265 research outputs found
Recommended from our members
Assessment of potential ORNL contributions to supply of molybdenum-99
The most widely used, and probably the most important, single radioisotope in commerce is {sup 99}Mo. Although the present supply is adequate, there are many vulnerabilities in the supply picture. Resources available at ORNL could be applied to help ensure the continued availability of this critically needed radioisotope. This assessment considers the ways in which ORNL might participate in DOE efforts to develop and maintain a domestic source of {sup 99}Mo for medical needs. The primary recommendation presented here is that ORNL obtain DOE support for development of an improved method for providing {sup 99}Mo to the user community. Specifically, development and demonstration of a system based on irradiation of enriched stable {sup 98}Mo, as opposed to fission of {sup 235}U, is recommended. Such a system would (1) alleviate the need for using highly enriched uranium as target material (nonproliferation and criticality safety concerns); (2) alleviate the need to produce a large volume of unwanted fission product wastes (safety and cost concerns); (3) promote the need for enriched {sup 98}Mo, which can be produced in the ORNL calutrons or plasma separation equipment; and (4) promote the need for a high-flux reactor, such as the High Flux Isotope Reactor (HFIR)
Recommended from our members
Development of the thermal denitration in-storage-can step in the CEUSP process
A thermal denitration in-the-storage-can process has been developed for use in the Consolidated Edison Uranium Solidification Program Facility. This process is being used to convert approx.1000 kg of highly fissile and radioactive uranium to a solid form for safe long-term storage. The material being solidified also contains approx.300 kg of cadmium and approx.40 kg of gadolinium which had been combined with the uranium to provide criticality safety. The unique thermal denitration process was found to be extremely susceptible to entrainment of solids by splattering, foaming, or expulsion actions. The process connection nozzle, through which the feed solution and purging air are supplied and the emerging off-gases are discharged, and the off-gas handling system were modified extensively to permit operation without development of nozzle or line pluggage due to accumulation of solid deposits. A process study was made to determine the effects of feed components and process variables on the tendency of the reacting mixture to splatter, foam, or be expelled. Because of the equipment modifications and the selection of appropriate processing conditions, the feed material is being denitrated without significant problems
Observability of Switched Linear Systems in Continuous Time
We study continuous-time switched linear systems with unobserved and exogeneous mode signals. We analyze the observability of the initial state and initial mode under arbitrary switching, and characterize both properties in both autonomous and non-autonomous cases
Fate of trace metals in anaerobic digestion
© Springer International Publishing Switzerland 2015. A challenging, and largely uncharted, area of research in the field of anaerobic digestion science and technology is in understanding the roles of trace metals in enabling biogas production. This is a major knowledge gap and a multifaceted problem involving metal chemistry; physical interactions of metal and solids; microbiology; and technology optimization. Moreover, the fate of trace metals, and the chemical speciation and transport of trace metals in environments— often agricultural lands receiving discharge waters from anaerobic digestion processes— simultaneously represents challenges for environmental protection and opportunities to close process loops in anaerobic digestion.The authors acknowledge funding within the framework of the COST Action 1302
(‘European Network on Ecological Roles of Trace Metals in Anaerobic
Biotechnologies’). GC is supported by a European Research Council Starting Grant
(‘3C-BIOTECH; No. 261330).Peer Reviewe
Extragenic suppressor mutations in ΔripA disrupt stability and function of LpxA
Background: Francisella tularensis is a Gram-negative bacterium that infects hundreds of species including humans, and has evolved to grow efficiently within a plethora of cell types. RipA is a conserved membrane protein of F. tularensis, which is required for growth inside host cells. As a means to determine RipA function we isolated and mapped independent extragenic suppressor mutants in ΔripA that restored growth in host cells. Each suppressor mutation mapped to one of two essential genes, lpxA or glmU, which are involved in lipid A synthesis. We repaired the suppressor mutation in lpxA (S102, LpxA T36N) and the mutation in glmU (S103, GlmU E57D), and demonstrated that each mutation was responsible for the suppressor phenotype in their respective strains. We hypothesize that the mutation in S102 altered the stability of LpxA, which can provide a clue to RipA function. LpxA is an UDP-N-acetylglucosamine acyltransferase that catalyzes the transfer of an acyl chain from acyl carrier protein (ACP) to UDP-N-acetylglucosamine (UDP-GlcNAc) to begin lipid A synthesis. Results: LpxA was more abundant in the presence of RipA. Induced expression of lpxA in the ΔripA strain stopped bacterial division. The LpxA T36N S102 protein was less stable and therefore less abundant than wild type LpxA protein. Conclusion: These data suggest RipA functions to modulate lipid A synthesis in F. tularensis as a way to adapt to the host cell environment by interacting with LpxA
Subprocess Size in Hard Exclusive Scattering
The interaction region of hard exclusive hadron scattering can have a large
transverse size due to endpoint contributions, where one parton carries most of
the hadron momentum. The endpoint region is enhanced and can dominate in
processes involving multiple scattering and quark helicity flip. The endpoint
Fock states have perturbatively short lifetimes and scatter softly in the
target. We give plausible arguments that endpoint contributions can explain the
apparent absence of color transparency in fixed angle exclusive scattering and
the dimensional scaling of transverse rho photoproduction at high momentum
transfer, which requires quark helicity flip. We also present a quantitative
estimate of Sudakov effects.Comment: 16 pages, 4 figures, JHEP style; v2: quantitative estimate of Sudakov
effects and more detailed discussion of endpoint behaviour of meson
distribution amplitude added, few other clarifications, version to appear in
Phys. Rev.
The temporal dynamics of Arc expression regulate cognitive flexibility
YesNeuronal activity regulates the transcription and
translation of the immediate-early gene Arc/Arg3.1,
a key mediator of synaptic plasticity. Proteasomedependent
degradation of Arc tightly limits its
temporal expression, yet the significance of this
regulation remains unknown. We disrupted the temporal
control of Arc degradation by creating an Arc
knockin mouse (ArcKR) where the predominant Arc
ubiquitination sites were mutated. ArcKR mice had
intact spatial learning but showed specific deficits
in selecting an optimal strategy during reversal
learning. This cognitive inflexibility was coupled to
changes in Arc mRNA and protein expression resulting
in a reduced threshold to induce mGluR-LTD and
enhanced mGluR-LTD amplitude. These findings
show that the abnormal persistence of Arc protein
limits the dynamic range of Arc signaling pathways
specifically during reversal learning. Our work
illuminates how the precise temporal control of activity-dependent
molecules, such as Arc, regulates synaptic
plasticity and is crucial for cognition.Open access funded by Biotechnology and Biological Sciences Research Counci
Limits on the monopole magnetic field from measurements of the electric dipole moments of atoms, molecules and the neutron
A radial magnetic field can induce a time invariance violating electric
dipole moment (EDM) in quantum systems. The EDMs of the Tl, Cs, Xe and Hg atoms
and the neutron that are produced by such a field are estimated. The
contributions of such a field to the constants, of the T,P-odd
interactions and are also estimated for the TlF, HgF and YbF molecules (where
() is the electron (nuclear) spin and is the molecular
axis). The best limit on the contact monopole field can be obtained from the
measured value of the Tl EDM. The possibility of such a field being produced
from polarization of the vacuum of electrically charged magnetic monopoles
(dyons) by a Coulomb field is discussed, as well as the limit on these dyons.
An alternative mechanism involves chromomagnetic and chromoelectric fields in
QCD.Comment: Uses RevTex, 16 pages, 4 postscript figures. An explanation of why
there is no orbital contribution to the EDM has been added, and the
presentation has been improved in genera
Pedagogic model for Deeply Virtual Compton Scattering with quark-hadron duality
We show how quark-hadron duality can emerge for valence spin averaged
structure functions, and for the non-forward distributions of Deeply Virtual
Compton Scattering. Novel factorisations of the non-forward amplitudes are
proposed. Some implications for large angle scattering and deviations from the
quark counting rules are illustrated.Comment: Version accepted by Phys. Rev.
- …