1,949 research outputs found
Brief Announcement: Erasure-Resilience Versus Tolerance to Errors
Get PDFWe describe work in progress on providing a separation between erasure-resilient and tolerant property testing. Specifically, we are able to exhibit a property which is testable (with the number of queries independent of the length of the input) in the presence of erasures, but is not testable tolerantly
New Sublinear Algorithms and Lower Bounds for LIS Estimation
Get PDFEstimating the length of the longest increasing subsequence (LIS) in an array is a problem of fundamental importance. Despite the significance of the LIS estimation problem and the amount of attention it has received, there are important aspects of the problem that are not yet fully understood. There are no better lower bounds for LIS estimation than the obvious bounds implied by testing monotonicity (for adaptive or nonadaptive algorithms). In this paper, we give the first nontrivial lower bound on the complexity of LIS estimation, and also provide novel algorithms that complement our lower bound.
Specifically, we show that for every ε ∈ (0,1), every nonadaptive algorithm that outputs an estimate of the LIS length in an array of length n to within an additive error of ε n has to make log^{Ω(log (1/ε))} n queries. Next, we design nonadaptive LIS estimation algorithms whose complexity decreases as the number of distinct values, r, in the array decreases. We first present a simple algorithm that makes Õ(r/ε³) queries and approximates the LIS length with an additive error bounded by ε n. This algorithm has better complexity than the best previously known adaptive algorithm (Saks and Seshadhri; 2017) for the same problem when r ≪ polylog (n). We use our algorithm to construct a nonadaptive algorithm with query complexity Õ(√r⋅ poly(1/λ)) that, when the LIS is of length at least λ n, outputs a multiplicative Ω(λ)-approximation to the LIS length. Our algorithm improves upon the state of the art nonadaptive LIS estimation algorithm (Rubinstein, Seddighin, Song, and Sun; 2019) in terms of the approximation guarantee.
Finally, we present a O(log n)-query nonadaptive erasure-resilient tester for monotonicity. Our result implies that lower bounds on erasure-resilient testing of monotonicity does not give good lower bounds for LIS estimation. It also implies that nonadaptive tolerant testing is strictly harder than nonadaptive erasure-resilient testing for the natural property of monotonicity
Modelling and testing of thermoplastic composite components using Building Block approach integrating process simulation.
Get PDFCurrently, the automotive sector is exploring the feasibility of replacing metals with composite materials for structural and non-structural applications. This is mainly driven by the demand for lighter and increasingly complex components, which will be extremely difficult to fabricate with the traditional metal forming approaches. This prompted the need for exploring textile reinforced composite materials, where they stand out about their ability to allow complex designs with high specific strength and stiffness. Which further helps to reduce mass and increase fuel efficiency. However, a disadvantage right now is the use of composites is limited by an inability to accurately analyse and predict these composite structures for its mechanical performance. This thesis presents methodology employing finite element techniques for predictive modelling of textile reinforced composite materials by considering the process simulations. The Building Block approach is introduced and implemented as a guideline, to efficiently substantiate the durability and performance of the component design sequentially.
FEA simulation of a composite component was done using two composite failure criterions for comparison, Crasurv (modified Tsai-Wu) and Hashin; after completing a detailed material characterisation and card fitting for creating FE material. The results of the structural simulations are compared against experimental results, which is kept as a benchmark for future comparisons and review.
The next step was to conduct process simulations to analyse the composite forming process to investigate the locally varying microstructure to account for the anisotropic behaviour in the composite part during its production that can alter the structural integrity of the component. An additive split between isotropic, elasto-plastic matrix and anisotropic hyper-elastic fibers material card is used in LS-Dyna explicit solver for conducting process simulations. A detailed material characterisation was done on the textile reinforced fabric and the composite laminate at forming temperature to study its tensile, shear, frictional and bending properties. The process simulation helps to obtain reliable structural simulation models by mapping
Strongly Sublinear Algorithms for Testing Pattern Freeness
Get PDFFor a permutation , a function contains a -appearance if there exists such that for all , if and only if . The function is -free if it has no -appearances. In this paper, we investigate the problem of testing whether an input function is -free or whether differs on at least values from every -free function. This is a generalization of the well-studied monotonicity testing and was first studied by Newman, Rabinovich, Rajendraprasad and Sohler (Random Structures and Algorithms 2019). We show that for all constants , , and permutation , there is a one-sided error -testing algorithm for -freeness of functions that makes queries. We improve significantly upon the previous best upper bound by Ben-Eliezer and Canonne (SODA 2018). Our algorithm is adaptive, while the earlier best upper bound is known to be tight for nonadaptive algorithms.28 pages, 2 figures; We thank anonymous reviewers for comments that helped us significantly improve the presentatio
Numerical device modeling for direct Z-scheme junctions using a solar cell simulator
Get PDFCarbon capture and utilization (CCU) is a promising solution for reducing reliance on fossil fuels and incentiviz-ing the capture of CO2. A key requirement for CCU is the development of effective photo/electrocatalysts with high CO2 reduction activity that can produce high-value products. Direct Z-scheme heterojunctions named after their charge transfer mechanism, use sunlight to conduct various photocatalytic reactions, similar to photosynthesis in plants. Solar cell simulation techniques can be used to obtain material properties and insights into the electronic characteristics of these materials. By solving semiconductor differential equations that model the behavior of semiconductors under different light intensities and applied biases, the solar cell simulator program (SCAPS) can evaluate the energy band edges, carrier concentrations, and output characteristics of the device. In this study, a method is proposed for modeling direct Z-scheme junctions in SCAPS by simulating the Shockley Read Hall (SRH) recombination using defect densities at the interface of the recombination junction (RJ). An example using a TiO2/CdIn2S4 Z-scheme junction is presented and the impact of defects on the performance of the junction is discussed. It is presented that the high recombination rates at the interface via these defects improve the device performance
sj-docx-1-pie-10.1177_09544089211042484 - Supplemental material for Microstructure modeling of a sintered Al–4Si–0.6Mg alloy extruded at semi-solid temperature ranges
No full textSupplemental material, sj-docx-1-pie-10.1177_09544089211042484 for Microstructure modeling of a sintered Al–4Si–0.6Mg alloy extruded at semi-solid temperature ranges by Abeyram M Nithin, M Joseph Davidson and Chilakalapalli Surya Prakash Rao in Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering</p
Modified phase-scheduled-command FxLMS algorithm for active sound profiling
Get PDFActive sound profiling, or active noise equalization strategies have been proposed to achieve spectral shaping of a primary disturbance signal. The control algorithms proposed to achieve such spectral shaping have either suffered from poor robustness to plant modelling uncertainties or required high levels of control effort. To improve the robustness of active sound profiling to uncertainties in the plant model, whilst avoiding increased control effort, a modified phase-scheduledcommand filtered-x least-mean-square (FxLMS) algorithm is proposed in this paper. The new algorithm provides improved stability, whilst requiring the minimum control effort. This improvement is achieved by replacing the plant model with an intelligent adaptive-hysteresis switching mechanism to allow the necessary estimation of the disturbance signal phase. The improved performance and robustness of the proposed algorithm is demonstrated through a series of simulations using measured acoustic responses
Dynamically Optimized Muscle Activity Patterns From A Novel Handle Based Propulsion Movement For A Wheelchair
No full textThe purpose of this study was to determine the muscle activity patterns resulting from dynamic optimization of a novel continuous wheelchair propulsion movement having a circularity ratio of 0.89.
For the study four major muscle groups were selected and a bang-bang control strategy was adopted to reduce the complexity and time for the optimization with a cost function to increase the net propulsion power. The successful completion of the optimization resulted in muscle excitation and activation curves for each actuator and a net power > 30 watts. The proposed propulsion mechanism can act as a substitute for the normal propulsion mechanisms used in daily life and sports activitie
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