Pilot workload and fatigue: A critical survey of concepts and assessment techniques

The principal unresolved issues in conceptualizing and measuring pilot workload and fatigue are discussed. These issues are seen as limiting the development of more useful working concepts and techniques and their application to systems engineering and management activities. A conceptual analysis of pilot workload and fatigue, an overview and critique of approaches to the assessment of these phenomena, and a discussion of current trends in the management of unwanted workload and fatigue effects are presented. Refinements and innovations in assessment methods are recommended for enhancing the practical significance of workload and fatigue studies

Simulator evaluation of display concepts for pilot monitoring and control of space shuttle approach and landing. Phase 2: Manual flight control

A study of the display requirements for final approach management of the space shuttle orbiter vehicle is presented. An experimental display concept, providing a more direct, pictorial representation of the vehicle's movement relative to the selected approach path and aiming points, was developed and assessed as an aid to manual flight path control. Both head-up, windshield projections and head-down, panel mounted presentations of the experimental display were evaluated in a series of simulated orbiter approach sequence. Data obtained indicate that the experimental display would enable orbiter pilots to exercise greater flexibility in implementing alternative final approach control strategies. Touchdown position and airspeed dispersion criteria were satisfied on 91 percent of the approach sequences, representing various profile and wind effect conditions. Flight path control and airspeed management satisfied operationally-relevant criteria for the two-segment, power-off orbiter approach and were consistently more accurate and less variable when the full set of experimental display elements was available to the pilot. Approach control tended to be more precise when the head-up display was used; however, the data also indicate that the head-down display would provide adequate support for the manual control task

Improved display support for flight management during low visibility approach and landing. A simulator evaluation of an ILS-independent runway perspective display Final report

Low visibility approach and landing simulation for jet transport

Specific Plateaus of the Quantum Hall Effect Induced by an Applied Bias

The spectrum and the eigenstates of a finite 2D tight-binding electronic system, with Dirichlet boundary conditions, in magnetic field and external linear potential are studied. The eigenstates show an equipotential character and may cross the plaquette in the direction perpendicular to the electric field. When leads are added to the plaquette, the channels carrying the current may be shortcut by equipotentials, resulting in additional plateaus situated inbetween the usual IQHE plateaus. This idea is confirmed by a numerical calculation within the four-terminal Landauer-B\"{u}ttiker approach.Comment: 9 pages, revtex, 2 gif figures and 5 postscript figure

Stochastic Yield Catastrophes and Robustness in Self-Assembly

A guiding principle in self-assembly is that, for high production yield, nucleation of structures must be significantly slower than their growth. However, details of the mechanism that impedes nucleation are broadly considered irrelevant. Here, we analyze self-assembly into finite-sized target structures employing mathematical modeling. We investigate two key scenarios to delay nucleation: (i) by introducing a slow activation step for the assembling constituents and, (ii) by decreasing the dimerization rate. These scenarios have widely different characteristics. While the dimerization scenario exhibits robust behavior, the activation scenario is highly sensitive to demographic fluctuations. These demographic fluctuations ultimately disfavor growth compared to nucleation and can suppress yield completely. The occurrence of this stochastic yield catastrophe does not depend on model details but is generic as soon as number fluctuations between constituents are taken into account. On a broader perspective, our results reveal that stochasticity is an important limiting factor for self-assembly and that the specific implementation of the nucleation process plays a significant role in determining the yield

Anomalous dephasing of bosonic excitons interacting with phonons in the vicinity of the Bose-Einstein condensation

The dephasing and relaxation kinetics of bosonic excitons interacting with a thermal bath of acoustic phonons is studied after coherent pulse excitation. The kinetics of the induced excitonic polarization is calculated within Markovian equations both for subcritical and supercritical excitation with respect to a Bose-Einstein condensation (BEC). For excited densities n below the critical density n_c, an exponential polarization decay is obtained, which is characterized by a dephasing rate G=1/T_2. This dephasing rate due to phonon scattering shows a pronounced exciton-density dependence in the vicinity of the phase transition. It is well described by the power law G (n-n_c)^2 that can be understood by linearization of the equations around the equilibrium solution. Above the critical density we get a non-exponential relaxation to the final condensate value p^0 with |p(t)|-|p^0| ~1/t that holds for all densities. Furthermore we include the full self-consistent Hartree-Fock-Bogoliubov (HFB) terms due to the exciton-exciton interaction and the kinetics of the anomalous functions F_k= . The collision terms are analyzed and an approximation is used which is consistent with the existence of BEC. The inclusion of the coherent x-x interaction does not change the dephasing laws. The anomalous function F_k exhibits a clear threshold behaviour at the critical density.Comment: European Physical Journal B (in print

Applications of thermal energy storage in the cement industry

In the manufacture of cement, literally trillions of Btu's are rejected to the environment each year. The purpose of this feasibility study program was to determine whether thermal energy storage could be used to conserve or allow alternative uses of this rejected energy. This study identifies and quantifies the sources of rejected energy in the cement manufacturing process, established use of this energy, investigates various storage system concepts, and selects energy conservation systems for further study. Thermal performance and economic analyses are performed on candidate storage systems for four typical cement plants representing various methods of manufacturing cement. Through the use of thermal energy storage in conjunction with waste heat electric power generation units, an estimated 2.4 x 10 to the 13th power Btu/year, or an equivalent on investment of the proposed systems are an incentive for further development

Parvovirus B19 infection in pediatric transplant patients

Evidence of recent parvovirus virus infection (as determined by the presence of a positive IgM antibody titer) without other identified causes of anemia was found in 5 of 26 pediatric solid-organ transplant recipients evaluated for moderate-to-severe anemia between June 1990 and July 1991. Anemia tended to be chronic (median duration of anemia at the time of diagnosis was 12 weeks) and was associated with normal red blood cell indices in the absence of reticulocytes. The median age of the children at the time of presentation with anemia due to parvovirus was 1.8 years at a median time of 8 months after transplantation. Four of the 5 children were treated with i.v. immunoglobulin because of persistance of anemia requiring blood transfusions. A response characterized by an increase in reticulocyte count and normalization of hemoglobin was seen in each of these patients 2-4 weeks after treatment. The remaining patient experienced a spontaneous recovery from her anemia. Parvovirus infection should be included in the differential diagnosis of solid-organ transplant recipients presenting with severe anemia associated with low or absent reticulocytes