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https://www.readbyqxmd.com/read/28241665/controlling-light-with-freeform-multifocal-lens-designed-with-supporting-quadric-method-sqm
#1
Vladimir Oliker
The SQM is a versatile methodology for designing freeform optics for irradiance redistribution. Recently it has often been applied in design of freeform lenses, mirrors and diffractive optical elements. Still, many questions regarding theory and performance of optics designed with the SQM are open. Here we investigate theoretically plano-freeform refractive lenses designed with the SQM when an incident collimated beam must be transformed into a beam illuminating with prescribed irradiances a large number of pixels on a flat screen...
February 20, 2017: Optics Express
https://www.readbyqxmd.com/read/28211734/positivity-of-curvature-squared-corrections-in-gravity
#2
Clifford Cheung, Grant N Remmen
We study the Gauss-Bonnet (GB) term as the leading higher-curvature correction to pure Einstein gravity. Assuming a tree-level ultraviolet completion free of ghosts or tachyons, we prove that the GB term has a nonnegative coefficient in dimensions greater than 4. Our result follows from unitarity of the spectral representation for a general ultraviolet completion of the GB term.
February 3, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28211455/supermode-density-wave-polariton-condensation-with-a-bose-einstein-condensate-in-a-multimode-cavity
#3
Alicia J Kollár, Alexander T Papageorge, Varun D Vaidya, Yudan Guo, Jonathan Keeling, Benjamin L Lev
Phase transitions, where observable properties of a many-body system change discontinuously, can occur in both open and closed systems. By placing cold atoms in optical cavities and inducing strong coupling between light and excitations of the atoms, one can experimentally study phase transitions of open quantum systems. Here we observe and study a non-equilibrium phase transition, the condensation of supermode-density-wave polaritons. These polaritons are formed from a superposition of cavity photon eigenmodes (a supermode), coupled to atomic density waves of a quantum gas...
February 17, 2017: Nature Communications
https://www.readbyqxmd.com/read/28208419/einstein-podolsky-rosen-paradox-implies-a-minimum-achievable-temperature
#4
David M Rogers
This work examines the thermodynamic consequences of the repeated partial projection model for coupling a quantum system to an arbitrary series of environments under feedback control. This paper provides observational definitions of heat and work that can be realized in current laboratory setups. In contrast to other definitions, it uses only properties of the environment and the measurement outcomes, avoiding references to the "measurement" of the central system's state in any basis. These definitions are consistent with the usual laws of thermodynamics at all temperatures, while never requiring complete projective measurement of the entire system...
January 2017: Physical Review. E
https://www.readbyqxmd.com/read/28208309/dimensional-reduction-in-bose-einstein-condensed-clouds-of-atoms-confined-in-tight-potentials-of-any-geometry-and-any-interaction-strength
#5
P Sandin, M Ögren, M Gulliksson, J Smyrnakis, M Magiropoulos, G M Kavoulakis
Motivated by numerous experiments on Bose-Einstein condensed atoms which have been performed in tight trapping potentials of various geometries [elongated and/or toroidal (annular)], we develop a general method which allows us to reduce the corresponding three-dimensional Gross-Pitaevskii equation for the order parameter into an effectively one-dimensional equation, taking into account the interactions (i.e., treating the width of the transverse profile variationally) and the curvature of the trapping potential...
January 2017: Physical Review. E
https://www.readbyqxmd.com/read/28196896/brownian-motion-of-solitons-in-a-bose-einstein-condensate
#6
Lauren M Aycock, Hilary M Hurst, Dmitry K Efimkin, Dina Genkina, Hsin-I Lu, Victor M Galitski, I B Spielman
We observed and controlled the Brownian motion of solitons. We launched solitonic excitations in highly elongated [Formula: see text] Bose-Einstein condensates (BECs) and showed that a dilute background of impurity atoms in a different internal state dramatically affects the soliton. With no impurities and in one dimension (1D), these solitons would have an infinite lifetime, a consequence of integrability. In our experiment, the added impurities scatter off the much larger soliton, contributing to its Brownian motion and decreasing its lifetime...
February 14, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28193284/selective-intra-dinucleotide-interactions-and-periodicities-of-bases-separated-by-k-sites-a-new-vision-and-tool-for-phylogeny-analyses
#7
REVIEW
Carlos Y Valenzuela
Direct tests of the random or non-random distribution of nucleotides on genomes have been devised to test the hypothesis of neutral, nearly-neutral or selective evolution. These tests are based on the direct base distribution and are independent of the functional (coding or non-coding) or structural (repeated or unique sequences) properties of the DNA. The first approach described the longitudinal distribution of bases in tandem repeats under the Bose-Einstein statistics. A huge deviation from randomness was found...
February 13, 2017: Biological Research
https://www.readbyqxmd.com/read/28191897/universal-lower-limit-on-vortex-creep-in-superconductors
#8
S Eley, M Miura, B Maiorov, L Civale
Superconductors are excellent testbeds for studying vortices, topological excitations that also appear in superfluids, liquid crystals and Bose-Einstein condensates. Vortex motion can be disruptive; it can cause phase transitions, glitches in pulsars, and losses in superconducting microwave circuits, and it limits the current-carrying capacity of superconductors. Understanding vortex dynamics is fundamentally and technologically important, and the competition between thermal energy and energy barriers defined by material disorder is not completely understood...
February 13, 2017: Nature Materials
https://www.readbyqxmd.com/read/28186806/casimir-forces-and-quantum-friction-from-ginzburg-radiation-in-atomic-bose-einstein-condensates
#9
Jamir Marino, Alessio Recati, Iacopo Carusotto
We theoretically propose an experimentally viable scheme to use an impurity atom in an atomic Bose-Einstein condensate, in order to realize condensed-matter analogs of quantum vacuum effects. In a suitable atomic level configuration, the collisional interaction between the impurity atom and the density fluctuations in the condensate can be tailored to closely reproduce the electric-dipole coupling of quantum electrodynamics. By virtue of this analogy, we recover and extend the paradigm of electromagnetic vacuum forces to the domain of cold atoms, showing in particular the emergence, at supersonic atomic speeds, of a novel power-law scaling of the Casimir force felt by the atomic impurity, as well as the occurrence of a quantum frictional force, accompanied by the Ginzburg emission of Bogoliubov quanta...
January 27, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28186803/linear-and-nonlinear-bullets-of-the-bogoliubov-de-gennes-excitations
#10
S Kumar, A M Perego, K Staliunas
We report on the focalization of Bogoliubov-de Gennes excitations of the nonlinear Schrödinger equation in the defocusing regime (Gross-Pitaevskii equation for repulsive Bose-Einstein condensates) with a spatially modulated periodic potential. Exploiting the modification of the dispersion relation induced by the modulation, we demonstrate the existence of localized structures of the Bogoliubov-de Gennes excitations, in both the linear and nonlinear regimes (linear and nonlinear "bullets"). These traveling Bogoliubov-de Gennes bullets, localized both spatially and temporally in the comoving reference frame, are robust and propagate remaining stable, without spreading or filamentation...
January 27, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28186789/meissner-like-effect-for-a-synthetic-gauge-field-in-multimode-cavity-qed
#11
Kyle E Ballantine, Benjamin L Lev, Jonathan Keeling
Previous realizations of synthetic gauge fields for ultracold atoms do not allow the spatial profile of the field to evolve freely. We propose a scheme which overcomes this restriction by using the light in a multimode cavity with many nearly degenerate transverse modes, in conjunction with Raman coupling, to realize an artificial magnetic field which acts on a Bose-Einstein condensate of neutral atoms. We describe the evolution of such a system and present the results of numerical simulations which show dynamical coupling between the effective field and the matter on which it acts...
January 27, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28183976/deterministic-entanglement-generation-from-driving-through-quantum-phase-transitions
#12
Xin-Yu Luo, Yi-Quan Zou, Ling-Na Wu, Qi Liu, Ming-Fei Han, Meng Khoon Tey, Li You
Many-body entanglement is often created through the system evolution, aided by nonlinear interactions between the constituting particles. These very dynamics, however, can also lead to fluctuations and degradation of the entanglement if the interactions cannot be controlled. Here, we demonstrate near-deterministic generation of an entangled twin-Fock condensate of ~11,000 atoms by driving a arubidium-87 Bose-Einstein condensate undergoing spin mixing through two consecutive quantum phase transitions (QPTs)...
February 10, 2017: Science
https://www.readbyqxmd.com/read/28179594/nuclear-cardiology-practice-in-asia-analysis-of-radiation-exposure-and-best-practice-for-myocardial-perfusion-imaging%C3%A3-results-from-the-iaea-nuclear-cardiology-protocols-cross-sectional-study-incaps
#13
Thomas N B Pascual, Mathew Mercuri, Noura El-Haj, Henry Hee-Sung Bom, Vikram Lele, Mouaz H Al-Mallah, Osnat Luxenburg, Ganesan Karthikeyan, Joao Vitola, John J Mahmarian, Nathan Better, Leslee J Shaw, Madan M Rehani, Ravi Kashyap, Diana Paez, Maurizio Dondi, Andrew J Einstein
BACKGROUND: This paper examines the current status of radiation exposure to patients in myocardial perfusion imaging (MPI) in Asia.Methods and Results:Laboratories voluntarily provided information on MPI performed over a 1-week period. Eight best practice criteria regarding MPI were predefined by an expert panel. Implementation of ≥6 best practices (quality index [QI] ≥6) was pre-specified as a desirable goal for keeping radiation exposure at a low level. Radiation effective dose (ED) in 1,469 patients and QI of 69 laboratories in Asia were compared against data from 239 laboratories in the rest of the world (RoW)...
February 8, 2017: Circulation Journal: Official Journal of the Japanese Circulation Society
https://www.readbyqxmd.com/read/28169331/nanosecond-time-resolved-characterization-of-a-pentacene-based-room-temperature-maser
#14
Enrico Salvadori, Jonathan D Breeze, Ke-Jie Tan, Juna Sathian, Benjamin Richards, Mei Wai Fung, Gary Wolfowicz, Mark Oxborrow, Neil McN Alford, Christopher W M Kay
The performance of a room temperature, zero-field MASER operating at 1.45 GHz has been examined. Nanosecond laser pulses, which are essentially instantaneous on the timescale of the spin dynamics, allow the visible-to-microwave conversion efficiency and temporal response of the MASER to be measured as a function of excitation energy. It is observed that the timing and amplitude of the MASER output pulse are correlated with the laser excitation energy: at higher laser energy, the microwave pulses have larger amplitude and appear after shorter delay than those recorded at lower laser energy...
February 7, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28147663/a-cylindrically-symmetric-magnetic-trap-for-compact-bose-einstein-condensate-atom-interferometer-gyroscopes
#15
R A Horne, C A Sackett
We present a variant of the time-orbiting potential trap suitable for Bose-Einstein condensate atom interferometers, which provides weak, cylindrically symmetric confinement as well as support for the atoms against gravity. This trapping configuration is well-suited for the implementation of a compact atom interferometer based gyroscope. The trap is made up of six coils, which were produced using photolithographic techniques and take up a modest volume of approximately 1 cubic inch inside a vacuum chamber. The trapping frequencies and thermal characteristics of the trap are presented, showing cylindrical symmetry and scalability of the trapping frequencies from 1 Hz to 8 Hz in the symmetry plane...
January 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28145899/vortices-and-vortex-lattices-in-quantum-ferrofluids
#16
A M Martin, N G Marchant, D H J O'Dell, N G Parker
The experimental realization of quantum-degenerate Bose gases made of atoms with sizeable magnetic dipole moments has created a new type of fluid, known as a quantum ferrofluid, which combines the extraordinary properties of superfluidity and ferrofluidity. A hallmark of superfluids is that they are constrained to rotate through vortices with quantized circulation. In quantum ferrofluids the long-range dipolar interactions add new ingredients by inducing magnetostriction and instabilities, and also affect the structural properties of vortices and vortex lattices...
March 15, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28138531/twist-induced-guidance-in-coreless-photonic-crystal-fiber-a-helical-channel-for-light
#17
Ramin Beravat, Gordon K L Wong, Michael H Frosz, Xiao Ming Xi, Philip St J Russell
A century ago, Einstein proposed that gravitational forces were the result of the curvature of space-time and predicted that light rays would deflect when passing a massive celestial object. We report that twisting the periodically structured "space" within a coreless photonic crystal fiber creates a helical channel where guided modes can form despite the absence of any discernible core structure. Using a Hamiltonian optics analysis, we show that the light rays follow closed spiral or oscillatory paths within the helical channel, in close analogy with the geodesics of motion in a two-dimensional gravitational field...
November 2016: Science Advances
https://www.readbyqxmd.com/read/28132422/probing-the-biology-of-cell-boundary-conditions-through-confinement-of-xenopus-cell-free-cytoplasmic-extracts
#18
REVIEW
Jessica G Bermudez, Hui Chen, Lily C Einstein, Matthew C Good
Cell-free cytoplasmic extracts prepared from Xenopus eggs and embryos have for decades provided a biochemical system with which to interrogate complex cell biological processes in vitro. Recently, the application of microfabrication and microfluidic strategies in biology has narrowed the gap between in vitro and in vivo studies by enabling formation of cell-size compartments containing functional cytoplasm. These approaches provide numerous advantages over traditional biochemical experiments performed in a test tube...
January 2017: Genesis: the Journal of Genetics and Development
https://www.readbyqxmd.com/read/28128618/dark-energy-from-violation-of-energy-conservation
#19
Thibaut Josset, Alejandro Perez, Daniel Sudarsky
In this Letter, we consider the possibility of reconciling metric theories of gravitation with a violation of the conservation of energy-momentum. Under some circumstances, this can be achieved in the context of unimodular gravity, and it leads to the emergence of an effective cosmological constant in Einstein's equation. We specifically investigate two potential sources of energy nonconservation-nonunitary modifications of quantum mechanics and phenomenological models motivated by quantum gravity theories with spacetime discreteness at the Planck scale-and show that such locally negligible phenomena can nevertheless become relevant at the cosmological scale...
January 13, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28125345/application-of-microrheology-in-food-science
#20
Nan Yang, Ruihe Lv, Junji Jia, Katsuyoshi Nishinari, Yapeng Fang
Microrheology provides a technique to probe the local viscoelastic properties and dynamics of soft materials at the microscopic level by observing the motion of tracer particles embedded within them. It is divided into passive and active microrheology according to the force exerted on the embedded particles. Particles are driven by thermal fluctuations in passive microrheology, and the linear viscoelasticity of samples can be obtained on the basis of the generalized Stokes-Einstein equation. In active microrheology, tracer particles are controlled by external forces, and measurements can be extended to the nonlinear regime...
January 12, 2017: Annual Review of Food Science and Technology
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