201 research outputs found
A Novel Synthesis of Symmetric Trienes
This paper describes a novel synthesis of trienes by treatment of trans-2-alkenyl triphenylphosphonium bromides with BuLi in THF solution. Compounds, 5,7,9-tetradecatriene, 1,6-diphenyl-1,3,5-hexatriene, and 2,6,11,16-tetramethyl-2,6,8,10,14-hexadecapentaene were prepared in the yields of 40%, 9%, and 46%, respectively. Cross-coupling of trans-2-heptenyltriphenylphosphonium bromide and trans-3-phenyl-2-propenyltriphenylphosphonium bromide gave a mixture of 5,7,9-tetradecatriene (10.6%), 1,6-diphenyl-1,3,5-hexatriene (0.5%), and 1-phenyl-1,3,5-decatriene (9.4%)
Numerical simulation of H2/air detonation using unstructured mesh
To explore the capability of unstructured mesh to simulate detonation wave propagation phenomena, numerical simulation of H2/air detonation using unstructured mesh was conducted. The unstructured mesh has several adv- antages such as easy mesh adaptation and flexibility to the complicated configurations. To examine the resolution dependency of the unstructured mesh, several simulations varying the mesh size were conducted and compared with a computed result using a structured mesh. The results show that the unstructured mesh solution captures the detailed structure of detonation wave, as well as the structured mesh solution. To capture the detailed detonation cell structure, the unstructured mesh simulations required at least twice, ideally 5times the resolution of structured mesh solution
Regression behavior of polylactic acid manufactured by fused filament fabrication for hybrid rocket propulsion
Advanced closed-loop control of thrust and mixture ratio of hybrid rockets is planned by combing a fuel mass flow rate control technique with a real-time fuel regression measurement. The latter technique is enabled by a multi-materialadditive-manufactured solid fuel with an integrated sensor probe structure. This work investigated the fuel regression behavior of polylactic acid (PLA) fuel used for the main material of this type of solid fuels. Rectangular slab fuels and cylindrical fuel grains were manufactured by Fused Filament Fabrication (FFF) and fired in an optically accessible slab burner and a lab-scale motor, respectively. The cylindrical fuel grains had more than 2 times larger regression rates than rectangular slab fuels even with the same PLA filament. One of the main factors causing this large difference can be an anisotropy in the fuel regression rate behavior of the solid fuels manufactured by FFF
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
Outburst of LS V+44 17 Observed by MAXI and RXTE, and Discovery of a Dip Structure in the Pulse Profile
We report on the first observation of an X-ray outburst of a Be/X-ray binary
pulsar LS V +44 17/RX J0440.9+4431, and the discovery of an absorption dip
structure in the pulse profile. An outburst of this source was discovered by
MAXI GSC in 2010 April. It was the first detection of the transient activity of
LS V +44 17 since the source was identified as a Be/X-ray binary in 1997. From
the data of the follow-up RXTE observation near the peak of the outburst, we
found a narrow dip structure in its pulse profile which was clearer in the
lower energy bands. The pulse-phase-averaged energy spectra in the 3100 keV
band can be fitted with a continuum model containing a power-law function with
an exponential cutoff and a blackbody component, which are modified at low
energy by an absorption component. A weak iron K emission line is also
detected in the spectra. From the pulse-phase-resolved spectroscopy we found
that the absorption column density at the dip phase was much higher than those
in the other phases. The dip was not seen in the subsequent RXTE observations
at lower flux levels. These results suggest that the dip in the pulse profile
originates from the eclipse of the radiation from the neutron star by the
accretion column.Comment: 18 pages, 7 figures, accepted for publication in PAS
Long-term Monitoring of the Black Hole Binary GX 339-4 in the High/Soft State during the 2010 Outburst with MAXI/GSC
We present the results of monitoring the Galactic black hole candidate GX
339-4 with the Monitor of All-sky X-ray Image (MAXI) / Gas Slit Camera (GSC) in
the high/soft state during the outburst in 2010. All the spectra throughout the
8-month period are well reproduced with a model consisting of multi-color disk
(MCD) emission and its Comptonization component, whose fraction is <= 25% in
the total flux. In spite of the flux variability over a factor of 3, the
innermost disk radius is constant at R_in = 61 +/- 2 km for the inclination
angle of i = 46 deg and the distance of d=8 kpc. This R_in value is consistent
with those of the past measurements with Tenma in the high/soft state. Assuming
that the disk extends to the innermost stable circular orbit of a non-spinning
black hole, we estimate the black hole mass to be M = 6.8 +/- 0.2 M_sun for i =
46 deg and d = 8 kpc, which is consistent with that estimated from the Suzaku
observation of the previous low/hard state. Further combined with the mass
function, we obtain the mass constraint of 4.3 M_sun < M < 13.3 M_sun for the
allowed range of d = 6-15 kpc and i < 60 deg. We also discuss the spin
parameter of the black hole in GX 339-4 by applying relativistic accretion disk
models to the Swift/XRT data.Comment: 9 pages, 8 figures, accepted for publication in PASJ (Suzaku+MAXI
special issue
A Spectral Study of the Black Hole Candidate XTE J1752-223 in the High/Soft State with MAXI, Suzaku and Swift
We report on the X-ray spectral analysis of the black hole candidate XTE\
J1752--223 in the 2009--2010 outburst, utilizing data obtained with the
MAXI/Gas Slit Camera (GSC), the Swift/XRT, and Suzaku, which work
complementarily. As already reported by Nakahira et al. (2010) MAXI monitored
the source continuously throughout the entire outburst for about eight months.
All the MAXI/GSC energy spectra in the high/soft state lasting for 2 months are
well represented by a multi-color disk plus power-law model. The innermost disk
temperature changed from 0.7 keV to 0.4 keV and the disk flux
decreased by an order of magnitude. Nevertheless, the innermost radius is
constant at 41 km, where is the
source distance in units of 3.5 kpc and the inclination. The multi-color
disk parameters obtained with the MAXI/GSC are consistent with those with the
Swift/XRT and Suzaku. The Suzaku data also suggests a possibility that the disk
emission is slightly Comptonized, which could account for broad iron-K features
reported previously. Assuming that the obtained innermost radius represents the
innermost stable circular orbit for a non-rotating black hole, we estimate the
mass of the black hole to be 5.510.28 , where the correction for the stress-free inner boundary condition
and color hardening factor of 1.7 are taken into account. If the inclination is
less than 49 as suggested from the radio monitoring of transient jets
and the soft-to-hard transition in 2010 April occurred at 1--4% of Eddignton
luminosity, the fitting of the Suzaku spectra with a relativistic
accretion-disk model derives constraints on the mass and the distance to be
3.1--55 and 2.3--22 {\rm kpc}, respectively. This confirms that the
compact object in XTE J1752--223 is a black hole.Comment: 12 pages including 7 figures and 4 tables, accepted for publication
in PAS
A Large X-ray Flare from a Single Weak-lined T Tauri Star TWA-7 Detected with MAXI GSC
We present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7
detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image
(MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of
ergs cm s in 2--20 keV band during the scan
transit starting at UT 2010-09-07 18:24:30.The estimated X-ray luminosity at
the scan in the energy band is 3 ergs s,indicating that
the event is among the largest X-ray flares fromT Tauri stars.Since MAXI GSC
monitors a target only during a scan transit of about a minute per 92 min
orbital cycle, the luminosity at the flare peak might have been higher than
that detected. At the scan transit, we observed a high X-ray-to-bolometric
luminosity ratio, log = ; i.e., the
X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has
neither an accreting disk nor a binary companion, the observed event implies
that none of those are essential to generate such big flares in T Tauri stars.Comment: 4 pages, 2 figures, 1 table accepted for publication in PAS
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