During the last decades, electronic textual information has become the world's largest and most important information source. Daily newspapers, books, scientific and governmental publications, blogs and private messages have grown into a wellspring of endless information and knowledge. Since neither existing nor new information can be read in its entirety, we rely increasingly on computers to extract and visualize meaningful or interesting topics and documents from this huge information reservoir. In this paper, we extend, improve and combine existing individual approaches into an overall framework that supports topologi-cal analysis of high dimensional document point clouds given by the well-known tf-idf document-term weighting method. We show that traditional distance-based approaches fail in very high dimensional spaces, and we describe an improved two-stage method for topology-based projections from the original high dimensional information space to both two dimensional (2-D) and three dimensional (3-D) visualizations. To demonstrate the accuracy and usability of this framework, we compare it to methods introduced recently and apply it to complex document and patent collections.
In this paper, we propose a masked photocathode inside a photoinjector for generating high brightness electron beam. Instead of mounting the photocathode onto an electrode, an electrode with small hole is used as a mask to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material easy by rotating the photocathode behind the electrode into the hole. Furthermore, this helps reduce the dark current or secondary electron emission from the photocathode material. The masked photocathode also provides transverse cut-off to a Gaussian laser beam that reduces electron beam emittance growth from nonlinear space-charge effects.
U .1 Presented at the IUPAC Meeting, Tokyo, Japan, September 1 - 11, 1977 LBL-6934 c.1 tAt-90ft ACTIVE SITES FOR HYDROCARBON CATALYSIS ON METAL SURFACES G. A. Somorjai October 18, 1977 Prepared for the U. S. Department of Energy under Contract W-740S-ENG-48 For Reference Not to be taken from this room
The characteristics of new prototype high gain photomultipliers having two microchannel plates in cascade for electron multiplication have been investigated. Measurements are given of the gain, dark current, quantum efficiency, anode pulse linearity, electron transit time, single and multiphotoelectron time spreads, and pulse height resolution of LEP PM137 8/II and PM137 7/I photomultipliers. The gain as a function of transverse magnetic field has been measured and is discussed. Emphasis is put on the determination of optimum photomultiplier operating conditions, particularly with respect to their pulse height resolution capability. Photomultiplier characteristics as a function of input pulse repetition frequency have been also investigated and discussed.
LBNL-42098 ~R~EST BERKELEY ~RLA~Da NA~IO~AL. L.AWFUZP4CE LABn RATa RY CFDSimulationof Infiltration Heat Recovery C.R.Buchananand M.H.Sherman EnvironmentalEnergy TechnologiesDivision July 1998
