1,933 research outputs found
Scalar and Tensor Force Contribution to the Nucleon-Nucleon Interaction Within a Chiral Constituent Quark Model
The nucleon-nucleon problem is studied as a six-quark system in a
nonrelativistic chiral constituent quark model where the Hamiltonian contains a
linear confinement and a pseudoscalar meson (Goldstone boson) exchange
interaction between the quarks. This hyperfine interaction has a long-range
Yukawa-type part, depending on the mass of the exchanged meson and a
short-range part, mainly responsible for the good description of the baryon
spectra.Comment: 6 pages (LaTeX with aip-6s.clo, aipproc.cls and aipxfm.sty packages),
2 eps figures. Presented at the II International Workshop on Hadron Physics,
25-29 September, 2002, Coimbra, Portuga
Important configurations for NN processes in a Goldstone boson exchange model
We study the short-range nucleon-nucleon interaction in a nonrelativistic
chiral constituent quark model by diagonalizing a Hamiltonian containing a
linear confinement and a Goldstone boson exchange interaction between quarks. A
finite six-quark basis obtained from single particle cluster model states was
previously used. Here we show that the configurations which appear naturally
through the use of molecular orbitals, instead of cluster model states, are
more efficient in lowering the six-quark energy.Comment: 17 pages, RevTe
Nucleon-Nucleon interaction in a chiral constituent quark model
We study the nucleon-nucleon (NN) problem as a six-quark system in a
nonrelativistic chiral constituent quark model where the Hamiltonian contains a
linear confinement and a pseudoscalar meson (Goldstone boson) exchange
interaction between the quarks. This interaction has a long range Yukawa-type
part, depending on the mass of the exchanged meson and a short range part,
mainly responsible for the good description of the baryon spectra. We calculate
the NN potential in the adiabatic approximation as a function of Z, the
separation distance between the centres of the two three-quark clusters. The
orbital part of the six-quark states is constructed either from the usual
cluster model states or from molecular orbital single particle states. The
latter are more realistic, having proper axially and reflectionally symmetries.
In both cases the potential presents an important hard core at short distances,
explained through the dominance of the [51]{FS} configuration. However in the
molecular orbital basis the core is less repulsive, as a consequence of the
fact that this basis gives a better upper bound for the energy of the six-quark
system. We calculate the potential for the 3S1 and 3S0 channels with two
different parametrizations. We find a small (few MeV) attractive pocket for one
of these parametrizations. A middle range attraction is simulated by the
addition of a sigma-meson exchange interaction between quarks, of a form
similar to that of the pseudoscalar meson exchange. The present study is an
intermediate, useful step towards dynamical calculations based on the
resonating group method.Comment: 12 pages, 3 eps figures (with aipproc.sty). Talk presented by D.
Bartz at the International Workshop on Hadron Physics "Effective Theories of
Low Energy QCD", Coimbra, Portugal, September 10-15, 199
Turbulent boundary-layer heat transfer from rapidly accelerating flow of rocket combustion gases and of heated air
Turbulent boundary layer heat transfer from fast accelerating flow of rocket exhaust gases and heated ai
Multicluster growth via irreversible cooperative filling on lattices
Consider irreversible cooperative filling of sites on an infinite lattice where the filling rates ki depend on the number, i, of occupied sites adjacent to the site(s) being filled. If clustering is significantly enhanced relative to nucleation (k1/k0≡ρ≫1), then the process is thought of as a competition between nucleation, growth, and (possible) coalescence of clusters. These could be Eden clusters with or without permanent voids, Eden trees, or have modified but compact structure (depending on the ki, i≥1).
Detailed analysis of the master equations in hierarchial form (exploiting an empty-site shielding property) produces results which are exact (approximate) in one (two or more) dimensions. For linear, square, and (hyper)cubic lattices, we consider the behavior of the average length of linear strings of filled sites, lav=J∞s=1 sls/J∞s=1 ls, where ls is the probability of a string of length s [lav=(1−CTHETA)−1 for random filling, at coverage CTHETA].
In one dimension, ls=ns gives the cluster size distribution, and we write lav=nav. We consider the scaling lav∼A(CTHETA)ρω as ρ→∞ (with CTHETA fixed), which is elucidated by the introduction of simpler models neglecting fluctuations in cluster growth or cluster interference. For an initially seeded lattice, there exists an upper bounding curve lav+ for lav (as a function of CTHETA), which is naturally obtained by switching off nucleation (setting k0=0). We consider scaling of lav+ as the initial seed coverage ε vanishes. The divergence, lav∼C(1−CTHETA)−1 as CTHETA→1, is also considered, focusing on the cooperativity dependence of C. Other results concerning single-cluster densities and ls behavior are discussed
The Evaluation of Stylized Facial Expressions
Stylized rendering aims to abstract information in an image making it useful not only for artistic but also for visualization purposes. Recent advances in computer graphics techniques have made it possible to render many varieties of stylized imagery efficiently. So far, however, few attempts have been made to characterize the perceptual impact and effectiveness of stylization. In this paper, we report several experiments that evaluate three different stylization techniques in the context of dynamic facial expressions. Going beyond the usual questionnaire approach, the experiments compare the techniques according to several criteria ranging from introspective measures (subjective preference) to task-dependent measures (recognizability, intensity). Our results shed light on how stylization of image contents affects the perception and subjective evaluation of facial expressions
PVD TBC experience on GE aircraft engines
The higher performance levels of modern gas turbine engines present significant challenges in the reliability of materials in the turbine. The increased engine temperatures required to achieve the higher performance levels reduce the strength of the materials used in the turbine sections of the engine. Various forms of Thermal Barrier Coatings (TBC's) have been used for many years to increase the reliability of gas turbine engine components. Recent experience with the Physical Vapor Deposition (PVD) process using ceramic material has demonstrated success in extending the service life of turbine blades and nozzles. Engine test results of turbine components with a 125 micrometer (0.005 in) PVD TBC have demonstrated component operating temperatures of 56-83 C (100-150 F) lower than uncoated components. Engine testing has also revealed the TBC is susceptible to high angle particle impact damage. Sand particles and other engine debris impact the TBC surface at the leading edge of airfoils and fracture the PVD columns. As the impacting continues the TBC erodes away in local areas. Analysis of the eroded areas has shown a slight increase in temperature over a fully coated area, however, a significant temperature reduction was realized over an airfoil without any TBC
Characterizing the Rigidly Rotating Magnetosphere Stars HD 345439 and HD 23478
The SDSS III APOGEE survey recently identified two new Ori E type
candidates, HD 345439 and HD 23478, which are a rare subset of rapidly rotating
massive stars whose large (kGauss) magnetic fields confine circumstellar
material around these systems. Our analysis of multi-epoch photometric
observations of HD 345439 from the KELT, SuperWASP, and ASAS surveys reveals
the presence of a 0.7701 day period in each dataset, suggesting the
system is amongst the faster known Ori E analogs. We also see clear
evidence that the strength of H-alpha, H I Brackett series lines, and He I
lines also vary on a 0.7701 day period from our analysis of multi-epoch,
multi-wavelength spectroscopic monitoring of the system from the APO 3.5m
telescope. We trace the evolution of select emission line profiles in the
system, and observe coherent line profile variability in both optical and
infrared H I lines, as expected for rigidly rotating magnetosphere stars. We
also analyze the evolution of the H I Br-11 line strength and line profile in
multi-epoch observations of HD 23478 from the SDSS-III APOGEE instrument. The
observed periodic behavior is consistent with that recently reported by Sikora
and collaborators in optical spectra.Comment: Accepted in ApJ
Measuring the Discernability of Virtual Objects in Conventional and Stylized Augmented Reality
In augmented reality, virtual graphical objects are overlaid over the real environment of the observer. Conventional augmented reality systems normally use standard real-time rendering methods for generating the graphical representations of virtual objects. These renderings contain the typical artifacts of computer generated graphics, e.g., aliasing caused by the rasterization process and unrealistic, manually configured illumination models. Due to these artifacts, virtual objects look artifical and can easily be distinguished from the real environment. A different approach to generating augmented reality images is the basis of stylized augmented reality [FBS05c]. Here, similar types of artistic or illustrative stylization are applied to the virtual objects and the camera image of the real enviroment. Therefore, real and virtual image elements look significantly more similar and are less distinguishable from each other. In this paper, we present the results of a psychophysical study on the effectiveness of stylized augmented reality. In this study, a number of participants were asked to decide whether objects shown in images of augmented reality scenes are virtual or real. Conventionally rendered as well as stylized augmented reality images and short video clips were presented to the participants. The correctness of the participants' responses and their reaction times were recorded. The results of our study show that an equalized level of realism is achieved by using stylized augmented reality, i.e., that it is significantly more difficult to distinguish virtual objects from real objects
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