Simulator study of the effect of control-system time delays on the occurrence of pilot-induced oscillations and on pilot tracking performance with a space-shuttle-orbiter configuration

Using a six degree-of-freedom motion-base simulator, the effect of control-system time delays on the occurrence of pilot-induced oscillations (PIO's) on the vehicle handling qualities and on pilot tracking performance for a landing-approach configuration of the Space Shuttle orbiter was studied. A linearized math model was employed which represented a 300-knot orbiter with almost all time delays removed. Additional time delays were then inserted following the pilot's hand-controller signals. Only pitch and roll commands were used for vehicle control. The simulation employed an air to air tracking task as a means of emphasizing PIO tendencies. Two astronauts, two research pilots, and one simulation engineer served as test subjects. Results showed that PIO's occurred when the amount of added time delay approximated that existing for the orbiter configuration flown in the approach and landing tests. Increasing the amount of delay increased PIO occurrences and resulted in degraded tracking performance. Decreasing the amount of time delay eliminated the PIO's

Comparison of analytical predictions of longitudinal short period pilot-induced oscillations with results from a simulation study of the space shuttle orbiter

An analytical analysis of conditions producing pilot induced oscillations (PIO's) was made for the space shuttle orbiter in a landing approach configuration for the task of milling the elevation angle of the line of sight to a target vehicle. The analysis yielded a value of PIO frequency and a value for the amount of total system time delay (pilot + control system) that can be tolerated before instability results. Calculations were performed showing the effect of varying the range to the target and of varying the handling qualities of the orbiter vehicle. Analytical predictions were compared with simulation results obtained using a visual motion simulator

Simulator study of the effect of visual-motion time delays on pilot tracking performance with an audio side task

The effect of time delay was determined in the visual and motion cues in a flight simulator on pilot performance in tracking a target aircraft that was oscillating sinusoidally in altitude only. An audio side task was used to assure the subject was fully occupied at all times. The results indicate that, within the test grid employed, about the same acceptable time delay (250 msec) was obtained for a single aircraft (fighter type) by each of two subjects for both fixed-base and motion-base conditions. Acceptable time delay is defined as the largest amount of delay that can be inserted simultaneously into the visual and motion cues before performance degradation occurs. A statistical analysis of the data was made to establish this value of time delay. Audio side task provided quantitative data that documented the subject's work level

Investigation of Halogenated Components Formed from Chlorination of Natural Waters: Preliminary Studies

Chlorination of power plant cooling water is extensively used as a means of controlling biofouling. This practice presents the potential for formation of halogenated organic compounds hazardous to man and his environment. Accordingly, the organic composition resulting from the chlorination of natural waters (northern Olympic Penn1sula sea water and the Columbia River in Washington State} has been investigated. Nonpolar lipophilic organic halogens were extracted by passing large volumes of water over columns of XAD-2 macroreticular resins. Examination of ether extracts from the resin columns using capillary gas chromatography revealed the presence of halogenated methanes, as well as other electron-capturing components~ that were not found when unchlorinated water was sampled. Examination of the chlorinated water extracts using gas chromatography/mass spectrometry revealed complex mixtures which generally were not separable into individual components~ even when high efficiency WCOT capillary columns were used. The samples were separated into fractions of increasing polarity using a water-deactivated silica gel column. Fractions were thus obtained which were more amenable to GC/MS investigation. Haloforms were identified as the major halogenated product from chlorination of the waters studied. Other halogenated products were found at much lower concentrations

KASR: A Reliable and Practical Approach to Attack Surface Reduction of Commodity OS Kernels

Commodity OS kernels have broad attack surfaces due to the large code base and the numerous features such as device drivers. For a real-world use case (e.g., an Apache Server), many kernel services are unused and only a small amount of kernel code is used. Within the used code, a certain part is invoked only at runtime while the rest are executed at startup and/or shutdown phases in the kernel's lifetime run. In this paper, we propose a reliable and practical system, named KASR, which transparently reduces attack surfaces of commodity OS kernels at runtime without requiring their source code. The KASR system, residing in a trusted hypervisor, achieves the attack surface reduction through a two-step approach: (1) reliably depriving unused code of executable permissions, and (2) transparently segmenting used code and selectively activating them. We implement a prototype of KASR on Xen-4.8.2 hypervisor and evaluate its security effectiveness on Linux kernel-4.4.0-87-generic. Our evaluation shows that KASR reduces the kernel attack surface by 64% and trims off 40% of CVE vulnerabilities. Besides, KASR successfully detects and blocks all 6 real-world kernel rootkits. We measure its performance overhead with three benchmark tools (i.e., SPECINT, httperf and bonnie++). The experimental results indicate that KASR imposes less than 1% performance overhead (compared to an unmodified Xen hypervisor) on all the benchmarks.Comment: The work has been accepted at the 21st International Symposium on Research in Attacks, Intrusions, and Defenses 201

Oscillatory oblique stagnation-point flow toward a plane wall

Two-dimensional oscillatory oblique stagnation-point flow toward a plane wall is investigated. The problem is a eneralisation of the steady oblique stagnation-point flow examined by previous workers. Far from the wall, the flow is composed of an irrotational orthogonal stagnation-point flow with a time-periodic strength, a simple shear flow of constant vorticity, and a time-periodic uniform stream. An exact solution of the Navier-Stokes equations is sought for which the flow streamfunction depends linearly on the coordinate parallel to the wall. The problem formulation reduces to a coupled pair of partial differential equations in time and one spatial variable. The first equation describes the oscillatory orthogonal stagnation-point flow discussed by previous workers. The second equation, which couples to the first, describes the oblique component of the flow. A description of the flow velocity field, the instantaneous streamlines, and the particle paths is sought through numerical solutions of the governing equations and via asymptotic analysis

Cost and Benefit Analysis of Tomato Spotted Wilt Virus (TSWV) Management Technology in Georgia.

Recent trend depicts that tomatoes and tomatoes products rank 2nd most important vegetable crop in the United States after potatoes and potatoes products contributing 20 percent of total vegetable production. More-so, tomato is equally ranked 2nd in the United States in terms of production value, generating $1.3 billion after head lettuce that contributed$1.4 billion in the same time period. In 2006, 422,000 acres of tomatoes were planted in the United States. Tomato is equally an important economic crop in the state of Georgia. In 2008, it ranked 14th in the Georgia vegetable acreage as 3,985 acres were planted. It also ranked 6th in terms of farm gate value in the same time period generating $51.2 million. Thrips-vectored tomato spotted wilt virus (TSWV) is a serious disease capable of causing damages to the plant, fruits, quality and reducing yields drastically. Managing TSWV can be complex. For instance, metalized UV-mulch may significantly reduce TSWV, but delay tomato maturity, potentially affecting price and market window. Also, resistant tomato lines may eliminate damages due to TSWV, but could have negative horticultural attributes that standard TSWV-susceptible hybrids do not. TSWV can induce irregular ripening in fruit after packing, affecting post harvest costs. This study is aimed at providing the optimal return per unit of enterprise using cost and benefit estimates of the combination of available inputs used in the various management strategies. Thereafter, the result of the differentially developed techniques and risk-rated cost and benefit budgets will be used to determine which of the risk-rated thrips, TSWV and IPM decision criteria would provide superior pareto-optimal economic and financial benefit to tomato growersTomatoes production, Tomato Spotted Wilt Virus (TSWV), inputs, fixed cost, variable costs, profitability, cost and benefit., Agribusiness, Agricultural and Food Policy, Agricultural Finance, Crop Production/Industries, Environmental Economics and Policy, Farm Management, Financial Economics, Health Economics and Policy, Marketing, Production Economics, Productivity Analysis, Research and Development/Tech Change/Emerging Technologies, Risk and Uncertainty, Teaching/Communication/Extension/Profession,