AN ESTIMATION OF THERMODYNAMIC AND TRANSPORT PROPERTIES OF CRYOGENIC HYDROGEN USING CLASSICAL MOLECULAR SIMULATION

ABSTRACT In this paper, we estimated the thermodynamic and transport properties of cryogenic hydrogen using classical molecular simulation to clarify the limit of classical method on the estimation of those properties of cryogenic hydrogen. Three empirical potentials, the Lennard-Jones (LJ) potential, twocenter Lennard-Jones (2CLJ) potential, and modified Buckingham (exp-6) potential, and an ab initio potential model derived by the molecular orbital (MO) calculation were applied. Molecular dynamics (MD) simulations were performed across a wide density-temperature range. Using these data, the equation of state (EOS) was obtained by Kataoka"s method, and these were compared with NIST (National Institute of Standards and Technology) data according to the principle of corresponding states. Moreover, we investigated transport coefficients (viscosity coefficient, diffusion coefficient and thermal conductivity) using time correlation function. As a result, it was confirmed that the potential model has a large effect on the estimated thermodynamic and transport properties of cryogenic hydrogen. On the other hand, from the viewpoint of the principle of corresponding states, we obtained the same results from the empirical potential models as from the ab initio potential, showing that the potential model has only a small effect on the reduced EOS: the classical MD results could not reproduce the NIST data in the high-density region. This difference is thought to arise from the quantum effect in actual liquid hydrogen. INTRODUCTION Currently liquid hydrogen is used as fuel for fuel cells and propellant for liquid rocket engines and the demand for liquid hydrogen is increasing. Therefore, it is very important to accurately ascertain the thermal flow phenomena which occur in the liquid hydrogen for safety and efficient use. Especially, in the case of analysis of nanoscale phenomena, molecular simulation is a powerful method. In recent years, studies that clarify the thermodynamic and transport properties of liquid hydrogen using molecular simulation [1-4] have attracted attention. It is possible to calculate macroscopic thermodynamic properties from the microscopic information using an intermolecular interaction. However there is a problem in the molecular simulation of liquid hydrogen. It is how to treat lowtemperature quantum effect. The rotational characteristic temperature of hydrogen is higher than those of other liquids, and the thermal de Broglie wavelength is on the same order as the molecular diameter of hydrogen. Therefore, it is not possible to simply apply the classical method to simulations of liquid hydrogen. Clearly, the non-classical approach for approximating quantum effects should be applied for such a system. It is especially desired in physics and chemistry to reproduce the time evolution of quantum many-body system, such as liquid hydrogen. Accordingly many studies of such simulations have been conducted and new methods have been propose

Reduction of T-Box 15 gene expression in tumor tissue is a prognostic biomarker for patients with hepatocellular carcinoma

Genome-wide analysis is widely applied to detect molecular alterations during oncogenesis and tumor progression. We analyzed DNA methylation profiles of hepatocellular carcinoma (HCC), and investigated the clinical role of most heypermethylated of tumor, encodes T-box 15 (TBX15), which was originally involved in mesodermal differentiation. We conducted a genome-wide analysis of DNA methylation of tumor and non-tumor tissue of 15 patients with HCC, and revealed TBX15 was the most hypermethylated gene of tumor (Beta-value in tumor tissue = 0.52 compared with non-tumor tissue). Another validation set, which comprised 58 HCC with radical resection, was analyzed to investigate the relationships between tumor phenotype and TBX15 mRNA expression. TBX15 mRNA levels in tumor tissues were significantly lower compared with those of nontumor tissues (p < 0.0001). When we assigned a cutoff value = 0.5-fold, the overall survival 5-year survival rates of the low-expression group (n = 17) were significantly shorter compared with those of the high-expression group (n = 41) (43.3% vs. 86.2%, p = 0.001). Multivariate analysis identified low TBX15 expression as an independent prognostic factor for overall and disease-free survival. Therefore, genome-wide DNA methylation profiling indicates that hypermethylation and reduced expression of TBX15 in tumor tissue represents a potential biomarker for predicting poor survival of patients with HCC

GULLY HEAD RETREAT OF AWACH-KANO GULLIES, NYANZA PROVINCE, KENYA: FIELD MEASUREMENTS ANF PIXED-BASED UPALOPE CATCHMENT ASSESSMENT

Gully erosion is a form of land degradation. Soil loss from croplands and residential areas and damage to human infrastructure caused by gully headcut retreat are particularly serious issues for developing countries in sub-Saharan Africa. We focused on the severe gully headcut retreat that incises agricultural land at the foot of the Kavirondo Rift escarpment in western Kenya. Between 2003 and 2004, measurements of the gully headcut retreat were taken. We investigated the topography, geology, and vegetation cover of the upslope catchment through field studies using remotely sensed imagery, analyzed using pixel-based data management. Analysis showed that factors sensitive to runoff were dominant and different overland flow paths caused different kinds of gully headcut retreat. Our pixel-based catchment assessment is a useful measure in the risk management of gully headcut retreat in this region

Importance of Fundamental sp, sp², and sp³ Hydrocarbon Radicals in the Growth of Polycyclic Aromatic Hydrocarbons

The most basic chemistry of products formation in hydrocarbons pyrolysis has been explored via a comparative experimental study on the roles of fundamental sp, sp², and sp³ hydrocarbon radicals/intermediates such as ethyne/ethynyl (C₂H₂/C₂H), ethene/ethenyl (C₂H₄/C₂H₃), and methane/methyl (CH₄/CH₃) in products formations. By using an in situ time-of-flight mass spectrometry technique, gas-phase products of pyrolysis of acetylene (ethyne, C₂H₂), ethylene (ethene, C₂H₄), and acetone (propanone, CH₃COCH₃) were detected and found to include small aliphatic products to large polycyclic aromatic hydrocarbons (PAHs) of mass 324 amu. Observed products mass spectra showed a remarkable sequence of mass peaks at regular mass number intervals of 24, 26, or 14 indicating the role of the particular corresponding radicals, ethynyl (C₂H), ethenyl (C₂H₃), or methyl (CH₃), in products formation. The analysis of results revealed the following: (a) product formation in hydrocarbon pyrolysis is dominated by hydrogen abstraction and a vinyl (ethenyl, C₂H₃) radical addition (HAVA) mechanism, (b) contrary to the existing concept of termination of products mass growth at cyclopenta fused species like acenaphthylene, novel pathways forming large PAHs were found succeeding beyond such cyclopenta fused species by the further addition of C₂H_<i>x</i> or CH₃ radicals, (c) production of cyclopenta ring-fused PAHs (CP-PAHs) such as fluoranthene/corannulene appeared as a preferred route over benzenoid species like pyrene/coronene, (d) because of the high reactivity of the CH₃ radical, it readily converts unbranched products into products with aliphatic chains (branched product), and (e) some interesting novel products such as dicarbon monoxide (C₂O), tricarbon monoxide (C₃O), and cyclic ketones were detected especially in acetone pyrolysis. These results finally suggest that existing kinetic models of product formation should be modified to include the reported novel species and their formation pathways. It is expected that outcomes of this study will be useful to understand the products formation from reactors to interstellar atmospheres as well as the growth mechanism of carbon nanomaterials