A new cationic poly(ester-anhydride): Synthesis, structure characterization, and biological properties

To improve the cytotoxicity and biocompatibility of cationic polymers used as gene carriers, new cationic poly(ester-anhydride) copolymers (Pea-PAs) bearing a quaternary ammonium group in the backbone were synthesized through a reaction between an aminoester dicarboxylic acid with a tertiary amine in the backbone and excess acetyl chloride. Their structure was characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectrometry (FTIR), and gel permeation chromatography (GPC). They degraded hydrolytically in 20 mM HEPES buffer at pH 7.4 at 37°C with a half-life of more than 70 h. Their cytotoxicity was substantially lower than that of PEI. The blood clotting index (BCI) and haemolysis ratio (HR) also showed that these newly synthesized Pea-PA polymer are biopolymers with good blood compatibility.     

A simple model for a two-stage chemical reaction with diffusion

We analyse the evolution of a two-stage chemical reaction betweentwo neighbouring plumes of reactants. Under the assumption thatthe plumes are approximately Gaussian we derive a system ofordinary differential equations for the total amount, the centroidand the variance of each reactant. We compare the solution ofthese equations with full numerical simulation of the reaction.Excellent agreement is obtained, with solution of the near-Gaussianmodel requiring considerably less computational effort thanthe full simulations. Of key importance is the yield of thereaction, and we discuss this feature in particular.     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.     

Morphology of epoxy/acrylic polymer‐dispersed liquid‐crystal film in DICY thermal cure

A polymer‐dispersed liquid‐crystal (PDLC) film was prepared from UV‐curable acrylic, thermally curable epoxy, and a liquid‐crystal (LC) mixture with a fixed LC content of 40 wt %. The UV irradiation and heat treatments were in sequential steps. At first, a phase diagram of a binary mixture of LC (E63) and epoxy [diglycidyl ether of polypropylene glycol (DER736)] was established to understand their miscibility. Then, the phase‐separation temperatures and morphologies of pre‐UV‐cured films with different equivalent DER736/dicyandiamide (DICY) molar ratios were observed. Finally, the polymerization‐induced phase‐separation behavior and morphology of the PDLC film were studied by real‐time observation while the film was maintained at 130 °C under the microscope. The results showed that the acrylic network would not affect the phase‐separation behavior of the E63/DER736 mixture. In both thermally induced and polymerization‐induced phase separations, the undissolved DICY particles acted as nucleation agents and were capable of inducing E63 to separate out early. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2033–2042, 2000     

空气中激光烧蚀Cu产生等离子体发射光谱的研究

利用Q-开关Nd:YAG激光器产生的1.06 μm、10 ns的脉冲激光聚焦在空气中的Cu靶上,观测了激光诱导的Cu等离子体发射光谱.采用不同的激光能量,分析了波长范围为440 nm到540 nm的空间分辨发射光谱.在局部热力学平衡(LTE)条件近似下,根据谱线的相对强度,得到了等离子体电子温度约在104 K以上,给出了靶面附近电子温度的空间演化规律,并探讨了N(Ⅱ)500.52 nm谱线的谱线强度和半高全宽随激光能量的变化规律.     

Steering in computational science: Mesoscale modelling and simulation

This paper outlines the benefits of computational steering for high performance computing applications. Lattice-Boltzmann mesoscale fluid simulations of binary and ternary amphiphilic fluids in two and three dimensions are used to illustrate the substantial improvements which computational steering offers in terms of resource efficiency and time to discover new physics. We discuss details of our current steering implementations and describe their future outlook with the advent of computational grids.     

Methylammonium formate as a mobile phase modifier for totally aqueous reversed-phase liquid chromatography

Although alkylammonium ionic liquids (ILs) such as ethylammonium nitrate and ethylammonium formate have been used as mobile phase "solvents" for liquid chromatography (LC), we have shown that the IL methylammonium formate (MAF), in part because of its lower viscosity as compared to other ILs, can be an effective replacement for methanol (MeOH) in reversed-phase LC. Plots of log retention factor versus the fraction of MeOH and MAF in the mobile phase indicate quite comparable solvent strength slope values of 2.50 and 2.05, respectively. Using a polar endcapped C18 column, furazolidone and nitrofurantoin using 20% MAF-80% water could be separated in 22 min but no baseline separation is possible using MeOH as the modifier, even down to 10%. Suppression of silanol peak broadening effects by MAF is important, permitting a baseline separation of pyridoxine, thiamine, and nicotinamide using 5% MAF-95% water at 0.7 mL/min. Using 5% MeOH-95% water, severe peak broadening for thiamine is evident. The compatibility of MAF as a mobile phase modifer at the 5% level for LC with mass spectrometry detection of water-soluble vitamins is also shown.     

High-speed vertical-cavity surface-emitting laser (VCSEL) absorption spectroscopy of ammonia (NH<Subscript>3</Subscript>) near 1.54 μm

A single-frequency VCSEL has been used for the first time for high-resolution spectroscopy near 1.5 μm. The incorporated buried-tunnel-junction technology enabled the realization of a long-wavelength InGaAlAs/InP VCSEL with low threshold current (0.925 mA), high output powers (0.576 mW) and low series resistance (60 Ω). The high-speed tuning capability of the long-wavelength VCSEL was investigated and used to conduct high-speed absorption spectroscopy. The peak tuning speed was measured to be 3.4 cm^-1/μs and a 4.5-cm^-1-wide NH₃ spectrum was recorded in 2 μs. The VCSEL was used to measure highly resolved low-pressure spectra for pressures ranging from 9.6 mbar to 1 bar. The measured Doppler-broadened linewidth of 0.02 cm^-1 agrees within 3% with the theoretical calculations. The availability and various advantages of 1.3–2-μm single-frequency VCSELs as compared to edge-emitting diode lasers, such as a large current tuning range even at very high tuning frequencies, and low production costs, should significantly expand the application fields for near-infrared laser gas sensors. Received: 17 July 2002 / Revised version: 4 December 2002 / Published online: 12 May 2003 RID="*" ID="*"Corresponding author. Fax: +43-1/58801-15999, E-mail: Gerhard@Totschnig.com     

Laryngeal Mechanisms During Human 4-kHz Vocalization Studied With CT, Videostroboscopy, and Color Doppler Imaging

The objective of this study was to investigate the underlying laryngeal mechanisms during the specific human 4-kHz vocalization. The laryngeal configuration during this vocalization was measured using high-resolution computerized tomographic scan and videostrobolaryngoscopy. The color Doppler imaging (CDI) of medical ultrasound was used to detect the vibrations of glottal and supraglottal mucosa. During the 4-kHz vocalization, the ventricular folds were adducted in the shape of a bimodal chink and the vocal folds were shaped as a "V" with an opening at the posterior glottis. In the coronal view, the laryngeal ventricles had collapsed and a divergent shaped conduit was observed at the posterior portion of the larynx. The surface mucosa vibration detected by CDI was noted over the bilateral ventricular folds and aryepiglottic folds. The vibration displacement was estimated to be on the order of 0.1mm. This vibration amplitude was too small to be detected in videostrobolaryngoscopy. The laryngeal configuration and CDI data suggested a diffuser jet with periodic vorticity bursts in the larynx producing 4 kHz voice.