Study of stability of large maneuvers of airplanes

A predictive method of nonlinear system analysis is used to investigate airplane stability and dynamic response during rolling maneuvers. The maneuver roll-rate is not assumed to be constant, and the airplane motion is represented by a set of coupled nonlinear differential equations. The general rolling maneuver is kinematically specified by its roll-rate variation p(t). A method for relating the airplane dynamic response to p(t) is developed. The method provides analytical expressions for the motion variables in terms of the maneuver descriptor p(t). A parameterized family of rolling maneuvers is considered, for which the method is used to predict specific dynamic response information, such as the dependence of the peak angle-of-attack excursion on the maneuver parameters. The stability and motion of the airplane in response to an arbitrary actuation of aileron input is considered. Analytical expressions relating motion variables to aileron input are obtained. Explicit analytical bounds on the motion variables are derived. A stability criterion which guarantees nondivergence of motion in response to aileron actuation is presented

Factors affecting the adoption and use of urban air mobility

Technological advances have recently led to the development of urban air mobility (UAM), an alternative transportation mode with several concepts including vehicles operated by on-demand fully-automated vertical take-off and landing aircraft (VTOL) for intra-city passenger transportation. However, despite a growing interest in UAM, understanding users’ perceptions to it remains limited. This research aims to identify and quantify the factors affecting the adoption and use of UAM, based on relevant tools from the literature, such as recurring factors in studies on aerial vehicle concepts, ground autonomous vehicles, but also acceptance models, such as the Technology Acceptance Model by Davis et al. (1989). A stated-preference survey was developed to assess the perception of users in terms of adoption time horizon, including options such as the first six years of the service’s implementation, “unsure”, and “never”. The obtained results were evaluated using exploratory factor analyses, and the specification and estimation of suitable discrete choice models, multinomial logit models (MNLs) and ordered logit models (OLMs), with adoption time horizon as dependent variable. Findings revealed the importance of safety and trust, affinity to automation, data concerns, social attitude, and socio-demographics for adoption. Factors, such as the value of time savings, the perception of automation costs, and service reliability, were also found to be highly influential. There was also an indication that skeptical respondents, i.e. answering “unsure”, had a behavior similar to late and non-adopters, i.e. adoption time horizon higher than six years or answering “never”. The summarized results were represented in an extended Technology Acceptance Model for urban air mobility, and provided insights for policymakers and industrial stakeholders

Selection of pomegranate (Punica granatum L.) in south-eastern Tunisia

Tunisia is one of the main producers and exporters of pomegranate (Punica granatum L.) in the world. Due to its international importance, the selection of both quantitative and qualitative most desirable varieties has become a necessity. To select new cultivars that are most appropriate for commercial use, 21 accessions were collected from different regions of south-east Tunisia. 24 morphological characters of the tree and fruit were studied for each accession. This study has revealed considerable diversity especially concerning the tree vigor, the fruit size and color and the acidity of juice. Taking into account all comments, some trees are considered particularly efficient in south-eastern Tunisia.Key words: South-east Tunisia, Punica granatum L., selection, morphological characters

Does Tropical Forest Fragmentation Increase Long-Term Variability of Butterfly Communities?

Habitat fragmentation is a major driver of biodiversity loss. Yet, the overall effects of fragmentation on biodiversity may be obscured by differences in responses among species. These opposing responses to fragmentation may be manifest in higher variability in species richness and abundance (termed hyperdynamism), and in predictable changes in community composition. We tested whether forest fragmentation causes long-term hyperdynamism in butterfly communities, a taxon that naturally displays large variations in species richness and community composition. Using a dataset from an experimentally fragmented landscape in the central Amazon that spanned 11 years, we evaluated the effect of fragmentation on changes in species richness and community composition through time. Overall, adjusted species richness (adjusted for survey duration) did not differ between fragmented forest and intact forest. However, spatial and temporal variation of adjusted species richness was significantly higher in fragmented forests relative to intact forest. This variation was associated with changes in butterfly community composition, specifically lower proportions of understory shade species and higher proportions of edge species in fragmented forest. Analysis of rarefied species richness, estimated using indices of butterfly abundance, showed no differences between fragmented and intact forest plots in spatial or temporal variation. These results do not contradict the results from adjusted species richness, but rather suggest that higher variability in butterfly adjusted species richness may be explained by changes in butterfly abundance. Combined, these results indicate that butterfly communities in fragmented tropical forests are more variable than in intact forest, and that the natural variability of butterflies was not a buffer against the effects of fragmentation on community dynamics

A New Sensorless Hybrid MPPT Algorithm Based on Fractional Short-Circuit Current Measurement and P&O MPPT

This paper presents a new maximum power point tracking (MPPT) method for photovoltaic (PV) systems. The proposed method improves the working of the conventional perturb and observe (P&O) method in changing environmental conditions by using the fractional short-circuit current (FSCC) method. It takes the initial operating point of a PV system by using the short-circuit current method and later shifts to the conventional P&O technique. The advantage of having this two-stage algorithm is rapid tracking under changing environmental conditions. In addition, this scheme offers low-power oscillations around MPP and, therefore, more power harvesting compared with the common P&O method. The proposed MPPT decides intelligently about the moment of measuring short-circuit current and is, therefore, an irradiance sensorless scheme. The proposed method is validated with computer software simulation followed by a dSPACE DS1104-based experimental setup. A buck-boost dc-dc converter is used for simulation and experimental confirmation. Furthermore, the reliability of the proposed method is also calculated. The results show that the proposed MPPT technique works satisfactorily under given environmental scenarios

Continuous Uniform Finite Time Stabilization of Planar Controllable Systems

Continuous homogeneous controllers are utilized in a full state feedback setting for the uniform finite time stabilization of a perturbed double integrator in the presence of uniformly decaying piecewise continuous disturbances. Semiglobal strong $\mathcal{C}^1$ Lyapunov functions are identified to establish uniform asymptotic stability of the closed-loop planar system. Uniform finite time stability is then proved by extending the homogeneity principle of discontinuous systems to the continuous case with uniformly decaying piecewise continuous nonhomogeneous disturbances. A finite upper bound on the settling time is also computed. The results extend the existing literature on homogeneity and finite time stability by both presenting uniform finite time stabilization and dealing with a broader class of nonhomogeneous disturbances for planar controllable systems while also proposing a new class of homogeneous continuous controllers

Fatigue and TSH Levels in Hypothyroid Patients

Background. Fatigue is often the complaint that initiates thyroid function investigation. Most available data related to fatigue and hypothyroidism involved patients with subclinical hypothyroidism where fatigue was not the primary outcome. This study investigated the association between TSH levels and fatigue and if there was a target TSH interval that was associated with lower incidence of fatigue in patients with hypothyroidism. Methods. An analytic, retrospective cohort study design assessed the relationship between TSH levels and fatigue. All adult patients at one endocrinology clinic who were diagnosed with hypothyroidism between January 1, 2006 and December 31, 2007 were included. Diagnoses were confirmed by biochemical testing. Data were abstracted from the clinic’s electronic medical record. Fatigue status was self-reported by the subject during examination by the endocrinologist. Fatigue status and TSH levels were obtained twice: at diagnosis and during the first follow-up visit. Results. A total of 135 patients met the inclusion criteria. After treatment, all patients had reductions in TSH levels. Those subjects reporting relief from fatigue tended to be males (p = 0.003), had lower TSH levels at follow-up (p < 0.001), had larger TSH differences from baseline (p =0.007), and had a primary diagnosis of acquired hypothyroidism (p < 0.001). Females were 2.9 times more likely to report persistent fatigue than males. Patients with primary diagnosis of thyroiditis were 3 times more likely to report persistent fatigue than those with acquired hypothyroidism. Conclusions. The observed relief from fatigue after treatment correlated with a higher TSH reduction compared to patients with persistent fatigue. It was unclear if fatigue relief was related to the level of TSH reduction (TSH difference) or to a lower absolute TSH level reached after treatment

Isotopic Production Cross Sections in Proton-Nucleus Collisions at 200 MeV

Intermediate mass fragments (IMF) from the interaction of $^{27}$Al, $^{59}$Co and $^{197}$Au with 200 MeV protons were measured in an angular range from 20 degree to 120 degree in the laboratory system. The fragments, ranging from isotopes of helium up to isotopes of carbon, were isotopically resolved. Double differential cross sections, energy differential cross sections and total cross sections were extracted.Comment: accepted by Phys. Rev.

Built‐in biaxial strain dependence of Γ‐X transport in GaAs/InxAl1−xAs/GaAs pseudomorphic heterojunction barriers (x=0, 0.03, and 0.06)

The effects of built‐in biaxial strain on Γ‐X transport in n‐GaAs/i‐InxAl1−xAs/n‐GaAs pseudomorphic single‐barrier structures (x=0, 0.03, and 0.06) are studied by measuring temperature‐dependent I‐V characteristics. For the accurate characterization of electron transport across each barrier, a self‐consistent numerical model is used to analyze the experimental results. For each structure, the four barrier parameters defined from the thermionic‐field‐emission theory, the effective Richardson constant A∗, the conduction‐band offsets ΔEc1,2, and a tunneling mass mn∗ are extracted by calculating the theoretical I‐V characteristics and fitting them to the experimental I‐V‐T data. The experimentally obtained X‐point conduction‐band shifts with the addition of indium are compared with the theoretical results calculated based on the model‐solid theory. The results indicate that the addition of indium not only splits the degenerate X minima of the InxAl1−xAs barrier, but also shifts the relative barrier heights of both longitudinal and transverse X valleys due to the alloy‐dependent band‐structure modification. The comparison between the experimental and theoretical results illustrates that the transverse X valleys are the main conduction channel for the Γ‐X transport across InxAl1−xAs pseudomorphic barriers. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70663/2/JAPIAU-76-12-7907-1.pd