825 research outputs found
Supplemental Material - Identifying and ranking the attributes of hospitals readiness to apply bring your own device: an explanatory sequential mixed study
No full textSupplemental Material for Identifying and ranking the attributes of hospitals readiness to apply bring your own device: an explanatory sequential mixed study by Maryam Jahanbakhsh, Mostafa Amini Rarani, Shahram Tahmasebian and Masoumeh Shahbazi in Proceedings of Singapore Healthcare</p
Salvesen’s Method for Added Resistance Revisited
No full textAlmost 4 years after the appearance of Salvesen–Tuck–Faltinsen (STF) strip theory (Salvesen et al., 1970, “Ship Motions and Sea Loads,” Annual Meeting of the Society of Naval Architecture and Marine Engineers (SNAME), New York, Nov. 12–13), Salvesen in 1974 published his popular method for calculation of added resistance (Salvesen, 1974, “Second-Order Steady State Forces and Moments on Surface Ships in Oblique Regular Waves,” Vol. 22; Salvesen, 1978, “Added Resistance of Ships in Waves,” J. Hydronautics, 12(1), pp. 24–34). His method is based on an exact near-field formulation; however, he applied the long-wave and the weak-scatterer assumptions to present his approximate method using the integrated quantities (hydrodynamic and geometrical coefficients). Considering the available computational powers in the 1970s, both of these assumptions were absolutely justifiable. The intention of this paper is to disseminate theresults of a recent study at the Technical University of Denmark, whereby the Salvesen’s formulation has been revisited and the added resistance is computed from the original exact equation without invoking the weak-scatterer or the long-wave assumptions. This is performed using the solutions of the radiation and the scattering problems, obtained by a low-order boundary element method and the two-dimensional free-surface Green function inside our in-house STF theory implementation (Bingham and Amini-Afshar, 2020, DTU_- Strip Theory Solver). The weak-scatterer assumption is then removed through a direct calculation of the x-derivatives of the velocity potentials and the normal vectors along the body.Knowing the velocity potentials over each panel, the long-wave assumption is also avoided by a piece-wise analytical integration of sectional Kochin Function (Kochin, 1936, “On the Wave Resistance and Lift of Bodies Submerged in Fluid,” Transactions of the Conference on the Theory of Wave Resistance, Moscow.). The presented results for five ship geometries testify that the correct treatment of the original equation is achieved only after both of the above-mentioned assumptions are removed. Implemented in this manner, Salvesen’s method proves to be relatively more accurate and robust than has been generally perceived during all these years. [DOI: 10.1115/1.4050213
Erratum: The role of visual preferences in architecture views
No full textThe article “The role of visual preferences in architecture views” by Ali Akbar Amini, Bahman Adibzadeh, published on 24 September 2020 in the Journal of Architecture and Urbanism, 44(2), 122–127, https://doi.org/10.3846/jau.2020.12582 contained a following errors on:
122 p. The source is incorrectly cited in the text. The correct citation is:
(de la Fuente Suárez, 2016)
126 p. The references incorrectly indicate author name, lastname and title of article. The correct citation is:
de la Fuente Suárez, L. A. (2016). Towards experiential representation in architecture. Journal of Architecture and Urbanism, 40(1), 47–58. https://doi.org/10.3846/20297955.2016.1163243
Corrected version of the article is available online.
The publisher apologises for this error
Sedimentation Processes in the Tinto and Odiel Salt Marshes in Huelva, Spain
No full textGlobal warming is a key factor to take into account when a study is conducted on tidal
wetlands. Both Odiel and Tinto salt marshes are the major wetlands in Andalusia (Spain).
From the mid-1950s to date, the land use changes (LUC) have caused a great landscape
alteration that along with the effects of climatic variables and sea wave energy have given
rise to a hard impact on the environment. The advent of new image processing procedures and use of high-resolution images from satellites gave precise patterns of erosion.
In this work, a new method patented by the author is presented and used to obtain the
total cubic meters of eroded soil in both salt marshes. Moreover, the different factors that
begin this phenomenon as well as the influence of intertidal processes are discussed. The
results show how the greater integration of remote sensing and geographical information
systems (GIS) technologies, with regression model, was most useful to describe, analyze
and predict the volumetric change process in both salt marshes
Optimal SVC allocation in power systems for loss minimization and voltage deviation reduction
No full textTransient stabilization of the power system network is of major importance in this era of the deregulated power systems. Static VAR compensator (SVC) proves to be more economical and efficient than its other counterparts. Due to installation cost of SVCs, there is an exigent requirement to optimize the SVC installation that could yield maximum benefit. In this paper, first the contingencies that result in maximum disturbance to the grid are realized and ranked accordingly. The measurement used for this purpose is the voltage profile index. Next, genetic algorithm has been used to find out the rating of the SVC and its location that could mitigate the contingency and minimize the weighted sum of the total power loss in the grid, sum of voltage deviations at all the buses, and the rating of SVC to be installed. The weights of each of the objective function terms are assigned according to their importance for the system. In order to evaluate the effectiveness of the proposed approach, it is applied to two test networks. It has been found out that the obtained SVC location and rating maintained voltage security and minimized power loss in the event of contingency.</p
Stability analysis of high-order finite-difference discretizations of the linearized forward-speed seakeeping problem
No full textA high-order finite-difference method solution of the linearized, potential flow, seakeeping problem for a ship at steady forward speed was recently presented by Amini-Afshar et al. [1,2]. In this paper, we provide a detailed matrix-based eigenvalue stability analysis of this model, highlighting the sources of instability and the effects of possible remedies. In particular, we illustrate how both boundary treatment and grid stretching are important factors which are not typically captured by a von Neumann-type analysis. The new analysis shows that when grid stretching is used together with centered finite difference schemes, the method is generally unstable. The source of the instability can in some cases be traced to an effective downwinding of the convective terms. Stable solutions can be obtained either by introducing upwind-biased schemes for computing the convective derivatives on the free-surface, or by application of a mild filter at each time-step. A second source of instability is associated with the treatment of the convective derivatives of the free-surface elevation at points close to the domain boundaries. Here it is necessary to consider whether the surrounding fluid points lie in an upwind or a downwind direction. For upwinded points, ordinary one-sided differencing can be used, but for downwinded points we instead impose a Neumann-type boundary condition derived from the body and free-surface boundary conditions. As an example application to complement those already given in [1], [2], the method is applied to solve the steady wave resistance problem and comparison is made to reference solutions for a two-dimensional floating cylinder and a submerged sphere. Estimates of the wave resistance of the Wigley hull are also compared with experimental measurements
LCDB 1.0: An Extensive Learning Curves Database for Classification Tasks
No full textThe use of learning curves for decision making in supervised machine learning is standard practice, yet understanding of their behavior is rather limited. To facilitate a deepening of our knowledge, we introduce the Learning Curve Database (LCDB), which contains empirical learning curves of 20 classification algorithms on 246 datasets. One of the LCDB’s unique strength is that it contains all (probabilistic) predictions, which allows for building learning curves of arbitrary metrics. Moreover, it unifies the properties of similar high quality databases in that it (i) defines clean splits between training, validation, and test data, (ii) provides training times, and (iii) provides an API for convenient access (pip install lcdb). We demonstrate the utility of LCDB by analyzing some learning curve phenomena, such as convexity, monotonicity, peaking, and curve shapes. Improving our understanding of these matters is essential for efficient use of learning curves for model selection, speeding up model training, and to determine the value of more training data.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Pattern Recognition and Bioinformatic
Adversarially Robust Decision Tree Relabeling
No full textDecision trees are popular models for their interpretation properties and their success in ensemble models for structured data. However, common decision tree learning algorithms produce models that suffer from adversarial examples. Recent work on robust decision tree learning mitigates this issue by taking adversarial perturbations into account during training. While these methods generate robust shallow trees, their relative quality reduces when training deeper trees due the methods being greedy. In this work we propose robust relabeling, a post-learning procedure that optimally changes the prediction labels of decision tree leaves to maximize adversarial robustness. We show this can be achieved in polynomial time in terms of the number of samples and leaves. Our results on 10 datasets show a significant improvement in adversarial accuracy both for single decision trees and tree ensembles. Decision trees and random forests trained with a state-of-the-art robust learning algorithm also benefited from robust relabeling.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Cyber Securit
Penalized FTRL with Time-Varying Constraints
No full textIn this paper we extend the classical Follow-The-Regularized-Leader (FTRL) algorithm to encompass time-varying constraints, through adaptive penalization. We establish sufficient conditions for the proposed Penalized FTRL algorithm to achieve O(t) regret and violation with respect to a strong benchmark X^tmax. Lacking prior knowledge of the constraints, this is probably the largest benchmark set that we can reasonably hope for. Our sufficient conditions are necessary in the sense that when they are violated there exist examples where O(t) regret and violation is not achieved. Compared to the best existing primal-dual algorithms, Penalized FTRL substantially extends the class of problems for which O(t) regret and violation performance is achievable.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Networked System
A bi-layer multi-objective techno-economical optimization model for optimal integration of distributed energy resources into smart/micro grids
No full textThe energy management system is executed in microgrids for optimal integration of distributed energy resources (DERs) into the power distribution grids. To this end, various strategies have been more focused on cost reduction, whereas effectively both economic and technical indices/factors have to be considered simultaneously. Therefore, in this paper, a two-layer optimization model is proposed to minimize the operation costs, voltage fluctuations, and power losses of smart microgrids. In the outer-layer, the size and capacity of DERs including renewable energy sources (RES), electric vehicles (EV) charging stations and energy storage systems (ESS), are obtained simultaneously. The inner-layer corresponds to the scheduled operation of EVs and ESSs using an integrated coordination model (ICM). The ICM is a fuzzy interface that has been adopted to address the multi-objectivity of the cost function developed based on hourly demand response, state of charges of EVs and ESS, and electricity price. Demand response is implemented in the ICM to investigate the effect of time-of-use electricity prices on optimal energy management. To solve the optimization problem and load-flow equations, hybrid genetic algorithm (GA)-particle swarm optimization (PSO) and backward-forward sweep algorithms are deployed, respectively. One-day simulation results confirm that the proposed model can reduce the power loss, voltage fluctuations and electricity supply cost by 51%, 40.77%, and 55.21%, respectively, which can considerably improve power system stability and energy efficiency
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