Outstanding Discrepancies Research Articles

Calculation of electron-impact 41P excitation of calcium

The convergent close-coupling method is applied to the calculation of 10 to 55 eV electron-impact 41P excitation of the calcium ground state. The results are compared with experiment and other theories. Though the overall agreement may be considered satisfactory there are some minor outstanding discrepancies that would benefit from further consideration, both theoretically and experimentally.

Absolute, time-resolved emission of non-LTE L-shell spectra from Ti-doped aerogels

Outstanding discrepancies between data and calculations of laser-produced plasmas in recombination have been observed since the 1980s. Although improvements in hydrodynamic modeling may reduce the discrepancies, there are indications that non-LTE atomic kinetics may be the dominant cause. Experiments to investigate non-LTE effects were recently performed at the NIKE KrF laser on low-density Ti-doped aerogels. The laser irradiated a 2 mm diameter, cylindrical sample of various lengths with a 4-ns square pulse to create a volumetrically heated plasma. Ti L-shell spectra spanning a range of 0.47–3 keV were obtained with a transmission grating coupled to Si photodiodes. The diagnostic can be configured to provide 1-dimensional spatial resolution at a single photon energy, or 18 discrete energies with a resolving power, λ / δ λ of 3–20. The data are examined and compared to calculations to develop absolute emission measurements that can provide new tests of the non-LTE physics.

A microscopically accurate continuum model for void formation during semiconductor silicon processing

A predictive continuum model for void growth in crystalline silicon is presented based on extensive atomistic calculations of vacancy cluster thermodynamic and structural properties. It is shown that the previously neglected internal configurational entropy of clusters dramatically alters the high temperature formation free energies and capture radii of small clusters, which in turn strongly impact the predicted evolution of the vacancy size distribution during Czochralski crystal growth. The new model is shown to resolve an outstanding discrepancy between experimentally measured and predicted void nucleation temperatures while at the same time providing an excellent representation of the final size distribution and void density under a variety of crystal growth conditions. All thermophysical parameters for describing point defect transport and thermodynamics used in the model were obtained independently using regression to other experimental systems. The results of this work demonstrate the potential utility, and perhaps necessity, of atomistic simulations for quantitatively accurate process modeling of complex solid-state aggregation phenomena.

Atomic data from the IRON Project

A new calculation of rate coefficients for electron collisional excitation of Fe XII is presented and compared to earlier calculations. Significant differences are found with all earlier work due to the inclusion of resonance processes that have not previously been considered and to the use of the intermediate coupling frame transformation method. The resulting dataset of collision strengths is shown to resolve many of the outstanding discrepancies between theory and solar observations. In particular, density sensitive line ratios in Fe XII now indicate electron densities close to those derived from other ions of comparable ionization potential.

Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: effect of precipitation-induced enhancement of the ionospheric Pedersen conductivity

Abstract. We consider the effect of precipitation-induced enhancement of the Jovian ionospheric Pedersen conductivity on the magnetosphere-ionosphere coupling current system which is associated with the breakdown of the corotation of iogenic plasma in Jupiter's middle magnetosphere. In previous studies the Pedersen conductivity has been taken to be simply a constant, while it is expected to be significantly enhanced in the regions of upward-directed auroral field-aligned current, implying downward precipitating electrons. We develop an empirical model of the modulation of the Pedersen conductivity with field-aligned current density based on the modelling results of Millward et al. and compute the currents flowing in the system with the conductivity self-consistently dependent on the auroral precipitation. In addition, we consider two simplified models of the conductivity which provide an insight into the behaviour of the solutions. We compare the results to those obtained when the conductivity is taken to be constant, and find that the empirical conductivity model helps resolve some outstanding discrepancies between theory and observation of the plasma angular velocity and current system. Specifically, we find that the field-aligned current is concentrated in a peak of magnitude ~0.25µAm-2 in the inner region of the middle magnetosphere at ~20 RJ, rather than being more uniformly distributed as found with constant conductivity models. This peak maps to ~17° in the ionosphere, and is consistent with the position of the main oval auroras. The energy flux associated with the field-aligned current is ~10mWm-2 (corresponding to a UV luminosity of ~100kR), in a region ~0.6° in width, and the Pedersen conductivity is elevated from a background of ~0.05mho to ~0.7mho. Correspondingly, the total equatorial radial current increases greatly in the region of peak field-aligned current, and plateaus with increasing distance thereafter. This form is consistent with the observed profile of the current derived from Galileo magnetic field data. In addition, we find that the solutions using the empirical conductivity model produce an angular velocity profile which maintains the plasma near to rigid corotation out to much further distances than the constant conductivity model would suggest. Again, this is consistent with observations. Our results therefore suggest that, while the constant conductivity solutions provide an important indication that the main oval is indeed a result of the breakdown of the corotation of iogenic plasma, they do not explain the details of the observations. In order to resolve some of these discrepancies, one must take into account the elevation of the Pedersen conductivity as a result of auroral electron precipitation.Key words. Magnetospheric physics (current systems, magnetosphere-ionosphere interactions, planetary magnetospheres)70d

On Global Energy Release Rate of a Permeable Crack in a Piezoelectric Ceramic

A permeable crack model is proposed to analyze crack growth in a piezoelectric ceramic. In this model, a permeable crack is modeled as a vanishing thin, finite dimension, rectangular slit with dielectric medium inside. A first-order approximation solution is derived in terms of the slit height, h0. The main contribution of this paper is that the newly proposed permeable crack model reveals that there exists a realistic leaky mode for electrical field, which allows applied electric field passing through the dielectric medium inside a crack. By taking into account the leaky mode effect, a correct estimation of electrical and mechanical fields in front of a crack tip in a piezoelectric ceramic is obtained. To demonstrate this new finding, a closed-form solution is obtained for a mode III permeable crack under both mechanical as well electrical loads. Both local and global energy release rates are calculated based on the permeable crack solution obtained. It is found that the global energy release rate derived for a permeable crack is in a broad agreement with some known experimental observations. It may be served as a fracture criterion for piezoelectric materials. This contribution reconciles the outstanding discrepancy between experimental observation and theoretical analysis on crack growth problem in piezoelectric materials.

The impact of government practice on the ability of project managers to manage

This paper examines the effect government policy has on the way managers of government-funded projects manage. The findings suggest that government reforms have improved the efficiency of processes undertaken during the life of the project, but have failed to address the issues arising from a lack of policy clarity relating to “what should be developed”. In addition, the findings suggest that the gains achieved through the implementation of government reforms are compromised by a lack of a management framework detailing the responsibility and authority of each government entity involved in the ownership of projects. In addition, there is presently no recourse to mediation for resolving outstanding contract discrepancies.

On the gradual character of the first-order spin reorientation transition in DyFe11Ti

Proceeding from recently published crystal field parameters, I demonstrate that the first-order spin reorientation transition point in DyFe12−xTix depends strongly on the value of titanium content x. This leads, due to inevitable small spatial variation of composition, to significant broadening of the first-order transition, giving it an appearance of a continuous process. Yet it can be unmistakably identified as a first-order phase transition, thanks to the characteristic shape of the temperature dependence of the spin orientation angle θ. What makes first- and second-order spin reorientation transitions clearly distinct is the shape, rather than width, of the “step” in the θ(T) dependence. Small differences of composition are also found to account for the outstanding discrepancies between the experimental studies carried out on different single crystals of DyFe11Ti, thus bringing the decade-long controversy to an end.

A quantitative study of tethered chains in various solution conditions using Langmuir diblock copolymer monolayers

This article summarizes our investigations of tethered chain systems using Langmuir monolayers of poly(dimethylsiloxane)-polystyrene (PDMS-PS) diblock copolymers on organic liquids. In this system, the PDMS block adsorbs strongly to the air surface while the PS block dangles into the subphase liquid. The air surface can be made either repulsive or attractive for the tethered PS chain segments by choosing a subphase liquid which has a surface tension less than or greater than that of PS, respectively. The segment profile of the PS block is determined by neutron reflection as a function of the surface density, the molecular weights of the PS and PDMS blocks, and the solution conditions. We cover the range of reduced surface density (Σ ) characteristic of the large body of data in the literature for systems of chains tethered onto solid surfaces from dilute solution in good or theta solvent conditions (Σ < 12). We emphasize quantitative comparisons with analytical profile forms and scaling predictions. We find that the strong-stretching limit assumed in analytical self-consistent field calculations (SCF) and scaling theories is not valid over this Σ range. On the other hand, over a large portion of this range (Σ ⪇ 5) tethered chain profiles are well described by a renormalization group theory for weakly interacting or noninteracting chains. Simultaneous with the study of the profile form, the free energy of the tethered chains is examined through the surface tension. A strong increase in the surface pressure is observed with increasing surface density which determines the maximum surface density which can be achieved. This effect is attributed to a combination of higher order osmotic interactions and configurational constraints. This effect may explain several outstanding discrepancies regarding the adsorption of end-functionalized chains and diblock copolymers onto solid surfaces.

Ar doping of CH4 plasmas for carbon film deposition

We have modeled the gas-phase chemistry of a typical radio frequency CH4/Ar plasma used for the deposition of diamond and diamond-like carbon films. Our simulations show that the most abundant carbon containing radical is CH3 in pure methane discharges, but it is the carbon dimer C2 in discharges of methane highly diluted by argon. Thus we propose that the gaseous precursor of the film is CH3 in methane plasmas, and C2 in CH4/Ar plasmas. This proposal resolves outstanding discrepancies and is consistent with recent experiments demonstrating the deposition of diamond from hydrogen deficient plasmas.

Atomic data from the IRON Project

We calculate collision strengths and thermally averaged collision strengths for electron excitation be- tween the forty energetically lowest levels of Fe 13+ .T he scattering calculation is more complete than any previous work on this ion and signicant dierences are found in the excitation rates for many of the extreme ultra-violet (EUV) transitions, compared to earlier work. A detailed comparison is made between predicted line intensity ratios and those observed in solar coronal spectra which shows that several outstanding discrepancies are resolved by the new atomic data.

Temporal phase control of soft-x-ray harmonic emission

We report a strong dependence of the soft-x-ray spectra generated by high harmonic emission on the chirp of the excitation pulse, when an ultrashort laser drives the process. For identical pulse durations, distinct harmonic peaks can be observed for positively chirped excitation pulses, while for negatively chirped pulses, the harmonic peaks become irregular. This behavior is explained by simulations that combine the chirp of the laser with the intrinsic phase shift of the harmonics. This work resolves an outstanding discrepancy between theory and experiment by demonstrating that high-order harmonic generation driven by short-duration pulses can result in distinct harmonic peaks. This work conclusively demonstrates the role of the intrinsic phase in determining harmonic emission spectra, and control this phase during the emission process.

Manifestation of halo size in scattering and reactions

Total reaction cross section and elastic scattering angular distribution calculations are discussed for composite (halo) nuclei with well-developed core and valence particle structures. We review the basis of few-body calculations of reaction cross sections and use a simple binary cluster model to clarify the inadequacy of optical limit Glauber calculations for determining the sizes of correlated nuclear systems. An outstanding discrepancy in the case of the 6Li and 6He systems is discussed. We show that under certain conditions complementary information on halo sizes could be obtained from precision elastic scattering measurements at lower energies.

Novel QCD Effects in the Production and Decay of Quarkonium

There are many outstanding discrepancies comparing the predictions of perturbative QCD and measurements of the rate of production and decay of heavy quark systems. The problems include the J/ψ → ρπ puzzle, leading charmed particle effects, the anomalous behavior of the heavy quark sea components of structure functions, anomalous nuclear target effects, and the large rates observed for single and double quarkonium production at large xF and large pT. I argue that these anomalies may be associated with nonperturbative effects in the higher Fock structure of hadron wavefunctions.

Implications of TeV flavor physics for the ΔI=1/2 rule and theBsemileptonic branching ratio

Two of the outstanding discrepancies between weak interaction phenomenology and the standard model come in the large size of the \ensuremath{\Delta}I=1/2 enhancement in K decays and in the small value of the B semileptonic branching ratio. We argue that these discrepancies are naturally explained by chromomagnetic dipole operators arising from new physics at the TeV scale. These operators are closely connected to diagrams which contribute to the quark mass matrix, and we show how the proper enhancement of the hadronic decays of s and b quarks can be linked to a generation of particular Cabibbo-Kobayashi-Maskawa mixing angles or quark masses. We confirm our model-independent analysis with detailed consideration of supersymmetric models and of technicolor models with techniscalars. This picture has additional phenomenological predictions for the B system: The branching ratio of charmless nonleptonic B decays should be of order 20%, due to a larger rate for b\ensuremath{\rightarrow}sg, while there are no dangerous new contributions to b\ensuremath{\rightarrow}s\ensuremath{\gamma}. Sizable contributions to b\ensuremath{\rightarrow}d\ensuremath{\gamma} are a common feature of models incorporating this mechanism. In techniscalar models the ${\mathit{Zb}}_{\mathit{L}}$b${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{L}}$ coupling is enhanced, in association with sizable contributions to b\ensuremath{\rightarrow}s${\mathrm{\ensuremath{\mu}}}^{+}$${\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}}$.

Small-polaron hopping in Mott-insulating UO2

The DC electrical conductivity in the extrinsic regime of a slightly hyperstoichiometric sample of polycrystalline UO2+x is re-analysed using the general framework of small-polaron theory, taking into account the Mott-insulating nature of the ground state of the stoichiometric material. It is established that above about 150 K the holes move by non-adiabatic hopping, with a mobility activation energy of 0.28+or-0.02 eV. There is no conflict between electrical and thermodynamic data, contrary to some earlier theories. The implications for existing empirical determinations of the Mott-Hubbard gap, U, and the associated entropy of formation of altered-valency cations in the intrinsic regime is investigated, and new (preferred) values presented. The relatively large carrier densities predicted near melting necessitate some further consideration of the Coulomb interaction and of its influence both on the magnitude of U and on the mobility activation energy. Finally, attention is drawn to some outstanding discrepancies between the semi-empirical values of the small-polaron self-energy and mobility activation energy determined in this work, using Lang-Firsov theory, and those yielded by fully microscopic HADES calculations.

A Petrogenetic Grid for the System MgO-Al2O3-SiO2

A comprehensive analysis of phase relations in the system (MAS) was carried out using primarily the data from phase equilibrium experiments in MAS spinel and garnet peridotite systems. The resulting phase relations were extended to the whole MAS system by maintaining internal consistency and using other relevant experimental data. Equilibria include cordierite and sapphirine, which are usually omitted in the construction of comprehensive petrogenetic grids. A larger number of petrologically important equilibria involving these and the other MAS phases appear to be stable and have not been enumerated previously. The analysis produced an internally consistent set of thermodynamic parameters that closely agree with the measured thermochemical values, although some outstanding discrepancies still remain. The result provides a simple and practical tool for calculating the phase relations in the MAS system, and potentially also in more complex chemical systems. This is demonstrated with calculated temperature-pressure phase diagrams.

The Status of the Solar Neutrino Problem

Perhaps the most outstanding discrepancy between prediction and measurements in current particle physics comes from the solar neutrino problem, in which a large deficit of high-energy solar neutrinos is observed. Many Nonstandard Solar Models have been invoked to try to reduce the predicted flux, but all have run into problems in trying to reproduce other measured parameters (e.g., the luminosity) of the Sun. Other explanations involving new physics such as neutrino decay and neutrino oscillations, etc. have also been proffered. Again, most of these explanations have been ruled out by either laboratory or astrophysical measurements. It appears that perhaps the most likely particle physics solution is that of matter enhanced neutrino oscillation, the Mikheyev-Smirnov-Wolfenstein (MSW) oscillations. Two new radiochemical gallium experiments, which have a low enough threshold to be sensitive to the dominant flux of low-energy p-p neutrinos, now also report a deficit and also favor a particle physics solution. The next generation of solar experiments promise to finally resolve the source of the ``solar neutrino problem`` by the end of this decade.

The heat of formation of NCO

The heat of formation of NCO has been determined rigorously by state-of-the-art ab initio electronic structure methods, including Mo/ller–Plesset perturbation theory from second through fifth order (MP2–MP5) and coupled-cluster and Brueckner methods incorporating various degrees of excitation [CCSD, CCSD(T), BD, BD(T), and BD(TQ)]. Five independent reactions were investigated to establish a consistent value for ΔHf,0○(NCO): (a) HNCO(X̃ 1A′)→H(2S)+NCO(2Π), (b) HNCO(X̃ 1A′)→H++NCO−, (c) N(4S)+CO→NCO(2Π), (d) HCN+O(3P)→H(2S)+NCO(2Π), and (e) NH(3Σ−)+CO→H(2S)+NCO(2Π). The one-particle basis sets employed in the study were comprised of as many as 377 contracted Gaussian functions and ranged in quality from [4s2p1d] to [14s9p6d4f] on the (C,N,O) atoms and from [2s1p] to [8s6p4d] on hydrogen. After the addition of bond additivity corrections evaluated from related reactions of precisely known thermochemistry, all five approaches were found to converge on the value ΔHf,0○(NCO)=31.4(5) kcal mol−1. Appurtenant refinements were obtained for the heat of formation of isocyanic acid, ΔHf,0○(HNCO)=−27.5(5) kcal mol−1, and hydrogen cyanide, ΔHf,0○(HCN)=31.9(5) kcal mol−1. The final proposals for ΔHf,0○(NCO) and ΔHf,0○(HNCO) resolve outstanding discrepancies with experiment and provide updates for thermochemical cycles of relevance to combustion chemistry.

The correct renormalization of the gluon operator in a covariant gauge

We give a correct prescription for the renormalization of composite operators containing gauge fields only. Using this procedure we are able to solve the long outstanding discrepancy which exists between the axial and covariant gauge calculations of the second-order anomalous dimension of the gluon operator. This discrepancy is due to an incorrect treatment of the mixing between gauge invariant (GI) and gauge variant (GV) operators in the literature. Contrary to what is usually claimed we show that in the general covariant-gauge radiative corrections to GV operators leads to counterterms corresponding to GI operators, which therefore contribute to the renormalization of the latter. Only if these counterterms are taken into account does the anomalous dimension of the gluon operator agree with the one obtained in the literature by choosing the axial gauge.