Order Of Magnitude Higher Precision Research Articles

High-precision electron affinity of oxygen

Negative ions are important in many areas of science and technology, e.g., in interstellar chemistry, for accelerator-based radionuclide dating, and in anti-matter research. They are unique quantum systems where electron-correlation effects govern their properties. Atomic anions are loosely bound systems, which with very few exceptions lack optically allowed transitions. This limits prospects for high-resolution spectroscopy, and related negative-ion detection methods. Here, we present a method to measure negative ion binding energies with an order of magnitude higher precision than what has been possible before. By laser-manipulation of quantum-state populations, we are able to strongly reduce the background from photodetachment of excited states using a cryogenic electrostatic ion-beam storage ring where keV ion beams can circulate for up to hours. The method is applicable to negative ions in general and here we report an electron affinity of 1.461 112 972(87) eV for 16O.

Removal of the highest energy POD mode for optimal construction of subgrid-scale parameters in a SPIV-measured turbulent mixing layer flow

Large eddy simulation is based on decomposition of turbulent flow structures to large energy-containing scales and small subgrid-scale (SGS) structures. The present study analyzes the effect of removing high-energy modes of flow to find the optimal construction of SGS parameters using the a priori approach. The data belong to a shear layer flow measured by stereoscopic particle image velocimetry (SPIV). The proper orthogonal decomposition (POD) method is used to capture all energy modes of the acquired velocity field. The missing/erroneous data are reconstructed using the gappy POD method. Particularly, similarity and mixed models are used to evaluate the SGS parameters. The results of the mixed model are compared via the a priori approach, before and after removing the high-energy modes. For the present flow, it is found that removal of just the first POD mode (as a representative of the mean flow) leads to the best SGS reconstruction, and this results in one order of magnitude higher precision of the average SGS stresses.

Spectroscopy on the AΠ1←XΣ+1 transition of buffer-gas-cooled AlCl

Aluminum monochloride (AlCl) has been proposed as an excellent candidate for laser cooling. Here we present absorption spectroscopy measurements on the $A^1\Pi \leftarrow X^1\Sigma^+$ transition in AlCl inside a cryogenic helium buffer-gas beam cell. The high resolution absorption data enables a rigorous, quantitative comparison with our high-level ab initio calculations of the electronic and rovibronic energies, providing a comprehensive picture of the AlCl quantum structure. The combination of high resolution spectral data and theory permits the evaluation of spectroscopic constants and associated properties, like equilibrium bond length, with an order of magnitude higher precision. Based on the measured molecular equilibrium constants of the $A^1\Pi$ state, we estimate a Franck-Condon factor of the $A^1\Pi \leftarrow X^1\Sigma^+$ of 99.88%, which confirms that AlCl is amenable to laser cooling.

2D Raman band splitting in graphene: Charge screening and lifting of the K-point Kohn anomaly

Pristine graphene encapsulated in hexagonal boron nitride has transport properties rivalling suspended graphene, while being protected from contamination and mechanical damage. For high quality devices, it is important to avoid and monitor accidental doping and charge fluctuations. The 2D Raman double peak in intrinsic graphene can be used to optically determine charge density, with decreasing peak split corresponding to increasing charge density. We find strong correlations between the 2D1 and 2D2 split vs 2D line widths, intensities, and peak positions. Charge density fluctuations can be measured with orders of magnitude higher precision than previously accomplished using the G-band shift with charge. The two 2D intrinsic peaks can be associated with the “inner” and “outer” Raman scattering processes, with the counterintuitive assignment of the phonon closer to the K point in the KM direction (outer process) as the higher energy peak. Even low charge screening lifts the phonon Kohn anomaly near the K point for graphene encapsulated in hBN, and shifts the dominant intensity from the lower to the higher energy peak.

Hydrogen molecular ions for improved determination of fundamental constants

The possible use of high-resolution rovibrational spectroscopy of the hydrogen molecular ions H + 2 and HD + for an independent determination of several fundamental constants is analyzed. While these molecules had been proposed for metrology of nuclear-to-electron mass ratios, we show that they are also sensitive to the radii of the proton and deuteron and to the Rydberg constant at the level of the current discrepancies colloquially known as the proton size puzzle. The required level of accuracy, in the 10 --12 range, can be reached both by experiments, using Doppler-free two-photon spectroscopy schemes, and by theoretical predictions. It is shown how the measurement of several well-chosen rovibrational transitions may shed new light on the proton-radius puzzle, provide an alternative accurate determination of the Rydberg constant, and yield new values of the proton-to-electron and deuteron-to-proton mass ratios with one order of magnitude higher precision.

Íntegro: Leveraging victim prediction for robust fake account detection in large scale OSNs

Detecting fake accounts in online social networks (OSNs) protects both OSN operators and their users from various malicious activities. Most detection mechanisms attempt to classify user accounts as real (i.e., benign, honest) or fake (i.e., malicious, Sybil) by analyzing either user-level activities or graph-level structures. These mechanisms, however, are not robust against adversarial attacks in which fake accounts cloak their operation with patterns resembling real user behavior.In this article, we show that victims – real accounts whose users have accepted friend requests sent by fakes – form a distinct classification category that is useful for designing robust detection mechanisms. In particular, we present Íntegro – a robust and scalable defense system that leverages victim classification to rank most real accounts higher than fakes, so that OSN operators can take actions against low-ranking fake accounts. Íntegro starts by identifying potential victims from user-level activities using supervised machine learning. After that, it annotates the graph by assigning lower weights to edges incident to potential victims. Finally, Íntegro ranks user accounts based on the landing probability of a short random walk that starts from a known real account. As this walk is unlikely to traverse low-weight edges in a few steps and land on fakes, Íntegro achieves the desired ranking.We implemented Íntegro using widely-used, open-source distributed computing platforms, where it scaled nearly linearly. We evaluated Íntegro against SybilRank, which is the state-of-the-art in fake account detection, using real-world datasets and a large-scale deployment at Tuenti – the largest OSN in Spain with more than 15 million active users. We show that Íntegro significantly outperforms SybilRank in user ranking quality, with the only requirement that the employed victim classifier is better than random. Moreover, the deployment of Íntegro at Tuenti resulted in up to an order of magnitude higher precision in fake account detection, as compared to SybilRank.

Ground-state binding energy of [formula omitted] from high-resolution decay-pion spectroscopy

A systematic study on the Λ ground state binding energy of hyperhydrogen HΛ4 measured at the Mainz Microtron MAMI is presented. The energy was deduced from the spectroscopy of mono-energetic pions from the two-body decays of hyperfragments, which were produced and stopped in a 9Be target. First data, taken in the year 2012 with a high resolution magnetic spectrometer, demonstrated an almost one order of magnitude higher precision than emulsion data, while being limited by systematic uncertainties. In 2014 an extended measurement campaign was performed with improved control over systematic effects, increasing the yield of hypernuclei and confirming the observation with two independent spectrometers and two targets of different thicknesses. The analysis of these data is in agreement with the previously published value for the HΛ4 binding energy as well as with a consistent re-analysis of the 2012 data. When compared to the HeΛ4 binding energy from emulsion data, a large charge symmetry breaking effect in the A=4 hypernuclear system is confirmed.

Active magnetoplasmonic ruler.

Plasmon rulers are an emerging concept in which the strong near-field coupling of plasmon nanoantenna elements is employed to obtain structural information at the nanoscale. Here, we combine nanoplasmonics and nanomagnetism to conceptualize a magnetoplasmonic dimer nanoantenna that would be able to report nanoscale distances while optimizing its own spatial orientation. The latter constitutes an active operation in which a dynamically optimized optical response per measured unit length allows for the measurement of small and large nanoscale distances with about 2 orders of magnitude higher precision than current state-of-the-art plasmon rulers. We further propose a concept to optically measure the nanoscale response to the controlled application of force with a magnetic field.

High resolution isotope shifts and hyperfine structure measurements of tungsten by laser-induced fluorescence spectroscopy

Isotope shifts and hyperfine structure of tungsten were studied in the near UV range. We have used laser-induced fluorescence spectroscopy on a pulsed supersonic beam to probe the 5D0 → 5F1 transition at 384.9 nm, 7S3 → 7P4 transition at 400.9 nm and 7S3 → 7P3 transition at 407.4 nm. Three new magnetic hyperfine constants are reported for 7P3,7P4 and 5F1 states. The isotope shifts of the 384.9 nm transition are presented for the first time, and the isotope shifts of 400.9 and 407.4 nm transitions are measured with an order of magnitude higher precision compared to the previous measurements. As a result, the nuclear parameters λ and λrel are extracted from the isotope shifts with an improved precision.

Treatment of Singular Integrals on Generalized Curvilinear Parametric Quadrilaterals in Higher Order Method of Moments

Singular integrals over the generalized curvilinear parametric quadrilaterals in higher order method of moments (MoM) are treated by a singularity cancellation technique. The singularities are eliminated via coordinate transformation, by which the singular integrals are converted into some regular integrals that can be numerically computed by using the Gauss-Legendre quadrature. Numerical results show that this proposed singular integral treatment approach converges much faster, yet achieves several orders of magnitude higher precision than the widely used singularity subtraction technique.

Precision Measurement ofLi11Moments: Influence of Halo Neutrons on theLi9Core

The electric quadrupole moment and the magnetic moment of the 11Li halo nucleus have been measured with more than an order of magnitude higher precision than before, |Q| = 33.3(5) mb and mu = +3.6712(3)muN, revealing a 8.8(1.5)% increase of the quadrupole moment relative to that of 9Li. This result is compared to various models that aim at describing the halo properties. In the shell model an increased quadrupole moment points to a significant occupation of the 1d orbits, whereas in a simple halo picture this can be explained by relating the quadrupole moments of the proton distribution to the charge radii. Advanced models so far fail to reproduce simultaneously the trends observed in the radii and quadrupole moments of the lithium isotopes.

Application of the third-law methodology to investigation of decomposition kinetics

The most important results obtained since the first application (in 2002) of the third-law methodology to kinetic studies of decomposition reactions are considered. The third-law method has been significantly improved and extended to powdered and melted materials. The use of the average values of molar entropy greatly simplified its application to materials with unknown product composition and/or unknown thermodynamic parameters. The order of magnitude higher precision and low susceptibility of the third-law method to the self-cooling compared with the Arrhenius-plots method, guarantees measurement of the E parameter with the error less than 2%. A significant reduction of experimental time and a possibility of simple evaluation of self-cooling are the additional advantages of this method.The application of the third-law method to decomposition studies permitted to support the basic assumptions underlying the physical approach to interpretation of decomposition kinetics. A good fit of experiment to theory for the ratio of the initial decomposition temperature to the E parameter, the peculiarities of carbonate decomposition in CO2 and regularities of solid and melted nitrate decomposition are in complete agreement with the mechanism of dissociative evaporation and consumption of a part τ of the condensation energy by reactant. It has become possible to evaluate the τ parameter a priori on the basis of thermodynamic features of the low-volatility product. From comparison of the E parameters with the molar enthalpies of the implied reactions, the decomposition mechanisms of 40 different reactants are identified. Some peculiarities in evolution of gaseous products in atomic and molecular forms are interpreted in accordance with the crystal symmetry of reactants. The earlier theoretical evaluations of the self-cooling effect, which can reach in high vacuum several ten degrees, are supported experimentally.

Interferometric Signatures of Single Molecules

We built an, interferometer where one of the two slits of a classical Young's setup is replaced by a single molecule embedded in a solid matrix. This enabled direct measurement of the first order coherence of the 0-0 single-molecule emission, which at high excitation powers proves to be split in coherent and incoherent parts. We demonstrate an order of magnitude higher precision in axial localization of single molecules in comparison with that of confocal microscopy. These experiments open a possibility for single-molecule holography. Detection of single molecules with low luminescence quantum yields could be another application of this technique.

The Soft X‐Ray Properties of a Complete Sample of Optically Selected Quasars. II. Final Results

We present the results of ROSAT position sensitive proportional counter (PSPC) observations of 10 quasars. These objects are part of our ROSAT program to observe a complete sample of optically selected quasars. This sample includes all 23 quasars from the bright quasar survey with a redshift z less than or = 0.400 and a Galactic H I column density N(sup Gal sub H I) less than 1.9 x 10(exp 20)/sq cm. These selection criteria, combined with the high sensitivity and improved energy resolution of the PSPC, allow us to determine the soft (approximately 0.2-2 keV) X-ray spectra of quasars with about an order of magnitude higher precision compared with earlier soft X-ray observations. The following main results are obtained: Strong correlations are suggested between the soft X-ray spectral slope alpha(sub x) and the following emission line parameters: H beta Full Width at Half Maximum (FWHM), L(sub O III), and the Fe II/H beta flux ratio. These correlations imply the following: (1) The quasar's environment is likely to be optically thin down to approximately 0.2 keV. (2) In most objects alpha(sub x) varies by less than approximately 10% on timescales shorter than a few years. (3) alpha(sub x) might be a useful absolute luminosity indicator in quasars. (4) The Galactic He I and H I column densities are well correlated. Most spectra are well characterized by a simple power law, with no evidence for either significant absorption excess or emission excess at low energies, to within approximately 30%. We find mean value of alpha(sub x) = -1.50 +/- 0.40, which is consistent with other ROSAT observations of quasars. However, this average is significantly steeper than suggested by earlier soft X-ray observations of the Einstein IPC. The 0.3 keV flux in our sample can be predicted to better than a factor of 2 once the 1.69 micrometer(s) flux is given. This implies that the X-ray variability power spectra of quasars flattens out between f approximately 10(exp -5) and f approximately 10(exp -8) Hz. A steep alpha(sub x) is mostly associated with a weak hard X-ray component, relative to the near-IR and optical emission, rather than a strong soft excess, and the scatter in the normalized 0.3 keV flux is significantly smaller than the scatter in the normalized 2 keV flux. This argues against either thin or thick accretion disks as the origin of the soft X-ray emission. Further possible implications of the results found here are briefly discussed.

The faintest stars

A determination of the luminosity and mass functions is given for field stars at the bottom of the main sequence as the first results from a 320 sq deg survey based on both optical and near-infrared photometry. The luminosity and mass functions are determined with an order of magnitude higher precision than previous studies achieve. No evidence is found for a mass function steepening toward the H-burning limit.

High precision relative locations of earthquakes at Mount St. Helens, Washington

Several earthquake sequences have occurred at Mount St. Helens as clusters of shallow events with nearly identical waveforms (multiplets). We present a technique that allows the relative relocation of events within a multiplet to at least an order of magnitude higher precision than is typically possible with traditional techniques. A multiplet is studied in pairs of events called doublets. Each doublet is made up of a reference event and one other event from the multiplet. The cross spectrum of a short window beginning just before the P arrival is used to compute differences in arrival times between seismograms from the same station for each doublet. These time differences, computed with a precision of 1–2 ms, are then used to locate each earthquake relative to the reference event. Engineering explosions with well‐known locations are used to test the relocation technique. Explosions can be relocated with accuracy better than 20 m for events within 250 m of the reference explosion. The relocation technique is applied to earthquakes preceding the September 10, 1984, and the May‐June 1985 dome‐building eruptions of Mount St. Helens. Forty events that occurred during a 12‐hour period in September 1984 are located in a volume, approximately 30 m in diameter, beneath the lava dome. The earthquakes following the extrusion do not occur in multiplets and appear to be distributed over a much larger volume. In the May‐June 1985 eruption we recognize three multiplet sets that took place successively in time. The multiplets are interpreted as repeated failure or slip within a relatively small volume due to high strain rates around the magma supply conduit.

Nuclear charge radii from muonic X-ray transitions in F, Na, Al, Si, P, S and K

Energies of muonic X-rays of the Lyman series of seven light natural elements (F, Na, Al, Si, P, S and K) have been determined with an accuracy of between 15 and 30 eV. Equivalent charge radii have been deduced. For μ −-K, transitions to the 2s state allowed an additional constraint on the Fermi c- t diagram. The results are in good agreement with, and generally of an order of magnitude higher precision than, comparable electron scattering data.