89 results on '"Rajagopalan Ramaswamy"'
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2. Fixed point theorem on an orthogonal extended interpolative ψF-contraction
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Menaha Dhanraj, Arul Joseph Gnanaprakasam, Gunaseelan Mani, Rajagopalan Ramaswamy, Khizar Hyatt Khan, Ola Ashour A. Abdelnaby, and Stojan Radenović
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complete $ \mathfrak{b} $-metric spaces ,fixed point ,orthogonal extended interpolative ciric reich-rus type $ \psi\mathcal{f} $-contraction ,Mathematics ,QA1-939 - Abstract
In this paper, we establish the fixed point results for an orthogonal extended interpolative Ciric Reich-Rus type $ \psi\mathcal{F} $-contraction mapping on an orthogonal complete $ \mathfrak{b} $-metric spaces and give an example to strengthen our main results. Furthermore, we present an application to fixed point results to find analytical solutions for functional equation.
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- 2023
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3. Application of fixed point results in the setting of F-contraction and simulation function in the setting of bipolar metric space
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Gunaseelan Mani, Rajagopalan Ramaswamy, Arul Joseph Gnanaprakasam, Vuk Stojiljković, Zaid. M. Fadail, and Stojan Radenović
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simulation function ,fixed point ,bpms ,Mathematics ,QA1-939 - Abstract
In the present work, simulation function is applied to establish fixed point results of F-contraction in the setting of Bi-polar metric space. Our results are extensions or generalizations of results proved in the literature. The derived results are substantiated with suitable examples and an application to find the solution to the integral equation.
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- 2023
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4. Exact Optical Solitons for Generalized Kudryashov’s Equation by Lie Symmetry Method
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Rajagopalan Ramaswamy, E. S. El-Shazly, M. S. Abdel Latif, Amr Elsonbaty, and A. H. Abdel Kader
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Mathematics ,QA1-939 - Abstract
In this article, we use Lie point symmetry analysis to extract some new optical soliton solutions for the generalized Kudryashov’s equation (GKE) with an arbitrary power nonlinearity. Using a traveling wave transformation, the GKE is transformed into a nonlinear second order ordinary differential equation (ODE). Using Lie point symmetry analysis, the nonlinear second-order ODE is reduced to a first-order ODE. This first-order ODE is solved in two cases to retrieve some new bright, dark, and kink soliton solutions of the GKE. These soliton solutions for the GKE are obtained here for the first time.
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- 2023
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5. CKD subpopulations defined by risk‐factors: A longitudinal analysis of electronic health records
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Rajagopalan Ramaswamy, Soon Nan Wee, Kavya George, Abhijit Ghosh, Joydeep Sarkar, Rolf Burghaus, and Jörg Lippert
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Therapeutics. Pharmacology ,RM1-950 - Abstract
Abstract Chronic kidney disease (CKD) is a progressive disease that evades early detection and is associated with various comorbidities. Although clinical comprehension and control of these comorbidities is crucial for CKD management, complex pathophysiological interactions and feedback loops make this a formidable task. We have developed a hybrid semimechanistic modeling methodology to investigate CKD progression. The model is represented as a system of ordinary differential equations with embedded neural networks and takes into account complex disease progression pathways, feedback loops, and effects of 53 medications to generate time trajectories of eight clinical biomarkers that capture CKD progression due to various risk factors. The model was applied to real world data of US patients with CKD to map the available longitudinal information onto a set of time‐invariant patient‐specific parameters with a clear biological interpretation. These parameters describing individual patients were used to segment the cohort using a clustering approach. Model‐based simulations were conducted to investigate cluster‐specific treatment strategies. The model was able to reliably reproduce the variability in biomarkers across the cohort. The clustering procedure segmented the cohort into five subpopulations – four with enhanced sensitivity to a specific risk factor (hypertension, hyperlipidemia, hyperglycemia, or impaired kidney) and one that is largely insensitive to any of the risk factors. Simulation studies were used to identify patient‐specific strategies to restrain or prevent CKD progression through management of specific risk factors. The semimechanistic model enables identification of disease progression phenotypes using longitudinal data that aid in prioritizing treatment strategies at individual patient level.
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- 2021
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6. Ulam–Hyers Stability and Well-Posedness of Fixed Point Problems in C*-Algebra Valued Bipolar b-Metric Spaces
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Manoj Kumar, Pankaj Kumar, Ali Mutlu, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, and Stojan Radenović
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C*-algebra valued bipolar b-metric space ,covariant mapping ,contravariant mapping ,fixed points ,Ulam–Hyers stability ,well-posdeness ,Mathematics ,QA1-939 - Abstract
Here, we shall introduce the new notion of C*-algebra valued bipolar b-metric spaces as a generalization of usual metric spaces, C*-algebra valued metric space, b-metric spaces. In the above-mentioned spaces, we shall define (αA−ψA) contractions and prove some fixed point theorems for these contractions. Some existing results from the literature are also proved by using our main results. As an application Ulam–Hyers stability and well-posedness of fixed point problems are also discussed. Some examples are also given to illustrate our results.
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- 2023
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7. Some Refinements of the Tensorial Inequalities in Hilbert Spaces
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Vuk Stojiljković, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, and Stojan Radenović
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tensorial product ,self-adjoint operators ,convex functions ,Mathematics ,QA1-939 - Abstract
Hermite–Hadamard inequalities and their refinements have been investigated for a long period of time. In this paper, we obtained refinements of the Hermite–Hadamard inequality of tensorial type for the convex functions of self-adjoint operators in Hilbert spaces. The obtained inequalities generalize the previously obtained inequalities by Dragomir. We also provide useful Lemmas which enabled us to obtain the results. The examples of the obtained inequalities for specific convex functions have been given in the example and consequences section. Symmetry in the upper and lower bounds can be seen in the last Theorem of the paper given, as the upper and lower bounds differ by a constant.
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- 2023
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8. New Exact Nematicon Solutions of Liquid Crystal Model With Different Types of Nonlinearities
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Rajagopalan Ramaswamy, A. H. Abdel Kader, and Amr Elsonbaty
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Jacobi elliptic function ,lie point symmetry ,liquid crystals ,nematicons ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
The aim of this work is to explore and find new closed-form nematicon solutions for different nonlinearities which occur in nematic liquid crystals (NLC) along with proposing optical system application that utilizes NLC nonlinearities. In particular, Lie point symmetry method is employed to scrupulously inspect and acquire solutions for some interesting cases of nonlinearities which have not been fully examined in literature such as quadratic, generalized dual-power law, and eighth-order nonlinearities. A variety of different nematicon dynamics are observed, including bright solitons, dark solitons and periodic behaviors. The explicit solution form for each dynamical behavior is obtained and the solution dependence on model parameters is investigated. The proposed optical system enables the flexible realization of different types of NLC nonlinearities. To the best of our knowledge, this is the first time to attain explicit exact nontrivial solutions for the particular cases of generalized dual-power law and eighth-order nonlinearities.
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- 2021
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9. On Ghost Attractor in Blinking Chaotic MVD Memristor-Based Circuit and its Application
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Rajagopalan Ramaswamy, A. M. A. El-Sayed, A. A. Elsadany, and Amr Elsonbaty
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Memristors ,pseudo-chaos encryption ,ghost attractors ,blinking circuit ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
This work is devoted to explore the possible existence of ghost attractors in a proposed nonautonomous blinking circuit with nonlinear memristors along with their potential application. The nonlinear dynamics of new memristor-based blinking circuit are significantly influenced by the speed of random switchings between its autonomous subcircuits. So, the effects of varying stochastic switching rate on the dynamical behaviors of blinking circuit are examined. It is demonstrated that it is possible to stimulate a non-stationary chaotic attractor for the blinking circuit which is surprisingly different from the attractors of composing subcircuits which exhibit simple periodic dynamics. A sufficiently small time period for random switchings in addition to precise tuning of circuit parameters are the major requirements for establishing these ghost attractors. The fascinating features of the induced ghost attractors render them appropriate noise-like source for secure communications applications. So, we proposed a new pseudo-chaos encryption algorithm that exploits the memristor-based blinking circuit in a more suitable digital platform. The proposed scheme overcomes the usual degradation in performance of digital chaos due to finite precision representation of floating numbers.
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- 2021
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10. NeuroBlu, an electronic health record (EHR) trusted research environment (TRE) to support mental healthcare analytics with real-world data
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Rashmi Patel, Miguel E Rentería, Soon Nan Wee, Rajagopalan Ramaswamy, Simran Thadani, Jesisca Tandi, Ruchir Garg, Nathan Calvanese, Matthew Valko, A John Rush, Joydeep Sarkar, and Scott H Kollins
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Medicine - Abstract
Purpose NeuroBlu is a real-world data (RWD) repository that contains deidentified electronic health record (EHR) data from US mental healthcare providers operating the MindLinc EHR system. NeuroBlu enables users to perform statistical analysis through a secure web-based interface. Structured data are available for sociodemographic characteristics, mental health service contacts, hospital admissions, International Classification of Diseases ICD-9/ICD-10 diagnosis, prescribed medications, family history of mental disorders, Clinical Global Impression—Severity and Improvement (CGI-S/CGI-I) and Global Assessment of Functioning (GAF). To further enhance the data set, natural language processing (NLP) tools have been applied to obtain mental state examination (MSE) and social/environmental data. This paper describes the development and implementation of NeuroBlu, the procedures to safeguard data integrity and security and how the data set supports the generation of real-world evidence (RWE) in mental health.Participants As of 31 July 2021, 562 940 individuals (48.9% men) were present in the data set with a mean age of 33.4 years (SD: 18.4 years). The most frequently recorded diagnoses were substance use disorders (1 52 790 patients), major depressive disorder (1 29 120 patients) and anxiety disorders (1 03 923 patients). The median duration of follow-up was 7 months (IQR: 1.3 to 24.4 months).Findings to date The data set has supported epidemiological studies demonstrating increased risk of psychiatric hospitalisation and reduced antidepressant treatment effectiveness among people with comorbid substance use disorders. It has also been used to develop data visualisation tools to support clinical decision-making, evaluate comparative effectiveness of medications, derive models to predict treatment response and develop NLP applications to obtain clinical information from unstructured EHR data.Future plans The NeuroBlu data set will be further analysed to better understand factors related to poor clinical outcome, treatment responsiveness and the development of predictive analytic tools that may be incorporated into the source EHR system to support real-time clinical decision-making in the delivery of mental healthcare services.
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- 2022
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11. Application of Fixed Points in Bipolar Controlled Metric Space to Solve Fractional Differential Equation
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Gunaseelan Mani, Rajagopalan Ramaswamy, Arul Joseph Gnanaprakasam, Amr Elsonbaty, Ola A. Ashour Abdelnaby, and Stojan Radenović
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bipolar metric space ,bipolar-controlled metric space ,fixed point ,covariant map ,contravariant map ,Thermodynamics ,QC310.15-319 ,Mathematics ,QA1-939 ,Analysis ,QA299.6-433 - Abstract
Fixed point results and metric fixed point theory play a vital role to find the unique solution to differential and integral equations. Likewise, fractal calculus has vast physical applications. In this article, we introduce the concept of bipolar-controlled metric space and prove fixed point theorems. The derived results expand and extend certain well-known results from the research literature and are supported with a non-trivial example. We have applied the fixed point result to find the analytical solution to the integral equation and fractional differential equation. The analytical solution has been supplemented with numerical simulation.
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- 2023
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12. (α − ψ) Meir–Keeler Contractions in Bipolar Metric Spaces
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Manoj Kumar, Pankaj Kumar, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, Amr Elsonbaty, and Stojan Radenović
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fixed point ,(α − ψ) Meir–Keeler contractive mappings ,covariant and contravariant mappings ,bipolar metric space ,Mathematics ,QA1-939 - Abstract
In this paper, we introduce the new notion of contravariant (α−ψ) Meir–Keeler contractive mappings by defining α-orbital admissible mappings and covariant Meir–Keeler contraction in bipolar metric spaces. We prove fixed point theorems for these contractions and also provide some corollaries of main results. An example is also be given in support of our main result. In the end, we also solve an integral equation using our result.
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- 2023
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13. Application of Fixed-Point Results to Integral Equation through F-Khan Contraction
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Arul Joseph Gnanaprakasam, Gunaseelan Mani, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, Khizar Hyatt Khan, and Stojan Radenović
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fixed point ,F-Khan contraction ,orthogonal set ,Mathematics ,QA1-939 - Abstract
In this article, we establish fixed point results by defining the concept of F-Khan contraction of an orthogonal set by modifying the symmetry of usual contractive conditions. We also provide illustrative examples to support our results. The derived results have been applied to find analytical solutions to integral equations. The analytical solutions are verified with numerical simulation.
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- 2023
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14. Solving an Integral Equation via Tricomplex-Valued Controlled Metric Spaces
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Rajagopalan Ramaswamy, Gunaseelan Mani, Arul Joseph Gnanaprakasam, Ola A. Ashour Abdelnaby, and Stojan Radenović
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controlled metric-type spaces ,tricomplex-valued controlled metric spaces ,fixed point ,integral equation ,Mathematics ,QA1-939 - Abstract
In this present study, we propose the concept of tricomplex-controlled metric spaces as a generalization of both controlled metric-type spaces and tricomplex metric-type spaces. In this work, we establish fixed point results using Banach, Kannan and Fisher-type contractions supported with nontrivial examples in the setting of the proposed space. We apply the derived result to find the analytical solution of an integral equation using the fixed point technique under the same metric.
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- 2023
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15. Some Novel Inequalities for LR-(k,h-m)-p Convex Interval Valued Functions by Means of Pseudo Order Relation
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Vuk Stojiljković, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, and Stojan Radenović
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convex set-valued functions ,left–right-(k,h-m)-p-convex set-valued functions ,Katugampola noninteger integral operators ,Hermite–Hadamard inequality ,Thermodynamics ,QC310.15-319 ,Mathematics ,QA1-939 ,Analysis ,QA299.6-433 - Abstract
In this paper, a new type of convexity is defined, namely, the left–right-(k,h-m)-p IVM (set-valued function) convexity. Utilizing the definition of this new convexity, we prove the Hadamard inequalities for noninteger Katugampola integrals. These inequalities generalize the noninteger Hadamard inequalities for a convex IVM, (p,h)-convex IVM, p-convex IVM, h-convex, s-convex in the second sense and many other related well-known classes of functions implicitly. An apt number of numerical examples are provided as supplements to the derived results.
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- 2022
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16. Fixed Points for (ξ,ω)-Weakly Cyclic Type Generalized Contraction Condition in Metric Spaces with an Application
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Penumarthy Parvateesam Murthy, Pusplata Sahu, Amr Elsonbaty, Khizar Hyatt Khan, Rajagopalan Ramaswamy, and Stojan Radenović
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fixed point ,cyclic representation ,altering distance function ,(ξ,ω)-weakly cyclic generalized contraction ,boundary value problem ,Mathematics ,QA1-939 - Abstract
In the present work, we have introduced a new type of (ξ,ω)-weakly cyclic generalized contraction in the setting of metric spaces and established some fixed-point results. Fixed-point results are useful in establishing the existence of unique solution to differential equations. We have supplemented the derived results with suitable non-trivial examples with an application to the Boundary Value Problem, generalizing some known results. The analytical result has been verified with numerical simulation.
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- 2022
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17. Fixed Points on Covariant and Contravariant Maps with an Application
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Rajagopalan Ramaswamy, Gunaseelan Mani, Arul Joseph Gnanaprakasam, Ola A. Ashour Abdelnaby, Vuk Stojiljković, Slobodan Radojevic, and Stojan Radenović
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C★-algebra-valued bipolar metric space ,covariant maps ,contravariant maps ,common fixed point ,Mathematics ,QA1-939 - Abstract
Fixed-point results on covariant maps and contravariant maps in a C★-algebra-valued bipolar metric space are proved. Our results generalize and extend some recently obtained results in the existing literature. Our theoretical results in this paper are supported with suitable examples. We have also provided an application to find an analytical solution to the integral equation and the electrical circuit differential equation.
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- 2022
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18. Common Fixed Point Theorems on Orthogonal Branciari Metric Spaces with an Application
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Gunaseelan Mani, Senthil Kumar Prakasam, Arul Joseph Gnanaprakasam, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, Khizar Hyatt Khan, and Stojan Radenović
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fixed point ,simulation functions ,orthogonal Rectangular metric space ,orthogonal α-admissible functions ,Mathematics ,QA1-939 - Abstract
In this article, we modify the symmetry of orthogonal metric spaces and we prove common fixed point theorems via simulation functions in orthogonal Rectangular metric spaces. We also provide an illustrative example to support our results. The derived results have been applied to find analytical solutions to integral equations. The analytical solutions are verified with a numerical simulation.
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- 2022
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19. Some New Results for (α, β)-Admissible Mappings in 𝔽-Metric Spaces with Applications to Integral Equations
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Hamid Faraji, Nikola Mirkov, Zoran D. Mitrović, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, and Stojan Radenović
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(α, β)-admissible mapping ,?-complete ,fixed point ,?-metric space ,Mathematics ,QA1-939 - Abstract
In this paper, we consider and extend some fixed point results in F-complete F-metric spaces by relaxing the symmetry of complete metric spaces. We generalize α,β-admissible mappings in the setting of F-metric spaces. The derived results are supplemented with suitable examples, and the obtained results are applied to find the existence of the solution to the integral equation. The analytical results are compared through numerical simulation. We pose certain open problems for extending and applying our results in the future.
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- 2022
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20. Common Fixed Point for Meir–Keeler Type Contraction in Bipolar Metric Space
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Penumarthy Parvateesam Murthy, Chandra Prakash Dhuri, Santosh Kumar, Rajagopalan Ramaswamy, Muhannad Abdullah Saud Alaskar, and Stojan Radenovi’c
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fixed points ,bipolar metric space ,covariant map ,compatible maps ,Cauchy bisequence ,Thermodynamics ,QC310.15-319 ,Mathematics ,QA1-939 ,Analysis ,QA299.6-433 - Abstract
In mathematical analysis, the Hausdorff derivatives or the fractal derivatives play an important role. Fixed-point theorems and metric fixed-point theory have varied applications in establishing a unique common solution to differential equations and integral equations. In the present work, some fixed-point theorems using the extension of Meir–Keeler contraction in the setting of bipolar metric spaces have been proved. The derived results have been supplemented with non-trivial examples. Our results extend and generalise the results established in the past. We have provided an application to find an analytical solution to an Integral Equation to supplement the derived result.
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- 2022
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21. Solution of Integral Equation with Neutrosophic Rectangular Triple Controlled Metric Spaces
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Gunaseelan Mani, Rajagopalan Ramaswamy, Arul Joseph Gnanaprakasam, Ola A Ashour Abdelnaby, Slobodan Radojevic, and Stojan Radenović
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neutrosophic metric space ,neutrosophic rectangular triple-controlled metric space ,fixed point results ,integral equation ,Mathematics ,QA1-939 - Abstract
In this paper, we introduce the notion of neutrosophic rectangular triple-controlled metric space, relaxing the symmetry requirement of neutrosophic metric spaces, by replacing triangular inequalities with rectangular inequalities, and prove fixed point theorems. We have derived several interesting results for contraction mappings supplemented with non-trivial examples. The derived results have been applied to prove the existence of a unique analytical solution as well as a closed form of the unique solution to the integral equation.
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- 2022
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22. An Application to Fixed-Point Results in Tricomplex-Valued Metric Spaces Using Control Functions
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Rajagopalan Ramaswamy, Gunaseelan Mani, Arul Joseph Gnanaprakasam, Ola A. Ashour Abdelnaby, and Stojan Radenović
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common fixed point ,TVMS ,complete TVMS ,Cauchy sequence ,fixed point ,Mathematics ,QA1-939 - Abstract
In the present work, we establish fixed-point results for a pair of mappings satisfying some contractive conditions on rational expressions with coefficients as point-dependent control functions in the setting of tricomplex-valued metric spaces. The proven results are extension and generalisation of some of the literature’s well-known results. We also explore some of the applications to our key results.
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- 2022
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23. Riemann-Liouville Fractional Inclusions for Convex Functions Using Interval Valued Setting
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Vuk Stojiljković, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, and Stojan Radenović
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convex interval-valued functions ,pseudo-order relations ,Hermite–Hadamard inequality ,Riemann–Liouville fractional integral operators ,fuzzy interval-valued analysis ,Mathematics ,QA1-939 - Abstract
In this work, various fractional convex inequalities of the Hermite–Hadamard type in the interval analysis setting have been established, and new inequalities have been derived thereon. Recently defined p interval-valued convexity is utilized to obtain many new fractional Hermite–Hadamard type convex inequalities. The derived results have been supplemented with suitable numerical examples. Our results generalize some recently reported results in the literature.
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- 2022
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24. Hermite–Hadamard Type Inequalities Involving (k-p) Fractional Operator for Various Types of Convex Functions
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Vuk Stojiljković, Rajagopalan Ramaswamy, Fahad Alshammari, Ola A. Ashour, Mohammed Lahy Hassan Alghazwani, and Stojan Radenović
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Hermite–Hadamard inequality ,(h,m)-convex function ,Hölder inequality ,(p,h)-convex function ,fractional inequality ,Thermodynamics ,QC310.15-319 ,Mathematics ,QA1-939 ,Analysis ,QA299.6-433 - Abstract
We establish various fractional convex inequalities of the Hermite–Hadamard type with addition to many other inequalities. Various types of such inequalities are obtained, such as (p,h) fractional type inequality and many others, as the (p,h)-convexity is the generalization of the other convex inequalities. As a consequence of the (h,m)-convexity, the fractional inequality of the (s,m)-type is obtained. Many consequences of such fractional inequalities and generalizations are obtained.
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- 2022
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25. A neural system dynamics modeling platform and its applications in randomized controlled trial data analysis
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Nadira Hamid, Joydeep Sarkar, Bjorn Redfors, Anisha Balani, Rajagopalan Ramaswamy, Abhijit Ghosh, Maria Alu, Aaron Crowley, Yiran Zhang, Martin B. Leon, Gregg W. Stone, and Juan F. Granada
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Clinical trials ,Analysis ,Neural networks ,System dynamics ,Computer applications to medicine. Medical informatics ,R858-859.7 - Abstract
Background: Conventional statistical methods used in clinical trials lack the ability to predict patient specific risk and very often do not consider the effects of time varying interventions. The aim of this study is to test a novel artificial neural network based model for clinical trial analysis to represent the continuous time evolution of risk. Methods: The novel methodology tested utilizes system dynamics and artificial neural networks. This methodology was applied to analyze data from 2,221 patients with acute myocardial infarction enrolled in a well characterized randomized study, the HORIZONS-AMI trial. Outcomes analyzed included: (1) target lesion revascularization (TLR) and (2) stent thrombosis. The proposed neural system dynamics (NSD) model was compared against traditional Cox Proportional Hazards (Cox PH) and Cox neural network (NN) models. Model performance was evaluated using C-statistic at 1, 2 -and 3- years follow-up and model-based simulation studies were performed to examine the effect of different variables on the predicted risk of TLR and stent thrombosis. Results: The NSD model achieved comparable performance to Cox models for TLR. For stent thrombosis, the NSD model outperformed Cox models (1-year C-statistic: Stent thrombosis – Cox PH: 0.60, Cox NN: 0.66, neural SD model: 0.69). The neural SD model identified clinically relevant variables such as stent count, stent type and multiple lesions treated as significant predictors for TLR; and stent count and peak platelet count for stent thrombosis. Simulations illustrated change in predicted TLR risk maximal for the neural SD model, compared to other models. For stent thrombosis, simulation scenario illustrated predicted event rate doubling when clopidogrel is discontinued at 6 months compared to extended use. Conclusions: We have demonstrated an alternative analytical methodology that combines system dynamics and artificial neural networks to analyze results from a randomized trial. This novel approach can incorporate patient-specific longitudinal data and provide personalized risk prediction.
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- 2021
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26. An Application of Urysohn Integral Equation via Complex Partial Metric Space
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Rajagopalan Ramaswamy, Gunaseelan Mani, Arul Joseph Gnanaprakasam, Ola A. Ashour Abdelnaby, and Stojan Radenović
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Urysohn integral equations ,common fixed points ,complex partial metric space ,Mathematics ,QA1-939 - Abstract
Metric fixed point theory has vast applications in various domain areas, as it helps in finding analytical solutions under various contractive conditions, including non-linear integral-type contractions. In our present work, we have established fixed point results in the setting of complex valued partial metric space. Our results extend the results proven in literature. Using our main result, we have provided an application to find the solution to the Urysohn-type integral equation.
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- 2022
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27. Room temperature magnetization switching in topological insulator-ferromagnet heterostructures by spin-orbit torques
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Yi Wang, Dapeng Zhu, Yang Wu, Yumeng Yang, Jiawei Yu, Rajagopalan Ramaswamy, Rahul Mishra, Shuyuan Shi, Mehrdad Elyasi, Kie-Leong Teo, Yihong Wu, and Hyunsoo Yang
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Science - Abstract
The application of spin-orbit torque in topological insulator heterostructures is limited only under low temperature. Here, the authors report room temperature magnetization switching in topological insulator-ferromagnet heterostructures by spin-orbit torques.
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- 2017
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28. Some Generalized Contraction Classes and Common Fixed Points in b-Metric Space Endowed with a Graph
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Reny George, Hossam A. Nabwey, Rajagopalan Ramaswamy, and Stojan Radenović
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(?, Ψ*, G, γs) contractions ,directed graph ,R-Weakly graph preserving ,rational contractions ,R-weakly α-admissible ,Mathematics ,QA1-939 - Abstract
We have introduced the new notions of R-weakly graph preserving and R-weakly α -admissible pair of multivalued mappings which includes the class of graph preserving mappings, weak graph preserving mappings as well as α -admissible mappings of type S, α * -admissible mappings of type S and α * - orbital admissible mappings of type S respectively. Some generalized contraction and rational contraction classes are also introduced for a pair of multivalued mappings and common fixed point theorems are proved in a b-metric space endowed with a graph. We have also applied our results to obtain common fixed point theorems for R-weakly α -admissible pair of multivalued mappings in a b-metric space which are the proper extension and generalization of many known results. Proper examples are provided in support of our results. Our main results and its consequences improve, generalize and extend many known fixed point results existing in literature.
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- 2019
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29. Application of fixed point results in the setting of $ \mathcal{F} $-contraction and simulation function in the setting of bipolar metric space
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Gunaseelan Mani, Rajagopalan Ramaswamy, Arul Joseph Gnanaprakasam, Vuk Stojiljković, Zaid. M. Fadail, and Stojan Radenović
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General Mathematics - Abstract
In the present work, simulation function is applied to establish fixed point results of $ \mathcal{F} $-contraction in the setting of Bi-polar metric space. Our results are extensions or generalizations of results proved in the literature. The derived results are substantiated with suitable examples and an application to find the solution to the integral equation.
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- 2023
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30. Fixed point theorem on an orthogonal extended interpolative $ \psi\mathcal{F} $-contraction
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Menaha Dhanraj, Arul Joseph Gnanaprakasam, Gunaseelan Mani, Rajagopalan Ramaswamy, Khizar Hyatt Khan, Ola Ashour A. Abdelnaby, and Stojan Radenović
- Subjects
General Mathematics - Abstract
In this paper, we establish the fixed point results for an orthogonal extended interpolative Ciric Reich-Rus type $ \psi\mathcal{F} $-contraction mapping on an orthogonal complete $ \mathfrak{b} $-metric spaces and give an example to strengthen our main results. Furthermore, we present an application to fixed point results to find analytical solutions for functional equation.
- Published
- 2023
- Full Text
- View/download PDF
31. (α − ψ) Meir–Keeler Contractions in Bipolar Metric Spaces
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Radenović, Manoj Kumar, Pankaj Kumar, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, Amr Elsonbaty, and Stojan
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fixed point ,(α − ψ) Meir–Keeler contractive mappings ,covariant and contravariant mappings ,bipolar metric space - Abstract
In this paper, we introduce the new notion of contravariant (α−ψ) Meir–Keeler contractive mappings by defining α-orbital admissible mappings and covariant Meir–Keeler contraction in bipolar metric spaces. We prove fixed point theorems for these contractions and also provide some corollaries of main results. An example is also be given in support of our main result. In the end, we also solve an integral equation using our result.
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- 2023
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32. Some New Results for (α, β)-Admissible Mappings in 𝔽-Metric Spaces with Applications to Integral Equations
- Author
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Radenović, Hamid Faraji, Nikola Mirkov, Zoran D. Mitrović, Rajagopalan Ramaswamy, Ola A. Ashour Abdelnaby, and Stojan
- Subjects
(α, β)-admissible mapping ,?-complete ,fixed point ,?-metric space - Abstract
In this paper, we consider and extend some fixed point results in F-complete F-metric spaces by relaxing the symmetry of complete metric spaces. We generalize α,β-admissible mappings in the setting of F-metric spaces. The derived results are supplemented with suitable examples, and the obtained results are applied to find the existence of the solution to the integral equation. The analytical results are compared through numerical simulation. We pose certain open problems for extending and applying our results in the future.
- Published
- 2022
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- View/download PDF
33. On exact solutions of fractional differential-difference equations with Ψ-Riemann–Liouville derivative
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Rajagopalan Ramaswamy, Mohamed S. Abdel Latif, Amr Elsonbaty, and Abas H. Abdel Kader
- Subjects
Mechanics of Materials ,Applied Mathematics ,Modeling and Simulation ,Computational Mechanics ,General Physics and Astronomy ,Statistical and Nonlinear Physics ,Engineering (miscellaneous) - Abstract
The aim of this work is to modify the invariant subspace method (ISM) in order to obtain closed form solutions of fractional differential-difference equations with Ψ-Riemann–Liouville (Ψ-RL) fractional derivative for first time. We have investigated the cases of two-dimensional and the three-dimensional invariant subspaces (ISs) in the suggested scheme. Using the modified ISM, new exact generalized solutions for the general fractional mKdV Lattice equation and the fractional Volterra lattice system are obtained. Compared with similar solution techniques in literature, the presented solution scheme is highly efficient and is capable to find new general exact solutions which cannot be attained by other methods.
- Published
- 2022
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- View/download PDF
34. DYNAMICAL ANALYSIS OF A NOVEL DISCRETE FRACTIONAL SITRS MODEL FOR COVID-19
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Waleed Adel, Zulqurnain Sabir, Amr Elsonbaty, and Rajagopalan Ramaswamy
- Subjects
2019-20 coronavirus outbreak ,Coronavirus disease 2019 (COVID-19) ,Applied Mathematics ,Modeling and Simulation ,Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ,Pandemic ,medicine ,Geometry and Topology ,Biology ,medicine.disease_cause ,Virology ,Coronavirus - Abstract
In this paper, a discrete fractional Susceptible-Infected-Treatment-Recovered-Susceptible (SITRS) model for simulating the coronavirus (COVID-19) pandemic is presented. The model is a modification to a recent continuous-time SITR model by taking into account the possibility that people who have been infected before can lose their temporary immunity and get reinfected. Moreover, a modification is suggested in the present model to correct the improper assumption that the infection rates of both normal susceptible and old aged/seriously diseased people are equal. This modification complies with experimental data. The equilibrium points for the proposed model are found and results of thorough stability analysis are discussed. A full numerical simulation is carried out and gives a better analysis of the disease spread, influences of model’s parameters, and how to control the virus. Comparisons with clinical data are also provided.
- Published
- 2021
- Full Text
- View/download PDF
35. Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO3–LaAlO3 Oxide Interface
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Mallikarjuna Rao Motapothula, Yi Wang, Jiawei Yu, Rajagopalan Ramaswamy, Thirumalai Venkatesan, Hyunsoo Yang, Kulothungasagaran Narayanapillai, and Dapeng Zhu
- Subjects
Band gap ,Oxide ,FOS: Physical sciences ,Bioengineering ,Insulator (electricity) ,02 engineering and technology ,01 natural sciences ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,General Materials Science ,010306 general physics ,Quantum tunnelling ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Spintronics ,Condensed matter physics ,Chemistry ,Mechanical Engineering ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Ferromagnetic resonance ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,Fermi gas - Abstract
Two-dimensional electron gas (2DEG) formed at the interface between SrTiO3 (STO) and LaAlO3 (LAO) insulating layer is supposed to possess strong Rashba spin-orbit coupling. To date, the inverse Edelstein effect (i.e. spin-to-charge conversion) in the 2DEG layer is reported. However, the direct effect of charge-to-spin conversion, an essential ingredient for spintronic devices in a current induced spin-orbit torque scheme, has not been demonstrated yet. Here we show, for the first time, a highly efficient spin generation with the efficiency of ~6.3 in the STO/LAO/CoFeB structure at room temperature by using spin torque ferromagnetic resonance. In addition, we suggest that the spin transmission through the LAO layer at high temperature range is attributed to the inelastic tunneling via localized states in the LAO band gap. Our findings may lead to potential applications in the oxide insulator based spintronic devices., Comment: 16 pages, 4 figures
- Published
- 2017
- Full Text
- View/download PDF
36. Room temperature magnetization switching in topological insulator-ferromagnet heterostructures by spin-orbit torques
- Author
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Yumeng Yang, Dapeng Zhu, Yang Wu, Hyunsoo Yang, Rajagopalan Ramaswamy, Rahul Mishra, Yihong Wu, Shuyuan Shi, Mehrdad Elyasi, Jiawei Yu, Kie Leong Teo, and Yi Wang
- Subjects
Materials science ,Kerr effect ,Science ,General Physics and Astronomy ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Article ,Magnetization ,Condensed Matter::Materials Science ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,010306 general physics ,lcsh:Science ,Surface states ,Condensed Matter - Materials Science ,Multidisciplinary ,Spintronics ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Ferromagnetism ,Topological insulator ,lcsh:Q ,Condensed Matter::Strongly Correlated Electrons ,Astrophysics::Earth and Planetary Astrophysics ,0210 nano-technology ,Current density ,Order of magnitude - Abstract
Topological insulators with spin-momentum-locked topological surface states are expected to exhibit a giant spin-orbit torque in the topological insulator/ferromagnet systems. To date, the topological insulator spin-orbit torque-driven magnetization switching is solely reported in a Cr-doped topological insulator at 1.9 K. Here we directly show giant spin-orbit torque-driven magnetization switching in a Bi2Se3/NiFe heterostructure at room temperature captured using a magneto-optic Kerr effect microscope. We identify a large charge-to-spin conversion efficiency of ~1–1.75 in the thin Bi2Se3 films, where the topological surface states are dominant. In addition, we find the current density required for the magnetization switching is extremely low, ~6 × 105 A cm–2, which is one to two orders of magnitude smaller than that with heavy metals. Our demonstration of room temperature magnetization switching of a conventional 3d ferromagnet using Bi2Se3 may lead to potential innovations in topological insulator-based spintronic applications., The application of spin-orbit torque in topological insulator heterostructures is limited only under low temperature. Here, the authors report room temperature magnetization switching in topological insulator-ferromagnet heterostructures by spin-orbit torques.
- Published
- 2017
37. Some Generalized Contraction Classes and Common Fixed Points in b-Metric Space Endowed with a Graph
- Author
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Hossam A. Nabwey, Reny George, Rajagopalan Ramaswamy, and Stojan Radenović
- Subjects
General Mathematics ,Fixed point ,directed graph ,01 natural sciences ,Combinatorics ,R-Weakly graph preserving ,Computer Science (miscellaneous) ,0101 mathematics ,Engineering (miscellaneous) ,Mathematics ,(C,Ψ*,G,γs) contractions ,lcsh:Mathematics ,010102 general mathematics ,Directed graph ,lcsh:QA1-939 ,R-weakly α-admissible ,010101 applied mathematics ,Metric space ,TheoryofComputation_MATHEMATICALLOGICANDFORMALLANGUAGES ,Generalized contraction ,Common fixed point ,Graph (abstract data type) ,Computer Science::Programming Languages ,rational contractions ,(?, Ψ*, G, γs) contractions - Abstract
We have introduced the new notions of R-weakly graph preserving and R-weakly &alpha, admissible pair of multivalued mappings which includes the class of graph preserving mappings, weak graph preserving mappings as well as &alpha, admissible mappings of type S, &alpha, * -admissible mappings of type S and &alpha, * - orbital admissible mappings of type S respectively. Some generalized contraction and rational contraction classes are also introduced for a pair of multivalued mappings and common fixed point theorems are proved in a b-metric space endowed with a graph. We have also applied our results to obtain common fixed point theorems for R-weakly &alpha, admissible pair of multivalued mappings in a b-metric space which are the proper extension and generalization of many known results. Proper examples are provided in support of our results. Our main results and its consequences improve, generalize and extend many known fixed point results existing in literature.
- Published
- 2019
- Full Text
- View/download PDF
38. Effect of (CoxFe1−x)80B20 Composition on the Magnetic Properties of the Free Layer in Double-Barrier Magnetic Tunnel Junctions
- Author
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Shalabh Srivastava, Hyunsoo Yang, Kangho Lee, Yuan Ping Feng, Kazutaka Yamane, Mohammad S. M. Saifullah, Tanmay Dutta, Jaesung Son, Rajagopalan Ramaswamy, Kie Leong Teo, and Andy Paul Chen
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Perpendicular magnetic anisotropy ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Double barrier ,01 natural sciences ,Magnetic anisotropy ,0103 physical sciences ,Thermal stability ,Current (fluid) ,0210 nano-technology ,Layer (electronics) - Abstract
The Co-Fe-B/MgO system with perpendicular magnetic anisotropy finds extensive application in modern magnetic memories. Critical issues for the practical usage of magnetic tunnel junctions (MTJs) include the limited thermal stability of bit storage, and low switching efficiency. This study elucidates the deterministic influence of Co-Fe-B composition and the MgO interface on an MTJ's fundamental magnetic properties, which affect both thermal stability and switching current. Furthermore, the authors observe an anomalous trend in saturation magnetization, which is attributed to a change in magnetic anisotropy.
- Published
- 2018
- Full Text
- View/download PDF
39. Long spin coherence length and bulk-like spin-orbit torque in ferrimagnetic multilayers
- Author
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Kyung Jin Lee, Rajagopalan Ramaswamy, Hyeon-Jong Park, Gyungchoon Go, Hyunsoo Yang, Rahul Mishra, Xuepeng Qiu, Shuyuan Shi, Jung Hyun Oh, Yi Wang, Do Bang, Hiroyuki Awano, Yunboo Jeong, Jiawei Yu, Pham Van Thach, Seo Won Lee, and Dongkyu Lee
- Subjects
Materials science ,FOS: Physical sciences ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Atomic units ,Condensed Matter::Materials Science ,Ferrimagnetism ,Torque ,General Materials Science ,Spin-½ ,Condensed Matter - Materials Science ,Spintronics ,Condensed matter physics ,Mechanical Engineering ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Coherence length ,Transverse plane ,Ferromagnetism ,Mechanics of Materials ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology - Abstract
Ferromagnetic spintronics has been a main focus as it offers non-volatile memory and logic applications through current-induced spin-transfer torques. Enabling wider applications of such magnetic devices requires a lower switching current for a smaller cell while keeping the thermal stability of magnetic cells for non-volatility. As the cell size reduces, however, it becomes extremely difficult to meet this requirement with ferromagnets because spin-transfer torque for ferromagnets is a surface torque due to rapid spin dephasing, leading to the 1/ferromagnet-thickness dependence of the spin-torque efficiency. Requirement of a larger switching current for a thicker and thus more thermally stable ferromagnetic cell is the fundamental obstacle for high-density non-volatile applications with ferromagnets. Theories predicted that antiferromagnets have a long spin coherence length due to the staggered spin order on an atomic scale, thereby resolving the above fundamental limitation. Despite several spin-torque experiments on antiferromagnets and ferrimagnetic alloys, this prediction has remained unexplored. Here we report a long spin coherence length and associated bulk-like-torque characteristic in an antiferromagnetically coupled ferrimagnetic multilayer. We find that a transverse spin current can pass through > 10 nm-thick ferrimagnetic Co/Tb multilayers whereas it is entirely absorbed by 1 nm-thick ferromagnetic Co/Ni multilayer. We also find that the switching efficiency of Co/Tb multilayers partially reflects a bulk-like-torque characteristic as it increases with the ferrimagnet-thickness up to 8 nm and then decreases, in clear contrast to 1/thickness-dependence of Co/Ni multilayers. Our results on antiferromagnetically coupled systems will invigorate researches towards energy-efficient spintronic technologies.
- Published
- 2018
40. Observation of Out-of-Plane Spin Texture in a SrTiO3(111) Two-Dimensional Electron Gas
- Author
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Hyunsoo Yang, Kaiming Cai, S. McKeown Walker, M. S. Bahramy, Jong Min Lee, Olle Heinonen, Steven S.-L. Zhang, Felix Baumberger, Giovanni Vignale, Rajagopalan Ramaswamy, Flavio Y. Bruno, and Pan He
- Subjects
Physics ,Condensed matter physics ,General Physics and Astronomy ,Order (ring theory) ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic field ,0103 physical sciences ,Texture (crystalline) ,010306 general physics ,0210 nano-technology ,Electronic band structure ,Fermi gas ,Rashba effect ,Spin-½ - Abstract
We explore the second order bilinear magnetoelectric resistance (BMER) effect in the $d$-electron-based two-dimensional electron gas $(2\mathrm{DEG})$ at the ${\mathrm{SrTiO}}_{3}(111)$ surface. We find evidence of a spin-split band structure with the archetypal spin-momentum locking of the Rashba effect for the in-plane component. Under an out-of-plane magnetic field, we find a BMER signal that breaks the sixfold symmetry of the electronic dispersion, which is a fingerprint for the presence of a momentum-dependent out-of-plane spin component. Relativistic electronic structure calculations reproduce this spin texture and indicate that the out-of-plane component is a ubiquitous property of oxide 2DEGs arising from strong crystal field effects. We further show that the BMER response of the ${\mathrm{SrTiO}}_{3}(111)$ 2DEG is tunable and unexpectedly large.
- Published
- 2018
- Full Text
- View/download PDF
41. Field-Free Spin-Orbit Torque Switching from Geometrical Domain-Wall Pinning
- Author
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Guang Yang, Hyunsoo Yang, Pan He, Yang Liu, Rajagopalan Ramaswamy, Kaiming Cai, and Jong Min Lee
- Subjects
Field (physics) ,FOS: Physical sciences ,Bioengineering ,02 engineering and technology ,01 natural sciences ,Magnetization ,0103 physical sciences ,Torque ,General Materials Science ,Spin-½ ,010302 applied physics ,Coupling ,Physics ,Condensed Matter - Materials Science ,Condensed matter physics ,Spintronics ,Mechanical Engineering ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Magnetic field ,Domain wall (magnetism) ,Condensed Matter::Strongly Correlated Electrons ,Astrophysics::Earth and Planetary Astrophysics ,0210 nano-technology - Abstract
Spin-orbit torques, which utilize spin currents arising from the spin-orbit coupling, offer a novel method to electrically switch the magnetization with perpendicular anisotropy. However, the necessity of an external magnetic field to achieve a deterministic switching is an obstacle for realizing practical spin-orbit torque devices with all-electric operation. Here, we report a field-free spin-orbit torque switching by exploiting the domain wall motion in an anti-notched microwire with perpendicular anisotropy, which exhibits multi-domain states stabilized by the domain wall surface tension. The combination of spin-orbit torque, Dzyaloshinskii-Moriya interaction, and domain wall surface tension induced geometrical pinning allows a deterministic control of the domain wall and offers a novel method to achieve a field-free spin-orbit torque switching. Our work demonstrates the proof of concept of a perpendicular memory cell which can be readily adopted in a three-terminal magnetic memory., 19 pages, 5 figures
- Published
- 2018
42. Observation of Out-of-Plane Spin Texture in a SrTiO_{3}(111) Two-Dimensional Electron Gas
- Author
-
Pan, He, S McKeown, Walker, Steven S-L, Zhang, F Y, Bruno, M S, Bahramy, Jong Min, Lee, Rajagopalan, Ramaswamy, Kaiming, Cai, Olle, Heinonen, Giovanni, Vignale, F, Baumberger, and Hyunsoo, Yang
- Abstract
We explore the second order bilinear magnetoelectric resistance (BMER) effect in the d-electron-based two-dimensional electron gas (2DEG) at the SrTiO_{3}(111) surface. We find evidence of a spin-split band structure with the archetypal spin-momentum locking of the Rashba effect for the in-plane component. Under an out-of-plane magnetic field, we find a BMER signal that breaks the sixfold symmetry of the electronic dispersion, which is a fingerprint for the presence of a momentum-dependent out-of-plane spin component. Relativistic electronic structure calculations reproduce this spin texture and indicate that the out-of-plane component is a ubiquitous property of oxide 2DEGs arising from strong crystal field effects. We further show that the BMER response of the SrTiO_{3}(111) 2DEG is tunable and unexpectedly large.
- Published
- 2018
43. Oscillatory spin-orbit torque switching induced by field-like torques
- Author
-
Shalabh Srivastava, Xuepeng Qiu, Hyunsoo Yang, Jaesung Son, Jong Min Lee, Rahul Mishra, Jungbum Yoon, Jae Hyun Kwon, Kaiming Cai, and Rajagopalan Ramaswamy
- Subjects
Magnetic domain ,Bistability ,Magnetism ,FOS: Physical sciences ,General Physics and Astronomy ,lcsh:Astrophysics ,02 engineering and technology ,01 natural sciences ,Magnetization ,lcsh:QB460-466 ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Torque ,010306 general physics ,Computer Science::Databases ,Physics ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Materials Science (cond-mat.mtrl-sci) ,Pulse duration ,021001 nanoscience & nanotechnology ,lcsh:QC1-999 ,Domain wall (magnetism) ,Magnet ,Astrophysics::Earth and Planetary Astrophysics ,0210 nano-technology ,lcsh:Physics - Abstract
Deterministic magnetization switching using spin-orbit torque (SOT) has recently emerged as an efficient means to electrically control the magnetic state of ultrathin magnets. The SOT switching still lacks in oscillatory switching characteristics over time, therefore, it is limited to bipolar operation where a change in polarity of the applied current or field is required for bistable switching. The coherent rotation based oscillatory switching schemes cannot be applied to SOT, because the SOT switching occurs through expansion of magnetic domains. Here we experimentally achieve oscillatory switching in incoherent SOT process by controlling domain wall dynamics. We find that a large field-like component can dynamically influence the domain wall chirality which determines the direction of SOT switching. Consequently, under nanosecond current pulses, the magnetization switches alternatively between the two stable states. By utilizing this oscillatory switching behavior, we demonstrate a unipolar deterministic SOT switching scheme by controlling the current pulse duration. Magnetism plays a key role in data storage devices. This paper reports on the experimental observation of spin-orbit torque-driven oscillatory switching due to field-like torque and finds that the magnetization can be switched back through using appropriate pulse duration.
- Published
- 2018
- Full Text
- View/download PDF
44. Efficient Charge-Spin Conversion and Magnetization Switching though Rashba Effect at Topological Insulator/Ag Interface
- Author
-
Lei Shen, Shuyuan Shi, Yuan Ping Feng, Yi Wang, Aizhu Wang, Seongshik Oh, Dapeng Zhu, Hyunsoo Yang, Rajagopalan Ramaswamy, Jisoo Moon, and Jiawei Yu
- Subjects
Physics ,Condensed Matter - Materials Science ,Spin polarization ,Condensed Matter - Mesoscale and Nanoscale Physics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Charge (physics) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferromagnetic resonance ,Magnetization ,Crystallography ,Topological insulator ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Nuclear Experiment ,Rashba effect ,Surface states ,Spin-½ - Abstract
We report the observation of efficient charge-to-spin conversion in the three-dimensional topological insulator (TI) $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ and Ag bilayer by the spin-torque ferromagnetic resonance technique. The spin-orbit-torque ratio in the $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}/\mathrm{Ag}/\mathrm{CoFeB}$ heterostructure shows a significant enhancement as the Ag thickness increases to \ensuremath{\sim}2 nm and reaches a value of 0.5 for 5 nm Ag, which is \ensuremath{\sim}3 times higher than that of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}/\mathrm{CoFeB}$ at room temperature. The observation reveals the interfacial effect of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}/\mathrm{Ag}$ exceeds that of the topological surface states (TSSs) in the $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ layer and plays a dominant role in the charge-to-spin conversion in the $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}/\mathrm{Ag}/\mathrm{CoFeB}$ system. Based on first-principles calculations, we attribute our observation to the large Rashba splitting bands which wrap the TSS band and have the same net spin polarization direction as the TSS of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$. Subsequently, we demonstrate Rashba-induced magnetization switching in $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}/\mathrm{Ag}/\mathrm{Py}$ with a low current density of $5.8\ifmmode\times\else\texttimes\fi{}{10}^{5}\phantom{\rule{0.16em}{0ex}}\mathrm{A}/\mathrm{c}{\mathrm{m}}^{2}$.
- Published
- 2018
45. Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO
- Author
-
Yi, Wang, Rajagopalan, Ramaswamy, Mallikarjuna, Motapothula, Kulothungasagaran, Narayanapillai, Dapeng, Zhu, Jiawei, Yu, Thirumalai, Venkatesan, and Hyunsoo, Yang
- Abstract
The two-dimensional electron gas (2DEG) formed at the interface between SrTiO
- Published
- 2017
46. Extrinsic Spin Hall Effect in Cu1−xPtx
- Author
-
Mallikarjuna Rao Motapothula, Rajagopalan Ramaswamy, T. Venkatesan, Xuepeng Qiu, Yi Wang, Mehrdad Elyasi, and Hyunsoo Yang
- Subjects
Materials science ,Condensed matter physics ,Spintronics ,Annealing (metallurgy) ,Alloy ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,01 natural sciences ,Copper ,Magnetization ,CMOS ,chemistry ,0103 physical sciences ,Spin Hall effect ,engineering ,010306 general physics ,0210 nano-technology ,Platinum - Abstract
The spin Hall effect (SHE) is a means to electrically control the magnetization of a ferromagnet---one of the prime goals in spintronics. The most-studied material for exploiting the SHE is platinum, but in CMOS electronics the preferred metal is copper, which has a weak SHE. The authors show that Pt-Cu alloy with just 28% Pt can be as efficient as pure Pt at generating spin current. This alloy can also withstand high annealing temperatures, and thus can be readily incorporated into CMOS technology, nudging spintronics that much closer to widespread use.
- Published
- 2017
- Full Text
- View/download PDF
47. Interfacial Rashba magnetoresistance of the two-dimensional electron gas at the LaAlO3 / SrTiO3 interface
- Author
-
Kalon Gopinadhan, Hyunsoo Yang, Rajagopalan Ramaswamy, Gyungchoon Go, Hyun-Woo Lee, Kulothungasagaran Narayanapillai, Dongwook Go, Kyung Jin Lee, and Thirumalai Venkatesan
- Subjects
Superconductivity ,Materials science ,Condensed matter physics ,Magnetoresistance ,Exchange interaction ,02 engineering and technology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Condensed Matter::Materials Science ,Ferromagnetism ,0103 physical sciences ,Spin Hall effect ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Fermi gas ,Spin (physics) - Abstract
We report the angular dependence of magnetoresistance in the two-dimensional electron gas at the ${\mathrm{LaAlO}}_{3}$/${\mathrm{SrTiO}}_{3}$ interface. We find that this interfacial magnetoresistance exhibits a similar angular dependence to the spin Hall magnetoresistance observed in ferromagnet/heavy metal bilayers, which has been so far discussed in the framework of the bulk spin Hall effect of the heavy metal layer. The observed magnetoresistance is in qualitative agreement with a theoretical model calculation including both Rashba spin-orbit coupling and an exchange interaction. Our result suggests that magnetic interfaces subject to spin-orbit coupling can generate a non-negligible contribution to the spin Hall magnetoresistance, and the interfacial spin-orbit coupling effect is therefore key to the understanding of various spin-orbit-coupling-related phenomena in magnetic/nonmagnetic bilayers.
- Published
- 2017
- Full Text
- View/download PDF
48. Spin orbit torque driven magnetization switching with sputtered Bi2Se3 spin current source
- Author
-
Tanmay Dutta, Shiheng Liang, Mohammad S. M. Saifullah, Guang Yang, Rajagopalan Ramaswamy, and Hyunsoo Yang
- Subjects
Materials science ,Acoustics and Ultrasonics ,Condensed matter physics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Magnetization ,Ferromagnetism ,Sputtering ,Topological insulator ,0103 physical sciences ,Orbit (dynamics) ,Torque ,010306 general physics ,0210 nano-technology ,Molecular beam epitaxy ,Spin-½ - Abstract
Current induced spin orbit torques (SOTs) offer an efficient pathway to manipulate the magnetization of a ferromagnet for future magnetic memories and logic devices. Among the various non-magnets utilized, the topological insulators, such as Bi2Se3, have proven to be one of most efficient spin current generators for SOTs. So far, the preferred growth technique for such materials is the molecular beam epitaxy technique which is not compatible with the magnetic memory industry. In this study, we utilize a sputter deposited Bi2Se3 to demonstrate highly efficient SOT generation and subsequently magnetization switching.
- Published
- 2019
- Full Text
- View/download PDF
49. Enhanced Spin-Orbit Torque via Modulation of Spin Current Absorption
- Author
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Pan He, Xuepeng Qiu, William Legrand, Rajagopalan Ramaswamy, Aurelien Manchon, Yang Wu, Jiawei Yu, and Hyunsoo Yang
- Subjects
Condensed Matter - Materials Science ,Materials science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,General Physics and Astronomy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Spin current ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferromagnetic resonance ,Metal ,Ferromagnetism ,Modulation ,visual_art ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,visual_art.visual_art_medium ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Absorption (electromagnetic radiation) ,Spin orbit torque ,Spin-½ - Abstract
The magnitude of spin-orbit torque (SOT), exerted to a ferromagnet (FM) from an adjacent heavy metal (HM), strongly depends on the amount of spin currents absorbed in the FM. We exploit the large spin absorption at the Ru interface to manipulate the SOTs in HM/FM/Ru multilayers. While the FM thickness is smaller than its spin dephasing length of 1.2 nm, the top Ru layer largely boosts the absorption of spin currents into the FM layer and substantially enhances the strength of SOT acting on the FM. Spin-pumping experiments induced by ferromagnetic resonance support our conclusions that the observed increase in the SOT efficiency can be attributed to an enhancement of the spin-current absorption. A theoretical model that considers both reflected and transmitted mixing conductances at the two interfaces of FM is developed to explain the results., Comment: Accepted for publication in Physical Review Letters
- Published
- 2016
50. Ferromagnet structural tuning of interfacial symmetry breaking and spin Hall angle in ferromagnet/heavy metal bilayers
- Author
-
Hyunsoo Yang, Xuepeng Qiu, Shiming Zhou, Meng Tang, Weijia Fan, Rajagopalan Ramaswamy, Huanglin Yang, and Zhong Shi
- Subjects
Permalloy ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,02 engineering and technology ,Substrate (electronics) ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferromagnetic resonance ,Ferromagnetism ,0103 physical sciences ,Texture (crystalline) ,Symmetry breaking ,010306 general physics ,0210 nano-technology ,Rashba effect ,Spin-½ - Abstract
We investigate the influence of ferromagnet crystalline structures on spin Hall angle (SHA) in ferromagnet (FM)/heavy metal (HM) bilayers with reversed stacking order. X-ray diffraction and transmission electron microscopy show that a pronounced permalloy (Py) (111) texture emerges in substrate/Ta/Py compared to that in substrate/Py/Ta. Spin torque ferromagnetic resonance measurements show that the out-of-plane SHA (θ⊥, associated with Rashba-like effective field) is ∼2 times larger in substrate/Ta/Py than that in substrate/Py/Ta, while in-plane SHA (θǁ, associated with spin Hall-like effective field) shows no distinct difference. We ascribe the FM structure dependent SHA to the interfacial symmetry breaking between the FM and HM, which is tuned by the work functions due to different crystalline structures of the FM. The emergence of the Py (111) structure enlarges the interfacial symmetry breaking and consequently enhances the Rashba effect at the FM/HM interface.
- Published
- 2018
- Full Text
- View/download PDF
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