Global state synchronization in networks of cyclic feedback systems

This technical note studies global asymptotic state synchronization in networks of identical systems. Conditions on the coupling strength required for the synchronization of nodes having a cyclic feedback structure are deduced using incremental dissipativity theory. The method takes advantage of the incremental passivity properties of the constituent subsystems of the network nodes to reformulate the synchronization problem as one of achieving incremental passivity by coupling. The method can be used in the framework of contraction theory to constructively build a contracting metric for the incremental system. The result is illustrated for a network of biochemical oscillators. © 2011 IEEE.

Effect of previous cyclic axial loads on pile groups

Numerous piles are often subjected to the combination of cyclic axial and cyclic lateral loads in service, such as piled foundations for offshore platforms which may suffer swaying and rocking motions owing to wind and wave actions. In this research, centrifuge tests were conducted to investigate the effect of previous cyclic axial loads on the performance of pile groups subjected to subsequent cyclic lateral loads. Different pile installation methods were also applied to study the different behaviour of bored and jacked pile groups subjected to cyclic loads. During lateral load cycling, it is seen that cyclic axial loads to which pile groups were previously subjected could reduce the pile cap permanent lateral displacement in the first lateral load cycle but do not influence the incremental rate of permanent displacement in the following lateral load cycles. Moreover, it is found that previous cyclic axial loads could improve the pile cap cyclic lateral secant stiffness, especially for the pre-jacked pile group. When rocking motions were induced by cyclic lateral loads, pile groups subjected to cyclic axial loads before have smaller permanent settlement than those without the cyclic axial loading effect. The designers of piles that are intended to resist significant lateral loads without excessive deformations in service may wish to deploy cyclic axial preloading, accordingly.

Aromaticity on the fly: cyclic transition state stabilization at finite temperature.

We study the transition state of pericyclic reactions at elevated temperature with unbiased ab initio molecular dynamics. We find that the transition state of the intramolecular rearrangements for barbaralane and bullvalene remains aromatic at high temperature despite the significant thermal atomic motions. Structural, magnetic, and electronic properties of the dynamical transition state show the concertedness and aromatic character. Free-energy calculations also support the validity of the transition state theory for the present rearrangement reactions. The calculations demonstrate that cyclic delocalization represents a strong force to synchronize the thermal atomic motions even at high temperatures.

Cyclic jacking of piles in silt and sand

Jacked piles are becoming a valuable installation method due to the low noise and vibration involved in the installation procedure. Cyclic jacking may be used in an attempt to decrease the required installation force. Small scale models of jacked piles were tested in sand and silt in a 10 m beam centrifuge. Two different piles were tested: smooth and rough. Piles were driven in two ways with monotonic and cyclically jacked installations. The cyclically jacked installation involves displacement reversal at certain depth for a fixed number of cycles. The depth of reversal and amplitude of the cycle vary for different tests. Data show that the base resistance increases during cyclic jacking due to soil compaction at the pile toe. On the other hand, shaft load decreases with the number of cycles applied due to densification of soil next to the pile shaft. Cyclic jacking may be used in unplugged tubular piles to decrease the required installation load. © 2013 Taylor & Francis Group, London.

An efficient approach of modelling the flexural cracking behaviour of un-notched plain concrete prisms subject to monotonic and cyclic loading

In the field of vibration-based damage detection of concrete structures efficient damage models are needed to better understand changes in the vibration properties of cracked structures. These models should quantitatively replicate the damage mechanisms in concrete and easily be used as damage detection tools. In this paper, the flexural cracking behaviour of plain concrete prisms subject to monotonic and cyclic loading regimes under displacement control is tested experimentally and modelled numerically. Four-point bending tests on simply supported un-notched prisms are conducted, where the cracking process is monitored using a digital image correlation system. A numerical model, with a single crack at midspan, is presented where the cracked zone is modelled using the fictitious crack approach and parts outside that zone are treated in a linear-elastic manner. The model considers crack initiation, growth and closure by adopting cyclic constitutive laws. A multi-variate Newton-Raphson iterative solver is used to solve the non-linear equations to ensure equilibrium and compatibility at the interface of the cracked zone. The numerical results agree well with the experiments for both loading scenarios. The model shows good predictions of the degradation of stiffness with increasing load. It also approximates the crack-mouth-opening-displacement when compared with the experimental data of the digital image correlation system. The model is found to be computationally efficient as it runs full analysis for cyclic loading in less than 2. min, and it can therefore be used within the damage detection process. © 2013 Elsevier Ltd.

Autoignition of alcohols and ethers in a rapid compression machine

The autoignition characteristics of methanol, ethanol and MTBE (methyl tert-butyl ether) have been investigated in a rapid compression machine at pressures in the range 20-40 atm and temperatures within 750-1000 K. All three oxygenated fuels tested show higher autoignition temperatures than paraffins, a trend consistent with the high octane number of these fuels. The autoignition delay time for methanol was slightly lower than predicted values using reported reaction mechanisms. However, the experimental and measured values for the activation energy are in very good agreement around 44 kcal/mol. The measured activation energy for ethanol autoignition is in good agreement with previous shock tube results (31 kcal/mol), although ignition times predicted by the shock tube correlation are a factor of three lower than the measured values. The measured activation energy for MTBE, 41.4 kcal/mol, was significantly higher than the value previously observed in shock tubes (28.1 kcal/mol). The onset of preignition, characterized by a slow energy release prior to early ignition was observed in some instances. Possible reasons for these ocurrences are discussed. © Copyright 1993 Society of Automotive engineers, Inc.

Modeling cyclic behavior of lightly overconsolidated clays in simple shear

Assessment of seismic performance and estimation of permanent displacements for submerged slopes require the accurate description of the soil's stress-strain-strength relationship under irregular cyclic loading. The geological profile of submerged slopes on the continental shelf typically consists of normally to lightly overconsolidated clays with depths ranging from a few meters to a few hundred meters and very low slope angles. This paper describes the formulation of a simplified effective-stress-based model, which is able to capture the key aspects of the cyclic behavior of normally consolidated clays. The proposed constitutive law incorporates anisotropic hardening and bounding surface principles to allow the user to simulate different shear strain and stress reversal histories as well as provide realistic descriptions of the accumulation of plastic shear strains and excess pore pressure during successive loading cycles. (C) 2000 Published by Elsevier Science Ltd. | Assessment of seismic performance and estimation of permanent displacements for submerged slopes require the accurate description of the soil's stress-strain-strength relationship under irregular cyclic loading. The geological profile of submerged slopes on the continental shelf typically consists of normally to lightly overconsolidated clays with depths ranging from a few meters to a few hundred meters and very low slope angles. This paper describes the formulation of a simplified effective-stress-based model, which is able to capture the key aspects of the cyclic behavior of normally consolidated clays. The proposed constitutive law incorporates anisotropic hardening and bounding surface principles to allow the user to simulate different shear strain and stress reversal histories as well as provide realistic descriptions of the accumulation of plastic shear strains and excess pore pressures during successive loading cycles.

The sensitivity of vibration characteristics of reinforced concrete beams under incremental static and cyclic loading

The use of changes in vibration properties for global damage detection and monitoring of existing concrete structures has received great research attention in the last three decades. To track changes in vibration properties experimentally, structures have been artificially damaged by a variety of scenarios. However, this procedure does not represent realistically the whole design-life degradation of concrete structures. This paper presents experimental work on a set of damaged reinforced concrete beams due to different loading regimes to assess the sensitivity of vibration characteristics. Of the total set, three beams were subject to incremental static loading up to failure to simulate overloading, and two beams subject to 15 million loading cycles with varying amplitudes to produce an accelerated whole-life degradation scenario. To assess the vibration behaviour in both cases, swept sine and harmonic excitations were conducted at every damage level. The results show that resonant frequencies are not sensitive enough to damage due to cyclic loading, whereas cosh spectral and root mean square distances are more sensitive, yet more scattered. In addition, changes in non-linearity follow a softening trend for beams under incremental static loading, whilst they are significantly inconsistent for beams under cyclic loading. Amongst all examined characteristics, changes in modal stiffness are found to be most sensitive to damage and least scattered, but modal stiffness is tedious to compute due mainly to the difficulty of constructing restoring force surfaces from field measurements. © (2013) Trans Tech Publications.

Centrifuge testing of monopiles subject to cyclic lateral loading

Monopiles supporting offshore wind turbines are subjected to cyclic lateral loading. The properties of the applied cyclic lateral load are known to have an effect on the accumulation of permanent displacement and rotation at the pile head. The results of centrifuge testing on model piles show that certain loading regimes lead to the development of locked in soil stresses around the pile. These locked in soil stresses change the stiffness of the monopile response to cyclic lateral loading and the natural frequency of the pile-soil system. © 2014 Taylor & Francis Group.

Polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs) monitored by tree bark in an E-waste recycling area

To investigate the environmental levels and profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs), tree bark samples (n = 22) were collected from Luqiao, an E-waste recycling area, in east China in July 11-13, 2006. The average concentrations of PCDD/Fs, PBDEs, and PCBs determined by isotope dilution-high resolution gas chromatography (HRGC) coupled with high resolution mass spectrometer (HRMS) were 0.1 +/- 0.0, 1.4 +/- 0.2, and 6.5 +/- 0.8 lg g (1) lipid weight, respectively. PCDD/F-toxic equivalent (TEQ, WHO-1998), PCB-TEQs, and total dioxin-like TEQs were 1.3 +/- 0.1, 0.5 +/- 0.0, and 1.8 +/- 0.2 ng g (1) lipid weight, respectively. The profiles of these pollutants in the tree bark were also discussed. Tetra-CDFs, deca-BDE and tri-CBs were the main homologues and accounted for 47% of total PCDD/Fs, 79.3% of total PBDEs, and 33.2% of total PCBs, respectively; As for TEQs, 2,3,4,7,8-PeCDF and PCB126 were the main contributors and accounted for 36% of the total PCDD/F-TEQs and 81.2% of the total PCB-TEQs, respectively. High accumulation of PCDD/Fs, PBDEs, and PCBs detected in the tree bark indicated heavy contaminations of these pollutants in Luqiao area. (C) 2008 Elsevier Ltd. All rights reserved.

Elevated levels of urinary 8-hydroxy-2'-deoxyguanosine in male electrical and electronic equipment dismantling workers exposed to high concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans, polybrominated diphenyl ethers, and polychlorinated biphenyls

To investigate the occupational exposure levels to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs), indoor dust (n = 3) in workshops and hair samples from male workers (n = 64) were collected at two electrical and electronic equipment waste (E-waste) dismantling factories located in the LQ area in east China in July 11-13, 2006. Pre- and postworkshift urines (64 of each) were also collected from the workers to study oxidative damage to DNA using 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a biomarker. The concentrations of PCDD/Fs, PCDD/F-WHO-TEQs, PBDEs, PCBs and PCB-WHO-TEQs were (50.0 +/- 8.1) x 10(3), 724.1 +/- 249.6, (27.5 +/- 5.8) x 10(6), (1.6 +/- 0.4) x 10(9), (26.2 +/- 3.0) x 10(3) pg/g dry weight (dw) in dust, and (2.6 +/- 0.6) x 10(3), 42.4 +/- 9.3, (870.8 +/- 205.4) x 10(3), (1.6 +/- 0.2) x 10(6), 41.5 +/- 5.5 pg/g dw in hair, respectively. The homologue and congener profiles in the samples demonstrated that high concentrations of PCDD/Fs, PBDEs, and PCBs were originated from open burning of E-waste. The 8-OHdG levels were detected at 6.40 +/- 1.64 mu mol/mol creatinine in preworkshift urines. However, the levels significantly increased to 24.55 +/- 5.96 mu mol/mol creatinine in postworkshift urines (p < 0.05). Then, it is concluded that there is a high cancer risk originated from oxidative stress indicated by the elevated 8-OHdG levels in the E-waste dismantling workers exposed to high concentrations of PCDD/Fs, PBDEs, and PCBs.

Detection of polybrominated diphenyl ethers in tilapia (Oreochromis mossambicus) from O'ahu, Hawai'i

Polybrominated diphenyl ethers (PBDEs) have been detected for the first time at a range from 231.58 to 685.61 ng g(-1) lipid weight in the muscles of tilapia ( Oreochromis mossambicus) collected from O'ahu, an island of the geographically isolated Hawaiian archipelago.