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81.
Adduct ions, [M + (CH3)3Si]+, were produced by bimolecular association reactions of trimethylsilyl ions, (CH3)3Si+, with acetone, cydohexaoone, anisole, dimethyl ether, 2,5-dimethylfuran, 2-methylfuran and furan in ion cyclotron resonance experiments at 300 K and at pressures of ~10?7 Torr (1 Torr = 133.3 Pa). The rate constants, ka, for the association reactions varied from 100% to 2% of the collision rate constants, kc. The rate constants were independent of pressure, except for furan. Measurements were also made of bond dissociation energies for these adduct ions, D[(CH3)3Si+–X], from equilibrium measurements. The association efficiency, ka/kc, increased with increasing bond dissociation energy and with increasing numbers of degrees of freedom, in qualitative agreement with theoretical predictions. Observations pertinent to the dependence of ka on reactant temperature and relative kinetic energy are discussed. The possibility of determining ion-neutral complex binding energies from radiative association rate constants is considered. 相似文献
82.
Ron Orlando Fred Strobel D. P. Ridge Burnaby Munson 《Journal of mass spectrometry : JMS》1987,22(9):597-605
Mixtures of tetramethylsilane and helium have been found to form [M + 73]+ adducts, hydrated trimethylsilyl ions and alkyl ions with aliphatic alcohols. The adduct ions were found to be formed by displacement of water from the hydrated trimethylsilyl ion. Ratios of the abundances of the adduct ions to the hydrated trimethylsilyl ion can be used to differentiate among primary, secondary and tertiary alcohols. Sensitivities for a number of alcohols with the tetramethylsilane/helium chemical ionization reagent system are approximately equal. 相似文献
83.
For two competing decompositions of the same molecular ion to give products [A1+] and [A2+], the ratio [A1+]/[A2+], is equal to the ratio of rate constants for the formation of the stable ions. Thr ratios, [Y C7H4O+]/[C7H5O+], were determined for several benzophenones for electron energies from 15 to 70 eV. Plots of log [Y C7H4O+]/[C7H5O+] vs.[ω+] gave good straight lines at all energies. Similar correlations have been reported for log [Y C7H6+]/[C7H7+] from substituted diphenyl ethanes and are also true for substituted acetophenones, log [YøCO+]/[CH3CO+]. A few charge exchange data were obtained which showed the same general trend as the electron-impact data and emphasize the contribution of low energy ions in the 70 eV mass spectra. Relatively poor correlations were obtained for the [Y C6H4+] and [C6H5+] ions that are formed by both one-step and two-step decompositions. 相似文献
84.
Chemical ionization mass spectra of several ethers obtained with He/(CH3)4Si mixtures as the reagent gases contain abundant [M + 73]+ adduct ions which identify the relative molecular mass. For the di-n-alkyl ethers, these [M + 73]+ ions are formed by sample ion/sample molecule reactions of the fragment ions, [M + 73 ? CnH2n]+ and [M + 73 ? 2CnH2n]+. Small amounts of [M + H]+ ions are also formed, predominantly by proton transfer reactions of the [M + 73 ? 2CnH2n]+ or [(CH3)3SiOH2]+ ions with the ethers. The di-s-alkyl ethers give no [M + 73] + ions, but do give [M + H]+ ions, which allow the determination of the relative molecular mass. These [M + H]+ ions result primarily from proton transfer reactions from the dominant fragment ion, [(CH3)3SiOH2]+ with the ether. Methyl phenyl ether gives only [M + 73]+ adduct ions, by a bimolecular addition of the trimethylsilyl ion to the ether, not by the two-step process found for the di-n-alkyl ethers. Ethyl phenyl ether gives [M + 73]+ by both the two-step process and the bimolecular addition. Although the mass spectra of the alkyl etherr are temperature-dependent, the sensitivities of the di-alkyl ethers and ethyl phenyl ether are independent of temperature. However, the sensitivity for methyl phenyl ether decreases significantly with increasing temperature. 相似文献
85.
Page PM McCarty TA Munson CA Bright FV 《Langmuir : the ACS journal of surfaces and colloids》2008,24(13):6616-6623
We report on the local microenvironment surrounding a free dansyl probe, dansyl attached to controlled pore glass (D-CPG), and dansyl molecules attached to trimethylsilyl-capped CPG (capped D-CPG) in pure and alcohol-modified supercritical CO2. These systems were selected to provide insights into the local microenvironment surrounding a reactive agent immobilized at a silica surface in contact with pure and cosolvent-modified supercritical CO2. Local surface-bound dansyl molecule solvation on the CPG surface depends on the dansyl molecule surface loading, the surface chemistry (uncapped versus capped), the bulk fluid density, and the alcohol gas phase absolute acidity. At high dansyl loadings, the surface-bound dansyl molecules are largely "solvated" by other dansyl molecules and these molecules are not affected significantly by the fluid phase. When the dansyl surface loading decreases, dansyl molecules can be accessed/solvated/wetted by the fluid phase. However, at the lowest dansyl loadings studied, the dansyl molecules are in a fluid inaccessible/restrictive environment and do not sense the fluid phase to any significant degree. In uncapped D-CPG, one can poise the system such that the local concentration of an environmentally less responsible cosolvent (alcohol) in the immediate vicinity of surface-immobilized dansyl molecules can approach 100% even though the bulk solution contains orders of magnitude less of this less environmentally responsible cosolvent. In capped C-CPG, the surface excess is attenuated in comparison to that of uncapped D-CPG. The extent of this cosolvent surface excess is discussed in terms of the dansyl surface loading, the local density fluctuations, the cosolvent and surface silanol gas phase acidities, and the silica surface chemistry. These results also have implications for cleanings, extractions, heterogeneous reactions, separations, and nanomaterial fabrication using supercritical fluids. 相似文献
86.
Several new interfaces have recently been developed requiring PATH to solve a mixed complementarity problem. To overcome the necessity of maintaining a different version of PATH for each interface, the code was reorganized using object-oriented design techniques. At the same time, robustness issues were considered and enhancements made to the algorithm. In this paper, we document the external interfaces to the PATH code and describe some of the new utilities using PATH. We then discuss the enhancements made and compare the results obtained from PATH 2.9 to the new version. 相似文献
87.
Feasible descent algorithms for mixed complementarity problems 总被引:6,自引:0,他引:6
In this paper we consider a general algorithmic framework for solving nonlinear mixed complementarity problems. The main features
of this framework are: (a) it is well-defined for an arbitrary mixed complementarity problem, (b) it generates only feasible
iterates, (c) it has a strong global convergence theory, and (d) it is locally fast convergent under standard regularity assumptions.
This framework is applied to the PATH solver in order to show viability of the approach. Numerical results for an appropriate
modification of the PATH solver indicate that this framework leads to substantial computational improvements.
Received April 9, 1998 / Revised version received November 23, 1998?Published online March 16, 1999 相似文献
88.
Yihsu Chen Benjamin F. Hobbs Sven Leyffer Todd S. Munson 《Computational Management Science》2006,3(4):307-330
This paper investigates the ability of the largest producer in an electricity market to manipulate both the electricity and emission allowances markets to its advantage. A Stackelberg game to analyze this situation is constructed in which the largest firm plays the role of the leader, while the medium-sized firms are treated as Cournot followers with price-taking fringes that behave competitively in both markets. Since there is no explicit representation of the best-reply function for each follower, this Stackelberg game is formulated as a large-scale mathematical program with equilibrium constraints. The best-reply functions are implicitly represented by a set of nonlinear complementarity conditions. Analysis of the computed solution for the Pennsylvania–New Jersey–Maryland electricity market shows that the leader can gain substantial profits by withholding allowances and driving up NO
x
allowance costs for rival producers. The allowances price is higher than the corresponding price in the Nash–Cournot case, although the electricity prices are essentially the same.We are grateful to two anonymous referees for their insightful comments that helped us improve the paper. This work is partially supported by NSF grants CS 0080577 and 0224817, by USEPA STAR grant R82873101-0, and by the Mathematical, Information, and Computational Sciences Division subprogram of the Office of Advanced Scientific Computing Research, Office of Science, U.S. Department of Energy, under Contract W-31-109-Eng-38. Any opinions or errors are the responsibility of the authors and not the sponsoring agencies. 相似文献
89.
90.
Bailey MM Gorman EM Munson EJ Berkland C 《Langmuir : the ACS journal of surfaces and colloids》2008,24(23):13614-13620
Diabetes is a set of diseases characterized by defects in insulin utilization, either through autoimmune destruction of insulin-producing cells (Type I) or insulin resistance (Type II). Treatment options can include regular injections of insulin, which can be painful and inconvenient, often leading to low patient compliance. To overcome this problem, novel formulations of insulin are being investigated, such as inhaled aerosols. Sufficient deposition of powder in the peripheral lung to maximize systemic absorption requires precise control over particle size and density, with particles between 1 and 5 microm in aerodynamic diameter being within the respirable range. Insulin nanoparticles were produced by titrating insulin dissolved at low pH up to the pI of the native protein, and were then further processed into microparticles using solvent displacement. Particle size, crystallinity, dissolution properties, structural stability, and bulk powder density were characterized. We have demonstrated that pure drug insulin microparticles can be produced from nanosuspensions with minimal processing steps without excipients, and with suitable properties for deposition in the peripheral lung. 相似文献