Radiation sterilized bone response to dynamic loading

Allogeneic bone grafts are used on a large scale in surgeries. To avoid the risk of infectious diseases, allografts should be radiation-sterilized. So far, no international consensus has been achieved regarding the optimal radiation dose. Many authors suggest that bone sterilization deteriorates bone mechanical properties. However, no data on the influence of ionizing radiation on bone dynamic mechanical properties are available. Bovine femurs from 2-year old animal were machine cut and irradiated with the doses 10, 15, 25, 35, 45 and 50 kGy. Dynamic mechanical analysis was performed at 1–10 Hz at the temperature range of 0–350 °C in 3-point bending configuration. No statistically significant differences in storage modulus were observed. However, there were significant decreased values of loss modulus between the samples irradiated with doses of 10 (↓14.3%), 15, 45 and 50 kGy (↓33.2%) and controls. It was stated that increased irradiation dose decreases the temperature where collagen denaturation process starts and increases the temperature where the collagen denaturation process finishes. It was shown that activation energy of denaturation process is significantly higher for the samples irradiated with the dose of 50 kGy (615 kJ/mol) in comparison with control samples and irradiation with other doses (100–135 kJ/mol).     

Interpolymer complexes comprising block copolymers due to specific interactions

Two kinds of supramolecular assembly, i.e., macromolecular complex comprising block copolymers were investigated by viscometry and static and dynamic light scattering. In the blend solutions of poly(styrene-co-methyl methacrylate) (PS-b-PMMA) and hydroxyl-containing modified polystyrene (PS(OH)), the hydrogen bonding between the PMMA block and PS(OH) leads to the complex formation. In the solutions of Zn sulfonated poly(styrene-b-ethylene-co-propylene) (ZnSSEP) and poly(butyl methacrylate-co-vinyl pyridine) (BVP), the ligand–metal coordination between BVP and the polystyrene ionomer block causes complexation. Both kinds of complexation induce nano-size, soluble complexes with micelle-like structure, which is stabilized in the solutions by the soluble, non-complexed blocks.     

Transient response of plates to travelling loads with application to slamming damage

There is a considerable range of slamming loads on hull plating which cause either elastic response or elastic-plastic response where the plastic deformation is of the same order as the elastic deformation. Failure criteria for plate design can likely be from pulses causing this range of deformation.

This paper summarizes the author's Master's thesis which gives a detailed analysis of the elastic response of hull plating to slamming pulses. A finite difference model of a plate strip is developed which accounts for membrane effects. The analysis shows detailed stress and deflection response to various pulses. The results of the elastic analysis give the combinations of typical pulses of 207–1380 K Pa peak pressures and decay times of 0.001–0.5 s leading to, but not exceeding, incipient yield at 276 and 414 MPa (40 000 and 60 000 psi) in various plate sizes.

The plate strip concept is then extended to the elastic-plastic range. The model is made of two rigid sections with deformable hinges at the center and ends. These hinges are comprised of layers of bar elements with elastic—plastic characteristics. The results of this analysis give the permanent deflections from pulses of two—six times those which cause incipient yield. Unexpected resonances of 5–30% occur in the elastic—plastic range, not noted in the elastic range.

While the slamming load is a pressure wave which propagates across a plate at some finite velocity, it is common in the analysis of hull plate slamming response to assume a spatially constant load. This paper gives justification for the approximation by analyzing the response to a travelling pressure front and specifies the criterion for which the approximation remains valid.     

Adapting second‐order response surface designs to specific needs

Experimental design strategies most often involve an initial choice of a classic factorial or response surface design and adapt that design to meet restrictions or unique requirements of the system under study. One such experience is described here, in which the objective was to develop an efficient experimental design strategy that would facilitate building second‐order response models with excellent prediction capabilities. In development, careful consideration was paid to the desirable properties of response surface designs. Once developed, the proposed design was evaluated using Monte Carlo simulation to prove the concept, a pilot implementation of the design carried out to evaluate the accuracy of the response models, and a set of validation runs enacted to look for potential weaknesses in the approach. The purpose of the exercise was to develop a procedure to efficiently and effectively calibrate strain‐gauge balances to be used in wind tunnel testing. The current calibration testing procedure is based on a time‐intensive one‐factor‐at‐a‐time method. In this study, response surface methods were used to reduce the number of calibration runs required during the labor‐intensive heavy load calibration, to leverage the prediction capabilities of response surface designs, and to provide an estimate of uncertainty for the calibration models. Results of the three‐phased approach for design evaluation are presented. The new calibration process will require significantly fewer tests to achieve the same or improved levels of precision in balance calibration. Copyright © 2008 John Wiley & Sons, Ltd.     

High cycle fatigue damage mechanisms in cast aluminium subject to complex loads

This article is dedicated to the high cycle fatigue behaviour of cast hypo-eutectic Al–Si alloys. In particular, the AlSi7Cu05Mg03 alloy is investigated. It presents the results of a vast experimental campaign undertaken to investigate the fatigue behaviour, and more specifically the fatigue damage mechanisms observed under complex loading conditions: plane bending with different load ratios, fully reversed torsion and equibiaxial bending with a load ratio of R = 0.1. A specific test set-up has been designed to create an equibiaxial stress state using disk shaped specimens. A tomographic analysis is also presented with the aim of characterising the micro-shrinkage pore population of the material.It is shown that two distinct and coexisting fatigue damage mechanisms occur in this material, depending on the presence of different microstructural heterogeneities (i.e. micro-shrinkage pores, Silicon particles in the eutectic zones, Fe-rich intermetallic phases, etc.). Furthermore, it is concluded that the effect of an equibiaxial tensile stress state is not detrimental in terms of high cycle fatigue. It is also shown that the Dang Van criterion is not able to simultaneously predict the multiaxial effect (i.e. torsion and equibiaxial tension) and the mean stress effect for this material.     

Radiation damage of bipolar SST due to γ rays of Co

In order to investigate radiation hardness of the bipolar SST transistors, transistor samples were exposed to gamma rays from an intense ⁶⁰Co source. The transistor samples were hard up to a total dose of the order of 10⁴ Gy.     

Radiation damage study of MeV ions-implanted Nd:YVO4 crystal

Damage formation mechanism of Nd:YVO₄ implanted with MeV ions is investigated. MeV Si⁺ ions were implanted into Nd:YVO₄ crystal, and the lattice damage was measured using Rutherford backscattering spectroscopy/channeling (RBS/C) method. The damage creation kinetic indicates a significant contribution from electronic energy loss to the surface damage. A detailed analysis allows us to deduce the different contributions from electronic and nuclear stopping powers to the lattice damage production. An obvious difference in extent of damage from 1 MeV and 3 MeV Si⁺ implantations also implies that there exists a threshold value of the electronic energy deposition for damage formation. The exact value of threshold is obtained by comparison with the experimental data obtained from 3 MeV O⁺, F⁺ and Si⁺ implantation results, which turns out to be (1.7 ± 0.1) keV/nm.     

Cognitive modeling and dynamic probabilistic simulation of operating crew response to complex system accidents: Part 3: IDAC operator response model

This is the third in a series of five papers describing the IDAC (Information, Decision, and Action in Crew context) model for human reliability analysis. An example application of this modeling technique is also discussed in this series. The model is developed to probabilistically predict the responses of the nuclear power plant control room operating crew in accident conditions. The operator response spectrum includes cognitive, emotional, and physical activities during the course of an accident. This paper discusses the modeling components and their process rules. An operator's problem-solving process is divided into three types: information pre-processing (I), diagnosis and decision-making (D), and action execution (A). Explicit and context-dependent behavior rules for each type of operator are developed in the form of tables, and logical or mathematical relations. These regulate the process and activities of each of the three types of response. The behavior rules are developed for three generic types of operator: Decision Maker, Action Taker, and Consultant. This paper also provides a simple approach to calculating normalized probabilities of alternative behaviors given a context.     

Monitoring ligand modulation of protein-protein interactions by mass spectrometry: estrogen receptor alpha-SRC1

Many drugs and chemicals exert their biological effect by modulating protein-protein interactions. In vitro approaches to characterize these mechanisms are often based on indirect measurements (e.g., fluorescence). Here, we used mass spectrometry (MS) to directly monitor the effect of small-molecule ligands on the binding of a coactivator peptide (SRC1) by the human estrogen receptor alpha ligand binding domain (hERalpha LBD). Nanoelectrospray mass spectrometry (nanoESI-MS) and high-mass matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with chemical cross-linking were employed to follow these processes. The chemical cross-linking protocol used prior to high-mass MALDI analysis allows detection of intact noncovalent complexes. The binding of intact hERalpha LBD homodimer with two coactivator peptides was detected with nanoESI-MS and high-mass MALDI-MS only in the presence of an agonist ligand. Furthermore, high-mass MALDI-MS revealed an increase of the homodimer abundance after incubating the receptor with a ligand, independent of the ligand character (i.e., agonist, antagonist). The binding characteristics of the compounds tested by MS correlate very well with their biological activity reported by cell-based assays. High-mass MALDI appears to be an efficient and simple tool for directly monitoring ligand regulation mechanisms involved in protein-protein interactions. Furthermore, the combination of both MS methods allows identifying and characterizing endocrine-disrupting compounds or new drug compounds in an efficient way.     

爆炸冲击下水底隧道的动态响应及毁伤模式研究

考虑炸药起爆、冲击波传播、冲击波与结构的相互作用以及结构的动态响应等复杂过程,基于Lagrange-Euler耦合算法,建立了水底隧道水下爆炸的全耦合数值仿真模型。通过与爆炸试验结果进行对比,验证了数值模型的可靠性;研究了水下爆炸冲击荷载作用下的水底隧道的毁伤破坏过程、空间分布规律及破坏模式。结果表明:水底隧道的破坏模式不仅与隧道自身的动力特性有关,还取决于起爆距离及炸药当量等;隧道的破坏模式为局部冲切或剥落破坏、弯曲破坏伴随着局部剥落破坏以及整体弯曲破坏。     

爆炸冲击下水底隧道的动态响应及毁伤模式研究

考虑炸药起爆、冲击波传播、冲击波与结构的相互作用以及结构的动态响应等复杂过程,基于Lagrange-Euler耦合算法,建立了水底隧道水下爆炸的全耦合数值仿真模型。通过与爆炸试验结果进行对比,验证了数值模型的可靠性;研究了水下爆炸冲击荷载作用下的水底隧道的毁伤破坏过程、空间分布规律及破坏模式。结果表明:水底隧道的破坏模式不仅与隧道自身的动力特性有关,还取决于起爆距离及炸药当量等;隧道的破坏模式为局部冲切或剥落破坏、弯曲破坏伴随着局部剥落破坏以及整体弯曲破坏。     

Contribution of time delays to p53 oscillation in DNA damage response

Although the oscillatory dynamics of the p53 network have been extensively studied, the understanding of the mechanism of delay‐induced oscillations is still limited. In this paper, a comprehensive mathematical model of p53 network is studied, which contains two delayed negative feedback loops. By studying the model with and without explicit delays, the results indicate that the time delay of Mdm2 protein synthesis can well control the pulse shape but cannot induce p53 oscillation alone, while the time delay required for Wip1 protein synthesis induces a Hopf bifurcation to drive p53 oscillation. In addition, the synergy of the two delays will cause the p53 network to oscillate in advance, indicating that p53 begins the repair process earlier in the damaged cell. Furthermore, the stability and bifurcation of the model are addressed, which may highlight the role of time delay in p53 oscillations.Inspec keywords: proteins, cellular biophysics, DNA, molecular biophysics, biomolecular effects of radiation, bifurcation, physiological models, cellular effects of radiation, oscillations, geneticsOther keywords: highlight, time delay, delayed negative feedback loops, murine double minute 2, Wip1 protein synthesis, explicit delays, Mdm2 protein synthesis, p53 network     

The response of composite structures with pre-stress subject to low velocity impact damage

The effect of an initial pre-stress on the response of carbon-fibre/epoxy laminated plates subjected to low velocity impact is investigated. Prior to being impacted, the samples are loaded either uniaxially or biaxially using a specially designed test rig which enables tension or compression loading, independent on each axis. Impact tests were carried out for two impact energies for uniaxial and biaxial tension, pure shear and the zero pre-stress cases. The effect of the pre-stress on the permanent indentation depth, absorbed energy and peak impact loads is experimentally quantified.

The results indicate that the penetration/perforation depth, peak load and absorbed energy are essentially independent of the nature and magnitude of the pre-stress at low levels of impact energy (6 J), becoming more significant at higher levels of impact energy (10 J).     

Radiation monitoring strategy: factors to be considered

In a nuclear or radiological emergency radiation measurements provide indispensable data needed in the management of the situation at hand. In order to assess the possible consequences correctly and to carry out proper countermeasures on time, the authorities must have a pre-prepared monitoring strategy at their disposal. There are, however, many different factors that affect a strategy. Thus, drawing up a comprehensive yet realistic emergency monitoring strategy is far from being an easy task. Some of the key factors related to strategies are reviewed and a simple way of producing a strategy plan is presented.     

Dynamic culture substrate that captures a specific extracellular matrix protein in response to light

The development of methods for the off–on switching of immobilization or presentation of cell-adhesive peptides and proteins during cell culture is important because such surfaces are useful for the analysis of the dynamic processes of cell adhesion and migration. This paper describes a chemically functionalized gold substrate that captures a genetically tagged extracellular matrix protein in response to light. The substrate was composed of mixed self-assembled monolayers (SAMs) of three disulfide compounds containing (i) a photocleavable poly(ethylene glycol) (PEG), (ii) nitrilotriacetic acid (NTA) and (iii) hepta(ethylene glycol) (EG₇). Although the NTA group has an intrinsic high affinity for oligohistidine tag (His-tag) sequences in its Ni²⁺-ion complex, the interaction was suppressed by the steric hindrance of coexisting PEG on the substrate surface. Upon photoirradiation of the substrate to release the PEG chain from the surface, this interaction became possible and hence the protein was captured at the irradiated regions, while keeping the non-specific adsorption of non-His-tagged proteins blocked by the EG₇ underbrush. In this way, we selectively immobilized a His-tagged fibronectin fragment (FNIII_7–10) to the irradiated regions. In contrast, when bovine serum albumin—a major serum protein—was added as a non-His-tagged protein, the surface did not permit its capture, with or without irradiation. In agreement with these results, cells were selectively attached to the irradiated patterns only when a His-tagged FNIII_7-10 was added to the medium. These results indicate that the present method is useful for studying the cellular behavior on the specific extracellular matrix protein in cell-culturing environments.     

Dynamic culture substrate that captures a specific extracellular matrix protein in response to light

Abstract

The development of methods for the off–on switching of immobilization or presentation of cell-adhesive peptides and proteins during cell culture is important because such surfaces are useful for the analysis of the dynamic processes of cell adhesion and migration. This paper describes a chemically functionalized gold substrate that captures a genetically tagged extracellular matrix protein in response to light. The substrate was composed of mixed self-assembled monolayers (SAMs) of three disulfide compounds containing (i) a photocleavable poly(ethylene glycol) (PEG), (ii) nitrilotriacetic acid (NTA) and (iii) hepta(ethylene glycol) (EG₇). Although the NTA group has an intrinsic high affinity for oligohistidine tag (His-tag) sequences in its Ni²⁺-ion complex, the interaction was suppressed by the steric hindrance of coexisting PEG on the substrate surface. Upon photoirradiation of the substrate to release the PEG chain from the surface, this interaction became possible and hence the protein was captured at the irradiated regions, while keeping the non-specific adsorption of non-His-tagged proteins blocked by the EG₇ underbrush. In this way, we selectively immobilized a His-tagged fibronectin fragment (FNIII_7–10) to the irradiated regions. In contrast, when bovine serum albumin—a major serum protein—was added as a non-His-tagged protein, the surface did not permit its capture, with or without irradiation. In agreement with these results, cells were selectively attached to the irradiated patterns only when a His-tagged FNIII_7-10 was added to the medium. These results indicate that the present method is useful for studying the cellular behavior on the specific extracellular matrix protein in cell-culturing environments.     

Numerical simulation of structural response and damage to simultaneous ground shock and airblast loads

Current practice in analysis and design of structures to withhold surface explosions considers only airblast forces on structures. A surface explosion, in fact, generates both ground shock and airblast pressure on a nearby structure. In this paper, the influences of simultaneous ground shock and airblast forces on structural responses are investigated. Blast-induced surface ground motions and airblast pressures estimated in a previous study are employed as input in the analysis. A previously developed three-dimensional homogenized material model for a masonry wall including the equivalent elastic properties, strength envelope and damage threshold is used to model masonry wall. Another material damage model developed for reinforced concrete structures is used for modelling RC behavior due to explosive loads. These material models are programmed and linked to an available computer program LS-DYNA3D through its user subroutine capability. A one-story masonry infilled RC frame is used as an example in the study. Dynamic response and damage of the example structure to simultaneous ground shock and airblast forces, or separately to ground shock only or airblast forces only are calculated. It is found that in general, airblast load governs structural response and damage when the scaled distance is small. However, under certain conditions, structural damage will be critically underestimated if ground shock is neglected. When the scale distance increases, the relative importance of the ground shock on structure response increases, and ground shock will dominate the surface explosion effects on structures at large scaled distance. At large scaled distance, the ground shock and airblast force effects on structures decoupled and structure response and damage to ground shock and airblast force can be analyzed separately.     

A reduced basis approach to quantifying damage dependent dynamic response of laminated composite structures

A finite element (FE) based formulation is utilized to represent the damage-dependent response of laminated composite structures. An internal-state-variable (ISV) approach provides a definition of the stiffness reduction caused by intralaminar crack propagation at the ply level. These ISVs are combined with simple stress criteria to accommodate ply property changes caused by fiber fracture, fiber microbuckling and interior delaminations. A set of orthogonal Ritz vectors are chosen as basis vectors to transform the dynamical equations of motion to a reduced coordinate space. The reduced basis form of the equations provides significant numerical efficiencies, especially for large ordered systems. Furthermore, damping and its variation with damage can be generally represented in any number of vibratory modes. The Newmark integration operator is used to solve the dynamic equations of motion, and equilibrium iterations are performed in each incremental time step to assure convergence. Results are given for laminated beam and plate geometries subjected to dynamic loads.