Energy dependence of directed flow over a wide range of pseudorapidity in Au + Au collisions at the BNL Relativistic Heavy Ion Collider

We report on measurements of directed flow as a function of pseudorapidity in Au + Au collisions at energies of square root of SNN = 19.6, 62.4, 130 and 200 GeV as measured by the PHOBOS detector at the BNL Relativistic Heavy Ion Collider. These results are particularly valuable because of the extensive, continuous pseudorapidity coverage of the PHOBOS detector. There is no significant indication of structure near midrapidity and the data surprisingly exhibit extended longitudinal scaling similar to that seen for elliptic flow and charged particle pseudorapidity density.     

Recent results from PHOBOS

The PHOBOS Collaboration has measured charged particles emitted over the range ?5.4<η<5.4 for Au+Au collisions at energies of $\sqrt {s_{NN} } = 19.6$ , 62.4, 130 and 200 GeV. In this contribution I will present recent results on the pseudorapidity distributions, total charged-particle production, and collective flow of particles obtained from these measurements.     

pH-dependent electron-transport properties of carbon nanotubes

Carbon nanotube electrochemical transistors integrated with microfluidic channels are utilized to examine the effects of aqueous electrolyte solutions on the electron-transport properties of single isolated carbon nanotubes. In particular, pH and concentration of supporting inert electrolytes are examined. A systematic threshold voltage shift with pH is observed while the transconductance and subthreshold swing remain independent of pH and concentration. Decreasing pH leads to a negative shift of the threshold voltage, indicating that protonation does not lead to hole doping. Changing the type of contact metal does not alter the observed pH response. The pH-dependent charging of SiO2 substrate is ruled out as the origin based on measurements with suspended nanotube transistors. Increasing the ionic strength leads to reduced pH response. Contributions from possible surface chargeable chemical groups are considered.     

Hydrogen sorption on palladium-doped sepiolite-derived carbon nanofibers

The hydrogen sorption behavior of novel Pd-doped sepiolite-derived carbon nanofibers (SDCNs) was investigated. Two chemical doping methods of ethanol/toluene reduction and a polyol process were applied to control Pd(0) formation in the SDCNs at different Pd doping levels. Hydrogen storage capacity was observed to vary depending on the Pd particle size and doping amount as the Pd particle surface area and the carbon Brunauer-Emmett-Teller (BET) surface area change with them, suggesting the existence of an optimum Pd doping level at each doping method for the best hydrogen storage capacity. Among the samples prepared using the polyol method at different Pd amounts, the maximum hydrogen uptake of about 0.41 wt % was obtained at 298 K and 90 bar for the 5 wt % Pd-doped SDCN that has a relatively high Pd particle surface area and carbon BET surface area. Samples prepared using the ethanol/toluene reduction method exhibited a higher hydrogen uptake of about 0.59 wt % at lower Pd doping levels (3 wt % Pd) due to a smaller Pd particle size and relatively high carbon BET surface area. The hydrogen desorption behavior investigated by differential scanning calorimeter exhibited that a higher amount of hydrogen desorbed at around 860 K from the Pd-doped SDCNs compared to that from the undoped SDCN. Fourier transform infrared (FTIR) spectroscopic analysis suggested that some of the weak chemisorbed hydrogen changes to a normal covalent bond during the heating and effuses at around 860 K.