Room-temperature Coulomb blockade of charge transport through composite nanostructures containing organic inter-links has recently been observed. A pronounced charging effect in combination with the softness of the molecular links implies that charge transfer gives rise to a significant deformation of these structures. For a simple model system containing one nanoscale metallic cluster connected by molecular links to two bulk metallic electrodes we show that self-excitation of periodic cluster oscillations in conjunction with sequential processes of cluster charging and decharging appears for a sufficiently large bias voltage. This new `electron shuttle' mechanism of discrete charge transfer gives rise to a current through the nanostructure, which is proportional to the cluster vibration frequency.Comment: 4 pages, 4 figure

Increasing evidence suggests that atherosclerosis is an inflammatory disease promoted by hypercholesterolemia. The role of adaptive immunity has been controversial, however. We hypothesized that proatherogenic T cells are controlled by immunoregulatory cytokines. Among them, TGF-β has been implied in atherosclerosis, but its mechanism of action remains unclear. We crossed atherosclerosisprone ApoE-knockout mice with transgenic mice carrying a dominant negative TGF-β receptor II in T cells. The ApoE-knockout mice with disrupted TGF-β signaling in T cells exhibited a sixfold increase in aortic lesion surface area, a threefold increase in aortic root lesion size, and a 125-fold increase in aortic IFN-γ mRNA when compared with age-matched ApoE-knockout littermates. When comparing size-matched lesions, those of mice with T cell-specific blockade of TGF-β signaling displayed increased T cells, activated macrophages, and reduced collagen, consistent with a more vulnerable phenotype. Ab's to oxidized LDL, circulating T cell cytokines, and spleen T cell activity were all increased in ApoE-knockout mice with dominant negative TGF-β receptors in T cells. Taken together, these results show that abrogation of TGF-β signaling in T cells increases atherosclerosis and suggest that TGF-β reduces atherosclerosis by dampening T cell activation. Inhibition of T cell activation may therefore represent a strategy for antiatherosclerotic therapy.This article was publised online in advance of the print addition. The date of publication is available from the JCI website, http://www.jci.org.

Abstract. -Effects of a coupling between the mechanical vibrations of a quantum dot placed between the two leads of a single electron transistor and coherent tunneling of electrons through a single level in the dot has been studied. We have found that for bias voltages exceeding a certain critical value a dynamical instability occurs and mechanical vibrations of the dot develop into a stable limit cycle. Introduction. -Nanoelectromechanics [1, 2] is a new, quickly developing field in condensed matter physics. A coupling between strongly pronounced mesoscopic features of the electronic degrees of freedom (such as quantum coherence and quantum correlations) and degrees of freedom connected to deformations of the material produces strong electromechanical effects on the nanometer scale. The mesoscopic force oscillations in nanowires [3-5] observed a few years ago is an example of such a phenomenon. Investigations of artificially-made nanomechanical devices, where the interplay between single-electron tunneling and a local mechanical degree of freedom significantly controls the electronic transport, is another line of nanoelectromechanics [6][7][8][9][10][11][12][13][14][15]. For one of the nanomechanical systems of this kind, the self-assembled single-electron transistor, a new electromechanical phenomena -the shuttle instability and a new so-called shuttle mechanism of the charge transport were recently predicted in [12]. It was shown that a small metallic grain attached to two metallic electrodes by elastically deformable links breaks into oscillations if a large enough bias voltage is applied between the leads. For the model system studied in [12], it was also shown that a finite friction is required for the oscillation amplitude to saturate and for a stable regime of oscillations to develop.An essential assumption made in [12] is that the relaxation mechanisms present are strong enough to keep the electron systems in each of the conducting parts of the transistor in local equilibrium (as assumed in the standard theory of Coulomb blockade [16,17]). Such relaxation, which destroys any phase coherence between electron tunneling events, allows a description of

An analytical analysis of quantum shuttle phenomena in a nanoelectromechanical single-electron transistor has been performed in the realistic case, when the electron tunneling length is much greater than the amplitude of the zero point oscillations of the central island. It is shown that when the dissipation is below a certain threshold value, the vibrational ground state of the central island is unstable. The steady state into which this instability develops is studied. It is found that if the electric field E between the leads is much greater than a characteristic value E(q), the quasiclassical shuttle picture is recovered, while if E<0) shuttle vibrations.