Strength and High-Temperature Stability of Dispersion Strengthened Nickel-MgO Alloys

Strength and high-temperature stability of dispersion strengthened nickel-magnesium oxide alloy

Prototype selection for parameter estimation in complex models

Parameter estimation in astrophysics often requires the use of complex physical models. In this paper we study the problem of estimating the parameters that describe star formation history (SFH) in galaxies. Here, high-dimensional spectral data from galaxies are appropriately modeled as linear combinations of physical components, called simple stellar populations (SSPs), plus some nonlinear distortions. Theoretical data for each SSP is produced for a fixed parameter vector via computer modeling. Though the parameters that define each SSP are continuous, optimizing the signal model over a large set of SSPs on a fine parameter grid is computationally infeasible and inefficient. The goal of this study is to estimate the set of parameters that describes the SFH of each galaxy. These target parameters, such as the average ages and chemical compositions of the galaxy's stellar populations, are derived from the SSP parameters and the component weights in the signal model. Here, we introduce a principled approach of choosing a small basis of SSP prototypes for SFH parameter estimation. The basic idea is to quantize the vector space and effective support of the model components. In addition to greater computational efficiency, we achieve better estimates of the SFH target parameters. In simulations, our proposed quantization method obtains a substantial improvement in estimating the target parameters over the common method of employing a parameter grid. Sparse coding techniques are not appropriate for this problem without proper constraints, while constrained sparse coding methods perform poorly for parameter estimation because their objective is signal reconstruction, not estimation of the target parameters.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS500 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Chiral Loops and Ghost States in the Quenched Scalar Propagator

The scalar, isovector meson propagator is analyzed in quenched QCD, using the MQA pole-shifting ansatz to study the chiral limit. In addition to the expected short-range exponential falloff characteristic of a heavy scalar meson, the propagator also exhibits a longer-range, negative metric contribution which becomes pronounced for smaller quark masses. We show that this is a quenched chiral loop effect associated with the anomalous structure of the $\eta '$ propagator in quenched QCD. Both the time dependence and the quark mass dependence of this effect are well-described by a chiral loop diagram corresponding to an $\eta '- \pi$ intermediate state, which is light and effectively of negative norm in the quenched approximation. The relevant parameters of the effective Lagrangian describing the scalar sector of the quenched theory are determined.Comment: 29 pages, 10 figures, Late

Observations and models for needle-tissue interactions

The asymmetry of a bevel-tip needle results in the needle naturally bending when it is inserted into soft tissue. In this study we present a mechanics-based model that calculates the deflection of the needle embedded in an elastic medium. Microscopic observations for several needle- gel interactions were used to characterize the interactions at the bevel tip and along the needle shaft. The model design was guided by microscopic observations of several needle- gel interactions. The energy-based model formulation incor- porates tissue-specific parameters such as rupture toughness, nonlinear material elasticity, and interaction stiffness, and needle geometric and material properties. Simulation results follow similar trends (deflection and radius of curvature) to those observed in macroscopic experimental studies of a robot- driven needle interacting with different kinds of gels. These results contribute to a mechanics-based model of robotic needle steering, extending previous work on kinematic models

The Ginzburg-Landau Free Energy Functional of Color Superconductivity at Weak Coupling

We derive the Ginzburg-Landau free energy functional of color superconductivity in terms of the thermal diagrams of QCD in its perturbative region. The zero mode of the quadratic term coefficient yields the same transition temperature, including the pre-exponential factor, as the one obtained previously from the Fredholm determinant of the two quark scattering amplitude. All coefficients of the free energy can be made identical to those of a BCS model by setting the Fermi velocity of the latter equal to the speed of light. We also calculate the induced symmetric color condensate near $T_c$ and find that it scales as the cubic power of the dominant antisymmetric color component. We show that in the presence of an inhomogeneity and a nonzero gauge potential, while the color-flavor locked condensate dominates in the bulk, the unlocked condensate, the octet, emerges as a result of a simultaneous color-flavor rotation in the core region of a vortex filament or at the junction of super and normal phases.Comment: 32 pages, Plain Tex, 3 figure

Improved Reliability Determination When Testing Cold-formed Steel Components

The objectives of this paper are to (a) determine the sensitivity of the reliability calculations in Chapter F of the AISI Specification (AISI-S100-07) to controlling load combinations and loading ratios, and (b) develop a more robust alternative for the use of Chapter F. To complete this study the bias factors and variances for all loading conditions are established. In addition, a range of practical load ratios is agreed upon. Parametric studies are performed to explore load case and load ratio dependency for use in the determination of the resistance factor, Φ; specifically, the pre-factor term CΦ and the load variance term VQ. The parametric studies are simplified into a table that provides load case dependent CΦ and VQ factors. The table is recommended for use in Chapter F reliability analysis of new products

A Critical Review of New Mobility Services for Urban Transport

The growing pressure on urban passenger transport systems has increased the demand for new and innovative solutions to increase its efficiency. One approach to tackle this challenge has been the slow but steady shift towards shared mobility services (car-, bike-sharing etc.). Building on these new modes and the developments in information and communication technologies, the concept of “Mobility as a Service” (MaaS) has recently come to light and offers convenient door-to-door transport without the need to own a private vehicle. The term Mobility as a Service (MaaS) stands for buying mobility services based on consumer needs instead of buying the means of mobility. In recent years, various MaaS schemes have been arisen around the world. The objective of this paper is to review these newly existing mobility services and develop an index to evaluate the level of mobility integration for each based on the assumption that higher level of integration is more appealing to travellers. The review presented in this paper allows a comparison among the schemes and provides the background and the key points of MaaS systems that the research community could use for designing surveys. It also provides significant insights to transport operators and authorities on the elements they should take into account to apply an attractive MaaS scheme that could effectively shift demand away from private vehicles

Feasibility Study for “Mobility as a Service” concept in London

Novel mobility services that heavily rely on technological advances could contribute to seamless mobility. Mobility as a Service (MaaS) is such a concept. The objective of the FS-MaaS project is to propose the design of a MaaS concept for London, the MaaS-London, and examine its feasibility. To work towards the concept of MaaS-London, first, the supply and the demand sides of the London transport market are analysed. There are a variety of mobility services supplied in London such as car clubs (car sharing), ride sharing, bike sharing, public transport, rail and taxi which altogether make London an ideal ground to exploit MaaS-London. The MaaS-London is an integrated platform that includes registration and package selection, intermodal journey planning, booking, smart ticketing and payment functions so that the entire chain of transport can be managed in this centralised platform. The most outstanding feature of MaaS-London is the provision of mobility packages, which consist of tailored bundles of mobility services customised to individual needs. The feasibility study indicates that the introduction of MaaS-London will benefit both the supply and the demand side. Transport operators will benefit by creating a larger market via the integrated platform. Travellers will also welcome the concept due to travel expense and time reduction, and better service experience. MaaS-London is a feasible product that can well serve London transport market and contribute to London’s 2020 vision

Behavior and Design of Axially Compressed Sheathed Wall Studs

The objective of this paper is to summarize efforts in a multi year project dedicated to developing a reliable design method for cold - formed steel wall studs that rely on sheathing for bracing. Testing on single columns with sheathing, and full - scale walls with sheathin g, are summarized. Particular emphasis is placed on the observed limit states given the different sheathing conditions. The sheathing supplies beneficial restraint to the wall studs and the stiffness of this sheathing - based restraint is characterized exper imentally and analytically. A unique application of the Direct Strength Method of design is explored where the sheathing - based restraint is used explicitly in determination of the elastic buckling loads of the wall studs, and then these elastic buckling lo ads are utilized to determine the strength. The test results are compared with the newly proposed design method as well as with previous design methods adopted by the AISI Specification. Good agreement is demonstrated for the new approach both in terms of strength an d limit states prediction