133 research outputs found
Phase Diagram of Lattice-Spin System RbCoBr
We study the lattice-spin model of RbCoBr which is proposed by Shirahata
and Nakamura, by mean field approximation. This model is an Ising spin system
on a distorted triangular lattice. There are two kinds of frustrated variables,
that is, the lattice and spin. We obtain a phase diagram of which phase
boundary is drawn continuously in a whole region. Intermediate phases that
include a partial disordered state appear. The model has the first-order phase
transitions in addition to the second-order phase transitions. We find a
three-sublattice ferrimagnetic state in the phase diagram. The three-sublattice
ferrimagnetic state does not appear when the lattice is not distorted.Comment: 5 pages, 4 figures, jpsj2.cls, to be published in J. Phys. Soc. Jpn.
Vol.75 (2006) No.
Transient down-regulation of beta1 integrin subtypes on kidney carcinoma cells is induced by mechanical contact with endothelial cell membranes
Adhesion molecules of the integrin beta1 family are thought to be involved in the malignant progression renal cell carcinoma (RCC). Still, it is not clear how they contribute to this process. Since the hematogenous phase of tumour dissemination is the rate-limiting step in the metastatic process, we explored beta1 integrin alterations on several RCC cell lines (A498, Caki1, KTC26) before and after contacting vascular endothelium in a tumour-endothelium (HUVEC) co-culture assay. Notably, alpha2, alpha3 and alpha5 integrins became down-regulated immediately after the tumour cells attached to HUVEC, followed by re-expression shortly thereafter. Integrin down-regulation on RCC cells was caused by direct contact with endothelial cells, since the isolated endothelial membrane fragments but not the cell culture supernatant contributed to the observed effects. Integrin loss was accompanied by a reduced focal adhesion kinase (FAK) expression, FAK activity and diminished binding of tumour cells to matrix proteins. Furthermore, intracellular signalling proteins RCC cells were altered in the presence of HUVEC membrane fragments, in particular 14-3-3 epsilon, ERK2, PKCdelta, PKCepsilon and RACK1, which are involved in regulating tumour cell motility. We, therefore, speculate that contact of RCC cells with the vascular endothelium converts integrin-dependent adhesion to integrin-independent cell movement. The process of dynamic integrin regulation may be an important part in tumour cell migration strategy, switching the cells from being adhesive to becoming motile and invasive
Dynamical Structure Factors of the Spin-1/2 XXZ Chain with Inverse-Square Exchange and Ising Anisotropy
The dynamical properties of the S=1/2 antiferromagnetic XXZ chain are studied
by the exact diagonalization and the recursion method of finite systems up to
24 sites. Two types of the exchange interaction are considered: one is the
nearest-neighbor type, and the other is the inverse-square one. As the Ising
anisotropy becomes larger, there appears a noticeable difference in the
transverse component S^{xx}(q,\omega) between the two types of the exchange.
For the nearest-neighbor type, the peak frequency of S^{xx}(q,\omega) for each
q approaches the center of the continuum spectrum. On the contrary, the peak
frequency for the inverse-square type moves to the upper edge of the continuum,
and separates from the continuum for the anisotropy larger than the threshold
value. Whether the interaction between domain walls (solitons) is absent or
repulsive in the Ising limit leads to this difference in the behavior of
S^{xx}(q,\omega). In the longitudinal component S^{zz}(q,\omega), on the other
hand, the feature of the dynamics is scarcely different between the two types.
The energy gap and the static properties are also discussed.Comment: 10 pages. A hard copy of 16 figures is available on request.
Submitted to J. Phys. Soc. Jp
Fluctuation-induced phase in CsCuCl3 in transverse magnetic field: Theory
CsCuCl3 is a quantum triangular antiferromagnet, ferromagnetically stacked,
with an incommensurate (IC) structure due to a Dzyaloshinskii-Moriya
interaction. Because of the classical degeneracy caused by the frustration,
fluctuations in CsCuCl3 have extraordinarily large effects, such as the phase
transition in longitudinal magnetic field (normal to the planes, parallel to
the IC wavenumber q) and the plateau in q in transverse field (perpendicular to
q). We argue that fluctuations are responsible also for the new IC phase
discovered in transverse field near the Neel temperature T_N, by T. Werner et
al. [Solid State Commun. 102, p.609 (1997)]. We develop and analyse the
corresponding minimal Landau theory; the effects of fluctuations on the
frustration are included phenomenologically, by means of a biquadratic term.
The Landau theory gives two IC phases, one familiar from previous studies;
properties of the new IC phase, which occupies a pocket of the
temperature-field phase diagram near T_N, agree qualitatively with those of the
new phase found experimentally.Comment: 12 pages, revtex, 4 postscript figures, submitted to J. Phys:
Condens. Matte
Electricity and disinfectant production from wastewater: Microbial Fuel Cell as a self-powered electrolyser
This study presents a simple and sustainable Microbial Fuel Cell as a standalone, self-powered reactor for in situ wastewater electrolysis, recovering nitrogen from wastewater. A process is proposed whereby the MFC electrical performance drives the electrolysis of wastewater towards the self-generation of catholyte within the same reactor. The MFCs were designed to harvest the generated catholyte in the internal chamber, which showed that liquid production rates are largely proportional to electrical current generation. The catholyte demonstrated bactericidal properties, compared to the control (open-circuit) diffusate, and reduced observable biofilm formation on the cathode electrode. Killing effects were confirmed using bacterial kill curves constructed by exposing a bioluminescent Escherichia coli target, as a surrogate coliform, to catholyte where a rapid kill rate was observed. Therefore, MFCs could serve as a water recovery system, a disinfectant/cleaner generator that limits undesired biofilm formation and as a washing agent in waterless urinals to improve sanitation. This simple and ready to implement MFC system can convert organic waste directly into electricity and self-driven nitrogen along with water recovery. This could lead to the development of energy positive bioprocesses for sustainable wastewater treatment
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