Surface characterization of selected LDEF tray clamps

The surface characterization of chromic acid anodized 6061-T6 aluminum alloy tray clamps has shown differences in surface chemistry depending upon the position on the Long Duration Exposure Facility (LDEF). Water contact angle results showed no changes in wettability of the tray clamps. The overall surface topography of the control, trailing edge(E3) and leading edge(D9) samples was similar. The thickness of the aluminum oxide layer for all samples determined by Auger depth profiling was less than one micron. X-ray photoelectron spectroscopy (XPS) analysis of the tray clamps showed significant differences in the surface composition. Carbon and silicon containing compounds were the primary contaminants detected

The interaction of fingermark deposits on metal surfaces and potential ways for visualisation

The interaction of fingermark deposits on metals has been examined by a variety of techniques. Visualisation by film growth has been the main area of investigation through: thermal oxidation, anodising, peroxide solution, and the interaction with vapour of iodine and ammonium sulphide. Corrosion of the underlying metal has also been examined as an alternative means of visualisation. Confocal microscopy was used to look at the film thickness and corrosion products around the prints. Scanning electron microscopy and energy dispersion of X-rays (SEM-EDX) examined a number of metal samples to investigate film growth and the elemental distribution. The observations suggest that differential oxidation was occurring as well as corrosion into the metal. Fingermark deposits on metals can corrode into the metal depending on the reactivity of the metal and leave a recoverable mark. However, fingermark deposits can also alter the rate of chemical reaction of the substrate metal by oxidation. In some cases organic matter can inhibit reaction, both when forming an oxide layer and when corroding the metal. However, signs of third level detail from pore contact may also be visible and the monovalent ions from salts could also influence film growth. Whilst further work would need to be carried out to decide whether any of these techniques may have application in fingermark recovery, this study does suggest that fingermarks on metals may be recoverable after incidents such as fires or immersion in water

Local states of free bose fields

These notes contain an extended version of lectures given at the ``Summer School on Large Coulomb Systems'' in Nordfjordeid, Norway, in august 2003. They furnish a short introduction to the theory of quantum harmonic systems, or free bose fields. The main issue addressed is the one of local states. I will adopt the definition of Knight of ``strictly local excitation of the vacuum'' and will then state and prove a generalization of Knight's Theorem which asserts that finite particle states cannot be perfectly localized. It will furthermore be explained how Knight's a priori counterintuitive result can be readily understood if one remembers the analogy between finite and infinite dimensional harmonic systems alluded to above. I will also discuss the link between the above result and the so-called Newton-Wigner position operator thereby illuminating, I believe, the difficulties associated with the latter. I will in particular argue that those difficulties do not find their origin in special relativity or in any form of causality violation, as is usually claimed

Quantum Electrodynamics in Two-Dimensions at Finite Temperature. Thermofield Bosonization Approach

The Schwinger model at finite temperature is analyzed using the Thermofield Dynamics formalism. The operator solution due to Lowenstein and Swieca is generalized to the case of finite temperature within the thermofield bosonization approach. The general properties of the statistical-mechanical ensemble averages of observables in the Hilbert subspace of gauge invariant thermal states are discussed. The bare charge and chirality of the Fermi thermofields are screened, giving rise to an infinite number of mutually orthogonal thermal ground states. One consequence of the bare charge and chirality selection rule at finite temperature is that there are innumerably many thermal vacuum states with the same total charge and chirality of the doubled system. The fermion charge and chirality selection rules at finite temperature turn out to imply the existence of a family of thermal theta vacua states parametrized with the same number of parameters as in zero temperature case. We compute the thermal theta-vacuum expectation value of the mass operator and show that the analytic expression of the chiral condensate for any temperature is easily obtained within this approach, as well as, the corresponding high-temperature behavior

Nonlinear Dynamics of the Perceived Pitch of Complex Sounds

We apply results from nonlinear dynamics to an old problem in acoustical physics: the mechanism of the perception of the pitch of sounds, especially the sounds known as complex tones that are important for music and speech intelligibility

On "full" twisted Poincare' symmetry and QFT on Moyal-Weyl spaces

We explore some general consequences of a proper, full enforcement of the "twisted Poincare'" covariance of Chaichian et al. [14], Wess [50], Koch et al. [34], Oeckl [41] upon many-particle quantum mechanics and field quantization on a Moyal-Weyl noncommutative space(time). This entails the associated braided tensor product with an involutive braiding (or $\star$-tensor product in the parlance of Aschieri et al. [3,4]) prescription for any coordinates pair of $x,y$ generating two different copies of the space(time); the associated nontrivial commutation relations between them imply that $x-y$ is central and its Poincar\'e transformation properties remain undeformed. As a consequence, in QFT (even with space-time noncommutativity) one can reproduce notions (like space-like separation, time- and normal-ordering, Wightman or Green's functions, etc), impose constraints (Wightman axioms), and construct free or interacting theories which essentially coincide with the undeformed ones, since the only observable quantities involve coordinate differences. In other words, one may thus well realize QM and QFT's where the effect of space(time) noncommutativity amounts to a practically unobservable common noncommutative translation of all reference frames.Comment: Latex file, 24 pages. Final version to appear in PR

Effective Lagrangians in 2+ϵ2 + \epsilon Dimensions

The failure of the the loop expansion and effective lagrangians in two dimensions, which traditionally hinges on a power counting argument is considered. We establish that the book keeping device for the loop expansion, a role played by (the reciprocal of) the pion-decay constant itself vanishes for $d=2$, thereby going beyond the power counting argument. We point the connection of our results to the distinct phases of the candidate for the effective lagrangians, the non-linear sigma model, in $d=2+\epsilon$, and eventually for $d=2$. In light of our results, we recall some of the relavant features of the multi-flavor Schwinger and large $N_f$ $QCD_2$ as candidates for the underlying theory in $d=2$.Comment: 13 pages plain LaTeX, to be run twice. Replaced with expanded and corrected version. One footnote adde

Two classes of generalized functions used in nonlocal field theory

We elucidate the relation between the two ways of formulating causality in nonlocal quantum field theory: using analytic test functions belonging to the space $S^0$ (which is the Fourier transform of the Schwartz space $\mathcal D$) and using test functions in the Gelfand-Shilov spaces $S^0_\alpha$. We prove that every functional defined on $S^0$ has the same carrier cones as its restrictions to the smaller spaces $S^0_\alpha$. As an application of this result, we derive a Paley-Wiener-Schwartz-type theorem for arbitrarily singular generalized functions of tempered growth and obtain the corresponding extension of Vladimirov's algebra of functions holomorphic on a tubular domain.Comment: AMS-LaTeX, 12 pages, no figure

Relativistic resonances: Their masses, widths, lifetimes, superposition, and causal evolution

Whether one starts form the analytic S-matrix definition or the requirement of gauge parameter independence in renormalization theory, a relativistic resonance is given by a pole at a complex value s of energy squared. The complex number s does not define the mass and width separately and this definition does not lead to interfering Breit-Wigner if two or more resonances are involved. To accomplish both we invoke the decaying particle aspect of a resonance and associate to each pole a space of relativistic Gamow kets which transform irreducibly under causal Poincare transformations. A Gamow state has an exponential time evolution and one can choose of the many possible width parameters, that parameter as the width of the relativistic resonance which equals the inverse lifetime. This uniquely defines the mass and width parameters for a relativistic resonance. Two or more poles in the same partial wave are given by the sum of Breit-Wigners in the scattering amplitude and by a superposition of Gamow vectors with each Gamow vector corresponding to one Breit-Wigner. In addition to the sum of Breit-Wigners the scattering amplitude contains a background amplitude representing direct production of the final state (contact terms).This contact amplitude is associated to a background vector which is a continuous superposition of Lippmann-Schwinger states. Omitting this continuum gives the Weisskopf-Wigner approximation.Comment: 22 pages, REVTe

Zitterbewegung and semiclassical observables for the Dirac equation

In a semiclassical context we investigate the Zitterbewegung of relativistic particles with spin 1/2 moving in external fields. It is shown that the analogue of Zitterbewegung for general observables can be removed to arbitrary order in \hbar by projecting to dynamically almost invariant subspaces of the quantum mechanical Hilbert space which are associated with particles and anti-particles. This not only allows to identify observables with a semiclassical meaning, but also to recover combined classical dynamics for the translational and spin degrees of freedom. Finally, we discuss properties of eigenspinors of a Dirac-Hamiltonian when these are projected to the almost invariant subspaces, including the phenomenon of quantum ergodicity