Investigation of the Effect of Artificial Internal Defects on the Tensile Behavior of Laser Powder Bed Fusion 17–4 Stainless Steel Samples: Simultaneous Tensile Testing and X-Ray Computed Tomography

Experimental Mechanics - Insufficient data are available to fully understand the effects of metal additive manufacturing (AM) defects for widespread adoption of the emerging technology....     

Matrices with positive principal minors

A new necessary and sufficient condition is given for all principal minors of a square matrix to be positive. A special subclass of such matrices, called quasidominant matrices, is also examined.     

Embedding euclidean lie algebras into quantum structures

We show that it is possible to express the basis elements of the Lie algebra of the Euclidean group,E(2), as simple irrational functions of certainq deformed expressions involving the generators of the quantum algebraU _q (so(2, 1)). We consider implications of these results for the representation theory of the Lie algebra ofE(2). We briefly discess analogous results forU _q (so(2, 2)). Presented at the 6th International Colloquium on Quantum Groups: “Quantum Groups and Integrable Systems”, Prague, 19–21 June 1997.     

Radiative reaction and quantum mechanics

According to the principles of quantum mechanics, the classical Lorentz-Dirac equations of the electron should follow from quantum electrodynamics in the classical limit. We show this is indeed true for the special case in which the charge does not radiate, provided the momentum operators in the Dirac theory are identified, in the classical limit, with the effective momenta of the Lorentz-Dirac equations.     

Solubility of water in polyimides: Quartz crystal microbalance measurements

The solubility of water vapor in four different polyimides at 100% relative humidity and 22°C was measured by means of a quartz crystal microbalance system. The results confirm earlier conclusions that diffusion in these polymers is Fickian, and are sufficiently precise that the order of solubilities is unambiguous. The differences between the values are interpreted in terms of morphological variations rather than variations in chemical affinity for water. Diffusion coefficients are also reported.     

Positive-energy irreps of the quantum anti de Sitter algebra

We obtain positive-energy irreducible representations of theq-deformed anti de Sitter algebraU _q (so(3, 2)) by deformation of the classical ones. When the deformation parameterq isN-th root of unity, all these irreducible representations become unitary and finite-dimensional. Generically, their dimensions are smaller than those of the corresponding finite-dimensional non-unitary representations ofso(3, 2). We discuss in detail the singleton representations, i.e. the Di and Rac. WhenN is odd, the Di has dimension 1/2(N ²–1) and the Rac has dimension 1/2(N ²+1), while ifN is even, both the Di and Rac have dimension 1/2N ². These dimensions are classical only forN=3 when the Di and Rac are deformations of the two fundamental non-unitary representations ofso(3, 2).Presented at the 4th Colloquium Quantum groups and integrable systems, Prague, 22–24 June 1995.On leave from Bulgarian Acad. Sci., Institute of Nuclear Research and Nuclear Energy, 72 Tsarigradsko Chaussee, 1784 Sofia, Bulgaria.On leave from Pennsylvania State University (Fulbright scholar).     

Localization and the Weyl algebras

Physics of Atomic Nuclei - Let W n (ℝ) be the Weyl algebra of index n. It is well known that so(p, q) Lie algebras can be viewed as quadratic polynomial (Lie) algebras in W n (ℝ) for p...     

LCVD of copper: Deposition rates and deposit shapes

Laser chemical vapor deposition of copper has been performed under a variety of conditions. The results are interpreted using the kinetic model of Ehrlich and Tsao. We find that the kinetics of the process are limited by the rates of surface reactions and not by diffusion of reactant molecules to the surface. Furthermore, we find that deposit shapes are quite sensitive to laser intensity and scan rate.     

Induced Representations and Invariant Integral Operators for SU (2, 2)

The elementary representations (ER) of SU (2, 2) induced from the three non-trivial parabolic subgroups P₀, P₁, P₂ are explicitly constructed in two equivalent realizations. We exhibit a one-to-one correspondence between the P₀ and P₂ induced representations. The corresponding representations are equivalent. We also exhibit a two-to-one correspondence between the P₁ ERs and a subset of the P₀ ERs; however, the corresponding representations are only partially equivalent. The Knapp-Stein integral intertwining operators are explicitly given for all representations in consideration.