12,668 research outputs found
Tensor models and 3-ary algebras
Full text linkTensor models are the generalization of matrix models, and are studied as
models of quantum gravity in general dimensions. In this paper, I discuss the
algebraic structure in the fuzzy space interpretation of the tensor models
which have a tensor with three indices as its only dynamical variable. The
algebraic structure is studied mainly from the perspective of 3-ary algebras.
It is shown that the tensor models have algebraic expressions, and that their
symmetries are represented by 3-ary algebras. It is also shown that the 3-ary
algebras of coordinates, which appear in the nonassociative fuzzy flat
spacetimes corresponding to a certain class of configurations with Gaussian
functions in the tensor models, form Lie triple systems, and the associated Lie
algebras are shown to agree with those of the Snyder's noncommutative
spacetimes. The Poincare transformations on the fuzzy flat spacetimes are shown
to be generated by 3-ary algebras.Comment: 21 pages, no essential changes of contents, but explanations added
for clarit
User's guide to the Mission Analysis Evaluation and Space Trajectory Operations program (MAESTRO)
Get PDFThe MAESTRO system is a mission analysis tool designed to present to the user information necessary to make the various decisions required in the design and execution of a spaceflight mission. The system was designed so that it can be used in both the pre-launch mission planning phase of a mission and during the flight as an in-flight decision making tool. A description of each of the following modes is presented: (1) trajectory propagation mode; (2) retro-fire determination mode; (3) midcourse analysis determination mode; (4) Monte Carlo mode; (5) verification mode; (6) orbit stability mode; and (7) post injection trim mode. A description of the inputs necessary to run the program mode is given along with a sample case
Multi-instantons in seven dimensions
Full text linkWe consider the self-dual Yang-Mills equations in seven dimensions. Modifying
the t'Hooft construction of instantons in , we find -instanton
solutions which depend on effective parameters and are -invariant.Comment: 9 pages, LaTeX, no figure
Treatment of failed articular cartilage reconstructive procedures of the knee: A systematic review
Get PDFBackground: Symptomatic articular cartilage lesions of the knee are common and are being treated surgically with increasing frequency. While many studies have reported outcomes following a variety of cartilage restoration procedures, few have investigated outcomes of revision surgery after a failed attempt at cartilage repair or reconstruction. Purpose: To investigate outcomes of revision cartilage restoration procedures for symptomatic articular cartilage lesions of the knee following a previously failed cartilage reconstructive procedure. Study Design: Systematic review; Level of evidence, 4. Methods: A literature search was performed by use of the PubMed, EMBASE, and MEDLINE/Ovid databases for relevant articles published between 1975 and 2017 that evaluated patients undergoing revision cartilage restoration procedure(s) and reported outcomes using validated outcome measures. For studies meeting inclusion criteria, relevant information was extracted. Results: Ten studies met the inclusion criteria. Lesions most commonly occurred in the medial femoral condyle (MFC) (52.8%), with marrow stimulation techniques (MST) the index procedure most frequently performed (70.7%). Three studies demonstrated inferior outcomes of autologous chondrocyte implantation (ACI) following a previous failed cartilage procedure compared with primary ACI. One study comparing osteochondral allograft (OCA) transplant following failed microfracture (MFX) with primary OCA transplant demonstrated similar clinical outcomes and graft survival at midterm follow-up. No studies reported outcomes following osteochondral autograft transfer (OAT) or newer techniques. Conclusion: This systematic review of the literature reporting outcomes following revision articular cartilage restoration procedures (most commonly involving the MFC) demonstrated a high proportion of patients who underwent prior MST. Evidence is sufficient to suggest that caution should be taken in performing ACI in the setting of prior MST, likely secondary to subchondral bone compromise. OCA appears to be a good revision treatment option even if the subchondral bone has been violated from prior surgery or fracture. </jats:sec
Towards the theory of coherent hard dijet production on hadrons and nuclei
Get PDFWe carry out a detailed calculation of the cross section of pion diffraction
dissociation into two jets with large transverse momenta, originating from a
hard gluon exchange between the pion constituents. Both the quark and the gluon
contribution are considered and in the latter case we present calculations both
in covariant and in axial gauges. We find that the standard collinear
factorization does not hold in this reaction. The structure of non-factorizable
contributions is discussed and the results are compared with the experimental
data. Our conclusion is that the existing theoretical uncertainties do not
allow, for the time being, for a quantitative extraction of the pion
distribution amplitude.Comment: 45 pages, latex, 17 figures, final version to appear in Nuclear
Physics
The Ginzburg-Landau Free Energy Functional of Color Superconductivity at Weak Coupling
Get PDFWe derive the Ginzburg-Landau free energy functional of color
superconductivity in terms of the thermal diagrams of QCD in its perturbative
region. The zero mode of the quadratic term coefficient yields the same
transition temperature, including the pre-exponential factor, as the one
obtained previously from the Fredholm determinant of the two quark scattering
amplitude. All coefficients of the free energy can be made identical to those
of a BCS model by setting the Fermi velocity of the latter equal to the speed
of light. We also calculate the induced symmetric color condensate near
and find that it scales as the cubic power of the dominant antisymmetric color
component. We show that in the presence of an inhomogeneity and a nonzero gauge
potential, while the color-flavor locked condensate dominates in the bulk, the
unlocked condensate, the octet, emerges as a result of a simultaneous
color-flavor rotation in the core region of a vortex filament or at the
junction of super and normal phases.Comment: 32 pages, Plain Tex, 3 figure
Effective Gap Equation for the Inhomogeneous LOFF Superconductive Phase
Full text linkWe present an approximate gap equation for different crystalline structures
of the LOFF phase of high density QCD at T=0. This equation is derived by using
an effective condensate term obtained by averaging the inhomogeneous condensate
over distances of the order of the crystal lattice size. The approximation is
expected to work better far off any second order phase transition. As a
function of the difference of the chemical potentials of the up and down
quarks, , we get that the octahedron is energetically favored from
to , where is the gap for
the homogeneous phase, while in the range the face
centered cube prevails. At a first order phase
transition to the normal phase occurs.Comment: 11 pages, 5 figure
Diquark Condensates and Compact Star Cooling
Full text linkThe effect of color superconductivity on the cooling of quark stars and
neutron stars with large quark cores is investigated. Various known and new
quark-neutrino processes are studied. As a result, stars being in the color
flavor locked (CFL) color superconducting phase cool down extremely fast. Quark
stars with no crust cool down too rapidly in disagreement with X-ray data. The
cooling of stars being in the N_f =2 color superconducting (2SC) phase with a
crust is compatible with existing X-ray data. Also the cooling history of stars
with hypothetic pion condensate nuclei and a crust does not contradict the
data.Comment: 10 pages, 5 figures, accepted for publication in Ap
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Replication: A Design Principle for Field Research
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