Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Statistics dependence of the entanglement entropy

The entanglement entropy of a distinguished region of a quantum many-body system reflects the entanglement in its pure ground state. Here we establish scaling laws for this entanglement in critical quasifree fermionic and bosonic lattice systems, without resorting to numerical means. We consider the setting of D-dimensional half-spaces which allows us to exploit a connection to the one-dimensional case. Intriguingly, we find a difference in the scaling properties depending on whether the system is bosonic-where an area law is proven to hold-or fermionic where we determine a logarithmic correction to the area law, which depends on the topology of the Fermi surface. We find Lifshitz quantum phase transitions accompanied with a nonanalyticity in the prefactor of the leading order term.     

A Fluorescent Molecular Probe for the Detection of Hydrogen Based on Oxidative Addition Reactions with Crabtree‐Type Hydrogenation Catalysts

A Crabtree‐type Ir^I complex tagged with a fluorescent dye (bodipy) was synthesized. The oxidative addition of H₂ converts the weakly fluorescent Ir^I complex (Φ=0.038) into a highly fluorescent Ir^III species (Φ=0.51). This fluorogenic reaction can be utilized for the detection of H₂ and to probe the oxidative addition step in the catalytic hydrogenation of olefins.     

Book reviews

A Philosopher Looks at Science. By John G. Kemeny. (Van Nostrand, 1959.) [Pp.xii+273.] 37s. 6d.

Principles of General Physiology. Vol. I : The Physico-Chemical Background. By L. E. Bayliss. (Longmans, 1959.) [Pp. xiii+520] 55s.

Dynamics. By A. E. Short. (London: University of London Press, Ltd., 1959.) [Pp. 384.] 30s.

The Human Element in Research Management. By B. E. Noltingk. (Elsevier, 1959.) [Pp. 92.] 9s. 6d.

Annual Report of the Advisory Council on Scientific Policy 1958-59. (Cmnd. 893, H.M.S.O., November 1959.) 1s.

Farbenphotographie und Farbenfilm. By Dr. Werner Schultze. (Berlin : Springer-Verlag, 1953.) [Pp. vii+ 318.] DM 40.

Extensive Air Showers. By W. Galbraith. (London: Butterworths, 1958.) [Pp. xvi + 211.] 40s.

The Chemistry of Organic Compounds. By J. B. Conant and A. H. Blatt. 5th Edition. (New York: The Macmillan Co., 1959.) [Pp. viii+652.] 54s.

Physics and Electronics in Physical Medicine. By A. Nightingale. (London : G. Bell &; Sons, 1959.) [Pp. x+292.] 30s.

Nuclear Reactor Materials. By B. R. T. Frost and M. B. Waldron. (London: Temple Press, 1959.) [Pp. vii + 79.] 12s. 6d.

Techniques Modernes et Applications de la Cryometrie. By Y. Doucet. (Paris : Dunod, 1959.) [Pp. 225.]

The General Properties of Matter. A 48-page handbook published and issued with the Home Scientist sets marketed by Kay (Sports and Games) Ltd., The Hyde, London, N.W.7.

The Prof: A Personal Memoir of Lord Cherwell. By R. F. Harrod. (London: Macmillan &; Co., 1959.) [Pp. xvi+282.] 25s.

Introductory Nuclear Theory. By Dr. L. R. B. Elton. (London : Pitman, 1959.) [Pp. xi+286.] 40s.

Les Satellites Artifciels et l'Astronautique. By R. Andre. (Paris: Dunod, 1959.) [Pp. 126.]

The Elements of Determinants, Matrices and Tensors for Engineers. By A. Austen Stigant. (London: Macdonald, 1959.) [pp. xi+133.] 60s.

Physikalisch-chemisches Rechnen in Wissenschaft und Technik. By Hans Fromherz. (Verlag Chemie, Weinheim/Bergstrasse.) [Pp. ix + 316.] DM 32.50.

University Entrance. The Basic Facts. Published by the National Union of Teachers, 1959. [Pp. 48.] 3s. 6d.

Teaching in Comprehensive Schools. A first report issued by the Incorporated Association (London : Cambridge University Press, of Assistant Masters in Secondary Schools. 1960 n.p.) [Pp. 48.]

The Advancement of Science, Vol. XVI, No. 3, December 1959. (The British Association for the Advancement of Science, London.) 7s. 6d.

Classical Dynamics. By R. H. Atkin. (London: Heinemann, 1959.) [Pp. ix +273.] 30s.

British Nuclear Reactors. By Gerard Gibbons and Kenneth Jay. (London: Chatto and Windus, 1960.) [Pp. 32.1 6s. 6d.

Materials and Processes of Electron Devices. By Max Knoll, assisted by B. Kazan. (Springer, 1959.) [Pp. xii+480.] DM 66.

Beam and Wave Electronics in Microwave Tubes. By R. G. E. Hutter. (D. Van Nostrand Co. Inc., 1960.) [Pp. xii+378.] 73s. 6d.

Space Flight. Volume 1: Environment and Celestial Mechanics. By K. A. Ehricke. (London: D. van Nostrand Company, Inc., 1960.) [Pp. x+513.] 109s.

Static Electrification. By Leonard B. Loeb. (Springer-Verlag, 1958.) [Pp. xii + 240.] DM 48.

Theory of Elementary Particles. By P. Roman. (Amsterdam : North-Holland Publishing Company.) [Pp. xii + 575.] (N.P.)

Molecular Structure-the Physical Approach. By J. C. D. Brand and J. C. Speakman. (London: Edward Arnold (Publishers) Ltd., 1960.) [Pp. viii + 300.] 30s.

Modern Physics. By H. A. Wilson. (London : Blackie &; Son Ltd., 4th edition, 1959.) [Pp. xv + 473] 40s.

Scientific and Engineering Manpower in Great Britain, 1959. Report of the Committee on Scientific Manpower of the Advisory Council on Scientific Policy. (Cmnd. 902, H.M.S.O., November 1959.) 3s.

Training in Radiological Health and Safety : Report of a Committee appointed by the United Kingdom Atomic Energy Authority. (London : H.M.S.O., 1960.) 5s. 6d.

Biographical Memoirs of Fellows of the Royal Society. Vol. 5 . (London: The Royal Society, 1960.) [Pp. 269.] 30s.     

Batchwise and Continuous Organophilic Nanofiltration of Grubbs‐Type Olefin Metathesis Catalysts

Retained : An N‐heterocyclic carbene with eight cyclohexyl groups (see figure) provides increased electron density for a highly active olefin metathesis catalyst as well as sufficient steric bulk to allow the efficient separation of such a complex from the organic products in the solvent‐resistant nanofiltration.

     

A Reversible Theory of Entanglement and its Relation to the Second Law

We consider the manipulation of multipartite entangled states in the limit of many copies under quantum operations that asymptotically cannot generate entanglement. In stark contrast to the manipulation of entanglement under local operations and classical communication, the entanglement shared by two or more parties can be reversibly interconverted in this setting. The unique entanglement measure is identified as the regularized relative entropy of entanglement, which is shown to be equal to a regularized and smoothed version of the logarithmic robustness of entanglement. Here we give a rigorous proof of this result, which is fundamentally based on a certain recent extension of quantum Stein’s Lemma, giving the best measurement strategy for discriminating several copies of an entangled state from an arbitrary sequence of non-entangled states, with an optimal distinguishability rate equal to the regularized relative entropy of entanglement. We moreover analyse the connection of our approach to axiomatic formulations of the second law of thermodynamics.     

Quantum many‐body phenomena in coupled cavity arrays

The increasing level of experimental control over atomic and optical systems gained in recent years has paved the way for the exploration of new physical regimes in quantum optics and atomic physics, characterised by the appearance of quantum many‐body phenomena, originally encountered only in condensed‐matter physics, and the possibility of experimentally accessing them in a more controlled manner. In this review article we survey recent theoretical studies concerning the use of cavity quantum electrodynamics to create quantum many‐body systems. Based on recent experimental progress in the fabrication of arrays of interacting micro‐cavities and on their coupling to atomic‐like structures in several different physical architectures, we review proposals on the realisation of paradigmatic many‐body models in such systems, such as the Bose‐Hubbard and the anisotropic Heisenberg models. Such arrays of coupled cavities offer interesting properties as simulators of quantum many‐body physics, including the full addressability of individual sites and the accessibility of inhomogeneous models.