Irregular speech rate dissociates auditory cortical entrainment, evoked responses, and frontal alpha

The entrainment of slow rhythmic auditory cortical activity to the temporal regularities in speech is considered to be a central mechanism underlying auditory perception. Previous work has shown that entrainment is reduced when the quality of the acoustic input is degraded, but has also linked rhythmic activity at similar time scales to the encoding of temporal expectations. To understand these bottom-up and top-down contributions to rhythmic entrainment, we manipulated the temporal predictive structure of speech by parametrically altering the distribution of pauses between syllables or words, thereby rendering the local speech rate irregular while preserving intelligibility and the envelope fluctuations of the acoustic signal. Recording EEG activity in human participants, we found that this manipulation did not alter neural processes reflecting the encoding of individual sound transients, such as evoked potentials. However, the manipulation significantly reduced the fidelity of auditory delta (but not theta) band entrainment to the speech envelope. It also reduced left frontal alpha power and this alpha reduction was predictive of the reduced delta entrainment across participants. Our results show that rhythmic auditory entrainment in delta and theta bands reflect functionally distinct processes. Furthermore, they reveal that delta entrainment is under top-down control and likely reflects prefrontal processes that are sensitive to acoustical regularities rather than the bottom-up encoding of acoustic features

Addressing the Majorana vs. Dirac Question with Neutrino Decays

The Majorana versus Dirac nature of neutrinos remains an open question. This is due, in part, to the fact that virtually all the experimentally accessible neutrinos are ultra-relativistic. Noting that Majorana neutrinos can behave quite differently from Dirac ones when they are non-relativistic, we show that, at leading order, the angular distribution of the daughters in the decay of a heavy neutrino into a lighter one and a self-conjugate boson is isotropic in the parent's rest frame if the neutrinos are Majorana, independent of the parent's polarization. If the neutrinos are Dirac fermions, this is, in general, not the case. This result follows from CPT invariance and is independent of the details of the physics responsible for the decay. We explore the feasibility of using these angular distributions -- or, equivalently, the energy distributions of the daughters in the laboratory frame -- in order to address the Majorana versus Dirac nature of neutrinos if a fourth, heavier neutrino mass eigenstate reveals itself in the current or next-generation of high-energy colliders, intense meson facilities, or neutrino beam experiments.Comment: 11 pages, 3 figure

Analysis of slow (theta) oscillations as a potential temporal reference frame for information coding in sensory cortices

While sensory neurons carry behaviorally relevant information in responses that often extend over hundreds of milliseconds, the key units of neural information likely consist of much shorter and temporally precise spike patterns. The mechanisms and temporal reference frames by which sensory networks partition responses into these shorter units of information remain unknown. One hypothesis holds that slow oscillations provide a network-intrinsic reference to temporally partitioned spike trains without exploiting the millisecond-precise alignment of spikes to sensory stimuli. We tested this hypothesis on neural responses recorded in visual and auditory cortices of macaque monkeys in response to natural stimuli. Comparing different schemes for response partitioning revealed that theta band oscillations provide a temporal reference that permits extracting significantly more information than can be obtained from spike counts, and sometimes almost as much information as obtained by partitioning spike trains using precisely stimulus-locked time bins. We further tested the robustness of these partitioning schemes to temporal uncertainty in the decoding process and to noise in the sensory input. This revealed that partitioning using an oscillatory reference provides greater robustness than partitioning using precisely stimulus-locked time bins. Overall, these results provide a computational proof of concept for the hypothesis that slow rhythmic network activity may serve as internal reference frame for information coding in sensory cortices and they foster the notion that slow oscillations serve as key elements for the computations underlying perception

Flavor and chiral oscillations with Dirac wave packets

We report about recent results on Dirac wave packets in the treatment of neutrino flavor oscillation where the initial localization of a spinor state implies an interference between positive and negative energy components of mass-eigenstate wave packets. A satisfactory description of fermionic particles requires the use of the Dirac equation as evolution equation for the mass-eigenstates. In this context, a new flavor conversion formula can be obtained when the effects of chiral oscillation are taken into account. Our study leads to the conclusion that the fermionic nature of the particles, where chiral oscillations and the interference between positive and negative frequency components of mass-eigenstate wave packets are implicitly assumed, modifies the standard oscillation probability. Nevertheless, for ultra-relativistic particles and sharply peaked momentum distributions, we can analytically demonstrate that these modifications introduce correction factors proportional to (m12/p0) square which are practically un-detectable by any experimental analysisComment: 16 pages, 2 figure

Additional time-dependent phase in the flavor-conversion formulas

In the framework of intermediate wave-packets for treating flavor oscillations, we quantify the modifications which appear when we assume a strictly peaked momentum distribution and consider the second-order corrections in a power series expansion of the energy. By following a sequence of analytic approximations, we point out that an extra time-dependent phase is merely the residue of second-order corrections. Such phase effects are usually ignored in the relativistic wave-packet treatment, but they do not vanish non-relativistically and can introduce some small modifications to the oscillation pattern even in the ultra-relativistic limit.Comment: 9 pages, 3 figure

How can we test seesaw experimentally?

The seesaw mechanism for the small neutrino mass has been a popular paradigm, yet it has been believed that there is no way to test it experimentally. We present a conceivable outcome from future experiments that would convince us of the seesaw mechanism. It would involve a variety of data from LHC, ILC, cosmology, underground, and low-energy flavor violation experiments to establish the case.Comment: 5 pages, 4 figure

Microlensing Detections of Moons of Exoplanets

We investigate the characteristic of microlensing signals of Earth-like moons orbiting ice-giant planets. From this, we find that non-negligible satellite signals occur when the planet-moon separation is similar to or greater than the Einstein radius of the planet. We find that the satellite signal does not diminish with the increase of the planet-moon separation beyond the Einstein radius of the planet unlike the planetary signal which vanishes when the planet is located well beyond the Einstein radius of the star. We also find that the satellite signal tends to have the same sign as that of the planetary signal. These tendencies are caused by the lensing effect of the star on the moon in addition to the effect of the planet. We determine the range of satellite separations where the microlensing technique is optimized for the detections of moons. By setting an upper limit as the angle-average of the projected Hill radius and a lower limit as the half of the Einstein radius of the planet, we find that the microlensing method would be sensitive to moons with projected separations from the planet of $0.05 {\rm AU} \lesssim d_{\rm p} \lesssim 0.24 {\rm AU}$ for a Jupiter-mass planet, $0.03 {\rm AU}\lesssim d_{\rm p} \lesssim 0.17 {\rm AU}$ for a Saturn-mass planet, and $0.01 {\rm AU} \lesssim d_{\rm p} \lesssim 0.08 {\rm AU}$ for a Uranus-mass planet. We compare the characteristics of the moons to be detected by the microlensing and transit techniquesComment: 6pages, 6 figure

Flavor Neutrino Oscillations and Time-Energy Uncertainty Relation

We consider neutrino oscillations as non stationary phenomenon based on Schrodinger evolution equation and mixed states of neutrinos with definite flavors. We show that time-energy uncertainty relation plays a crucial role in neutrino oscillations. We compare neutrino oscillations with $B_{d}^{0}\leftrightarrows\bar B_{d}^{0}$ oscillations.Comment: A report at the 2nd Scandinavian Neutrino Workshop, SNOW 2006, Stockholm, May 2-6, 200

Optical measurements of the droplet size distribution in the case of fuel atomization in swirl nozzles and planar airblast diffusers

The theoretical principles of optical methods for the determination of the particle sizes of sprays are considered and aspects of the experimental implementation of these principles are discussed. An experimental device for point-intensity measurements makes use of a helium-neon laser. The cross-sectional area of the laser beam is enlarged with the aid of a lens system to the size of the measurement cross-section. The intensity of the laser light scattered by the spray particles is measured as a function of light direction. Approaches which take into account the total energy of the diffractively scattered light are also discussed and an investigation is conducted regarding the measurement error sources. A description is presented of experimental results obtained in studies of a number of fuel nozzle sprays