Neural network modeling of memory deterioration in Alzheimer's disease

The clinical course of Alzheimer's disease (AD) is generally characterized by progressive gradual deterioration, although large clinical variability exists. Motivated by the recent quantitative reports of synaptic changes in AD, we use a neural network model to investigate how the interplay between synaptic deletion and compensation determines the pattern of memory deterioration, a clinical hallmark of AD. Within the model we show that the deterioration of memory retrieval due to synaptic deletion can be much delayed by multiplying all the remaining synaptic weights by a common factor, which keeps the average input to each neuron at the same level. This parallels the experimental observation that the total synaptic area per unit volume (TSA) is initially preserved when synaptic deletion occurs. By using different dependencies of the compensatory factor on the amount of synaptic deletion one can define various compensation strategies, which can account for the observed variation in the severity and progression rate of AD

Catalytic RNA and synthesis of the peptide bond

We are studying whether the L-19 IVS ribozyme from Tetrahymena thermophila can catalyze the formation of the peptide bond when it is supplied with synthetic aminoacyl oligonucleotides. If this reaction works, it could give us some insight into the mechanism of peptide bond formation and the origin of coded protein synthesis. Two short oligoribonucleotides, CCCCC and a protected form of CCCCU were prepared; the former was made by the controlled hydrolysis of Poly(C), and the later by multistep chemical synthesis from the protected monomers. The homopentamer was then aminocylated using C-14 labelled Boc-protected glycine imidazolide. This aminoacylated oligo-nucleotide has now been shown to enter the active site of the L-19 IVS, and aminoacyl transfer, and peptide bond formation reactions are being sought. Our synthesis of CCCCU made us aware of the inadequacy of many of the 2'- hydroxyl protecting groups that are in use today and we therefore designed a new 2'- protecting group that is presently being tested

Carneades' quip : Orality, philosophy, wit, and the poetics of impromptu quotation

In spite of a long and influential philosophical career, when Carneades of Cyrene (214-129 BC), head of the Academy in its skeptical phase, died at age eighty-five, he left behind no written works. There were, we are told, some letters extant in Diogenes Laertius' time addressed to Ariarathes, king of Cappadocia, but Carneades' philosophical opinions were conveyed orally and transmitted to posterity in written form only by his students (D.L. 4.65).1 In this respect Carneades resembles not only Pythagoras and Socrates before him and Epictetus later, but also his Skeptic predecessors Pyrrho and Arcesilaus, whose refusal to commit their ideas to writing was a conscious protest against philosophical dogmatism.2/

The impact of the mode of thought in complex decisions: intuitive decisions are better

A number of recent studies have reported that decision quality is enhanced under conditions of inattention or distraction (unconscious thought; Dijksterhuis, 2004; Dijksterhuis and Nordgren, 2006; Dijksterhuis et al., 2006). These reports have generated considerable controversy, for both experimental (problems of replication) and theoretical reasons (interpretation). Here we report the results of four experiments. The first experiment replicates the unconscious thought effect, under conditions that validate and control the subjective criterion of decision quality. The second and third experiments examine the impact of a mode of thought manipulation (without distraction) on decision quality in immediate decisions. Here we find that intuitive or affective manipulations improve decision quality compared to analytic/deliberation manipulations. The fourth experiment combines the two methods (distraction and mode of thought manipulations) and demonstrates enhanced decision quality, in a situation that attempts to preserve ecological validity. The results are interpreted within a framework that is based on two interacting subsystems of decision-making: an affective/intuition based system and an analytic/deliberation system

Suppression of switchable polarization in KDP by ionizing radiation

Switching curves were obtained from KH2PO4 single crystals exposed to x-ray radiation for various time intervals, up to 8 h. The applied electric field was varied between 370 and 740 V/cm, as well. The temperature was held constant at 99 K. The switching curves were fit to a three-parameter nucleation and growth model based on the original works by Johnson and Mehl, and independently by Avrami. The two dynamic parameters, characteristic time tc, and effective domain wall dimensionality n, produced values consistent with unirradiated studies, however, they did not show any clear dependancy on exposure time. The switchable polarization P decreased with increasing exposure time. A simple exponential decay is used to describe P as a function of exposure time. The rate coefficient k for the exponential, decreases with increasing electric field

Exobiology in Earth orbit: The results of science workshops held at NASA, Ames Research Center

The Workshops on Exobiology in Earth Orbit were held to explore concepts for orbital experiments of exobiological interest and make recommendations on which classes of experiments should be carried out. Various observational and experimental opportunities in Earth orbit are described including those associated with the Space Shuttle laboratories, spacecraft deployed from the Space Shuttle and expendable launch vehicles, the Space Station, and lunar bases. Specific science issues and technology needs are summarized. Finally, a list of recommended experiments in the areas of observational exobiology, cosmic dust collection, and in situ experiments is presented

The reception of Homer as oral poetry

For me, one of the most interesting directions in oral tradition studies focuses on the reception of Homeric poetry as oral poetry in classical and later antiquity. The topics and materials for study here are wide-ranging. They include the internalization of Homeric poetics by lyric and elegiac poets; "rhapsodic" variation and conflation of lines in authors who quote Homer; the adaptation of Homeric tags in Cynic street sermons; the pastiche form known as the cento; even the re-use of Homeric poetry in magical incantations, to name just a few avenues of investigation.Not

Operation and monitoring guidelines and the development of a screening tool for irrigating with coal mine water in Mpumalanga Province, South Africa

It is predicted that vast volumes of impacted mine water will be produced by mining activities in the Mpumalanga coalfields of South Africa. Irrigation provides for a novel approach to the utilisation and disposal of mine water, under the correct conditions. The significance of these findings lies in the versatility of this irrigation. Communities which often have veryfew other resources can utilise mine water to generate livelihoods. Research over a period of more than 10 years has shown that this water can be used successfully for the irrigation of a range of crops. The potential environmental impact of this excess water is of great concern in a water-scarce country like South Africa. There is, however, continuing concern from the local regulators regarding the long-term impact that large-scale mine-water irrigation may have on groundwater quality andquantity. Detailed research has been undertaken over the past number of years on both undisturbed soils and in coal-mining spoils. These sites range from sandy soils to very clayey soils. The results indicate that many of the soils have considerable attenuation capacities and that over the period of irrigation, a large proportion of the salts are contained in the upper portions of the unsaturated zones below each irrigation pivot. The volumes and quality of water leaching through to the aquifers have been quantified at each site. From these data mixing ratios were calculated in order to determine the effect of the irrigation water on the underlying aquifers. One of the outcomes from this study was to define the conditions under which mine-water irrigation can be implemented and the associated operational and monitoring guidelines that should be followed. These have been based on the findings from this study, the fundamental  considerations of mine-water irrigation, the regulatory environment and, as far as possible, the practical implementation of mine-water irrigation as part of optimal mine-water management. In an attempt to standardise decision-making regarding mine-water irrigation, the criteria, data, rules and fundamentals discussed have been combined in a user-friendly tool, called GIMI (Groundwater Impacts from Minewater Irrigation). This tool should assist in the practical implementation of mine-water irrigation as part of optimal mine-water management

Almucantar radio telescope report 1: A preliminary study of the capabilities of large partially steerable paraboloidal antennas

The almucantar radio telescope development and characteristics are presented. The radio telescope consists of a paraboloidal reflector free to rotate in azimuth but limited in altitude between two fixed angles from the zenith. The fixed angles are designed to provide the capability where sources lying between two small circles parallel with the horizon (almucantars) are accessible at any one instant. Basic geometrical considerations in the almucantar design are presented. The capabilities of the almucantar telescope for source counting and for monitoring which are essential to a resolution of the cosmological problem are described