4,798 research outputs found
Convergence of approximate deconvolution models to the mean Magnetohydrodynamics Equations: Analysis of two models
We consider two Large Eddy Simulation (LES) models for the approximation of
large scales of the equations of Magnetohydrodynamics (MHD in the sequel). We
study two -models, which are obtained adapting to the MHD the approach
by Stolz and Adams with van Cittert approximate deconvolution operators. First,
we prove existence and uniqueness of a regular weak solution for a system with
filtering and deconvolution in both equations. Then we study the behavior of
solutions as the deconvolution parameter goes to infinity. The main result of
this paper is the convergence to a solution of the filtered MHD equations. In
the final section we study also the problem with filtering acting only on the
velocity equation
Loop constraints: A habitat and their algebra
This work introduces a new space \T'_* of `vertex-smooth' states for use in
the loop approach to quantum gravity. Such states provide a natural domain for
Euclidean Hamiltonian constraint operators of the type introduced by Thiemann
(and using certain ideas of Rovelli and Smolin). In particular, such operators
map \T'_* into itself, and so are actual operators in this space. Their
commutator can be computed on \T'_* and compared with the classical
hypersurface deformation algebra. Although the classical Poisson bracket of
Hamiltonian constraints yields an inverse metric times an infinitesimal
diffeomorphism generator, and despite the fact that the diffeomorphism
generator has a well-defined non-trivial action on \T'_*, the commutator of
quantum constraints vanishes identically for a large class of proposals.Comment: 30 pages RevTex, 2 figures include
CR Structures and Asymptotically Flat Space-Times
We discuss the unique existence, arising by analogy to that in algebraically
special space-times, of a CR structure realized on null infinity for any
asymptotically flat Einstein or Einstein-Maxwell space-time.Comment: 6 page
On the consistency of the constraint algebra in spin network quantum gravity
We point out several features of the quantum Hamiltonian constraints recently
introduced by Thiemann for Euclidean gravity. In particular we discuss the
issue of the constraint algebra and of the quantum realization of the object
, which is classically the Poisson Bracket of two Hamiltonians.Comment: 13 pages, RevTex, 2 figures include
Eicosapentaenoic acid and oxypurinol in the treatment of muscle wasting in a mouse model of cancer cachexia
Cancer cachexia is a wasting condition, driven by systemic inflammation and oxidative stress. This study investigated eicosapentaenoic acid (EPA) in combination with oxypurinol as a treatment in a mouse model of cancer cachexia. Mice with cancer cachexia were randomized into 4 treatment groups (EPA (0.4 g/kg/day), oxypurinol (1 mmol/L ad-lib), combination, or control), and euthanized after 29 days. Analysis of oxidative damage to DNA, mRNA analysis of pro-oxidant, antioxidant and proteolytic pathway components, along with enzyme activity of pro- and antioxidants were completed on gastrocnemius muscle. The control group displayed earlier onset of tumor compared to EPA and oxypurinol groups (P<0.001). The EPA group maintained body weight for an extended duration (20 days) compared to the oxypurinol (5 days) and combination (8 days) groups (P<0.05). EPA (18.2±3.2 pg/ml) and combination (18.4±3.7 pg/ml) groups had significantly higher 8-OH-dG levels than the control group (12.9±1.4 pg/ml, P≤0.05) indicating increased oxidative damage to DNA. mRNA levels of GPx1, MURF1 and MAFbx were higher following EPA treatment compared to control (P≤0.05). Whereas oxypurinol was associated with higher GPx1, MnSOD, CAT, XDH, MURF1, MAFbx and UbB mRNA compared to control (P≤0.05). Activity of total SOD was higher in the oxypurinol group (32.2±1.5 U/ml) compared to control (27.0±1.3 U/ml, P<0.01), GPx activity was lower in the EPA group (8.76±2.0 U/ml) compared to control (14.0±1.9 U/ml, P<0.05), and catalase activity was lower in the combination group (14.4±2.8 U/ml) compared to control (20.9±2.0 U/ml, P<0.01). There was no change in XO activity. The increased rate of weight decline in mice treated with oxypurinol indicates that XO may play a protective role during the progression of cancer cachexia, and its inhibition is detrimental to outcomes. In combination with EPA, there was little significant improvement from control, indicating oxypurinol is unlikely to be a viable treatment compound in cancer cachexia.<br /
On the Bardina’s model in the whole space
We consider the Bardina’s model for turbulent incompressible flows in the whole space with a cut-off frequency of order α^(-1)> 0. We show that for any α> 0 fixed, the model has a unique regular solution defined for all t ∈ [0, ∞[
Efficient Stark deceleration of cold polar molecules
Stark deceleration has been utilized for slowing and trapping several species
of neutral, ground-state polar molecules generated in a supersonic beam
expansion. Due to the finite physical dimension of the electrode array and
practical limitations of the applicable electric fields, only molecules within
a specific range of velocities and positions can be efficiently slowed and
trapped. These constraints result in a restricted phase space acceptance of the
decelerator in directions both transverse and parallel to the molecular beam
axis; hence, careful modeling is required for understanding and achieving
efficient Stark decelerator operation. We present work on slowing of the
hydroxyl radical (OH) elucidating the physics controlling the evolution of the
molecular phase space packets both with experimental results and model
calculations. From these results we deduce experimental conditions necessary
for efficient operation of a Stark decelerator.Comment: 8 pages, 9 figure
Volume and Quantizations
The aim of this letter is to indicate the differences between the
Rovelli-Smolin quantum volume operator and other quantum volume operators
existing in the literature. The formulas for the operators are written in a
unifying notation of the graph projective framework. It is clarified whose
results apply to which operators and why.Comment: 8 page
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