New theory explaining Griffith strength results on nano-cracked glass fibres.

The purpose of this paper is to propose a mechanism and theory that can explain the extraordinary increase in measured strength that Griffith observed for glass fibres containing nano-cracks. His 1921 theory (Griffith 1921 Phil. Trans. R. Soc. Lond. A 221, 163-198. (doi:10.1098/rsta.1921.0006)) predicted that the strength of a cracked sample should be independent of sample size, yet his results on stretched glass fibres gave strength increasing almost as the inverse of fibre diameter. He proposed a 'flaw statistics' argument in an attempt to explain these bizarre results, suggesting strength increased because large defects were less likely in the smaller volumes. But this 'flaw statistics' concept is unnecessary because the Griffith energy criterion of cracking must give a size effect, as demonstrated in many different crack-testing configurations. In general, the Griffith energy criterion for crack equilibrium predicts strength rising for smaller samples because such samples contain less volume energy to create new crack surface energy. The problem is that this 'size effect' idea has not until now been properly defined for the simple tension crack test. The new idea proposed is that many nano-cracks are likely to exist in an experimental glass sample, so these must also obey the thermodynamic analysis. A problem then arises because, as the main crack propagates, other cracks may close, but healing is not reversible in glass so thermodynamics does not apply completely to these secondary cracks. Crack healing is in the Griffith theory, which is perfectly reversible mathematically, though not explicitly stated. This article is part of the theme issue 'Nanocracks in nature and industry'.

Nano-samples give higher brittle strength by the Griffith energy principle.

The purpose of this paper is to show that brittle test samples give a huge size effect that can take several different forms depending on the sample geometry, crack position and mode of force application. Sometimes crack equilibrium force depends on sample dimension d or d1/2 and sometimes the force is independent of area, for example in peel or lap joint cracking. This big size effect arises from the potential energy term in the conservation theory, not considered by Griffith but dominating certain cracks. These examples illustrate the fact that strength of a brittle material containing a crack is an unsatisfactory concept because the cracks absorb surface energy driven by volume energy terms or by potential energy terms or a mixture of the two, leading to a disconnection between applied cracking force and sample cross-section area. The flaw statistics argument mentioned by Griffith is unnecessary, though strength can be affected in certain circumstances by the presence of random flaws. An unusually large size effect is shown experimentally for thermal shock of ceramic tubes, in which the cracking force increases as the cube of diameter goes down. This thermal shock resistance of fine tubes has proved important for application of ceramic fuel cells but cannot be explained by fracture mechanics theory at present. The conclusion is that experimental results show the Griffith energy criterion for cracking is correct whereas the Galilean stress criterion fails. The concept 'strength of brittle materials' is therefore untenable for most crack testing geometries. This article is part of the theme issue 'Nanocracks in nature and industry'.

Calculations on compact disc cracking.

The Griffith equation for brittle cracking has three problems. First, it applies to an infinite sheet whereas a laboratory test sample is typically near 100 × 100 mm. Second, it describes a central crack instead of the more dangerous and easily observable edge crack. Third, the theory assumes a uniform stress field, instead of tensile force application used in the laboratory. The purpose of this paper is to avoid these difficulties by employing Gregory's solution in calculating the crack behaviour of PMMA (Poly Methyl Meth Acrylate) discs, pin loaded in tension. Our calculations showed that axial disc loading gave nominal strengths comparable with Griffith theory, but the force went to zero as the crack fully crossed the disc, fitting experimental results. Off-axis loading was more interesting because the predicted strength was lower than in axial testing, but also gave unexpected behaviour at short crack lengths, where nominal strength did not rise indefinitely but dropped as crack length went below D/10, quite different from Griffith, where strength rose continuously as cracks were shortened. Such off-axis loading leads to a size effect in which larger discs are weaker, reminiscent of the fine fibre strengthening phenomenon reported in Griffith's early paper (Griffith 1921 Phil. Trans. R. Soc. Lond. A 221, 163-198. (doi:10.1098/rsta.1921.0006)). This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.

Energizing ASTM lap joint fracture standards.

Several ASTM standards on the fracture of glued and welded joints need attention because they do not consider the Griffith energy criterion of cracking which was proposed a century ago. It is almost as if Griffith never existed because the ASTM definition of failure is the stress criterion postulated by Galileo in 1638 in which stress at failure (i.e. strength = force/area) is defined as the determinant of fracture. Irene Martinez Villegas (Villegas, Rans 2021 Phil. Trans. R. Soc. A 376, 20200296. (doi:10.1098/rsta.2020.0296)) shows in this volume that attempts to use ASTM D5868 to standardize welded composite (carbon fibre reinforced polymer, CFRP) lap joints reveal major problems. First, the test is a low angle bend-peel test; not shear. Second, the energy required to break the joint is not emphasized so that joints may have high strength properties but also low toughness; third, the fracture force is not proportional to the lap joint area so the concept of strength independent of sample size is false; fourth, as the CFRP panels are made thicker, the strength rises at constant overlap area so the strength can be any value you want; fifth, the strength of larger joints goes down; this is the size effect noted in many bend-cracking tests, much as Galileo suggested for bent beam fracture in his famous book 'the larger the machine, the greater its weakness'. The purpose of this paper is to demonstrate that poor ASTM 'shear strength' standards should be replaced by a definition of welded lap joint performance based on Griffith's energy conservation argument in which fracture surface energy is the main parameter resisting failure. The foundation of this Griffith-style lap joint analysis for long cracks goes back to 1975 but has been largely ignored until now because it does not fit the Griffith equation for cracked sheets, has no 'stress intensity factor', and travels at constant speed, not accelerating like the standard Griffith tension crack. This study of tensile delamination shows that a long lap crack is not driven by stress near the crack but by changes in stored elastic energy in the stretched strips remote from the crack tip, while strain energy release rate is negative. It would be more appropriate to call this lap failure a tensile delamination crack. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.

Complete Genome Sequence of Campylobacter jejuni subsp. jejuni ATCC 35925.

Here, we report the complete genome sequence of Campylobacter jejuni ATCC 35925, an avian isolate from Sweden. The genome gives insight into the ATCC 35925 strain's remarkable ability to tolerate copper and its permissiveness to plasmid transformation.

Calculation of normal contact forces between silica nanospheres.

In this work, interaction forces between two silica nanospheres after contact, including the van der Waals (vdW) attraction, Born repulsion, and mechanical contact forces are studied by molecular dynamics (MD) simulations. The effects of interaction path (approach or departure), initial relative velocity, and relative orientations of two nanospheres are first examined. The results show that the interparticle forces are, to a large degree, independent of these variables. Then, emphasis is given to other important variables. At a small contact deformation, the size dependence of the vdW attraction and Born repulsion qualitatively agrees with the prediction based on the conventional theories, but this becomes vague upon further deformation due to the gradually flattened shape of deformed particles. An alternative approach is provided to calculate the interparticle vdW attraction and Born repulsion forces. Moreover, the MD simulations show that the Hertz model still holds to describe the mechanical contact force at low compression, which is obtained by subtracting the vdW attraction and Born repulsion forces from the total normal force. Comparisons with the Johnson-Kendall-Roberts (JKR) and Derjaguin-Muller-Toporov (DMT) models, in terms of force-displacement relationships and contact radius, show that the two models can be used to provide the first approximation, but there is some deviation from the MD simulated results. The origins of the quantitative difference are analyzed. New equations are formulated to estimate the interaction forces between silica nanospheres, which should be useful in the dynamic simulation of silica nanoparticle systems.

Surfactant protein D (SP-D) alters cellular uptake of particles and nanoparticles.

Surfactant protein D (SP-D) is primarily expressed in the lungs and modulates pro- and anti-inflammatory processes to toxic challenge, maintaining lung homeostasis. We investigated the interaction between NPs and SP-D and subsequent uptake by cells involved in lung immunity. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) measured NP aggregation, particle size and charge in native human SP-D (NhSP-D) and recombinant fragment SP-D (rfhSP-D). SP-D aggregated NPs, especially following the addition of calcium. Immunohistochemical analysis of A549 epithelial cells investigated the co-localization of NPs and rfhSP-D. rfhSP-D enhanced the co-localisation of NPs to epithelial A549 cells in vitro. NP uptake by alveolar macrophages (AMs) and lung dendritic cells (LDCs) from C57BL/6 and SP-D knock-out mice were compared. AMs and LDCs showed decreased uptake of NPs in SP-D deficient mice compared to wild-type mice. These data confirmed an interaction between SP-D and NPs, and subsequent enhanced NP uptake.

Red blood cell transfusion: experience in a rural aeromedical transport service.

INTRODUCTION: The administration of blood products to critically ill patients can be life-saving, but is not without risk. During helicopter transport, confined work space, communication challenges, distractions of multi-tasking, and patient clinical challenges increase the potential for error. This paper describes the in-flight red blood cell transfusion practice of a rural aeromedical transport service (AMTS) with respect to whether (1) transfusion following an established protocol can be safely and effectively performed, and (2) patients who receive transfusions demonstrate evidence of improvement in condition. METHODS: A two-year retrospective review of the in-flight transfusion experience of a single-system AMTS servicing a rural state was conducted. Data elements recorded contemporaneously for each transfusion were analyzed, and included hematocrit and hemodynamic status before and after transfusion. Compliance with an established transfusion protocol was determined through structured review by a multidisciplinary quality review committee. RESULTS: During the study, 2,566 missions were flown with 45 subjects (1.7%) receiving in-flight transfusion. Seventeen (38%) of these transports were scene-to-facility and 28 (62%) were inter-facility. Mean bedside and in-flight times were 22 minutes (range 3-109 minutes) and 24 minutes (range 8-76 minutes), respectively. The most common conditions requiring transfusion were trauma (71%), cardiovascular (13%) and gastrointestinal (11%). An average of 2.4 liters (L) of crystalloid was administered pre-transfusion. The mean transfusion was 1.4 units of packed red blood cells. The percentages of subjects with pre- and post-transfusion systolic blood pressures of <90 mmHg were 71% and 29%, respectively. The pre- and post-transfusion mean arterial pressures were 62 mmHg and 82 mmHg, respectively. The pre- and post- transfusion mean hematocrit levels were 17.8% and 30.4%, respectively. At the receiving institution, 9% of subjects died in the Emergency Department, 18% received additional transfusion within 30 minutes of arrival, 36% went directly to the operating room, and 36% were directly admitted to intensive care. Thirty-one percent of subjects died prior to hospital discharge. There were no protocol violations or reported high-risk provider blood exposure incidents or transfusion complications. All transfusions were categorized as appropriate. CONCLUSIONS: In this rural AMTS, transfusion was an infrequent, likely life-saving, and potentially high-risk emergent therapy. Strict compliance with an established transfusion protocol resulted in appropriate and effective decisions, and transfusion proved to be a safe in-flight procedure for both patients and providers.

Adhesion of alumina surfaces through confined water layers containing various molecules.

When two surfaces confine water layers between them at the nanoscale, the behavior of these confined water molecules can deviate significantly from the behavior of bulk water, and it could reflect on the adhesion of such surfaces. Thus, the aim of this study is to assess the role of confined water layers on the adhesion of hydrophilic surfaces and how sensitive this adhesion is to the presence of contaminants. Our methodology used under water AFM force measurements with an alumina-sputtered sphere-tipped cantilever and a flat alumina single crystal and then added fractions of ethanol, dimethylformamide, formamide, trimethylamine, and trehalose to water as contaminants. Such solutions were designed to illuminate the influences of dielectric constant, molecular size, refractive index, and number of hydrogen bonds from donors and acceptors of solutes to water. Apart from very dilute solutions of dimethylformamide, all solutions decreased the ability of confined water to give adhesion of the alumina surfaces. The predicted theoretical contribution of van der Waals and electrostatic forces was not observed when the contaminants distorted the way water organizes itself in confinement. The conclusion was that adhesion was sensitive mostly to the hydrogen-bonding network within water layers confined by the hydrophilic alumina surfaces.

Particle and nanoparticle interactions with fibrinogen: the importance of aggregation in nanotoxicology.

Ingested, inhaled or injected particles come into contact with biological fluids containing polymers, such as the protein fibrinogen. We studied interactions between well-characterized submicron particles or nanoparticles (NPs) and human fibrinogen. In vitro aggregation and zeta potential measurements of different sized and functionalized polystyrene, carbon black and silica NPs suspended in fibrinogen solutions were made. Particle size, surface charge and aggregation behaviour significantly changed in the presence of fibrinogen. Polymer (protein) bridging and bridge flocculation was observed. We concluded: (1) NP aggregation rate in a fibrinogen solution depended on particle surface type; (2) amine-functionalized particles aggregated more slowly in fibrinogen; and (3) particle morphology strongly influenced biologically available surface for protein attachment, but this did not correlate well with particle surface area for complex particles (calculated or measured). Interaction of particles and NPs with pro-coagulant polymers may therefore dictate the NP surface dose presentation to cells/organs and subsequent cellular effects, in and ex vivo.

A new measure of molecular attractions between nanoparticles near kT adhesion energy.

The weak molecular attractions of nanoparticles are important because they drive self-assembly mechanisms, allow processing in dispersions e.g. of pigments, catalysts or device structures, influence disease through the attraction of viruses to cells and also cause potential toxic effects through nanoparticle interference with biomolecules and organs. The problem is to understand these small forces which pull nanoparticles into intimate contact; forces which are comparable with 3kT/2z the thermal impact force experienced by an average Brownian particle hitting a linear repulsive potential of range z. Here we describe a new method for measuring the atomic attractions of nanoparticles based on the observation of aggregates produced by these small forces. The method is based on the tracking of individual monosize nanoparticles whose diameter can be calculated from the Stokes-Einstein analysis of the tracks in aqueous suspensions. Then the doublet aggregates are distinguished because they move slower and are also very much brighter than the dispersed nanoparticles. By finding the ratio of doublets to singlets, the adhesive energy between the particles can be calculated from known statistical thermodynamic theory using assumptions about the shape of the interaction potential. In this way, very small adhesion energies of 2kT have been measured, smaller than those seen previously by atomic force microscopy (AFM) and scanning tunneling microscopy (STM).

Cold Hearts: a case study of therapeutic hypothermia in helicopter emergency medical services (HEMS).

A 36-year-old white man hit a home run in the seventh inning of a community baseball game. The patient ran the bases successfully and returned to home plate. As he was bending over to pick up the bat, he suddenly collapsed. Bystander cardiopulmonary resuscitation (CPR) was immediately initiated, and defibrillation occurred within 5 minutes per the local emergency medical services (EMS) service. The automated external defibrillator (AED) shocked the patient a total of three times, and he was transported to a local hospital at the basic life support level. Helicopter emergency service (HEMS) was activated by local medical control, and LifeFlight of Maine responded to transfer this patient to a tertiary care center.

Performance of endotracheal intubation and rescue techniques by emergency services personnel in an air medical service.

BACKGROUND: Literature spanning the last two decades has identified potential harm associated with out-of-hospital endotracheal intubation performed by ground paramedics. Previous researchers have reported intubation success rates of 66% to 97% in the air medical setting. OBJECTIVE: To examine the success of endotracheal intubation and rescue techniques performed by air medical personnel during the first eight years of operation of the air ambulance service. METHODS: This study was a retrospective survey of health records utilizing data from LifeFlight of Maine's airway procedure quality review database, covering the first eight years of system encounters. RESULTS: During the study period, 369 intubation encounters occurred. Rapid-sequence intubation medications were administered in 345 (93.5%) cases. Flight personnel successfully performed endotracheal intubation in 340 (92.1%) encounters. Unsuccessful intubations were managed with an alternative definitive airway, rescue airway, or bag-valve-mask. Laryngeal mask airway (n = 11) was the most commonly used rescue airway device. CONCLUSIONS: During the first eight years of operation of this air medical transport system, flight personnel were able to successfully perform endotracheal intubation in 92.1% of cases.

Developing the reaction kinetics for a biodiesel reactor.

The aim of this paper was to investigate the kinetics of the biodiesel reaction in order to find out how best to reach 96.5% methyl ester. The purity of the biodiesel product was examined using gas chromatography to the EN14214 FAME standard and real-time optical microscopy was used to observe the reaction. The problem was the reaction does not reach completion and the mechanism is not understood. It was observed that droplet size had a major influence on reaction end point and that the reaction was mass-transfer limited. This observation was confirmed by developing a mass-transfer based reaction model using the data from the batch reactor which agreed with results from other researchers. The model predicted better conversion with more mixing intensity. The results show that significant improvements could be made to the conventional FAME process.

Aggregation and surface properties of iron oxide nanoparticles: influence of pH and natural organic matter.

The interactions between unpurified manufactured nanoparticles (NPs; iron oxide NPs, approximately 7 nm) and standard Suwannee River humic acid (SRHA) were investigated under a range of environmentally relevant conditions. At low pH, approximately 35% of the total iron was in the dissolved phase (< 1 kDa), present from the initial synthesis, whereas at pH more than 4, this concentration was negligible because of the formation of new particles via hydrolysis. Dynamic light scattering results indicated that extensive aggregation of NPs began at approximately pH 5 to 6 and reached a maximum at approximately pH 8.5, whereas with added SRHA, aggregation was shifted to lower pH values of 4 to 5 and was affected by SRHA concentration. Aggregation could be explained mainly by charge neutralization. Further, more detailed investigations by flow field-flow fractionation and transmission-electron microscopy were performed under a more restricted set of conditions (pH 2-6) to examine the aggregation process. Results indicated the formation of SRHA surface coating on iron oxide NPs of approximately 1 nm and the increase in thickness of this coating with the increase of SRHA concentration. Iron oxide NPs were shown to form increasingly large aggregates with increases in both pH (from 2 to 6) and SRHA concentration (from 0 to 25 mg/L). The structure and aggregation mechanism of these aggregates were found to be both pH and SRHA concentration dependent, with open, porous aggregates in the absence of SRHA and compact aggregates in the presence of SRHA.

Steam reforming of biodiesel by-product to make renewable hydrogen.

The aim of this paper was to investigate the viability of steam reforming the combined glycerol and water by-product streams of a biodiesel plant. A platinum alumina catalyst was used to optimise the operating conditions for glycerol steam reforming and mass spectroscopy was chosen to measure reformer gas yield. The problem is that glycerol steam reforming is relatively untested even with pure glycerol and the by-product quality may be too poor. The strategy was therefore to optimise the process using pure glycerol and compare the performance with by-product glycerol. To test catalyst degradation caused by carbon deposition, a Solid Oxide fuel cell (SOFC) was used as a separate reformer and electrical performance was measured to indicate carbon deposition. This is the first time a SOFC has been run on glycerol. The results showed that thermodynamic theory can be used to predict reformer performance. At high temperatures high gas yield can be reached (almost 100%) and selectivities of 70% (dry basis) obtained. The optimum conditions for glycerol reforming were 860 degrees C temperature (maximum tested), 0.12 mols/min glycerol flow per kg of catalyst and 2.5 steam/carbon ratio. Reforming catalysts lasted for several days of continuous operation with minimal degradation, 0.4% of feed deposited. By-product glycerol performed slightly worse with a lower yield and more carbon deposition, 2% of feed. The results show that glycerol steam reforming is a viable alternative use for glycerol and potentially a better option than purification.