Net Cross Research Articles

Gain properties of an Er3+ complex in a poly(methylmethacrylate) matrix for 1540nm broadband optical amplification

Emission properties of an erbium organic complex embedded in a polymer matrix are investigated for laser and optical amplification applications in the 1550nm telecommunication range. The evaluation of stimulated emission cross sections is inferred from the Judd-Ofelt model [B. R. Judd et al., Phys. Rev. 169, 130 (1968); G. S. Ofelt, J. Chem. Phys. 37, 511 (1962)] based on experimental spectroscopic data, resulting in the determination of the three Ω2=1.92×10−19, Ω4=1.82×10−20, and Ω6=1.65×10−20 Judd-Ofelt coefficients. These parameters are then used to calculate the oscillator strengths between states and allow us to evaluate spontaneous emission probabilities, radiative lifetimes, branching ratios, and quantum efficiencies of levels. Stimulated emission cross-sections are determined using the McCumber method [D. E. Mc Cumber, Phys. Rev. 134, A299 (1964)]. Net gain cross sections are calculated for different values of the inversion population in Er3+ ions. Results show that organic polymer hosts doped with erbium complexes are very attractive materials for amplification in the telecommunication spectral range, as they display high gain cross section as compared to other erbium-containing materials, coupled with a wide and relatively flat amplification spectrum (up to 70nm) which covers the whole spectral range currently used for wavelength division multiplexing operation.

Time-dependent density functional theory calculations for collisions of bare ions with helium

We present net capture and ionisation cross sections for the collision systems p-He and He 2+–He with emphasis on microscopic response effects during the collision. The calculations rely on the basis generator method (BGM). In both collision systems the response of the effective electronic interaction to the time-dependent density leads to a significant change of the net cross sections.

The Molecular Effect in the Multiple Ionization of Diatom Molecules by Fast Ion Impact

The multiple ionization process is investigated for the molecular targets on the basis of the recently developed contracted independent electron model (CIEM), where the impact-parameter-dependent ionization probability plays a key role. We found that the multiple ionization cross sections strongly depend on the angle between the incident beam direction and the molecular axis. Also the molecular effect is found that the ionization cross section for a molecular target is not equal to the sum of those for the constituent isolated atoms. Moreover, we proved the sum rule on the net ionization cross section. Numerical estimation shows that the multiple ionization cross sections for N 2 and CO molecules, bombarded by the ions at the energies of more than 100 keV/u, are in better agreement with the experimental data than the other models.

Enantioselective Synthesis of Cyclic Allylboronates by Mo‐Catalyzed Asymmetric Ring‐Closing Metathesis (ARCM). A One‐Pot Protocol for Net Catalytic Enantioselective Cross Metathesis.

Mo-catalyzed asymmetric ring-closing metathesis (ARCM) reactions are used to synthesize cyclic allylboronates of high optical purity (89% ee to >98% ee). A one-pot procedure involving formation of allylboronates, Mo-catalyzed ARCM and functionalization of the optically enriched cyclic allylboronates constitutes net asymmetric cross metathesis (ACM). Structural modification of ARCM products include reactions with aldehydes to afford optically enriched compounds that bear quaternary carbon centers with excellent diastereoselectivity. These studies emphasize the significance of the availability of chiral Mo-based complex as a class of chiral metathesis catalysts that frequently complement one another in terms of reactivity and selectivity.

Effect of internal optical loss on threshold characteristics of semiconductor lasers with a quantum-confined active region

We develop a general approach to including the internal optical loss in the description of semiconductor lasers with a quantum-confined active region. We assume that the internal absorption loss coefficient is linear in the free-carrier density in the optical confinement layer and is characterized by two parameters, the constant component and the net cross section for all absorption loss processes. We show that, in any structure where the free-carrier density does not pin in the presence of light generation, the free-carrier-density dependence of internal loss gives rise to the existence of a second lasing threshold above the conventional threshold. Above the second threshold, the light-current characteristic is two-valued up to a maximum current at which the lasing is quenched. We show that the presence of internal loss narrows considerably the region of tolerable structure parameters in which the lasing is attainable; for example, the minimum cavity length is significantly increased. Our approach is quite general but the numerical examples presented are specific for quantum dot (QD) lasers. Our calculations suggest that the internal loss is likely to be a major limiting factor to lasing in short-cavity QD structures.

Enantioselective synthesis of cyclic allylboronates by Mo-catalyzed asymmetric ring-closing metathesis (ARCM). A one-pot protocol for net catalytic enantioselective cross metathesis

Mo-catalyzed asymmetric ring-closing metathesis (ARCM) reactions are used to synthesize cyclic allylboronates of high optical purity (89% ee to >98% ee). A one-pot procedure involving formation of allylboronates, Mo-catalyzed ARCM and functionalization of the optically enriched cyclic allylboronates constitutes net asymmetric cross metathesis (ACM). Structural modification of ARCM products include reactions with aldehydes to afford optically enriched compounds that bear quaternary carbon centers with excellent diastereoselectivity. These studies emphasize the significance of the availability of chiral Mo-based complex as a class of chiral metathesis catalysts that frequently complement one another in terms of reactivity and selectivity.

Time-dependent independent-particle model calculation of multiple capture and ionization processes inp−Ar,p¯−Ar,andHe2+−Arcollisions

Previous work on multielectron transitions in proton, antiproton, and ${\mathrm{He}}^{2+}$-ion impact on neon is extended to the case of argon targets for collision energies in the 5--1000 keV/amu range. Global quantities such as net electron loss from the target, net capture, and net ionization are predicted within experimental errors using a spherically symmetric optimized effective target atom potential with dynamical screening effects based on the time-dependent net ionization probability. The inclusion of target response is crucial in order to obtain correct positions and heights for the peaks in the net ionization cross sections. Effects due to cascading following multiple outer-shell excitation are found to be appreciable at energies between 10 and 100 keV/amu, but are overestimated by the statistical model. L-shell vacancy production is reported to affect recoil charge state production at energies above 200 keV/amu for charge states $q>~3.$ At low and intermediate energies, the independent-particle model is shown to overestimate q-fold recoil ion production significantly for $q>~3$ for proton impact signaling the role of electronic correlations for these channels. For antiproton impact the $q=3$ cross section is consistent with the independent-particle model.

A Study of the Vacuum γ-Radiolysis of Two Aromatic Polyimide Fluoropolymers Containing Phenylphosphine Oxide

The vacuum γ-radiolysis of two fluorinated polyimides containing phenylphosphine oxide units, TOR-RC and TOR-RC ODPA, have been studied at 77 K and 300 K. The phenyl phosphine oxide units provide protection of the polymers towards oxidation by oxygen atoms and the bulky fluoromethyl groups reduce the colouration of the polymers by limiting donor–acceptor complex formation through the aromatic units. At 77 K the radicals formed were identified to be a mixture of neutral radicals (60%) and anion radicals. At 300 K only neutral radicals were found. The G-values for radical formation were found to be 0.50 and 0.42 at 77 K and 0.051 and 0.052 at 300 K for TOR-RC and TOR-RC ODPA, respectively. Little change was observed in the visible spectra of the polyimides following vacuum radiolysis at 300 K up to a dose of 3.3 MGy, and the polymers were shown to undergo net cross linking with a gel dose of 0.45 MGy.

Interaction of hydrogen and deuterium with dislocations in palladium as observed by small angle neutron scattering

Small angle neutron scattering (SANS) measurements on Pd samples containing dislocations with a density of a few 10 11 cm −2 reveal an additional intensity for a scattering vector of 0.02 Å −1 to 0.2 Å −1 after loading with hydrogen (H) or deuterium (D). The corresponding net cross section is inversely proportional to the scattering vector as expected for line type scattering objects with a superimposed exponential decrease stemming from scattering within the Guinier-regime. This experimental finding is in accordance with a model where extended segregation of H or D within the dilated regions of edge dislocations occurs. In a first order approximation this corresponds to a precipitation of cylindrically shaped hydrides along the dislocation line and can be treated quantitatively yielding radii in agreement with SANS data. Whereas gas volumetric measurements at the same total concentration reveal no difference for the amount of H- and D-segregation, there is a pronounced effective difference in SANS intensities which cannot be explained by the different scattering lengths alone. However, the different sign of the latter quantity in combinations with an expected volume expansion within the hydride/deuteride region provides a reasonable explanation of the intensity difference observed. Knowing the amount of segregated H or D from gas volumetry and the dislocation density from electron microscopy the SANS results can be explained in a self consistent way.

Deeply boundπ−states in207Pbformed in the208Pb(d,3He)reaction. I. Experimental method and results

The deeply bound pionic states ${(1s,2p)}_{{\ensuremath{\pi}}^{\ensuremath{-}}}{\ensuremath{\bigotimes}}^{207}\mathrm{Pb}$ were observed for the first time, by investigating the ${}^{208}\mathrm{Pb}{(d,}^{3}\mathrm{He})$ reaction at a beam energy of ${T}_{d}=604.3\mathrm{MeV}$ and at ejectile angles around 0\ifmmode^\circ\else\textdegree\fi{}. The measured momentum distribution of the ${}^{3}\mathrm{He}$ particles was used to determine the Q value spectrum in the region $\ensuremath{-}145\mathrm{MeV}lQl\ensuremath{-}120\mathrm{MeV}$ with a systematic uncertainty of \ifmmode\pm\else\textpm\fi{}120 keV and a full width at half maximum resolution of $480\ifmmode\pm\else\textpm\fi{}60\mathrm{keV}.$ This spectrum shows a prominent peak at $Q\ensuremath{\simeq}\ensuremath{-}135.5\mathrm{MeV},$ corresponding to the pionic $2p$ state, coupled mainly to the ${3p}_{1/2}$ and ${3p}_{3/2}$ neutron hole states in ${}^{207}\mathrm{Pb}.$ A shoulder is seen on the tail of this dominant peak, and is attributed to the population of the pionic $1s$ state. The cross section for the continuum component at these high excitation energies is ${d}^{2}\ensuremath{\sigma}/(d\ensuremath{\Omega}dE)=4.7\ensuremath{\mu}\mathrm{b}/\mathrm{s}\mathrm{r}\mathrm{}\mathrm{MeV}.$ The net cross section for production of ${\ensuremath{\pi}}^{\ensuremath{-}}$ states in the bound pion region $\ensuremath{-}140\mathrm{MeV}lQl\ensuremath{-}133\mathrm{MeV}$ above the continuum amounts to $d\ensuremath{\sigma}/d\ensuremath{\Omega}=76\ensuremath{\mu}\mathrm{b}/\mathrm{s}\mathrm{r}.$

Routability Crossing Distribution and Floating Pin Assignment for T-type Junction Region

Based on non-crossing relations, vertical constraint relations and net-geometry relations in one T-type junction region, two kinds of routability crossing distributions are proposed to improve routing performance in one T-type junction region. For routability crossing distribution in one T-type junction region, a routability-ordering graph is built to decide a net ordering in O(n2) time. For routability quota crossing distribution in one T-type junction region, if the number of net crossings in base channel is more than a given quota, this net ordering in routability crossing distribution will be further adjusted to satisfy the quota requirement by using a net interchange operation in O(n) time. For floating pin assignment in one T-type junction region, global nets are assigned on the boundary between top channel and base channel by interleaving vacant pins in O(n) time according to a net ordering in routability crossing distribution.

Visible absorption cross sections and integrated absorption intensities of molecular oxygen (O2 and O4)

Absorption spectra of gas‐phase molecular oxygen and zero air at temperatures of 223 and 283 K have been measured in the laboratory using a coolable multipass‐optics gas cell and Fourier transform spectroscopy in the wavelength range 455 to 830 nm (12,000–22,000 cm−1). Net absorption cross sections of the O2A−, B−, and γ‐bands at <0.002 nm spectral resolution, and pressures of 100 and 1000 hPa zero air have been determined. Binary absorption cross sections of the collision‐induced O4 bands at <0.18 nm spectral resolution and a pressure of 1000 hPa pure oxygen have been determined, with corrections for the O2 γ‐band absorption. Calculated integrated absorption intensities and, for the O2A− and B−bands, “effective” Einstein A‐coefficients are compared with previous literature values.

Positron scattering from atomic sodium

Close-coupling calculations of positron scattering from atomic sodium are performed from threshold to 100 eV. The alkali atom is represented by a frozen-core model based upon the Hartree - Fock approximation. The close-coupling calculations are performed in a model containing multiple sodium (3s, 3p, 4s, 3d, 4p) and positronium states (1s, 2s, 2p, 3s, 3p, 3d). Subsidiary calculations with three and ten positronium states were performed at selected energies to test the convergence of the positronium formation cross section. The predicted total cross sections agree with the experimental data of Kwan et al but there are differences with the data of Kauppila et al. The net positronium formation cross section underestimates the experimental data of Zhou et al.

Small-angle neutron scattering study of dislocations in deformed single-crystal copper

Small-angle neutron scattering measurements of deformed single-crystal copper have been performed over a wavevector transfer range of 0.0655 ≤ Q ≤ 1.32 nm−1. The measurements included four samples deformed in compression at room temperature along the [110] direction to 6.8, 15.6, 35.0 and 54.3% reduction in thickness and an undeformed reference sample. The response of the reference sample followed the Porod law at lowest (Q and was, at least in part, the result of scattering from the external surfaces of the sample. The radially averaged net cross sections were found to increase with increasing deformation, while the power-law exponent n (dΣ/dΩ ∝ 1/Qn) decreased from n ≃ 3 to n ≃ 2.2 with increasing deformation. The scattering response of the two most deformed samples was noticeably anisotropic. Analysis of this anisotropy revealed strong 1/Q2 scattering perpendicular to the {111} dislocation slip planes, in agreement with the theoretical work of Seeger [J. Appl. Phys. (1959), 30, 629–637]. The decrease in the radially averaged power-law exponent is therefore attributed to strong 1/Q2 behavior at the highest levels of deformation. Bulk-averaged edge dislocation densities that varied systematically from approximately 1 × 1010 to 5 × 1010 cm−2 were obtained from the measured data.

Damage and Residual Properties of Notched [0/± 45/90]s and [0/90]2s Graphite/PEEK Woven Laminates Under Reversed Fatigue

Two lay-ups [0/±45/90] s and [0/90]2 s made of a T300 five-harness satin, woven-fabric-reinforced PEEK and containing a 12.7 mm diameter hole were charac terized in static tension. The high fracture toughness, GIC, of the thermoplastic matrix per mitted very little damage with no fiber breakage until final failure. In contrast, under reversed fatigue conditions, at a cyclic applied load equal to 55 % of the compressive strength, a large damage zone including fiber breakage developed. This was due to a rapid decrease of the resistance to splitting and to tow debonding in fatigue. The stiffness decreased with increasing size of the damage for both laminates. The [0/±45/90] s lay-up showed little variation of the residual tensile strength with increasing size of the fatigue- induced damage zone, whereas the [0/90]2 s showed a 30% increase. After the damage zone grew to 40 % and 15 % of the net cross section for the [0/90]2 s and the [0/ ± 45/90] s, respectively, the residual strength started to decrease.

Net ionisation cross sections of rare gas targets in collisions with swift highly charged ions

Net ionisation cross sections of rare gas targets in collisions with swift highly charged ions

Acoustic emission measurements of PWR weld material with inserted defects : Scruby, C.B.; Stacey, K.A. United Kingdom Atomic Energy Authority, Harwell, AERE-R-12386, 39 pp. (Jan. 1987)

Following an early phase of limited activity at the University of Pisa on small stainless steel pipes containing axial cracks, in 1981 ENEA, the Italian Committee for Research and Development of Nuclear Energy and Alternative Energies, has started a massive research campaign on fracture of carbon and stainless steel piping containing through and part-through cracks loaded either under pressure or in bending. The purpose of the program was to develop a better understanding on pipes fracture behaviour in order to set new design criteria more realistic, yet conservative, than the guillotine break and prepare acceptance criteria for in-service flaws particularly under the growing pressure of IGSCC that has merciless affected worldwide practically any BWR piping system.The analysis of more than 100 tests carried out at CISE research centre, in Milano, on 4 inch, 6 inch, 8 inch and 10 inch pipes has indicated that unstable fracture requires at least 150° through wall crack under ASME maximum design stresses. The leak area, before instability takes place, is always less than 10% of the net cross section area of the pipe. This has led ENEA to consider a 10% break area as a reasonable value to calculate jet forces. Further, it was found that the net section collapse load criterion by far underestimates the actual collapse load and that 360° part-through cracks tend to switch from ductile to brittle failure mode of a pipe loaded in bending.Further work is planned for the next 3 years including high temperature tests, stainless steel weldments and HAZ tests, high compliance tests and eventually burst tests. Besides the ENEA's research program, Ansaldo AMN, the Italian Nuclear Architect Engineer, is developing theoretical studies and codes to treat the problem of pipe fracture.

Production of multiply charged recoil ions in collisions of 50 and 100 keV amu-1 C and Ne ions with Ne

An experimental study was made on the production of recoil ions in collisions of C and Ne ions with Ne. Absolute values of the Nei+ recoil ion production cross section sigma i were measured. The plot of sigma i against i shows a shoulder at i=3 and 4 in the Neq+-Ne collisions, which becomes conspicuous at the incident energy of 100 keV amu-1. This phenomenon is ascribed to the contribution of transfer ionisation to the recoil ion production. The net ionisation cross section, sigma += Sigma i i sigma i, was compared with a theoretical prediction based on a classical scaling rule.

Registration of Net Blotch Resistant Barley Composite Cross XLV Germplasm

Crop ScienceVolume 28, Issue 1 cropsci1988.199a.rgp p. 199-199 Registration of Germplasm Registration of Net Blotch Resistant Barley Composite Cross XLV Germplasm H. E. Bockelman, Corresponding Author H. E. Bockelman n/[email protected] USDA-ARS, Univ of Idaho Res. and Extension Ctr., P.O. Box AA, Aberdeen, ID, 83210 Dep. of Plant Pathology, Montana State Univ., Bozeman, MT, 59717Corresponding author.Search for more papers by this authorE. L. Sharp, E. L. Sharp Dep. of Plant Pathology, Montana State Univ.Search for more papers by this authorM. M. Harrabi, M. M. Harrabi Laboratoire Genetique, Institut National Agronomique de Tunisie, 43 Ave. Charles Nicolle, 1002 Tunis-Belvedere, TunisiaSearch for more papers by this authorM. Cherif, M. Cherif Laboratoire Genetique, Institut National Agronomique de Tunisie, 43 Ave. Charles Nicolle, 1002 Tunis-Belvedere, TunisiaSearch for more papers by this author H. E. Bockelman, Corresponding Author H. E. Bockelman n/[email protected] USDA-ARS, Univ of Idaho Res. and Extension Ctr., P.O. Box AA, Aberdeen, ID, 83210 Dep. of Plant Pathology, Montana State Univ., Bozeman, MT, 59717Corresponding author.Search for more papers by this authorE. L. Sharp, E. L. Sharp Dep. of Plant Pathology, Montana State Univ.Search for more papers by this authorM. M. Harrabi, M. M. Harrabi Laboratoire Genetique, Institut National Agronomique de Tunisie, 43 Ave. Charles Nicolle, 1002 Tunis-Belvedere, TunisiaSearch for more papers by this authorM. Cherif, M. Cherif Laboratoire Genetique, Institut National Agronomique de Tunisie, 43 Ave. Charles Nicolle, 1002 Tunis-Belvedere, TunisiaSearch for more papers by this author First published: 01 January 1988 https://doi.org/10.2135/cropsci1988.199a.rgpCitations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume28, Issue1January–February 1988Pages 199-199 RelatedInformation

Failure modes of specimens containing surface flaws under cyclic torsion

Turbine-generator shafts are often subjected to a complex transient torsional loading. Such a torsional loading may initiate yielding at the outer radius of the shaft or in the fillets. The methods for predicting turbine-shaft fatigue life due to transient loading depent upon the mode of crack growth from an undetected crack. The most common location for the existence of a crack is the fillets or shoulders of the shaft. Specimens were designed from AISI 4340 steel with two diametrically opposed flat surfaces. Initial defect orientations of 0 deg, 45 deg and 90 deg with respect to the sepcimen axis on the fillet were studied. The specimens were subjected to cyclic torsion with zero mean torque and with a torque amplitude necessary to cause yielding at the outer radius of the specimen. When initial defects were aligned with a plane of maximum shear stress (0 deg and 90 deg), the cracks propagated along that plane. For 45-deg defects (aligned to a plane of maximum tensile stress) the crack still propagated along the plane of maximum shear. However, the number of cycles to initiate and to propagate the crack to failure for 45-deg defects were (two to three times) larger than those for 0-deg and 90-deg defects. Mode II and Mode III crack-growth rates were measured from specimens containing 0-deg and 90-deg defects. It was found that the crack-growth rate in Mode II was higher than in Mode III. However, all the specimens failed due to reduction of the net cross section, mostly attributed to Mode III crack growth. Similar results were obtained from specimens of turbine-shaft material (A469 steel), and 2024 aluminum with different rolling directions. Fatigue-crack-growth rates in Mode III were measured from circumferentially notched bar. They were found to be a unique function of ΔK III alternating stress intensity in Mode III. It was found that the mechanism of crack growth is produced by the formation and linkage of elongated cavities at the crack tip.