1,108 research outputs found
Near-Ultraviolet and Visible Spectroscopy of HAYABUSA Spacecraft Re-entry
HAYABUSA is the first spacecraft ever to land on and lift off from any
celestial body other than the moon. The mission, which returned asteroid
samples to the Earth while overcoming various technical hurdles, ended on June
13, 2010, with the planned atmospheric re-entry. In order to safely deliver the
sample return capsule, the HAYABUSA spacecraft ended its 7-year journey in a
brilliant "artificial fireball" over the Australian desert. Spectroscopic
observation was carried out in the near-ultraviolet and visible wavelengths
between 3000 and 7500 \AA at 3 - 20 \AA resolution. Approximately 100 atomic
lines such as Fe I, Mg I, Na I, Al I, Cr I, Mn I, Ni I, Ti I, Li I, Zn I, O I,
and N I were identified from the spacecraft. Exotic atoms such as Cu I, Mo I,
Xe I and Hg I were also detected. A strong Li I line (6708 \AA) at a height of
~55 km originated from the onboard Li-Ion batteries. The FeO molecule bands at
a height of ~63 km were probably formed in the wake of the spacecraft. The
effective excitation temperature as determined from the atomic lines varied
from 4500 K to 6000 K. The observed number density of Fe I was about 10 times
more abundant than Mg I after the spacecraft explosion. N2+(1-) bands from a
shock layer and CN violet bands from the sample return capsule's ablating heat
shield were dominant molecular bands in the near-ultraviolet region of 3000 -
4000 \AA. OH(A-X) band was likely to exist around 3092 \AA. A strong shock
layer from the HAYABUSA spacecraft was rapidly formed at heights between 93 km
and 83 km, which was confirmed by detection of N2+(1-) bands with a vibration
temperature of ~13000 K. Gray-body temperature of the capsule at a height of
~42 km was estimated to be ~2437 K which is matched to a theoretical
prediction. The final message of the HAYABUSA spacecraft and its sample return
capsule are discussed through our spectroscopy.Comment: Accepted for publication in PASJ, 22 pages, 7 figures, 6 table
The B Lymphocyte Adaptor Molecule of 32 kD (Bam32) Regulates B Cell Antigen Receptor Signaling and Cell Survival
The B lymphocyte–associated adaptor protein 32 kD in size (Bam32) is expressed at high levels in germinal center (GC) B cells. It has an NH2-terminal src homology 2 (SH2) domain which binds phospholipase C (PLC)γ2, and a COOH-terminal pleckstrin homology (PH) domain. Thus, Bam32 may function to integrate protein tyrosine kinase (PTK) and phosphatidylinositol 3-kinase (PI3K) signaling pathways in B cells. To further define the role Bam32 plays in B cells, we generated Bam32-deficient DT40 cells. These Bam32−/− cells exhibited lower levels of B cell antigen receptor (BCR)-induced calcium mobilization with modest decreases in tyrosine phosphorylation of phospholipase C (PLC)γ2. Moreover, BCR-induced activation of extracellular signal-regulated kinase (ERK), c-jun NH2-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) pathways was impaired in Bam32−/− cells but not the activation of Akt-related pathways. Activation of downstream transcription factors such as nuclear factor of activated T cells (NF-AT) and nuclear factor of κ binding (NF-κB) was also impaired in Bam32−/− cells. Furthermore, Bam32−/− cells were more susceptible to BCR-induced death. Taken together, these findings suggest that Bam32 functions to regulate BCR-induced signaling and cell survival most likely in germinal centers
High-precision molecular dynamics simulation of UO2-PuO2: superionic transition in uranium dioxide
Our series of articles is devoted to high-precision molecular dynamics
simulation of mixed actinide-oxide (MOX) fuel in the rigid ions approximation
using high-performance graphics processors (GPU). In this article we assess the
10 most relevant interatomic sets of pair potential (SPP) by reproduction of
the Bredig superionic phase transition (anion sublattice premelting) in uranium
dioxide. The measurements carried out in a wide temperature range from 300K up
to melting point with 1K accuracy allowed reliable detection of this phase
transition with each SPP. The {\lambda}-peaks obtained are smoother and wider
than it was assumed previously. In addition, for the first time a pressure
dependence of the {\lambda}-peak characteristics was measured, in a range from
-5 GPa to 5 GPa its amplitudes had parabolic plot and temperatures had linear
(that is similar to the Clausius-Clapeyron equation for melting temperature).Comment: 7 pages, 6 figures, 1 tabl
Absence of a Spin Liquid Phase in the Hubbard Model on the Honeycomb Lattice
A spin liquid is a novel quantum state of matter with no conventional order
parameter where a finite charge gap exists even though the band theory would
predict metallic behavior. Finding a stable spin liquid in two or higher
spatial dimensions is one of the most challenging and debated issues in
condensed matter physics. Very recently, it has been reported that a model of
graphene, i.e., the Hubbard model on the honeycomb lattice, can show a spin
liquid ground state in a wide region of the phase diagram, between a semi-metal
(SM) and an antiferromagnetic insulator (AFMI). Here, by performing numerically
exact quantum Monte Carlo simulations, we extend the previous study to much
larger clusters (containing up to 2592 sites), and find, if any, a very weak
evidence of this spin liquid region. Instead, our calculations strongly
indicate a direct and continuous quantum phase transition between SM and AFMI.Comment: 15 pages with 7 figures and 9 tables including supplementary
information, accepted for publication in Scientific Report
Spin-Wave Theory of the Multiple-Spin Exchange Model on a Triangular Lattice in a Magnetic Field : 3-Sublattice Structures
We study the spin wave in the S=1/2 multiple-spin exchange model on a
triangular lattice in a magnetic field within the linear spin-wave theory. We
take only two-, three- and four-spin exchange interactions into account and
restrict ourselves to the region where a coplanar three-sublattice state is the
mean-field ground state. We found that the Y-shape ground state survives
quantum fluctuations and the phase transition to a phase with a 6-sublattice
structure occurs with softening of the spin wave. We estimated the quantum
corrections to the ground state sublattice magnetizations due to zero-point
spin-wave fluctuations.Comment: 8 pages, 20 figure
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