A creep model for metallic composites based on matrix testing: Application to Kanthal composites

An anisotropic creep model is formulated for metallic composites with strong fibers and low to moderate fiber volume percent (less than 40 percent). The idealization admits no creep in the local fiber direction and assumes equal creep strength in longitudinal and transverse shear. Identification of the matrix behavior with that of the isotropic limit of the theory permits characterization of the composite through uniaxial creep tests on the matrix material. Constant and step-wise creep tests are required as a data base. The model provides an upper bound on the transverse creep strength of a composite having strong fibers embedded in a particular matrix material. Comparison of the measured transverse strength with the upper bound gives an assessment of the integrity of the composite. Application is made to a Kanthal composite, a model high-temperature composite system. Predictions are made of the creep response of fiber reinforced Kanthal tubes under interior pressure

Heavy flavor diffusion in weakly coupled N=4 Super Yang-Mills theory

We use perturbation theory to compute the diffusion coefficient of a heavy quark or scalar moving in N=4 SU(N_c) Super Yang-Mills plasma to leading order in the coupling and the ratio T/M<<1. The result is compared both to recent strong coupling calculations in the same theory and to the corresponding weak coupling result in QCD. Finally, we present a compact and simple formulation of the Lagrangian of our theory, N=4 SYM coupled to a massive fundamental N=2 hypermultiplet, which is well-suited for weak coupling expansions.Comment: 22 pages, 4 figures; v3: error corrected in calculations, figures and discussion modified accordingl

Decision-Tree Based Transceiver Selection for Medium Access Control in Wireless Sensor Networks

The primary contribution of this paper lies in evaluating the potential benefits of using decision tree based transceiver selection algorithms for multi-hub wireless sensor networks (WSNs) to improve network performance and stability. The classification algorithm helps improve network throughput and reduce unnecessary transceiver handovers by considering multiple decision factors, without any additional hardware complexity at the sensor nodes. The algorithms allow the nodes to use information included in the reference messages from the transceivers, and the Receiver Signal Strength Indicator (RSSI) as decision factors. This paper demonstrates the effectiveness of decision tree based algorithms (Decision Tree and Random Forest) through simulation, and the results show that this approach can enhance throughput and provide extra stability to the WSN in the scenarios considered, compared to traditional approach using distance or RSSI

Using Information from Rendezvous Missions for Best-Case Appraisals of Impact Damage to Planet Earth Caused by Natural Objects

The Asteroid Threat Assessment Project (ATAP), a part of NASAs Planetary Defense Coordination Office (PDCO) has the responsibility to appraise the range of surface damage by potential asteroid impacts on land or water. If a threat is realized, the project will provide appraisals to officials empowered to make decisions about potential mitigation actions. This paper describes a scenario for assessment of surface damage when characterization of an asteroid had been accomplished by a rendezvous mission that would be conducted by the international planetary defense community. It is shown that the combination of data from ground and in-situ measurements on an asteroid provides knowledge that can be used to pin-point its impact location and predict the level of devastation it would cause. The hypothetical asteroid 2017 PDC with a size range of 160 to 290 m in diameter to be discussed at the PDC 2017 is used as an example. In order of importance for appraising potential damage, information required is: (1) where will the surface impact occur? (2) what is the mass, shape and size of the asteroid and what is its entry state (speed and entry angle) at the 100 km atmospheric pierce point? And (3) is the asteroid a monolith or a rubble pile? If it is a rubble pile, what is its structure and heterogeneity from the surface and throughout its interior? Item (1) is of first order importance to determine levels of devastation (loss of life and infrastructure damage) because it varies strongly on the impact location. Items (2) and (3) are used as inputs for ATAPs simulations to define the level of surface hazards: winds, overpressure, thermal exposure; all created by the deposition of energy during the objects atmospheric flight, andor cratering. Topics presented in this paper include: (i) the devastation predicted by 2017 PDCs impact on land based on initial observations using ATAPs risk assessment capability, (ii) how information corresponding to items (1) to (3) could be obtained from a rendezvous mission, and (iii) how information from a rendezvous mission could be used, along with that from ground observations and data from the literature to provide input for a new risk analysis capability that is emerging from ATAPs research. It is concluded that this approach would result in the creation of an appraisal of the threat from 2017 PDC with the least uncertainty possible, herein called the best-case

Ultrarapid cerium(III)–NHC catalysts for high molar mass cyclic polylactide

The EPSRC are acknowledged for research funding through the Centre for Doctoral Training in Critical Resource Catalysis (CRITICAT, EP/ L016419/1, R. W. F. K., P. M. D. A. E.), EP/J018139/1, the UK Catalysis Hub (EP/K014714/1, P. L. A., C. K. W., S. K. R.), EP/M010554/1 (P. L. A.) and EP/S018603/1 (C. K. W.). This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 740311, P.L.A.).Cyclic polyesters could improve the properties of degradable plastics, but routes to them that provide a product with faster rates, higher molar mass, and greater selectivity for cyclic vs linear polymer are needed. Here, homogeneous Ce(III)–N-heterocyclic carbene (NHC) catalysts show outstanding activities (turn-over-frequency (TOF) > 864 000 h–1), excellent control, and selectivity for cyclic polylactide (PLA) topology (>95%), yielding high molar mass PLA (60 < Mn < 250 kg mol–1). They efficiently produce cyclic PLA from rac-lactide or l-lactide and aliphatic cyclic polyesters from ε-caprolactone or β-butyrolactone. The enhanced performances are only achievable from combining cooperative Lewis acidic cerium(III) and hemilabile N-heterocyclic carbene functionalities.PostprintPostprintPeer reviewe

Pilot Study Comparing Closed Versus Open Tracheal Suctioning in Postoperative Neonates and Infants With Complex Congenital Heart Disease

Objectives: To determine the hemodynamic effect of tracheal suction method in the first 36 hours after high-risk infant heart surgery on the PICU and to compare open and closed suctioning techniques. Design: Pilot randomized crossover study. Setting: Single PICU in United Kingdom. Participants: Infants undergoing surgical palliation with Norwood Sano, modified Blalock-Taussig shunt, or pulmonary artery banding in the first 36 hours postoperatively. Interventions: Infants were randomized to receive open or closed (in-line) tracheal suctioning either for their first or second study tracheal suction in the first 36 hours postoperatively. Measurements and Main Results: Twenty-four infants were enrolled over 18 months, 11 after modified Blalock-Taussig shunt, seven after Norwood Sano, and six after pulmonary artery banding. Thirteen patients received the open suction method first followed by the closed suction method second, and 11 patients received the closed suction method first followed by the open suction method second in the first 36 hours after their surgery. There were statistically significant larger changes in heart rate (p = 0.002), systolic blood pressure (p = 0.022), diastolic blood pressure (p = 0.009), mean blood pressure (p = 0.007), and arterial saturation (p = 0.040) using the open suction method, compared with closed suctioning, although none were clinically significant (defined as requiring any intervention). Conclusions: There were no clinically significant differences between closed and open tracheal suction methods; however, there were statistically significant greater changes in some hemodynamic variables with open tracheal suctioning, suggesting that closed technique may be safer in children with more precarious physiology. (Pediatr Crit Care Med 2017; XX:00–00

Iatrogenic Spinal Cord Injury Resulting From Cervical Spine Surgery.

STUDY DESIGN: Retrospective cohort study of prospectively collected data. OBJECTIVE: To examine the incidence of iatrogenic spinal cord injury following elective cervical spine surgery. METHODS: A retrospective multicenter case series study involving 21 high-volume surgical centers from the AOSpine North America Clinical Research Network was conducted. Medical records for 17 625 patients who received cervical spine surgery (levels from C2 to C7) between January 1, 2005, and December 31, 2011, were reviewed to identify occurrence of iatrogenic spinal cord injury. RESULTS: In total, 3 cases of iatrogenic spinal cord injury following cervical spine surgery were identified. Institutional incidence rates ranged from 0.0% to 0.24%. Of the 3 patients with quadriplegia, one underwent anterior-only surgery with 2-level cervical corpectomy, one underwent anterior surgery with corpectomy in addition to posterior surgery, and one underwent posterior decompression and fusion surgery alone. One patient had complete neurologic recovery, one partially recovered, and one did not recover motor function. CONCLUSION: Iatrogenic spinal cord injury following cervical spine surgery is a rare and devastating adverse event. No standard protocol exists that can guarantee prevention of this complication, and there is a lack of consensus regarding evaluation and treatment when it does occur. Emergent imaging with magnetic resonance imaging or computed tomography myelography to evaluate for compressive etiology or malpositioned instrumentation and avoidance of hypotension should be performed in cases of intraoperative and postoperative spinal cord injury

On the screening of static electromagnetic fields in hot QED plasmas

We study the screening of static magnetic and electric fields in massless quantum electrodynamics (QED) and massless scalar electrodynamics (SQED) at temperature $T$. Various exact relations for the static polarisation tensor are first reviewed and then verified perturbatively to fifth order (in the coupling) in QED and fourth order in SQED, using different resummation techniques. The magnetic and electric screening masses squared, as defined through the pole of the static propagators, are also calculated to fifth order in QED and fourth order in SQED, and their gauge-independence and renormalisation-group invariance is checked. Finally, we provide arguments for the vanishing of the magnetic mass to all orders in perturbation theory.Comment: 37 pages, 8 figure