Biomedical subjects

D E Presti

Publications and source records attributed to D E Presti.

3 recordsLinked to original sources

PubMed1992

The context of smoking initiation and maintenance: findings from interviews with youths.

The characteristics of initial cigarette-smoking situations and subsequent situations in which adolescents received an offer to smoke were examined by means of interviews with 287 youths in grades 7 through 10. Initiation of smoking generally took place in a social context (89%), with small groups (2.7 people) of same-gender, older (2.1 years), peers (and siblings) who were smokers (60%). In one-third of these onset situations, another novice smoked for the first time. Most subjects (81%) reported that they smoked their first cigarette because they accepted an offer. The characteristics of the onset situation did not significantly differ between regular and experimental smokers. The situations for later offers to smoke were similar: small groups of same-gender, slightly older, cigarette-smoking peers (and siblings). Descriptive and comparative data also are presented on procurement, perceived prevalence, parental influence, cravings, quit attempts, beliefs about ease of quitting, and intention to smoke. These data suggest that school-based interventions may not be sufficient to address the broad social context surrounding adolescent tobacco use. Community-wide interventions are advocated.

Adolescent↗

PubMed1986

Does attention affect visual feature integration?

Two questions are investigated in this work: first, whether the integration of color and shape information is affected by attending to the stimulus location, and second, whether attending to a stimulus location enhances the perceptual representation of the stimulus or merely affects decision processes. In three experiments, subjects were briefly presented with colored letters. On most trials, subjects were precued to the stimulus location (valid cue); on some trials, a nonstimulus location was cued (invalid cue). Subjects were less likely to incorrectly combine colors and letter shapes following a valid cue. The attentional facilitation afforded by the cue was not limited to feature integration but also affected the registration of features. However, when the amount of feature information was strictly controlled, attention still affected feature integration. The results indicate that orienting attention to the location of the cue affects the quality of the perceptual representation for features and their integration.

Adolescent↗

PubMed1975

Electronic structures of cephalosporins and penicillins. 4. Modeling acylation by the beta-lactam ring.

Molecular orbital calculations by the CNDO/2 method are used to study the molecular and electronic details involved in the initial phases of the opening of the beta-lactam ring of a model cephalosporin structure, 7-amino-3-acetoxymethyl-3-cephem. The effect of a simple nucleophile, OH-, approaching the carbonyl carbon center of the beta-lactam ring is monitored by following the charge redistributions that occur in the bicyclic system and in the 3 side chain. A migration of electron density to the ester oxygen of the CH2OAc group is observed with concomitant weakening of the CH2-OAc bond. The results are discussed in relation to the mechanism of acylation of bacterial cell wall enzymes by beta-lactam antibiotics and in relation to the hydrolysis of these molecules. The results indicate that the ability of the 3' substituent of cephalosporins to stabilize electron density transferred to it, i.e., the leavability of the 3' moiety, can be an important factor in activating the beta-lactam toward nucleophilic attack.

Acylation↗