1,175 research outputs found

    Selected field trips in and near Boston for classes in the social studies

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    Thesis (Ed.M.)--Boston University, 1949. This item was digitized by the Internet Archive

    The Morphologically Divided Redshift Distribution of Faint Galaxies

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    We have constructed a morphologically divided redshift distribution of faint field galaxies using a statistically unbiased sample of 196 galaxies brighter than I = 21.5 for which detailed morphological information (from the Hubble Space Telescope) as well as ground-based spectroscopic redshifts are available. Galaxies are classified into 3 rough morphological types according to their visual appearance (E/S0s, Spirals, Sdm/dE/Irr/Pec's), and redshift distributions are constructed for each type. The most striking feature is the abundance of low to moderate redshift Sdm/dE/Irr/Pec's at I < 19.5. This confirms that the faint end slope of the luminosity function (LF) is steep (alpha < -1.4) for these objects. We also find that Sdm/dE/Irr/Pec's are fairly abundant at moderate redshifts, and this can be explained by strong luminosity evolution. However, the normalization factor (or the number density) of the LF of Sdm/dE/Irr/Pec's is not much higher than that of the local LF of Sdm/dE/Irr/Pec's. Furthermore, as we go to fainter magnitudes, the abundance of moderate to high redshift Irr/Pec's increases considerably. This cannot be explained by strong luminosity evolution of the dwarf galaxy populations alone: these Irr/Pec's are probably the progenitors of present day ellipticals and spiral galaxies which are undergoing rapid star formation or merging with their neighbors. On the other hand, the redshift distributions of E/S0s and spirals are fairly consistent those expected from passive luminosity evolution, and are only in slight disagreement with the non-evolving model.Comment: 11 pages, 4 figures (published in ApJ

    Event-Related Potentials Reveal Differential Brain Regions Implicated in Discounting in Two Tasks

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    The way people make decisions about future benefits termed discounting - has important implications for both financial planning and health behaviour. Several theories assume that, when delaying gratification, the lower weight given to future benefits (the discount rate) declines exponentially. However there is considerable evidence that it declines hyperbolically with the rate of discount being proportionate to the delay distance. There is relatively little evidence as to whether neural areas mediating timedependent discounting processes differ according to the nature of the task. The present study investigates the potential neurological mechanisms underpinning domain-specific discounting processes. We present high-density event-related potentials (ERPs) data from a task in which participants were asked to make decisions about financial rewards or their health over short and long time-horizons. Participants (n=17) made a button-press response to their preference for an immediate or delayed gain (in the case of finance) or loss (in the case of health), with the discrepancy in the size of benefits/losses varying between alternatives. Waveform components elicited during the task were similar for both domains and included posterior N1, frontal P2 and posterior P3 components. We provide source dipole evidence that differential brain activation does occur across domains with results suggesting the possible involvement of the right cingulate gyrus and left claustrum for the health domain and the left medial and right superior frontal gyri for the finance domain. However, little evidence for differential activation across time horizons is found.

    Event-related Potentials reveal differential Brain Regions implicated in Discounting in Two Tasks

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    The way people make decisions about future benefits – termed discounting - has important implications for both financial planning and health behaviour. Several theories assume that, when delaying gratification, the lower weight given to future benefits (the discount rate) declines exponentially. However there is considerable evidence that it declines hyperbolically with the rate of discount being proportionate to the delay distance. There is relatively little evidence as to whether neural areas mediating time- dependent discounting processes differ according to the nature of the task. The present study investigates the potential neurological mechanisms underpinning domain-specific discounting processes. We present high-density event-related potentials (ERPs) data from a task in which participants were asked to make decisions about financial rewards or their health over short and long time-horizons. Participants (n=17) made a button-press response to their preference for an immediate or delayed gain (in the case of finance) or loss (in the case of health), with the discrepancy in the size of benefits/losses varying between alternatives. Waveform components elicited during the task were similar for both domains and included posterior N1, frontal P2 and posterior P3 components. We provide source dipole evidence that differential brain activation does occur across domains with results suggesting the possible involvement of the right cingulate gyrus and left claustrum for the health domain and the left medial and right superior frontal gyri for the finance domain. However, little evidence for differential activation across time horizons is found.Decision Making, Domain-Specific Discounting, Event-Related Potentials

    High-density event-related potentials: Current theories and practice

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    Event-Related Potentials (ERPs) are changes in the ongoing electrical activity of the brain (Electroencephalograms, or EEGs) which are caused by the specific occurrence of a cognitive, motor or perceptual event. Any changes in EEG due to the demands of the task are amplified, averaged and extracted as ERP waveforms (see Figure 1). These wave-forms are measured as the difference between the electrical activity of a baseline reference electrode attached to an electrically inactive site, such as the mastoid bone below the ear or the naison on the nose, and the electrical activity of the areas of the brain covered by the electrodes. These changes allow neuroscientists to determine what areas of brain are being stimulated at a given time (and therefore which brain areas are involved in a given process), precisely when these areas become activated and what happens in these areas when people make an error

    Securities Law: Seventh Circuit Review of Remedies, Definitions, Standing and Sanctions

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    Design of a solar energy centre for providing lighting and income-generating activities for off-grid rural communities in Kenya

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    One of the biggest challenges in the developing world is the provision of affordable and reliable electricity access to rural and marginalized people where grid extension is prohibitively expensive. Many off-grid schemes to date have focused on household lighting with mixed success. Some of the greatest difficulties have been around affordability and sustainability of the service provided, with systems being abandoned or removed due to broken equipment or inability of the user to continue paying for the service. It has been reported that key to the success of the best programs has been the means to improve the economic prospects of the users. In this paper the design of a solar energy centre for a rural village in Kenya, that enables income-generating activities for the community in addition to basic lighting and mobile phone charging provision, will be reported. We have found that it is possible to use the energy centre model to provide power for activities that could offer a source of income for the community, at an affordable cost with equipment available in Kenya today. It is believed that this will allow the community to develop economically and therefore ensure the sustainability of the off-grid power supply
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