48 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
Theory of spin-2 Bose-Einstein condensates: spin-correlations, magnetic response, and excitation spectra
The ground states of Bose-Einstein condensates of spin-2 bosons are
classified into three distinct (ferromagnetic, ^^ ^^ antiferromagnetic", and
cyclic) phases depending on the s-wave scattering lengths of binary collisions
for total-spin 0, 2, and 4 channels. Many-body spin correlations and magnetic
response of the condensate in each of these phases are studied in a mesoscopic
regime, while low-lying excitation spectra are investigated in the hermodynamic
regime. In the mesoscopic regime, where the system is so tightly confined that
the spatial degrees of freedom are frozen, the exact, many-body ground state
for each phase is found to be expressed in terms of the creation operators of
pair or trio bosons having spin correlations. These pairwise and trio-wise
units are shown to bring about some unique features of spin-2 BECs such as a
huge jump in magnetization from minimum to maximum possible values and the
robustness of the minimum-magnetization state against an applied agnetic field.
In the thermodynamic regime, where the system is spatially uniform, low-lying
excitation spectra in the presence of magnetic field are obtained analytically
using the Bogoliubov approximation. In the ferromagnetic phase, the excitation
spectrum consists of one Goldstone mode and four single-particle modes. In the
antiferromagnetic phase, where spin-singlet ^^ ^^ pairs" undergo Bose-Einstein
condensation, the spectrum consists of two Goldstone modes and three massive
ones, all of which become massless when magnetic field vanishes. In the cyclic
phase, where boson ^^ ^^ trios" condense into a spin-singlet state, the
spectrum is characterized by two Goldstone modes, one single-particle mode
having a magnetic-field-independent energy gap, and a gapless single-particle
mode that becomes massless in the absence of magnetic field.Comment: 28 pages, 4 figure
Exact Eigenstates and Magnetic Response of Spin-1 and Spin-2 Vectorial Bose-Einstein Condensates
The exact eigenspectra and eigenstates of spin-1 and spin-2 vectorial
Bose-Einstein condensates (BECs) are found, and their response to a weak
magnetic field is studied and compared with their mean-field counterparts.
Whereas mean-field theory predicts the vanishing population of the zero
magnetic-quantum-number component of a spin-1 antiferromagnetic BEC, the
component is found to become populated as the magnetic field decreases. The
spin-2 BEC exhibits an even richer magnetic response due to quantum correlation
between 3 bosons.Comment: 5 pages, no figures. LaTeX20
Topological Excitations in Spinor Bose-Einstein Condensates
A rich variety of order parameter manifolds of multicomponent Bose-Einstein
condensates (BECs) admit various kinds of topological excitations, such as
fractional vortices, monopoles, skyrmions, and knots. In this paper, we discuss
two topological excitations in spinor BECs: non-Abelian vortices and knots.
Unlike conventional vortices, non-Abelian vortices neither reconnect themselves
nor pass through each other, but create a rung between them in a topologically
stable manner. We discuss the collision dynamics of non-Abelian vortices in the
cyclic phase of a spin-2 BEC. In the latter part, we show that a knot, which is
a unique topological object characterized by a linking number or a Hopf
invariant [], can be created using a conventional quadrupole
magnetic field in a cold atomic system.Comment: Proceedings of the workshop "New Frontiers in QCD 2010
Quantum Phase Transition of Spin-2 Cold Bosons in an Optical Lattice
The Bose-Hubbard Hamiltonian of spin-2 cold bosons with repulsive interaction
in an optical lattice is proposed. After neglecting the hopping term, the
site-independent Hamiltonian and its energy eigenvalues and eigenstates are
obtained. We consider the hopping term as a perturbation to do the calculations
in second order and draw the phase diagrams for different cases. The phase
diagrams show that there is a phase transition from Mott insulator with integer
number bosons to superfluid when the ratio ( is the
spin-independent on-site interaction and the hopping matrix element between
adjacent lattice sites) is decreased to a critical value and that there is
different phase boundary between superfluid and Mott insulator phase for
different Zeeman level component in some ground states. We find that the
position of phase boundary for different Zeeman level component is related to
its average population in the Mott ground state.Comment: 16 pages, 6 figure
Streptococcus anginosus のプロリルトリペプチジルペプチダーゼの産生と酵素性状
Streptococcus anginosus is considered to be implicated in the etiology of oral infectious diseases as well as abscess formation in various body sites. We investigated the production and the enzymatic properties of PTP of S. anginosus NCTC 10713. This enzyme was found only in cell extract and active on tripeptide substrates containing proline residue at P1 position, particularly H−Ala−Ala−Pro−p−nitroanilide. The enzyme was produced by all 8 species of tested streptococci, indicating occurrence of this enzyme is rather ubiquitous within streptococci. This PTP was purified to homogeneity from the cell extract by the procedures including ammonium sulfate precipitation, chromatography, gel filtration and electrophoresis. The enzyme was inhibited by serine enzyme inhibitors and chelating reagents, indicating this PTP is a serine metalloenzyme with a molecular mass of 66 kDa. The enzyme was active against H−Ala−Ala−Pro−p−nitroanilide and H−Ala−Phe−Pro−p−nitroanilide in neutral pH solutions. The activity was completely lost by heating at 50°C for 10min
Solutions of multi-component NLS models and spinor Bose-Einstein condensates
A three- and five-component nonlinear Schrodinger-type models, which describe
spinor Bose-Einstein condensates (BEC's) with hyperfine structures F=1 and F=2
respectively, are studied. These models for particular values of the coupling
constants are integrable by the inverse scattering method. They are related to
symmetric spaces of BD.I-type SO(2r+1)/(SO(2) x SO(2r-1)) for r=2 and r=3.
Using conveniently modified Zakharov-Shabat dressing procedure we obtain
different types of soliton solutions.Comment: 12 pages, LaTeX, no figures, elsart styl
Topological defects in spinor condensates
We investigate the structure of topological defects in the ground states of
spinor Bose-Einstein condensates with spin F=1 or F=2. The type and number of
defects are determined by calculating the first and second homotopy groups of
the order-parameter space. The order-parameter space is identified with a set
of degenerate ground state spinors. Because the structure of the ground state
depends on whether or not there is an external magnetic field applied to the
system, defects are sensitive to the magnetic field. We study both cases and
find that the defects in zero and non-zero field are different.Comment: 10 pages, 1 figure. Published versio
Abe homotopy classification of topological excitations under the topological influence of vortices
Topological excitations are usually classified by the th homotopy group
. However, for topological excitations that coexist with vortices, there
are case in which an element of cannot properly describe the charge of
a topological excitation due to the influence of the vortices. This is because
an element of corresponding to the charge of a topological excitation
may change when the topological excitation circumnavigates a vortex. This
phenomenon is referred to as the action of on . In this paper,
we show that topological excitations coexisting with vortices are classified by
the Abe homotopy group . The th Abe homotopy group is
defined as a semi-direct product of and . In this framework, the
action of on is understood as originating from noncommutativity
between and . We show that a physical charge of a topological
excitation can be described in terms of the conjugacy class of the Abe homotopy
group. Moreover, the Abe homotopy group naturally describes vortex-pair
creation and annihilation processes, which also influence topological
excitations. We calculate the influence of vortices on topological excitations
for the case in which the order parameter manifold is , where is
an -dimensional sphere and is a discrete subgroup of . We show
that the influence of vortices on a topological excitation exists only if
is even and includes a nontrivial element of .Comment: 36 pages, 12 figure
On the single mode approximation in spinor-1 atomic condensate
We investigate the validity conditions of the single mode approximation (SMA)
in spinor-1 atomic condensate when effects due to residual magnetic fields are
negligible. For atomic interactions of the ferromagnetic type, the SMA is shown
to be exact, with a mode function different from what is commonly used.
However, the quantitative deviation is small under current experimental
conditions (for Rb atoms). For anti-ferromagnetic interactions, we find
that the SMA becomes invalid in general. The differences among the mean field
mode functions for the three spin components are shown to depend strongly on
the system magnetization. Our results can be important for studies of beyond
mean field quantum correlations, such as fragmentation, spin squeezing, and
multi-partite entanglement.Comment: Revised, newly found analytic proof adde