Aircraft woods: their properties, selection, and characteristics

Strength values of various woods for aircraft design for a 15 per cent moisture condition of material and a 3-second duration of stress are presented, and also a discussion of the various factors affecting the values. The toughness-test method of selecting wood is discussed, and a table of acceptance values for several species is given

The optical counterparts of Accreting Millisecond X-Ray Pulsars during quiescence

Eight Accreting Millisecond X-ray Pulsars (AMXPs) are known to date. Optical and NIR observations carried out during quiescence give a unique opportunity to constrain the nature of the donor star and to investigate the origin of the observed quiescent luminosity at long wavelengths. Using data obtained with the ESO-Very Large Telescope, we performed a deep optical and NIR photometric study of the fields of XTE J1814-338 and of the ultracompact systems XTE J0929-314 and XTE J1807-294 during quiescence in order to look for the presence of a variable counterpart. If suitable candidates were found, we also carried out optical spectroscopy. We present here the first multi-band (VR) detection of the optical counterpart of XTE J1814-338 in quiescence together with its optical spectrum. The optical light curve shows variability in both bands consistent with a sinusoidal modulation at the known 4.3 hr orbital period and presents a puzzling decrease of the V-band flux around superior conjunction that may be interpreted as a partial eclipse. The marginal detection of the very faint counterpart of XTE J0929-314 and deep upper limits for the optical/NIR counterpart of XTE J1807-294 are also reported. We also briefly discuss the results reported in the literature for the optical/NIR counterpart of XTE J1751-305. Our findings are consistent with AMXPs being systems containing an old, weakly magnetized neutron star, reactivated as a millisecond radio pulsar during quiescence which irradiates the low-mass companion star. The absence of type I X-ray bursts and of hydrogen and helium lines in outburst spectra of ultracompact (P_orb < 1 hr) AMXPs suggests that the companion stars are likely evolved dwarf stars.Comment: Accepted for publication by A&A; 12 pages, 12 figure

Swift Observations of Hard X-ray Emitting White Dwarfs in Symbiotic Stars

The X-ray emission from most accreting white dwarfs (WDs) in symbiotic binary stars is quite soft. Several symbiotic WDs, however, produce strong X-ray emission at energies greater than ~20 keV. The Swift BAT instrument has detected hard X-ray emission from 4 such accreting WDs in symbiotic stars: RT Cru, T CrB, CD -57 3057, and CH Cyg. In one case (RT Cru), Swift detected X-rays out to greater than 50 keV at a > 5 sigma confidence level. Combining data from the XRT and BAT detectors, we find that the 0.3-150 keV spectra of RT Cru, T CrB, and CD -57 3057 are well described by emission from a single-temperature, optically thin thermal plasma, plus an unresolved 6.4-6.9 keV Fe line complex. The X-ray spectrum of CH Cyg contains an additional bright soft component. For all 4 systems, the spectra suffer high levels of absorption from material that both fully and partially covers the source of hard X-rays. The XRT data did not show any of the rapid, periodic variations that one would expect if the X-ray emission were due to accretion onto a rotating, highly magnetized WD. The X-rays were thus more likely from the accretion-disk boundary layer around a massive, non-magnetic WD in each binary. The X-ray emission from RT Cru varied on timescales of a few days. This variability is consistent with being due to changes in the absorber that partially covers the source, suggesting localized absorption from a clumpy medium moving into the line of sight. The X-ray emission from CD -57 3057 and T CrB also varied during the 9 months of Swift observations, in a manner that was also consistent with variable absorption.Comment: Accepted for publication in ApJ. 9 pages, 6 figure

Nonlinear electrodynamics and the Pioneer 10/11 spacecraft anomaly

The occurrence of the phenomenon known as photon acceleration is a natural prediction of nonlinear electrodynamics (NLED). This would appear as an anomalous frequency shift in any modeling of the electromagnetic field that only takes into account the classical Maxwell theory. Thus, it is tempting to address the unresolved anomalous, steady; but time-dependent, blueshift of the Pioneer 10/11 spacecrafts within the framework of NLED. Here we show that astrophysical data on the strength of the magnetic field in both the Galaxy and the local (super)cluster of galaxies support the view on the major Pioneer anomaly as a consequence of the phenomenon of photon acceleration. If confirmed, through further observations or lab experiments, the reality of this phenomenon should prompt to take it into account in any forthcoming research on both cosmological evolution and origin and dynamical effects of primordial magnetic fields, whose seeds are estimated to be very weak.Comment: Final version accepted for publication in Europhysics Letters, uses EPL style, 7 page

Contour identical implants to bridge mandibular continuity defects - individually generated by LaserCUSING® - A feasibility study in animal cadavers

Background Ablative tumor surgery often results in continuity defects of the mandible. When an immediate reconstruction using autologous bone grafts is not possible the bridging of the defects with a variety of bridging plates might be achieved. However, those bridging plates have the risk of plate fractures or exposure. Customized titanium implants manufactured using CAD/CAM and the LaserCUSING® technique might be an alternative. Methods In the present study, computed tomographies (CT) of porcine cadaver mandibles were generated and transferred into DICOM data. Following, different continuity defects were surgically created in the mandibles. Based on the DICOM data customized titanium implants were manufactured using CAD/CAM procedures and the LaserCUSING® technique. The implants were fixed to the remaining stumps with screws. Subsequently, the accuracy of the reconstructed mandibles was tested using plaster casts. Results The workflow from the CT to the application of the customized implants was proved to be practicable. Furthermore, a stable fixation of the customized implant to the remaining stumps could be achieved. The control of the accuracy showed no frictions or obstacles. Conclusion The customized titanium implant seems to be a promising approach to bridge continuity defects of the mandible whenever an immediate reconstruction with autologous bone is not possible

The long-term evolution of the spin, pulse shape, and orbit of the accretion-powered millisecond pulsar SAX J1808.4-3658

We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658, an X-ray transient with a recurrence time of ~2 yr, using data from the Rossi X-ray Timing Explorer covering 4 transient outbursts (1998-2005). We verify that the 401 Hz pulsation traces the spin frequency fundamental and not a harmonic. Substantial pulse shape variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse shape changes suggests that, as an outburst dims, the X-ray "hot spot" on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse shape variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous nudot measurements of this source into question), with typical upper limits of |nudot| < 2.5x10^{-14} Hz/s (2 sigma). However, combining data from all the outbursts shows with high (6 sigma) significance that the pulsar is undergoing long-term spin down at a rate nudot = (-5.6+/-2.0)x10^{-16} Hz/s, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of B < 1.5x10^8 G for the pulsar's surface dipole magnetic field and and Q/I < 5x10^{-9} for the fractional mass quadrupole moment. We also measured an orbital period derivative of Pdot = (3.5+/-0.2)x10^{-12} s/s. This surprising large Pdot is reminiscent of the large and quasi-cyclic orbital period variation observed in the so-called "black widow" millisecond radio pulsars, supporting speculation that SAX J1808.4-3658 may turn on as a radio pulsar during quiescence. In an appendix we derive an improved (0.15 arcsec) source position from optical data.Comment: 22 pages, 10 figures; accepted for publication in Ap

A Compton Up-scattering Model for Soft Lags in the Lower Kilohertz QPO in 4U1608-52

An empirical Compton up-scattering model is described which reproduces both the fractional amplitude (RMS) vs. energy and the soft time lags in the 830 Hz QPO observed in 4U1608-52 on Mar. 3, 1996. A combination of two coherent variations in the coronal and soft photon temperatures (with their relative contributions determined by enforcing energy conservation) gives rise to the QPO's energy dependent characteristics. All input parameters to the model, save a characteristic plasma size and the fraction of Comptonized photons impinging on the soft photon source, are derived from the time-averaged photon energy spectrum of the same observation. Fits to the fractional RMS and phase lag data for this kilohertz QPO imply that the spatial extent of the plasma is in the range from 4 to 15 km.Comment: 4 pages, 2 figure

New Indicators for AGN Power: The Correlation Between [O IV] lambda 25.89 micron and Hard X-ray Luminosity for Nearby Seyfert Galaxies

We have studied the relationship between the [O IV] lambda 25.89 micron emission line luminosities, obtained from Spitzer spectra, the X-ray continua in the 2-10 keV band, primarily from ASCA, and the 14-195 keV band obtained with the SWIFT/Burst Alert Telescope (BAT), for a sample of nearby (z < 0.08) Seyfert galaxies. For comparison, we have examined the relationship between the [O III] 5007, the 2-10 keV and the 14-195 keV luminosities for the same set of objects. We find that both the [O IV] and [O III] luminosities are well-correlated with the BAT luminosities. On the other hand, the [O III] luminosities are better-correlated with 2-10 keV luminosities than are those of [O IV]. When comparing [O IV] and [O III] luminosities for the different types of galaxies, we find that the Seyfert 2's have significantly lower [O III] to [O IV] ratios than the Seyfert 1's. We suggest that this is due to more reddening of the narrow line region (NLR) of the Seyfert 2's. Assuming Galactic dust to gas ratios, the average amount of extra reddening corresponds to a hydrogen column density of ~ few times 10^21 cm^-2, which is a small fraction of the X-ray absorbing columns in the Seyfert 2's. The combined effects of reddening and the X-ray absorption are the probable reason why the [O III] versus 2-10 keV correlation is better than the [O IV] versus 2-10 keV, since the [O IV] emission line is much less affected by extinction. Overall, we find the [O IV] to be an accurate and truly isotropic indicator of the power of the AGN. This suggests that it can be useful in deconvolving the contribution of the AGN and starburst to the spectrum of Compton-thick and/or X-ray weak sources.Comment: Accepted for publication in the Astrophysical Journal. 31 pages, 6 figures, 4 table