Impact of mechanical deformation on guest diffusion in zeolitic imidazolate frameworks.

The effect of the mechanical deformation of metal-organic frameworks on guest diffusion was investigated by employing molecular dynamics simulations. Two basic deformation modes, uniaxial tensile and shear deformation, were considered. The computed shear modulus of the zeolitic imidazolate framework-8 (ZIF-8) model system was much lower than the Young's modulus, which is in agreement with the experimental results. The diffusion rate in ZIF-8 was calculated for two types of guest molecules: the nonpolar H2 and the quadrupolar CO2. Under tensile strain, the diffusion of both H2 and CO2 was found to be enhanced, whereas the diffusion rates did not change significantly under shear loading. The evolution of the internal structure of ZIF-8 was studied to determine its effect on guest diffusion. The organic-inorganic connection was identified as the source of the framework's flexibility, and therefore we focused on the N-Zn bond and the N-Zn-N angle. Under stretching deformation, the N-Zn bond is elongated and the N-Zn-N angle remains constant. Thus, the length of the C2-C2 long bond, determining the size of the 6-membered ring (6MR) gate, increases and the gate is opened, allowing for faster guest diffusion. Under shear deformation, the N-Zn bond length changes very little and the N-Zn-N angle is distorted. This results in the occurrence of three peaks in the C2-C2 bond length distribution. Although the 6MR gate is distorted, the variation of its average size is small, resulting in a very small effect on the guest diffusivity. In addition, we found that the fluctuation of the ZIF-8 cell can enhance the impact of the mechanical deformation of the host on guest diffusion.

An adolescent presenting with malignant fibrous histiocytoma of the testis: a case report.

INTRODUCTION: Malignant fibrous histiocytoma is a very common subtype of soft-tissue sarcoma in middle and late adulthood. However, malignant fibrous histiocytoma of the testis is very rare in adolescents. CASE PRESENTATION: We report here the case of a 14-year-old Han Chinese boy, who presented with left scrotal mass lasting for 20 days along with distending pain for 5 days. A physical examination revealed a chicken egg-sized, firm, well-defined mass and unclear epididymis. A B-scan ultrasonography of the left scrotum displayed a 9.0×5.2×4.5cm medium- or low-echoic lobulated mass, which suggested a left testicular neoplasm. A fine needle aspiration cytology examination revealed that the cells obtained from the patient's testicular neoplasm were composed of myxoid spindle, and ovoid cells with nuclear atypia and mitotic activity, and arranged in a whirlpool or storiform pattern. Under histological examination, the tumor cells were arranged in a storiform pattern, which displayed mucoid matrix degeneration, and grew invasively. Consequently, a histopathological diagnosis suggested myxofibrosarcoma (or myxoid malignant fibrous histiocytoma). CONCLUSIONS: An ultrasonic examination combined with fine needle aspiration cytology should be helpful for the initial differential diagnosis of testicular malignant fibrous histiocytoma. However, the final confirmation relies on histopathological examination. To the best of our knowledge, this is the first reported case of malignant fibrous histiocytoma of the testis in an adolescent.

[Effect of temperature, rainfall and soil properties on farmland soil nitrification].

Climate conditions, soil properties and management practices control soil nitrification process which affects nitrogen cycling and balance in agro-ecosystems. The interaction of temperature, rainfall, soil type and fertilization on the soil nitrification process was studied by a soil transplantation experiment installed in 3 experiment stations of Chinese Ecological Research Network, i.e., Hailun, Fenqiu and Yingtan Agroecological Experiment Station, which represents middle temperature, warm temperature and middle subtropical zone, respectively. Three types of cropland soils were selected, i.e., neutral black soil (Phaeozem), alkaline Chao soil (Cambisol) and acidic red soil (Acrisol). Then one-meter depth soil profiles for each soil were transplanted in 3 stations to build the field experiment. The two-year experimental results (2006-2007) showed soil nitrification intensity (SNI) changed with the temperature and rainfall during the maize tasseling stage. From Hailun to Yingtan, with an increase of monthly average temperature from 22.3 degrees C to 26.8 degrees C and the monthly rainfall from 100.8 mm to 199.6 mm, SNI decreased by 64.2%-67.2% for black soil, 52.1%-52.5% for Chao soil, and 41.7%-75.2% for red soil, respectively. There were significant negative correlations between SNI and temperature and rainfall, with a correlation coefficient of r = -0.354 (p < 0.01) and r = -0.290 (p < 0.01), respectively. The total number of soil nitrobacteria and the intensity of soil nitrification was affected by soil types, which increased in a sequence of Chao soil > black soil > red soil. Among soil properties, pH affected SNI significantly, with a correlation coefficient of r = 0.551 (p < 0.01). In generally, climate condition (temperature and rainfall), soil type and fertilization present an integrated impact on soil nitrification process, and there were significant interactions of climate x soil type, climate x fertilization, soil type x fertilization, and climate x soil type x fertilization.