3,227 research outputs found
Numerical renormalization group approach to a quartet quantum-dot array connected to reservoirs:gate-voltage dependence of the conductance
The ground-state properties of quartet quantum-dot arrays are studied using
the numerical renormalization group (NRG) method with a four-site Hubbard model
connected to two non-interacting leads. Specifically, we calculate the
conductance and local charge in the dots from the many-body phase shifts, which
can be deduced from the fixed-point eigenvalues of NRG. As a function of the
on-site energy which corresponds to the gate voltage, the
conductance shows alternatively wide peak and valley. Simultaneously, the total
number of electrons in the four dots shows a quantized stair case
behavior due to a large Coulomb interaction . The conductance plateaus of
the Unitary limit emerging for odd are caused by the Kondo effect.
The valleys of the conductance emerge for even , and their width
becomes substantially large at half-filling. It can be regarded as a kind of
the Mott-Hubbard insulating behavior manifesting in a small system. These
structures of the plateaus and valleys become weak for large values of the
hybridization strength between the chain and leads. We also discuss
the parallel conductance for the array connected to four leads.Comment: 8 pages, 9 figure
Mixed-state aspects of an out-of-equilibrium Kondo problem in a quantum dot
We reexamine basic aspects of a nonequilibrium steady state in the Kondo
problem for a quantum dot under a bias voltage using a reduced density matrix,
which is obtained in the Fock space by integrating out one of the two
conduction channels. The integration has been carried out by discretizing the
conduction channels preserving the two-fold degeneracy due to the left-going
and right-going scattering states. The remaining subspace is described by a
single-channel Anderson model, and the statistical weight is determined by the
reduced density matrix. In the noninteracting case, it can be constructed as
the mixed states that show a close similarity to the high-temperature
distribution in equilibrium. Specifically, if the system has an inversion
symmetry, the one-particle states in an energy window between the two chemical
potentials \mu_R and \mu_L are occupied, or unoccupied, completely at random
with an equal weight. The Coulomb interaction preserves these aspects, and the
correlation functions can be expressed in a Lehmann-representation form using
the mixed-state statistical weight.Comment: 8 pages, 3 figure
Population-only decay map for n-qubit n-partite inseparability detection
We introduce a new positive linear map for a single qubit. This map is a
decay only in populations of a single-qubit density operator. It is shown that
an n-fold product of this map may be used for a detection of n-partite
inseparability of an n-qubit density operator (i.e., detection of impossibility
of representing a density operator in the form of a convex combination of
products of density operators of individual qubits). This product map is also
investigated in relation to a variant of the entanglement detection method
mentioned by Laskowski and Zukowski.Comment: 5 pages, 1 figure, RevTex4, v2 minor grammatical changes, typos
correcte
Correlated electron transport through double quantum dots coupled to normal and superconducting leads
We study Andreev transport through double quantum dots connected in series
normal and superconducting (SC) leads, using the numerical renormalization
group. The ground state of this system shows a crossover between a local
Cooper-pairing singlet state and a Kondo singlet state, which is caused by the
competition between the Coulomb interaction and the SC proximity. We show that
the ground-state properties reflect this crossover especially for small values
of the inter-dot coupling , while in the opposite case, for large ,
another singlet with an inter-dot character becomes dominant. We find that the
conductance for the local SC singlet state has a peak with the unitary-limit
value . In contrast, the Andreev reflection is suppressed in the Kondo
regime by the Coulomb interaction. Furthermore, the conductance has two
successive peaks in the transient region of the crossover. It is further
elucidated that the gate voltage gives a different variation into the
crossover. Specifically, as the energy level of the dot that is coupled to the
normal lead varies, the Kondo screening cloud is deformed to a long-range
singlet bond.Comment: 11 pages, 10 figure
Effects of phlebotomy on the growth of ferric nitrilotriacetate-induced renal cell carcinoma.
The ferric nitrilotriacetate-induced carcinogenesis model is unique in that reactive oxygen species-free radicals are involved in the carcinogenic process. But the effects of iron-withdrawal in the progression of renal cell carcinoma are not well understood. We performed repeated phlebotomies on animals that had been administered ferric nitrilotriacetate in the initiation stage of renal cell carcinoma (phlebotomy group), and compared the development of renal tumors with those not receiving repeated phlebotomies (non-phlebotomy group). Ferric nitrilotriacetate-treated male Wistar rats were randomly divided into 2 groups: a phlebotomy group (21 rats) and a non-phlebotomy group (17 rats). Ten age-adjusted normal rats were also observed as a normal group. Hematocrit was maintained under 25% in the phlebotomy group. Hematocrit levels in the normal group and in the non-phlebotomy group were not significantly different. As a result, the incidence of renal cell carcinoma was not significantly different between phlebotomy and non-phlebotomy animals. However, the total weight of the renal cell carcinoma was significantly heavier in the animals from non-phlebotomy group than in those from the phlebotomy group (23.64 g +/- 18.54 vs. 54.40 g +/- 42.40, P < 0.05). The present study demonstrated that phlebotomy after the administration of ferric nitrilotriacetate did not reduce the incidence of renal cell carcinoma. In addition, we showed that iron withdrawal at the promotion stage of carcinogenesis will retard tumor growth.</p
Phase transition in compressible Ising systems at fixed volume
Using a Ginzburg-Landau model, we study the phase transition behavior of
compressible Ising systems at constant volume by varying the temperature
and the applied magnetic field . We show that two phases can coexist
macroscopically in equilibrium within a closed region in the - plane. It
occurence is favored near tricriticality. We find a field-induced critical
point, where the correlation length diverges, the difference of the coexisting
two phases and the surface tension vanish, but the isothermal magnetic
susceptibility does not diverge in the mean field theory. We also investigate
phase ordering numerically.Comment: 13 figure
The United States and Japan in the Postwar World
A major phenomenon in the post-World War II world is the rise of Japan as a leading international economic and industrial power. This advance began with American aid in rebuilding the nation after the war, but it has now seen Japan rival and even outstrip the United States on several fronts. The relations between the two powers and the impact that they have on economic and political factors during the postwar years are the focus of this important book. The editors, Akira Iriye and Warren I. Cohen, themselves noted authorities on Asian affairs, have gathered here contributions from a distinguished group of American and Japanese scholars. The resulting collection represents a unique blend of viewpoints from each side of the American-Japanese relationship.
Akira Iriye is Charles Warren Professor of American History at Harvard University.
Warren I. Cohen is Distinguished University Professor at the University of Maryland, Baltimore County.
A rich volume that will be of interest not only to specialists, but also especially to government officials and the business and financial community. —History
A useful guide to an understanding of the strains and stresses between the United States and Japan as the two countries move toward the end of the twentieth century. —Journal of American Historyhttps://uknowledge.uky.edu/upk_political_science_international_relations/1022/thumbnail.jp
Re/Os constraint on the time-variability of the fine-structure constant
We argue that the accuracy by which the isochron parameters of the decay
are determined by dating iron meteorites may
not directly constrain the possible time-dependence of the decay rate and hence
of the fine-structure constant . From this point of view, some of the
attempts to analyze the Oklo constraint and the results of the QSO absorption
lines are re-examined.Comment: 7 pages, 3 figures; v2, revised top sentence on p.
Ecological damage, human rights and Oil: local advocacy NGOs dialogic action and alternative accounting practices
This study explores why local NGOs in the Niger Delta integrate dialogic action and accounts into their campaigns to protect the human, economic and environmental rights of indigenous communities. The NGOs considered their alternative-accounts effective in problematizing the need for greater accountability, giving greater visibilities to unsustainable practices, building the capacity of the indigenous people, creating networks of engagement, giving voice to indigenous communities and addressing some of the power imbalances in this region. NGOs and local community representatives asserted that the production and communication of accounts of their suffering were making a difference and creating hope for future change
Explosions inside Ejecta and Most Luminous Supernovae
The extremely luminous supernova SN2006gy is explained in the same way as
other SNIIn events: light is produced by a radiative shock propagating in a
dense circumstellar envelope formed by a previous weak explosion. The problems
in the theory and observations of multiple-explosion SNe IIn are briefly
reviewed.Comment: 9 pages, 6 figures, LateX aipproc.cls. A bit more details and color
added to Fig.3. The 10th International Symposium on Origin of Matter and
Evolution of Galaxies (OMEG07), Sapporo, Japan, December 200
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