14088655
The Mock LISA data challenges: from challenge 1B to challenge 3
The Mock LISA Data Challenges are a programme to demonstrate and encourage the development of LISA data-analysis capabilities, tools and techniques. At the time of this workshop, three rounds of challenges had been completed, and the next was about to start. In this paper we provide a critical analysis of the entries to the latest completed round, Challenge 1B. The entries confirm the consolidation of a range of data-analysis techniques for galactic and massive-black-hole binaries, and they include the first convincing examples of detection and parameter estimation of extreme-mass-ratio inspiral sources. In this paper we also introduce the next round, Challenge 3. Its data sets feature more realistic waveform models (e.g., galactic binaries may now chirp, and massive-black-hole binaries may precess due to spin interactions), as well as new source classes (bursts from cosmic strings, isotropic stochastic backgrounds) and more complicated nonsymmetric instrument noise.
41820397
Fast detection and automatic parameter estimation of a gravitational wave signal with a novel method
The detection of gravitational wave usually requires to match the measurement data with a large number of templates, which is computationally very expensive. Compressed sensing methods allow one to match the data with a small number of templates and interpolate the rest. However, the interpolation process is still computationally expensive. In this article, we designed a novel method that only requires to match the data with a few templates, yet without needing any interpolation process. The algorithm worked well for signals with relatively high SNRs. It also showed promise for low SNRs signals.
17506970
System identification of the linac RF system using a wavelet method and its applications in the SNS LLRF control system
For a pulsed LINAC such as the SNS, an adaptive feed-forward algorithm plays an important role in reducing the repetitive disturbance caused by the pulsed operation conditions. In most modern feed-forward control algorithms, accurate real time system identification is required to make the algorithm more effective. In this paper, an efficient wavelet method is applied to the system identification in which the Haar function is used as the base wavelet. The advantage of this method is that the Fourier transform of the Haar function in the time domain is a sinc function in the frequency domain. Thus we can directly obtain the system transfer function in the frequency domain from the coefficients of the time domain system response.
45170690
Towards more realistic forecasting of dark energy constraints from galaxy redshift surveys
Galaxy redshift surveys are becoming increasingly important as a dark energy probe. We 
improve the forecasting of dark energy constraints from galaxy redshift surveys by using the 
‘dewiggled’ galaxy power spectrum, P_(dw)(k), in the Fisher matrix calculations. Since P_(dw)(k) is 
a good fit to real galaxy clustering data over most of the scale range of interest, our approach is 
more realistic compared to previous work in forecasting dark energy constraints from galaxy 
redshift surveys. We find that our new approach gives results in excellent agreement when 
compared to the results from the actual data analysis of the clustering of the Sloan Digital 
Sky Survey Data Release 7 luminous red galaxies. We provide forecasts of the dark energy 
constraints from a plausible Stage IV galaxy redshift survey.
9230144
Future Type Ia Supernova Data as Tests of Dark Energy from Modified Friedmann Equations
In the Cardassian model, dark energy density arises from modifications to the Friedmann equation, which becomes H2 = g(ρM), where g(ρM) is a new function of the energy density. The universe is flat, matter dominated, and accelerating. The distance-redshift relation predictions of generalized Cardassian models can be very different from generic quintessence models, and can be differentiated with data from upcoming pencil beam surveys of Type Ia supernovae such as Supernova/Acceleration Probe (SNAP). We have found the interesting result that, once Ωm is known to 10% accuracy, SNAP will be able to determine the sign of the time dependence of the dark energy density. Knowledge of this sign (which is related to the weak energy condition) will provide a first discrimination between various cosmological models that fit the current observational data (cosmological constant, quintessence, Cardassian expansion). Further, we have performed Monte Carlo simulations to illustrate how well one can reproduce the form of the dark energy density with SNAP. To be concrete we study a class of two-parameter (n, q) generalized Cardassian models that includes the original Cardassian model (parameterized by n only) as a special case. Examples are given of modified polytropic (MP) Cardassian models that fit current supernova and cosmic microwave background data, and prospects for differentiating between MP Cardassian and other models in future data are discussed. We also note that some Cardassian models can satisfy the weak energy condition w > -1 even with a dark energy component that has an effective equation of state wX < -1.
118163168
Three-dimensional two-layer outer gap model: the third peak of vela pulsar
We extend the two-dimensional two-layer outer gap model to a three-dimensional geometry and use it to study the high-energy emission of the Vela pulsar. We apply this three-dimensional two-layer model to the Vela pulsar and compare the model light curves, the phase-averaged spectrum and the phase-resolved spectra with the recent Fermi observations, which also reveals the existence of the third peak between two main peaks. The phase position of the third peak moves with the photon energy, which cannot be explained by the geometry of magnetic field structure and the caustic effect of the photon propagation. We suggest that the existence of the third peak and its energy dependent movement results from the azimuthal structure of the outer gap.
6120041
N-body simulations for testing the stability of triaxial galaxies in MOND
We perform a stability test of triaxial models in Modified Newtonian Dynamics (MOND) using N-body simulations. The triaxial models considered here have densities that vary with r −1 in the centre and r −4 at large radii. The total mass of the model varies from 10 8 to 10 10 M� , representing the mass scale of dwarfs to medium-mass elliptical galaxies, respectively, from deep MOND to quasi-Newtonian gravity. We build triaxial galaxy models using the Schwarzschild technique, and evolve the systems for 200 Keplerian dynamical times (at the typical length-scale of 1.0 kpc). We find that the systems are virial overheating, and in quasi-equilibrium with the relaxation taking approximately 5 Keplerian dynamical times (1.0 kpc). For all systems, the change of the inertial (kinetic) energy is less than 10 per cent (20 per cent) after relaxation. However, the central profile of the model is flattened during the relaxation and the (overall) axis ratios change by roughly 10 per cent within 200 Keplerian dynamical times (at 1.0 kpc) in our simulations. We further find that the systems are stable once they reach the equilibrium state.