A dc to dc converter

The object of the invention is to provide an improved converter for converting one direct current voltage to another. A plurality of phased square wave voltages are provided from a ring counter through amplifiers to a like plurality of output transformers. Each of these transformers has two windings, and S(1) winding and an S(2) winding. The S(1) windings are connected in series, then the S(2) windings are connected in series, and finally, the two sets of windings are connected in series. One of six SCRs is connected between each two series connected windings to a positive output terminal and one of diodes is connected between each set of two windings of a zero output terminal. By virtue of this configuration, a quite high average direct current voltage is obtained, which varies between full voltage and two-thirds full voltage rather than from full voltage to zero. Further, its variation, ripple frequency, is reduced to one-sixth of that present in a single phase system. Application to raising battery voltage for an ion propulsion system is mentioned

Alley Cropping: An Agroforestry Practice

Alley cropping is an agroforestry practice intended to place trees within agricultural cropland systems. The purpose is to enhance or add income diversity (both long and short range), reduce wind and water erosion, improve crop production, improve utilization of nutrients, improve wildlife habitat or aesthetics, and/or convert cropland to forest. The practice is especially attractive to landowners wishing to add economic stability to their farming system while protecting soil from erosion, water from contamination, and improving wildlife habitat

Alley Cropping: An Agroforestry Practice

Alley cropping is an agroforestry practice intended to place trees within agricultural cropland systems. The purpose is to enhance or add income diversity (both long and short range), reduce wind and water erosion, improve crop production, improve utilization of nutrients, improve wildlife habitat or aesthetics, and/or convert cropland to forest. The practice is especially attractive to landowners wishing to add economic stability to their farming system while protecting soil from erosion, water from contamination, and improving wildlife habitat

Walnut agroforestry (1996)

Agroforestry, or growing trees and other crops together on the same land, has been practiced for years in other countries to achieve more sustainable and productive use of limited land resources. In the U.S., forestry and agriculture historically have been considered mutually exclusive land use alternatives. But with clear management objectives, careful planning and skillful intensive management, combining crops and trees can provide advantages that outweigh any perceived disadvantages. Agroforestry is a potential alternative to conventional mechanical methods for soil erosion control. It also allows for gradual removal of highly erodible cropland from row-crop production.New 1/92, Reprinted 5/96/5

High-z radio starbursts host obscured X-ray AGN

We use Virtual Observatory methods to investigate the association between radio and X-ray emission at high redshifts. Fifty-five of the 92 HDF(N) sources resolved by combining MERLIN+VLA data were detected by Chandra, of which 18 are hard enough and bright enough to be obscured AGN. The high-z population of microJy radio sources is dominated by starbursts an order of magnitude more active and more extended than any found at z<1 and at least a quarter of these simultaneously host highly X-ray-luminous obscured AGN.Comment: 4 pages, 2 figures, To appear in the proceedings of 'At the Edge of the Universe' (9-13 October 2006, Sintra, Portugal

Growth-Quality Evaluation of Black Walnut Wood. Part II-Color Analyses of Veneer Produced on Different Sites

Heartwood color is an important wood quality parameter in the grading of black walnut veneer. One of the primary factors that causes a reduction in veneer grade is variability in heartwood color. This variability may be in the form of streaked heartwood or in coloration not of a uniform light chocolate brown nature. Black walnut trees from four distinctly different sites were selected to describe wood color of commercially prepared veneer sheets, using standard color measurement techniques, so that within-tree, between-tree, and between-site variations could be determined. Selected logs were sliced into veneer by a commercial process and the veneer was graded according to industrial standards. Reflectance data were obtained from selected veneer samples and these data were transformed into standard color parameters. Wide ranges in luminance and purity parameters were obtained. However, only the differences in luminance were detectable upon visual examination. This suggests that variability in luminance (i.e., darkness or lightness) is the primary cause of heartwood color variability. These analyses revealed statistically significant within-site differences in heartwood luminance, but within-tree differences were also observed. Between-site differences were considered less important than within-site differences

Using Technical Performance Measures

All programs have requirements. For these requirements to be met, there must be a means of measurement. A Technical Performance Measure (TPM) is defined to produce a measured quantity that can be compared to the requirement. In practice, the TPM is often expressed as a maximum or minimum and a goal. Example TPMs for a rocket program are: vacuum or sea level specific impulse (lsp), weight, reliability (often expressed as a failure rate), schedule, operability (turn-around time), design and development cost, production cost, and operating cost. Program status is evaluated by comparing the TPMs against specified values of the requirements. During the program many design decisions are made and most of them affect some or all of the TPMs. Often, the same design decision changes some TPMs favorably while affecting other TPMs unfavorably. The problem then becomes how to compare the effects of a design decision on different TPMs. How much failure rate is one second of specific impulse worth? How many days of schedule is one pound of weight worth? In other words, how to compare dissimilar quantities in order to trade and manage the TPMs to meet all requirements. One method that has been used successfully and has a mathematical basis is Utility Analysis. Utility Analysis enables quantitative comparison among dissimilar attributes. It uses a mathematical model that maps decision maker preferences over the tradeable range of each attribute. It is capable of modeling both independent and dependent attributes. Utility Analysis is well supported in the literature on Decision Theory. It has been used at Pratt & Whitney Rocketdyne for internal programs and for contracted work such as the J-2X rocket engine program. This paper describes the construction of TPMs and describes Utility Analysis. It then discusses the use of TPMs in design trades and to manage margin during a program using Utility Analysis

Increase woodland products through timber stand improvement

"Timber Stand Improvement (TSI) denotes management practices that improve the vigor, productivity, and quality of stands of trees."--First page.John Slusher and H.E. Garrett (School of Forestry, Fisheries and Wildlife), Clell Solomon (Missouri Department of Conservation), and Ivan L. Sander (U.S. Forest Service)Revised 5/84/5