Program konačnih razlika četvrtog reda točnosti za simulaciju rasprostiranja SH-vala u heterogenom viskoelastičnom sredstvu

This article presents a staggered grid time-domain finite-difference (FD) program for the simulation of sH-wave propagation in a viscoelastic heteroge¬neous medium. The incorporation of realistic damping in FD program is based on a rheological model widely known as generalized maxwell body (gmB-EK). The accuracy of implementation of realistic damping is validated by comparing the numerically computed frequency dependent quality factors and phase velocity with the same computed using gmB-EK rheological model and the Futterman’s relationship. The accuracy was also validated by comparing the numerically com¬puted soil amplification at resonance frequency for different damping with the analytical solutions. The stability and grid dispersion are also studied in details.Prikazan je program konačnih razlika (FD) na razmaknutoj mreži u vremenskoj domeni za simulaciju rasprostiranja sH-vala u viskoelastičnom heterogenom sredstvu. Uključivanje realističnog prigušenja u program temelji se na reološkom modelu poznatom kao generalizirano maxwellovo tijelo (gmB-EK). Valjanost implementiranog prigušenja je potvrđena usporedbom numerički dobivenih frekventno ovisnih kvalitativnih faktora i fazne brzine s onima izračunatim gmB-EK reološkim modelom i korištenjem Futter¬manove relacije. Točnost je potvrđena i usporedbom numerički izračunate amplifikacije tla pri rezonantnoj frekvenciji za različito prigušenje s analitičkim rješenjima. stabilnost i disperzija mreže su također detaljno istraženi

EFFECTS OF MEDU AND COASTAL TOPOGRAPHY ON THE DAMAGE PATTERN DURING THE RECENT INDIAN OCEAN TSUNAMI ALONG THE COAST OF TAMILNADU

Effects of Medu (naturally elevated landmass very close to the seashore and elongated parallel to the coast) and coastal topography on the damage pattern during the deadliest Indian Ocean tsunami of December 26, 2004 is reported. The tsunami caused severe damage and claimed many victims in the coastal areas of eleven countries bordering the Indian Ocean. The damage survey revealed large variation in damage along the coastal region of Tamilnadu (India).The most severe damage was observed in the Nagapattinam district on the east coast and the west coast of Kanyakumari district. Decrease of damage from Nagapattinam to Kanchipuram district was observed. Intense damage again appeared to the north of Adyar River (from Srinivaspuri to Anna Samadhi Park). Almost, no damage was observed along the coast of Thanjavur, Puddukkotai and Ramnathpuram districts in Palk Strait, situated in the shadow zone of Sri Lanka.It was concluded that the width of continental shelf has played a major role in the pattern of tsunami damage. It was inferred that the width of the continental shelf and the interference of reflected waves from Sri Lanka and Maldives Islands with direct waves and receding waves was responsible for intense damage in Nagapattinam and Kanyakumari districts, respectively. During the damage survey authors also noted that there was almost no damage or much lesser damage to houses situated on or behind the Medu. Many people observed the first arrival. The largest tsunami amplitude occurred as the first arrival on the eastern coast and in the second arrival on the western coast

Bio-energetic preservation of cones in a mouse model of retinitis pigmentosa

ARVO Annual Meeting AbstractDaniel Narayan, Glyn Chidlow, John P M Wood, Robert James Casso

P-SV valni algoritam konačnih razlika četvrtog reda točnosti na razmaknutoj mreži s varijabilnom veličinom mreže i VGR-metodom dijagnostike napetosti

The implementation of VGR-stress imaging technique, as a free surface boundary condition, in a (2, 4) staggered grid P-SV wave finite difference (FD) algorithm with a variable size of a grid cell is presented in this paper. VGR is acronym for \u27vertical grid-size reduction\u27. The qualitative and quantitative results confirmed that the effective thickness (ETH) of the first soil layer become less by one-half of the vertical size of a grid cell than the assigned thickness (ATH), if stress imaging technique is used as a free surface boundary condition. The results of various numerical experiments revealed that the stress imaging technique causes significant numerical dispersion of Rayleigh waves and the VGR-stress imaging technique is efficient enough to avoid the same. So, superiority associated with the VGR-stress imaging technique over the well stress imaging technique is that it avoids both the significant numerical dispersion of Rayleigh waves in homogeneous medium and the soil thickness discrepancy. The maximum grid spacing ratio (ratio of largest to smallest size of a grid cell) up to 6.0 did not affect the accuracy of FD algorithm with a variable size of a grid cell. In case of a variable size of a grid cell, the required computational memory and time for a particular basin-edge model was 6.43 and 16.62 times lesser than that required in case of uniform grid.Prikazana je primjena VGR-metode dijagnostike napetosti (engl. VGR-stress imaging technique), kao slobodnog rubnog uvjeta na površini, u (2,4) P-SV valnom algoritmu konačnih razlika (engl. finite difference, FD) na razmaknutoj mreži s varijabilnom veličinom mrežne ćelije. VGR je akronim za smanjenje vertikalne veličine mreže (engl. vertical grid-size reduction). Kvalitativni i kvantitativni rezultati potvrdili su da efektivna debljina (engl. effective thickness, ETH) prvog sloja tla postaje za polovinu vertikalnog koraka mreže manja od pridijeljene debljine (engl. assigned thickness, ATH), ukoliko se metoda dijagnostike napetosti koristi kao slobodan rubni uvjet na površini. Rezultati različitih numeričkih eksperimenata otkrili su da uobičajeno korištena metoda dijagnostike naprezanja dovodi do značajne numeričke disperzije Rayleighevih valova, dok je VGR-metoda dovoljno učinkovita da to izbjegne. Nadmoć VGR-metode nad dobro poznatom metodom dijagnostike napetosti se stoga očituje u izbjegavanju značajne numeričke disperzije Rayleighevih valova u homogenom sredstvu, kao i manjem odstupanju u debljini sloja tla. Maksimalni omjer koraka mreže (tj. omjer najveće prema najmanjoj veličini mrežne ćelije) do 6.0 nije utjecao na točnost FD algoritma s varijabilnom veličinom mrežne ćelije. U slučaju varijabilne mreže, računalna memorija i vrijeme računanja potrebni za određeni model ruba bazena bili su 6.43, odnosno 16.62 puta manji nego u slučaju jednolike mreže

Vector lattice model for stresses in granular materials

A vector lattice model for stresses in granular materials is proposed. A two dimensional pile built by pouring from a point is constructed numerically according to this model. Remarkably, the pile violates the Mohr Coulomb stability criterion for granular matter, probably because of the inherent anisotropy of such poured piles. The numerical results are also compared to the earlier continuum FPA model and the (scalar) lattice $q$-model

Low-Luminosity Accretion in Black Hole X-ray Binaries and Active Galactic Nuclei

At luminosities below a few percent of Eddington, accreting black holes switch to a hard spectral state which is very different from the soft blackbody-like spectral state that is found at higher luminosities. The hard state is well-described by a two-temperature, optically thin, geometrically thick, advection-dominated accretion flow (ADAF) in which the ions are extremely hot (up to $10^{12}$ K near the black hole), the electrons are also hot ($\sim10^{9-10.5}$ K), and thermal Comptonization dominates the X-ray emission. The radiative efficiency of an ADAF decreases rapidly with decreasing mass accretion rate, becoming extremely low when a source reaches quiescence. ADAFs are expected to have strong outflows, which may explain why relativistic jets are often inferred from the radio emission of these sources. It has been suggested that most of the X-ray emission also comes from a jet, but this is less well established.Comment: To appear in "From X-ray Binaries to Quasars: Black Hole Accretion on All Mass Scales" edited by T. Maccarone, R. Fender, L. Ho, to be published as a special edition of "Astrophysics and Space Science" by Kluwe

Universal energy distribution for interfaces in a random field environment

We study the energy distribution function $\rho (E)$ for interfaces in a random field environment at zero temperature by summing the leading terms in the perturbation expansion of $\rho (E)$ in powers of the disorder strength, and by taking into account the non perturbational effects of the disorder using the functional renormalization group. We have found that the average and the variance of the energy for one-dimensional interface of length $L$ behave as, $_{R}\propto L\ln L$, $\Delta E_{R}\propto L$, while the distribution function of the energy tends for large $L$ to the Gumbel distribution of the extreme value statistics.Comment: 4 pages, 2 figures, revtex4; the distribution function of the total and the disorder energy is include

Clues on black hole feedback from simulated and observed X-ray properties of elliptical galaxies

The centers of elliptical galaxies host supermassive black holes that significantly affect the surrounding interstellar medium through feedback resulting from the accretion process. The evolution of this gas and of the nuclear emission during the galaxies' lifetime has been studied recently with high-resolution hydrodynamical simulations. These included gas cooling and heating specific for an average AGN spectral energy distribution, a radiative efficiency declining at low mass accretion rates, and mechanical coupling between the hot gas and AGN winds. Here we present a short summary of the observational properties resulting from the simulations, focussing on 1) the nuclear luminosity; 2) the global luminosity and temperature of the hot gas; 3) its temperature profile and X-ray brightness profile. These properties are compared with those of galaxies of the local universe, pointing out the successes of the adopted feedback and the needs for new input in the simulations.Comment: 15 pages, 6 figures, accepted for publication in Advances in Space Researc

Random walks and polymers in the presence of quenched disorder

After a general introduction to the field, we describe some recent results concerning disorder effects on both `random walk models', where the random walk is a dynamical process generated by local transition rules, and on `polymer models', where each random walk trajectory representing the configuration of a polymer chain is associated to a global Boltzmann weight. For random walk models, we explain, on the specific examples of the Sinai model and of the trap model, how disorder induces anomalous diffusion, aging behaviours and Golosov localization, and how these properties can be understood via a strong disorder renormalization approach. For polymer models, we discuss the critical properties of various delocalization transitions involving random polymers. We first summarize some recent progresses in the general theory of random critical points : thermodynamic observables are not self-averaging at criticality whenever disorder is relevant, and this lack of self-averaging is directly related to the probability distribution of pseudo-critical temperatures $T_c(i,L)$ over the ensemble of samples $(i)$ of size $L$. We describe the results of this analysis for the bidimensional wetting and for the Poland-Scheraga model of DNA denaturation.Comment: 17 pages, Conference Proceedings "Mathematics and Physics", I.H.E.S., France, November 200

Universal interface width distributions at the depinning threshold

We compute the probability distribution of the interface width at the depinning threshold, using recent powerful algorithms. It confirms the universality classes found previously. In all cases, the distribution is surprisingly well approximated by a generalized Gaussian theory of independant modes which decay with a characteristic propagator G(q)=1/q^(d+2 zeta); zeta, the roughness exponent, is computed independently. A functional renormalization analysis explains this result and allows to compute the small deviations, i.e. a universal kurtosis ratio, in agreement with numerics. We stress the importance of the Gaussian theory to interpret numerical data and experiments.Comment: 4 pages revtex4. See also the following article cond-mat/030146