Individual differences in alpha frequency drive crossmodal illusory perception

Perception routinely integrates inputs from different senses. Stimulus temporal proximity critically determines whether or not these inputs are bound together. Despite the temporal window of integration being a widely accepted notion, its neurophysiological substrate remains unclear. Many types of common audio-visual interactions occur within a time window of -100ms [1-5]. For example, in the sound- induced double-flash illusion, when two beeps are presented within -100ms together with one flash, a second illusory flash is often perceived [2]. Due to their intrinsic rhythmic nature, brain oscillations are one candidate mechanism for gating the temporal window of integration. Interestingly, occipital alpha-band oscillations cycle on average every -100ms with peak frequencies ranging between 8-14Hz (i.e. 120-60ms cycle). Moreover, presenting a brief tone can phase-reset such oscillations in visual cortex [6, 7]. Based on these observations, we hypothesized that the duration of each alpha cycle might provide the temporal unit to bind audio-visual events. Here we first recorded EEG while participants performed the sound-induced double-flash illusion task [4] and found positive correlation between individual alpha-frequency (IAF) peak and the size of the temporal window of the illusion. Participants then performed the same task while receiving occipital transcranial alternating current stimulation (tACS), to modulate oscillatory activity [8] either at their IAF or at off-peak alpha-frequencies (IAF±2Hz). Compared to IAF tACS, IAF-2Hz and IAF+2Hz tACS respectively enlarged and shrunk the temporal window of illusion, suggesting that alpha oscillations might represent the temporal unit of visual processing that cyclically gates perception and the neurophysiological substrate promoting audio-visual interactions

Encoding of temporal probabilities in the human brain

Anticipating the timing of future events is a necessary precursor to preparing actions and allocating resources to sensory processing. This requires elapsed time to be represented in the brain and used to predict the temporal probability of upcoming events. While neuropsychological, imaging, magnetic stimulation studies, and single-unit recordings implicate the role of higher parietal and motor-related areas in temporal estimation, the role of earlier, purely sensory structures remains more controversial. Here we demonstrate that the temporal probability of expected visual events is encoded not by a single area but by a wide network that importantly includes neuronal populations at the very earliest cortical stages of visual processing. Moreover, we show that activity in those areas changes dynamically in a manner that closely accords with temporal expectations

Nitrogen transfer between clover and wheat in an intercropping experiment

A novel approach to the problem of improving nitrogen supply in organic farming is to use intercropping of cereals with a legume to provide nitrogen transfer within a season and/or to following crops. The affects of intercropping were studied in a column experiment using mixtures of winter wheat (Triticum aestivum cv. Claire), with white clover (w.c.) (Trifolium repens cv. Barblanca) and with red clover (r.c.) (Trifolium pratense cv. Britta). The effects of cutting and removal above ground clover material with and without additional soil disturbance were compared to leaving clover plants in situ and intercropped with wheat in a split root design. Wheat and clover plants, as monocultures, were used for the controls. 15N ammonium nitrate solution was applied. The wheat seeds were sown into the column without nitrogen. We found that the cutting treatment produced the highest yield of wheat. Available ammonium-N in the soil was greatest in the clover control treatment for the column with only red clover roots and in the cutting+soil disturbance treatment for the column with only white clover roots. Available nitrate-N was greatest in the soil disturbance treatment in the column with clover and wheat roots for both red and white clover. The cutting treatment produced the highest yield of wheat

Meson Synchrotron Emission from Central Engines of Gamma-Ray Bursts with Strong Magnetic Fields

Gamma-ray bursts (GRBs) are presumed to be powered by still unknown central engines for the timescales in the range $1ms \sim$ a few s. We propose that the GRB central engines would be a viable site for strong meson synchrotron emission if they were the compact astrophysical objects such as neutron stars or rotating black holes with extremely strong magnetic fields $H \sim10^{12} - 10^{17}G$ and if protons or heavy nuclei were accelerated to ultra-relativistic energies of order $\sim 10^{12}-10^{22}eV$. We show that the charged scalar mesons like $\pi^{\pm}$ and heavy vector mesons like $\rho$, which have several decay modes onto $\pi^{\pm}$, could be emitted with high intensity a thousand times larger than photons through strong couplings to ultra-relativistic nucleons. These meson synchrotron emission processes eventually produce a burst of very high-energy cosmic neutrinos with $10^{12} eV \leq E_{\nu}$. These neutrinos are to be detected during the early time duration of short GRBs.Comment: 12 pages, 4 figures. Accepted for publication in the Astrophysical Journal Letter

Internal Migration and Regional Population Dynamics in Europe: Romanian Case Study

The report analyses population migration and change in Romania over the period 1984-1994. The analysis of population change is conducted for 2948 communes and towns, the finest administrative division for which population data are available. The lack of migration data on the level of communes and towns makes in-depth analysis of the migration for small spatial units impossible. For that reason analysis of the patterns of migration is conducted for 40 Judete (also referred to as counties or regions) and the capital city of Bucharest, i.e. 41 units altogether. Council of Europe Publishing, F-67075 Strasbourg - Cedex, France

Physical parameters and emission mechanism in Gamma-Ray Bursts

Detailed information on the physical parameters in the sources of cosmological Gamma-Ray Bursts (GRBs) is obtained from few plausible assumptions consistent with observations. Model-independent requirements posed by these assumptions on the emission mechanism in GRBs are formulated. It is found that the observed radiation in sub-MeV energy range is generated by the synchrotron emission mechanism, though about ten per cent of the total GRB energy should be converted via the inverse Compton process into ultra-hard spectral domain (above 100 GeV). We estimate the magnetic field strength in the emitting region, the Lorentz factor of accelerated electrons, and the typical energy of IC photons. We show that there is a "line-of-death" relation for GRBs and derive from this relation the lower limits on both GRB duration and GRB variability timescale. The upper limit on the Lorentz factor of GRB fireballs is also found. We demonstrate that steady-state electron distribution consistent with the Compton losses may produce different spectral indices, e.g., 3/4 as opposed to the figure 1/2 widely discussed in the literature. It is suggested that the changes in the decline rate observed in the lightcurves of several GRB afterglows may be due to the time evolution of spectral break, which appears in the synchrotron emission generated by steady-state self-consistent electron distribution.Comment: Journal reference added, introduction extended, minor changes in notation

On ammonia futile cycling in a marine unicellular alga

AbstractFutile cycling of ammonia, involving passive release of NH3 and active transport of NH4+, is potentially a major energetic cost to a unicellular organism. Nitrogen-starved cells of the marine diatom Phaeodactylum tricornutum possess a sodium-dependent transport system for the ammonium (NH4+) analogue methylammonium (CH3NH3+). In nitrogen-replete cells and nitrogen-starved cells incubated in the absence of sodium the rate of methylamine uptake was low and increased as a linear function of increasing methylamine concentration. Cells incubated with 21 μM ammonia or 500 μM methylamine (which give the same concentration of uncharged base), had similar rates of uptake in both nitrogen-replete and nitrogen-starved cells. In nitrogen-replete cells there was no inhibition of ammonia or methylamine uptake in the absence of sodium, but there was a marked inhibition for both with nitrogen-starved cells. However, despite the abolition of active CH3NH3+ and NH4+ uptake by nitrogen-starved cells in the absence of sodium, these cells did not release ammonia. Moreover, neither urea or low pH (which decreased the rate of ammonia uptake) induced release of ammonia in the absence of sodium. In contrast, nitrogen-replete cells released ammonia in darkness, with greater release occurring in the absence of sodium. Absence of sodium was as effective as the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) in inhibiting methylamine uptake by nitrogen-starved cells. However, release of preaccumulated methylamine by nitrogen-starved cells only occurred in the presence of CCCP; there was little release in the absence of sodium. These results suggest that futile cycling of ammonia across the plasma membrane of P. tricornutum is not quantitatively significant

Neutrinos from Early-Phase, Pulsar-Driven Supernovae

Neutron stars, just after their formation, are surrounded by expanding, dense, and very hot envelopes which radiate thermal photons. Iron nuclei can be accelerated in the wind zones of such energetic pulsars to very high energies. These nuclei photo-disintegrate and their products lose energy efficiently in collisions with thermal photons and with the matter of the envelope, mainly via pion production. When the temperature of the radiation inside the envelope of the supernova drops below $\sim 3\times 10^6$ K, these pions decay before losing energy and produce high energy neutrinos. We estimate the flux of muon neutrinos emitted during such an early phase of the pulsar - supernova envelope interaction. We find that a 1 km$^2$ neutrino detector should be able to detect neutrinos above 1 TeV within about one year after the explosion from a supernova in our Galaxy. This result holds if these pulsars are able to efficiently accelerate nuclei to energies $\sim 10^{20}$ eV, as postulated recently by some authors for models of Galactic acceleration of the extremely high energy cosmic rays (EHE CRs).Comment: 16 pages, 3 figures, revised version submitted to Ap

Postcard: John D Knox & Company

This black and white printed postcard contains correspondence from John D. Knox & Co. in Topeka, Kansas to a man serving as treasurer in Minneapolis, Kansas. Printed text and handwriting are on the front of the card. Handwriting is on the back of the card.https://scholars.fhsu.edu/tj_postcards/2162/thumbnail.jp