there has arisen an increased awareness of the 

 potential of enhancing imaging and sensing under 

 normally obscured visibility by using submillime- 

 ter techniques. Consequently, there has been in- 

 creasing activity in research on coherent sources, 

 propagation, and detection as part of a coordinat- 

 ed Army-wide program. Contractors participating 

 in the program are the Georgia Institute of Tech- 

 nology and Lincoln Laboratories. In-house work 

 is in progress at the Army Missile Command, 

 Harry Diamond Laboratories, and the Army Elec- 

 tronics Command. 



Research on Percolation Theory 



Percolation theory is a computer simulation 

 technique which permits prediction of the distribu- 

 tion of phases in multiphase systems, and thereby 

 mechanical, electrical, and thermal properties of 

 alloys and a wide variety of composite materials. 



Thus far, the results of in-house efforts at the 

 Army Materials and Mechanics Research Center 

 have been beneficially applied toward the predic- 

 tion of optimized structures of materials for a 

 host of diverse end uses, such as gradient armor, 

 reduction of blast damage, and noise suppression 

 (e.g., optimum pore structures in foamed materi- 

 als). Further improvements in the technique and 

 applications of the technique are in process. 



Reference: 



"Phase Connectivity in a Two-Phase Microstructure Monte- 

 Carlo Calculation of Topological and Percolation Properties". 

 George D. Qiiinn. George H. Bishop, and Ralph J. Harrison. 

 Pub. in Nuclear Metallurgy. 20. 1215-1225, 1976. The Proceed- 

 ings of 1976 International Conference on Computer Simulation 

 for Materials Applications, NBS, April 1976. 



Pulsed Positive Negative Ion Chemical 

 Ionization Mass Spectrometry 



Conventional mass spectrometry, a technique 

 based on the generation of positive ions by the 

 impact of electrons upon a vaporized sample, has 

 long provided the most effective way to identify 

 complex chemical compounds. The ions in general 

 acquire considerable energy in the course of their 

 formation, and as a result rapidly undergo exten- 

 sive fragmentation, limiting the amount of struc- 

 tural information obtainable in the analysis. In the 

 chemical ionization approach, electron transfer to 

 form sample ions occurs in an indirect manner: 

 Ions are formed by electron impact upon relative- 

 ly stable gases, which then transfer electrons to or 

 from the sample molecules. Less excess energy is 

 present, and comparable concentrations of posi- 

 tive and negative ions are produced. 



Professor Donald F. Hunt of the University of 

 Virginia, a pioneer in the development and appli- 



cation of the chemical ionization technique, has 

 succeeded in coupling it with an effective means 

 to detect positive and negative ions simultaneous- 

 ly. This he has accomplished by using convention- 

 al electrostatic techniques to draw alternate bursts 

 of positive and negative ions from the ionization 

 chamber, and then analyzing the beam with a 

 quadripole filter. Two matched electron multi- 

 pliers, one each for positive and negative ions, 

 allow simultaneous display of each signal as a 

 function of ionic mass (or more correctly, mass/ 

 charge ratio). The instrumentation and its use 

 have been described and its potential assessed in 

 detail. 



The reduction in ion fragmentation, the en- 

 hanced generation of negative ions, and the added 

 information provided by the analysis for both posi- 

 tive and negative species, provide a dramatic im- 

 provement in the diagnostic capability. This is ac- 

 companied by a hundred-to-thousand-fold in- 

 crease in sample ion current at the detectors, 

 translating into an increase in sensitivity to the 10'- 

 or 10-1'* gram level. The basic technique is being 

 further developed for the detection, identification, 

 and quantification of volatile and nonvolatile or- 

 ganic and inorganic substances at the nanogram 

 (10-9) to femtogram (lO-i"^) level. 



Remote Sensing of Wind and Atmospheric 

 Structure by Lidar 



Dr. J. A. Weinman and his group at the Uni- 

 versity of Wisconsin have developed a high resolu- 

 tion monostatic lidar (laser radar) system for 

 probing the lower atmosphere. Light pulses from 

 the lidar are scattered from aerosols which occur 

 naturally in the atmosphere boundary layer. The 

 time that elapses between the emission and return 

 of this light is used to determine the range at 

 which the aerosols are located. The magnitude of 

 the return signal has been determined to be pro- 

 portional to the densities of aerosols at that range. 

 The aerosols are not uniformly distributed in the 

 boundary layer, and the motion of these natural 

 aerosol density inhomogeneities can be tracked. 

 Measurement of the rate of displacement of the 

 inhomogeneities renders it feasible to measure 

 wind remotely in near real time. By changing the 

 lidar elevation and digitally processing the data, 

 near real time vertical cross-section displays of 

 optically "clear" atmospheric convection can be 

 made visible, and such diverse atmospheric struc- 

 tures as inversions, convective plumes, incipient 

 clouds, and waves are observable. Time series of 

 such pictures permit the complex motion field 

 under cumulus clouds to be observed. Thus, at- 

 mospheric structure and wind can be obtained on 

 a time scale and resolution not feasible with cur- 

 rent meteorological observation systems. 



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