Maximization of eigenvalues using topology optimization

Topology optimization is used to optimize the eigenvalues of plates. The results are intended especially for MicroElectroMechanical Systems (MEMS) but can be seen as more general. The problem is not formulated as a case of reinforcement of an existing structure, so there is a problem related to localized modes in low density areas. The topology optimization problem is formulated using the SIMP method. Special attention is paid to a numerical method for removing localized eigenmodes in low density areas. The method is applied to numerical examples of maximizing the first eigenfrequency. One example is a practical MEMS application; a probe used in an Atomic Force Microscope (AFM). For the AFM probe the optimization is complicated by a constraint on the stiffness and constraints on higher order eigenvalues. Received June 10, 1999     

Interesting Interest Points

Not all interest points are equally interesting. The most valuable interest points lead to optimal performance of the computer vision method in which they are employed. But a measure of this kind will be dependent on the chosen vision application. We propose a more general performance measure based on spatial invariance of interest points under changing acquisition parameters by measuring the spatial recall rate. The scope of this paper is to investigate the performance of a number of existing well-established interest point detection methods. Automatic performance evaluation of interest points is hard because the true correspondence is generally unknown. We overcome this by providing an extensive data set with known spatial correspondence. The data is acquired with a camera mounted on a 6-axis industrial robot providing very accurate camera positioning. Furthermore the scene is scanned with a structured light scanner resulting in precise 3D surface information. In total 60 scenes are depicted ranging from model houses, building material, fruit and vegetables, fabric, printed media and more. Each scene is depicted from 119 camera positions and 19 individual LED illuminations are used for each position. The LED illumination provides the option for artificially relighting the scene from a range of light directions. This data set has given us the ability to systematically evaluate the performance of a number of interest point detectors. The highlights of the conclusions are that the fixed scale Harris corner detector performs overall best followed by the Hessian based detectors and the difference of Gaussian (DoG). The methods based on scale space features have an overall better performance than other methods especially when varying the distance to the scene, where especially FAST corner detector, Edge Based Regions (EBR) and Intensity Based Regions (IBR) have a poor performance. The performance of Maximally Stable Extremal Regions (MSER) is moderate. We observe a relatively large decline in performance with both changes in viewpoint and light direction. Some of our observations support previous findings while others contradict these findings.     

In-network performance of handheld mobile terminals

This paper considers a realistic evaluation of the power mobile handsets are able to transmit and receive. It has been suggested to use the so-called total radiated power (TRP) and the total isotropic sensitivity (TIS) for the uplink and downlink, respectively, which may be seen as special cases of the general mean-effective-gain (MEG) measure. These measures are computed from the spherical radiation pattern of the handset and the different measures are obtained by using different models of the mobile propagation environment. In this paper, the results obtained via the spherical radiation patterns are compared with the equivalent performance obtained in a live Global System for Mobile Communications (GSM) network using data from the Abis network interface. This method does not require altering of the handsets and the testing uses normal calls in the network. The investigation is based on measurements with four different commercially available handsets carried out in two different indoor environments and involving 22 test users. In addition, a series of measurements were also made with a phantom simulating the handset user, allowing a test of how well the phantom represents the average user.     

Optimization of practical trusses with constraints on eigenfrequencies, displacements, stresses, and buckling

In this paper we consider the optimization of general 3D truss structures. The design variables are the cross-sections of the truss bars together with the joint coordinates, and are considered to be continuous variables. Using these design variables we simultaneously carry out size optimization (areas) and shape optimization (joint positions). Topology optimization (removal and introduction of bars) is only considered in the sense that bars of minimum cross-sectional area will have a negligible influence on the performance of the structure. The structures are subjected to multiple load cases and the objective of the optimizations is minimum mass with constraints on (possibly multiple) eigenfrequencies, displacements, and stresses. For the case of stress constraints, we deal differently with tensile and compressive stresses, for which we control buckling on the element level. The stress constraints are imposed in correlation with industrial standards, to make the optimized designs valuable from a practical point of view. The optimization problem is solved using SLP (Sequential Linear Programming).     

Diffractive optical coupling element for surface plasmon resonance sensors

Design, technological features, and performance of polymeric diffractive optical coupling elements (DOCEs), developed for surface plasmon resonance (SPR) sensors are reported. The concept is based on input and output coupling of collimated and perpendicularly incident light beams to exchangeable SPR sensor chips. In the SPR sensor chips, one DOCE couples the input light beam to a (bio-)chemical sensor surface and another DOCE images the output light beam onto a detector array. The manufacturing technique is based on an injection moulding process similarly to the manufacturing process of compact discs allowing precision manufacturing and reproduction of the grating topography of the DOCEs. The DOCE-based SPR sensor chip is specifically suitable for miniaturisation and large scale production, while maintaining high optical quality and performance.     

Designing on-site: Facilitating participatory contextual architecture with mobile phones

Some movements within modern architecture particularly emphasise the importance of matching buildings to their surroundings. However, practicing such “contextual architecture” is highly challenging and typically not something the future inhabitants of a building are well equipped for participating in. This paper explores the potentials of using mobile phone technology for facilitating such client participation in the parts of an architecture process that take place on the building site. For this we introduce ArchiLens, a mobile system for interactive on-site 3D visualisation of houses, and findings from a field study with 40 participants in the process of building or modifying their home. The study showed that using the system helped evoke people’s imagination of the look and feel of their future house, and envision it in context. This enabled them to participate more closely in the design process on-site by iteratively reviewing design alternatives and exploring, for example, other placements and materials.     

Study of the impact of reactants utilization on the performance of PEMFC commercial stacks by impedance spectroscopy

Reactants utilization is a key stake for a PEMFC system: a too low utilization leads to a waste of reactant but a too high utilization may result in a detrimental starvation. To study these impacts, two commercial stacks were characterised by impedance spectroscopy under different hydrogen and oxygen utilizations (from nominal conditions to quasi-starvation). One was fresh while the other was operated on-field during 10,000 h. This study shows that the two capacitive loops in the lowest frequency range (1 Hz and below) correspond respectively to oxygen and hydrogen mass transfer limitations: the limiting reactant can be clearly identified from the impacted frequencies. The size of these loops was increased by up to 30% when the cell operated at high reactant utilizations. These results could therefore pave the way to the development of algorithms able to estimate the degree of starvation of some cells.     

Antennas for next generation mobile communications

In future mobile communications many antennas will coexist on the device. This creates a number of problems related to bandwidth, efficiency, and correlation. Remedies are discussed in the paper, and attention is called to the promising area of adaptive matching, which also can solve problems related to the user.     

Steady and transient inflow dynamics with actuator disk vortex theory

The actuator disk is a well‐known and widely used theoretical tool in wind engineering. This work proposes a new theory based on an actuator surface, capable of treating time‐varying vectorial load distributions and yaw/pitch misalignment. A simplified representation of vortex motion is used to arrive at a tractable problem. The theory is not restricted to disks; arbitrary coplanar (optionally disjoint) actuator surfaces may be modeled. Some of the theoretical novelties used in the modeling includes use of the fractional Laplacian and extensive use of the Fourier transform on . Promising experimental validation based on pitch‐step experiments at the Tjæreborg turbine is furnished. Comparisons are also made to existing methodologies. Analysis and numerical work shows that the model encapsulates Coleman's vortex theory.     

Ligand Binding to Dynamically Populated G-Quadruplex DNA

Several small-molecule ligands specifically bind and stabilize G-quadruplex (G4) nucleic acid structures, which are considered to be promising therapeutic targets. G4s are polymorphic structures of varying stability, and their formation is dynamic. Here, we investigate the mechanisms of ligand binding to dynamically populated human telomere G4 DNA by using the bisquinolinium based ligand Phen-DC3 and a combination of single-molecule FRET microscopy, ensemble FRET and CD spectroscopies. Different cations are used to tune G4 polymorphism and folding dynamics. We find that ligand binding occurs to pre-folded G4 structures and that Phen-DC3 also induces G4 formation in unfolded single strands. Following ligand binding to dynamically populated G4s, the DNA undergoes pronounced conformational redistributions that do not involve direct ligand-induced G4 conformational interconversion. On the contrary, the redistribution is driven by ligand-induced G4 folding and trapping of dynamically populated short-lived conformation states. Thus, ligand-induced stabilization does not necessarily require the initial presence of stably folded G4s.