| 11. |
- Merlis, Timothy M., et al.
(författare)
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Changes in Poleward Atmospheric Energy Transport over a Wide Range of Climates : Energetic and Diffusive Perspectives and A Priori Theories
- 2022
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Ingår i: Journal of Climate. - : American Meteorological Society. - 0894-8755 .- 1520-0442. ; 35:20, s. 2933-2948
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Tidskriftsartikel (refereegranskat)abstract
- The midlatitude poleward atmospheric energy transport increases in radiatively forced simulations of warmed climates across a range of models from comprehensive coupled general circulation models (GCMs) to idealized aquaplanet moist GCMs to diffusive moist energy balance models. These increases have been rationalized from two perspectives. The energetic (or radiative) perspective takes the atmospheric energy budget and decomposes energy flux changes (radiative forcing, feedbacks, or surface fluxes) to determine the energy transport changes required by the budget. The diffusive perspective takes the net effect of atmospheric macroturbulence to be a diffusive energy transport down-gradient, so transport changes can arise from changes in mean energy gradients or turbulent diffusivity. Here, we compare these perspectives in idealized moist, gray-radiation GCM simulations over a wide range of climates. The energetic perspective has a dominant role for radiative forcing in this GCM, with cancellation between the temperature feedback components that account for the GCM’s nonmonotonic energy transport changes in response to warming. Comprehensive CMIP5 simulations have similarities in the Northern Hemisphere to the idealized GCM, although a comprehensive GCM over several CO2 doublings has a distinctly different feedback evolution structure. The diffusive perspective requires a non-constant diffusivity to account for the idealized GCM-simulated changes, with important roles for the eddy velocity, dry static stability, and horizontal energy gradients. Beyond diagnostic analysis, GCM-independent a priori theories for components of the temperature feedback are presented that account for changes without knowledge of a perturbed climate state, suggesting that the energetic perspective is the more parsimonious one.
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| 12. |
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| 13. |
- Rostedt Punga, Anna, 1978-
(författare)
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MuSK Antibody(+) Versus AChR Antibody(+) Myasthenia Gravis : Clinical, Neurophysiological and Morphological Aspects
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Myasthenia gravis (MG) is an autoimmune neuromuscular disorder that causes fluctuating muscle weakness. MG may be divided into an ocular form and a generalized form based on the involved muscles. Treatment differs between these different MG forms. The majority (80%) of patients with generalized MG are seropositive for antibodies against the acetylcholine receptor (AChR-Ab). Recently a new antibody was detected against muscle specific tyrosine kinase (MuSK) in about 40% of patients who are AChR-Ab seronegative. A few patients with MuSK-Abs have muscular atrophies, as well as electrophysiological myopathy.In this thesis we have characterized MuSK-Ab seropositive [MuSK(+)] patients using clinical parameters, including health-related quality of life (hrQoL), neurophysiology and muscle morphology, and compared them to patients with and without AChR-Abs. The question concerned which factors contribute to their muscle weakness. Additionally, we wanted to determine if single-fiber electromyography (SFEMG) in a limb muscle has any predictive value for generalization of ocular MG. Our results suggest that MuSK(+) patients more often have a myopathic electromyography pattern, although this pattern is found also in other immunological subtypes of MG. The myopathic pattern may be associated with the frequently found mitochondrial abnormalities. However, disturbed neuromuscular transmission is the primary cause of muscle weakness in the majority of MuSK(+) patients, as well as in AChR-Ab seropositive patients. The disease-specific hrQoL MG questionnaire was successfully validated into Swedish and these scores correlated with disturbed neuromuscular transmission in a proximal arm muscle. Abnormal SFEMG findings occur also in muscles outside of the facial area in ocular MG, although this is not predictive of subsequent generalization. MuSK (+) patients have little or no beneficial effect of acetylcholine esterase inhibitors (AChEI). On the contrary AChEI may produce profound adverse effects. We present the hypothesis that this effect of AChEI is due to abnormal receptor morphology in MuSK(+) patients.
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| 14. |
- Espin Delgado, Angela
(författare)
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Propagation of Supraharmonics in Low-Voltage Networks
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The need for measures towards a sustainable use of energy has incited the proliferation of devices and systems for the efficient use of electricity. Energy-efficient appliances, equipment for the electrification of transportation, electricity generators from renewable energy sources, and communication protocols, e.g., for smart metering are sources of supraharmonic distortion in electrical networks. Supraharmonics are voltage and current waveform distortion in the frequency range from 2 up to 150 kHz.The increase in sources of supraharmonics in the last decades and the propagation of this type of distortion have triggered a variety of unwanted consequences (interference) in the electrical networks. Interference associated to supraharmonics such as audible noise, degradation or failure in the operation of electrical equipment, and breakdown of insulation materials, have been reported around the world. A standardized framework for supraharmonics as a power quality phenomenon that involves both grid operators and equipment manufacturers is needed to limit these interferences. The limits to be set shall not hinder the modernization of the electrical system and the consequential energy transition.There are gaps in the standardization framework for supraharmonics as a power quality phenomenon. The study of supraharmonics as a power quality parameter should consider variables that affect emission levels and propagation of supraharmonics. At the same time, an assessment of the severity of given supraharmonics levels regarding their consequences is needed to settle realistic reference levels. Deterministic methods have been generally used to study supraharmonic propagation but they might not be suitable when considering many possible scenarios.This research introduces forefront methods and results on the study of supraharmonics emission, propagation, and consequences. The study has two focal points: 1) to study the impact of the impedance of the grid and low-voltage devices on the emission and propagation of supraharmonics; 2) to assess the severity of propagated supraharmonics in terms of the characteristics of the distortion and the probability of interference. Experimental and theoretical case studies are built to carry out the research. Measured and synthetic signals representative of supraharmonic distortion present in low-voltage networks are used.The main results of this research are summarized as:The levels of emitted and propagated supraharmonics depend on the impedance of the grid, the emitting device and the neighboring devices. Resonance can lead to significant levels of supraharmonics anywhere in the grid. The variability and diversity of low-voltage devices lead to high uncertainty in the estimation of their impedance. Stochastic methods are recommended to assess the probability of interference.Different attributes of supraharmonics are responsible for different interference phenomena. Indications of the severity of supraharmonics attributes are given for three phenomena: audible noise, negative impacton residual current devices, and light flicker of LED lamps.This research contributes to the establishment of supraharmonics as a power quality phenomenon with standardized solutions. It introduces methods for the assessment of: 1) supraharmonic emission from installations needed to recommend planning levels; 2) supraharmonic propagation in low-voltage networks, and 3) the probability of interference needed to define reference levels.
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| 15. |
- Tschudin, Christian, et al.
(författare)
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Network Pointers
- 2002
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Ingår i: SIGCOMM Communications Review. - 0146-4833. ; 33:1
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Tidskriftsartikel (refereegranskat)
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