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Methylation of the fragile X mental retardation 1 (FMR1) exon 1/intron 1 boundary positioned fragile X related epigenetic element 2 (FREE2), reveals skewed X-chromosome inactivation (XCI) in fragile X syndrome full mutation (FM: CGG > 200) females. XCI skewing has been also linked to abnormal X-linked gene expression with the broader clinical impact for sex chromosome aneuploidies (SCAs). In this study, 10 FREE2 CpG sites were targeted using methylation specific quantitative melt analysis (MS-QMA), including 3 sites that could not be analysed with previously used EpiTYPER system. The method was applied for detection of skewed XCI in FM females and in different types of SCA. We tested venous blood and saliva DNA collected from 107 controls (CGG < 40), and 148 FM and 90 SCA individuals. MS-QMA identified: (i) most SCAs if combined with a Y chromosome test; (ii) locus-specific XCI skewing towards the hypomethylated state in FM females; and (iii) skewed XCI towards the hypermethylated state in SCA with 3 or more X chromosomes, and in 5% of the 47,XXY individuals. MS-QMA output also showed significant correlation with the EpiTYPER reference method in FM males and females (P < 0.0001) and SCAs (P < 0.05). In conclusion, we demonstrate use of MS-QMA to quantify skewed XCI in two applications with diagnostic utility.
Despite many advances in recent years for patients with critical paediatric and congenital cardiac disease, significant variation in outcomes remains across hospitals. Collaborative quality improvement has enhanced the quality and value of health care across specialties, partly by determining the reasons for variation and targeting strategies to reduce it. Developing an infrastructure for collaborative quality improvement in paediatric cardiac critical care holds promise for developing benchmarks of quality, to reduce preventable mortality and morbidity, optimise the long-term health of patients with critical congenital cardiovascular disease, and reduce unnecessary resource utilisation in the cardiac intensive care unit environment. The Pediatric Cardiac Critical Care Consortium (PC4) has been modelled after successful collaborative quality improvement initiatives, and is positioned to provide the data platform necessary to realise these objectives. We describe the development of PC4 including the philosophical, organisational, and infrastructural components that will facilitate collaborative quality improvement in paediatric cardiac critical care.
We report a means of directly controlling DNA dehybridization by radio frequency magnetic field coupling to a nanometer scale antenna covalently linked to the DNA. The method of control relies on induction heating of an Au nanocrystal, which raises the temperature of a biomolecule to which it is covalently bound, while leaving surrounding molecules relatively unaffected. Because heat dissipation in biomolecules in solution is rapid(<50 picoseconds) this switching is reversible. This technique is specific, reversible, and non-optical. Since it can be used in solution, it has the potential to be extended to systems in vivo. The ability to differentially control local temperature forms the basis of control of properties such as hybridization and enzyme activity, and has the potential of controlling many biological processes.
Classical plasticity theories generally assume that the stress at a point is a function of strain at that point only. However, when gradients in strain become significant, this localization assumption is no longer valid. These conventional models fail to display a ‘size effect’. This effect is seen experimentally when the scale of the phenomenon of interest is on the order of several microns. Under these conditions, strain gradients are of a significant magnitude as compared to the overall strain and must be considered for models to accurately capture observed phenomena.
The mechanics community has been actively involved in the development of strain gradient theories for many years. Recently, interest in this area has been rekindled and several new approaches have appeared in the literature. Two different approaches are currently being evaluated. One approach considers strain gradients as internal variables that do not introduce work conjugate higher order stresses. Another approach considers the strain gradients as internal degrees of freedom that requires work conjugate higher order stresses. Experiments are being performed to determine which approach models material behavior accurately with the least amount of complexity. A key difference between the two models considered here is the nature of the assumed boundary conditions at material interfaces. Therefore, we are investigating the deformation behavior of aluminum/sapphire interfaces loaded under simple shear. Samples are fabricated using ultra-high vacuum diffusion bonding. To determine the lattice rotations near the boundary, we are examining the samples with both electron backscatter diffraction methods (EBSD) in the scanning electron microscope and with a variety of diffraction techniques in the transmission electron microscope. The experimentally found boundary conditions shall be subsequently used to determine whether the simpler internal variable model is adequately descriptive or if the greater complexity associated with the internal degree of freedom approach is warranted.
The electronic structure of Pu materials is examined using photoelectron spectroscopy. For delta-phase Pu metal as well as PuCoGa5 and PuIn3, the 5f electrons appear to be at the threshold between localized and itinerant character. A mixed level model computational scheme is used which results in non-magnetic solutions for the electronic structure and agrees well with the photoemission measurements. Several other computational schemes are assessed against photoemission results for delta Pu. Additional insight is provided by O2 and H2 dosing of the delta Pu samples and consideration of surface effects. The experimental and computational results are consistent with the 5f electrons in Pu materials exhibiting a dual nature with some fraction of the 5f levels localized and not participating in the bonding while the other fraction of 5f character is involved in bonding and hybridization with the conduction electrons.
The 5f electronic states in elemental Pu and Pu compounds exhibit elements of both itinerant and localized behavior. Several first-principles calculations have been presented to describe this balance, differing in the manner in which electron correlation is included in the calculation. This paper describes a calculations performed with the Mixed Level Model (MLM), presenting calculated results for the two Pu compounds, PuRhGa5 and PuCoGa5. The MLM results are compared with other calculations and the differences discussed.
The purpose of this paper is to provide an introduction for non-experts to first-principles electronic structure methods that are widely used in the field of condensed-matter physics, including applications to actinide materials. The methods I describe are based on density functional theory (DFT) within the local density approximation (LDA) and the generalized gradient approximation (GGA). In addition to explaining the meaning of this terminology I also describe the underlying theory itself in some detail in order to enable a better understanding of the relative strengths and weaknesses of the methods. I briefly mention some particular numerical implementations of DFT, including the linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods, as well as general methodologies that go beyond DFT and specifically address some of the weaknesses of the theory. The last third of the paper is devoted to a few selected applications that illustrate the ideas discussed in the first two-thirds. In particular, I conclude by addressing the current controversy regarding magnetic DFT calculations for actinide materials. Throughout this paper particular emphasis is placed on providing the appropriate background to enable the non-expert to gain a better appreciation of the application of first-principles electronic structure methods to the study of actinide and other materials.
The application of TiAl-based alloys as an exhaust valve material would allow automotive engines to operate at higher temperatures with increased efficiencies. Development of these materials at Ford initially concentrated on the Ti-48A1-1V (at%) system. This included; 1) room and elevated temperature fatigue, 2) creep and 3) tensile ductility optimization. Results from this test program in conjunction with other available data, previous ceramic experience and limited engine testing led to the conclusion that the major roadblock to implementation was not optimizing mechanical properties, but rather low cost and reliable valve manufacturing technology. When a cost effective manufacturing technology is developed, then the emphasis will shift to ensuring the product durability. Hence, the focus of the current program is the development of valve manufacturing technologies, in particular valve blank fabrication. Currently, casting appears to be the lowest cost alternative for valve blank fabrication. This paper reviews the technology development process as it pertains to TiAl-based valves.
Al2Ti is a promising material for use in elevated temperature structural applications. It has a lower density than Ti3Al and TiAl. We have previously shown that the compressive yield strength of Al2Ti is higher than that of similarly processed TiAl and Al3Ti between room temperature and 900°C. In this study, two additional processing methods were utilized to produce the material: uniaxial hot pressing of rapidly solidified powder and hot forging of cast ingots. Effects of hot forging or annealing of as-cast Al2Ti on the microhardness and load for crack initiation were studied. The microhardness and crack initiation load were also used to compare powder processed material consolidated either by hot pressing or hot isostatic pressing. The oxidation behavior of as-cast, cast & hot isostatically pressed (cast & hip’ed), and powder processed & hip’ed (PP) Al2Ti was also investigated. The oxidation tests were performed in air at 815°C and 982°C for 100 hr. PP Al2Ti exhibited the lowest weight gain and as-cast exhibited the highest. Al2Ti shows superior oxidation resistance compared to Ti3Al- and TiAl- based alloys tested under similar conditions and shows comparable oxidation resistance to Al3Ti at 800°C. SEM/EDS was used to study the morphological development of the oxide scale and to identify the chemical constituents present in the various layers of the scale.
The stability of bcc-based phases in the Ti-Al-Nb alloy system has been studied from first-principles using a combination of ab-initio total energy and cluster variation method (CVM) calculations. Total energies have been computed for 18 binary and ternary bcc superstructures in order to determine low temperature ordering tendencies. From the results of these calculations a set of effective cluster interaction parameters have been derived. These interaction parameters are required input for CVM computations of alloy thermodynamic properties. The CVM has been used to study the effect of composition on finite-temperature ordering tendencies and site preferences for bcc-based phases. Strong ordering tendencies are observed for binary Nb-Al and Ti-Al bcc phases as well as for ternary alloys with compositions near Ti2AlNb. For selected superstructures we have also analyzed structural stabilities with respect to tetragonal distortions which transform the bcc into an fcc lattice. Instabilities with respect to such distortions are found to exist for binary but not ternary bcc compounds.
The mechanical properties of interfaces in Ti/Al2O3 composites were characterized by four point bending and fiber pushout tests. To determine the bi-material fracture toughness with four point bending tests, planar interfaces were evaluated as sandwich composites. By changing the processing temperature from 700°C to 1000°C, the interfacial fracture energy was found to increase ug to 950°C. It then decreases when the processing temperature is further increased to 1000°C. This is because of the formation of the intermetallic compound (Ti3Al). Interfacial shear strength and interfacial frictional stress of 323MPa and 312 MPa were obtained, respectively, by performing pushout tests of the Al2O3 fiber reinforced Ti matrix composites. These values are smaller than the shear yielding strength of the Ti matrix which is 525 MPa.
A systematic study of photoluminescence (PL) of Er and O ion implanted and annealed n-type GaN grown on R-plane sapphire (A12O3) was performed. The Er implants ranged from 2 × 1013 to 1 × 1015 Er++/cm2, and the O co-implants ranged from 1014 to 1016 O+/cm2. The resulting nine different combinations of GaN:Er,O were annealed at 600 °C (4 hrs. in N2), 700 °C (1.5 hrs. in N2), 800 °C (0.75 hr. in NH3), and 900 °C (0.5 hr. in NH3) Following each annealing step, the Er3 -related PL at 1.54 μm was measured from each sample at 77K, when pumped directly with 135 mW of power at 980 nm. The three samples with the highest dose of Er (1 × 1015 Er++/ cm 2), regardless of O co-dopant dose, yielded the strongest PL peak intensity at 1.54 μm after all the anneals. The integrated PL from 1.52 to 1.58 μm was reduced by 62 % when going from 77 K to room temperature (RT).
The nonlinear optical properties of epitaxial KNbO3 were studied for films grown by metalorganic chemical vapor deposition on different substrates. X-ray diffraction revealed epitaxial KNbO3 with a (110) orientation for layers deposited on single crystal strontium titanate. Whereas, films grown on (100) spinel exhibited a multi-variant structure, consisting of the (110) and (001) orientations. The volume fraction of each crystallographic variant in the film was calculated. Second harmonic generation measurements at 532 nm were performed to determine the ferroelectric domain variants present. The Maker-fringe technique was employed to obtain the effective nonlinear optical susceptibility of the films, which ranged from 0.1 - 1.8 pm/V. The SHG intensity profiles reveal a strong dependence upon substrate type.