2,235 research outputs found
Dissipative quantum disordered models
This article reviews recent studies of mean-field and one dimensional quantum
disordered spin systems coupled to different types of dissipative environments.
The main issues discussed are: (i) The real-time dynamics in the glassy phase
and how they compare to the behaviour of the same models in their classical
limit. (ii) The phase transition separating the ordered -- glassy -- phase from
the disordered phase that, for some long-range interactions, is of second order
at high temperatures and of first order close to the quantum critical point
(similarly to what has been observed in random dipolar magnets). (iii) The
static properties of the Griffiths phase in random Ising chains. (iv) The
dependence of all these properties on the environment. The analytic and numeric
techniques used to derive these results are briefly mentioned.Comment: Contribution to the 12th International Conference on Recent Progress
in Many-Body Theories, Santa Fe, New Mexico, USA, August 2004; 10 pages no
fig
Sensitizing Ability and Toxicity of Iodoacetamide in Radiotherapy of a C3H Mouse Mammary Carcinoma
The radiosensitizing effect of iodoacetamide was studied in a C3H mouse mammary carcinoma together with its toxicity to the host. TCD50 or radiation dose to yield 50% tumour control frequency was determined in tumours treated or untreated with the agent. Results indicated that 15 mg/kg of iodoacetamide sensitized hypoxic tumour cells, as did atmospheric oxygen, and the sensitization was not detectable below this dose. Experiments with fractionated treatments suggested that the reoxygenation occurring during the treatment intervals of 24 hours might be more important in the sterilization of tumour cells than the agent
Low Temperature Symmetry of Pyrochlore Oxide Cd2Re2O7
We report the X-ray study for the pyrochlore oxide Cd2Re2O7. Two
symmetry-lowering structural transitions were observed at Ts1=200K and
Ts2=120K. The former is of the second order from the ideal cubic pyrochlore
structure with space group Fd-3m to a tetragonally distorted structure with
I-4m2, while the latter is of the first order likely to another tetragonal
space group I4122. We discuss the feature of the lattice deformation.Comment: 4 pages, 4 figure
Gravitational GUT Breaking and the GUT-Planck Hierarchy
It is shown that non-renormalizable gravitational interactions in the Higgs
sector of supersymmetric grand unified theories (GUT's) can produce the
breaking of the unifying gauge group at the GUT scale ~GeV. Such a breaking offers an attractive alternative to the
traditional method where the superheavy GUT scale mass parameters are added ad
hoc into the theory. The mechanism also offers a natural explanation for the
closeness of the GUT breaking scale to the Planck scale. A study of the minimal
SU(5) model endowed with this mechanism is presented and shown to be
phenomenologically viable. A second model is examined where the Higgs doublets
are kept naturally light as Goldstone modes. This latter model also achieves
breaking of at but cannot easily satisfy the current
experimental proton decay bound.Comment: 11 pages, REVTeX, 1 figure included as an uuencoded Z-compressed
PostScript file. Our Web page at
http://physics.tamu.edu/~urano/research/gutplanck.html contains ready to
print PostScript version (with figures) as well as color version of plot
Itinerant-Electron Magnet of the Pyrochlore Lattice: Indium-Doped YMn2Zn20
We report on a ternary intermetallic compound, "YMn2Zn20", comprising a
pyrochlore lattice made of Mn atoms. A series of In-doped single crystals
undergo no magnetic long-range order down to 0.4 K, in spite of the fact that
the Mn atom carries a local magnetic moment at high temperatures, showing
Curie-Weiss magnetism. However, In-rich crystals exhibit spin-glass transitions
at approximately 10 K due to a disorder arising from the substitution, while,
with decreasing In content, the spin-glass transition temperature is reduced to
1 K. Then, heat capacity divided by temperature approaches a large value of 280
mJ K-2 mol-1, suggesting a significantly large mass enhancement for conduction
electrons. This heavy-fermion-like behavior is not induced by the Kondo effect
as in ordinary f-electron compounds, but by an alternative mechanism related to
the geometrical frustration on the pyrochlore lattice, as in (Y,Sc)Mn2 and
LiV2O4, which may allow spin entropy to survive down to low temperatures and to
couple with conduction electrons.Comment: 5 pages, 4 figures, J. Phys. Soc. Jpn., in pres
Thermal and Electrical Properties of gamma-NaxCoO2 (0.70 < x < 0.78)
We have performed specific heat and electric resistivity measurements of
NaCoO (-0.78). Two anomalies have been observed in the
specific heat data for , corresponding to magnetic transitions at
K and K reported previously. In the electrical
resistivity, a steep decrease at and a bending-like variation at
(=120K for ) have been observed. Moreover, we have investigated
the -dependence of these parameters in detail. The physical properties of
this system are very sensitive to , and the inconsistent results of previous
reports can be explained by a small difference in . Furthermore, for a
higher value, a phase separation into Na-rich and Na-poor domains occurs as
we previously proposed, while for a lower value, from characteristic
behaviors of the specific heat and the electrical resistivity at the
low-temperature region, the system is expected to be in the vicinity of the
magnetic instability which virtually exists below .Comment: 4 pages (3 figures included) and an extra figure (gif), to be
published in J. Phys. Soc. Jpn. 73 (9) with possible minor revision
Analysis of ELM stability with extended MHD models in JET, JT-60U and future JT-60SA tokamak plasmas
The stability with respect to a peeling–ballooning mode (PBM) was investigated numerically with
extended MHD simulation codes in JET, JT-60U and future JT-60SA plasmas. The MINERVA-DI
code was used to analyze the linear stability, including the effects of rotation and ion diamagnetic drift
( *w i), in JET-ILW and JT-60SA plasmas, and the JOREK code was used to simulate nonlinear
dynamics with rotation, viscosity and resistivity in JT-60U plasmas. It was validated quantitatively
that the ELM trigger condition in JET-ILW plasmas can be reasonably explained by taking into
account both the rotation and *w i effects in the numerical analysis. When deuterium poloidal rotation
is evaluated based on neoclassical theory, an increase in the effective charge of plasma destabilizes
the PBM because of an acceleration of rotation and a decrease in *w i. The difference in the amount of
ELM energy loss in JT-60U plasmas rotating in opposite directions was reproduced qualitatively with
JOREK. By comparing the ELM affected areas with linear eigenfunctions, it was confirmed that the
difference in the linear stability property, due not to the rotation direction but to the plasma density
profile, is thought to be responsible for changing the ELM energy loss just after the ELM crash. A
predictive study to determine the pedestal profiles in JT-60SA was performed by updating the EPED1 model to include the rotation and *w i effects in the PBM stability analysis. It was shown that the plasma rotation predicted with the neoclassical toroidal viscosity degrades the pedestal performance by about 10% by destabilizing the PBM, but the pressure pedestal height will be high enough to achieve the target parameters required for the ITER-like shape inductive scenario in JT-60SA.JSPS KAKENHI 15K06656EURATOM 63305
Unification Picture in Minimal Supersymmetric SU(5) Model with String Remnants
The significant heavy threshold effect is found in the supersymmetric SU(5)
model with two adjoint scalars, one of which is interpreted as a massive string
mode decoupled from the lower-energy particle spectra. This threshold related
with the generic mass splitting of the basic adjoint moduli is shown to alter
properly the running of gauge couplings, thus giving a natural solution to the
string-scale grand unification as prescribed at low energies by LEP precision
measurements and minimal particle content. The further symmetry condition of
the (top-bottom) Yukawa and gauge coupling superunification at a string scale
results in the perfectly working predictions for the top and bottom quark
masses in the absence of any large supersymmetric threshold corrections.Comment: published versio
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