ALBERT

Description: Pathogenic bacteria adhere despite severe mechanical perturbations induced by the host, such as coughing. In Gram-positive bacteria, extracellular protein appendages termed pili are necessary for adherence under mechanical stress. However, little is known about the behavior of Gram-positive pili under force. Here, we demonstrate a mechanism by which Gram-positive pili...

Description: Author(s): J. Janušonis, C. L. Chang, T. Jansma, A. Gatilova, V. S. Vlasov, A. M. Lomonosov, V. V. Temnov, and R. I. Tobey We generate in-plane magnetoelastic waves in nickel films using the all-optical transient grating technique. When performed on amorphous glass substrates, two dominant magnetoelastic excitations can be resonantly driven by the underlying elastic distortions, the Rayleigh surface acoustic wave and th… [Phys. Rev. B 94, 024415] Published Wed Jul 13, 2016

Description: We use the transient grating technique to generate narrow-band, widely tunable, in-plane surface magnetoelastic waves in a nickel film. We monitor both the structural deformation of the acoustic wave and the accompanying magnetic precession and witness their intimate coupling in the time domain. Strikingly, when an in plane magnetic field is applied parallel to the acoustic propagation direction, we witness its resonant coupling to the ferromagnetic resonance.

Description: Polar ionospheric heaters have generated ULF/ELF/VLF waves by modulating the auroral electrojet at D/E region altitudes. We present theoretical/computational results indicating that modulated F-region HF heating can generate ionospheric currents even in the absence of electrojet currents. The ELF currents are driven in a two-step process. First, the pressure gradient associated with F-region electron heating drives a local diamagnetic current. This acts as an antenna to inject Magneto-Sonic (MS) waves in the ionospheric plasma. Second, the electric field of the magneto-sonic wave drives Hall currents when it reaches the E region of the ionosphere. The Hall currents act as a secondary antenna that injects waves in the Earth-Ionosphere Waveguide below and Shear Alfven waves upwards to the conjugate regions. The paper examines the scaling and limitations of the concept and suggests proof-of-principle experiments using the HAARP ionospheric heater.

Description: We report results from numerical and experimental studies of the excitation of ULF shear Alfvén waves inside the ionospheric Alfvén resonator (IAR) by heating the ionosphere with powerful HF waves launched from the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. Numerical simulations of the two-fluid MHD model describing IAR in a dipole magnetic field geometry with plasma parameters taken from the observations at HAARP during the October–November 2010 experimental campaign reveal that the IAR quality is higher during nighttime conditions, when the ionospheric conductivity is very low. Simulations also reveal that the resonance wave cannot be identified from the magnetic measurements on the ground or at an altitude above 600 km because the magnetic field in this wave has nodes on both ends of the resonator, and the best way to detect IAR modes is by measuring the electric field on low Earth orbit satellites. These theoretical predictions are in good, quantitative agreement with results from observations: In particular, (1) observations from the ground-based magnetometer at the HAARP site demonstrate no significant difference in the amplitudes of the magnetic field generated by HAARP in the frequency range from 0 to 5 Hz, and (2) the DEMETER satellite detected the electric field of the IAR first harmonic at an altitude of 670 km above HAARP during the heating experiment.

Description: The first experimental demonstration of HF driven currents in the ionosphere at low ELF/ULF frequencies without relying in the presence of electrojets is presented. The effect was predicted by theoretical/computational means in a recent letter and given the name Ionospheric Current Drive (ICD). The effect relies on modulated F-region HF heating to generate Magneto-Sonic (MS) waves that drive Hall currents when they reach the E-region. The Hall currents inject ELF waves into the Earth-Ionosphere waveguide and helicon and Shear Alfven (SA) waves in the magnetosphere. The proof-of-concept experiments were conducted using the HAARP heater in Alaska under the BRIOCHE program. Waves between 0.1–70 Hz were measured at both near and far sites. The letter discusses the differences between ICD generated waves and those relying on modulation of electrojets.

Description: Author(s): C. L. Chang, S. Mieszczak, M. Zelent, V. Besse, U. Martens, R.R. Tamming, J. Janusonis, P. Graczyk, M. Münzenberg, J.W. Kłos, and R. I. Tobey Creating and controlling spin waves is a central topic in spintronics. Spatially shaped optical fields can be used to create lateral texture in the magnetization profile of a uniformly magnetized sample. When implemented with fast pulses of light, this provides a method to generate user-defined, transient magnetization texture and its accompanying band structure for spin waves. The authors demonstrate this effect using femtosecond laser pulses in the transient-grating geometry, for elastic excitation of a variety of spin waves in a modified magnetic landscape. Comparing experiments to calculations, the authors identify the various elastically activated spin-wave modes. [Phys. Rev. Applied 10, 064051] Published Thu Dec 20, 2018

Description: Nature Materials 15, 601 (2016). doi:10.1038/nmat4641 Authors: M. P. M. Dean, Y. Cao, X. Liu, S. Wall, D. Zhu, R. Mankowsky, V. Thampy, X. M. Chen, J. G. Vale, D. Casa, Jungho Kim, A. H. Said, P. Juhas, R. Alonso-Mori, J. M. Glownia, A. Robert, J. Robinson, M. Sikorski, S. Song, M. Kozina, H. Lemke, L. Patthey, S. Owada, T. Katayama, M. Yabashi, Yoshikazu Tanaka, T. Togashi, J. Liu, C. Rayan Serrao, B. J. Kim, L. Huber, C.-L. Chang, D. F. McMorrow, M. Först & J. P. Hill Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.

Description: In the cores of some clusters of galaxies the hot intracluster plasma is dense enough that it should cool radiatively in the cluster's lifetime, leading to continuous 'cooling flows' of gas sinking towards the cluster centre, yet no such cooling flow has been observed. The low observed star-formation rates and cool gas masses for these 'cool-core' clusters suggest that much of the cooling must be offset by feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical and infrared observations of the galaxy cluster SPT-CLJ2344-4243 (ref. 11) at redshift z = 0.596. These observations reveal an exceptionally luminous (8.2 x 10(45) erg s(-1)) galaxy cluster that hosts an extremely strong cooling flow (around 3,820 solar masses a year). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (formation of around 740 solar masses a year), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool-core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star-formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form through accretion of the intracluster medium, rather than (as is currently thought) assembling entirely via mergers.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McDonald, M -- Bayliss, M -- Benson, B A -- Foley, R J -- Ruel, J -- Sullivan, P -- Veilleux, S -- Aird, K A -- Ashby, M L N -- Bautz, M -- Bazin, G -- Bleem, L E -- Brodwin, M -- Carlstrom, J E -- Chang, C L -- Cho, H M -- Clocchiatti, A -- Crawford, T M -- Crites, A T -- de Haan, T -- Desai, S -- Dobbs, M A -- Dudley, J P -- Egami, E -- Forman, W R -- Garmire, G P -- George, E M -- Gladders, M D -- Gonzalez, A H -- Halverson, N W -- Harrington, N L -- High, F W -- Holder, G P -- Holzapfel, W L -- Hoover, S -- Hrubes, J D -- Jones, C -- Joy, M -- Keisler, R -- Knox, L -- Lee, A T -- Leitch, E M -- Liu, J -- Lueker, M -- Luong-Van, D -- Mantz, A -- Marrone, D P -- McMahon, J J -- Mehl, J -- Meyer, S S -- Miller, E D -- Mocanu, L -- Mohr, J J -- Montroy, T E -- Murray, S S -- Natoli, T -- Padin, S -- Plagge, T -- Pryke, C -- Rawle, T D -- Reichardt, C L -- Rest, A -- Rex, M -- Ruhl, J E -- Saliwanchik, B R -- Saro, A -- Sayre, J T -- Schaffer, K K -- Shaw, L -- Shirokoff, E -- Simcoe, R -- Song, J -- Spieler, H G -- Stalder, B -- Staniszewski, Z -- Stark, A A -- Story, K -- Stubbs, C W -- Suhada, R -- van Engelen, A -- Vanderlinde, K -- Vieira, J D -- Vikhlinin, A -- Williamson, R -- Zahn, O -- Zenteno, A -- England -- Nature. 2012 Aug 16;488(7411):349-52. doi: 10.1038/nature11379.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. mcdonald@space.mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22895340" target="_blank"〉PubMed〈/a〉

Description: In the past decade, our understanding of galaxy evolution has been revolutionized by the discovery that luminous, dusty starburst galaxies were 1,000 times more abundant in the early Universe than at present. It has, however, been difficult to measure the complete redshift distribution of these objects, especially at the highest redshifts (z 〉 4). Here we report a redshift survey at a wavelength of three millimetres, targeting carbon monoxide line emission from the star-forming molecular gas in the direction of extraordinarily bright millimetre-wave-selected sources. High-resolution imaging demonstrates that these sources are strongly gravitationally lensed by foreground galaxies. We detect spectral lines in 23 out of 26 sources and multiple lines in 12 of those 23 sources, from which we obtain robust, unambiguous redshifts. At least 10 of the sources are found to lie at z 〉 4, indicating that the fraction of dusty starburst galaxies at high redshifts is greater than previously thought. Models of lens geometries in the sample indicate that the background objects are ultra-luminous infrared galaxies, powered by extreme bursts of star formation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Vieira, J D -- Marrone, D P -- Chapman, S C -- De Breuck, C -- Hezaveh, Y D -- Weibeta, A -- Aguirre, J E -- Aird, K A -- Aravena, M -- Ashby, M L N -- Bayliss, M -- Benson, B A -- Biggs, A D -- Bleem, L E -- Bock, J J -- Bothwell, M -- Bradford, C M -- Brodwin, M -- Carlstrom, J E -- Chang, C L -- Crawford, T M -- Crites, A T -- de Haan, T -- Dobbs, M A -- Fomalont, E B -- Fassnacht, C D -- George, E M -- Gladders, M D -- Gonzalez, A H -- Greve, T R -- Gullberg, B -- Halverson, N W -- High, F W -- Holder, G P -- Holzapfel, W L -- Hoover, S -- Hrubes, J D -- Hunter, T R -- Keisler, R -- Lee, A T -- Leitch, E M -- Lueker, M -- Luong-Van, D -- Malkan, M -- McIntyre, V -- McMahon, J J -- Mehl, J -- Menten, K M -- Meyer, S S -- Mocanu, L M -- Murphy, E J -- Natoli, T -- Padin, S -- Plagge, T -- Reichardt, C L -- Rest, A -- Ruel, J -- Ruhl, J E -- Sharon, K -- Schaffer, K K -- Shaw, L -- Shirokoff, E -- Spilker, J S -- Stalder, B -- Staniszewski, Z -- Stark, A A -- Story, K -- Vanderlinde, K -- Welikala, N -- Williamson, R -- England -- Nature. 2013 Mar 21;495(7441):344-7. doi: 10.1038/nature12001. Epub 2013 Mar 13.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA. vieira@caltech.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23485967" target="_blank"〉PubMed〈/a〉