AC Cycle Research Articles

Structural transition kinetics and activated behavior in the superconducting vortex lattice

Using small-angle neutron scattering, we investigated the behavior of a metastable vortex lattice state in MgB2 as it is driven towards equilibrium by an AC magnetic field. This shows an activated behavior, where the AC field amplitude and cycle count are equivalent to, respectively, an effective "temperature" and "time". The activation barrier increases as the metastable state is suppressed, corresponding to an aging of the vortex lattice. Furthermore, we find a cross-over from a partial to a complete suppression of metastable domains depending on the AC field amplitude, which may empirically be described by a single free parameter. This represents a novel kind of collective vortex behavior, most likely governed by the nucleation and growth of equilibrium vortex lattice domains.

Ozone Production in Coaxial DBD Using an Amplitude-Modulated AC Power Supply in Air

ABSTRACTIn this study, a traditional tubular reactor and an amplitude-modulated AC power supply are employed to develop a unique practical ozone generator with a widely adjustable ozone concentration and simultaneously a constant ozone yield. The amplitude-modulated AC high-voltage waveform driving the discharge consists of the TON (burst of four consecutive AC cycles) and TOFF periods. The characteristics of the ozone generation in air were experimentally investigated at different energy densities, duty cycles and air flow rates, as well as cooling conditions and frequencies. The experimental results show that a unique ozone generator has an almost constant ozone yield of 51.68 ± 2.97 g/kWh in the energy density range of 50–350 kJ/m3, while a wide range of ozone concentration and output can be developed through changing the applied voltage amplitude. A higher ozone yield of can be achieved by decreasing the duty cycle and increasing gas flow rate, while higher ozone concentration can be easily achieved by changing air flow rate. The maximum ozone yield of 92 g/kWh is achieved. In contrast to only a single AC cycle in one complete TON period, changing duty cycle for a consecutive AC cycles in one complete TON period cannot be employed to develop a unique ozone generator with a widely adjustable ozone concentration and simultaneously a constant ozone yield because of different Lissajous figures, discharge energies, positive peaks, negative peaks and their differences for each AC cycle. In addition, the total capacitance of the reactor is not only independent of energy density, duty cycle and cooling condition, but also of AC frequency. A higher AC frequency of the applied high-voltage waveforms leads to a lower dielectric capacitance while increasing gap capacitance.

Flexible, transparent resistive switching device based on topological insulator Bi2Se3-organic composite

Two-dimensional topological insulator bismuth selenide (Bi2Se3) nanosheets (NSs) embedded in poly-methyl methacrylate (PMMA) are employed for the first time for the resistive switching (RS) application. Hexagonal 2D Bi2Se3 NSs are synthesized by a simple solvothermal method and combine with PMMA at different weight percentages of 2D Bi2Se3. Field emission scanning electron microscopy and transmission electron microscopy along with other characterizations such as X-ray photoelectron spectroscopy and Raman spectroscopy were performed for the characterization of Bi2Se3@PMMA hybrid system. The composite was deposited on a transparent, flexible polyethylene terephthalate substrate to form Ag/Bi2Se3@PMMA/indium doped tin oxide memory cell. I-V characteristics of the device revealed a stable and non-volatile memory effect. The device shows a significantly high resistance (RHRS/RLRS) ratio, more than 103, high retention time (more than 9000 s) with high reproducibility over a large number of (105) ac cycles. From the experimental data, RS performances are explained by using a charge trapping–detrapping mechanism. Owing to the increasing interest in flexible electronics, bending tests are carried out at various bending diameters (10–30 mm) to show the mechanical robustness of the proposed device.

Characteristics of the Discharge and Ozone Generation in Oxygen-Fed Coaxial DBD Using an Amplitude-Modulated AC Power Supply

In this study, a traditional tubular reactor and an amplitude-modulated AC power supply were employed to develop a unique practical ozone generator with a widely adjustable ozone concentration and simultaneously a constant ozone yield. The characteristics regarding discharge and ozone generation in oxygen were experimentally investigated in detail. The amplitude-modulated AC waveform consisted of TON (burst of four consecutive AC cycles) and TOFF with a duty cycle of 0.4. The experimental results show that a unique ozone generator can be developed through changing the applied voltage amplitude when an amplitude-modulated AC power supply producing periodic bursts of several consecutive AC cycles during the TON period is used. A quite high and stable ozone yield of 165 ± 16 g/kWh was achieved and a wide range of ozone concentrations could be obtained. Moreover, we observed a very interesting phenomenon that the discharge energy and voltage peak for every AC cycle showed some difference, resulting from the accumulation and release of charge on the dielectric. The first AC cycle had the highest discharge energy and positive voltage peak as well as the lowest negative voltage peak, which was particularly obvious at a high energy density. Additionally, water cooling of the grounded electrode seemed to have a small influence on the basic electrical characteristics of the discharge and had a positive effect on the concentration and yield of ozone due to a reduction in gas temperature in the discharge gap.

Four cycles of adriamycin and cyclophosphamide followed by four cycles of docetaxel (NSABP-B27) with concomitant trastuzumab as neoadjuvant therapy for high-risk, early-stage, HER2-positive breast cancer patients.

BackgroundThe majority of breast cancer patients in Jordan are diagnosed at a young age and present with metastatic or locally advanced disease. The National Surgical Adjuvant Breast and Bowel Project Protocol B27 (NSABP-B27) (four cycles of adriamycin and cyclophosphamide [AC] followed by four cycles of docetaxel) is a standard neoadjuvant regimen in our institution. In this study, we report the efficacy of adding trastuzumab to docetaxel in this regimen for high-risk human epidermal growth factor receptor 2 (HER2)-positive early-stage disease.Patients and methodsConsecutive HER2-positive breast cancer patients treated with this regimen were included. Treatment was given at standard doses and schedules as reported in NSABP-B27. Trastuzumab was given with docetaxel and then continued for 1 year.ResultsA total of 121 patients (mean age 45.4 years) were included. The majority had high-risk features including large tumor size, positive axillary lymph nodes, and grade III disease. Three patients did not complete the planned cycles of AC due to a lack of response. Eight (6.6%) patients missed at least one cycle of docetaxel. Following neoadjuvant therapy, 119 patients underwent surgery, of whom 59 (49.6%) patients achieved pathological complete response. The response was higher in node-negative patients (64.0 vs 45.7%; P=0.03) and in hormone receptor-negative disease patients (69.7 vs 41.9%; P=0.018). Breast-conserving surgery was performed in 21.5% of the patients. The median disease-free survival (DFS) for the whole group was not reached while the 3- and 5-year DFS rates were 84.2 and 74.1%, respectively.ConclusionTrastuzumab added to the NSABP-B27 regimen is a unique combination. When used in high-risk patients, as in our study, outcomes similar to reported data were achieved without unexpected toxicities.

Influence of Duty Cycle on Ozone Generation and Discharge Using Volume Dielectric Barrier Discharge

The influence of duty cycle on ozone generation and discharge characteristics was investigated experimentally using volume dielectric barrier discharge in both synthetic air and pure oxygen at atmospheric pressure. The discharge was driven by an amplitude-modulated AC high voltage–power supply producing TON (a single AC cycle) and TOFF periods with a widely variable duty cycle. The experimental results show that the energy delivered to the discharge during each AC cycle remains roughly constant and is independent of feed gas, duty cycle and TOFF. Both average discharge power and ozone concentration show an initial linear increase with duty cycle, and deviate gradually from linearity owing to an increase in gas temperature at higher duty cycles. Nevertheless, ozone yield remains nearly constant (45.7 ± 3.5 g/kWh in synthetic air and 94.7 ± 3.1 g/kWh in pure oxygen) over a wide range of applied duty cycles (0.02–1). This property can be conveniently employed to develop a unique ozone generator with a widely adjustable ozone concentration and simultaneously a constant ozone yield. Additionally, the discharges in synthetic air and pure oxygen have similar electrical characteristics; however, there are observable differences in apparent luminosity, which is weak and white-toned for synthetic air discharge, and bright and blue-toned for pure oxygen discharge.

Effects of the Third Harmonic Demagnetization Field on the ac Losses of a Granular FeSeTe Superconductor in ac Field

The first harmonics of the magnetic response, of inter- and intragranular volume fractions of a FeSe0.5Te0.5 granular superconducting sample in an alternate magnetic field, have been numerically extracted from the measured magnetization of the whole system by using a model which considers the effects of the fundamental demagnetization fields generated by the magnetization itself. This allowed us to obtain the temperature and field behaviors of the inter- and intragranular ac losses during an ac cycle. These parameters have been found sensitive to the existence of the third harmonic components of the demagnetization field produced by the corresponding magnetization harmonics of the sample. This confirms that the effects of the magnetic response third harmonic components on the sample magnetization, through the demagnetization field, should be taken into account for a more detailed analysis of the measured ac magnetic curves.

Bistable transport properties of a quasi-one-dimensional Wigner solid on liquid helium under continuous driving

We investigate low-frequency fluctuations in the transport characteristics of a quasi-1D Wigner solid (WS) moving along a liquid helium substrate in response to a sinusoidal driving voltage. The fluctuations occur between distinct transport modes in which the decoupling of the WS from ripplonic polarons (or 'dimple lattice', DL) formed on the helium surface does, or does not, occur during each ac cycle. We demonstrate that a Gaussian-like distribution in the decoupling threshold force gives rise to this bistability, as the low-frequency switching occurs when the probability of decoupling during each ac cycle is small but finite. We attribute the distribution in the decoupling threshold force to the range of structural configurations allowed for the quasi-1D electron lattice, which influences the strength of the WS-DL coupling. Hence, the switching rate between the ac transport modes is extremely sensitive to the microscopic properties of the electron solid.

CHEMOTHERAPY REGIMEN AC (DOXORUBICIN AND CYCLOPHOSPHAMIDE) IN BREAST CANCER – PREVENTION OF NAUSEA AND VOMITING

Chemotherapy regimen AС (doxorubicin and cyclophosphamide) is the most often used in adjuvant chemotherapy of breast cancer. AC regimen is high emetogenic. Objective – to evaluate the effectiveness of the combination of aprepitant, ondansetron and dexamethasone for the prevention of nausea and vomiting in patients with breast cancer receiving chemotherapy regimen AC. Materials and methods : 82 female patients with breast cancer received adjuvant chemotherapy regimen AC: doxorubicin 60 mg/ m 2 , cyclophosphamide 600 mg/m 2 in day 1, each 21 day 4 cycle. Patients received an triple-therapy regimen (aprepitant 125 mg p.o. in day 1, 80 mg in days 2 and 3, ondansetron 8 mg i.v. in 1 day, dexamethasone 12 mg i.v.in 1 day, then to 8 mg/day p.o. in days 2–4) for prevention of nausea and vomiting. Results : During the first cycle of chemotherapy in acute phase (0-24 hours from the start of chemotherapy) complete control of nausea and vomiting was achieved at 72 (87.8%) patients. During delayed phase (25-120 hours from the start of chemotherapy) complete control achieved at 56 (68.3%)patients . 57.3% of patients had complete control of nausea and vomiting during all 4 cycles. Conclusion: Adequate regimen for prevention of nausea and vomiting is combination of NK1 receptor antagonist, 5-HT3 receptor antagonist and dexamethasone. Triple-therapy regimen allows more than half of the patients undergo 4 cycles of AC without nausea and vomiting.

Polymer Gating White Flexible Field‐Induced Lighting Device

The development of field‐induced electroluminescence (EL) devices holds great promise for the production of extremely flexible and efficient large‐area light sources. Here, a novel flexible polymeric gate layer for alternating current driven organic electroluminescence (AC‐OEL) devices is presented. The charge‐valve mechanism of carrier manipulation in forward and reversed bias of the applied AC cycles is fully detailed. With a low‐doping strategy of two phosphors in the fluorescent host, a flexible polyethylene(PET)‐based AC‐OEL device with poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethylammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] gate exhibits incredible stability on EL performance with a superior color rendering index, over 81 at 2800 K color temperature and a power efficiency of 2.8 lm W−1 at 1000 cd m−2 with high bending ability (−90° to +90°).

CORALLEEN: A phase 2 clinical trial of chemotherapy or letrozole plus ribociclib as neoadjuvant treatment for postmenopausal patients with luminal B/HER2-negative breast cancer.

TPS594 Background: Dysregulation of cyclin D-CDK4/6-Rb pathway is associated with endocrine resistance in hormone receptor–positive (HR+) breast cancer. Recently, a CDK4/6 inhibitor has shown unprecedented efficacy in metastatic disease, leading to its regulatory approval. Several others are currently in clinical development for the management of HR+ breast cancer in the early and advanced settings. However, it is vital to gain insights into the molecular and biological effects of this class of agents and could identify patients who can benefit the most, delaying or avoiding the use of chemotherapy.The neoadjuvant setting provides an ideal scenario to carry out these investigations. Hence, we propose to conduct an exploratory study to evaluate the biological effects and the efficacy of ribociclib in patients with primary luminal B tumors.We hypothesize that the combination of ribociclib plus letrozole may offer clinical benefit in the preoperative setting. Methods: This is a parallel, multicenter, two-arm, randomized exploratory study in postmenopausal women with primary operable HR+/HER2-negative Luminal B breast cancer designed to evaluate the clinical benefit of ribociclib plus letrozole. Eligibility includes stage I-III operable breast cancer, Luminal B by PAM50, ECOG 0-1. They will be randomized 1:1 to receive either six 28-days cycles of ribociclib (600mg; 3-weeks-on/1-week-off) plus daily letrozole (2.5mg) or chemotherapy: four cycles of AC (doxorubicin 60 mg/m2, cyclophosphamide 600 mg/m2 every 21 days) followed by weekly paclitaxel during 12 weeks. Baseline, Day 15 on-treatment, and surgical specimens will be collected for molecular characterization and evaluation of response (decrease in Ki67, change to ROR low disease) The primary endpoint is the rate of Residual Cancer Burden (RCB) per MD Anderson Cancer Center procedures. A rate of RCB 0 and 1 score at surgery, with a rank between 20% to 25% with 47 evaluable patients by group of treatment will offer a precision between 11.5% and 12.4%, respectively (95%CI). Ninety-four patients will be enrolled in 20 sites across Spain.

Two methods of AC loss calculation in numerical modelling of superconducting coils

Numerical methods are widely utilised in the prediction of AC loss in superconducting coils. A commonly used approach is based on determination of the local dissipation calculated from the distributions of electrical field and current density throughout the winding, as well as its evolution over the AC cycle. This quantity reflects the heat release on a microscopic scale, and its integration throughout the coil winding over one AC cycle provides the value of loss per cycle in the coil. On the other hand, one can look at global quantities characterising the energy flow from a power supply to the coil: the electrical current supplied and the voltage on its terminals. Averaging, with respect to time, of the voltage times current product also gives the coil loss per cycle. Here we show that a comparison of results obtained with ‘local’ and ‘global’ methodologies can be useful in identifying the numerical errors caused by calculation techniques. However, this is possible only when the modelling method allows for determination of the essential physical quantities as independent variables. We illustrate this approach with an example utilising the A-φ and H-formulations for the AC loss evaluation in a ten-turn pancake coil wound from coated conductor tape.

Effect of arc current on droplet ejection from tungsten-based electrode in multiphase AC arc

The dynamic behavior of droplet ejection from a tungsten electrode was successfully visualized using a high-speed camera and an appropriate band-pass filter. The effect of arc current on droplet ejection was investigated to understand the electrode erosion mechanism in the multiphase AC arc. The rate of erosion by droplet ejection increased with increasing current. This result was examined on the basis of the time variation in forces on a pending droplet at the electrode tip during the AC cycle. The relationship among electromagnetic force, surface tension, and ion pressure on the molten tip during the cathodic period is crucial for controling droplet ejection. The molten tip becomes hemispherical forming the pending droplet with an increase in the instantaneous value of arc current during the AC cycle. The pending droplet detaches from the electrode surface when electromagnetic force becomes the dominant force. Consequently, a higher rate of erosion by droplet ejection with a higher arc current resulted from a stronger electromagnetic force.

Plasma Actuator Performance Driven by Dual-Power Supply Voltage—AC High Voltage Superimposed With Pulse Bias Voltage

Many studies have demonstrated the utility of surface dielectric barrier discharge (SDBD) plasma actuators driven by different voltage waveforms for airflow control. In this paper, a new dual-power supply voltage consisting of ac high voltage with a superimposed positive or negative pulse bias voltage is applied to a two-electrode structure SDBD actuator to compare the actuator performance with that driven by a single ac voltage waveform. The ionic wind velocity, the thrust force, and the schlieren visualization images are studied under three types of voltage waveforms: single ac voltage, ac voltage superimposed with a positive pulse bias voltage (ACPP), and ac voltage superimposed with a negative pulse bias voltage (ACNP). The influences of different pulse parameters including pulse voltage, pulse repetition frequency (PRF), and pulsewidth on the actuator performance are studied in detail. Experimental results show that pulse voltage and PRF have more notable influence on the actuator performance when the actuator is driven by ACPP, while the pulsewidth has little effect on the actuator performance. In contrast, the actuator performance is little changed when the actuator is driven by ACNP. The positive and negative pulse discharges have different effects on the actuator performance, the reason is positive pulse discharge increases the discharge of glow-like region while negative pulse discharge increases the discharge of streamer region in the following ac cycle. The schlieren images further indicate pulse discharge exerts its effects on the SDBD actuator performance by affecting the electric field of ac discharge.

Light emission characteristics during the initiation of the electric tree in insulating polymers

The light emission during the growing of the electric tree has been studied before, but very little is known about it before the electric tree initiation. The aim of this work is to study the light emission before electric tree initiation in insulate materials under high AC stress. The ultra-sensitive photomultiplier tube is used to detect the photons in a darkroom and a series of optical filters are used to investigate the spectrum of the photons. The existence of photons before tree initiation is proved and the pattern of them during an AC cycle is observed. The spectrums of the light emission in different dielectric materials are acquired and provide some evidence for the interaction between free charges and polymer molecules. Although the investigation of the light emission is far from being complete, it is found that the light emission under AC voltage starts with the recombination of opposite charges and the interaction process begins under a higher electric field. Based on the experimental results, a brief charge behaviour model is built up.

Effects of airflow on the distribution of filaments in atmospheric AC dielectric barrier discharge

Atmospheric-pressure dielectric barrier discharge (DBD) accompanied by airflow has attracted a significant attention for its extensive applications. In this paper, the effects of airflow on the characteristics of the atmospheric air DBD plasma are experimentally investigated using the DBD reactor excited by a 15 kHz AC power source. In order to study the discharge filaments distribution at different flow rates, transparent conductive indium tin oxide film is used as the upper electrode, and quartz glasses are used as insulated dielectrics. Experiment results prove that the breakdown voltage is decreased and more current pulses with declined amplitudes are produced when the airflow is introduced into the discharge gap. It is confirmed that although the discharge seems to be diffuse in the presence of airflow to the naked eyes, the discharge mode remains filamentary in the intensified charge-coupled device images within a single AC cycle. By acquiring the images with a different exposure time, it can be recognized that the discharge filaments move along the flow field direction with a velocity less than the corresponding flow rate. The movement of discharge filaments is attributed to the motion of the charge induced by the airflow.

Vortex activation energy in the AC magnetic response of superconducting YBa2Cu3O7 thin films with complex pinning structures

The vortex activation energy UAC in the AC magnetic response of superconductors exhibits a logarithmic variation with the screening current density J (regardless of the pinning structure details), and takes surprisingly high values in the vicinity of the DC irreversibility line, especially at low external DC magnetic fields, as often reported. This is essentially different from the behaviour of the vortex-creep activation energy at long relaxation time scales in DC magnetic measurements, and is not completely understood. We investigated the DC relaxation and the AC response for YBa2Cu3O7 films containing nanorods and nanoparticles, with the DC and AC fields oriented perpendicular to the film surface. It is shown that the large UAC values in the vicinity of the DC irreversibility line, where the critical-state-related AC signal occurs, are generated by a non-diffusive vortex motion during the AC cycle, with the mean vortex hopping length longer than the average distance between the pinning centres. In these conditions, the smearing of the vortex pinning potential by thermally induced vortex fluctuations is weak, and UAC mainly results from the strong influence of the pinning-enhanced viscous drag on the vortex hopping process. The logarithmic UAC(J) dependence is consistent with a high UAC.

Zero-Bias Shapiro Steps in Asymmetric Pinning Nanolandscapes

The coherent nonlinear dynamics of Abrikosov vortices in asymmetric pinning nanolandscapes is studied by theoretical modeling and combined microwave and dc electrical resistance measurements. The problem is considered on the basis of a single-vortex Langevin equation within the framework of a stochastic model of anisotropic pinning. When the distance over which Abrikosov vortices are driven during one half ac cycle coincides with one or a multiple of the nanostructure period, Shapiro steps appear in the current-voltage curves (CVCs) as a general feature of systems whose evolution in time can be described in terms of a particle moving in a periodic potential under combined dc and ac stimuli. While a dc voltage appears in response to the ac drive, the addition of a dc bias allows one to diminish the rectified voltage and eventually to change its sign when the extrinsic dc bias-induced asymmetry of the pinning potential starts to dominate the intrinsic one. This rectified negative voltage in the CVCs becomes apparent as \emph{zero-bias} Shapiro steps, which are theoretically predicted and experimentally observed for the first time.

Abrikosov fluxonics in washboard nanolandscapes

Abrikosov fluxonics, a domain of science and engineering at the interface of superconductivity research and nanotechnology, is concerned with the study of the properties and dynamics of Abrikosov vortices in nanopatterned superconductors, with particular focus on their confinement, manipulation, and exploitation for emerging functionalities. Vortex pinning, guided vortex motion, and the ratchet effect are three main fluxonic “tools” which allow for the dynamical (pinned or moving), the directional (angle-dependent), and the orientational (current polarity-sensitive) control of the fluxons, respectively. Thanks to the periodicity of the vortex lattice, several groups of effects emerge when the vortices move in a periodic pinning landscape: Spatial commensurability of the location of vortices with the underlying pinning nanolandscape leads to a reduction of the dc resistance and the microwave loss at the so-called matching fields. Temporal synchronization of the displacement of vortices with the number of pinning sites visited during one half ac cycle manifests itself as Shapiro steps in the current-voltage curves. Delocalization of vortices oscillating under the action of a high-frequency ac drive can be tuned by a superimposed dc bias. In this short review a set of experimental results on the vortex dynamics in the presence of periodic pinning potentials in Nb thin films is presented. The consideration is limited to one particular type of artificial pinning structures — directly written nanolandscapes of the washboard type, which are fabricated by focused ion beam milling and focused electron beam induced deposition. The reported results are relevant for the development of fluxonic devices and the reduction of microwave losses in superconducting planar transmission lines.

Improving thrust by pulse-induced breakdown enhancement in AC surface dielectric barrier discharge actuators for airflow control

The characteristics of a plate-to-plate AC surface dielectric barrier discharge (SDBD) actuator using the pulse-induced breakdown enhancing method are experimentally investigated. The encapsulated electrode is supplied with a sine high AC voltage, while the exposed electrode is feed by a synchronized pulse voltage. Based on the thrust force and power consumption measurements, a parametric study was performed using a positive pulse applied at the trough phase of the AC cycles in which the thrust force was observed to increase by about 100% to 300% and the efficiency up to about 100% compared with the AC-only supply conditions for different AC voltages within the tested range. The pulse-induced breakdown effect was analyzed from the electrical and light emission waveforms to reveal the underlying mechanism. The surface potential due to the charge deposition effect was also measured using a specially designed corona-like discharge potential probe. It is shown that the pulse-induced breakdown was able to cause a temporarily intensified local electric field to enhance the glow-like discharge and meanwhile increase the time-average surface potential in the region further downstream. The improvement in the force by the enhancement in the pulse-induced breakdown was mainly due to enhancements in the glow-like discharge and the surface potential increment, with the latter being more important when the AC voltage is higher.