159 research outputs found
Whirling spin order in the quasicrystal approximant AuAlTb
Neutron powder diffraction experiment has been performed on the quasicrystal
approximant AuAlTb, a body-center-cubic crystal of
icosahedral spin clusters. The long-range antiferromagnetic order was confirmed
at the transition temperature K. The magnetic structure
consists of noncoplanar whirling spins on the icosahedral clusters, arranging
antiferroic-manner. A simple icosahedral spin-cluster model with uniaxial
anisotropy accounts well the whirling spin order as well as the in-field
metamagnetic transition, indicating that the icosahedral symmetry is essential.Comment: 6 pages, 4 figure
White Patchy Materials Formed in a Scoriacious Road-cut Profile on Miyake Island(Plant Production Science Soil Science)
Sulfurous gas, sulfur or sulfates are frequently contained in volcanic ejecta. We found white patchy materials (WPM) in a road-cut profile on Miyake Island, Japan. The layer containing WPM consists of scoria deposit in 1874. The major materials we identified in the WPM were CaSO_4・2H_2O and amorphous silica according to X-ray diffraction and energy dispersive X-ray analyses. A possible process for crystallization of CaSO_4・2H_2O in the WPM is the dissolution of CaSO_4・2H_2O contained in the overlying 2000 ash and its re-precipitation on the surface of the scoriacious road-cut profile. Emission of sulfur dioxide gas, converted to sulfuric acid in water, has been so abundant since the 2000 eruption that we further examined reaction products between crushed scoria and dilute H_2SO_4 (0.1-2.5mol L^). CaSO_4・2H_2O was also identified in the reaction products as well as alunogen, iron sulfate, etc. Because alunogen is highly soluble in water, CaSO_4・2H_2O was the major crystalline product after rinsing with water
Stepwise Assembly of Fibrinogen Is Assisted by the Endoplasmic Reticulum Lectin-Chaperone System in HepG2 Cells
The endoplasmic reticulum (ER) plays essential roles in protein folding and assembly of secretory proteins. ER-resident molecular chaperones and related enzymes assist in protein maturation by co-operated interactions and modifications. However, the folding/assembly of multimeric proteins is not well understood. Here, we show that the maturation of fibrinogen, a hexameric secretory protein (two trimers from a, b and c subunits), occurs in a stepwise manner. The ac complex, a precursor for the trimer, is retained in the ER by lectin-like chaperones, and the b subunit is incorporated into the ac complex immediately after translation. ERp57, a protein disulfide isomerase homologue, is involved in the hexamer formation from two trimers. Our results indicate that the fibrinogen hexamer is formed sequentially, rather than simultaneously, using kinetic pause by lectin chaperones. This study provides a novel insight into the assembly of most abundant multi-subunit secretory proteins
Atomic structure and magnetism of the Au-Ga-Ce 1/1 approximant crystal
We report a new Au-Ga-Ce 1/1 approximant crystal (AC) which possesses a
significantly wide single-phase region of 53 - 70 at% Au and 13.6 - 15.1 at%
Ce. Single crystal X-ray structural analyses reveal the existence of two types
of structural degrees of freedom, i.e., the Au/Ga mixing sites and the
fractional Ce occupancy site: the former enables a large variation in the
electron concentration and the latter allows a variation in the occupancy of a
magnetic impurity atom at the center of the Tsai-type cluster. Following these
findings, the influences of two types of structural modifications on the
magnetism are thoroughly investigated by means of magnetic susceptibility and
specific heat measurements on the Au-Ga-Ce 1/1 AC. The spin-glass (SG) state is
found to be the ground state over the entire single-phase region, showing a
robust nature of the SG state against both structural modifications. In
addition, a gigantic specific heat (C/T) is commonly observed at low
temperatures for all the compositions, which is consistently explained as a
consequence of the spin-freezing phenomenon, not of a heavy Fermion behavior as
reported elsewhere. Moreover, the origin of the SG state in the 1/1 Au-Ga-Ce AC
is attributed to the existence of non-magnetic atom disorder in the Au/Ga
mixing sites. Furthermore, a Kondo behavior is observed in the electrical
resistivity at low temperatures, which is enhanced by increasing the Ce
concentration, verifying that a Ce atom introduced at the cluster center
behaves as a Kondo impurity for the first time.Comment: 8 pages, 4 figure
Unveiling exotic magnetic phase diagram of a non-Heisenberg quasicrystal approximant
A magnetic phase diagram of the non-Heisenberg Tsai-type 1/1 Au-Ga-Tb
approximant crystal (AC) has been established across a wide electron-per-atom
(e/a) range via magnetization and powder neutron diffraction measurements. The
diagram revealed exotic ferromagnetic (FM) and antiferromagnetic (AFM) orders
that originate from the unique local spin icosahedron common to icosahedral
quasicrystals (iQCs) and ACs; The noncoplanar whirling AFM order is stabilized
as the ground state at the e/a of 1.72 or less whereas a noncoplanar whirling
FM order was found at the larger e/a of 1.80, with magnetic moments tangential
to the Tb icosahedron in both cases. Moreover, the FM/AFM phase selection rule
was unveiled in terms of the nearest neighbour (J1) and next nearest neighbour
(J2) interactions by numerical calculations on a non-Heisenberg single
icosahedron. The present findings will pave the way for understanding the
intriguing magnetic orders of not only non-Heisenberg FM/AFM ACs but also
non-Heisenberg FM/AFM iQCs, the latter of which are yet to be discovered
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