943 research outputs found
Hadronic production calculated in the NRQCD factorization formalism
The NRQCD factorization formalism of Bodwin, Braaten, and Lepage prescribes
how to write quarkonium production rates as a sum of products of short-distance
coefficients times non-perturbative long-distance NRQCD matrix elements. We
present, in the true spirit of the factorization formalism, a detailed
calculation of the inclusive cross section for hadronic production. We
find that in addition to the well known {\it color-singlet} production
mechanisms, there are equally important mechanisms in which the pair
that forms the is initially produced in a {\it color-octet} state, in
either a , , or angular-momentum
configuration. In our presentation, we emphasize the ``matching'' procedure,
which %is the method that allows us to determine the short-distance
coefficients appearing in the factorization formula. We also point out how one
may systematically include relativistic corrections in these calculations.Comment: 25 pages, 3 postscript figures, use Revtex and epsfig.sty We fixed
some typos, added some text regarding a reference, and changed some
equations. The file will be available at http://phenom.physics.wisc.edu
Nearly Perfect Durable Superhydrophobic Surfaces Fabricated by a Simple One-Step Plasma Treatment
Fabrication of superhydrophobic surfaces is an area of great interest because it can be applicable to various engineering fields. A simple, safe and inexpensive fabrication process is required to fabricate applicable superhydrophobic surfaces. In this study, we developed a facile fabrication method of nearly perfect superhydrophobic surfaces through plasma treatment with argon and oxygen gases. A polytetrafluoroethylene (PTFE) sheet was selected as a substrate material. We optimized the fabrication parameters to produce superhydrophobic surfaces of superior performance using the Taguchi method. The contact angle of the pristine PTFE surface is approximately 111.0�� �� 2.4��, with a sliding angle of 12.3�� �� 6.4��. After the plasma treatment, nano-sized spherical tips, which looked like crown-structures, were created. This PTFE sheet exhibits the maximum contact angle of 178.9��, with a sliding angle less than 1��. As a result, this superhydrophobic surface requires a small external force to detach water droplets dripped on the surface. The contact angle of the fabricated superhydrophobic surface is almost retained, even after performing an air-aging test for 80 days and a droplet impacting test for 6 h. This fabrication method can provide superb superhydrophobic surface using simple one-step plasma etching. ? 2017 The Author(s).114Ysciescopu
Added Value of Computed Tomography Virtual Intravascular Endoscopy in the Evaluation of Coronary Arteries with Stents or Plaques
Coronary computed tomography angiography (CCTA) is a widely used imaging modality for diagnosing coronary artery disease (CAD) but is limited by a high false positive rate when evaluating coronary arteries with stents and heavy calcifications. Virtual intravascular endoscopy (VIE) images generated from CCTA can be used to qualitatively assess the vascular lumen and might be helpful for overcoming this challenge. In this study, one hundred subjects with coronary stents underwent both CCTA and invasive coronary angiography (ICA). A total of 902 vessel segments were analyzed using CCTA and VIE. The vessel segments were first analyzed on CCTA alone. Then, using VIE, the segments were classified qualitatively as either negative or positive for in-stent restenosis (ISR) or CAD. These results were compared, using ICA as the reference, to determine the added diagnostic value of VIE. Of the 902 analyzed vessel segments, CCTA/VIE had sensitivity, specificity, accuracy, positive predictive value, and negative predictive value (shown in %) of 93.9/90.2, 96.2/98.2, 96.0/97.7, 70.0/83.1, and 99.4/99.0, respectively, in diagnosing ISR or CAD, with significantly improved specificity (p = 0.025), accuracy (p = 0.046), and positive predictive value (p = 0.047). VIE can be a helpful addition to CCTA when evaluating coronary arterie
Electromagnetic form factors of charged and neutral kaons in an extended vector-meson-dominance model
A model is developed for electromagnetic form factors of the charged and
neutral K-mesons. The formalism is based on ChPT Lagrangians with vector
mesons. The form factors, calculated without fitting parameters, are in a good
agreement with experiment for space-like and time-like photon momenta.
Contribution of the two-kaon channels to the muon anomalous magnetic moment
a_\mu is calculated.Comment: 23 pages, 11 figures, accepted for publication in Eur. Phys. J.
Rebirth of X-ray Emission from the Born-Again Planetary Nebula A 30
The planetary nebula (PN) A30 is believed to have undergone a very late
thermal pulse resulting in the ejection of knots of hydrogen-poor material.
Using HST images we have detected the angular expansion of these knots and
derived an age of 850+280-150 yr. To investigate the spectral and spatial
properties of the soft X-ray emission detected by ROSAT, we have obtained
Chandra and XMM-Newton observations of A30. The X-ray emission from A30 can be
separated into two components: a point-source at the central star and diffuse
emission associated with the hydrogen-poor knots and the cloverleaf structure
inside the nebular shell. To help us assess the role of the current stellar
wind in powering this X-ray emission, we have determined the stellar parameters
of the central star of A 30 using a non-LTE model fit to its optical and UV
spectrum. The spatial distribution and spectral properties of the diffuse X-ray
emission is suggestive that it is generated by the post-born-again and present
fast stellar winds interacting with the hydrogen-poor ejecta of the born-again
event. This emission can be attributed to shock-heated plasma, as the
hydrogen-poor knots are ablated by the stellar winds, under which circumstances
the efficient mass-loading of the present fast stellar wind raises its density
and damps its velocity to produce the observed diffuse soft X-rays. Charge
transfer reactions between the ions of the stellar winds and material of the
born-again ejecta has also been considered as a possible mechanism for the
production of diffuse X-ray emission, and upper limits on the expected X-ray
production by this mechanism have been derived. The origin of the X-ray
emission from the central star of A 30 is puzzling: shocks in the present fast
stellar wind and photospheric emission can be ruled out, while the development
of a new, compact hot bubble confining the fast stellar wind seems implausible.Comment: 29 pages, 11 figures, 4 tables; accepted for publication by Ap
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA
An investigation of the hadronic final state in diffractive and
non--diffractive deep--inelastic electron--proton scattering at HERA is
presented, where diffractive data are selected experimentally by demanding a
large gap in pseudo --rapidity around the proton remnant direction. The
transverse energy flow in the hadronic final state is evaluated using a set of
estimators which quantify topological properties. Using available Monte Carlo
QCD calculations, it is demonstrated that the final state in diffractive DIS
exhibits the features expected if the interaction is interpreted as the
scattering of an electron off a current quark with associated effects of
perturbative QCD. A model in which deep--inelastic diffraction is taken to be
the exchange of a pomeron with partonic structure is found to reproduce the
measurements well. Models for deep--inelastic scattering, in which a
sizeable diffractive contribution is present because of non--perturbative
effects in the production of the hadronic final state, reproduce the general
tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil
Evidence of Color Coherence Effects in W+jets Events from ppbar Collisions at sqrt(s) = 1.8 TeV
We report the results of a study of color coherence effects in ppbar
collisions based on data collected by the D0 detector during the 1994-1995 run
of the Fermilab Tevatron Collider, at a center of mass energy sqrt(s) = 1.8
TeV. Initial-to-final state color interference effects are studied by examining
particle distribution patterns in events with a W boson and at least one jet.
The data are compared to Monte Carlo simulations with different color coherence
implementations and to an analytic modified-leading-logarithm perturbative
calculation based on the local parton-hadron duality hypothesis.Comment: 13 pages, 6 figures. Submitted to Physics Letters
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