Effective space utilization is an important consideration in logistics systems and is especially important in dense storage environments. Dense storage systems provide high-space utilization; however, because not all items are immediately accessible, storage and retrieval operations often require shifting of other stored items in order to access the desired item, which results in item location uncertainty when asset tracking is insufficient. Given an initial certainty in item location, we use Markovian principles to quantify the growth of uncertainty as a function of retrieval requests and discover that the steady state probability distribution for any communicating class of storage locations approaches uniform. Using this result, an expected search time model is developed and applied to the systems analyzed. We also develop metrics that quantify and characterize uncertainty in item location to aid in understanding the nature of that uncertainty. By incorporating uncertainty into our logistics model and conducting numerical experiments, we gain valuable insights into the uncertainty problem such as the benefit of multiple item copies in reducing expected search time and the varied response to different retrieval policies in otherwise identical systems.

Most of the physically realizable optical sources are radiating in a random manner given the random nature of the radiation of a large number of atoms that constitute the source. Besides, a lot of natural and synthetic materials are fluctuating randomly. Hence, the optical fields that one encounters, in most of the applications are fluctuating and must be treated using random or stochastic functions. Within the framework of the scalar-coherence theory, one can describe changes of the properties of any stochastic field such as the spectral density and the spectral degree of coherence on propagation in any linear medium, deterministic or random. One of the frequently encountered random media is the atmospheric turbulence, where the fluctuating refractive index of such medium severely degrades any signal propagating through it; especially it causes intensity fades of the signal. The usage of stochastic beams at the transmitter instead of deterministic ones has been suggested sometime ago to suppress the severe effects of intensity fluctuations caused by the atmospheric turbulence. In this dissertation, we study the usage of partially coherent beams in long path propagation schemes through turbulent atmosphere such as one frequently encounters in remote sensing, in the use of communication systems, and in guiding. Also the used detection scheme at the receiver is important to quantify the received signal efficiently, hence we compare the performance of incoherent (direct) detection versus coherent (heterodyne) detection upon the use of either one of them at the receiver of the communication system of beams propagating in turbulent atmosphere and namely we evaluate the signal-to-noise-ratio (SNR) for each case. The scalar-coherence theory ignored the vector nature of stochastic fields, which should be taken into account for some applications such as the ones that depend on the change of the polarization of the field. Recently generalization for the scalar-coherence theory including the vector aspects of the stochastic beams has been formulated and it is well-known as the unified theory of coherence and polarization of stochastic beams. The use of the unified theory of coherence and polarization makes it possible to study both the coherence properties and the polarization properties of stochastic electromagnetic beams on propagation in any linear media. The central quantity in this theory is a 2 × 2 matrix that describes the statistical ensemble of any stochastic electromagnetic beam in the space-frequency domain or its Fourier transform in the space-time domain. In this dissertation we derive the conditions that the cross-spectral density matrix of a so-called planar, secondary, electromagnetic Gaussian Schell-model source has to satisfy in order to generate a beam propagating in vacuum. Also based on the unified-theory of coherence and polarization we investigate the subtle relationship between coherence and polarization under general circumstances. Besides we show the effects of turbulent atmosphere on the degree of polarization and the polarization state of a partially coherent electromagnetic beam, which propagates through it and we compare with the propagation in vacuum. The detection of the optical signals is important; hence it affects the fidelity of the communication system. In this dissertation we present a general analysis for the optical heterodyne detection of stochastic electromagnetic beams. We derive an expression for the SNR when two stochastic electromagnetic beams are mixed coherently on a detector surface in terms of the space-time domain representation of the beams, the beam coherence polarization matrices. We evaluate also the heterodyne efficiency of a heterodyne detection system for stochastic beams propagating in vacuum and we discuss the dependence of the heterodyne efficiency of the detection process on the changes in the beam parameters as the beam propagates in free space.

By nature discrete solitons represent self-trapped wavepackets in nonlinear periodic structures and result from the interplay between lattice diffraction (or dispersion) and material nonlinearity. In optics, this class of self-localized states has been successfully observed in both one-and two-dimensional nonlinear waveguide arrays. In recent years such lattice structures have been implemented or induced in a variety of material systems including those with cubic (Kerr), quadratic, photorefractive, and liquid-crystal nonlinearities. In all cases the underlying periodicity or discreteness leads to new families of optical solitons that have no counterpart whatsoever in continuous systems. In the first part of this dissertation, a theoretical investigation of linear and nonlinear optical wave propagation in semi-infinite waveguide arrays is presented. In particular, the properties and the stability of surface solitons at the edge of Kerr (AlGaAs) and quadratic (LiNbO3) lattices are examined. Hetero-structures of two dissimilar semi-infinite arrays are also considered. The existence of hybrid solitons in these latter types of structures is demonstrated. Rabi-type optical transitions in z-modulated waveguide arrays are theoretically demonstrated. The corresponding coupled mode equations, that govern the energy oscillations between two different transmission bands, are derived. The results are compared with direct beam propagation simulations and are found to be in excellent agreement with coupled mode theory formulations. In the second part of this thesis, the concept of parity-time-symmetry is introduced in the context of optics. More specifically, periodic potentials associated with PT-symmetric Hamiltonians are numerically explored. These new optical structures are found to exhibit surprising characteristics. These include the possibility of abrupt phase transitions, band merging, non-orthogonality, non-reciprocity, double refraction, secondary emissions, as well as power oscillations. Even though gain/loss is present in this class of periodic potentials, the propagation eigenvalues are entirely real. This is a direct outcome of the PT-symmetry. Finally, discrete solitons in PT-symmetric optical lattices are examined in detail.

京都大学 / 新制・論文博士 / 博士(医学) / 乙第13525号 / 論医博第2271号 / 新制||医||1062(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 井上 治久, 教授 大森 孝一, 教授 古川 壽亮 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

It is reasonable to assume that an aircraft might experience some in-flight discrete source damage caused by various incidents. It is, thus, necessary to evaluate the impact of such damage on the performance of the aircraft. This study is focused on evaluating the effect of a simple discrete damage in an aircraft wing on its static and dynamic response. The damaged wing is modeled by a thin-walled beam with a longitudinal crack the response of which can be obtained analytically. As uncertainties are present in the location and size of the crack as well as in the applied loads, their effects are incorporated into the framework consisting of structural response, crack propagation and aeroelasticity. The first objective of this study is to examine the effect of damage represented by a crack on the wing flexibility that influences its deformation and aero-elastic divergence characteristics. To study this, the thin-walled beam is modeled by Benscoter thin-walled beam theory combined with Gunnlaugsson and Pedersen compatibility conditions to accurately account for the discontinuity at the interface of the cracked and uncracked beam segments. Instead of conducting a detailed finite element analysis, the solution is obtained in an exact sense for general distributed loads representing the wind pressure effects. This analytical approach is shown to provide very accurate values for the global beam response compared with the detailed finite element shell analysis. This analytical solution is, then, used to study the beam response probabilistically. The crack location and size are assumed to be uncertain and are, thus, characterized by random variable. For a specified limit state, the probability of failure can be conveniently calculated by the first order second moment analysis using the safety index approach. The same analytical solution is also used to study the aero-elastic divergence characteristics of a wing, the inner structure of which is represented by a thin-walled beam with a crack of uncertain size and position along the beam. The second objective of this study is to examine the time growth of a crack under dynamic gust type of loading to which a wing is likely to be exposed during flight. Damage propagating during operation further deteriorates the safety of the aircraft and it is necessary to study its time growth so that its impact on the performance can be evaluated before it reaches its unstable state. The proposed framework for the crack growth analysis is based on classical fracture mechanics where the remaining flight time is obtained by Monte Carlo simulation in which various uncertainties are taken into account. To obtain equivalent cyclic loading required for crack growth analysis, random vibration analysis of the thin-walled beam is conducted for stochastic wind load defined by a gust load spectral density function. The probability of failure represented by the crack size approaching the critical crack size within the flight duration or the remaining flight time before a crack reaches its limiting value are obtained. This study with a simple representation of a wing and damage is anticipated to provide initial guidance for future studies to examine the impact of discrete source damage on the in-flight performance of the aircrafts, with the ultimate goal of minimizing the adverse effect and enhancing the safety of aircrafts experiencing damage. / Ph. D.

In this study, the properties of the reflected paths and scattering phenomena were investigated in the LMDS band (28 GHz). We used the newly developed sampling swept time delay short pulse (SSTDSP) sounder to collect field data in certain locations on the Virginia Tech campus. The sounder collected the channel impulse response analog waveform, sampled, digitized and reconstructed it. The stored data were used to produce the power delay profile and other channel parameters. In particular, we collected scattered and reflected data regarding the channel response with different incident angle and distance set-ups from brick and limestone walls. We used the reflected pulse width and maximum excess delay derived from each power delay profile to analyze the rough surface scattering phenomena. We found that limestone and brick walls exhibited some diffuse scattering. The reflected pulse of a limestone wall had more maximum excess delay spread than did a brick wall at -15dB power threshold. The mean maximum excess delay for the reflected pulse of the limestone wall measurement set-ups was more than two times that of the brick wall. With equal transmitter and receiver distances to the wall, we found that as the incident angle increased, the maximum excess delay decreased but the perpendicular reflection coefficient increased. It is recommended that for future study, a second generation SSTDSP sounder will replicate the measurement with larger distance and angle set-ups as well as in non-line-of-sight areas. / Master of Science

This thesis takes the reader through an overview of issues pertinent to Local Multi-point Distribution Services (LMDS). The reader will first learn what LMDS is and then review the system architectures that are made available for LMDS technologies. After summarizing the basics of LMDS, we will compare it with some competing technologies. The reader will then be guided through the aspects of millimeter (mm) wave radio link design. This should be a good lead into the experiment section, since it is suspected that the reader would want to be aware of what design techniques are involved in mm-wave radio link design and what issues may pose potential problems and how they may be mitigated. Of the potential problems posed in the mm-wave radio link design section, one will be further investigated experimentally. This is the investigation of the effect of vegetation on the magnitude, phase and error vector magnitude (EVM) performance of an LMDS channel. The motivation for this experiment came from the review earlier work, which showed an unexpected relationship between carrier to noise ratio (C/N) and bit error rate BER. / Master of Science

This decade will hopefully see the first human stepping on the Martian soil. Thus, supporting and enhancing the life quality of a future crew should be the driving theme for accomplishing manned missions on Mars. In this regard, an on-demand, ubiquitous, reliable, wideband, and low-latency connectivity seems of vital importance, both for in-situ and deep-space communications. Hence, this PhD dissertation aims to introduce innovation on this multi-faceted topic, to propose a new set of solutions which we refer to as Next Generation Communications on Mars (NGC-M). First, we discuss through extensive simulations the viability of an Extraterrestrial Long Term Evolution (E-LTE) porting, where a lander and a rover are re-allocated to compose a wireless local mobile network as the base station (BS) and user equipment (UE), respectively. Next, in order to model realistic Martian channels for further solid evaluations, we present a study on large and small-scale phenomena through a three-dimensional (3D) ray-tracing algorithm executed over 3D tile-based rendering of high-resolution Digital Elevation Model (DEM) of the ``Red Planet" surface. Then, we formulate a framework for the design of heterogeneous ground-to-space multi-layered (3D) networks implementing Cloud Radio Access Networks (C-RAN) for ``Towards 6G" Martian connectivity. The results will spread from simulations of the so-called splitting options, for the virtualization of baseband functionalities on non-dedicated hardware, to end-to-end (E2E) network emulations and on-hardware assessments. Finally, a decode-and-forward (DF) optical wireless multi-relay network (OWmRN), based on satellites orbiting the Lagrangian points (LPs), will be proposed for wideband exchanges of data between Mars and Earth. Data rate over time will be measured with respect to the selected shortest-path for relaying. The analysis of the various techniques, performed in a holistic and systemic view, focuses on viability and performance, taking into account trade-offs and constraints inherent to the unusual and challenging Martian application environment.

The safe and efficient propagation of the Deflagration to Detonation Transition (DDT) is a topic that has been researched for many years due to its applications in Aerospace and Mechanical Engineering. DDT is when fire caused by the burning of fuel is accelerated to the upper CJ point on the Rankine Hugoniot curve due to instabilities in the flame and the turbulence caused by these instabilities. The complex flame dynamics that go along with DDT have ensured that the process is yet to be fully understood and defined. This research will work towards observing the early stages of burning hydrogen-air mixtures in DDT conditions in order to better understand the processes that cause DDT. The research will also involve the testing of multiple different equivalence ratios of hydrogen known to undergo DDT. This research will assist in making places that store reactive gasses such as hydrogen safer by searching for the method of DDT formation and ways to prevent it. This research will also allow for safer commercial use of DDT in Detonation Based Engines. The research was tested in a secure facility and observed the first four inches of ignition and deflagration using schlieren and chemiluminescence imaging techniques. Through the research, it was found that flames at higher equivalence ratios tend to be longer, more top-biased, and have more instabilities than flames of lower equivalence ratios, better preparing them for DDT. This study will be elaborated on in future research using a variety of different fuels to solidify the findings of the research performed and to assist in the ability to innovate using DDT.

<p> A method for the measurement of the microwave conductivity of a semiconductor subjected to a high electric field is described, which provides for varying angles between the microwave and applied electric field vectors. The results of measurements on 10 ohm-em. n-type germanium at 9.522 GHz with applied electric fields up to 3KV/cm are given. </p> <p> The measurements show that the microwave conductivity is controlled by the differential carrier mobility (∂V/∂E) for the condition of microwave and applied electric field vectors parallel. For the case of the fields at right angles the microwave conductivity is controlled by a carrier mobility intermediate between the d. c. mobility (v/B) and the differential mobility (∂V/∂E). </p> <p> Theoretical expressions for the performance of a proposed "Hot Electron Microwave Rotator" are developed. </p> / Thesis / Master of Engineering (MEngr)