Biomedical subjects

R Levitan

Publications and source records attributed to R Levitan.

At least 19 recordsLinked to original sources

PubMed1991

Protein and other compositional differences of the extracellular material from slimy and non-slimy colonies of non-mucoid Pseudomonas aeruginosa.

The composition of extracellular material produced by non-mucoid strains of Pseudomonas aeruginosa differed when grown on surfaces that either did or did not induce the formation of slime under conditions where the medium was identical. The nature of the changes in protein composition indicated that protein expression differed in the course of growth on the two surfaces, and hence that there were physiological consequences associated with growth under conditions which do or do not lead to slime formation. The compositional differences also included elevated levels in extracellular material from the slimy colonies of two virulence factors, protease and rhamnolipids.

Bacterial Capsules↗

PubMed1990

Auditory grouping based on fundamental frequency and formant peak frequency.

The perceptual grouping of a four-tone cycle was studied as a function of differences in fundamental frequencies and the frequencies of spectral peaks. Each tone had a single formant and at least 13 harmonics. In Experiment 1 the formant was created by filtering a flat spectrum and in Experiment 2 by adding harmonics. Fundamental frequency was found to be capable of controlling grouping even when the spectra spanned exactly the same frequency range. Formant peak separation became more effective as the sharpness (amplitude of the peak relative to a spectral pedestal) increased. The effect of each type of acoustic difference depended on the task. Listeners could group the tones by either sort of difference but were also capable of resisting the disruptive effect of the other one. This was taken as evidence for the presence of a schema-based process of perceptual grouping and the relative weakness of primitive segregation.

Adult↗

PubMed1990

Fusion of auditory components: effects of the frequency of amplitude modulation.

The fusion of two amplitude-modulated (AM) tones presented simultaneously was studied. Subjects were presented with an AM tone (A) followed by a copy of itself (B) which was accompanied by another AM tone (C). In different experiments, the subjects were asked either to rate how clearly they could hear Tone B in the BC mixture or whether Tone B was present or not. The stronger the fusion of Tones B and C, the harder it was to "hear out" Tone B. It was found that fusion was strongest when Tones B and C were modulated at the same rate; segregation curves were obtained for the degree of mismatch of modulation frequency.

Adult↗

PubMed1989

GI problems in the elderly, Part II: Prevalent diseases and disorders.

When ambulatory geriatric patients present with gastrointestinal (GI) complaints, a complete workup is necessary to determine whether the cause is a functional problem or organic disease. Some of the more common organic diseases found in the elderly GI patient include peptic ulcer disease, neoplasms, inflammatory bowel diseases, and diverticular disease. Special considerations that must be given the geriatric patient during workup, diagnosis, and treatment are discussed.

Age Factors↗

PubMed1989

GI problems in the elderly, Part I: Aging-related considerations.

Gastrointestinal problems are very common in the elderly; they account for 20% of all geriatric deaths. The evaluation of gastrointestinal ailments is difficult in the aged due to variation in signs and symptoms, coexisting nutritional problems, lack of patient cooperation, presence of comorbidity, and effects of polypharmacy. Poor clinical histories are common and gastrointestinal ailments may be atypical. Non-compliance with therapy and testing is a common problem and unrealistic expectations from interventions are the rule rather than the exception. Iatrogenic disorders must be ruled out in all patients with gastrointestinal symptoms; an accurate drug and nutritional history is critical for achieving success in the management of the elderly.

Aged↗

PubMed1975