1,267 research outputs found

    Compressed Sensing based Dynamic PSD Map Construction in Cognitive Radio Networks

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    In the context of spectrum sensing in cognitive radio networks, collaborative spectrum sensing has been proposed as a way to overcome multipath and shadowing, and hence increasing the reliability of the sensing. Due to the high amount of information to be transmitted, a dynamic compressive sensing approach is proposed to map the PSD estimate to a sparse domain which is then transmitted to the fusion center. In this regard, CRs send a compressed version of their estimated PSD to the fusion center, whose job is to reconstruct the PSD estimates of the CRs, fuse them, and make a global decision on the availability of the spectrum in space and frequency domains at a given time. The proposed compressive sensing based method considers the dynamic nature of the PSD map, and uses this dynamicity in order to decrease the amount of data needed to be transmitted between CR sensors’ and the fusion center. By using the proposed method, an acceptable PSD map for cognitive radio purposes can be achieved by only 20 % of full data transmission between sensors and master node. Also, simulation results show the robustness of the proposed method against the channel variations, diverse compression ratios and processing times in comparison with static methods

    Meta-analyses: Does long-term PPI use increase the risk of gastric premalignant lesions?

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    Background: Proton pump inhibitors (PPIs) are the most effective agents available for reducing acid secretion. They are used for medical treatment of various acid-related disorders. PPIs are used extensively and for extended periods of time in gastroesophageal reflux disease (GERD). A troublesome issue regarding maintenance therapy has been the propensity of PPI-treated patients to develop chronic atrophic gastritis while on therapy that could theoretically lead to an increased incidence of gastric cancer. In addition, animal studies have raised concern for development of enterochromaffin-like cell hyperplasia and carcinoid tumors in the stomachs of mice receiving high dose PPIs. Current literature does not provide a clear-cut conclusion on the subject and the reports are sometimes contradictory. Therefore, this study is a systematic review of the available literature to address the safety of long-term PPI use and its relation to the development of malignant/premalignant gastric lesions. Methods: A literature search of biomedical databases was performed. The reference lists of retrieved articles were reviewed to further identify relevant trials. We hand-searched the abstracts of the American Digestive Disease Week (DDW) and the United European Gastroenterology Week (UEGW) from 1995 to 2013. Only randomized clinical trials (RCTs) that used PPIs as the primary treatment for at least six month versus no treatment, placebo, antacid or anti-reflux surgery (ARS) were included. Two reviewers independently extracted the data. Discrepancies in the interpretation were resolved by consensus. All analyses of outcomes were based on the intention-to-treat principle. We performed statistical analysis using Review Manager software. The effect measure of choice was relative risk (RR) for dichotomous data. Results: Six RCTs with a total of 785 patients met the inclusion criteria. Two multicenter RCTs compared Esomeprazole with placebo. One RCT compared omeprazole with ARS. Two RCTs compared omeprazole with ranitidine and one RCT compared lansoprazole with ranitidine. Four of the included RCTs had moderate risk of bias and two had low risk of bias. The number of patients with increased corporal atrophy score, intestinal metaplasia score and chronic antral inflammation did not statistically differ between the PPI maintenance group and controls. Similar results were found when ECL-cell hyperplasia was assessed between the groups. ConclusionS: Maintenance PPIs did not have an association with increased gastric atrophic changes or ECL-cell hyperplasia for at least three years in RCTs

    Stretching An Anisotropic DNA

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    We present a perturbation theory to find the response of an anisotropic DNA to the external tension. It is shown that the anisotropy has a nonzero but small contribution to the force-extension curve of the DNA. Thus an anisotropic DNA behaves like an isotropic one with an effective bending constant equal to the harmonic average of its soft and hard bending constants.Comment: 29 pages and 4 figure. To appear in J. Chem. Phy

    Extreme bendability of DNA double helix due to bending asymmetry

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    Experimental data of the DNA cyclization (J-factor) at short length scales, as a way to study the elastic behavior of tightly bent DNA, exceed the theoretical expectation based on the wormlike chain (WLC) model by several orders of magnitude. Here, we propose that asymmetric bending rigidity of the double helix in the groove direction can be responsible for extreme bendability of DNA at short length scales and it also facilitates DNA loop formation at these lengths. To account for the bending asymmetry, we consider the asymmetric elastic rod (AER) model which has been introduced and parametrized in an earlier study (B. Eslami-Mossallam and M. Ejtehadi, Phys. Rev. E 80, 011919 (2009)). Exploiting a coarse grained representation of DNA molecule at base pair (bp) level, and using the Monte Carlo simulation method in combination with the umbrella sampling technique, we calculate the loop formation probability of DNA in the AER model. We show that, for DNA molecule has a larger J-factor compared to the WLC model which is in excellent agreement with recent experimental data.Comment: 8 pages, 9 figure

    Search Bias Quantification: Investigating Political Bias in Social Media and Web Search

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    Users frequently use search systems on the Web as well as online social media to learn about ongoing events and public opinion on personalities. Prior studies have shown that the top-ranked results returned by these search engines can shape user opinion about the topic (e.g., event or person) being searched. In case of polarizing topics like politics, where multiple competing perspectives exist, the political bias in the top search results can play a significant role in shaping public opinion towards (or away from) certain perspectives. Given the considerable impact that search bias can have on the user, we propose a generalizable search bias quantification framework that not only measures the political bias in ranked list output by the search system but also decouples the bias introduced by the different sources—input data and ranking system. We apply our framework to study the political bias in searches related to 2016 US Presidential primaries in Twitter social media search and find that both input data and ranking system matter in determining the final search output bias seen by the users. And finally, we use the framework to compare the relative bias for two popular search systems—Twitter social media search and Google web search—for queries related to politicians and political events. We end by discussing some potential solutions to signal the bias in the search results to make the users more aware of them.publishe

    Effects of Peer Education and Orientation Tour on Anxiety in Patient Candidates for Coronary Angiography

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    Background: Coronary angiography is a stressful procedure for most patients. The physiological responses caused by anxiety during coronary angiography increase the likelihood of dysrhythmia, coronary artery spasm, and rupture. Objectives: This study compared the effects of peer education and an orientation tour on anxiety in patients who were candidates for coronary artery angiography. Patients and Methods: This single blind quasi-experimental study was conducted in 2014. A total of 177 patients who were candidates for coronary artery angiography were divided into three groups: a peer education group, an orientation tour group, and a control group. The patients in the peer education group were trained by a peer educator, and the patients in in the orientation tour group were trained by the researcher, who worked in the angiography unit. The DASS-21 questionnaire was used to measure the patients’ anxiety levels before the intervention and two hours before undergoing the coronary angiography. The data were analyzed using a Chi-square test, analysis of variance, the Kruskal-Wallis, Wilcoxon, Mann-Whitney U tests, and an interquartile range. Results: The three groups did not significantly differ regarding the mean anxiety scores before the intervention. However, a significant difference was observed between the mean anxiety scores of the three groups after the intervention (P = 0.0001). In the peer education group, the mean anxiety score was 5.34 ± 2.52 and decreased to 3.69 ± 2.87 after the intervention (P = 0.0001). In the orientation tour group, the mean anxiety was 5.53 ± 3.49, which and changed to 3.10 ± 2.22 (P = 0.0001). However, the mean anxiety score significantly increased in the control group (5.66 ± 2.94 vs. 6.53 ± 3.43, P = 0.017). Conclusions: Both methods of peer education and orientation tour decreased the anxiety levels in patients undergoing coronary artery angiography. Therefore, these approaches should be carried out according to the hospital condition and facilities

    Generative Temporal Models with Spatial Memory for Partially Observed Environments

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    In model-based reinforcement learning, generative and temporal models of environments can be leveraged to boost agent performance, either by tuning the agent's representations during training or via use as part of an explicit planning mechanism. However, their application in practice has been limited to simplistic environments, due to the difficulty of training such models in larger, potentially partially-observed and 3D environments. In this work we introduce a novel action-conditioned generative model of such challenging environments. The model features a non-parametric spatial memory system in which we store learned, disentangled representations of the environment. Low-dimensional spatial updates are computed using a state-space model that makes use of knowledge on the prior dynamics of the moving agent, and high-dimensional visual observations are modelled with a Variational Auto-Encoder. The result is a scalable architecture capable of performing coherent predictions over hundreds of time steps across a range of partially observed 2D and 3D environments.Comment: ICML 201
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