ABSTRACT
Ortho-benzyne is a potentially important precursor for polycyclic aromatic hydrocarbon formation, but much is still unknown about its chemistry. In this work, we report on a combined experimental and theoretical study of the o-benzyne + acetylene reaction and employ double imaging threshold photoelectron photoion coincidence spectroscopy to investigate the reaction products with isomer specificity. Based on photoion mass-selected threshold photoelectron spectra, Franck-Condon simulations, and ionization cross section calculations, we conclude that phenylacetylene and benzocyclobutadiene (PA : BCBdiene) are formed at a non-equilibrium ratio of 2 : 1, respectively, in a pyrolysis microreactor at a temperature of 1050 K and a pressure of â¼20 mbar. The C8H6 potential energy surface (PES) is explored to rationalize the formation of the reaction products. Previously unidentified pathways have been found by considering the open-shell singlet (OSS) character of various C8H6 reactive intermediates. Based on the PES data, a kinetic model is constructed to estimate equilibrium abundances of the two products. New insights into the reaction mechanism - with a focus on the OSS intermediates - and the products formed in the o-benzyne + acetylene reaction provide a greater level of understanding of the o-benzyne reactivity during the formation of aromatic hydrocarbons in combustion environments as well as in outflows of carbon-rich stars.
ABSTRACT
This study evaluated the Digitizing Computer System (DCS Production) for computer-controlled fabrication of titanium copings. The three-dimensional shape of the crown preparations was acquired through micropalpation with a contact digitizer on the master cast. In this in vitro study the marginal fit of computer-machined titanium frameworks for veneered crowns was assessed using scanning electron microscopy. Measurement of the marginal gap between the framework and the tooth was performed along the entire length of the finish line. The evaluation was based on 1,475 individual measurements on 10 test specimens. The mean values of marginal fit for the individual crowns ranged from 21.2 +/- 14.6 microns to 81.6 +/- 25.1 microns. The mean value for all crowns was 47.0 +/- 31.5 microns.
Subject(s)
Computer-Aided Design , Crowns , Dental Alloys , Dental Marginal Adaptation , Denture Design/methods , Titanium , Computer-Aided Design/statistics & numerical data , Crowns/statistics & numerical data , Dental Casting Technique , Denture Design/statistics & numerical data , Humans , Models, DentalABSTRACT
Some results of a study done in 1975/76 in Basle are presented (N=422 people working in administrative and industrial firms). Generally medicine takers are to be found in a high percentage already in the group with little symptoms. On the other side many of those reporting a high number of symptoms do not consult a physician. The number of symptoms reported is higher with progressive age, women and lower socio-economic status. Nevertheless we do not find an increase of consultations with a physician in the same direction.
Subject(s)
Sick Role , Adult , Age Factors , Female , Humans , Male , Middle Aged , Occupations , Sex Factors , Socioeconomic Factors , SwitzerlandABSTRACT
A large gap is existing between the system of medical services and the "consumer". It is necessary to reinforce preventive attitudes and behavior should prepare the fundamental concepts. A research design is presented.
Subject(s)
Attitude to Health , Health Services/statistics & numerical data , Sick Role , Delivery of Health Care , Demography , Health Expenditures , Humans , Preventive Health Services/statistics & numerical data , Socioeconomic Factors , SwitzerlandABSTRACT
Preliminary data of inquiry on illness behavior are presented. 94% of the subjects (N =472 people working in administrative and industrial firms) reported at least one symptom within 1 month. Their consecutive activities are described.
