The acoustic characteristics of a point-reacting duct liner that consists of a porous facing sheet backed by cellular cavities are derived by examining the wave propagation within the liner. The relation between the derived expression for the liner acoustic admittance and a semi-empirical formula that is widely used in the literature is discussed. The influence of the liner on acoustic propagation in a duct is examined for the case of a plane duct that carries a uniform mean flow. Numerical results for the attenuation rates vs. frequency are presented. These results. are of three types: (1) comparisons with previously published results for no backing cavity and no mean flow are made, and these results are extended to include the effects of the mean flow; (2) results of parametric variations of the liner dimensions are presented to assess the relative influence of the facing-sheet thickness and the cavity depth; (3) results from the derived expression for liner specific admittance and from the semi-empirical formula are compared in order to determine the significance of the wave propagation within the porous material and to determine the range of validity of the semi-empirical formula. / Master of Science

Clasts within the Fincastle conglomerate indicate that more than 15,000 ft of structural relief had developed between the axis of the Blue Ridge anticlinorium and the trough of the Salem synclinorium by Middle Ordovician time. The Fincastle conglomerate is restricted to the northeast depression of the Salem synclinorium, south of the Southern and Central Appalachian boundary. Evidence indicates the Fincastle conglomerate is a northeastern lithofacies of the Bays Formation. The Fincastle has an average thickness of 48 to 69 ft, a maximum thickness of 300 ft, and is absent to the southwest where it has fined to siltstone and shale. Each conglomerate zone may grade up into diamictite or graywacke which, in turn, grades upward into shale. Clasts of well-foliated basement gneiss, vein quartz, quartz pebble conglomerate, sandstone and carbonate clasts were derived from the complementary Blue Ridge anticlinorium and perhaps the Piedmont. Calcite-cemented sandstone, sandstone conglomerate and micritic, black limestone clasts were probably derived from within the basin. The deposit is characterized by subrounded to rounded, elongate clasts (up to 17 in long) in a graywacke matrix. The Fincastle conglomerate was deposited in broad, shallow, marine channels. Sedimentary features indicate it was resedimented from a stream environment during flooding or high river stages. The textural and compositional immaturity of the Fincastle sediments indicate they bypassed the nearshore marine environment. The Fincastle conglomerate indicates erosion of a local culmination on the Blue Ridge anticlinorium or a geanticline in Middle Ordovician time to the southeast in the vicinity of the Goose Creek window. / Master of Science

This paper extends an existing mathematical model of rain depolarization and attenuation to include the expected variances as well as the usually predicted mean values. It emphasizes depolarization and develops data for waves with frequencies ranging from 4 to 34.8 GHz propagating in rain cells which vary in intensity from light to severe. General causes of output scatter are included, and the scatter induced by the rain drop size distribution is examined in detail. Predicted cross polarization variances in excess of 9 dB for certain frequencies are shown. This variance is significant in that it can easily exceed system threshold criteria of mean value designs. Methods for extending the depolarization predictions to attenuation variances are discussed. The paper concludes with a brief examination of resonance encountered when drop diameters are multiples or submultiples of critical wavelengths. Conclusions drawn are applicable to polarization diversity design; multiple hop systems requiring frequency reuse and systems constrained to operate under fixed polarizations. / Master of Science

M.S.

Reconnaissance investigation of the Cu-Fe-Zn-S system has been conducted into the phase equilibria of the geologically significant portion containing pyrrhotite, pyrite, bornite, chalcopyrite, cubanite, and sphalerite. Chalcopyrite-sphalerite relationships were emphasized because of their common association as intimately intergrown phases (interpreted as exsolution or replacement) in major Cu-Zn ore bodies. The investigation employed silica tube-type experiments in the temperature range 800°C to 500°C. Data indicate that solid solubility of ZnS in intermediate solid solution (a high temperature chalcopyrite-like phase) and of .CuS and FeS in sphalerite depend on temperature, sulfur content, and metal:metal ratios, Illustrations of temperature and sulfur controls are listed below: CuS in sphalerite - temperature - 800°C, 11.74 mole percent 500°C, 3.36 mole percent sulfur content - excess - 800°C, decreases from 11.74 to 6.03 deficiency - 800°C, decreases from 11.74 to 5.98 ZnS in iss - temperature - 800°C, 22.73 mole percent 500°C, 4.67 mole percent sulfur content - excess - 800°C, decreases from 22.73 to 7.1 (with Fe) Variation of Cu/Fe ratios in iss from 23.93/53.88 to 40.51/50.08 produces a change of ZnS solubility in iss from 22.73 mole. percent to 9.4 mole percent. It is concluded that intergrowths found in ores may result from reduction in temperature, change in sulfur activity or ordering in a crystal structure. The low levels of impurity found in natural sphalerites and chalcopyrites indicate their virtual total expulsion on cooling. / Master of Science

Research was initiated in April, 1973, to evaluate the use of artificial reefs in Smith Mountain Lake, Virginia. Twelve areas of the reservoir were selected for study. The sites were chosen from SCUBA and fathometer survey data on the basis of uniformity of water depth, substrate type, amount of submerged cover, and bottom topography. Four reefs were constructed of scrap automobile tires and four were made of discarded Christmas trees. The remaining four sites were designated control areas. Experimental fishing surveys, SCUBA surveys, and trapping and netting surveys revealed several trends: 1. That sunfishes preferred tree reefs to tire reefs during the spring sampling period, and 2. that reefs effectively concentrated fishes as compared to control areas during the sampling period. / M.S.

The central problem of this study was to identify competencies which are important for success as a Consumer and Homemaking Teacher in Virginia. The objectives of the study were to identify the philosophy held by Consumer and Homemaking teachers·in Virginia; to determine the tasks which are needed to implement\the philosophy; to determine the consensus among various groups of home economists as to which competencies are important for effective teaching. The approach to meeting these objectives was to have a number of home economics teachers create lists of basic beliefs, tasks, and competencies which they felt were important for successful teaching of home economics; to have professionals in the field of home economics review and react to these lists and; to construct refined lists of the philosophy, tasks, and competencies needed for successful teaching of home economics. The initial lists were prepared by sixty-eight home economics teachers who were taking classes on competency based education. The participants in these classes also reviewed and revised the philosophy and task lists. The competency statements were assembled in a Likert-Scale questionnaire and were rated as Very Important, Important, Neither Impor- tant or Unimportant, Unimportant, or Very Unimportant by three Reactor Groups. The competency statements which were rated important or very important by all groups who evaluated them were considered to be necessary for successful teaching of home economics. Refined philosophy, task, and competency lists were developed which can be used in evaluating and redesigning teacher education programs and by teachers and supervisors for self-improvement. / M.S.

Even though the ability to produce vocalizations by the vibration of a membrane is widespread throughout the lizard suborder, only the sounds of geckos (Gekkonidae) have been closely studied. The purposes of this study were to describe the physical structure, social significance, and means of sound production by Anolis g. grahami, one of the 13 anoline species known to vocalize. Recordings were made of 16 adult males and five adult females within two general situations: (1) while held in an experimenter's hand, and (2) while unrestrained within a cage. Hand-held lizards produced five types of vocalizations: (1) two kinds of growls, (2) two kinds of squeals, and (3) a chirp. Unrestrained lizards vocalized during fights only, producing one type of sound in attacks and another during prolonged fights. Lizards responded only slightly to recorded vocalizations and little more to environmental sounds. This suggests that they do not respond to sounds generally and that vocalizations therefore have little intraspecific use. The most important use of vocalizations is probably in defense against predators, and it is a preadaptation for social communication. Vocalization is scattered throughout the genus and therefore seems to be produced by a structure present in most species which is more highly elaborated in vocal species. Dissections revealed that vocal cords are absent, but that the larynx is nevertheless the site of sound production. A thin membrane within the glottis is proposed as the vibrating structure. / M.S.

In this exploratory work, several premixed flames were operated beneath the surface of liquid nitrogen in hopes that some unusual intermediates would be obtained from the resulting quenching process. This quenching would prevent the further reaction of the intermediates which would lead to the final products that are observed under more ordinary conditions. The reactor consisted of a three-port cylindrical vessel with an observation port. The walls of the reactor were insulated from the ambient atmosphere with fiberglass and styrofoam. The flame was introduced into the reactor through a flame holder port in the center of the bottom of the reactor. Since a cold flame holder would quench a flame, it was equipped with a heater which could be controlled to keep the flame holder near room temperature even though it was submerged in liquid nitrogen. Three premixed flames, CH₄-O₂, C₃H₈-O₂, and C₂H₂-O₂, were studied. The submerged stoichiometric combustion yielded condensed products, which, when mass spectrometrically analyzed at room temperature, consisted of nitrogen oxides, carbon oxides, water and nitric acid. The presence of NO₂, CO₂ and HNO₃ was clear, but the confirmation of NO, N₂O, CO, CH₄ or OCH₂ was somewhat equivocal due to overlapping peaks from several compounds. A 10 to 15 per cent deviation of either fuel or oxidant from stoichiometric mixture did not produce any change in the over-all chemistry that was observed. / M.S.

No description available.