Development and Experimental Validation of a Dispersity Model for In Silico RAFT Polymerization

The exploitation of computational techniques to predict the outcome of chemical reactions is becoming commonplace, enabling a reduction in the number of physical experiments required to optimize a reaction. Here, we adapt and combine models for polymerization kinetics and molar mass dispersity as a function of conversion for reversible addition fragmentation chain transfer (RAFT) solution polymerization, including the introduction of a novel expression accounting for termination. A flow reactor operating under isothermal conditions was used to experimentally validate the models for the RAFT polymerization of dimethyl acrylamide with an additional term to accommodate the effect of residence time distribution. Further validation is conducted in a batch reactor, where a previously recorded in situ temperature monitoring provides the ability to model the system under more representative batch conditions, accounting for slow heat transfer and the observed exotherm. The model also shows agreement with several literature examples of the RAFT polymerization of acrylamide and acrylate monomers in batch reactors. In principle, the model not only provides a tool for polymer chemists to estimate ideal conditions for a polymerization, but it can also automatically define the initial parameter space for exploration by computationally controlled reactor platforms provided a reliable estimation of rate constants is available. The model is compiled into an easily accessible application to enable simulation of RAFT polymerization of several monomers

Well-defined networks from DGEBF - the importance of regioisomerism in epoxy resin networks

The previously ignored or unreported impact of regiosomerism within diglycidyl ether of bisphenol F (DGEBF) on its network properties is presented. Routes to the isomers of DGEBF were explored: high-performance liquid chromatography showed good separation of the three isomers [para–para-DGEBF (ppDGEBF), para–ortho-DGEBF (poDGEBF), and ortho–ortho-DGEBF (ooDGEBF)] with small yields; column chromatography gave good separation of pp- + po- from oo-DGEBF but pp-/po- separation was not achieved. Synthesis was optimized to crude yields of 76% for pp-; 87% for po-, and 86% for oo-. Subsequently, crosslinked networks were prepared with meta-xylylenediamine. With increasing ortho content, degradation of chemical resistance and an inherent weakening of the network was observed, that is, glass transition temperature (Tg), beta transition temperature (Tβ), density, crosslink density, and the desorption diffusion coefficient decreased, whereas sorption diffusion coefficient and ultimate solvent uptake increased. This clearly shows that a subtle chemical structure change can significantly impact network performance

Can inflationary models of cosmic perturbations evade the secondary oscillation test?

We consider the consequences of an observed Cosmic Microwave Background (CMB) temperature anisotropy spectrum containing no secondary oscillations. While such a spectrum is generally considered to be a robust signature of active structure formation, we show that such a spectrum {\em can} be produced by (very unusual) inflationary models or other passive evolution models. However, we show that for all these passive models the characteristic oscillations would show up in other observable spectra. Our work shows that when CMB polarization and matter power spectra are taken into account secondary oscillations are indeed a signature of even these very exotic passive models. We construct a measure of the observability of secondary oscillations in a given experiment, and show that even with foregrounds both the MAP and \pk satellites should be able to distinguish between models with and without oscillations. Thus we conclude that inflationary and other passive models can {\em not} evade the secondary oscillation test.Comment: Final version accepted for publication in PRD. Minor improvements have been made to the discussion and new data has been included. The conclusions are unchagne

Continuous-Flow Laboratory SAXS for In Situ Determination of the Impact of Hydrophilic Block Length on Spherical Nano-Object Formation during Polymerization-Induced Self-Assembly

In situ small-angle X-ray scattering (SAXS) is a powerful technique for characterizing block-copolymer nano-object formation during polymerization-induced self-assembly. To work effectively in situ, it requires high intensity X-rays which enable the short acquisition times required for real-time measurements. However, routine access to synchrotron X-ray sources is expensive and highly competitive. Flow reactors provide an opportunity to obtain temporal resolution by operating at a consistent flow rate. Here, we equip a flow-reactor with an X-ray transparent flow-cell at the outlet which facilitates the use of a low-flux laboratory SAXS instrument for in situ monitoring. The formation and morphological evolution of spherical block copolymer nano-objects was characterized during reversible addition fragmentation chain transfer polymerization of diacetone acrylamide in the presence of a series of poly(dimethylacrylamide) (PDMAm) macromolecular chain transfer agents with varying degrees of polymerization. SAXS analysis indicated that during the polymerization, highly solvated, loosely defined aggregates form after approximately 100 s, followed by expulsion of solvent to form well-defined spherical particles with PDAAm cores and PDMAm stabilizer chains, which then grow as the polymerization proceeds. Analysis also indicates that the aggregation number (Nagg) increases during the reaction, likely due to collisions between swollen, growing nanoparticles. In situ SAXS conducted on PISA syntheses using different PDMAm DPs indicated a varying conformation of the chains in the particle cores, from collapsed chains for PDMAm47 to extended chains for PDMAm143. At high conversion, the final Nagg decreased as a function of increasing PDMAm DP, indicating increased steric stabilization afforded by the longer chains which is reflected by a decrease in both core diameter (from SAXS) and hydrodynamic diameter (from DLS) for a constant core DP of 400

Guidelines for chemotherapy of biliary tract and ampullary carcinomas

Few randomized controlled trials (RCTs) with large numbers of patients have been conducted to date in patients with biliary tract cancer, and standard chemotherapy has not been established yet. In this article we review previous studies and clinical trials regarding chemotherapy for unresectable biliary tract cancer, and we present guidelines for the appropriate use of chemotherapy in patients with biliary tract cancer. According to an RCT comparing chemotherapy and best supportive care for these patients, survival was significantly longer and quality of life was significantly better in the chemotherapy group than in the control group. Thus, chemotherapy for patients with biliary tract cancer seems to be a significant treatment of choice. However, chemotherapy for patients with biliary tract cancer should be indicated for those with unresectable, locally advanced disease or distant metastasis, or for those with recurrence after resection. That is why making the diagnosis of unresectable disease should be done with greatest care. As a rule, pathological diagnosis, including cytology or histopathological diagnosis, is preferable. Chemotherapy is recommended in patients with a good general condition, because in patients with general deterioration, such as those with a performance status of 2 or 3 or those with insufficient biliary decompression, the benefit of chemotherapy is limited. As chemotherapy for unresectable biliary tract cancer, the use of gemcitabine or tegafur/gimeracil/oteracil potassium is recommended. As postoperative adjuvant chemotherapy, no effective adjuvant therapy has been established at the present time. It is recommended that further clinical trials, especially large multi-institutional RCTs (phase III studies) using novel agents such as gemcitabine should be performed as soon as possible in order to establish a standard treatment

Guidelines for the management of biliary tract and ampullary carcinomas: surgical treatment

The only curative treatment in biliary tract cancer is surgical treatment. Therefore, the suitability of curative resection should be investigated in the first place. In the presence of metastasis to the liver, lung, peritoneum, or distant lymph nodes, curative resection is not suitable. No definite consensus has been reached on local extension factors and curability. Measures of hepatic functional reserve in the jaundiced liver include future liver remnant volume and the indocyanine green (ICG) clearance test. Preoperative portal vein embolization may be considered in patients in whom right hepatectomy or more, or hepatectomy with a resection rate exceeding 50%–60% is planned. Postoperative complications and surgery-related mortality may be reduced with the use of portal vein embolization. Although hepatectomy and/or pancreaticoduodenectomy are preferable for the curative resection of bile duct cancer, extrahepatic bile duct resection alone is also considered in patients for whom it is judged that curative resection would be achieved after a strict diagnosis of its local extension. Also, combined caudate lobe resection is recommended for hilar cholangiocarcinoma. Because the prognosis of patients treated with combined portal vein resection is significantly better than that of unresected patients, combined portal vein resection may be carried out. Prognostic factors after resection for bile duct cancer include positive surgical margins, especially in the ductal stump; lymph node metastasis; perineural invasion; and combined vascular resection due to portal vein and/or hepatic artery invasion. For patients with suspected gallbladder cancer, laparoscopic cholecystectomy is not recommended, and open cholecystectomy should be performed as a rule. When gallbladder cancer invading the subserosal layer or deeper has been detected after simple cholecystectomy, additional resection should be considered. Prognostic factors after resection for gallbladder cancer include the depth of mural invasion; lymph node metastasis; extramural extension, especially into the hepatoduodenal ligament; perineural invasion; and the degree of curability. Pancreaticoduodenectomy is indicated for ampullary carcinoma, and limited operation is also indicated for carcinoma in adenoma. The prognostic factors after resection for ampullary carcinoma include lymph node metastasis, pancreatic invasion, and perineural invasion

Phase locking and periodic evolution of solitons in passively mode-locked fiber lasers with a semiconductor saturable absorber

Passively mode-locked lasers with intracavity weakly birefringent fiber are theoretically analyzed based on two coupled complex one-dimensional Ginzburg-Landau equations. The model includes fiber birefringence, spectral filtering, saturable gain, and saturable loss. Phase-locked soliton solutions are found for small amounts of birefringence and several types of soliton with periodic polarization evolution for higher amounts of birefringence. Numerical simulations show qualitative agreement with experimental results. © 1998 Optical Society of America.The research of J. M. Soto-Crespo was supported by Comunidad de Madrid contract 06T/039/96 and by Direcci´on Generale de Ense ˜ nanza Superior contract PB96-0819.Peer Reviewe

Observation of polarization-locked vector solitons in an optical fiber

Polarization-locked vector solitons (PLVS) were observed in an optical fiber lasers with well-controlled birefringence. Couple-nonlinear Schrodinger equations were used to describe the evolution of the polarization components along the axes of the fibers. The fiber laser allowed the monitoring of vector solitons in a transmission system.Peer Reviewe

Mode-locking Ultrafast Solid-state Lasers With Saturable Bragg Reflectors

We discuss mode-locking of low-gain solid-state lasers using a semiconductor saturable Bragg reflector structure. This recently developed low-loss mode-locking device consists of a single quantum well which acts as a saturable absorber incorporated into a high-reflectivity Bragg mirror. Highly stable mode-locking in solid-state lasers results from an ultrafast transient reflectivity in the device that is caused by saturation of the excitonic absorption in near-resonant conditions.23454464Asaki, M.T., Huang, C.P., Garvey, D., Zhou, J., Kapteyn, H.C., Murnane, M.M., Generation of 11 femtosecond pulses from a self mode-locked Ti:sapphire laser (1993) Opt. Lett., 18, pp. 977-979Keller, U., Knox, W.H., 'Thooft, G.W., Ultrafast solid-state mode-locked lasers using resonant nonlinearities (1992) IEEE J. Quantum Electron., 28, pp. 2123-2133Keller, U., Chiu, T.H., Ferguson, J.F., Self-starting and self-Q-switching dynamics of passively mode-locked Nd:YLF and Nd:YAG lasers (1993) Opt. Lett., 18, p. 217Hönninger, C., Kärtner, F.X., Zhang, G., Keller, U., Giesen, A., Passively mode-locked femtosecond Yb:YAG laser using semiconductor saturable absorbers Opt. Lett., , to be publishedConlon, P.J., Tong, Y.P., French, P.M.W., Taylor, J.R., Shestakov, A.V., Passive mode locking and dispersion measurement of a sub-100-fs Cr 4+:YAG laser (1994) Opt. Lett., 19, pp. 1468-1470Ishida, Y., Naganuma, K., Characteristics of femtosecond pulses near 1.5 μm in a self-mode-locked Cr 4+:YAG laser (1994) Opt. Lett, 19, pp. 2003-2005Collings, B.C., Stark, J.B., Tsuda, S., Knox, W.H., Cunningham, J.E., Jan, W.Y., Pathak, R., Bergman, K., Saturable Bragg Reflector self-starting passive modelocking of a Cr 4+:YAG laser pumped with a diode-pumped Nd:YVO4 laser (1996) Opt. Lett, 21, pp. 1171-1173Rizvi, N.H., French, P.M.W., Taylor, J.R., 50-fs pulse generation from a self-starting cw passively mode-locked Cr:LiSrAlF 6 laser (1992) Opt. Lett., 17, pp. 877-879Evans, J.M., Spence, D.E., Sibbett, W., Chai, B.H.T., Miller, A., 50-fs pulse generation from a self-mode-locked Cr:LiSrAlF 6 laser (1992) Opt. Lett, 15, pp. 1447-1449Dymott, M.J.P., Botheroyd, I.M., Hall, G.J., Lincoln, J.R., Ferguson, A.I., All-solid-state actively mode-locked Cr:LiSAF laser (1994) Opt. Lett., 19, pp. 634-636Kopf, D., Weingarten, K.J., Brovelli, L.R., Kamp, M., Keller, U., Diode-pumped 100-fs passively mode-locked Cr:LiSAF laser with an antiresonant Fabry-Perot saturable absorber (1994) Opt. Lett., 19, pp. 2143-02145Tsuda, S., Knox, W.H., De Souza, E.A., Jan, W.Y., Cunningham, J.E., Low loss intracavity AlAs/AlGaAs saturable Bragg reflector for femtosecond mode lockinng in solid-state lasers (1995) Opt. Lett., 20, pp. 1406-1408Yanovsky, V.P., Wise, F.W., Self-starting femtosecond diodepumped Cr:LiSGaF laser (1996) OSA TOPS Advanced Solid State Lasers, 1, p. 261Wa, P.L.K., Chai, B.H.T., Miller, A., Modelocked Cr 3+:LiSr 0.8Ca 0.2AlF 6 laser producing 150 fs pulses (1991) Electron. Lett., 27, pp. 2350-2351Sorokina, I.T., Sorokin, E., Wintner, E., Cassanho, A., Jenssen, H.P., Noginov, M.A., Efficient continuous-wave TEM 00 and femtosecond Kerr-lens mode-locked Cr:LiSrGaF laser (1996) Opt. Lett., 21, pp. 204-206Hanson, F., Bendall, C., Poirier, P., Gain measurements and average power capabilities of Cr 3+:LiSrAlF 6 (1993) Opt. Lett., 18, pp. 1423-1425Beaud, P., Richardson, M.C., Chen, Y.-F., Chai, B.H.T., Optical amplification characteristics of Cr:LiSAF and Cr:LiCAF under flashlamppumping (1994) IEEE J. Quantum Electron., 30, pp. 1259-1266Stalder, M., Bass, M., Chai, B.H.T., Thermal quenching of fluorescence in chromium-doped fluoride laser crystals (1992) J. Opt. Soc. Amer., B9, pp. 2271-2273Ippen, E.P., Haus, H.A., Liu, L.Y., Additive pulse mode locking (1989) J. Opt. Soc. Amer. B, 6, p. 1736Rizvi, N.H., French, P.M.W., Taylor, J.R., Delfyett, P.J., Florez, L.T., Generation of pulses as short as 93 fs from self-starting femtosecond Cr:LiSrAlF 6 lasers by exploiting multiple-quantum well absorbers (1993) Opt. Lett., 18, pp. 983-985Keller, U., Miller, D.A.B., Boyd, G.D., Chiu, T.H., Ferguson, J.E., Asom, M.T., Solid-state los-loss intracavity saturable absorber for Nd:YLF lasers: An antiresonant semiconductor Fabry-Perot saturable absorber (1992) Opt. Lett., 17, p. 505Miller, D.A.B., Lasers tuners and wavelength-sensitive detectors based on absorbers in standing waves (1994) IEEE J. Quantum Electron., 30, pp. 732-749Feldmann, J., Sacher, J., Göbel, E., Mode locking using a type II multiple-quantum-well structure as a fast saturable absorber (1991) Opt. 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