Thermal Oscillations and Peroxide Bombs: Design and Simulation of a Calorimetric Explosives Detector

2013 ◽  
Author(s):  
R. Ball
Keyword(s):  
Thermal Oscillations

A Superconducting Microscope

1971 ◽  
Vol 29 ◽  
pp. 10-11 ◽  
Author(s):  
R. E. Worsham ◽  
J. E. Mann ◽  
E. G. Richardson
Keyword(s):  
Liquid Helium ◽  
Focal Length ◽  
Vacuum System ◽  
Objective Lens ◽  
Electrical Instability ◽  
Radiation Shields ◽  
And Control ◽  
Thermal Oscillations ◽  
Flux Pump

This superconducting microscope, Figure 1, was first operated in May, 1970. The column, which started life as a Siemens Elmiskop I, was modified by removing the objective and intermediate lenses, the specimen chamber, and the complete vacuum system. The large cryostat contains the objective lens and stage. They are attached to the bottom of the 7-liter helium vessel and are surrounded by two vapor-cooled radiation shields.In the initial operational period 5-mm and 2-mm focal length objective lens pole pieces were used giving magnification up to 45000X. Without a stigmator and precision ground pole pieces, a resolution of about 50-100Å was achieved. The boil-off rate of the liquid helium was reduced to 0.2-0.3ℓ/hour after elimination of thermal oscillations in the cryostat. The calculated boil-off was 0.2ℓ/hour. No effect caused by mechanical or electrical instability was found. Both 4.2°K and 1.7-1.9°K operation were routine. Flux pump excitation and control of the lens were quite smooth, simple, and, apparently highly stable. Alignment of the objective lens proved quite awkward, however, with the long-thin epoxy glass posts used for supporting the lens.

Thermionic constants of metals and semiconductors - IV. Monovalent metals (continued)

1954 ◽  
Vol 225 (1161) ◽  
pp. 159-172
Keyword(s):  
Thermal Expansion ◽  
Work Function ◽  
Temperature Variation ◽  
Condensed Phase ◽  
Energy Barrier ◽  
External Pressure ◽  
Detailed Calculation ◽  
Free Electrons ◽  
Saturation Vapour Pressure ◽  
Thermal Oscillations

In a monovalent metal, in which the valency electrons may be regarded as forming a free-electron assemblage, the assumption of a temperature-independent energy barrier at the surface of the metal is shown to be equivalent to taking the free electrons in the condensed phase, namely, the metal, and the electrons in the gaseous phase in thermal equilibrium with it, as forming a homogeneous single component system . The temperature variation of the work function is then determined by the temperature variation of the therm odynamic potential of the electrons in the condensed phase, when the external pressure is kept constant a t the value of the saturation vapour pressure of the electrons, which is equivalent to keeping the pressure of the electron assemblage in the condensed phase also constant, since the energy barrier at the surface is independent of temperature. It is further shown that for a degenerate, or nearly degenerate, electron assemblage the specific heat at constant pressure is the same as that at constant volume, and it is easily calculated. The temperature coefficient of the work function calculated therefrom corresponds to an apparent lowering of about 8 to 10% in the value of the A coefficient in therm ionic emission. This agrees with observation. On the other hand, the thermal expansion of the lattice is found to be about 25 to 50 times that to be expected thermodynamically for the electron assemblage in the condensed phase. This result, when viewed against the nearly normal observed value of the A coefficient, shows that the energy barrier at the surface of the metal should decrease with increase of temperature by the same amount by which the thermodynamic potential of the electrons in the condensed phase decreases as a result of the thermal expansion of the lattice. A detailed calculation is made of the effect of both the thermal expansion of the lattice, and the increased thermal oscillations of the atoms in the lattice, associated with the rise in temperature, on the energy of the barrier at the surface. The net effect is found to be a lowering of this energy of the required magnitude.

scholarly journals Direct observation of surface-state thermal oscillations in SmB6 oscillators

2018 ◽  
Vol 97 (3) ◽  
Author(s):  
Brian Casas ◽  
Alex Stern ◽  
Dmitry K. Efimkin ◽  
Zachary Fisk ◽  
Jing Xia
Keyword(s):  
Direct Observation ◽  
Surface State ◽  
Thermal Oscillations

The Molecular Structure and Arrangement in Stretched Natural Rubber

1949 ◽  
Vol 22 (3) ◽  
pp. 617-633
Author(s):  
Dorothy G. Fisher
Keyword(s):  
Natural Rubber ◽  
Complex Form ◽  
Crystalline Lattice ◽  
Complex Molecules ◽  
Oriented Molecules ◽  
Molecular Pattern ◽  
Diffuse Zone ◽  
Direct Indication ◽  
Zone Pattern ◽  
Thermal Oscillations

Abstract Although there are still some minor discrepancies to be resolved, the appearance of the diffuse-zone electron-diffraction pattern arising from thin films of stretched natural rubber is adequately explained on the basis of the thermal oscillations of the long-chain rubber molecules in the crystalline regions, this pattern being analogous to that which would be given by a stream of oriented molecules in a pseudo-gaseous condition. As Charlesby, Finch and Wilman pointed out, the diffuse-zone pattern has distinct advantages in the examination of complex molecules, since it gives a direct indication of the configuration of the molecule, independent of its mode of fitting into any particular crystalline lattice. In spite of the diffuseness of the patterns with which we are dealing a study of the diffuse zone or molecular pattern has shown that it is possible to discriminate decisively between two postulated atomic configurations which do not differ greatly. In the case of natural rubber, neither of the two configurations investigated agrees in every respect with experiment, but the evidence brought forward above supports the view that the atomic arrangement in the stretched rubber molecule approximates to a simple form having planar units and standard bond lengths and angles, rather than to the more complex form hitherto considered.

The stability of thermal oscillations in a reactive slab: reduction to Hill’s equation

1982 ◽  
Vol 384 (1787) ◽  
pp. 455-462
Keyword(s):  
Surface Temperature ◽  
Hill’S Equation ◽  
Periodic Surface ◽  
Temperature Oscillations ◽  
Hill's Equation ◽  
Chemically Reacting ◽  
The Stability ◽  
Thermal Oscillations ◽  
Surface Temperature Variation ◽  
Time Periodic

The thermal stability of an exothermic chemically reacting slab with time-periodic surface temperature variation is examined. It is shown, on the basis of a good approximation due to Boddington, Gray and Walker, that the behaviour depends on the solutions of an ordinary differential equation of first order. The equation contains a modified amplitude, for small values of which it can be reduced to a particular form of Hill’s equation. Critical values of the Frank-Kamenetskii parameter, as a function of the amplitude ϵ and frequency ω of the surface temperature oscillations, are derived from the latter equation. For ω = 2π and 0 ≼ ϵ ≼ 2 the values are in good agreement with previously calculated ones.

Thermal oscillations during the catalytic hydrogenation of nitrobenzene

1989 ◽  
Vol 54 (2) ◽  
pp. 237-242 ◽  
Author(s):  
L. Petrov ◽  
Ch. Vladov ◽  
A. Eliyas ◽  
N. Kirkov ◽  
K. Tenchev ◽  
...  
Keyword(s):  
Catalytic Hydrogenation ◽  
Thermal Oscillations

Observations of Complex Oscillations in a Closed Thermosyphon

1985 ◽  
Vol 107 (4) ◽  
pp. 833-839 ◽  
Author(s):  
J. E. Hart
Keyword(s):  
Isothermal Section ◽  
Temperature Difference ◽  
Periodic Flow ◽  
Wide Range ◽  
Tube Assembly ◽  
Thermal Oscillations ◽  
Steady Convection

Observations have been made of thermal oscillations in a slightly inclined closed thermosyphon. The thermosyphon is made up of two isothermal tubes, capped at the outer ends, and joined along their axes by an insulating section. The tube assembly is filled with liquid and inclined slightly with respect to the vertical. The lower isothermal section is hotter than the upper one and convection is driven across the insulating region. Between the applied temperature difference at which simple steady convection occurs, and that required for persistent turbulent motions, there is a wide range over which thermal oscillations are observed. These oscillations reflect quasi-periodic flow as well as a type of periodic chaos.

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