428 research outputs found
Physical Nucleon Properties from Lattice QCD
We demonstrate that the extremely accurate lattice QCD data for the mass of
the nucleon recently obtained by CP-PACS, combined with modern chiral
extrapolation techniques, leads to a value for the mass of the physical nucleon
which has a systematic error of less than one percent.Comment: 4 pages, 2 figure
Interplay of Spin and Orbital Angular Momentum in the Proton
We derive the consequences of the Myhrer-Thomas explanation of the proton
spin problem for the distribution of orbital angular momentum on the valence
and sea quarks. After QCD evolution these results are found to be in very good
agreement with both recent lattice QCD calculations and the experimental
constraints from Hermes and JLab
Assessment of a novel 32-channel phased array for cardiovascular hybrid PET/MRI imaging: MRI performance.
BACKGROUND: Cardiovascular imaging using hybrid positron emission tomography (PET) and magnetic resonance imaging (MRI) requires a radio frequency phased array resonator capable of high acceleration factors in order to achieve the shortest breath-holds while maintaining optimal MRI signal-to-noise ratio (SNR) and minimum PET photon attenuation. To our knowledge, the only two arrays used today for hybrid PET/MRI cardiovascular imaging are either incapable of achieving high acceleration or affect the PET photon count greatly.
PURPOSE: This study is focused on the evaluation of the MRI performance of a novel third-party prototype 32-channel phased array designed for simultaneous PET/MRI cardiovascular imaging. The study compares the quality parameters of MRI parallel imaging, such as g-factor, noise correlation coefficients, and SNR, to the conventional arrays (mMR 12-channel and MRI-only 32-channel) currently used with hybrid PET/MRI systems. The quality parameters of parallel imaging were estimated for multiple acceleration factors on a phantom and three healthy volunteers. Using a Germanium-68 (Ge-68) phantom, preliminary measurements of PET photon attenuation caused by the novel array were briefly compared to the photon counts produced from no-array measurements.
RESULTS: The global mean of the g-factor and SNR
CONCLUSIONS: The MRI performance of the novel PET/MRI 32-channel array qualifies it to be a viable alternative to the conventional arrays for cardiovascular hybrid PET/MRI. A detailed evaluation of the novel array\u27s PET performance remains to be conducted, but cursory assessment promises significantly reduced attenuation
Gut Microbiome: Profound Implications For Diet And Disease
The gut microbiome plays an important role in human health and influences the development of chronic diseases ranging from metabolic disease to gastrointestinal disorders and colorectal cancer. Of increasing prevalence in Western societies, these conditions carry a high burden of care. Dietary patterns and environmental factors have a profound effect on shaping gut microbiota in real time. Diverse populations of intestinal bacteria mediate their beneficial effects through the fermentation of dietary fiber to produce short-chain fatty acids, endogenous signals with important roles in lipid homeostasis and reducing inflammation. Recent progress shows that an individual’s starting microbial profile is a key determinant in predicting their response to intervention with live probiotics. The gut microbiota is complex and challenging to characterize. Enterotypes have been proposed using metrics such as alpha species diversity, the ratio of Firmicutes to Bacteroidetes phyla, and the relative abundance of beneficial genera (e.g., Bifidobacterium, Akkermansia) versus facultative anaerobes (E. coli), pro-inflammatory Ruminococcus, or nonbacterial microbes. Microbiota composition and relative populations of bacterial species are linked to physiologic health along different axes. We review the role of diet quality, carbohydrate intake, fermentable FODMAPs, and prebiotic fiber in maintaining healthy gut flora. The implications are discussed for various conditions including obesity, diabetes, irritable bowel syndrome, inflammatory bowel disease, depression, and cardiovascular disease
Quark-meson coupling model for finite nuclei
A Quark-Meson Coupling (QMC) model is extended to finite nuclei in the
relativistic mean-field or Hartree approximation. The ultra-relativistic quarks
are assumed to be bound in non-overlapping nucleon bags, and the interaction
between nucleons arises from a coupling of vector and scalar meson fields to
the quarks. We develop a perturbative scheme for treating the spatial
nonuniformity of the meson fields over the volume of the nucleon as well as the
nucleus. Results of calculations for spherical nuclei are given, based on a fit
to the equilibrium properties of nuclear matter. Several possible extensions of
the model are also considered.Comment: 33 pages REVTeX plus 2 postscript figure
Nucleon mass and pion loops: Renormalization
Using Dyson--Schwinger equations, the nucleon propagator is analyzed
nonperturbatively in a field--theoretical model for the pion--nucleon
interaction. Infinities are circumvented by using pion--nucleon form factors
which define the physical scale. It is shown that the correct, finite,
on--shell nucleon renormalization is important for the value of the mass--shift
and the propagator. For physically acceptable forms of the pion--nucleon form
factor the rainbow approximation together with renormalization is inconsistent.
Going beyond the rainbow approximation, the full pion--nucleon vertex is
modelled by its bare part plus a one--loop correction including an effective
. It is found that a consistent value for the nucleon mass--shift can
be obtained as a consequence of a subtle interplay between wave function and
vertex renormalization. Furthermore, the bare and renormalized pion--nucleon
coupling constant are approximately equal, consistent with results from the
Cloudy Bag Model.Comment: 14 pages, 6 figure
Strange nucleon form factors in the perturbative chiral quark model
We apply the perturbative chiral quark model at one loop to calculate the
strange form factors of the nucleon. A detailed numerical analysis of the
strange magnetic moments and radii of the nucleon, and also the momentum
dependence of the form factors is presented.Comment: 18 pages, 6 figure
Death and Communal Mass-Mourning: Vin Diesel and the Remembrance of Paul Walker
This article examines Vin Diesel’s use of his public Facebook Page to mourn the loss of his friend and co-actor Paul Walker in the period from 2013-2015. It discusses how Vin Diesel performed his grief and how his mourning process was communally reflected and repeated by both Vin Diesel and Walker fans, who used Vin Diesel’s page to share and verbalise their own feelings of loss in a both public and safe space. An analysis of Vin Diesel’s own status updates and 1800 comments reacting to three popular status updates related to the death of Paul Walk posted over the course of more than a year show that commentary was used to make condolences to both Vin Diesel and Walker’s familes and to affectively express the users’ immediate feelings, both verbally and through the use of emojis. However, over time, both the form and intensity of expression of both Vin Diesel and his followers changed, pointing to the need to further study celebrity mourning processes on social media over extended periods of time
Drop Traffic in Microfluidic Ladder Networks with Fore-Aft Structural Asymmetry
We investigate the dynamics of pairs of drops in microfluidic ladder networks
with slanted bypasses, which break the fore-aft structural symmetry. Our
analytical results indicate that unlike symmetric ladder networks, structural
asymmetry introduced by a single slanted bypass can be used to modulate the
relative drop spacing, enabling them to contract, synchronize, expand, or even
flip at the ladder exit. Our experiments confirm all these behaviors predicted
by theory. Numerical analysis further shows that while ladder networks
containing several identical bypasses are limited to nearly linear
transformation of input delay between drops, mixed combination of bypasses can
cause significant non-linear transformation enabling coding and decoding of
input delays.Comment: 4 pages, 5 figure
Baryon-Baryon Interactions
After a short survey of some topics of interest in the study of baryon-baryon
scattering, the recent Nijmegen energy dependent partial wave analysis (PWA) of
the nucleon-nucleon data is reviewed. In this PWA the energy range for both pp
and np is now 0 < Tlab < 350 MeV and a chi^2_{d.o.f.}=1.08 was reached. The
implications for the pion-nucleon coupling constants are discussed. Comments
are made with respect to recent discussions around this coupling constant in
the literature. In the second part, we briefly sketch the picture of the baryon
in several, more or less QCD-based, quark-models that have been rather
prominent in the literature. Inspired by these pictures we constructed a new
soft-core model for the nucleon-nucleon interaction and present the first
results of this model in a chi^2 -fit to the new multi-energy Nijmegen PWA.
With this new model we succeeded in narrowing the gap between theory and
experiment at low energies. For the energies Tlab = 25-320 MeV we reached a
record low chi^2_{p.d.p.} = 1.16. We finish the paper with some conclusions and
an outlook describing the extension of the new model to baryon-baryon
scattering.Comment: 12 pages LaTeX and one postscript figure included. Invited talk
presented at the XIVth European Conference of Few-Body Problems in Physics,
Amsterdam, August 23-28, 199
- …