Search Results (26)

Multiple sclerosis (MS) is a chronic progressive neurodegenerative disease that leads to disabilities such as difficulty moving and slowed cognitive processing. It is the leading non-traumatic cause of disability worldwide. MS also has a high potential to become a model for neurodegenerative diseases with a progression like Alzheimer’s or Parkinson’s. Cardiovascular diseases (CVDs) remain the leading cause of global deaths and have a considerable economic impact. The higher incidence of cardiovascular comorbidities in patients with MS compared to healthy individuals of the same age worsens the prognosis of neurological pathology, leading to a higher level of disability, poorer physical outcomes, higher depression scores, cognitive aging, and diminished quality of life. Classical observational studies often have questionable elements that can represent a source of error, making it difficult to establish a causal relationship between MS and CVD. Genetic studies, including genome-wide evaluation, may resolve this issue and may represent a topic for future research. We report the case of a 31-year-old male patient with a history of multiple sclerosis (MS) diagnosed seven years prior, who presented with acute chest pain upon returning from vacation. Despite the previous recommendation for disease-modifying therapy, the patient had discontinued treatment by personal choice. Electrocardiography (ECG) revealed ST-segment elevation in inferior leads, and emergent coronary angiography identified severe multi-vessel coronary artery disease (CAD), requiring immediate revascularization. This case highlights the potential cardiovascular risks in young patients with MS and the importance of continuous medical supervision. Full article

The widespread practice of deliberate human displacement for biodiversity conservation remains a contentious issue in the Anthropocene era. This study explores the ecological impacts of conservation-led resettlement (ER) in Nepal’s Terai Arc Landscape (TAL), a biodiverse region under significant conservation and development pressures. Although ER aims to enhance ecological integrity, the role of displacement in conservation has been understudied. Using case studies from the TAL, we examined ecological indicators in vacated settlement areas within parks and newly resettled sites outside protected zones. Data were collected through a review of secondary literature, 240 household interviews, 5 focus group discussions, 25 key informant interviews, and multiple field visits across resettlement sites. Between 1973 and 2019, TAL gained 922.52 sq. km of core protected areas (displacing over 4800 households) and dispossessed communities from 2120.12 sq. km of buffer zones, significantly expanding protected areas and upgrading conservation standards from IUCN category IV to II. This contributed to the recovery of key species such as tigers, rhinos, and elephants. However, resettlements, often located along critical biological corridors and buffer zones, led to habitat fragmentation, endangering the gene pool flow and creating isolated habitats. Results show that, in general, most ecosystem and environmental variables were perceived significantly different (p < 0.05) among resettled communities in the study area. The cultural and land-based attachments of displaced communities were overlooked. These findings highlight the risks of short-term resettlement planning, which can exacerbate pressures on critical corridors, escalate human–wildlife conflicts, and provide a clear indication of the trade-off between conservation benefits and social costs. Full article

With the advancement of science and technology, industrial robots have become indispensable equipment in advanced manufacturing and a critical benchmark for assessing a nation’s manufacturing and technological capabilities. Enhancing the reliability of industrial robots is therefore a pressing priority. This paper investigates the drive system of industrial robots, modeling it as a series system comprising multiple components (n) with a repairman who operates under a single vacation policy. The system assumes that each component’s lifespan follows an exponential distribution, while the repairman’s repair and vacation times adhere to general distributions. Notably, the repairman initiates a vacation at the system’s outset. Using the supplementary variable method, a mathematical model of the system is constructed and formulated within an appropriate Banach space, leading to the derivation of the system’s abstract development equation. Leveraging functional analysis and the $C_0$-semigroup theory of bounded operators, the study examines the system’s adaptability, stability, and key reliability indices. Furthermore, numerical simulations are employed to analyze how system reliability indices vary with parameter values. This work contributes to the field of industrial robot reliability analysis by introducing a novel methodological framework that integrates vacation policies and general distribution assumptions, offering new insights into system behavior and reliability optimization. The findings have significant implications for improving the design and maintenance strategies of industrial robots in real-world applications. Full article

In this paper, we developed a new standby system that combines a retrial strategy with multiple working vacations, and we performed a dynamic analysis of the system. We investigated its well−posedness and asymptotic behavior using the theory of the $C_0-$semigroup in the functional analysis. First, the corresponding model was transformed into an abstract Cauchy problem in Banach space by introducing the state space, the main operator, and its domain of definition. Second, we demonstrated that the model had a unique non−negative time−dependent solution. Using Greiner’s boundary perturbation idea and the spectral properties of the corresponding operator, the non−negative time−dependent solution strongly converged to its steady−state solution. We also provide numerical examples to illustrate the effect of different parameters on the system’s reliability metrics. Full article

Recent progress has seen multiple Ta₂O₅ polymorphs generated by different synthesis techniques. However, discrepancies arise when these polymorphs are produced in widely varying thermodynamic conditions and characterized using different techniques. This work aimed to characterize and compare Ta₂O₅ particles formed at high and low temperatures using nanosecond pulsed laser ablation (PLA) and continuous wave (CW) laser heating of a local area of tantalum in either air or an ¹⁸O₂ atmosphere. Scanning electron microscopy (SEM) and Raman spectroscopy of the micrometer-sized particles generated by PLA were consistent with either a localized amorphous Ta₂O₅ phase or a similar, but not identical, crystalline β-Ta₂O₅ phase. The Raman spectrum of the material formed at the point of CW laser impingement was in good agreement with the previously established ceramic “H-Ta₂O₅” phase. TEM and electron diffraction analysis of these particles indicated the phase structure matched an oxygen-vacated superstructure of monoclinic H-Ta₂O₅. Further from the point of laser impingement, CW heating produced particles with a Raman spectrum that matched β-Ta₂O₅. We confirmed that the high-temperature ceramic phase characterized in previous work by Raman spectroscopy was the same monoclinic phase characterized in different work by TEM and could be produced by direct laser heating of metal in air. Full article

To ensure the efficient functioning of solar energy generation systems, it is crucial to have dependable designs and regular maintenance. However, when these systems or their components operate at multiple working levels, optimizing reliability becomes a complex task for models and analyses. In the context of reliability modeling in solar energy generation systems, researchers often assume that random variables follow an exponential distribution (binary-state representation) as a simplification, although this may not always hold true for real-world engineering systems. In the present paper, a multi-state solar energy generating system with inverters in series configuration is investigated, in which unreliable by-pass changeover switches, common cause failures (CCFs), and multiple repairman vacations are also considered. Furthermore, the arrivals of CCFs and the repair processes of the failed system due to CCFs are governed by different Markovian arrival processes (MAPs), and the lifetimes and repair times of inverters and by-pass changeover switches and the repairman vacation time in the system have different phase-type (PH) distributions. Therefore, the behavior of the system is represented using a Markov process methodology, and reliability measures for the proposed system are derived utilizing aggregated stochastic process theory. Finally, a numerical example and a comparison analysis are presented to demonstrate the findings. Full article

In this paper, a bulk arrival and two-phase bulk service with active Bernoulli feedback, vacation, and breakdown is considered. The server provides service in two phases as mandatory according to the general bulk service rule, with minimum bulk size ${}^{\prime }{a}^{\prime }$ and maximum bulk size ${}^{\prime }{b}^{\prime }$. In the first essential service (FES) completion epoch, if the server fails, with probability ${}^{\prime }{\mathsf{\delta }}^{\prime }$, then the renewal of the service station is considered. On the other hand, if there is no server failure, with a probability ${}^{\prime }1-{\delta }^{\prime }$, then the server switches to a second essential service (SES) in succession. A customer who requires further service as feedback is given priority, and they join the head of the queue with probability $\beta$. On the contrary, a customer who does not require feedback leaves the system with a probability ${}^{\prime }1-{\beta }^{\prime }$. If the queue length is less than ${}^{\prime }{a}^{\prime }$ after SES, the server may leave for a single vacation with probability ${}^{\prime }1-{\beta }^{\prime }$. When the server finds an inadequate number of customers in the queue after vacation completion, the server becomes dormant. After vacation completion, the server requires some time to start service, which is attained by including setup time. The setup time is initiated only when the queue length is at least ${}^{\prime }{a}^{\prime }$. Even after setup time completion, the service process begins only with a queue length ‘N’ (N > b). The novelty of this paper is that it introduces an essential two-phase bulk service, immediate Bernoulli feedback for customers, and renewal service time of the first essential service for the bulk arrival and bulk service queueing model. We aim to develop a model that investigates the probability-generating function of the queue size at any time. Additionally, we analyzed various performance characteristics using numerical examples to demonstrate the model’s effectiveness. An optimum cost analysis was also carried out to minimize the total average cost with appropriate practical applications in existing data transmission and data processing in LTE-A networks using the DRX mechanism. Full article

Motivated by observing real-world instances of multi-aisle automated storage and retrieval systems (AS/RSs) with shared storage, we introduced a new optimization problem called the parallel crane scheduling (PCS) problem. Unlike the single crane scheduling (SCS) problem, the decisions of the PCS problem include not only the request sequencing and storage/retrieval location selection, but also assigning requests to cranes. The PCS problem better reflects the real-life situation, but it is more complex, since these three decisions are interrelated and interact with one another. In this study, since the empty location vacated by any retrieval operation is instantly available, we introduced a new dynamic programming model combined with a mixed-integer linear programming model to describe this complex problem. Considering the feature of location-dependent processing time, we transformed the PCS problem into a variant of the unrelated parallel machine scheduling problem. We developed an apparent tardiness cost-based construction heuristic and an ant colony system algorithm with a problem-specific local optimization. Our experiments demonstrated that the proposed algorithms provide excellent performance, along with the insight that globally scheduling multiple aisles could be considered to reduce the total tardiness when designing an operation scheme for multi-aisle AS/RSs. Full article

The basic information survey on homesteads requires understanding the shape of homesteads, and the shape of the homesteads based on the spatial location can reflect information such as their outline and regularity, but the current shape classification of rural homesteads at the parcel scale lacks analytical methods. In this study, we endeavor to explore a classification model suitable for characterizing homestead shapes at the parcel scale by assessing the impact of various research methods. Additionally, we aim to uncover the evolutionary patterns in homestead shapes. The study focuses on Yangdun Village, located in Deqing County, Zhejiang Province, as the research area. The data utilized comprise Google Earth satellite imagery and a vector layer representing homesteads at the parcel scale. To classify the shapes of homesteads and compare classification accuracy, we employ a combination of methods, including the fast Fourier transform (FFT), Hu invariant moments (HIM), the Boyce and Clark shape index (BCSI), and the AlexNet model. Our findings reveal the following: (1) The random forest method, when coupled with FFT, demonstrates the highest effectiveness in identifying the shape categories of homesteads, achieving an average accuracy rate of 88.6%. (2) Combining multiple methods does not enhance recognition accuracy; for instance, the accuracy of the FFT + HIM combination was 88.4%. (3) The Boyce and Clark shape index (BCSI) proves unsuitable for classifying homestead shapes, yielding an average accuracy rate of only 58%. Furthermore, there is no precise numerical correlation between the homestead category and the shape index. (4) It is noteworthy that over half of the homesteads in Yangdun Village exhibit rectangular-like shapes. Following the “homesteads reform”, square-like homesteads have experienced significant vacating, resulting in a mixed arrangement of homesteads overall. The research findings can serve as a methodological reference for the investigation of rural homestead shapes. Proficiency in homestead shape classification holds significant importance in the realms of information investigation, regular management, and layout optimization of rural land. Full article

This article analyses a four-dimensional stochastic queueing-inventory system with multiple server vacations and a state-dependent arrival process. The server can start multiple vacations at a random time only when there is no customer in the waiting hall and the inventory level is zero. The arrival flow of customers in the system is state-dependent. Whenever the arriving customer finds that the waiting hall is full, they enter into the infinite orbit and they retry to enter the waiting hall. If there is at least one space in the waiting hall, the orbital customer enters the waiting hall. When the server is on vacation, the primary (retrial) customer enters the system with a rate of ${\lambda }_1\left({\theta }_1\right)$. If the server is not on vacation, the primary (retrial) arrival occurs with a rate of ${\lambda }_2\left({\theta }_2\right)$. Each arrival rate follows an independent Poisson distribution. The service is provided to customers one by one in a positive time with the rate of $\mu$, which follows exponential distribution. When the inventory level drops to a fixed s, reorder of Q items is triggered immediately under $(s,Q)$ ordering policy. The stability of the system has been analysed, and using the Neuts matrix geometric approach, the stationary probability vectors have been obtained. Moreover, various system performance measures are derived. The expected total cost analysis explores and verifies the characteristics of the assumed parameters of this model. The average waiting time of a customer in the waiting hall and orbit are investigated using all the parameters. The monotonicity of the parameters is verified with its characteristics by the numerical simulation. The discussion about the fraction time server being on vacation suggests that as the server’s vacation duration reduces, its fraction time also reduces. The mean number of customers in the waiting hall and orbit is reduced whenever the average service time per customer and average replenishment time are reduced. Full article

The present study deals with the stock-dependent Markovian demand of a retrial queueing system with a single server and multiple server vacation. The items are restocked under a continuous review $(s,Q)$ ordering policy. When there is no item in the system, the server goes on vacation. Further, any arrival demand permits entry into an infinite orbit whenever the server is on vacation. In the Matrix geometric approach with the Neuts-Rao truncation technique, the steady-state joint distribution of the number of customers in orbit, the server status, and the inventory level is obtained. Under the steady-state conditions, some significant system performance measures, including the long-run total cost rate, are derived, and the Laplace-Stieltjes transform is also used to investigate the waiting time distribution. According to various considerations of uncontrollable parameters and costs, the merits of the proposed model, especially the important characteristics of the system with stock dependency over non-stock dependency, are explored. Ultimately, the important facts and ideas behind this model are given in conclusion. Full article

An autonomous driving environment poses a very stringent requirement for the timely delivery of safety messages in vehicular ad hoc networks (VANETs). Time division multiple access (TDMA)-based medium access control (MAC) protocols are considered a promising solution because of their time-bound message delivery. However, in the event of mobility-caused packet collisions, they may experience an unpredicted and extended delay in delivering messages, which can cause catastrophic accidents. To solve this problem, a distributed TDMA-based MAC protocol with mobility-caused collision mitigation (MCCM-MAC) is presented in this paper. The protocol uses a novel mechanism to detect merging collisions and mitigates them by avoiding subsequent access collisions. One vehicle in the merging collisions retains the time slot, and the others release the slot. The common neighboring vehicles can timely suggest a suitable new time slot for the vacating vehicles, which can avoid access collisions between their packet transmissions. A tie-breakup mechanism is employed to avoid further access collisions. Simulation results show that the proposed protocol reduces packet loss more than the existing methods. Consequently, the average delay between the successfully delivered periodic messages is also reduced. Full article

The complex adaptation system (CAS) theory of “adaptability to produce complexity” is a new theoretical perspective for the spatio-temporal evolution of rural tourism systems. Based on the CAS theory, the theoretical framework, structural composition, formation process, and evolution mechanism of the rural tourism complex system were examined and revealed. The suburban country region of Wuhan was taken as the area of focus for empirical research. The state of the rural tourism destination system in Wuhan has gone through various periods of development: the embryonic stage of the system (before 2000), formation (2001–2007), rapid development (2008–2015), and consolidation and transformation (since 2016). Under the environments stimulating external physical geography, social economy, market demand, and emergencies, multiple agents such as government, enterprises, residents, and tourists in Wuhan have actively adapted to the environment and other agents, and the interaction intensity and complexity have gradually increased, driving the emergence of system agent types, functional structures, and spatial patterns. The agents continue to grow, differentiate, and aggregate. The tourism product has shifted from the dominance of a rural ecological scenery and leisure agriculture to diversified development, and with the main function changing from sightseeing to leisure and vacation. The rural communities have been renovated and beautified, transforming them from a provider of rural service facilities to a co-builder of a rural-imaged tourism space. Full article

The transient behavior of the finite-buffer queueing model with batch arrivals and generally distributed repeated vacations is analyzed. Such a system has potential applications in modeling the functioning of production systems, computer and telecommunication networks with energy saving mechanism based on cyclic monitoring the queue state (Internet of Things, wireless sensors networks, etc.). Identifying renewal moments in the evolution of the system and applying continuous total probability law, a system of Volterra-type integral equations for the time-dependent queue-size distribution, conditioned by the initial buffer state, is derived. A compact-form solution for the corresponding system written for Laplace transforms is obtained using an algebraic approach based on Korolyuk’s potential method. An illustrative numerical example presenting the impact of the service rate, arrival rate, initial buffer state and single vacation duration on the queue-size distribution is attached as well. Full article

We consider a $MAP/PH/1$-type queueing system with server vacations as a model that is useful for the analysis of multiple access systems with polling discipline without transmission interruption. Vacation of the server corresponds to the service providing competitive information flows to the polling system. In this paper, we consider a vacation queueing model under pretty general assumptions about the probabilistic distributions describing the behavior of the system and the realistic assumption, in many real-world systems, that ongoing service cannot be terminated ahead of schedule. We derive the criterion of the stable operation of the system and the stationary distributions of the system states and the waiting time. An illustrative numerical example is presented. Full article