Algorithms for Replica Placement in High-Availability Storage

A new model of causal failure is presented and used to solve a novel replica placement problem in data centers. The model describes dependencies among system components as a directed graph. A replica placement is defined as a subset of vertices in such a graph. A criterion for optimizing replica placements is formalized and explained. In this work, the optimization goal is to avoid choosing placements in which a single failure event is likely to wipe out multiple replicas. Using this criterion, a fast algorithm is given for the scenario in which the dependency model is a tree. The main contribution of the paper is an $O(n + \rho \log \rho)$ dynamic programming algorithm for placing $\rho$ replicas on a tree with $n$ vertices. This algorithm exhibits the interesting property that only two subproblems need to be recursively considered at each stage. An $O(n^2 \rho)$ greedy algorithm is also briefly reported.Comment: 22 pages, 7 figures, 4 algorithm listing

Current Animal Models of Postoperative Spine Infection and Potential Future Advances.

Implant related infection following spine surgery is a devastating complication for patients and can potentially lead to significant neurological compromise, disability, morbidity, and even mortality. This paper provides an overview of the existing animal models of postoperative spine infection and highlights the strengths and weaknesses of each model. In addition, there is discussion regarding potential modifications to these animal models to better evaluate preventative and treatment strategies for this challenging complication. Current models are effective in simulating surgical procedures but fail to evaluate infection longitudinally using multiple techniques. Potential future modifications to these models include using advanced imaging technologies to evaluate infection, use of bioluminescent bacterial species, and testing of novel treatment strategies against multiple bacterial strains. There is potential to establish a postoperative spine infection model using smaller animals, such as mice, as these would be a more cost-effective screening tool for potential therapeutic interventions

Dyschromatosis symmetrica hereditaria: Report of a sporadic case in a Nigerian child

Dyschromatosissymmetricahereditaria (DSH) is one of a group of reticulate pigment disorders of the skin. It is a rare autosomal dominantly inheritedgenodermatosis, presenting as mottled admixtures of hypopigmented and hyperpigmented macules on the dorsa of the extremities. It is predominantly found among persons of Oriental origin. We hereby  document the first case of dyschromatosissymmetricahereditaria in a four year old Nigerian boy who presented with progressive symmetric dyschromic lesions on the dorsa of the hands and feet, with no family history of similar lesions. The diagnosis was confirmed by the typical histologic finding of basal hyperpigmentation with normal number of melanocytes and absence of melanin incontinence from a hyperpigmented lesionKeywords: DyschromatosisSymmetricaHereditaria, Nigerian, Sporadi

Towards segmentation and spatial alignment of the human embryonic brain using deep learning for atlas-based registration

We propose an unsupervised deep learning method for atlas based registration to achieve segmentation and spatial alignment of the embryonic brain in a single framework. Our approach consists of two sequential networks with a specifically designed loss function to address the challenges in 3D first trimester ultrasound. The first part learns the affine transformation and the second part learns the voxelwise nonrigid deformation between the target image and the atlas. We trained this network end-to-end and validated it against a ground truth on synthetic datasets designed to resemble the challenges present in 3D first trimester ultrasound. The method was tested on a dataset of human embryonic ultrasound volumes acquired at 9 weeks gestational age, which showed alignment of the brain in some cases and gave insight in open challenges for the proposed method. We conclude that our method is a promising approach towards fully automated spatial alignment and segmentation of embryonic brains in 3D ultrasound

Modelling the Effect of Road Grade on the CO2 and NOx Emissions of a Passenger Car through a Real World-Urban Traffic Network

A Portable Emission Measurement System (PEMS) was utilised to record the on-road Carbon Dioxide (CO2) emission of a EURO 4 petrol vehicle over 48 test runs through an urban-traffic network. The tests were conducted over a 780 metre micro-scale road segment between Headingley and the City of Leeds, UK, with measurement on both the inbound (Section A) and outbound lanes (Section B). The monitored test runs were conducted under a range of traffic flow conditions from heavily congested to free-flowing traffic. Vehicle exhaust emission simulations using an instantaneous power-emission model have the capability to generate estimates of real-world vehicle emissions over micro-scale road sections. The Technical University of Graz’s (TUG) Passenger car and Heavy duty Emission Model (PHEM) was used to calculate a CO2 emission estimate for each of the 48 test runs through Sections A and B. The model CO2 emission estimates were then compared to the real-world PEMS emission measurements, to determine the accuracy of the modelling methodology. Whilst instrumented vehicles can adequately capture second-by-second (1Hz) absolute position and vehicle speed there is significant instrument error in the measurement of real-world elevation using a Global Positioning System (GPS) as part of a PEMS set-up. These errors make it very difficult to accurately calculate a 1Hz road grade with GPS systems. However, as road grade can have an important influence on engine power demand and hence fuel consumption and exhaust emission it is essential to include a representative road grade estimate for micro-scale emission estimation. Rather than using a GPS recorded elevation, this study developed a simple road grade estimation methodology which employs Geographic Information System (GIS) software to interpolate the elevation at each second of PEMS data from a 5-metre resolution Digital Terrain Map (DTM) derived from Light Detection And Ranging (LiDAR) data. The method applies an algorithm to compute the road grade from the LiDAR-GIS elevation values and vehicle speed, and alleviates errors resulting from absolute position measurement inaccuracy of the GPS at low speed. The addition of the LiDAR-GIS road grade to the PHEM modelling was found to improve the accuracy of the PHEM estimate of the PEMS measured real-world CO2 emission. From the 48 test runs the average PHEM estimate (including road grade) of the real-world measured CO2 emission through Section A was 93%, and through Section B was 94%. Of the total 96 test runs over Section A and B 91% of the PHEM estimates were between 80% and 110% of the PEMS recorded value. In further analysis, an assessment of the effect of road grade on both CO2 and NOx emission was conducted. Sections A and B were combined for each test run to form Segment AB, which has a net flat road grade. The PEMS recorded speed profiles for each of the test runs through sections A and B were input into PHEM and emission estimates generated under four road grade scenarios. The scenarios were formed by decreasing and exaggerating the LiDAR-GIS road grade for each second of data, multiplying it by coefficients of 0 (flat), 0.5 (half the grade), 1, and 2 (double the grade). The results indicate that assuming a flat profile in PHEM would result in an average underestimate of the segment emission by 2.7% for CO2 and 7.0% for NOx when calculated with road grade, and by 7.9% for CO2 and 20.4% for NOx were the road grade doubled. The method developed in this study provides a simple methodology for calculating 1Hz road grade, and has been shown to improve the modelling of CO2 emission for this data set. This research suggest that using the PHEM model with a LiDAR-GIS calculated road grade provides a practical method for accurately estimating real-world micro-scale emission. On-road emission monitoring by PEMS is scheduled to be introduced for Euro 6c type approval from September 2017. In order to accurately determine road load during the real-world test procedure it will be important to develop a suitable methodology for calculating a 1Hz road grade

Predator-Induced Vertical Behavior of a Ctenophore

Although many studies have focused on Mnemiopsis leidyi predation, little is known about the role of this ctenophore as prey when abundant in native and invaded pelagic systems. We examined the response of the ctenophore M. leidyi to the predatory ctenophore Beroe ovata in an experiment in which the two species could potentially sense each other while being physically separated. On average, M. leidyi responded to the predator’s presence by increasing variability in swimming speeds and by lowering their vertical distribution. Such behavior may help explain field records of vertical migration, as well as stratified and near-bottom distributions of M. leidyi