Crossover Phase Research Articles

Analysis of an Online Stability Monitoring Approach for DC Microgrid Power Converters

An online approach to evaluate and monitor the stability margins of dc microgrid power converters is presented in this paper. The discussed online stability monitoring technique is based on the Middlebrook's loop-gain measurement technique, adapted to the digitally controlled power converters. In this approach, a perturbation is injected into a specific digital control loop of the converter and after measuring the loop gain, its crossover frequency and phase margin are continuously evaluated and monitored. The complete analytical derivation of the model, as well as detailed design aspects, are reported. In addition, the presence of multiple power converters connected to the same dc bus, all having the stability monitoring unit, is also investigated. An experimental microgrid prototype is implemented and considered to validate the theoretical analysis and simulation results, and to evaluate the effectiveness of the digital implementation of the technique for different control loops. The obtained results confirm the expected performance of the stability monitoring tool in steady-state and transient operating conditions. The proposed method can be extended to generic control loops in power converters operating in dc microgrids.

Finite-volume and magnetic effects on the phase structure of the three-flavor Nambu–Jona-Lasinio model

In this work we analyze the finite-volume and magnetic effects on the phase structure of a generalized version of Nambu--Jona-Lasinio model with three quark flavors. By making use of mean-field approximation and Schwinger's proper-time method in a toroidal topology with antiperiodic conditions, we investigate the gap equation solutions under the change of the size of compactified coordinates, strength of magnetic field, temperature and chemical potential. The 't Hooft interaction contributions are also evaluated. The thermodynamic behavior is strongly affected by the combined effects of relevant variables. The findings suggest that the broken phase is disfavored due to both increasing of temperature and chemical potential, and the drop of the cubic volume of size $L$, whereas it is stimulated with the augmentation of magnetic field. In particular, the reduction of $L$ (remarkably at $L\approx 0.5 - 3 $~fm) engenders a reduction of the constituent masses for $u,d,s$-quarks through a crossover phase transition to the their corresponding current quark masses. On the other hand, the presence of a magnetic background generates greater values constituent quark masses, inducing smaller sizes and greater temperatures at which the constituent quark masses drop to the respective current ones.

Analytical Design of PI Controllers for Second Order plus Time Delay Systems

Analytical design scheme of a Proportional Integral controllers for the stability and performance of second order plus time delay systems is presented in this paper. The method proposed in the study achieves general computation equations for mentioned systems. Inspired from the Bode’s ideal transfer function characteristics, gain crossover frequency and phase margin specifications are considered for the system. Then, these specifications are used to obtain the parameters of the controller. Analytically derived formulas by the proposed method are tested with existing plants in the literature and the results are illustrated graphically. It is shown that the tuning method satisfies desired gain crossover frequency and phase margin specifications.

İkinci Derece Zaman Gecikmeli Sistemler için Analitik PD Denetleyici Tasarımı

This paper intends to present the design scheme of a Proportional Derivative controller for stability and performance of time delay systems in the second order. Inspired from Bode’s ideal system characteristics, phase margin and gain crossover frequency specifications are considered for the system. Then, these specifications are used to obtain the parameters of the controller. The method proposed in the study achieves general computation equations for mentioned systems. Analytically derived formulas by the proposed method are tested with existing plants in the literature and the results are illustrated graphically. It is shown that the tuning method satisfies desired gain crossover frequency and phase margin specifications.

ODENZA: A study of patient preference between ODM-201 (darolutamide) and enzalutamide in men with metastatic castrate-resistant prostate cancer (mCRPC).

TPS334 Background: In recent years, the treatment of mCRPC has evolved and next-generation androgen receptor (AR)-axis targeting drugs (enzalutamide (ENZ), and abiraterone) have been approved and are routinely used. Darolutamide (DARO) is a new next-generation AR inhibitor which has shown strong activity and minimal toxicity in two phase I-II trials ARADES (Fizazi, Lancet Oncol 2014) and ARAFOR (Massard, Eur Urol 2016) and is currently evaluated in a study in men with non-metastatic CRPC (ARAMIS trial). In contrast to ENZ, DARO does not significantly penetrate the blood-brain barrier in vivo, and this may reduce the risk of fatigue, cognitive impairment, and seizure. Assessing patient preference between DARO and ENZ may contribute further differentiating between these two agents. Methods: ODENZA is a prospective, randomized, open-label, multicenter, cross-over phase II trial assessing patient preference between DARO and ENZ. It was initiated in November 2017. Eligibility criteria include: men with asymptomatic or mildly symptomatic mCRPC, performance status 0-1, no prior next generation AR axis-targeted agent. The randomization is stratified on performance status and prior treatment with a taxane for CSPC. 250 patients will be randomized 1:1 to: 12-week ENZ followed by 12-week DARO or 12-week DARO followed by 12-week ENZ. The primary endpoint is patient preference between DARO and ENZ, assessed after the second treatment period. A two-sided binomial test with a power of 80% and a bilateral α of 0.05 will be used. Secondary endpoints include: reasons for patient preference, dose modifications and time to dose modification, safety, fatigue (BFI), cognitive function as assessed by Cogstate computerized cognitive tests, depression screening (CES-D) test, frequency of falls, PSA declines using Waterfall plots after each treatment period, Progression-Free Survival (PFS), association between 4-weeks PSA value and PFS, incidence of cancer progression or death, and tumor response. The study is recruiting. By October 23, 2018, 75 patients have been screened and 66 have been randomized. Clinical trial information: NCT03314324.

Design of FOPI Controller for Time Delay Systems and Its Experimental Validation

In this paper, we report on the identification and modeling of unknown and higher order processes into first order plus dead time (FOPDT) plants based on the limit cycle information obtained from a single relay feedback test with an online fractional order proportional integral (FOPI) controller. The parameters of the test processes are accurately determined by the state space method while the FOPI controller settings are re-tuned to achieve enhanced performance based on the identified model parameters based on the balanced-tuning method. A new performance index, integral time fractional order absolute error (ITFIAE) is introduced in this paper for balanced tuning of fractional order (FO) controllers. It requires minimum design specifications without a-priori knowledge of gain and phase crossover frequencies and is done non-iteratively without disrupting the closed loop. Four test processes and experimental analysis on a coupled tank system (CTS) validate the theory proposed.

Abstract P6-21-11: Final results from IMPROVE: A randomized, controlled, open-label, cross-over phase IV study to determine the patients' preference for either combined endocrine therapy (exemestane plus everolimus) or immunochemotherapy (capecitabine plus bevacizumab) as first line treatment for advanced HR+/HER2- breast cancer

Abstract For patients (pts) with advanced HR+/HER2- breast cancer various treatment options exist. Endocrine therapy or chemotherapy are the recommended 1st-line treatment options according to international guidelines. With comparable efficacy, it is of utmost importance to identify the treatment that has the least negative impact on the pts' quality of life (QoL). Randomized studies to determine the pts' preference (pref) for equi-effective treatment concepts, are lacking. IMPROVE compared both therapeutic concepts by assessing the pts' pref for either a combined antihormonal approach (everolimus /exemestane (E/E)) or chemotherapy (capecitabine /bevacizumab (C/B)). In total, 77 pts were recruited from 10/14 until 04/17 at 26 sites in GER. Upon diagnosis of locally advanced, inoperable or metastatic disease, pts were randomized to receive 1st-line C/B until disease progression followed by 2nd-line E/E (Arm A) or vice versa (Arm B). Primary objective was the patient-reported pref for either treatment protocol 12 weeks after switching therapy. Key secondary endpoints include PFS, OS, safety and QoL. Descriptive statistics were used to to analyse data, PFS and OS were calculated by using the Kaplan-Meier method. Baseline characteristics were well balanced with a slightly shorter disease-free interval after primary diagnosis and more prior treatments in Arm B.In Arm A [95% CI], 39% [13.9-68.4] vs 23% [5.0-53.8] of pts preferred E/E compared to C/B, 23% [5.0-53.8] were undecided. In Arm B, 56% [30.8-78.5] vs 11% [1.4-34.7] preferred C/B, 22% [6.4-47.6] undecided. Overall, 42% [24.5-60.9] vs 23% [9.6-41.1] of pts preferred C/B, 23% [9.6-41.1] were undecided. Physicians' pref had a tendency for C/B treatment (Arm A, 62% [31.6-86.1] vs 39% [13.9-68.4] for C/B. Arm B, 56% [30.8-78.5] vs 28% [9.7-53.5] for C/B, no pref 17% [3.6-41.4]). Median 1st-line PFS [months, 95% CI] was 11.1 [7.8-18.0] for C/B (Arm A) vs 3.5 [2.7-5.5] for E/E (Arm B). Median 2nd-line PFS was 3.7 [2.4-7.8] for E/E (Arm A) vs 3.6 [2.3-5.5] for C/B (Arm B). Median OS [months, 95% CI] was 28.8 [19.7-NA] (Arm A) and 24.7 [13.9-28.8] (Arm B). 73.0% and 52.6% (1st and 2nd line, C/B) vs 54.1% and 52.9% (1st and 2nd line, E/E) of pts developed grade 3/4 AEs. Most common grade 3/4 AEs (%) were hand-foot syndrome (18.9), fatigue (17.6), hypertension (13.5) for C/B and anaemia (23.5), fatigue, dyspnoea, cough (each 17.6) for E/E (either line). No treatment-related deaths occurred. Patient-reported QoL (EORTC-QLQC30) and treatment satisfaction were not significantly different between arms in either treatment phase. In the IMPROVE study, pts had no pref for either endocrine therapy or immunochemotherapy. Overall, there was a tendency in favour of the chemotherapeutic approach (C/B), which was in line with the therapy pref reported by the physicians. C/B was found to have slightly better efficacy results but at the cost of a higher frequency of grade 3/4 AEs, bearing in mind the difference in duration of therapy between the two regimens. Patient-reported QoL, however, was similar in both arms. Citation Format: Kurbacher CM, Söling U, Hahn A, Chiabudini M, Maintz C, Rieger L, Falkenstein J, Runkel E, Potthoff K, Decker T. Final results from IMPROVE: A randomized, controlled, open-label, cross-over phase IV study to determine the patients' preference for either combined endocrine therapy (exemestane plus everolimus) or immunochemotherapy (capecitabine plus bevacizumab) as first line treatment for advanced HR+/HER2- breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-21-11.

Entropy production and reheating at the chiral phase transition

We study the production of entropy in the context of a nonequilibrium chiral phase transition. The dynamical symmetry breaking is modeled by a Langevin equation for the order parameter coupled to the Bjorken dynamics of a quark plasma. We investigate the impact of dissipation and noise on the entropy and explore the possibility of reheating for crossover and first-order phase transitions, depending on the expansion rate of the fluid. The relative increase in S/N is estimated to range from 10% for a crossover to 100% for a first-order phase transition at low beam energies, which could be detected in the pion-to-proton ratio as a function of beam energy.

Effects of Multiple Waveforms on Patient Preferences and Clinical Outcomes in Patients Treated With Spinal Cord Stimulation for Leg and/or Back Pain

We present the results of a prospective, randomized, crossover, single-blind, study in which each patient is in control of himself. The aim was to evaluate subperception-based (SP-SCS) waveforms in previously implanted spinal cord stimulation (SCS) patients with leg and/or back pain due to failed back surgery syndrome, who experienced only paresthesia-based stimulation (PB-SCS). Patients with PB-SCS experience in SCS was 4.7 years (SD 2.9). We enrolled 28 consecutive patients. Treatment consisted of seven days of PB-SCS, followed by a randomized, crossover phase to test SP-SCS waveforms (burst or 1 kHz frequency, seven days each). A maximum of three-day washout period separated each stimulation program. Statistically significant pain relief was maintained using both SP-SCS waveforms, as indicated by the differences between the pre-PB-SCS numeric pain rating score (mean 9) and the pain score after using the burst program (pain relief 52%) or the 1 kHz program (pain relief 51%). There was no statistically significant superiority among PB-SCS, burst, and 1 kHz stimulation. Overall, 50% of patients preferred PB-SCS, 42% chose to move to SP-SCS stimulation, one patient was unable to give feedback, and one patient was unsuccessful with any type of stimulation. Overall, SCS has shown to be successful in pain relief and the patients switched to a SP-SCS waveform only for having higher pain relief. There was a high heterogeneity regarding waveform preference, with patients who preferred to feel the tingling sensation and those who chose a SP-SCS option, mainly for greater pain relief. In general, SCS is successful, resulting in high pain relief, improvements in quality of life, and little depression. Overall, 42% patients benefited from the novel SP-SCS stimulation waveforms.

Recent Results and Methods on Higher Order and Off-diagonal Cumulants of Identified Net-particle Multiplicity Distributions in Au+Au Collisions at STAR

We present recent results on the cumulants of net-particle distributions in Au+Au collisions at the STAR experiment. Beam energy dependence of net-Λ cumulants and off-diagonal cumulants are measured. These measurements provide additional constraints on the chemical freeze-out conditions. The sixth-order cumulant of net-charge and net-proton distributions is measured at sNN=200GeV to search for the signal of the crossover phase transition. Finally, an unfolding technique is developed and applied to the net-proton distributions at 19.6 GeV to account for the non-binomial effects of the detector.

An exact solution of spherical mean-field plus orbit-dependent non-separable pairing model with two non-degenerate j-orbits

An exact solution of nuclear spherical mean-field plus orbit-dependent non-separable pairing model with two non-degenerate j-orbits is presented. The extended one-variable Heine–Stieltjes polynomials associated to the Bethe ansatz equations of the solution are determined, of which the sets of the zeros give the solution of the model, and can be determined relatively easily. A comparison of the solution to that of the standard pairing interaction with constant interaction strength among pairs in any orbit is made. It is shown that the overlaps of eigenstates of the model with those of the standard pairing model are always large, especially for the ground and the first excited state. However, the quantum phase crossover in the non-separable pairing model cannot be accounted for by the standard pairing interaction.

Spin crossover and structural phase transition in homochiral and heterochiral Fe[(pybox)2]2+ complexes.

Spin crossover and structural phase transition in three pairs of homochiral and heterochiral [Fe(pybox)2]2+ diastereomers were investigated through magnetic and crystallographic studies. Herein, we show that the spin transition properties of these compounds are strongly related to the homochiral or heterochiral assembly of the ligands and structural phase transition. Our work demonstrates that chirality is a feasible factor to modulate and influence the molecular geometry and thus the spin-crossover properties of complexes.

Phase structure and surface tension in quark meson model

In a mean-field approximation, we study the in-medium effective potential of the two-flavor quark meson model in the presence of a fermionic vacuum term at a finite temperature and density. There exists a crossover phase transition in the low-density region, and also there is a first-order phase transition in the high-density region accompanied by a critical end point. For the first-order phase transition, when the temperature is close to the critical temperature, the values of surface tension are calculated at various chemical potentials and we find that our results are very close to the results recently found in other chiral models with two flavors. Some consequences and possible applications of our results are also pointed out for the experiments on heavy ion collisions and the evolutions of the compact stars in their early stages.

Width-dependent phase crossover in transition metal dichalcogenide nanoribbons

Two-dimensional (2D) transition metal dichalcogenides MX2 (M = Mo, W; X = S, Se) exhibit two phases: the ground state 2H and the metastable 1T. Here, WSe2 and MoS2 monolayers have been studied, and we show by comprehensive first-principles calculations that the stability of the two phases can be switched in MX2 nanoribbons. The 2H phase is found to have increasingly higher energy than the 1T phase at a smaller ribbon width, and the width for favoring the 1T phase reaches up to 2.50 nm for WSe2. The phase crossover is due to higher coordination of edge M atoms in 1T phase than in 2H phase and an interesting electronic reconstruction of 1T lattice in the ribbon interior. The edge configuration of 1T phase diminishes the edge dangling bonds and thereby enhances the stability of MX2 nanoribbons. Our findings underscore the importance of edges in determining the structures of 2D MX2 and are crucial for their future scientific studies and potential applications.

Computer-Aided Design of Digital Compensators for DC/DC Power Converters

Digital control of high-frequency power converters has been used extensively in recent years, providing flexibility, enhancing integration, and allowing for smart control strategies. The core of standard digital control is the discrete linear compensator, which can be calculated in the frequency domain using well-known methods based on the frequency response requirements (crossover frequency, fc, and phase margin, PM). However, for a given compensator topology, it is not possible to fulfill all combinations of crossover frequency and phase margin, due to the frequency response of the controlled plant and the limitations of the compensator. This paper studies the performance space (fc, PM) that includes the set of achievable crossover frequencies and phase margin requirements for a combination of converter topology, compensator topology, and sensors, taking into account the effects of digital implementation, such as delays and limit cycling. Regarding limit cycling, two different conditions have been considered, which are related to the design of the digital compensator: a limited compensator integral gain, and a minimum gain margin. This approach can be easily implemented by a computer to speed up the calculations. The performance space provides significant insight into the control design, and can be used to compare compensator designs, select the simplest compensator topology to achieve a given requirement, determine the dynamic limitations of a given configuration, and analyze the effects of delays in the performance of the control loop. Moreover, a figure of merit is proposed to compare the dynamic performance of the different designs. The main goal is to provide a tool that identifies the most suitable compensator design in terms of the dynamic performance, the complexity of the implementation, and the computational resources. The proposed procedure to design the compensator has been validated in the laboratory using an actual DC/DC converter and a digital hardware controller. The tests also validate the theoretical performance space and the most suitable compensator design for a given dynamic specification.

An indirect optimization scheme for tuning a fractional order PI controller using extremum seeking

The increasing amount of researches have proven the advantages of fractional order PID controllers. For fractional order PI (FO-PI) controller, the classical tuning approach is based on specifying a certain gain crossover frequency, a phase margin and a robustness to plants gain variations, it can be implemented by applying a series of open-loop experiments without an accurate process model. Additionally, the performance optimization is a widely used auto-tuning method, it searches online for the controller parameters that minimize a cost function which quantifies the closed-loop performance. Based on extremum seeking (ES) algorithm, a novel indirect optimization scheme for tuning a FO-PI controller which combines the regular ES optimization with the classical tuning approach is proposed in this paper. Instead of optimizing the controller parameters directly, we parametrize all the controllers leading to the given performance specifications (cross-over freq, phase margin, iso-damping) and then do the optimization of the cross-over freq and phase margin to achieve the best step-response performance. Simulation and experimental results demonstrate that the proposed ES optimization scheme can achieve a great balance between robustness and performance.

Deep learning and holographic QCD

We apply the relation between deep learning (DL) and the AdS/CFT correspondence to a holographic model of QCD. Using a lattice QCD data of the chiral condensate at a finite temperature as our training data, the deep learning procedure holographically determines an emergent bulk metric as neural network weights. The emergent bulk metric is found to have both a black hole horizon and a finite-height IR wall, so shares both the confining and deconfining phases, signaling the cross-over thermal phase transition of QCD. In fact, a quark antiquark potential holographically calculated by the emergent bulk metric turns out to possess both the linear confining part and the Debye screening part, as is often observed in lattice QCD. From this we argue the discrepancy between the chiral symmetry breaking and the quark confinement in the holographic QCD. The DL method is shown to provide a novel data-driven holographic modeling of QCD, and sheds light on the mechanism of emergence of the bulk geometries in the AdS/CFT correspondence.

Complexity growth rate during phase transitions

We present evidences for the connection between the potential of different fields and complexity growth rates both in conformal and confining cases. By studying different models, we also establish a strong connection between phase transitions and the discontinuities in the complexity growth rates. In the first example, for the dyonic black holes which are dual to van der Waals fluids, we find a similar first order phase transition in the behavior of complexity growth rate. We then compare the Schwinger effect and also the behavior of complexity in the AdS and AdS soliton backgrounds and comment on the connection between them. Finally, in a general Gubser model of QCD, we present the connections between the potentials, entropies, speed of sounds and complexity growth rates during crossover, first and second order phase transitions and also the behavior of quasinormal modes.

Mechanism of dynamic phase transition and synchronous stability in Hindmarsh–Rose neuronal network

The neuronal dynamics plays an important role in understanding the neurological phenomena. We study the mechanism of the dynamic phase transition and its Lyapunov stability of a single Hindmarsh–Rose (HR) neuronal model. We propose an index [Formula: see text] to express the dynamical phase of the HR neurons. When [Formula: see text] the neuron is in the pure resting state, and when [Formula: see text] the neuron closes to the pure spiking phase, while when [Formula: see text] the neuron runs in the bursting phase. Based on this method, we investigate numerically the phase diagram of the HR neuronal model in the parameter space. We find that two mechanisms governed the HR neuronal dynamic phase transition, the phase transition and crossover transition in the different regions of the parameter space. Moreover, we analyze the equilibrium point stability of the HR neuronal model based on the Lyapunov stability method. We study the synchronous stability of the HR neuronal network based on the master stability function method and give the phase diagrams of the maximum Lyapunov exponents in the parameter space of networks. The regions of the synchronous stabilities in the parameter space depend on the couplings of the HR neurons of the membrane potential and the flux of the fast ion channel between the HR neurons. These results help to understand the HR neuronal dynamics and the synchronous stability of the HR neuronal networks.

Frequency frame approach on loop shaping of first order plus time delay systems using fractional order PI controller

This study proposes an analytical design method of fractional order proportional integral (FOPI) controllers for first order plus time delay (FOPTD) systems. Suggested technique obtains the general computation equations of controllers for such systems. These equations are used to tune controller parameters to meet specified frequency and phase properties to satisfy the stability of whole system. It is found that the designed controllers not only make the system stable, but also have positive effect on the performance and robustness of the system. Main contribution of the paper lays on this thought. There proposed a concept, “frequency frame” which encloses the curves between phase and gain crossover frequencies in Bode plot. Robustness of the control system can be improved by expanding or constricting the edges of this frame and flattening the curves inside the frame. Thus, any case that leads the system to instability can be avoided. Analytically derived equations are tested with proper examples and the results are shown illustratively. Advantages and disadvantages of the method are comparatively given.