Sequential Components Research Articles

Accuracy Enhancement of CNC Multi-Axis Machine Tools through an On-Line Error Identification and Compensation Strategy

In order to improve multi-axis machine accuracy, error compensation techniques have been widely applied. However, the lack of reliable methods for direct, global and comprehensive estimation implies that all compensation techniques are based on off-line sequential error components measurement. These measurements provide static results, and cannot reflect the actual machine conditions. Thus, these results are not representative of the real working conditions because of disturbances from thermal distortions and dynamic perturbations. This paper presents an on-line error identification and compensation approach for CNC multi-axis machine tools. Based on the simultaneous measurement of error components, the proposed identification scheme is built to ensure volumetric error prediction for an adaptive error compensation system. Implemented on a moving bridge type CMM, the approach led to a significant improvement of the three-dimensional measurement accuracy.Compared to the conventional off-line error compensation techniques, the proposed identification and compensation approach can further improve the compensation adaptability and efficiency.

A Novel Hierarchical Section Protection Based on the Solid State Transformer for the Future Renewable Electric Energy Delivery and Management (FREEDM) System

The effectiveness of a protection scheme in any power grid is essential to the reliability of the supply. One of the main goals of the FREEDM systems is to increase supply reliability to end users. However, traditional protection methods, including over current, sequential components, and wide differential area protection, are not suitable for this system for several reasons that will be explained in the paper. A new protection strategy is presented in this paper. This protection scheme takes advantage not only of the system configuration but mostly of the solid state transformer capability and design to minimize any circuit and communication that are needed for a successful protection strategy. A real time digital simulator (RTDS) is used to model a sample FREEDM system in order to verify the proposed protection scheme. Hardware-in-the-loop (HIL) testing was performed to verify the proposed protection scheme.

Dual-CCD Complete Stokes Simultaneously Imaging Polarimeter and Experimental Data Analysis

Polarization imaging technology that is on the basis of the polarization measurement can change the obtained polarization information into two-dimensional image, from which we can acquire polarization characteristics of target scene just like normal gray image so that this technique is widely used in the fields of military investigation, medical testing, space exploration, meteorology and so on. Traditional imaging polarimeter is time sequence polarization imaging, which is to use sequential rotational polarization components (line polarizer or wave plate etc.) and to combine Fourier analysis method to acquire final Stokes components. But because of the sacrificing of temporal resolution, this technique does not meet the needs of the situation of high-speed dynamic changing scene. While current simultaneously polarization imaging technique commonly uses multiple sets of optical systems and at least four CCD cameras, which have the problems of low energy utilization rate and non-matching performance among the optical sets. To solve the aforementioned problems, we design and implement a set of non-mechanical rotating parts, double Wollaston prisms-based high resolution simultaneously imaging polarimeter. This system uses the specific combination of non-polarizing beam splitter, Wollaston prisms and wave plates to divide the incident target space beam into four optical paths of different polarization states which can be taken into two types: two paths in the reflection part and two paths in the transmission part. Finally the imaging lens converge the beam to different regions of two large array CCD to image four images. To achieve the goal of extracting complete Stokes information, we apply the Stokes vector and Mueller matrix analysis. The article presents systems structure, working theory, calibration method, experiment data analysis and system polarization performance, which provides a good reference for the simultaneously high-speed polarization imaging.

Mammographical mass detection and classification using Local Seed Region Growing–Spherical Wavelet Transform (LSRG–SWT) hybrid scheme

The purpose of this study is to implement accurate methods of detection and classification of benign and malignant breast masses in mammograms. Our new proposed method, which can be used as a diagnostic tool, is denoted Local Seed Region Growing–Spherical Wavelet Transform (LSRG–SWT), and consists of four steps. The first step is homomorphic filtering for enhancement, and the second is detection of the region of interests (ROIs) using a Local Seed Region Growing (LSRG) algorithm, which we developed. The third step incoporates Spherical Wavelet Transform (SWT) and feature extraction. Finally the fourth step is classification, which consists of two sequential components: the 1st classification distinguishes the ROIs as either mass or non-mass and the 2nd classification distinguishes the masses as either benign or malignant using a Support Vector Machine (SVM). The mammograms used in this study were acquired from the hospital of Istanbul University (I.U.) in Turkey and the Mammographic Image Analysis Society (MIAS). The results demonstrate that the proposed scheme LSRG–SWT achieves 96% and 93.59% accuracy in mass/non-mass classification (1st component) and benign/malignant classification (2nd component) respectively when using the I.U. database with k-fold cross validation. The system achieves 94% and 91.67% accuracy in mass/non-mass classification and benign/malignant classification respectively when using the I.U. database as a training set and the MIAS database as a test set with external validation.

Sequential Projection Pursuit Principal Component Analysis – Dealing with Missing Data Associated with New -Omics Technologies

Principal Component Analysis (PCA) is a common exploratory tool used to evaluate large complex data sets. The resulting lower-dimensional representations are often valuable for pattern visualization, clustering, or classification of the data. However, PCA cannot be applied directly to many -omics data sets generated by newer technologies such as label-free mass spectrometry due to large numbers of non-random missing values. Here we present a sequential projection pursuit PCA (sppPCA) method for defining principal components in the presence of missing data. Our results demonstrate that this approach generates robust and informative low-dimensional data representations compared to commonly used imputation approaches.

A unified current control scheme for voltage source converter high voltage direct current under unbalanced grid conditions

This paper presents a novel unified dynamic model and vector current control strategy to improve voltage source converter (VSC) based high voltage direct current (HVDC) (VSC-HVDC) transmission system performance under unbalanced system conditions. Both the AC- and DC-side models are developed in the unique positive synchronously rotating reference (dq-p) frame with respect to both the positive- and negative-sequence components. Based on the model, the active power (or DC voltage) control is schemed with a proportional-integral regulator plus a resonant integrator, intended to eliminate the 2ω ripple in the DC-link, and reactive power control resorts to a resonant filter to mitigate the current harmonic distortion due to the ripple component. To prevent the sequential component decomposition, the current control of both the positive- and negative-sequence components is designed in a unified way in the stationary alphabeta frame. The proposed strategy can maintain rather low level AC current harmonics along with the DC-link 2ω ripple elimination, enhancing the VSC-HVDC operational ability under AC unbalanced conditions. The PSCAD/EMTDC simulation results verify the validity of the proposed strategy.

A Unified Current Control Scheme for Voltage Source Converter High Voltage Direct Current Under Unbalanced Grid Conditions

This paper presents a novel unified dynamic model and vector current control strategy to improve voltage source converter (VSC) based high voltage direct current (HVDC) (VSC-HVDC) transmission system performance under unbalanced system conditions. Both the AC- and DC-side models are developed in the unique positive synchronously rotating reference (dq-p) frame with respect to both the positive- and negative-sequence components. Based on the model, the active power (or DC voltage) control is schemed with a proportional-integral regulator plus a resonant integrator, intended to eliminate the 2ω ripple in the DC-link, and reactive power control resorts to a resonant filter to mitigate the current harmonic distortion due to the ripple component. To prevent the sequential component decomposition, the current control of both the positive- and negative-sequence components is designed in a unified way in the stationary αβ frame. The proposed strategy can maintain rather low level AC current harmonics along with the DC-link 2ω ripple elimination, enhancing the VSC-HVDC operational ability under AC unbalanced conditions. The PSCAD/EMTDC simulation results verify the validity of the proposed strategy.

The Research of The Pulse Power Source Sequential Control System

The pulse power source; Control system; Sequential control; Trigger control Abstract. In this essay, the working process of Capacitor-Based Pulsed-Power System and the requirement of the sequential control component applied in such system has been discussed. Based on that, further description of the composition and working principle of the sequential control system has been made .The diagram of each block of the sequential control system are displayed to illustrate the working process in engineering application and problems would confront in engineering designing process. Finally, the charging and discharging test and electromagnetic emission experiments have been conducted and prove that such sequential control system can function stably and reliably in strong electromagnetic interference environment and it also has good expansibility.

Improvement of dynamic performance of doubly fed induction generator-based wind turbine power system under an unbalanced grid voltage condition

With the current increase in wind power penetration into the energy market, control and operation of wind turbine generators becomes a major research topic. Wind turbine based on doubly fed induction generator (DFIG), which is sensitive to grid disturbances, is widely used. Under an unbalanced grid voltage condition, oscillations of the DFIG's electromagnetic torque and instantaneous stator powers strongly affect the dynamic performance of the DFIG. In this study, a new configuration based on vector proportional'integral (VPI) controller is proposed to eliminate such oscillations. This new configuration is employed in the rotor side converter (RSC) of the DFIG. With the proposed VPI control strategy, decomposition of sequential components and mathematical complexity are reduced. Compared with the conventional field-oriented control based on the standard single PI controller, the VPI controller can successfully eliminate torque and stator power oscillations. The effectiveness of the proposed control strategy is validated through simulation results obtained on a 1.5'MW DFIG-based wind turbine system model built in MATLAB/Simulink.

Transient currents in a molecular photo-diode

Light-induced charge transmission through a molecular junction (molecular diode) is studied in the framework of a HOMO–LUMO model and in using a kinetic description. Expressions are presented for the sequential (hopping) and direct (tunneling) transient current components together with kinetic equations governing the time-dependent populations of the neutral and charged molecular states which participate in the current formation. Resonant and off-resonant charge transmission processes are analyzed in detail. It is demonstrated that the transient currents are associated with a molecular charging process which is initiated by photo excitation of the molecule. If the coupling of the molecule to the electrodes is strongly asymmetric the transient currents can significantly exceed the steady state current.

Using Online Learning and Interactive Simulation To Teach Spiritual and Cultural Aspects of Palliative Care to Interprofessional Students

To meet the complex needs of patients with serious illness, health professional students require education in basics aspects of palliative care, including how to work collaboratively on an interprofessional team. An educational program was created, implemented, and evaluated with students in medicine, nursing, chaplaincy, and social work. Five learning objectives emphasized spiritual, cultural, and interprofessional aspects of palliative care. The program blended two sequential components: an online interactive, case-based learning module, and a live, dynamic simulation workshop. Content analysis was used to analyze students' free-text responses to four reflections in the online case, as well as open-ended questions on students' postworkshop questionnaires, which were also analyzed quantitatively. Analysis of 217 students' free-text responses indicated that students of all professions recognized important issues beyond their own discipline, the roles of other professionals, and the value of team collaboration. Quantitative analysis of 309 questionnaires indicated that students of all professions perceived that the program met its five learning objectives (mean response values>4 on a 5-point Likert scale), and highly rated the program and its two components for both educational quality and usefulness for future professional work (mean response values approximately>4). This innovative interprofessional educational program combines online learning with live interactive simulation to teach professionally diverse students spiritual, cultural, and interprofessional aspects of palliative care. Despite the challenge of balanced professional representation, this innovative interprofessional educational program met its learning objectives, and may be transferable for use in other educational settings.

Steady state vapor compression refrigeration cycle simulation for a monovalent inverter-driven water-to-water heat pump with a desuperheater for low energy houses

A steady-state simulation is presented for a monovalent inverter-driven water-to-water heat pump with a desuperheater. For design-oriented simulations, superheating or subcooling degrees are used as input. However, the proposed simulation only uses the system's refrigerant charge, environmental, and control parameters, which make it particularly useful for off-design evaluations, including the annual performance factor calculation. Block models were used for the compressor and electronic expansion valve, while novel adaptive zone models were used for the heat exchangers. A multivariable error minimization algorithm was used over a sequential component scheme to provide global convergence. The numerical calculations were compared with 118 experimental results. The resulting COP agrees within 10% for 95.77% of the data. The mapping results reveal a maximum COP deviation of 8.78%. Computational results for the studied system reveal that a constant degree of superheating might not always maximize the COP.

Employing a RGB-D sensor for real-time tracking of humans across multiple re-entries in a smart environment

The term smart environment refers to physical spaces equipped with sensors feeding into adaptive algorithms that enable the environment to become sensitive and responsive to the presence and needs of its occupants. People with special needs, such as the elderly or disabled people, stand to benefit most from such environments as they offer sophisticated assistive functionalities supporting independent living and improved safety. In a smart environment, the key issue is to sense the location and identity of its users. In this paper, we intend to tackle the problems of detecting and tracking humans in a realistic home environment by exploiting the complementary nature of (synchronized) color and depth images produced by a low-cost consumer-level RGB-D camera. Our system selectively feeds the complementary data emanating from the two vision sensors to different algorithmic modules which together implement three sequential components: (1) object labeling based on depth data clustering, (2) human re-entry identification based on comparing visual signatures extracted from the color (RGB) information, and (3) human tracking based on the fusion of both depth and RGB data. Experimental results show that this division of labor improves the system?s efficiency and classification performance.

Operation of Wind-Turbine-Driven DFIG Systems Under Distorted Grid Voltage Conditions: Analysis and Experimental Validations

This paper presents enhanced control strategies for doubly fed induction generator (DFIG)-based wind power generation systems under distorted grid voltage conditions. The mathematical model of DFIG, in view of the fifth- and seventh-order components of grid voltage harmonics, is proposed and analyzed in detail. Based on the analytical model, further studies are conducted on the distortions of stator/rotor currents and the oscillations in the stator active/reactive powers as well as the electromagnetic torque, where the impact of DFIG's load conditions is considered. Meanwhile, alternative rotor current references are calculated to enhance the uninterruptable operation capability of the wind-turbine-driven DFIG systems under distorted grid conditions. An improved software PLL is designed, which is capable of accurately and rapidly tracking the frequency and phase angle of the fundamental grid voltage under distorted grid conditions. A proportional integral plus resonant (PI-R) current controller in the synchronously rotating (dq) reference frame is employed to simultaneously regulate the fundamental and harmonic components of rotor currents without any sequential component decomposition. Experiment results on a 3-kW DFIG prototype demonstrate the correctness of the analytical results and the effectiveness of the software PLL and PI-R current controller when the grid voltage is distorted.

Typology of engineering mathematics learners in a Singapore polytechnic: a socio-psychological perspective

This study aims to understand how engineering mathematics students form intentions in mathematics learning from a socio-psychological perspective. A grounded theory approach was adopted and 21 engineering students and six tutors participated in the study. The main findings in this study show that a student's intention in engineering mathematics learning is made up of a number of sequential components – their critical trigger, internalized significance, aim and perceived intention-related consequences in engineering mathematics learning. Accordingly, the participants may be broadly classified into five types of learners: idealistic learners, competitive learners, pragmatic learners, fatalistic learners and dissonant learners according to their intentions in engineering mathematics learning.

Brain glycogen—new perspectives on its metabolic function and regulation at the subcellular level

Glycogen is a complex glucose polymer found in a variety of tissues, including brain, where it is localized primarily in astrocytes. The small quantity found in brain compared to e.g., liver has led to the understanding that brain glycogen is merely used during hypoglycemia or ischemia. In this review evidence is brought forward highlighting what has been an emerging understanding in brain energy metabolism: that glycogen is more than just a convenient way to store energy for use in emergencies—it is a highly dynamic molecule with versatile implications in brain function, i.e., synaptic activity and memory formation. In line with the great spatiotemporal complexity of the brain and thereof derived focus on the basis for ensuring the availability of the right amount of energy at the right time and place, we here encourage a closer look into the molecular and subcellular mechanisms underlying glycogen metabolism. Based on (1) the compartmentation of the interconnected second messenger pathways controlling glycogen metabolism (calcium and cAMP), (2) alterations in the subcellular location of glycogen-associated enzymes and proteins induced by the metabolic status and (3) a sequential component in the intermolecular mechanisms of glycogen metabolism, we suggest that glycogen metabolism in astrocytes is compartmentalized at the subcellular level. As a consequence, the meaning and importance of conventional terms used to describe glycogen metabolism (e.g., turnover) is challenged. Overall, this review represents an overview of contemporary knowledge about brain glycogen and its metabolism and function. However, it also has a sharp focus on what we do not know, which is perhaps even more important for the future quest of uncovering the roles of glycogen in brain physiology and pathology.

Performance Enhancement of Stand-Alone DFIG Systems With Control of Rotor and Load Side Converters Using Resonant Controllers

In this paper, the control of a stand-alone doubly fed induction generator (DFIG)-based wind power conversion system with unbalanced and nonlinear loads is investigated. Under these load conditions, the quality of stator voltage and current waveforms of the DFIG is strongly affected due to the negative and distorted components, reducing the performance of other normal loads connected to the DFIG. To tackle this problem, the control strategy is comprehensively developed in both rotor-side converter (RSC) and load-side converter (LSC) of the DFIG. The LSC is used as an active power filter to compensate for unbalanced and distorted stator currents whereas the RSC is developed to fully eliminate unbalanced and harmonic voltages at the point of common coupling. The proposed compensation method is based on current controllers in either the RSC or the LSC, which employ a proportional integral plus a resonant controller. These current controllers are controlled in the positive synchronous reference frame so that the rotor current and stator current are directly regulated without decomposing sequential components. Analytical issues on how to eliminate unbalanced and distorted components in the stator voltage and current are also described in this paper. To verify the effectiveness of the proposed control strategy, experimental results with 2.2-kW DFIG topology are presented and discussed in the paper.

Different Signaling Pathways Stimulate a Disintegrin and Metalloprotease-17 (ADAM17) in Neutrophils during Apoptosis and Activation

ADAM17 is a membrane-associated metalloprotease that cleaves proteins from the surface of neutrophils and modulates the density of various receptors and adhesion molecules. The protease activity of ADAM17 is highly inducible and occurs upon neutrophil activation as well as apoptosis. At this time, little is known about the signal transduction pathway that promotes ADAM17 activity in neutrophils upon the induction of apoptosis. We show that caspase-8 activation, Bid cleavage, and the release of mitochondrial reactive oxygen species are sequential transduction components of the Fas signaling cascade that induces ADAM17. This is different from ADAM17 stimulation upon overt neutrophil activation, which requires MAPK p38 or ERK, but not caspases and reactive oxygen species. ADAM17 activity in apoptotic neutrophils may serve to inactivate select effector molecules that promote the pro-inflammatory activity of recruited neutrophils. For instance, TNFα receptors TNF-RI and TNF-RII are substrates of ADAM17, and we show that they are shed during apoptosis, decreasing neutrophil sensitivity to TNFα. Altogether, our findings provide significant new insights into the signal transduction pathway that stimulates ADAM17 during induced neutrophil apoptosis. ADAM17 induction during apoptosis may rapidly diminish neutrophil sensitivity to the inflammatory environment, complementing other anti-inflammatory activities by these cells during inflammation resolution.

Efficiently speeding up sequential computation through the n-way programming model

With core counts on the rise, the sequential components of applications are becoming the major bottleneck in performance scaling as predicted by Amdahl's law. We are therefore faced with the simultaneous problems of occupying an increasing number of cores and speeding up sequential sections. In this work, we reconcile these two seemingly incompatible problems with a novel programming model called N-way. The core idea behind N-way is to benefit from the algorithmic diversity available to express certain key computational steps. By simultaneously launching in parallel multiple ways to solve a given computation, a runtime can just-in-time pick the best (for example the fastest) way and therefore achieve speedup. Previous work has demonstrated the benefits of such an approach but has not addressed its inherent waste. In this work, we focus on providing a mathematically sound learning-based statistical model that can be used by a runtime to determine the optimal balance between resources used and benefits obtainable through N-way. We further describe a dynamic culling mechanism to further reduce resource waste. We present abstractions and a runtime support to cleanly encapsulate the computational-options and monitor their progress. We demonstrate a low-overhead runtime that achieves significant speedup over a range of widely used kernels. Our results demonstrate super-linear speedups in certain cases.

Insight into low frequency noise induced by gate leakage current in AlGaAs/GaAs high electron mobility transistors at 4.2 K

The bias-cooling method—the gate being kept biased at Vgc during the cooling—has been used to investigate the low frequency noise (LFN) in an AlGaAs/GaAs two-dimensional electron gas high electron mobility transistor at 4.2 K. For a chosen working point (i.e., a chosen drain bias/current), its gate bias Vgs, gate leakage current Igs, and LFN depend on Vgc. With the help of the heterostructure band diagram simulation for each Vgc, the relation between Igs and the LFN can be elucidated by the gate Fermi level with regard to the heterostructure band diagram. The LFN originated from Igs is caused by its sequential tunnelling component.