Virtual Layer Research Articles

Prediction of Elastic Properties for a Wound Oxide Ceramic Matrix Composite Material

This study presents enhanced studies of inverse approach of the classical laminate theory for prediction of the elastic properties of a wound oxide ceramic matrix composites material (CMC). Based on mechanical tests and microstructure analysis, elastic properties of virtual equivalent unidirectional layers were calculated. To adapt the analytical model to CMCs from different batches which show various fiber volume contents, porosities, and different fiber orientations, a scaling factor Ω was introduced with the help of modified mixing considering these specific properties. A good correlation between experimental and analytically calculated results showed in this study.

Spatial resolution recovery utilizing multi-ray tracing and graphic processing unit in PET image reconstruction

Depth-of-interaction (DOI) poses a major challenge for a PET system to achieve uniform spatial resolution across the field-of-view, particularly for small animal and organ-dedicated PET systems. In this work, we implemented an analytical method to model system matrix for resolution recovery, which was then incorporated in PET image reconstruction on a graphical processing unit platform, due to its parallel processing capacity. The method utilizes the concepts of virtual DOI layers and multi-ray tracing to calculate the coincidence detection response function for a given line-of-response. The accuracy of the proposed method was validated for a small-bore PET insert to be used for simultaneous PET/MR breast imaging. In addition, the performance comparisons were studied among the following three cases: 1) no physical DOI and no resolution modeling; 2) two physical DOI layers and no resolution modeling; and 3) no physical DOI design but with a different number of virtual DOI layers. The image quality was quantitatively evaluated in terms of spatial resolution (full-width-half-maximum and position offset), contrast recovery coefficient and noise. The results indicate that the proposed method has the potential to be used as an alternative to other physical DOI designs and achieve comparable imaging performances, while reducing detector/system design cost and complexity.

A novel cost based model for energy consumption in cloud computing.

Cloud data centers consume enormous amounts of electrical energy. To support green cloud computing, providers also need to minimize cloud infrastructure energy consumption while conducting the QoS. In this study, for cloud environments an energy consumption model is proposed for time-shared policy in virtualization layer. The cost and energy usage of time-shared policy were modeled in the CloudSim simulator based upon the results obtained from the real system and then proposed model was evaluated by different scenarios. In the proposed model, the cache interference costs were considered. These costs were based upon the size of data. The proposed model was implemented in the CloudSim simulator and the related simulation results indicate that the energy consumption may be considerable and that it can vary with different parameters such as the quantum parameter, data size, and the number of VMs on a host. Measured results validate the model and demonstrate that there is a tradeoff between energy consumption and QoS in the cloud environment. Also, measured results validate the model and demonstrate that there is a tradeoff between energy consumption and QoS in the cloud environment.

A Stratified Monitoring Model for Hybrid Cloud

Hybrid clouds integrate different cloud solutions. Its inherent complexity and short of standard urge for a careful analysis, systematizing and understanding of monitoring. In this context, this paper provides a deep insight into hybrid cloud monitoring. It proposes a layered monitoring model for hybrid clouds, identifying the multiple layers of monitoring, focusing on physical infrastructure layer, virtual infrastructure layer, network, application/service layer, while combining the perspectives of service providers and clients. This process involves the identification of relevant parameters and metrics for each layer. Due to its flexibiliity and intelligence, using Agent technology, an agent-based monitoring architecture is presented. It enables to eliminate the complexity among different cloud platforms.This study contributes to achieve a clearer and more efficient approach to hybrid cloud monitoring.

Cirsoid aneurysm of scalp: Value of multidetector CT scan in pre-operative evaluation

Cirsoid aneurysm of scalp is a rare arteriovenous malformation (AVM) of external carotid branches and scalp veins. This malformation of scalp is also synonymously called as plexiform angioma, aneurysma racesomsum, and aneurysm cirsoide, aneurysma serpentinum. This AVM can be congenital or acquired; a congenital form will be present at birth, however, becomes overt only after puberty. Superficial temporal artery is the feeder in approximately 70-80% of the cases, followed by occipital and supraorbital artery. Multidetector computed tomography angiography reconstructed images can provide excellent detail of the feeders, draining veins and their soft tissue relations. Volume rendering data sets in computer workstations we can actually perform virtual dissection layers of the lesion for operative planning. Well planned surgical excision can have least surgical recurrence rates and complications.

Linatron Mi6, the X-Ray Source for Cargo Inspection

Since its inception in 2008, Linatron Mi6 has been the standard x-ray source for cargo inspection. It produces interlaced dual energy (6MV and 3.5MV) x-ray pulses that enable material discrimination scan in a single pass. Both pulse-to-pulse and longer term stability has been improved. With Linatron Mi6 as the x-ray source, it is now possible to achieve a continuous material discrimination scale, instead of only dividing materials into four classes: organic material, inorganic material, metals and high atomic metals. Other advanced material discrimination features include virtual layer peeling and trust rating. Energy sensitive imaging detectors can extend material discrimination in thin-object region. Although our Linatron Mi9 Linatron, which produces interlaced pulses of 9MV and 6MV x-ray pulses, provides even better material discrimination performance as well as better radiographic performance, it is not as widely used due to increased imaging system size and higher cost of safety shielding.

Efficient load balancing algorithm for distributed systems using mobile agents

In this paper, we present a new load balancing algorithm for parallel virtual architectures based on mobile agents. The proposed model is based on a reference diagnostic test performed by the host agent at the deployment time of the parallel application. This diagnostic test allows evaluating the computation performance and the communication latency of each node of the distributed system. The parallel tasks to execute are assigned to the distributed virtual processing units (VPUs) according to the performance offered by each node. The VPUs, represented by mobile agents, are associated in a parallel virtual layer, according to the parallel architecture topology required by the application. This model can also use metadata, of the parallel tasks to be distributed, to estimate more accurately the required times to perform the current parallel task. This feature allows predicting the performance offered by the distributed system according to the selected configuration of the selected computational model. When the system detects unbalanced loads, during the execution of any iterative computation, the system determines the required migrations of the VPUs from overloaded to under loaded nodes in order to keep the distributed system in a perfect balanced stat. To describe the proposed approach, the established mathematical model and a SPMD parallel application example are presented to prove the effectiveness of the proposed model. 246 M. Youssfi, O. Bouattane and M. O. Bensalah

Software-Defined Networking: A Comprehensive Survey

The Internet has led to the creation of a digital society, where (almost) everything is connected and is accessible from anywhere. However, despite their widespread adoption, traditional IP networks are complex and very hard to manage. It is both difficult to configure the network according to predefined policies, and to reconfigure it to respond to faults, load, and changes. To make matters even more difficult, current networks are also vertically integrated: the control and data planes are bundled together. Software-defined networking (SDN) is an emerging paradigm that promises to change this state of affairs, by breaking vertical integration, separating the network's control logic from the underlying routers and switches, promoting (logical) centralization of network control, and introducing the ability to program the network. The separation of concerns, introduced between the definition of network policies, their implementation in switching hardware, and the forwarding of traffic, is key to the desired flexibility: by breaking the network control problem into tractable pieces, SDN makes it easier to create and introduce new abstractions in networking, simplifying network management and facilitating network evolution. In this paper, we present a comprehensive survey on SDN. We start by introducing the motivation for SDN, explain its main concepts and how it differs from traditional networking, its roots, and the standardization activities regarding this novel paradigm. Next, we present the key building blocks of an SDN infrastructure using a bottom-up, layered approach. We provide an in-depth analysis of the hardware infrastructure, southbound and northbound application programming interfaces (APIs), network virtualization layers, network operating systems (SDN controllers), network programming languages, and network applications. We also look at cross-layer problems such as debugging and troubleshooting. In an effort to anticipate the future evolution of this new paradigm, we discuss the main ongoing research efforts and challenges of SDN. In particular, we address the design of switches and control platforms - with a focus on aspects such as resiliency, scalability, performance, security, and dependability - as well as new opportunities for carrier transport networks and cloud providers. Last but not least, we analyze the position of SDN as a key enabler of a software-defined environment.

Adding NTFS Support to Android Operating System Via Kernel

Android is a nascent mobile operating system based on the Linux kernel that is developed by Google but lacks support for disks partitioned with the NTFS. Currently in the Google Play Store there are some third party applications to provide NTFS support to Android OS. But the main disadvantage of such applications is that the phone needs to be rooted (flashed) which may be tedious for a lay user and in many cases may void the device’s warranty. And above all, a custom ROM needs to be installed to avail the NTFS functionality. This paper covers a technique to provide native support for NTFS (New Technology File System) in the Android operating system by avoiding the rooting process. Hence to use NTFS-SD card or NTFS HDD we won’t require any third party applications to perform basic read/write operations. This is implemented with the help of the Virtual Filesystem layer (VFS) which is a subsystem of the kernel that implements the file and the file system-related interfaces provided to user-space programs. The NTFS will rely on the VFS layer to enable programs to use standard UNIX system calls to make basic operations like read/write as well as advanced features which NTFS has.

Numerical evaluation of the effect of multiple roughness changes

The effect of multiple roughness changes close to a building site was examined through three dimensional computational fluid dynamics (CFD) simulations conducted in a virtual boundary layer wind tunnel (V-BLWT). The results obtained were compared with existing wind speed models, namely ESDU-82026 and Wang and Stathopoulos (WS) model. The latter was verified by wind tunnel tests of sixty nine cases of multiple roughness patches, and also with a simplified 2D numerical model. This work extends that numerical study to three dimensions and also models roughness elements explicitly. The current numerical study shows better agreement with the WS model, that has shown better agreements with BLWT tests, than the ESDU model. This is in contrast to previous results of Wang and Stathopoulos, who concluded that CFD shows better agreement with the ESDU model. Many cases were simulated in a V-BLWT that has same dimensions as BLWT used in the original experiment and also in a reduced symmetrical version (S-BLWT) that takes advantage of regular arrangement of roughness blocks. The S-BLWT gives results almost identical to V-BLWT simulations, while achieving significant reduction on computational time and resources.

A Virtualization Layer Approach to Survivability

Network virtualization facilitates sharing and effi- cient utilization of computing and bandwidth resources of an underlying substrate network. As network virtualization becomes popular, it is important to efficiently map a virtual infrastructure (VI) onto a substrate network, such that the survivability of the former can be guaranteed against failures in the latter. In this paper, we study a virtualization layer approach to survivability, whereby the virtualization layer customizes a VI request with redundant nodes and links according to its reliability require- ments and then passes limited information about the augmented VI to the physical layer, where the mapping of the augmented VI takes place. More specifically, we develop a flexible scheme to enhance the original VI graph with K redundant nodes, in order to fight against an arbitrary substrate node failure. In addition, a scenario-based component group (SBCG) concept is proposed to describe resource sharing of enhanced VI requests at the physical layer. We also develop an efficient heuristic that takes advantage of the limited information on SBCG to reduce costs when mapping the enhanced VI to the substrate network. The efficiency of the proposed solution is compared using extensive simulation under various performance metrics. It is shown that the K-redundant-node scheme with SBCG information is more cost efficient than the existing 1-redundant-node solution.

Network virtualization for disaster resilience of cloud services

Today's businesses and consumer applications are becoming increasingly dependent on cloud solutions, making them vulnerable to service outages that can result in a loss of communication or access to business-critical services and data. Are we really prepared for such failure scenarios? Given that failures can occur on both the network and data center sides, is it possible to have efficient end-to-end recovery? The answer is mostly negative due to the separate operation of these domains. This article offers a solution to this problem based on network virtualization, and discusses the necessary architecture and algorithm details. It also answers the question of whether it is better to provide resilience in the virtual or physical layer from a cost effectiveness and failure coverage perspective.

Toward Scalable Indexing for Top-<inline-formula> <tex-math notation="TeX">\(k\) </tex-math></inline-formula> Queries

A top- k query retrieves the best \(k\) tuples by assigning scores for each tuple in a target relation with respect to a user-specific scoring function. This paper studies the problem of constructing an indexing structure for supporting top- k queries over varying scoring functions and retrieval sizes. The existing research efforts can be categorized into three approaches: list- , layer- , and view-based approaches. In this paper, we mainly focus on the layer-based approach that pre-materializes tuples into consecutive multiple layers. We first propose a dual-resolution layer that consists of coarse-level and fine-level layers. Specifically, we build coarse-level layers using skylines , and divide each coarse-level layer into fine-level sublayers using convex skylines . To make our proposed dual-resolution layer scalable , we then address the following optimization directions: 1) index construction; 2) disk-based storage scheme; 3) the design of the virtual layer; and 4) index maintenance for tuple updates. Our evaluation results show that our proposed method is more scalable than the state-of-the-art methods.

Design and Implementation of a Large Scale Tree-Based QR Decomposition Using a 3D Virtual Systolic Array and a Lightweight Runtime

A systolic array provides an alternative computing paradigm to the von Neumann architecture. Though its hardware implementation has failed as a paradigm to design integrated circuits in the past, we are now discovering that the systolic array as a software virtualization layer can lead to an extremely scalable execution paradigm. To demonstrate this scalability, in this paper, we design and implement a 3D virtual systolic array to compute a tile QR decomposition of a tall-and-skinny dense matrix. Our implementation is based on a state-of-the-art algorithm that factorizes a panel based on a tree-reduction. Freed from the constraint of a planar layout, we present a three-dimensional virtual systolic array architecture for this algorithm. Using a runtime developed as a part of the Parallel Ultra Light Systolic Array Runtime (PULSAR) project, we demonstrate on a Cray-XT5 machine how our virtual systolic array can be mapped to a large-scale machine and obtain excellent parallel performance. This is an important contribution since such a QR decomposition is used, for example, to compute a least squares solution of an overdetermined system, which arises in many scientific and engineering problems.

Study of Migration Policies in Energy-Aware Virtual Router Networks

The definition of a virtual router layer allows the application of energy saving techniques based on the migration of virtual routers within the physical infrastructure as traffic conditions change. As traffic decreases, physical resources can be vacated through virtual router migration, thus, saving energy. Such resources can be reclaimed if needed because of traffic increase. Unfortunately, the migration of virtual routers involves reconfiguration costs depending on implementation details and characterized, for instance, by the revenue loss due to quality-of-service (QoS) degradation during the migration process. In this paper, we propose a methodology based on the Markov decision processes for the evaluation of optimal migration policies taking into account both the operation (in terms of energy consumption) and reconfiguration costs.

TinCan: User-Defined P2P Virtual Network Overlays for Ad-hoc Collaboration

Virtual private networking (VPN) has become an increasingly important component of a collaboration environment because it ensures private, authenticated communication among participants, using existing collaboration tools, where users are distributed across multiple institutions and can be mobile. The majority of current VPN solutions are based on a centralized VPN model, where all IP traffic is tunneled through a VPN gateway. Nonetheless, there are several use case scenarios that require a model where end-to-end VPN links are tunneled upon existing Internet infrastructure in a peer-to-peer (P2P) fashion, removing the bottleneck of a centralized VPN gateway. We propose a novel virtual network — TinCan — based on peerto-peer private network tunnels. It reuses existing standards and implementations of services for discovery notification (XMPP), reflection (STUN) and relaying (TURN), facilitating configuration. In this approach, trust relationships maintained by centralized (or federated) services are automatically mapped to TinCan links. In one use scenario, TinCan allows unstructured P2P overlays connecting trusted end-user devices — while only requiring VPN software on user devices and leveraging online social network (OSN) infrastructure already widely deployed. This paper describes the architecture and design of TinCan and presents an experimental evaluation of a prototype supporting Windows, Linux, and Android mobile devices. Results quantify the overhead introduced by the network virtualization layer, and the resource requirements imposed on services needed to bootstrap TinCan links.

Hardware-software collaboration for secure coexistence with kernel extensions

Our society is dependent upon computer systems that are the target of a never-ending siege against their resources. One powerful avenue for exploitation is the operating system kernel, which has complete control of a computer system's resources. The current methodology for kernel design, which involves loadable extensions from third parties, facilitates compromises. Most of these extensions are benign, but in general they pose a threat to system trustworthiness: they run as part of the kernel and some of them can be vulnerable or malicious. This situation is paradoxical from a security point of view: modern OSes depend, and must co-exist, with untrustworthy but needed extensions. Similarly, the immune system is continuously at war against various types of invaders and, through evolution, has developed highly successful defense mechanisms. Collaboration is one of these mechanisms, where many players throughout the body effectively communicate to share attack intelligence. Another mechanism is foreign body co-existence with its microbiota. Remarkably, these properties are not leveraged in kernel defense approaches. Security approaches at the OS and virtual machine layers do not cooperate with each other or with the hardware. This paper advocates a new paradigm for OS defense based on close collaboration between an OS and the hardware infrastructure, and describes a hardware-software architecture realizing this vision. It also discusses the architecture design at the OS and hardware levels, including experimental results from an emulator-based prototype, and aspects of an ongoing hardware implementation. The emulator-based proof-of-concept prototype, Ianus, uses Linux as the OS and the Bochs x86 emulator as the architecture layer. It successfully minimized kernel extensions interactions with the original kernel. Its security was evaluated with real rootkits and benign extensions. Ianus' performance was analyzed with system and CPU benchmarks and it caused a small overhead to the system (approximately 12%).

XtratuM hypervisor redesign for LEON4 multicore processor

XtratuM is an open source hypervisor that uses para-virtualization techniques designed to comply with safety critical real-time requirements. Several projects aimed to define a reference architecture for space on-board systems have adopted XtratuM as a virtualization layer in order to enforce the strong spatial and temporal isolation between software components that is required on real-time airborne systems. Given the shift in the general trend in processor development towards multicore processors, the European Space Agency (ESA) is commissioning a set of studies in order to evaluate their suitability for their use on the space market. This paper focuses on the porting of XtratuM to the LEON4 multicore processor, in the frame of a ESA study that pursues to assess its fitness for its use in future space missions.

Analysis of Load Transfer Efficiency at Joints of Monolithic Track-Bed under New City Tramcar Loading

Joint load transfer ability is the key part of the analysis of the rigid pavement structure. This paper is focused on the load transfer efficiency at joints of monolithic track-bed under new city tramcar loading. Based on the general finite element analysis software ABAQUS, the relationship between the modulus of virtual materials in virtual material layer method and joint load transfer ability is analyzed. Meanwhile, bending stress and deflection for monolithic track-bed structure on edge loading case are calculated under different thickness of the pavement structure.

OPTIMIZING SERVERS THROUGH VIRTUALIZATION

This paper represents a comparison of using multiple server services and how virtualization brings down to the utilization of servers . Virtualization of Servers helps in enabling application isolation, mobility, and partitioning of individual servers in the cloud. The physical servers having a virtual server layer above them handles the resource utilization from various clients. This extra layer creates resource utilization considerably.