Implicit admission control

Internet protocols currently use packet-level mechanisms to detect and react to congestion. Although these controls are essential to ensure fair sharing of the available resource between multiple flows, in some cases they are insufficient to ensure overall network stability. We believe that it is also necessary to take account of higher level concepts, such as connections, flows, and sessions when controlling network congestion. This becomes of increasing importance as more real-time traffic is carried on the Internet, since this traffic is less elastic in nature than traditional Web traffic. We argue that, in order to achieve better utility of the network as a whole, higher level congestion controls are required. By way of example, we present a simple connection admission control (CAC) scheme which can significantly improve the overall performance. This paper discusses our motivation for the use of admission control in the Internet, focusing specifically on control for TCP flows. The technique is not TCP specific, and can be applied to any type of flow in a modern IP infrastructure. Simulation results are used to show that it can drastically improve the performance of TCP over bottleneck links. We go on to describe an implementation of our algorithm for a router running the Linux 2.2.9 operating system. We show that by giving routers at bottlenecks the ability to intelligently deny admission to TCP connections, the goodput of existing connections can be significantly increased. Furthermore, the fairness of the resource allocation achieved by TCP is improved     

3D Knitting for Pneumatic Soft Robotics

Soft robots adapt passively to complex environments due to their inherent compliance, allowing them to interact safely with fragile or irregular objects and traverse uneven terrain. The vast tunability and ubiquity of textiles has enabled new soft robotic capabilities, especially in the field of wearable robots, but existing textile processing techniques (e.g., cut-and-sew, thermal bonding) are limited in terms of rapid, additive, accessible, and waste-free manufacturing. While 3D knitting has the potential to address these limitations, an incomplete understanding of the impact of structure and material on knit-scale mechanical properties and macro-scale device performance has precluded the widespread adoption of knitted robots. In this work, the roles of knit structure and yarn material properties on textile mechanics spanning three regimes–unfolding, geometric rearrangement, and yarn stretching–are elucidated and shown to be tailorable across unique knit architectures and yarn materials. Based on this understanding, 3D knit soft actuators for extension, contraction, and bending are constructed. Combining these actuation primitives enables the monolithic fabrication of entire soft grippers and robots in a single-step additive manufacturing procedure suitable for a variety of applications. This approach represents a first step in seamlessly “printing” conformal, low-cost, customizable textile-based soft robots on-demand.     

Modelling of electrostatic gate operations in the Kane solid state quantum computer

The nuclear spin quantum computer proposed by Kane [Nature 393 (1998) 133] exploits as a qubit array ³¹P dopants embedded within a silicon matrix. Single-qubit operations are controlled by the application of electrostatic potentials via a set of metallic ‘A’ gates, situated above the donors, on the silicon surface, that tune the resonance frequency of individual nuclear spins, and a globally applied RF magnetic field that flips spins at resonance. Coupling between qubits is controlled by the application of potentials via a set of ‘J’ gates, between the donors, that induce an electron-mediated coupling between nuclear spins. We report the results of the study of the electric field and potential profiles arising within the Kane device from typical gate operations. The extent to which a single nuclear spin can be tuned independently of its neighbours, by operation of an associated A-gate, is examined and key design parameters in the Kane architecture are addressed. Implications for current fabrication strategies involving the implantation of ³¹P atoms are discussed. Solution of the Poisson equation has been carried out by simulation using a TCAD modelling package (Integrated Systems Engineering AG).     

Serial communication circuit with optimized skew characteristics

This letter highlights features of an optimized serial communication system, including an oversampling technique of data recovery, issues related to off-board communications and a modified universal asynchronous receiver transmitter (UART) implemented in a programmable logic device (PLD). The resulting system provides high skew tolerance at 44 Mb/s data rate and has achieved a transmission distance of 130 m, at this rate, with the aid of an enhanced differential transceiver circuit. The principal application is for embedded systems with medium distance communication requirements. This UART can be integrated with other communication functions, such as packet routing switches, in a PLD device     

Measuring thermal and mechanical stresses on optical fiber in a DC module using fiber Bragg gratings

Fiber Bragg gratings (FBGs) can be used as sensors to monitor stress and test temperature during the processing and handling of optical fiber. As the FBG experiences a combination of mechanical and thermal loading, the return Bragg wavelength will shift proportionately to the magnitude of the load. This paper discusses the use of these sensors in quantifying induced stress on fiber during the packaging of a dispersion-compensating module (DCM) and the ensuing environmental exposure. There are two potential fiber-failure modes for fiber wound in DCMs, namely microbend-induced attenuation and fiber failure from fatigue. The ability to quantify fiber stress provides a useful feedback tool in the design phase of these modules that can aid in reducing the risk of mechanical and optical failure modes. A practical characterization process was developed to decouple thermal and stress effects on FBGs based on results from current literature and from this study. Uncoated Bragg sensors were found to respond linearly between -40 to 80/spl deg/C. Gratings with a protective polymer recoat departed from the linear behavior of the uncoated gratings below -5/spl deg/C. It was determined that the recoat material places less than 25 MPa (3.6 klbf/in/sup 2/) of axial compression on the fiber at -40/spl deg/C. Four gratings with different Bragg wavelengths were spliced into 10 km of fiber and wound into a DCM. The wind-induced stress on all four gratings quickly relaxed. The module was then thermal cycled between -40 and +75/spl deg/C. The overall stress on each grating was acceptably low for reliability purposes. The maximum stress of 17 MPa (2.5 klbf/in/sup 2/) was observed at the lowest temperature.     

Bayesian Multi-Object Filtering With Amplitude Feature Likelihood for Unknown Object SNR

In many tracking scenarios, the amplitude of target returns are stronger than those coming from false alarms. This information can be used to improve the multiple-target state estimation by obtaining more accurate target and false-alarm likelihoods. Target amplitude feature is well known to improve data association in conventional tracking filters, such as probabilistic data association and multiple hypothesis tracking, and results in better tracking performance of low signal-to-noise ratio (SNR) targets. The advantage of using the target amplitude approach is that targets can be identified earlier through the enhanced discrimination between target and false alarms. One of the limitations of this approach is that it is usually assumed that the SNR of the target is known. We show that the reliable estimation of the SNR requires a significant number of measurements, and so we propose an alternative approach for situations where the SNR is unknown. We illustrate this approach in the context of multiple targets for different SNRs in the framework of finite set statistics (FISST). Furthermore, we illustrate how this can be incorporated into approximate multiple-object filters derived from FISST, including probability hypothesis density (PHD) and cardinalized PHD (CPHD) filters. We present simulation results for Gaussian mixture implementations of the filters that demonstrate a significant improvement in performance over just using location measurements.     

Amplification of tunable, picosecond pulses from a single-mode, short cavity dye laser

The design and performance of an Nd⁺³:YAG pumped, short cavity dye laser-dye amplifier system is reported. This system produces narrow bandwidth, broadly tunable picosecond pulses with energies in the millijoule range.     

Simulation,assessment and technical conclusions from a major accident investigation

This paper is the third in a series which describes and discusses the scientific and technical analysis used to assist the investigation of a major accident involving a Royal Australian Navy helicopter. This particular investigation was a particularly complex one that required transportation of the wreckage from the crash site in Indonesia, at the end of the on-site investigation, to laboratories in Australia for detailed assessment. This paper describes the simulations used to assist the investigation, and the technical conclusions reached about the loss of control of the aircraft. Finally the paper outlines the sequence of events which occurred during the accident, and discusses some key issues involved in the formal investigative processes associated with the Board of Inquiry, and the lessons learned in the process.