Real-time detection of electron tunnelling in a quantum dot

Nanostructures in which strong (Coulomb) interactions exist between electrons are predicted to exhibit temporal electronic correlations. Although there is ample experimental evidence that such correlations exist, electron dynamics in engineered nanostructures have been observed directly only on long timescales. The faster dynamics associated with electrical currents or charge fluctuations are usually inferred from direct (or quasi-direct) current measurements. Recently, interest in electron dynamics has risen, in part owing to the realization that additional information about electronic interactions can be found in the shot noise or higher statistical moments of a direct current. Furthermore, interest in quantum computation has stimulated investigation of quantum bit (qubit) readout techniques, which for many condensed-matter systems ultimately reduces to single-shot measurements of individual electronic charges. Here we report real-time observation of individual electron tunnelling events in a quantum dot using an integrated radio-frequency single-electron transistor. We use electron counting to measure directly the quantum dot's tunnelling rate and the occupational probabilities of its charge state. Our results provide evidence in favour of long (10 micros or more) inelastic scattering times in nearly isolated dots.     

A preliminary study of crassulacean acid metabolism (CAM) in the endangered aquatic quillwortIsoetes sinensis Palmer in China

Isoetes sinensis Palmer (Isoetaceae) is an aquatic or amphibious plant that is critically endangered in China. Previous studies have revealed the crassulacean acid metabolism (CAM)-like photosynthetic pathway occurs commonly in submerged leaves in genusIsoetes. Water chemistry parameters and the titratable acidity content of the plant extract were measured from samples obtained in the early morning (7∶00) and late afternoon (15∶00) from twoI. sinensis populations in China. One population occurs in the eulittoral zone of a freshwater tidal river at low elevation (134 m) and another occurs in a densely vegetated, high elevation (1 100 m) alpine shallow pool. Significant differences in pH and titratable acidity of the plant extract were detected between the morning and afternoon samples. These changes are associated with diurnal changes in water chemistry. Our results provide the first evidence for the existence of the CAM pathway in the East Asian endemicIsoetes sinensis Palmer. The magnitude of fluctuations in the titratable acidity of the plant extract may be correlated with the severe carbon limitation imposed on the plants by its aquatic habitat. Foundation item: Supported by the State Key Basic Research and Development Plan (G2000046805) Biography:Pang Xin-an (1974-), male, Master candidate, research direction: conservation biology.     

Human immunodeficiency virus induces phosphorylation of its cell surface receptor

AIDS is an immunoregulatory disorder characterized by depletion of the CD4+, helper/inducer lymphocyte population. The causative agent of this disease is the human immunodeficiency virus, HIV, which infects CD4+ cells and leads to cytopathic effects characterized by syncytia formation and cell death. Recent studies have demonstrated that binding of HIV to its cellular receptor CD4 is necessary for viral entry. We find that binding of HIV to CD4 induces rapid and sustained phosphorylation of CD4 which could involve protein kinase C. HIV-induced CD4 phosphorylation can be blocked by antibody against CD4 and monoclonal antibody against the HIV envelope glycoprotein gp120, indicating that a specific interaction between CD4 and gp120 is required for phosphorylation. Electron microscopy shows that a protein kinase C inhibitor does not impair binding of HIV to CD4+ cells, but causes an apparent accumulation of virus particles at the cell surface, at the same time inhibiting viral infectivity. These results indicate a possible role for HIV-induced CD4 phosphorylation in viral entry and identify a potential target for antiviral therapy.     

The gene lin-3 encodes an inductive signal for vulval development in C. elegans.

The lin-3 gene is necessary for induction of the Caenorhabditis elegans vulva by the anchor cell. It encodes a molecule similar to epidermal growth factor and to transforming growth factor-alpha and acts through the epidermal growth factor receptor homologue let-23. Expression of lin-3 in the anchor cell stimulates vulval induction; lin-3 may encode the vulval inducing signal.