Ejection Forces and Friction Coefficients from Injection Molding Experiments Using Rapid Tooling Inserts

Experiments have been performed with injection mold inserts made using solid freeform fabrication processes in an effort to further study such applications for economic production of small quantities of parts. Static friction coefficients were determined for HDPE and HIPS against P-20 steel, sintered LaserForm ST-100, and stereolithography SL 5170 using the ASTM D 1894 standard. Injection mold inserts were constructed of the same three materials and were used to inject cylindrical parts using HDPE and HIPS. Ejection forces were measured, and a model was used to calculate ejection forces and apparent coefficients of static friction. Statistical analyses were used to determine the effects of packing time, cooling time and packing pressure on ejection force for the three insert types. This paper compares experimental and calculated ejection forces, compares standard friction test results to calculated apparent coefficients of friction, summarizes the statistical results, and comments on the feasibility of using rapid tooled inserts for injection molding.Mechanical Engineerin

Prospects for Internet technology

This paper surveys the current developments in Internet technology, with a particular emphasis on performance, and the growing need for various guarantees of quality of service. It discusses hardware technologies for increased bandwidth, mechanisms for requesting and providing specific qualities of service, and various scaling issues. Fi-nally it discusses mechanisms needed for (but not the economics of) the Internet in the mass market. To this end, we survey changes in the areas of addressing, and flow management. 1

Statistical Properties of Avalanches in Networks

We characterize the distributions of size and duration of avalanches propagating in complex networks. By an avalanche we mean the sequence of events initiated by the externally stimulated `excitation' of a network node, which may, with some probability, then stimulate subsequent firings of the nodes to which it is connected, resulting in a cascade of firings. This type of process is relevant to a wide variety of situations, including neuroscience, cascading failures on electrical power grids, and epidemology. We find that the statistics of avalanches can be characterized in terms of the largest eigenvalue and corresponding eigenvector of an appropriate adjacency matrix which encodes the structure of the network. By using mean-field analyses, previous studies of avalanches in networks have not considered the effect of network structure on the distribution of size and duration of avalanches. Our results apply to individual networks (rather than network ensembles) and provide expressions for the distributions of size and duration of avalanches starting at particular nodes in the network. These findings might find application in the analysis of branching processes in networks, such as cascading power grid failures and critical brain dynamics. In particular, our results show that some experimental signatures of critical brain dynamics (i.e., power-law distributions of size and duration of neuronal avalanches), are robust to complex underlying network topologies.Comment: 11 pages, 7 figure

Brain neurons as quantum computers: {\it in vivo} support of background physics

The question: whether quantum coherent states can sustain decoherence, heating and dissipation over time scales comparable to the dynamical timescales of the brain neurons, is actively discussed in the last years. Positive answer on this question is crucial, in particular, for consideration of brain neurons as quantum computers. This discussion was mainly based on theoretical arguments. In present paper nonlinear statistical properties of the Ventral Tegmental Area (VTA) of genetically depressive limbic brain are studied {\it in vivo} on the Flinders Sensitive Line of rats (FSL). VTA plays a key role in generation of pleasure and in development of psychological drug addiction. We found that the FSL VTA (dopaminergic) neuron signals exhibit multifractal properties for interspike frequencies on the scales where healthy VTA dopaminergic neurons exhibit bursting activity. For high moments the observed multifractal (generalized dimensions) spectrum coincides with the generalized dimensions spectrum calculated for a spectral measure of a {\it quantum} system (so-called kicked Harper model, actively used as a model of quantum chaos). This observation can be considered as a first experimental ({\it in vivo}) indication in the favour of the quantum (at least partially) nature of the brain neurons activity

Reconstituting Digital Counterpublics in Times of Crisis: The Case of the United States and the Republic of Georgia

Since the advent of social media at the turn of the 21st century, scholars of communication, cultural studies, and media studies have long been invested in the question of the relationship between social media platforms and the discursive formation of counterpublics for social movement mobilization. In this article, we seek to pose a new question for scholarly inquiry: How do citizens leverage the tools of social media platforms to reconstitute counterpublics in times of crisis? Toward this end, we conduct a comparative case study of the way citizens leverage platforms for counterpublic formation in the Republic of Georgia and the United States. Both cases represent two ends of the Janus-face of the 21st-century Internet: The Internet as a tool for public will-formation that can enrich the flowering of democracy across digital spaces, and the Internet as a tool capable of undermining traditional norms of public will formation predicated on shared understanding across the public sphere(s)

Unstable and Stable Classifications of Scombroid Fishes

Many cladists believe that a classification should strictly reflect a cladistic hypothesis. Consequently, they propose classifications that often differ markedly from existing ones and are potentially unstable due to phylogenetic uncertainty. This is problematic for economically or ecologically important organisms since changing classifications can cause confusion in their management as resources. The classification of the 44 genera of scombroid fishes (the mackerels, tunas, billfishes, and their relatives) illustrates this problem of instability. Previous cladistic analyses and analyses presented in this paper, using different data sets, result in many different cladistic hypotheses. In addition, the inferred cladograms are unstable because of different plausible interpretations of character coding. A slight change in coding of a single character, the presence of splint-like gill rakers, changes cladistic relationships substantially. These many alternative cladistic hypotheses for scombroids can be converted into various cladistic classifications, all of which are substantially different from the classification currently in use. In contrast, a quantitative evolutionary systematic method produces a classification that is unchanged despite variations in the cladistic hypothesis. The evolutionary classification has the advantage of being consistent with the classification currently in use, it summarizes anagenetic information, and it can be considered a new form of cladistic classification since a cladistic hypothesis can-be unequivocally retrieved from an annotated form of the classification

Sequence of phase transitions induced in an array of Josephson junctions by their crossover to pi-state

We show that the transition of Josephson junctions between the conventional and pi states caused by the decrease in temperature induces in a regular two-dimensional array of such junctions not just a single phase transition between two phases with different ordering but a sequence of two, three or four phase transitions. The corresponding phase diagrams are constructed for the cases of bipartite (square or honeycomb) and triangular lattices.Comment: 5 pages, v2: as published in EP

New, efficient, and accurate high order derivative and dissipation operators satisfying summation by parts, and applications in three-dimensional multi-block evolutions

We construct new, efficient, and accurate high-order finite differencing operators which satisfy summation by parts. Since these operators are not uniquely defined, we consider several optimization criteria: minimizing the bandwidth, the truncation error on the boundary points, the spectral radius, or a combination of these. We examine in detail a set of operators that are up to tenth order accurate in the interior, and we surprisingly find that a combination of these optimizations can improve the operators' spectral radius and accuracy by orders of magnitude in certain cases. We also construct high-order dissipation operators that are compatible with these new finite difference operators and which are semi-definite with respect to the appropriate summation by parts scalar product. We test the stability and accuracy of these new difference and dissipation operators by evolving a three-dimensional scalar wave equation on a spherical domain consisting of seven blocks, each discretized with a structured grid, and connected through penalty boundary conditions.Comment: 16 pages, 9 figures. The files with the coefficients for the derivative and dissipation operators can be accessed by downloading the source code for the document. The files are located in the "coeffs" subdirector

Next Generation Solar Array Technologies for Small Satellites

Recent advances in Shape Memory Alloy (SMA), Elastic Memory Composites (EMC), and ultra- light composites along with thin-film Copper-Indium- Diselinide (CIS) photovoltaics have offered the potential to provide solar array systems for small satellites that are significantly lighter than the current state of the practice. The Air Force Research Laboratory (AFRL), National Aeronautics and Space Administration (NASA) Langley, Defense Advanced Research Projects Agency (DARPA), and Lockheed Martin are jointly sponsoring an effort that will develop and, in partnership with AeroAstro, demonstrate advanced technologies for solar array applications. These technologies will result in advances that include cost, weight, risk, reliability, and power. Conventional state-of-the-practice solar arrays utilize rigid honeycomb panels to provide the structural support for the crystalline Silicon (Si) or Gallium Arsenide (GaAs) solar cells. Rigid composite panel structural and manufacturing methods have placed a practical producible limit on the power to weight efficiency of today’s solar panels. This limit is about 60 Watts per kilogram (W/kg). New technologies are needed to break this power to weight barrier and meet future DOD and NASA space power requirements. A potential solution to this problem, are the technologies that are being developed under the Lightweight Flexible Solar Array (LFSA) program. The LFSA will demonstrate key technologies on four space flights. The first space opportunity consisted of a flight experiment of a Shape Memory Alloy (SMA) deployment hinge that was demonstrated on the Space Shuttle Columbia (STS-93) in July 1999. The second flight opportunity consisted of a sub-scale twopanel solar array that was demonstrated on NASA’s Earth Observing-1 spacecraft in November 2000. The third and fourth flight opportunities will transition thin-film solar arrays into SSC02-II-2 Fosness, Eugene 2 16th Annual/USU Conference on Small Satellites operational spacecraft systems, specifically on the AeroAstro/Astronautic Technology Sdn. Bhd. (ATSB) Small Payload ORbit Transfer (SPORT™) vehicle in 2003 and the Team Encounter solar sail in 2004. The synergistic merging of the new, innovative technologies into an advanced lightweight thin- film solar array will meet the requirements of the emerging next generation of small satellites. The implementation of these new techno logies directed at lightweight solar arrays will result in significant weight and volume reductions over current satellite systems. The SMA devices will provide a controlled shock-less deployment of the solar array and improved testability due to mechanism re-set capability. Additionally, the SMA actuators will eliminate or minimize deployment motors, mechanisms, and part count. The LFSA program is a pathfinder for next generation rollout arrays that increase specific power densities to \u3e200 W/kg