Mantle Source Regions and Magma Evolution along the Juan de Fuca Ridge, Pacific Ocean

Magmas are intruded and erupted along the axes of mid-ocean ridges. As part of a larger effort to understand crustal accretion at these plate boundaries, we are studying the petrology and geochemistry of erupted lavas to characterize magma plumbing systems and to determine the processes that occur during magma ascent and evolution. The focus of this research is the Juan de Fuca Ridge (JdF) which extends from the Blanco fracture zone at ~ 44.5° N to a triple junction with the Nootka Fault and the Sovanco fracture zone at 48.7° N in the northeastern Pacific ocean. Petrologic studies indicate that partial crystallization of magmas occurs in reservoirs located at various depths in the crust, and magmas evolve via crystallization in these reservoirs. A study of the trace element geochemistry of erupted lavas was undertaken to ascertain whether crystallization is the only process occurring during magma evolution and to probe the mantle source regions of the magmas. Geochemical data were compiled from Gale et al. (2013), and individual analyses were normalized to the composition of average Normal Mid-Ocean Ridge basalt (NMORB), CI chondrites, and the primitive mantle to aid interpretation of geochemical variations. Ratios of La/Sm, K/U, K/Ti, and K/P were calculated and plotted against latitude in order to determine the extent of crustal assimilation affecting the magmas, as well as to gain insight into the enrichment of the mantle sources. Furthermore, Na8 values from Scott et al. (2012) were examined to determine if different regions of the ridge had undergone different degrees of mantle melting. From this information, we determined that there are at least two mantle sources for the Juan de Fuca ridge: a Depleted MORB Mantle (DMM) source in the south, and a Normal Mid-Ocean Ridge Basalt (NMORB) source in the north. In addition, trace element data normalized to N-MORB show similar patterns of relative enrichment within ridges, but with large ranges of enrichment among different samples, particularly in segments 1, 2, 3, and 4, indicating that extensive fractional crystallization has occurred in those regions. Strontium anomalies also indicate that plagioclase played a major role in crystallization.A three-year embargo was granted for this item

Contribution of primary motor cortex to compensatory balance reactions

<p>Abstract</p> <p>Background</p> <p>Rapid compensatory arm reactions represent important response strategies following an unexpected loss of balance. While it has been assumed that early corrective actions arise largely from sub-cortical networks, recent findings have prompted speculation about the potential role of cortical involvement. To test the idea that cortical motor regions are involved in early compensatory arm reactions, we used continuous theta burst stimulation (cTBS) to temporarily suppress the hand area of primary motor cortex (M1) in participants prior to evoking upper limb balance reactions in response to whole body perturbation. We hypothesized that following cTBS to the M1 hand area evoked EMG responses in the stimulated hand would be diminished. To isolate balance reactions to the upper limb participants were seated in an elevated tilt-chair while holding a stable handle with both hands. The chair was held vertical by a magnet and was triggered to fall backward unpredictably. To regain balance, participants used the handle to restore upright stability as quickly as possible with both hands. Muscle activity was recorded from proximal and distal muscles of both upper limbs.</p> <p>Results</p> <p>Our results revealed an impact of cTBS on the amplitude of the EMG responses in the stimulated hand muscles often manifest as inhibition in the stimulated hand. The change in EMG amplitude was specific to the target hand muscles and occasionally their homologous pairs on the non-stimulated hand with no consistent effects on the remaining more proximal arm muscles.</p> <p>Conclusions</p> <p>Present findings offer support for cortical contributions to the control of early compensatory arm reactions following whole-body perturbation.</p

Can Monkeys Choose Optimally When Faced with Noisy Stimuli and Unequal Rewards?

We review the leaky competing accumulator model for two-alternative forced-choice decisions with cued responses, and propose extensions to account for the influence of unequal rewards. Assuming that stimulus information is integrated until the cue to respond arrives and that firing rates of stimulus-selective neurons remain well within physiological bounds, the model reduces to an Ornstein-Uhlenbeck (OU) process that yields explicit expressions for the psychometric function that describes accuracy. From these we compute strategies that optimize the rewards expected over blocks of trials administered with mixed difficulty and reward contingencies. The psychometric function is characterized by two parameters: its midpoint slope, which quantifies a subject's ability to extract signal from noise, and its shift, which measures the bias applied to account for unequal rewards. We fit these to data from two monkeys performing the moving dots task with mixed coherences and reward schedules. We find that their behaviors averaged over multiple sessions are close to optimal, with shifts erring in the direction of smaller penalties. We propose two methods for biasing the OU process to produce such shifts

Integration of Sensory and Reward Information during Perceptual Decision-Making in Lateral Intraparietal Cortex (LIP) of the Macaque Monkey

Single neurons in cortical area LIP are known to carry information relevant to both sensory and value-based decisions that are reported by eye movements. It is not known, however, how sensory and value information are combined in LIP when individual decisions must be based on a combination of these variables. To investigate this issue, we conducted behavioral and electrophysiological experiments in rhesus monkeys during performance of a two-alternative, forced-choice discrimination of motion direction (sensory component). Monkeys reported each decision by making an eye movement to one of two visual targets associated with the two possible directions of motion. We introduced choice biases to the monkeys' decision process (value component) by randomly interleaving balanced reward conditions (equal reward value for the two choices) with unbalanced conditions (one alternative worth twice as much as the other). The monkeys' behavior, as well as that of most LIP neurons, reflected the influence of all relevant variables: the strength of the sensory information, the value of the target in the neuron's response field, and the value of the target outside the response field. Overall, detailed analysis and computer simulation reveal that our data are consistent with a two-stage drift diffusion model proposed by Diederich and Bussmeyer [1] for the effect of payoffs in the context of sensory discrimination tasks. Initial processing of payoff information strongly influences the starting point for the accumulation of sensory evidence, while exerting little if any effect on the rate of accumulation of sensory evidence

The Ballad of Sam Bass

The Ballad of Sam Bass is an original. play based on the life of Sam Bass the outlaw. Cowboys camped on the Chisholm trail are entertained by a stranger who sings a song about Sam Bass. Bass was a good-hearted individual who was seduced by his vices, drinking and gambling, and fell into the life of an outlaw. He was successful in eluding the law until he was betrayed by one of his own men, Jim Murphy. In the course of his song, the stranger reveals himself to be Frank Jackson, the only surviving member of Bass's gang. Jackson had talked Bass out of killing Murphy when Bass became suspicious. Creating the song serves as a catharsis for Jackson's guilt

Autograph letters. What they are worth - The importance the pursuit of collecting has attained in this country. Some manuscripts of famous authors ... New York [189-].

Title.; On verso: M.C. # 09-82-038.244

Eulogy on Chief-Justice Chase, delivered by William M. Evarts before the alumni of Dartmouth college, at Hanover, June 24, 1874. Pub. at their request.

This pamphlet contains, the eulogy on Chief-Justice Chase, delivered by William M. Evarts before the alumni of Dartmouth college, at Hanover, June 24, 1874. Pub. at their request.https://scholarsjunction.msstate.edu/fvw-pamphlets/1028/thumbnail.jp

Arguments and speeches of William Maxwell Evarts,

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Eulogy on Chief-Justice Chase,

Mode of access: Internet

Memorandum : the sum awarded by the Tribunal at Geneva a mere equivalent of the losses of ships and cargoes destroyed, including the losses of masters and seamen by such destruction

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