find that Eq. (1) does indeed give n 0 (T) values which are independent of r for r ^ 6 A, and, further, that these values exhibit a very reasonable temperature dependence and are consistent with the best theoretical estimates of n 0 {0). This certainly lends credence to Eq, (1) and leads us to believe that our new values are the most realistic estimates of n 0 (T) obtained to date. They should, however, still be treated with caution since existing derivations 15 ' 16 of Eq. (1) rely heavily on physical intuition. It would be desirable to obtain the relation between g{r) and n Q from a systematic theory that clearly establishes its limits of validity, and we hope that the success of the present study will stimulate further theoretical work in this direction.

Local high current densities in areas around dislocations with a screw component might be responsible for the observed high leakage currents in GaN-based electronic devices. Using ballistic electron emission microscopy, threading dislocations with a screw component are found to be accompanied by high current densities and low effective Schottky barrier heights. The electronic states responsible for this extremely nonuniform behavior of GaN films are metastable trap states. The experimental results show that acceptor- and donor-like charge traps coexist in the vicinity of dislocations with a screw component.

ZIF-8 nanocrystals have exhibited different mechanisms for rhodamine B degradation in water under various circumstances.

Radical cyclization made easy Metalloenzymes contain metal cofactors that can sometimes be exploited to catalyze reactions distinct from their natural function. Drawing on inspiration from heme-based radical polymerizations, Zhou et al . screened a panel of metalloproteins for candidates that could catalyze an atom-transfer radical cyclization, producing a lactam from an amide substrate bearing bromoalkyl and alkene functional groups (see the Perspective by Zhang and Dydio). Cytochrome P-450 derivatives were effective catalysts, and a series of enzyme variants were generated by directed evolution to access the full range of enantiomer and diastereomer products for model substrates. Such biocatalysts are valuable additions to the synthetic chemistry toolkit and reiterate the potential of metalloenzymes in catalyzing useful unnatural reactions. —MAF

Ultrafast subpicosecond optical pulse generation is achieved by passive colliding-pulse mode locking of monolithic multiple quantum well InGaAsP semiconductor lasers. Transform-limited optical pulses with durations of 1.1, 0.83, 1.0, and 0.64 ps are achieved at repetition rates of 40, 80, 160, and 350 GHz, respectively, without using any external ac sources.