Gas Adsorption and Diffusion Behaviors in Interfacial Systems Composed of a Polymer of Intrinsic Microporosity and Amorphous Silica: A Molecular Simulation Study.

We investigate the adsorption and diffusion behaviors of CO2, CH4, and N2 in interfacial systems composed of a polymer of intrinsic microporosity (PIM-1) and amorphous silica using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. We build model systems of mixed matrix membranes (MMMs) with PIM-1 chains sandwiched between silica surfaces. Gas adsorption analysis using GCMC simulations shows that gas molecules are preferentially adsorbed in microcavities distributed near silica surfaces, resulting in an increase in the solubility coefficients of CO2, CH4, and N2 compared to bulk PIM-1. In contrast, diffusion coefficients obtained from MD simulations and then calibrated using the dual-mode sorption model show different tendencies depending on gas species: CO2 diffusivity decreases in MMMs compared to PIM-1, whereas CH4 and N2 diffusivities increase. These differences are attributed to competing effects of silica surfaces: the emergence of larger pores as a result of chain packing disruption, which enhances gas diffusion, and a quadrupole-dipole interaction between gas molecules and silica surface hydroxyl groups, which retards gas diffusion. The former has a greater impact on CH4 and N2 diffusivities, whereas the latter has a greater impact on CO2 diffusivity due to the strong quadrupole-dipole interaction between CO2 and surface hydroxyls. These findings add to our understanding of gas adsorption and diffusion behaviors in the vicinity of PIM-1/silica interfaces, which are unobtainable in experimental studies.

Cdc2-like kinase 2 (Clk2) promotes early neural development in Xenopus embryos.

Neural induction and patterning in vertebrates are regulated during early development by several morphogens, such as bone morphogenetic proteins (BMPs) and fibroblast growth factors (FGFs). Ventral ectoderm differentiates into epidermis in response to BMPs, whereas BMP signaling is tightly inhibited in the dorsal ectoderm which develops into neural tissues. Here, we show that Cdc2-like kinase 2 (Clk2) promotes early neural development and inhibits epidermis differentiation in Xenopus embryos. clk2 is specifically expressed in neural tissues along the anterior-posterior axis during early Xenopus embryogenesis. When overexpressed in ectodermal explants, Clk2 induces the expression of both anterior and posterior neural marker genes. In agreement with this observation, overexpression of Clk2 in whole embryos expands the neural plate at the expense of epidermal ectoderm. Interestingly, the neural-inducing activity of Clk2 is increased following BMP inhibition and activation of the FGF signaling pathway in ectodermal explants. Clk2 also downregulates the level of p-Smad1/5/8 in cooperation with BMP inhibition, in addition to increasing the level of activated MAPK together with FGF. These results suggest that Clk2 plays a role in early neural development of Xenopus possibly via modulation of morphogen signals such as the BMP and FGF pathways.

First case of a bloodstream infection caused by the genus Brachybacterium.

An 83-year-old previously self-sufficient man was referred to our hospital for a fever, severe tenderness over the lumbar spine, and elevated C-reactive protein levels. Computed tomography revealed fluid collection in the intervertebral space of L3/4. Gram-positive, short rod-shaped bacteria were isolated from two sets of blood cultures. A 16S rRNA sequence analysis of an isolate showed a similarity of 98.1% to the nearest type strain Brachybacterium squillarum JCM 16464T. Biochemical characteristics of the presently isolated strain differed from those of the most closely related species of the genus Brachybacterium. The patient was successfully discharged on day 73 of admission with antimicrobial therapies and showed no recurrence during outpatient visits. Brachybacterium spp. have mainly been isolated from the environment, and human Brachybacterium infections have rarely been documented to date. To our knowledge, this is the first clinical isolation of Brachybacterium sp. as a causative pathogen of bloodstream infection.

Construction of non-Markovian coarse-grained models employing the Mori-Zwanzig formalism and iterative Boltzmann inversion.

We propose a new coarse-grained (CG) molecular simulation technique based on the Mori-Zwanzig (MZ) formalism along with the iterative Boltzmann inversion (IBI). Non-Markovian dissipative particle dynamics (NMDPD) taking into account memory effects is derived in a pairwise interaction form from the MZ-guided generalized Langevin equation. It is based on the introduction of auxiliary variables that allow for the replacement of a non-Markovian equation with a Markovian one in a higher dimensional space. We demonstrate that the NMDPD model exploiting MZ-guided memory kernels can successfully reproduce the dynamic properties such as the mean square displacement and velocity autocorrelation function of a Lennard-Jones system, as long as the memory kernels are appropriately evaluated based on the Volterra integral equation using the force-velocity and velocity-velocity correlations. Furthermore, we find that the IBI correction of a pair CG potential significantly improves the representation of static properties characterized by a radial distribution function and pressure, while it has little influence on the dynamic processes. Our findings suggest that combining the advantages of both the MZ formalism and IBI leads to an accurate representation of both the static and dynamic properties of microscopic systems that exhibit non-Markovian behavior.

A fundamental study of cryoablation on normal bone: diagnostic imaging and histopathology.

Cryoablation is a minimally invasive cancer treatment. In this study, the effects of cryoablation on normal rabbit bone were evaluated using imaging and histopathological examinations. Cryoablation was performed using a Cryo-Hit (Galil Medical, Yokneam, Israel). Under anesthesia, one cryoablation needle was inserted at the center of the femur (day 0). To create an ice ball (2 x 3 cm), two 10-min freeze cycles were performed, separated by a 5-min thaw cycle. During cryoablation, changes in the bone and regional tissue were monitored using magnetic resonance imaging (MRI). MRI scans, computed tomography (CT) scans, and collections from the femur (for histopathological evaluation) were performed on days 7, 14, 28, and 56. In terms of the all rabbits' general conditions, we did not observe lameness, decreased appetite, or any other side effects during the experimental periods. Histopathological evaluations of the femur were performed using hematoxylin and eosin staining. MRI indicated inflammation around the ice ball on day 7. Subsequently, the area of inflammation gradually decreased from days 14 to 56. In the histopathological examination, necrosis of bone marrow cells and endosteum were observed from days 7 to 56. No regeneration of bone marrow cells was observed during the experimental period. On the other hand, cryoablation did not influence osteoblasts. Furthermore, there was no pathologic fracture during the experimental period. Our results suggest that cryoablation does not induce severe adverse effects on normal bone, and therefore has potential as a therapeutic option for bone tumors, including metastatic tumors to bone.

Evaluation of gas permeability in porous separators for polymer electrolyte fuel cells: Computational fluid dynamics simulation based on micro-x-ray computed tomography images.

Pore structures and gas transport properties in porous separators for polymer electrolyte fuel cells are evaluated both experimentally and through simulations. In the experiments, the gas permeabilities of two porous samples, a conventional sample and one with low electrical resistivity, are measured by a capillary flow porometer, and the pore size distributions are evaluated with mercury porosimetry. Local pore structures are directly observed with micro-x-ray computed tomography (CT). In the simulations, the effective diffusion coefficients of oxygen and the air permeability in porous samples are calculated using random walk Monte Carlo simulations and computational fluid dynamics (CFD) simulations, respectively, based on the x-ray CT images. The calculated porosities and air permeabilities of the porous samples are in good agreement with the experimental values. The simulation results also show that the in-plane permeability is twice the through-plane permeability in the conventional sample, whereas it is slightly higher in the low-resistivity sample. The results of this study show that CFD simulation based on micro-x-ray CT images makes it possible to evaluate anisotropic gas permeabilities in anisotropic porous media.

In vitro efficacy of combinations of eight antimicrobial agents against Mycobacteroides abscessus complex.

OBJECTIVES: A standard treatment regimen against Mycobacteroides abscessus complex (MABC) infections has not yet been established, making MABC difficult to treat successfully. In this study, we sought to develop an active ingredient for the clinical treatment of MABC infections. METHODS: We screened 102 MABC strains isolated from clinical specimens using DNA sequence analysis with the housekeeping genes hsp65 and rpoB. Drug susceptibility testing was performed against two subspecies-Mycobacteroides abscessus subsp. abscessus (M. abscessus) and Mycobacteroides abscessus subsp. massiliense (M. massiliense)-using eight antimicrobial agents (clarithromycin, amikacin, doxycycline, imipenem, linezolid, moxifloxacin, faropenem, and rifampicin). The combined efficacy of the antimicrobial agents was investigated using a checkerboard method. RESULTS: We identified 51 isolates as M. abscessus, 46 as M. massiliense, and five as others. Most of the M. abscessus isolates (83.0 %) exhibited inducible resistance to clarithromycin via the expression of the erm(41) gene. Combinations of imipenem with linezolid, moxifloxacin, and rifampicin exhibited additive effects against 81.0 %, 40.7 %, and 26.9 % of M. abscessus, respectively, and against 54.5 %, 69.2 %, and 30.8 % of M. massiliense, respectively. CONCLUSIONS: These results demonstrated the potential efficacy of a regimen containing imipenem against M. abscessus and M. massiliense infections.

Mutual influence of molecular diffusion in gas and surface phases.

We develop molecular transport simulation methods that simultaneously deal with gas- and surface-phase diffusions to determine the effect of surface diffusion on the overall diffusion coefficients. The phenomenon of surface diffusion is incorporated into the test particle method and the mean square displacement method, which are typically employed only for gas-phase transport. It is found that for a simple cylindrical pore, the diffusion coefficients in the presence of surface diffusion calculated by these two methods show good agreement. We also confirm that both methods reproduce the analytical solution. Then, the diffusion coefficients for ink-bottle-shaped pores are calculated using the developed method. Our results show that surface diffusion assists molecular transport in the gas phase. Moreover, the surface tortuosity factor, which is known to be uniquely determined by physical structure, is influenced by the presence of gas-phase diffusion. This mutual influence of gas-phase diffusion and surface diffusion indicates that their simultaneous calculation is necessary for an accurate evaluation of the diffusion coefficients.

Effect of capillary condensation on gas transport properties in porous media.

We investigate the effect of capillary condensation on gas diffusivity in porous media composed of randomly packed spheres with moderate wettability. To simulate capillary phenomena at the pore scale while retaining complex pore networks of the porous media, we employ density functional theory (DFT) for coarse-grained lattice gas models. The lattice DFT simulations reveal that capillary condensations preferentially occur at confined pores surrounded by solid walls, leading to the occlusion of narrow pores. Consequently, the characteristic lengths of the partially wet structures are larger than those of the corresponding dry structures with the same porosities. Subsequent gas diffusion simulations exploiting the mean-square displacement method indicate that while the effective diffusion coefficients significantly decrease in the presence of partially condensed liquids, they are larger than those in the dry structures with the same porosities. Moreover, we find that the ratio of the porosity to the tortuosity factor, which is a crucial parameter that determines an effective diffusion coefficient, can be reasonably related to the porosity even for the partially wet porous media.

Hyperthermal molecular beam source using a non-diaphragm-type small shock tube.

We have developed a hyperthermal molecular beam source employing a non-diaphragm-type small shock tube for gas-surface interaction studies. Unlike conventional shock-heated beam sources, the capability of repetitive beam generation without the need for replacing a diaphragm makes our beam source suitable for scattering experiments, which require signal accumulation for a large number of beam pulses. The short duration of shock heating alleviates the usual temperature limit due to the nozzle material, enabling the generation of a molecular beam with higher translational energy or that containing dissociated species. The shock-heated beam is substantially free from surface-contaminating impurities that are pronounced in arc-heated beams. We characterize the properties of nitrogen and oxygen molecular beams using the time-of-flight method. When both the timing of beam extraction and the supply quantity of nitrogen gas are appropriately regulated, our beam source can generate a nitrogen molecular beam with translational energy of approximately 1 eV, which corresponds to the typical activation energy of surface reactions. Furthermore, our beam source can generate an oxygen molecular beam containing dissociated oxygen atoms, which can be a useful probe for surface oxidation. The dissociation fraction along with the translational energy can be adjusted through the supply quantity of oxygen gas.

A non-diaphragm type small shock tube for application to a molecular beam source.

A non-diaphragm type small shock tube was developed for application to a molecular beam source, which can generate beams in the energy range from 1 to several electron volts and beams containing dissociated species such as atomic oxygen. Since repetitive high-frequency operation is indispensable for rapid signal acquisition in beam scattering experiments, the dimensions of the shock tube were miniaturized to reduce the evacuation time between shots. The designed shock tube is 2-4 mm in diameter and can operate at 0.5 Hz. Moreover, a high shock Mach number at the tube end is required for high-energy molecular beam generation. To reduce the shock attenuation caused by the wall boundary layer, which becomes significant in small-diameter tubes, we developed a high-speed response valve employing the current-loop mechanism. The response time of this mechanism is about 100 µs, which is shorter than the rupture time of conventional diaphragms. We show that the current-loop valve generates shock waves with shorter formation distances (about 200-300 mm) than those of conventional shock tubes. In addition, the converging geometry efficiently accelerates shock wave in the small-diameter tubes. The optimal geometry of the shock tube yields shock Mach number around 7, which indicates that the translation energy of molecular beams can exceed 1 eV even in the presence of the real gas effect.

Bottom-up construction of interaction models of non-Markovian dissipative particle dynamics.

We derive the equation of motion for non-Markovian dissipative particle dynamics (NMDPD) by introducing the history effects on the time evolution of the system. Our formulation is based on the generalized Langevin equation, which describes the motions of the centers of mass of clusters comprising microscopic particles. The mean, friction, and fluctuating forces in the NMDPD model are directly constructed from an underlying molecular dynamics (MD) system without any scaling procedure. For the validation of our formulation, we construct NMDPD models from high-density Lennard-Jones systems, in which the typical time scales of the coarse-grained particle motions and the fluctuating forces are not fully separable. The NMDPD models reproduce the temperatures, diffusion coefficients, and viscosities of the corresponding MD systems more accurately than the dissipative particle dynamics models based on a Markovian approximation. Our results suggest that the NMDPD method is a promising alternative for simulating mesoscale flows where a Markovian approximation is not valid.