The Size-Frequency Distribution of the Zodiacal Cloud: Evidence from the Solar System Dust Bands

Recent observations of the size-frequency distribution of zodiacal cloud particles obtained from the cratering record on the LDEF satellite (Love and Brownlee 1993) reveal a significant large particle population (100 micron diameter or greater) near 1 AU. Our previous modeling of the Solar System dust bands (Grogan et al 1997), features of the zodiacal cloud associated with the comminution of Hirayama family asteroids, has been limited by the fact that only small particles (25 micron diameter or smaller) have been considered. This was due to the prohibitively large amount of computing power required to numerically analyze the dynamics of larger particles. The recent availability of cheap, fast processors has finally made this work possible. Models of the dust bands are created, built from individual dust particle orbits, taking into account a size-frequency distribution of the material and the dynamical history of the constituent particles. These models are able to match both the shapes and amplitudes of the dust band structures observed by IRAS in multiple wavebands. The size-frequency index, q, that best matches the observations is approximately 1.4, consistent with the LDEF results in that large particles are shown to dominate. However, in order to successfully model the `ten degree' band, which is usually associated with collisional activity within the Eos family, we find that the mean proper inclination of the dust particle orbits has to be approximately 9.35 degrees, significantly different to the mean proper inclination of the Eos family (10.08 degrees).Comment: 49 pages total, including 27 figure pages. Submitted to Icaru

Collaborative Intrusion Detection in Federated Cloud Environments

Moving services to the Cloud is a trend that has steadily gained popularity over recent years, with a constant increase in sophistication and complexity of such services. Today, critical infrastructure operators are considering moving their services and data to the Cloud. Infrastructure vendors will inevitably take advantage of the benefits Cloud Computing has to offer. As Cloud Computing grows in popularity, new models are deployed to exploit even further its full capacity, one of which is the deployment of Cloud federations. A Cloud federation is an association among different Cloud Service Providers (CSPs) with the goal of sharing resources and data. In providing a larger-scale and higher performance infrastructure, federation enables on-demand provisioning of complex services. In this paper we convey our contribution to this area by outlining our proposed methodology that develops a robust collaborative intrusion detection methodology in a federated Cloud environment. For collaborative intrusion detection we use the Dempster-Shafer theory of evidence to fuse the beliefs provided by the monitoring entities, taking the final decision regarding a possible attack. Protecting the federated Cloud against cyber attacks is a vital concern, due to the potential for significant economic consequences

An elastic scaling method for cloud security

Cloud computing is being adopted in critical sectors such as transport, energy and finance. This makes cloud computing services critical in themselves. When cyber attacks and cyber disruptions happen, millions of users are affected. A cyber disruption in this context means a temporary or permanent loss of service, with impact on users of the cloud service who rely on its continuity. Intrusion detection and prevention methods are being developed to protect this sensitive information being stored, and the services being deployed. There needs to be an assurance that the confidentiality, integrity and availability of the data and resources are maintained. This paper presents a background to the critical infrastructure and cloud computing progression, and an overview to the cloud security conundrum. Analysis of existing intrusion detection methods is provided, in addition to our observation and proposed elastic scaling method for cloud security

Distributed attack prevention using Dempster-Shafer theory of evidence

This paper details a robust collaborative intrusion detection methodology for detecting attacks within a Cloud federation. It is a proactive model and the responsibility for managing the elements of the Cloud is distributed among several monitoring nodes. Since there are a wide range of elements to manage, complexity grows proportionally with the size of the Cloud, so a suitable communication and monitoring hierarchy is adopted. Our architecture consists of four major entities: the Cloud Broker, the monitoring nodes, the local coordinator (Super Nodes), and the global coordinator (Command and Control server - C2). Utilising monitoring nodes into our architecture enhances the performance and response time, yet achieves higher accuracy and a broader spectrum of protection. For collaborative intrusion detection, we use the Dempster Shafer theory of evidence via the role of the Cloud Broker. Dempster Shafer executes as a main fusion node, with the role to collect and fuse the information provided by the monitors, taking the final decision regarding a possible attack

RESONANT STRUCTURE IN THE KUIPER DISK: AN ASYMMETRIC PLUTINO DISK

In order to develop a dynamical model of the Kuiper disk, we run numerical integrations of particles originating from source bodies trapped in the 3 : 2 external mean motion resonance with Neptune to determine what percentage of particles remain in the resonance for a variety of particle and source body sizes. The dynamical evolution of the particles is followed from source to sink with Poynting-Robertson light drag, solar wind drag, radiation pressure, the Lorentz force, neutral interstellar gas drag, and the effects of planetary gravitational perturbations included. We find that the number of particles in the 3 : 2 resonance increases with decreasing � (i.e., increasing particle size) for the cases in which the initial source bodies are small (� 10 km in diameter) and that the percentage of particles in resonance is not significantly changed by either the addition of the Lorentz force, as long as the potential of the particles is small (� 5 V), or the effect of neutral interstellar gas drag. The brightness of the entire Kuiper disk is calculated using a model composed of 500 lm diameter particles and fits well with upper limits to the Kuiper disk brightness and previous estimates. A disk with a size-frequency distribution weighted toward large particles, which are more likely to remain in resonance, may have a stronger, more easily identifiable resonant signature than a disk composed of small particles

How Observations of Circumstellar Disk Asymmetries Can Reveal Hidden Planets: Pericenter Glow and its Application to the HR 4796 Disk

Recent images of the disks of dust around the young stars HR 4796A and Fomalhaut show, in each case, a double-lobed feature that may be asymmetric (one lobe may be brighter than the other). A symmetric double-lobed structure is that expected from a disk of dust with a central hole that is observed nearly edge-on (i.e., close to the plane of the disk). This paper shows how the gravitational influence of a second body in the system with an eccentric orbit would cause a brightness asymmetry in such a disk by imposing a "forced eccentricity" on the orbits of the constituent dust particles, thus shifting the center of symmetry of the disk away from the star and causing the dust near the forced pericenter of the perturbed disk to glow. Dynamic modeling of the HR 4796 disk shows that its 5% brightness asymmetry could be the result of a forced eccentricity as small as 0.02 imposed on the disk by either the binary companion HR 4796B, or by an unseen planet close to the inner edge of the disk. Since it is likely that a forced eccentricity of 0.01 or higher would be imposed on a disk in a system in which there are planets, but no binary companion, the corresponding asymmetry in the disk's structure could serve as a sensitive indicator of these planets that might otherwise remain undetected.Comment: 61 pages, 10 figures, accepted for publication in the Astrophysical Journal (scheduled for January 10, 2000

Cognitive and cognitive-behavioral therapies

In this chapter we will provide a brief review of some of the major historical forces that lead to the development of the cognitive behavioral therapies. We will then define what are the common characteristics among this increasingly diverse set of interventions, and in doing so also attempt to differentiate the cognitive-behavioral therapies from related approaches to psychotherapy. We will then turn our primary focus to a description of the major models within the cognitive-behavioral paradigm, and to discussing their current empirical status. The chapter will conclude with a discussion of current issues related to the cognitive-behavioral therapies, and with predictions and suggestions for the future development of the approach

Deep 10 and 18 micron Imaging of the HR 4796A Circumstellar Disk: Transient Dust Particles & Tentative Evidence for a Brightness Asymmetry

We present new 10.8 and 18.2 micron images of HR 4796A, a young A0V star that was recently discovered to have a spectacular, nearly edge-on, circumstellar disk prominent at ~20 microns (Jayawardhana et al. 1998; Koerner et al. 1998). These new images, obtained with OSCIR at Keck II, show that the disk's size at 10 microns is comparable to its size at 18 microns. Therefore, the 18 micron-emitting dust may also emit some, or all, of the 10 micron radiation. Using these multi-wavelength images, we determine a "characteristic" diameter of 2-3 microns for the mid-infrared-emitting dust particles if they are spherical and composed of astronomical silicates. Particles this small are expected to be blown out of the system by radiation pressure in a few hundred years, and therefore these particles are unlikely to be primordial. Dynamical modeling of the disk (Wyatt et al. 2000) indicates that the disk surface density is relatively sharply peaked near 70 AU, which agrees with the mean annular radius deduced by Schneider et al. (1999) from their NICMOS images. We present evidence (~1.8 sigma significance) for a brightness asymmetry that may result from the presence of the hole and the gravitational perturbation of the disk particle orbits by the low-mass stellar companion or a planet. This "pericenter glow," which must still be confirmed, results from a very small (a few AU) shift of the disk's center of symmetry relative to the central star HR 4796A; one side of the inner boundary of the annulus is shifted towards HR 4796A, thereby becoming warmer and more infrared-emitting. The possible detection of pericenter glow implies that the detection of even complex dynamical effects of planets on disks is within reach.Comment: 18 pages. 9 GIF images. Total size ~800 kB. High resolution images available upon request. Accepted for publication in the Astrophysical Journal (scheduled for January 10, 2000