Constitutive equation with fractional derivatives for the generalized UCM model

A fundamental problem on the constitutive equation with fractional derivatives for the generalized upper convected Maxwell model (UCM) is studied. The existing investigations on the constitutive equation are reviewed and their limitations or deficiencies are highlighted. By utilizing the convected coordinates approach, a mathematically rigorous constitutive equation with fractional derivatives for the generalized UCM model is proposed, which has an explicit expression for the stress tensor. This model can be reduced to the linear generalized Maxwell model with fractional derivatives, the UCM model and some other existing models. In addition, the rheological properties of this proposed model in the start-up of simple shear and elongation flows are investigated. It is shown that this generalized UCM model can describe the various stress evolution processes and the strain hardening effect of the viscoelastic fluids.     

Probing enantioselectivity on chirally modified Cu(110), Cu(100), and Cu(111) surfaces

Temperature programmed desorption methods have been used to probe the enantioselectivity of achiral Cu(100), Cu(110), and Cu(111) single crystal surfaces modified by chiral organic molecules including amino acids, alcohols, alkoxides, and amino-alcohols. The following combinations of chiral probes and chiral modifiers on Cu surfaces were included in this study: propylene oxide (PO) on L-alanine modified Cu(110), PO on L-alaninol modified Cu(111), PO on 2-butanol modified Cu(111), PO on 2-butoxide modified Cu(100), PO on 2-butoxide modified Cu(111), R-3-methylcyclohexanone (R-3-MCHO) on 2-butoxide modified Cu(100), and R-3-MCHO on 2-butoxide modified Cu(111). In contrast with the fact that these and other chiral probe/modifier systems have exhibited enantioselectivity on Pd(111) and Pt(111) surfaces, none of these probe/modifier/Cu systems exhibit enantioselectivity at either low or high modifier coverages. The nature of the underlying substrate plays a significant role in the mechanism of hydrogen-bonding interactions and could be critical to observing enantioselectivity. While hydrogen-bonding interactions between modifier and probe molecule are believed to induce enantioselectivity on Pd surfaces (Gao, F.; Wang, Y.; Burkholder, L.; Tysoe, W. T. J. Am. Chem. Soc. 2007, 129, 15240-15249), such critical interactions may be missing on Cu surfaces where hydrogen-bonding interactions are believed to occur between adjacent modifier molecules, enabling them to form clusters or islands.     

Structure‐Based Design of Platinum(II) Complexes as c‐myc Oncogene Down‐Regulators and Luminescent Probes for G‐Quadruplex DNA

A series of platinum(II) complexes with tridentate ligands was synthesized and their interactions with G‐quadruplex DNA within the c‐myc gene promoter were evaluated. Complex 1 , which has a flat planar 2,6‐bis(benzimidazol‐2‐yl)pyridine (bzimpy) scaffold, was found to stabilize the c‐myc G‐quadruplex structure in a cell‐free system. An in silico G‐quadruplex DNA model has been constructed for structure‐based virtual screening to develop new Pt^II‐based complexes with superior inhibitory activities. By using complex 1 as the initial structure for hit‐to‐lead optimization, bzimpy and related 2,6‐bis(pyrazol‐3‐yl)pyridine (dPzPy) scaffolds containing amine side‐chains emerge as the top candidates. Six of the top‐scoring complexes were synthesized and their interactions with c‐myc G‐quadruplex DNA have been investigated. The results revealed that all of the complexes have the ability to stabilize the c‐myc G‐quadruplex. Complex 3 a ([Pt^II L2R ] ⁺ ; L2 =2,6‐bis[1‐(3‐piperidinepropyl)‐1H‐enzo[d]imidazol‐2‐yl]pyridine, R =Cl) displayed the strongest inhibition in a cell‐free system (IC₅₀=2.2 μM ) and was 3.3‐fold more potent than that of 1 . Complexes 3 a and 4 a ([Pt^II L3R ]⁺; L3 =2,6‐bis[1‐(3‐morpholinopropyl)‐1H‐pyrazol‐3‐yl]pyridine, R =Cl) were found to effectively inhibit c‐myc gene expression in human hepatocarcinoma cells with IC₅₀ values of ≈17 μM , whereas initial hit 1 displayed no significant effect on gene expression at concentrations up to 50 μM . Complexes 3 a and 4 a have a strong preference for G‐quadruplex DNA over duplex DNA, as revealed by competition dialysis experiments and absorption titration; 3 a and 4 a bind G‐quadruplex DNA with binding constants (K) of approximately 10⁶–10⁷ dm³ mol^?1, which are at least an order of magnitude higher than the K values for duplex DNA. NMR spectroscopic titration experiments and molecular modeling showed that 4 a binds c‐myc G‐quadruplex DNA through an external end‐stacking mode at the 3′‐terminal face of the G‐quadruplex. Intriguingly, binding of c‐myc G‐quadruplex DNA by 3 b is accompanied by an increase of up to 38‐fold in photoluminescence intensity at λ_max=622 nm.     

Size selective assembly of colloidal particles on a template by directed self-assembly technique

We report a simple and effective approach to organize micron- and submicron-sized particles in a size selective manner. This approach utilizes the template assisted directed self-assembly technique. A topographically patterned photoresist surface is fabricated and used to create an ordered array of colloidal particles from their aqueous suspensions. Assembly of particles on this template is then achieved by using a conventional spin coating technique. Feasibility of this technique to form a large area of patterned particle assemblies has been investigated. To arrange the particles on the template, the physical confinement offered by the surface topography must overcome a joint effect of centrifugal force and the hydrophobic nature of the photoresist surface. This concept has been extended to the size selective sorting of colloidal particles. The capability of this technique for sorting and organizing colloidal particles of a particular diameter from a mixture of microspheres is demonstrated.     

High-throughput determination of seven trace elements in food samples by inductively coupled plasma-mass spectrometry

A method was developed for high-throughput determinations of 7 elements in food samples, namely antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and tin (Sn). The samples were digested by closed-vessel microwave-assisted digestion using concentrated nitric acid (HNO3) as the medium, followed by microwave- assisted evaporation to concentrate the sample solutions before dilution to the desired volume. The microwave-assisted evaporation procedure effectively reduced the final acid concentration to around 8% before analysis by inductively coupled plasma-mass spectrometry (ICP-MS). This reduction allows determination by ICP-MS to proceed without further sample dilution, which would affect the detection limit. The method was validated, and method recoveries for As, Cd, Cr, Pb, and Hg were within the certified ranges of the chosen certified reference materials. Recoveries of the 7 elements from spiked samples ranged from 93.1 to 103.6%. The standard uncertainties of precision for the 7 elements were between 3.1 and 4.3%. Interlaboratory comparison studies for As, Cd, and Pb gave z-scores ranging from -0.2 to 0.3.     

High frequency formulation for the acoustic power spectrum due to cascade-turbulence interaction

This paper investigates the noise radiated by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. An analytic formulation for the spectrum of acoustic power of a two-dimensional flat-plate is derived. The main finding of this paper is that the acoustic power spectrum from the cascade of flat airfoils may be split into two distinct frequency regions of low frequency and high frequency, separated by a critical frequency. Below this frequency, cascade effects due to the interaction between neighboring airfoils are shown to be important. At frequencies above the critical frequency, cascade effects are shown to be relatively weak. In this frequency range, acoustic power is shown to be approximately proportional to the number of blades. Based on this finding at high frequencies, an approximate expression is derived for the power spectrum that is valid above the critical frequency and which is in excellent agreement with the exact expression for the broadband power spectrum. The formulation is used to perform a parametric study on the effects on the power spectrum of the blade number, stagger angle, gap-chord ratio, and Mach number. The theory is also shown to provide a close fit to the measured spectrum of rotor-stator interaction.     

Determination of the hyperpolarizability components of hemicyanine dyes by measuring the anisotropic fluorescence and second harmonic of the dyes uniformly aligned within zeolite channels

A unidirectional ensemble of hemicyanine molecules was prepared by inserting the molecules into the vertical channels of a uniformly oriented zeolite (silicalite-1) film grown on a glass substrate. Fluorescence from this sample excited with light polarized along the vertical channel was 50 times larger than that excited with light polarized orthogonal to the vertical channel direction. These vertically aligned hemicyanine dyes were used to determine the ratio of the molecular hyperpolarizability components beta(zxx)/beta(zzz) of hemicyanine.     

Optical depth and multiple scattering depolarization in liquid clouds

In this paper, we calculate multiply scattered lidar signals with Monte Carlo method for measuring optical depth (extinction coefficient), effective size of water droplets, and liquid water content of clouds, and present algorithms that implement our method. We calculated multiply scattered lidar signals for various water droplet sizes and liquid water contents using a Monte Carlo method. A simple correspondence between water droplet optical depth and the degree of polarization in a modified gamma size distribution (C₁ cloud) is found. We also calculated the degree of polarization of a lidar signal for a given liquid water content, finding that the degree of polarization is only dependent on optical depth. Since the Raman lidar signal of liquid water depends on the total volume of the water droplet, the effective radius of the water droplet can thus be recovered from the degree of polarization of the lidar signal and the Raman signal of the liquid water.     

Simultaneous determination of water-soluble vitamins excreted in human urine after eating an overdose of vitamin pills by a HPLC method coupled with a solid phase extraction

We have applied a quick and convenient method for determining water-soluble vitamins excreted in human urine. We found that the Sep-Pak C(18) cartridge was useful for preconcentration and recovery of water-soluble vitamins in urine with minimized loss of vitamins. The recovery of vitamins was well over 90%. The separation was carried out by gradient elution with 90/10 (v/v%) methanol/water with 0.1% trifluoroacetic acid (TFA) and water with 0.1% TFA on a muBondapak C(18) column. The separation was completed within 15 min. We measured concentrations of water-soluble vitamins excreted in urine after swallowing an overdose of vitamin pills on purpose, and found that the concentration of each vitamin increased rapidly to the maximum in 2-3 h and decreased swiftly.