33 research outputs found
About Zitterbewegung and electron structure
We start from the spinning electron theory by Barut and Zanghi, which has
been recently translated into the Clifford algebra language. We "complete" such
a translation, first of all, by expressing in the Clifford formalism a
particular Barut-Zanghi (BZ) solution, which refers (at the classical limit) to
an internal helical motion with a time-like speed [and is here shown to
originate from the superposition of positive and negative frequency solutions
of the Dirac equation]. Then, we show how to construct solutions of the Dirac
equation describing helical motions with light-like speed, which meet very well
the standard interpretation of the velocity operator in the Dirac equation
theory (and agree with the solution proposed by Hestenes, on the basis
--however-- of ad-hoc assumptions that are unnecessary in the present
approach). The above results appear to support the conjecture that the
Zitterbewegung motion (a helical motion, at the classical limit) is responsible
for the electron spin.Comment: LaTeX; 11 pages; this is a corrected version of work appeared partly
in Phys. Lett. B318 (1993) 623 and partly in "Particles, Gravity and
Space-Time" (ed.by P.I.Pronin & G.A.Sardanashvily; World Scient., Singapore,
1996), p.34
Electron structure, Zitterbewegung, and the new non-linear Dirac-like equation
The recent literature shows a renewed interest, with various independent
approaches, in the classical theories for spin. Considering the possible
interest of those results, at least for the electron case, we purpose in this
paper to explore their physical and mathematical meaning, by the natural and
powerful language of Clifford algebras (which, incidentally, will allow us to
unify those different approaches). In such theories, the ordinary electron is
in general associated to the mean motion of a point-like "constituent" Q, whose
trajectory is a cylindrical helix. We find, in particular, that the object Q
obeys a new, non-linear Dirac-like equation, such that --when averaging over an
internal cycle (which corresponds to linearization)-- it transforms into the
ordinary Dirac equation (valid for the electron as a whole).Comment: LaTeX; 19 pages; this is a corrected version of work appeared partly
in Hadronic J. 18 (1995) 97 and partly in Phys.Lett. B318 (1993) 48
Shear Viscosity and Oscillations of Neutron Star Crusts
We calculate the electron shear viscosity (determined by Coulomb electron
collisions) for a dense matter in a wide range of parameters typical for white
dwarf cores and neutron star crusts. In the density range from ~10^3 g cm^-3 to
10^7-10^10 g cm^-3 we consider the matter composed of widely abundant
astrophysical elements, from H to Fe. For higher densities, 10^10-10^14 g
cm^-3, we employ the ground-state nuclear composition, taking into account
finite sizes of atomic nuclei and the distribution of proton charge over the
nucleus. Numerical values of the viscosity are approximated by an analytic
expression convenient for applications. Using the approximation of
plane-parallel layer we study eigenfrequencies, eigenmodes and viscous damping
times of oscillations of high multipolarity, l~500-1000, localized in the outer
crust of a neutron star. For instance, at l~500 oscillations have frequencies f
>= 40 kHz and are localized not deeper than ~300 m from the surface. When the
crust temperature decreases from 10^9 K to 10^7 K, the dissipation time of
these oscillations (with a few radial nodes) decreases from ~1 year to 10-15
days.Comment: 23 pages, 13 figure
Hippocampal state-dependent behavioral reflex to an identical sensory input in rats.
We examined the local field potential of the hippocampus to monitor brain states during a conditional discrimination task, in order to elucidate the relationship between ongoing brain states and a conditioned motor reflex. Five 10-week-old Wistar/ST male rats underwent a serial feature positive conditional discrimination task in eyeblink conditioning using a preceding light stimulus as a conditional cue for reinforced trials. In this task, a 2-s light stimulus signaled that the following 350-ms tone (conditioned stimulus) was reinforced with a co-terminating 100-ms periorbital electrical shock. The interval between the end of conditional cue and the onset of the conditioned stimulus was 4±1 s. The conditioned stimulus was not reinforced when the light was not presented. Animals successfully utilized the light stimulus as a conditional cue to drive differential responses to the identical conditioned stimulus. We found that presentation of the conditional cue elicited hippocampal theta oscillations, which persisted during the interval of conditional cue and the conditioned stimulus. Moreover, expression of the conditioned response to the tone (conditioned stimulus) was correlated with the appearance of theta oscillations immediately before the conditioned stimulus. These data support hippocampal involvement in the network underlying a conditional discrimination task in eyeblink conditioning. They also suggest that the preceding hippocampal activity can determine information processing of the tone stimulus in the cerebellum and its associated circuits
Sur la transition entre la combustion conductive et la combustion convective dans les matériaux poreux
La transition de la déflagration à la détonation (DDT) dans les propulsifs poreux est précédée par une première transition : la transition d’une combustion conductive à une combustion convective (CCT).On a donné une condition de stabilité pour la combustion conductive pour ces propulsifs poreux dont la densité à l’état fondu est supérieure à la densité à l'état solide non brûlé
Pontine stimulation overcomes developmental limitations in the neural mechanisms of eyeblink conditioning
Pontine neuronal activation during auditory stimuli increases ontogenetically between postnatal days (P) P17 and P24 in rats. Pontine neurons are an essential component of the conditioned stimulus (CS) pathway for eyeblink conditioning, providing mossy fiber input to the cerebellum. Here we examined whether the developmental limitation in pontine responsiveness to a CS in P17 rats could be overcome by direct stimulation of the CS pathway. Eyeblink conditioning was established in infant rats on P17-P18 and P24-P25 using pontine stimulation as a CS. There were no significant age-related differences in the rate or level of conditioning. Eyeblink conditioned responses established with the stimulation CS were abolished by inactivation of the ipsilateral cerebellar nuclei and overlying cortex in both age groups. The findings suggest that developmental changes in the CS pathway play an important role in the ontogeny of eyeblink conditioning