Freedom of Mind

This is the text of The Lindley Lecture for 1961, given by Stuart Hampshire (1914-2004), a British philosopher

Investigation of Oleic Acid As A Dispersant For Hydroxyapatite Powders For Use In Ceramic Filled Photo-Curable Resins For Stereolithography

Stereolithography allows production of porous hydroxyapatite scaffolds for bone regeneration but is limited by the challenging rheology of ceramic filled resins. Oleic acid, a natural fatty acid, was applied in concentrations of 0.0–0.3 wt% to improve the rheological properties of HAp resins for the fabrication of solid cylinders and scaffolds by digital light processing (DLP) printing in a wiperless system. Bonding by chemisorption was confirmed by FTIR analysis. The powders were then incorporated into a photo-curable resin of 1–6 hexanediol diacrylate at 18–30 vol%. The shear viscosity and sedimentation rates of photocurable resins containing HAp powder decreased with increasing concentration of oleic acid. The curing depth and width of resins containing the HAp were unchanged as a result of the presence of oleic acid. Oleic acid improved the printing behaviour of the resins allowing the fabrication of scaffolds with continuous macro-porosity on a wiperless DLP system

Propagation of woody plants, Station Bulletin, no.465

The Bulletin is a publication of the New Hampshire Agricultural Experiment Station, College of Life Sciences and Agriculture, University of New Hampshire, Durham, New Hampshire

The influence of waste bark on plant growth. The comparative value of bark as a surface mulch for apples, blueberries, and raspberries., Station Bulletin, no.435

The Bulletin is a publication of the New Hampshire Agricultural Experiment Station, College of Life Sciences and Agriculture, University of New Hampshire, Durham, New Hampshire

Mechanical Properties of Hydroxyapatite-Zirconia Compacts Sintered by Two Different Sintering Methods

Microwave sintering is traditionally employed to reduce the sintering temperature required to densify powder compacts. The effect of microwave heating on hydroxyapatite (HA)-zirconia (ZrO2) green bodies has been investigated in order to understand how microwave energy may affect the physical and mechanical properties of the resultant densified composites. Laboratory synthesised nano-sized HA and a commercial nano-sized ZrO2 powder have been ball milled to create mixtures containing 0-5 wt% ZrO2 loadings. Compacts were microwave sintered at either 700, 1000 or 1200°C with a 1 h hold time. Comparative firings were also performed in a resistive element furnace using the same heating profile in order to assess the differences between conventional and microwave heating on the physical, mechanical and microstructural properties of the composites. Samples sintered at 700°C show little sign of densification with open porosities of approximately 50%. Composites conventionally sintered at 1000°C were between 65 and 75% dense, whereas the samples microwave sintered at this temperature were between 55 and 65% dense. Samples sintered at 1200°C showed the greatest degree of densification (\u3e80%) with a corresponding reduction in open porosities. TCP generation occurred as a consequence of sintering at 1200°C, even with 0 wt% ZrO2, and increased degradation of the HA phase to form significant amounts of TCP occurred with increasing additions of ZrO2, along with increasing open porosity. Nanosized ZrO2 prevents the densification of the HA matrix by effectively pinning grain boundaries and this effect is more pronounced in the MS materials. Similar strengths are achieved between the microwave and conventionally sintered samples. Greater amount of open porosity and pore interconnectivity are seen in the MS samples, which are considered to be useful for biomedical applications as they can promote osteo-integration. © 2009 Springer Science+Business Media, LLC

Investigating the Effect of SiO2-TiO2-CaO-Na 2O-ZnO Bioactive Glass Doped Hydroxyapatite: Characterisation and Structural Evaluation

The effects of increasing bioactive glass additions, SiO2-TiO2-CaO-Na2O-ZnO up to 25 wt% in increments of 5 wt%, on the physical and mechanical properties of hydroxyapatite (HA) sintered at 900, 1000, 1100 and 1200°C for 2 h was investigated. Increasing both the glass content and the temperature resulted in increased HA decomposition. This resulted in the formation of a number of bioactive phases. However the presence of the liquidus glass phase did not result in increased densification levels. At 1000 and 1100°C the additions of 5 wt% glass resulted in a decrease in density which never recovered with increasing glass content. At 1200°C a cyclic pattern resulted from increasing glass content. There was no direct relationship between strength and density with all samples experiencing no change or a decrease in strength with increasing glass content. Weibull statistics displayed no pattern with increasing glass content. © 2014 Springer Science+Business Media

Reflections on a crisis: political disenchantment, moral desolation, and political integrity

Declining levels of political trust and voter turnout, the shift towards populist politics marked by appeals to ‘the people’ and a rejection of ‘politics-as-usual’, are just some of the commonly cited manifestations of our culture of political disaffection. Democratic politics, it is argued, is in crisis. Whilst considerable energy has been expended on the task of lamenting the status of our politics and pondering over recommendations to tackle this perceived crisis, amid this raft of complaints and solutions lurks confusion. This paper seeks to explore the neglected question of what the precise nature of the crisis with which we are confronted involves, and, in so doing, to go some way towards untangling our confusion. Taking my cue from Machiavelli and his value-pluralist heirs, I argue that there is a rift between a morally admirable and a virtuous political life. Failure to appreciate this possibility causes narrations of crisis to misconstrue the moral messiness of politics in ways that lead us to misunderstand how we should respond to disenchantment. Specifically, I suggest that: (i) we think that there is a moral crisis in politics because we have an unsatisfactorily idealistic understanding of political integrity in the first place; and (ii) it is a mistake to imagine that the moral purification of politics is possible or desirable. Put simply, our crisis is not moral per se but primarily philosophical in nature: it relates to the very concepts we employ—the qualities of character and context we presuppose whilst pondering over political integrity

Effect of Nitrogen on Properties of Na2O-CaO-SrO-ZnO-SiO2 Glasses

Glasses in the Na2O-CaO-SrO-ZnO-SiO2 system have previously been investigated for suitability as a reagent in Al-free glass polyalkenoate cements (GPCs). These materials have many properties that offer potential in orthopedics. However, their applicability has been limited, to date, because of their poor strength. This study was undertaken with the aim of increasing the mechanical properties of a series of these Zn-based GPC glasses by doping with nitrogen to give overall compositions of: 10Na2O-10CaO-20SrO-20ZnO-(40-3x)SiO2-xSi3N4 (x is the no. of moles of Si3N4). The density, glass-transition temperature, hardness, and elastic modulus of each glass were found to increase fairly linearly with nitrogen content. Indentation fracture resistance also increases with nitrogen content according to a power law relationship. These increases are consistent with the incorporation of N into the glass structure in threefold coordination with silicon resulting in extra cross-linking of the glass network. This was confirmed using 29Si MAS-NMR which showed that an increasing number of Q2 units and some Q3 units with extra bridging anions are formed as nitrogen content increases at the expense of Q1 units. A small proportion of Zn ions are found to be in tetrahedral coordination in the base oxide glass and the proportion of these increases with the presence of nitrogen

CT colonography: external clinical validation of an algorithm for computer-assisted prone and supine registration

Purpose To perform external validation of a computer-assisted registration algorithm for prone and supine computed tomographic (CT) colonography and to compare the results with those of an existing centerline method. Materials and Methods All contributing centers had institutional review board approval; participants provided informed consent. A validation sample of CT colonographic examinations of 51 patients with 68 polyps (6–55 mm) was selected from a publicly available, HIPAA compliant, anonymized archive. No patients were excluded because of poor preparation or inadequate distension. Corresponding prone and supine polyp coordinates were recorded, and endoluminal surfaces were registered automatically by using a computer algorithm. Two observers independently scored three-dimensional endoluminal polyp registration success. Results were compared with those obtained by using the normalized distance along the colonic centerline (NDACC) method. Pairwise Wilcoxon signed rank tests were used to compare gross registration error and McNemar tests were used to compare polyp conspicuity. Results Registration was possible in all 51 patients, and 136 paired polyp coordinates were generated (68 polyps) to test the algorithm. Overall mean three-dimensional polyp registration error (mean ± standard deviation, 19.9 mm ± 20.4) was significantly less than that for the NDACC method (mean, 27.4 mm ± 15.1; P = .001). Accuracy was unaffected by colonic segment (P = .76) or luminal collapse (P = .066). During endoluminal review by two observers (272 matching tasks, 68 polyps, prone to supine and supine to prone coordinates), 223 (82%) polyp matches were visible (120° field of view) compared with just 129 (47%) when the NDACC method was used (P < .001). By using multiplanar visualization, 48 (70%) polyps were visible after scrolling ± 15 mm in any multiplanar axis compared with 16 (24%) for NDACC (P < .001). Conclusion Computer-assisted registration is more accurate than the NDACC method for mapping the endoluminal surface and matching the location of polyps in corresponding prone and supine CT colonographic acquisitions

Mechanical properties, structure, bioactivity and cytotoxicity of bioactive Na-Ca-Si-PO-(N) glasses

peer-reviewedBioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids. However, because of their poor strength their use is restricted to non-load-bearing applications. The effects of nitrogen addition on the physical and mechanical properties and structure of bioactive oxynitride glasses in the system Na–Ca–Si–P–O–N have been studied. Glasses with compositions (mol.%): 29Na2O–13.5CaO–2.5P2O5–(55 −3x)SiO2–xSi3N4 (x is the no. of moles of Si3N4) were synthesised with up to 1.5 at% P and 4.1 at% N. A novel 3-step process was used for addition of P and N and this proved successful in minimising weight losses and producing homogeneous glasses with such high SiO2 contents. The substitution of 4.12 at% N for oxygen results in linear increases in density (1.6%), glass transition temperature (6%), hardness (18%) and Young’s modulus (74%). Vickers Indentation Fracture (VIF) resistance (Kifr) was calculated from various relationships depending on the load, indent diagonal, crack lengths and Young’s modulus to hardness (E/H) ratio. Firstly, Meyer’s index n is calculated from the slope of the logarithmic plot of load versus indent diagonal. Then by comparing the experimental slopes of the logarithmic plots of crack lengths versus load it is concluded that the cracking mode is Radial Median type. The substitution of 4.12 at% N for oxygen results in an increase in Kifr of 40%. These increases in properties are consistent with the incorporation of N into the glass structure in three-fold coordination with silicon which results in extra cross-linking of the glass network. The structure of these bioactive oxynitride glasses was investigated by solid state nuclear magnetic resonance (MAS NMR) of 31P and 29Si. The structure reveals that all the N atoms are bonded to Si atoms with the formation of SiO3N, SiO2N2 and Q4 structural units with extra bridging anions at the expense of Q3 units. The bioactivity of the glasses has been evaluated by soaking them in simulated body fluid (SBF) and results confirm that all these oxynitride glasses are bioactive. Cytotoxicity tests based on different concentrations of these bioactive glass powders in a cell growth environment have also shown that they are not cytotoxic