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Einstein’s forgotten model of the universe (Vol. 45 No.2)
An image of the blackboard used in Einstein’s 2nd Rhodes lecture at Oxford in April 1931.Credit: Museum of the History of Science, University of Oxford, UK.
New insights into Einstein’s view of the cosmos from the translation and study of one of his least known papers.
This work provides the first English translation and an analysis of one of Albert Einstein’s little-known papers, “On the cosmological problem of the general theory of relativity.” Published in 1931, it features a forgotten model of the universe, while refuting Einstein’s own earlier static model of 1917. In this paper, Einstein introduces a cosmic model in which the universe undergoes an expansion followed by a contraction. This interpretation contrasts with the monotonically expanding universe of the widely known Einstein-de Sitter model of 1932.
The authors provide insights into Einstein’s view of cosmology. At that time, the first pieces of evidence for an expanding universe emerged, among others, stemming from Hubble’s observations of the expanding universe. In this paper, the authors also discuss Einstein’s view of issues such as the curvature of space and the timespan of the expansion, while also uncovering some anomalies in Einstein’s calculations.
C. O’Raifeartaigh and B. McCann (2014), “Einstein’s cosmic model of 1931 revisited”, Eur. Phys. J. H, 39, 63 (2014)
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Ferroelectric tunnel junction for memory and logic design (Vol. 45 No.2)
The structure of Co/BaTiO3/La0.67Sr0.33MnO3 FTJ and DC simulation curves with proposed model
Ferroelectric tunnel junction (FTJ) is an emerging nonvolatile binary data storage device. Unlike conventional tunnel junctions, FTJ is switched via a pure electronic mechanism, and it exhibits higher OFF/ON resistance ratio and larger resistance-area product. Considering great potential of FTJ as next generation memory, the authors aimed to develop the first compact model of FTJ for associated circuits design and simulation.
They presented a SPICE-compatible model of Co/BaTiO3/La0.67Sr0.33MnO3 FTJ through investigating a variety of physical theories including Brinkman model, JKD semi-empirical scaling law, KAI model, and Merz’s law. These theories quantitatively explain the experimental data of tunnel resistance and switching process, and hence verify the accuracy of proposed model. This model has been programmed with Verilog-A language and integrated on Cadence platform. With the proposed model, the authors researched the reading reliability and power dissipation of FTJ based on CMOS 40nm technology node. Simulation results demonstrated the advantages of FTJ over magnetic tunnel junction (MTJ) in high reliability and ultralow power.
The authors have added this model into the open source device library SPINLIB to allow IC designers to simulate FTJ-based circuits efficiently.
Z. H. Wang, W. S. Zhao, W. Kang, A. Bouchenak-Khelladi, Y. Zhang, J.-O. Klein, D. Ravelosona and C. Chappert, “A physics-based compact model of ferroelectric tunnel junction for memory and logic design”, J. Phys. D: Appl. Phys. 47, 045001 (2014)
[Abstract]
Finding and verifying Quantumness in “Classical” States (Vol. 45 No.2)
Changes in conditional marginal distributions as signature of discord.
Separable states were previously treated as “classical” states due to the lack of entanglement. Recently, quantum discord was proposed as a general quantification of quantumness that is able to reveal nonclassical correlations beyond entanglement. This measure suggests that for bipartite Gaussian states, quantum correlations are nonzero for all but product states. This implies that even a non-entangled bipartite state prepared by splitting a thermal state on beamsplitter could display nonzero quantumness. To examine such nonclassical correlations, experimental methods to verify the presence of discord are of particular interest.
In this paper, the authors demonstrated a simple yet efficient technique for certifying quantum discord in continuous variable states. By checking the difference between conditioned marginal distributions, such as peak separation, the authors were able to reveal discord in bipartite Gaussian states and a certain class of non-Gaussian states. Hence, the presence of informational contents greater than that attributed to classical correlations in these separable states was verified. With some prior knowledge about the bipartite states, the proposed method could detect quantum correlations with minimal resources, thus serves as an indispensable tool for the testing of quantumness.
S. Hosseini, S. Rahimi-Keshari, J. Y. Haw, S. M. Assad, H. M. Chrzanoswki, J. Janousek, T. Symul, T. C. Ralph and P. K. Lam, "Experimental verification of quantum discord in continuous-variable states" J. Phys. B: At. Mol. Opt. Phys., 47 025503 (2014)
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How hypergravity impacts electric arcs (Vol. 45 No.2)
Glide arc discharge under normal gravity conditions.Credit: J. Sperka et al.
A new study focused on electric discharge behaviour under intense gravitational forces shows that its dynamic changes as gravity increases.
Arc discharges are common in everyday conditions like welding or in lightning storms. But in altered gravity, not as much is known about their behaviour. For the first time, the authors studied the behaviour of a special type of arc discharge, so-called glide arc, in varying hypergravity conditions, up to 18 G. In this work they demonstrate how the plasma channel of this glide arc discharge moves due to external forces of buoyancy in varying gravity conditions. These results could have implications for improved safety precautions in manned space flights and in the design of ion thrusters used for spacecraft propulsion.
The authors performed measurements on atmospheric pressure glide arc helium plasma under the forces of hypergravity. They established a model showing that gravity strongly influences the glide arc discharge. These effects stem from thermal buoyancy, which increases with gravity, they conclude.
J. Sperka, P.Souček, J. J.W.A. Van Loon, A. Dowson, C. Schwarz, J. Krause, G. Kroesen and V.Kudrle, “Hypergravity Effects on Glide Arc Plasma”, Eur. Phys. J. D, 67, 261 (2013)
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