Classical Direct Method Research Articles

Target Reconstruction with a Reference Point Scatterer using Phaseless Far Field Patterns

An important property of the phaseless far field patterns with incident plane waves is the translation invariance. Thus it is impossible to reconstruct the location of the underlying scatterers. By adding a reference point scatterer into the model, we design a novel direct sampling method using the phaseless data directly. The reference point technique not only overcomes the translation invariance, but also brings a practical phase retrieval algorithm. Based on this, we propose a hybrid method combining the novel phase retrieval algorithm and the classical direct sampling methods. Numerical examples in two dimensions are presented to demonstrate their effectiveness and robustness.

A modified two-stage randomized response model for estimating the proportion of stigmatized attribute

ABSTRACTThe survey related to stigmatized characteristics leads to the non-response problem if it is conducted according to classical (direct) methods, especially, developed for non-sensitive issues; therefore, it needs to be applied appropriate survey methodology to get a reliable response from respondents in incriminating issues. Randomized response model is one of the most recent methods which is attracting the attention of survey practitioners to deal with the problems of non-response because it protects the privacy of individuals in order to acquire the truthful response. The present work proposes a new two-stage randomized response model to get rid of misleading response or non-response due to the stigmatized nature of attribute under the study. The proposed randomized response model results in the unbiased estimator of population proportion possessing the sensitive attribute. The properties of the resultant estimator have been studied and empirical comparisons are performed to show its dominance over existing estimators. Suitable recommendations have been put forward to the survey practitioners.

Prediction error identification of linear dynamic networks with rank-reduced noise

Dynamic networks are interconnected dynamic systems with measured node signals and dynamic modules reflecting the links between the nodes. We address the problem of identifying a dynamic network with known topology, on the basis of measured signals, for the situation of additive process noise on the node signals that is spatially correlated and that is allowed to have a spectral density that is singular. A prediction error approach is followed in which all node signals in the network are jointly predicted. The resulting joint-direct identification method, generalizes the classical direct method for closed-loop identification to handle situations of mutually correlated noise on inputs and outputs. When applied to general dynamic networks with rank-reduced noise, it appears that the natural identification criterion becomes a weighted LS criterion that is subject to a constraint. This constrained criterion is shown to lead to maximum likelihood estimates of the dynamic network and therefore to minimum variance properties, reaching the Cramér–Rao lower bound in the case of Gaussian noise. In order to reduce technical complexity, the analysis is restricted to dynamic networks with strictly proper modules.

Rapid and economical protocols for genomic and metagenomic DNA extraction from oak (Quercus brantii Lindl.)

Two new efficient, fast and low-cost metagenomic DNA extraction methods were developed for different Persian oak tissues (leaf, stem, root, and rhizospheric) and soil samples. The new “omics” studies on the genus Quercus are of importance to help finding efficient strategies for overcoming environmental challenges, and to do this, presence of efficient DNA extraction protocols for different Quercus species are very critical. The objective of the present study was to develop new efficient methods for extraction of metagenomic DNA (mDNA) from of Persian oak (Quercus brantii Lindl.) tissues. The efficiency of two newly developed mDNA extraction methods, including indirect SDS-based (ISB or concentrate method) and one spin column-based method (SCB) were compared to that of two classical direct methods, including CTAB-based and SDS-based methods, and two commercial mDNA extraction kits. The maximum average yield of mDNA for all samples (leaf, stem, root, bulk, and rhizospheric soils) was obtained by SCB (258 ng/μl) and ISB (189 ng/μl) methods, respectively. Successful PCR amplification for 16SrRNA and ITS sequence was consistently observed for ISB, SCB, and kit-extracted mDNAs, which confirmed the high purity of mDNA extracted by these methods. The new methods showed more than 96% quantitative PCR efficiency, and partial restriction digestion and metagenomic library construction confirmed the high efficiency of the newly developed methods. It could be concluded that two new protocols enhanced efficiency (yield, purity, and cost) of mDNA extraction from different tissues of Persian oak.

Transient Stability Assessment Using Individual Machine Equal Area Criterion Part II: Stability Margin

In the second part of this two-paper series, the stability margin of a critical machine and that of the system are first proposed, and then the concept of the nonglobal stability margin is illustrated. Based on the crucial statuses of the leading unstable critical machine and the most severely disturbed critical machine, the critical stability of the system from the perspective of an individual machine is analyzed. At the end of this paper, comparisons between the proposed method and classic global direct methods are demonstrated.

A Generalized Reduced Gradient Method for the Optimal Control of Very-Large-Scale Robotic Systems

This paper develops a new indirect method for distributed optimal control (DOC) that is applicable to optimal planning for very-large-scale robotic (VLSR) systems in complex environments. The method is inspired by the nested analysis and design method known as generalized reduced gradient (GRG). The computational complexity analysis presented in this paper shows that the GRG method is significantly more efficient than classical optimal control or direct DOC methods. The GRG method is demonstrated for VLSR path planning in obstacle-populated environments in which robots are subject to external forces and disturbances. The results show that the method significantly improves performance compared to the existing direct DOC and stochastic gradient methods.

Direct Torque Control of Induction Motor with Common-Mode Voltage Elimination

If the common-mode voltage in the induction motor drive is not eliminated, it may cause failure of motor bearings and malfunctioning of the electrical equipment associated with the drive. This article proposes the modified direct torque control technique to control the induction motor fed by three-level inverter, commonly called a neutral-point-clamped inverter. The selective voltage vectors in three-level inverter determine elimination of the common-mode voltage. The classic three-level direct torque control based on selection of 6-full, 6-half, and 2-zero voltage vectors out of available 27 is modified so that the 6-intermediate voltage vectors and a zero voltage vector are employed. A comparative investigation with another three-level direct torque control method which reduces both common-mode voltage and torque ripple is also carried out. These methods are compared with classic two-level direct torque control method in context of common-mode voltage, torque ripple, current total harmonic distortion (THD) and DC-link utilization. The simulation and experimental results validate the proposed common-mode voltage elimination and common-mode voltage reduction direct torque control techniques.

Evaluating the reliability of multi-body mechanisms: A method considering the uncertainties of dynamic performance

Mechanism reliability is defined as the ability of a certain mechanism to maintain output accuracy under specified conditions. Mechanism reliability is generally assessed by the classical direct probability method (DPM) derived from the first order second moment (FOSM) method. The DPM relies strongly on the analytical form of the dynamic solution so it is not applicable to multi-body mechanisms that have only numerical solutions. In this paper, an indirect probability model (IPM) is proposed for mechanism reliability evaluation of multi-body mechanisms. IPM combines the dynamic equation, degradation function and Kaplan–Meier estimator to evaluate mechanism reliability comprehensively. Furthermore, to reduce the amount of computation in practical applications, the IPM is simplified into the indirect probability step model (IPSM). A case study of a crank–slider mechanism with clearance is investigated. Results show that relative errors between the theoretical and experimental results of mechanism reliability are less than 5%, demonstrating the effectiveness of the proposed method.

Constraints in Identification of Multi-Loop Feedforward Human Control Models

Abstract: The human controller (HC) can greatly improve target-tracking performance by utilizing a feedforward operation on the target signal, in addition to a feedback response. System identification methods are used to determine the correct HC model structure: purely feedback or a combined feedforward/feedback model. In this paper, we investigate three central issues that complicate this objective. First, the identification method should not require prior assumptions regarding the dynamics of the feedforward and feedback components. Second, severe biases might be introduced by high levels of noise in the data measured under closed-loop conditions. To address the first two issues, we will consider two identification methods that make use of linear ARX models: the classic direct method and the two-stage indirect method of van den Hof and Schrama (1993). Third, model complexity should be considered in the selection of the ‘best’ ARX model to prevent ‘false-positive’ feedforward identification. Various model selection criteria, that make an explicit trade-off between model quality and model complexity, are considered. Based on computer simulations with a HC model, we conclude that 1) the direct method provides more accurate estimates in the frequency range of interest, and 2) existing model selection criteria do not prevent false-positive feedforward identification. Copyright ©2016 IFAC

The impact of next-generation sequencing technologies on HLA research.

In the past decade, the development of next-generation sequencing (NGS) has paved the way for whole-genome analysis in individuals. Research on the human leukocyte antigen (HLA), an extensively studied molecule involved in immunity, has benefitted from NGS technologies. The HLA region, a 3.6-Mb segment of the human genome at 6p21, has been associated with more than 100 different diseases, primarily autoimmune diseases. Recently, the HLA region has received much attention because severe adverse effects of various drugs are associated with particular HLA alleles. Owing to the complex nature of the HLA genes, classical direct sequencing methods cannot comprehensively elucidate the genomic makeup of HLA genes. Thus far, several high-throughput HLA-typing methods using NGS have been developed. In HLA research, NGS facilitates complete HLA sequencing and is expected to improve our understanding of the mechanisms through which HLA genes are modulated, including transcription, regulation of gene expression and epigenetics. Most importantly, NGS may also permit the analysis of HLA-omics. In this review, we summarize the impact of NGS on HLA research, with a focus on the potential for clinical applications.

Life Prediction of FRP Composites by a Direct Method

AbstractA direct computational approach for lifetime prediction of fibre‐reinforced polymer (FRP) composites is presented. The approach is based on a direct method which allows predicting the fatigue life from the stabilised damage state. The classical direct method is generalised to the case of coupled plasticity with damage mechanics of the UD‐FRP composite materials [1]. The constitutive model is based on a continuous damage meso‐scale approach [2]. By analysing damage variables and thermodynamical forces associated with damage at the stabilised state, fatigue life prediction law is proposed as a power law function of stabilised thermodynamic forces. The obtained numerical results have been validated by experimental test results on standard glass‐fibre/epoxy angle‐ply and cross‐ply laminate plates. The proposed approach could serve as a useful tool for the design of FRP composites. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of a new bis(perfluoroalkyl oxirane) dioxyethylene ether

Classic direct synthetic methods failed to transform bis(perfluororalkylallyl) dioxyethylene ether into the corresponding bis(perfluoroalkyl oxirane). This transformation was instead realized using a mixture of mercuric acetate/bromine to produce the corresponding bromoacetate, which was subsequently transformed to a bromohydrin and further to bis(perfluoroalkyl oxirane) through the use of triethylbenzyl ammonium chloride as a phase transfer catalyst in alkaline media.

SHELXT: Integrating space group determination and structure solution

SHELXT is intended for robust routine solution of small molecule crystal structures. It makes the simple but powerful assumption that the structure consists of resolved atoms, but unlike classical direct methods it is not required that the atoms are 'equal'. This enables it to succeed with poor or incomplete data but makes it unsuitable for structures that are twinned, modulated or contain severe (e.g. 'whole molecule') disorder. SHELXT is a dual-space program that starts with a Patterson minimum superposition and iteratively applies the random omit procedure (also used in SHELXD) with data expanded to space group P1, but does not use phase probability relations or solvent flipping. In the SHELX system it will probably obsolete SHELXS but not SHELXD, which is better for large equal-atom and twinned structures. SHELXT reads any legal SHELX format .ins and (HKLF3 or 4) .hkl files. It extracts the Laue group and tries to find space groups in this Laue group and origin shifts to fit the phases from the best P1 solution, and makes an approximate assignment of element types using the elements specified on the SFAC instruction (and maybe a couple more). This is followed by an isotropic refinement and an attempt to assign the absolute structure if the space group is non-centrosymmetric. It is hoped to release SHELXT as part of the SHELX system (http://shelx.uni-ac.gwdg.de/SHELX/index.php) in time for the 2014 Montreal IUCr Meeting.

A method for measuring the contact area in instrumented indentation testing by tip scanning probe microscopy imaging

The determination of the contact area is a key step in deriving mechanical properties such as hardness or an elastic modulus by instrumented indentation testing. Two families of procedures are dedicated to extracting this area: on the one hand, post-mortem measurements that require residual imprint imaging, and on the other hand, direct methods that only rely on the load vs. penetration depth curve. With the development of built-in scanning probe microscopy imaging capabilities such as atomic force microscopy and indentation tip scanning probe microscopy, last-generation indentation devices have made systematic residual imprint imaging much faster and more reliable. In this paper, a new post-mortem method is introduced and further compared to three existing classical direct methods by means of a numerical and experimental benchmark covering a large range of materials. It is shown that the new method systematically leads to lower error levels regardless of the type of material. The pros and cons of the new method vs. direct methods are also discussed, demonstrating its efficiency in easily extracting mechanical properties with enhanced confidence.

A Liquid Inorganic Electrolyte Showing an Unusually High Lithium Ion Transference Number: A Concentrated Solution of LiAlCl4 in Sulfur Dioxide

We report on studies of an inorganic electrolyte: LiAlCl4 in liquid sulfur dioxide. Concentrated solutions show a very high conductivity when compared with typical electrolytes for lithium ion batteries that are based on organic solvents. Our investigations include conductivity measurements and measurements of transference numbers via nuclear magnetic resonance (NMR) and by a classical direct method, Hittorf’s method. For the use of Hittorf’s method, it is necessary to measure the concentration of the electrolyte in a selected cell compartment before and after electrochemical polarization very precisely. This task was finally performed by potentiometric titration after hydrolysis of the salt. The Haven ratio was determined to estimate the association behavior of this very concentrated electrolyte solution. The measured unusually high transference number of the lithium cation of the studied most concentrated solution, a molten solvate LiAlCl4 × 1.6SO2, makes this electrolyte a promising alternative for lithium ion cells with high power ability.

Effects of a Destabilization Heat Treatment on the Microstructure and Abrasive Wear Behavior of High-Chromium White Cast Iron Investigated Using Different Characterization Techniques

The hypoeutectic white cast iron was subjected to various destabilization heat treatment temperatures of 1173 K, 1273 K, and 1373 K (900 °C, 1000 °C, and 1100 °C) for 2 hours. The as-cast and destabilized specimens were characterized by optical metallography, classical direct comparison, and the Rietveld method. The volume fractions of carbides were measured by optical metallography. Moreover, the volume fractions of retained austenite and martensite were measured by the classical direct comparison method. Despite the limitations of optical metallography and the classical direct comparison method, the Rietveld method was successively and accurately applied to determine the volume fractions of all phases. In addition, the Rietveld analysis yielded certain results, such as the crystallographic properties of the phases that can be used to explain the relationship between the microstructural parameters and the wear behavior. Abrasive wear tests with different sliding speeds were carried out on the as-cast and destabilized alloys to identify the effect of microstructural parameters on the wear behavior. The results indicated that the morphologies of secondary carbides, the crystallographic properties of the phases, and the proper combination of the amount of martensite, retained austenite, and carbides were the principle parameters that affect the hardness and wear behavior of the alloy.

Modified Smith predictor design for unstable processes with step and periodic disturbances

In this article, a modified Smith predictor control scheme is proposed for step and periodic disturbance rejection for unstable processes with time delay. The scheme consists of three controllers: first one for set-point tracking, second one for nonperiodic disturbance rejection, and the third one for rejecting the periodic disturbances and improving the robustness. The set-point tracking controller is designed using the classical direct synthesis method based on the process model without considering the time delay. The nonperiodic disturbance rejection controller is also designed using the direct synthesis method. For further improved disturbance attenuation, a periodic disturbance rejection controller is designed. An analysis for the selection of the closed-loop tuning parameters of the controllers is carried out with the peak value of sensitivity function ( MS) as a robustness measure. The present method gives improved nominal and robust performances for step and periodic disturbances and also improved closed-loop performances when compared to recently reported methods.

Leapfrogging and synoptic Leapfrogging: A new optimization approach

A novel optimization technique is introduced and demonstrated. Leapfrogging starts with a randomly located set of trial solutions (termed players) within the feasible decision variable (DV) space. At each iteration, the player with the worst objective function (OF) value is relocated to a random position within its DV-space reflection on the other side of the player with the best OF value. Test cases reveal that this simple algorithm has benefits over classic direct and gradient-based methods and particle swarm in speed of finding the optimum and in handling surface aberrations, including ridges, multi-optima, and stochastic objective functions. Potential limitations and analysis opportunities are discussed.

A review of gradient algorithms for numerical computation of optimal trajectories

In this paper, two classic direct methods for numerical computation of optimal trajectories were revisited: the steepest descent method and the direct one based upon the second variation theory. The steepest descent method was developed for a 0ayer problem of optimal control, with free onal state and o(ed terminal times. Terminal constraints on the state variables were considered through the penalty function method. The second method was based upon the theory of second variation and it involves the closed-loop solutions of a linear quadratic optimal control problem. The algorithm was developed for a Bolza problem of optimal control, with o(ed terminal times and constrained initial and onal states. 3roblems with free onal time are also considered by using a transformation approach. $n algorithm that combines the main characteristics of these methods was also presented. The methods were applied for solving two classic optimization problems 阂 Brachistochrone and Zermelo 阂 and their main advantages and disadvantages were discussed. Finally, the optimal space trajectories transference between coplanar circular orbits for different times of ?ight was calculated, using the proposed algorithm.

Beamforming regularization matrix and inverse problems applied to sound field measurement and extrapolation using microphone array

For sound field reproduction using multichannel spatial sound systems such as Wave Field Synthesis and Ambisonics, sound field extrapolation is a useful tool for the measurement, description and characterization of a sound environment to be reproduced in a listening area. In this paper, the inverse problem theory is adapted to sound field extrapolation around a microphone array for further spatial sound and sound environment reproduction. A general review of inverse problem theory and analysis tools is given and used for the comparative evaluation of various microphone array configurations. Classical direct regularization methods such as truncated singular value decomposition and Tikhonov regularization are recalled. On the basis of the reviewed background, a new regularization method adapted to the problem at hand is introduced. This method involves the use of an a priori beamforming measurement to define a data-dependent discrete smoothing norm for the regularization of the inverse problem. This method which represents the main contribution of this paper shows promising results and opens new research avenues.