Nonlinear and Inertant Acoustic Metamaterials and Their Device Implications

Acoustic Metamaterials (AM) are a class of artificial structural materials that derive their unique dynamic properties, not just from material constituents but more so from engineered local configurations. Tailoring these local configurations have been shown to impart unusual mechanical wave manipulation capabilities to AM with potentially novel applications in protective structures; acoustic devices for sensing, noise control, and energy harvesting; and MEMS devices. Most AM require the presence of periodic features that locally exhibit dynamic phenomena like resonance or instability within a host material or structure. A key advantage of the AM design approach is the latitude to explore new local configurations to further enrich their dynamic behavior. The present study focusses on nonlinear and inertant AM configurations and their device implications. Using the method of multiple scales applied to a lumped-parameter effective-mass model, approximate analytical solutions were derived for the amplitude-dependent dispersion curve shifts in nonlinear AM owing to the presence of cubically hardening or softening nonlinearities in local oscillators. Discrete element simulations predict the possibility of realizing passive acoustic control devices such as selective filters, amplitude band-pass filters and direction-biased waveguides using nonlinear AM. A numerical routine to generate root profile geometries that enable contact-based hardening response in tip-loaded cantilever beam resonators was developed and implemented. Experiments on a structural waveguide test article verify the existence and extent of bandgaps and also provide an indication of the passive direction-bias phenomenon. Whereas, incorporating inerters, which are mechanical elements that display a force proportional to the relative acceleration across them, could create structural devices that display frequency-dependent negative and even extreme effective-mass and stiffness regimes. Such devices have implications for passive high-pass filters with ultra-low frequency bandgaps that encompass the long wavelength limit and can be realized without the use of any mechanical grounding elements and even for structural networks that can act as a nearly complete mechanical wave inhibitor. Further research on the interactive synergies between nonlinear and inertant configurations and practical strategies to scale and fabricate them could have promise for realizing a new class of AM with enriched dynamics beyond those found in predominantly locally resonant variants that are currently being developed.Mechanical & Aerospace Engineerin

Querying Streaming System Monitoring Data for Enterprise System Anomaly Detection

The need for countering Advanced Persistent Threat (APT) attacks has led to the solutions that ubiquitously monitor system activities in each enterprise host, and perform timely abnormal system behavior detection over the stream of monitoring data. However, existing stream-based solutions lack explicit language constructs for expressing anomaly models that capture abnormal system behaviors, thus facing challenges in incorporating expert knowledge to perform timely anomaly detection over the large-scale monitoring data. To address these limitations, we build SAQL, a novel stream-based query system that takes as input, a real-time event feed aggregated from multiple hosts in an enterprise, and provides an anomaly query engine that queries the event feed to identify abnormal behaviors based on the specified anomaly models. SAQL provides a domain-specific query language, Stream-based Anomaly Query Language (SAQL), that uniquely integrates critical primitives for expressing major types of anomaly models. In the demo, we aim to show the complete usage scenario of SAQL by (1) performing an APT attack in a controlled environment, and (2) using SAQL to detect the abnormal behaviors in real time by querying the collected stream of system monitoring data that contains the attack traces. The audience will have the option to interact with the system and detect the attack footprints in real time via issuing queries and checking the query results through a command-line UI.Comment: Accepted paper at ICDE 2020 demonstrations track. arXiv admin note: text overlap with arXiv:1806.0933

Singleton: System-wide Page Deduplication in Virtual Environments

ABSTRACT We consider the problem of providing memory-management in hypervisors and propose Singleton, a KVM-based systemwide page deduplication solution to increase memory usage efficiency. Specifically, we address the problem of doublecaching that occurs in KVM-the same disk blocks are cached at both the host(hypervisor) and the guest(VM) page-caches. Singleton's main components are identical-page sharing across guest virtual machines and an implementation of an exclusivecache for the host and guest page-cache hierarchy. We use and improve KSM-Kernel SamePage Merging to identify and share pages across guest virtual machines. We utilize guest memory-snapshots to scrub the host page-cache and maintain a single copy of a page across the host and the guests. Singleton operates on a completely black-box assumption-we do not modify the guest or assume anything about it's behaviour. We show that conventional operating system cache management techniques are sub-optimal for virtual environments, and how Singleton supplements and improves the existing Linux kernel memory management mechanisms. Singleton is able to improve the utilization of the host cache by reducing its size(by upto an order of magnitude), and increasing the cache-hit ratio(by factor of 2x). This translates into better VM performance(40% faster I/O). Singleton's unified page deduplication and host cache scrubbing is able to reclaim large amounts of memory and facilitates higher levels of memory overcommitment. The optimizations to page deduplication we have implemented keep the overhead down to less than 20% CPU utilization

A five year learning experience with sequence of events in a child with closed femur shaft fracture

Femur shaft fractures are the most common fractures requiring hospitalization in children. Management of these fractures mainly depend on the age of the child. Associated injuries, fracture pattern, weight of the child and overlying soft tissue condition also influence the management. Still, the definitive treatment remains controversial in children between 5-16 years. We present our experience in management of 5 year old boy with mid shaft femur fracture and its complications. In his paper we want to highlight the importance of sticking to the basic principles and the recommendations in the management of the paediatric femur shaft fractures