The correlation of indentation size effect experiments with pyramidal and spherical indenters

Experiments were conducted in annealed iridium using pyramidal and spherical indenters over a wide range of load. For a Berkovich pyramidal indenter, the hardness increased with decreasing depth of penetration. However, for spherical indenters, hardness increased with decreasing sphere radius. Based on the number of geometrically necessary dislocations generated during indentation, a theory that takes into account the work hardening differences between pyramidal and spherical indenters is developed to correlate the indentation size effects measured with the two indenters. The experimental results verify the theoretical correlation.

The correlation of the indentation size effect measured with indenters of various shapes

Experimental results are presented which show that the indentation size effect for pyramidal and spherical indenters can be correlated. For a pyramidal indenter, the hardness measured in crystalline materials usually increases with decreasing depth of penetration, which is known as the indentation size effect. Spherical indentation also shows an indentation size effect. However, for a spherical indenter, hardness is not affected by depth, but increases with decreasing sphere radius. The correlation for pyramidal and spherical indenter shapes is based on geometrically necessary dislocations and work-hardening. The Nix and Gao indentation size effect model (J. Mech. Phys. Solids 46 (1998) 411) for conical indenters is extended to indenters of various shapes and compared to the experimental results. © 2002 Elsevier Science Ltd. All rights reserved.

A mechanistic description of combined hardening and size effects

Mechanistic models based on geometrically necessary dislocations are re-examined in light of recent experiments exhibiting the indentation size effect. A simple method is developed to combine work hardening, solid solution hardening, radiation hardening and size effects. The model is verified by experiments in ionic salt crystals. © 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Unfolding grain size effects in barium titanate ferroelectric ceramics

Grain size effects on the physical properties of polycrystalline ferroelectrics have been extensively studied for decades; however there are still major controversies regarding the dependence of the piezoelectric and ferroelectric properties on the grain size. Dense BaTiO3 ceramics with different grain sizes were fabricated by either conventional sintering or spark plasma sintering using micro- and nano-sized powders. The results show that the grain size effect on the dielectric permittivity is nearly independent of the sintering method and starting powder used. A peak in the permittivity is observed in all the ceramics with a grain size near 1μm and can be attributed to a maximum domain wall density and mobility. The piezoelectric coefficient d33 and remnant polarization Pr show diverse grain size effects depending on the particle size of the starting powder and sintering temperature. This suggests that besides domain wall density, other factors such as back fields and point defects, which influence the domain wall mobility, could be responsible for the different grain size dependence observed in the dielectric and piezoelectric/ferroelectric properties. In cases where point defects are not the dominant contributor, the piezoelectric constant d33 and the remnant polarization Pr increase with increasing grain size.

Bayesian error bars for regression

Regression problems are concerned with predicting the values of one or more continuous quantities, given the values of a number of input variables. For virtually every application of regression, however, it is also important to have an indication of the uncertainty in the predictions. Such uncertainties are expressed in terms of the error bars, which specify the standard deviation of the distribution of predictions about the mean. Accurate estimate of error bars is of practical importance especially when safety and reliability is an issue. The Bayesian view of regression leads naturally to two contributions to the error bars. The first arises from the intrinsic noise on the target data, while the second comes from the uncertainty in the values of the model parameters which manifests itself in the finite width of the posterior distribution over the space of these parameters. The Hessian matrix which involves the second derivatives of the error function with respect to the weights is needed for implementing the Bayesian formalism in general and estimating the error bars in particular. A study of different methods for evaluating this matrix is given with special emphasis on the outer product approximation method. The contribution of the uncertainty in model parameters to the error bars is a finite data size effect, which becomes negligible as the number of data points in the training set increases. A study of this contribution is given in relation to the distribution of data in input space. It is shown that the addition of data points to the training set can only reduce the local magnitude of the error bars or leave it unchanged. Using the asymptotic limit of an infinite data set, it is shown that the error bars have an approximate relation to the density of data in input space.

A cross-cultural study of factors influencing helping behaviour

The burgeoning research into altruism and helping behaviour has examined the effect of many variables that enhance or inhibit helpfulness, but little attention has been given to the influence of culture. In the present research, data on various aspects of helping behaviour were collected in both the UK and the Sudan so that the importance of cultural influences could be investigated. In addition this research also tested the validity of current models of helping. In a repertory grid study, urgency and cost emerged as the main constructs people in the two countries use to distinguish between various helpful situations. A laboratory experiment designed to test existing models of intervention behaviour found significant main effects of country, group, size, cost and urgency; and a group size/urgency interaction. Subjects in the Sudan intervened faster than subjects in the UK; lone subjects intervened faster than subjects in small and large groups; subjects in low cost intervened faster than subjects in high cost conditions; and subjects in high urgency intervened faster than subjects in low urgency conditions. Group size effect was stronger in low than in high urgency conditions. Two field studies further investigated the effect of urgency and cost in urban-nonurban context. Significant main effects of urgency and cost were found in cities but not in towns; and people in cities were less helpful than people in towns. A questionnaire survey found that in both countries there were significant urban-nonurban differences in the incidence of reported social contacts and exchange of helpful acts between acquaintances, neighbours and strangers. However, there were no urban-nonurban differences between relatives and close friends. Finally, attitudes to altruism and helpfulness did not differ between the two countries or between urban and nonurban residents. The results highlight the need to incorporate urgency and cultural variables in theoretical models of helping behaviour.

Statnote 32 : the partial correlation coefficient

In previous statnotes, the application of correlation and regression methods to the analysis of two variables (X,Y) was described. The most important statistic used to measure the degree of correlation between two variables is Pearson’s ‘product moment correlation coefficient’ (‘r’). The correlation between two variables may be due to their common relation to other variables. Hence, investigators using correlation studies need to be alert to the possibilities of spurious correlation and the methods of ‘partial correlation’ are one method of taking this into account. This statnote applies the methods of partial correlation to three scenarios. First, to a fairly obvious example of a spurious correlation resulting from the ‘size effect’ involving the relationship between the number of general practitioners (GP) and the number of deaths of patients in a town. Second, to the relationship between the abundance of the nitrogen-fixing bacterium Azotobacter in soil and three soil variables, and finally, to a more complex scenario, first introduced in Statnote 24involving the relationship between the growth of lichens in the field and climate.

Exact solution for the energy spectrum of Kelvin-wave turbulence in superfluids

We study the statistical and dynamical behavior of turbulent Kelvin waves propagating on quantized vortices in superfluids and address the controversy concerning the energy spectrum that is associated with these excitations. Finding the correct energy spectrum is important because Kelvin waves play a major role in the dissipation of energy in superfluid turbulence at near-zero temperatures. In this paper, we show analytically that the solution proposed by [L’vov and Nazarenko, JETP Lett. 91, 428 (2010)] enjoys existence, uniqueness, and regularity of the prefactor. Furthermore, we present numerical results of the dynamical equation that describes to leading order the nonlocal regime of the Kelvin-wave dynamics. We compare our findings with the analytical results from the proposed local and nonlocal theories for Kelvin-wave dynamics and show an agreement with the nonlocal predictions. Accordingly, the spectrum proposed by L’vov and Nazarenko should be used in future theories of quantum turbulence. Finally, for weaker wave forcing we observe an intermittent behavior of the wave spectrum with a fluctuating dissipative scale, which we interpreted as a finite-size effect characteristic of mesoscopic wave turbulence.

Effect of vesicle size on tissue localization and immunogenicity of liposomal DNA vaccines

The formulation of plasmid DNA (pDNA) in cationic liposomes is a promising strategy to improve the potency of DNA vaccines. In this respect, physicochemical parameters such as liposome size may be important for their efficacy. The aim of the current study was to investigate the effect of vesicle size on the in vivo performance of liposomal pDNA vaccines after subcutaneous vaccination in mice. The tissue distribution of cationic liposomes of two sizes, 500 nm (PDI 0.6) and 140 nm (PDI 0.15), composed of egg PC, DOPE and DOTAP, with encapsulated OVA-encoding pDNA, was studied by using dual radiolabeled pDNA-liposomes. Their potency to elicit cellular and humoral immune responses was investigated upon application in a homologous and heterologous vaccination schedule with 3 week intervals. It was shown that encapsulation of pDNA into cationic lipsomes resulted in deposition at the site of injection, and strongest retention was observed at large vesicle size. The vaccination studies demonstrated a more robust induction of OVA-specific, functional CD8+ T-cells and higher antibody levels upon vaccination with small monodisperse pDNA-liposomes, as compared to large heterodisperse liposomes or naked pDNA. The introduction of a PEG-coating on the small cationic liposomes resulted in enhanced lymphatic drainage, but immune responses were not improved when compared to non-PEGylated liposomes. In conclusion, it was shown that the physicochemical properties of the liposomes are of crucial importance for their performance as pDNA vaccine carrier, and cationic charge and small size are favorable properties for subcutaneous DNA vaccination.

The effect of rock surface aspect on growth, size structure and competition in the lichen Rhizocarpon geographicum

Rhizocarpon geographicum is a crustose lichen found frequently on rock surfaces of southern aspect and less frequently on rock surfaces of northern aspect in Gwynedd, North Wales. This study tested the hypothesis that the radial growth of R. geographicum thalli predicts aspect distribution. Thalli of all sizes, however, exhibited significantly greater radial growth over 18 months on northwest compared with southeast facing surfaces. The hypothesis that a more intense competitive environment on northwest facing surfaces may explain the aspect distribution of R. geographicum was then tested. The size frequency distributions of thalli revealed a higher proportion of thalli in the smallest size class and a more restricted thallus size range on the northwest facing surfaces. In addition, thallus mortality appeared to be greater on northwest facing surfaces. Significantly more associated lichen species were present on rock surfaces of northern aspect at sites where R. geographicum was present. The mean frequency of the associated lichen species, however, was significantly lower on surfaces of northern aspect where R. geographicum was present. In addition, two common foliose species at these sites were demonstrated experimentally to overgrow thalli of R. geographicum. It is concluded that the growth of R. geographicum over the study period did not predict aspect distribution and that differences in the competitive environments on northwest and southeast surfaces may be an important factor determining aspect distribution. © 2002 Elsevier Science B.V. All rights reserved.

A CFD approach on the effect of particle size on char entrainment in bubbling fluidised bed reactors

The fluid – particle interaction inside a 41.7 mg s-1 fluidised bed reactor is modelled. Three char particles of sizes 500 µm, 250 µm, and 100 µm are injected into the fluidised bed and the momentum transport from the fluidising gas and fluidised sand is modelled. Due to the fluidising conditions and reactor design the char particles will either be entrained from the reactor or remain inside the bubbling bed. The particle size is the factor that differentiates the particle motion inside the reactor and their efficient entrainment out of it. A 3-Dimensional simulation has been performed with a completele revised momentum transport model for bubble three-phase flow according to the literature as an extension to the commercial finite volume code FLUENT 6.2.

The vesicle size of DDA:TDB liposomal adjuvants plays a role in the cell-mediated immune response but has no significant effect on antibody production

The use of cationic liposomes as experimental adjuvants for subunit peptide of protein vaccines is well documented. Recently the cationic liposome CAF01, composed of dimethyldioctadecylammonium (DDA) and trehalose dibehenate (TDB), has entered Phase I clinical trials for use in a tuberculosis (TB) vaccine. CAF01 liposomes are a heterogeneous population with a mean vesicle size of 500 nm; a strong retention of antigen at the injection site and a Th1-biassed immune response are noted. The purpose of this study was to investigate whether CAF01 liposomes of significantly different vesicle sizes exhibited altered pharmacokinetics in vivo and cellular uptake with activation in vitro. Furthermore, the immune response against the TB antigen Ag85B-ESAT-6 was followed when various sized CAF01 liposomes were used as vaccine adjuvants. The results showed no differences in vaccine (liposome or antigen) draining from the injection site, however, significant differences in the movement of liposomes to the popliteal lymph node were noted. Liposome uptake by THP-1 vitamin D3 stimulated macrophage-like cells did not show a liposome size-dependent pattern of uptake. Finally, whilst there were no significant differences in the IgG1/2 regardless of the liposome size used as a delivery vehicle for Ag85B-ESAT-6, vesicle size has a size dependent effect on cell proliferation and IL-10 production with larger liposomes (in excess of 2 µm) promoting the highest proliferation and lowest IL-10 responses, yet vesicles of ~500 nm promoting higher IFN-? cytokine production from splenocytes and higher IL-1ß at the site of injection.