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At least 811 records · Page 45Linked to original sources
PubMed2001

Contribution of heat transfer to turbine blades and vanes for high temperature industrial gas turbines. Part 2: Heat transfer on serpentine flow passage.

The improvement of the heat transfer coefficient of the 1st row blades in high temperature industrial gas turbines is one of the most important issues to ensure reliable performance of these components and to attain high thermal efficiency of the facility. This paper deals with the contribution of heat transfer to increase the turbine inlet temperature of such gas turbines in order to attain efficient and environmentally benign engines. Following the experiments described in Part 1, a set of trials was conducted to clarify the influence of the blade's rotating motion on the heat transfer coefficient for internal serpentine flow passages with turbulence promoters. Test results are shown and discussed in this second part of the contribution.

Journal Article↗
PubMed1979

Effects of temperature on tension, tension-dependent heat, and activation heat in twitches of frog skeletal muscle.

1. The effects of temperature on muscle energy liberation (heat plus work production) and isometric twitch force production were measured at rest length (l o) and at long muscle lengths (approx. 1.35 l o) where twitch force was greatly depressed. 2. Force production and energy liberation at l o declined progressively as muscle temperature was elevated from 0 to 20 degrees C. Force production decreased to a greater extent than did energy liberation. A plot of energy liberation vs. twitch force suggested that a fraction of the l o energy liberation was produced independent of temperature. 3. The energy liberated at long muscle lengths, the activation heat, was independent of muscle temperature. The activation heat is interpreted as reflecting the energy dissipated during Ca2+ cycling and thus suggests that, under the conditions of these experiments, the amount of Ca2+ released with stimulation is independent of muscle temperature and subsequent muscle force production. 4. Analysis of the results also supports the conclusions that skeletal muscle energy liberation is dependent on muscle force production and that the energy liberation associated with Ca2+ cycling is essentially independent of muscle length in the range of l o--1.35 l o.

Animals↗
PubMed1994

A small artery heat transfer model for self-heated thermistor measurements of perfusion in the kidney cortex.

A small artery model (SAM) for self-heated thermistor measurements of perfusion in the canine kidney is developed based on the anatomy of the cortex vasculature. In this model interlobular arteries and veins play a dominant role in the heat transfer due to blood flow. Effective thermal conductivity, kss, is calculated from steady state thermistor measurements of heat transfer in the kidney cortex. This small artery and vein model of perfusion correctly indicates the shape of the measured kss versus perfusion curve. It also correctly predicts that the sinusoidal response of the thermistor can be used to measure intrinsic tissue conductivity, km, in perfused tissue. Although this model is specific for the canine kidney cortex, the modeling approach is applicable for a wide variety of biologic tissues.

Animals↗
PubMed1976

Heat-induced requirements for sucrose or magnesium for expression of heat resistance in Bacillus cereus forespores.

The addition of 0.6 M sucrose of 0.016 M Mg2+ to the enumeration medium was required for early expression of heat resistance (10 min at 70 degrees C) in stage V Bacillus cereus forspores. The addition of Mg2+ to the sporulation medium did not remove this requirment for sucrose of Mg2+. The heat damage did not affect forespore germination or outgrowth, but injured cells in the absence of sucrose or Mg2+ were not capable of cell division. The heat-induced sublethal damage apparently affected the forspore component(s) that could be repaired or was capable of normal function in the presence of added Mg2+ or sucrose.

Bacillus cereus↗
PubMed1978

Dry-heat destruction of lipopolysaccharide: design and construction of dry-heat destruction apparatus.

A dry-heat oven with automatic, multiple-sample introduction and withdrawal has been constructed to achieve instantaneous heating and cooling of samples. The oven temperature fluctuation at set points of 170 to 250 degrees C was +/- 0.1 degrees C, with temperature variation between the replicate samples of +/- 0.2 degrees C. Correction required for a sample come-up time was minimal, i.e., less than 0.25 min of the dry-heat destruction time.

Hot Temperature↗
PubMed1977

Immunological interrelationships between cholera toxin and the heat-labile and heat-stable enterotoxins of coliform bacteria.

Cholera toxin (CT) and the heat-labile (LT) toxin of Escherichia coli are known to share antigenic properties. The present study examined the immunological relationship of CT and the LT and heat-stable (ST) toxins of E. coli, Klebsiella pneumoniae, and Enterobacter cloacae. The neutralizing capacity of equine CT antiserum and of antiserum raised in rabbits to the LT toxin of the three species of coliform bacteria was evaluated by determining their capacity to inhibit the action of purified CT and semipurified ultrafiltration preparations of the coliform LT and ST toxins in inducing water secretion as assayed by the in vivo marker perfusion technique in the rat jejunum. One milliliter of antiserum to CT and to E. coli and Klebsiella LT completely neutralized the secretory action of each of these three toxins; effective serial dilutions of CT antiserum extended to 1 to 4, whereas those of the antisera to LT were limited to 1 to 2 in most instances. One milliliter of antiserum to E. cloacae LT partially neutralized each of the three coliform LT toxins; serial dilutions were inactive. Antiserum to E. cloacae LT did not neutralize CT. Antiserum to CT and to each of the three coliform LT toxins also had a weak neutralizing effect on the ST toxins of E. coli and Klebsiella, but they did not affect E. cloacae ST. Adsorption of the antiserum to CT and to each of the three LT toxins by incubation with a heat-inactivated preparation of either the homologous or a heterologous LT toxin completely abolished the neutralizing capacity of the antisera towards both LT and ST. These observations indicate that the immunological interrelationship of CT and E. coli LT extends to the LT toxins of Klebsiella and E. cloacae and, further, that these immunological properties are shared to a lesser extent by the ST toxins of E. coli and Klebsiella.

Antigen-Antibody Reactions↗
PubMed1985

A completely synthetic toxoid vaccine containing Escherichia coli heat-stable toxin and antigenic determinants of the heat-labile toxin B subunit.

The immunodeterminant regions of the Escherichia coli heat-labile toxin B subunit were identified by determining the antigenicity, by using enzyme-linked immunosorbent assays, of synthetically produced peptides corresponding to various segments of its 124-amino-acid sequence. The addition of the 18-amino-acid sequence of heat-stable toxin (ST) to some of these peptides enhanced their B subunit antigenicity. Peptide residues containing the 26 amino acids of B subunit sequence 58 to 83 joined to the 18-amino-acid sequence of ST yielded a 44-amino-acid peptide whose antigenicity was 50% that of both native B subunit and ST. This peptide was completely nontoxic when tested in Chinese hamster ovary tissue culture, suckling mouse, and rat ligated ileal loop assays. Peroral immunization of rats with the polymeric form of this peptide yielded a dose-dependent response of intestinal immunoglobulin A antitoxin titers to both the ST and B subunit components and provided strong protection against challenge with viable ST- and heat-labile toxin-producing E. coli strains. The immunogenicity of the synthetic peptide in rats was the same as that of ST and about 50% that of native B subunit. The completely synthetic peptide vaccine has the following advantages over previously described toxoid vaccines that consist of synthetic ST chemically cross-linked to native B subunit derived from bacterial cultures: it is produced by a single synthetic process, it is completely nontoxic, and it is immunogenic for both ST and B subunit.

Amino Acid Sequence↗
PubMed1989

Citrobacter freundii produces an 18-amino-acid heat-stable enterotoxin identical to the 18-amino-acid Escherichia coli heat-stable enterotoxin (ST Ia).

We purified and sequenced the heat-stable enterotoxin produced by Citrobacter freundii. The toxin was detected during purification by reaction with monoclonal antibody to Escherichia coli heat-stable enterotoxin. The C. freundii toxin amino acid sequence was identical to that of the 18-amino-acid heat-stable enterotoxin (STa) produced by toxigenic E. coli.

Amino Acid Sequence↗
PubMed1999

Native and mutant forms of cholera toxin and heat-labile enterotoxin effectively enhance protective efficacy of live attenuated and heat-killed Shigella vaccines.

Both native and mutant forms of cholera toxin (CT) and heat-labile enterotoxin (LT) are effective adjuvants for antigens and killed whole-cell preparations. To determine whether these toxin molecules could also boost the immunogenicity and efficacy of live attenuated vaccines directed against shigellosis, the guinea pig keratoconjunctivitis model was used to evaluate the adjuvant effect of these toxin molecules on EcSf2a-3, a DeltavirG DeltaaroD Escherichia coli-Shigella flexneri 2a hybrid vaccine strain that was previously found to be less protective than its parent strain in the guinea pig model. Experiments using native and mutant toxin molecules showed that both CT and LT and mutant derivatives were effective as an adjuvant for EcSf2a-3 and that the mutant toxin molecules, which were developed to retain adjuvanticity without the toxicity associated with the native molecules, were as effective as the native toxin molecules as adjuvants. Protective efficacy was enhanced for both the oral and intranasal routes of immunization. Serum antibody response to the S. flexneri 2a O antigen, the primary antigen for protective immunity, was not dependent on the addition of an adjuvant. However, enumeration of the O-antigen-specific immunoglobulin G (IgG) and IgA antibody-secreting cells in the spleen and draining lymph nodes following intranasal immunization suggested that enhancement of the local immune response by the toxin molecules may contribute to the observed increase in protective efficacy. The efficacy of heat-killed S. flexneri 2a was enhanced only by mutant LT molecules. These results suggest that the best candidates for enhancing the efficacy of both live attenuated and heat-killed Shigella vaccines with minimal reactogenicity are the mutant toxin molecules.

Adjuvants, Immunologic↗
PubMed1987

Fusion of Escherichia coli heat-stable enterotoxin and heat-labile enterotoxin B subunit.

The 3' terminus of the DNA coding for the extracellular Escherichia coli heat-stable enterotoxin (ST) devoid of transcription and translation stop signals was fused to the 5' terminus of the DNA coding for the periplasmic B subunit of the heat-labile enterotoxin (LTB) deleted of ribosomal binding sites and leader peptide. By RNA-DNA hybridization analysis, it was shown that the fused DNA was transcribed in vivo into an RNA species in close agreement with the expected molecular weight inferred from the nucleotide sequence. The translation products of the fused DNA resulted in a hybrid molecule recognized in Western blots (immunoblots) with antibodies directed against the heat-labile moiety. Anti-LTB antibodies coupled to a solid support bound ST and LTB simultaneously when incubated with ST-LTB cellular extracts. By [35S]cysteine pulse-chase experiments, it was shown that the fused ST-LTB polypeptide was converted from a precursor with an equivalent electrophoretic mobility of 20,800 daltons to an approximately 18,500-dalton species, which accumulated within the cell. The data suggest that wild-type ST undergoes at least two processing steps during its export to the culture supernatant. Blocking the natural carboxy terminus of ST inhibited the second proteolytic step and extracellular delivery of the hybrid molecule.

Amino Acid Sequence↗
PubMed1989

Simultaneous detection of Escherichia coli heat-stable and heat-labile enterotoxin genes with a single RNA probe.

A single RNA probe was synthesized and used to detect simultaneously the methanol-soluble heat-stable enterotoxin and heat-labile enterotoxin genes in Escherichia coli strains. The results with the biotinylated or radioactive probe correlated 100% with the biological assay results for both toxins. The RNA probe detected the three known heat-stable enterotoxin A alleles.

Alleles↗
PubMed1978

Heat inactivation of vaccinia virus particle-associated functions: properties of heated particles in vivo and in vitro.

The heat inactivation characteristics of several vaccinia virus particle-associated functions known to be involved in the transcription of the genome were examined. All functions were more resistant to heat than infectivity. Noninfectious particles were generated which exhibited significant levels of activity of all enzymes examined, and their properties were investigaed both in vitro and in vivo. RNA was synthesized in vitro by such particles, although transport of the RNA into the surrounding medium was defective. This RNA was larger than that made in normal particles but it was polyadenylated and functioned in vitro as a message coding for normal early proteins. The sequences transcribed were similar to those transcribed in normal particles, and we suggest that the production of abnormally large RNA is due to a defect in transcriptional termination. We could not detect any virus-specific protein or RNA synthesis in cells exposed to these inactivated particles and conclude that the loss of infectivity caused by heating is due to a general decline in the activities of a number of particle functions.

Cell Line↗
PubMed1975

A technique for obtaining linear heat-survivor curves with Staphylococcus aureus and its application to the assay of sublethal heat injury.

Staphylococcus aureus was grown in a complex (HK) medium either by a batch technique or by a modified batch technique after growth in a chemostat. These cultures were heat-treated at 52 degrees C, and counted on trypticase soy agar (TSA) or trypticase soy agar containing 7.5% NaCl (TSAS). When linear heat-survivor curves were obtained decimal reduction times (D52 degrees C) could be calculated from the TSA counts and pseudodecimal reduction times (D' 52 degrees C) from the TSAS counts. The D or D' values of batch-grown cells varied from 22 to 133 min and from 3 to 12 min, respectively. With cells grown by the modified technique the values were less variable (D was 22-51 min and D' was 3-7 min). D and D' values could be calculated from the same heat treatment in two of the six estimations with cells grown by the modified technique.

Bacteriological Techniques↗
PubMed1980

Angiotensin II inhibits both heat production and heat loss mechanisms in the rat.

The effects of intracerebroventricular injections of angiotensin II on thermoregulatory responses of conscious rats to ambient temperatures (Ta) of 8, 22, and 30 degrees C were assessed. Administration of angiotensin II produced dose-dependent hypothermia in rats at both Ta 8 and 22 degrees C. The hypothermia in response to angiotensin II was due to decreased metabolic heat production. In addition, angiotensin II produced cutaneous vasoconstriction at Ta 8-22 degrees C. However, at Ta 30 degrees C angiotensin II produced no change in rectal temperature or other thermoregulatory responses. Furthermore, the hypothermia induced by angiotension II was antagonized by pretreatment with 6-hydroxytryptamine (a selective catecholamine neurotoxin) and propranolol (a selective beta-adrenergic antagonist) but not either 5,6-dihydroxytryptamine (a selective serotonin neurotoxin), atropine (a cholinergic antagonist), or phentolamine (a selective alpha-adrenergic antagonist). The data indicate that angiotension II inhibits both heat production and heat loss mechanisms which lead to an alteration in body temperature, probably via the activation of central adrenergic receptors.

5,6-Dihydroxytryptamine↗
PubMed1983

Work in progress: the effect of heat on bleomycin cytotoxicity in vitro and on the accumulation of 57Co-bleomycin in heat-treated rat tumors.

The cytotoxic effects of the sequence and timing in combined hyperthermia and bleomycin treatment were tested in vitro using V79 Chinese hamster cells. The order of treatment was important; heat treatment followed by the administration of bleomycin yielded greater cytotoxicity than when the opposite order was used. To determine whether heat-treated tumors have an altered uptake of bleomycin, rat rhabdomyosarcoma (BA 1112) tumors were heated locally with RF current (43 degrees C, 90 min.), injected with 57Co-bleomycin, and imaged on a radioisotope camera. Results of tumor-to-background (T/B) ratio analysis indicate that (a) local hyperthermia (43 degrees C) does not appear to alter tumor uptake patterns of 57Co-bleomycin; and (b) intravenous and intraperitoneal injections produce similar T/B uptake ratios, typically between 2 and 3 at 120 minutes postinjection. In the BA 1112/WAG/Rij tumor system, local hyperthermia treatment does not seem to interfere with the subsequent accumulation of bleomycin in the tumor.

Animals↗
PubMed2004

Assessment of heat production, heat loss, and core temperature during nitrous oxide exposure: a new paradigm for studying drug effects and opponent responses.

Studies using core temperature (T(c)) have contributed greatly to theoretical explanations of drug tolerance and its relationship to key features of addiction, including dependence, withdrawal, and relapse. Many theoretical accounts of tolerance propose that a given drug-induced psychobiological disturbance elicits opponent responses that contribute to tolerance development. This proposal and its theoretical extensions (e.g., conditioning as a mechanism of chronic tolerance) have been inferred from dependent variables, such as T(c), which represent the summation of multiple underlying determinants. Direct measurements of determinants could increase the understanding of opponent processes in tolerance, dependence, and withdrawal. The proximal determinants of T(c) are metabolic heat production (HP) and heat loss (HL). We developed a novel system for simultaneously quantifying HP (indirect calorimetry), HL (direct gradient layer calorimetry), and T(c) (telemetry) during steady-state administrations of nitrous oxide (N(2)O), an inhalant with abuse potential that has been previously used to study acute and chronic tolerance development to its hypothermia-inducing property. Rats were administered 60% N(2)O (n = 18) or placebo gas (n = 16) for 5 h after a 2-h placebo baseline exposure. On average, N(2)O rapidly but transiently lowered HP and increased HL, each by approximately 16% (P < 0.001). On average, rats reestablished and maintained thermal equilibrium (HP = HL) at a hypothermic T(c) (-1.6 degrees C). However, some rats entered positive heat balance (HP > HL) after becoming hypothermic such that acute tolerance developed, i.e., T(c) rose despite continued drug administration. This work is the first to directly quantify the thermal determinants of T(c) during administration of a drug of abuse and establishes a new paradigm for studying opponent processes involved in acute and chronic hypothermic tolerance development.

Administration, Inhalation↗
PubMed1975

Effect of ambient temperature on heat production and heat loss in burn patients.

Four controls and eight burned patients with thermal injury ranging from 7 to 84% total body surface were studied in an environmental chamber at 25 and 33 degrees C ambient temperature and a constant vapor pressure during two consecutive 24-h periods. Hypermetabolism was present in the burn patients in both ambient temperatures and core and skin temperatures were consistently higher than in the normal men despite increased evaporative water loss. The higher environmental temperature decreased metabolic rate in patients with large thermal injuries in whom the decrement in dry heat loss produced by higher ambient temperature exceeded the increase of wet heat loss. In patients with burns smaller than 60%, these changes equaled one another and higher environmental temperature exerted no effect on metabolic rate. Core-skin heat conductivity increased with burn size; patients with large burns were characterized by inadequate core-skin insulation when exposed to the cooler environment, necessitating the compensatory increase of metabolic rate. This increase, however, was small and of the order of 5-8 kcal times m-2 times h-1.

Adolescent↗
PubMed1997

Spirometry with a Fleisch pneumotachograph: upstream heat exchanger replaces heating requirement.

The exact temperature of the head of an unheated Fleisch pneumotachograph (PT) during recording is not known, and variation in its temperature may lead to errors in measuring spirometric indexes. We measured PT head temperature during blows from five normal subjects, recorded by using a PT with and without an upstream heat exchanger to condition the air to the ambient temperature that was set in a climate chamber. Group mean (+/- SD) temperature of a thermocouple (TC) placed inside the PT head was 11.8 +/- 1.9 degrees C with 7 degrees C ambient, 25.4 +/- 1.3 degrees C at 23 degrees C, and was 37.2 +/- 0.3 degrees C at 37 degrees C. The between-subject range of temperature for this TC was 7.5 degrees at 7 degrees C, 5.5 degrees at 23 degrees C, and 1.1 degrees at 37 degrees C. The mean within-subject within-blow variation of temperature for this TC was 10.0 degrees and 3.3 degrees C for ambient of 7 degrees and 23 degrees C, respectively. At the usual ambient temperature in a laboratory, these differences in temperature lead to a 3.6% between-subject bias in recording, and the within-subject differences lead to 2.6% underreading of peak expiratory flow and a 0.5% overreading later in the blow, which makes ATPS-to-BTPS correction erroneous or difficult to perform. With the use of an upstream heat exchanger, the group mean temperature was 8.7 +/- 0.4 degrees, 23.2 +/- 0.2 degrees, and 37.1 +/- 0.2 degrees C at the three ambient temperatures, respectively, and the within-subject within-blow variation was reduced to < 1 degrees C. A heat exchanger placed upstream of the PT satisfactorily conditioned expired air to the ambient temperature and removed the error.

Adult↗