The Bailey Point Region and Other Muskox Refugia in the Canadian Arctic: A Short Review

The muskox (Ovibos moschatus) is widely distributed over much of arctic Canada but only at a few locations do their densities remain high and populations relatively stable. These refugia constitute the most favourable muskox ranges in the Canadian Arctic Archipelago .... Refugia for muskoxen in the High Arctic include lowlands on eastern Axel Heiberg Island in the Mokka Fiord region, the lowlands of northeastern Devon Island, and the Bailey Point region of Melville Island .... All of those regions historically have supported high densities of muskoxen from time to time but the Bailey Point region must be considered the best habitat for muskoxen in the Canadian High Arctic. ..

55% conversion efficiency to green in bulk quasi-phase-matching lithium niobate

High voltage and liquid electrodes were used for periodic poling of lithium niobate. A sample with a period of 6.80 µm was used for first-order frequency doubling of 1064 nm Q-switched Nd:YAG light with an average power conversion of 55%, implying greater than 90% power conversion at the peak of the pulse. The effective nonlinear coefficient for both Q-switched and continuous-wave measurements was ~15 pm/V

Quasi-phase matching lithium niobate, periodically poled via liquid electrodes

We have achieved reliable periodic poling of z-cut lithium niobate in 0.2 mm thick samples, patterned with photoresist on one face and subjected to pulsed electric fields via liquid electrodes. Our set-up was a further development of the one used by Camlibel. Filter paper was soaked in a solution of LiCl in water and placed on both sides of a sample with a photoresist pattern on one side (1 micrometre of standard photoresist acts as an effective barrier to domain inversion). This sandwich was then clamped between electrodes connected to ground and a high-voltage pulse generator. The pulse amplitude was 4.5 kV. We found that the single most important feature during inversion is that the transferred charge should be twice the spontaneous polarization times the desired area of inversion. The domains went all the way through the substrate, with a slight random variation in the position of the domain walls on the planar electrode side

Energy and force analysis of Ti-6Al-4V linear friction welds for computational modeling input and validation data

The linear friction welding (LFW) process is finding increasing use as a manufacturing technology for the production of titanium alloy Ti-6Al-4V aerospace components. Computational models give an insight into the process, however, there is limited experimental data that can be used for either modeling inputs or validation. To address this problem, a design of experiments approach was used to investigate the influence of the LFW process inputs on various outputs for experimental Ti-6Al-4V welds. The finite element analysis software DEFORM was also used in conjunction with the experimental findings to investigate the heating of the workpieces. Key findings showed that the average interface force and coefficient of friction during each phase of the process were insensitive to the rubbing velocity; the coefficient of friction was not coulombic and varied between 0.3 and 1.3 depending on the process conditions; and the interface of the workpieces reached a temperature of approximately approximately 1273 K (1000 °C) at the end of phase 1. This work has enabled a greater insight into the underlying process physics and will aid future modeling investigations.EPSRC, Boeing Company, Welding Institut

Self-organised light-induced scattering in periodically poled lithium niobate

A new species of self-organized light-induced scattering, appearing only in bulk periodically poled lithium niobate, is reported. Clearly defined diffracted beams develop on exposure to 532 nm light from a frequency-doubled, Q-switched, and mode-locked Nd:YAG laser. The structure thus created also diffracts light at 1064 nm. The effect is strongly dependent on temperature, the polarization state of the light, and the period of domain reversal. It exhibits a sharply defined nonlinear threshold at which the far-field pattern of the diffracted light evolves rapidly.[This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.

Green-light generation of picosecond pulses in first-order quasi-phase-matched lithium niobate

Bulk periodically poled lithium niobate has been used for efficient first-order quasi-phase matched second harmonic generation of green light in the picosecond regime. We measured an effective nonlinear coefficient of ~14 pm/V

Photorefractive scattering in bulk periodically poled lithium niobate

We report a new species of self-organised light-induced scattering, appearing only in bulk periodically poled lithium niobate. Clearly defined diffracted beams develop on exposure to 532 nm light from a frequency-doubled, Q-switched and mode-locked Nd:YAG laser. The structure thus created also diffracts light at 1064 nm. The effect is strongly dependent on temperature, the polarization state of the light and the period of domain reversal. It exhibits a sharply defined nonlinear threshold at which the far-field pattern of the diffracted light evolves rapidly

Highly-efficient cw blue light generation via first-order quasi-phase-matched frequency-doubling of a diode-pumped 946nm Nd:YAG laser

49 mW of cw blue light have been generated with a conversion efficiency of 4.6% by first-order quasi-phase-matched frequency doubling of a high-power diode-pumped 946 nm Nd:YAG laser. A sample of periodically poled LiNbO3, with domain reversal period of 4.6 µm and length of 6 mm was used in the experiment. The measured effective nonlinear coefficient of 19 pm/V and the bandwidth of 3 °C for the quasi-phase-matching curve (second harmonic power vs. temperature) are very close to the theoretical limits.<br/

The mixed problem in L^p for some two-dimensional Lipschitz domains

We consider the mixed problem for the Laplace operator in a class of Lipschitz graph domains in two dimensions with Lipschitz constant at most 1. The boundary of the domain is decomposed into two disjoint sets D and N. We suppose the Dirichlet data, f_D has one derivative in L^p(D) of the boundary and the Neumann data is in L^p(N). We find conditions on the domain and the sets D and N so that there is a p_0>1 so that for p in the interval (1,p_0), we may find a unique solution to the mixed problem and the gradient of the solution lies in L^p

Magnetic Fields, Relativistic Particles, and Shock Waves in Cluster Outskirts

It is only now, with low-frequency radio telescopes, long exposures with high-resolution X-ray satellites and gamma-ray telescopes, that we are beginning to learn about the physics in the periphery of galaxy clusters. In the coming years, Sunyaev-Zeldovich telescopes are going to deliver further great insights into the plasma physics of these special regions in the Universe. The last years have already shown tremendous progress with detections of shocks, estimates of magnetic field strengths and constraints on the particle acceleration efficiency. X-ray observations have revealed shock fronts in cluster outskirts which have allowed inferences about the microphysical structure of shocks fronts in such extreme environments. The best indications for magnetic fields and relativistic particles in cluster outskirts come from observations of so-called radio relics, which are megaparsec-sized regions of radio emission from the edges of galaxy clusters. As these are difficult to detect due to their low surface brightness, only few of these objects are known. But they have provided unprecedented evidence for the acceleration of relativistic particles at shock fronts and the existence of muG strength fields as far out as the virial radius of clusters. In this review we summarise the observational and theoretical state of our knowledge of magnetic fields, relativistic particles and shocks in cluster outskirts.Comment: 34 pages, to be published in Space Science Review