Size‐Specific Interactions Between Single‐ and Double‐Stranded Oligonucleotides and Cationic Water‐Soluble Oligofluorenes

An improved synthetic approach was developed for the synthesis of 1,4‐bis[9′,9′‐bis(6″‐(N,N,N‐trimethylammonium)‐hexyl)‐fluoren‐2′‐yl]benzene tetrabromide ( 1a ), 1,4‐bis[9′,9′;9″,9″‐tetra(6″′‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″‐bisfluoren‐2′‐yl] benzene octabromide ( 1b ) and 1,4‐bis[9′,9′;9″,9″;9″′,9″′‐hexakis(6″″‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″,7″,2″′‐trifluoren‐2′‐yl] benzene dodecabromide ( 1c ). These molecules provide a size‐specific series of water‐soluble oligofluorene molecules with increasing numbers of repeat units to model the interactions between cationic conjugated polymers and DNA. Fluorescence quenching and energy‐transfer measurements were performed with 1a – c and single‐stranded (ss) DNA and double‐stranded (ds) DNA, with and without fluorescein (Fl). These studies show that, on a per‐negative‐charge basis, ssDNA quenches the emission of 1a – c more effectively than dsDNA. Furthermore, we show that the energy‐transfer ratios dsDNA–Fl/ssDNA–Fl are dependent on the number of repeat units in 1a – c .     

Cholesterol in eggs from different species of poultry determined by capillary GLC

This study compared two methods of egg cholesterol extraction and determination by gas liquid chromatography (GLC), validated by comparison with standard reference material (SRM 1845). The two extraction procedures were of comparable accuracy with dried whole egg samples of 0·25–0·5 g, but the direct saponification method was rapid, reduced occupational hazard, and quantitative precision was within 2% coefficient of variation. The validated procedure was used to determine cholesterol in eggs of several domestic avian species. Eggs produced by commercial types of chicken (White Leghorn) had the lowest cholesterol (11·5–11·8 mg/g yolk) compared to 13·0, 14·6, 15·2, 15·6, 16·5, 16·8 and 18·1 mg/g for Rhode Island Red chicken, guinea fowl, New Hampshire chicken, duck, pea fowl, domestic turkey and wild turkey eggs, respectively. Yolk cholesterol concentration of commercial White Leghorn chicken eggs was not influenced by age. However, eggs from older birds contained about 23% more cholesterol on a per egg basis (220 versus 179 mg) because of the larger yolk.     

Influence of milk fat, milk solids, and light intensity on the light stability of vitamin A and riboflavin in lowfat milk

Retinyl palmitate and riboflavin were quantified in milk samples exposed to fluorescent light. Effects of compositional factors were determined by comparing rates of loss of riboflavin and vitamin A in milks with different amounts of milk fat and milk solids. Upon exposure to fluorescent light, rates of vitamin A and riboflavin loss were lower in whole milk than in skim milk. Riboflavin degraded more slowly in skim milk with 1% added nonfat dry milk than in skim milk with no added solids. No additional protective effect for riboflavin was found when added solids were increased from 1 to 3%. Compared with milk with no added solids, 1% added nonfat dry milk did not increased protection for vitamin A, but a protective effect was noted when the skim milk was fortified with 3% nonfat dry milk. Increasing light intensity increased the rates of loss of both vitamins, and riboflavin was lost at a greater rate.     

Residual-stress relaxation and densification in CO₂-laser-induced long-period fiber gratings

The first concurrent measurements of the three-dimensional refractive-index and residual-stress distributions in a CO₂-laser-irradiated fiber are presented. A Corning SMF-28 fiber was exposed from one side to focused pulses with durations of 100-500?ms. The cross-sectional form of the index modulation is asymmetric with changes concentrated on the side of the fiber facing the exposure. The longitudinal form is Gaussian-like with a wide top and extends approximately 100 μm from the center of the exposure. Relaxation of frozen-in viscoelasticity results in a maximum index modulation of 5×10^-4 on the side of the fiber facing the exposure with mechanical stress relaxation contributing changes of less than 1×10^-4.     

The corrosion of INCONEL alloy 740 in simulated environments for pulverized coal-fired boiler

The corrosion of a new nickel base superalloy, INCONEL alloy 740, has been studied at 550 and 700 °C on exposure to the synthetic coal ash/flue gas environments by means of XRD, SEM, and EDX. Low temperature hot corrosion of the new alloy occurred at two temperatures. The corrosion started to form the thin Cr₂O₃ scale on the alloy at 550 °C and developed as pitting attack resulted from sulfidation. The frontal attack at 700 °C consisted of two successive stages in which the corrosion mechanism started from the sulfidation and ended up in the fluxing of oxide. The compact and protective Cr₂O₃ scale formed and the internal sulfidation took place during the initial stage. The severe hot corrosion occurred due to the presence of the molten CoSO₄ during the propagation stage. The loose and porous outer layer and the compact inner layer consisted of spinels and oxides, respectively. The sulfides of Cr, Ti, and Nb formed on the front of oxide scale and in Cr-depletion zone. The rapid degradation of corrosion resistance of the alloy can be attributed to the dissolution of both cobalt and cobalt oxide on the surface. The alloy of 25% Cr exhibited better resistance to coal ash/flue gas corrosion as compared to the alloy of 23% Cr in the present case.     

Hypoxia Inhibits Subretinal Inflammation Resolution Thrombospondin-1 Dependently

Hypoxia is potentially one of the essential triggers in the pathogenesis of wet age-related macular degeneration (wetAMD), characterized by choroidal neovascularization (CNV) which is driven by the accumulation of subretinal mononuclear phagocytes (MP) that include monocyte-derived cells. Here we show that systemic hypoxia (10% O₂) increased subretinal MP infiltration and inhibited inflammation resolution after laser-induced subretinal injury in vivo. Accordingly, hypoxic (2% O₂) human monocytes (Mo) resisted elimination by RPE cells in co-culture. In Mos from hypoxic mice, Thrombospondin 1 mRNA (Thbs1) was most downregulated compared to normoxic animals and hypoxia repressed Thbs-1 expression in human monocytes in vitro. Hypoxic ambient air inhibited MP clearance during the resolution phase of laser-injury in wildtype animals, but had no effect on the exaggerated subretinal MP infiltration observed in normoxic Thbs1^−/−-mice. Recombinant Thrombospondin 1 protein (TSP-1) completely reversed the pathogenic effect of hypoxia in Thbs1^−/−-mice, and accelerated inflammation resolution and inhibited CNV in wildtype mice. Together, our results demonstrate that systemic hypoxia disturbs TSP-1-dependent subretinal immune suppression and promotes pathogenic subretinal inflammation and can be therapeutically countered by local recombinant TSP-1.     

Quantum-well infrared photodetector structure synthesis: methodology and experimental verification

A numerical method for global optimization of quantum-well infrared photodetector (QWIP) performance parameters is presented and experimentally verified. The single-band effective-mass Schroedinger equation is solved by employing the argument principle method (APM) to extract both the bound and quasibound eigen-energies of the quantum heterostructure. APM is combined with a simulated annealing algorithm to determine a set of device design parameters such as potential barrier height V/sub i/, layer thickness d/sub i/, number of material layers N, total device length, applied bias V/sub Bias/ etc., for which the QWIP performance is within a predetermined convergence criterion. The method presented incorporates the effect of energy-dependent effective mass of electrons in nonparabolic conduction bands. The present model can handle many optimization parameters and can incorporate fabrication constraints to achieve physically realizable devices. In addition, the method is not limited to the optimization of absorption structures, and can be used for other intersubband devices such as electron-wave Fabry-Perot filters and quantum-cascade lasers. The strength and versatility of the present method are demonstrated by the design of a bicolor equal-absorption-peak QWIP structure, and experimental verification of the zero-bias absorption spectrum is presented.     

Diffraction of ballistic electrons by semiconductor gratings:Rigorous analysis, approximate analyses, and device design

A rigorous coupled-wave analysis is developed to model ballistic electron diffraction by semiconductor gratings with periodic effective mass and for potential energy variations. This analysis includes expressions for diffracted angles, evanescent and propagating orders, the Bragg condition, and diffraction efficiencies. Two approximate diffraction regimes, Bragg and Raman-Nath, are defined in which the rigorous coupled-wave equations (RCWEs) can be solved analytically, and the approximations required, the approximate solutions, and the restrictions placed on the grating parameters for each regime are given. It is shown that both the Bragg regime and the Raman-Nath regime are achievable with physically fabricated semiconductor grating structures. In addition, it is shown that both narrow and broad angular and energy selectivities can be achieved through control of the effective thickness of the grating. These results are used in the design of a two-dimensional electron gas (2-DEG) switch and a 2-DEG broadcast device     

The localization model of rubber elasticity and the stress-strain behavior of a network formed by cross-linking a deformed melt

This paper examines the copolymerzation of methyl acrylate (MA) and isobutylene (IB) with a complexed initiating system of AlEtCl₂ and benzoyl peroxide (BPO). The effects of monomer ratio, monomer concentration, initiator composition and polymerization conditions on copolymer composition, degree of alternation, intrinsic viscosity and conversion were studied. An alternating copolymer was obtained when the [IB] / [MA] mole ratio was equal or greater than one.