The Droplet Group Micro-Explosions, Viscosity and Atomization Characteristics of W/O Emulsions

The spray of emulsified fuel, composed of diesel fuel, water and methanol can make micro-explosion under high temperature conditions, and the viscosity and the atomization characteristics of emulsion have significant effects on the micro- explosion of emulsions. To clarify the combustion mechanism of water-in-oil emulsion sprays, combustion bomb experiments were carried out, and the droplet group micro- explosions in W/O fuel emulsion sprays in a high-pressure, high-temperature bomb were observed clearly by a multi-pulsed, off-axis, image-plane ruby laser holocamera and continuously by a high-speed CCD camera.The viscosity and atomization characteristics of emulsions were also studied experimentally. The experimental results show that the higher concentration of the aqueous phase (water-methanol) (<50%) increases the viscosity of the emulsions, especially for higher agent concentration, and higher aqueous phase concentration and higher viscosity results in lager Sauter Mean Diameter (SMD). The experiment results also show that the different kinds of emulsifying agents, with different Hydrophile-Lipophile Balance (HLB) values, have significant influence on the viscosity of the emulsions.

The Influence of Viscosity and Surface Tension on Atomization of Water/Methanol and Diesel Emulsions

This paper shows the result of experimental studies of the influence of viscosities, surface tensions on atomization characteristics of water/methanol and diesel emulsions. Three emulsifying agents Y01, Y02 and Y03, with viscosity of 1.32 ～ 1.5 Pa·s and HLB values of 5.36, 4.83 and 4.51 respectively was produced by Span 80 and Tween 60. In the W/O emulsions, the aqueous phase is between 10% and 50%; the agent concentration added is 0.8 ～ 8.0%. The viscosity of the emulsions is 0.003 ～ 0.02 Pa·s, and the surface tension is 0.04 ～ 0.1 N/m. The types and concentrations of agents and the aqueous phase ( < 50%) significantly influence the viscosity of the emulsions and the Sauter Mean Diameter, measured by Malvern Particle Analyzer SERIES 2600.

Experimental Characterization Of Electrical Current Leakage In Poly(Dimethylsiloxane) Microfluidic Devices

Poly(dimethylsiloxane) (PDMS) is usually considered as a dielectric material and the PDMS microchannel wall can be treated as an electrically insulated boundary in an applied electric field. However, in certain layouts of microfluidic networks, electrical leakage through the PDMS microfluidic channel walls may not be negligible, which must be carefully considered in the microfluidic circuit design. In this paper, we report on the experimental characterization of the electrical leakage current through PDMS microfluidic channel walls of different configurations. Our numerical and experimental studies indicate that for tens of microns thick PDMS channel walls, electrical leakage through the PDMS wall could significantly alter the electrical field in the main channel. We further show that we can use the electrical leakage through the PDMS microfluidic channel wall to control the electrolyte flow inside the microfluidic channel and manipulate the particle motion inside the microfluidic channel. More specifically, we can trap individual particles at different locations inside the microfluidic channel by balancing the electroosmotic flow and the electrophoretic migration of the particle.

Nuclear Hartree-Fock calculations on parallel computers

Hartree-Fock (HF) calculations have had remarkable success in describing large nuclei at high spin, temperature and deformation. To allow full range of possible deformations, the Skyrme HF equations can be discretized on a three-dimensional mesh. However, such calculations are currently limited by the computational resources provided by traditional supercomputers. To take advantage of recent developments in massively parallel computing technology, we have implemented the LLNL Skyrme-force static and rotational HF codes on Intel's DELTA and GAMMA systems at Caltech.

We decomposed the HF code by assigning a portion of the mesh to each node, with nearest neighbor meshes assigned to nodes connected by communication· channels. This kind of decomposition is well-suited for the DELTA and the GAMMA architecture because the only non-local operations are wave function orthogonalization and the boundary conditions of the Poisson equation for the Coulomb field.

Our first application of the HF code on parallel computers has been the study of identical superdeformed (SD) rotational bands in the Hg region. In the last ten years, many SD rotational bands have been found experimentally. One very surprising feature found in these SD rotational bands is that many pairs of bands in nuclei that differ by one or two mass units have nearly identical deexcitation gamma-ray energies. Our calculations of the five rotational bands in ^(192)Hg and ^(194)Pb show that the filling of specific orbitals can lead to bands with deexcitation gamma-ray energies differing by at most 2 keV in nuclei differing by two mass units and over a range of angular momenta comparable to that observed experimentally. Our calculations of SD rotational bands in the Dy region also show that twinning can be achieved by filling or emptying some specific orbitals.

The interpretation of future precise experiments on atomic parity nonconservation (PNC) in terms of parameters of the Standard Model could be hampered by uncertainties in the atomic and nuclear structure. As a further application of the massively parallel HF calculations, we calculated the proton and neutron densities of the Cesium isotopes from A = 125 to A = 139. Based on our good agreement with experimental charge radii, binding energies, and ground state spins, we conclude that the uncertainties in the ratios of weak charges are less than 10^(-3), comfortably smaller than the anticipated experimental error.

Quantum Mechanics Studies of Fuel Cell Catalysts and Proton Conducting Ceramics with Validation by Experiment

We carried out quantum mechanics (QM) studies aimed at improving the performance of hydrogen fuel cells. This led to predictions of improved materials, some of which were subsequently validated with experiments by our collaborators.

In part I, the challenge was to find a replacement for the Pt cathode that would lead to improved performance for the Oxygen Reduction Reaction (ORR) while remaining stable under operational conditions and decreasing cost. Our design strategy was to find an alloy with composition Pt3M that would lead to surface segregation such that the top layer would be pure Pt, with the second and subsequent layers richer in M. Under operating conditions we expect the surface to have significant O and/or OH chemisorbed on the surface, and hence we searched for M that would remain segregated under these conditions. Using QM we examined surface segregation for 28 Pt₃M alloys, where M is a transition metal. We found that only Pt₃Os and Pt₃Ir showed significant surface segregation when O and OH are chemisorbed on the catalyst surfaces. This result indicates that Pt₃Os and Pt3Ir favor formation of a Pt-skin surface layer structure that would resist the acidic electrolyte corrosion during fuel cell operation environments. We chose to focus on Os because the phase diagram for Pt-Ir indicated that Pt-Ir could not form a homogeneous alloy at lower temperature. To determine the performance for ORR, we used QM to examine all intermediates, reaction pathways, and reaction barriers involved in the processes for which protons from the anode reactions react with O₂ to form H₂O. These QM calculations used our Poisson-Boltzmann implicit solvation model include the effects of the solvent (water with dielectric constant 78 with pH 7 at 298K). We found that the rate determination step (RDS) was the O_ad hydration reaction (O_ad + H₂O_ad -> OH_ad + OH_ad) in both cases, but that the barrier for pure Pt of 0.50 eV is reduced to 0.48 eV for Pt₃Os, which at 80 degrees C would increase the rate by 218%. We collaborated with the Pu-Wei Wu’s group to carry out experiments, where we found that the dealloying process-treated Pt2Os catalyst showed two-fold higher activity at 25 degrees C than pure Pt and that the alloy had 272% improved stability, validating our theoretical predictions.

We also carried out similar QM studies followed by experimental validation for the Os/Pt core-shell catalyst fabricated by the underpotential deposition (UPD) method. The QM results indicated that the RDS for ORR is a compromise between the OOH formation step (0.37 eV for Pt, 0.23 eV for Pt_2ML/Os core-shell) and H₂O formation steps (0.32 eV for Pt, 0.22 eV for Pt_2ML/Os core-shell). We found that Pt_2ML/Os has the highest activity (compared to pure Pt and to the Pt₃Os alloy) because the 0.37 eV barrier decreases to 0.23 eV. To understand what aspects of the core shell structure lead to this improved performance, we considered the effect on ORR of compressing the alloy slab to the dimensions of pure Pt. However this had little effect, with the same RDS barrier 0.37 eV. This shows that the ligand effect (the electronic structure modification resulting from the Os substrate) plays a more important role than the strain effect, and is responsible for the improved activity of the core- shell catalyst. Experimental materials characterization proves the core-shell feature of our catalyst. The electrochemical experiment for Pt_2ML/Os/C showed 3.5 to 5 times better ORR activity at 0.9V (vs. NHE) in 0.1M HClO₄ solution at 25 degrees C as compared to those of commercially available Pt/C. The excellent correlation between experimental half potential and the OH binding energies and RDS barriers validate the feasibility of predicting catalyst activity using QM calculation and a simple Langmuir–Hinshelwood model.

In part II, we used QM calculations to study methane stream reforming on a Ni-alloy catalyst surfaces for solid oxide fuel cell (SOFC) application. SOFC has wide fuel adaptability but the coking and sulfur poisoning will reduce its stability. Experimental results suggested that the Ni4Fe alloy improves both its activity and stability compared to pure Ni. To understand the atomistic origin of this, we carried out QM calculations on surface segregation and found that the most stable configuration for Ni₄Fe has a Fe atom distribution of (0%, 50%, 25%, 25%, 0%) starting at the bottom layer. We calculated that the binding of C atoms on the Ni4Fe surface is 142.9 Kcal/mol, which is about 10 Kcal/mol weaker compared to the pure Ni surface. This weaker C binding energy is expected to make coke formation less favorable, explaining why Ni₄Fe has better coking resistance. This result confirms the experimental observation. The reaction energy barriers for CHx decomposition and C binding on various alloy surface, Ni₄X (X=Fe, Co, Mn, and Mo), showed Ni₄Fe, Ni₄Co, and Fe₄Mn all have better coking resistance than pure Ni, but that only Ni₄Fe and Fe₄Mn have (slightly) improved activity compared to pure Ni.

In part III, we used QM to examine the proton transport in doped perovskite-ceramics. Here we used a 2x2x2 supercell of perovskite with composition Ba₈X₇M₁(OH)₁O₂₃ where X=Ce or Zr and M=Y, Gd, or Dy. Thus in each case a 4⁺ X is replace by a 3⁺ M plus a proton on one O. Here we predicted the barriers for proton diffusion allowing both includes intra-octahedron and inter-octahedra proton transfer. Without any restriction, we only observed the inter-octahedra proton transfer with similar energy barrier as previous computational work but 0.2 eV higher than experimental result for Y doped zirconate. For one restriction in our calculations is that the O_donor-O_acceptor atoms were kept at fixed distances, we found that the barrier difference between cerates/zirconates with various dopants are only 0.02~0.03 eV. To fully address performance one would need to examine proton transfer at grain boundaries, which will require larger scale ReaxFF reactive dynamics for systems with millions of atoms. The QM calculations used here will be used to train the ReaxFF force field.

Isotope shift studies in the rare earths and lead

Isotope shifts of K_α1 x-ray transitions were measured for the Neodymium isotopes Nd 142, 143, 144, 145, 146, 148 and 150, the Samarium isotopes Sm 147, 148, 149, 150, 152 and 154, the Gadolinium isotopes Gd 154, 155, 156, 157, 158 and 160, the Dysprosium isotopes Dy 162 and 164, the Erbium isotopes Er 166, 168 and 170, the Hafnium isotopes Hf 178 and 180 and the Lead isotopes Pb 204, 206, 207 and 208. A curved crystal Cauchois spectrometer was used. The analysis of the measurement furnished the variation of the mean square charge radius of the nucleus, δ˂r²˃, for 23 isotope pairs. The experimental results were compared with theoretical values from nuclear models. Combining the x-ray shifts and the optical shifts in Nd and Sm yielded the optical mass shifts. An anomaly was observed in the odd-even shifts when the optical and the x-ray shifts were plotted against each other.

杂质对掺钕磷酸盐激光玻璃光谱性质的影响

综述了过渡金属杂质（Cu，Fe）和稀土杂质（Dy，Pr，Sm，Ce）对掺钕磷酸盐激光玻璃吸收损耗及Nd^3＋荧光猝灭影响的研究状况。

Low loss waveguide in Nd3+-doped silicate glass fabricated by carbon ion implantation

Low loss index enhanced planar waveguides in Nd3+-doped silicate glass were fabricated by 3.0 MeV C+ ion implantation. The enhancement of the refractive index confined the light propagating in the waveguide. The prism-coupling method was used to measure dark modes in the waveguide. The effective refractive indices of the waveguide were obtained based on the dark modes. The moving fiber method was applied to measure the waveguide propagation loss. Loss measured in non-annealed samples is about 0.6 dB/cm. And the waveguide mode optical near-field output at 633 nm was presented. (c) 2005 Elsevier B.V. All rights reserved.

Property studies of optical waveguide formed by 6.0 MeV carbon ion implantation into Nd : silicate glass

Nd:silicate glass was implanted at room temperature by 6.0 MeV C3+ ions with a dose of 2.0 x 10(15) ions cm(-2). A waveguide with thickness of about 6.3 mu m was formed. The prism-coupling method was used to observe the dark modes of the waveguide at 633 nm and 1539 nm, respectively. There are three dark modes at 633 nm, of which one is the enhanced-index mode. The propagation loss of the enhanced-index mode in the waveguide measured at 633 nm is 0.42 dB cm(-1) after annealing at 217 degrees C for 35 min. The reflectivity calculation method was applied to simulate the refractive index profiles in the waveguide. The mode optical near-field output at 633 nm was presented.

Optimizing the Curie temperature of pseudo-binary RxR2-x ' Fe-17 (R, R ' = rare earth) for magnetic refrigeration

Several pseudo-binary RxR2-x'Fe-17 alloys (with R = Y, Ce, Pr, Gd and Dy) were synthesized with rhombohedral Th2Zn17-type crystal structure determined from x-ray and neutron powder diffraction. The choice of compositions was done with the aim of tuning the Curie temperature (T-C) in the 270 +/- 20 K temperature range, in order to obtain the maximum magneto-caloric effect around room temperature. The investigated compounds exhibit broad isothermal magnetic entropy changes, Delta S-M(T), with moderate values of the refrigerant capacity, even though the values of Delta S-M(Peak) are relatively low compared with those of the R2Fe17 compounds with R = Pr or Nd. The reduction on the Delta S-M(Peak) is explained in terms of the diminution in the saturation magnetization value. Furthermore, the Delta S-M(T) curves exhibit a similar caret-like behavior, suggesting that the magneto-caloric effect is mainly governed by the Fe-sublattice. A single master curve for Delta S-M/Delta S-M(Peak)(T) under different values of the magnetic field change are obtained for each compound by rescaling of the temperature axis.