Dynamic Job-shop Scheduling Program (DJSP) Analysis for Preventive Military Helicopter Maintenance System (PMS)

Republic of Korea Army(ROKA) has been founding new attack helicopter troops since last year by adopting US main attack helicopter, AH-64E Apache, and peripheral system like pilots and mechanics training systems and their organization. The AH-64E Apache is a major attack helicopter of the US Army and all of its systems are verified in terms of the effectiveness in real operations for several decades. However, ROKA still needs their own version of systems including tactics, template, and maintenance which are suitable for Korean terrain, climate, personnel, and so on. At least ROKA needs to have a chance to verify that the adopted system is working well with different circumstances, especially with a different maintenance system. As basic characteristics, routine maintenance and management are essential for accident prevention for a helicopter, there are specially formalized maintenance systems for every kind of helicopter respectively. It was established by a manufacturer in maintenance manuals and can be modified and integrated by users and operators. Apache also has its own maintenance schedule and system including 25-hour, 50-hour, 125-hour, and 250-hour maintenance and inspections which are implemented according to the operation hours. Those schedules are done by a task force or temporary maintenance team which is led by one or two inspectors and supported by 3~4 mechanics. Maintenance troops restrict the number of aircraft to get in the process by managing the flight hours considering the limit of manpower and equipment so that the operation rate stays above at least 80%. It is important to stipulate their capacity in need and max capacity with given personnel and facility for newly founding military troops. Especially since ROKA aviation branch is applying a more strict maintenance process, it might cause insufficiency of resources if organized by same template and procedure with the US Army. The goal of this study is to verify if existing personnel organization is affordable for new maintenance system of AH-64 Apache helicopters. As a further step ahead, this research found the most critical personnel pool and their relationship by sensitivity analysis. This research specified actual maintenance procedure and restrictions on computer and simulated virtually. During the repetition of the test, existing organization was found inadequate to satisfy all restrictions and requirements. Test pilot and inspector pool are critical to secure the successful maintenance support and to prepare for contingency. Also, there were interesting relationships between the mechanics groups. They are in supplemental relationships with each other because of the condition of one pool affects the other

Master of Science

thesisTo get reliable location and time information for specific objects, the U. S. Department of Defense (DOD) developed the Global Positioning System (GPS). In spite of its enormous advantages, it encounters limitations in GPS-denied or compromised environments. To address these limitations, Inertial Motion Units (IMUs), consisting of gyroscopic devices, have been substituted for GPS in these harsh environments. However, they are also limited by bias, which increases error growth by integrating signals. This research project allows for tracking a pedestrian in GPS-limited environments by adding another portable localization system to the IMU, the Ground Reaction Sensor Cluster (GRSC). The GRSC measures the precise velocity of an object by applying zero velocity updating (ZUPTing) events, and seeks to compensate for the limitations of the IMU to give the precise position of the pedestrian. This project addresses the testing environment developed to evaluate the reliability of a shoe-mounted GRSC. This environment consisted of both physical measurements and analysis of the data. Through this testing, we check whether this device would meet the Defense Advanced Research Projects Agency's (DARPA) requirement to resolve the zero-velocity error biases of 4000, 250 and 20 um/s with a typical 0.3s midstance measurement time. To ensure an adequate amount of data, the process was automated and run for several different cycle lengths

High-speed and high-SNR photoacoustic microscopy based on a galvanometer mirror in non-conducting liquid

Optical-resolution photoacoustic microscopy (OR-PAM), a promising microscopic imaging technique with high ultrasound resolution and superior optical sensitivity, can provide anatomical, functional, and molecular information at scales ranging from the microvasculature to single red blood cells. In particular, real-time OR-PAM imaging with a high signal-to-noise ratio (SNR) is a prerequisite for widespread use in preclinical and clinical applications. Although several technical approaches have been pursued to simultaneously improve the imaging speed and SNR of OR-PAM, they are bulky, complex, not sensitive, and/or not actually real-time. In this paper, we demonstrate a simple and novel OR-PAM technique which is based on a typical galvanometer immersed in non-conducting liquid. Using an opto-ultrasound combiner, this OR-PAM system achieves a high SNR and fast imaging speed. It takes only 2 seconds to acquire a volumetric image with a wide field of view (FOV) of 4 x 8 mm(2) along the X and Y axes, respectively. The measured lateral and axial resolutions are 6.0 and 37.7 mu m, respectively. Finally, as a demonstration of the system's capability, we successfully imaged the microvasculature in a mouse ear in vivo. Our new method will contribute substantially to the popularization and commercialization of OR-PAM in various preclinical and clinical applications.11Ysciescopu

2D Genus Topology of 21-cm differential brightness temperature during cosmic radiation

A novel method to characterize the topology of the early-universe intergalactic medium during the epoch of cosmic reionization is presented. The 21-cm radiation background from high redshift is analyzed through calculation of the 2-dimensional (2D) genus. The radiative transfer of hydrogen-ionizing photons and ionization-rate equations are calculated in a suite of numerical simulations under various input parameters. The 2D genus is calculated from the mock 21-cm images of high-redshift universe. We construct the 2D genus curve by varying the threshold differential brightness temperature, and compare this to the 2D genus curve of the underlying density field. We find that (1) the 2D genus curve reflects the evolutionary track of cosmic reionization and (2) the 2D genus curve can discriminate between certain reionization scenarios and thus indirectly probe the properties of radiation-sources. Choosing the right beam shape of a radio antenna is found crucial for this analysis. Square Kilometer Array (SKA) is found to be a suitable apparatus for this analysis in terms of sensitivity, even though some deterioration of the data for this purpose is unavoidable under the planned size of the antenna core

The impact of inhomogeneous subgrid clumping on cosmic reionization

Cosmic reionization was driven by the imbalance between early sources and sinks of ionizing radiation, both of which were dominated by small-scale structure and are thus usually treated in cosmological reionization simulations by subgrid modelling. The recombination rate of intergalactic hydrogen is customarily boosted by a subgrid clumping factor, {\left/\left^2}, which corrects for unresolved fluctuations in gas density ${n}$ on scales below the grid-spacing of coarse-grained simulations. We investigate in detail the impact of this inhomogeneous subgrid clumping on reionization and its observables, as follows: (1) Previous attempts generally underestimated the clumping factor because of insufficient mass resolution. We perform a high-resolution $N$-body simulation that resolves haloes down to the pre-reionization Jeans mass to derive the time-dependent, spatially-varying local clumping factor and a fitting formula for its correlation with local overdensity. (2) We then perform a large-scale $N$-body and radiative transfer simulation that accounts for this inhomogeneous subgrid clumping by applying this clumping factor-overdensity correlation. Boosting recombination significantly slows the expansion of ionized regions, which delays completion of reionization and suppresses 21 cm power spectra on large scales in the later stages of reionization. (3) We also consider a simplified prescription in which the globally-averaged, time-evolving clumping factor from the same high-resolution $N$-body simulation is applied uniformly to all cells in the reionization simulation, instead. Observables computed with this model agree fairly well with those from the inhomogeneous clumping model, e.g. predicting 21 cm power spectra to within 20% error, suggesting it may be a useful approximation.Comment: 23 pages, 16 figures, 4 tables. MNRAS accepte