scholarly journals Heats of Chemical Reactions and Submarine Heat Production

1974 ◽  
Vol 37 (1) ◽  
pp. 213-215 ◽  
Author(s):  
W. S. Fyfe
Keyword(s):  
Chemical Reactions ◽  
Heat Production

The priority of the heat production in a muscle twitch

1958 ◽  
Vol 148 (932) ◽  
pp. 397-402 ◽  
Keyword(s):  
Chemical Reactions ◽  
Heat Production ◽  
Mechanical Response ◽  
Substantial Part ◽  
Hypertonic Solution ◽  
Isotonic Solution ◽  
Muscle Twitch ◽  
Previous Conclusion

When a muscle has been soaked in a moderately hypertonic solution its mechanical response to a shock is delayed, but its heat production is almost normal and starts considerably earlier than its shortening. After a more hypertonic solution the mechanical response is abolished, but a substantial part of the heat production remains. These effects are rapidly reversed by soaking in a normal isotonic solution. They strengthen the previous conclusion that chemical reactions triggered by a stimulus precede the mechanical response.

Heat production in oscillating chemical reactions: three examples

1987 ◽  
Vol 112 (1) ◽  
pp. 95-100 ◽  
Author(s):  
I. Lamprecht ◽  
B. Schaarschmidt ◽  
T. Plesser
Keyword(s):  
Chemical Reactions ◽  
Heat Production

The positive and negative heat production associated with a nerve impulse

1958 ◽  
Vol 148 (931) ◽  
pp. 149-187 ◽  
Keyword(s):  
Chemical Reactions ◽  
Heat Production ◽  
Surface Membrane ◽  
Nerve Impulse ◽  
Active Phase ◽  
Fibre Surface ◽  
Excitable Membrane ◽  
Substantial Part ◽  
Recording Equipment ◽  
Muscle Twitch

The ‘initial’ heat production of a non-medullated nerve ( Maia ) has been reinvestigated with more rapid recording equipment than was previously available. In a single impulse at 0° C a positive heat production was observed averaging about 9 x 10 -6 cal/g nerve: this is rapid and is probably associated with the active phase of the impulse. It is followed by a rather slower heat absorption averaging about 7 x 10 -6 cal/g nerve and lasting for about 300 ms. Previous methods were too slow to do more than record the difference between the two, the ‘net heat’, viz. about 2 x 10 -6 cal/g nerve: this is about one-third greater at 0°C than at 18° C. Maia nerves contain fibres from 20 to 0.3 µ in diameter, and about half the heat is probably derived from fibres less than 3.0 µ . The velocities of impulses in them at 0° C vary from 1.4 to 0.1 m/s, so impulses reach the recording thermojunctions throughout a long interval. Thus the observed course of the heat production is the resultant of positive and negative components in different fibres, and a substantial part of each is masked. The real positive and negative heats, therefore, are substantially greater than those observed: on the most likely estimate of velocity distribution, in a single impulse at 0° C they are about 14 x 10 -6 cal/g and — 12 x 10 -6 cal/g, respectively. Heat production, like ionic interchange, is probably proportional to fibre surface, which in 1 g of Maia nerve is estimated as 10 4 cm 2 . If the fibre surface is taken as 50 Å thick, the heats just calculated, if reckoned per gram of surface material, are 2.8 x 10 -3 cal and — 2.4 x 10 -3 cal, respectively. The former is about the same as the heat produced per gram in a muscle twitch. During the passage of an impulse there is known to be an interchange of Na and K ions between the axoplasm and the outside fluid. When isotonic solutions of NaCl and KCl are mixed there is a production of heat. A substantial part of the heat during an impulse may be derived from the interchange of Na and K. Another part may be associated with chemical reactions occurring in the excitable membrane during the cycle of permeability change accompanying the passage of an impulse. The negative heat production is discussed. It cannot be connected with ‘pumping back’ the Na and K ions; this is a much slower process and anyhow would probably involve a positive heat production. It may be a sign of endothermic chemical reactions, representing a first (anaerobic) stage in recovery, which occur in the surface membrane following the completion of the permeability cycle. The question is considered whether the positive and negative phases of the heat production could be due to the discharge and recharge, during the action potential, of the condenser residing in the excitable membrane. The heats so calculated are of the right order of size, but on present evidence the time relations seem to be quite wrong. The amount of K which escapes per impulse from Maia nerve during slow repetitive stimulation at 0° C was measured. It depends greatly on frequency of stimulation; at ‘zero frequency’ it was about 9 X 10 -8 mole/g x impulse.

scholarly journals On the relation between the output of uric acid and the rate of heat production the body

1907 ◽  
Vol 79 (535) ◽  
pp. 541-545
Keyword(s):  
Uric Acid ◽  
Total Nitrogen ◽  
Chemical Reactions ◽  
Heat Production ◽  
Acid Production ◽  
Muscular Activity ◽  
The Body ◽  
Considerable Degree ◽  
Purine Derivatives ◽  
Pathological Conditions

The rate at which uric acid is turned out of the body is very different at different times of the day, even when the food contains no ready-made purine derivatives. It is higher during the early hours of the day than at anytime, and it is considerably lower at night. The reason for this, as was pointed out by one of us, is not likely to be that the excretory functions are depressed at night, since these functions, to judge from the total nitrogen of the urine, are more active during the first hours of sleep than at any time in the 24 hours. And since, when the diet is confined to bread, butter, and milk, the uric acid must be derived from the body substance and not from the food, it seems probable that there is some function of the body which is in abeyance during sleep and is, to a considerable degree, responsible for the output of uric acid; some function, that is to say, which is effected by chemical reactions involving the production of uric acid, and possibly in some measure creatinine. If it is possible to identify this function, the activity of which can, on a suitable diet, be measured by the amount of the uric acid excreted, it may be possible to give a clearer account of the processes by which, at the onset of fever, the temperature of the body can be sent up independently of any voluntary muscular activity; for while the temperature is rising, the output of uric acid may be four times as great as it otherwise would be. Similarly, in the study of other pathological conditions in which uric acid plays a part, it must be of importance to be able to point to the kind of activity which is accompanied by increased uric acid production.

Surface reactions observed by photoemission electron microscopy (PEEM)

1992 ◽  
Vol 50 (1) ◽  
pp. 286-287
Author(s):  
H.H. Rotermund
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Work Function ◽  
Chemical Reactions ◽  
Reaction Diffusion ◽  
Dynamic Processes ◽  
Clean Surface ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Photoemission Electron

Chemical reactions at a surface will in most cases show a measurable influence on the work function of the clean surface. This change of the work function δφ can be used to image the local distributions of the investigated reaction,.if one of the reacting partners is adsorbed at the surface in form of islands of sufficient size (Δ>0.2μm). These can than be visualized via a photoemission electron microscope (PEEM). Changes of φ as low as 2 meV give already a change in the total intensity of a PEEM picture. To achieve reasonable contrast for an image several 10 meV of δφ are needed. Dynamic processes as surface diffusion of CO or O on single crystal surfaces as well as reaction / diffusion fronts have been observed in real time and space.

Microwaves: Application in Electron Microscopy

1990 ◽  
Vol 48 (3) ◽  
pp. 140-141
Author(s):  
Anthony S-Y Leong ◽  
David W Gove
Keyword(s):  
Electron Microscopy ◽  
Light Microscopy ◽  
Chemical Reactions ◽  
Electromagnetic Waves ◽  
Tissue Fixation ◽  
Primary Method ◽  
Dipolar Molecules ◽  
Wide Range ◽  
Time Required ◽  
Cryostat Sections

Microwaves (MW) are electromagnetic waves which are commonly generated at a frequency of 2.45 GHz. When dipolar molecules such as water, the polar side chains of proteins and other molecules with an uneven distribution of electrical charge are exposed to such non-ionizing radiation, they oscillate through 180° at a rate of 2,450 million cycles/s. This rapid kinetic movement results in accelerated chemical reactions and produces instantaneous heat. MWs have recently been applied to a wide range of procedures for light microscopy. MWs generated by domestic ovens have been used as a primary method of tissue fixation, it has been applied to the various stages of tissue processing as well as to a wide variety of staining procedures. This use of MWs has not only resulted in drastic reductions in the time required for tissue fixation, processing and staining, but have also produced better cytologic images in cryostat sections, and more importantly, have resulted in better preservation of cellular antigens.

Fine structure and properties of defects in naturally occurring silicates and oxides

1990 ◽  
Vol 48 (4) ◽  
pp. 460-461
Author(s):  
David R. Veblen
Keyword(s):  
Chemical Reactions ◽  
High Resolution Electron Microscopy ◽  
Extended Defects ◽  
Single Chain ◽  
Naturally Occurring ◽  
Resolution Electron ◽  
Fine Structures ◽  
Image Simulations ◽  
Similar Crystal Structure

Extended defects and interfaces control many processes in rock-forming minerals, from chemical reactions to rock deformation. In many cases, it is not the average structure of a defect or interface that is most important, but rather the structure of defect terminations or offsets in an interface. One of the major thrusts of high-resolution electron microscopy in the earth sciences has been to identify the role of defect fine structures in reactions and to determine the structures of such features. This paper will review studies using HREM and image simulations to determine the structures of defects in silicate and oxide minerals and present several examples of the role of defects in mineral chemical reactions. In some cases, the geological occurrence can be used to constrain the diffusional properties of defects.The simplest reactions in minerals involve exsolution (precipitation) of one mineral from another with a similar crystal structure, and pyroxenes (single-chain silicates) provide a good example. Although conventional TEM studies have led to a basic understanding of this sort of phase separation in pyroxenes via spinodal decomposition or nucleation and growth, HREM has provided a much more detailed appreciation of the processes involved.

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