First Observation of Self-Amplified Spontaneous Emission in a Free-Electron Laser at 109 nm Wavelength

We present the first observation of Self-Amplified Spontaneous Emission (SASE) in a free-electron laser (FEL) in the Vacuum Ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approx. 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width and intensity fluctuations all corroborate the existing models for SASE FELs.Comment: 6 pages including 6 figures; e-mail: [email protected]

Electromagnetic Shaft Current Problems A User's Viewpoint

PaperPg. 191-197.This article covers a user’s experience, viewpoint and resolution, with destructive stray shaft currents on a centrifugal split-case design compressor. The compressor is driven by a 33,000 HP 13-stage condensing turbine. Shaft currents have been noted by many rotating equipment users for years and had been mostly associated with wet turbine steam causing a static current. A common type grounding brush, in continuous contact with the shaft, was used to bleed off all excess currents to ground. These brushes generally proved successful where “static” conditions were present. However, at times severe currents were generated causing quick bearing deterioration. The brushes simply could not carry the current away. Approximately ten years ago, a theory that stray currents could also be generated by high magnetic levels and fields within the equipment itself evolved. Currents generated in this manner were then termed “electromagnetic” in nature. Electromagnetic currents are definitely more destructive than static currents. The tell-tale signs are distractive from static currents as metal can actually be removed from the shaft, definite erosion (frosting) patterns are set up and frosting can and does appear at different locations throughout the machine during the magnetic destructive process. These stray currents have been present on this particular compressor since plant start-up in September of 1971. Necessary outages, as a direct result of bearing failure, have occurred as frequently as one month and as infrequently as 1 ½ years. Many paths have been followed in the attempt to resolve the bearing failures prior to implementing the electromagnetic current history. Solutions ranged from installation and modification of current drain brushes, to a total radial bearing redesign by the original equipment manufacturer (OEM). The following represents Northern Petrochemical Company’s (NPC) complete history and thrust into the electromagnetic theory and a final resolve

Cardiovascular and thermal responses evoked from the periaqueductal grey require neuronal activity in the hypothalamus

Stimulation of neurons in the lateral/dorsolateral periaqueductal grey (l/dlPAG) produces increases in heart rate (HR) and mean arterial pressure (MAP) that are, according to traditional views, mediated through projections to medullary autonomic centres and independent of forebrain mechanisms. Recent studies in rats suggest that neurons in the l/dlPAG are downstream effectors responsible for responses evoked from the dorsomedial hypothalamus (DMH) from which similar cardiovascular changes and increase in core body temperature (Tco) can be elicited. We hypothesized that, instead, autonomic effects evoked from the l/dlPAG depend on neuronal activity in the DMH. Thus, we examined the effect of microinjection of the neuronal inhibitor muscimol into the DMH on increases in HR, MAP and Tco produced by microinjection of N-methyl-d-aspartate (NMDA) into the l/dlPAG in conscious rats. Microinjection of muscimol alone modestly decreased baseline HR and MAP but failed to alter Tco. Microinjection of NMDA into the l/dlPAG caused marked increases in all three variables, and these were virtually abolished by prior injection of muscimol into the DMH. Similar microinjection of glutamate receptor antagonists into the DMH also suppressed increases in HR and abolished increases in Tco evoked from the PAG. In contrast, microinjection of muscimol into the hypothalamic paraventricular nucleus failed to reduce changes evoked from the PAG and actually enhanced the increase in Tco. Thus, our data suggest that increases in HR, MAP and Tco evoked from the l/dlPAG require neuronal activity in the DMH, challenging traditional views of the place of the PAG in central autonomic neural circuitry