A true concurrent model of smart contracts executions

The development of blockchain technologies has enabled the trustless execution of so-called smart contracts, i.e. programs that regulate the exchange of assets (e.g., cryptocurrency) between users. In a decentralized blockchain, the state of smart contracts is collaboratively maintained by a peer-to-peer network of mutually untrusted nodes, which collect from users a set of transactions (representing the required actions on contracts), and execute them in some order. Once this sequence of transactions is appended to the blockchain, the other nodes validate it, re-executing the transactions in the same order. The serial execution of transactions does not take advantage of the multi-core architecture of modern processors, so contributing to limit the throughput. In this paper we propose a true concurrent model of smart contract execution. Based on this, we show how static analysis of smart contracts can be exploited to parallelize the execution of transactions.Comment: Full version of the paper presented at COORDINATION 202

Laxatives Do Not Improve Symptoms of Opioid-Induced Constipation: Results of a Patient Survey

Introduction.:  Laxatives are commonly used to treat opioid-induced constipation, the commonest and most bothersome complication of opioids. However, laxatives have a nonspecific action and do not target underlying mechanisms of opioid-induced constipation; their use is associated with abdominal symptoms that negatively impact quality of life. Objective.:  To assess the effects of laxatives in patients taking opioids for chronic pain. Methods.:  One hundred ninety-eight UK patients who had taken opioid analgesics for at least one month completed a cross-sectional online or telephone survey. Questions addressed their pain condition, medication, and laxative use (including efficacy and side effects). The survey also assessed bowel function using the Bowel Function Index. Results.:  Since starting their current opioid, 134 of 184 patients (73%) had used laxatives at some point and 122 (91%) of these were currently taking them. The most common laxatives were osmotics and stimulants. Laxative side effects were reported in 75%, most commonly gas, bloating/fullness, and a sudden urge to defecate. Side effects were more common in patients less than 40 years of age. Approximately half of patients said laxatives interfered with work and social activities, and one-fifth needed an overnight hospital stay because of their pain condition and/or constipation. Laxatives did not improve the symptoms of constipation, as assessed by the Bowel Function Index. Constipation was not related to opioid strength, dose of opioid, or number of laxatives taken. Conclusions.:  Use of laxatives to treat opioid-induced constipation is often ineffective and associated with side effects. Instead of relieving the burden of opioid-induced constipation, laxative use is associated with a negative impact

Developing Active Learning Exercises for Any Content

Teaching and learning both should be fun, engaging, and impactful in lasting ways. Studies show that student engagement and information retention increases when students are immersed in active learning - hands-on usage of the information. Modern faculty members are seeking methods of incorporating active learning into their teaching, but may not know where to start when creating their own active learning materials. This paper will outline a process for creating new activities. Included are appendices full of creative active-learning formats (hot topics borrowed from primary and secondary education), as well as guidelines on when to use them that will make teaching and learning fun and practical. These media are also useful for developing transferable skills that students will bring into the workplace

A Precision Angle Sensor using an Optical Lever inside a Sagnac Interferometer

We built an ultra low noise angle sensor by combining a folded optical lever and a Sagnac interferometer. The instrument has a measured noise floor of 1.3 prad / Hz^(1/2) at 2.4 kHz. We achieve this record angle sensitivity using a proof-of-concept apparatus with a conservative N=11 bounces in the optical lever. This technique could be extended to reach sub-picoradian / Hz^(1/2) sensitivities with an optimized design.Comment: 3 pages, 4 figure

Heat conductivity of DNA double helix

Thermal conductivity of isolated single molecule DNA fragments is of importance for nanotechnology, but has not yet been measured experimentally. Theoretical estimates based on simplified (1D) models predict anomalously high thermal conductivity. To investigate thermal properties of single molecule DNA we have developed a 3D coarse-grained (CG) model that retains the realism of the full all-atom description, but is significantly more efficient. Within the proposed model each nucleotide is represented by 6 particles or grains; the grains interact via effective potentials inferred from classical molecular dynamics (MD) trajectories based on a well-established all-atom potential function. Comparisons of 10 ns long MD trajectories between the CG and the corresponding all-atom model show similar root-mean-square deviations from the canonical B-form DNA, and similar structural fluctuations. At the same time, the CG model is 10 to 100 times faster depending on the length of the DNA fragment in the simulation. Analysis of dispersion curves derived from the CG model yields longitudinal sound velocity and torsional stiffness in close agreement with existing experiments. The computational efficiency of the CG model makes it possible to calculate thermal conductivity of a single DNA molecule not yet available experimentally. For a uniform (polyG-polyC) DNA, the estimated conductivity coefficient is 0.3 W/mK which is half the value of thermal conductivity for water. This result is in stark contrast with estimates of thermal conductivity for simplified, effectively 1D chains ("beads on a spring") that predict anomalous (infinite) thermal conductivity. Thus, full 3D character of DNA double-helix retained in the proposed model appears to be essential for describing its thermal properties at a single molecule level.Comment: 16 pages, 12 figure