Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

A trust region algorithm with a worst-case iteration complexity of $$\mathcal{O}(\epsilon ^{-3/2})$$O(∈-3/2) for nonconvex optimization

Abstract: We propose a trust region algorithm for solving nonconvex smooth optimization problems. For any $$\overline{\epsilon }\in (0,\infty )$$∈¯?(0,?), the algorithm requires at most $$\mathcal{O}(\epsilon ^{-3/2})$$O(∈-3/2) iterations, function evaluations, and derivative evaluations to drive the norm of the gradient of the objective function below any $$\epsilon \in (0,\overline{\epsilon }]$$∈?(0,∈¯]. This improves upon the $$\mathcal{O}(\epsilon ^{-2})$$O(∈-2) bound known to hold for some other trust region algorithms and matches the $$\mathcal{O}(\epsilon ^{-3/2})$$O(∈-3/2) bound for the recently proposed Adaptive Regularisation framework using Cubics, also known as the arc algorithm. Our algorithm, entitled trace, follows a trust region framework, but employs modified step acceptance criteria and a novel trust region update mechanism that allow the algorithm to achieve such a worst-case global complexity bound. Importantly, we prove that our algorithm also attains global and fast local convergence guarantees under similar assumptions as for other trust region algorithms. We also prove a worst-case upper bound on the number of iterations, function evaluations, and derivative evaluations that the algorithm requires to obtain an approximate second-order stationary point.

Nanoindentation measurements on Cu–Sn and Ag–Sn intermetallics formed in Pb-free solder joints

Abstract: Nanoindentation testing has been used to measure the hardness and elastic modulus of Ag3Sn, Cu6Sn5, and Cu3Sn intermetallics, as well as Sn–Ag–Cu solder and pure Sn and Cu. The intermetallics were fabricated by solid-state annealing of diffusion couples prepared from a substrate (Cu or Ag) and a solder material (Sn or Sn–Ag–Cu solder), providing geometries and length scales as close as possible to a real solder joint. Nanoindentation results for the intermetallics, representing penetration depths of 20–220 nm and loads from 0.7 to 9.5 mN, reveal elastic/plastic deformation without evidence of fracture. Measured hardness values of Cu6Sn5 (6.5 ± 0.3 GPa) and Cu3Sn (6.2 ± 0.4 GPa) indicate a potential for brittle behavior, while Ag3Sn (2.9 ± 0.2 GPa) appears much softer and ductile. Using a bulk Cu6Sn5 sample, Vickers hardness testing revealed an indentation size effect for this compound, with a hardness of 4.3 GPa measured at a load of 9.8 N. An energy balance model is used to explain the dependence of hardness with load or depth, where the observation of an increasing amount of fracture with applied load is identified as the primary mechanism. This result explains discrepancies between nanoindentation and Vickers results previously reported.

Trainee nondisclosure in supervision: What are they not telling you?

Abstract: Aims: The purposes of this study were to examine: (1) the content of and reasons for trainee nondisclosure in supervision, and (2) the influence of trainee anxiety and perception of the supervisory working alliance on amount of nondisclosure and willingness to disclose. Method: As the focus of the study was a single supervision session, qualitative and quantitative data were collected from 204 trainees about their most recent supervision session. Results: Within the single supervision session on which they reported, 84.3% of trainees withheld information from their supervisors. Trainees reported an average of 2.68 nondisclosures occurring in the session, with the most common nondisclosure involving a negative supervision experience. Trainee perception of a better supervisory working alliance was related to less nondisclosure and greater overall willingness to disclose in supervision. Higher trainee anxiety was related to greater nondisclosure and lower overall willingness to disclose in supervision. Implications: The implications of the findings for the practice of supervision are discussed and areas for further research are suggested.

RockSalt: better, faster, stronger SFI for the x86

Abstract: Software-based fault isolation (SFI), as used in Google's Native Client (NaCl), relies upon a conceptually simple machine-code analysis to enforce a security policy. But for complicated architectures such as the x86, it is all too easy to get the details of the analysis wrong. We have built a new checker that is smaller, faster, and has a much reduced trusted computing base when compared to Google's original analysis. The key to our approach is automatically generating the bulk of the analysis from a declarative description which we relate to a formal model of a subset of the x86 instruction set architecture. The x86 model, developed in Coq, is of independent interest and should be usable for a wide range of machine-level verification tasks.