Work functions, ionization potentials, and in-between: Scaling relations based on the image charge model

We revisit a model in which the ionization energy of a metal particle is associated with the work done by the image charge force in moving the electron from infinity to a small cut-off distance just outside the surface. We show that this model can be compactly, and productively, employed to study the size dependence of electron removal energies over the range encompassing bulk surfaces, finite clusters, and individual atoms. It accounts in a straightforward manner for the empirically known correlation between the atomic ionization potential (IP) and the metal work function (WF), IP/WF$\sim$2. We formulate simple expressions for the model parameters, requiring only a single property (the atomic polarizability or the nearest neighbor distance) as input. Without any additional adjustable parameters, the model yields both the IP and the WF within $\sim$10% for all metallic elements, as well as matches the size evolution of the ionization potentials of finite metal clusters for a large fraction of the experimental data. The parametrization takes advantage of a remarkably constant numerical correlation between the nearest-neighbor distance in a crystal, the cube root of the atomic polarizability, and the image force cutoff length. The paper also includes an analytical derivation of the relation of the outer radius of a cluster of close-packed spheres to its geometric structure.Comment: Original submission: 8 pages with 7 figures incorporated in the text. Revised submission (added one more paragraph about alloy work functions): 18 double spaced pages + 8 separate figures. Accepted for publication in PR

Direct aerosol chemical composition measurements to evaluate the physicochemical differences between controlled sea spray aerosol generation schemes

Controlled laboratory studies of the physical and chemical properties of sea spray aerosol (SSA) must be under-pinned by a physically and chemically accurate representation of the bubble-mediated production of nascent SSA particles. Bubble bursting is sensitive to the physico-chemical properties of seawater. For a sample of seawater, any important differences in the SSA production mechanism are projected into the composition of the aerosol particles produced. Using direct chemical measurements of SSA at the single-particle level, this study presents an intercomparison of three laboratory-based, bubble-mediated SSA production schemes: gas forced through submerged sintered glass filters ("frits"), a pulsed plunging-waterfall apparatus, and breaking waves in a wave channel filled with natural seawater. The size-resolved chemical composition of SSA particles produced by breaking waves is more similar to particles produced by the plunging waterfall than those produced by sintered glass filters. Aerosol generated by disintegrating foam produced by sintered glass filters contained a larger fraction of organic-enriched particles and a different size-resolved elemental composition, especially in the 0.8–2 μm dry diameter range. Interestingly, chemical differences between the methods only emerged when the particles were chemically analyzed at the single-particle level as a function of size; averaging the elemental composition of all particles across all sizes masked the differences between the SSA samples. When dried, SSA generated by the sintered glass filters had the highest fraction of particles with spherical morphology compared to the more cubic structure expected for pure NaCl particles produced when the particle contains relatively little organic carbon. In addition to an intercomparison of three SSA production methods, the role of the episodic or "pulsed" nature of the waterfall method on SSA composition was under-taken. In organic-enriched seawater, the continuous operation of the plunging waterfall resulted in the accumulation of surface foam and an over-expression of organic matter in SSA particles compared to those produced by a pulsed plunging waterfall. Throughout this set of experiments, comparative differences in the SSA number size distribution were coincident with differences in aerosol particle composition, indicating that the production mechanism of SSA exerts important controls on both the physical and chemical properties of the resulting aerosol with respect to both the internal and external mixing state of particles. This study provides insight into the inextricable physicochemical differences between each of the bubble-mediated SSA generation mechanisms tested and the aerosol particles that they produce, and also serves as a guideline for future laboratory studies of SSA particles

Bathymetry Beneath Ice Shelves of Western Dronning Maud Land, East Antarctica, and Implications on Ice Shelf Stability

Antarctica's ice shelves play a key role in stabilizing the ice streams that feed them. Since basal melting largely depends on ice-ocean interactions, it is vital to attain consistent bathymetry models to estimate water and heat exchange beneath ice shelves. We have constructed bathymetry models beneath the ice shelves of western Dronning Maud Land by inverting airborne gravity data and incorporating seismic, multibeam, and radar depth references. Our models reveal deep glacial troughs beneath the ice shelves and terminal moraines close to the continental shelf breaks, which currently limit the entry of Warm Deep Water from the Southern Ocean. The ice shelves buttress a catchment that comprises an ice volume equivalent to nearly 1 m of eustatic sea level rise, partly susceptible to ocean forcing. Changes in water temperature and thermocline depth may accelerate marine-based ice sheet drainage and constitute an underestimated contribution to future global sea level rise

H.E.S.S. observations of gamma-ray bursts in 2003-2007

Very-high-energy (VHE; >~100 GeV) gamma-rays are expected from gamma-ray bursts (GRBs) in some scenarios. Exploring this photon energy regime is necessary for understanding the energetics and properties of GRBs. GRBs have been one of the prime targets for the H.E.S.S. experiment, which makes use of four Imaging Atmospheric Cherenkov Telescopes (IACTs) to detect VHE gamma-rays. Dedicated observations of 32 GRB positions were made in the years 2003-2007 and a search for VHE gamma-ray counterparts of these GRBs was made. Depending on the visibility and observing conditions, the observations mostly start minutes to hours after the burst and typically last two hours. Results from observations of 22 GRB positions are presented and evidence of a VHE signal was found neither in observations of any individual GRBs, nor from stacking data from subsets of GRBs with higher expected VHE flux according to a model-independent ranking scheme. Upper limits for the VHE gamma-ray flux from the GRB positions were derived. For those GRBs with measured redshifts, differential upper limits at the energy threshold after correcting for absorption due to extra-galactic background light are also presented.Comment: 9 pages, 4 tables, 3 figure

Discovery of VHE gamma-rays from the high-frequency-peaked BL Lac object RGB J0152+017

Aims: The BL Lac object RGB J0152+017 (z=0.080) was predicted to be a very high-energy (VHE; > 100 GeV) gamma-ray source, due to its high X-ray and radio fluxes. Our aim is to understand the radiative processes by investigating the observed emission and its production mechanism using the High Energy Stereoscopic System (H.E.S.S.) experiment. Methods: We report recent observations of the BL Lac source RGB J0152+017 made in late October and November 2007 with the H.E.S.S. array consisting of four imaging atmospheric Cherenkov telescopes. Contemporaneous observations were made in X-rays by the Swift and RXTE satellites, in the optical band with the ATOM telescope, and in the radio band with the Nancay Radio Telescope. Results: A signal of 173 gamma-ray photons corresponding to a statistical significance of 6.6 sigma was found in the data. The energy spectrum of the source can be described by a powerlaw with a spectral index of 2.95+/-0.36stat+/-0.20syst. The integral flux above 300 GeV corresponds to ~2% of the flux of the Crab nebula. The source spectral energy distribution (SED) can be described using a two-component non-thermal synchrotron self-Compton (SSC) leptonic model, except in the optical band, which is dominated by a thermal host galaxy component. The parameters that are found are very close to those found in similar SSC studies in TeV blazars. Conclusions: RGB J0152+017 is discovered as a source of VHE gamma-rays by H.E.S.S. The location of its synchrotron peak, as derived from the SED in Swift data, allows clearly classification it as a high-frequency-peaked BL Lac (HBL).Comment: Accepted for publication in A&A Letters (5 pages, 4 figures

Rubbery taproot disease of sugar beet in Serbia associated with 'Candidatus phytoplasma solani'

Rubbery taproot disease (RTD) of sugar beet was observed in Serbia for the first time in the 1960s. The disease was already described in neighboring Bulgaria and Romania at the time but it was associated with abiotic factors. In this study on RTD of sugar beet in its main growing area of Serbia, we provide evidence of the association between 'Candidatus Phytoplasma solani' (stolbur phytoplasma) infection and the occurrence of typical RTD symptomatology. 'Ca. P. solani' was identified by PCR and the sequence analyses of 16S ribosomal RNA, tuf, secY, and stamp genes. In contrast, the causative agent of the syndrome “basses richesses” of sugar beet-namely, 'Ca. Arsenophonus phytopathogenicus'-was not detected. Sequence analysis of the stolbur strain's tuf gene confirmed a previously reported and a new, distinct tuf stolbur genotype (named 'tuf d') that is prevalent in sugar beet. The sequence signatures of the tuf gene as well as the one of stamp both correlate with the epidemiological cycle and reservoir plant host. This study provides knowledge that, for the first time, enables the differentiation of stolbur strains associated with RTD of sugar beet from closely related strains, thereby providing necessary information for further epidemiological work seeking to identify insect vectors and reservoir plant hosts. The results of this study indicate that there are differences in hybrid susceptibility. Clarifying the etiology of RTD as a long-known and economically important disease is certainly the first step toward disease management in Serbia and neighboring countries.This is the peer reviewed version of the following article: Ćurčić Ž., Stepanović J., Zübert C., Taški-Ajduković K., Kosovac A., Rekanović E., Kube M., Duduk B. Rubbery taproot disease of sugar beet in Serbia associated with 'Candidatus phytoplasma solani'. Plant Disease 2021, 105 (2), 255 – 263. [https://doi.org/10.1094/PDIS-07-20-1602-RE]

A Replication of Failure, Not a Failure to Replicate

Purpose: The increasing role of systematic reviews in knowledge production demands greater rigor in the literature search process. The performance of the Social Work Abstracts (SWA) database has been examined multiple times over the past three decades. The current study is a replication within this line of research. Method: Issue level coverage was examined for the same 33 SWA core journals and the same time period as our 2009 study. Results: The mean percentage of issues missing in the current study was 20%. The mean percentage of issues missing in the current study was significantly greater than the mean percentage of issues missing in the 2009 study. Discussion: The research of other groups, and that of our own, has failed to prompt NASW Press to act. SWA was failing, it is failing and NASW Press has failed to correct those failures

Study of the reaction e^{+}e^{-} -->J/psi\pi^{+}\pi^{-} via initial-state radiation at BaBar

We study the process $e^+e^-\to J/\psi\pi^{+}\pi^{-}$ with initial-state-radiation events produced at the PEP-II asymmetric-energy collider. The data were recorded with the BaBar detector at center-of-mass energies 10.58 and 10.54 GeV, and correspond to an integrated luminosity of 454 $\mathrm{fb^{-1}}$. We investigate the $J/\psi \pi^{+}\pi^{-}$ mass distribution in the region from 3.5 to 5.5 $\mathrm{GeV/c^{2}}$. Below 3.7 $\mathrm{GeV/c^{2}}$ the $\psi(2S)$ signal dominates, and above 4 $\mathrm{GeV/c^{2}}$ there is a significant peak due to the Y(4260). A fit to the data in the range 3.74 -- 5.50 $\mathrm{GeV/c^{2}}$ yields a mass value $4244 \pm 5$ (stat) $\pm 4$ (syst)$\mathrm{MeV/c^{2}}$ and a width value $114 ^{+16}_{-15}$ (stat)$\pm 7$(syst)$\mathrm{MeV}$ for this state. We do not confirm the report from the Belle collaboration of a broad structure at 4.01 $\mathrm{GeV/c^{2}}$. In addition, we investigate the $\pi^{+}\pi^{-}$ system which results from Y(4260) decay

Early Inception of the Laramide Orogeny in Southwestern Montana and Northern Wyoming: Implications for Models of Flat‐Slab Subduction

Timing and distribution of magmatism, deformation, exhumation, and basin development have been used to reconstruct the history of Laramide flat-slab subduction under North America during Late Cretaceous-early Cenozoic time. Existing geodynamic models, however, ignore a large (40,000-km(2)) sector of the Laramide foreland in southwestern Montana. The Montana Laramide ranges consist of Archean basement arches (fault-propagation folds) that were elevated by thrust and reverse faults. We present new thermochronological and geochronological data from six Laramide ranges in southwestern Montana (the Beartooth, Gravelly, Ruby and Madison Ranges, and the Tobacco Root and Highland Mountains) that show significant cooling and exhumation during the Early to mid-Cretaceous, much earlier than the record of Laramide exhumation in Wyoming. These data suggest that Laramide-style deformation-driven exhumation slightly predates the eastward sweep of magmatism in western Montana, consistent with geodynamic models involving initial strain propagation into North American cratonic rocks due to stresses associated with a northeastward expanding region of flat-slab subduction. Our results also indicate various degrees of Cenozoic heating and cooling possibly associated with westward rollback of the subducting Farallon slab, followed by Basin-and-Range extension. Plain Language Summary The Laramide region in the western U.S. is characterized by some of the highest topography in North America including the Wind River Range in WY and the Beartooth Range of WY and Montana. These ranges have fed detritus to surrounding basins for millions of years and contributed to modern ecosystems. These high topographic features and basins have significantly impacted paleoenvironmental conditions over geological time. The formation of these high-relief ranges has been linked to deep Earth, geodynamic, processes involving subduction of a flat slab under the North American Plate. Models of flat-slab subduction rely on the timing and pattern of deformation and exhumation of Laramide ranges, which remains poorly understood. Our study provides new data on the timing of deformation and exhumation of Laramide ranges in SW Montana and northern WY capable of testing current models of flat-slab subduction.NSF-Tectonics [EAR-1524151]6 month embargo; published online: 9 January 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]