Energy deposition stochastics and track structure: what about the target?

The broad field of microdosimetry, as reflected in the proceedings of the 13 previous symposia in this series, has been largely concerned with the microscopic stochastics of energy deposition from ionising radiations of different qualities, the ways in which these can be described and the information that they can provide towards mechanistic understanding of the biological effects of radiation and for practical applications. Directions of the research have been strongly influenced by technical developments at particular times, most notably the tissue-equivalent proportional counter and later Monte Carlo track-structure simulation methods. Essential to the research have been evolving notions as to characteristics of the relevant biological targets, and in particular their sizes and structures in relation to the microscopic features of the radiation. Over the decades since the first Symposium on Microdosimetry, in 1967, emphasis has fluctuated from key targets being assumed to be of nanometre dimensions, then up to one micrometer, ten micrometers, and then back again to a few nanometres. Some of these historical threads are traced through the successive symposia, culminating in current emphasis on the predominant importance of clustered damage in DNA, first revealed by track-structure simulations, but tempered by recognition also of the contribution that novel 'non-targeted' effects may play in the overall biological consequences of radiation.     

Evaluating the performance of the Harshaw™ DXTRAD LiF:Mg,Cu,P finger ring with two different thickness filters

Amongst the dosemeters offered by the Health Protection Agency (HPA) Personal Dosimetry Service are finger rings, which use the Harshaw? DXTRAD element. This paper describes restricted-type testing carried out by HPA on the previously untried combination of the LiF:Mg,Cu,P material and a thicker filter (42 mg cm(-2)). The tests were based on ISO 12794 [International Organization for Standardization. ISO 12794:2000 nuclear energy--radiation protection--individual thermoluminescence dosemeters for the extremities and eyes. ISO (2000)] and included energy and angle dependence of response for photons. The conclusion was, for photon dosimetry applications the thicker filter is acceptable for use in the HPA service.     

How the sensitivity in PIXE elemental analysis is affected by the type of particle, cross-sections, background radiation and other factors?

The purpose of this paper is to review the relevant factors to be taken into account to obtain a more sensitive PIXE (Particle induced X-ray emission) elemental analysis. In quantitative PIXE analysis, matrix effects become a fundamental factor. Depending on the analyzed element, the projectile particle type and its energy, material composition can have a major effect on the X-ray yields. Background in the X-ray spectrum, detection limits, particle stopping powers and X-ray photons attenuation, should be considered. Also the ionization cross-sections could be affected by the previous state of the projectile, conditioned by the passage in the material producing multiple ionizations and changes in its state of charge. A variety of experimental results and theoretical models, are analyzed here for protons, deuterons and heavier incident ions.     

Why is combinatorial communication rare in the natural world,and why is language an exception to this trend?

In a combinatorial communication system, some signals consist of the combinations of other signals. Such systems are more efficient than equivalent, non-combinatorial systems, yet despite this they are rare in nature. Why? Previous explanations have focused on the adaptive limits of combinatorial communication, or on its purported cognitive difficulties, but neither of these explains the full distribution of combinatorial communication in the natural world. Here, we present a nonlinear dynamical model of the emergence of combinatorial communication that, unlike previous models, considers how initially non-communicative behaviour evolves to take on a communicative function. We derive three basic principles about the emergence of combinatorial communication. We hence show that the interdependence of signals and responses places significant constraints on the historical pathways by which combinatorial signals might emerge, to the extent that anything other than the most simple form of combinatorial communication is extremely unlikely. We also argue that these constraints can be bypassed if individuals have the socio-cognitive capacity to engage in ostensive communication. Humans, but probably no other species, have this ability. This may explain why language, which is massively combinatorial, is such an extreme exception to nature''s general trend for non-combinatorial communication.     

Optimisation of the composition of an acrylic bone cement: application to relative amounts of the initiator and the activator/co-initiator in Surgical Simplex®P

In cemented arthroplasties, the two-part self-curing acrylic bone cement is currently the only material used for anchoring the total joint replacement to the contiguous bone. In virtually all commercially available formulations of this cement, the agents used for the initiation and activation/co-initiation of the radical polymerisation reaction are benzoyl peroxide (BPO) and N, N dimethyl-para-toluidine (DMPT), respectively. There are no reports in the open literature on the rationale for the amounts of these and other constituents in the formulations of the cement. Given the concerns that have been raised in the literature regarding the effect of residual DMPT on the body, it is important to keep the starting amounts of BPO and DMPT as high and as low, respectively, as possible. In the present work, the focus is on the relative amounts of these two agents in the case of one widely used commercial formulation, Surgical Simplex(R) P. Thirty variants of this cement were formulated, covering three concentrations of the co-polymer/BPO (75%, 80%, and 85% of the mass of the powder) and DMPT amounts (ranging from 0.8 %v/v to 2.4% v/v.) The setting time (t(set)), the peak temperature reached during the cement polymerisation process (T(max)), and the ultimate compressive strength (UCS) of each of the formulations were determined in accordance with procedures specified in ISO 5833. A critical examination of all the results indicated that the optimum ratio of the concentration of the initiator (BPO embedded in the PMMA-sytrene co-polymer) to that of the activator/co-initiator (DMPT) in Surgical Simplex(R) P is 57.14 (80%w/w co-polymer + BPO per 1.4%v/v DMPT). The mean values of t(set), T(max), and UCS of this optimum formulation were determined to be 12.30 min, 68 degrees C, and 101 MPa, respectively, all of which are within the limits specified in ISO 5833. The commercially available formulation of this cement contains 2.5%v/v DMPT, while the optimum formulation, as found in the present work, has 44% less DMPT, which may translate to a smaller amount of residual DMPT that is available for elution into the periprosthetic tissue in a cemented arthroplasty, over the in vivo life of the joint replacement.     

Effects of Cu and Al on the crystal structure and composition of η (MgZn2) phase in over-aged Al–Zn–Mg–Cu alloys

Heat treatable Al–Zn–Mg alloys can be strengthened by the precipitation of second phase particles. In this paper, Al–6.57%Zn–2.83%Mg and Al–6.57%Zn–2.83%Mg–3.92%Cu alloys (in wt%) in T7 state (140 °C for 96 h) have been prepared. The effects of Cu and Al on the concentration and structure of equilibrium η (MgZn₂) phase have been investigated by high resolution transmission electron microscopy, aberration-corrected scanning transmission electron microscopy, selected election diffraction pattern simulations, and first-principles calculations. The effects of Cu and Al substitution on the diffraction characteristics of the η phase and the general rule of Cu and Al substitution in the η phase have been discussed.     

Atomic structure of hardening precipitates in an Al–Mg–Zn–Cu alloy determined by HAADF-STEM and first-principles calculations: relation to η-MgZn2

The structures of two nanoscale plate precipitates prevalent at maximum strength and over-aged conditions in a 7449 Al–Mg–Zn–Cu alloy were investigated. Models derived from images of high angle annular dark field scanning transmission electron microscopy were supported by first-principles calculations. Both structures are closely linked to the η-MgZn₂ Laves phase through similar layers of a rhombohedral atomic subunit. The finest plate contains one such layer together with a layer of an orthorhombic unit. The second plate contains rhombohedral layers only, normally four, but rotated relatively to form different stacking variants, one of which may be likened to η. For both structures, the same atomic planes describe the main interface with Al. Both plates could be described in space group P3. The unit cells comprise interface and arbitrary numbers of {111}Al (habit) planes. Eight Al-planes were included in the first-principles calculations. The enthalpy indicates high layer/unit stability. The plate thickness can be understood by a simple mismatch formulation.     

Coronavirus mapping in scientific publications: When science advances rapidly and collectively,is access to this knowledge open to society?

Scientometrics - The COVID-19 pandemic is creating a global health emergency. Mapping this health emergency in scientific publications demands multiple approaches to obtain a picture as complete as...     

On the properties of ?111? {110} dissociated superdislocation in B2 structure YAg and YCu: Core structure and Peierls stress

The simplified one-dimensional dislocation equation for mixed dislocations is derived briefly from the two-dimensional modified Peierls-Nabarro equation taking into account the discreteness effect of crystals. The collinear dissociated core structure of 〈111〉 {110} superdislocations in the novel B2 structure YAg and YCu are investigated with the simplified equation. Both the core width and the dissociated width are increasing with the increases in the dislocation angle of superdislocations. The dissociated width determined by continuum elastic theory is inaccurate for the high antiphase boundary energy but is recovered for the low antiphase boundary energy. The Peierls stress of the dissociated dislocation is replaced by that of superpartials. The results show that both the unstable stacking fault energy and the core width are crucial for the Peierls stress in the case of a narrow core structure. However, the core width becomes the main factor in controlling the Peierls stress in the case of a wide core.     

An analysis of dimensionality using factor analysis (true-score theory) and Rasch measurement: what is the difference? Which method is better?

One often hears the question asked, "For questionnaire data measuring a variable, what difference does it make to use factor analysis/principal components analysis (true-score theory) or Rasch measurement in testing for dimensionality?" This paper reports both factor analysis and Rasch measurement analysis for two sets of data. One set of data measures social anxiety for primary school students (N=436, I=10) and the second measures attitude to mathematics for primary-aged students (N=774, I=10). For both sets of data, the factor analysis suggests that the scores are reliable, and that inferences can be made that are valid for measuring school anxiety and attitude to mathematics. For both sets of data analyzed with Rasch measurement techniques, the reliability of the measures, the dimensionality of the measures, and the initial conceptualisation of the items, are called into question. It suggests that one cannot make valid inferences from the measures that were initially set up for true-score theory. The Rasch analysis suggests that items intended to measure a variable should be initially developed on a conceptualized scale from easy to hard, and that students should answer the items from this perspective, so that the Rasch analysis of the data tests this conceptualisation, and a linear scale can be created based on a mathematical measurement model with consistent units (logits).     

Is farming a belief in Northern Ghana? Exploring the dual-system theory for commerce,culture, religion and technology

Rice production encountered several challenges, especially among rural farmers in Northern Ghana. The current debate encompasses the belief of cultural norms and religious values as the right theory for the sustainability of agriculture. The belief in abstracts is prioritised to the adoption of improved rice. This paper examined the value attached to traditional rice varieties as a result of societal beliefs, and theoretically underpinned by the Dual-system hypothesis. The finding from three ethnic and religious groups through a survey indicates heterogeneity in the results but also demonstrates the factual importance of culture and religion. This paper, therefore, proposes a new way of categorising farming; as a business and a belief and that policy stream aim at small scale, rural farmers with belief peculiarities needs to adopt cultural and religious strategies to promote adoption.     

Who is in control of road safety? A STAMP control structure analysis of the road transport system in Queensland,Australia

Despite significant progress, road trauma continues to represent a global safety issue. In Queensland (Qld), Australia, there is currently a focus on preventing the ‘fatal five’ behaviours underpinning road trauma (drug and drink driving, distraction, seat belt wearing, speeding, and fatigue), along with an emphasis on a shared responsibility for road safety that spans road users, vehicle manufacturers, designers, policy makers etc. The aim of this article is to clarify who shares the responsibility for road safety in Qld and to determine what control measures are enacted to prevent the fatal five behaviours. This is achieved through the presentation of a control structure model that depicts the actors and organisations within the Qld road transport system along with the control and feedback relationships that exist between them. Validated through a Delphi study, the model shows a diverse set of actors and organisations who share the responsibility for road safety that goes beyond those discussed in road safety policies and strategies. The analysis also shows that, compared to other safety critical domains, there are less formal control structures in road transport and that opportunities exist to add new controls and strengthen existing ones. Relationships that influence rather than control are also prominent. Finally, when compared to other safety critical domains, the strength of road safety controls is brought into question.     

Effect of beryllium on age hardening,defect structure,and S′ formation in Al–2·5Cu–1·2Mg alloy

Abstract

The effect of micro additions of Be on the aging behaviour, defect structure, and S′ phase formation in Al–2·5Cu–1·2Mg alloy is investigated. It is shown that the addition of 0·15%Be significantly increases the peak hardness and overall precipitation rate for the alloy. An analysis of the kinetic data shows that S′ precipitation obeys the Avrami equation, and that the Be addition does not affect the growth dependent parameter or activation energy, but significantly increases the nuclei density dependent parameter, which is consistent with the higher density of S precipitates in the microstructures of the alloy containing Be. Analysis using transmission electron microscopy shows that Be reduces the dislocation loop density during the early stages of aging, which is attributed to the high Be–vacancy binding energy, and promotes formation of dislocation helices. The enhanced nucleation of S′, notwithstanding the lower density of dislocation loops, which stimulate S′ nucleation, suggests the operation of a non-heterogeneous nucleation mechanism.

MST /1977     

Modelling of particle nucleation and growth in binary alloys under elastic deformation: An application to a Cu–0.95 wt%Co alloy

This study incorporates the effect of elastic deformation in a previously proposed model for the nucleation and growth of precipitates. We adapt the KWN-model by Robson [20] to incorporate the effect of strain energy arising from elastic deformation on the homogeneous nucleation and growth of Co particles in a Cu–Co system at constant temperatures. The finite-volume method is used for the KWN-model and the finite-element method is used to simulate elastic deformations within a cylindrical tension test specimen. Simulations of the nucleation and growth of Co particles in a Cu–Co system on the cylindrical region show that the incorporation of elastic strain energies has a noticeable impact on the process. The derived quantities of homogeneous nucleation and growth, such as the particle volume fraction and the particle number density, show a clear spatial correlation with the calculated strain energy. The results also show that the currently presented algorithm, which incorporates the influence of elastic deformation, has low computational cost with respect to full simulations, with just a minimal loss of accuracy.     

Bilateral Comparison Between CEM and LACOMET in the Range from 83.8058?K to 933.473?K, Linking to CCT Comparisons

A bilateral comparison between Centro Español de Metrología (CEM) and Laboratorio Costarricense de Metrología (LACOMET) in the range from 83.8058 K to 933.473 K was carried out during 2009, and it is aimed to provide linkage of the CCT key comparisons K3 and K4 to LACOMET. This comparison gives support to the calibration measurement capabilities requested by LACOMET. The participation of CEM in the EURAMET regional comparisons EUROMET-T.K3 and EUROMET-T.K4 is the basis of the link. Two 25 ?? standard platinum resistance thermometers (SPRTs) were used as travelling standards and were hand carried. One of them was used only in the aluminum freezing point while the other one covered the remaining fixed points. At the temperature of the argon triple point (83.8058 K), CEM performed the measurements in an argon triple-point apparatus, but LACOMET calibrated the SPRT at a temperature close to the argon point using a liquid-nitrogen boiling-point apparatus. Both SPRTs were provided by LACOMET, and LACOMET measured them before and after CEM. The SPRTs showed no significant drifts during the comparison. The results for both laboratories agreed within their expanded uncertainties and are summarized. A proposal for the linkage to the results of CCT-K3 and CCT-K4 is presented.     

Textile industry and environment: can the use of bacterial cellulose in the manufacture of biotextiles contribute to the sector?

Clean Technologies and Environmental Policy - The textile industry is one of the most complex sectors in relation to environmental degradation, both with regard to the materials used from petroleum...     

Changes to the morphology,structure and properties as a consequence of polyethylene working in a polymer–metal kinematic pair

A change is presented of the orientation of lamellar structure, degree of crystallinity, the degree of the spatial arrangement of the structure, micromechanical properties, and the surface morphology and thickness of a plastically deformed upper layer. These changes are the effect of work in a polymer–metal kinematic pair, which have occurred as a result of plastic deformation of polyethylene during its service. It has been shown that, as a result of selecting proper parameters of UHMW polyethylene via the initial draft and electron-beam irradiation, such a structure of the polymer can be obtained, which will enable the above-mentioned changes in morphology and structure to take place during service. This in turn, will allow a reduction of the susceptibility of the polymer to permanent deformation by 3–6 times, and its wear by more than 5 times, compared to the initial material.