In this paper, we introduce Collabra, a distributed intrusion detection platform based on Xen hypervisors to maintain the security of the cloud based on virtualized network. While the concept of virtual machine monitor (VMM) signifies implementing an abstraction layer between the underlying host and the guest operating system (OS) to enforce security, its kernel is required to be free of vulnerabilities that intruders can use to compromise the host. In Xen, guest applications make resource requests through the hyper-call API to transfer the privilege to the VMM kernel for executing privileged operations. On a cloud scale, there exist hundreds of VM networks and thousands of guest operating systems (OSes) running on virtual domains. There is every possibility of intruders trying to misuse the hyper-call interface to compromise guest OS kernels and finally the host OS kernel itself. Sophisticated attacks can be launched in the distributed and collaborative style thereby bypassing most current intrusion detection systems. Collabra acts as a filtering layer which is completely integrated with every VMM. It scans through each call by incorporating integrity checking and collaborative detection mechanisms. It exists in multiple instances, and acts concurrently over a VMM network interacting with other instances to detect (possibly collaborative) attacks and prevent illicit access to the VMM and the host. An admin version of Collabra exists on a privileged domain in the VM network to perform filtering of malicious add-ons to hyper-calls at the guest OS level itself before routing the call to the VMM.
Quantitative fluid velocity and turbulence measurements, which were obtained using laser Doppler velocimetry (LDV) during the course of the physical modeling of the molten steel flow in a continuous casting billet mold, are presented. The experimental findings are compared to the results obtained by the computational simulation of the flow using the high-Reynolds-number and five lowReynolds-number k-ε turbulence models. The predictive capabilities of these turbulence models were assessed in comparison to the experimentally measured axial velocity and turbulence kinetic energy values. The measured turbulence velocity fluctuations in various directions strongly suggest the nonisotropic nature of the flow field, which cannot be predicted with the k-ε models. The extent of deviations between the measurements and computations was quantified.
The connected dominating set (CDS) has been extensively used for routing and broadcast in mobile ad hoc networks. While existing CDS protocols are successful in constructing CDS of competitive size with localized information, they either lack the mechanism to properly handle nodal mobility or require lengthy period of time to recover when CDS becomes corrupted. In this paper, a novel protocol, namely Multi-Initiator Connected Dominating Set protocol (MI-CDS), is proposed that constructs and maintains CDS of competitive size efficiently without introducing much communication overhead. The simulation results demonstrate that MI-CDS permits CDS to be available for the highest percentage of time in the mobile network scenario compared with the other CDS protocols.
This paper is dedicated to the memory of Derlon Chu (Nov. 20, 1959-June 19, 2003)-a colleague and a friend who has contributed much to make CFD impact the design of automotive components. Derlon Chu spearheaded the formation of the "Partnership on CFD Codes and Models for the Automotive Industry" to address error issues in CFD. This paper presents and evaluates a method for estimating grid-induced errors in CFD solutions that recognizes error at one location in the flow domain may not be generated there, but rather generated elsewhere and then transported there. This paper derives a system of discrete error-transport equations (DETEs) to compute the evolution of grid-induced errors in finite-volume solutions of the Euler equations for compressible flows in two dimensions. The finite-volume method to which the DETEs were derived is one which can be applied to structured or unstructured meshes with cells that can be triangular, rectangular, or other polygons. Results for a test problem involving an oblique shock wave show that if the residuals in the DETEs are modeled accurately, then the DETEs can predict grid-induced errors accurately.
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