Enlarging the library of poly‐(L‐lysine citramide) polyelectrolytic drug carriers

Poly‐(L ‐lysine citramide) is a degradable drug carrier of the polyelectrolyte type that is composed of citric acid and L ‐lysine building blocks. In a previous work, poly‐(L ‐lysine citramide) was synthesized by the interfacial polycondensation of α‐hydroxy acid protected citryl dichloride with COOH‐protected lysine diamine. Because of head‐to‐head and head‐to‐tail and tail‐to‐tail linkages in the chains as well as various side reactions such as deprotection of the α‐hydroxy acid moieties and intramolecular imide ring formation, a very large family of degradable polyelectrolyte copolymers was obtained. All the members of this family hydrolytically degrade to the same end products. In this study, another route was explored based on the polycondensation of α‐hydroxy acid protected citric acid pentafluorophenyl diesters, namely, citrobenzal dipentafluorophenyl and citrochloral dipentafluorophenyl with N‐N′‐trimethylsilylated COOH‐protected L ‐lysine. The resulting polymers were characterized by IR, NMR, and size exclusion chromatographic analyses. The resulting chain structures and repeat units were identified from these characterizations and are discussed as compared with characteristics exhibited by analogous polymers resulting from interfacial polycondensation. Differences observed at the intermediate stage involving protected polymers were largely erased during the final deprotection stage because of imide formation during final hydrolysis under the selected conditions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3475–3484, 2001     

Sway Reduction on Container Cranes Using Delayed Feedback Controller

Traditionally, container cranes are modeled as a simple pendulum, witheither a flexible or a rigid hoisting cable, and a lumped mass at theend of that cable. In the case of large container cranes, the actualconfiguration of the hoisting mechanism is significantly different. Itconsists typically of an arrangement of four hoisting cables, which arehoisted from four different points on the trolley and attached on theload side to four points on a spreader bar used to lift containers.Thus, the dynamics of the actual container-crane hoisting assembly isdifferent from that of a simple pendulum. A controller design based onthe actual model is more likely to result in an improved response. Inthis work, a mathematical model of the actual container crane isdeveloped. Then, a simplified version of this model is used to calculatethe gain and delay for the delay controller developed earlier. Numericalsimulations are performed by applying the delay controller to the fullnonlinear model of the container crane.     

External energy transfer in amplified spontaneous emissions from MEH-PPV conjugated polymer

We observed amplified spontaneous emissions (ASEs) in solutions of conjugated polymer under high power neodymium-doped yttrium aluminum garnet (Nd:YAG) laser excitation. A solution of coumarin-485 dye (C₄₈₅) and conjugated polymer (MEH-PPV) was prepared in tetrahydrofuran (THF). Here, C₄₈₅ acted as a donor (with different ratios) while MEH-PPV served as an acceptor (with a constant ratio). Without the donor, MEH-PPV exhibited ASE only in the excimeric state; with the donor, however, it produced ASE in both the monomeric and excimeric states simultaneously. These results clearly show that it is possible to monitor and manipulate the excited state behavior of molecules by using an energy transfer process using laser-excited conjugated polymer.     

Surface plasmons reveal spin crossover in nanometric layers

Nano-objects and thin films displaying molecular spin-crossover phenomena have recently attracted much attention. However, the investigation of spin crossover at reduced sizes is still a big challenge. Here we demonstrate that surface plasmon polariton waves propagating along the interface between a metal and a dielectric layer can be used to detect the spin-state changes in the latter with high sensitivity, even at the nanometer scale.     

Photonic band-gap enhanced second-harmonic generation in a planar lithium niobate waveguide

Enhanced second-harmonic generation (SHG) conversion efficiency was theoretically predicted in waveguide geometry with coupling to a one-dimensional grating photonic band gap (PBG). We report a series of experiments using samples made with lithium niobate. A waveguide was fabricated near the surface by applying the proton-exchange technique. The characteristics of waveguide modes were determined by several techniques: prism coupling, diffraction, and Cherenkov radiation. The WKB method was used to analyze the results. Ultraviolet laser lithography was applied to make PBG gratings on the sample. We further investigated Cherenkov second-harmonic generation (CSHG), i.e., SHG radiated into the substrate, under the condition of a band-edge PBG resonance in the waveguides. The SHG inside planar waveguides was also experimentally investigated. We fabricated waveguides with multiple pump modes and found that the second mode was more efficient in enhancing the second harmonic signal. This result is explained by our model. Several samples were investigated in detail; the highest conversion efficiency of CSHG with a PBG was enhanced around 50 times above the CSHG signal without a PBG. A numerical model was constructed with parameters calculated from our sample characterization data to interpret the experimental results.     

Application of heat pipe technology in thermal analysis of metals

Summary Thermal analysis has been used in foundry applications to assess the quality of the melt before casting. The high-end thermal analysis techniques such as DSC or DTA are expensive and not suitable for foundry applications. The Computer-Aided Cooling Curve Analysis (CA-CCA) method based on one thermocouple has been widely used as a batch process with poor control over heat extraction and cooling rates during solidification. A heat pipe apparatus has been developed as a thermal analysis tool. The apparatus can assess the melt quality more accurately, as well as, allow for better control of heating and cooling rates. Moreover, the solidification process can be modeled more accurately, and thus the casting parameters affecting the casting quality can be closely simulated and consequently controlled. In this paper the principles of a heat-pipe assisted thermal analysis system are highlighted. The advantages of the new system are described and the possibility of its adoption in melt assessments is discussed.     

Design and Development of D‒α‒Tocopheryl Polyethylene Glycol Succinate‒block‒Poly(ε-Caprolactone) (TPGS−b−PCL) Nanocarriers for Solubilization and Controlled Release of Paclitaxel

The objective of this study was to synthesize and characterize a set of biodegradable block copolymers based on TPGS-block-poly(ε-caprolactone) (TPGS-b-PCL) and to assess their self-assembled structures as a nanodelivery system for paclitaxel (PAX). The conjugation of PCL to TPGS was hypothesized to increase the stability and the drug solubilization characteristics of TPGS micelles. TPGS-b-PCL copolymer with various PCL/TPGS ratios were synthesized via ring opening bulk polymerization of ε-caprolactone using TPGS, with different molecular weights of PEG (1–5 kDa), as initiators and stannous octoate as a catalyst. The synthesized copolymers were characterized using ¹H NMR, GPC, FTIR, XRD, and DSC. Assembly of block copolymers was achieved via the cosolvent evaporation method. The self-assembled structures were characterized for their size, polydispersity, and CMC using dynamic light scattering (DLS) technique. The results from the spectroscopic and thermal analyses confirmed the successful synthesis of the copolymers. Only copolymers that consisted of TPGS with PEG molecular weights ≥ 2000 Da were able to self-assemble and form nanocarriers of ≤200 nm in diameter. Moreover, TPGS₂₀₀₀-b-PCL₄₀₀₀, TPGS₃₅₀₀-b-PCL₇₀₀₀, and TPGS₅₀₀₀-b-PCL₁₅₀₀₀ micelles enhanced the aqueous solubility of PAX from 0.3 µg/mL up to 88.4 ug/mL in TPGS₅₀₀₀-b-PCL₁₅₀₀₀. Of the abovementioned micellar formulations, TPGS₅₀₀₀-b-PCL₁₅₀₀₀ showed the slowest in vitro release of PAX. Specifically, the PAX-loaded TPGS₅₀₀₀-b-PCL₁₅₀₀₀ micellar formulation showed less than 10% drug release within the first 12 h, and around 36% cumulative drug release within 72 h compared to 61% and 100% PAX release, respectively, from the commercially available formulation (Ebetaxel^®) at the same time points. Our results point to a great potential for TPGS-b-PCL micelles to efficiently solubilize and control the release of PAX.     

Effect of electromagnetic actuations on the dynamics of a harmonically excited cantilever beam

The influence of electromagnetic actuators (EMAs) on the frequency response of a harmonically excited cantilever beam is investigated analytically, numerically and experimentally in this paper. Specifically, the intensity of the current generating the EMAs force is varied and its effect on the dynamic behavior of the system is analyzed. Analytical treatment based on perturbation analysis is performed on a simplified equation modeling the one mode vibration of the cantilever beam. Results indicated that EMAs produce a softening behavior in the system. Further, it is shown that as the current intensity of EMAs increases, the resonance curve shifts toward smaller values of frequency and the non-linear characteristic of the system becomes softer. The analytical predictions have been verified numerically and confirmed experimentally using a test rig.     

A simple Abel inversion method of interferometric data for temperature measurement in axisymmetric medium

In this work, we describe a simple method of Abel inversion for temperature measurement in a natural convection axisymmetric flow. The essence of the method is that the measured lateral fringe shift profile is fitted with a polynomial with only even powers and then Abel inverse integral is evaluated analytically. This technique is compared with recent existing methods to test the accuracy and error propagation using a simulated interferogram of natural convection flow below a downward-facing heated horizontal disk in air. For this comparison, lateral fringe profiles are simulated using temperature fields computed by solving Navier Stokes and energy equations. Through random-number generation, noise profile is artificially added to the simulated noise-free lateral fringe shift profile. The results showed that the proposed technique for Abel inversion leads to accurate temperature profiles when the lateral fringe shift profile is fitted with even-power polynomials having degrees ranging from 20 to 30.