scholarly journals A Fragmentation Region-based Skyline Computation Framework for a Group of Users

2021 ◽  
Author(s):  
Ghoncheh Babanejad Dehaki ◽  
Hamidah Ibrahim ◽  
Nur Izura Udzir ◽  
Fatimah Sidi ◽  
Ali Amer Alwan

Skyline processing, an established preference evaluation technique, aims at discovering the best, most preferred objects, i.e. those that are not dominated by other objects, in satisfying the user’s preferences. In today’s society, due to the advancement of technology, ad-hoc meetings or impromptu gathering are becoming more and more common. Deciding on a suitable meeting point (object)for a group of people (users) to meet is not a straightforward task especially when these users are located at different places with distinct preferences. A place which is close by to the users might not provide the facilities/services that meet all the users’ preferences; while a place having the facilities/services that meet most of the users’ preferences might be too distant from these users. Although the skyline operator can be utilised to filter the dominated objects among the objects that fall in the region of interest of these users, computing the skylines for various groups of users in similar region would mean rescanning the objects of the region and repeating the process of pair wise comparisons among the objects which are undoubtedly unwise. On this account, this study presents a region-based skyline computation framework which attempts to resolve the above issues by fragmenting the search region of a group of users and utilising the past computed skyline results of the fragments. The skylines, which are the objects recommended to be visited by a group of users, are derived by analysing both the locations of the users, i.e. spatial attributes, as well as the spatial and non-spatial attributes of the objects. Several experiments have been conducted and the results show that our proposed framework outperforms the previous works with respect to CPU time.

2018 ◽  
Vol 13 (4) ◽  
pp. 34
Author(s):  
T.A. Bubba ◽  
D. Labate ◽  
G. Zanghirati ◽  
S. Bonettini

Region of interest (ROI) tomography has gained increasing attention in recent years due to its potential to reducing radiation exposure and shortening the scanning time. However, tomographic reconstruction from ROI-focused illumination involves truncated projection data and typically results in higher numerical instability even when the reconstruction problem has unique solution. To address this problem, bothad hocanalytic formulas and iterative numerical schemes have been proposed in the literature. In this paper, we introduce a novel approach for ROI tomographic reconstruction, formulated as a convex optimization problem with a regularized term based on shearlets. Our numerical implementation consists of an iterative scheme based on the scaled gradient projection method and it is tested in the context of fan-beam CT. Our results show that our approach is essentially insensitive to the location of the ROI and remains very stable also when the ROI size is rather small.


1972 ◽  
Vol 25 (2) ◽  
pp. 207 ◽  
Author(s):  
DT Pegg

In conventional electrodynamic theory, the advanced potential solution of Maxwell's equations is discarded on the ad hoc basis that information can be received from the past only and not from the future. This difficulty is overcome by the Wheeler?Feynman absorber theory, but unfortunately the existence of a completely retarded solution in this theory requires a steady-state universe. In the present paper conventional electrodynamics is used to obtain a condition which, if satisfied, allows information to be received from the past only, and ensures that the retarded potential is the only consistent solution. The condition is that a function Ua of the future structure of the universe is infinite, while the corresponding function Ur of the past structure is finite. Of the currently acceptable cosmological models, only the steady-state, the open big-bang, and the Eddington-Lema�tre models satisfy this condition. In these models there is no need for an ad hoc reason for the preclusion of advanced potentials.


Author(s):  
María Teresa Martínez-Romero ◽  
Antonio Cejudo ◽  
Pilar Sainz de Baranda

Puberty is a vulnerable period for musculoskeletal disorders due to the existence of a wide inter-individual variation in growth and development. The main objective of the present study was to describe the prevalence of back pain (BP) in the past year and month in school-aged children according to sex, age, maturity status, body mass index (BMI) and pain characteristics. This study involved 513 students aged between 9 and 16 years. Anthropometric measures were recorded to calculate the maturity stage of the students using a regression equation comprising measures for age, body mass, body height, sitting height and leg length. An ad hoc questionnaire composed of eight questions was used to describe BP prevalence in school-aged children. The results showed that the prevalence of BP in school-aged children was observed in 35.1% over the last year (45% boys and 55% girls), and 17.3% (40.4% boys and 59.6% girls, with an association found between female sex and BP) in the last month. The prevalence of back pain in the past year and month was higher the older the students were, or the more pubertal development they had experienced. The prevalence of BP in the last year was also higher in those with overweight or obesity. After adjustment for sex, there was an association between BP and older age and higher BMI in boys and an association between BP and higher pubertal development in girls. In summary, the present study showed that the prevalence of BP was related to the maturity stage and weight of the participants, with different prevalence patterns found according to sex.


2019 ◽  
Vol 7 (3) ◽  
pp. 227-236 ◽  
Author(s):  
Niels Gheyle

In the past 20 years, two related literature strands have gradually moved centre stage of the attention of EU Studies scholars. The first is preoccupied with the ‘politicization of European integration’, a multi-faceted concept that aims to tie together a multitude of political and societal manifestations underlying an increasing controversiality of the EU. A second concerns the parliamentarization of the EU, referring to the changing (institutional) role and EU-related activities national parliaments engage in. The key point of this contribution is simple, but often overlooked: We can and should be seeing parliamentarization as a necessary, yet insufficient, component of a wider process of politicization. Doing so goes beyond the often ad hoc or pars pro toto theoretical assumptions in both literature strands, sheds new light on the normative consequences attached to these phenomena, and furthers a more complete understanding of how a ‘comprehensive’ politicization of European policies develops.


Hypertension ◽  
2021 ◽  
Vol 78 (Suppl_1) ◽  
Author(s):  
Stephen P Juraschek ◽  
Lawrence J Appel ◽  
Edgar R Miller

Background: Hypertension trials that monitor orthostatic hypotension (OH) compare standing to seated blood pressure (BP) rather than supine BP. We determined the impact of a supine vs seated position on OH prevalence and its relationship with fall risk and orthostatic symptoms. Methods: The Study to Understand Fall Reduction and Vitamin D in You (STURDY) was a randomized trial testing the effects of vitamin D3 dose on falls in adults age ≥70 years at higher risk of falls. OH was determined at baseline, 3, 12, and 24 months with each of 2 protocols: (1) seated to standing and (2) supine to standing. OH was defined as a drop in systolic or diastolic BP of at least 20 or 10 mm Hg. Participants were asked about orthostatic symptoms in the past month. Falls were ascertained via daily fall calendar, ad hoc reporting, and scheduled interviews. Results: Among 522 participants with 953 OH assessments (mean age 76 ± 5 years, 42% women, 18% Black), mean baseline BP was 129 ± 18/68 ± 11 mm Hg. Mean BP increased 3.4/2.6 mm Hg after sitting, but decreased -3.7/-0.7 mm Hg after being supine. OH was detected in 2.2% of seated vs 14.8% of supine assessments. Supine OH better predicted falls (HR 1.60; 95% CI: 0.98, 2.61; P =0.06) than seated OH (HR 0.70; 95% CI: 0.30, 1.60; P =0.39), although both were non-significant ( Figure ). While seated OH was not associated with orthostatic symptoms, supine OH was associated with a greater risk of fainting, blacking out, seeing spots, room spinning, and headache in the prior month ( P -values of 0.048 to 0.002). Conclusions: Supine OH was more prevalent and appeared to better predict falls and orthostatic symptoms than seated OH. These findings support a supine protocol for OH in clinical practice.


Sensors ◽  
2019 ◽  
Vol 19 (9) ◽  
pp. 2120
Author(s):  
Annan Yang ◽  
Bo Li ◽  
Zhongjiang Yan ◽  
Mao Yang

From the perspective of media protocol control and routing of directional wireless ad hoc sensors networks, neighbor discovery protocol is an important problem to be solved first. In the past period of time, some methods have been studied on neighbor discovery protocol, but they have a common defect of link collision. The collision is caused by mutual interference of multiple transmitting nodes which are in one reception beam of the receiving node. To solve this problem, we propose a neighbor discovery algorithm using a bi-directional carrier sense collision avoidance and multi subchannels based on a scan-based algorithm (BD-SBA). Based on a scan-based algorithm (SBA), bi-directional carrier sense of the BD-SBA algorithm is performed in the first broadcast step which can reduce the collision of broadcasting the scanning request (SREQ) frames. In the second step (the reply step), the mechanism of multiple subchannels and multiple slots is applied to reduce the collision of the scanning response (SRES) frames. From the analysis and simulation, we can see that nodes using proposed algorithm can discover their neighbor nodes in fewer time. Moreover, the proposed algorithm has better performance for different beamwidths and densely distributed scenes. So it has great significance in engineering application.


2016 ◽  
Vol 17 (1) ◽  
Author(s):  
Ingrid Landau ◽  
John Howe

Trade unions in Australia have long played an important role in the enforcement of minimum employment standards. The legislative framework today continues to recognize this enforcement role, but in a way that is more individualistic and legalistic than in the past. At the same time that the law has evolved to emphasize the representation and servicing role of trade unions, the Australian union movement has sought to revitalize and grow through the adoption of an “organizing model” of unionism that emphasizes workplace-level activism. This Article explores how these seemingly opposing trends have manifested themselves in the enforcement-related activities of five trade unions. Considerable diversity was found among the unions in relation to the extent to which and how the unions performed enforcement-related activities. However, all five unions spent significant time and resources on monitoring and enforcing employer compliance with minimum standards and saw this work as a core part of what they do. The case studies suggest, however, that the way in which this work is undertaken within unions and by whom has changed significantly in recent decades. While there was evidence that enforcement work was used tactically by unions in certain cases, this was largely on an ad hoc basis and there was little indication that the enforcement work was integrated into broader organizing objectives and strategies. Overall, the unions were ambivalent, if not skeptical, as to the capacity for enforcement work to grow unions through building workplace activism and collective strength.


2013 ◽  
Vol 45 (04) ◽  
pp. 1083-1110 ◽  
Author(s):  
Sergey Foss ◽  
Stan Zachary

Many regenerative arguments in stochastic processes use random times which are akin to stopping times, but which are determined by the future as well as the past behaviour of the process of interest. Such arguments based on ‘conditioning on the future’ are usually developed in an ad-hoc way in the context of the application under consideration, thereby obscuring the underlying structure. In this paper we give a simple, unified, and more general treatment of such conditioning theory. We further give a number of novel applications to various particle system models, in particular to various flavours of contact processes and to infinite-bin models. We give a number of new results for existing and new models. We further make connections with the theory of Harris ergodicity.


1994 ◽  
Vol 25 (6) ◽  
pp. 559
Author(s):  
James W. Wilson ◽  
Catherine A. Brown ◽  
Carolyn Kieran ◽  
Frank K. Lester

This special issue of the Journal for Research in Mathematics Education was prepared to help celebrate the 25th anniversary year of the journal. President Mary Lindquist appointed an ad hoc task force to develop activities to mark this 25th year. Input was solicited from former editorial board members and editors and from others throughout mathematics education. We came to a recognition that doing something to reflect on the journal's journey over the past 25 years, while underscoring the scholarship that guides our work, would be a vehicle to help look ahead to the next 25 years.


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