The standard model of labor is one in which individuals trade their time and energy in return for monetary rewards. Building on Fiske's relational theory (1992), we propose that there are two types of markets that determine relationships between effort and payment: monetary and social. We hypothesize that monetary markets are highly sensitive to the magnitude of compensation, whereas social markets are not. This perspective can shed light on the well-established observation that people sometimes expend more effort in exchange for no payment (a social market) than they expend when they receive low payment (a monetary market). Three experiments support these ideas. The experimental evidence also demonstrates that mixed markets (markets that include aspects of both social and monetary markets) more closely resemble monetary than social markets.

he wide adoption of dynamic second-price auctions as the format of choice for Internet-based (online) transactions has created an interest in understanding how individuals behave in such environments. The current work concentrates on two dynamic effects, which we call quasi-endowment and opponent effect, and finds that these effects may result in over-bidding.The results of two experimental auctions-one involving hypothetical bids and the other real-money bids-demonstrate that bids reflect valuations that include the nonnormative influences of the two factors. Quasi-endowment and opponent effects could lead to the behaviors of repeated bidding and sniping commonly observed in second-price online auctions such as eBay.

We have studied terahertz ͑THz͒ emission from InAs and GaAs in a magnetic field, and find that the emitted radiation is produced by coupled cyclotron-plasma charge oscillations. Ultrashort pulses of THz radiation were produced at semiconductor surfaces by photoexcitation with a femtosecond Ti-sapphire laser. We recorded the integrated THz power and the THz emission spectrum as a function of magnetic field at fields up to 5.5 T, and as function of temperature for Tϭ10-280 K. The maximum observed THz power is ϳ1.6ϫ10 Ϫ13 J/pulse ͑12 W average power͒ from n-InAs (1.8ϫ10 16 cm Ϫ3 ͒ at Bϭ3.2 T. We compare our results to semiclassical models of magnetoplasma oscillations of bulk free carriers and damped motion of free carriers in a twodimensional electron gas. The bulk model describes THz emission from n-GaAs at all magnetic fields, and InAs at Bϭ0. It fails to describe THz emission from InAs at nonzero magnetic fields. We show that a model including both bulk plasma oscillations and THz emission from a surface accumulation layer describes THz emission from InAs in a moderate magnetic field, but this model does not completely describe emission at fields ͉B͉Ͼ1.0 T.

We study terahertz (THz) emission from GaAs as a function of photon energy and electric field. THz radiation arises from transport of photogenerated charge in an electric field and by hot carrier diffusion (the photo-Dember effect). These mechanisms can be separated by experiments in which either the electric field or the kinetic energy of the carriers is varied. For electric fields E∼4 kV/cm, we find that the electric field controls THz emission for carrier temperatures kBTC⩽0.1 eV, while hot-carrier diffusion dominates for kBTC≈1 eV. Both mechanisms contribute at intermediate fields and carrier temperatures. Our results are consistent with estimates of the relative magnitudes of these two effects.

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