398 research outputs found
Multicycle dynamics of fault systems and static and dynamic triggering of earthquakes
Get PDFDynamic simulations of rupture propagation and multiple earthquake cycles for varying fault geometries are presented. We investigate the role of both dynamic and static stress changes on earthquake triggering. Dynamic stress triggering of earthquakes is caused by the passage of seismic waves, whereas static stress triggering is due to net slippage on a fault resulting from an earthquake. Static stress changes represented by a Coulomb failure function and its relationship to seismicity rate change is a relatively well-known mechanism, whereas the physical origin of dynamic triggering remains one of the least understood aspects of earthquake nucleation. We investigate these mechanisms by analysing seismicity patterns with varying fault separation, geometry and with and without dynamic triggering present
Galaxy Counterparts of metal-rich Damped Lyman-alpha Absorbers - I: The case of the z=2.35 DLA towards Q2222-0946
Full text linkWe have initiated a survey using the newly commissioned X-shooter
spectrograph to target candidate relatively metal-rich damped Lyman-alpha
absorbers (DLAs). The spectral coverage of X-shooter allows us to search for
not only Lyman-alpha emission, but also rest-frame optical emission lines. We
have chosen DLAs where the strongest rest-frame optical lines ([OII], [OIII],
Hbeta and Halpha) fall in the NIR atmospheric transmission bands. In this first
paper resulting from the survey, we report on the discovery of the galaxy
counterpart of the z_abs = 2.354 DLA towards the z=2.926 quasar Q2222$-0946.
This DLA is amongst the most metal-rich z>2 DLAs studied so far at comparable
redshifts and there is evidence for substantial depletion of refractory
elements onto dust grains. We measure metallicities from ZnII, SiII, NiII, MnII
and FeII of -0.46+/-0.07, -0.51+/-0.06, -0.85+/-0.06, -1.23+/-0.06, and
-0.99+/-0.06, respectively. The galaxy is detected in the Lyman-alpha, [OIII]
lambda4959,5007 Halpha emission lines at an impact parameter of about 0.8
arcsec (6 kpc at z_abs = 2.354). We infer a star-formation rate of 10 M_sun
yr^-1, which is a lower limit due to the possibility of slit-loss. Compared to
the recently determined Halpha luminosity function for z=2.2 galaxies the
DLA-galaxy counterpart has a luminosity of L~0.1L^*_Halpha. The emission-line
ratios are 4.0 (Lyalpha/Halpha) and 1.2 ([OIII]/Halpha). The Lyalpha line shows
clear evidence for resonant scattering effects, namely an asymmetric,
redshifted (relative to the systemic redshift) component and a much weaker
blueshifted component. The fact that the blueshifted component is relatively
weak indicates the presence of a galactic wind. The properties of the galaxy
counterpart of this DLA is consistent with the prediction that metal-rich DLAs
are associated with the most luminous of the DLA-galaxy counterparts.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
Ghosts of the Milky Way: a search for topology in new quasar catalogues
Full text linkWe revisit the possibility that we inhabit a compact multi-connected flat, or
nearly-flat, Universe. Analysis of COBE data has shown that, for such a case,
the size of the fundamental domain must be a substantial fraction of the
horizon size. Nevertheless, there could be several copies of the Universe
within the horizon. If the Milky Way was once a quasar we might detect its
`ghost' images. Using new large quasar catalogues we repeat the search by
Fagundes & Wichoski for antipodal quasar pairs. By applying linear theory to
account for the peculiar velocity of the local group, we are able to narrow the
search radius to 134 arcsec. We find seven candidate antipodal quasar pairs
within this search radius. However, a similar number would be expected by
chance. We argue that, even with larger quasar catalogues, and more accurate
values of the cosmological parameters, it is unlikely to be possible to
identify putative ghost pairs unambiguously, because of the uncertainty of the
correction for peculiar motion of the Milky Way.Comment: MNRAS Letters, Accepted, 5 pages, 3 figure
On the sizes of z>2 Damped Lyman-alpha Absorbing Galaxies
Full text linkRecently, the number of detected galaxy counterparts of z > 2 Damped
Lyman-alpha Absorbers in QSO spectra has increased substantially so that we
today have a sample of 10 detections. M{\o}ller et al. in 2004 made the
prediction, based on a hint of a luminosity-metallicity relation for DLAs, that
HI size should increase with increasing metallicity. In this paper we
investigate the distribution of impact parameter and metallicity that would
result from the correlation between galaxy size and metallicity. We compare our
observations with simulated data sets given the relation of size and
metallicity. The observed sample presented here supports the metallicity-size
prediction: The present sample of DLA galaxies is consistent with the model
distribution. Our data also show a strong relation between impact parameter and
column density of HI. We furthermore compare the observations with several
numerical simulations and demonstrate that the observations support a scenario
where the relation between size and metallicity is driven by feedback
mechanisms controlling the star-formation efficiency and outflow of enriched
gas.Comment: Accepted for publishing in MNRAS lette
Cosmic crystallography using short-lived objects - active galactic nuclei
Full text linkCosmic crystallography is based on the principle that peaks in the pair
separation histogram (PSH) of objects in a catalogue should be induced by the
high number of topologically lensed pairs that are separated by Clifford
translations, in excess to ``random'' pairs of objects. Here we present
modifications of this method that successively improve the signal-to-noise
ratio by removing a large part of the noise and then false signals induced by
selection effects. Given the transient nature of the most readily available
tracer objects, active galactic nuclei (AGNs), the former is possible because a
natural filter for removing many of the noise pairs is available: when counting
pairs of objects in order to create PSHs, only those with nearly identical
redshifts need to be counted. This redshift filter (a maximum value of ) was applied to a compilation of AGN catalogues. Further noise was
removed by applying a second filter, a maximum angle
rad, and a minimum number of pairs \protect\npairs=3 to find each ``bunch of
pairs'' (BoP) where the {\em vectors} (in Euclidean comoving space) defined by
pairs are required to be nearly equal, whereas in the PSH only the {\em
lengths} must be nearly equal. These filters reveal significant signals, which,
however, are due to selection effects. A third filter, a minimum length
\Lselec=150 {\hMpc} between the (parallel) vectors in a BoP, is found to
effectively remove these selection effect pairs. After application of these
successive filters, no significant topological signal was found.Comment: 9 pages, 8 figures, matches the version accepted by Astronomy &
Astrophysic
The use of the SAEM algorithm in MONOLIX software for estimation of population pharmacokinetic-pharmacodynamic-viral dynamics parameters of maraviroc in asymptomatic HIV subjects
Get PDFUsing simulated viral load data for a given maraviroc monotherapy study design, the feasibility of different algorithms to perform parameter estimation for a pharmacokinetic-pharmacodynamic-viral dynamics (PKPD-VD) model was assessed. The assessed algorithms are the first-order conditional estimation method with interaction (FOCEI) implemented in NONMEM VI and the SAEM algorithm implemented in MONOLIX version 2.4. Simulated data were also used to test if an effect compartment and/or a lag time could be distinguished to describe an observed delay in onset of viral inhibition using SAEM. The preferred model was then used to describe the observed maraviroc monotherapy plasma concentration and viral load data using SAEM. In this last step, three modelling approaches were compared; (i) sequential PKPD-VD with fixed individual Empirical Bayesian Estimates (EBE) for PK, (ii) sequential PKPD-VD with fixed population PK parameters and including concentrations, and (iii) simultaneous PKPD-VD. Using FOCEI, many convergence problems (56%) were experienced with fitting the sequential PKPD-VD model to the simulated data. For the sequential modelling approach, SAEM (with default settings) took less time to generate population and individual estimates including diagnostics than with FOCEI without diagnostics. For the given maraviroc monotherapy sampling design, it was difficult to separate the viral dynamics system delay from a pharmacokinetic distributional delay or delay due to receptor binding and subsequent cellular signalling. The preferred model included a viral load lag time without inter-individual variability. Parameter estimates from the SAEM analysis of observed data were comparable among the three modelling approaches. For the sequential methods, computation time is approximately 25% less when fixing individual EBE of PK parameters with omission of the concentration data compared with fixed population PK parameters and retention of concentration data in the PD-VD estimation step. Computation times were similar for the sequential method with fixed population PK parameters and the simultaneous PKPD-VD modelling approach. The current analysis demonstrated that the SAEM algorithm in MONOLIX is useful for fitting complex mechanistic models requiring multiple differential equations. The SAEM algorithm allowed simultaneous estimation of PKPD and viral dynamics parameters, as well as investigation of different model sub-components during the model building process. This was not possible with the FOCEI method (NONMEM version VI or below). SAEM provides a more feasible alternative to FOCEI when facing lengthy computation times and convergence problems with complex models
Association studies and direct DNA sequencing implicate some known genetic susceptibility loci in the etiology of nonsyndromic orofacial clefts in sub-Saharan African populations
Get PDFRelationships among growth and different NOR phenotypes in a specific stock of rainbow trout (Oncorhynchus mykiss)
Full text linkThe significance of the largest scale CMB fluctuations in WMAP
Full text linkWe investigate anomalies reported in the Cosmic Microwave Background maps
from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite on very large
angular scales and discuss possible interpretations. Three independent
anomalies involve the quadrupole and octopole:
1. The cosmic quadrupole on its own is anomalous at the 1-in-20 level by
being low (the cut-sky quadrupole measured by the WMAP team is more strikingly
low, apparently due to a coincidence in the orientation of our Galaxy of no
cosmological significance);
2. The cosmic octopole on its own is anomalous at the 1-in-20 level by being
very planar;
3. The alignment between the quadrupole and octopole is anomalous at the
1-in-60 level.
Although the a priori chance of all three occurring is 1 in 24000, the
multitude of alternative anomalies one could have looked for dilutes the
significance of such a posteriori statistics. The simplest small universe model
where the universe has toroidal topology with one small dimension of order half
the horizon scale, in the direction towards Virgo, could explain the three
items above. However, we rule this model out using two topological tests: the
S-statistic and the matched circle test.Comment: N.B. that our results do not rule out the recently proposed
dodecahedron model of Luminet, Weeks, Riazuelo, Lehoucq & Uzan, which has a
36 degree twist between matched circles. 12 pages, 5 figs; more info at
http://www.hep.upenn.edu/~angelica/topology.htm
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