Origin and prevention of high contact resistance in multilevel metal-polyimide structures

When polyimide is used as the insulating dielectric in multilevel-metal structures, a high contact resistance can result within the interconnecting vias. This paper examines the particular case of oxygen plasma patterning of the polyimide using a photoresist mask. Auger analysis in combination with compositional depth profiling was employed on a series of samples to measure surface composition of etched vias in polyimide. Results show two effects which, together, can account for high contact resistance: first, there is a thicker than normal aluminum oxide layer on the first level metal surface (due to exposure to the oxygen plasma); second, there is a thin, etch-resistant carbonaceous film (due to redeposition of organic material during plasma etching) that prevents oxide thinning through chemical means. It was found that by lowering the plasma pressure to 50 mTorr near the end of the etch, the organic film can be removed. In the absence of the carbonaceous layer, the oxide can then be chemically thinned to produce clean aluminum surfaces within the vias.     

Development of the Utah Artificial Arm

The development of a practical multifunction, electronically controlled artificial arm is an extremely complex undertaking. Various technical factors such as the limited capability of man-made components, together with problems in the development of adequate control systems, impair the ultimate performance of any prosthesis. Also, nontechnical problems in clinical, marketing, and economic areas strongly influence the potential success of any system. Consequently, the realization of a practical system with the possibility of near-term application requires simultaneous and coordinated work by personnel in a number of normally unrelated areas of medicine and engineering. The opinions of engineers, physicians, amputees, industrial entities, and institutions responsible for funding the fitting of artificial limnbs must be understood and must influence the design process. This paper begins with a discussion of the natural limb and those design objectives and compromises which govern the development of its artificial counterpart Specific details of the Utah Arm are then reviewed, along with general comments regarding the area of prosthetic limb research and application.     

Reduced adipose 18∶3ω3 with weight loss by very low calorie dieting

The human undergoing rapid and sustained weight loss by very low calorie dieting (VLCD) derives the majority of daily energy needs from adipose fatty acids. To evaluate the rates of metabolic utilization of individual fatty acids in humans, two groups of adult women outpatients were studied during major weight loss by VLCD. The diets used were either food or formula, providing the recommended dietary allowance for minerals and vitamins, with fat contents of 2–20 g/d. Group 1 consisted of 10 subjects [initial body mass index (BMI) 32.7, 157% of ideal body weight (IBW)] with a mean loss of 17.7 kg in 3–5 months. Group 2 consisted of 14 subjects (initial BMI 36.7, 167% of IBW) with a mean loss of 25.6 kg in 4–5 months. Adipose tissue biopsies were obtained by needle aspiration from Group 1 before and after weight loss and from Group 2 before, at the midpoint, and after weight loss. With weight loss in Group 1, the adipose tissue content of 18∶1ω9, 18∶2ω6, and 20∶4ω6 did not change, but 18∶3ω3 fell (0.67 to 0.56 wt%, p<0.0001) as did 20∶5ω3 (0.08 to 0.05, p<0.01). Adipose tissue 22∶6ω3 rose from 0.03 to 0.07 (p<0.01). In Group 2, only 18∶3ω3 showed a change, falling from 0.71 to 0.69 to 0.59 wt% across weight loss (p=0.03 by analysis of variance). We conclude that the major fatty acids are oxidized in proportion to their composition in adipose triglyceride. The significant reduction in the concentration of 18∶3ω3 during weight loss is unique among fatty acids. Its accelerated removal from adipose tissue indicates either a preferential step in β-oxidation or a defined need during supplemented fasting which exceeds its rate of provision from adipose stores. This work was presented in part at the Annual Meeting of the American Society for Clinical Nutrition, Washington, D.C., 1988.     

Role of Grain Size in the Strength and R-Curve Properties of Alumina

An investigation of the interrelationships between strength, crack-resistance ( R -curve) characteristics, and grain size for alumina ceramics has been carried out. Results of identation-strength measurements on high-density aluminas with uniform grain structures in the size range 2 to 80 μm are presented. A theoretical fit to the data, obtained by adjusting parameters of a constitutive frictional-pullout relation in a grain-bridging model, allows determination of the critical microstructural parameters controlling the R -curve behavior of these aluminas. The primary role of grain size in the toughness characteristic is to determine the scale of grain pullout at the bridged interface. It is shown that the strength properties are a complex function of the bridged microstructure, governed at all but the finest grain sizes by the stabilizing effect of the R -curve. The analysis confirms the usual negative dependence of strength on grain size for natural flaws that are small relative to the grain size, but the dependence does not conform exactly to the −1/2 power predicted on the basis of classical "Griffith-Orowan" flaws. The analysis provides a self-consistent account of the well-documented transition from "Orowan" to "Petch" behavior.     

Netted radar: Network communications design and optimisation

Networks of phased array radars are generally able to provide better counter stealth target detection and classification. Each radar sensor (or node) generates information which requires transmission to a central authority that is able to evaluate the information. This requires a communications network to be established to allow transmission of information to and from any node. Each radar node is limited by range and degree and relies on the formation of a multi-hop network to facilitate these transmissions.This paper presents a model whereby the radar beam itself is used in the formation of a multi-hop network. The phased array’s multi-functional nature allows rapid switching between communications and radar function. A model of how the communication system could operate is presented, and an evolutionary optimisation algorithm based upon the concept of Pareto optimality is used for the topological design of the network. Finally, a simulation environment is presented to show the simulated performance of the communication model and designed networks.     

Microwave backscatter modeling of erg surfaces in the Sahara desert

The Sahara desert includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. Previous study shows that Saharan ergs exhibit significant radar backscatter (/spl sigma//spl deg/) modulation with azimuth angle (f). We use /spl sigma//spl deg/ measurements observed at various incidence angles and f from the NASA Scatterometer (NSCAT), the SeaWinds scatterometer, the ERS scatterometer (ESCAT), and the Tropical Rainfall Measuring Mission's Precipitation Radar to model the /spl sigma//spl deg/ response from sand dunes. Observations reveal a characteristic relationship between the backscatter modulation and the dune type, i.e., the number and orientation of the dune slopes. Sand dunes are modeled as a composite of tilted rough facets, which are characterized by a probability distribution of tilt with a mean value, and small ripples on the facet surface. The small ripples are modeled as cosinusoidal surface waves that contribute to the return signal at Bragg angles only. Longitudinal and transverse dunes are modeled with rough facets having Gaussian tilt distributions. The model results in a /spl sigma//spl deg/ response similar to NSCAT and ESCAT observations over areas of known dune types in the Sahara. The response is high at look angles equal to the mean tilts of the rough facets and is lower elsewhere. This analysis provides a unique insight into scattering by large-scale sand bedforms.     

FastFabric: Scaling hyperledger fabric to 20 000 transactions per second

Blockchain technologies are expected to make a significant impact on a variety of industries. However, one issue holding them back is their limited transaction throughput, especially compared to established solutions such as distributed database systems. In this paper, we rearchitect a modern permissioned blockchain system, Hyperledger Fabric, to increase transaction throughput from 3000 to 20 000 transactions per second. We focus on performance bottlenecks beyond the consensus mechanism, and we propose architectural changes that reduce computation and I/O overhead during transaction ordering and validation to greatly improve throughput. Notably, our optimizations are fully plug‐and‐play and do not require any interface changes to Hyperledger Fabric.     

Predicting fingertip forces by imaging coloration changes in the fingernail and surrounding skin

This paper presents an external camera method for measuring fingertip forces by imaging the fingernail and surrounding skin. A 3-D model of the fingernail surface and skin is obtained with a stereo camera and laser striping system. Subsequent images from a single camera are registered to the 3-D model by adding fiducial markings to the fingernail. Calibration results with a force sensor show that the measurement range depends on the region of the fingernail and skin. A generalized least squares model is developed to predict fingertip force given coloration changes, and results for normal and shear force measurement are presented.     

Low‐loss TCP/IP header compression for wireless networks

Wireless is becoming a popular way to connect mobile computers to the Internet and other networks. The bandwidth of wireless links will probably always be limited due to properties of the physical medium and regulatory limits on the use of frequencies for radio communication. Therefore, it is necessary for network protocols to utilize the available bandwidth efficiently. Headers of IP packets are growing and the bandwidth required for transmitting headers is increasing. With the coming of IPv6 the address size increases from 4 to 16 bytes and the basic IP header increases from 20 to 40 bytes. Moreover, most mobility schemes tunnel packets addressed to mobile hosts by adding an extra IP header or extra routing information, typically increasing the size of TCP/IPv4 headers to 60 bytes and TCP/IPv6 headers to 100 bytes. In this paper, we provide new header compression schemes for UDP/IP and TCP/IP protocols. We show how to reduce the size of UDP/IP headers by an order of magnitude, down to four to five bytes. Our method works over simplex links, lossy links, multi‐access links, and supports multicast communication. We also show how to generalize the most commonly used method for header compression for TCP/IPv4, developed by Jacobson, to IPv6 and multiple IP headers. The resulting scheme unfortunately reduces TCP throughput over lossy links due to unfavorable interaction with TCP's congestion control mechanisms. However, by adding two simple mechanisms the potential gain from header compression can be realized over lossy wireless networks as well as point‐to‐point modem links. This revised version was published online in June 2006 with corrections to the Cover Date.     

Performance analysis of session oriented data communications for mobile computing in cellular systems

Future cellular communication systems must seamlessly support services for a wide range of user needs, including voice, data, video and multi‐media. It is envisioned that mobile users may do much computer processing in an off‐line mode but must occasionally connect to a network in order to exchange data and/or files. For this purpose a communication session is initiated. During the session the user has access to network resources, although this access may be shared with others. Owing to the mobile environment, the user's connection to the network during a session may be severed. Since the mobile user can act semi‐autonomously, such disconnections can be transparent. That is, the mobile user can continue to function in an off‐line mode while the system will begin transparent automatic reconnection attempts to reestablish a link to the network. Only after a fixed (given) number of such attempts to reconnect have failed, is the session deemed to have failed. The issue is complicated by the hostile mobile radio environment and by user mobility. We consider session‐oriented communications and develop a tractable analytical model for traffic performance based on multi‐dimensional birth–death processes. The approach allows consideration of various platform types, such as pedestrians, automobiles, and buses, which may have very different mobility characteristics. Performance characteristics, such as: blocking, forced session termination, carried traffic, the average time per suspension, and the average number of suspensions per session, are calculated. This revised version was published online in July 2006 with corrections to the Cover Date.