Perturbation Study of the Conductance through an Interacting Region Connected to Multi-Mode Leads

We study the effects of electron correlation on transport through an interacting region connected to multi-mode leads based on the perturbation expansion with respect to the inter-electron interaction. At zero temperature the conductance defined in the Kubo formalism can be written in terms of a single-particle Green's function at the Fermi energy, and it can be mapped onto a transmission coefficient of the free quasiparticles described by an effective Hamiltonian. We apply this formulation to a two-dimensional Hubbard model of finite size connected to two noninteracting leads. We calculate the conductance in the electron-hole symmetric case using the order $U^2$ self-energy. The conductance shows several maximums in the $U$ dependence in some parameter regions of $t_y/t_x$, where $t_x$ ($t_y$) is the hopping matrix element in the $x$- ($y$-) directions. This is caused by the resonance occurring in some of the subbands, and is related with the $U$ dependence of the eigenvalues of the effective Hamiltonian.Comment: 17 pages, 12 figures, to be published in J.Phys.Soc.Jpn. 71(2002)No.

Quasi-particle description for the transport through a small interacting system

We study effects of electron correlation on the transport through a small interacting system connected to reservoirs using an effective Hamiltonian which describes the free quasi-particles of a Fermi liquid. The effective Hamiltonian is defined microscopically with the value of the self-energy at $\omega=0$. Specifically, we apply the method to a Hubbard chain of finite size $N$ ($=1, 2, 3, ...$), and calculate the self-energy within the second order in $U$ in the electron-hole symmetric case. When the couplings between the chain and the reservoirs on the left and right are small, the conductance for even $N$ decreases with increasing $N$ showing a tendency toward a Mott-Hubbard insulator. This is caused by the off-diagonal element of the self-energy, and this behavior is qualitatively different from that in the special case examined in the previous work. We also study the effects of the asymmetry in the two couplings. While the perfect transmission due to the Kondo resonance occurs for any odd $N$ in the symmetric coupling, the conductance for odd $N$ decreases with increasing $N$ in the case of the asymmetric coupling.Comment: 27 pages, RevTeX, 14 figures, to be published in Phys. Rev.

Sfrp5 Modulates Both Wnt and BMP Signaling and Regulates Gastrointestinal Organogensis in the Zebrafish, Danio rerio

Sfrp5 belongs to the family of secreted frizzled related proteins (Sfrp), secreted inhibitors of Wingless-MMTV Integration Site (Wnt) signaling, which play an important role in cancer and development. We selected sfrp5 because of its compelling expression profile in the developing endoderm in zebrafish, Danio rerio. In this study, overexpression of sfrp5 in embryos results in defects in both convergent extension (CE) by inhibition of non-canonical Wnt signaling and defects in dorsoventral patterning by inhibition of Tolloid-mediated proteolysis of the BMP inhibitor Chordin. From 25 hours post fertilization (hpf) to 3 days post fertilization (dpf), both overexpression and knockdown of Sfrp5 decrease the size of the endoderm, significantly reducing liver cell number. At 3 dpf, insulin-positive endodermal cells fail to coalesce into a single pancreatic islet. We show that Sfrp5 inhibits both canonical and non-canonical Wnt signaling during embryonic and endodermal development, resulting in endodermal abnormalities. © 2013 Stuckenholz et al

A new experimental rat model of osteosarcoma established by intrafemoral tumor cell inoculation, useful for biology and therapy investigations

Satisfactory experimental models for preclinical cancer studies must follow several criteria: (1) reproducibility of the method used to induce the tumor and (2) clinical, pathological and kinetic similarity with the corresponding human tumors. We developed a model of osteosarcoma locally induced by the intrafemoral injection of osteosarcoma (OSR) cells in Sprague-Dawley rats. This method yields nearly 80% of bone tumors at the injection site. These tumors double their volume fairly slowly (in approximately 20 days) and lung metastases occur in 96% of the animals. The OSR cell-induced tumor is characterized by a direct production of mineralized matrix by the tumor cells themselves, as revealed by histochemical analysis. The microarchitectural parameters which were quantified by a microscanner show an increased trabecular bone volume (+238%) when OSR cells were injected in the femur, as compared to controls injected with vehicle. Osteoblastic markers such as alkaline phosphatase, osteopontin, osteocalcin and bone sialoprotein were expressed by the tumor in vivo, whereas the initially injected OSR cells did not express some of these markers, suggesting that OSR cells reacquired an osteoblastic phenotype in a favorable environment. The clinical, radiological and histological data show that this model shares high similarities with the osteocondensing forms of osteosarcoma in humans

Shh-mediated degradation of Hhip allows cell autonomous and non-cell autonomous Shh signalling

The distribution of Sonic Hedgehog (Shh) is a highly regulated and critical process for development. Several negative feedback mechanisms are in place, including the Shh-induced upregulation of Hedgehog-interacting protein (Hhip). Hhip sequesters Shh, leading to a non-cell autonomous inhibition of the pathway. Hhip overexpression has a severe effect on neural tube development, raising the question why normal sites of Hhip expression have a seemingly unimpaired response to Shh. Here we show that although Hhip is able to leave its sites of synthesis to inhibit Shh non-cell autonomously, activation of Smoothened (Smo) drastically increases Hhip internalization and degradation cell autonomously. Although Hhip is unable to cell autonomously inhibit the consequences of Smo activation, it can inhibit the Shh response non-cell autonomously. Our data provide a mechanism by which the Shh ligand can activate the response and negate cell autonomous effects of Hhip, while Hhip can still induce non-cell autonomous inhibitio