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Cloud data centers, such as Amazon EC2, host myriad big data applications using Virtual Machines (VMs). As these applications are communication-intensive, optimizing network transfer between VMs is critical to the performance of these applications and network utilization of data centers. Previous studies have addressed this issue by scheduling network flows with coflow semantics or optimizing VM placement with traffic considerations. However, coflow scheduling and VM placement have been conducted orthogonally. In fact, these two mechanisms are mutually dependent, and optimizing these two complementary degrees of freedom independently turns out to be suboptimal. In this paper, we present VirtCO, a practical framework that jointly schedules coflows and places VMs ahead of VM launch to optimize the overall performance of data center applications. We model the joint coflow scheduling and VM placement optimization problem, and propose effective heuristics for solving it. We further implement VirtCO with OpenStack and deploy it in a testbed environment. Extensive evaluation of real-world traces shows that compared with state-of-the-art solutions, VirtCO greatly reduces the average coflow completion time by up to 36.5%. This new framework is also compatible with and readily deployable within existing data center architectures.

Transverse fracture of the skull base is common both in the crushing of temporal regions of the skull and in the case of force acting on one temporal region. However, the mechanism of transverse skull base fracture caused by maxillofacial force has not been fully clarified. To provide an injury identification basis for forensic pathologists and clinicians, this paper combines accident reconstruction and finite element analysis methods to study the injury mechanism of an incomplete transverse fracture of skull base after the injured individual’s mandible was subjected to violence in a traffic accident. The results show that after the injured individual’s mandible was subjected to violence, forces in the direction of the left mandibular fossa and the right mandibular fossa were generated, creating the component forces. The combination of the two forces can produce a crushing effect toward the center of the skull base, as if the left and right temporal regions are being crushed, and the stress is concentrated at the joint of the mandible, the middle cranial fossa and the hypophyseal fossa. When the stress exceeds a certain limit, it will cause a transverse fracture of the skull base.