Steady-state analysis of the constant-frequency clamped seriesresonant converter

A constant-frequency diode-clamped series resonant converter (CFCSRC) is proposed as a solution to problems associated with frequency-controlled resonant converters. This converter has two resonant frequencies, and control is achieved by varying the relative time spent at each switching frequency. Two zero-current-switching (ZCS) modes are examined and plotted in the output plane. An equation is given for the boundary between the two ZCS modes, as well as an expression for the boundary between ZCS and non-ZCS operation; both are plotted in the output plane. The output equation for the main mode is shown to be hyperbolic. Converter peak voltages limited to the input voltages, and peak currents are less than those of the frequency-controlled clamped series resonant converter over a large operating range. Data from a prototype converter are compared with theoretical data and are shown to be in good agreement with the theoretical model     

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Bistatic RCS of Complex Objects near Forward Scatter

A technique is presented for predicting the bistatic radar cross section (RCS) of an opaque, arbitrarily shaped object at angles near forward scatter. Babinet's principle is employed to approximate the object's scattering pattern as the two-dimensional Fourier transform of its silhouette. Calculations for spheres and right-circular cylinders are shown to agree with predictions based on exact Mie theory, method of moments, and physical optics. Restrictions on the applicability of the method are presented.     

煤水浆的雾化与磨损的实验研究

本煤水浆喷嘴采用内混合式空气雾化喷嘴(图1)。煤水浆通道设计成形状简单的直通道。主流雾化空气高速旋转喷出,在内混合室与煤水浆混合,形成气浆薄液膜,它在内混合室出口处再与次流雾化空气相撞,进一步雾化破碎。 实验用煤粉成份为固体碳68.0％.挥发份23.2％,灰分7.8％和硫0.84％.实验用煤水浆按重量比为70％的磨细煤粉、1％的附加剂和29％的水组成。最大煤粒尺寸为250um。混     

Application of time-variable process noise in terrestrial reference frames determined from VLBI data

In recent years, Kalman filtering has emerged as a suitable technique to determine terrestrial reference frames (TRFs), a prime example being JTRF2014. The time series approach allows variations of station coordinates that are neither reduced by observational corrections nor considered in the functional model to be taken into account. These variations are primarily due to non-tidal geophysical loading effects that are not reduced according to the current IERS Conventions (2010). It is standard practice that the process noise models applied in Kalman filter TRF solutions are derived from time series of loading displacements and account for station dependent differences. So far, it has been assumed that the parameters of these process noise models are constant over time. However, due to the presence of seasonal and irregular variations, this assumption does not truly reflect reality. In this study, we derive a station coordinate process noise model allowing for such temporal variations. This process noise model and one that is a parameterized version of the former are applied in the computation of TRF solutions based on very long baseline interferometry data. In comparison with a solution based on a constant process noise model, we find that the station coordinates are affected at the millimeter level.     

Locating potential biosignatures on Europa from surface geology observations

We evaluated the astrobiological potential of the major classes of geologic units on Europa with respect to possible biosignatures preservation on the basis of surface geology observations. These observations are independent of any formational model and therefore provide an objective, though preliminary, evaluation. The assessment criteria include high mobility of material, surface concentration of non-ice components, relative youth, textural roughness, and environmental stability. Our review determined that, as feature classes, low-albedo smooth plains, smooth bands, and chaos hold the highest potential, primarily because of their relative young age, the emplacement of low-viscosity material, and indications of material exchange with the subsurface. Some lineaments and impact craters may be promising sites for closer study despite the comparatively lower astrobiological potential of their classes. This assessment will be expanded by multidisciplinary examination of the potential for habitability of specific features.     

Shaping a legal framework for the commercial use of outer space: recommendations and conclusions from Project 2001

Private and commercial activity in outer space still poses challenges to space law and policy. Within ‘Project 2001’—a legal research project by the University of Cologne's Institute of Air and Space Law and the German Aerospace Center (DLR)—six international expert working groups examined international and national laws, in order to identify gaps and, where necessary, propose improvements to the present legal framework for private space activities. The results were presented and discussed at an international colloquium in May 2001 in Cologne, Germany, where final conclusions have been drawn. This report presents a summary of the project's work and main conclusions, which are documented in full in a comprehensive book to be published in May 2002.     

Drilling systems for extraterrestrial subsurface exploration

Drilling consists of 2 processes: breaking the formation with a bit and removing the drilled cuttings. In rotary drilling, rotational speed and weight on bit are used to control drilling, and the optimization of these parameters can markedly improve drilling performance. Although fluids are used for cuttings removal in terrestrial drilling, most planetary drilling systems conduct dry drilling with an auger. Chip removal via water-ice sublimation (when excavating water-ice-bound formations at pressure below the triple point of water) and pneumatic systems are also possible. Pneumatic systems use the gas or vaporization products of a high-density liquid brought from Earth, gas provided by an in situ compressor, or combustion products of a monopropellant. Drill bits can be divided into coring bits, which excavate an annular shaped hole, and full-faced bits. While cylindrical cores are generally superior as scientific samples, and coring drills have better performance characteristics, full-faced bits are simpler systems because the handling of a core requires a very complex robotic mechanism. The greatest constraints to extraterrestrial drilling are (1) the extreme environmental conditions, such as temperature, dust, and pressure; (2) the light-time communications delay, which necessitates highly autonomous systems; and (3) the mission and science constraints, such as mass and power budgets and the types of drilled samples needed for scientific analysis. A classification scheme based on drilling depth is proposed. Each of the 4 depth categories (surface drills, 1-meter class drills, 10-meter class drills, and deep drills) has distinct technological profiles and scientific ramifications.