The folding fingerprint of visual cortex reveals the timing of human V1 and V2

Primate neocortex contains over 30 visual areas. Recent techniques such as functional magnetic resonance imaging (fMRI) have successfully identified many of these areas in the human brain, but have been of limited value for revealing the temporal dynamics between adjacent visual areas, a critical component of understanding visual cognition. The voltages recorded at the scalp, electroencephalography (EEG), is a direct measure of neural activity that reflects the summed activity across all brain areas. Identifying the cortical sources that contribute to the EEG is a difficult problem. We developed an anatomically constrained dipole search method that solves the traditional problems by combining fMRI, EEG and many stimuli that activate small cortical regions. The method provides a means to validate the extracted waveforms. Both V1 and V2 waveforms have similar onset latencies as well as dynamics that can explain previous controversial findings about the responses of these areas

Nature of stochastic ion heating in the solar wind: testing the dependence on plasma beta and turbulence amplitude

The solar wind undergoes significant heating as it propagates away from the Sun; the exact mechanisms responsible for this heating are not yet fully understood. We present for the first time a statistical test for one of the proposed mechanisms, stochastic ion heating. We use the amplitude of magnetic field fluctuations near the proton gyroscale as a proxy for the ratio of gyroscale velocity fluctuations to perpendicular (with respect to the magnetic field) proton thermal speed, defined as $\epsilon_p$. Enhanced proton temperatures are observed when $\epsilon_p$ is larger than a critical value ($\sim 0.019 - 0.025$). This enhancement strongly depends on the proton plasma beta ($\beta_{||p}$); when $\beta_{||p} \ll 1$ only the perpendicular proton temperature $T_{\perp}$ increases, while for $\beta_{||p} \sim 1$ increased parallel and perpendicular proton temperatures are both observed. For $\epsilon_p$ smaller than the critical value and $\beta_{||p} \ll 1$ no enhancement of $T_p$ is observed while for $\beta_{||p} \sim 1$ minor increases in $T_{\parallel}$ are measured. The observed change of proton temperatures across a critical threshold for velocity fluctuations is in agreement with the stochastic ion heating model of Chandran et al. (2010). We find that $\epsilon_p > \epsilon_{\rm crit}$ in 76\% of the studied periods implying that stochastic heating may operate most of the time in the solar wind at 1 AU.Comment: Accepted for publication in The Astrophysical Journal Letter

Magnetic Reconnection May Control the Ion-Scale Spectral Break of Solar Wind Turbulence

The power spectral density of magnetic fluctuations in the solar wind exhibits several power-law-like frequency ranges with a well defined break between approximately 0.1 and 1 Hz in the spacecraft frame. The exact dependence of this break scale on solar wind parameters has been extensively studied but is not yet fully understood. Recent studies have suggested that reconnection may induce a break in the spectrum at a "disruption scale" $\lambda_D$, which may be larger than the fundamental ion kinetic scales, producing an unusually steep spectrum just below the break. We present a statistical investigation of the dependence of the break scale on the proton gyroradius $\rho_i$, ion inertial length $d_i$, ion sound radius $\rho_s$, proton-cyclotron resonance scale $\rho_c$ and disruption scale $\lambda_D$ as a function of $\beta_{\perp i}$. We find that the steepest spectral indices of the dissipation range occur when $\beta_e$ is in the range of 0.1-1 and the break scale is only slightly larger than the ion sound scale (a situation occurring 41% of the time at 1 AU), in qualitative agreement with the reconnection model. In this range the break scale shows remarkably good correlation with $\lambda_D$. Our findings suggest that, at least at low $\beta_e$, reconnection may play an important role in the development of the dissipation range turbulent cascade and causes unusually steep (steeper than -3) spectral indices.Comment: Accepted in ApJ

The Civil Justice System Bridges the Great Divide in Consumer Protection

This article discusses the tendency of American consumers to place their confidence -- often blindly -- in agencies such as the FDA and the Consumer Product Safety Commission. It further analyzes the issue that recent events related to the pharmaceutical industry and the FDA raise serious doubts as to whether that blind trust is uniformly justified

Influence of quark boundary conditions on the pion mass in finite volume

We calculate the mass shift for the pion in a finite volume with renormalization group (RG) methods in the framework of the quark-mesons model. In particular, we investigate the importance of the quark effects on the pion mass. As in lattice gauge theory, the choice of quark boundary conditions has a noticeable effect on the pion mass shift in small volumes, in addition to the shift due to pion interactions. We compare our results to chiral perturbation theory calculations and find differences due to the fact that chiral perturbation theory only considers pion effects in the finite volume.Comment: 24 pages, 5 figures, RevTex4, published version, discussion of lattice results extende

Strong Preferential Ion Heating is Limited to within the Solar Alfvén Surface

The decay of the solar wind helium-to-hydrogen temperature ratio due to Coulomb thermalization can be used to measure how far from the Sun strong preferential ion heating occurs. Previous work has shown that a zone of preferential ion heating, resulting in mass-proportional temperatures, extends about 20-40 R-circle dot from the Sun on average. Here we look at the motion of the outer boundary of this zone with time and compare it to other physically meaningful distances. We report that the boundary moves in lockstep with the Alfven point over the solar cycle, contracting and expanding with solar activity with a correlation coefficient of better than 0.95 and with an rms difference of 4.23 R-circle dot. Strong preferential ion heating is apparently predominately active below the Alfven surface. To definitively identify the underlying preferential heating mechanisms, it will be necessary to make in situ measurements of the local plasma conditions below the Alfven surface. We predict that the Parker Solar Probe (PSP) will be the first spacecraft to directly observe this heating in action, but only a couple of years after launch as activity increases, the zone expands, and PSP's perihelion drops.Wind grant [NNX14AR78G]; NASA HSR grant [NNX16AM23G]Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Cohort-Specific Online Discussion Experiences: A Collaborative And Multidisciplinary Approach To Improving Student Learning

Research addressing the effects of cohort size on student success in asynchronous online discussions is sparse.  As such, the following study attempted to determine an optimal student cohort size to enhance success and engagement within online discussions in general education courses at a large post-secondary university consisting of predominately adult learners.  Experimental courses split mandatory discussions into one, two, or three cohorts to maintain a discussion size of no more than ten students per cohort per week.  The effects of cohort size on student grade-point-average (GPA), withdraw rate, fail rate, and progression rate was evaluated in addition to effects on student satisfaction as measured by end-of-course surveys (EoCS).  Results showed no significant difference in either student success or student satisfaction between courses with one, two, or three online discussion cohorts.  Future online education research should focuses on upper division courses where students might benefit from smaller group discussions

Volume Dependence of the Pion Mass in the Quark-Meson-Model

We consider the quark-meson-model in a finite three-dimensional volume using the Schwinger proper-time renormalization group. We derive and solve the flow equations for finite volume in local potential approximation. In order to break chiral symmetry in the finite volume, we introduce a small current quark mass. The corresponding effective meson potential breaks chiral O(4) symmetry explicitly, depending on sigma and pion fields separately. We calculate the volume dependence of the pion mass and of the pion decay constant with the renormalization group flow equations and compare with recent results from chiral perturbation theory in a finite volume.Comment: 28 pages, 5 figures, v2: minor changes, references updated, final version published in Phys. Rev.

Large-scale Control of Kinetic Dissipation in the Solar Wind

In this Letter we study the connection between the large-scale dynamics of the turbulence cascade and particle heating on kinetic scales. We find that the inertial range turbulence amplitude ($\delta B_i$; measured in the range of 0.01-0.1 Hz) is a simple and effective proxy to identify the onset of significant ion heating and when it is combined with $\beta_{||p}$, it characterizes the energy partitioning between protons and electrons ($T_p/T_e$), proton temperature anisotropy ($T_{\perp}/T_{||}$) and scalar proton temperature ($T_p$) in a way that is consistent with previous predictions. For a fixed $\delta B_i$, the ratio of linear to nonlinear timescales is strongly correlated with the scalar proton temperature in agreement with Matthaeus et al., though for solar wind intervals with $\beta_{||p}>1$ some discrepancies are found. For a fixed $\beta_{||p}$, an increase of the turbulence amplitude leads to higher $T_p/T_e$ ratios, which is consistent with the models of Chandran et al. and Wu et al. We discuss the implications of these findings for our understanding of plasma turbulence.Comment: Accepted in ApJ

A zone of preferential ion heating extends tens of solar radii from Sun

The extreme temperatures and non-thermal nature of the solar corona and solar wind arise from an unidentified physical mechanism that preferentially heats certain ion species relative to others. Spectroscopic indicators of unequal temperatures commence within a fraction of a solar radius above the surface of the Sun, but the outer reach of this mechanism has yet to be determined. Here we present an empirical procedure for combining interplanetary solar wind measurements and a modeled energy equation including Coulomb relaxation to solve for the typical outer boundary of this zone of preferential heating. Applied to two decades of observations by the Wind spacecraft, our results are consistent with preferential heating being active in a zone extending from the transition region in the lower corona to an outer boundary 20-40 solar radii from the Sun, producing a steady state super-mass-proportional $\alpha$-to-proton temperature ratio of $5.2-5.3$. Preferential ion heating continues far beyond the transition region and is important for the evolution of both the outer corona and the solar wind. The outer boundary of this zone is well below the orbits of spacecraft at 1 AU and even closer missions such as Helios and MESSENGER, meaning it is likely that no existing mission has directly observed intense preferential heating, just residual signatures. We predict that {Parker Solar Probe} will be the first spacecraft with a perihelia sufficiently close to the Sun to pass through the outer boundary, enter the zone of preferential heating, and directly observe the physical mechanism in action.Comment: 11 pages, 7 figures, accepted for publication in the Astrophysical Journal on 1 August 201