Class-E, Class-C, and Class-F power amplifiers based upon a finitenumber of harmonics

Class-E operation at UHF and microwave frequencies is achieved by using transmission-line networks to provide the drain harmonic impedances of an ideal class-E power amplifier (PA). This paper develops a technique for analysis of such amplifiers that are based upon a finite number of harmonics. The technique is generally applicable to classes E, C, and F as well as PAs with harmonic reactances not corresponding to those of established classes. The analysis shows that the maximum achievable efficiency depends not upon the class of operation, but upon the number of harmonics employed. For any set of harmonic reactances, the same maximum efficiency can be achieved by proper adjustment of the waveforms and the fundamental-frequency load reactance. The power-output capability depends upon the harmonic reactances and is maximum for class F     

Obtaining a nanostructure in titanium by equal-channel angular pressing

Conclusions 1. We have developed a technological setup for isothermal equal-channel angular pressing (ECAP) for hard-to-deform materials that serve at up to 500°C and specific loads on the punch of up to 2000 MPa. 2. We established the process parameters that provide fabrication of defectless preforms from titanium of grade VT1-0 with a nanostructure and obtained specimens 100 mm long and 20 mm in diameter. 3. We used the method of grids to study the strain state of preforms obtained by the ECAP method and established the great influence of the geometry of the channels, in particular, of the back angle of intersection of the pressing channels, on the uniformity of the distribution of shear strain in the plane of flow of the material. 4. Rotation of a preform of titanium VT1-0 after each cycle of ECAP by 90° about the longitudinal axis provides a homogeneous structure with grains 0.2 – 0.5 μm in size after eight treatment cycles. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 27 – 31, September, 2000.     

Efficiency of Doherty RF Power-Amplifier Systems

A Doherty system combines the outputs of two or more linear RF power amplifiers (PAs) through an impedance-inverting coupler such as a quarter-wave transmission line. At low output levels, the first PA operates linearly, reaching saturation (and maximum efficiency) at some transition voltage below the system peak-output voltage. At higher output levels, the first PA remains saturated and the second PA operates linearly. The instantaneous efficiency and power characteristics of a Doherty system are derived using ideal class-B RF PAs so that the results can easily be scaled for use with real-world PAs. The average efficiency and maximum-efficiency transition points are then determined for a variety of amplitude-modulated signals. The Doherty amplifier can be considerably more efficient than a conventional class-B linear PA. For example, the 28-and 8.9-percent average efficiencies of a class-B PA with Rayleigh-distri buted envelopes with 10-and 20-dB peak-to-average ratios are improved to 60 and 48 percent, respectively, by a two-stage Doherty system. The addition of a third stage further improves the efficiencies to 70 and 66 percent, respectively.     

Market basket survey shows elevated levels of As in South Central U.S. processed rice compared to California: consequences for human dietary exposure

We report the largest market basket survey of arsenic (As) in U.S. rice to date. Our findings show differences in transitional-metal levels between polished and unpolished rice and geographical variation in As and selenium (Se) between rice processed in California and the South Central U.S. The mean and median As grain levels for the South Central U.S. were 0.30 and 0.27 mimcrog As g(-1), respectively, for 107 samples. Levels for California were 41% lower than the South Central U.S., with a mean of 0.17 microg As g(-1) and a median of 0.16 microg As g(-1) for 27 samples. The mean and median Se grain levels for the South Central U.S. were 0.19 microg Se g(-1). Californian rice levels were lower, averaging only 0.08 and 0.06 microg Se g(-1) for mean and median values, respectively. The difference between the two regions was found to be significant for As and Se (General Linear Model (GLM): As p < 0.001; Se p < 0.001). No statistically significant differences were observed in As or Se levels between polished and unpolished rice (GLM: As p= 0.213; Se p= 0.113). No significant differences in grain levels of manganese (Mn), cobalt (Co), copper (Cu), or zinc (Zn) were observed between California and the South Central U.S. Modeling arsenic intake for the U.S. population based on this survey shows that for certain groups (namely Hispanics, Asians, sufferers of Celiac disease, and infants) dietary exposure to inorganic As from elevated levels in rice potentially exceeds the maximum intake of As from drinking water (based on consumption of 1 L of 0.01 mg L(-1) In. As) and Californian state exposure limits. Further studies on the transformation of As in soil, grain As bioavailability in the human gastrointestinal tract, and grain elemental speciation trends are critical.     

Formation of a nanostructure and properties of titanium rods during equal-channel angular pressing CONFORM followed by drawing

Severe plastic deformation by equal-channel angular pressing according to the Conform schedule (ECAP-Conform) is used for the first time to produce long titanium rods in a nanostructured state. As a result of ECAP-Conform followed by drawing, the ultimate strength of Grade 4 titanium increases to 1350 MPa, and its yield strength increases to 1300 MPa at a high retained plasticity. The high efficiency and output of the ECAP-Conform method allow the development (on its basis) of a commercial technology for the production of high-strength nanostructured titanium, which is a promising material for medical implants.     

Energy production from grassland – Assessing the sustainability of different process chains under German conditions

In many regions of Europe, grassland shapes the landscape and fulfils important functions in protecting nature, soil, and water. However, the traditional uses of grassland for forage production are vanishing with progress in breeding and structural adaptations in agriculture. On the other hand, the demand for biomass energy is rising due to political sustainability goals and financial measures to support renewable energy. Against this background, the Institute for Technology Assessment and Systems Analysis investigated the applicability, economic efficiency, and sustainability of different techniques for energy production from grassland as well as from grassland converted into maize fields or short-rotation poplars under German conditions. The results show that despite relatively high energy prices and the financial support for bioenergy, the effects of energy production from grassland on employment in agriculture and farmers' income are modest. What is beneficial are savings in non-renewable energy, reductions in greenhouse gas emissions, and local provision of energy carriers. If grassland biomass (grass silage or hay) is used for energy purposes, this brings the further advantages of preserving biodiversity and the cultural landscape and protecting of soil and groundwater. Negative impacts on sustainable development result from an increase in emissions, which leads to acidification, eutrophication, and risks to human health. The overall evaluation indicates that short-rotation poplars are comparatively advantageous from the economic and ecological point of view. Therefore, a development plan for grassland is required to identify areas where grassland could be used as an energy resource or where it would be favourable to install energy plantations with fast-growing perennial plants.     

How to Render Frames and Influence People

Rendering systems generally treat the production of images as an objective process governed by the laws of physics. However, perception and understanding on the part of viewers are subjective processes influenced by a variety offactors. For example, in the presentation of architectural drawings, the apparent precision with which the drawings are made will affect whether the viewer considers the design as part of a preliminary design or as part of a final polished project, and to some extent the level of confidence the viewer has in the encoded information. In this paper we develop techniques for rendering images in a way that differs from the usual photorealistic or wire-frame output of renderers. In particular, our techniques allow a user to adjust the rendering of a scene to produce images using primitives with variable degrees of precision, from approximations that resemble vague “five-minute-sketches” to more mature but still hand-drawn images. We provide a theoretical framework for analysing the information flow from the computer to the user via such images. Finally, we describe the design and implementation of a prototypical renderer and show examples of its output.     

Trends in incidence of and mortality from invasive cancer of the uterine cervix in Scotland (1975-1994)

BACKGROUND: Among the victims of floods, earthquakes, and hurricanes, there is an increased prevalence of post-traumatic stress disorder and depression, which are risk factors for suicidal thinking. We conducted this study to determine whether natural disasters affect suicide rates. METHODS: From a list of all the events declared by the U.S. government to be federal disasters between 1982 and 1989, we selected the 377 counties that had each been affected by a single natural disaster during that period. We collected data on suicides during the 36 months before and the 48 months after the disaster and aligned the data around the month of the disaster. Pooled rates were calculated according to the type of disaster. Comparisons were made between the suicide rates before and those after disasters in the affected counties and in the entire United States. RESULTS: Suicide rates increased in the four years after floods by 13.8 percent, from 12.1 to 13.8 per 100,000 (P<0.001), in the two years after hurricanes by 31.0 percent, from 12.0 to 15.7 per 100,000 (P<0.001), and in the first year after earthquakes by 62.9 percent, from 19.2 to 31.3 per 100,000 (P<0.001). The four-year increase of 19.7 percent after earthquakes was not statistically significant. Rates computed in a similar manner for the entire United States were stable. The increases in suicide rates were found for both sexes and for all age groups. The suicide rates did not change significantly after tornadoes or severe storms. CONCLUSIONS: Our study shows that suicide rates increase after severe earthquakes, floods, and hurricanes and confirms the need for mental health support after severe disasters.     

Formation of a submicrocrystalline structure in St10 and 08R steels during equal-channel angular pressing

The effect of cold equal-channel angular pressing (ECAP) on the structure and properties of low-carbon St10 and 08R steels in the initially ferritic-pearlitic and bainitic states is studied. Directly after ECAP, only a partially submicrocrystalline structure with a grain size of 150–300 nm (depending on alloying and the initial state) can be obtained. Along with a granular structure, a subgrain and/or cellular structure, including an oriented structure, are observed. The finest structure forms in a boron-containing 08R steel with a structural-element size of 190 nm. The strength of the 08R steel subjected to cold ECAP (σ_u = 805–1235 MPa) corresponds to a hardware strength class of 8.8–12.9. The strength of the deformed St10 steel is close to a strength class of 8.8.