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.     

Polychlorinated biphenyl concentrations in adult chinook salmon (Oncorhynchus tshawytscha) returning to coastal and Puget Sound hatcheries of Washington State

Identifying the source of polychlorinated biphenyls (PCBs) is the first step to eliminating contamination within anadromous salmonids and other aquatic species. We evaluated PCB concentrations in the muscle tissue of 4-year old Puget Sound and coastal hatchery Chinook salmon in an effortto identify potential locations where contamination occurs. Ten muscle samples were taken from each of two Puget Sound hatcheries and two coastal hatcheries in Washington State to determine PCB concentrations. Two technical mixtures of PCBs, Aroclor 1254 and Aroclor 1260, were measured in the tissue samples collected. Aroclor 1254 was detected in all samples, while Aroclor 1260 was detected in 16 of 40 samples. Generalized linear modeling (GLM) was used to evaluate the influence of region (Puget Sound and coast), hatchery, sex, fish length, and percent lipids on PCB concentrations. Twenty different GLMs representing multiple null hypotheses were ranked using Akaike Information Criterion (AIC). Six of the 20 models evaluated had substantial support for being the best model to describe PCB concentrations in Chinook salmon. The six models with substantial support were region and lipids; region; hatchery and lipid; region and sex; region, sex, and lipids; and region and length. Region appears to be the most influential variable explaining the variation in PCB concentrations in Chinook salmon in the Pacific Northwest. PCB concentrations in Chinook salmon muscle tissue from Puget Sound hatcheries were significantly greater (mean 49.26 microg/kg wet weight and standard deviation 40.55 microg/kg) than those from coastal hatcheries (mean 17.41 microg/kg wet weight and standard deviation 6.8 microg/kg). Our results suggest that some contamination likely occurs in the Pacific Ocean. However, a larger source likely exists within Puget Sound or along the migratory route of Puget Sound Chinook salmon. The observation of PCBs in Chinook salmon also has important implications for human health and salmon carcass supplementation.     

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.     

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.     

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.