scholarly journals Feeling the heat: source–sink mismatch as a mechanism underlying the failure of thermal tolerance

2020 ◽  
Vol 223 (16) ◽  
pp. jeb225680 ◽  
Author(s):  
Matti Vornanen
Keyword(s):  
High Temperature ◽  
High Temperatures ◽  
Signal Transmission ◽  
Mechanistic Explanation ◽  
Ion Current ◽  
Electrical Excitability ◽  
Temperature Dependent ◽  
Branching Points ◽  
Low Pass ◽  
Source Sink

ABSTRACTA mechanistic explanation for the tolerance limits of animals at high temperatures is still missing, but one potential target for thermal failure is the electrical signaling off cells and tissues. With this in mind, here I review the effects of high temperature on the electrical excitability of heart, muscle and nerves, and refine a hypothesis regarding high temperature-induced failure of electrical excitation and signal transfer [the temperature-dependent deterioration of electrical excitability (TDEE) hypothesis]. A central tenet of the hypothesis is temperature-dependent mismatch between the depolarizing ion current (i.e. source) of the signaling cell and the repolarizing ion current (i.e. sink) of the receiving cell, which prevents the generation of action potentials (APs) in the latter. A source–sink mismatch can develop in heart, muscles and nerves at high temperatures owing to opposite effects of temperature on source and sink currents. AP propagation is more likely to fail at the sites of structural discontinuities, including electrically coupled cells, synapses and branching points of nerves and muscle, which impose an increased demand of inward current. At these sites, temperature-induced source–sink mismatch can reduce AP frequency, resulting in low-pass filtering or a complete block of signal transmission. In principle, this hypothesis can explain a number of heat-induced effects, including reduced heart rate, reduced synaptic transmission between neurons and reduced impulse transfer from neurons to muscles. The hypothesis is equally valid for ectothermic and endothermic animals, and for both aquatic and terrestrial species. Importantly, the hypothesis is strictly mechanistic and lends itself to experimental falsification.

Improvement of Dielectric Performance of a Prototype AlN High Temperature Chip-level Package

2011 ◽  
Vol 2011 (HITEN) ◽  
pp. 000052-000057 ◽  
Author(s):  
Liang-Yu Chen
Keyword(s):  
High Temperature ◽  
Dielectric Properties ◽  
High Temperatures ◽  
Substrate Surface ◽  
Substrate Material ◽  
Glass Coating ◽  
Temperature Dependent ◽  
High Temperature Electronics ◽  
Dielectric Performance ◽  
Parasitic Parameters

Aluminum nitride (AlN) has been proposed as a packaging substrate material for reliable high temperature electronics operating in a wide temperature range. However, it was discovered in a recent study that the dielectric properties of some commercial polycrystalline AlN materials change quite significantly with temperature at high temperatures. These material properties resulted in undesired large and temperature-dependent parasitic parameters for a prototype chip-level package based on an AlN substrate with the yttrium oxide dopant. This paper reports a method using a coating layer of a commercial thick-film glass on the AlN substrate surface to significantly reduce both the parasitic capacitances and parasitic conductances between neighboring inputs/outputs (I/Os) of a prototype AlN chip-level package. The parasitic parameters of 8-I/Os low power chip-level packages with the insulating glass coating were characterized at frequencies from 120 Hz to 1 MHz between room temperature and 500°C. These results were compared with the parameters of AlN packages without the glass coating. The results indicate that the parasitic capacitances and conductances between I/Os of the improved prototype AlN packages are significantly reduced and stable at high temperatures. The method using a glass coating provides a feasible way to mitigate the temperature dependence of dielectric properties of AlN and further utilize AlN as a reliable packaging substrate material for high temperature applications.

scholarly journals Depression of heart rate in fish at critically high temperatures is due to atrioventricular block

2020 ◽  
Author(s):  
Jaakko Haverinen ◽  
Matti Vornanen
Keyword(s):  
Heart Rate ◽  
Cardiac Output ◽  
High Temperature ◽  
Cardiac Function ◽  
High Temperatures ◽  
Ventricular Myocytes ◽  
Mechanistic Explanation ◽  
Excitation Threshold ◽  
Av Block ◽  
Peak Value

ABSTRACTAt critically high temperature, cardiac output in fish collapses due to depression of heart rate (bradycardia). However, the cause of bradycardia remains unresolved. Here we provide a mechanistic explanation for the temperature induced bradycardia. To this end rainbow trout (Oncorhynchus mykiss; acclimated at +12°C) were exposed to acute warming, while cardiac function was followed from electrocardiograms. From +12°C to +25.3°C, electrical excitation between different parts of the heart was coordinated but above +25.3°C atrial and ventricular beating rates became partly dissociated due to 2:1 atrioventricular (AV) block. With further warming atrial rate increased to the peak value of 188 ± 22 bpm at +27°C, while the rate of the ventricle reached the peak value of 124 ± 10 bpm at +25.3°C and thereafter dropped to 111 ± 15 bpm at +27°C. In single ventricular myocytes, warming from +12°C to +25°C attenuated electrical excitability as evidenced by increases in rheobase current and critical depolarization required to trigger action potential. The depression of excitability was caused by temperature induced decrease in input resistance (sarcolemmal K+ leak via the outward IK1 current) of resting myocytes and decrease in inward charge transfer by the Na+ current (INa) of active myocytes. Collectively these findings show that at critically high temperatures AV block causes ventricular bradycardia which is an outcome from the increased excitation threshold of the ventricle due to changes in passive (resting ion leak) and active (inward charge movement) electrical properties of ventricular myocytes. The sequence of events from the level of ion channels to the cardiac function in vivo provides a mechanistic explanation for the depression of cardiac output in fish at critically high temperature.

Temperature-Dependent Coefficient of Thermal Expansion of Silicon Nitride Films Used in Microelectromechanical Systems

1999 ◽  
Vol 605 ◽  
Author(s):  
Melissa Bargmann ◽  
Amy Kumpel ◽  
Haruna Tada ◽  
Patricia Nieva ◽  
Paul Zavracky ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Silicon Nitride ◽  
Cantilever Beam ◽  
High Temperatures ◽  
Microelectromechanical Systems ◽  
Coefficient Of Thermal Expansion ◽  
Temperature Dependent ◽  
Temperature Property ◽  
Silicon Nitride Films

AbstractMicroelectromechanical systems (MEMS) have potential application in high temperature environments such as in thermal processing of microelectronics. The MEMS designs require an accurate knowledge of the temperature dependent thermomechanical properties of the materials. Techniques used at room temperature often cannot be used for high-temperature property measurements. MEMS test structures have been developed in conjunction with a novel imaging apparatus designed to measure either the modulus of elasticity or thermal expansion coefficient of thin films at high temperatures. The MEMS test structure is the common bi-layered cantilever beam which undergoes thermally induced deflection at high temperatures. An individual cantilever beam on the order of 100 νm long can be viewed up to approximately 800°C. With image analysis, the curvature of the beam can be determined; and then the difference in coefficient of thermal expansion between the two layers can be determined using numerical modeling. The results of studying silicon nitride films on silicon oxide are presented for a range of temperatures.

Sterile intersexuality in an isopod induced by the interaction between a bacterium (Wolbachia) and the environment

1998 ◽  
Vol 76 (3) ◽  
pp. 493-499 ◽  
Author(s):  
T Rigaud ◽  
P Juchault
Keyword(s):  
High Temperature ◽  
High Temperatures ◽  
Lethal Effect ◽  
Autosomal Gene ◽  
Temperature Dependent ◽  
Armadillidium Vulgare ◽  
Genomic Conflict ◽  
Heritable Trait ◽  
Partial Destruction

An endocellular bacterium of the genus Wolbachia changes chromosomic (ZZ) males into functional females in a number of populations of the woodlouse Armadillidium vulgare. The interaction between the feminizing effect of Wolbachia and the lethal effect of high temperature on these bacteria is shown to be responsible for the appearance of high proportions of sterile intersexes (Si). Wolbachia-infected females produced an average of 15% Si when reared for 200 days under a daily thermoperiodic regime that included 4 h at 30°C. A temperature of 30°C is known to destroy Wolbachia. The Si phenotype may therefore be due to the partial destruction (or inhibition) of the feminizing bacteria by high temperature during development. This induction of a proportion of Si differs in two ways from the intersexuality induced by the conflict between the feminizing agent and a host autosomal gene. First, the genomic conflict does not lead to the production of numerous Si, and second, the temperature-dependent production of Si is a sporadic event induced by the environment, rather than being a heritable trait. The overproduction of sterile offspring at high temperatures can result inWolbachia-infected females of A. vulgare suffering a loss of fitness.

High Temperature n- and p-type Doped Microcrystalline Silicon Layers Grown by VHF PECVD Layer-by-Layer Deposition

2003 ◽  
Vol 762 ◽  
Author(s):  
A. Gordijn ◽  
J.K. Rath ◽  
R.E.I. Schropp
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
High Temperatures ◽  
Continuous Wave ◽  
Hydrogen Plasma ◽  
Silicon Layer ◽  
Dark Conductivity ◽  
High Deposition Rate ◽  
Layer By Layer ◽  
Microcrystalline Silicon

AbstractDue to the high temperatures used for high deposition rate microcrystalline (μc-Si:H) and polycrystalline silicon, there is a need for compact and temperature-stable doped layers. In this study we report on films grown by the layer-by-layer method (LbL) using VHF PECVD. Growth of an amorphous silicon layer is alternated by a hydrogen plasma treatment. In LbL, the surface reactions are separated time-wise from the nucleation in the bulk. We observed that it is possible to incorporate dopant atoms in the layer, without disturbing the nucleation. Even at high substrate temperatures (up to 400°C) doped layers can be made microcrystalline. At these temperatures, in the continuous wave case, crystallinity is hindered, which is generally attributed to the out-diffusion of hydrogen from the surface and the presence of impurities (dopants).We observe that the parameter window for the treatment time for p-layers is smaller compared to n-layers. Moreover we observe that for high temperatures, the nucleation of p-layers is more adversely affected than for n-layers. Thin, doped layers have been structurally, optically and electrically characterized. The best n-layer made at 400°C, with a thickness of only 31 nm, had an activation energy of 0.056 eV and a dark conductivity of 2.7 S/cm, while the best p-layer made at 350°C, with a thickness of 29 nm, had an activation energy of 0.11 V and a dark conductivity of 0.1 S/cm. The suitability of these high temperature n-layers has been demonstrated in an n-i-p microcrystalline silicon solar cell with an unoptimized μc-Si:H i-layer deposited at 250°C and without buffer. The Voc of the cell is 0.48 V and the fill factor is 70 %.

NICROFER 5520 Co

Alloy Digest ◽  
1995 ◽  
Vol 44 (3) ◽  
Keyword(s):  
High Temperature ◽  
Chemical Composition ◽  
Physical Properties ◽  
Tensile Properties ◽  
High Temperatures ◽  
Heat Treating ◽  
High Temperature Corrosion ◽  
Creep Properties ◽  
Nickel Chromium ◽  
Temperature Performance

Abstract NICROFER 5520 Co is a nickel-chromium-cobalt-molybdenum alloy with excellent strength and creep properties up to high temperatures. Due to its balanced chemical composition the alloy shows outstanding resistance to high temperature corrosion in the form of oxidation and carburization. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on high temperature performance as well as forming, heat treating, machining, and joining. Filing Code: Ni-480. Producer or source: VDM Technologies Corporation.

CARLSON ALLOY C601

Alloy Digest ◽  
1994 ◽  
Vol 43 (7) ◽  
Keyword(s):  
High Temperature ◽  
Physical Properties ◽  
Stress Corrosion ◽  
Tensile Properties ◽  
High Temperatures ◽  
Stress Corrosion Cracking ◽  
Heat Treating ◽  
Resistance To Stress ◽  
Extended Exposure ◽  
Sulfur Containing

Abstract Carlson Alloy C601 is characterized by high tensile, yield and creep-rupture strengths for high temperature service. The alloy is not embrittled by extended exposure to high temperatures and has excellent resistance to stress-corrosion cracking, to carburizing, nitriding and sulfur containing environments. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as creep. It also includes information on forming, heat treating, machining, and joining. Filing Code: Ni-458. Producer or source: G.O. Carlson Inc.

INCOTHERM TD

Alloy Digest ◽  
2005 ◽  
Vol 54 (11) ◽  
Keyword(s):  
Corrosion Resistance ◽  
High Temperature ◽  
Physical Properties ◽  
Tensile Properties ◽  
Oxidation Resistance ◽  
High Temperatures ◽  
Rare Earths ◽  
Temperature Performance

Abstract Incotherm TD is a thermocouple-sheathing alloy with elements of silicon and rare earths to enhance oxidation resistance at high temperatures. This datasheet provides information on composition, physical properties, and tensile properties as well as deformation. It also includes information on high temperature performance and corrosion resistance as well as forming. Filing Code: Ni-628. Producer or source: Special Metals Corporation.

HASTELLOY ALLOY X

Alloy Digest ◽  
1954 ◽  
Vol 3 (12) ◽  
Keyword(s):  
High Temperature ◽  
Physical Properties ◽  
Tensile Properties ◽  
Oxidation Resistance ◽  
High Temperatures ◽  
Heat Treating ◽  
Operating Conditions ◽  
Molybdenum Alloy ◽  
High Temperature Strength ◽  
Nickel Chromium

Abstract HASTELLOY Alloy X is a nickel-chromium-iron-molybdenum alloy recommended for high-temperature applications. It has outstanding oxidation resistance at high temperatures under most operating conditions, and good high-temperature strength. This datasheet provides information on composition, physical properties, and tensile properties as well as creep. It also includes information on forming, heat treating, and machining. Filing Code: Ni-14. Producer or source: Haynes Stellite Company.

KUBOTA ALLOY HT

Alloy Digest ◽  
2011 ◽  
Vol 60 (11) ◽  
Keyword(s):  
High Temperature ◽  
Physical Properties ◽  
Tensile Properties ◽  
Nickel Alloy ◽  
Oxidation Resistance ◽  
High Temperatures ◽  
Temperature Performance ◽  
Iron Chromium

Abstract Kubota Alloy HT is an iron-chromium-nickel alloy that has both strength and oxidation resistance at high temperatures. This datasheet provides information on composition, physical properties, and tensile properties as well as creep. It also includes information on high temperature performance as well as casting and joining. Filing Code: SS-1108. Producer or source: Kubota Metal Corporation, Fahramet Division.

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