Shadow kernels: A general mechanism for kernel specialization in existing operating systems

Existing operating systems share a common kernel text section amongst all processes. It is not possible to perform kernel specialization or tuning such that different applications execute text optimized for their kernel use despite the benefits of kernel specialization for performance guided optimization, exokernels, kernel fastpaths, and cheaper hardware access. Current specialization primitives involve system wide changes to kernel text, which can have adverse effects on other processes sharing the kernel due to the global side-effects. We present shadow kernels: a primitive that allows multiple kernel text sections to coexist in a contemporary operating system. By remapping kernel virtual memory on a context-switch, or for individual system calls, we specialize the kernel on a fine-grained basis. Our implementation of shadow kernels uses the Xen hypervisor so can be applied to any operating system that runs on Xen.This work was principally supported by internal funds from the Computer Laboratory at the University of Cambridge; and also by the Engineering and Physical Sciences Research Council [grant number EP/K503009/1].This is the final version of the article. It first appeared from ACM via http://dx.doi.org/10.1145/2797022.279702

Comparison of Joint Compression and Pull- Out Strength of 6.5-mm Self-Drilling Screws With Headed and Headless in Subtalar Arthrodesis: A Pilot Study

Background: In patients with degenerative osteoarthritis of the subtalar joint, surgical treatment can include subtalar arthrodesis. Notably, mechanical factors such as compression and pull-out strength contribute to successful union, which can be achieved through use of headed or headless cannulate screws. The purpose of this study was to compare the resultant joint compressive force and pull-out strength between use of a headless 6.5-mm self-drilling cannulated compression screw and a more traditional headed 6.5- mm self-drilling cannulated compression screw. Methods: This study used the calcaneus and talus from six paired fresh frozen specimens. The soft tissues were stripped and the joint was separated. Fujifilm Prescale Compression Paper (Minato, Tokyo, Japan) was placed in the subtalar joint, and both the talus and calcaneus were fixed with either traditional headed or a headless cannulated screw. Pull-out strength was measured by fixing the fused subtalar joints to a servohydraulic activator and measuring peak load at failure in distraction. Imaging analysis of the compression paper determined peak compression across the joint. Results: The resultant joint compressive force and pull-out strength were not statistically different between use of headed and headless cannulated compression screws (P = 0.30 and P = 0.67, respectively). Conclusions: In a small sample, use of headless cannulated compression screws offered equivalent joint compression as that of a headed screw in subtalar arthrodesis and showed equivalent resistance to pullout force

Percutaneous Interventional Radiology-Operated Endoscopy for Foreign Body Removal

Image-guided retrieval of endovascular devices such as inferior vena cava filters, guidewires, and stents is well reported, though there is a paucity of published reports on biliary, genitourinary, or gastrointestinal foreign body retrieval utilizing percutaneous endoscopy, particularly when it is performed solely by interventional radiologists. In cases of failed traditional endoscopic techniques or to evade more invasive surgical options, percutaneous endoscopy can be an adjunctive tool employed by interventional radiologists to extract foreign bodies. In this article, clinical evaluation, perioperative management, and procedural techniques for biliary, genitourinary, and gastrointestinal endoscopy for foreign body retrieval are reviewed

Collaboration is Key – Bridging the Gap and Building an IR Endoscopy Practice

While the tools and techniques employed by interventional radiologists on a day-to-day basis translate well to learning the skills required to perform basic endoscopic interventions, collaboration with other specialties is crucial to the success of an interventional radiology endoscopy program. As in any field in medicine, the paramount goal is to improve patient care. Adding the ability to directly visualize structures through an endoscope to certain interventional radiologic procedures may greatly augment the efficacy, safety, and success of interventional radiology procedures. Colleagues in urology, gastroenterology, and surgery should be involved in decision-making and treatment planning to ensure that a shared vision for optimal patient care is achieved

Billing, Coding, and Credentialing for Interventional Radiology-Operated Endoscopy

A sound understanding of billing and coding is essential to start a successful interventional radiology endoscopy practice. While the codes utilized are similar to gastrointestinal and genitourinary endoscopy codes, physicians and institutional coders need to be familiar with the codes used for these types of procedures in the interventional radiology setting. The following manuscript gives a brief overview of aspects relating to credentialing, billing, and coding in interventional radiology endoscopy

When is a polymorph not a polymorph? Helical trimeric O-H···O synthons in trans-1,4-diethynylcyclohexane-1,4-diol

Two polymorphs (A and B) of trans-1,4-diethynylcyclohexane-1,4-diol represent a unique example of the simultaneous occurrence of both conformational polymorphism and conformational isomorphism, while a pseudopolymorphic monohydrate is closely related

Biomechanical Strength and Bulk Comparisons Between the Open-Book Technique and the Pulvertaft Method for Peroneal Tendon Transfer: A Pilot Study

Background: The Pulvertaft method has classically been used for the transfer of various tendon injuries owing to its biomechanical strength; however, this method has been shown to be bulky. We describe the open-book technique, which can offer comparable structural integrity with a decreased bulk. The purpose of this study was to determine whether the openbook technique is biomechanically equivalent to the Pulvertaft method for treating peroneal tendon injuries. Methods: We evaluated five pairs of human cadaveric ankles. Within each pair, one specimen was randomly assigned to either the Pulvertaft or the open-book group. Using sharp dissection, the tendons were severed in a standardized method. Transfer was performed using one of the two randomly assigned techniques. The transferred peroneal tendons were stressed on a mechanical tensioning device until failure. Data were recorded and analysis was performed. Results: There was a statistically significant difference (P \u3c 0.001) between the thickness of the Pulvertaft method (7.6 mm) and open-book technique (5.7 mm). There was also a statistically significant difference in elongation, with the Pulvertaft undergoing more elongation at yield (9.7 mm vs 3.7 mm, respectively; P = 0.04). No statistical difference was detected in elongation at peak (P = 0.52), load at yield (P = 0.9), or peak load (P = 0.69). Conclusions: The open-book technique appears to be a viable biomechanical alternative to the Pulvertaft method for peroneal tendon transfer. The peak load, load at yield, and elongation at peak were biomechanically equivalent. The open-book technique was found to provide a significant decrease in thickness, which could prove advantageous when dealing with anatomical locations

Interaction of reed and acoustic resonator in clarinetlike systems

Sound emergence in clarinetlike instruments is investigated in terms of instability of the static regime. Various models of reed-bore coupling are considered, from the pioneering work of Wilson and Beavers ["Operating modes of the clarinet", J. Acoust. Soc. Am. 56, 653--658 (1974)] to more recent modeling including viscothermal bore losses and vena contracta at the reed inlet. The pressure threshold above which these models may oscillate as well as the frequency of oscillation at threshold are calculated. In addition to Wilson and Beavers' previous conclusions concerning the role of the reed damping in the selection of the register the instrument will play on, the influence of the reed motion induced flow is also emphasized, particularly its effect on playing frequencies, contributing to reduce discrepancies between Wilson and Beavers' experimental results and theory, despite discrepancies still remain concerning the pressure threshold. Finally, analytical approximations of the oscillating solution based on Fourier series expansion are obtained in the vicinity of the threshold of oscillation. This allows to emphasize the conditions which determine the nature of the bifurcation (direct or inverse) through which the note may emerge, with therefore important consequences on the musical playing performances