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Humanities and Social Sciences40%

Selected Abstracts

Hippocampal granule cells opt for early retirement

HIPPOCAMPUS, Issue 10 2010
C.B. Alme
Abstract Increased excitability and plasticity of adult-generated hippocampal granule cells during a critical period suggests that they may "orthogonalize" memories according to time. One version of this "temporal tag" hypothesis suggests that young granule cells are particularly responsive during a specific time period after their genesis, allowing them to play a significant role in sculpting CA3 representations, after which they become much less responsive to any input. An alternative possibility is that the granule cells active during their window of increased plasticity, and excitability become selectively tuned to events that occurred during that time and participate in later reinstatement of those experiences, to the exclusion of other cells. To discriminate between these possibilities, rats were exposed to different environments at different times over many weeks, and cell activation was subsequently assessed during a single session in which all environments were revisited. Dispersing the initial experiences in time did not lead to the increase in total recruitment at reinstatement time predicted by the selective tuning hypothesis. The data indicate that, during a given time frame, only a very small number of granule cells participate in many experiences, with most not participating significantly in any. Based on these and previous data, the small excitable population of granule cells probably correspond to the most recently generated cells. It appears that, rather than contributing to the recollection of long past events, most granule cells, possibly 90,95%, are effectively "retired." If granule cells indeed sculpt CA3 representations (which remains to be shown), then a possible consequence of having a new set of granule cells participate when old memories are reinstated is that new representations of these experiences might be generated in CA3. Whatever the case, the present data may be interpreted to undermine the standard "orthogonalizer" theory of the role of the dentate gyrus in memory. © 2010 Wiley-Liss, Inc. [source]

Multiple Realizability Intuitions and the Functionalist Conception of the Mind

METAPHILOSOPHY, Issue 1 2006
WILLIAM RAMSEY
Abstract: A popular argument supporting functionalism has been what is commonly called the "multiple realizability" argument. One version of this argument uses thought experiments designed to show that minds could be composed of different types of material. This article offers a metaphilosophical analysis of this argument and shows that it fails to provide a strong case for functionalism. The multiple realizability argument is best understood as an inference-to-the-best-explanation argument, whereby a functionalist account of our mental concepts serves to explain our multiple realizability intuitions. I show that the argument is inadequate because alternative accounts of our mental concepts exist that provide equally plausible explanations for these intuitions. Moreover, in the case of our qualia concepts, a nonfunctionalist account explains several other intuitions that functionalism cannot explain. Thus, despite its popularity, the intuition-based version of the multiple realizability argument is a poor reason for accepting functionalism. [source]

On holographic transform compression of images

INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 5 2000
Alfred M. Bruckstein
Abstract Lossy transform compression of images is successful and widespread. The JPEG standard uses the discrete cosine transform on blocks of the image and a bit allocation process that takes advantage of the uneven energy distribution in the transform domain. For most images, 10:1 compression ratios can be achieved with no visible degradations. However, suppose that multiple versions of the compressed image exist in a distributed environment such as the internet, and several of them could be made available upon request. The classical approach would provide no improvement in the image quality if more than one version of the compressed image became available. In this paper, we propose a method, based on multiple description scalar quantization, that yields decompressed image quality that improves with the number of compressed versions available. © 2001 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 11, 292,314, 2000 [source]

Equations to predict precipitation onset and bubblepoint pressures of asphaltenic reservoir fluids

AICHE JOURNAL, Issue 7 2009
J. M. del Rio
Abstract A set of algebraic equations to predict upper onset-of-precipitation and bubble-point pressures of asphaltene-containing reservoir fluids in wide temperature ranges are proposed. In developing the equations, laboratory data of 11 Mexican and 12 more live oils have been analyzed, and a correlation of these data with temperature has been found. A modified least-squares regression method has been used to develop two versions of the proposed equations. In one version, a single pressure/temperature data point is required to predict the entire onset/bubble-point curves at any temperature. For oils with no experimental precipitation data available at all, a second version of the proposed expressions employs standard chromatographic data of the reservoir fluid to provide a reasonable prediction. The average absolute deviations in calculated onset and bubble-point pressures by the proposed equations are 2.53 and 0.45MPa by the one-point correlations, respectively, and 3.96 and 1.62 MPa by the compositionally-based correlations, respectively. The developed expressions are simple and can be used to provide reasonable predictions of upper onset and bubble-point pressures of asphaltenic live oils in cases where laboratory data are scarce. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Integrating Hume's Accounts of Belief and Justification

PHILOSOPHY AND PHENOMENOLOGICAL RESEARCH, Issue 2 2001
LOUIS E. LOEB
Hume's claim that a state is a belief is often intertwined,though without his remarking on this fact,with epistemic approval of the state. This requires explanation. Beliefs, in Hume's view, are steady dispositions (not lively ideas), nature's provision for a steady influence on the will and action. Hume's epistemic distinctions call attention to circumstances in which the presence of conflicting beliefs undermine a belief's influence and thereby its natural function. On one version of this interpretation, to say that a belief is justified, ceteris paribus, is to say that for all that has been shown the belief would be steady in its influence under suitable reflection. On a second version, it is to say that prima facie justification is an intrinsic property of the state, in virtue of its steadiness. These versions generate different understandings of the relationship between Parts iii and iv of Book I of the Treatise. [source]