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Modular Hamiltonians on the null plane and the Markov property of the vacuum state
http://iopscience.iop.org/1751-8121/50/36/364001
We compute the modular Hamiltonians of regions having the future horizon lying on a null plane. For
a CFT this is equivalent to regions with a boundary of arbitrary shape lying on the null cone. These
Hamiltonians have a local expression on the horizon formed by integrals of the stress tensor. We
prove this result in two different ways, and show that the modular Hamiltonians of these regions
form an infinite dimensional Lie algebra. The corresponding group of unitary transformations moves
the fields on the null surface locally along the null generators with arbitrary null line dependent
velocities, but act non-locally outside the null plane. We regain this result in greater generality
using more abstract tools on the algebraic quantum field theory. Finally, we show that modular
Hamiltonians on the null surface satisfy a Markov property that leads to the saturation of the
strong sub-additive inequality for the entropies and to the strong super-additivity of the relative
entropy.<...Horacio Casini, Eduardo Testé and Gonzalo Torroba2017-08-07T23:00:00ZJournal of Physics A: Mathematical and TheoreticalHoracio Casini <em>et al</em>Horacio Casini <em>et al</em> 2017 <em>J. Phys. A: Math. Theor.</em> <b>50</b> 364001http://iopscience.iop.org/1751-8121/50/36/364001/pdf/a_50_36_364001.pdf08/September/20173650Journal of Physics A: Mathematical and Theoretical36400110.1088/1751-8121/aa7eaaA note on magnetic generalizations of the Kerr and Kerr–Newman solutions
http://iopscience.iop.org/0264-9381/34/17/177002
A concise form of the asymptotically flat metrics describing the simplest magnetic generalizations
of the Kerr and Kerr–Newman spacetimes is presented. The explicit formulae for the corresponding
electromagnetic potentials are also given, together with simple expressions of all metric functions
in the equatorial plane. It is shown that the magnetic field changes the structure of the
gravitational multipole moments of the vacuum Kerr solution.V S Manko2017-08-01T23:00:00ZClassical and Quantum GravityV S MankoV S Manko 2017 <em>Class. Quantum Grav.</em> <b>34</b> 177002http://iopscience.iop.org/0264-9381/34/17/177002/pdf/cqg_34_17_177002.pdf07/September/20171734Classical and Quantum Gravity17700210.1088/1361-6382/aa80bbEffect of doping on lattice dynamics and electron–phonon coupling of the actinides Ac–Th alloy
http://iopscience.iop.org/0953-8984/29/35/355401
We have studied the electronic, lattice dynamical, and electron–phonon properties of the actinides
##IMG## [http://ej.iop.org/images/0953-8984/29/35/355401/cmaa7c05ieqn001.gif] {${\rm Ac}_{1-x}$} Th
x alloy within the framework of density functional perturbation theory. The self-consistent virtual
crystal approximation is used for the alloy modeling, and spin–orbit coupling is included in the
calculation of all relevant quantities. An overall decrease of the electron–phonon coupling ( λ ) by
##IMG## [http://ej.iop.org/images/0953-8984/29/35/355401/cmaa7c05ieqn002.gif] {$53\%$} from Ac to Th
was observed. However, its dependence on x shows a non-linear behavior. λ reduces just 6% from Ac to
a Th content of ##IMG## [http://ej.iop.org/images/0953-8984/29/35/355401/cmaa7c05ieqn003.gif]
{$x=0.4$} , then drops drastically (∼ ##IMG## [http://ej.iop.org/i...] {$47\%$}R de Coss-Martínez, P González-Castelazo, O De la Peña-Seaman, R Heid and K-P Bohnen2017-07-30T23:00:00ZJournal of Physics: Condensed MatterR de Coss-Martínez <em>et al</em>R de Coss-Martínez <em>et al</em> 2017 <em>J. Phys.: Condens. Matter</em> <b>29</b> 355401http://iopscience.iop.org/0953-8984/29/35/355401/pdf/cm_29_35_355401.pdf06/September/20173529Journal of Physics: Condensed Matter35540110.1088/1361-648X/aa7c05Geometric mechanics of ray optics as particle dynamics: refraction index with cylindrical symmetry
http://iopscience.iop.org/0143-0807/38/5/055302
Starting from the Fermat principle of geometrical optics, we analyse the ray dynamics in a graded
refractive index system device with cylindrical symmetry and a refractive index that decreases
parabolically with the radial coordinate. By applying Hamiltonian dynamics to the study of the ray
path we obtain the strict equivalence of this optical system with the dynamics of a particle with an
equivalent mass moving in a potential function that may exhibit a well, depending on the value of
some associated parameters. We analyse the features of this potential function as well as the energy
values and the symmetries of the system and see that both the azimuthal and axial components of the
optical conjugate momentum are two constants of motion. The phase space relation for the momentum
radial component is obtained analytically, and then we can obtain the components of the momentum
vector at any point, given the value of the radial coordinate, and from this we have the direction
...Emilio Cortés and Melina Ruiz2017-08-07T23:00:00ZEuropean Journal of PhysicsEmilio Cortés and Melina RuizEmilio Cortés and Melina Ruiz 2017 <em>Eur. J. Phys.</em> <b>38</b> 055302http://iopscience.iop.org/0143-0807/38/5/055302/pdf/ejp_38_5_055302.pdf01/September/2017538European Journal of Physics05530210.1088/1361-6404/aa7610Twisting dirac fermions: circular dichroism in bilayer graphene
http://iopscience.iop.org/2053-1583/4/3/035015
Twisted bilayer graphene is a chiral system which has been recently shown to present circular
dichroism. In this work we show that the origin of this optical activity is the rotation of the
Dirac fermions’ helicities in the top and bottom layer. Starting from the Kubo formula, we obtain a
compact expression for the Hall conductivity that takes into account the dephasing of the
electromagnetic field between the top and bottom layers and gathers all the symmetries of the
system. Our results are based in both a continuum and a tight-binding model, and they can be
generalized to any two-dimensional Dirac material with a chiral stacking between layers.E Suárez Morell, Leonor Chico and Luis Brey2017-07-23T23:00:00Z2D MaterialsE Suárez Morell <em>et al</em>E Suárez Morell <em>et al</em> 2017 <em>2D Mater.</em> <b>4</b> 035015http://iopscience.iop.org/2053-1583/4/3/035015/pdf/tdm_4_3_035015.pdf01/September/2017342D Materials03501510.1088/2053-1583/aa7eb6Control of base-excited dynamical systems through piezoelectric energy harvesting absorber
http://iopscience.iop.org/0964-1726/26/9/095013
The spring-mass absorber usually offers a good control to dynamical systems under direct base
excitations for a specific value of the excitation frequency. As the vibrational energy of a primary
dynamical system is transferred to the absorber, it gets dissipated. In this study, this energy is
no longer dissipated but converted to available electrical power by designing efficient energy
harvesters. A novel design of a piezoelectric beam installed inside an elastically-mounted dynamical
system undergoing base excitations is considered. A design is carried out in order to determine the
properties and dimensions of the energy harvester with the constraint of simultaneously decreasing
the oscillating amplitudes of the primary dynamical system and increasing the harvested power of the
energy harvesting absorber. An analytical model for the coupled system is constructed using
Euler–Lagrange principle and Galerkin discretization. Different strategies for controlling the
primary structur...H Abdelmoula, H L Dai, A Abdelkefi and L Wang2017-08-08T23:00:00ZSmart Materials and StructuresH Abdelmoula <em>et al</em>H Abdelmoula <em>et al</em> 2017 <em>Smart Mater. Struct.</em> <b>26</b> 095013http://iopscience.iop.org/0964-1726/26/9/095013/pdf/sms_26_9_095013.pdf01/September/2017926Smart Materials and Structures09501310.1088/1361-665X/aa76b3Strong influence of the oxygen stoichiometry on the vortex bundle size and critical current
densities J c of GdBa 2 Cu 3 O x -coated conductors grown by co-evaporation
http://iopscience.iop.org/0953-2048/30/9/095009
We report on the influence of oxygen stoichiometry on the vortex creep mechanism of GdBa 2 Cu 3 O x
-coated conductors produced by co-evaporation. The oxygen stoichiometry of the films, x , was
modified in a controlled way between 6.85 and 7, which resulted in systematic and reversible control
of the superconducting critical temperature between about 78 and 93 K. The change in the oxygen
stoichiometry produces a strong reduction in the self-field critical current densities J c without
significantly modifying the power-law dependence at intermediate magnetic fields, which indicates a
negligible contribution of oxygen vacancies to the pinning. In addition, the characteristic glassy
exponent μ shows a systematic diminution from about 1.63 at x = 7 to about 1.12 at x = 6.85. The
results are compared with those obtained for proton- and oxygen-irradiated films, in which the
vortex dynamics is determined b...N Haberkorn, J Guimpel, S Suárez, H Troiani, P Granell, F Golmar, Jae-Hun Lee, S H Moon and Hunju Lee2017-08-10T23:00:00ZSuperconductor Science and TechnologyN Haberkorn <em>et al</em>N Haberkorn <em>et al</em> 2017 <em>Supercond. Sci. Technol.</em> <b>30</b> 095009http://iopscience.iop.org/0953-2048/30/9/095009/pdf/sust_30_9_095009.pdf01/September/2017930Superconductor Science and Technology09500910.1088/1361-6668/aa7d19Spectral tunability of two-photon states generated by spontaneous four-wave mixing: fibre tapering,
temperature variation and longitudinal stress
http://iopscience.iop.org/2058-9565/2/3/034015
We explore three different mechanisms designed to controllably tune the joint spectrum of photon
pairs produced by the spontaneous four-wave mixing (SFWM) process in optical fibres. The first of
these is fibre tapering, which exploits the modified optical dispersion resulting from reducing the
core radius. We have presented a theory of SFWM for tapered fibres, as well as experimental results
for the SFWM coincidence spectra as a function of the reduction in core radius due to tapering. The
other two techniques that we have explored are temperature variation and application of longitudinal
stress. While the maximum spectral shift observed with these two techniques is smaller than for
fibre tapering, they are considerably simpler to implement and have the important advantage that
they are based on the use of a single, suitably controlled, fibre specimen.E Ortiz-Ricardo, C Bertoni-Ocampo, Z Ibarra-Borja, R Ramirez-Alarcon, D Cruz-Delgado, H Cruz-Ramirez, K Garay-Palmett and A B U’Ren2017-08-01T23:00:00ZQuantum Science and TechnologyE Ortiz-Ricardo <em>et al</em>E Ortiz-Ricardo <em>et al</em> 2017 <em>Quantum Sci. Technol.</em> <b>2</b> 034015http://iopscience.iop.org/2058-9565/2/3/034015/pdf/qst_2_3_034015.pdf01/September/201732Quantum Science and Technology03401510.1088/2058-9565/aa7a37Active learning of geometrical optics in high school: the ALOP approach
http://iopscience.iop.org/0031-9120/52/5/055005
A group comparison experiment of two high school classes with pre and post instruction testing has
been carried out to study the suitability and advantages of using the active learning of optics and
photonics (ALOP) curricula in high schools of developing countries. Two parallel, mixed gender, 12th
grade classes of a high school run by the local university were chosen. One course was randomly
selected to follow the experimental instruction, based on teacher and student activities contained
in the ALOP Manual. The other course followed the traditional, teacher-centered, instruction
previously practiced. Conceptual knowledge of the characteristics of image formation by plane
mirrors and single convergent and divergent lenses was measured by applying, in both courses, the
multiple-choice test, light and optics conceptual evaluation (LOCE). Measurement before instruction
showed that initial knowledge was almost null, and therefore equivalent, in both courses. After
instruction testi...Alejandra Alborch, Susana Pandiella and Julio Benegas2017-07-31T23:00:00ZPhysics EducationAlejandra Alborch <em>et al</em>Alejandra Alborch <em>et al</em> 2017 <em>Phys. Educ.</em> <b>52</b> 055005http://iopscience.iop.org/0031-9120/52/5/055005/pdf/ped_52_5_055005.pdf01/September/2017552Physics Education05500510.1088/1361-6552/aa7cceAbsolute Magnitudes and Colors of RR Lyrae Stars in DECam Passbands from Photometry of the Globular
Cluster M5
http://iopscience.iop.org/1538-3881/154/3/85
We characterize the absolute magnitudes and colors of RR Lyrae stars in the globular cluster M5 in
the ugriz filter system of the Dark Energy Camera (DECam). We provide empirical period–luminosity
(P–L) relationships in all five bands based on 47 RR Lyrae stars of the type ab and 14 stars of the
type c. The P–L relationships were found to be better constrained for the fundamental-mode RR Lyrae
stars in the riz passbands, with dispersions of 0.03, 0.02 and 0.02 mag, respectively. The
dispersion of the color at minimum light was found to be small, supporting the use of this parameter
as a means to obtain accurate interstellar extinctions along the line of sight up to the distance of
the RR Lyrae star. We found a trend of color at minimum light with a pulsational period that, if
taken into account, brings the dispersion in color at minimum light to ##IMG##
[http://ej.iop.org/images/1538-3881/154/3/85/ajaa7fedieqn1.gif] {$\leqslant 0.016$} mag for...A. Katherina Vivas, Abhijit Saha, Knut Olsen, Robert Blum, Edward W. Olszewski, Jennifer Claver, Francisco Valdes, Tim Axelrod, Catherine Kaleida, Andrea Kunder, Gautham Narayan, Thomas Matheson, and Alistair Walker2017-08-03T23:00:00ZThe Astronomical JournalA. Katherina Vivas <em>et al.</em>A. Katherina Vivas <em>et al.</em> 2017 <em>AJ</em> <b>154</b> 85http://iopscience.iop.org/1538-3881/154/3/85/pdf/aj_154_3_85.pdf01/September/20173154The Astronomical Journal8510.3847/1538-3881/aa7fed