Scottish Executive asked public bodies to prepare business continuity plans based upon the National Health Service Scotland‘s contingency plan and scenarios, and this briefing paper is a consequence of that request