| 11. |
- Jianfeng, Lin, 1994, et al.
(författare)
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Intelligent ship anti-rolling control system based on a deep deterministic policy gradient algorithm and the Magnus effect
- 2022
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Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 34:5
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Tidskriftsartikel (refereegranskat)abstract
- Anti-rolling devices are widely used in modern shipboard components. In particular, ship anti-rolling control systems are developed to achieve a wide range of ship speeds and efficient anti-rolling capabilities. However, factors that are challenging to solve accurately, such as strong nonlinearities, a complex working environment, and hydrodynamic system parameters, limit the investigation of the rolling motion of ships at sea. Moreover, current anti-rolling control systems still face several challenges, such as poor nonlinear adaptability and manual parameter adjustment. In this regard, this study developed a dynamic model for a ship anti-rolling system. In addition, based on deep reinforcement learning (DRL), an efficient anti-rolling controller was developed using a deep deterministic policy gradient (DDPG) algorithm. Finally, the developed system was applied to a ship anti-rolling device based on the Magnus effect. The advantages of reinforcement learning adaptive control enable controlling an anti-rolling system under various wave angles, ship speeds, and wavelengths. The results revealed that the anti-rolling efficiency of the intelligent ship anti-rolling control method using the DDPG algorithm surpassed 95% and had fast convergence. This study lays the foundation for developing a DRL anti-rolling controller for full-scale ships.
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| 12. |
- Jianfeng, Lin, 1994, et al.
(författare)
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Shape optimization and hydrodynamic simulation of a Magnus anti-rolling device based on fully parametric modeling
- 2023
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Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 35:5
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Tidskriftsartikel (refereegranskat)abstract
- Ship anti-rolling devices are an essential component of modern vessels. The core component of the Magnus effect-based ship anti-rolling device is a rotating cylinder, hereinafter referred to as the Magnus cylinders. In this paper, fully parametric three-dimensional modeling of Magnus cylinders was performed, and the design space dimension was reduced using the Sobol design optimization method while still providing accurate and reliable results. The Sobol method generates quasi-random sequences that are more uniformly spaced in the search space and can more efficiently cover the entire solution space. The shape optimization study of the Magnus cylinder was carried out in conjunction with the computational fluid dynamics method to find the geometry of the Magnus cylinder with excellent hydrodynamic performance. Critical design parameters include the diameters of the cylinder ends and the length of the cylinder. The hydrodynamic and flow field characteristics of Magnus cylinders before and after the optimization were compared. The results show that there can be multiple local optimal values for lift and drag of Magnus cylinders within the design space to increase the lift and decrease the drag. The Magnus effect primarily influences the position of the vortex-shedding separation point at the surface of Magnus cylinders and deflects the wake to one side. For the optimized Magnus cylinder, the distribution of pressure and velocity in the flow field is significantly different. This research forms the basis for improving the practical application of Magnus anti-rolling devices.
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| 13. |
- Lin, Jianfeng, et al.
(författare)
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Experimental investigation and intelligent control of the magnus anti-rolling device for ship stability at zero speed
- 2024
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Ingår i: Ocean Engineering. - 0029-8018. ; 308
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Tidskriftsartikel (refereegranskat)abstract
- Under zero-speed conditions, ships are particularly susceptible to the effects of waves, which directly impact the safety of the vessel. A ship anti-rolling device based on the Magnus effect is designed to mitigate rolling motions across a full range of speeds, thereby enhancing the vessel's stability. This study presents an experimental investigation and intelligent control of Magnus anti-rolling devices aimed at enhancing ship stability at zero speed. The test setup, intelligent control algorithm, and experimental procedures specifically tailored for evaluating the Magnus anti-rolling device were designed. Following this, a comprehensive analysis was conducted to assess the effects of different cylinder geometries, swinging speeds, initial roll angles, and control methods on the anti-rolling characteristics of the device. Results demonstrate that the intelligent control method achieves an average anti-rolling efficiency of 89%. Additionally, the optimised geometric model of the Magnus anti-rolling device exhibits improved anti-rolling efficiency relative to the original model. The study confirms the stability and robustness of the intelligent Magnus anti-rolling device and suggests future research directions for practical applications aboard full-scale vessels in complex marine environments.
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| 14. |
- Link, Yumin, et al.
(författare)
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The Importance of Optical Coherence Tomography in the Diagnosis of Atypical or Subclinical Optic Neuritis : A Case Series Study
- 2023
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Ingår i: Journal of Clinical Medicine. - : MDPI. - 2077-0383. ; 12:4
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Tidskriftsartikel (refereegranskat)abstract
- Background: Optic neuritis (ON) is an inflammatory condition of the optic nerve. ON is associated with development of demyelinating diseases of the central nervous system (CNS). CNS lesions visualized by magnetic resonance imaging (MRI) and the finding of oligoclonal IgG bands (OB) in the cerebrospinal fluid (CSF) are used to stratify the risk of MS after a "first" episode of ON. However, the diagnosis of ON in absence of typical clinical manifestations can be challenging. Methods and Materials: Here we present three cases with changes in the optic nerve and ganglion cell layer in the retina over the disease course. (1) A 34-year-old female with a history of migraine and hypertension had suspect amaurosis fugax (transient vision loss) in the right eye. This patient developed MS four years later. Optical coherence tomography (OCT) showed dynamic changes of the thickness of peripapillary retinal nerve fiber layer (RNFL) and macular ganglion cell-inner plexiform layer (GCIPL) over time. (2) A 29-year-old male with spastic hemiparesis and lesions in the spinal cord and brainstem. Six years later he showed bilateral subclinical ON identified using OCT, visual evoked potentials (VEP) and MRI. The patient fulfilled diagnosis criteria of seronegative neuromyelitis optica (NMO). (3) A 23-year-old female with overweight and headache had bilateral optic disc swelling. With OCT and lumbar puncture, idiopathic intracranial hypertension (IIH) was excluded. Further investigation showed positive antibody for myelin oligodendrocyte glycoprotein (MOG). Conclusions: These three cases illustrate the importance of using OCT to facilitate quick, objective and accurate diagnosis of atypical or subclinical ON, and thus proper therapy.
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| 15. |
- Sabir Rashid, Avan, et al.
(författare)
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Homonymous visual field defect and retinal thinning after occipital stroke
- 2021
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Ingår i: Brain and Behavior. - : Wiley-Blackwell. - 2162-3279 .- 2162-3279. ; 11:10
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Tidskriftsartikel (refereegranskat)abstract
- Introduction Stroke is the most common cause of homonymous visual field defects (VFD). About half of the stroke patients recover from VFD. However, relationship between VFD and retinal changes remains elusive. Purpose To investigate the association between occurrence of VFD, changes of macular ganglion cell and inner plexiform layer (GCIPL) and its axon retinal nerve fiber layer (RNFL) detected with optical coherence tomography (OCT). Patients and methods The study consists of retrospective review of medical records and follow-up examinations. Patients with acute occipital stroke were registered. VFD was identified with confrontation and/or perimetry tests at the onset. At follow-up, the patients were examined with visual field tests and OCT measurements. Results Thirty-six patients met the inclusion criteria. At onset, 26 patients (72%) had VFD. At follow-up >1 year after stroke, 13 patients (36%) had remaining VFD: 5 had homonymous hemianopia, 5 had homonymous quadrantanopia, and 3 had homonymous scotomas. Average thickness of GCIPL and RNFL were significantly reduced in each eye in patients with VFD compared to non-VFD (NVFD) (p < .01 for all comparisons). Thickness of superior and inferior RNFL quadrants was significantly reduced in VFD compared to NVFD (p < .01 for both). Among these 13 patients, 4 had characteristic homonymous quadrant-GCIPL thinning, 2 had characteristic homonymous hemi-GCIPL thinning, and 7 had diffuse GCIPL thinning. Conclusion GCIPL and RNFL thinning were observed in the patients with VFD. GCIPL thinning appears in two forms: atypical diffuse thinning, or homonymous hemi-GCIPL thinning. Examining GCIPL and RNFL provides easy and reliable objective measures and is therefore proposed to be of predictive value on visual function.
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| 16. |
- Sator, Lea, et al.
(författare)
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Overdiagnosis of COPD in Subjects With Unobstructed Spirometry A BOLD Analysis
- 2019
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Ingår i: Chest. - : Elsevier BV. - 0012-3692 .- 1931-3543. ; 156:2, s. 277-288
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: There are several reports on underdiagnosis of COPD, while little is known about COPD overdiagnosis and overtreatment. We describe the overdiagnosis and the prevalence of spirometrically defined false positive COPD, as well as their relationship with overtreatment across 23 population samples in 20 countries participating in the BOLD Study between 2003 and 2012.METHODS: A false positive diagnosis of COPD was considered when participants reported a doctor's diagnosis of COPD, but postbronchodilator spirometry was unobstructed (FEV1/FVC > LLN). Additional analyses were performed using the fixed ratio criterion (FEV1/FVC < 0.7).RESULTS: Among 16,177 participants, 919 (5.7%) reported a previous medical diagnosis of COPD. Postbronchodilator spirometry was unobstructed in 569 subjects (61.9%): false positive COPD. A similar rate of overdiagnosis was seen when using the fixed ratio criterion (55.3%). In a subgroup analysis excluding participants who reported a diagnosis of "chronic bronchitis" or "emphysema" (n = 220), 37.7% had no airflow limitation. The site-specific prevalence of false positive COPD varied greatly, from 1.9% in low- to middle-income countries to 4.9% in high-income countries. In multivariate analysis, overdiagnosis was more common among women, and was associated with higher education; former and current smoking; the presence of wheeze, cough, and phlegm; and concomitant medical diagnosis of asthma or heart disease. Among the subjects with false positive COPD, 45.7% reported current use of respiratory medication. Excluding patients with reported asthma, 34.4% of those with normal spirometry still used a respiratory medication.CONCLUSIONS: False positive COPD is frequent. This might expose nonobstructed subjects to possible adverse effects of respiratory medication.
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| 17. |
- Studnicka, Michael, et al.
(författare)
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COPD : Should Diagnosis Match Physiology?
- 2020
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Ingår i: Chest. - : Elsevier BV. - 0012-3692 .- 1931-3543. ; 157:2, s. 473-475
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 18. |
- Wang, Yuanji, et al.
(författare)
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The diversity of microbial community and function varied in response to different agricultural residues composting
- 2020
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Ingår i: Science of the Total Environment. - : Elsevier B.V.. - 0048-9697 .- 1879-1026. ; 715
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Tidskriftsartikel (refereegranskat)abstract
- Microbial activities are the dynamic core in the soil nutrient cycle. To improve the knowledges about the responses of soil microbial community structure and potential function to long-term cover crops practice. The co-occurrence patterns of soil microbial community structure and functional genes were evaluated using 16SrRNA, ITS and metagenomic technique in 13 years cover crops of orchard grass (OG, Dactylis glomerata L.) with high C/N and white clover (WC, Trifolium repens L.) with low C/N. Conventional tillage (CT) was control. The experiment was implemented in an apple orchard located on the Loess Plateau, China, from 2006 to 2018. We also measured soil physicochemical properties and enzyme activities related to carbon and nitrogen cycling. The conclusions showed that the dominant bacterial phyla were Actinobacteria 27.68% in OG treatment and Proteobacteria 25.89% in WC treatment. Organic matter inputs stimulated growth of the phyla of Actinobacteria, Firmicutes, Chloroflexi, Ascomycota and genera of Bacillus, Blastococcus, Streptomyces and Penicillium. Interestingly, the OG and WC treatments promoted the fungal and bacterial alpha-diversity compared to CT treatment, respectively. In addition, compared to CT treatment, OG treatment was beneficial to the increase of C-cycle enzyme activity, while WC treatment tended to increase the N-cycle enzyme activity. Notably, compared to CT treatment, they both enriched carbon fixation and cycle pathways genes, while WC treatment increased the nitrogen metabolism pathway genes. Moreover, OG treatment was more conducive to the enrichment of carbohydrate enzymes genes involved in the hydrolysis of cellulose and hemicellulose compared to WC treatment. Overall, different quality of plant residues stimulated the specific expressions of soil microbial community structure and function. Long-term planted white clover was effective strategy to improve soil quality. © 2020 Elsevier B.V.
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