Efficient use of iterative solvers in nested topology optimization

In the nested approach to structural optimization, most of the computational effort is invested in the solution of the analysis equations. In this study, it is suggested to reduce this computational cost by using an approximation to the solution of the analysis problem, generated by a Krylov subspace iterative solver. By choosing convergence criteria for the iterative solver that are strongly related to the optimization objective and to the design sensitivities, it is possible to terminate the iterative solution of the nested equations earlier compared to traditional convergence measures. The approximation is computationally shown to be sufficiently accurate for the purpose of optimization though the nested equation system is not necessarily solved accurately. The approach is tested on several large-scale topology optimization problems, including minimum compliance problems and compliant mechanism design problems. The optimized designs are practically identical while the time spent on the analysis is reduced significantly.     

Remote sensing of vital signs using an ultra-wide-band radar

Remote vital signs monitoring and tracking are of great importance for various applications including but not limited to baby monitoring, elderly care, human activity behind barriers, bio-medical and more. This paper deals with the extraction of micro-Doppler (uDoppler) signatures of a person’s respiration and heart-beat using a single transmitter (TX), single receiver (RX) Ultra Wide Band (UWB) impulse radar. The received spectrum contains the respiration and heart fundamental beat frequencies and their corresponding integer multiplicity harmonies as well as their mutual inter-modulations that appears due to the micro-Doppler frequency-modulation of the sinusoidal nature of the moving torso and heart, a fact that poses a difficulty in extracting the correct heart-beat fundamental harmony. Moreover, the commonly used Discrete Fourier Transform (DFT) is insufficient for differentiating close proximity spectral components, thus, an adaptive, real-time, novel, spectral estimation algorithm is proposed and experimental results are given.     

Temporary Tasks Assignment Resolved

Abstract. Among all basic on-line load balancing problems, the only unresolved problem was load balancing of temporary tasks on unrelated machines. This open problem existed for almost a decade, see [12]. We resolve this problem by providing an inapproximability result. In addition, a newer open question is to identify the dependency of the competitive ratio on the durations of jobs in the case where durations are known. We resolve this problem by characterizing this dependency. Finally, we provide a PTAS for the off-line problem with a fixed number of machines and show a 2 -inapproximability result for the general case.     

High-Order Analysis of Reinforced Concrete Slabs Strengthened with Circular Composite Laminated Patches of General Layup

A high-order model for the analysis of reinforced concrete (RC) slabs strengthened with externally bonded composite laminated patches of a general layup is presented. The model follows the concepts of the high-order theory and it is based on variational principles, equilibrium, and compatibility requirements. The classical lamination theory is adopted for the composite patch and it yields a set of coordinate dependent constitutive relations. The governing equations form a set of partial differential equations with variable coefficients. The solution procedure adopts the Galerkin and the multiple-shooting methods in the circumferential and radial directions, respectively. The proposed model is used for the numerical study of a square RC slab strengthened with a circular cross-ply laminated patch. The results focus on the overall behavior of the slab and the localized shear and vertical normal stresses near the edge of the bonded patch. Comparison with results obtained using a simplified axisymmetric model is also presented and discussed. The study reveals that the anisotropy of the bonded patch affects the overall and the localized response of the strengthened slab. It also shows that the simplified axisymmetric analysis tends to underestimate the stresses and stress resultants, and thus may be considered unsafe.     

An improved parallel algorithm for integer GCD

We present a simple parallel algorithm for computing the greatest common divisor (gcd) of twon-bit integers in the Common version of the CRCW model of computation. The run-time of the algorithm in terms of bit operations isO(n/logn), usingn ¹⁺ processors, where is any positive constant. This improves on the algorithm of Kannan, Miller, and Rudolph, the only sublinear algorithm known previously, both in run time and in number of processors; they requireO(n log logn/logn),n ² log² n, respectively, in the same CRCW model.We give an alternative implementation of our algorithm in the CREW model. Its run-time isO(n log logn/logn), usingn ¹⁺ processors. Both implementations can be modified to yield the extended gcd, within the same complexity bounds.Supported in part by an IBM Graduate Fellowship and a Bantrell Postdoctoral Fellowship.Supported in part by a Weizmann Postdoctoral Fellowship.4 All logarithms are to base 2.     

Self‐Assembled SERS Substrates with Tunable Surface Plasmon Resonances

The fabrication of surface‐enhanced Raman spectroscopy (SERS) substrates that are optimized for use with specific laser wavelength–analyte combinations is addressed. In order to achieve large signal enhancement, temporal stability, and reproducibility over large substrate areas at low cost, only self‐assembly and templating processes are employed. The resulting substrates consist of arrays of gold nanospheres with controlled diameter and spacing, properties that dictate the optical response of the structure. Tunability of the extended surface plasmon resonance is observed in the range of 520–1000 nm. It is demonstrated that the enhancement factor is maximized when the surface plasmon resonance is red‐shifted with respect to the SERS instrument laser line. Despite relying on self‐organization, site‐to‐site enhancement factor variations smaller than 10% are obtained.     

Stress Analysis of Monolithic Circular Arches Strengthened with Composite Materials

This paper presents an analytical approach for the elastic stress analysis of monolithic circular arches strengthened with externally bonded fiber-reinforced polymer (FRP) strips. Emphasis is placed on the interfacial stresses between the existing structure and the supplemental reinforcement layers. Two analytical models are presented: The first model formulates the governing equations in terms of the displacements in the arch and the FRP strip and the tangential distribution of the shear stresses in the adhesive layer as unknowns without involving any assumptions on the stress and displacement fields in the adhesive layer. The second model uses the functional form of the displacement field derived in the first model yielding a formulation in terms of displacement unknowns only. Two numerical examples that examine the capabilities of the analytical approach are discussed. The first example focuses on the stress analysis of a strengthened arch under a localized load. The second example studies the elastic response of a partially strengthened arch to a symmetric load and a horizontal support settlement. The numerical study quantifies the interfacial shear and peeling stresses between the old and the new components underlining the stress concentrations. Finally, conclusions are presented and directions for future research on the application of the theory to masonry arches are outlined.