Exact Analysis of TTL Cache Networks: The Case of Caching Policies driven by Stopping Times

TTL caching models have recently regained significant research interest, largely due to their ability to fit popular caching policies such as LRU. This paper advances the state-of-the-art analysis of TTL-based cache networks by developing two exact methods with orthogonal generality and computational complexity. The first method generalizes existing results for line networks under renewal requests to the broad class of caching policies whereby evictions are driven by stopping times. The obtained results are further generalized, using the second method, to feedforward networks with Markov arrival processes (MAP) requests. MAPs are particularly suitable for non-line networks because they are closed not only under superposition and splitting, as known, but also under input-output caching operations as proven herein for phase-type TTL distributions. The crucial benefit of the two closure properties is that they jointly enable the first exact analysis of feedforward networks of TTL caches in great generality

Mitigating the Performance Impact of Network Failures in Public Clouds

Some faults in data center networks require hours to days to repair because they may need reboots, re-imaging, or manual work by technicians. To reduce traffic impact, cloud providers \textit{mitigate} the effect of faults, for example, by steering traffic to alternate paths. The state-of-art in automatic network mitigations uses simple safety checks and proxy metrics to determine mitigations. SWARM, the approach described in this paper, can pick orders of magnitude better mitigations by estimating end-to-end connection-level performance (CLP) metrics. At its core is a scalable CLP estimator that quickly ranks mitigations with high fidelity and, on failures observed at a large cloud provider, outperforms the state-of-the-art by over 700$\times$ in some cases

Hyperbolic outer billiards : a first example

We present the first example of a hyperbolic outer billiard. More precisely we construct a one parameter family of examples which in some sense correspond to the Bunimovich billiards.Comment: 11 pages, 8 figures, to appear in Nonlinearit

Ultrasound imaging of the sciatic nerve division in the popliteal fossa: A volunteer study

Background and Objectives: A sciatic nerve block at the level of the popliteal fossa is frequently administered for post-operative analgesia for surgery below the knee. While ultrasound continues to gain popularity as the technique of choice for guiding needle positioning during peripheral nerve blocks, practitioners can begin to utilize ultrasound to look for patterns of anatomical significance. Recognizing anatomical variations among different demographic populations can help practitioners improve in performing nerve blocks. We aim to determine if predictable variability exists in sciatic nerve bifurcation location and depth at the level of the popliteal fossa. Methods: After IRB approval, eligible subjects were screened for ASA I or II status and demographic data was collected. Fifty subjects were enrolled. The SonoSite MicroMaxx® with 38-mm broadband linear array, 13-6 MHz probe with color Doppler and image capturing capabilities was used for ultrasound measurements. With subject lying prone, the location of the sciatic nerve in relation to the popliteal crease and skin-to-nerve distance were assessed via ultrasound. Two independent investigators confirmed nerve location for measurements. Analyses were performed with SAS version 9.1 using Pearson Correlation Coefficients and regression analysis. Results: Gender stratification revealed that, while males were both taller and heavier, skin-nerve measurements for depth were consistently deeper in females (p-value 0.02). Independent of the right or left leg, male gender and increased height decreases the skin-nerve distance, while increased weight increases the distance. There was no correlation between patient characteristics and crease-nerve distance. In some subjects, variability of crease-nerve distance even existed between their right and left leg. Conclusion: We show that significant variability exists for actual sciatic nerve bifurcation location, or target injection site, with consistently deeper skin depth values for female patients when compared to male patients, accounting for height and weight. These findings suggest visualization techniques such as ultrasound may lead to better localization of ideal injection sites

Predicting postoperative day 1 hematocrit levels after uncomplicated hysterectomy

ObjectiveTo develop a model for predicting postoperative hematocrit levels after uncomplicated hysterectomy.MethodsIn a retrospective study, data were analyzed from the Michigan Surgery Quality Collaborative for non‐emergent hysterectomies performed for benign indications among women aged at least 18 years between January 1, 2012, and April 4, 2014. Linear mixed models were used for univariate and multivariate analyses.ResultsThe model was developed with data from 4747 hysterectomies and validated on 1184 cases. In the mixed multivariate analysis, higher postoperative day 1 (POD1) hematocrit levels were associated with higher weight (B = 0.03222, P < 0.001), higher preoperative hematocrit (B = 0.6587, P < 0.001), and non‐vaginal hysterectomy (B = 0.2815, P = 0.0055). Lower POD1 hematocrit was associated with higher preoperative platelet count (B = − 0.00457, P < 0.001), greater estimated blood loss (B = − 0.00652, P < 0.001), and larger intraoperative crystalloid volume (B = − 0.3303, P < 0.001). The final model predicted POD1 hematocrit within 4% points of the actual value for 91.7% of cases in the validation set.ConclusionUse of the model after uncomplicated hysterectomy might help to support the practice of selectively conducting postoperative hematocrit tests after hysterectomy in a clinically thoughtful and cost‐effective manner.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135182/1/ijgo19.pd

International clinical rotations during U.S. residency training: Creating an accreditation council for graduate medical education-approved rotation

Healthcare professionals increasingly report interest in global health and participation in international healthcare delivery. Growth opportunities exist for trainees to improve knowledge, skills and attitudes through international experiences. Professional development via international medicine may have lasting effects on patient care and practice patterns following training. In 2010, the first resident took part in an international, exchange elective between The George Washington University’s Department of Anesthesiology in Washington, DC and La Universidad de San Francisco’s Department of Anesthesiology in Quito, Ecuador. This resident elective rotation resulted from a strategic partnership, initiated in 2008, between two training institutions with an established track record of medical student educational exchange programs. The goal of any resident elective rotation should be to enhance an educational experience, to improve upon a perceived training deficiency, or to create a unique offering that takes advantage of local assets and connections. International electives, if properly conceived, can accomplish all three goals. This guide for program leadership addresses the rationale and challenges, from concept to Accreditation Council for Graduate Medical Education approval, of creating an international clinical rotation for residents

THE COST STRUCTURE OF MICROFINANCE INSTITUTIONS IN EASTERN EUROPE AND CENTRAL ASIA

Microfinance institutions are important, particularly in developing countries, because they expand the frontier of financial intermediation by providing loans to those traditionally excluded from formal financial markets. This paper presents the first systematic statistical examination of the performance of MFIs operating in Eastern Europe and Central Asia. A cost function is estimated for MFIs in the region from 1999-2004. First, the presence of subsidies is found to be associated with higher MFI costs. When output is measured as the number of loans made, we find that MFIs become more efficient over time and that MFIs involved in the provision of group loans and loans to women have lower costs. However, when output is measured as volume of loans rather than their number, this last finding is reversed. This may be due to the fact that such loans are smaller in size; thus for a given volume more loans must be made.http://deepblue.lib.umich.edu/bitstream/2027.42/40195/3/wp809.pd