Final Channel Research Articles

Laser-assisted free-free transition in electron-atom collisions

The free-free transition is studied for an electron-hydrogen atom system in the ground state at very low incident energies in the presence of an external homogeneous, monochromatic, and linearly polarized laser field. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing the Volkov solutions in both the initial and final channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the effect of electron-exchange interactions, short-range interactions, as well as of long-range interactions. The laser-assisted differential as well as total elastic cross sections are calculated for single-photon absorption or emission in the soft photon limit, the laser intensity being much less than the atomic field intensity. A strong suppression is noted in the laser-assisted cross sections as compared to the field-free situations. A significant difference is noted in the singlet and the triplet cross sections.

Double ionization of helium by bare ions: Theoretical study of the fully differential cross sections

This work presents a theoretical study of fully differential cross sections (FDCSs) for the double ionization of an He target by ion impact within a distorted wave model. The initial atomic system is described by two approximated wave functions of different accuracy proposed by Bonham and Kohl. For the final channel several models are considered based upon improvements and simplifications of the well-known three-body Coulomb (3C) model. The influence of the receding projectile on the resulting fragments is also studied by implementing a model with effective charges that depend on the momenta of the four particles. The FDCSs resulting for different electron energy sharing are discussed. The sensitivity of the FDCSs to the projectile charge sign and magnitude is explored over the energy range 700 keV/amu through 6 MeV/amu.

THEORETICAL STUDY OF THE 11Li β DECAY INTO THE DEUTERON CHANNEL IN A CLUSTER MODEL

The β-decay process of the 11 Li halo nucleus into 9 Li and d is reanalyzed within a three-body model. The 11 Li nucleus is described as a 9 Li +n+n system in hyperspherical coordinates. The transition probability per time and energy units measured in a recent experiment can be reproduced with a broad resonance located around 0.8 MeV and a weak absorption from the 9 Li + d final channel.

Coherent electron emission for dissociative ionization of molecular hydrogen by electron impact

The single ionization of hydrogen molecules is studied theoretically as a function of the molecular alignment. Within the framework of the two-effective center model, multiple differential cross sections as a function of both electron momenta in the final channel of the reaction, and the internuclear orientation, are computed for both non-dissociative and dissociative final H+2 states. Preliminary results show that the interference pattern arising from the two-center character of the molecular target changes strongly with the final state of the residual molecular ion.

Single-electron-capture processes in collisions of He2+, Liq+ (q=1,2,3),C6+, andO8+ions with helium

Cross sections for single-electron capture in collisions of He${}^{2+}$, Li${}^{q+}$ ($q$ = 1,2,3), ${\mathrm{C}}^{6+}$, and ${\mathrm{O}}^{8+}$ ions with helium atoms at incident energy ranging from 50 to 5000 keV/amu have been calculated in the framework of four-body boundary-corrected continuum intermediate state (BCCIS-4B) approximation in both prior and post forms. In this formalism, distortion in the final channel related to the Coulomb continuum states of the projectile ion and the active electron in the field of residual target ion are included. In all cases, total single-electron-capture cross sections have been calculated by summing over all contributions up to $n$ = 3 shells and subshells, respectively. It has been observed that the contribution of the capture cross section into the excited states is significant for asymmetric collision (${Z}_{P}>{Z}_{T}$) and is insignificant for symmetric collision. Numerical results for the total cross sections show good agreement with the available experimental findings, particularly in the post form. Post-prior discrepancy has been found to be within 30% except for Li${}^{+}$ + He interactions below 150 keV/amu.

Metal microchannel lamination using surface mount adhesives for low-temperature heat exchangers

This paper reports the feasibility of using surface mount adhesives to produce low temperature microchannel arrays in a wide variety of metals. Sheet metal embossing and chemical etching processes have been used to produce sealing bosses that eliminate channel laminae, resulting in approximately 50% material savings over traditional methods. An assembly process using adhesive dispense and cure is outlined to produce leak-free devices. Optimal fill ratios were determined to be between 1.1 and 1.25. Bond strength investigation reveals robustness to surface conditions and a bond strength of 5.5–8.5 MPa using a 3X safety factor. Dimensional characterization reveals a two sigma (95%) post-bonded channel height tolerance under 10% after bonding. Patterning tolerance and surface roughness of the laminae faying surfaces were found to have a significant influence on the final post-bonded channel height. Leakage and burst pressure testing on several samples has established confidence that adhesive bonding can produce leak-free joints. Operating pressures up to 413 kPa have been satisfied, equating to tensile pressure on bond joints of 1.9 MPa. Higher operating pressures can be accommodated by increasing the bond area of devices.

Three-Body Model Calculation of Spin Distribution in Two-Nucleon Transfer Reaction for the System of 238U(18O,16O)240U Reaction

The differential cross sections of two-nucleon transfer reactions 238U(18O,16O)240U around 180 MeV are calculated by one-step Born approximation with a 16O+2 n+238U three-body model. The wave function in the initial channel is obtained by the continuum-discretized coupled-channels method, and that in the final channel is evaluated by adiabatic approximation. The cross sections have a peak around the grazing angle, and the spin distribution, i.e., the cross section at the peak as a function of the transferred spin, is investigated. The shape of the spin distribution is found to be not sensitive to the incident energies, optical potentials, and treatment of the breakup channels, whereas it depends on the excitation energy of the residual nucleus 240U. To fulfill the condition that the peak position should not exceeds 10ħ, which is necessary for the surrogate ratio method to work, it is concluded that the excitation energy must be less than 10 MeV.

Study of differential cross section using different bound state potentials

In this study, heavy ion reactions of ^6Li + (^{58}Ni, ^{28}Si, ^{12}C) and ^7Li + ^{12}C are studied using different bound state potentials, within the framework of the Distorted Wave Bourn Approximation (DWBA) calculations. Woods-Saxon potential is expressed as the optical potential in the initial and final channels together with a Coulomb potential. The calculations of the angular distributions are found to be in a good agreement with the experimental data. The extracted spectroscopic factors are reasonable.

Experimental Optimization of Flow Distributors for Pressure-Driven Separations and Reactions in Flat-Rectangular Microchannels

We report on the results of an experimental study established to optimize the design of microfabricated flow distributors for use in pressure-driven separations and reactions in flat-rectangular channels. For this purpose, the performance of a wide variety of possible flow distributor designs etched in glass/silicon wafers was compared, using CCD camera detection to study the shape and variance of the bands eluting from them. The best performance was obtained with radially interconnected distributors with a diverging inlet section and filled with diamond-shaped pillars, oriented perpendicular to the main flow direction and with a high transversal over axial aspect ratio. It was found that the best distributor designs start with a diverging section containing some 10-12 subsequent rows of high aspect ratio pillars (with a transversal width making up 10-15% of the final channel width) and with a divergence angle selected such that the sloped side-walls run parallel with the sides of the diamond-shaped pillars. After this zone, one or more regions with pillars with a smaller aspect ratio should be provided to increase the number of exit points. To prevent the formation of dead zones in these subsequent zones, so-called distributor wedges can be used to prevent the formation of any dead zones in the wake of the large aspect ratio pillars of the preceding section.

State-selective charge transfer in ion–ion interactions at intermediate and high energies

The total and state-selective cross sections for charge transfer in H++He+, He2++Li2+, He2++He+ and Li3++Li2+ collisions were calculated using the boundary corrected continuum intermediate state approximation with an energy range of 30–2000 keV amu−1. In this model, distortion in the final channel related to the Coulomb continuum states of the projectile ion and the electron in the field of the residual target is included. The sub-shell distribution of total charge transfer cross section has been reported in tabular form. Comparison of the results is made with those of other recent theoretical investigations and experimental findings. The present results are found to be in very good agreement with the available experimental findings.

Self-organization of linear nanochannel networks

A theoretical study has been conducted to explore the mechanics of self-organizing channel networks with dimensions in the submicron range and nanorange. The channels form by the partial release and bond back of prestressed thin films. In the release phase, the film spontaneously buckles into wrinkles of a certain wavelength, followed by a bond-back phase in which the final channel geometry is established through cohesive interface attractions. Results are presented in terms of the channel spacing, height, and width as a function of the film stiffness, thickness, eigenstrain, etch width, and interface energy. We have identified two dimensionless parameters that fully quantify the network assembly, showing excellent agreement with experiments. Our results provide valuable insight for the design of submicron and nanoscale channel networks with specific geometries.

ERRATUM: “THE IONIC PATHWAYS OF LITHIUM CHEMISTRY IN THE EARLY UNIVERSE: QUANTUM CALCULATIONS FOR LiH+REACTING WITH H” (ApJ, 708, 1560)

Due to an error at the publisher, Equations (6), (9), (13), and (14) were incorrectly printed. We present the correct equations below. IOP Publishing sincerely regrets this error. where EJ coll. represents a fixed value of the collision energy for a preselected internal state of the target, taken to be independent of the labels (j, ν) (Parker & Pack 1978). where E is the center-of-mass collision energy, kB is the Boltzmann constant, T is the temperature, and ν' and j' are all possible final vibrational and rotational channels of the product.

An inverse geometry design problem for optimization of single serpentine flow field of PEM fuel cell

The cathode flow-field design of a proton exchange membrane fuel cell (PEMFC) determines its reactant transport rates to the catalyst layer and removal rates of liquid water from the cell. This study optimizes the cathode flow field for a single serpentine PEM fuel cell with 5 channels using the heights of channels 2–5 as search parameters. This work describes an optimization approach that integrates the simplified conjugated-gradient scheme and a three-dimensional, two-phase, non-isothermal fuel cell model. The proposed optimal serpentine design, which is composed of three tapered channels (channels 2–4) and a final diverging channel (channel 5), increases cell output power by 11.9% over that of a cell with straight channels. These tapered channels enhance main channel flow and sub-rib convection, both increasing the local oxygen transport rate and, hence, local electrical current density. A diverging, final channel is preferred, conversely, to minimize reactant leakage to the outlet. The proposed combined approach is effective in optimizing the cathode flow-field design for a single serpentine PEMFC. The role of sub-rib convection on cell performance is demonstrated.

Associated photoproduction ofK+mesons off protons within a coupled-channelsK-matrix approach

We investigate the $p(\ensuremath{\gamma},{K}^{+})\ensuremath{\Lambda}$ and $p(\ensuremath{\gamma},{K}^{+}){\ensuremath{\Sigma}}^{0}$ reactions within a coupled-channels effective-Lagrangian method that is based on the $\mathsf{K}$-matrix approach. The two-body final channels included are $\ensuremath{\pi}N$, $\ensuremath{\eta}N$, $\ensuremath{\phi}N$, $\ensuremath{\rho}N$, $\ensuremath{\gamma}N$, $K\ensuremath{\Lambda}$, and $K\ensuremath{\Sigma}$. Nonresonant meson-baryon interactions are included in the model via nucleon intermediate states in the $s$ and $u$ channels and meson exchanges in the $t$-channel amplitude and the $u$-channel resonances. The nucleon resonances ${S}_{11}(1535)$, ${S}_{11}(1650)$, ${S}_{31}(1620)$, ${P}_{11}(1440)$, ${P}_{11}(1710)$, ${\mathrm{P}}_{13}(1720)$, ${P}_{33}(1232)$, ${P}_{33}(1600)$, ${\mathrm{D}}_{13}(1520)$, ${D}_{13}(1700)$, and ${D}_{33}(1700)$ are included explicitly in the calculations. With a single parameter set that was derived earlier from our analysis of $\ensuremath{\eta}$-meson photoproduction, the model describes all the available cross-section and polarization data of the SAPHIR Collaboration well for the two investigated channels. The description of the data from the CLAS Collaboration, however, is not of the same quality. In contrast to some previous studies, we do not find any compelling need to include a ${D}_{13}$ state with a mass of about $2.0$ GeV to reproduce the data for the $p(\ensuremath{\gamma},{K}^{+})\ensuremath{\Lambda}$ reaction at photon energies corresponding to the invariant mass around $1.9$ GeV.

Multi-channel medium access control protocol with channel distribution for mobile ad hoc networks

This study proposes a novel multi-channel medium access control protocol for mobile ad hoc networks that enables nodes to transmit packets in distributed channels. In our protocol, the ad hoc traffic indication message window is divided into two windows. The first window is called the deciding channel window (DCW). Source and destination nodes can negotiate with each other in deciding a channel that can be used to compete for the final data channel in the DCW. The second window is called the exchanging packet window (EPW). Pair source and destination nodes can compete to obtain a channel to transfer packets in the EPW. This mechanism can distribute pair source and destination nodes to compete for a data channel. Hence, because of this, collisions can be avoided greatly and throughput can be increased. The simulation results show that our protocol successfully exploits the use of the bandwidth of multiple channels effectively.

Outer-Bank Bars: A New Intra-Channel Architectural Element within Sinuous Submarine Slope Channels

Abstract This study describes for the first time “outer-bank bars,” an intra-channel architectural element that is unique to sinuous submarine channels. The study is based on interpretation of 3D seismic data of sinuous channels in the upper slope of the Amazon Fan, offshore Brazil. Outer-bank bars comprise channel-fill deposits found in tight meander loops at outer corners of bend apices or slightly upstream or downstream of apices. This architectural element can be up to 1.5 km wide and up to 150 m thick with continuous internal reflectors dipping 1–20° towards the inner bend of the meander loop, a direction of dip opposed to that of fluvial point bars or submarine lateral-accretion packages. The angles of outer-bank bar surfaces increased to a maximum at bend apices. Outer-bank bars occur in the final aggradational channel fill in the two separated channel–levee systems in the Amazon data set. They may have been formed as a result of enhanced deposition on the outside of the bend caused by a combination of flow-volume reduction and flow superelevation. Accretion of outer-bank bars may cause the thalweg position to shift towards the inner bends leading to sinuosity reduction. Since this architectural element is likely to be sand prone, its recognition may have significant implications for prediction of hydrocarbon reservoirs.

Fabrication of metallic micromolds by laser and electro-discharge micromachining

A method of creating metallic micromolds with features that have high-aspect ratios is described in this paper. The proposed manufacturing process utilizes laser micromachining to cut the negative two-dimensional profiles of the desired microfeatures and fluidic network patterns on a 100 μm thick brass sheet. The positive relief of the cut pattern is then created by using electro-discharge micromachining (micro-EDM) die-sinking the metallic mask onto a brass substrate. The final substrate with the desired relief pattern becomes the molding tool used for either elastomer casting or thermoplastic hot embossing. To validate the proposed fabrication methodology and evaluate the quality of surface finishes, a brass mold master of a T-channel micromixer (50 μm width, 25 μm height) is developed and multiple replicated devices are cast on this mold using poly-di-methyl-siloxane (PDMS). The surface finish of both the original micromold master and final molded channels on PDMS are measured using an optical profiler and found to have a roughness of approximately 400 nm Ra. The ability of the proposed fabrication technique to create high-aspect ratio features is illustrated by manufacturing a Y-channel micromixer with an aspect ratio of 4. Experimental results are discussed and suggestions for improvement are presented.

Scaling laws in (e,3e) processes

We study the double ionization of helium-like ions by impact of electrons with high incident energy. Within the isoelectronic sequence, an approximate scaling law for (e,3e) differential cross sections is proposed and confirmed by calculations. The latter are performed using 14-parameters Hylleraas-like wave functions to represent the bound electrons in the initial channel, plane waves for the fast incoming and scattered electrons, and a continuum distorted wave approach for the two ejected electrons in the final channel.

A Four-Body Fully Distorted Wave-Eikonal Initial State model for ionization of He by ion impact

A Four-Body Fully Distorted Wave-Eikonal Initial State (4B-FDW-EIS) model is developed for the case of single electron ionization of He by bare ion impact, taking into account both electrons as active ones. The projectile is considered to influence them on equal footing, in both the initial and final channels. Doubly differential cross sections (DDCS) are calculated and effects due to electron correlation are shown for the case of protons impinging over He atoms.

Multiple parton interactions inZ+4j,W±W±+0/2jandW+W−+2jproduction at the LHC

The expected rate for Multiple Parton Interactions (MPI) at the LHC is large. This requires an estimate of their impact on all measurement foreseen at the LHC. Conversely it provides new means of studying MPI at the LHC. In this paper we examine the role of MPI at the LHC, with the design energy of 14 TeV, in - Z production in association with four jets, - W\pm W\pm in association with zero or two jets. -W+ W- in association with two jets. In all cases the vector bosons are assumed to decay leptonically. The MPI contribution to Z+4j is dominated by events with two jets with balancing transverse momentum. It is possible to achieve a good signal to background ratio, close to 20%, for MPI compared to Single Interaction processes by selecting events with two jets with large separation in the transverse plane. The corresponding statistical significance for a luminosity of 1 inverse fb is about 6.9 for the mu+mu- channel alone. The final state channel in which only two same-sign high transverse momentum charged leptons are required and additional hard jets are vetoed is dominated by MPI, with an expected yield of 2500 events with the full LHC luminosity.