Kolbeinn Karlsson
Cornell University
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Publication
Featured researches published by Kolbeinn Karlsson.
Medical Image Analysis | 2014
Ruogu Fang; Kolbeinn Karlsson; Tsuhan Chen; Pina C. Sanelli
Blood-brain barrier permeability (BBBP) measurements extracted from the perfusion computed tomography (PCT) using the Patlak model can be a valuable indicator to predict hemorrhagic transformation in patients with acute stroke. Unfortunately, the standard Patlak model based PCT requires excessive radiation exposure, which raised attention on radiation safety. Minimizing radiation dose is of high value in clinical practice but can degrade the image quality due to the introduced severe noise. The purpose of this work is to construct high quality BBBP maps from low-dose PCT data by using the brain structural similarity between different individuals and the relations between the high- and low-dose maps. The proposed sparse high-dose induced (shd-Patlak) model performs by building a high-dose induced prior for the Patlak model with a set of location adaptive dictionaries, followed by an optimized estimation of BBBP map with the prior regularized Patlak model. Evaluation with the simulated low-dose clinical brain PCT datasets clearly demonstrate that the shd-Patlak model can achieve more significant gains than the standard Patlak model with improved visual quality, higher fidelity to the gold standard and more accurate details for clinical analysis.
international conference on image processing | 2014
Kuan-Chuan Peng; Kolbeinn Karlsson; Tsuhan Chen; Dongqing Zhang; Hong Heather Yu
Most works about affective image classification in computer vision treat each emotion category independently and predict hard labels, ignoring the correlation between emotion categories. In this work, inspired by psychological theories, we adopt a dimensional emotion model to model the correlation among certain emotion categories. We also propose a framework of changing image emotion by using our emotion predictor. Easily extendable to other feature transformations, our framework changes image emotion by color histogram specification, relaxing the limitation of the previous method that each emotion is associated with a monotonic palette. Effective and comparable to the previous work of changing image emotion shown by user study, our proposed framework provides users with more flexible control in changing image emotion compared with the previous work.
PLOS ONE | 2015
Abdurrahman Gumus; Seoho Lee; Syed Saad Ahsan; Kolbeinn Karlsson; Richard M. Gabrielson; Christopher G. Guglielmo; David W. Winkler; David Erickson
The metabolism of birds is finely tuned to their activities and environments, and thus research on avian systems can play an important role in understanding organismal responses to environmental changes. At present, however, the physiological monitoring of bird metabolism is limited by the inability to take real-time measurements of key metabolites during flight. In this study, we present an implantable biosensor system that can be used for continuous monitoring of uric acid levels of birds during various activities including flight. The system consists of a needle-type enzymatic biosensor for the amperometric detection of uric acid in interstitial fluids. A lightweight two-electrode potentiostat system drives the biosensor, reads the corresponding output current and wirelessly transfers the data or records to flash memory. We show how the device can be used to monitor, in real time, the effects of short-term flight and rest cycles on the uric acid levels of pigeons. In addition, we demonstrate that our device has the ability to measure uric acid level increase in homing pigeons while they fly freely. Successful application of the sensor in migratory birds could open up a new way of studying birds in flight which would lead to a better understanding of the ecology and biology of avian movements.
acm multimedia | 2014
Kolbeinn Karlsson; Wei Jiang; Dongqing Zhang
Traditional photo browsing systems developed for PCs are inefficient for browsing and searching of large photo albums on mobile devices due to the small screen size and limited mobile processing power. We propose a new concept in this paper, the multiscale timeline, where photos are grouped into clusters and displayed sequentially on a scaled timeline with user controllable time scales, enabling multiscale overview of the photo album for efficient browsing and searching. To address the slow speed of re-clustering when new photos are added, a new incremental spectral clustering algorithm is further developed, which is an order of magnitude faster than the traditional spectral clustering algorithm and its conventional incremental version. Our implementation of the system on mobile devices shows a better user experience and browsing efficiency based on the experiments over large real-world photo collections.
symposium on cloud computing | 2018
Kolbeinn Karlsson; Danny Adams; Gloire Rubambiza; Zangyueyang Xian; Robbert van Renesse; Hakim Weatherspoon; Stephen B. Wicker
The popularity surrounding blockchains has naturally led to research into its applicability in many areas. However, Nakamoto-style blockchains possess several characteristics that make them inappropriate for many purposes in the Internet of Things (IoT) domain. Notably, they are powerintensive and require high network connectivity. These requirements are fundamentally incompatible with IoT where nodes may have limited power and sporadic network access. We are designing a blockchain approach for IoT environments called Vegvisir. Vegvisir is a partition-tolerant blockchain for use in power-constrained IoT environments with limited network access. Under the hood, it is a membership-based, directed acyclic graph (DAG)-structured blockchain [1]. It is motivated by and ideally suited for paramedics and firefighters in disaster scenarios. For instance, it can be used to aid in many tasks during disaster response where network connectivity is poor or nonexistent; namely, it is a blockchain, so provides the abstraction of an append-only log of transactions that is tamperproof. Utilizing a distributed trust model, Nakamoto-style blockchains are free from centralized control and single
Communications of The ACM | 2017
Stephen B. Wicker; Kolbeinn Karlsson
Exploring the technical and ethical issues surrounding Internet advertising and ad blocking.
hawaii international conference on system sciences | 2016
Kolbeinn Karlsson; Stephen B. Wicker
Privacy issues related to location-based services have been extensively studied in recent years, but the focus has mainly been on providing what is commonly referred to as k-anonymity. The underlying assumptions in this approach, however, are often flawed, since the users identity is often already known to the service provider. This paper studies the effect of location obfuscation on semantic location attacks, i.e. attacks inferring which places the user has visited, against an adversary with a prior distribution over the possible semantic locations. The prior is estimated using Foursquare venue data from five U. S. cities of varying sizes. Our results indicate that location data must be very low resolution to guarantee that an adversary can never infer a users location with significant confidence, but the resolution can be increased by an order of magnitude if a low expected probability of a successful inference suffices.
PLOS ONE | 2014
Vlad Oncescu; Seoho Lee; Abdurrahman Gumus; Kolbeinn Karlsson; David Erickson
Hemorrhagic shock (HS) is the leading cause of death for people with traumatic injuries. The onset of HS is correlated with marked changes in the plasma vasopressin levels and some studies indicate that administrating vasopressin in the bloodstream can help stabilize the situation. This situation calls naturally for the use of implantable devices for both the monitoring and treatment of HS. In this work, we present a self-powered hemorrhagic-shock autonomous integrated device (hemoAID) that continuously monitors vasopressin levels and releases vasopressin automatically when levels drop below a certain threshold. We demonstrate that the device can operate at physiological concentrations of vasopressin, in sheep serum, thus paving the way towards the development of an autonomous implantable device for HS prevention.
Analyst | 2014
Abdurrahman Gumus; Seoho Lee; Kolbeinn Karlsson; Richard M. Gabrielson; David W. Winkler; David Erickson
international conference on distributed computing systems | 2018
Kolbeinn Karlsson; Weitao Jiang; Stephen B. Wicker; Danny Adams; Edwin Ma; Robbert van Renesse; Hakim Weatherspoon