Oak Ridge National Laboratory

About: Oak Ridge National Laboratory is a facility organization based out in Oak Ridge, Tennessee, United States. It is known for research contribution in the topics: Neutron & Ion. The organization has 31868 authors who have published 73724 publications receiving 2633689 citations. The organization is also known as: ORNL.

A Mutation in Rab27a causes the vesicle transport defects observed in ashen mice

Abstract: The dilute (d), leaden (ln), and ashen (ash) mutations provide a unique model system for studying vesicle transport in mammals. All three mutations produce a lightened coat color because of defects in pigment granule transport. In addition, all three mutations are suppressed by the semidominant dilute-suppressor (dsu), providing genetic evidence that these mutations function in the same or overlapping transport pathways. Previous studies showed that d encodes a major vesicle transport motor, myosin-VA, which is mutated in Griscelli syndrome patients. Here, using positional cloning and bacterial artificial chromosome rescue, we show that ash encodes Rab27a. Rab GTPases represent the largest branch of the p21 Ras superfamily and are recognized as key players in vesicular transport and organelle dynamics in eukaryotic cells. We also show that ash mice have platelet defects resulting in increased bleeding times and a reduction in the number of platelet dense granules. These defects have not been reported for d and ln mice. Collectively, our studies identify Rab27a as a critical gene for organelle-specific protein trafficking in melanocytes and platelets and suggest that Rab27a functions in both MyoVa dependent and independent pathways.

Power-law scaling and fractal nature of medium-range order in metallic glasses.

Abstract: Understanding the short- and medium-range structure of metallic glasses remains a difficult challenge The observation that the medium-range order has the characteristics of a fractal network may have broader implications in the understanding of the relation between structure and mechanical properties in metallic glasses The atomic structure of metallic glasses has been a long-standing scientific problem Unlike crystalline metals, where long-range ordering is established by periodic stacking of fundamental building blocks known as unit cells, a metallic glass has no long-range translational or orientational order, although some degrees of short- and medium-range order do exist1,2,3 Previous studies1,2,3,4 have identified solute- (minority atom)-centred clusters as the fundamental building blocks or short-range order in metallic glasses Idealized cluster packing schemes, such as efficient cluster packing on a cubic lattice1 and icosahedral packing3 as in a quasicrystal, have been proposed and provided first insights on the medium-range order in metallic glasses However, these packing schemes break down beyond a length scale of a few clusters Here, on the basis of neutron and X-ray diffraction experiments, we propose a new packing scheme—self-similar packing of atomic clusters We show that the medium-range order has the characteristics of a fractal network with a dimension of 231, and is described by a power-law correlation function over the medium-range length scale Our finding provides a new perspective of order in disordered materials and has broad implications for understanding their structure–property relationship, particularly those involving a change in length scales

Cloud Quantum Computing of an Atomic Nucleus

Abstract: We report a quantum simulation of the deuteron binding energy on quantum processors accessed via cloud servers. We use a Hamiltonian from pionless effective field theory at leading order. We design a low-depth version of the unitary coupled-cluster ansatz, use the variational quantum eigensolver algorithm, and compute the binding energy to within a few percent. Our work is the first step towards scalable nuclear structure computations on a quantum processor via the cloud, and it sheds light on how to map scientific computing applications onto nascent quantum devices.

Facile ionothermal synthesis of microporous and mesoporous carbons from task specific ionic liquids.

Abstract: An expedient, template-free, high-yield, and solventless route to nitrogen-rich micro- and mesoporous carbons is reported based on direct, atmospheric-pressure carbonization of task-specific ionic liquids bearing one or more nitrile side chains. The resulting textural properties (pore regime, surface area) are highly dependent upon the structural motifs of the ions comprising the corresponding parent ionic liquid, and uniform carbon films are routinely deposited with this novel methodology, highlighting excited new opportunities in the development of advanced functional carbon composites.

Softening caused by profuse shear banding in a bulk metallic glass.

Abstract: By controlling the specimen aspect ratio and strain rate, compressive strains as high as 80% were obtained in an otherwise brittle metallic glass. Physical and mechanical properties were measured after deformation, and a systematic strain-induced softening was observed which contrasts sharply with the hardening typically observed in crystalline metals. If the deformed glass is treated as a composite of hard amorphous grains surrounded by soft shear-band boundaries, analogous to nanocrystalline materials that exhibit inverse Hall-Petch behavior, the correct functional form for the dependence of hardness on shear-band spacing is obtained. Deformation-induced softening leads naturally to shear localization and brittle fracture.