L1 Control Research Articles

Delay Robustness and Compensation in L1 Adaptive Control

Stability analysis of an L1 adaptive control design decomposes into i) the derivation of an inequality condition imposed on a filter in the control channel that guarantees transient performance bounds on the state and control input for a theoretical nonadaptive reference system, and ii) a Lyapunov-type proof of the decay of a predictor error as the inverse square root of the adaptive gain, which in turn can be made arbitrarily large without sacrificing robustness to time delay in the control input. This paper reviewsrecent results on the robustness to input and communication time delays for L1 control systems with uncertain nonlinearities and in nontrivial network configurations, as well as a possible scheme for compensating for large, constant input delays.

Delay‐dependent output feedback L1 control for positive Markovian jump systems with mode‐dependent time‐varying delays and partly known transition rates

SummaryThe paper deals with the problem of delay‐dependent output feedback L1 control for positive Markovian jump systems with mode‐dependent time‐varying delays and partly known transition rates. First, by constructing an appropriate co‐positive type Lyapunov function, sufficient conditions for stochastic stability and L1‐gain performance of the open‐loop system are developed. Then, an effective method is proposed to construct the output feedback controller. These sufficient criteria are derived in the form of linear programming. A key point of this paper is to extend the special requirement of completely known transition rates to more general form that covers completely known and completely unknown transition rates as two special cases. Finally, a numerical example is given to illustrate the validity of the main results. Copyright © 2016 John Wiley & Sons, Ltd.

A robust L1 controller design for continuous-time TS systems with persistent bounded disturbance and actuator saturation

This paper proposes a novel approach for L1 performance controller design of saturated input nonlinear systems described by Takagi-Sugeno (TS) fuzzy systems. The proposed method utilizes parallel distributed compensation (PDC) approach to minimize the effect of persistent bounded disturbances on the system output and the design conditions are formulated in terms of linear matrix inequalities (LMIs) and a generalized eigenvalue problem (GEVP). The novelty of this paper is to design a saturated robust L1 PDC controller whose procedure comprises new techniques for both minimizing the L1 performance gain and handling actuator saturation constraint. These techniques lead to less conservative results compared to recently published papers in the viewpoint of L1 performance criterion gain as well as the control input saturation. The advantages of the proposed approach in each above-mentioned viewpoint are shown via numerical examples by comparing our results with the existing literatures. Finally, a nonlinear electromagnetic suspension (EMS) system is considered to verify the applicability and efficiency of this novel design method.

Orthographic Activation in L2 Spoken Word Recognition Depends on Proficiency: Evidence from Eye-Tracking.

The use of orthographic and phonological information in spoken word recognition was studied in a visual world task where L1 Finnish learners of L2 French (n = 64) and L1 French native speakers (n = 24) were asked to match spoken word forms with printed words while their eye movements were recorded. In Experiment 1, French target words were contrasted with competitors having a longer (<base> vs. <bague>) or a shorter word initial phonological overlap (<base> vs. <bain>) and an identical orthographic overlap. In Experiment 2, target words were contrasted with competitors of either longer (<mince> vs. <mite>) or shorter word initial orthographic overlap (<mince> vs. <mythe>) and of an identical phonological overlap. A general phonological effect was observed in the L2 listener group but not in the L1 control group. No general orthographic effects were observed in the L2 or L1 groups, but a significant effect of proficiency was observed for orthographic overlap over time: higher proficiency L2 listeners used also orthographic information in the matching task in a time-window from 400 to 700 ms, whereas no such effect was observed for lower proficiency listeners. These results suggest that the activation of orthographic information in L2 spoken word recognition depends on proficiency in L2.

Set-based modeling and observer design for planar structure from motion

Sets that are defined either from closed contours or from a set of points are generic descriptors for several kinds of objects in binary images. In this paper, we derive a novel model in the space of sets and design an observer for the proposed model to estimate the depth and orientation of planar objects from a camera. This problem is well known as structure from motion. When the objects are only partially projected on the image plane of the camera, our model makes object depth and orientation estimation possible without feature tracking and matching between distinct image frames (i.e., the so-called correspondence problem), which is an advantage over the image moments-based model. However, the proposed model fails in some situations (the failures can be seen as brief instabilities), and it is not always continuous. To compensate for these drawbacks, we designed a fast observer based on L1 control theory with a binary signal for the proposed model. Stability analysis with respect to a certain asymptotic instability ratio is also presented in this paper. The effectiveness of the proposed model and observer is demonstrated through simulations and experimental results.

Quantum Optimal Control Problems with a Sparsity Cost Functional

ABSTRACTIn this article, the investigation of a class of quantum optimal control problems with L1 sparsity cost functionals is presented. The focus is on quantum systems modeled by Schrödinger-type equations with a bilinear control structure as it appears in many applications in nuclear magnetic resonance spectroscopy, quantum imaging, quantum computing, and in chemical and photochemical processes. In these problems, the choice of L1 control spaces promotes sparse optimal control functions that are conveniently produced by laboratory pulse shapers. The characterization of L1 quantum optimal controls and an efficient numerical semi-smooth Newton solution procedure are discussed.

Absolute exponential L1-gain analysis and synthesis of switched nonlinear positive systems with time-varying delay

This paper investigates absolute exponential stability and stabilization with L1-gain performance of switched nonlinear positive systems with time-varying delay. Nonlinear functions considered in the paper are located in a sector field and the time-varying delay is unknown but bounded. The notion of absolute exponential L1 stability of switched nonlinear positive systems is first introduced. A nonlinear Lyapunov–Krasovskii functional is constructed for the underlying systems. By using the Lyapunov–Krasovskii functional, a sufficient condition for absolute exponential L1 stability of the systems is established in terms of linear programming. Then, absolute exponential L1 control synthesis of the systems is addressed. A feedback control law containing nonlinear functions and a state-feedback control law are designed, respectively. By comparing with existing results, it is shown that the present design is less conservative. Finally, an illustrative example is provided to illustrate the effectiveness of the results.

Robust L1 dynamic output feedback control for a class of networked control systems based on T–S fuzzy model

This paper investigates the robust L1 dynamic output feedback control problem for a class of nonlinear networked control systems (NCSs) represented by Takagi–Sugeno (T–S) fuzzy model. In consideration with the imperfect networked environment with signal transmission delay and data packet dropout, a fuzzy NCS via dynamic output feedback is established by utilizing the parallel distributed compensation (PDC) technique. The attention is focused on designing the robust L1 controller that guarantees being asymptotically stable of the fuzzy NCS and satisfies a prescribed L1 noise attenuation level γ with respect to all persistent and amplitude-bounded disturbance input signals. In particular, we concentrate on constructing a delay- and basis- dependent Lyapunov–Krasovskii function which is in favor of reducing the conservatism, and furthermore, by using the integral inequality method and the Projection Lemma, the peak-to-peak performance criterion is first established. In this way, the design problem of the admissible L1 dynamic output feedback controller can be converted into a convex optimization problem of solving a set of linear matrix inequalities (LMIs). Simulation results are provided to illustrate the effectiveness of the proposed method.

Transfer into L3 English

AbstractThis study is concerned with L3 acquisition in heritage speakers (HSs). The goals are to incorporate HSs into L3 acquisition research and investigate the role of language dominance for predicting L3 transfer. We analyze global accent in German-Turkish early bilinguals, HSs of Turkish, who acquired English as their L3. Twenty native-speaker judges determined accent strength and accent source in the speech of 18 bilinguals as well as 15 controls (L1 English, L1 German, L1 Turkish) when speaking English. Results show, firstly, that bilinguals are perceived as less accented than L1 Turkish speakers and similar to L1 German speakers. Secondly, unlike L1 controls, there is no uniform accent source for HSs when speaking their L3. Our results question the role of age of acquisition, while being generally consistent with the TPM. However, HSs seem to benefit from bilingual experience and structure-based transfer can be overpowered by high proficiency.

How does language distance between L1 and L2 affect the L2 brain network? An fMRI study of Korean–Chinese–English trilinguals

The present study tested the hypothesis that language distance between first language (L1) and second language (L2) influences the assimilation and accommodation pattern in Korean–Chinese–English trilinguals. The distance between English and Korean is smaller than that between Chinese and Korean in terms of orthographic transparency, because both English and Korean are alphabetic, whereas Chinese is logographic. During fMRI, Korean trilingual participants performed a visual rhyming judgment task in three languages (Korean: KK, Chinese: KC, English: KE). Two L1 control groups were native Chinese and English speakers performing the task in their native languages (CC and EE, respectively). The general pattern of brain activation of KC was more similar to that of CC than KK, suggesting accommodation. Higher accuracy in KC was associated with decreased activation in regions of the KK network, suggesting reduced assimilation. In contrast, the brain activation of KE was more similar to that of KK than EE, suggesting assimilation. Higher accuracy in KE was associated with decreased activation in regions of the EE network, suggesting reduced accommodation. Finally, an ROI analysis on the left middle frontal gyrus revealed greater activation for KC than for KE, suggesting its selective involvement in the L2 with more arbitrary mapping between orthography and phonology (i.e., Chinese). Taken together, the brain network involved in L2 reading is similar to the L1 network when L2 and L1 are similar in orthographic transparency, while significant accommodation is expected when L2 is more opaque than L1.

Finite-Time $$L_1$$ L 1 Control for Positive Markovian Jump Systems with Partly Known Transition Rates

The paper deals with the problem of finite-time $$L_1$$L1 control for positive Markovian jump systems with partly known transition rates. Firstly, by constructing a linear co-positive Lyapunov function, sufficient conditions for finite-time boundedness and $$L_1$$L1 finite-time boundedness of the open-loop system are developed. Then, an effective method is proposed for the construction of the state feedback controller. These sufficient criteria are derived in the form of linear programming. A key point of this paper is to extend the special requirement of completely known transition rates to more general form that covers completely known and completely unknown transition rates as two special cases. Finally, two examples are given, which include a mathematical model of virus mutation treatment to illustrate the validity of the obtained results.

Application of L&lt;sub&gt;1&lt;/sub&gt; Adaptive Control to a High Maneuverability Aircraft

The L1 Adaptive control technique is applied to the F-18 HARV (High Alpha Research Vehicle) aircraft. This control architecture compensates for both the matched and the unmatched uncertainties of the full nonlinear aircraft dynamics. This paper describes the L1 control architecture used to control the nonlinear dynamics of the aircraft and the final part presents the detailed simulation results for the lateral channel

An optimal culture medium for growing Karlodinium veneficum: Progress towards a microalgal dinoflagellate-based bioprocess

In addressing a potential bioprocess for bioactives production from microalgae, the choice of a proper culture medium is a key factor. In the present work, an optimal culture medium for producing the marine dinoflagellate microalga Karlodinium veneficum was formulated using a stochastic search strategy based on genetic algorithm. The optimized formulation had 25 components including the macronutrients, trace elements and vitamins. With this medium, the final attainable cell concentration during batch growth was enhanced by 120% relative to the control culture grown in the L1 medium. The final titer of the bioactive karlotoxins measured using the hemolytic activity of the culture filtrate was enhanced by 190% relative to the L1 control. These results are a promising basis for further development of photobioreactor culture strategies for microalgal dinoflagellates.

$$L_1$$ L 1 Control for Positive Markovian Jump Systems with Time-Varying Delays and Partly Known Transition Rates

This paper deals with the problem of $$L_1$$L1 control for positive Markovian jump systems with time-varying delays and partly known transition rates. Firstly, by the use of appropriate co-positive type Lyapunov function, sufficient conditions for stochastic stability of positive Markovian jump systems with time-varying delays and partly known transition rates are proposed. Then, $$L_1$$L1-gain performance of the system considered is analyzed. Based on the results obtained, a state feedback controller is constructed such that the closed-loop Markovian jump system is positive and stochastically stable with $$L_1$$L1-gain performance. All the proposed conditions are derived in linear programming. Finally, an example is given to demonstrate the validity of the main results.

Production and on-line comprehension of definiteness in English and Dutch by monolingual and sequential bilingual children

The present article examines production and on-line processing of definite articles in Turkish-speaking sequential bilingual children acquiring English and Dutch as second languages (L2) in the UK and in the Netherlands, respectively. Thirty-nine 6–8-year-old L2 children and 48 monolingual (L1) age-matched children participated in two separate studies examining the production of definite articles in English and Dutch in conditions manipulating semantic context, that is, the anaphoric and the bridging contexts. Sensitivity to article omission was examined in the same groups of children using an on-line processing task involving article use in the same semantic contexts as in the production task. The results indicate that both L2 children and L1 controls are less accurate when definiteness is established by keeping track of the discourse referents (anaphoric) than when it is established via world knowledge (bridging). Moreover, despite variable production, all groups of children were sensitive to the omission of definite articles in the on-line comprehension task. This suggests that the errors of omission are not due to the lack of abstract syntactic representations, but could result from processes implicated in the spell-out of definite articles. The findings are in line with the idea that variable production in child L2 learners does not necessarily indicate lack of abstract representations (Haznedar and Schwartz, 1997).

Phonetic accommodation in Russian-Estonian bilingual speech

The influence of L1 phonological knowledge on L2 bilingual speech has long been a fruitful topic of speech perception and production research (Piske et al., J. Phonetics 29, 191–215). Recent research examining phonetic accommodation in bilingual speech has demonstrated that L1 and L2 phonologies interact in a bidirectional, dynamic manner (Fowler et al., J. Phonetics 36, 649–663). My study builds on these results by examining the acoustic outcomes of phonetic accommodation in vowels produced by bilingual Russian(L1)-Estonian(L2) speakers. Specifically, I aim to test the hypotheses that L2 knowledge can significantly affect robust aspects of L1 speech, i.e., vowel quality, and that there is a correlation between the extent of L2 exposure and the degree of phonetic accommodation. The preliminary results of acoustic analysis suggest that bilingual speakers produce L1 vowels with formant values that are intermediate from both L1 and L2 monolingual controls, indicating that L2 exposure influences significant aspects of L1 speech. Presently, I am conducting analyses which compare individual speaker differences in the extent of phonetic convergence to the amount of their L2 use and exposure. My overarching objective is to present novel empirical evidence that expands our current understanding of phonetic accommodation in bilingual speech production.

Fetal Cyclophosphamide Exposure Induces Testicular Cancer and Reduced Spermatogenesis and Ovarian Follicle Numbers in Mice

Exposure to radiation during fetal development induces testicular germ cell tumors (TGCT) and reduces spermatogenesis in mice. However, whether DNA damaging chemotherapeutic agents elicit these effects in mice remains unclear. Among such agents, cyclophosphamide (CP) is currently used to treat breast cancer in pregnant women, and the effects of fetal exposure to this drug manifested in the offspring must be better understood to offer such patients suitable counseling. The present study was designed to determine whether fetal exposure to CP induces testicular cancer and/or gonadal toxicity in 129 and in 129.MOLF congenic (L1) mice. Exposure to CP on embryonic days 10.5 and 11.5 dramatically increased TGCT incidence to 28% in offspring of 129 mice (control value, 2%) and to 80% in the male offspring of L1 (control value 33%). These increases are similar to those observed in both lines of mice by radiation. In utero exposure to CP also significantly reduced testis weights at 4 weeks of age to ∼70% of control and induced atrophic seminiferous tubules in ∼30% of the testes. When the in utero CP-exposed 129 mice reached adulthood, there were significant reductions in testicular and epididymal sperm counts to 62% and 70%, respectively, of controls. In female offspring, CP caused the loss of 77% of primordial follicles and increased follicle growth activation. The results indicate that i) DNA damage is a common mechanism leading to induction of testicular cancer, ii) increased induction of testis cancer by external agents is proportional to the spontaneous incidence due to inherent genetic susceptibility, and iii) children exposed to radiation or DNA damaging chemotherapeutic agents in utero may have increased risks of developing testis cancer and having reduced spermatogenic potential or diminished reproductive lifespan.

Asynchronous L1 control of delayed switched positive systems with mode-dependent average dwell time

This paper investigates the stability and asynchronous L1 control problems for a class of switched positive linear systems (SPLSs) with time-varying delays by using the mode-dependent average dwell time (MDADT) approach. By allowing the co-positive type Lyapunov–Krasovskii functional to increase during the running time of active subsystems, a new stability criterion for the underlying system with MDADT is first derived. Then, the obtained results are extended to study the issue of asynchronous L1 control, where “asynchronous” means that the switching of the controllers has a lag with respect to that of system modes. Sufficient conditions are provided to guarantee that the resulting closed-loop system is exponentially stable and has an L1-gain performance. Finally, two numerical examples are given to show the effectiveness of the developed results.

Finite-time L1 control for positive switched linear systems with time-varying delay

This paper is concerned with the problem of finite-time L1 control for a class of positive switched linear systems with time-varying delay. Firstly, by using the average dwell time approach, sufficient conditions which can guarantee the L1 finite-time boundedness of the underlying system are given. Then, in virtue of the results obtained, a state feedback controller is designed to ensure that the resulting closed-loop system is finite-time bounded with L1-gain performance. All the obtained results are formulated in terms of linear matrix inequalities (LMIs), which can be solved conveniently. Finally, an example is given to illustrate the efficiency of the proposed method.

Parsing the Passive: Comparing Children With Specific Language Impairment to Sequential Bilingual Children

Twenty-five monolingual (L1) children with specific language impairment (SLI), 32 sequential bilingual (L2) children, and 29 L1 controls completed the Test of Active & Passive Sentences-Revised (van der Lely 1996) and the Self-Paced Listening Task with Picture Verification for actives and passives (Marinis 2007). These revealed important between-group differences in both tasks. The children with SLI showed difficulties in both actives and passives when they had to reanalyse thematic roles on-line. Their error pattern provided evidence for working memory limitations. The L2 children showed difficulties only in passives both on-line and off-line. We suggest that these relate to the complex syntactic algorithm in passives and reflect an earlier developmental stage due to reduced exposure to the L2. The results are discussed in relation to theories of SLI and can be best accommodated within accounts proposing that difficulties in the comprehension of passives stem from processing limitations.