Support of Rock Cuts at Washington-Dulles International Airport

Expansions at the Washington-Dulles International Airport since 1999 have required extensive vertical, open-cut rock excavations in Triassic age siltstone bedrock. These excavations have extended to depths of up to approximately 65 ft (20 m) adjacent to existing infrastructure for construction of new below-ground stations for the new Automated People Mover (APM) light rail system. The selection of design support pressures for the rock excavations was an important decision, balancing the projects’ risks and construction costs. At the center of this issue was the development of a geotechnical model of the rock mass and its primary failure mechanism. Thus, a comprehensive subsurface characterization was required. The rock mass characterization included observation and mapping of excavation faces, detailed logging of rock cores, use of optical and acoustic televiewer, testing of discontinuity samples for shear strength evaluation, groundwater monitoring, and inclinometer monitoring of supported faces. The televiewer data, combined with site observations, allowed for a more complete understanding of the engineering characteristics of the bedding plane and joint discontinuities within the siltstone rock mass. Based on the pattern of the predominant discontinuities, it was concluded that bedding planes dipping into the excavation at approximately 30 degrees intersecting near-vertical joints would present the greatest risk for rock cut failures. Extensive laboratory testing and field inspections at a variety of exposed cuts with varying bedding plane and joint orientations suggested that the potential for a large slide along a bedding plane was relatively low. This conclusion was based on observations of discontinuous clay seams of limited number, the first- and second-order roughness of joint and bedding plane surfaces, and the limited persistence of joint and bedding plane discontinuities. Previous design lateral pressures for permanent station walls had been based on an assumed potential failure model of a large, excavation-scale block failure. However, using the recent characterization data, the rock mass failure mechanism of a local joint- and bedding-controlled sliding block mechanism was considered more appropriate. The resulting design lateral pressure necessary to support a rock face using this mechanism and the shear strength of discontinuities and intact rock was significantly lower than the initial design values. Construction-phase observations and monitoring, which included detailed field mapping, automated instrumentation monitoring, and groundwater monitoring, have verified the rock characterization and design assumptions. The reduction in design pressures for the permanent below-grade walls for the APM station structures resulted in major cost savings for the projects now in design and construction. Based on the scale of future expansion plans at Dulles, the projected total cost savings resulting from the reduced design lateral rock pressures will be considerable

The Use of the Concept “Entitlement” in Management Literature: A Historical Review, Synthesis, and Discussion of Compensation Policy Implications

Individuals\u27 perceptions of what they are entitled to have long been regarded as an important area of debate. We examine the various uses of entitlement perceptions across fields to develop a typology that identifies two dimensions: employee entitlement perceptions and reciprocity in the employee–employer relationship. We discuss how our typology informs management practice. In particular, we describe the implications of our typology on employee reactions to different pay plans. Directions for future research are suggested

Investigation of photorefractive subharmonics in the absence of wavemixing

Using a new optical configuration free from the influence of photorefractive optical nonlinearity, we investigate the main characteristics of the spatial subharmonic K/2 excited in a Bi12SiO20 crystal by a light-intensity pattern with wave vector K and frequency O. It is shown that in a large region of intensity and applied electric field the optimum value O of the frequency corresponds to the conditions of parametric excitation of the weakly damped eigenmodes of the medium: the space-charge waves. The threshold and above-threshold characteristics of the subharmonic regime are in good agreement with the theory

Eigen modes for the problem of anomalous light transmission through subwavelength holes

We show that the wide-spread concept of optical eigen modes in lossless waveguide structures, which assumes the separation on propagating and evanescent modes, fails in the case of metal-dielectric structures, including photonic crystals. In addition to these modes, there is a sequence of new eigen-states with complex values of the propagation constant and non-vanishing circulating energy flow. The whole eigen-problem ceases to be hermitian because of changing sign of the optical dielectric constant. The new anomalous modes are shown to be of prime importance for the description of the anomalous light transmission through subwavelength holes.Comment: 5 pages, 4 figure

Orbital mechanism of the circular photogalvanic effect in quantum wells

It is shown that the free-carrier (Drude) absorption of circularly polarized radiation in quantum well structures leads to an electric current flow. The photocurrent reverses its direction upon switching the light helicity. A pure orbital mechanism of such a circular photogalvanic effect is proposed that is based on interference of different pathways contributing to the light absorption. Calculation shows that the magnitude of the helicity dependent photocurrent in $n$-doped quantum well structures corresponds to recent experimental observations.Comment: 5 pages, 2 figures, to be published in JETP Letter

Opto-Electronic Characterization of Three Dimensional Topological Insulators

We demonstrate that the terahertz/infrared radiation induced photogalvanic effect, which is sensitive to the surface symmetry and scattering details, can be applied to study the high frequency conductivity of the surface states in (Bi1-xSbx)2Te3 based three dimensional (3D) topological insulators (TI). In particular, measuring the polarization dependence of the photogalvanic current and scanning with a micrometre sized beam spot across the sample, provides access to (i) topographical inhomogeneity's in the electronic properties of the surface states and (ii) the local domain orientation. An important advantage of the proposed method is that it can be applied to study TIs at room temperature and even in materials with a high electron density of bulk carriers.Comment: 6 pages, 4 figure

Spin photocurrents and circular photon drag effect in (110)-grown quantum well structures

We report on the study of spin photocurrents in (110)-grown quantum well structures. Investigated effects comprise the circular photogalvanic effect and so far not observed circular photon drag effect. The experimental data can be described by an analytical expression derived from a phenomenological theory. A microscopic model of the circular photon drag effect is developed demonstrating that the generated current has spin dependent origin.Comment: 6 pages, 3 figure

Exact solution of the Bragg-diffraction problem in sillenites

A method for the exact solution of the Bragg-difrraction problem for a photorefractive grating in sillenite crystals based on Pauli matrices is proposed. For the two main optical configurations explicit analytical expressions are found for the diffraction efficiency and the polarization of the scattered wave. The exact solution is applied to a detailed analysis of a number of particular cases. For the known limiting cases there is agreement with the published results

Quantum kinetic theory of shift current electron pumping in semiconductors

We develop a theory of laser beam generation of shift currents in non-centrosymmetric semiconductors. The currents originate when the excited electrons transfer between different bands or scatter inside these bands, and asymmetrically shift their centers of mass in elementary cells. Quantum kinetic equations for hot-carrier distributions and expressions for the induced currents are derived by nonequilibrium Green functions. In applications, we simplify the approach to the Boltzmann limit and use it to model laser-excited GaAs in the presence of LO phonon scattering. The shift currents are calculated in a steady-state regime.Comment: 23 pages, 5 figures (Latex

Excitonic effects on the two-color coherent control of interband transitions in bulk semiconductors

Quantum interference between one- and two-photon absorption pathways allows coherent control of interband transitions in unbiased bulk semiconductors; carrier population, carrier spin polarization, photocurrent injection, and spin current injection may all be controlled. We extend the theory of these processes to include the electron-hole interaction. Our focus is on photon energies that excite carriers above the band edge, but close enough to it so that transition amplitudes based on low order expansions in $\mathbf{k}$ are applicable; both allowed-allowed and allowed-forbidden two-photon transition amplitudes are included. Analytic solutions are obtained using the effective mass theory of Wannier excitons; degenerate bands are accounted for, but envelope-hole coupling is neglected. We find a Coulomb enhancement of two-color coherent control process, and relate it to the Coulomb enhancements of one- and two-photon absorption. In addition, we find a frequency dependent phase shift in the dependence of photocurrent and spin current on the optical phases. The phase shift decreases monotonically from $\pi /2$ at the band edge to 0 over an energy range governed by the exciton binding energy. It is the difference between the partial wave phase shifts of the electron-hole envelope function reached by one- and two-photon pathways.Comment: 31 pages, 4 figures, to be published in Phys. Rev.