A three-component protocol for the enantiodifferentiation of amines using triphenyl borate and BINOL: is it an ion pair or an amine-coordinated complex?

The structure of the borate complex responsible for the enantiodifferentiation of amines using a previously reported three-component protocol has been established. The choice between an ion pair and an amine-coordinated complex with the N atom of the amine coordinated to the B atom is favored for the former structure based on the DFT-calculated B-11 NMR chemical shifts. In contrast to expectations, the anisotropies of the quadrupolar B-11 nucleus for the two structures were calculated to be indistinguishable with regard to their effect on the linewidth of the NMR signal. (C) 2014 Elsevier Ltd. All rights reserved.

Pair dispersion of turbulent premixed flame elements

Flame particles are mathematical points comoving with a reacting isoscalar surface in a premixed flame. In this Rapid Communication, we investigate mean square pair separation of flame particles as a function of time from their positions tracked in two sets of direct numerical simulation solutions of H-2-air turbulent premixed flames with detailed chemistry. We find that, despite flame particles and fluid particles being very different concepts, a modified Batchelor's scaling of the form = C-F ( (F)(0) Delta(F)(0))(2/3)t(2) holds for flame particle pair dispersion. The proportionality constant, however, is not universal and depends on the isosurface temperature value on which the flame particles reside. Following this, we attempt to analytically investigate the rationale behind such an observation.

Suspensions of polymer-grafted nanoparticles with added polymers-Structure and effective pair-interactions

We present the results of combined experimental and theoretical (molecular dynamics simulations and integral equation theory) studies of the structure and effective interactions of suspensions of polymer grafted nanoparticles (PGNPs) in the presence of linear polymers. Due to the absence of systematic experimental and theoretical studies of PGNPs, it is widely believed that the structure and effective interactions in such binary mixtures would be very similar to those of an analogous soft colloidal material-star polymers. In our study, polystyrene-grafted gold nanoparticles with functionality f = 70 were mixed with linear polystyrene (PS) of two different molecular weights for obtaining two PGNP: PS size ratios, xi = 0.14 and 2.76 (where, xi = M-g/M-m, M-g and M-m being the molecular weights of grafting and matrix polymers, respectively). The experimental structure factor of PGNPs could be modeled with an effective potential (Model-X), which has been found to be widely applicable for star polymers. Similarly, the structure factor of the blends with xi = 0.14 could be modeled reasonably well, while the structure of blends with xi = 2.76 could not be captured, especially for high density of added polymers. A model (Model-Y) for effective interactions between PGNPs in a melt of matrix polymers also failed to provide good agreement with the experimental data for samples with xi = 2.76 and high density of added polymers. We tentatively attribute this anomaly in modeling the structure factor of blends with xi = 2.76 to the questionable assumption of Model-X in describing the added polymers as star polymers with functionality 2, which gets manifested in both polymer-polymer and polymer-PGNP interactions especially at higher fractions of added polymers. The failure of Model-Y may be due to the neglect of possible many-body interactions among PGNPs mediated by matrix polymers when the fraction of added polymers is high. These observations point to the need for a new framework to understand not only the structural behavior of PGNPs but also possibly their dynamics and thermo-mechanical properties as well. (C) 2015 AIP Publishing LLC.

Insight into the Evaporation Dynamics of a Pair of Sessile Droplets on a Hydrophobic Substrate

In this work, we have demonstrated three unique regimes in the evaporation lifecycle of a pair of sessile droplets placed in variable proximity on a hydrophobic substrate. For small separation distance, the droplets undergo asymmetric spatiotemporal,evaporation leading to contact angle hysteresis and suppressed vaporization. The reduced evaporation has been attributed quantitatively to the existence of a constrained vapor-rich dome between the two droplets. However, a dynamic decrease in the droplet radius due to solvent removal marks a return to symmetry in terms of evaporation and contact angle. We have described the variation in evaporation flux using a universal correction factor. We have also demonstrated the existence of a critical separation distance beyond which the droplets in the, droplet pair do not affect each other. The results are crucial to a plethora of applications ranging from surface patterning to lab-on-a-chip devices.

Insight into the Evaporation Dynamics of a Pair of Sessile Droplets on a Hydrophobic Substrate

In this work, we have demonstrated three unique regimes in the evaporation lifecycle of a pair of sessile droplets placed in variable proximity on a hydrophobic substrate. For small separation distance, the droplets undergo asymmetric spatiotemporal,evaporation leading to contact angle hysteresis and suppressed vaporization. The reduced evaporation has been attributed quantitatively to the existence of a constrained vapor-rich dome between the two droplets. However, a dynamic decrease in the droplet radius due to solvent removal marks a return to symmetry in terms of evaporation and contact angle. We have described the variation in evaporation flux using a universal correction factor. We have also demonstrated the existence of a critical separation distance beyond which the droplets in the, droplet pair do not affect each other. The results are crucial to a plethora of applications ranging from surface patterning to lab-on-a-chip devices.

Effect of strain rate response and pin diameter on mechanically mixed layer formation and wear mechanisms in a Ti6Al4V-SS316L pair

Three mechanisms operate during wear of materials. These mechanisms include the Strain Rate Response (SRR - effect of strain rate on plastic deformation), Tribo-Chemical Reactions (TCR) and formation of Mechanically Mixed Layers (MML). The present work investigates the effect of these three in context of the formation of MML. For this wear experiments are done on a pin-on-disc machine using Ti64 as the pin and SS316L as the disc. It is seen that apart from the speed and load, which control the SRR and TCR, the diameter of the pin controls the formation of MML, especially at higher speeds.

I. Numerical solution of exact pair equations. II. Numerical solution of first-order pair equations

Part I

Numerical solutions to the S-limit equations for the helium ground state and excited triplet state and the hydride ion ground state are obtained with the second and fourth difference approximations. The results for the ground states are superior to previously reported values. The coupled equations resulting from the partial wave expansion of the exact helium atom wavefunction were solved giving accurate S-, P-, D-, F-, and G-limits. The G-limit is -2.90351 a.u. compared to the exact value of the energy of -2.90372 a.u.

Part II

The pair functions which determine the exact first-order wavefunction for the ground state of the three-electron atom are found with the matrix finite difference method. The second- and third-order energies for the (1s1s)¹S, (1s2s)³S, and (1s2s)¹S states of the two-electron atom are presented along with contour and perspective plots of the pair functions. The total energy for the three-electron atom with a nuclear charge Z is found to be E(Z) = -1.125•Z² +1.022805•Z-0.408138-0.025515•(1/Z)+O(1/Z²)a.u.

Supernovae explosions induced by pair production instability

Stars with a core mass greater than about 30 M_⊙ become dynamically unstable due to electron-positron pair production when their central temperature reaches 1.5-2.0 x 10^{9 0}K. The collapse and subsequent explosion of stars with core masses of 45, 52, and 60 M_⊙ is calculated. The range of the final velocity of expansion (3,400 – 8,500 km/sec) and of the mass ejected (1 – 40 M_⊙) is comparable to that observed for type II supernovae.

An implicit scheme of hydrodynamic difference equations (stable for large time steps) used for the calculation of the evolution is described.

For fast evolution the turbulence caused by convective instability does not produce the zero entropy gradient and perfect mixing found for slower evolution. A dynamical model of the convection is derived from the equations of motion and then incorporated into the difference equations.

Experimental study study of antiproton-proton annihilation into a pair of charged Pi-Mesons or K-Mesons for incident antiproton mementa in the range from 0.72 GeV/c to 2.62 GeV/c

The cross sections for the two antiproton-proton annihilation-in-flight modes,

ˉp + p → π⁺ + π^-

ˉp + p → k⁺ + k^-

were measured for fifteen laboratory antiproton beam momenta ranging from 0.72 to 2.62 GeV/c. No magnets were used to determine the charges in the final state. As a result, the angular distributions were obtained in the form [dσ/dΩ (Θ_C.M.) + dσ/dΩ (π – Θ_C.M.)] for 45 ≲ Θ_C.M. ≲ 135°.

A hodoscope-counter system was used to discriminate against events with final states having more than two particles and antiproton-proton elastic scattering events. One spark chamber was used to record the track of each of the two charged final particles. A total of about 40,000 pictures were taken. The events were analyzed by measuring the laboratory angle of the track in each chamber. The value of the square of the mass of the final particles was calculated for each event assuming the reaction

ˉp + p → a pair of particles with equal masses.

About 20,000 events were found to be either annihilation into π ^±-pair or k ^±-pair events. The two different charged meson pair modes were also distinctly separated.

The average differential cross section of ˉp + p → π⁺ + π^- varied from ~ 25 µb/sr at antiproton beam momentum 0.72 GeV/c (total energy in center-of-mass system, √s = 2.0 GeV) to ~ 2 µb/sr at beam momentum 2.62 GeV/c (√s = 2.64 GeV). The most striking feature in the angular distribution was a peak at Θ_C.M. = 90° (cos Θ_C.M. = 0) which increased with √s and reached a maximum at √s ~ 2.1 GeV (beam momentum ~ 1.1 GeV/c). Then it diminished and seemed to disappear completely at √s ~ 2.5 GeV (beam momentum ~ 2.13 GeV/c). A valley in the angular distribution occurred at cos Θ_C.M. ≈ 0.4. The differential cross section then increased as cos Θ_C.M. approached 1.

The average differential cross section for ˉp + p → k⁺ + k^- was about one third of that of the π^±-pair mode throughout the energy range of this experiment. At the lower energies, the angular distribution, unlike that of the π^±-pair mode, was quite isotropic. However, a peak at Θ_C.M. = 90° seemed to develop at √s ~ 2.37 GeV (antiproton beam momentum ~ 1.82 GeV/c). No observable change was seen at that energy in the π^±-pair cross section.

The possible connection of these features with the observed meson resonances at 2.2 GeV and 2.38 GeV, and its implications, were discussed.

Observations of the 1992 U.S. Pelagic Pair Trawl Fishery in the Northwest Atlantic

Pelagic pair trawling for tuna, Thunnus spp., and swordfish, Xiphias gladius, was introduced in U.S. Northwest Atlantic waters in 1991. During autumn (October-November) of 1992 under the authority oft he Federal Atlantic Swordfish Regulations, the National Marine Fisheries Service placed observers aboard pelagic pair trawl vessels to document the catch, bycatch, discard, and gear used in this new fishery. The fishery is conducted primarily at night along shelf-edge waters from June to November. In late 1991, revised regulations restricted swordfish to bycatch in this fishery resulting in pelagic pair trawl vessels targeting tuna throughout 1992. Analyses of 1992 data indicate that albacore, T. alalunga, was the predominant species caught, although yellowfin tuna, T. albaeares, and bigeye tuna, T. obesus, were the preferred target species. Bycatch also included swordfish, large sharks, pelagic rays and other pelagic fishes, other tunas, and marine mammals.

Commercial small craft pair trawling trials Lake Chilwa, Malawi 1971

The results are reported of commercial small craft pair trawling trials conducted on Lake Chilwa from May to August 1971. Type of vessels and equipment used and the fishing method and operation employed are described and design data given for the different trawls used. The effects on catching efficiency of varying amounts of small mesh netting trawls are dealt with and recommendations made for trawls design modifications.

On-going generation of multiple forms of HIV-1 intersubtype recombinants in the Yunnan Province of China

Objectives: To investigate the molecular epidemiology of HIV in China's Yunnan Province, where the initial HIV-1 outbreak among injecting drug users (IDU) occurred in 1989, and to analyse the genesis and interrelationship of the epidemic with that in surrounding areas. Design: A molecular epidemiological investigation was conducted among IDU in three prefectures in Yunnan Province, including Wenshan (east), Honghe (southeast) and Dehong (west). Methods: Thirty-nine specimens were collected from consenting IDU in 2000-2001. The nucleotide sequences of 2.6 kb gag-RT and 340 base pair (bp) env (C2/V3) regions were determined. Phylogenetic tree and recombination breakpoint analyses were performed. Results: The circulating recombinant form (CRF), CRF08_BC, predominated in east Yunnan near Guangxi Province (89% in Wenshan and 81% in Honghe), whereas it was not detected in Dehong(0/14) in the west. In contrast, 71% (10/14) of the Dehong isolates were unique recombinant forms (URF), mostly between subtypes B' (Thailand variant of subtype B) and C, with distinct profiles of recombination breakpoints. The subtype B' accounts for the remaining 29% (4/14) of Dehong isolates. Interestingly, two Honghe isolates (2/16) shared some of the precise B'/C recombination breakpoints with CRF07_BC. Conclusion: New recombinant strains are arising continually in west Yunnan near the Myanmar border. Some appeared to be secondary recombinants derived from CRF07_BC that had further recombined with other strains. The uneven distribution of subtypes, CRF and URF, suggests the presence of independent transmission networks and clusters among IDU in Yunnan. (C) 2002 Lippincott Williams Wilkins.

Narrow line-width resonant cavity enhanced photodetectors operating at 1.55 mu m

A method for fabrication of long-wavelength narrow line-width InGaAs resonant cavity enhanced (RCE) photodetectors in a silicon substrate operating at the wavelength range of 1.3-1.6 mu m has been developed. A full width at half maximum (FWHM) of 0.7 nm and a peak responsivity of 0. 16 A/W at the resonance wavelength of 1.55 mu m have been accomplished by using a thick InP layer as part of the resonant cavity. The effects of roughness and tilt of the InP layer surface, and its free carrier absorption, as well as the thickness deviation of the mirror pair on the resonance wavelength shift and the peak quantum efficiency of the RCE photodetectors are analyzed in detail, and approaches for minimizing them toward superior performance are suggested. (C) 2007 Elsevier B.V. All rights reserved.

1.55 mu m GaInNAs resonant-cavity-enhanced photodetector grown on GaAs

We report the design, growth, fabrication, and characterization of a GaAs-based resonant-cavity-enhanced (RCE) GaInNAs photodetector operating at 1.55 mu m. The structure of the device was designed using a transfer-matrix method (TMM). By optimizing the molecular-beam epitaxy growth conditions, six GaInNAs quantum wells were used as the absorption layers. Twenty-five (25)- and 9-pair GaAs/AlAs-distributed Bragg reflectors were grown as the bottom and top mirrors. At 1.55 mu m, a quantum efficiency of 33% with a full width at half maximum of 10 nm was obtained. The dark current density was 3x10(-7) A/cm(2) at a bias of 0 V and 4.3x10(-5) A/cm(2) at a reverse bias of 5 V. The primary time response measurement shows that the device has a rise time of less than 800 ps. (c) 2005 American Institute of Physics.

High-performance 1.55 mu m low-temperature-grown GaAs resonant-cavity-enhanced photodetector

A 1.55 mu m low-temperature-grown GaAs (LT-GaAs) photodetector with a resonant-cavityenhanced structure was designed and fabricated. A LT-GaAs layer grown at 200 degrees C was used as the absorption layer. Twenty- and fifteen-pair GaAs/AlAs-distributed Bragg reflectors were grown as the bottom and top mirrors. A responsivity of 7.1 mA/W with a full width at half maximum of 4 nm was obtained at 1.61 mu m. The dark current densities are 1.28x10(-7) A/cm(2) at the bias of 0 V and 3.5x10(-5) A/cm(2) at the reverse bias of 4.0 V. The transient response measurement showed that the photocarrier lifetime in LT-GaAs is 220 fs. (c) 2006 American Institute of Physics.