Experimental study of the effect of external electric fields on interfacial dynamics of colloidal particles

The interaction of colloidal particles with a planar surface (i.e., wall) in the presence of an electric field applied parallel to the planar surface is of interest in various microfluidic devices. Evanescent wave-based particle-tracking velocimetry was used to investigate the dynamics of a dilute suspension of polystyrene and silica particles (radii a = 110-463 nm) in a monovalent electrolyte solution with a Debye length of 6.8 nm driven through a microchannel by external electric fields E = 15-31 V/cm over the first 300 nm next to the channel wall. The particle velocity parallel to the wall due to electrophoresis and electroosmosis was in good agreement with the Helmholtz-Smoluchowski relation, and the hydrodynamic interactions between the wall and the particles were negligible, for all particle types. Measurements of the distribution of particles along the wall-normal coordinate, however, suggest that an additional force as great as 30 fN that repels the negatively charged particles away from the wall is induced by nonzero E. The results suggest that the magnitude of this force scales as E(2) and a(2) but is independent of the particle ζ-potential, in agreement with previous theoretical studies. However, estimates of the force assuming that the particles have a Boltzmann distribution were up to 40 times greater than the theoretical predictions, which only considered "remote" particle-wall interactions. These results are, to our knowledge, the first to observe a repulsive wall-normal force due to an applied electric field for near-wall colloidal particles.     

Two Bessel Bridges Conditioned Never to Collide,Double Dirichlet Series,and Jacobi Theta Function

It is known that the moments of the maximum value of a one-dimensional conditional Brownian motion, the three-dimensional Bessel bridge with duration 1 started from the origin, are expressed using the Riemann zeta function. We consider a system of two Bessel bridges, in which noncolliding condition is imposed. We show that the moments of the maximum value is then expressed using the double Dirichlet series, or using the integrals of products of the Jacobi theta functions and its derivatives. Since the present system will be provided as a diffusion scaling limit of a version of vicious walker model, the ensemble of 2-watermelons with a wall, the dominant terms in long-time asymptotics of moments of height of 2-watermelons are completely determined. For the height of 2-watermelons with a wall, the average value was recently studied by Fulmek by a method of enumerative combinatorics.     

Scanning laser microscope for imaging nanostructured superconductors

The nanofabrication of superconductors yields various interesting features in superconducting properties. A variety of different imaging techniques have been developed for probing the local superconducting profiles. A scanning pulsed laser microscope has been developed by the combination of the XYZ piezo-driven stages and an optical fiber with an aspheric focusing lens. The scanning laser microscope is used to understand the position-dependent properties of a superconducting MgB₂ stripline of length 100 μm and width of 3 μm under constant bias current. Our results show that the superconducting stripline can clearly be seen in the contour image of the scanning laser microscope on the signal voltage. It is suggested from the observed image that the inhomogeneity is relevant in specifying the operating conditions such as detection efficiency of the sensor.     

How have they started? – A brief guide for pedestrians

I shall present a very brief summary of subjects selected from what Prof. Akito Arima has done in the past years. I will focus on the initial works on the configuration mixing and on the Interacting Boson Model. Since there are many literatures on these subjects, I shall concentrate what have been done at the initial or at the pre-history stages. By doing this, we shall see how Prof. Akito Arima started from the scratch.     

The Most Effective Model for Describing the Universal Behavior of a Noisy Kuramoto–Sivashinsky Equation as a Paradigmatic Model

We study a noisy Kuramoto–Sivashinsky (KS) equation which describes unstable surface growth and chemical turbulence. It has been conjectured that the universal long-wavelength behavior of the equation, which is characterized by scale-dependent parameters, is described by a Kardar–Parisi–Zhang (KPZ) equation. We consider this conjecture by analyzing a renormalization-group equation for a class of generalized KPZ equations. We then uniquely determine the parameter values of the KPZ equation that most effectively describes the universal long-wavelength behavior of the noisy KS equation.     

Ionic Liquids as Performance Ingredients in Space Lubricants

Low vapor pressure and several other outstanding properties make room-temperature ionic liquids attractive candidates as lubricants for machine elements in space applications. Ensuring sufficient liquid lubricant supply under space conditions is challenging, and consequently, such tribological systems may operate in boundary lubrication conditions. Under such circumstances, effective lubrication requires the formation of adsorbed or chemically reacted boundary films to prevent excessive friction and wear. In this work, we evaluated hydrocarbon-mimicking ionic liquids, designated P-SiSO, as performance ingredients in multiply alkylated cyclopentane (MAC). The tribological properties under vacuum or various atmospheres (air, nitrogen, carbon dioxide) were measured and analyzed. Thermal vacuum outgassing and electric conductivity were meas- ured to evaluate ‘MAC & P-SiSO’ compatibility to the space environment, including the secondary effects of radiation. Heritage space lubricants—MAC and perfluoroalkyl polyethers (PFPE)—were employed as references. The results corroborate the beneficial lubricating performance of incorporating P-SiSO in MAC, under vacuum as well as under various atmospheres, and demonstrates the feasibility for use as a multifunctional additive in hydrocarbon base oils, for use in space exploration applications.     

Hydroxymethylfurfural as an Intermediate of Cellulose Carbonization

Hydrogen bond donor solvents such as aromatic solvents inhibit the secondary degradation of cellulose-derived primary pyrolysis products. In a previous study, we found that the formation of solid carbonized products was completely inhibited during cellulose pyrolysis in aromatic solvents, with 5-hydroxymethylfurfural (5-HMF) recovered in certain yields instead. This indicated that 5-HMF is an intermediate in cellulose carbonization. To confirm this hypothesis, the thermal reactivity of 5-HMF was investigated. At 280 °C, pure 5-HMF polymerized into a hard glassy substance through OH group elimination, but further conversion was slow. When pyrolyzed in the presence of glycerol, a model of coexisting primary pyrolysis products from cellulose, a coupling reaction proceeded. Reactions characteristic of cellulose carbonization then occurred, including the formation of acidic groups and benzene-type structures in the solid products. These results confirmed the above hypothesis. The molecular mechanism of cellulose carbonization is discussed, focusing on the crystalline nature.     

White and Taylor Type Guest Host Displays Without Scattering Effects Using the Tilted Boundary Conditions

White and Taylor type guest host displays using the tilted boundary condition have been reported. The parallel or the perpendicular boundary condition is usually used for these displays and both conditions cause scattering phemomena after the electric field removal. The present paper reports the relaxation processes of samples with the tilted boundary after the field removal. Using the tilted boundary, two types of nonscattering conditions depending on the thickness of the liquid crystal layer (d), the natural pitch (Po) and the boundary condition (φ) exist. Both types of conditions are discussed in detail.     

Construction of α-phosphonolactams via rhodium (II)-catalyzed intramolecular C?H insertion reactions

The Rh(II)-catalyzed intramolecular C H insertion reactions of N,N-dialkyl-α-diazo-α-(diethylphosphono)acetamides 2a , f–j in CHCl₃ or ClCH₂CH₂Cl were found to give monocyclic and bicyclic α-phosphono-β-lactams, 3a and 3f–j , in 43–67% yields via regiospecific α-C H insertion of the N-alkyl groups. Similar treatment of N-benzyl-N-isopropyl-α-diazo-α-(diethylphosphono)acetamide ( 2b ) and the corresponding N-isobutyl-N-methylacetamide 2d in ClCH₂CH₂Cl afforded mixtures of β-lactams 3b (35%) and and 3b ′ (16%), β-lactam 3d (47%), and γ-lactam 4d (10%), respectively, each of which is formed by the competitive C H insertion reaction between benzylic and isopropyl α-C H bonds and between methyl α-C H and methine β-C H bonds, respectively. For the formation of β-lactams, the selectivity in the rhodium-mediated C H insertion in ClCH₂CH₂Cl follows the order methyl > methine > benzylic α-C H bond on N-substituents. The N,N-dibutyl-α-diazo homologue 2c and Nα[α-diazo-α-(diethylphosphono)acetyl]-2-methylindoline ( 2k ) exclusively produced γ-lactams 4c (67%) and 4k (81%) via insertion into the methylene β-C H and methyl β-C H bonds. tert-Butyl N-[α-diazo-α-(dibenzylphosphono)acetyl]-piperidine-2-carboxylate ( 2m ) on similar treatment, followed by deprotection of the benzyl ester afforded the 7-phosphono carbacepham 6 in 32% overall yield. Similar Rh(II)-catalyzed cyclization of N-methyl-N[4-benzyloxy-α-(diethylphosphono)-phenyl(diethyl-phosphono)methyl]-α-diazo-acetamide ( 2n ) led to 1-[4′-benzylphenyl(diethylphosphono)methyl] -3-(diethyl-phosphono)azetidin-2-one ( 3n ) in 78% yicld. The phosphono group at C-7 of 3f was converted into the acetylamino group via a four-step reaction. Application of chiral rhodium(II) carboxylates 12a–c to the insertion reactions of 2b , c produced α-phosphono-β-and γ-lactams, 3b and 4c , in 6–24% ee and 25–29% ee, respectively.