On the exceptional damage-tolerance of gradient metallic materials

An experimental study is described on the fracture toughness and micro-mechanisms associated with the initiation and propagation of cracks in metallic nickel containing marked gradients in grain size, ranging from ∼30 nm to ∼4 μm. Specifically, cracks are grown in a gradient structured (GS) nickel with grain-size gradient ranging from the coarse macro-scale to nano-scale (CG → NG) and vice versa (NG → CG), with the measured crack-resistance R-curves compared to the corresponding behavior in uniform nano-grained (NG) and coarse-grained (CG) materials. It is found that the gradient structures display a much-improved combination of high strength and toughness compared to uniform grain-sized materials. However, based on J-integral measurements in the gradient materials, the crack-initiation toughness is far higher for cracks grown in the direction of the coarse-to-nano grained gradient than vice versa, a result which we ascribe primarily to excessive crack-tip blunting in the coarse-grained microstructure. Both gradient structures, however, display marked rising R-curve behavior with exceptional crack-growth toughnesses exceeding 200 MPa.m½

Swift UVOT Grism Observations of Nearby Type Ia Supernovae - I. Observations and Data Reduction

Ultraviolet (UV) observations of Type Ia supernovae (SNe Ia) are useful tools for understanding progenitor systems and explosion physics. In particular, UV spectra of SNe Ia, which probe the outermost layers, are strongly affected by the progenitor metallicity. In this work, we present 120 Neil Gehrels Swift Observatory UV spectra of 39 nearby SNe Ia. This sample is the largest UV (lambda < 2900 A) spectroscopic sample of SNe Ia to date, doubling the number of UV spectra and tripling the number of SNe with UV spectra. The sample spans nearly the full range of SN Ia light-curve shapes (delta m(B) ~ 0.6-1.8 mag). The fast turnaround of Swift allows us to obtain UV spectra at very early times, with 13 out of 39 SNe having their first spectra observed >~ 1 week before peak brightness and the earliest epoch being 16.5 days before peak brightness. The slitless design of the Swift UV grism complicates the data reduction, which requires separating SN light from underlying host-galaxy light and occasional overlapping stellar light. We present a new data-reduction procedure to mitigate these issues, producing spectra that are significantly improved over those of standard methods. For a subset of the spectra we have nearly simultaneous Hubble Space Telescope UV spectra; the Swift spectra are consistent with these comparison data.Comment: Accepted for publication in MNRA

Chimera order in spin systems

Homogeneous populations of oscillators have recently been shown to exhibit stable coexistence of coherent and incoherent regions. Generalizing the concept of chimera states to the context of order-disorder transition in systems at thermal equilibrium, we show analytically that such complex ordering can appear in a system of Ising spins, possibly the simplest physical system exhibiting this phenomenon. We also show numerically the existence of chimera ordering in 3-dimensional spin systems that model layered magnetic materials, suggesting possible means of experimentally observing such states.Comment: 5 pages, 3 figure

Photoemission Spectroscopy of Magnetic and Non-magnetic Impurities on the Surface of the Bi2_2Se3_3 Topological Insulator

Dirac-like surface states on surfaces of topological insulators have a chiral spin structure that suppresses back-scattering and protects the coherence of these states in the presence of non-magnetic scatterers. In contrast, magnetic scatterers should open the back- scattering channel via the spin-flip processes and degrade the state's coherence. We present angle-resolved photoemission spectroscopy studies of the electronic structure and the scattering rates upon adsorption of various magnetic and non-magnetic impurities on the surface of Bi$_2$Se$_3$, a model topological insulator. We reveal a remarkable insensitivity of the topological surface state to both non-magnetic and magnetic impurities in the low impurity concentration regime. Scattering channels open up with the emergence of hexagonal warping in the high-doping regime, irrespective of the impurity's magnetic moment.Comment: 5 pages, 4 figure

Multilevel semantic analysis and problem-solving in the flight domain

A computer based cockpit system which is capable of assisting the pilot in such important tasks as monitoring, diagnosis, and trend analysis was developed. The system is properly organized and is endowed with a knowledge base so that it enhances the pilot's control over the aircraft while simultaneously reducing his workload

Impact of Building Information Modeling Implementation on the Acceptance of Integrated Delivery Systems: Structural Equation Modeling Analysis

In recent years, building information modeling (BIM) has been increasingly employed by the architecture, engineering and construction industry worldwide as a result of digital government initiatives. In spite of some promising early evidence on the benefits of BIM, the momentum of this top-down drive should build upon after-implementation empirical evidence. Through the structural equation modeling analysis of survey returns from 145 Chinese BIM-enabled projects, this research demonstrates that BIM’s degree of implementation can positively affect the acceptability of integrated project delivery (IPD) in the future via increased perception of the need for supply chain incentivization and improved communication quality enabled by BIM. Rolling out BIM on a wider scale may yield an additional benefit in lowering the barrier to the implementation of IPD systems. This finding can serve as evidential support for government mandates that require the compulsory adoption of BIM in public projects

Hurst parameter analysis of radio pulsar timing noise

We present an analysis of timing residual (noise) of 54 pulsars obtained from 25-m radio telescope at Urumqi Observatory with a time span of 5~8 years, dealing with statistics of the Hurst parameter. The majority of these pulsars were selected to have timing noise that look like white noise rather than smooth curves. The results are compared with artificial series of different constant pairwise covariances. Despite the noise like appearance, many timing residual series showed Hurst parameters significantly deviated from that of independent series. We concluded that Hurst parameter may be capable of detecting dependence in timing residual and of distinguishing chaotic behavior from random processes.Comment: 7 pages, 3 figures, 2 tables, Submitted to MNRA