In this paper, we analytically study the performance of opportunistic multi-channel bonding protocol supporting delay-sensitive multimedia services. We consider a multi-channel system shared by IEEE ...802.11ac users who can transmit over multiple channels and legacy users who can only transmit over one single channel. By analyzing the channel bonding behavior of IEEE 802.11ac users and the random access of legacy users, bonding probability and successful bonding probability of IEEE 802.11ac users can be derived. Furthermore, the access delays of both legacy and 802.11ac users are analyzed. According to the analytical results, the network capacity which quantifies the maximum number of multimedia flows that can be supported with guaranteed delay is then presented. Additionally, the impacts of different parameters such as traffic data rate on the network capacity are investigated. Our analytical results show that channel bonding is favorable when the secondary channels are underutilized. But channel bonding should be disabled when there are already intense contentions from legacy users. Based on the analytical results, we propose a heuristic bonding policy which can provide important guidelines to control the number of flows to satisfy the QoS requirement and achieve the maximum network capacity. Extensive simulations have been conducted to validate the analytical results.
Highlights 1) To train our young neurosurgeons eye to pick up the physical signs and to enhance the visual memory. 2) To elaborate the importance of full neurological exam. 3) The clinical finding ...can change the surgical plan and surgical priority for similar patients. 4) Enhance the correlation between clinical spine finding and brain lesion and the need for full radiological study of the spine for such patient before proceeding with surgery.
In many computational science and engineering applications, the output of a system of interest corresponding to a given input can be queried at different levels of fidelity with different costs. ...Typically, low-fidelity data is cheap and abundant, while high-fidelity data is expensive and scarce. In this work we study the reinforcement learning (RL) problem in the presence of multiple environments with different levels of fidelity for a given control task. We focus on improving the RL agent’s performance with multifidelity data. Specifically, a multifidelity estimator that exploits the cross-correlations between the low- and high-fidelity returns is proposed to reduce the variance in the estimation of the state–action value function. The proposed estimator, which is based on the method of control variates, is used to design a multifidelity Monte Carlo RL (MFMCRL) algorithm that improves the learning of the agent in the high-fidelity environment. The impacts of variance reduction on policy evaluation and policy improvement are theoretically analyzed by using probability bounds. Our theoretical analysis and numerical experiments demonstrate that for a finite budget of high-fidelity data samples, our proposed MFMCRL agent attains superior performance compared with that of a standard RL agent that uses only the high-fidelity environment data for learning the optimal policy. 22This article is an extended version of a paper originally presented at the ESANN (European Symposium on Artificial Neural Networks) conference in 2023.
•Proposed an unbiased reduced-variance multifidelity estimator for the state–action value function in multifidelity reinforcement learning (RL).•Theoretically analyzed the impacts of variance reduction in estimating the state–action value function on both policy evaluation and policy improvement.•Designed a multifidelity Monte Carlo RL algorithm, MFMCRL, to improve policy learning for RL agents operating in high-fidelity environments.•Demonstrated empirical performance gains in synthetic multifidelity RL environments and a neural architecture search (NAS) use case.
Craniopharyngioma (CP) is a rare intracranial tumor arising from the epithelial remnants of Rathke's pouch, most frequently originating in the sellar/parasellar region. Histologically, CP is a benign ...low-grade tumor (WHO grade 1) with two distinct phenotypes: adamantinomatous CP (ACP) and papillary CP (PCP). Craniopharyngioma constitutes 1–3% of all primary intracranial tumors in adults and 5–10 % of intracranial tumors in children. The annual incidence ranges from 0.13 to 2 per 100,000 population per year with no gender predilection. Due to its unique anatomical locations, the most frequently reported clinical manifestations are headache, visual impairment, nausea/vomiting, and endocrine deficiencies resulting in sexual dysfunction in adults and growth failure in children. Growth hormone deficiency is the most predominant endocrinological disturbance associated with craniopharyngioma. Computed tomography (CT) is gold standard to detect calcifications in CP tissue (found in 90 % of these tumors). Magnetic Resonance Imaging (MRI) further characterizes craniopharyngiomas and helps to narrow down the differential diagnoses. In almost all craniopharyngioma cases, surgery is indicated to: establish the diagnosis, relieve mass-related symptoms, and remove as much tumor as is safely possible. Recent neurosurgical technical advances, including innovative surgical approaches, detailed radiotherapy protocols, targeted therapy, replacement of lost hormonal functions and quality of life all have the potential to improve the outcome of patients with craniopharyngioma. In this article, we present extensive literature on craniopharyngioma clinical presentation, radiological findings, management, and future prospective. The present article helps to identify further research areas that set the basis for the management of such a complex tumor.
•Craniopharyngioma is a rare intracranial tumor arising from the epithelial remnants of Rathke's pouch.•Growth hormone deficiency is the most predominant endocrinological disturbance associated with craniopharyngioma.•Surgery is indicated to: establish the diagnosis, relieve mass-related symptoms, and remove as much tumor as is safely possible.
Background. Ganglioneuroma (GN) is a rare, benign tumor that originates from neural crest cells and can potentially affect any anatomical site within the sympathetic nervous system. Typically, GNs ...are more frequently reported in children and young adults, with a slightly higher prevalence in females. We are reporting a rare case of a giant lumbar spine ganglioneuroma by outlining the clinical presentation, radiological finding, management, and outcome. Case Description. A 37-year-old female presented with low back pain radiating to the right lower limb for few years. Neurological examination revealed bilateral lower limb hyperreflexia (+3). Lumbar spine CT and MRI revealed a right paravertebral soft tissue lesion with heterogeneous signal intensity and enhancement at L1 to L3. The patient underwent complete resection of the lesion via a retroperitoneal approach. The surgery was uneventful. The histopathological sections were suggestive of mature ganglioneuroma. She was discharged in stable condition with follow-up at neurosurgery clinic. Conclusion. Giant ganglioneuromas are rare, benign tumors of sympathetic neurons. Complete surgical resection is the most effective therapeutic option for ganglioneuroma to avoid recurrence. Given the benign nature of ganglioneuroma, chemotherapy and radiotherapy tend to have a limited role following surgical resection.
Giant Colloid Cyst Alkhaibary, Ali; Khairy, Sami
World neurosurgery,
September 2022, 2022-09-00, 20220901, Letnik:
165
Journal Article
Recenzirano
Giant colloid cysts are defined as cysts of more than 3 cm in maximal diameter. Few cases of giant colloid cysts have been reported in the literature. We herein describe a giant colloid cyst. A ...15-year-old female presented with headache, blurred vision, and episodic behavioral changes for 3 months. Neurological examination was limited due to agitation and confusion. Fundoscopy was notable for bilateral papilledema. Brain computed tomography revealed a giant third-ventricular lesion, causing obstructive hydrocephalus. The patient underwent urgent ventriculoperitoneal shunt insertion initially and then cyst excision. The histopathological sections of the lesion were compatible with a colloid cyst. Five years following surgical resection, a brain magnetic resonance imaging did not demonstrate any evidence of residual or cyst recurrence. To our knowledge, giant colloid cysts have been rarely reported and pose a management dilemma in the literature. The present article highlights the symptomatology, radiological findings, and outcome of a giant colloid cyst.
Abstract This study aimed to assess the level of knowledge, attitudes, and practices (KAP) concerning malaria and malaria prevention among rural populations residing in the southwestern region of ...Saudi Arabia. This was a household-based cross-sectional survey, using structured questionnaire that was developed and distributed among households selected randomly from 19 villages (clusters) located in a southwestern region of Saudi Arabia, north of the border with Yemen. The data collected were analyzed using SPSS version 20. A majority of respondents (98.4%) reported that they had heard about malaria, but only 21.7% reported that they had sufficient information about the disease. Surprisingly, the most popular source of information was the internet and social media (proportion responding positively in parenthesis) (25.5%), followed by family (21.7%), while information from health facilities contributed only 12.4%. A majority of respondents were aware that malaria is a communicable (89.1%) and deadly (70%) disease; however, only 30.2% of the respondents responded that malaria is a treatable disease. Almost all of the aware respondents (97.5%) were inclined to seek treatment from health facilities, and 63.2% preferred to seek treatment within 24 h of presenting with symptoms. Regarding personal precautions, the most common practice adopted by respondents was indoor residual spraying IRS (47.3%), followed by anti-mosquito spraying (29.8%), mosquito bed nets (13.2%) and combined anti-mosquito sprays and nets on windows (4.7%). This KAP study did not show any statistically significant differences in KAP due to age; however the practices of preventive measures against malaria differed significantly by nationality (Saudi versus non-Saudi). We conclude that most populations living in the villages have an acceptable level of knowledge and awareness about malaria and seek timely treatment. However, the positive attitudes and practices in relation to personal protection and prevention measures against malaria require marked improvement. The obvious gap between the knowledge and practice related to malaria prevention requires innovative strategies based on local evidence that well suits the local circumstances to promote and encourage the adoption and practice of personal protective measures.
Spinal dural arteriovenous fistulas account for the majority of spinal vascular malformations. They are typically located in the thoracolumbar region and are diagnosed in the middle-aged and elderly ...populations. Although spinal dural arteriovenous fistulas have been postulated to be acquired, their exact development remains uncertain. Typically, the arteriovenous shunt is situated close to the spinal nerve root, inside the dura mater, where the blood from the radiculomeningeal artery and radicular vein intermix. Throughout history, there have been multiple classification systems of spinal arteriovenous shunts since 1967. Those were mainly based on the evolution of diagnostic studies as well as the treatment of these lesions. Such classification systems have undergone significant changes over the years. Unlike intracranial dural arteriovenous fistula, spinal dural arteriovenous fistula is progressive in nature. The neurological manifestations, due to venous congestion, tend to be insidious as well as non-specific. These include sensory deficits, such as paresthesia, bilateral and/or unilateral radicular pain affecting the lower limbs, and gait disturbances. Spinal dural arteriovenous fistulas can be suspected on magnetic resonance imaging/magnetic resonance angiography and confirmed by digital subtraction angiography (DSA). The management includes surgery, endovascular therapy, and in selected cases, radiotherapy. The treatment goal of spinal dural arteriovenous fistula is to halt the progression of the disease. The prognosis depends on both the duration of symptoms as well as the clinical condition prior to therapy. The present article comprehensively reviews the pathophysiology, changes in classification systems, natural history, clinical manifestations, radiological features, management, and prognosis.
Background. Hypothalamic lipomas are benign developmental lesions that tend to be discovered incidentally. This article describes the radiological features, outcome, and the postulated theories ...behind hypothalamic lipomas development. Methods. The electronic archive of neurosurgery was retrospectively reviewed. All patients with a neuroradiological diagnosis of hypothalamic lipoma, between 2005 and 2020, were included. Results. Out of 246 patients with intracranial lipomas, a total of six patients with hypothalamic lipomas have been identified. On computed tomography images, one of the hypothalamic lipomas demonstrated calcification. On magnetic resonance imaging, peripheral enhancement after contrast administration was noted in one of the lesions. Considering the benign nature of the lesions, neurosurgical intervention was not indicated. Conclusion. The majority of patients with hypothalamic lipomas are asymptomatic and undergo brain imaging for other indications. Although uncommon, such developmental lesions can be identified in the general population, especially with the advancement of neuroimaging techniques.
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