A theoretical interpretation of isotope effects in mixtures of light and heavy water—II

Solvent isotope effects for H₂O---D₂O mixtures and for ionic hydration equilibria in such mixtures can be calculated from the structure difference between D₂O and H₂O and that between HDO and H₂O and the relative amounts of the three waters. The behavior of acids in H₂O---D₂O mixtures is considered in detail. Dissociation constants of acetic acid are calculated over the complete range of deuterium concentrations and found to agree with the experimentally determined ones. The Gross equation for the dependence of isotope effect on mole fraction of deuterium for acid-catalyzed reaction of substrates S proceeding via SL⁺ transition states (L=H or D) is derived from first principles.     

{\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}} \viewkind4\uc1\pard\f0\fs24 Status of software for PGNAA bulk analysis by the Monte Carlo - Library Least-Squares (MCLLS) approach \par }

Summary {\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}} \viewkind4\uc1\pard\f0\fs24 The Center for Engineering Applications of Radioisotopes (CEAR) has been working for about ten years on the Monte Carlo - Library Least-Squares (MCLLS) approach for treating the nonlinear inverse analysis problem for PGNAA bulk analysis. This approach consists essentially of using Monte Carlo simulation to generate the libraries of all the elements to be analyzed plus any other required libraries. These libraries are then used in the linear Library Least-Squares (LLS) approach with unknown sample spectra to analyze for all elements in the sample. The other libraries include all sources of background which includes: (1) gamma-rays emitted by the neutron source, (2) prompt gamma-rays produced in the analyzer construction materials, (3) natural gamma-rays from K-40 and the uranium and thorium decay chains, and (4) prompt and decay gamma-rays produced in the NaI detector by neutron activation. A number of unforeseen problems have arisen in pursuing this approach including: (1) the neutron activation of the most common detector (NaI) used in bulk analysis PGNAA systems, (2) the nonlinearity of this detector, and (3) difficulties in obtaining detector response functions for this (and other) detectors. These problems have been addressed by CEAR recently and have either been solved or are almost solved at the present time. We have now finished the development of Monte Carlo simulation for all of the libraries except the prompt gamma-ray library from the activation of the NaI detector. We must first determine a treatment for the coincidence schemes for Na and particularly I to complete the Monte Carlo simulation of this last library. \par }     

An evaluation of voltammetric titration procedures for the determination of trace metal complexation in natural waters by use of computers simulation

The impact of random analytical errors on the determination of metal complexation parameters of natural waters by metal titration procedures based on cathodic stripping (CSV) or anodic stripping (ASV) voltammetry is investigated by means of computer simulation. The results indicate that random analytical errors are of overriding importance in establishing the range of ligand concentrations and conditional stability constants that can be accurately determined by these techniques. Simulations incorporating realistic estimates of random analytical error show that only stability constants lying within a relatively narrow range, typically three orders of magnitude, can be determined accurately by the ASV procedure. The CSV procedure suffers from the same limitations, but is potentially more flexible in that the available detection window can be moved (but not widened) by adjustments to the method. Both techniques are capable of accurately determining ligand concentrations provided that the corresponding stability constant, K′, is greater than a threshold value which corresponds to the lower end of the available detection window for the stability constant. Realistically attainable improvements in analytical precision did not greatly improve the performance of either technique. Two graphical treatments for the evaluation of metal complexation parameters from titration data are compared: the Scatchard and Van den Berg/Ruzic plots. Simulations indicate that at least for the single-ligand model of complexation, the Van den Berg/Ruzic method is superior. The importance of the simulation results with respect to determining metal complexation parameters in natural waters is discussed. This study illustrates the value of computer simulation when complex, time-consuming analytical techniques are applied and the need for rigorous analysis of errors in producing data of environmental relevance.     

A counterexample to a ‘simplex algorithm’ for convex bodies

A counterexample, in E ³, is given to the following conjecture. Suppose f ^* is a linear functional, and e an exposed point of a convex body K such that f ^* does not attain its maximum on K at e; then there is an f ^*-strictly increasing path in the one-skeleton of K emanating from e. The counterexample shows that a certain generalized simplex algorithm fails. Furthermore for a different linear functional f, there are no three disjoint f-strictly increasing paths in the one-skeleton of K leading to e.     

Material Design in Poly(Lactic Acid) Systems: Block Copolymers,Star Homo- and Copolymers,and Stereocomplexes

Abstract

This paper gives a general overview of several approaches we have investigated for designing new PLA-based polymers with a broad range of properties and improved processability. These approaches include: copolymerization (block and stereoblock copolymers), microstructure and architecture control, and stereocomplexation. Multiblock copolymers with alternating “soft” and “hard” segments, synthesized over a broad range of chemical compositions, show properties ranging from hard plastics to elastomers. Stereoblock copolymers with alternating amorphous and semicrystalline PLA blocks combine the advantages of PLA homopolymers (crystallinity) and random copolymers (processability). Independent control of polymer architecture and microstructure allows for the synthesis of star polymers with various arm morphologies. A new method for stereocomplex formation between L-PLA and D-PLA, which combines in-situ polymerization with stereocomplexation, is also described. For the synthesis of these new materials we took advantage of: 1) chirality of lactide monomer, 2) retention of configuration during polymerization, 3) living nature of the ring-opening polymerization (ROP) of lactide in the presence of active hydrogen groups such as OH and NH₂, and 4) control of the level of transesterification reactions.     

Effect of the External Mirror Feedback Strength in the Dynamics and Spectrum of the Injected Semiconductor Lasers

We analytically investigate the effect of an external mirror on the stability of an injected semiconductor laser, the latter treated as injected damped oscillators. In the studied configuration, the injected semiconductor laser with an external mirror is under the influence of a chaotic oscillating optical signal that is generated by a similar semiconductor master laser. We derive our results in terms of the damping rate and resonance frequency. We show that the external mirror can eliminate the unstable modes of the injected laser at low frequencies. Furthermore, the mirror can enhance the damping of the oscillation modes of the injected semiconductor laser; consequently, the driven response of the injected laser may have a broad spectrum, even wider than that of the chaotic driving signal. We also show results for the bandwidths of the injection amplitude and phase increment as functions of the injection rate and feedback strength of the external mirror. In addition, we use bifurcation and time-series curves to describe the dynamical behavior of the injected laser. We identify the feedback strength of injected laser, relative to that of the master laser, which induces synchronization between the injected-laser oscillation modes and the master laser.     

Electrophilic aromatic prenylation via cascade cyclization

To gain access to prenylated hexahydroxanthenes, tandem cascade cyclization–electrophilic aromatic substitution reactions have been studied on substrates bearing allylic and propargylic substituents. Both BF₃·OEt₂ and TMSOTf can be used to initiate this reaction sequence, resulting in different ratios of the C-2 and C-6 substitution products. Even though allylic transposition is observed in some cases, the results of a crossover experiment are consistent with an intramolecular reaction sequence. Taken together, these studies now allow preparation of either the C-2 or C-6 prenylated hexahydroxanthene products.     

Combined OX40 Agonist and PD-1 Inhibitor Immunotherapy Improves the Efficacy of Vascular Targeted Photodynamic Therapy in a Urothelial Tumor Model

Purpose: Vascular targeted photodynamic therapy (VTP) is a nonsurgical tumor ablation approach used to treat early-stage prostate cancer and may also be effective for upper tract urothelial cancer (UTUC) based on preclinical data. Toward increasing response rates to VTP, we evaluated its efficacy in combination with concurrent PD-1 inhibitor/OX40 agonist immunotherapy in a urothelial tumor-bearing model. Experimental design: In mice allografted with MB-49 UTUC cells, we compared the effects of combined VTP with PD-1 inhibitor/OX40 agonist with those of the component treatments on tumor growth, survival, lung metastasis, and antitumor immune responses. Results: The combination of VTP with both PD-1 inhibitor and OX40 agonist inhibited tumor growth and prolonged survival to a greater degree than VTP with either immunotherapeutic individually. These effects result from increased tumor infiltration and intratumoral proliferation of cytotoxic and helper T cells, depletion of Treg cells, and suppression of myeloid-derived suppressor cells. Conclusions: Our findings suggest that VTP synergizes with PD-1 blockade and OX40 agonist to promote strong antitumor immune responses, yielding therapeutic efficacy in an animal model of urothelial cancer.