Final Channel Research Articles

Non-adiabatic dynamics in the α+6He scattering and the nuclear breakup of 10Be

The α+6 He low-energy reactions and the structural changes of 10 Be in the microscopic α+α+N+N model are studied by the generalized two-center cluster model with the Kohn-Hulthén-Kato variation method. It is found that, in the inelastic scattering to the [Formula: see text] channel, characteristic enhancements are expected as the results of the parity-dependent non-adiabatic dynamics. In the positive parity state, the enhancement originates from the excited eigenstate generated by the resonance pole of the final channel, while that in the negative parity state is induced by the Landau-Zener level-crossing. The reaction mechanism in breakup of 10 Be into the 5 He +5 He and α+6 He continuums is also studied. The strong enhancement in the breakup of [Formula: see text] is discussed in connection with the non-adiabatic dynamics.

Formation of channelized lava flows on an unconfined slope

The formation of channelized lava flows on a wide uniform slope is investigated both theoretically and experimentally. When a lava is released at a constant flow rate from a point source, we predict that it flows both down and across the slope at the same rate in a early time regime before undergoing a transition to a long‐time regime where down‐slope flow is faster than lateral flow. Eventually, the lateral flow is stopped by the strength of the growing surface crust, and the flow then travels down slope in a channel of constant width. Using scaling analysis, we derive expressions for the final channel width in both flow regimes, as a function of the flow rate, the slope, the density difference driving the flow, the lava viscosity, the thermal diffusivity, and the yield strength of the crust. We also find a dimensionless flow morphology parameter that controls whether the subsequent channel flow occurs in a “mobile crust” regime or in a “tube” regime. These theoretical predictions are in good agreement with laboratory experiments in which polyethylene glycol wax flows down a wide uniform slope under cold water. The theory is also applied to the understanding of the formation of a basaltic sheet flow lobe in Hawaii, which had an estimated crust yield strength of order 6 × 104 Pa.

Pass-Through of Exchange Rates to Consumption Prices: What has Changed and Why

In this paper, we use cross-county and time series evidence to argue that retail price sensitivity to exchange rates may have increased over the past decade. This finding applies to traded goods, as well as to non-traded goods. We highlight three reasons for changing pass through at the level of retail prices of goods. First, pass through may have declined at the level of import prices, but the evidence is mixed over types of goods and countries. Second, there has been a large expansion of imported input use across sectors. This means that the costs of imported goods as well as home tradable goods have heightened sensitivity to import prices and exchange rates. The final channel we consider is whether there have been changing sectoral expenditures on distribution services, with the direction of change negatively correlated with pass through into final consumption prices. We find that this channel, which has been a means of insulating consumption prices from import content and exchange rates, has not systematically changed in recent years. The balance of effects weighs in favor of increased sensitivity of consumption prices to exchange rates, even if exchange-rate pass-through into import prices has declined for some types of goods.

Continuum distorted wave theory for positronium formation reactions

The formation of ground-state positronium in collisions of positrons on hydrogen atoms is considered. In previous theoretical works, two-center distorted wave functions were employed to approximate either the initial or the final channel. Here we report results obtained by means of the eikonal final state-continuum distorted wave (EFS-CDW) approximation for which asymptotically correct distorted wave functions are used for both the initial and final states of the scattering system. Comparison of the present theoretical total cross sections with experimental data reveals that distortion effects become important in both channels as the impact energy decreases. This work also shows that the EFS-CDW model is suitable for capture process in the scattering system at unexpected low energies.

Dissociative recombination of small carbon cluster cations

The dissociative recombination of small cluster cations with free, zero-energy electrons was studied at the ASTRID storage ring. It was found that only two-body fragmentation channels contribute: C+C{sub 2} for C{sub 3}{sup +}, C{sub 2}+C{sub 2} and C+C{sub 3} for C{sub 4}{sup +}. For C{sub 5}{sup +} and C{sub 6}{sup +} the final channels were also characterized by two-body fragmentation, but the specific channels were not identified because of limited mass resolution. It is being speculated whether cluster ions larger than C{sub 6}{sup +} may undergo recombination without dissociation. These clusters have a large heat capacity and a correspondingly lower temperature after electron capture. The decay of the intermediate neutral clusters may be influenced by infrared emission, which provides cooling and prevents dissociation.

Electron correlation in Xe 4d Auger decay studied by slow photoelectron–Auger electron coincidence spectroscopy

Two different experimental methods, namely threshold electron–Auger electron coincidences and slow photoelectron–Auger electron coincidences are applied to investigate the Xe 4d Auger decay in the near-threshold region and reveal the essential role of electron correlation. The coincidences allow us to select the different channels for the 4d hole Auger decay which lead to different final states of the Xe2+ ion: 5s−2(1S0), 5s−15p−1(1P1), 5p−2(1S0), 5p−2(1D2), 5p−2(3P0,1) and 5p−2(3P2). Measurements of the threshold electrons with the first method reveal strong PCI distortion of electron spectra in all channels. Comparison with calculations carried out in the framework of the quantum-mechanical PCI model allows us to clarify the dynamics of threshold electron production. In the 5p−2(1S0) channel, the main contribution comes from the PCI retardation of slow photoelectrons. In the 5p−2(1D2) and 5p−2(3P) final state channels, additional processes of PCI recapture followed by valence multiplet decays play a role at and below the N4 and N5 thresholds. The slow photoelectron spectra measured by the second method reveal also a strong PCI distortion. Analysis within the framework of the eikonal model shows the influence of the Auger electron on the PCI distorted line shapes.

On the dissociation of the 2-pentanone ion studied by threshold photoelectron photoion coincidence spectroscopy

The photodissociation of 2-pentanone has been studied by threshold photoelectron photoion coincidence (TPEPICO) spectroscopy, in which ion time-of-flight (TOF) mass spectra are recorded as a function of the photon energy in the range of 9.6–12.2 eV. 2-Pentanone ions dissociate via four competitive channels: ethylene (C 2H 4) loss to produce the propen-2-ol ion, n-propyl ( C 3H 7) loss to produce the acetyl ion, and two parallel methyl ( CH 3) loss channels, producing the butanoyl ion at low energies and the but-3-en-2-ol ion at higher energies. The latter dissociates further via ethylene (C 2H 4) loss providing a second pathway to the acetyl ion. This final dissociation channel is observed experimentally by the appearance of an asymmetric ion peak in the time-of-flight (TOF) distribution at photon energies greater than 11.5 eV. The ion TOF distributions and breakdown diagram have been modeled in terms of the statistical RRKM theory for unimolecular reactions, yielding the 0 K dissociation onsets of 10.239 ± 0.015 eV for the butanoyl ion and 10.259 ± 0.019 eV for the propen-2-ol (acetone enolate) ion. By relating the measured onsets with other well established heats of formation, the 298 K heat of formation of the butanoyl and propen-2-ol ions were determined to be 586.9 ± 2.1 and 680.7 ± 1.8 kJ/mol, respectively. The acetone enolate ion is thus 37 kJ/mol more stable than the acetone ion, a value supported by G3B3, and CBS-QB3 calculations. The but-3-en-2-ol ion was found to lose ethylene to produce the acetyl ion without an energy barrier.

Positronium formation in collisions of fast positrons impacting on vapour water molecules

Positronium formation through electron capture by fast positrons impinging on vapour water molecules is studied theoretically at intermediate and high impact energies. This multi-electron system is treated within the framework of the independent electron model. The charge transfer process is described by employing the continuum distorted-wave final-state approximation. In this model, the final state of the collision is distorted by two Coulomb wavefunctions associated with the interactions of both the positron and the active electron (the captured one) with the residual ionic target. The water molecule is described by an expansion of monocentric Slater-like functions centred on the oxygen atom. Total cross sections are computed by using a partial-wave technique and compared with results obtained using the simpler Coulomb–Born approximation. Theoretical results for the production of H2O+ ions in the final channel of the reaction through charge transfer processes (positronium formation and ionization) are also presented.

Break-up of positronium (Ps) atom in collision with a He+ ion

The dynamics of electron loss to the continuum (ELC) from the light neutral projectile positronium (Ps) atom in collision with He+ ion is studied in the framework of post-collisional Eikonal approximation. The full three-body interaction, which is crucial for such ELC process is taken into account in the final channel. Both the triple differential cross sections (TDCS) and the double differential cross sections (DDCS) are studied at some intermediate and high incident energies, with respect to the threshold energy for this process. A distinct broad ELC peak centred around ve (velocity of the ejected electron) ≈vp (velocity of the positron) is noted in the ejected electron energy spectrum (DDCS) for forward ejection of e/e+, corroborating the experimental findings for the ELC process. The probability of emission of the e+ at higher angles is almost negligible as compared to its forward emission. Another salient feature noted in the present work is the shifting of the ELC DDCS (summed over the electron ejection angles) peak towards higher value of the ratio ve/vp with increasing incident energy, in agreement with the experimental findings of Armitage et al for Ps–He break-up process.

Formation of theH−ion in the positronium–hydrogen-atom collision

The cross sections (both differential and total) for ${\mathrm{H}}^{\ensuremath{-}}$ formation in the process $\mathrm{Ps}(1s)+\mathrm{H}(1s)\ensuremath{\rightarrow}{e}^{+}+{\mathrm{H}}^{\ensuremath{-}}$ in the energy range $10--500\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ have been studied. The calculations have been performed in the framework of the Coulomb-modified eikonal approximation and take account of the long-range Coulomb attraction between the outgoing ${e}^{+}$ and ${\mathrm{H}}^{\ensuremath{-}}$ ion in the final channel.

Search for Θ+(1540) in exclusive proton-induced reaction $$p + C(N) \to \Theta ^ + \bar \kappa ^0 + C(N)$$ at the energy of 70 GeV

A search for narrow Θ+(1540), a candidate for a pentaquark baryon with positive strangeness, has been performed in an exclusive proton-induced reaction \(p + C(N) \to \Theta ^ + \bar \kappa ^0 + C(N)\) on carbon nuclei or quasifree nucleons at \(E_{beam} = 70GeV(\sqrt s = 11.5GeV)\) studying nK+, pKS0, and pKL0 decay channels of Θ+(1540) in four different final states of the \(\Theta ^ + \bar K^0 \) system. In order to assess the quality of the identification of the final states with neutron or KL0, we reconstructed Λ(1520) → nKS0 and ϕ → KL0KS0 decays in the calibration reactions p + C(N) → Λ (1520)K++C(N) and p+C(N) → pϕ+C(N). We found no evidence for a narrow pentaquark peak in any of the studied final states and decay channels. Assuming that the production characteristics of the \(\Theta ^ + \bar K^0 \) system are not drastically different from those of the Λ(1520)K+ and pϕ systems, we established upper limits on the cross-section ratios \(\sigma (\Theta ^ + \bar K^0 )/\sigma (\Lambda (1520)K^ + ) < 0.02\) and \(\sigma (\Theta ^ + \bar K^0 )/\sigma (p\phi ) < 0.15\) at 90% C.L. and a preliminary upper limit for the forward-hemisphere cross section \(\sigma (\Theta ^ + \bar K^0 )\) nb/nucleon.

Experiments of influence of discharge process on channel pattern

Based on experimental data and theory, by means of simplified discharge durations in a small flume, the influence of discharge process on channel morphology and channel pattern was analyzed in this paper. It was concluded that on the same original channel, different discharge and channel conditions would end with different river morphology, including thalwegs and radius of bends. Different discharge process resulted in two kinds of change: tiny change in the process of "big-small-big" and distinct change in the process of "small-big-small". Flood discharge duration was verified to be the main cause in the discharge process. Proper discharge process will change the morphologies of river, even can led to channel pattern transformation. The influences based on the relationship between the flow and the channel itself, including slope and riverbed constitution. Although not be a main cause, original channel morphology may influence its final channel pattern. Neglecting the influence of channel itself will hamper the understanding of channel patterns.

Effect of polarization on photodetachment thresholds

We have measured the near-threshold cross sections for the photodetachment of ${\mathrm{Li}}^{\ensuremath{-}}$ into the ${e}^{\ensuremath{-}}(ks,d)\text{\ensuremath{-}}\mathrm{Li}(2{p}_{1∕2})$, ${e}^{\ensuremath{-}}(ks,d)\text{\ensuremath{-}}\mathrm{Li}(3p)$, ${e}^{\ensuremath{-}}(kp)\text{\ensuremath{-}}\mathrm{Li}(3s)$, and ${e}^{\ensuremath{-}}(kp)\text{\ensuremath{-}}\mathrm{Li}(4s)$ continuum channels and the photodetachment of ${\mathrm{K}}^{\ensuremath{-}}$ into the ${e}^{\ensuremath{-}}(ks,d)\text{\ensuremath{-}}\mathrm{K}(4{p}_{3∕2})$ continuum channel. The data was analyzed using both a top-of-barrier model and a modified effective range theory. Both approaches explicitly take into account the significant polarization potential in the final continuum channels. The study involving both experiment and theory enabled us to investigate the effect of the polarization on near-threshold photodetachment. Furthermore, since photodetachment and electron scattering are related in the half-collision concept, we were able to determine low-energy electron scattering quantities such as phase shifts, elastic cross sections, and $s$ wave scattering lengths for electron scattering on excited Li and K atoms. The results allowed us to predict a virtual state in the ${e}^{\ensuremath{-}}(ks)\text{\ensuremath{-}}\mathrm{Li}(3p)$ system.

Cold forging method for polymer microfabrication

AbstractA polymer micro cold forging process was investigated. This method, derived from polymer solid‐phase forming, resembles more the metal‐forging method than the standard thermoplastic molding protocol. A micro‐forging die set was designed and fabricated and a series of cold forging experiments were carried out with varied process conditions, including forging speed, forging pressure, and dwell time. High‐aspect‐ratio microchannels were fabricated on polytetrafluoroethylene (PTFE) substrates. The dimension of replicated channels was found to be consistent from shot to shot. Owing to instantaneous elastic recovery, the channel has a width about 30% smaller than that on the die. The final channel size is contingent upon the forging process conditions, as well as upon the post‐recovery process. Upsetting experiments of PTFE cylindrical samples were carried out to study the fundamental issues on dimensional recovery so as to predict and consequently control the dimensional changes in polymer cold forging. Polym. Eng. Sci. 44:1998–2004, 2004. © 2004 Society of Plastics Engineers.

Ionization ofArby energetic proton impact

Available theoretical total and differential cross sections for the ionization of argon atoms by energetic proton impact are discussed and compared with our present calculations. The results depend sensitively on the model potential used for the description of the unperturbed atomic orbitals. Remarkable post-prior discrepancies are found when the electron-target interactions are calculated with respect to different potentials for the initial and final channels, respectively. Not only the orthogonality between bound and continuum wave functions, but also the correct asymptotic behavior of the exchange part of the potential is crucial for a satisfactory description of the experimental data.

UV-to-red relaxation pathways in CaTiO3:Pr3+

The radiationless relaxation pathways leading to the quenching of 3P0 emission and subsequent atypical single red luminescence from 1D2 level in CaTiO3:Pr3+ are studied under UV excitation. Self-trapped excitons are shown to participate in the relaxation process and Pr3+/Ti4+⇋Pr4+/Ti3+ charge transfer state (CTS) is proposed as the final relaxation channel to the emitting 1D2 level. This mechanism is supported by EPR investigations showing an increase of paramagnetic [Pr4+Ti3+O3]+ clusters upon optical excitation in the CTS.

Electron Correlation in the Final Continuum of IonizationHydrogen by 150-eV Electron Impact

Electron correlation in triple differential cross sections forionization of atomic hydrogen by electron impact is analysed forthe case of coplanar asymmetric geometry within the framework of thetwo-potential formulae. Based on the approximations of projectile andfaster-electron plane wave, the transition matrix element isanalytically expressed to be a product of two factors: the correlationfactor of two electrons in the final channel and thestructure-scattering factor. The contribution of both the factors tothe angular distribution of the triple differential cross section iscalculated. The present results are compared with the experimental dataand the other theoretical calculations for the incident energy of 150 eV.

Search for ${\rm\Theta}(1540)^ + $ in the exclusive proton-induced reaction ${\rm p + {C(N)\to \Theta^ + \bar{K}^0 + {C}(N)}}$ at the energy of 70 GeV

A search for narrow Theta(1540)^+, a candidate for pentaquark baryon with positive strangeness, has been performed in an exclusive proton-induced reaction p+C(N) \to Theta^+ \bar{K}^0 + C(N) on carbon nuclei or quasifree nucleons at E_{beam}=70 GeV (sqrt{s} = 11.5 GeV) studying nK^+, pK_S and pK_L decay channels of Theta(1540)^+ in four different final states of the Theta^+ \bar{K}^0 system. In order to assess the quality of the identification of the final states with neutron or K_L we reconstructed Lambda(1520)\to nK_S and phi\to K_LK_S decays in the calibration reactions p+C(N)\to Lambda(1520)K^+ + C(N) and p+C(N)\to p\phi + C(N). We found no evidence for narrow pentaquark peak in any of the studied final states and decay channels. Assuming that the production characteristics of the Theta^+ \bar{K^0} system are not drastically different from those of the Lambda(1520)K^+ and p\phi systems, we established upper limits on the cross section ratios sigma(Theta^+\bar{K}^0)/sigma(Lambda(1520)K^+) < 0.02 and sigma(Theta^+\bar{K}^0)/sigma(p\phi) < 0.15 at 90% CL and a preliminary upper limit for the forward hemisphere cross section sigma(Theta^+\bar{K}^0) < 30 nb/nucleon.

Triple-differential cross sections for inner-shell electron-impact ionization of carbon

Triple-differential cross sections (TDCS) have been calculated for the $K$-shell ionization of carbon atom by fast electron impact for highly asymmetric kinematics. In the present calculation the three Coulomb two-body interaction, the dynamic screening modification of these interactions and the correlation in the final channel, the screening effect of the multielectron target, and the distortion of Coulomb force in the initial channel have been taken into account. Results are compared with the relative measurement performed on the ${\mathrm{C}}_{2}{\mathrm{H}}_{2}$ molecule as target. The present TDCS is found to be in better accord with experiment.

Simultaneous transfer ionization of a negative hydrogen ion by positron impact

A model has been proposed to investigate theoretically, the simultaneous electron capture and the ejection of another electron by which a bare hydrogen ion and a positronium atom (Ps) are produced in a single collision between a positron and a negative hydrogen ion $({\mathrm{H}}^{\ensuremath{-}}).$ The angular distributions of the scattered Ps atom as well as of the ejected electron are studied in the intermediate- and high-energy regimes (40--200 eV) with respect to the threshold energy for this particular transfer ionization (TI) process. The electron-electron correlation effect that mainly governs such two-electron transition processes in this energy regime has been taken into account in both the initial and final channels. The long-range Coulomb attraction between the incident positron and the negative hydrogen ion in the initial channel has also been incorporated properly. Signature of the so-called Thomas peak (a double-peak structure) predicted for charge-transfer or transfer-ionization process for heavy-particle projectiles in the high-energy regime has also been noted in the present TI process (for light projectile ${e}^{+})$ and could be attributed to the correlated ${e}^{+}\ensuremath{-}e\ensuremath{-}e$ scattering mechanism. In addition, the fully differential (triple) cross sections for different kinematics reveal some structures unusual for a pure transfer or a pure ionization process which are to be verified by the future experiments.