Fast Adaptive S-ALOHA Scheme for Event-driven Machine-to-Machine Communications

Machine-to-Machine (M2M) communication is now playing a market-changing role in a wide range of business world. However, in event-driven M2M communications, a large number of devices activate within a short period of time, which in turn causes high radio congestions and severe access delay. To address this issue, we propose a Fast Adaptive S-ALOHA (FASA) scheme for M2M communication systems with bursty traffic. The statistics of consecutive idle and collision slots, rather than the observation in a single slot, are used in FASA to accelerate the tracking process of network status. Furthermore, the fast convergence property of FASA is guaranteed by using drift analysis. Simulation results demonstrate that the proposed FASA scheme achieves near-optimal performance in reducing access delay, which outperforms that of traditional additive schemes such as PB-ALOHA. Moreover, compared to multiplicative schemes, FASA shows its robustness even under heavy traffic load in addition to better delay performance.Comment: 5 pages, 3 figures, accepted to IEEE VTC2012-Fal

Direct observation of pitting corrosion evolutions on carbon steel surfaces at the nano-to-micro- scales.

The Cl--induced corrosion of metals and alloys is of relevance to a wide range of engineered materials, structures, and systems. Because of the challenges in studying pitting corrosion in a quantitative and statistically significant manner, its kinetics remain poorly understood. Herein, by direct, nano- to micro-scale observations using vertical scanning interferometry (VSI), we examine the temporal evolution of pitting corrosion on AISI 1045 carbon steel over large surface areas in Cl--free, and Cl--enriched solutions. Special focus is paid to examine the nucleation and growth of pits, and the associated formation of roughened regions on steel surfaces. By statistical analysis of hundreds of individual pits, three stages of pitting corrosion, namely, induction, propagation, and saturation, are quantitatively distinguished. By quantifying the kinetics of these processes, we contextualize our current understanding of electrochemical corrosion within a framework that considers spatial dynamics and morphology evolutions. In the presence of Cl- ions, corrosion is highly accelerated due to multiple autocatalytic factors including destabilization of protective surface oxide films and preservation of aggressive microenvironments within the pits, both of which promote continued pit nucleation and growth. These findings offer new insights into predicting and modeling steel corrosion processes in mid-pH aqueous environments

Globalizing Hayden White

This conversation originated in a plenary session organized by Ewa Domańska and María Inés La Greca under the same title of ‘Globalizing Hayden White’ at the III International Network for Theory of History Conference ‘Place and Displacement: The Spacing of History’ held at Södertörn University, Stockholm, in August 2018. In order to pay homage to Hayden White’s life work 5 months after his passing we knew that what was needed–and what he himself would have wanted–was a vibrant intellectual exchange. Our ‘celebration by discussion’ contains elaborated and revised versions of the presentations by scholars from China (Xin Chen), Latin America (María Inés La Greca, Veronica Tozzi Thompson), United States (Paul Roth), Western (Kalle Pihlainen) and East-Central Europe (Ewa Domańska). We took this opportunity of gathering scholars who represent different parts of the world, different cultures and approaches to reflect on White’s ideas in a global context. Our interest was in discussing how his work has been read and used (or even misread and misused) and how it has influenced theoretical discussions in different parts of the globe. Rather than just offering an account as experts, we mainly wanted to reflect on the current state of our field and the ways that White’s inheritance might and should be carried forward in the future.Fil: Domanska, Ewa. Adam Mickiewicz University in Poznań; PoloniaFil: la Greca, María Inés. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tres de Febrero. Departamento de Metodología, Estadística y Matemáticas; Argentina. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Departamento de Filosofía; ArgentinaFil: Roth, Paul A.. University of California at Santa Cruz; Estados UnidosFil: Chen, Xin. Zhejiang University; ChinaFil: Tozzi, María Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tres de Febrero. Departamento de Metodología, Estadística y Matemáticas; Argentina. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Departamento de Filosofía; ArgentinaFil: Pihlainen, Kalle. Tallinn University; Estoni

Optical Properties of Organometallic Perovskite: An ab initio Study using Relativistic GW Correction and Bethe-Salpeter Equation

In the development of highly efficient photovoltaic cells, solid perovskite systems have demonstrated unprecedented promise, with the figure of merit exceeding nineteen percent of efficiency. In this paper, we investigate the optical and vibrational properties of organometallic cubic perovskite CH3NH3PbI3 using first-principles calculations. For accurate theoretical description, we go beyond conventional density functional theory (DFT), and calculated optical conductivity using relativist quasi-particle (GW) correction. Incorporating these many-body effects, we further solve Bethe-Salpeter equations (BSE) for excitons, and found enhanced optical conductivity near the gap edge. Due to the presence of organic methylammonium cations near the center of the perovskite cell, the system is sensitive to low energy vibrational modes. We estimate the phonon modes of CH3NH3PbI3 using small displacement approach, and further calculate the infrared absorption (IR) spectra. Qualitatively, our calculations of low-energy phonon frequencies are in good agreement with our terahertz measurements. Therefore, for both energy scales (around 2 eV and 0-20 meV), our calculations reveal the importance of many-body effects and their contributions to the desirable optical properties in the cubic organometallic perovskites system.Comment: 5 pages, 4 figure

Magnetic quantum oscillations in YBa2_2Cu3_3O6.61_{6.61} and YBa2_2Cu3_3O6.69_{6.69} in fields of up to 85 T; patching the hole in the roof of the superconducting dome

We measure magnetic quantum oscillations in the underdoped cuprates YBa$_2$Cu$_3$O$_{6+x}$ with $x=0.61$, 0.69, using fields of up to 85 T. The quantum-oscillation frequencies and effective masses obtained suggest that the Fermi energy in the cuprates has a maximum at $p\approx 0.11-0.12$. On either side, the effective mass may diverge, possibly due to phase transitions associated with the T=0 limit of the metal-insulator crossover (low-$p$ side), and the postulated topological transition from small to large Fermi surface close to optimal doping (high $p$ side)

Mutations on the N-terminal edge of the DELSEED loop in either the α or β subunit of the mitochondrial F 1 -ATPase enhance ATP hydrolysis in the absence of the central γ rotor

F1-ATPase is a rotary molecular machine with a subunit stoichiometry of α3 β3 γ1 δ1 ε1. It has a robust ATP-hydrolyzing activity due to effective cooperativity between the three catalytic sites. It is believed that the central γ rotor dictates the

q-Deformation of W(2,2) Lie algebra associated with quantum groups

An explicit realization of the W(2,2) Lie algebra is presented using the famous bosonic and fermionic oscillators in physics, which is then used to construct the q-deformation of this Lie algebra. Furthermore, the quantum group structures on the q-deformation of this Lie algebra are completely determined.Comment: 12 page