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Anna Pavlova, Jerry M Parks, James C Gumbart
Corrinoid cofactors such as cobalamin are used by many enzymes and are essential for most living organisms. Therefore, there is broad interest in investigating cobalamin-protein interactions with molecular dynamics simulations. Previously developed parameters for cobalamins are based mainly on crystal structure data. Here, we report CHARMM-compatible force field parameters for several corrinoids developed from quantum mechanical calculations. We provide parameters for corrinoids in three oxidation states, Co3+, Co2+ and Co1+, and with various axial ligands...
January 15, 2018: Journal of Chemical Theory and Computation
X Zheng, Y R Sun, J-J Chen, W Jiang, K Pachucki, S-M Hu
The 2 ^{3}S-2 ^{3}P transition of ^{4}He was measured by comb-linked laser spectroscopy using a transverse-cooled atomic beam. The centroid frequency was determined to be 276 736 495 600.0(1.4) kHz, with a fractional uncertainty of 5.1×10^{-12}. This value is not only more accurate but also differs by as much as -49.5  kHz (20σ) from the previous result given by [Cancio Pastor et al., Phys. Rev. Lett. 92, 023001 (2004)PRLTAO0031-900710.1103/PhysRevLett.92.023001; Cancio Pastor et al.Phys. Rev...
December 29, 2017: Physical Review Letters
Yvan Castin, Alice Sinatra, Hadrien Kurkjian
Liquid helium and spin-1/2 cold-atom Fermi gases both exhibit in their superfluid phase two distinct types of excitations, gapless phonons and gapped rotons or fermionic pair-breaking excitations. In the long wavelength limit, revising and extending the theory of Landau and Khalatnikov initially developed for helium [Zh. Exp. Teor. Fiz. 19, 637 (1949)], we obtain universal expressions for three- and four-body couplings among these two types of excitations. We calculate the corresponding phonon damping rates at low temperature and compare them to those of a pure phononic origin in high-pressure liquid helium and in strongly interacting Fermi gases, paving the way to experimental observations...
December 29, 2017: Physical Review Letters
Qilai Zhao, Kaijun Zhou, Zisheng Wu, Changsheng Yang, Zhouming Feng, Huihui Cheng, Jiulin Gan, Mingying Peng, Zhongmin Yang, Shanhui Xu
The Earth's magnetic field has significant effects that protect us from cosmic radiation and provide navigation for biological migration. However, slow temporal variations originating in the liquid outer core invariably exist. To understand the working mechanism of the geomagnetic field and improve accuracy of navigation systems, a high-precision magnetometer is essential to measure the absolute magnetic field. A helium optically pumping magnetometer is an advanced approach, but its sensitivity and accuracy are directly limited by the low-frequency relative intensity noise and frequency stability characteristics of a light source...
January 1, 2018: Optics Letters
V Gayathri Devi, Amit Sircar, Deepak Yadav, Jayraj Parmar
In the fusion fuel cycle, the accurate analysis and understanding of the chemical composition of any gas mixture is of great importance for the efficient design of a tritium extraction and purification system or any tritium handling system. Methods like laser Raman spectroscopy and gas chromatography with thermal conductivity detector have been considered for hydrogen isotopes analyses in fuel cycles. Gas chromatography with a cryogenic separation column has been used for the analysis of hydrogen isotopes gas mixtures in general due to its high reliability and ease of operation...
January 12, 2018: Journal of Separation Science
Yang Yang, Yong Gang Li, Michael P Short, Chung-Soo Kim, Karl K Berggren, Ju Li
Full three dimensional (3D) simulations of ion implantation are necessary in a wide range of nanoscience and nanotechnology applications to capture the increasing effect of ion leakage out of surfaces. Using a recently developed 3D Monte Carlo simulation code IM3D, we first quantify the relative error of the 1D approach in three applications of nano-scale ion implantation: (1) nano-beam for nitrogen-vacancy (NV) center creation, (2) implantation of nanowires to fabricate p-n junctions, and (3) irradiation of nano-pillars for small-scale mechanical testing of irradiated materials...
January 11, 2018: Nanoscale
Maximilian Lasserus, Martin Schnedlitz, Daniel Knez, Roman Messner, Alexander Schiffmann, Florian Lackner, Andreas W Hauser, Ferdinand Hofer, Wolfgang E Ernst
Alloying processes in nanometre-sized Ag@Au and Au@Ag core@shell particles with average radii of 2 nm are studied via high resolution Transmission Electron Microscopy (TEM) imaging on in situ heatable carbon substrates. The bimetallic clusters are synthesized in small droplets of superfluid helium under fully inert conditions. After deposition, they are monitored during a heating cycle to 600 K and subsequent cooling. The core-shell structure, a sharply defined feature of the TEM High-Angle Annular Dark-Field images taken at room temperature, begins to blur with increasing temperature and transforms into a fully mixed alloy around 573 K...
January 10, 2018: Nanoscale
M Briant, E Mengesha, M-A Gaveau, B Soep, J-M Mestdagh, L Poisson
The CH antisymmetric stretch of the C2H2 moieties in acetylene dimers was explored over the range 3270-3290 cm-1 using the helium nanodroplet isolation (HENDI) technique. This work is part of a general investigation which addresses the dynamical consequences of coupling the deformation motions of weakly bound complexes with a finite size quantum liquid (the helium droplet). The acetylene dimer is attractive from this point of view because one of its deformation coordinates promotes a tunneling isomerization process...
January 10, 2018: Physical Chemistry Chemical Physics: PCCP
Thomas Tessonnier, Andrea Mairani, Wenjing Chen, Paola Sala, Francesco Cerutti, Alfredo Ferrari, Thomas Haberer, Jürgen Debus, Katia Parodi
BACKGROUND: Due to their favorable physical and biological properties, helium ion beams are increasingly considered a promising alternative to proton beams for radiation therapy. Hence, this work aims at comparing in-silico the treatment of brain and ocular meningiomas with protons and helium ions, using for the first time a dedicated Monte Carlo (MC) based treatment planning engine (MCTP) thoroughly validated both in terms of physical and biological models. METHODS: Starting from clinical treatment plans of four patients undergoing proton therapy with a fixed relative biological effectiveness (RBE) of 1...
January 9, 2018: Radiation Oncology
Jessica Lo, Sanja Zivanovic, Alan Lunt, Mireia Alcazar-Paris, Gwendolyn Andradi, Mark Thomas, Neil Marlow, Sandy Calvert, Janet Peacock, Anne Greenough
OBJECTIVES: To assess longitudinally small airway function in children born extremely prematurely and whether there was a correlation between airway function in infancy and at 11-14 years. WORKING HYPOTHESES: There would be tracking of airways obstruction and small airway function would deteriorate during childhood in those born extremely prematurely. STUDY DESIGN: A longitudinal study. PATIENT-SUBJECT SELECTION: Thirty-five children with a mean gestational age of 26 weeks had lung function assessed at 1 year corrected and 11-14 years of age...
January 9, 2018: Pediatric Pulmonology
Habtewold D Waktola, Svein A Mjos
The chromatographic efficiency that could be achieved in temperature-programmed gas chromatography was compared for four capillary columns that are typically applied for analysis of fatty acid methyl esters (FAME). Three different carrier gases, hydrogen, helium and nitrogen, were applied. For each experiment, the carrier gas velocities and the temperature rates were varied with a full 9 × 3 design, with nine levels on the carrier gas velocity and temperature rates of 1, 2 or 3°C/min. Response surface methodology was used to create models of chromatographic efficiency as a function of temperature rate and carrier gas velocity...
January 4, 2018: Journal of Separation Science
Shin Kajita, Shota Kawaguchi, Noriyasu Ohno, Naoaki Yoshida
Helium plasma irradiation on metal surfaces leads to the formation of metallic fuzzy nanostructures accompanied by the growth of helium bubbles in metals. The mechanism of the growth process, its impact for fusion devices, and potential application have been explored. Here we show enhanced growth of large-scale fuzz by precipitating additional metallic particles during helium plasma irradiation. The growth rate of the fuzzy structures became orders of magnitude greater than conventional fuzz growth; in an hour of irradiation, 1 mm-thick visible tungsten and molybdenum fuzzy fur structures covered a tungsten metal substrate...
January 8, 2018: Scientific Reports
Tim Gehrke, Carlo Amato, Simon Berke, Maria Martisikova
Ion-beam radiography (iRAD) could potentially improve the quality control of ion-beam therapy. The main advantage of iRAD is the possibility to directly measure the integrated stopping power. Until now there is no clinical implementation of iRAD. Topics of ongoing research include developing dedicated detection systems to achieve the desired spatial resolution (SR) and investigating different ion types as imaging radiation. This work focuses on the theoretical and experimental comparison of proton (pRAD) and helium-beam radiography (αRAD)...
January 9, 2018: Physics in Medicine and Biology
Miroslaw Karbowiak, Czeslaw Rudowicz, Jakub Cichos
The virtual lack of information on electronic spectra of divalent lanthanide elements (Ln2+) other than Sm2+, Eu2+, Tm2+ and Yb2+ has prompted us to set for synthesis and characterization of novel Ln2+ systems. First successful attempt concerned SrCl2:Nd2+ single crystals. Here, we report stabilization of divalent dysprosium in a chloride host. Importantly this has been accomplished with Dy ions introduced in a divalent state during synthesis, unlike by -irradiation of Dy3+ systems employed previously. This synthesis method yields good quality SrCl2:Dy2+ single crystals...
January 5, 2018: Journal of Physical Chemistry. A
Yuri Bedjanian
The kinetics and products of the reaction of OH radicals with ClNO have been studied in a flow reactor coupled with an electron impact ionization mass spectrometer at nearly 2 Torr total pressure of helium and over a wide temperature range, T = 220 - 940 K. The rate constant of the reaction OH + ClNO  products (1) was determined under pseudo-first order conditions, monitoring the kinetics of OH consumption in excess of ClNO: k1 = 1.48 × 10-18 × T2.12 exp(146/T) cm3molecule-1s-1 (uncertainty of 15%). HOCl, Cl and HONO were observed as the reaction products...
January 5, 2018: Journal of Physical Chemistry. A
M I Dykman, K Kono, D Konstantinov, M J Lea
We study the shift of the energy levels of electrons on a helium surface due to the coupling to the quantum field of surface vibrations. As in quantum electrodynamics, the coupling is known, and it is known to lead to an ultraviolet divergence of the level shifts. We show that there are diverging terms of different nature and use the Bethe-type approach to show that they cancel each other, to leading order. This resolves the long-standing theoretical controversy and explains the existing experiments. The results allow us to study the temperature dependence of the level shift...
December 22, 2017: Physical Review Letters
M Aguilar, L Ali Cavasonza, B Alpat, G Ambrosi, L Arruda, N Attig, S Aupetit, P Azzarello, A Bachlechner, F Barao, A Barrau, L Barrin, A Bartoloni, L Basara, S Başeğmez-du Pree, M Battarbee, R Battiston, U Becker, M Behlmann, B Beischer, J Berdugo, B Bertucci, K F Bindel, V Bindi, W de Boer, K Bollweg, V Bonnivard, B Borgia, M J Boschini, M Bourquin, E F Bueno, J Burger, W J Burger, F Cadoux, X D Cai, M Capell, S Caroff, J Casaus, G Castellini, F Cervelli, M J Chae, Y H Chang, A I Chen, G M Chen, H S Chen, L Cheng, H Y Chou, E Choumilov, V Choutko, C H Chung, C Clark, R Clavero, G Coignet, C Consolandi, A Contin, C Corti, W Creus, M Crispoltoni, Z Cui, K Dadzie, Y M Dai, A Datta, C Delgado, S Della Torre, O Demakov, M B Demirköz, L Derome, S Di Falco, F Dimiccoli, C Díaz, P von Doetinchem, F Dong, F Donnini, M Duranti, D D'Urso, A Egorov, A Eline, T Eronen, J Feng, E Fiandrini, P Fisher, V Formato, Y Galaktionov, G Gallucci, R J García-López, C Gargiulo, H Gast, I Gebauer, M Gervasi, A Ghelfi, F Giovacchini, D M Gómez-Coral, J Gong, C Goy, V Grabski, D Grandi, M Graziani, K H Guo, S Haino, K C Han, Z H He, M Heil, J Hoffman, T H Hsieh, H Huang, Z C Huang, C Huh, M Incagli, M Ionica, W Y Jang, Yi Jia, H Jinchi, S C Kang, K Kanishev, B Khiali, G N Kim, K S Kim, Th Kirn, C Konak, O Kounina, A Kounine, V Koutsenko, A Kulemzin, G La Vacca, E Laudi, G Laurenti, I Lazzizzera, A Lebedev, H T Lee, S C Lee, C Leluc, H S Li, J Q Li, Q Li, T X Li, Y Li, Z H Li, Z Y Li, S Lim, C H Lin, P Lipari, T Lippert, D Liu, Hu Liu, V D Lordello, S Q Lu, Y S Lu, K Luebelsmeyer, F Luo, J Z Luo, S S Lyu, F Machate, C Mañá, J Marín, T Martin, G Martínez, N Masi, D Maurin, A Menchaca-Rocha, Q Meng, V M Mikuni, D C Mo, P Mott, T Nelson, J Q Ni, N Nikonov, F Nozzoli, A Oliva, M Orcinha, F Palmonari, C Palomares, M Paniccia, M Pauluzzi, S Pensotti, C Perrina, H D Phan, N Picot-Clemente, F Pilo, C Pizzolotto, V Plyaskin, M Pohl, V Poireau, L Quadrani, X M Qi, X Qin, Z Y Qu, T Räihä, P G Rancoita, D Rapin, J S Ricol, S Rosier-Lees, A Rozhkov, D Rozza, R Sagdeev, S Schael, S M Schmidt, A Schulz von Dratzig, G Schwering, E S Seo, B S Shan, J Y Shi, T Siedenburg, D Son, J W Song, M Tacconi, X W Tang, Z C Tang, D Tescaro, Samuel C C Ting, S M Ting, N Tomassetti, J Torsti, C Türkoğlu, T Urban, V Vagelli, E Valente, E Valtonen, M Vázquez Acosta, M Vecchi, M Velasco, J P Vialle, V Vitale, S Vitillo, L Q Wang, N H Wang, Q L Wang, X Wang, X Q Wang, Z X Wang, C C Wei, Z L Weng, K Whitman, H Wu, X Wu, R Q Xiong, W Xu, Q Yan, J Yang, M Yang, Y Yang, H Yi, Y J Yu, Z Q Yu, M Zannoni, S Zeissler, C Zhang, F Zhang, J Zhang, J H Zhang, S W Zhang, Z Zhang, Z M Zheng, H L Zhuang, V Zhukov, A Zichichi, N Zimmermann, P Zuccon
We report the observation of new properties of primary cosmic rays He, C, and O measured in the rigidity (momentum/charge) range 2 GV to 3 TV with 90×10^{6} helium, 8.4×10^{6} carbon, and 7.0×10^{6} oxygen nuclei collected by the Alpha Magnetic Spectrometer (AMS) during the first five years of operation. Above 60 GV, these three spectra have identical rigidity dependence. They all deviate from a single power law above 200 GV and harden in an identical way.
December 22, 2017: Physical Review Letters
J Y Zhao, W Bi, S Sinogeikin, M Y Hu, E E Alp, X C Wang, C Q Jin, J F Lin
A new miniature panoramic diamond anvil cell (mini-pDAC) as well as a unique gas membrane-driven mechanism is developed and implemented to measure electronic, magnetic, vibrational, and thermodynamic properties of materials using the nuclear resonant inelastic X-ray scattering (NRIXS) and the synchrotron Mössbauer spectroscopy (SMS) simultaneously at high pressure (over Mbar) and low temperature (T < 10 K). The gas membrane system allows in situ pressure tuning of the mini-pDAC at low temperature. The mini-pDAC fits into a specially designed compact liquid helium flow cryostat system to achieve low temperatures, where liquid helium flows through the holder of the mini-pDAC to cool the sample more efficiently...
December 2017: Review of Scientific Instruments
V Zhelyazkova, S D Hogan
We present the results of experiments demonstrating the spectroscopic detection of Förster resonance energy transfer from NH3 in the X1A1 ground electronic state to helium atoms in 1sns 3S1 Rydberg levels, where n = 37 and n = 40. For these values of n, the 1sns 3S1 → 1snp 3PJ transitions in helium lie close to resonance with the ground-state inversion transitions in NH3 and can be tuned through resonance using electric fields of less than 10 V/cm. In the experiments, energy transfer was detected by direct state-selective electric field ionization of the 3S1 and 3PJ Rydberg levels and by monitoring the population of the 3DJ levels following pulsed microwave transfer from the 3PJ levels...
December 28, 2017: Journal of Chemical Physics
Friethjof Theel, Antonia Karamatskou, Robin Santra
The Hartree-Fock method is an important approximation for the ground-state electronic wave function of atoms and molecules so that its usage is widespread in computational chemistry and physics. The Hartree-Fock method is an iterative procedure in which the electronic wave functions of the occupied orbitals are determined. The set of functions found in one step builds the basis for the next iteration step. In this work, we interpret the Hartree-Fock method as a dynamical system since dynamical systems are iterations where iteration steps represent the time development of the system, as encountered in the theory of fractals...
December 2017: Chaos
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