4,742 research outputs found
START: Smoothed particle hydrodynamics with tree-based accelerated radiative transfer
We present a novel radiation hydrodynamics code, START, which is a smoothed
particle hydrodynamics (SPH) scheme coupled with accelerated radiative
transfer. The basic idea for the acceleration of radiative transfer is parallel
to the tree algorithm that is hitherto used to speed up the gravitational force
calculation in an N-body system. It is demonstrated that the radiative transfer
calculations can be dramatically accelerated, where the computational time is
scaled as Np log Ns for Np SPH particles and Ns radiation sources. Such
acceleration allows us to readily include not only numerous sources but also
scattering photons, even if the total number of radiation sources is comparable
to that of SPH particles. Here, a test simulation is presented for a multiple
source problem, where the results with START are compared to those with a
radiation SPH code without tree-based acceleration. We find that the results
agree well with each other if we set the tolerance parameter as < 1.0, and then
it demonstrates that START can solve radiative transfer faster without reducing
the accuracy. One of important applications with START is to solve the transfer
of diffuse ionizing photons, where each SPH particle is regarded as an emitter.
To illustrate the competence of START, we simulate the shadowing effect by
dense clumps around an ionizing source. As a result, it is found that the
erosion of shadows by diffuse recombination photons can be solved. Such an
effect is of great significance to reveal the cosmic reionization process.Comment: 14 pages, 23 figures, accepted for publication in MNRA
Formation and Disruption of Cosmological Low Mass Objects
We investigate the evolution of cosmological low mass (low virial
temperature) objects and the formation of the first luminous objects. First,
the `cooling diagram' for low mass objects is shown. We assess the cooling rate
taking into account the contribution of H_2, which is not in chemical
equilibrium generally, with a simple argument of time scales. The reaction
rates and the cooling rate of H_2 are taken from the recent results by Galli &
Palla (1998). Using this cooling diagram, we also estimate the formation
condition of luminous objects taking into account the supernova (SN) disruption
of virialized clouds. We find that the mass of the first luminous object is
several times 10^7 solar mass, because smaller objects may be disrupted by the
SNe before they become luminous. Metal pollution of low mass (Ly-alpha) clouds
also discussed. The resultant metallicity of the clouds is about 1/1000 of the
solar metallicity.Comment: 11 pages, 2 figures, To appear in ApJ
Correlations in optically-controlled quantum emitters
We address the problem of optically controlling and quantifying the
dissipative dynamics of quantum and classical correlations in a set-up of
individual quantum emitters under external laser excitation. We show that both
types of correlations, the former measured by the quantum discord, are present
in the system's evolution even though the emitters may exhibit an early stage
disentanglement. In the absence of external laser pumping,we demonstrate
analytically, for a set of suitable initial states, that there is an entropy
bound for which quantum discord and entanglement of the emitters are always
greater than classical correlations, thus disproving an early conjecture that
classical correlations are greater than quantum correlations. Furthermore, we
show that quantum correlations can also be greater than classical correlations
when the system is driven by a laser field. For scenarios where the emitters'
quantum correlations are below their classical counterparts, an optimization of
the evolution of the quantum correlations can be carried out by appropriately
tailoring the amplitude of the laser field and the emitters' dipole-dipole
interaction. We stress the importance of using the entanglement of formation,
rather than the concurrence, as the entanglement measure, since the latter can
grow beyond the total correlations and thus give incorrect results on the
actual system's degree of entanglement.Comment: 11 pages, 10 figures, this version contains minor modifications; to
appear in Phys. Rev.
Regulated star formation in forming disk galaxies under ultraviolet radiation background
We perform radiation hydrodynamics simulations on the evolution of galactic
gas disks irradiated by ultraviolet radiation background. We find gas disks
with N_H > 10^21 cm^-2 exposed to ultraviolet radiation at a level of I_21=1
can be self-shielded from photoheating, whereas the disk with N_H < 10^21 cm^-2
cannot. We also find that the unshielded disks keep smooth density distribution
without any sign of fragmentation, while the self-shielded disks easily
fragment into small pieces by self-gravity, possibly followed by star
formation. The suppression of star formation in unshielded disks is different
from photoevaporation effect, since the assumed dark halo potential is deep
enough to keep the photoheated gas. Presence of such critical threshold column
density would be one of the reason for the so-called down-sizing feature of
present-day galaxies.Comment: 12pages, 10figures, ApJ accepte
Radiative Regulation of Population III Star Formation
We explore the impact of ultraviolet (UV) radiation from massive Population
III (Pop III) stars of 25, 40, 80, and 120 M_sun on the subsequent Pop III star
formation. In this paper, particular attention is paid to the dependence of
radiative feedback on the mass of source Pop III star. UV radiation from the
source star can work to impede the secondary star formation through the
photoheating and photodissociation processes. Recently, Susa & Umemura (2006)
have shown that the ionizing radiation alleviates the negative effect by
H_2-dissociating radiation from 120$M_sun PopIII star, since an H_2 shell
formed ahead of an ionizing front can effectively shield H_2-dissociating
radiation. On the other hand, it is expected that the negative feedback by
H_2-dissociating radiation can be predominant if a source star is less massive,
since a ratio of the H_2-dissociating photon number to the ionizing photon
number becomes higher. In order to investigate the radiative feedback effects
from such less massive stars, we perform three-dimensional radiation
hydrodynamic simulations, incorporating the radiative transfer effect of
ionizing and H_2-dissociating radiation. As a result, we find that if a source
star is less massive than ~25M_sun, the ionizing radiation cannot suppress the
negative feedback of H_2-dissociating radiation. Therefore, the fate of the
neighboring clouds around such less massive stars is determined solely by the
flux of H_2-dissociating radiation from source stars. With making analytic
estimates of H_2 shell formation and its shielding effect, we derive the
criteria for radiation hydrodynamic feedback depending on the source star mass.Comment: 8 pages, 9 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Drug delivery applications of three-dimensional printed (3DP) mesoporous scaffolds
Mesoporous materials are structures characterized by a well-ordered large pore system with uniform porous dimensions ranging between 2 and 50 nm. Typical samples are zeolite, carbon molecular sieves, porous metal oxides, organic and inorganic porous hybrid and pillared materials, silica clathrate and clathrate hydrates compounds. Improvement in biochemistry and materials science led to the design and implementation of different types of porous materials ranging from rigid to soft two-dimensional (2D) and three-dimensional (3D) skeletons. The present review focuses on the use of three-dimensional printed (3DP) mesoporous scaffolds suitable for a wide range of drug delivery applications, due to their intrinsic high surface area and high pore volume. In the first part, the importance of the porosity of materials employed for drug delivery application was discussed focusing on mesoporous materials. At the end of the introduction, hard and soft templating synthesis for the realization of ordered 2D/3D mesostructured porous materials were described. In the second part, 3DP fabrication techniques, including fused deposition modelling, material jetting as inkjet printing, electron beam melting, selective laser sintering, stereolithography and digital light processing, electrospinning, and two-photon polymerization were described. In the last section, through recent bibliographic research, a wide number of 3D printed mesoporous materials, for in vitro and in vivo drug delivery applications, most of which relate to bone cells and tissues, were presented and summarized in a table in which all the technical and bibliographical details were reported. This review highlights, to a very cross-sectional audience, how the interdisciplinarity of certain branches of knowledge, as those of materials science and nano-microfabrication are, represent a growing valuable aid in the advanced forum for the science and technology of pharmaceutics and biopharmaceutics
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