On Eulerian extensions and their application to no-wait flowshop scheduling

We consider a variant of no-wait flowshop scheduling that is motivated by continuous casting in the multistage production process in steel manufacturing. The task is to find a feasible schedule with a minimum number of interruptions, i.e., continuous idle time intervals on the last production stage. Based on an interpretation as Eulerian Extension Problems, we fully settle the complexity status of any particular problem case: We give a very intuitive optimal algorithm for scheduling on two processing stages with one machine in the first stage, and we show that all other problem variants are strongly NP-hard. We also discuss alternative idle time related scheduling models and their justification in the considered steel manufacturing environment. Here, we derive constant factor approximations.     

Representation Theorems for Analytic Machines and Computability of Analytic Functions

We present results concerning analytic machines, a model of real computation introduced by Hotz which extends the well-known Blum, Shub and Smale machines (BSS machines) by infinite converging computations. The well-known representation theorem for BSS machines elucidates the structure of the functions computable in the BSS model: the domain of such a function partitions into countably many semi-algebraic sets, and on each of those sets the function is a polynomial resp. rational function. In this paper, we study whether the representation theorem can, in the univariate case, be extended to analytic machines, i.e. whether functions computable by analytic machines can be represented by power series in some part of their domain. We show that this question can be answered in the negative over the real numbers but positive under certain restrictions for functions over the complex numbers. We then use the machine model to define computability of univariate complex analytic (i.e. holomorphic) functions and examine in particular the class of analytic functions which have analytically computable power series expansions. We show that this class is closed under the basic analytic operations composition, local inversion and analytic continuation.     

Robotic Assembly Processes as a Driver in Architectural Design

Over the last couple of years industrial robots have increasingly gained the interest of architects and designers. Robotics in architecture and construction has mainly been looked at from an engineering perspective during the latter half of the twentieth century, with the main purpose of automating the building process. Today the focus has turned towards realizing non-standardized designs and developing custom fabrication processes. However, the specific characteristics of the robot, which distinguish it from common computer numerically controlled machines, are often overlooked. Industrial robots are universal fabrication machines that lend themselves especially well to assembly tasks. Applied to architecture this resolves to the ability to control and manipulate the building process. As such, applying industrial robots emphasizes construction as an integral part of architectural design. Moreover, designing and manipulating robotic assembly processes can become a driver in architectural design. The potential of such an approach is discussed on the basis of several design experiments that illustrate that by applying such methods, form is not derived from computation or geometry, but from a physical process.     

Ego noise cancellation of a robot using missing feature masks

We describe an architecture that gives a robot the capability to recognize speech by cancelling ego noise, even while the robot is moving. The system consists of three blocks: (1) a multi-channel noise reduction block, comprising consequent stages of microphone-array-based sound localization, geometric source separation and post-filtering; (2) a single-channel noise reduction block utilizing template subtraction; and (3) an automatic speech recognition block. In this work, we specifically investigate a missing feature theory-based automatic speech recognition (MFT-ASR) approach in block (3). This approach makes use of spectro-temporal elements derived from (1) and (2) to measure the reliability of the acoustic features, and generates masks to filter unreliable acoustic features. We then evaluated this system on a robot using word correct rates. Furthermore, we present a detailed analysis of recognition accuracy to determine optimal parameters. Implementation of the proposed MFT-ASR approach resulted in significantly higher recognition performance than single or multi-channel noise reduction methods.     

Elastic constants of metal/ceramic composites with lamellar microstructures: Finite element modelling and ultrasonic experiments

The elastic properties of single domains of lamellar AlSi12/Al₂O₃ composites produced by metal infiltration of freeze cast preforms have been examined. The anisotropic elastic constants determined from ultrasonic phase spectroscopy (UPS) experiments have been compared to microstructure based FE-models created with the program OOF2, micromechanical models (Mori–Tanaka and inverse Mori–Tanaka) and an analytical model for an ideal laminate. The influences of lamellae orientations and ceramic contents on the elastic constants have been investigated. Along the lamellae directions the microstructure based FE model and the inverse Mori–Tanaka model are in good agreement with experimental results. Perpendicular to the lamellae the experiment shows a stiffer than expected elastic behaviour.     

Automatically mimicking unique hand-drawn pencil lines

In applications such as architecture, early design sketches containing accurate line drawings often mislead the target audience. Approximate human-drawn sketches are typically accepted as a better way of demonstrating fundamental design concepts. To this end we have designed an algorithm that creates lines that perceptually resemble human-drawn lines. Our algorithm works directly with input point data and a physically based mathematical model of human arm movement. Our algorithm generates unique lines of arbitrary length given the end points of a line, without relying on a database of human-drawn lines. We found that an observational analysis obtained through various user studies of human lines made a bigger impact on the algorithm than a statistical analysis. Additional studies have shown that the algorithm produces lines that are perceptually indistinguishable from that of a hand-drawn straight pencil line. A further expansion to the system resulted in mimicked dashed lines.     

Degradation and destruction of optical surfaces by hypervelocity impact

This study investigates the damage caused by impacts of space debris and micrometeoroids (SD/MM) on mirrors of placed on spacecrafts in an orbit of 700 km and 1400 km altitude with an inclination of 48°. For the investigated orbits the maximum damage from impact degradation of the optical surface as well as the probability of total destruction by single particle hit has been calculated. Based on the NASA statistical standard model ORDEM 96, the calculation of SD particle fluxes shows that at 700 km altitude an average of 62000 impact damages per m² and per year are caused by particles with a diameter equal or larger than 1 μm. At 1400 km altitude the figure is reduced by 30%. The corresponding MM fluxes have been calculated with the Grün model and are 1.5 orders of magnitude smaller than the SD fluxes. For the generation of a damage law and for the determination of the total destruction limits, 50 impact damages were produced on coated and uncoated quartz glass samples, employing the impact facilities of the Ernst-Mach-Institute (EMI) and the Aerospace Department of the Technical University Munich (TUM/LRT). The particle sizes were varied between 3 μm and 1000 μm. The impact velocities were between 2.0 km/s and 16.1 km/s. Due to the irregular damages a clear correlation with the impact angle (0°, 30°, 60°) could not be proven. The diameter of the optically inactive surface after impact is proportional to E^0.458 (where E = kinetic energy of the impact). The experimental total destruction limit of 5 mm thick quartz glasses is reached with an impact energy of 13.5 J (Aluminum sphere, 0.9 mm diameter, 5 km/s impact velocity). The degradation analysis showed that 3.5 % of the optical surfaces of the mirrors in 700 km orbits (48 ° inclination) is destroyed within 10 years by space debris and micro-meteoroids. The probability of total destruction for the considered mirrors in 700 km altitude is in the percent range for an operational period of 10 years. Degradation damages and the probability of total destruction in an orbit in 1400 km is slightly below the values for the 700 km orbit.     

Multiscale homogenization models for the elastic behaviour of metal/ceramic composites with lamellar domains

This study predicts the elastic properties of an innovative metal–ceramic composite with statistically oriented domains of parallel ceramic platelets embedded in a eutectic Al–Si-alloy. For this purpose, a two-step homogenization procedure was employed by finite element- and micromechanical modelling. In a first step, the microstructure of the specimen was divided in domains with the same orientation of lamellae and the elastic properties of single domains were calculated while a precise representation of the shape of the lamellae was attempted. In a second step the elastic constants of a large specimen consisting of many domains were computed both by finite element and micromechanical modelling. The experimental Young’s modulus of such poly-domain specimens was determined by an acoustic resonance method and was lower than predicted. The differences can be explained by microcracks caused by large residual microstresses produced in these materials when they are cooled from the manufacturing temperature.     

Fundamental experiments as benchmark problems for modeling ultrasonic micro-impact processes

Many ultrasonic processes are based on the mechanical contact of oscillating parts. Within ultrasonic machining (drilling, milling, grinding) micro impacts lead to abrasion at the processed workpiece and hopefully do not damage the tool. In ultrasonic motors ideally neither part gets worn. Thus the appropriate design of contact partners as well as their kinematics is a substantial task during the development of such devices. A first step to optimize contact mechanics is to understand their behavior and dependencies on parameter variations, such as vibration amplitude and pre-stress of the impacting parts. For a detailed understanding models validated with convincing experimental data from measurements are absolutely essential. This paper focuses on simple vibro-impact experiments which can be used as benchmark data for future models. The setup of the experiment and first experimental investigations are described in detail.