3,467 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
New results for hadronic collisions in the framework of the Parton-Based Gribov-Regge Theory
We recently proposed a new approach to high energy nuclear scattering, which
treats hadronic collisions in a sophisticated way. Demanding theoretical
consistency as a minimal requirement for a realistic model, we provide a
solution for the energy conservation, screening problems and identical
elementary interactions, the so-called "Parton-Based Gribov-Regge Theory"
including enhanced diagrams. We can now present some of our results for SPS and
RHIC energies.Comment: 4 pages, 3 figures, To appear in the proceedings of Quark Matter 2002
(QM 2002), Nantes, France, 18-24 Jul 200
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
Canonical aspects of strangeness enhancement
Strangeness enhancement (SE) in heavy ion collisions can be understood in the
statistical model on the basis of canonical suppression. In this formulation,SE
is a consequence of the transition from canonical to the asymptotic grand
canonical limit and is predicted to be a decreasing function of collision
energy. This model predictions are consistent with the recent NA49 data on
enhancement at GeV.Comment: 4 pages, 4 figures. To appear in the proceedings of Quark Matter 2002
(Nantes, France
Strange Particle Production in p+p, p+Pb and Pb+Pb Interactions from NA49
Recent NA49 results on Lambda, Antilambda, Xi- and Antixi+ production in
minimum bias p+p and centrality selected p+Pb collisions at 158 GeV/c, and the
results on Lambda, Antilambda, K+ and K- production in central Pb+Pb collisions
at 40, 80 and 158 A GeV are discussed and compared with other available data.
By comparing the energy dependence of Lambda and Antilambda production at
mid-rapidity a striking similarity is observed between p+p and A+A data. This
is also seen in the energy dependence of the Lambda/pi ratio. K+/pi at
mid-rapidity is affected in a similar way, due to the associated production of
K+ together with Lambda particles. The observed yields increase faster than the
number of wounded nucleons when comparing p+Pb to p+p. As already observed in
A+A collisions, the increase is larger for multistrange than for strange
baryons and for baryons than for anti-baryons.Comment: 8 pages, 10 figures, To appear in proceedings of Strange Quark in
Matter 2001-A Flavourspace Odyssey, Frankfurt am Main, Germany, 24-29. Sept.
200
A study of random laser modes in disordered photonic crystals
We studied lasing modes in a disordered photonic crystal. The scaling of the
lasing threshold with the system size depends on the strength of disorder. For
sufficiently large size, the minimum of the lasing threshold occurs at some
finite value of disorder strength. The highest random cavity quality factor was
comparable to that of an intentionally introduced single defect. At the
minimum, the lasing threshold showed a super-exponential decrease with the size
of the system. We explain it through a migration of the lasing mode frequencies
toward the photonic bandgap center, where the localization length takes the
minimum value. Random lasers with exponentially low thresholds are predicted.Comment: 4 pages, 4 figure
An Application of Kerr Blackhole Fly-Wheel Model to Statistical Properties of QSOs/AGNs
The aim of this work is to demonstrate the properties of the magnetospheric
model around Kerr blackholes (BHs), so-called the fly-wheel (rotation driven)
model. The fly-wheel engine of the BH-accretion disk system is applied to the
statistics of QSOs/AGNs. In the model, the central BH is assumed to be formed
at and obtains nearly maximum but finite rotation energy (
extreme Kerr BH) at the formation stage. The inherently obtained rotation
energy of the Kerr BH is released through an magnetohydrodynamic process. This
model naturally leads finite lifetime of AGN activity.
Nitta et al. (1991) clarified individual evolution of Kerr BH fly-wheel
engine which is parametrized by BH mass, initial Kerr parameter, magnetic field
near the horizon and a dimension-less small parameter. We impose a statistical
model for the initial mass function (IMF) of ensemble of BHs by the
Press-Schechter formalism. By the help of additional assumptions, we can
discuss the evolution of the luminosity function and the spatial number density
of QSOs/AGNs.Comment: 12 pages, 7 figures Fig.7 has been replace
Inhibition of ABCB1 (MDR1) Expression by an siRNA Nanoparticulate Delivery System to Overcome Drug Resistance in Osteosarcoma
Background: The use of neo-adjuvant chemotherapy in treating osteosarcoma has improved patients’ average 5 year survival rate from 20% to 70% in the past 30 years. However, for patients who progress after chemotherapy, its effectiveness diminishes due to the emergence of multi-drug resistance (MDR) after prolonged therapy.
Methodology/Principal Findings: In order to overcome both the dose-limiting side effects of conventional chemotherapeutic agents and the therapeutic failure resulting from MDR, we designed and evaluated a novel drug delivery system for MDR1 siRNA delivery. Novel biocompatible, lipid-modified dextran-based polymeric nanoparticles were used as the platform for MDR1 siRNA delivery; and the efficacy of combination therapy with this system was evaluated. In this study, multi-drug resistant osteosarcoma cell lines (KHOSR2 and U-2OSR2) were treated with the MDR1 siRNA nanocarriers and MDR1 protein (P-gp) expression, drug retention, and immunofluoresence were analyzed. Combination therapy of the MDR1 siRNA loaded nanocarriers with increasing concentrations of doxorubicin was also analyzed. We observed that MDR1 siRNA loaded dextran nanoparticles efficiently suppresses P-gp expression in the drug resistant osteosarcoma cell lines. The results also demonstrated that this approach may be capable of reversing drug resistance by increasing the amount of drug accumulation in MDR cell lines.
Conclusions/Significance: Lipid-modified dextran-based polymeric nanoparticles are a promising platform for siRNA delivery. Nanocarriers loaded with MDR1 siRNA are a potential treatment strategy for reversing MDR in osteosarcoma
Robotic Defect Inspection with Visual and Tactile Perception for Large-scale Components
In manufacturing processes, surface inspection is a key requirement for
quality assessment and damage localization. Due to this, automated surface
anomaly detection has become a promising area of research in various industrial
inspection systems. A particular challenge in industries with large-scale
components, like aircraft and heavy machinery, is inspecting large parts with
very small defect dimensions. Moreover, these parts can be of curved shapes. To
address this challenge, we present a 2-stage multi-modal inspection pipeline
with visual and tactile sensing. Our approach combines the best of both visual
and tactile sensing by identifying and localizing defects using a global view
(vision) and using the localized area for tactile scanning for identifying
remaining defects. To benchmark our approach, we propose a novel real-world
dataset with multiple metallic defect types per image, collected in the
production environments on real aerospace manufacturing parts, as well as
online robot experiments in two environments. Our approach is able to identify
85% defects using Stage I and identify 100% defects after Stage II. The dataset
is publicly available at https://zenodo.org/record/8327713Comment: This is a pre-print for International Conference on Intelligent
Robots and Systems 2023 publicatio
Facial Identification at a Virtual Reality Airport
Person identification at airports requires the comparison of a passport photograph with its bearer. In psychology, this process is typically studied with static pairs of face photographs that require identity-match (same person shown) versus mismatch (two different people) decisions, but this approach provides a limited proxy for studying how environment and social interaction factors affect this task. In this study, we explore the feasibility of virtual reality (VR) as a solution to this problem, by examining the identity matching of avatars in a VR airport. We show that facial photographs of real people can be rendered into VR avatars in a manner that preserves image and identity information (Experiments 1 to 3). We then show that identity matching of avatar pairs reflects similar cognitive processes to the matching of face photographs (Experiments 4 and 5). This pattern holds when avatar matching is assessed in a VR airport (Experiments 6 and 7). These findings demonstrate the feasibility of VR as a new method for investigating face matching in complex environments
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