Near-infrared emission bands of Er-doped YAP and LSO crystals

The ground state absorption (GSA), photoluminescence (PL) and photoluminescence excitation (PLE) spectra for Er(1.0 at%):YAP and Er(0.5 at%):LSO were measured at room temperature. Based on the GSA spectra, the radiative transition rates and luminescence branch ratios of erbium ions were determined by the Judd-Ofelt (J-O) method. In the range of 1400-1700 nm Er(1.0 at%):YAP has intense absorption at 1509 nm (0.96×10⁻²⁰ cm²), which is almost two times larger than the peak absorption of Er(0.5 at%):LSO. From the PL and PLE spectra, four intense emission bands around 850 nm (⁴S_3/2→⁴I_13/2), 980 nm (⁴I_11/2→⁴I_15/2), 1230 nm (⁴S_3/2→⁴I_11/2) and 1520 nm (⁴I_13/2→⁴I_15/2) were observed. The stimulated emission cross-sections of the four bands were calculated by the Fuchtbauer-Ladenberg (F-L) equation. The results suggest that Er(1.0 at%):YAP has potential to realize laser oscillation at 858 nm because of the relatively large simulated emission cross-section (1.76×10⁻²⁰ cm²). The temperature dependences of the PL spectra for the two crystals were also investigated in the range of 290-12 K. The ∼1520 nm emission presents continuous increase with temperature, while the emissions around 850, 1230 and 980 nm firstly increase with temperature, then reach their own largest values at the transition temperatures (about 100 K), and finally decrease with temperature. These results were well interpreted by the temperature dependence of multi-phonon process.     

40 Gb/s, secure optical communication based upon fast reconfigurable time domain spectral phase en/decoding with 40 Gchip/s optical code and symbol overlapping

We propose and experimentally demonstrate a 40 Gb/s secure optical communication system with on-off-keying (OOK) modulation format by using a time domain spectral phase en/decoding scheme, which employs a highly dispersive element and high-speed phase modulator for introducing significant symbol overlapping for both the encoded and incorrectly decoded noiselike signals to enhance the information security against eavesdropping using a power detector. The influence of dispersion and chip modulation rate on the symbol overlapping of the incorrectly decoded signal has been analytically investigated and experimentally verified. Security enhancement for 40 Gb/s OOK data using fast reconfigurable 40 Gchip/s optical codes with code lengths of up to 1024 has been demonstrated and compared with a 10 Gb/s system.     

Curdlan as a Polymeric Starting Material to Access C6-Modified Glucose Derivatives

We evaluated the potential of a linear β-1,3-glucan (curdlan) as a starting material to access C6-modified glucose derivatives and found that 6-bromo-6-deoxyglucose, 6-azide-6-deoxyglucose, and 6-acetamido-6-deoxyglucose could be readily prepared from curdlan through its C6-selective and quantitative modifications and subsequent acid-catalyzed hydrolysis.     

On the volume and surface area of hyperbolic polyhedra

A truncated tetrahedron is a building block of hyperbolic 3-manifolds with totally geodesic boundary. We study the relation between the volume of a truncated tetrahedron and the area of its faces which form the boundary of manifolds.     

Discrimination Between 8‐Oxo‐2′‐Deoxyguanosine and 2′‐Deoxyguanosine in DNA by the Single Nucleotide Primer Extension Reaction with Adap Triphosphate

The adenosine derivative of 2‐oxo‐1,3‐diazaphenoxazine (Adap) exhibits a superb ability to recognize and form base pairs with 8‐oxo‐2′‐deoxyguanosine (8‐oxo‐dG) in duplex DNA. In this study, the triphosphate of Adap (dAdapTP) was synthesized and tested for single nucleotide incorporation into primer strands using the Klenow Fragment. The efficiency of dAdapTP incorporation into 8‐oxo‐dG‐containing templates was more than 36‐fold higher than with dG‐containing templates, and provides better discrimination than does the incorporation of natural 2′‐deoxyadenosine triphosphate (dATP). The selective incorporation of dAdapTP into 8‐oxo‐dG templates was therefore applied to the detection of 8‐oxo‐dG in human telomeric DNA sequences extracted from H₂O₂‐treated HeLa cells. The enzymatic incorporation of dAdapTP into 8‐oxo‐dG‐containing templates may provide a novel basis for sequencing oxidative DNA damage in the genome.     

Influence of RNA Strand Rigidity on Polyion Complex Formation with Block Catiomers

Polyion complexes (b‐PICs) are prepared by mixing single‐ or double‐stranded oligo RNA (aniomer) with poly(ethylene glycol)‐b‐poly(l ‐lysine) (PEG‐PLL) (block catiomer) to clarify the effect of aniomer chain rigidity on association behaviors at varying concentrations. Here, a 21‐mer single‐stranded RNA (ssRNA) (persistence length: 1.0 nm) and a 21‐mer double‐stranded RNA (small interfering RNA, siRNA) (persistence length: 62 nm) are compared. Both oligo RNAs form a minimal charge‐neutralized ionomer pair with a single PEG‐PLL chain, termed unit b‐PIC (uPIC), at low concentrations (<≈0.01 mg mL⁻¹). Above the critical association concentration (≈0.01 mg mL⁻¹), ssRNA b‐PICs form secondary associates, PIC micelles, with sizes up to 30–70 nm, while no such multimolecular assembly is observed for siRNA b‐PICs. The entropy gain associated with the formation of a segregated PIC phase in the multimolecular PIC micelles may not be large enough for rigid siRNA strands to compensate with appreciably high steric repulsion derived from PEG chains. Chain rigidity appears to be a critical parameter in polyion complex association.

     

The rheology of suspensions of vinylon fibers in polymer liquids. II. Suspensions in polymer solutions

Summary The rheological properties of vinylon fiber suspensions in polymer solutions were studied in steady shear flow. Shear viscosity, first normal-stress difference, yield stress, relative viscosity, and other properties were discussed. Three kinds of flexible vinylon fibers of uniform length and three kinds of polymer solutions as mediums which exhibited remarkable non-Newtonian behaviors were employed. The shear viscosity and relative viscosity ( _r ) increased with the fiber content and the aspect ratio, and depended upon the shear rate. Shear rate dependence of _r was found only in the low shear rate region. This result was different from that of vinylon fiber suspensions in Newtonian fluids. The first normal-stress difference increased at first slightly with increasing fiber content but rather decreased and showed lower values for high content suspensions than that of the medium. A yield stress could be determined by using a modified equation of Casson type. The flow properties of the fiber suspensions depended on the viscosity of the medium in the suspensions under consideration.With 16 figures and 1 table     

Viscosity of particle filled polymer melts

Summary Viscosities of particle filled polymer melts were measured at fairly low shear rate. Particles were glass beads, glass balloons, and silas balloons. Polymers were polyethylene and polystyrene. Flow curves were superimposed with respect to concentration of filler. The relative viscosity defined as the ratio of viscosity of filled polymer to that of unfilled polymer at the same shear stress is obtained as an asymptotic value even for highly filled material. The relation between relative viscosity and volume fraction of filler was represented by the equations derived byMaron andPierce orMooney. Only the distribution of particle size had influence on relative viscosity at a defined filler concentration. Yield stresses were estimated, and found to increase exponentially in the range of volume fraction from 0.1 to 0.5.

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Zusammenfassung Viskositäten von Polymerschmelzen, die mit Teilchen gefüllt worden waren, wurden bei mittleren Schergeschwindigkeiten bestimmt. Als Teilchen wurden Voll- und Hohlkugeln aus Glas, sowie sog. silas balloons, als Polymere Polyäthylen und Polystyrol verwendet. Die Fließkurven für verschiedene Füllstoffkonzentrationen wurden überlagert. Die relative Viskosität, definiert als das Verhältnis der Viskositäten von gefülltem und ungefülltem Polymer bei gleicher Schubspannung, besitzt einen asymptotischen Wert selbst für hoch gefülltes Material. Die Beziehung zwischen relativer Viskosität und Füllstoff-Volumenkonzentration läßt sich durch eine vonMaron undPierce oder eine vonMooney abgeleitete Gleichung beschreiben. Nur die Teilchengrößenverteilung hat bei einer definierten Füllstoffkonzentration einen Einfluß auf die relative Viskosität. Fließspannungen werden abgeschätzt und dafür in einem Konzentrationsbereich zwischen 0,1 und 0,5 ein exponentieller Anstieg gefunden.

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With 13 figures and 2 tables     

Current developments and future trends in solid-phase microextraction techniques for pharmaceutical and biomedical analyses

Sample preparation is important for the isolation and concentration of desired trace components from complex matrices. Sample preparation is the most labor-intensive and error-prone process in analytical methodology, and greatly influences the reliable and accurate determination of analytes. The integration of sample preparation with various analytical instruments is most conveniently achieved by using microextraction techniques and/or microdevices. Solid-phase microextraction (SPME) is both simple and effective, enabling miniaturization, automation and high-throughput performance. Moreover, SPME has reduced analysis times, as well as the costs of solvents and disposal. This review describes current developments and future trends in novel SPME techniques, including fiber SPME, in-tube SPME and related new microextraction techniques. Especially innovative SPME approaches, including multi-well high-throughput sampling, ligand-receptor binding study for pharmacokinetics, direct in vivo sampling, chip-based microfluidic system, and new sampling techniques using intelligent carbon nanotube and temperature-response polymer in pharmaceutical and biomedical analysis are focused items.     

Differential Effects of Cold Exposure on Gene Expression Profiles in White Versus Brown Adipose Tissue

The thermogenic function of brown adipose tissue (BAT) is known to be markedly elevated when animals are exposed to the cold, and intensive studies have been carried out to understand the molecular basis enabling effective thermogenesis in cold-exposed animals. In this study, we used microarray analysis to examine the effects of cold exposure of animals on their gene expression profiles in white adipose tissue (WAT), which seems to function as a counterpart tissue of BAT. The results indicate that the effects of cold exposure on the gene expression profiles of WAT were much more moderate than the effects on those of BAT. Possible reasons for the different responses of BAT and WAT to cold exposure are discussed.