bluuebunny/crossref_metadata_2025 huggingface dataset:
Preoperative Hyponatremia is a Risk Factor for Adverse 30-Day Outcomes Following Total Hip Arthroplasty
Authors: Tanenbaum Joseph E. , Bomberger Thomas T. , Knapik Derrick M. , Fitzgerald Steven J. , Shah Nihar S. , Wera Glenn D.
Published: February 2020

The relationship between preoperative hyponatremia and 30-day outcomes following total hip arthroplasty (THA) is currently unknown. The present study used prospectively collected data to quantify the association between preoperative hyponatremia and odds of major morbidity (MM), longer length of stay, readmission, and reoperation within 30 days following THA. Patients who underwent THA between 2012 and 2014 were identified in the National Surgical Quality Improvement Program database using validated Current Procedural Terminology codes. Patients were included if they were either normonatremic or hyponatremic preoperatively. The outcome measures in this study were 30-day MM, hospital length of stay, 30-day readmission, and 30-day reoperation. A unique multivariable logistic regression model was used for each outcome to identify statistically significant associations between hyponatremia and the outcome of interest after adjusting for covariates. From 2012 to 2014, 59,236 THA procedures were recorded in National Surgical Quality Improvement Program, of which 55,611 patients were normonatremic and 3,051 patients were hyponatremic. After adjusting for covariates, preoperative hyponatremia was significantly associated with increased odds of MM (odds ratio [OR] = 1.14; 99% confidence interval [CI]: 1.01–1.30), 30-day reoperation (OR = 1.18; 99% CI: 1.02–1.36), and longer hospital length of stay (OR = 1.20; 99% CI: 1.13–1.27). Hyponatremia was not significantly associated with greater odds of 30-day readmission (OR = 0.91; 99% CI: 0.82–1.01). Preoperative hyponatremia was significantly associated with adverse 30-day outcomes following THA. As the U.S. health care system continues to transition toward value-based reimbursement that emphasizes health care quality, the results of the present study can be used to improve patient selection and preoperative counseling.
Loaded objects: addressing gun violence through art in the gallery and beyond
Authors: Dell’Aria Annie
Published: February 2020

Gun violence impacts our experience of public spaces, including how we represent and memorialize tragic events stemming from guns in public ways. Immediate memorials, complete with flowers and other ephemera, frequently appear at the sites of gun violence, at times to be followed by permanent memorials with contemplative spaces and names of victims etched in stone. While communicating loss and grief, both of these strategies usually evade any real political action or consideration of the complexities of gun violence or its causes. Mirroring the stalemate in our political dialogue around guns and their proliferation, our dominant strategies of memorialization similarly offer little more than “thoughts and prayers”. In what ways can contemporary art break through these evasions and even prompt dialogue or change around the complex array of issues that arise with the increased presence of guns in American society? How can art generate experiences for viewers that allow for a more complex consideration of gun-related violence than the cycle of grief seen in immediate and permanent memorials? In this paper, I survey works of art that produce possibilities for transformative conversation around the issue by considering guns as what Bruno Latour calls “actants”. I begin by examining guns in the gallery, first offering a new readings of Chris Burden’s Shoot (1971) and Marina Abramović’s Rhythm 0 (1974), both of which notoriously included real firearms, and then turning to sculptural projects that literally disarm guns, rendering them deliberately strange and prompting complex conversations about their material presence in American life. I then shift focus towards the public sphere to consider works by Krzysztof Wodiczko, Jenny Holzer, and Michael Rakowitz, artists who rewire established circuits of monumental commemoration, public space advertising, and vernacular immediate memorials to generate a sense of distance, and even a safe space for dialogue in the public realm.
Community and authority in ROAR Magazine
Authors: Buts Jan
Published: February 2020

This article responds to a common critique of corpus-based studies as decontextualized exercises in linguistic analysis by illustrating how, in the case of internet-based data, the concordance line can reveal rather than obscure aspects of a textual body’s cultural constitution. The data for the study consists of 100 articles of the online political journal ROAR (Reflections on a Revolution) Magazine, which has reported on global instances of public unrest and dissent since 2011. After sketching the relation between the financial crisis commencing in 2007 and the global protests that followed in its wake, the article investigates textual patterns within ROAR’s varied output. These patterns, ranging from the collocational profile of the keyword democracy to quotation practices, are shown to be constitutive of a virtual sense of community. This process of identity formation is then shown to have a mythopoetic effect, which ultimately impacts the emplotment of the various events covered and considered by the magazine. Additional attention is paid to ROAR as a cross-platform enterprise. In this respect, the fragmentary nature of the Internet is shown to both facilitate and frustrate the creation of a symbolic sense of community.
Degenerations of Filippov algebras
Authors: Kaygorodov Ivan , Volkov Yury
Published: February 2020

We consider the variety of Filippov (n-Lie) algebra structures on an (n + 1)-dimensional vector space. The group GLn(K) acts on it, and we study the orbit closures with respect to the Zariski topology. This leads to the definition of Filippov algebra degenerations. We present some fundamental results on such degenerations, including trace invariants and necessary degeneration criteria. Finally, we classify all orbit closures in the variety of complex (n + 1)-dimensional Filippov n-ary algebras.
Magnetocaloric effect in Tb2O3 and Dy2O3 nanoparticles at cryogenic temperatures
Authors: Shinde K. P. , Tien V. M. , Huang L. , Park H.-R. , Yu S.-C. , Chung K. C. , Kim D.-H.
Published: February 2020

Magnetic refrigeration is a cooling technology based on the magnetocaloric effect, which has greater energy efficiency than conventional refrigeration, and has attracted much attention for low and room temperature cooling applications. Here, we report magnetocaloric effects at cryogenic temperatures in nanostructured rare earth oxides prepared by rare earth nitride formation and successive oxidation that guarantees chemical stabilities and finer particle sizes of rare earth oxide nanoparticles. Tb2O3 and Dy2O3 rare earth oxides with a cubic structure were prepared that undergo a second-order magnetic transition at Néel temperatures of 8 K and 4 K, respectively. Magnetic entropy changes (−ΔSM) were 6.6 and 18.2 J/kg K, respectively, at an applied magnetic field of 6 T.
Geometry free materials enabled by transformation optics for enhancing the intensity of electromagnetic waves in an arbitrary domain
Authors: Abdolali Ali , Barati Sedeh Hooman , Fakheri Mohammad Hosein
Published: February 2020

The concentration of electromagnetic waves is of utmost importance in many engineering applications such as energy harvesting devices. According to the transformation optics methodology, a feasible approach for obtaining arbitrary shape concentrators is proposed. Contrary to the previous works, the obtained materials are homogeneous and independent of the concentrator shape. That is, regardless of the input geometry, always one constant material, which is optic-null medium (ONM), is used, and the performance of the device will not alter. This competency will ease the design process and circumvent the sophisticated calculations of the necessitating materials. To demonstrate such a capability, several numerical full-wave simulations were performed for different shapes of concentrators. Furthermore, with the aid of effective medium theory (EMT), the ONM was realized using split-ring resonator-meander line metamaterial blocks. Then, as a proof of concept, an arbitrary shape concentrator was designed according to EMT and by exploiting the retrieved parameters of the realized metamaterials. It was observed that the realization results exhibit strong agreement with the theoretical investigations and corroborate the generality and effectiveness of the proposed designing method.
Spray droplet size distribution and droplet velocity measurements in a firing optical engine
Authors: Sharma Nikhil , Bachalo William D. , Agarwal Avinash Kumar
Published: February 2020

Macroscopic spray characteristics of a fuel injection system in an internal combustion (IC) engine have a direct impact on engine performance, emissions, and combustion characteristics. Nonintrusive in-cylinder measurements provide insights into the spray formation process for greater understanding of fuel-air mixing and combustion processes in an IC engine. In this paper, there are two parts: (a) procedure and methodology to configure the Artium phase Doppler interferometer (PDI) for in situ measurements through a cylindrical window and (b) comparative macroscopic spray characteristics in a firing Gasoline Direct Injection (GDI) optical engine to a constant volume spray chamber (CVSC) for spray droplet size-velocity distributions. Binned average velocity and average Sauter mean diameter of spray droplets in a firing engine were compared with that of a CVSC. Probability density function of droplet diameters in the CVSC under ambient conditions and in the engine combustion chamber provides an insight into the comparative droplet size distributions and droplet dynamics. Discussion on challenges encountered during PDI measurements in the firing engine environment, safety protocols, and tools required is also included. In addition, shadowgraphy images have been used to discuss the details on spray boundaries and spray evolution. The droplet size distribution inside the engine combustion chamber was found to be significantly different from the one observed in the CVSC. An engine simulation model can be developed/validated by using the data reported in this manuscript for attaining superior accuracy in the model. This paper describes the comparisons of the spray droplet size and velocity distributions in a CVSC and in situ for a working GDI engine. Maximum spray droplet velocity components (Vx, Vy) under engine combustion chamber conditions were 29.8 m/s, 14.2 m/s whereas the corresponding velocities in the CVSC under ambient conditions they were 78.41 m/s, 23.92 m/s, respectively, showing a large difference between the traditional measurements in the CVSC simulating engine conditions, and actual firing engine conditions. This study also reports the very first attempt in the open literature to measure spray droplet size and velocity distribution measurements in a firing IC engine.
Investigation on the generation of high voltage quasi-square pulses with a specific two-node PFN-Marx circuit
Authors: Zhang Haoran , Li Zhiqiang , Zhang Zicheng , Shu Ting
Published: February 2020

A specific multi-stage two-node pulse forming network (PFN)-Marx topology circuit, which can produce high voltage quasi-square pulses, is investigated and designed in this paper. The specificity of this circuit is that the PFN-Marx is formed by several uniform ladder networks that have two sections of the LC unit and a ladder network formed by four-node capacitors. Compared with conventional PFN-Marx generators formed by equal-value capacitors and inductors with more than four nodes, the number of capacitors in the circuit designed here can be reduced significantly. A five-stage two-node PFN-Marx is assembled to verify the validity of the topology circuit. The experimental results show that the PFN-Marx can generate a quasi-square pulse with a pulse width of 105 ns, flat-top of 50 ns, and amplitude of 80 kV with ±3% voltage variation. The topology circuit design is promising to achieve higher voltage (more stages) and longer pulse width.
Experimental study on monitoring system of clinical beam purity in multiple-ion beam operation for heavy-ion radiotherapy
Authors: Mizushima K. , Iwata Y. , Muramatsu M. , Lee S. H. , Shirai T.
Published: February 2020

The National Institute of Radiological Sciences has investigated multiple-ion therapy using energetic beams of helium, carbon, oxygen, and neon ions, to improve treatment outcomes of refractory cancer. For this therapy, it is necessary to ensure the helium-ion beam purity to avoid irradiation by unwanted ions. Here, we develop a measurement method for monitoring beam purity. This method can measure the charge number of the ions in a high-purity beam using an ionization chamber and Faraday cup. In addition, it can be used to detect the contamination of the clinical helium-ion beam. We perform beam experiments to evaluate our beam-purity monitoring method and predict that our method is capable of detecting contamination below 1%.
Optimization of quasi-axisymmetric stellarators with varied elongation
Authors: Feng Zhichen , Gates David A. , Lazerson Samuel A. , Landreman Matt , Pomphrey Neil , Fu GuoYong
Published: February 2020

An optimization study of Quasi-Axisymmetric (QA) stellarators with varied elongation has been carried out using the optimization code STELLOPT. The starting point of our optimization is a previously obtained QA stellarator with three field periods and an aspect ratio of 6. A series of QA stellarators are obtained at zero plasma beta with the varied elongation value ranging from 2.5 to 3.7. A good quasi-symmetry is kept when the elongation value is reduced from the original value of 3.7. The rotational transform profile and aspect ratio are kept fixed. The plasma volume is ether kept fixed or varied linearly with elongation. Furthermore, finite beta QA stellarators are considered. The corresponding bootstrap currents are calculated using the kinetic code SFINCS. A series of kink-stable QA stellarators are obtained via optimization with varied plasma beta up to 5% and self-consistent bootstrap current. This work demonstrates that good QA stellarators with finite beta and varied elongation exist that are stable to external kink modes.
Parametric controllability of the personalized PageRank: Classic model vs biplex approach
Authors: Flores Julio , García Esther , Pedroche Francisco , Romance Miguel
Published: February 2020

Measures of centrality in networks defined by means of matrix algebra, like PageRank-type centralities, have been used for over 70 years. Recently, new extensions of PageRank have been formulated and may include a personalization (or teleportation) vector. It is accepted that one of the key issues for any centrality measure formulation is to what extent someone can control its variability. In this paper, we compare the limits of variability of two centrality measures for complex networks that we call classic PageRank (PR) and biplex approach PageRank (BPR). Both centrality measures depend on the so-called damping parameter α that controls the quantity of teleportation. Our first result is that the intersection of the intervals of variation of both centrality measures is always a nonempty set. Our second result is that when α is lower that 0.48 (and, therefore, the ranking is highly affected by teleportation effects) then the upper limits of PR are more controllable than the upper limits of BPR; on the contrary, when α is greater than 0.5 (and we recall that the usual PageRank algorithm uses the value 0.85), then the upper limits of PR are less controllable than the upper limits of BPR, provided certain mild assumptions on the local structure of the graph. Regarding the lower limits of variability, we give a result for small values of α. We illustrate the results with some analytical networks and also with a real Facebook network.
Phononic comb generation in high-Q quartz resonators
Authors: Kubena R. L. , Wall W. S. , Koehl J. , Joyce R. J.
Published: February 2020

We report on the observation of high-fidelity, high-Q, phononic combs in AT-cut 100-MHz shear-mode quartz resonators. The comb generation was observed on the first spurious mode above the fundamental mode resonance when driven a few kHz off resonance at power levels between +11 and +18 dBm. These combs exhibit the expected phase coherence between the teeth with no measurable line broadening from the nonlinear generation. Interestingly, the combs can exhibit a complex structure at particular temperatures. These changes in the comb structure over temperature are thought to be driven by the relative frequency shifts between the interacting modes. Teeth with both much larger and smaller frequency sensitivities to the drive frequency have been observed. These characteristics may be useful for enhancing the sensitivity of resonant-mode MEMS sensors or improving the phase stability of oscillators. In addition, if cryogenically cooled, these highly coherent combs may provide a component for phononic quantum processing studies.
On the stability of a heated rotating-disk boundary layer in a temperature-dependent viscosity fluid
Authors: Miller R. , Griffiths P. T. , Hussain Z. , Garrett S. J.
Published: February 2020

The paper presents a linear stability analysis of the temperature-dependent boundary-layer flow over a rotating disk. Gas- and liquid-type responses of the viscosity to temperature are considered, and the disk rotates in both a quiescent and an incident axial flow. Temperature-dependent-viscosity flows are typically found to be less stable than the temperature independent cases, with temperature dependences that produce high wall viscosities yielding the least stable flows. Conversely, increasing the incident axial flow strength produces greater flow stability. Transitional Reynolds numbers for these flows are then approximated through an eN-type analysis and are found to vary in approximate concordance with the critical Reynolds number. Examination of the component energy contributions shows that flow stability is affected exclusively through changes to the mean flow. The results are discussed in the context of chemical vapor deposition reactors.
Strong-field control of H3+ production from methanol dications: Selecting between local and extended formation mechanisms
Authors: Iwamoto Naoki , Schwartz Charles J. , Jochim Bethany , Raju P. Kanaka , Feizollah Peyman , Napierala J. L. , Severt T. , Tegegn S. N. , Solomon A. , Zhao S. , Lam Huynh , Wangjam Tomthin Nganba , Kumarappan V. , Carnes K. D. , Ben-Itzhak I. , Wells E.
Published: February 2020

Using the CD3OH isotopologue of methanol, the ratio of D2H+ to D3+ formation is manipulated by changing the characteristics of the intense femtosecond laser pulse. Detection of D2H+ indicates a formation process involving two hydrogen atoms from the methyl side of the molecule and a proton from the hydroxyl side, while detection of D3+ indicates local formation involving only the methyl group. Both mechanisms are thought to involve a neutral D2 moiety. An adaptive control strategy that employs image-based feedback to guide the learning algorithm results in an enhancement of the D2H+/D3+ ratio by a factor of approximately two. The optimized pulses have secondary structures 110–210 fs after the main pulse and result in photofragments that have different kinetic energy release distributions than those produced from near transform limited pulses. Systematic changes to the linear chirp and higher order dispersion terms of the laser pulse are compared to the results obtained with the optimized pulse shapes.
Precursor effects and field-induced short-range order above the Verwey transition in single Fe3O4 crystals
Authors: Boekema Carolus , Morante Carlos
Published: February 2020

The internal fields in single crystals of magnetite (Fe3O4) have been previously studied through muon-spin rotation (μSR). By Maximum-Entropy (ME) μSR, we analyze Fe3O4 μSR data with external fields parallel to the <111>, <110> or <100> axis. The ME peak-to-noise ratio is optimized by varying the filter time and time interval. Several μSR time series indicate a beat pattern. Using MEμSR, a second frequency signal is seen at non-zero fields in the temperature range above the Verwey transition (TV = ∼123 K). At zero field, MEμSR confirms with much-improved precision the existence of one frequency signal found earlier by curve fitting (CF) and Fourier transformation (FT). We compare our room temperature (RT) field-dependent MEμSR transforms for <110> Fe3O4 with those found at 205 K to study a second order phase transition at the Wigner temperature (TW = ∼247 K). At RT and 205 K for fields below the demagnetization field and parallel to <110> Fe3O4, a second MEμSR frequency is observed, missed by CF and FT. These extra magnetic fields fall on the extended magnetization curves below and above TW. At RT, a small field induces a short-range order similar to the precursor effects in the TV – TW interval. At 205 K within that precursor T-interval, we observe a comparable RT-disordered state. The existence of these additional internal fields is likely related to phonon-assisted 3d-electron(-spin) hopping and short-range order behaviors. Our MEμSR studies lead to a better understanding of the local magnetism in this Mott-Wigner glass.
Achievement of stable negative ion production with Cs-seeded for long pulse beam operation in the prototype of Cs-seeded negative ion source for JT-60SA
Authors: Ichikawa Masahiro , Kojima Atsushi , Hiratsuka Junichi , Yoshida Masafumi , Umeda Naotaka , Squilayan G. Q. , Watanabe Kazuhiro , Tobari Hiroyuki , Kashiwagi Mieko
Published: February 2020

Long pulse negative ion beams of 500 keV and 154 A/m2 for 118 s have been achieved for the first time, which exceeds the requirement of the JT-60SA negative ion source. In order to solve the issues of such long pulse beams, the fast cutoff system of the power supply aims to reduce the surge current and to extend the lifetime of filaments and the suppression method of excess cesium (Cs) accumulation on the plasma grid (PG) to achieve stable negative ion production. By developing the fast cutoff system using a field programmable gate array unit for the arc power supply, the cutoff time has been reduced to 1/10 that of the original system and the lifetime of the filament was extended by three times. In order to achieve stable negative ion production, incoming Cs on the PG surface has been reduced by keeping the chamber wall temperature below 40 °C. As a result, a stable beam current drift of <6% has been achieved for the 118 s duration.
What do we learn from the classical turning surface of the Kohn–Sham potential as electron number is varied continuously?
Authors: Gould Tim , Liberles Benjamin T. , Perdew John P.
Published: February 2020

The classical Kohn–Sham turning radius Rt of an atom can be defined as the radius where the Kohn–Sham potential is equal to the negative ionization potential of the atom, i.e., where vs(Rt) = ϵh. It was recently shown [E. Ospadov et al., Proc. Natl. Acad. Sci. U. S. A. 115, E11578–E11585 (2018)] to yield chemically relevant bonding distances, in line with known empirical values. In this work, we show that extension of the concept to non-integer electron number yields additional information about atomic systems and can be used to detect the difficulty of adding or subtracting electrons. Notably, it reflects the ease of bonding in open p-shells and its greater difficulty in open s-shells. The latter manifests in significant discontinuities in the turning radius as the electron number changes the principal quantum number of the outermost electronic shell (e.g., going from Na to Na2+). We then show that a non-integer picture is required to correctly interpret bonding and dissociation in H2+. Results are consistent when properties are calculated exactly or via an appropriate approximation. They can be interpreted in the context of conceptual density functional theory.
Point defects in PbCdTe solid solutions
Authors: Horichok I. V. , Parashchuk T. O.
Published: February 2020

The defect subsystem of PbCdTe crystals was analyzed using the method of thermodynamic potential. The predominant type of point defects and their effect on the concentration of free charge carriers have been estimated. It was established that the electroneutral substitution defect CdPb is the dominant point defect in the investigated system. Furthermore, the carrier concentration of a solid solution is determined by the concentration of single-ionized interstitial cadmium atoms and single- and double-ionized vacancies of lead. The donor effect of cadmium in lead telluride is rather weak due to the efficient self-compensation processes. Consequently, n- or p-type conductivity materials with the optimal composition for thermoelectric application carrier concentrations (1018–1019 cm−3) could be obtained by introducing the stoichiometric metal/chalcogenide component of the base material (Pb/Te) or by the implementation of additional donor/acceptor impurities.
Study of correlation between plasma parameter and beam optics
Authors: Kisaki M. , Nakano H. , Tsumori K. , Ikeda K. , Masaki S. , Haba Y. , Fujiwara Y. , Nagaoak K. , Osakabe M.
Published: February 2020

Simultaneous measurement of negative ion source plasma and extracted beam is carried out in order to clarify a key plasma parameter governing the meniscus formation in negative ion sources for fusion. The plasma discharge is performed with various discharge powers at different bias voltages in order to vary the plasma parameters. It is shown that the beam width changes along the same curve with respect to the negative ion density at any bias voltage while it varies along different curves with other plasma parameters depending on the bias voltage. This implies that the mechanism of meniscus formation in negative ion sources could be described along the similar manner as positive ion sources.
Numerical investigations on the flow over cuboids with different aspect ratios and the emitted noise
Authors: Wang Yanan , Thompson David , Hu Zhiwei
Published: February 2020

The effect of aspect ratio on the flow over cuboids in cross-flow is investigated numerically, together with the noise emitted to the far field. The near-field flow features are obtained using the delayed detached eddy simulation approach and the far-field noise is predicted using the Ffowcs Williams–Hawkings acoustic analogy. Ten values of aspect ratio are studied in the current work ranging from 1/6 to 12 at three Reynolds numbers between 50 000 and 200 000. Aerodynamic coefficients, flow patterns, and pressure distributions along the cuboid surfaces are studied in detail with respect to cuboid aspect ratio for different Reynolds numbers. It is found that the separated flow from the leading edge reattaches to the lateral surfaces of cuboids with aspect ratios smaller than unity, while a secondary vortex is formed near the trailing edge for larger aspect ratios. In addition, the aspect ratio has considerable effect on the tonal peak in the far-field noise spectra from the cuboids occurring for aspect ratios greater than 1.
Modeling the effects of slip on dipole–wall collision problems using a lattice Boltzmann equation method
Authors: Mohammed S. , Graham D. I. , Reis T.
Published: February 2020

We study the physics of flow due to the interaction between a viscous dipole and boundaries that permit slip. This includes partial and free slip, and interactions near corners. The problem is investigated by using a two relaxation time lattice Boltzmann equation with moment-based boundary conditions. Navier-slip conditions, which involve gradients of the velocity, are formulated and applied locally. The implementation of free-slip conditions with the moment-based approach is discussed. Collision angles of 0°, 30°, and 45° are investigated. Stable simulations are shown for Reynolds numbers between 625 and 10 000 and various slip lengths. Vorticity generation on the wall is shown to be affected by slip length, angle of incidence, and Reynolds number. An increase in wall slippage causes a reduction in the number of higher-order dipoles created. This leads to a decrease in the magnitude of the enstrophy peaks and reduces the dissipation of energy. The dissipation of the energy and its relation to the enstrophy are also investigated theoretically, confirming quantitatively how the presence of slip modifies this relation.
Desorption of neutrals, cations, and anions from core-excited amorphous solid water
Authors: Dupuy R. , Féraud G. , Bertin M. , Romanzin C. , Philippe L. , Putaud T. , Michaut X. , Cimino R. , Baglin V. , Fillion J.-H.
Published: February 2020

Core-excitation of water ice releases many different molecules and ions in the gas phase. Studying these desorbed species and the underlying desorption mechanisms can provide useful information on the effects of x-ray irradiation in ice. We report a detailed study of the x-ray induced desorption of a number of neutral, cationic, and anionic species from amorphous solid water. We discuss the desorption mechanisms and the relative contributions of Auger and secondary electrons (x-ray induced electron stimulated desorption) and initial excitation (direct desorption) as well as the role of photochemistry. Anions are shown to desorb not just through processes linked with secondary electrons but also through direct dissociation of the core-excited molecule. The desorption spectra of oxygen ions (O+, OH+, H2O+, O−, and OH−) give a new perspective on their previously reported very low desorption yields for most types of irradiations of water, showing that they mostly originate from the dissociation of photoproducts such as H2O2.
Anti-crossing property of strong coupling system of silver nanoparticle dimers coated with thin dye molecular films analyzed by electromagnetism
Authors: Itoh Tamitake , Yamamoto Yuko S. , Okamoto Takayuki
Published: February 2020

Evidence of strong coupling between plasmons and molecular excitons for plasmonic nanoparticle (NP) dimers exhibiting ultra-sensitive surface enhanced resonant Raman scattering is the observation of anti-crossing in the coupled resonance. However, experimentally tuning the plasmon resonance of such dimers for the observation is difficult. In this work, we calculate the anti-crossing property of dimers coated with thin dye films according to the classical electromagnetism. This property is quantitatively evaluated according to the coupled oscillator model composed of a plasmon and a molecular exciton representing the molecular multi-level system. A comparison of the film thickness dependences of dimer spectral changes with those of silver ellipsoidal NPs indicates that the dipole plasmons localized in the dimer gap are coupled with molecular excitons of the film much stronger than the dipole plasmons of ellipsoidal NPs. Furthermore, the anti-crossing behavior of coupled resonances is investigated while tuning plasmon resonance by changing the morphology and refractive index of the surrounding medium. The spectral changes observed for ellipsoidal NPs clearly exhibit anti-crossing property; however, the anti-crossing behavior of dimers is more complex due to the strong coupling of dipoles and higher-order plasmons with multiple molecular excitons. We find that the anti-crossing for dimers is clearly confirmed by the refractive index dependence of coupled resonance.
Nanoscale density variations in sputtered amorphous TaOx functional layers in resistive switching devices
Authors: Xu Qiyun , Ma Yuanzhi , Skowronski Marek
Published: February 2020

The density variations in reactively sputtered amorphous TaOx thin films deposited on planar and patterned substrates have been quantified by high-angle annular dark-field scanning transmission electron microscopy. The experiments have been performed both in plan-view and cross-sectional geometries. The planar films exhibit a cellular structure consisting of high-density cells with low-density boundaries. Laterally, cell sizes varied from 5 to 20 nm as the deposition temperature was changed from 298 K to 573 K. The corresponding density ratio of the cell boundary over the cell interior varied between 0.98 and 0.93 corresponding to 2%–7% free volume in the functional layer. The film microstructure is consistent with the self-shadowing effect of surface roughness. Similar low-density areas were found at the locations of steps of the patterned substrates with a local density decrease of up to 9%. The influence of the low-density region in the resistive random-access memory device is discussed.
Cooperative torus mode emission of O-ring lasers
Authors: Saito Mitsunori , Kubota Atsushi , Yagi Ryohei
Published: February 2020

Deformable ring lasers were fabricated by dispersing fluorescent dye (rhodamine 6G) in silicone rubber rings, i.e., the so-called O-rings. When excited with a pulsed green laser, an O-ring of 750 µm diameter exhibited a stimulated emission with a threshold fluence of 20 µJ/mm2. The wavelength and directionality of the emission were tunable by expansion or distortion of the ring with a needle. Because of this flexibility, the fluorescent peak of the O-ring lasers was not too sharp (a low-Q emission) and its wavelength differed slightly with individual rings. These features were advantageous for inducing a cooperative emission through an optical coupling of the rings. The optical coupling could be attained by exciting a cross-sectional circulation mode (torus mode), which the O-ring held in addition to the ordinary whispering gallery mode. When an O-ring was spitted with a glass fiber, for example, the torus mode coupled with the fiber mode, and consequently, the ring fluorescence emerged from the fiber end. Multiple O-rings, which individually exhibited a different emission wavelength, generated a single emission peak due to the optical coupling when they were arranged together on a spit fiber.
Anisotropic index of refraction and structural properties of hexagonal boron nitride epilayers probed by spectroscopic ellipsometry
Authors: McKay M. A. , Li J. , Lin J. Y. , Jiang H. X.
Published: February 2020

The anisotropic index of refraction of 200 μm thick boron-10 enriched hexagonal boron nitride (h-BN) freestanding epilayers grown by metalorganic chemical vapor deposition has been measured using spectroscopic ellipsometry in the UV (4.0–5.1 eV) spectral range. It was found that the index of refraction for the polarization mode with an electric field perpendicular to the c-axis (ordinary, no) is much higher than that with an electric field parallel to the c-axis (extraordinary, ne). By inclusion of turbostratic- (t-) phase layers within h-BN having an average inclination angle (θ) with respect to the ideal c-plane, a simple method for quantifying θ has been deduced. Our results revealed that the presence of t-phase layers decreases the optical anisotropy of h-BN and that a signature of improved crystalline quality is an increase in the ordinary index of refraction (no) as a result of the average incline angle θ approaching 0° and predicted that no = 2.7 and ne = 1.5 at 280 nm for single crystalline h-BN epilayers. More importantly, our results demonstrated that spectroscopic ellipsometry is an effective technique for characterizing the crystalline quality of h-BN epilayers with the advantages of being noninvasive and highly sensitive.
Dynamic heterogeneity and collective motion in star polymer melts
Authors: Fan Jinpeng , Emamy Hamed , Chremos Alexandros , Douglas Jack F. , Starr Francis W.
Published: February 2020

While glass formation of linear chain polymer melts has widely been explored, comparatively little is known about glass formation in star polymer melts. We study the segmental dynamics of star polymer melts via molecular dynamics simulations and examine the cooperative nature of segmental motion in star melts. In particular, we quantify how the molecular architecture of star polymers, i.e., the number of arms and the length of those arms, affects the glass transition temperature Tg, the non-Gaussian nature of molecular displacements, the collective string-like motion of monomers, and the role of chain connectivity in the cooperative motion. Although varying the number of arms f and the molecular mass Ma of the star arms can significantly influence the average star molecular shape, all our relaxation data can be quantitatively described in a unified way by the string model of glass formation, an activated transport model that derives from the Adam–Gibbs model, where the degree of cooperative motion is identified with the average length L of string-like particle exchange motions observed in our simulations. Previous work has shown the consistency of the string model with simulations of linear polymers at constant volume and constant pressure, as well as for thin supported polymer films and nanocomposites with variable polymer–surface interactions, where there are likewise large mobility gradients as in the star polymer melts studied in the present paper.
Probing structural changes upon carbon monoxide coordination to single metal adatoms
Authors: Ryan P. T. P. , Meier M. , Jakub Z. , Balajka J. , Hulva J. , Payne D. J. , Lee T.-L. , Franchini C. , Allegretti F. , Parkinson G. S. , Duncan D. A.
Published: February 2020

In this work, the adsorption height of Ag adatoms on the Fe3O4(001) surface after exposure to CO was determined using normal incidence x-ray standing waves. The Ag adatoms bound to CO (Ag1CO) are found to be pulled out of the surface to an adsorption height of 1.15 Å ± 0.08 Å, compared to the previously measured height of 0.96 Å ± 0.03 Å for bare Ag adatoms and clusters. Utilizing DFT+vdW+U calculations with the substrate unit cell dimension fixed to the experimental value, the predicted adsorption height for Ag1CO was 1.16 Å, in remarkably good agreement with the experimental results.
Enhanced magnetostriction of Tb–Dy–Fe via simultaneous ⟨111⟩-crystallographic orientation and -morphological alignment induced by directional solidification in high magnetic fields
Authors: Dong Shulin , Liu Tie , Dong Meng , Guo Xiaoyu , Yuan Shuang , Wang Qiang
Published: February 2020

The giant magnetostriction exhibited by pseudobinary Tb–Dy–Fe compounds has attracted considerable attention for use in magneto-mechanical actuators and sensors. However, simultaneously producing a crystallographic orientation and a morphological alignment of the (Tb,Dy)Fe2 phase along the ⟨111⟩ direction has proven difficult and inhibits further increase in the desired property. This work demonstrates that, by coupling the directional solidification and a high magnetic field, a ⟨111⟩-orientation and -alignment were simultaneously created. In addition, the pores and the defects in the alloys were eliminated, leading to an enhancement of the magnetostrictive performance. Analyses indicate that the controlled growth of the (Tb,Dy)Fe2 crystal was owing to the collaboration of the multiple magnetic field effects on both the liquid and the solid phases during the directional solidification. Specifically, the magnetic torque induced a rotation of the crystals aligning their easy axis of magnetization (i.e., ⟨111⟩) along the magnetic field direction. Further, the Lorentz force stabilized the directional growth of the crystals by suppressing the convection, while the magnetic force exerted a compressive stress on the paramagnetic alloy melt to remove the gases in the melt. As a result, a highly ⟨111⟩-oriented and -aligned and defect-free Tb–Dy–Fe compound was produced. This strategy may also be expanded to other alloy systems whose phases exhibit a magnetic anisotropy and thereby fabricate anisotropic functional compounds.
Entire crystallization process of Lennard-Jones liquids: A large-scale molecular dynamics study
Authors: Ouyang Wenze , Sun Bin , Sun Zhiwei , Xu Shenghua
Published: February 2020

By using a graphics processing unit-accelerated parallel algorithm on a compute unified device architecture platform, we perform large-scale molecular dynamics simulations in a Lennard-Jones system to observe the entire crystallization process, including metastable stage, critical nuclei formation, and the stage of crystal growth. Although the intermediated precursors that play a role in determining the polymorphs are predominantly bcc ordered, the polymorph selection is rather different at different stages. The precursors that have a relatively high orientational order will be on average in a denser region than uniform liquids, but microscopically the crystal nucleation happens without a density change. The average density of nuclei first increases significantly, and then almost keeps independent on the crystallite size after the growing post-critical nucleus becomes large enough. With such a large enough system, the crystal growth rate is able to be calculated directly by doing a linear fit to the temporal evolution of growing crystallite size. The obtained value of the growth rate indicates that the actual crystal growth in the Lennard-Jones system where the crystal–liquid interface has several kinds of structures is possibly driven by both collision-controlled and diffusion-controlled mechanisms.
Polarization controlled fine structure of diffraction spots from an optically induced grating
Authors: Jelken Joachim , Henkel Carsten , Santer Svetlana
Published: February 2020

We report on the remote control of the fine structure of a diffraction spot from optically induced dual gratings within a photosensitive polymer film. The material contains azobenzene in the polymer side chains and develops a surface relief under two-beam holographic irradiation. The diffraction of a polarized probe beam is sensitive to the orientation of the azobenzene groups forming a permanently stored birefringence grating within the film. We demonstrate that the fine structure of the probe diffraction spot switches from a Gaussian to a hollow or a hollow to a “Saturn”-like structure by a change in polarization. This makes it potentially useful in photonic devices because the beam shape can be easily inverted by an external stimulus.
Enhanced particle flux due to localized divertor MHD instability in DIII-D tokamak
Authors: Wang H. Q. , Watkins J. G. , Guo H. Y. , Leonard A. W. , Thomas D. M. , Stepanenko A. A. , Krasheninnikov S. I.
Published: February 2020

An MHD mode with a frequency of  <10 kHz has been identified near the inner strike point from various diagnostics, i.e., divertor Langmuir probes, magnetics sensors, and interferometers, but does not appear in the upstream and core diagnostics. This MHD mode is associated with magnetic oscillations of ≳5 G, has a long wavelength in the toroidal direction with toroidal mode number n = 1, but is localized in a narrow radial region of a few cm. The mode appears when the outer strike point remains attached and the inner strike point nearly detaches, grows with increasing density, and eventually weakens and vanishes as the outer strike point detaches. This mode results in particle flux with an order of magnitude higher than the background plasmas near the inner strike point. The mode characteristics are consistent with the Current-Convective-Instability theory prediction. Initial simulations based on experimental input have found oscillations with similar frequencies but weaker amplitude.
Giant shifts of photoluminescence bands in GaN
Authors: Reshchikov Michael A.
Published: February 2020

Unusually large shifts of photoluminescence (PL) bands with excitation intensity or with temperature are sometimes observed in GaN. In particular, the ultraviolet luminescence band with a maximum at 3.28 eV is attributed to transitions from the conduction band (or shallow donors) to the shallow MgGa acceptor. In semi-insulating GaN samples doped with Mg, enormous redshift (up to 0.6 eV) and broadening of this PL band can be observed with variation of temperature or excitation intensity. A similar behavior of PL was observed in semi-insulating GaN doped with Zn. The blue band with a maximum at 2.9 eV in GaN:Zn is attributed to electron transitions from the conduction band or from shallow donors to the ZnGa acceptor level located at 0.4 eV above the valence band. In conductive n-type GaN, this PL band redshifts by only 7 meV with decreasing excitation intensity by five orders of magnitude, and the shift is explained with the donor–acceptor pair model. However, in semi-insulating GaN:Zn samples, a gradual shift by up to 0.8 eV with decreasing excitation intensity has been observed. Finally, the yellow luminescence band shifts by not more than 7 meV in high-quality, undoped GaN samples, while a redshift by more than 0.1 eV can be observed in GaN heavily doped with Si. The giant shifts are attributed to the presence of electric fields in high-resistivity or heavily doped n-type GaN.
Device and method for nonlinear ultrasonic measurements on highly irradiated 304 stainless steel specimens in a hot cell environment
Authors: Kim J.-Y. , Wall J. J. , Joo Y.-S. , Park D.-G. , Jacobs L. J.
Published: February 2020

This paper reports on the first successful nonlinear ultrasonic measurement on highly irradiated specimens in a hot cell environment. The specimens are ANSI 304 stainless steel specimens for which the microstructure characterization and ultrasonic velocity measurement have been previously conducted. The critical part of this research is the development of an automatic fixture device that can facilitate repeatable loading and unloading to place the contact ultrasonic transducers on and off of the specimen. The key step to achieve high measurement repeatability is a careful adjustment of the support-spring constants such that the contact force at the interface between the transducer face and specimen surface is as uniform and constant as possible. The longitudinal ultrasonic velocities, which are obtained as a by-product of the nonlinear ultrasonic measurements, show a level of random variation in terms of (max-min)/average (%) below 0.2%, and the velocity distributions and magnitudes are in good agreement with those from the previous work. The ultrasonic nonlinearity parameters show the level of random variation below 4.7%, which is extremely low, considering that the measurements are conducted in a hot cell environment. The nonlinearity parameters also show a strong dependence on the measurement location in a particular specimen with respect to the radiation source, demonstrating a possible inhomogeneous microstructure evolution in these 12.7 mm thick specimens. This research demonstrates the feasibility of making nonlinear ultrasonic measurement on highly radioactive materials and/or in a highly radioactive environment using the device and procedure developed.
Smart optically induced nonlinear photonic crystals for frequency conversion and control
Authors: Liu Dawei , Liu Shan , Mazur Leszek Mateusz , Wang Bingxia , Lu Peixiang , Krolikowski Wieslaw , Sheng Yan
Published: February 2020

We extend the functionality of nonlinear photonic crystals by fabricating a structure combining a few individual optical transformations in second harmonic generation. In particular, we employed all-optical spontaneous polarization reversal in ferroelectrics to create nonlinear holograms with curved fork-like spatial modulation of nonlinearity for the generation of second harmonic optical vortices. The curved fork-like structure represents a combination of a standard vortex harmonic generator (fork structure) and an axicon, thereby allowing us to realize the second harmonic “perfect vortices” whose diameter remains constant independently of their topological charge.