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Liang Hu, Nicola Poli, Leonardo Salvi, Guglielmo M Tino
We report on the realization of a matter-wave interferometer based on single-photon interaction on the ultranarrow optical clock transition of strontium atoms. We experimentally demonstrate its operation as a gravimeter and as a gravity gradiometer. No reduction of interferometric contrast was observed for a total interferometer time up to ∼10  ms, limited by geometric constraints of the apparatus. Single-photon interferometers represent a new class of high-precision sensors that could be used for the detection of gravitational waves in so far unexplored frequency ranges and to enlighten the boundary between quantum mechanics and general relativity...
December 29, 2017: Physical Review Letters
Monica Pate, Ana-Maria Raclariu, Andrew Strominger
A transient color flux across null infinity in classical Yang-Mills theory is considered. It is shown that a pair of test "quarks" initially in a color singlet generically acquire net color as a result of the flux. A nonlinear formula is derived for the relative color rotation of the quarks. For a weak color flux, the formula linearizes to the Fourier transform of the soft gluon theorem. This color memory effect is the Yang-Mills analog of the gravitational memory effect.
December 29, 2017: Physical Review Letters
Christopher J Moore, Deyan P Mihaylov, Anthony Lasenby, Gerard Gilmore
Gravitational waves (GWs) cause the apparent position of distant stars to oscillate with a characteristic pattern on the sky. Astrometric measurements (e.g., those made by Gaia) provide a new way to search for GWs. The main difficulty facing such a search is the large size of the data set; Gaia observes more than one billion stars. In this Letter the problem of searching for GWs from individually resolvable supermassive black hole binaries using astrometry is addressed for the first time; it is demonstrated how the data set can be compressed by a factor of more than 10^{6}, with a loss of sensitivity of less than 1%...
December 29, 2017: Physical Review Letters
Donglin Ma
Recently, China is planning to construct a new large optical-infrared telescope (LOT), in which the aperture of the primary mirror is as large as 12m. China's LOT is a general-purpose telescope, which is aimed to work with multiple scientific instruments such as spectrographs. Based on the requirements of LOT telescope, we have compared the performance of Ritchey-Chrétien (RC) design and Aplanatic-Gregorian (AG) design from the perspective of scientific performance and construction cost. By taking the primary focal ratio, Nasmyth focal ratio, and telescope's site condition into consideration, we finally recommend a RC f/1...
January 8, 2018: Optics Express
S Longhi
Einstein's equivalence principle (EP) states the complete physical equivalence of a gravitational field and corresponding inertial field in an accelerated reference frame. However, to what extent the EP remains valid in non-relativistic quantum mechanics is a controversial issue. To avoid violation of the EP, Bargmann's superselection rule forbids a coherent superposition of states with different masses. Here we suggest a quantum simulation of non-relativistic Schrödinger particle dynamics in non-inertial reference frames, which is based on the propagation of polarization-entangled photon pairs in curved and birefringent optical waveguides and Hong-Ou-Mandel quantum interference measurement...
January 15, 2018: Optics Letters
Akihisa Miayagawa, Makoto Harada, Tetsuo Okada
We present a novel analytical principle in which an analyte (according to its concentration) induces a change in the density of a microparticle, which is measured as a vertical coordinate in a coupled acoustic-gravitational (CAG) field. The density change is caused by the binding of gold nanoparticles (AuNPs) on a polystyrene (PS) microparticle through avidin-biotin association. The density of a 10-m PS particle increases by 2 % when 500 100-nm AuNPs are bound to the PS. The CAG can detect this density change as a 5-10-m shift of the levitation coordinate of the PS...
January 12, 2018: Analytical Chemistry
D Hammond, R Welbury, G Sammons, E Toman, M Harland, S Rice
Craniofacial trauma results in distracting injuries that are easy to see, and as oral and maxillofacial surgeons (OMFS) we gravitate towards injuries that can be seen and are treatable surgically. However, we do tend not to involve ourselves (and may potentially overlook) injuries that are not obvious either visually or radiographically, and concussion is one such. We reviewed the records of 500 consecutive patients who presented with facial fractures at the Queen Elizabeth Hospital, Birmingham, to identify whether patients had been screened for concussion, and how they had been managed...
January 8, 2018: British Journal of Oral & Maxillofacial Surgery
Sisi Zhou, Mengzhen Zhang, John Preskill, Liang Jiang
Quantum metrology has many important applications in science and technology, ranging from frequency spectroscopy to gravitational wave detection. Quantum mechanics imposes a fundamental limit on measurement precision, called the Heisenberg limit, which can be achieved for noiseless quantum systems, but is not achievable in general for systems subject to noise. Here we study how measurement precision can be enhanced through quantum error correction, a general method for protecting a quantum system from the damaging effects of noise...
January 8, 2018: Nature Communications
Jeremy Sakstein, Bhuvnesh Jain
The LIGO and VIRGO Collaborations have recently announced the detection of gravitational waves from a neutron star-neutron star merger (GW170817) and the simultaneous measurement of an optical counterpart (the γ-ray burst GRB 170817A). The close arrival time of the gravitational and electromagnetic waves limits the difference in speed of photons and gravitons to be less than about 1 part in 10^{15}. This has three important implications for cosmological scalar-tensor gravity theories that are often touted as dark energy candidates and alternatives to the Λ cold dark matter model...
December 22, 2017: Physical Review Letters
Pedro V P Cunha, Emanuele Berti, Carlos A R Herdeiro
We prove the following theorem: axisymmetric, stationary solutions of the Einstein field equations formed from classical gravitational collapse of matter obeying the null energy condition, that are everywhere smooth and ultracompact (i.e., they have a light ring) must have at least two light rings, and one of them is stable. It has been argued that stable light rings generally lead to nonlinear spacetime instabilities. Our result implies that smooth, physically and dynamically reasonable ultracompact objects are not viable as observational alternatives to black holes whenever these instabilities occur on astrophysically short time scales...
December 22, 2017: Physical Review Letters
T Baker, E Bellini, P G Ferreira, M Lagos, J Noller, I Sawicki
The detection of an electromagnetic counterpart (GRB 170817A) to the gravitational-wave signal (GW170817) from the merger of two neutron stars opens a completely new arena for testing theories of gravity. We show that this measurement allows us to place stringent constraints on general scalar-tensor and vector-tensor theories, while allowing us to place an independent bound on the graviton mass in bimetric theories of gravity. These constraints severely reduce the viable range of cosmological models that have been proposed as alternatives to general relativistic cosmology...
December 22, 2017: Physical Review Letters
G D'Amico, G Rosi, S Zhan, L Cacciapuoti, M Fattori, G M Tino
Gravity gradients represent a major obstacle in high-precision measurements by atom interferometry. Controlling their effects to the required stability and accuracy imposes very stringent requirements on the relative positioning of freely falling atomic clouds, as in the case of precise tests of Einstein's equivalence principle. We demonstrate a new method to exactly compensate the effects introduced by gravity gradients in a Raman-pulse atom interferometer. By shifting the frequency of the Raman lasers during the central π pulse, it is possible to cancel the initial position- and velocity-dependent phase shift produced by gravity gradients...
December 22, 2017: Physical Review Letters
Florian Niedermann, Antonio Padilla
Gravitational models of self-tuning are those in which vacuum energy has no observable effect on spacetime curvature, even though it is a priori unsuppressed below the cutoff. We complement Weinberg's no-go theorem by studying field-theoretic completions of self-adjustment allowing for broken translations as well as other generalizations, and identify new obstructions. Our analysis uses a very general Källén-Lehmann spectral representation of the exchange amplitude for conserved sources of energy-momentum and exploits unitarity and Lorentz invariance to show that a transition from self-tuning of long wavelength sources to near general relativity (GR) on shorter scales is generically not possible...
December 22, 2017: Physical Review Letters
Paolo Creminelli, Filippo Vernizzi
The observation of GW170817 and its electromagnetic counterpart implies that gravitational waves travel at the speed of light, with deviations smaller than a few×10^{-15}. We discuss the consequences of this experimental result for models of dark energy and modified gravity characterized by a single scalar degree of freedom. To avoid tuning, the speed of gravitational waves must be unaffected not only for our particular cosmological solution but also for nearby solutions obtained by slightly changing the matter abundance...
December 22, 2017: Physical Review Letters
Jose María Ezquiaga, Miguel Zumalacárregui
Multimessenger gravitational-wave (GW) astronomy has commenced with the detection of the binary neutron star merger GW170817 and its associated electromagnetic counterparts. The almost coincident observation of both signals places an exquisite bound on the GW speed |c_{g}/c-1|≤5×10^{-16}. We use this result to probe the nature of dark energy (DE), showing that a large class of scalar-tensor theories and DE models are highly disfavored. As an example we consider the covariant Galileon, a cosmologically viable, well motivated gravity theory which predicts a variable GW speed at low redshift...
December 22, 2017: Physical Review Letters
Salvatore Vitale, Davide Gerosa, Carl-Johan Haster, Katerina Chatziioannou, Aaron Zimmerman
In a regime where data are only mildly informative, prior choices can play a significant role in Bayesian statistical inference, potentially affecting the inferred physics. We show this is indeed the case for some of the parameters inferred from current gravitational-wave measurements of binary black hole coalescences. We reanalyze the first detections performed by the twin LIGO interferometers using alternative (and astrophysically motivated) prior assumptions. We find different prior distributions can introduce deviations in the resulting posteriors that impact the physical interpretation of these systems...
December 22, 2017: Physical Review Letters
J R Fleck, C L Rains, D S Weeraratne, C T Nguyen, D M Brand, S M Klein, J M McGehee, J M Rincon, C Martinez, P L Olson
Segregation of the iron core from rocky silicates is a massive evolutionary event in planetary accretion, yet the process of metal segregation remains obscure, due to obstacles in simulating the extreme physical properties of liquid iron and silicates at finite length scales. We present new experimental results studying gravitational instability of an emulsified liquid gallium layer, initially at rest at the interface between two glucose solutions. Metal settling coats liquid metal drops with a film of low density material...
January 4, 2018: Nature Communications
Orso Pusterla, Gregor Sommer, Francesco Santini, Mark Wiese, Didier Lardinois, Michael Tamm, Jens Bremerich, Grzegorz Bauman, Oliver Bieri
BACKGROUND: Lung perfusion MRI after i.v. gadolinium (Gd) contrast administration is commonly based on spoiled gradient-echo acquisitions, such as volume-interpolated breath-hold examinations (VIBE), suffering from low signal-to-noise in the parenchyma. PURPOSE: To investigate the lung signal enhancement ratio (SER) with ultra-fast steady-state free precession (ufSSFP) after Gd-administration. STUDY TYPE: Retrospective. SUBJECTS: Ten subjects with healthy lungs; nine patients with pulmonary diseases (chronic obstructive pulmonary disease [COPD], lung cancer, pulmonary fibrosis, lung contusion)...
January 3, 2018: Journal of Magnetic Resonance Imaging: JMRI
Luciano Gattinoni, Tommaso Tonetti, Michael Quintel
The acute respiratory distress (ARDS) lung is usually characterized by a high degree of inhomogeneity. Indeed, the same lung may show a wide spectrum of aeration alterations, ranging from completely gasless regions, up to hyperinflated areas. This inhomogeneity is normally caused by the presence of lung edema and/or anatomical variations, and is deeply influenced by the gravitational forces.For any given airway pressure generated by the ventilator, the pressure acting directly on the lung (i.e., the transpulmonary pressure or lung stress) is determined by two main factors: 1) the ratio between lung elastance and the total elastance of the respiratory system (which has been shown to vary widely in ARDS patients, between 0...
December 28, 2017: Critical Care: the Official Journal of the Critical Care Forum
Gregory L Peck, Manish Garg, Bonnie Arquilla, Vicente H Gracias, Harry L Anderson Iii, Andrew C Miller, Bhakti Hansoti, Paula Ferrada, Michael S Firstenberg, Sagar C Galwankar, Ramon E Gist, Donald Jeanmonod, Rebecca Jeanmonod, Elizabeth Krebs, Marian P McDonald, Benedict Nwomeh, James P Orlando, Lorenzo Paladino, Thomas J Papadimos, Robert L Ricca, Joseph V Sakran, Richard P Sharpe, Mamta Swaroop, Stanislaw P Stawicki
The growth of academic international medicine (AIM) as a distinct field of expertise resulted in increasing participation by individual and institutional actors from both high-income and low-and-middle-income countries. This trend resulted in the gradual evolution of international medical programs (IMPs). With the growing number of students, residents, and educators who gravitate toward nontraditional forms of academic contribution, the need arose for a system of formalized metrics and quantitative assessment of AIM- and IMP-related efforts...
October 2017: International Journal of Critical Illness and Injury Science
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