SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Relative density

34

Estimates of body mass often represent the founding assumption on which biomechanical and macroevolutionary hypotheses are based. Recently, a scaling equation was applied to a newly discovered titanosaurian sauropod dinosaur (Dreadnoughtus), yielding a 59 300 kg body mass estimate for this animal. Herein, we use a modelling approach to examine the plausibility of this mass estimate for Dreadnoughtus. We find that 59 300 kg for Dreadnoughtus is highly implausible and demonstrate that masses above 40 000 kg require high body densities and expansions of soft tissue volume outside the skeleton several times greater than found in living quadrupedal mammals. Similar results from a small sample of other archosaurs suggests that lower-end mass estimates derived from scaling equations are most plausible for Dreadnoughtus, based on existing volumetric and density data from extant animals. Although volumetric models appear to more tightly constrain dinosaur body mass, there remains a clear need to further support these models with more exhaustive data from living animals. The relative and absolute discrepancies in mass predictions between volumetric models and scaling equations also indicate a need to systematically compare predictions across a wide size and taxonomic range to better inform studies of dinosaur body size.

Concepts: Fundamental physics concepts, Density, Volume, Animal, Mass, Kilogram, Relative density, Dinosaur

29

Alcohol contributes to intentional and unintentional injury. We explored on-premise licensed alcohol establishments (LAEs) and emergency medical service (EMS) ambulance calls.We completed a retrospective population-based study in the Region of Peel, Ontario, 2005 to 2014, where alcohol sales are tightly regulated and healthcare is universally available. We included participants age ≥ 19 years. Longitude-latitude coordinates of all 696 LAEs and all 267,477 EMS ambulance calls were ascertained, and then assigned to 1 of 1568 dissemination areas (DA) in Peel. Relative risks (RRs) described the association between density of on-premise LAEs (by DA deciles) and the rate of EMS calls, adjusted for material deprivation, and density of beer/liquor stores in each DA.There was a curvilinear relation between LAE density and EMS calls for trauma, rising from 45.3 per 1000 in DAs with no LAEs to 381.0 per 1000 in decile-10 (adjusted RR 7.83, 95% confidence interval [CI] 6.15-9.97). This relation was more pronounced for alcohol-focused LAEs, and highest among younger males. Calls for assault (RR 2.67, 95% CI 1.26-5.65) and intoxication (RR 4.00, 95% CI 1.41-11.38) were more likely on the last day of the month and the day thereafter, compared to 1 week prior. At 02:00 hours, when LAEs must stop selling alcohol, there was a considerable rise in assault-related calls in DAs with LAE but not in DAs without LAEs.On-premise LAEs contribute to EMS calls for trauma and assault, especially among young males, around last call, and when monthly pay cheques are cashed.

Concepts: Relative risk, Retrospective, Law, Emergency medical services, Emergency medical technician, Relative density, Ontario, Regional Municipality of Peel

26

The Bristol Stool Form scale classifies the relative density of stool. In a prospective cohort study, we investigated the associations between stool density, C. difficile assay positivity, hospital-onset C. difficile infection, complications and severity of C. difficile. We describe associations between Bristol Score, assay positivity, and clinical C. difficile infection.

Concepts: Cohort study, Gut flora, Density, Clostridium difficile, Clostridium, Relative density, Clostridia, Bristol Stool Scale

23

Late sodium channel current (late INa) is considered to be an anti-arrhythmic target. The prime anti-arrhythmic mechanisms of late INa inhibition have been suggested to be 1) suppression of intracellular calcium [Cai]-mediated rhythmic activity (via reduction of Cai secondary to the decrease of intracellular sodium [Nai]) and 2) normalization of repolarization. Endogenous late INa is a small current and acceleration of heart rate decreases late INa density. Late INa influx may significantly contribute to Nai loading, but it appears to largely occur in the combined conditions of augmented late INa density, bradycardia, and prolonged repolarization. At the same time, the relative contribution of late INa (including endogenous) in any types of prolonged cardiac repolarization is critical. Sodium channel blockers inhibit both late INa and peak INa, and a specific block of late INa might be achieved at slow and normal but seems not at rapid activation rates, at which peak INa, a much greater current, is likely to be inhibited also. The anti-arrhythmic potential of a specific inhibition of late INa appears to best fit for, or may be limited to, the prevention of arrhythmias associated with prolonged repolarization, but it seems to be applicable to all types of arrhythmic abnormalities with elongated cardiac repolarization.

Concepts: Water, Electrophysiology, Cardiac arrest, Cardiac electrophysiology, Sodium, Relative density, Antiarrhythmic agents, Electrical conduction system of the heart

11

Stomach fullness is a determinant of satiety. Although both the viscosity and energy content have been shown to delay gastric emptying, their relative importance is not well understood.

Concepts: Energy, Fundamental physics concepts, Density, Randomized controlled trial, Muscle, Stomach, Energy density, Relative density

8

The low conductivity of two-dimensional covalent organic frameworks (2D COFs), and most related coordination polymers, limits their applicability in optoelectronic and electrical energy storage (EES) devices. Although some networks exhibit promising conductivity, these examples generally lack structural versatility, one of the most attractive features of framework materials design. Here we enhance the electrical conductivity of a redox-active 2D COF film by electropolymerizing 3,4-ethylenedioxythiophene (EDOT) within its pores. The resulting poly(3,4-ethylenedioxythiophene) (PEDOT)-infiltrated COF films exhibit dramatically improved electrochemical responses, including quantitative access to their redox-active groups, even for 1 μm-thick COF films that otherwise provide poor electrochemical performance. PEDOT-modified COF films can accommodate high charging rates (10-1600 C) without compromising performance and exhibit both a 10-fold higher current response relative to unmodified films and stable capacitances for at least 10 000 cycles. This work represents the first time that electroactive COFs or crystalline framework materials have shown volumetric energy and power densities comparable with other porous carbon-based electrodes, thereby demonstrating the promise of redox-active COFs for EES devices.

Concepts: Electric charge, Electricity, Fundamental physics concepts, Density, Water, Electrochemistry, Physical quantities, Relative density

4

BACKGROUND: The relative roles of climate variability and population related effects in malaria transmission could be better understood if regional-scale dynamical malaria models could account for these factors. METHODS: A new dynamical community malaria model is introduced that accounts for the temperature and rainfall influences on the parasite and vector life cycles which are finely resolved in order to correctly represent the delay between the rains and the malaria season. The rainfall drives a simple but physically based representation of the surface hydrology. The model accounts for the population density in the calculation of daily biting rates. RESULTS: Model simulations of entomological inoculation rate and circumsporozoite protein rate compare well to data from field studies from a wide range of locations in West Africa that encompass both seasonal endemic and epidemic fringe areas. A focus on Bobo-Dioulasso shows the ability of the model to represent the differences in transmission rates between rural and peri-urban areas in addition to the seasonality of malaria. Fine spatial resolution regional integrations for Eastern Africa reproduce the malaria atlas project (MAP) spatial distribution of the parasite ratio, and integrations for West and Eastern Africa show that the model grossly reproduces the reduction in parasite ratio as a function of population density observed in a large number of field surveys, although it underestimates malaria prevalence at high densities likely due to the neglect of population migration. CONCLUSIONS: A new dynamical community malaria model is publicly available that accounts for climate and population density to simulate malaria transmission on a regional scale. The model structure facilitates future development to incorporate migration, immunity and interventions.

Concepts: Mathematics, Malaria, Africa, Water, Weather, Population density, Madagascar, Relative density

3

Commercial hydrogen production by electrocatalytic water splitting will benefit from the realization of more efficient and less expensive catalysts compared with noble metal catalysts, especially for the oxygen evolution reaction, which requires a current density of 500 mA/cm(2) at an overpotential below 300 mV with long-term stability. Here we report a robust oxygen-evolving electrocatalyst consisting of ferrous metaphosphate on self-supported conductive nickel foam that is commercially available in large scale. We find that this catalyst, which may be associated with the in situ generated nickel-iron oxide/hydroxide and iron oxyhydroxide catalysts at the surface, yields current densities of 10 mA/cm(2) at an overpotential of 177 mV, 500 mA/cm(2) at only 265 mV, and 1,705 mA/cm(2) at 300 mV, with high durability in alkaline electrolyte of 1 M KOH even after 10,000 cycles, representing activity enhancement by a factor of 49 in boosting water oxidation at 300 mV relative to the state-of-the-art IrO2 catalyst.

Concepts: Oxygen, Iron, Density, Water, Hydrogen, Electrochemistry, Nitrogen, Relative density

3

Hierarchical cellular structures are ubiquitous in nature because of their low-density, high-specific properties, and multifunctionality. Inspired by these systems, we created lightweight ceramic architectures composed of closed-cell porous struts patterned in the form of hexagonal and triangular honeycombs by direct foam writing. The foam ink contains bubbles stabilized by attractive colloidal particles suspended in an aqueous solution. The printed and sintered ceramic foam honeycombs possess low relative density (∼6%). By tailoring their microstructure and geometry, we created honeycombs with different modes of deformation, exceptional specific stiffness, and stiffness values that span over an order of magnitude. This capability represents an important step toward the scalable fabrication of hierarchical porous materials for applications, including lightweight structures, thermal insulation, tissue scaffolds, catalyst supports, and electrodes.

Concepts: Density, Colloid, Materials science, Ceramic, Relative density, Clay

3

Prions are composed of the misfolded prion protein (PrP(Sc)) organized in a variety of aggregates. An important question in the prion field has been to determine the identity of functional PrP(Sc) aggregates. In this study, we used equilibrium sedimentation in sucrose density gradients to separate PrP(Sc) aggregates from three hamster prion strains (Hyper, Drowsy, SSLOW) subjected to minimal manipulations. We show that PrP(Sc) aggregates distribute in a wide range of arrangements and the relative proportion of each species depends on the prion strain. We observed a direct correlation between the density of the predominant PrP(Sc) aggregates and the incubation periods for the strains studied. The relative presence of PrP(Sc) in fractions of different sucrose densities was indicative of the protein deposits present in the brain as analyzed by histology. Interestingly, no association was found between sensitivity to proteolytic degradation and aggregation profiles. Therefore, the organization of PrP molecules in terms of the density of aggregates generated may determine some of the particular strain properties, whereas others are independent from it. Our findings may contribute to understand the mechanisms of strain variation and the role of PrP(Sc) aggregates in prion-induced neurodegeneration.

Concepts: Protein, Density, Protein folding, Prion, Transmissible spongiform encephalopathy, Relative density, Fatal familial insomnia