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S Gandolfi, H-W Hammer, P Klos, J E Lynn, A Schwenk
We present quantum Monte Carlo calculations of few-neutron systems confined in external potentials based on local chiral interactions at next-to-next-to-leading order in chiral effective field theory. The energy and radial densities for these systems are calculated in different external Woods-Saxon potentials. We assume that their extrapolation to zero external-potential depth provides a quantitative estimate of three- and four-neutron resonances. The validity of this assumption is demonstrated by benchmarking with an exact diagonalization in the two-body case...
June 9, 2017: Physical Review Letters
Graeme J Ackland, Mihindra Dunuwille, Miguel Martinez-Canales, Ingo Loa, Rong Zhang, Stanislav Sinogeikin, Weizhao Cai, Shanti Deemyad
The crystal structure of elements at zero pressure and temperature is the most fundamental information in condensed matter physics. For decades it has been believed that lithium, the simplest metallic element, has a complicated ground-state crystal structure. Using synchrotron x-ray diffraction in diamond anvil cells and multiscale simulations with density functional theory and molecular dynamics, we show that the previously accepted martensitic ground state is metastable. The actual ground state is face-centered cubic (fcc)...
June 23, 2017: Science
Daniele Ongari, Peter G Boyd, Senja Barthel, Matthew Witman, Maciej Haranczyk, Berend Smit
Pore volume is one of the main properties for the characterization of microporous crystals. It is experimentally measurable and it can also be obtained from the refined unit cell by a number of computational techniques. In this work we assess the accuracy and the discrepancies between the different computational methods which are commonly used for this purpose, i.e, geometric, helium and probe center pore volume, by studying a database of more than 5000 frameworks. We developed a new technique to fully characterize the internal void of a microporous material and to compute the probe accessible and occupiable pore volume...
June 21, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Francesca Nunzi, Diego Cesario, Fernando Pirani, Leonardo Belpassi, Gernot Frenking, Felice Grandinetti, Francesco Tarantelli
We studied the puzzling stability and short distances predicted by theory for helium adducts with some highly polar molecules, such as BeO or AuF. On the basis of high-level quantum-chemical calculations, we carried out a detailed analysis of the charge displacement occurring upon adduct formation. For the first time we have unambiguously ascertained that helium is able not only to donate electron density, but also, unexpectedly, to accept electron density in the formation of weakly bound adducts with highly polar substrates...
June 21, 2017: Journal of Physical Chemistry Letters
Qing Su, Shinsuke Inoue, Manabu Ishimaru, Jonathan Gigax, Tianyao Wang, Hepeng Ding, Michael J Demkowicz, Lin Shao, Michael Nastasi
Despite recent interest in amorphous ceramics for a variety of nuclear applications, many details of their structure before and after irradiation/implantation remain unknown. Here we investigated the short-range order of amorphous silicon oxycarbide (SiOC) alloys by using the atomic pair-distribution function (PDF) obtained from electron diffraction. The PDF results show that the structure of SiOC alloys are nearly unchanged after both irradiation up to 30 dpa and He implantation up to 113 at%. TEM characterization shows no sign of crystallization, He bubble or void formation, or segregation in all irradiated samples...
June 20, 2017: Scientific Reports
Kirk Richard Jensen, Toshinobu Hondo, Hirochika Sumino, Michisato Toyoda
Helium isotope determination may be useful in measuring volcanic activity and issuing earlier warnings of possible eruptions. A method is presented for measuring the (3)He/(4)He ratio in a gas sample using the multi-turn time-of-flight mass spectrometer infiTOF-UHV (MSI-Tokyo Inc., Tokyo Japan) (infiTOF). In contrast to conventional waveform averaging, peaks are determined by counting ion pulses from each time-of-flight trigger. Samples were also measured by conventional magnetic-sector mass spectrometry for comparison...
June 20, 2017: Analytical Chemistry
Peter Mygind Leth, Birgitte Schmidt Astrup
Suicide using a combination of a plastic bag over the head and inhalation of a non-irritating gas, such as helium, argon or nitrogen, has been reported in the literature. Here an unusual suicide method in a 17-year old man by suffocation from covering the face with household plastic wrap, combined with nitrous oxide inhalation, is presented. The case was reviewed based on police, autopsy and hospital reports. A PubMed search for scientific literature related to nitrous oxide abuse and suicide by suffocation was performed and our findings discussed in relation to the scientific literature found...
June 19, 2017: Forensic Science, Medicine, and Pathology
Nadine Erbeldinger, Felicitas Rapp, Svetlana Ktitareva, Philipp Wendel, Anna S Bothe, Till Dettmering, Marco Durante, Thomas Friedrich, Bianca Bertulat, Stephanie Meyer, M C Cardoso, Stephanie Hehlgans, Franz Rödel, Claudia Fournier
The vascular endothelium interacts with all types of blood cells and is a key modulator of local and systemic inflammatory processes, for example, in the adhesion of blood leukocytes to endothelial cells (EC) and the following extravasation into the injured tissue. The endothelium is constantly exposed to mechanical forces caused by blood flow, and the resulting shear stress is essential for the maintenance of endothelial function. Changes in local hemodynamics are sensed by EC, leading to acute or persistent changes...
2017: Frontiers in Immunology
P Moroshkin, P Leiderer, Th B Möller, K Kono
Electrically charged metallic micro- and nanoparticles are trapped under a free surface of superfluid He in a vertical static electric field. We observe a static deformation of the charged liquid surface in the form of a Taylor cone and the emission of a charged liquid helium jet (electrospray). Our numeric calculations reproduce the static shape of the cone.
May 2017: Physical Review. E
D T Banuti, M Raju, M Ihme
The coexistence line of a fluid separates liquid and gaseous states at subcritical pressures, ending at the critical point. Only recently, it became clear that the supercritical state space can likewise be divided into regions with liquidlike and gaslike properties, separated by an extension to the coexistence line. This crossover line is commonly referred to as the Widom line, and is characterized by large changes in density or enthalpy, manifesting as maxima in the thermodynamic response functions. Thus, a reliable representation of the coexistence line and the Widom line is important for sub- and supercritical applications that depend on an accurate prediction of fluid properties...
May 2017: Physical Review. E
D Campi, M Bernasconi, G Benedek, A P Graham, J P Toennies
The phonon dispersion curves of ultrathin films of Cs(110) on Pt(111) measured with inelastic helium atom scattering (HAS) are reported and compared with density-functional perturbation theory (DFPT) calculations. The combined HAS and DFPT analysis also sheds light on the bulk phonon dynamics of bcc-Cs, on which very little is known from neutron scattering due to its large neutron capture cross-section. Moreover the temperature dependence of the elastic HAS Debye-Waller exponent of Cs(110)/Cu(111) ultrathin films allows for an estimation of the electron-phonon coupling strength λ as a function of the film thickness...
June 14, 2017: Physical Chemistry Chemical Physics: PCCP
Elif Eren Gültekin
The scope of the present study is to investigate the change of elastic modulus with the physical and mechanical properties of porcelain tiles. In the study, porcelain tiles were sintered at different temperatures and at different heating rates to obtain minimum water absorption (%). After this, the time of flight of longitudinal and shear ultrasonic waves was measured through the tile. The time of flight of ultrasonic waves was measured using contact ultrasonic transducers operating on a pulse-echo mode. Using the time of flight of the ultrasonic waves and the thickness of the tiles, the velocity of the waves was determined...
June 3, 2017: Ultrasonics
Bhaskar Mani Adhikari, Tuyen Truong, Nidhi Bansal, Bhesh Bhandari
Use of gases (air, carbon dioxide and nitrogen) has been practiced in the manufacture of dairy products (i.e. ice cream, whipped cream and butter) to improve their texture, mouthfeel and shelf-life extension. Many attempts have also been made to incorporate other gases such as hydrogen, nitrous oxide, argon, xenon, and helium into the dairy systems for various product functionalities such as whipping, foaming, texture, aroma enhancement and therapeutic properties. The gases can be dissolved in aqueous and fat phases or remain in the form of bubbles stabilised by protein or fat particles...
June 13, 2017: Critical Reviews in Food Science and Nutrition
Kristína Štrbová, Helena Raclavská, Jiří Bílek
The aim of the study was to characterize vertical distribution of particulate matter, in an area well known by highest air pollution levels in Europe. A balloon filled with helium with measuring instrumentation was used for vertical observation of air pollution over the fugitive sources in Moravian-Silesian metropolitan area during spring and summer. Synchronously, selected meteorological parameters were recorded together with particulate matter for exploration its relationship with particulate matter. Concentrations of particulate matter in the vertical profile were significantly higher in the spring than in the summer...
June 9, 2017: Journal of Environmental Management
Nancy Quiros, Naima Tariq, Timur V Tscherbul, Jacek Kłos, Jonathan D Weinstein
We have used laser ablation and helium buffer-gas cooling to produce titanium-helium van der Waals molecules at cryogenic temperatures. The molecules were detected through laser-induced fluorescence spectroscopy. Ground-state Ti(a^{3}F_{2})-He binding energies were determined for the ground and first rotationally excited states from studying equilibrium thermodynamic properties, and found to agree well with theoretical calculations based on newly calculated ab initio Ti-He interaction potentials, opening up novel possibilities for studying the formation, dynamics, and nonuniversal chemistry of van der Waals clusters at low temperatures...
May 26, 2017: Physical Review Letters
Benjamin Jäger, Eckard Bich
A new potential energy curve for the krypton-helium atom pair was developed using supermolecular ab initio computations for 34 interatomic distances. Values for the interaction energies at the complete basis set limit were obtained from calculations with the coupled-cluster method with single, double, and perturbative triple excitations and correlation consistent basis sets up to sextuple-zeta quality augmented with mid-bond functions. Higher-order coupled-cluster excitations up to the full quadruple level were accounted for in a scheme of successive correction terms...
June 7, 2017: Journal of Chemical Physics
Andhika Kiswandhi, Peter Niedbalski, Christopher Parish, Qing Wang, Lloyd Lumata
We report on the assembly and performance evaluation of a 180 GHz/6.4 T dynamic nuclear polarization (DNP) system based on a cryogen-free superconducting magnet. The DNP system utilizes a variable-field superconducting magnet that can be ramped up to 9 T and equipped with cryocoolers that can cool the sample space with the DNP assembly down to 1.8 K via the Joule-Thomson effect. A homebuilt DNP probe insert with top-tuned NMR coil and microwave port was incorporated into the sample space in which the effective sample temperature is approximately 1...
June 7, 2017: Magnetic Resonance in Chemistry: MRC
Fekri Abroug, Lamia Ouanes-Besbes, Zeineb Hammouda, Saoussen Benabidallah, Fahmi Dachraoui, Islem Ouanes, Philippe Jolliet
When used as a driving gas during NIV in hypercapnic COPD exacerbation, a helium-oxygen (He/O2) mixture reduces the work of breathing and gas trapping. The potential for He/O2 to reduce the rate of NIV failure leading to intubation and invasive mechanical ventilation has been evaluated in several RCTs. The goal of this meta-analysis is to assess the effect of NIV driven by He/O2 compared to air/O2 on patient-centered outcomes in hypercapnic COPD exacerbation. Relevant RCTs were searched using standard procedures...
December 2017: Annals of Intensive Care
Sang-Hee Jo, Ki-Hyun Kim
To develop accurate quantitation methods for two major permanent gases, N2 and O2, a series of calibration experiments were carried out using a gas chromatograph (GC)/barrier discharge ionization detector (BID) equipped with a large-volume injection (LVI) system. To this end, gaseous working standards (WSs) diluted with helium gas were prepared at ten different concentration levels representing three different concentration ranges (in ppm) in 1-L polyester aluminum (PEA) bags ((1) low, 209~2090 (O2) and 791~7910 (N2); (2) moderate, 2090 ~ 20,900 (O2) and 7910~79,100 (N2); and (3) high, 20,900~209,000 (O2) and 79,100~791,000 (N2))...
July 2017: Environmental Monitoring and Assessment
Patricia A Dailey, Robert Harwood, Kyle Walsh, James B Fink, Tina Thayer, Greg Gagnon, Arzu Ari
BACKGROUND: Heliox (helium-oxygen mixture) has been shown to reduce turbulence and improve aerosol delivery in a range of clinical settings. We questioned whether heliox as compared with oxygen via high-flow nasal cannula (HFNC) would affect aerosol delivery. We hypothesized that heliox would have a significant effect on aerosol delivery as compared with oxygen with both quiet and distressed breathing patterns. METHODS: A vibrating mesh nebulizer was placed at the inlet of a humidifier via HFNC with small adult cannula distal to the heated-wire circuit with prongs placed into simulated nares with a T-shaped trap and absolute filter connected to a breath simulator set to adult quiet and distressed breathing parameters...
June 6, 2017: Respiratory Care
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