73 research outputs found

    The Teaching Of Controversial Issues In Geography

    Get PDF
    A Geographical Education Magazine article.The cognitive approach appears to reign in most geography classrooms. The emotive and the psychic approaches receive only cursory attention. The result has been a lack of deeper understanding of the issues involved in a topic. This contributes to the partial or biased education of our students and we suspect it also contributes to poor results in the ‘O’ and ‘A’ level examinations. This paper presents points in favor of the emotive approach and describes how controversial issues can be tackled in the ‘O’ and ‘A’ level geography classrooms

    Von Humboldt and Ritter: Contributions to Geographical Methodology

    Get PDF
    A GEM article

    Selected aims in teaching Geography at the Junior Secondary Level in Zimbabwe

    Get PDF
    A GEM article on the aims of teaching geography at junior secondary school level.There are various factors that influence one’s thinking when it comes to the description of aims in teaching geography at school level. Firstly, there are changes in the curriculum at the secondary school level. These involve longer schooling periods in that all children proceed from form 1 to form 4; the growing complexity of our society; the earlier maturation of pupils and the demands that our education system should be more socialistic in outlook. These have had the effect of widening the aims of secondary school geography

    Generalized Fokker-Planck equation, Brownian motion, and ergodicity

    Full text link
    Microscopic theory of Brownian motion of a particle of mass MM in a bath of molecules of mass m≪Mm\ll M is considered beyond lowest order in the mass ratio m/Mm/M. The corresponding Langevin equation contains nonlinear corrections to the dissipative force, and the generalized Fokker-Planck equation involves derivatives of order higher than two. These equations are derived from first principles with coefficients expressed in terms of correlation functions of microscopic force on the particle. The coefficients are evaluated explicitly for a generalized Rayleigh model with a finite time of molecule-particle collisions. In the limit of a low-density bath, we recover the results obtained previously for a model with instantaneous binary collisions. In general case, the equations contain additional corrections, quadratic in bath density, originating from a finite collision time. These corrections survive to order (m/M)2(m/M)^2 and are found to make the stationary distribution non-Maxwellian. Some relevant numerical simulations are also presented

    Several small Josephson junctions in a Resonant Cavity: Deviation from the Dicke Model

    Full text link
    We have studied quantum-mechanically a system of several small identical Josephson junctions in a lossless single-mode cavity for different initial states, under conditions such that the system is at resonance. This system is analogous to a collection of identical atoms in a cavity, which is described under appropriate conditions by the Dicke model. We find that our system can be well approximated by a reduced Hamiltonian consisting of two levels per junction. The reduced Hamiltonian is similar to the Dicke Hamiltonian, but contains an additional term resembling a dipole-dipole interaction between the junctions. This extra term arises when states outside the degenerate group are included via degenerate second-order (L\"{o}wdin) perturbation theory. As in the Dicke model, we find that, when N junctions are present in the cavity, the oscillation frequency due to the junction-cavity interaction is enhanced by N\sqrt{N}. The corresponding decrease in the Rabi oscillation period may cause it to be smaller than the decoherence time due to dissipation, making these oscillations observable. Finally, we find that the frequency enhancement survives even if the junctions differ slightly from one another, as expected in a realistic system.Comment: 11 pages. To be published in Phys. Rev.

    Spontaneous emission and lifetime modification caused by an intense electromagnetic field

    Full text link
    We study the temporal evolution of a three-level system (such as an atom or a molecule), initially prepared in an excited state, bathed in a laser field tuned at the transition frequency of the other level. The features of the spontaneous emission are investigated and the lifetime of the initial state is evaluated: a Fermi "golden rule" still applies, but the on-shell matrix elements depend on the intensity of the laser field. In general, the lifetime is a decreasing function of the laser intensity. The phenomenon we discuss can be viewed as an "inverse" quantum Zeno effect and can be analyzed in terms of dressed states.Comment: 25 pages, 6 figure

    A new perturbative expansion of the time evolution operator associated with a quantum system

    Full text link
    A novel expansion of the evolution operator associated with a -- in general, time-dependent -- perturbed quantum Hamiltonian is presented. It is shown that it has a wide range of possible realizations that can be fitted according to computational convenience or to satisfy specific requirements. As a remarkable example, the quantum Hamiltonian describing a laser-driven trapped ion is studied in detail.Comment: 32 pages; modified version with examples of my previous paper quant-ph/0404056; to appear on the J. of Optics B: Quantum and Semiclassical Optics, Special Issue on 'Optics and Squeeze Transformations after Einstein

    Transport theory yields renormalization group equations

    Full text link
    We show that dissipative transport and renormalization can be described in a single theoretical framework. The appropriate mathematical tool is the Nakajima-Zwanzig projection technique. We illustrate our result in the case of interacting quantum gases, where we use the Nakajima-Zwanzig approach to investigate the renormalization group flow of the effective two-body interaction.Comment: 11 pages REVTeX, twocolumn, no figures; revised version with additional examples, to appear in Phys. Rev.
    • …
    corecore