Morphological and ecological divergence of Lilium and Nomocharis within the Hengduan Mountains and Qinghai-Tibetan Plateau may result from habitat specialization and hybridization

Background: Several previous studies have shown that some morphologically distinctive, small genera of vascular plants that are endemic to the Qinghai-Tibetan Plateau and adjacent Hengduan Mountains appear to have unexpected and complex phylogenetic relationships with their putative sisters, which are typically more widespread and more species rich. In particular, the endemic genera may form one or more poorly resolved paraphyletic clades within the sister group despite distinctive morphology. Plausible explanations for this evolutionary and biogeographic pattern include extreme habitat specialization and hybridization. One genus consistent with this pattern is Nomocharis Franchet. Nomocharis comprises 7 - 15 species bearing showy-flowers that are endemic to the H-D Mountains. Nomocharis has long been treated as sister to Lilium L., which is comprised of more than 120 species distributed throughout the temperate Northern Hemisphere. Although Nomocharis appears morphologically distinctive, recent molecular studies have shown that it is nested within Lilium, from which is exhibits very little sequence divergence. In this study, we have used a dated molecular phylogenetic framework to gain insight into the timing of morphological and ecological divergence in Lilium-Nomocharis and to preliminarily explore possible hybridization events. We accomplished our objectives using dated phylogenies reconstructed from nuclear internal transcribed spacers (ITS) and six chloroplast markers.Results: Our phylogenetic reconstruction revealed several Lilium species nested within a clade of Nomocharis, which evolved ca. 12 million years ago and is itself nested within the rest of Lilium. Flat/open and horizon oriented flowers are ancestral in Nomocharis. Species of Lilium nested within Nomocharis diverged from Nomocharis ca. 6.5 million years ago. These Lilium evolved recurved and campanifolium flowers as well as the nodding habit by at least 3.5 million years ago. Nomocharis and the nested Lilium species had relatively low elevation ancestors (<1000 m) and underwent diversification into new, higher elevational habitats 3.5 and 5.5 million years ago, respectively. Our phylogeny reveals signatures of hybridization including incongruence between the plastid and nuclear gene trees, geographic clustering of the maternal (i.e., plastid) lineages, and divergence ages of the nuclear gene trees consistent with speciation and secondary contact, respectively.Conclusions: The timing of speciation and ecological and morphological evolutionary events in Nomocharis are temporally consistent with uplift in the Qinghai-Tibetan Plateau and of the Hengduan Mountains 7 and 3 - 4 million years ago, respectively. Thus, we speculate that the mountain building may have provided new habitats that led to specialization of morphological and ecological features in Nomocharis and the nested Lilium along ecological gradients. Additionally, we suspect that the mountain building may have led to secondary contact events that enabled hybridization in Lilium-Nomocharis. Both the habitat specialization and hybridization have probably played a role in generating the striking morphological differences between Lilium and Nomocharis.Peer reviewedBotan

Stress effects on stability and diffusion behavior of sulfur impurity in nickel: A first-principles study

A systematic investigation regarding the effect of stress on the stability and diffusion behavior of S impurity in Ni was carried out via first-principles methods. A comparison of the formation energy of S in Ni indicated that S more easily forms as a solution atom with increasing S concentration in Ni supercells, but the binding energy showed that as the concentration of S that dissolved into Ni increased, the structure became less stable. The diffusion barrier via the octahedral-tetrahedral-octahedral site path was always lower than that via the octahedral-octahedral site path. The diffusion barrier of single S decreased with increase in tensile stress. S diffusion accelerated under applied tensile stress, which was disadvantageous in suppressing S retention in Ni. These results implied that even at a low concentration, dissolved S still had a tendency of precipitating from the Ni matrix, to further increase the stability of the system. (C) 2014 Elsevier B. V. All rights reserved

Performance of Multi-Layer and Stator-Shifting Fractional-Slot Concentrated Windings for Superconducting Wind Turbine Generators under Normal and Short-Circuit Operation Conditions

High temperature superconducting (HTS) generators are being considered for large offshore direct-drive (DD) wind turbines as they are expected to be lightweight and compact. However, short circuit torques of an HTS generator with integral-slot distributed windings (ISDWs) are too high for wind turbine constructions, mainly due to the large magnetic air gap. Fractional-slot concentrated windings (FSCWs) can be considered to address this issue since their high leakage inductance can limit short circuit currents and torques. Unlike ISDWs, FSCWs produce great contents of space harmonics that induce excessive losses in rotor components. Multi-layer and stator-shifting windings have been proposed to effectively reduce such losses. Based on a conventional 12-slot 10-pole configuration, this paper evaluates the effects of multi-layer and stator-shifting FSCWs on torque production and loss reduction in a 10 MW DD HTS generator. The examined losses include eddy current losses in the rotor shields and AC losses in the HTS field winding. This paper also checks if these FSCW schemes maintain the advantage of achieving a low short circuit torque. The results show that a 6-phase stator-shifting winding is the best choice for applying FSCWs to HTS generators.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

A free wake vortex model for floating wind turbine aerodynamics

In order to significantly increase the share of wind energy produced worldwide, wind energy technology is moving from onshore to offshore and from shallow water to deep water. Floating offshore wind turbines (FOWTs) are expected to be economically better than bottom-mounted turbines when placed in water deeper than 60 metres. Despite key initiatives such as the installation of the world’s first floating wind farm off the coast of Scotland in 2017, many design and operational challenges need to be solved to make floating offshore wind turbines economically attractive.Wind Energ

Data Driven Fault Tolerant Control: A Subspace Approach

The main stream research on fault detection and fault tolerant control has been focused on model based methods. As far as a model is concerned, changes therein due to faults have to be extracted from measured data. Generally speaking, existing approaches process measured inputs and outputs either by a filter designed based on a known model (e.g. for additive faults), or by an identification scheme to estimate the changed model parameters (e.g. due to multiplicative faults). Since the classical system identification methods are usually more involved than solving a linear least-squares problem, they can hardly be implemented online. The contribution of this thesis is hence the development of reliable numerical methods that try to extract fault information from data, in a manner as easy as solving a linear least-squares problem. These methods include “data driven” controller reconfiguration (CR) and fault detection and identification (FDI), and online experiment design to ensure that the “data” are informative enough to discover the changed system properties due to faults. The focus of Chapter 2 is on the development of the “data driven” controller reconfiguration approach, i.e. the closed-loop subspace predictive control (SPC). The key step in this approach is identifying a future output predictor (in terms of Markov parameters), which maps the past I/Os and future inputs to the future outputs of a system. A predictive controller is then parameterized by the identified predictor. The closed-loop SPC skips the realization of the system model and relies only on its Markov parameters; and can therefore be easily implemented online to adaptively accommodate multiplicative faults. It has been proven that with infinitely long measurement and prediction horizons, the closed-loop SPC is equivalent to the classical LQG design for LTI systems. In the case of a limited number of noisy data samples, the identified Markov parameters are biased and noisy, which then lead to a stochastic uncertainty in the output predictor of the SPC. This chapter develops a probabilistic robust solution in an explicit form, which is “cautious” to this uncertainty. The closed-loop SPC for LTI systems is extended to linear parameter varying systems. Chapter 3 focuses on developing Fault detection and Identification approaches Connected to Subspace Identification (FICSI) for both LTI and LPV systems. FICSI avoids projecting a residual vector onto the left null space of the extended observability matrix, as the classical parity space approach (PSA) requires. The advantage of avoiding this projection is the preservation of the degree of freedom in the residual vector, and consequently, the fault information contained therein. The thesis proves that FICSI produces residualsmore sensitive to faults than PSA does. It then proves the asymptotic unbiasedness of the FICSI fault estimation schemes. The novelty of the FICSI algorithms compared to the existing fault detection and estimation approaches based on PSA or unknown input observer (UIO), can also be attributed to the fact that FICSI requires only a sequence of Markov parameters mapping the I/O measurements to the residual. As a consequence, the FICSI detector and estimation filters can be directly identified from I/O measurements in a closed-loop plant, without modeling its dynamics in a state-space form. Both the SPC and FICSI algorithms rely on a sequence of Markov parameters identified from data. To identify these parameters, the inputs to the plant have to be “informative” enough; i.e. they must persistently excite the system to a sufficient order. Classical experiment design and the recent literatures on identification for control parameterize the spectrum of input signals in frequency domain. The persistency of excitation condition is ensured, if the input autocorrelation coefficients are nonzero up to a sufficient order. In recently developed identification for control approaches, optimal input signals (in terms of robust closed-loop performance achievable by the identified model) need to be searched on a grid of frequency points. This is unfortunately not suitable for online implementations. This thesis hence develops in Chapter 4 an online input design approach in time domain, which avoids parameterizing the input spectrum. This approach requires constraining input signals by a set of LMIs, and can be incorporated into a convex optimization problem. The combination of these input constraints with the SPC approach leads to an adaptive predictive control scheme with guaranteed parametric convergence. Due to its convexity and the recursive nature, this online design approach is more suitable than the classical approaches to capture the abruptly changed system conditions due to faults in a timely manner.Delft Center for Systems and ControlMechanical, Maritime and Materials Engineerin

High resolution soil moisture mapping using distributed temperature sensing: A data assimilation framework

Water Resource

The aerodynamics of floating offshore wind turbines in different working states during surge motion

The rotor of floating offshore wind turbines with platform motions may undergo different working states during its operation, e.g. from windmill working state to vortex ring and propeller working state. In this paper, an aerodynamic model based on a free wake vortex method is used to simulate the rotor undergoing surge motion. The associated change of working states of the rotor is evaluated quantitatively and visually. The results show that during a full cycle of the surge motion of the floating platform, the rotor experiences alternative onset of the windmill state, vortex ring state, and propeller state, while the later two occur only during the downwind motion of the rotor. The aerodynamic load change corresponding to different working states of the rotor indicates that the vortex ring state is the most unstable phase of the three.Wind Energ

Predicting the occurrence of the vortex ring state for floating offshore wind turbines

The local aerodynamic loading on floating offshore wind turbines (FOWTs) is more complex than on bottom-fixed wind turbines due to the platform motions. In particular, the FOWT rotor may start to interact with its own wake and enter a so-called vortex ring state (VRS). However, it is still unclear when, and to what extent, the VRS may happen to floating offshore wind turbines. In this paper, we quantitatively predict the VRS using Wolkovitch's criterion during the operating conditions of different FOWTs simulated by FAST. The results show that the type of floating foundation has a significant influence on the aerodynamic performance of the rotor. Also, the probability of occurrence of VRS is bigger for the floating platforms that are more sensitive to wave excitations.Wind Energ

Identification and Robust Control of the Nonlinear Photoelectrothermal Dynamics of LED Systems

In lighting systems consisting light-emitting diodes (LEDs), excessive temperature is a main cause of degraded luminous efficacy, which leads to reduced average illuminance and distorted illumination rendering. Modeling the thermal dynamics of LEDs is hence essential in designing thermal dissipators and controllers for maintaining constant illuminance or chromaticity. In the existing literature, both physical modeling and system identification have been proposed, which all find the dependence of the temperature on the input power. When the power fluctuates, e.g., due to dimming control, the thermal dynamics becomes nonlinear. Moreover, when a photoelectrothermal model is used in the control synthesis, the nonlinearity due to the product of the temperature-dependent efficacy and the input power must be considered. These nonlinearities are either ignored or linearized in most existing methods. The main contribution of this work is treating the aforementioned nonlinearities in a linear parameter varying (LPV) framework. First, the nonlinear thermal dynamics is identified by LPV system identification techniques. Then, a controller to track reference illuminance is designed by H∞ control techniques to be robust to both the temperature and the disturbance from ambient light. The identification data and the designed controller are collected from and verified on a real experimental setup.Electronic Components, Technology and Material

Comparative analysis of different criteria for the prediction of vortex ring state of floating offshore wind turbines

The wind condition around floating offshore wind turbines (FOWTs) can be largely different from that developed around bottom-mounted wind turbines due to the platform motions. The existing literature identifies four working state of FOWTs, one of them being the vortex ring state (VRS) which may occur as the rotor moves in its own wake. It is potentially a problem that influences the aerodynamic performance and lifetime of FOWTs. It is still unclear when, and to what extent, does the VRS happen to floating offshore wind turbines. The aim of this paper is to quantitatively predict the occurrence of VRS during the operation of FOWTs. Three different criteria are used and compared: the axial induction factor, Wolkovitch's criterion and Peters’ criterion. The results show that the VRS phenomena may occur for a large range of operating conditions and can be correlated with the minima in the relative wind speed normal to the rotor plane. Also, the probability of occurrence of VRS is smaller for the floating platforms that exhibit the least motions such as the TLP. Finally, Wolkovitch's criterion seems to be the most suitable one for the VRS prediction, while Peters criterion indicates the initial aerodynamic change and is thus suitable for early warning of VRS.Wind Energ