5,342 research outputs found
Isolated nano-tendril bundles on tungsten surfaces exposed to radiofrequency helium plasma
The DIONISOS experiment is used to study the impact of RF helium (He) plasma on the surface morphology of tungsten (W) at a frequency of 13.56 MHz. Helium ion energy distributions with a span of 70–75 eV, while still below the sputtering threshold result in nano-tendril bundles (NTBs) and free-standing W whiskers on surfaces at 1020 K. The NTBs are distributed intragranularly with coverage of less than 10% while reaching up to 30 µm normal to the surface for He ion fluence of 7.6 × 10²⁵m⁻² and flux density of 10²²m⁻²s⁻¹. Analysis of the NTB interior and sub-surface structure is provided through focused ion beam cross section. Keywords: Tungsten fuzz; Helium; Nano-tendril; RF sheathUnited States. Department of Energy (Award DE-SC00-02060)United States. Department of Energy (Grant DE-FC02-99ER54512
Transport coefficients of He+ ions in helium
Recent theoretical advances have made it possible to calculate ab initio interaction potentials for atomic ionatom collisions that are highly accurate, and to use the potentials to calculate gaseous ion transport coefficients that meet or exceed the accuracy with which they can be measured1-4. Hence gaseous ion transport data serve as stringent tests of the interaction potentials. Advances in the calculation of transport properties, unfortunately, have not included the situation where atomic ions move through their parent gases, where resonant charge transfer (RCT) can occur. The purpose of this paper is to fill this void
A two-way photonic interface for linking Sr+ transition at 422 nm to the telecommunications C-band
We report a single-stage bi-directional interface capable of linking Sr+
trapped ion qubits in a long-distance quantum network. Our interface converts
photons between the Sr+ emission wavelength at 422 nm and the telecoms C-band
to enable low-loss transmission over optical fiber. We have achieved both up-
and down-conversion at the single photon level with efficiencies of 9.4% and
1.1% respectively. Furthermore we demonstrate noise levels that are low enough
to allow for genuine quantum operation in the future.Comment: 5 pages, 4 figure
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Late Paleocene event chronology: unconformities, not diachrony
The chronology of the events associated with the late Paleocene thermal maximum (LPTM, Chron C24r) has been established through the construction of a composite reference section that involved chemomagnetobiostratigraphic correlations and assumed minimum diachrony of biostratigraphic events. On this basis, discrepancies between correlations in different sections were explained by inferred unconformities. However, diachrony between distant sections cannot be ruled out. We report here on two geographically close sections drilled onshore New Jersey that yield different records of chemomagnetobiostratigraphic correlations in the interval representing Chron C24r. Because of their proximity (approximately 40 km apart), diachrony of biostratigraphic events between the two sections can be ruled out. In contrast, the marked lithologic disconformities in the sections explain well the different records of events. We thus conclude that the current relative chronology for Chron C24r is firmly based and that the upper Paleocene-lower Eocene stratigraphic record yields multiple unconformities, with Subzone NP9b rarely sampled. We examine the implications that undeciphered unconformities may have on the identification of proxies for paleoceanographic reconstruction, in particular with regard to the identification of the carbon isotope excursion (CIE) that reflects a dramatic latest Paleocene disturbance of the carbon cycle. We propose biostratigraphic means (short-lived calcareous nannoplankton and planktonic foraminifera taxa) that permit the unequivocal identification of the CIE not only in the oceanic realm but also in neritic settings
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An Exceptional Chronologic, Isotopic, and Clay Mineralogic Record of the Latest Paleocene Thermal Maximum, Bass River, NJ, ODP 174AX
A thick, apparently continuous section recording events of the latest Paleocene thermal maximum in a neritic setting was drilled at Bass River State Forest, New Jersey as part of ODP Leg l74AX [Miller, Sugarman, Browning et al., 1998]. Integrated nannofossil and magneto-stratigraphy provides a firm chronology supplemented by planktonic foraminiferal biostratigraphy. This chronologic study indicates that this neritic section rivals the best deep-sea sections in providing a complete record of late Paleocene climatic events. Carbon and oxygen isotopes measured on benthic foraminifera show a major (4.0 %o in carbon, 2.3 %o in oxygen) negative shift correlative with the global latest Paleocene carbon isotope excursion (CIE). A sharp increase in kaolinite content coincides with the isotope shift in the Bass River section, analogous to increases found in several other records. Carbon and oxygen isotopes remain low and kaolinite content remains high for the remainder of the depositional sequence above the CIE (32.5 ft, 9.9 m), which we estimate to represent 300-500 k.y. We interpret these data as indicative of an abrupt shift to a warmer and wetter climate along the North American mid-Atlantic coast, in concert with global events associated with the CIE
Hot Disks And Delayed Bar Formation
We present observational evidence for the inhibition of bar formation in
dispersion-dominated (dynamically hot) galaxies by studying the relationship
between galactic structure and host galaxy kinematics in a sample of 257
galaxies between 0.1 z 0.84 from the All-Wavelength Extended Groth
Strip International Survey (AEGIS) and the Deep Extragalactic Evolutionary
Probe 2 (DEEP2) survey. We find that bars are preferentially found in galaxies
that are massive and dynamically cold (rotation-dominated) and on the stellar
Tully-Fisher relationship, as is the case for barred spirals in the local
Universe. The data provide at least one explanation for the steep (3)
decline in the overall bar fraction from z=0 to z=0.84 in L and brighter
disks seen in previous studies. The decline in the bar fraction at high
redshift is almost exclusively in the lower mass (10 log M(\Msun)
11), later-type and bluer galaxies. A proposed explanation for this
"downsizing" of the bar formation / stellar structure formation is that the
lower mass galaxies may not form bars because they could be dynamically hotter
than more massive systems from the increased turbulence of accreting gas,
elevated star formation, and/or increased interaction/merger rate at higher
redshifts. The evidence presented here provides observational support for this
hypothesis. However, the data also show that not every disk galaxy that is
massive and cold has a stellar bar, suggesting that mass and dynamic coldness
of a disk are necessary but not sufficient conditions for bar formation -- a
secondary process, perhaps the interaction history between the dark matter halo
and the baryonic matter, may play an important role in bar formation.Comment: In press, ApJ, 13 pages, 5 figures (3 color
Recent Advances in Electron Cryotomography and their Application to Imaging Purified Protein Complexes, Isolated Organelles, and Small Cells
Human Resources and the Resource Based View of the Firm
The resource-based view (RBV) of the firm has influenced the field of strategic human resource management (SHRM) in a number of ways. This paper explores the impact of the RBV on the theoretical and empirical development of SHRM. It explores how the fields of strategy and SHRM are beginning to converge around a number of issues, and proposes a number of implications of this convergence
Maximum gravitational-wave energy emissible in magnetar flares
Recent searches of gravitational-wave (GW) data raise the question of what
maximum GW energies could be emitted during gamma-ray flares of highly
magnetized neutron stars (magnetars). The highest energies (\sim 10^{49} erg)
predicted so far come from a model [K. Ioka, Mon. Not. Roy. Astron. Soc. 327,
639 (2001)] in which the internal magnetic field of a magnetar experiences a
global reconfiguration, changing the hydromagnetic equilibrium structure of the
star and tapping the gravitational potential energy without changing the
magnetic potential energy. The largest energies in this model assume very
special conditions, including a large change in moment of inertia (which was
observed in at most one flare), a very high internal magnetic field, and a very
soft equation of state. Here we show that energies of 10^{48}-10^{49} erg are
possible under more generic conditions by tapping the magnetic energy, and we
note that similar energies may also be available through cracking of exotic
solid cores. Current observational limits on gravitational waves from magnetar
fundamental modes are just reaching these energies and will beat them in the
era of advanced interferometers.Comment: 16 pages, 5 figures, 1 tabl
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