Theory of Interaction of Memory Patterns in Layered Associative Networks

A synfire chain is a network that can generate repeated spike patterns with millisecond precision. Although synfire chains with only one activity propagation mode have been intensively analyzed with several neuron models, those with several stable propagation modes have not been thoroughly investigated. By using the leaky integrate-and-fire neuron model, we constructed a layered associative network embedded with memory patterns. We analyzed the network dynamics with the Fokker-Planck equation. First, we addressed the stability of one memory pattern as a propagating spike volley. We showed that memory patterns propagate as pulse packets. Second, we investigated the activity when we activated two different memory patterns. Simultaneous activation of two memory patterns with the same strength led the propagating pattern to a mixed state. In contrast, when the activations had different strengths, the pulse packet converged to a two-peak state. Finally, we studied the effect of the preceding pulse packet on the following pulse packet. The following pulse packet was modified from its original activated memory pattern, and it converged to a two-peak state, mixed state or non-spike state depending on the time interval

Transport Coefficients of the Yukawa One Component Plasma

We present equilibrium molecular-dynamics computations of the thermal conductivity and the two viscosities of the Yukawa one-component plasma. The simulations were performed within periodic boundary conditions and Ewald sums were implemented for the potentials, the forces, and for all the currents which enter the Kubo formulas. For large values of the screening parameter, our estimates of the shear viscosity and the thermal conductivity are in good agreement with the predictions of the Chapman-Enskog theory.Comment: 11 pages, 2 figure

Monte Carlo simulations of the screening potential of the Yukawa one-component plasma

A Monte Carlo scheme to sample the screening potential H(r) of Yukawa plasmas notably at short distances is presented. This scheme is based on an importance sampling technique. Comparisons with former results for the Coulombic one-component plasma are given. Our Monte Carlo simulations yield an accurate estimate of H(r) as well for short range and long range interparticle distances.Comment: to be published in Journal of Physics A: Mathematical and Genera

Cavitation Inception on the I.T.T.C. Standard Head Form

Cavitation inception measurements were made on the I.T.T.C. Standard Head Form over a range of speeds and dissolved air content. The results were similar to those observed in other water tunnels with resorbers. Cavitation inception indices were observed as low as 0. 4 as compared with the minimum calculated pressure coefficient of O.6. As in previous measurements a pronounced velocity scale effect was observed

Discovery of Extremely Embedded X-ray Sources in the R Coronae Australis Star Forming Core

With the XMM-Newton and Chandra observatories, we detected two extremely embedded X-ray sources in the R Corona Australis (R CrA) star forming core, near IRS 7. These sources, designated as XB and XA, have X-ray absorption columns of ~3e23 cm-2 equivalent to AV ~180 mag. They are associated with the VLA centimeter radio sources 10E and 10W, respectively. XA is the counterpart of the near-infrared source IRS 7, whereas XB has no K-band counterpart above 19.4 mag. This indicates that XB is younger than typical Class I protostars, probably a Class 0 protostar or in an intermediate phase between Class 0 and Class I. The X-ray luminosity of XB varied between 29<log LX <31.2 ergs s-1 on timescales of 3-30 months. XB also showed a monotonic increase in X-ray brightness by a factor of two in 30 ksec during an XMM-Newton observation. The XMM-Newton spectra indicate emission from a hot plasma with kT ~3-4 keV and also show fluorescent emission from cold iron. Though the X-ray spectrum from XB is similar to flare spectra from Class I protostars in luminosity and temperature, the light curve does not resemble the lightcurves of magnetically generated X-ray flares because the variability timescale of XB is too long and because variations in X-ray count rate were not accompanied by variations in spectral hardness. The short-term variation of XB may be caused by the partial blocking of the X-ray plasma, while the month-long flux enhancement may be driven by mass accretion.Comment: 26 pages, 8 figures, To be published in ApJ in April 200

Forster energy transfer signatures in optically driven quantum dot molecules

The Forster resonant energy transfer mechanism (FRET) is investigated in optically driven and electrically gated tunnel coupled quantum dot molecules. Two novel FRET induced optical signatures are found in the dressed excitonic spectrum. This is constructed from exciton level occupation as function of pump laser energy and applied bias, resembling a level anticrossing spectroscopy measurement. We observe a redistribution of spectral weight and splitting of the exciton spectral lines. FRET among single excitons induces a splitting in the spatially-direct exciton lines, away from the anticrossing due to charge tunneling in the molecule. However, near the anticrossing, a novel signature appears as a weak satellite line following an indirect exciton line. FRET signatures may also occur among indirect excitons, appearing as split indirect lines. In that case, the signatures appear also in the direct biexciton states, as the indirect satellite mixes in near the tunneling anticrossing region