Large Break Research Articles

Poly Methacrylic Acid Sodium Salt (PMANa)/Polyurethane (PU) Latex-Polyelectrolyte Colloid Systems Enabling One-Pot Fabrication of Nonperiodic Structured Mechanoresponsive Smart Windows.

Mechanoresponsive smart windows can modulate optical transparency by mechanical actuation, showing the advantages of low cost, energy efficiency, and chemical stability. To date, mechanoresponsive smart windows are mainly built on periodic nano- or microstructures such as arrays, wrinkles, 3D photonic crystals, and polymeric nanocomposites. However, the production of periodic structures requires multiple and complicated processes, which restricts large-scale manufacturing of mechanoresponsive smart windows for practical application. Here, we report one-pot fabrication of poly methacrylic acid sodium salt (PMANa)/polyurethane (PU) mechanoresponsive smart windows with a nonperiodic naturally occurring microsized structure. The obtained smart windows display a high contrast ratio and stable transparency switching behavior under 80% tensile strain over 1000 cycles and have a large breaking elongation of 820%. It offers a promising platform for designing and fabricating multifunctional optical devices including anticounterfeiting labels and dynamical light gratings.

Stretchable and Superelastic Fibrous Sponges Tailored by "Stiff-Soft" Bicomponent Electrospun Fibers for Warmth Retention.

Health risks in an extremely cold environment make warm retention equipment highly desirable. However, creating materials with a high warm retention performance and robust mechanical property to durably prevent against the harsh conditions is highly challenging. Herein, we report on a one-step and facile strategy to fabricate stretchable and superelastic fibrous sponges by creating unique "stiff-soft" polymer networks within fibers and bonding architecture among fibers. The premise of this design is that stiff polystyrene can endow materials with rigidity and soft polyurethane can absorb energy during mechanical deformation. Benefiting from this systematic tailoring for the polymer and assembling networks, the resultant fibrous sponges exhibit a unique tensile recovery property, a large breaking elongation of 70%, and an outstanding resilience for resisting 100 cyclic compressions with 50% strain under -50 °C. Moreover, the fibrous sponges possess dramatic characteristics of high porosity (∼99.31%), ultralight property (volume density = 7.68 mg cm-3), and effective warmth retention (thermal conductivity = 27.6 mW m-1 K-1), as well as technical features of the simple assembly process to scale up easily. The preparation of fibrous sponges provides a new vision for developing ultralight and efficient warmth retention materials.

Stochastic ion and electron heating on drift instabilities at the bow shock

Abstract The analysis of the wave content inside a perpendicular bow shock indicates that heating of ions is related to the lower hybrid drift (LHD) instability, and heating of electrons is related to the electron cyclotron drift (ECD) instability. Both processes represent stochastic acceleration caused by the electric field gradients on the electron gyroradius scales, produced by the two instabilities. Stochastic heating is a single-particle mechanism where large gradients break adiabatic invariants and expose particles to direct acceleration by the direct current and wave fields. The acceleration is controlled by function $\chi = m_iq_i^{-1} B^{-2}$div(E), which represents a general diagnostic tool for processes of energy transfer between electromagnetic fields and particles, and the measure of the local charge non-neutrality. The identification was made with multipoint measurements obtained from the Magnetospheric Multiscale spacecraft. The source for the LHD instability is the diamagnetic drift of ions, and for the ECD instability the source is ExB drift of electrons. The conclusions are supported by laboratory diagnostics of the ECD instability in Hall ion thrusters.

Estimation and inference of change points in high-dimensional factor models

In this paper, we consider the estimation of break points in high-dimensional factor models where the unobserved factors are estimated by principal component analysis (PCA). The factor loading matrix is assumed to have a structural break at an unknown time. We establish the conditions under which the least squares (LS) estimator is consistent for the break date. Our consistency result holds for both large and small breaks. We also find the LS estimator’s asymptotic distribution. Simulation results confirm that the break date can be accurately estimated by the LS even if the magnitudes of breaks are small. In two empirical applications, we implement the method to estimate break points in the U.S. stock market and U.S. macroeconomy, respectively.

Study the effects of various parameters on hydrogen production in the WWER1000/V446

Hydrogen generation and its deflagration or explosion can damage the containment integrity during severe accidents (SAs). In this paper, the total amount of the produced hydrogen during Station Black-Out (SBO), SBO along with Large Break Loss of Coolant Accident (LBLOCA) and SBO along with Small Break Loss of Coolant accident (SBLOCA) for the WWER1000/V446 reactor is estimated by the MELCOR code. Parametric analysis on the SA type, passive safety systems, coating materials of the reactor pressure vessel (RPV), cavity's concrete type and condition is discussed to determine their effects on the H2 production. The obtained results showed that the SBO could produce more H2 (450 kg) compared with other SAs. Passive safety systems increase the amount of the hydrogen production. In addition, CRBR concrete produces low amount of the hydrogen compared with other concrete types.

Water-Enabled Room-Temperature Self-Healing and Recyclable Polyurea Materials with Super-Strong Strength, Toughness, and Large Stretchability.

The synthesis of polymeric materials that simultaneously possess multiple excellent mechanical properties and high-efficient self-healability at room temperature is always a huge challenge. Here, we report the synthesis of a transparent polyurea material that can self-heal at room temperature with the aid of water and, meanwhile, has multiple remarkable mechanical performances, including super-high strength, excellent toughness, and large stretchability. Thanks to the synergistic enhancement of both dynamic imine bonds and hierarchical hydrogen bonds within the networks, the resulting polyureas have a world-record tensile strength of 41.2 MPa when compared with other polyurethanes that can self-heal at room temperature and, at the same time, a large breaking strain of 823.0% and a superior toughness of 127.2 MJ/m3. Besides the influence of imine bonds, the mechanical properties of the polyureas are also strongly related to the density and strength of the hierarchical hydrogen bonds within the polyurea networks, and these two factors could be finely controlled by adjusting the mass ratio of the soft segments with different chain lengths and the types of diisocyanates used for polyurea synthesis, respectively. More importantly, the highly dynamic characteristic of both imine bonds and hierarchical hydrogen bonds within the polyureas endows the materials with repeated water-enabled room-temperature self-healing capacity with a high healing efficiency of 92.2%. Moreover, the polyureas can also be recycled or remolded under mild conditions by the hot-pressing or dissolution/casting process. The synthesized polyureas also show great potential in damping applications with a loss factor larger than 0.3 over the temperature range from 12 to 75 °C. It is believed that polyureas with super-high and well-tunable mechanical properties and high-efficient room-temperature self-healing ability have great potential to substitute traditional irreparable polymers in diverse practical applications.

Experimental study on thermo-mechanical deformation of PHWR channel at elevated temperature

The severe accidents in PHWR type reactors are less probabilistic events owing to extensive safety features, but the consequences of these accidents are serious if not mitigated. Severe accidents progress with the channel deformation due to thermal load, internal pressure and weight of its components. Channel’s sagging behaviour and its failure will define the accident progression under the event of low-pressure inside the channel. Sagging deformation determines the nature of early debris or suspended debris formation. Also, sagging of channel results in the pull-out force on the Calandria end-shield. Therefore, it becomes imperative to know the nature of the event in order to provide any mitigating countermeasures.The present paper aims to study the sagging of coolant channels of standard 220 MWe Indian PHWR under the hypothesis of postulated severe accidents with large break LOCA and loss of ECCS as an initiating event. The moderator cooling system is postulated as impaired with no make-up system. It is difficult to perform a full-scale channel sagging experiments in laboratory. Hence, a novel scale-down approach (1:3) has been adopted for laboratory experiments for the channel sagging study.Experiments have indicated a significant initial sagging with sudden power ramp. The sagging of channel was significant as the temperature of CT reached to 460 °C. The pull-force was not dominant during the transient heat-up, but significant pull or end-load has been observed at the end of the channel cooling. The rate-dependent plasticity (creep) is found to be a dominating mechanism for sagging of the channel.

Comparative study on the breaking waves by a piston-type wavemaker in experiments and SPH simulations

ABSTRACT The wave transfer function derived from the linear wavemaker theory has been widely applied to validate the accuracy of the regular wave. However, it is limited to analyze the waves with large wave steepness, short wavelength, or breaking wave generated right on the wave paddle. By introducing the piston stroke-to-water depth ratio, the empirical formula in the literature is modified to predict both regular and breaking waves according to the wave steepness. Using an experimental wave flume, regular and breaking waves are generated by manipulating the target wave steepness and stroke-to-water depth ratio. The proposed equation is verified in accordance with the experiment results, and optimal variables including energy loss coefficient and breaker index are presented by analyzing the root-mean-square errors. With the developed equation, wave heights and relative depths from any type of piston-type wavemaker can be predicted if the variables of the proposed equation are properly adjusted. Additionally, the numerical wave tank (NWT) is modeled by smoothed particle hydrodynamics (SPH), and the numerically calculated wave heights show good agreement with the proposed equation. The developed methodology can be employed as a guideline toward further studies including analyses of structural behavior under the breaking wave.

Uncertainty quantification for TRACE simulation of FIX-II No. 5052 test

The Best Estimate Plus Uncertainty approach requires the knowledge of input uncertainties for the uncertainty propagation with best-estimate codes. Inaccurate judgement of some model parameter uncertainties related to the dominant physical phenomena may result in misestimation of the safety margin. This paper presents a framework of inverse uncertainty quantification (UQ) to quantify model parameter uncertainties in order to address this issue. It is applied to TRACE simulation of a large break loss of coolant accident conducted on the FIX-II facility, and peak cladding temperature (PCT) is the simulation output. Sensitivity analysis identifies the parameters of the critical flow model as the most influential to the PCT. The inverse UQ is performed based on Bayesian framework, which adopts Markov Chain Monte Carlo sampling and surrogate modelling algorithms. The quantified uncertainties of the model parameters are the desired results from the inverse UQ process, which are useful in BEPU studies.

Dynamic Semiparametric Factor Model With Structural Breaks

For the change-point analysis of a high-dimensional time series, we consider a semiparametric model with dynamic structural break factors. With our model, the observations are described by a few low-dimensional factors with time-invariant loading functions of the covariates. Regarding the structural break, the factors are assumed to be nonstationary and follow a vector autoregression process with a change in the parameter values. In addition, to account for the known spatial discrepancies, we introduce discrete loading functions. We study the theoretical properties of the estimates of the loading functions and the factors. Moreover, we provide both the consistency and the asymptotic normality for making an inference on the estimated breakpoint. Importantly, our results hold for both large and small breaks in the factor dependency structure. The estimation precision is further illustrated via a simulation study. Finally, we present two empirical applications in modeling the dynamics of the minimum wage policy in China and analyzing a limit order book dataset. Supplementary materials for this article are available online.

Do only tax incentives matter? Labor supply and demand responses to an unusually large and salient tax break

I explore labor supply responses to an unusually large and salient notch generated by the “Mini-Job” program in Germany. Using administrative data, I document three findings. First, despite the unusually large magnitude of incentives, earnings elasticities are modest, even after accounting for frictions. Second, the observed response cannot be fully attributed to labor supply alone; rather, the observed outcomes are highly dependent on the availability of jobs and, so are strongly influenced by labor demand incentives. Third, I show that these firm incentives are likely driven by the fact that mini-job workers receive lower fringe-benefit payments.

Preliminary optimization of emergency core cooling system with accident-tolerant fuels

Based on the excellent performance of accident-tolerant fuels (ATFs), the optimization schemes for the safety system of Chinese advanced three-loop pressurized water reactor during loss of coolant accident (LOCA) were proposed and corresponding feasibility analysis was carried out in this study. The modified system analysis code was used to safety evaluation and four ATF systems were investigated. Several modifications were made to the rod geometries in partial ATF systems to make up the poor neutron economic performance of FeCrAl and MoMAX. The emergency core cooling system (ECCS) was optimized during LOCA with different break sizes. The results show that it is feasible for all ATF systems to cancel the high pressure safety injection (HPSI) or cancel both HPSI and low pressure safety injection (LPSI) but add an extra accumulator (ACC). Also the safety of reactors fueled with ATFs can be guaranteed with only 0.35 times the original flowrate of LPSI during large break LOCA (LB-LOCA). In the scheme of replacing the original ECCS with two extra ACCs during LB-LOCA, reactors loaded with partial ATFs are safe, while UO2-Zr systems are in danger as a contrast. This work could provide reference for the design of reactor safety system in the future.

Preliminary neutronic/thermal-hydraulic evaluation and safety system optimization of PWR loaded with fully ceramic microencapsulated fuel

As one of the Accident Tolerant Fuels (ATFs), Fully Ceramic Microencapsulated (FCM) presents advantageous safety performance in the severe accidents compared with UO2 owing to its high melting point, superior heat transfer ability and proliferation resistance capability. In this study, preliminary neutronic and thermal-hydraulic analysis of Chinese improved three-loop Pressurized Water Reactor (PWR) with FCM pellet and SiC cladding (FCM-SiC) were conducted to demonstrate the fuel performance of ATFs. First, a three dimensional full core model loaded with FCM-SiC was developed to acquire the cycle length, power distribution and isotopic inventories. And low reactor power and high fuel enrichment were used to satisfy the annual reload requirement. Then, the reactor thermal-hydraulic safety evaluation was carried out by the modified subchannel and system analysis codes, which depicts lower Fuel Centerline Temperature (FCT) and Peak Cladding Temperature (PCT) in FCM-SiC reactor compared to the reactor with traditional fuels. The Minimum Departure from Nucleate Boiling Ratio (MDNBR) of cladding is much higher than the criterion of 1.3 as well. Furthermore, the reactor safety system was simplified and optimized by taking full advantage of the preponderance of ATFs, and the results show that the reactor of FCM-SiC can operate safely with only 10% initial flowrate of Low Pressure Safety Injection (LPSI) or without Accumulators (ACCs) during Large Break Loss of Coolant Accident (LBLOCA), while the conventional zircaloy is failed under the same conditions. This work could provide guidelines for the optimized design of the reactor safety system in the future.

Encapsulating Tin Nanoflowers into Microcapsules for High‐Rate‐Performance Secondary Battery Anodes through In Situ Polymerizing Oil‐in‐Water Interface

Large volume expansion and structural breaking have been severe issues for emerging high‐performance secondary battery anodes. Herein, a novel microcapsule anode filled with tin (Sn) nanoflowers is presented, which is prepared through in situ interface polymerization of an oil‐in‐water emulsion system. The carbon shell of the microcapsules reduces the pulverization of the encapsulated Sn, and the voids inside the capsules provide efficient spaces for the volume change of Sn during lithiation–delithiation. The Sn‐filled microcapsules exhibit a high rate performance with a capacity decay rate as low as 0.38%, even after three rounds of repeated tests, and a stable capacity of 800 mAh g−1 after 200 cycles at 380 mA g−1. In addition, the electron transfer kinetics and Li‐ion diffusion are investigated, which indicate that the microcapsule system enables a good environment for both electron and ion transfer.

Submacular perfluorocarbon liquid: long-term follow-up.

To report the long-term follow-up of patients with inadvertent retained submacular perfluorocarbon liquid (PFCL) bubbles after vitrectomy surgery. PFCL has unique chemical and physical features which facilitate displacement of subretinal fluid from central toward periphery allowing intraoperative reattachment of the mobile retina and manipulation of the anterior part of the detached retina without performing drainage retinotomy. Despite these advantages, PFCL droplets may be inadvertently retained in the submacular space. A retrospective case series study was conducted. We reviewed 1224 consecutive patients who had undergone primary pars plana vitrectomy at one vitreoretinal center operated by single surgeon (Hammouda Ghoraba). Chart review was performed to identify patients and procedural factors that could predispose to retained submacular PFCL with anatomical and functional outcomes with follow-up at least 18months. The retina was completely attached in 97% of eyes where PFCL was used after one or two vitrectomy surgeries. Submacular PFCL was found in 12 (0.98%) eyes. There was no statistical difference between perfluorodecalin and perfluoro-n-octane as regards retention rate. The possible risk factors associated with submacular retention of PFCL phenomenon are the presence of post-equatorial retinal breaks in six patients (50%) and large retinal break (2-3 clock hours) in three patients (25%). Submacular PFC migration occurs in nearly 1% of cases when it is used. It occurred in cases of RRD with post-equatorial or large breaks. Using perfluoro-n-octane or perfluorodecalin had no statistical difference. Different behaviors of submacular PFC droplets occurred. Some cases of small submacular PFC droplets maintained fair VA for a long period.

Damping HVDC Circuit Breaker With Current Commutation and Limiting Integrated

The fault current limiting in high-voltage dc (HVdc) grids is critical to reducing the breaking stress of dc circuit breaker and improving the breaking reliability. However, the existing HVdc circuit breakers rarely consider the rapid limiting of fault current in the breaking process. In this article, a novel HVdc circuit breaker integrating current commutation and damping is presented, which can realize fast current limiting and interruption while preserving large breaking capability and low cost. Simulation analysis of current commutation capability is carried out to determine the optimal parameters in the current damping module. Then, the fault current breaking performance of the proposed HVdc breaker is evaluated and compared with conventional hybrid HVdc breaker theoretically. Finally, a low-power prototype of the current damping dc breaker is built and tested to verify the validity of the proposed topology.

Global sensitivity analysis of LOFT large break loss of coolant accident with optimized moment-independent method

Best estimate plus uncertainty (BEPU) analysis has been widely adopted for safety evaluation of the nuclear reactor, and the sensitivity analysis is an important part of the BEPU methodology. Local sensitivity analysis methods are still widely utilized in the methodology, which is not suitable for complex non-linear nuclear systems. The global sensitivity analysis is essential but the biggest problem is that the computational cost can hardly be accepted. In this study, the moment-independent global method was adopted and optimized, and a low-cost method was obtained and assessed. The sensitivity analysis of a large break loss of coolant accident (LBLOCA) of the LOFT facility was carried out by using the method. Results show that the optimized method can well evaluate the sensitivity indices with very low cost and relatively high accuracy, and the result obtained through the optimized method is much more reliable than that of the local sensitivity analysis method.

Thermodynamics of laser plasma removal of micro and nano-particles

Micro-impurity pollution is always one of the key factors affecting the quality and service life of precision devices. Micro-nano impurity particles are difficult to remove by traditional cleaning methods (ultrasonic cleaning, etc.) and low removal efficiency by laser cleaning methods (dry laser cleaning, etc.). The laser plasma shock wave has high pressure and high temperature characteristics, which can remove nano-scaled impurity particles, and has great potential applications. In this work, we mainly study the thermodynamic effect of the laser plasma in the process of removing micro- and nano-particles. In this work, the Al particles on the Si substrate are removed by laser plasma shock wave, and the transformation of the particle state is discussed through the changes of the experimental sample morphology after different pulse effects. The experimental results show as follows With the increase of the pulse number, the micro- and nano-particle residues gradually decrease. At the same time, on the surface of the sample after these particles are removed, it can be found that large particles break up into small particles, and some of the particles will change into smooth spheres when their temperatures reach the melting point. These phenomena are the result of the interaction of the thermodynamic effect of the plasma. In order to study the transformation process of particle state, based on the plasma shock wave propagation theory, the evolution law of pressure characteristic and temperature characteristic of shock wave are obtained. From the evolution law, it can be seen that with the increase of shock wave radius, the pressure and temperature gradually decrease. When the shock wave propagates to the surface of a sample, it can reach the compression threshold and correspondingly the surface temperature arrives at melting temperature of particles, which are consistent with the experimental results. By using the finite element simulation method, the pressure and temperature of laser plasma shock wave acting on particles are studied. The stress distribution and temperature distribution in particles varying with time are obtained. The analysis results are consistent with the experimental results, and therefore the thermodynamic mechanism of plasma on particles is obtained.

ПРОСТРАНСТВЕННЫЕ РАЗЛИЧИЯ ПЛОТНОСТИ РАЗРЫВОВ В ЛЕДЯНОМ ПОКРОВЕ ПРИАТЛАНТИЧЕСКОЙ ЧАСТИ АРКТИЧЕСКОГО БАССЕЙНА

We analyzed data on the spatial distribution (density) of large breaks (gaps) in the drifting sea ice cover in the Western Arctic for the period from October 2005 to September 2017, obtained through decoding of lowresolution images from the NOAA satellites. The specific length of gaps, which is the total length of them over an area of 1 km2, is used as a characteristic of the spatial density. It was found that along the continental slope, approximately from the meridian 70° E to the Lincoln Sea, there is a well-defined area of high density, which remains throughout most part of the ice cycle. In this area, the values of the specific gap length averaged over two-month periods exceeded 24 m/km2. In the near-polar region, the density of breaks was smaller throughout the whole ice cycle. The least values of the specific length take place in May–June that is caused by changes in the general state of the ice cover. It was determined that the density of gaps in this area of the Arctic basin well correlated with the speed of wind drift of ice: the more intensive the drift, the larger the density. On the continental slope, two local zones with maximum values of the specific length of breaks reaching 32 m/km2 are considered. It is suggested that the stability of their location in space and time is connected with the increased influence of tidal processes on the deformation of the ice cover over local bottom elevations on the continental slope. A correlation between the bottom profile and the values of the specific length of the gaps along two conditional lines passing through the maximum value zones did show that the largest values of the density are noticed in areas with significant gradients of the depth.

Best estimate plus uncertainty analysis of the China advanced large-scale PWR during LBLOCA scenarios

China advanced large-scale Pressurized Water Reactor (PWR) implements series of passive safety systems to provide core cooling and decay heat removal in case of some unexpected accidents. The development of reactor best estimate system analysis codes has realized the transition from conservative safety analysis to Best Estimate plus Uncertainty (BEPU) analysis for the purpose of achieving more realistic results and digging larger safety margins. The BEPU analysis during Large Break Loss of Coolant Accident (LBLOCA) has been widely used for the licensing application of Nuclear Power Plants (NPPs). In this paper, the BEPU analysis of China advanced large-scale PWR was performed under the conditions of LBLOCA scenarios employing RELAP5 code. The models of reactor coolant system with all the passive safety systems were established and the influence of uncertainties of important parameters on the Peak Cladding Temperature (PCT) was evaluated. The results show the obtained PTC (1314 K) through the BEPU analysis is far below the 10CFR50.46 PCT acceptance criteria (1477 K) in case of LBLOCA and is also lower than the conservative calculation value (1348 K), indicating a larger safety margin. This work provides a meaningful evaluation method for China advanced large-scale PWR safety assessment.