A precursor in waterhammer analysis : rediscovering Johannes von Kries

In 1883 Johannes von Kries published the theory of waterhammer in a study of blood flow in arteries. He derived the “Joukowsky formula ” before Joukowsky (1898) and Frizell (1898) did. He considered skin friction in unsteady laminar flow and thus derived formulas for wave attenuation and line pack. The theory was confirmed by experimental results obtained in rubber hoses. In 1892 he published the first textbook describing “classical ” waterhammer. It presents formulas for phase-velocity and damping that are frequency-dependent because of skin friction, and in this sense it is the first contribution to the – these days popular – subject of unsteady friction

Thomas Young's research on fluid transients : 200 years on

Thomas Young published in 1808 his famous paper (1) in which he derived the pressure wave speed in an incompressible liquid contained in an elastic tube. Unfortunately, Young's analysis was obscure and the wave speed was not explicitly formulated, so his achievement passed unnoticed until it was rediscovered nearly half a century later by the German brothers Weber. This paper briefly reviews Young's life and work, and concentrates on his achievements in the area of hydraulics and waterhammer. Young's 1808 paper is "translated" into modern terminology. Young's discoveries, though difficult for modern readers to identify, appear to include most if not all of the key elements which would subsequently be combined into the pressure rise equation of Joukowsky

Polar Jahn-Teller centers and magnetic neutron scattering cross-section in copper oxides

In the framework of the model of the polar singlet-triplet Jahn-Teller centers the cross-section is obtained for magnetic neutron scattering in high-$T_{c}$ cuprates. Multi-mode character of the $CuO_{4}$ cluster ground manifold in the new phase of polar centers determines the dependence of magnetic form-factor on the local structure and charge state of the center. It is shown that magnetic inelastic neutron scattering in the system of the polar singlet-triplet Jahn-Teller centers permits to investigate the non-magnetic charge and structure excitations.Comment: 13 pages, LaTe

Coordination of an Asynchronous Multi-Agent System via Averaging

This paper is concerned with the coordination of a group of n > 1 mobile autonomous agents which all move in the plane with the same speed but with di®erent headings. Each agent updates its heading from time to time to a new value equal to the average of its present heading and the headings of its current \neighbors". Although all agents use the same rule, individual updates are executed asynchronously. By appealing to the concept of \analytic synchronization", it is shown that under mild connectivity assumptions of the underlying directed graph characterizing neighbor relationships, the local update rules under consideration can cause all agents to eventually move in the same direction despite the absence of centralized coordination and despite the fact that each agent's set of neighbors change with time as the system evolves