Intrinsic factors responsible for brittle versus ductile nature of refractory high-entropy alloys.

Refractory high-entropy alloys (RHEAs) are of interest for ultrahigh-temperature applications. To overcome their drawbacks - low-temperature brittleness and poor creep strength at high temperatures - improved fundamental understanding is needed. Using experiments, theory, and modeling, we investigated prototypical body-centered cubic (BCC) RHEAs, TiZrHfNbTa and VNbMoTaW. The former is compressible to 77 K, whereas the latter is not below 298 K. Hexagonal close-packed (HCP) elements in TiZrHfNbTa lower its dislocation core energy, increase lattice distortion, and lower its shear modulus relative to VNbMoTaW whose elements are all BCC. Screw dislocations dominate TiZrHfNbTa plasticity, but equal numbers of edges and screws exist in VNbTaMoW. Dislocation cores are compact in VNbTaMoW and extended in TiZrHfNbTa, and different macroscopic slip planes are activated in the two RHEAs, which we attribute to the concentration of HCP elements. Our findings demonstrate how ductility and strength can be controlled through the ratio of HCP to BCC elements in RHEAs.

Tick Paralysis Case Series: An 11-Year Institutional Case Series.

OBJECTIVES: The aims of the study were to identify and to describe cases of pediatric tick paralysis presenting to an emergency department in southern Louisiana during an 11-year period. METHODS: We conducted a retrospective chart review of patients aged 0 to 18 years with a diagnostic code of toxic effect of venom, tick-borne viral encephalitis, Guillain-Barré syndrome, acute infective polyneuritis, or abnormality of gait from July 2005 to June 2016. Data were collected on visit month, patient age, race and sex, tick's attachment site, location of tick removal, symptoms and length of symptoms, initial diagnosis, time to appropriate diagnosis, and hospital length of stay. RESULTS: Nine patients aged 2 to 10 years presented with lower limb weakness and varying degrees of upper extremity ataxia or paralysis, areflexia, dysarthria, diplopia, or petechia. Five cases were accurately and rapidly diagnosed; 4 cases involved a delay in accurate diagnosis. Treatment of the misdiagnosed cases ranged from septic workup to neurologic workup, including magnetic resonance imaging. The tick was discovered by the patients' relative in 4 cases, by a primary care or emergency care physician at another facility in 3 cases, and by 1 of our emergency care physicians in 2 patients. CONCLUSIONS: The incidence of tick paralysis in southern Louisiana is unknown. However, our case series indicates that it is likely higher than expected. Although most cases in our facility were quickly diagnosed and treated through tick removal, delayed diagnosis results in unnecessary tests, procedures, and medical costs. All of our cases fully recovered after tick removal.

Hepatocellular carcinoma in body builders; an emerging rare but serious complication of androgenic anabolic steroid use.

Illicit use of androgenic anabolic steroids (AAS) is a known problem amongst certain groups including body builders and other athletes. Use of these drugs is thought to be high in some areas of South Wales. A number of adverse effects have been associated with use of AAS including the development of hepatic adenomas. There have been a handful of rare cases of the development of hepatocellular carcinoma following AAS use. We report two such cases presenting to the same surgical centre in South Wales within six months. We do this with reference to data from Public Health Wales, including the Harm Reduction Wales Needle and Syringe provision report, which indicate a particularly high rate of use of AAS in the surrounding area. We believe these cases are important from the public health point of view. They demonstrate a rare and not widely known about, but potentially fatal adverse effect of AAS, now becoming prevalent with the high use of these drugs. This is important for doctors to be aware of, but also could form the focus of a public health campaign targeted at AAS users.

Correlating Free-Volume Hole Distribution to the Glass Transition Temperature of Epoxy Polymers.

A new algorithm is developed to quantify the free-volume hole distribution and its evolution in coarse-grained molecular dynamics simulations of polymeric networks. This is achieved by analyzing the geometry of the network rather than a voxelized image of the structure to accurately and efficiently find and quantify free-volume hole distributions within large scale simulations of polymer networks. The free-volume holes are quantified by fitting the largest ellipsoids and spheres in the free-volumes between polymer chains. The free-volume hole distributions calculated from this algorithm are shown to be in excellent agreement with those measured from positron annihilation lifetime spectroscopy (PALS) experiments at different temperature and pressures. Based on the results predicted using this algorithm, an evolution model is proposed for the thermal behavior of an individual free-volume hole. This model is calibrated such that the average radius of free-volumes holes mimics the one predicted from the simulations. The model is then employed to predict the glass-transition temperature of epoxy polymers with different degrees of cross-linking and lengths of prepolymers. Comparison between the predicted glass-transition temperatures and those measured from simulations or experiments implies that this model is capable of successfully predicting the glass-transition temperature of the material using only a PDF of the initial free-volume holes radii of each microstructure. This provides an effective approach for the optimized design of polymeric systems on the basis of the glass-transition temperature, degree of cross-linking, and average length of prepolymers.

Coarse-Grained Molecular Dynamics Study of the Curing and Properties of Highly Cross-Linked Epoxy Polymers.

In this work, a coarse-grained model is developed for highly cross-linked bisphenol A diglycidyl ether epoxy resin with diaminobutane hardener. In this model, all conformationally relevant coarse-grained degrees of freedom are accounted for by sampling over the free-energy surfaces of the atomic structures using quantum mechanical simulations. The interaction potentials between nonbonded coarse-grained particles are optimized to accurately predict the experimentally measured density and glass-transition temperature of the system. In addition, a new curing algorithm is also developed to model the creation of highly cross-linked epoxy networks. In this algorithm, to create a highly cross-linked network, the reactants are redistributed from regions with an excessive number of reactive molecules to regions with a lower number of reactants to increase the chances of cross-linking. This new algorithm also dynamically controls the rate of cross-linking at each local region to ensure uniformity of the resulting network. The curing simulation conducted using this algorithm is able to develop polymeric networks having a higher average degree of cross-linking, which is more uniform throughout the simulation cell as compared to that in the networks cured using other curing algorithms. The predicted gel point from the current curing algorithm is in the acceptable theoretical and experimental range of measured values. Also, the resulting cross-linked microstructure shows a volume shrinkage of 5%, which is close to the experimentally measured volume shrinkage of the cured epoxy. Finally, the thermal expansion coefficients of materials in the glassy and rubbery states show good agreement with the experimental values.

Suicide attempts presenting to trauma centers: trends across age groups using the National Trauma Data Bank.

BACKGROUND: This study sought to examine the epidemiology and mortality of violent suicide attempts presenting to trauma centers and to describe differences in male and female suicide attempters presenting to trauma centers by decade of age. METHOD: Data from the National Trauma Data Bank (American College of Surgeons) years 2010-2012 were used for this study. E-codes indicative of self-inflicted injury (e950-e959) were used to identify violent suicide attempts. Incidents were categorized by decade of age at admission. We examined the effects of age and sex on rates of violent suicide attempts, mechanism used, and mortality. RESULTS: In all, 36035 violent suicide attempts were identified in the National Trauma Data Bank. Proportion of in-hospital mortality differed significantly with age (P< .001). Individuals aged 20 to 29 years had a significantly higher number of attempts with 15.6% mortality, whereas individuals aged 80 plus year had fewer attempts but with 45.9% mortality. There were significant interactions between sex and age on lethality of suicide attempts (P< .01) and mechanism chosen (P< .01), with men being more likely to use firearms across age groups. CONCLUSION: This study highlights the importance of examining the epidemiology of suicide attempts across sex and age. There are significant differences in rate of attempts, lethality of mechanism, and in-hospital mortality. Future studies should continue to investigate violent suicide attempts to design and implement effective treatment strategies targeted toward specific populations.

Clinically relevant interaction between warfarin and scuppernongs, a quercetin containing muscadine grape: continued questions surrounding flavonoid-induced warfarin interactions.

We present a case of clinically relevant and probable interaction between warfarin and scuppernongs in a 73-year-old woman where ingestion of scuppernongs, a variety of quercetin-containing muscadine grapes, over a period of 2 months was associated with elevations in the International Normalised Ratio to supratherapeutic levels. While muscadine grapes and specifically scuppernongs are found primarily in Southeastern USA, the flavonoid in questionand quercetin is found worldwide as a dietary supplement.

Quasi-periodic events in crystal plasticity and the self-organized avalanche oscillator.

When external stresses in a system--physical, social or virtual--are relieved through impulsive events, it is natural to focus on the attributes of these avalanches. However, during the quiescent periods between them, stresses may be relieved through competing processes, such as slowly flowing water between earthquakes or thermally activated dislocation flow between plastic bursts in crystals. Such smooth responses can in turn have marked effects on the avalanche properties. Here we report an experimental investigation of slowly compressed nickel microcrystals, covering three orders of magnitude in nominal strain rate, in which we observe unconventional quasi-periodic avalanche bursts and higher critical exponents as the strain rate is decreased. Our experiments are faithfully reproduced by analytic and computational dislocation avalanche modelling that we have extended to incorporate dislocation relaxation, revealing the emergence of the self-organized avalanche oscillator: a novel critical state exhibiting oscillatory approaches towards a depinning critical point. This theory suggests that whenever avalanches compete with slow relaxation--in settings ranging from crystal microplasticity to earthquakes--dynamical quasi-periodic scale invariance ought to emerge.

The role of distal third radius dual energy X-ray absorptiometry (DXA) and central DXA in evaluating for osteopenia and osteoporosis in men receiving androgen deprivation therapy for prostate cancer.

The authors assessed the use of distal third radius dual energy X-ray absorptiometry (DXA) concomitantly with central (hip and lumbar spine) DXA to identify men with osteopenia or osteoporosis receiving androgen deprivation therapy (ADT) for prostate cancer. Initial classification with central DXA demonstrated 60 (17%) normal, 187 (55%) osteopenic, and 96 (28%) osteoporotic patients. Sixteen of 60 (27%) normal patients were reclassified as osteopenic (14) or osteoporotic (2), and 20 of 187 (11%) osteopenic patients were reclassified as osteoporotic with the combination of central DXA plus distal third radius DXA. The difference in reclassification was statistically significant. The addition of distal third radius to central DXA scanning in men with bone loss associated with ADT identifies a statistically significant number of men being reclassified as having osteopenia or osteoporosis. Combined central and distal third radius DXA scanning should be considered routine in the evaluation of all men suspected of bone loss associated with ADT. This has specific significant clinical relevance because of the large number of men with nonevaluable central DXA studies. Fracture risk prediction and treatment recommendations based on this reclassification will need to be determined by follow-up studies.

Quantitative prediction of solute strengthening in aluminium alloys.

Despite significant advances in computational materials science, a quantitative, parameter-free prediction of the mechanical properties of alloys has been difficult to achieve from first principles. Here, we present a new analytic theory that, with input from first-principles calculations, is able to predict the strengthening of aluminium by substitutional solute atoms. Solute-dislocation interaction energies in and around the dislocation core are first calculated using density functional theory and a flexible-boundary-condition method. An analytic model for the strength, or stress to move a dislocation, owing to the random field of solutes, is then presented. The theory, which has no adjustable parameters and is extendable to other metallic alloys, predicts both the energy barriers to dislocation motion and the zero-temperature flow stress, allowing for predictions of finite-temperature flow stresses. Quantitative comparisons with experimental flow stresses at temperature T=78 K are made for Al-X alloys (X=Mg, Si, Cu, Cr) and good agreement is obtained.

The chemistry of deformation: how solutes soften pure metals.

Solutes have been added to strengthen elemental metals, generating usable materials for millennia; in the 1960s, solutes were found to also soften metals. Despite the empirical correlation between the "electron number" of the solute and the change in strength of the material to which it is added, the mechanism responsible for softening is poorly understood. Using state-of-the-art quantum-mechanical methods, we studied the direct interaction of transition-metal solutes with dislocations in molybdenum. The interaction increases dramatically with increasing electron number and strongly influences the mechanisms responsible for plasticity in these materials. Our quantitative model explains solution softening of metals by using changes in energy and stress scales of plasticity from solutes.

Origin of brittle cleavage in iridium.

Iridium is unique among the face-centered cubic metals in that it undergoes brittle cleavage after a period of plastic deformation under tensile stress. Atomistic simulation using a quantum-mechanically derived bond-order potential shows that in iridium, two core structures for the screw dislocation are possible: a glissile planar core and a metastable nonplanar core. Transformation between the two core structures is athermal and leads to exceptionally high rates of cross slip during plastic deformation. Associated with this athermal cross slip is an exponential increase in the dislocation density and strong work hardening from which brittle cleavage is a natural consequence.