Local moment formation in quantum point contacts

Spin-density-functional theory of quantum point contacts (QPCs) reveals the formation of a local moment with a net of one electron spin in the vicinity of the point contact - supporting the recent report of a Kondo effect in a QPC. The hybridization of the local moment to the leads decreases as the QPC becomes longer, while the onsite Coulomb-interaction energy remains almost constant.Comment: 10 pages, 3 figures, accepted for publication in Physical Review Letter

Extreme sensitivity of the spin-splitting and 0.7 anomaly to confining potential in one-dimensional nanoelectronic devices

Quantum point contacts (QPCs) have shown promise as nanoscale spin-selective components for spintronic applications and are of fundamental interest in the study of electron many-body effects such as the 0.7 x 2e^2/h anomaly. We report on the dependence of the 1D Lande g-factor g* and 0.7 anomaly on electron density and confinement in QPCs with two different top-gate architectures. We obtain g* values up to 2.8 for the lowest 1D subband, significantly exceeding previous in-plane g-factor values in AlGaAs/GaAs QPCs, and approaching that in InGaAs/InP QPCs. We show that g* is highly sensitive to confinement potential, particularly for the lowest 1D subband. This suggests careful management of the QPC's confinement potential may enable the high g* desirable for spintronic applications without resorting to narrow-gap materials such as InAs or InSb. The 0.7 anomaly and zero-bias peak are also highly sensitive to confining potential, explaining the conflicting density dependencies of the 0.7 anomaly in the literature.Comment: 23 pages, 7 figure

The Low-Temperature Fate of the 0.7 Structure in a Point Contact: A Kondo-like Correlated State in an Open System

Besides the usual conductance plateaus at multiples of 2e2/h, quantum point contacts typically show an extra plateau at ~ 0.7(2e2/h), believed to arise from electron-electron interactions that prohibit the two spin channels from being simultaneously occupied. We present evidence that the disappearance of the 0.7 structure at very low temperature signals the formation of a Kondo-like correlated spin state. Evidence includes a zero-bias conductance peak that splits in a parallel field, scaling of conductance to a modified Kondo form, and consistency between peak width and the Kondo temperature

Characterization of in vitro growth of bovine preantral ovarian follicles : a preliminary study

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Characterization of in vitro growth of bovine preantral ovarian follicles: A preliminary study.

Preantral follicles were mechanically extracted from bovine ovaries collected at slaughter. On average 90 early growing follicles were collected per ovary. The follicles were cultured for 7 days in Dulbecco's modified Eagle medium F-12 nutrient mixture + 10% fetal calf serum + 10% newborn calf serum. The individual follicular diameter and the follicular DNA content were recorded at the start and the end of culture. The follicular DNA content was estimated by a microfluorometric method using the fluorochrome, 4'-6 diamidino-2-phenylindol-2HCl (DAPI). After culture, 86% of the follicles looked morphologically normal. Of the surviving follicles, 73% showed an increase in diameter varying between 5 and 30 mum, and the follicular DNA content increased from 1 to 72% under the same culture conditions. These results indicate that bovine preantral follicles can survive in vitro and even grow in a single medium

Histologic and autoradiographic study of the in vitro effects of FGF-2 and FSH on isolated bovine preantral follicles: preliminary investigation.

Bovine early preantral follicles (40 to 65 microm diameter) were cultured for 24 or 48 h in the presence of 0, 10, 50 or 100 ng/ml of basic fibroblast growth factor (FGF-2), porcine FSH (pFSH) or both (ratio 1:1); the follicles were also exposed throughout the entire culture period to 2 microCi/ml ((3)H) thymidine. The effects of these factors on oocyte morphology and follicular DNA synthesis were then analyzed. Autoradiography was performed on histological serial sections of follicles after the culture period. Oocyte morphology of each follicle and the rate of follicular DNA synthesis were evaluated at the same time. Oocyte morphology was considerably altered in the presence of exogenous FSH. This effect seemed to be reduced by FGF-2, at least up to 24 h of culture. Analyzable incorporation of ((3)H) thymidine was only detected after 48 h of culture. The FGF-2 significantly increased the number of labeled nuclei per follicle whereas pFSH did not. This responsiveness of granulosa cells to FGF-2 disappeared in the presence of pFSH. No correlation was found between the number of labeled nuclei per follicle and the morphology of its oocyte. These results suggest that in cultured bovine early preantral follicles, pFSH induces oocyte degeneration and that this degeneration seems to be attenuated by FGF-2. In addition, FGF-2 lead to an increase in follicular DNA synthesis that disappeared in the presence of pFSH

Characterization of in vitro growth of bovine preantral ovarian follicles : a preliminary study

International audienc