Improved search for galactic white dwarf binaries in Mock LISA Data Challenge 1B using an F-statistic template bank

We report on our F-statistic search for white-dwarf binary signals in the Mock LISA Data Challenge 1B (MLDC1B). We focus in particular on the improvements in our search pipeline since MLDC1, namely refinements in the search pipeline and the use of a more accurate detector response (rigid adiabatic approximation). The search method employs a hierarchical template-grid based exploration of the parameter space, using a coincidence step to distinguish between primary (``true'') and secondary maxima, followed by a final (multi-TDI) ``zoom'' stage to provide an accurate parameter estimation of the final candidates.Comment: 11 pages, 4 included figures, submitted to Classical and Quantum Gravity for GWDAW12 proceeding

Risk factors for extubation failure in mechanically ventilated children in pediatric intensive care unit

Background: Mechanical ventilation is lifesaving in children with respiratory failure. However, its unnecessary prolongation once a child is capable of sustaining spontaneous effective ventilation is associated with significant complications. Objective: To identify the factors that lead to higher chance of extubation failure in mechanically ventilated children. Materials and Methods: A prospective, observational study was conducted over a period of 1 year. Children admitted to pediatric intensive care unit of a tertiary care hospital of Northern India aged 1 month–17 years, needing mechanical ventilation were included in the study. Predefined criteria were used to decide the timing of extubation. Relevant details were recorded to study various patient-related parameters and their association with extubation outcome. Results: Mean age of the study group was 50 months with a male:female ratio of 3:1. Extubation failure rate was 14.5%. Extubation failure was significantly higher in patients ventilated for >7 days (p=0.01), those with the pediatric risk of mortality score >10 at admission (p=0.009), in addition to peak inspiratory pressure >16 cm H2O (p=0.009) and FiO2 ≥0.35 (p=0.01) before extubation. Accidental extubation was also associated with higher extubation failure (p<0.001). Conclusion: Our study demonstrates that even though sicker patients requiring ventilation for longer duration are more prone to failed extubations, protocol based, and planned extubations lead to better extubation success

Searching for Galactic White Dwarf Binaries in Mock LISA Data using an F-Statistic Template Bank

We describe an F-statistic search for continuous gravitational waves from galactic white-dwarf binaries in simulated LISA Data. Our search method employs a hierarchical template-grid based exploration of the parameter space. In the first stage, candidate sources are identified in searches using different simulated laser signal combinations (known as TDI variables). Since each source generates a primary maximum near its true "Doppler parameters" (intrinsic frequency and sky position) as well as numerous secondary maxima of the F-statistic in Doppler parameter space, a search for multiple sources needs to distinguish between true signals and secondary maxima associated with other, "louder" signals. Our method does this by applying a coincidence test to reject candidates which are not found at nearby parameter space positions in searches using each of the three TDI variables. For signals surviving the coincidence test, we perform a fully coherent search over a refined parameter grid to provide an accurate parameter estimation for the final candidates. Suitably tuned, the pipeline is able to extract 1989 true signals with only 5 false alarms. The use of the rigid adiabatic approximation allows recovery of signal parameters with errors comparable to statistical expectations, although there is still some systematic excess with respect to statistical errors expected from Gaussian noise. An experimental iterative pipeline with seven rounds of signal subtraction and re-analysis of the residuals allows us to increase the number of signals recovered to a total of 3419 with 29 false alarms.Comment: 29 pages, 11 figures; submitted to Classical and Quantum Gravit

Charge stability and charge-state-based spin readout of shallow nitrogen-vacancy centers in diamond

Spin-based applications of the negatively charged nitrogen-vacancy (NV) center in diamonds require efficient spin readout. One approach is the spin-to-charge conversion (SCC), relying on mapping the spin states onto the neutral (NV$^0$) and negative (NV$^-$) charge states followed by a subsequent charge readout. With high charge-state stability, SCC enables extended measurement times, increasing precision and minimizing noise in the readout compared to the commonly used fluorescence detection. Nano-scale sensing applications, however, require shallow NV centers within a few \si{\nano \meter} distance from the surface where surface related effects might degrade the NV charge state. In this article, we investigate the charge state initialization and stability of single NV centers implanted \approx \SI{5}{\nano \meter} below the surface of a flat diamond plate. We demonstrate the SCC protocol on four shallow NV centers suitable for nano-scale sensing, obtaining a reduced readout noise of 5--6 times the spin-projection noise limit. We investigate the general applicability of SCC for shallow NV centers and observe a correlation between NV charge-state stability and readout noise. Coating the diamond with glycerol improves both charge initialization and stability. Our results reveal the influence of the surface-related charge environment on the NV charge properties and motivate further investigations to functionalize the diamond surface with glycerol or other materials for charge-state stabilization and efficient spin-state readout of shallow NV centers suitable for nano-scale sensing.Comment: 9 pages, 5 figure

Black Hole Mergers and Unstable Circular Orbits

We describe recent numerical simulations of the merger of a class of equal mass, non-spinning, eccentric binary black hole systems in general relativity. We show that with appropriate fine-tuning of the initial conditions to a region of parameter space we denote the threshold of immediate merger, the binary enters a phase of close interaction in a near-circular orbit, stays there for an amount of time proportional to logarithmic distance from the threshold in parameter space, then either separates or merges to form a single Kerr black hole. To gain a better understanding of this phenomena we study an analogous problem in the evolution of equatorial geodesics about a central Kerr black hole. A similar threshold of capture exists for appropriate classes of initial conditions, and tuning to threshold the geodesics approach one of the unstable circular geodesics of the Kerr spacetime. Remarkably, with a natural mapping of the parameters of the geodesic to that of the equal mass system, the scaling exponent describing the whirl phase of each system turns out to be quite similar. Armed with this lone piece of evidence that an approximate correspondence might exist between near-threshold evolution of geodesics and generic binary mergers, we illustrate how this information can be used to estimate the cross section and energy emitted in the ultra relativistic black hole scattering problem. This could eventually be of use in providing estimates for the related problem of parton collisions at the Large Hadron Collider in extra dimension scenarios where black holes are produced.Comment: 16 pages, 12 figures; updated to coincide with journal versio