scholarly journals On Space Efficiency of Algorithms Working on Structural Decompositions of Graphs

2018 ◽  
Vol 9 (4) ◽  
pp. 1-36 ◽  
Author(s):  
Michał Pilipczuk ◽  
Marcin Wrochna
Keyword(s):  
Space Efficiency ◽  
Efficiency Of Algorithms ◽  
Structural Decompositions

scholarly journals Revisiting Modified Greedy Algorithm for Monotone Submodular Maximization with a Knapsack Constraint

2021 ◽  
Vol 5 (1) ◽  
pp. 1-22
Author(s):  
Jing Tang ◽  
Xueyan Tang ◽  
Andrew Lim ◽  
Kai Han ◽  
Chongshou Li ◽  
...  
Keyword(s):  
Approximation Algorithms ◽  
Greedy Algorithm ◽  
Branch And Bound ◽  
Upper Bound ◽  
Optimization Problem ◽  
Approximation Factor ◽  
Real World Application ◽  
Efficiency Of Algorithms ◽  
Knapsack Constraint ◽  
Submodular Maximization

Monotone submodular maximization with a knapsack constraint is NP-hard. Various approximation algorithms have been devised to address this optimization problem. In this paper, we revisit the widely known modified greedy algorithm. First, we show that this algorithm can achieve an approximation factor of 0.405, which significantly improves the known factors of 0.357 given by Wolsey and (1-1/e)/2\approx 0.316 given by Khuller et al. More importantly, our analysis closes a gap in Khuller et al.'s proof for the extensively mentioned approximation factor of (1-1/\sqrte )\approx 0.393 in the literature to clarify a long-standing misconception on this issue. Second, we enhance the modified greedy algorithm to derive a data-dependent upper bound on the optimum. We empirically demonstrate the tightness of our upper bound with a real-world application. The bound enables us to obtain a data-dependent ratio typically much higher than 0.405 between the solution value of the modified greedy algorithm and the optimum. It can also be used to significantly improve the efficiency of algorithms such as branch and bound.

scholarly journals Practical Prediction of the Boil-Off Rate of Independent-Type Storage Tanks

2021 ◽  
Vol 9 (1) ◽  
pp. 36
Author(s):  
Dong-Ha Lee ◽  
Seung-Joo Cha ◽  
Jeong-Dae Kim ◽  
Jeong-Hyeon Kim ◽  
Seul-Kee Kim ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Environmentally Friendly ◽  
Fuel Tank ◽  
Computational Time ◽  
Insulation Material ◽  
Element Analysis ◽  
Vertical Temperature Profile ◽  
Space Efficiency ◽  
Key Aspects

Because environmentally-friendly fuels such as natural gas and hydrogen are primarily stored in the form of cryogenic liquids to enable efficient transportation, the demand for cryogenic fuel (LNG, LH) ships has been increasing as the primary carriers of environmentally-friendly fuels. In such ships, insulation systems must be used to prevent heat inflow to the tank to suppress the generation of boil-off gas (BOG). The presence of BOG can lead to an increased internal pressure, and thus, its control and prediction are key aspects in the design of fuel tanks. In this regard, although the thermal analysis of the phase change through a finite element analysis requires less computational time than that implemented through computational fluid dynamics, the former is relatively more error-prone. Therefore, in this study, a cryogenic fuel tank to be incorporated in ships was established, and the boil-off rate (BOR), measured considering liquid nitrogen, was compared with that obtained using the finite element method. Insulation material with a cubic structure was applied to the cylindrical tank to increase the insulation performance and space efficiency. To predict the BOR through finite element analysis, the effective thermal conductivity was calculated through an empirical correlation and applied to the designed fuel tank. The calculation was predicted to within 1% of the minimum error, and the internal fluid behavior was evaluated by analyzing the vertical temperature profile according to the filling ratio.

scholarly journals Hybrid Image Encryption Technique Using Genetic Algorithm and Lorenz Chaotic System

2020 ◽  
Vol 32 ◽  
pp. 03009
Author(s):  
Vishwanath Chikkareddi ◽  
Anurag Ghosh ◽  
Preksha Jagtap ◽  
Sahil Joshi ◽  
Jeel Kanzaria
Keyword(s):  
Genetic Algorithm ◽  
Image Encryption ◽  
Chaotic System ◽  
Random Number ◽  
Current Image ◽  
Space Efficiency ◽  
Highly Sensitive ◽  
Key Sensitivity ◽  
Lorenz Chaotic System ◽  
Time And Space Complexity

One of the important application of image encryption is storing confidential and important images on a local device or a database in such a way that only the authorized party can view or perceive it. The current image encryption technique employs the genetic algorithm to increase confusion in the image, but compromises in time and space complexity. The other method employs chaos or pseudo random number generating systems which have fast and highly sensitive keys but fails to make the image sufficiently noisy and is risky due to its deterministic nature. We propose a technique which employs the non-deterministic, optimizing power of genetic algorithm and the space efficiency and key sensitivity of chaotic systems into a unified, efficient algorithm which will retain the merits of both the methods whereas tries to minimize their demerits in a software system. The encryption process proceeds in two steps, generating two keys. First, an encryption sequence is generated using Lorenz Chaotic system of differential equation. The seed values used are the user’s actual key having key sensitivity of 10-14. Second, the encrypted image’s genetic encryption sequence is generated which will result in an encrypted image with entropy value greater than 7.999 thus ensuring the image is very noisy. Proposed technique uses variations of Lorenz system seed sets to generate all random mutations and candidate solutions in Genetic encryption. Since only the seed sets leading to desired solution is stored, space efficiency is higher compared to storing the entire sequences. Using this image encryption technique we will ensure that the images are hidden securely under two layers of security, one chaotic and other non-deterministic.

scholarly journals On structural decompositions of finite frames

2015 ◽  
Vol 42 (3) ◽  
pp. 721-756
Author(s):  
Alice Z.-Y. Chan ◽  
Martin S. Copenhaver ◽  
Sivaram K. Narayan ◽  
Logan Stokols ◽  
Allison Theobold
Keyword(s):  
Finite Frames ◽  
Structural Decompositions

scholarly journals Structural decompositions, width parameters, and graph labelings

2005 ◽  
Vol 145 (2) ◽  
pp. 141-142 ◽  
Author(s):  
Jan Kratochvíl ◽  
Andrzej Proskurowski ◽  
Oriol Serra
Keyword(s):  
Structural Decompositions

Research on Efficient Spatial Keyword Queries Supporting Wildcard

2013 ◽  
Vol 427-429 ◽  
pp. 2554-2557
Author(s):  
Jin Kun Pan ◽  
Dong Sheng Li
Keyword(s):  
Bloom Filter ◽  
Location Based Services ◽  
High Time ◽  
Exact Match ◽  
Inverted File ◽  
Space Efficiency ◽  
Integrated Index ◽  
Web Contents ◽  
High Space ◽  
Realistic Scenes

With the popularity of location-based services, Web contents are being geo-tagged and spatial keyword queries that retrieve objects satisfying both spatial and keyword conditions are gaining in prevalence. The existing spatial keyword queries focus on exact match or prefix match of the keywords cannot satisfy the demand of wildcard based imprecise match in many realistic scenes. Aiming to solve this problem, two methods which are fit for different situation are put forward: the inverted file and R-tree integrated index which fits for the situation that requires high time efficiency and the Prefix Bloom Filter and R-tree integrated index which fits for the situation requiring high space efficiency. The effectiveness of the two indexes is valid through experiments.

Use of Integrated Viscous Dampers to Control Wind Induced Vibrations in Tall Buildings

2019 ◽  
Author(s):  
Ian Ashcroft ◽  
Melissa Burton ◽  
David Farnsworth
Keyword(s):  
New York ◽  
Real Life ◽  
Tall Buildings ◽  
Cost Effective ◽  
Design Stage ◽  
Viscous Dampers ◽  
High Performing ◽  
Space Efficiency ◽  
Wind Events ◽  
Wind Comfort

<p>The tall building world is seeing a trend pushing building heights and slenderness ratios to levels previously unseen. The design of these buildings for both strength and serviceability is typically governed by the dynamic response of the building to wind. Comfort of building occupants during relatively low return period wind events is a key challenge, and engineers are increasingly turning to damping technologies to limit building accelerations rather than adding stiffness or mass. Large tuned mass dampers (TMDs) are a commonly used solution.</p><p>This paper suggests that integrating viscous dampers within a tall building’s structure can deliver a cost- effective alternative to TMDs, delivering high performing buildings with additional benefits in terms of robustness and space efficiency.</p><p>Two case studies are presented. Firstly, measured data from a tower in New York with viscous dampers integrated into the structure is provided, comparing design stage predictions to real-life performance. Furthermore, a case study for a super-slender tower is described, demonstrating the potential for enhanced performance and significant cost and space savings using integrated damping.</p>

Staff and students’ perception of implementing flexible working arrangements in institution of higher education

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Sam M. Mwando ◽  
Amin Issa ◽  
Verinjaerako Kangotue
Keyword(s):  
Higher Education ◽  
Information Technologies ◽  
Academic Staff ◽  
Work Productivity ◽  
Successful Implementation ◽  
Employee Productivity ◽  
University Staff ◽  
Content Type ◽  
Space Efficiency ◽  
Flexible Working

Purpose The purpose of this paper is to examine the perception of university staff and students in implementing flexible working arrangements (FWA) to increase space efficiency, lower overheads and improve productivity at the Namibia University of Science and Technology. Design/methodology/approach Data was collected using questionnaires, interviews and document searches. A total of 253 university staff (academic and support) and students were surveyed to solicit their perceptions on the extent to which FWA could be implemented to ensure space optimisation, minimise property related costs and improve employee productivity. Findings The study confirms that the successful implementation of FWA needs coordinated institutional policy to effectively support and cater to university staff’s different needs while meeting those of the university. Implementing FWA may reduce demand on utilities resulting in lower overheads for the institution. Based on the findings, the study is inconclusive on whether FWA improves or reduces staff productivity. Practical implications In the era of austerity measures in institutions of higher education (IHE), with rapid advances in communication information technologies, FWA are not only a possibility but inevitable to ensure optimal use of space, lower operating costs and improved work productivity. This study provides a cursory understanding of the possibility to implementing FWA in higher education. Originality/value This study contributes to the FWA body of knowledge from the perspective of both academic, non-academic staff and students in IHE.

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