Linear Reference Research Articles

Measured Performance and Stability Analysis of Large-Scale Reinforced Model Embankments at Different Moisture Contents

This paper describes construction and instrumentation of two 1.65-m high reinforced embankment models that were tested at two different gravitational water contents (GWC) on the dry and wet sides of the optimum moisture content (OMC); i.e. OMC−2 % and OMC+2 %. The embankment models were constructed using a clayey sand that was reinforced with four layers of instrumented geotextile with a uniform vertical spacing of 300 mm. Each model embankment was subjected to a line surcharge load (strip footing) near its crest until failure. The magnitudes of GWC, earth pressure, geotextile strains, footing settlement and embankment deformations were measured using EC-5 sensors, earth pressure cells, wire potentiometers, linear variable deferential transformers and reference plates, respectively during the construction and loading phases of each test. The GWC values in each model embankment were measured using EC-5 sensors and the oven drying method to ensure that they were close to the target values. Slope stability analysis was carried out to study the equilibrium of embankment models and to validate the predicted bearing capacity and factor of safety results against the experimental data. Results of this study show that the embankment model constructed on the dry side of OMC (i.e. OMC−2 %) had a 10 % greater serviceability failure load than the model built at OMC+2 %. Meanwhile, stability analysis results indicate that the bearing capacity of an unreinforced model embankment at OMC−2 % would be 72 % lower than that of the corresponding reinforced model. It is also found that compaction-induced energy could increase the earth pressure within the embankment by up to 70 % of the vertical stress in the soil mass due to gravity.

A Novel Approach to Beam Steering Using Arrays Composed of Multiple Unique Radiating Modes

A novel approach to beam steering is presented using an array composed of elements each supporting a unique radiating mode. The one-dimensional (1-D) beam synthesis properties of the novel ideal multiple mode dipole array are quantified using Fourier synthesis and shown to have significant improvement in scan range compared to a conventional linear dipole reference array. A hybrid phased array composed of multiple mode subarrays is also proposed and shown to be an efficient tradeoff between performance improvement and design complexity. Reasonable agreement is obtained between the simulated and measured impedance and radiation pattern properties of a four-element multiple mode array. Finally, a 16-element hybrid phased array composed of four four-element multiple mode subarrays is fabricated and measured. The array is shown to have a 3-dB scan range of $\pm 68^{\circ}$ , which is in good agreement with the simulated value of $\pm 69^{\circ}$ at the design frequency of 4.6 GHz. Additionally, the 3-dB bandwidth of the array is more than 1 GHz at broadside. This bandwidth reduces to approximately 300 MHz at the widest scan angles, which is consistent with an equivalent conventional linear array.

TH-CD-207-03: A Constrained Linear Reference Region Model For DCE-MRI

Purpose: Dynamic contrast enhanced (DCE)-MRI characterizes perfusion in tissues using time-series data and a quantitative model. This study presents a modification to the linear reference region model (LRRM) that uses two fitting parameters instead of three, resulting in improved accuracy and precision of estimated parameters. Methods: The number of fitting parameters in the LRRM is reduced by noting that the 1st and 2nd parameters are related by the kep of the reference region. This relation is accounted by the proposed constrained LRRM (CLRRM). The performance of CLRRM was compared against LRRM through simulations of concentration-time curves produced using the Tofts model, with KTrans=0.1, v_ e=0.1 for reference tissue, and KTrans=0.25, v_e=0.4 for tumour. SNR in reference curve is generally high, therefore Gaussian noise was added only to the tumour curves for an SNR range of 5 to 50 in 10 steps with temporal resolutions of 1s, 10s, 30s and 60s. 10,000 realizations were simulated for each SNR and temporal resolution combination. The in-vivo performance of both methods was evaluated by applying them to data acquired in sarcoma. Results: The accuracy was evaluated through the mean percent error, and precision was judged by the standard deviation of the percent error. Both CLRRM and LRRM had similar accuracy at high SNR, but CLRRM was more accurate at lower SNR, especially for kep. The mean percent error for kep was-36% for LRRM and-6% for CLRRM at SNR 5 and 30s temporal resolution. The standard deviation for CLRRM was roughly 5 times lower. The in-vivo results showed that CLRRM produced kep maps with less noise and higher values in the solid tumour region. Conclusion: A modified version of the linear reference region model improves quantitative DCE-MRI parameter estimates at low SNR and low temporal resolution. Funding from the RI-MUHC (Montreal General Hospital Foundation), NSERC CREATE MPRTN (Grant no. 432290), and McGill University Faculty of Medicine Fellowships.

State constrained tracking control for nonlinear systems

This work addresses the model reference tracking control problem. It aims to highlight the encountered difficulties and the proposed solutions to achieve the tracking objective.Based on a literature overview of linear and nonlinear reference tracking, the achievements and the limitations of the existing strategies are highlighted. This motivates the present work to propose clear control algorithms for perfect and approximate tracking controls of nonlinear systems described by Takagi–Sugeno models. First, perfect nonlinear tracking control is addressed and necessary structural conditions are stated. If these conditions do not hold, approximate tracking control is proposed and the choice of the reference model to be tracked as well as the choice of the criterion to be minimized are discussed with respect to the desired objectives. The case of constrained control input is also considered in order to anticipate and counteract the effect of the control saturation.

Constitutive characteristics and microstructure evolution of 7150 aluminum alloy during isothermal and non-isothermal multistage hot compression

Isothermal and non-isothermal multistage hot compression tests were carried out on 7150 aluminum alloy at temperature range of 325–425°C and strain rate range of 0.01−1s−1. During isothermal multistage hot compression, the flow stress decreased with increasing temperature, accumulative strain as well as decreasing strain rate and pass strain. However, the interval time had a complex influence on flow stress, which ascended flow stress values with increasing interval time at 425°C. The isothermal and non-isothermal constitutive characteristics were studied based on hyperbolic-sine law, indicating complex influences of various processing parameters on material constants. Non-isothermal multistage flow stresses were found to be easier than normal continuous single pass method to manipulate for constitutive equations calculation with better linear fitting reference and comparable activation energy. Precipitation at low temperature and its dissolution at high temperature were found to affect flow behavior and constitutive characteristics remarkably based on microstructural observation of deformed sample.

Use of Gestalt Theory and Random Sets for Automatic Detection of Linear Geological Features

This paper presents the calibration and application of a Gestalt-based line segment method for automatic geological lineament detection from remote sensing images. This method involves estimation of the scale factor, the angle tolerance and a threshold on the false alarm rate. It identifies major lineaments as objects characterized by two edges on the image, which appear as transitions from dark to bright and vice versa. These objects were modelled as random sets with parameters drawn from their distributions. Following the geometry of detected segments, a novel validation method assesses the accuracy with respect to a linear vector reference. The methodology was applied to a study area in Kenya where lineaments are prominent in the landscape and are well identifiable from an ASTER image. Error rates were based on distance and local orientation, and the study showed that the existence and size of the objects were sensitive to parameter variation. False detection rate and missing detection rate were both equal to 0.50, which is better than values equal to 0.65 and 0.63, observed using the Canny edge detection. Modelling the uncertainty of geological lineaments with random sets further showed that no core set is formed, indicating that there is an inherent uncertainty in their existence and position, and that the variance is relatively high. Comparing the test area with four areas in the same region showed similar results. Despite some shortcomings in identifying full lineaments from partially observed lineaments, it is concluded that the procedure in this paper is well able to automatically extract lineaments from a remote sensing image and validate their existence.

Analysis of [formula omitted] adaptive state feedback control. Why does it approximate an implementable LTI controller?

The analysis in this paper shows that L1 adaptive state feedback control approximates an implementable LTI controller because: (1) the addition of a low-pass filter in the controller structure leads to an internal loop in the controller and (2) high gain feedback within this loop leads to inversion of the linear reference model and cancellation of non-linear characteristics of the adaptation law. This result holds for a variety of adaptation laws and the achieved performance does not depend on the exact formulation of this law.

The Application of Pulse Altimeter for Linear References Detection

Abstract Algorithm of linear references detection is based on statistical processing of reflected pulse altimeter signal. It is assumed that linear references formed from two underlying surfaces and differences between statistical distribution of pulse amplitude depend on the type of underlying surface. The differences allow us to decide which type of surface reflects our signal. To do this we use the method of maximum posteriori probability. This paper describes how to determine the position of linear reference and what the accuracy of this process is. The minimum of maximum posteriori probability is closely connected with linear reference position. We use this fact to detect the linear reference position. This algorithm allows us to realise autonomous navigation. We use Doppler sharpening to increase the accuracy of detection of linear reference position and increase the number of discriminated surfaces.

線形参照モデルを用いた速度飽和を含むシステムの安定化

Actuator rate saturation has characteristics to increase the phase lag of the system and it can be one of the factors that destabilize the motion control system for a higher control response. We propose a new control method that can stabilize the system with rate limited actuators. First, it is shown that the actuator rate limited characteristics causes control systems to be unstable using both describing function analysis and nonlinear simulations. Next, the proposed method using linear actuator reference model is described. It can avoid the rate saturation of actuators to improve the phase lag characteristics. Then, the effectiveness of proposed method is demonstrated through stability analysis and nonlinear simulations.

Map-based control method for vehicle stability enhancement

This work proposes a map-based control method to improve a vehicle’s lateral stability, and the performance of the proposed method is compared with that of the conventional model-referenced control method. Model-referenced control uses the sliding mode method to determine the compensated yaw moment; in contrast, the proposed map-based control uses the compensated yaw moment map acquired by vehicle stability analysis. The vehicle stability region is calculated by a topological method based on the trajectory reversal method. A 2-DOF vehicle model and Pacejka’s tire model are used to evaluate the proposed map-based control method. The properties of model-referenced control and map-based control are compared under various road conditions and driving inputs. Model-referenced control uses a control input to satisfy the linear reference model, and it generates unnecessary tire lateral forces that may lead to worse performance than an uncontrolled vehicle with step steering input on a road with a low friction coefficient. However, map-based control determines a compensated yaw moment to maintain the vehicle within the stability region, so the typical responses of vehicle enable to converge rapidly. The simulation results with sine and step steering show that map-based control provides better the tracking responsibility and control performance than model-referenced control.

Pattern Synchronization of Nonlinear Heterogeneous Multiagent Networks With Jointly Connected Topologies

In this paper, a decentralized control algorithm is proposed for a group of heterogeneous agents with nonlinear dynamics such that it achieves synchronization in diverse collective motion patterns. With the aid of a group of deliberately designed linear homogeneous reference models, the synchronization problem is converted into a class of regulation problem. The regulation problem is hence solved using the nonlinear output feedback control technique. The conversion and, hence, the decentralized synchronization algorithm are valid when the multiagent system is jointly connected in terms of its time-varying network topologies. The effectiveness of the algorithm is verified through theoretical analysis.

Experimental Analysis of a Coupled Energy Harvesting System with Monostable and Bistable Configuration

In this paper we present experimental results from an energy harvesting system with two coupled energy harvesters. The energy conversion mechanism of the two coupled energy harvesters is based on the electromagnetic principle. The coupling is generated by two magnets in a repulsive arrangement. In this manner a bistable configuration can be obtained if the gap between the magnets is sufficiently small. We demonstrate that the total power output can be increased in comparison to a linear reference system, if specific conditions are fulfilled. In this respect, the highest power output occurs in the nonlinear region of a monostable system configuration, mostly near the transition to a bistable configuration. On the other hand, the results also indicate, that a bistable operating mode does not necessarily enhance the power output of the coupled system.

Aroma-Active Compounds in Jinhua Ham Produced With Different Fermentation Periods

The aroma-active compounds in Jinhua ham processed and stored for 9, 12, 15 and 18 months were extracted by dynamic headspace sampling (DHS) and solvent-assisted flavor evaporation (SAFE) and analyzed by gas chromatography-olfactometry-mass spectrometry (GC-O-MS). In GC-O-MS, volatile compounds were identified based on their mass spectrum, linear retention index (LRI), odor properties, or reference compound comparisons. The results showed that a total number of 81 aroma-active compounds were identified by GC-O-MS. Among them, acids (such as acetic acid, butanoic acid and 3-methylbutanoic acid), saturated aldehydes (such as hexanal, heptanal, octanal and 3-methylbutanal), benzene derivatives (such as benzeneacetic acid), ester and lactone (such as γ-nonalactone and γ-decalactone) were identified as critical compounds in Jinhua ham aroma. The results also indicated that the type and content of the odorants increased significantly with the duration of the fermentation period.

Computational modeling of individual differences in behavioral estimates of cochlear nonlinearities.

Temporal masking curves (TMCs) are often used to estimate cochlear compression in individuals with normal and impaired hearing. These estimates may yield a wide range of individual differences, even among subjects with similar quiet thresholds. This study used an auditory model to assess potential sources of variance in TMCs from 51 listeners in Poling et al. [J Assoc Res Otolaryngol, 13:91-108 (2012)]. These sources included threshold elevation, the contribution of outer and inner hair cell dysfunction to threshold elevation, compression of the off-frequency linear reference, and detection efficiency. Simulations suggest that detection efficiency is a primary factor contributing to individual differences in TMCs measured in normal-hearing subjects, while threshold elevation and the contribution of outer and inner hair cell dysfunction are primary factors in hearing-impaired subjects. Approximating the most compressive growth rate of the cochlear response from TMCs was achieved only in subjects with the highest detection efficiency. Simulations included off-frequency nonlinearity in basilar membrane and inner hair cell processing; however, this nonlinearity did not improve predictions, suggesting that other sources, such as the decay of masking and the strength of the medial olivocochlear reflex, may mimic off-frequency nonlinearity. Findings from this study suggest that sources of individual differences can play a strong role in behavioral estimates of compression, and these sources should be considered when using forward masking to study cochlear function in individual listeners or across groups of listeners.

A renormalized potential-following propagation algorithm for solving the coupled-channels equations.

We derive a general renormalized potential-following propagation method that efficiently solves the coupled-channels equations. The step size is variable, the method is compatible with reactive boundary conditions, and the algorithm may be combined with other renormalized algorithms, such as renormalized Numerov. We diagonalize the coupling matrix and consider piece-wise constant and linear reference potentials. The constant reference potential algorithm is very simple to implement, yet for multichannel problems almost as accurate as the linear reference potential method. The applicability of the proposed algorithms to realistic problems is demonstrated for cold collisions of NH radicals. The renormalized approach has the advantage of producing wave functions in a straightforward way, which is illustrated for a shape resonance in NH-NH collisions. These scattering wave functions can be used to study ultracold photoassociation and near-threshold photodissociation.

Volatile constituents of mini-watermelon fruits

Aroma is one of the essential factors for evaluating fruit quality, and the volatile constituents in mini-watermelon fruits were here determined by a headspace-solid-phase micro-extraction and gas chromatography–mass spectrometry method (HS-SPME-GC–MS). The plants, Citrullus lanatus [Thumb.] Matsum. and Nakai cv. Minirossa (Cucurbitaceae), were cultivated in Pachino, Sicily (Italy) under greenhouse conditions. The fruits were collected in two different production years. Sixty-eight volatile compounds have been identified and quantified; among these, the impact aroma compounds are also included. The volatile compounds have been identified by linear retention index, mass spectra, standard injection and reference data; the quantification has been carried out by the standard addition technique. The main compounds were (Z)-3-nonen-1-ol, (E)-2-nonenal and (Z,Z)-3,6-nonadien-1-ol, which are characteristic volatiles in the Cucurbitaceae family.

Adaptive Control for Nonlinear Singular Systems

Nonlinear singular systems present a general mathematical framework for the modeling and controlling of complicated systems, however the complex nature of this type of systems causes many difficulties in control strategy. In this paper, a model reference control approach is addressed for nonlinear affine singular systems. First, a basic control system is proposed based on the Lyapunov stability theorem so that nonlinear singular system can asymptotically track the desired linear reference model. After that, in the second design, it has been considered that systems’ parameters are unknown and two adaptive approaches are investigated. For better illustration, simulation has been done and the results show the tracking performance for both presented control systems. DOI: http://dx.doi.org/10.5755/j01.itc.43.2.4958

Repetitive controller for improving grid‐connected photovoltaic systems

This study presents the modelling and design steps of a discrete time recursive repetitive controller (RC) to be used in a grid-connected photovoltaic (PV) system. It is shown that the linear synchronous reference frame proportional-integral controller, originally designed to control the converter's output currents, may have its effectiveness compromised because of non-linearities in the system components. A RC is introduced as an alternative to overcome this drawback and improve the system's output currents. The performance of the designed hybrid controller is tested, under both steady-state and transient operations, for variations on the power generated by a 30 kWp PV power plant. Experimental results obtained from the operation of the PV system connected to a distribution network, without output passive filters, only through a transformer that operates in a non-linear region are presented. The results are used to evaluate the performance of the proposed compensation method and to validate the designed hybrid controller.

Homogeneous reprocessing of GPS, GLONASS and SLR observations

The International GNSS Service (IGS) provides operational products for the GPS and GLONASS constellation. Homogeneously processed time series of parameters from the IGS are only available for GPS. Reprocessed GLONASS series are provided only by individual Analysis Centers (i. e. CODE and ESA), making it difficult to fully include the GLONASS system into a rigorous GNSS analysis. In view of the increasing number of active GLONASS satellites and a steadily growing number of GPS+GLONASS-tracking stations available over the past few years, Technische Universitat Dresden, Technische Universitat Munchen, Universitat Bern and Eidgenossische Technische Hochschule Zurich performed a combined reprocessing of GPS and GLONASS observations. Also, SLR observations to GPS and GLONASS are included in this reprocessing effort. Here, we show only SLR results from a GNSS orbit validation. In total, 18 years of data (1994–2011) have been processed from altogether 340 GNSS and 70 SLR stations. The use of GLONASS observations in addition to GPS has no impact on the estimated linear terrestrial reference frame parameters. However, daily station positions show an RMS reduction of 0.3 mm on average for the height component when additional GLONASS observations can be used for the time series determination. Analyzing satellite orbit overlaps, the rigorous combination of GPS and GLONASS neither improves nor degrades the GPS orbit precision. For GLONASS, however, the quality of the microwave-derived GLONASS orbits improves due to the combination. These findings are confirmed using independent SLR observations for a GNSS orbit validation. In comparison to previous studies, mean SLR biases for satellites GPS-35 and GPS-36 could be reduced in magnitude from $$-35$$ and $$-38$$ mm to $$-12$$ and $$-13$$ mm, respectively. Our results show that remaining SLR biases depend on the satellite type and the use of coated or uncoated retro-reflectors. For Earth rotation parameters, the increasing number of GLONASS satellites and tracking stations over the past few years leads to differences between GPS-only and GPS+GLONASS combined solutions which are most pronounced in the pole rate estimates with maximum 0.2 mas/day in magnitude. At the same time, the difference between GLONASS-only and combined solutions decreases. Derived GNSS orbits are used to estimate combined GPS+GLONASS satellite clocks, with first results presented in this paper. Phase observation residuals from a precise point positioning are at the level of 2 mm and particularly reveal poorly modeled yaw maneuver periods.

Interactive metadiscourse in research articles: A comparative study of paradigmatic and disciplinary influences

This article reports a comparative study of interactive metadiscourse in quantitative and qualitative research articles across the disciplines of applied linguistics, education, and psychology. Drawing on Hyland's metadiscourse framework, the study examined the use of five types of interactive metadiscourse, together with their subtypes, in a corpus of 120 research articles. Quantitative and qualitative analyses revealed clear cross-paradigmatic differences in the incidence of reformulators, comparative and inferential transitions, sequencers, and non-linear references. The analyses also identified marked cross-disciplinary differences in the use of exemplifiers, comparative transitions, linear references, and integral citations. These observed differences are interpretable in terms of the contrasting epistemologies underlying the qualitative and quantitative research paradigms and the different knowledge-knower structures prevailing in the disciplines under investigation.