Backpropagating constraints-based trajectory tracking control of a quadrotor with constrained actuator dynamics and complex unknowns

In this paper, a backpropagating constraints-based trajectory tracking control (BCTTC) scheme is addressed for trajectory tracking of a quadrotor with complex unknowns and cascade constraints arising from constrained actuator dynamics, including saturations and dead zones. The entire quadrotor system including actuator dynamics is decomposed into five cascade subsystems connected by intermediate saturated nonlinearities. By virtue of the cascade structure, backpropagating constraints (BCs) on intermediate signals are derived from constrained actuator dynamics suffering from nonreversible rotations and nonnegative squares of rotors, and decouple subsystems with saturated connections. Combining with sliding-mode errors, BC-based virtual controls are individually designed by addressing underactuation and cascade constraints. In order to remove smoothness requirements on intermediate controls, first-order filters are employed, and thereby contributing to backstepping-like subcontrollers synthesizing in a recursive manner. Moreover, universal adaptive compensators are exclusively devised to dominate intermediate tracking residuals and complex unknowns. Eventually, the closed-loop BCTTC system stability can be ensured by the Lyapunov synthesis, and trajectory tracking errors can be made arbitrarily small. Simulation studies demonstrate the effectiveness and superiority of the proposed BCTTC scheme for a quadrotor with complex constrains and unknowns

Fast and accurate trajectory tracking control of an autonomous surface vehicle with unmodeled dynamics and disturbances

In this paper, fast and accurate trajectory tracking control of an autonomous surface vehicle (ASV) with complex unknowns including unmodeled dynamics, uncertainties and/or unknown disturbances is addressed within a proposed homogeneity-based finite-time control (HFC) framework. Major contributions are as follows: (1) In the absence of external disturbances, a nominal HFC framework is established to achieve exact trajectory tracking control of an ASV, whereby global finitetime stability is ensured by combining homogeneous analysis and Lyapunov approach; (2) Within the HFC scheme, a finite-time disturbance observer (FDO) is further nested to rapidly and accurately reject complex disturbances, and thereby contributing to an FDO-based HFC (FDO-HFC) scheme which can realize exactness of trajectory tracking and disturbance observation; (3) Aiming to exactly deal with complicated unknowns including unmodeled dynamics and/or disturbances, a finite-time unknown observer (FUO) is deployed as a patch for the nominal HFC framework, and eventually results in an FUO-based HFC (FUOHFC) scheme which guarantees that accurate trajectory tracking can be achieved for an ASV under harsh environments. Simulation studies and comprehensive comparisons conducted on a benchmark ship demonstrate the effectiveness and superiority of the proposed HFC schemes

Wright-Fisher diffusion bridges

The trajectory of the frequency of an allele which begins at $x$ at time $0$ and is known to have frequency $z$ at time $T$ can be modelled by the bridge process of the Wright-Fisher diffusion. Bridges when $x=z=0$ are particularly interesting because they model the trajectory of the frequency of an allele which appears at a time, then is lost by random drift or mutation after a time $T$. The coalescent genealogy back in time of a population in a neutral Wright-Fisher diffusion process is well understood. In this paper we obtain a new interpretation of the coalescent genealogy of the population in a bridge from a time $t\in (0,T)$. In a bridge with allele frequencies of 0 at times 0 and $T$ the coalescence structure is that the population coalesces in two directions from $t$ to $0$ and $t$ to $T$ such that there is just one lineage of the allele under consideration at times $0$ and $T$. The genealogy in Wright-Fisher diffusion bridges with selection is more complex than in the neutral model, but still with the property of the population branching and coalescing in two directions from time $t\in (0,T)$. The density of the frequency of an allele at time $t$ is expressed in a way that shows coalescence in the two directions. A new algorithm for exact simulation of a neutral Wright-Fisher bridge is derived. This follows from knowing the density of the frequency in a bridge and exact simulation from the Wright-Fisher diffusion. The genealogy of the neutral Wright-Fisher bridge is also modelled by branching P\'olya urns, extending a representation in a Wright-Fisher diffusion. This is a new very interesting representation that relates Wright-Fisher bridges to classical urn models in a Bayesian setting. This paper is dedicated to the memory of Paul Joyce

An investigation of School-Based Curriculum Development in Chinese state-run high schools: A multi-cases study on curriculum leadership and teacher participation

This study aims to investigate the implementation of SBCD in high school context of mainland China based on Marsh’s matrix of SBCD variations (1990; 2009). It also investigates the roles and responsibilities of school leaders and teachers in the process of implementation. Most empirical studies in the field have been written in primary and middle school contexts, but few studies were carried out at high schools with a deep consideration of the Chinese University Entrance Examination (UEE). As the fact that UEE has long been deeply embedded in Chinese high school context, little is known about how UEE would affect the implementation of SBCD.A mixed-method design was used to collect and analyse the study data in two state-run high schools of mainland China. The aim of using both quantitative and qualitative data collection tools is to illuminate the way leaders and teachers implement SBCD in a high school, and how they implement and understand the SBCD to afford the existing school structure in relation to the school needs and improvement. Data were collected sequentially according to the explanatory sequential design. In the first phase of the study, a questionnaire was employed to investigate the whole teacher population of two focused schools. In the second phase, 20 participants including leaders and teachers were interviewed through a semi-structured interview. Descriptive statistics and thematic analysis were undertaken.Eight themes with twenty associated sub-themes were identified from the analysis. The findings indicated that the implementation of SBCD mainly depended on the school culture, history and leadership. The results revealed two leader roles and three main responsibilities in leading SBCD, and two different patterns of teacher participation in SBCD such as individual with self-actualisation and passive with a lack of agency. Also, this study confirmed a dilemma of SBCD caused by long-standing traditional exam culture in Chinese state-run high schools.</div

Consumer-oriented incoming call connection service for the ubiquitous consumer wireless world

This thesis proposes a novel consumer-oriented Incoming Call Connection (ICC) service as an important enabling infrastructural component of the recently proposed ubiquitous consumer wireless world (UCWW), a new Consumer-centric Business Model (CBM) environment for wireless communications. The ICC solution proposed here will be offered by third-party providers who are autonomous of the access network providers. Compared to the present ICC service in the legacy subscriber-based networks, the consumeroriented ICC service will offer to mobile users greater flexibility and management control over incoming calls, enable users to receive incoming calls via multiple access networks/providers by means of a single identity, support user-driven, seamless, network-transparent Hot Access network Change (HAC), largely eliminate roaming charges and develop a new wireless networking business opportunity among other benefits. This thesis advocates for a coming paradigm change from the existing ICC service established on the Subscriber-based Business Model (SBM-ICC) towards the CBM-based ICC (CBM-ICC) service. The investigation, design and implementation of all the protocols and other elements required for building the CBM-ICC service especially in terms of transport, signaling and mobility support are addressed. The existence of other key UCWW infrastructural components of third-party authentication, authorization and accounting (3P-AAA) service provision, IPv6 personal address, and service offerings advertisements over wireless billboard channels (WBCs) is assumed. An architecture and protocol infrastructure for the CBMICC service is elaborated. Components and interfaces relying upon existing protocols or requiring new signaling protocols (or modification/new elements of existing protocols) are identified and for the latter solutions are suggested. The concept of user-driven HAC is promoted and described. The introduction of the Stream Control Transmission Protocol (SCTP) as a potential solution for enabling this HAC is motivated. Furthermore, the thesis elaborates a generic CBM-ICC service scenario, which shows how the CBM-ICC service offers to mobile users greater freedom and operation control over incoming calls, enables the novel attribute of users being empowered to receive incoming calls simultaneously, and otherwise, from various homogeneous and heterogeneous access networks, owned by the same or different providers, and enables user-driven HAC on active calls in keeping with, or matched to, user’s Always Best Connected and Best Served (ABC&S) policies. A CBM-ICC proof-of-concept system-level testbed is implemented to perform experimental tests, probe different communications scenarios, evaluate the service performance, and further elaborate the service architecture. In this, approaches towards evaluating the performance of the CBM-ICC service based on designed testbed are elaborated, and sample numerical results are presented and analyzed

Appendix and data files

Appendix 1 and 2 were used in the main text. Four original data files were used to conduct the analyses

Tailoring Membrane Surface Properties and Ultrafiltration Performances via the Self-Assembly of Polyethylene Glycol-<i>block</i>-Polysulfone-<i>block</i>-Polyethylene Glycol Block Copolymer upon Thermal and Solvent Annealing

Recently, ultrafiltration (UF) membranes have faced great challenges including the fine control of membrane surfaces for high filtration performances and antifouling properties in treating complex solution systems. Here, a particular type of amphiphilic block copolymer polyethylene glycol-<i>block</i>-polysulfone-<i>block</i>-polyethylene glycol (PEG-<i>b</i>-PSf-<i>b</i>-PEG) was synthesized through one-pot step-growth polymerization with mPEG [monomethylpoly­(ethylene glycol)] as two ends to achieve the mobility of hydrophilic polymer chains. Without any other polymers or additives involved, the PEG-<i>b</i>-PSf-<i>b</i>-PEG triblock copolymer UF membrane was fabricated through the non-solvent-induced phase separation (NIPS) method. The surface properties and filtration performances of UF membranes were tailored through the self-assembly of PEG-<i>b</i>-PSf-<i>b</i>-PEG triblock copolymers combining the thermal and solvent annealing treatments in water at 90 °C for 16 h. The annealed PEG-<i>b</i>-PSf-<i>b</i>-PEG triblock copolymer membrane significantly enhanced its water flux resulting from the increased mean pore size with the improved porosity, as well as the decreased skin layer thickness, upon annealing. More importantly, the PEG-<i>b</i>-PSf-<i>b</i>-PEG triblock copolymer membrane surface turned from hydrophobic to hydrophilic upon annealing with the PEG enrichment on the surface, and exhibited improved protein antifouling performances. Our research opens a new avenue to tailor the membrane structure and surface properties by self-assembly of amphiphilic block copolymers upon thermal and solvent annealing treatments

Image_4_Impacts of different fencing periods and grazing intensities on insect diversity in the desert steppe in Inner Mongolia.tif

For the past several decades, both species biodiversity and productivity of desert steppe have been reduced due to excessive use and climate factors. To counteract this, Chinese government has supported large-scale grassland ecological restoration programs since the year 2000. The policy needs a standard for the evaluation of the effects of such restorative measures on the grasslands after decades. Grassland insect diversity plays an important role in the maintenance of plant species and functional diversity. To understand the relation of grazing management and insect diversity, we use a complete two factor design, two fencing periods (3 or 7 years) and three grazing intensities (0, 6, or 12 sheep per ha), to examine the response of the insect diversity to fencing and grazing in desert steppe. We found almost no significant differences in either plant or insect species diversity between the sites fenced for 3 and 7 years, as the pressure of grazing increased, insect diversity decreased to a greater extent at 7-year enclosure sites than at 3-year sites. We recommend the most suitable grazing intensity for the sustainability of biodiversity of the desert steppe in Inner Mongolia is light grazing (8 sheep/ha 0.5 yr−1), and the most suitable fencing period is three years, which suggest that policies that remove livestock from the desert grassland for long periods (7 + years) are not beneficial for maintaining insect diversity, and heavy grazing lead ecological environment weaker and insect diversity decreasing. Thus, periodic livestock grazing is important in the design of management actions to preserve biodiversity.</p

Table_2_Impacts of different fencing periods and grazing intensities on insect diversity in the desert steppe in Inner Mongolia.xlsx

For the past several decades, both species biodiversity and productivity of desert steppe have been reduced due to excessive use and climate factors. To counteract this, Chinese government has supported large-scale grassland ecological restoration programs since the year 2000. The policy needs a standard for the evaluation of the effects of such restorative measures on the grasslands after decades. Grassland insect diversity plays an important role in the maintenance of plant species and functional diversity. To understand the relation of grazing management and insect diversity, we use a complete two factor design, two fencing periods (3 or 7 years) and three grazing intensities (0, 6, or 12 sheep per ha), to examine the response of the insect diversity to fencing and grazing in desert steppe. We found almost no significant differences in either plant or insect species diversity between the sites fenced for 3 and 7 years, as the pressure of grazing increased, insect diversity decreased to a greater extent at 7-year enclosure sites than at 3-year sites. We recommend the most suitable grazing intensity for the sustainability of biodiversity of the desert steppe in Inner Mongolia is light grazing (8 sheep/ha 0.5 yr−1), and the most suitable fencing period is three years, which suggest that policies that remove livestock from the desert grassland for long periods (7 + years) are not beneficial for maintaining insect diversity, and heavy grazing lead ecological environment weaker and insect diversity decreasing. Thus, periodic livestock grazing is important in the design of management actions to preserve biodiversity.</p

Image_1_Impacts of different fencing periods and grazing intensities on insect diversity in the desert steppe in Inner Mongolia.tif

For the past several decades, both species biodiversity and productivity of desert steppe have been reduced due to excessive use and climate factors. To counteract this, Chinese government has supported large-scale grassland ecological restoration programs since the year 2000. The policy needs a standard for the evaluation of the effects of such restorative measures on the grasslands after decades. Grassland insect diversity plays an important role in the maintenance of plant species and functional diversity. To understand the relation of grazing management and insect diversity, we use a complete two factor design, two fencing periods (3 or 7 years) and three grazing intensities (0, 6, or 12 sheep per ha), to examine the response of the insect diversity to fencing and grazing in desert steppe. We found almost no significant differences in either plant or insect species diversity between the sites fenced for 3 and 7 years, as the pressure of grazing increased, insect diversity decreased to a greater extent at 7-year enclosure sites than at 3-year sites. We recommend the most suitable grazing intensity for the sustainability of biodiversity of the desert steppe in Inner Mongolia is light grazing (8 sheep/ha 0.5 yr−1), and the most suitable fencing period is three years, which suggest that policies that remove livestock from the desert grassland for long periods (7 + years) are not beneficial for maintaining insect diversity, and heavy grazing lead ecological environment weaker and insect diversity decreasing. Thus, periodic livestock grazing is important in the design of management actions to preserve biodiversity.</p