In distributed systems, if a hardware fault corrupts the state of a process, this error might propagate as a corrupt message and contaminate other processes in the system, causing severe outages. Recently, state corruptions of this nature have been observed surprisingly often in large computer populations, e.g., in large-scale data centers. Moreover, since the resilience of processors is expected to decline in the near future, the likelihood of state corruptions will increase even further. In this work, we argue that preventing the propagation of state corruption should be a first-class requirement for large-scale fault-tolerant distributed systems. In particular, we propose developers to target error isolation, the property in which each correct process ignores any corrupt message it receives. Typically, a process cannot decide whether a received message is corrupt or not. Therefore, we introduce hardening as a class of principled approaches to implement error isolation in distributed systems. Hardening techniques are (semi-)automatic transformations that enforce that each process appends an evidence of good behavior in the form of error codes to all messages it sends. The techniques “virtualize” state corruptions into more benign failures such as crashes and message omissions: if a faulty process fails to detect its state corruption and abort, then hardening guarantees that any corrupt message the process sends has invalid error codes. Correct processes can then inspect received messages and drop them in case they are corrupt. With this dissertation, we contribute theoretically and practically to the state of the art in fault-tolerant distributed systems. To show that hardening is possible, we design, formalize, and prove correct different hardening techniques that enable existing crash-tolerant designs to handle state corruption with minimal developer intervention. To show that hardening is practical, we implement and evaluate these techniques, analyzing their effect on the system performance and their ability to detect state corruptions in practice.

The algebra of SU(2) is ubiquitous in physics, applicable both to the atomic spin states and the polarisation states of light. The method developed by Majorana and Schwinger to represent pure, symmetric spin-states of arbitrary value as a product of spin-1/2 states is a powerful tool that allows for a great conceptual and practical simplification. Foremost, it allows the representation of a qudit on the same geometry as a qubit, i.e., the Bloch sphere. An experimental implementation of the Majorana representation in the realm of quantum optics is presented. The technique allows the projection of arbitrary quantum states from a coherent state input. It is also shown that the method can be used to synthesise arbitrary interference patterns with unit visibility, and without resorting to quantum resources. In this context, it is argued that neither the shape nor the visibility of the interference pattern is a good measure of quantumness. It is only the measurement scheme that allows for the perceived quantum behaviour. The Majorana representation also proves useful in delineating uncertainty limits of states with a particular spin value. Issues with traditional uncertainty relations involving the SU(2) operators, such as trivial bounds for certain states and non-invariance, are thereby resolved with the presented pictorial solution. / <p>QC 20170428</p>

The ultimate goal of this research is to develop the capability of direct numerical simulation of a flow containing numerous rigid finite size particles. In order to reach this goal, we have implemented the smoothed profile method (SPM) in the University of Iowa in-house solver, pELAFINT3D and overcame several challenges related to the method. This includes a proposed formulation for the interface thickness and many validations and comparisons with experimental data as well as with a second-order accurate sharp interface method. As one of the issues related to low-density particles is the instability, SPM has been improved by developing to a fully implicit scheme. Moreover, use of higher order integration formulation and implementation of Euler parameters have been shown to be helpful in stabilization of the calculations. To preserve the efficiency when the number of the particles increases, local mesh refinement is shown to be a very effective tool. A revised version of SPM that has only one projection step is proposed to improve the efficiency of the method. A comprehensive efficiency study is performed and it has been shown that the new method is less expensive in problems with high added mass effect when strongly coupled fluid-structure interaction schemes are used. Moreover, the code is massively parallelized using MPI and PETSc libraries. The parallelization includes I/O, operations leading to construction of the linear solver as well as the solver itself. Simulation of a particle laden flow involves particles collisions. Two novel collision models are suggested which are able to avoid particle overlapping for arbitrary shape particles. The methods are efficient as they are not involved with extra grid refinement related to implementing lubrication forces. The issue of handling continuously changing number of particles in a particle laden flow is solved by implementation of a linked list data structure for the particles. By studying a flow over a constricted region we showed that the platelets’ activation is more likely to happen for the particles that pass from the middle of the upper bump region because those particles will have longer exposure time to the high shear flow behind the bump. PDF contour of particles’ presence show the more concentrated presence of the particles near the bump. Moreover, the interaction of RBCs and platelets pushes the platelets toward the wall after the bottom wall.

<p>The paper explores theoretical shortcomings in the egalitarian theory by John Rawls and provides a complementary view on the problem of morally arbitrary contingencies. The conception of natural lottery, which Rawls presents to signify the starting range of morally arbitrary inequalities, falls short in philosophical grounding. According to critics, the notion of natural lottery appeals to the philosophical conception of moral luck which undermines ascription of moral responsibility. Since moral responsibility is a basic prerequisite for egalitarian justice, the appeal to morally arbitrary contingencies of the natural lottery may be self-defeating for the theory.</p><p>Criticizing Rawls’s approach to morally arbitrary contingencies Susan Hurley investigates philosophical groundings for judgment of moral responsibility. Philosophical inquiries into moral luck differentiate four categories of luck and expose the difficulties of ascription of moral responsibility for it. The conception of moral luck implies epistemological shortcomings in the rational judgment of moral responsibility. Hurley claims that ascription of moral responsibility requires another logical strategy.</p><p>The critical discussion by Norman Daniels refers to another egalitarian theory by Ronald Dworkin which suggests ascription of moral responsibility on a gradual scale. The theory divides the naturally contingent recourses into categories of brute luck and option luck. This strategy stratifies normative standards of responsibility by the criteria of individual choice and circumstances.</p><p>Considering the strategy of gradual ascription of responsibility, I suggest to apply a moral developmental perspective as an additional outlook on the moral responsibility in egalitarian theory. The theory of moral development by Lawrence Kohlberg provides an explanation of a gradual development of moral responsibility through a natural order of developmental stages. It stratifies the moral responsibility into a hierarchical model of measurement and systematizes the order of normative standards.</p>

Multiquadric collocation method is highly efficient for solving partial differential equations due to its exponential error convergence rate. More amazingly, there are two ways to reduce the error: the traditional way of refining the grid, and the unexpected way of simply increasing the value of shape constant $c$ contained in the multiquadric basis function, $sqrt{r^2 + c^2}$. The latter is accomplished without increasing computational cost. It has been speculated that in a numerical solution without roundoff error, infinite accuracy can be achieved by letting $c ightarrow infty$. The ability to obtain infinitely accurate solution is limited only by the roundoff error induced instability of matrix solution with large condition number. Using the arbitrary precision computation capability of {it Mathematica}, this paper tests the above conjecture. A sharper error estimate than previously obtained is presented in this paper. A formula for a finite, optimal $c$ value that minimizes the solution error for a given grid size is obtained. Using residual errors, constants in error estimate and optimal $c$ formula can be obtained. These results are supported by numerical examples.

In this work, we have reported the design, MBE-growth and fabrication of strain-balanced n-type modulation-doped (MD) InGaAlAs/InGaAs multiple quantum wells laser/SOAs on InP. The quantum well contains a lattice-matched InGaAs core, a compressive-strained InGaAs padding, and a tensile-strained InGaAlAs spacer. Two kinds of samples having similar structure but different fundamental transition wavelength of 1.55 £gm and 1.48 £gm are separately prepared for investigating their characteristics in optical amplification under forward bias and electro-absorption under reversed bias. Also, the technique of growing high-quality InGaAlAs with solid-source molecular beam epitaxy has been established and the resulting InGaAlAs bulk and QWs samples are extensively characterized by double-crystal X-ray diffraction, transmission electron microscopy, electroluminescence, and photoluminescence measurements. For £f = 1.55 £gm samples, ridge-waveguide lasers of Fabry-Perot (FP) type and tilted-end-facet (TEF) type were fabricated by a new developed multi-step wet-etching process. When injection current density > 20A/cm^2, electroluminescence spectra show higher optical gain for the quantum well e1-hh2 transition at £f = 1460 nm than the e1-hh1 transition at £f = 1550 nm. The FP laser shows a lasing peak of £f = 1514 nm at threshold. Additional lasing wavelength at £f =1528 nm and 1545 nm were observed sequentially as the injection current increased. However, for the TEF laser, only the emission at £f = 1511 nm was observed. These TE-polarized lasing wavelengths are consistent with the £_-like absorption peaks in photocurrent spectra. The lasing performance is possible attributed to optical transitions within quantum dots/wires which are formed by the strain-field profile and alloy segregation/migration. For £f = 1.48 £gm samples, the differential absorption spectroscopy, which measures the change of transmission (£GT/T) in the presence of electric field, is used to study the electro-absorption modulation behavior of MD-SOA¡¦s. A sample with n-type modulation-doping amounting to a sheet density of 3.5 ¡Ñ 10^11 cm^-2 per QW and combining with a hole-stopping barrier represents the largest chirp parameter (£Gn/£Gk) under reversed bias, which offers an excellent platform to realize electro-refractive devices with larger refractive index changes (£Gn) but lower differential absorption (£G£\) near £f = 1.55 £gm, which is also our interested region of operation. In addition, we have succeeded in reducing the length of conventional constant-width multimode interference (MMI) coupler of K = 0.15 and 0.28 more than 32% by a novel stepped-width design concept. By extending the stepped-with idea, we show that it is possible to obtain 2x2 waveguide couplers with new power splitting ratios of 7%, 64%, 80% and 93% for cross coupling by cascading two short MMI sections. We further realize freely chosen power splitting ratio by interconnecting a pair of unequal-width waveguides as the phase-tuning section into the middle of two short MMI sections. These compact and low loss MMI-based devices use only rectangular geometry without any bent, curved, and tapered waveguides. They offer valuable new possibilities for designing waveguide-based photonic integrated circuits.

Many types of radial basis functions, such as multiquadrics, contain a free parameter called shape factor, which controls the flatness of RBFs. In the 1-D problems, Fornberg et al. [2] proved that with simple conditions on the increasingly flat radial basis function, the solutions converge to the Lagrange interpolating. In this report, we study and extend it to the 1-D Poisson equation RBFs direct solver, and observed that the interpolants converge to the Spectral Collocation Method using Polynomial. In 2-D, however, Fornberg et al. [2] observed that limit of interpolants fails to exist in cases of highly regular grid layouts. We also test this in the PDEs solver and found the error behavior is different from interpolating problem.

Rotordynamics is an important area in mechanical engineering. Many machines contain rotating parts. It is well known that rotating components can develop large amplitude lateral vibrations near certain speeds called critical speeds. This large amplitude vibration is called rotor whirl. This thesis is about rotor whirl. Conventional treatments in rotordynamics use what are called gyroscopic terms and treat the rotor as a one-dimensional structure (Euler-Bernoulli or Timoshenko) with or without rigid masses added to them. Gyroscopic terms are macroscopic inertial terms that arise due to tilting of spinning cross-sections. This approach, while applicable to a large class of industrially important rotors, is not applicable to a general rotor geometry. In this thesis we develop a genuine continuum level three dimensional formulation for rotordynamics that can be used for many arbitrarily shaped rotors. The key insight that guides our formulation is that gyroscopic terms are macroscopic manifestations of the prestress induced due to spin of the rotor. Using this insight, we develop two modal projection techniques for calculating the critical speed of arbitrarily shaped rotors. These techniques along with our prestress based formulation are the primary contributions of the thesis. In addition, we also present two different nonlinear finite element based implementations of our formulation. One is a laborious load-stepping based calculation performed using ANSYS (a commercially available finite element package). The other uses our nonlinear finite element code. The latter two techniques are primarily developed to provide us with an accurate answer for comparison with the results obtained using the modal projection methods. Having developed our formulation and the subsequent modal projection approximations, we proceed to validation. First, we analytically study several examples whose solutions can be easily obtained using routine methods. Second, we consider the problem of a rotating cylinder under axial loads. We use a semi-analytical approach for this problem and offer some insights into the role played by the chosen kinematics for our virtual work calculations. The excellent match with known results obtained using Timoshenko theory validates the accuracy of our formulation. Third, we consider several rotors of arbitrary shape in numerical examples and show that our modal projection methods accurately estimate the critical speeds of these rotors. After validation, we consider efficiency. For axisymmetric rotor geometries, we implement our formulation using harmonic elements. This reduces the dimension of our problem from three to two and considerable savings in time are obtained. Finally, we apply our formulation to describe asynchronous whirl and internal viscous damping phenomena in rotors.

The paper explores theoretical shortcomings in the egalitarian theory by John Rawls and provides a complementary view on the problem of morally arbitrary contingencies. The conception of natural lottery, which Rawls presents to signify the starting range of morally arbitrary inequalities, falls short in philosophical grounding. According to critics, the notion of natural lottery appeals to the philosophical conception of moral luck which undermines ascription of moral responsibility. Since moral responsibility is a basic prerequisite for egalitarian justice, the appeal to morally arbitrary contingencies of the natural lottery may be self-defeating for the theory. Criticizing Rawls’s approach to morally arbitrary contingencies Susan Hurley investigates philosophical groundings for judgment of moral responsibility. Philosophical inquiries into moral luck differentiate four categories of luck and expose the difficulties of ascription of moral responsibility for it. The conception of moral luck implies epistemological shortcomings in the rational judgment of moral responsibility. Hurley claims that ascription of moral responsibility requires another logical strategy. The critical discussion by Norman Daniels refers to another egalitarian theory by Ronald Dworkin which suggests ascription of moral responsibility on a gradual scale. The theory divides the naturally contingent recourses into categories of brute luck and option luck. This strategy stratifies normative standards of responsibility by the criteria of individual choice and circumstances. Considering the strategy of gradual ascription of responsibility, I suggest to apply a moral developmental perspective as an additional outlook on the moral responsibility in egalitarian theory. The theory of moral development by Lawrence Kohlberg provides an explanation of a gradual development of moral responsibility through a natural order of developmental stages. It stratifies the moral responsibility into a hierarchical model of measurement and systematizes the order of normative standards.

A three-dimensional, parallel, finite volume solver which uses Roe&#039 / s upwind flux differencing scheme for spatial and Runge-Kutta explicit multistage time stepping scheme for temporal discretization on unstructured meshes is developed for the unsteady solution of external viscous flow around rotating bodies. The main aim of this study is to evaluate the aerodynamic dynamic stability derivative coefficients for rotating missile configurations. Arbitrary Lagrangian Eulerian (ALE) formulation is adapted to the solver for the simulation of the rotation of the body. Eigenvalues of the Euler equations in ALE form has been derived. Body rotation is simply performed by rotating the entire computational domain including the body of the projectile by means of rotation matrices. Spalart-Allmaras one-euqation turbulence model is implemented to the solver. The solver developed is first verified in 3-D for inviscid flow over two missile configurations. Then inviscid flow over a rotating missile is tested. Viscous flux computation algorithms and Spalarat-Allmaras turbulence model implementation are validated in 2-D by performing calculations for viscous flow over flat plate, NACA0012 airfoil and NLR 7301 airfoil with trailing edge flap. The ALE formulation is validated in 2-D on a rapidly pitching NACA0012 airfoil. Afterwards three-dimensional validation studies for viscous, laminar and turbulent flow calculations are performed on 3-D flat plate problem. At last, as a validation test case, unsteady laminar and turbulent viscous flow calculations over a spinning M910 projectile configuration are performed. Results are qualitatively in agreement with the analytical solutions, experimental measurements and previous studies for steady and unsteady flow calculations.