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R Johnson

Publications and source records attributed to R Johnson.

At least 523 records · Page 29Linked to original sources
PubMed1984

Ultrasonic acoustic emissions from the sapwood of cedar and hemlock : an examination of three hypotheses regarding cavitations.

Measurements are reported of ultrasonic acoustic emissions (AEs) measured from sapwood samples of Thuja occidentalis L. and Tsuga canadensis (L.) Carr. during air dehydration. The measurements were undertaken to test the following three hypotheses: (a) Each cavitation event produces one ultrasonic AE. (b) Large tracheids are more likely to cavitate than small tracheids. (c) When stem water potentials are >-0.4 MPa, a significant fraction of the water content of sapwood is held by ;capillary forces.' The last two hypotheses were recently discussed at length by M. H. Zimmermann. Experimental evidence consistent with all three hypotheses was obtained. The evidence for each hypothesis respectively is: (a) the cumulative number of AEs nearly equals the number of tracheids in small samples; (b) more water is lost per AE event at the beginning of the dehydration process than at the end, and (c) sapwood samples dehydrated from an initial water potential of 0 MPa lost significantly more water before AEs started than lost by samples dehydrated from an initial water potential of about -0.4 MPa. The extra water held by fully hydrated sapwood samples may have been capillary water as defined by Zimmerman.We also report an improved method for the measurement of the ;intensity' of ultrasonic AEs. Intensity is defined here as the area under the positive spikes of the AE signal (plotted as voltage versus time). This method was applied to produce a frequency histogram of the number of AEs versus intensity. A large fraction of the total number of AEs were of low intensity even in small samples (4 mm diameter by 10 mm length). This suggests that the effective ;listening distance' for most AEs was less than 5 to 10 mm.

Journal Article↗
PubMed1984

Phage-typing and drug-resistance patterns as tools in mycobacterial epidemiology.

Phage-typing by itself was not sufficient to delineate the boundaries of a mini-epidemic of tuberculosis in upstate New York. Drug-resistance patterns were needed as well. In a small upstate community, 79% of 14 isolates tested were resistant to one or more of the antituberculosis drugs. Of 15 isolates with phage types determined, 47% were type 1(13), 27% were type 7(7, 13), and 27% were type 1(7, 12, 13). By combining phage-typing and sensitivity testing, we were able to demonstrate that 4 or possibly 5 of the 7 phage-type 1(13) strains are epidemiologically related.

Bacteriophage Typing↗
PubMed1984

Differential effects of age versus glycemic stimulation on the maturation of insulin stimulus-secretion coupling during culture of fetal rat islets.

We have cultured islets from 21.5-day-old fetal rats for 1-7 days in RMPI 1640/10% fetal calf serum containing 2.8 or 11.1 mM glucose to evaluate the differential effects of age vis-à-vis glycemic stimulation on the maturation of selected components of stimulus-secretion coupling. After 1 day of culture in either media, acute stimulation with 3.0 mg/ml glucose during basal perifusion with 0.5 mg/ml glucose elicited only a small first phase of stimulated insulin secretion and no second phase. The acute exposure to 3.0 mg/ml glucose produced no change in the prevailing high rates of oxygen consumption (QO2) and caused only minor increments in phosphate efflux (i.e., peak values for phosphate flush of 126 +/- 16% of baseline for islets that had been cultured in 11.1 mM glucose and 162 +/- 30% for islets cultured in 2.8 mM glucose). After 7 days of culture in 11.1 mM glucose, acute stimulation with 3.0 mg/ml glucose increased Qo2 (as in adult islets) and effected acute increases in the AT32P and GT32P content of prelabeled islets. The 3.0 mg/ml glucose also triggered phosphate flush to 599 +/- 45% of baseline and elicited first as well as early second phases of stimulated insulin secretion that replicated the performance of adult islets. By contrast, after 7 days of culture in 2.8 mM glucose, similar acute exposures of fetal islets to 3.0 mg/ml glucose effected only a small first phase and a negligible second phase of stimulated insulin secretion despite the occurrence of the same increments in Qo2 as after culture in 11.1 mM glucose, highly significant increases in AT32P and GT32P, and phosphate flushes that peaked at 306 +/- 16% of basal values. Thus, the ontogeny of individual components of stimulus-secretion coupling may occur in asynchronous fashion and varying require glycemic stimulation in addition to aging per se. The capacities to augment efflux of orthophosphate, enhance respiration, and heighten nucleotide turnover in response to acute stimulation with glucose seem to mature in large measure in time-dependent fashion, whereas some chronic exposure to ambient glucose in excess of basal levels may be required to establish and/or maintain the other coupled components that underlie biphasic stimulated insulin release. However, we did not achieve full exocytotic maturation even after 7 days of culture with 11.1 mM glucose.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1984

Transcutaneous electrical nerve stimulation: its role in the control of chronic pain.

An assessment was made of the effectiveness of long-term transcutaneous electrical nerve stimulation (TENS) in the treatment of chronic posttraumatic pain. Compensation Board files showed that 846 patients received TENS from 1975 to 1979, with more than 70% having intractable back pain. Of this group using TENS, 44.6% were free of disability, and an additional 36.2% were capable of modified work. Questionnaire responses were obtained from 563 of 637 patients receiving TENS in 1978 or 1979. At the six-month follow-up, most respondents (472, 83.8%) reported continuing benefit from TENS, including a reduction of pain (418, 74.2%), less need for medication (322, 57.2%), and improved sleep patterns (331, 58.8%). Only 13.6% of those who had returned to work reported no benefit from TENS, while 18.4% of those still unemployed reported no benefit. Among those who had returned to work (264 cases, 46.9% of respondents), benefit was reported equally by those with back injuries and by those with other injuries. The responses observed in this trial seem larger and more long-lasting than could be obtained by a placebo effect, and further attempts at a controlled trial may be warranted. However, there are major practical difficulties to such an investigation, and the resulting controversy could reduce the therapeutic effectiveness of TENS in conditions where alternative treatments are either ineffective or undesirable.

Back Pain↗
PubMed1984

Hepatic and renal erythropoietin production during various intervals of short-term hypoxia.

Hypoxia stimulates erythropoietin (Ep) production and subsequent stimulation of erythropoiesis. Chronically applied hypoxia results in a variety of physiological alterations including polycythemia, hemoglobinemia, and vascular and metabolic changes. As red cell mass increases to such an extent to allow for adequate tissue oxygenation, plasma Ep levels drop and the rate of erythropoiesis is lowered. In the present work, the precise contribution of the kidney and the liver to the Ep response to acutely administered hypoxia (6-24 hr/0.4 atm) was determined using an in situ tandem perfusion of the liver and kidneys. The results indicate that hepatic and renal Ep production during different intervals of acute hypoxia is not uniform. This alteration may be partially explained by the reported reduction in splanchnic blood flow and a possible redistribution of hepatic microcirculation, which may cause the liver to become more hypoxic than the kidney under the same ambient pO2. The role of the liver becomes more pronounced as the time of acute hypoxic exposure increases, whereas the Ep content of renal perfusates is not drastically altered. At certain intervals during hypoxia, the liver displays a greater potential to elaborate Ep.

Animals↗
PubMed1984

The maximum exercise stress test: is it a behavior-modification tool?

The controlled study presented demonstrates the results obtained when using the maximum exercise stress test (MEST) as a behavior-modification tool for coronary artery disease risk factors. Changes in attitudes, behaviors, and objective measurements of health were assessed in a low-risk population. Only exercise level was significantly altered (P less than .03). Changes in the other measured parameters were insignificant. The MEST test is also expensive, and no benefit has been demonstrated in terms of its ability to decrease the morbidity and mortality seen in coronary artery disease.

Adult↗
PubMed1983

Gliadin subfraction skin test for the diagnosis of coeliac disease.

Skin hypersensitivity to a gliadin subfraction (Fraction 3) was tested in patients with coeliac disease, patients with inflammatory bowel disease, and controls. Those with coeliac disease showed substantially greater hypersensitivity than controls, but there was no significant difference between the frequency of hypersensitivity in patients with coeliac disease and in those with inflammatory bowel disease. Fraction 3 did not provide a sufficiently specific skin reaction to be of use in the diagnosis of coeliac disease.

Adolescent↗
PubMed1983

Arrangement of MP26 in lens junctional membranes: analysis with proteases and antibodies.

The major membrane protein of the bovine lens fiber cell is a 26-kilodalton (kD) protein (MP26), which appears to be a component of the extensive junctional specializations found in these cells. To examine the arrangement of MP26 within the junctional membranes, various proteases were incubated with fiber cell membranes that had been isolated with or without urea and/or detergents. These membranes were analyzed with electron microscopy and SDS-PAGE to determine whether the junctional specializations or the proteins were altered by proteolysis. Microscopy revealed no obvious structural changes. Electrophoresis showed that chymotrypsin, papain, and trypsin degraded MP26 to 21-22 kD species. A variety of protease treatments, including overnight digestions, failed to generate additional proteolysis. Regions on MP26 which were sensitive to these three proteases overlapped. Smaller peptides were cleaved from MP26 with V8 protease and carboxypeptidases A and B. Protein domains cleaved by these proteases also overlapped with regions sensitive to chymotrypsin, papain, and trypsin. Specific inhibition of the carboxypeptidases suggested that cleavage obtained with these preparations was not likely due to contaminating endoproteases. Since antibodies are not thought to readily penetrate the 2-3 nm extracellular gap in the fiber cell junctions, antibodies to MP26 were used to analyze the location of the protease-sensitive domains. Antisera were applied to control (26 kD) and proteolyzed (22 kD) membranes, with binding being evaluated by means of ELISA reactions on intact membranes. Antibody labeling was also done following SDS-PAGE and transfer to derivatized paper. Both assays showed a significant decrease in binding following proteolysis, with the 22 kD product showing no reaction with the anti-MP26 sera. These investigations suggest that MP26 is arranged with approximately four-fifths of the primary sequence "protected" by the lipid bilayer and the narrow extracellular gap. One-fifth of the molecule, including the C-terminus, appears to be exposed on the cytoplasmic side of the membrane.

Animals↗
PubMed1983

Manipulation of P3 latency: speed vs. accuracy instructions.

Twelve young female subjects were presented with a series of horizontal line-pairs of same or different length in a two-alternative, forced-choice RT task, with 60 of each type pair in each block of trials. In one block (Easy) lines differed by 30%, in another block (Difficult) lines differed by 7%. Subjects were first given 60 practice trials with the Easy discrimination and with the instruction that speed and accuracy should be emphasized equally. For the next block of trials, accuracy was emphasized with a monetary bonus for accurate performance. Finally, in the last block of trials, speed was emphasized with a monetary bonus for speedy performance. Additionally, a penalty was incurred for RTs that exceeded a criterion level based on each individual subject's performance. The order of Easy and Difficult discrimination blocks was maintained within a subject but balanced across subjects. From the latency-adjusted P3s recorded from Pz, we obtained P3 latencies, amplitudes and single-trial P3 latency/RT correlations. RT to correct and incorrect trials and error data were also collected. P3 was considerably larger during the Speed than Accuracy conditions. The single-trial P3 latency/RT correlation was higher in Speed than in Accuracy runs. RT was 235 msec faster and P3 was 40 msec earlier during the Speed than during the Accuracy runs. On the other hand, discrimination difficulty delayed P3 and RT about equally, 28 and 43 msec respectively. This pattern suggests that speed instructions and discrimination difficulty affect stimulus processing time and response production time differently.

Adult↗