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Mathematics, Volume 9, Issue 8

2021 April-2 - 124 articles

Cover Story: A change in temperature drastically modifies the lifetime of a product. AFT models relate the distribution of the time-to-failure for usual conditions with the distribution of the accelerated failure times. Different optimal designs can be combined to obtain the best temperatures in which to take observations such that the most accurate estimates of the lifetime distribution parameters can be derived. View this paper.
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Articles (124)

  • Article
  • Open Access
17 Citations
4,588 Views
21 Pages

μ-Synthesis for Fractional-Order Robust Controllers

  • Vlad Mihaly,
  • Mircea Şuşcă,
  • Dora Morar,
  • Mihai Stănese and
  • Petru Dobra

20 April 2021

The current article presents a design procedure for obtaining robust multiple-input and multiple-output (MIMO) fractional-order controllers using a μ-synthesis design procedure with DK iteration. μ-synthesis uses the generalized Robust Control frame...

  • Article
  • Open Access
2 Citations
2,072 Views
10 Pages

Non-Stationary Model of Cerebral Oxygen Transport with Unknown Sources

  • Andrey Kovtanyuk,
  • Alexander Chebotarev,
  • Varvara Turova,
  • Irina Sidorenko and
  • Renée Lampe

20 April 2021

An inverse problem for a system of equations modeling oxygen transport in the brain is studied. The problem consists of finding the right-hand side of the equation for the blood oxygen transport, which is a linear combination of given functionals des...

  • Article
  • Open Access
2,235 Views
22 Pages

20 April 2021

In this article, we consider the Qian–Sheng model in the Landau–de Gennes framework describing nematic liquid crystal flows when the inertial effect is neglected. By taking the limit of elastic constant to zero (also called the uniaxial limit) and ut...

  • Article
  • Open Access
11 Citations
2,669 Views
29 Pages

20 April 2021

A complex multi-state redundant system with preventive maintenance subject to multiple events is considered. The online unit can undergo several types of failure: both internal and those provoked by external shocks. Multiple degradation levels are as...

  • Review
  • Open Access
40 Citations
6,338 Views
20 Pages

20 April 2021

Systems of fractional-order differential equations present stability properties which differ in a substantial way from those of systems of integer order. In this paper, a detailed analysis of the stability of linear systems of fractional differential...

  • Article
  • Open Access
5 Citations
3,639 Views
20 Pages

20 April 2021

This paper introduces a new methodology to estimate time-varying alphas and betas in conditional factor models, which allows substantial flexibility in a time-varying framework. To circumvent problems associated with the previous approaches, we intro...

  • Feature Paper
  • Article
  • Open Access
49 Citations
7,546 Views
20 Pages

19 April 2021

This paper examines the interdependence between green financial instruments, represented by green bonds and green stocks, and a set of major conventional assets, such as Treasury, investment-grade and high-yield corporate bonds, general stocks, crude...

  • Article
  • Open Access
4 Citations
5,705 Views
16 Pages

19 April 2021

The study of the assessment and reflection of biological assets in the economic processes of agricultural enterprises can be represented as a chain of phenomena in which scientists and practitioners try to study and understand the nature and essence...

  • Article
  • Open Access
9 Citations
3,102 Views
16 Pages

Nonlinear Control of Hydrostatic Thrust Bearing Using Multivariable Optimization

  • Waheed Ur Rehman,
  • Wakeel Khan,
  • Nasim Ullah,
  • M. D. Shahariar Chowdhury,
  • Kuaanan Techato and
  • Muhammad Haneef

19 April 2021

This research work is focused on the nonlinear modeling and control of a hydrostatic thrust bearing. In the proposed work, a mathematical model is formulated for a hydrostatic thrust bearing system that includes the effects of uncertainties, unmodell...

  • Article
  • Open Access
4,526 Views
17 Pages

The Impact of Candidates’ Profile and Campaign Decisions in Electoral Results: A Data Analytics Approach

  • Camilo Campos-Valdés,
  • Eduardo Álvarez-Miranda,
  • Mauricio Morales Quiroga,
  • Jordi Pereira and
  • Félix Liberona Durán

19 April 2021

In recent years, a wide range of techniques has been developed to predict electoral results and to measure the influence of different factors in these results. In this paper, we analyze the influence of the political profile of candidates (characteri...

  • Article
  • Open Access
5 Citations
3,134 Views
10 Pages

19 April 2021

In this paper, we discuss the question of finding an optimal control for the solutions of the problem with dry friction quasistatic contact, in the case that the friction law is modeled by a nonlocal version of Coulomb’s law. In order to get the nece...

  • Article
  • Open Access
4 Citations
3,398 Views
15 Pages

19 April 2021

The nonhomogeneous Poisson process model with power law intensity, also known as the Army Materiel Systems Analysis Activity (AMSAA) model, is commonly used to model the reliability growth process of many repairable systems. In practice, it is necess...

  • Article
  • Open Access
4 Citations
4,566 Views
27 Pages

Coping with Challenges in Teaching Foreign Languages to Children with Mild Intellectual Disabilities: Stakeholders’ Perspectives

  • Cristina Pérez-Valverde,
  • Raúl Ruiz-Cecilia,
  • Leopoldo Medina-Sánchez and
  • Juan Ramón Guijarro-Ojeda

19 April 2021

In this qualitative study, we aim to gain insight into the stakeholders’ perspectives around the inclusion of a mild intellectual disability (MID) student of perinatal origin in the foreign language (FL) classroom, and their perspectives on the stude...

  • Article
  • Open Access
3 Citations
3,120 Views
20 Pages

19 April 2021

The Analytic Target Cascading (ATC) is an effective method for solving hierarchical Multidisciplinary Design Optimization (MDO) problems. At the same time, this method suffers from poor convergence and low accuracy, which is caused by the inconsisten...

  • Article
  • Open Access
13 Citations
3,083 Views
22 Pages

19 April 2021

In the traditional nonlinear optimization theory, the Karush-Kuhn-Tucker (KKT) optimality conditions for constrained optimization problems with inequality constraints play an essential role. The situation becomes challenging when the theory of tradit...

  • Article
  • Open Access
19 Citations
3,612 Views
22 Pages

Advanced Metaheuristic Method for Decision-Making in a Dynamic Job Shop Scheduling Environment

  • Hankun Zhang,
  • Borut Buchmeister,
  • Xueyan Li and
  • Robert Ojstersek

19 April 2021

As a well-known NP-hard problem, the dynamic job shop scheduling problem has significant practical value, so this paper proposes an Improved Heuristic Kalman Algorithm to solve this problem. In Improved Heuristic Kalman Algorithm, the cellular neighb...

  • Article
  • Open Access
1 Citations
2,659 Views
17 Pages

18 April 2021

We are interested in a contact problem for a thin fixed beam with an internal point obstacle with possible rotation and shift depending on a given swivel and sliding friction. This problem belongs to the most basic practical problems in, for instance...

  • Article
  • Open Access
4 Citations
2,547 Views
14 Pages

Factorization à la Dirac Applied to Some Equations of Classical Physics

  • Zine El Abiddine Fellah,
  • Erick Ogam,
  • Mohamed Fellah and
  • Claude Depollier

18 April 2021

In this paper, we present an application of Dirac’s factorization method to three types of the partial differential equations, i.e., the wave equation, the scattering equation, and the telegrapher’s equation. This method gives results that contribute...

  • Article
  • Open Access
13 Citations
1,952 Views
11 Pages

17 April 2021

In this paper, by using the new concept of (ϱ,ψ,ω)-quasiinvexity associated with interval-valued path-independent curvilinear integral functionals, we establish some duality results for a new class of multiobjective variational control problems with...

  • Article
  • Open Access
10 Citations
2,104 Views
12 Pages

17 April 2021

The present paper deals with a duality study associated with a new class of multiobjective optimization problems that include the interval-valued components of the ratio vector. More precisely, by using the new notion of (ρ,ψ,d)-quasiinvexity associa...

  • Review
  • Open Access
63 Citations
12,601 Views
48 Pages

Graph Metrics for Network Robustness—A Survey

  • Milena Oehlers and
  • Benjamin Fabian

17 April 2021

Research on the robustness of networks, and in particular the Internet, has gained critical importance in recent decades because more and more individuals, societies and firms rely on this global network infrastructure for communication, knowledge tr...

  • Article
  • Open Access
46 Citations
4,585 Views
28 Pages

17 April 2021

Gravity and flexibility will cause fluctuations of the rotation angle in the servo system for flexible manipulators. The fluctuation will seriously affect the motion accuracy of end-effectors. Therefore, this paper adopts a control method combining t...

  • Article
  • Open Access
9 Citations
2,433 Views
25 Pages

17 April 2021

The direct strong-form collocation method with reproducing kernel approximation is introduced to efficiently and effectively solve the natural convection problem within a parallelogrammic enclosure. As the convection behavior in the fluid-saturated p...

  • Article
  • Open Access
10 Citations
2,678 Views
12 Pages

16 April 2021

This paper is concerned with complete synchronization of fractional-order chaotic systems with both model uncertainty and external disturbance. Firstly, we propose a new dynamic feedback control method for complete synchronization of fractional-order...

  • Article
  • Open Access
70 Citations
4,045 Views
14 Pages

Hybrid Nanofluid Flow over a Permeable Shrinking Sheet Embedded in a Porous Medium with Radiation and Slip Impacts

  • Shahirah Abu Bakar,
  • Norihan Md Arifin,
  • Najiyah Safwa Khashi’ie and
  • Norfifah Bachok

16 April 2021

The study of hybrid nanofluid and its thermophysical properties is emerging since the early of 2000s and the purpose of this paper is to investigate the flow of hybrid nanofluid over a permeable Darcy porous medium with slip, radiation and shrinking...

  • Article
  • Open Access
5 Citations
4,902 Views
14 Pages

16 April 2021

This research aims to determine the existence of inflection points when companies’ credit risk goes from being minimal (Hedge) to being high (Ponzi). We propose an analysis methodology that determines the probability of hedge credits to migrate to sp...

  • Feature Paper
  • Article
  • Open Access
2 Citations
2,400 Views
11 Pages

16 April 2021

In this research, we continue studying limit theorems for combinatorial numbers satisfying a class of triangular arrays. Using the general results of Hwang and Bender, we obtain a constructive proof of the central limit theorem, specifying the rate o...

  • Article
  • Open Access
58 Citations
4,328 Views
22 Pages

16 April 2021

In this study, thermal performance and flow characteristics of a shell and tube heat exchanger equipped with various baffle angles were studied. The heat exchanger was operated with distilled water, and a hybrid nanofluid at three concentrations of 0...

  • Article
  • Open Access
16 Citations
3,830 Views
26 Pages

A New Ensemble Method for Detecting Anomalies in Gene Expression Matrices

  • Laura Selicato,
  • Flavia Esposito,
  • Grazia Gargano,
  • Maria Carmela Vegliante,
  • Giuseppina Opinto,
  • Gian Maria Zaccaria,
  • Sabino Ciavarella,
  • Attilio Guarini and
  • Nicoletta Del Buono

16 April 2021

One of the main problems in the analysis of real data is often related to the presence of anomalies. Namely, anomalous cases can both spoil the resulting analysis and contain valuable information at the same time. In both cases, the ability to detect...

  • Article
  • Open Access
18 Citations
4,152 Views
16 Pages

16 April 2021

Agriculture decision support systems (DSSs) play an important role in facilitating evidence-based agricultural decision-making for improving agribusiness productivity. Evaluating and selecting the most appropriate agriculture DSS for sustainable agri...

  • Article
  • Open Access
2 Citations
3,084 Views
8 Pages

16 April 2021

The existing spatial panel structural vector auto-regressive model can effectively capture the time and spatial dynamic dependence of endogenous variables. However, the hypothesis that the common factors have the same effect for all spatial units is...

  • Article
  • Open Access
1 Citations
2,082 Views
52 Pages

16 April 2021

The uncertainty for the continuous-time linear programming problem with time-dependent matrices is considered in this paper. In this case, the robust counterpart of the continuous-time linear programming problem is introduced. In order to solve the r...

  • Article
  • Open Access
141 Citations
11,995 Views
27 Pages

16 April 2021

With the effects of the COVID-19 pandemic, the e-commerce trend is driving faster, significantly impacting supply chains around the world. Thus, the importance of logistics and supply chain functions has been amplified in almost every business that s...

  • Article
  • Open Access
5 Citations
2,087 Views
18 Pages

16 April 2021

Let p(z) be a polynomial of degree n having no zeros in |z|<1. In this paper, we generalize and extend a well-known result proven by Ankeny and Rivlin for the sth derivative of the polynomial. Furthermore, another well-known result proven by Rivli...

  • Feature Paper
  • Article
  • Open Access
2,488 Views
11 Pages

16 April 2021

This paper is concerned with an SIS epidemic reaction-diffusion model. The purpose of this paper is to derive some effects of the spatial heterogeneity of the recovery rate on the total population of infected and the reproduction number. The proof is...

  • Article
  • Open Access
30 Citations
4,607 Views
19 Pages

16 April 2021

Sustainable development has become a global catchphrase in the recent development age. This leads to the growth of various methodologies in evaluating environmental efficiency, such as the Data Envelopment Analysis (DEA) method. The purpose of this s...

  • Article
  • Open Access
5 Citations
2,781 Views
14 Pages

16 April 2021

In this research, we study the convex minimization problem in the form of the sum of two proper, lower-semicontinuous, and convex functions. We introduce a new projected forward-backward algorithm using linesearch and inertial techniques. We then est...

  • Article
  • Open Access
5 Citations
4,252 Views
20 Pages

16 April 2021

This work provides a procedure with which to construct and visualize profiles, i.e., groups of individuals with similar characteristics, for weighted and mixed data by combining two classical multivariate techniques, multidimensional scaling (MDS) an...

  • Article
  • Open Access
22 Citations
5,397 Views
23 Pages

16 April 2021

This study analyzes business performance through efficiency score estimation in two sustainable tourism models: cultural tourism and rural tourism. The study uses microeconomic data (microdata) of Spanish firms with different characteristics in terms...

  • Article
  • Open Access
38 Citations
3,148 Views
20 Pages

15 April 2021

A discrete-time predator–prey system incorporating fear effect of the prey with the predator has other food resource is proposed in this paper. The trivial equilibrium and the predator free equilibrium are both unstable. A set of sufficient condition...

  • Article
  • Open Access
1 Citations
2,570 Views
10 Pages

Period-Life of a Branching Process with Migration and Continuous Time

  • Khrystyna Prysyazhnyk,
  • Iryna Bazylevych,
  • Ludmila Mitkova and
  • Iryna Ivanochko

15 April 2021

The homogeneous branching process with migration and continuous time is considered. We investigated the distribution of the period-life τ, i.e., the length of the time interval between the moment when the process is initiated by a positive number of...

  • Feature Paper
  • Article
  • Open Access
1 Citations
2,669 Views
7 Pages

A Liouville’s Formula for Systems with Reflection

  • Santiago Codesido and
  • F. Adrián F. Tojo

15 April 2021

In this work, we derived an Abel–Jacobi–Liouville identity for the case of two-dimensional linear systems of ODEs (ordinary differential equations) with reflection. We also present a conjecture for the general case and an application to coupled harmo...

  • Article
  • Open Access
5 Citations
1,904 Views
19 Pages

15 April 2021

This paper analyzes cost sharing in uncapacitated lot-sizing models with backlogging and heterogeneous costs. It is assumed that several firms participate in a consortium aiming at satisfying their demand over the planning horizon with minimal operat...

  • Article
  • Open Access
6 Citations
2,638 Views
15 Pages

Portability of Predictive Academic Performance Models: An Empirical Sensitivity Analysis

  • Jose Luis Arroyo-Barrigüete,
  • Susana Carabias-López,
  • Tomas Curto-González and
  • Adolfo Hernández

15 April 2021

The portability of predictive models of academic performance has been widely studied in the field of learning platforms, but there are few studies in which the results of previous evaluations are used as factors. The aim of this work was to analyze p...

  • Article
  • Open Access
89 Citations
6,574 Views
16 Pages

Deep Learning for Wave Energy Converter Modeling Using Long Short-Term Memory

  • Seyed Milad Mousavi,
  • Majid Ghasemi,
  • Mahsa Dehghan Manshadi and
  • Amir Mosavi

15 April 2021

Accurate forecasts of ocean waves energy can not only reduce costs for investment, but it is also essential for the management and operation of electrical power. This paper presents an innovative approach based on long short-term memory (LSTM) to pre...

  • Article
  • Open Access
8 Citations
6,342 Views
13 Pages

15 April 2021

The analytic hierarchy process (AHP) is a well-known approach in decision-making because of its simplicity and rationality. However, in conventional AHP, it cannot account for the correlation effect between criteria. In this paper, we use the lexical...

  • Article
  • Open Access
2,365 Views
27 Pages

15 April 2021

In this paper, an adaptive proximal bundle method is proposed for a class of nonconvex and nonsmooth composite problems with inexact information. The composite problems are the sum of a finite convex function with inexact information and a nonconvex...

  • Article
  • Open Access
9 Citations
3,999 Views
15 Pages

A Conceptual Probabilistic Framework for Annotation Aggregation of Citizen Science Data

  • Jesus Cerquides,
  • Mehmet Oğuz Mülâyim,
  • Jerónimo Hernández-González,
  • Amudha Ravi Shankar and
  • Jose Luis Fernandez-Marquez

15 April 2021

Over the last decade, hundreds of thousands of volunteers have contributed to science by collecting or analyzing data. This public participation in science, also known as citizen science, has contributed to significant discoveries and led to publicat...

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Mathematics - ISSN 2227-7390