Abstract: A semiconductor wafer with variable transmittance, serves as a saturable absorber for performing passive Q-switching in a laser system to produce laser pulses having defined output characteristics. By translating or rotating the semiconductor saturable absorber, loss properties of a laser cavity may be altered. In this manner, the output characteristics of the laser pulses can be varied without changing other parameters of laser operation. The output characteristics may include pulse duration, pulse repetition rate, peak power and average output power of the laser pulses. The semiconductor wafer can be made of doped or undoped GaAs, AlGaAs, InP, etc. Furthermore, the tunable Q-switch may simultaneously serve as an output coupler for the laser cavity.

Abstract: Compounds, compositions and methods for modulating the activity of receptors are provided. In particular compounds and compositions are provided for modulating the activity of receptors and for the treatment, prevention, or amelioration of one or more symptoms of disease or disorder directly or indirectly related to the activity of the receptors.

Abstract: The invention is based in part on the discovery that nonselective &kgr; agonists that possess &mgr; receptor-mediated effects in addition to their &kgr; agonist effects can decrease cocaine self-administration more effectively and with fewer undesirable side effects than can highly selective &kgr; agonists. The invention includes a number of new compounds having both nonselective &kgr; opioid receptor agonist activity and additional activity at &mgr; opioid receptors. These compounds are useful for the treatment of cocaine abuse, and can also be radiolabeled for use as imaging agents, e.g., the N-fluoroalkyl and iodoalkyl derivatives can be used, respectively, for positron emission tomography (PET) and single photon computed tomography (SPECT) brain imaging.