Daubert’s Naïve Realist Challenge to Husserl

Despite extensive discussion of naïve realism in the wider philosophical literature, those influenced by the phenomenological movement who work in the philosophy of perception have hardly weighed in on the matter. It is thus interesting to discover that Edmund Husserl’s close philosophical interlocutor and friend, the early twentieth-century phenomenologist Johannes Daubert, held the naive realist view. This article presents Daubert’s views on the fundamental nature of perceptual experience and shows how they differ radically from those of Husserl’s. The author argues, in conclusion, that Daubert’s views are superior to those of Husserl’s specifically in the way that they deal with the phenomenon of perceptual constancy

Development of composite material test methodology for fractue toughness/damage tolerance

Fracture toughness testing techniques for composite materials are reviewed for simplicity, applicability to filament wound systems, and correlation with fracture mechanics preinciples. Toughness test results are repesented for homogeneous epoxy and graphite reinforced epoxy

Synthesis of pyrrone polymers, 21 June 1967 - 21 June 1968

Synthesis of pyrrone polymers by reactions of dianhydride and diacetoamido diamines or with tetramin

Radio Variability of Sagittarius A* - A 106 Day Cycle

We report the presence of a 106-day cycle in the radio variability of Sgr A* based on an analysis of data observed with the Very Large Array (VLA) over the past 20 years. The pulsed signal is most clearly seen at 1.3 cm with a ratio of cycle frequency to frequency width f/Delta_f= 2.2+/-0.3. The periodic signal is also clearly observed at 2 cm. At 3.6 cm the detection of a periodic signal is marginal. No significant periodicity is detected at both 6 and 20 cm. Since the sampling function is irregular we performed a number of tests to insure that the observed periodicity is not the result of noise. Similar results were found for a maximum entropy method and periodogram with CLEAN method. The probability of false detection for several different noise distributions is less than 5% based on Monte Carlo tests. The radio properties of the pulsed component at 1.3 cm are spectral index alpha ~ 1.0+/- 0.1 (for S nu^alpha), amplitude Delta S=0.42 +/- 0.04 Jy and characteristic time scale Delta t_FWHM ~ 25 +/- 5 days. The lack of VLBI detection of a secondary component suggests that the variability occurs within Sgr A* on a scale of ~5 AU, suggesting an instability of the accretion disk.Comment: 14 Pages, 3 figures. ApJ Lett 2000 accepte

A computer simulation of oscillatory behavior in primary visual cortex

Periodic variations in correlated cellular activity have been observed in many regions of the cerebral cortex. The recent discovery of stimulus-dependent, spatially-coherent oscillations in primary visual cortex of the cat has led to suggestions of neural information encoding schemes based on phase and/or frequency variation. To explore the mechanisms underlying this behavior and their possible functional consequences, we have developed a realistic neural model, based on structural features of visual cortex, which replicates observed oscillatory phenomena. In the model, this oscillatory behavior emerges directly from the structure of the cortical network and the properties of its intrinsic neurons; however, phase coherence is shown to be an average phenomenon seen only when measurements are made over multiple trials. Because average coherence does not ensure synchrony of firing over the course of single stimuli, oscillatory phase may not be a robust strategy for directly encoding stimulus-specific information. Instead, the phase and frequency of cortical oscillations may reflect the coordination of general computational processes within and between cortical areas. Under this interpretation, coherence emerges as a result of horizontal interactions that could be involved in the formation of receptive field properties

Spike frequency adaptation affects the synchronization properties of networks of cortical oscillators

Oscillations in many regions of the cortex have common temporal characteristics with dominant frequencies centered around the 40 Hz (gamma) frequency range and the 5–10 Hz (theta) frequency range. Experimental results also reveal spatially synchronous oscillations, which are stimulus dependent (Gray&Singer, 1987;Gray, König, Engel, & Singer, 1989; Engel, König, Kreiter, Schillen, & Singer, 1992). This rhythmic activity suggests that the coherence of neural populations is a crucial feature of cortical dynamics (Gray, 1994). Using both simulations and a theoretical coupled oscillator approach, we demonstrate that the spike frequency adaptation seen in many pyramidal cells plays a subtle but important role in the dynamics of cortical networks. Without adaptation, excitatory connections among model pyramidal cells are desynchronizing. However, the slow processes associated with adaptation encourage stable synchronous behavior