Plateau Phenomenon Research Articles

A Universal Power Flow Model for Dual Active Bridge-Based Converters With Phase Shift Modulation

In this article, a universal power flow model for the dual active bridge (DAB)-based dc-dc converters with phase-shift modulation is derived. The model considers the lossy components, the dead time, and the resonant commutations of the converters. A power flow model for the partial parallel dual active bridge (P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> DAB) converter is generated from the universal power flow model. Based on the calculations, the power plateau phenomenon and the antipower phenomenon, as well as their causes and influences are discussed. Because of the zero-reactive power loss in the lagging full bridge, the zero-voltage turn on of all of the switches, and the zero-current commutation of the switches in the lagging full bridge during the power plateau, a hypothesis, which claims that the converter is more efficient in the power plateau operation than in other operation modes, is made. A laboratory prototype of the P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> DAB converter is constructed. The analysis about the power plateau and the antipower phenomenon is verified, as well as the proposed hypothesis is proved. Compared against the measured power, the model for the (P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> DAB) converter has the maximum error less than 10%. Therefore, the validity of the universal power flow model is verified.

Plateau dynamics with quantized oscillations of a strongly driven qubit

We present an interesting dynamical temporal localization of a strongly driven two-level system (TLS), a plateau with quantized oscillation, by an analytical and transparent method, the counter-rotating-hybridized rotating-wave (CHRW) method. This approach, which is based on unitary transformations with a single parameter, treats the rotating and counter-rotating terms on equal footing. In the unitarily transformed representation, we find that it is the multiple-harmonic terms shown in the transformed Hamiltonian that make a crucial contribution to the generation of the exotic plateau phenomenon. By comparing the results of the numerically exact calculation and several other methods, we show that the CHRW results obtained by analytical formalism involving the collective effects of multiple harmonics are in good agreement with the numerical results, which illustrates not only the general tendency of the dynamical evolution of strongly driven TLS, but also the interesting phenomena of plateaus. The developed CHRW method reveals two kinds of plateau patterns: zigzag plateau and armchair plateau. The plateau phenomenon has a periodical pattern whose frequency is double the driving frequency, and possesses quantized oscillations the number of which has a certain, precise value. Besides, fast oscillation is produced on every plateau which is determined by the relevant driving parameters of the TLS. Our main results are as follows: (i) in the large-amplitude oscillatory case, it turns out that the collective effects of all even harmonics contribute to the generation of zigzag plateau with quantized oscillation; (ii) in the small-amplitude oscillatory case, the dynamics of the coherent destruction of tunneling under strong driving is exactly exhibited by including the odd-harmonic effect, namely, armchair plateau possessing a two-stair structure rather than the complete destruction.

Association between Obesity and Microvascular Diseases in Patients with Type 2 Diabetes Mellitus

Background: The association between obesity and microvascular diseases, especially in extremely obese patients with type 2 diabetes mellitus, has not been well examined. This study aimed to investigate this association and further compare the magnitude of the associations of fat mass index (FMI), body mass index (BMI), waist circumference (WC), and waist-to-height (W-t-H), with the risk of microvascular diseases in type 2 diabetes mellites(T2DM). Methods: We mainly used FMI as an indicator of obesity to study the association with microvascular diseases and performed a post hoc analysis of the ACCORD study. The primary microvascular outcomes of the present study included severe renal hypofunction, retinopathy, or neuropathy. Findings: After confounding factors were adjusted for, patients with the highest quartile of FMI had a higher risk of severe renal hypofunction (hazard ratio [HR]: 1·26, 95% confidence interval [CI]: 1·16–1·36) and neuropathy (HR: 1·93, 95% CI: 1·74–2·15) but not higher risk of retinopathy (HR: 1·17, 95% CI: 0·96–1·43) than those with the lowest quartile. A “plateau phenomenon” for severe renal hypofunction and neuropathy was found when the extent of obesity exceeded a certain point. Quartiles, deciles or standardized measure (1-SD increment) of obesity indicators analysis showed inconsistent results on which obesity indicator had a stronger association with the risk of microvascular disease. Interpretation: Obesity is associated with renal function deterioration and neuropathy but not with retinopathy. Compared to BMI, WC, and W-t-H, FMI did not show a stronger association with the risk of microvascular diseases. Funding Statement: None. Declaration of Interests: All authors declare to have no conflict of interest.

Progress Update and Challenges on O2max Testing and Interpretation.

The maximal oxygen uptake (O2max) is the primary determinant of endurance performance in heterogeneous populations and has predictive value for clinical outcomes and all-cause mortality. Accurate and precise measurement of O2max requires the adherence to quality control procedures, including combustion testing and the use of standardized incremental exercise protocols with a verification phase preceded by an adequate familiarization. The data averaging strategy employed to calculate the O2max from the breath-by-breath data can change the O2max value by 4–10%. The lower the number of breaths or smaller the number of seconds included in the averaging block, the higher the calculated O2max value with this effect being more prominent in untrained subjects. Smaller averaging strategies in number of breaths or seconds (less than 30 breaths or seconds) facilitate the identification of the plateau phenomenon without reducing the reliability of the measurements. When employing metabolic carts, averaging intervals including 15–20 breaths or seconds are preferable as a compromise between capturing the true O2max and identifying the plateau. In training studies, clinical interventions and meta-analysis, reporting of O2max in absolute values and inclusion of protocols and the averaging strategies arise as imperative to permit adequate comparisons. Newly developed correction equations can be used to normalize O2max to similar averaging strategies. A lack of improvement of O2max with training does not mean that the training program has elicited no adaptations, since peak cardiac output and mitochondrial oxidative capacity may be increased without changes in O2max.

Variational quantum eigensolver for frustrated quantum systems

Hybrid quantum-classical algorithms have been proposed as a potentially viable application of quantum computers. A particular example - the variational quantum eigensolver, or VQE - is designed to determine a global minimum in an energy landscape specified by a quantum Hamiltonian, which makes it appealing for the needs of quantum chemistry. Experimental realizations have been reported in recent years and theoretical estimates of its efficiency are a subject of intense effort. Here we consider the performance of the VQE technique for a Hubbard-like model describing a one-dimensional chain of fermions with competing nearest- and next-nearest-neighbor interactions. We find that recovering the VQE solution allows one to obtain the correlation function of the ground state consistent with the exact result. We also study the barren plateau phenomenon for the Hamiltonian in question and find that the severity of this effect depends on the encoding of fermions to qubits. Our results are consistent with the current knowledge about the barren plateaus in quantum optimization.

Self-reported Morisky Eight-item Medication Adherence Scale for Statins Concords with the Pill Count Method and Correlates with Serum Lipid Profile Parameters and Serum HMGCoA Reductase Levels.

BackgroundIt is imperative that non-compliance with statins be identified and addressed to maximize their clinical benefits. Patient self-reporting methods are convenient to apply in clinical practice but need to be validated.ObjectiveWe studied the concordance of a patient self-report method, Morisky eight-item medication adherence scale (MMAS)), with the pill count method in measuring adherence with statins and their correlation with extended lipid profile parameters and serum hydroxyl-methylglutaryl coenzyme A reductase (HMGCoA-R) enzyme levels.MethodsMMAS and the pill count method were used to measure the adherence with statins in patients on statins for any duration. Patients were subjected to an estimation of extended lipid profile and serum HMGCoA-R levels at the end of three months follow-up.ResultsOut of a total of 200 patients included in the study, 117 patients had a low adherence (score less than 6 on MMAS) whereas 65 and 18 patients had medium (score 6 or 7) and high adherence (score of 8), respectively. The majority of patients who had low adherence to statins by MMAS were nonadherent by the pill count method yielding a concordance of 96.5%. Medium or high adherence to statins by the MMAS method had a concordance of 89.1% with the pill count method. The levels of total cholesterol, low-density lipoprotein-cholesterol, apolipoprotein B, and HMGCoA-R were negatively correlated with compliance measured by pill count and MMAS in a statistically significant way and with similar correlation coefficients. HMGCoA-R levels demonstrated a plateau phenomenon, with levels being 9-10 ng/ml when compliance with statin therapy was greater than 60% by pill count and greater than 6 on the Morisky scale.ConclusionIn conclusion, MMAS and the pill count method showed concordance in measuring adherence to statins. These methods need to be explored further for their interchangeability as surrogates for biomarker levels.

Longer-term liraglutide administration at the highest dose approved for obesity increases reward-related orbitofrontal cortex activation in response to food cues: Implications for plateauing weight loss in response to anti-obesity therapies.

GLP-1 analogs have recently risen to the forefront as effective medications for lowering weight through actions in the central nervous system (CNS). However, their actions in the CNS have not yet been studied in the human brain after longer-term administration at the highest dose approved for obesity (liraglutide 3.0 mg). A total of 20 participants with obesity were treated with placebo and liraglutide (3.0 mg) in the context of a randomized, placebo-controlled, double-blind, cross-over trial after 5 weeks of dose escalation. Neurocognitive and neuroimaging (fMRI) responses to food cues were examined at the clinical research center of Beth Israel Deaconess Medical Center. While using liraglutide, patients lost more weight (placebo-subtracted -2.7%; P < .001), had decreased fasting glucose (P < .001) and showed improved cholesterol levels. In an uncontrolled analysis, brain activation in response to food images was not altered by liraglutide vs placebo. When controlled for BMI/weight, liraglutide increased activation of the right orbitofrontal cortex (OFC) in response to food cues (P < .016, corrected for multiple comparisons). In contrast to prior studies, we demonstrate for the first time that liraglutide treatment, administered over a longer period at the highest doses approved for obesity, does not alter brain activation in response to food cues. A counter-regulatory increase in reward-related OFC activation in response to food cues can be observed when neuroimaging data are controlled for BMI changes, indicating changes in CNS that could lead to later plateaus of weight loss. These data point to a promising focus for additional interventions which, by contributing to the CNS reward system, could provide tangible benefits in reversing the plateauing phenomenon and promoting further weight loss.

Statistical mechanical analysis of learning dynamics of two-layer perceptron with multiple output units

The plateau phenomenon, wherein the loss value stops decreasing during the process of learning, is troubling. Various studies suggest that the plateau phenomenon is frequently caused by the network being trapped in the singular region on the loss surface, a region that stems from the symmetrical structure of neural networks. However, these studies all deal with networks that have a one-dimensional output, and networks with a multidimensional output are overlooked. This paper uses a statistical mechanical formalization to analyze the dynamics of learning in a two-layer perceptron with multidimensional output. We derive order parameters that capture macroscopic characteristics of connection weights and the differential equations that they follow. We show that singular-region-driven plateaus diminish or vanish with multidimensional output, in a simple setting. We found that the more non-degenerative (i.e. far from one-dimensional output) the model is, the more plateaus are alleviated. Furthermore, we showed theoretically that singular-region-driven plateaus seldom occur in the learning process in the case of orthogonalized initializations.

On the role of Zr content into Portevin-Le Chatelier (PLC) effect of selective laser melted high strength Al-Cu-Mg-Mn alloy

Portevin-Le Chatelier (PLC) effect manifests itself as an unstable plastic flow during the tensile tests of aluminum alloys. With the increase of Zr content in high strength Al-Cu-Mg-Mn alloys, the stress-strain curves transform from smooth flow to serrated flow. The transition is attributed to the grain refinement as well as the interaction among Al3Zr precipitates, solute atoms and dislocations. What’s more, yield plateau (YP) phenomenon starts to appear when the Zr content reaches 1 wt.%. These findings provide a new perspective on tailoring mechanical behavior by alloy design for selective laser melting (SLM).

Numerical analysis near singularities in RBF networks

The existence of singularities often affects the learning dynamics in feedforward neural networks. In this paper, based on theoretical analysis results, we numerically analyze the learning dynamics of radial basis function (RBF) networks near singularities to understand to what extent singularities influence the learning dynamics. First, we show the explicit expression of the Fisher information matrix for RBF networks. Second, we demonstrate through numerical simulations that the singularities have a significant impact on the learning dynamics of RBF networks. Our results show that overlap singularities mainly have influence on the low dimensional RBF networks and elimination singularities have a more significant impact to the learning processes than overlap singularities in both low and high dimensional RBF networks, whereas the plateau phenomena are mainly caused by the elimination singularities. The results can also be the foundation to investigate the singular learning dynamics in deep feedforward neural networks.

Dynamics of Learning in MLP: Natural Gradient and Singularity Revisited.

The dynamics of supervised learning play a main role in deep learning, which takes place in the parameter space of a multilayer perceptron (MLP). We review the history of supervised stochastic gradient learning, focusing on its singular structure and natural gradient. The parameter space includes singular regions in which parameters are not identifiable. One of our results is a full exploration of the dynamical behaviors of stochastic gradient learning in an elementary singular network. The bad news is its pathological nature, in which part of the singular region becomes an attractor and another part a repulser at the same time, forming a Milnor attractor. A learning trajectory is attracted by the attractor region, staying in it for a long time, before it escapes the singular region through the repulser region. This is typical of plateau phenomena in learning. We demonstrate the strange topology of a singular region by introducing blow-down coordinates, which are useful for analyzing the natural gradient dynamics. We confirm that the natural gradient dynamics are free of critical slowdown. The second main result is the good news: the interactions of elementary singular networks eliminate the attractor part and the Milnor-type attractors disappear. This explains why large-scale networks do not suffer from serious critical slowdowns due to singularities. We finally show that the unit-wise natural gradient is effective for learning in spite of its low computational cost.

Development and Validation of a ROM Incorporated By a Semi-Empirical Aging Model for a Large-Format LiFePO4/Graphite Cell

Lithium iron phosphate (LFP) as cathode materials was firstly introduced by Padhi etc. in 1997. It has undergone remarkable developments and been widely used in commercial Li-ion batteries because of its good electrochemical and thermal stability. In order to overcome the low conductivity and high-current capability, carbon coating and nanoparticles are used to achieve a high rate capability with low cost. LFP as cathode materials has caused great interest in the field of electric and hybrid electric vehicles. The research aims to develop an online algorithms for LFP/Graphite cells to detailed describe lithiation and delithiation process during galvanostatic discharging and charging. The model is based on the electrochemical thermal principles. A reduced order model (ROM) has been developed for both fresh and aged lithium iron phosphate (LFP) based cells (nominal capacity: 20Ah), in which plateau and path dependence phenomena caused by two-phase transition during charging and discharging have been taken into consideration. Two-phase transition during lithium intercalation/deintercalation into/from LFP particles is approximately modeled by a shrinking core with a moving boundary at the interface between two phases, lithium-rich phase and lithium-deficiency phase. Moreover, it is also described by the modified diffusion equations with consideration of multiple layers that formed in cathode particles. Polynomial approach, state space approach and some other reduction assumptions, such as linearization of Bulter-Volmer equations, are used for solid concentration, electrolyte concentration and potentials, separately. For fresh cells, the physics-based ROM has been validated by experimental data obtained through galvanostatic charging and discharging at different C-rate (1C, 3C, 4C) and temperature (25, 45). Path dependence experiments are also conducted and then used to do comparable analysis with simulation results. The simulation results of single cycles, multiple cycles and pulse cycles show great consistent with experiment results. Furthermore, parameter sensitivity of ROM has also been analyzed. Therefore, the model is able to represent the characteristics of plateau and path dependence of LFP cells. For aged cells, a semi-empirical degradation model has been incorporated into the former ROM. By fitting the semi-empirical degradation model, three important parameters, resistance, electrolyte diffusion coefficient and volume fraction of anode active materials, are extracted from the experimental voltage curve. Five cells are stored in a thermal chamber at 25 for six months at different SOC (10%, 30%, 50%, 70%, 90%). Five cells are cycled under 4C/4C charging/discharging procedure at different temperature (25, 45), SOC cycling range (5%-75%, 25%-95%) and number of cycles. The capacity fade of these five cells are 5.81%, 10.95%, 12.17%, 14.17%, and 23.54%, separately. Experiment results illustrate that high temperature and SOC could accelerate the battery aging. EIS and capacity measurements are conducted every 30 cycles during cycling. EIS results show that the impedance curve shifts rightwards as the increase of ohmic resistance and SEI resistance caused by side reactions. Post-mortem analysis, XRD and SEM, are used to analyze the change of morphology and composition for aged cells The impedances are increased as the number of cycles on the rise. It shows that there is no structure change in both cathode and anode. The model with semi-empirical degradation model incorporated is validated against cycling experiments and shows good consistency.

A new constitutive model for simulation of softening, plateau, and densification phenomena for trabecular bone under compression

A new type of constitutive model and its computational implementation procedure for the simulation of a trabecular bone are proposed in the present study. A yield surface-independent Frank–Brockman elasto-viscoplastic model is introduced to express the nonlinear material behavior such as softening beyond yield point, plateau, and densification under compressive loads. In particular, the hardening- and softening-dominant material functions are introduced and adopted in the plastic multiplier to describe each nonlinear material behavior separately. In addition, the elasto-viscoplastic model is transformed into an implicit type discrete model, and is programmed as a user-defined material subroutine in commercial finite element analysis code. In particular, the consistent tangent modulus method is proposed to improve the computational convergence and to save computational time during finite element analysis. Through the developed material library, the nonlinear stress–strain relationship is analyzed qualitatively and quantitatively, and the simulation results are compared with the results of compression test on the trabecular bone to validate the proposed constitutive model, computational method, and material library.

A numerical method for predicting O-forming gap in UOE pipe manufacturing

Large diameter welded pipes used in oil and gas pipelines are primarily manufactured by the UOE process, which consists of U-forming, O-forming, and expansion procedures. The formation of O-forming gap in the O-forming stage is a key processing factor and it involves complex plastic deformation and springback of the steel plate. In this paper, a numerical method is proposed for predicting geometric configuration and O-forming gap of steel plate after C–U–O-forming. A combined hardening model for characterizing the loading–unloading–reverse loading deformation of pipe steels is developed based on the Chaboche hardening model. The yield plateau phenomenon and the variation of elastic modulus with the increase of pre-strain are incorporated. Industrial experiments are carried out, and the proposed method is validated through comparison between experimental and calculated results. Furthermore, the influence of material and processing parameters on O-forming gap is numerically investigated. The results reveal that U-forming radius is the most important factor in C- and U-forming stages to determine O-forming gap, and the opening gap width increases with increasing of compression ratio in O-forming stage. Finally, the established numerical method is combined with a genetic algorithm and applied to optimize UOE process parameters for obtaining an ideal opening gap. The proposed method provides an effective and efficient tool for UOE process design.

Learning dynamics of a single polar variable complex-valued neuron.

This letter investigates the characteristics of the complex-valued neuron model with parameters represented by polar coordinates (called polar variable complex-valued neuron). The parameters of the polar variable complex-valued neuron are unidentifiable. The plateau phenomenon can occur during learning of the polar variable complex-valued neuron. Furthermore, computer simulations suggest that a single polar variable complex-valued neuron has the following characteristics in the case of using the steepest gradient-descent method with square error: (1) unidentifiable parameters (singular points) degrade the learning speed and (2) a plateau can occur during learning. When the weight is attracted to the singular point, the learning tends to become stuck. However, computer simulations also show that the steepest gradient-descent method with amplitude-phase error and the complex-valued natural gradient method could reduce the effects of the singular points. The learning dynamics near singular points depends on the error functions and the training algorithms used.

Novel polymorphism behavior of poly(butylene adipate) in its nanocomposites with carbon nanofibers

Carbon nanofibers prominently enhance the formation of α-form crystal poly(butylene adipate) at low temperature and lead to a novel plateau phenomenon of α-form crystal content in their composites through specific CH–π interactions.

The Career Plateau of Chinese Public Servants: Construct, Measurement and Its Psychological and Behavioral Influence

中国公共组织中基层公务员的职业生涯高原是值得关注的重要问题。首先通过深度访谈和开放式问卷调查，归纳出公务员职业生涯高原的典型特征与表现，然后通过问卷调查获得三批处级以下公务员的数据。基于样本一（n：279）的探索性因素分析发现，公务员职业生涯高原为两维度的结构：升迁停滞、职位边缘化。基于样本二（n=517）的验证性因素分析证实了公务员职业生涯高原两维度结构模型，公务员职业生涯高原测量工具有较理想的信度和效度。基于样本三（n=520）、样本四（n=230）的研究表明，职业生涯高原对公务员的组织承诺、职业倦怠、工作退缩行为均有不同程度的消极的影响，但相对于升迁停滞，公务员职业边缘化对于上述效果变量的影响更为显著。

Fire behaviour of continuous reinforced concrete slabs in a full-scale multi-storey steel-framed building

To further understand the fire behaviour of reinforced concrete floor slabs, a fire test was performed on six continuous panels (two by three) in a full-scale three-storey steel-framed building. In this paper, the test building, specially designed furnace and relevant experimental phenomena are briefly introduced. The furnace temperatures, temperature distributions, failure patterns as well as horizontal and vertical displacements of some structural components during the heat-up and cool-down phases were recorded and discussed in detail. The test data indicate that deformations of the heated panels have an important relationship with the boundary constraints around the heat panels. The plateau phenomenon of deflections at various measuring points mainly depends on the heated beams around the heated panels. The steel beams do not show partial buckling or failures due to constraints provided by other structural elements. Thus, taking advantage of the intrinsic design strength of the steel beams without applying fire retardant coatings can provide sufficient safety margins in similar engineering design scenarios. Moreover, the cracking characteristics at the upper surface of the heated panels have a direct relationship with the number and location of the heated panels in the floor. Several rational suggestions for the renovation of buildings subjected to fire can be quickly provided by utilising the cracking information.

The mechanism of shape instability for a vesicle in extensional flow

AbstractWhen a flexible vesicle is placed in an extensional flow (planar or uniaxial), it undergoes two unique sets of shape transitions that to the best of the authors’ knowledge have not been observed for droplets. At intermediate reduced volumes (i.e. intermediate particle aspect ratio) and high extension rates, the vesicle stretches into an asymmetric dumbbell separated by a long, cylindrical thread. At low reduced volumes (i.e. high particle aspect ratio), the vesicle extends symmetrically without bound, in a manner similar to the breakup of liquid droplets. During this ‘burst’ phase, ‘pearling’ occasionally occurs, where the vesicle develops a series of periodic beads in its central neck. In this paper, we describe the physical mechanisms behind these seemingly unrelated instabilities by solving the Stokes flow equations around a single, fluid-filled particle whose interfacial dynamics is governed by a Helfrich energy (i.e. the membranes are inextensible with bending resistance). By examining the linear stability of the steady-state shapes, we determine that vesicles are destabilized by curvature changes on its interface, similar to the Rayleigh–Plateau phenomenon. This result suggests that the vesicle’s initial geometry plays a large role in its shape transitions under tension. The stability criteria calculated by our simulations and scaling analyses agree well with available experiments. We hope that this work will lend insight into the stretching dynamics of other types of biological particles with nearly incompressible membranes, such as cells.

Career Plateauing: Is It Still A Matter of Concern?

Hierarchical plateauing has been an issue and a challenge for most organizations in almost all sectors. The volatile global market conditions and the limited availability of higher positions has made the competition for openings much more intense. Many researchers have associated plateauing with negative consequences such as lower levels of job satisfaction, poor commitment, high absenteeism, greater stress, low motivation and high employee turnover. The literature also indicates that in most organizations, plateauing is often considered as one of the contributing factors to employee’s intention to leave in most organizations. However, very few realize that plateaued employees can actually be turned into the most valuable assets and can enhance an organization’s competitiveness if the employers are able to manage this group effectively. This paper investigates the relationship between hierarchical plateauing and intention to leave among nurses in public hospitals. Questionnaires were distributed to 700 nurses in 11 public hospitals in Peninsular Malaysia to examine the current perception of employees towards hierarchical plateauing in their career . The results showed that hierarchical plateauing was not significantly related to the intention to leave. The results provide some new insight in the sense that they support the recent notion that the plateauing phenomenon has become unavoidable and that many employees have no choices but to experience it sooner or later in their career and sometimes even earlier than they anticipate. The implications of the study and future research suggestions are also discussed. DOI: 10.5901/mjss.2014.v5n7p224