Pulsar Timing and its Application for Navigation and Gravitational Wave Detection

Pulsars are natural cosmic clocks. On long timescales they rival the precision of terrestrial atomic clocks. Using a technique called pulsar timing, the exact measurement of pulse arrival times allows a number of applications, ranging from testing theories of gravity to detecting gravitational waves. Also an external reference system suitable for autonomous space navigation can be defined by pulsars, using them as natural navigation beacons, not unlike the use of GPS satellites for navigation on Earth. By comparing pulse arrival times measured on-board a spacecraft with predicted pulse arrivals at a reference location (e.g. the solar system barycenter), the spacecraft position can be determined autonomously and with high accuracy everywhere in the solar system and beyond. We describe the unique properties of pulsars that suggest that such a navigation system will certainly have its application in future astronautics. We also describe the on-going experiments to use the clock-like nature of pulsars to "construct" a galactic-sized gravitational wave detector for low-frequency (f_GW ~1E-9 - 1E-7 Hz) gravitational waves. We present the current status and provide an outlook for the future.Comment: 30 pages, 9 figures. To appear in Vol 63: High Performance Clocks, Springer Space Science Review

Structural isotopic effects in the smallest chiral amino acid observation of a structural phase transition in fully deuterated alanine

A first study of possible changes instigated by deuteration in amino acids was carried out using neutron diffraction, inelastic neutron scattering and Raman scattering in L alanine, C2H4 NH2 COOH. Careful analysis of the structural parameters shows that deuteration of L alanine engenders significant geometric changes as a function of temperature, which can be directly related to the observation of new lattice vibration modes in the Raman spectra. The combination of the experimental data suggests that C2D4 ND2 COOD undergoes a structural phase transition or a structural rearrangement at about 170 K. Considering that this particular amino acid is a hydrogen bonded system with short hydrogen bonds O H 1.8 , we evoke the Ubbelohde effect to conclude that substitution of hydrogen for deuterium gives rise to changes in the hydrogen bonding interactions. The structural differences suggest distinct relative stabilities for the hydrogenous and deuterated L alanin