Numerical investigation of seismic amplification characteristics in loess ridge region of Xiji, northwest China.

The seismic effects on sloped terrain, which are of paramount importance for engineering design and earthquake risk mitigation, have always been a central focus of earthquake engineering research. In this study, generalized geometric models of loess ridges at varying heights were created, and a three-dimensional nonlinear numerical model was established using FLAC3D. Seismic ground motion time histories at different frequencies and actual earthquake ground motion records were input into the model to analyze the peak acceleration amplification effects experienced by the surface of loess ridges when subjected to SV waves. The study's outcomes reveal that seismic amplification on the slopes of loess ridges is characterized by non-linearity with respect to slope height. Instead, it exhibits rhythmic variations, with the rate of change in these rhythms increasing in correspondence with the frequency of seismic motion and the height of the slope. Under low-intensity seismic motion, a linear increase in acceleration amplification is observed at the ridge's crest concerning the height of the loess ridge. However, under high-intensity seismic motion, the relationship between amplification and slope height becomes less significant. Typically, the peak acceleration at the ridge's crest is reported to be 1.5 to 2.5 times that observed at the slope's base. The amplification effect at the ridge's crest is more pronounced in the low-frequency and high-frequency segments when compared to the mid-frequency range. Conversely, significant amplification is observed in the high-frequency range in the lower sections of the slope near the base. It is further noted that the amplification effect at the ridge's crest displays distinct behavior at different frequencies, characterized by narrow frequency bands of maximum amplification, with peak amplification factors exceeding 10 in some cases. These research findings have practical significance and provide valuable references for engineering construction and seismic risk mitigation planning in loess regions.

The influence of seismic frequency spectrum on the instability of loess slope.

The input of seismic wave with different frequency has a significant impact on loess slope instability. On the basis of field investigation and experiments, the particle flow software PFC2D was used to explore the effect of seismic frequency spectrum on slope instability through the process of calibrating soil microscopic parameters, model establishment, seismic wave input and other processes. The results show that: 1. The low-frequency component of the input wave is the main frequency band that causes the slope instability, the slope has amplifying effect on the low-frequency input wave, and the slope has a "filtering" effect on the high-frequency input wave; 2. The instability of the slope will cause an increase in frequency components above 10 Hz; 3. The special structure of the slope is one of the main reasons for the instability of the slope. This result has theoretical and practical significance for earthquake landslide prevention and monitoring and early warning.

Transgenerational effects of BDE-209 on male reproduction in F3 offspring rats.

Decabromodiphenyl ether (BDE-209), a congener of polybrominated diphenyl ethers, is a commonly used brominated flame retardant and a known endocrine disrupting chemical (EDC). Knowledge about the effects of prenatal BDE-209 exposure on male reproduction and whether transgenerational effects occur in subsequent generations are scant. Therefore, in this study, we tested the hypothesis that prenatal exposure to BDE-209 disrupted sperm function in the F1, F2, and F3 generations of male rats. Pregnant Sprague-Dawley rats were treated by gavage from gestation day 0 to birth with 5 mg BDE-209/kg/day. This treatment was based on the lowest-observed-adverse-effect level for DNA damage to sperm in male offspring. On postnatal day 84 for all generations, epididymal sperm counts, motility, morphology, reactive oxygen species generation, sperm chromatin DNA structure integrity, testicular DNA content in spermatogenesis, and serum testosterone levels were assessed. DNA methyltransferase (Dnmts) mRNA expression and methyl-CpG binding domain sequencing were also examined to analyze DNA methylation status in the F3 generation. In the F1 generation, prenatal exposure to BDE-209 disrupted body weight, decreased anogenital distance (AGD), sperm count, and motility; and increased bent tail rates of sperm. In the F2 generation, exposure to BDE-209 decreased AGD, sperm count, normal morphology rates, Dnmt1 expression, and increased Dnmt3a expression. In the F3 generation, BDE-209 exposure decreased AGD and normal sperm morphology, disrupted testicular elongated spermatid and round spermatid rates, reduced serum testosterone levels, and inhibited the mRNA expression of Dnmt1 and Dnmt3b. Compared with the control group, there existed 215 differentially hyper-methylated and 83 hypo-methylated genes in the BDE-209 group. BDE-209 is an EDC to disrupt the male reproduction from F1 to F3. BDE-209-induced changes in sperm function and hyper- or hypo-DNA methylation in the F3 generation might therefore explain the possible mechanism underlying BDE-209-mediated epigenetic transgenerational effects on the male reproductive system.

Study on the dynamic characteristics of soft soil.

Soft soil is a special type of under-consolidated soil widely distributed in coastal areas of China. In recent years, with the rapid development of Tianjin, an increasing number of public and civil buildings have been built on soft soil. Soft soil poses an imperceptible risk to the safety of buildings in the area. This paper statistically analyzes the physical and dynamic properties of soft soil in Tianjin, and gives the corresponding range values. The results are as follows. (1) Except for the liquidity index, there is a certain correlation between other physical properties; (2) analyzed by experiment, the effects of consolidation time, consolidation ratio, and effective confining pressure on the dynamic shear modulus ratio and damping ratio of soft soil are given. (3) A model of the relationship between shear wave velocity and burial depth of clay and silty clay in the region is given. (4) The influence of different kinetic parameters on the design response spectrum is analyzed. The work described in this article is valuable for workers engaged in soft soil research.

Evaluation of unpredictable critical conditions of patients treated in the observation unit of the Emergency Department.

We evaluated unpredictable critical conditions of patients treated in the Emergency Department (ED) observation unit, who were transferred into the emergency resuscitation room from January 1 through June 30, 2001. A total of 175 patients were observed for the following critical conditions: dyspnea (51 patients; 29.14%), hypotension (28; 16.00%), chest pain (18; 10.29%), dysrhythmia (15; 8.57%), hematemesis (15; 8.57%), altered mental status (12; 6.85%), shock (10; 5.71%), coma (8; 4.57%), apnea (5; 2.86%), hematochezia (3; 1.72%), seizure (3; 1.72%), and others (7; 4.00%). The 27 patients who had cardiopulmonary resuscitation (CPR), endotracheal tube intubation, or cardioversion/defibrillation in the ED suffered an in-ED mortality of 25.9% (7) and an in-hospital mortality of 59.2% (16). The remaining 148 patients who received appropriate treatment, except for the above, had a lower in-hospital mortality (20.28%, 30 patients) (p < 0.05). We should limit the number of patients in the observation unit to avoid overloading, and classify patients according to their clinical conditions. We should determine whether or not they have definite diagnoses or are waiting for hospital admission while receiving simple treatments. The observation unit must be provided with well-trained staff and suitable physical facilities with support services, and rapid specialty consultations must be available.