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Naval air defense is a critical facility for ship survivability and has been subject of a number of studies. We investigate here three different approaches to modeling it with computer software. One approach focuses on the problems of information processing and communication for the air-defense team, and is good for analyzing its efficiency. Another approach focuses on the inference of the nature of observed tracks, and is based on the novel psychological theory of conceptual blending. A third approach uses an expert-systems approach that can learn from experience and be more substantially automated than the other two approaches. Each approach has its own advantages: The first provides insights for organizing and managing air-defense personnel, the second provides insights into cognitive biases in analysis that should be examined during training, and the third suggests a way to mostly automate the air-defense process to save money. This work suggests the value of multiple simulations of the same process when that process is important to understand.

Pilin withan M,of16,500 was purified tohomogeneity fromNeisseria meningitidis SP3428. Procedures whichprovided useful separation during purification included high-pressure liquid chromatography witha TSKsize exclusion column, Sephacryl S-200 columnchromatography, ion-exchange chromatography with SP-Sephadex, andpreparative sodiumdodecyl sulfate-polyacrylamide gelelectrophoresis. Theaminoacid composition ofthis pilin wassimilar tothat previously reported forthis species. Thesequence oftheN-terminal 51aminoacids was alsodetermined. Theprotein lacked a modified phenylalanine attheaminoterminus and displayed sixresidues whichwere different fromNeisseria gonorrhoeae inthatregion ofthemolecule determined tobethelectin-binding domain. Monoclonal antibody raised tothis pilin was employed, alongwith a monoclonal antibody toan epitope common toallgonococcal pilins, toanalyze theintra- andinterstrain heterogeneity ofmeningococcal piliation. Theresults indicate thatN.meningitidis displays considerable intra- andinterstrain heterogeneity with respect tobothpilus subunit size andantigenicity. TheMrofsubunits ranged from13,000 to20,000. Aconsiderable amountofevidence now exists that fibrous proteins attached tothecell surface ofsome gram-negative

The first identified vexillifers (4.4, 6.0 mm HL) and 2 juveniles (10.5, 11.4 mm HL) of Pyramodon ventralis are described and compared with vexillifer larvae of Snyderidia canina (3.6,5.7 mm HL). The presence of pelvic fins, a visceral cradle, and a greater number of pectoral-fin rays distinguishes larvae of P. ventralis from larvae of S. canina. Pyramodontine vexillifers are characterized as follows: a deep, compressed head and trunk with a depth at the first anal ray of 0.77-0.92 HL; a short predorsal distance of 1.12-1.27 HL; more than 24 pectoral-fin rays; a proximal vexillum radial with a descending anterior process, a wavy ventral contour, and a posterior process passing under the anterior dorsal-fin radials; a pronounced second neural spine; and long anal-fin radials. Identification of a vexillifer larva of Pyramodon establishes the vexillifer larva as a unique specialization of all Carapidae and reinforces the classification of Pyramodon as a close relative of Snyderidia.

Observations in sapling stands of unthinned Douglas'fir (.Pteudotvlga menzie:ii) sh<;wed thzt mountain beaver (Apladotut;a nfa) are Usrally associated with the treeless openings. Vegetation found iD these openings provides the majority of their food and nesting material. Mountain beaver damage to saplings usually occurs in the border areas around these openings. The levels of damage appear related to stand chara.teristics such as age, size, and density of trees and to the degree of canopy closure. In this study, the heaviest damage by mounrain beaver occulred to ttees nine to twelve years old aod coincided with the approximate time of canopy closure. The distribution of animals, their use o{ vegetation, and the patterns of damage suggest that as the tree canopy closes, understory vegetation is suppressed and damage levels increase as moudtain beaver are then forced to rely .on Douglas-fir for food. Slab and increment core samples provide an e{fective means of darrog camage. lnlroduction Mountain beavet (Aplodantia rut'a'1 datna.ge saplings of Douglas-fir (Pseutlotsuga nenziesi.i) and other species in the 10- to 25-yeat age class, sometimes causing serious stocking reductions and ecoflomic losses. Basal girdling and uodemitring of roots are the most selious injuries inflicted on saplings ( Hooven, 1977; l awrence et al., 1961). Observations repofied io rhis paper suggesr characteristics of mouotain beaver distti- bution and their habirat use which may aid in understanding the problem and in con-

Results demonstrate how the economic feasibility of commercial hardwood thinning is impacted by tree diameter. product mix. and primary product markets. These results indicate that multi- product harvesting can increase revenues by $0.01/ft3 to $0.32/f t3; and that small shifts in price levels or haul distance can postpone commercial thinning approximately 10 years.