Fundamental Limits of Communication with Low Probability of Detection

This paper considers the problem of communication over a discrete memoryless channel (DMC) or an additive white Gaussian noise (AWGN) channel subject to the constraint that the probability that an adversary who observes the channel outputs can detect the communication is low. Specifically, the relative entropy between the output distributions when a codeword is transmitted and when no input is provided to the channel must be sufficiently small. For a DMC whose output distribution induced by the "off" input symbol is not a mixture of the output distributions induced by other input symbols, it is shown that the maximum amount of information that can be transmitted under this criterion scales like the square root of the blocklength. The same is true for the AWGN channel. Exact expressions for the scaling constant are also derived.Comment: Version to appear in IEEE Transactions on Information Theory; minor typos in v2 corrected. Part of this work was presented at ISIT 2015 in Hong Kon

R-Wave Dispersion Analysis in Transversely Isotropic Stratum

With dynamic stiffness of elastic half-space, the Rayleigh wave dispersion in transversely isotropic soil is analyzed by Finite-layer and Semi-infinite layer method. Only is matrix eigenvalue involved, avoiding the calculation procedure encountered in analytical method. Two examples prove the deduction correctly and show that soil anisotropy influences dispersion dramatically. It is possible to study soil anisotropy and characteristics of its dynamical responses from its surface wave dispersion

BBR-induced Stark shifts and level broadening in helium atom

The precise calculations of blackbody radiation (BBR)-induced Stark shifts and depopulation rates for low-lying states of helium atom with the use of variational approach are presented. An effect of the BBR-induced induced Stark-mixing of energy levels is considered. It is shown that this effect leads to a significant reduction of lifetimes of helium excited states. As a consequence the influence of Stark-mixing effect on the decay rates of metastable states in helium is discussed in context of formation processes of the cosmic microwave background

Design for Deconstruction for Sustainable Composite Steel-Concrete Floor Systems

[EN ] Conventional steel-concrete composite floor systems utilizing steel headed stud anchors and metal decks are cost-effective and widely used solutions for non-residential multi-story buildings, due in part to their enhanced strength and stiffness relative to non-composite systems. Because these systems use steel headed stud anchors welded onto steel flanges and encased in cast-in-place concrete slabs to achieve composite action, it is not possible to readily deconstruct and reuse the steel beams and concrete slabs. As the building industry is moving towards sustainability, there are clear needs for developing sustainable steel-concrete composite floor systems to facilitate material reuse, minimize consumption of raw materials, and reduce end-of-life building waste. This paper presents the behavior and design strategies for a sustainable steel-concrete composite floor system. In this system, deconstructable clamping connectors are utilized to attach precast concrete planks to steel beams to achieve composite action. The load-slip behavior of the clamping connectors was studied in pushout tests, and the test results showed that the clamping connectors possess similar shear strength to 19 mm diameter shear studs and much greater slip capacity. Four full-scale beam tests were performed to investigate the flexural behavior of the deconstructable composite beams under gravity loading and validate the connector behavior attained from the pushout tests. All the beams behaved in a ductile manner. The flexural strengths of the composite beam specimens closely match the strengths predicted for composite beams by the design provisions of the American Institute of Steel Construction (AISC).This material is based upon work supported by the National Science Foundation under Grants No. CMMI-1200820 and No. IIS1328816, the American Institute of Steel Construction, Northeastern University, and Simpson Gumpertz & Heger. In-kind support is provided by Benevento Companies, Capone Iron Corporation, Fastenal, Halfen, Lehigh Cement Company, Lindapter, Meadow Burke, Souza Concrete, and S&F Concrete. This support is gratefully acknowledged.Wang, L.; Webster, M.; Hajjar, J. (2018). Design for Deconstruction for Sustainable Composite Steel-Concrete Floor Systems. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 191-198. https://doi.org/10.4995/ASCCS2018.2018.7060OCS19119

3D elastoplastic model for fine-grained gassy soil considering the gas-dependent yield surface shape and stress-dilatancy

Fine-grained sediments containing large discrete gas bubbles are widely distributed in the five continents throughout the world. The presence of gas bubbles could either degrade or enhance the hardening behavior and undrained shear strength (su) of the soil, depending on the initial pore water pressure (uw0) and initial gas volume fraction (ψ0). The existing constitutive models, however, can solely capture either detrimental or beneficial effect owing to the presence of gas. This study presents a new three-dimensional (3D) elastoplastic constitutive model that describes both the damaging and beneficial effects of gas bubbles on the stress–strain behavior of fine-grained gassy soil in a unified manner. This was achieved by incorporating (1) a versatile expression of yield function that simulates a wide range of yield curve shapes in a unified context, and (2) a dilatancy function capturing the distinct stress–dilatancy behavior of fine-grained gassy soil. Given the lack of direct experimental evidence on the shape of the yield curve of fine-grained gassy soil, new experiments were performed. This has led to the identification of three distinct shapes of yield curve—bullet, ellipse, and teardrop—as well as the formulation of the yield function considering the dependency of yield curve shapes on uw0 and ψ0. The new model was shown to reasonably capture both the damaging and beneficial effects of gas on the compression and shear behavior of three types of fine-grained gassy soils with a broad range of uw0 and ψ0 by using a unified set of parameters