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

How can the Financial Sector Better Serve People and the Planet? The Need to Reimagine Finance

This article analyses two events in 2010, which attempted to reimagine the role of the financial sector in promoting international development. Several strategies for reimagining are identified and described, and mutually reinforcing barriers to reimagining are outlined. The challenges for moving from ideas to action are particularly difficult for a sector that is often impenetrable to those outside of it. The global nature of the sector is also key to the challenge of reimagining, whether proponents for change are inside or outside of it

Using the Financial Crisis to Reimagine the Private Sector

This article uses a workshop, organised by the think tank, Tomorrow's Company, to explore attempts to reimagine the role of business in development. In trying to envisage new ways of working between businesses and INGOs, workshop participants grappled with the tension between abstract thinking and the need to be practical and tangible. The challenges of imagining new ways of working together are highlighted in this article. Ultimately, it is the failure to visualise how change happens in a macro?setting that is seen as the key stumbling block to progress

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

Stories as personal coaching philosophy

The importance of coaches developing and articulating a personal coaching philosophy which encapsulates their values and beliefs is widely recognised. Yet it is also acknowledged that many coaches resist what appears an abstract task or find it to be of limited use in their day-to-day practice. In this paper we explore the potential of an alternative approach to developing and articulating a personal coaching philosophy: storytelling. Following a discussion of the potential of stories, we present a story written by one coach which expresses her personal philosophy in a way that is firmly rooted in her coaching practice. Storytelling approaches, we suggest, can reveal the connections between abstract/general philosophy and the personal embodied experience of coaching. We reflect on the possibilities and problems of using stories as philosophy and offer some suggestions for how coaches may be supported in developing their coaching philosophy through storytelling

Reimagining Aid for the Next Ten Years: What do Donors Think?

This article reports on a workshop facilitated by IDS for representatives of six European development donor agencies. The aim was to create some space for reflection on how aid agencies will need to adapt to, and influence, the changes in the external environment over the next ten years. We identified three key aims for development assistance: narrow national interest, the achievement of the Millennium Development Goals and sustainable global management. The trade?offs and overlaps between these three aims were explored and their implications for the approach, form, capacities and accountabilities of future development agencies were outlined. The authors observed that the space for reflection was much valued by the participants, and argue that the existence of these spaces will come under increased pressure if the results agenda is not sufficiently innovative

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