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  1. Buch ; Online: Distributed saddle point problems for strongly concave-convex functions

    Qureshi, Muhammad I. / Khan, Usman A.

    2022  

    Abstract: In this paper, we propose GT-GDA, a distributed optimization method to solve saddle point problems of the form: $\min_{\mathbf{x}} \max_{\mathbf{y}} \{F(\mathbf{x},\mathbf{y}) :=G(\mathbf{x}) + \langle \mathbf{y}, \overline{P} \mathbf{x} \rangle - H(\ ... ...

    Abstract In this paper, we propose GT-GDA, a distributed optimization method to solve saddle point problems of the form: $\min_{\mathbf{x}} \max_{\mathbf{y}} \{F(\mathbf{x},\mathbf{y}) :=G(\mathbf{x}) + \langle \mathbf{y}, \overline{P} \mathbf{x} \rangle - H(\mathbf{y})\}$, where the functions $G(\cdot)$, $H(\cdot)$, and the the coupling matrix $\overline{P}$ are distributed over a strongly connected network of nodes. GT-GDA is a first-order method that uses gradient tracking to eliminate the dissimilarity caused by heterogeneous data distribution among the nodes. In the most general form, GT-GDA includes a consensus over the local coupling matrices to achieve the optimal (unique) saddle point, however, at the expense of increased communication. To avoid this, we propose a more efficient variant GT-GDA-Lite that does not incur the additional communication and analyze its convergence in various scenarios. We show that GT-GDA converges linearly to the unique saddle point solution when $G(\cdot)$ is smooth and convex, $H(\cdot)$ is smooth and strongly convex, and the global coupling matrix $\overline{P}$ has full column rank. We further characterize the regime under which GT-GDA exhibits a network topology-independent convergence behavior. We next show the linear convergence of GT-GDA to an error around the unique saddle point, which goes to zero when the coupling cost ${\langle \mathbf y, \overline{P} \mathbf x \rangle}$ is common to all nodes, or when $G(\cdot)$ and $H(\cdot)$ are quadratic. Numerical experiments illustrate the convergence properties and importance of GT-GDA and GT-GDA-Lite for several applications.
    Schlagwörter Mathematics - Optimization and Control ; Computer Science - Machine Learning ; Computer Science - Multiagent Systems ; Statistics - Machine Learning
    Thema/Rubrik (Code) 006
    Erscheinungsdatum 2022-02-11
    Erscheinungsland us
    Dokumenttyp Buch ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  2. Buch ; Online: Consensus-based Networked Tracking in Presence of Heterogeneous Time-Delays

    Doostmohammadian, Mohammadreza / Pirani, Mohammad / Khan, Usman A.

    2023  

    Abstract: We propose a distributed (single) target tracking scheme based on networked estimation and consensus algorithms over static sensor networks. The tracking part is based on linear time-difference-of-arrival (TDOA) measurement proposed in our previous works. ...

    Abstract We propose a distributed (single) target tracking scheme based on networked estimation and consensus algorithms over static sensor networks. The tracking part is based on linear time-difference-of-arrival (TDOA) measurement proposed in our previous works. This paper, in particular, develops delay-tolerant distributed filtering solutions over sparse data-transmission networks. We assume general arbitrary heterogeneous delays at different links. This may occur in many realistic large-scale applications where the data-sharing between different nodes is subject to latency due to communication-resource constraints or large spatially distributed sensor networks. The solution we propose in this work shows improved performance (verified by both theory and simulations) in such scenarios. Another privilege of such distributed schemes is the possibility to add localized fault-detection and isolation (FDI) strategies along with survivable graph-theoretic design, which opens many follow-up venues to this research. To our best knowledge no such delay-tolerant distributed linear algorithm is given in the existing distributed tracking literature.

    Comment: ICRoM22
    Schlagwörter Electrical Engineering and Systems Science - Systems and Control ; Electrical Engineering and Systems Science - Signal Processing ; Mathematics - Dynamical Systems
    Thema/Rubrik (Code) 006
    Erscheinungsdatum 2023-02-15
    Erscheinungsland us
    Dokumenttyp Buch ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  3. Artikel: A Case of Bilateral Adrenal Hemorrhage: The Exceptional Cause of Adrenal Insufficiency.

    Khakwani, Aemen S / Waqar, Fatima / Khan, Usman A / Anwar, Muhammad Nadeem

    Cureus

    2022  Band 14, Heft 3, Seite(n) e23413

    Abstract: Bilateral adrenal hemorrhage is an extremely uncommon and life-threatening condition. It is caused by multiple etiologies, including antiphospholipid syndrome, disseminated histoplasmosis, trauma, severe stress, and granulomatous disease. The authors ... ...

    Abstract Bilateral adrenal hemorrhage is an extremely uncommon and life-threatening condition. It is caused by multiple etiologies, including antiphospholipid syndrome, disseminated histoplasmosis, trauma, severe stress, and granulomatous disease. The authors present a unique case of a 64-year-old alcoholic male, who was admitted after fall and right hip fracture. On day seven of admission, the patient started to develop hypotension, leukocytosis, and tachycardia. CT abdomen was done, which ruled out infectious causes, however, it showed bilateral adrenal hemorrhages. Patient adrenocorticotrophic hormone (ACTH) stimulation test was positive for adrenal insufficiency and was started on hydrocortisone replacement. Our case highlights the fact that adrenal insufficiency after bilateral adrenal hemorrhage can be slow and can manifest as late as seven days and prompt therapy with steroids is warranted to avoid life-threatening adrenal insufficiency.
    Sprache Englisch
    Erscheinungsdatum 2022-03-23
    Erscheinungsland United States
    Dokumenttyp Case Reports
    ZDB-ID 2747273-5
    ISSN 2168-8184
    ISSN 2168-8184
    DOI 10.7759/cureus.23413
    Datenquelle MEDical Literature Analysis and Retrieval System OnLINE

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  4. Artikel ; Online: Surgical management of Rathke cleft cysts in pediatric patients: a single institution experience.

    Brandel, Michael G / Lin, Christine / Rennert, Robert C / Plonsker, Jillian H / Khan, Usman A / Crawford, John R / Nation, Javan / Levy, Michael L

    Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery

    2024  Band 40, Heft 5, Seite(n) 1367–1375

    Abstract: Objective: Rathke cleft cysts (RCCs) are benign, epithelial-lined sellar lesions that arise from remnants of the craniopharyngeal duct. Due to their rarity in the pediatric population, data are limited regarding the natural history and optimal ... ...

    Abstract Objective: Rathke cleft cysts (RCCs) are benign, epithelial-lined sellar lesions that arise from remnants of the craniopharyngeal duct. Due to their rarity in the pediatric population, data are limited regarding the natural history and optimal management of growing or symptomatic RCCs. We present our institutional experience with the surgical management of RCCs.
    Methods: We performed a retrospective study of consecutive RCC patients ≤ 18 years old treated surgically at our institution between 2006 and 2022.
    Results: Overall, 567 patients with a diagnosis of pituitary mass or cyst were identified. Of these, 31 had a histopathological diagnosis of RCC, 58% female and 42% male. The mean age was 13.2 ± 4.2 years. Presenting symptoms included headache (58%), visual changes (32%), and endocrinopathies or growth delay (26%); 13% were identified incidentally and subsequently demonstrated growth on serial imaging. Six percent presented with symptomatic intralesional hemorrhage. Surgical approach was transsphenoidal for 90% of patients and orbitozygomatic for 10%. Preoperative headaches resolved in 61% of patients and preoperative visual deficits improvement in 55% after surgery. New pituitary axis deficits were seen in 9.7% of patients. Only two complications occurred from a first-time surgery: one cerebrospinal fluid leak requiring lumbar drain placement, and one case of epistaxis requiring cauterization. No patients experienced new visual or neurological deficits. Patients were followed postoperatively with serial imaging at a mean follow-up was 62.9 ± 58.4 months. Recurrence requiring reoperation occurred in 32% of patients. Five-year progression-free survival was 47.9%. Except for one patient with multiple neurological deficits from a concurrent tectal glioma, all patients had a modified Rankin Scale score of 0 or 1 (good outcome) at last follow-up.
    Conclusion: Due to their secretory epithelium, pediatric RCCs may demonstrate rapid growth and can cause symptoms due to local mass effect. Surgical management of symptomatic or growing pediatric RCCs via cyst fenestration or partial resection of the cyst wall can be performed safely, with good neurologic outcomes. There is a nontrivial risk of endocrinologic injury, and long-term follow up is needed due to high recurrence rates.
    Mesh-Begriff(e) Humans ; Child ; Male ; Female ; Adolescent ; Retrospective Studies ; Carcinoma, Renal Cell ; Central Nervous System Cysts/surgery ; Kidney Neoplasms ; Cysts
    Sprache Englisch
    Erscheinungsdatum 2024-01-19
    Erscheinungsland Germany
    Dokumenttyp Journal Article
    ZDB-ID 605988-0
    ISSN 1433-0350 ; 0302-2803 ; 0256-7040
    ISSN (online) 1433-0350
    ISSN 0302-2803 ; 0256-7040
    DOI 10.1007/s00381-024-06277-z
    Datenquelle MEDical Literature Analysis and Retrieval System OnLINE

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  5. Artikel ; Online: Combined translabyrinthine, anterior petrosal approach for resection of collision vestibular schwannoma and petrous apex meningioma in neurofibromatosis type 2, with auditory brainstem implant placement.

    Khan, Usman A / Plonsker, Jillian H / Friedman, Rick A / Schwartz, Marc S

    Neurosurgical focus: Video

    2021  Band 5, Heft 2, Seite(n) V17

    Abstract: The natural history of neurofibromatosis type 2 (NF2) is profound bilateral hearing loss. The decision to pursue microsurgery may be more complicated in NF2 than with sporadic tumors. Schwannomas in NF2 often occur with other skull base tumors. Treatment ...

    Abstract The natural history of neurofibromatosis type 2 (NF2) is profound bilateral hearing loss. The decision to pursue microsurgery may be more complicated in NF2 than with sporadic tumors. Schwannomas in NF2 often occur with other skull base tumors. Treatment should be tailored to preserve auditory perception for as long as possible. The authors present the case of a man with NF2 and a vestibular schwannoma who has poor hearing on the same side as a large petrous apex meningioma, both opposite to a well-hearing ear. This case highlights surgical decision-making and technical nuances during resection of collision tumors in NF2. The video can be found here: https://stream.cadmore.media/r10.3171/2021.7.FOCVID21130.
    Sprache Englisch
    Erscheinungsdatum 2021-10-01
    Erscheinungsland United States
    Dokumenttyp Journal Article
    ISSN 2643-5217
    ISSN (online) 2643-5217
    DOI 10.3171/2021.7.FOCVID21130
    Datenquelle MEDical Literature Analysis and Retrieval System OnLINE

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  6. Artikel ; Online: Going the distance in acoustic neuroma resection: microsurgical outcomes at high-volume centers of excellence.

    Brandel, Michael G / Plonsker, Jillian H / Khan, Usman A / Rennert, Robert C / Friedman, Rick A / Schwartz, Marc S

    Journal of neuro-oncology

    2023  Band 163, Heft 1, Seite(n) 105–114

    Abstract: Purpose: High-volume hospitals are associated with improved surgical outcomes for acoustic neuromas (ANs). Due to the benign and slow-growing nature of ANs, many patients travel to geographically distant cities, states, or countries for their treatment. ...

    Abstract Purpose: High-volume hospitals are associated with improved surgical outcomes for acoustic neuromas (ANs). Due to the benign and slow-growing nature of ANs, many patients travel to geographically distant cities, states, or countries for their treatment. However, the impact of travel burden to high-volume centers, as well as its relative benefit are poorly understood. We compared post-operative outcomes between AN patients that underwent treatment at local, low-volume hospitals with those that traveled long distances to high-volume hospitals.
    Methods: The National Cancer Database was used to analyze AN patients that underwent surgery (2004-2015). Patients in the lowest quartile of travel distance and volume (Short-travel/Low-Volume: STLV) were compared to patients in the highest quartile of travel distance and volume (Long-travel/High-Volume: LTHV). Only STLV and LTHV cases were included for analysis.
    Results: Of 13,370 cases, 2,408 met inclusion criteria. STLV patients (n = 1,305) traveled a median of 6 miles (Interquartile range [IQR] 3-9) to low-volume centers (median 2, IQR 1-3 annual cases) and LTHV patients (n = 1,103) traveled a median of 143 miles [IQR 103-230, maximum 4,797] to high-volume centers (median 34, IQR 28-42 annual cases). LTHV patients had lower Charlson/Deyo scores (p = 0.001), mostly received care at academic centers (81.7% vs. 39.4%, p < 0.001), and were less likely to be minorities (7.0% vs. 24.2%, p < 0.001) or underinsured (4.2% vs. 13.8%, p < 0.001). There was no difference in average tumor size. On multivariable analysis, LTHV predicted increased likelihood of gross total resection (odds ratio [OR] 5.6, 95% confidence interval [CI] 3.8-8.4, p < 0.001), longer duration between diagnosis and surgery (OR 1.3, 95% CI 1.0-1.6, p = 0.040), decreased length of hospital stay (OR 0.5, 95% CI 0.4-0.7, p < 0.001), and greater overall survival (Hazard Ratio [HR] 0.6, 95% CI 0.4-0.95, p = 0.029). There was no significant difference in 30-day readmission on adjusted analysis.
    Conclusion: Although traveling farther to high-volume centers was associated with greater time between diagnosis and treatment for AN patients, they experienced superior postoperative outcomes compared to patients who received treatment locally at low-volume centers. Enabling access and travel to high-volume centers may improve AN patient outcomes.
    Mesh-Begriff(e) Humans ; Neuroma, Acoustic/surgery ; Proportional Hazards Models ; Medically Uninsured ; Travel ; Hospitals, High-Volume ; Retrospective Studies
    Sprache Englisch
    Erscheinungsdatum 2023-04-21
    Erscheinungsland United States
    Dokumenttyp Journal Article
    ZDB-ID 604875-4
    ISSN 1573-7373 ; 0167-594X
    ISSN (online) 1573-7373
    ISSN 0167-594X
    DOI 10.1007/s11060-023-04313-7
    Datenquelle MEDical Literature Analysis and Retrieval System OnLINE

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  7. Buch ; Online: Distributed Delay-Tolerant Strategies for Equality-Constraint Sum-Preserving Resource Allocation

    Doostmohammadian, Mohammadreza / Aghasi, Alireza / Vrakopoulou, Maria / Rabiee, Hamid R. / Khan, Usman A. / Charalambou, Themistoklis

    2023  

    Abstract: This paper proposes two nonlinear dynamics to solve constrained distributed optimization problem for resource allocation over a multi-agent network. In this setup, coupling constraint refers to resource-demand balance which is preserved at all-times. The ...

    Abstract This paper proposes two nonlinear dynamics to solve constrained distributed optimization problem for resource allocation over a multi-agent network. In this setup, coupling constraint refers to resource-demand balance which is preserved at all-times. The proposed solutions can address various model nonlinearities, for example, due to quantization and/or saturation. Further, it allows to reach faster convergence or to robustify the solution against impulsive noise or uncertainties. We prove convergence over weakly connected networks using convex analysis and Lyapunov theory. Our findings show that convergence can be reached for general sign-preserving odd nonlinearity. We further propose delay-tolerant mechanisms to handle general bounded heterogeneous time-varying delays over the communication network of agents while preserving all-time feasibility. This work finds application in CPU scheduling and coverage control among others. This paper advances the state-of-the-art by addressing (i) possible nonlinearity on the agents/links, meanwhile handling (ii) resource-demand feasibility at all times, (iii) uniform-connectivity instead of all-time connectivity, and (iv) possible heterogeneous and time-varying delays. To our best knowledge, no existing work addresses contributions (i)-(iv) altogether. Simulations and comparative analysis are provided to corroborate our contributions.
    Schlagwörter Electrical Engineering and Systems Science - Systems and Control ; Computer Science - Multiagent Systems ; Mathematics - Optimization and Control
    Thema/Rubrik (Code) 006
    Erscheinungsdatum 2023-10-27
    Erscheinungsland us
    Dokumenttyp Buch ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  8. Buch ; Online: Minimal Sufficient Conditions for Structural Observability/Controllability of Composite Networks via Kronecker Product

    Doostmohammadian, Mohammadreza / Khan, Usman A.

    2019  

    Abstract: In this paper, we consider composite networks formed from the Kronecker product of smaller networks. We find the observability and controllability properties of the product network from those of its constituent smaller networks. The overall network is ... ...

    Abstract In this paper, we consider composite networks formed from the Kronecker product of smaller networks. We find the observability and controllability properties of the product network from those of its constituent smaller networks. The overall network is modeled as a Linear-Structure-Invariant (LSI) dynamical system where the underlying matrices have a fixed zero/non-zero structure but the non-zero elements are potentially time-varying. This approach allows to model the system parameters as free variables whose values may only be known within a certain tolerance. We particularly look for minimal sufficient conditions on the observability and controllability of the composite network, which have a direct application in distributed estimation and in the design of networked control systems. The methodology in this paper is based on the structured systems analysis and graph theory, and therefore, the results are generic, i.e., they apply to almost all non-zero choices of free parameters. We show the controllability/observability results for composite product networks resulting from full structural-rank systems and self-damped networks. We provide an illustrative example of estimation based on Kalman filtering over a composite network to verify our results.

    Comment: Accepted for publication in IEEE TSIPN
    Schlagwörter Electrical Engineering and Systems Science - Systems and Control ; Computer Science - Multiagent Systems ; Computer Science - Social and Information Networks
    Erscheinungsdatum 2019-12-07
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    Dokumenttyp Buch ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  9. Buch ; Online: A Hybrid Variance-Reduced Method for Decentralized Stochastic Non-Convex Optimization

    Xin, Ran / Khan, Usman A. / Kar, Soummya

    2021  

    Abstract: This paper considers decentralized stochastic optimization over a network of $n$ nodes, where each node possesses a smooth non-convex local cost function and the goal of the networked nodes is to find an $\epsilon$-accurate first-order stationary point ... ...

    Abstract This paper considers decentralized stochastic optimization over a network of $n$ nodes, where each node possesses a smooth non-convex local cost function and the goal of the networked nodes is to find an $\epsilon$-accurate first-order stationary point of the sum of the local costs. We focus on an online setting, where each node accesses its local cost only by means of a stochastic first-order oracle that returns a noisy version of the exact gradient. In this context, we propose a novel single-loop decentralized hybrid variance-reduced stochastic gradient method, called GT-HSGD, that outperforms the existing approaches in terms of both the oracle complexity and practical implementation. The GT-HSGD algorithm implements specialized local hybrid stochastic gradient estimators that are fused over the network to track the global gradient. Remarkably, GT-HSGD achieves a network topology-independent oracle complexity of $O(n^{-1}\epsilon^{-3})$ when the required error tolerance $\epsilon$ is small enough, leading to a linear speedup with respect to the centralized optimal online variance-reduced approaches that operate on a single node. Numerical experiments are provided to illustrate our main technical results.

    Comment: Accepted in ICML 2021
    Schlagwörter Mathematics - Optimization and Control ; Computer Science - Distributed ; Parallel ; and Cluster Computing ; Computer Science - Machine Learning ; Computer Science - Multiagent Systems ; Statistics - Machine Learning
    Thema/Rubrik (Code) 510
    Erscheinungsdatum 2021-02-12
    Erscheinungsland us
    Dokumenttyp Buch ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  10. Buch ; Online: Distributed Constraint-Coupled Optimization over Lossy Networks

    Doostmohammadian, Mohammadreza / Khan, Usman A. / Aghasi, Alireza / Charalambous, Themistoklis

    2022  

    Abstract: This paper considers distributed resource allocation and sum-preserving constrained optimization over lossy networks, where the links are unreliable and subject to packet drops. We define the conditions to ensure convergence under packet drops and link ... ...

    Abstract This paper considers distributed resource allocation and sum-preserving constrained optimization over lossy networks, where the links are unreliable and subject to packet drops. We define the conditions to ensure convergence under packet drops and link removal by focusing on two main properties of our allocation algorithm: (i) The weight-stochastic condition in typical consensus schemes is reduced to balanced weights, with no need for readjusting the weights to satisfy stochasticity. (ii) The algorithm does not require all-time connectivity but instead uniform connectivity over some non-overlapping finite time intervals. First, we prove that our algorithm provides primal-feasible allocation at every iteration step and converges under the conditions (i)-(ii) and some other mild conditions on the nonlinear iterative dynamics. These nonlinearities address possible practical constraints in real applications due to, for example, saturation or quantization among others. Then, using (i)-(ii) and the notion of bond-percolation theory, we relate the packet drop rate and the network percolation threshold to the (finite) number of iterations ensuring uniform connectivity and, thus, convergence towards the optimum value.
    Schlagwörter Electrical Engineering and Systems Science - Systems and Control ; Computer Science - Multiagent Systems ; Mathematics - Optimization and Control
    Thema/Rubrik (Code) 510
    Erscheinungsdatum 2022-08-30
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    Dokumenttyp Buch ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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