Fast high--voltage amplifiers for driving electro-optic modulators

We describe five high-voltage (60 to 550V peak to peak), high-speed (1-300ns rise time; 1.3-300MHz bandwidth) linear amplifiers for driving capacitive or resistive loads such as electro-optic modulators. The amplifiers use bipolar transistors in various topologies. Two use electron tubes to overcome the speed limitations of high-voltage semiconductors. All amplifiers have been built. Measured performance data is given for each.Comment: 9pages, 6figures, 6tables, to appear in Review of Scientific Instrument

A simple model of price formation

A simple Ising spin model which can describe the mechanism of price formation in financial markets is proposed. In contrast to other agent-based models, the influence does not flow inward from the surrounding neighbors to the center site, but spreads outward from the center to the neighbors. The model thus describes the spread of opinions among traders. It is shown via standard Monte Carlo simulations that very simple rules lead to dynamics that duplicate those of asset prices.Comment: Version 2: 4 pages, 4 figures; added more stringent statistical analysis; to appear in Int. J. Modern Physics C, Vol. 13, No. 1 (2002

Open shells in reduced-density-matrix-functional theory

Reduced-density-matrix-functional theory is applied to open-shell systems. We introduce a spin-restricted formulation by appropriately expressing approximate correlation-energy functionals in terms of spin-dependent occupation numbers and spin-independent natural orbitals. We demonstrate that the additional constraint of total-spin conservation is indispensable for the proper treatment of open-shell systems. The formalism is applied to the first-row open-shell atoms. The obtained ground-state energies are in very good agreement with the exact values as well as other state of the art quantum chemistry calculationsComment: 4 pages, 2 figures, corrected typo

Competing spin transfer and dissipation at Co/Cu(001) interfaces on femtosecond timescales

By combining interface-sensitive non-linear magneto-optical experiments with femtosecond time resolution and ab-initio time-dependent density functional theory, we show that optically excited spin dynamics at Co/Cu(001) interfaces proceeds via spin-dependent charge transfer and backtransfer between Co and Cu. This ultrafast spin transfer competes with dissipation of spin angular momentum mediated by spin-orbit coupling already on sub 100 fs timescales. We thereby identify the fundamental microscopic processes during laser-induced spin transfer at a model interface for technologically relevant ferromagnetic heterostructures.Comment: 5 pages, 4 figure

Migration in far West Nepal. Challenging migration categories and theoretical lenses

In this reply to Ronald Skeldon’s comment on their article, “Migration in Far West Nepal” (Critical Asian Studies 43 (1) 2011), the authors stress the need to overcome the categorical dichotomy between “international” and “internal” migration by thoroughly considering the conditions and characteristics different types of cross-border regimes encompass for migrants. They furthermore argue that choosing the “right” theoretical approach or conceptual framework depends on the kinds of research questions that need to be answered. By understanding migration as a social practice, the authors favor a multi-dimensional approach to migration, one that does not place economic motives over others. Ultimately, they call for a reconciliation of different—competing—perspectives on migration

COMPLETE SOLUTION OF THE XXZ-MODEL ON FINITE RINGS. DYNAMICAL STRUCTURE FACTORS AT ZERO TEMPERATURE.

The finite size effects of the dynamical structure factors in the XXZ-model are studied in the euclidean time $(\tau)$-representation. Away from the critical momentum $p=\pi$ finite size effects turn out to be small except for the large $\tau$ limit. The large finite size effects at the critical momentum $p=\pi$ signal the emergence of infrared singularities in the spectral $(\omega)$-representation of the dynamical structure factors.Comment: PostScript file with 12 pages + 11 figures uuencoded compresse

Propagação do cupuaçuzeiro.

bitstream/item/18771/1/com.tec.116.pd

Níveis de tolerância e letal de umidade em sementes de pupunheira, Bactris gasipaes.

Sementes de pupunheira (Bactris gasipaes Kunth) foram submetidas a dessecamento, em ambiente com ar condicionado (23 mais ou menos 1oC e umidade relativa do ar de 72 mais ou menos 5%), com o objetivo de determinar os níveis de tolerância e letal de umidade, assim como verificar as implica coes do dessecamento sobre o tempo médio e a uniformidade de germinação. A exposição das sementes, nesse ambiente, durante 0 (testemunha), 24, 48, 72, 96, 120 e 168 horas, possibilitou a obtenção dos seguintes graus de umidade: 48,0%; 36,8%; 30,9%; 22,7%; 20,2%; 15,8% e 12,6%, respectivamente. Imediatamente após cada período de secagem, as sementes foram semeadas em substrato de areia e serragem, misturadas na proporção volumétrica de 1:1. Os testes de germinação foram conduzidos nas condições de temperatura ambiente (26, 6oC, em media), com quatro repetições de 50 sementes e tiveram a duração de 120 dias

Nocturnal air, road, and rail traffic noise and daytime cognitive performance and annoyance

Various studies indicate that at the same noise level and during the daytime, annoyance increases in the order of rail, road, and aircraft noise. The present study investigates if the same ranking can be found for annoyance to nocturnal exposure and next day cognitive performance. Annoyance ratings and performance change during combined noise exposure were also tested. In the laboratory 72 participants were exposed to air, road, or rail traffic noise and all combinations. The number of noise events and LAS,eq were kept constant. Each morning noise annoyance questionnaires and performance tasks were administered. Aircraft noise annoyance ranked first followed by railway and road noise. A possible explanation is the longer duration of aircraft noise events used in this study compared to road and railway noise events. In contrast to road and rail traffic, aircraft noise annoyance was higher after nights with combined exposure. Pooled noise exposure data showed small but significant impairments in reaction times (6 ms) compared to nights without noise. The noise sources did not have a differential impact on performance. Combined exposure to multiple traffic noise sources did not induce stronger impairments than a single noise source. This was reflected also in low workload ratings