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Jonathan Jerke, Bill Poirier
Using a combination of ideas, the ground and several excited electronic states of the helium atom and the hydrogen molecule are computed to chemical accuracy-i.e., to within 1-2 mhartree or better. The basic strategy is very different from the standard electronic structure approach in that the full two-electron six-dimensional (6D) problem is tackled directly, rather than starting from a single-electron Hartree-Fock approximation. Electron correlation is thus treated exactly, even though computational requirements remain modest...
March 14, 2018: Journal of Chemical Physics
Christoph Schran, Felix Uhl, Jörg Behler, Dominik Marx
The design of accurate helium-solute interaction potentials for the simulation of chemically complex molecules solvated in superfluid helium has long been a cumbersome task due to the rather weak but strongly anisotropic nature of the interactions. We show that this challenge can be met by using a combination of an effective pair potential for the He-He interactions and a flexible high-dimensional neural network potential (NNP) for describing the complex interaction between helium and the solute in a pairwise additive manner...
March 14, 2018: Journal of Chemical Physics
Massimo Boninsegni
The momentum distribution and atomic kinetic energy of the two isotopes of helium in a liquid mixture at temperature T = 2 K are computed by quantum Monte Carlo simulations. Quantum statistics is fully included for4 He, whereas3 He atoms are treated as distinguishable. Comparison of theoretical estimates with a collection of the most recent experimental measurements shows reasonable agreement for the energetics of4 He and pure3 He. On the other hand, a significant discrepancy (already observed in previous studies) is reported between computed and measured values of the3 He kinetic energy in the mixture, especially in the limit of low3 He concentration...
March 14, 2018: Journal of Chemical Physics
Vipan K Parihar, Mattia Maroso, Amber Syage, Barrett D Allen, Maria C Angulo, Ivan Soltesz, Charles L Limoli
Of the many perils associated with deep space travel to Mars, neurocognitive complications associated with cosmic radiation exposure are of particular concern. Despite these realizations, whether and how realistic doses of cosmic radiation cause cognitive deficits and neuronal circuitry alterations several months after exposure remains unclear. In addition, even less is known about the temporal progression of cosmic radiation-induced changes transpiring over the duration of a time period commensurate with a flight to Mars...
March 11, 2018: Experimental Neurology
Francesca Nunzi, Diego Cesario, Fernando Pirani, Leonardo Belpassi, Francesco Tarantelli
We studied the nature of the interaction of the weakly bound Be-He adduct, by means of an integrated theoretical approach, based on high-level quantum chemical calculations for the characterization of the potential energy surfaces and charge displaced upon adduct formation, together with the development of a semi-empirical analytical formulation of the interaction potential. Our results show that Be is able to form stable adduct with He when the Be(1D) (1s2 2s2  1s2 2s0 2p2) excited state is involved, with a binding energy of as much as 10...
March 14, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Thomas K F Foo, Evangelos Laskaris, Mark Vermilyea, Minfeng Xu, Paul Thompson, Gene Conte, Christopher Van Epps, Christopher Immer, Seung-Kyun Lee, Ek T Tan, Dominic Graziani, Jean-Baptise Mathieu, Christopher J Hardy, John F Schenck, Eric Fiveland, Wolfgang Stautner, Justin Ricci, Joseph Piel, Keith Park, Yihe Hua, Ye Bai, Alex Kagan, David Stanley, Paul T Weavers, Erin Gray, Yunhong Shu, Matthew A Frick, Norbert G Campeau, Joshua Trzasko, John Huston, Matt A Bernstein
PURPOSE: To build and evaluate a small-footprint, lightweight, high-performance 3T MRI scanner for advanced brain imaging with image quality that is equal to or better than conventional whole-body clinical 3T MRI scanners, while achieving substantial reductions in installation costs. METHODS: A conduction-cooled magnet was developed that uses less than 12 liters of liquid helium in a gas-charged sealed system, and standard NbTi wire, and weighs approximately 2000 kg...
March 13, 2018: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Yoshiaki Iwase, Yoji Horie, Sawao Honda, Yusuke Daiko, Yuji Iwamoto
Polyalkoxysilsesquiazanes ([ROSi(NH)1.5 ]n , ROSZ, R = Et, nPr, iPr, nBu, sBu, nHex, sHex, cHex, decahydronaphthyl (DHNp)) were synthesized by ammonolysis at -78 °C of alkoxytrichlorosilane (ROSiCl₃), which was isolated by distillation as a reaction product of SiCl₄ and ROH. The simultaneous thermogravimetric and mass spectrometry analyses of the ROSZs under helium revealed a common decomposition reaction, the cleavage of the oxygen-carbon bond of the RO group to evolve alkene as a main gaseous species formed in-situ, leading to the formation of microporous amorphous Si-O-N at 550 °C to 800 °C...
March 13, 2018: Materials
M D Rotondaro, B V Zhdanov, M K Shaffer, R J Knize
We performed a measurement of the beam quality of an optimized moderate power cesium Diode Pumped Alkali Laser (DPAL). The DPAL used a stable resonator and operated in continuous wave mode using a static cell filled with metallic cesium and a mixture of methane and helium at 200 and 400 torr respectively. In this work, we characterized the spatial quality of the DPAL output beam. As a result of these experiments we determined the output beam quality was excellent (M2 < 1.2) in the whole range of pump power used (up to 11...
March 5, 2018: Optics Express
Jyun-Hong Chen, Yuan-Liang Zhong, Lain-Jong Li, Chii-Dong Chen
Two-dimensional electron gas (2DEG) is crucial in condensed matter physics and is present on the surface of liquid helium and at the interface of semiconductors. Monolayer MoS2 of 2D materials also contains 2DEG in an atomic layer as field effect transistor (FET) ultrathin channel. In this study, we synthesized double triangular MoS&lt;sub&gt;2&lt;/sub&gt; through a chemical vapor deposition method to obtain grain boundaries for forming a ripple structure in FET channel. When the temperature was higher than approximately 175 K, the temperature dependence of the electron mobility μ was consistent with those in previous experiments and theoretical predictions...
March 12, 2018: Nanotechnology
J J Wittmann, T V Can, M Eckardt, W Harneit, R G Griffin, B Corzilius
The electronic g factor carries highly useful information about the electronic structure of a paramagnetic species, such as spin-orbit coupling and dia- or paramagnetic (de-)shielding due to local fields of surrounding electron pairs. However, in many cases, a near "spin-only" case is observed, in particular for light elements, necessitating accurate and precise measurement of the g factors. Such measurement is typically impeded by a "chicken and egg situation": internal or external reference standards are used for relative comparison of electron paramagnetic resonance (EPR) Larmor frequencies...
March 6, 2018: Journal of Magnetic Resonance
Pieter Cools, Mahtab Asadian, Wannes Nicolaus, Heidi Declercq, Rino Morent, Nathalie De Geyter
This work describes the surface modification of 300PEO-PEOT/PBT 55/45 thin films using a medium pressure dielectric barrier discharge system operated in argon, helium, nitrogen or dry air to improve cell-surface interactions of this established biomaterial. The first part of the paper describes the optimization of the plasma processing parameters using water contact angle goniometry. The optimized samples are then characterized for changes in surface topography and surface chemical composition using atomic force microscopy (AFM) and X-ray fluorescence spectroscopy (XPS) respectively...
March 7, 2018: Materials
Anna N Bagdinova, Evgeny I Demikhov, Nataliya G Borisenko, Sergei M Tolokonnikov, Gennadii V Mishakov, Andrei V Sharkov
The free boundary of smectic A (SmA), nematic and isotropic liquid phases were studied using a polarized optical microscope, an interferometric surface structure analyzer (ISSA), an atomic force microscope (AFM) and a scanning near-field optical microscope (SNOM). Images of the SmA phase free surface obtained by the polarized microscope and ISSA are in good correlation and show a well-known focal domain structure. The new periodic stripe structure was observed by scanning near-field optical microscopy on the surface of the smectic A, nematic and isotropic phases...
2018: Beilstein Journal of Nanotechnology
Yuri Bedjanian
The kinetics and products of the reaction of F + C2H4  products (1) have been studied in a discharge flow reactor combined with an electron impact ionization mass spectrometer at nearly 2 Torr total pressure of helium in the temperature range 298 - 950 K. The total rate constant of the reaction, k1 = (1.78 ± 0.30)×10-10 cm3molecule-1s-1, determined under pseudo-first order conditions, monitoring the kinetics of F-atom consumption in excess of C2H4, was found to be temperature independent in the temperature range used...
March 7, 2018: Journal of Physical Chemistry. A
Justin C Sowder, Mar Janna Dahl, Kaitlin R Zuspan, Kurt H Albertine, Donald M Null, Mitchell D Barneck, J Fredrik Grimmer
Objective To (1) compare physiologic changes during rigid bronchoscopy during spontaneous and mechanical ventilation and (2) evaluate the efficacy of a helium-oxygen (heliox) gas mixture as compared with room air during rigid bronchoscopy. Study Design Crossover animal study evaluating physiologic parameters during rigid bronchoscopy. Outcomes were compared with predicted computational fluid analysis. Setting Simulated ventilation via computational fluid dynamics analysis and term lambs undergoing rigid bronchoscopy...
March 1, 2018: Otolaryngology—Head and Neck Surgery
Francesco Borgatti, Piero Torelli, Marco Brucale, Denis Gentili, Giancarlo Panaccione, Celia Castan Guerrero, Bernhard Schäfer, Mario Ruben, Massimiliano Cavallini
We investigate the solvatochromic effect of a Fe-based spin crossover (SCO) compound via Ambient Pressure soft X-ray Absorption Spectroscopy (AP-XAS) and atomic force microscopy (AFM). AP-XAS provides the direct evidence of the spin configuration for the Fe(II) 3d states of the SCO material upon in situ exposure to specific gas or vapor mixtures; concurrent changes in nanoscale topography and mechanical characteristics are revealed via AFM imaging and AFM-based force spectroscopy respectively. We find that exposing the SCO material to gaseous helium promotes an effective decrease of the transition temperature of its surface layers, while the exposure to methanol vapor causes opposite surfacial and bulk solvatochromic effects...
March 6, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
Salah Awel, Richard A Kirian, Max O Wiedorn, Kenneth R Beyerlein, Nils Roth, Daniel A Horke, Dominik Oberthür, Juraj Knoska, Valerio Mariani, Andrew Morgan, Luigi Adriano, Alexandra Tolstikova, P Lourdu Xavier, Oleksandr Yefanov, Andrew Aquila, Anton Barty, Shatabdi Roy-Chowdhury, Mark S Hunter, Daniel James, Joseph S Robinson, Uwe Weierstall, Andrei V Rode, Saša Bajt, Jochen Küpper, Henry N Chapman
High-resolution Bragg diffraction from aerosolized single granulovirus nanocrystals using an X-ray free-electron laser is demonstrated. The outer dimensions of the in-vacuum aerosol injector components are identical to conventional liquid-microjet nozzles used in serial diffraction experiments, which allows the injector to be utilized with standard mountings. As compared with liquid-jet injection, the X-ray scattering background is reduced by several orders of magnitude by the use of helium carrier gas rather than liquid...
February 1, 2018: Journal of Applied Crystallography
Zhen Liu, Jorge Botana, Andreas Hermann, Steven Valdez, Eva Zurek, Dadong Yan, Hai-Qing Lin, Mao-Sheng Miao
Until very recently, helium had remained the last naturally occurring element that was known not to form stable solid compounds. Here we propose and demonstrate that there is a general driving force for helium to react with ionic compounds that contain an unequal number of cations and anions. The corresponding reaction products are stabilized not by local chemical bonds but by long-range Coulomb interactions that are significantly modified by the insertion of helium atoms, especially under high pressure. This mechanism also explains the recently discovered reactivity of He and Na under pressure...
March 5, 2018: Nature Communications
Huong Giang T Nguyen, Jarod C Horn, Matthias Thommes, Roger D van Zee, Laura Espinal
Addressing reproducibility issues in adsorption measurements is critical to accelerating the path to discovery of new industrial adsorbents and to understanding adsorption processes. A National Institute of Standards and Technology Reference Material, RM 8852 (ammonium ZSM-5 zeolite), and two gravimetric instruments with asymmetric two-beam balances were used to measure high-pressure adsorption isotherms. This work demonstrates how common approaches to buoyancy correction, a key factor in obtaining the mass change due to surface excess gas uptake from the apparent mass change, can impact the adsorption isotherm data...
December 2017: Measurement Science & Technology
Arnab Ganguly, Jason Stewart, Alan Rhoden, Michael Volny, Nabil Saad
Mass Spectrometry has commonly been used in the semi-conductor industry where maintaining a clean environment with minimum contaminants under high vacuum is crucial for successful manufacturing. Since the technology's early usage for pharmaceutical manufacturing in the early '80s, particularly in the freeze-drying environment, much has changed. The focus of the current work is aimed at asking some key questions regarding the maturity of the technology, its challenges and importance of having an application-specific instrument for quantitative process analyses applied to freeze-drying...
March 1, 2018: European Journal of Pharmaceutics and Biopharmaceutics
Shaoning Jiang, Zhiming Wang
The effect of post-irradiation annealing on the microstructures and mechanical properties of V-4Cr-4Ti alloys was studied. Helium-hydrogen-irradiated sequentially V-4Cr-4Ti alloys at room temperature (RT) were undergone post-irradiation annealing at 450 °C over periods of up to 30 h. These samples were carried out by high-resolution transmission electron microscopy (HRTEM) observation and nanoindentation test. With the holding time, large amounts of point defects produced during irradiation at RT accumulated into large dislocation loops and then dislocation nets which promoted the irradiation hardening...
March 2, 2018: Nanoscale Research Letters
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