Afrika Matematika最新文献

{"title":"On the Reynolds stress and inviscid solution to the hydrodynamic stability problem","authors":"Nagarohini Challa,&nbsp;S. Prakash","doi":"10.1007/s13370-026-01466-2","DOIUrl":"10.1007/s13370-026-01466-2","url":null,"abstract":"<div><p>The linear instability of inviscid, incompressible annular flows, a problem commonly known as the Circular Rayleigh Problem in hydrodynamic stability, is analyzed. Tollmien’s series solutions are presented for the problem under consideration. A neutrally stable eigensolution is demonstrated to exist for wave numbers <span>(k_s &gt; 0)</span>, and it is established that instability arises exclusively for wave numbers within the interval <span>(0&lt; k &lt; k_s)</span>. Furthermore, the behavior of the imaginary part of the complex wave speed <span>( c )</span>, namely <span>( c_i )</span>, as <span>( k )</span> approaches <span>( k_s^{-} )</span> in the context of the Circular Rayleigh problem, is studied using Tollmien–Lin’s perturbation formula. For singular neutral modes, the Reynolds stress (<span>(tau )</span>) decreases proportionally to the inverse square of the radial distance, unlike the parallel flow case where it is constant.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148009837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A mathematical perspective into the p53 protein on the expression of the transcription factor E2F in CycD/Cdk4(6) subsystem","authors":"Nkululeko Qwabe,&nbsp;Kesh Govinder","doi":"10.1007/s13370-026-01450-w","DOIUrl":"10.1007/s13370-026-01450-w","url":null,"abstract":"<div><p>Inhibitors play a significant role in the monitoring of cellular pathways. In this investigation, we evaluate the impact of p53 protein production in the CycD/Cdk4(6) subsystem. This protein assumes a crucial role in the regulation of cellular processes, including DNA repair, cell quiescence, and apoptosis. The occurrence of these processes takes place during the <span>(hbox {G}_textbf{1})</span> phase, which represents the growth stage of a cell. Although the expression of the p53 protein is not fully understood, it is known to be pulsatile and produced in response to DNA damage. As a result, the severity of cell DNA damage directly affects the level of p53 protein expression within the cell system. To further comprehend the cancerous activity of a cell in this subsystem, we have developed a novel mathematical model for the behaviour of the CycD/CDK4(6) subsystem. Our observations reveal that the system exhibits a Hopf-bifurcation, which is consistent with laboratory findings. In addition to the mathematical analysis, we have also conducted simulations of the cell processes, which successfully mimic the results obtained in the laboratory. We hope that this model will contribute to a deeper understanding of the impact of the p53 protein on cellular processes in averting oncogenic activities.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13370-026-01450-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148009661","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modeling a smooth surface by a constrained biharmonic equation with application in soil science","authors":"Samson Seifu Bekele,&nbsp;Maregnesh Mechal Wolde,&nbsp;Claus Führer,&nbsp;Nils-Otto Kitterød,&nbsp;Anne Kværnø","doi":"10.1007/s13370-026-01465-3","DOIUrl":"10.1007/s13370-026-01465-3","url":null,"abstract":"<div><p>This paper presents a method for mathematical modelling of surfaces conditioned on empirical data. It is based on solving a discrete biharmonic equation over a domain with given inner point and inner curve data. The inner curve data is used to model boundary values while the inner point data is used for modeling a load vector with the goal to generate a smooth surface. The construction of boundary data is an ill-posed problem, for which a special regularization approach is suggested. The method is designed for surface construction problems with a very limited amount of measured data. In the paper we apply the method by using empirical data of soil thickness and geological maps indicating exposed bedrock regions.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13370-026-01465-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147796914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An ecological generalized model with r-Kirchhoff-type problem","authors":"J. Vanterler da C. Sousa,&nbsp;Junior C. A. Soares,&nbsp;Felix S. Costa","doi":"10.1007/s13370-026-01463-5","DOIUrl":"10.1007/s13370-026-01463-5","url":null,"abstract":"<div><p>In the present paper we investigate the existence of solutions for an ecological generalized model with <i>r</i>-Kirchhoff problem via the method of sub-supersolutions in <span>(zeta )</span>-generalized space <span>(mathcal {H}^{alpha , eta ;zeta }_{r}(Lambda ))</span>. We also discuss some special cases.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13370-026-01463-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147737464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Computing the Sombor index in annihilating-ideal graphs","authors":"M. J. Nikmehr,&nbsp;R. Nikandish,&nbsp;M. Mehrara","doi":"10.1007/s13370-026-01456-4","DOIUrl":"10.1007/s13370-026-01456-4","url":null,"abstract":"<div><p>The Sombor index for a graph <i>G</i> with vertex set <i>V</i> and edge set <i>E</i> is defined as <span>(sum _{vwin E}sqrt{d_v^2+d_w^2})</span>, where <span>(d_v)</span> denotes the number of edges incident on the vertex <span>(vin V)</span>. The annihilating-ideal graph of a commutative ring <i>R</i> consists the set of non-trivial ideals with non-zero annihilator as the vertex set and two distinct vertices are joined by an edge if their product is zero. In this paper, the Sombor index of annihilating-ideal graphs associated with <span>(mathbb {Z}_n)</span>, the ring of integers modulo <i>n</i>, is discussed.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147642548","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A parameterized block-splitting preconditioner for indefinite least squares problem","authors":"Davod Khojasteh Salkuyeh","doi":"10.1007/s13370-026-01451-9","DOIUrl":"10.1007/s13370-026-01451-9","url":null,"abstract":"<div><p>We present a stationary iteration method based upon a block splitting for a class of indefinite least squares problem. Convergence of the proposed method is investigated and optimal value of the involving parameter is computed. The induced preconditioner is applied to accelerate convergence of the GMRES method for solving the problem. We also analysed the eigenpair distribution of the preconditioned matrix. We assess the efficiency of the proposed preconditioner by presenting results from a numerical comparison with several existing preconditioners.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147606834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"GPU-based program for computing the strong fuzzy degree of hypergroupoids","authors":"Yuming Feng,&nbsp;Violeta Leoreanu-Fotea","doi":"10.1007/s13370-026-01418-w","DOIUrl":"10.1007/s13370-026-01418-w","url":null,"abstract":"<div><p>In this paper, we present algorithms to determine the strong fuzzy grade of a hypergroupoid, exemplifying two types of hypergroupoids. Programs involved with GPU computing for calculating the strong fuzzy grade of the hypergroupoids with large cardinality are given, and a comparison of programs between using GPU and CPU is presented. We also give programs for the Corsini method named <i>join2fuzzy</i> and <i>fuzzy2join</i>. All programs are applicable for any hypergroupoid, except the program <i>GenH</i>, with which the hypergroupoid <i>H</i> to be studied is introduced.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147607379","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Plane symmetric Renyi holographic dark energy in Brans–Dicke theory","authors":"Y. Prasanthi,&nbsp;D. Neelima,&nbsp;K. Suresh","doi":"10.1007/s13370-026-01452-8","DOIUrl":"10.1007/s13370-026-01452-8","url":null,"abstract":"<div><p>In this study, we investigate the cosmological implications of Renyi holographic dark energy (RHDE) in the framework of Brans–Dicke (BD) theory, considering a plane symmetric Cosmological model. We consider both the Hubble horizon and the Granda-Oliveros (GO) scale as infrared (IR) cutoffs to explore the dynamical evolution of the universe. To ascertain the solutions, we depend on the premises of (i) the correlation between metric potentials and (ii) the exponential relationship between the scale factor and the scalar field. For each cutoff, we derive the corresponding field equations, analyze the behavior of key cosmological parameters such as the deceleration parameter, equation of state (EoS), and BD scalar field dynamics and discuss the conditions for accelerated expansion. The results indicate that the RHDE component exhibits negative pressure and stable behavior for suitable ranges of model parameters under both infrared cutoffs. Although the present model does not describe a dynamical transition from decelerated to accelerated expansion, it provides a mathematical and kinematical exploration of Rényi holographic dark energy in an anisotropic Brans–Dicke background. The study emphasizes the qualitative differences caused by the choice of infrared cutoff and serves as a foundation for more general theoretical investigations.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147606994","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Certain generating matrix functions of Charlier matrix polynomials using Weisner’s group theoretic method","authors":"Ayman Shehata","doi":"10.1007/s13370-026-01445-7","DOIUrl":"10.1007/s13370-026-01445-7","url":null,"abstract":"<div><p>The present paper discusses a study of a class of Charlier matrix polynomials (CMPs) and its generalized analogue. Certain generating matrix functions, recurrence matrix relations, matrix differential equation, summation formulas and many new results have been discussed for these matrix polynomials. Weisner’s group theoretic method is used to obtain matrix generating relations for Charlier matrix polynomials and the details of this method were given in this paper. Finally, we will discuss only briefly the procedure followed.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13370-026-01445-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147560424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A secure watermarking technique to address security concerns of modern telemedicine applications: a chaotic map-based approach","authors":"Haris Aziz,&nbsp;Taha Aziz,&nbsp;Asim Aziz,&nbsp;E. Momoniat,&nbsp;Syed Mushad Mustuzhar Gilani","doi":"10.1007/s13370-026-01462-6","DOIUrl":"10.1007/s13370-026-01462-6","url":null,"abstract":"<div><p>The modern era has witnessed an immense propagation of multimedia applications. Authentication and copyright are hot topics with these next-generation multimedia platforms. Telemedicine is one perspective domain that customs the benefits of multimedia ecosystems to deliver efficient medical services. In addition, the recent COVID-19 pandemic aids as a catalyst to put telemedicine in the spotlight of modern research. The spike in telemedicine usage has led to a rapid escalation in the generation and sharing of electronic medical data. Medical image watermarking is a complementary security mechanism to address the issues of integrity, copyright, and confidentiality. This manuscript presents a robust, imperceptible, and efficient scheme for watermarking medical images to protect legitimate ownership and privacy. The architecture integrates three heterogeneous chaotic maps (Chebyshev, Tangent Delay Ellipse Reflecting Cavity System, and an Extended logistic map) to significantly expand the effective key space and enhance key sensitivity. The resiliency of the algorithm is further enriched by supplementing confusion operation in the watermark using a 4 × 4 Substitution box. Three unique chaotic maps are used to amplify the endurance of the proposed scheme, which specifies the location for watermark insertion The chaotic sequences mutually govern the spatial and frame-wise watermark embedding locations. Experimental evaluations conducted on medical images demonstrate excellent visual imperceptibility by having peak signal-to-noise ratio (PSNR) values exceeding 55 dB and structural similarity index (SSIM) values close to unity. Statistical integrity is validated by Chi-Square analysis (<i>X</i>² = 18,695,731), confirming histogram preservation. Security is bolstered by an extensive key space of 10¹⁰⁸, equivalent to 256-bit protection, while a Crest Factor of 5.0989 ensures a noise-like encrypted distribution. Robustness analysis under noise addition and cropping, yields low bit error rate values, validating reliable blind watermark extraction without the original carrier image. Results show that the scheme has excellent attributes to handle authentication and copyright issues for real-time medical applications.</p></div>","PeriodicalId":46107,"journal":{"name":"Afrika Matematika","volume":"37 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147559667","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}