Bulk and shear mechanical loss of titania-doped tantala

We report on the mechanical loss from bulk and shear stresses in thin film, ion beam deposited, titania-doped tantala. The numerical values of these mechanical losses are necessary to fully calculate the Brownian thermal noise in precision optical cavities, including interferometric gravitational wave detectors like LIGO. We found the values from measuring the normal mode mechanical quality factors, Q's, in the frequency range of about 2000-10,000 Hz, of silica disks coated with titania-doped tantala coupled with calculating the elastic energy in shear and bulk stresses in the coating using a finite element model. We fit the results to both a frequency independent and frequency dependent model and find ${?}_{\mathrm{shear}}=(8.3\pm 1.1)\times {10}^{?4}$, ${?}_{\mathrm{bulk}}=(6.6\pm 3.8)\times {10}^{?4}$ with a frequency independent model and ${?}_{\mathrm{shear}}\left(f\right)=(5.0\pm 0.7)\times {10}^{?4}+(5.4\pm 1.1)\times {10}^{?8}f$, ${?}_{\mathrm{bulk}}\left(f\right)=(11\pm 2.8)\times {10}^{?4}?(8.7\pm 4.7)\times {10}^{?8}f$ with a frequency dependent (linear) model. The ratio of these values suggest that modest improvement in the coating thermal noise may be possible in future gravitational wave detector optics made with titania-doped tantala as the high index coating material by optimizing the coating design to take advantage of the two different mechanical loss angles.     

Gravitational-wave stochastic background from cosmic strings

We consider the stochastic background of gravitational waves produced by a network of cosmic strings and assess their accessibility to current and planned gravitational wave detectors, as well as to big bang nucleosynthesis (BBN), cosmic microwave background (CMB), and pulsar timing constraints. We find that current data from interferometric gravitational wave detectors, such as Laser Interferometer Gravitational Wave Observatory (LIGO), are sensitive to areas of parameter space of cosmic string models complementary to those accessible to pulsar, BBN, and CMB bounds. Future more sensitive LIGO runs and interferometers such as Advanced LIGO and Laser Interferometer Space Antenna (LISA) will be able to explore substantial parts of the parameter space.     

Magnetized strange quark matter solutions in f(R,T) gravity with cosmological constant

In this research, we have studied magnetized strange quark matter (SQM) solutions for Friedmann-Robertson-Walker (FRW) universe in f(R, T) gravity. To obtain exact solutions of modified field equations we have used $f(R,T)=R+2f\left(T\right)$ and $f(R,T)=f_1\left(R\right)+f_2\left(T\right)$ models given by Harko et al. (Harko et al. in Phys. Rev. D 84:024020, 2011) and $f(R,T)=R+f_3\left(T\right)$ model (here f₃ is an arbitrary function) with cosmological constant Λ. For t → ∞ we obtain $p=?\rho$ dark energy situation with small constant values of cosmological constant in three different f(R, T) gravitation models. In our solutions magnetic field does not observe also we have transformed our solutions from FRW universe to Static Einstein Universe (SEU) and we get f(R, T) gravity results for SEU universe. Finally we discussed our physical solutions.     

Gravitational wave bursts from cosmic strings

Cusps of cosmic strings emit strong beams of high-frequency gravitational waves (GW). As a consequence of these beams, the stochastic ensemble of gravitational waves generated by a cosmological network of oscillating loops is strongly non-Gaussian, and includes occasional sharp bursts that stand above the rms GW background. These bursts might be detectable by the planned GW detectors LIGO/VIRGO and LISA for string tensions as small as G&mgr; approximately 10(-13). The GW bursts discussed here might be accompanied by gamma ray bursts.     

Upper limits on the mechanical loss of silicate bonds in a silicon tuning fork oscillator

Silicon optics suspended by silicon ribbons or silicon fibers and kept at low temperature are being considered, because of promising optical and mechanical properties, for the test masses of third generation interferometric gravitational-wave detectors. To interconnect the suspension elements the technique of hydroxide catalysis (or silicate) bonding can be used. In order to estimate the bond loss a tuning fork was fabricated from silicon ribbons, which were then silicate bonded. The temperature dependence of mechanical loss of this tuning fork was measured in the temperature range of 95–295 K. The ratio of the energy stored in the bond layer to the total energy of the tuning fork was calculated by numerical simulation. This provided an upper limit of the bond loss as a function of the temperature. It is $(5\pm 2)\times {10}^{?3}$ at 123 K, a proposed operating temperature of cryogenically operating ground based interferometric gravitational-wave detectors.     

On constraining the speed of gravitational waves following GW150914

We point out that the observed time delay between the detection of the signal at the Hanford and Livingston LIGO sites from the gravitational wave event GW150914 places an upper bound on the speed of propagation of gravitational waves, c_gw ? 1.7 in the units of speed of light. Combined with the lower bound from the absence of gravitational Cherenkov losses by cosmic rays that rules out most of subluminal velocities, this gives a model-independent double-sided constraint 1 ? c_gw ? 1.7. We compare this result to model-specific constraints from pulsar timing and cosmology.     

Application of medium energy plasma focus device in study of radioisotopes

Pulsed neutrons generated in a plasma focus device are used for the thermal neutron activation analysis (TNAA) of selected three elements having widely different half-lives varying from a few seconds to a few days [Dysprosium (Dy), Manganese (Mn) and Gold (Au)]. Neutron pulse having strength of $(1.2\pm 0.3)\times {10}^9$ neutrons/pulse with a pulse width of $46\pm 5\text{ns}$ is produced by “MEPF-12” device operated at a filling gas (deuterium + 0.5% krypton) pressure of 3 mbar. The fast 2.45 MeV D–D neutrons are thermalized before irradiating the sample. The decay gammas from the radioisotopes ^165mDy ($T_{1/2}=1.26\text{min.}$), ⁵⁶Mn ($T_{1/2}=2.58\text{hrs.}$), and ¹⁹⁸Au ($T_{1/2}=2.69\text{days}$) produced via reactions, ¹⁶⁴Dy($n,\gamma$)^165mDy, ⁵⁵Mn($n,\gamma$) ⁵⁶Mn, and ¹⁹⁷Au($n,\gamma$) ¹⁹⁸Au respectively are counted off-line in a lead shielded well type $76\times 76{\text{mm}}^2$ NaI(Tl) detector coupled to a calibrated 2048 channel analyzer. The values of half-lives evaluated from the measured decay gammas, $1.43\pm 0.3\text{min.}$, $2.56\pm 0.5\text{hrs.}$ and $2.84\pm 0.6\text{days}$ respectively for the radioisotopes of Dy, Mn and Au, are seen to be close to the values reported in literature.     

Ultra-low dissipation resonators for improving the sensitivity of gravitational wave detectors

Broadband enhancement of the sensitivity of gravitational wave detectors can be achieved by the use of negative dispersion filters to create white light signal recycling cavities. This filter should have mechanical frequency of 300 kHz or higher and $T/Q_{\mathrm{m}}～6\times {10}^{?10}$ K, in order to achieve appreciable sensitivity enhancement in the range of 1–2 kHz. This paper investigates the possibility of using optical dilution of GaAs/AlGaAs-coated Si and GaAs “cat-flap” micro-resonators to achieve such performance. We analyse the loss contributions to such resonators, particularly thermoelastic loss, suspension loss and acceleration loss. Sufficient reduction of thermoelastic loss is possible when operating near the zero thermal expansion point with temperature control of ～1 K for both materials. Acceleration loss and suspension losses can be minimised in the frequency range ${10}^4\text{–}{10}^5\text{Hz}$, allowing Q-factors in the range ${10}^{11}\text{–}{10}^{12}$, but these are reduced at the target 400 kHz frequency. Results are subject to assumptions regarding material losses. Fabrication techniques for creating GaAs and SiN_x suspended silicon cat-flap resonators are presented.     

Lattice dynamics and phase transition of NiTi alloy

We have performed detailed first-principles calculations to investigate the structural and lattice dynamical properties of NiTi alloy. The calculated static structures consist well with the experimental data and other theoretical results. With quasi harmonic approximation, the phase boundary between B19′ and BCO phases can be described as a five order polynomial $T=100?89.28P+296.75P^2?717.94P^3+734.62P^4?274.25P^5$. The change of vibrational entropy is $0.07k_B$/atom at the transition temperature 100 K under zero pressure.     

Examining the fragmentation of 158 A GeV lead ions on copper target: Charge-changing cross sections

A stack of plastic CR-39 Track Detectors were exposed to 158 A GeV ²⁰⁷Pb ions at the CERN-SPS beam facility. The exposure of stack was performed at normal incidence with a fluence of about $1500\mathrm{ions}/{\mathrm{cm}}^2$. The total number of lead ions in each spill was about $7.8\times {10}^4$ with eight spills on each stack. For the stack with the Cu target, the lengths of etched cones on one face of the CR-39 detectors (before and after the target) were measured. Using these measurements and charge identification methodology in CR-39 track detectors, total and partial charge changing cross sections of 158 A GeV ${\mathrm{Pb}}^{82+}$ ions on Cu and CR-39 targets are determined in the charge region $63⩽Z⩽82$. The possibilities of presence and absence of odd–even effect in measured partial charge changing cross sections of 158 A GeV Pb ions for Cu and CR-39 targets are described. The charge resolution $({\sigma }_Z)$ achieved in the present experiment is $\sim 0.18\mathrm{e}$–0.21e. The analysis of discrepancies between our experimental results and other published results for the identical reaction is also presented.