Thermal Properties of Tissue Equivalent Phantom Materials

Thermal conductivity, specific heat, density, and thermal diffusivity were determined for standard RF and microwave phantom materials. Thermal conductivity data for seven phantom materials of varying aluminum content were analyzed using mixture theories. With the thermal diffusivity values obtained, worst case errors in SAR determination due to thermal conduction for adipose-muscle planar phantoms were estimated.     

The Linguistic Subversion of Mental Representation

Embedded and embodied approaches to cognition urge that (1) complicated internal representations may be avoided by letting features of the environment drive behavior, and (2) environmental structures can play an enabling role in cognition, allowing prior cognitive processes to solve novel tasks. Such approaches are thus in a natural position to oppose the ??thesis of linguistic structuring??: The claim that the ability to use language results in a wholesale recapitulation of linguistic structure in onboard mental representation. Prominent examples of researchers adopting this critical stance include Andy Clark, Michael Wheeler, and Mark Rowlands. But is such opposition warranted? Since each of these authors advocate accounts of mental representation that are broadly connectionist, I survey research on formal language computation in artificial neural networks, and argue that results indicate a strong form of the linguistic structuring thesis is true: Internal representational systems recapitulate significant linguistic structure, even on a connectionist account of mental representation. I conclude by sketching how my conclusion can nonetheless be viewed as consistent with and complimentary to an embedded/embodied account of the role of linguistic structure in cognition.     

影响力的艺术

在灾难面前，中国互联网和两亿网民爆发出的力量，在抗震救灾中发挥了独特的作用。     

Cognition and the Power of Continuous Dynamical Systems

Traditional approaches to modeling cognitive systems are computational, based on utilizing the standard tools and concepts of the theory of computation. More recently, a number of philosophers have argued that cognition is too subtle or complex for these tools to handle. These philosophers propose an alternative based on dynamical systems theory. Proponents of this view characterize dynamical systems as (i) utilizing continuous rather than discrete mathematics, and, as a result, (ii) being computationally more powerful than traditional computational automata. Indeed, the logical possibility of such super-powerful systems has been demonstrated in the form of analog artificial neural networks. In this paper I consider three arguments against the nomological possibility of these automata. While the first two arguments fail, the third succeeds. In particular, the presence of noise reduces the computational power of analog networks to that of traditional computational automata, and noise is a pervasive feature of information processing in biological systems. Consequently, as an empirical thesis, the proposed dynamical alternative is under-motivated: What is required is an account of how continuously valued systems could be realized in physical systems despite the ubiquity of noise.     

Information technologies and intuitive expertise: a method for implementing complex organizational change among New York City Transit Authority’s Bus Maintainers

This paper describes an attempt to implement a complex information technology system with the New York City Transit Authority’s (NYCTA) Bus Maintainers intended to help better track and coordinate bus maintenance schedules. IT implementation is notorious for high failure rates among so-called “low level” workers. We believe that many IT implementation efforts make erroneous assumptions about front line worker’s expertise, which creates tension between the IT implementation effort and the “cultures of practice” among the front line workers. We designed an aggressive “learning intervention” to address this issue and called “Operational Simulation”. Rather than requiring the expected 12 months for implementation, the hourly staff reached independence with the new system in 2 weeks and line supervisors (who do more) managed in 6 weeks. Additionally, the NYCTA shifted from a reactive to a proactive maintenance approach, reduced cycle times, and increased the “mean distance between failure”, resulting in a estimated $40 million cost savings. Implications for cognition, expertise, and training are discussed.     

Varieties of Analog and Digital Representation

The ‘received view’ of the analog–digital distinction holds that analog representations are continuous while digital representations are discrete. In this paper I first provide support for the received view by showing how it (1) emerges from the theory of computation, and (2) explains engineering practices. Second, I critically assess several recently offered alternatives, arguing that to the degree they are justified they demonstrate not that the received view is incorrect, but rather that distinct senses of the terms have become entrenched specific fields, perhaps most notably in the cognitive psychology of mental imagery.