Modal response and frequency shift of the cantilever in a noncontact atomic force microscope

The force-sensing cantilever in a noncontact atomic force microscope is a continuous system with infinite number of eigenmodes. Although the frequently used point mass model was found sufficient in many cases, its conditions for validity and the insights on how higher eigen-modes could affect the selection of operation parameters were not established. In this letter, we formulate the cantilever motion using modal response analysis, a powerful means enabling an efficient numerical solution and a first order analytical solution. The origins and impacts of the higher eigenfrequency oscillation are then investigated, which sheds lights on achieving optimal imaging conditions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87824/2/183506_1.pd

Second order conic approximation for disassembly line design with joint probabilistic constraints

A problem of profit oriented disassembly line design and balancing with possible partial disassembly and presence of hazardous parts is studied. The objective is to design a production line providing a maximal revenue with balanced workload. Task times are assumed to be random variables with known normal probability distributions. The cycle time constraints are to be jointly satisfied with at least a predetermined probability level. An AND/OR graph is used to model the precedence relationships among tasks. Several lower and upper–bounding schemes are developed using second order cone programming and convex piecewise linear approximation. To show the relevance and applicability of the proposed approach, a set of instances from the literature are solved to optimality

Modeling and analysis of multi‐stage transfer lines with unreliable machines and finite buffers

This paper models and analyzes multi‐stage transfer lines with unreliable machines and finite buffers. The machines have exponential operation, failure, and repair processes. First, a mixed vector–scalar Markov process model is presented based on some notations of mixed vector–scalar operations. Then, several steady‐state system properties are deduced from this model. These include the reversibility and duality of transfer lines, conservation of flow, and the flow rate–idle time relationship. Finally, a four‐stage transfer line case is used to compare and evaluate the accuracy of some approximation methods presented in the literature with the exact numerical solutions this model can provide. The properties and their proofs in this paper lay the theoretic foundation for some widely held assumptions in decomposition techniques of long transfer lines in the area of manufacturing systems engineering.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44292/1/10479_2004_Article_326042.pd

Optimal door fitting with systematic fixture adjustment

A systematic approach is presented to obtain the best door gap quality through optimal door fitting in automobile body manufacturing. First, three indexes of gap quality are defined; they are: (1) door gap width deviation relative to design nominal; (2) door gap parallelism; and (3) car-to-car gap consistency. Then the door-fitting problem is formulated into a general constrained optimization problem. The effects of optimal door fitting on the three quality indexes are evaluated through computer simulation. These results provide a lower bound on the design of nominal door gap by considering process capability. Finally, a computer-aided fixture adjustment scheme is developed to orient a door in a body side opening to achieve the optimal fitting. The amount of adjustment, with the desired orientation obtained from optimization, is calculated based on parametrically modeled local surface features of the fixture and the door. The adequacy of door feature modeling is verified through a door-fitting experiment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45560/1/10696_2005_Article_BF01328807.pd

uPAR Induces Expression of Transforming Growth Factor β and Interleukin-4 in Cancer Cells to Promote Tumor-Permissive Conditioning of Macrophages

Cancer cells condition macrophages and other inflammatory cells in the tumor microenvironment so that these cells are more permissive for cancer growth and metastasis. Conditioning of inflammatory cells reflects, at least in part, soluble mediators (such as transforming growth factor β and IL-4) that are released by cancer cells and alter the phenotype of cells of the innate immune system. Signaling pathways in cancer cells that potentiate this activity are incompletely understood. The urokinase receptor (uPAR) is a cell-signaling receptor known to promote cancer cell survival, proliferation, metastasis, and cancer stem cell–like properties. The present findings show that uPAR expression in diverse cancer cells, including breast cancer, pancreatic cancer, and glioblastoma cells, promotes the ability of these cells to condition co-cultured bone marrow–derived macrophages so that the macrophages express significantly increased levels of arginase 1, a biomarker of the alternatively activated M2 macrophage phenotype. Expression of transforming growth factor β was substantially increased in uPAR-expressing cancer cells via a mechanism that requires uPA-initiated cell signaling. uPAR also controlled expression of IL-4 in cancer cells via a mechanism that involves activation of ERK1/2. The ability of uPAR to induce expression of factors that condition macrophages in the tumor microenvironment may constitute an important mechanism by which uPAR promotes cancer progression

Electrical conductance between conductors with dissimilar temperature-dependent material properties

The method of Greenwood and Williamson is extended to give a general solution for the coupled nonlinear problem of steady-state electrical and thermal conduction across an interface between two conductors of dissimilar materials, for both of which the electrical resistivity and thermal conductivity are functions of temperature. The method presented is sufficiently general to cover all combinations of conductor geometry, material properties and boundary values provided that (i) the current enters and leaves the conductor through two equipotential isothermal surfaces, (ii) the remaining boundaries of the conductor are thermally and electrically insulated and (iii) the interface(s) between different materials would be equipotential surfaces in the corresponding linear problem. Under these restrictions, the problem can be decomposed into the solution of a pair of nonlinear algebraic equations involving the boundary values and the material properties, followed by a linear mapping of the resulting one-dimensional solution into the actual conductor geometry. Examples are given involving single and multiple contact areas between dissimilar half spaces.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48905/2/d82204.pd

Quantum trajectories for Brownian motion

We present the stochastic Schroedinger equation for the dynamics of a quantum particle coupled to a high temperature environment and apply it the dynamics of a driven, damped, nonlinear quantum oscillator. Apart from an initial slip on the environmental memory time scale, in the mean, our result recovers the solution of the known non-Lindblad quantum Brownian motion master equation. A remarkable feature of our approach is its localization property: individual quantum trajectories remain localized wave packets for all times, even for the classically chaotic system considered here, the localization being stronger the smaller $\hbar$.Comment: 4 pages, 3 eps figure