Nonlinear penetration of liquid drops into radial capillaries

The nonlinear dynamics of the impact and penetration of a liquid droplet in a radial capillary is studied numerically. The radial capillary is formed by two parallel plates at a distance of delta(g). The top plate has an orifice at its center. A droplet impacting on the orifice-plate partly spreads over the top plate, and the rest penetrates into the capillary gap between the two plates. The rate of spread of the fluid on the orifice plate, xi(out), is governed by the contact angle, beta, between the liquid and the orifice plate and the droplet initial momentum, whereas the rate of fluid spread inside the capillary gap, xi(in), is decided by the contact angles with both plates and the plate gap, delta(g).     

Synthesis and Characterization of Copper(I) Complexes Containing Tri(2‐Pyridylmethyl)Amine Ligand

Reaction of copper halides CuX (X=Cl, Br, I) with tri(2‐pyridylmethyl)amine) (TPMA) in THF under N₂ affords a series of monomeric copper(I) complexes CuX(TPMA) (X=Cl ( 1 ), Br ( 2 ) and I ( 3 )). Treatment of [CuCl(TPMA)] ( 1 ) with 0.5 equivalent of 1,4‐diisocyanobenzene following by equimolar amount of NaBF₄ affords a novel binuclear complex [(TPMA)Cu(μ‐1,4‐CNC₆H₄NC)Cu(TPMA)](BF₄)₂ ( 4 ). The copper(I) halide TPMA complexes show interesting fluxional behaviors in temperature dependence in the ¹H NMR spectrum that can be explained by the dissociation and reassociation of the pyridyl group and alkylamine nitrogen of TPMA ligand. The crystal structures of 1 , 3 and 4 are determined by an X‐ray diffractometer. Complexes 1 and 3 are distorted tetrahedral coordinates with strong bonding between three pyridyl N atoms and the corresponding halide donor. Crystallographic results of 4 clearly indicates two Cu(I) ions are bridged by 1,4‐diisocyanobenzene, forming a centro‐symmetrical homobinuclear complex with a “dangling” uncoordinated pyridyl group.     

Properties of acetate kinase activity inClostridium thermocellum cell extracts

Acetate kinase (EC 2.7.2.1) is involved in the wasteful production of acetate during conversion of cellulose to ethanol byClostridium thermocellum. The properties of this enzyme activity inC. thermocellum cell extracts were determined. Optimum enzyme activity was at 60 degrees C and between pH 7.5 and 9.0. In the presence of air, acetate kinase was stable to temperatures up to 60 degrees C, retaining 90% activity after 2 h, and was inactivated rapidly at higher temperatures. The enzyme exhibited a wide range of stability to pH (5.0-9.0) when incubated at 50 degrees C for 2 h. As with other acetate kinases, a divalent cation, such as Mg(2+), was required for enzyme activity. Optimum activity was observed at 20mM MgCl(2) when ATP was held constant at 10 mM. Acetate kinase activity was adversely affected by KCl, a salt commonly used in ion-exchange or affinity chromatography, with 0.3M KCl inhibiting by 50%. These results will be important in optimizing the direct microbial conversion process of cellulose to ethanol usingC. thermocellum in coculture withClostridium thermosaccharolyticum.     

Nitrogen speciation of polar petroleum compounds by compound class separation and on-line liquid chromatography – mass spectrometry (LC-MS)

Chromatography on Attapulgus clay and on silicic acid has been used to isolate ‘neutral’ and ‘basic’ nitrogen fractions from the 650–1050 °F distillate of an off-shore Californian crude oil. These polar compounds were subjected to on-line liquid chromatography – mass spectrometric (LC-MS) analysis using low voltage electron-impact ionization high resolution mass spectrometry (LVEI HRMS) and deuterated ammonia chemical ionization (ND₃ Cl) to determine the molecules' elemental composition and number of exchangeable hydrogen atoms. On-line separation of heavy oils into saturated, 1–4 ring aromatic, and polar compounds was performed by normal phase high performance liquid chromatography (HPLC) on a dinitroanilinopropyl (DNAP) silica column.     

Electrophoresis of a charge-regulated sphere normal to a large disk

The electrophoresis of a rigid, charge-regulated, spherical particle normal to a large disk is investigated under the conditions of low surface potential and weak applied electric field. We show that, although the presence of a charged disk does not generate an electroosmotic flow, it affects particle motion appreciably through inducing charge on its surface and establishing an osmotic pressure field. The competition between the hydrodynamic force and the electric force may yields a local extremum in mobility; it is also possible that the direction of particle movement is reversed. In general, if a particle remains at constant surface potential, a decrease in the thickness of double layer has the effect of increasing the electrostatic force acting on it so that its mobility increases. However, this might not be the case for a charged-regulated particle because an excess hydrodynamic force is enhanced. For a fixed separation distance, the influence of a charged disk on mobility may reduce to a minimum if the bulk concentration of hydrogen ion is equal to the dissociation constant of the monoprotic acidic functional groups on particle surface.     

Boundary Effects on Diffusiophoresis of Cylindrical Particles in Nonelectrolyte Gradients

The diffusiophoretic motion of a long circular cylinder in a transversely imposed gradient of a nonionic solute near a large plane wall parallel to its axis is analyzed. The range of the interaction between the solute and the solid surfaces is assumed to be small relative to the particle radius and to the gap width between the particle and the wall, but the polarization effect of the mobile solute in the thin diffuse layers adjacent to the solid surfaces caused by the strong adsorption of the solute is incorporated. A normal flux of the solute and a slip velocity of the fluid at the outer edge of the diffuse layers are used as the boundary conditions for the fluid domain outside the diffuse layers. Through the use of cylindrical bipolar coordinates along with these boundary conditions, a set of transport equations governing this problem is solved in the quasisteady situation and the wall effects on the diffusiophoresis of the cylinder are computed for various cases. For the diffusiophoretic motion of a cylinder normal to a plane, the particle mobility decreases monotonically with the decrease of the distance of the particle axis from the wall. The stronger the polarization effect in the diffuse layer, the weaker the wall effect on the diffusiophoresis. The effect of the normal plane on the diffusiophoresis of a cylinder is much more significant than that for a sphere at the same separation. For the diffusiophoresis of a cylinder parallel to a plane, the boundary effect is a complicated function of the relevant parameters (not necessarily varies monotonically with the extent of separation) mainly due to the existence of a diffusio-osmotic flow caused by the tangential fluid velocity at the plane wall. Copyright 2000 Academic Press.     

Electronic-to-vibrational energy transfer reactions: Na(3 2P) + CO (X1Σ+, υ=0)

The vibrational distribution of CO produced from the electronic-to-vibrational energy transfer reaction: Na(3²P) + CO(X¹Σ⁺, υ=0)→Na(3²S) + CO(X¹Σ⁺, υ?8) has been determined by means of infrared resonance absorption measurements employing a cw CO laser. A flash-lamp-pumped dye laser is used to excite the ground state Na to the 3²P_{$\text{1}\text{2}$} and 3²P_{$\text{3}\text{2}$} states. The CO molecules formed in the reaction were found to be vibrationally excited up to the limits of available electronic energies carried by the excited Na atoms, and the vibrational population exhibits a maximum at υ=2. The efficiency of E→V energy transfer was determined to be 35%. Our present results were found to be consistent with the impulsive (half-collision) and curve-crossing models.     

Fabrication on uniform plating-based flip chip solder bumps after reflow process using a polishing mechanism

This paper presents an innovative polishing process aimed at leveling rough surface of plating-based flip chip solder bumps so as to get uniform coplanarity across the whole substrate after both electroplating and reflow processes. This polishing mechanism is characteristic of combining mechanical-dominated polishing force with slight chemical reaction together. A large number of extremely but inevitably rugged mushroom-like structures after electroplating are drastically smoothed down with the help of this newly-developed polishing process. Nearly 70 μm solder bumps in height with two different profiles as square and circle on the substrates reach as flatly as ±3 μm between different substrates after reflow process; ±2.5 μm in single substrate; and even ±1 μm in die, respectively. Besides, surface roughness among the solder bumps is simultaneously narrowed down from Ra 0.6 to Ra 0.03 along with the coplanarity improvement. Excellent uniformity and smooth surface roughness in solder bumps are absolutely beneficial to pile up and deposit in the following steps in MEMS and semiconductor fields.     

Blue Electroluminescence Enhancement of Poly{2,7‐(9,9′‐dioctylfluorene)‐co‐4‐diphenylamino‐4′‐bipenylmethylsulfide} Incorporating Side‐Chain‐Tethered Gold Nanoparticles

Through in situ reduction of a gold precursor, we have tethered gold nanoparticles (Au NPs) to the side chains of poly{2,7‐(9,9′‐dioctylfluorene)‐co‐4‐diphenylamino‐4′‐bipenylmethylsulfide} (PF‐DBMS) through its ArSCH₃ anchor groups. The presence of 1 wt % of the tethered Au NPs led to a reduction in the degree of aggregation of the polymer chains, resulting in a 50 % increase in its quantum yield. The electroluminescence of a 1 wt % Au/PF‐DBMS device was almost four times higher in terms of its maximum brightness and its full‐width‐at‐half‐maximum emission peak was much narrower than that of a pure PF‐DBMS device; the presence of a small amount of Au NPs significantly enhances the electron injection and transport and suppresses the photo‐oxidation of PF‐DBMS.     

Effective Work Function Engineering of TaxCy Metal Gate on Hf-Based Dielectrics

This letter reports the engineering of effective work function (EWF) for tantalum carbide (TaC) metal gate on high-k gate dielectrics. The dependence of EWF on Si concentration in HfSiO as well as nitridation techniques is revealed. The EWF was extracted by both terraced oxide and terraced high-k techniques with the bulk and interface charges taken into account. The incorporation of Si in Hf-based dielectrics results in an increase of EWF, while the presence of N tends to decrease the EWF. Plasma nitridation is found to be more effective in lowering the EWF than a thermal nitridation. The phenomena can be explained by the modification of TaC/high-k interface dipole moment, which arises from the electronegativity difference for various interface bonds. Based on the above findings, we proposed a novel approach to reduce the EWF of TaC on HfSiON by using a thin HfO₂ cap layer after optimizing the nitridation. The MOSFET results show that this technique is able to achieve a lower V_t without degrading the device performance