Interaction Between Gravity Compensation Suspension System and Deployable Structure

Gravity compensation suspension systems are essential to support space structures during tests on Earth, but also impose constraints on the structures that have the effect of changing their behavior. A computational and experimental study of the interaction of a rigid panel solar array model with a manually adjustable suspension system during quasi-static deployment tests in the 1-g environment of the laboratory is presented. A methodology is established for modeling this interaction, for predicting the effects of suspension system adjustments, and for optimization of the suspension system through these adjustments. Some improvements can be achieved by manual adjustments, but further optimization requires an active system

Modeling and Control of a Flexible Structure Incorporating Inertial Slip-Stick Actuators

Shape and vibration control of a linear flexible structure by means of a new type of inertial slip-stick actuator are investigated. A nonlinear model representing the interaction between the structure and a six-degree-of-freedom Stewart platform system containing six actuators is derived, and closed-loop stability and performance of the controlled systems are investigated. A linearized model is also derived for design purposes. Quasistatic alignment of a payload attached to the platform is solved simply by using a proportional controller based on a linear kinematic model. The stability of this controller is examined using a dynamic model of the complete system and is validated experimentally by introducing random thermal elongations of several structural members. Vibration control is solved using an H∞ loop-shaping controller and, although its performance is found to be less satisfactory than desired, the nonlinear model gives good predictions of the performance and stability of the closed-loop system

Deployable Tensegrity Reflectors for Small Satellites

Future small satellite missions require low-cost, precision reflector structures with large aperture that can be packaged in a small envelope. Existing furlable reflectors form a compact package which, although narrow, is too tall for many applications.An alternative approach is proposed, consisting of a deployable “tensegrity” prism forming a ring structure that deploys two identical cable nets (front and rear nets) interconnected by tension ties; the reflecting mesh is attached to the front net. The geometric configuration of the structure has been optimized to reduce the compression in the struts of the tensegrity prism. A small-scale physical model has been constructed to demonstrate the proposed concept. A preliminary design of a 3-m-diam, 10-GHz reflector with a focal-length-to-diameter ratio of 0.4 that can be packaged within an envelope of 0.1 x 0.2 x 0.8 m^3 is presented

Thermal behaviour of single ply triaxial woven fabric composites

This paper studies the complex thermal deformation of single-ply triaxial weave com- posites. This behaviour is studied experimentally, by testing ?at plates and narrow strips of TWF, and numerically, by carrying out ?nite-element simulations that capture the e?ects of the thermo-mechanical anisotropy of the individual tows that make up the composite. It is shown that the dominating e?ect is the development of a thermally-induced twist

Position estimation delays in signal injection-based sensorless PMSM drives

The causes of position estimation delays and their effects on the sensorless control of permanent magnet synchronous motor drives are investigated. The position of a permanent magnet synchronous machine is estimated via the injection of high frequency voltage signals. The delays under investigation are due to the digital implementation of the control algorithm and to the digital filters adopted for decoupling the inspection signals from the fundamental components of the stator current measures. If not correctly modeled and compensated, such delays can reduce the performance of the control scheme. Experimental results are provided, proving the accuracy of the modeling approach and the effectiveness of the related compensation strateg

Evaporative cooling of a small number of atoms in a single-beam microscopic dipole trap

We demonstrate experimentally the evaporative cooling of a few hundred rubidium 87 atoms in a single-beam microscopic dipole trap. Starting from 800 atoms at a temperature of 125microKelvins, we produce an unpolarized sample of 40 atoms at 110nK, within 3s. The phase-space density at the end of the evaporation reaches unity, close to quantum degeneracy. The gain in phase-space density after evaporation is 10^3. We find that the scaling laws used for much larger numbers of atoms are still valid despite the small number of atoms involved in the evaporative cooling process. We also compare our results to a simple kinetic model describing the evaporation process and find good agreement with the data.Comment: 7 pages, 5 figure

LHCb Scintillating Fiber detector front end electronics design and quality assurance

The on-detector electronics of the LHCb Scintillating Fiber Detector consists of multiple PCBs assembled in a unit called Read Out Box, capable of reading out 2048 channels with an output rate of 70 Gbps. There are three types of boards: PACIFIC, Clusterization and Master Board. The Pacific Boards host PACIFIC ASICs, with pre-amplifier and comparator stages producing two bits of data per channel. A cluster-finding algorithm is then run in an FPGA on the Clusterization Board. The Master Board distributes fast and slow control, and power. We describe the design, production and test of prototype PCBs.</p

Magnetic hallmarks of viscous electron flow in graphene

We propose a protocol to identify spatial hallmarks of viscous electron flow in graphene and other two-dimensional viscous electron fluids. We predict that the profile of the magnetic field generated by hydrodynamic electron currents flowing in confined geometries displays unambiguous features linked to whirlpools and backflow near current injectors. We also show that the same profile sheds light on the nature of the boundary conditions describing friction exerted on the electron fluid by the edges of the sample. Our predictions are within reach of vector magnetometry based on nitrogen-vacancy centers embedded in a diamond slab mounted onto a graphene layer.Comment: 5 pages, 6 figure

Shades of Dispossession: Neoliberalism and the Social Production of Credibility, In Machu Picchu, Peru

This dissertation ethnographically examines the inconsistencies experienced by district residents in the historic and nature Sanctuary of Machu Picchu, over the Peruvian government\u27s drive to implement neoliberal policies. Heritage conservation in the southern Peruvian Andes is increasingly shaped by current neoliberal policies. The people who live in the district of Machu Picchu live in a protected area that gives the state expropriating powers to claim the land as a public good. The central problem is that under neoliberalism, a public asset is used for private gain at the expense of residents. Inhabitants experience changing juridical relationships as a contradiction between the neoliberal claim of a free market, and the hand of the government creating conditions that select some over others. My inquiry focuses on the actions of a mobilization formed out of small-middle scale entrepreneurs\u27 operating in a tourism economy. I explore the intersection between governance and the market economy through the lens of dispossession, and I argue that by reframing public goods in neoliberal terms, the stage was set for dispossessing inhabitants. Heritage conservation and economic structural adjustment involve incompatible forms of credibility that either justify the takings of rights, civil-status and the public resources accommodating larger capital investments, or discredit the legitimacy of governing authorities