Models that depict innovation as a smooth, well-behaved linear process badly misspecify the nature and direction of the causal factors at work. Innovation is complex, uncertain, somewhat disorderly, and subject to changes of many sorts. Innovation is also difficult to measure and demands close coordination of adequate technical knowledge and excellent market judgment in order to satisfy economic, technological, and other types of constraints—all simultaneously. The process of innovation must be viewed as a series of changes in a complete system not only of hardware, but also of market environment, production facilities and knowledge, and the social contexts of the innovation organization.

An Overview of Innovation

The Auger recombination coefficient in quasi-bulk InxGa1−xN (x∼9%–15%) layers grown on GaN (0001) is measured by a photoluminescence technique. The samples vary in InN composition, thickness, and threading dislocation density. Throughout this sample set, the measured Auger coefficient ranges from 1.4×10−30to2.0×10−30cm6s−1. The authors argue that an Auger coefficient of this magnitude, combined with the high carrier densities reached in blue and green InGaN∕GaN (0001) quantum well light-emitting diodes (LEDs), is the reason why the maximum external quantum efficiency in these devices is observed at very low current densities. Thus, Auger recombination is the primary nonradiative path for carriers at typical LED operating currents and is the reason behind the drop in efficiency with increasing current even under room-temperature (short-pulsed, low-duty-factor) injection conditions.

Auger recombination in InGaN measured by photoluminescence

Bose–Einstein condensation (BEC), a form of matter first postulated in 1924, has famously been demonstrated in dilute atomic gases at ultra-low temperatures. Much effort is now being devoted to exploring solid-state systems in which BEC can occur. In theory semiconductor microcavities, where photons are confined and coupled to electronic excitations leading to the creation of polaritons, could allow BEC at standard cryogenic temperatures. Kasprzak et al. now present experiments in which polaritons are excited in such a microcavity. Above a critical polariton density, spontaneous onset of a macroscopic quantum phase occurs, indicating a solid-state BEC. BEC should also be possible at higher temperatures if coupling of light with solid excitations is sufficiently strong. Demokritov et al. have achieved just that, BEC at room temperature in a gas of magnons, which are a type of magnetic excitation. Bose–Einstein condensation, the formation of a collective quantum state of identical particles, called bosons, is observed at room temperature in a gas of magnons, which are a type of magnetic excitation. Bose–Einstein condensation1,2 is one of the most fascinating phenomena predicted by quantum mechanics. It involves the formation of a collective quantum state composed of identical particles with integer angular momentum (bosons), if the particle density exceeds a critical value. To achieve Bose–Einstein condensation, one can either decrease the temperature or increase the density of bosons. It has been predicted3,4 that a quasi-equilibrium system of bosons could undergo Bose–Einstein condensation even at relatively high temperatures, if the flow rate of energy pumped into the system exceeds a critical value. Here we report the observation of Bose–Einstein condensation in a gas of magnons at room temperature. Magnons are the quanta of magnetic excitations in a magnetically ordered ensemble of magnetic moments. In thermal equilibrium, they can be described by Bose–Einstein statistics with zero chemical potential and a temperature-dependent density. In the experiments presented here, we show that by using a technique of microwave pumping it is possible to excite additional magnons and to create a gas of quasi-equilibrium magnons with a non-zero chemical potential. With increasing pumping intensity, the chemical potential reaches the energy of the lowest magnon state, and a Bose condensate of magnons is formed.

Bose–Einstein condensation of quasi-equilibrium magnons at room temperature under pumping

When a gas of bosonic particles is cooled below a critical temperature, it condenses into a Bose-Ei…

Bose-Einstein condensation

Chemical Science Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352; Department of Chemistry, ShelbyHall, University of Alabama, Box 870336, Tuscaloosa, Alabama 35487-0336; Notre Dame Radiation Laboratory, University of Notre Dame,Notre Dame, Indiana 46556; Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 0520-8107; Argonne NationalLaboratory, 9700 South Cass Avenue, Argonne, Illinois 60439; Department of Computer Science and Department of Physics, 2710 University Drive,Washington State University, Richland, Washington 99352-1671; Lawrence Berkeley National Laboratory, 1 Cyclotron Road Mailstop 1-0472,Berkeley, California 94720; Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300,Austin, Texas 78712; Office of Basic Energy Sciences, U.S. Department of Energy, SC-141/Germantown Building, 1000 Independence Avenue,S.W., Washington, D.C. 20585-1290; Department of Physics and Engineering Physics, Stevens Institute of Technology, Castle Point on Hudson,Hoboken, New Jersey 07030; Department of Chemistry, Johns Hopkins University, 34th and Charles Streets, Baltimore, Maryland 21218;Department of Chemistry, University of Southern California, Los Angeles, California 90089-1062; Department of Chemistry, The Ohio StateUniversity, 100 West 18th Avenue, Columbus, Ohio 43210-1185; Department of Chemistry, Columbia University, Box 3107, Havemeyer Hall,New York, New York 10027; Department of Chemistry, University of Pittsburgh, Parkman Avenue and University Drive,Pittsburgh, Pennsylvania 15260; Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000; Department of Physics andAstronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, New Jersey 08854-8019; Department of Chemistry,516 Rowland Hall, University of California, Irvine, Irvine, California 92697-2025; Stanford Synchrotron Radiation Laboratory, Stanford LinearAccelerator Center, 2575 Sand Hill Road, Mail Stop 69, Menlo Park, California 94025; School of Chemistry and Biochemistry, Georgia Institute ofTechnology, 770 State Street, Atlanta, Georgia 30332-0400; Geology Department, University of California, Davis, One Shields Avenue,Davis, California 95616-8605; Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,Cambridge, Massachusetts 02139-4307; Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084Received July 23, 2004

http://casey.brown.edu/chemistry/research/LSWang/publications/194.pdf

Role of water in electron-initiated processes and radical chemistry: issues and scientific advances.

Production and optical properties of steady-state photoinjected plasmas in quantum wires

It is summarized what can be considered as the present situation with regards to the construction of an ensemble formalism—Gibbs’ style—for the case of far-from-equilibrium systems. The main questions involved are subsummed and the construction of a general nonequilibrium grand-canonical ensemble is presented. Very brief considerations on statistics differing from the conventional Boltzmann–Gibbs one are presented.

Nonequilibrium ensemble formalism

An optical investigation of the transport properties of carriers in a thick GaAs layer is presented. The electron transport is monitored by time-resolved luminescence from the GaAs layer and an InGaAs quantum well beneath. The transients are mostly insensitive to the presence of external electric fields of both polarities, which indicates a carrier transport dominated by ambipolar diffusion. Spin measurements under a continuous-wave low-density regime show a strong conservation of the electron spin during the diffusion of electrons through the thick GaAs layer and their capture by the InGaAs well, but only for an applied field polarity that accelerates the electrons towards the well.

/pdf/carrier-dynamics-investigated-by-time-resolved-optical-5dlr4wo1y6.pdf

Carrier Dynamics Investigated by Time-Resolved Optical Spectroscopy

Nonlinear transport phenomena and relaxation processes in highly photoexcited polar direct-gap semiconductors are considered. The rates of energy transfer between subsystems are calculated and it is shown that for ultra-short laser pulses lattice heating is unimportant. However, for cw laser-light illumination a pronounced enhancement of the lattice temperature is expected when laser power approaches, or surpasses, a critical value, leading the system to melting conditions.



Es werden nichtlineare Transportphanomene und Relaxationsprozesse in optisch hoch-angeregten, polaren, direkten Halbleitern untersucht. Die Geschwindigkeiten des Energietransfer zwischen Subsystemen werden berechnet und es wird gezeigt, das fur ultrakurze Laserimpulse Gitterauf-heizung unwesentlich ist. Jedoch wird fur Belichtung mit kontinuierlichem Laserlicht eine be-trachtliche Erhohung der Gittertemperatur erwartet, wenn die Laserleistung einen kritischen Wert erreicht oder ubersteigt und das System zu Schmelzbedingungen gefuhrt wird.

On Laser‐Induced Lattice Heating in a Polar Semiconductor

This article studies the dissipative thermodynamic regime of an electron system in bulk matter under the action of an external source of energy, which generates electron-hole pairs with a nonequilibrium distribution in energy space. It is shown that with increasing values of the source power (furthering the distance from equilibrium), and strictly in the case of a p-doped material, the carrier system displays complex behavior characterized by undergoing a succession of transitions between synergetically self-organized dissipative structures. The sequence goes from the homogeneous steady state (or stochastic thermal chaos), to sinusoidal spatial deviations (morphological ordering), to intricate ordered states (subharmonic bifurcations), to deterministic turbulent-like chaos (large amount of nonlinear periodic spatial organization of the Landau-Prigogine's type). The phenomenon may arise, for example, in semiconductor systems, molecular polymers, and protein molecular chains in biosystems. © 1997 John Wiley & Sons, Inc.

Áurea R. Vasconcellos

Papers

Production and optical properties of steady-state photoinjected plasmas in quantum wires

Nonequilibrium ensemble formalism

Carrier Dynamics Investigated by Time-Resolved Optical Spectroscopy

On Laser‐Induced Lattice Heating in a Polar Semiconductor

Complex behavior in condensed matter: morphological ordering in dissipative carrier systems