Oscillatory Finite-Time Singularities in Finance, Population and Rupture

We present a simple two-dimensional dynamical system where two nonlinear terms, exerting respectively positive feedback and reversal, compete to create a singularity in finite time decorated by accelerating oscillations. The power law singularity results from the increasing growth rate. The oscillations result from the restoring mechanism. As a function of the order of the nonlinearity of the growth rate and of the restoring term, a rich variety of behavior is documented analytically and numerically. The dynamical behavior is traced back fundamentally to the self-similar spiral structure of trajectories in phase space unfolding around an unstable spiral point at the origin. The interplay between the restoring mechanism and the nonlinear growth rate leads to approximately log-periodic oscillations with remarkable scaling properties. Three domains of applications are discussed: (1) the stock market with a competition between nonlinear trend-followers and nonlinear value investors; (2) the world human population with a competition between a population-dependent growth rate and a nonlinear dependence on a finite carrying capacity; (3) the failure of a material subjected to a time-varying stress with a competition between positive geometrical feedback on the damage variable and nonlinear healing.Comment: Latex document of 59 pages including 20 eps figure

Coloured overlays and precision-tinted lenses: poor repeatability in a sample of adults diagnosed with visual stress (vol 37, pg 542, 2017)

Purpose Visual stress consists of perceived distortions or discomfort while reading. It is claimed that these symptoms are alleviated by viewing through coloured lenses or overlays, with a specific colour required for each individual. This has been explained on the basis of altered visual cortex excitation as affected by the spectral content of the viewing light. If symptoms are indeed alleviated by a particular colour that has an impact on the individual's visual system, we would expect that selection of the most beneficial colour would be repeatable. The aim of this study was to determine whether this is the case. Methods Twenty-one participants (mean age 26 years (range 8–55 years); 12 female, nine male) with visual stress and no other uncorrected ocular or visual anomaly were recruited. Each participant selected the colour most beneficial in alleviating their symptoms from a standard set of 10 coloured overlays, and underwent intuitive colorimetry in which the most beneficial of a wide range of chromatic illuminance settings was selected. Without prescribing an overlay at the first appointment, this process was repeated on a second occasion at a mean of 25 days later. Results About half of the participants (n = 10) chose the same (n = 7) or similar (with one common colour in both choices; n = 3) coloured overlay on the two occasions, while 11 participants chose a completely different overlay colour. Across all participants, the colorimetry setting shifted by, on average, 9.6 just noticeable differences, indicating that the colours were perceptually very different. Conclusion These findings suggest that people with visual stress are unlikely to find exactly the same colour to be optimal on different occasions, and raise questions about the need for precise colour specification in tinted lenses for visual stress

A Proposed Policy-Based Management Architecture for Wireless Clients Operating in a Heterogeneous Mobile Environment

The objective of this paper is to provide a managed always best connected service to mobile entities over underlying heterogeneous wireless and mobile platforms while maintaining negotiated security and quality of service (QoS). This paper proposes a new model and its architecture which is based upon Policy-based Management but provides a new framework based on layered-approach for the centralised management of mobile clients. In particular, we propose and implement a new model of a policy-managed mobile client and its architecture to support seamless handoff across multiple access networks. The proposed mobile client supports multi-domain authentication, authorisation and security based on user profiles as well as the ability to negotiate management services over interconnected heterogeneous mobile platforms. We have also proposed a new handoff initiation algorithm to select an optimum time to handoff. This algorithm combines metrics in a novel way using standard deviations without resorting to other computationally intensive methods. Finally, this paper describes a proof-of-concept implementation based upon Microsoft Windows presenting a performance analysis to validate our architectural approach

Flexible Booms, Momentum Wheels, and Subtle Gravity-Gradient Instabilities

A gravity-gradient boom and a momentum wheel provides a passive, three-axis attitude control system for a small satellite requiring 10° Earth-oriented pointing In a low Earth orbit. The Polar BEAR satellite Is a small satellite using just such a system that has experienced unexpected attitude instabilities during some of Its full-sun orbit periods. This paper examines the attitude dynamles and disturbances associated with gravlty-gradientlmomentum-wheel systems In an attempt to identify potential destabilizing mechanisms common to the configuration. Polar BEAR is not the only such configuration to experience problems In full sun. and several other examples are briefiy discussed. Although we place particular emphasis on trying to understand Polar BEAR\u27s anomaly, Its performance may be symptomatic of problems with the Dexible-boom/momentum-wheel configuration

Development and Evaluation of a Secure Web Gateway Using Existing ICAP Open Source Tools

This work in progress paper discusses the development and evaluation of an open source secure web gateway. The proof of concept system uses a combination of open source software (including the Greasyspoon ICAP Server, Squid HTTP proxy, and Clam Antivirus) to perform the various security tasks that range from simple (such as passive content insertion) to more advanced (such as active content alteration) by modules installed on the server. After discussing the makeup of the proof of concept system we discuss our evaluation methodology for both effectiveness and performance. The effectiveness was tested using comparative analysis of groups of self-browsing high interaction client honeypots (employing a variety of security measures) and recording different system alteration rates. Performance was tested across a wide range of variables to determine the failure conditions and optimal set up for the components used

A Novel Design and Implementation of Dos-Resistant Authentication and Seamless Handoff Scheme for Enterprise WLANs

With the advance of wireless access technologies, the IEEE 802.11 wireless local area network (WLAN) has gained significant increase in popularity and deployment due to the substantially improved transmission rate and decreased deployment costs. However, this same widespread deployment makes WLANs an attractive target for network attacks. Several vulnerabilities have been identified and reported regarding the security of the current 802.11 standards. To address those security weaknesses, IEEE standard committees proposed the 802.11i amendment to enhance WLAN security. The 802.11i standard has demonstrated the capability of providing satisfactory mutual authentication, better data confidentiality, and key management support, however, the design of 802.11i does not consider network availability. Thus 802.11i is highly susceptible to malicious denial-of-service (DoS) attacks, which exploit the vulnerability of unprotected management frames. This paper proposes, tests and evaluates a combination of three novel methods by which the exploitation of 802.11i by DoS attacks can be improved. These three methods include an access point nonce dialogue scheme, a fast access point transition protocol handoff scheme and a location management based selective scanning scheme. This combination is of particular value to real-time users running time-dependant applications such as VoIP. In order to acquire practical data to evaluate the proposed schemes, a prototype network has been implemented as an experimental testbed using open source tools and drivers. This testbed allows practical data to be collected and analysed. The result demonstrates that not only the proposed authentication scheme eradicates most of the DoS vulnerabilities, but also substantially improved the handoff performance to a level suitable for supporting real-time services

New Approaches to Mitigation of Malicious Traffic in VoIP Networks

Voice over IP (VoIP) telephony is becoming widespread in use, and is often integrated into computer networks. Because of this, malicious software threatens VoIP systems in the same way that traditional computer systems have been attacked by viruses, worms, and other automated agents. VoIP networks are a challenge to secure against such malware as much of the network intelligence is focused on the edge devices and access environment. This paper describes the design and implementation of a novel VoIP security architecture in which evaluation of, and mitigation against, malicious traffic is demonstrated by the use of virtual machines to emulate vulnerable clients and servers through the use of apparent attack vectors. This new architecture, which is part of an ongoing research project, establishes interaction between the VoIP backend and the end users, thus providing information about ongoing and unknown attacks to users

A glassy contribution to the heat capacity of hcp 4^4He solids

We model the low-temperature specific heat of solid $^4$He in the hexagonal closed packed structure by invoking two-level tunneling states in addition to the usual phonon contribution of a Debye crystal for temperatures far below the Debye temperature, $T < \Theta_D/50$. By introducing a cutoff energy in the two-level tunneling density of states, we can describe the excess specific heat observed in solid hcp $^4$He, as well as the low-temperature linear term in the specific heat. Agreement is found with recent measurements of the temperature behavior of both specific heat and pressure. These results suggest the presence of a very small fraction, at the parts-per-million (ppm) level, of two-level tunneling systems in solid $^4$He, irrespective of the existence of supersolidity.Comment: 11 pages, 4 figure