Analysis of photoinitiated polymerization in a membrane mimetic film using infrared spectroscopy and near-IR Raman microscopy

A method has been developed to investigate the extent of polymer cross-linking that results following in situ photopolymerization of an acrylate-functionalized phospholipid assembly adsorbed onto a stabilized, membrane-mimetic film produced from a polyelectrolyte multilayer (PEM) on polytetrafluoroethylene (PTFE) grafts. The acrylate phospholipid monomer was synthesized, prepared as a unilamellar vesicle, and fused onto closed-packed acyl chains that make up the PEM membrane-mimetic barrier on the PTFE graft. Both broad band white light and 514.5 nm laser radiation were used as excitation sources for photoinitiation; eosin Y was used as the photoinitiator. The use of 514.5 nm excitation reduced the time for maximum polymerization of the acrylate lipid from 60 min to 240 s. Infrared spectroscopy was successfully used to analyze the extent of photopolymerization in simplified model acrylate lipid systems; however, this method could not be used to analyze acrylate polymerization in heterogeneous, multicomponent PEM membrane-mimetic barriers on PTFE grafts. A near-infrared Raman microscopy method based on the ratio of the integrated areas of the CC and CN vibrations was shown to provide equivalent information to the IR method for analysis of the extent of polymerization efficiency in acrylate lipids. In addition, it proved feasible to extend this near-IR Raman method to the in situ analysis of the extent of polymerization in a stabilized acrylate lipid membrane on a PEM film in a PTFE vascular graft. This work describes a new approach for generating and analyzing the robustness of a membrane-mimetic coating on biomaterial surfaces, and may improve our ability to predict the long-term stability of polymeric membrane-mimetic films on implantable medical devices.     

Vibrational spectral studies of L-citrullinium perchlorate

Infrared and Raman spectra of L-citrullinium perchlorate crystals have been recorded at room temperature. The vibrational assignments of the observed wavenumbers are proposed on the basis of group theoretical analysis. The presence of carbonyl group indicates that the molecule exists in the ionic form. The shifting of stretching and bending wavenumbers indicates the presence of extensive hydrogen bonding in the crystal. The anion fundamentals however continue to be degenerated. This suggests that its symmetry is not affected in the crystal.     

Vibrational spectroscopic studies of (3-mercaptopropyl)trimethoxylsilane sol-gel and its coating

Organosilane sol-gels have been prepared under different conditions from mercaptopropyltrimethoxysilane (MPTMS) and mercaptopropyltriethoxysilane (MPTES). These sol-gels were applied for the thin film coating on aluminum. Vibrational spectroscopy has been employed to trace and to study the proceeding of the sol-gel formation and the curing of the coated films on Al. Based on the group frequencies as well as their spectral behavior under different conditions, vibrational assignments have been made for most of the observed bands. Surface enhanced Raman scattering has revealed the chemical adsorption of MPTMS sol-gel on silver particles. Recorded reflection and absorption infrared (RAIR) spectra of coated tiles cured at different temperatures have indicated that surface reaction may occur at high temperature. The anticorrosion characters of the coated metals have been evaluated with the measured electrochemical data. Results from cyclic voltammographs have indicated that each layer of sol-gel coating would reduce the redox current across the electrode/electrolyte solution interface. Tafel plots have shown that the anodic current of the coated electrode decreases significantly and the corrosion potentials shift to the positive side.     

Asymptotic Analysis for Random Walks with Nonidentically Distributed Jumps Having Finite Variance

Let ξ₁,ξ₂,... be independent random variables with distributions F₁F₂,... in a triangular array scheme (F _i may depend on some parameter). Assume that Eξ _i = 0, Eξ _i ² < ∞, and put \(S_n = \sum {_{i = 1}^n \;} \xi _i ,\;\overline S _n = \max _{k \leqslant n} S_k\). Assuming further that some regularly varying functions majorize or minorize the “averaged” distribution \(F = \frac{1}{n}\sum {_{i = 1}^n F_i }\), we find upper and lower bounds for the probabilities P(S _n > x) and \(P(\bar S_n > x)\). We also study the asymptotics of these probabilities and of the probabilities that a trajectory {S _k } crosses the remote boundary {g(k)}; that is, the asymptotics of P(max_k≤n(S _k ? g(k)) > 0). The case n = ∞ is not excluded. We also estimate the distribution of the first crossing time.     

On the Functions on Linear Spaces

In this paper are considered the authors results that have been received in the last few years and are devoted to the research of functions mapping a finite linear space to itself. The characteristics of functions representing interest from the point of view of cryptography, geometrical properties of functions are resulted. This research is supported by RFFI (grants 99-01-00929 and 99-01-00941).Mathematics Subject Classifications (2000) 51E15, 51E20.     

Beeinflussung der Turbulenzstruktur in der ebenen Mischungsschicht zweier Ströme durch Polymerzusätze

Zusammenfassung Ausgehend von der Frage, ob beim Phänomen der Widerstandsverminderung (Toms-Effekt) die Wirkung der Polymeren nur auf die Strömung in den wandnahen Bereichen beschränkt ist oder eine solche auch in wandferneren Gebieten gefunden werden kann, hat die vorliegende Untersuchung zum Ziel, den Einfluß derartiger Zusätze in der sog. Freien Turbulenz zu analysieren, bei denen also keine Wechselwirkungen mit festen Wänden vorhanden sind. Als besonders einfaches Beispiel einer solchen Strömung wurde diejenige in einer ebenen turbulenten Mischungsschicht ausgewählt, die sich zwischen zwei mit verschiedener Geschwindigkeit bewegten Parallelströmen ausbildet. In derartigen Strömungen existiert eine charakteristische Wirbelstruktur, die von einer turbulenten Mikrostruktur überlagert wird, und es sollte untersucht werden, wie diese Strukturen sich bei Zugabe von widerstandsvermindernden Polymeren ändern.Als Untersuchungsmethode wurde die raum-zeitliche Korrelationsanalyse mittels Laser-Doppler-Anemometern verwendet. Da aber die bekannten Systeme hierfür nur bedingt einsetzbar sind, wurde eine für diesen Zweck besser geeignete optische Anordnung neu entwickelt.Als wichtigstes Ergebnis wurde gefunden, daß durch den Polymerzusatz die Intensität und die Kohärenzlänge der turbulenten Makrostrukturen erheblich anwachsen, wohingegen die turbulenten Mikrostrukturen weitgehend unterdrückt werden. Größe und Abstand der Wirbel werden zwar verkleinert, doch wird ihre Aufeinanderfolge vergleichmäßigt, und ihre Lebensdauer nimmt entsprechend zu. Weiter wurde nachgewiesen, daß die mit der Polymerzugabe verbundene Viskositätserhöhung nicht die Hauptursache für diese Effekte sein kann, da solche bei newtonschen Flüssigkeiten mit vergleichbarer Viskosität längst nicht in so ausgeprägter Weise auftreten.Das ebenfalls beobachtete verringerte Dickenwachstum vor allem im Anfangsbereich der Mischungsschicht in Verbindung mit einer Verstärkung der Intensität der langsameren turbulenten Längsschwankungen legt die Deutung nahe, daß durch die Hauptströmung infolge Entknäuelung und Orientierung der Polymermolekeln eine Fließanisotropie erzeugt wird. Dagegen läßt sich die Verlangsamung des Wirbelwachstums und die Unterdrückung der Mikroturbulenz am ehesten durch die Behinderung lokaler Dehnströmungen infolge einer stark erhöhten Dehnviskosität erklären. Die Vorstellung, daß bei den Austauschvorgängen in einer freien turbulenten Mischungsschicht die Flüssigkeitseigenschaften keine Rolle spielen, ist somit durch diese Untersuchung als zumindest für viskoelastische Flüssigkeiten nicht zutreffend nachgewiesen worden.

---

An important question concerning the phenomenon of drag reduction (Toms effect) is whether the influence of polymer additives is restricted to regions near the wall or whether it also extends to the core. Therefore the aim of the present investigation was to analyse the influence of such additives on socalled free turbulence in which there are no interactions with rigid walls. A plane turbulent mixing layer formed between two parallel streams moving with different velocities was chosen as a particularly simple example of such a flow. There exists in these flows a characteristic vortex structure with a superimposed turbulent micro-structure. The influence on these structures of an addition of drag reducing polymers was investigated.Space-time correlation analysis using Laser-Doppler Anemometry was chosen as the technique for investigating the turbulent flow field. Because commercially available systems are not particularly well suited for such measurements, a special optical arrangement was developed.The most important result was that the polymer additive significantly raised the intensity and coherence length of the turbulent macro-structure whereas the turbulent micro-structure was strongly attenuated. The size and separation of the vortices were decreased but their occurrence became more regular and their lifetimes increased. Furthermore it was demonstrated that the viscosity increase associated with the addition of polymer could not be the main reason for these effects, as such effects were far less pronounced in Newtonian liquids of comparable viscosity.The slower growth in the thickness of the mixing layer, observed particularly in the initial region, as well as the increase in the intensity of the slower longitudinal turbulent fluctuations suggest that the main flow induces a flow anisotropy as a result of uncoiling and orientation of the polymer molecules. On the other hand the decrease in the vortex growth rate and the suppression of the micro-turbulence can best be explained by a hindrance of local extensional flows resulting from a strong increase in the extensional viscosity. The notion that fluid properties do not play a role in the process of momentum exchange in a free turbulent mixing layer has been shown by these investigations to be inappropriate at least for viscoelastic liquids.

Von der Abteilung Chemietechnik der Universität Dortmund genehmigte Dissertation; auszugsweise vorgetragen auf der Jahrestagung der Deutschen Rheologischen Gesellschaft in Aachen vom 5.–7. März 1979 und auf dem VIII. Internationalen Rheologie-Kongreß in Neapel vom 1.–5. September 1980.     

对线性规划单纯形法的注记

为了更有效地应用单纯形算法求解线性规划问题,本文提出了以下几点注记。(1)人工变量列不必参与数值计算,也不占存储空间,从而可大量节省计算量和存储量;(2)使用基变量指标集来判断人工变量是否离基,可避免舍人误差的影响;(3)虚设人工变量的最终非零值对于修改存在矛盾的数学模型将起着关键性作用;(4)可将大M法与两阶段法统一处理,且M可不取具体的数值,也不参与数值计算;(5)实际计算中宜将Dantzig算法与Bland算法结合起来使用,既可对一般问题达到快速收敛的目的,又可避免退化问题可能产生的循环现象,而且在软件设计与实现上要比字典序方法等简单容易;(6)对于大型稀疏矩阵的计算机数据录入,建议采用二元数组的数据结构逐行录入,则可节省三分之一的录入工作量。     

Frequency doubling of a fibre-amplified 1083 nm DBR laser

A good frequency standard is required at 1083 nm for measurements on the fine structure of helium and of the fine structure constant. Several milliwatts of CW frequency-doubled light offers the prospect of stabilisation to a Doppler-free hyperfine transition in molecular iodine. The 1083 nm emission of an extended-cavity DBR diode laser has been amplified using an ytterbium-doped fibre amplifier, and applied to a type-I phase matched Mg:LiNbO₃ crystal in a high-Q fundamental-resonant cavity for frequency doubling. The amplifier gain at 1083 nm under typical operating conditions was 13.8 dB, with a coherent output power up to 63 mW, limited by the maximum signal input power. The doubling cavity Q was , and about 70% of the incident power was coupled in. The maximum 2nd-harmonic conversion efficiency exceeded 20% and provided an output power of 3.7 mW for making continuous frequency scans of up to 600 MHz in the green. An optical spectrum analyser at 541.5 nm showed fringes of 4.6 MHz full width half maximum, close to the instrumental width. Received: 25 February 1998 / Revised and Accepted: 28 May 1998     

A photodiode array detection system: Design concept and implementation

Summary Use of a linear photodiode array as the elemental detector for an HPLC UV/Visible detector can provide both quantitative and semi-qualitative information for the analytical chemist. This paper discusses the primary needs of the analyst, the goals to be achieved in hardware and software, and possible applications for such a detection system.