Appropriate age range for introduction of complementary feeding into an infant’s diet

Peer reviewedPublisher PD

L₁adaptive control of a generic fighter aircraft

This master's thesis was performed at the section of Flight Control Systems at SAAB Aeronautics in Linköping as a part of my Master of Science in Aerospace Engineering at KTH, Stockholm. This report examines the use of L₁ adaptive control to stabilize the inner longitudinal and lateral loops of a generic fighter aircraft, in the event of failure of the system that measures current speed and altitude. The philosophy of the L₁ adaptive controller is to decouple the adaptation from the control loop by using a state-predictor based adaptation scheme, still only compensating for the uncertainties within the bandwidth of the control channel by the use of low-pass filters. The main goal of the project was to investigate in the tuning of the L₁ adaptive controller with respect to the nonlinear uncertainties related to the failure, and with a limited sampling rate of 60 Hz. The desired closed-loop dynamics for the statepredictor was designed by linearising the aircraft dynamics in a point in the middle of the flight envelope and placing the poles of the system with respect to flying qualities. The modified piecewise constant adaptation law was chosen as adaptation law, which achieves faster adaptation by increasing the sampling rate, yielding better performance at a given sample rate compared to the piecewise constant adaptation law [1]. All the states were transformed to discrete time in order to be implementable digitally. Results have shown that augmenting a state-feedback controller with a L₁ adaptive controller increases robustness in the whole flying envelope, with good flying qualities. Problems were discovered in the low speed regions of the envelope, where the L₁ adaptive controller did not provide the desired performance. A switching scheme between two L1 adaptive controllers was examined. The switch between the controllers was done by knowing when the landing gear was up or down. The second state-predictor was designed with linearised dynamics in landing speed and altitude. The switching scheme was own in a simulator with a nonlinear generic fighter aircraft model with good resultsDetta examensarbete utfördes vid sektionen för styrsystem på SAAB Aeronautics i Linköoping som en del av min Master of Science i Aerospace Engineering vid KTH, Stockholm. Rapporten undersöker användningen av L₁adaptiv reglering för att stabilisera de inre longitudinella och laterala looparna i ett generisk stridsflygplan, i händelse av ett fel på det system som mäter aktuell hastighet och höjd. Filosofin med L₁ adaptiv reglering ar att frånkoppla anpassning från reglerkretsen med en prediktorbaserad anpassningslag, men kompenserar bara för osäkerheterna inom bandbredden för styrkanalen med hjälp av lågpassfilter. Det huvudsakliga målet med projektet var att undersöka finjusteringen av en L₁ adaptiv regulator med avseende på de olinjära osäkerheterna i händelse av ett fel, och med en begränsad samplingsfrekvens på 60 Hz. Den önskade dynamiken för det slutna systemet i prediktorn designades genom att linjärisera flygplanets dynamik i en punkt i mitten av flygenveloppen och placera polerna för systemet med avseende på flygegenskaper. Den modifierade styckvis konstanta anpassninglagen valdes som anpassninglag. Den uppnår snabbare anpassning genom att öka samplingshastigheten och ger bättre prestanda vid en given samplingsfrekvens jämfört med den styckvis konstant anpassninglagen [1]. Alla tillstånd transformerades till diskret tid för att kunna implementeras digitalt. Resultaten har visat att genom att utöka en vanlig tillståndsåterkoppling med en L₁ adaptiv regulator ökar robustheten i hela flygenveloppen med goda flygegenskaper. Problem upptäcktes i de låga hastighetsregionerna, där den L₁ adaptiva regulatorn inte ger önskad prestanda. En växlingsmetodik mellan två L₁ adaptiva regulatorer undersöktes. Växlingen mellan regulatorerna gjordes genom att veta när landningsstället är uppe eller nere. Den andra tillståndsprediktorn utformades med linjäriserad dynamik i landningshastighet och höjd. Växlingsmetodiken flögs i en simulator med en olinjär generisk flygplansmodell med goda resulta

On the diagnosis of childhood coeliac disease: Past and present

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On the diagnosis of childhood coeliac disease: Past and present

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Maternal and perinatal conditions and the risk of developing celiac disease during childhood

Background: Celiac disease (CD) is increasing worldwide, which might be due to the changing environmental and lifestyle exposures. We aimed to explore how conditions related to maternity, delivery and the neonatal period influence CD onset during childhood. Methods: Using Sweden's national registers we had access to information on 1 912 204 children born between 1991 and 2009, 6 596 of whom developed CD before 15 years of age. Logistic regression analyses were performed to determine how CD is associated with maternity, delivery and the neonatal period. Results: Regardless of sex, a reduction in CD risk was observed in children born to mothers aged >= 35 years (odds ratio [OR] 0.8; 95 % confidence interval [CI] 0.7-0.9) and with high maternal income (OR 0.9; 95 % CI 0.8-0.9). Being a second-born child, however, was positively associated with CD. Among boys, elective caesarean delivery increased the risk of CD (OR 1.2; 95 % CI 1.0-1.4), while maternal overweight (OR 0.9; 95 % CI 0.8-0.9), premature rupture of the membrane (OR 0.4; 95 % CI 0.2-0.8) and low birth weight showed a negative association. Girls had an increased CD risk compared to boys and in girls the risk was increased by repeated maternal urinary tract infections (OR 1.1; 95 % CI 1.0-1.2). Conclusions: Elective caesarean delivery and repeated maternal urinary tract infections during pregnancy are associated with increased risk of CD onset during childhood, suggesting the role of dysbiosis during early life. High maternal age and high income reduced the risk of CD, which might be due to infant-feeding practices and life style