High Levels Of Heat Research Articles

Curing characteristics of acrylic bone cement.

Commercial acrylic bone cements are supplied as two components, a polymer powder and a liquid monomer. Mixing of the two components is followed by a progressive polymerization of the liquid monomer to yield a solid mass, a high level of heat being generated during this exothermic reaction. The exposure of bone to high temperatures has led to incidences of bone necrosis and tissue damage, ultimately resulting in failure of the prosthetic fixation. The aim of this study was to determine the thermal properties of two acrylic bone cements as they progress through their polymerization cycles. It was also felt that there was a need to quantify the variations in the curing characteristics as a function of preparing bone cement by different techniques, hand mixing and vacuum mixing. A number of parameters were calculated using the data gathered from the investigation: peak temperature, cure temperature, cure time, and the cumulative thermal necrosis damage index. The results show the temperature profile recorded during polymerization was lowest when the cement was prepared using the Howmedica Mix-Kit I system: 36 degrees C for Palacos R and 41 degrees C for CMW3 respectively. When the acrylic cements were prepared in any vacuum mixing system there was evidence of an increase in the cure temperature. The main factor that contributed to this rise in temperature was an imbalance in the polymer powder : liquid monomer ratio, there was a high incidence of unmixed powder visible in the mixing barrel of some contemporary vacuum mixing devices. Observing the thermal characteristics of the polymethyl methacrylate (PMMA) bone cements assessed, it was found that particular formulations of bone cements are suited to certain mixing methodologies. It is vital that a full investigation is conducted on a cement mixing/delivery system prior to its introduction into the orthopaedic market.

Physics and technology of spallation neutron sources

A substantial body of research is necessary in order to be able to make reliable predictions on the performance and safety of Accelerator Driven Systems (ADS), in particular of their spallation targets. So far, practical experience has resulted from the development of research neutron sources only. Next to fission and fusion, spallation is an efficient process for releasing neutrons from nuclei. Unlike the other two reactions, it is an endothermal process and can, therefore, not be used per se in energy generation. In order to sustain a spallation reaction, an energetic beam of particles, most commonly protons, must be supplied onto a heavy target. Spallation can, however, play an important role as a source of neutrons whose flux can be easily controlled via the driving beam. Although sophisticated Monte Carlo codes exist to compute all aspects of a spallation facility, many features can be understood on the basis of simple physics arguments. Technically a spallation facility is very demanding, not only because a reliable and economic accelerator of high power is needed to drive the reaction, but also, and in particular, because high levels of radiation and heat are generated in the target which are difficult to cope with. Radiation effects in a spallation environment are different from those commonly encountered in a reactor and are probably even more temperature dependent than the latter because of the high gas production rate. A commonly favored solution is the use of molten heavy metal targets. While radiation damage is not a problem in this case, except for the container, other issues need to be considered. R&D carried out for the development of spallation neutron sources will thus be beneficial also directly for ADS.

Thermal characteristics of curing acrylic bone cement

Commercial acrylic bone cements are supplied as two components, a polymer powder and a liquid monomer. Mixing of the two components is followed by a progressive polymerisation of the liquid monomer to yield a solid mass, a high level of heat being generated during this exothermic reaction. The exposure of bone to high temperatures has led to incidences of bone necrosis and tissue damage, ultimately resulting in failure of the prosthetic fixation. The aim of this study was to determine the thermal properties of various acrylic bone cements as they progress through their polymerisation cycles. It was also felt that there was a need to quantify variations in the curing characteristics as a function of preparing bone cement by different techniques, hand mixing and vacuum mixing. A number of parameters were calculated using the data gathered from the investigation; peak temperature, cure temperature, cure time, and the cumulative thermal necrosis damage index. Observing the thermal characteristics of the polymethyl methacrylate bone cements assessed, it was found that particular formulations of bone cements are suited to certain m xing methodologies. It is vital that a full investigation is conducted on a cement mixing/delivery system prior to its introduction into the orthopaedic market.

Pain

Pain

Cerebral blood-flow changes evoked by two levels of painful heat stimulation: a positron emission tomography study in humans

Positron emission tomography (PET) and accumulation of H 2 15O as a marker of neuronal activity were used to create maps of cerebral blood-flow changes evoked by painful heat stimulation in 10 subjects. Two levels of painful tonic and phasic heat stimuli were applied with use of a newly developed contact heat thermode on the volar surface of the dominant (right) arm. The subjects participated in two separate PET sessions. Maps reflecting low and high levels of painful tonic heat were obtained in the first session, and low and high levels of painful phasic heat in the second session. The subjects scored their peak pain intensity and unpleasantness on 10-cm visual analogue scales. For each subject, PET images were aligned to nuclear magnetic resonance (NMR) images and remapped into the standardized co-ordinate system of Talairach. After normalization of the PET volumes, subtraction images were formed voxel-by-voxel and converted to a t-statistic volume. The perceived pain intensity and unpleasantness were identical with painful tonic and phasic heat stimulation. Directed searches revealed significant blood-flow increases in the contralateral primary sensorimotor cortex (MI/SI), SII, insular cortex and cingulate cortex when the low tonic heat map was subtracted from the high. A similar, but not identical, pain-processing network was observed for the maps representing the subtraction of low and high phasic heat. In this subtraction, the blood-flow increases in MSI/SI did not reach statistical significance, and significant blood flow decreases were found in the contralateral middle temporal gyrus. Finally, the location of the activation site in the cingulate cortex was different from that observed during tonic heat pain. This study has provided more evidence for the existence of a common pain-processing network engaged during the perception of different levels of toxic and phasic heat pain.

Effect of radiant heat on the surface hardness of glass polyalkenoate (ionomer) cement

The use of heat to improve mechanical properties of materials is a widely accepted phenomenon. It has been studied in dentistry with a view to improving the properties of resin composite. Dental cements may benefit by the application of heat, in particular with regard to their early surface properties. This study was carried out to examine the effect of the application of radiant heat to the surface hardness of one type of glass polyalkenoate cement. It was found that raising the temperature of the surface of the cement to a maximum of 60°C significantly improved the early surface hardness of the material. The application of a high level of heat also improved the surface hardness of the cement after 24 h compared to cement which had not been heat treated. The use of heat would appear to accelerate the matrix-forming reaction of the material and although further work is necessary this technique may have clinical application.

Packaging of GaAs signal processors on multichip modules

The extensions that must be made to the deposited multichip module (MCM-D) fabrication technology and to the design and layout of these structures in order to accommodate high clock rate ECL and GaAs digital integrated circuits are discussed. Techniques for attachment of the high clock rate chips to the MCM-Ds are discussed, including wire bond, tape automated bond (TAB), flip-chip solder attachment, and flip adhesives. The tradeoffs between these different approaches are noted. Electrical issues are addressed. The problem of launching fast rise time, wide bandwidth signals onto and retrieving such signals from the MCM-Ds are noted. The thermal problems associated with the packing of 10-50 high power dissipation chips onto such small structures are discussed, along with methods of removing such high levels of heat by changes in materials incorporated into the stacked structures. Several MCM-D design and fabrication projects under way which attempt to address and solve some of the problems are described, along with some of the initial results of these studies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analgesic properties of a systemically-administered synthetic dipeptide of 5-hydroxytryptophan

Synthetic peptides of 5-hydroxytryptophan (5-HTP), including N-acetyl-5-HTP-5-HTP amide (5-HTP-ACETYL-DP), specifically inhibit the binding of serotonin to serotonin binding protein. 5-HTP-ACETYL-DP also produces a long-lasting, opiate-sensitive analgesia following central, but not systemic administration. The present study evaluated an apolar derivative of 5-HTP dipeptide, N-hexanoyl-5-HTP-5-HTP amide (5-HTP-HEX-DP), for its analgesic properties in rats following systemic administration. 5-HTP-HEX-DP (5–50 mg/kg) significantly increased jump thresholds in a dose-dependent manner with peak analgesia occurring at 2.5 hr after injection, and lasting up to 5 hr. In the tail-flick assay, 5-HTP-HEX-DP (20 mg/kg) produced a significant antinociceptive effect at 1 hr post-injection using both high and low intensity levels of radiant heat. While 5-HTP-HEX-DP and morphine each elicited analgesia following acute administration, chronic (14 days) incremental dosing with 5-HTP-HEX-DP or morphine resulted in persistent analgesia in 5-HTP-HEX-DP-treated animals, and a loss of analgesia in morphine-treated rats. Thus, significant tolerance to morphine, but not 5-HTP-HEX-DP analgesia developed using this protocol. Hence, 5-HTP-HEX-DP is a systemically-active analgesic which fails to develop tolerance when administered daily over 14 days.

Reduction of Oxygen Consumption, Insensible Water Loss, and Radiant Heat Demand with Use of a Plastic Blanket for Low-Birth-Weight Infants Under Radiant Warmers

Eight very low-birth-weight premature infants (mean birth weight 1.11 +/- 0.05 [SEM]kg, mean gestation 30 +/- 1 weeks, and mean age 9 +/- 2 days) were studied under servocontrolled radiant warmers with and without a loosely fitted, transparent, and flexible Saran plastic blanket. Metabolic rate was significantly less in all infants when covered by the blanket (oxygen consumption was 7.99 +/- 1.13 mL/kg/min v 9.00 +/- 1.10 mL/kg/min uncovered, P less than .001). There were also significant reductions in insensible water loss (1.86 +/- 0.18 v 1.25 +/- 0.20 mL/kg/h, P less than .01) and in heat demand from the radiant warmer (14.3 +/- 1.3 v 9.9 +/- 1.4 mW/cm2, P less than .001) when infants were nursed under the blanket compared with the control condition, respectively. Covering the critically ill, very low-birth-weight infant nursed under a radiant heater with a thin, transparent layer of Saran is beneficial in reducing oxygen consumption, insensible water loss, and the need for exposure to high levels of radiant heat. Further investigation to confirm the benefits and possible complications of plastic blankets should be conducted before routine use can be recommended.

The Development of a Superior Form of Fire-Protective Cladding for Quarters at Ekofisk, Norwegian North Sea

The safety of personnel residing in a living-quarters module on an offshore platform can be greatly improved by the installation of a heat-shield wall platform can be greatly improved by the installation of a heat-shield wall on the inboard side of the quarters. This paper describes the study that developed the heat-shield wall and that helped develop a tool for predicting the mechanics and consequences of certain platform disasters. predicting the mechanics and consequences of certain platform disasters. Introduction Early 1973 heralded the expected increase in offshore activity on Phase 2 constructions at the Ekofisk field, and launched the designs of future Phase 3 installations.The first installation to be engineered in the Phase 3 development program was the Cod field platform, to stand in about 230 ft of water in Block 7/11 and to lie about 50 miles northwest of Ekofisk Center. The platform was to be a combined drilling, production. and platform was to be a combined drilling, production. and accommodations platform with a production rate of 17,400 BOPD and 118.5 MMscf/D of gas. Because of its remote location it had to be fully self-supporting a compact production facility with its own living quarters and with its products pipelined to Ekoflsk Center.The quarters were to be permanent and were designed toaccommodate all drilling and well service company crews during well drilling, completion, and testing;accommodate all work crews during production equipment and line hook-up; andeventually house the operations and maintenance personnel during the production life of the field. production life of the field. To the regulatory authorities involved, the concept of permanent living quarters on a production platform close permanent living quarters on a production platform close to hydrocarbon-handling equipment was highly innovative, and was considered unsafe and of unsound practice.To assure the regulatory authorities to the contrary, it was decided to prepare certain theoretical analyses for Cod. The intent was to demonstrate that in the event of failures, selected platform disasters, or normal operating upsets, personnel on board were protected within the confines of the quarters for an adequate period.The documentation for these analyses was called the safety study. This study examined production flaring during equipment malfunctions, calculated normal and abnormal operating noise levels, and predicted the sequence and consequences of certain major platform accidents occurring as a result of possible material or equipment failure.The section of the study that analyzed these catastrophies (as the major accidents were called), although rudimentary in its approach, did produce parameters and predict effects that clearly indicated that a superior type predict effects that clearly indicated that a superior type of fire protection was required for the quarters. It showed that the quarters, where the personnel would ultimately assemble in an emergency, had to be protected on its inboard side and roof by a construction that could withstand high, intense thermal shocks, continually high radiant heat levels, and the errosive effects of convective heat fluxes.To meet these conditions a special wall was devised, called the heat-shield wall; similar types of high-grade fire barriers were designed for the roof and skid.Materials were selected and fire-tested individually. Components of these materials were assembled into sample wall panels and subjected to ad hoc fire tests, where the loading criterion was the heat flux and the upper test limit was the temperature level at which their steel support structure began to lose its physical properties. p. 221

Studies with Chicks on the Growth Depressing Factor(s) in Faba Beans (Vicia faba L. var. minor)

The growth response of broiler chicks was improved when they were fed diet containing high levels (greater than 85%) of heat treated as compared to raw faba beans. Pelleting and microwave treatment of faba beans containing 10% moisture resulted in maximal improvements in chick growth rates and feed efficiency of only 6% and 8%, respectively. Steam autoclaving (121 degrees for 20 minutes), extrusion (130 degrees or 152 degrees), or microwave treatment of faba beans containing 18% added water resulted in maximal improvements of 16% in growth rates and 19% in feed: gain ratios. the above study, a time course study of the relationship between faba beans autoclaving time anc chick growth response, and studies with individual faba bean fractions (starch isolate and protein isolate) suggests that processing improves the utilization of faba bean mainly through its effects on components associated with the protein and possibly the hull portions of faba beans. The utilization of faba bean starch is not improved with processing. Although the nature of the growth depressing factor(s) has not been established, the results from this study indicated that the major component does not appear to be a tryspin inhibitor, hemagglutinin, some other heat labile protein, or vicine.