F.Z. Li

Tensile strength of single-walled carbon nanotubes directly measured from their macroscopic ropes

20 mm long ropes consisting of soundly aligned single-walled carbon nanotube (SWNT) ropes, synthesized by the catalytic decomposition of hydrocarbons, were employed for direct tensile strength measurements. The average tensile strength of SWNT rope composites is as high as 3.6 +/-0.4 GPa, similar to that of carbon fibers. The tensile strength of SWNT bundles was extrapolated from the strength of the composites to be 2.3 +/-0.2 to 14.2 +/-1.4 GPa after simply taking into account the volume fraction of SWNT bundles in the minicomposite, and the tensile strength of single SWNTs was estimated to be as high as 22.2 +/-2.2 GPa. The excellent mechanical properties of SWNTs will make them an ideal reinforcement agent for high performance composite materials

Synthesis of macroscopically long ropes of well-aligned single-walled carbon nanotubes

chinese acad sci, inst met res, int ctr mat phys, shenyang 110015, peoples r china. mit, dept elect engn & comp sci, cambridge, ma 02139 usa. mit, dept phys, cambridge, ma 02139 usa.;cheng, hm (reprint author), chinese acad sci, inst met res, int ctr mat phys, 72 wenhua rd, shenyang 110015, peoples r china

Frequency response characteristic of single-walled carbon nanotubes as supercapacitor electrode material

Impedance analysis was employed to study the frequency response characteristics of supercapacitors utilizing single-walled carbon nanotubes (SWNTs) as electrode material. The knee frequency is around 631 Hz for the electrochemically oxidized SWNT supercapacitor, much higher than that of the as-prepared one (around 316 Hz) and the common activated carbon supercapacitor (< 1 Hz). The good frequency response observed in this work is due to the introduction of nanosized mesopores and oxygen-containing groups formed during the electrochemical oxidization of SWNTs. The capacitance of electrochemically oxidized SWNT supercapacitor is 113 F/g, which is much higher than the value of the as-prepared one (20 F/g)

Regulation of Transforming Growth Factor-β1–Induced Apoptosis and Epithelial-to-Mesenchymal Transition by Protein Kinase A and Signal Transducers and Activators of Transcription 3

Apoptosis and epithelial-to-mesenchymal transdifferentiation or transition (EMT) are crucial for normal development and body homeostasis. The alterations of these events are closely related to some pathologic processes, such as tumor formation and metastasis, fibrotic diseases of liver and kidney, and abnormal development of embryos. The mechanism that underlies the simultaneously occurring apoptosis and EMT induced by transforming growth factor-beta (TGF-beta) has not been well studied. In this report, we investigated the potential mechanism that underlies TGF-beta1-induced apoptosis and EMT. TGF-beta1-induced apoptosis and EMT were associated with the activation of protein kinase A (PKA) and signal transducers and activators of transcription 3 (STAT3). Inhibition of PKA by specific PKA inhibitor H89 or by PKA inhibitor peptide blocked STAT3 activation and suppressed TGF-beta1-induced apoptosis and EMT. Furthermore, overexpression of a phosphorylation-deficient form of STAT3, but not wild-type STAT3, produced an inhibitory effect on TGF-beta1-induced apoptosis and EMT. The results indicate that PKA is an upstream regulator for TGF-beta1-induced STAT3 activation and plays an important role in TGF-beta1-mediated apoptosis and EMT. These studies provided a new insight into the signaling mechanism underlying the apoptosis and EMT, which could be of importance in understanding some related physiologic and pathologic processes.

Theoretical investigation of A-element atom diffusion in Ti2AC (A=Sn, Ga, Cd, In, and Pb)

The phase stability and mechanical properties of Ti(2)AC (A=Ga, Cd, Sn, In, and Pb) have close relationship with the behavior of group-A element atoms in these compounds. This letter shows that although the Al, Ga, and In (or Si, Sn, and Pb) are in the same group, the migration energy and vacancy formation energy of group-A atom in Ti(2)GaC/Ti(2)InC (or Ti(2)SnC/Ti(2)PbC) are noticeable lower than those in Ti(2)AlC (or Ti(3)SiC(2)). The present results are helpful for a better understanding of easy out diffusion and self-extrusion of group-A atoms in these compounds.

Protein kinase A suppresses the differentiation of 3T3-L1 preadipocytes

cAMP and protein kinase A (PKA) are widely known as signaling molecules that are important for the induction of adipogenesis. Here we show that a strong increase in the amount of cAMP inhibits the adipogenesis of 3T3-L1 fibroblast cells. Stimulation of PKA activity suppresses adipogenesis and, in contrast, inhibition of PKA activity markedly accelerates the adipogenic process. As adipogenesis progresses, there is a significant increase in the expression level of PKA regulatory subunits and a corresponding decrease in PKA activity. Moreover, treatment of 3T3-L1 cells with epidermal growth factor (EGF) stimulates PKA activity and blocks adipogenesis. Inhibition of PKA activity abolishes this suppressive effect of EGF on adipogenesis. Moreover, activation of PKA induces serine/threonine phosphorylation, reduces tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1) and the association between PKA and IRS-1. Taken together, our study demonstrates that PKA has a pivotal role in the suppression of adipogenesis. cAMP at high concentrations can suppress adipogenesis through PKA activation. These findings could be important and useful for understanding the mechanisms of adipogenesis and the relevant physiological events.

A self-similar array model of single-walled carbon nanotubes

To describe single-walled carbon nanotube (SWNT) arrays, we propose a self-similar array model. For isolated SWNT bundles, the self-similar array model is consistent with the classical triangular array model; for SWNT bundle arrays, it can present hierarchy structures and specify different array configurations. Based on this self-similar array model, we calculated the energetics of SWNT arrays, investigated the driving force for the formation of macroscopic SWNT arrays, and briefly discussed the hierarchy structures in real macroscopic SWNT arrays. (c) 2005 American Institute of Physics.

Photovoltaic effect and its polarity in Si doping superlattices

We have studied the photovoltaic effects in Si doping superlattices (nipi) under different excitation conditions with and without additional cw optical biasing using a He-Ne laser. On the basis of the photovoltaic theory of carrier spatial separation in superlattices, we propose the concept of spatial fixity of the photovoltage polarity in type-II superlattices and examine the experimental results. The photovoltaic effect in Si nipi is found mainly from the direct transitions related with shallow impurities in real space, not the electron-hole band-to-band process as in GaAs nipi.