Search

Abstract As multiple {11 2 ¯ 2} twin variants are often formed during deformation in hexagonal close-packed (hcp) titanium, the twin-twin interaction structure has a profound influence on mechanical properties. In this paper, the twin-twin interaction structures of the {11 2 ¯ 2} contraction twin in cold-rolled commercial purity titanium were studied by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Formation of the {11 2 ¯ 2} twin variants was found to deviate the rank of Schmid factor, and the non-Schmid behavior was explained by the high-angle grain boundary nucleation mechanism. All the observed twin-twin pairs manifested a quilted-looking structure, which consists of the incoming twins being arrested by the obstacle twins. Furthermore, the quilted-looking {11 2 ¯ 2} twin-twin boundary was revealed by TEM and high resolution TEM observations. De-twinning, lattice rotation and curved twin boundary were observed in the obstacle twin due to the twin-twin reaction with the impinging twin. A twin-twin interaction mechanism for the {11 2 ¯ 2} twin variants was proposed in terms of the dislocation dissociation, which will enrich the understanding for the propagation of twins and twinning-induced hardening in hcp metals and alloys. [ABSTRACT FROM AUTHOR]

With the push towards control and elimination of soil-transmitted helminthiasis and schistosomiasis in low- and middle-income countries, there is a need to develop alternative diagnostic assays that complement the current in-country resources, preferably at a lower cost. Here, we describe a novel high-resolution melt (HRM) curve assay with six PCR primer pairs, designed to sub-regions of the nuclear ribosomal locus. Used within a single reaction and dye detection channel, they are able to discriminate Ancylostoma duodenale , Necator americanus , Strongyloides stercoralis , Ascaris lumbricoides , Trichuris trichiuria and Schistosoma spp. by HRM curve analysis. Here we describe the primers and the results of a pilot assessment whereby the HRM assay was tested against a selection of archived fecal samples from Ghanaian children as characterized by Kato–Katz and real-time PCR analysis with species-specific TaqMan hydrolysis probes. The resulting sensitivity and specificity of the HRM was 80 and 98.6% respectively. We judge the assay to be appropriate in modestly equipped and resourced laboratories. This method provides a potentially cheaper alternative to the TaqMan method for laboratories in lower resource settings. However, the assay requires a more extensive assessment as the samples used were not representative of all target organisms. [ABSTRACT FROM AUTHOR]

The article discusses the physiology of the oxyhemoglobin dissociation curve. The oxyhemoglobin dissociation curve reflects the relationship between the oxygen saturation of hemoglobin and the partial pressure of arterial oxygen, which can shift depending on various factors. It discusses how the body delivers oxygen to the tissues with the help of right and left shifts.

Present study concerns the development of a new approach for chemical reaction modelling in DSMC technique. The conventional quantum-kinetic (QK) method based on the VHS collision model is usually applied by the DSMC algorithm to simulate chemical reactions in rarefied gas flowfield. In this paper, a modified quantum-kinetic model (MQK) is presented to remove some limitation of the QK chemical model. The MQK method uses the GSS collision model based on the Stockmayer potential function which can capture both the attractive and repulsive intermolecular forces and polarization effect of the molecules in the reactive flow. To investigate the accuracy and capability of the proposed model, firstly, dissociation of the nitrogen (non-polar gas) and water vapour (polar gas) are simulated in a single cell DSMC for equilibrium and non-equilibrium conditions. The results of the MQK are assessed with those of the QK methods, analytical models and experimental data. Secondly, dissociation of these two types of gases is studies in the rarefied gas flowfield along the stagnation line of a typical hypersonic atmospheric blunt body problem. The flowfield properties including the density, velocity, transient, vibrational and total temperature along the stagnation line and surface properties including the surface pressure and heatflux at the stagnation point obtained by the MQK model are compared with results of the QK method and available analytical and experimental data. The results show that the MQK model provides more accurate results when the polarization effects and both the attractive-repulsive intermolecular forces are dominant especially at high temperature. Also, comparison of the computational cost between two models indicates higher efficiency using the proposed method rather than the QK model due to reduction of number of the collision pairs. [ABSTRACT FROM AUTHOR]

The purpose of the current work is the theoretical and computational comparison of selected models for the energetics of dislocation dissociation resulting in stacking fault and partial dislocation (core) formation in fcc crystals as based on the (generalized) Peierls–Nabarro (GPN: e.g., Xiang et al., 2008; Shen et al., 2014 ), and phase-field (PF: e.g., Shen and Wang, 2004; Hunter et al., 2011, 2013; Mianroodi and Svendsen, 2015 ), methodologies (e.g., Wang and Li, 2010 ). More specifically, in the current work, the GPN-based model of Xiang et al. (2008) is compared theoretically with the PF-based models of Shen and Wang (2004) , Hunter et al. (2011, 2013) , and Mianroodi and Svendsen (2015) . This is carried out here with the help of a unified formulation for these models via a generalization of the approach of Cahn and Hilliard (1958) to mechanics. Differences among these include the model forms for the free energy density ψ ela of the lattice and the free energy density ψ sli associated with dislocation slip. In the PF-based models, for example, ψ ela is formulated with respect to the residual distortion H R due to dislocation slip (e.g., Khachaturyan, 1983; Mura, 1987 ), and with respect to the dislocation tensor curl H R in the GPN model (e.g., Xiang et al., 2008 ). As shown here, both model forms for ψ ela are in fact mathematically equal and so physically equivalent. On the other hand, model forms for ψ sli differ in the assumed dependence on the phase or disregistry fields ϕ , whose spatial variation represents the transition from unslipped to slipped regions in the crystal. In particular, Xiang et al. (2008) and Hunter et al. (2011, 2013) work with ψ sli ( ϕ ) . On the other hand, Shen and Wang (2004) and Mianroodi and Svendsen (2015) employ ψ sli ( ϕ , ∇ ϕ ) . To investigate the consequences of these differences for the modeling of the dislocation core, dissociation, and stacking fault formation, predictions from the models of Hunter et al. (2011, 2013) and Mianroodi and Svendsen (2015) are compared with results from molecular statics (MS) for the deformation field of dissociated edge and screw dipoles in Al and Au. Particularly notable is the agreement of the MS and PF strain field results for the case of perfect screw dissociation which, in contrast to the edge case, are characterized by asymmetric displacement and strain fields. The degree of this asymmetry is apparently related to the corresponding anisotropy ratio. As well, comparison of MS and PF disregistry fields implies that the gradient dependence of ψ sli results in a broadening of the (otherwise too narrow) disregistry profile to the form predicted by MS. [ABSTRACT FROM AUTHOR]

Pulsed laser excitation of a dense ultracold Cs vapor has been used to study the pairwise interactions between Cs atoms excited to np3/2 Rydberg states of principal quantum numbers in the range n = 22-36. Molecular resonances were observed that correspond to excitation of Rydberg-atom-pair states correlated not only to the np3/2 + np3/2 dissociation asymptotes, but also to ns1/2 + (n + 1)s1/2, ns1/2 + n'f1, and (n -- 4)fi + (n -- 3) fj (j = 5/2,7/2) dissociation asymptotes. These pair resonances are interpreted as arising from dipole-dipole and higher-order long-range-interaction terms between the Rydberg atoms on the basis of (i) their spectral positions, (ii) their response to static and pulsed electric fields, and (iii) millimeter-wave spectra between pair states correlated to different pair-dissociation asymptotes. The Rydberg-atom-pair states were found to spontaneously decay by Penning ionization and the dynamics of the ionization process were investigated during the first 15 jus following initial photoexcitation. To interpret the experimental observations, a potential model was derived that is based on the numerical determination of the eigenvalues and eigenfunctions of the long-range interaction Hamiltonian. With ihis potential model, which does not include adjustable parameters, all experimental observations could be accounted for, and the results demonstrate that long-range-interaction models provide a global and accurate description of interactions in ultracold Rydberg gases and that they correctly account for, and enable the analysis of, phenomena as diverse as the formation of Rydberg macrodimers, Penning ionization in dense Rydberg gases, and Rydberg-excitation-blockade effects. [ABSTRACT FROM AUTHOR]

We report Lyman-series emission cross sections of neutral hydrogen dissociation fragments after valence (15-34 eV) and inner-shell (533-542 eV) excitation of water vapor with monochromatic synchrotron radiation as functions of the exciting-photon energy. In the valence excitation energy region, the thermodynamical limits of the production of the differently excited hydrogen fragments are directly observed and absolute emission cross sections are determined. For resonant inner-shell excitations, the fluorescing excited hydrogen state is found to be strongly dependent on the molecular or Rydberg-like character of the excitation. [ABSTRACT FROM AUTHOR]

A model for determining the hyperfine structure of the excited electronic states of diatomic bialkali heteronuclear molecules is formulated from the atomic hyperfine interactions and is applied to the case of bosonic, 39KCs and fermionic 40KCs molecules. The hyperfine structure of the potential-energy curves of the states correlated to the K(4s ²S1/2)+ Cs(6p ²P)1/2/3/2) dissociation limits is described in tenus of different coupling schemes depending on the internuclear distance R. These results provide a step in the calculation of the hyperfine structure of rovibrational levels of these excited molecular states in the perspective of the identification of efficient paths for creating ultracold ground-state KCs molecules. [ABSTRACT FROM AUTHOR]

In a gas of ultracold atoms whose scattering length is controlled by a magnetic Feshbach resonance, atoms can be associated into universal dimers by an oscillating longitudinal magnetic field. In addition to the harmonic resonance with frequency near that determined by the dimer binding energy, there is a subharmonic resonance with half that frequency. If the thermal gas contains dimers, they can be dissociated into unbound atoms by the oscillating magnetic field. We show that the transition rates for association and dissociation can be calculated by treating the oscillating magnetic field as a sinusoidal time-dependent perturbation proportional to the contact operator. Many-body effects are taken into account through transition matrix elements of the contact operator. We calculate both the harmonic and subharmonic transition rates analytically for association in a thermal gas of atoms and for dissociation in a thermal gas of dimers. [ABSTRACT FROM AUTHOR]

In this paper we study double-ionization-induced charge asymmetric dissociation (CAD) in heteronuclear diatomic molecules. In CO we find a selective charge distribution in two CAD channels, i.e., C2+ + O is abundantly produced but C + O2+ is nearly nonexistent. This cannot be explained by the ionization energy difference between the two channels alone. Our study shows that the C2+ + O channel is sequentially formed through an intermediate state C+ + O and the selective charge distribution is the result of electron distribution in CO when exposed to intense laser fields. [ABSTRACT FROM AUTHOR]

A formulation of a multiconfiguration time-dependent Hartree-Fock (MCTDHF) method with nuclear motion is tested by application to a three-body breakup problem, the dissociative photoionization cross section of the HJ ion. The representation of the wave function in terms of a set of Slater determinants used for all nuclear geometries, with a prescribed parametric dependence upon the nuclear geometry such that the cusps follow the nuclei, times a complete basis expansion in the nuclear degrees of freedom shows promise as a method for treating nonadiabatic electronic and nuclear motion in molecules. However, the method used here for diatomics, in which the parametric dependence is prescribed through the choice of prolate spheroidal coordinates, produces qualitatively incorrect steplike behavior in the calculated cross section near onset. Modifications to the prolate spheroidal coordinate system that would improve this nonadiabatic diatomic MCTDHF representation are proposed. [ABSTRACT FROM AUTHOR]

We study electron-impact-induced dissociation of small van der Waals-bound argon complexes at a projectile energy of 120 eV. Kinetic-energy-release (KER) spectra of the Ar2 and Ar3 parent species for the final charge states 2Ar+, Ar++Ar2+, and Ar2++Ar+ and electron energies have been measured together with angular distributions of fragment ions. They are used to identify dissociation mechanisms such as interatomic Coulombic decay (ICD). [ABSTRACT FROM AUTHOR]

Dissociative electron attachment (DEA) to gas phase CO2 has been probed using a velocity slice imaging technique. DEA to CO2 produces only an O- ionic fragment and shows two major resonances located at 4.4 and 8.2 eV, respectively. The kinetic energy and angular distribution of the O- ions are measured around the second resonance with higher efficiency and sensitivity that provide details of the DEA dynamics. The kinetic energy distributions are in good agreement with the previous reports. However, the distinct angular distributions show substantial difference from the two recent studies within the limited electron energies. Our angular distribution results show two negative ion resonant states are involved in the underlying DEA process at the entire electron energies over the second resonance. We discussed the recent conflicting findings in the angular distribution results. The forward-backward asymmetry observed in the angular distributions is explained due to the interference effect of different partial waves associated with the attaching electron. [ABSTRACT FROM AUTHOR]

The purpose of the current work is the development of a phase field model for dislocation dissociation, slip and stacking fault formation in single crystals amenable to determination via atomistic or ab initio methods in the spirit of computational material design. The current approach is based in particular on periodic microelasticity ( Wang and Jin, 2001; Bulatov and Cai, 2006; Wang and Li, 2010 ) to model the strongly non-local elastic interaction of dislocation lines via their (residual) strain fields. These strain fields depend in turn on phase fields which are used to parameterize the energy stored in dislocation lines and stacking faults. This energy storage is modeled here with the help of the ”interface” energy concept and model of Cahn and Hilliard (1958) (see also Allen and Cahn, 1979; Wang and Li, 2010 ). In particular, the “homogeneous” part of this energy is related to the “rigid” (i.e., purely translational) part of the displacement of atoms across the slip plane, while the “gradient” part accounts for energy storage in those regions near the slip plane where atomic displacements deviate from being rigid, e.g., in the dislocation core. Via the attendant global energy scaling, the interface energy model facilitates an atomistic determination of the entire phase field energy as an optimal approximation of the (exact) atomistic energy; no adjustable parameters remain. For simplicity, an interatomic potential and molecular statics are employed for this purpose here; alternatively, ab initio (i.e., DFT-based) methods can be used. To illustrate the current approach, it is applied to determine the phase field free energy for fcc aluminum and copper. The identified models are then applied to modeling of dislocation dissociation, stacking fault formation, glide and dislocation reactions in these materials. As well, the tensile loading of a dislocation loop is considered. In the process, the current thermodynamic picture is compared with the classical mechanical one as based on the Peach-Köhler force. [ABSTRACT FROM AUTHOR]

This paper reports a crossed-beam velocity-map imaging study into the electron ionization dynamics of jet-cooled N2 and O2 molecules at electron collision energies from 35 to 100 eV. The use of velocity-map imaging detection provides insight into the detailed ionization dynamics through the dimension of the product ion kinetic energy associated with impulsive dissociation. In particular, "mesoscopic" cross sections corresponding to ionization from manifolds of energetically close states converging to the same dissociation asymptote are reported for a number of single-ionization channels. In addition, a range of double-ionization cross sections have been characterized, including those yielding X22+ dications. These are found to be in excellent agreement with other cross sections determined in coincidence measurements. This agreement supports a meaningful and accurate determination of the single-ionization channels. [ABSTRACT FROM AUTHOR]

Absolute cross sections for electron-impact dissociation of O3- ions yielding an O+ fragment are measured. The animated electron-ion crossed-beam method is applied in the energy range from 1 eV to 2.5 keV. The maximum total cross section for O+ fragment production is found to be (3.6 ± 0.3) x 10-16 cm² at 75 eV and such a large value of the cross section extends down to low energies. The threshold energy is found to be below 2 eV. Contributions of dissociative excitation and dissociative ionization to 0 + fragment production are determined separately. The total kinetic energy release distributions are determined at select electron energies. Present data are discussed and compared with recent results [S. H. M. Deng et al, Phys. Rev. A 82, 062715 (2010)]. [ABSTRACT FROM AUTHOR]

We simulate the time-dependent Schrödinger equation and observe the rescattering dissociation of H2 in strong infrared laser fields. Two dissociation pathways are identified, i.e., the dissociation of H2+ in the 2pσu state and the dissociation of H2 in doubly excited states. The former accounts for larger proportions as the rescattering energy is larger. The kinetic energy release of dissociative fragments reflects the temporal internuclear distance at the moment the rescattering happens. [ABSTRACT FROM AUTHOR]

We systematically study the influence of laser intensities on the dissociation of H2+ in strong laser fields by numerically solving the time-dependent Schrödinger equation. In Ti:sapphire infrared (IR) laser fields, H2+ mainly dissociates along 1sσg and 2pσu states. The mixture of these dissociative states results in the laser-intensity-dependent electron asymmetric localization. When the dissociation process is dressed by a laser field with a very long wavelength, the potential surfaces 1sσg and 2pσu degenerate due to the Stark effect, hence the kinetic energy release is changed. When H2+ is exposed to a strong ultraviolet (UV) pulse, H2+ is pumped to several excited states by absorbing a few energetic photons, resulting in the molecular dissociation ending with several kinetic energy peaks. The discrepancy of simulation results from the numerical models with and without Born-Oppenheimer approximation are analyzed. [ABSTRACT FROM AUTHOR]

Within the Born-Oppenheimer approximation, we build a multichannel model to simulate the dissociation of H2+ in strong laser fields. Two applications of this model are presented: first, orthogonally polarized UV and infrared pulses are used to dissociate H2+ into 2pπu and 3dπg states, whose superposition results in asymmetric electron localization after the dissociation; second, two orthogonally polarized UV pulses are introduced to trigger competing Rabi oscillations among 1sσg, 2pσu, 3dσg and 2pπu states. This study shows the dissociation of H2+ can be steered into selected electronic states with controllable probabilities with state-of-the-art laser technologies. [ABSTRACT FROM AUTHOR]

We experimentally studied the dissociation dynamics of a highly charged Ar3 cluster initiated by a high-energy electron. The dissociation patterns of the correlated ions from a two-body and a three-body Coulombic explosion (CE) of (Ar3)2+ suggest that predissociation alters the evolution of radiative charge transfer. The three-body CE in (Ar3)4+ and (Ar3)5+ is driven, after double ionization of one constituent Ar atom, by single ionization with a simultaneous interatomic Coulombic decay process. [ABSTRACT FROM AUTHOR]

We explore the effect of nuclear mass on the laser-driven electron localization process. We dissociate a mixed H2 and D2 target with intense, carrier-envelope-phase (CEP) stable 6 fs laser pulses and detect the products in a reaction microscope. We observe a very strong CEP-dependent asymmetry in proton and deuteron emission for low dissociation energy channels. This asymmetry is stronger for H2 than for D2. We also observe a large CEP offset between the asymmetry spectra for H2 and D2. Our theoretical simulations, based on a one-dimensional two-channel model, agree very well with the asymmetry spectra, but fail to account properly for the phase difference between the two isotopes. [ABSTRACT FROM AUTHOR]

Data on the (5S1/2+5p1/2)1g 87Rb2 state under the D\ limit, provided by a photoassociation experiment on cold atoms, have been analyzed by an improved LeRoy-Bernstein (LRB) approach including linear and nonlinear terms and provide a C6 value of the potential. To do that, using a model for hyperfine structure shifts, we have first subtracted the hyperfine effects in the split Unes and deduced the vibrational energies. Then, we have compared three LRB-type models to fit the data. We conclude that the second-order improved LRB is well suited and allows us to deduce an experimental value of C6 [C6 = (15.14 ± 0.05) x 104 a.u.]. [ABSTRACT FROM AUTHOR]

We present experimental results on the ionization and dissociation of methane in femtosecond pulses of radiation. Angular- and intensity-dependent yields of singly and doubly charged species were measured using an imaging mass spectrometer. The measured data show that all fragment yields exhibit some degree of anisotropy as a result of them being preferably ejected parallel to the polarization direction. Additionally, an anomalous perpendicular fragmentation pattern is found for CH22+. We find evidence of multiple dissociation mechanisms including statistical decay, field-assisted dissociation, and Coulomb explosion. [ABSTRACT FROM AUTHOR]

We propose a scheme to achieve extremely asymmetric electron localization during molecular dissociations. Hydrogen molecular ion (H2+) dissociation is investigated theoretically. A THz pulse is used to steer the electron motion after the molecular ion is excited by an ultrashort ultraviolet laser pulse. A high probability, as high as 99.3%, to localize electrons on one of the two nuclei is demonstrated, with a dissociation probability of 6.14% and almost no ionization, by optimizing the peak intensities and time delay of the two pulses. Even when the total dissociation probability is increased to 25.6%, more than 96.3% electrons can be localized in all dissociation events. These results represent a significant advancement in the electronic dynamics control in molecules. [ABSTRACT FROM AUTHOR]

Dissociative ionization of NiAr was experimentally studied in an intense femtosecond laser field. The break of the weak van der Waals bond generates an argon atomic ion and a nitrogen molecular ion. Both of them can recapture the tunneling electron. The probability measurement indicates that the tunneling electron prefers to be recaptured by the atomic ion. [ABSTRACT FROM AUTHOR]

The time-dependent surface flux method developed for the description of electronic spectra [L. Tao and A. Scrinzi, New J. Phys. 14, 013021 (2012); A. Scrinzi, New J. Phys. 14, 085008 (2012)] is extended to treat dissociation and dissociative ionization processes of H2+ interacting with strong laser pulses. By dividing the simulation volume into proper spatial regions associated with the individual reaction channels and monitoring the probability flux, the joint energy spectrum for the dissociative ionization process and the energy spectrum for dissociation is obtained. The methodology is illustrated by solving the time-dependent Schrödinger equation for a collinear one-dimensional model of H2+ with electronic and nuclear motions treated exactly and validated by comparison with published results for dissociative ionization. The results for dissociation are qualitatively explained by analysis based on dressed diabatic Floquet potential energy curves, and the method is used to investigate the breakdown of the two-surface model. [ABSTRACT FROM AUTHOR]

We experimentally investigate lasing behaviors of population-inverted N2+ ions for the transitions between the vibrational level (v' = 0) of excited electronic B 2Σu+ state and the two lowest vibrational levels (v = 0, 1) of the ground X 2Σu+ state in an elliptically polarized laser field. It is found that, as the polarization of the pump laser evolves from linear to circular, the lasing signal for the 0 → 0 transition at 391 nm first increases with a maximum enhancement of ∼40% at the ellipticity of 0.3 and then decreases, whereas for the 0 → 1 transition at 428 nm, the lasing signal decreases monotonically. This difference between the 391 - and 428-nm lasing signals is ascribed to the high sensitivity of the strong-field response of the molecular ion to molecular vibrations, which indicates the possibility to control the vibrational state distribution of molecules by tuning the ellipticity of the laser pulse. [ABSTRACT FROM AUTHOR]

Perfluorocarbons (PFCs) are man-made compounds whose ion physics exhibit complex interplays between statistical and nonstatistical fragmentation and intramolecular rearrangement processes. One probe of such processes is the energy-dependent electron-impact-ionization cross section. Partial electron-impact-ionization cross sections are reported for the fragments arising from five C2 to C4 PFCs, namely, C2F6, C3F8, CsF6, CF2=CF-CF=CF2, and CF3-C=C-CF3, over the energy range from threshold to ∼210 eV. Care was taken to maximize ion collection efficiency and to minimize discrimination against ions produced with high kinetic-energy release, and the measured cross sections have been calibrated using independent absolute total (gross) ionization efficiency curves measured previously in the same laboratory with an instrument that was designed to essentially have unit detection efficiency. Total ionization cross sections have also been modeled using the binary-encounter Bethe model, and the shortcomings of the model when applied to perfluorinated compounds are discussed. Analysis of the mass spectral fragmentation patterns in combination with ab initio energetics suggests that nonstatistical dissociative ionization processes play a significant role in the fragmentation dynamics of saturated PFCs. In contrast, unsaturated PFCs exhibit long-lived parent ions, which tend to undergo a higher degree of statistical dissociation following ionization, involving considerable intramolecular rearrangement. [ABSTRACT FROM AUTHOR]

We present both experimental and theoretical results for the dissociative ionization of D2 molecules induced by electron impact. Cross sections are determined in the molecular frame and are fully differential in the energies and emission angles of the dissociation fragments. Transitions are considered from the X1Σg+ electronic ground state of D2 to the 2sσg, 2pπu and 2pσu excited states of D2+. The experimental results are compared to calculations performed within the molecular four-body distorted-wave framework to describe the multicenter nature of the scattering process. The cross sections reveal a dramatic dependence on both the alignment of the internuclear axis with respect to the direction of the projectile momentum and on the symmetry of the excited dissociating state which is energetically resolved. [ABSTRACT FROM AUTHOR]

Abstract: To model the deformation of single crystal nickel based superalloys (SCNBS) with low stacking fault energy (SFE), three-dimensional discrete dislocation dynamics (3D-DDD) is extended by incorporating dislocation dissociation mechanism. The present 3D-DDD simulations show that, consistent with the existing TEM observation, the leading partial can enter the matrix channel efficiently while the trailing partial can hardly glide into it when the dislocation dissociation is taken into account. To determine whether the dislocation dissociation can occur or not, a critical percolation stress (CPS) based criterion is suggested. According to this CPS criterion, for SCNBS there exists a critical matrix channel width. When the channel width is lower than this critical value, the dislocation tends to dissociate into an extended configuration and vice versa. To clarify the influence of dislocation dissociation on CPS, the classical Orowan formula is improved by incorporating the SFE. Moreover, the present 3D-DDD simulations also show that the yielding stress of SCNBSs with low SFE may be overestimated up to 30% if the dislocation dissociation is ignored. With dislocation dissociation being considered, the size effect due to the width of γ matrix channel and the length of γ′ precipitates on the stress–strain responses of SCNBS can be enhanced remarkably. In addition, due to the strong constraint effect by the two-phase microstructure in SCNBS, the configuration of formed junctions is quite different from that in single phase crystals such as Cu. The present results not only provide clear understanding of the two-phase microstructure levelled microplastic mechanisms in SCNBSs with low SFE, but also help to develop new continuum-levelled constitutive laws for SCNBSs. [Copyright &y& Elsevier]

We discuss how a recent pump-probe study [Kelkensberg et al., Phys. Rev. Lett. 103, 123005 (2009)] of the dissociative ionization of H2, under the combined effect of a single extreme ultraviolet attosecond pulse and an intense near-infrared pulse, actually represents a transition-state spectroscopy of the strong-field dissociation step, i.e., of the (probe-pulse-)dressed H2+ molecular ion. The way the dissociation dynamics is influenced by the duration of the near-infrared probe pulse, and by the time delay between the two pulses, is discussed in terms of adiabatic versus nonadiabatic preparation and transport of time-parametrized Floquet resonances associated with the dissociating molecular ion. Under a long probe pulse, the field-free vibrational states of the initial wave packet are transported, in a one-to-one manner, onto the Floquet resonances defined by the field intensity of the probe pulse and propagated adiabatically under the pulse. As the probe pulse duration shortens, nonadiabatic transitions between the Floquet resonances become important and manifest themselves in two respects: first, as a vibrational shake-up effect occurring near the peak of the short pulse, and second, through strong interference patterns in the fragment's kinetic energy spectrum, viewed as a function of the time delay between the pump and the probe pulses. [ABSTRACT FROM AUTHOR]

We present a detailed study of the exact-exchange (EXX) kernel of time-dependent density-functional theory with an emphasis on its discontinuity at integer particle numbers. It was recently found that this exact property leads to sharp peaks and step features in the kernel that diverge in the dissociation limit of diatomic systems [Hell-gren and Gross, Phys. Rev. A 85,022514 (2012)]. To further analyze the discontinuity of the kernel, we here make use of two different approximations to the EXX kernel: the Petersilka Gossmann Gross (PGG) approximation and a common energy denominator approximation (CEDA). It is demonstrated that whereas the PGG approximation neglects the discontinuity, the CEDA includes it explicitly. By studying model molecular systems it is shown thai the so-called field-counteracting effect in the density-functional description of molecular chains can be viewed in terms of the discontinuity of the static kernel. The role of the frequency dependence is also investigated, highlighting its importance for long-range charge-transfer excitations as well as inner-shell excitations. [ABSTRACT FROM AUTHOR]

The relative dissociation fractions for the production of fragment ions and ion pairs of SF6 are studied for H- and C- impact in the energy range from 15 to 30 keV. Recoil ions (SF4+, SF3+, SF2+, SF+, S+, F+, SF42+, SF22+) and ion pairs (SF3++F+,SF2++F+,SF++F+,S++F+, F++F+) are detected and identified in coincidence with scattered projectiles in two charge states (q=0 and q=+1) by using a time-of-flight spectrometer. The relative dissociation fractions are energy dependent for both single-electron-loss (SL) channel and double-electron-loss (DL) channel processes for certain negative ions. It is also found that the relative dissociation fractions for DL are larger than those for SL. In addition, the degree of fragmentation will become greater with a larger mass number of the projectiles at the same impact energy for the same electron-loss channel. A comparison of the time-of-flight spectra is made between that under negative-ion impact and that under electron impact, and it is found that the probability of production of SFn+ ions with n odd is higher than that of similar ions with n even, and the probability of production of SFn2+ ions with n even is higher than that of similar ions withn odd under H-, C-, positive-ion, and electron impact. We analyze this interesting phenomenon from the bond-dissociation energies of SFn+ and SFn2+. We also analyze the coincident time-of-flight spectra of two fragment ions resulting from double ionization of SF6 by H- and C- impact and describe the major dissociation pathways of SF62+ for H- and C- impact in the energy range from 15 to 30 keV. [ABSTRACT FROM AUTHOR]

We present experimental results for dissociative electron attachment to carbon dioxide near the 8-eV Feshbach resonance. In particular, the dissociation channel leading to O- production has been investigated with a momentum imaging technique that utilizes a supersonic gas jet to form a low-temperature, confined molecular target. Angular fragmentation and kinetic energy release distributions are compared to recent results by Slaughter et al. [J. Phys. B 44, 205203 (2012)] and Wu et al. [Phys. Rev. A 85, 052709 (2012)] using similar techniques. We show that careful attention to weighting of the O- fragmentation momentum space is required to interpret the kinetic energy release observations and that there is no appreciable change in the angular distribution of CT fragments at different energies around the resonance peak, as previously reported by Wu et al. The present O- momentum distribution and kinetic energy release differ from previous results and provide alternative guidance for the theoretical consideration of potential energy surface dynamics that takes place during attachment. [ABSTRACT FROM AUTHOR]

We numerically model the dissociation dynamics of the noble-gas dimer ions He+², Ne+², Ar+², Kr+², and Xe+² in ultrashort pump and probe laser pulses of different wavelengths. Our calculations reveal a distinguished "gap" in the kinetic energy spectra, observed experimentally for the Ar2 dimer [J. Wu et al., Phys. Rev. Lett. 110, 033005 (2013)], for all noble-gas dimers for appropriate wavelength combinations. This striking phenomenon can be explained by the dissociation of dimer ions on dipole-coupled Born-Oppenheimer adiabatic potential curves. Comparing pump-probe-pulse-delay-dependent kinetic-energy-release spectra for different noble-gas dimer cations of increasing mass, we discuss increasingly prominent (i) fine-structure effects in and (ii) classical aspects of the nuclear vibrational motion. [ABSTRACT FROM AUTHOR]

Total and partial cross sections for breakup of the ground rovibronic state of H+² by photon impact are calculated using the exact nonadiabatic nonrelativistic Hamiltonian without approximation. The converged results span six orders of magnitude. The breakup cross section is divided into dissociative excitation and dissociative ionization. The dissociative excitation channels are divided into contributions from principal quantum numbers 1-4. For dissociative ionization, the fully differential cross section is calculated using a formally exact expression. These results are compared with approximate expressions. The Born-Oppenheimer expression for the dissociative ionization amplitude is shown to be deficient near onset. A Born-Oppenheimer approximation to the final state is shown to give accurate results for the sharing of kinetic energy between the electronic and the internuclear degrees of freedom--the doubly differential cross section. To accurately calculate the triply differential cross section, including the angular behavior, it is shown that nonadiabatic wave functions for both initial and final states are required at low electron energies. [ABSTRACT FROM AUTHOR]

We have experimentally studied the formation of ultracold RbCs molecules by photoassociation at short internuclear range followed by spontaneous emission. The observation of new excited levels with respect to our previous work [Gabbanini and Dulieu, Phys. Chem. Chem. Phys. 13, 18905 (2011)] on both sides of the Rb(5S1/2) + Cs(6p3/2) dissociation limit gives information on the state responsible for molecule formation. The molecules are mainly formed in deeply bound levels of the electronic triplet ground state. The observed photoassociation transitions present differences in terms of saturation. [ABSTRACT FROM AUTHOR]

We study the directional dissociative ionization of diatomic molecules (H2, N2, Ar2, and CO) by intense phase-controlled elliptically polarized two-color pulses. The phase between the two colors of our elliptically polarized two-color pulse is unambiguously and straightforwardly assigned by tracing the momentum of the released electron, streaked by the rotating laser field, which is imprinted in the momentum of the correlated ion. The laser-driven electron motion, electron-localization-assisted enhanced multielectron ionization, and role of the orbital shape for the asymmetric dissociative ionizations of various molecules are discussed. [ABSTRACT FROM AUTHOR]

The shifts in the four-body recombination peaks, due to an effective range correction to the zero-range model close to the unitary limit, are obtained and used to extract the corresponding effective range of a given atomic system. The approach is applied to an ultracold gas of cesium atoms close to broad Feshbach resonances, where deviations of experimental values from universal model predictions are associated with effective range corrections. The effective range correction is extracted with a weighted average given by 3.9 ± 0.8ftvdw, where Rvdw is the van der Waals length scale, which is consistent with the van der Waals potential tail for the Cs2 system. The method can be generally applied to other cold atom experimental setups to determine the contribution of the effective range to the tetramer dissociation position. [ABSTRACT FROM AUTHOR]

Charge asymmetric dissociation into C2+ + O following ionization of a CO+ molecular-ion beam with intense ultrashort (7-40-fs) laser pulses is studied using a coincidence three-dimensional momentum imaging method. The data suggest that allowing the molecule enough time to stretch within a laser pulse such that it ionizes beyond the curve crossings of the C2+ + O and C+ + 0+ potentials enhances the otherwise hard-to-reach charge asymmetric dissociation channel. [ABSTRACT FROM AUTHOR]

The photofragmentation of the water cation H2O+ through dicationic states has been studied at 35.0±0.2 nm (35.4±0.3 eV) and 21.8±0.2 nm (56.8±0.5 eV) with a crossed ion-photon beams experiment at the free electron laser FLASH. The dissociation of the dications is found to be similar at the two wavelengths and to proceed into O0+2H+, OH++H+, and O++H2+, with determined ratios sOH++H+/sO++H2+=4.2±0.3 and sOH++H+/sO0+2H+>0.7. The measured kinetic-energy releases for these processes are consistent with three-body breakup (O0+2H+) occurring mainly through the 23A" and 21A" states of H2O2+ and two-body breakup (OH++H+) occurring through X3A", 13A", and 11A" states of H2O2+, as predicted in a recent theoretical study [Gervais , J. Chem. Phys.0021-960610.1063/1.3157164 131, 024302 (2009)]. In addition to the kinetic-energy releases, we also report on fragment correlation in the three-body channel where the two protons carry the major part of the released momentum. [ABSTRACT FROM AUTHOR]

Time-sliced velocity imaging experiments have been performed for the low-energy electron dissociative attachment to CFCI3 in the gas phase. The time-sliced velocity images of the F- anionic fragment, recorded at different electron attachment energies (2.0-7.0 eV), indicate image pattern evolutions. The angular and kinetic energy distributions of the F- fragment are interpreted with two shape-resonant states of CFC13~ and thermochemistry calculations for dissociation thresholds. The dramatic reduction of the F- kinetic energy observed at higher attachment energies is possibly due to two-body dissociation with an electronically excited state of CCI3 (2A") or three-body dissociations. [ABSTRACT FROM AUTHOR]

We present ab initio calculations for the dissociative recombination rates of LiHe+ ions. The study involves first a realistic understanding of the electronic structure of the ion and neutral LiHe molecule and then carrying out the nuclear dynamics the system undergoes during the dissociation process. For the electronic part we employ R-matrix calculations to describe the situation of low-energy electrons scattered by LiHe+ ions. These results are further extended by additional quantum chemistry calculations of the higher Rydberg states of the neutral LiHe molecule as a compound state after the primary ionic interaction. We demonstrate that the two separate and independent results are smoothly connected via the use of Seaton's theorem. The subsequent motion of the nuclei is then incorporated via a rovibrational frame transformation based on the use of Siegert pseudostates. Finally, the resulting thermal dissociative recombination rates are shown for different initial states of the target LiHe+ ion in the presence of the impinging electron. [ABSTRACT FROM AUTHOR]

Long-range states of diatomic molecules have average values of internuclear separations (R) at least one order of magnitude larger than the equilibrium value of R. For example, the helium dimer 4He2 has a single bound state with (R) of about 50 A. We show that the properties of these states, such as (R), the dissociation energy, or the s-wave scattering length, can be related by simple, yet very accurate, formulas if a potential-energy curve is known. By examining a range of ab initio and empirical helium dimer potentials as well as scaling these potentials, we found that the formulas remain accurate, even if very approximate potentials were used. In addition to 4He2, we present results for 9Be2, 20Ne2, and KRb. [ABSTRACT FROM AUTHOR]

We report an upper bound to the ionization energy of 85Rb2 of 31 348.0(6) cm"1, which also provides a lower bound to the dissociation energy D0 of 85Rb2+ of 6307.5(6) cm-1. These bounds were measured by the onset of autoionization of the excited states of 85Rb2 below the 5s + 7p atomic limit. We form 85Rb2 molecules via photoassociation of ultracold 85Rb atoms and subsequently excite the molecules by single-photon uv transitions to states above the ionization threshold. [ABSTRACT FROM AUTHOR]

We estimate rates for the dissociative recombination (DR) of NO2+ + e-. Although accurate excited-state potential-energy curves for the excited states of the neutral are not available, we estimate that the 1 2Φg and the 1 2πg states of the neutral may intersect the ground-state cation potential-energy surface near its equilibrium geometry. Using fixed nuclei scattering calculations, we estimate the rate for direct DR via these states and find it to be significant. We also perform approximate calculations of DR triggered by the indirect mechanism, which suggest that the indirect DR rate for NO2 is insignificant compared to the direct rate. [ABSTRACT FROM AUTHOR]

We propose that the evolution of superfluidity from the Bardeen-Cooper-Schrieffer (BCS) regime to the Bose-Einstein condensation (BEC) regime can be realized using ultracold Fermi gas coupled to a single-mode cavity. By the functional integral formalism, we derive an effective atom-only action, which mimics the two-component Fermi gas with tunable two-body interaction. First, we address the features of the cavity-mediated interaction. We find that the matter-light coupling creates an effective s-wave scattering whose sign and amplitude are controlled by parameters of the cavity. Second, we discuss the fermionic superfluidity on the mean-field level, including the order parameter, chemical potential, quasiparticle excitation spectrum, momentum distribution, and dissociation temperature. It is shown that by varying the atom-cavity detuning, a BCS to BEC crossover occurs. In addition, the influences of the atomic collaborative effect and external pumping field on the pairing correlation are also studied. [ABSTRACT FROM AUTHOR]

The ionization and dissociation fractions of the CO2 molecule under the impact of 10-30-keV negative ions H-, C-, and O- are studied. The four recoil ions originating from the target molecule CO2 (CO2+, CO+, O+, and C+) are measured and identified in coincidence with projectiles in two final charge states (q = 0 and q = +1) by using a time-of flight spectrometer. The ionization and dissociation fractions of CO2 are found to associate with the momentum of the impacting ions. We also analyze the fractions for ionization and dissociation from a physical point. No comparison is given since no other experimental and theoretical data exist in the investigated energy range. [ABSTRACT FROM AUTHOR]

The integral relations formalism introduced in [P. Barletta et al., Phys. Rev. Lett. 103, 090402 (2009); C. Romero-Redondo et al., Phys. Rev. A 83, 022705 (2011)] and designed to describe 1 + A' reactions is extended here to collision energies above the threshold for the target breakup. These two relations are completely general, and in this work they are used together with the adiabatic expansion method for the description of 1 + 2 reactions. The neutron-deuteron breakup, for which benchmark calculations are available, is taken as a test of the method. The j-wave collision between the 4He atom and 4He2 dimer above the breakup threshold and the possibility of using soft-core two-body potentials plus a short-range three-body force will be investigated. Comparisons to previous calculations for the three-body recombination and collision dissociation rates will be shown. [ABSTRACT FROM AUTHOR]

Using pump-probe spectroscopy, strong-field enhanced-ionization is found in an inner orbital of I2. A wave packet is launched in the B state of I2, whose valence orbitals are σg2πu4πg3σu1, and singly ionized to the I +I+ dissociation channel. The ionization signal peaks at two different internuclear separations: ∼7.3 and ∼8.7 a.u. The latter shows enhanced ionization of the σu state which has been studied before with the I2+ signal. However, the peak at smaller R corresponds to enhanced ionization of the σ8 state. The peak at ∼8.7 a.u. in the dissociating channel reveals that there could be strong mixing of different molecular orbitals when the two iodine atoms are pulled apart. [ABSTRACT FROM AUTHOR]