Graph Signal Processing: Overview, Challenges and Applications

Research in Graph Signal Processing (GSP) aims to develop tools for processing data defined on irregular graph domains. In this paper we first provide an overview of core ideas in GSP and their connection to conventional digital signal processing. We then summarize recent developments in developing basic GSP tools, including methods for sampling, filtering or graph learning. Next, we review progress in several application areas using GSP, including processing and analysis of sensor network data, biological data, and applications to image processing and machine learning. We finish by providing a brief historical perspective to highlight how concepts recently developed in GSP build on top of prior research in other areas.Comment: To appear, Proceedings of the IEE

Rotation and scale invariant shape representation and recognition using Matching Pursuit

Using a low-level representation of images, like matching pursuit, we introduce a new way of describing objects through a general description using a translation, rotation, and isotropic scale invariant dictionary of basis functions. We then use this description as a predefined dictionary of the object to conduct a shape recognition task. We show some promising results for the detection with simple shapes

Affine invariant Matching Pursuit-based shape representation and recognition using scale-space

In this paper, we propose an analytical low-level representation of images, obtained by a decomposition process, here the matching pursuit (MP) algorithm, as a new way of describing objects through a general continuous description using an affine invariant dictionary of basis functions. This description is used to recognize objects in images. In the learning phase, a template object is decomposed, and the extracted subset of basis functions, called meta-atom, gives the description of our object. We then extend naturally this description into the linear scale-space using the definition of our basis functions, and thus bringing a more general representation of our object. We use this enhanced description as a predefined dictionary of the object to conduct an MP-based shape recognition (MPSR) task into the linear scale-space. The introduction of the scale-space approach improves the robustness of our method, and permits to avoid local minima problems encountered when minimizing a non-convex energy function. We show results for the detection of complex synthetic shapes, as well as natural (aerial and medical) images

Ridgelet transform applied to motion compensated images

Wavelet transform is a powerful instrument in catching zero-dimensional singularities. Ridgelets are a powerful instrument in catching and representing mono-dimensional singularities in bidimensional space. In this paper we propose a hybrid video coder scheme using ridgelet transform for the first approximation of line-edge singularities in displaced frame difference images. We demonstrate the potential of ridgelets and results show substantial improvements when compared to wavelet only based coder

New Dictionary and Fast Atom Searching Methods for Matching Pursuit Representation of Displaced Frame Difference

Matching pursuit decomposes a signal into a linear expansion of functions selected from a redundant dictionary, isolating the signal structures that are coherent with respect to a given dictionary. In this paper we focus on the Matching Pursuit representation of the displaced frame difference (dfd). In particular, we introduce a new dictionary for matching pursuit that efficiently exploits the signal structures of the dfd. We also propose a fast strategy to find the atoms exploiting the maximum of the absolute value of the error in the motion predicted image and the convergence of the MSE with the rotation of the atoms. Results show that the fast strategy is quite robust when compared to exhaustive search techniques and it improves the results of a suboptimal search strategy based on a genetic algorithm

Dynamic Region and Block-Based Motion Estimation for Video Compression

The aim of this project is to find a motion estimation method that works in combination with block matching in order to reduce the visible artifacts. The proposed solution tries to extract the real motions taking place in a sequence. The developed algorithm is a region based motion estimator. We associate to regions of general shape motion parameters which describe an ane transformation on the plane. The traditional block matching is then used for smaller transformations. The developed algorithm is iterative. It alternatively considers the motion and the region as being constant and renes the other one according to this hypothesis. The results will show that it converges and leads to good results if big objects are moving in a sequence

Incidence and prognosis of dysnatraemia in critically ill patients: Analysis of a large prevalence study

Background: The objective of this study is to assess the impact of dysnatraemia on mortality among intensive care unit (ICU) patients in a large, international cohort. Material and methods: Analysis of the Extended Prevalence of Infection in Intensive Care (EPIC II) study, a 1-day (8 May 2007) worldwide multicenter, prospective point prevalence study. Hyponatraemia was categorized as mild (130-134 mM/L), moderate (125-129 mM/L) or severe ( 155 mM/L). Patients with normal serum sodium (135-145 mM/L) constituted the reference group. The main outcome was hospital mortality. Analysis was conducted separately for patients admitted on the study day (25·8%) and those already present on the ICU (74·2%). Results: Serum sodium was measured in 13 276 of the 13 796 patients (96·2%). A total of 3815 patients (28·7%) had dysnatraemia: 12·9% with hyponatraemia and 15·8% with hypernatraemia. The prevalence of dysnatraemia was significantly greater in patients already present on the ICU prior to the study day than for those just admitted (13·1% vs. 12·3% for hyponatraemia and 17·1% vs. 12·1% for hypernatraemia, both P < 0·001). Hospital mortality rates were higher in patients with dysnatraemia than in those with normal sodium levels and were directly related to the severity of hypo- and hypernatraemia. This association between dysnatraemia and mortality was similar in infected and noninfected patients (P = 0·061). Conclusions: Dysnatraemia is more frequent during the ICU stay than on the day of admission. Dysnatraemia in the ICU - even mild - is an independent predictor of increased hospital mortality

Proceedings of the second "international Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST'14)

The implicit objective of the biennial "international - Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST) is to foster collaboration between international scientific teams by disseminating ideas through both specific oral/poster presentations and free discussions. For its second edition, the iTWIST workshop took place in the medieval and picturesque town of Namur in Belgium, from Wednesday August 27th till Friday August 29th, 2014. The workshop was conveniently located in "The Arsenal" building within walking distance of both hotels and town center. iTWIST'14 has gathered about 70 international participants and has featured 9 invited talks, 10 oral presentations, and 14 posters on the following themes, all related to the theory, application and generalization of the "sparsity paradigm": Sparsity-driven data sensing and processing; Union of low dimensional subspaces; Beyond linear and convex inverse problem; Matrix/manifold/graph sensing/processing; Blind inverse problems and dictionary learning; Sparsity and computational neuroscience; Information theory, geometry and randomness; Complexity/accuracy tradeoffs in numerical methods; Sparsity? What's next?; Sparse machine learning and inference.Comment: 69 pages, 24 extended abstracts, iTWIST'14 website: http://sites.google.com/site/itwist1

Silicone adhesive multilayer foam dressings as adjuvant prophylactic therapy to prevent hospital-acquired pressure ulcers : a pragmatic noncommercial multicentre randomized open-label parallel-group medical device trial

Background: Silicone adhesive multilayer foam dressings are used as adjuvant therapy to prevent hospital‐acquired pressure ulcers (PUs). Objectives: Determine if silicone foam dressings in addition to standard prevention reduce PU incidence category 2 or worse compared to standard prevention alone. Methods: Multicentre, randomised controlled, medical device trial conducted in eight Belgian hospitals. At risk adult patients were centrally randomised (n=1633) to study groups based on a 1:1:1 allocation: experimental group 1 (n=542) and 2 (n=545) ‐ pooled as the treatment group ‐ and the control group (n=546). Experimental groups received PU prevention according to hospital protocol, and a silicone foam dressing on these body sites. The control group received standard of care. The primary endpoint was the incidence of a new PU category 2 or worse at these body sites. Results: In the intention‐to‐treat population (n=1605); 4.0% of patients developed PUs category 2 or worse in the treatment group and 6.3% in the control group (RR=0.64, 95% CI 0.41 to 0.99, P=0.04). Sacral PUs were observed in 2.8% and 4.8% of the patients in the treatment group and the control group, respectively (RR=0.59, 95% CI 0.35 to 0.98, P=0.04). Heel PUs occurred in 1.4% and 1.9% of patients in the treatment and control group respectively (RR=0.76, 95% CI 0.34 to 1.68, P=0.49). Conclusions: Silicone foam dressings reduce the incidence of PUs category 2 or worse in hospitalised at‐risk patients when used in addition to standard of care. Results show a decrease for sacrum, but no statistical difference for heel/trochanter areas

Selection of Conditions for Cellulase and Xylanase Extraction from Switchgrass Colonized by Acidothermus cellulolyticus

Solid-state fermentation has been widely used for enzyme production. However, secreted enzymes often bind to the solid substrate preventing their detection and recovery. A series of screening studies was performed to examine the role of extraction buffer composition including NaCl, ethylene glycol, sodium acetate buffer, and Tween 80, on xylanase and cellulase recovery from switchgrass. Our results indicated that the selection of an extraction buffer is highly dependent on the nature and source of the enzyme being extracted. While a buffer containing 50 mM sodium acetate at pH 5 was found to have a positive effect on the recovery of commercial fungal-derived cellulase and xylanase amended to switchgrass, the same buffer had a significant negative effect on enzyme extraction from solid fermentation samples colonized by the bacterium Acidothermus cellulolyticus. Xylanase activity was more affected by components in the extraction buffers compared to cellulase. This study demonstrated that extraction followed by diafiltration is important for assessing enzyme recovery from solid fermentation samples. Reduction in activity due to compounds present in the switchgrass extracts is reversible when the compounds are removed via diafiltration