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We investigate the temperature dependence of three major Raman modes of black phosphorus (BP) prepared by mechanical exfoliation from room temperature to 325 C. With increasing temperature, all the Raman peaks show redshift in peak position and broadening in linewidth, but they depend on the film thickness. The first-order temperature coefficients of A g

have revealed a shape-independent hyperbolic scaling rule for the exciton binding energy versus the exciton Bohr radius in semiconductor quantum wires, and an enhancement in the exciton binding energy in a quantum wire with respect to a quantum well for a given exciton Bohr radius. These findings were attributed to the existence of a constant ͑shapeand/or size-independent͒ virial theorem value ͑potentialto kinetic-energy ratio͒, respectively, for the wires and wells, and its value was found to be larger ͑ϭ4͒ for wires than ͑ϭ2͒ for wells. In order to elucidate the physics underlying the above results, we reexamine this subject by calculating the exciton binding energy and the corresponding virial theorem value in quantum wells and wires with infinite confinement barriers. We find the following. ͑i͒ The virial theorem value is nonconstant but approaches 2 from above when reducing the finite extension of the electron and hole wave functions in the confined directions. This is because the origin of the virial theorem value of 2 lies in the inverse square Coulomb force being the only interaction seen by the electron and hole. ͑ii͒ The scaling rule is nonhyperbolic, because the virial theorem value is not a constant. ͑iii͒ The virial theorem value and the exciton binding energy are larger in a wire than in a well for a given exciton Bohr radius, because the wire exciton has a smaller kinetic energy in the nonconfined direction. ͑iv͒ The origin of the shape-independent scaling rule for wires lies in the close similarity of the effective Coulomb potentials for wires with different shapes and widths. The virial theorem value being or not being a constant is irrelevant to the scaling rule. ͑v͒ There exists a more fundamental and practically more useful shape-independent scaling rule. ͓S0163-1829͑99͒11803-4͔

Storage‐stable styrene‐butadiene‐styrene triblock copolymer (SBS)‐modified asphalt was prepared by dynamic vulcanization. The vulcanization characteristics of the asphalt/SBS/sulfur blend were studied using a strain‐controlled rheometer. The vulcanization of SBS in the asphalt resulted in a marked increase in the torque of the blend. In addition, the vulcanization of a butadiene rubber (BR)/sulfur blend was significantly influenced by the addition of asphalt through a curemeter. The existence of asphalt can accelerate the vulcanization of BR/sulfur blend and reduce its reversion. The preparation process of storage‐stable SBS‐modified asphalt by dynamic vulcanization was identified by a plot of the electric current versus time. The addition of sulfur to the SBS‐modified asphalts resulted in the formation of chemically vulcanized network structures in the modified binders. The physical properties of the SBS‐modified asphalt containing sulfur were compared to those of the modified binders without sulfur. The storage stability of the SBS‐modified asphalt was effectively improved by the addition of sulfur. The rheological properties of the SBS‐modified asphalts before and after adding sulfur were characterized by using dynamic shear rheometry and a rotational viscometer. As indicated by the monitored morphology, the compatibility and high‐temperature storage stability of SBS‐modified asphalts were improved by the addition of sulfur.

We have used first principles methods to systematically investigate the quantum confinement effect on the electronic properties of zinc-blende (ZB) and wurtzite (WZ) InAs nanowires (NWs) with different orientations and diameters, and compared their electronic properties before and after pseudo-hydrogen passivation. The results show that the calculated carrier effective masses are dependent on the NW diameter, except for [110] ZB NWs, and the hole effective masses of [111] ZB NWs are larger than the electron effective masses when the NW diameter is ≥26 Å. The band alignments of [111] ZB and [0001] WZ NWs reveal that the effect of quantum confinement on the conduction bands is greater than on the valence bands, and the position of the valence band maximum level changes little with increasing NW diameter. The pseudo-hydrogen passivated NWs have larger band gaps than the corresponding unpassivated NWs. The carrier effective masses and mobilities can be adjusted by passivating the surface dangling bonds.

s u m m a r yThe complex dynamics of partial bed-load transport in a series of well-controlled laboratory experiments are explored systematically and simulated by a stochastic model in this study. Flume experiments show that the leading front of bed-load on a 20-m-long, mixed-size gravel-bed moves anomalously, where the transient transport rate of the accelerating front varies with the observation time scale. In addition, observations show that moving particles may experience bimodal transport (i.e., coexistence of long trapping time and large jump length) related to bed coarsening and the formation of clusters on a heterogeneous gravel-bed, which is distinguished from the traditional theory of hiding-exposing interactions among mixed-size particles. A fractional derivative model is finally applied to characterize the overall behavior of partial bed-load transport, including the coexistence of the sub-diffusion and non-local feature caused by turbulence and the micro-relief within an armor layer.