Combustion: Structural interaction in a viscoelastic material

The effect of interaction between combustion processes and structural deformation of solid propellant was considered. The combustion analysis was performed on the basis of deformed crack geometry, which was determined from the structural analysis. On the other hand, input data for the structural analysis, such as pressure distribution along the crack boundary and ablation velocity of the crack, were determined from the combustion analysis. The interaction analysis was conducted by combining two computer codes, a combustion analysis code and a general purpose finite element structural analysis code

Pulse Profiles, Spectra and Polarization Characteristics of Non-Thermal Emissions from the Crab-Like Pulsars

We discuss non-thermal emission mechanism of the Crab-like pulsars with both a two-dimensional electrodynamical study and a three-dimensional model. We investigate the emission process in the outer gap accelerator. In the two-dimensional electrodynamical study, we solve the Poisson equation of the accelerating electric field in the outer gap and the equation of motion of the primary particles with the synchrotron and the curvature radiation process and the pair-creation process. We show a solved gap structure which produces a consistent gamma-ray spectrum with EGRET observation. Based on the two-dimensional model, we conduct a three-dimensional emission model to calculate the synchrotron and the inverse-Compton processes of the secondary pairs produced outside the outer gap. We calculate the pulse profiles, the phase-resolved spectra and the polarization characteristics in optical to $\gamma$-ray bands to compare the observation of the Crab pulsar and PSR B0540-69. For the Crab pulsar, we find that the outer gap geometry extending from near the stellar surface to near the light cylinder produces a complex morphology change of the pulse profiles as a function of the photon energy. This predicted morphology change is quite similar with that of the observations. The calculated phase-resolved spectra are consistent with the data through optical to the $\gamma$-ray bands. We demonstrate that the 10$\sim$20 % of the polarization degree in the optical emissions from the Crab pulsar and the Vela pulsar are explained by the synchrotron emissions with the particle gyration motion.Comment: 39 pages, 11 figures, Accepted for publication in Ap

Edge currents and nanopore arrays in zigzag and chiral graphene nanoribbons as a route toward high-ZTZT thermoelectrics

We analyze electronic and phononic quantum transport through zigzag or chiral graphene nanoribbons (GNRs) perforated with an array of nanopores. Since local charge current profiles in these GNRs are peaked around their edges, drilling nanopores in their interior does not affect such edge charge currents while drastically reducing heat current carried by phonons in sufficiently long wires. The combination of these two effects can yield highly efficient thermoelectric devices with maximum $ZT \simeq 11$ at liquid nitrogen temperature and $ZT \simeq 4$ at room temperature achieved in $\sim 1$ $\mu$m long zigzag GNRs with nanopores of variable diameter and spacing between them. Our analysis is based on the $\pi$-orbital tight-binding Hamiltonian with up to third nearest-neighbor hopping for electronic subsystem, the empirical fourth-nearest-neighbor model for phononic subsystem, and nonequilibrium Green function formalism to study quantum transport in both of these models.Comment: 5 pages, 5 figures, PDFLaTe

Analyzing Android Browser Apps for file:// Vulnerabilities

Securing browsers in mobile devices is very challenging, because these browser apps usually provide browsing services to other apps in the same device. A malicious app installed in a device can potentially obtain sensitive information through a browser app. In this paper, we identify four types of attacks in Android, collectively known as FileCross, that exploits the vulnerable file:// to obtain users' private files, such as cookies, bookmarks, and browsing histories. We design an automated system to dynamically test 115 browser apps collected from Google Play and find that 64 of them are vulnerable to the attacks. Among them are the popular Firefox, Baidu and Maxthon browsers, and the more application-specific ones, including UC Browser HD for tablet users, Wikipedia Browser, and Kids Safe Browser. A detailed analysis of these browsers further shows that 26 browsers (23%) expose their browsing interfaces unintentionally. In response to our reports, the developers concerned promptly patched their browsers by forbidding file:// access to private file zones, disabling JavaScript execution in file:// URLs, or even blocking external file:// URLs. We employ the same system to validate the ten patches received from the developers and find one still failing to block the vulnerability.Comment: The paper has been accepted by ISC'14 as a regular paper (see https://daoyuan14.github.io/). This is a Technical Report version for referenc