Cold spray surface patterning of aluminum on aluminum, silicon, glass, and printed circuit board substrates

17 USC 105 interim-entered record; under review.The aim of the present study is to investigate the feasibility and the criteria of using the cold spray technique for surface patterning to create two-dimensional surface features on various substrates. Metal meshes (16, 45, 170, 200, 400, and 5/16″) were used as screens for surface patterning in this investigation; fabricated features were characterized with optical microscope, scanning electron microscope, and optical profilometer. Processing parameters like mesh size, standoff distance, gun traverse speed, and number of spray passes were examined to study their influence to the morphology of the fabricated features. Two-dimensional aluminum features were successfully fabricated on aluminum, soda-lime glass, silicon wafer, and the copper foil-layer of printed circuit board. The smallest feature created with −45 to +5 μm aluminum feedstock powders, has an average size of 67.4 μm. It was determined that the pore size of a mesh needs to be at least 3.3 times bigger than the average size of feedstock powders in order to create features successfully. To estimate the probability of feedstock powders passing through a mesh and simulate the topography of the fabricated features, a Monte Carlo simulation incorporating the particle size distribution and the geometries of meshes was developed. With the capability of creating features on diverse substrates, the cold spray surface patterning technique shows promising potential to create heterogeneous two-dimensional functional features or devices at micron-sized with high efficiency.This work was funded by the Department of Mechanical and Aerospace Engineering of the Naval Postgraduate School

Smearing effect due to the spread of a probe-particle on the Brownian motion near a perfectly reflecting boundary

Quantum fluctuations of electromagnetic vacuum are investigated in a half-space bounded by a perfectly reflecting plate by introducing a probe described by a charged wave-packet distribution in time-direction. The wave-packet distribution of the probe enables one to investigate the smearing effect upon the measured vacuum fluctuations caused by the quantum nature of the probe particle. It is shown that the wave-packet spread of the probe particle significantly influences the measured velocity dispersion of the probe. In particular, the asymptotic late-time behavior of its $z$-component, $$, for the wave-packet case is quite different from the test point-particle case ($z$ is the coordinate normal to the plate). The result for the wave-packet is \sim 1/\t^2 in the late time (\t is the measuring time), in stead of the reported late-time behavior $\sim 1/z^2$ for a point-particle probe. This result can be quite significant for further investigations on the measurement of vacuum fluctuations.Comment: 8 page

Quantum Stress Tensor Fluctuations and their Physical Effects

We summarize several aspects of recent work on quantum stress tensor fluctuations and their role in driving fluctuations of the gravitational field. The role of correlations and anticorrelations is emphasized. We begin with a review of the properties of the stress tensor correlation function. We next consider some illuminating examples of non-gravitational effects of stress tensors fluctuations, specifically fluctuations of the Casimir force and radiation pressure fluctuations. We next discuss passive fluctuations of spacetime geometry and some of their operational signatures. These include luminosity fluctuations, line broadening, and angular blurring of a source viewed through a fluctuating gravitational field. Finally, we discuss the possible role of quantum stress tensor fluctuations in the early universe, especially in inflation. The fluctuations of the expansion of a congruence of comoving geodesics grows during the inflationary era, due to non-cancellation of anticorrelations that would have occurred in flat spacetime. This results in subsequent non-Gaussian density perturbations and allows one to infer an upper bound on the duration of inflation. This bound is consistent with adequate inflation to solve the horizon and flatness problems.Comment: 15 pages, 1 figure; invited talk presented at the 3rd Mexican Meeting on Experimental and Theoretical Physics, Mexico City, September 10-14, 200

Switching effect upon the quantum Brownian motion near a reflecting boundary

The quantum Brownian motion of a charged particle in the electromagnetic vacuum fluctuations is investigated near a perfectly reflecting flat boundary, taking into account the smooth switching process in the measurement. Constructing a smooth switching function by gluing together a plateau and the Lorentzian switching tails, it is shown that the switching tails have a great influence on the measurement of the Brownian motion in the quantum vacuum. Indeed, it turns out that the result with a smooth switching function and the one with a sudden switching function are qualitatively quite different. It is also shown that anti-correlations between the switching tails and the main measuring part plays an essential role in this switching effect. The switching function can also be interpreted as a prototype of an non-equilibrium process in a realistic measurement, so that the switching effect found here is expected to be significant in actual applications in vacuum physics.Comment: 12 pages, 2 figures This version is just to correct the author-lis

Improving the flexibility of the desktop PC supply chain

Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering; in conjunction with the Leaders for Manufacturing Program at MIT, 2006.Vita.Includes bibliographical references (leaves 83-84).Dell Inc. is a company headquartered in Round Rock, TX founded by entrepreneur Michael Dell in 1984. In its 20+ years of history, Dell has revolutionized the PC industry by deploying the "Dell Direct" model--eliminating the "middleman" retailers in the PC supply chain-and achieved the Number 1 market share in the PC market. In managing its supply chain, Dell also utilizes its direct model and owns strategic relationships with many of the contract manufacturers, most of which have factories in China. For desktop PCs, these contract manufacturers produce semi-completed products and ship these products to Dell's U.S. and Ireland factories, and then Dell factory workers complete the remainder of the desktop PC assembly process by installing the components that are customized by Dell's customers. In order for Dell to remain low-cost and readily respond to customer demand, Dell's suppliers maintain a minimum amount of semi-completed goods inventory in a hub near each of Dell's manufacturing facilities. Foxconn (Hon Hai Precision Industry Co., Ltd.) was founded in 1974 by Taiwanese entrepreneur Tai-ming Terry Gou. Besides its home base in Taiwan, Foxconn has major manufacturing operations in mainland China, U.S., and Europe.(cont.) Originally a maker of plastic parts, connectors and cable assemblies, Foxconn has since established manufacturing facilities worldwide that produce a variety of high-tech products, including electrical and mechanical components, modules and sub-systems for PCs, consumer electronics, handsets, networking, and display products. Foxconn's eCMMS (e-enabled components, modules, move and service) model and its high degree of vertical integration in supply chain allow Foxconn to address clients' needs from a single source. Foxconn services name-brand clients, such as Dell. Similar to Dell's inventory management strategies, Foxconn also requires its suppliers to keep a minimum amount of raw materials at its inbound warehouse. Dell and Foxconn's shared strategy is to maintain a minimum level of inventory while balancing it with a continuity of supply, in order to maximize sales and minimize the inventory-holding cost. However, this inventory management policy has been disrupted by a continuous shortage of chipset supply from Dell's chipset manufacturer since July 2004. A chipset is a critical component of the desktop motherboard manufactured by Foxconn in China.(cont.) After manufacturing the motherboard, Foxconn is also responsible for installing the motherboard into the desktop chassis before shipping the motherboard-inside chassis from China to U.S. or Ireland by ocean. The chipset supply shortage has caused Foxconn not to be able to procure chipsets in order to manufacture the motherboards in China. As a result, some chassis are shipped empty by ocean first, and motherboards are air-freighted later. This leads Dell to utilize Third-Party Integrators (3PI) in the U.S. to install the motherboards into the chassis. The continuous shortfall of chipset supply increases the volume of motherboard-chassis integration in the U.S. and further increases Dell's overall manufacturing costs. Thus, the goal of this thesis is to create a framework for improving the flexibility of the Desktop PC Supply Chain. This framework examines how the various players contribute to the supply chain, the dynamics among these players that led to the current supply chain design, and how Dell can work with its suppliers and other strategic partners to more effectively balance demand and supply.(cont.) This thesis will explain the symptoms as well as the root causes of the problem, present the original direction of my internship and the exogenous factors that caused the direction to change, and describe the renewed direction. It will also examine Dell's decision-making process, organizational processes, and leadership issues involved. In addition, it will discuss how other industries structure their manufacturing given a supply shortage and the importance of trust and innovating contracting in cultivating more collaborative relationships in a supply chain.by Johnson Wu.S.M.M.B.A