Since its inception, the blockchain technology has shown promising application prospects. From the initial cryptocurrency to the current smart contract, blockchain has been applied to many fields. Although there are some studies on the security and privacy issues of blockchain, there lacks a systematic examination on the security of blockchain systems. In this paper, we conduct a systematic study on the security threats to blockchain and survey the corresponding real attacks by examining popular blockchain systems. We also review the security enhancement solutions for blockchain, which could be used in the development of various blockchain systems, and suggest some future directions to stir research efforts into this area.
Smart contracts are full-fledged programs that run on blockchains (e.g., Ethereum, one of the most popular blockchains). In Ethereum, gas (in Ether, a cryptographic currency like Bitcoin) is the execution fee compensating the computing resources of miners for running smart contracts. However, we find that under-optimized smart contracts cost more gas than necessary, and therefore the creators or users will be overcharged. In this work, we conduct the first investigation on Solidity, the recommended compiler, and reveal that it fails to optimize gascostly programming patterns. In particular, we identify 7 gascostly patterns and group them to 2 categories. Then, we propose and develop GASPER, a new tool for automatically locating gascostly patterns by analyzing smart contracts' bytecodes. The preliminary results on discovering 3 representative patterns from 4,240 real smart contracts show that 93.5%, 90.1% and 80% contracts suffer from these 3 patterns, respectively.
Diffusion tensor imaging (DTI) is a recent imaging technique that assesses the microstructure of the cerebral white matter (WM) based on anisotropic diffusion (i.e., water molecules move faster in parallel to nerve fibers than perpendicular to them). Fractional anisotropy (FA), which ranges from 0 to 1.0, increases with myelination of WM tracts and is sensitive to diffuse axonal injury (DAI) in adults with traumatic brain injury (TBI). However, previous DTI studies of pediatric TBI were case reports without detailed outcome measures. Using mean FA derived from DTI fiber tractography, we compared DTI findings of the corpus callosum for 16 children who were at least 1 year (mean 3.1 years) post-severe TBI and individually matched, uninjured children. Interexaminer and intraexaminer reliability in measuring FA was satisfactory. FA was significantly lower in the patients for the genu, body, and splenium of the corpus callosum. Higher FA was related to increased cognitive processing speed and faster interference resolution on an inhibition task. In the TBI patients, higher FA was related to better functional outcome as measured by the dichotomized Glasgow Outcome Scale (GOS). FA also increased as a function of the area of specific regions of the corpus callosum such as the genu and splenium, and FA in the splenium was reduced with greater volume of lesions in this region. DTI may be useful in identifying biomarkers related to DAI and outcome of TBI in children.
Objective To investigate the efficacy and safety of ixekizumab in patients with active radiographic axial spondyloarthritis (SpA) and prior inadequate response to or intolerance of 1 or 2 tumor necrosis factor inhibitors ( TNF i). Methods In this phase III randomized, double‐blind, placebo‐controlled trial, adult patients with an inadequate response to or intolerance of 1 or 2 TNF i and an established diagnosis of axial SpA (according to the Assessment of SpondyloArthritis international Society [ ASAS ] criteria for radiographic axial SpA, with radiographic sacroiliitis defined according to the modified New York criteria and ≥1 feature of SpA) were recruited and randomized 1:1:1 to receive placebo or 80‐mg subcutaneous ixekizumab every 2 weeks ( IXE Q2W) or 4 weeks ( IXEQ4W ), with an 80‐mg or 160‐mg starting dose. The primary end point was 40% improvement in disease activity according to the ASAS criteria ( ASAS 40) at week 16. Secondary outcomes and safety were also assessed. Results A total of 316 patients were randomized to receive placebo (n = 104), IXEQ2W (n = 98), or IXEQ4W (n = 114). At week 16, significantly higher proportions of IXEQ2W patients (n = 30 [30.6%]; P = 0.003) or IXEQ4W patients (n = 29 [25.4%]; P = 0.017) had achieved an ASAS 40 response versus the placebo group (n = 13 [12.5%]), with statistically significant differences reported as early as week 1 with ixekizumab treatment. Statistically significant improvements in disease activity, function, quality of life, and spinal magnetic resonance imaging–evident inflammation were observed after 16 weeks of ixekizumab treatment versus placebo. Treatment‐emergent adverse events ( AE s) with ixekizumab treatment were more frequent than with placebo. Serious AE s were similar across treatment arms. One death was reported ( IXEQ2W group). Conclusion Ixekizumab treatment for 16 weeks in patients with active radiographic axial SpA and previous inadequate response to or intolerance of 1 or 2 TNF i yields rapid and significant improvements in the signs and symptoms of radiographic axial SpA versus placebo.
To evaluate the effects of mild to moderate blast-related traumatic brain injury (TBI) on the microstructure of brain white matter (WM) and neurobehavioral outcomes, we studied 37 veterans and service members (mean age 31.5 years, SD = 7.2; post-injury interval 871.5 days; SD = 343.1), whose report of acute neurological status was consistent with sustaining mild to moderate TBI due to blast while serving in Iraq or Afghanistan. Fifteen veterans without a history of TBI or exposure to blast (mean age 31.4 years, SD = 5.4) served as a comparison group, including seven subjects with extracranial injury (post-injury interval 919.5 days, SD = 455.1), and eight who were uninjured. Magnetic resonance imaging disclosed focal lesions in five TBI participants. Post-concussion symptoms (Neurobehavioral Symptom Inventory), post-traumatic stress disorder (PTSD) symptoms (PTSD Checklist-Civilian), and global distress and depression (Brief Symptom Inventory) were worse in the TBI participants than the comparison group, but no group differences were found in perceived physical or mental functioning (SF-12). Verbal memory (Selective Reminding) was less efficient in the TBI group, but there were no group differences in nonverbal memory (Selective Reminding) or decision making (Iowa Gambling Task). Verbal memory in the TBI group was unrelated to PTSD severity. Diffusion tensor imaging (DTI) using tractography, standard single-slice region-of-interest measurement, and voxel-based analysis disclosed no group differences in fractional anisotropy (FA) and apparent diffusion coefficient (ADC). However, FA of the left and right posterior internal capsule and left corticospinal tract was positively correlated with total words consistently recalled, whereas ADC for the left and right uncinate fasciculi and left posterior internal capsule was negatively correlated with this measure of verbal memory. Correlations of DTI variables with symptom measures were non-significant and inconsistent. Our data do not show WM injury in mild to moderate blast-related TBI in veterans despite their residual symptoms and difficulty in verbal memory. Limitations of the study and implications for future research are also discussed.
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