Analysis of transient characteristics and design improvement of the passive residual heat removal system of NHR-200-II

NHR-200-II is a small integrated pressurized water reactor with 200 MW core thermal power. The core heat is transferred to two independent intermediate circuits via fourteen in-vessel primary heat exchangers (PHE), and the heat in the intermediate circuits is transferred to feedwater by two steam generators (SG) in the two intermediate circuits respectively. A passive residual heat removal (PRHR) branch is connected to each intermediate circuit to remove core decay heat under postulated accidents. During normal operation, PRHR branches are isolated by valves while SG branches in intermediate circuits are open. The valves in PRHR branches will be opened and the isolation valves of SG branches will be closed during decay heat removal scenarios. The decay heat removal capacity of NHR-200-II PRHRS could be seriously deteriorated once the isolation valves for SG branches fail to close, which was confirmed in a scaled integral test loop previously. Current understanding of PRHRS’s thermal-hydraulic characteristics with possible isolation failure in SG branches is limited. In this paper, the NHR-200-II PRHRS is modeled with RELAP5 considering the case of success and fail to isolate SG branches. A series of numerical simulations are carried out to study the impact of various parameters, such as the initial temperature, the size of the intermediate circuits’ header, and the initial flow direction in the intermediate circuits. Oscillatory flow is found when SG branches fail to be isolated under certain parameters combinations. An improved PRHRS design is purposed to eliminate possible flow oscillations, and the purposed improved design are tested by numerical simulations

Methane detection scheme based upon the changing optical constants of a zinc oxide/platinum matrix created by a redox reaction and their effect upon surface plasmons

We detect changes in the optical properties of a metal oxide semiconductor (MOS), ZnO, in a multi-thin-film matrix with platinum in the presence of the hydrocarbon gas methane. A limit of detection of 2% by volume with concentrations from 0 to 10% and maximum resolution of 0.15% with concentrations ranging from 30% to 80% at room temperature are demonstrated along with a selective chemical response to methane over carbon dioxide and the other alkane gases. The device yields the equivalent maximum bulk refractive index spectral sensitivity of 1.8 × 105 nm/RIU. This is the first time that the optical properties of MOS have been monitored to detect the presence of a specific gas. This single observation is a significant result, as MOS have a potentially large number of target gases, thus offering a new paradigm for gas sensing using MOSs

Changes in Precipitation and Drought Extremes over the Past Half Century in China

Changes in climate extremes have become a hot issue in the research field of climate change recently. Many studies have reported that climate extremes have occurred more frequently and with increasing intensity in recent decades. In this study, thresholds of precipitation and drought extremes were determined by the cumulative distribution function, and their spatiotemporal changes over the past half-century in China were analyzed by relative change rate. The results show that: (1) precipitation extremes increased in all regions except North China, while increasing trends of drought extremes were detected in all regions except Northwest China and the Qing–Tibet Plateau; (2) the maximum change rates in frequency of precipitation extremes were found in Northwest China and the Qing–Tibet Plateau, with values of 16.13% and 8.12%, and the maximum change rates in frequency of drought extremes were in Southwest and Southeast China, whose increases in intensity of drought extremes were also the maximum; (3) variation in precipitation extremes showed a relatively mixed pattern with higher heterogeneity compared to that of drought extremes; and (4) changes in precipitation and drought extremes relate to mid-intensity, lower-intensity, and annual precipitation

Early Diagnosis of Brain Injury in Premature Infants Based on Amplitude-Integrated EEG Scoring System

Analyzing and discussing the relationship between brain injury in preterm infants and related risk factors can provide evidence for perinatal prevention and early intervention of brain injury in preterm infants, thereby improving the quality of life of preterm infants. This paper selects term preterm infants diagnosed with preterm infant asphyxia in the NICU of a university’s First Affiliated Hospital from January 2018 to February 2019 as the research object. In addition, healthy term infants born at the same time in the obstetric department of this hospital are selected as the control group. Both groups of premature infants were monitored for brain function within 6 hours after birth. The aEEG results range from background activity (continuous normal voltage, discontinuous normal voltage, burst suppression, continuous low voltage, and plateau) and sleep-wake cycle (no sleep-wake cycle, immature, and mature sleep-wake cycle) to epileptic activity (single seizures, recurrent seizures, and status epilepticus), three aspects to judge. Statistical analysis uses SPSS 17.0 software. Amplitude-integrated EEG is a simplified form of continuous EEG recording. The trace of the trace represents the voltage change signal of the entire EEG background activity, which can reflect the EEG amplitude, frequency, burst-inhibition, and other pieces of information. aEEG can reflect the degree of HIE lesions in premature infants and the long-term prognosis. It is easy to operate and effective in diagnosis and can be continuously monitored. It is worthy of clinical popularization. There is a good correlation between the expression of EEG and biomarkers. Combining multiple methods can diagnose HIE earlier and evaluate the prognosis

Gradual chlorination at different positions of D-π-A copolymers based on benzodithiophene and isoindigo for organic solar cells

Isoindigo (IID) has been widely used as strong acceptor unit (A) to construct narrow bandgap polymers in organic field effect transistors (OFETs) and organic solar cells (OSCs). Combing with IID, we chose benzodithiophene (BDT) as the donor unit (D) and thieno [3,2-b]thiophene (TT) as the π bridge to construct a new type of D-π-A polymer PE70. Based on PE70, we adopt the chlorination strategy to fine-tune photoelectric characteristics and film morphology, and then developed PE74 and PE75. By blending with non-fullerene acceptor (NFA) Y6, device based on PE74 with chloride substitution on the BDT unit showed increasing photovoltaic performance. In addition, further chlorine substitution on the IID (PE75) would greatly reduce the non-radiative voltage loss (ΔV3), and the distorted molecular conformation also took responsible for the excessive recombination. As results, PE74:Y6-based device achieves a power conversion efficiency (PCE) of 11.06% with open-circuit voltage (VOC) of 0.76 ​V, which are higher than those of PE70:Y6 (PCE of 10.40% and VOC of 0.72 ​V) and PE75: Y6-based device (PCE of 6.24% and VOC of 0.84 ​V). This work demonstrates the regularity of the photovoltaic performance caused by chlorination strategy in polymer in the non-fullerene OSC devices, which provide important insights into high-performance photovoltaic materials

Influence of Key Processing Technology on the Quality of Freshly-squeezed Lettuce Juice

In order to realize the effects of blanching (95 ℃/2 min), separation (6000×g/10 min) and sterilization (600 MPa, 25 ℃/2 min) on the processing quality of freshly-squeezed lettuce juice, hydroponic green rosa lettuce were chosen as the test material. Changes of microorganisms, color, physical and chemical parameters, enzyme activities and antioxidant capacity were evaluated. The results suggested that the total aerobic bacteria of freshly-squeezed lettuce juice was less than 2 lgCFU/mL and the mold and yeast were less than 1.3 lgCFU/mL after sterilization process, all of which were within the national standard limit (GB 7101-2015). Separation process significantly affected the color and chlorophyll content of lettuce juice. The L*, a*, b* and C* values of fresh clear lettuce juice were significantly increased (P<0.05), and the clear juice was brighter, lighter in green, deeper in yellow and higher in saturation, and the total chlorophyl content decreased by 56.44%. Blanching process significantly decreased the a* value (P<0.05), and the green color became brighter. The inactivation rates of polyphenoloxidase, peroxidase and catalase were 83.76%, 84.87% and 90.80% after blanching, respectively. Blanching and sterilization both affected the active components and antioxidant capacity of freshly-squeezed lettuce juice, the soluble sugar content retention rate was 91.24% and 88.3%, the soluble protein retention rate was 64.22% and 60.60%, the total phenolic content was decreased by 53.31% and 56.28%, the antioxidant capacity decreased by 82.61% and 73.91%, respectively. This study could provide technical reference for processing of freshly-squeezed vegetable juice

Self-Assembly of Four-Claw Discotic Mesogenic Molecules: Influence of Core on Chirality

The morphology of self-assembled monolayers determined by molecular structure and involved interactions plays a crucial role in their properties. Herein, we report a study on 2D self-assembly of two kinds of triphenylene-submitted discotic mesogenic species, which have similar four TP moieties with alkyne spacer but different rigid aromatic cores pyrene and carbazole. Two types of stable periodic long-ranged supramolecular networks on the highly oriented pyrolytic graphite surface have been visualized via high-resolution scanning tunneling microscopy technique. A comparative study reveals how the aromatic core of molecular building blocks affects achiral and chiral arrangement of discotic molecule on surface. The asymmetry backbone results in molecular orientation and varied van der Waals forces between molecule–molecule and molecule–substrate. Our results demonstrate that design of functional molecules plays an important role in the construction of 2D supramolecular assembly possessing desirable structure for the specific applications