989 research outputs found
An In Vitro Comparison of the Rake Angles Between K3 and ProFile Endodontic File Systems
The purpose of this study was to compare rake angles of the ProFile and K3 file systems. Twenty-five 40/0.06 taper files were obtained for each system. Five files from the same manufacturer were placed perpendicularly into a vial of Epoxicure Resin and left to set for 24 h. The set-ups were removed from the vials and each were sectioned 5 mm from the tip of the files and polished. A photomicrograph was taken of each file with 100× magnification. Five sets of ProFile and five sets of K3 files were processed in this manner. Images were captured digitally, and rake angles of each file were measured. Multivariate ANOVA found a significant difference (p \u3c 0.001) among the three negative rake angles of the ProFile system compared with the K3 system
Diffractive Meson Production and the Quark-Pomeron Coupling
Diffractive meson production at HERA offers interesting possibilities to
investigate diffractive processes and thus to learn something about the
properties of the pomeron. The most succesful phenomenological description of
the pomeron so far assumes it to couple like a isoscalar photon to
single quarks. This coupling leads, however, to problems for exclusive
diffractive reactions. We propose a new phenomenological pomeron vertex, which
leads to very good fits to the known data, but avoids the problems of the old
vertex.Comment: 20 pages, latex with uuencoded postscript, revised versio
Dielectric resonances of ordered passive arrays
The electrical and optical properties of ordered passive arrays, constituted
of inductive and capacitive components, are usually deduced from Kirchhoff's
rules. Under the assumption of periodic boundary conditions, comparable results
may be obtained via an approach employing transfer matrices. In particular,
resonances in the dielectric spectrum are demonstrated to occur if all
eigenvalues of the transfer matrix of the entire array are unity. The latter
condition, which is shown to be equivalent to the habitual definition of a
resonance in impedance for an array between electrodes, allows for a convenient
and accurate determination of the resonance frequencies, and may thus be used
as a tool for the design of materials with a specific dielectric response. For
the opposite case of linear arrays in a large network, where periodic boundary
condition do not apply, several asymptotic properties are derived. Throughout
the article, the derived analytic results are compared to numerical models,
based on either Exact Numerical Renormalisation or the spectral method.Comment: 12 pages, 12 figure
QCD sum rules with finite masses
The concept of QCD sum rules is extended to bound states composed of
particles with finite mass such as scalar quarks or strange quarks. It turns
out that mass corrections become important in this context. The number of
relevant corrections is analyzed in a systematic discussion of the IR- and
UV-divergencies, leading in general to a finite number of corrections. The
results are demonstrated for a system of two massless quarks and two heavy
scalar quarks.Comment: 15 pages, including two pictures to be found in an extra file. Latex
neads epsf.st
Orthogonal Linear Combinations of Gaussian Type Orbitals
The set of Gaussian Type Orbitals g(n1,n2,n3) of order (n+1)(n+2)/2, of
common n=n1+n2+n3<=7, common center and exponential, is customized to define a
set of 2n+1 linear combinations t(n,m) (-n<=m<=n) such that each t(n,m) depends
on the azimuthal and polar angle of the spherical coordinate system like the
real or imaginary part of the associated Spherical Harmonic. (Results cover
both Hermite and Cartesian Gaussian Type Orbitals.) Overlap, kinetic energy and
Coulomb energy matrix elements are presented for generalized basis functions of
the type r^s*t(n,m) (s=0,2,4,...). In addition, normalization integrals int
|g(n1,n2,n3)|d^3r are calculated up to n=7 and normalization integrals int
|r^s*t(n,m)|d^3r up to n=5.Comment: 13 pages, no figures, REVTeX4. Corrected eqs. (23) and (C4
COALESCING NEUTRON STARS AS GAMMA RAY BURSTERS ?
We investigate the dynamics and evolution of coalescing neutron stars. The
three-dimensional Newtonian equations of hydrodynamics are integrated by the
`Piecewise Parabolic Method' However, we do include the effects of the emission
of gravitational waves on the hydrodynamics. The properties of neutron star
matter are described by the equation of state of Lattimer & Swesty. In addition
to the fundamental hydrodynamic quantities, density, momentum, and energy, we
follow the time evolution of the electron density in the stellar gas. Energy
losses and changes of the electron abundance due to the emission of neutrinos
are taken into account by an elaborate ``neutrino leakage scheme'', which
employs a careful calculation of the lepton number and energy source terms of
all neutrino types. The grid is Cartesian and equidistant with a resolution of
64**3 or 128**3, which allows us to calculate the self-gravity via fast Fourier
transforms.Comment: extended abstract contribution to the proceedings of the 17th Texas
Symposium, 2 pages, uuencoded compressed postscript
Correlation functions of scattering matrix elements in microwave cavities with strong absorption
The scattering matrix was measured for microwave cavities with two antennas.
It was analyzed in the regime of overlapping resonances. The theoretical
description in terms of a statistical scattering matrix and the rescaled
Breit-Wigner approximation has been applied to this regime. The experimental
results for the auto-correlation function show that the absorption in the
cavity walls yields an exponential decay. This behavior can only be modeled
using a large number of weakly coupled channels. In comparison to the
auto-correlation functions, the cross-correlation functions of the diagonal
S-matrix elements display a more pronounced difference between regular and
chaotic systems
Reciprocal regulation of PKA and rac signaling
Activated G protein-coupled receptors (GPCRs) and receptor tyrosine kinases relay extracellular signals through spatial and temporal controlled kinase and GTPase entities. These enzymes are coordinated by multifunctional scaffolding proteins for precise intracellular signal processing. The cAMP-dependent protein kinase A (PKA) is the prime example for compartmentalized signal transmission downstream of distinct GPCRs. A-kinase anchoring proteins tether PKA to specific intracellular sites to ensure precision and directionality of PKA phosphorylation events. Here, we show that the Rho-GTPase Rac contains A-kinase anchoring protein properties and forms a dynamic cellular protein complex with PKA. The formation of this transient core complex depends on binary interactions with PKA subunits, cAMP levels and cellular GTP-loading accounting for bidirectional consequences on PKA and Rac downstream signaling. We show that GTP-Rac stabilizes the inactive PKA holoenzyme. However, β-adrenergic receptor-mediated activation of GTP-Rac–bound PKA routes signals to the Raf-Mek-Erk cascade, which is critically implicated in cell proliferation. We describe a further mechanism of how cAMP enhances nuclear Erk1/2 signaling: It emanates from transphosphorylation of p21-activated kinases in their evolutionary conserved kinase-activation loop through GTP-Rac compartmentalized PKA activities. Sole transphosphorylation of p21-activated kinases is not sufficient to activate Erk1/2. It requires complex formation of both kinases with GTP-Rac1 to unleash cAMP-PKA–boosted activation of Raf-Mek-Erk. Consequently GTP-Rac functions as a dual kinase-tuning scaffold that favors the PKA holoenzyme and contributes to potentiate Erk1/2 signaling. Our findings offer additional mechanistic insights how β-adrenergic receptor-controlled PKA activities enhance GTP-Rac–mediated activation of nuclear Erk1/2 signaling
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