Study of 42 and 85 GHz coupled cavity traveling-wave tubes for space use

Designs were formulated for four CW, millimeter wavelength traveling-wave tubes having high efficiency and long life. Three of these tubes, in the 42 to 44 GHz frequency region, develop power outputs of 100 to 300 watts with overall efficiencies of typically 45 percent. Another tube, which covers the frequency range of 84 to 86 GHz, provides a power output of 200 watts at 25 percent efficiency. The cathode current density in each design was 1A/sq cm. Each tube includes: metal-ceramic construction, periodic permanent magnet focusing, a two step velocity taper, an electron beam refocusing section, and a radiation cooled three-stage depressed collector. The electrical and mechanical design for each tube type is discussed in detail. The results of thermal and mechanical analyses are presented

Receipt for Soldiers\u27 Effects (6 March 1864)

Receipt for 6 dollars from J.L. Dodd, private Co. D., to Thomas Reberhttps://egrove.olemiss.edu/ciwar_milrec/1080/thumbnail.jp

Data Rate Determination for Fixed, Matched Filter Channels

In today\u27s world, with ever rising data rate requirements and ever shrinking budgets, the use of existing equipment to perform new tasks is highly desirable. Often the need to increase the data transmission rates through an existing system is clear, yet financial or logistical constraints do not permit complete redesign of the system. Other situations do not allow the designer access to all of the system components, as in satellite systems. Whatever the circumstances, the desirable result is to maximize the data rates through existing channels. This paper presents a method for determination of the allowable data rates in existing channels. In addition, a measure of the expected degradation associated with the use of a pre-existing receive filter and matched transmit filter pair at increased transmit data rates is determined. Examples are given for different filter types and data modulation formats

A Comparison of Modulation Schemes in Bandlimited AWGN Channels

In recent years, as data rates rise for seemingly decreasing available bandwidths, a great deal of research has been directed toward finding bandwidth efficient modulation schemes. Two such methods are partial-response signaling and trellis-coded modulation. Both of which promise performance gains in a bandlimited channel when compared to uncoded systems. This paper will compare the performance of these schemes, when applied to a QPSK system over various channel bandwidths

Uplink-Noise Limited Satellite Channels

Many applications, current and emerging, are faced with a relatively new and interesting channel model. Systems which transmit data through a nonlinear relay, such as a satellite, must deal with a composite channel that can be separated into two distinct channels - the uplink channel between the user and the relay, and the downlink channel between the relay and the final destination. If the system has a strict power limitation and high data rate demands, such as a small satellite transmitting through NASA\u27s TDRSS Network, the dominant noise is present on the uplink rather than the downlink channel. Such a system is deemed to be uplink-noise limited and presents the designer with a number of problems not encountered in a more typical downlink-noise limited channel. Whereas the transmitted signal constellation can be pre-distorted to take into account the effect of the nonlinearity in the down-link limited channel, no amount of pre-distortion will solve the problems encountered when the majority of the noise is present before the nonlinearity. Instead, the receiver must be modified to reflect the non- Gaussian noise due to the operation of the nonlinearity on Gaussian noise. Under three assumptions - there is no downlink-noise present, the downlink channel is wideband relative to the data, and the filter proceeding the nonlinearity meets both matched filter and Nyquist requirements - such modifications can be made based on the nature of the nonlinearity. By mapping the ideal decision region through the nonlinearity, performance almost identical to that of a linear-wideband AWGN channel can be achieved. This paper will develop the theoretical performance of the receiver described for a nonlinearity typical of a satellite channel. Performance curves will be presented for QPSK, SPSK, 16PSK and 16QAM modulation schemes

Temperature and Moisture Influence on Compression-Recovery Behavior of Wood

The primary limitation of non-veneer wood composites for applications in moist environments is dimensional instability. Thickness instabilities from moisture absorption primarily result from damaged cell structures that recover upon absorption of moisture. Previous research has shown that manipulating the pressing parameters involved in the manufacture of non-veneer wood composites (i.e., temperature and moisture) can lead to a more dimensionally stable product. However, the precise phenomena controlling these changes are not fully defined. To understand development of pressing-induced damage, the large strain, compression-recovery behavior of wood and polyurethane (PUR) foam (i.e., as a model system) was studied at a variety of compression temperatures spanning the glassy to rubber transition. The behavior is then related to polymer phase transitions to discern the role of viscoelastic behavior in damage evolution. The elastic modulus (E) and yield stress (σy) were used to characterize the elastic region of compression, whereas fractional recovery (R) and dissipated energy (ΔE) represented the inelastic component. The PUR foam displayed a distinct glassy plateau region dominated by E, σy, and ΔE as well as low R. Wood with 22 and 12% MC behaved similarly to the elastomeric PUR foam; however, limits on environmental control prevented testing in the rubbery regime for the 12% MC samples. The E and σy also decreased with increasing compression temperature for ovendried yellow-poplar. However, in contrast to yellow-poplar with either 12 or 22% MC, an increase in ΔE was accompanied by a decrease in R with increasing compression temperature of the oven-dried yellow-poplar. An apparent change in mechanism occurs when compressing wood at high temperatures without moisture present. This change was attributed to kinetic effects such as thermal degradation or crosslinking reactions

A Model for Viscoelastic Consolidation of Wood-Strand Mats. Part II: Static Stress-Strain Behavior of the Mat

A solid mechanics model is developed to predict the static stress-strain behavior of randomly formed wood-strand mats during pressing. The procedure includes a Monte Carlo simulation for reconstructing the mat structure. During the early stages of mat displacement, the model computes the cumulative stress development from strand bending. As consolidation continues, the overlapping strands form solid columns. Hooke's Law, modified by a nonlinear strain function, governs the stress development in a finite number of these imaginary columns comprising the mat. Experimental results showed good agreement with the predicted stress response

A Model for Viscoelastic Consolidation of Wood-Strand Mats. Part I. Structural Characterization of the Mat Via Monte Carlo Simulation

A procedure using Monte Carlo simulation was developed to characterize the spatial structure of randomly formed, wood-strand mats. The simulation reproduces the number of strands in the centroids of imaginary strand columns of finite size. The vertical distances between the adjacent strands and the location of the column centroid relative to the constant length of each strand are also simulated. A data base was collected on realistic mats produced from strands of constant size and non-planar geometries (i.e., random bow, cup, and twist). The procedure can be used in a model for predicting the mechanical behavior of random strand mats during consolidation

Reducing Moisture Swell of Densified Wood With Polycarboxylic Acid Resin

A water-soluble polycarboxylic acid (PCA) resin was assessed for ability to limit moisture swelling of densified wood. Aspen flakes were treated in 0 (control), 1, 5, 10, and 20% PCA resin solutions and drained for 1, 10, and 20-min time periods. Following treatments, flakes were compressed to roughly 50% strain at 170°C. The PCA content of flakes significantly increased with increasing concentration and drain time. Water absorption and thickness swell of flakes decreased with increasing PCA content. Both water absorption and thickness swell of untreated flakes were over 100%; but for PCA-treated flakes, water absorption and thickness swell as low as 45% and 16%, respectively, were achieved. Irreversible thickness swell decreased with increasing PCA content, while reversible thickness swell remained relatively constant. The swelling coefficient decreased with increasing PCA content, a behavior that often is associated with bulking agents for treated, uncompressed wood. However, dynamic mechanical analysis further suggested that PCA resin acts as a cross-linking agent to stabilize the position of the collapsed cell walls