Large Number Of Levels Research Articles

Handling categorical features with many levels using a product partition model

A common difficulty in data analysis is how to handle categorical predictors with a large number of levels or categories. Few proposals have been developed to tackle this important and frequent problem. We introduce a generative model that simultaneously carries out the model fitting and the aggregation of the categorical levels into larger groups. We represent the categorical predictor by a graph where the nodes are the categories and establish a probability distribution over meaningful partitions of this graph. Conditionally on the observed data, we obtain a posterior distribution for the levels aggregation, allowing the inference about the most probable clustering for the categories. Simultaneously, we extract inference about all the other regression model parameters. We compare our and state-of-art methods showing that it has equally good predictive performance and more interpretable results. Our approach balances out accuracy vs. interpretability, a current important concern in statistics and machine learning.

Insurance pricing with hierarchically structured data an illustration with a workers' compensation insurance portfolio

Actuaries use predictive modeling techniques to assess the loss cost on a contract as a function of observable risk characteristics. State-of-the-art statistical and machine learning methods are not well equipped to handle hierarchically structured risk factors with a large number of levels. In this paper, we demonstrate the data-driven construction of an insurance pricing model when hierarchically structured risk factors, contract-specific as well as externally collected risk factors are available. We examine the pricing of a workers' compensation insurance product with a hierarchical credibility model [Jewell, W. S. (1975). The use of collateral data in credibility theory: A hierarchical model. Laxenburg: IIASA], Ohlsson's combination of a generalized linear and a hierarchical credibility model [Ohlsson, E. (2008). Combining generalized linear models and credibility models in practice. Scandinavian Actuarial Journal 2008(4), 301–314] and mixed models. We compare the predictive performance of these models and evaluate the effect of the distributional assumption on the target variable by comparing linear mixed models with Tweedie generalized linear mixed models. For our case-study the Tweedie distribution is well suited to model and predict the loss cost on a contract. Moreover, incorporating contract-specific risk factors in the model improves the predictive performance and the risk differentiation in our workers' compensation insurance portfolio.

DESIGN AND SYNTHESIS OF TERNARY LOGIC ELEMENTS

The aim of this paper is creating some ternary elements. The threshold element of ternary logic on bipolar transistors and elements of ternary systems based on it are considered. The main disadvantages of this approach are identified. The multi-threshold element of multivalued logic and its specific four-threshold implementation are considered. The scientific nowelty is the using of a multithreshold element of multivalued logic as a basis for constructing elements of ternary systems. It is shown that the advantages of a multi-threshold element of multi-valued logic are a larger number of thresholds of input signals, a larger number of levels that it can distinguish and a larger number of output signals. The implementation of some ternary elements, such as half-adder, disjunction and strong conjunction, is given. The practical significance of obtained results is that the multithreshold element of multivalued logic allows us to use it for synthesis basic elements of ternary logic and use one approach for all of them. Additional practical advantage is that in practice it allows you to build more diverse logical and arithmetic devices with a simplified implementation. The implementation of ternary devices based on threshold logic is a way to create ternary devices that can compete with binary devices in terms of equipment, capacity, operational capabilities, and variety. This, in turn, leads to greater speed and simplification of the structure of devices, as well as increasing the speed of data processing. These advantages are significant in such areas of computer use as intelligent data processing systems, expert systems, decision theory, i.e., where data analysis is performed. Prospects for further research are to use the method of construction and synthesis of nodes of ternary computer systems, based on MTEML. Their optimization, and development of principles of mathematical modeling and software of such systems and their elements is expedient.

Correction to: Sobolev analysis of methanimine with large number of levels: requirement of collisional rate coefficients

Correction to: Sobolev analysis of methanimine with large number of levels: requirement of collisional rate coefficients

Non-Life Insurance Risk Classification Using Categorical Embedding

This article presents several actuarial applications of categorical embedding in the context of non-life insurance risk classification. In non-life insurance, many rating factors are naturally categorical, and often the categorical variables have a large number of levels. The high cardinality of categorical rating variables presents challenges in the implementation of traditional actuarial methods. Categorical embedding that is proposed in the machine learning literature for handling categorical variables has recently received attention in actuarial studies. The method is inspired by the neural network language models for learning text data and maps a categorical variable into a real-valued representation in the Euclidean space. Using a property insurance claims we demonstrate the use of categorical embedding in three applications. The first shows how embeddings are used to construct rating classes and calculate rating relativities for a single insurance risk. The second concerns predictive modeling for multivariate insurance risks and emphasizes the effects of dependence on tail risks. The third focuses on pricing new products where transfer learning is used to gather knowledge from existing products.

Sobolev analysis of methanimine with large number of levels: requirement of collisional rate coefficients

Sobolev analysis of methanimine with large number of levels: requirement of collisional rate coefficients

Studi Analisis Perbandingan Pwm Carrier Untuk Multilevel Inverter Tiga Fasa Lima Belas Level Dengan Sumber Input Simetris Terpisah

Inverters are used to convert direct current or DC (Direct Current) sources into alternating current sources or AC (Alternating Current). A method is needed to make the output waveform close to a sinusoidal waveform. The Multi Level Inverter (MLI) method has a large number of levels and is closer to a sinusoidal wave. The three-phase MLI design with a separate symmetrical input source in this study is able to produce a three-phase output wave, where the resulting Total Harmonic Distortion (THD) value is smaller, namely 5.65% when using the Modified PWM method where the carrier signal has no frequency

Space Vector Techniques for a Binary-Cascaded Multilevel Inverter Operating Under Reduced Common-Mode Voltage With Reduced Commutations

This paper presents a novel space vector pulse width modulation (SVPWM) for a three-phase binary cascaded multilevel inverter. The SVPWM could become impractical in multilevel inverters (MLIs) because of its increasing complexity with a larger number of levels. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gh</i> coordinate system can ease the digital implementation, but to generate the inverter's <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc</i> states from the nearest three vectors (NTVs), iterative computations are required every sampling instant. This paper proposes further reduction of computations by directly generating the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc</i> state with minimum common-mode voltage (CMV) from a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gh</i> vector. Subsequently, only one vector among the NTVs is required for implementing the proposed SVPWM. The reduced CMV profile within the NTVs further permits the reduction of commutations by clamping one phase during a sampling period. The presented technique exhibits full dc bus utilization capability and can be implemented in the binary cascaded MLI (BCMLI) and further applied to any <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -level MLI. Also, if <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> is considerably large or if switching losses and electromagnetic interference emissions must be minimized, nearest vector modulation with reduced CMV along with line-frequency operation of high-voltage cells can be implemented to reduce the switching losses. Experiment results of a BCMLI is presented to verify the effectiveness of the proposed technique.

Submodule fault-tolerant control based adaptive carrier-PDPWM for modular multilevel converters

The modular multilevel converter (MMC) is considered a very promising candidate for medium-voltage and/or high-power grids. One of the major concerns in half-bridge MMCs, especially with large number of levels, is the fault occurs at the converter submodule (SM). Hence, an appropriate control with an SM fault tolerance of the MMC is required to enhance its reliability. This paper addresses the issue and proposes a fault tolerant control-based adaptive carrier phase disposition pulse width modulation (AC-PDPWM) technique for MMCs with superior symmetrical and asymmetrical fault-tolerant capabilities. The proposed control-based AC-PDPWM acts to regulate the flow of energy between arms, rebalance the SM capacitors, and redistribute the pulses to the SM switches. In this study, a single-phase grid connected MMC having both symmetrical and asymmetrical fault conditions is investigated. Compared with other control methods, the proposed control can tolerate the SM fault conditions without requiring redundant SMs or additional computational burden, which decreases the cost and volume of the MMC design and simplifies its control. Simulation and experimental results are included to verify the fault-tolerant capability of the proposed control.

Laryngoscopic Screening Before Revision Anterior Cervical Spine Surgery: Is Vocal Cord Palsy a Relevant Factor in Deciding the Approach Direction?

Retrospective study. The aim was to evaluate the exact incidence of vocal cord palsy (VCP) caused by previous anterior cervical spine surgery (ACSS) and aid surgeons in deciding the approach direction in revision ACSS. The incidence of VCP detected by preoperative laryngoscopic screening before revision ACSS appeared to be much higher in previous reports than in our experience. We reviewed the data of 64 patients who underwent revision ACSS. Preoperative laryngoscopy was performed in all patients to detect VCP and/or structural abnormalities of the vocal cords. The patients' characteristics, laryngoscopy results, and symptoms before revision surgery that were potentially caused by previous recurrent laryngeal nerve injuries (voice change, foreign body sensation, and chronic aspiration) were recorded. Laryngoscopy demonstrated no complete VCP or decreased vocal cord motility. Eleven patients (17.2%) showed vocal cord-related symptoms and 13 patients (20.3%) showed abnormal laryngoscopic findings without VCP. Four patients (6.2%) showed vocal cord-related symptoms and abnormal laryngoscopic findings simultaneously. At the initial operative level, no significant differences in vocal cord-related symptoms were observed between the upper and lower levels (C3-4-5 vs. C5-6-7). However, the frequency of vocal cord-related symptoms was significantly high at the larger number of levels (≥3 segments) (P=0.010). In contrast to previous reports, this study demonstrated that VCP is rarely detected before revision ACSS. Therefore, deciding the approach direction with only vocal cord motility can be dangerous, and more attention is required in setting the approach direction in patients who show both vocal cord-related symptoms and abnormal laryngoscopic finding. In other cases, a contralateral approach which has a low risk of bilateral VCP could be utilized if necessary.

Optimal Denial-of-Service Attack Strategy on State Estimation Over Infinite-Time Horizon

Security issues of cyber-physical systems have become a timely and hot topic in recent years. In this brief, we investigate the power-constrained optimal denial-of-service (DoS) attack strategy with multiple power levels on state estimation over infinite-time horizon. We start from the two-level case and explicitly derive out the basic form of optimal attack strategy. In order to handle the intractability brought about by the larger number of levels, we develop an equivalent property for general multi-level cases that the multi-level scheduling can be viewed as a feasible combination of several sub-schedules with a designed stochastic-triggered manner, which provides a necessary condition of optimal solution. Moreover, based on the practical communication model, we give the condition under which the optimal schedule can be uniquely and explicitly determined for the two-pick strategy. Numerical simulations are accomplished to verify the effectiveness of our proposed methods.

Nonparametric modeling via two-way mixed effects design

The classical F-test for testing the hypothesis of no fixed main effects in a mixed effects design is valid under the assumption of normality, symmetry and variance homogeneity of the error terms assumption. We consider the two-way mixed effects design which does not require these three assumptions. A test procedure for the hypothesis of no main fixed effects is developed under this flexible model. The asymptotic distribution of the test statistic is studied for a large number of levels of the random effects.

A new boost switched capacitor seven‐level grid‐tied inverter

In this paper, a new switched capacitor-based multilevel inverter structure is suggested. The proposed topology can generate seven-level output voltage waveform using ten power electronic switches and two floating capacitors. This structure has the ability to boost the input DC voltage, up to 1.5 times. Although this topology can generate an output waveform with large number of levels, it does not increase the voltage stress on the power electronic switches. There is no need for capacitor voltage balancing in this structure since the capacitors are balanced through charging and discharging modes of operation. In addition, the suggested switched capacitor inverter reduces the number of input dc power supplies and uses a single dc source such as a photovoltaic (PV) panel. Since the proposed inverter is an neutral point clamp based multilevel inverter topology, the leakage current is minimized and as a result the overall efficiency of the proposed system is increased. The operation modes and steady-state analysis of the proposed structure are explained in detail. In order to validate the feasibility of the proposed topology, some experimental results are presented in the grid connected mode of operation.

Optimal design of a cascaded rectangular‐type and circle‐type multilevel inverters with a new switching technique

Multilevel inverters (MLIs) are extensively used in industrial and renewable energy applications. They are a promising solution for the effective transformation of dc to ac. Researchers are developing auspicious topologies to mitigate the use of an output filter, which reduces cost and complexity. Hence, it is necessary to develop a topology that is capable of increasing output voltage levels with an optimum number of power electronic components. However, in developed topologies, a large number of switches, gate driver circuits, and dc sources are used. To solve this problem, a new MLI structure is introduced. The proposed structure is cascaded to form cascaded rectangular-type and circle-type topologies capable of engendering maximum output voltage levels and incorporating an optimum number of switches, gate driver circuits, and dc-sources. Moreover, conventional switching techniques have become more complex, while generating a staircase output contains a large number of levels. Therefore, this study proposes a novel switching technique that is easy to implement in MLIs with large output voltage levels. To show the competency of the proposed topology, a comprehensive comparison is performed with various structures. At the end of this study, validation of the proposed switching technique and topology is verified by simulations and experimentations.

Multilevel axicon for perfect optical vortex generation

We present the fabrication of a beam shaper with 32 levels for the generation of nondiffractive optical fields representing quasi-Bessel beams of order zero. This optical element is designed for visible light (λ=633 nm) and fabricated using standard photolithography and a fine calibrated reactive ion etching process. A large number of levels approximates a continuous conical surface so that the optical quality of the element is very good. It is investigated the possibility of generating perfect optical vortices with this class of optical elements.

New Selective Harmonic Elimination-Pulse-Width Modulation for Cascaded H-bridge Multilevel Inverters

AbstractThis paper presents a univariate equation-based selective harmonic elimination-pulse-width modulation (USHE-PWM) method for cascaded H-bridge (CHB) multilevel inverters (MLIs). Using equal-area criteria, the selection of voltage rating of dc-links have been done. The output voltage is controlled by inserting switching notch at the centre of each level of output voltage. Instead of conventional transcendental SHE-PWM equations, all these calculations are accomplished using univariate equations. This simplifies the real-time implementation of the proposed method greatly, even for the MLI with a large number of levels. The USHE-PWM method can eliminate more harmonics compared with the conventional SHE-PWM methods. While controlling the output voltage, the harmonic pattern remains unaffected. The validity of the proposed method is confirmed by the simulation and experimental studies.

Chain of magnetic tunnel junctions as a spintronic memristor

In the context of neuromorphic computation, spintronic memristors are investigated for their use as synaptic weights. In this paper, we propose and experimentally demonstrate a resistive synaptic device based on ten magnetic tunnel junctions (MTJs) connected in a serial configuration. Our device exhibits multiple resistance levels that support its use as a synaptic element. It allows for two operating knobs: external magnetic field and voltage pulses (Spin-Transfer Torque). Moreover, it can be operated in different ways. When varying continuously the amplitude of the voltage pulse and/or the magnetic field, eleven resistance states can be reached. In contrast, if the initial state of the chain is reset between every step, a very large number of levels are reached. Ideally, a total of 2N resistance levels could be accessible. This coincides well with the desired analog-like behavior in ideal memristors. Since this device consists of a scalable number of N MTJs, and MTJ technology is continuously optimized and improved, the proposed memristor shows promise as a scalable synapse solution for neuromorphic hardware implementations.

A Developed Two-Leg Ladder Multilevel Converter Structure

The applications of multilevel converters (MCs) in industry have been increased because of their advantages such as high quality output waveform and lower harmonic distortions. This paper proposes an improved two-leg ladder topology for MC. For generating all levels at output voltage waveform, two methods are investigated for selecting the values of dc sources. The suggested structure generates a large number of levels at output voltage waveform with the least number of power electronic components such as insulated gate bipolar transistors, gate driver circuits, dc voltage sources and anti-parallel diodes in comparison with other similar topologies. Also, the magnitude of blocked voltage by switches is low. Power losses analysis on the proposed topology is provided. It is shown that the number of on-state switches in the presented structure is less than other similar topologies, which causes the voltage drop and power losses of proposed topology to be reduced. To show the merits of the proposed structure, comparison results are provided with other structures. To validate the analytical results of proposed topology, an experimental work for a 9-level converter and the simulation results for a 25-level converter are provided. PSCAD/EMTDC software is used for simulation works.

Radiative rates for E1, E2, M1, and M2 transitions in Ne-like Hf LXIII, Ta LXIV and Re LXVI

Calculations for energy levels, radiative rates and lifetimes have been performed for three Ne-like ions, namely Hf LXIII, Ta LXIV and Re LXVI, for which the general-purpose relativistic atomic structure package (GRASP) has been adopted. Results are presented among the lowest 121 levels of these ions, which belong to the 2s22p6, 2s22p53ℓ, 2s2p63ℓ, 2s22p54ℓ, 2s2p64ℓ, and 2s22p55ℓ configurations, but CI (configuration interaction) has been considered among a much larger number of levels. No measurements for energy levels are available but comparisons have been made with the earlier similar theoretical results. Additionally, calculations have also been performed with the flexible atomic code (FAC) in order to assess the effect of (much) larger CI on energy levels.

Middle-Level SHE Pulse-Amplitude Modulation for Cascaded Multilevel Inverters

This letter presents a novel middle-level selective harmonic elimination-pulse-amplitude modulation (SHE-PAM) method to calculate switching angles and to synthesize reference voltage for variable dc voltage sources connected to multilevel inverter. Instead of conventional multivariable nonlinear transcendental SHE-pulse-width modulation (SHE-PWM) equations or polynomial equations derived from them, the proposed method works on univariate linear equations. Due to reduced computational complexities, it can be implemented in real-time for the inverter having a large number of levels. Without amplifying the magnitude of higher order harmonics, proposed method eliminates a significant number of harmonics as compared to SHE-PWM and conventional SHE-PAM methods. The total harmonic distortion (THD) of the output voltage is a function of only number of voltage levels and remains constant for a whole range of modulation index. The theoretical analysis and working characteristics of suggested method are validated by simulation and experimental studies.