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.

34-Sulfatobastadin 13 [1] was isolated from the sponge Ianthella sp. Its structure was elucidated by nmr techniques and chemical transformation to bastadin 13 [2]. Compound 1 weakly inhibited binding to the endothelin A receptor (ETA), while compound 2 inhibited growth of Bacillus subtilis.

Ballistic electron emission microscopy (BEEM) has been used to study transport in a double barrier resonant tunneling structure. Unlike conventional transport techniques, BEEM allows the injected electron energy to be varied independent of the band profile. We report the observation of quasi-bound states and band-structure effects as deduced from the temperature evolution of the BEEM spectra. The BEEM thresholds are found to be in good agreement with the calculated energetically favorable levels. Our results show that BEEM is a powerful spectroscopic tool for studying quantum structures.

The shifts in the absorption edge with hydrostatic pressure have been measured for four ternary semiconductors. In all cases the energy gap increases with pressure. From the data the pressure dependence of the energy gap (dE,/dP) was determined as 2.2 meV/kbar for AgGaS2, 3.4 meV/kbar for CuGaS"5.3 meV/kbar for AgGaSe, , and 2.7 meV/kbar for AgInSe, . These shifts are compared with the corresponding II-VI compounds and discussed. Some optical effects associated with the pressure-induced phase transitions in some of the I-III-VI, compounds and II-VI compounds are described and discussed.