Formation and Radiative Feedback of First Objects and First Galaxies

First, the formation of first objects driven by dark matter is revisited by high-resolution hydrodynamic simulations. It is revealed that dark matter haloes of ~10^4M_sun can produce first luminous objects with the aid of dark matter cusps. Therefore, the mass of first objects is smaller by roughly two orders of magnitude than in the previous prediction. This implies that the number of Pop III stars formed in the early universe could be significantly larger than hitherto thought. Secondly, the feedback by photo-ionization and photo-dissociation photons in the first objects is explored with radiation hydrodynamic simulations, and it is demonstrated that multiple stars can form in a 10^5M_sun halo. Thirdly, the fragmentation of an accretion disk around a primordial protostar is explored with photo-dissociation feedback. As a result, it is found that the photo-dissociation can reduce the mass accretion rate onto protostars. Also, protostars as small as 0.8M_sun may be ejected and evolve with keeping their mass, which might be detected as "real first stars" in the Galactic halo. Finally, state-of-the-art radiation hydrodynamic simulations are performed to investigate the internal ionization of first galaxies and the escape of ionizing photons. We find that UV feedback by forming massive stars enhances the escape fraction even in a halo as massive as > 6* 10^9M_sun, while it reduces the star formation rate significantly. This may have a momentous impact on the cosmic reionization.Comment: 26 pages, 14 figure

Synthesis of Porous Materials and Their Microstructural Control through Ice Templating

Ice-templating is a simple, practical kind of template synthesis which consists of sol-gel polycondensation, unidirectional freezing of hydrosols or hydrogels, and pore-preserving drying method, such as freeze drying, thereby resulting in desirable porous materials. The unidirectional freezing may be achieved by either immersion freezing or contact freezing. Freeze-dried materials contain porous microstructures that are replicas of the ice crystals formed during the unidirectional freezing process. Two similar but slightly different applications of ice-templating will be investigated here. Fabrication of macroporous foam materials by unidirectional freezing of an aqueous suspension of carbon nanotubes (CNTs) dispersed by chitosan is a concrete example of functionalization of an electroconductive foam, which is a composite material made from a polymer and CNTs. As expected, their electroconductive properties can be controlled by the fabrication method and condition. Additional examples of porous materials synthesized by ice-templating are porous microfibers and microhoneycombs of silica, titania, silica-alumina, titania-silica, and even carbon. In the preparation, the morphology and porous structure can be controlled by the freezing conditions and synthesis conditions of the corresponding hydrogels, respectively

Исследование влияния термической обработки на вид излома ударных образцов и трещиностойкость сталей типа 06Г2МБТ

В работе исследованы образцы Шарпи низкоуглеродистых трубных сталей типа 06Г2МБТ после контролируемой прокатки и ускоренного охлаждения и термической обработки по различным режимам. На основе литературных данных и результатов собственных экспериментов проведен анализ поверхностей разрушения, изучено влияние температуры нагрева на уровень ударной вязкости стали и вид поверхности излома

Synthesis of single and multi unit-wall MgB[sub 2] nanotubes by arc plasma in inert liquid via self-curling mechanism

Magnesium diboride (MgB2) is known as a promising superconductor due to its high transmission temperature. Similarly to single-wall carbon nanotube, unique characteristics would be seen if a nanotube structure of MgB2 having a unit-wall of Mg and B atomic bilayer is prepared. However, such MgB2 nanotubes have not ever been synthesized. In this article, formation mechanism of unit-wall MgB2 nanotube is elucidated by molecular mechanics calculation. From the viewpoint of energetic stability, the unit-wall will be curled up to form nanotube structure when MgB2 crystal is disassembled to an isolated unit-wall layer. An experiment using arc plasma in inert liquid was utilized to produce unit-wall MgB2 nanotubes. As a result, a single and multiunit-wall MgB2 nanotube was successfully synthesized. In this reaction field, the arc plasma may play a role to produce isolated MgB2 unit-wall fragment, and the cold cathode surface can contribute to preserve MgB2 nanotube structure

Cr as a key factor for direct synthesis of multi-walled carbon nanotubes on industrial alloys

Six kinds of industrial alloys, SUS316, FCH2, Invar, Permalloy, Inconel, and Nichrome, and three kinds of pure metals, Fe, Ni, and Cr, were used for substrates on which multi-walled carbon nanotubes (MWCNTs) were directly synthesized from ethylene. To activate their surfaces for the MWCNT formation, their surfaces were modified by two steps, (1) oxidation step in Ar–O2 mixture gas and (1) following reduction step in Ar–H2 mixture gas. It was discovered that Cr is a key component to realize the catalytic growth of MWCNTs on Fe and Ni emerged from the alloys. Using SUS316 to observe the influence of oxidation duration on MWCNT diameter, it was seen that increasing the oxidation duration resulted in the increase of the MWCNT diameter. This tendency can be explained by diffusion of Fe through Cr-rich layer, which causes the increase of catalyst particle diameters. The excess Fe diffusion through the Cr-rich layer resulted in the formation of a unique mushroom structure. These effects seen in the observation on the oxidation duration did not appear when reduction duration was prolonged because the Cr-rich layer could inhibit the Fe diffusion. Instead, the length of the MWCNTs can became maximum by employing an appropriate reduction duration

Effects of synthesis conditions on the structural features and methane adsorption properties of single-walled carbon nanohorns prepared by a gas-injected arc-in-water method

Single-walled carbon nanohorns (SWCNHs) can be easily synthesized via a gas-injected arc-in-water method that is considered to be a cost-effective technique. The electrode configuration and duration of arc discharge were modified in order to enhance the yield and methane-adsorption properties of SWCNHs. As a result, the yield of the SWCNHs was significantly increased by increasing the discharge time and the size of the cathode. Using these modified conditions, the horn units in the SWCNH aggregates increased in size, and the thermal stability of SWCNHs in an oxidative environment increased accordingly. Ab initio molecular orbital calculations were used to explain the trend in the thermal stability. When the conventional conditions were applied, a burn-off of about 40% was necessary in order to achieve the maximum specific surface area and micropore volume. Remarkably, by enlarging the cathode size, the burn-off can be reduced by almost half to achieve the enhanced micropore volume. As a result, SWCNHs obtained using the modified conditions adsorbed a larger amount of methane than did SWCNHs obtained from the conventional synthetic conditions. The effect of a mild oxidation treatment on SWCNHs on their methane adsorption suggested that SWCNHs with micropores would be more flexible than pristine SWCNHs. This tendency was elucidated using a molecular mechanics calculation

Fabrication of carbon nanotube film directly grown on conductive stainless steel film and application to dielectrophoretic nanoparticle capture

Multi-walled carbon nanotubes (CNTs) were synthesized directly on stainless steel film thermally deposited on an alumina plate. To activate the growth of CNTs, the stainless steel film was reduced in H2 stream without oxidation step. The electrical resistivity of the CNT film synthesized by this way turned to be 1/190 of CNT film synthesized by a conventional way using catalyst preparation method with magnetron sputtering. Dielectrophoretic (DEP) particle capture was demonstrated using the patterned CNT film synthesized on stainless steel film, and it was observed that carbon nanohorns (CNHs) dispersed with Pd nanoparticles (Pd-CNHs) and Pd-Au alloy nanoparticles (Pd/Au-CNHs) were captured at the CNT electrodes due to the high electric field strength there. In this DEP capture, Pd-CNHs were enriched in the present condition. The temperature to deposit stainless steel film and the influence of oxidation step were also investigated for the growth of CNTs

Porous microfibers and microhoneycombs synthesized by ice templating

Recently we introduced the “ice templating” method, a new method which allows the synthesis of nanoporous materials with unique morphology, such as microfibers and microhoneycombs. In this method, materials are synthesized by freezing their parent hydrosols or hydrogels unidirectionally. Ice crystals which grow within the precursor during freezing act as the template. Therefore, the template can be easily removed through simple thawing and drying, which is a unique and beneficial feature of this method. This paper will first describe the outline of this new method and next, the details about methods to control the dimensions of the materials obtained through it. Comments about the range of applicability of this method will also be provided