Microwave Gaseous Discharges

Contains reports on three research projects.United States Atomic Energy Commission (Contract AT(30-1) 1842

Spectral isolation of naturally reductive metrics on simple Lie groups

We show that within the class of left-invariant naturally reductive metrics $\mathcal{M}_{\operatorname{Nat}}(G)$ on a compact simple Lie group $G$, every metric is spectrally isolated. We also observe that any collection of isospectral compact symmetric spaces is finite; this follows from a somewhat stronger statement involving only a finite part of the spectrum.Comment: 19 pages, new title and abstract, revised introduction, new result demonstrating that any collection of isospectral compact symmetric spaces must be finite, to appear Math Z. (published online Dec. 2009

Microwave Gaseous Discharges

Contains reports on five research projects.United States Atomic Energy Commission (Contract AT(30-1) 1842

One-Parameter Squeezed Gaussian States of Time-Dependent Harmonic Oscillator and Selection Rule for Vacuum States

By using the invariant method we find one-parameter squeezed Gaussian states for both time-independent and time-dependent oscillators. The squeezing parameter is expressed in terms of energy expectation value for time-independent case and represents the degree of mixing positive and negative frequency solutions for time-dependent case. A {\it minimum uncertainty proposal} is advanced to select uniquely vacuum states at each moment of time. We show that the Gaussian states with minimum uncertainty coincide with the true vacuum state for time-independent oscillator and the Bunch-Davies vacuum for a massive scalar field in a de Sitter spacetime.Comment: 13 Pages, ReVTeX, no figure

Microwave Gaseous Discharges

Contains research objectives and reports on five research projects

Oxidation in a temperature gradient

The effects of a temperature gradient and heat flux on point defect diffusion in protective oxide scales were examined. Irreversible thermodynamics were used to expand Fick's first law of diffusion to include a heat flux term--a Soret effect. Oxidation kinetics were developed for the oxidation of cobalt and for nickel doped with chromium. Research in progress is described to verify the effects of a heat flux by oxidizing pure cobalt in a temperature gradient above 800 C, and comparing the kinetics to isothermal oxidation. The tests are being carried out in the new high temperature gaseous corrosion and corrosion/erosion facility at the Albany Research Center

Hot Corrosion at Air-Ports in Kraft Recovery Boilers

Hot corrosion can occur on the cold-side of airports in Kraft recovery boilers. The primary corrosion mechanism involves the migration of sodium hydroxide and potassium hydroxide vapors through leaks in the furnace wall at the airports and their subsequent condensation. It has been reported that stainless steel is attacked much faster than carbon steel in composite tubes, and that carbon steel tubing, when used with a low-chromium refractory, does not exhibit this type of corrosion. For hot corrosion fluxing of metal oxides, either acidic or basic fluxing takes place, with a solubility minimum at the basicity of transition between the two reactions. For stainless steel, if the basicity of the fused salt is between the iron and chromium oxide solubility minima, then a synergistic effect can occur that leads to rapid corrosion. The products of one reaction are the reactants of the other, which eliminates the need for rate-controlling diffusion. This effect can explain why stainless steel is attacked more readily than carbon steel

Specific heat study of single crystalline Pr0.63_{0.63} Ca0.37_{0.37} MnO3_{3} in presence of a magnetic field

We present the results of a study of specific heat on a single crystal of Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ performed over a temperature range 3K-300K in presence of 0 and 8T magnetic fields. An estimate of the entropy and latent heat in a magnetic field at the first order charge ordering (CO) transition is presented. The total entropy change at the CO transition which is $\approx$ 1.8 J/mol K at 0T, decreases to $\sim$ 1.5 J/mol K in presence of 8T magnetic field. Our measurements enable us to estimate the latent heat $L_{CO}$ $\approx$ 235 J/mol involved in the CO transition. Since the entropy of the ferromagnetic metallic (FMM) state is comparable to that of the charge-ordered insulating (COI) state, a subtle change in entropy stabilises either of these two states. Our low temperature specific heat measurements reveal that the linear term is absent in 0T and surprisingly not seen even in the metallic FMM state.Comment: 8 pages (in RevTEX format), 12 figures (in postscript format) Submitted to Phys. Rev.

State-of-the-art review of electrochemical noise sensors

There are a number of different techniques capable of being used to measure corrosion within equipment. The most simple, the use of metal coupons, usually causes the process to be shut down, is manpower intensive, and has a time delay in getting the required corrosion information. Electrical Resistance (ER) techniques are often used but their response is very sensitive to temperature and they cannot differentiate between general and localized corrosion. Electrochemical techniques, such as linear polarization resistance (LPR), electrochemical noise (EN), electrochemical impedance spectroscopy (EIS), harmonic distortion analysis (HDA), and electrochemical frequency modulation (EFM), have the capability of solving most of those drawbacks. Electrochemical probes can be mounted permanently in most equipment, give regular measurements of the intensity of corrosion, and some can detect localized corrosion. Of all of the electrochemical techniques, EN has the most potential for being used successfully to measure general and localized corrosion rates of equipment. The EN technique was studied in the late 1970s and early 80s as a means of detecting localized (stochastic) corrosion phenomena, such as occurs with pitting, crevice and cavitation attack. EN measurements are based on fluctuations in electrochemical potential and corrosion current that occur during corrosion. Electrochemical potential is related to the driving force (thermodynamics) of the reaction, while corrosion current is related to the rate of reaction (kinetics) of the reaction. The idea is that random electrochemical events on the surface of a corroding metal will generate noise in the overall potential and current signals. Each type of corrosion (for example general corrosion, pitting corrosion, crevice corrosion, and stress corrosion cracking) will have a characteristic “fingerprint” or “signature” in the signal noise. This “fingerprint” can be used to predict the type and severity of corrosion that is occurring. By comparison, conventional electrochemical techniques such as LPR, EIS, HDA and EFM rely on a steady-state analogy for the determination of general corrosion rates. Early studies were carried out using potential EN measurements, using time domain, statistical and frequency domain analyses to characterise the electrochemical response of systems undergoing localised corrosion. Current EN measurements followed quickly using zero resistance ammetry to study the current noise between two identical electrodes. For general corrosion processes, EN has been demonstrated independently by several workers to provide information similar to LPR. Noise technology has been used to study systems undergoing very low to very high rates of corrosion, for example, coatings performance, passive systems undergoing pit initiation/propagation, condensing systems, systems undergoing stress corrosion cracking, and general corrosion through to the very high corrosion rates experienced during chemical cleaning processes. This review will describe: state of the art methods and probes used to measure EN, data acquisition requirements, theory to analyze the signal and to relate the signal to corrosion rates and types, the results of EN field trials, and laboratory results in environments similar to gaspipelines

Momentum of an electromagnetic wave in dielectric media

Almost a hundred years ago, two different expressions were proposed for the energy--momentum tensor of an electromagnetic wave in a dielectric. Minkowski's tensor predicted an increase in the linear momentum of the wave on entering a dielectric medium, whereas Abraham's tensor predicted its decrease. Theoretical arguments were advanced in favour of both sides, and experiments proved incapable of distinguishing between the two. Yet more forms were proposed, each with their advocates who considered the form that they were proposing to be the one true tensor. This paper reviews the debate and its eventual conclusion: that no electromagnetic wave energy--momentum tensor is complete on its own. When the appropriate accompanying energy--momentum tensor for the material medium is also considered, experimental predictions of all the various proposed tensors will always be the same, and the preferred form is therefore effectively a matter of personal choice.Comment: 23 pages, 3 figures, RevTeX 4. Removed erroneous factor of mu/mu_0 from Eq.(44