Unconventional order-disorder phase transition in improper ferroelectric hexagonal manganites

The improper ferroelectricity in YMnO$_3$ and other related multiferroic hexagonal manganites are known to cause topologically protected ferroelectric domains that give rise to rich and diverse physical phenomena. The local structure and structural coherence across the ferroelectric transition, however, were previously not well understood. Here we reveal the evolution of the local structure with temperature in YMnO$_3$ using neutron total scattering techniques, and interpret them with the help of first-principles calculations. The results show that, at room temperature, the local and average structures are consistent with the established ferroelectric $P6_3cm$ symmetry. On heating, both local and average structural analyses show striking anomalies from $\sim 800$ K up to the Curie temperature consistent with increasing fluctuations of the order parameter angle. These fluctuations result in an unusual local symmetry lowering into a \textit{continuum of structures} on heating. This local symmetry breaking persists into the high-symmetry non-polar phase, constituting an unconventional type of order-disorder transition.Comment: 10 pages, 5 figure

The Extraction and Analytical Profiling of Bioactive Phospho- and Sphingolipids from Commercial Whey Protein Phospholipid Concentrate

Milk is the first source of nutrition for all mammalian neonates. The complex matrix that constitutes milk has evolved to provide optimal nutrition for the newborn, for each species, respectively. Milk fat, originating in mammary epithelial, forms lipid droplets which are stabilized in the aqueous environment by bioactive polar lipids and proteins called the milk fat globular membrane (MFGM). The fluid phase of the membrane is made of amphiphilic polar lipids, largely glycerophospholipids and sphingolipids. The MFGM acts to compartmentalize the milk fat in the aqueous phase of milk and likewise, stabilize the oil in water emulsion. Polar lipids, specifically phospholipids, make up the cellular membranes of all living things. Infants require milk polar lipids for growth and development, but also have specific benefits in neurological/neurobehavioral develop, gastrointestinal development, and establishment of the gut microbiome reported in pre-clinical and clinical trials. Adults also benefit from the consumption of milk polar lipids, with positive effects in lipid metabolism, reduced inflammation, and reduced cardiovascular disease risk. Polar lipids also play a role in the neurological health of aging adults and are associated with reduced risk of colon cancer in pre-clinical trials. In the dairy industry, MFGM can be concentrated into several different products, including cream, beta serum, buttermilk, whey cream and MFGM enriched whey. The fat dominant fractions, such as cream, buttermilk, and whey cream, previously were the focus of a large body of research using new technologies to recover milk polar lipids. MFGM enriched whey is available commercially as whey protein phospholipid concentrate (WPPC), a co-product of the production of high purity whey protein by membrane filtration technologies. However, there are no standards for phospholipid content in WPPC. Determination of phospholipid content of WPPC would give a better understanding of value this product has as a source of milk polar lipids, compared to other MFGM enriched products. Polar lipids are also valuable functional ingredients, acting as emulsifiers, commonly used throughout the food industry. These polar lipids are usually sourced from plants, such as soy and sunflower, called lecithins. Plant based lecithins are regularly used in dairy products because of their emulsifying properties. Milk and dairy products are a potential source of polar lipids; however, no common commercial processes exist to extract phospholipids at concentrations high enough to serve as dairy-based lecithins. During this project, a validated method for quantitating milk phospholipids was developed using hydrophilic interaction high performance liquid chromatography coupled to evaporative light scattering detection (HILIC HPLC-ELSD). This method was developed in collaboration with the dairy industry to be used as a standard method for future quality assurance testing and production of new MFGM and milk polar lipid products. Lipids are extracted using the Folch method, modified to reduce the required volumes of halogenated solvents. A final sample preparation step using solid phase extraction is used to remove neutral lipids and concentrate polar lipids. This HPLC method utilizes a quaternary solvent system which results in baseline resolution of phospholipid classes allowing for confident, reproducible quantitation of major milk polar lipids. The method was validated using spike-recovery, injection stability, and intermediate precision tests. The sample preparation steps also successfully isolated phospholipids for accurate quantitation when challenged with high protein, lactose, and fat content dairy products and plant based lecithins. Next, the use of a food-grade solvent, ethanol, as an extraction solvent for the recovery of polar lipids from WPPC was investigated. The ethanol extraction procedures developed allowed for the recovery of a total lipid residue, and avoided specialized equipment reported by other methods in the literature. Using absolute ethanol and the boiling point of the reaction mixture as an indicator of temperature, a total of 20 mass equivalents of solvent was used to recovery lipids over four extraction cycles. Additionally, the potential for polar lipids to be fractionated from neutral lipids using ethanol was also investigated. Total lipids dissolved in ethanol extraction solvent were concentrated slightly and then partitioned using fractional crystallization to produce a polar lipid-enriched fraction. Neutral lipids are crystallized away from polar lipids when incubated at 15oC due to temperature-dependent solubility in high ethanol concentration solutions. The resulting polar lipid fraction was analyzed by HPLC and determined to contain 38% total phospholipids by mass. Sphingomyelin was observed to concentrate into the polar lipid fraction during ethanol fractionation. Finally, mass spectrometry-based lipidomics methods were applied to the ethanol extracted lipids from WPPC to profile polar lipids present in the commercially available product. Detailed structural information can be obtained from mass spectrometry, allowing for the identification of fatty acids attached to individual lipids species and the identification of the sphingoid backbone of sphingolipids. A total of 33 sphingomyelin species were detected and represented more than 27% of the total polar lipids detected in the total lipid extract. In the previous experiment some phospholipid species decreased in concentration after fractional crystallization, this observation was confirmed by the LC-MS analysis. Phosphatidylserine, phosphatidylinositol, and several glycosylated ceramide species were observed to co-crystallize with neutral lipids during fractionation. Correlation diagrams and principal component analysis (PCA) support the claim that phospholipids, specifically sphingomyelin and phosphatidylcholine, are recovered in a polar lipid-enriched residue after ethanol extraction and fractionation

The effects of under-sleeper pads on sleeper-ballast interaction

Under-sleeper pads (USPs), typically made from polyurethane, are used by railways in certain parts of the world to reduce ballast settlement and consequently lengthen the ballast tamping cycle. The rationale behind this relatively new addition to the conventional ballasted track structure is that the pad increases the contact area between the angular ballast particles and the underside of the concrete sleeper, with the effect that ballast breakdown and total track settlement are reduced. This paper describes two experiments on the effects of USPs on four aspects of sleeper–ballast interaction, namely contact area, contact pressure, ballast settlement and ballast breakdown. Static and dynamic tests up to 1 million loading cycles were performed under controlled laboratory conditions on concrete sleepers with and without USPs. Sophisticated pressure sensors revealed an increase in contact area from 12% to 35% for static loading tests, and from 8% to 20% for dynamic tests, with a resulting 70% reduction in contact pressure. In addition, a 44% reduction in ballast settlement and a 23% reduction in ballast breakdown were achieved by the introduction of USPs. In conclusion it is argued that the introduction of USPs specifically on heavy-haul lines would offer significant advantages with respect to ballast settlement and breakdown. These advantages are most likely to lengthen general ballast tamping and screening cycles, resulting in significant life cycle cost savings.Transnet Freight Rail is gratefully acknowledged for financial support to the Chair in Railway Engineering at the University of Pretoria.http://www.journals.co.za/ej/ejour_civileng.htmlam2016Civil Engineerin