Analysis of a Splitting Estimator for Rare Event Probabilities in Jackson Networks

We consider a standard splitting algorithm for the rare-event simulation of overflow probabilities in any subset of stations in a Jackson network at level n, starting at a fixed initial position. It was shown in DeanDup09 that a subsolution to the Isaacs equation guarantees that a subexponential number of function evaluations (in n) suffice to estimate such overflow probabilities within a given relative accuracy. Our analysis here shows that in fact O(n^{2{\beta}+1}) function evaluations suffice to achieve a given relative precision, where {\beta} is the number of bottleneck stations in the network. This is the first rigorous analysis that allows to favorably compare splitting against directly computing the overflow probability of interest, which can be evaluated by solving a linear system of equations with O(n^{d}) variables.Comment: 23 page

Rare Events in Stochastic Systems: Modeling, Simulation Design and Algorithm Analysis

This dissertation explores a few topics in the study of rare events in stochastic systems, with a particular emphasis on the simulation aspect. This line of research has been receiving a substantial amount of interest in recent years, mainly motivated by scientific and industrial applications in which system performance is frequently measured in terms of events with very small probabilities.The topics mainly break down into the following themes: Algorithm Analysis: Chapters 2, 3, 4 and 5. Simulation Design: Chapters 3, 4 and 5. Modeling: Chapter 5. The titles of the main chapters are detailed as follows: Chapter 2: Analysis of a Splitting Estimator for Rare Event Probabilities in Jackson Networks Chapter 3: Splitting for Heavy-tailed Systems: An Exploration with Two Algorithms Chapter 4: State Dependent Importance Sampling with Cross Entropy for Heavy-tailed Systems Chapter 5: Stochastic Insurance-Reinsurance Networks: Modeling, Analysis and Efficient Monte Carl

Magnetic structures, spin-flop transition and coupling of Eu and Mn magnetism in the Dirac semimetal EuMnBi2_2

We report here a comprehensive study of the AFM structures of the Eu and Mn magnetic sublattices as well as the interplay between Eu and Mn magnetism in this compound by using both polarized and non-polarized single-crystal neutron diffraction. Magnetic susceptibility, specific heat capacity measurements and the temperature dependence of magnetic diffractions suggest that the AFM ordering temperature of the Eu and Mn moments is at 22 and 337 K, respectively. The magnetic moments of both Eu and Mn ions are oriented along the crystallographic $c$ axis, and the respective magnetic propagation vector is $\textbf{k}_{Eu} = (0,0,1)$ and $\textbf{k}_{Mn}=(0,0,0)$. With proper neutron absorption correction, the ordered moments are refined at 3 K as 7.7(1) $\mu_B$ and 4.1(1) $\mu_B$ for the Eu and Mn ions, respectively. In addition, a spin-flop (SF) phase transition of the Eu moments in an applied magnetic field along the $c$ axis was confirmed to take place at a critical field of B$_c$ $\sim$ 5.3 T. The evolution of the Eu magnetic moment direction as a function of the applied magnetic field in the SF phase was also determined. Clear kinks in both field and temperature dependence of the magnetic reflections ($\pm1$, 0, 1) of Mn were observed at the onset of the SF phase transition and the AFM order of the Eu moments, respectively. This unambiguously indicates the existence of a strong coupling between Eu and Mn magnetism. The interplay between two magnetic sublattices could bring new possibilities to tune Dirac fermions via changing magnetic structures by applied fields in this class of magnetic topological semimetals.Comment: 15 pages, 12 figures, accepted by Physical Review Researc

Reproductive Biology of Yellowfin Tuna (<i>Thunnus albacares</i>) in Tropical Western and Central Pacific Ocean

A total of 756 yellowfin tuna (Thunnus albacares) caught by a Chinese drifting longliner in the tropical western and central Pacific Ocean (WCPO) from May 2018 to March 2019 were investigated to describe the reproductive biology of the species. Generalized linear model and polytomous logistic regression for the ordinal response model were employed to assess the effects of biometric and spatiotemporal factors (such as individual fork length (FL), fishing depth, dissolved oxygen, and month) on the reproductive traits of yellowfin tuna. The results showed that FLs ranged from 87 to 163 cm, averaging 115.8 cm (SD = ±14.2) for females and 121.8 cm (SD = ±16.8) for males. The proportion of males in the sampled fish was 0.61 (SD = ±0.29), and larger males (>130 cm) were proportionally predominant. Analyses based on the monthly variation of the gonadosomatic index and monthly proportion of sexual maturity stages of the gonads showed that the main spawning period of yellowfin tuna lasts from September to December. In addition, the 50% first maturity FLs of males and females were 111.96 cm (SD = ±1.04) and 119.64 cm (SD = ±1.30), respectively. This study provides new information on the reproductive development of T. albacares in the tropical WCPO region. These reproductive parameters reduce uncertainty in current stock assessment models, which will ultimately assist the fishery in becoming sustainable for future generations

Morphometric measurement of lumbar pedicle in different regions: a systematic review

Abstract Objective To collect the data of pedicle width and height in different areas, and to investigate the difference and variation rule of pedicle width and height. Methods Comprehensive search of PubMed, Ovid Medline, and Web of science databases was performed. Collected data were imported into SPSS, and one-way ANOVA test and post hoc test were used to determine whether there were statistical differences in pedicle width and height between the different regions. Results Oceania had the largest pedicle width and height, followed by Americans. West Asian had the largest pedicle width in Asia, followed by East and Southeast Asian, and Chinese and South Asian had similar pedicle width. Different from the variation pattern of pedicle width, the pedicle height of Chinese, East and Southeast Asian and West Asian in Asian range is similar, but the pedicle height of South Asian is significantly smaller than the first three, and has statistical significance. Conclusions People in different regions have similar patterns of variation in pedicle width and height even though they belong to different ethnic groups. This phenomenon is particularly prominent and pronounced in populations in geographically close areas, which may be related to inter-ethnic integration due to population movement between adjacent areas. There is a relationship between the morphological characteristics of the human lumbar pedicle and geographical location

Uncovering the Efficiency and Performance of Ground-Source Heat Pumps in Cold Regions: A Case Study of a Public Building in Northern China

In cold regions, due o the impact of climatic conditions, the heat load in winter and the cooling load in summer are unbalanced. In the long-term operation of the ground-source heat pump (GSHP), the soil heat imbalance phenomenon has still not been successfully solved. Therefore, this study took the GSHP of a public building in the cold area of northern China as the research object. Based on the unit performance data of the system over 8 years and the measured data of the soil temperature field, the long-term operation efficiency of the GSHP in the cold region and the variation law of the soil temperature field were explored. In order to further study the problem of soil heat imbalance, the effect of heat exchange hole groups at different intervals on the underground soil thermal environment after 30 years of operation in the system was simulated, and the optimization scheme of heat exchange hole spacing was proposed. The research results support the improvement and optimization of GSHP design and construction, and have important practical significance for the popularization of GSHPs in cold regions

Physical properties and magnetic structure of a layered antiferromagnet PrPd0.82_{0.82}Bi2_2

We report the physical properties, crystalline and magnetic structures of singe crystals of a new layered antiferromagnetic (AFM) material PrPd0.82Bi2. The measurements of magnetic properties and heat capacity indicate an AFM phase transition at T N ~ 7 K. A large Sommerfeld coefficient of 329.23 mJ⋅mol−1⋅K−2 is estimated based on the heat capacity data, implying a possible heavy-fermion behavior. The magnetic structure of this compound is investigated by a combined study of neutron powder and single-crystal diffraction. It is found that an A-type AFM structure with magnetic propagation wavevector k = (0 0 0) is formed below T N. The Pr3+ magnetic moment is aligned along the crystallographic c-axis with an ordered moment of 1.694(3) μ B at 4 K, which is smaller than the effective moment of the free Pr3+ ion of 3.58 μ B. PrPd0.82Bi2 can be grown as large as 1 mm×1 cm in area with a layered shape, and is very easy to be cleaved, providing a unique opportunity to study the interplay between magnetism, possible heavy fermions, and superconductivity

Analysis of clinical features and identification of risk factors in patients with non-alcoholic fatty liver disease based on FibroTouch

Abstract Our aim was to explore the correlation between ultrasound attenuation parameter (UAP) and liver stiffness measurement (LSM) based on FibroTouch (China) and clinical features in patients with non-alcoholic fatty liver disease (NAFLD), so as to provide a certain basis for the clinical application of FibroTouch in NAFLD. Hepatic steatosis and fibrosis in patients with NAFLD were graded according to FibroTouch, and the relationship between steatosis and fibrosis levels and clinical characteristics was retrospectively analyzed. Hepatic steatosis was positively related with weight, BMI, waist, hyperlipidemia, hyperuricemia, FBG, UA, TG, ALT, AST, GGT, LSM and hepatic fibrosis grading, and was negatively related with gender (male), age and AST/ALT ratio. Hepatic fibrosis was positively related with age, BMI, waist, hypertension, FBG, ALT, AST, GGT, NFS, APRI, FIB-4, UAP and hepatic steatosis grading, and was negatively related with blood platelet (PLT) counts. Moreover, BMI, waist, TG, ALT and LSM were independent risk factors of hepatic steatosis, while decreased PLT counts, AST and UAP were independent risk factors of hepatic fibrosis. Body mass parameters, metabolic risk factors and liver function indicators increase the risk of hepatic steatosis and fibrosis in patients with NAFLD, and UAP and LSM can interact with each other

Effect of Microwave Treatments Combined with Hot-Air Drying on Phytochemical Profiles and Antioxidant Activities in Lily Bulbs (<i>Lilium lancifolium</i>)

Lily bulbs (Lilium lancifolium Thunb.) are rich in phytochemicals and have many potential biological activities which could be deep-processed for food or medicine purposes. This study investigated the effects of microwaves combined with hot-air drying on phytochemical profiles and antioxidant activities in lily bulbs. The results showed that six characteristic phytochemicals were identified in lily bulbs. They also showed that with an increase in microwave power and treatment time, regaloside A, regaloside B, regaloside E, and chlorogenic acid increased dramatically in lily bulbs. The 900 W (2 min) and the 500 W (5 min) groups could significantly suppress the browning of lily bulbs, with total color difference values of 28.97 ± 4.05 and 28.58 ± 3.31, respectively, and increase the content of detected phytochemicals. The highest oxygen radical absorbance activity was found in the 500 W, 5 min group, a 1.6-fold increase as compared with the control (57.16 ± 1.07 μmol TE/g DW), which was significantly relevant to the group’s phytochemical composition. Microwaves enhanced the phytochemicals and antioxidant capacity of lily bulbs, which could be an efficient and environmentally friendly strategy for improving the nutrition quality of lily bulbs during dehydration processing

Rare-earth based intermetallic triangular lattice antiferromagnets REZn3_3As3_3: Crystal growth and physical properties

Inspired by the recent extensive investigations of the ground-state magnetic properties in the rare-earth based triangular lattice antiferromagnet YbMgGaO$_4$ and the related insulating oxide compounds, we have recently carried out the single-crystal growth of the rare-earth based triangular lattice intermetallic compounds REZn$_3$As$_3$ (RE=Ce, Nd, Pr). These materials are strongly frustrated two-dimensional antiferromagnets with the rare-earth ions forming triangular lattice layers. Our studies of the physical properties of the grown high-quality single-crystal samples, including X-ray diffraction, low-temperature heat capacity and magnetic susceptibility measurements etc., have suggested complex magnetic ground states for the studied compounds, likely due to the interplay between geometric frustration, Kondo coupling and RKKY interactions. Further investigations via neutron scattering have been planned