124,956 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Intrasubband and intersubband scattering in semiconductor quantum wires
No full textWe have performed low-density (< 10(5) cm(-1)) time-resolved photoluminescence experiments that probe the relaxation of photo-excited carriers in a quantum wire. Our results show that carrier-carrier collisions are dominant at very short times both for intra- and for inter-subband scattering as only expected if non-Markovian effects are taken into account. (C) 1999 Elsevier Science B.V. All rights reserved.LOEQLPNSwiss Fed Inst Technol, IMO, Dept Phys, CH-1015 Lausanne, Switzerland. Deveaud, B, Swiss Fed Inst Technol, IMO, Dept Phys, CH-1015 Lausanne, Switzerland.ISI Document Delivery No.: 267TPCited Reference Count: 6Cited References:CHAVEZPIRSON A, 1996, APPL PHYS LETT, V69, P218MACIEL AC, 1995, APPL PHYS LETT, V66, P3039OGAWA T, 1991, PHYS REV B, V44, P8138PRENGEL F, 1999, PHYS REV B, V59, P5806SIRIGU L, 1999, IN PRESSVOUILLOZ F, 1997, PHYS REV LETT, V78, P158
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Towards a room-temperature polariton amplifier
No full textMicrocavity exciton polaritons, the fundamental optical excitations of semiconductor microcavities with quantum wells inside, have been proposed as promising candidates for observing stimulated scattering, condensation and other phenomena related to the bosonic nature of excitons. Having a light mass, quantum degeneracy of polaritons can be reached at low densities and high temperatures. But the radiative time of polaritons is very short (in the picosecond range) and usually prevents an efficient thermalization and cooling of the excited cloud of polaritons. A 'coherently driven condensate', not corresponding to a thermal equilibrium, but featuring multiple occupation of single-particle states, can however be created by an external laser source resonantly exciting polaritons. Under this condition, stimulated parametric scattering of polaritons can provide huge optical gain on a weak probe pulse shined on the sample. In this work we demonstrate that this phenomenon can survive at temperatures close to room temperature and could be achieved in the future even above this limit. Clever sample designs favour the thermal robustness of polariton parametric amplification, but from the experimental data it turns out that the parameter that ultimately limits the highest temperature for polariton parametric scattering is the exciton binding energy
Femtosecond dynamics and non-linearities of exciton-photon coupling in semiconductor microstructures
No full textWe have studied the femtosecond dynamics of excitonic resonances in quantum well microcavities under strong excitation. Very strong non-linearities are observed, which bear clear resemblance to the non-linearities of an atomic two-level system. The fact that the excitonic system undergoes Rabi flopping and AC Stark splitting is clearly evidenced in a number of cases. Excitation induced dephasing shows an effect much stronger than the light dressing and prevents the observation of the Rabi flopping only when exciting in the continuum. Most of the experimental findings are well reproduced by a dynamical solution of the Maxwell-Bloch equations for an ensemble of two-level systems. This allows in particular understanding of the occurrence of strong coherent gain in microcavitics. An exhaustive description of the experiments is given within the framework of semiconductor Maxwell-Bloch optical equations at the Hartree-Fock level. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS
Polariton amplification in semiconductor microcavities
No full textMicrocavity exciton polaritons, the fundamental optical excitations of semiconductor microcavities with quantum wells inside, have been proposed as promising candidates for observing stimulated scattering, condensation and other phenomena related to the bosonic nature of excitons. Having a light mass, quantum degeneracy of polaritons can be reached at low densities and high temperatures. But the radiative time of polaritons is very short (in the picosecond range) and usually prevents an efficient thermalization and cooling of the excited cloud of polaritons. A 'coherently-driven condensate', not corresponding to a thermal equilibrium, but featuring multiple occupation of single-particle states, can however be created by an external laser source resonantly exciting polaritons. Under this condition, stimulated parametric scattering of polaritons can provide huge optical gain on a weak probe pulse shined on the sample. In this work we demonstrate that this phenomenon can survive at temperatures close to room temperature and could be achieved in the next future even above this limit. Clever sample designs favour the thermal robustness of polariton parametric amplification, but from the experimental data it turns out that the parameter that ultimately limits the highest temperature for polariton parametric scattering is the exciton binding energy. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Non-linear dynamical effects in semiconductor microcavities
No full textAn investigation of the parametric amplification and its coherent control in a semiconductor microcavity is presented. The time and angle resolved pump and probe experiments show that several picoseconds after pumping the polaritons are still coherent and parametric scattering is still going on. The experimental data concerning the time integrated measurements are in qualitative agreement with the numerical data obtained from a relatively simple theoretical model based on three polarisation components, pump, probe, and idler. As for the dynamics of parametric amplification in real time, the measurements reveal that often stimulation is considerably delayed with respect to the arrival of pump and probe. Even though the observed dynamics is complex, our simple theoretical model permits to reproduce several of the experimental features. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Determination of the exciton formation in quantum wells from time-resolved interband luminescence
No full textWe present the results of a detailed time-resolved luminescence study carried out on a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated. We perform this experiment with a spectral resolution and a sensitivity of the setup, allowing us to keep the observation of these two separate contributions over a broad range of times and densities. This allows us to directly evidence the exciton formation time, which depends on the density as expected from theory. We also denote the dominant contribution of excitons to the luminescence signal, and the lack of thermodynamical equilibrium at low densities.LOEQEcole Polytech Fed Lausanne, Inst Photon & Elect Quant, CH-1015 Lausanne, Switzerland. Szczytko, J, Ecole Polytech Fed Lausanne, Inst Photon & Elect Quant, CH-1015 Lausanne, Switzerland., ISI Document Delivery No.: 857PS, Times Cited: 5, Cited Reference Count: 27, Cited References: , AGRANOVICH VM, 1966, JETP LETT, V3, P223, CHATTERJEE S, 2004, PHYS REV LETT, V92, DAMEN TC, 1990, PHYS REV B, V42, P7434, DEVEAUD B, 1987, APPL PHYS LETT, V51, P828, DEVEAUD B, 1991, PHYS REV LETT, V67, P2355, DEVEAUD B, 1993, J PHYS IV, V3, P11, HANNEWALD K, 2000, PHYS REV B, V62, P4519, HAYES GR, 2002, PHYS STATUS SOLIDI A, V190, P637, HOYER W, 2003, PHYS REV B, V67, KAINDL RA, 2003, NATURE, V423, P734, KIRA M, 1998, PHYS REV LETT, V81, P3263, KIRA M, 1999, PHYS REV LETT, V82, P3544, LASHER G, 1964, PHYS REV, V133, A553, LEO K, 1988, PHYS REV B, V38, P1947, MATSUSUE T, 1987, APPL PHYS LETT, V50, P1429, MILLER DAB, 1982, APPL PHYS LETT, V41, P679, PHILLIPS RT, 1996, SOLID STATE COMMUN, V98, P287, PIERMAROCCHI C, 1996, PHYS REV B, V53, P15834, PIERMAROCCHI C, 1997, PHYS REV B, V55, P1333, RIDLEY BK, 1990, PHYS REV B, V41, P12190, ROBART D, 1995, SOLID STATE COMMUN, V95, P287, RUHLE WW, 1989, PHYS REV B, V40, P1756, SHAH J, 1996, SOLID STATE SCI, V115, P161, SZCZYTKO J, 2004, PHYS STATUS SOLIDI C, V1, P493, THILAGAM A, 1993, J LUMIN, V55, P11, WEISBUCH C, 1981, SOLID STATE COMMUN, V37, P219, YOON HW, 1996, PHYS REV B, V54, P2763, 13740
Pragmatic Case Studies as a Source of Unity in Applied Psychology
No full textTo unify or not to unify applied psychology: that is the question. In this article we review pendulum swings in the historical efforts to answer this question—from a comprehensive, positivist, “top-down,” deductive yes between the 1930s and the early 60s, to a postmodern no since then. A rationale and proposal for a limited, “bottom-up,” inductive yes in applied psychology is then presented, employing a case-based paradigm that integrates both positivist and postmodern themes and components. This paradigm is labeled “pragmatic psychology” and, its specific use of case studies, the “Pragmatic Case Study Method” (“PCS Method”). We call for the creation of peer-reviewed journal-databases of pragmatic case studies as a foundational source of unifying applied knowledge in our discipline. As one example, the potential of the PCS Method for unifying different angles of theoretical regard is illustrated in an area of applied psychology, psychotherapy, via the case of Mrs. B. The article then turns to the broader historical and epistemological arguments for the unifying nature of the PCS Method in both applied and basic psychology.Peer reviewe
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