Archive for November, 2007
The Effect of Working Memory Load on Task Choice in Voluntary Task Switching
The voluntary task switching (VTS) paradigm allows subjects to choose the specific task to be performed on each trial. Subjects are instructed to perform each task equally often and in a random order; however, they tend to show a repetition bias, performing fewer switches than would be expected in a random sequence. Lack of executive resources
was assessed as a contributor to this repetition bias. A memory load manipulation was used to limit the executive resources available during VTS. Simple memory storage tasks, which required only the maintenance of memory letters, had no impact on VTS performance. However, a working memory load, which required the active manipulation
of memory letters during VTS, differentially reduced the proportion of switches such that greater repetition bias was found under greater working memory loads. The availability of executive resources at the time of task performance appears to influence task choice.
PTRANSP Simulations of Toroidal Momentum Transport in Neutral Beam Heated Tokamak Plasmas
The PTRANSP code is used to predict self-consistently the toroidal rotational frequency, electron temperature, ion temperature, and EB flow shear rate. Turbulence-driven thermal transport and toroidal momentum transport are computed using several transport models. A neoclassical contribution is added to the turbulence-driven toroidal momentum transport and thermal transport. It is found that inward fluxes of momentum can be generated by the Reynolds stress in the Weiland transport model. The neutral beam injection torque input, computed using the NUBEAM code, drives rotation in the plasma core, while charge exchange can drive rotation near the plasma edge. The poloidal velocity is computed using neoclassical theory. In H-mode discharges, it is found that the largest contribution to the EB flow shear is usually a consequence of toroidal rotation. The rotation frequency is investigated as a function of plasma parameters including the torque per particle. The simulated radial profiles of the toroidal rotational frequency, ion temperature, and electron temperature are compared with experimental data.
The Lambert W Function
The Lambert W function is the inverse of the complex-valued function f(x) = xex. It has been studied since the 1700s by the likes of Johann Lambert, Leonhard Euler, and E.M. Wright, and it has applications to problems in calculus, differential equations, graph theory, and computer science. This talk will present a survey of the most important properties of W and describe some of its applications in detail.
Consumption And Granular Flow In A Vibro-Fluidized Stirred Granular Bed
This work examines the behavior of a deep granular bed subject to simultaneous vertical vibration and stirring. The power necessary to stir a 5.6 cm diameter and 20 cm deep granular bed of 150 micron glass beads using a 4-blade vane impeller was measured over a wide range of forcing conditions. Impeller rotation rates from 0 – 1000 rpms and vibration accelerations in the range 0 < gamma < 4.0 were explored. Both the power required for stirring and vibration were recorded. Sharp changes in vane power draw indicate flow transitions from dense granular flow to vibro-fluidized flow at a critical acceleration. The total power profile (vane plus vibration power) demonstrates a minimum just above the critical acceleration. Progressive increases or decreases n both vane speed and gamma independently show hysteresis as the flow bifurcates between two primary states of dense granular flow and loose-packed, vibrofluidized behavior. These observations are compared to those found in fluidized systems and flows generated in high-shear granulators.
Shared sequences of the aromatase transcript in neurons and glia of the zebra finch brain.
In many vertebrates, the P450 enzyme aromatase (CYP19a; E-synthase) is expressed in multiple tissues including the brain and gonad. In the zebra finch (Taeniopygia guttata), the aromatase gene is alternatively spliced in the 5 untranslated region (UTR) resulting in two known transcripts expressed preferentially in the brain (Exon 1a) and ovary (Exon 1b). These transcripts share identical sequences from the beginning of their protein translational start sites (Exon 2), the coding region (Exons 3-9) and through the 3 UTR (Exons 9-10). In addition to these constitutively expressed transcripts, an inducible aromatase is expressed in reactive glia following damage to the zebra finch neuropil. Inducible aromatase is detectable 6 hours following mechanical injury and persists for at least 6 weeks. Towards understanding the regulation and expression of glial aromatase, we hypothesized that inducible (glial) aromatase represents a novel transcript in the zebra finch. To test this hypothesis, we: (i) examined the upregulation of specific amplicons within the aromatase transcript following mechanical injury using quantitative PCR (qPCR), (ii) performed 5 and 3 rapid amplification of cDNA ends (RACE) from RNA extracted from injured and non-injured brain, (iii) ran northern blot analysis on injured and non-injured telencephalic RNA and (iv) isolated the transcript in glial enriched cultures of the developing zebra finch telencephalon.