Finite element modelling of cold formed stainless steel columns

This paper describes the results obtained from a finite element investigation into the load capacity of column members of lipped channel cross-section, cold formed from Type 304 stainless steel, subjected to concentric and eccentric compression loading. The main aims of this investigation were to determine the effects which the non-linearity of the stress-strain behaviour of the material would have on the column behaviour under concentric or eccentric loading. Stress-strain curves derived from tests and design codes are incorporated into non-linear finite element analyses of eccentrically loaded columns and the results obtained are compared with those obtained on the basis of experiments on stainless steel channel columns with the same properties and dimensions. Comparisons of the finite element results and the test results are also made with existing design specifications and conclusions are drawn on the basis of the comparisons

Extension of earth orbits using low-thrust propulsion

The primary motivation for the utilization of space for environmental science, and in-particular Earth Observation, is the unique vantage point which a spacecraft can provide. For example, a spacecraft can provide a global dataset with a much higher temporal resolution than any other platform. Earth Observation spacecraft are increasingly focused on a single primary application, typically conducted from a small set of classical orbits which limits the range of vantage points and hence the type of observations which can be made. The next generation of innovative Earth Observation spacecraft may however only be enabled through new orbit options not considered in the past. The objective of the study was therefore to enlarge the set of potential Earth orbits by considering the use of low-thrust propulsion to extend the conventional Molniya orbit. These new orbits will use existing, or near-term low-thrust propulsion technology to enable new Earth Observation science and offer a radically new set of tools for mission design. Continuous low-thrust propulsion was applied in the radial, transverse and normal directions to vary the critical inclination of the Molniya orbit, while maintaining the zero change in argument of perigee condition. As such the inclination can be freely altered from the expected critical inclination of 63.4 deg, to, for example 90 deg, creating a Polar-Molniya orbit. Analytical expressions were developed which were then validated using a numerical model, to show that not only was the argument of perigee unchanged but all other orbital elements were also unaffected by the applied low-thrust. It was shown that thrusting in the transverse direction allowed the spacecraft to achieve any inclination with the lowest thrust magnitude in any single direction; this value was however found to be further reduced by combining both radial and transverse thrust. Real-time continuous observation of the Arctic Circle is then enabled using current electric propulsion technology, with fewer spacecraft than the traditional Sun-synchronous polar orbit, and at reduced range than a 'pole-sitter'. Applications of such an orbit would include more accurate Arctic weather predictions and severe weather event warnings for this region

Solar sail mission applications and future advancement

Solar sailing has long been envisaged as an enabling technology. The promise of open-ended missions allows consideration of radically new trajectories and the delivery of spacecraft to previously unreachable or unsustainable observation outposts. A mission catalogue is presented of an extensive range of potential solar sail applications, allowing identification of the key features of missions which are enabled, or significantly enhance, through solar sail propulsion. Through these considerations a solar sail application-pull technology development roadmap is established, using each mission as a technology stepping-stone to the next. Having identified and developed a solar sail application-pull technology development roadmap, this is incorporated into a new vision for solar sailing. The development of new technologies, especially for space applications, is high-risk. The advancement difficulty of low technology readiness level research is typically underestimated due to a lack of recognition of the advancement degree of difficulty scale. Recognising the currently low technology readiness level of traditional solar sailing concepts, along with their high advancement degree of difficulty and a lack of near-term applications a new vision for solar sailing is presented which increases the technology readiness level and reduces the advancement degree of difficulty of solar sailing. Just as the basic principles of solar sailing are not new, they have also been long proven and utilised in spacecraft as a low-risk, high-return limited-capability propulsion system. It is therefore proposed that this significant heritage be used to enable rapid, near-term solar sail future advancement through coupling currently mature solar sail, and other, technologies with current solar sail technology developments. As such the near-term technology readiness level of traditional solar sailing is increased, while simultaneously reducing the advancement degree of difficulty along the solar sail application-pull technology development roadmap

Collision and evaporation avoidance for spacecraft formation

<p>Formation flying is an extremely promising approach to space operations with the potential to enable new types of missions and providing substantial increase in the performance of future space science and Earth observation applications. To successfully validate formation flying however requires the development of specific technologies and methodologies, which are beyond current state-of-the art in a wide range of diverse fields such as metrology and spacecraft guidance, navigation and control. A number of missions are currently under different stages of development to implement some of these stringent requirements.</p> <p>The paper develops and compares collision avoidance algorithms, demonstrating them within a 6 degrees of freedom, multi-spacecraft environment. At first a number of different collision avoidance scenarios will be identified alongside the triggers that will cause the algorithms to be activated. Once activated the collision avoidance algorithm must ensure corrective action to avoid catastrophic consequences to the mission.</p&gt

CONCENTRATION IN AGRIBUSINESS

Industrial Organization,

The Economic Organization of U.S. Broiler Production

Broiler production in the United States is coordinated almost entirely through systems of production contracts, in which a grower’s compensation is based, in part, on how the grower’s performance compares with that of other growers. The industry is undergoing a gradual structural change as production shifts to larger broiler enterprises that provide larger shares of an operator’s household income. Larger enterprises require substantially larger investments in broiler housing, and new or retrofitted houses are also an important source of productivity growth in the industry. This report, based on a large and representative survey of broiler operations, describes the industry’s organization, housing features, contract design, fees and enterprise cost structures, and farm and household finances.broilers, chickens, production contracts, broiler grower financial performance, chicken housing, chicken litter, poultry, Farm Management, Production Economics,

Solar sailing

An introduction to solar sailing is presented. The physical principles are briefly reviewed along with an introduction to the historical context of solar sailing. Potential solar sail configurations are briefly introduced, while placing these in the context of the current hardware development programmes. Following the introduction to solar sailing we progress onto a discussion of solar sail orbital dynamics in a planet-centred environment. The development of solar sail trajectory generation is presented, from Earth escape trajectories through to lunar fly-by trajectories and more accurate Earth escape methods. Much of this work relies on assumptions to generate near-optimal solutions rather than true globally optimal solutions, which are computationally difficult to determine for multiple revolution trajectories. Many of these traditional planet-centred solar sail applications, such as Earth escape, also require rapid attitude slew manoeuvres to achieve. This first lecture is based on theory development and application with a view towards future missions, such as planetary sample return

Asymptotically exact trial wave functions for yrast states of rotating Bose gases

We revisit the composite fermion (CF) construction of the lowest angular momentum yrast states of rotating Bose gases with weak short range interaction. For angular momenta at and below the single vortex, $L \leq N$, the overlaps between these trial wave functions and the corresponding exact solutions {\it increase} with increasing system size and appear to approach unity in the thermodynamic limit. In the special case $L=N$, this remarkable behaviour was previously observed numerically. Here we present methods to address this point analytically, and find strongly suggestive evidence in favour of similar behaviour for all $L \leq N$. While not constituting a fully conclusive proof of the converging overlaps, our results do demonstrate a striking similarity between the analytic structure of the exact ground state wave functions at $L \leq N$, and that of their CF counterparts. Results are given for two different projection methods commonly used in the CF approach

Magnetic Oscillations of a Fractional Hall Dot

We show that a quantum dot in the fractional Hall regime exhibits mesoscopic magnetic oscillations with a period which is a multiple of the period for free electrons. Our calculations are performed for parabolic quantum dots with hard-core electron-electron interactions and are exact in the strong field limit for $k_B T$ smaller than the fractional Hall gap. Explicit expressions are given for the temperature dependence of the amplitude of the oscillations.Comment: 11 pages, IUCM-004, plain te