1,210 research outputs found
Conservation in two-particle self-consistent extensions of dynamical-mean-field-theory
Extensions of dynamical-mean-field-theory (DMFT) make use of quantum impurity
models as non-perturbative and exactly solvable reference systems which are
essential to treat the strong electronic correlations. Through the introduction
of retarded interactions on the impurity, these approximations can be made
two-particle self-consistent. This is of interest for the Hubbard model,
because it allows to suppress the antiferromagnetic phase transition in
two-dimensions in accordance with the Mermin-Wagner theorem, and to include the
effects of bosonic fluctuations. For a physically sound description of the
latter, the approximation should be conserving. In this paper we show that the
mutual requirements of two-particle self-consistency and conservation lead to
fundamental problems. For an approximation that is two-particle self-consistent
in the charge- and longitudinal spin channel, the double occupancy of the
lattice and the impurity are no longer consistent when computed from
single-particle properties. For the case of self-consistency in the charge- and
longitudinal as well as transversal spin channels, these requirements are even
mutually exclusive so that no conserving approximation can exist. We illustrate
these findings for a two-particle self-consistent and conserving DMFT
approximation.Comment: 17 pages, 9 figure
Electronic Order with Staggered Kondo and Crystalline Electric Field Singlets
Novel electronic order is found theoretically for a system where even number
of localized electrons per site are coupled with conduction electrons. For
precise quantitative study, a variant of the Kondo lattice model is taken with
crystalline electric field (CEF) singlet and triplet states for each site.
Using the dynamical mean-field theory combined with the continuous-time quantum
Monte Carlo method, a staggered order with alternating Kondo and CEF singlets
is identified for a case with one conduction electron per site being
distributed in two conduction bands each of which is quarter-filled. This
electronic order accompanies a charge density wave (CDW) of conduction
electrons that accumulate more on Kondo-singlet sites than on CEF-singlet
sites. Possible relevance of the present order to the scalar order in
PrFeP is discussed.Comment: 11 pages, 17 figure
Effect of Disorder on Fermi surface in Heavy Electron Systems
The Kondo lattice model with substitutional disorder is studied with
attention to the size of the Fermi surface and the associated Dingle
temperature. The model serves for understanding heavy-fermion Ce compounds
alloyed with La according to substitution Ce{x}La{1-x}. The Fermi surface is
identified from the steepest change of the momentum distribution of conduction
electrons, and is derived at low enough temperature by the dynamical mean-field
theory (DMFT) combined with the coherent potential approximation (CPA). The
Fermi surface without magnetic field increases in size with decreasing x from
x=1 (Ce end), and disappears at such x that gives the same number of localized
spins as that of conduction electrons. From the opposite limit of x=0 (La end),
the Fermi surface broadens quickly as x increases, but stays at the same
position as that of the La end. With increasing magnetic field, a metamagnetic
transition occurs, and the Fermi surface above the critical field changes
continuously across the whole range of x. The Dingle temperature takes a
maximum around x=0.5. Implication of the results to experimental observation is
discussed.Comment: 5 pages, 5 figure
Excitonic Bound State in the Extended Anderson Model with c-f Coulomb Interaction
The Anderson model with the Coulomb interaction between the local and
conduction electrons is studied in the semiconducting phase. Based on a
perturbation theory from the atomic limit, leading contributions for the c-f
Coulomb interaction are incorporated as a vertex correction to hybridization.
An analytical solution shows that the effective attraction in the intermediate
states leads to a bound state localized at the local electron site.
Self-consistent equations are constructed as an extension of the non-crossing
approximation (NCA) to include the vertex part yielding the bound state. A
numerical calculation demonstrates the excitonic bound state inside the
semiconducting gap for single-particle excitations, and a discontinuity at the
gap edge for magnetic excitations.Comment: 15 pages, 20 figures, submitted to J. Phys. Soc. Jp
Explosive nucleosynthesis in core-collapse supernovae
The specific mechanism and astrophysical site for the production of half of
the elements heavier than iron via rapid neutron capture (r-process) remains to
be found. In order to reproduce the abundances of the solar system and of the
old halo stars, at least two components are required: the heavy r-process
nuclei (A>130) and the weak r-process which correspond to the lighter heavy
nuclei (A<130). In this work, we present nucleosynthesis studies based on
trajectories of hydrodynamical simulations for core-collapse supernovae and
their subsequent neutrino-driven winds. We show that the weak r-process
elements can be produced in neutrino-driven winds and we relate their
abundances to the neutrino emission from the nascent neutron star. Based on the
latest hydrodynamical simulations, heavy r-process elements cannot be
synthesized in the neutrino-driven winds. However, by artificially increasing
the wind entropy, elements up to A=195 can be made. In this way one can mimic
the general behavior of an ejecta where the r-process occurs. We use this to
study the impact of the nuclear physics input (nuclear masses, neutron capture
cross sections, and beta-delayed neutron emission) and of the long-time
dynamical evolution on the final abundances.Comment: 10 pages, 8 figures, invited talk, INPC 2010 Vancouver, Journal of
Physics: Conference Serie
Minimum alveolar concentrations and hemodynamic effects of two different preparations of sevoflurane in pigs
BACKGROUND: Original sevoflurane (Sevo A) is made with water, while a generic sevoflurane (Sevocris) is produced with propylene glycol as a stabilizing additive. We investigated whether the original and generic sevoflurane preparations differed in terms of their minimum alveolar concentration (MAC) values and hemodynamic effects. METHODS: Sixteen pigs weighing 31.6±1.8 kg were randomly assigned to the Sevo A or Sevocris groups. After anesthesia induction via mask with the appropriate sevoflurane preparation (6% in 100% oxygen), the MAC was determined for each animal. Hemodynamic and oxygenation parameters were measured at 0.5 MAC, 1 MAC and 1.5 MAC. Histopathological analyses of lung parenchyma were performed. RESULTS: The MAC in the Sevo A group was 4.4±0.5%, and the MAC in the Sevocris group was 4.1±0.7%. Hemodynamic and metabolic parameters presented significant differences in a dose-dependent pattern as expected, but they did not differ between groups. Cardiac indices and arterial pressures decreased in both groups when the sevoflurane concentration increased from 0.5 to 1 and 1.5 MAC. The oxygen delivery index (DO2I) decreased significantly at 1.5 MAC. CONCLUSION: Propylene glycol as an additive for sevoflurane seems to be as safe as a water additive, at least in terms of hemodynamic and pulmonary effects
Role of p-f Hybridization in the Metal-Non-Metal Transition of PrRu4P12
Electronic state evolution in the metal-non-metal transition of PrRu4P12 has
been studied by X-ray and polarized neutron diffraction experiments. It has
been revealed that, in the low-temperature non-metallic phase, two inequivalent
crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2)
ground states are located at Pr1 and Pr2 sites forming the bcc unit cell
surrounded by the smaller and larger cubic Ru-ion sublattices, respectively.
This modulated electronic state can be explained by the p-f hybridization
mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f
hybridization effect plays an important role for the electronic energy gain in
the metal-non-metal transition originated from the Fermi surface nesting.Comment: 5 pages, 5 figures. Accepted by J. Phys. Soc. Jp
Vortex jamming in superconductors and granular rheology
We demonstrate that a highly frustrated anisotropic Josephson junction
array(JJA) on a square lattice exhibits a zero-temperature jamming transition,
which shares much in common with those in granular systems. Anisotropy of the
Josephson couplings along the horizontal and vertical directions plays roles
similar to normal load or density in granular systems. We studied numerically
static and dynamic response of the system against shear, i. e. injection of
external electric current at zero temperature. Current-voltage curves at
various strength of the anisotropy exhibit universal scaling features around
the jamming point much as do the flow curves in granular rheology, shear-stress
vs shear-rate. It turns out that at zero temperature the jamming transition
occurs right at the isotropic coupling and anisotropic JJA behaves as an exotic
fragile vortex matter : it behaves as superconductor (vortex glass) into one
direction while normal conductor (vortex liquid) into the other direction even
at zero temperature. Furthermore we find a variant of the theoretical model for
the anisotropic JJA quantitatively reproduces universal master flow-curves of
the granular systems. Our results suggest an unexpected common paradigm
stretching over seemingly unrelated fields - the rheology of soft materials and
superconductivity.Comment: 10 pages, 5 figures. To appear in New Journal of Physic
The endogenous soluble VEGF receptor-2 isoform suppresses lymph node metastasis in a mouse immunocompetent mammary cancer model
BACKGROUND: Cancer metastasis contributes significantly to cancer mortality and is facilitated by lymphangiogenesis and angiogenesis. A new splicing variant, endogenous soluble vascular endothelial growth factor receptor-2 (esVEGFR-2) that we recently identified is an endogenous selective inhibitor of lymphangiogenesis. To evaluate the antimetastatic potential of esVEGFR-2, gene therapy with vector expressing esVEGFR-2 (pesVEGFR-2) or endostatin (pEndo) as a positive control was conducted on murine metastatic mammary cancer.
METHODS: Syngeneic inoculated metastatic mammary cancers received direct intratumoral injection of pesVEGFR-2, pEndo or pVec as control, once a week for six weeks. In vivo gene electrotransfer was performed on the tumors after each injection.
RESULTS: Deaths from metastasis were much lower in the pesVEGFR-2 and pEndo groups than in those of the pVec. Tumor volume was significantly lower in the pesVEGFR-2 and the pEndo groups throughout the study. Multiplicity of lymph node and lung metastatic nodules was significantly suppressed in the pesVEGFR-2 and pEndo groups. Moreover, the total number of overall metastasis including the other organs was also decreased in these groups. However, pesVEGFR-2 was not able to decrease the number of lungs, ovaries, kidneys and adrenals with metastasis as counted by unilateral or bilateral metastasis. The number of CD34+/Lyve-1⁻ blood microvessels was significantly decreased in the pEndo group, while the number of CD34⁻/Lyve-1+ lymphatic vessels was significantly decreased in the pesVEGFR-2 and pEndo groups. In addition, a significant reduction in the number of dilated lymphatic vessels containing intraluminal cancer cells was observed in the pesVEGFR-2 and pEndo groups. Levels of apoptosis were significantly increased in the pEndo group, whereas the rates of cell proliferation were significantly decreased in the pesVEGFR-2 and pEndo groups.
CONCLUSIONS: Our data demonstrate that esVEGFR-2 can inhibit mainly lymph node metastasis. The antimetastatic activity of esVEGFR-2 may be of high clinical significance in the treatment of metastatic breast cancer because lymph node involvement is a most important prognostic factor in cancer patients
Continuous-Time Quantum Monte Carlo Approach to Singlet-Triplet Kondo Systems
Dynamical properties are studied numerically for a variant of the Kondo model
with singlet and triplet crystalline electric field (CEF) levels where Kondo
and CEF singlets compete for the ground state. Using the continuous-time
quantum Monte Carlo method, we derive the -matrix of conduction electrons
and dynamical susceptibilities of local electrons without encountering the
negative sign problem. When the CEF splitting is comparable to the Kondo
temperature, the dynamical response has only a quasi-elastic peak.
Nevertheless, the local single-particle spectrum shows an energy gap in strong
contrast with the ordinary Kondo model.Comment: 9 pages, 10 figure
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