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Filip Ficek, Pavel Fadeev, Victor V Flambaum, Derek F Jackson Kimball, Mikhail G Kozlov, Yevgeny V Stadnik, Dmitry Budker
Heretofore undiscovered spin-0 or spin-1 bosons can mediate exotic spin-dependent interactions between standard model particles. Here, we carry out the first search for semileptonic spin-dependent interactions between matter and antimatter. We compare theoretical calculations and spectroscopic measurements of the hyperfine structure of antiprotonic helium to constrain exotic spin- and velocity-dependent interactions between electrons and antiprotons.
May 4, 2018: Physical Review Letters
Luca Giannessi, Enrico Allaria, Kevin C Prince, Carlo Callegari, Giuseppe Sansone, Kiyoshi Ueda, Toru Morishita, Chien Nan Liu, Alexei N Grum-Grzhimailo, Elena V Gryzlova, Nicolas Douguet, Klaus Bartschat
The seeded Free-Electron Laser (FEL) FERMI is the first source of short-wavelength light possessing the full coherence of optical lasers, together with the extreme power available from FELs. FERMI provides longitudinally coherent radiation in the Extreme Ultraviolet and soft x-ray spectral regions, and therefore opens up wide new fields of investigation in physics. We first propose experiments exploiting this property to provide coherent control of the photoionization of neon and helium, carry out numerical calculations to find optimum experimental parameters, and then describe how these experiments may be realized...
May 17, 2018: Scientific Reports
Chan Gao, Xueyong Zhang, Chuanchao Zhang, Zhilei Sui, Meng Hou, Rucheng Dai, Zhongping Wang, Xianxu Zheng, Zengming Zhang
Herein, pressure-induced phase transitions of RDX up to 50 GPa were systematically studied under different compression conditions. Precise phase transition points were obtained based on high-quality Raman spectra with small pressure intervals. This favors the correctness of the theoretical formula for detonation and the design of a precision weapon. The experimental results indicated that α-RDX immediately transformed to γ-RDX at 3.5 GPa due to hydrostatic conditions and possible interaction between the penetrating helium and RDX, with helium gas as the pressure-transmitting medium (PTM)...
May 17, 2018: Physical Chemistry Chemical Physics: PCCP
Y Jiang, M Lawrence, M P Ansell, A Hussain
This paper, for the first time, fully characterizes the intrinsic physical parameters of hemp shiv including cell wall microstructure, pore size distribution and absolute density. Scanning electron microscopy revealed microstructural features similar to hardwoods. Confocal microscopy revealed three major layers in the cell wall: middle lamella, primary cell wall and secondary cell wall. Computed tomography improved the visualization of pore shape and pore connectivity in three dimensions. Mercury intrusion porosimetry (MIP) showed that the average accessible porosity was 76...
April 2018: Royal Society Open Science
Mario Hernández Vera, Ersin Yurtsever, Roland Wester, Franco A Gianturco
We present an extensive range of accurate ab initio calculations, which map in detail the spatial electronic potential energy surface that describes the interaction between the molecular anion NH2 - (1 A1 ) in its ground electronic state and the He atom. The time-independent close-coupling method is employed to generate the corresponding rotationally inelastic cross sections, and then the state-changing rates over a range of temperatures from 10 to 30 K, which is expected to realistically represent the experimental trapping conditions for this ion in a radio frequency ion trap filled with helium buffer gas...
May 14, 2018: Journal of Chemical Physics
H J Williams, L Caldwell, N J Fitch, S Truppe, J Rodewald, E A Hinds, B E Sauer, M R Tarbutt
We demonstrate coherent microwave control of the rotational, hyperfine, and Zeeman states of ultracold CaF molecules, and the magnetic trapping of these molecules in a single, selectable quantum state. We trap about 5×10^{3} molecules for almost 2 s at a temperature of 70(8)  μK and a density of 1.2×10^{5}  cm^{-3}. We measure the state-specific loss rate due to collisions with background helium.
April 20, 2018: Physical Review Letters
Jinhyuk Lim, Choong-Shik Yoo
The phase diagram of hydrogen-helium mixtures is presented to 75 GPa, underscoring the formation of metastable H_{2}-rich crystallite in He-rich fluid mixtures and the structural phase transition in He lattice at ∼52  GPa. The Raman data also indicate a significant level of mixing between H_{2} and He even in solids, giving rise to new vibrational bands in He-rich solid at ∼2400  cm^{-1} for H-He stretching and 140  cm^{-1} for the lattice phonon of H_{2} incorporated hcp He. Therefore, the present result signifies unexpected, strong chemical association of the interstitial-filled guest molecules (H_{2} or He) with the host lattice (hcp He or H_{2}) in this quantum solid mixture...
April 20, 2018: Physical Review Letters
Yang Yang, Petr Dementyev, Niklas Biere, Daniel Emmrich, Patrick Stohmann, Riko Korzetz, Xianghui Zhang, André Beyer, Sascha Koch, Dario Anselmetti, Armin Gölzhäuser
The provision of clean water is a global challenge, and membrane filtration is a key technology to address it. Conventional filtration membranes are constrained by a trade-off between permeance and selectivity. Recently, some nanostructured membranes demonstrated the ability to overcome this limitation by utilizing well-defined carbon nanoconduits that allow a coordinated passage of water molecules. The fabrication of these materials is still very challenging, but their performance inspires research toward nanofabricated membranes...
May 9, 2018: ACS Nano
Masoomeh Mahmoodi-Darian, Stefan Raggl, Michael Renzler, Marcelo Goulart, Stefan E Huber, Andreas Mauracher, Paul Scheier, Olof Echt
The smallest doubly charged coronene cluster ions reported so far, Cor15 2+ , were produced by charge exchange between bare coronene clusters and He2+ [H. A. B. Johansson et al., Phys. Rev. A 84, 043201 (2011)]. These dications are at least five times larger than the estimated Rayleigh limit, i.e., the size at which the activation barrier for charge separation vanishes. Such a large discrepancy is unheard of for doubly charged atomic or molecular clusters. Here we report the mass spectrometric observation of doubly charged coronene trimers, produced by electron ionization of helium nanodroplets doped with coronene...
May 7, 2018: Journal of Chemical Physics
Z V Gagkaeva, E S Zhukova, V Grinenko, A K Grebenko, K V Sidoruk, T A Voeikova, M Dressel, B P Gorshunov
Employing optical spectroscopy we have performed a comparative study of the dielectric response of extracellular matrix and filaments of electrogenic bacteria Shewanella oneidensis MR-1, cytochrome c, and bovine serum albumin. Combining infrared transmission measurements on thin layers with data of the terahertz spectra, we obtain the dielectric permittivity and AC conductivity spectra of the materials in a broad frequency band from a few cm-1 up to 7000 cm-1 in the temperature range from 5 to 300 K. Strong absorption bands are observed in the three materials that cover the range from 10 to 300 cm-1 and mainly determine the terahertz absorption...
May 7, 2018: Journal of Biological Physics
R W Pattie, N B Callahan, C Cude-Woods, E R Adamek, L J Broussard, S M Clayton, S A Currie, E B Dees, X Ding, E M Engel, D E Fellers, W Fox, P Geltenbort, K P Hickerson, M A Hoffbauer, A T Holley, A Komives, C-Y Liu, S W T MacDonald, M Makela, C L Morris, J D Ortiz, J Ramsey, D J Salvat, A Saunders, S J Seestrom, E I Sharapov, S K Sjue, Z Tang, J Vanderwerp, B Vogelaar, P L Walstrom, Z Wang, W Wei, H L Weaver, J W Wexler, T L Womack, A R Young, B A Zeck
The precise value of the mean neutron lifetime, τn , plays an important role in nuclear and particle physics and cosmology. It is used to predict the ratio of protons to helium atoms in the primordial universe and to search for physics beyond the Standard Model of particle physics. We eliminated loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls...
May 6, 2018: Science
Pierluigi Piersimoni, Bruce A Faddegon, José Ramos Méndez, Reinhard W Schulte, Lennart Volz, Joao Seco
PURPOSE: To evaluate the accuracy of relative stopping power reconstructed with simulated helium CT (HeCT) in comparison to proton CT (pCT). METHODS: A Monte Carlo (MC) study with the TOPAS tool was performed to compare the accuracy of relative stopping power (RSP) reconstruction and spatial resolution of low-fluence HeCT to pCT, both using 200 MeV/u particles. An ideal setup consisting of a flat beam source and a totally absorbing energy-range detector was implemented to estimate the theoretically best achievable RSP accuracy for the calibration and reconstruction methods currently used for pCT...
May 4, 2018: Medical Physics
T Inaniwa, N Kanematsu
The microdosimetric kinetic (MK) model underestimates the cell-survival fractions for high linear energy transfer (LET) and high dose irradiations. To address the issue, some researchers previously extended the MK model to the stochastic microdosimetric kinetic (SMK) model. In the SMK model, the radiation induced cell-survival fractions were estimated from the specific energies z d and z n absorbed by a microscopic subnuclear structure domain and a cell nucleus, respectively. By taking the stochastic nature of z n as well as that of z d into account, the SMK model could reproduce the measured cell-survival fractions for radiations with wide LET and dose ranges...
May 4, 2018: Physics in Medicine and Biology
Rosa Lo Frano, Monica Puccini, Eleonora Stefanelli, Daniele Del Serra, Stefano Malquori
An open issue for the fusion power reactor is the choice of breeding blanket material. The possible use of Helium-Cooled Pebble Breeder ceramic material in the form of pebble beds is of great interest worldwide as demonstrated by the numerous studies and research on this subject. Lithium orthosilicate (Li₄SiO₄) is a promising breeding material investigated in this present study because the neutron capture of Li-6 allows the production of tritium, 6Li (n, t) 4He. Furthermore, lithium orthosilicate has the advantages of low activation characteristics, low thermal expansion coefficient, high thermal conductivity, high density and stability...
May 2, 2018: Materials
J J Spake, D K Sing, T M Evans, A Oklopčić, V Bourrier, L Kreidberg, B V Rackham, J Irwin, D Ehrenreich, A Wyttenbach, H R Wakeford, Y Zhou, K L Chubb, N Nikolov, J M Goyal, G W Henry, M H Williamson, S Blumenthal, D R Anderson, C Hellier, D Charbonneau, S Udry, N Madhusudhan
Helium is the second-most abundant element in the Universe after hydrogen and is one of the main constituents of gas-giant planets in our Solar System. Early theoretical models predicted helium to be among the most readily detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres 1 . Searches for helium, however, have hitherto been unsuccessful 2 . Here we report observations of helium on an exoplanet, at a confidence level of 4.5 standard deviations. We measured the near-infrared transmission spectrum of the warm gas giant 3 WASP-107b and identified the narrow absorption feature of excited metastable helium at 10,833 angstroms...
May 2018: Nature
Drake Deming
No abstract text is available yet for this article.
May 2018: Nature
M Holler, J Raabe, A Diaz, M Guizar-Sicairos, R Wepf, M Odstrcil, F R Shaik, V Panneels, A Menzel, B Sarafimov, S Maag, X Wang, V Thominet, H Walther, T Lachat, M Vitins, O Bunk
For many scientific questions gaining three-dimensional insight into a specimen can provide valuable information. We here present an instrument called "tOMography Nano crYo (OMNY)," dedicated to high resolution 3D scanning x-ray microscopy at cryogenic conditions via hard X-ray ptychography. Ptychography is a lens-less imaging method requiring accurate sample positioning. In OMNY, this in achieved via dedicated laser interferometry and closed-loop position control reaching sub-10 nm positioning accuracy...
April 2018: Review of Scientific Instruments
Cédric Schmidt, Yoann Pertot, Tadas Balciunas, Kristina Zinchenko, Mary Matthews, Hans Jakob Wörner, Jean-Pierre Wolf
We present a 0.2 TW sub-two-cycle 1.8 µm carrier-envelope-phase stable source based on two-stage pulse compression by filamentation for driving high-order harmonic generation extending beyond the oxygen K absorption edge. The 1 kHz repetition rate, high temporal resolution enabled by the short 11.8 fs driving pulse duration, and bright high-order harmonics generated in helium make this an attractive source for solid-state and molecular-dynamics studies.
April 30, 2018: Optics Express
Przemysław Wachulak, Martin Duda, Andrzej Bartnik, Antoni Sarzyński, Łukasz Węgrzyński, Michał Nowak, Alexandr Jancarek, Henryk Fiedorowicz
We present a compact laboratory system for near edge soft X-ray fine structure (NEXAFS) spectroscopy that was developed using a laser-plasma light source. The source is based on a double stream gas puff target. The plasma is formed by the interaction of a laser beam with the double stream gas puff target approach. The laser plasma source was optimized for efficient soft X-ray emission from a krypton/helium target in the range of 1.5 to 5 nm wavelength. This emission is used to acquire simultaneously the emission and absorption spectra of soft X-ray light from the source and from the investigated sample using a grazing incidence spectrometer...
April 2, 2018: Optics Express
Wanderley de Souza, Marcia Attias
Scanning electron microscopy has been used to observe and study parasitic protozoa for at least 40 years. However, field emission electron sources, as well as improvements in lenses and detectors, brought the resolution power of scanning electron microscopes (SEM) to a new level. Parallel to the refinement of instruments, protocols for preservation of the ultrastructure, immunolabeling, exposure of cytoskeleton and inner structures of parasites and host cells were developed. This review is focused on protozoan parasites of medical and veterinary relevance, e...
April 24, 2018: Experimental Parasitology
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