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The NINJA-2 project: detecting and characterizing gravitational waveforms modelled using numerical binary black hole simulations
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)The Numerical INJection Analysis (NINJA) project is a collaborative effort between members of the numerical relativity and gravitational-wave (GW) astrophysics communities. The purpose of NINJA is to study the ability to detect GWs emitted from merging binary black holes (BBH) and recover their parameters with next-generation GW observatories. We report here on the results of the second NINJA project, NINJA-2, which employs 60 complete BBH hybrid waveforms consisting of a numerical portion modelling the late inspiral, merger, and ringdown stitched to a post-Newtonian portion modelling the early inspiral. In a 'blind injection challenge' similar to that conducted in recent Laser Interferometer Gravitational Wave Observatory (LIGO) and Virgo science runs, we added seven hybrid waveforms to two months of data recoloured to predictions of Advanced LIGO (aLIGO) and Advanced Virgo (AdV) sensitivity curves during their first observing runs. The resulting data was analysed by GW detection algorithms and 6 of the waveforms were recovered with false alarm rates smaller than 1 in a thousand years. Parameter-estimation algorithms were run on each of these waveforms to explore the ability to constrain the masses, component angular momenta and sky position of these waveforms. We find that the strong degeneracy between the mass ratio and the BHs' angular momenta will make it difficult to precisely estimate these parameters with aLIGO and AdV. We also perform a large-scale Monte Carlo study to assess the ability to recover each of the 60 hybrid waveforms with early aLIGO and AdV sensitivity curves. Our results predict that early aLIGO and AdV will have a volume-weighted average sensitive distance of 300 Mpc (1 Gpc) for 10M⊙ + 10M⊙ (50M⊙ + 50M⊙) BBH coalescences. We demonstrate that neglecting the component angular momenta in the waveform models used in matched-filtering will result in a reduction in sensitivity for systems with large component angular momenta. This reduction is estimated to be up to ~15% for 50M⊙ + 50M⊙ BBH coalescences with almost maximal angular momenta aligned with the orbit when using early aLIGO and AdV sensitivity curves
The role of defects in the nonlinear optical absorption behavior of carbon and ZnO nanostructures
No full textRestricted Access.In bulk materials, defects are usually considered to be unwanted since deviations from perfect lattices may degrade device performance. Interestingly, the presence of defects throws open new possibilities in the case of nanostructures due to the properties related to their limited size scale. Defects and disorders which alter the electronic structure of nanostructures can significantly influence their electronic, magnetic and nonlinear optical properties. Here, we show that defect engineering is an effective strategy for tailoring the nonlinear optical (NLO) properties of carbon and ZnO nanostructures. The effects of surface states, lattice disorders, polycrystalline interfaces and heterogeneous dopants on the nonlinear absorption behaviour of these nanostructures are discussed in detail. Realistic tunable NLO features achieved by controlling such defects enhance the scope of these nanostructures in device applications such as optical limiting, optical switching, pulse shaping, pulse compression and optical diode action
Deep searches for decametre-wavelength pulsed emission from radio-quiet gamma-ray pulsars
No full textOpen AccessWe report the results of extensive follow-up observations of the gamma-ray pulsar J1732−3131, which has recently been detected at decametre wavelengths, and the results of deep searches for the counterparts of nine other radio-quiet gamma-ray pulsars at 34 MHz, using the Gauribidanur radio telescope. No periodic signal from J1732−3131 could be detected above a detection threshold of 8σ, even with an effective integration time of more than 40 h. However, the average profile obtained by combining data from several epochs, at a dispersion measure of 15.44 pc cm−3, is found to be consistent with that from the earlier detection of this pulsar at a confidence level of 99.2 per cent. We present this consistency between the two profiles as evidence that J1732−3131 is a faint radio pulsar with an average flux density of 200–400 mJy at 34 MHz. Despite the extremely bright sky background at such low frequencies, the detection sensitivity of our deep searches is generally comparable to that of higher frequency searches for these pulsars, when scaled using reasonable assumptions about the underlying pulsar spectrum. We provide details of our deep searches, and put stringent upper limits on the decametre-wavelength flux densities of several radio-quiet gamma-ray pulsars
Growth, structural and mechanical analysis of a single crystal of L-prolinium tartrate: a promising material for nonlinear optical applications
No full textRestricted Access.A single crystal of L-prolinium tartrate (LPT), which is an organic non linear optical material, was successfully synthesized and grown using a slow evaporation solution growth technique (SEST). The crystal structure and lattice parameters of the crystal were confirmed by powder X-ray diffraction and it was found that it belongs to the monoclinic crystal system with β = 100.380 and a noncentrosymmetric space group. The presence of strain in the grown ingot was calculated from powder X-ray diffraction measurements. The crystalline perfection was examined by high resolution X-ray diffractometry, which revealed that the crystal contained structural grain boundaries. The optical behavior of the grown specimen was analyzed by photoluminescence (PL) spectroscopy and its time resolved PL decay was calculated. The grown crystal adopted a step wise growth pattern with parallel striations, which was confirmed from the etching technique. Its ferroelectric and piezoelectric properties were also assessed. Its third order non linearity was assessed using an open aperture Z-scan technique. The thermal parameters of the LPT single crystal were calculated using a photopyroelectric technique. The mechanical strength of the single crystal at the micro level was observed by nanoindentation using the Oliver–Pharr method
Photo-disintegration of heavy nuclei at the core of Cen A
No full textOpen AccessFermi LAT has detected gamma ray emissions from the core of Cen A. More recently, a new component in the gamma ray spectrum from the core has been reported in the energy range of 4 GeV to tens of GeV. We show that the new component and the HESS detected spectrum of gamma rays from the core at higher energy have possibly a common origin in photo-disintegration of heavy nuclei. Assuming the cosmic rays are mostly Fe nuclei inside the core and their spectrum has a low energy cut-off at 52 TeV in the wind frame moving with a Doppler factor 0.25 with respect to the observer on earth, the cosmic ray luminosity required to explain the observed gamma ray flux above 1 GeV is found to be 1.5 × 1043 erg/sec
Mutually ordered self-assembly of discotic liquid crystal-graphene nanocomposites.
No full textRestricted Access.The room temperature anthraquinone discotic 1,5-dihydroxy-2,3,6,7-tetrakis(3,7-dimethyloctyloxy)-9,10-anthraquinone (RTAQ) self-assembles in the presence of octadecylamine functionalized graphene (f-graphene) into an ordered sandwich like structure, where the discotic molecules form columnar structures on graphene sheets. Cryo-SEM and SEM images provide evidence for this ordering. This behaviour is also supported by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and conductivity studies of nanocomposites
Light beams with general direction and polarization: Global description and geometric phase
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We construct the manifold describing the family of plane monochromatic light waves with all directions, polarizations, phases and intensities. A smooth description of polarization, valid over the entire sphere S2S2 of directions, is given through the construction of an orthogonal basis pair of complex polarization vectors for each direction; any light beam is then uniquely and smoothly specified by giving its direction and two complex amplitudes. This implies that the space of all light beams is the six dimensional manifold View the MathML sourceS2×C2∖{0}, the (untwisted) Cartesian product of a sphere and a two dimensional complex vector space minus the origin. A Hopf map (i.e. mapping the two complex amplitudes to the Stokes parameters) then leads to the four dimensional manifold S2×S2S2×S2 which describes beams with all directions and polarization states. This product of two spheres can be viewed as an ordered pair of two points on a single sphere, in contrast to earlier work in which the same system was represented using Majorana’s mapping of the states of a spin one quantum system to an unordered pair of points on a sphere. This is a different manifold, CP2CP2, two dimensional complex projective space, which does not faithfully represent the full space of all directions and polarizations. Following the now-standard framework, we exhibit the fibre bundle whose total space is the set of all light beams of non-zero intensity, and base space S2×S2S2×S2. We give the U(1)U(1) connection which determines the geometric phase as the line integral of a one-form along a closed curve in the total space. Bases are classified as globally smooth, global but singular, and local, with the last type of basis being defined only when the curve traversed by the system is given. Existing as well as new formulae for the geometric phase are presented in this overall framework
